JPH07166034A - Polyester film - Google Patents

Abstract

PURPOSE:To improve the resistances to shaving and scratch of a polyester film by incorporating a fine chromium oxide powder as the lubricant into the film. CONSTITUTION:A polyester resin having an intrinsic viscosity (in o-chlorophenol at 35 deg.C) of 0.4-0.9dl/g is compound with 0.05-1wt.% fine chromium oxide powder having an average particle size of 0.05-0.5mum as the lubricant, if necessary together with 0.01-2.0wt.% inert particles having an average particle size of 0.3-2.0mum and is extruded in the temp. range from the m.p. (Tm deg.C) of the resin to (Tm+70) deg.C to give an unstretched film having an intrinsic viscosity of 0.35-0.9dl/g. The film is stretched monoaxially by 2.5-5.0 times in the temp. range from (Tg-10) deg.C to (Tg+70) deg.C (wherein Tg is the glass transition point of the resin), then stretched in the direction vertical to the foregoing stretching by 2.5-5 times in the temp. range from Tg to (Tg+70) deg.C, and thermally set in the temp. range from (Tg+70) to Tm deg.C.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a polyester film, and more particularly to a polyester film which is excellent in abrasion resistance and scratch resistance and is particularly useful as a base film for magnetic recording media.

[0002]

2. Description of the Related Art Biaxially oriented polyester films represented by polyethylene terephthalate films are widely used for various applications, especially for magnetic recording media because of their excellent physical and chemical properties.

In a biaxially oriented polyester film, its slipperiness and abrasion resistance are major factors that affect the workability of the film manufacturing process and processing process and the product quality. If these are insufficient, for example, when the magnetic layer is applied to the surface of the biaxially oriented polyester film and used as a magnetic tape, the friction between the coating roll and the film surface is severe, and shavings are generated,
Scratches occur on the film surface. Also when used as a VTR or data cartridge, shavings and scratches are generated in the process of winding the cassette at a high speed, which causes dropout.

Particularly in VTR applications, a metal guide or a plastic guide whose surface is not sufficiently finished may be used for a guide post fixed in a cassette for the purpose of cost reduction recently, but the surface of these guide posts is extremely high. rough. Therefore, a conventional technique for improving the slipperiness and abrasion resistance of a film, for example, a method of adding inorganic particles such as silicon oxide, titanium dioxide, calcium carbonate, talc, clay and calcined kaolin (for example, JP-A-54).
No. 57562) or a method of precipitating fine particles containing calcium, lithium or phosphorus in the polymerization system (see, for example, Japanese Examined Patent Publication No. 52-32914) to produce a film and provide a magnetic film without providing a back coat. When tape is used, shavings and scratches are generated in the process of winding the tape into the cassette at a high speed, and the dropout level is increased.

To solve such a problem, for example, Japanese Patent Laid-Open No.
Japanese Patent Laid-Open No. 2-43450 proposes a method of reducing scratch resistance by adding porous alumina, silica, titania particles or the like having a large porosity. However, this publication does not disclose or suggest the present invention.

[0006]

SUMMARY OF THE INVENTION An object of the present invention is to provide a polyester film which has good abrasion resistance and scratch resistance even for a rough metal guide or a plastic guide, and is particularly useful for a magnetic recording medium. Especially.

[0007]

According to the present invention, there is provided a polyester film containing, as a lubricant, fine particles of chromium oxide having an average particle diameter of 0.05 to 0.5 μm. The purpose of is achieved. Hereinafter, the present invention will be described in detail, with which other objects, configurations, advantages and effects of the present invention will be apparent.

The polyester in the present invention is a polyester having an aromatic dicarboxylic acid as a main acid component and an aliphatic glycol as a main glycol component. Such polyesters are substantially linear and have film forming properties, especially film forming properties by melt molding.

Examples of the aromatic dicarboxylic acid include terephthalic acid, naphthalene dicarboxylic acid, isophthalic acid, diphenoxyethane dicarboxylic acid, diphenyl sulfone dicarboxylic acid, diphenyl ketone dicarboxylic acid and anthracene dicarboxylic acid.

Examples of the aliphatic glycol include polymethylene glycol having 2 to 10 carbon atoms such as ethylene glycol, trimethylene glycol, tetramethylene glycol, pentamethylene glycol, hexamethylene glycol and decamethylene glycol, and cyclohexanedimethanol. Examples thereof include alicyclic diol.

In the present invention, as the polyester, those having alkylene terephthalate and / or alkylene naphthalene dicarboxylate as a main repeating unit are preferably used.

