Chapter II: Part 2

TABLE 2.—_Tar-acid resins: United States production and sales, by type of raw material, 1933-37_

----+--------------------------------+---------------------------------
| Phenol | Tar-acid mixtures[1]
+----------+----------+----------+----------+----------------------
| | Sales | | Sales
Year|Production+----------+----------+Production+----------+-----------
|(net resin| Quantity | |(net resin| Quantity |
| content) |(net resin| Value | content) |(net resin| Value
| | content) | | | content) |
----+----------+----------+----------+----------+----------+-----------
| _1,000 | _1,000 | _1,000 | _1,000 | _1,000 | _1,000
| pounds_ | pounds_ | dollars_ | pounds_ | pounds_ | dollars_
| | | | | |
1933| 25,163 | 21,851 | 5,383 | 6,535 | 6,152 | 1,182
1934| 29,777 | 27,995 | 7,332 | 10,887 | 8,091 | 1,705
1935| 36,323 | 34,597 | 6,568 | 16,654 | 12,371 | 2,200
1936| 51,603 | 49,053 | 9,419 | 18,747 | 12,908 | 2,325
1937| 52,472 | 50,209 | 8,616 | 27,373 | 23,337 | 4,685
+----------+----------+----------+----------+----------+-----------
| Phenol-cresol | Cresol-cresylic | Cresol-xylenol
| mixtures | acid mixtures | mixtures
+----------+----------+----------+----------+----------+-----------
| | | | | |
|Production|Sales (net|Production|Sales (net|Production|Sales (net
|(net resin| resin |(net resin| resin |(net resin| resin
| content) | content) | content) | content) | content) | content)
+----------+----------+----------+----------+----------+-----------
| _1,000 | _1,000 | _1,000 | _1,000 | _1,000 | _1,000
| pounds_ | pounds_ | pounds_ | pounds_ | pounds_ | pounds_
1937| 14,046 | 13,238 | 10,702 | 8,467 | 2,625 | 1,632
----+----------+----------+----------+----------+----------+-----------

[1] Includes phenol-cresol mixtures, cresol-cresylic acid
mixtures, and cresol-xylenol mixtures. For 1937, where it is
possible, the totals of tar-acid mixtures are broken down into
these three groups.

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

Processes of resin manufacture.

The processes of and patents for the manufacture of tar-acid-formaldehyde resins are numerous. No attempt is made here to describe in detail the several processes of manufacture or the endless number of variations and modifications. In general the processes in operation may be designated (_a_) one stage wet, (_b_) two stage wet, and (_c_) dry.

The one-stage wet process consists in heating molecular proportions of tar acid and formaldehyde (40-percent solution) in the presence of an acid or alkaline catalyst. The formaldehyde is added all at once and the reaction proceeds with the elimination of water. The difficulty with this process is that of obtaining uniform batches because it cannot be controlled exactly.

The two-stage process is probably the one most widely used today and consists in introducing formaldehyde in two or more stages as the reaction progresses. Much better process control and more uniform results are so obtained. A soluble, fusible resin is formed from which the water is easily removed. Fillers and pigments may be added during the latter part of the operation.

The dry process is the least important and is used only where cast resins are being made. Light-colored, transparent resins are obtained and the operation is carried on to the final stage (C resin). In this process the aldehyde used is solid paraformaldehyde or hexamethylenetetramine. These materials are more costly than formaldehyde solution.

Proportions of raw materials used vary widely—Baekeland suggested 7 mols of formaldehyde and 6 mols of phenol (210 parts of 100-percent formaldehyde to 564 parts of phenol), with a yield of resin equivalent to 118 percent of the phenol. Larger proportions of formaldehyde are said to increase the yield to as much as 140 percent of the phenol.

Catalysts used to aid in the condensation of the reacting bodies may be acids or bases. Certain properties of the resins may be varied by the kind and quantity of catalyst used. Large proportions of basic or acidic catalysts may affect the filler or metal inserts. Basic catalysts used include caustic soda, caustic potash, ammonia, carbonates, and alkali sulphites. Acid catalysts are usually one of the mineral acids such as hydrochloric acid or sulphuric acid.

While formaldehyde in the form of a 40-percent solution is the principal aldehyde used with the tar acids, certain other aldehydes are used in small amounts. Among these are acetaldehyde, butyraldehyde, benzaldehyde, and others. Resins from furfural and phenol are discussed as “Furfural Resins,” page 51.

Production in the United States.

The production of tar-acid resins in the United States has increased markedly in the last 10 years. Table 3 shows the production and sales of all coal-tar resins in 1927 and 1928 (when there was no further break-down available but when this classification was made up chiefly of tar-acid resins) and of tar-acid resins from 1929 to 1937. The figures given are in net resin content and do not include fillers, modifiers, or pigments. From 1929 to 1937 production increased from 26 million pounds to 80 million pounds; sales from 25 million pounds valued at 9.9 million dollars to 74 million pounds valued at 13.3 million dollars; the value per pound dropped from 39 cents to 19 cents.

In 1937 the production of tar-acid resins for molding accounted for about 40 percent of the total; those for surface coatings, about 25 percent; those for lamination, about 20 percent; and those for miscellaneous uses, about 15 percent.

TABLE 3. _Tar-acid resins: United States production and sales 1927-37_

--------+-------------+----------------------------------------
| | Sales
| Production +------------+--------------+------------
Year | (net resin | Quantity | |
| content) | (net resin | Value | Unit value
| | content) | |
--------+-------------+------------+--------------+------------
| _Pounds_ | _Pounds_ | |
1927[1] | 13,452,230 | 13,084,313 | $6,094,656 | $0.47
1928[1] | 20,411,465 | 20,778,856 | 7,211,958 | .35
1929[2] | 26,235,792 | 25,129,701 | 9,869,274 | .39
1930[2] | 18,338,389 | 17,428,687 | 6,576,023 | .38
1931[2] | 22,647,000 | 21,496,000 | 6,646,000 | .31
1932[2] | 17,163,000 | 15,042,000 | 3,946,000 | .26
1933[2] | 31,697,780 | 28,002,799 | 6,564,670 | .23
1934[2] | 40,663,565 | 36,086,008 | 9,037,861 | .25
1935[2] | 52,731,728 | 46,733,378 | 8,730,438 | .19
1936[2] | 70,349,328 | 61,961,200 | 11,743,978 | .19
1937[2] | 79,844,825 | 73,545,880 | 13,300,870 | .19
--------+-------------+------------+--------------+----------

[1] All coal-tar resins.

