KR100248728B1 - Biaxially oriented polyester film for magnetic recording media and process for the preparation thereof - Google Patents

Abstract

In the present invention, a lubricant slurry obtained using a milling machine is added to a polyester resin, and then extruded and stretched to produce a polyester film. The calcined kaolin (A) having an average particle diameter of 0.05 to 0.5 μm and an average particle diameter of 0.51 to 3 μm Calcined kaolin (B) was dispersed in glycol under the conditions of a circumferential speed of 8 to 15 m / min of the mill and a residence time of 50 to 150 minutes of the particles in the mill to obtain lubricant slurries (A) and (B), followed by polyester Based on the weight of the film, active slurries (A) and (B) were added to the polyester resin so that calcined kaolin (A) was contained in an amount of 0.01 to 2% by weight and calcined kaolin (B) in an amount of 0.05 to 1% by weight. To provide a method for producing a biaxially oriented polyester film, and a polyester film produced thereby, the polyester film produced according to the present invention , Abrasion resistance and the scratch resistance is excellent while excellent in elimination of the high-speed driving friction characteristics and inorganic lubricant is particularly suitable for use in magnetic recording media.

Description

Biaxially Oriented Polyester Film For Magnetic Recording Media And Method Of Manufacturing The Same

The present invention relates to a polyester film and a method for manufacturing the same. Specifically, by using a lubricant slurry prepared under specific conditions using a specific amount of specific inorganic particles, the surface properties, abrasion resistance, and scratch resistance are excellent and friction at high speeds is achieved. A biaxially oriented polyester film having improved properties and dropping resistance of an inorganic lubricant, and a method of manufacturing the same.

Polyester film represented by polyethylene terephthalate ("PET") has a stable chemical structure, high mechanical strength, excellent heat resistance, durability, chemical resistance, etc., capacitors, medical, industrial, packaging, It is used in many applications such as photographic films, labels, as well as substrates of magnetic recording media.

In order to impart runability, processability and surface properties to such a polyester film, inorganic particles such as calcium carbonate, silica and kaolin are added as lubricants to form irregularities on the surface of the polyester.

However, when kaolin is used among these inorganic lubricants, it is advantageous to control the surface properties of the polyester film. However, due to the large generation of macroparticles due to undispersed particles, it is dropped when manufactured for magnetic tape and data storage. There are problems such as drop-out and error occurrence, and the particle size distribution is wide, so that the number of required projections per single area of the film is insufficient after the production of the film, and the dropping resistance of the aggregated inorganic lubricant after high-speed driving There was a problem of this deterioration.

The present inventors have solved the above problems, excellent surface properties, abrasion resistance and scratch resistance, and continued research to develop a polyester film excellent in friction characteristics and dropping resistance of the inorganic lubricant during high-speed driving, The present invention has been completed by discovering that the above problems can be solved by using two calcined kaolin particles having different particle diameters and contents, and using a slurry prepared by adjusting the circumferential speed and particle residence time of the mill.

SUMMARY OF THE INVENTION An object of the present invention is to provide a polyester film having excellent surface properties, abrasion resistance, and scratch resistance, significantly improved dropout, excellent frictional properties and dropping resistance of an inorganic lubricant at high speeds, and a method of manufacturing the same.

In order to achieve the above object, in the present invention, a lubricant slurry obtained by using a milling machine is added to a polyester resin, and then extruded and stretched to produce a polyester film. The calcined kaolin (A) having an average particle diameter of 0.05 to 0.5 μm and The calcined kaolin (B) having an average particle diameter of 0.51 to 3 µm was dispersed in glycol under the conditions of the circumferential speed of the milling machine at 8 to 15 m / min and the residence time of the particles in the mill to 50 to 150 minutes, respectively, to obtain lubricant slurries (A) and (B). After obtaining, the active slurries (A) and (B) are contained in an amount of 0.01 to 2% by weight of calcined kaolin (A) and 0.05 to 1% by weight of calcined kaolin (B), based on the weight of the polyester film. It provides to the polyester resin, the manufacturing method of the biaxially-oriented polyester film, and the polyester film manufactured by the said method are provided.

Hereinafter, the present invention will be described in more detail.

