Vinyl resins, acrylate resins, and polystyrene resins are at present produced in much smaller volume than those just listed. If and when the volume of production is increased the price may be decreased. In 1937, the price per pound of pure resin[12] was as follows:
| Type of resin: | Average sales price
of net resin, 1937
(per pound) |
|---|
| Vinyl | $0.69 |
| Acrylate | 1.66 |
Early in 1938, acrylate resins were being offered for sale at 85 cents per pound for molding powder and $1.25 per pound for the cast material; polystyrene resins at 72 cents per pound.
Petroleum resins, in 1937, sold for an average of 2 cents per pound net resin content.[12] This low price puts them beyond competition of the other synthetic resins in the uses in laminating and coating to which they are adapted.
The physical properties of a resin and its uses.
A more expensive resin will be used in preference to a cheaper one, only if the higher cost is more than offset by some physical property, such as color, which makes it more desirable in a particular use. The most common molding resin at present is the tar-acid type, but it is available only in the darker colors and therefore has been at a disadvantage, where a light color is desired, in competition with cellulose nitrate (celluloid) and cellulose acetate plastics or with urea and cast phenolic resins. In recent years the production of cellulose acetate molding compounds and of urea resins has increased rapidly, largely under this stimulus. The desire for color also promises well for the future of the acrylate and polystyrene resins which are produced in water-clear grades or colored with dyes or pigments.
Table 17.—Synthetic resins and other plastics: Properties that affect appearance
| Type | Machining qualities | Clarity | Color possibilities | Burning rate | Effect of age | Effect of sunlight | Refractive index No1 |
|---|
| Synthetic resins: | | | | | | | |
| Tar-acid—Formaldehyde: | | | | | | | |
| Molded, wood flour filler. | Fair to good. | Opaque | Limited | Very low | None | Light shades discolor | |
| Molded, mineral filler. | do | do | do | Nil | do | do | |
| Molded, fabric filler. | do | do | do | Approximately nil | do | do | |
| Laminated, paper base. | Fair to excellent. | do | do | Very low | Improves mechanical and electrical properties. | Lowers surface resistance. | |
| Laminated, fabric base. | do | do | do | do | do | do | |
| Laminated, asbestos cloth base. | do | do | do | Approximately nil | do | | |
| Cast | Excellent | Transparent, translucent, opaque. | Unlimited | Very low | Hardens slightly | Colors may fade | 1.5-1.7 |
| Tar-acid—Furfural: | | | | | | | |
| Wood flour filler. | Fair to good | Opaque | Limited | do | do | Light shades discolor | |
| Mineral filler. | do | do | do | Nil | do | do | |
| Fabric filler. | do | do | do | do | do | do | |
| Urea—Formaldehyde. | Fair | Translucent, opaque | Unlimited pastel shades | Very low | do | None | 1.54-1.6 |
| Vinyl, unfilled. | Good | Transparent, translucent, opaque | Unlimited pastels to black | Nil | Strength unaffected | Darkens | 1.53 |
| Vinyl, filled. | Excellent (organic filler). | do | do | Approximately nil | None | Discolors | |
| Acrylate | Very good | Transparent (95% light transmission). | Unlimited | Slow | do | None | 1.49 |
| Polystyrene | Poor to good | Transparent, translucent, opaque. | do | do | do | Yellows | 1.67 |
| Other plastics: | | | | | | | |
| Shellac compound. | do | Opaque | Limited, pastels excluded | High (wood filler) | | None | |
| Cold molded: | | | | | | | |
| Nonrefractory. | Poor | do | Dark colors only | Nil | | | |
| Refractory. | do | do | Gray | do | | | |
| Rubber compounds: | | | | | | | |
| Chlorinated rubber. | | Translucent, opaque | Unlimited | do | Slight embrittlement | Darkens | 1.56 |
| Modified isomerized rubber. | Good | Transparent | do | Slow | None | Slight surface crazing | |
| Hard rubber. | Fair | Opaque | Limited | Medium | do | Discolors surface, resistivity decrease. | |
| Casein | Good | Translucent, opaque | Unlimited | Very low | Hardens slightly | Colors may fade | |
| Cellulose compounds: | | | | | | | |
| Ethyl cellulose | do | Transparent, translucent, opaque | do | Slow | Slight | Slight | 1.47 |
| Cellulose acetate sheet | do | do | do | do | do | do | 1.49-1.50 |
| Cellulose acetate molding | do | do | do | do | do | do | 1.47-1.50 |
| Cellulose nitrate | do | do | do | Very high | Slight hardening | Discolors and becomes brittle | 1.50 |