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Michigan State
University

 

 

 

This is to certify that the
thesis entitled

THE EFFECT OF SURFACE MODIFICATION
ON THE PRINTABILITY OF POLYOLEFIN FILM

presented by

CHANIN KULSETTHANCHALEE

has been accepted towards fulfillment
of the requirements for

MASTER Jegree in W

30:“. gm;
0

Major profes or

Date AUGUST 20, 1998

 

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we WM“

THE EFFECT OF SURFACE MODIFICATION

ON THE PRINTABILITY OF POLYOLEFIN FILM

By

Chanin Kulsetthanchalee

A THESIS

submitted to
Michigan State University
in partial fulfillment of the requirements
for the degree of

MASTER OF SCIENCE

School Of Packaging

Summer 1998

ABSTRACT

THE EFFECT OF SURFACE MODIFICATION
ON THE PRINTABILITY OF POLYOLEFIN FILM
By

Chanin Kulsetthanchalee

Presently, there are several types of surface modification techniques used
in industry. Corona treatment, was employed in the present study because
of its availability and ease of treatment, as compared to other techniques
such as chemical treatment. The effect of surface modification on the
printability of polyolefin films was evaluated after contact angle
measurements were performed and surface free energy values had been
determined, respectively. A modified application of the SPEC‘SCAN 2000
computer software was employed for estimation of the area percent of printed
surface peeled from the printed film. Electron Spectroscopy for Chemical
Analysis (ESCA) was performed to characterize the surface composition of
film samples. The results obtained were not conclusive. However, the results
of surface free energy estimations proved satisfactory, as anticipated; The
higher the corona treatment level, the higher the surface free energy value,

as well as the better adhesion of the ink to the film.

"for my Tarents and Jill? Beloved Ones...

iii

ACKNOWLEDGMENTS

The author wishes to express the appreciation to his advisor, Professor

Jack R. Giacin, for all of his time of the guidance, effort, patience and many more which
lead to this work success. i felt truly in debt for his perpetual kindness, perspiration, and
inspiration.

I would also like to thank all the committee members for their time and helpful
suggestion for this work i.e., Professor Susan Selke, Professor Joe Kuszai.

it is impossible to finish this work without all the experimental effort contributed
by many people helpful hint from the Composite Materials and Structures Center, MSU.
Many thanks go to the Tredegar film products for the supplies of the film samples. I also
have to express my thank to the friends at Department of Pulp and Paper Science at
Western Michigan University for many help on the use of the SPEC*SCAN 2000 system for
testing the percentage of ink peeled.

And I would like to show my gratitude to Ms.Chaweewon Wongwarangkul
for her inspiration and devotion as well as my fn'ends’ helpfulness throughout my
work; Ms.Prapassara Nilagupta, Mr.Takeshi Ueda and Dr.Rath Pichyangkura.

Sincerely,

Chanin Kulsetthanchalee

iv

TABLE OF CONTENTS

ListofTables......................

LIstofFIgures
Chapter1 Introduction and ObjectIves
Chapter2 Surface phenomena background...............

2.1 Wetting and adhesion theory.........

2.2Surfacefreeenergy(SFE)estimation................................... ..
2.2.1 Solid surface energy determination using SFE components ........
2.2.2 Solution forthework ofadhesion..........................................
2.3 Calculations of both contributions to SFE of polymer...
2.3.1 Determinant method
2.3.2 The least square method

2.3.3 Derivation of least squares method... ..

Chapter3 Surfaceactivationofpolymers.....................................
3.1 Flametreatment............................
3.2 Chemical treatment
3.3 Plasma treatment............. ..

3.4 Corona dischargetreatment (CDT)......

.viii

14

.15

16

17

19

.22

.25

.26

...27

.29

Chapter4 Experimental Procedures..........................................35
4.1 Methods ofcontact angle measurement...................................35

4.1.1 Apparatus and materials used for contact angle measurements..36

4.1.2 Sample preparation for contact angle measurements... .36
4.1.3 Calculation of surface energy of solid... ...40
4.2 Application of printing lnk...... ...41

4.3 Sample preparation for the peel adhesion test... ...43
4.4 Peel adhesion test43
4.5 Method for measuring printing ink adhesion by peel test... ..45

4.6 Quantitative measurement of the peeled areas of the sample film 47

4.7 ESCA (Electron Spectroscopy for Chemical Analysis) ...49
Chapter5 Resultsanddiscussion..................'.............................51
5.1 Contact angle measurement of liquids on the films... ..51
5.2 Surfacefreeenergyoffilm samples..........................................54
5.3 Discussion on peel tested areas of the samples... 57
5.4TheresultsofESCAsurveymethodanalysis........................... 62
Summaryand COI‘iCIUSlOl‘i63

vi

APPENDIX A...

Samples of calculation program used to determine the

surface free energy of the film samples

APPENDIX B...

Samples of the analysis data from the Electron Spectroscopy ...

for Chemical Analysis (ESCA)

APPENDIX C...

Samples of original databbtaIned from the

SPEC" SCAN 2000 system

vii

. ...66

...7O

...74

79

LIST OF TABLES

Table 1 : Surface tension of various solvents at 20°C...
Table 2 : Surface free energy oftypical polymers...

Table 3 : Surface energy of liquids used in the experiment...

treated HDPE film sample

Table 5: Surface free energy of corona discharge treated ....

HDPE film

Table 6 :The percentage area of the peeled area at different

level of treatment (%)

Table 7 : ESCA determination for the surface compositions... ....

...15
...27

......35

Table 4 : Contact angle values obtained for corona discharge... .52

...54

...57

.....62

of the film sample at variable exposure levels of corona treated

viii

Figure 1:

Figure 2:

Figure 3:

Figure 4:

Figure 5:
Figure 6 :
Figure 7 :

Figure 8:

Figure 9 :

Figure 10 :

Figure 11

Figure 12 :

LIST OF FIGURES

The surface tension balance at a point of three-phase... ..

Typical individual relationship of (y,6 )"S versus.

(739)” deduced from one of the equation [18] or [19]

Effect of storage after corona discharge treatment on...

the wetting tension of a polyethylene surface.

Apparatus for surface activation of plastic film by corona...

discharge with equivalent electrical circuit.

Eyepiece view of goniometer and sessile drop on sample...
Goniometer (model 100-00 115, Rama-Hart, lnc.)...............
Peel testing apparatus scheme.......

Contact angle measurement of the corona treated ..

film using different liquids

Effect of corona treatment level on the polar, dispersive

and total surface free energy values

and the total surface energy

: The illustration of printed specimen after peel test...

the percentage of the area which was peeled off

Relationship between the corresponded components

The relationship between the level of treatment and...

...18

31

.32

.38

.39

.46

.53

.55

56

.58

.60

Chapter 1

INTRODUCTION

Polyolefin films are of widespread use, especially in packaging
applications. Several important applications such as adhesive bonding,
lamination, printing and painting require good adhesion to polymer surfaces.
Printing, as a major method of producing printed media, is one of the major types
of today’s communication and has become the focus of attention in the
packaging industry. As a result of this concern, materials used to produce good
quality and effective printing are also the focus of concern.

Since polyolefin film is a non-absorbing substrate, it is difficult to employ it
as a printing substrate, unless surface modification is achieved. As a result, it is
usually necessary to carry out a pre-treatment to achieve the required adhesion
level. The requirement for printability is that the printing ink must wet the
surface and adhere to the polymeric substrate. Polyolefins, which refer to
polyethylene and polypropylene, are generally known to be difficult to print
materials, due to their low surface free energy and poor wetting ability.

Oriented polypropylene (OPP) was first introduced in 1960 (Marra,19‘88).
Since then, it has replaced several other commercially used packaging materials
in a variety of packaging applications, and has become one of the leading

commodity flexible packaging films. This dramatic growth is attributed to

oriented polypropylenes outstanding physical properties and relatively low cost.
OPP also offers a number of additional important properties such as:

(i) moisture protection; (ii) longer product shelf-life; (iii) better optical
clarity; (iv) excellent mechanical properties; and (v) chemical inertness
(Adamson,1976) The inertness of the polymer surface, however, results in poor
ink adhesion. Therefore, surface treatment is required to activate the substrate.
This is usually done by a high voltage discharge treatment (corona treatment) ,
and to a lesser extent, by flame treatment (Brewis,1985).

Mangipudi et al.(1995) suggested and showed that to obtain true surface
free energy values, measurements should be made with a Surface Forces
Apparatus (SFA), which was originally developed by lsraelachvili et al.(1972),
rather than through contact angle measurements. The authors evaluated corona
treated polyethylene film and confirmed that an increase in surface modification
led to an increase of surface energy. Mangipudi et al. also proposed that contact
angle measurements gave only an estimation of surface free energy values,
since it was not sensitive to small changes in surface composition.

Hollander et al.(1994) found that a combination of contact angle
measurements (goniometry) and chemical derivatization reactions could supply
semi-quantitative information about functional groups on the upper most surface
layers of polymer film. Further, the authors found that when there is little, or a
lack of information relative to the chemical structure of the polymer surface, this
combination, rather than simple contact angle measurements, was regarded as

valuable complimentary methods for the surface analysis of a polymer.

Strobel et al.(1990) studied the aging in air of corona treated
polypropylene film and found that the effects of aging on such film were minimal.
They also found that aging did not affect ink adhesion for the particular
polypropylene film and ink studied.

In these studies, the tests for ink adhesion were performed manually,
although based on the following ASTM standards :

ASTM D 3359-93 Standard test method for measuring adhesion by tape test

ASTM D 897-78 Standard test method for Tensile properties of adhesive bonds

ASTM D 1876-93 Standard test method for Peel resistance of adhesives
(T-Peel test)

ASTM D 903-93 Standard test method for Peel or stripping strength of adhesive
bonds

ASTM 02979-88 Standard test method for Pressure-sensitive tack of adhesives
using an Inverted probe machine.

