JPH0543717A - Abrasive sheet and its production - Google Patents

Abstract

PURPOSE:An abrasive sheet produced by holding abrasive grains having a specific average particle diameter on the surface layer of an aromatic polyimide film in the state that a part of each particle is embedded and that many projections comprising the partially exposed abrasive grains are formed over the whole region, and reduced in the amount of the expensive abrasive grains used. CONSTITUTION:An aromatic polyamic acid solution is extruded from a polymer-feeding opening 9 on a support 15 through an extrusion die 10, and the formed thin film 4 is thermally dried with a heater 5 in a casting oven 6 to obtain an aromatic polyamic acid film 4'. The film 4' is dipped in a dispersion 8 comprising an organic solvent and abrasive grains homogeneously dispersed in the solvent to coat the surface of the film. The film is dried in a drying region 14 and treated at a high temperature with a heater 11 in a curing oven 13 to imidate the polymer, followed by winding up on a roll 30 to obtain the abrasive sheet 1 in which the abrasive grains having an average particle diameter of 0.1-100mum are held on the surface layer of the aromatic polyimide film in the state that the abrasive grains are partially embedded in the layer and that many projections in a rate of 1-5X10<7> projections/mm over the whole region of the film are formed from the partially exposed abrasive grains.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The first invention of the present application is summarized as follows.
Abrasive grains are held by embedding a part of each grain in the surface layer of the aromatic polyimide film, and a large number of protrusions of the partially exposed abrasive grains are formed uniformly over the entire surface layer of the film. The present invention relates to a flexible abrasive sheet made of a heat-resistant aromatic polyimide film.

Since the polishing sheet of the present invention does not use any binder resin or the like, a large number of abrasive grains directly and firmly hold a part of each particle by the polyimide resin of the surface layer thereof. The partially exposed abrasive grains forming a large number of protrusions fully utilize the characteristics of the particles, and the binder resin, etc., which has conventionally deteriorated the heat resistance, is not used. It is possible to make full use of the high level of heat resistance and mechanical properties inherent to the group polyimide film.

The second invention of this application is that "abrasive grains have a low boiling point on the surface of a" self-supporting film composed of an aromatic polyamic acid and an organic polar solvent "formed from an aromatic polyamic acid solution. Of the dispersion liquid uniformly dispersed in the organic solvent, and the coating layer of the dispersion liquid is dried,
Further, the self-supporting film is heat-treated at a high temperature to reproducibly produce a flexible polishing sheet made of an aromatic polyimide film having "a large number of protrusions consisting of the partially exposed abrasive grains" uniformly. Involved in the method.

The polishing sheet of the present invention is an aromatic polyimide film in which a large number of projections of exposed abrasive grains are formed without using a binder or the like while maintaining high heat resistance, and the initial polishing property is Is an excellent flexible polishing sheet.

[0005]

Description of the Prior Art Since aromatic polyimide films have high heat resistance and mechanical properties, it has been proposed that they can be used as a flexible polishing sheet in which abrasive particles are mixed in a specific polyimide film. .. (Japanese Patent Laid-Open No. 62-74577) However, since the above-mentioned polishing sheet has abrasive grains mixed therein, extremely expensive abrasive grains (for example, diamond abrasive grains and the like) are not included. There is a problem that it is wasted without being used for polishing in a considerable proportion.

As a method of imparting abrasiveness to one surface of the film, a polymer (binder resin) solution containing abrasive grains is applied to the surface of the film and dried, and the abrasive grains are attached to the film with a binder. A method of making an abrasive sheet is practiced. In this known coating method, the adhesiveness between the binder layer and the aromatic polyimide film may not always be sufficient, or the heat resistance may decrease due to the binder,
Further, since it is difficult to uniformly form a coating layer composed of abrasive grains and a binder, there is a problem that the flatness of the film is considerably lowered.

Further, in the above-mentioned method of attaching the abrasive grains using the known binder to the film surface, the abrasive grains are easily aggregated by the influence of the binder resin, and moreover, the peripheral surface of the particles is coated with the binder resin. Therefore, there is a problem that the abrasiveness of the abrasive grains is not sufficiently reflected from the beginning when used for polishing.

[0008]

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention The object of the present invention is to "expose on the surface of an aromatic polyimide film without being coated with a resin component, which does not have the problems in the above-mentioned known ones. Many projections made of fine abrasive grains
The present invention is to newly provide a heat-resistant polishing sheet which is uniformly formed over the entire surface, and further to provide an industrial manufacturing method for the polishing sheet.

