THE USE OF PLASTlCS IN WOOD FURNITURE Thesis for the Degree of M. S. MlCHlGAN STATE UNIVERSITY CHING YUNG CHIANG 1975 ‘0 IBESlS I by g“ .1 (FT. ' ABSTRACT THE USE OF PLASTICS IN WOOD FURNITURE BY Ching Yung Chiang This study tries to analyze the acceptance of plastics in the furniture industry in the United States and tries to find possibilities for similar developments acceptable to the Taiwanese furniture industry. Analyses on the furniture industries of these two countries shows that there exists similarity and difference; rising labor costs, rising purchasing power and sophisticated domestic markets are the similar characteristics, but the size of the factory, the mechanization of the furniture industry and the customer's taste are the differences. The study also reveals that the Taiwanese furniture industry can not only strengthen its aggressive exportation but also can improve its position in the domestic market. The basic chemistry of plastics is discussed with particular emphasis on: (1) molding plastics: polystyrenes, (2) casting plastics: polyurethanes and polyesters, (3) mold-making plastics: silicones, and "(4) laminating plastics: polyvinyls, phenolics and melamines. The processes of manufacturing decorative or structural items for furniture are presented in such a way that detailed discussions are limited to the most frequently used methods and materials; injection Ching Yung Chiang molding of polystyrenes and flexible RTV silicone rubber mold casting of polyurethanes and polyesters. Various laminating processes are also discussed. The manufacture of intricate, ornate, whole wood furniture for export markets, the use of wood—grained cast plastic parts, wood- grained, laminated furniture panels on particleboard core stock for domestic markets are recommended to the furniture industry in Taiwan. THE USE OF PLASTICS IN WOOD FURNITURE By Ching Yung Chiang A THESIS Submitted to Michigan State University in partial fulfillment of the requirements for the degree of MASTER OF SCIENCE DEPARTMENT OF FORESTRY 1975 ACKNOWLEDGMENTS The author wishes to express his deepest appreciation to Dr. Otto Suchsland, of the Department of Forestry, not only for his guidance in the construction of this thesis but also for his help with which the author is able to continue and finish his academic study. Thanks and appreciation also go to the author's wife, Chin Mei Tsai, for her continuous encouragement and patience while the author is far away from her, and for the author not being available to the many things that a growing family requests and needs. 11 AcmOWIIEDGMT S O 0 O O O O O O O O O O O O O 0 LIST OF TABLE S I O O I O O O O O O O O O O O O O O 0 LIST OF FIGURES. . . . . . . . . . . . . TABLE OF CONTENTS CHAPTER 1. 2. 4. INTRODUCTION . . . . . . . . . . . . . . . . . . PROFILE OF THE FURNITURE INDUSTRY AND INNOVATION WITH PLASTICS IN THE UNITED STATES. . . . . . . . . . . . . l) The Characteristics of the Furniture Industry. . . 2) Innovation with Plastics . . . . . . . . . . . . . a) Product Performance. . . . . . . . . . . . . . b) Product Processing . . . . . . . . . . . . . . c) Product Cost . . . . . . . . . . . . . . . . . 3) The Bright Future. . . . . . . . . . . . . . . . . BASIC CHEMISTRY OF PLASTICS. . . . . . . . . . l) Polymerization Reactions . . . . . . . . . . . . . a) Addition Polymerization. . . . . . . . . . . . (1) Initiation. . . . . . . . . . . . . . . . (2) Propagation . . . . . . . . . . . . . . . (3) Termination . . . . . . . . . . . . . . . (4) Molecular Weight. . . . . . . . . . . . . b) Condensation Polymerization. . . . . . . . . . c) Rearrangement Polymerication . . . . . . . . . 2) Termoplastics Versus Thermosets. . . . . . . . . . 3) Copolymers . . . . . . . . . . . . . . . . . . . . 4) Common Plastics in Wood Furniture. . . . . . . . . a) Polystyrenes . . . . . . . . . . . . . . . . . b) Polyurethanes. . . . . . . . . . . . . . . . . c) Polyesters . . . . . . . . . . . . . . . . . . d) Silicones. .‘. . . . . . . . . . . . . . . . . e) Polyvinyls . . . . . . . . . . . . . . . . . . f) Phenolics and Melamines. . . . . . . . . . . . PROCESSING O O O O O O O O O O O O O O O O O 0 iii PAGE ii vi vii 11 13 13 13 18 18 18 19 19 19 20 20 21 21 22 23 23 25 26 28 29 30 32 1) a) C) 2) a) b) e) 3) 4) a) b) e) d) e) f) s) COATING. 1) 2) 3) 4) FURNITURE INDUSTRY IN TAIWAN 1) 2) TABLE OF CONTENTS CONTINUED Injection Molding. . . . MOIdS. O O O I O O O b) MOld Making 0 O O O 0 Casting. . . Molding Process. . . iv Advantages and Disadvantages M01d Making 0 O O O C (1) Materials for Mold Making (2) Model . . . . . (3) Mold Fabrication. (4) Extending Mold Life . . . . . . Casting Polyurethanes and Polyesters Rotational Molding . . . Finishing Molded Parts . Barrier Coat . . . . Stains and Toners. . Filler . . . . . . . Sealer . . . . . . . Pigment Stains and Glaze Topcoating . . . . . Finishing Polyurethane and Polyester' St Roller Coating . . . . . . . . . Embossing and Printing The Film. Low Pressure Laminating. . . . . a) b) e) The Paper. (1) Overlay Paper . . . . . . (2) Pattern Sheet (Decorative (3) Bonding Kraft (Barrier Paper) . . . . (4) Balancing Paper Impregnation . . . . Press. . . . . . . . Vinyl Laminating . . . . Status Of Taiwan Furniture a) The High Growth Rate Industry. . b) A Further Study On The Furniture Potential Market In Domestic Consumption ,a) Disposable Annual Income . . . . . . Structure In Taiwan. ains. Pa Industry. b) Residential Construction . . . . d) Social Attitude. . . per Industry c) Number of Newly Married Couples. . . PAGE 32 33 33 35 39 40 4O 4O 41 41 43 44 45 48 49 50 51 51 51 51 51 53 53 56 56 57 57 57 S7 58 58 58 6O 63 63 63 65 67 69 69 69 71 TABLE OF CONTENTS CONTINUED 3) Foreign Market Analysis. . . . . . . . . . . . . a) Growth Of Export Market. . . . . . . . . . . b) Export Of Labor. . . . . . . . . . . . . . . 4) Recommendations. . . . . . . . . . . . . . . . . Products For Foreign Markets . . . . . . . . b) Products For Domestic Markets. . . . . . . . a) (1) (2) (3) 7. CONCLUSIONS. REFERENCES WOod-Grained Cast Plastic Parts . .'. . Wood-Grained Laminated Furniture Panels . Part1¢1€board o o o o o o o o o o o o o O O O O O O O O O O 0 O O O O 0 O O O 0 PAGE 71 71 71 74 76 77 77 77 78 80 82 TABLE 10. 11. 12. 13. 14. 15. 16. 17. 18. LIST OF TABLES Household Furniture - U.S. General Statistics, By Employment Size of Establishment: 1972. . . . . . . 1974 Profile, Household Furniture. . . . . . . . . . FMM Survey Showing Use of Plastics in Furniture. . . Plastic Consumption Characteristics by Furniture Manufacturers Based on Plant Size. . . . . . . . . . Plastics In Furniture. . . . . . . . . . . . . . . . Properties of WOod and Plastics. . . . . . . . . . . Household Furniture: Trends and Projections 1967-75 Properties of Polystyrene and Polyester. . . . . . . Estimated Annual Growth of Manufacturing Industries In Taiwan 0 O O O O O O O O O O O O O O O O O O O O 0 Size of Factory Based on Number of Employees in Furniture Industry of Taiwan (1970). . . . . . . . . Logs Imported into Taiwan. . . . . . . . . . . . . . Product Cost Analysis Of Some Furniture Items Manufactured In Taiwan. . . . . . . . . . . . . . . . . . . . . . Residential Construction In Taiwan . . . . . . . . . Number of Annual Married Couples in Taiwan . . . . . wood Products Exported From Taiwan . . . . . . . . . Export Countries For Taiwanese Furniture . . . . . . Average Mbnthly wages In The Furniture Industry Of T a iwan O O O O O O O O O O O O O O O O O O O O O O 0 Furniture Items Exported From Taiwan . . . . . . . . vi PAGE 10 11 12 14 17 24 64 65 66 68 7O 7O 72 73 73 75 FIGURE LIST OF FIGURES Growth of Furniture Shipments Parallels Disposable Income 0 O O O O O O O O O O O O O O C O O O O O O O Single-Stage Screw Type Plastic Injection Molding MaChine O I O O I O O O O O O O O O O O O O O O O O O O O In the Reciprocating Screw Cylinder, The Material Is Plasticated by the Screw While The Later Moves Backward in the Cylinder; For Injection, The Screw MOves Forward, Acting as a Ram. . . . . . . . . . . . . . . . . . . . . A Multiple-Spindle, or Carousel-Type Rotational Molding Machine. Each Spindle Carries a Group of Molds or a Single Large Mold Through Heating and Cooling Enclosures Prior to Loading and Unloading of the Mold . . . . . . . The Three-Roll Reverse-Roll Coater . . . . . . . . . . . Temperature and Pressure Diagram of a 12-0pening Particleboard Laminating Press . . . . . . . . . . . . . Build-Up of One Board per Opening. . . . . . . . . . . . Typical Direct Roll Coating System for Application of v1ny1 Film to PartiCIeboard O O O O O O O O I O O O O O 0 vii PAGE 15 36 38 47 54 59 61 62 1. INTRODUCTION (4) (7) Plastics is the name of a family of synthetic materials which have large molecules made up of chains of atoms. The official defini- tion of plastics accepted by the Society of Plastic Engineers (SPE) and the Society of the Plastics Industry (SP1) is "a large and varied group of materials which consist of or contain as an essential ingredient a substance of high molecular weight which, while solid in the finished state, at some stage of its manufacture is soft enough to be formed into various shapes -- most usually through the application (either singly or together) of heat and pressure." Natural rubber was one of the first materials to be considered moldable plastic. In 1839, Charles Goodyear mixed the masticated raw rubber with sulphur and found that he could vulcanize the rubber into its final shape by heating it in the mold. In 1846, Dr. Friedrich Schonbein found that he could convert the cellulose in wood and other plant products into a clear tough, horny material by treating it with nitric acid. Schanbein's nitrocellulose became the basis of our modern plastics industry. In 1862, Alexander Parkes found that he could dissolve nitrocell- ulose in molten camphor. As the solution cooled, it passed through a putty-like plastic stage during which it could be molded. Then it set a flexible horny material. In 1897, W. Krische and Adolf Spittler discovered that casein could be waterproofed and hardened by treating it with formaldehyde. 