Thus, according to the studies described above, Strobel et al. (1990)
assumed that the choice of probe liquids used for contact angle measurements
was appropriate for estimating surface free energy values. Further, the method
used in calculation and interpretation was well defined by Park (1994).

In the present study, high density polyethylene film will be subjected to
various levels of corona discharge treatment, in order to determine the effect of
the corona treatment on the surface free energy of the polyolefin film, and its
effect on ink adhesion to the film surface. Therefore, the primary objectives of

this study include:

Objectives

1. To determine the effect of corona discharge treatment of high density
polyethylene (HDPE) films on surface free energies, as well as the
corresponding dispersive and polar free energy components of the total
surface free energy, by measuring the contact angles of various liquids on
the respective film samples.

2. To determine printability and related characteristics of the corona treated and
non-treated polyolefin films, such as wettability and ink adhesion properties
through a modification of typical test methods and ASTM standards. The
ASTM standard method of test for ink adhesion on the film samples will be
modified, so as to minimize the effect of tape application pressure, storage
time, peel rate and the peel angle on the ink adhesion peel test.

3. To evaluate the use of the Spec*Scan 2000 system, to estimate and compare
ink adhesion to the polyolefin surface, as a function of different corona
treatment levels.

4. To evaluate and analyze the obtained data to determine a correlation

between corona treatment level and ink adhesion.

Chapter 2

SURFACE PHENOMENA BACKGROUND

Kraus (Kraus,1954) has summarized the results of many direct
measurements of the work of adhesion. These measurements were made
using precision calorimeters, with the solid in a finely powdered form having a
known surface area. The value of work of adhesion for a large class of solid-
liquid systems is in the range of 200 to 300 ergslcmz, the adhesion in these
systems being due, presumably, to dispersion forces. If the liquid has a dipole
moment, the work of adhesion is usually increased by 100 to 200 ergs/cm2
because of the electrostatic attractions resulting from the dipole. Those liquids
capable of hydrogen bonding show the largest values of work of adhesion, 700
to 1000 ergs/cm2 being observed with metal oxides and water.

Two dissimilar substances, brought into intimate contact, exert
attractive forces on each other across their common interface. Often these
forces are of sufficient magnitude so that the substances tenaciously resist
separation. This phenomenon is called adhesion. It is essentially a surface
phenomenon, being strongly dependent upon the nature of the surfaces and
upon the intimacy of contact of the surfaces.

An interface is an essential feature of an adhesive bond. A related
phenomenon, cohesion, refers to attractive forces acting among like molecules

and is a bulk rather than a surface phenomenon” Cohesive forces are

responsible for the close packing of molecules in solids and liquids, as
contrasted with gases.

Adhesion is an important aspect of bonding operations such as
extrusion coating and thermoplastic laminating. In other bonding operations
such as heat sealing, an adhesive bond is formed initially, but because of
chain diffusion, the interface gradually disappears and the bond becomes
cohesive in nature (Marra 1988).

In order to make printing ink adhere to various polymer films, it is
necessary to activate the surface of the film. Activation is a surface
phenomenon, in which a change in the chemical or physical nature of the
surface is induced by passing the film through a gas flame or a corona
discharge.

The effect of surface treatment is typically characterized by changes in
the surface free energy components, namely the dispersive (nonpolar or
London, 75") and non-dispersive (polar or acid-base, ys") (Carley etal.,1978)
These surface free energy components can be calculated by analyzing contact
angle measurements of a liquid phase on the polymer film surface.
(Kaelble,1971)

Based on the work of Zisman (1964) for critical surface tension of
wetting (7c) and Fowkes (1990) for surface energy based on dispersive
components, Dann (1970) carried out contact angle measurements using a
series of liquids on polymer surfaces and found that polar force components

and dispersive force components should be additive, to evaluate surface

tension and surface energy of low energy surfaces. Carley and Kitze (1978)
have well developed the relationship of the respective surface free energy
contributions, to characterize adhesion properties and estimate the effect of
corona treatment of polyethylene (PE) films. These investigators also
measured the films adhesion strength directly, using an adhesive-tape peel
test and surface tension tests. Based on the results of their studies, Carley
and Kitze (1978) proposed that the polar component of surface free energy
was a key to understanding the changes in adhesion properties of the PE film,

following corona-discharge treatment.

2.1 Wetting and Adhesion Theory

Wetting is defined as the extent to which a liquid makes contact with a
solid surface. The wettability of liquids with a respective surface can be
characterized by measuring the peripheral contact angles between the surface
of a small sessile drop of the liquid and the horizontal surface of the solid.
Adhesion is the intimate bonding together of surfaces on which interfacial
forces are acting. The work required to pull the interface apart from two faces
can also be estimated. (Kinloch, et al. 1991)

Contact angle measurements provide a simple, inexpensive method to
obtain direct information on wetting by the contact angle of a liquid, and can
estimate the surface free energy in terms of a solid, as described in Figure 1.
At equilibrium, and in the absence of interfacial reactions, the extent of wetting

on the surface by the liquid is determined by the force balance between the

three phase contacts, as illustrated in Figure 1. This balance of interfacial
forces was initially described by Young in 1805 (Adamson 1976), and it is now

known as Young’s equation:

757 = is: + 11., cos 0 [1]
where the terms my and ysv are the surface tension of the liquid and the
solid in equilibrium with the vapor, respectively, and 7;. represents the
interfacial tension between liquid and solid with the contact angle (0).
The equivalent equation was expressed in algebraic form by Dupre’ in

1869, along with the definition of work of adhesion (Adamson 1976).

Y . .
LV Uld

Figure 1 : The surface tension balance at a point of three-phase

 

contact at equilibrium for ideal surface

An ideal surface is a smooth surface, without interfacial reactions with a
liquid drop. The surface free energy (SFE) ( ys ) of a polymer can also be
expressed by the equilibrium spreading pressure ( Tl: ) of a test vapor due to the

adsorption of vapor molecules, as described in equation [2].

‘Ys = 'YsI + TE [2]

where (n) is defined as the reduction of (75) due to the adsorption of vapor by

the surface, when the vapor obeys the ideal gas laws as in equation [3]

n = RT l"° rdun p) [3]

where ( p) is the vapor pressure, (p0) is the saturation vapor pressure; R
and T are the gas constant and temperature, respectively, and I“ is the surface
concentration of absorbed vapor. For a polymer with low surface energy, (1!)

can usually be neglected so that equation [1] is approximated by:

75 = Ysl + 'Ylv COS 9 [4]

Equation [4] provides a means to describe the spreadability (or
wettability) of liquids on a solid surface. The criteria of the spreading of a
liquid on a solid can be expressed by defining the parameter S. the equilibrium

spreading coefficient.

Se = 73 ’ (Ysl + 'Ylv I = Ylv (COS 9 '1) [5]

When (0) is zero, i.e. cos 6 = 1, S6 = 0, the liquid spontaneously
spreads over the surface because of the negative free energy associated with
the process. When (0) is not zero, i.e. cos 0 <1 and Se <0, then the liquid is
non-spreading over the surface.

The work of adhesion involves the separation of two phases, which are
originally in intimate contact with each other. The work of adhesion, WA, can
be combined with equation [4] to give a direct relationship between WA and

wetting, yielding;

WA = st+ Ylv ' 'Ysl = Ylv ( 1 + cos 6) [6]

Equation [6] indicates that WA. can be maximized when the liquid
exhibits a zero or near zero contact angle. In addition to the concept of the
wetting equilibria being described by thermodynamic relationships with contact
angles, the rate at which the contact angle equilibrium is approached depends
on such factors as the driving force for wetting, the viscosity of the liquid, and

the roughness of the solid surface.

10

2.2 Surface Free Energy Estimation

Surface energies of solids such as a polymer film are usually estimated
from the contact angle measurements using probe liquids of known surface
characteristics. Most of the contact angle methods developed to estimate the
surface free energy of a solid are based on Young’s equation as shown in
Equation [1], by using a liquid drop on the smooth and undeformed surface of
the solid. Since the surface free energy of a solid cannot be directly measured,
various methods of estimating the surface free energy of a solid have been

developed and the one used for this work was described in the Appendix .A.

2.2.1 Solid Surface Energy Determination using SFE components

This method is based as Fowkes’ proposal that surface free energy
components exist, which are due to particular types of intermolecular forces,
including dispersion forces, dipole-dipole forces, or hydrogen-bonding
interaction. (Fowkes, 1964). It has been recognized that the surface free
energy is the result of two major components; namely dispersion forces (or
London forces) and polar forces, which are considered as acid/base

interactions, and is expressed as follows:
1 = 7" + 1" [7]

where the superscripts d and p, respectively, are dispersion and polar

force components of the surface energy of a solid, such as a polymer film.

11

Fowkes (1964) then applied the geometric mean to the dispersive force
components for estimating the surface energies involving only dispersion

forces:

77.7 = Ya + imp-2 [(77d vbdll "2 [8]

where y. and 7., are the surface energies of the two phases, and
superscript " is the dispersive component of the interfacial energy.

Owens et al. (1969) presented an equation to describe the interfacial
energy between two surfaces by combining all interactions, including
dispersion forces, into a single 1" term. They assumed that the geometric
mean expression could be extended to polar interactions and subsequently to

Equation [9] in the solid/liquid system, as follows;

78! = 'st T 'Ylv ' 2 “78“ Via” m " 2 KY: YIPII 112 [9]

where d and p denote the dispersion and polar components of the
interfacial free energy, respectively.

Finally an equation to allow estimating the surface free energy of a solid
can be described by combining equation [9] with equations [4] and [7], which

eliminates the interfacial energy of the solid and liquid phrases:

12

7. (1+ cos e>= 2 to.“ 701‘” + 2 to." 701‘” [10]

where y. is the surface tension of the liquid, which is the sum of both

the dispersion and polar force components.

