JPH07244835A - Polyester film for magnetic recording medium - Google Patents

Abstract

PURPOSE:To obtain the smoothness and the scratch-resistance which do not deteriorate electromagnetic conversion characteristics and the excellent running properties under high temperature and high humidity conditions by a method wherein the required number of colloidal silica particles are contained. CONSTITUTION:Colloidal silica particles whose diameters are 10-1000mmu, preferably 15-500mmu, more preferably 55-300mmu, are employed. It is preferred that the silica particles have a uniform particle size distribution. If the average diameter of the silica particles is denoted by (a) (mmu), it is preferred that not less than 95wt.% of the particles belong to the diameter range not larger than 2a (mmu), more preferably, not larger than 1.5a (mmu). The respective circle equivalent diameters of at least 200 colloidal silica particles are measured and the average diameter and the particle size distribution can be calculated in accordance with the sectioned weight shares of the respective circle equivalent diameters.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a polyester film for magnetic recording media.

[0002]

2. Description of the Related Art Conventionally, polyester films for magnetic recording media have been used in order to improve workability such as winding and slitting.
Alternatively, in order to provide tape running property in a video tape recorder, countless minute protrusions are provided on the film surface. However, these minute projections deteriorate the electromagnetic conversion characteristics necessary for magnetic recording, and cause dropout (recording loss) and color noise.

The problem here is that the projections on the surface of the film have hitherto not been able to obtain fine projections that do not deteriorate the electromagnetic conversion characteristics, and that the average projection diameter has a relatively small particle size but a wide particle size distribution. This is because the coarse particles had a large adverse effect.

For example, in a vapor deposition type video tape in which a magnetic substance is vapor-deposited on the surface of a polyester film, since the magnetic layer is very thin, the surface morphology of the base film used is as it is after the magnetic substance is vapor-deposited. The surface morphology of the deposited thin film becomes Therefore, if the surface roughness of the base film is rough, the electromagnetic conversion characteristics of the vapor-deposited video tape are significantly deteriorated. Considering this electromagnetic conversion property, a base film having a smooth and completely mirror-finished surface is preferable, but a vapor-deposited film formed on such a base film has a very smooth slip surface because the vapor-deposited surface keeps the mirror-like surface as it is. Unfavorably, unless a protective film layer is provided on the vapor deposition surface, a large amount of scratches will occur in the tape forming process after the vapor deposition step,
It loses practicality at all.

A serious problem in practical use of the vapor-deposited video tape is the runnability of the vapor-deposited surface. In the case of a coating type video tape in which a conventional magnetic powder is mixed with an organic binder and applied to a base film, a lubricant can be added to the binder to improve the running property of the magnetic surface.
In the case of vapor-deposited video tape, the runnability of the vapor-deposited surface cannot generally be used unless a protective film layer is provided, and it is difficult to uniformly provide a protective film layer on the vapor-deposited surface. However, there is a drawback in that the running property of the surface cannot be improved, especially under the severe conditions of actual use, that is, under high temperature and high humidity conditions.

[0006]

An object of the present invention is to provide a base for a magnetic recording medium which can obtain smoothness which does not deteriorate electromagnetic conversion characteristics, scratch resistance, and good running property even under high temperature and high humidity conditions. To provide a film.

[0007]

Means for Solving the Problems The above object of the present invention is to provide a magnetic material containing 95% by weight or more of colloidal silica in the range of 2a (mμ) when the average particle size is a (mμ). Achieved by polyester film for recording media.

The polyester referred to in the present invention may be any polyester as long as it is mainly composed of linear polyester. For example, polyethylene terephthalate, polytetramethylene terephthalate, poly-1,4-dichlorohexylene dimethylene terephthalate, polyethylene-2,
6-naphthalene dicarboxylate, polyethylene-P
-Oxybenzoate is a typical example.

The above polyester may be a homopolyester or a copolyester. In the case of copolyester, the components to be copolymerized include, for example, diethylene glycol, propylene glycol,
Neopentyl glycol, polyethylene glycol, P
Diol components such as xylylene glycol and 1,4-cyclohexanedimethanol, dicarboxylic acid components such as adipic acid, sebacic acid, phthalic acid, isophthalic acid, 2,6-naphthalene dicarboxylic acid and 5-sodium sulfoisophthalic acid Examples thereof include polyfunctional carboxylic acid components such as mellitic acid and pyromellitic acid, and P-oxyethoxybenzoic acid. In the case of copolymerization, the component to be copolymerized is 20 mol% or less.

