KR100558566B1 - Biaxially Stretched Polyester Film for Magnetic Recording Media - Google Patents

Abstract

The present invention relates to a biaxially stretched polyester film having excellent smoothness and dimensional stability and excellent electron conversion characteristics when made of magnetic tape and hardly causing dropout, and its technical configuration is 90 mol% or more of ethylene terephthalate units. In preparing a polyester resin having an intrinsic viscosity of 0.45 or more and 0.70 or less, inert particles having an average particle diameter of 0.05 μm to 3.0 μm in the polymer contain 0.05 wt% to 2.0 wt% of calcium carbonate particles and an average particle diameter of 0.04 μm. 0.01 wt% to 1.0 wt% of silica particles having a primary particle size of 5 to 60 nm, adjusted to ˜0.4 μm, and biaxially stretching the unstretched film obtained therefrom by a conventional method, and then 180 ° C. to 230 ° C. Biaxially stretched polyester film for magnetic recording media heat-fixed at ℃.

Description

Biaxially Stretched Polyester Film for Magnetic Recording Media

The present invention relates to a biaxially stretched polyester film having excellent smoothness and dimensional stability and exhibiting excellent electron conversion characteristics when made of magnetic tape and hardly causing drop-outs. The present invention relates to a biaxially stretched polyester film for a magnetic recording medium, comprising adding calcium carbonate particles and silica particles having a particle diameter as an external particle into a film.

In general, polyesters represented by polyethylene terephthalate have been used for various purposes such as magnetic tape, electrical insulation, condensation, photography, graphic arts, packaging, etc., due to their excellent physical and chemical properties. . However, in spite of the excellent properties, when the film is formed only by polyethylene terephthalate itself, the workability in the film forming process is inferior because the friction coefficient is large and the static electricity is generated. It is also not suitable for a magnetic recording medium because it does not impart the required characteristics as a magnetic recording medium. The electrostatic properties, migration activity, abrasion resistance, running resistance, and smoothness of polyester films have a major influence on the quality of the product as well as the manufacturing process and processing of the film. If the adhesion thickness with the cooling roll becomes uneven in the process, and if the activity, abrasion resistance, and durability are poor, a large amount of scratches and abrasions are generated due to friction between the surface of the film and the roll during film forming, and the smoothness of the film surface is reduced. If not, it acts as a deterioration factor of the electron conversion characteristics in the magnetic recording medium.

In addition, the winding property of the polyester film has a great effect on the quality of the film. When the film is wound, air flows between the film and the film, and as the winding speed of the film increases, the amount of air introduced increases and the winding property is deteriorated. .

In general, in order to give a polyester film an active activity, abrasion resistance, running resistance, and winding properties, it is known to give these characteristics by generating a large number of protrusions on the surface of the film. In addition, as a method of imparting projections, methods of adding external particles such as inert inorganic fine particles into a film during polyester production, and an internal particle method in which particles are generated by arbitrary catalyst precipitation in the film are well known. However, since the internal particle type has excellent affinity with the polymer and thus wear resistance due to particle dropping is small, wear resistance can be given, but particle size control of the precipitated particles during the polyester manufacturing process is difficult and uniform properties are difficult to obtain.

In the external particle addition method, inorganic particles such as barium sulfate, kaolin, silica, calcium carbonate, titanium dioxide, and alumina are added to the film during the preparation of the polyester and added into the film. The characteristics of the film can be given.

However, in the external particle method, the durability of polyester film and the degree of agglomeration of particles are different depending on the point of particle injection, condition of particle, particle type, particle shape and particle size. It is easy to cause defects. Therefore, it is necessary to provide limited conditions such as the size, shape, particle treatment method and the like of these particles.