VI = yI°+yI° [11]

By making contact angle measurements with two probe liquids of known
characteristics; two equations can be set up for one common solid surface and
the equation solved for the unknowns, y.“ and 7.? The surface energy of the

solid, 7, is then the sum of these two components.

78 = 'st'I'Ysp I12]

Dann (1970)evaluated the surface energy of many liquids used for
contact-angle measurements from the previously reviewed equations.
Basically, Dann determined only the dispersion-force components of the liquid
surface tension, 7.“ , by measuring contact angles against a solid that was
intended to have only a dispersion-type surface energy. The author measured
contact angles of various liquids on paraffin, assuming 7, " as zero, and

evaluated the dispersion component of the liquid using equation [ 13 ]

l3

y.d= 4ypd(COSB)/ y. [13]

where 'y .d is the dispersion force component of the liquid surface free
energy; 7. is the total surface free energy of the liquid, which can be directly
measured by using the Du Nouy ring method (1919) or the Wilhemy plate
technique (1863); and y pd is the paraffin surface free energy of the
dispersion-force component, which was known to be 25.5 [dynes/cm]. Then y I”,
the polar (or non-dispersion) component of the liquids surface tension, was
calculated by using equation [7]

Some typical liquids used in the contact angle method to characterize
the solid surface free energy and their associated solvents are summarized in

Table1.

2.2.2 Solution for the work of adhesion

This method is based on the surface tension that can be divided into two
components, the dispersion force and polar force components, and is
represented by y = y“ + 7" (Equation [7]). The equation w = 2(y.y. )V'
can be extended with the concept of Owens, et al.(1969) by the following

equafion;

WA: 2(73‘ 15')"2 + 2(1:p rip)"2 I14]

Combining this equation with the Young-Dupre Equation [6] yields:

7. (1+ cos a) = 2 <7.“ mm 2 (7." In“ [15]

14

 

 

 

Table 1 : Surface Tension of various solvents at 20°C "’
Solvent dynes/cm Solvent dynes/cm
n-Heptane 19.5 Butyl cellosolve 27.3
lsopropyl acetate 21.2 n-Butyl acetate 27.6
lsopropyl alcohol 21.4 Cyclohexanone 27.7
Ethyl alcohol 22.3 Toluene 27.7
Acetone 22.3 Cellosolve 29.4
Methyl alcohol 22.6 2-Nitropropane 30.0
lsobutyl alcohol 22.8 Methyl Cellosolve 33.0
sec-Butyl alcohol 23.0 Cellosolve acetate 33.6
Diethylene glycol 23.0 Dimethylforrnamide 35.0
Methyl isobutyl ketone 23.6 Methyl Cellosolve 35.1
acetate
Ethyl acetate 23.9 1 ,1 ,2,2- 36.0
Tetrachloroethane

Methyl ethyl ketone 24.6 Dimethyl sulfoxide 43.0
Cyclohexane 25.5 Ethylene glycol 48.4
Tetrahydrofuran 26.4 Fonnamide 58.2
Carbon tetrachloride 27.0 Glycerol 63.4
Chlorofonn 27.1 Water 70.8

 

 

(a) Satas, D., Plastics Finishing and Decoration. VanNostrand Reinhold, 1986

Contact angle measurements have been widely used to calculate the

15

2.3 Calculations of both contributions to SFE of polymer

values of the dispersion force, 7,“ and polar force, 7.”, components to the total

surface free energy, 7, , by solution of equation [10] or [14] .

 

Kaelble and

Cirlin (1971) used two fluids to calculate the surface energy from geometric
mean approximations. Carey et al.(1978) used four liquids rather than two
liquids to characterize the surface free energy of a series of test surfaces and
Kinloch etal. (1991) have developed a series of equations to reduce errors
during calculation of surface energies on the solids by using four liquids.

The following details the derivation of equations and methods.

2.3.1 Determinant method

Kaelble, et al.(1971) analyzed the experimental values of work of
adhesion acquired by using the equation w = 7. (1+ cos 0). In their analysis a
pair of simultaneous equations is derived for two liquids, m and n, on a
common solid surface:

2(1:")"' (incl )my'+ 2(1sp)%(1ri'°)my' [15]

(WA )m

2(13)” (1nd )ny'+ 2(17")%( VIP )ny’ [17]

(WA )n

where 0 is the contact angle of the liquid on the soild surface. Thus, if

the values of 0 13,7." for the two liquids are known, these equations may
be solved to yield the dispersion and polar force components to the surface
free energy of the solid surface. The total surface energy is then simply the
sum of these components. However, this method has some limitations when
using contact angle data for only two liquids, and suffers errors when

calculation of the surface energies is performed with other liquids.

l6

Equations [16] and [17] have a linear relationship in the schematic
representation of (y 3)” versus ( y. 9 )V‘ as shown in Figure 2, where four linear
relationships obtained from four individual liquid contact angle analyses are
illustrated. Previously reported studies have solved for the two unknowns by
solving for each individual pair of lines and then averaging the results. This
direct approach was found, however, to lead to considerable errors in the
values of y," and 7.", which had been calculated.

Kaelble et al.(1971) suggested that the pairs of lines having values
exceeding the boundary conditions should be excluded to minimize errors,

where 0mm” is given by:

Dboundary = [(vndlm (1nd)n]V'-[(YI°)m(1IP)n] V' 2i10I18]

Though this condition was shown to contribute somewhat to reducing the
scattering, the conditions of Dboundary remain an unverified condition. According
to this method, point A and B in Figure 2 are disregarded in the calculation of

the surface energy of solids, which may lead to some errors.

2.3.2 The least square method
Kinloch (1987) proposed this method to make it possible not only to
calculate the surface energy values by including all the contact angle data, but

also to reduce errors in calculations, based on the slopes of the straight lines

17

shown graphically in Figure 2. It is possible to use Equation [15] and [17] with
the method of least squares to obtain the best values of the dispersion force,

y 5", and polar force, y 5", components for each treated surface. This is based
on the data obtained from a number of liquids instead of just two (Park 1994).
The derivation of this procedure and a computer program for solving equations

are detailed below.

 

 

    
  

 

(l) Distilled Water

(2) Formamidc

(3) Methane diiodidc
(4) Tricrecly Phosphate

IS

 

 

 

8

ldync I cm] 0'5

 

0.5
u

(1:)

 

 

 

 

 

 

(‘4’) [dynclcml 0‘5

 

 

 

Figure 2 Typical individual relationship of (73)" versus

(1:9)” deduced from one of the equation [16] or [17]

18

2.3.3 Derivation of least squares method
Equation [15] can be rewritten for each liquid used for the contact angle

measurement on the common film surface as follows:

2(1I“)V’/ vI-lvs°)"'+ 2(vapl”/1I-(vs")"' = 1+0039 [19]
When k number of liquids are used for the contact angle measurement,
Equation [20] can be simplified as in the matrix form with two unknown

components of the surface free energy:

[Alkxz IX]sz = IBIkxI +Ielkx1 [20]
where matrix [A] represents the constant coefficients of the two unknowns,
(19)” and (7," ')"’ , in Matrix [X]. Matrix [8] represents the constant values from
the right-hand side of Equation [19] (i.e. 1+ cos 9), and matrix [e] is the error
involved in balancing the individual equation.
When m number of contact angle measurements for each liquid on a film are

recorded, then equation [20] can be extended as:

[Alm [X]2xm = [Blkxm + [elkxm [21]
Matrix [B] is taken to the left-hand side of the equation [21], and multiplied by

both sides of the equality with the transpose of the left-hand side:

19

{[AlkX2[X]2XM ' I B lkxmf {[AlkX2[X]2Xfl1 '[ B lkxm}
={IAIkx2Ix12xm'IBlkmeTIIeII [22]
where superscript T presents the transpose of the matrix concerned. The

equation can be expanded to:

{[X]T[A]'[A][X]}mm-{[X]T[A]T[B]}mm
-{[BIT[AI[X]}mm+'{[BlTlBl}mxm = [Elmxm [23]
When the partial derivative of matrix [E] is employed for the two unknowns (X1

and X2) and made to zero to minimize the error then:

MEI/6X1 = [AITIAIIXI‘r [XITIAITIAl-[AITIB] - [BITIA]=0
[24]
MEI/6X: = [A]T[A][X]+ IXITIAITIAl-[AITIB] - [BITIA] =0

Since the above two equations are the same, rearranging one of the equations
gives:
{[AITlAllxl-[AlTlBllzxm+{IXITlAlTlAl- [BlTlAllmz = 0

[25]

Equation 25 is in the form of [ z ] + [ z ]T = 0. In order to satisfy the equality to
zero, then both matrixes should be individually equal to zero. Therefore:

{IAITIAIIXIhxm = {IAITIBlhxm [25]

20

and
{IXITIAITIAIMn = {IBITIAILMIZ [27]
Equation [26] is the transpose of equation [27] Therefore one of these two
equations is required for analysis for contact angle measurements. Matrix [X]
in the above equations can be solved by one of equations below:
[x12xm = inverseHAlTlAl} {[A]T[B]}2xm [281
and

IX)...“= inversetlAlTlAl} {IBI'IAIIM [291

There are several advantages to using this method, namely: this method yields
the least errors, it accepts all the data, and it is very simple to employ into a
computer program. A computer program to solve this equation can be written
by using fortran, basic, or any software which can calculate the matrix. In the
present study. “Microsoft Excel” TM ® (Microsoft corp.) software has been used

to solve the matrix [X] in Equation [28].

21

Chapter 3

SURFACE ACTIVATION OF POLYMERS

The author has reviewed in detail the topic of surface activation corona
discharge and since the detailed review of this topic is considered beyond the
scope of this dissertation, an abbreviated summary of the topic area as
described by McKelvey (1962) is presented below.