[0009]

The first invention of this application is that the average particle size of the aromatic polyimide film is 0.
Abrasive grains having a size of 1 to 100 μm are held by embedding a part of each grain, and a large number of exposed protrusions of the abrasive grains are formed over the entire surface layer of the film.
The polishing sheet is characterized by being uniformly formed at a rate of 5 × 10 ⁷ pieces / mm ² .

The second invention of this application is that an aromatic polyamic acid solution is cast on a support to form a thin film of the solution, and the thin film on the support is dried to form an aromatic polyamic acid and an organic compound. A self-supporting film consisting of a polar solvent is formed, then the film is peeled off from the support, and the surface of the film has an average particle size of 0.1 to 100.
A dispersion liquid in which abrasive particles having a diameter of μm are uniformly dispersed in an organic solvent having a low boiling point is applied, and a coating layer of the dispersion liquid is dried to retain fine abrasive particles on the surface layer of the film. , A method for producing an abrasive sheet, characterized in that the self-supporting film is heat-treated at a high temperature.

Hereinafter, the present invention will be described in more detail with reference to the drawings. FIG. 1 is a sectional view showing an example of the polishing sheet of the present invention. FIG. 2 is a cross-sectional view showing an enlarged portion X of FIG. FIG. 3 is a cross-sectional view schematically showing an example of a film forming apparatus used in the method for manufacturing the polishing sheet of the present invention.

The polishing sheet of the present invention has an average particle size of 0.1 to 100 μm as shown in FIGS.
m, preferably about 0.2 to 60 μm, “a large number of abrasive grains” 3 are partially embedded in the surface layer 2 of the aromatic polyimide film 1 and firmly held, and Many projections consisting of abrasive grains 3 "
5 × 10 ⁷ pieces / mm ² , preferably 2 to 5 × 10 ⁶ pieces / mm ²
A polishing sheet made of an aromatic polyimide film, which is formed uniformly at a ratio of mm ² and has an inner layer portion which is continuous with the surface layer 2 and substantially does not contain abrasive grains.

In the method of manufacturing an abrasive sheet of the present invention, for example, as shown in FIG. 3, a film forming apparatus equipped with an extrusion forming die 1 is used to apply an "aromatic polyamic acid solution" to the die 10. It is supplied and extruded as a thin film body 4 from a discharge port of a die onto a support (belt) 15 to form a thin film having a uniform thickness, and the thin film is dried in a casting furnace 6 to mostly remove the solvent. After removing and forming a self-supporting film 4'of polyamic acid, the film is peeled from the support 15, and the "abrasive-dispersed solution" is applied to the surface layer of the film to form a coating layer. Is dried, and finally, the self-supporting film 4 ″ on which the abrasive grains are held is heat-treated in the curing furnace 13 to continuously form the polishing sheet 1 of the present invention.

The aromatic polyimide forming the polishing sheet of the present invention may be a heat resistant high molecular weight polymer obtained by polymerization and imidization from an aromatic tetracarboxylic acid component and an aromatic diamine component. Examples of the aromatic tetracarboxylic acid component include 3,3 ′,
Biphenyltetracarboxylic acids such as 4,4′-biphenyltetracarboxylic acid or an acid dianhydride, 2,3,3 ′, 4′-biphenyltetracarboxylic acid or an acid dianhydride, pyromet acid or an acid anhydride thereof Examples thereof include pyromellitic acid, 3,3 ′, 4,4′-benzophenonetetracarboxylic acid or an acid dianhydride thereof.

Further, as the aromatic diamine,
Diphenyl ether-based diamine compounds such as 4,4′-diaminodiphenyl ether and 3,4′-diaminodiphenyl ether, diphenylsulfone-based diamine compounds such as 4,4′-diaminodiphenyl sulfone and 3,4′-diaminodiphenyl sulfone, o ⁻ , m ^- or p
^- and the like phenylene-based diamine compounds such as phenylenediamine.

In the present invention, the amount of (a) biphenyltetracarboxylic acids is 50 mol% or more, especially 6
An aromatic tetracarboxylic acid component containing 0 to 100 mol% and phenylenediamine or diaminodiphenyl ether are 50 mol% or more, especially 60
Aromatic diamine component containing more than mol%, or,
(B) An aromatic tetracarboxylic acid component composed of biphenyltetracarboxylic acids (containing 50 mol% or more, particularly 55 to 90 mol%) and pyromellitic acid (less than 50 mol%, particularly 10 to 45 mol%), and phenylene Aromatic diamine component containing diamine (50 mol% or more, especially 55 to 95 mol% contained) and diphenyl ether diamine (less than 50 mol%, especially contained about 5 to 45 mol%) as main components, both components equimolar polymerization And an aromatic polyimide obtained by imidization is preferable.

