Document M48KJYaRN3bZn7EDJoXwN8gjy

PVC FABRICATION AND APPLICATIONS by W. C. DOUGLAS J. M. GYENGE GEORGE HACKIM A. J. HANLEY ucc 006184 BIOGRAPHIES W. C. Douglas was graduated from Purdue University in 1958 with a Bachelor of Science degree in Chemical Engineering. He initially joined Standard Oil Com* pany of Ohio where Iris work centered around the development and technical applications of secondary plasticizers for vinyl resins. Since 1963 he has been employed by The General Tire & Rubber Company as Technical Service Chemist in the field of polyurethane foams. He is a member of the Society of Plastics Engineers. J. M. Gyenge was graduated from Baldwin Wallace College in 1943 with a Bachelor of Science degree in Chemistry-. He has done graduate work at Akron University in polymer chemistry. From 1946 to 1956, he was a development chemist at the Akron Government Development Laboratories of Rubber Reserve. In The General Tire & Rubber Company's Chemical Division he has served as both Technical Service Representative and as Sales Development Engineer. He was appointed to his present position. Manager, Technical Service, in 1959. Mr. Gyenge ia a member of the American Chemical Society. George Hackim was graduated from the University of Akron in 1947 with the degree of Bachelor of Science in Chemistry. First employed by the Sun Rubber Company, he came to The General Tire & Rubber Company in 1948 in the production training program. From a first assignment in Research, he was transferred to the Chemical Division in 1950 as Manager of Technical Service and later became Sales Manager. In the newly formed Chemical Plastics Division he was: Assistant Director of Sales, 1962; General Sales Manager, 1963; and has been Vice PresidentIndustrial Sales since early 1964. Mr. Hackim is a member of the American Chem ical Society, the Society of the Plastics Industry, end is former chairmen of the Akron Rubber Group. Albert J. Hanley ia Section Head of Plastic Evaluation and Application for The General Tire & Rubber Company. Graduated in 1920 from Massachusetts Institute of Technology with a Bachelor of Science degree in Chemical Engi neering, he went on to serve as head of the chemistry department at Mount Saint Mary's College, Maryland, until 1926. He became, in turn, chief chemist at Textileather and Technical Director for Respro, Inc., plastics manufacturers, until these firms were absorbed by the parent company in 1955. At that time he became Group Head of Plastic Evaluation- and Application until appointed to his present post in 1962. Mr. Hanley is a member of the American Chemical Society, the Society of Plastics Engineers, and the Society of Plastics Indus tries, ucc 006185 TABLE OF CONTENTS I. Introduction II. End Use Applications III. PVC Besin Types IV. Conversion of Besin to Product A. Compounding 1. Stsbilixstion 2. Plssticixstion 3. Lubrication 4. Pigmentation B. Processes end Febricetion 1. Dryblending 2. Benburying 3. Milling 4. Calendering S. Extrusion a. Bigid Vinyl b. Vinyl Foam 6. Blow Molding 7. Compression Molding 8. Injection Molding 9. Fluidised Bed Coatings 10. Contour Forming 11. Assembly of PVC Products C. Decoretive Effects 1. Embossing 2. Printing * ucc 006186 D. Mixing and Processing of Plastisol Resins 1. Dip Coating 2. Slush Molding 3. Rotational Molding 4. PVC Foaaa ucc 006187 FABRICATION AND APPLICATIONS I. Introduction The previous papers have described how polyvinyl chloride is obtained as-.-''-' a granular powder. In this state, PVC has very limited use and the eonversion of PVC into commercial products depends upon its modification through compounding. The many compositions obtainable from PVC are highly adaptable to a number of operations which convert the materials into usable products. Most PVC products are obtained by calendering, extrusion, and coating techniques. Other conversion methods such as blow molding, compression molding, injection molding, and fluidized bed are used to a lesser degree.' The molecular weight of the resin, compounding, processing, and finishing all contribute to the performance and appearance of the final product. The great variety of end uses for PVC make it one of America's most thriving and expanding industries. PVC, more than any other polymer, is aynonomoua with versatility. II, End Use Applications In 1962, PVC became the world's first billion pound plastic. Figure 1 shows the sales volumes of the various classifications of vinyl for 1962 and 1963. It can be seen from the curves that calendering and extrusion captures the bulk of the market. Poundage for 1963 was greater than in 1962 in every classification except miscellaneous, and thetotal increase for the one year period is 18%. Indications are that 1964 will show a similar increase over 1963 and PVC seems headed toward a two billion pound market in the near future. As PVC has grown in volume, the price has dropped accordingly, further accelerating the plastics industry's interest in the material. The current low price of 164/lb. contributes toward