Background of the Invention Coated abrasive materials such as abrasive cloth or paper, and the like, is produced generally by fixing abrasive particles on the surface of a substrate using a bonding agent. For example, abrasive particles are first bonded to a backing material by a first bonding agent which is usually called a make coating, and then a second bonding agent which is usually called a size coating, and is applied so that it covers the make coat and abrasive particles to reinforce the abrasive particles.

As the bonding agent, thermosetting resins such as a glue, phenolic resin, urea resin, epoxy resin, and the like, and radiation setting resins in which a monomer or oligomer having a unsaturated double bond such as an acrylate, and the like, is cured by an electron ray or ultraviolet ray, are usually used.

Among the above-described resins, a phenolic resin is often used due to excellent hardness and heat resistance, however, a long and wide heating oven is required to raise productivity since curing speed thereof is slow. The urea resin has a high curing speed, however, it can not be used for an abrasive material used under severe abrasion condition or in the presence of water due to its low strength and water resistance. The curing speed of the radiation setting resin can be increased by design, however, a radiation source and a special apparatus to prevent leakage of radiation are required.

Further, when the above-described resin as a first bonding agent is applied on a porous substrate such as paper or cloth, the permeation thereof into the substrate is extreme if the substrate is not treated. Consequently the particle adhesive layer does not remain on the surface and the flexibility of the substrate is lost. To prevent this phenomenon, the porous substrate is sealed with a primer as described, for example, in Japanese Patent Application Laid-Open (JP-A) No.

63(1988)-256368. However, this method is complicated and expensive since a - separate sealing process is required.

As a method for applying a first bonding agent directly on a porous substrate, Japanese Patent Application Laid-Open (JP-A) No. 7(1995)-1344 and EPO Patent No. 620083 Al disclose a method in which a hot melt adhesive is applied on a substrate, adhesive particles are applied on it, then the adhesive is cured by radiation. However, this method requires a special applicator to apply the hot melt adhesive and a radiation source for radiation curing.

Epoxy resin has been widely used since it has an excellent adhesion with abrasive particles and a substrate, can increase curing speed, and improve productivity.

Japanese Patent Application Laid-Open (JP-A) No. 56(1981)-10525; Japanese Patent Application Publication (JP-B) No.63(1988)-33488; and U.S. Pat.

No. 4,225,460 disclose the use of a latent Lewis acid catalyst obtained by putting a Lewis acid-glycerin complex into a micro-capsule as a curing agent for an epoxy resin.

Japanese Patent Application Laid-Open (JP-A) No. 63(1988)-256368 discloses a method in which an epoxy resin comprising a cationic photo-initiator is irradiated with a ultraviolet ray, and further cured with heating to a bonding agent used for an abrasive material.

Japanese Patent Application Laid-Open (JP-A) No. 5(1993)-261666 describes a method in which a water-dispersed epoxy resin is used as a bonding agent for an abrasive material.

However, none of these prior techniques disclose a technique in which the production process of a coated abrasive material is totally simplified and the production time is shortened.

Summarv of the Invention The present invention intends to solve the above-mentioned problems by omitting the step of sealing a porous substrate and by shortening the curing time of a bonding agent when a coated abrasive material is produced using a porous substrate.

The present invention provides a process for producing a coated abrasive - material comprising the steps of: providing a porous substrate; applying a first bonding agent on at least one surface of the porous substrate to form a make coat layer; placing abrasive particles on the make coat layer; and applying a second bonding agent on the make coat layer and the abrasive particles to make a size coat layer, wherein, said first bonding agent, second bonding agent or both agents comprise (i) a solid epoxy resin having a melt viscosity coefficient of 1,000 cps (1 Parts) or more at 1200C and (ii) a curing catalyst.

In this specification, "solid epoxy resin" means a resin which exists in a solid state at room temperature and has an epoxy group which can be subjected to ring opening polymerization. In general, this resin has a softening point of not less than 60"C, preferably from 60 to 3000C, more preferably from 60 to 1600C.

When the softening point of the solid epoxy resin is less than 60"C, the solid epoxy resin is softened and fluidized earlier and the abrasive layer is easily deformed when it is heated for curing. If the abrasive layer is cured when it is in deformed condition, the resulting bonding agent matrix will be strained, retaining of the abrasive particles becomes ununiform, and the abrasion ability decreases.

