JPH0822931B2 - Film for magnetic recording media - Google Patents

Description

The present invention relates to a film for a magnetic recording medium, and more particularly to a magnetic tape having excellent electromagnetic conversion characteristics, running property and durability and capable of recording for a long time, particularly a VTR. TECHNICAL FIELD The present invention relates to a biaxially oriented film useful for manufacturing a magnetic tape for use.

[Prior Art] Conventionally, as a VTR magnetic tape, a magnetic tape having a biaxially oriented polyethylene terephthalate film as a support and having a magnetic layer mainly composed of a magnetic material and a polymer binder formed on at least one surface thereof has been used. However, this technique has the following drawbacks.

(1) Electromagnetic conversion characteristics are low.

(2) When the tape thickness is made thin, the running property and durability of the tape become poor, so that there is a limit to the thickness, and as a result, there is a limit to the amount of tape that can be wound in a cassette of a predetermined size, and recording takes a long time. Can not.

For these improvements, it is necessary to make the surface of the magnetic tape as flat as possible to improve the contact with the magnetic head. For this purpose, it is effective to flatten the surface of the base film that is the support of the magnetic layer. Is. However, if the base film is excessively flattened, the magnetic tape becomes difficult to run.

As a solution to this problem, a base film has been proposed as a heterogeneous film having a flat surface and a rougher surface, and a method of ensuring running performance on a rougher surface has been proposed.As a typical film, a laminated film by coextrusion is proposed. Is proposed. With this method, the surface roughness of the front and back can be designed almost freely, but it is necessary to prepare several kinds of polymer raw materials and to prepare a die for coextrusion, which causes a problem that film production becomes complicated. . Further, a method has been carried out in which both surfaces have very flat surfaces and a back coat is provided on the surface opposite to the magnetic layer of the tape to improve the running property. Although the back coat makes it possible to improve the slippage, there is a problem that the conventional cassette cannot be used as it is if the tape thickness is to be made as thin as possible to increase the recording capacity. Further, in the case of manufacturing a thin base film having both flat surfaces, there are problems that wrinkles occur when wound in a roll shape and the end surface of the roll tends to have a high edge shape.

In recent years, with the miniaturization of household VTRs, the tape width has become 12.
Although the size has been reduced from 7 mm to 8 mm and the cassette has been downsized, due to the above-mentioned drawbacks, none of the magnetic tapes having a thin tape thickness that can deal with this has been satisfied.

[Object of the Invention] An object of the present invention is to solve the above-mentioned drawbacks, to have good electromagnetic conversion characteristics, and to be useful in the production of a magnetic tape which is excellent in running property and durability of the tape even if it is thin. To provide.

Another object of the present invention is to provide a roll-shaped winding film in which wrinkles and high edges of the film are prevented.

[Structure of the Invention] The present invention comprises polyethylene-2,6-naphthalate containing inert solid fine particles, the film has a Young's modulus in the width direction of 670 Kg / mm ² or more, and a Young's modulus in the length direction of the film is It is larger than the Young's modulus in the width direction by 30 kg / mm ² or more, and the surface roughness (Ra) of one side of the film is 0.002 to 0.010 μm.
And the surface roughness (Ra) of the other surface is 0.007 to 0.030.
The biaxially oriented film for a magnetic recording medium is characterized by having a difference in surface roughness on both sides of 0.005 μm or more.

The polyethylene-2,6-naphthalate in the present invention includes not only homopolymers but also those in which the third component is copolymerized in a small proportion and those in which a small proportion of other polymers are mixed. The intrinsic viscosity number of such polyethylene-2,6-naphthalate is preferably 0.45 to 0.75. Such polyethylene-2,6-naphthalate can be produced by a known method.

The biaxially oriented film in the present invention is made of such polyethylene-2,6-naphthalate, and the width direction Young's modulus of the film is 670 Kg / mm ² or more, preferably 680 Kg / mm ² or more, and the length direction Young's modulus of the film is. The Young's modulus in the width direction is 30 Kg / mm ² or more. The Young's modulus in the length direction is preferably 750 Kg / mm ² or more. Width Young's modulus is 670 Kg / mm ²
When it is smaller than the above range, in the case of a video tape, the contact between the rotary cylinder head and the tape is not sufficient and the electromagnetic conversion characteristics are deteriorated, which is not preferable. The Young's modulus in the longitudinal direction is 700 kg / mm ²
When it gets smaller, it causes trouble in the tape running system,
If it cannot withstand repeated running and the difference from the Young's modulus in the width direction is less than 30 kg / mm ² , the head contact is insufficient and the electromagnetic conversion characteristics are not sufficient, which is not preferable.