'With this discovery they had laid the foundation to the casein plastics industry. In 1909, Dr. Leo Henrik Baekeland had found that the product formed from phenol and formaldehyde was a resinous substance. It was- the first synthetic plastic. Rubber was a natural resinous substance obtained from a tree; celluloid had been based on cellulose, a plant product. Casein was an animal material obtained from milk. But Bakelite, named after Baekeland, was different. This time, the chemist had made his plastic from the simplest of raw materials in the form of coal tar chemicals. With the discovery of Bakelite, plastics became a part of organic chemistry and'the possibility of making other materials with this property of plasticity, thus, had been stimulated. Within a short time, the study of plastic materials was to become a complex and specialized branch of scientific research. Although its foundations were laid in the 1920's, rapid growth in plastics was brought about, in part, by the shortages of materials during the Second WOrld war. This permitted the evaluation of plastics in a wide variety of applications and markets. Plastics offered a unique combination of availability, properties, economics, style, and ease of processing. Building construction, packaging, electronics, agriculture, automobile, housewares, and toys are examples of major markets. Low cost, durability, and insulating properties, lightweight, resistance to chemdcals and ease of fabrication make plastics competi- tive with metals, glass, wood, and other materials. Versatility in fabrication is a major advantage especially with respect to economics. Another major advantage of using plastics is that large quantities of intricate parts can be duplicated rapidly with a relatively high degree of dimensional accuracy. From one mold thousands of identical parts can be made. Furthermore, parts require little or no work after they come from the mold. An extremely important consideration in practically all applica- tions of plastics is their light weight. In making parts, the primary concern is with volume, and the low specific gravity of plastics, compared to metals, gives them an advantage in terms of economics and applicability. Other advantages include corrosion resistance, fire control characterisitcs, weatherability and aesthelic appeal. According to most economic industry indicators the plastics industry is rapidly approaching the number one position as a producer of basic materials and fabricated products. It is calculated that by the year 2000 plastics will constitute three-quarters of all engineer- ing materials in terms of volume. At first, plastics penetrated the conventional wood furniture industry in the form of resin adhesives. By 1935, phenol and urea formaldehyde were used owing to their superior properties, such as extreme durability and ease of application. After the Second WOrld war the decorative high-pressure laminates were introduced into this field. Ten years later, in 1965 injection polystyrene parts appeared in the furniture industry. Cast polyurethane and cast polyester successively showed up in 1966 and 1967 respectively. The revolution with plastics in furniture, then, spread. The technical revolution in the furniture industry with plastics started with the introduction of highly styled Mediterranean and Spanish designs which required intricate replicas and ornate carvings and decorations. Plastics made it possible to produce these styles within the price range of the mass market by eliminating expensive labor in carving and machining operations. Rising labor costs, a shortage of skilled and semi-skilled labor and shortages of conventional raw material have been the factors contributing to the use of plastics. Furthermore with plastics, the designers have been given a greater freedom of expression without having to resort to more expensive production techniques. To date, plastics appear in the furniture world in the form of total plastic furniture as well as solid furniture parts. The entrance of plastics into the furniture industry is following the course of what took place earlier in other industries where plastics replaced conventional materials. Costs began to rise and labor became expensive. However, wood is cheaper than plastic on a pound for pound basis and wood is difficult to displace because of its natural texture and superior properties. Even though it was overwhelmed in some areas, plastics still cannot compete when wood is used to produce a flat or fairly simple nonornate piece of furniture. In addition, the soaring prices of plastic raw materials derived from oil and its petrochemicals due to energy shortage leads to an uncertain circumstance for the plastics development in the wood furniture industry. The furniture industry in Taiwan is very different from that of the United States in size, mechanization, furniture styles and customers' taste. Relatively small capital investment has limited the size and the degree of mechanization of the typical furniture factory. Inadequate and inaccurate equipment in Taiwan has produced low quality furniture in small quantities to provide the local necessities. The majority of the local consumers have been satisfied with low quality products at a low price for a long time. However, Taiwan also faces rising labor costs, rising purchasing power and more sophisticated local markets which will lead into improved techniques and innovation in the furniture industry. Besides, increased exports also prove that the men, materials, and methods revolution is extremely necessary to meet the quality and quantity requirement. By observing the innovation with plastics in the United States, we realize that the possibility of using plastics in furniture might become attractive today or sometime in the future in Taiwan. This study will try to analyze the use of plastics in the United States and will try to explore the possibility for similar developments in Taiwan. 2. PROFILE OF THE FURNITURE INDUSTRY AND INNOVATION. WITH PLASTICS IN THE UNITED STATES l) The Characteristics of the Furniture Industry It may be said that furniture manufacture is more of an art than a science or a technology, even though significant advances have been made in the more recent past. The furniture industry has existed as long as human civilization and has developed certain distinguishable characteristics. First, the industry is largely composed of small and medium-size family controlled and long established manufacturing units. 1) Almost 65% of the wood furniture plants employ less than 20 people, (Table l) and 2) the number of establishments has remained at a figure of some 5300 without signi- ficant change during the last decade; they were 5211 in 1958 and 5365 and 5302 for 1973 and 1974 (Table 2) respectively. Secondly, the industry is monopolized by a few large companies. A tendency shows that the profitability rates seem to increase in accordance with the size of the company (49). The top 50 factories produce almost half of the furniture products (49). It further appears that the industry is becoming more densely concentrated as a result of consolidation. Thirdly, furniture has been traditionally a 10w paying industry. The problem gets more serious because the labor constitutes a large percentage of the total cost. 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Furthermore, the plastic product performs better in terms of physical and thermal properties and its greater resistance to chemical and environmental damage as compared to the conventional raw material (Table 6). b) Product Processing It is possible to design plastic parts in a way which is impos- sible, uneconomic, or impractical with wood parts. For example, radical designs can be duplicated in great quantities. Assembling problems encountered in wood products do not exist in plastics, since the plastics are molded with tolerances between i 0.005 and i 0.010 inches. Furthermore, there are almost no limitations to the size of plastics that are usually found in the wood industry, and this will reduce assembling operation and labor cost. c) Product Cost Basically speaking, pound for pound, plastics are more expensive than wood. But they are inexpensive on the basis of unit price due to the greater productivity and the one step molding process. 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Growth of Furniture Shipments Parallels Disposable Income (54). 