Examples of the abrasive grains used in the present invention include diamond abrasive grains, SiC abrasive grains (carborundum,
Suitable examples include green SiC, black SiC, etc., boron nitride abrasive grains, alumina abrasive grains, chromium oxide abrasive grains, cerium oxide abrasive grains, and the like.

In the polishing sheet of the present invention, abrasive grains are not substantially contained in the inner layer of the aromatic polyimide film which is the base film, and the film basically has the original mechanical properties and heat resistance. While, in addition, FIGS.
As shown in, the abrasive grains without using a binder,
Is firmly held on the surface layer 2 of the film 1,
Further, the abrasive grains 3 partially exposed to the outside are a novel polishing sheet in which a large number of protrusions are uniformly formed, and such a polishing sheet has never been known.

According to the method for producing the polishing sheet of the present invention, the aromatic polyamic acid solution is cast on a flat support surface such as a glass plate, a copper plate, a metal belt or the like to have a thickness of 10 to 1
A thin film of a 000 μm solution was formed, and the thin film was partially dried to form a self-supporting film composed of an aromatic polyamic acid and a residual organic polar solvent, and then the self-supporting film was peeled off. After that, on the surface of the film,
A dispersion containing abrasive particles is applied and dried to hold the abrasive particles on a self-supporting film of polyamic acid, and then subjected to heat treatment for imidization and removal of residual solvent to form a flexible polishing sheet. Done in the way you get.

In the manufacturing method of the present invention, the manufacturing steps described above can be divided into batches, and for example, as shown in FIG.
Using a film forming apparatus having an extrusion molding mechanism as shown in, by a film forming method combining a solution casting method and a coating method, the aromatic polyimide film polishing sheet described above can be continuously and reproducibly produced. The method of obtaining is preferred.

That is, in the production method of the present invention, the "aromatic polyamic acid solution" is first produced from the polymer solution supply port 9 of the extrusion die 10 by using the film production apparatus shown in FIG. Extrusion molding mechanism of the device [die 10,
Support (belt) 15, heater 5, casting furnace 6, etc.], and then the thin film 4 is wound around the pair of drive wheels 16 from the discharge port of the die 10 and is rotated. The thin film 4 on the upper surface of the support 15 is continuously extruded on the upper surface of a smooth support 15 (metal belt or the like) by a heater or a hot air blowing device 5 inside the casting furnace 6. It is appropriately dried on the body to remove most of the solvent to form a self-supporting film 4 ′, and then the self-supporting film 4 ′ is peeled off from the support to prepare a self-supporting film (aromatic polyamic acid). Film) is formed.

The polyamic acid solution may be composed of an aromatic polyamic acid (aromatic polyimide precursor) obtained from an aromatic tetracarboxylic acid component and an aromatic diamine component and an organic polar solvent. And
The polymer solution has an aromatic polyamic acid content of 5
It is preferably about 40 to 40% by weight, particularly about 10 to 30% by weight.

The above-mentioned polyamic acid solution has a "solution viscosity (rotational viscosity)" of about 50 to 10000 poises, particularly about 100 to 6000 poises at the temperature of discharge from the extrusion die 10 during the above-mentioned extrusion molding. Preferably.

The aromatic polyamic acid used in the above polyamic acid solution has a logarithmic viscosity of the polymer (measurement temperature: 30 ° C., concentration: 0.5 g / 100 ml solvent, and solvent: N-methyl-2-pyrrolidone). But about 0.5
-6, especially 1.0-5, and more preferably about 1.5-4.

The organic polar solvent used in the polyamic acid solution is, for example, N-methyl-2-pyrrolidone, N, N-dimethylacetamide, N, N-diethylacetamide, N, N-dimethylformamide, N,
Examples thereof include amide-based organic solvents such as N-diethylformamide, or mixed solvents containing them as a main component.

The temperature of the aromatic polyamic acid solution discharged from the extrusion die during the above-mentioned extrusion molding is 0 to 15
0 ° C, particularly 5 to 100 ° C, more preferably 10 to 80
C., and the temperature at which the thin film on the support is dried (casting temperature) after the polymer solution is discharged may be about 50 to 180.degree. C., especially about 80 to 150.degree. C. The drying time is preferably 1 to 60 minutes, particularly 5 to 30 minutes.

