JPH0618064B2 - Magnetic recording tape - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic recording tape, and more specifically, the tape may be disturbed due to abrupt changes in environmental conditions, particularly temperature changes, or running failure due to collapse may occur. The present invention relates to a magnetic recording tape.

Prior Art Magnetic recording tapes are used in audio, computers, video, etc. Such a magnetic recording tape is usually
A magnetic layer made of an organic polymer substance containing magnetic powder is formed on one surface of a non-magnetic support typified by a polyester film. This magnetic layer may optionally have
In addition to the magnetic powder, a small amount of an antifriction agent such as alumina, carbon black for imparting a light-shielding property, a lubricant, a dispersant, an antistatic agent, etc. are added. Furthermore, the tape is made to easily run on the other surface of the non-magnetic support, or the running-side non-magnetic support is damaged by running, and the tension of the running tape increases to disturb running. In order to avoid troubles such as the transfer of powder generated by scratches on the non-magnetic support to the magnetic layer or the contamination of the rotating drum, which may cause loss of recording / playback, a back coat is applied as necessary. A layer may be provided in some cases.

A magnetic recording tape is manufactured in the order of several hundreds to ten.
A magnetic layer is coated on one side of a non-magnetic support with a width of about 00 mm, and after drying, it is formed into a tape shape as slits with a width according to each specification. This tape is a cassette for audio and video, for example. Even if you put it in a box, it is usually a pancake that is rolled up as a long tape and then rolled separately into a cassette.

This pancake may be transported because it is located in the in-cassette location or sold in the state of the pancake. Therefore, the quality retention of the pancake is a very important quality point in terms of product yield. Becomes
In other words, changes in temperature and humidity during storage, transportation, etc., especially temperature changes, have a subtle effect on pancakes, causing gaps in some of the pancakes, and in some cases even misalignment. As a result, the form of the pancake may be disturbed, and the workability of the in-cassette may be significantly deteriorated.
Therefore, there is a demand for a material that does not cause these troubles, in other words, a material that is excellent in shape retention.

OBJECT OF THE INVENTION The object of the present invention is to provide an environment in which a pancake of a magnetic recording tape coated with a magnetic layer containing a magnetic powder on one side of a non-magnetic support of a biaxially oriented polyester film undergoes storage and transportation. It is an object of the present invention to provide a magnetic recording tape that maintains good shape retention without being affected by changes, that is, changes in temperature and humidity, particularly changes in temperature.

According to the present invention, there is provided a magnetic recording tape having a magnetic layer formed on one side of a non-magnetic support of a biaxially oriented polyester film, and the residual shrinkage rate of the tape. (3
Residual shrinkage in the longitudinal direction of the tape when the tape was heated from 25 ° C to 40 ° C under a load of 00g / mm ² , kept at 40 ° C for 1 hour, and then allowed to cool to 25 ° C again. )
Is 0.005% or less, the longitudinal stiffness of the tape is 1.5 g / mm ² or more, and the tape pull-out coefficient (F) is the following formula (1) 3F ≦ 15 (1) It is achieved by a magnetic recording tape characterized by satisfying the following.

In the present invention, the magnetic layer may be a coating type or a metal thin film type. The magnetic powder used in the coating type magnetic layer is not particularly limited as long as it has a ferromagnetic property, and for example, γ-Fe ₂ O ₃ , Co-γ-Fe ₂ O ₃ , CrO ₂ , pure iron, Fine particles of iron alloy, barium ferrite, etc. (needle-shaped, disk-shaped fine particles, etc.) are preferable. As the binder, for example, a thermoplastic resin such as a vinyl chloride-vinyl acetate copolymer, a polyurethane resin, a nitrocellulose, a saturated polyester resin, or an epoxy resin, or a crosslinking agent such as a polyisocyanate compound is added to the thermoplastic resin. Preferable examples are thermosetting resins, and further polyfunctional acrylates which are crosslinked by heat, actinic rays and the like. Furthermore, as the lubricant, for example, silicone oil, various fatty acids and fatty acid esters are preferably mentioned, and as the anti-friction agent (abrasive), for example, Al ₂ O ₃ , Cr ₂ O ₃ , SiC, α-iron oxide and the like are used. Preferred examples include: In addition, examples of the dispersant include lecithin and surfactants.