[2] Resins from tar acids only.

Source: Compiled from annual reports of the Tariff Commission on
dyes and other synthetic organic chemicals in the United States.

Imports into the United States.

Imports of tar-acid resins into the United States are dutiable under paragraph 28 at 7 cents per pound and 45 percent ad valorem based upon American selling price. Discussion of this rate, other restrictions upon imports in the earlier years, and of the rates upon articles made of these resins will be found on pages 59 to 61.

Imports of tar-acid resins are not shown separately in official statistics; the classification under which such imports are entered includes all synthetic resins of coal-tar origin. Table 4 shows the quantity and value of imports of all coal-tar resins since 1918, and table 5 shows the principal sources of imports for certain years.

Invoice analyses of imports in the last 3 years show only very small quantities of phenolic resins being imported. In 1934 there was an importation of 950 pounds of Bakelite molding compound; in 1935 imports of 100 pounds of molding compound and 22 pounds of aminophenol resin are recorded, and in 1936 imports of Bakelite filament compound totaled 250 pounds and other resins 8,851 pounds.

Even if in the years up to 1933 all of the imports of resins of coal-tar origin were tar-acid resins, imports of tar-acid resins have been negligible when compared with production. The smallness of imports may be accounted for by a combination of factors, (1) the prohibition of imports of certain types, which conflicted with patent rights; (2) the rate of duty upon imports; (3) the fact that the manufacture of tar-acid resins developed more rapidly in the United States than in most foreign countries; and (4) the allocation of markets through agreements between affiliated producers in different countries. (See p. 58.)

TABLE 4.—_Synthetic resins of coal-tar origin: United States imports for consumption, 1919-37_

--------+----------+----------+-----------+------------+---------------
| | | | Computed | Computed
Year | Quantity | Dutiable | Value per | ad valorem | specific
| | value | pound | rate | rate
--------+----------+----------+-----------+------------+---------------
| _Pounds_ | | | _Percent_ | _Per pound_
1919 | 1,114 | $2,860 | $2.57 | 32.0 | $0.82
1920 | 2,479 | 2,681 | 1.08 | 34.6 | .37
1921 | 1,420 | 2,366 | 1.67 | 33.0 | .55
1922 | 2,518 | 3,498 | 1.39 | 52.3 | .73
1923 | 3,183 | 10,512 | 3.30 | 62.1 | .20
1924 | 8,756 | 4,183 | .48 | 68.9 | .33
1925 | 1,537 | 889 | .58 | 57.1 | .33
1926 | 1,649 | 1,298 | .79 | 53.9 | .42
1927 | 11,359 | 4,266 | .38 | 63.6 | .24
1928 | 60,547 | 10,984 | .18 | 83.6 | .15
1929 | 67,529 | 17,503 | .26 | 72.0 | .19
1930 | 46,464 | 10,417 | .22 | 76.2 | .17
1931 | 6,074 | 6,180 | 1.02 | 51.9 | .53
1932 | 6,403 | 3,905 | .61 | 56.5 | .34
1933 | 3,776 | 2,508 | .66 | 55.5 | .37
1934 | 15,711 | 8,680 | .55 | 57.7 | .32
1935 | 18,015 | 6,075 | .34 | 65.8 | .22
1936 | 18,598 | 13,643 | .73 | 54.5 | .40
1937[1] | 18,977 | 14,278 | .75 | 54.3 | .41
--------+----------+----------+-----------+------------+---------------

[1] Preliminary.

Source: Foreign Commerce and Navigation of the United States.

TABLE 5.—_Synthetic resins of coal-tar origin: United States imports for consumption, by principal sources, in specified years, 1929-37_

---------------+--------+-------+-------+-------+-------+-------+-------
Imported from— | 1929 | 1931 | 1933 | 1934 | 1935 | 1936 |1937[1]
+--------+-------+-------+-------+-------+-------+-------
| Quantity (pounds)
+-------+-------+-------+-------+-------+-------+-------
Germany | 50,770 | 3,166 | 2,724 | 9,801 | 2,220 |10,750 | 13,950
France | 20 | 2,331 | 740 | | 297 | 168 |
United Kingdom | 336 | | | 1,065 |13,242 | 1,979 | 2,215
Switzerland | 3,473 | 1,781 | 4,384 | 1,716 | | |
Canada | 1,372 | 135 | 1,266 | 594 | | |
All other | | | | | | |
countries | 16,403 | 577 | 312 | | 340 | 51 | 502
+--------+-------+-------+-------+-------+-------+-------
Total | 67,529 | 6,074 | 3,776 |15,711 |18,015 |18,598 | 18,977
+--------+-------+-------+-------+-------+-------+-------
| Value
+-------+-------+-------+-------+-------+-------+-------
Germany |$11,771 |$4,053 |$1,913 |$5,303 |$1,959 |$9,700 |$11,960
France | 21 | 1,760 | 465 | | 236 | 177 |
United Kingdom | 2,235 | | | 255 | 2,476 | 1,090 | 659
Switzerland | | | | 2,621 | 1,308 | 2,154 | 1,197
Canada | | | | 501 | 46 | 486 | 214
All other | | | | | | |
countries | 3,476 | 367 | 130 | | 50 | 36 | 248
+--------+-------+-------+-------+-------+-------+-------
Total | 17,503 | 6,180 | 2,508 | 8,680 | 6,075 |13,643 | 14,278
+--------+-------+-------+-------+---------------+-------
| Unit value
+--------+-------+-------+-------+-------+-------+-------
Germany | $0.23 | $1.28 | $0.70 | $0.54 | $0.88 | $0.90 | $0.86
France | 1.05 | .76 | .63 | | .79 | 1.05 |
United Kingdom | 6.65 | | | .24 | .19 | .55 | .30
Switzerland | | | | .75 | .73 | .49 | .70
Canada | | | | .37 | .34 | .38 | .36
All other | | | | | | |
countries | .21 | .64 | .42 | | .15 | .71 | .49
+--------+-------+-------+-------+-------+-------+-------
Average | .26 | 1.02 | .66 | .55 | .34 | .73 | .75
+--------+-------+-------+-------+-------+-------+-------
| Percent of total quantity
+--------+-------+-------+-------+-------+-------+-------
Germany | 75.2 | 52.1 | 72.1 | 62.4 | 12.3 | 57.8 | 73.5
France | .1 | 38.4 | 19.6 | | 1.6 | .9 |
United Kingdom | .5 | | | 6.8 | 73.5 | 10.6 | 11.7
Switzerland | | | | 22.1 | 9.9 | 23.6 | 9.1
Canada | | | | 8.7 | .8 | 6.8 | 3.1
All other | | | | | | |
countries | 24.2 | 9.5 | 8.3 | | 1.9 | .3 | 2.6
---------------+--------+-------+-------+-------+-------+-------+-------

