Vinyl CHloride Monomer Emissions From The Polyvinyl Chloride Processing Industries. Report to U. S. Environmental Protection Agency, Research Triangle Park, North Carolina. Lita Nelsen Jack Milgrom Robert Eller May 1975 76086-11

VINYL CHLORIDE MONOMER EMISSIONS
FROM THE POLYVINYL CHLORIDE PROCESSING INDUSTRIES

Report to
U. S. Environmental Protection Agency
Research Triangle Park, North Carolina

Plastic products based on polyvinyl chloride (PVC) are among the oldest of the major plastic materials. The first commercial plant to make PVC resin was constructed in 1939, and consumption has now grown to over 4.5 billion pounds per year--the second largest plastic (after polyethylene) consumed in the United States. PVC is the most versatile type of synthetic resin produced and is used in more individual end products than any other type of plastic material. This versatility arises from the relatively low cost of PVC, its ease of fabrication, its solvent, weather and abrasion resistance, and the fact that its mechanical properties can be varied by proper adjustment of additives to yield products ranging from rigid, brittle materials to soft, rubbery ones.

There are three major processes in the conversion of vinyl chloride monomer to a finished polyvinyl chloride product: (1) polymerization of the monomer to the polymer; (2) compounding, or addition of additives to the polymer to yield the desired properties for handling the polymer and in the final product; and (3) fabricating, in which the compound is melted and then formed into the final shape required. Because of the wide variety of uses to which PVC is put, there is a considerable variety of polymerization processes, compounding operations and fabricating processes which must be used to arrive at the desired end properties. Figure II-1 presents a schematic of the types of polymerization processes used to produce each end product. These processes are discussed in some detail in the following subsections.

PVC resins vary in molecular weight and in chemical composition. The molecular weight of most commercial PVC resins lies between 50,000 and 120,000 and most PVC resins are homopolymers made from vinyl chloride alone. About 15% of the vinyl chloride polymers are copolymers containing vinyl chloride and other monomers, with vinyl acetate being the most common comonomer. The processing and performance characteristics of PVC depend upon the nature of the polymer itself and on the additives used in the compound.

Although it is the purpose of this present program to assess vinyl chloride monomer emissions only from the compounding and fabricating steps of this process, the details of the polymerization processes also impact on the monomer emitted. The different polymerization processes result in different amounts of residual monomer remaining in the raw resins, which may later be emitted during fabrication operations.

End Product             Fabrication Process      Compound
Pipe & Conduit              E                       R
Panel & Siding              E                       R
Flooring                    CP, C                   P, F
Upholstery                  CP, C                   P, F
Pipe Fittings               IM                      R
Lighting Fixtures           E                       R
Film (Packaging)            E, CP, C                F, S, R
Sheet (Packaging)           C, E                    R
Rainwater Systems           E                       R
Bottles                     BM                      R
Weather Stripping           E                       F
Wire & Cable                E                       F
Baby Pants                  C                       F
Footwear                    LP, IM, SM, CP, C       P, F
Outerwear                   CP, C                   P, F
Windows                     E                       R
Hose                        E                       F
Phonograph Records          CM                      R
Toys                        RC, IM, LP              P, F. R
Auto Mats                   CP                      P
Auto Tops                   C, CP                   P, F
Medical Tubing              E                       F
Tool Handles                CP                      P
Credit Cards                E                       R
Wallcoverings               C                       F
Can Coating                 CP                      S, 0
Exterior Paint                                      L
Closure Gaskets             LP                      P

Figure II-lb. Polyvinyl Chloride Manufacturing Processes
(For key to processes and compounds see Figure II-la above)

1. Description of Processes
There are four commercial processes currently employed in the U.S. for the manufacture of PVC resin: suspension, emulsion, bilk, and solution polymerization. All four processes are based on free-radical polymerization of vinyl chloride monomer, using initiators such as organic peroxides. The choice of polymerization method depends on the ultimate application of the resin and the economics of the processes.