More specifically, the solid epoxy resin used in the present invention has a viscosity of not less than 1,000 cps (1 Pa's) at a curing temperature of 1200C, preferably not less than 1,000 cps (1 Parts) at 1 500C, more preferably not less than 1500 cps (1.5 Pa's) at 1500C.

Detailed Description of the Invention In the present invention, solid epoxy resins having various molecular weights and epoxy equivalents can be used depending on the production method of the abrasive material, the use of the abrasive material, and performance required.

Preferably, a cresol novolak type epoxy resin, phenol novolak type epoxy resin, bisphenol A type epoxy resin, bisphenol F type epoxy resin, brominated epoxy resin, triglycidyl isocyanurate, naphthalene based epoxy resin, fluorene based epoxy resin, trishydroxyphenylmethane type epoxy resin, tetraphenylolethane type epoxy resin, biphenyl type epoxy resin, DPP novolak type

epoxy resin, and the like can be used. These can be used alone Qr in a suitable combination of two or more.

A particularly preferable solid epoxy resin is a cresol novolak type epoxy resin which is obtained by reacting epichlorohydrin with o-cresol novolak. The cresol novolak type epoxy resin has a short curing time and has a high hardness and high heat resistance after curing and, therefore, providing an article having a high abrasion ability in a short production time.

For example, useful solid o-cresol novolak epoxy resins have an epoxy equivalent from 170 to 300, a number average molecular weight from 500 to 1500 (weight average molecular weight from 1,500 to 5,000), and a softening point from about 60"C to 1000C. Specific commercially available examples include "SUMI- EPOXY ESCN-220HH" and "SUMI-EPOXY ESCN-195XL" manufactured by Sumitomo Chemical Co., Ltd., "Epitoto YDCN-701" and "Epitoto YDCN-703P" manufactured by Toto Kasei K.K., "EPON RESIN 164" manufactured by Shell Chemical Corp. and "EOCN-104S" manufactured by Nippon Kayaku Co., Ltd.

Further, another preferred resin is a bisphenol A based epoxy resin obtained by polymerization of epichlorohydrin and bisphenol A. The bisphenol A based epoxy resin has a short curing time and a high hardness and high toughness (impact resistance) after curing and, therefore, provides a high abrasive particle retaining force and cutting ability in a short production time.

For example, useful solid bisphenol A epoxy resins have an epoxy equivalent from 450 to 6,000, a number average molecular weight from 900 to 10,000, and a softening point from about 60"C to 1600C. Specific useful commercially available bisphenol A based resins include "SUMI-EPOXY ESA- 014", "SUMI-EPOXY ESA-Ol 111 and "SUMI-EPOXY ESA-017" manufactured by Sumitomo Chemical Co., Ltd., "Epitoto YD-01 1", "Epitoto YD-014" and "Epitoto YD-01711 manufactured by Toto Kasei K.K. and "EPON 1001" and "EPON 1004" manufactured by Shell Chemical Corp.

In addition, phenol novolak type epoxy resins obtained by reacting epichlorohydrin and a phenol novolak (for example, "EPPN-201" manufactured by Nippon Kayaku Co., Ltd.), trishydroxyphenylmethane type epoxy resin (for

example, "EPPN-502H" manufactured by Nippon Kayaku Co., Ltd.) and naphthalene based epoxy resin (for example, 'INC-7000" manufactured by Nippon Kayaku Co., Ltd. and "ESN-375" manufactured by Nippon Steal Chemical Co., Ltd.) are also preferred.

The curing catalyst used in the present invention is a component which cures the above-described solid epoxy resins. A catalyst providing a high curing speed is preferred in order to further shorten the production time. Useful epoxy resin catalysts include acidic and basic catalysts.

An acidic catalyst is a substance which catalytically accelerates the polymerization between epoxy groups by functioning as an acid in the ring opening polymerization reaction of an epoxy resin. Preferred examples include metal halide compounds such as tin chloride (IV); salts of Lewis acids and amines such as a salt of boron trifluoride and monoethylamine or piperidine; aromatic sulfonium salts and aromatic diazonium salts which generate Lewis acids or Broensted acids by ultraviolet irradiation; boron trifluoride etherate; and a complex of antimony pentafluoride and diethylaniline.