Preferred examples of the metal thin film include those obtained by layering CO, CO—Cr, and other metals by a physical vapor deposition method such as vacuum vapor deposition, sputtering, and ion plating.

In the present invention, the base nonmagnetic support on which the magnetic layer is provided is a biaxially oriented polyester film. This polyester is substantially linear, and is preferably a polyester having an aromatic dicarboxylic acid as a main acid component and an aliphatic glycol as a main glycol component. Examples of the aromatic dicarboxylic acid include terephthalic acid, naphthalenedicarboxylic acid, isophthalic acid, diphenoxyethanedicarboxylic acid, diphenyldicarboxylic acid, diphenylethercarboxylic acid, diphenylsulfonedicarboxylic acid, diphenylketonedicarboxylic acid, anthracenedicarboxylic acid and the like. . Examples of the aliphatic glycol include polymethylene glycol having 2 to 10 carbon atoms such as ethylene glycol, trimethylene glycol, tetramethylene glycol, pentamethylene glycol, hexamethylene glycol and decamethylene glycol, and alicyclic diols such as cyclohexanedimethanol. Etc.

As the polyester, those having alkylene terephthalate and / or alkylene naphthalate as a main constituent component are preferable. Among such polyesters, not only polyethylene terephthalate and polyethylene-2,6-naphthalate but also, for example, 80 mol% or more of the total dicarboxylic acid component is terephthalic acid and / or 2,6-naphthalenedicarboxylic acid, and the total glycol component is A copolymer in which 80 mol% or more is ethylene glycol is particularly preferable. At that time, the other dicarboxylic acid of 20 mol% or less of the total acid component may be the above aromatic dicarboxylic acid,
Further, it can be, for example, an aliphatic carboxylic acid such as adipic acid or sebacic acid; an aliphatic dicarboxylic acid such as cyclohexane-1,4-dicarboxylic acid. 20 mol% or less of the total glycol component may be the above glycol other than ethylene glycol, or an aromatic diol such as hydroquinone, resorcin, 2,2-bis (4-hydroxyphenyl) propane; Aliphatic diols containing aromatics such as 4-dihydroxymethylbenzene; polyalkylene glycols (polyoxyalkylene glycols) such as polyethylene glycol, polypropylene glycol, polytetramethylene glycol
And so on.

In the polyester, for example, an aromatic oxyacid such as hydroxybenzoic acid; a component derived from an oxycarboxylic acid such as an aliphatic oxyacid such as ω-hydroxycaproic acid, a total amount of a dicarboxylic acid component and an oxycarboxylic acid component. In addition, those containing 20 mol% or less are also included. Further, in the polyester, a tricarboxylic or polyfunctional polycarboxylic acid or polyhydroxy compound such as trimellitic acid or pentaerythritol is used in an amount in a substantially linear range, for example, an amount of 2 mol% or less based on all acid components. Polymerized ones are also included.

The polyester is known per se and can be produced by a method known per se.

The polyester has an intrinsic viscosity of about 0.4-measured as a solution in o-chlorophenol at 35 ° C.
A value of about 0.9 is preferred.

Further, the above-mentioned polyester may contain additives such as a stabilizer, a colorant, and an antioxidant, if necessary.

