Thermosetting acrylamide resin

A number of thermosetting acrylic resins for use as surface coatings have appeared during recent years. These are generally complex copolymers and terpolymers such as a styrene-ethyl acrylate-alkoxy methyl acrylamide... 

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... 

The thermoset acrylics (20) of major importance in the coating industry, in recent years, have been developed primarily by Canadian Industry Ltd. and by Pittsburgh Plate Glass Co. in this country (4). Raw materials are acrylamide, acrylic acid, acrylates, and styrene. Cross-linking agents are amino and epoxy resins. The materials are also self-cross-linking. They are usually sold as solutions in paint solvents. 

Thermosetting acrylics are produced by incorporating functional carboxyl, hydroxyl, or amide groups during free radical polymerization. Acrylamide and acrylic acid are often used as functional monomers for this purpose. The thermosetting acrylics are formulated with other reactive resins, such as epoxies, to provide a crosslinked film on heating. These films are considerably harder, tougher and more chemically resistant than those attainable from thermoplastic acrylics. 

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). 

Thermosetting (crosslinking) acrylics normally require a crossUnker to be present. Their actual cure behaviour is dependent upon the pendant (side chain) functionality of the copolymerised co-monomers. Acrylamide will crosslink with itself, epoxy or amino resins, whilst amino or melamine crosslinkers will react with hydroxyl or acid groups. Isocyanates can react with hydroxyl groups at room temperature. To reduce the hazards of isocyanates and the inconvenience of two pack systems, blocked isocyanates can be used. At elevated temperatures used for stoving they can unblock generating an alcohol and an isocyanate which will react with any hydroxyl or acid groups on the acryUc resin. 

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