KR960003819B1 - Polyester for magnetic recording media - Google Patents

Abstract

The biaxial oriented polyester base film for magnetic recording medium contains calcium carbonate having a form to satisfy the condition of : 0.4 micron <=2a<=1.2 micron; 0.2 micron <=2b<=0.8 micron; 2b<=a; b<=c<=a. Pref. the calcium carbonate has 0.1-1.0 wt. pt. of 0.1-1.0 micron of ave. particle size. The difference of refractive index of length and width direction. is above 0.010. The obtd. polyester base film has good running property, surface smoothness and abrasion resistance.

Description

Biaxially Oriented Polyester Base Film for Magnetic Recording Media

1 is a particle shape displayed in three-dimensional coordinates

2 is a tester for measuring the runability of the present invention

* Explanation of symbols for main parts of the drawings

1: Shear tension measuring unit 2: 6mm hard chrome plated pin

3: back end tension measurement part θ: 135 ° C

The present invention relates to a biaxially oriented polyester base film for magnetic recording media, and more particularly, to running, surface smoothness and wear resistance produced by adding calcium carbonate having a unique shape different from ordinary calcium carbonate or spherical silica particles. A base film for excellent magnetic recording media.

Japanese Patent Application Laid-Open No. 64-128, No. 63-251434, and the like are disclosed as methods for producing a polyester film for a magnetic recording medium.

In Japanese Patent Laid-Open No. 64-128, 0.01-3.0 wt% of substantially amorphous spherical silica (particle A) having an average particle diameter of 0.01-1.0 µ, a [d ₁₀ / d ₉₀ ] value of 1.1-2.7, and a Mohs hardness of 4.0 A polyester film characterized by containing 0.005 to 0.5wt% of Particle B having a [D 2 / D ₁] value of 1.1 to 4.0 and below was prepared. In No. 63-251435, a polyester film was prepared. 63-251435 contains 0.005 to 3 wt% of spherical silica particles (A) having an average particle diameter of 0.05 to 4 µ, a particle diameter ratio (long diameter / short diameter) of 1.0 to 1.2, and 0.005 to 3 wt% of terephthalic acid metal salt particles (B). It has been produced a biaxially oriented polyester film characterized in that.

However, this conventional technique is extremely good surface smoothness of the film when using only spherical silica particles, but poor running characteristics, and thus wear resistance, such as the occurrence of white powder and scratches on the surface of the film due to repeated driving or high-speed driving, etc. Since the defect is poor, the technology to improve the running property of the film by introducing a second particle component having a larger particle size than the spherical silica or the shape of the film surface projections caused by the spherical silica is not only weak to wear but also to improve the running property. The second particle component also forms coarse coarse particles in the film to form coarse protrusions or cause powder generation due to particle dropout when the film or the magnetic tape made of the film travels, and thus the electromagnetic conversion characteristics and the dropout of the magnetic recording tape. Resulting in poor quality.

Therefore, in the present invention, by adding a calcium carbonate having a unique shape different from ordinary calcium carbonate or spherical colloidal silica, the shape of the surface forming protrusion of the film is wider than that of the normal calcium carbonate or colloidal silica. Because of this large film, it has good sliding property by these particles when running the film, so it has good resistance to abrasion and excellent surface smoothness due to uniformity of the projections. Therefore, when it is applied as a magnetic recording medium, especially a high density, high quality video base film, A tape having excellent electromagnetic conversion characteristics and wear resistance can be obtained.

The polyester of the present invention is obtained by condensation reaction between a dicarboxylic acid component and a glycol component, and terephthalic acid, naphthalene dicarboxylic acid and ester compounds thereof may be used as the dicarboxylic acid component, and ethylene glycol is preferable as the glycol component. .

As other copolymerization components, in the case of dicarboxylic acid, isophthalic acid, phthalic acid, adipic acid, sebacic acid, etc. may be used in a small amount. A small amount may be copolymerized.

