Synthetic resins and their raw materials

Chapter III: Part 3

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Source: Dyes and Other Synthetic Organic Chemicals in the United
States, U. S. Tariff Commission.

In 1933 there were 6 makers of resins from phthalic anhydride, in 1935 there were 15, and in 1937 there were 35. The 1937 output of alkyd resins from phthalic anhydride was 58,450,032 pounds net resin, with sales of 32,583,307 pounds valued at $6,446,011. Producing plants are well scattered through northern and eastern United States. In 1936 fewer than one-third of the makers accounted for about 90 percent of the output.

The domestic production of resins from maleic anhydride was reported for the first time in 1933. The output in that year consisted of experimental quantities produced by two firms. A small increase in production occurred in 1934 when another maker began operation. In 1936 there were eight producers and the output was many times that of 1934. In 1937 there were 12 makers of these resins with an output of 2,803,987 pounds and sales of 2,154,988 pounds, valued at $418,183. It is the opinion of some persons in the industry that in volume of production and sales the resins from maleic anhydride will in the near future approach that obtained from phthalic anhydride.

Imports into and exports from the United States.

No imports of alkyd resins have been recorded in official statistics.

Exports of alkyd resin coatings and finishes are not separately shown, but data collected from the several producers show that appreciable quantities were exported in recent years, principally to Central and South American countries.

5. UREA RESINS

One of the most important series of thermosetting resins is the group made by condensing urea and formaldehyde. As early as 1897 it was discovered that an amorphous condensation product was obtained from the reaction of urea and formaldehyde. The clear glass-like mass obtained led to considerable research work toward the development of a substitute for glass. It was found, however, that the resin obtained absorbed moisture, resulting in a dimming of its luster, and that on standing for a time, the condensation continued producing cracks, fissures, and disfigurements in the molded article. In 1926 a successful commercial product was developed in England by the use of thiourea. Cost of production, however, was high. The addition of thiourea gave the product greater strength and water resistance than that obtained with urea alone but retarded the rate of cure. Also the sulphur present attacked steel molds, which necessitated the use of expensive chromium plated or stainless steel molds.

About 1929 the first successful straight urea product was perfected in the United States. It was found that a filler, such as highly refined alpha cellulose, minimized the stresses. The filler (as much as 30 to 40 percent is usually incorporated), destroys the transparency but permits the manufacture of translucent articles in a wide range of color. Many of the colors possible with the urea resins, particularly the light shades, cannot at present be obtained in molded tar-acid resins.

An interesting fact concerning these resins is that they are produced indirectly from four gases: Ammonia, carbon dioxide, hydrogen, and carbon monoxide. Ammonia and carbon dioxide react to form urea, and hydrogen and carbon monoxide yield methyl alcohol which is converted to formaldehyde.

Description and uses.

The urea resins are outstanding largely because of their brilliancy and depth of color, properties not readily obtained in other thermosetting resins. Being odorless and tasteless and completely resistant to oils and greases, they are adapted to use in the manufacture of cosmetic containers. Concentrated acids and alkalies attack the resin. The electrical properties of the urea resins compare favorably with those of the tar-acid resins. They have a lower power factor at high-frequencies than the tar-acid resins, and are replacing, to some extent, established materials in heavy duty electrical equipment where “tracking” causes trouble. Molded articles made from urea resins are resilient but not unbreakable.

Source: Plaskon Company, Inc., 2112 Sylvan Avenue, Toledo, Ohio.]

The important uses of the urea resins are dictated by their pleasing color and appearance. In 1935 the largest outlets were in buttons and buckles, in bottle closures, and in such premium items as biscuit cutters and cereal bowls distributed by a large food manufacturer. Tableware, bathroom fixtures, all sorts of containers and closures, housings for radios, clocks, scales, and other machines for retail stores, and light-colored wall plates and switches, knobs, handles, and trim on dash panels of automobiles, and handles and trimming on gas and electric ranges were among the widespread applications of the urea resins. In 1938 probably the fastest growing outlet for urea resins is in lighting equipment. Use in packaging, in closures, and in housings, is also increasing. Tableware, the principal outlet for a number of years, is declining markedly.

