JPH0781020B2 - Polyester film for magnetic recording media - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to a polyester film having excellent characteristics, running properties and abrasion resistance when used as a magnetic tape. More specifically, the present invention relates to a base film for high density magnetic recording, which has extremely few scratches and abrasion powder generated when the tape is running and has excellent magnetic tape cutting properties.

[Problems to be Solved by Prior Art and Invention]

The polyester film has excellent physical and chemical properties and is widely used in industry. In particular, biaxially stretched polyethylene terephthalate film is now indispensable as a base material for magnetic recording media because it is superior in flatness, mechanical strength and dimensional stability to other films.

On the other hand, in recent years, improvements in magnetic recording media have been made rapidly, and along with this, the demand for base films has become more severe. For example, in the case of high density recording such as video tape, the surface of the base film is required to be flatter. However, as is well known, when the film surface becomes flat,
Friction and abrasion with a portion that comes into contact with the film become large, and scratches on the film and generation of abrasion powder increase, causing various adverse effects.

For example, if abrasion powder is generated before the magnetic layer coating process including the film manufacturing process, it may cause dropout increase due to magnetic layer coating omission or transfer of abrasion powder to the magnetic layer surface. If abrasion powder is generated in the calendering process performed for the purpose of making the surface of the calender roll, it becomes white powder and adheres to the surface of the calender roll, resulting in deterioration of the surface roughness of the magnetic layer. Furthermore, if the abrasion resistance is poor even after the product is made into a product, the abrasion powder generated in the running system in the tape deck often causes the characteristic deterioration and the dropout.

In addition, in recent years, there has been an increasing demand for the base film to have improved abrasion resistance as well as abrasion resistance. This is because, in the tape dubbing process or the like, the portion where the tape comes into contact is damaged, and the abrasion powder generated may damage the film.
Not only are these scratches unfavorable in appearance, they also cause process contamination and increased dropouts.

In order to improve the abrasion resistance and scratch resistance of such a film or tape, it is known that inert fine particles are present in the polyester film to roughen the film surface appropriately. Such moderate roughening can contribute not only to improvement of abrasion resistance and scratch resistance but also to improvement of handling workability of the film and running property as a magnetic tape, but it can sufficiently meet recent severe requirements. It wasn't something. The reason is that in order to sufficiently satisfy these characteristics, it is necessary to increase the amount of fine particles to be blended or the diameter of particles, but these methods increase the average roughness too much or cause coarse particles due to the inclusion of coarse particles. As a result, the number of protrusions is increased and the electromagnetic conversion characteristics of the magnetic tape are deteriorated and the dropout is increased. Thus it is extremely difficult to achieve this trade-off. The only known effective method is the so-called back coating method, in which a suitable coating is applied to the surface opposite to the magnetic layer, but it is extremely costly and has various problems in its characteristics. It wasn't the way.

On the other hand, one of the main characteristics required for a base film of a magnetic recording material is easiness of cutting. This is a phenomenon in which, when a magnetic tape is cut into a certain width, in the case of a base film having poor cuttability, the cut surface is turned into a streak, and in some cases, it becomes a cutting powder and falls off. When this phenomenon is further aggravated, powder is also dropped from the magnetic layer, and these fallen powder causes dropout.

As a method of improving the cuttability, for example, a method of increasing the crystallinity of the film is known. However, since the increase in crystallinity deteriorates the wear resistance, it is not possible to extremely increase the crystallinity in practical use, and the fact is that the base film is designed at the sacrifice of cuttability to some extent. .

As described above, it is industrially very useful if the abrasion resistance, scratch resistance and easy cutting property of the base film for a magnetic recording medium can be effectively improved by a simple means.

[Means for solving problems]

In view of the above circumstances, the present inventors have conducted diligent studies on polyester films for magnetic recording media, and as a result, polyester films containing certain specific fine particles are excellent in abrasion resistance, scratch resistance, and easy cutting. And has reached the present invention.

That is, the gist of the present invention is that the particle size distribution defined below is 2.0 or less,
Al ₂ O ₃ particles (a) having a volume shape factor (f) of 0.1 to π / 6 and an average particle diameter of 0.005 to 0.1 μm defined below are 0.05 to 5.0 wt%,
And a polyester film containing 0.05 to 2.0 wt% of inert particles (b) having an average particle size larger than that of the particles (a) and having an average particle size of 0.1 to 3 μm, and refraction in the thickness direction of the film. The polyester film for a magnetic recording medium is characterized in that the ratio is 1.492 or more and the intrinsic viscosity of the film is in the range of 0.52 to 0.62.