Further, the above polyester contains at least one of an alkali metal salt derivative of sulfonic acid which is non-reactive with the polyester and a polyalkylene glycol which is substantially insoluble in the polyester in an amount not exceeding 5% by weight. You may mix in.

The colloidal silica referred to in the present invention has a fine single particle size. Specifically, silica particles obtained from water glass by a treatment such as an ion exchange method or dialysis are attached to fine silica particles. It is possible to use, for example, a water glass method of growing by growth and a method synthesized by an alkoxide method of hydrolyzing a silicate ester in an alcohol solvent. Each of them has a uniform particle size distribution, few agglomerated particles, and a particle shape that is extremely spherical.

Conventionally, a method of adding fine inert inorganic particles has been known as a method of forming protrusions on the film surface to improve running property and the like. Examples of these inert inorganic particles include kaolin, calcium carbonate, titanium oxide,
Particles such as silica have been applied. However, these particles have irregular shapes, and silica, titanium oxide, etc. have a shape in which a large number of fine particles are aggregated, and the particle size is non-uniform, and there are also many coarse particles and a wide particle size distribution. have. In order to improve these drawbacks, it has been attempted to make the particle diameter uniform by using crushing treatment and dispersion treatment together, but the effect is insufficient and the projection shape to be formed is not uniform. Was insufficient.

In the present invention, conventional silica, that is, conventional wet silica, agglomerated silica such as dry silica synthesized by thermal decomposition of silicon halide, particles of calcium carbonate, titanium oxide, kaolin, etc., etc. It is characterized by the fact that there are few coarse projections due to coarse particles and a large number of uniform projections are formed due to the effect of uniform fine single particles of colloidal silica, uniform particle size, etc.

The colloidal silica used in the present invention preferably has a particle size of 10 to 1000 mμ, more preferably 15 to 500 mμ, and particularly preferably 55 to 300 mμ. The comparison area is preferably ² to 200 m ² / g, more preferably 5 to 181 m ² / g, and particularly 14 to
49 m ² / g is preferred.

The particle size distribution of the particles is preferably uniform, and the colloidal silica of the present invention has an average particle size of a
(Mμ), 95 wt% or more of particles are 2a (m
It is characterized by having a distribution of
It is preferably distributed within a range of a (mμ) or less. More specifically, for at least 200 particles of colloidal silica, the equivalent circle diameter is determined for each particle by electron microscope observation, and the average diameter and particle size distribution are determined by the weight fraction of each divided equivalent circle diameter. Can be calculated. Furthermore, when the film is observed with a transmission electron microscope (magnification: 30,000), it is preferable that about 10 or more particles are dispersed in the film so that they do not aggregate.

The amount of colloidal silica particles added is preferably 0.005 to 5 wt%, more preferably 0.05 wt%.
2 to 1.0 wt%, more preferably 0.05 to 0.8
wt%.

Further, when the film is stretched, internal particles composed of a polymerization residue which causes film surface protrusions or inert particles other than colloidal silica added from the outside may be contained. Its content is, when it contains inert particles other than colloidal silica, inhibits the projections due to the colloidal silica due to the projections, so as not to impair the effect of the present invention, the particle size is equal to or less than the particle size of the colloidal silica. Preferably. When the protrusions of the inactive particles are smaller than the protrusions of colloidal silica, the protrusions derived from colloidal silica substantially dominate the effect of the present invention, and a good effect can be obtained. Similarly, colloidal silica having two different particle sizes may be used together.

The polyester film of the present invention is a polyester film formed by mixing the above polyester with the above colloidal silica by a conventional method,
That is, a film formed by melting polyester and extruding it into a sheet or a cylindrical shape, stretching it in at least one direction, and as the mechanical properties of the film, a normal balance type, a uniaxially strengthened type, It is preferably of the biaxially strengthened type.

