KR19980054877A - Biaxially stretched polyester film for data storage media - Google Patents

Abstract

The present invention is characterized in that the ratio of the central line average roughness (SRa) to the ten-point average roughness (SRa) is 0.030 to 0.050 by additionally containing main particles giving surface smoothness and larger sub- By weight of kaolinite-type calcium carbonate particles or plate-like kaolin, and the sub-particles contain 0.05-0.4% by weight of calcium carbonate having an average particle diameter of 600-1500 nm, and the physical properties Relates to a biaxially stretched polyester film for a data storage medium which satisfies the following conditions.

Where μ _k denotes a dynamic friction coefficient, t-3 is the average refractive index, n _T is the thickness direction of the refractive index of the film, R is a difference between the maximum and minimum values of the thickness, t-12 has an average thickness, [R / t-12 × 100] indicates the thickness non-uniformity.

Description

Biaxially stretched polyester film for data storage media

The present invention relates to a biaxially stretched polyester film for use in a magnetic recording medium such as an audio or video magnetic recording tape or a magnetic recording disk. More particularly, the present invention relates to a biaxially stretched polyester film for a data storage medium, High-smoothness data storage media showing abrasion resistance and excellent electronic conversion characteristics.

In general, polyesters such as polyethylene terephthalate have excellent mechanical and chemical properties and are used in various products of films and fibers. Especially when used as a polyester base film for magnetic recording media such as audio or video tape, their running properties, winding properties, abrasion resistance, smoothness and electronic variation characteristics affect productivity and quality improvement. For example, increasing the production speed in the current film or magnetic tape production process affects the productivity and quality because the film surface and the friction of the rolls may cause a relatively large amount of scratches and / or scratches in comparison with the low speed production. For example, increasing the production rate in the current or magnetic tape production process affects the productivity and quality as it may cause a relatively large amount of scratches or scratches due to the friction between the film surface and the roll as compared to the low speed production. Further, in the case of a film having surface roughness favorable for running property and windability, there is a possibility that the electron conversion characteristic is lowered.

In order to solve such a problem, in order to improve the running property, winding property and abrasion resistance of the base film within a range that does not cause deterioration of the electron conversion characteristics, a water-soluble polymer having a proper molecular weight, polysiloxane, styrene butadiene rubber (USP 4,550,049) or a method in which fine particles having a large hardness and particles having a larger particle diameter are mixed and used (Japanese Patent Laid- 316316, JP 62-214518, JP 63-108037, JP 06-84445, JP 04-40375, etc.) are mainstream, and the fine particles impart abrasion resistance in view of the function of bottom reinforcement. . Commonly used particles are spherical silica, calcium carbonate, alumina, titinia, zirconia, kaolin, crosslinked polymers, and combinations thereof, and have been steadily changing to improve the properties of such film substrates.

In general, the coating thickness of the magnetic recording medium is about 3-5 占 퐉, but the thickness of the coating layer is becoming thinner for the purpose of cost reduction and productivity improvement. The polyester base film obtained by the conventional method described above has good elastic modulus, Mechanical strength and chemical properties, but it was impossible to produce a film having excellent surface smoothness, running property and abrasion resistance in terms of cost, productivity and quality. Therefore, the object of the present invention is to provide a biaxially stretched polyester base film for a data storage medium in which a polyester base film is produced, and this problem is solved.

In order to solve this problem, the inventor of the present invention has found that, in order to make the ratio of the center line average roughness (SRa) to the ten-point average roughness (SRz) 0.030-0.050 by additionally including the main particles giving the surface smoothness and the sub- 0.01 to 1.0% by weight of hexahedral calcium carbonate or plate-like kaolin having an average particle diameter of 300 to 800 nm and a calenderite structure, and 0.05 to 0.4% by weight of calcium carbonate of 600 to 1,500 nm as sub- The physical properties of the film thus obtained were able to complete the present invention so as to satisfy the following conditions.

(Where mu _k represents the coefficient of dynamic friction, N _T is the refractive index in the thickness direction of the film, R is the difference between the maximum value and the minimum value of the film thickness, The average thickness of the film, Is the thickness non-uniformity.)