In general, when the particle size of the particles contained in the polyester polymer is large or when coarse particles are formed by agglomeration of particles in the polyester, the film shows excellent results in the activity and runability of the film, but may cause defects in the film during winding. In the precise fields such as recording media, not only the electronic conversion characteristics of the magnetic recording medium are deteriorated, but also the occurrence of wear particles due to particle dropout is increased. Too small particle diameters result in winding and running characteristics of the polyester film. Will lower. In addition, it is necessary to select the ratio of the actual surface area to the primary particle size under limited conditions. At this time, if the ratio of the actual surface area to the theoretical surface area of the primary particle diameter is less than 0.62, the bonding strength between the primary particles is strong, so that even if the particles are treated in the slurry step, the effect is less. Since agglomeration occurs and the electron conversion property is lowered, it is necessary to give the polyester film properties through combination of small particles and large particles in a limited condition and treatment of the particles.

In order to satisfy the properties of such a polyester film, in the present invention, specific particles are selected, the particles are completely dispersed in an ethylene glycol slurry state, and the number of coarse particles is reduced to a specific range or less by treatment in the slurry step. By producing polyester in a controlled state, it is excellent in winding property, activating property, abrasion resistance, scratch resistance, running resistance, etc. of polyester film, and controls coarse particles in the film by agglomeration of particles to drop out when manufacturing into a magnetic recording medium. It is possible to provide a film having a low electron conversion property and excellent electron conversion characteristics.

As a specific polyester production method that can satisfy the two properties described above, a method of forming a discontinuous coating by applying a specific coating on the film surface is disclosed in Japanese Patent Application Laid-Open No. 3-80410, Japanese Patent Application Laid-Open No. 60- 180837, SO 60-180838, SO 60-180839 and the like.

In addition, when the polyester film is used as a magnetic tape, the laminated polyimide improves the electron conversion characteristics and the driving performance in the film manufacturing process when the magnetic film is made of magnetic tape by changing the surface design of the film surface on which the magnetic material is applied or deposited and the opposite surface thereof. Japanese Patent Laid-Open Publication Nos. Hei 1-26337, Hei 1-26338 and Japanese Laid-Open Patent Publication No. Hei 3-325674 and the like are known.

However, such a film may cause blocking, abrasion, and scratches due to friction with metal rolls in the film manufacturing process due to extremely low surface roughness of the film surface on which the magnetic material is applied or deposited. In spite of the low surface roughness of the film, when made of magnetic tape, the electron conversion characteristics such as dropout can be deteriorated. Thus, in the related art, in order to improve wear resistance of a film, a method of adding high-hardness microparticles such as alumina oxide to the front surface of a film is disclosed in Japanese Patent Application Laid-Open Nos. 6-64034, 6-143409, 6-179762 and 6-200064 or the like.

However, the polyethylene terephthalate film obtained by the conventional technique described above can obtain good elastic modulus, heat resistance, mechanical strength, and chemical properties. However, due to insufficient running performance during high-speed radiation for magnetic recording, problems such as dropping of powder are generated, resulting in various magnetic recording applications. Could not be applied to. Accordingly, an object of the present invention is to provide a biaxially oriented polyethylene terephthalate film for a magnetic recording medium capable of simultaneously satisfying cutting property, scratch resistance, abrasion resistance and winding resistance as well as excellent running performance when producing a polyethylene terephthalate film. .

In order to solve this problem, the present invention controls the appropriate particle size and mixing ratio of the external particles (A) and the external particles (B) added in the process of producing a polyethylene terephthalate resin having an intrinsic viscosity of 0.45 or more and 0.70 or less, and in particular, a polyester film. In order to disperse the added external particles (B) in the ethylene glycol slurry state in order to give the wear resistance characteristics of the slurry, it is used to satisfy the following equation through the particle treatment in the slurry step,

0.04 μm ≤ D50 ≤ 0.4 μm

2.0μm or more Particles 40ppm or less

In addition, as for the silica particles as external particles (B), the ratio Rsa of the actual surface area to the theoretical surface area of the primary particle diameter satisfies the following equation,

0.62 ≤ Rsa ≤ 0.90

By producing polyester, the center line average roughness (SRa) is 0.010 to 0.020, and the number of sheets with a height of 0.5 µm or more per unit area (mm2) satisfies 10 to 200, and the film has excellent reactivity, wear resistance, and scratch resistance. When manufacturing a magnetic recording medium, it was possible to produce a film having excellent electron conversion characteristics.

