Melamine formaldehyde-cured acrylic

Acrylate Copolymer (AC) A copolymer of eight parts of n-butyl methacrylate, one part of ethyl methacrylate and one part of styrene was prepared. 800 g of n-butyl methacrylate, 100 g of ethyl methacrylate and 100 g of styrene were heated with stirring in a 2000 cc three-necked flask, equipped with a reflux condenser and nitrogen inlet. The reaction was carried out at 80°C until a prepolymer of syrupy consistency was obtained. The polymer was very similar in nature to the polyacrylate used in a previous study (7,8), except that it contained no pendant hydroxyl or carboxyl groups needed for the melamine-formaldehyde cure. 

FTIR techniques in combination with or as complement to other measurement techniques have been used in a wide range of photochemistry studies on polymers. These include bisphenol-A polycarbonate [173], polycarbonate coatings on mirrors [174], PMMA [175], poly( -butyl acrylate) [176] and polypropylene [177]. DSC and FTIR studies have been used in conjunction to investigate the nature of y-radiation-induced degradation and its effect on the 19°C and 30°C phase transitions in PTFE [178]. IR studies of the hydrolysis of melamine-formaldehyde crosslinked acrylic copolymer films have shown that copolymer-melamine formaldehyde crosslinks are broken and that crosslinks between melamine molecules are formed [179]. The thermal and photo-degradation mechanisms in an IR study of cured epoxy resins were found to be related to the autoxidative degradation processes for aliphatic hydrocarbons [180]. 

Good quality steel is used and electrozinc is preferred for washing machines. Steel is pretreated with iron phosphate for economy electrozinc with a fine crystal zinc phosphate. No primer is normally used 25-40/im of finish is applied direct to metal. The required properties are best obtained with a thermosetting acrylic or polyester/melamine-formaldehyde finish. Self-reactive acrylics are usually preferred these resins contain about 15 Vo 7V-butoxymethyl acrylamide (CH2=CH —CO —NH —CHj—O —C4H,) monomer and cure in a manner similar to butylated melamine-formaldehyde resins. Resistance or anti-corrosive properties may be upgraded by the inclusion of small amounts of epoxy resin. Application is usually by electrostatic spray application from disc or bell. Shapes are complex enough to require convected hot-air curing. Schedules of 20 min at 150-175°C are... 

Chem. Descrip. Etherified acrylated melamine/formaldehyde resin (62-68%) in tripropylene glycol diacrylate Uses Crosslinking agent in radiation-cure applies, such as polyester and epoxy acrylates, unsat. polyesters, aliphatic and aromatic urethane acrylates, and most acrylate monomer diluents imparts hardness and gloss, stain and chem. resist, to coatings, paper coatings Features Cured by free radical polymerization initiated by U V or thermal processing... 

Classification Butylated melamine-formaldehyde resin Uses Crosslinking agent for alkyd/polyester or acrylic resins, for use in solv.-borne coatings, acid curing wood finishes... 

Suggested adhesives include modified acrylics, epoxies, polyesters, resorcinol-formaldehyde, furane, phenol-formaldehyde, polyvinyl formal-phenolic, polyvinyl butyral, nitrile rubber-phenolic, polyisobutylene rubber, polyurethane rubber, reclaimed rubber, melamine-formaldehyde, epoxy-phenolic, and cyanoacrylates. For maximum adhesion primers should be used. Nitrile-phenoUcs give excellent bonds if cured under pressure at temperatures of 149 C. Lower-strength bonds are obtained with most rubber-based adhesives. 

Baner, D. R., and Dickie, R. A., Cure response in acrylic copolymer-melamine formaldehyde crosslinked coatings, J. Coat. Tech., 54, 1982. 

Hydroxy functional acrylics will cure with all types of amino resins, including urea formaldehyde, melamine formaldehyde (MF) and benzoguanamine formaldehyde types. Urea formaldehyde resins are faster curing and cheaper than the other two main types, but they are rarely used with acrylics due to inferior film performance (e.g. resistance properties and exterior durability). 

In the early days, although paint manufacturers flirted with acrylamide chemistry for automotive topcoats, their higher curing temperatures of 150 C and above precluded commercialisation in this end use. Carboxy functional acrylics have inferior weathering performance. Consequently, thermosetting acrylic topcoats are almost exclusively based on hydroxyl functional polymers. These are crosslinked with either alkylated melamine formaldehyde resins or as 2 component (2K) systems, with aliphatic isocyanate adducts. The 2 component systems are an extremely important class used mainly in automotive repair applications and warrant a chapter in their own right (see Chapter V on component isocyanate curing systems). 

In the resultant paint, the acrylic polymer is cured with an etherified (normally butylated) melamine formaldehyde resin at temperatures of around 120°C. The cross linking reaction has been shown earlier in Figure 4. 

The clear lacquer is based on an hydroxy thermosetting acrylic resin as described earlier, and it is cured with a melamine formaldehyde resin. The binder is modified with a UV absorber system comprising ... 

The commercial pressures in the general metal finishing area mean that the much cheaper styrene monomer must be utilised to keep the resin cost down. The otho monomer consideration for the two markets is adhesion to substrates. In the general metal finishing area, substrate pretreatment will often be limited and therefore the acrylic will have to be quite adaptable. The paint formulation alone caimot compensate for a substrate intolerable acrylic Epoxy functionality is commonly included to improve substrate adhesion, particularly when there is no priming scheme. If the curing schedule allows it, modification of the acrylic/melamine formaldehyde binder with up to 15% epoxy resin will enhance metal adhesion, chemical resistance and film flexibility. 

Melamine formaldehyde can be crosslinked at elevated temperatures with both hydroxyl and carboxyl functional groups. (See thermosetting acrylics chapter for reaction mechanisms.) The temperature required is at least 120°C, at which point the hydroxyl group will react, but the carboxyl group needs a slightly higher heat input, approximately 150°C. Systems are unlikely to require an acid catalyst because of the catalytic effects of the polymerisation catalysts and surfactants in the acrylic latices. If required, p-toluene sulphonic acid is the most suitable (typically at levels of 0.2 - 0.4%). Alternatively, the melamine resin could be incorporated in an unneutralised, acidic emulsion, which reduces the cure temperature, but will sacrifice stability. 

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