The important uses of the urea resins are dictated by their pleasing color and appearance. In 1935 the largest outlets were in buttons and buckles, in bottle closures, and in such premium items as biscuit cutters and cereal bowls distributed by a large food manufacturer. Tableware, bathroom fixtures, all sorts of containers and closures, housings for radios, clocks, scales, and other machines for retail stores, and light-colored wall plates and switches, knobs, handles, and trim on dash panels of automobiles, and handles and trimming on gas and electric ranges were among the widespread applications of the urea resins. In 1938 probably the fastest growing outlet for urea resins is in lighting equipment. Use in packaging, in closures, and in housings, is also increasing. Tableware, the principal outlet for a number of years, is declining markedly.
A comparatively new use is in shades and reflectors, replacing opal glass. The unpigmented resin is highly translucent and gives high light transmission and an exceptional degree of light diffusion. These properties, together with low unit manufacturing costs, reduced shipping costs, and resistance to breakage make the urea resins an ideal material for all sorts of shades and reflectors for direct and indirect lighting fixtures. Many of the shades used in railway cars are of this material. The resin is available in degrees of denseness and opacity to give particular ratios of reflection and transmission. Reflectors as large as 28 inches in diameter are on the market.
Although molded articles are the large outlets for the urea resins, other applications are of increasing importance. Sirups used to impregnate paper and cloth are used in laminating and the resulting materials have unusual decorative possibilities. The surface is hard and durable and the wide range of colors possible permits very attractive applications. The urea resins are used both as the principal binding material for laminated sheets or on the surface laminae of sheets where tar-acid resins are used as the chief binder. The latter practice permits a wide color range in decorative materials without loss of strength or other characteristics of the tar-acid resins. In 1937 there were seven makers, and their production of urea resins for laminating accounted for slightly less than 10 percent of the total of all urea resins.
Another application of urea resins which has grown rapidly in the past 2 years is in combination with alkyd resins in surface coatings. In 1937 there were three makers, and their output of urea resins for coatings amounted to more than 10 percent of the total production of urea. Until recently the use of urea resins in paints and varnishes was discouraged by their insolubility in organic solvents and their instability. On the other hand, their lack of color, their high transparency, their hardness, and their freedom from after-yellowing were desirable characteristics. The development of methods for preparing condensates, which overcome the undesirable properties, has made available resins for this use. They are marketed as water-white viscous solutions in a mixture of organic solvents and are intended for use in baking finishes. They cannot be used alone because the cured resin is extremely hard and brittle and lacks adhesion. When combined with more elastic film-forming materials such as drying or nondrying oil alkyd resins, they produce coatings that are mar-proof, resistant to alcohol, grease, oil, and fruit acids, and available in a full range of colors. Applications are in metal furniture finishes, toys, refrigerators, can, and drum coatings.
The value of urea resins as adhesives has been known for many years and one of the first patents issued for such use was United States Patent No. 1,355,834 granted in 1920. Commercial development and application, however, did not take place until the last 2 years. Several brands of urea adhesives are now on the market. These meet the need for a hot-press adhesive which is applied in liquid form, cures rapidly at moderate temperatures, and is economical. For greater economy, the urea adhesive may be mixed with various proportions of flour (up to 50 percent) without affecting its water resistance. Diluted thus it comes within the cost range of animal and vegetable glues and is more durable. At present, it sells for 18 to 20 cents per pound; mixing it with 50 percent flour gives an adhesive for plywood, costing about 10 cents per pound. In 1937 three producers made urea resins for this use.
Other uses are in the treatment of textiles to obtain crease-proof properties and in the impregnation of wood. United States Patent No. 1,951,994 issued on March 20, 1934, reports the preparation of artificial silk from urea resins.
Production in the United States.
Commercial production of urea resins in the United States was reported for the first time in 1929. Early in that year the American Cyanamid Co. concluded an arrangement with the British Cyanides Co. of England for the American rights to manufacture and sell in the United States a resin made from urea, thiourea, and formaldehyde and marketed as Beetle molding powder. A manufacturing unit was built at Bound Brook, N. J., and in 1930 the output was substantial.
In 1931 another producer, the Toledo Synthetic Products Co., began manufacture of urea resins. Several years prior to that time the Toledo Scale Co. started a search for a material light in weight to replace the heavy porcelain-on-steel used in cases for scales. The search led to the urea resins and to commercial production by their subsidiary. In 1935 the Toledo Synthetic Products Company reached an agreement with the Imperial Chemical Industries of England for the interchange of technical and commercial information and of free patent licenses on urea molding and laminating resins. The name of the domestic firm was later changed to the Plaskon Co.