[1] Preliminary.

Source: Foreign Commerce and Navigation of the United States.

Exports from the United States.

Appreciable quantities of phenolic resins are exported annually in the form of molding compounds and as finished articles of wide variety. Statistics of these exports are not compiled separately by the Department of Commerce.

Exportation is limited by a number of factors, such as licensing agreements, patents, allocation of markets, and high tariffs or embargoes in certain countries. The largest domestic maker is affiliated with producers in Great Britain, Germany, France, Italy, Canada, and Japan. Other domestic firms have agreements as to patents and markets with producers in England, Germany, and other countries.

TAR-ACID RESINS FOR MOLDING

The tar-acid resins were first developed for molding and they are still used in large volume in this way. An article produced in large quantity is more likely to be made of molded resin. The cost of the mold, which may amount to several thousand dollars, then becomes very small per unit produced. If the article is of such a shape that it would require a great deal of labor to produce in metal or wood, it may be produced in quantity much more cheaply from resin, since it will come from the mold almost in finished form.

A few of the large molders find it economical to make their own resins when they use one type in large volume or desire some special modification. Most of the molders buy resins for molding in the form of either powder or pre-formed pellets ready for use.

Molding powders and pellets.

Molding powder is made from B-stage resin (see p. 13), a filler, a pigment, a lubricant, and a plasticizer. These materials are mixed and put through rolls at a moderate heat and pressure. The resin softens and amalgamates with the other materials. It hardens upon cooling and is ground to powder. A pre-formed pellet may be made from the powder by pressure; use in this form saves the time of the molder when filling the mold, since he is not required to measure the powder.

The proper selection of the filler in a molding powder is important in influencing the quality of the molded article. Fibrous fillers improve the mechanical strength and shock resistance of the finished article. Wood flour is the most widely used filler in tar-acid resins as well as in other thermosetting resins. Pine, spruce, and fir are the principal kinds used, and consideration must be given to the bulk, gum content, color, and the size and shape of the wood particles. Color is the least important since most of the tar-acid resins give brown or black moldings. When the molding must withstand high temperatures, asbestos fiber is used as a filler. In articles requiring high shock resistance, such as golf club heads, a filler of paper pulp is used. Where high electrical insulation and dielectric properties are required, ground mica is used as the filler. Certain inorganic fillers such as powdered slate, gypsum, barium sulphate, calcium sulphate, china clay, zinc oxide, and infusorial earths, are sometimes used. Large proportions of these may be used where hardness is more important than strength, as in phonograph records. Other materials used include rubber, graphite, horn, bone, starch, pumice, and cork.

Coloring matter used may be coal-tar dyes or pigments such as bone black, carbon black, and iron oxides. Pigments are usually more satisfactory, although dyes are sometimes preferred in articles for insulation.

A lubricant is added to the molding mixture to overcome the tendency to stick in the mold. Metallic soaps, stearates, and stearic acid are those most commonly used.

Sometimes a plasticizer is included, its function being to act as a solvent for the resin, thus increasing the flow of the material in the mold. The plasticizer should be one which will become infusible or at least remain solid in the molded article.

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

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

Source: Bakelite Corporation, 217 Park Avenue, New York, N. Y.]

A typical molding powder or pre-form pellet will contain by weight:

Resin 40 to 50 percent
Filler 35 to 50 percent
Plasticizer 5 percent
Lubricant 1 percent
Pigment 1 percent

The molding of tar-acid resins.

Ordinarily the molds used are made of hardened steel, highly polished. They must stand working pressures of several thousand pounds per square inch. The mold is placed in a hydraulic press, heated by steam, electricity, or gas, and the molding material is placed in the mold. The press is closed and heat and pressure are applied. The temperatures used range between 250° F. and 365° F., and the pressures between 1,000 and 8,000 pounds per square inch. The molding time depends on the shape and size of the article and on the composition of the molding material. As little as one-half minute is required for small objects and as long as 10 minutes for large objects. Average molding time is about 3 minutes. The article is removed from the mold, allowed to cool, and is then trimmed, sanded, filed, or polished. Since the mold is highly polished, the finishing operation is usually needed only to remove the flash. Inserts, such as metal parts (binding posts, electrical contacts, etc.), or inlays of polished metal in name plates, and signs, are often molded in; gear shift knobs are molded over a hollow metal core; rubber inserts are used in castors, electrical plugs, and similar objects.

The molding operation is an art, and has made remarkable progress in recent years. Many articles molded of tar-acid resins are well-known to the public. The automotive industry is the best customer, using such molded parts as gear shift knobs, horn buttons, accelerator pedals, light switches, ignition parts, and distributor heads. Other well-known applications are builders’ hardware, electrical switch plates, switches and fixtures, fountain pens, radio parts, telephone parts, handles for stoves, vacuum cleaners, and other appliances, buttons, buckles, costume jewelry, camera cases, radio cabinets, small containers, and hundreds of others.

The importance of tar-acid resins in molded articles is shown by the fact that more than 75 percent of all synthetic resin molded articles made in 1937 used this type of resin as a binder.

Production of tar-acid molding resins.

Domestic production of tar-acid molding powders and pellets was reported to the Tariff Commission by 15 makers in 1937. Most of these firms have specialized in resin development and manufacture. Among the well-known brands are Bakelite, Durez, Durite, Resinox, Indur, and others (see p. 153 for list of trade names).