In the present invention, the polyester may contain a suitable amount of a thermal stabilizer, UV stabilizer, antioxidant, dye, antistatic agent, etc. as necessary.

Calcium carbonate, which is a particle component of the present invention, is prepared by reacting calcium hydroxide aqueous solution or suspension with carbonic acid gas in the presence of natural polymers, as disclosed in Japanese Patent Publication No. Hei 48-35195. It can be prepared by the carbonation by adding ammonia to the aqueous solution of calcium hydroxide as described above, there is no limitation on the production method.

There is no restriction on the particle size distribution of calcium carbonate in the present invention, but the narrower the particle size distribution ratio represented by the following formula, the more suitable for achieving the present invention.

d ₂₅ / d ₇₅

(Where d ₂₅ is the positive mean particle size of 25% from the maximum particle size of the total 100% cumulative distribution, d ₇₅ is the mean particle size of the cumulative 75% point, d ₂₅ / d ₇₅ is 1.8 or less, preferably If it satisfies 1.5 or less, more preferably 1.3 or less, it is suitable for achieving the present invention.)

In the present invention, for the purpose of increasing the affinity of ethylene glycol, polyester and calcium carbonate, calcium carbonate acryl copolymers or other carboxylic acid compounds, polymers or metal salts thereof, phosphorus compounds, silane and titanium coupling agents or sulfonic acid compounds and their The surface treatment or dispersion treatment may be performed alone or in combination, such as a polymer or a metal salt.

There is no restriction on the specific surface area of calcium carbonate in the present invention, but the specific surface area of 20 m 2 gr (BET method) or less solid type is advantageous to achieve the present invention.

In the present invention, when the shape of the calcium carbonate is expressed in three-dimensional coordinates as in the second degree, the particle shape coefficients a, b, and c must satisfy the following four conditions.

① 2a values should be in the range of 0.4 µm to 1.2 µm, and ② 2b values should satisfy the range of 0.2 µm and 0.8 µm. Also, ③a must be greater than or equal to 2b, and ④c must be greater than or equal to b and greater than or equal to a.

If the 2a value is less than 0.4 or the 2b value is less than 0.2, the surface roughness of the film is too low, and the running performance is poor. If the 2a value is more than 1.2, and the 2b value is more than 0.8, the film surface roughness is increased and the electromagnetic conversion characteristic of the magnetic recording tape is poor. Dropout increases.

When the a value is less than 2b value, the particle formation is close to the spherical shape, so that the smoothness of the film is good, but poor running and abrasion resistance as in the prior art.

If the c value is less than the b value, the particle shape is close to linear, and thus the running property of the film is poor, and the electromagnetic conversion characteristics and dropout of the magnetic recording tape are deteriorated. On the contrary, four conditions are possible for the condition that the c value exceeds the a value, and double conditions 1 and 2 are the same as the claims when the a and c are reversed. Compared to the production of wider projections, rather than worsening wear resistance.

c> a, c = 1.2, a <1.2 condition 1

c> a, c> 1.2, a <1.2 condition 2

c> a, c> 1.2, a = 1.2 condition 3

c> a, c> 1.2, a <1.2 condition 4

In this invention, the average particle diameter of calcium carbonate needed to satisfy | fill the range of 0.1-1.0 micrometer, and content in a film 0.1-1.0 weight%. When the average particle size is less than 0.1μ or the content is less than 0.1% by weight, the film has poor running characteristics and is not suitable for magnetic recording media.When the average particle size is over 1.0μ, the film surface roughness is increased and the electromagnetic conversion characteristics of the magnetic recording tape are poor. Therefore, it is disadvantageous for high density and low quality recording of the magnetic material, and the dropout of the magnetic tape becomes worse due to the increase of the powder due to the dropping of coarse particles during the slitting after the magnetic layer is introduced or the repeated running of the tape.

In addition, when the particle content exceeds 1.0% by weight, coarse protrusions are formed on the surface of the film as a result of particle aggregation, which is not good for deteriorating electromagnetic conversion characteristics and causing dropout.

