JPH0644342B2 - Base film for magnetic recording medium - Google Patents

Description

TECHNICAL FIELD The present invention relates to a base film for a magnetic recording medium, and more particularly to a suitable base film for a video tape or a floppy disk.

[Prior Art] A polyethylene terephthalate film containing inert inorganic particles is known as a base film for a magnetic recording medium. (For example, Japanese Patent Publication No. 57-31205).

[Problems to be Solved by the Invention] However, the conventional base film for a magnetic recording medium described above is
In order to reduce the cost of video tapes, especially video tapes, there is a drawback in that the running property is insufficient when the video tape is used without a back coat.

It is an object of the present invention to provide a base film for a magnetic recording medium, which has improved such problems and has excellent running properties without deteriorating electromagnetic conversion characteristics when the magnetic recording medium is used.

[Means for Solving Problems] The present invention contains a polyester having the following structural unit as a main repeating unit and 0.03 to 2.0% by weight of inorganic fine particles having an average particle diameter of 0.03 to 2.5 μm. Is a biaxially oriented film containing the composition as a main component, and the inorganic fine particles have a volume fraction of particles having a particle size of 1.3 times or more of the average particle size of 5% of the total.
Magnetic recording characterized in that the average particle size of the particles having a particle size of ˜45% and 5% (volume%) from the larger particle size is 1.3 to 10 times the average particle size of all particles. The present invention relates to a base film for media.

It is at least one kind of dicarboxylic acid residue selected from

The polyester in the present invention is a polyester having the above structural unit as a main repeating unit, and R is At least one dicarboxylic acid residue selected from In this case, the running property is further improved, which is particularly desirable. Further, within the range that does not inhibit the present invention, preferably 10
Other components than the above may be copolymerized as long as they are within the mol%.

The average particle size of the inorganic fine particles in the present invention is 0.03 to 2.
It should be in the range of 5 μm, preferably 0.07 to 2.3 μm, and more preferably 0.10 to 2.0 μm. If the average particle size is smaller than the above range, the running property becomes poor, and conversely if it is large, the electromagnetic conversion property becomes poor, which is not preferable.

The composition used in the present invention contains the above inorganic fine particles in an amount of 0.03 to
It is necessary to contain 2.0% by weight, preferably 0.05 to 1.5% by weight, more preferably 0.1 to 1.0% by weight. If the content is less than the above range, the running property becomes poor, and conversely if the content is too large, the electromagnetic conversion characteristics become poor, which is not preferable.

When two or more kinds of inorganic fine particles are used, the total amount thereof needs to satisfy the above content.

Further, the inorganic fine particles in the invention have an average particle size of 1.3.
It is necessary that the volume fraction of particles having a particle size of twice or more is 5 to 45%, preferably 10 to 40% of the whole. If the volume fraction is smaller than the above range, the running property becomes poor,
On the contrary, if it is large, the electromagnetic conversion characteristics become poor, which is not preferable.

Further, in the inorganic fine particles according to the present invention, the average particle diameter of 5% (volume%) particles from the larger particle diameter is 1.3 to 10 times, preferably 1.5 to 8 times the average particle diameter of all particles. .0
It is necessary to be in the range of, preferably 1.5 to 6.0 times. If the average particle size of 5% (volume%) particles from the larger particle size is smaller than the above range, the running property becomes poor, and conversely if the average particle size becomes large, the electromagnetic conversion characteristics become poor, which is not preferable.

In addition, the average particle diameter (μm) of 5% (volume%) particles from the larger particle diameter of the inorganic fine particles in the present invention is φ ₂
And the thickness (μm) of the magnetic layer is φ ₃ , φ ₂ and φ
_A magnetic recording medium having a ratio of ₃ (φ ₃ / φ ₂ ) in the range of 0.2 to 8.0 is particularly preferable because the running properties and electromagnetic conversion characteristics are further improved.

The fine particles of the present invention are particularly desirable when the Mohs hardness is 5 or less, because the improvement of the running property is particularly remarkable due to the limitation of the particle size characteristics.

