CURL-RESISTANT BACKSIDE COATING LAYER FOR ABRASIVE PAPER

Abstract: A curl-resistant backside layer for an abrasive paper which includes a surfactant-free, film-forming, carboxy group-containing latex polymer. The latex polymer may be ammonia- or amine-dispersed and the curl-resistant backside layer additionally may contain a crosslinking agent. Also provided is a curl-resistant abrasive backing which includes a polymer-reinforced paper having a first surface and a second surface; a synthetic polymeric layer bonded to the first surface; and a surfactant-free, film-forming, carboxy group-containing latex polymer layer bonded to the second surface. Further provided is a curl-resistant abrasive paper which includes a polymer-reinforced paper having a first surface and a second surface; a synthetic polymeric layer bonded to the first surface; a layer of abrasive particles bonded to the synthetic polymer layer; and a surfactant-free, film-forming, carboxy group-containing latex polymer layer bonded to the second surface. In both the abrasive backing and the abrasive paper, the latex polymer may be ammonia- or amine-dispersed and the latex polymer layer may contain a crosslinking agent. The layer also may contain particles to impart antislip properties to the layer.

Description: CURL-RESISTANT BACKSIDE COATING LAYER FOR ABRASIVE PAPER Background of the Invention The present invention relates to an abrasive substrate. More particularly, the present invention relates to a latex-impregnated paper intended for use as an abrasive backing. The reinforcement of paper by latex polymer impregnation (commonly referred to as latex saturation) is a long-established practice. The polymer employed typically is a synthetic material, most often a latex, and the paper may consist solely of cellulosic fibers or of a mixture of cellulosic and noncellulosic fibers. Polymer reinforcement is employed to improve one or more of such properties as dimensional stability, resistance to chemical and environmental degradation, resistance to tearing, embossability, resiliency, conformability, moisture and vapor transmission, and abrasion resistance, among others. Latex saturated papers typically have been used as label print stock, base substrates for abrasive papers, and similar applications where strength is an essential requirement. Currently, backside coatings for abrasive papers provide antislip properties when wet, some degree of water repellency, and perhaps some curl prevention. Nevertheless, there still is an opportunity for improved curl resistance in backside coatings for abrasive papers. Summary of the Invention The present invention addresses some of the difficulties and problems discussed above by providing a curl-resistant backside layer for an abrasive paper which includes a surfactant-free, film-forming, carboxy group-containing latex polymer. By way of example, the latex polymer may be ammonia- or amine-dispersed. The curl-resistant backside layer additionally may contain a crosslinking agent. It also may contain particles such as silica or diatomaceous earth particles to provide antislip properties. The present invention also provides a curl-resistant abrasive backing which includes a polymer-reinforced paper having a first surface and a second surface; a synthetic polymeric layer bonded to the first surface; and a surfactant-free, film-forming, carboxy group-containing latex polymer layer bonded to the second surface. Again, the latex polymer may be ammonia- or amine-dispersed and the latex polymer layer may contain a crosslinking agent. Such layer also may contain particles as described above. The present invention further provides a curl-resistant abrasive paper which includes a polymer-reinforced paper having a first surface and a second surface; a synthetic polymeric layer bonded to the first surface; a layer of abrasive particles bonded to the synthetic polymer layer; and a surfactant-free, film-forming, carboxy group-containing latex polymer layer bonded to the second surface. The latex polymer may be ammonia- or amine- dispersed and the latex polymer layer may contain a crosslinking agent. It also may contain particles which provide antislip properties, such as silica and diatomaceous earth particles, and the like. Detailed Description of the Invention As used herein, the term "backside layer" refers to a layer or coating on the backside of an abrasive paper, i.e., the side of the abrasive paper which does not have the layer of abrasive particles thereon. The term "abrasive backing" is used herein to mean a paper, typically a polymer- reinforced paper, which is intended to be provided with a layer of abrasive particles. The term "abrasive paper" refers to the combination of an abrasive backing and a layer of abrasive particles. As used herein, the term "paper" is meant to include any web or sheet-like material which contains at least about 50 percent by weight of cellulosic fibers. In addition to cellulosic fibers, the web may contain other natural fibers, synthetic fibers, or mixtures thereof. Cellulosic nonwoven webs may be prepared by air laying or wet laying relatively short fibers to form a web or sheet. Thus, the term includes sheets prepared from a papermaking furnish. Such furnish may