In the present invention, in addition to the calcium carbonate of the claims, polyester and inert inorganic substances, internal precipitated particles, heat resistant polymer fine particles and the like may be used in combination.

Inert inorganic particulates include titanium oxide (TiO₂), silicon dioxide (SiO₂), silicon oxide (SiO), aluminum oxide (Al₂O₃), calcium carbonate (CaCO₃), clay (Talc) and aluminosilicate ( Aluminosilicate), and the internally precipitated particles are precipitated during the polymerization of the polyester, and may be a reactant of a transesterification catalyst with a dicarboxylic acid, a transesterification catalyst with a phosphorus compound, and a polyester linear oligomer. As the heat-resistant polymer microparticles, a crosslinking degree of vinyl, acryl copolymer, crosslinking ester, crosslinking amide resin and thermosetting resin such as phenol, epoxy and urea It is possible to have a chemically unreacted carboxyl group or to have a porous structure.

In the present invention, it is preferable to go through the usual processes such as particle dispersion, classification, removal of coarse particles, etc., and there are no limitations on the method of use, conditions, types of expectations, processing time, and the like.

In the present invention, there is no limitation on the method of adding the particles or the time of adding the particles, but it is preferable to disperse them in the glycol component and to add the particles at the initial stage of the polycondensation.

In addition, when introducing a particle component other than calcium carbonate may be added together in a polycondensation reactor, after the production of each polymer may be prepared by mixing to extrude the final concentration before film formation.

In the present invention, it is necessary to satisfy that the difference Δn (= n _TD −n _MD ) between the widthwise refractive index n _TD and the axial refractive index n _MD of the film is 0.010 or more.

The film having an n value of less than 0.010 has a rough cross section of the slits at a predetermined width after the magnetic layer is introduced and increases dropout due to the dropping of powder or magnetic layer components. When Δn value is 0.010 or more, there is no such problem, and more preferably, Δn value is 0.020 or more.

However, when the Δn value is more than 0.060, the anisotropy of the film is too large, so that adverse effects such as heat shrinkage are caused.

Such a film can be produced by the following method.

First, the polyester chip is dried under reduced pressure at 160 ° C. and then melted at 280 to 310 ° C. to prepare an amorphous sheet by an electrostatically applied cooling solidification method, followed by stretching 3 to 4 times at 90 to 105 ° C. in the axial direction. It is produced by stretching 4 to 6 times at 95-125 degreeC in the width direction continuously, and heat-setting at 200-240 degreeC.

Although there is no restriction | limiting in the thickness direction refractive index value or average refractive index value of a film in this invention, the thickness direction refractive index value is ideally in the range of 1.490-1.515, and the average refractive index value is preferable in the range of 1.595-1.605.

When the refractive index of the thickness is less than 1.490, the running and abrasion resistance is poor, and when the thickness is higher than 1.515, the film forming operation is poor and the improvement effect is insignificant.

In addition, when the average refractive index value is less than 1.595, thermal shrinkage is severe and curling of the magnetic recording tape is not good. When the average refractive index is higher than 1.605, the surface is easily scratched or broken when friction occurs.

There is no restriction on film strength in the present invention, but when the film thickness is 12.5μ or more, MD, TD direction F-5 value is 11kg / mm², more preferably 12kg / mm² or more, and in order to increase the effect of the present invention, the TD direction It is recommended that the F-5 value be more than 13 kg / mm². When the film thickness is less than 12.5 µ, the effect is great when the F-5 value in the MD direction is 14 kg / mm² or more.

There is no restriction on the surface roughness of the film in the present invention, but the average surface roughness is in the range of 2 to 11 mm, preferably 3 to 9 mm, more preferably 4 to 7 mm, and is suitable for achieving the present invention.

That is, the present invention is a base film for a magnetic recording medium, wherein the average particle diameter is 0.1 to 1.0 mu and the first degree particle shape contains 0.1 to 1.0 wt% of calcium carbonate satisfying the following formula.