The biaxially oriented polyester film has a center line average roughness (Ra) in the range of 0.008 to 0.060 μm, and a protrusion height (h: μm) measured by a multiple interference reflection microscope (Tl monochromatic light). ) And the number of protrusions (pieces / mm ² ) are 2.0>h> 1.5 5 pieces / mm ² or less 1.5h> 1.0 10 pieces / mm ² or less 1.0h> 0.75 1 to 25 pieces / mm ² 0.75h> 0.530 It is preferable to satisfy the following condition: 100 pieces / mm ² 0.5h> 0.25 80 pieces / mm ² or more. The surface roughness is preferably formed by incorporating inactive inorganic fine particles or organic fine particles into the film. Such inert fine particles have an average particle diameter of 0.01 to 10 μm, and further 0.03.
The content is preferably 0.01 to 5% by weight, more preferably 0.01 to 1.5% by weight. In this case, the inert fine particles may be a single component, or may be two components or more.

The inert fine particles are preferably silicon dioxide (including hydrates, diatomaceous earth, silica sand, quartz, etc.); alumina; silicates containing 30% by weight or more of SiO ₂ (for example, amorphous or Is a crystalline clay mineral, aluminosilicate (including fired products and hydrates), hot asbestos, zircon, fly ash, etc.), Mg, Zn, Zr and Ti oxides; C
a and Ba sulfates; Li, Na and Ca phosphates (1
(Including hydrogen and dihydrogen salts); Li, Na, and K benzoates; Ca, Ba, Zn, and Mn terephthalates; Mg,
Ca, Ba, Zn, Cd, Pb, Sr, Mn, Fe, Co, and Ni titanates; Ba and Pb chromates; Carbon (eg, carbon black, graphite); Glass (eg, glass powder, Glass beads and the like); Ca and Mg carbonates; fluorspar; and ZnS. More preferably, silicic acid anhydride, hydrous silicic acid, aluminum oxide, aluminum silicate (including calcined products and hydrates), 1 lithium phosphate, 3 lithium phosphate, sodium phosphate, barium phosphate,
Titanium oxide, lithium benzoate, double salts of these compounds (including hydrates) glass powder, clay (including kaolin, bentonite, clay etc.), talc, diatomaceous earth, calcium carbonate and the like are exemplified.

The polyester containing these inert fine particles is usually used at any time during the reaction for forming the polyester, for example, during the transesterification reaction or the polycondensation reaction in the case of the transesterification method or at the direct polymerization method. It can be produced by adding inert fine particles (preferably as a slurry of glycol) to the reaction system during the period. It is preferable to add the inert fine particles to the reaction system at the initial stage of the polycondensation reaction, for example, until the intrinsic viscosity reaches about 0.3.

The biaxially oriented polyester film is not particularly limited by its production method, but preferably, polyester containing a predetermined proportion of fine particles is melted, extruded in a sheet form from a slit die, and cooled and solidified by a casting drum. An unstretched sheet is formed, and then the unstretched sheet is biaxially stretched to form a product (film), which is further subjected to heat treatment (heat set), lateral heat shrinkage adjustment treatment, and then longitudinal relaxation treatment. Manufactured by

At that time, in order to preferably satisfy the requirements of the present invention, for example, the stretching temperature is the first stage stretching temperature (for example, the longitudinal stretching temperature:
T ₁ ) in the range of (Tg-10) to (Tg + 45) ° C (however, T 1
g: glass transition temperature of polyester), and the second stage stretching temperature (for example, transverse stretching temperature: T ₂ ) is (T ₁ +15)
To (T ₁ +40) ° C., the stretching ratio is 2.5 to 6.0 in the first stage stretching, particularly 3.5 to 5.5 times, and 2. in the second stage stretching.
It is preferably 5 to 4.0 times, particularly 2.8 to 3.7 times. The biaxially stretched film obtained is preferably 1 to 20 at a temperature in the range of 150 to 245 ° C, more preferably 170 to 240 ° C.
Heat fix for about 0 seconds. Furthermore, it is preferable that the heat treatment conditions in a normal tenter are adjusted to adjust the heat shrinkage ratio in the lateral direction, and then the longitudinal relaxation treatment is performed.