The polyester used in the present invention is made from aromatic dicarboxylic acid such as terephthalic acid, 2,6-naphthalenedicarboxylic acid and ethylene glycol as starting materials, but may also contain another third component. At this time, the dicarboxylic acid component of the starting material of the present invention includes isophthalic acid, terephthalic acid, 2,6-naphthalenedicarboxylic acid, phthalic acid, adipic acid, sebacic acid. Such acid components may be used alone or in combination of two or more. Another starting material, the glycol component includes, for example, ethylene glycol, propylene glycol, butanediol, neopentyl glycol, and the like, and one or two or more thereof may be used. In the present invention, the polyester may also include additives of heat stabilizers, antiblocking agents, antioxidants, antistatic agents, anti-ultraviolet and other materials to improve the pinning properties when forming the sheet. The polyester obtained in this way has an intrinsic viscosity of 0.45 or more and 0.70 or less, and inert inorganic particles (A) for imparting active activity and running characteristics in the polymer during the preparation of the polyester resin have an average particle diameter of 0.05 µm to 3.0 µm. It is preferable to contain phosphorus calcium carbonate particles and the addition amount is 0.05 wt%-2.0 wt%. Particle size of calcium carbonate particles

When it is 3.0 mu m or more, coarse protrusions are formed in the film, which is not suitable for use as a magnetic recording medium. Therefore, excellent characteristics are shown at 0.10 µm to 1.5 µm. In addition, the inert inorganic fine particles (B) added in order to impart the wear resistance characteristics of the polyester film are silica particles having a primary particle size of 5 to 60 nm with a flat particle diameter adjusted to 0.04 μm to 0.4 μm, and an addition amount of 0.01 wt% to It is preferable to set it as 1.0wt%, More preferably, it is more preferable to add 0.05wt%-0.5wt% that the primary particle diameter adjusted to 0.07 micrometer-0.3 micrometer is 10-50 mm. In this case, the ratio (Rsa) of the actual surface area to the theoretical surface area of the primary particle diameter was 0.62 to 0.90.

In this case, the inorganic fine particles (B) are treated at the particle slurry production step to have a mean particle size of 0.04 µm to 0.4 µm and a number of particles having a size of 2.0 µm or larger existing on the particle slurry at 40 ppm or less, and theoretically at a surface area of the primary particle diameter. Particles having an actual surface area to particle ratio of 0.62 to 0.90 are added to the polycondensation reaction to adjust the number of coarse particles present in the polyester to a specific range or less, thereby improving wear resistance and scratch resistance of the polyester film. It has become possible to improve the electron conversion characteristics of the magnetic recording medium. At this time, the treatment method of the particle slurry includes a classification treatment method, a milling method, a filtering method, a dispersant treatment method, and the like.

A non-stretched film is made of a polyethylene terephthalate resin prepared by the above method, stretched 2.0 to 5.0 times in the longitudinal direction at 90 ° C. to 130 ° C., and then stretched 2.0 to 5.0 times at 90 ° C. to 140 ° C. in the transverse direction, Obtain a biaxially oriented polyester film for magnetic recording media which is made by thermal curing at 180 ° C. to 230 ° C. for 1 second to 10 minutes, and tensile stress (hereinafter referred to as F-5 value) at 5% elongation is used in both longitudinal and transverse directions. 10kg / mm2 or more, Young's modulus is 400kg / mm2 or more in both longitudinal and transverse directions, Heat shrinkage is 2% or less in both longitudinal and transverse directions, Centerline average roughness SRa is between 0.01µm and 0.02µm, and 10-point average roughness SRz A biaxially oriented polyester film for magnetic recording media, characterized by satisfying a maximum roughness SRmax of 0.2 µm to 0.5 µm and a centerline roughness SRmax of 0.4 µm to 0.65 µm, and having a number of 10 to 200 or more with a height of 0.5 µm per unit area (mm 2). Get it There.