- doing -

0.4μ≤2a≤1.2μ

0.2μ≤2b≤0.8μ

2b≤a

b≤c≤a

<Measurement method>

Measurement of the physical properties of the particles and the film was evaluated by the following method.

1) Average particle size (μ) and particle size distribution

It measured by SA-CP3 of Shimadju Corporation of Japan.

The mean particle size was the cumulative 50% of the equivalent spherical particle size distribution, and the particle size distribution was expressed as the ratio d ₂₅ / d ₇₅ between the 25% and 75% points.

2) particle shape

The measurement of the particle-related coefficients a, b, and c (μ) in FIG. 1 was carried out using an electron microscope.

3) Surface roughness of film (SRa (mm))

Average surface roughness was measured by a non-contact three-dimensional surface roughness measuring instrument TOPO-3D of the USA.

4) Film runability

Figure 2 is expressed by this value by calculating the friction coefficient (μf) of the following equation from the tension difference of the front and rear stage when the film is run at a speed of 1m / min using a film running tester.

5) refractive index and refractive index difference of the film

The axial direction (n _MD ) and the width direction (n _TD ) refractive index were measured with Abbe's refractometer from Atago, Japan, and the difference was calculated based on the following equation.

※ △ n = n _TD -n _MD

6) Wear resistance of film (Ⅰ)

The stainless steel pin of diameter 6mm was mounted on the runability tester of FIG. 2, and the film was run at a speed of 50 gr and a running speed of 250 m / min. .

★ Grade 1: Almost no powder attached

Class 3: Attach small amount of powder

Grade 5: large amount of powder

Grades are judged on an average of 10 times, grade 2 is in the middle of grades 1 and 3, grade 4 is in the middle of grades 3 and 5, and grades 4 and 5 are unusable.

7) Wear Resistance of Film (Ⅱ)

The stainless steel pin having a diameter of 6 mm was attached to the runability tester of FIG. 2, and the film was scratched by visual observation of the degree of scratching after running a 100 meter film at a driving tension of 30 gr and a traveling speed of 250 m / min.

★ Grade 1: No scratch

Class 3: Has Shallow Scratch

Class 5: Have a lot of deep scratches

The grade is judged as an average of 10 times, grade 2 is in the middle of grades 1 and 3, grade 4 is in the middle of 3 and 5, and films of grades 4 and 5 are unusable.

Hereinafter, the present invention will be described in more detail with reference to the following examples.

However, it is not limited to the Example of this invention.

Example 1

100 parts of dimethyl terephthalate, 60 parts of ethylene glycol, 0.1 part of magnesium acetate tetrahydrate, 0.05 parts of antimony trioxide were added to a transesterification reactor, and the transesterification reaction was carried out from 140 DEG C to 230 DEG C over 4 hours while removing methanol out of the reactor. The average particle diameter was 0.62μ, and the particle shape coefficients a were 0.5, b was 0.3, and c was 0.3. Then, 0.3% by weight of calcium carbonate and 0.05% by weight of triethylphosphate were added to the polycondensation reactor, followed by high vacuum for 4 hours. Polycondensation reaction was carried out to obtain polyester (A) having an intrinsic viscosity of 0.610.

Dry polyester (A) at 160 ° C, extrude at 300 ° C, produce amorphous sheet by electrostatic applied cooling method, 3.5 times in axial direction at 100 ° C, 3.8 times in width direction at 110 ° C, crystallize at 220 ° C, relax) A 3% film was obtained.

Example 2

In the same manner as in Example 1, 0.3 wt% of calcium carbonate having an average particle diameter of 0.3 μ, a of 0.3, b of 0.15, and c of 0.15, and polyester (B) is the same as that of polyester (A). A method of preparing a polyester (B) was prepared by adding 0.3 μg of calcium carbonate to 0.8 wt%.

After mixing polyester (A) and polyester (B) at 10: 1, a film having a thickness of 14.5 µ was obtained in the same manner as in Example 1.

