Curing melamine resins

Melamine resins were introduced about ten years after the Beetle molding compound. They were very similar to those based on urea but had superior quaHties. Henkel in Germany was issued a patent for a melamine resin in 1936 (7). Melamine resins rapidly supplanted urea resins and were soon used in molding, laminating, and bonding formulations, as well as for textile and paper treatments. The remarkable stabiHty of the symmetrical triazine ring made these products resistant to chemical change once the resin had been cured to the insoluble, cross-linked state. 

Tire Cord. Melamine resins are also used to improve the adhesion of mbber to reinforcing cord in tires. Textile cord is normally coated with a latex dip solution composed of a vinylpyridine—styrene—butadiene latex mbber containing resorcinol—formaldehyde resin.. The dip coat is cured prior to use. The dip coat improves the adhesion of the textile cord to mbber. Further improvement in adhesion is provided by adding resorcinol and hexa(methoxymethyl) melamine [3089-11 -0] (HMMM) to the mbber compound which is in contact with the textile cord. The HMMM resin and resorcinol cross-link during mbber vulcanization and cure to form an interpenetrating polymer within the mbber matrix which strengthens or reinforces the mbber and increases adhesion to the textile cord. Brass-coated steel cord is also widely used in tires for reinforcement. Steel belts and bead wire are common apphcations. Again, HMMM resins and resorcinol [108-46-3] are used in the mbber compound which is in contact with the steel cord to reinforce the mbber and increase the adhesion of the mbber to the steel cord. This use of melamine resins is described in the patent Hterature (49). 

The recovery of fiber from broke (off-specification paper or trim produced in the paper mill) is compHcated by high levels of urea—formaldehyde and melamine—formaldehyde wet-strength resin. The urea resins present a lesser problem than the melamine resins because they cure slower and are not as resistant to hydrolysis. Broke from either resin treatment may be reclaimed by hot acidic repulping. Even the melamine resin is hydrolyzed rapidly under acidic conditions at high temperature. The cellulose is far more resistant and is not harmed if the acid is neutralized as soon as repulping is complete. 

Properties. The outstanding characteristic of melamine, usually a white crystalline matrial, is its insolubiUty in most organic solvents. This property is also evident in melamine resins after they are cured. On the other hand, melamine is appreciably soluble in water, its solubiUty increasing with increased temperature. The properties of melamine are Hsted in Table 5. 

Decorative laminates have a core or base of Kraft paper impregnated with a phenolic resin. A printed pattern layer impregnated with a melamine-formaldehyde or urea-thiourea-formaldehyde resin is then laid on the core and on top of this a melamine resin-impregnated protective translucent outer sheet. The assembly is then cured at 125-150°C in multi-daylight presses in the usual way. 

Galperin etal. (1995) has reviewed the work undertaken in the Byelorussian Institute of Technology, including work with PF, UF and melamine resins. Apart from resin curing using conventional heating, microwave curing was also studied. 

Lukowsky, D., Peek, R.D. and Rapp, A.O. (1998). Curing conditions for a low formaldehyde etherificated melamine resin. International Research Group on Wood Preservation, Doc. No. IRG/WP 98-40108. 

Enamel Properties. Clear coatings were formed by crosslinking the PHBA-modified oligomers with a standard melamine resin. Baking at 175° was necessary to obtain optimal properties. The cured films were glossy and nearly transparent except for films made from 60/40 PHBA ratio polyol. Adhesion was excellent. 

Melamine resins are used from this group of thermosets for the manufacture of food contact materials. The melamine can be used in mixtures with urea and in some applications with phenol (< 1 %). The polymerization process is catalyzed in the presence of organic acids (e.g. acetic acid, lactic acid, tartaric acid, citric acid), hydrochloric acid, sulfuric acid, phosphoric acid, sodium and potassium hydroxide, ammonia, calcium or magnesium hydroxide as well as salts of these substances (total < 1 %) which cause the elimination of water and lead to a cured resin system. Stearic acid can be used as a lubricant as can zinc, calcium and magnesium salts, esters of montanic acid with ethandiol and 1,3-butandiol, as well as silicone oil (total < 1 %). 

As a result of their properties, melamines are often used as decorative laminates. The melamine resins cure via an addition reaction mechanism so no reaction by-products can be produced on postcure as with the phenolic resins. The specific surface preparation for adhesive bonding and the preferred adhesives for bonding melamine and urea parts are similar to those suggested for phenolic resins. 

DORESCO AKW6-8 is an ammoniacal water solution of a soya oil alkyd resin. The alkyd is not completely esterifled so that it is suspendible in alkaline water solution however, it is sufficiently esterified so that it will cure with melamine resin and other cross linking resins. This resin solution should be stirred before use to achieve uniformity. 

Phase segregation affects the dependence of the viscosity growth on the applied stress of shear rate [88], It is possible to see Such an effect is seen experimentally in a sufficiently extended part of flow ability after a microphase segregation i.e. the ratio ijt is relatively small, for example, in curing melamine-formaldehyde resins in solution [87], However, the case of tp/t close to unity, this effect may not always be revealed due to experimental difficulties. 

Polyester resins possess premium performance properties such as exterior durability, gloss, flexibility hardness, color stability, and versatility of cure. Polyesters are used in product finishes for household appliances, food and beverage containers, aircraft and equipment, automotive primers and bake coats, metal furniture, and fixtures. For example, water-soluble saturated polyesters are used in industrial baking paints, and in combination with melamine resin. Polyesters can be formulated in high solids and waterborne formulations to meet the requirements for the low VOC coatings being mandated by the EPA. 

Micarta [Westinghouse], TM for a group of laminated plastics composed of paper or fabric made from cellulose, glass, asbestos or synthetic fibers bonded with phenolic or melamine resins and cured at elevated temperature and pressure. 

Affect both C and kg. This would be the case for finish foils. These are urea or melamine resin saturated paper foils which are bonded to the panel with urea adhesive. Another example is acid-curing lacquers which contain formaldehyde and, at least for a limited period of time, substantially increase the emission potential, but at the same time is an efficient diffusion barrier for the formaldehyde from the particleboard underneath. 

The acrylic resin used was Rohm and Haas Co.s QR-496 ( 4), so the exact nature of the polymer is not known. It is hydroxy functional, thus requiring an aminoplast for proper cure commercially modified hexa-methylol melamine resin was used for this purpose. During the first part of the investigation the acrylic resin was used without the melamine resin, but for final evaluation it was incorporated to give a more realistic commercial coating system. 

Another type of primer is based on a styrene/al ly 1 alcohol copolymer (Monsanto RJ-lOO). This polymer can be modified with fatty acids and cured with melamine resin (19). 

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