JPS63235337A - Biaxially oriented polyester film - Google Patents

Abstract

PURPOSE:To obtain the title film low in a content of voids and excellent in lubricity, chipping resistance and scratching resistance, by adding specified spherical silica particles and other inert inorganic particles to a polyester. CONSTITUTION:An unstretched film is obtained by melt-extruding a polyester of an intrinsic viscosity of 0.4-0.9, produced by adding 0.005-2wt.% spherical silica particles (A) having an average particle diameter of 0.4-3mum, a particle diameter ratio (major diameter/minor diameter) of 1.0-1.2 and a relative standard deviation of the formula <=0.5 and 0.5-2wt.% other inert inorganic microparticles (B) (e.g., kaolin) of an average particle diameter in the range of 0.05-2.9mum (<= that of component A) to the reaction system during esterification or polycondensation into a film. This film is stretched in one direction in a temperature range (T1) from the glass transition temperature (Tg) minus 10 to (Tg+45) deg.C, and in the other direction in a temperature range from (T1+5) deg.C to (T1+40) deg.C, and heat-set at 180-250 deg.C.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a biaxially oriented polyester film, more specifically, it contains specific spherical silica fine particles and spherical inert inorganic fine particles of smaller particle size, and has excellent slip properties. This invention relates to a biaxially oriented polyester film with excellent scratch resistance and crack resistance.

[Prior Art] Polyester films, represented by polyethylene terephthalate films, have excellent physical properties.

Because of its chemical properties, it is used in a wide range of applications, such as magnetic tape, capacitors, photography, and packaging.

It is used for OHP etc.

In a polyester film, its slipperiness and abrasion resistance are major factors that determine the workability of the film manufacturing process and processing process in each application, as well as the quality of the product.

If these are insufficient, for example, when applying a magnetic layer to the surface of a polyester film and using it as a magnetic tape,
The friction between the coating roll and the film surface during application of the magnetic layer is intense, and the film surface is also severely abraded due to this, and in extreme cases, wrinkles, scratches, etc. may occur on the film surface.

Furthermore, even after slitting a film coated with a magnetic layer and processing it into audio, video, or computer tape, there are many guide parts, playback heads, etc. when pulling it out from a reel or cassette, winding it, or other operations. Significant abrasion occurs between the polyester film, causing scratches and distortion, and furthermore, the surface of the polyester film is scratched and a white powdery substance is deposited, which is often a major cause of missing magnetic recording signals, that is, dropouts.

Generally, to improve the slipperiness of a film, a method is adopted in which the contact area between guide rolls, etc. is reduced by adding unevenness to the film raw material.
01) A method in which inert fine particles are precipitated from a polymeric catalyst residue using a film raw material, and 01) A method in which inert fine particles are added. Generally speaking, the larger the size of the fine particles in these raw polymers, the greater the effect of improving slipperiness. Since this itself can cause defects such as dropouts, the unevenness of the film surface must be as m and w as possible, and there are currently demands to satisfy these contradictory characteristics at the same time. be.

In addition, in a film made of polyester containing the above-mentioned inert fine particles, peeling occurs at the boundary between the fine particles and the polyester due to biaxial stretching, and voids are formed around the fine particles. The larger the particle is, the larger the void is.
The shape becomes larger when the shape is more spherical than plate-like, when the fine particles are a single particle and are less likely to deform, when the unstretched film is stretched, the stretching area magnification is higher, and when stretching is carried out at a lower temperature. As these voids get larger, the shape of the protrusions becomes gentler, increasing the coefficient of friction, and small I (scratches) on the voids of the biaxially oriented polyester film that occur during repeated use also cause particles to fall off. This reduces durability and causes the generation of shavings. It has traditionally been common practice to add IN or two or more (a combination of large particles and small particles) of calcium carbonate, titanium oxide, kaolin, etc. as inert particles (JP-A-51-34272.52- 7895
3. 52-78954, 53-41355.53-
No. 71154), these fine particles form large voids, which causes the above-mentioned problems, and also results in a film with poor scratch resistance, and improvements in this problem are desired.

[Purpose of the Invention] The present inventor has solved these disadvantages, and has improved the slipperiness and abrasion resistance of the film by reducing the voids around the inert particles and making the film surface moderately rough. The present invention was developed as a result of intensive studies to obtain a biaxially oriented polyester film with surface characteristics suitable for the intended use.