The adjustment of the heat shrinkage ratio in the lateral direction is usually performed before the longitudinal relaxation treatment. It is usually adjusted during heat treatment in a tenter. For example, when the heat shrinkage in the lateral direction is insufficient, the film may be stretched in the width direction during the heat treatment, and when the heat shrinkage is too large, the film may be relaxed in the width direction during the heat treatment. good. More specifically, the heat treatment temperature 16
When the temperature is 0 ° C, it may be relaxed by 9 to 13% with respect to the entire width, and when 170 ° C, it may be relaxed by 5 to 11%.
It is recommended to relax 1-8% at 180 ° C.
When it is ℃, it's good to relax or relax 0-5%,
When the temperature is 205 ° C., it may be extended or relaxed by 3 to −2%, and when the temperature is 220 ° C., it may be extended or relaxed by 1 to −6%.

As a method of relaxing in the longitudinal direction, for example, a method of relaxing in a non-contact state under heating and low tension by a floating treatment method by aerodynamic force; a method of relaxing by giving a speed difference between a heating roll and a cooling roll each having a nip roll. Alternatively, there is a method of relaxing in the longitudinal direction by successively narrowing the traveling speed of the clip holding the film in the tenter, but any method can be used as long as it can relax in the longitudinal direction.

The temperature when relaxing in the longitudinal direction is preferably (Tg + 20) ° C. or higher (heat treatment temperature −30) ° C. or lower, and more preferably (Tg + 30) ° C. or higher (heat treatment temperature −40) ° C. or lower. (Tg +
At a temperature lower than 20) ° C, the heat shrinkage ratio in the vicinity of Tg cannot be sufficiently reduced, and (heat treatment temperature -30) ° C.
At higher temperatures, the amount of relaxation in the vertical direction increases, but the shrinkage in the horizontal direction also increases, which makes it impossible to satisfy the thermal shrinkage ratio in the horizontal direction and also reduces the mechanical properties in the horizontal direction. In the case of a system in which the unevenness is aggravated and the relaxation is performed by the speed difference between the two rolls, scratches are generated laterally on the film surface due to the width contraction on the heating roll, which is not preferable. Relaxation of longitudinal varies depending the heat treatment temperature, but the film tension during relaxation 10 Kg / cm ² or more 80 Kg / cm ² or less, preferably 20 Kg / cm ² or more 60 Kg / cm ²
As will be described below, for example, in the case where the relaxation is performed by the speed difference between the two rolls, it is preferable to adjust the speed of the cooling roll with respect to the heating roll. Film tension is 10 kg
If it is less than / cm ² , the film sags and wrinkles occur, and if the tension is more than 80 kg / cm ^{2, the} heat shrinkage cannot be lowered sufficiently.

By the above-mentioned relaxation treatment, the heat shrinkage ratio in the vertical direction at the temperature of the relaxation treatment or higher does not affect the winding of the coating material. According to the conventional longitudinal relaxation, not only the relaxation in the longitudinal direction but also the contraction rate in the lateral direction occurs, so that the thermal contraction rate in the lateral direction becomes too small. If the heat shrinkage in the transverse direction is too small, wrinkles are generated on the surface of the film roll, or wrinkles are formed during coating of the magnetic paint, which causes coating unevenness, which is not preferable.

The biaxially oriented polyester film thus obtained usually exhibits the same surface characteristics on the front and back surfaces. In this case, the surface on which the magnetic layer is provided may be the front surface or the back surface.

