Abrasive sheet and method of manufacturing the same

Abstract: Disclosed is an abrasive sheet (10) having an abrasive particle (13) layer formed on a surface of a thin flexible resin film (11). The abrasive sheet (10) is produced by the steps of: preparing a releasable film; forming a thin flexible resin film (11) layer on a release agent applied surface of said releasable film; forming an abrasive particle (13) layer on an upper surface of said resin film (11) layer; thereafter, removing said resin film (11) having said abrasive particle (13) layer formed thereon from said releasable film; and cutting said resin film (11) having said abrasive particle (13) layer formed thereon into any suitable size. The abrasive sheet (10) can provide higher polishing power during the polishing operation, but it polishes a surface while tracing or following any orange peel on the surface. Therefore, the abrasive sheet (10) is effective for use as the polishing tool that can replace with the fine compound buffing process currently utilized in the automobile repairing industry.

Description: BACKGROUND OF THE INVENTION Field of the Invention The present invention relates to an abrasive sheet as per the preamble of claim 1 and a method of manufacturing the same, and more particularly; to such abrasive sheet that is effective for use in an automobile repairing industry, and method of manufacturing the same. An example of such a sheet is disclosed in EP 552 782 A. Description of the Prior Art At the present state of the art of automobile repairing industry, a various kinds of techniques are utilized for repairing external plates of automobiles such as bonnets, doors and the like as damaged due to automobile accidents within shorter period of time and at lower cost in order to meet the customer's demands. In the prior art, the damaged portions on the external plates of the automobiles are typically repaired in the following manner. Initially, a damaged recess portion of a plate is processed for restoration to its original shape by a panel beating process. Thereafter, any previous paint, if remaining, on the surface to be repaired is removed by using, for example, an abrasive paper of coarse grains to such degree that an underlying steel material becomes exposed. Then, cleaning of the surface is effected using some solvent, and the surface is coated with a putty. After the putty is hardened up to such point that the sanding can be done, the surface is sanded to flat condition by use of the abrasive paper of coarse grains. Then, the surrounding surface thereof is made flatened with the use of the abrasive paper by feather edging and giving teeth. Next, the surface is coated with a primer surfacer by a spray gun, and after it is hardened, the abrasive paper of fine grains is used for smoothing the surface. Then, the surface is coated with an over-coating paint by a spray gun. Furthermore, any dust, if present on the surface, is removed by using a water-proof abrasive paper of very fine grains, and a skin or surface conditioning is effected using the water-proof·abrasive paper and/or a fine compound buffing. Finaly, a polishing is performed by using a very fine and/or a super fine compound. In the prior art repairing procedure as described above, due to the spraying operation of the over coating paint by the spray gun in atomized form, it is unavoidable that there is an orange peel always produced after hardening and drying of the paint material. More particularly, such orange peel may have a different form or shape depending upon several factors including viscosity, surface tension and fluidity of the paint material when a particle in atomized paint material is re-combined with other particle on the painted surface; velocity of volatilization of the solvent; diameter of the spray gun; pressure and flow rate of air; flow rate of the paint material; distance to the surface to be painted; angle of atomization; and the surrounding conditions such as temperature, humidity, etc,. Although it is normally required in a repair-painting operation that an orange peel on a newly painted surface should substantially be matched to the existing orange peel on the surrounding area, there may frequently be some difference therebetween due to the effect of the factors as above. In order to match both orange peels, it is common practice that the newly painted surface is polished a buffing process using a compound for closely conforming to the surrounding surface. Such operation is referred to as "surface-conditioning" or "skin-conditioning". The surface-conditioning is generally effected in such manner that if the orange peel is more finer and is larger in number than that of the surrounding surface a rised portion is firstly sanded by using a water-proof abrasive paper of No. 1000 (P1000) to No. 2000 for conforming to the surrounding surface. Then, any sanding trace produced by this water-proof abrasive paper is eliminated by using a fine compound buffing process. In addition, any polishing trace produced by this fine compound buffing is eliminated, and at the same time, the surface-conditioning is effected with the use of a