making PVC one of the first materi als considered when production of a new plastic article is being planned, Though the 1.40 specific gravity of the unplasticized resin ia relatively high, the pound-volume costs of the plasticized compounds are much more favorable. This poundage is not consumed as a single product or application. PVC has widespread utility in products ranging in stiffness from rigid sheet for construction applications to flexible film for food wrapping. This extreme difference in end product application is possible because the basic vinyl polymer can be solvated by plasticizers over a range of concentrations. All of these PVC compounds are thermoplastic in character end acquire at some critical elevated temperature a rubber-like consistency! Therefore, it is not surprising that in the early days plasticized vinyl compounds were converted or formed to shape on equipment found in the rubber industry. Experience soon demonstrated that calendering, tubing, extruding, and pressing machines for rubber were inefficient for making quality vinyl products. These same types of converting machines were modified in basic engineering design, temperature range, and automatic control in order to manufacture vinyl end-products to extremely close dimensional tolerances. - 1- ucc 006188 . SUBTOTAL USAGE OF PVC RESIN (000,000 OF LBS.) FIGURE 1. YEARLY CONSUMPTION OF PVC RESIN o c 00 ^ (O </ GRAND TOTAL IN BILLION LBS. Ill. PVC Resin Types As outlined earlier, the basic polyvinyl chloride can be polymerized or copolymerized by suspension, emulsion, or solution techniques. For the purposes of this paper, the emphasis will be placed on the suspension type of resin. PVC polymer can be made in a wide range of chain lengths or molecular weights. For control and identification purposes, the molecular weight is characterized by the polymer's intrinsic viscosity in a solvent solution. The higher molecular weight polymers possess higher tensile strength and hardness, better resistance to flow at elevated temperatures, and improved solvent resistance, when compared to their lower molecular weight homologs. Table 1 Effect of Molecular Wei ght on PVC Prop ertiea Resin Molecular Weight* Intrinsic Viscosity Vygen 85 74,000 .80 Vygen 105 83,000 .93 Yx&g" 110 93,000 1.03 Tensile Strength, psi** Ultimate Elongation, %** Tensile Stress at 100% Elongation, psi** Shore A Hardness, . 0 Sec. 10 Sec. 2160 230 1290 91 80 2490 300 1400 91 80 2730 340 1420 91 81 Formulation Resin 100 parts * DOP - 50 parts Ba-Cd Stab iliter 2 parts Vygen 120 107,000 1.18 2890 350 1460 92 82 * D. J. Mead and R. M. Fuoss, J. American Chemical Society, 64, 277, (1942) * ASTM D-412-61T In a typical formulation using 50 parts of dioctyl phthslate (DOP) plas ticizer per hundred parts of resin and resins of differing intrinsic viscosity ranging from 0.80 to 1.18, it can be seen that the tensile strength, elon gation at break, and Shore A hardness increase with increasing molecular weight. Figures 2 and .7 show these points graphically.. -3- UCC 006190 TENSILE STRENGTH, PSI FIGURE 2. EFFECT OF MOLECULAR WEIGHT ON TENSILE SThtNU'W FIGURE 3. EFFECT OF MOLECULAR WEIGHT ON ELONGATION UCC 006191 Calendering temperatures increase from a 300 to 330F level with a 0.80 viscosity resin to a 330 to 360F level for the 1.18 viscosity resin, as shown in Figure 4. FIGURE 4. EFFECT OF MOLECULAR WEIGHT ON CALENDERING TEMPERATURE Higher processing temperatures tend to create resin instability problems if the processing cycle is of long duration. A compromise must often be made between the molecular weight resin selected and the processing tech* nique. The higher molecular weight resins are used in extrusions of flexible tubing, welting, electrical components, garden hose, and calendered film which require short dwell times at the elevated processing temperatures. Intermediste molecular weight resins are used in film snd sheet, costed fabrics snd rigid applications. Low molecular weight resins are used in fluidised bed coatings, phonograph records snd injection molded parts. * 5- ucc 006192 IV. Conversion of Resin to Product A. Compounding 1. StabiLi ration Very few polymers inherently possess outstanding heat or light resistance on long term exposure, and polyvinyl chloride is no exception. The science of PVC degradation is well established and, although complicated, is known to involve the loss of a chlorine and a hydrogen atom from adjacent carbon atoms on the backbone chain. Strong alkali promotes this loss of hydrogen chloride. A slightly alkaline metallic salt will act as an acid acceptor and prevent further generation of 11C1 along t)ie polymer chain. Lead aalta such as basic lead carbonate or lead silicate were the earli* est stabilizers used in polyvinyl chloride. Lead atabilizers are atill used in electrical insulation where the service specifications require up to a 10SC temperature rating. Organo-tin compounds such as dibutyl tin dilaurate or tin maleate are liquid at processing temperatures and can be dispersed through the PVC compound more readily than solid metallic salts. They also protect the polymer by saturating the double bond created wherever HC1 is lost in the first stage of decomposition. A major advance in stabilization was the discovery that organocadmium compounds are synergized in their stabilizing action by companion barium organic compounds. These systems are readily dispersed end have limited solubility in plasticized PVC compounds and make possible haze-free products of good clarity and color. 