Statistics of production and sales of tar-acid resins used in molding were collected separately for the first time in 1935. They show a net resin output of about 21,000,000 pounds, with sales of 18,000,000 pounds or about 40 percent of the total tar-acid resins. The average unit value was 17 cents per pound. In 1937 the production of tar-acid resins for molding exceeded 32,000,000 pounds, again about 40 percent of the total. These statistics are based on net resin and do not include fillers, modifiers, pigments, or inert material of any kind.

CAST PHENOLIC RESINS

Process of manufacture.

The production of cast phenolic resins requires pure materials, expensive equipment, and extreme care in the control of the operation. A mixture of phenol and formaldehyde and a catalyst (usually sodium or potassium hydroxide) is charged into a nickel-lined reaction kettle and heated until the water separates and is removed. The reaction is then allowed to proceed to the desired point. Glycerin is added to aid in forming a transparent product. All equipment, including pipe lines, valves, and pumps, is nickel or nickel lined except that used for formaldehyde, which is made of aluminum.

The resin is usually made in 1,000 pound batches, and the reaction cycle ranges from 6 to 18 hours. It is colored with soluble coal-tar dyes and cast into lead molds. These are placed in a heated room and allowed to cure for 3 to 6 days. The resin is removed from the mold with air hammers, and the lead molds are melted.

The appearance of the resin may be changed by varying its water content, by the addition of dyes and fillers, and by the addition of other substances to produce some desired effect, such as imitation ivory or marble. The clarity of the resin depends upon its water content—the greater the degree of dehydration the clearer the product. Range of colors is complete, from crystal clear to the darker shades, with any degree of transparency, translucency, or opaqueness.

Casting is in the form of sheets, rods, tubes, or special forms suitable for the production of buckles, jewelry, and other small products. Molds of complicated shape cannot be used, which means that most articles if produced of cast resin must be produced from standard shapes by subsequent working. Recently small radio cabinets have been cast.

Uses.

Cast phenolic resin can be machined in the same manner as hard wood. It must be polished after machining, usually by tumbling with shoe pegs and pumice or with muslin wheels. The smooth finish and low degree of heat conduction give the material a pleasant feel, not cold to the touch as is metal. The coloring is not superficial and therefore does not chip or wear off. Electrical properties are excellent. A slow polymerization continues for some time after fabrication, resulting in slight shrinkage.

Cast phenolic resins are marketed by the producers as rods, sheets, cylinders, and special castings. Standard round rods range from ⅜ inch to more than 5 inches in diameter. Special rods are available in such forms as square, hexagon, octagon, and fluted. Standard sheets are in sizes from 12 by 24 inches to 36 by 72 inches, and from ⅛ to 1 inch thick. Stock cylinders are available in a wide range of inside and outside diameters.

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

Stock material is fabricated by a number of firms into an endless variety of articles. Among these are toilet articles such as combs, backs for brushes, cosmetic containers, and trinkets; fittings for automobiles, electrical appliances, furniture, and display fixtures; jewelry, dress ornaments, clock cases, handbag frames, vanity cases, smokers’ articles, signs and advertising specialties, picture frames, handles for cutlery, chessmen, pens, desk penholders, pencils, and many others. Probably the largest consumption is in the making of buttons and buckles.

The cast phenolic resins are odorless, tasteless, nonflammable, resistant to oils and greases, and practically nonbreakable.

Patents and licensing.

The basic patent covering the manufacture of cast phenolic resins is United States Patent No. 1,854,600, issued April 19, 1932, to F. Poliak and A. Ostersetzer, of Vienna, and assigned to Pollopas, Ltd., of London. Many other patents have been granted on variations and modifications of this one. The basic process is also patented in England, France, Germany, and other countries.

United States and Canadian patent rights were purchased by the American Catalin Corporation; German rights by the Interessen Gemeinschaft Industrie A. G. (German I. G.); French rights by Kuhlmann Co., and British rights by the Imperial Chemical Industries. These licensing arrangements limited the licensee to sales in his own and, in some instances, nearby countries.

The American Catalin Corporation has successfully defended the validity of this patent and has licensed a number of domestic manufacturers to produce cast phenolic resins on a royalty basis.

In 1937 there were seven domestic makers of cast phenolic resins located in New Jersey, New York, Massachusetts, and Pennsylvania. These firms produce and market resins under the following trade names: Catalin, Prystal, Joanite, Fiberlon, Phenolin, and Marblette.

Production of cast phenolic resins.

Production was initiated about 1929 by the American Catalin Corporation. The output increased substantially every year from that year through 1933. Statistics of production and sales are not publishable for the years prior to 1934 because they would reveal the operations of individual firms; they are given in table 6 for subsequent years.

TABLE 6.—_Cast phenolic resins: United States production and sales, 1934-37_

------+-------------+---------------------------------------
| | Sales
Year | Production +------------+-------------+------------
| | Quantity | Value | Unit value
------+-------------+------------+-------------+------------
| _Pounds_ | _Pounds_ | |
1934 | 4,968,445 | 4,793,658 | $2,099,035 | $0.44
1935 | 5,566,621 | 5,454,490 | 2,205,879 | .40
1936 | 6,111,632 | 6,013,855 | 2,476,619 | .41
1937 | 5,459,654 | 5,335,746 | 2,180,620 | .41
------+-------------+------------+-------------+------------

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

Imports and exports.

The licensing agreements, as outlined above, provide for the allocation of markets for cast phenolic resins. Because of this arrangement there are little or no imports and exports of this material.

TAR-ACID RESINS FOR LAMINATING

By laminating is meant the impregnation of sheets of paper, fiber, or cloth with a solution of synthetic resin and the building up of these layers into sheets of reinforced synthetic resin of various thicknesses. When a tar-acid resin is used the paper or cloth is immersed in or coated with a solution of the B-stage resin, dried, and layers of the material are compressed and consolidated, under heat and pressure to form sheets, rods, tubes, blocks, and other forms, in the infusible C-stage.

