Stock material or miscellaneous articles – Structurally defined web or sheet – Continuous and nonuniform or irregular surface on layer or...
Patent
1995-09-28
1997-12-09
Robinson, Ellis
Stock material or miscellaneous articles
Structurally defined web or sheet
Continuous and nonuniform or irregular surface on layer or...
428 357, 4284111, 428412, 428405, 428447, 428451, 428483, 428331, 428429, 428442, 428520, 428522, 522 84, 522 99, 522 83, 522 64, 522172, C08K 336, B32B 1902, B32B 2720, B32B 1710
Patent
active
056958510
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
This invention relates to coating compositions which, when exposed to high-energy radiation, can form a cured film having excellent abrasion resistance and weather resistance, and to molded articles (in particular, synthetic resin molded articles) having a surface coated with the cured product of such a coating composition.
BACKGROUND ART
In recent years, transparent plastic materials having high fracture resistance are being widely used as substitutes for transparent glass. However, transparent plastic materials have serious disadvantages in that their surfaces are less hard than that of glass, are easily damaged by scratching, and have insufficient abrasion resistance.
Accordingly, many attempts have hitherto been made to improve the abrasion resistance of transparent plastic materials. One of the most common methods is to apply a curable fluid consisting essentially of a compound having a plurality of acryloyloxy or methacryloyloxy groups in the molecule to a surface of a molded article, cure it by the application of heat or by exposure to high-energy radiation such as ultraviolet light, and thereby form a highly mar-resistant coating on the surface of the molded article, as described, for example, in Japanese Patent Laid-Open Nos. 102936/'78, 104638/'78 and 97633/'79.
The curable fluid used in this method is readily available at a relatively low cost. However, since the resulting cured film is an organic material, it is a matter of fact that the abrasion resistance of molded articles having such a coating is more or less limited.
On the other hand, several methods for imparting higher surface hardness to plastic molded articles are known. They include, for example, a method which comprises applying an alkoxysilane compound to a surface of a plastic molded article and curing it by the application of heat to obtain a coated molded article, as described in Japanese Patent Laid-Open Nos. 26822/'73 and 64671/'84; and a method which comprises applying a coating composition composed of colloidal silica and a curable fluid to a surface of a plastic molded article and curing it by the application of heat to obtain a coated molded article, as described in Japanese Patent Laid-Open Nos. 106969/'81 and 272041/'90.
However, the coating compositions used in these methods contain an organic solvent in order to improve their application properties. As a result, the plastic molded article being coated may be cracked in the drying step, the coating film is liable to defects such as unevenness of coating, and the resulting coated molded article tends to present a poor appearance. Moreover, the organic solvent is unavoidably released to the atmosphere in the coating step, and this is undesirable from the viewpoint of global environmental protection on which much attention has been focused in recent years. Furthermore, these coating compositions using a curable fluid are disadvantageous for industrial purposes because their thermal cure requires a large energy consumption and a long curing time.
On the other hand, coating compositions comprising colloidal silica, an alkoxysilane having an acryl or methacryl group, and a polyfunctional acrylate are disclosed in Japanese Patent Publication Nos. 21815/'87, 55307/'89, 2168/'91 and 6190/'91, and Japanese Patent Laid-Open Nos. 204669/'84, 256874/'87, 64138/'90, 18423/'92, 214743/'92, 220411/'92, 98189/'93, 306374/'93, 25363/'94, 41468/'94 and 151694/'94.
These coating compositions can also be used as solventless coating materials and can yield plastic molded articles having fairly high surface hardness. However, they have the disadvantage of being insufficient in weather resistance because the cured film may be hydrolyzed at the interface between the colloidal silica and the alkoxysilane, resulting in cracking or whitening thereof.
In order to solve these problems, the present inventors discovered that a coating composition comprising finely divided silica having its surfaces modified by a hydrolyzate of an alkoxysilane having a styryl group, a polyfunctional
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Ige Hitoshi
Watanabe Hiroyuki
Yanagase Akira
Mitsubishi Rayon Co. Ltd.
Robinson Ellis
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