10. VINYL RESINS
Vinyl acetate, vinyl chloride, and to a lesser extent vinyl chloroacetate, are the raw materials (monomers) for the several vinyl resins commercially produced in the United States, Canada, and Germany. These are all esters of the hypothetical vinyl alcohol and are made by the action of acetic and hydrochloric acids on acetylene.
The spontaneous polymerization of vinyl derivatives has been known for many years, although its significance and industrial application have been realized only recently. Vinyl acetate, probably the most important of the vinyl esters, was discovered in 1912 and first made in Canada in 1917.
Vinyl resins may be classified into (a) polyvinyl acetate, (b) copolymers of vinyl acetate and vinyl chloride, (c) polyvinyl chloride, and (d) polyvinyl chloroacetate.
Polyvinyl acetate resins.—The several commercial types of vinyl acetate resins are marketed under the trade names Vinyloid A, Alvar, Gelva, Formvar, and Mowilith. The first of these is a product of Carbide and Carbon Chemicals Co., New York, the next three are products of Shawinigan Chemicals Limited, Shawinigan Falls, Canada, and the last is made by the Interessen Gemeinschaft Industrie A. G., Germany. Vinyloid A and Gelva represent the simplest series of vinyl acetate resins and are made by polymerizing the monomer. The softening point and viscosity of the polyvinyl acetate resins increase with higher polymerization. Such resins are colorless, tasteless, odorless, thermoplastic products. They are soluble in coal-tar solvents and are compatible with certain alkyd resins, tar-acid resins, and natural resins. Films of polyvinyl acetate resin are not discolored by exposure, and after irradiation they become opaque to ultraviolet light, are hard and tough, and have good adherence and endurance. Their dielectric strength is good and they do not show a carbon track after the passage of an electric arc. Various grades having softening points from 80° to 200° C. are available.
Polyvinyl acetate resins are used in making transparent papers, paper to metal laminations, glassine papers for food packaging, as a substitute for chicle in chewing gum, and as a component of paints, varnishes, and lacquers. They have the desirable properties of compatibility, durability, resistance to abrasion, and rust inhibition in the surface-coating use. Having the same refractive index as pyrex glass, they leave no line of demarcation when used as a cement for that material. They have been used to stiffen toe-caps in shoes and articles made from paper pulp suspensions. Gelvas are not molded as such because of their tendency to cold flow. They are used, however, as a binder for ground mineral fillers in advertising signs and for wood flour in molded artificial wood carvings. In nitrocellulose lacquers they improve the adhesion, luster, and toughness.
Alvars are made by replacing part or all of the acetate groups in Gelva with acetaldehyde. Their viscosity varies with the degree of polymerization and their properties vary according to the extent of replacement of the acetate groups. The Alvar types do not cold flow when molded, are tougher, harder, and have better adhesion but are less resistant to weathering than the Gelva types. Other properties are about the same as those of the Gelvas. Alvars having 70 to 80 percent acetate group replacement are used chiefly in spirit type varnishes, lacquers, and enamels that must stand exposure to weather. Another Alvar type is used in injection and press molding. The high binding power of the resin permits the use of large percentages of filler without loss of desirable properties. Such moldings may be machined and polished, and take inserts, such as the wood core in shoe heels. Flexible phonograph and transcription records made from the Alvars have gained wide approval. An 85 percent (acetate replacement) type has better impact strength and is used in toilet articles. Sheets, rods, and tubes of this resin may be machined in much the same way as nitrocellulose plastic and used where noninflammability is an asset.
Formvars are made by replacing part or all of the acetate groups in Gelva with formaldehyde. These resins are colorless, odorless,tasteless, and thermoplastic. They have higher softening points and greater tensile and impact strength than the Alvars. They are resistant to alcohols, coal-tar solvents, fats, oils, or water. Moisture transmission rate through a film of this resin is about one-tenth that through regenerated cellulose and one-fourth that through cellulose acetate.
The grades of the Formvars available are designated by the extent of replacement of the acetate group. The 75-percent replacement type has excellent mechanical strength and flexibility and is unaffected by sunlight. Formvars of 95 percent acetate displacement have a tensile strength as high as 10,000 pounds per square inch and offer possibilities in the manufacture of artificial silk and photographic film.
The vinyl resins have made possible a new type of safety glass superior to any heretofore marketed. By condensing butylaldehyde with vinyl acetate, a polymer is obtained which is used as the inner layer between two sheets of glass. Heat and pressure secure complete adhesion and yield a sheet with greater resistance to breakage at low temperatures than the types now in general use.