include only cellulose fibers or a mixture of cellulose fibers with other natural fibers and/or synthetic fibers. The furnish also may contain additives and other materials, such as fillers, e.g., clay and titanium dioxide, surfactants, antifoaming agents, and the like, as is well known in the papermaking art. As a practical matter, the abrasive paper of the present invention will be prepared from latex-impregnated paper. By way of illustration only, the latex-impregnated paper may be a water leaf sheet of wood pulp fibers or alpha pulp fibers impregnated with a reactive acrylic polymer latex such as Rhoplex ® B-15 (Rohm and Haas Company, Philadelphia, Pennsylvania). However, any of a number of other latices may be used, if desired, some examples of which are summarized in Table A, which follows. Table A Suitable Latices for Impregnation of Paper The impregnating dispersion typically will contain clay and an opacifier such as titanium dioxide. Exemplary amounts of these two materials are 16 parts and 4 parts, respectively, per 100 parts of polymer on a dry weight basis. By way of example only, the first layer may have a basis weight of 13.3 lbs/1300 ft 2 (50 g/m 2 ) before impregnation. The impregnated paper generally may contain impregnant in a range of from about 5 to about 50 percent by weight, on a dry weight basis, although in some cases higher levels of impregnant in the paper may be suitable. As an illustration, the paper may contain 18 parts impregnating solids per 100 parts fiber by weight, and may have a basis weight of 15.6 lbs/1300 ft 2 (58 g/m 2 ), both on a dry weight basis. A suitable caliper is 3.8 ± 0.3 mil (97 ± 8 micrometers). As stated earlier, the curl-resistant backside layer of the present invention includes a surfactant-free, film-forming, carboxy group-containing latex polymer. The layer generally is water-resistant; that is, a film of the polymer absorbs little or no water upon being immersed. By way of example, the latex polymer may be ammonia- or amine-dispersed. For example, the latex polymer may be an acrylic polymer. As another example, the latex polymer may be an ammonia-dispersed acrylic polymer. As a further example, the latex polymer may be a dispersible poly(vinyl acetate). The curl-resistant backside layer additionally may contain a crosslinking agent. Examples of suitable crosslinking agents include polyfucntional aziridine oligomers. The crosslinking agent may be present, by way of example, in an amount of from about 1 to about 15 percent by weight, based on the amount of the latex polymer. As another example, the crosslinking agent may be present in an amount of from about 2 to about 10 percent by weight. The curl-resistant backside layer also may contain particles such as silica or diatomaceous earth particles to provide antislip properties. While such particles, if present, typically will be inorganic particles, particles of organic materials also may be employed. Exemplary of inorganic particles are the following: silica; clay; calcium carbonate; talc; barium sulfate; diatomaceous earth; titanium dioxide; alumina; aluminum silicate; calcium silicate; kaolin; magnesium silicate; magnesium oxalate; magnesium-calcium carbonate; magnesium oxide; and magnesium hydroxide. Such particles generally may be present in an amount sufficient to impart antislip properties to the backside layer. For example, the particles may be present in an amount of from about 1 to about 50 percent, based on the amount of the carboxy group-containing latex polymer. As another example, the particles may be present in an amount of from about 5 to about 30 percent by weight. As a further example, the particles may be present in an amount of from about 5 to about 15 percent by weight. The present invention also provides a curl-resistant abrasive backing which includes a polymer-reinforced paper having a first surface and a second surface; a synthetic polymeric layer bonded to the first surface; and a surfactant-free, film-forming, carboxy group-containing latex polymer layer bonded to the second surface. Again, the latex polymer may be ammonia- or amine-dispersed and the latex polymer layer may contain a crosslinking agent and particles as described above. The present invention further provides a curl-resistant abrasive paper which includes a polymer-reinforced paper having a first surface and a second surface; a synthetic polymeric layer bonded to the first surface; a layer of abrasive particles bonded to the synthetic polymer layer; and a surfactant-free, film-forming, carboxy group-containing latex polymer layer bonded to the second surface. The latex polymer may be ammonia- or amine- dispersed and the latex polymer layer may contain a crosslinking agent and particles, again as described above. The present invention is further described by the example which follows. Such example, however, is not to be construed as limiting in any way either the spirit or the scope of the present invention. Example The paper used in this example was a commercially available saturated paper (Type S-91082 or Duraflex Dark Olive Waterproof Paper, Kimberly-Clark Corporation, Roswell, Georgia). Sheet size was 8.5 x 11 inches (about 22 x 28 cm). The paper contained 97 percent by weight recycled wood