Suspension polymerization is the most commonly used process in the U.S. today, accounting for about 80% of PVC production. This process can be used to prepare both homopolymers and copolymers of a variety of molecular weights. In the suspension process vinyl chloride monomer is suspended in water with a small amount of a suspending agent. The molecular weight of the resulting polymer is generally controlled by the reaction temperature and by the addition of modifiers. After completion of the polymerization reaction, the solid polymer, which is in the form of fine beads, is recovered by centrifugation and drying. Depending upon the ultimate application, the product may be sold as (1) an unstabilized polymer, usually in the powder form as it is obtained from the reactor; (2) a dry powder blend with additives and/or colorants; or (3) a pelletized compound. Suspension resins are used for both rigid and flexible formulations.

About 11% of the PVC resin produced in the United States in 1974 was produced by emulsion polymerization, which is basically very similar to the suspension process, except that relatively large amounts of emulsifying agents are used. This process produces resins with a very small particle size and typically of higher molecular weight than the suspension resins. To maintain the small particle size, emulsion resins are usually dried using a spray drying technique. (Complete removal of the emulsifiers is never achieved in resins produced by this process so that products requiring high clarity, for example, packaging film or very low water adsorption, such as wire insulation, cannot. be produced from emulsion resins. The resulting powders, which are called paste resins or dispersion resins are sold either to independent compounders or to fabricators. In the United States all plastisols are made from dispersion resins, primarily homopolymers. About lox of the polymers made by the emulsion process--or a total of about 50 million pounds of PVC in 1974--were sold as latices for coating app applications; all of these are copolymers.

Bulk polymerization is a relatively new process in the United States. It was developed in France (by Pechiney) and is used by Hooker Chemical Corporation,

the Goodyear Tire & Rubber Company, and the B.F. Goodrich Company. About 6% of the PVC resins produced in the U.S. in 1974 was made this way.

In this process the monomer is polymerized in the absence of solvent. The reactors are specially designed to handle bulk polyvinyl chloride at elevated temperatures.

These bulk polymers have several desirable features--high porosity (desirable in making flexible compound), clarity, and relatively uniform shape and size of the particles. They also have remarkably good heat stability and improved fusion properties, and can be processed with the ease of conventional vinyl chloride-vinyl acetate copolymers. Bulk-polymerized resins resemble the suspension resins and are used in the same applications.

Although solution polymerization is over 40 years old, only about 3% of the PVC resins produced in the United States in 1974 were produced by this method. At present vinyl chloride solution polymerization is used only for the production of copolymers of vinyl chloride and vinyl acetate (usually containing 10-25x vinyl acetate). Union Carbide is currently the only U.S. producer of solution-polymerized resins.

In the solution process the monomers are dissolved in organic solvents such as n-butane or cyclohexane. The polymerization is carried out in an autoclave, and the polymer precipitates as the reaction proceeds. The resulting resins are usually dried and sold as powders or beads. Most solution process resins are sold to formulators who prepare solutions containing these resins for various coating applications.

Table II-1 shows the U.S. production of PVC resins in the last five years categorized by polymerization process. (Appendix Table A-I lists the major U.S. resin manufacturers.) As shown in Table II-1, in the period 1969-73, PVC production increased at an annual growth rate of about 11%.

Production growth slowed to about 7% last year. Most of this growth has been the production of suspension homopolymer resins. (Table II-1 resins made by the bulk process are included with the suspension resins.) Because of the improvement in the processibility of suspension and bulk hompolymers, the need for easier-processing copolymers has diminished over the past few years.

Pure polyvinyl chloride resin is usually unsatisfactory as a material for packaging, construction, upholstery, and many of the other applications for which it is used. Its brittleness, difficulty of processing, degradability, etc., require that the raw resin be "compounded" with a variety

          Suspension    Suspension     Dispersion
        Homopolymers^a   Copolymers   Resins and Latex    Total
1969         2052           592            388          3032
1970         2232           519            364          3115
1971         2475           504            458          3437
1972         3149           559            550          4258
1973         3433           540            589          4562
1974^c        3687           581            632^d          4900

Annual Growth (%)
1969-1973    13.8          -2.5           11.0          10.7
1974          7.3           7.6            7.3           7.5

^a Includes polymers made by bulk process.
^b Includes polymers made by solution process.
^c Estimated by Modern Plastics, January, 1975.
^d We estimate the production of dispersion resins in 1974 amounted to 475 MM lbs.