Example 1 [Comparative Examples 1 to 5]

In Example 1, the size, shape factor and content of the particles were changed, and the conditions are shown in Table 1.

Example 4

After changing the size and shape coefficient of the particles in Example 1 to prepare a polyester (A) through the same process as in Example 1 to prepare an amorphous sheet 3.8 times in the axial direction at 100 ℃, 4.2 times in the width direction at 112 ℃ After stretching, crystallization was performed at 225 ° C., and a film having a thickness of 14.2 μm was prepared under a condition of Rex 3.2%.

Example 5

In the polyester (B) of Example 2, 0.3 wt% of aluminum oxide (Al₂O₃) instead of calcium carbonate (CaCO₃) was mixed with polyester (A) of Example 1 in a 5: 5 ratio. After drying, extruding, and cooling to prepare an amorphous sheet, the film was stretched 4.0 times in the axial direction at 100 ° C. and 4.3 times in the width direction at 115 ° C., and a film having a thickness of 11.5 μ after heat treatment at 230 ° C. and 2.8% of Rex was prepared. .

Example 6

100 parts of polyester (A) and dimethyl terephthalate of Example 2, 70 parts of ethylene glycol, 0.1 part of calcium acetate monohydrate, and 0.15 part of lithium acetate dihydrate were added to a transesterification reactor, and methanol was removed from the reactor from 140 ° C. After transesterification to 230 ° C. over time, 0.2 parts of trimethyl phosphate, 0.03 parts of phosphoric acid, antimony trioxide and 0.05 parts were added, and then transferred to a polycondensation reactor to carry out a condensation reaction for 4 hours at high vacuum to obtain an intrinsic viscosity of 0.610. After mixing the polyester (B) of 5: 1 in the same manner as in Example 1.

Example 7

In the polyester (B) of Example 5, the polyester (B) prepared by adding 0.3 wt% of the heat resistant polymer particles prepared by the following method instead of aluminum oxide was mixed with the polyester (A) at 5: 5.

100 parts of methyl methacrylate, 25 parts of styrene monomer, 30 parts of ethylene glycol dimethacrylate, 1.0 part of benzoyl peroxide, 5 parts of acrylic acid were mixed uniformly with 100 parts of toluene, and then dispersed in 700 parts of distilled water for 8 hours at 80 ° C. After the reaction, the mixture is washed with distilled water, and unreacted monomer and linear polymer are extracted with toluene and dried.

The obtained 0.1 mm crosslinked crosslinker is pulverized to 20 mu using a grinder, and then mixed with the glycol component at 50 wt%, and treated with a sand grinder to obtain a particle slurry having an average particle diameter of 0.2 mu.

Comparative Example 6

The polyester (A) of Example 1 was dried at 160 ° C., extruded at 300 ° C., and an amorphous sheet was produced by electrostatic applied cooling, 4.0 times in the axial direction at 100 ° C., 3.7 times in the width direction at 110 ° C., and crystallized at 220 ° C. And a Relex 3% process to obtain a film having a thickness of 14.5μ.

TABLE 1

※ * S Ra: Surface roughness of film

** μf: Running property of film

** Δn: refractive index of film

Claims (4)

A biaxially oriented polyester base film for magnetic recording media, characterized by containing calcium carbonate having a shape satisfying the following formula in producing a biaxially oriented polyester film for magnetic recording media. 0.4μ≤2a≤1.2μ 0.2μ≤2b≤0.8μ 2b≤a b≤c≤a The biaxially oriented polyester base film for magnetic recording media according to claim 1, wherein the average particle diameter of calcium carbonate is 0.1 to 1.0 mu. A biaxially oriented polyester base film for magnetic recording media according to claim 1, wherein the content of calcium carbonate is 0.1 to 1.0 wt%. The biaxially oriented polyester base film for magnetic recording media according to claim 1, wherein the difference between the widthwise refractive index and the axial refractive index of the film is 0.010 or more.