The coating of sheets of paper with solutions of natural resin and the compacting of these sheets by heat and pressure is an old practice, especially for electrical uses. Shellac and copal have been widely used and yield a laminated board of good electrical and mechanical properties when used at temperatures under 70° C. Above 70° C. the resin softens and the desirable properties are lost. Since temperatures above 70° C. are not uncommon in electrical equipment, the limitations of these natural resins in this use can readily be seen. The use of tar-acid resins to impregnate insulation material removes the temperature limitation and otherwise improves the product; insulators so made are widely used in all sorts of electrical and radio equipment.

Uses of tar-acid resin laminated products.

Laminated sheets of tar-acid resin are made with paper, canvas, duck, linen, pulpboard, vulcanized fiber, plywood, and other materials. Paper is the material generally used for electrical insulation, although cloth is sometimes used when greater strength is needed. Canvas is used where maximum strength is required, as in gears for automobiles and industrial machinery. Impregnated linen is adapted to punched parts and small gears.

These laminated materials are uniformly dense, tough, resilient and light in weight. They are nonabsorptive, have low thermal conductivity, and a low coefficient of expansion. Their dielectric strength is excellent and chemically they are inert to oils, brine, most acids, weak alkalies, and many solvents. Structurally they are strong under tension, compression, flexion, or impact; they are easy to machine and are sound absorbing.

Gears made of laminated canvas are widely used; they are silent and outwear those made of metal. The development of such gears was brought about by the demand for a positive drive without the clash and clatter resulting from metal to metal contact. The laminated gear absorbs vibrations, eliminates noise, and reduces wear. The laminated material is one-seventh the weight of brass, one-sixth the weight of steel, one-fifth the weight of cast iron and one-half the weight of aluminum. Laminated gear blanks may be cut on automatic machines into helical, spur, bevel, or worm gears.

Timing gears in automobiles are frequently of this type; they require no adjustment and seldom need replacement during the life of the motor. The light weight of the material reduces to a minimum flywheel effect on the camshaft. Where lubrication is difficult a graphite impregnated blank may be used.

Bearings made from laminated fabric are successfully used in heavy rolling mills where they reduce replacement costs and decrease power consumption. The laminated material possesses strength, smooth surface, density, good load carrying capacity, high impact resistance, nonscoring properties, and is practically frictionless. Power consumption is said to be reduced as much as 40 to 60 percent of that of metal bearings and the life of the laminated bearing has been as much as 10 times that of the metal ones. It replaces Babbitt metal, brass, bronze, white metal, gun metal, or lignum vitae in this application.

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

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

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

In decorative uses, laminated materials have made remarkable progress in recent years. In this application the material made from laminated paper is veneered on wood or fiber board, and the surface is so durable that refinishing is probably not necessary during the life of the equipment. Table tops for public rooms such as restaurants, cafeterias, and bars are widely used because of the beautiful designs obtainable and because the material is not discolored by lighted cigarettes, alcohol or other liquids, and does not chip or crack. Laminated sheets are used for bathroom and kitchen walls, doors, window sills, store and theater fronts, lobby walls in hotel and office buildings, and counter tops in banks and post offices. The liner _Queen Mary_ is equipped with panels of this material as is also the new Library of Congress Annex. Most of the leading hotels have installed bar and cocktail lounges of laminated materials because of the range of color and the ease with which novel designs may be carried out.

Almost any solid color, design, or imitation of another material may be given the laminated sheet simply by printing it upon the top sheet of paper used in the impregnated assembly. Thus a beautiful piece of walnut or mahogany may be photographed, inexpensively reproduced upon paper, and the finished laminated sheet will closely imitate the polished wood. The combination of beauty with long life should permit the widespread use of this type of material in all sorts of building and equipment. It has been suggested as a possibility in automobile body construction.

Other important uses are in trim and door strips for mechanical refrigerators, in cafeteria trays, buckets and special containers, tires for factory trucks, textile spools, miners’ safety helmets, gaskets, valve discs and rings for pumps, pulleys, besides many others.

Production of tar-acid resins for laminating.

Statistics of production and sales of synthetic resins for laminating were not separately compiled prior to 1935. Since that year the resins made from cresylic acid have been used to the greatest extent in laminating, followed by those made from phenol. Tar-acid resins reported as “used in paints, varnishes, and lacquers” may include appreciable quantities of resin varnishes used for laminating. The total production and sale in 1937 of tar-acid resins used in laminating, therefore, would be the sum of the 20 percent of the total (see table 3) reported for laminating plus some part of the 25 percent reported for surface coatings.

Domestic producers of tar-acid resins for laminating are located in Delaware, New Jersey, New York, Illinois, Massachusetts, and Pennsylvania. The makers of the laminated materials are located in Delaware, New Jersey, New York, Ohio, Illinois, Pennsylvania, Indiana, and Connecticut. Their products are marketed under a number of trade names, including Micarta, Dilecto, Celoron, Formica, Textolite, Phenolite, Insurok, Spauldite, Synthane and Phenol Fibre.

Imports into the United States.

There has been practically no importation of synthetic resins for laminating. Imports of laminated products (rods, tubes, blocks, strips, blanks, or other forms) of which synthetic resin is the chief binding agent totaled only 215 pounds, valued at $612 in 1931 (principally from the United Kingdom); 13 pounds, valued at $71 in 1932; none in 1933 and 1934; 609 pounds, valued at $579 in 1935 from Canada, Germany, and the Netherlands; and 3,260 pounds, valued at $9,468 in 1936 from Austria, Germany, and the United Kingdom.

Exports from the United States.

Exports of phenolic or other synthetic resins for laminating and of laminated articles are not separately recorded in official statistics. It is known that appreciable quantities of laminated articles are exported to Canada, England, and other countries.

TAR-ACID RESINS FOR SURFACE COATINGS

Synthetic resins are widely used for surface coatings, chiefly because of the ease with which new types can be produced to meet special requirements and because of their uniformity. Tar-acid resin coatings may be varied in composition and properties to meet a particular purpose. Possible variations depend on the type or mixture of tar acid used (phenol, cresols, xylenols, tertiary amyl phenol, tertiary butyl phenol, phenyl phenol), whether the condensation takes place in the presence of an acid or an alkali, and on the proportion of formaldehyde used. The resin so formed may be modified with natural resins, synthetic resins of the alkyd type, fatty acids, or other materials. The almost endless opportunities for different types can, therefore, readily be appreciated.

