Stock material or miscellaneous articles – Structurally defined web or sheet – Continuous and nonuniform or irregular surface on layer or...
Reexamination Certificate
2002-09-26
2004-09-14
Berman, Susan (Department: 1711)
Stock material or miscellaneous articles
Structurally defined web or sheet
Continuous and nonuniform or irregular surface on layer or...
C428S141000, C428S142000, C428S143000, C428S149000, C428S339000
Reexamination Certificate
active
06790512
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates generally to a coating composition and process for making and applying the coating. More specifically, the invention relates to radiation-cured and thermally-cured coatings having a macroscopic texture that provides superior abrasion resistance and unique aesthetic qualities.
2. Description of Related Art
Radiation-curable coatings are used in many applications throughout the coatings industry, such as protective coatings for various substrates, including plastic, metal, wood, ceramic, and others, and the advantages of radiation-curing compared to thermal curing are well known in the art. These coatings are typically resin-based mixtures that are usually cured using ultraviolet (UV) radiation. The resins are typically mixtures of oligomers and monomers that polymerize upon exposure to UV radiation resulting in a cured coating.
Various other components may be added to the resin mixture. A photosensitizer or photoinitiator may be added to cause cross-linkage of the polymers upon exposure to UV radiation. Flatting agents, such as silica, may be added to reduce or control the level of gloss in the cured coating; however, U.S. Pat. No. 4,358,476 discloses that excessive concentrations of flatting agents may result in undesirably high viscosities impeding proper application of the coating to a substrate, potential separation of the resin into separate phases, and a deleterious effect on the efficacy of the UV radiation. U.S. Pat. No. 5,585,415 describes the use of a pigmented composition and various photoinitiators that produce a uniform microscopic surface wrinkling that provides a low gloss surface without the use of flatting agents. Various other components, such as fillers, plasticizers, antioxidants, optical brighteners, defoamers, stabilizers, wetting agents, mildewcides and fungicides, surfactants, adhesion promoters, colorants, dyes, pigments, slip agents, fire and flame retardants, and release agents, may also be added to the resin mixture to provide additional functionality.
An important aspect of these coatings is their level of scratch or abrasion resistance. Good abrasion resistance is desirable so that the integrity and appearance of the coating is maintained. For example, a superior abrasion-resistant coating would be desirable for a flooring substrate, since flooring is typically exposed to a variety of abrasives. Improvements in the abrasion-resistance of coatings has been accomplished through various techniques. U.S. Pat. No. 4,478,876 describes the addition of colloidal silica to hydrolyzable silanes and polymers derived from a combination of acryloxy functional silanes and polyfunctional acrylate monomers. Another technique is the use of compositions containing acrylate or methacrylate functionalities on a monomer, oligomer, or resin. U.S. Pat. No. 5,104,929 describes the use of colloidal silica dispersions in certain acrylate or methacrylate ester monomers or mixtures thereof. U.S. Pat. No. 5,316,855 describes the use of a cohydrolyzed metal alkoxide sol with a trialkoxysilane-containing organic component having the trialkoxysilane.
These radiation-cured coatings generally have a substantially smooth, exposed surface such that there is no macroscopic texture or texture visible to the naked eye. This type of smooth surface provides for ease of cleaning. Some radiation-cured coatings have a microscopic texture as described in U.S. Pat. No. 5,585,415. The individual features of this texture are not visible to the naked eye, but the combined effect of the microscopic texture results in the scattering of visible light that results in a matte or low gloss appearance. This texture is provided by the coating curing process which results in microscopic wrinkles on the surface of the coating. While the microscopic dimensions of this texture provide a matte finish, these dimensions also make the coating susceptible to particle entrapment within the microscopic wrinkles. This particle entrapment results in a visibly dirty surface that is difficult to clean. Another microscopic texture found in radiation-curable coatings results from the addition of flatting agents to the uncured coating mixture. During the curing process these flatting agents, which are small inorganic or organic particles, concentrate at the coating surface to form a microscopically rough surface that scatters visible light resulting in a matte finish. The size of the particle used is typically such that it is no larger in diameter than the average thickness of the cured coating. Particles much larger than the coating thickness do not result in a matte finish and are not desired. Since most radiation-cured coatings are no more than 75-100 &mgr;m thick, and since UV radiation can not typically penetrate any deeper, typical flatting agent particles for UV-cured coatings range in size from 0.1-100 &mgr;m, depending upon average coating thickness.
Flatting agents are well known in the art as described, for example, in F. D.C. Gallouedec et al., “Optimization of Ultrafine Microporous Powders to Obtain Low-Gloss UV Curable Coatings,” Radtech Report, September/October 1995, pp 18-24.
To produce such macroscopically smooth surfaces requires the application of a coating mixture that can be easily distributed across the substrate to be coated. If the coating mixture has a high viscosity, for example, the coating will not distribute smoothly. Therefore, it is preferable to use a lower viscosity coating to produce such a macroscopically smooth coating surface. Thermally-cured coatings are also used in many applications throughout the coatings industry for various substrates such as plastic, metal, wood, ceramic, and others. Thermally-cured coatings are similar to radiation-cured coatings in that they typically comprise resin-based mixtures of oligomers and monomers that polymerize upon curing. Instead of using radiation to cure or polymerize the resin, however, heat is used to affect polymerization. As such, a thermally-activated initiator is used to initiate polymerization, rather than a photosensitizer or photoinitiator. However, various other components may be added to the thermally-curable resin mixture, including the same components that are added to radiation-curable resin mixture, such as flatting agents, fillers, plasticizers, antioxidants, optical brighteners, defoamers, stabilizers, wetting agents, mildewcides and fungicides, surfactants, adhesion promoters, colorants, dyes, pigments, slip agents, fire and flame retardants, and release agents.
Similar to the radiation-cured coatings, however, thermally-cured coatings are also substantially smooth from a macroscopic perspective. Also, to produce such macroscopically smooth surfaces requires the application of a coating mixture that can be easily distributed across the substrate to be coated. If the coating mixture has a high viscosity, for example, the coating will not distribute smoothly. Therefore, as with radiation-cured coatings, it is preferable to use a lower viscosity coating to produce such a macroscopically smooth coating surface.
Other coatings provide a macroscopically textured surface but by methods other than radiation-curing or thermal-curing. In chemical embossing, for example, a macroscopic texture is formed based upon the use of various chemicals added to the substrate. In mechanical embossing, the substrate itself is imprinted with the desired textural pattern. In both types of embossing, the subsequently applied coating naturally conforms to the shape of the substrate textural pattern. However, any desired change to the textural pattern requires changes in the amount and type of chemicals added to the substrate and/or the replacement of the roller used to mechanically imprint the pattern on the substrate, which can be significantly expensive and time consuming. Furthermore, neither the coating itself or its application are inherently providing the desired texture. In another form of mechanical embossing, texture may be achieved by impressing a given pattern on the
Burcham Loyd J.
Ferguson Donald C.
Henry Donald B.
MacQueen Richard C.
Parker Anthony A.
Berman Susan
Congoleum Corporation
Morgan & Lewis & Bockius, LLP
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