The projections formed on at least one surface of the film of the present invention preferably have (a) an area average diameter [D ₁ ] of 0.3 to 5 μm, more preferably 0.4 to 2 μm. is there. 0.3
If it is less than μ, the running property of the vapor-deposited magnetic surface is deteriorated, and if it exceeds 5 μ, the electromagnetic conversion characteristics are deteriorated, which may not be preferable. (B) Ratio [D ₁ ] / of the area average diameter [D ₁ ] and the number average diameter [D ₂ ] expressing the sharpness of the distribution of the surface projection diameter
[D ₂ ] is preferably more than 1 and less than 2.5,
More preferably, it is more than 1 and 2.0 or less. If it is 2.5 or more, the distribution of the projection diameter becomes too wide, which may lead to deterioration of electromagnetic conversion characteristics due to the coarse projection, particularly dropout. It is practically impossible that only protrusions having exactly the same diameter such that the ratio becomes 1. (C) The maximum protrusion height [P] is preferably 0.10 μm or less, more preferably 0.05 μm or less, and further preferably 0.005 to 0.03 μm. If it exceeds 0.10 μm, the electromagnetic conversion characteristics may deteriorate. (D) The number of protrusions [N] is 5 × 10 ³ to 1 × 10 ⁵ pieces / mm
² is preferable, and more preferably 1 × 10 ⁴ to 4 × 10 ^4.
K / mm ² . If it is less than 5 × 10 ³ pieces / mm ² , the running property of the vapor-deposited magnetic surface may deteriorate, and if it exceeds 1 × 10 ⁵ pieces / mm ² , the electromagnetic conversion characteristics may deteriorate.

From the viewpoint of controlling the state of surface protrusions, it is most preferable to add colloidal silica to the polyester which forms an optically flat surface.

The surface of the polyester film is preferably smooth. Specifically, the roughness of the film is 0.08 mm, which is the cutoff value of a stylus surface roughness meter.
Ra value is 0.030μ or less, preferably 0.020μ,
More preferably, it is 0.015μ.

The Ra value means a center line (a portion above the center line) in a roughness curve without undulations by using an appropriate cutoff value from a sectional curve obtained from a stylus type surface roughness meter. Is obtained by making the areas of the lower part and the lower part equal to each other), and is a calculated average of absolute values of height (lowness) of the roughness curve (according to DIN 4768).

The polyester film of the present invention can be applied to stamping foils, optical recording materials, capacitors, electrostatic recording materials and various other applications, but it is a base film for magnetic recording media, especially a base for forming a ferromagnetic metal thin film. It is preferably applied to a film.

As the means for forming the ferromagnetic metal thin film, all conventionally known methods can be used, but a sputtering method, an electroless plating method, an ion plating method, or a vacuum deposition method can be used. The vacuum deposition method is particularly preferable. As the ferromagnetic metal material, iron, cobalt, nickel, alloys thereof, cobalt-chromium alloy, or the like can be used.

The thickness of the vapor-deposited metal film is generally 0.0 in view of the necessity of providing sufficient output as a high density magnetic recording medium.
About 2 to 0.5 μ is preferable. The thickness of the metal vapor deposition film formed in this way is very thin, and as described above, the surface condition of the base film directly becomes the surface condition of the vapor deposition film, satisfying both the electromagnetic conversion characteristics and the running property of the vapor deposition magnetic surface. In order to do so, it is preferable that the above-mentioned projections are present on the vapor deposition surface of the base film.

The polyester film of the present invention is preferably coated with a solution prepared by dispersing a lubricant in water or a solvent for imparting slipperiness on the surface opposite to the vapor-deposited magnetic surface. As a method for imparting slipperiness, all conventionally known methods can be used. For example, a non-evaporated film obtained by unstretching, uniaxially stretching, or biaxially stretching a water-based or solvent-based solution of lubricant + polymer binder + surfactant is used. Sliding properties can be imparted by coating and drying the magnetic surface during or after film formation.

The method of measuring and evaluating the characteristics of the film and tape will be described below.

(1) Average particle size and particle size distribution of particles For at least 200 or more colloidal silica particles, the equivalent circle diameter is determined by using an electron microscope, and the average particle diameter is determined by the weight fraction of each divided equivalent circle diameter particle. Determine the diameter and particle size distribution. In the case of a colloidal silica solution, a centrifugal sedimentation method or the like may be adopted if necessary.

(2) Film protrusions (b) Area average diameter [D ₁ ] and number average diameter [D ₂ ], number of protrusions [N] Cambridge Instruments (UK) "Quanti
met "720 was used. 400 on the surface of the film to be observed.
Aluminum is vacuum-deposited to a thickness of ~ 500 ohm strong, and a reflective metallurgical microscope (32x objective, 8x eyepiece)
Then, the observation of 100 fields of view is performed, and the image of the protrusion is observed by detecting that it is observed in black.

Image processing measures the number of protrusions and the area of protrusions,
The area range of 3.14 × 10 ^{-2 to} 78.5 μm ² is 15
Divide the protrusion of each area into steps that are divided into months. The projection diameter is calculated as an equivalent circle diameter from the intermediate area of each step, and the number of projections [N _n ] of the surface projection diameter [D _n ] of each step consisting of 15 steps and the surface projection diameter [D _n ] of each step The relationship with the sum of areas [A _n ] is understood. The area average diameter [D ₁ ] and number average diameter [D ₁ ]
₂ ] is calculated by the following equations.

