1. Field of the Invention
This invention relates to phenolic molding compounds using phenol-aldehyde Novolac resins. More specifically, it relates to such resins modified to improve arc resistance, arc track voltage and flame retardance by the incorporation of melamine. Still more specifically, it relates to phenolic resin comprising 10.5-20 percent by weight of melmine based on the weight of the total composition.
2. State of the Prior Art
No prior art has been found for the use of melamine for improving the arc resistance or arc track voltage of phenolic molding compounds.
Moreover, while phenolic molding resins may be improved in flame or fire retardance by the addition of mineral modifiers, the use of sufficient amounts of mineral modifiers, such as hydrated alumina, to produce the desired flame retardant effect may have an adverse effect on other properties such as flow, cure rate and high specific gravity. Therefore it would be desirable to replace such mineral additives with melamine. However, when melamine has been used as one of the resin components such as in a phenol-melamine-aldehyde resin, the product has the normal post shrinkage for the resin.
French Pat. No. 1,480,362 shows the use of melamine in foam phenolic resins but makes no mention of its use in phenolic molding compounds. French Pat. No. 2,003,124 shows the use of a combination of a mineral or inorganic material having water of crystallization from which the water is released at high temperatures, together with an organic material, such as melamine.
In the parent application, the Examiner cited U.S. Pat. Nos. 2,387,256; 2,593,926 and 2,816,085; and Matsuda et al., Chem. Abstracts, Vol. 70, 1969, 7875z. In the final rejection, the Examiner relied only on the Groten U.S. Pat. No. 2,387,256 and the Matsuda et al. reference.
Groten, U.S. Pat. No. 2,387,256 shows the use of a melamine-formaldehyde resin instead of hexamethylenetetramine (hexa) as a curing agent for phenol-formaldehyde resins. As discussed later herein, the reaction of a preformed melamine-formaldehyde resin with a phenolic resin does not produce the same results as the reaction of the phenolic resin with a mixture of free melamine and hexamethylenetetramine.
The Matsuda Chem. Abstract reference describes briefly the production of a colorless resin solution by first reacting a Novolac resin with aqueous formaldehyde to form a methylolated product which is then reacted with melamine and aqueous formaldehyde for a sufficient period to produce a resin solution. This does not teach applicant's composition of a water-insoluble, solid Novolac resin mixed with unreacted melamine, and hexa which produces a molded product having a substantial amount of unreacted melamine therein.