JPH0684445B2 - Biaxially oriented 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 which provides excellent running properties, electromagnetic conversion properties, abrasion resistance and slit properties when used as a magnetic recording medium. More specifically, the present invention relates to a base film that is extremely suitable for high-density magnetic recording applications because it is extremely resistant to scratches and abrasion powder during running of the tape and has excellent slitting properties, and can suppress the occurrence of dropouts.

[Problems to be Solved by Prior Art and Invention]

The polyester film has excellent physical and chemical properties and is widely used as an industrial base material. In particular, the biaxially oriented polyethylene terephthalate film is now indispensable as a base film for magnetic recording media due to its excellent mechanical strength, dimensional stability and flatness. By the way, in recent years, magnetic recording media have been rapidly improved, and accordingly, the demand for a base film has become more severe. For example, in the case of a video tape that requires high density recording, the magnetic layer is thinned. In this case, the unevenness of the base film itself is reflected on the surface of the magnetic layer. The loss causes deterioration of electromagnetic conversion characteristics and causes dropout. Therefore, it is desired that the surface of the base film be as flat as possible. However, when the film surface becomes flat, not only the runnability of the film deteriorates, but also friction and wear between the film and the base material, for example, the guide pin, become large, and scratches or abrasion powder are generated on the film. become. The generated abrasion powder is often transferred to the surface of the magnetic layer and causes a dropout when the magnetic tape is stacked and wound up.

If the scratch resistance of the film is insufficient, the film is likely to be scratched before and after coating the magnetic layer, which is reflected on the surface of the magnetic layer, resulting in poor electromagnetic characteristics. Also, the presence of the scraped white powdery substance often deteriorates the electromagnetic characteristics.

Further, the quality of the slitting property of the magnetic tape has a great influence on its performance. That is, the magnetic tape is subjected to so-called calendering, which is a mirror surface on the surface of the magnetic layer, and then slit with a desired width by using a shear cutter, but in this case, powder or whiskers is often generated from the cut end. When this foreign substance adheres to the surface of the magnetic layer, dropout is induced, so improvement of the slit property has been strongly desired.

The inventors of the present invention have made extensive studies as to the improvement of various characteristics desired for these magnetic recording media, and as a result, previously disclosed Japanese Patent Application No. 63-14241.
An epoch-making method was proposed in the specification of JP-A-9-131131.

It has a high Mohs hardness, for example, aluminum oxide particles, is added to the base film in order to highly satisfy scratch resistance, which has not been improved in the past, while maintaining running properties and wear resistance as necessary. The skeleton is the technical idea of using in combination with other particles having an appropriate particle size and hardness for improvement.

Such a novel method certainly made it possible to satisfy these properties to a high degree. However, the generation of dust and whiskers at the time of slitting, which causes most of dropouts, is still insufficient, especially during long-term continuous operation, and further improvement has been required.

Regarding the improvement of the slit property of the polyester film,
Methods for increasing the crystallinity of conventional films and Japanese Patent Application No. 63-95933
There is known a method of using a copolyethylene terephthalate film in which the plane orientation coefficient and the number of microvoids are kept in a specific range as described in Japanese Patent Publication, but it is not always satisfactory in terms of practicality and effect. Was not. Moreover, these films are remarkably inferior in terms of scratch resistance, and the emergence of a base film capable of reducing dropout has been strongly desired.

[Means for solving problems]

The inventors of the present invention have desired runnability for these magnetic recording media,
As a result of comprehensively examining electromagnetic conversion characteristics, abrasion resistance, scratch resistance, and slitting property, a film containing two kinds of particles having certain characteristics and having a surface state in a specific range is obtained. The present invention has been completed by finding that a base film having a high degree of satisfaction with all of these properties, especially scratch resistance and slitting property, and particularly having a markedly reduced dropout is provided.

That is, the gist of the present invention is 0.1 to 2% by weight of inorganic particles (A) having an average particle size of 1 μm or less and a Mohs hardness of 8 or more, and inert particles having an average particle size larger than that of the particles (A) and a Mohs hardness of 5 or less ( A film containing 0.05 to 2% by weight of B),
A biaxially oriented polyester film for a magnetic recording medium is characterized in that the fine projection density on the film surface is 100 to 500 pieces / mm.

Hereinafter, the present invention will be described in detail.

