DUST VACUUMINGABRASIVE TOOL

Technical Field

The present invention relates to a dust vacuuming abrasive tool having an abrasive sheet material with perforations, and a supporting pad with perforations and a ventilative member, for vacuuming dust during abrading work.

Background Art

Painting coat, clear coat, putty filler, primer and the like are abraded in automobile repairing work and the like. When painting coat, clear coat, putty filler, primer or the like is abraded, a large amount of abraded dust, or swarf, is created. This swarf has to be removed otherwise the surface of the abrasive material would become clogged, resulting in reduced abrading efficiency. Therefore, conventional dust vacuuming abrasive tools having perforations in an abrasive surface are well known.

Such abrasive tools are generally formed of an abrasive sheet material (abrasive cloth or the like) and a pad for supporting the abrasive material, sometimes called a back-up pad. In an exemplary pad, about 6 or 7 perforations for vacuuming dust having a diameter of approximately 10 mm are formed at predetermined positions in the abrasive material and in the pad. Thus, the abrasive sheet material is mounted on the surface for attaching an abrasive material of the pad, so that the perforations overlap, and perforations which penetrate through to the rear side are formed in the abrasive surface of the abrasive tool.

Abrading work is carried out by attaching a sander having a vacuuming function to the rear surface of the abrasive tool, and abraded swarf is vacuumed through the perforations in the abrasive surface and discharged.

When an abrasive material is mounted on the pad, the work of attaching the abrasive material while visually confirming the alignment of the perforations in the pad and in the abrasive material is troublesome. In the case where the perforations in the abrasive material do not align with the perforations in the pad, the number of perforations in the abrasive surface is effectively reduced, and therefore, sufficient dust vacuuming performance cannot be obtained. Therefore, when the type of abrasive material is changed, and the alignment of the perforations, or the format of the perforations changes, it also may be necessary to change the back-up pad accordingly, which is time-consuming and inefficient.

Brief Description of the Drawings

Fig. 1, A cross sectional diagram showing the structure (portion) of an abrasive sheet material having perforations.

Fig. 2, A diagram showing the abrasive surface of an abrasive sheet material used in the present invention. Fig. 3, A cross sectional diagram showing one example of a backup pad suitable for use in the present invention.

Fig. 4, A diagram showing the support surface of a backup pad suitable for use in the present invention.

Fig. 5, A diagram showing the support surface of a backup pad suitable for use in the present invention.

Fig. 6, A cross sectional diagram showing one example of an intermediate pad suitable for use in the present invention.

Fig. 7, A diagram showing another example of the support surface or back surface of an intermediate pad suitable for use in the present invention. Fig. 8, A diagram showing another example of the support surface or back surface of an intermediate pad suitable for use in the present invention.

Fig. 9, A diagram showing another example of the support surface or back surface of an intermediate pad suitable for use in the present invention.

Fig. 10, A diagram showing how the condition of overlap of perforations changes with the angle at which the perforated structures are shifted.

Explanation of Numerals

11... Base

12 ... Binder 13 ... Abrasive particle

14, 14' ... Perforations

20 ... Abrasive sheet material

24, 24' ... Perforations

30 ... Backup pad 31 ... Rigid material layer

32 ... Elastic resin layer

33 ... Bolt

34, 34' ... Perforations 40 ... Backup pad 44, 44' ... Perforations

50 ... Backup pad 54, 54' ... Perforations 55 ... Channels 60 ... Intermediate pad 61 ... Sponge layer

64, 64' ... Perforations

70, 80, 90 ... Intermediate pad

74, 74', 84, 84', 94, 94' ... Perforations

75, 85, 95 ... Channels

Disclosure of the Invention

The present invention is provided in order to solve the above-described problems with the prior art, and an object thereof is to make it unnecessary to align the perforations of an abrasive sheet material with those of the support pad, and to reduce the labor for replacing abrasive materials.

The present invention provides a dust vacuuming abrasive tool comprising: a) an abrasive sheet material having an abrasive surface, a back surface and 20 or more perforations; and b) a backup pad having a support surface, a back surface and i) 20 or more perforations, or ii) a plurality of perforations and also having, in the supporting surface, channels which interconnect the perforations and extend along lines connecting the 20 or more perforations of the abrasive sheet material; the back surface of the abrasive sheet material being fixed detachably on the

support surface of the backup pad wherein the 20 or more perforations of the abrasive sheet material are approximately adjacent the backup pad perforations and are arranged in a lattice of equally spaced equilateral triangles, wherein the diameter of the abrasive sheet material perforations are 2 to 8 mm, wherein the distance between two adjacent perforations is not greater than 1.5 times the diameter of the perforations, and wherein the diameter of the backup pad perforations is 80 to 120% of the diameter of the abrasive sheet material perforations.

