1. Field of the Invention
This invention relates to a process for preparing a foamed body having chemically embossed patterns.
2. Description of the Prior Art
In general, there are two methods for forming embossed patterns. One is the so-called "ballet" printing method in which embossing is effected simultaneously with printing, and the other is the so-called chemical-embossing method. Many proposals have been made particularly with regard to the latter method.
U.S. Pat. No. 3,293,094 and Japanese Patent Publication No. 43-28636, for example, disclose methods for producing embossed patterns in which the surface of a sheet of an unfoamed resin composition containing a foaming agent, is printed with an ink which contains a decomposition inhibitor. The latter ingredient inhibits the decomposiition of the foaming agent, so that the decomposition process at the printed surfaces is retarded whereby embossed patterns are produced.
Japanese Patent Publication No. 43-15713 discloses a method for producing printed chemically embossed patterns in which a sheet of an unfoamed resin composition containing a foaming agent is printed with an ink which contains substances serving to lower the decomposition temperature, such as a so-called "kicker" and the like. As a result, the foaming process at the printed surfaces is accelerated resulting in an embossing effect.
In addition, U.S. Pat. No. 3,804,933, and Japanese Laid-Open Patent Applications No. 48-84158 and 49-105853 disclose methods for producing printed chemically embossed patterns which utilize sheets of a monomer having unsaturated bonds or of an unfoamed resin composition containing a reactive plasticizer and a foaming agent. The surfaces of these sheets are printed with an ink containing peroxides or amines whereby the printed products are inhibited from foaming, resulting in production of embossed patterns.
However, the methods of the first three mentioned references require extreme control on the heating conditions used to decompose the foaming agent. Moreover, the methods of the last three mentioned references suffer from the disadvantage that evenness of the sheet is not assured because the surface finish depends greatly upon the degree of bridging in the composition. As a result, it is difficult to obtain a uniform sheet. Furthermore, since the thickness of the sheet is not constant or uniform, the printed portions often are discolored, e.g., are whitened, and become cracked. Consequently, there continues to exist a need for improved techniques for chemically embossing foamed compositions.