Therefore, an object of the present invention is to provide a biaxially oriented polyester film with small voids and excellent slipperiness, abrasion resistance, and scratch resistance.

[Configuration and Effects of the Invention] According to the present invention, an object of the present invention is to
Contains 0.005 to 2% by weight of spherical silica particles with an average particle diameter of 0.4 to 3 μm and a particle size ratio (major axis/minor axis) of 1.0 to 1.2 as the first component. And the second
As a component, the average particle size is smaller than the first component, but 0.05~
Other inert inorganic fine particles in the range of 2.9μm are 0.5
This is achieved by a biaxially oriented polyester film characterized in that the content is greater than 2% by weight and less than 2% by weight.

Here, the major axis and minor axis of the spherical silica particles are determined using an electron microscope, for example, after depositing metal on the particle surface.
It is determined from an image magnified 10,000 to 30,000 times, and the average particle size/particle size ratio is determined by the following formula.

Average particle diameter 2 Sum of area equivalent diameters of measured particles / Number of particle diameter ratio of measured particles = Average major diameter of silica particles / Average minor diameter of core particles The polyester in the present invention has an aromatic dicarboxylic acid as the main acid component, It is a polyester whose main glycol component is aliphatic glycol.

Such polyesters are substantially linear and have film forming properties, particularly by melt molding. Examples of aromatic dicarboxylic acids include terephthalic acid,
Examples include naphthalenedicarboxylic acid, isophthalic acid, diphenylethanedicarboxylic acid, diphenyldicarboxylic acid, diphenyletherdicarboxylic acid, diphenylsulfonedicarboxylic acid, diphenylketonedicarboxylic acid, anthracenedicarboxylic acid, and the like. Examples of aliphatic glycols include ethylene glycol, trimethylene glycol, and tetramethylene glycol.

Examples include alkylene glycols having 2 to 10 carbon atoms such as pentamethylene glycol, hexamethylene glycol, decamethylene glycol, etc., alicyclic diols such as polyethylene glycol, and cyclohexane dimetatool.

In the present invention, polyesters containing, for example, alkylene terephthalate and/or alkylene naphthalate as main constituents are preferably used.

Among such polyesters, for example, not only polyethylene terephthalate and polyethylene-2,6-naphthalate, but also terephthalic acid and/or 2,6-naphthalenedicarboxylic acid account for 80 mol% or more of the total dicarboxylic acid component, and all glycol Preference is given to copolymers in which 80 moles or more of the component is ethylene glycol, in which case up to 20 mole % of the total acid component can be the above-mentioned aromatic dicarboxylic acids other than terephthalic acid and/or naphthalene dicarboxylic acid, and for example Aliphatic dicarboxylic acids such as adipic acid, sepatic acid, etc.; cyclohexane-1,4-
It can be an alicyclic dicarboxylic acid such as dicarboxylic acid. 20 mol% or less of the total glycol component is
It can be any of the above glycols other than ethylene glycol, or for example hydroquinone, resorcinol, 2
．． Aromatic diols such as 2-bis(4-hydroxyphenyl)propane; aliphatic diols containing an aromatic ring such as 1,4-dihydroxymethylbenzene; polyalkylene glycols such as polyethylene glycol, polypropylene glycol, and polytetramethylene glycol; Polyoxyalkylene glycol) and the like can also be used.

In addition, the polyester used in the present invention contains a dicarboxylic acid component and a component derived from an oxycarboxylic acid such as an aromatic oxyacid such as hydroxybenzoic acid; an aliphatic oxyacid such as ω-droxycaproic acid; Those copolymerized or combined in an amount of 20 mol % or less based on the total amount of carboxylic acid components are also included.

Furthermore, the polyester in the present invention contains a trifunctional or higher functional polycarboxylic acid or a polyhydroxy compound, such as trimellitate, in a substantially linear amount, for example, 2 mol % or less based on the total acid component. Also included are those copolymerized with acids, pentaerinlitol, and the like.

The above polyester is known per se, and can be produced by a method known per se.

The above polyester has an intrinsic viscosity of about 0.4 measured as a solution in 0-thaloloyenol at 35°C.
~0.9 is preferred.

The biaxially oriented polyester film of the present invention has many fine protrusions on its surface.