Further, this biaxially oriented film has a single layer structure and a surface roughness (Ra) of one surface (I) of 0.002 to 0.010 m.
And the surface roughness (Ra) of the other surface (II) is 0.007.
~ 0.030 μm and the difference in surface roughness on both sides is 0.005 μm
That is all. If the surface roughness (Ra) on the flat side is larger than 0.010 μm, the surface of the magnetic surface cannot maintain the electromagnetic conversion characteristics required for a high-quality magnetic recording tape, which is not preferable. The preferred surface roughness of this surface (I) is 0.007 μm or less and 0.002 μm or more. Further, the surface roughness of the other side (II) of the film needs to be rougher. If this is not the case, the tape will not slide well and the running durability will be insufficient. The surface roughness of this surface (II) is in the range of 0.007 to 0.030 μm, more preferably 0.01
It is in the range of 0 to 0.025 μm.

The surface roughness is basically polyethylene-2,6-
It can be formed by dispersing inert solid fine particles in naphthalate.

The inert solid fine particles are preferably silicon dioxide (including hydrate, diatomaceous earth, silica sand, quartz, etc.); alumina; silicate containing 30% by weight or more of SiO ₂ (for example, amorphous or Are crystalline clay minerals, aluminosilicates (including calcined and hydrated), hot asbestos, zircon, fly ash, etc .; oxides of Mg, Zn, Zr and Ti;
Ca and Ba sulfates; Li, Na and Ca phosphates (including monohydrogen and dihydrogen salts); Li, Na and K benzoates; Ca, Ba, Zn and Mn terephthalates; Mg, Ca, Ba, Z
Titanate of n, Cd, Pb, Sr, Mn, Fe, Co and Ni; Ba and Pb
Chromates; carbon (eg lamp black, thermal black, furnace black, carbon black such as acetylene black, graphite, etc.); glass (eg glass powder, glass beads, etc.); Ca and Mg carbonates: fluorite and ZnS Is exemplified. More preferably, silicic acid anhydride, hydrous silicic acid, aluminum oxide, aluminum silicate (including calcined products and hydrates), phosphoric acid 1
Lithium, trilithium phosphate, sodium phosphate, calcium phosphate, barium sulfate, titanium oxide, lithium benzoate, double salts of these compounds (including hydrates), glass powder, clay (including kaolin, bentonite, clay etc.) ，
Examples are talc, diatomaceous earth, calcium carbonate and the like. Particularly preferred are carbonaceous fine particles, silicon dioxide, titanium oxide, and calcium carbonate. The average particle diameter of these inert solid fine particles is 0.01 to 0.6 μm, and more preferably 0.05 to 0.6 μm.
It is preferably 0.6 μm, particularly 0.08 to 0.4 μm, and the addition amount is 0.01 to 1.5% by weight (relative to polymer), further 0.03 to 1.0% by weight (same), and particularly 0.05 to 1.0% by weight.
(Same), preferably 0.05 to 0.6% by weight (same). These characteristics are due to the flat surface (I) of the biaxially oriented film.
It is preferable to determine the surface roughness (Ra) of the above. The surface roughness (Ra) of the rough surface (II) of the biaxially oriented film can be controlled by a combination of the characteristics of the inert solid fine particles and the stretching treatment conditions described later.

The biaxially oriented film of the present invention can be manufactured, for example, as follows.