The above polyamic acid self-supporting film has an imidization ratio of the polymer contained of about 0-8.
When the film is continuously peeled from the support, the content of the solvent is about 0%, particularly about 5 to 70%, the solvent content is about 5 to 60% by weight, and particularly about 10 to 50% by weight.
And, in the next coating / drying process of the dispersion liquid of abrasive grains,
It is sufficient that the film has such strength that the film is not easily broken.

In the production method of the present invention, as shown in FIG. 3, abrasive grains are uniformly dispersed in an organic solvent in the surface layer of the self-supporting film 4'of polyamic acid produced as described above. The dispersion is coated, and the coating layer of the dispersion is dried by a suitable means in the drying area 14 to substantially remove the solvent in the coating layer, and the surface layer of the film 4 ″ is allowed to retain abrasive grains. Then, the self-supporting film 4 ″ is heat-treated at a high temperature in the curing oven 13 to imidize the polymer and substantially remove the remaining organic polar solvent to produce a polishing sheet.

The solvent used to prepare the above dispersion is
Lower alcohols such as isopropanol, n-propanol, isobutanol, n-butanol, and ethanol,
Ketone solvents such as acetone, ethyl-methyl ketone, methyl-propyl ketone, methyl-isobutyl ketone, N
Examples include amide solvents such as -methyl-2-pyrrolidone, N, N-dimethylacetamide, N, N-diethylacetamide, N, N-dimethylformamide, N, N-diethylformamide, etc., and boiling points 50 to 250.
It is preferably an organic solvent having a boiling point of about 100 to 220 ° C.

The solvent for preparing the above-mentioned dispersion liquid contains 50% by weight or more, particularly 60% by weight or more, of a good solvent capable of dissolving 5% by weight or more of polyamic acid (for example, the above-mentioned amide solvent). It is preferable that the dispersion of the polyamic acid on the surface of the self-supporting film described above is wettable and the abrasive grains are retained on the film.

In the above dispersion liquid, the concentration of the abrasive grains is preferably about 0.1 to 30% by weight, particularly about 1 to 20% by weight from the viewpoint of stability in the dispersibility of the abrasive grains. In the production method of the present invention, the dispersion liquid does not substantially agglomerate fine abrasive grains, and in order to uniformly disperse each single particle, a binder, a resin component such as a polymer are substantially contained. It is also a characteristic that the dispersion does not particularly require the binder component or the like.

The coating operation of the above-mentioned dispersion liquid is carried out at a temperature lower than the boiling point of the solvent, and is 60 ° C. or lower, particularly 0 to 50 ° C.
A gravure method, a reverse method, a dipping method (the coating operation is performed by continuously dipping the self-supporting film in the dispersion liquid 8 in the film forming apparatus of FIG. 3) at a coating temperature of a certain degree. It is preferable to use a coating method. The coating film of the above-mentioned dispersion liquid has a thickness of 0.
The thickness is preferably 5 to 100 μm, particularly preferably 1 to 80 μm.

The self-supporting film 4 "coated with the above-mentioned dispersion liquid is blown with dry hot air (heating air) in the drying area 14, is irradiated with heat rays with a heater, or is under reduced pressure (vacuum method). By a suitable drying means such as drying at about 5 to 250 ° C., especially 50 to 220 ° C. to evaporate the solvent of the coating layer of the dispersion liquid to remove substantially all of the abrasive grains. Is uniformly and firmly held on the surface of the self-supporting film in a single particle state.

In the manufacturing method of the present invention, as shown in FIG.
Self-supporting film 4 "holding abrasive grains as described above
Is passed through a curing furnace 13 in which a plurality of heaters 11 are installed to perform heat treatment to form the polishing sheet 1 of the present invention, and further cooled to room temperature (about 0 to 50 ° C.), and a guide roll It is wound on a winding roll 30 of a winding machine (not shown in the figure) having 31 or the like.

The heat treatment of the polyamic acid self-supporting film coated with the dispersion and dried at a heat treatment temperature of about 2
The heat treatment time at about 50 to 600 ° C., especially about 300 to 550 ° C., for about 1 to 60 minutes, especially about 2 to 30 minutes imidizes the polymer in the film, and the organic matter in the film. Preferred to substantially remove the solvent. In the method for producing a polishing sheet of the present invention, if the film forming apparatus shown in FIG.
The polishing sheet having the above-mentioned performance can be continuously produced at 10 m / min, particularly 0.2 to 5 m / min.

