JPH02208323A - Film for magnetic recording medium - Google Patents

Abstract

PURPOSE:To obtain the title film improved in electromagnetic transduction properties, travelling properties and durability and being capable of long-term recording by specifying the Young's modulus of the film in the crosswise direction and its surface roughness. CONSTITUTION:Polyethylene 2,6-naphthalate of an intrinsic viscosity of 0.45-0.65, containing inert solid particles (e.g. SiO2) of a mean particle diameter of 0.01-0.60mum, is melt-extruded at about 300 deg.C, and is adhered to a specular drum to obtain an unoriented film. This film is stretched in the machine direction at 120-135 deg.C in a stretch ratio >=1.8 and then in the crosswise direction at 135-140 deg.C in a stretch ratio >=3.5, and heat-set. After one surface of the obtained film is heated to a temperature higher than the temperature of the surface by 5-30 deg.C and the temperature of the side which forms the face is set at 160-180 deg.C, the film is again stretched in the machine direction in a stretch ratio >=2.0 and then in the crosswise direction at 170-210 deg.C in a stretch ratio >=1.5, and heat-set to obtain a film for a magnetic recording medium having a Young's modulus >=670kg/mm<2> in the machine direction which is higher than that in the crosswise direction by at least 30kg/mm<2>, a surface roughness of one surface of 0.002-0.010mum and a surface roughness of the other surface of 0.007-0.030mum and a difference between these roughnesses >=0.005mum.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a film for magnetic recording media, and more particularly to a film for magnetic recording media that has excellent electromagnetic characteristics, runnability, and durability, and is capable of long-term recording, especially for VTRs. The present invention relates to a biaxially oriented film useful in the production of magnetic tapes.

[Prior Art] Conventionally, magnetic tapes for VTRs have been used in which a biaxially oriented polyethylene terephthalate film is used as a support and a magnetic layer mainly composed of a magnetic material and a polymeric binder is formed on at least one surface of the support. However, this technique had the following drawbacks.

(1) Poor electromagnetic conversion characteristics.

(a) If the tape thickness is made thinner, the running performance and durability of the tape will deteriorate, so there is a limit to the tape thickness.As a result, there is a limit to the amount of tape that can be wrapped around a cassette of a given size, making it impossible to record for a long time. do not have.

These improvements require making the surface of the magnetic tape as flat as possible to improve contact with the magnetic head.
For this purpose, it is effective to flatten the surface of the base film that is the support for the magnetic layer. However, if the base film is too flattened, a problem arises in that it becomes difficult for the magnetic tape to run.

As a solution to this problem, a method has been proposed in which the base film is made of a different surface film with a flat surface and a rougher surface to ensure runnability on the rougher surface, and a typical example of this method is lamination by coextrusion. A film is proposed.

Although this method allows the surface roughness of the front and back surfaces to be designed almost freely, it requires the preparation of multiple types of polymer raw materials and the preparation of dies for coextrusion, making film production complicated. . Another method has been implemented in which running properties are improved by making both surfaces very flat and applying a back coat to the opposite side of the magnetic layer of the tape. A back coat can improve slippage, but if you want to increase the recording capacity by making the tape as thin as possible, there is also the problem that it cannot be inserted into a conventional cassette as is. Furthermore, when producing a thin base film with flat surfaces on both sides, there are problems in that wrinkles occur when the base film is wound into a roll, and the end faces of the roll tend to have high edges.

In addition, in recent years, with the miniaturization of home VTRs, the tape width has increased to 1
2,7 # becomes smaller from 1m to 8mm and has a cassette of 1~
However, due to the above-mentioned drawbacks, there has been no satisfactory magnetic tape with a thin tape thickness that can cope with this trend.

[Object of the Invention] The object of the present invention is to provide a biaxially oriented film which eliminates the above-mentioned drawbacks, has good electromagnetic conversion characteristics, and is useful for manufacturing magnetic tapes which have extremely good tape runnability and durability even when made thin. Our goal is to provide the following.

Another object of the present invention is to provide a rolled film that is free from wrinkles and high edges.

[Structure of the Invention] The present invention provides polyethylene containing inert solid fine particles.
2,6-naphthalate, the Young's modulus in the width direction of the film is 670 Ky/- or more, the Young's modulus in the longitudinal direction of the film is greater than the Young's modulus in the width direction by 30'J/- or more, and one of the films is made of 2,6-naphthalate. The surface roughness (Ra) of the surface is 0
．． 002 to 0.010 μm, the other side has a surface roughness (Ra) of 0.007 to 0.030 μm, and the difference in surface roughness on both sides is 0.005 μm or more. This is a biaxially oriented film for recording media.