2. Plaaticization It was stated previously that polyvinyl chloride reaina ere capable of being compounded into a wide variety of products hsving different degrees of flexibility end hardness. This great versatility is poaaibla because of the softening action of plasticizers on the hard horny resin. In general, the degree of softness of the com pound will be in direct proportion to the plasticizer-resin ratio. By varying this ratio, a wide range of PVC properties can be achieved. The chemical function of a plasticizer is dependent upon the presence of polar groups in its molecular structure. This polarity allows the plasticizer molecules to be inserted between PVC resin molecules, neutralizing the Van der Waal or secondary valence bonds. This weakening of the Van der Wnal forces creates localized flexible areas intermingled with resin strength sreas. The combination re sults in s strong, yet pliable, polymer. There is evidence that the plasticizer swells the amorphous regions end that' the small regions of crystallites are unettacked or unaffected by the plasticizer. This situation ia unique to polyvinyl -6- UCC 006193 chloride. It permits the creation of products which are flexible without being weak, are resilient without being snappy, are more leather-like than rubbery, have surface slip without tack, and have good abrasion resistance. Commercial products of satisfactory durability require that the solvent or plasticiiing agent have long term permanence. The plasticizer should be at least as permanent as the properly stabilized resin. To be permanent, the plasticizer must either be a true solvent or be associated with a true solvent for the PVC resin. The plasticizer must resist oxidation both during processing and during long term in-use aging for periods up to five or more years. Its affinity to the resin must be greater than to foreign substances which would normally contact the PVC product in service. For upholstery, these substances would include resistance to wicking into clothing, dust or dirt, and soapy water washing. It must have a very low volatility to eliminate evaporation. It should be odorleas and colorless in order to have widespread utility. When the material in question meets these speczfications to a practical degree, it becomes known as a primary PVC plasticizer. Ordinarily, a plasticizer will be a high molecular weight ester formed by the reaction of an aliphatic alcohol of eight to twelve carbon chain length with an acid which may be either phthalic, azelaic, adipic, or sebacic. Polymeric forms of esters are usually in the 2000-500U molecular weight range. These plasticizers are used where special permanence is required. Plasticizers are commonly liquids with viscosities which may be as low as a light oil or as thick as honey. They vary widely in their efficiency in flexibilizirig the PVC resin and the particular proper ties contributed to the PVC product. For this reason, it is common practice to blend a mixture of plasticizers to obtain a compromise of their individual assets and defects. It is this type of blending that makes vinyl products so versatile. Figures S, 6, and 7 show the effect of DOP plasticizer (di-octyl phthslate) concentration on the tensile strength, elongation, and Shore A Hardness of a Vygen 120 formulation. Where exceptional permanence or dimensional stability is demanded, chemically bound copolymers and physical polymer blends provide the answer. Nitrile rubber (butadieim/ocrylonitrile) can be used, although its poor color limits it to dark colored applications. Other polymers used for modification are chlorinated polyethylene, scrylica, and aerylonitrile-butadiene-styrnne (ABS) resins. -7- ucc 006194 POUNDS/SQUARE INCH FiGuHE 5. Lftc.Cl' OF DuP LEVw. ON TENSIII EiHhNuili FIGURE 6. EFFECT OF OOP LEVEL ON ELONGATION 8 ucc 006195 FIGURE 7. EFFECT OF DOP LEVEL ON SHORE A HARDNESS SHORE A HARDNESS. 10 SEC. 3. Lubrication Vinyl is processed and formed by metallic parts which may be a set of rolls, a forming die, a mold, or some other device. During this processing, the vinyl must adhere to the metal so that the plastic draws in, fills, and flows with the forming surfaces. However, this adhesion must not be great enough to cause distortion when the article is removed-from these metal surfaces. Adequate parting is obtained by including in the compound trace quantities of lubricants that act as metal release agents. The release agents are soluble to only a limited degree in the vinyl compound at the processing temperatures. Thus, minute particles of the release agent are deposited on the hot metal surfaces and form a semicontinuous coating. Excessive quantities of the release agent should be avoided to prevent exudation on the finished PVC surface. Exudation of lubricant appears after processing and is not only unsightly, but can interfere with the application of decorative finishes or subsequent dielectric heat sealing. Stearic acid is a common release agent, but metallic stearates, waxes, or poly ethylene have been used. Proper technology in the use of lubricants is an important factor in successful production of vinyl products. 