pulp fibers and 3 percent by weight polyester fibers having a denier of 3 and a length of 0.25 inch (about 6.4 mm). The basis weight of the paper before saturation was 87 grams per square meter (gsm). The saturant was a styrene-butadiene rubber latex and was present at a level sufficient to give the saturated paper a basis weight of 110 gsm. One side (the first side) of the paper was coated by means of extrusion casting with a 0.5-mil (about 6.4-mm) thick polyethylene layer to give an abrasive backing. By way of explanation, the polyethylene layer is water resistant, while the paper itself can absorb water and expand. This differential expansion results in curl when the paper is wet. The other side (the second side) of the paper was coated with two different dispersions. The first, Dispersion A, had a solids content of 27 percent by weight. The dispersion consisted of 100 dry parts of an acrylic latex (Hycar ® 26672, B. F. Goodrich Company, Cleveland, Ohio), 10 dry parts of a diatomaceous earth silica (Celite ® 263, (Manville Products Corporation, Denver, Colorado), and 10 dry parts of a polyfunctional aziridine crosslinking agent (Xama-7 ® , B. F. Goodrich Company, Cleveland, OH). The dry coating weight was 15 gsm. The second dispersion, Dispersion B, was similar to Dispersion A, except the Hycar ® 26672 was replaced with a like amount of an ammonia-dispersed ethylene-acrylic acid copolymer (Michem ® Prime 4983, Michelman, Inc., Cincinnati, Ohio). The coating weight from Dispersion B was 14 gsm. Sheets of the abrasive backing and sheets having backside coatings of Dispersions A and B, respectively, were placed in water. The abrasive backing, i.e., the sheet lacking a backside coating, curled immediately and curled into a tube having about two complete circles of paper. The sample having a backside coating of Dispersion A remained fairly flat for about 2 hours, then slowly curled into a tube having about 1.5 circles of paper after 24 hours. The sample having a backside coating of Dispersion B remained flat for about 8 hours, then slowly curled into a tube having about 0.25 circle of paper after 24 hours. The sample having a backside coating of Dispersion B was notably stiffer than either the sample having a backside coating of Dispersion A or lacking a backside coating. While the specification has been described in detail with respect to specific embodiments thereof, it will be appreciated by those skilled in the art, upon attaining an understanding of the foregoing, may readily conceive of alterations to, variations of, and equivalents to these embodiments. Accordingly, the scope of the present invention should be assessed as that of the appended claims and any equivalents thereto.

Claims: WHAT IS CLAIMED IS: 1. A curl-resistant backside layer for an abrasive paper comprising a surfactant- free, film-forming, carboxy group-containing latex polymer. 2. The curl-resistant backside layer of claim 1 , in which the latex polymer is ammonia- or amine-dispersed. 3. The curl-resistant backside layer of claim 1 , in which the layer further comprises a crosslinking agent. 4. The curl-resistant backside layer of claim 2, in which the layer further comprises a crosslinking agent. 5. The curl-resistant backside layer of claim 1 , in which the layer further comprises particles in an amount sufficient to impart antislip properties to the layer. 6. A curl-resistant abrasive backing comprising: a polymer-reinforced paper having a first surface and a second surface; a synthetic polymeric layer bonded to the first surface; and a surfactant-free, film-forming, carboxy group-containing latex polymer layer bonded to the second surface. 7. The curl-resistant abrasive backing of claim 6, in which the latex polymer is ammonia- or amine-dispersed. 8. The curl-resistant abrasive backing of claim 6, in which the latex polymer layer further comprises a crosslinking agent. 9. The curl-resistant abrasive backing of claim 7, in which the latex polymer layer further comprises a crosslinking agent. 10. The curl-resistant backside layer of claim 6, in which the layer further comprises particles in an amount sufficient to impart antislip properties to the layer. 11. A curl-resistant abrasive paper comprising: a polymer-reinforced paper having a first surface and a second surface; a synthetic polymeric layer bonded to the first surface; a layer of abrasive particles bonded to the synthetic polymer layer; and a surfactant-free, film-forming, carboxy group-containing latex polymer layer bonded to the second surface. 12. The curl-resistant abrasive paper of claim 11 , in which the latex polymer is ammonia- or amine-dispersed. 13. The curl-resistant abrasive paper of claim 11 in which the latex polymer layer further comprises a crosslinking agent. 14. The curl-resistant abrasive paper of claim 12, in which the latex polymer layer further comprises a crosslinking agent. 15. The curl-resistant backside layer of claim 11 , in which the layer further comprises particles in an amount sufficient to impart antislip properties to the layer.

Inventors: KRONZER FRANCIS JOSEPH, KRONZER, FRANCIS, JOSEPH
Applicants: KIMBERLY CLARK CO, KIMBERLY-CLARK WORLDWIDE, INC.
Application year: 1999
Main classification: B24D
IPC codes: B24D3, B24D11