Polyethylene-2,6-naphthalene in the present invention includes not only pomopolymers, but also those copolymerized with a small proportion of a third component and those mixed with a small proportion of other polymers. The intrinsic viscosity 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 film has a Young's modulus in the width direction of 670 to 9/mA or more, preferably 680 kg
/rruA or more, and the Young's modulus in the longitudinal direction of the film is greater than the Young's modulus in the width direction by 30.9/mtA or more.

The Young's modulus in the longitudinal direction is preferably 750 Ky/- or more. If the Young's modulus in the width direction is less than 670/9/mA, the contact between the rotating cylinder head and the tape will not be sufficient in the case of a videotape, which is undesirable since the electromagnetic conversion characteristics will deteriorate. Also, if the Young's modulus in the longitudinal direction is less than 700 Ky/mA, trouble will occur in the tape running system and it will not be able to withstand repeated running. is not sufficient, resulting in insufficient electromagnetic conversion characteristics, which is undesirable.

Furthermore, this biaxially oriented film has a single layer structure and has a surface roughness (Ra) of 0.002 to 0.002 on one surface (I).
The surface roughness (Ra) of the other surface (II) is 0.007 to 0.030 μm, and the difference in surface roughness between both surfaces is 0.005 μm or more.

If the surface roughness (Ra) of the flat side is greater than o, oio μm, it is not preferable because the magnetic surface cannot maintain the electromagnetic conversion characteristics necessary for a high-quality magnetic recording tape. The preferred surface roughness of this surface <I> is 0
．． 0.007 μm or less and 0.002 μm or more. Also,
The surface roughness of the other side (n) of the film needs to be rougher. If this is not the case, slippage will be poor when used as a tape, and running durability will not be sufficient. This side (I
The surface roughness of [> is in the range of 0.007 to 0.030 μm,
More preferably, it is in the range of 0.010 to 0.025 μm.

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

The inert solid fine particles are preferably ■Silicon oxide (including hydrates, diatomaceous earth, silica sand diquartz, etc.):■
Alumina: ■ Silicates containing 30% by weight or more of 5iOz (e.g. amorphous or crystalline clay minerals, aluminosilicates (including calcined products and hydrated products), hot asbestos, zircon, fly ash, etc.) ; ■ Oxides of vg, zn, zr and Ti; Sulfates of OCa and Ba; ■ Phosphates of L+, xa and Ca (including monohydrogen salts and dihydrogen salts); ■li
, benzoates of Na and K; OCa, Ba.

Terephthalates of Zn and Mn; 0M (1, Ca.

Ba, Zn, Cd, Pb, Sr, Mn, FeC0 and N
Titanate of i: @Chromate of JBa and Pb: 0 carbon (e.g. carbon black such as lamp black, thermal black, furnace black, acetylene black, graphite, etc.); @Glass (e.g. glass powder, glass peas, etc.) ; OCa and M (+ carbonate: 0 fluorspar and ■ ZnS are exemplified. More preferably, anhydrous silicic acid, hydrated silicic acid, aluminum oxide, aluminum silicate (including calcined products, hydrates, etc.) , monolithium phosphate, monolithium phosphate, sodium phosphate, calcium phosphate, fi
barium, titanium oxide, lithium benzoate, double salts of these compounds (including hydrates), glass powder, clay (including kaolin, bentonite, clay, etc.), talc,
Examples include silica gravel and kerfrusium carbonate. Particularly preferred are carbonaceous fine particles, silicon dioxide, titanium oxide, and calcium carbonate. These inert solid fine particles have an average particle size of 0.
．． 01 to 0.6 μm, more preferably 0.05 to 0.6 μm, especially 0.08 to 0.4 μm, and the amount added is 0.01 to 1.5% by weight (based on the polymer), and 0.03-1.0% by weight (same), especially 0.05-1
．． 0% by weight (same), especially 0.05-0.6% by weight (same)
It is preferable that

These characteristics are preferably determined from the point of defining the surface roughness (Ra) of the flat surface (I) of the biaxially oriented film.

Also, the surface roughness of the rough surface (II) of the biaxially oriented film (
Ra) can be controlled by a combination of the characteristics of the inert solid fine particles and the stretching conditions described below.

The biaxially oriented film in the present invention can be produced, for example, as follows.

