JPH01311131A - Polyester film for magnetic recording medium - Google Patents

Abstract

PURPOSE:To obtain the subject polyester film having excellent scratching resistance, readily cutting properties, slipperiness, etc., containing inactive inorganic particles having specific hardness and inactive particles having larger average particle diameter than the inorganic particles and having intrinsic viscosity in a specific range. CONSTITUTION:The aimed polyester film containing (A) inactive inorganic particles (e.g., Al2O3 or SiC) having >=6, preferably >=8 Mohs hardness and (B) inactive particles (e.g., SiO2 or kaolin) having a larger average particle diameter than the component A and having 0.52-0.62 intrinsic viscosity. Particles having 0.0050.1mu average particle diameter are used as the component A and the amount of the particles used is preferably 0.05-5wt.% based on the polyester. Particles having 0.1-3.0mu average particle diameter are used as the component B and the amount of the particles used is preferably 0.05-2.0wt.% based on the polyester.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a polyester film that has excellent electrical properties, runnability, and abrasion resistance when used as a magnetic tape. More specifically, the present invention relates to a base film for high-density magnetic recording that has extremely few scratches and generation of abrasion powder during tape running (and has excellent magnetic tape cutting properties).

[Problems to be solved by conventional technology and invention]

Polyester films have excellent physical and chemical properties and are widely used in industry. In particular, biaxially oriented polyethylene terephthalate film is now indispensable as a base material for magnetic recording media because of its superior flatness, mechanical strength, and dimensional stability compared to other films.

On the other hand, improvements in magnetic recording media have been made at a rapid pace in recent years, and as a result, requirements for base films have become even more stringent. For example, in applications requiring high-density recording, such as videotapes, a flatter base film surface is required. However, if the film surface becomes flat (as is known),
Friction and abrasion between the parts that come into contact with the film become a problem, causing damage to the film and increased generation of abrasion powder, causing various problems.

For example, if abrasion powder is generated before the magnetic layer coating process, which includes the film manufacturing process, it can cause dropouts due to missing magnetic layer coating or transfer of abrasion powder to the magnetic layer surface. When abrasion powder is generated in the calendering process performed for the purpose of oxidation, it adheres as white powder to the surface of the calender roll, roughening the surface of the magnetic layer and causing a decrease in charge. Furthermore, if the abrasion resistance is poor even after the product is manufactured, abrasion powder generated in the running system within the tape deck will cause a decrease in charge and frequent dropouts.

Furthermore, in recent years, there has been an increasing demand for improved scratch resistance in addition to abrasion resistance for base films. This is because the tape may be damaged at the contact point during the tape dubbing process or the like, or the film may be damaged from abrasion powder generated.

These scratches not only have an undesirable appearance, but also cause process contamination and increased dropouts.

In order to improve the abrasion resistance and scratch resistance of such films or tapes, it is known that K can be used to appropriately roughen the surface of the film by making inactive fine particles present in the polyester film.

Such appropriate surface roughening not only improves abrasion resistance and scratch resistance, but also contributes to improvements in film handling workability and running properties as a magnetic tape, and is sufficient to meet recent strict demands. 5. In order to fully satisfy these characteristics, it is necessary to increase the amount of fine particles mixed or increase the particle diameter, but these methods may raise the average roughness too much. This leads to an increase in the number of coarse protrusions due to the presence of coarse particles, resulting in a decrease in the electromagnetic conversion characteristics of the magnetic tape and an increase in dropouts. It is extremely difficult to achieve this contradictory phenomenon.

The only effective method known is the so-called back coating method, in which a suitable coating is applied to the opposite side of the magnetic layer, but it is extremely expensive and has various problems with its characteristics, making it impractical for practical use. It wasn't the way it was.

On the other hand, one of the main properties required for a base film of a magnetic recording material is ease of cutting.

This is because when cutting magnetic tape to a certain width, if the base film has poor cuttability, the cut surface may turn over in a striped manner. This is a phenomenon in which the powder turns into powder and flakes off. If this phenomenon worsens further, powder may fall from the magnetic layer, and these fallen powder may cause dropouts.

