EP1423239A1

EP1423239A1 - Sheet-form abrasive with dimples or perforations

Info

Publication number: EP1423239A1
Application number: EP02757524A
Authority: EP
Inventors: Kazuo Suzuki; Hajime Ebisawa
Original assignee: 3M Innovative Properties Co
Current assignee: 3M Innovative Properties Co
Priority date: 2001-09-03
Filing date: 2002-09-03
Publication date: 2004-06-02
Also published as: BR0212275A; CN1549757A; WO2003020474A1; JP2003071731A

Abstract

A sheet-form abrasive material having a substrate (11), a binder (12) coated on a surface of the substrate, and abrasive grains bonded to the substrate by the binder, wherein the abrasive material has a plurality of dimples or perforations (14), each having a mutually independent shape that are placed over an entire abrasive surface, and an effective contact area to an object to be abraded of 50% to 96%.

Description

SHEET-FORM ABRASIVE WITH DIMPLES OR PERFORATIONS

FIELD

The present invention relates to an abrasive material, and, more particularly, relates to a sheet-form abrasive material that is suitably used for a finishing process of an organic material such as resin or coated films.

BACKGROUND

When an abrasive product having a flat abrasive layer is used in an abrasive process, it is not possible to obtain a stable abrasive effect and abrasive accuracy. This is because abrasive wastes are accumulated between the abrasive product and the surface to be abraded, with the result that the surface to be abraded is scratched by the abrasive wastes, or the abrasive wastes adhere to the surface to be abraded, causing degradation in the abrasive accuracy.

In order to solve this problem, a technique has been known in which protrusions and recesses are formed on a surface of an abrasive product so that abrasive wastes and dropped abrasive material particles are collected in the recesses and thereby removed. For example, Japanese Patent Publication No. 3012261 discloses an abrasive material in which an abrasive layer has steric structure. This abrasive material is provided with a substrate, a supporting layer formed on the substrate and an abrasive layer coated on the supporting layer, and the supporting layer is formed into a regular, uniform concave-convex shape. Japanese Patent Laid-Open Publication No. Sho 63-16980 discloses an abrasive material in which, a binder and abrasive grains have been applied to a substrate and dried, this is subjected to an embossing process by using a roll having a concave-convex pattern, such as a pressing process using a calendar roll with a concave-convex printing cylinder, so that protrusions and recesses are formed on the abrasive layer.

Japanese Patent Laid-Open Publication No. Hei 1-171771 discloses an abrasive material which has a binder, and abrasive grains bonded to a substrate by the binder on a surface of the substrate that has been preliminarily subjected to an embossing process to provide a concave-convex pattern.

In these abrasive materials, with respect to the protrusions and recesses formed on the abrasive layer, the recesses are formed in the structure so that the recesses surround one protrusion or are placed in parallel with one protrusion; and the recesses form continuous grooves. As described above, protrusions and recesses are formed on the abrasive layer so as to collect in the recesses or to remove abrasive wastes and dropped abrasive material particles. However, in the case when the recesses are formed as continuous grooves, it is highly possible to cause scratches on a surface to be abraded by the edges of the recesses, or by the collected abrasive wastes, etc., that can move through the recesses comparatively freely.

Abrasive articles designed for attachment to a sander having a plurality of perforations are also known. Examples include the abrasive discs commercially available under the trade designations "3M HOOKIT FILM DISC DUST FREE" and "3M IMPERIAL STIKIT DISC DUST FREE" from 3M Company, St. Paul, MN. The perforations in the abrasive discs are used as suction openings for removing dust and are not placed over the entire surface of the abrasive material.

Moreover, in the above-mentioned abrasives, the abrasive process is carried out by abrasive grains bonded to the protrusions, and the outstanding protrusions tend to have a greater load, causing acceleration in the wear of the abrasive grains, and resulting short service life of the abrasive material. SUMMARY

The present provides a sheet-form abrasive material that can abrade a surface with high accuracy, without damaging the surface to be abraded, and is superior in abrasive efficiency and service life. The abrasive material of the present invention is suitably used for a finishing process of an organic material such as resin or coated films.