The polyester referred to in the present invention means terephthalic acid, 2,6-
An aromatic dicarboxylic acid such as naphthalenedicarboxylic acid or an ester thereof and a polyester obtained by using ethylene glycol as a main starting material are shown, but other third component may be contained. In this case, examples of the dicarboxylic acid component include isophthalic acid, phthalic acid, 2,6-naphthalenedicarboxylic acid, terephthalic acid, adipic acid, sebacic acid, and oxycarboxylic acid components such as p-oxyethoxybenzoic acid. Two or more kinds can be used. As the glycol component, diethylene glycol, propylene glycol, butanediol, 1,4-
One or more of cyclohexanedimethanol and neopentyl glycol can be used. In any case, the polyester of the present invention refers to a polyester in which 80% or more of repeating structural units have ethylene terephthalate units or ethylene-2,6-naphthalene units.

Further, the polyester film of the present invention refers to a biaxially oriented polyester film using such polyester as a starting material, and a known method can be used as a production method thereof. For example, usually melt-extruded in a sheet form at 270 to 320 ° C., then cooled and solidified at 40 to 80 ° C. to obtain an amorphous sheet, and then biaxially stretched in the longitudinal and transverse directions sequentially or simultaneously, 160 to 250 ° C. A method such as heat treatment in (for example, the method described in JP-B-30-5639) can be used. In the case of stretching in the longitudinal and transverse directions, each may be stretched in one stage, or if necessary, may be stretched in multiple stages, or a heat treatment section for orientation relaxation may be provided between the multiple stages of stretching. You can also Further, after biaxial stretching, it is also possible to perform stretching again before being subjected to the heat treatment step of the next step. This re-stretching can be carried out in either the longitudinal or lateral directions, or in both directions.

The film of the present invention contains 0.1 to 2% by weight of an inorganic particle size (A) having an average particle size of 1 μm or less and a Mohs hardness of 8 or more. The particle size (A) is mainly oriented in the film in order to improve the scratch resistance of the film, but specifically, aluminum oxide, silicon carbide, zircon carbide, vanadium carbide, titanium carbide, boron carbide, boride. Tungsten, boron nitride, etc. may be used. Among these, aluminum oxide or silicon carbide, and especially calcium oxide, which are industrially easily available, are preferably used.

Even if the average particle size of the particles (A) exceeds 1 μm, the scratch resistance is sufficiently exhibited, but the base material contacting the film may be strongly damaged depending on the running speed and tension of the magnetic tape. Therefore, this value is 1 μm or less, preferably 0.
It is preferable that the thickness is 1 μm or less. Further, when the amount of the polyester compounded is less than 0.1% by weight, the effect of scratch resistance becomes slightly inferior, and when it exceeds 2% by weight, the substrate is often damaged.

Examples of particles that can be particularly preferably used in the present invention include aluminum oxide produced by a so-called thermal decomposition method. These particles are usually produced by flame hydrolysis using anhydrous aluminum chloride as a raw material, and their particle size is about 10 mμ to 100 μm. Further, in the present invention, aluminum oxide particles obtained by a hydrolysis method of alkoxide can also be preferably used. In this case, usually Al (OC
₃ H ₇ ) ₃ or Al (OC ₄ H ₉ ) is used as a starting material, and the hydrolysis conditions are appropriately selected to obtain fine particles of 1 μm or less.
Of course, in this case, it is also possible to employ a method in which an acid is added to the synthesized slurry to obtain a transparent sol, which is then gelled and then heated to 500 ° C. or higher to obtain a sintered body.

Alternatively, another method, that is, aluminum acetate fine powder obtained by adding methyl acetate or ethyl acetate to a sodium aluminate solution and stirring to obtain AlOOH, and then heating this may be used. In any case, aluminum oxide having an average particle diameter of 1 μm or less is particularly preferably used in the present invention. In the present invention, it is preferable to completely disperse the aluminum oxide particles up to the primary particles before use, but it may be a little aggregated and behave as the secondary particles as long as the surface condition of the film is not adversely affected. However, in this case also, the apparent average particle size is preferably 1 μm or less, and particularly preferably 0.1 μm or less. In these cases, part of the aluminum oxide, for example 30% by weight
It does not matter if less than is replaced by oxides such as Si, Ti, Fe, Na, and K.

The film of the present invention contains 0.05 to 2% by weight of the inorganic particles (A) and the inert particles (B) having an average particle size larger than that of the particles (A) and a Mohs hardness of 5 or less.

The particles (B) are mainly used for improving the running property and abrasion resistance of the film, but so-called additive particles or precipitated particles may be used, or both may be used in combination if necessary. Good. However, in any case, the average particle size thereof needs to be larger than that of the particles (A) and the Mohs hardness thereof needs to be 5 or less. This is because it is desirable that the particles forming relatively large protrusions on the film surface, which have a high probability of coming into contact with the substrate, have low hardness. If these requirements are not met, the film often causes catastrophic wear to the substrate.