As a method for improving cuttability, for example, a method of increasing the crystallinity of the film is known. However, increasing the degree of crystallinity deteriorates abrasion resistance, so in practice, it is not possible to increase the degree of crystallinity to an extreme degree, and the reality is that the base film is designed at the expense of cuttability to some extent. .

As described above, it would be extremely useful industrially if the abrasion resistance, scratch resistance and easy cutting properties of base films for magnetic recording media could be effectively improved by simple means.

[Means for solving problems]

In view of the above circumstances, the present inventors conducted intensive studies on polyester films for magnetic recording media, and found that polyester films containing specific fine particles have excellent abrasion resistance, scratch resistance, and ease of cutting. This discovery led to the present invention.

That is, the gist of the present invention is a polyester film containing inert inorganic particles (a) having a Mohs hardness of 6 or more and inert particles (b) having a larger average particle size than the particles (a); The intrinsic viscosity of the film is o,! ;2
The present invention relates to a polyester film for magnetic recording media, characterized in that the polyester film is in the range of .

The present invention will be explained in more detail below.

The polyester referred to in the present invention is a polyester that can be obtained by polycondensing terephthalic acid or its ester and glycol.

This polyester can be obtained by directly reacting terephthalic acid and glycol, or by polycondensation after transesterification of an alkyl ester of terephthalic acid and glycol, or by polycondensation of glycol ester of terephthalic acid. It can also be obtained by

In the present invention, two or more types of particles having different hardness and particle size are used in combination with polyester,
Furthermore, it is characterized by its intrinsic viscosity when formed into a film. That is, in order to improve the handling workability and abrasion resistance of polyester film, and to improve the runnability, abrasion resistance, and scratch resistance after making it into a magnetic tape, it is necessary to incorporate inert fine particles into polyester. It is already known that this is the case. The present inventors have found that if particles (a) having a Mohs hardness of 6 or more are used in combination with other particles (b) having a larger particle size, these properties can be significantly improved, especially scratch resistance. It has been found that the properties can be significantly improved. Furthermore, in addition to these characteristics, the inventors have discovered that in order to improve the cutting properties when cutting magnetic tape into a certain width, it is sufficient to set the intrinsic viscosity of the film to 0.32 to 0.62, thereby achieving the present invention.

Particles Ca) having a Mohs hardness of 6 or more used in the present invention include, for example, S i 02, T i 02, Alz O3, S
iC.

Examples include zeolite and celite, but the particles are not limited to these as long as they have a Mohs hardness of 6 or more. Among these, Al2O3, SiC%T, which has a Mohs hardness of
i C, titanium black, especially At203 is preferably used.

Al2O3 which is particularly preferably used in the present invention is usually obtained by a so-called thermal decomposition method, and is generally 1
It has a particle size of about 0 mμ to 100 mμ.

In this case, a part of A1□o3, for example less than 30% by weight, is Si.
It may also be substituted with an oxide such as Na, K, or the like.

Note that the particle size distribution of particles (a) is not particularly limited, but particles with a sharper particle size, for example, when integrated from the smallest particle size, the weight fraction is 75% and the particle size ratio of 2j% is 2.
．． θ or less, preferably /, j or less, more preferably /,
J or less is preferably used.

Furthermore, there is no particular restriction on the shape of the particles (a), but
Those that are more lumpy or spherical than usual are preferably used. Specifically, particles having a volumetric shape coefficient Theo, / to π/6, preferably 0.2 to T are preferred.

There is also no particular restriction on the specific surface area of the particles (a) used. For example, particles with an average particle diameter of O, Sμ have a specific surface area of about 4 m2 /I assuming that they are true spheres and have a density of 2ji/an3, but even porous particles of uoom''/11100 can be suitably used.

The surfaces of these particles (,l) may be modified with various surface treatment agents.

These surface treatment agents, which are normally used for the purpose of improving the affinity with ethylene glycol and polyester, are generally applied in an amount of less than 1% by weight relative to the particles, such as silane coupling agents and titanium cup Mention may be made of ring agents.