In one aspect the present invention provides a sheet-form abrasive material having a substrate, a binder coated on a surface of the substrate, and abrasive grains bonded to the substrate by the binder, wherein the abrasive material has a plurality of dimples or perforations each having a mutually independent shape distributed over the entire abrasive surface. The abrasive material has an effective contact area to an object to be abraded of about 50% to about 96%.

In one embodiment, the dimples or perforations of the abrasive material are round in shape with a diameter ranging from 0.5 mm to 10 mm, more preferably ranging from 2 mm to 6 mm. In another embodiment the dimples or perforations of the abrasive material are square with a side length ranging from 0.2 mm to 10 mm, more preferably ranging from 2 mm to 6 mm.

Ixi another embodiment the dimples or perforations of the abrasive material have a chamfered edge.

In yet another embodiment the abrasive material has an effective contact area ranging from about 75% to about 90%, more preferably ranging from about 80% to about

85%.

In yet another embodiment the dimples or perforations on the abrasive article have a diameter ranging from 2% to 8% of the outer diameter of the abrasive material.

In yet another embodiment the abrasive grains of the abrasive material are coated (preferably electrostatically coated) substantially in the form of a single layer.

In another aspect the present invention provides a manual abrasive block or manual sander having attached thereto an abrasive article of the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view of an abrasive material of the present invention. FIG. 2a is a schematic cross-sectional view that shows an electrostatic spray coating method.

FIG. 2b is a cross-sectional view of an abrasive coating produced using the electrostatic coating method of FIG. 2a.

FIG. 3 a is a schematic cross-sectional view of a slurry coating method. FIG. 3b is a cross-sectional view of an abrasive coating produced using the slurry coating method of FIG. 3 a.

FIG. 4a is a schematic cross-sectional view that shows an electrostatic coating method.

FIG. 4b is a cross-sectional view of an abrasive coating produced using the electrostatic coating method of FIG. 4a.

FIGS. 5a-5d are front views of embodiments of abrasive materials of the present invention.

FIGS. 6a-6c are front views of embodiments of abrasive materials of the present invention. FIG. 7 is a schematic representation of an electrostatic spray coating apparatus.

DETAILED DESCRIPTION

FIG. 1 is a cross-sectional view of one embodiment of an abrasive material in accordance with the present invention. The surface of a substrate 11 is coated with a binder 12, and abrasive grains 13 are bonded to the substrate 11 by the binder 12.

A plurality of perforations 14 are formed in the abrasive material. Instead of perforations, dimples that do not penetrate to the rear face of the substrate may also be used. Abrasive swarf and sloughed abrasive particles are collected and held in the perforations or dimples so that it becomes possible to effectively prevent line-shaped scratches that tend to be formed on a surface to be abraded from forming. Moreover, in the case of the perforations, the abrasive surface is effectively prevented from adhering to a coated surface, thereby providing improved abrasive efficiency.

The shape of the dimples or perforations is not particularly limited, as long as they are formed in a mutually independent manner without forming continuous grooves. For example, the shape is properly selected from the group consisting of a round shape, an elliptical shape and a polygonal shape, for example, a hexagon, square, rhombus or triangle.

With respect to the dimples or perforations, when they are too small, clogging may occur thereby causing degradation in the efficiency of collecting abrasive swarf, etc.

When the dimples or perforations are too big, the abrasive material is reduced in strength and abrading efficiency. Therefore, the dimension of the dimples or perforations is preferably from about 2% to about 8 % based on the outer dimension (diameter ratio) of the abrasive material.

More specifically, with respect to the dimension of the dimples or perforations, in the case of round dimples or perforations, the diameter ranges from about 0.5 mm to about 10 mm, more preferably, about 2 mm to about 6 mm, and in the case of square dimples or perforations, the length of the side of the square ranges from about 0.2 mm to about 10 mm, more preferably, about 2 mm to about 6 mm.

The dimples or the perforations are preferably placed over the entire abrasive surface of the abrasive material. In the case when there is an area lacking the dimples or perforations on the abrasive surface, abrasive swarf is not collected in this area, and the abrasive material tends to adhere to the object to be abraded, causing reduction in abrasive efficiency.