Types of resin used and the resultant coatings.

The tar-acid resins used in varnishes and other surface coatings are usually oil-soluble types. They may be divided into three general classes: (1) Phenol-formaldehyde condensation products rendered oil-soluble by chemical combination or physical dispersion in other materials, such as rosin and copal; (2) condensation products made from tar acids other than simple phenol, which are themselves soluble in drying oils and thinners; and (3) products from the condensation of the substituted phenols and formaldehyde. These three classes of oil-soluble tar-acid resins differ widely in their chemical and physical properties and in their functions. The first group are usually called modified phenolic resins, the second group are referred to as unmodified or 100-percent soluble, and the third group are known as substituted phenolic resins.

The unmodified resins are extensively used in long-oil tung varnishes, to which they impart greater drying speed, durability, and resistance to alkalis and gases. The modified types impart the same properties to tung oil varnishes but to a lesser extent. In addition the modified types possess considerable hardness so that greater gloss and fullness are obtained. Modifiers are either drying oils or natural resins; tung oil is the most widely used oil and rosin the principal natural resin. Substituted phenols such as para tertiary amyl phenol and para tertiary butyl phenol may be used in place of simple phenol; while these are relatively high priced components, the resins made therefrom have increased in recent years to an appreciable volume because of their improved properties.

Other synthetic resins, such as those of the alkyd, petroleum, urea, and vinyl types, are sometimes incorporated with the phenolics in the same surface coating to obtain some desired property. The addition of a plasticizer, such as tricresyl phosphate or dibutyl phthalate, improves the flexibility of the film.

Spirit varnishes, in which the synthetic resin is dissolved in a solvent, are also available. In this type the soluble fusible resin (form A) is dissolved in an organic solvent such as acetone or the various alcohols, and conversion of the resin to the insoluble, infusible state (form C) is effected by baking the film.

Coatings made from tar-acid resins are widely used in so-called 4-hour enamels and varnishes, for both interior and exterior application. They are also used in the manufacture of linoleum, artificial leather, adhesives, and printing inks. When incorporated with nitrocellulose or cellulose acetate lacquers they improve the adhesion, luster, and resistance to alkalies.

Production in the United States.

In 1937 the output of tar-acid resins for surface coatings exceeded 20 million pounds (net resin). Those from phenol and the substituted phenols accounted for a very large part of the total. They were followed by resins from cresylic acids and the xylenols in that order.

In 1937 there were about 20 domestic makers of this type of synthetic resin, with factories located in California, Connecticut, Illinois, Indiana, New Jersey, New York, Massachusetts, Michigan, Missouri, Ohio, Pennsylvania, and Rhode Island.

Imports into and exports from the United States.

Imports of oil-soluble phenolic resins have been negligible. This is due, in part, to licenses and agreements between certain domestic and foreign makers, to the remarkable advancement and pioneering work done in this country, to the holding of many basic patents by Americans, and to the relatively high duty on imports.

Exports of these products, usually in the form of enamels, varnishes, and lacquers, have been appreciable and are probably increasing each year. Official statistics are not reported separately.

TAR-ACID RESINS IN ADHESIVES

A comparatively new use for tar-acid resins is in the manufacture of wood adhesives. Ordinary vegetable and animal glues have long been used, although their deficiencies in certain characteristics are well known. These include (a) their inability to produce uniform products, (b) the tendency of most alkaline glues to stain wood, (c) the bad effects of moisture on them, and of bacteria and fungi in the case of animal glues. The tar-acid resins have none of these objectionable qualities. Being chemically inert they are free from attack by fungi and bacteria. Moisture does not affect them, and they do not stain wood.

Three types of resins are used as wood adhesives, principally in bonding plywoods and veneers: (1) Hot press liquid, (2) cold press liquid, and (3) resin film. Furniture, radio cabinets, games, and building products constructed from plywoods bonded with resins can be shipped to tropical countries, the bond not being affected by extreme climatic conditions.

These resin adhesives are more expensive than the usual animal and vegetable glues, a factor which has limited their application. Their advantages may, however, open up to resin bonded plywoods uses in which the more ordinary types are not satisfactory.

TAR-ACID RESINS FOR OTHER USES

The application of tar-acid resins in casting, molding, laminating, surface coatings, and adhesives has been described. There are many other uses, but most of them approach the types of application dealt with.

Impregnation of all sorts of materials with tar-acid resins is an increasing use; such applications are in fabrics for aircraft, crease resistant textiles, wood, asbestos, concrete, and electrical coils. Wood with resin forced into the fiber under pressure is used for furniture, flooring, heads for golf clubs, and handles for utensils. Resin is used as a binder in the manufacture of brake linings for automobiles, as well as in the manufacture of abrasive and grinding wheels.

An interesting application is in the construction of corrosion-resistant chemical plant equipment. In 1922 the German firm of Saureschutz Gesellschaft was incorporated to fabricate equipment composed of a special acid-resisting type of phenolic resin and asbestos. Sometime later its manufacture was started in the United States. All sorts of industrial plant equipment is now available, including cylindrical and rectangular tanks up to 9 feet in diameter and 12 feet high, piping for corrosive liquids and gases, valves, pumps, fans and ventilators, filter press plates and frames, buckets, dippers, etc.

Another new use is for making matrices in which to mold rubber printing plates. Such plates are used at present chiefly in printing cotton and paper bags but extensive experimentation promises to broaden their use. The matrix is made of fiber board of very open structure impregnated with tar-acid resin in the process of manufacture.

4. ALKYD RESINS

Description and uses.

The alkyd resins, used principally in paints, varnishes, and lacquers, are a group of condensation products synthesized by reacting polyhydric alcohols, such as glycerin and the glycols, with dibasic organic acids, such as phthalic, maleic, succinic, and sebacic. The condensation product is almost always modified to give properties to the resin desirable or essential to the specific application contemplated. The modifying agent may be a drying, semidrying, or nondrying oil; the fatty acid of an oil; a natural resin, such as rosin; a synthetic resin of the tar-acid group or of the urea-formaldehyde type; or other substance. Up to the present time unmodified alkyd resins have not been commercially important.