Known polyethylene-2,6 having an intrinsic viscosity of 0.45 to 0.65
-Naphthalate is melt extruded at a temperature of about 300 ° C and brought into close contact with a mirror surface drum to obtain a substantially non-oriented film, and then the non-oriented film is formed in a longitudinal direction and then in a transverse direction by a conventionally known method. Stretching is sequentially performed in the transverse direction and the longitudinal direction at a desired magnification. One side of the resulting film is 5 more than the other side.
-30 ° C high temperature, preferably 10-30 ° C high temperature, more preferably
Heat to a high temperature of 20-30 ° C and stretch again in the machine direction. At that time, it is preferable that the high temperature side surface of the film slips on the heating roll to some extent. The surface roughness (Ra) where the high temperature side surface is rough is shown. As a heating method at the time of re-longitudinal stretching,
It is not particularly limited as long as the above-mentioned temperature difference occurs on both sides of the film, and examples thereof include radiant heating, contact heating with liquid and solid, hot air heating and the like. Of these, the contact heating method, particularly the roll heating method, is preferable. Examples of the heating roll used for re-longitudinal stretching include a Teflon coating roll, a ceramic coating roll, and a silicone rubber coating roll. After the completion of the stretching in the longitudinal direction again, the film is stretched in the transverse direction again with a stenter, further heat-fixed, and wound as a film roll. The film is slit into a desired width to form a product roll.
The first stage of longitudinal stretching is at a temperature of 120-135 ° C, stretch ratio 1.8 times or more,
Furthermore, it is preferable to carry out at 1.8 to 2.5 times. In the first stage transverse stretching, the temperature is 135 to 140 ° C, the stretching ratio is 3.5 times or more, and further 3.5 to 4.
It is preferable to carry out 3 times. A heat setting treatment is usually performed after the first-stage transverse stretching, but this treatment is performed at a temperature higher than the transverse stretching temperature and at a temperature at which the film does not whiten. In the second-stage longitudinal stretching (re-longitudinal stretching), the temperature on the surface (I) forming side is 160 to 1
It is preferably carried out at 80 ° C, more preferably 170 to 180 ° C. The re-longitudinal stretching ratio is determined from the viewpoint that the Young's modulus in the longitudinal direction is 700 kg / mm ² or more, but it is preferably at least 2.0 times. The total longitudinal stretching ratio is preferably 4.7 times or more. The second stage transverse stretching (re-transverse stretching) is performed at a temperature of 170 to 210.
It is preferably carried out at a temperature of 180 ° C to 210 ° C. The transverse re-stretching ratio is determined from the viewpoint that the transverse Young's modulus is 670 kg / mm ² or more, but it is preferably at least 1.5 times. The total transverse stretching ratio is preferably 5.1 times or more. The final heat setting treatment is performed at a temperature higher than the transverse re-stretching temperature.

[Examples] The present invention will be further described based on Examples below. Various physical properties and characteristics in the present invention can be measured and defined as follows.

(1) Young's modulus film is cut into a sample width of 10 mm and a length of 15 cm, and the gap between chucks is 1
The Young's modulus is calculated from the tangent line of the rising part of the obtained load-elongation curve by setting it to 00 mm and pulling at a tensile speed of 10 mm / min and a chart speed of 100 mm / min with an Instron type universal tensile tester.

(2) Film surface roughness (Ra) Center line average roughness: Ra (unit: μm) is a value defined by JIS-B0601.

In the present invention, using a stylus type surface roughness meter (SURFCORDER SE-30C) of Kosaka Laboratory Ltd., under the conditions of stylus radius: 2 μm, measurement morning: 0.03 g, cutoff value: 0.25 mm. Draw a film surface roughness curve, extract a portion of the measured length L from the obtained film surface roughness curve in the direction of its center line, use the center line of this extracted portion as the X axis, and set the longitudinal magnification direction to Y.
When the roughness curve is represented by Y = f (x) as an axis, the value (Ra: μm) given by the following equation is defined as the film surface roughness.

Ra = (1 / L) ▲ ∫ ^L ₀ ▼ | f (x) | dx In the present invention, 5 pieces are measured with a reference length of 2.5 mm, and Ra is taken as an average value of 4 pieces by removing one piece from the larger value. Represents

(3) Running performance of magnetic tape The magnetic tape was set on a home video tape recorder (helical scan), and running for 100 hours was repeated while starting and stopping running, and the running state was checked and the output was measured. When all of the following items were satisfied in this run, the runnability was determined to be good, and otherwise the runnability was determined to be poor.

 The end of the tape does not break or wakame.

 No squeaking of the tape while driving.

 The tape does not tear or break.

(4) Electromagnetic conversion characteristics of magnetic tape The video characteristics are the values obtained by measuring the playback output at 4MHz using a VHS method VTR (Product name "HR 7300" manufactured by Victor Company of Japan, Ltd.) in which the recording / playback head was modified to Sendust alloy. Is. The standard tape is a commercially available γ-Fe ₂ O ₃ layer coating type 1 / 2VHS tape.

The C / N ratio is a C / N ratio in which a carrier signal of 4 MHz is recorded and the level of the reproduced amplitude-modulated signal at 30 MHz is used as a noise level.

Example 1 and Comparative Example 1 Pellets of polyethylene-2,6-naphthalate (PEN) having an intrinsic viscosity of 0.65 and containing 0.15% by weight of true spherical silica having an average particle size of 0.27 μm were dried at 180 ° C. for 4 hours. , Supply to the extruder hopper, melt at a melting temperature of 300 ~ 305 ℃,
This molten polymer was molded and extruded on a rotary cooling drum having a surface finish of about 0.3 S and a surface temperature of 70 ° C. through a 0.8 mm opening slit die to obtain an unstretched film having a thickness of 354 μm.