The inorganic fine particles in the invention are not particularly limited, but in the case of a metal halide compound having a fluorite structure or a rutile structure, the improvement of the running property is particularly remarkable due to the limitation of the particle size characteristics of the inorganic fine particles as described above. In particular, when the halogen is fluorine, the effect due to the limitation of the particle size characteristic is more remarkable, and among them, CaF ₂ , SrF ₂ ,
Particularly desirable because runnability further becomes better than in the case of MgF _2, MnF _2.

The film of the present invention contains the above composition as a main component, but may be blended with other polymers within a range that does not impair the object of the present invention, and may further contain an antioxidant, a heat stabilizer, a lubricant, an ultraviolet absorber. Inorganic or organic additives such as nucleating agents may be added to the extent that they are usually added. Further, inorganic particles outside the scope of the present invention may be added within a range that does not impair the object of the present invention.

The film of the present invention is a film obtained by biaxially orienting the above composition. An unoriented film and a uniaxially oriented film are not preferable because they have poor running properties and electromagnetic conversion characteristics.

The plane orientation index of the film of the present invention is 0.935 to
In the case of 0.975, particularly 0.940 to 0.970, the running property is further improved, which is particularly desirable.

The density index of the film of the present invention is 0.02 to 0.0.
When it is in the range of 5, the runnability is further improved, which is particularly desirable.

The film of the present invention is particularly desirable when the coefficient of static friction in the width direction between the films is in the range of 0.4 to 4.0, particularly 0.6 to 3.0, because the running property is further improved.

The film of the present invention has a surface average roughness Ra in the width direction of 0.0.
04-0.025μm, especially 0.005-0.020μ
When it is in the range of m, the running property and the electromagnetic conversion characteristics are further improved, which is particularly desirable.

The film of the present invention has a melt viscosity at 290 ° C. and 200 sec ⁻¹ of 800 to 10000 poise, particularly 1000 to 700.
When it is in the range of 0 poise, the running property and the electromagnetic conversion characteristics are further improved, which is particularly desirable.

Next, a method for manufacturing the base film for a magnetic recording medium of the present invention will be described.

First, the method of incorporating the inert inorganic fine particles having a predetermined average particle diameter can be performed by a known method,
A method of mixing and dispersing the polyester diol component in the form of a slurry is effective for obtaining the average particle diameter of the present invention. Further, a method for obtaining the particle size characteristic range of the present invention, that is, the volume fraction of particles having a particle size of 1.3 times or more of the average particle size is set to 5 to 45% of the whole, and the particle size is larger 5%
As a method of setting the average particle size of (volume%) particles to 1.3 to 10 times the average particle size of all particles, two or more types of particles having different average particle sizes are used in the form of a slurry in a polyester diol component. Or by dispersing inorganic particles having an average particle size of 1.5 to 3.0 times larger than the average particle size range of the present invention in the form of a slurry in the diol component of the polyester, and then 1 to 50 per minute. ON / OFF at one frequency
The method of dispersing with a mixer that repeats is effective, but the latter method is particularly effective, and in this case, the rotation speed of the mixer is preferably 10 to 1000 rpm.

Next, the diol component containing the inorganic particles thus obtained and a predetermined dicarboxylic acid (or ester thereof) are polycondensed by a known method to obtain a predetermined polyester.

After sufficiently drying the polyester pellets, the pellets are supplied to a known melt extruder and melt-extruded into a sheet form from a slit die at a temperature not lower than the temperature at which the pellets melt and not higher than the temperature at which the polymer decomposes, followed by cooling and solidification. To make an unstretched film. In this case, the method of extruding by passing through a filter having a 95% cut diameter measured by a Coulter counter of 2 to 40 times, particularly 3 to 20 times the desired average particle diameter, has a particle diameter characteristic within the range of the present invention, that is, The volume fraction of particles having a particle diameter of 1.3 times or more of the average particle diameter is 5 to 45% of the whole, and the average particle diameter of particles having a larger particle diameter is 5% (volume%). It is extremely effective to make the average particle diameter 1.3 to 10 times.