Furthermore, the present invention provides a dust vacuuming abrasive tool comprising: a) an abrasive sheet material having an abrasive surface, a back surface and 20 or more perforations; b) an intermediate pad having a supporting surface, a back surface and i) 20 or more perforations, or ii) a plurality of perforations and also having, in the supporting surface and/or the back surface, channels which interconnect the perforations and extend along lines connecting the 20 or more perforations of the abrasive sheet material, and c) a backup pad having a supporting surface, a back surface and a plurality of perforations; the back surface of the abrasive sheet material being fixed detachably on the supporting surface of the intermediate pad and the back surface of the intermediate pad being fixed detachably on the supporting surface of the backup pad; wherein the 20 or more perforations of the abrasive sheet material are

approximately adjacent the intermediate pad perforations and are arranged in a lattice of equally spaced equilateral triangles; wherein the diameters of the perforations of the abrasive sheet material is 2 to 8 mm, wherein the distance between two adjacent perforations is not greater than 1.5 times the diameters of the perforations, and wherein the diameter of the perforations of the intermediate pad is 80 to 120% of the diameter of the perforations of the abrasive sheet material

It becomes possible to mount an abrasive sheet material at an arbitrary angle to a pad, thereby reducing the problem of aligning the perforations when an abrasive sheet material is attached to a pad.

The dust vacuuming abrasive tool of the present invention comprises a combination of an abrasive sheet material which has 20 or more dust vacuuming perforations arranged in a predetermined size and formation, and an intermediate pad and/or backup pad having a plurality of dust vacuuming perforations. Hereinafter, a plurality of dust vacuuming perforations arranged in a predetermined size and formation are sometimes referred to collectively as a perforated structure.

In the present specification, "effective perforations" means the portions where perforations in an abrasive material and perforations in a pad overlap. That is to say, "effective perforations in the abrasive surface" are passageways which penetrate through the abrasive surface of the abrasive tool to the rear surface, and have the function of vacuuming abraded swarf through the sander. In addition, "perforations" means through holes,

excluding recesses.

Abrasive Sheet Material

Fig. 1 is a cross sectional diagram showing the structure (portion) of an abrasive sheet material having dust vacuuming perforations. The surface of a base 11 is coated with a binder 12, and abrasive particles 13 are adhered to the base 11 with binder 12. A surface of the base on which abrasive particles are provided is an abrasive surface, and a surface on which no abrasive particles are provided is a back surface. An attaching member is, if needed, provided on the back surface of the abrasive material in sheet form. The abrasive material is provided with dust vacuuming perforations 14, 14', ... penetrating from the abrasive surface to the back surface.

It is preferable for any protruding edge of the perforations on the abrasive surface side be removed, otherwise there is a risk that the surface to be abraded may be scratched.

The perforations are preferably formed by carrying out a punching process on an abrasive material in sheet form, or alternatively, laser converted. When an abrasive material is punched, it is preferable for the blade to enter in the direction from the abrasive surface to the rear surface of the base. As a result it prevents the perforated edge from protruding from the abrasive surface. In addition, the perforations may be formed by punching out the base in advance.

The base may be any material which is conventionally used as a base for an abrasive material in sheet form. For example, a polymer film, a woven cloth, a non-woven cloth, a sheet of paper, an impregnated sheet of paper, a polymer coated sheet of paper, an

elastomer in foam form or the like can be used. Particularly preferable bases are oil or resin impregnated sheets of paper, polymer coated sheets of paper, polyester films, such as polyethylene terephthalate, and such sheets of paper and films on which a metal has been vapor deposited. The thickness of the base is generally 12 micrometers (μm) to 5000 μm, and preferably 38 μm to 3000 μm.

Abrasive particles are adhered to the surface of the base with a binder. As for the binder, binders which can secure sufficient adhesive strength and are conventionally used for an abrasive material for repairing automobiles are used. Phenol resin, epoxy resin, polyester resin, urethane resin, acryl resin, urea resin and the like can be cited as examples.