[0031]

[Chemical 1] (B) Maximum protrusion height [P] High precision thin film step measuring instrument (model: E, manufactured by Kosaka Research Institute, Ltd.
T-10) using stylus diameter cone type 0.5μR, needle pressure 5
mg, measurement speed 4 μ / sec, longitudinal magnification 1 million times, lateral magnification 1000 times, cut-off condition 0.016 mm. The portion of is extracted, and the difference between the maximum peak and the minimum valley during the measurement of the five surfaces is defined as the maximum protrusion height [P].

(3) Tape characteristics The tape characteristics were evaluated by repeating recording and reproducing using a general commercially available VHS VTR. The tape running property was evaluated by performing reproduction under two conditions of normal temperature and normal humidity and high temperature and high humidity, and observing the fluctuation of the screen due to the disturbance of the tape running. The evaluation criteria are as follows. ○: The running screen was smooth and there was no fluctuation on the playback screen. X: Traveling becomes slower in some places, causing fluctuations in the playback screen.

(4) Scratch resistance The scratch resistance was evaluated by observing scratches on the tape thin film after repeatedly running 100 times under normal temperature and normal humidity and high temperature and high humidity conditions. The evaluation criteria are as follows. ◯: Occurrence of extremely weak scratches is slightly observed on the tape thin film surface. X: Tight scratches occur on the tape thin film surface. The room temperature and normal humidity are conditions of 25 ° C. and 60% RH, and the high temperature and high humidity are conditions of 40 ° C. and 80% RH.

(5) S / N ratio The S / N ratio is a signal S contained in the video duplication signal at the time of reproduction by recording a 50% white level signal at the optimum recording current of each tape.
The ratio of noise and noise N is calculated by using a video noise meter
The HS standard tape was set to 0 dB for comparative measurement.

(6) Dropout Dropout is a drop in which the recorded signal of the three-stage step is recorded on the magnetic recording tape with the optimum recording current, the attenuation of the output of the video head amplifier at the time of reproduction is 18 dB, and the connection time is 2.0 μsec or more. The outs were measured with a dropout counter for 10 minutes, and averaged per minute. The S / N ratio and the dropout measurement were performed under normal temperature and normal humidity conditions.

The ferromagnetic thin film provided on the polyester film for a magnetic recording medium of the present invention, particularly the vapor-deposited magnetic thin film, is provided on at least one side of the polyester film. The surface area of the film of the present invention is large, and in particular, the contact area with the magnetic head is very small, so that the running property of the ferromagnetic thin film surface is extremely good.

Next, a method for producing the polyester film of the present invention will be described with reference to specific examples. First, colloidal silica obtained by the water glass method or the alkoxide method is contained in polyester. The aqueous colloidal silica obtained by removing the alkali content from the colloidal silica obtained by the water glass method is careful in the subsequent step of aggregation, and in the point that it is finally present in the state of almost primary particles by special treatment. Most preferred. The colloidal silica may be used by mixing it with glycol while containing water, or by replacing water with glycol. Further, colloidal silica is mixed with a glycol solution containing a required concentration of colloidal silica immediately before the final addition to the polymerization system.
Under reduced pressure of 0 mmHg or less, preferably 1 to 10 mmHg, for example, oscillation frequency 20 KHz, oscillation output 150 W
The above ultrasonic treatment is performed for 30 minutes or more. It is effective to remove the low boiling point substance which is considered to be the cause of the secondary aggregation by this special treatment, by utilizing the characteristic of the colloidal silica having a very sharp particle size distribution and preventing the secondary aggregation.

The thus prepared polyester polymer containing uniformly dispersed ultrafine single particle diameter colloidal silica particles is melt-extruded by an ordinary extruder and cooled by a cooling drum to obtain an unoriented film. , In the usual way,
After stretching in one direction, stretching is performed in a right angle direction, or after stretching in a right angle direction, re-stretching is further performed in the one direction and heat treatment is performed. Further, specifically, the polyester raw material described above is used, melt extrusion is performed by a normal film forming machine, and after cooling, 3 to 5
Uniaxially stretched twice, and 90 at the preheater of the stenter after biaxial stretching.
After preheating at ~ 120 ° C, at a stretching temperature of 90-120 ° C, 25 ~
Stretch horizontally 4.5 times. At this stage, the polyester film having the surface protrusions of the present invention is substantially obtained. Furthermore, this transversely stretched film is heat-treated at 180 ° C. to 220 ° C., or 1.1 to 1.8 times, and 180 to 180 ° C. after re-longitudinal stretching.
The biaxially stretched polyester film of the present invention is obtained by heat treatment at 220 ° C.