Particle size distribution: Particle size ratio (d25 / d75) when the weight fraction is 75% (d75) and 25% (d25) when integrated from the larger particle size Volume shape factor (f): V / D ³ (V is the volume of the inert particles,
D represents the diameter of the inert fine particles) The present invention will be described 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 subjecting an alkyl ester of terephthalic acid and glycol to an ester-esterification reaction followed by polymerization condensation or polycondensation of glycol ester of terephthalic acid. It can also be obtained by a method such as.

In the present invention, two or more kinds of particles having different hardness and particle diameters blended with polyester are used in combination.
Further, it is characterized in that it has an intrinsic viscosity when formed into a film. That is, in order to improve the handling workability and abrasion resistance of the polyester film, and to improve the running property, abrasion resistance, and scratch resistance after forming the magnetic tape, fine particles inert to the polyester are contained. It is already known that it is good. If the present inventors jointly use Al ₂ O ₃ particles (a) having a specific average particle size, particle size distribution and volume shape factor as such particles and other particles (b) having a larger particle size than that, It has been found that these properties can be remarkably improved, and especially scratch resistance can be remarkably improved. In addition to these characteristics, the inventors have found that in order to improve the cuttability when the magnetic tape is cut into a certain width, the limiting viscosity of the film may be set to 0.52 to 0.62 and the present invention has been completed.

Al ₂ O _{3 which} is particularly preferably used in the present invention is usually obtained by a so-called thermal decomposition method, and is generally 10 mμ.
To a particle size of about 100 mμ. In this case Al
A part of ₂ O ₃ , for example, less than 30% by weight, may be replaced with an oxide such as Si, Na or K.

The particle size distribution (d25 / d75) of the particles (a) used in the present invention is 2.0
Or less, preferably 1.5 or less, more preferably 1.3 or less. If the particle size distribution exceeds 2.0, the scratch resistance and abrasion resistance of the film will be poor, and when the magnetic tape is used, the dropout will increase, and the output will decrease and fluctuate significantly, which is not preferable.

The volume shape factor (f) of the particles (a) is 0.1 to π / 6,
It is preferably 0.2 to π / 6. Volume shape factor is less than 0.1,
That is, the effect of improving the scratch resistance and slipperiness of the film becomes insufficient as the shape moves away from the spherical shape.

The specific surface area of the particles (a) used is also not particularly limited. For example, particles with an average particle size of 0.5μ are spherical and have a density of 2 g /
Assuming cm ³ has a specific surface area of about 6 m ² / g, but 40
Even a porous material of about 0 m ² / g can be suitably used.

The surface of these particles (a) may be modified with various surface treatment agents.

These surface treatment agents, which are usually used for the purpose of improving the affinity with ethylene glycol or polyester, are generally applied in an amount of 5% by weight or less based on the particles, and examples thereof include silane coupling agents and titanium cups. A ring agent can be mentioned.

Although the mechanism by which the particles (a) give good results in scratch resistance is not clarified, the particles having a hardness higher than the hardness of the contact portion of the film have a remarkable effect, so that the particles forming a film surface protrusion are It is considered that scratches on the film surface are reduced by abrading the sharp parts where the particles come into contact. Furthermore, the present invention is characterized in that other particles (b) having a larger average particle size than the high hardness particles (a) are used in combination. The particles (b) may be either inorganic particles or organic particles as long as they are particles inactive to polyester.

The Mohs hardness of the particles (b) is not particularly limited, but preferably lower than that of the particles (a). Moreover, you may use together 2 or more types of particles as needed.

The present invention further has an intrinsic viscosity of 0.52 to 0 when formed into a film.
It is characterized by being in the range of 62. The lower the intrinsic viscosity is, the better the cuttability is. However, if the intrinsic viscosity is less than 0.52, breakage frequently occurs during film formation and productivity is impaired. On the other hand, if it exceeds 0.62, the effect of improving the cuttability becomes insufficient. Particularly preferably, it is in the range of 0.54 to 0.60.