The complex of antimony pentafluoride and diethylaniline is particularly preferable. This compound has a high latent property at normal or ambient temperature and provides a high curing speed at high temperature and, therefore, provides a long usable time at room temperature and can be cured in a short time at a high temperature. Consequently, the production or process time can be easily controlled, and minimized, resulting in more efficient process.

The basic catalyst is a substance which catalytically accelerates the polymerization between epoxy groups by functioning as a base in the ring opening polymerization reaction of an epoxy resin. Preferable examples include metal alkoxides such as sodium methoxide and potassium butoxide; metal phenoxides such as sodium phenoxide and potassium phenoxide; metal hydroxides; tertiary amines such as dimethylbenzylamine, triethylamine and 2,4,6- tris(dimethylaminomethyl)phenol ("DMP-3011 manufactured by Rohm & Haas Corp.); and imidazole derivatives such as 2-methylimidazole, 2-ethyl-4-

methylimidazole and 2-phenylimidazole. The imidazole derivatives are particularly preferred.

The bonding agent used in the present invention is obtained by mixing a solid epoxy resin and a catalyst. The catalyst is contained in the bonding agent in an amount typically from 1 to 20 parts by weight, preferably from 1 to 10 parts by weight, more preferably from 2 to 5 parts by weight based on 100 parts by weight of the epoxy resin.

When the amount of the catalyst is less than 1 part by weight, the curing time of the bonding agent is substantially lengthened, and when over 20 parts by weight, the strength of the bonding agent matrix after curing is lowered and the cutting ability of the resulting abrasive material decreases.

Various additives known to those skilled in the art can be appropriately blended into the bonding agent. For example, a coupling agent to enhance adhesion between the abrasive particles and the bonding agent, a plasticizer, dispersing agent, antistatic agent, and the like can be blended.

The bonding agent may be used as a first bonding agent which forms a make coat layer or as a second bonding agent which forms a size coat layer.

A volatile solvent can be blended into the bonding agent in a suitable amount so to provide a suitable viscosity for the applying process described below.

When used as a first bonding agent for forming a make coat layer, the above-described bonding agent has a viscosity from 200 to 100,000 cps (0.2 to 100 Pa s), preferably from 300 to 50,000 cps (0.3 to 50 Pa. s), more preferably from 400 to 10,000 cps (0.4 to 10 Pa s) at a temperature of 25°C. When the viscosity is less than 200 cps (0.2 Pa s), if the porous substrate is not sealed, the bonding agent permeates into the substrate. When the viscosity of the bonding agent is over 100,000 cps (100 Pa s), the bonding agent cannot be applied to a substrate evenly.

In particular, the above-described conditions are suitable for an abrasive particle having a grit size ranging from JIS #20 to #240.

When used as a second bonding agent for forming a size coat layer, the above-described bonding agent has a viscosity from 10 to 10,000 cps (0.01 to 10

Pa s), preferably from 20 to 5,000 cps (0.02 to 5 Pa s), more preferably from 30 to 2,000 cps (0.03 to 2 Pea. 5) at a temperature of 25"C. When the viscosity is less than 10 cps (0.01 Pars), the coating thickness tends to be uneven due to flowability after coating. When the viscosity is over 10,000 cps (10 Pa s), the second bonding agent does not sufficiently permeate between respective abrasive particles, allowing bubbles to remain in the second bonding agent layer which causes a reduction in strength.

In particular, the above-described conditions are suitable for an abrasive particle having a grit sizing from JIS #120 to JIS #4000.

Examples of preferred volatile solvent include ketone-based solvents such methyl ethyl ketone, methyl isobutyl ketone, and cyclohexanone; ester based- solvents such as ethyl acetate and butyl acetate; aromatic hydrocarbon solvents such as benzene, toluene, and xylene; and alcohol-based or ether-based solvents such as dioxane, tetrahydrofuran, and propylene glycol monomethyl ether.

When the above bonding agents are used as a first bonding agent, the bonding agent does not permeate into the substrate and can support the abrasive particles even if the porous substrate is not prior sealed. As a result, the process in which the porous substrate is sealed with a primer can be omitted in the production of a coated abrasive material, and the production process can be remarkably simplified.