“Even though nonpolar polymers, such as PE, PP, do not adhere well to
other materials, there are still many applications in which they are bonded to
paper, metals, inks, and other plastics. It is necessary to activate the surface of
the nonpolar material before it comes in contact with the other adherend in order
to achieve satisfactory adhesion in these bonding operations."

“A wide variety of techniques have been used for surface activation.
These include sundry chemical treatments involving chlorine gas, ozone, and
other oxidizing agents, exposure to hot gases and flames, and exposure to
various types of electrical discharges.”

“According to Allan (1959), complete wetting is a necessary condition for
good adhesion. Activation increases the wettability (decreases the contact
angle) of a surface toward a polar liquid. Because materials such as
polyethylene are wet by printing inks only after being activated, surface

activation is a necessary prerequisite to the printing of polyethylene.”

22

“In addition to making polyethylene compatible with printing inks,
activation appears to increase its adhesion to metals and metal oxide surfaces. It
has been reported that the adhesion of polyethylene to stainless steel increases
with the degree of oxidation of the polyethylene.”

“Most investigators agree that activation is the result of the formation of
polar groups in the surface. Rossman (1956) activated polyethylene film
samples with a flame, a glow discharge, and a brush discharge from a Tesla coil.
Spectrophotometric examination indicated that oxidation occurred in all three
cases. Hines (1957) conducted similar studies on polyethylene film that had
been flame activated. He concluded that hydroxyl and ether groups, probably in
the form of formals and hemiformals, were formed on the surface. Various
chemical treatments for the activation of polymer film surfaces have been
reported and are reviewed by Bloyer(1955) .The simultaneous action of chlorine
gas and ultra-violet radiation proved moderately successful. Wolinski
(1955) reported that films could be activated with a combination of ozone and a
hydrogen halide or ozone with nitrous oxide. Horton (1954) patented a process
for surface activation via oxidation with chromic acid and other strong oxidizing
agents. Kreidl et.al.(1955) reported that activation is obtained by exposing the
surface of polyethylene to a high temperature, while the bulk of the material is
kept at a low temperature. He proposes using hot combustion gases, hot air,
exposure to open flame without actual contact, and exposure to electric heating

elements.”

23

“There are two activation processes of commercial importance. One
process, patented by Kritchever (1953), involves the direct exposure of the film
surface to an open flame. The other process, patented by Traver (1957),
involves passing the film through an electric field in which rapid electron
bombardment of the surface occurs.”

Brewis (1994) stated that adhesion to polymer surfaces needed for good
printing required surface pretreatment, such as the use of corona discharge or
flame treatment, in order to attain the required adhesion level. In practice,
there are various types of surface pretreatments which are essential for
providing good adhesion to polymer surfaces. These include flame treatment,
chemical etching treatment, plasma treatment, and corona discharge treatment.

According to Lane and Hourston (1993), various commercial applications
of polyolefins, such as adhesive bonding, printing, and extrusion coating, which
, require good adhesion, may give rise to some problems.

The effects of corona discharge treatment on ink adhesion to high density
polyethylene are described in detail below. The effects of the other pretreatment
techniques on polyolefins are also briefly discussed.

Pretreatment techniques other than corona discharge are described

initially, followed by a detailed review of the corona discharge procedure.

24

3.1 Flame treatment

Flame treatment: It is used to improve ink adhesion to molded polyolefin,
acetal copolymer and polyethylene terephthalate containers. That is, an object
is passed over one or more burners, which consist of a large number of closely-
spaced jets which are fed with an air-gas mixture.

( Brewis 1985)

Flame treatment is believed to help oxidize and make the surface easily
wettable, because flames generally consist of excited species of O, NO, OH, and
NH, that will remove hydrogen from the plastic surface, which is contacted for a
period of less than 1 second with the oxidizing portion of the flame. Ayres and
Shofner (1972) found that the optimum treatment time for an unspecified
polyolefin was 0.02 seconds.

The treatment level may be affected by variables such as the air-to-gas
ratio, distance of surface to be treated from the visible blue tips of the flame, and
speed of the part passing through the flame.(Satas, 1986)

The treatment is suited to various'shapes of objects. Round containers,
for example, can be treated on all sides by rotating them, or by dropping them
through a ring burner. The treatment can also be used in, in-line processing.
When applied prior to corona discharge, flame treatment helps improve the
printing quality, since the flame will break down the crystallites, and render the
surface more susceptible to corona discharge treatment. Moreover, the
treatment allows additives, which are usually restricted to antioxidants and anti-

static agents, to survive during the process (Brewis,1985)

25

For sheeted objects, the process is preferred for use with sheeting with a

thickness greater, rather than less than 0.6 mm (23.6 mil)

3.2 Chemical treatment

Chemical treatmentzThe polymer surface is exposed to certain types of
chemical oxidizing agents such as chromic acid, permanganate compounds, and
or sulfonate compounds, which results in chemical reactions and
microroughness on the surface of the object (Satas,1986). Brewis (1985)
accumulated several interesting formulations of compounds for this treatment.

Chemical treatment is not an easy or convenient process, because it
requires immersion and exposure to chemical reagents within a specific period
, of time. Further, it requires that the object be precleaned and replaced by a new
one at a certain time interval, in order to avoid contamination. Thus, this
treatment can be employed with irregular shaped objects, or only after other
simpler and lower cost methods have proven to be unsuccessful. Polyethylene,
polypropylene, acrylonitriIe—butadiene-styrene terpolymer (ABS), poly(phenylene
oxide), polyether, and polystyrene can either be treated by this method or by one
of the other treatments described. The surface energy of these polymers are
summarized, as shown in Table 2. (Lekan 1988)

ABS and PP parts, for instance, may be chemically etched for metallic
plating. Conversely, fluorocarbon polymers are more likely to be treated by this
chemical treatment procedure. The major disadvantages of chemical treatment

are its corrosive nature and the effluent problem. However, chromic acid etching

26

improves bondability by removing amorphous or rubbery areas and forming

cavities, since surface oxidation might occur and leads to surface wettability.

Table 2 : Surface free energy of typical polymers I”

 

 

Polymer type dyne/cm Polymer type dyne/cm
Polypropylene -PP,OPP 29-31 Polyethylene - PE 30-31
Polytetrafluoroethylene 19-20 Polyvinyl fluoride (T edlar) 28
(Teflon) - PTFE

Polystyrene - PS 38 PET 41-44
ABS 35-42 Polycarbonate - PC 46
Polyamide < 36 Polyimide 40
PMMA < 36 Polyaryl ether ketone < 36
Epoxy < 36 Polyacetal < 36
Fluorinated ethylene 18-22 Polyphenylene oxide - 47
propylene - FEP PPO

Riqid PVC 39 PBT 32
Plasticized PVC 33-38 Polysulfone 41
Polyester 41-44 Polyethersulfone 50
Polyvinylidene fluoride 25 Polyarylsulfone 41
Nylon 33-46 Polyphenylene sulfide 38

 

 

 

 

(a) Lekan S.F., “Corona treatment as an adhesion promoter for U V/EB curable coatings”
Journal of Radiation Technology, 1988.

To achieve maximum adhesion strength, the degree of surface porosity must be

compatible with the level of etching.

3.3 Plasma treatment
Plasma treatment: The interaction of the surface of a monolayer material

with a chemical plasma (ions, electrons, atoms and radicals), which is formed

27

when power is applied to a typical gas like oxygen, nitrogen, hydrogen, argon
and the like at low pressure, leads to rapid chemical modification of the surface,
which improves wettability and adhesion characteristics.

Compared to ozone and corona discharge treatments, plasma treatment
is a more rapid process and leaves less damage to the polymer surface.
Schonhorn and Hansen (1966), as cited in Satas (1986), showed that a
polyethylene surface can be effectively treated by an inert gas plasma produced
by a radio frequency field, which improved the polymer films bondability.
Commercially, this method is used for difficult-to-treat polymer surfaces.
Garbassi et al. (1994) stated that plasma treatment is required to be carried out
in a vacuum chamber and gas feed, to maintain appropriate pressure and
composition of gaseous mixtures.

Parameters which affect plasma treatment are sample and chamber
geometry, pressure, gas flow rate, and the electromagnetic force.

There are two types of plasma treatment: cold and hot plasma treatment.
The former treatment is carried at a low temperature and at a low pressure, while
the latter treatment is carried out at very high temperatures (5,000 - 10,000° K)
and at atmospheric pressure. Cold plasma treatment is used in micro-electronic
fabrication, which deals with plasma etching of inorganic substrates such as
silicon. Hot plasma treatment deals with hard or wear resistant coatings, which
involve melting an inorganic powder such as a ceramic and spraying the molten

substance on metal surfaces.

28

3.4 Corona discharge treatment (CDT)

Corona discharge treatment (CDT): It occurs in the electromagnetic field
between two electrodes, one of which is at a high potential and the other is
grounded. The treatment is carried out at atmospheric pressure, and at
relatively low temperature. The gases in the field are ionized yielding oxygen-
containing excited species which react with the polymer surface.

Several theories for the observed increased adhesion after CDT have
been proposed. The most important ones involve degradation, cross—linking,
oxidation, hydrogen bonding, ozonation, and electret formation.