As for the abrasive particles, abrasive particles that can be used for an abrasive material for repairing automobiles are used. As for the material thereof, for example, aluminum oxide, cerium oxide, silicon carbide, diamond, alumina oxide, including melt alumina, ceramic alumina (including sol-gel alumina) and the like can be cited. In addition, the abrasive particles may be fine particles made of plastic, such as polymethacrylate ester, polystyrene, polyolefm and the like. As for the dimensions of the abrasive particles, the average particle diameter is generally approximately 500 μm to 0.45 μm. That is to say, the average particle diameter is 500 μm (JIS #36) to 0.45 μm (JIS #20000), and preferably, the average particle diameter is 5 μm (JIS #2500) to 300 μm (JIS #60).

The abrasive sheet material may be made from a coated abrasive, which is subsequently perforated. Alternatively, the backing material may be perforated, after which it may be coated with a binder and abrasive particles, then cured according to established methods known to those of ordinary skill in the art.

Fig. 2 is a diagram showing the abrasive surface of an abrasive sheet material used in the present invention. This abrasive material 20 in sheet form is provided with 61 perforations 24, 24', .... on the abrasive surface. The number of perforations 24 is at least about 20, preferably from about 20 to 150, and more preferably from about 30 to 100.

Arrangement of perforations 24, 24', ... is configured to be contiguous lattice where the centers of three adjacent perforations form an equilateral triangle. The distance between adjacent perforations, which are located at vertices of an equilateral triangle, is not greater than 1.5 times, and preferably from 0.5 to 1.5 times the diameters of the perforations. If the distance between adjacent perforations is greater than 1.5 times the diameters of the perforations, the perforations of the abrasive sheet material and those of the backup pad, or those the intermediate pad, may not be adequately aligned when such pads or abrasive sheet materials are moved about their respective axis of rotation. Consequently, the dust vacuuming efficiency of the tool is reduced.

The diameter of the perforations 24 is 2 to 8 mm, and preferably 3 to 7 mm. If the diameter of the perforations is too small, abraded swarf will tend to clog the hole, whereas a too large a diameter, will reduce the vacuuming force per perforation.

It is not always necessary for the perforations to be uniformly arranged throughout the entire abrasive surface. This is because the amount of swarf generated is not uniform throughout the abrasive surface. For example, since the abrasive power is weak in the center of the axis of rotation of the abrasive surface and the amount of swarf is small, the dust vacuuming performance does not decrease even if some dust vacuuming perforations

are omitted. For some applications, it may be desirable to enhance the abrading power in a peripheral area of an abrasive surface by forming an area having fewer, or even no perforations, in the peripheral area.

An appropriate form in a plan view and the dimensions of the abrasive sheet material may be determined in accordance with the application. Disc form, for example, is generally used. This is also true for the described pad below.

Backup Pad An abrasive sheet material is poor in self-supporting ability and therefore it is difficult to apply adequate abrasive pressure to a surface to be sanded. Therefore, the abrasive sheet material is attached to a sufficiently hard backup pad in order to apply adequate abrasive pressure to the surface to be sanded.

The pad includes several kinds, such as a backup pad and an intermediate pad, depending on applications. The backup pad is a pad which is used while being mounted directly to a sander. Fig. 3 is a cross sectional diagram showing one example of a backup pad suitable for use in the present invention. This backup pad 30 has a structure where an elastic resin layer 32 is disposed on a rigid material layer 31. The exposed surface of the elastic resin layer 32 side is a supporting surface. The exposed surface of the rigid material layer 31 side is a back surface. The supporting surface may be provided with a attachment member, if needed. The back surface is provided with means for mounting the backup pad to a sander, for example, a bolt 33. Moreover, the backup pad has perforations 34, 34', ... penetrating from the support surface to the back surface.

Fig. 4 is a diagram showing the support surface of a backup pad suitable for use in the present invention. This backup pad 40 has many perforations 44, 44', ... in its support surface. The number of perforations 44 is at least about 20, preferably from about 20 to 150, and more preferably from about 30 to 100.

The arrangement of the perforations 44 is almost the same as that of the abrasive sheet material in sheet form. Namely, the size of an equilateral triangle formed by the centers of three adjacent perforations is the same between the abrasive sheet material and the backup pad. However, it is not necessary to make the number of the perforations of the backup pad exactly equal to that of the abrasive sheet material. This is because, as mentioned above, it is not always necessary to arrange perforations uniformly throughout the support surface and the arrangement may be changed depending upon required performance or applications.