Among such polyesters, not only polyethylene terephthalate and polyethylene-2,6-naphthalenedicarboxylate, but especially 80 mol% or more of all dicarboxylic acid components are terephthalic acid and / or 2,6-naphthalenedicarboxylic acid. A copolymer which is an acid and in which 80 mol% or more of all glycol components is ethylene glycol is preferable. 20 mol% or less of the total acid component may be the above aromatic dicarboxylic acids other than terephthalic acid and / or 2,6-naphthalenedicarboxylic acid, and aliphatic dicarboxylic acids such as adipic acid and sebacic acid. Acids; can be alicyclic dicarboxylic acids such as cyclohexane-1,4-dicarboxylic acid and the like.
Further, 20 mol% or less of the total glycol component may be the above-mentioned glycol other than ethylene glycol, and aromatic diols such as hydroquinone, resorcin, 2,2-bis (4-hydroxyphenyl) propane and the like; 1 It can also be an aliphatic diol having an aromatic ring such as 4,4-dihydroxydimethylbenzene; a polyalkylene glycol (polyoxyalkylene glycol) such as polyethylene glycol, polypropylene glycol, polytetramethylene glycol and the like.

Further, the polyester in the present invention includes
Aromatic oxy acids such as hydroxybenzoic acid, ω-
Those in which a component derived from an oxycarboxylic acid such as an aliphatic oxyacid such as hydroxycaproic acid is copolymerized or bonded with 20 mol% or less based on the total amount of the dicarboxylic acid component and the oxycarboxylic acid component are also included.

Further, in the polyester of the present invention, the tricarboxylic or polyfunctional polycarboxylic acid or polyhydroxy compound, such as trimellitate, is contained in a substantially linear range, for example, in an amount of 2 mol% or less based on the total acid components. A copolymer of acid, pentaerythritol and the like is also included.

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

The polyester preferably has an intrinsic viscosity of about 0.4 to about 0.9 dl / g as determined by measuring at 35 ° C. in an o-chlorophenol solvent.

Chromium oxide used as a lubricant in the present invention is an oxide of chromium from divalent to hexavalent, which is also known in the literature [see, for example, "Chromium oxide", published by Kyoritsu Shuppan Co., Ltd.]. And chromium trioxide can be preferably mentioned for practical use. Further, two or more kinds of chromium oxide may be used.

In the present invention, the average particle size of the chromium oxide fine particles is 0.05 to 0.5 μm, preferably 0.05.
Is about 0.3 μm. By using the chromium oxide fine particles having the average particle diameter within the above range, it becomes possible to obtain a polyester film having excellent scratch resistance and abrasion resistance.

The average particle size of the chromium oxide fine particles is defined as a value measured in the state of being present in the polyester film. However, in many cases, it can be represented by the value measured for the powder before being mixed with the polyester.

The above-mentioned chromium oxide fine particles are preferably agglomerates of primary particles having an average particle diameter of 0.1 μm or less. Use of such chromium oxide fine particles has good dispersibility and small addition amount. It has advantages such as being completed and less likely to generate shavings.

From the viewpoint of scratch resistance and abrasion resistance of the polyester film of the present invention, the amount of chromium oxide fine particles is preferably 0.05 to 1.0% by weight based on the polyester. More preferable results are obtained when the content is 0.1 to 0.5% by weight.

Chromium oxide fine particles are dispersed in glycols such as ethylene glycol to form a slurry before being added to polyester, if necessary, and then finely pulverized by using a medium stirring type mill, or a wet classifier, Coarse particles can be removed by a filter or the like to obtain a predetermined average particle size. At this time, a dispersant or the like can be added before the above treatment. Further, a predetermined average particle diameter can be obtained by performing a crushing treatment or a classification treatment by a dry method.

In the present invention, in addition to the above chromium oxide fine particles, inert particles having an average particle diameter of 0.3 to 2.0 μm can be blended in the polyester film. The presence of inert particles other than the chromium oxide fine particles gives the polyester film more excellent results in scratch resistance and abrasion resistance, and improves the handleability in the step of producing the film, and further the magnetic recording of the film. The runnability when used as a base film for a medium is improved.
However, it is not preferable to mix inert particles having an excessively large average particle diameter because the surface flatness is deteriorated and the electromagnetic conversion characteristics of the magnetic recording medium are deteriorated.

The amount of such inert particles is preferably 0.01 to 2.0% by weight based on the polyester, which gives preferable results.

The type of the inert particles is not particularly limited, and examples thereof include inorganic inert particles such as calcium carbonate, silicon dioxide, titanium oxide, aluminum oxide and kaolin, and organic inert particles such as silicone resin and crosslinked polystyrene. Particles, particles internally deposited by the polymerization catalyst, and the like can be used.