16 1967-1974, was 7.7 percent. Tables 2 and 7 depict some more detail. Manufacturer's shipments of household furniture in 1975 are expected to show an increase of 7 percent over that of 1974, despite the economic depression. A survey, conducted by the Bureau of Census, revealed that besides disposable personal income, the age of household head played an important role regarding household expenditures on household durables. Households headed by persons under 35 years of age spent the most on furniture and appliances. In addition, the survey also pointed out that more and more families will be headed by persons under 35 years of age. According to William J. Hodge, Consumer Goods and Services Division, "A continuing high level of consumer expenditures for durables and increased formation of new households are expected to have a favorable effect on sales of house furniture during the reminder of the decade." (54). 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BASIC CHEMISTRY OF PLASTICS Plastics are made from simple molecular monomers by a mechanism known as polymerization. In recent years the highly sophisticated understanding of structure-property relationships and the introduction of new monomers have resulted in the capability to "tailor make" plastics. l) Bolymerization Reactions There are three methods to synthesize larger molecules. First, the reacting molecules simply add together end to end; this is known as addition polymerization. Second, the reacting molecules are joined together through the elimination of a small molecule, usually water or alcohol; this is known as condensation polymerization. And lastly,the reaction involves the rearrangement of atoms and bonds between adjacent molecules; this is known as rearrangement polymerization (27). a) Addition Polymerization The great bulk of commercially produced polymers is made by the addition method. For instance, ethylene is the monomer for polyethylene. Its formula can be written as CH2 = CH2. The existence of the double bond in the monomer is necessary in all addition polymerization processes (27). 18 19 (l) Initiation Under certain conditions the two unshared valences present in the double bond can become available for reactions. CH2 = CH2 + -CH2-CH2- Some high evergy sources such as radiation and thermal energy, or an ionic type of catalyst such as peroxides are employed to do this job. Heat is usually used because it is relatively inexpensive (20) (51). CH2 = CHZ- R +’R-CHZDCHZ” Where R' is called a free radical. (2) Propagation The ethylene molecule becomes active and tends to react with neighboring molecules. R-CHz-CHZ- + -CH2-CH2- + R-CHz-CHZ-CHz-CHZ- Then, the reaction continues, 6, 10, ... more and more carbon molecules are linked to each other. It occurs very quickly, and many hundreds of ethylene molecules join the chain within a second. There is a remaining active end (20) (51). (3) Termination When the active ends meet each other, they will deactivate each other. Therefore some of the molecular chains might be very long but some shorter (27). R ~~~~~~~~ ' + ' ~~~~~~~~~~~~ R‘+ R ~~~~~~~~~~~~~~~ R or R~~~ +.~~~~R+R~ ~~~~~~~~~ R 20 (4) Molecular Weight The moment of termination of any chain is quite random. The mass of polymer therefore consists of many chains of different lengths. The average molecular weight and the molecular weight distribution thus are used to identify a particular polymer instead of a unique molecular weight as used in inorganic compounds. The average molecular weight and the molecular weight distribution are of great technological importance, because the chemical, mechanical and aging properties of a polymer depend to a considerable extent on them (27). b) Condensation Polymerization This type of reaction does not involve double bonds. For example, + + CZHSOH HOOCCH3 + CZHSOOCCH3 H20 The product of this reaction is ethyle acetate (ester). However the monobasic acids and alcohols cannot react any further, because there is only one functional group (OH- or COOH—) on each molecule available. Terephthalic acid which has two carboxyle groups, and ethylene glycol which has two hydroxyl groups can produce a polymer by condensation polymerization. The polyesterification involves condensation of hydroxyl and carboxyl groups. For example, (38) HOOC—Q— coon + Hocuzcnzou + Hooc—Q-coonzcnzon + H20 Terephthalic acid Ethylene glycol HOCHZCHZOH + HOOC—Q—COOCHZCHZOH + HOOC-Q— COOH Ethylene glycol Terephthalic acid Hocnzcnzooc @— coocuzcnzooc —©— coon 21 and so on ... These molecules often increase to a molecular weight of 10 or 20 thou- sand and are known as Dacron. c) Rearrangement Polymerization (27) Just like the condensation polymerization, for a rearrangement reaction to occur, the reactants must have two or more functional groups. For example, OCN(CH2)6NCO + H0(CH2)40H + OCN(CH NHCOO(CH2)40H 2)6 Hexamethylene Butane diol di-isocyanate In this reaction some atoms from the isocymate group (-NCO) and the hydroxyl group (-OH) have to rearrange themselves to form the -NHCOO- linkage. The resulting molecule still has functional ends and can react further. HO(CH -OOCHN-(CH2)6-NHCOO-(CH2)4-00CHN-(CH2)6- Polyurethane 2’4 and so on ... 2) Thermoplastics Versus Thermosets (20) (27) (51) Those polymers that contain repeated units in a linear or chain- like form are referred to as thermoplastic. They become moldable when heated and can be repeatedly heated until soft and remolded. The plastics mentioned so far are all linear or have chain-like forms, therefore, they are all thermoplastics. 'But polyurethanes for example, form crosslinkages rather than linear chains by further reactions and are thermosetting. 22 Polyesterification can be made more complex by using tri- or quadri— functional molecules instead of mono- or di- functional molecules. For example, if we use a trihydric alcohol such as glycerol, the reaction will be: (CHZ-CH-CHZ)n + ( )n'+ <:::> + n H20 I OH 0H 0H HOOC COOH “H COOC \COOCHv 2 OH Glycerol Orthophthalic (trifunctional) acid (difunctional) TI —1— l P QR _L__ __l_ 2 7' After the linear reaction, they develop further into cross-links. Once the cross-links have formed, the molecules are set and solidified. These are called the thermosets. 3) lggpolymers (2Q) The polymer chain can be made not only from identical monomers but also from non-identical ones. The latter type of polymer is also called copolymer. Their properties are infinitely variable and depend on the proportions of the different compounds used. For example, by polymerizing mixtures of vinyl chloride and vinyl acetate, molecular chains can be built up in which the links consist partly of polyvinyl chloride (PVC) and partly of polyvinyl acetate (PVA). These copolymers combine the properties of the PVA and PVC, the nature of the copolymer depending upon the proportion of the constituents that are present. Another example, ABS plastics used in molding furniture parts, are copolymers which combine styrene with butadiene and acrylonitrile. 23 4) Common Plastics In Wood Furniture There is no other family of materials with so many variations in forms like plastics. Plastics can appear as molding compounds, liquid casting resins, solid structural shapes, coatings, adhesives, laminates, fibers, etc. a) Polystyrenes (20) (30) (48) Styrene in the common name for vinyl benzene. Commercially, the reaction of benzene with ethylene is universally used to produce the styrene monomer. Styrene, then, polymerizes very fast under heat into polystyrene. The reaction can be visualized as: CH CH CH = CH ©+CH2=CH2+023+02 2" styrene Polystyrene -FH-CH -CH-CH - 2 2 Polystyrene homopolymer which is made of styrene identical monomers is noted primarily for excellent balance of characteristics rather than for one or two unique properties. One of polystyrene's defects as a plastic is its brittleness and a tendency to craze on aging. Polymeri- zation with acrylonitrile gives the copolymer better chemical and aging properties than polystyrene alone. ABS copolymer is made with improved impact strength, elongation characteristics and is accepted as one of the best quality materials for molding furniture parts. Polystyrene is by far the major plastic being used in simulated wood in the furniture industry because of its low price and good properties (Table 8). Polystyrene parts are generally injection molded. TABLE 8. 