Source: Society of Plastics Industries, Annual Statistical Reports, and Modern Plastics, January, 1975, and ADL.

of additives in order to achieve the required properties. The concentration of additives in these compounds can vary from 3% to over 100% (based on the weight of resin). Four major categories of compounding are considered: (1) rigid PVC compounding; (2) flexible compounding; (3) compounding (or formulating) of plastisols and organosols; and (4) formulating of PVC solutions.

Rigid compounds, which are supplied as powders or pellets, contain from 80 to 97% PVC depending upon the end application. Three to five percent of an elastomeric product is often added as an impact modifier to rigid compounds used for pipe applications. Rigid compounds often require pigments such as titanium oxide in addition to lubricants and stabilizers.

Although most rigid compounds are homopolymers, some copolymers are also sold. These are usually lower in molecular weight than the homopolymers, and contain vinyl acetate as the comonomer.

Dry blending is typically used to prepare rigid compounds of PVC in powder form. These powders are usually used to manufacture PVC pipe. Dry blend powders are economical, particularly if compounding is done directly in the polymerization vessel prior to discharging the resin. Robintech today manufactures a suspension resin which is compounded in the polymerization kettle and used to fabricate pipe, and which does not require further dry blend compounding.

Flexible PVC products require plasticizer to soften the hard resin; the types and concentration of plasticizers used are very varied. Flexible compounds are made by mixing the dry PVC resin with plasticizer and other additives, frequently followed by fusing and pelletizing of the compound. In these compounds, the dry resin accounts for 33-60% of the composition, with the plasticizers, fillers, antioxidants, lubricants, and other additives comprising the remainder. Resins used are primarily high-molecular-weight homopolymers; the molecular weight is usually higher than resins used in making rigid compounds. Resins for flexible compounds, like those for rigid compounds, are made by the suspension or bulk process.

Most flexible PVC coatings and a small fraction of flexible molded products are made from plastisols. These plastisols are dispersions of PVC resins in plasticizer with other compounding ingredients such as stabilizers, fillers, and pigments. Some plastisols are very thin liquids, and others are heavy, doughy pastes. The manufacture of plastisols requires PVC dispersion resins, which are made primarily by the emulsion process (although a very small percentage is produced by the solution process). Plastisols are made primarily from homopolymers.

Because the dispersion resins are more expensive than those made by the suspension process, small amounts of suspension resins are often added to lower the costs of a plastisol formulation. Suspension resins used for this application are called blending resins.

Organosols are similar in constitution to plastisols, except that they are thinned with solvents to control the viscosity for certain coating processes. Organosols are often used in coating processes, such as metal coating, where low viscosities are needed and where evaporation of the volatile thinner does not affect the appearance of the product.

Plastisols and organosols are not sold by the resin producers. They are sold either by an independent formulator or are prepared by the fabricator.

PVC solutions are also used for coating applications. Most PVC can coatings are formed from such solutions. Resins for this application are prepared primarily by solution polymerization although some are synthesized by the suspension polymerization process. Because the dispersing agents in suspension resins interfere with the properties of the solution, they must be removed after polymerization; otherwise, the coating resin will not possess maximum clarity and water resistance properties.

Most PVC solution coating resins are copolymers, typically containing 3 to 161 vinyl acetate as the comonomer; copolymers with vinylidene chloride or vinyl ethers are also available.

Because of the limited solubility of vinyl copolymers, strong solvents such as ketones and esters are used by the formulators, as the base of PVC coating solutions.

PVC compounds, both flexible and rigid, are converted to end products by a number of processing techniques including extrusion, calendering, injection molding, blow molding and compression molding. Flexible compounds are usually processed at lower temperatures than rigid ones, because the increased plasticizer compound lowers the softening point of the resins. Plastisol processing techniques include coating, casting, slush molding, rotational moldings and low-pressure injection molding.