The present invention will be described in detail. Recently, media companies have been increasing the coating speed and the thickness of the coating layer for the purpose of cost reduction and productivity improvement. Therefore, the running property, windability, abrasion resistance, and electronic conversion characteristics of the polyester base film greatly affect the productivity of the magnetic tape and the processability. For example, when a polyester base film lacking such characteristics is used for a magnetic material high-speed coating for magnetic tape production, the friction between the coating roll and the film becomes large, causing the film to scratch and scratch. In addition, Dropouts cause defects such as dropouts.

At this time, many studies have been made on a method for judging excellent running property or sliding property and electron conversion characteristic of a polyester film. For example, a method (USP 4,680,217) for evaluating the properties of the surface of a polyester film as a function of the number of projections and surface roughness (SRa) (USP 4,708,902: USP 5,087,526) It has been progressing.

However, when this method is applied to this study, it is difficult to solve problems such as coating irregularities or scratches occurring during high speed coating of magnetic materials. Therefore, the inventors of the present invention have developed a method that is simpler and more easily predictable than the above-mentioned complicated methods. That is, when the centerline average roughness value (SRa) showing the surface smoothness is small, the electronic conversion characteristic is excellent, but the running property and slippery property are bad, so that the scratch due to wear is easy, and if the average roughness value (SRz) There are few problems. Therefore, the relative ratio of these two values, ie, the centrality average roughness (SRa / SRz) to the ten-point average roughness, can be considered as a method that can simultaneously consider the above two problems.

The injector used in the present invention adjusts the appropriate center line average roughness (SRa), and the large sub-particles added additionally are used to control the ten point average roughness (SRz), which leads to better running, abrasion resistance and electron conversion characteristics I created a shared product.

Furthermore, polyester basic properties which can evaluate the excellent running property without causing deformation such as heat shrinkage or thermal expansion of the polyester film due to the frictional heat occurring between the coating roll and the back-up rate in the magnetic material coating process include average refractive index and refractive index in the thickness direction have. The average refractive index (t-3) gives an excellent running characteristic when it is in the range of 1,600 or more and better than 1,603-1,605. Also, when the refractive index in the thickness direction (n _T ) is between 1,490 and 1,500, the running property is excellent. In the present invention, a product satisfying the range of 1,491-1,493 was developed.

When the thickness of the polyester base film is non-uniform, there may be a difference in pressure between the coating roll and the backup roll in the magnetic coating process, and the coating unevenness may cause problems with the adhesion between the head of the tape and the coated base film have. Therefore, a polyester base film having a uniform thickness is required (USP 4,610,833; USP 4,680,217). In the present invention, the thickness non-uniformity of the polyester base film was made to be 30% or less. The polyester used in the present invention may contain an aromatic dicarboxylic acid or an ester-forming compound thereof and an alkylene glycol as main components and another third component. Terephthalic acid and dimethyl terephthalate are mainly used as the dicarboxylic acid and its ester forming compound, and ethylene glycol is mainly used as the alkylene glycol component. The produced polyester has repeating structural units of ethylene terephthalate and 80% And the better the content ratio of the repeating structural units, the better. In the present invention, the polyester may include additives such as a flame retardant, a stabilizer, a filler, a plasticizer, a colorant, an antioxidant, an antistatic agent, an ultraviolet absorber and the like.

The average particle size of the calcium carbonate or kaolin particles used as the impregnator for imparting surface smoothness is preferably from 0.2 to 1.6 μm, but is preferably from 300 to 800 nm for the data storage medium, 1.0% by weight is generally used, and in the case of the sub-particles, 0.05-0.4% by weight is preferable. At this time, when the average particle size of the injector is 1.6 占 퐉 or more, or when the content exceeds 1.0% by weight, the value of the center line average roughness (SRa) becomes 20 nm or more, The coarse particles having a particle diameter of 2.5 탆 or more in the case of the sub-particles may cause problems in dropout or electron conversion characteristics after coating with the magnetic material, so they are classified and removed. When the content is less than 200 nm or the content is less than 0.01% by weight, the value of dynamic friction coefficient becomes equal to or greater than the expected value, and the running property and the abrasion resistance can not be achieved.

