Urea-formaldehyde resins molding powder

The urea-formaldehyde (UF) Molding powder will contain a number of ingredients. Most commonly these include resin, filler, pigment, accelerator, stabilizer, lubricant, and plasticizer. 

UREA-FORMALDEHYDE RESIN. An important class of amino resin. Urea and formaldehyde are united in a two-stage process in the presence of pyridine, ammonia, or certain alcohols with heat and control of pH to form intermediates (methylolurea, dimenthylolurea) that are mixed with fillers to produce molding powders. These are converted to thermosetting resins by further controlled heating and pressure in the presence of catalysts. These were first plastics that could be made in white, pastel, and colored products. See also Amino Acids Melamine. 

The largest use is for binding fibrous and granulated wood into indoor composition board. Smaller uses are for wet-strength paper and permanent-crease textiles. About 4 percent of urea-formaldehyde resin is combined with alpha-cellulose to make molding powders (Table 15.18). These find use mainly in electrical parts such as switches, wall plates and receptacles, circuit breakers, electric blankets, handles and knobs. 

The first commercially successful synthetic polymer was phenol-formaldehyde (PF) [Smith, 1899]. The resin was introduced in 1909 by Baekeland as Bakelite . The urea-formaldehyde resins (UF), were discovered in 1884, but production of Beetle moldable resin commenced in 1928. Three years later, Formica , phenolic paper covered with decorative layer protected by UF, was introduced. The thiourea-formaldehyde molding powders were commercialized in 1920, while in 1935, Ciba introduced Cibanite , anihne-formaldehyde (AF) molding materials, then two years later, the melamine-formaldehyde (MF). 

Molding Powders. Urea-formaldehyde resins are compounded with alpha-cellulose cotton fiber reinforcement to produce molding powders (4 percent) for compression, transfer, and injection molding. Typical molding conditions are 127 to 182°C and 2000 to 8000 psi. They are superior to phenolics in white color, electrical resistance, and low cost, but are limited by moisture sensitivity (Table 3.13). They are used primarily in electrical wiring devices such as wall outlets, receptacles, electric blanket controls, circuit breakers, and knob handles. Smaller amounts are used in bottle caps, housewares, buttons, and sanitary ware. 

Urea formaldehyde molding powders are used primarily where particularly short molding cycles are desired for low unit costs (e.g., wiring devices and plastic closures) [8]. Important end uses of this resin can be found in industries dealing with plywood, particle-board, plastic closures, wiring devices, textile resins, paper resins, coatings, bondings, furfuryl alcohol modified foundry resins, etc. 

Several copolymers and condensates of oxidized starches with polymers have been developed. For example, products of starch dialdehyde condensation with acrylamide were prepared for further copolymerization with various monomers to form resins for coatings, molding powders,585 and materials for immobilization of enzymes, for instance, alpha amylase.586 Hypochlorite-oxidized starches were also reacted with acrylonitrile.507,521 Hypochlorite-oxidized starches were allowed to react with allylated starch dialdehyde,587 polycondensates of ammonia-dimethylamine-epichlorohydrin,588 polycondensates of starch dialdehyde with melamine,589 urea433,541,590 capable of precipitation of tannin591, carboxyamides,411 urea and formaldehyde,592 proteins,524,593,594 polyfyinyl alcohol),595 alkylammonium salts,519,596 alkoxyalkylamines,597... 

Contributions to the urea resins technolc were made by Goldschmidt and Neuss in 1921 and by Poliak and Ripper in 1923. Molding resins, based on condensation products of urea and thiourea with formaldehyde (Beetle) were produced in England in 1926. Toledo Scales introduced a urea-formaldehyde molding powder (Plaskon) in 1928. Paper impregnated with urea resin was used as the outer surface layer of Formica decorative laminates in 1931. 

To a resin flask equipped with mechanical stirrer and condenser is added 63 gm (0.5 mole) of melamine and 120 gm (2.0 moles) or urea. Then 435 gm (31% aq 4.5 moles) of neutral formaldehyde is added with stirring and heated by means of a water bath to dissolve the solids (approximately 0.5 hr). If a sample is cooled at this point, the resin will precipitate. The solution is now blended with 120gm of cellulose, and the entire mass is dried and ground. The resulting molding powder flows well when heated for 3 min at 145°C. Thiourea may be used in place of urea to give similar resins. 

To a resin flask equipped with a mechanical stirrer and condenser is added 26.3 gm (10.14 moles) of benzoguanamine, 3.7 gm (0.026 mole) of hexamine, and 79 gm (0.98 mole) of formaldehyde. The mixture is heated to 80 -85 C and the pH adjusted with ammonium hydroxide. Then a solution containing 740 gm of 37% (9.0 moles) formaldehyde and 370 gm (6.2 moles) of urea is added and the mixture stirred and heated for 40 min at 75 -80°C and pH 7.5-8.0. The resulting reaction mixture is treated with 0.4 gm of ammonium chloride at 60°C, and 250 gm of wood pulp is added. The mixture is agitated 20 min, dried, and pulverized to give a molding powder. 

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