Next, this unstretched film is biaxially stretched and oriented. As the stretching method, a sequential biaxial stretching method or a simultaneous biaxial stretching method can be used, but the sequential biaxial stretching method is particularly preferable. The stretching conditions in this case include the longitudinal direction,
A method in which the film is stretched 3.0 to 4.0 times in the longitudinal direction and then 3.2 to 4.5 times in the width direction at a temperature in the range from the glass transition point of the polymer to the cold crystallization temperature both in the width direction. Is preferred. The stretching speed is preferably in the range of 10 ³ to 10 ⁷ % / min. Further, a method of further stretching the stretched film in at least one direction is effective in further improving the running property of the film.

Next, the stretched film is heat treated, and the heat treatment condition in this case is a temperature of 180 ° C. to 230 ° C., preferably 19 ° C.
The method of heat-treating for 0.5 to 60 seconds in the range of 0 ° C to 220 ° C is effective for further improving the running property of the film. Further, it is effective to carry out the heat treatment under a fixed length in order to further improve the running property.

Hereinafter, the base film for a magnetic recording medium of the present invention has been described. However, the film of the present invention may be subjected to known corona discharge treatment, and may be provided with adhesiveness, moisture resistance, heat sealability, lubricity and the like. For this purpose, other polymers may be laminated or coated with other organic or inorganic composition.

[Operation] Since the present invention is a film in which inert inorganic particles having a specific average particle size and particle size distribution are contained in polyester, the accompanying air flow associated with running when used as a magnetic tape etc. The effect of the present invention has been obtained by improving.

[Physical property measuring method and effect evaluation method] The characteristic value measuring method and effect evaluating method of the present invention are as follows.

(1) Average particle size of inorganic fine particles Polyester was removed from the film by a plasma ashing method or a 0-chlorophenol dissolution method, and this was dispersed in ethanol, followed by a stretching sedimentation method (Horiba Seisakusho, CAPA50).
It is the volume average diameter measured in 0 use).

(2) Content of inorganic fine particles After adding 0-chlorophenol 1.0 to 100 g of polyester and heating at 120 ° C. for 3 hours, an ultracentrifuge 55P-72 manufactured by Hitachi Koki Co., Ltd. was used and 40 at 30,000 rpm. Centrifugation is performed for a minute, and the obtained particles are vacuum dried at 100 ° C. If a melting peak corresponding to the polymer is observed when the fine particles are measured with a scanning differential calorimeter, the fine particles are heated and cooled with 0-chlorophenol and then centrifuged again. When no melting peak is observed, fine particles are defined as precipitated particles. Normally, two centrifugation operations are sufficient.

(3) Glass transition point Tg, cold crystallization temperature Tcc It was measured using DSC (Differential Scanning Calorimeter) II type manufactured by Perkin Elmer. The measurement conditions of DSC are as follows. That is, 10 mg of a sample film is set in a DSC apparatus, melted at a temperature of (melting point + 30 ° C.) for 5 minutes, and then rapidly cooled in liquid nitrogen. The temperature of this quenched sample is raised at 10 ° C./min, and the glass transition point Tg is detected. Continue to raise the temperature further,
The crystallization exothermic peak temperature from the glass state was defined as the cold crystallization temperature Tcc.

(4) Plane Orientation Index Using an Atsube refractometer with sodium D line (wavelength 589 nm) as a light source, the biaxially oriented film has a refractive index (A) in the thickness direction and is rapidly cooled into water at 10 ° C. after melt pressing. The refractive index (denoted as B) in the thickness direction of the non-oriented (amorphous) film produced in this way was measured, and A / B was taken as the plane orientation index. Use methylene iodide as the mount solution, and
It was measured at 65 ° C. and 65% RH.