If the Mohs hardness of the particles (a) is less than 6, the effect of improving scratch resistance will be insufficient, so a Mohs hardness of 6 or more is an essential requirement. The mechanism by which particles with a high Mohs hardness give good results in terms of scratch resistance is not clear, but the effect is more pronounced for particles with a higher hardness than the areas in contact with the film, which suggests that they form protrusions on the film surface. It is thought that the particles abrade the sharp parts that they come into contact with, thereby reducing damage to the film surface. Furthermore, the present invention is characterized in that other particles (b) having a larger average particle diameter than the highly hard particles (a) are used in combination. This particle (
As b), either inorganic particles or organic particles may be used as long as they are inert to polyester.

The Mohs hardness of the particles (b) is also not particularly limited, but it is preferably lower than the hardness of the particles (a). Furthermore, two or more types of particles may be used in combination, if necessary.

The present invention further has an intrinsic viscosity of 0.32 when made into a film.
It is characterized by being in the range of ~0.4. The lower the intrinsic viscosity, the better the ease of cutting is, but the lower the intrinsic viscosity, the better.
If it is less than 2, it is not preferable because breakage occurs frequently during film formation, which impedes productivity.

On the other hand, if it exceeds 0.6:l, the effect of improving cuttability becomes poor. Particularly preferably, it is in the range of 11 to 0.60.

In addition, in the present invention, the particles (a) usually have an average particle diameter of 0.00! The content is usually 0.03 to Swt%, preferably 0.7 to Swt%, based on the polyester.
), the average particle size is usually 0.7 to 3.0 μm, preferably 0.0 μm. ．． 7~/, jμm is used, and the content is usually 0.01 A-co, Owt%, based on polyester.
Preferably it is o, /~/, Owt%. particle (a
) If the average particle size of particles (a) exceeds 0.7 μm, the effect of the large particles used in combination will be insufficient, resulting in poor slipperiness and wear resistance.On the other hand, if the average particle size of particles (a) is less than o, o o s μm, ,
The effect of improving scratch resistance is inferior and is not preferred. Further, the content of the particles is 0. If the content is less than 5 wt%, the effect of improving scratch resistance will not be observed, and on the other hand, if the content exceeds 5 wt%, coarse protrusions will occur due to aggregation, resulting in a decrease in the electromagnetic conversion characteristics of the magnetic tape and an increase in dropouts. If the particle size exceeds 3 μm, the roughness of the film becomes undesirable. This is undesirable because it increases the cost, which leads to deterioration of electromagnetic conversion characteristics after forming into a magnetic tape. The content of the particles is 0.0! ;w
If it is less than t%, the handling properties and abrasion resistance of the film, and the running properties and abrasion resistance of the magnetic tape will be poor, and if it exceeds 2wt%, the roughness of the film will become too high and coarse protrusions will be formed due to particle aggregation. 5, which is undesirable as it causes a decrease in the retention of the magnetic tape and an increase in dropouts.

The particles used in the present invention are preferably subjected to generally used crushing treatment, classification treatment, and filtration treatment to remove coarse particles. For example, a rod mill, a ball mill, a vibrating rod mill, a vibrating ball mill, a pan mill, a roller mill, an impact mill, a disc mill, an agitating grinding mill, a fluid energy mill, etc. can be used for the crushing process. One or more of the semi-free swirl method, forced swirl method, hydrocyclone method, centrifugation method, etc. can be used.

In the present invention, the particles may be added to the polyester in any manner before the start of polycondensation, during polycondensation, or after polycondensation, but particularly preferably before polycondensation and at the beginning of polycondensation reaction. In the present invention, in order to coexist one or more types of particles in the film, each particle is added individually to the polyester, and a predetermined amount of each polyester is blended at the time of film formation, or the particles are added to the polyester. In this case, it may be obtained by blending a predetermined amount of each particle.

In addition, the polycondensation reaction catalyst used is usually sb, Ti%
Examples include Sn and Si compounds.

In the present invention, the refractive index in the thickness direction of the film is 1. If it is 2 or more, the running properties, abrasion resistance, and scratch resistance are further improved.