The magnetic recording tape of the present invention comprises a magnetic layer provided on one surface of the above-mentioned non-magnetic support. The tape has a heat shrinkage ratio in the longitudinal direction (300 g / mm ² , preferably 400 g / m 2).
When the tape was heated from 25 ° C to 40 ° C at a heating rate of 2 ° C / min under a load of m ² , held for 1 hour, and then returned to 25 ° C by allowing it to cool, Direction thermal shrinkage)
0.005% or less, preferably 0.003% or less, more preferably
Must be 0.002% or less. As a result, it is possible to prevent the tape pancake from causing troubles such as winding collapse due to changes in temperature and humidity during storage, transportation, etc., and in particular, the tape in cassette can be smoothly performed. , The commercial value of pancakes will be maintained.

The longitudinal direction of the magnetic recording tape refers to the longitudinal direction of the base film, that is, the extrusion direction during film formation.

In order to keep the residual shrinkage in the longitudinal direction of the magnetic recording tape small, it is necessary not only that the residual shrinkage in the longitudinal direction of the base film itself is small, but the property of the magnetic layer, that is, the adhesion to the base film. It is presumed that the degree of expansion and contraction due to temperature, the fluctuation of tension in the working process, etc. also act, and they all act together to determine the residual shrinkage rate of the magnetic recording tape.

The magnetic recording tape has a longitudinal stability of 1.
It should be 5 g / mm ² or more, preferably 2.0 g / mm ² or more, and more preferably 2.5 g / mm ² or more. by this,
The rigidity of the tape is enhanced, and for example, when the web coated with the magnetic layer is slit into the width of the tape and wound into a pancake, the tape can be wound into a good shape. If the stayness is too small, the tape will not be soft enough to cause "fatigue."
Occurs, the running property of the tape becomes unstable, the tape end face is likely to be stretched and bent, and it is difficult to wind it into a pancake with a good shape and a good winding tension for both the inner and outer layers. Of the pancake may lose its shape-retaining property.

For magnetic recording tapes, the tape pull-out coefficient (F) is expressed by the following formula (1) 3F15 (1) Need to be satisfied. Preferably, the above extraction coefficient
(F) satisfies the following equation (2) 4F10 ... (2).

The withdrawal coefficient (F) is slit under a predetermined condition, using a rolled pancake, the core of the pancake is fixed, and the winding end portion of the pancake is hung vertically.
The tape end is fixed to the detection part of the load cell, the load is moved vertically at a constant speed, and the load cell is moved until the tape is no longer pulled out from the pancake. The pull-out force is drawn on the chart, read as the average force (average tension), and calculated from the above definition. When the tape cannot be pulled out of the pancake, the tension indicated by the load cell rises rapidly and abnormally, but this tension is excluded from the reading of the average tension.

When the pull-out coefficient (F) of the tape satisfies the above formula (1), a pancake that is resistant to environmental changes, that is, has good shape retention can be obtained. If this pull-out factor (F) is too small, in other words, if the tape pull-out length is too short, or if the tape pull-out force (average tension) is too large, the pancake roll will be hard and the environmental change (especially temperature change) will ), The pancake morphology is directly affected by the degree of residual shrinkage, and the winding tension is partially concentrated, resulting in poor pancake shape retention. On the other hand, if the pull-out coefficient (F) is too large, the pancake will be softly wound before the expansion and contraction of the tape due to environmental changes (especially temperature changes) and the effects of residual shrinkage will be taken into consideration. As a result, the tape may not be in the desired shape, and the tape may run in an unstable manner, causing rubbing or wrinkling by rubbing against the guides.

The drawing coefficient (F) is greatly influenced by the surface roughness of the base film, especially the surface roughness of the back surface, and in general, this coefficient (F) is small for flat base films, while this coefficient ( F) becomes large. From this point of view, the base film has a surface roughness of the running surface of 0.008 to 0.060 μm in terms of center line average roughness (Ra), or is provided with a back coat layer which imparts slipperiness to the running surface. When the slipperiness equivalent to that is given, there is a feature that running defects due to collapse of winding do not occur, and trouble does not occur during in-cassette, for example. And, it can be advantageously used as a magnetic recording tape for audio, video, computer and the like.