Although safety glass was invented in 1905, and many substitutes for the original nitrocellulose inner layer have been proposed, only two reached commercial importance before the development of the vinyl resins. These are cellulose acetate and the acrylate resins. Safety glass used in automobile windshields up to about 1930 discolored after a year or two of service. This discoloration was due to the action of the actinic rays of the sun on the nitrocellulose layer. Since 1930 this difficulty has been largely overcome by using an actinic ray filter glass (a special glass with a high iron content) in front of the nitrocellulose sheet, or by using cellulose acetate, which is not discolored to the same extent by light, as a substitute for nitrocellulose. Both cellulose nitrate and cellulose acetate, however, have a tendency to lose toughness and strength at low temperatures, to absorb moisture, and to separate from the glass around the edge unless sealed, and to lose their plasticizer and shrink.
Although a vast improvement over ordinary plate glass, laminated glass made with cellulose nitrate or acetate has the serious defect of being brittle at low temperatures, such as prevail in the winters of northern States. It is easily shattered at zero Fahrenheit, while at 60° F. and above it is quite strong. This shortcoming led to the development of the vinyl resin sheet for safety glass with a remarkable degree of toughness. At normal temperatures it has rubberlike toughness which, although decreased at low temperatures, is not punctured by the impact of a half-pound steel ball falling from a 30-foot height at minus 10° F., whereas nitrocellulose or acetate laminated glass withstands the impact of a fall from not greater than one-tenth this height. A further advantage of the vinyl sheet is that it is water resistant, making the sealing of the edges of the glass unnecessary and thus reducing costs. Exposure to ultraviolet light in Florida sunlight for more than 2 years did not discolor it.
The many desirable properties of the vinyl resins, as outlined above, indicate their widespread use in laminated safety glass when it is available in sufficient quantities. It is estimated that our annual output of safety glass interlayer sheets exceeds 17,000,000 pounds,of which 25 to 30 percent are for windshields, and 70 to 75 percent for side and back windows of automobiles.
At least one of the series of Mowiliths made in Germany is polymerized vinyl acetate. It is recommended as an ingredient of water-white lacquers. It is compatible with nitrocellulose and is extremely durable and not disintegrated or discolored on exposure to weather.
Copolymers of vinyl acetate and vinyl chloride.—The simultaneous polymerization of mixtures of vinyl acetate and vinyl chloride yields resins with the desirable properties of the two reactants. The extent of plasticity is largely controlled by varying the ratio of the vinyl derivatives. Resins high in vinyl chloride content are better suited to molding, and those high in vinyl acetate are better lacquer ingredients. These resins are marketed as Vinylites by the Carbide and Carbon Chemicals Co., New York. They are thermoplastic, odorless, tasteless, and practically nonflammable. Their outstanding properties are resistance to water, soap, acids, alkalies, and alcohol, and their strength and good dielectric properties. Their stability to light is improved by the addition of ultraviolet absorbing compounds and their stability to heat by the addition of lead oleate, calcium stearate, or other bases. Water absorption and compatibility with other resins is increased as the chloride content increases.
The principal types of copolymers are:
Vinylite VYN, high molecular weight. This resin is used in dentures where good fatigue resistance, impact strength, and tensile strength are required. It contains 85 to 88 percent vinyl chloride.
Vinylite VYN, medium molecular weight. This resin is used in general molding and extending applications including sheets, rods, and tubes. Its vinyl chloride content averages 85 to 88 percent.
Vinylite VYN, low molecular weight. This resin is used in moldings, coated paper, lacquers, floor tile, phonograph records, and felt impregnation. It contains 85 to 88 percent vinyl chloride.
Vinylite VYC. This resin of low molecular weight is compatible with nitrocellulose and is used in lacquers and finishes for industrial applications. Lacquers from the Vinylites are called Vinyloids.
The Vinylites for molding are thermoplastic and shrink very little, making them applicable to large moldings. They may be used in extension processes such as tooth-brush preforms, pipe lining, and wall trim. Fillers and pigments may be added, although pigments containing iron and zinc have harmful effects on the stability of the resin. The fillers used are wood flour, mica, talc, and alpha cellulose. Fillers reduce the mechanical strength of the resin and lessen its resistance to water. Plasticizers, such as dibutyl phthalate or tricresyl phosphate, give a softer, more flexible resin. Resins from the copolymers resemble the cellulose derivatives in their molding characteristics, mechanical strength, and appearance.