(5) Density index The density of the film measured using a density gradient tube consisting of n-heptane / carbon tetrachloride was d ₁ (g / cm ³ ), and this film was melt-pressed and then rapidly cooled in water at 10 ° C. Difference from the density d _{2 of} the non-oriented (amorphous) film made by
(D ₁ −d ₂ ) was used as the density index.

(6) Static friction coefficient (width direction) Using a slip tester manufactured by Toyo Tester, ASTM-D-
According to 1894-63, the film was measured by sliding it in the width direction.

(7) Melt viscosity The temperature was 290 ° C. and the shear rate was 200 sec ^−1, which was measured using a flow tester for enhancing melt viscosity.

(8) Surface average roughness Ra It was measured according to JIS-B-0601 using a stylus type surface roughness meter. However, the cutoff was 0.08 mm and the measurement length was 1 mm.

(9) Electromagnetic conversion characteristics γ-Fe ₂ O ₃ 100 parts by weight, vinyl chloride-vinyl acetate copolymer 15 parts by weight, polyurethane elastomer 15 parts by weight, carbon black 8 parts by weight, methyl ethyl ketone 120 parts by weight, methyl isobutyl ketone 130 parts by weight. Department,
A mixture of 2 parts by weight of myristylic acid was thoroughly mixed and dispersed by a sand mill to prepare a magnetic paint, and 15 parts by weight of polyisocyanate (Coronate L) was added to the magnetic paint, which was added to a sample polyester film to a thickness of 4.0 μm.
(Dry thickness) Coating, calendering (temperature 90 ° C., linear pressure 200 kg / cm), and slitting to 1/2 inch width to give a tape. This tape was incorporated into a VHS system video cassette (120 minutes) to make a video cassette tape.

Using a VTR on this tape, a signal from a TV test signal generator (TG-7 / 1 type manufactured by Shibasoku Co., Ltd.) was recorded, and 100 passes (120 ° C) at 25 ° C and 50% RH were recorded.
(Minute x 100 passes) Using a dropout counter, a tape having a dropout width of 5 μsec or more and a reproduced signal attenuation of −16 dB or more was picked up and dropped out from this tape. The measurement was carried out for 10 video cassettes, and when the number of dropouts converted per minute was less than 10, the electromagnetic conversion characteristics were good, and when the number was 10 or more, it was considered bad.

(10) Runnability Set the above tape on VTR, 25 ℃, 50% RH
After running 100 passes at 40 ° C and 80% RH for 100 passes, the following items were ranked in 5 grades with a maximum of 5 points, and when the total score of all items was 15 to 10, the runnability was good, When 9 or less, the runnability was determined to be poor.

It should be noted that, in the ranking of 5 levels, the number of samples of 50 volumes is 0 to 1 even if the following items are not satisfied.
The case of 5 pieces, the case of 2 to 3 pieces was 4 points, the case of 4 to 6 pieces was 3 points, the case of 7 to 9 pieces was 2 points, and the case of 10 or more pieces was 1 point.

a) Tape edge does not break (does not buckle) b) Tape does not become wakame-like c) Tape does not generate fine powder due to abrasion (magnetic layer and base film layer) [Example] Implementation of the present invention An explanation will be given based on an example.

Examples 1 to 4 and Comparative Examples 1 to 8 Calcium fluoride manufactured by Kanto Kagaku (CaF ₂ , first-class reagent)
Alternatively, silica (TT-600) manufactured by Nippon Aerosil Co., Ltd. was changed to various dispersion methods in ethylene glycol, mixed and dispersed in the form of a slurry, and transesterified with dimethyl terephthalate, polycondensed, and shown in Table 1. Average particle size,
Polyethylene terephthalate was prepared containing calcium fluoride and silica having particle size characteristics in the amounts shown in Table 1.

The polyethylene terephthalate pellets are heated to 180 ° C.
It was dried under reduced pressure (3 Torr) for 3 hours. The pellets were supplied to an extruder, melt-extruded at 300 ° C., wound around a casting drum having a surface temperature of 30 ° C. and cooled and solidified by an electrostatically applied casting method to prepare an unstretched film having a thickness of about 170 μm. This unstretched film was stretched at 90 ° C. in the longitudinal direction by 3.4 times.