In the present invention, the characteristic values and the overall physical properties were measured by the following method.

(1) Average particle size of particles

The average particle diameter of all the particles used was measured using a particle size distribution analyzer (Granulometer HR-850) in the state dispersed in ethylene glycol as the average particle diameter was the point of the volume fraction 50% of the particles converted into a sphere.

(2) Number of coarse particles

The number of coarse particles in the particle slurry was measured in PPM units by using TA-II of COULTER COUNTER.

(3) surface area (SA) and Rsa of the particles;

Gas nitrogen is adsorbed inside the pore and the surface area is measured (BET method). This method is applied to the formula produced by Brunauer, Emmett, Teller. The measurement method is that when nitrogen gas is adsorbed on the surface of particles under liquid nitrogen temperature, the gas causes phase transition to liquid and monolayer up to the relative pressure (P / Po) of 0.3. It can be calculated by using the following formula.

P / Po 1 C-1

-------- = ----- + -------- P / Po

V (1-Po) VmC VmC

Vm (mono layer adsorption volume) can be obtained from the above equation and substituted into the following equation to obtain the surface area.

          Vm

SA = -------- × 6.023E23 × 16.2E-20 [㎡ / g]

         22414

The ratio of the actual surface area and the theoretical surface area for the primary particle diameter was obtained by substituting the following equation with the value obtained from the above equation.

                  SA

Rsa = -------------------------

          Difference about theoretical surface area

(4) F-5 value

This value represents the tensile stress measured when a 10 mm wide film sample was stretched 5% with a tensile tester at a temperature of 25 ° C., a distance of 100 mm between chucks, and a tensile speed of 20 mm / min.

(5) YOUNG'S MODULUS

Young's modulus is represented by the initial Young's modulus at the time of tension | tensile_strength measured when the film sample of 10 mm width is extended | stretched at the temperature of 25 degreeC, the distance of 100 mm between chucks, and the tensile speed of 20 mm / min.

(6) heat shrinkage

Heat shrinkage was measured after leaving the film specimen in an oven at 105 ° C. for 30 minutes.

Thermal shrinkage is calculated as [(l0-l) / l0] × 100 (%), where l0 is the original length and l is the length measured after heat treatment.

(7) The center line average roughness (SRa), ten point average roughness (SRz), and center line maximum roughness (SRmax) of the film were measured using a three-dimensional surface roughness meter manufactured by KOSAKA of Japan.

(8) bifunctional

The polyester film was made of a roll tape of a certain width, fixed to a metal guide roll, and then driven while contacting for a long time. The degree of scratching on the surface of the film was observed under a microscope, and the percentage of the guide roll was visually observed to determine as follows. .

Level 1: Almost no scratch on the film surface after friction with the guide roll.

Level 2: Small scratches on the film surface after friction with the guide roll.

Level 3: Scratches on the film surface after friction with the guide roll.

(9) Evaluation of wear resistance

As shown in the drawing, a specimen was subjected to forced repeated friction between a film and a guide pin at a specially designed sample loading site using a traveling system of a Haydon friction coefficient measuring device. KOSAKA SE-3300) calculated the volume of protrusions by height and volume to quantify the rate of volume change before and after friction. The lower the value shown here, the better the wear resistance.

The formula for measuring the measurement conditions and the volume change rate is as follows.

-Load: 50g-Measuring length: 50㎜ Measuring speed: 50㎜ / sec-Number of repeated runs: 200

Σ [Ni ' ³ × n)-(Ni ³ -n)]

Volume change rate (ΔV) = ------------------------------- × 100

Σ [Ni ' ³ × n)]

Where Ni 'is SLICE LEVEL, Ni is the height after friction, and n is the number of each height.

(10) dropout

The biaxially oriented polyester film was coated with a magnetic layer having a thickness of 4 μm using a conventional method to produce a video tape, and then the optimum current was recorded on the video tape as a five-step disparity signal, and the attenuation of the video head output was 20 dB, A duration of 15 µsec or more was regarded as a dropout, measured continuously for 30 minutes, and averaged per minute, divided into grades A to D for evaluation.