The diameter of the perforations of the backup pad is 80 to 120%, preferably 90 to 110%, of the diameter of the perforations of the abrasive material in sheet form. If the ratio is less than 80%, the dust vacuum efficiency will fall. On the other hand, if it is over 120%, the support provided by the backup pad adjacent the abrasive sheet material perforations will adversely affect the abrasive performance.

In the support surface of the backup pad, channels may be formed along lines connecting all or part of the perforations 44, 44' .... Such channels, will efficiently guide the swarf that has passed through the abrasive sheet perforations to the perforations 44, 44 ... of the backup pad.

The width of the channels is from 1 to 8 mm, and preferably from 2 to 7 mm. If the channels are too narrow, the swarf will not be effectively guided toward the perforations in the backup pad. If the channels are too wide, the backup pad may not hold the abrasive sheet material effectively during the sanding operation. The depth of the channels is from 0.5 to 5.0 mm, and preferably from 1.0 to 3.0 mm. If the channels are too shallow, the guiding dust- vacuuming property will fail to be exerted sufficiently, because each small swarf is condensed (agglutinated) into larger lamp (mass). On the other hand if the channels are too deep, insufficient vacuum may cause the swarf to become trapped in the channels, because each swarf is piled up (accumulated) on the bottom of the channels as sediment (deposit).

Fig. 5 is a diagram showing the support surface of a backup pad suitable for use in the present invention. This backup pad 50 has seven perforations 54, 54', ... in its support surface. The number of perforations 54 is not particularly limited and may be appropriately determined, for example, within the range of from 3 to 70 or from 5 to 19.

The diameter and arrangement of perforations 54 are also not particularly restricted and may be determined by taking into consideration the supporting function and dust vacuuming function of the backup pad.

Moreover, the supporting surface of this backup pad 50 is provided with channels 55. The channels 55 are arranged along lines connecting the 20 or more perforations of the abrasive sheet material. The channels 55 interconnect dust vacuuming perforations 54, 54' .... Swarf which has passed through perforations 24, 24' ..of the abrasive sheet material travels along the channels 55 and is guided to dust vacuuming perforations 54, 54' ... of the backup pad.

The channels in the supporting surface of the backup pad need not be arranged along all the lines connecting the 20 or more dust vacuuming opening of the abrasive sheet material and may be arranged partly along the lines.

Intermediate Pad

The intermediate pad means a pad which is used to adjust the hardness or compliancy of the backup according to the needs of the sanding operation. It is mounted between the abrasive sheet material and the backup pad. For example, in the case of abrading an object with a curved surface, if a surface supporting the abrasive sheet material is made of elastic resin, the surface is so hard that the abrasive material does not come into contact uniformly with the entire curved surface of the object. As a result, uneven abrasion causes a problem in that it is impossible to abrade the entire surface uniformly. As a solution of this problem, a sponge pad is mounted between an abrasive sheet material and a backup pad to reduce the hardness of the supporting surface. Fig. 6 is a cross sectional diagram showing one example of an intermediate pad suitable for use in the present invention. This intermediate pad 60 is composed of a sponge layer 61. One exposed surface is a supporting surface and the other exposed surface is a back surface. The supporting surface and the back surface may be provided with a attachment member, if needed. The intermediate pad has perforations 64, 64', ... penetrating from the support surface to the back surface. The number, arrangement and size of perforations may be determined like those of the backup pad. For example, the opening structure shown in Fig. 2 may be used as arrangement of perforations.

Fig. 7 is a diagram showing another example of the supporting surface or back surface of an intermediate pad suitable for use in the present invention. This intermediate pad 70 has seven perforations 74, 74', ... in its supporting surface. The number of the perforations 74 is not particularly limited and may be appropriately determined, for example, within the range of from 3 to 70 or from 5 to 19. The diameter and arrangement of perforations 74 are also not particularly restricted and may be determined by taking into consideration the supporting function and dust vacuuming function of the intermediate pad.