In the present invention, the particles (a) have an average particle size of 0.005.
.About.0.1 .mu.m, the content of which is 0.05 to 5% by weight, preferably 0.1 to 2% by weight, based on the polyester, and the particles (b) used in combination therewith have an average particle size of 0.1 to 3.0 .mu.m.
m, preferably 0.3 to 1.5 μm, and the content is 0.05 to 2.0 wt% with respect to the polyester, preferably 0.1 to 1.0 w
t%. If the average particle size of the particles (a) exceeds 0.1 μm, the effect of the large particles used in combination becomes insufficient, and the slipperiness and wear resistance are poor. On the other hand, if the average particle size of the particles (a) is less than 0.005 μm, However, the effect of improving scratch resistance is inferior, which is not preferable. Also,
If the content of the particles is less than 0.1 wt%, the effect of improving the scratch resistance is not seen, which is not preferable. On the contrary, if the content exceeds 5 wt%, coarse projections due to aggregation occur and the electromagnetic conversion characteristics of the magnetic tape deteriorate. This leads to an increase in dropouts, which is not desirable.

On the other hand, if the average particle diameter of the particles (b) is less than 0.1 μm, the handling property, abrasion resistance, running property and abrasion resistance of the magnetic tape become poor, and if the particle diameter exceeds 3 μm, the film becomes inferior. The surface roughness becomes unnecessarily high and the electromagnetic conversion characteristics after magnetic tape formation are deteriorated, which is not preferable.
If the content of the particles is less than 0.05 wt%, the handling property of the film, abrasion resistance, the running property and abrasion resistance of the magnetic tape will be inferior, and if it exceeds 2 wt%, the film roughness will be too high, Coarse protrusions are generated due to particle agglomeration, resulting in a decrease in characteristics of the magnetic tape and an increase in dropout, which is not preferable.

The particles used in the present invention are preferably subjected to commonly used crushing treatment, classification treatment and overtreatment to remove coarse particles. For the crushing treatment, for example, a lot 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 agitation mill, a fluid energy mill, etc. can be used.
For classification, one or more of a semi-free vortex type, a forced vortex type, a hydrocyclone type, a centrifugal separation method and the like can be used.

The particles in the present invention may be added to the polyester either before the polycondensation starts, during the polycondensation, or after the polycondensation, but particularly preferably before the polycondensation and at the initial stage of the polycondensation reaction. In order to make two or more kinds of particles coexist in the film in the present invention, each of the particles may be added alone to the polyester, and each polyester may be blended in a predetermined amount at the time of film formation.
Alternatively, when it is added to the polyester, it may be obtained by blending each particle in a predetermined amount, or any of them may be used. The polycondensation reaction catalyst to be used usually includes Sb, Ti, Sn, and Si compounds.

In the present invention, the refractive index in the thickness direction of the film is 1.492.
When it is above, running property, 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-transverse sequential biaxial stretching, it can be obtained by setting the longitudinal stretching temperature to about 105 to 115 ° C, which is 5 to 30 ° C higher than the normal stretching temperature. Alternatively, it can also be obtained by performing a significant lateral relaxation after the biaxial stretching and before the heat treatment. In the present invention, the upper limit of n _α is preferably about 1.510.

〔Example〕

Hereinafter, the present invention will be described in more detail with reference to Examples.
The present invention is not limited to the following examples unless it exceeds the gist. The measuring methods and definitions of various physical properties and characteristics in the examples are as follows.
In the examples, "part" or "%" means "part by weight" or "% by weight", respectively.

(1) Sliding property It measured using the apparatus of FIG. That is, the film is wrapped around a fixed hard chrome-plated metal roll (diameter 6 mm) at an angle of 135 ° (θ), a load of 53 g (T ₂ ) is applied to one end and it is run at a speed of 1 m / min, and the other end The resistance (T ₁ , g) is measured and the friction coefficient (μ
d) was determined.

(2) Abrasion resistance Using the device shown in FIG.
The amount of white powder adhering to the fixed pin was visually judged, and the wear resistance rank was A (excellent adhesion amount and excellent),
It was divided into three ranks: B (small adhesion amount and practically no problem) and C (high adhesion amount and poor practicability).

(3) Intrinsic viscosity [η] 1 g of polymer is phenol / tetrachloroethane = 50/50
It was dissolved in 100 ml of a mixed solvent (weight ratio) and measured at 30 ° C.

(4) Refractive index in film thickness direction (n _α ) The refractive index in the film thickness direction with respect to sodium D ray was measured at 23 ° C. using an Atsube type refractometer manufactured by Atago Optical Co., Ltd.