A: less than 10 / min

B: 10 or more / min-less than 30 / min

C: 30 or more / min-less than 50 / min

D: 50 or more per minute

Hereinafter, the present invention will be described in detail with reference to Examples and Comparative Examples.

Example 1

A mixture of 100 parts of dimethyl terephthalate, 70 parts of ethylene glycol, 0.07 parts of manganese acetate tetrahydrate, and 0.03 parts of antimony trioxide was heated in a reactor to carry out methanol exchange and transesterification. 0.03 parts of trimethyl phosphate and two inorganic fine particles (calcium carbonate, silica) were added to the reaction mixture, followed by a polycondensation reaction for 4 hours. The silica particles were prepared in an ethylene glycol slurry state and then milled. After the addition, the polycondensation reaction was completed, a polyester chip was obtained. It is dried and then extruded through an extruder to obtain an unstretched film, the unstretched sheet is stretched 4.7 times in the longitudinal direction at 120 ° C., and then stretched 4.7 times in the transverse direction at 110 ° C. to 130 ° C., preferably in the transverse direction. The film was thermally cured at 210 ° C. for 30 seconds while relaxing to 1% to 30%, thereby obtaining a film having a thickness of 14.2 μm. As a result of evaluating the physical properties of this oriented film, as shown in Table 1, since it exhibited excellent reactivity, scratch resistance, and abrasion resistance, and eliminated large projections on the surface of the film, it hardly caused dropout when manufacturing magnetic tape. Polyester film was obtained and the physical properties of the film are shown in Table 1.

Example 2

In Example 1, except that the primary particle diameter of the silica particles was 20nm and the surface area was 90m 2 / g was carried out in the same manner as in Example 1 to obtain a film and the physical properties of the film are shown in Table 1.

Example 3

Except that the content of silica particles in the polyester film in Example 1 is 0.12wt% was carried out in the same manner as in Example 1 to obtain a film and the film properties are shown in Table 1.

Comparative Example 1

Except for using alumina particles in place of silica particles in Example 1 was carried out in the same manner as in Example 1 to obtain a film and the film properties are shown in Table 1.

Comparative Example 2

Except for using anatase-type titanium particles in place of the silica particles in Example 1 was carried out in the same manner as in Example 1 to obtain a film and the physical properties of the film are shown in Table 1.

Comparative Example 3

In Example 1, except that silica particles were used in the form of colloidal spherical silica, the same procedure as in Example 1 was carried out to obtain a film. Table 1 shows physical properties of the film.

Table 1

The biaxially stretched polyester film for magnetic recording media of the present invention has excellent smoothness and dimensional stability, extremely low abrasion and scratches during friction, and small coarse protrusions on the film.

1 is a view showing an apparatus for forcibly repeated friction of the film surface to evaluate the wear resistance of the film

<Explanation of symbols on the main parts of the drawing>

1 film fixing fixture 2 fixing plate

3: film 4: guide pin (rotation)

5: Guide pin (fixed) W: Load

Claims (1)

A polyester film prepared by using a polyester resin containing 90 mol% or more of ethylene terephthalate units and having an intrinsic viscosity of 0.45 or more and 0.70 or less, wherein the film contains calcium carbonate particles having an average particle diameter of 0.05 μm to 3.0 μm in the polymer. 0.05 wt% to 2.0 wt%, the primary particle size is 5 to 60 nm, completely dispersed in an ethylene glycol slurry state, and the average particle size and the number of coarse particles satisfy the following formula by treatment in the slurry stage, Theoretically, the ratio (Rsa) of the actual surface area of the particles to the surface area of the primary particle diameter contained 0.01 wt% to 1.0 wt% of silica particles of 0.62 to 0.90. Biaxially stretched polyester films for magnetic recording media heat-set at 230 캜; 0.04 μm ≤ D50 ≤ 0.4 μm 2.0 micrometers or more and particle | grains 40 ppm or less.