Moreover, the supporting surface and/or the back surface of this intermediate pad 70 is provided with channels 75. The channels 75 are arranged along lines connecting the 20 or more dust vacuuming perforations of the abrasive material in sheet form. The channels 75 cross the perforations 74, 74' ... to interconnect them. Swarf which has passed through perforations 24, 24' .... of the abrasive sheet material travels along the channels 75 and is guided to perforations 74, 74' ... of the intermediate pad.

The channels in the support surface or back surface of the intermediate pad need not be arranged along all the lines connecting the 20 or more perforations of the abrasive sheet material and may be arranged partly along the lines. The width and depth of the channels may be determined like those of the backup pad.

Fig. 8 is a diagram showing another example of the support surface or back surface of an intermediate pad for use in the present invention. This intermediate pad 80 has channels 85 in addition to 61 perforations 84, 84', .... The channels 85 are arranged along lines interconnecting all the perforations 84, 84', ....

Fig. 9 is a diagram showing another example of the supporting surface or back surface of an intermediate pad for use in the present invention. The channels in the supporting surface or back surface are arranged along lines connecting the dust vacuuming perforations 94, 94', ... in a series of concentric loops.

Dust vacuuming abrasive tool

The back surface of an abrasive sheet material as described above is removeably attached to the supporting surface of a pad, and thereby, a dust vacuuming abrasive tool of the present invention is obtained. When an intermediate pad is used as the pad, the back surface of the intermediate pad is further removeably attached to the supporting surface of a backup pad, and thereby, a dust vacuuming abrasive tool of the present invention is obtained. A conventional attachment member may be used. Examples of preferable members include 2-part hook and loop mechanical fasteners and adhesives. In the case where a 2-part hook and loop mechanical fastener is used, a clearance is created between the abrasive material and the backup pad, and this clearance functions as a channel for vacuuming abraded swarf, and therefore, the efficiency of dust vacuum can further be increased. The hook part of the mechanical fastener may be attached to either the rear surface of the abrasive sheet material and the loop part of the mechanical fastener attached to the support surface of the backup pad, or vice versa. The height of the clearance may be adjusted using the height of the loops, and it is not smaller than 0.5 mm, preferably not smaller than 1 mm to 2 mm, in order to make it function as a channel for vacuuming dust.

In the dust vacuuming abrasive tool according to the present embodiment, it is not necessary to match the positions of perforations of the backup pad or intermediate pad and

the abrasive sheet material when attaching the abrasive sheet material to the intermediate pad or backup pad. That is to say, whichever the direction in which the abrasive sheet material or the pad is placed, the area of the effective perforations in the abrasive surface can be secured so as to have not less than a certain value, and the dust vacuuming performance of the abrasive surface is maintained.

Though the present invention is accurately described using the following examples, the present invention is not limited to these.

Examples

Example 1

A nylon pile loop material of a mechanical fastener was attached to the back surface of an abrasive material "Disc Unicut P400" having a diameter of 125 mm, made by Sumitomo 3M Ltd. Perforations were formed in the abrasive material to form an opening structure shown in Fig. 2. Thus, an abrasive sheet material was obtained. The total number of circular perforations was 61, all having a diameter of 5.0 millimeters (mm). The centers of three adjacent perforations form an equilateral triangle of length. The distance between adjacent perforations is 6.8 mm.

A lO mm-thick sponge sheet was punched into a circle 125 mm in diameter. A hook material of a mechanical fastener was attached to the supporting surface of the resultant sponge disc and a loop material of the mechanical fastener was attached to the back surface. Perforations were formed in the disc material to form an opening structure shown in Fig. 2. Thus, an intermediate pad was obtained. The 5.5 mm diameter perforations were the in the same arrangement as the abrasive sheet material. The

diameter of the intermediate pad perforations were 110% of the diameter of the abrasive sheet material perforations.

A hook material of a mechanical fastener was attached to the supporting surface of a solid (unperforated) backup pad "Sander Pad (without perforations)" having a diameter of 125 mm, made by Shinano Inc. Perforations were formed in this pad material to form an opening structure shown in Fig. 2. Thus, a backup pad was obtained. The 5.5 mm diameter perforations were the in the same arrangement as the abrasive sheet material. The diameter of the backup pad perforations were 110% of the diameter of the abrasive sheet material perforations.

The back surface of the abrasive sheet material was fixed to the support surface of the intermediate pad and the back surface of the intermediate pad was fixed to the support surface of the backup pad. Thus, a dust vacuuming abrasive tool was obtained. The clearance between the back surface and the support surface was adjusted to 2 mm.