As described above, the present invention is a polyester film having ultra-fine single surface protrusions, and the vapor-deposited thin film formed on the surface has dramatically improved surface running performance. Moreover, the electromagnetic conversion characteristics of the vapor deposition tape are not impaired, and the dropout does not increase because there is no coarse protrusion.

[0040]

EXAMPLES Next, production examples of the base film of the present invention and production examples of video tapes using the base film will be described.

Example 1 While adding ethylene glycol (EG) little by little to water-based colloidal silica having an average particle diameter of 60 mμ and a concentration of 20 wt%, water was carefully distilled off to obtain a silica concentration of 10 wt%.
EG-substituted colloidal silica was prepared. A small amount of silica aggregate was found on the liquid surface and the vessel wall, and this was filtered.

Dimethyl terephthalate (DMT) 100
Part, and 0.02 part of Zn acetate, the above EG-substituted colloidal silica and additional EG are 0.2 wt% with respect to the weight of the produced polyester, and the molar ratio of the total EG to DMT is 2.5. 1 to 1 such EG solution
Under a reduced pressure of 2 mmHg, it was treated with an ultrasonic disperser having an oscillation frequency of 20 KHz and an oscillation output of 300 W for about 2 hours. Observation of 500 particles of this colloidal silica with an electron microscope confirmed that the average particle diameter was 60 mμ, and the particles having a particle size of 120 mμ or more were 0.5 wt%. Further, no aggregate of two or more particles was observed. Further, when calculating the area-equivalent diameter, the ratio of the major axis and the minor axis was determined, and the average ratio was 1.03, which was a shape close to a true sphere.

This treatment solution was added and a transesterification reaction was carried out at 180 to 240 ° C. Then 0.035 parts of antimony trioxide and 0.04 of trimethyl phosphonate
Then, prepolymerization was carried out at 240 to 270 ° C. under a gentle reduced pressure, and further polycondensation reaction was carried out at 270 to 280 ° C. under high vacuum to complete the reaction in 4 hours.

The intrinsic viscosity of the obtained polyethylene terephthalate was 0.65. This polymer was dried after being made into chips, extruded at 290 to 300 ° C. with a film molding machine and cooled with a cooling drum to prepare a 210 μ unstretched film, which was 3.5 times at 90 ° C. in the longitudinal direction and 100 in the lateral direction. Biaxial stretching is carried out 4.0 times at ℃, and further at 205 ℃ for 3 times.
After fixing for 0 seconds, a polyethylene terephthalate film having a thickness of 14 μm was produced.

Thereafter, an easy-sliding treatment coating liquid containing calcium carbonate and silicone in a binder of polyurethane resin and vinyl chloride-vinyl acetate copolymer was applied to one side of the film and dried. Subsequently, a cobalt-nickel alloy thin film having a film thickness of 0.1 μm was formed on the opposite surface coated with the slippery coating liquid by vacuum vapor deposition, cut into a predetermined width in the machine direction of the film, and a magnetic tape having a thickness of 15 μm was formed. did. This characteristic is shown in Table 1.

Example 2 A magnetic tape was obtained in the same manner as in Example 1 except that the concentration of the colloidal silica used in the production of the base film of Example 1 was 0.1 wt%. Table 1 shows tape characteristics
It was shown to.

Example 3 In the production of the base film of Example 1, the average particle size was 1
A magnetic tape was obtained in the same manner as in Example 1 except that 00 mμ of colloidal silica was used at an addition concentration of 0.1 wt%. The tape properties are shown in Table 1.

Comparative Example 1 Instead of EG containing 10 wt% concentration of colloidal silica at the time of preparing the polymer of Example 1, dry method silica having an average particle diameter of 60 mμ dispersed with a high-speed stirrer was added at a concentration of 1
A magnetic tape was obtained in the same manner as in Example 1 except that EG containing 0 wt% was used. The tape properties are shown in Table 1.

[0049]

[Table 1]

[0050]

As described above, the present invention is a film in which colloidal silica having a specific particle size distribution is added to polyester, and when a magnetic layer is provided on the film,
It was possible to obtain smoothness with good electromagnetic conversion characteristics, scratch resistance, and good runnability at high temperature and high humidity.

Claims (1)

[Claims] 1. When the average particle size is a (mμ), 95
A polyester film for a magnetic recording medium, which comprises colloidal silica having a particle content of 2 wt% or more within a range of 2a (mμ).