It is not necessary for all the dimples or perforations to have the same shape and the same dimension. Those having different shapes and different dimensions may be formed in a mixed manner, as long as they are placed over the entire surface of the abrasive material. However, they are preferably arranged with regularity.

The edge of each dimple or perforation on the side of the abrasive surface is preferably chamfered. In the case when the edge of each dimple or perforation on the side of the abrasive surface is sharp or stands out, this might damage the surface to be abraded. The perforations are preferably formed by subjecting the abrasive material to a punching process. When the abrasive material is punched, it is preferable to insert the blade in the direction from the abrasive surface toward the rear surface of the substrate. This makes it possible to provide a chamfered edge in each perforation on the side of the abrasive surface. However, the perforations may also be formed by punching the substrate prior to coating of the abrasive material. Dimples are preferably formed by subjecting the substrate to an embossing process.

Moreover, dimples may be formed by a replica method. These methods make it possible to form dimples having a uniform, regular shape with high reproducibility, to improve accuracy and finish quality imparted by the abrasive material, and also to provide a chamfered edge in each dimple on the side of the abrasive surface. With respect to the abrasive material of the present invention, the effective contact area of the abrasive surface to the object to be abraded is preferably in the range of about 50% to about 96%. More preferably, in the case of a manual abrasive block for use in wet sanding, the effective contact area is preferably in the range of about 75% to about 90%, more preferably, about 80% to about 85%. The effective contact area refers to the ratio (%) of the area of the abrasive material surface excluding the dimples or perforations based on the area ofthe abrasive material surface having no dimples or perforations. An effective contact area of less than about 50% increases the load imposed on the abrasive grains during the abrasive process causing an increase in isolated grains, and a resulting reduction in the abrasive efficiency. An effective contact area exceeding about 96% fails to provide improved abrasive efficiency. With respect to the substrate used for the abrasive material of the present invention, all the material usually used as a substrate for a sheet-form abrasive material may be used. More specifically, materials, such as a polymer film, woven cloth, nonwoven cloth, paper, impregnated paper and polymer coated paper, may be used. Particularly preferred substrates include for example, oil-impregnated paper, polymer-coated paper, polyester such as polyethylene terephthalate (PET), and metal-vapor-deposited paper, or films of these. The thickness of the substrate is generally in the range of 12 μm to 150 μm, more preferably, in the range of 38 μm to 100 μm.

The abrasive grains are bonded to the surface of the substrate with a binder. Examples of binders include phenol resins, epoxy resins, polyester resins, urethane resins, acrylic resins, etc.

Examples of abrasive grains include aluminum oxide, cerium oxide, silicon carbide and diamond; and with respect to the aluminum oxide, fused alumina, ceramic alumina (including sol-gel alumina), etc. may be used. The abrasive grains may be fine particles made of plastics such as polymethacrylate, polystyrene, polyolefin and the like. The particle size of the abrasive grains is usually from 53 μm to 0.45 μm in average particle size, i other words, the average particle size is from 53 μm (JIS #220) to 0.45 μm (JIS #20000), more preferably, 5 μm (JIS #2500) to 40 μm (JIS #360).

To manufacture an abrasive material of the present invention, first, a substrate having neither dimples or perforations is used to form an abrasive material having a flat abrasive surface. Next, a plurality of dimples or perforations that have a mutually independent shape are formed over the entire surface of the substrate. Alternatively, a plurality of dimples or perforations that have a mutually independent shape may be first formed over the entire surface of the substrate. Next, a binder and abrasive grains are applied to the substrate. The material is then heated to cure the binder.

The abrasive grains are preferably formed as a single coated layer so that they are aligned on the surface of the substrate substantially in one layer. This arrangement makes it possible to improve the retaining force of the abrasive grains and efficiency of use of the abrasive grains. This arrangement also maintains the protrusions and recesses on the film surface.

The abrasive grains are preferably applied using an electrostatic spray coating method. This allows arrangement of the abrasive grains to have proper orientation, and consequently to improve abrasive efficiency of the abrasive material. FIG. 2a is a schematic cross-sectional view that shows the principle of the electrostatic spray coating method. Object 56 to be coated is placed in front of spray nozzle 54 so as to face it with a predetermined gap. Abrasive grains 51 and a binder (not shown) are charged by a DC high- voltage power-supply 52, and discharged through a spray nozzle 54 by an air flow flowing in the direction shown by arrow 53.

