JP2507606B2 - Polyester film for magnetic recording media - Google Patents

Description

TECHNICAL FIELD The present invention relates to a polyester film for a magnetic tape, which has excellent characteristics, low dropout, scratch resistance and durability. More specifically, the present invention relates to a base film for high-density magnetic recording, which has very few scratches and abrasion powder generated during tape running and has excellent adhesiveness to a magnetic layer.

[Problems to be Solved by Conventional Techniques and Inventions] In recent years, magnetic recording media have been rapidly improved, and along with this, demands for base films have become more severe. For example, the surface of a base film that requires high-density recording such as a video tape is required to have a flatter surface in order to improve electromagnetic characteristics. However, when the film surface becomes flat, friction and wear increase, scratches on the film surface and generation of abrasion powder remarkably occur, causing various adverse effects.

Further, in recent years, there is an increasing demand for improvement in scratch resistance. This is due to an increase in demand for video soft tape applications, but a large amount of scratches are caused by contact between the tape running at high speed and the device base material in the soft tape production process, that is, the magnetic transfer process and the cassette winding process. And abrasion powder is generated, which causes deterioration of electromagnetic conversion characteristics and frequent dropouts.

In order to improve the scratch resistance and abrasion resistance of the film,
The presence of inert fine particles in the polyester film,
It is known that the surface may be roughened appropriately. Such appropriate roughening can contribute not only to improvement of scratch resistance and abrasion 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. This is because it is necessary to increase the content of fine particles or increase the average diameter of the particles in order to sufficiently satisfy these characteristics. This causes an increase in coarse projections due to the mixture, which results in a decrease in the electromagnetic conversion characteristics of the magnetic tape and an increase in dropout. 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 surface, but it is not a practical method due to problems such as extremely high cost. .

Further, the main property required as a base film of a magnetic recording material is adhesiveness with a magnetic layer. The adverse effects due to poor adhesion include an increase in dropout after repeated running and an increase in dropout due to powder falling off of the magnetic layer during tape slitting.

As a method for improving the adhesiveness of the biaxially stretched polyester film, for example, a method of copolymerizing a specific polyester-forming component, a method of blending a specific resin or the like with polyester to form a film, a flame treatment of a polyester film, a corona Surface treatment methods such as discharge treatment, plasma discharge treatment, ultraviolet irradiation treatment, and chemical treatment using a specific organic compound or inorganic compound are known. However, the method by copolymerization, the method by a composition, and the method by surface treatment are not always satisfactory for magnetic recording because the adhesive force changes with time or the adhesive force is slightly inferior.

Thus, it has been required to effectively improve scratch resistance, adhesiveness and abrasion resistance of a high density base film for a magnetic recording medium by a simple means.

[Means for Solving the Problems] In view of the above circumstances, the present inventors have conducted diligent studies on a polyester film for a magnetic recording medium, and as a result, contain certain specific fine particles and apply it to one surface of the film. A polyester film provided with a layer has scratch resistance,
The inventors have found that they have excellent adhesiveness, abrasion resistance, etc., and completed the present invention.

That is, the gist of the present invention is that the particle size distribution is 2.0 or less, the volume shape factor is 0.1 to π / 6, the Mohs hardness is 8 or more, and the average particle size is 0.01 to
A polyester film for a magnetic recording medium comprising 0.05 to 5 wt% of particles of 5 μm and having a center line average roughness of 0.005 to 0.040 μm on the film surface and having a coating layer provided on one side thereof.

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

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 with glycol, or by subjecting an alkyl ester of terephthalic acid and glycol to transesterification, followed by polycondensation or polycondensation of glycol ester of terephthalic acid. Can also be obtained by

The present invention is characterized in that the type of particles contained in the polyester film and the coating layer provided on one side of the film.

That is, in order to improve the handling workability and abrasion resistance of the polyester film, and the scratch resistance after magnetic tape formation,
In order to improve durability and electromagnetic conversion characteristics, it is already known that fine particles inactive to polyester may be contained, but the present inventors have found that such particles have a Mohs hardness of 8 or more. It was found that the effect of improving scratch resistance is remarkable among these characteristics by using. Further, in order to remarkably improve dropout, durability and electric characteristics, it has been found that a coating layer for improving adhesion to the magnetic layer, slipperiness, etc. may be provided on the magnetic layer surface of the film, and the present invention has been reached. did.