24 Properties of Polystyrene and Polyester (6). QUALITY PARAMETERS POLYESTERS POLYSTYRENE Appearance Excellent Very good Feel Excellent Good Knocking Excellent Poor Acceptance of finishes Very good Good Resistance to solvents Good Poor Nailability Excellent Good Screw-holding power Excellent Good Tensile strength Excellent if reinforced Good Shear strength Excellent if reinforced Good Compression Excellent if reinforced Good Creep Excellent if reinforced Fairly good at high Impact resistance Stress cracking Use for overlays Use for whole doors and drawers Use for picture frames Use for very thin parts (under 1/8") Use for headboards Use for very small parts Use for structural parts large sofa ends, pedestals, etc. Use for flexible parts Performance at extreme cold temperatures Performance at extreme high temperatures Dimensional Stability Excellent for semi- rigid overlays, flex- ible molding strips and reinforced parts Very good Excellent Fair Fair Good Very good Fair Excellent if reinforced Excellent Fair Very good Very good loads and long times. Poor at elevated temp. Good Good Good Very good Good Excellent Good Good Good, if no exposed to long times of high loads and tempera- tures Not possible Good Very good Excellent 25 b) Polyurethanes (4) (5) (6) (20) (31) A polyurethane is made by reacting a polyol (hydroxy compounds) with an isocyanate (l-c rearrangement polymerization). Polyurethanes represent one of the most complex areas of plastics chemistry. There are almost an infinite number of polyurethane materials. Because the ability to use a number of different raw materials makes it possible to produce polymers of different densities. In addition, a gas which is either generated by the reaction or introduced into the reaction creates a foamed material of cellular form. The finished polymer may be flexible or rigid, depending on the degree the reaction is allowed to progress. As with polystyrene, rigid polyurethanes started out in the decorative areas. Now they are used more and more in the structural areas and in the fabrication of complete furniture units. It is hard to find any area of furniture where rigid polyurethanes are not used. Casting is generally employed to mold the urethane articles, even though injection molding can also be used. Some outstanding character- istics of polyurethane foam casting parts are: 1, Densities can be varied from 4 to 50 pounds per cubic foot. The widespread use of rigid polyurethanes is due in large part to the great variety of densities that can be produced. As the density changes so does the strength of the material. For instance, beams and wall plaques for decorative purposes ~would run about 3.5 pounds per cubic foot, mirror frames can range from 8 to 27 pounds per cubic foot, and kitchen cabinets would range from 25 to 30 pounds per cubic foot. 26 2. Equipment cost and mold cost are low. The casting for rigid polyurethanes is a low pressure process which uses inexpensive molds and constraining frames. Polyurethane parts can be cast economically when production runs are only a few parts per day up to a few thousand parts per day. In contrast, the injection molding of polystyrene components is economi- cal only when thousands of parts are turned out per day. 3. Styling is virtually unlimited in designing. Polyurethanes employ elastomeric molds. A more intricate design can be produced without worrying about draft angles. The flexible mold allows under cuts in the design. 4. Molds can be easily and quickly made. 5. Polyurethane parts can be finished and worked like wood and feel and have the sound of wood. 6, Dyes and pigments can be added to give uniform color throughout the foam. 7, A barrier coat is unnecessary. Polyurethanes as well as polystyrenes show a fast projected growth in their application as furniture parts. 1968 1970 1974 Unit: million pounds Polystyrenes 52 85 127 Polyesters 22 23 33 Polyurethanes 15 28 42 c) Polyesters (5) (6) (27) (32) Polyesters are produced by condensating an acid and an alcohol. Rigid polyesters are usually made from maleic acid (CHCOOH), Phthalic CHCOOH 27 COOH acid [:::I’ and glycols, while flexible polyesters contain adipic \COOH (H00(CH COOH), and glycols. 2’4 The properties and appearance of polyester, and rate of cure can be tailored by means of blending the flexible and the rigid polymers in suitable proportion. For example, a resin consisting of 70 percent flexible type, 30 percent rigid type and combined with an equal quantity of filler would have a density of about 94 pounds per cubic foot. The product would have 2,500 psi tensile strength and 6,500 psi compressive strength. Such a material could be easily stapled, nailed, sanded, and sawed. Furthermore, the filler such as wood flour, not only lowers the price but also provides a receptive surface for stains and it makes polyester components easier to finish than other plastic materials. The melting point of a polyester is usually an indicator for flexibility of rigidity of the final products. Resins that are liquids or show a low melting point give generally flexible products. Resins that have a higher melting point usually are rigid. Polyesters are cast in a manner somewhat similar to that of rigid polyurethanes. Both of these polymers are not a single material but rather a range of materials. Polyesters parts can be made to range from very flexible to highly rigid materials. Like polyurethanes, polyesters also have the advantages of the casting process such as lower mold cost, remarkable time-saving in preparing a mold, perfect reproduction of wood surfaces, etc. Table 8 depicts the outstanding end product prOperties of polyesters. 28 d) Silicones (20) (29) (53) In general, organic chemicals which are compounds of carbon, are inflammable and will decompose when heated. That is what happens when we burn wood or coal. It is inevitable, therefore, that synthetic plastics should suffer defects characteristics of organic compounds. They are subject to chemical change under the effect of heat and atmos- pheric degradation. They will often dissolve in solvents such as alcohol or benzene, and under suitable conditions they will be decomposed and burnt. These tendencies are inherent in most of the synthetic plastics for they are organic compounds. On the other hand, inorganic compounds are often inert, unchanging materials. Stone, asbestos, clay, or glass are not readily changed to other compounds by combustion or atmospheric attack. They do not lend themselves to such intricate chemical changes as do the compounds of carbon. Silicone is an element that occurs in inorganic substances such as quartz and.glass; relatively inert and resistant to the effects of heat or atmospheric inflences. However, silicone possesses certain proper- ties similar to those of carbon, and the two elements belong to the same chemical group. Silicone is capable of forming compounds with the same structure as the corresponding carbon compounds. For instance, the hydride silane, SiHA, is analogous to methane, CH4. Thermoplastic polymers and thermosetting polymers can be produced by the hydrolysis of dimethyldichlorosilane and methyltrichlorosilane respectively. ‘ 3 Cl—Si-Cl + H20 +--0-Si-O-Si-0- CH3 CH3 CH3 CH3 CH3 CH 29 CH3 Cl-Si-Cl + H20'+ CH3-Si-O-Si-O-Si-O- I C1 0 O 0 III CH3-Si-O-Si-O-Si-O- O CH O |3| Besides methyl CH3-, phenyl C6H5- or vinyl CH=CH— group can be attached to silicone derivates. These groups impart characteristics, such as solvent resistance, lubricity, compatibility, and reactibility with organic chemicals and polymers. Silicones, combining organic and inorganic substances, not only look like, but act like organic materials on one hand. On the other hand, they also are like their inorganic ancestor, silica $102, resistant to heat, cold, chemicals and weathering. Instead of being a molding material for decorative items or struc- tural parts, silicones in the furniture industry play an important role as mold-making materials, which will be discussed in detail later. e) Polyvinyls (20) (38) (39) (40) Vinyl polymers and copolymers consist of a large family of thermo- plastics. Their general structure can be presented as follows: 2 I R -- CH -CH —- 1,, When R is C1-, it is polyvinyl R is CH 000-, it is polyvinyl acetate 3 R is H-, it is polyethylene R is Q: it is polystyrene and R could be others. 30 In general, the lower the molecular weight, the poorer the mechanical properties of the polymer will be, and the lower is its thermal stability. Polyvinyls are light in weight, often transparent and glass-like. The solid plastics are tough and strong, and can be cast into films. When they are softened, they are suitable for modern mass- productive techniques employing injection molding. Polyvinyls can be modified by plasticizers, fillers, and stabi- lizers to produce rigid or flexible materials as desired. Stabilizers are used to prevent polyvinyls from the effects of oxidation, of heat, and of light. Plasticizers are used to soften polyvinyls, and to make them flexible when the products are cool. The plasticizer molecules machanically rather than chemically penetrate between the vinyl chains and separate them apart on cooling. Therefore the cooled polymers remain soft and flexible. In the furniture industry, polyvinyls are employed as laminates rather than structural or decorative parts. Polyvinyl sheets, engraved and printed with wood grain, are laminated to solid vertical or hori- zontal surfaces. f) Phenolics and Melamines (20) (38) (39) (40) Phenolic plastics are made by chemical reaction between phenol or cresol, and formaldehyde. The phenol has three non-specific reactive sites instead of two. When phenol and formaldehyde begin to join together into a chain in the presence of heat and a small amount of alkaline catalyst such as ammonia, they join head to tail to give a straightforward thread-like molecule. The product is a thick sticky resin and it is thermoplastic. However, as the heating continues, the 31 molecule tends to branch out here and there from the three non-specific reactive sites of the phenol and the branching chains begin to join up with formaldehyde. The polymer, then, develops a rigid network struc- ture and sets. Melamines are produced by reacting amino-bearing melamine with formaldehyde at temperatures of 160 to 195°F with pH values exceeding 8.5. Basically, the melamines are similar to phenolics. As in the case of phenolic plastics, the molecule of the melamine polymer is not a simple straightforward chain; it develops branches, as a result of which the molecules can eventually join themselves together to form a three-dimensional network. For adhesive purposes, the material is pre—condensated and cooled to 70°F. For the purposes of impregnating laminated, modifying media are added to enhance the elasticity of the hardened melamine resins and to prevent the films from sticking to the press plates. Both phenolics and melamines are hard, durable and are highly resistant to heat and scratch. Bearing those excellent properties, they are commonly used in the production of laminated materials from cloth or paper. 