The polyester film of the present invention is prepared, for example, by extruding the polyester at a temperature of Tm to (Tm + 70) ° C. (where Tm is the melting point of the polyester) and having an intrinsic viscosity of 0.35 to 0.9 dl / g. To obtain a stretched film,
The unstretched film is uniaxially (longitudinal or lateral) at a temperature of (Tg-10) to (Tg + 70) ° C (here, T
g is the glass transition temperature of polyester) and is 2.5 to
The film is stretched at a draw ratio of 5.0 times, and then at a temperature of Tg to (Tg + 70) ° C. in a direction perpendicular to the above stretching direction (when the first stage stretching is the longitudinal direction, the second stage stretching is the transverse direction). .5
It can be produced by stretching at a draw ratio of 5.0 times. In this case, the area stretching ratio is preferably 9 to 22 times, more preferably 12 to 22 times. The stretching means may be simultaneous biaxial stretching or sequential biaxial stretching.

Further, the obtained film has (Tg + 7
It can be heat-set at a temperature of 0) to Tm (° C.). For example, for polyethylene terephthalate film, 1
It is preferable to heat-set at 90 to 230 ° C. The heat setting time is, for example, 1 to 60 seconds.

The reason why the polyester film of the present invention is excellent in abrasion resistance and scratch resistance is not clear, but it is considered that the shape and hardness of the particles are appropriate in particular.

The polyester film of the present invention has excellent abrasion resistance and scratch resistance, and is particularly useful as a base film for magnetic recording media.

[0030]

EXAMPLES The present invention will be described in more detail with reference to the following examples. In addition, each characteristic value in the examples is based on the following method.

(1) Average Particle Size of Particles (i) When Obtaining Average Particle Size from Powder CP-50 Model Centrifugal Particle Size Analyzer (Centrifugal) manufactured by Shimadzu Corporation
The particle size corresponding to 50 mass% is read from the integrated curve of the particle size calculated based on the centrifugal sedimentation curve obtained using the Particle Size Analyzer) and the abundance of particles having that particle size, and this value is read as above. The average particle size is used (see the book “Particle size measurement technology” published by Nikkan Kogyo Shimbun, 1975, pages 242 to 247).

(Ii) In the case of particles in the film A small piece of the sample film was fixed on a sample stage for a scanning electron microscope, and a sputtering device (JFC-made by JEOL Ltd.) was used.
1100 type ion etching apparatus) is used to perform ion etching treatment on the film surface under the following conditions. The condition is that the sample is placed in a bell jar, the degree of vacuum is raised to a vacuum state of about 10 ^-3 Torr, the voltage is 0.25 KV, and the current is 1
Ion etching is performed at 2.5 mA for about 10 minutes. Further, gold spatter was applied to the film surface with the same apparatus, and observed with a scanning electron microscope at a magnification of 50,000 to 10,000, and Luzex 5 manufactured by Nippon Regulator Co., Ltd.
At 00, the equivalent spherical diameter distribution of at least 100 particles is obtained and calculated from the point of 50% weight integration.

(2) Running friction coefficient of film (μk) The friction coefficient is measured as follows using the device shown in FIG.
In FIG. 1, 1 is an unwind reel, 2 is a tension controller, 3, 5, 6, 8, 9 and 11 are free rollers,
4 is tension detector (inlet), 7 is stainless steel SU
Fixed rod made of S304 (outer diameter 5 mmφ, surface roughness Ra =
0.02 μm), 10 is a tension detector (exit), 1
Reference numeral 2 is a guide roller, and 13 is a take-up reel.

At a temperature of 20 ° C. and a humidity of 60%, the width is 1 /
A film slit into 2 inches is attached to the fixed rod 7 at an angle θ =
It is brought into contact with (152/180) π radial (152 °) and moved (rubbed) at a speed of 200 cm per minute. The exit tension (T ₂ : g) when the tension controller 2 is adjusted so that the entrance tension T ₁ is 35 g is detected by the exit tension detector after the film has run 90 m, and the running friction coefficient μk is calculated by the following formula. calculate. μk = (2.303 / θ) log (T 2 / T 1) = 0.868log (T 2/35)

(3) Flatness of film surface Ra (center line average roughness) is measured according to JIS B 0601. Using a stylus-type surface roughness meter (SURFCOM3B) manufactured by Tokyo Seimitsu Co., Ltd., a chart (film surface roughness curve) is drawn under the conditions of a needle radius of 2 μ and a load of 0.07 g to obtain a film. A portion of the measurement length L is extracted from the surface roughness curve in the direction of the center line, the center line of the extracted portion is taken as the X axis, the longitudinal magnification direction is taken as the Y axis, and the roughness curve Y = f (x) When expressed, the value (Ra: μm) given by the following equation is defined as the flatness of the film surface.