In lacquers the Vinylites offer high resistance to water, oils, and chemicals. The drying of such lacquers is by evaporation rather than by oxidation. They are suitable for lining food containers, coating concrete, coating paper for bottle cap liners, and as a stiffener for box toes of shoes. Their most successful application at present is as an inside coating for beer cans. Floor tile containing these resins mixed with slate flour or other filler has good possibilities.
Polyvinyl chloride resins.—Vinyl chloride may be polymerized to give nonflammable resins of varying solubilities. The completely polymerized resin is practically insoluble at ordinary temperatures and is used as a rubber substitute. It is marketed as Koroseal by B. F. Goodrich Rubber Co., Akron, O. Compared with natural rubber, it has greater resistance to acids, alkalies, oils, and alcohol, more flexing life, better resistance to sunlight, water, and oxidation. Solutions of this resin marketed as Korolac are used in special types of varnishes.
Polyvinyl chloroacetate resins.—These resins known as Mowiliths are made in Germany. Application is largely for surface coating. Practically no information on this type is available.
Divinyl acetylene and synthetic rubber.—Two products closely related to those described above but probably not synthetic resins as defined for this discussion are divinyl acetylene, a synthetic drying oil, and Neoprene, a synthetic rubber.
Acetylene, when passed into a solution of copper chloride and ammonium chloride, combines with itself. When two molecules of acetylene react monovinyl acetylene is formed, and when three molecules of acetylene react divinyl acetylene is formed. Monovinyl acetylene reacts with hydrochloric acid to give chloroprene, which is polymerized to synthetic rubber or Neoprene.
Divinyl acetylene is a colorless liquid which darkens on exposure to light and which has an onionlike odor. When polymerized liquids are formed, then as the reaction progresses viscous products and finally insoluble, infusible, inert resins. By arresting the reaction before the gel point is reached, an amber colored heavy liquid, soluble in aromatic hydrocarbons, is obtained. Since divinyl acetylene will continue to polymerize at ordinary temperatures, this property is taken advantage of in using it as a basis for paints, under the name “synthetic drying oil.” Clear, amber films are obtained from solutions of this oil in solvent naphtha. Divinyl acetylene is quick drying, is many times more impervious to moisture than linseed oil, and is thermosetting. It is not attacked by solvents but is attacked by strong oxidizing agents, and the gelled material may ignite spontaneously.
Although not classified as a resin, synthetic rubber is discussed here because of its close chemical relationship to the vinyl resins. It is made commercially by E. I. du Pont de Nemours & Co., Wilmington, Del., and is marketed as Neoprene. It is sold as a plastic polymer which is vulcanized and processed much the same as natural rubber except that sulphur is not essential to vulcanization. Synthetic rubber is higher in price than natural rubber, but it has certain properties which make it suitable for service conditions where natural rubber is unsatisfactory. Among these properties are its resistance to gasoline, oils, and greases, and to elevated temperatures. It does not check or crack on exposure to sunlight, nor does it oxidize as rapidly as natural rubber. Its principal applications are in special gaskets, printing rolls, jackets for high tension cable, linings for gasoline or oil hose lines, balloon fabrics, diaphragms for regulators, and packing for compressors. Its existence acts as a limit to the increase in the price of natural rubber and assures a supply in emergencies.
Some of the products described are commercially produced in the United States; others in Canada or in Germany. Those made in the United States are usually not made by more than one firm, so that statistics of production and sales are not publishable. The vinyl acetate resins have been produced principally in Canada; the copolymers of vinyl chloride and vinyl acetate are domestic products. In 1935 the United States output of all vinyl resins exceeded 1,000,000 pounds, a figure that was increased in 1936 and 1937.
The Canadian output of Gelva and Alvar has reached commercial quantities; that of Formvar is still confined to experimental plant lots.
The acceptance of vinyl resin sheets for safety glass will greatly increase the output in 1938. The basic patent, known as the Morrison-Blaike patent, United States No. 2,036,092 issued on March 31, 1936, is owned by Shawinigan Chemicals, Ltd., Montreal, Canada, who have licensed several domestic producers. The monomer (vinyl acetate) is now produced at Niagara Falls, N. Y., by the Niacet Chemicals Corp., which is jointly owned by this Canadian firm, Carbide and Carbon Chemicals Corporation, and E. I. du Pont de Nemours & Co. It is also produced by du Pont at Belle, W. Va. It is shipped, in tank cars, to polymerization and sheet-forming plants at Indian Orchard, Mass., Arlington, N. J., and Charleston, W. Va. The Indian Orchard plant, known as the Shawinigan Resin Products Co., and jointly owned by the Canadian firm and the Fiberloid Corporation, is now in operation. The plant of the du Pont Company at Arlington, N. J., began production in May 1938, and that of Carbide and Carbon Chemicals Corp, at Charleston, W. Va., is in production. These plants have a combined annual capacity of about 10 million pounds of vinyl resin sheets. According to present plans this new safety glass will be available for 1939 model automobiles. The resin sheet to be used is 0.0015 inch thick as compared with the 0.0025 inch thickness of the present cellulose acetate and nitrocellulose sheet. Several trade names have been adopted for the vinyl resin sheets, among which are Vinylite X, and Butvar. The licenses granted to domestic makers under the Morrison-Blaike patent also permit them to make vinyl acetate resins for purposes other than safety-glass sheets. Considerable progress has been made in adapting these resins to injection molding operations for the production of tooth-brush handles, combs, closures, and other parts.
