Лако-красочные материалы — производство

Properties

Fully disperse the millbase. Premix the let down components and add to millbase to reduce flocculation of the pigment. Primal WL-51 (Rohm and Haas) has excellent adhesion to plastics.

(ii) A Clear Waterborne Plastic Coating

Properties

nvc 29%

pH 9.0

Premix water and the additives. Then add to the resin with stirring. Primal WL-81 (Rohm and Haas) is an aqueous thermoplastic acrylic resin, 41.5% nvc with an MFFT of 57°C. It does not contain co-solvents, which maximises formulating latitude. It can be crosslinked with monomeric methoxy melamines, e. g. Cymel 303, to give harder, more resistant films.

Viscosity can be adjusted for different application methods, such as spray and brush, without external thickeners, which often detract from resistance properties, by the addition of amines. Less volatile amines result in slower hardness development. Under high relative humidity drying conditions, morpholine is superior for sprayability.

Butyl glycol is a very good coalescent for Primal WL-81, but can be combined with other coalescents for optimum application characteristics.

(iii) Water Based Metallic Basecoat for Plastics

Properties

nvc 18.5%

pH 7.5

Add the diluted NeoRez R-974 to the premixed resin and adjust the pH to 9.5 — 10.0 with ammonia. Let down slowly other premixes in order under good stirring. Adjust final pH to 7.5.

NeoCryl A-639 (Zeneca) is an acrylic/styrene copolymer, 45% nvc. Butyl glycol is used as the coalescent. NeoRez R-974 (Zeneca) is a polyurethane dispersion to improve abrasion resistance. It also helps coalescence. Primal RM-5 (Rohm & Haas) is a thickener. Acid resistant grades of aluminium, such as SS 3334AR WD from Silberline, should be used.

The formulation is recoatable after 5 minutes at 50°C. Two pack urethane clearcoats and water based clearcoats are suitable as overcoats.

(iv) Waterborne Coating for Polystyrene :

Properties

Viscosity 35-40 secs B4 @ 20°C

Density 1.03-1.05

Black WBF is from Systeem Chemie. Neocry 1 A661 (Ex Zeneca) is a water based acrylic emulsion with high Tg 80°C, giving it maximum solvent resistance. Tego 1488 (Tego Chemie) is an extremely effective defoamer. It is let down with water prior to incorporation into the coating, best added at the earliest possible opportunity to prevent the formation of a stable foam during manufacture. Microspersion 250 (Micro Powders Inc.) is a polyethylene wax dispersion, which is included to improve the abrasion resistance and performance under crockmeter tests. Dapro W77 (Daniel Products) and Surfynol 104E (Air Products) are surfactants used to modify the surface tension of the paint, enabling it to wet and adhere to the surface of the polystyrene. The blend is more efficient than either product alone, though the reasons for this are not fully understood. Tego Glide 450 (Tego Chemie) is a slip additive. A higher percentage is required in the water based system because this type of silicone material does not diffuse to the surface of the coating as in conventional systems, but is resident in the disperse phase, evenly distributed throughout the coating. Flat Ayd (Daniel Products) is a pre-dispersed matting agent for gloss control. Aerosil R972 (Degussa) is included to control viscosity and aid application. The viscosity increase in the applied coating, which results from the application of conventional systems as solvent evaporates from the film, does not occur in water based systems, hence the addition of thixotropes will be required to reproduce this effect. Kodaflex TXIB (Eastman Kodak) aids the film coalescence of the high Tg polymer, this is also improved by the two coalescing solvents butyl glycol and Texanol.

Resins suitable for use in plastics coatings include :