Grinding Cloth And Method For The Preparation Thereof

Abstract

The present invention relates to a grinding cloth of excellent grinding properties and process for the preparation thereof. The novel grinding cloth comprises preparing fiber filaments in such a manner e.g. by compressing them as to have spaces between them, thereby forming a fiber base. The said base is fixed in a matrix by means of a synthetic resin adhesive containing grinding particles. Globular crystals are formed on said matrix by spraying a mixture of said synthetic adhesives containing grinding particles and having a higher surface tension than said matrix.

Description

SPECIFICATION

This invention relates to a grinding and polishing cloth to be used for the surface treatment of various metals, glass, stones, wood, synthetic resins, etc., and method for the preparation thereof. The term "grinding cloth" as used herein denotes "a grinding cloth, a polishing cloth, and/or a grinding and polishing cloth." More particularly, the present invention is concerned with the grinding cloth which comprises fiber filaments mixed with each other in such a manner as to have spaces in between them, e.g. as by compressing them, thereby forming a fiber base, The said fiber base is fixed by means of synthetic resin adhesives containing grinding particles and further causing globular crystals to be formed on the filaments by means of synthetic resin adhesives containing grinding particles and having a higher surface tension than the resin already coating the filaments.

Sandpaper, rotary buffers, etc., have heretofore been generally used for grinding and polishing. They are prepared by pasting grinding materials to the surface of paper, cloth, etc., by using glue as an adhesive or alternatively, the grinding and polishing materials are fixed thereon by electrodeposition or by spraying a resin such as a phenolic resin on the paper or cloth etc. However, glue fails under conditions of high temperature or humidity. It becomes starchy and hardens, softens or deteriorates, depending upon atmospheric conditions. Thus, glue is of limited utility. Phenolic resins are somewhat satisfactory in terms of their water and humidity resistance; however, there is a drawback in that when the curing time of the diluted resin in drying temperatures are not accurately controlled, said resins become starchy and hard and are thus useless.

Further, the conventional types of grinding and polishing cloths consist of grinding particles which are evenly and uniformly adhered to the surface of the fiber base. The area of contact of the grinding particles to the base is small with the result that poor adherence is obtained. While capable of grinding and polishing, these conventional materials cannot withstand irregular and uneven impact and friction. Grinding particles are abraided or scattered during the grinding and polishing. Moreover, such irregular and uneven forces reach the fiber base through the grinding particles, thereby shortening the life of said fiber base. Such have been the drawbacks of the prior art. The objects of the present invention are to overcome the aforementioned disadvantages. More particularly, an object of this invention is to improve adherence of the filaments of the fiber base and to moderate the irregular shocks caused during grinding and polishing throughout the fiber base. This object is accomplished by fixing the fiber base in an adhesive resin matrix containing grinding particles. This matrix is then dried and a mixture containing synthetic resin adhesives of higher surface tension than that of the matrix and grinding materials are sprayed on the surface of said matrix, thereby causing adherence of mixture of resins and adhesives in the form of globular crystals. This step enlarges the adhesive surface and prevents grinding particles from becoming dislodged and scattering. Also, a larger grinding surface is realized.

The result of the above steps is the formation of a grinding and polishing cloth which is durable and excellent in its grinding and polishing performance.

The accompanying drawing illustrates the preferred embodiment of the present invention. The left and right portions of FIG. 1 are respectively, magnified front and cross-sectional views of the grinding and polishing cloth of this invention.

FIG. 2 is a prospective of a rotary grinding wheel.

FIG. 3 is a perspective of a set of fabricated rotary grinding wheels in the shape of a cylinder.

With reference to FIG. 1, reference numerals 1, 1' and 1" designate the various kinds of fiber filaments. Typical examples of fiber used alone or in combination include such natural fibers as cotton, hemp-palm, coconut palm, hemp, etc. Synthetic fibers include materials such as polypropylene, polyester, nylon, etc. Mineral fibers such as asbestos, etc., can be employed.

Numeral 2 designates grinding and polishing particles. Suitable materials include emery powder, silicon carbide, aluminum oxide and artificial diamond powder, etc.

The resins in the present invention are noncritical except for the requirements that the matrix of the resin and the fiber base must have good adhesive properties and a lower surface tension when dried than the resin forming the globular crystals which contain grinding particles. Suitable materials for the matrix of resin and fiber base include the polyester resin such as that prepared by ethylene glycol, adipic acid and propylene glycol. Such resin may be cured at 120.degree. C. for 25 minutes. Such resins are available commercially as "Vurnock D 380," manufactured by the Japan Reichold Company. Admixed with the polyester resin is a toluene diisocyanate resin such as one prepared by reacting toluene diisocyanate and triethanolpropane cured at 120.degree. C. for 25 minutes. Such a resin is commercially available as "Vurnock D 750" from the Japan Reichold Company. For the adhesive resin used in the formation of globular crystals, an epoxide resin such as "Epikote 815" manufactured by Shell Chemical Company, which has an epoxide equivalent of 183 to 193, a molecular weight of approximately 306, is liquid at normal temperature, prepared from condensation of bisphenol A and epichlorohydrin and has a viscosity of 8 to 11 poises is suitable. Admixed with such epoxide resin is a phenolic resin as for example, a phenol-formaldehyde resin cured at 135.degree. C. for 45 minutes. Such a resin is commercially available from the Japan Reichold Company as "Becksol 1303." Admixed with the above resins is a silicone resin with repeating silicon-oxygen bonds. Such a material is TSR 113 manufactured by Tokyo Shibaura Electric Company, Ltd. This product has a specific gravity of 25.degree. C. of 1 plus or minus 0.04, a viscosity of 1.0 to 2.5 poises and is dried at 250.degree. C. for 2 hours. The silicon atoms are attached to hydrocarbon radicals. The following examples are illustrative:

EXAMPLE 1

A felt-like fiber base is prepared by blending: nylon filaments (1) (20 to 30 denier thick), 35 to 45 mm long, (glass fibers) (1') (15 to 25 deniers thick, 30 to 40 mm long) and white hemp filaments (1") (10 to 15 deniers thick, 25 to 30 mm long). The numerals (1), (1') and (1") are with reference to FIG. 1. The fiber filaments are formed into a mat by compressing them.