4. Pigmentation The growing use of PVC has been due in part to the color possibilities of the plastic. - 9- UCC 006196 Automotive and household upholstery are presently made in high style colors to match or contrast with any color scheme. PVC sheeting having superior durability is produced in colors and tex tures which'offer unlimited creative styling possibilities to the designer. The pigments used must be acid resistant, stable to the processing temperatures up to 400F, nonmigratory, and light stable. The pigments are dispersed to a fine particle size by grinding in a three-roll paint mill with part of the plasticizer. Satisfactory pigments include titanium dioxide, phthalocyanine blues and greens, and high tint carbon blacks. Fillers are often used for coat reduction. Finely divided calcium carbonate is most often used, but clay, asbestos, and other fillers are common. Certain electrical properties are improved through the use of fillers. Flame resistance is bolstered through the incorporation of antimony trioxide and phosphate plaaticisere. Electrical properties are improved with the addition of calcined clay. B. Processes and Fabrication 1, Dryblending A PVC compound initially is a heterogeneous mixture of the many components. The major ingredients are a PVC resin powder and a liquid plasticizer which must solvate the resin. The solvation rate of this type of system is time and temperature dependent. The most economical method of solvating the resin is through the use of inexpensive mixing equipment with large capacities. Thus, large stainless steel chambers jacketed for heating are used to churn, tumble, or agitate three to five thousand pounds of the compound. At this stage, only the colorant is omitted. The temper ature is maintained at 180 to 200F for about an hour. This equip ment is often a ribbon blender. 2. Banburying Part of the presolvated resin-p1asticizer masterbatch from the pre blender, together with the pigment paste, is fused into a homogeneous mass in an intensive shear internal mixer such as a Banbury. This machine consists of a two cylindered stator containing two powered rotors. Their operation is such that the plastic compound is sheared against and around the stator's surfaces. The stators and/or the rotors are heated to raise the temperature of the vinyl compound to its fusing temperature between 300-350F. A plunger retains the compound within the chambers and a sliding door in the bottom of the chambers allows the fused homogeneous compound to be discharged. The capacity of production size Banburys for the vinyl industry varies from a 110 to a 600 lb. batch delivered on five minute cycles. Milling Normally, a Banbury batch is delivered to one or more 60" to 90* wide two-roll mills designed for high temperature operation. The 10 - ucc 006197 threefold function of the Mill is: (1) to free the plastic of entrapped air whipped in by a high speed Banbury; (2) to bring the plastic to a controlled temperature (and, therefore, a constant plastic viscosity); and (3) to deliver the plastic in a ribbon of predetermined width and gauge of thickness. This ribbon stock may be fed directly to a calender or an extruder in practically an ideal plastic state, or it may be partially cooled and fed to a dicer or pelletizer to make a reserve compound inventory for future processing. Calendering A large percentage of the above mill-prepared vinyl plastic com pound is fed to a calender which converts the crudely shaped ribbon into continuous lengths of film, sheeting, or coating for a sub strate (i.e., woven cloth, knit fabrics, or paper, etc.) of surprisingly accurate widths and thicknesses. For example, a modern plastic calender is capable of delivering a 0.0018* gauge film with a maximum variation in gauge of 0.0001*. Normally, film of this gauge can be more economically produced by extrusion, since a two million dollar calender train must have a high poundage output to justify its capital investment. A modern calender engineered for handling plastics has four cast chilled iron rolls mounted in a Z type frame so that the influences of forces on any one roll can affect only one adjacent roll. A roll with a working face of 66* width will be from 20* to 24* in diameter while a 96" width roll face will have from 30* to 36* in diameter. This calender will be automated both to control the gauge of the film and also to emboss, cool, and deliver the film to