Specific examples of such particles (B) include inorganic particles such as kaolin, talc, carbon, molybdenum sulfide, gypsum, rock salt, calcium carbonate, barium sulfate, lithium fluoride, calcium fluoride, zeolite, and calcium phosphate. However, mainly from the viewpoint of dispersibility in polyester, calcium carbonate, barium sulfate, zeolite,
Calcium phosphate is preferably used.

Further, as the particles (B), a heat resistant polymer fine powder can be used. As a typical example in this case, for example, as described in JP-B-59-5216, a monovinyl compound having only one aliphatic unsaturated bond in the molecule and a divinyl compound in the molecule as a cross-linking agent. Examples thereof include copolymers with a compound having one or more aliphatic unsaturated bonds, but are not limited thereto, and examples thereof include thermosetting phenol resin, thermosetting epoxy resin, and thermosetting. It is also possible to use a fine powder of a fluorinated resin such as a hydrophilic urea resin benzoguanamine resin or polytetrafluoroethylene.

Further, precipitated particles can be mentioned as another example of the particles (B). The deposited particles are those in which the metal compound is deposited as fine particles in the polyester manufacturing process,
For example, an alkali metal compound or an alkaline earth metal compound is present during or before and after the transesterification reaction or esterification reaction, and is precipitated as particles of about 0.1 to 3 μm in the presence or absence of a phosphorus compound.

In any case, in the present invention, it is necessary to allow particles (B) having a larger average particle size and a lower Mohs hardness than the particles (A) to be present, but the average particle size of the particles (B) is usually
It is 2 times or more, preferably 5 times or more that of the particles (A). Further, the average particle diameter of the particles (B) is preferably 3 μm or less in order to keep good electromagnetic conversion characteristics.

If the content of the particles (B) in the polyester film is less than 0.05% by weight, the running property and abrasion resistance will be insufficient, and if it exceeds 2% by weight, the electromagnetic conversion characteristics will often deteriorate. .

As described above in detail, in the present invention, it is indispensable to use two particles of a certain different specific type, but the eye of the present invention further has a certain fine protrusion density on the film surface in order to improve the slit property. To keep it in range. That is, the present inventors have found that if a very large number of different components are finely dispersed in the film, the slit property can be improved without impairing other properties, but the extent of the improvement is due to the presence of such different components. As a result, it was found that there is a very good correlation with the density of the fine protrusions on the surface of the film that develops.

Although the reason why such a phenomenon occurs is not clear, it is considered that the number of different components are finely dispersed in the film and the polyester molecule and crystal structure are appropriately disturbed to improve the slit property.

The fine protrusion density in the present invention can be measured by a stylus type surface roughness meter. At this time, the radius of the stylus is 2 μm and the stylus pressure is 30
mg, cutoff value 0.08 mm, vertical magnification 100,000 times,
The lateral magnification is set to 500 times and the film surface is measured 1 mm. Fine protrusions are defined as those in which the difference between the peak level on the chart of the obtained roughness curve and the valley level on the left side thereof is 1.0 mm or more.

The fine projection density of the film surface of the present invention is 100 to 500 pieces / mm
Must be If this value is less than 100, the improvement of the slit property will be insufficient, and if it exceeds 500, the overlap between the projections will increase and the electromagnetic conversion characteristics will deteriorate, which is not preferable.

Such microprojections can be developed in several ways. First, the first method is a method of providing such fine protrusions in a system using only particles (A) and particles (B). That is a method of providing such fine protrusions. Because such fine protrusions usually have an average particle size of 0.1 to 1 μm,
Particles (A) can be achieved by adding 0.1 to 0.6 μm particles to the polyester film in an amount of 0.1 to 5% by weight, preferably 0.2 to 3% by weight.
It is also possible to develop such a surface state by carefully adjusting the particle size and amount of the particles (B).

However, more simply, there is a method of blending the third particles (C) which plays a role of expressing fine protrusions.
The particles (C) are usually selected from the above range of particle size and amount, and in this case as well, the Mohs hardness of the particles is preferably 5 or less. Further, it is desirable to select the average particle diameter so that the particles (A), the particles (C), and the particles (B) are arranged in ascending order. As the particles (C), in addition to inorganic particles, heat-resistant polymer fine powder or precipitated particles can be used.

