Patent Publication Number: US-5024126-A

Title: Slip-resistant plastic surface and process for producing such

Description:
This is a continuation of copending application Ser. No. 157,894, filed on Feb. 19, 1988, now abandoned. 
    
    
     FIELD OF THE INVENTION 
     The invention concerns a method for producing coarse surfaces on components made from plastic, and particularly components made by injection molding. The invention is most applicable for plastic devices and articles for which the gripping ability or slip resistance is to be improved, as, for example, tool handles, stairway covers, etc. 
     BACKGROUND OF THE INVENTION 
     It is known to produce coarse matte surfaces on injection molded components by texturing the injection molds, as, for example, by electronic discharge machining or photo-chemical etching. However, this process is suitable only for relatively thin-walled injection-molded components which cool in the mold to such an extent that the temperature is below that at which the material becomes plasticly deformable. Thicker-walled components, are often still so hot during removal from the mold that the heat remaining in the surrounding portions of the mold cause any existing texture to disappear. Thus, the desired effects of improved gripping ability and slip resistance are not attained. In such cases, the surface may be highly roughed by blasting it with a slightly abrasive medium, such as nut-shell fines. The disadvantage of such blasting treatment is that small particles are torn out of the surface of the plastic component, and the dust caused therefrom must be removed. Another disadvantage is that the color of the surface is changed somewhat. 
    
    
     OBJECTS AND SUMMARY OF THE INVENTION 
     It is an object of this invention to produce plastic articles with coarse surfaces which articles have a uniform surface, have a controllable degree of coarseness, do not require further finishing, and do not exhibit color changes. 
     According to the invention, polymer material from which the particular article is made is dissolved in a suitable solvent, whereby the ratio of solvent to polymer is approximately in the range of 7 to 1 to 15 to 1. For example, if the article is made from polycarbonate, the solvent, as is well known in the art, may be dimethylacetamide dimethylformamide, or dimethylsulfoxide, among others. Fine crystalline material is stirred into the solution, in the approximate range of about 7 to 1 to 20 to 1 of solution to crystalline material, thereby forming a dispersion. The relative proportions of the components depend upon the specific gravity of the polymer, the crystalline material and the desired degree of coarseness. The article is then immersed into the dispersion, causing a partial solvation and softening of the surface layer of the article. Upon removal of the article from the dispersion bath, a film of the dispersion remains intricately bonded to the partially solvated surface layer of the plastic article. 
     The solvent is then removed from the layer coating the workpiece by, for example, evaporation and/or washing, leaving behind a layer of polymer in which the crystalline material is finely distributed and firmly anchored. 
     By selecting the size of the crystalline particles and its concentration, the degree of coarseness may be precisely controlled. 
     The process of this invention permits a highly uniform texturing of the entire surface of a workpiece. Because the crystalline material is firmly embedded in the polymer, the coarse texture is maintained even after prolonged use. This is of particular importance in tool handles and grips, for example. Any color changes are minimal and controllable by adjusting the composition of the dispersion solution.