very fine compound buffing process. Finaly, a polishing is conducted by using a super fine compound. In general, in automobile repairing industry, only a few repair shops or painters have a complete painting booth equipped with an air cleaner, but most of the repair shops or painters have a simplified painting booth or some of them have no such booth. Therefore, it may frequently happen that any fine particles or dust in the air are deposited on the painted surface and they tend to absorb the paint on the surrounding surface to form a rised portion on the surface or to make the surface rough. When such surface is sanded by using the prior art water-proof abrasive paper, some sanding trace may remain thereon. In addition, the roughness on the recess portion can not be eliminated by use of such water-proof abrasive paper. Such roughness on the recess portion and the sanding trace can be eliminated only by using the compound, thereby effecting surface-conditioning. The buffing process is generally performed using a polisher which is electrically or pneumatically driven at the rotation speed of 1500 to 3000rpm. A towel buff, a wool buff or a sponge buff is commonly used between the polisher and the painted surface. A compound used in the buffing process consists of an emulsion including such particles that have lower hardness and are likely to be weared and collapsed for the purpose of providing the glossy. The buffing process is performed while dropping such liquid compound onto the painted surface. The water-proof abrasive paper of the finest grains currently available is No. 2000. Any sanding trace produced by such abrasive paper is generally eliminated by the buffing process using the compound. Because of free particles used for such buffing process, the polishing efficiency is lower, and longer period of time and much labor is necessary. On the other hand, the sanding process using the abrasive paper or cloth provides higher efficiency, but the sanding trace produced thereby becomes more coarser. Furthermore, such abrasive paper or cloth can sand only a rised portion of the orange peel, but not a recess portion thereof. In the prior art, another abrasive member has been proposed in which a flexible adhesive layer having abrasive particles incorporated therein is deposited onto a film or any other layers. Such abrasive member has deficiency in that the abrasive particles may be removed earlier, leading to loss of the abrasion capability, and that the sanding of a recess portion can not be attained. A further abrasive member has also been proposed in which abrasive particles are deposited onto a sponge pad in the same manner as the case where they are deposited onto a paper or cloth. Such abrasive member, however, is not practical because of coarse sanding trace and a lot of waste produced after it is used. The EP 0 552 782 shows a cloth- or paper-backed abrasive member which comprising a backing, a make coat consisting of a polymer and overlaying the backing, a plurality of abrasive grains embedded in the make coat and a size coat which is coated over the make coat and the abrasive grains. Such abrasive member provides a high efficiency, but produces coarse sanding traces, which makes a long buffing process necessary. Further, such an abrasive member can sand only a raised portion of the surface, not a recess portion thereof. The US 4 753 838 discloses a polishing sheet consisting of a supporting layer in form of a flexible synthetic resin sheet and suede-like layer having microporous and macroporous cells. The polishing sheet comprises an adhesive agent on the reverse side of the supporting layer covered by a releasing paper. Such a polishing sheet enables an improved surface quality in a polishing process, but can not be used in a sanding process in which more material has to be removed. The efficiency required in such a sanding process can not be achieved by such a polishing sheet without abrasive grains. It is the object of the invention to provide an improved abrasive sheet which provides a higher abrasive capability and produces a finer sanding trace and to provide a method for manufacturing such an improved abrasive sheet. This object is fulfilled by an abrasive sheet having the features disclosed in claim 1 and a method comprising the steps disclosed in claim 6. Preferred embodiments are defined in the dependent subclaims. The present invention provides an abrasive sheet consisting of a thin flexible resin film and an abrasive particle layer formed on the surface of said resin film. The film being characterized by features as further described in claim 1. Said resin film has thickness of between 10 and 100 µm, 100%M of between 98 and 1960 N/cm 2 (10 and 200Kgf/cm 2 ), tensile strength of between 1,96 and 8,82 kN/cm 2 (200 and 900Kgf/cm 2 ), and elongation of between 250 and 1000%; and said abrasive particle layer has abrasive particles of No. 400 (P400) to No. 4000. According to a preferred embodiment of the present invention, said resin film has thickness of between 20 and 50 µm, 100%M of between 147 and 294 N/cm 2 (15 and 30Kgf/cm 2 ), tensile strength of between 3,43 and 5,39 