A comparatively new use is in shades and reflectors, replacing opal glass. The unpigmented resin is highly translucent and gives high light transmission and an exceptional degree of light diffusion. These properties, together with low unit manufacturing costs, reduced shipping costs, and resistance to breakage make the urea resins an ideal material for all sorts of shades and reflectors for direct and indirect lighting fixtures. Many of the shades used in railway cars are of this material. The resin is available in degrees of denseness and opacity to give particular ratios of reflection and transmission. Reflectors as large as 28 inches in diameter are on the market.

Although molded articles are the large outlets for the urea resins, other applications are of increasing importance. Sirups used to impregnate paper and cloth are used in laminating and the resulting materials have unusual decorative possibilities. The surface is hard and durable and the wide range of colors possible permits very attractive applications. The urea resins are used both as the principal binding material for laminated sheets or on the surface laminae of sheets where tar-acid resins are used as the chief binder. The latter practice permits a wide color range in decorative materials without loss of strength or other characteristics of the tar-acid resins. In 1937 there were seven makers, and their production of urea resins for laminating accounted for slightly less than 10 percent of the total of all urea resins.

Another application of urea resins which has grown rapidly in the past 2 years is in combination with alkyd resins in surface coatings. In 1937 there were three makers, and their output of urea resins for coatings amounted to more than 10 percent of the total production of urea. Until recently the use of urea resins in paints and varnishes was discouraged by their insolubility in organic solvents and their instability. On the other hand, their lack of color, their high transparency, their hardness, and their freedom from after-yellowing were desirable characteristics. The development of methods for preparing condensates, which overcome the undesirable properties, has made available resins for this use. They are marketed as water-white viscous solutions in a mixture of organic solvents and are intended for use in baking finishes. They cannot be used alone because the cured resin is extremely hard and brittle and lacks adhesion. When combined with more elastic film-forming materials such as drying or nondrying oil alkyd resins, they produce coatings that are mar-proof, resistant to alcohol, grease, oil, and fruit acids, and available in a full range of colors. Applications are in metal furniture finishes, toys, refrigerators, can, and drum coatings.

The value of urea resins as adhesives has been known for many years and one of the first patents issued for such use was United States Patent No. 1,355,834 granted in 1920. Commercial development and application, however, did not take place until the last 2 years. Several brands of urea adhesives are now on the market. These meet the need for a hot-press adhesive which is applied in liquid form, cures rapidly at moderate temperatures, and is economical. For greater economy, the urea adhesive may be mixed with various proportions of flour (up to 50 percent) without affecting its water resistance. Diluted thus it comes within the cost range of animal and vegetable glues and is more durable. At present, it sells for 18 to 20 cents per pound; mixing it with 50 percent flour gives an adhesive for plywood, costing about 10 cents per pound. In 1937 three producers made urea resins for this use.

Other uses are in the treatment of textiles to obtain crease-proof properties and in the impregnation of wood. United States Patent No. 1,951,994 issued on March 20, 1934, reports the preparation of artificial silk from urea resins.

Production in the United States.

Commercial production of urea resins in the United States was reported for the first time in 1929. Early in that year the American Cyanamid Co. concluded an arrangement with the British Cyanides Co. of England for the American rights to manufacture and sell in the United States a resin made from urea, thiourea, and formaldehyde and marketed as Beetle molding powder. A manufacturing unit was built at Bound Brook, N. J., and in 1930 the output was substantial.

In 1931 another producer, the Toledo Synthetic Products Co., began manufacture of urea resins. Several years prior to that time the Toledo Scale Co. started a search for a material light in weight to replace the heavy porcelain-on-steel used in cases for scales. The search led to the urea resins and to commercial production by their subsidiary. In 1935 the Toledo Synthetic Products Company reached an agreement with the Imperial Chemical Industries of England for the interchange of technical and commercial information and of free patent licenses on urea molding and laminating resins. The name of the domestic firm was later changed to the Plaskon Co.