the packaging unit. These devices and their controls in the calender train repre sent an investment of a million dollars. The output production of a calender is dependent upon the gauge of the plastic delivered and generally falls in the range of 2000 to 3000 lbs. per hour for a 66" width machine. The ordinary plastic calender produces film between 0.003" and 0.005* gauges to be used for raincoats, shower or window curtains, aprons, baby pants, food covers, and similar articles. Film be tween 0.005" and 0.010* gauges is used for inflatable toys, air mattresses, industrial protective covering, and electrical tape. Sheeting between 0.016" and 0.022" is used for novelty purposes such as ladies handbags, belts, wallets, and briefcases. All of these gauges are used for coating fabrics or paper that are widely uaed in upholstery, rainwear, apparel, boat decking, shoe trimmings, book covers, and many other uses. Table 2 shows a typical formulation for a General Purpose Film. - 11 - ucc 006198 Table'2 Typical PVC Formulation General Purpose Film Parts Benin: Plasticitors: Processing aid: Stabi1izer: Vygen 110 DOP Cresyl diphenyl phosphate Monomeric epoxy plasticizer Stearic acid Ba-Cd 100.00 37.00 8.00 5.00 0.25 2.00 5. Extrusion A second method for shaping a molten plastic into a desired shape is with an extruder. This device consists of a smooth bore cylinder with a close fitting worm screw rotating inside the cylinder. PVC compound as cold pellets, cold dry blended powder, or hot mill ribbon is fed to the extruder. It is homogeneously mixed and brought to its proper working viscosity for ultimate forming by the mechanical energy of the screw and the heat provided by the controlled temperature cylinder or barrel. The changed pitch of the screw at its end alters the screw's function from masticating and mixing to that of a positive displacement pump. The orifice or die mounted at the head of the screw is similar in shape to the desired product. The shaped extrudate is drawn in a measured degree from the die to the cooling medium, usually water. The die must be designed in such a fashion as to compensate for the change in dimensions and shape that this pull or draft exerts on the hot extrudate. The extruder can form flat film, sheeting, and coated products simi lar to the products of a calender and, in addition, make hollow articles and complex shapes impossible to obtain from a calender. It is considerably less costly to install, but has only a small fraction of the capacity of a calender. Film as thin as K mil can be extruded by the blown film technique. A tube with a wall thickness of 0.012* is extruded. As the tube of hot plastic issues from the extruder, air is introduced inside the tube in sufficient quantity to expand the plastic to a 72* diameter cylinder. This simultaneously widens the film and reduces the gauge of the wall thickness. The percentage gauge tolerance of this film is far greater than the -- 5% allowable for calendered film, hut it is adequate for film used in packaging applications. An alternate procedure to blown film is the use of a slit die with dimensions approximately equal to that of the film desired. This die requires a high degree of engineering sophistication to.produce uniform flow of the PVC plastic across wide widths and especially to prevent any sectional areas in the flow of the PVC plastic that are slow moving or 'dead.* This latter condition can lead to 12 degradation of the PVC doe to the excessive heat history. Slit die extrusion is true plastic forming. The films produced readily conform to close tolerances in gauge not possible with blown film. Lamination of the hot film directly to a preheated substrate such as a fabric or paper is possible with slit die extrusion. Milk carton paper is often coated in this manner. The extruder is used for making film, monofilament strips, rods, tubing, hose and profile shapes such as refrigerator gasketing. Table 3 shows a typical PVC refrigerator gasket compound. Table 3 Extruded Refrigerator Gasket Parts Resin: Plasticizers; Filler: Stabilizer: Processing aid: Vygen 120 Polymeric epoxy plasticiser Polymeric plasticiser Calcium carbonate Ba-Cd Lubricant 100.00 10.00 80.00 25.00 1.50 0.25 The extruder is the universal device used for PVC coating of elec trical wire. In this latter application, the copper wire is pre heated, passed through a cross head'on the extruder and carefully centered in a circular stream of extruding plastic so that an even coating surrounds the wire. The wire is pulled at a constant race of speed and actually aids the production rate of the extruder in assisting the flow of the plastic. A cross head is a device for changing the flow of the plastic to a right angle with its normal flow. The capacity of an extruder is rated by the diameter of its cylin der. Extruders are available in a range from 1)4* to 12* with the 214", 414*, and 6* the moat popular sites. Their output capacities are about 175,500, and 1000 pounds per hour, respectively. The technology of the action