The basic machine is the extruder, which consists of a metal barrel, a closefitting internal screw(s) connected to a drive mechanism and a means for applying heat to the barrel in one or more zones. The process consists basically of mixing and melting a continuous stream of plastic and

pushing it through a specially designed orifice or die by the turning action of the screw(s). In general, the extruder is very versatile with respect to the type of materials it can process.

Extrusion is used for marking continuous lengths of profiles. (A "profile" varies only in two dimensions, as opposed to molded products which vary in three.) Major profile products include: film and sheet, wire coating, pipe rod, and siding. Both flexible and rigid PVC compounds in either powder or pellet form are used in this process; either suspension or bulk process resins may be used.

Wire and cable insulation accounts for a significant portion of the flexible compound that is extruded. In wire and cable coating, the compound is extruded around a continuous length of the wire or cable.

Typically, pelletized compound is used in this process. The concentration of plasticizer in the compound varies with the application. For example, communication wire contains about 60% PVC. Most fabricators in this segment of the industry do their own compounding, although a few purchase the compound.

Rigid pipe and tubing are formed as continuous extrusions through an annular die approximating the desired profile; cooling is usually effected by passing the extrudate through a water bath or trough. Pipe as large as one meter in diameter can be prepared this way.

Pipe extrusion requires the use of rigid compounds, containing 85 to 95% PVC. Most PVC resins used in pipe manufacture are compounded into powder blends by the pipe producer. However, Robintech sells pipe compound made by the in-kettle-compounding process.

Siding, Rain Gutters and Other Special Profiles are made in a similar way to rigid pipe. However, because these profiles are somewhat more difficult to extrude than pipe, manufacturers use rigid compound in pellet form for these processes. This segment of the industry typically uses single-screw extruders and purchases the compound.

Flexible Profiles are extruded from flexible compounds and include such items as medical tubing, garden hose, gaskets, weather stripping, water-stop sheet, and cove base. Pelletized compound is used, typically containing about 60% PVC, with the remainder being plasticizers, pigments, and stabilizers. Major manufacturers of flexible profiles do their own compounding; smaller manufacturers usually purchase compound.

PVC film can be made either by extrusion or calendering. In the blown-film extrusion process, which is the preferred method for packaging films, pellets of homopolymer compound are melted and extruded through a die with a thin, annular opening to produce a thin-walled tube.

Shrink film is made by stretching the film either as it is made or in a subsequent stretching operation. Stretching introduces orientation (the alignment of polymer chains).

A small amount of film is produced by flat die (slit-die) extrusion. This involves extruding molten resin from an extruder through a wide slit die with adjustable lips into a cooling system. These films typically have a lower degree of orientation than the blown film.

Sheet products (films greater than 10 mils in thickness) are manufactured by the slit-die extrusion technique. Most sheet extrusion processes use rigid compounds, although some may contain up to 10% plasticizer, depending upon the exact physical requirements of the end application. Sheet compounds usually are made from homopolymers; both pellets and powders can be used. Most fabricators purchase sheet compound, but a few of the larger fabricators do their own compounding.

A large portion of the sheet products are used in construction applications. such as transparent corrugated sheets. Sheet is corrugated by passing it through forming rolls after extrusion. Rigid sheet is also used in various packaging applications.

Calendering is used primarily in the production of flexible sheet although a small fraction of rigid sheet is produced by this method. Calendering is capable of producing high-quality material at very high rates of output. In this process, the compound is passed between a series of three or four large heated revolving rollers which squeeze the material into sheet or film. The thickness of the finished material is controlled by the space between the final rolls. The resulting surface of the film or sheeting may be smooth, matted., or embossed, depending on the surface of the final rollers.

Calendering also can be used to coat PVC onto textiles or other supporting materials. In applying a coating, the compound is passed between two top horizontal rollers on a calender, while the uncoated material is passed between two bottom rollers. Finally, the substrate and film converge and are passed between a single set of rollers; the product emerges as a smooth film or sheet anchored to the substrate.- The alternative process to calender coating is post-calender laminating. In this process, the vinyl coating is prepared in advance and then laminated onto fabric by passing the two materials through pressure rolls.