According to the present invention, these many fine protrusions are dispersed in the polyester, and a large number of contained spherical silica particles (first component) and other inert inert fine particles (second component) having a smaller particle size are dispersed in the polyester. derived from ingredients).

The polyester containing these inert particles dispersed is usually produced at any time during the reaction to form the polyester, such as during the transesterification reaction or polycondensation reaction when using the transesterification method, or at any time during the polycondensation reaction when using the direct polymerization method. It can be produced by adding spherical silica particles and other inert R fine particles individually or together (preferably as a slurry in glycol) into the reaction system at the time of . Preferably, these inert fine particles are added to the reaction system at the beginning of the polycondensation reaction, for example, until the intrinsic viscosity reaches about 0.3.

In the present invention, the spherical silica particles as the first component dispersed in the polyester have an average particle size of 0.4 to 3 μm.
These are silica particles having a particle size ratio (major axis/breadth axis) of 1.0 to 1.2. These spherical silica particles have individual shapes that are extremely close to true spheres, and the silica particles conventionally known as lubricants are either ultra-fine platform particles of about 10 mμ, or aggregates of these particles have a diameter of about 0.5 μm. It is characterized by a marked difference from the formation of aggregates (agglomerated particles).

The average particle diameter of the spherical silica particles is preferably 0.5 to 2.
It is 0 μm, more preferably 0.6 to 1.5 μm.

If the average particle size is less than 0.4 μm, the effect of improving slipperiness, abrasion resistance, and scratch resistance is insufficient, which is undesirable. If the average particle size exceeds 3 μm, the film surface becomes too rough. The particle size ratio of the spherical silica particles is preferably 1.0 to 1.15°, more preferably 1.
．． It is 0 to 1.1.

In addition, it is preferable that the spherical silica particles have a sharp particle size distribution, and the relative standard deviation representing the steepness of the distribution is 0,
This relative standard deviation, which is preferably 5 or less, more preferably 0.4 or less, particularly 0.3 or less, is expressed by the following formula.

Relative standard deviation = where, Di; area circle equivalent diameter of individual particle (μm) D =
Average diameter equivalent to sum of surface areas (=(Σ Di)/n) (μm) i=1 n: represents the number of particles measured.

When spherical silica particles with a relative standard deviation of 0.5 or less are used, since the particles are spherical and have an extremely steep particle size distribution, the height of the large protrusions on the film surface becomes extremely uniform, and furthermore, the height of the large protrusions on the film surface becomes extremely uniform. The large protrusion has a very sharp protrusion shape because the voids around the lubricant are small.
Therefore, even with the same number of large protrusions, the slipperiness is extremely good compared to those using other lubricants.

The spherical silica particles are not limited in any way, including the manufacturing method, as long as the above-mentioned conditions are satisfied. For example, spherical silica particles can be formed by ethyl orthosilicate [S t (OC2H!
From the hydrolysis of hydrated silica [3i (O
H) a ] Monodisperse spheres are created, and this hydrous silica monodisperse region is further dehydrated to form silica bonds [=Si-0-8t
It can be produced by three-dimensionally growing microorganisms (Journal of the Chemical Society of Japan' 81. No. 9°P, 1503).

S i (OC2Ha) a +4
H20→S i (OH) 4 +4C2H! l
OH-:S i -OH+ HO-3i =→=
S i OS i =+820 In the present invention, the amount of spherical silica particles added as the first component must be 0.005 to 2% by weight, preferably 0.01 to 1% by weight, based on the polyester. ,
More preferably, it is 0.02 to 0.5% by weight. If the amount added is 0.005% by weight without grooves, the effect of improving slipperiness and abrasion resistance will be insufficient, while if it exceeds 2% by weight, the film will break frequently, which is not preferable.

In the present invention, other inert particles as the second component to be dispersed and contained in the polyester are particularly limited as long as they have an average particle diameter smaller than that of the first component but within the range of 0.05 to 2.9 μm. Examples of other inert inorganic fine particles that are not used include calcium carbonate.

Magnesium carbonate, kaolin, clay, bentonite,
Titanium oxide, porous silica, barium sulfate.

Examples include calcium titanate, barium titanate, fluorite, barium chromate, glass peas, and the like. These can be used alone or in combination of two or more.