This stretching was performed with a difference in peripheral speed between the two sets of rolls, and the stretching speed was 10,000% / min. This uniaxial film was stretched at a stretching rate of 2000% / min at 100 ° C. for 3.6 times in the width direction using a stenter and heat-treated at 210 ° C. for 5 seconds under a constant length to obtain a film having a thickness of 14 μm. The average particle size, particle size characteristics, and content of the inorganic particles in this film were as shown in Table 1.

As shown in Table 1, the runnability and electromagnetic conversion characteristics of this base film when used as a magnetic recording medium are, as shown in Table 1, the average particle size of the inorganic fine particles and the average particle size of 1.5 times or more. When the volume fraction and the average particle diameter of 5% (volume%) particles having the largest particle diameter were within the range of the present invention, excellent running properties and electromagnetic conversion characteristics were obtained (Table 1). , Examples 1-4).

However, when the particle size characteristics were out of the range of the present invention, it was not possible to obtain the one having both the traveling property and the electromagnetic conversion property (Table 1, Comparative Examples 1 to 8).

Examples 5 to 10 Magnesium fluoride (MgF ₂ , manufactured by Kanto Kagaku, reagent Extr)
a pure grade) and calcium carbonate (CaCO ₃ ) are mixed and dispersed in ethylene glycol in the form of a slurry, and α, β-bis (2-chlorophenoxy) ethane 4,
Polyethylene containing magnesium fluoride and calcium carbonate having the average particle size and particle size characteristics shown in Table 2 in the amounts shown in Table 2 after transesterification and polycondensation with 4'-dimethyl dicarboxylate. α, β-Bis (2-chlorophenoxy) ethane 4,4′-dicarboxylate was obtained.

The polyester pellets were dried under reduced pressure (3 Torr) at 180 ° C. for 3 hours. The pellets were supplied to an extruder, melt-extruded at 300 ° C., wound around a casting drum having a surface temperature of 30 ° C. by an electrostatic cast method, and cooled and solidified to form an unstretched film having a thickness of about 220 μm. This unstretched film was stretched in the longitudinal direction at 120 ° C.
It was stretched 8 times.

This stretching was performed with a difference in peripheral speed between the two sets of rolls, and the stretching speed was 10,000% / min. This uniaxial film was stretched 4.2 times in the width direction at 120 ° C. at a stretching speed of 2000% / min using a stenter and heat-treated at 210 ° C. for 5 seconds under a constant length to obtain a film having a thickness of 14 μm. The average particle size, particle size characteristics, and content of the inorganic particles in this film were as shown in Table 2.

As shown in Table 2, the runnability and electromagnetic conversion characteristics when these base films were used as magnetic recording media were good.

EFFECTS OF THE INVENTION Since the present invention uses a polyester film having a specific particle size and particle size parameter, a base film having excellent electromagnetic conversion characteristics and running properties when used as a magnetic recording medium can be obtained. is there.

The base film for a magnetic recording medium of the present invention can be used for various magnetic recording medium applications, but it is used for a video tape or a magnetic disk, especially a video tape without a back coat, etc. by utilizing its excellent running property. It is preferably used.

Claims (1)

[Claims] 1. A composition comprising a polyester containing the following structural unit as a main repeating unit and a composition containing 0.03 to 2.0% by weight of inorganic fine particles having an average particle size of 0.03 to 2.5 μm. In the axially oriented film, the inorganic fine particles have a volume fraction of particles having a particle diameter of 1.3 times or more the average particle diameter of 5 to 45% of the whole, and 5% from the larger particle diameter ( The average particle size of the particles of (% by volume) is 1.3 to 10 times the average particle size of all the particles, a base film for a magnetic recording medium. It is at least one kind of dicarboxylic acid residue selected from