Although the cost of the calender together with the auxiliary equipment is very high (a typical calender train costs 2 to 3 million dollars), calendering is the most economical method for producing thick PVC film and sheeting. Film and sheeting of the middle-gauge range between 3 and 25 mils is almost entirely produced by calendering. Today's calender lines are designed with throughput capacities of from 2,000 to 10,000 pounds of compound

per hour, or 70 - 100 yards per minute. Widths of film and sheet usually run to 72 inches, with some as wide as 92 inches.

Because calender fabrication is economical only if the production volume is high, only a few end users can use the calendering process. The main products made on calender equipment are: vinyl sheeting, coated vinyls, and floor tile. Coated fabrics are widely used for upholstery. Unsupported vinyl film and sheet is used to manufacture inflatables, footwear, purses, handbags, wallets, raincoats, tablecloths, shower curtains, luggage, and other similar products. Over 90% of the PVC-coated fabrics used in furniture upholstery are produced by calendering. Only a relatively small quantity of high-style, "expanded vinyls" is cast from plastisol (see section below). In these products, the vinyl is foamed to give it a "hand" that is similar to leather. Expanded vinyl products can be made either by the casting or calendering process.

Most motor vehicles today use vinyl-coated fabrics as the primary upholstery material. The backing material is largely cotton. About 85% of these coated fabrics are made by the calendering process and the remainder by the casting or knife-coating process. Unsupported vinyl sheet also is used in a variety of automotive applications such as Landau tops and panel coverings. Crash pads are covered with a calendered sheet that is made from a blend of ABS and PVC. These products typically contain about 35% PVC, although some may contain as much as 70% PVC.

While the major application for vinyls in home furnishings is upholstery, the second largest application is wall covering. The wall covering product consists of PVC film laminated to paper, cotton, or other backing material. Window shades are frequently made from vinyl sheet. Light-gauge, clear, rigid, and semi-rigid PVC film is used in the manufacture of prefinished plywood and particle board. In this method, clear film is printed with a wood grain pattern and laminated to the board with the print on the inside. The prefinished product is used to manufacture such items as office furniture and stereo cabinets.

made by the calendering process are also used extensively as surface finishes for construction products. For example, large quantities of gypsum board are finished with printed, embossed, opaque sheet which is adhered to the surface to yield a decorative and abrasion-resistant finished panel.

For the most part, calender operators buy raw resin and carry out the compounding in their own facilities. Homopolymer made either by suspension or bulk polymerization process is used to make these compounds.

is another large outlet for calendered PVC. The resins used in this application are mostly- vinyl chloride vinyl acetate copolymers with 8 to 18% vinyl acetate. These polymers can bind large amounts of the mineral fillers that are used in these products. Resin

and plasticizer account for about 17% of the formulation, with the resin alone accounting for only about

Flexible tile is also made by the calendering process. In this case, a relatively low-molecular-weight homopolymer is used with calcium carbonate as the filler. Typically, the plasticizer content of the calendered compound is about 40%, and the resin is 30x. A third type of flooring is made by the coating process (see section below). The fabricator, who manufactures tile flooring by the calendering process, normally does his own compounding.

In this process rigid or flexible compound is melted in a heating chamber, and the melt is forced through a nozzle under high pressure into a closed mold. The resins most frequently used in rigid PVC injection molding are medium-molecular-weight homopolymers; some lower molecular weight vinyl chloride-vinyl acetate copolymers are also used. These resins are derived from suspension or bulk polymerization processes. The feedstock may be in the form of pellets or powder, but most injection molding of PVC is done from pellets compounded by the resin manufacturer. In the future, large-scale manufacturers of pipe fittings may use powder compounded in their own plant.

Two major products made by injection molding are pipe fittings (from rigid compound) and shoe components, such as heels and soles (made from flexible compound).- Other products include industrial parts, such as fan blades, handles, etc.

Blow molding of rigid PVC is generally limited to the manufacture of bottles. This process is usually coupled with extrusion, using singlescrew extruders.