The average particle size of such inert inorganic fine particles is 0.1 to 1.9μ.
In order to obtain particles with a predetermined average particle size, which is preferably 0.1 to 1.4 μm, conventionally known particle preparation methods can be used, such as pulverization and 1-class preparation. It is preferable to perform the above steps to obtain a particle size distribution with a predetermined average particle size of 9.

In the present invention, the content of inert inorganic fine particles as the second component is more than 0.5% by weight based on the polyester.
It is necessary to make the proportion less than 0.5% by weight, preferably 0.5
More than 1.5% by weight and 0.6 fiJ
It is 1% to 1% by weight. This content is 0,005% by weight
If it is less than that, the effect of improving slipperiness and abrasion resistance will be insufficient.
On the other hand, if it exceeds 2% by weight, the film will frequently break, which is not preferable.

The biaxially oriented polyester film of the present invention can be manufactured according to the conventional methods for manufacturing biaxially oriented films.
For example, polyester containing spherical silica particles and other inert inorganic fine particles is melt-cast to form an amorphous unstretched film, and then the unstretched film is biaxially stretched, heat-set, and as required. If so, it is produced by a relaxation heat treatment. At this time, the surface properties of the film vary depending on the particle size, amount, etc. of the spherical silica particles and other inert fine particles, and also depending on the stretching conditions, so they are appropriately selected from conventional stretching conditions. In addition, the density, thermal shrinkage rate, etc. change depending on the temperature, magnification, speed, etc. during stretching and heat treatment.For example, the stretching temperature is 1.
The stage stretching temperature (e.g. longitudinal stretching temperature 2T1) is ('f
'g-10) to (Tg+45>'C range (however, T
g: glass transition temperature of polyester), the second-stage stretching temperature (for example, lateral stretching temperature 2 T2) is (T1+5) ~
It is recommended to select from the range of (T1+40)'C, and
The stretching ratio is preferably selected from a range in which the uniaxial stretching ratio is 2.5 or more, especially 3 times or more, and the area magnification is 8 times or more, especially 10 times or more.Furthermore, the heat setting temperature is 18
It is preferable to select from the range of 0 to 250°C, more preferably 200 to 230°C.

The biaxially oriented polyester film of the present invention has smaller voids than conventional films, and is characterized by smaller voids, especially around the spherical silica particles. The reason why the voids around the spherical silica particles are small is because the spherical silica particles have a good affinity for polyester, and because the particles themselves are very close to true spheres, the stress around the lubricant propagates evenly during stretching, allowing the polyester to bond with the polyester. It is presumed that this is because stress is not concentrated on a part of the lubricant interface.

In the present invention, the distribution of large protrusions formed on the surface of the polyester film is extremely uniform due to the addition of spherical silica particles whose particle size distribution is extremely sharp.
A polyester film with uniform protrusion heights can be obtained. By further containing inert inorganic fine particles in this film, it is possible to further improve the slipperiness while maintaining the abrasion resistance.

The biaxially oriented polyester film of the present invention has uniform uneven surface characteristics, excellent slipperiness and abrasion resistance, and is characterized in that it generates significantly less scum, white powder, and the like. Taking advantage of these characteristics, this biaxially oriented polyester film can be widely used in a variety of applications4.For example, when used as a base film for magnetic recording, such as video, audio, and computer applications, it exhibits excellent electromagnetic conversion properties. , slipperiness, running durability, etc. can be obtained.

It also has a low coefficient of friction when used in capacitor applications.

Excellent windability, low crushing load, high transparency, etc. can be obtained. As mentioned above, this biaxially oriented polyester film is preferably used as a base film for magnetic recording media, particularly as a base film for magnetic tapes, but is also suitable for use in electrical applications, packaging applications, vapor deposition films, etc. It can be widely applied to other fields as well. Furthermore, the biaxially oriented polyester may be subjected to surface treatment such as easy adhesion treatment (for example, easy adhesion layer coating, corona treatment, etc.) on one or both sides, and may also be treated with antistatic agents, ultraviolet absorbers, colorants, etc. It may also contain a third component.

[Example] The present invention will be further explained below with reference to Examples.

Note that various physical property values and characteristics in the present invention were measured as follows.

rl+ Particle size of spherical silica particles There are the following conditions for particle size measurement.

1) When determining the average particle size, particle size ratio, etc. from powder 2) When determining the average particle size, particle size ratio, etc. in a film.