In order to obtain a film having such physical properties, for example, in the case of longitudinal-horizontal sequential biaxial stretching, it can be obtained by setting the longitudinal stretching temperature to about 3 to Jθ °C higher than the normal stretching temperature, ior to its °C. However, it can also be obtained by performing significant transverse relaxation after biaxial stretching and before heat treatment. In the present invention, the upper limit of na is /,
It is preferably about t/0.

〔Example〕

Hereinafter, the present invention will be explained in more detail with reference to Examples.
The present invention is not limited to the following examples unless it exceeds the gist thereof.

The methods and definitions for determining σII+ of various physical properties and characteristics in the examples are as follows. Further, in the examples, "part" or "%" means "part by weight" or "% by weight", respectively.

(1) Slip property Measured using the apparatus shown in Figure 1. That is, the film is wound around a fixed hard chrome-plated metal roll (diameter 6 mm) and brought into contact at an angle of /35° (θ), r, y fl (T2
) with a load on one end, run it at a speed of /m/7FLi, measure the resistance (T+,,!/) at the other end,
The coefficient of friction (μd) during running was determined using the following formula.

(2) Abrasion resistance Using the device shown in Figure 2, the film was run for 200 m, and the amount of white powder adhering to the fixing pin was visually judged. ') Less and better 6.7. ), I((The amount of adhesion is small (no problem in practice)
It was divided into three ranks: , C (poor practicality due to large amount of adhesion).

(3) Intrinsic viscosity [η] Polymer/I = phenol/tetrachloroethane! 0
Dissolved in 100me of mixed solvent of 7!0 (weight ratio), 3
Measured at 0°C.

(4) Refractive index (na) in the film thickness direction Sodium D
The refractive index in the film thickness direction with respect to the line was measured.

(5) Weight integration S in uniform sphere diameter distribution obtained by average particle diameter microscopy
A point of 0% was used.

(6) Manufacture of magnetic tape The magnetic paint shown below was applied to a polyester film to form a magnetic layer having a thickness of 2 μm after drying. That is, 200 parts of magnetic fine powder 1, l-'' IJ urethane resin 30
70 parts of nitrocellulose, IO part of vinyl chloride-vinyl acetate copolymer, lecithin S part, 100 parts of cyclohexanone, 200 parts of methyl isobutyrate, and 300 parts of methyl ethyl ketone were mixed and dispersed in a ball mill for tIt hours. After adding the isocyanate compound S part to make a magnetic paint and applying it to a polyester film,
Magnetic orientation was applied before the paint was sufficiently dried and solidified, and then dried. Further, this coated film was subjected to surface treatment using a supercalender, and was slit into 4-inch widths to make a videotape. This videotape is Matsushita Electric Ryo 3 NV-
The following magnetic tape characteristics were evaluated using a 3700-type video deck at regular speed.

The VTR head output at a measurement frequency of Hiromegahertz was measured using an OVTR head output synchroscope, and the relative value was expressed in decibels with a blank as θ decibels.

0 Number of dropouts q, playback the tape recorded with a signal of q megahertz, measure the number of dropouts with a dropout counter for about 20 minutes, and
It was converted into the number of dropouts per minute.

(7) Scratch resistance A magnetic tape cut into inch pieces is attached to a hard chrome-plated metal pin (diameter 61II11, surface roughness 3S) under tension θ.
I. Wrapping is at an angle of 35°, and rubbing is performed 7 times at a running speed of 1 m/sec. Aluminum vapor deposition was performed on the scratched surface of the magnetic tape, and the amount of scratches was visually determined and ranked as follows.

Rank L: The amount of damage is extremely large.

Rank-2: A large amount of damage.

Rank 3: The amount of damage is between rank λ and da.

Rank tI: The amount of damage is small.

Rank S: No scratches.

The practical limit of use is rank 3 or higher.

(8) Cutting property A, r3. was obtained by observing the state of the cut surface of the magnetic tape with an electron microscope when the magnetic tape coated with a wide width was cut into a width of about an inch. It was divided into three ranks: C.

A is a product in very good condition with no streaks or chips on the cut surface, C is a product with many stripes on the cut surface (and some chips were also observed), and B is an intermediate between the two. .

