Acrylic coatings hydroxy functional

Kinetic Model. All of the coatings used in this study are hydroxy functional acrylic copolymers crosslinked with melamine formaldehyde crosslinkers. The chemistry of crosslinking with melamine formaldehyde crosslinkers has been discussed in detail elsewhere (5.11). The type and rate of the reactions depend primarily on... 

Polyurethane-acrylic coatings with interpenetrating polymer networks (IPNs) were synthesized from a two-component polyurethane (PU) and an unsaturated urethane-modified acrylic copolymer. The two-component PU was prepared from hydroxyethylacrylate-butylmethacrylate copolymer with or without reacting with c-caprolactonc and cured with an aliphatic polyisocyanate. The unsaturated acrylic copolymer was made from the same hydroxy-functional acrylic copolymer modified with isocyanatoethyl methacrylate. IPNs were prepared simultaneously from the two-polymer systems at various ratios. The IPNs were characterized by their mechanical properties and glass transition temperatures. 

The clear-coat is referred to as a two-component (2K) clear-coat when isocyanate is used as the cross-linker. The isocyanate must be added to the hydroxy functional acrylic just prior to spray application to prevent premature cross-linking (or gelation). For this reason, the two-part mixing is referred to as 2K. Cure conditions for isocyanate-cured clear-coat range from room temperature (car refinish) to 250°F for 30 min. 

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. 

The ether linkage formed during the crosslinking reaction of amino formaldehyde resins with hydroxy functional polymers is sensitive to acid hydrolysis. [2.197] Exposure to acid rain is sufficient to damage high solids acrylic/melamine coatings. The use of either active CH [2.198] or NH functional polymers [2.199] creates linkages... 

Coating powders for exterior use are mainly based on the SP-TGIC system. Of some importance is the SP-PUR system, i.e., the combination of hydroxy-functional polyester resins with caprolactam-blocked isocyanate adducts (primarily based on isophorone diisocyanate). The newly developed SP-HAA and SP-glycidyl estermix systems avoid the problems of TGIC as regards toxicology. Acrylic resins are of importance mainly in the United States (AY-PUR) and in Japan (AY-DDA). The AY-PUR system is used for automotive components and in domestic appliances. The PUR systems based on uretdione (a dimerization product of isocyanates) do not... 

Chem. Descrip. Acrylic resin (50%) in xylene Uses Acrylic for fast-drying two-pack coatings, air-drying and forced-drying two-component industrial lacquers Features Hydroxy-functional crosslinkable with polyisocyanates Properties Hazen < 200 color dilutable with toluene, xylene, acetone, MEK, MIBK, methoxypropyl acetate, ethyl acetate, butyl acetate dens. = 0.98 g/cm (20 C) dynamic vise. 600-1200 mPa s hyd. no. 60-70 flash pt. = 26 C 48-52% NV... 

Chem. Descrip. Acrylic resin (65%) in methoxypropyl acetate Uses Acrylic for air-drying and stoving two-component industrial coatings, wood coatings, metal coatings, plastic coatings Features Hydroxy-functional crosslinkable with polyisocyanates exc. 

Uses Acrylic for fast drying two-pack coatings, industrial lacquers Features Hydroxy-functional crosslinkable with polyisocyanates Properties Hazen < 80 color dens. = 1.00 g/cm (20 C) dynamic vise. 

Chem. Descrip. Modified acrylic resin (80%) in butyl acetate Uses Acrylic for ultra-high-solids two-pack industrial coatings, lacquers, thick-layer coatings, airless appliable paints Features Hydroxy-functional crosslinkable with polyisocyanates high gloss very good mech. props., chem. resist. ease of applic. Properties Hazen < 200 color dens. = 1.09 g/cm (20 C) dynamic vise. 

Chem. Descrip. Low m.w. hydroxy-functional silicone-based additive Uses Mar resist, aid, slip agent, flow aid for powd. coatings based on epoxy, polyester, acrylic, and PU resins Features Does not reduce gloss or heat stability, even at over cure Properties Grans. sp.gr. 1.23 g/cm m.p. 85 C 96.6% act. 

In order to complete coverage of powder coatings, we must mention here the urethane cross-linked powders. In these cases we have hydroxy functional resins, which may be either polyester or acrylic. These are cross-linked by blocked isocyanate cross-linkers, principally those blocked with e-caprolactam as will be described in the next chapter. 

Diethyl malonate blocked diisocyanates cross-fink polyols at 120°C for 30 min. The reaction with alcohols does not srield urethanes, rather transesterification occurs (134), and reaction with amines srields amides, not ureas. Storage-stable coatings can be formulated by using monofimctional alcohol in the solvent (135). Clear coats for automobiles that have both excellent environmental etch and abrasion resistance have been formulated with a combination of a hydroxy-functional acrylic resin, malonic ester blocked HDI and IPDI trimers, and an ME resin (136). 

The hydroxy-functional polyurethane dispersions can be cross-linked with MF resins or blocked isocyanates. Blocked isocyanates can also be used with water-reducible anionic acrylic or polyester resins instead of an MF resin oxime blocked isocyanates are commonly used, owing to their high reactivity. Oxime blocked aliphatic isocyanates are more stable to hydrolysis than oxime blocked aromatic isocyanates (32). As mentioned earlier alcohol blocked isocyanates are used in cationic electrodeposition coatings. 

Hydroxy functional acrylics are used in general industrial (GI) stoving rinishes in two distinct capacities. They are used to impart highly durable finishes for exterior components such as tractor sheet metal and cabs, fenders for earth moving equipment, or as one coat finishes in more wide ranging metal finishing such as office furniture, irons, microwave ovens, toasters, food mixers and blenders. 

Frequently, hydroxyl functional monomers are used as part of the copolymer with the hydroxy group providing the site for crosslinking with, for example, an amino crosslinker, when the coating is stoved. Two hydroxy functional types have been shown. Hydroxyl ethyl has a terminal (primary) hydroxyl group which is more reactive than the secondary hydroxy group on the hydroxy propyl chain. It is thus possible to get more rapid cure response by incorporation of hydroxy ethyl rather than hydroxy propyl functionality in the acrylic copolymer. This, however, may not always be advantageous as frequently rapid cure can lead to poor adhesion. 

Transesterification yields oligomeric esters analogous to 34. Reactive HAS containing hydroxy, oxirane or carboxy groups in position 4 can be chemically attached to acrylic PUR by condensation. The products obtained are intended as persistent stabilizers for coatings, transformed into oligomeric condensates with cyanuric chloride or used for endcapping of terminally functionalized macromonomers [293],... 

---