10 observation fields of particles with a magnification of 200,000 obtained by a transmission electron microscope were used to measure 10 fields of view using image analysis of Quantimet 500 type manufactured by Leica. The average particle diameter (d50) is expressed as the particle diameter when the weight fraction is 50% by converting the particles here into a sphere and integrating from the larger particle diameter. In addition, the particle size distribution is the particle size when the weight fraction is 25% and 75% (d25 and d7, respectively).
It was expressed by the ratio of 5) (d25 / d75). The volume shape factor f was calculated by the following equation, with the maximum value of each particle measured and the average value being D.

f = V / D ³ (however, V = d50 (π / 6)) (6) Production of magnetic tape The following magnetic paint is applied to a polyester film, and a magnetic layer is formed so that the film thickness after drying is 2 μm. Formed. That is, 200 parts of magnetic part powder, 30 parts of polyurethane resin, 10 parts of nitrocellulose, 10 parts of vinyl chloride-vinyl acetate copolymer, 5 parts of lecithin, 100 parts of cyclohexanone, 100 parts of methyl isobutyl ketone and 300 parts of methyl ethyl ketone by a ball mill. After time mixing and dispersion, polyisocyanate compound 5
After adding parts, a magnetic paint was applied, which was applied to a polyester film, magnetically oriented before the paint was sufficiently dried and solidified, and then dried. Further, this coated film was surface-treated with a super calendar and slit into a 1/2 inch width to obtain a video tape. The following magnetic tape characteristics of this video tape were evaluated at a constant speed using an NV-3700 type video deck manufactured by Matsushita Electric Industrial Co., Ltd.

VTR head output The VTR head output at a measurement frequency of 4 MHz was measured with a synchroscope, and the blank was set to 0 decibels and the relative value was displayed in decibels.

Dropout number A videotape recorded with a signal of 4.4 MHz was played back, and the number of dropouts was measured for about 20 minutes with a dropout counter of Okura Industry Co., Ltd. and converted into the number of dropouts per minute.

(7) Scratch resistance A magnetic tape cut to a width of 1/2 inch is rubbed once on a hard chrome-plated metal pin (diameter 6 mm, surface roughness 3S) at a tension of 50 g, a winding angle of 135 °, and a running speed of 4 m / sec. Let Aluminum was vapor-deposited on the rubbing surface of the magnetic tape, and the amount of scratches was visually determined and ranked as follows.

Rank 1: The amount of scratches is extremely large.

Rank 2: A lot of scratches.

Rank 3: The amount of damage is between ranks 2 and 4.

Rank 4: The amount of scratches is small.

Rank 5: Not scratched.

The practical use limit is rank 3 or higher.

(8) Cleaving property The magnetic tape coated with a wide width was cut into 1/2 inch width, and the state of the cut surface of the magnetic tape was observed with an electron microscope to classify it into three ranks A, B and C.

A is a very good result with no streaks on the cut surface and no cutting powder is generated, C is a large number of streaks on the cutting surface, and the invention of cutting powder is also seen, and B is between the two.

Example 1 (Production of polyester film) 100 parts of dimethyl terephthalate and 60 of ethylene glycol
Part and magnesium acetate / tetrahydrate 0.09 part are placed in a reactor, heated and heated, and methanol is distilled off to carry out a transesterification reaction. It takes 4 hours from the start of the reaction to 230 ° C.
The temperature was raised to 0 and the transesterification reaction was substantially completed. Next, 0.5% of Al ₂ O ₃ particles having a particle size distribution of 1.30, a volume shape factor of 0.25 and an average particle size of 0.02 μm, which had been previously crushed, classified and passed, were further added, and 0.04 part of ethyl acid phosphate and 0.04 part of antimony trioxide were added. Polycondensation reaction was carried out for 4 hours to obtain a polyester (A) having an intrinsic viscosity of 0.61. Also, separately
Instead of Al ₂ O ₃ particles, SiO ₂ particles with an average particle size of 0.7 μm are 1.0
%, And transesterification reaction and polycondensation reaction were carried out in the same manner to obtain a polyester (B) having an intrinsic viscosity of 0.60.

80% polyester (A) and 20 polyester (B)
% Evenly blended and dried at a temperature of 180 ° C, then 290
It was extruded into a sheet form from an extruder at a temperature of ℃, and an amorphous film of 200 μm was obtained by electrostatic contact cooling method.

The amorphous film is then placed 110 in the direction of film flow.
3.5 times at ℃, 110 ℃ in the direction orthogonal to the film flow
Was stretched 3.5 times, heat treated at 220 ° C. for 3 seconds, and then cooled to obtain a biaxially stretched polyester film having a thickness of 15 μm.