A known polyethylene-2,6-naphthalate having an intrinsic viscosity of 0.45 to 0.65 is melt-extruded at a temperature of about 300°C and brought into close contact with a mirror drum to obtain a substantially non-oriented film. The non-oriented film is sequentially stretched in the longitudinal direction and in the transverse direction, or in the transverse direction and in the longitudinal direction, at a desired magnification by a conventionally known method. Next, one side of the obtained film is heated to a temperature higher than the other side by 5 to 30° C., preferably 10 to 30° C., more preferably 20 to 30° C., and stretched again in the longitudinal direction.

At this time, it is preferable that the high temperature side surface of the film slips on the heating roll to some extent. The surface on the high temperature side shows roughness (Ra). The heating method during longitudinal re-stretching is not particularly limited as long as it produces the above-mentioned temperature difference on both sides of the film, such as radiation heating, contact heating with a liquid or solid.

Examples include hot air heating. Among these, the contact heating method, particularly the roll heating method, is preferred. Examples of heating rolls used for longitudinal re-stretching include Teflon coated rolls and ceramic coated rolls.

Examples include silicone rubber sheeting rolls. After this second stretching in the longitudinal direction, the film is stretched in the transverse direction again using a stenter, further heat-set, and wound up as a film roll. This film is slit to a desired width to form a product roll. The first stage longitudinal stretching was performed at a temperature of 120 to 135°C.
It is preferable to carry out the stretching at a stretching ratio of 1.8 times or more, more preferably 1.8 to 2.5 times. The temperature of the first stage lateral stretching is 135-140
'C1 Draw ratio is preferably 3.5 times or more, more preferably 3.5 to 4.3 times. After the first stage of lateral stretching, a heat setting treatment is usually performed, and this treatment is carried out at a temperature higher than the temperature of the lateral stretching and at a temperature that does not whiten the film. In the second stage of longitudinal stretching (re-longitudinal stretching), the temperature of the side where the surface (I> is formed) is set to 160 to 1
The temperature is preferably 80°C, more preferably 170 to 180°C. The longitudinal re-stretching ratio is 7001 (9/-
It is determined based on the above points, but it is preferable to set it to at least 2.0 times. The total longitudinal stretching ratio is preferably 4.7 times or more. In addition, the second stage of transverse stretching (re-transverse stretching) is carried out at a temperature of 170 to 210°C, furthermore 180 to 210°C.
It is preferable to do so. The re-transverse stretching magnification is determined from the point that the transverse Young's modulus is 670/9/mA or more, and is preferably at least 1.5 times. The total lateral stretching ratio is preferably 5.1 times or more. The final heat setting treatment is performed at a higher temperature than the re-transverse stretching temperature.

[Examples] The present invention will be further explained based on Examples below. Note that various physical property values and characteristics in the present invention are measured and defined as follows.

(1) Cut a Young's modulus film into a sample with a length of 15 Gm, and pull it with an Instron type universal tensile tester at a chuck distance of 100 m, a tension speed of 10 mm for 1 minute, and a chart speed of 100 m/min. Obtained load - Calculate Young's modulus from the tangent to the rising part of the elongation curve.

(2) Film surface roughness (Ra) Center line average roughness: Ra (unit: μm) is a value defined by JIS-B 0601.

In the present invention, ■Stylus type surface roughness meter (SUR) of Koita Research Institute
FCORDER5E-30G), stylus radius: 2
μm, measurement phase: 0.03 ej cutoff value:
Draw a film surface roughness curve under the condition of 0.25 mm, extract a part of the measured length from the obtained film surface roughness curve in the direction of its center line, and align the center line of this extracted part with the X axis. If the roughness curve is expressed as Y=f(x) with the vertical magnification direction as the Y axis, then the value (Ra: μm) given by the following equation is defined as the film surface roughness.

Ra - (1/L) f, If (x) ldx In the present invention, the standard length is 2.5#, 5 measurements are taken, and the average value of the 4 measurements, excluding the one with the largest value, is calculated as Ra. represent

(3) Running properties of magnetic tape A magnetic tape was set in a home video tape recorder (helical scan) and run for 100 hours while repeatedly starting and stopping running, and the running condition was examined and the output was measured. During this run, if all of the following items were satisfied, the running performance was determined to be good, and if not, the running performance was determined to be poor.

■ The edges of the tape will not bend or become seaweed-like.

■ No tape squeal occurs while driving.

■ The tape will not tear or break.

(41vA magnetic tape electromagnetic conversion characteristics video characteristics are VH8 type VTR (manufactured by Victor Japan, product name: r
1@R7300j) is the value obtained by measuring the reproduction output at 4MHz. Standard tape is commercially available γ-r
This is a tape for 1/2 Vl-1s with e20 3 layer coating type.