kN/cm 2 (350 and 550Kgf/cm 2 ), and elongation of between 600 and 800%; and said abrasive particle layer has abrasive particles of No. 1000 (P1000) to No. 2000. According to one embodiment of the present invention, said abrasive particle layer includes a flexible resin layer which sandwiches abrasive particles and an adhesive layer for affixing these abrasive particles to said resin film between the flexible resin layer and said resin film. According to another embodiment of the present invention, said resin layer has the same characteristics as those of said resin film. According to a further embodiment of the present invention, a rear surface of said resin film is provided with a pressure sensitive adhesion(PSA) layer for facilitating the use of the abrasive sheet by affixing said resin film to a sponge pad. The method of manufacturing an abrasive sheet, comprises the steps of: preparing a releasable film; forming a thin flexible resin film layer on a release agent applied surface of said releasable film; forming an abrasive particle layer on an upper surface of said resin film layer; removing said resin film having said abrasive particle layer formed thereon from said releasable film; and cutting said resin film with said abrasive particle layer formed thereon into any suitable size to form an abrasive sheet, wherein the film has the further features as detailed in method claim 6. According to one embodiment of the present invention, said step of forming the resin film layer further includes: coating said release agent applied surface of said releasable film with a polyurethane resin, an emulsion including NBR, SBR or the like, and drying said coating. BRIEF DESCRIPTION OF THE DRAWINGS The present invention and its preferred embodiments will be described in greater detail with reference to the accompanying drawings, in which: Fig. 1 is a perspective view showing a combination of an abrasive sheet according to one embodiment of the present invention and a sponge pad on which the abrasive sheet is mounted; Fig. 2 is a perspective view showing an abrasive sheet with some exaggeration in the side edges thereof, which abrasive sheet is to be used for mounting on a sponge pad, as shown in Fig. 1; Figs. 3(A) to 3(E) are schematic views for sequentially explaining method of manufacturing an abrasive sheet according to one embodiment of the present invention; Figs. 4(A) to 4(C) are graphs showing roughness of the painted surfaces, as measured by a surface roughness measuring instrument (stylus tip angle at 90 degree and cone size of 5µmR) in perpendicular to the sanding direction, in which the abscissa is graduated by a division of 500 µm and the ordinate by a division of 2 µm; and Fig. 5(A) to 5(E) are graphs showing roughness of the painted surfaces, as measured by a surface roughness measuring instrument (stylus tip angle at 90 degree and cone size of 5 µmR) in perpendicular to the sanding direction by water-proof abrasive paper, in which the abscissa is graduated at a division of 100 µm and the ordinate at a division of 1 µm. DESCRIPTION OF THE PREFERRED EMBODIMENTS Fig. 1 is a perspective view showing a combination of an abrasive sheet according to the present invention and a sponge pad on which the abrasive sheet is mounted; and Fig. 2 is a perspective view showing only an abrasive sheet which is to be used for mounting on a sponge pad, as shown in Fig. 1. As shown in Figs. 1 and 2, the abrasive sheet 10 according to one embodiment of the present invention includes a flexible thin resin film 11; a very thin adhesive layer 12 formed on the surface of the resin film 11; abrasive particles 13 deposited on the adhesive layer 12; and an additional flexible thin resin film 14 formed on the abrasive particles 13. Referring to Fig. 2, the abrasive sheet 10 may be affixed to a releasable bese board 30 through a PSA layer 15 formed on the resin film 11 at the opposite side to said thin resin film 14 to form an abrasive sheet assembly. Such abrasive sheet assembly comprising the abrasive sheet 10 and the releasable bese board 30 is extremely usefull in the view point of handling and storage therefor. When the sanding process for sanding, for example, a painted surface on an external plate of an automobile is to be done using the abrasive sheet 10, the abrasive sheet 10 together with the PSA layer 15 formed on the resin film 11 is removed from the releasable bese board 30 of the abrasive sheet assembly. Thereafter, the abrasive sheet 10 is affixed to a flat surface 21 of a sponge pad 20 by putting the PSA layer 15 thereon. Then, the sanding or surface-conditioning process can rapidly and efficiently be done by using the abrasive sheet 10 while flowing the water from the sponge pad 20 onto the painted surface. In the embodiment as above, the resin film 11 of the abrasive sheet 10 may consist of any one of the water-proof flexible resins such as polyurethane resin, NBR, SBR and the like. The resin film 11 has the thickness of between 10 and 100 µm, and more preferably between 20 and 50 µm. The abrasive particles 13 on the resin film 11 has the grains of No. 400 (P400) to No. 4000, and more preferably