Example/ (Polyester/U, production of film) 700 parts of dimethyl terephthalate, 60 parts of ethylene glycol, and four pieces of magnesium acetate ':J', 0.
09 parts were placed in a reactor, heated to raise the temperature, and methanol was distilled off to carry out a transesterification reaction. After a while from the start of the reaction, the temperature was raised to 230°C, and the transesterification reaction was substantially completed.

Next, the average particle size o, 02, which has been crushed, classified, and filtered in advance, is
/1m of Al2O3 particles were added as O, S%, and 0.0% of ethyla/tudphosphate was added. Part OII, 41 parts of antimony trioxide, o,
Ta. In addition, instead of Al2O3 particles, T″ average particle size o
, 7 μm S i 02 particles were added in an amount of 0%, and transesterification and polycondensation reactions were performed in the same manner, until the intrinsic viscosity was 0. A polyester (B) of AO was obtained.

Next, 10% polyester (A) and polyester (B) were added.
) was uniformly blended with 20%, dried at a temperature of 10° C., and then extruded into a sheet from an extruder at a temperature of 290° C. to obtain an amorphous film of 200 μm in length using an electrostatic contact cooling method.

Then, the amorphous film is rolled 77 in the film machine direction.
Stretched 7.5 times at 0°C and further 2j times at 770°C in the direction perpendicular to the flow of the film, heat-treated at 220°C for 3 seconds, and then cooled to obtain a biaxially stretched polyester film with a thickness of 754 m. Ta.

(Manufacture of magnetic tape) A magnetic layer was applied to the obtained biaxially stretched polyester film, and the ease of cutting and electromagnetic properties were measured. The results are shown in Table 1.

Examples - ~ q In Examples -/, the particle type and particle size contained in polyester (A) and hypopolyester (B) were changed as shown in Table/, so that the contents of both polyesters were as shown in Table 7. A polyester film and a magnetic tape were produced in the same manner as in Example 1, except that the stretching conditions were appropriately changed so that the refractive index in the thickness direction of the film became the value shown in Table 7.

These results are shown in Table-1.

Comparative Example A polyester film was obtained by variously changing the particles added to the polyesters (A) and (B), the intrinsic viscosity of the polyester, and the film stretching conditions. Table 7 shows the properties of the obtained polyester film and the properties after forming it into a magnetic tape.

All of the films of Examples/-4 < that meet the requirements of the present invention have excellent runnability and abrasion resistance, do not shed powder when cut into a predetermined width as a magnetic tape, and have particularly good scratch resistance at high speeds. It was extremely good.

On the other hand, Comparative Example 1 is an example in which the Mohs hardness of the particles does not meet the requirements of the present invention, but the scratch resistance was poor and the magnetic tape had many scratches.

Comparative Example C is an example in which the intrinsic viscosity of the film exceeds the upper limit of the range of the present invention. It was inferior.

Comparative Example 3, Da, is an example in which the requirements of the present invention were not met in terms of the Mohs hardness of the particles or the inclusion of single particles, and the refractive index in the thickness direction was below the preferred range. In this case, the abrasion resistance and abrasion resistance were poor, and many abrasion powders fell off and the magnetic tape was scratched, which was poor.

〔Effect of the invention〕

The film of the present invention contains two or more types of specific inert particles and has an intrinsic viscosity within a specific range, so that the film has excellent scratch resistance, cuttability, abrasion resistance, and slipperiness. Therefore, its industrial value is high.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram of a running system of an apparatus for evaluating film running properties. (I) in the diagram is 6 Ryuda, 5US-qko0-J
2 fixed pins, (II) is the inlet tension meter,
(III) shows the exit tension meter, and the winding is at the corner (0) / 3! ;''. Figure 2 is a schematic diagram of the running system of the apparatus for evaluating the abrasion resistance of films. In the figure, (IV) is A 11! 11 da, SUS -& 20-
JJ fixing pin, ('v) shows a tension meter, and the winding angle (θ) is /35°.

Claims (1)

[Claims] (1) Inert inorganic particles (a) having a Mohs hardness of 6 or more
and a polyester film containing inert particles (b) having a larger average particle size than particles (a), and characterized in that the intrinsic viscosity of the film is in the range of 0.52 to 0.62. Polyester film for magnetic recording media.