The unstretched film thus obtained was stretched 2.3 times in the machine direction while heating at 125 ° C. by a known roll stretching method, and further 3.7 times in the transverse direction while heating at 135 ° C. by a known stenter method. It was stretched and then heat set at 155 ° C. Subsequently, both sides of the film were heated to 155 ° C with a hard chrome plating roll, and then only one side of the film was heated to 190 ° C with a Teflon coating roll (at this time, the temperature of the other side of the film was 170 ° C). It was stretched 2.6 times in the machine direction. The surface temperature of the film was measured with a radiation thermometer. Subsequently, the re-longitudinal stretched film was stretched 1.65 times in the transverse direction while being heated to 200 ° C. by a stenter method, and then heat fixed at 220 ° C. to obtain a biaxially oriented PEN film having a thickness of 9.7 μm (Examples 1).

For comparison, a PEN film was obtained in the same manner as in Example 1 except that the temperature on both sides of the film was heated to 170 ° C. and stretched when the Teflon coating roll was heated (Comparative Example 1).

The films of Example 1 and Comparative Example 1 were slit by slitters to a width of 500 mm and a length of 2000 m, respectively, and wound into a roll. The film roll of Example 1 had a good winding shape without any high edges or wrinkles. On the other hand, in the film of Comparative Example 1, the edge rose and became a high edge. The film was pulled out from this roll and both ends were observed, but it was in a so-called wakame shape.

On the other hand, α-Fe ₂ O ₃ obtained by thermally decomposing needle-shaped α-FeOOH containing 6% cobalt was hydrogen-reduced to obtain ferromagnetic iron powder having an average needle-shaped length of 0.23 μm.

100 parts by weight of the above ferromagnetic iron powder (hereinafter simply referred to as "part")
The following composition was kneaded and dispersed in a ball mill for 12 hours.

Polyester polyurethane 12 parts Vinyl chloride-vinyl acetate-maleic anhydride copolymer 10 parts α-alumina 5 parts Carbon black 1 part Butyl acetate 70 parts Methyl ethyl ketone 35 parts Cyclohexanone 100 parts Further after dispersion And knead for 15 to 30 minutes. Further, 7 parts of a 25% ethyl acetate solution of a triisocyanate compound was added, and the mixture was subjected to high-speed shear dispersion for 1 hour to prepare a magnetic coating solution.

The obtained coating solution was applied onto the flat surface of the PEN film of Example 1 and Comparative Example 1 so that the dry film thickness was 3.4 μm.

Then, after orientation treatment in a direct current magnetic field, it was dried at 100 ° C. After drying, it was calendered and slit into a 1/2 inch width to obtain a magnetic tape for video having a thickness of 13.7 μm.

The results of evaluating the magnetic tapes thus obtained are shown in Table 1.

The magnetic tape using the film of Example 1 has a reproduction output, C
Both / N were large and the durability was also good. On the other hand, the magnetic tape using the film of Comparative Example 1 was excellent in both reproduction output and C / N, but the edge portion was bent after repeated running five times and the durability was poor. This is because the tape is hard to slip.

The maximum tape length that can be stored in a commercially available VHS video cassette has increased by a factor of 1.5.

Examples 2 to 4 and Comparative Examples 2 and 3 The unstretched film obtained in the same manner as in Example 1 was stretched 2.3 times in the longitudinal direction while heating at 130 ° C. by a known roll stretching method, and further, a known stenter method. Was stretched in the transverse direction by 3.6 times while being heated to 135 ° C. Subsequently, both sides of the film were heated to 155 ° C. with a hard chrome plating roll. Then, only one side of the film was heated to a predetermined temperature shown in Table 2 by a ceramic coating roll by changing the temperature of the roll. At this time, the draw ratio was also changed as shown in Table 2. The surface temperature of the film was measured with a radiation thermometer. This film is further 20 in the stenter (ST)
Stretch up to 1.70 times in the transverse direction while heating to 0 ° C, then
Heat setting was performed at 10 ° C. to obtain a biaxially oriented PEN film having a thickness of 9.7 μm. A magnetic tape was prepared in the same manner as in Example 1 based on these films. The magnetic tape thus obtained was evaluated and the results are shown in Table 2.

The magnetic tapes of Examples 2, 3 and 4 were good in reproduction output, C / N and durability. On the other hand, the Young's modulus of the film of the magnetic tape of Comparative Example 2 was almost the same as that of the Example, but
Since the running surface (the surface opposite to the magnetic layer coated surface) was flat, running durability was poor.

Further, the magnetic tape of Comparative Example 3 was excellent in running durability, but the reproduction output and C / N were insufficient because the surface roughness of the film was rough. This is because the rough surface of the base film was transferred to the flat surface of the magnetic layer.

