This invention relates to the application of colorant in a desired pattern to an embossed electrically uncharged polymeric surface.
It is often desirable to decorate items having polymeric surfaces, such as suitcases, automobile seats, and furniture upholstery with colorants. Where a surface is smooth, these are various methods to decorate it including spraying with spray masks, lamination, printing, and the like. However, if the polymeric surface is embossed, lamination, spraying with spray masks, and printing methods are not highly desirable. Lamination and spray with spray masks will not seal against the various peaks and valleys of an embossed surface and printing methods also have disadvantages. Electrostatic printing methods normally require that the substrate, in this case the polymeric surface, be electrostatically neutral or that a uniform field can be produced between the printing screen and the substrate surface. To obtain a uniform electrical field between an embossed surface and the printing screen is difficult because of the uneven surface. Moreover, when a non-uniform electrostatic field is established between the substrate and the printing screen, the uneven surface may cause the designs to have feathered edges. Thus, designs are not as attractive and distinct as desired.
The prior art, e.g., U.S. Pat. No. 3,058,444 uses a rotatably mounted magnetic roller to deposit a mixture of magnetic powder and toner to an electrophotographically formed electrostatic latent image. The necessity of charging the surface and application of electrophotographic coating to the surface requires specialized equipment with its appurtenant cost. Moreover, variations in the amount of the electrostatic charge in the latent image could vary the concentration of the deposited mixture and/or cause a feathered effect at the edge of a design. Coatings have been applied to embossed surfaces but generally an adhesive method is used, e.g., see U.S. Pat. No. 3,616,135.
The present invention has the distinct advantage of not requiring the substrate to be electrically charged. That is, the material which has a polymeric surface is electrically uncharged although alternately it may be charged if desired. The theory on which the present invention is based is that if a colorant made of a polymeric material is pressed against another polymeric surface, the friction itself will cause an electrostatic attraction known as a triboelectric effect. This triboelectric effect at least temporarily holds the colorant against the polymeric surface until it can be subsequently coated with a coating of some type such as hydroxy functional acrylic with urethane and 1,6 diacrylate.
Another apsect of this invention is the use of a roller magnet bounded by generally non-magnetic walls on both sides thereof which extend radially outwardly so that the magnetic carrier and polymeric colorant is attracted and distributed in a straight line. The wheel-shaped magnet is biased against the polymeric surface so that it presses the mixture against the surface and deposits it thereon. The walls prevent any feathering of the stripe or other desired design.
Different methods for holding a polymeric material in position on the polymeric surface are the applications of heat and resins. However, if heat and resins are not used in precise amounts, they will distort the polymeric surface. The subject invention has the advantage of less risk of damage to the surface. The coating is simply applied and permitted to dry by dehydration or by application of ultraviolet light.