The C/N ratio is the C/N ratio when a 4MH2 carrier signal is recorded and the level at 30M I-I Z of the reproduced amplitude modulation signal is set as the noise level.

Example 1 and Comparative Example 1 0.15% by weight of true spherical silica with an average particle size of 0.27 μm
polyethylene-2 with an intrinsic viscosity of 0.65,
After drying pellets 1 to 6-naphthalate (PEN) at 180°C for 4 hours, they were fed into an extruder hopper and melted at a melting temperature of 300-305°C, and the molten polymer was
Surface finishing 0.3S through Surin 1-shaped die with partial opening degree
The mixture was extruded onto a rotating cooling drum with a surface temperature of 70° C. to obtain an unstretched film having a thickness of 354 μm.

The thus obtained unstretched film was stretched by a known roll stretching method while being heated to 125°C in the longitudinal direction.
Stretched to 135°C by a known stenter method.
Stretched to 3.7 times in the transverse direction while heating, then stretched to 15
Heat-fixed at 5°C. Subsequently, both sides of the film were heated to 155°C with a hard chrome roll, and then only one side of the film was heated to 190°C with a Teflon coated roll. At this time, the density of the square side of the film was 170°C.
'C) and stretched 2.6 times in the longitudinal direction. In addition,
The surface temperature of the film was measured using a radiation thermometer. Subsequently, the re-stretched film was stretched 1.65 times in the transverse direction while heating it to 200'C using a stenter method, and then stretched at 22°C.
A biaxially oriented PEN film having a thickness of 9.7 μm was obtained by heat setting at 0° C. (Example 1).

In addition, 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 during heating of the Teflon coating roll, and the stretching was performed in the same manner as in Example 1 (Comparative Example 1).
).

Example 1. The film of Comparative Example 1 was slit into pieces each having a width of 500# and a length of 2000 m using a slitter, and then wound up into a roll. The film roll of Example 1 had no high edges or wrinkles and had a good rolled appearance. On the other hand, in the film of Comparative Example 1, the edges rose and became high edges. When the film was pulled out from this roll and both ends were observed, it was found to have a so-called seaweed shape.

On the other hand, α-Fe 203 obtained by thermally decomposing acicular αFe0OH containing 6% cobalt was subjected to hydrogen reduction to obtain ferromagnetic iron powder with an average acicular length of 0.23 μm.

100 parts by weight of the above ferromagnetic iron powder (hereinafter simply referred to as 1 part)
The following composition was mixed 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
7 parts methyl ethyl ketone 35 parts cyclohexanone 100 parts After dispersing, 1 part of fatty acid ester (amyl stearate) is further added and kneaded for another 15 to 30 minutes. Furthermore, 7 parts of a 25% ethyl acetate solution of a triincyanate compound was added and dispersed under high-speed shearing for 1 hour to prepare a magnetic coating solution.

The obtained coating liquid was used in Example 1. Each coating was applied onto the flat surface of the PEN film of Comparative Example 1 so that the dry film thickness was 3.4 μm.

Next, after orientation treatment in a DC magnetic field, it was dried at 100°C. After drying, calendering treatment was performed to obtain a video magnetic tape having a thickness of 13.7 .mu.7 nm by sliving it into 1/2 inch width.

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

The magnetic tape using the film of Example 1 had a reproduction output of C
/N were large and the durability was also good. On the other hand, the magnetic tape using the film of Comparative Example 1 has a reproduction output, C/N
Although both were very good, the edges were bent after 5 repeated runs and the durability was poor. This is because the tape is difficult to slip.

Note that the maximum tape length that can be stored in a commercially available VHS video cassette has increased by 1.5 times.

Table 1 Examples 2 to 4 and Comparative Examples 2.3 An unstretched film obtained in the same manner as in Example 1 was stretched in the longitudinal direction by a known roll stretching method while being heated to 130°C.
Stretched 3 times and further by the known stenter method 135
The film was stretched 3.6 times in the transverse direction while heating at .degree. Subsequently, both sides of the film were heated to 155° C. using a hard chrome plated roll. Next, only one side of the film was heated using a ceramic coating roll to a predetermined temperature shown in Table 2 by changing the temperature of the roll. At this time, the stretching ratio was also changed as shown in Table 2. Note that the surface temperature of the film was measured using a radiation thermometer. This film was further heated to 200°C using a stenter (ST) and was heated to 1.7°C in the transverse direction.
The film was stretched to 0 times and then heat-set at 210° C. to obtain a biaxially oriented PEN film with a thickness of 9.7 μm. Using these films as a base, magnetic tapes were prepared in the same manner as in Example 1. The results of evaluating the thus obtained magnetic tape are shown in Table 2.

