Method of producing dull paint surfaces

Details Method of producing dull paint surfaces Method of producing dull paint surfaces

1994-02-01

1995-10-24

Padgett, Marianne

Coating processes

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

Polymerization of coating utilizing direct application of...

427500, 427504, 427167, 427203, 427204, 428172, 428216, 428446, 428452, 428442, B05D 306, B05D 506, B32B 300, B32B 2700

Patent

active

054608570

DESCRIPTION:

BRIEF SUMMARY
The present invention relates to a method of producing dull paint surfaces, in which initially a first paint layer is applied in a first layer thickness and at least one second paint layer is then applied on top of the first paint layer, at least the paint layer applied last being provided with dulling agents and having a dry film layer thickness which is less than the average particle size of the dulling agent.
To apply paint to various materials, especially furniture foils or chipboard, high-solids paints systems are predominantly used which are distinguished by particularly low pollution of the environment and by great economy of the painting devices used. Among such paints, the paint systems curable by UV radiation are of particular importance. However, paints are also known which are cured by ionizing radiation, in particular by electron beams. This method has the advantage over UV curing that even layers which contain hiding pigments can be cured within a short time to give hard coatings. In addition, the presence of photoinitiators is not necessary.
When using both the paints curable by UV radiation and those curable by ionizing radiation, high-gloss to silk-gloss coatings, having a degree of gloss of between 100 and 40 units according to DIN 67530 under an angle of observation of 60 degrees, can be produced without problems. By contrast, it is extraordinarily difficult to produce dull surfaces, which are demanded for many applications. These problems can not be overcome even by the usual methods of dulling paints by means of using highly disperse silicas or polyolefin powder, metal salts or mineral fillers.
This is true especially if coatings having a very high scratch resistance are to be produced, as is the case, for example, for coatings of furniture foils. To ensure high scratch resistance, the paint applied must, as is known, have a certain minimum layer thickness in order to ensure adequate mechanical stability of the paint layer. When producing dull surfaces, the difficulty therefore is that the dulling agents, because of their small particle diameter, sink to such a depth within the paint layer, in the case of an unduly large layer thickness, that they can no longer protrude from the surface and the desired dull appearance is therefore no longer produced.
In German Patent 3,721,071, a two-stage process is therefore proposed for producing dull surfaces, in which initially a first paint layer and then at least one second paint layer are applied, at least the paint layer applied last being provided with dulling agents. The paint layers are cured by means of UV radiation.
This procedure has, however, the disadvantage that, in the coating of impregnated or porous substrates such as, for example, decorative papers, filters, gypsum, concrete or the like, there is a considerable risk of uncured paint constituents (monomers, binders) remaining in the coating, which lead to emission problems and entail a deterioration in the surface quality. A further disadvantage is that it is necessary to apply a plurality of layers if relatively large overall layer thicknesses are to be obtained. Problems also arise if pigmented coatings are to be produced by this method. Finally, it is also a disadvantage that photoinitiators must be added to the coating agents for curing. Fragments and secondary products of the initiators also cause emission problems.
German Auslegeschrift 2,947,597 likewise describes a method of producing dull surfaces. In this method, a coating agent is applied and cured by subjecting the system to the successive combined action of ionizing radiation or UV radiation and of heat radiation or hot air until the entire film or coating has been cured. The disadvantage in this method is, however, that heat-sensitive substrates can be coated only with restrictions or not at all, since additional thermal curing of the coating agents is absolutely necessary in order to obtain the desired properties of the resulting coatings.
The greatest disadvantage is, however, that formaldehyde is eliminated in the

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1984 Annual Book of ASTMS Standards, Sec. 6, Paints, Relates Coating and Aromatics*, vol. 06.02 "Paint-Pigments, Resins & Polymers Exerpt" p. Designation D1483-60 and D1544-80 Philadelphia, Pa. 1984 (no month.

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