The electret formation theory is contradictory to radical-based
degradation, oxidation, and hydrogen bonding concepts. Electret as an
electrical counterpart of a permanent magnet, by which the electrical potential is
caused, consists of different phenomena such as homocharges and
heterocharges. ( Kim et al. 1971)

Homocharges are developed from external polarization, which is affected
by the injection and subsequent trapping of charge carriers (electron from the
ionized air molecules), while heterocharges are developed from internal
polarization. The term ‘homocharges’ refers to the surface charge, which has
the same polarity as the electrodes.

lntemal polarization consists of atomic—, dipole-, barrier- and space-
charge polariziation, which results in net charges at the surface, with an

opposite polarity to that of the electrodes.(Stradal et al. 1975)

29

Electrons, protons, excited atoms and ions in the plasma of corona
discharge could cause carbon-to carbon and carbon to hydrogen bond breakage
on the polymer surface. (Satas,1986), resulting in the formation of free radicals.
The radicals formed are long-lived and can react with oxygen and/or nitrogen,
resulting in the introduction of polar groups on the polymer surface, thus making
it more easily wettable. Other changes also occur during the corona discharge
treatment. Low molecular weight material, which might be on the surface may
cross-link, and consequently modify the surface properties. For example, the
heat sealing temperature of the treated film is lower than the one without
treatment.(Blythe et al.1978) It has been proposed by Baszkin et al. (1976) that
the wettability of a treated polyethylene surface is decreased, if its temperature
was raised to 85°C. This can be explained by the redistribution of external
groups, due to incremental chain mobility at the temperature of testing. Some of
the lower molecular weight scission products, such. as various processing
additives, may migrate into the bulk polymer, therefore depriving the surface of
lower molecular weight polar materials.

The corona discharge treatment can be erased from the film by
contacting with a metallic surface. Therefore, contact of a corona treated
surface with metal should be avoided. The wetting tension of corona treatment
film may also change during storage. This change can be attributed to the
migration of low molecular weight compounds to the surface. This is illustrated
in Figure 3, where the wetting tension of a corona treated polyethylene surface

is plotted as a function of time following Corona treatment.

30

01
O
1

h
01
r

 

Wetting Tension - dynes [cm
a
O
r

 

L l l l l

o 5 10 15 20 25
Storage Time days

Figure 3 : Effect of storage after corona discharge treatment on the

wetting tension of a polyethylene surface.

Surface activation by corona discharge requires relatively simple
equipment, is easy to control, and yields uniform and reproducible results. The
process, which has considerable commercial importance, is shown schematically
in Figure 4. The equipment consists of a power supply that provides a high
voltage alternating potential to a sharp-edged electrode. A rotating metal drum,
maintained at ground potential, is located so that there is a narrow gap between
its surface and the edge of the electrode. The films are carried by the drum
through the gap, thus exposing its free surface to the electrical discharge.

An equivalent electrical circuit for the process is also shown in Figure 4.

It assumes that the plastic film is nonconducting, and thus introduces only

capacitance into the circuit. In its unionized state, the air in the gap is essentially

nonconducting, but when ions are present, an electric current can be carried

across the gap. The air, therefore, is represented as a capacitor and a
resistance in parallel, with one or the other predominating, depending upon the
condition of the air. Hence, before breakdown of the air (ionization), the
equivalent electrical circuit consists of two capacitors in series and, after
breakdown, of a capacitor and resistance in series.

Corona discharges, which are characterized by high voltages and low
currents, occur at atmospheric pressure when one of the electrodes has sharp
edges or points. The discharge begins when the electrode potential increases to
the point where partial ionization of the gas takes place. The gap becomes filled

with a pale violet glow, a hissing noise is heard, and the odor of ozone

 

.25—5.5;

CORONA 51 g
GENERATOR\ 3: 1? E

o- e

GLASS - ‘3
METAL 5

TUBE ROD L_ ‘4]:

 

 

 

 

METALLIC ROLL

 

E? FILM

Figure 4 : Apparatus for surface activation of plastic film by corona

discharge with equivalent electrical circuit.

32

can be detected. Bright blue streamers emerge from sharp points on the
electrode and terminate in the gap. If the plastic film were not present, or if it
should rupture so that the streamers could reach the other electrode, sparking
and then arcing would result, and the current would increase drastically.

The current in the corona discharge is carried by electrons and ions.
During the first half cycle, charged particles of the same polarity as the electrode
collect on the film surface. This reduces the effective field strength and thus
quenches the corona before the end of the half cycle. When the polarity of the
electrode changes, the oppositely charged particles now on the film surface
cause an increase in the gradient in the gap, and the corona starts at a lower
applied potential than in the initial half cycle. Therefore the plastic film has the
effect of enabling the discharge to be sustained at a lower applied potential. The
primary operating variables in the activation process are the 'voltage and
frequency. applied to the electrode, the distance between the electrode and the
1 film surface, and the linear speed of the film. The following kinetic analysis of
surface activation via corona discharge attempts to relate these variables to the
degree of activation of the film. The key assumptions in the analysis are
as follows :

l. Activation is due to the production of polar groups on the surface of the film.

2. Polar groups can be produced only at certain reactive sites on the surface of
the film.

3. The key step in the formation of a polar group is the collision of a charged

particle with a reactive site.

33

Leach and Pierce (1993) stated that good quality ink should remain on
the surface of the printed packages for as long as the paint’s lifespan. They add
that the adhesive properties of the ink depends upon its compatibility with the
vehicle system, the type of pigments and their percentage, as well as the
degree of dispersion in the final ink. Of the three, the vehicle system seems to
be the most influential factor in determining the ink's adhesive properties;
namely, the degree of vehicle penetration into an absorbent substrate and the
film-forming ability of the ink resin, with a molecular affinity for the substrate on
non-absorbent substrates. Thus, it is very crucial which type of ink resin should
be employed. There are two means by which the vehicle system has an
influence over the adhesion of an ink. That is, it produces wetting and flow-out
of ink, which provides a continuous film essential for good adhesion. Moreover,
the 'vehicle system is good for penetrating the substrate. The surface of
Poly(vinyl chloride) PVC, for example, can be softened, which causes chemical

and physical bonding.(Satas,1986)

34

Chapter 4

EXPERIMENTAL PROCEDURES

4.1 Methods of Contact Angle Measurement

The surface energy of non-treated and treated films was calculated from
the analysis of contact angle of the following liquids on polymer surfaces:
distilled water, formamide, di-iodomethane, and tricresyl phosphate. The values
of surface energy of the four liquids are shown in the Table 3.

Table 3 : Surface energy of liquids used in the experiment “"

 

 

 

 

 

 

Surface energy of the corresponding component (dynes/cm)
Liquids Dispersive Polar Total
Fonnamide 32.3 26.0 58.3
Distilled water 22.0 50.2 72.2
Di-iodomethane 48.5 2.3 50.8
Tn'cresyl phosphate 36.2 4.5 40.7

 

 

 

 

 

 

(a) Feast WJ. et.al. 1992. Polymer Surfaces and Interfaces 11. John Wileyd’cSons

4.1.1. Apparatus and materials used for contact angle measurements

A contact angle Goniometer (Model 100-00 115, Rama-Hart corporation,
Mountain Lake, New Jersey) was ,used to measure the contact angle of liquids
on polymer surfaces in this study. Apart from the Goniometer, contact angle

measurements required the following : glass slides, double-side adhesive tape,

35

the four contact angle liquids mentioned above, a pipette ‘Pipetman’ (0-200 pi),
and polymer test films.
Materials
. Film sample
Corona discharge treated high density polyethylene films (1.5 mil
thickness) obtained from Tredegar Film Products ( Richmond, Virginia) were
used in the present study. Treatment levels were 0, 1.8, 2.2, 2.6 and 3.0 Kw,
respectively.
. Liquids used in Contact angle measurement
Distilled water (Deionized grade)
Formamide CAs 75-12-7
(super pure grade 2 95 %)
Methylene Iodide, CA8 75-11-6
(purified grade)
Tricresyl Phosphate, CAs 1330-78-5
(technical grade : 80% para, 20% meta)

All above were supplied by Fisher Scientific (Fairlawn, N.J.07410)

4.1.2. Sample preparation for contact angle measurements

Pre-cleaned and air-dried films approximately 2 x 1 inch2 were mounted
very smoothly on a glass slide by using double adhesive tape. The sessile drop
method of measuring contact angles was used in this study, at ambient

atmosphere at room temperature. Droplets of 5~7 ul size were formed on the

36

polymer film surfaces delivered from a Pipetman ® pipet (0~200 III) in such a
way as to make the angles advance. A minimum of 12 contact angle
measurements were made to calculate the surface energy of the test polymer
film by the computer software program, as detailed in the appendices section.
Angles were read to the closest degree by using a 10 x microscope with a
protractor eyepiece. The procedure employed to measure the contact angle for

the respective film samples was as follows :

1. The polymer test film was mounted on top of the adhesive tape after a
piece of double-side adhesive tape had been placed on a glass slide of
2.5 x 1.25 inches. It is crucial that air bubbles be avoided from the space
between the laminates. Within 48 hours, the film sample will reach the
equilibrium state where the air will gradually disappear.

2.The microscope was focused on the nearest edge of the film surface
and the film surface and ‘base-line’ adjusted to achieve coincidence. This
setting was not changed during the reading of the contact angle. (See Figure 5)

3. A pipette was set to produce droplets of 5-7 III on polymer film samples,
depending on the test liquids, to form the droplets deposited onto the film as a
sessile drop of about 2.5 mm diameter with the Pipetman ® pipet (0~200 [.11). At
least 12 contact angle values for each liquid were measured within an error of 3

degrees. The contact angle values were then converted into surface energy

37

 

 

Sample specimen
ky"
Base fine
Specimen stage

m Sessile droplet of test liquid (5-7 pl )

..........

 

 

 

 

 

 

 

   
 

Glass slide (2.5m. x 1.25 in.)

 

 

 

—- Film specimen Double faced Adhesive tape

 

 

 

Figure 5 : The view from eyepiece Ien of Goniometer and sessile drop on sample

values of the polymer film, by the computerized software, as described in the
appendices.

4. After the glass slide with polymer sample was placed face-up on the
specimen stage of the Goniometer, the microscope was adjusted to aim at the
horizontal reference line in order to measure contact angle values.

5. The specimen stage was adjusted to be able to view the nearest edge
of the left angle of the sessile drop. The microscope, again, was reset by
shifting the cross hair line which it, at the beginning, would be perpendicular to

the base line when looked in the eyepiece lens, as shown in Figure 5.