In 1932 the Unyte Corporation started commercial production of urea resins at Grasselli, N. J. This firm was affiliated with the American I. G. Corporation. Late in 1936 the Plaskon Co. took over the Unyte Corporation.

The output of urea resins increased markedly in 1936 and 1937. Statistics for those years cannot be published without disclosing operations of individual firms. It may be stated, however, that the increase in both years over the previous year was considerably greater than for any earlier period. Most of the production was used in molded articles although appreciable quantities were consumed in laminated articles, in surface coatings, in the impregnation of fabric, and in adhesives.

There were 10 domestic makers of these resins in 1937.

Domestic production and sales of urea resins are shown in table 8.

TABLE 8.—_Urea resins: United States production and sales, 1933-37_

--------+------------+------------------------------------
| | Sales
Year | Production +-----------+------------+-----------
| | Quantity | Value | Unit value
--------+------------+-----------+------------+-----------
| _Pounds_ | _Pounds_ | |
1933 | 3,234,356 | 2,977,791 | $1,422,671 | $0.48
1934 | 3,470,916 | 3,115,608 | 1,290,802 | .41
1935 | 4,202,536 | 4,005,083 | 1,828,565 | .46
1936-37 | ([1]) | ([1]) | ([1]) |

[1] Not publishable; figures would reveal operations of
individual firms.

Source: Dyes and Other Synthetic Organic Chemicals in the United
States, U. S. Tariff Commission.

United States imports and exports.

Resins obtained from urea and thiourea, if imported, would probably be classified under paragraph 11 of the Tariff Act of 1930. The present rate of duty under this classification is 4 cents per pound and 30 percent ad valorem.

There has been no importation of these resins. This is due principally to the international licensing arrangements which usually include the allocation of markets.

Exports are not shown separately in official statistics.

6. ACRYLATE RESINS

A new development of widespread importance in the synthetic resin industry is the commercial production of the polymers of certain derivatives of acrylic acid. The commercial exploitation of the acrylates is another example of the belated realization of the value of substances known for many years. Acrylic acid has been known for about a hundred years, and the polymer of methyl acrylate was first described in 1880. It was not until 1927, however, that a suitable method for their commercial production was developed. The study of the many derivatives of acrylic and methacrylic acids leads to the conclusion that those of greatest practical application in the resin field are the lower esters, such as methyl and ethyl, polymerized separately or together.

Colorless transparency, stability against aging, thermoplasticity, and chemical resistance to many reagents are the general characteristics of the acrylate resins. In consistency they range from soft, sticky, semiliquids to hard, tough, thermoplastic solids. Since these widely varying properties are obtained by control of manufacturing conditions, rather than by the use of plasticizers, the resins retain their initial properties indefinitely. Aging and weathering have no effect as they are stable under exposure to heat, light, and oxidizing agents. The methacrylates are harder and tougher but less elastic than the acrylates.

Properties and uses.

The acrylate resins are marketed in a number of forms, such as solutions in organic solvents, dispersions in water, solid cast sheets, rods and tubes, and molding powders. All of these are distinguishable from many other resins by their colorless transparency, adhesive qualities, great elasticity, and chemical resistance. The brilliant water-white color makes it possible to secure masses having a high degree of light transmission and great optical clarity.

The earliest commercial use of the acrylate resins was in laminated safety glass marketed as Plexigum in the United States and as Luglas and Sigla in Europe. The extensibility and elasticity of the resin film gives the laminated glass a flexible or yielding type of break when subjected to a hard impact. Having excellent adhesion to glass there is no need of an auxiliary cement to bond the resin to the glass, nor is it necessary to seal the edges since the resin has good resistance to moisture. The acrylate resin used for this purpose is in the form of a viscous solution in an organic solvent. A film is applied to each sheet of glass, the solvent removed by drying, and the sheets are pressed together.