Another means for producing the fine projections required in the present invention is so-called polymer blend. That is, it is a method of blending a polymer which, when added to and mixed with polyester in addition to particles (A) and particles (B), has a sea-island structure and can give fine projections to the film surface. Examples of such a polymer include polyethylene, polypropylene, polymethylmethacrylate, polycarbonate, polyamide, polystyrene, polysulfone, polyethersulfone, polyphenylene sulfide, polyalkylene glycol, and polyester liquid crystal polymers. Among these, the polyester-based liquid crystal polymer has suitable compatibility with the polyester and easily gives a preferable surface state, so that it can be preferably used.

In any case, in the present invention, by maintaining the fine projection density of the film surface in a certain specific range, it is possible to achieve the improvement of the slit property without impairing other properties, but such an effect is a biaxially stretched film. Refractive index η
_When the difference Δn between _TD and the refractive index η _{MD in the} longitudinal direction is 0.010 or more, preferably 0.020 or more, more preferably 0.025 or more,
It is more prominent.

〔Example〕

Hereinafter, the present invention will be described in more detail with reference to Examples, but the present invention is not limited to the following Examples as long as the gist thereof is not exceeded. In addition, "part" in Examples and Comparative Examples means "part by weight".

The measuring method used in the present invention is as follows.

(1) Average particle size The particle size is measured with a microscope, and the volume fraction of equivalent sphere is 50%.
The particle size (diameter) at the point is defined as the average particle size.

(2) Abrasion resistance Using the device shown in FIG.
The amount of white powder adhering to the fixing pin is visually judged and the wear resistance rank is A (excellent adhesion amount is excellent) ~
It was divided into three ranks, C (high adhesion amount and poor practical use).

(3) Runnability The slip property of the film was evaluated. The slipperiness was measured using the apparatus shown in FIG. That is, the film is wound around a fixed coin chrome-plated metal roll (diameter 6 mm) at a rotation angle of 135 °, that is, at 2.356 rad (θ), a load of 53 g (T ₂ ) is applied to one end, and this is run at a speed of 1 m / mm, The resistance force (T ₁ , g) at the other end is measured, and the friction coefficient (μ
d) was determined.

(4) Scratch resistance First, a magnetic tape was manufactured. That is, the following magnetic paint was applied to a polyester film, and the film thickness after drying was 2 μm.
The magnetic layer was formed so that That is, 200 parts of magnetic fine powder,
Polyisocyanate compound after 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 were dispersed in a ball mill for 48 hours. After adding 5 parts to make a magnetic paint, this 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.

Next, attach the magnetic tape to a coin chrome-plated metal pin (diameter
A wrap angle of 135 ° and a tension of 50 g were applied to a 6 mm surface roughness 3S) and rubbed at a running speed of 4 m / sec.

Next, aluminum was vapor-deposited on the rubbing surface of the magnetic tape, and the degree of scratches was visually judged and divided into the following 5 ranks.

Rank 1 There are many scratches and often deep scratches.

Rank 2 The amount of damage is relatively large, and there are deep flaws in some places.

Rank 3 The degree of scratches is relatively small and the number of deep scratches is small.

Rank 4 Some scratches are observed, but it is a satisfactory level.

Rank 5 Almost no scratches.

(5) Slitting property The magnetic sheet after calendering was slit into a 1/2 inch width with a shear cutter. At this time, the slit portions were observed and the degree of beard and powder generation was divided into the following three ranks.

Rank A: Very good with no beards or powder even if slit continuously for 1 hour. Rank B: Intermediate between A and C. Rank C: Slits continuously produced for 1 hour and then whiskers and powder were gradually generated. Will be available.

(6) Electromagnetic properties The electromagnetic properties of the above magnetic tapes were measured using a Matsushita Electric NV-3700 type video deck.

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

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.

Example 1 100 parts of dimethyl terephthalate and 70 parts of ethylene glycol
Parts and 0.09 parts of magnesium acetate tetrahydrate in a reactor,
While heating and heating, methanol was distilled off, and about 4 hours after the start of the reaction, the temperature was raised to 230 ° C. to complete the transesterification reaction. Then the average particle size obtained by the pyrolysis method is 0.
After adding 1 part of 02 μm aluminum oxide, 0.04 part of triethyl phosphate and 0.04 part of antimony trioxide were further added, and polycondensation reaction was carried out by a conventional method to obtain polyethylene terephthalate having an intrinsic viscosity of 0.62. (Polyester (A)) The aluminum oxide particles were extremely uniformly dispersed in the polyester (A), and substantially no aggregated particles were observed.

