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.
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:
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.
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.
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.