The harder acrylic resins are used in the form of solid thermoplastics. Methyl methacrylate is of special interest. As the monomer is a mobile liquid it can be cast-polymerized to a solid of any desired shape in predesigned molds or produced in finely divided form for use as molding powder. The cast resin is marketed in this country as Crystalite, Plexiglas and Lucite, and in England as Diakon.

The solid acrylate resins are clearer than cast phenolic resins, not as brittle as the polystyrene resins, and not as tough as cellulose acetate or nitrocellulose plastics. Their transparency and resistance to aging and weather permit their use in applications not previously considered for synthetic resins. Sheets of this resin may be formed or molded into many useful shapes. The aircraft industry has found them suitable for windshields and cockpit enclosures to effect streamlining and thus greatly reduce wind resistance.

Methyl methacrylate is probably the nearest approach to organic glass thus far developed. Its optical properties make it suitable for spectacle lenses, camera lenses, magnifying glasses, and protective goggles. Spectacle lenses are now being made to prescription by molding. It is estimated that 900 molds will supply the requirements of about 98 percent of the prescriptions. The excellent light transmitting quality of methyl methacrylate permits its use in edge lighting, advertising displays, and instrument dials. It is also used in inspection windows in various types of machinery where curved sections are necessary and where glass might be broken.

A synthetic resin combining the properties mentioned, together with high tensile and impact strength, good dielectric properties, ultraviolet transmission, and resistance to water, oil, acids, and alkalies is an important contribution. The acrylates may be colored or have fillers added to give any desired translucency or opaqueness. They can be sawed, cut, blanked, turned, drilled, ground, polished, and sanded much the same as are nitrocellulose plastics.

Source: Rohm & Haas Company, 222 W. Washington Square, Philadelphia, Pa.]

A new and interesting application of the acrylate resins is as molded reflectors in a system of indirect highway lighting. The reflectors are pressed from colorless, transparent methyl methacrylate resin and are 1⅝ inches in diameter. They are assembled in a pressed metal housing to form a double facing marker which is snap-locked to the top of an angle iron post. The posts are so located that the reflectors are accurately aligned 3 feet above the pavement edge. An installation has been made on U. S. Highway No. 16 between Detroit and Lansing, Mich., at a cost of about $340 per mile. The motorist provides his own light from his headlights which strikes the reflectors and is returned as a narrow beam of brilliant illumination. The chief of the United States Bureau of Public Roads states that this is a definite contribution to the safety and utility of the highways at night. The reflector is a group of tiny cube corners, over 300 in each disk. Each cube corner is a complete retrodirective optical system; a light ray entering the front surface is reflected from surface to surface of the cube and after the third reflection is directed back toward the headlight regardless of the entrance angle. If the cubes are made with a high degree of dimensional accuracy, the reflected light has a high candlepower, strong enough to be seen for a mile.

Other uses for these resins are in sound recording records, dentures, telephone and radio transmitter diaphragms, novelties, and lighting fixtures.

The monomer (unpolymerized methyl methacrylate) may be used to impregnate wood, cloth, wallboard, cork, paper, electrical coils, tile, or stone, and then polymerized to form the resin. Paper and cloth so treated have many uses, such as in the electrical and food-packaging industries. Laminated sheets find wide possibilities for use in the aircraft field, and for lamp shades. Wood may be impregnated with as much as 60 percent of the monomer. Solutions of these resins in organic solvents, such as ethylene dichloride, ethyl acetate, and toluol, are used in surface coatings, undercoats on difficult adhesion jobs, to impregnate paper and textiles, and in insulation. These coating solutions are marketed in the United States under the trade name Acryloids and in Europe under the trade names, Borron, Plexigum, and Acronol. They may be brushed, sprayed, dipped, and baked. Baking is recommended to give a higher gloss, better adhesion, and a harder film. The dried film has an elasticity of 1,000 percent at ordinary room temperature and the light transmission of clear films is intermediate between ordinary window glass and quartz.

Acrysol is an adhesive consisting of a dispersion of the resin in water and is recommended for use where adhesion is difficult, as on rubber or rubberized surfaces.