4. PROCESSING There are three ways to produce plastics, namely: by molding, casting, and thermoforming. Molding processes in the furniture industry are custom operations most of the time, while casting processes are captive operation. Injection molding represents a major portion of the plastics production. Here, productivity must be high for economic reasons. In contrast, flexible mold casting gives flexibility in the quantities of production and still has economic advantages. The methods of molding and casting will be discussed in great detail in this part and additional discussion will be given the rotational molding (rotomolding) for its versatile characteristics. 1) Injection Molding (2) (ll) (24) (30) (34) (45) The largest fraction of furniture parts such as decorative articles and structural items, is molded by injection molding. This trend is believed to continue for some time to come. The important factors which make the injection molding so widespread are: 1. Technology is well advanced. 2. Equipment is readily available in all sizes. 3, This method produces unifomm parts at high volumes. 4, Good simulation of wood is possible. 32 33 There are, however, some shortcomings associated with this process, such as: 1. Machinery and auxiliary equipment are expensive. 2. Processing is complicated. 3. Mass production is required for acceptable unit cost. 4. No undercuts of design are possible. a) Molds The molds used in injection molding are of very high quality, machined to close tolerances and thus are very expensive. The mold must be designed to be able to withstand the very high pressures it will be exposed to during the injection process. Since the cycle time' depends largely on the cure time of the plasticized material in the mold, the thermal conductivity of the mold for cooling the molten plastic is also one of the critical factors. The shorter the cycle time, the greater the quantitives the machine will produce, and thus the more economic the operation will be. b) Mold Making Aluminum, steel, and beryllium-copper, can be employed as mold- making materials. Usually, beryllium-copper is used for the injection mold. To make a mold, selection of a fine model carefully made with desired grain structure and appearance is most essential. In addition, the mold should be free from undercuts and a draft of two to seven degrees is desirable. Mbreover, the model should be about two hundredth 34 of an inch larger than the desired part to allow for shrinkage of the metal mold and the plastic part. It takes about three weeks or more to make a beryllium-copper mold. A flexible silicone rubber prototype mold is first cast from the model. Then, a ceramic mold is cast from the prototype mold. At last berylliumrcopper is cast in the ceramic mold. The plastic products are made in the berylliumrcopper mold and the features produced are repli- cates of the mold. Flexible mold casting will be discussed in the next part. However, there is a better process - the Shaw process. The Shaw process is recognized as a superior technique for casting a rigid mold by shortening the time needed for the cast sequence described above and without sacrificing faithful duplication. The outstanding char- acteristics lie in the fact that when a slurry mold, which is made of a compound of refractory powders with an ethyl silicate binder and a jelling agent, from the rubber prototype mold is ignited, a microcrazed structure is formed in the mold. This microcrazed structure mold can be used for the casting of the beryllium-copper mold. The rigid mold is usually cored with drilled intersecting channels for circulating heat transfer medium, such as water, to cool the incoming molten plastic. In addition to shortening the cycle time of the molding process, the cooling design also plays an important role in influencing physical prOperties of the end products to some extent, such as uniformity of the plastics. 35 c) Molding Process Injection molding is the major method employed for molding ther- moplastics, especially for polystyrenes. There are four types of injection machines operating in the United States. The reciprocating screw type (the single-stage screw type) is the most popular (Figure 2). It has some advantages, such as: l. A better preparation of the plastic material for molding. 2. A higher pressure on the material when it is injected into the mold. 3. A better color dispersion when using dry coloring or color concentrate. 4. A quicker change from one material or color to another. During the molding cycle, the plastic pellets are forced from the hopper into a heating cyclinder. There, the material is plasticized and screwed forward into the injection chamber (Figure 2). In the second step, when the chamber loaded with sufficient quantity of molten plastic, the screw moves forward, acting as a ram (Figure 3) and forcing the accumulated plasticized material through the nozzle into the sprue bushing through the runs, the gates and then into the cavity of the mold. Then, the cavities are quickly filled and uniformly cooled. Other important factors in the molding operation are: l. Drying and blending the plastic compound. Drying reduces the moisture content of the molding pellet to a point where it will not affect the molding process or cause defects in - the molded parts. Blending is used to tailor material properties to desired end products and sufficiently use up the scrap. FIGURE 2 . 36 Single-Stage Screw Type Plastic Injection Molding Machine (2). ._.__..,_'-' w _——.—-——_ 37 coma coma ucaofi 58E 38 FEED l/,INJECTION CYLINDER HOPPER —— / (”(Iy % /' § / 1 ’/////// N O z ZL E W\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\ / l7»- ‘5“ " 35131575 A ' _‘r . I o. meavumfimmwnnnufeummm§ ‘Daagkég? \ - ‘0'. ‘ '0 o \‘:“" » “:.:\: HEATER f Vs 2k NON-RETURN ROTATING AND _ FLOW VALVE RECIPTROCATING SCREW;PISTON ASSEMBLY SCREW SHAFT FIGURE 3. In the Reciprocating Screw Cylinder, The Material Is Plasticated by the Screw While The Later Moves Backward in the Cylinder; For Injection, The Screw Moves Forward, Acting as a Ram (2). 39 2. Feeding the plastic compound. The plastic material can be fed to the heating cylinder on either a volume or weight basis. Generally speaking, the latter is more precise than the former. Improper feeding, such as caused by inventory fluctuation in the heat cylinder will cause short shots, part shrinkage, etc. 3. Plastication. To plasticate the molding compound thoroughly and uniformly into a homogenous melt plastic with controlled viscosity is essential for the production of sound parts. In order to obtain an even melt plastic, and to avoid degrading, a balance must be maintained between the need to provide adequate time for proper heat exposure of material in the cylinder and the need to move more material through the cylinder as fast as possible. 2) Casting Casting is a relatively simpler process for the production of plastic components if compared to the molding systems. In short, the process includes pouring resins into the mold, allowing to cure at room temperature and ejecting the solid item. As a general rule, thermoset- ting resins are employed in casting and thermoplastics in injection molding, with some exceptions. However, thermOplastics can also be cast, and thermosets can be injection-molded. 40 a) Advantages and Disadvantages The investment in casting equipments is not high and production can be carried out economically at just a few parts a day. Mbld costs are much lower than in injection molding and molds can be easily made by the furniture maker. In addition, flexible casting molds can be made for highly ornate parts, having a high degree of undercutting which is absolutely impossible in injection molding. In other words, we can get more precise wood grain duplicate than we do in injection molding. The main disadvantage is that the number of parts obtainable from a flexible mold is limited to a range of 80 to 200 due to chemical, mechanical action and slower heat transfer. b) Mold Making (1) Materials for Mold Making (23) Several materials can be employed for the mold-forming. Among those, latex, urethane and silicone elastomers are most commonly used. Latex elastomers are very cheap and are useful for casting all kinds of materials. But its excessive shrinkage and high labor-requirement reduce its attractiveness. urethane elastomer molds have to be treated ‘with the troublesome wax or silicone type release agents before molding. In addition, the urethane elastomer used for mold-making has a short pot life which makes the fabricating operation difficult. For these reasons, latex elastomers and urethane elastomers, lose their ground to the silicone elastomers, even though they are excellent in resistance to solvents in the coatings and chemicals produced by the molded parts and are very tough. 41 Silicone room temperature vulcanizing (RTV) rubbers have certain outstanding characteristics, such as: 1. Thermal and oxidation stability from -100°F to 500°F. 2. Chemical inertness. 3. Surface stability to prevent other materials from sticking. 4. Ability to precisely reproduce fine detail figure. 