EXAMPLES Hereinafter, the present invention will be further described with reference to examples. Incidentally, various physical properties and characteristics in the present invention are measured and defined as follows.

(1) Film surface roughness (Ra) It was measured according to JIS B 0601. Using a stylus type surface roughness meter (SURFCOM 3B) manufactured by Tokyo Seimitsu Co., Ltd., a chart (film surface roughness curve) was drawn under the conditions of a needle radius of 2 μ and a load of 0.07 g. From the film surface roughness curve, a portion of the measurement length L is extracted in the direction of the center line, the center line of the extracted portion is the X axis, and the vertical magnification direction is the Y axis.
When the roughness curve is represented by Y = f (x), the value (Ra: μm) given by the following equation is defined as the film surface roughness.

In the present invention, 8 pieces were measured with a reference length of 0.25 mm, and Ra was expressed as an average value of 5 pieces excluding 3 pieces having the larger values.

(2) Number of surface protrusions Aluminum is uniformly vacuum-deposited on the surface of the film to a thickness of 400 to 500 Å or less, and a non-deposited surface (film surface) opposite to which is coated with collodion, and dried. Tl monochromatic multiplex interference reflection microscope (eg Carl Zeiss
Using JENA), an arbitrary 100 cm ² of the aluminum vapor deposition surface is observed at 100 times magnification, and the number of protrusions having interference fringes corresponding to the protrusion height of the protrusions in the microscope field is counted.

(3) Stayness Using loop stiffener tester "Type D" manufactured by Toyo Seiki Co., Ltd., loop length 50 mm, crushing amount 10 mm,
It is measured with a load of 10 gr, and the average value of n = 5 is displayed in units of g / mm ² .

(4) Residual shrinkage rate Vacuum Mechanical Engineering Co., Ltd. thermomechanical tester "Type TM-3000"
Both ends of a predetermined test piece are gripped with a chuck by using, and the temperature is raised from 25 ° C. to 40 ° C. at a heating rate of 2 ° C./min under a predetermined load, kept for 1 hour and then allowed to cool to 25 Return to ℃.

The dimensional change before and after the temperature treatment is read from the chart, and the residual shrinkage rate is calculated by the following formula. In addition, it measures about 5 samples and displays as an average value as an absolute value.

However, test piece length (between chucks): 15.0 mm Test piece width: 3.8 mm Load: 400 g / mm ² , 900 g / mm ² .

(5) Average particle size of lubricant particles Shimadzu CP-50 type Centrifuge particle
Size Analyzer (Centrifugal Particle Size An
alyser). From the cumulative curve of the particles of each particle size calculated based on the obtained stretched sedimentation curve and the abundance thereof, the particle size reaching 50 mass percent is read, and this value is taken as the average particle size.

(6) Pancake roll form Place the pancake horizontally on a flat plate that is hard, flat and difficult to transfer heat, and store the pancake in a constant temperature bath that can change the temperature in the range of 40 ° C to -10 ° C. ℃ or -10 ℃
After being kept at room temperature (25 ° C.) for a certain period of time (24 hours), the state in which the shape of the pancake collapses (partially shifts) as the temperature of the pancake changes is visually determined. At that time, the temperature of the pancake is measured at a position about 1 cm away from the surface of the pancake using a non-contact temperature detector (a pyroelectric infrared radiation thermometer “ER 2008” manufactured by Matsushita Electric Co., Ltd.).

The visual judgment criteria are as follows.

◯: No change in pancake morphology was observed in response to temperature changes, and no problems with tape running occurred even after in-cassette at room temperature.

Δ: The shape of the pancake is partially staggered with respect to the temperature change, but when the tape is in-cassetted at room temperature thereafter, almost no trouble in running the tape is felt.

X: The pancake morphology showed a clear step shift with respect to the temperature change, and in-cassette was impossible.