Further, when the bonding agents of the invention are used as second bonding agents, a substrate can be wound up irrespective of the reaction rate of the curing reaction since a bonding agent layer in solid state is generated only if the solvent is removed, therefore, retention time in a heating oven can be shorten and the productivity can be raised.

In a preferred embodiment of the present invention, a first bonding agent is first applied on at least one surface of a porous substrate to form a make coat layer.

It is not necessary to first seal the porous substrate with a primer, as the first bonding agent may be directly applied on the surface. The application method is not particularly restricted, and the application can be conducted using a roll coating method, and the like.

The make coat layer is usually formed so that the thickness thereof after - curing will be 500 to 5 llm though it varies depending on the grit of the abrasive particles. In general, the coating weight of the make coat layer is from 500 to 5 g/m2, and preferably from 300 to 20 g/m2 on the make coat layer. The make coat layer remains tacky or adhesive directly after the application and, therefore, the abrasive particles adhere to it and are supported. Then, the make coat layer is dried and cured. In general, the make coat layer is first dried for a short time at about 50 to 1 500C before curing. The curing is conducted generally by maintaining the layer at about 100 to 1 800C for about 0.5 minutes to about 1 hour, preferably from about 1 to about 30 minutes, or at about 120 to 1600C for about 0.5 minutes to about 30 minutes, preferably from about 1 to about 10 minutes.

This curing reaction is not required to be conducted completely, and after a size coat layer is formed, the make and size coat layers may be cured completely together.

Then, a second bonding agent is applied on the make coat layer and abrasive particles to form a size coat layer. The application method is the same as in the case of the make coat layer. The size coat layer is generally formed so that the thickness thereof after curing is from 100 to 1 pm. Then, the size coat layer is dried and cured in the same manner as described above for the make coat layer.

The porous substrate used in the present invention is one that is usually used in the abrasive art such as paper, cloth, and nonwoven fabrics. These porous substrates may either be treated or untreated substrates in accordance with accepted practices used in the art. Further, the useful abrasive particles are those which are usually used in the art. Typical examples thereof include aluminum oxide, silicon carbide, silicon nitride, zirconium oxide, chromium oxide, iron oxide, diamond, cubic boron nitride, alumina zirconia, emery, and the like.

The grit of the abrasive particle is not particularly restricted, for example, a particle having a grit from JIS #20 to JIS #4000, preferably from JIS #24 to JIS #3000 prescribed in JIS R 6001 can be used.

Examples The following Examples further illustrate the present invention in detail, but are not to be construed to limit the scope thereof. In the Examples, all amounts blended are by weight unless otherwise stated.

The epoxy resins used in the present Examples are shown in Table 1.

Table 1 No. Type Product Name Property and Melt viscosity condition (250C) (1500C) Bisphenol A ELA-128 (Mfg. By Liquid state (viscosity About 30 cps Sumitomo Chemical Co., 13,000 cps) (13 Pas) (0.03 Pa's) Ltd.) 2 Cresol ESCN-220 (Mfg. By Solid (softening point 1,600-2,400 novolak Sumitomo Chemical Co., 92"C) cps Ltd.) (1.6 to 2.4 Parts) 3 Bisphenol A ESA-014 (Mfg. By Solid (softening point About 2,000 Sumitomo Chemical Co., 92 to 1020C) cps Ltd.) (2 Parts) The curing catalysts used in the present Examples are shown in Table 2.

Table 2 No. Compound Name 1 2-ethyl-4-methylimidazole 2 Antimony pentachloride-diethylanilne complex Example 1 One hundred parts of a cresol novolak type epoxy resin "ESCN-220" manufactured by Sumitomo Chemical Co., Ltd.; 3.8 parts of 2-ethyl-4- methylimidazole; 15.1 parts of 2-ethoxymethanol; 42.9 parts of methyl ethyl ketone; and 100 parts of calcium carbonate were mixed to obtain a bonding agent having a non-volatile content of 78% and a viscosity of 478 cps (0.478 Pa.s) at 25"C.