The particles having a Mohs hardness of 8 or more used in the present invention are, for example,
_{SiC 4, Al 2 O 3,} ZrO 2, Si 3 N 4, but the diamond and the like, not limited to these as long as Mohs hardness of 8 or more particles. Of these, Al ₂ O ₃ is preferably used.

Al ₂ O ₃ preferably used in the present invention is usually obtained by a so-called thermal decomposition method, but since the compound as a raw material, the conditions of thermal decomposition, the shape and distribution are different,
It is necessary to select a manufacturing method that satisfies the requirements of the present invention.
In this case, part of Al ₂ O ₃ , for example, less than 30% by weight is Si or Na,
It may be substituted with an oxide such as K.

The particles used in the present invention have a sharp particle size distribution, that is, a weight fraction of 75% when integrated from the smaller particle size.
And the particle size ratio of 25% is 2.0 or less, preferably 1.5 or less, more preferably 1.3 or less. Further, the shape of the particles used is closer to a lump or a sphere. Volume shape factor is 0.1 to π / 6, preferably 0.2 to π / 6
Particles in the range of are used. If the particle size distribution of the particles to be used exceeds 2.0, the presence of large particles increases, which not only lowers the characteristics but increases dropouts, but also causes the large particles to damage the magnetic layer, which is not preferable. If the volumetric shape factor of the particles used is less than 0.1, the scratch resistance will be poor. Also, the specific surface area of the particles used is not particularly limited. For example, particles having an average particle size of 0.5 μm have a specific surface area of about 6 m ² / g assuming that they are true spheres and have a density of 2 g / cm ³ , but porous particles of about 400 m ² / g can be preferably used. The surface of these particles may be modified with various surface treatment agents. Usually, these surface treatment agents used for the purpose of improving the affinity with ethylene glycol or polyester are generally used in an amount of 5% by weight or less based on the particles, and examples thereof include a silane coupling agent and a titanium coupling agent. Can be mentioned.

Incidentally, these particles are generally used for crushing treatment,
It is preferable to remove coarse particles by performing classification treatment and overtreatment. For the crushing treatment, for example, a rod mill, ball mill, pan mill, roller mill, impact mill, etc. can be used, and for classification treatment, a semi-free vortex type, forced vortex type, hydrocyclone type, centrifugal separation, etc. The above can be used.

The particles in the present invention may be added to the polyester either before the initiation of polycondensation or after the polycondensation, but particularly preferably before the polycondensation and at the initial stage of the polycondensation reaction.

The average particle size of the particles used in the present invention is 0.01 to 5 μm, preferably 0.01 to 1 μm. Average particle size is
If it is less than 0.01 μm, the interaction between particles is increased and it is difficult to uniformly disperse it in the polyester, and the height of protrusions on the film surface is low, and the scratch resistance effect is insufficient, which is not preferable. On the other hand, if the average particle size exceeds 5 μm, the surface roughness of the film becomes unnecessarily high and the electromagnetic conversion characteristics of the magnetic tape are deteriorated, which is not preferable.

Further, in the present invention, the content of particles in the polyester film is 0.05 to 5% by weight, preferably 0.1 to 1% by weight. If the content of particles is less than 0.05 w%, the effect of improving scratch resistance is not seen, which is not preferable. Conversely, if the content exceeds 5 wt%, coarse projections due to aggregation occur and the electromagnetic conversion characteristics of the magnetic tape drop or drop. This leads to an increase in out, which is not preferable.

The present invention further has a center line average roughness of the film surface of 0.00
It is characterized by being in the range of 5 to 0.040 μm. When the center line average roughness is less than 0.005 μm, the workability of the film is
It is not preferable because the abrasion resistance becomes poor. On the other hand, when the center line roughness exceeds 0.040 μm, the electromagnetic conversion characteristics of the magnetic tape, especially the output and S / N ratio are poor, which is not preferable.