[0036]

The present invention will be described in more detail below by showing Examples and Comparative Examples of the present invention. In the examples and the like, each measurement test was performed by the following method. For the average surface roughness (Ra), a tally step surface roughness meter (manufactured by Rank Taylor Hobson) using a stylus having a conical tip with a radius of 12.5 μm, a load of 10 mg, and a roughness direction magnification of 5 The center line average roughness was measured under measurement conditions of 10,000 times to 50,000 times and a measurement length of 1 mm.

The number of fine projections is 50 with an optical or electron microscope.
Observe a photograph of the film surface taken twice or more (preferably 100 times or more), and 0.1 μ for fine projections due to abrasive grains (slippery agent) added for the purpose of roughening (sliding).
It was measured by counting the number of fine protrusion diameters of m or more.

The holding power of the abrasive particles held on the surface layer of the polishing sheet is determined by sticking a commercially available adhesive tape (cellophane tape) on the surface layer of the polishing sheet and press-bonding the adhesive tape, and then peeling off the adhesive tape. Measure the number of abrasive grains attached to the adhesive layer of the tape by observing with an optical or electron microscope,
The number of pieces / mm ² indicates the degree of holding power.

With respect to the polishing performance of the polishing sheet, the surface of fine ceramics Al ₂ O ₃ was 25
The cumulative polishing amount at the time of polishing at ° C is shown for each polishing time. Further, the folding endurance showing the flexibility of this polishing sheet was shown by the number of times the polishing sheet was folded back 180 degrees many times and the polishing sheet was partially broken.

Example 1 An aromatic tetracarboxylic acid component consisting of 3,3 ', 4,4'-biphenyltetracarboxylic dianhydride and 4,4'
An aromatic diamine component composed of diaminodiphenyl ether, N, N-dimethylacetamide (DMAC)
In an N, N-dimethylacetamide (DMAC) solution of an aromatic polyamic acid (R type) [polymer concentration: 18% by weight, logarithmic viscosity of polymer at 30 ° C .; 3.0, 30 ° C.]. Solution viscosity (rotational viscosity) at 21;
00 poise] was prepared.

Further, a dispersion liquid was prepared by uniformly dispersing diamond abrasive grains (average particle diameter: 12 μm) at a concentration of 5% by weight in a N, N-dimethylacetamide (DMAC) solvent.

The above-mentioned aromatic polyamic acid solution is extruded from the polymer solution supply port 9 using a film forming apparatus provided with an extrusion die (multi-manifold type two-layer die) as shown in FIG. It is supplied to an extrusion molding mechanism having a die 1, and the thin film 4 is discharged from the discharge port of the die 1.
At a discharge temperature of 30 ° C., a support having a smooth surface (metal belt) which is wound around a pair of drive wheels 16 and rotates.
15 is continuously extruded on the upper surface of 15 and the thin film 4 on the upper surface of the support 15 is dried in a casting furnace 6 by a heater and a hot air blowing device 5 at a temperature of about 140 ° C. for 6 minutes to obtain a self-supporting property. Film 4 '
(Solvent content: about 30-40% by weight) was formed, and then the self-supporting film 4'was peeled from the support.

As shown in FIG. 3, the self-supporting film 4'of polyamic acid was continuously immersed in the dispersion 8 at room temperature to form a coating layer of the dispersion on the surface of the film. Further, in the drying zone 14, dry air was blown onto the coating layer to dry the coating layer to substantially remove the organic solvent in the coating layer, and fine diamond abrasive grains were firmly held on the surface layer of the film. A self-supporting film 4 "of polyamic acid was formed.

Finally, the polyamic acid self-supporting film 4 "holding the fine diamond abrasive grains.
Is passed through a curing furnace 13 in which an infrared heater 11 is installed, and heat-treated for 4 minutes in a temperature range in which the temperature is raised stepwise from about 150 to 450 ° C. to form a polishing sheet 1, and Then, the polishing sheet 1 was cooled to room temperature and wound on a winding roll 30 of a winding machine 31 (the whole is not shown) to manufacture a flexible polishing sheet having a thickness of 75 μm. The film forming speed is 0.6 m
/ Min.

A tensile test was conducted on the above-mentioned abrasive sheet, and as a result, the tensile strength was 14 kg / mm ² and the elongation was 46%. Further, the surface condition of the above-mentioned polishing sheet was monitored with an electron microscope or the like, and various surface data were measured. The results are shown in Table 1. Table 1 shows the results of the abrasive property test performed at high temperature on the abrasive sheet.