A wide variety of types is obtained by the use of different materials and different modifiers. The variations begin with the dibasic acid used, and with the polyhydric alcohol used. The modifications possible are practically endless, and almost any fixed oil or the corresponding fatty acid, and most of the natural or synthetic resins may be used. The importance of the modifier is shown by the proportion used in most alkyd resins. On the average, approximately 50 percent of the total weight of the drying and semidrying alkyd resin products is modifier, 30 percent dibasic acid, and 20 percent polyhydric alcohol. The proportions will, of course, vary with individual types. Certain types on the market contain only 25 percent modifier while others have as much as 75 percent.

In a new industry such as this, rapid changes in types and applications must be expected. Extensive research is being carried on by various groups. The raw material makers are seeking cheaper products or those with special properties; the resin makers are investigating an endless number of modifications, and the makers of surface coatings are testing most of the new types offered.

Development and patents.

Probably the earliest record of research leading to the development of the alkyds was that of van Bemmelen, who reported in a German technical journal in 1856 the sirupy products obtained by heating together succinic acid and glycerin or citric acid and glycerin. The first investigation of the phthalic anhydride-glycerin resins was recorded in 1901.[3] Watson Smith, while engaged in research on phthalein dyes, obtained a transparent, highly refractive resinlike substance when glycerin and phthalic anhydride were heated together. Smith recommended the product as a cement for ceramic wares.

During the period 1910-16 the research laboratories of the General Electric Co., engaged in research on a synthetic resin from glycerin and phthalic anhydride. As a result of these studies numerous patents were granted for this type of resin to which the trade name Glyptal was applied. Intensive research was carried on by several firms, many variations were developed, and literally hundreds of patents were granted.

The paint and varnish industry has been undergoing radical readjustment. Methods and natural products, which for decades or centuries had changed very little, are giving way to synthetic creations of our laboratories. The first important departure from the traditional practices was the development of nitrocellulose lacquers. The commercial application of the alkyd resins followed, and their use is increasing rapidly. Because this development is still comparatively young, the large number of modifications offered has confused the coating manufacturer. It is probable that many of the synthetic products now being marketed have no special technical or economic justification and that they will in time lose out in competition with better products known at present, or still to be developed.

United States Patent No. 1,893,873, dated January 10, 1933, granted to R. H. Kienle and assigned to the General Electric Co., was considered one of the basic patents in this field. Early in 1936 it was declared invalid in a suit claiming infringement brought against the Paramet Chemical Co. of Brooklyn, N. Y. The decision in this case seems to have opened the glycerin-phthalic anhydride resins to a large number of manufacturers.

Among the principal brands of alkyd resins now on the domestic market are Beckosol, Dulux, Esterol, Glyptal, Rezyl, and Teglac. Each of these trade names identifies a series of products.

Classification of alkyd resins.

A number of classifications of the alkyd resins are possible and practical. Since by far the most important applications are in surface coatings, and their use in molding compositions is relatively unimportant, it seems advisable at this time to emphasize the more important use. For the purpose of this survey the following classification is used:

(1) Drying alkyd resins.
(a) Unmodified.
(b) Modified with natural materials.
(c) Modified with other synthetic resins.
(d) Modified with other synthetic resins and oil extended.
(2) Semidrying alkyd resins.
(3) Nondrying alkyd resins.
(4) Miscellaneous modified alkyd resins.
(5) Alkyd resins in water dispersion.
(6) Alkyd resins in molding compositions.

At least 75 percent of the alkyd resin finishes used at present are of the drying type and about 15 percent of the nondrying type.

_Unmodified drying alkyd resins._—This class of alkyd resins consists of a series of compounds made from polyhydric alcohols, polybasic acids, and fatty acids in chemical combination. The alcohol is usually glycerin, and the polybasic acid largely phthalic anhydride or acid, although others, such as maleic anhydride (acid) are increasing rapidly in importance. The fatty acid or oil used may be linseed, tung, perilla, hempseed, soybean, sunflower, safflower, or other drying oil. It is believed that tung oil and perilla oil are the most important at this time.

Unmodified drying alkyd resins are characterized by excellent durability but limited resistance to water in air-dried finishes. Both in air-dried and in baked finishes they are outstanding as to flexibility, quick drying, long luster life, and permanent adhesion. Their principal uses are in finishes for interior walls and woodwork, automobiles, coatings on steel such as for refrigerators, railway equipment, bridges, advertising signs, and lithographed containers. In these applications the products of this type compete with nitrocellulose lacquers and the older types of varnishes and paints. While the initial cost is higher, greater durability is obtained together with faster drying, flexibility, and hardness.

Probably the largest field for surface coatings is outdoor wood finishes. Several attempts have been made to adapt pure alkyd finishes to this use but with limited success because the hard and non-porous finish does not permit the escape of moisture contained in the wood and the pressure developed from vaporization of the moisture by the sun’s rays tends to lift the coating from the wood surface. Recently it has been found practicable to incorporate from 15 to 20 percent alkyd resins in conventional types of outdoor paints for wood. Here the use of alkyds has contributed greater durability and retention of fresh appearance over a longer period. Paints of this type are now on the retail market.

_Drying alkyd resins modified with natural materials._—This type of alkyd resin is modified principally with natural resins, such as rosin, damar, mastic, shellac, or copal. The use of these natural resins imparts hardness to the resin but shortens its durability. They make the product less expensive, permit easier incorporation of the drying oil, and in some instances increase the water resistance.

Their principal application is to modify nitrocellulose lacquers and lacquer sealers, in order to impart gloss, hardness, and easy sanding. It has been said that the commercial production of drying alkyds modified with natural resins was as important a development in the surface coating industry as the discovery of the alkyds themselves.

_Drying alkyd resins modified with other synthetic resins._—Drying alkyd resins may be modified with tar-acid formaldehyde resins, tar-acid furfural resins, urea-formaldehyde resins, petroleum resins, and the coumarone and indene resins.

Modification with tar-acid resins gives a quicker setting, harder drying finish with a higher gloss. Alkyd resins so modified are adapted to both air-drying and baked undercoats and finishes; they have good durability and adhesion and good resistance to grease, oils, alcohol and abrasion. For some uses the tar-acid resin modification gives better qualities than either component possesses alone, but in light colored finishes it has a tendency to cause the finish to yellow. Coatings made of drying alkyd resins modified with tar acid resins are widely used on automobile chassis, fenders, and bodies, machinery coatings, steel fixtures and toys; they are especially suitable for primers, undercoats, and finishes on metal.