No. 1000 (P1000) to No. 2000. In addition, the following factors for the flexibility that the resin film 11 should provide for attaining the advantageous effects as described below: a factor 100%M (modulus) in the range of between 98 and 1960 N/cm 2 (10 and 200 Kgf/cm 2 ), and more preferably between 147 and 294 N/cm 2 (15 and 30Kgf/cm 2 ); a tensile strength in the range of between 1,96 and 8,82 kN/cm 2 (200 and 900 Kgf/cm 2 ), and more preferably between 3,43 and 5,39 kN/cm 2 (350 and 550Kgf/cm 2 ); and an elongation in the range of between 250 and 1000%, and more preferably between 600 and 800%. It is noted, here, that the factor "100%M" means the tensile strength at the elongation of 100% (i.e., when elongated at double). The manufacturing process for the abrasive sheet 10 according to the present invention will be described below in more detail. Fig. 3 schematically shows one embodiment of the manufacturing process for the abrasive sheet according to the present invention. More particularly, as shown in Fig. 3(A), a rigid releasable film 40 having suitable thickness is prepared; a release agent applied surface 41 of the film 40 is coated with a polyurethane resin, an emulsion including NBR, SBR or the like; and after drying, a thin flexible resin film 11 having the thickness of between 10 and 100 µm is formed thereon. The rigidity required for the releasable film 40 may be at such degree that it can prevent the thin flexible resin film 11 formed thereon from unnecessarily elongating and contracting in the subsequent manufacturing steps. Then, as shown in Fig. 3(B), an upper surface of the thin flexible resin film 11 is coated with a solution including epoxy resin, phenolic resin, acrylic resine or the like, and abrasive particles 13 of No. 1000 (P1000) to No. 2000 are deposited thereon by an electrostatic deposition process (Fig. 3(C)). After drying of said solution, an adhesive layer 12 having the abrasive particles 13 deposited therein is formed. Then, as shown in Fig. 3(D), a solusion including a flexible resin is applied over the adhesive layer 12 to form a thin flexible resin layer 14. It is preferable that the resin layer 14 is formed from the same material and has the same characteristics as those of the resin film 11, and the thickness of the resin layer 14 is about 70% of the height of the abrasive particles 13. In this embodiment the adhesive layer 12, the abrasive particles 13 and the resin layer 14 form "an abrasive particle layer". Thereafter, as shown in Fig. 3(E), the resin film 11, together with the abrasive particle layer formed thereon, is removed from the release agent applied surface 41 of the releasable film 40. Then, a PSA layer 15 is formed on a rear surface of the resin film 11 at the opposite side to the abrasive particle layer. The abrasive sheet 10 having the PSA layer 15 formed on the rear side therof is then affixed to a releasable base board 30 to form an abrasive sheet assembly, as already described above. Finally, such abrasive sheet assembly comprising the abrasive sheet 10 and the releasable base board 30 is cut into any desired size, as shown in Fig. 2. The abrasive sheet 10 thus produced was tested in order to demonstrate its effectiveness and advantageous effects for an actual sanding operation of a painted surface, as described below. A painted surface having the roughness (or the orange peel) as shown in Fig. 4(A) was selected for an object to be sanded. Such painted surface was manually sanded by using a commercially available water-proof abrasive paper of No. 1500 while flowing the water onto the surface. The roughness of the surface produced by this sanding operation is shown in Fig. 4(B). For comparison, the painted surface as shown in Fig. 4(A) was similarly sanded, but by using No. 1500 abrasive sheet 10 of the present invention which was affixed to the sponge pad 20 as shown in Fig. 1. The roughness of the surface produced by this sanding is shown in Fig. 4(C). It is noted, in the graph of Fig. 4, that the abscissa is graduated at a division of 500 µm and the ordinate at a division of 2 µm (refer to upper right portion of Fig. 4). Another test was conducted in order to compare the abrasion capability or sanding power provided by the prior art abrasive paper and the abrasive sheet of the present invention. Fig. 5(A) represents the roughness of a painted surface after it was manually sanded by using the commercially available water-proof abrasive paper of No. 1500, as measured in perpendicular to the sanding direction. Then, the painted surface having the roughness as shown in Fig. 5(A) was further sanded by using No. 1500 abrasive sheet 10 of the present invention which was affixed to the sponge pad 20 as shown in Fig. 1. This polishing operation was done on the surface area of 75mm x 200mm for a period of 30 seconds, while flowing the water, but in the direction orthogonal to the polishing direction in the case of Fig. 5(A). The test result indicating the roughness of the surface produced by this polishing operation is shown in Fig. 5(B). In contrast thereto, Fig. 5(C) shows the test result for another case in which the painted surface