The resulted bonding agent was applied on a paper substrate having a basic weight of 167 g/m2, a thickness of 0.187 mm, and a gas permeation rate of 83 second/100 cc, in an amount applied of about 70 g/m2 by a roll coating method, and was dried and cured at 1 450C for about 5 minutes. Then, the substrate was

observed for permeation of the bonding agent into the substrate. The results are shown in Table 4.

Examples 2 and 3 and Comparative Example 1 Bonding agents were obtained in the same manner as in Example 1 except that formulations shown in Table 3 were used, and permeability into the paper substrate was evaluated, respectively. The results are shown in Table 4.

Table 3 Raw material Example 1 Example 2 Example 3 Comparative Example 1 ELA-128 (liquid) - - 100 ESCN-220 (solid) 100 50 - ESA-014 (solid) - 50 100 2-ethyl-4-imidazole 3.8 3.8 3.8 3.8 2-ethoxyethanol 15.1 44.5 15.1 15.1 Methyl ethyl ketone (MEK) 42.9 21.4 - Methyl isobutyl ketone (MIBK) - 21.4 42.9 Calcium carbonate (filling agent) 100 100 100 100 Non-volatile component (Z) 78 70 70 93 Viscosity (cps) 478 983 7260 4060 Table 4 Bonding agent Permeability bonding agent into paper substrate Evaluation Example 1 A cured layer of the bonding agent was formed on the 0 surface. Example 2 A cured layer of the bonding agent was formed on the 0 surface. Example 3 A cured layer of the bonding agent was formed on the 0 surface. Comparative The bonding agent permeated through the substrate to the X Example 1 reverse side, and no cured layer of the bonding agent remained on the surface.

The results shown in Table 4 show that the bonding agents of Examples 1 to 3 generated a make coat layer on the surface of the substrate after curing and could support the abrasive particles even when applied on the porous substrate that had not been sealed. On the other hand, the bonding agent of Comparative Examples 1 did not generate a make coat layer which remained on the surface of the substrate after curing and which could not support the abrasive particles when applied on the porous substrate that had not been sealed.

Example 4 An abrasive article was obtained by using a solid epoxy resin-containing bonding agent as a make coat layer About 80 g/m2 of the solid epoxy resin- containing bonding agent obtained in Example 2 was applied on the above- described paper substrate using a roll coating method. About 150 g/m2 of an aluminum oxide abrasive particle of JIS #100 was applied on the formed make coat layer by an electrostatic coating method, and the make coat layer was heated and cured at about 145"C for about 3 minutes. About 150 g/m2 of a phenolic resin bonding agent shown in Table 5 was applied on the make coat layer and abrasive particles by a roll coating method. The formed size coat layer was dried by heating at about 120"C for about 4 minutes, and further heated and cured at about 80 to 120"C for about 15 hours. A loop material was laminated on the reverse side of this coated abrasive material, and was punched or cut-out in the form of a disk having a diameter of 125 mm to obtain an abrasive material disk.

Table 5 Raw Material - ~~~~ ~~ Parts by weight Resol phenolic resin (non-volatile content 78%) 61.54 Water 13.86 2-ethoxyethanol 5.93 Calcium carbonate (filling agent) 52 Non-volatile content (%) 75 Comparative Example 2 About 80 g/m2 of the phenolic resin bonding agent shown in Table 5 was applied on the above-described paper substrate using a roll coating method. About 150 g/m2 of an aluminum oxide abrasive particle of JIS #100 was applied on the formed make coat layer by an electrostatic coating method, and the make coat layer was heated and cured at about 110"C for about 2 hours. About 150 g/m2 of the phenolic resin bonding agent shown in Table 5 was applied on the make coat layer and abrasive particles by a roll coating method. The formed size coat layer was dried with heating at about 1200C for about 4 minutes, and further heated and

cured at about 80 to 1000C for about 15 hours. A loop material was laminated on the reverse side of this coated abrasive material, and was punched or cut-out in the form of a disk having a diameter of 125 mm to obtain an abrasive material disk.

Comparison of Example 4 with Comparative Example 2 (1) Production method In Example 4 using the solid epoxy resin-containing bonding agent as a make coat layer, the curing time of the make coat layer is remarkably shortened as compared with that in Comparative Example 2 using the phenolic resin bonding agent.

(2) Abrasion ability The abrasive disks of Example 4 and Comparative Example 2 were installed in a double action thunder, and subjected to steel abrasion, respectively.