The properties of the particles and the polyester film used in the present invention, such as running property, abrasion resistance, electron conversion characteristic, thickness non-uniformity, and the like, are measured by the following methods.

(1) Average Particle Size

All particles used were measured with a particle size analyzer (Granulometer HR-850, or Zeat sizer) in an ethylene glycol slurry and the particle size on the final film was measured using an electron microscope (SEM) Of 50% by volume calculated as an average particle diameter.

(2) Surface roughness (contact type three-dimensional illuminometer)

The surface roughness is measured with a contact type 3-dimensional roughness meter (SE-3300, KOSAKA) based on JIS BO 601-1994, the curved diameter of the contact needle tip is 2 μm and the needle pressure is 30 mg. The standard measurement length (L) is 1.1 nm and the surface roughness curve is the value obtained by the following equation when y = f (x).

The ten-point mean roughness (Rz) is the difference between the height of five mountains and the depth of five bones in the section curve.

(3) Film running ability

The angle of the part where the film was wound on a metal roll (diameter: 6 mm) plated with a fixed hard chrome was contacted at 180 ° (3.142 rad (?)), A load of 50g (T ₂ ) was applied to one end, / Second, measure the tension (T ₁ ) at the other end and calculate the coefficient of friction (μ _k ) during running according to the following formula.

(4) Evaluation of abrasion resistance

(SE-3300, KOSAKA) using the Haydon coefficient of friction measuring system and the specially designed loading area to cause forced repetitive friction between the film and the guide pin, And the number of protrusions by the height is measured in terms of volume, and quantified by the rate of change in volume before and after the friction. The lower the value, the better the abrasion resistance. Calculation formula of measurement condition and volume change rate is as follows.

Measuring conditions

- Load: 90g

- Measuring length: 50mm

- Measurement speed: 50mm / sec

- Number of repeated driving: 200 times

Here, Ni 'is the friction level (SLICE LEVEL), Ni is the height after friction, and n is the number of each height.

(5) Refractive index of film

The Abbe refractometer is measured at 25 ° C using sodium D radiation as a light source, and the longitudinal and transverse thickness directions are defined as n _MD , n _TD , and n _T , respectively.

(6) Film thickness non-uniformity

The thickness of the film was measured using a micrometer at intervals of 10 cm in the transverse direction.

(R is the difference between the maximum value and the minimum value of the film thickness, The average thickness of the film)

(7) Magnetic tape and cartridge characteristics

Tape or cartridge sample

The resulting polyester film was coated with a magnetic paint using a reverse roll as shown in the following composition, self-aligned, and then calendered at a temperature of 70 ° C using a steel / nylon five-stage calender roll at a feed rate of 200 kg / cm And aged at 70 DEG C for 48 hours.

The above-mentioned tape master was slit into a tape or a cartridge by slitting at 1/2 inch, and the characteristic properties were measured by the following method.

[Composition of magnetic paint]

Iron oxide: 100 parts by weight

Vinyl chloride / vinyl acetate copolymer 10 parts by weight

Polyurethane elastomer: 10 parts by weight

Lecithin: 1 part by weight

Methyl ethyl ketone: 75 parts by weight

Methyl isophthalate: 75 parts by weight

Toluene: 75 parts by weight

Lauric acid: 1.5 parts by weight

Evaluation of head adhesion by number of dropouts

In the case of VHS, a video tape on which a signal of 0-4.4 MHz is recorded is reproduced, and the number of dropouts is measured for a specific time using a dropout counter device VH01-CZ manufactured by Shiba Soaku, Switch to the number of outs.

Evaluation of the Electromagnetic Reflection Characteristics (C-S / N, Y-S / N)

Measure the color noise (C-S / N) and luminance noise (Y-S / N) of the tape or cartridge made of the polyester film produced by using the device manufactured by Shiba soaku with 0 dB of the home VTR.

The present invention will be described with reference to Examples and Comparative Examples.

