Resins Melamine

Melamine resins are included in urea—formaldehyde resins. 

Formaldehyde—Alcohol Solutions. These solutions are blends of concentrated aqueous formaldehyde, the alcohol, and the hemiacetal. Methanol decreases the average molecular weight of formaldehyde oligomers by formation of lower molecular weight hemiacetals. These solutions are used to produce urea and melamine resins the alcohol can act as the resin solvent and as a reactant. The low water content can improve reactivity and reduce waste disposal and losses. Typical specifications for commercially available products are shown in Table 7 (117). 

Grade G-9, glass fabric with moisture-resistant melamine resin binder, is similar to Grade G-5 but with better electric strength properties under wet conditions. Electrical appHcations should be limited to operating temperatures of 50°C (122°F) or less. 

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. 

Since melamine resins are derived from urea, they are more cosdy and are therefore restricted to appHcations requiring superior performance. Essentially ad of the melamine produced is used for making amino resins and plastics. 

Formaldehyde. Pure formaldehyde, CH2O, is a colorless, pungent smelling reactive gas (see Formaldehyde). The commercial product is handled either as soHd polymer, paraformaldehyde (13), or in aqueous or alcohoHc solutions. Marketed under the trade name Formcel, solutions in methanol, / -butanol, and isobutyl alcohol, made by Hoechst-Celanese, are widely used for making alcohol-modified urea and melamine resins for surface coatings and treating textiles. 

Phenohc resins are generally used in alcohohc solution, whereas melamine resins are best handled in water or water—alcohol mixtures. The paper or cloth web is passed through a dip tank containing resin solution, adjusted for pick-up on squeeze rohs, and then passed through a heated drying oven. 

Uron Resins. In the textile industry, the term uron resin usually refers to the mixture of a minor amount of melamine resin and so-called uron, which in turn is predorninantly N,]S -bis(methoxymethyl)uron [7388-44-5] plus 15—25% methylated urea—formaldehyde resins, a by-product. 

Melamine—Formaldehyde Resins. The most versatile textile-finishing resins are the melamine—formaldehyde resins. They provide wash-and-wear properties to ceUulosic fabrics, and enhance the wash durabiHty of flame-retardant finishes. Butylated melamine —formaldehyde resins of the type used in surface coatings may be used in textile printing-ink formulations. A typical textile melamine resin is the dimethyl ether of trimethylolmelamine [1852-22-8] which can be prepared as follows ... 

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. 

Resin-B sedFinishes. Resin-based water repeUents are durable finishes that are modified melamine resins, blended with waxes. In some cases, the resin helps disperse the wax in the repeUent formulation. The resin provides water repeUency and binds the wax onto the fabric. 

Most of the surface sizes used in North America are modified styrene maleic anhydride (SMA) copolymers. Commercially available materials include Scripset (Monsanto/Hercules Inc.), Cypres (Cytec), Sursize (Akzo Nobel), MSA (Morton), NovaCote (Georgia Pacific), and HTl (Hopton Technologies). Styrene acrylate emulsions that are commonly used include Jetsize and Unibond (Akzo Nobel), Basoplast (BASF), and Cypres (Cytec). Other materials used as surface sizes include acrylonitrile acrylate copolymer (Basoplast, BASF), stearylated melamine resin (Sequapel, Sequa), polyurethane (Graphsize, Vining Chemicals), and diisobutylene maleic anhydride copolymers (Baysynthol, Bayer). 

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. 

The paper-impregnation drying oven exhausts contain high concentrations (10—20% LEL) of alcohols and some resin monomer. Vinyl resins and melamine resins, which sometimes also contain organic phosphate fire retardants, may be used for air filters. The organic phosphates could shorten catalyst life depending on the mechanism of reduction of catalyst activity. Mild acid leaching removes iron and phosphoms from partially deactivated catalyst and has restored activity in at least one known case. 

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. 

Modified melamine resins are also employed commercially. Alkylated resins analogous to the alkylated urea-formaldehyde resins provide superior coatings but are more expensive than the urea-based products. 

Paper with enhanced wet-strength may be obtained by incorporating melamine resin acid colloid into the pulp. Melamine resin acid colloid is obtained by dissolving a lightly condensed melamine resin or trihydroxymethylmelamine, which are both normally basic in nature, in dilute hydrochloric acid. Further condensation occurs in solution and eventually a colloidal solution is formed in which the particles have a positive charge. Careful control over the constitution of the colloidal solution must be exercised in order to obtain products of maximum stability. 

Formulated Melamine resin + epoxy-functional silane... 

Chemical compounds manufactured at petrochemical plants include methanol, formaldehyde, and halogenated hydrocarbons. Formaldehyde is used in the manufacture of plastic resins, including phenolic, urea, and melamine resins. Halogenated hydrocarbons are used in the manufacture of silicone, solvents, refrigerants, and degreasing agents. 

Amino resins are characterized by being more clear and harder (tensile strength) than phenolics. However, their impact strength (breakabil-ity) and heat resistance are lower. Melamine resins have better heat and moisture resistance and better hardness than their urea analogs. 

Compression and injection molding are used with amino resins to produce articles such as radio cabinets, buttons, and cover plates. Because melamine resins have lower water absorption and better chemical and heat resistance than urea resins, they are used to produce dinnerware and laminates used to cover furniture. Almost ah molded objects use fillers such as cellulose, asbestos, glass, wood flour, glass fiber and paper. The 1997 U.S. production of amino resins was 2.6 billion pounds. 

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