The abrasion conditions included a load: thunder self weight + 2 kg, an air pressure: 5 kg/cm2, and an abrasion time: 5 minutes x 6 times (total 30 minutes).

The amounts abraded (g) are shown in Table 6.

Table 6 Example 2 Comparative Example 2 First time 13.9 13.9 Second time 14.5 14.1 Average 14.2 14.0 The results in Table 6 show that the abrasive material disk of Example 4 using the solid epoxy resin-containing bonding agent as a make coat layer has the same abrasion ability as the abrasive material disk of Comparative Example 2 using the phenolic resin.

Example 5 An abrasive article was obtained by using a solid epoxy resin-containing bonding agent as a size coat layer. About 10 g/m2 of a liquid epoxy resin- containing bonding agent shown in Table 7 was applied on a Cw paper substrate (JIS R 6252) which was sealed by oil impregnation using a roll coating method.

About 40 g/m2 of an aluminum oxide abrasive particle of JIS P 400 was applied on the formed make coat layer by an electrostatic coating method, and the make coat layer was heated and cured at about 140"C for about 5 minutes. About 40 g/m2 of a solid epoxy resin-containing bonding agent shown in Table 8 was applied on the make coat layer and abrasive particles by a roll coating method. The formed size coat layer was dried and cured with heating at about 140"C for about 5 minutes.

An adhesive was applied on the reverse side of this coated abrasive material, and was punched or cut-out in the form of a rectangle of 100 mm x 175 mm to obtain an abrasive material sheet carrying the adhesive.

Table 7 Raw Material Parts by weight ELA-128 (liquid) 50 Polyamide curing agent ("Versamide 125" manufactured by Henkel Hakusui K.K.) 50 Xylene 33.33 7< Non-volatile content (%) 75 Table 8 Raw Material Parts by weight ESCN-220 (solid) 100 Antimony pentafluoride-diethylamiline complex 3 MEK 66.67 Non-volatile content (°/O) 60.7 Comparative Example 3 About 10 g/m2 of the liquid epoxy resin-containing bonding agent shown in Table 7 was applied on the above-described sealed paper substrate using a roll coating method. About 40 g/m2 of an aluminum oxide abrasive particle of JIS #400 was applied on the formed make coat layer by an electrostatic coating method, and the make coat layer was heated and cured at about 140"C for about 5 minutes. About 40 g/m2 of the phenolic resin bonding agent shown in table 9 was applied on the make coat layer and abrasive particles by a roll coating method.

The formed size coat layer was dried with heating at about 1 200C for about 4 minutes, and further heated and cured at about 110"C for about 24 hours. An adhesive was applied on the reverse side of this coated abrasive material, and was punched or cut-out in the form of a rectangle of 100 mm x 175 mm to obtain an abrasive material sheet carrying the adhesive.

Table 9 Raw Material Parts by weight Resol phenolic resin (non-volatile content 75%) 100 2-ethoxyethanol 25 Non-volatile content (%) 60.7 Comparison of Example 5 with Comparative Example 3 (1) Production method In Example 5 which used the solid epoxy resin-containing bonding agent as a size coat layer, the curing time of the size coat layer is remarkably shortened as compared with that in Comparative Example 3 using the phenolic resin bonding agent.

(2) Abrasion ability The abrasive material disks of Example 5 and Comparative Example 3 were installed in a double action thunder, and subjected to steel abrasion, respectively.

The abrasion conditions included a load: thunder self weight + 2 kg, an air pressure: 5 kg/cm2, and an abrasion time: 5 minutes. The amounts abraded (g) are shown in Table 10.

Table 10 Example 5 Comparative Example 3 First time 10.7 4.7 Second time 8.4 6.8 Average 9.6 5.8 The results shown in Table 10 show that the abrasive material disk of Example 5 using the solid epoxy resin-containing bonding agent as a size coat layer has the same abrasion ability as the abrasive material disk of Comparative Example 3 using the phenolic resin.

According to the present invention, in producing a coated abrasive material using a porous substrate, sealing of the porous substrate could be omitted, the curing time of a bonding agent could be shortened, and the production process of the coated abrasive material was totally simplified to shorten the production time.