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Coloring Finishing And Painting Wood
Alkyd finishes made with a China-wood oil modifier will air-dry in about 16 hours. Usually, alkyd finishes are made, in part at least, with soya-bean oil, which is slow or almost non-drying; and, in this case, baked-on finish is required. The baking type placed on metal requires for drying only 1 to 11/2 hours at a temperature of 275° F. to 325° F. The Ford factory recently was using sprayed-on enamel finishes of the alkyd type and baking them on under both heat and light by use of thousands of 260 watt electric lamps. The bodies passed thru tunnels or moving ovens powerfully lighted for both heat and light lumination during the drying process. Some repair shops are said to "spray on" an enamel and dry it out under a big lamp or group of lamps.
At present there is a tendency toward the alkyd or phthalic type of enamels for baked-on metal finishes, such as are used on automobiles, articles of tin, and refrigerators. Alkyd resins are also in some of the present-day lacquers.
The Rezyls and Teglacs are other alkyd resins made by using modifying agents which are generally fatty acids. The Rezyls are used in house paints, lacquers, and in some baking enamels. The Teglacs are also modified alkyds, which are combined with some natural resin acid as the modifying agent.
329. Nevindene Resins.—It is from reactive chemicals known as coumarone and indene, which are found in certain coal-tar naphthas, that the cumar type of synthetic resins called Nevindene is obtained. Reactions of coumarone and indene thru treatment with polymerizing agents produce the Nevindene resins which are manufactured in several grades. The most valuable seem to be the hard grades. Tho not soluble in alcohol, they are soluble in varying proportions in the light coal-tar solvents and petroleum naphthas. The Nevindenes blend well with some of the needed drying oils, with other synthetic resins, and also with fossil resins sometimes mixed with them for special purposes. It has been found, however, that the phenol-modified indene types of resins are most easily blended with other varnish ingredients ; consequently, they are especially valuable for use in plastics, adhesives, chlorinated rubber coatings, and varnishes. The Nevindene resins are used in blends sometimes to reduce the acidity of the mixtures, being almost neutral or containing practically no acid themselves. Another reason for blending with other resins is because Nevindene sells at a lower price than most resins of other types. The Neville resins are manufactured for use in varnishes, bronzing liquids, and paints; and such finishes are resistant to moisture, alkali, and acids. The earliest types of Nevindene resin varnishes and enamels showed afteryel lowing, which made them unsuitable where white enamels and transparent light finishes were desired. This quality has been somewhat improved recently by use of purer materials.