[0036]

[Equation 1]

In the present invention, 8 pieces are measured with a reference length of 0.25 mm, and Ra (μm) is expressed as an average value of 5 pieces excluding 3 pieces having a larger value.

(4) Scratch resistance and abrasion resistance In the same apparatus as in FIG. 1 used for measuring the running friction coefficient μk, the winding tension was 30 degrees and the inlet tension was 25 g at a speed of 300 m / min. And run for 200m. The shavings adhering to the fixed rod 7 after running and the scratches of the tape after running are evaluated. At this time, as the fixing rod 7, a 6φ tape guide (surface roughness Ra = 0.15 μm) obtained by bending a SUS sintered plate into a cylindrical shape and having an insufficient surface finish
The method using A is used as method A, and the method using a 6φ tape guide made of carbon black-containing polyacetal is used as method B.

<Scraping powder determination> ◎: Shavings powder is not seen at all ◯: Slightly shavings powder is seen △: Presence of shavings powder can be seen at a glance ×: Shavings powder is badly adhered

<Scratch Judgment> ⊚: No scratches were found ◯: 1 to 5 scratches were found Δ: 6 to 15 scratches were found ×: 16 or more scratches were found

[0041]

Examples 1 to 6, Comparative Examples 1 to 3 Dimethyl terephthalate and ethylene glycol, manganese acetate as a transesterification catalyst, and antimony trioxide as a polymerization catalyst,
Phosphorous acid was added as a stabilizer, and the additive particles shown in Tables 1 and 2 were added as a lubricant, and the mixture was polymerized by an ordinary method to obtain polyethylene terephthalate having an intrinsic viscosity of 0.62 dl / g. .

The polyethylene terephthalate pellets were dried at 170 ° C. for 3 hours, then fed to an extruder hopper and melted at a melting temperature of 280 to 300 ° C. The molten polymer was surface-finished through a 1 mm slit die to a surface finish of 0.1.
It was extruded onto a rotary cooling drum having a surface temperature of 20 ° C. for about 3 s to obtain a 200 μm unstretched film.

The unstretched film thus obtained is preheated at 75 ° C., and further 15 m between low speed and high speed rolls.
From above, a single infrared heater having a surface temperature of 900 ° C. was used to heat the film to draw it up to 3.6 times, quench it, and then supply it to a stenter and draw it laterally at 105 ° C. to 3.9 times.
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 14 μm. The characteristics of this film are shown in Tables 1 and 2.

[Example 7] Dimethyl-2,6-naphthalenedicarboxylate was used in place of dimethyl terephthalate, the surface temperature of the rotary cooling drum was 60 ° C, the preheating temperature during longitudinal stretching was 120 ° C, and the surface of the infrared heater was Temperature 9
50 ° C, transverse stretching temperature 125 ° C, heat setting 215
A biaxially oriented film was obtained in the same manner as in Example 2 except that the temperature was kept at 10 ° C for 10 seconds. The film properties are shown in Table 1.

[Comparative Example 4] A biaxially oriented film was obtained in the same manner as in Example 7, except that the particles shown in Table 2 were used as the lubricant. The characteristics are shown in Table 2.

[0046]

[Table 1]

[0047]

[Table 2]

As is clear from the results shown in Tables 1 and 2, when chromium oxide fine particles are used, a polyester film having excellent abrasion resistance and scratch resistance, which is useful as a base film of a magnetic recording medium, can be obtained.

[0049]

According to the present invention, it is possible to provide a polyester film which is excellent in abrasion resistance and scratch resistance and is particularly useful as a base film of a magnetic recording medium.

[Brief description of drawings]

FIG. 1 is a schematic view of an apparatus for measuring a running friction coefficient (μk).

[Explanation of symbols]

 1 Unwinding reel 2 Tension controller 3 Free roller 4 Tension detector (inlet) 5 Free roller 6 Free roller 7 Fixing rod 8 Free roller 9 Free roller 10 Tension detector (outlet) 11 Free roller 12 Guide roller 13 Take-up reel

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI technical display area B29K 105: 16 B29L 7:00

Claims (4)

[Claims] 1. A polyester film comprising chromium oxide fine particles having an average particle diameter of 0.05 to 0.5 μm as a lubricant. 2. The polyester film according to claim 1, wherein the chromium oxide fine particles are contained in an amount of 0.05 to 1% by weight based on polyester. 3. The polyester according to claim 1, which contains 0.01 to 2% by weight of inert particles other than chromium oxide particles having an average particle diameter of 0.3 to 2.0 μm with respect to the polyester. the film. 4. The polyester film according to claim 1, wherein the polyester film is biaxially oriented.