The present invention is characterized by using calcined kaolin as lubricating particles, but using two kinds of particle size distribution, and characterizing the circumferential speed of the mill and the particle residence time in the mill used when these kaolin particles are prepared in slurry. The average particle diameter of the first calcined kaolin particles used in the production of the polyester film of the present invention is in the range of 0.01 to 0.5 μm, preferably 0.05 to 0.2 μm, and preferably 0.01 to 2% by weight, based on the weight of the polyester. Can be dispersed in glycol in an amount of 0.05 to 1% by weight to obtain a lubricant slurry. When the average particle diameter of the first calcined kaolin is smaller than 0.01 μm, the surface roughness in the film is lowered, so that the friction coefficient is increased, so that the runability is poor, and when the first calcined kaolin is used at less than 0.01% by weight, the running friction coefficient High workability becomes poor. In particular, when more than 2% by weight of calcined kaolin particles having an average particle diameter of more than 0.5 μm is used, coarse particles are generated due to the coagulation of lubricant and the formation of large amounts of particles. Errors occur during manufacture of tapes, which is undesirable.

The second calcined kaolin particles used in the production of the polyester film of the present invention have an average particle diameter in the range of 0.51 to 3 µm, which is used for the purpose of improving runability. When the average particle diameter of the second calcined kaolin is smaller than 0.51 μm, the running property is not improved. When the average particle diameter is larger than 3 μm, the film surface is roughened due to the formation of large protrusions on the film surface due to the large particles. Dropouts occur and become poor due to errors in the manufacture of data storage tapes. In addition, the second calcined kaolin particles can be dispersed in glycol in an amount of 0.05 to 1% by weight, preferably 0.05 to 0.5% by weight, to obtain a lubricant slurry. If used more than 1% by weight, the dispersibility is poor, and since the physical properties of the film are lowered, it is not preferable.

In the present invention, in the preparation of the lubricant slurry, the mill may be selected either horizontally or vertically, but the disk circumferential speed of the mill should be 8 to 15 m / sec, and the residence time of the kaolin particles in the mill should be 50 to 150 minutes. . If the disk circumferential speed of the mill is less than 8m / sec, even if the residence time is in the range of 50 to 150 minutes, due to the lack of stress of the disk separating each particle, the cohesiveness is extremely poor during film preparation, the circumferential speed is 15m / second If exceeded, re-agglomeration of the crushed particles due to overdispersion occurs, which is not preferable.

In addition, if the residence time of the particles in the milling machine is less than 50 minutes, the undispersed particles are present, which is not preferable because of the high viscosity. If the particles are longer than 150 minutes, the viscosity of the slurry increases due to the cohesion of the superdispersed particles. It is not preferable because the fluidity and shelf life are lowered.

In addition, in the preparation of the slurry of the lubricant particles, a dispersing agent may be used to improve dispersibility. As the dispersing agent, for example, an acryl-based compound such as sodium polyacrylate, sodium methacrylate or ammonium acrylate, or benzenesulfonate-based Compounds and the like, and among them, those which are soluble in glycol can be selected and used.

At least 80 mol% of the repeating unit of the polyester resin used in the film of the present invention is composed of ethylene terephthalate, and other copolymerizing components are isophthalic acid, para-betaoxyethoxybenzoic acid, 2,6-naphthalene dicar Acids, 4,4'-dicarboxyl diphenyl, 4,4'-dicarboxylbenzophenone, bis (4-carboxydiphenyl) ethane, adipic acid, sephasinic acid, 5-sodium sulfoisophthalic acid Dicarboxylic acid components, such as propylene glycol, butadiol, neopentylglycol, diethylene glycol, cyclohexane dimethanol, and paraoxybenzoic acid, etc. can be used, selecting arbitrarily.

As a polyester resin used for this invention, the polyethylene terephthalate obtained by polycondensing dimethyl terephthalate and ethylene glycol is especially preferable.

The lubricant slurry prepared under the above conditions can be added to the polyester when the polyester resin is in the absence of production, preferably before the completion of the polycondensation.

The manufacturing method of the polyester film of this invention is not specifically limited, You may use either a transesterification method or a direct polymerization method, and you may use either a batch type or a continuous type. In addition, a polyester resin having a molecular weight of about 20,000 including the above additives may be prepared by biaxially stretching an unstretched sheet melt-extruded by a T-die method or the like.

When the transesterification method is used, there is no restriction on the transesterification catalyst that can be used, and any conventionally known one can be used.

Moreover, a polymerization catalyst is not specifically limited, either, It is preferable to select suitably from an antimony compound, a germanium compound, and a titanium compound, and to use.