of various thermoplastic materials during extrusion has received intensive study during the past five years and many plaatica have had their behaviour reduced to mathematical terms. For example, screw design has been keyed to specific thermo plastic compositions and the proper ratio of the length of the screw to its diameter (L/D) has been established. Plastic extruders nor mally have an L/D of at least 20/1 and often are 30/1. As in the case of calendering, the process of cooling the extrudate and handling during postforming ore highly developed operations which affect the surface characteristics, clarity, flatness, shape, and gauge of the product. Rigid Vinyl Rigid PVC contains only a small amount of plasticiser or none at all. Two types of rigid PVC are available. Type 1 possesses - 13 - ucc 006200 excellent chemical resistance, physical properties, heat distortion, and weather resistance. Type 2 has slightly lower chemical and physical properties but has better impact resist ance, up to 20 times that of Type 1. The impact strength is provided by inclusion of nitrile rubbers or modifying resins, along with stabilizers, fillers, and additives. Fabrication of Type 2 is easier and surface defects are less of a problem. Types 1 and 2 PVC are used in electrical conduit, pipe, con struction panels, tank linings, valves and skylights, and many other rigid applications. Table 4 shows the effect of molecular weight and resin modifier on the physical properties of rigid PVC. The use of the A8S resin provides a substantial increase in impact resistance. Table 4 Effect of Molecular Weight and Modifying Resin on Rigid PVC Properties Intrinsic Resin Viscosity _1_ 2_ 3_ i. Vygen 65 Vygen 85 Vygen 120 ABS* 0.70 0.80 1.18 100 - 100 70 - - 100 - - - * 30 _5_ - 70 30 Properties Tensile Strength, psi 7,750 7,775 7,850 6,150 6,250 Flexural Strength, psi Flexural Modulus, psi 11,750 12,000 12,500 9,225 9,600 4.2 x 10s 4.2 x 10s 4.4 x 105 3.3 x 10s 3.6 x 105 Notched Izod 77F, ft. lb./in. 0.44 0.50 0.80 14.0 18.0 Heat Distortion a 264 psi, C 10 mil deflection 69 69 75 66 72 60 mil deflection 75 76 80 74 78 Rockwell "R" Hardness 115 115 116 107 108 * Acrylonitrile-Butadiene-Styrene resin b. Vinyl Foam Vinyl foam may be prepared from suspension resin by extrusion. Nitrogen compounds which decompose under heat are used to pro vide the gas needed for expansion. The decomposition temper ature is adjustable by a post expansion technique. In this process, the material is extruded at a temperature below the blowing agent decomposition temperature; subsequent expansion - 14 UCC 006201 of the foam is accomplished by heating. Minimum practical density is seven pounds per cubic foot by post expansion. High density <40 lb./cu. ft. and higher) closed cell foam may be produced by direct extrusion and blowing of the compound within the barrel of the extruder. Expansion occurs upon the emergence of the compound from the extruder head. Closed cell vinyl foams are also made from blends of vinyl and nitrile rubber. The proper relationship must be maintained between the cure of the nitrile and the decomposition of the blowing agent, since the curing nitrile supports the cellular matrix. Too rapid a cure leads to ruptured cells; too slow s cure results in lost gas, giving high densities. Proper balancing of the system gives densities ss low as four to six pounds per cubic foot. 6. Blow Molding Blow molding is a well-accepted process for the production of plastic bottles especially, but the use of vinyl in this process in the U.S.A. has not reached the volume which it enjoya in Europe. The alower growth of blown PVC bottles in this country has been due to a lack of stabilizers which will permit clarity of the finished bottle and still pass the toxicity requirements of the Pood end Drug Administration. Blown PVC bottles do show superior properties to polyethylene types. In addition to high clarity and good oil resistance, PVC bottles have 1/10 the oxygen permeability of similar PE bottles. Due to the high rigidity of PVC, thinner walls can be used. An extruder is the source of the prepared hot plastic compound for blow molding. In this process a cylinder of hot plastic falls in a vertical position below the extruder head and between the opening of a split mold. The split mold closes to pinch the ends of the plastic, making a sealed tube. A hypodermic needle pene trates the interior of the sealed tube, end presaurized air is injected to expand the sealed tube until it fills the mold cavity. The cold or relatively cold mold converts the plastic to its hardened condition in a few seconds. The mold opens and discharges the molded object, and the cycle repeats itself automatically. The formed object may be a waste basket, an automobile arm rest, or a part of e toy doll, although PVC bottles have one of the most interesting possibilities for future markets. This is an intricate art requiring extremely accurate control of the temperature (i.e., viscosity) of the PVC compound. Clarity is achieved through proper