Production of polyester

100 parts of dimethyl terephthalate, 70 parts of ethylene glycol, and 0.09 parts of manganese acetate tetrahydrate 0.04 part of antimony trioxide were charged into a reactor, and the methanol was distilled out by heating. After transesterification for 4 hours, calcium carbonate The particles or the spherical silica particles were subjected to an ester exchange reaction at the end of the initial stage, 0.06 part of phosphoric acid was added to the reaction product, and the reaction was carried out for 4 hours to obtain a polyester having an intrinsic viscosity of 0.63 part. In this case, the calcium carbonate particles having an average particle diameter of 300 to 800 nm are surface-treated with a polyacrylic salt, the coarse particles having a particle size of 1.6 mu m are removed with a classifier, and then added to prepare a polyester (A). Kaolin particles are then added (B). In the case of calcium carbonate having an average particle diameter of 600-1500 nm, which is additionally used as a large particle, a copolymer of an olefin-maleic salt is surface-treated and a coarse particle of 2.5 μm or more is classified to produce a polyester (C) .

(D) having an intrinsic viscosity of 0.62 was obtained without the addition of inorganic particles. All of these polyesters were processed into chips in order to facilitate the input of the film manufacturing process.

[Example 1]

After drying the polyester chips (A), (C), and (D) synthesized above at 150 ° C. and 10 Torr for about 6 hours, a two-dimensional sheet having a certain thickness was discharged and cooled and solidified at 30-50 ° C. I made an unstretched film.

The film was stretched 3.5 times at 100-130 占 폚 in the longitudinal direction, stretched 4.0 占 퐉 at 100-140 占 폚 in the transverse direction, and immediately subjected to heat treatment at 230 占 폚 to produce a film. The physical properties of the prepared two-side stretched polyester film were measured in accordance with the above-mentioned method, and the results are shown in the following table.

[Example 2]

The unstretched film used in Example 1 was stretched 4.2 times at 90-110 占 폚 in the longitudinal direction, 4.2 times at 100-140 占 폚 in the transverse direction, and immediately heat-treated at 210 占 폚 to prepare a biaxially stretched film. The results of physical properties are shown in the following table.

[Example 3]

A biaxially stretched polyester film was prepared in the same manner as in Example 1 except that the polyester chips (B), (C) and (D) synthesized above were used, .

[Comparative Example 1]

A biaxially stretched polyester film was produced in the same manner as in Example 1 except that the polyester chips (A) and (D) were used, and the results of the physical properties thereof are shown in the following table.

[Comparative Example 2]

A biaxially stretched polyester film was produced in the same manner as in Example 2 except that the polyester chips (A) and (D) were used, and the results of the physical properties thereof are shown in the following table.

[table]

Claims (4)

Wherein the ratio of the centerline average roughness (SRa) to the ten-point average roughness (SRz) is 0.030 to 0.050 by including an additional major particle that imparts surface smoothness and a larger minor particle. [Claim 3] The method according to claim 1, wherein the injector comprises 0.01-1.0 wt% of hexahedral calcium carbonate particles having a mean particle diameter of 300-800nm or a plate-like kaolin having a calcite structure and the subparticles are calcium carbonate having an average particle diameter of 600-1500nm -0.4% by weight of the polyisocyanate and the physical properties of the finally produced film satisfy the following conditions. Here, μ _k represents the coefficient of dynamic friction, N _r is the refractive index in the direction of thickness of the film, R is the difference between the maximum value and the minimum value of the film thickness, Is the average thickness of the film, and [R / t-12 x 100] is the thickness non-uniformity. The method according to claim 1, wherein the injector used in the finally produced film is surface treated with a plyacrylic salt in the case of calcium carbonate having an average particle diameter of 300 to 800 nm, and coarse particles having a particle size of 1.6 탆 or more are classified and used, Characterized in that in the case of calcium carbonate having a particle diameter of 600 to 1500 nm, the surface treatment is performed with a copolymer of an olefin and a maleic salt, and coarse particles of 2.5 m or more are classified and used. The polyester film according to any one of claims 1, 2 and 3, wherein the polyester film comprises at least one of a flame retardant, a stabilizer, a filler, a plasticizer, a colorant, an antioxidant, an antistatic agent or an ultraviolet absorber Biaxially stretched polyester film for data storage media .0