Stretching can use the conventionally well-known polyester stretching method, and there is no change of a process by the said additive. It is preferable that extending | stretching temperature is 60-150 degreeC, and the draw ratio is 2.5 to 6.0 times in the longitudinal direction, and 2.5 to 6.0 times in the transverse direction.

The polyester film produced according to the present invention has an average agglomeration degree of film-like lubricant of 2 to 10, a distance (pv) between the highest and lowest projections on the film surface of 0.05 to 0.6 µm, and a height of 0.1 µm or more on the surface of the film. The number of protrusions having a length of 8 to 30 per 5 mm. If the average agglomeration exceeds 10, the electronic properties of the magnetic tape are degraded, and an error occurs in manufacturing the data storage tape, which is not preferable.

The polyester film produced according to the present invention can be designed in a suitable thickness depending on the use, but it is usually preferred to have a thickness in the range of 2.0 to 200 ㎛.

Hereinafter, the present invention will be described in more detail based on the following examples. However, the following examples are only for illustrating the present invention, and the scope of the present invention is not limited thereto.

The measuring method used in the following Examples is as follows.

1) Average particle diameter

It is the volume average particle diameter which measured the ethylene glycol slurry using the centrifugal particle size measuring device of Shimadzu, Japan.

2) surface smoothness

The surface roughness of the film of 30 mm in length, 20 mm in width, and 20 micrometers in thickness was measured by the contact type using the surface roughness meter of Kosaka Institute of Japan.

Center line average roughness (Ra): When drawing a straight line parallel to the average line of the roughness curve, the height of the straight line where both areas of the straight line are equal

Peak & valley distance (PV): distance between the maximum height and the minimum depth in the measurement section

The lower the average roughness and the maximum height, the better the smoothness and the better the cohesiveness.

3) Cohesive

The area of the film 500 cm 2 was analyzed by an optical microscope to measure the number of large particles and evaluated in the following four steps:

0 or more particles with a height of 1 µm or more are present: ◎

5 or more particles 1m in height or more are present.

15 particles or more with a height of 1 µm or more are present: △

15 or more particles having a height of 1 µm or more are present.

4) average cohesion

Using a projection electron microscope of Japan's Zolsa, cut the film to a thickness of 100 nm, observe the particles on the shear plane at a magnification of 100,000 times, and analyze how many primary particles are the aggregated particles. Averaged.

5) Number of protrusions

Using a surface roughness meter from Kosaka Institute of Japan, a surface roughness of 30 mm in length, 20 mm in width and 20 μm in thickness was measured by 5 mm in the contact manner and the surface roughness was evaluated in the following four steps:

8 or more projection heights of 0.1㎛ or more: ◎

In case of 6 to 7 protrusion heights of 0.1 µm or more: ○

In case of 4 to 5 protrusion heights of 0.1 µm or more: △

In case of 0 to 3 protrusion heights of 0.1㎛ or more: ×

6) dropout

Magnetically coated films were measured for 1 minute using a dropout counter from I & I, Japan, and error occurrences of more than 5 μs × 20 dB were called dropouts and evaluated in four steps:

Dropout occurrences below 5: ◎

Dropout occurrences 5 to 10: ○

10 to 15 dropout occurrences: △

15 or more dropouts: ×

7) Drop resistance

Using tape running tester of Yokohama Systems Research Institute, Japan, the film was slept 1/2 inch wide at 20 ° C and 60% RH atmosphere, and 200m long at 300m / min. Observation by dropping resistance as a percentage of occurrence of the powder around the guide pin when viewed under a microscope was evaluated in four steps:

If there is no powder on guide pin: ◎

100% buried, 1/5 area of guide pin: ○

Percentage of powder, 1/2 area of guide pin: △

Percentage Buried, Occurs Overall on Guide Pin: ×

Example 1

Calcined kaolin A with a 0.3 µm particle diameter and calcined kaolin B with a 0.7 µm particle diameter were respectively 9 m / sec in the mill, and the residence time of the calcined kaolin A and B in the mill was 55 minutes. Slurry A and B were prepared by dispersion in concentration.

Dimethyl terephthalate and ethylene glycol were mixed in an equivalent ratio of 1: 2, 0.04% by weight of calcium acetate was added to the reactor as a transesterification catalyst, and transesterified for 2 hours to substantially complete the transesterification system. Slurry A and Slurry B were added in an amount such that 0.3% by weight of calcined kaolin A and 0.1% by weight of calcined kaolin B were added thereto, and then 0.04% by weight of trimethylphosphate and 0.03% by weight of antimony trioxide were added thereto. Time-polymerization reaction was performed and polyester was obtained.

