In 1937 approximately 66 percent of the United States production of tar-acid resins was made from phenol; 18 percent from phenol-cresol mixtures; 13 percent from cresol-cresylic acid mixtures; and 3 percent from cresol-xylenol mixtures. Table [2] shows for recent years production and sales of tar-acid resins by type of raw material. Pure phenol is used for cast resins. Molding resins are usually made from pure phenol or from tar-acid mixtures, chiefly phenol. Laminating and coating resins are usually made from mixtures containing substantial amounts of the cresols and xylenols (frequently spoken of by the trade as cresylic acid).
Table 2.—Tar-acid resins: United States production and sales, by type of raw material, 1933-37
| Year | Phenol | Tar-acid mixtures1 | ||||
|---|---|---|---|---|---|---|
| Production (net resin content) | Sales | Production (net resin content) | Sales | |||
| Quantity (net resin content) | Value | Quantity (net resin content) | Value | |||
| 1,000 pounds | 1,000 pounds | 1,000 dollars | 1,000 pounds | 1,000 pounds | 1,000 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 mixtures | Cresol-cresylic acid mixtures | Cresol-xylenol mixtures | ||||
| Production (net resin content) | Sales (net resin content) | Production (net resin content) | Sales (net resin content) | Production (net resin content) | Sales (net resin content) | |
| 1,000 pounds | 1,000 pounds | 1,000 pounds | 1,000 pounds | 1,000 pounds | 1,000 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.