The official statistics of imports of vinyl resins prior to 1936 are not satisfactory for purposes of comparison. Imports could be entered under either paragraph 2 or paragraph 11 and could be included either with the statistics of imports of vinyl acetate (see table91, page141) or be thrown into a general group of non-coal-tar synthetic gums and resins, n. s. p. f., which in addition to vinyl resins would include the acrylates and ureas. Table10gives imports of synthetic resins under paragraph 11 of the Tariff Act of 1930.
Table 10.—Synthetic resins classified under paragraph 11:1United States imports for consumption 1931-37
1Statistical classification 838.914, synthetic gums and resins, n. s. p. f. (not coal tar) 1931-35; 838.939 same, other than those in chief value of vinyl acetate, 1936 and 1937.2Preliminary.Source: Compiled by the U. S. Tariff Commission from official statistics of the U. S. Department of Commerce.
1Statistical classification 838.914, synthetic gums and resins, n. s. p. f. (not coal tar) 1931-35; 838.939 same, other than those in chief value of vinyl acetate, 1936 and 1937.
2Preliminary.
Source: Compiled by the U. S. Tariff Commission from official statistics of the U. S. Department of Commerce.
A better idea of the imports of vinyl resins prior to 1936 is obtained by an invoice analysis of imports through the Port of New York under paragraphs 2 and 11. Table11shows imports of vinyl acetate resins based on such an analysis for 1934 and 1935 and on official statistics for the years 1936 and 1937.
Similarly table12shows imports of Mowilith resins based upon import analysis for the period 1932-1935, and upon official statistics for 1936 and 1937.
Table 11.—Vinyl acetate resins: United States imports for consumption, 1934-37
1Invoice analysis of imports entered through the New York customs district.2Statistical classification 817.58 (par. 2), vinyl acetate, polymerized, and synthetic resins made in chief value from vinyl acetate, n. s. p. f. (excluding imports from Germany) and 838.938 (par. 11), synthetic resins made in chief value from vinyl acetate, n. e. s.3Preliminary.Source: Compiled by the U. S. Tariff Commission from official statistics of the U. S. Department of Commerce.
1Invoice analysis of imports entered through the New York customs district.
2Statistical classification 817.58 (par. 2), vinyl acetate, polymerized, and synthetic resins made in chief value from vinyl acetate, n. s. p. f. (excluding imports from Germany) and 838.938 (par. 11), synthetic resins made in chief value from vinyl acetate, n. e. s.
3Preliminary.
Source: Compiled by the U. S. Tariff Commission from official statistics of the U. S. Department of Commerce.
Table 12.—Mowilith resins: United States imports for consumption, 1932-37
1Analysis of invoices of imports entered through the New York customs district.2Imports from Germany under statistical classification 817.58 (par. 2), vinyl acetate, polymerized, and synthetic resins made in chief value of vinyl acetate.3Preliminary.Source: Compiled by the U. S. Tariff Commission from official statistics of the U. S. Department of Commerce.
1Analysis of invoices of imports entered through the New York customs district.
2Imports from Germany under statistical classification 817.58 (par. 2), vinyl acetate, polymerized, and synthetic resins made in chief value of vinyl acetate.
3Preliminary.
Source: Compiled by the U. S. Tariff Commission from official statistics of the U. S. Department of Commerce.
Prior to January 1, 1936, the rate of duty on imports of vinyl resins was 6 cents per pound and 30 percent ad valorem under paragraph 2, and 4 cents per pound and 30 percent ad valorem under paragraph 11 of the Tariff Act of 1930. Under the terms of the trade agreement with Canada, the duty under both paragraphs was reduced to 3 cents per pound and 15 percent ad valorem. This rate was generalized to the other countries from which we have received imports, with the exception of Germany.
Exports of vinyl resins are not separately shown in official statistics.