In the present invention, as long as the gist is not exceeded,
Other particles than the particles having a Mohs hardness of 8 or more, which is essential in the present invention, may be included, and in some cases, it is more preferable. For example, when the average particle size of particles having a Mohs hardness of 8 or more is 0.3 μm or less, the scratch resistance is improved, but as described above, the handling workability is poor and the wear resistance is insufficient. As described above, in the present invention, the particles may be used in combination with other particles, if necessary.
Examples of particles that can be used in combination include, for example, a catalyst residue in a polyester reaction system in the presence or absence of a phosphorus compound.
Particles deposited as particles of ˜5 μm, inorganic or organic particles such as kaolin, talc, calcium carbonate, calcium phosphate, silicon dioxide, titanium dioxide and heat-resistant organic crosslinked polymer particles, Mohs hardness with different average particle diameters 8 The above particles can be mentioned.

The present invention is further characterized in that a coating layer is provided on one side of the film. The compound constituting the coating layer may be either a low molecular weight compound or a high molecular weight compound, but a compound having a composition capable of improving the adhesiveness to the magnetic layer is preferably used. Of course, the coating material can be selected according to the characteristics to be exhibited. For example, compounds having properties such as lubricants and antistatic agents, thermoplastic resins for slipperiness and flattening, crosslinkable resins and coating agents are required from organic solvent-soluble type to aqueous dispersions. Various compounds and compositions may be used depending on the means.

Specifically, for example, antistatic surfactants such as alkyl sulfonates and alkylbenzene sulfonates, vinyl-based anionic or cation-based polymer antistatic agents, various phenol-based ultraviolet absorbers, etc. , Antioxidant, organic solvent-soluble thermoplastic polyester, water-dispersible thermoplastic polyester containing sulfonate,
Alkyd polyester, organic solvent soluble or water dispersible polyurethane resin, polyisocyanate compound,
End-blocked polyurethane resin, vinyl chloride-vinyl acetate type, vinylidene chloride type, styrene type, vinyl acetate type, acrylic type and other organic solvent soluble or water dispersible vinyl type resin, epoxy resin, silicone type resin, urea Examples thereof include, but are not limited to, a resin and a melamine resin. These coating layers may contain inorganic or organic fine particles, dyes, pigments, surfactants, lubricants and the like.

The application to the polyester film may be applied to what has already been formed into a film, or may be within the film manufacturing process. Particularly in the case of a biaxially stretched polyester film, a coating treatment is performed after uniaxial stretching by roll stretching, and a method of heat-treating this by stretching it in a direction perpendicular to the previous stretching direction without drying or drying is a film-forming and coating treatment at the same time. It is extremely useful because it can be implemented.

As a coating method, a well-known reverse coater, gravure coater, kiss coater, or other roll coater method or a bar coater method can be used, but the coating method is not limited thereto. The coating thickness can be changed as necessary, but the range is 0.001 to 1.0 μm, preferably 0.01 to 0.5 μm, and more preferably 0.01 to 0.1 μm.

[Examples] 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 unless the gist thereof is exceeded. 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) Average particle size, particle size distribution, and volumetric shape factor 10 fields of view of the particles observed with a transmission electron microscope at a magnification of 200,000 were measured using an image analyzer of Quantimet 500 type manufactured by Leica. It was The average particle size is expressed as the particle size when the weight fraction is 50% by converting the individual particles into a permeation sphere and integrating from the smaller particle size. The particle size distribution was expressed as the ratio of particle size when the weight fraction was 25% and 75% (25% / 75%). The volume shape factor (f) is obtained by measuring the maximum diameter of each particle, and letting this average value be D, f = V / D ³ (where V is (average particle diameter) ³ × (π / 6)) Calculated from

(2) Center line average roughness (Ra) It was determined as follows using a surface roughness measuring device (SE-3F) manufactured by Kosaka Laboratory Ltd. That is, a portion having a reference length L (2.5 mm) is extracted from the film cross-section curve in the direction of its center line, and the center line of this extracted portion is taken as the x-axis, and the direction of longitudinal magnification is taken as the y-axis. The value given by the following equation when represented by x) is represented by [μm]. Twelve points were measured for each sample, and the average value of 10 points, excluding the maximum and minimum values, was used. The tip radius of the stylus is 2
μm, the load was 30 mg, and the cutoff value was 0.08 mm.