Example 5 and Comparative Example 4 PEN pellets containing 0.55% by weight of true spherical silica having an average particle diameter of 0.46 μm and an intrinsic viscosity of 0.60 were dried at 170 ° C. for 5 hours and melt-extruded to obtain an unstretched film. . Subsequently, the unstretched film was stretched 2.3 times in the machine direction by heating at 130 ° C. by a roll stretching method, and further 3.7 times in the transverse direction while heating at 135 ° C. by a known tenter method. Continue to 160 ℃ with hard chrome plating roll on both sides of film
Then, the ceramic coating roll was used to heat only one side of the film to a predetermined temperature shown in Table 3 by changing the temperature of the roll. At this time, the draw ratio was also changed as shown in Table 3. This film is further stretched in the transverse direction while being heated to 200 ° C by a stenter (ST),
Then heat set at 220 ° C and perform biaxially oriented PE with a thickness of 9.7 μm.
I got N films. A magnetic tape was prepared in the same manner as in Example 1 based on these films. The results of evaluating the magnetic tapes thus obtained are as shown in Table 3.

The magnetic tape of Example 5 had good reproduction output, C / N, and durability. On the other hand, since the magnetic tape of Comparative Example 4 has a low lateral Young's modulus, when the tape was repeatedly run, wakame-like defects were generated at the edges of the tape.

Example 6 0.4% by weight of carbon black having an average particle size of 0.35 μm was added and PEN was melted by a conventional method, extruded on a cooled mirror surface drum, and cooled to obtain an unstretched film (thickness 425 μm).
I got Subsequently, this unstretched film is heated to 128 ° C by a roll stretching method and stretched 2.2 times in the longitudinal direction, and further stretched 3.6 times in the transverse direction while heating at 135 ° C by a known stenter method, and then heated at 165 ° C. Fixed Subsequently, both sides of the film were heated to 160 ° C with a hard chrome plating roll. Then, only one side of the film was stretched to 2.8 times while heating to 195 ° C. with an infrared heater. In addition, the stenter (S
T) was stretched 1.25 times while heating at 180 ° C, then 1.35 times while heating at 200 ° C, and finally heat fixed at 210 ° C. The thickness of the obtained PEN film was 10.5μ. This film was slit into a width of 300 mm by a slitter to a length of 4000 m and wound into a roll. Wrinkles and high edges of this product did not occur at all. The Young's modulus of the obtained film longitudinal direction 800 Kg / mm ^2, lateral 750 kg / mm ^2, the surface roughness (Ra) flat surface 10 nm, the surface of the opposite was 18 nm.

Using this film as a base, a magnetic layer was applied on a flat surface in the same manner as in Example 1 to prepare a magnetic tape. The thickness of the tape was 14.5μ. The evaluation result of the magnetic tape thus obtained was good. That is, the tape of this example had a reproduction output of +8.0 dB and a C / N of 7.3 dB and was extremely excellent in durability. The maximum tape length that can be stored in the video cassette was increased by 1.5 times.

[Advantages of the Invention] The biaxially oriented film for magnetic recording media of the present invention provides head touch and running durability of the tape even if the thickness thereof is smaller than that of the conventional base film, that is, even if the thickness of the base film of the magnetic tape is reduced. It is excellent and has the characteristics of being able to record for a long time because it has the same characteristics as conventional tapes. Further, it has a feature that it is possible to manufacture a tape having excellent running durability without a back coat. Furthermore, the base film of the present invention has a flat surface on which the magnetic layer is applied, but since the opposite surface is rougher, it has the advantage that wrinkles and high edges do not occur when wound on a slit roll. Have.

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Claims (4)

[Claims] 1. A polyethylene-2,6-naphthalate containing inert solid fine particles, wherein the Young's modulus in the width direction of the film is 670 kg / mm ² or more, and the Young's modulus in the length direction of the film is the Young's modulus in the width direction. 30kg / mm ² or more, and the surface roughness (Ra) of one side of the film is 0.002-0.010μm
And the surface roughness (Ra) of the other surface is 0.007 to 0.030.
A biaxially oriented film for a magnetic recording medium, which is characterized in that the difference in surface roughness between both surfaces is 0.005 μm or more. 2. The average particle size of the inert solid fine particles is 0.01 to 0.60.
The biaxially oriented film according to claim 1, wherein the biaxially oriented film is fine particles having a size of μm. 3. The biaxially oriented film according to claim 1, wherein the inert solid fine particles are carbonaceous fine particles. 4. The biaxially oriented film according to claim 1, 2 or 3, wherein the content of the inert solid fine particles is 0.05 to 1% by weight.