Similarly, polyester containing 1% by weight of calcium carbonate having an average particle size of 0.6 μm was obtained. (Polyester (B)) On the other hand, a heat-resistant crosslinked polymer having an average particle diameter of 0.2 μm was obtained. That is, monodispersed crosslinked polymer particles were obtained by an emulsion polymerization method using 90 parts of styrene and 10 parts of divinylbenzene as starting materials, and then polyester containing 1% by weight of the particles was produced in the same manner as above. (Polyester (C)) The polyester (A), polyester (B), and polyester (C) obtained as described above are mixed at a weight ratio of 30:20:50, dried, and then dried at 290 ° C. by an extruder to form a sheet. To obtain an amorphous sheet. The sheet is then lengthwise 90
The film was stretched 3.5 times at ℃ and 4.3 times at 110 ℃ in the width direction and heat treated at 210 ℃ to obtain a biaxially oriented polyester film having a thickness of 15 μm. The widthwise refractive index of the obtained film is 1.67.
2. The refractive index in the longitudinal direction was 1.644 and the difference was 0.028. The density of fine projections on the film surface was 254 / mm.

A magnetic layer was applied to the obtained film to prepare a magnetic recording medium, and its characteristics were evaluated.

Example 2 A film was obtained by using liquid crystal polyester instead of the crosslinked polymer particles of Example 1. That is, in place of 50 parts of polyester (C), 19.4 parts of polyethylene terephthalate, 18.2 parts of p-acetoxybenzoic acid, 0.01 parts of magnesium acetate and 0.01 parts of antimony trioxide were mixed and reacted at a temperature of 275 ° C. A biaxially oriented polyethylene terephthalate film having a thickness of 15 μm was obtained in the same manner as in the production of the polyester film of Example 1 using 2 parts of liquid crystalline polyester and 48 parts of particle-free polyethylene terephthalate.

Next, using the film, a magnetic recording medium was obtained in the same manner as in Example 1 and its characteristics were evaluated.

Examples 3 and 4 The same operation as in Example 1 was carried out except that the particles contained in the polyester film were changed as shown in Table 1.
However, in Example 3, the average particle diameter of the third component was 0.2 μm.
0.5 part of calcium carbonate, and in Example 4, 0.6 part of a cross-linked polymer having an average particle size of 0.3 μm as a third component was mixed with the film.

Comparative Example 1 A film was obtained in the same manner as in Example 1 except that the crosslinked polymer particles were not blended, and then a magnetic recording medium was obtained.

Comparative Examples 2 and 3 As shown in Table 1, the same operation as in Example 1 was performed except that the particles contained in the polyester film were changed. However, in Comparative Example 2, the average particle size of the third component was 0.
A 7 μm cross-linked polymer was blended in an amount of 3% by weight with respect to polyester. In Example 4, the second component was used as the second component.
20% by weight of the liquid crystal polyester used in Example 2 was blended with the polyester.

The films of Examples 1 to 4 satisfying the requirements of the invention are all excellent in various properties such as slit property and electromagnetic property, and the dropout is remarkably reduced, but the fine protrusion density is not suitable in Comparative Examples 1 to 3. Film was inadequate in terms of electromagnetic conversion characteristics and dropout.

[Effects of the Invention] The film of the present invention is useful for high-density magnetic recording applications having excellent running properties, electromagnetic conversion characteristics, abrasion resistance, slit resistance and scratch resistance, and its industrial value is high.

[Brief description of drawings]

FIG. 1 is a diagram showing a running system for evaluating the abrasion resistance of a film. (I) is a stainless steel fixing pin with a diameter of 6 mm,
(II) shows a tension meter, and θ is 135 °. FIG. 2 is a diagram showing a running system for evaluating the running property of the film. (V) is a stainless steel fixing pin with a diameter of 6 mm, (I
II) and (IV) are tension meters, and θ is 135
°.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification code Internal reference number FI Technical display location B29L 7:00 4F (72) Inventor Toshifumi Takizawa 1000 Kamoshida-cho, Midori-ku, Yokohama-shi, Kanagawa Daifoil stocks 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-59-227421 (JP, A) JP-A-61-240431 (JP, A)

Claims (1)

[Claims] 1. Inorganic particles (A) having an average particle size of 1 μm or less and a Mohs hardness of 8 or more, 0.1 to 2% by weight, and inert particles (B) having an average particle size larger than that of the particles (A) and a Mohs hardness of 5 or less. A biaxially oriented polyester film for magnetic recording media, characterized in that the film has a fine protrusion density of 100 to 500 / mm.