Production in the United States.

Commercial production of acrylate resins in the United States was started in 1931 by Rohm and Haas, Philadelphia, Pa., under United States Patents Nos. 1,388,016 of August 16, 1921, and 1,829,208 of October 27, 1931.

Commercial production of methyl methacrylate resins was started in 1937 by E. I. du Pont de Nemours & Co. This development is under United States Patent No. 1,980,483, issued in 1934. The liquid monomer is produced at Belle, W. Va., and shipped to Arlington, N. J., where it is polymerized by heat to the solid resin.

The output of acrylate resins was hardly more than experimental in 1935 but increased somewhat in 1936 and very appreciably in 1937. Although statistics of production are not publishable, it can be stated that in 1937 the output approached that of other synthetic resins made in commercial quantities. The properties of these resins indicate very large commercial production in the near future. Prices of the several types are still high as compared with other resins but should eventually be somewhat lower than those of cellulose acetate and nitrocellulose plastics and slightly higher than those of cast phenolic resins.

Imports into and exports from the United States.

There have been no recorded imports of acrylate resins. The two domestic producers have agreements, licenses, or affiliations with the principal foreign makers of these products, one in England and one in Germany. Such arrangements would account for the absence of imports, except for sample or experimental lots, and might also limit export markets.

7. COUMARONE AND INDENE RESINS

Coumarone and indene are present in appreciable quantities in certain coal-tar fractions, especially in the solvent naphtha fractions distilling between 160° and 190° C. No attempt is made to isolate them from the solvent naphtha. Such a procedure would be difficult and expensive and, since polymerization readily takes place in dilute solutions, it is more economical to use fractions of solvent naphtha rich in these substances. The resins obtained are mixtures of polymerized coumarone and polymerized indene.

The solvent naphtha must be refined by fractional distillation and the polymerization very carefully controlled. The polymerizing agent is usually sulphuric acid although metallic salts, such as aluminum chloride, are sometimes used. The yield and color of the resin are affected by temperature and amount of acid used. Light colored resins are the most desirable. After polymerization the acid or metallic salt is removed, the product washed and neutralized and finally distilled. Several byproducts, such as naphtha, paracoumarone soap, and high boiling oils, are also obtained.

Description and uses.

Coumarone and indene resins are produced and marketed in the United States under the trade names Cumar and Neville. A number of grades are available, including the following:

Designation: _Melting point_
Rubber grade, soft 50°- 65° C.
Medium soft 65°- 85° C.
Rubber grade, hard 85°-100° C.
Medium hard 100°-135° C.
Varnish grade 135°-160° C.

In addition to these, certain types are produced for special purposes.

The coumarone and indene resins are used to a large extent in varnishes for metal and wood. In this application they may be used to replace all or part of the higher priced natural resins and, to some extent, ester gum. Their application is somewhat limited by their rather short durability and elasticity. They are neutral, nonoxidizing and nonsaponifiable and impart to varnishes greater inertness and adhesion, fair dielectric strength, and shorter drying time than many of the natural resins. They cannot be used in nitrocellulose lacquer since they are not compatible with that plastic.

Another important use of these resins is as an ingredient in mastic floor tile, in the production of which a thermoplastic binder is used. Originally, asphalt was used, but demand for light colored tile necessitated some other binder, the requirements for which were met by the coumarone and indene resins.

The next largest application of these resins is in rubber compounding, their effect being to soften the rubber during milling and to facilitate its handling on rolls. They do not affect the aging qualities of rubber and are used as a softener for reclaimed as well as for new rubber.

Coumarone and indene resins are used, to some extent, in linoleum, for impregnating roofing felt, in electrical and friction tapes, paper and cloth sizing, printing inks, brake linings, adhesives, artificial leather, oil cloth, and shoe polishes. As a substitute for chicle as much as 10 percent may be incorporated in the chewing gum mixture. Their application in molded articles is very limited because of their brittleness and low tensile strength.

Production in the United States.