having the roughness as shown in Fig. 5(A) was further polished by using the prior art abrasive means comprising a fine compound deposited on a sponge pad. This polishing operation was performed on the surface area of 75mm x 200mm for a period of 30 seconds, but in the direction orthogonal to the polishing direction in the case of Fig. 5(A). Fig. 5(D) shows the roughness of the surface when such polishing operation was further continued for a period of 90 seconds, and Fig. 5(E) shows the roughness of the surface when such polishing operation was yet further continued for a period of 120 seconds. In the graph of Fig. 5, the abscissa is graduated at a division of 100 µm and the ordinate at a division of 1 µm (refer to upper right portion of Fig. 5). The No. 1500 abrasive sheet according to the present invention used in the above tests had the following specifications: Resin film 11: Thickness: 30 µm 100%M: 216 N/cm 2 (22Kgf/cm 2 ) Tensile strength: 4,4 kN/cm 2 (450Kgf/cm 2 ) Elongation: 700% Adhesive layer 12: Epoxy resin (epoxy equivalent: 200) Curing agent: polyamide (amine value: 200) Thickness: 3 µm Voltage at deposition of abrasive particles: DC 40,000 volts Flexible resine layer 14: Same resin as the resine film 11 Thickness: 7 µm An analysis of the test results will be described below. First, referring back to Fig. 4, the curve of Fig.4(B) indicates that the recess portion of the surface can not be ground with the use of the water-proof abrasive paper, while the curve of Fig.4(C) clearly indicates that such recess portion of the surface can surely be ground with the use of the abrasive sheet according to the present invention. In addition, by comparison of the curves of Figs.4(B) and (C), it is clearly apparent that the roughness of the surface produced by using No. 1500 abrasive sheet of the present invention becomes more finer than that produced by No. 1500 water-proof abrasive paper (for comparison, the same grains of No. 1500 was used for both case). Referring now to Fig. 5, by comparison of the curve of Fig.5(A) representing the roughness of the surface produced by No. 1500 water-proof abrasive paper with the curve of Fig.5(B) representing the roughness produced by No. 1500 abrasive sheet of the present invention, it is obvious that the roughness produced by the abrasive sheet of the present invention is extremely fine, although the measuring direction is different for both cases. In addition, as is also apparent by comparison of the curves of Figs.5(B) and (C) for which the polishing was effected during the same time period of 30 seconds, the polishing power of the abrasive sheet of the present invention is much greater. The curve of Fig.5(D) indicates that the coarse roughness still remains on the surface, and the curve of Fig.5(E) indicates that the almost same fine roughness as in the case of the present invention is ultimately attained after the polishing for longer time period of 120 seconds. The reason why such excellent polishing can be achived with the abrasive sheet according to the present invention is not clearly analyzed at present. It can, however, be considered that, due to the construction wherein the abrasive particle layer is formed on the flexible resin film, an expansion and contraction of such resin film can freely be produced during the polishing operation so that the abrasive particles in the abrasive particle layer can surely be made contact with the surface to be repaired, irrespective of any rised and/or recess portions present thereon. It can also be considered that if the adhesive layer having the abrasive particles held therein is extremely thin and flexible, and especially, if the abrasive particles 13 and the adhesive layer 12 for affixing these particles 13 to the resin film 11 are sandwiched between the resin film 11 and the resin layer 14, because of highly toughness and good expantion/contraction characteristics of both the resin film 11 and the resin layer 14, the degree that the abrasive particles 13 can freely move becomes much greater, and therefore, there is no such possibility that the abrasive particles can deeply cut into the surface to be repaired, with the result that the roughness of the surface after the polishing operation becomes very finer, and the higher polishing power can be attained as compaired to the prior art buffing process. Furthermore, when the abrasive sheet according to the present invention is affixed to the sponge pad, the abrasive sheet can behave as if it is a part of the sponge pad, which enables the reliable polishing of any uneven surface having rised/recess portions thereon. It is apparent from the foregoing that an abrasive sheet according to the present invention can provide higher polishing power during a polishing operation, but it polishes a surface while tracing or following any unevenness or orange peel on the surface. Therefore, the present invention provides a new and improved polishing tool that can replace with the fine compound buffing process currently utilized in the automobile repairing industry in order to greately reduce the labor and the time period required for such polishing operation.