The abrasive particles 51 and the binder are allowed to adhere to the object 56 to be coated (e.g., a film substrate of an abrasive material) by coulomb force derived from corona discharging current flowing from gun top needle electrode 55 having a high voltage to the object to be coated 56. In this method, an electrostatic field 57 is formed between the gun top needle electrode 55 and the object to be coated 56 so that the abrasive grains 51, ionized at the top of the electrostatic spray, are allowed to fly along the electrostatic field 57 and to adhere to the surface of the object to be coated 56 in a uniform manner. As a result, as illustrated in FIG. 2b, in comparison with the slurry method, the abrasive particles 51 on the surface of the film substrate 56 are allowed to have proper orientation, thereby making it possible to provide an abrasive material that is superior in abrasive force. Moreover, subsequently applied abrasive grains do not adhere onto the abrasive grains that have already adhered due to electrostatic repulsion between the subsequently applied abrasive grains and the adhered abrasive grains. In this way, the surface of the film substrate 56 is coated with abrasive particles 51 substantially in the form of a single layer. Thus, it is possible to improve the retaining force of the abrasive grains and the efficiency in using the abrasive grain.

The binder and the abrasive grains may be applied separately, or a mixture of the binder and the abrasive grains may be preliminarily prepared, and directly applied to the substrate by the electrostatic spray coating method.

After the abrasive grains and the binder have been applied to the substrate, the binder is cured to obtain an abrasive material. The binder is typically cured by applying heat.

With respect to the method for applying abrasive grains to a substrate, other methods such as a slurry coating method and an electrostatic coating method similar to the electrostatic spray coating method may be used.

FIG. 3(a) is a schematic cross-sectional view that shows the principle of a slurry coating method. A slurry coating liquid 61 containing abrasive grains 63 and a binder 64 is flattened using a blade 62, and the abrasive material as shown in FIG. 3(b) is obtained. FIG. 4(a) is a schematic cross-sectional view that shows the principle of the electrostatic coating method. Abrasive grains 71 are placed on hot plate 73 and aligned face-to-face with an object to be coated 74 separated with a predetermined gap. High voltage is applied to hot plate 73 by an AC high-voltage power supply 72 (2.5 to 60 Hz, 0 to 60 kV) so that the abrasive grains 71 are charged as shown by the (+) and (-) symbols in FIG. 4(a). Simultaneously, an electrostatic field 75 is formed between the hot plate 71 and the object to be coated 74 so that the abrasive grains 72 are attracted toward the surface of the object to be coated 74 by a coulomb force and are allowed to adhere thereto. Thus, an abrasive material as shown in FIG. 4(b) is obtained.

The abrasive material of the present invention is suitably applied to an abrasive process on an organic material such as a resin. The present invention makes it possible to effectively prevent the abrasive material from adhering to the surface to be abraded, and consequently to improve the abrasive efficiency. For example, the abrasive material of the present invention may be used to remove coated film defects existing on a coated film formed on sheet metal and to adjust the texture of the coated surface. In this case, the abrasive material of the present invention may be used in either a dry abrasive process or a wet abrasive process.

In these applications, the abrasive material is usually attached to a manual abrasive block or a sander. With respect to the manual abrasive block, Japanese Utility Model Laid-Open Publication No. Hei 5-67465 discloses one example thereof. With respect to the sander, Japanese Patent Laid-Open Publication No. Hei 7-314318 discloses one example thereof.