When the two opening structures shown in Fig. 2 are overlapped, the degree of overlap, or alignment, of dust vacuuming perforations changes with the angle at which the opening structures are shifted about the axis of rotation. Fig. 10 is a diagram showing how the degree of overlap of perforations changes with the angle at which the perforated structures are shifted. In the diagram, one of perforations which at least partly overlap together is shaded. When the angle is changed by 5° over the range 0° to 30°, the number of overlapping perforations changes, as shown in the diagram. The number of dust vacuuming perforations overlapping becomes maximum at a shift angle of 0° and it becomes minimum at a shift angle of 10°.

Sanding test performed under the conditions shown Table 1 while changing the shift angle between an abrasive sheet material and an intermediate pad and the shift angle between an intermediate pad and a backup pad in a dust vacuuming abrasive tool. In the test, the ratio of the discharge amount of abraded swarf to the total abraded amount was defined as dust vacuum efficiency.

The results are shown in Table 2.

Table 1

Table 2

The results of the abrading test show that the dust vacuum efficiency of the dust

vacuuming abrasive tool of the present invention does not fall so much even when abrasive sheet material and the backup pad perforations are not exactly aligned . Therefore, when attaching an intermediate pad or an abrasive material to a backup pad, it is not necessary to exactly align the respective perforations and the work of attachment is easy.

Example 2

In the supporting surface and back surface of an intermediate pad prepared in the same manner as in Example 1 , channels were formed along lines connecting the perforations in concentric loops. Fig. 9 is a diagram showing the support surface and the back surface of the intermediate pad. The channels were formed by removing the hook element on the supporting surface and the loop element on the back surface with a width of 3 mm. A dust vacuuming abrasive tool was obtained in the same manner as in Example 1 , except that this intermediate pad was used, and a sanding test performed. The results are shown in Table 3.

Example 3

In the supporting surface and back surface of an intermediate pad prepared in the same manner as Example 1 , channels were formed along lines completely connecting the perforations. Fig. 8 is a diagram showing the support surface and the back surface of the intermediate pad. The channels were formed by removing the hook element on the supporting surface and the loop element on the back surface with a width of 3 mm by a melting (fusion) removing method. A dust vacuuming abrasive tool was obtained in the same manner as in Example 1 , except that this intermediate pad was used, and a sanding test performed. The results are shown in Table 3.

Example 4

A lO mm-thick sponge sheet was punched into a circle 125 mm in diameter. A hook material of a mechanical fastener was attached to the support surface of the resultant sponge disc and a loop material of the mechanical fastener was attached to the back surface. In this disc material, seven perforations were formed so that the perforations overlapped with the perforations provided in a backup pad made by Shinano Inc. "Sander Pad (with perforations)." The opening at the center had a diameter of 20 mm and the perforations in the peripheral portion had a diameter of 11 mm. In the supporting surface and back surface of this pad material, channels were formed along lines connecting all the abrasive sheet material perforations. Fig. 7 is a diagram showing the supporting surface and the back surface of the intermediate pad. The channels were formed by removing the hook element on the supporting surface and the loop element on the back surface with a width of 3 mm by a melting (fusion) removing method. A dust vacuuming abrasive tool was obtained in the same manner as in Example 1 , except that this intermediate pad was used, and a sanding test was performed. The results are shown in Table 3.

Example 5

An dust vacuuming abrasive tool was prepared in the same manner as in Example 1 , except that a backup pad with seven perforations made by Shinano Inc. "Sander Pad (with perforations)" and an intermediate pad the same as that used in Example 4 were used, and a sanding test was performed. The results are shown in Table 3.

Comparative Example

An intermediate pad having seven perforations was prepared in the same manner as in

Example 4, except that no channels were formed in the supporting surface or the back surface. A dust vacuuming abrasive tool was prepared in the same manner as in Example

1, except that a backup pad with seven perforations made by Shinano Inc. "Sander Pad

(with perforations)" and this intermediate pad were used, and a sanding test was performed.

The results are shown in Table 3. Table 3

The results of the sanding tests show that even if the number and arrangement of perforations in an intermediate pad and a backup pad are the same as those of conventional products, the forming of channels along lines connecting the perforations in an abrasive sheet material lead to effects the same as those in the case of forming the perforated structure of the present invention.