TECHNICAL FIELD

The present invention relates to a polishing method and a polishing pad.

BACKGROUND ART

There has been known a buffing process as a processing method to smooth a polished object having a curved surface, for example, a painted surface of a vehicle body such as a vehicle (for example, PTL 1). The buffing process is a method that applies various kinds of abrading agents or the like to a peripheral area (a surface) of a grinding wheel (a buff) made of any material including a cloth and rotates the grinding wheel to polish an object to be polished.

However, the buffing process cannot remove an undulation of a surface of the polished object; therefore, it was difficult to achieve beautiful surface finish.

In response to this, the inventors have proposed a polishing method that can remove an undulation of a surface of a polished object having a curved surface (see PTL 2).

CITATION LIST

Patent Literature

PTL 1: JP 2012-251099 A

PTL 2: JP 2016-47566 A

SUMMARY OF INVENTION

Technical Problem

A method of PTL 2 uses a polishing pad having a polishing surface formed of a hard resin layer; therefore, especially when a comparatively soft concave curved surface such as a coated film is polished, reducing polishing scratches becomes an object.

A first object of the present invention is to provide a polishing method that can reduce polishing scratches even when a polished surface is a comparatively soft concave curved surface such as a coated film.

Meanwhile, when polishing with polishing slurry (slurry containing abrasives) is performed using a polishing pad made of a porous material having an interconnected cell structure such as foamed polyurethane, the slurry soaks through the polishing pad and the soaked slurry disperses, and therefore the slurry is not used for polishing, causing a problem of low usage efficiency of the slurry.

A second object of the present invention is to provide a polishing pad featuring usage efficiency of slurry higher than that of the conventional product as a polishing pad used for polishing with polishing slurry.

Solution to Problem

To achieve the first object, a polishing method as a first aspect of the present invention features having the following configurations (1) to (3).

(1) A disc-shaped polishing pad is used. The polishing pad has a peripheral surface at a polishing surface side in an axial direction of the disc. The peripheral surface is a tapered surface having a diameter reduced to the polishing surface. An angle formed by the peripheral surface at the polishing surface side and the polishing surface is 125° or more and less than 180°.
(2) The used polishing pad has hardness of 40 or more. The hardness is hardness (hereinafter referred to as “C hardness”) immediately after a pressing surface is in close contact by a testing method specified in an appendix 2 of JIS K7312: 1996, “Spring Hardness Test Type C Testing Method”.

This testing method uses a spring hardness testing machine having a structure that indicates a distance of an indenter protruding from a hole at a center of the pressing surface by spring pressure being pressed to return by a test specimen when the pressing surface of the testing machine is brought into close contact with a surface of the test specimen by scale as the hardness. The measured surface of the test specimen has a size at least equal to or more than the pressing surface of the testing machine.

(3) Slurry containing abrasives is supplied to a polished surface (a surface of a polished object) larger than the polishing surface. The polishing surface is pressed against the polished surface and the polishing pad is moved to polish the polished surface.

The polishing method having the configuration (3) is likely to generate a polishing scratch on the polished surface compared with a polishing method where a polished surface is smaller than a polishing surface.

To achieve the first object, a polishing method as a second aspect of the present invention features having the configurations (2) and (3) and the following configuration (4).

(4) The polishing pad has a disc shape, and a peripheral surface at the polishing surface side in an axial direction of the disc is an arc surface.

To achieve the first object, a polishing method as a third aspect of the present invention features having the following configurations (11) to (13).

(11) Slurry containing abrasives is supplied to a polished surface (a surface of a polished object).

(12) A polishing pad has hardness of 40 or more and 80 or less is used. The hardness is hardness (hereinafter referred to as “C hardness”) immediately after a pressing surface is in close contact by a testing method specified in an appendix 2 of JIS K7312: 1996, “Spring Hardness Test Type C Testing Method”.

This testing method uses a spring hardness testing machine having a structure that indicates a distance of an indenter protruding from a hole at a center of the pressing surface by spring pressure being pressed to return by a test specimen when the pressing surface of the testing machine is brought into close contact with a surface of the test specimen by scale as the hardness. The measured surface of the test specimen has a size at least equal to or more than the pressing surface of the testing machine.

(13) A polishing surface is pressed against the polished surface and the polishing pad is moved to polish the polished surface.

To achieve the second object, a polishing pad as a fourth aspect of the present invention features the following. The polishing pad is a polishing pad used for polishing with polishing slurry. A water stop portion is formed at a part of or an entire surface.

Advantageous Effects of Invention

According to the polishing methods of the first to the third aspects of the present invention, even when the polished surface is a comparatively soft concave curved surface such as a coated film, polishing scratches can be reduced.

According to the polishing pad of the fourth aspect of the present invention, usage efficiency of the slurry becomes higher than a conventional product in which a water stop portion is not formed.