(3) Manufacture of magnetic tape and S / N, DO evaluation The following magnetic paint was applied to a polyester film,
The magnetic layer was formed so that the film thickness after drying was 2.5 μm.
That is, 220 parts of magnetic fine powder, 30 parts of polyurethane resin, 10 parts of nitrocellulose, vinyl chloride-vinyl acetate copolymer 8
Parts, lecithin 5 parts, cyclohexanone 100 parts, methyl isobutyl ketone 100 parts and methyl ethyl ketone 280 parts are mixed and dispersed in a ball mill for 48 hours and then 4 parts of a polyisocyanate compound is added to obtain a magnetic paint, which is applied to a polyester film, and then the paint. Was magnetically oriented before being 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 was measured with a synchroscope at a measurement frequency of 4 MHz, and the blank was set to 0 decibels and the relative value was displayed in decibels.

-Number of dropouts (DO) The number of dropouts per minute was measured by playing back a video tape recording a signal of 4.4 MHz and measuring the number of dropouts with a dropout counter of Okura Industry Co., Ltd. for about 20 minutes.

(4) Scratch resistance A magnetic tape cut into 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. . 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.

(5) 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 during running (μ
d) was determined.

(6) Durability A tape recording a signal of 4.4 MHz was recorded at a constant speed of 500 with a NV-3700 type video deck manufactured by Matsushita Electric Industrial Co., Ltd.
Measure the number of dropouts after running repeatedly,
It was expressed as a ratio to the number of dropouts before repeated running.

(7) Magnetic layer adhesiveness A double-sided adhesive tape is pasted on a stainless steel plate with a thickness of 1 m / m, and the magnetic tape is slit so that the magnetic layer surface of the 1/2 inch slit is in contact with the adhesive tape. to paste together. Then, the peel resistance when the polyester film is peeled from the magnetic layer at an angle of 180 ° is measured by a tensile test at a speed of 500 mm / min.

Example 1 100 parts of dimethyl terephthalate and ethylene glycol 6
0 part, magnesium acetate and 0.09 part of tetrahydrate 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 reach 230 ° C.
The temperature was raised to 0 and the transesterification reaction was substantially completed. Next, using aluminum chloride as a raw material, 10 parts of Al ₂ O ₃ particles obtained by combustion hydrolysis in an oxyhydrogen flame were mixed with ethylene glycol 90 parts.
Scattered into parts and sand grinder (Igarashi SGL-1
/ 2G) was added to 8 times the slurry that had been crushed for 100 minutes, 0.04 parts of ethyl acid phosphate and 0.04 parts of antimony trioxide were added, and polycondensation reaction was carried out for 4 hours to obtain a polyester with an intrinsic viscosity of 0.62. (A) was obtained. Also, separately
In place of Al ₂ O ₃ particles, CaCO ₃ particles with an average particle size of 0.7 μm are added to 0.6
%, 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.

The obtained polyester (A) and polyester (B) are blended uniformly ((A) / (B) = 50/50) and 180 ° C.
After being dried at a temperature of 290 ° C., it was extruded into a sheet at a temperature of 290 ° C. by an extruder, and an amorphous film having a thickness of 200 μm was obtained by electrostatic contact cooling method.

The amorphous film is then placed in the film flow direction 95
It was stretched 3.5 times at ℃. An aqueous dispersion of polyester resin (Finetex ES-650 manufactured by Dainippon Ink and Chemicals, Inc.) and an aqueous dispersion of polyurethane resin (Implanil DLH manufactured by Bayer Co.) were used as solid components on each side of the longitudinally stretched film.
After coating with a bar coater, an aqueous dispersion with a concentration of 0% and 80% at a concentration of 10% was drawn, stretched 3.9 times at 110 ° C in the direction orthogonal to the flow direction of the film, and heat-treated at 220 ° C for 3 seconds. After that, the mixture was cooled to obtain a biaxially stretched polyester film having a thickness of 15 μm.