The magnetic tapes of Examples 2, 3 and 4 are playback outputs.

C/N and durability were all good. On the other hand, comparative example 2
Although the Young's modulus of the film of the magnetic tape was almost the same as that of the example, the running durability was poor because the running surface (the opposite side to which the magnetic layer was applied) was flat.

In addition, although the magnetic tape of Comparative Example 3 had excellent running durability, due to the rough surface of the film, the playback output and C/N
was insufficient. 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 1 having an intrinsic viscosity of 0.60 and containing 0.55% by weight of true spherical silica with an average particle diameter of 0.46 μm
- was dried at 170°C for 5 hours and then melt-extruded to obtain an unstretched film. Subsequently, the unstretched film was stretched 2.3 times in the machine direction while being heated to 130°C using a roll stretching method, and further stretched 3.7 times in the transverse direction while being heated to 135°C using a known tenter method.

Next, roll both sides of the film with a hard chrome roll for 16 minutes.
The film was heated to 0° C., and then only one side of the film was heated to a predetermined temperature shown in Table 3 by changing the temperature of the roll using a ceramic coating roll. At this time, the stretching ratio was also changed as shown in Table 3. This film was further stretched in the transverse direction while being heated to 200°C using a stenter (ST), and then heat-set at 220°C to a thickness of 9.7 μm.
A biaxially oriented PEN film of m was obtained. A magnetic tape was prepared using these films as a base in the same manner as in Example 1. The results of evaluating the thus obtained IC magnetic tape are shown in Table 3.

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

Example 6 0.4% by weight of carbon black with an average particle size of 0.35 μm
PEN is melted by a conventional method, extruded onto a cooled mirror drum, cooled and made into an unstretched film (thickness: 42 mm).
5 μm) is 19. Subsequently, this unstretched film was heated to 128°C by a roll stretching method and stretched 2.2 times in the machine direction, and further stretched 3.6 times in the transverse direction while heated to 135°C by a known stenter method. Then, it was heat-set at 165°C. Subsequently, both sides of the film were heated to 160° C. using a hard chrome plated roll. 2. After that, while heating only one side of the film to 195°C with an infrared heater.
It was stretched up to 8 times. Furthermore, 180 at Stenter (ST)
It was stretched 1.25 times while heating at .degree. C., then 1.35 times while heating at 200.degree. C., and finally heat-set at 210.degree. The thickness of the obtained PEN film was 10.5μ. Cut this film into a slitter with a width of 300 mm and a width of 4,000 mm.
711 and rolled into a roll. No wrinkles or high edges occurred on this product. The Young's modulus of the obtained film was gooKg/mtA in the longitudinal direction and 750KFI/mtR in the lateral direction, and the surface roughness (Ra) was 100 m1 on the flat side and 18 μm on the opposite side.

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 results of the magnetic tape thus obtained were good. In other words, the tape of this embodiment has a playback output of +8. Od3.

The durability was also extremely excellent with a C/N+7.3 clB. Note that the maximum tape length that can be stored in a video cassette was increased by 1.5 times.

[Effects of the Invention] Even if the biaxially oriented film for magnetic recording media of the present invention is made thinner than the conventional base film, that is, even if the thickness of the base film of the magnetic tape is made thinner, the tape hand touch,
It has good running durability and has the same characteristics as conventional tape, so it has the advantage of being able to record for a long time. Another feature is that it is possible to manufacture tapes with excellent running durability even without a back coat.

Furthermore, the base film of the present invention has a flat surface on which the magnetic layer is applied, but the opposite surface is rougher, so wrinkles and high edges do not occur when it is wound onto a slit roll. has.

Claims (1)

[Claims] 1. Polyethylene-2,6 containing inert solid fine particles
- Made of naphthalate, 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 longitudinal direction of the film is 30 kg/mm^2 higher than the Young's modulus in the width direction.
The surface roughness (Ra) of one side of the film is 0.002 to 0.010 μm, the surface roughness (Ra) of the other side is 0.007 to 0.030 μm, and A biaxially oriented film for a magnetic recording medium, characterized in that the difference in surface roughness is 0.005 μm or more. 2. The average particle size of the inert solid particles is 0.01 to 0.60.
The biaxially oriented film according to claim 1, wherein the biaxially oriented film is microparticles having a diameter of .mu.m. 3. The biaxially oriented film according to claim 1 or 2, 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 inert solid fine particles is 0.05 to 1% by weight.