compounding and is based mainly on the stabilizer used, although the chilling rate of ths hot article, particularly bottles, is also important. A rapid chill usually improves the clarity. Some degree of clarity is lost due to the increased molecular weight needed for impact strength. - 15 - ucc 006202 Higher molecular weight also necessitates the use of higher proceasing temperatures. Stabilizers sanctioned by FDA are primarily zinc and calcium types. However, these materials give less protection at processing temper* atures than the barium-cadmium and tin types. The success of PVC blow molding in Europe is due to the use of di-octyl tin compounds, which are as yet unacceptable in this country. As more acceptable stabilizers are developed, a large market will be created for PVC bottles where other thermoplastics are unaccept able. The future should see PVC bottles used to package gasoline, motor and mineral oils, polishes and insecticides, cosmetics, per fumes, disinfectants, detergents, foods, and soft drinks. 7. Compression Molding The molders of phonograph player records consume lsrge tonnage of vinyl compounds for compression molding of their disks. They use a low molecular weight homopolymer or copolymer resin for this purpose and the application is a specialized industry. Clear rigid sheeting as windows for instrument panels, flexible clear sheeting as rear windows in automobiles and novelty applications, are also press molded. 8. Injection Molding PVC compounds are used to a limited extent in injection molded parts. The rotating plasticating screw plunger type of machine is definitely preferred in processing vinyl. 9. Fluidized Bed Coatings The fluidized bed coating technique is excellent for coating intricate metallic parts. This can be done with a powder blend containing all plasticizers, pigments, and stabilizers. The more popular and successful method is to fuse the powder blend and to then pulverize it into a fine powder. The coating technique is to heat the part to be coated to a temper ature in excess of 4S0F. The heated part is then suspended in an environment of the powdered resin- blend which is fluidized with a stream of sir. The thickness of the fused layers can be controlled very accurately. Repeated dippings can build up thick and uniform coatings. 10. Contour Forming Irregular formed parts, such as automotive crash pads, are usually made from flat sheets which are postformed to the desired shape. The most common procedure is to use the vacuum forming system. In this technique the flat sheeting is softened by radiant heat to the forming temperature. The preheated sheet is then placed over - 16 - ijrr 006203 a female mold, a vacuum is drawn in the mold and the atmospheric air preasure cause* the vinyl sheeting to flow and fill the con tours of the mold. Since the mold is cold, the vinyl sheet loses its heat rapidly and can be lifted from the mold a minute or two later. An alternative type of molding to. vacuum forming uses air pressure to distort the hot vinyl sheeting into a female mold providing it is equipped with holes for the escape of air entrapped in the molds, The use of matched male and female molds results in products with the closest dimensional tolerance. 11. Assembly of PVC Products PVC products arc readily cut to size in multiple layers by the commonly employed motor driven circular knives or by cutting with pattern shaped dies. Dielectric heat sealing is often used to seal PVC films and flexible sheets. In the process, the PVC to be joined is placed between two electrode scaling bars which transmit a high frequency current to the PVC and exert the required pressure on it. Heat provided by friction from shifting of the polar chains within the material causes the films to flow together and seal. The resultant seams have bond strengths equal to the strength of the goods. The use of recommended solvent cements to make assemblies is as satisfactory as dielectric sealing and are used for large objects such as in tent-making or swimming pools. Fabric backed or sup ported PVC products are sewn with thread as in upholstery assembly. C, Decorative Effects A high percentage of vinyl resin products are consumer items and depend ent upon their attractive surface appearance and style to sell. These effects are obtained by either embossing or printing the colored surface, or both. 1. Embossing Embossing of the plastic is achieved using steel rolls engraved with impressions that will give a pleasing appearance. These rolls are mounted over rubber backup rolls in the calender or extruder train es close to the forming orifice as possible. At this loca tion, the plastic sheet is in its ideal rheological condition to form into and permanently retain the configuration of the delicate engraving pattern of the embossing roll. 2. Printing The majority of automotive upholstery is currently finished in metallic effects across the entire surface. These chrome tones cannot be obtained directly from the calender since the aluminum flake does not have an