Acrylic copolymers, thermosetting

Hand building finishes that retain their stiffening and fullness effects after repeated launderings are considered to be durable. These products are usually aqueous emulsions of polymers that form water-insoluble films on the fibre surface when dried. The three main types of products are vinyl acetate-containing polymers, acrylic copolymers and thermosetting polymers. 

The paint studied is a typical automotive thermosetting enamel which consists of an epoxy functional acrylic copolymer and butylated melamine crosslinking agent. The acrylic copolymer is composed of methyl methacrylate, n-butyl methacrylate, n-butyl acrylate, styrene, acrylonitrile, 2-ethyl hexyl acrylate and 2-hydroxyethyl methacrylate. Carbon black was used as the pigment. 

Rhoplex [Rohm Haas], TM for aqueous dispersions of acrylic copolymers. White, opaque emulsions various grades differing in hardness, flexibility, adhesion, and tack of film some thermosetting. Produce colorless, transparent films with outstanding permanence, durability, adhesion, and pigment-binding capacity. 

Diplast D Diplast 0 Diplast R Diplast TM Diplast TM8 Lexorez 1100-220 Trioctyl trimellltate veNde, pigment grinding Beetle 227-8 Polyester resin, thermosetting, Styrene/acrylates copolymer... 

It can be concluded that the beverage can coating is a methyl melhacrylate/eth-ylhexyl acrylate copolymer modified polyester. The polyester is an adipic acid-modified neopentyl glycol iso-/orthophthalic acid type. The electrical appliance coating is a butylated amino resin cross-linked pentaerythritol-orlhophthalic thermosetting alkyd enamel. 

In general, the thermosetting acrylic copolymers are terpolymers. The first monomer confers hardness and rigidity to the copolymer, the second monomer contributes to the flexibility of the copolymer and the third monomer provides pendant reactive groups which are the sites for subsequent cross-linking. Table 6.3 shows examples of each of the three classes of monomer which are used commercially. 

Table 6.3. Comonomers used in the preparation of thermosetting acrylic copolymers.

Thermosetting acrylic copolymers containing epoxy groups are usually cross-linked by poly functional amines, e.g. ... 

Figure 2.30. Hydroxyl functional thermosetting acrylic copolymer resin...

Several acrylic copolymers have been mentioned in the preceding sections, but generally the products described contain a preponderance of one monomer with minor amounts of other monomer(s). There also exists a large number of acrylic copolymers in which one monomer does not predominate to any great extent. Such copolymers find widespread use in surface coatings. Two distinct types of copolymers are used in surface coatings, namely thermoplastic acrylics and thermosetting acrylics and it is these materials which are the subject of this section. 

Thermosetting acrylic binder systems utilize copolymers of functional and nonfunctional acrylic (or similar) monomers. The functional monomers are incorporated for reactivity with crosslinkers. The most common functional monomer for reactions is the hydroxyl group. The hydroxyl groups on the acrylic copolymers react with melamine and urea resins (amino resins) and with polyisocyanates. These reactions are shown in Figure 11. The reaction of hydroxy functional polymers with amino resins require acid catalysis and heat. The reaction with polyisocyanates can occur at room temperature as well as at higher temperatures. A number of materials will catalyze the hydroxyl/isocyanate reaction (organotin compounds, acids, amines, metal salts, etc.)(9). 

In September 1964 the Du Pont company announced materials that had characteristics of both thermoplastics and thermosetting materials. These materials, known as ionomers, are prepared by copolymerising ethylene with a small amount (1-10 % in the basic patent) of an unsaturated carboxylic acid such as acrylic acid using the high-pressure process. Such copolymers are then treated... 

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... 

Sanding is carried out at this stage and, after clean-up, the final colour or top-coat is applied. There is some variation in the resin chemistry used. Alkyds crosslinked with melamine-formaldehyde are widely used for non-metallic pigmentation. Metallics are usually based on acrylics for better durability. The acrylic may be thermoset with melamine-formaldehyde or a thermoplastic lacquer (plasticised copolymer of methyl methacrylate). A thickness of about 50ftm is applied and stoved for 20 min at 130°C (lacquers receive a bake-sand-bake process for a smoother appearance). 

Plastics can be classified as thermoplastic or thermosetting. Thermoplastics are materials that can be repeatedly softened by heat and hardened by cooling. Typical of the thermoplastic family are the styrene polymers and copolymers, acrylics, cellulosics, polyethylenes, polypropylenes, vinyls, and nylons. Thermoset polymers are those that undergo chemical reactions induced by heat, pressure, catalysts, and ultraviolet (UV) light, leading to an infusible state. Typical plastics in the thermosetting family are amines (melamine. 

The principal kinds of thermoplastic resins include (1) acrylonitrile-butadiene-styrene (ABS) resins (2) acetals (3) acrylics (4) cellulosics (5) chlorinated polyelliers (6) fluorocarbons, sucli as polytelra-fluorclliy lene (TFE), polychlorotrifluoroethylene (CTFE), and fluorinated ethylene propylene (FEP) (7) nylons (polyamides) (8) polycarbonates (9) poly elliylenes (including copolymers) (10) polypropylene (including copolymers) ( ll) polystyrenes and (12) vinyls (polyvinyl chloride). The principal kinds of thermosetting resins include (1) alkyds (2) allylics (3) die aminos (melamine and urea) (4) epoxies (5) phenolics (6) polyesters (7) silicones and (8) urethanes,... 

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