38

 

lens microscope objectwe lens green filter

I 1 l specimen\stage I /

illuminator

  

..................................................................................

353'“? ....
..........
...............
.53.};

5.3.1. ......
.....

......

 

 

 

   

illuminator control

I

image focus knob cross-travel adjustor

 

 

 

 

*— optical bench

 

 

 

 

 

Figure 6 : Goniometer schematic (model 100-00 115, Rame-Hart, Inc.)

6. The measuring cross line was adjusted to tangency above the base of
the drop to create a wedge of light bounded by the two cross lines and the drop
profile.

7. The cross line was slowly rotated in order to measure it, while adjusting
the cross travel of the specimen stage so that the wedge of light would be
gradually extinguished and the cross-line would attain tangency with the drop
profile at the base of the drop.

8. At least 12 measurements of contact angle values were measured for
each liquid on the same samples which the process was repeated as above.

For water and fonnamide which have high surface tension, as they form
relatively large contact angles on the film, the contact angle readings were able
to be taken after 30 seconds. Meanwhile, the other two liquids
(i.e., di-iodomethane and tricresyl phosphate), which have low surface tension,
spread rapidly on the film. Therefore, the contact angle must be read as soon as

the droplets formed, within a 30 second period.

39

4.1.3. Calculation of surface energy of solid

The measured contact angle values on the film surfaces from the four
liquids were used to calculate surface free energies, and the corresponding
dispersion and polar components, according to the method of solving the
equations described by Park (1994).

The following equation, which describes the interaction of liquids with a
solid surface, was based on the geometric means of the force interactions and

the sum of the dispersive and polar terms.

1: (1+ COS 9) = 2 (17d 7i“)1m + 2 (7.” if)"2 [301

where y.“ and y." can be calculated by solving two equations which were
set up by contact angle measurements with four liquids of known surface tension
values. The least square method was used to obtain the best values of the
surface energy of the test solid.

A computer based program was developed by Park (1994) in order to
calculate the surface free energy of polymers with polar and dispersive
components and for providing a graphic representation of (y.d )" versus (y.P ) " 2
, where the four linear relationships are plotted using one of the simultaneous
equations given in the above equation. The procedure of Kaelble (1971) , using

the determinant method, and of Kinloch et al.(1991), using the least square

method, were fully detailed in the theoretical sections.

40

4.2 Application of Printing Ink
Materials and apparatus

a Film sample

Corona discharge treated high density polyethylene films (1.5 mil
thickness) obtained from Tredegar Film Products ( Richmond, Virginia) were
used in the present study. Treatment levels were 0, 1.8, 2.2, 2.6 and 3.0 Kw,
respectively.

. Printing inks

A B87DTM opaque white, flexographic printing ink, manufactured by Sun
Chemical Corporation, (Carlstadt New Jersey) and provided by Cellofoil film
lnc., (Battle creek, Michigan) was used in the present study.

The composition of the printed ink is as follows :

Ingredients [°/o by weight of total formula]

Solids components 50.3
Ethyl alcohol 22.8
n-propyl acetate 12.9
n-propyl alcohol 8.5
lsopropyl alcohol 5.4
MP naphtha 0.3
Total 100.0

. Anilox roller with a 2.5 inches bandwidth

41

1. Samples from the five film rolls were removed and were cut into pieces
of 12 x 5 inches each.

2. The external side of the film, which was treated by corona discharge at
4 different levels, were marked in order to differentiate it from the non-treated
side.

3. The cut pieces of film were placed on white paper, with the non-
treated facing the paper and they were attached together by an adhesive tape.

4. Multi B&D opaque white ink, contained in a disposable glass pipet,
was dropped on an Anilox roller with a 2.5 inches bandwidth. The ink was then
rolled onto the treated side of the cut film to provide a printed surface.

5. The film was then left to dry at room temperature for approximately 30
minutes.

6. After drying, the printed film samples were again cut into stripes of
(1.5 - 2) x 11 inches, which consisted of no stains or any other visible printing
flaws.

7. Each piece of the selected printed film was labeled to identify its level
of corona discharge treatment.

The entire process was repeated until acceptable results were obtained

for each film sample.

42

4.3 Sample preparation for the Peel Adhesion Test

1. The Scotch brand tape (No. 610) was placed on the printed surface of
a film sample of 1.5 to 2x 11 inches.

2. A rubber roller of 5.2 lbs. was used to apply the tape at a constant
pressure, so as to provide uniformity from sample to sample.

3. The printed sample film was then cut into a piece of 1 inch in width
and 11 inches in length.

4. The sample film was wrapped in aluminum foil and stored at ambient

temperature to be used within 48 hours.

4.4 Peel Adhesion Test

Traditionally, the peel adhesion test is conducted manually, with no
standardized methods. In the present study, the test procedures were designed
to be more scientifically oriented and standardized. Namely, the terms and
procedures employed in the present study were based upon the ASTM
standards. The ASTM standard methods modified for application in this study
are as follows:
ASTM D 3359-93 Standard test method for measuring adhesion by tape test
ASTM D 897-78 Standard test method for Tensile properties of adhesive bonds
ASTM D 1876-93 Standard test method for Peel resistance of adhesives

(T-Peel test)

ASTM D 903-93 Standard test method for Peel or stripping strength of adhesive

bonds

43

ASTM 02979-88 Standard test method for Pressure-sensitive tack of adhesives
using an Inverted probe machine.

One of the objectives of the study was to assess the relationship between
changes in surface energies of the film and ink adhesion, in order to evaluate
the effects of surface modification of polyolefin films on the films printability.
The test methods employed were designed to determine the adhering ability of
an ink coatings, to a film substrate, by using pressure-sensitive adhesive tape,
under a specific set of test conditions. The test for untreated film is employed as
a control.

Apparatus 8. Test specimen

oTensile Testing Machine -lnstron Universal Tensile tester model SFM-
20, (United Calibration Corporation, Huntington Beach, California).

A power-driven machine, with a constant rate-of-jaw separation which shall have
the following features :

- The applied tension, as measured and recorded, should be accurate within one
percentage.

- Specimens shall be held in the testing machine by grips which clamp firmly
and prevent slipping during the test.

- The rate of travel of the power-actuated grip shall be uniform throughout the
tests. In this study, a crosshead speed of 20 inch per minute was used for each
samples tested.

- The machine shall be autographic giving a chart having the distance of

separation as one axis and the applied load as the other axis of coordinates.

44

A 500 gram load cell was employed to utilize the sensitivity of the
machine during test and to make possible the measurement of the force with
minimal fluctuations during the test. The test system was operated by using a
computer controlled system ( United Calibration Corporation) at the Composite
Material and Structure Center (CMSC), MSU.

. Polyethylene film samples were coated with printing ink and cut into
strips of the size of 1.5 x 11.0 inch

oTape test - Scotch tape No.610 ® (TM of 3 M Products, St.Paul,
Minnesota)

Conditioning

Test condition at room atmosphere (23 i 2 °C and 50 i 5 % R.H.). Prior
to tastings an alignment check was made by placing the provided metal plate
between the upper and lower jaws to insure that the tension is uniform and
symmetrical.

4.5 Method for Measuring Printing ink Adhesion by Peel Test

The tensile machine used in the test was initially standardized with a 500
gram load cell and programmed by a computer to run at a rate of 20 inches per
minute.

A length of 1 inch from one end of the adhesive tape was attached to the
upper clamp jaw and a 1 inch length from the same end of the sample film was
attached to the lower clamp jaw. The substrates were then thoroughly separated
by the clamp jaws. A schematic diagram of the test apparatus is presented in

Figure 7. The sample -tape composite for testing ink adhesion is shown as well.

45

 

Upper Grip

I].

f<— Test Specimen

      
 

 

 

 

Figure 7 : Peel Testing Apparatus scheme

When the tape was peeled from the sample film, the differences between
the extension(%) and the load (grns) as a function of different corona treatment
levels were recorded. The peeled area was observed to determine the degree
of ink adhesion. The ink on the film which was treated at a higher corona
treatment levels was expected to show a lesser degree of peeling from the film
surface, than from film exposed to lower treatment levels.

The load, which measures the force of peeling the tape from the film, was
recorded. An autographic plot of the load (lbs) and extension of peeled distance
was obtained.

The appearance of the ink coated film surface was observed and the

condition of the surface recorded. For further analysis, the ink-stained tapes

46

and the ink-peeled film samples were stored in resealable bags, for further

analysis with the application of the SPEC * SCAN 2000 system.

4.6 Quantitative measurement of the peeled areas of the sample film

In this study, the SPEC*SCAN 2000 system, (Apogee Systems), which is
a pulp & paper gray scale visual impact dirt counting system, was adapted for
use with polymer film. It should be noted that the SPEC*SCAN 2000 system is
normally used for dirt and fiber content analysis of the pulp and paper, based
upon the TAPPI T 437 om-90 standard developed by Apogee Systems, Inc.
These measurements were conducted at the Department of Pulp and Paper
Science, Western Michigan University, Kalamazoo, Michigan.

The SPEC*SCAN 2000 system is computerized with a high resolution flat
bed image scanner. It operates on the SPEC*SCAN 2000 software supplied by
Apogee Systems, Incorporated.

For analysis, the peeled film was placed on the scanner, covered with
black paper simulating dirt, and the area of grayness (the peeled area) was then
scanned and quantified by the apparatus. The peeled area was determined in
square millimeter (sq. mm) and then converted in proportion to the total printed
area of 1x10 sq. in (6451.6 sq. mm). The calculated data was reported in
tabular form. The results of the measurement of the peeled areas of the
respective test films were compared with one another, in terms of the different

levels of corona treatment film.