5. Hardness to resist foaming pressures. RTV rubbers are the best materials for making the flexible mold, though they are expensive. (2) Model (50) Caution must be taken in making the mold from a model to account for an average shrinkage of the plastics of 2 percent. The grain pattern should be accentuated to produce a more realistic wood-like part. In the case of a wood model, this grain accentuation can be accomplished by rubbing a soft wire brush over the pattern part in the direction of the grain. A mixture of 5 percent petroleum jelly and 95 percent methylene chloride serves as a release agent. It is sprayed on the model and makes the mold separate easily and cleanly from the pattern. (3) Mold Fabrication (12) (23) (50) All of the RTV silicone rubbers used for mold making are two- component systems containing a polymer and a catalyst. The mixture is 91 percent polymer and 9 percent catalyst by weight. There are four steps to fabricate a mold: 1. Mix the two parts thoroughly by hand or with a power mixer until the color of the catalyst disappears. 42 Deair the mixture in a chamber which has a minimum vacuum of 29- inches of mercury. During the deairation, the mixture will expand as much as four times the original volume, then the mixture will recede after a few minutes. A vibrating table can also be used for the deairation purpose. The entrained aix“bubblesare forced out by vibrating and can be broken with compressed air. Pour the desired mixture over a framed model. There are three types of molds generally used nowadays. (a) The flatback or open face construction mold. This is used to produce five sided furniture parts. After pouring the desired mixture a lid drilled with 1/16 inch bleed holes and coated with the release agent is fastened on the confining frame. The elastomer, the RTV silicone rubber, should be forced out the holes to make sure there is no entrained air between the lid and the mold back. After curing the silicone rubber at room temperature, the bottom of the frame is removed first and then the model. (b) The split mold. This is used to produce furniture leg, lamps bases or other similar parts. The frame for this type of mold is split into two parts. The elastomer is poured over the bottom just as in the case of the flatback mold. After the bottom half has cured completely a release agent is sprayed or brushed over the matching surfaces. At least, the top half is fastened in place and the elastomer is poured into the existing cavity. 43 (c) The six sided construction mold. This is used to produce cabinet doors or the like. A sheet of about 3/8 inch thickness of RTV silicone rubber with the desired pattern and size of one side of the cabinet door is fastened to the lid. After the elastomer is poured over the flat back mold, the impressed lid is then clamped on. A six sided mold thus is made after the elastomer has cured. 4. Aging the mold. Generally, the mold should be allowed to cure for 24 hours before removing the model. Furthermore, three more days are needed for aging the mold at room temperature. Before using the mold, it is recommended to allow seven days for developing complete physical properties after pouring. (4) Extending Mold Life (22) (50) Mold life primarily depends on the materials cast in the mold and the maintenance of the mold. Usually proper application of a barrier coat will at least double the life of the silicone rubber mold. In developing a barrier, every part of the mold must be evenly coated every time. For the deep undercuts, a pencil type air brush or extension nozzle is needed to accomplish the coating job. A qualified barrier coat should provide two functions: 1. During the mold cycle, the coating penetrates to the casting parts to make them compatible with the succeeding finishing without further treatment after demolding. 2. When applied to the mold surface, it protects the mold from chemi- cal attack. 44 Before applying the barrier coat, a release agent is sprayed on the mold which is then laid aside to dry completely. If not completely dried, the heat generated by the thermoplastic and residual solvent will cause a defective part owing to the broken barrier. Soap was used as release agent for a long time, but it does not do the job well. Wax in petroleum solvent generally serves the purpose. The problems of rapid deterioration of the molds such as swelling, hardening of the surface, brittleness, broken surface, and discoloration of the surface stem from either too much release agent or the solvent of the release agent remaining in the mold. Mold temperature built up during the casting runs due to the exothermic reaction should not exceed 100 to 110°F. Otherwise, the protection of the release agent will be lost and the mold exposed to the chemical such as isocynate of the polyurethanes. Polyesters can also cause trouble, like sticking to the mold after many repeated runs. It is recommended to heat the mold to 550°F for about an hour after every five-or-so coatings to melt polyester residue and improve mold life. The parts should be ejected from the mold as soon as possible, since mold life is directly proportional to the accumulated contact time. c) Casting Polyurethanes and Polyesters (12) (23) (28) Plastic parts of polyurethanes and polyesters not only perform the same functions in the furniture item, but also are cast almost in 45 the same way in many respects. Some of the main differences between these two materials are: l. Polyester exerts no pressure on molds, therefore no clamping or back-up operations are necessary for the mold. 2. Mbld life is longer when polyester is used. 3. Mold release agents, when used, are more readily cleaned from polyester parts. 4. Polyester parts are denser than those of polyurethanes.‘ 5. Polyesters tend to shrink more than polyurethane foams, therefore molds must be built to allow for this shrinkage. 3) Rotational Molding_(3)~(2l)_(42) (56) Getting more and more attention in the furniture industry in recent years is rotational molding, a process in which a fixed quantity of plastic compound, either powder or liquid, is sealed in the mold and rotated in biaxial direction while being heated. The molten plastic is then distributed evenly in the cavities. The mold keeps rotating biaxially during the cooling phase. The plastic item is then cured and ejected (Figure 4). The reasons for favoring the rotational molding lie mainly in the fact that it can mold parts of various shapes and sizes. The more complex the shape is, the more suitable the rotational molding is. The larger the size of the part is, the better the rota- tional molding operates. FIGURE 4. 46 A Multiple-Spindle, or Carousel-Type Rotational Molding Machine. Each Spindle Carries a Group of Molds or a Single Large Mold Through Heating and Cooling Enclosures Prior to Loading and Unloading of the Mold (3). 47 MOVABLE SPINDLES , SLOTTED COOLING AREA SLOTTED OVEN / \ v :' [ch-('3 'V~,’ ’4 I/ ‘/ \\‘ \ , \ \ , , \ 2 SPIDERS MOLDS ’ ‘ ‘ ‘l. ’—;\-" \ -" /\/1 \ [I I /\ ’ ’ x’ I noon OPENING t \ / OPENING OOOR \ ’ LOADING Auo’ UNLOAOING AREA FIGURE 4 . 48 The following are the advantages of rotational molding for the furniture industry: 1. Products are made seamless and stress free. In addition, there is a tendency to make the wall thicker at the corners where most often extra strength is needed. 2. The wall thickness of the part except for the corner is uniform. 3. Fine appearance can easily be gained. 4. The tooling costs are relatively low. 5. Any shape and size can be molded especially hollow parts or parts of angular shape. 4) Finishing Molded Parts (14) (36) (43) One of the most essential factors, which help plastics make inroads into the furniture industry is that the developed finishing technology makes the finished wood-grain plastic components indistin- guishable in decorative appearance from real wood. Some plastic articles, such as a mirror frame or a waste basket, can be finished separately. However, the plastics which serve as components of wood furniture should be finished right along with the wood parts. In the latter case, the finishing not only furnishes the wood-grain plastics with satisfactory finishing effects, but also makes the plastics indistinguishable from the other wood components in the piece of furniture. In separate finishing, special topcoats can be developed to give adequate adhesion to the plastic, but in simultaneous finishing the conventional finishing materials for wood are being used step by step along with the wood parts. Unfortunately, the solvents of 49 the finishing materials tend to attack the plastics. Therefore a special treatment, a barrier coat should be applied first, before the plastic parts are attached to the wood base. a) Barrier Coat (1) (l3) (17) (25) (33) (46) The first and the most important step in finishing the plastic parts is the application of a proper barrier coat (base coat). A barrier coat should: 1. Provide proper color background. Since the plastic will be assembled with wood after the barrier coat has been applied, it will be treated simultaneously with wood step by step from then on. Therefore, the barrier coat should be formulated in a color as close to the natural wood color as possible. Practically, it should always be somewhat darker than the uncoated wood substrate, since the plastic is much less porous than wood and will not absorb the succeeding stain to the same degree as wood. This must be compensated by adjusting the color of the basecoat. In most cases, the color is molded into the plastic in such a way as to match the color of the furniture. In case the finished furniture is scratched, the plastic part will not appear so signifi- cantly different from the wood part. 2. Provide adhesion not only to the molded plastic but also to the subsequent finishing coats. Most of the conventional lacquers used in wood finishing have no adhesion to polystyrene. So, a barrier coat should be formulated to bond the plastic and the conventional nitrocellulose lacquers. 