Thereafter the fiber base is dipped into a liquid mixture (viscosity 2,000 to 3,500 cps) consisting of: 50 g. of a glycol adipic acid-propylene glycol polyester resin (Vurnock D 380), 50 g. of a toluene diisocyanate-triethanol-propane resin, (Vurnock D 750), 70 g. butyl acetate and 150 g. grinding particles.

The excess liquid is removed from the above mixture by squeezing between rollers. Said mixture is then dried at 140.degree. C. for about 15 minutes thereby being cured. The fiber base obtained in such manner consists of the mixed filaments (1), (1') and (1") which are thoroughly combined with each other and are fixed. The fiber-resin matrix thus formed is strong, excellent in its elasticity and chemical resistance.

Then the mixture of grinding and polishing particles blended with synthetic resins which have chemical resistance as well as high surface tension with respect to the fiber resin matrix, is sprayed onto said matrix. More specifically, a liquid mixture consisting of:

A. epoxide resin (Epikote 815) 10 grams B. acetic anhydride 0.5 grams C. phenol-formaldehyde resin (Beckosol 1303) 70 grams D. silicone resin (TSR 113) 10 grams E. Cellosolve acetate 10 grams F. methylethyl ketone 40 grams G. ethyl acetate 10 grams H. grinding and polishing particles 200 grams

is sprayed through a spray nozzle at pressure of 0.5 to 2.5 atmospheres and is dried at 140.degree. C. to 160.degree. C. for 15 to 20 minutes.

Then said liquid mixture and grinding and polishing particles are caused to adhere to the mixed filaments (1), (1') and (1") in the form of globular crystals (3) as a result of the high surface tension of the phenol-formaldehyde-epoxide resin formed in the liquid mixture.

EXAMPLE 2

The grinding and polishing cloth of example 1 is dipped into a liquid mixture of (1) polyester resin (Vurnock D 380)- 50 grams, toluene diisocyanate resin (Vurnock D 750)- 50 grams, solvent naphtha-20 grams, butyl acetate-50 grams, ethyl acetate-30 grams and grinding and polishing particles-100 grams. Then, after removing the excess liquid therefrom, said mixture is dried at 150.degree. C. for 20 minutes and is thus cured. In such a manner there is provided a grinding and polishing cloth which is excellent in thermal resistance, abrasion resistance, elasticity and tensile strength.

In the first step of the above-mentioned process, the resin-filament mixture is, in the drying step, converted into a urethane resin by the reaction of the polyester and isocyanate.

In the second drying step, a resin of excellent heat resistance, abrasion resistance, elasticity and tensile strength is realized by the reaction of said urethane resin with the phenol-formaldehyde-epoxide resin of the liquid mixture. If the third coating step of the process, as set forth in example 2 is employed, the resin should be substantially the same as that of the first step in terms of composition and properties. Thus, the resultant product has improved heat resistance, abrasion resistance, elasticity and tensile strength. In such manner, the filaments are more thoroughly fixed and in the aforementioned steps the resin is formed into a body. The grinding and polishing cloth of the present invention is prepared in the form of a rotary grinding wheel as shown in FIG. 2. As shown in FIG. 3, a sufficient number of such wheels are put onto a shaft so that the grinding and polishing cloth of the present invention may be used in a cylindrical form.

The fiber base of the present invention if subjected to the above-discussed pre-treatment (i.e. the mixed filaments having been fixed by the resin containing the grinding and polishing particles) avoids the undesirable consequences of irregular shock when grinding and polishing. This is accomplished by the fact that the shock does not effect a single point of the grinding surface alone, but is absorbed and moderated throughout the entirety of the grinding and polishing cloth. Said cloth has a great deal of elasticity and is especially good for grinding and polishing uneven surfaces.

The grinding and polishing resins are caused to adhere to the filaments in the form of globular crystals by means of synthetic resin adhesives having a higher surface tension than the resin-filament matrix supporting said globular crystals. Therefore, the grinding and polishing particles are not scattered. Grinding and polishing particles, adhesives, and pre-treated fiber base are uniformly abraded and in this manner there is provided a sheet having long life and excellent grinding and polishing properties.

Claims

We claim:

1. A process for the production of a grinding and polishing cloth which comprises:

a. dipping a fiber base comprising compressed fiber filaments in a mixture comprising toluene diisocyanate and polyester resins and grinding particles;

b. removing the excess mixture therefrom;

c. drying by heating the mixture, thereby fixing the fiber base and forming a fiber base-resin matrix;

d. spraying said matrix with a liquid mixture comprising grinding particles and synthetic resins comprising a mixture of epoxide, phenol-formaldehyde and silicone resins, said resin mixture having a higher surface tension than the matrix of step c, and

e. drying by heating said liquid mixture on said matrix thereby causing globular crystals to form thereon and adhere thereto.

2. The grinding and polishing cloth of the process of claim 1.

3. A process according to claim 1 wherein the globular crystals of step e are further fixed by dipping in the same mixture employed in step a and curing.

4. The grinding and polishing cloth of claim 3.