Rigid compounds used in this process contain about 90 to 95Z are normally fed to the blow molding machine in pellet or cube form. Polymers used in this process are primarily homopolymers that are made by the suspension or bulk profess. The bottle fabricator usually purchases his compound from the resin producer. Two compound grades are used: a food grade and a general-purpose grade, which differ primarily in the stabilizers used. Food-grade compound contains additives approved by the FDA, and is-used to blow-mold bottles for products that may be ingested. The general-purpose grade compound is used to manufacture containers for such products as shampoo and liquid detergents.

Compression molding of PVC is limited and is used primarily for processing rigid compounds into phonograph records. Record compounds use primarily

copolymers containing about 15% vinyl acetate; the compounds themselves contain about 3% additives.

Most record molders manufacture their own compound; however, a significant fraction of record compound is manufactured by one major independent compounder, who specifically manufactures for this industry. This compounder alone accounts for almost one-third of the PVC used by record molders. The manufacturer of phonograph records generally recycles returned records, and about 25% of the compound used by the industry is derived from this type of scrap.

Most PVC emulsion polymers (dispersion resins) are used to manufacture plastisol compounds. These compounds typically contain about 50% PVC; most are made from homopolymer resins. Some plastisol compounds are formulated with blending resins made by the suspension process which are added to the compound primarily to lower the cost. Blending resins are also effective in reducing the viscosity of the plastisol systems. These resins are mostly homopolymers and are intermediate in particle size between dispersion and general-purpose suspension resins.

Plastisols are processed as fluids by a variety of processes including knife coating, roller coating, casting, rotational molding, dipping, and hot spraying.

Although the majority of PVC emulsion polymerization products are used to make dispersion resins, about 10%--50 million pounds in 1974--was used as latex rather than in the coagulated form. Most latex resins are copolymers of vinyl chloride with minor amounts of vinyl acetate. Others contain small amounts of acrylate monomers, or vinylidene chloride. Major applications of latices include: (1) outdoor house paint; (2) saturation and coating of paper and paperboard; (3) impregnation of non-wovens used in automotive trim such as door panels; and (4) vinyl wall coverings.

Coating. Most plastisol compounds are used to compounds are used to coat substrates such as textiles, paper, and sheet metal. Coating equipment generally consists of an adjustable doctor knife or spreading blade supported over a steel plate or roller. Rollers are sometimes used instead of doctor blades. Major fabricators of such products as coated fabrics and vinyl flooring usually do their own compounding.

Coated Flooring. The major plastisol product made by a coating process is flooring. In recent years, plastisol-coated felts have been used as an inexpensive floor covering, and have made inroads in the flooring market at the expense of calendered vinyl-asbestos tile.

Coated flooring is made in a number of ways. The base material can be felt, thick paper, or asbestos. In one method, the base is laminated with a printed PVC sheet and a coating of a clear (unfilled) plastisol

is applied as a protective top layer. PVC foam, made from a plastisol compound can be used in place of the vinyl sheet. The foam can be embossed or decorated and then top coated with a clear plastisol. In still another method, the base can be coated with a "filled" acrylic polymer and then finished with a top coat of the clear plastisol. Coatings are usually applied using a roll coater and then fused in an oven.

Dip and Slush Molding. Slush molding is a process for making thin-walled, flexible products. In this process, excess liquid plastisol is charged to a hollow mold of the desired contour. Heat, which is applied to the outside of the mold, fuses only the plastisol that is in contact with the hot mold surface; the unfused excess liquid plastisol is dumped out and used again. This process is used primarily to produce overshoes, rubbers, bathing caps, and similar products.

Dip molding is also used to produce skin-like products such as gloves, and handle-bar grips. In the dipping process, preheated products, particularly metal, are coated by dipping-into a plastisol solution and then dried.

Rotational Casting or Molding. This is another major method of processing plastisols. In this case, a measured amount of liquid plastisol is charged into a rotating split mold. The speed of rotation is comparatively slow, so that the plastisol flows by the effect of gravity to form a layer of uniform thickness over the entire mold cavity. The plastisol layer is fused during rotation. The mold is then removed from the oven and cooled by water: The mold is opened and the molded article is removed.