50 3. Provide some absorptivity to hold stains. This makes it easier to match color with wood parts. 4. Act as a barrier in preventing a solvent attack by lacquer topcoats containing strong solvents. Polystyrenes are very sensitive to those solvents such as naph- thas, ketones, and esters which are the major components of common finishing products. Plastics attacked by the solvent will develop a number of surface irregularities such as wrinkling, cracking, alliga- toring, and other unique effects. These are categorically defined as "crazing". Generally speaking, plastic parts tend to craze in stressed areas during the finishing operation. The stresses are usually set up around the sprue area and in certain places where excessive shrinkage occurs in the mold. The cooling cycle and the flow characteristics of the polystyrene are factors influencing the development of shrinkage. b) Stains and Toners (1) (17) This adds color to the wood and enhances the grain. The synthetic parts are finished in conjunction with wood after base coating. Non-grain-raising (NGR) stains or dye stains have little effect on polystyrene because of its non-porous surfaces. The NGR stains or dye stains are therefore not used for polystyrene. Toner with binder is sometimes used to give additional depth to the basecoated plastic and adjacent wood parts. 51 c) Filler (l) (17) The function of fillers is to add color and to close the pores of the wood. Since plastic does not absorb stain and the barrier coat absorbs only slightly, therefore, generally, filler has little effect on the finish of plastics. d) Sealer (1) (17) The sealer is applied over stain or filler to seal off the surface and provide a smooth foundation for the topcoats. Between-coat sandings of wood can be accomplished in a normal manner, but plastics require no sanding in order to perfectly match the completed finish. e) Pigment stains and glaze stains (1) (l7) Pigment glazing gives the furniture piece a highlighted, shaded or antique appearance. Pigment stains or glaze stains contributes more to the realistic woody appearance of plastic furniture components than any other finishing steps. f) Topcoating (l) (17) A shellac, varnish, or lacquer topcoat can be applied after sealing. Usually, two or more coats are required. g) Finishing polyurethane and polyester parts (1) So far, the discussion has dealt with finishes for polystyrenes which represent the largest quantity of plastics consumed in the furniture industry and which appear to be more difficult to finish. Polyurethanes and polyesters basically need no basecoat because they are not attacked by the chemicals in the solvents of conventional 52 lacquers or varnishes. Therefore the basecoat is used for the purposes of providing a uniform and consistent color. After basecoating, poly- urethanes and polyesters can be finished like polystyrenes. However, because of the porous nature, polyurethanes and polyesters will be more like wood in their ability to receive and absorb the various finishing steps. 5. COATING Furniture finishing with wood grain can be done in three ways. First, on the plastic molding or cast parts. Second, on an overlay material which will then be applied to the wood-base substrate. Third, on the wood-base substrate directly. These finishing processes involve embossing, printing, coating, overlaying, and laminating. The first method has been discussed previously and the other two will be discussed here. Basically, no matter what process is employed in finishing flat stock, a series of rolls are used to accomplish the coating, even though some alternatives are available, such as a press plate. A discussion of coating is basic to the understanding of these other finishing processes: embossing, printing, overlaying and laminating. For embossing and printing, the roll surface is engraved with the desired pattern instead of the plain roll used in coating. After printing and embossing usually on the vinyl film or on the phenolic- or melamine-impregnated craft paper, overlaying or laminating is then performed on the flat stock. 1) Roller Coating (7) (26) (35) The reverse roll coater is one of the prime coaters used in the furniture industry. The three-roll reverse-roll coater (Figure 5), modified from one-roll and two-roll coaters, will be discussed for 53 54 Rubber Chrome Plated Metering Roll Doctor / Chrone Pl. Transfer -—~ Roll FIGURE 5. The Three-Roll Reverse-Roll Coater 55 supplying basic technical information. On the basis of operation prin- ciple, there is no difference between the more sophisticated coaters and this three-roll coater. The coating material is supplied from a reservoir. Roll B picks up the coating material which is metered at the nip between the roll B and the roll C by adjusting roll C. A doctor on roll C removes the excess coating material so that the surface of this roll will be clean when it arrives at the nip. The substrate runs between roll A and roll B in a direction opposite to the direction of rotation of roll B. An even coating thus is applied to the substrate. Most finishing materials contain three ingredients; the solvent, the vehicle, and the pigment. Color and shininess are due to the pigment. The vehicle (resin and oil) in which the pigment is dispersed presents the dry film binding the pigment to the substrate. The solvent regulates the viscosity of the coating material for easy operation. Synthetic resins are normally used as the vehicle solids in the furniture industry nowadays. But natural resin and nitrocellulose resin are still used in this industry also. Plasticizers such as oxidizing oils and non-drying oils provide the dry film flexibility. The roll can be a hollow or solid steel cylinder. Surfaces are chrome-plated or covered with synthetic rubber. During operation, control of proper viscosity of the finishing material is essential. Ropings which are small ridges formed at right angles to the coating roll, are most often caused by high viscosity owing to solvent evaporation before coating operation. There are two other factors contributing to ropings: (1) unevenly worn roll, and (2) bad condition of the roll surface. 56 2) Embossing and Printing The Film In the furniture industry, horizontal tops are often overlayed or laminated for prevention of mechanical destruction and chemical attack. The embossed and/or printed film is employed as the material for laminating or for overlaying. Direct printing and embossing of the wood-based substrate are common also. Embossing is carried out by forcing a metal roll, which carries an engraved pattern raised above the roll surface, against the heated plastic followed by cooling. As for printing operation, a back roll is provided to transfer ink from the engraved roll to the film. If multi- color is needed, a series of three or more engraved rolls should be aligned. The first one carries yellow ink, for example, the second, red and then blue for the third, etc. The rolls are prepared from color separations produced by photographing the subject through color filters. 3) Low Pressure Laminating (15) (16) (44) (47)_ The wood-base substrate, most often a particleboard, can be laminated with (1) high pressure laminate, (2) low pressure laminate, and (3) either paper, cloth, or plastic films overlay. Laminating can be accomplished by cold press, hot press, and rotary press for high- volume production, and by manual methods in low volume. Cold press and hot press methods are used for bonding rigid laminate to particleboard, while the rotary press is used for bonding flexible films as well as rigid material. The following will discuss the low pressure laminating. 57 a) The Paper Usually, there are three layers of alpha cellulose paper which is decorated with wood grain and/or impregnated with resin on the face of the substrate and a sheet of resin impregnated cellulose paper on the back. The paper should have the right porosity and resin reception and must have a high wet tearing strength as well. (1) Overlay Paper This paper, with 2.0 to 4.5 grams per square foot in weight, is made of unfilled alpha cellulose and saturated with melamine resin up to 300 percent, based on dry paper weight. It will be fused and give good transparency and good protection after hot pressing. (2) Pattern Sheet (Decorative Paper) This paper, with a basic weight of between 8.0 and 15.0 grams per square foot, is made of filled alpha cellulose and is saturated with the same resin used for overlay paper to a range of 100 to 150 percent related to the basic paper weight. The wood grain pattern on the paper is printed by rotogravue. The ink used should possess the follow properties: 1. It should be compatible with melamine resin. 2. It should be insoluble in the solvents of the resin. 