Claims: An abrasive sheet which consists of a thin flexible resin film (11) and an abrasive particle layer (13) formed on the surface of said resin film, characterized in that said resin film (11) has a thickness of between 10 and 100 µm, 100%M of between 98 and 1960 N/cm 2 (10 and 200 Kgf/cm 2 ), a tensile strength of between 1,96 and 8,82 kN/cm 2 (200 and 900 Kgf/cm 2 ), and an elongation of between 250 and 1000 %; and said abrasive particle layer (13) has abrasive particles of No. 400 (P400) to No. 4000. An abrasive sheet according to claim 1, characterized in that said resin film (11) has a thickness of between 20 and 50 µm, 100%M of between 147 and 294 N/cm 2 (15 and 30 Kgf/cm 2 ), tensile strength of between 3,43 and 5,39 kN/cm 2 (350 and 550 Kgf/cm 2 ), and elongation of between 600 and 800%; and said abrasive particle layer (13) has abrasive particles of No. 1000 (P1000) to No. 2000. An abrasive sheet according to claim 1 or 2, characterized in that said abrasive particle layer (13) includes a flexible resin layer (14) which sandwiches abrasive particles and an adhesive layer for affixing these abrasive particles to said resin film between the flexible resin layer (14) and said resin film (14). An abrasive sheet according to Claim 3, characterized in that said resin layer (13) has the same characteristics as those of said resin film (11); An abrasive sheet according to any one of Claims 1 to 4, characterized in that a rear surface of said resin film (11) is additionally provided with a pressure sensitive adhesion (PSA) layer for facilitating the use of the abrasive sheet by affixing said resin film (11) to a sponge pad. A method of manufacturing an abrasive sheet, characterized in that it comprises the steps of: preparing a releasable film; forming a thin flexible resin film layer (11) on a release agent applied surface of said releasable film, said resin film (11) having thickness of between 10 and 100 µm, 100%M of between 98 and 1960 N/cm 2 (10 and 200 Kgf/cm 2 ), tensile strength of between 1,96 and 8,82 kN/cm 2 (200 and 900 Kgf/cm 2 ), and elongation of between 250 and 1000%; forming an abrasive particle layer (13) on an upper surface of said resin film (11) layer, said abrasive particle layer (13) having abrasive particles of No. 400 (P400) to No. 4000; removing said resin film having said abrasive particle layer (13) formed thereon from said releasable film; and cutting said resin film (11) with said abrasive particle layer (13) formed thereon into any suitable size to form an abrasive sheet. A method of manufacturing an abrasive sheet according to Claim 6, characterized in that said step of forming said resin film (11) layer further includes: coating said release agent applied surface of said releasable film with a polyurethane resin, an emulsion including NBR, SBR or the like, and drying said coating.

Inventors: USUI AKIRA, YOSHIDA YUKIO, USUI, AKIRA, YOSHIDA, YUKIO, Usui, Akira, c/o Kovax Corporation, Yoshida, Yukio, c/o Kovax Corporation
Applicants: KOVAX CORP, KOVAX CORPORATION
Application year: 1996
Main classification: B24D3
IPC codes: B24D3, B32B5, B24D11