Method of coating and compositions for use therein

Details Method of coating and compositions for use therein Method of coating and compositions for use therein

1998-11-19

2000-12-19

Pianalto, Bernard

Coating processes

Direct application of electrical, magnetic, wave, or...

Polymerization of coating utilizing direct application of...

106285, 106400, 252600, 427299, 4273855, 427558, 427559, 427595, C08J 718

Patent

active

061625116

DESCRIPTION:

BRIEF SUMMARY
The invention relates to coatings and in particular to a method of coating and to coating compositions.
Commonly used coatings are composed of resins or polymers, and one or more of solvents (except in the case of powder coating) together with pigments or filler components and other additives to provide stability or other desirable properties. The traditionally used coatings are classified into thermoplastic and thermosettable coatings and more recently radiation curable coatings have been used in some applications. Ideally a coating composition should allow quick curing, have good film forming properties and provide good adhesion to the substrate.
Thermoplastic, thermosetting and radiation curable compositions require the presence of solvent or diluent to reduce the viscosity and provide film formation. In the case of radiation curable compositions the diluent is generally in the form of a monomer which on curing is incorporated into the polymer network. Thermosetting and radiation curable compositions require less solvent or diluent however higher solids contents reduce storage stability, film forming properties and produce less efficient curing. These problems are further exacerbated when significant proportions of filler or pigment are present.
We have now found that good coating adhesion and uniformity can be provided even in the presence of high filler and pigment content by applying a radiation curable coating at a temperature above ambient temperature.
We have also found that when the coating is to be applied to a wettable substrate that a significant improvement in coating properties are provided when the coating is applied to the substrate when wet. The use of a wet substrate surface leads to more efficient use of the coating and generally provides improved adhesion.
Accordingly we provide a method of preparing a coated substrate comprising: including an unsaturated monomer and at least one of an unsaturated prepolymer and binder or mixture thereof; temperature, preferably from 35.degree. C. to 150.degree. C. to the substrate; and
The radiation curable composition is applied to the substrate at a temperature above ambient temperature and preferably in the range of from 35 to 150.degree. C. More preferably the temperature is from 50 to 120.degree. C. and most preferably from 60 to 80.degree. C.
The composition is preferably curable by electron beam or ultraviolet radiation. UV curable compositions are preferred due to convenience and the cost advantage provided by UV-curing techniques. UV curable compositions may include a photoinitiator.
Throughout the description and claims of this specification, the word "comprise" and variations of the word, such as "comprising" and "comprises", is not intended to exclude other additives or components or integers.
The method of the invention provides considerable advantages in application of coatings containing pigment. The use of significant quantities of fillers or pigments tends to mask penetration of UV light significantly reducing the quality of resultant coating. Radiation curing of pigmented systems in air especially for exterior use, has proved to be particularly difficult. The presence of air results in surface inhibition reducing the quality, adhesion and durability of the cured coating. Although curing under nitrogen reduces these difficulties the use of nitrogen is inconvenient and increases the expense of forming coatings. Furthermore previous attempts to coat substrates using UV curable coatings have generally required the use of relatively thin coatings of for example 10 microns. The formation of thicker coatings has therefore required the application of a number of layers. We have now found that the process of the present invention, particularly when used in conjunction with particular photoinitiators, allows radiation curable coating to be applied even at significant thicknesses such as 30 microns or more and with high pigment or filler loadings. This enables a better coverage density to be obtained than was generally previously practicable wi

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Copy of PCT International Search Report for PCT/AU97/00307 dated Jul. 11, 1997.

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