Examples 2 to 3 Diamond abrasive grains having an average particle size of 35 μm (Example 2) and 70 μm (Example 3) were used, and the compounding ratio was 7 with respect to the dimethylacetamide solvent. .5 by weight% (example 2), and, in addition to a 15 wt% (example 3) a dispersion was prepared in the same manner as in example 1, respectively. Example 1 except that each dispersion was used
By the same film forming method as above, a polishing sheet made of a flexible aromatic polyimide film having a thickness of 75 μm was manufactured.

As a result of performing a tensile test on each of the above-mentioned polishing sheets, each polishing sheet was found to have almost the same tensile strength and elongation as the polishing sheet obtained in Example 1. Further, various tests similar to those in Example 1 were performed on each of the above polishing sheets, and the test results are shown in Table 1.

Example 5 An aromatic tetracarboxylic acid component consisting of 3,3 ′, 4,4′-biphenyltetracarboxylic dianhydride and an aromatic diamine component consisting of paraphenylenediamine were mixed with N,
Polymerization in N-dimethylacetamide (DMAC) at 30 ° C. to produce aromatic polyamic acid (S type) DMAC
A solution [polymer concentration: 18% by weight, logarithmic viscosity of polymer (30 ° C.); 3.5, solution viscosity at 30 ° C. (rotary viscosity); 5000 poise] was prepared.

A flexible polishing sheet was produced in the same manner as in Example 1 except that the above polyamic acid solution was used. As a result of performing a tensile test on the above-mentioned abrasive sheet, the tensile strength is 20 kg / mm ² and the elongation is 1.
It was 0%. Table 1 shows other various properties of the polishing sheet.

[0050]

[Table 1]

[0051]

In the polishing sheet of the present invention, a large number of abrasive grains are directly and firmly held by the polyimide resin of the surface layer thereof, without using any binder resin or the like. Due to the partially exposed abrasive grains, while exhibiting sufficiently high abrasivity from the initial stage, since the binder resin etc. that had reduced the heat resistance in the conventional coating type film is not used,
Aromatic polyimide film, which is the base film, is capable of fully utilizing the original high level of heat resistance, mechanical properties, flexibility, etc. Furthermore, since abrasive grains are attached only to the surface layer of the polishing sheet, This has the effect that the amount of expensive abrasive particles used can be made extremely smaller than that of conventionally known polishing sheets.

The second invention of this application is that "abrasive grains have a low boiling point on the surface of a" self-supporting film consisting of an aromatic polyamic acid and an organic polar solvent "formed from an aromatic polyamic acid solution. Of the dispersion liquid uniformly dispersed in the organic solvent, and the coating layer of the dispersion liquid is dried,
Further, by heat-treating the self-supporting film at a high temperature, a flexible polishing sheet having "a large number of protrusions composed of partially exposed abrasive grains" is produced with good reproducibility industrially or continuously. Is the way to do it.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing a part of an example of a polishing sheet of the present invention.

FIG. 2 is a cross-sectional view showing an enlarged part X of FIG.

FIG. 3 is a schematic view of a film forming apparatus used in the manufacturing method of the present invention.

[Explanation of symbols]

1: Polishing sheet 2: Surface 3: Abrasive grains 4, 4'and 4 ": Thin film (self-supporting film of polyamic acid) 6: Casting furnace 8: Dispersion liquid 10: Die for film formation 11: Heater 13: Cure furnace 14: Drying area 15: Belt 30: Winding roll

Claims (2)

[Claims] 1. Abrasive grains having an average particle size of 0.1 to 100 μm are embedded in a surface layer of an aromatic polyimide film by embedding a part of each grain, and the partially exposed abrasive grains. The polishing sheet is characterized in that a large number of projections consisting of 1 are uniformly formed at a rate of 1 to 5 × 10 ⁷ pieces / mm ² over the entire surface layer of the film. 2. A self-support comprising an aromatic polyamic acid and an organic polar solvent by casting an aromatic polyamic acid solution on a support to form a thin film of the solution and drying the thin film on the support. A transparent film is formed, and then the film is peeled off from the support, and then, on the surface of the film,
A dispersion liquid in which abrasive grains having an average particle diameter of 0.1 to 100 μm are uniformly dispersed in a low boiling point organic solvent is applied, and a coating layer of the dispersion liquid is dried to form a fine surface layer on the film. A method for producing a polishing sheet, which comprises holding abrasive grains and finally heat-treating the self-supporting film at a high temperature.