After drying, the polyester was extruded into a sheet by an extruder at 290 ° C. to a rotating cooling drum to obtain a sheet in an amorphous form. Thereafter, the film was stretched 3.0 times in the longitudinal direction and 3.0 times in the transverse direction at 90 ° C. to obtain a film having a thickness of 20 μm.

Physical property test results of the polyester film obtained above are shown in Table 1 below.

Example 2 to 3

In the manufacture of a polyester film, the particle size and content of the calcined kaolins A and B; And a polyester film was prepared in the same manner as in Example 1, except that the disc circumferential speed and residence time of the mill during slurry production were changed within the scope of the present invention as shown in Table 1 below.

Physical property test results of the obtained film are summarized in Table 1.

Comparative Examples 1 to 8

In manufacture of a polyester film, the kind, particle diameter, and content of a lubricating particle; And the polyester film was prepared in the same manner as in Example 1, except that the circumferential speed and residence time of the mill during slurry production to deviate from the scope of the present invention as shown in Table 1.

Physical property test results of the obtained film are summarized in Table 1.

Particle Type Average particle size (㎛) Content (% by weight) Mill Surface smoothness Cohesive Mean coagulation Number of protrusions Dropout Falling Resistance Disk speed (m / s) Retention time (minutes) Center line average roughness (Ra: ㎛) Center Line Maximum Height (PV) Example 1 Kaolin A Kaolin B 0.30.7 0.30.1 9 55 0.017 0.155 ◎ 6 ◎ ◎ ◎ Example 2 Kaolin A Kaolin B 0.30.8 0.30.09 10 65 0.017 0.168 ◎ 4 ◎ ◎ ◎ Example 3 Kaolin A Kaolin B 0.30.9 0.20.08 12 75 0.019 0.198 ◎ 3 ◎ ◎ ◎ Comparative Example 1 Kaolin 0.3 0.3 7 55 0.021 0.225 × 15 △ × ○ Comparative Example 2 Kaolin 0.7 0.09 9 40 0.025 0.298 × 16 △ × △ Comparative Example 3 Kaolin 0.9 0.08 7 45 0.033 0.435 × 20 × × △ Comparative Example 4 Calcium carbonate 0.8 0.2 9 40 0.027 0.321 ○ 18 △ × △ Comparative Example 5 Silica 0.5 0.3 6 45 0.021 0.255 ○ 11 △ △ ○ Comparative Example 6 Kaolin A Kaolin B 0.30.7 0.30.1 7 40 0.034 0.329 × 28 × × × Comparative Example 7 Kaolin A Kaolin B 0.30.9 0.20.08 11 40 0.041 0.501 × 35 × × × Comparative Example 8 Kaolin A Kaolin B 0.30.8 0.30.09 11 160 0.051 0.652 × 49 × × ×

As shown in Table 1, the polyester film of the present invention is particularly suitable for magnetic recording tapes because of excellent surface characteristics, wear resistance and scratch resistance, and excellent friction characteristics and high dropping resistance of inorganic lubricants at high speeds. It can be widely used in various applications requiring surface properties, abrasion resistance and scratch resistance.

Claims (4)

A lubricant slurry obtained by using a milling machine is added to a polyester resin, followed by extrusion molding and stretching to prepare a polyester film. (B) was dispersed in glycol under the conditions of a circumferential speed of 8 to 15 m / min of the mill and a residence time of 50 to 150 minutes of the particles in the mill to obtain lubricant slurries (A) and (B), and then the weight of the polyester film Based on the calcined kaolin (A) is 0.01 to 2% by weight and calcined kaolin (B) is characterized in that the addition of the active slurry (A) and (B) to the polyester resin The manufacturing method of the biaxially-oriented polyester film made. The method of claim 1, Method of using a dispersant in the preparation of the lubricant slurry. A biaxially oriented polyester film produced by the method of claim 1 or 2. The method of claim 3, wherein The polyester film has an average agglomeration degree of film-like lubricant of 2 to 10, a distance (pv) between the highest and lowest protrusions on the film surface is 0.05 to 0.6 μm, and the number of protrusions having a height of 0.1 μm or more on the film surface is measured. Polyester film, characterized in that 8 to 30 per 5mm length.