Figs. 5 and 6 are front views that show embodiments of the abrasive material of the present invention. Those shown in Figs. 5a, 5b, 5c, and 5d are abrasive discs 100 that are designed to be attached to a manual sanding block. An opening 102 in the center provides a passageway through which lubrication liquid (e.g. water) may be supplied to the abrasive surface. The opening has no function for collecting abrasive waste. The abrasive discs include a plurality holes 104 distributed over the entire abrasive surface 106, each of the holes having a mutually independent shape. Representative specifications for the abrasive discs are shown in Table 1 : TABLE 1

Those shown in Figs. 6a to 6c are abrasive discs designed for attachment to a sander. The abrasive discs 110 include plurality holes 112 distributed over the entire abrasive surface 114, each of the holes having a mutually independent shape. Representative specifications for these abrasive discs are shown in Table 2: TABLE 2

In the following examples, objects and advantages of this invention are further illustrated by various embodiments thereof but the details of those examples should not be construed to unduly limit the invention.

EXAMPLES Examples 1 to 4

A PET film having a thickness of 75 μm was used as a substrate. First, an abrasive coating liquid was formed by blending 100 g of aluminum oxide having a grain size JIS#2000 (available from Nanko Ceramics), 20 g of epoxy resin available under the trade designation "EPOTOHTO YD128R" (available from Tohto Kasei), 20 g of

"VERSAMIDE 125" (available from Henkel-Hakusui) and 75 g of propylene glycol monomethyl ether (available from Dow Coming, Inc.).

FIG. 7 is a schematic drawing of a coating device used in the electrostatic spray coating method. The abrasive coating liquid was sent under pressure from holding tank 81 (equipped with an air mixer) to diaphragm pump 82 and was circulated through a pressure difference between paint regulator 83 and back pressure regulator 84. The pressure difference was set at not less than 0.15 Mps as measured on gauges 85 and 86.

The coating liquid flowing from the holding tank 81 was sent to an electrostatic spray gun where an atomized stream of coating liquid and air was formed. The output of the spray gun 87 was controlled by an accuracy paint regulator 88 placed at the inlet ofthe gun. A voltage was applied to the electrode of the gun by a low-voltage control device 89 so as to form an electrostatic field. The air was ionized at the top of the electrode so that the particles of coating liquid passing through the ionized area were negatively charged. The coating liquid was applied to PET film 90 in the direction of the electrostatic field.

With respect to the coating device, an electrostatic spray gun commercially available as "REA-90 FOR 75785 SOLVENT-BASED PAFNT" and a low-voltage control unit commercially available as "9040 CASCADE LOW- VOLTAGE CONTROL UNIT" (from Lanzburg Industry Ltd.) were used. The coating conditions were set as follows:

TABLE 3

Thereafter, a size coating process was carried out using a phenol type resin (available from Showa Koubunshi K.K.). The size coating was cured at 140°C for three minutes. The resulting continuous abrasive sheet was then subjected to a punching process from the direction from the abrasive surface toward the rear face, so that perforations were formed over the entire surface of the abrasive sheet. Four types of abrasive discs were formed by changing the number of perforations (Examples 1 to 4). Abrasive discs having a diameter of 100mm were punched from the perforated abrasive sheets. An abrasive disc having no perforations was used as a control sample. Table 4 shows the specifications of the resulting abrasive discs.

TABLE 4

An abrasive testing machine (available under the trade designation "SCIEFFER" abrasion machine from Frazier Precision Company, Gaithersburg, MD) was used to carry out abrasive testing on the resulting abrasive discs. An acrylic plate having a diameter of 100 mm and a thickness of 8 mm was used as an object to be abraded. The abrasive load was set to 4.5 kg. The amount of abrasion was measured by rotating the object to be abraded and measuring the weight loss of the acrylic plate in grams. Table 5 shows the results of the test. Moreover, the abraded surfaces formed on the plates were visually evaluated, and no line-shaped scratches were found in any of the abrasive discs.

TABLE 5

Example 5

The same processes as described in Examples 1 to 4 were carried out except that a PET film having a thickness of 3 mil (75 μm) was used. The PET film included pin-point dimples having a diameter of 650μm and a depth of lOOμm formed in a lattice pattern over the entire surface. The effective contact area of the abrasive disc was 83.6%.