47

Definition of terms used

Pressure-sensitive adhesive - a viscoelastic material which in solvent-
free form remains permanently tacky. Such material will adhere instantaneously
to most solid surfaces with the application of very slight pressure. (Refer to
Scotch brand TM number 610)

Flexible — indicates a material of the proper flexural strength and
thickness to permit a turn back at an appropriate 180° angle in the expected

loading range of the test without failure.

48

4.7 ESCA Analysis

The surface composition of the films was determined by Electron
Spectroscopy for Chemical Analysis (ESCA), using a Perkin-Elmer PMI model
5400 system with a standard Magnesium source ( Ka l, 2 ) operated with 1253
Ev at 300 w 15 Kv, 20 mA at the Composite Materials and Structure Center
(CMSC) MSU. The instrument employed a 180°hemispherical energy analyzer
operated in the fixed analyzer transmission mode at a pass energy of 89.75eV
and a position sensitive detector for signal collection. Spectra were collected
using an analysis area of 3x lOmm. Spectra were collected using a 45 ° take off
angle between the sample and the analyzer lens. Survey spectra were collected
for each of the samples to identify elements present and surface atomic
concentration was calculated.

In the ESCA experiment, identification of elements and their compounds
is based on peak position, expressed as binding energy, and peak shape. When
only one type of bonding is present, the peak shape will be symmetrical. For
multiple types of bonds it is possible to see asymmetric peak shapes due to
differing binding energies leading to overlapping peaks.

Error in quantitative results from the ESCA experiment has been generally
accepted to be within ten percent for survey analyses and within five percent for
high resolution work.

Quantitation in the ESCA experiment is described as surface atomic
concentration. For example, if a sample is composed of 57% sulfur, 6% oxygen

and 37% carbon this is interpreted as: for a surface consisting of 100 atoms, 57

49

are sulfur, 6 are oxygen and 37 are carbon atoms. The limits of detection for the
ESCA experiment are generally accepted to be more than 0.2%.

Surface atomic concentrations are calculated using sensitivity factors.
These factors include instrumental factors and the photoelectron cross section
for each element. X-ray photoelectron spectroscopy is very sensitive to fluorine,
which has a large photoelectron cross section. In the Perkin-Elmer PHI XPS
spectrometers, the sensitivity factor of fluorine is set equal to one and all other
factors are scaled accordingly. Surface atomic concentrations are calculated by
the following equation:

C X: surface atomic concentration of a given element, where there are i elements
I x = area of the given element's peak in the ESCA spectrum

8 ,7 = sensitivity factor of a given element

0.: I,/s, [31]
2 Il [Si

50

Chapter 5

RESULTS AND DISCUSSION

5.1 Contact angle measurements

A Rama-Hart Goniometer model 100-00-115 was employed to measure
the contact angles of liquids with weak polar properties, such as di-iodomethane
and tricresylphosphate and those with strong polar properties, such as
formamide and distilled water, on solid surfaces. The results of the
measurement of the contact angles of the test liquids on high density
polyethylene films which were treated at different levels of corona discharge are
summarized in Table 4. The results of the non-treated HDPE film are also
summarized for comparison. For better illustration, the results are presented
graphically in Figure 7, where histograms of the contact angles measured for the
respective HDPE film samples are given.

As shown, significant changes in the contact angle values of the probe
liquids were observed for the HDPE film following corona treatment. For the test
liquids with strong polar properties, the contact angle values showed a continual
decrease with increased corona treatment time, while for the test liquids with
weak polar properties, the contact angle values appeared to be fairy constant
following the 1.8 kw treatment condition. This implies that the polar component
of the surface free energy increases incrementally with the treatment level, while
the dispersive surface free energy component showed no significant change with

corona treatment level.

51

Table 4 : Contact angle values obtained for Corona discharge
treated HDPE film samples

 

Contact Angle Measurement, average mean (degrees) (*1

 

 

 

 

 

 

 

 

 

 

 

Samples
Distilled water Formamide Di- Tricresyl

Iodomethane Phosphate
Non-treated 89.00:2.0 67.00:1.0 46.00:].0 34.50: 1.5
P-1.8 R 66.00: 1.0 50.00:].0 27.00:1.0 23.00: 1.0
P-2.2 k 60.00: 1.0 44.00:1.0 29.50:2.0 15.00:1.0
P-2.6 I: 55.50: 1.5 43.50:O.5 29.50:1.5 15.50: 1.5
P-3.0 k 54.00: 1.0 39.00:1.0 27.50:2.5 20.00:2.0

 

(a) Averaged values of at least 10 different measurements, performed on different positions of the sample

surface.

52

 

 

 

 
   
     

;.;.;,-,-.;,;.;.;.3.; r” ::

......
...............

W

 

 

 

Ki*Ii-I'iii-Ll-I’I-I-L'I‘I

..............................

\‘

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

888889“

seaasfiap ‘ejfiuv petuoo

P-2.6 It P-3.0 k

P-2.2 k
Level of treatment (kw)

P-1.8 k

Non-treated

LU Distilled water Cl Formamide B Di-lodomethane I Tricresyl Phosphate I

 

 

 

 

53

Figure 8 : Contact angle measurement of the corona treated film using different liquids

5.2 Surface free energy of film samples

Surface free energies and their corresponding polar and dispersive
components were calculated using a Microsoft Excel software program together
with “The least square method” adapted by Park (1994).

The polarity, defined as the ratio of the polar component to the total surface
free energy (7 .Pl 7.7 ) was also determined (Wu, 1982). The results of surface
free energy determinations are summarized in Table 5, which provides a
comparison of the surface free energy values of the untreated and corona treated

film samples.

Table 5 : Surface Free Energy of Corona Discharge Treated HDPE film

 

 

 

 

 

 

 

SURFACE FREE ENERGY OF FILMS Polarity
(dyne / cm)

Samples Dispersive component Polar component Total (°/o percent)
Non-treated 33.1879 2.0860 , 35.2739 5.9137
P-1.8 k 33.3725 9.7337 43.1063 22.580
P-2.2 k 32.0673 13.7144 45.7817 29.956
P-2.6 1: 30.7980 16.0161 46.8141 34.212
P-3.0 k 30.0632 17.8541 47.9172 37.260

 

 

 

 

 

 

 

For better illustration the results are presented graphically in Figure 9,
where histograms of the surface free energy and the associated polar and

dispersive components, determined for the respective HDPE film samples, are

54

given. The effect of corona treatment level on the polar, dispersive and total

surface free energy values is also presented graphically in Figure 10, where the

respective surface free energy values are plotted as a function of corona

discharge level.

As shown, the observed increase in the values of the total surface free

energies for the corona treated HDPE films can be attributed to the increased

contribution of the polar component.

 

 

 

 

 

 

.5225! 3.2.0 on... neat—6

Level of treatment (kw)

[- Dispersive Component I Polar Component ITotall

 

 

 

 

Figure 9 : Effect of corona treatment level on the polar, dispersive and total

surface free energy values

55

>965 center. .33 65 can mucocanoo noucoamotoe 65 c3252. 35:23.61 0 9.. 2:9...

 

 

regs IOI Eugen—=60 ..Eom 1.11 32.2339 ethonua .1ng

 

93. v 2253.... been—.200 Co .05..
m ON N.N

  

 

 

S.

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3......

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on.

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w...

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5

 

 

 

 

 

 

 

 

 

5.3 Ink Adhesion

The results obtained from the SPEC*SCAN 2000 system used in this
study showed that the ink on the tested areas of the non-treated polymers was
totally or nearly completely peeled from the film, while the ink applied to the
corona treated polymers showed significantly less transfer to the adhesive tape
surface, at all levels of treatment. The area percent peeled, ranged from
approximately 98 % for the untreated film to less than 2 % for the high corona

treatment (3 KW), as illustrated in Table 6.

Table 6 : The area percent of ink peeled as a function of corona
treatment level.

 

 

 

 

 

 

 

 

 

 

 

 

SAMPLE # UNTREATED P-1.8 KW P-2.2 KW P-2.6 KW 113.0 KW
1 97.09 27.62 9.09 6.89 1.12
2 97.78 24.43 14.74 7.04 2.89
3 96.35 21.15 12.71 4.94 0.25
4 95.61 26.34 12.48 5.06 2.14
5 98.82 23.74 15.04 5.87 2.56
6 99.11 23.13 12.59 4.33 1.87
7 98.44 24.07 15.27 6.28 0.83
8 96.79 20.61 14.11 4.65 2.03
9 98.53 26.82 13.12 6.52 0.47
Average 97.61 24.21 13.24 5.73 1.57
SD. 1.2149 2.4175 1.9002 1.0129 0.9388

 

 

 

 

 

 

 

 

57

Thus, showing that corona treatment of polyolefin polymers is a significant aid

for enhancement of ink adhesion.

 

Ink Printed

 

Peel area afler tape test

Test Specimen ( 11 " x 2 " )

 

 

 

Figure 11 : The illustration of printed specimen after peel test

As shown in Figure 11, where the image of the printed film sample is
displayed, a portion of the ink coating was removed by the peel test. By using
this modified ink adhesion technique, as previously described, the area
percent of the ink surface which was peeled away can be described as being a
portion of the total area of the printed ink surface. However, it is necessary to
point out here that, according to the data in Table 6, the values of the peeled
areas, measured on a percentage basis, were based on an approximation
scale. Here the peeled area percent is calculated using some type of grid or a
small rectangular area and the numerical area percent values are averaged.

Thus, the peeled area adjacent to both sides of these regions would be

58

difficult to interpret. As a result, an error from this procedure still exists, due to
the reading limitation of the software. In terms of practical use in industry, the
ink peel test is typically evaluated by a single, visual inspection. This might
somehow affect the ability to differentiation between the treatments even at
different treatment levels.