1) In the case of powder, scatter the powder on an electric sample stage so that the individual particles do not overlap as much as possible, and form a thin gold film vapor deposited layer on the surface using a gold sputtering device to a thickness of 200 to 300 people. For example, 10,000 to 30,00 with a scanning electronic closed microscope.
Observe at 00x magnification and use Luzex 500 manufactured by Nippon Regulator ■ to determine the long diameter (Dl) of at least 100 particles.
i), determine the minor axis (Dsi) and area circle equivalent diameter <Di). Then, with the number average value expressed by these following formulas, the major axis (D I ) and the minor axis (Ds) of the silica particles are
, represents the average particle size (D).

n
nDI=(Σ D Ii) /n, D s = (Σ
Dsi) / n1 = 1 i = 1 D = (Σ D i ) / n 1 = 1 2) In the case of particles in a film, a small piece of sample film was fixed on a scanning electron microscope sample stage and sputtered by JEOL ■. Equipment (JFC-110
0 type ion sputtering device) is used to perform ion etching on the film surface under the following conditions.The four conditions are to place the sample in a Pel jar, increase the degree of vacuum to approximately 10''3 Torr, and apply a voltage of 0. 25KV, current 1.
25 Perform ion etching at IIA for about 10 minutes. Furthermore, gold sputtering is applied to the surface of the film using the same equipment, and the film is stained with gold sputtering using a scanning electron microscope.
Observe at 00x magnification and measure the long diameter of at least 100 particles (D Ii
), the short axis (DSi), and the area circle equivalent diameter (Di). The following steps are carried out in the same manner as in 1) above.

(2) Particle size, etc. of inorganic particles other than silica particles 1) Average particle size CP-SO type Centrif Nigel Particle Size Analyzer (Centrifuaal
Particle 5iza Analyser)
The particle size corresponding to 50 mass percent is read from the integrated curve of particles of each particle size and their abundance calculated based on the obtained centrifugal sedimentation curve, and this value is calculated as the above average particle size. (See Book Particle Size Measuring Techniques, Nikkan Kogyo Shimbun, 1975, pp. 1, 242-247).

2) Particle size ratio A small piece of the film is fixedly molded using an epoxy resin G trowel, and an ultra-thin section (cut parallel to the direction of film flow) with a thickness of approximately 600 mm is created using a microtome. The cross-sectional shape of the glides 1 (particles) in the film was observed using a transmission electron microscope (manufactured by Hitachi, Ltd., model I-800), and expressed as the ratio of the long axis of the slick E to the short axis.

3) Measure the relative standard deviation value in the same way as for silica particles (~), and for non-spherical particles, calculate the volume from the particle size ratio of f electrons, and calculate the volume from the particle size ratio of f electrons. The diameter at that time is taken as the particle size, and the relative standard deviation value is calculated.

(3 film surface roughness Ra) This is the value defined in JIS-BO601 as center i average roughness Ra), and in the present invention C
C) Measure 1. The measurement conditions are as follows.

(a) Stylus tip radius = 2μm (b) Measuring pressure: 30mm (C) Cutoff: 0.25+m (d) Measuring length: 0.5mm (e) How to summarize the data - Repeat 5 times for the same sample Measure and set the largest value to 1
The average value of the remaining four data is rounded off to the fourth decimal place and displayed to the third decimal place.

(4) Void ratio in the film (surface) according to the method (1)-2) above.
The area around the lubricant is exposed, and the major axis of at least 50 solid particles and the major axis of the voids are measured, and the void ratio is expressed as the number average value of the void ratio determined by the following formula: void ratio = major axis of void / major axis of solid fine particles.

(5) Film friction coefficient (μk) In an environment with a temperature of 20°C and a humidity of 60%, a film cut into medium 1/2 inch pieces was held at a fixed rod (surface roughness 0.2 μm) at an angle θ = (152
/18G) in contact at π radians (152°) 2 per minute
Move (friction) at a speed of 00 cm. The exit tension (Tz: g) when the tension controller is adjusted so that the entrance tension T1 is 35 g is detected by the exit tension detector after the film has traveled 90 m, and the running wear coefficient μk is calculated using the following formula.