A magnetic layer was applied to the coated surface of the obtained biaxially stretched polyester film to obtain a magnetic tape.

Examples 2 and 3 As in Example 1, the polyester (A) and the polyester (B) in Example 1 were blended so that the content and content shown in Table 1 were changed by changing the particle type and particle size. To produce a biaxially oriented polyester film and a magnetic tape.

Comparative Example 1 In Example 2, the particles added to the polyester (A) were changed to Al ₂ O ₃ to use CaCO ₃ particles having a low Mohs hardness, and the particles in the polyester (B) were changed as shown in Table-1. In the same manner, a biaxially stretched polyester film and a magnetic tape were obtained.

Comparative Example 2 In Example 1, a biaxially stretched film and a magnetic tape were obtained without performing coating after longitudinal stretching.

Comparative Example 3 Aluminum hydroxide obtained by hydrolyzing organic aluminum was separated and fired to obtain Al ₂ O ₃ particles having a BT specific surface area of 170 m ² / g. The obtained particles were made into an ethylene glycol slurry in the same manner as in Example 1. Microscopic observation of the particles in the slurry showed that the particles were needle-shaped and had an average particle size of
The shape factor was 0.04 μm and 0.03. A biaxially stretched film and a magnetic tape were obtained in the same manner as in Example 1 except that this slurry was used.

 The results obtained above are summarized in Table 1.

Comparative Example 4 In the method for producing Al ₂ O ₃ particles of Comparative Example 3, the average particle diameter was 0.08 μm by changing the firing temperature and time of aluminum hydroxide.
m, shape factor 0.17, particle size distribution 0.17, particle size distribution 2.54 were obtained, and a biaxially stretched film and a magnetic tape were obtained in the same manner as in Comparative Example 3 except that such particles were used.

The magnetic tapes using the polyester films of Examples 1 to 3 satisfying the requirements of the present invention were excellent in magnetic layer adhesion and scratch resistance, and were sufficiently satisfactory in reproduction output and dropout number. In particular, there was almost no increase in dropout after running many times, which 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 is inferior.
Many scratches were found on the magnetic tape, the number of dropouts was large, and the durability was slightly inferior.

Comparative Example 2 is an example in which the coating layer is not provided on one side of the polyester film, but the adhesiveness between the magnetic layer and the polyester film surface is extremely low compared to the case where the coating layer is provided, and the dropout increases and the durability is increased. It was not preferable because it deteriorated the property.

Comparative Example 3 is an example in which the center line average roughness of the film surface exceeds the upper limit of the range of the present invention, but in this case, electromagnetic conversion characteristics are poor and dropout increases, which is not preferable. It was

Comparative Examples 3 and 4 are examples in which the particle size distribution and the volume shape factor do not satisfy the requirements of the present invention, but the scratch resistance is poor and scratches occur on the running surface side of the magnetic tape. The number of outs was large and the durability was poor.

[Effect of the Invention] The film of the present invention contains specific inert particles,
Furthermore, by providing a coating layer on one surface of the film, a film having excellent scratch resistance and magnetic layer adhesiveness is provided, and its industrial value is high.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Takashi Harada, 1000, Kamoshida-cho, Midori-ku, Yokohama, Kanagawa Prefecture, Central Research Laboratory, DIAFOIL Co., Ltd. 58-215427 (JP, A) JP 60-71225 (JP, A) JP 61-133017 (JP, A)

Claims (1)

(57) [Claims] 1. A particle size distribution of 2.0 or less, a volume shape factor of 0.1 to π /
6, particles with a Mohs hardness of 8 or more and an average particle size of 0.01 to 5 μm
A polyester film for a magnetic recording medium, which comprises 0.05 to 5 wt% and has a coating layer on one side of a polyester film having a center line average roughness of 0.005 to 0.040 μm on the film surface.