Based on the result of the highest corona treatment level (3.0 kw)
evaluated in this study, which had the least peeled area (1.57%), it can be
assumed that if such polymers had been treated at a higher level that the
peeled area may have been further diminished or even showed no ink peel.
Therefore, the plot of the percentage of the peel area versus the level of
treatment can be seen, as shown in Figure 12. Typical results indicated that
the film without treatment showed little or no ink adhesion and thus gave the
highest percentage value of the ink peeled. Further, test films with the higher
levels of corona treatment showed the least amount of the ink, which was
peeled away. At the highest level of the treatment, there is such a minimal
amount of ink peeled that only one percent of ink coating was peeled from the
substrate when tested.

By using a tensile testing procedure, the data for the peel test were
recorded graphically in a manner typical of tensile testing curves. The peeled
area on the sample was generated during this process. In practice, the upper
grip of the tensile tester held the sample and the lower grip held the tape
specimen affixed to the printed surface. However, the results did not represent

a satisfactory level of agreement and many fluctuations occurred during the

59

testing. The force of adhesion, therefore, could not be calculated accurately
due to the significant level of error. Thus, this study employed the peeling
procedure only to create the peeled area, which provided samples for
quantitative measurement, using the modification technique for the

SPEC*SCAN 2000.

 

 

Percentage of the Peel area (%)

 

 

 

 

Level of treatment (kw)

 

 

 

Figure 12 : The relationship between the level of treatment and

the percentage of the area which was peeled off

60

5.4 The results of ESCA survey method analysis

Operating the photoelectron spectrophotometer with a wide scan and
low resolution allows for the identification of elements at the polymer surface.
Quantitative analysis of the amount present for each element is 4; 5-10%. No
chemical state information is available, due to low resolution of the seen.

A high resolution scan with a narrow window and better resolution
allows employment of peak position, along with the shape of the peak to
determine chemical state information from the sample surfaces. Curve fitting
can be done where peaks are fitted under the spectral envelopes to interpret
. data as different functional groups presented.

When comparing the ESCA analysis of corona treated polyethylene
treated at 3.0 versus 1.8 kw, there were no significant differences in either
surfaces within experimental errors for C 89 i 1% and O 11: 1%, as shown
in Table 7.

Only a high resolution scan can indicate whether there are differences
in the chemical state of the treated polyethylene at 3.0 versus 1.8 kw corona
discharge treatment. The 0 1s and C 13 peak shapes and position are
similar. Therefore, there appears to be no significance difference between the
two sample treatments with respect to surface atomic composition.

The C 15 peak shape indicates the surface of PE film has been
oxidized. Non-oxidized C 1s peaks are very symmetric. There are no
shoulders to the higher binding energy side indicating oxidation had occurred

and also the absence of any other atoms such as nitrogen and sulfur. Curve

61

fitting could provide a better idea on group functionality, however an initial
survey of the data indicates oxidation, probably C-O ( could be C-O-C or C-O-
H ) When oxides are present, for example, the C-0 bond , the binding energy
will shift + 1.5 eV from 285.0 eV to C-0 at 286.5 eV as compared to 288.0 eV

for the C=O group.

Table 7 : ESCA determination for the surface compositions of the film sample at

variable exposure levels of the corona treatment.

 

 

 

 

 

 

 

Percentage Atomic Concentration (a) 7 (Cl

Sample Corona treated C O
. 09”) CM (%)

Non-treated 0.0 100.0 0.0
P-1.8 1.8 90.04 9.96
P-2.2 2.2 89.55 10.45
P-2.6 2.6 88.0 12.0

P-3.0 3.0 87.0 12.0 0’)

 

 

 

 

 

 

(a) Averaged values of at least 3 measurements, performed on different positions of the
sample.

(b) ESCA survey found other possible elements e. g. Si on sample surface
(c) This interpretation of the ESCA data was edited from the comments and opinion of

Dr.Cara L.Weitzsacker at CMSC, Michigan State University

62

Summag 8. Conclusion

Polyethylene is a saturated hydrocarbon structure, of the class of
polymer called polyolefins. Like other saturated hydrocarbon substances, it
has very low polarity and very low reactivity. lts surface wetting tension is low,
approximately 30 dynes I cm. This inertness implied that wetting and adhesion
of inks will not occur unless the surface is activated.

It has been demonstrated that the level of corona treatment depends on
the power applied in the air gap and perhaps the machine speed, as well as
wattage, unit area and unit time. At the highest treatment level for the test
films, this study has shown that the total surface free energy was comprised
primarily of the polar component of the total surface free energy. This result
was confirmed by the ink peel area test. The printed ink area remained
sustainable on the corona treated films after the peel tape test. Whereas the
non-treated sample showed nearly total removal of the printed ink from the
polymer surface. The amount of ink which was removed by the peel test was
quantitatively evaluated by using a modification of the SPEC*SCAN 2000
technique and the test procedure developed. As a result, the percentage of ink
peeled from the film surface could be estimated more accurately than by the
more traditional method typically employed. It was found that the film exposed
to the highest level of corona treatment showed the least amount of the ink

peeled from its surface i.e.1.57 % As the corona treatment level was reduced,

63

the results showed that increasingly higher percentages of the printed surface
were peeled from the polyethylene film.

Analysis of the film surfaces using the ESCA technique was ineffective
in determining chemical changes of the substrate with respect to surface
functionality. It did show, however that the surface was oxidized as a result of

corona treatment.

64

APPENDIX A

Samples of calculation program used to

determine the

Surface free energy of the film samples

65

Water

90.0000
89.0000
90.0000
88.0000
87.0000
90.0000
89.0000
88.0000
87.0000
90.0000

0.0000
0.0175
0.0000
0.0349
0.0523
0.0000
0.0175
0.0349
0.0523
0.0000

1.4051
0.7292

F
68.0000
67.0000
67.0000
66.0000
68.0000
68.0000
68.0000
67.0000
66.0000
67.0000

0.3746
0.3907
0.3907
0.4067
0.3746
0.3746
0.3746
0.3907
0.4067
0.3907

1.4071
0.7347

D
45.0000
46.0000
45.0000
47.0000
47.0000
46.0000
47.0000
47.0000
45.0000
46.0000

0.7071
0.6947
0.7071
0.6820
0.6820
0.6947
0.6820
0.6820
0.7071
0.6947

1.0000 1.3746 1.7071
1.0175 1.3907 1.6947
1.0000 1.3907 1.7071
1 .0349 1 .4067 1.6820
1 .0523 1.3746 1.6820
1 .0000 1.3746 1 .6947
1.0175 1.3746 1.6820
1.0349 1.3907 1.6820
1.0523 1 .4067 1 .7071
1.0000 1.3907 1.6947
(Step 4 : Product of transpose matrix from step 3)
1.0000 1.0175 1.0000
1.3746 1.3907 1.3907
1.7071 1.6947 1.7071
1 .8290 1.8290 1 .8290

1.4083
0.7321

66

p
34.0000
34.0000
34.0000
35.0000
36.0000
35.0000
34.0000
36.0000
34.0000
36.0000

(Step 2: Convert step 1 data to be a product of cosine as below)

0.8290
0.8290
0.8290
0.8192
0.8090
0.8192
0.8290
0.8090
0.8290
0.8090

(Step 3 : Product of addition of 1+ cosine from step 2)

1 .8290
1 .8290
1 .8290
1 .8192
1 .8090
1 .8192
1 .8290
1 .8090
1 .8290
1 .8090

1.0349
1.4067
1.6820
1.8192

(Step 5 : Product of Mutiplication of Matrix of step 3.1 8 step 4)

1.4061
0.7392

(Step 1: List all measurements of contact angles taken from film samples)

1 .0523
1 .3746
1 .6820
1.8090

1.3990
0.7359

1.0175
1.3746
1.6820
1.8290

1.4005
0.7312

5.7589
1.4135

5.7842
1 .4241

1 .0349
1 .3907
1 .6820
1 .8090

1 .3999
0.7353

5.6872
1.5547

5.8406
1.3201

1.0523
1.4067
1.7071
1.8290

1.4181
0.7451

(Step 6 : The result of surface energy as shown)

5.7568
1.5834

5.7020
1 .5821

67

(Step 4 : Product of transpose matrix from step 3) <continued>

1 .0000
1 .3907
1 .6947
1 .8090

(Step 5 : Product of Mutiplication of Matrix of step 3.1 8 step 4) <continued>

1 .3989
0.7292

5.7703
1 .3759

5.6666
1.5881

(Step 1.1 : List the SFE of liquids used for calculation )

Dispersion Polar Total
21.8000 51.0000 72.8000 W
32.3000 26.0000 58.3000 F
48.5000 2.3000 50.8000 D
36.2000 4.5000 40.7000 P

(Step 2.1: Product of 2 X sq.root of each component by total SFE "A")

Dispersion Polar
0.1283 0.1962
0.1950 0.1749
0.2742 0.0597
0.2957 0.1042

(Step 3.1 : Transpose number of step 2.1 "A' ")
0.1283 0.1950 0.2742 0.2957
0.1962 0.1749 0.0597 0.1042

(Step 3.2 : Product of A'*A)
0.2171 0.1065 1.0000 0.0000
0.1065 0.0835 0.0000 1.0000

[Step 3.3 Product of inversion of (A"A) ]
12.2920 -15.6681 0.2171 0.1065
-15.6681 31.9444 0.1065 0.0835

68

APPENDIX B

Samples of the analysis data
from the
Electron Spectroscopy for Chemical Analysis

(ESCA)

69

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ed

3/(3)N

72

APPENDIX C

Samples of original data
obtained from

the SPEC * SCAN 2000 system

73

 

 

 

... 11111 1111. 1111
11111

111111 ’ 111 11.

111111111 1 1111111. 1111111111111 111111111
:21

111 11 11 111
1 111111 11
1111.111 1.

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111 111
111111 111 1111111 1111 1111 11111 1111

D 2 1111111
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77

BIBLIOGRAPHY

78

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83

 

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