Applications for rotational moldings include flexible toys, automobile arm rests and dash pads, beach balls, basketballs, etc.

Rotational molding is particularly suitable for the manufacture of hollow items. The process has the advantage that the equipment is relatively inexpensive, and the process is not very complex. Molds can be made from aluminum, and they are easy to produce. The process affords a high degree of flexibility and is economically attractive for short runs, frequent color changes, intricate designs and relatively thick walls.

Producers of products using slush molding and rotational casting typically purchase the plastisol compound from independent formulators.

Low pressure Injection Molding. This technique, which resembles conventional injection molding, can be used for molding such items as shoe soles, and gaskets for glass containers and crown caps used as closures for glass beverage containers. Some companies also use liquid plastisols to manufacture the so-called "roll-on gaskets" which are used in aluminum "convenience" caps for beverage containers. Others form these compounds from PVC tape.

Typical formulations of liquid plastisols used for glass-container gaskets consist of 75 parts dispersion resin, 25 parts blending resin, and 100 parts of plasticizer and other additives. The major manufacturer who use plastisols for gasketing material used in packaging do their own compounding.

In general, low-pressure injection molding, just as other plastisol processing, uses relatively inexpensive equipment. The costs of the machines and molds are lower than for conventional injection molding.

PVC-solution coatings or enamels are normally used as coatings for metal. PVC coating solutions are made from copolymers containing about 15% vinyl acetate, formed primarily by the "solution polymerization" process. Some suspension resins are also used.

The majority of PVC enamels are used as can and closure coatings, especially for interior top coatings for beer and soft drink cans. All aluminum end for soft drink cans are coated with PVC, some of which are based on organosols rather than enamels. Beverage cans made from tinplate or tinfree steel are coated exclusively with PVC enamel. Approximately 25% of all food cans also are coated with the vinyl enamel.

PVC enamels are also used as coatings for the inside of metal closures such as jar lids. These coatings are usually modified with epoxy or phenolic resins. Minor amounts of PVC enamels are also used in combination with phenolics in exterior decorative coatings for some beverage cans.

In addition to their use as can coatings, PVC solution resins are used in a variety of other metal-coating applications, such as finishes for appliances, metal furniture, building panels and some non-electrical machinery. PVC enamels are also used in maintenance and marine-coating applications. In many of these latter applications, vinyls are used in combination with other resins.

Solution-based resin systems made from suspension resins are used to prepare cast film. Such cast film is of higher quality than film made by the blown-film extrusion process, with substantially improved clarity and brillance and low gel content. Film thickness is also more easily controlled.

Table II-2 summarizes the reported domestic PVC resin consumption for the years 1969 to 1974, according to fabrication process. Note that extrusion and calendering consumed about 70% of all PVC resins.

In the four-year period, 1969-1973, consumption of all types of PVC resins grew an average of about 14% per year. During this same period, the use of PVC resins in the extrusion process increased at an average annual

rate of 23%, with most of the growth occurring between 1971 and 1972. In contrast, the consumption of PVC resins in the calendering process showed little growth during this time period.

An analysis of the consumption of PVC resins by product within each fabrication category is shown in Table II-3. This table indicates that the rapid growth in the consumption of PVC by the extrusion process was due primarily to the increased use of rigid PVC pipe and conduit. Between 1971 and 1973, the consumption of PVC for this end use increased about 60% per year.

Film and sheet products accounted for the major growth in calendering. During the 1971-1973 period, the use of PVC resins in this application increased 8% per year. During this same period, the consumption of PVC resin in the blow molding process (the process used to make bottles) increased, on the average, 63% per year.

The use of PVC plastisol resins grew at a rate of approximately 14% per year. Textile and paper coating processes were the major factors responsible for the growth in plastisols.

Source: Modern Plastics, January Issues, and Society of Plastics Industries, Annual Statistical Reports.

* Includes applications where PVC is used as a latex. About 9-lox of the total consumed in this category are coatings applied from a latex.
** The largest application under this category is rotational molding.