There are three domestic makers of these resins. Statistics of production and sales cannot be published without disclosing the operations of individual companies. The output, however, has increased appreciably in recent years and this type of synthetic resin is now among the most important produced.

Imports into and exports from the United States.

There have been no recorded imports of coumarone and indene resins in recent years. This is understandable because the duty alone would usually be more than the domestic price.[4]

Official export statistics do not separately record these resins, although quantities are exported to nearby countries, including Canada.

8. PETROLEUM RESINS

Considerable research work has been done on the synthesis of resins from petroleum. It has long been known that cracked petroleum distillates, when stored for a time, have a tendency to form gums. This tendency is so pronounced that inhibitors are added to arrest such formation. These gums are of little value as resins, but it is possible to obtain good varnish resins by oxidation or controlled polymerization of certain distillates of petroleum cracking. By carefully controlling operations, resins of varied properties are obtained and several of them have become commercially important. The unsaturated compounds, largely olefins and diolefins, present in highly cracked petroleum distillates can be polymerized, with certain catalysts. The resin produced depends upon the types of unsaturated hydrocarbons present and upon the conditions of polymerization.

Properties and uses.

Several types of petroleum resins are on the market, one made from the “polymer slop” obtained in the high temperature, vapor-phase cracking operation, and the other prepared primarily for the production of resin. The former is marketed under the trade name Petropol and the latter as Santoresin.

The “Petropol” resins are marketed in two grades, No. 1158 and No. 2138. The specifications for these are as follows:

Miscible in all proportions with petroleum solvents.

Petropol No. 1158 is used by core oil makers to replace such vegetable oils as linseed, tung, and perilla. It is used also as a binder and waterproofing agent on rock wool insulation, replacing rosin and mineral oil. For spraying coal to minimize dusting, it has the advantage over calcium chloride of increasing the B. t. u. content of the fuel.

Petropol No. 2138 is a surface coating material which dries by polymerization. A low cost paint is obtained by combining a pigment and a plasticizer with the resin. Such paint dries in about one-fourth the time of linseed oil paints, adheres better to metal, and has greater resistance to water, acids, and alkalies. In varnishes and enamels it replaces 12 to 15 percent of tar-acid resin, minimizes skinning, and gives a higher luster and better flow. Another use of this Petropol is as a binder in brake linings, replacing certain tar-acid resins.

These two Petropol resins are among the lowest priced synthetics, selling at present (1938), in tank carlots, for 2 to 5 cents per pound.

The Santoresins are clear, hard, neutral products, melting at 100° C. They are soluble in drying oils, accelerate the gelatination of tung oil, are nonreactive with pigments, do not yellow on outdoor exposure, and are resistant to alkalies, acids, alcohol, and water. Applications are in protective coatings for wood, metal, paper, leather, cement, plaster, and other materials, in printing inks, plastic tile, linoleum, and fiber packages. Being odorless and tasteless they may be used to line food containers. Their high resiliency and purity recommend their use as a base for chewing gum. Other uses are as an agent for wetting and dispersing pigments in rubber and in surface coatings, to replace ester gum or modified tar-acid resins.

At present the Santoresins are offered at 15 cents per pound in lots of 20,000 pounds or more. Their approximate specifications are:

Appearance A clear hard resin.
Melting point 110° to 120° C. A. S. T. M. (Ring & Ball).
Acid value 0 to 1.
Iodine value 125 to 135.
Specific gravity (at 20° C.) 1.02 or 8.5 lbs. per gallon.
Color (50 percent solution
by weight in toluol) 13 to 15 Gardner Holt standard.

Odor slight when cold, sweet and aromatic when melted. Soluble in aromatic hydrocarbons, petroleum thinners, turpentine, and varnish oils. Insoluble in alcohols, esters, ketones, and not completely compatible with nitrocellulose.

Production.

In the United States two makers of petroleum resins are producing in commercial quantities and several others are carrying on extensive research. Production was small in 1935, but increased in 1936 and in 1937. The development and expansion of these resins over the past 2 years indicate that they will become important.