3. It should be fade-resistant and be able to withstand the laminating process. (3) Bonding Kraft (Barrier Paper) This is either a filled alpha cellulose paper impregnated with melamine resin or a natural colored soda kraft paper impregnated with 58 phenolic resin. The basic weight of the paper varies from 8.0 to 15.0 grams per square foot. The saturant which is phenolic or melamine resin ranges between 60 to 100 percent. It is used to provide a smooth surface for the board to laminate. (4) Balancing Paper This is filled cellulose paper with a basic weight between 8.0 to 15.0 grams per square foot depending on the weight of the face sheets. Its principal function is to prevent warpage and to equalize the moisture vapor transmission rates during service. b) Impregnation The paper unwinds from a roll, then is immersed in and emerges from a watery solution of resin. The absorbed water then is evaporated in an oven. The resin quantity is adjusted by the concentration and the viscosity of the resin solution and by squeezing off the excess resin by way of rolls or wipers. The films should be wet enough for further processing, but it should not be too wet, as this will cause stains. c) Press The prOper flow of the resin in the paper and the final cure are all depending on a time and temperature-pressure relationship. A workable laminating cycle (Figure 6) is presented in the following description. The specific pressures for laminating particleboard is about 355 psi and is about 570 psi for hardboard. There are two combinations of time-temperature relationship for the pressing processes; pressing at 275°F with longer curing times of 8 to 10 minutes for a total cycle xiii... Ill!!! llli.llllilll I?“ 59 .33 $on wsaumswawa vumoooaofluumm mafiaomoéa m mo Snowman musmmoum can ououmuoaaou. .o mama: . ZHZ mH .uH MH NH HH OH m w h o n .V m N H G O h p - . . p p p . . . p p p L o I a n I . gmmmmm I I. I. I ... I ¢ . gfiémaH I a a I - mHH omw ..--------------------- own Hmm 0N." omH oom 0mm oom omm mo 60 time of about 16 to 18 minutes and pressing at 310°F with a shorter curing time of about 5 minutes for a total cycle time of 10 minutes. The lower temperature decreases the possibility of fracturing later, but has a tendency to increase shrinkage of the particleboard. One press build-up for melamine resin impregnated paper is shown in Figure 7. The particleboard for conventional laminating should have densities ranging between 45 and 47 pounds per cubic foot and the opti- mum.moisture contant ranges between 6 and 7.5 percent. Furthermore, thickness should be controlled to a tolerance of plus or minus 0.005 inch. Of course, the surfaces must be made of fine chips. 4) Vinyl Laminating (41) Wood-grained vinyl is widely used in laminating by the direct roll coater. The direct roll coater system for application of vinyl film to particleboard (Figure 8) is a high speed production layout. At first the particleboard is cleaned by the brush roll, then it goes through the glue spreader and a resin coat is applied and the glue is dried in the succeeding oven. Then, the gluing and curing processes are repeated again. After that, the substrate passes under heaters to make the adhesive sticky. Simultaneously, the vinyl film is unwound from the roll to meet the in-coming particleboard. A heated laminating nip roll applies pressure to bond the substrate and the film together. Then, the laminated particleboard is embossed and cut to size. WONQNO‘UI 61 HEATING PLATEN CARRIER PLATE PAD , . ONE-SIDED PRESSPLATE DECORATIVE FILM UNDERLAY FILM PHENOLIC FILM PARTICLE BOARD mNO‘M-bWN-l-‘ FIGURE 7. Build-Up of One Board per Opening (16). HNLADb 62 .Aaqv oumonoaoauum . a on same Haafl> mo cognac HHQQ< now amummm wafiumo o Haas uumuflo HmUHaaa .w go; 2.2 e: as . w :25 $ 2.2 22 223.. 8:8 \ :25 2.2 usage” 2.2 MEEEES _\ «=8 8.2:: ..v . p Edie: 6. FURNITURE INDUSTRY IN TAIWAN Taiwan is a densely populated country and her manufacturing industries have experienced periods of growth and development. The dense population has contributed to these developmentsby providing low cost labor. This labor force with at least a seven-year education on the average is basically skillful, intelligent, and industrious in nature. Besides, the ever-green climate of the island provides an ideal environment for running factories by eliminating a lot of auxiliary facilities and equipment. Taiwan is at a stage between a developing and a developed country. This shows in the prosperity of labor intensive industries which have a relatively low level of technology, such as the textile industry and the wood products industry. 1) Status of Taiwan Furniture Industry a) The High Growth Rate Industry Sources from the Industry Bureau of Taiwan, Republic of China, point out that the manufacturing industries will continue to grow steadily and rapidly. A long term estimation (Table 9) depicts an annual growth of 10 percent or more, during the next five years. WOod products industries rank the highest among all industries and will have a high growth potential even after the country will switch its emphasis from light industries to heavy industries. Table 9 shows that 63 64 .mafleo mo UHHpsamm .am3Hm9 mo ammuom muumsocH "mounom 0.5 m.HH 0.0H 0.NH 0.m .maH Hounds: oHHmumZIGoz .0 o.NH o.mH m.mH n.0H n.0H .0GH muosvoum 0003 .m ~.0 0.0 n.0H 0.0a ~.0H .0GH onuKMH .N m.m 0.0 0.0 0.0 0.0 .ocH voom .H 0.0 5.0 H.0H m.mH m.~H moauumnvaH uawwq o.HH H.NH m.NH o.mH 0.0H .maH sowumuuommamuy .m ~.m m.ma n.0a 0.0H m.- .maH owaouuomam 0am ofiuuomam .N 0.NH 0.0 0.0 m.NH 0.0 .maH mom can .ouumm .H m.w m.NH 0.0H n.5H m.mH mmfiuumsonH h>mmm 00.1Hm. 00.105. 0an whoa quad ucouuom Haas: .AOHV fim3HMH. CH mQHHumDVGH wfifihfiuommfifig HO SU3OHU HMSfig fimugfiumm om mgm<fi 65 the growth rate of heavy industries will leave light industries behind after 1976. b) A Further Study on the Furniture Industry Structure in Taiwan A census conducted by the Ministry of Economy of Taiwan in 1960 revealed that at least 90 percent of the furniture factories employed less than six workers per factory. However, the census of 1970 showed that 68 percent of the establishments employed less than 20 workers each with a total of 12 percent of the labor force in the furniture industry. The census also showed that two big factories were estab- lished in that period and absorbed 42 percent of the furniture employees (Table 10). TABLE 10. Size of Factory Based on Number of Employees in Furniture Industry of Taiwan (1970) (8). Eggigfirg: EggigfiIgHMENTS PERCENT EMPLOYEES PERCENT 1 - 19 52 68 379 12 2o - 39 8 10 197 6 4o - 99 12 16 708 23 100-199 2 2.5 295 10 200-499 1 1 203 7 flAbove 500 2 2.5 1286 42 Total 77 100 3068 100 Sources: Ministry of Economy, Republic of China. II 3" Id." Alll. » 66 It should be noted that almost two-thirds of the furniture industries are still operated under family controlled, non-efficient condition. On the other hand, large sized, modern plants have operated in this field for the past three years. In contrast to its population surplus, Taiwan lacks resources. Forests cover almost three-fifths of this tiny island, unfortunately, most of them are unaccessible and uneconomical for wood harvesting. Most of the wood for furniture is imported from South East Asia; teak from Thailand,and lauan, meranti and similar species from the Philippines and Indonesia (Table 11). Almost all the teak logs go into the furniture industry, while 80 percent of lauan logs are processed in plywood factories (8). TABLE 11. Logs Imported into Taiwan (8). Unit: Cubic Meter. YEAR LAUAN TEAK 1961 168,029 27 1962 275,958 762 1963 446,492 397 1964 562,307 383 1965 625,102 190 1966 691,878 1,204 1967 727,150 1,490 1968 1,090,149 501 1969 1,183,022 1,564 1970 1,489,298 3,776 1971 2,205,287 - 3,938 Source: Import and Export Statistics of Republic of China. 67 A production cost analysis conducted by the United Nation's forestry and forest industry development plan in 1968 in Taiwan is shown in Table 12. The analysis revealed the following: First, log cost in furniture-making was about 50 percent or more, depending on what the end products were. Second, direct labor varied over a wide range depending on the degree of mechanization. The lower the degree of mechanization, the higher was the percentage of the direct labor cost. Third, selling expenses, administrative, and profit were relatively low, compared to equivalent figures for the United States furniture industry, because there are few sales-promotion activities such as public exhibits or services after the sale. In all, the fragmented, raw material lacking and inefficient furniture with rather primitive processing and selling-promotion techniques is backed up inexpensive and high quality labor and offers a very attractive investment environment. As a rule, the development of an island style economy, dense in population and poor in resources, depends much more on foreign trade than on domestic sales, as Japan has shown. However, some factors favoring domestic consumptions are worthy of consideration. 2) Potential Market In Domestic Consumption It was mentioned previously that sales of furniture have related significantly to disposable personal income, residential construction and the number of young families. They are the main factors to provide a potential market. 68 .w0ma ca swam ucoamoao>mn muumnvcH powwow 0cm huumouom m.coaumz wouwcb "mousom N OOH N O.ON N O.HN N O.O N O.OO OONO AmsmuO amass N OOH N O.ON N N.OH N m.ma N O.Om HOOO ONHOO amass N OOH N O.ON N ~.O N N.~N N m.Nm AOOOOAO x669 N OOH N O.NN N O.O N H.mm N m.OO assay OOOOOO News OHOONO NOO OOOOO HOOO OHa