μ = (2,303/θ) loQ (T2 /
'T'1)=0.868 log(Tz/35)(6
1. Abrasion resistance The abrasion resistance of the running surface of the base film is evaluated using a 5-stage mini super calendar. The calendar is a 5-stage calendar with nylon rolls and steel rolls, the processing temperature is 80°C, and the linear pressure applied to the film is 200 kg.
/ cm, and the film speed was 50 m/min. After running the running film for a total length of 2000 m, the abrasion resistance of the base film was evaluated based on the dirt that adhered to the top roller of the calendar.

4-level judgment> ◎: No stains on the nylon roll ○: Almost no stains on the nylon roll ×: Stain on the nylon roll × × = Severe stain on the nylon roll (a) A film cut to a scratch judgment width of 172 inches was tested as described above. (Using a palm friction coefficient measuring device No. 51, it was placed in contact with a fixed rod at an angle of 152°, was run for 10 m at a speed of 203/Sec, and after repeating this 50 times, the 1/2 inch wide base film The thickness, depth, and number of scratches on the surface are evaluated in the following five stages.

◎ No scratches observed on 1/2 inch wide base film 0 Almost no scratches observed on 1/2 inch medium base film Δ Scratches observed on 1/2 inch wide base film (No scratches observed on 1/2 inch wide base film) × Several thick scratches are observed on the 1/2 inch wide base film xx Many thick and deep scratches are observed all over the 1/2 inch wide base film Comparative Examples 1 to 6 Dimethyl terephthalate and ethylene glycol , polymerization was carried out by a conventional method using manganese acetate as a transesterification catalyst, antimony trioxide as a polymerization catalyst, phosphorous acid as a stabilizer, and inorganic fine particles shown in Table 1 as a lubricant, and the intrinsic viscosity (orthochlorophenol, 35℃)0.
62 polyethylene terephthalate was obtained.

This polyethylene terephthalate pellet was heated to 170°C.
, after drying for 3 hours, fed to the extruder hopper, melting temperature 28
The molten polymer is melted at 0 to 300°C.
The surface finish is about 0.3 S through the slit die.
Extruded onto a rotating cooling drum with a surface temperature of 20℃, 290μ
An unstretched film of m was obtained.

The unstretched film thus obtained was preheated at 75°C, and further heated between low speed and high speed rolls with one IR heater with a surface temperature of 900°C from above 15III, and stretched to 3.6°C. The film was then rapidly cooled, then supplied to a stenter and stretched 3.7 times in the transverse direction at 105°C. The obtained biaxially oriented film was heat set at a temperature of 205° C. for 5 seconds to obtain a heat set biaxially oriented film having a thickness of 15 μm.

The properties of these films are shown in Table 1.

Examples 1 to 8 and Comparative Example 7 Except for using spherical silica (manufactured by Nippon Shokubai Kagaku Kogyo ■) as the first component and other inert inorganic fine particles as the second component, which are not shown in Table 2, instead of kaolin. A biaxially oriented polyester film was obtained in the same manner as in Comparative Example 1.

The properties of these films are shown in Table 2.

According to Table 2, by using spherical silica particles as the first component, the scratch resistance of the film with a high concentration of the second component was improved, and the runnability and abrasion resistance were improved.

It can be seen that a film with excellent scratch resistance can be obtained.

Claims (1)

[Claims] 1. As the first component in polyester, the average particle size is 0.4.
~3 μm and particle size ratio (major axis/breadth axis) of 1.0 to 1
．． Other inert materials containing 0.005 to 2% by weight of spherical silica particles, and having an average particle size smaller than that of the first component but in the range of 0.05 to 2.9 μm as the second component. A biaxially oriented polyester film containing inorganic fine particles in a proportion of more than 0.5% by weight and less than 2% by weight. 2. The biaxially oriented polyester film according to claim 1, wherein the relative standard deviation of the spherical silica particles expressed by the following formula is 0.5 or less. Relative standard deviation = ▲There are mathematical formulas, chemical formulas, tables, etc.▼ Here, Di: Area circle equivalent diameter of each particle (μm) @D@: Average value of area circle equivalent diameter ▲ There are mathematical formulas, chemical formulas, tables, etc.▼ (μm) n: represents the number of particles. 3. The biaxially oriented polyester film according to claim 1 or 2, wherein the other inert fine particles are at least one selected from the group consisting of kaolin, bentonite, titanium oxide, calcium carbonate, and porous silica. .