Modification with urea resins produces baked-finish coatings. As much as 40 percent of the urea resin is incorporated. It makes possible coatings with a full range of permanent colors and improves their hardness and mar-proofness, whereas without the ureas the combination of color range with hardness had been difficult to obtain. The urea resin modified alkyds find use on metal surfaces of articles which must stand rough handling, such as toys, furniture, and motors.

Modification with petroleum resins produces air-dried finishes. For industrial use on metal they give coatings with better adhesion, dispersion of pigments, and resistance to acids, alkalies, and moisture at a lower cost than is obtained by ester gum or tar-acid resin modification. The petroleum resin modification minimizes skinning and improves the luster and the flow.

_Drying alkyd resins modified with other synthetic resins and oil extended._—Excellent water resistance and versatility are the characteristics of finishes made of alkyd resins modified with other synthetic resins (usually tar-acid) and oil extended. The incorporation of drying oils gives a low cost finish with better compatibility and brushing and with the combined properties of a quick-setting varnish and an alkyd resin. Although not so durable or quick setting as the unmodified finishes, they have better water resistance. These finishes may be brushed or sprayed, air-dried or baked. They have wide industrial and architectural uses.

_Semidrying alkyd resins._—Cottonseed oil is the principal modifier in semidrying alkyd resins. Alkyd resins of this type are used in finishes requiring maximum gloss and color retention. When baked on metal at high temperatures they show no tendency to wrinkle. They are used as reinforcing agents to increase flexibility and durability, and to plasticize other finishes.

_Nondrying alkyd resins._—The nondrying or nonoxidizing alkyd resins are those containing a nondrying oil, such as castor oil or coconut oil, or the fatty acid of a nondrying oil, such as stearic, palmitic, or oleic acid. Nondrying oils make the resin less sensitive to heat hardening and impart greater flexibility. These resins are used principally as plasticizers in nitrocellulose lacquers. In this use they have the advantage of better retention of plasticizing efficiency than other plasticizers, many of which are lost by evaporation, migration, absorption, or oxidation. These modified nitrocellulose lacquers, either clear or pigmented, are used for coating wood, composition board, cloth, paper, rubber, leather, and similar surfaces.

_Miscellaneous modified alkyd resins._—This group includes alkyd resins modified with materials other than those already discussed. To date (1938) there has been little, if any, commercial production of such resins. There are many modifiers which have been suggested and which might be used but for the fact that they are too expensive. Among these are butyl alcohol and benzoic acid.

_Alkyd resins in water dispersion._—Emulsions of alkyd resins in water are now available for use in clear and pigmented coatings. These are sold in the form of paste containing 40 to 50 percent solids and are diluted with water at the time of application. They are especially suitable for coating porous surfaces, such as brick, concrete, plaster, stucco, and masonry of all kinds. They are applied by brushing or spraying and they combine the ease of application of water paints with the durability, washability, and hardness of oil paints. They dry quickly, and the dried film cannot again be dissolved or suspended in water; the coating can therefore be washed or, after several weeks, scrubbed with cleansers. Compared with oil paints, they give better coverage, are easier to apply, and cost appreciably less. Compared with other types of water paints, such as kalsomine, they give a glossier coating of greater durability and superior appearance; they seal porous surfaces better; their covering capacity is greater; and their applied cost is slightly less per square yard of surface.

Coatings of this type may be applied directly over fresh plaster without a sizing coat, since they allow the curing of the plaster to continue. The usual paint pigments may be incorporated.

A special use of the water dispersed alkyds is on asphalt or tar since they are nonbleeding in the solvents of these materials. This quality permits their use for traffic and zone markers on streets.

_Alkyd resins in molding compositions and other uses._—The alkyd resins are much less important as binders in molded articles than in coatings and finishes. Conversion of the resin to the insoluble infusible form is extremely slow, requiring days as compared with minutes for the tar-acid and urea resins.

The alkyds are used as binders for flake, powder, and split mica to produce insulation material of high electrical strength. Other uses are in the production of linoleums; gaskets; brake linings; laminated fabric, paper, and cardboard sheets; printing inks; and coated paper, textiles, and leathers.

Pigments and solvents in alkyd finishes.

Since the alkyd resins are largely used in surface coatings and finishes and since this application in this field is producing great changes in the industry, it is appropriate to consider the effect of their use on other materials.

The average alkyd resin consists of 50 percent glycerol phthalate modified with 50 percent oil, fatty acid, natural resin, or synthetic resin. The alkyd and modifier are dissolved in a solvent, usually a coal-tar light oil such as toluol, or xylol, or a petroleum solvent, and pigmented with titanium dioxide or other pigment. Highly basic pigments such as zinc oxide, carbonate white lead, whiting and aluminum hydrate (all important pigments in the conventional types of finishes) are not used in alkyd finishes.

Production in the United States.

Prior to 1929, the domestic production of resins from phthalic anhydride was confined largely to one maker. The quantities produced were relatively small. In 1929 there were three producers, the volume of whose production exceeded one million pounds for the first time. Beginning with 1933 the Tariff Commission collected and compiled production and sales statistics for these resins. They are shown in table 7.

TABLE 7.—_Alkyd resins from phthalic and maleic anhydride: United States production and sales, 1933-37_

--------+-----------+------------+------------------------------------
| | | Sales
Year | Number of | Production +------------+-----------+-----------
| makers | | | |
| | | Quantity | Value | Unit value
--------+-----------+------------+------------+-----------+-----------
| | _Pounds_ | _Pounds_ | |
1933 | 6| 9,930,705| 3,654,854 | $673,890 | $0.18
1934 | 10| 15,219,247 | 7,084,602 | 1,022,436 | .14
1935 | 15| 34,312,713 | 15,836,942 | 3,482,078 | .22
1936[1] | 31| 46,952,452 | 24,252,535 | 5,312,121 | .22
1937[1] | 39| 61,254,019 | 34,738,295 | 6,864,194 | .20
--------+-----------+------------+------------+-----------+-----------

[1] Includes resins from maleic anhydride.