opportunity to *leaf* as it does in a highly - 17 - ucc 006204 fluid vehicle. The finish must be from a colored solution using a rotogravure print technique. The fabric is aubsequently dried free of solvent. Design print falls into two classes. There are the delicate and subtle shadings associated with high grade leather effects and the gaudy and often multi-color effects of houseware and apparel mate rials. These are also applied on rotogravure print machines equipped with print rolls having the appropriate design engraved into their surface. At times, print machines must have up to eight stations applying different colors which print in register to make a flower reproduction. D. Mixing and Processing of Plastisol Resins So far we have discussed how PVC suspension produced reaina are com pounded and processed. Plastisol resins ere handled and processed in an entirely different manner. Plescisol compounds are made so that whan the resin ia blended with a liquid plesticixer, the mixture ie in the form of e fluid. Plastisol resins are often termed "stir-in reaina,* for a common method of blending a plastisol resin formulation is the use of e simple agitstor. Hi-shear mixers are quite common, although practically any method by which the resin can be dispersed uniformly in the plasticiser end/or solvents is acceptable. In the blending process, the liquids in s formulation are charged to a vessel and agitated until mixed. Then the plastisol resin and other powders are added gradually under agitation until all materials are charged end a uniform liquid, called a "plastisol,V is'produced. When organic solvents are included in the formulation, the liquid ia termed an 'organosol,* The solvents are used as viscosity reducing agents. The rheology of these liquid systems is quite critical, since they are processed by methods where the `flowability muat be cloaely controlled. Plaatiaola ere ueed in the following ways: 1. Dip Coating A widely uaed process is dip costing. In this process, an article, such as a wire dish drainer, is dipped into the plastisol and re moved. The coating ia then fused on to the dipped article in forced draft ovena.- When en organosol is used, the heating of the article muat be carried out in two stages. The first stage consists of evaporation of the solvent under low heat; the second stage consists of fusion of the vinyl. In this way, surface imperfections due to - boiling solvent during fusion are eliminated. Usually, a solvent recovery system ia installed in plants using organosols for reasons of economy. In a variation of this process, cotton gloves on metal hands are dip coated in order to impart chemical protection and solvent resistance to work gloves. Articles too large for dip coating may be sprayed with plastisol and subsequently fused. 18 ucc 006205 2. Slush Molding Slush molding is, in s sense, the reverse process of dip coating. In this process the plastisol is poured into s heated mold. The mold is then inverted and only a coating of the gelled vinyl remains in the mold. Fusion and stripping of the article from the mold complete the process. Boots are made by such a technique. The main restriction of slush molding is that the article must have at least one sizeable opening to the interior to permit filling and emptying the mold of plastisol. 3. Rotational Molding Rotational molding is much like slush molding, except that there need be no opening in the article for the introduction of plastisol. It is used for complex shapes like dolls' heads, arms, etc. It is also used for play balls, footballs, and basketballs. In the tech* nique, a quantity of plastisol is poured into a mold, the mold is closed and rotated in three dimensions while heat is used to fuse the formulation inside. Temperatures must be controlled so as to permit even fusion and uniform flow characteristics. 4. PVC Foams PVC foams are easily prepared from plastisols. Either a chemical which decomposes under heat or a mechanical entrapment of gas may be used. The plastisol is often laid down as a thin coating over another vinyl layer which may or may not be fused. When blown, the combination is effectively used as an insulating material resembling leather for use in outerwear. The areas of cushioning and insulating are more often captured by urethanes or polystyrenes. - 19 - UCC 006206 1 If > 1. Saith, Wa. Mayo, Vinyl Resins. Reinhold, New York, 1958 2. Schildknecht, Calrin Everett, Vinyl Polymers, Wiley and Sona, New York, 1952 3. Bernhardt, Ernest C., Processing of Plastic Materials. Reinhold, New York, 1959 4. Cope, Dwight, Plastic Materials. Goodheart*Wilcox Co., Chicago, 1956 5. Esterez, J. M. J. and Powell, D. C., Manipulation of Theraoplastic Sheet. Rod and Tube. Iliffe & Sons Ltd., London, 1960 6. Simonds, Herbert Rumsey, Source Book of the New Plastics. Reinhold. New York. 1959 7. Frados, Joel (Editor), Modern Plastics Encyclopedia for 1964, Vol. 41/ No.'1A, Hildreth Press, Inc. , Bristol, Connecticut, 1963 8. SPI Plastics Engineering Handbook, 1960 . 20 ucc 006207