An acrylic plate having a diameter of 100 mm and a thickness of 2 mm was abraded through one-direction reciprocal movements by using a manual abrasive block The abrasive processes were carried out using both a wet abrasive process and a dry abrasive process. Evaluations were made of the wet abrasive operability, abrasive property, and finish according to the criteria set forth in Tables 6-8. The average surface roughness Ra (μm) was measured according to JIS measuring method (JISB0601-1994) using a 525 Series Photoracer (high-accuracy surface roughness measuring apparatus SV- C600) available from Mitsutoyo K.K. The results are set forth in Table 9. TABLE 6 Wet Abrasive Operability

Smooth cutting without adhering, and without uneven revolution is conducted

O during an abrasive process of coated film.

X Adhering and uneven revolution occurs during an abrasive process of coated film.

TABLE 7 Abrasive Property

An abrasive amount of not less than about 20% by comparison with a

O conventional product is obtained.

X An abrasive amount of less than about 20% by comparison with a conventional product is obtained.

TABLE 8 Finish Quality

O No line-form scratches were found on the abraded surface.

X Line-form scratched were found on the abraded surface.

Comparative Example 1

An abrasive disc was obtained according to the same manner as described in Example 5, except that a PET film having a thickness of 3 mil (75 μm) without any protrusions or recesses on the surface was used as the substrate. This disc was tested as described for Example 5. The results are presented in Table 9. Comparative Example 2

An abrasive disc was obtained according to the same manner as described in Example 5, except that the abrasive qoating was applied to the other surface of the PET film having pin-point protrusions having a diameter of 650 μm and a height of 100 μm were formed over the entire surface. The resulting abrasive disc had an effective contact area of 16.4%. The disc was tested as described for Example 5. The results are presented in Table 9. Comparative Example 3

An abrasive disc was obtained according to the same manner as described in Example 5 except that the PET film substrate had a plurality of diamond-shaped protrusions (having a short diameter of 1220 μm, a long diameter of 1750 μm and a height of 40 μm) formed in a pattern of continuous grooves with a width of 580 μm. The resulting abrasive disc had an effective contact area of 42.7%. The disc was tested as described in Example 5. The results are presented in Table 9.

TABLE 9

The results show that in comparison with the abrasive material having protrusions, the abrasive material having dimples on the abrasive surface thereof is less likely to cause scratches on the surface to be abraded, and has a superior operability. Various modifications and alterations of this invention will become apparent to those skilled in the art from the foregoing description without departing from the scope and spirit of this invention.

Claims

WHAT IS CLAIMED IS:

1. A sheet-form abrasive material comprising: a substrate; a binder coated on a surface of the substrate; and abrasive grains bonded to the substrate by the binder forming an abrasive surface; wherein the abrasive material has a plurality of dimples or perforations distributed over the entire abrasive surface, each of said dimples or perforations having a mutually independent shape, wherein the abrasive material has an effective contact area to an object to be abraded of about 50% to about 96%.

2. The abrasive material according to claim 1, wherein said dimples or perforations have a round shape having a diameter of 0.5 mm to 10 mm.

3. The abrasive material according to claim 1, wherein said dimples or perforations have a round shape having a diameter of 2 mm to 6 mm.

4. The abrasive material according to claim 1, wherein said dimples or perforations have a square shape having a side length of 0.2 mm to 10 mm.

5. The abrasive material according to claim 1, wherein said dimples or perforation have a square shape having a side length of 2 mm to 6 mm.

6. The abrasive material according to claim 1, wherein each of said dimples or perforations has a chamfered edge.

7. The abrasive material according to claim 1, wherein said abrasive material has a plurality of dimples.

8. The abrasive material according to claim 1, wherein said abrasive material has a plurality of perforations.

9. The abrasive material according to claim 1, wherein said abrasive material has an effective contact area ranging from about 75% to about 90%.

10. The abrasive material according to claim 1, wherein said abrasive material has an effective contact area ranging from about 80% to about 85%.

11. The abrasive material according to claim 1, wherein said dimples or perforations have a diameter ranging from 2% to 8 % of an outer diameter of the abrasive material.

12. The abrasive material according to claim 1, wherein said abrasive grains are substantially in the form of a single layer.

13. The abrasive material according to claim 1, wherein said abrasive grains are applied using an electrostatic spay coating method.

14. The abrasive material according to claim 1, wherein said abrasive material is attached to a manual abrasion block or a sander.