(Production of Magnetic Tape) The obtained biaxially stretched polyester film was coated with a magnetic layer, and the cuttability and electromagnetic characteristics were measured. The results are shown in Table 1.

Examples 2 and 3 In Example-1, the type of particles, the particle size, the particle size distribution, and the volumetric shape factor to be contained in the polyester (A) and the polyester (B) were changed as shown in Table 1, and both polyesters were used.
The polyester film and the magnetic film were prepared in the same manner as in Example 1 except that the content was blended so that the refractive index in the thickness direction of the film became the value shown in Table-1. A tape was manufactured.

The results are shown in Table-1.

Comparative Examples 1 to 8 Polyester films were obtained by variously changing the particles added to the polyesters (A) and (B), the intrinsic viscosity of the polyester, and the stretching conditions of the film. The properties of the obtained polyester film and the properties after forming the magnetic tape are shown in Table 1.

The films of Examples 1 to 3 satisfying the requirements of the present invention are all excellent in running property and abrasion resistance, there is no powder drop when cut into a predetermined width as a magnetic tape, and particularly scratch resistance at high speed is extremely high. It was good.

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

Comparative Example 2 is an example in which the intrinsic viscosity of the film exceeds the upper limit of the range of the present invention, but in this case, cutting property is poor, cutting chips are generated, and dropout due to powder falling off of the magnetic layer is increased. It was inferior.

Comparative Examples 3 and 4 are examples in which the requirements of the present invention are not satisfied in terms of the Mohs hardness of particles or the inclusion of single particles, and the refractive index in the thickness direction is below the preferable range. In this case, the abrasion resistance and the scratch resistance were poor, and many of the abrasion powder fell off and the magnetic tape was scratched, which was inferior.

Since Comparative Examples 5 and 6 do not contain Al ₂ O ₃ particles, the scratch resistance is poor.

Comparative Examples 7 and 8 are examples in which the volume shape factor and the particle size distribution do not satisfy the requirements of the present invention, but scratch resistance and abrasion resistance are poor, and deterioration of the characteristics of the magnetic tape was observed.

The film of the present invention is excellent in scratch resistance, easy cutting property, abrasion resistance and slipperiness by containing two or more kinds of specific inert particles and further limiting the intrinsic viscosity of the film to a specific range. It provides a film, and its industrial value is high.

[Brief description of drawings]

FIG. 1 is a schematic diagram of a running system of an apparatus for evaluating the running property of a film. In the figure, (I) is a 6 mmφ, SUS-420-J2 fixing pin, (II) is an inlet tension meter, (III) is an outlet tension meter, and the winding angle (θ) is 135 °. FIG. 2 is a schematic diagram of a running system of an apparatus for evaluating the abrasion resistance of a film. In the figure, (IV) is 6 mmφ, SUS-42
0-J2 fixing pin, (V) shows the tension meter,
The winding angle (θ) is 135 °.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification number Internal reference number FI Technical display location C08L 67:02 (72) Inventor Toshifumi Takizawa 1000 Kamoshida-cho, Midori-ku, Yokohama-shi, Kanagawa Daia Foil Co., Ltd. Central Research Laboratory (72) Inventor Kei Harada 1000 Kamoshida-cho, Midori-ku, Yokohama-shi, Kanagawa Daifoil Co., Ltd. Central Research Laboratory (56) Reference JP-A-52-78953 (JP, A) JP-A-62-164733 ( JP, A) JP-A-61-293832 (JP, A)

Claims (1)

[Claims] 1. A particle size distribution defined below is 2.0 or less, a volume shape factor (f) defined below is 0.1 to π / 6, and an average particle size is 0.005 to.
The Al ₂ O ₃ particles (a) having a diameter of 0.1 μm are 0.05 to 5.0 wt%, and the average particle size is larger than that of the particles (a) and the average particle size is 0.1.
A polyester film containing 0.05 to 2.0 wt% of inert particles (b) of 3 to 3 μm, a refractive index in the thickness direction of the film is 1.492 or more, and an intrinsic viscosity of the film is in the range of 0.52 to 0.62. A polyester film for a magnetic recording medium, characterized by being present. Particle size distribution: Particle size ratio (d25 / d75) when the weight fraction is 75% (d75) and 25% (d25) when integrated from the larger particle size Volume shape factor: V / D ³ (V is Volume of inert fine particles, D represents the diameter of the inert fine particles)