Imports into and exports from the United States.

There has been no importation of petroleum resins into the United States. Exports have been confined to samples and experimental quantities.

9. POLYSTYRENE RESINS

The polystyrene resins are thermoplastic products discovered about 100 years ago and are therefore the oldest synthetic resins known. Their practical application has been greatly retarded by the lack of inexpensive raw materials of high purity and by the difficulties experienced in their manufacture.

Ethylene, from petroleum or natural gas, is combined with benzene, from byproduct coke-oven operations, to form ethyl benzene, which is cracked to vinyl benzene or styrene. This monomer is polymerized by heat at 100°-150° C. The resin may be extremely tough or very brittle, depending on the conditions of polymerization. Products having different properties are obtained by (_a_) low temperature polymerization, (_b_) high temperature polymerization, and (_c_) catalytic polymerization.

The low-temperature polymers, sometimes designated as alpha-metastyrol, are produced by polymerizations of vinyl benzene at temperatures under 175° C. A transparent resin, colorless to light yellow, is produced which is remarkably tough, has excellent tensile strength, unusually good dielectric properties, and is resistant to most chemicals.

Polymerization at high temperatures (above 175° C.) yields a brittle resin designated as beta-metastyrol. This type is transparent but usually dark in color, has low tensile strength and shock resistance.

When vinyl benzene is polymerized in the presence of catalysts, the resulting resin is similar to resins obtained at high temperatures, except that it is lighter in color. It is sometimes designated as gamma-metastyrol. Oxidizing agents are usually the catalysts. Clear, colorless, vitreous resins are obtained by excluding air during polymerization.

Properties and uses.

Polystyrene resin is a clear, colorless, highly thermoplastic molding material with high insulating property, moisture resistance, inertness, dimensional stability, and impact strength. It can be molded directly by heat and pressure, and the molded articles are remarkably resistant to discoloration by light. Polystyrene has a dielectric constant of 2.6, a power factor of 0.02 percent, and is equivalent to fused quartz as an electrical insulator of low dielectric loss. Films of 0.002 inch thickness have a dielectric strength of more than 2,000 volts per mil thickness, which is better than that of any other available synthetic resin and even better than that of shellac. The tensile strength of the resin is 5,500 to 7,000 pounds per square inch, and its impact resistance remains unchanged at temperatures as low as minus 70° C. It transmits all wave lengths of light down to 3,000 Angstrom units.

Polystyrene is adapted to large scale production of transparent, translucent, and opaque moldings in a wide variety of colors. It is easily molded by injection processes, softening at about 150° F. and is molded at 300° to 375° F., under 3,000 to 30,000 pounds pressure per square inch. As much as 40 percent filler may be used without seriously affecting the tensile strength, although the filler does affect the dielectric properties. Since the resin is thermoplastic there is no waste in the molding operation; scrap material may be reground and used again.

The unusual properties of these polystyrene resins should give them widespread applications when the cost is low enough to make them competitive with other materials. Potentially large volume outlets are in radio frequency insulation; in dentures because of the strength, low specific gravity, ease of coloring, and absence of odor and taste of the material; in electrical parts for submarine and aircraft storage battery cases and separators; and for the manufacture of glass eyes.

Other possible applications of polystyrene resins are in metal lacquers and in light colored enamels. Their toughness and light color, together with their solubility in cheap solvents, suggest their use for these purposes. Such lacquers are said to be quick-drying, resistant to water, and moderately so to acids and alkalies.

Production in the United States.

For a number of years, the Naugatuck Chemical Division of the United States Rubber Co. produced small quantities of polystyrene resins, which were marketed under the trade name Victron when for general purposes and under the trade name Marvelyn when for use in dentures. Little progress was made because of high costs and failure to produce a water-white product. The sales price was between $1.50 and $2 per pound. Early in 1937 the Naugatuck Chemical Division transferred its patents on polystyrene resins to the Carbide and Carbon Chemicals Corporation.

The Dow Chemical Co., Midland, Mich., late in 1937 announced commercial production of clear, colorless polystyrene in several forms. Styron is the trade name for the resin from this source. In January 1938, the Bakelite Corporation announced Bakelite Polystyrene. The plants manufacturing polystyrene have a capacity in excess of 2,000,000 pounds a year, and the resin is currently offered at 72 cents per pound.

At least one other domestic firm is doing research on the polystyrenes and expects to produce commercially in the near future.

Imports into and exports from the United States.

At least two commercial types of polystyrene resins are produced abroad. Both are made in Germany and marketed under the trade names Resoglas and Trolitul. Resoglas is a water-white, transparent thermoplastic resin softening at about 150° C. Its water absorption is low, it is nonoxidizing, and does not discolor on weathering and baking. Appreciable quantities are produced in Germany and the sales price there was reported to have been 40 cents per pound during 1936.

Source: Bakelite Corporation, 247 Park Avenue, New York, N. Y.]

Small quantities of Resoglas and Trolitul have been imported from Germany in recent years. Table 9 shows the quantities imported in recent years.

TABLE 9.—_Resoglas and Trolitul: United States imports for consumption, 1933-37_

--------+-----------------------------+---------------------------
| Resoglas (polystyrol) | Trolitul
Year +----------+-------+----------+--------+-------+----------
| Quantity | Value |Unit value|Quantity| Value |Unit value
--------+----------+-------+----------+--------+-------+----------
| _Pounds_ | | |_Pounds_| |
1933 | 771 | ([1]) | | 672 | ([1]) |
1934 | 991 | ([1]) | | 200 | ([1]) |
1935 | 110 | $97 | $0.88 | 4,608 |$3,782 | $0.82
1936 | 2,220 | 1,901 | .86 | 4,671 | 3,641 | .78
1937[2] | None | None | | 6,788 | 4,077 | .60
--------+----------+-------+----------+--------+-------+----------

[1] Not available.

[2] Preliminary.

Source: Analyses of invoices of paragraph 28, act of 1930—U. S.
Tariff Commission.

With the more advanced development of polystyrol resins in Germany prior to 1938, evidenced by larger commercial production, by wider application, by the marketing of a water-white product at a considerably lower price, it might be expected that imports into the United States would have been in considerably larger amount than shown in table 9. That they were small was probably due to the high rate of duty which made them expensive as compared with other synthetic resins in the United States and thus limited their market to uses in which the others were less satisfactory. Resoglas was reported to have been selling for 40 cents per pound in Germany. The imported resin is assessed for duty under the provisions of paragraph 28 of the Tariff Act of 1930 at 45 percent ad valorem based on American selling price (as a competitive product) and 7 cents per pound. The American selling price of the resin made in the United States until late in 1937, as determined by the Bureau of Customs, Treasury Department, was $1.85 per pound. The duty was therefore 90 cents per pound. Imports of Trolitul were valued at 75 cents per pound, giving a cost of $1.75 per pound laid down, duty paid, in domestic markets. With the present American selling price of 72 cents per pound, the duty would be approximately 36 cents per pound.

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.

Description and uses.

_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.

Production in the United States.

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.

Imports into the United States.

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 table 91, page 141) 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. Table 10 gives imports of synthetic resins under paragraph 11 of the Tariff Act of 1930.

TABLE 10.—_Synthetic resins classified under paragraph 11:[1] United States imports for consumption 1931-37_

--------+----------+-------+-----------
Year | Quantity | Value | Unit value
--------+----------+-------+-----------
| _Pounds_ | |
1931 | 453 | $173 | $0.38
1932 | 454 | 29 | .06
1933 | 1,120 | 496 | .44
1934 | 4,084 | 1,576 | .39
1935 | 3,105 | 1,804 | .58
1936 | 146 | 65 | .45
1937[2] | 1,963 | 439 | .22
--------+----------+-------+-----------

[1] Statistical 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.

[2] Preliminary.

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. Table 11 shows 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 table 12 shows 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_

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Synthetic resins and their raw materialsChapter III: Part 3

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