(7) Tape pull-out factor (F) Using a shear type slitter (RT type manufactured by Nishimura Seisakusho Co., Ltd.), tape with 3/20 inch micro slits
Using the apparatus shown in FIG. 1, the pancake (rolling width 5 cm) is rolled up under conditions of a winding speed of 10 m / min and a winding tension of 30 g.

The pancake is made vertical and the hub (core) is fixed, the tape is laid vertically from the outermost layer of the pancake, the tape end is fixed to the load cell, and the load cell is set to 2 mm in the vertical direction.
The tape is pulled out by moving at a speed of / sec. When the tension of the load cell suddenly increases, stop the load cell,
The average tension (g / tape width) is read as the pull-out tension from the chart, and the tape pull-out length is measured on the tape.

Let the average value of the measured values of n = 5 be the tape pull-out coefficient (F).

Example 1 10 parts by weight of calcium carbonate (average particle size: 1.5 μm) was added to 90 parts by weight of ethylene glycol (hereinafter abbreviated as EG), and then mixed and stirred to obtain a slurry.

Next, 100 parts by weight of dimethyl terephthalate and EG70
After transesterification using 0.035 part by weight of manganese acetate tetrahydrate as a catalyst, the calcium carbonate (concentration 0.4% by weight vs. polymer) obtained above was added under stirring. Subsequently, 0.03 part by weight of trimethyl phosphate and 0.03 part by weight of antimony trioxide were added, and then polycondensation reaction was carried out in a usual manner under a high temperature vacuum to obtain a polyethylene terephthalate pellet having an intrinsic viscosity of 0.620.

Furthermore, this polyethylene terephthalate pellet is 170
After drying at ℃ for 3 hours, supply to extruder hopper and melt temperature 2
It is melted at 80-300 ° C, and this molten polymer is molded and extruded through a 1 mm slit die onto a rotary cooling drum with a surface finish of about 0.3 S and a surface temperature of 20 ° C, and a thickness of about 160
An unstretched film of μm was obtained.

The unstretched film thus obtained was preheated to 75 ° C., and then, between the lower speed roll and the higher speed roll, it was placed at 9 mm from above 15 mm.
It is heated by one IR heater having a surface temperature of 00 ° C., stretched 1.6 times by the low and high roll surface speeds, and then rapidly cooled and then heated again to the above temperature condition and stretched 1.5 times, Further, this rapid cooling-heat stretching was repeated (total magnification of re-stretching was 3.6 times) to stretch in the machine direction. This longitudinally stretched film is then stretched 3.9 times in the transverse direction at a temperature of 105 ° C. in hot air, and then heat treated at 230 ° C. for 7 seconds to give 11 μm.
A biaxially oriented film with a thickness of m was obtained. The stretching speed at this time was 20 m / min.

Then, this biaxially oriented film is heated at 120 ° C. with a heating roll.
After the heating, a relaxation treatment was applied between the cooling roll and the cooling roll while applying tension corresponding to shrinkage according to the heat treatment temperature. The characteristics of the obtained film are shown in Table 1.

Further, a coating consisting of 70 wt% γ-Fe ₂ O ₂ and 30 wt% binder was applied to the film thus obtained. This binder is 5 wt% urethane rubber, 3.5 wt%
Nitrocellulose, 1.5wt% vinyl chloride, 90wt%
Of methyl ethyl ketone and an isocyanate compound as a curing agent added to the resin in an amount of 15% by weight.
A 600 mm wide magnetic material coating stock (magnetic layer thickness: 4 μm) was obtained by coating according to a conventional method.

Using a shear slitter, this coating stock was subjected to a 3 / 20-inch micro slit using [Nishimura Seisakusho's RT bridge], and then the winding speed was 10 m / min using the device shown in FIG. It was wound on a pancake (roll width 5 cm) under a tension of 30 g.

The characteristics of the obtained magnetic tape were measured by the following methods, and the results are shown in Table 1.

Audio characteristic measurement method and evaluation Using Tektronix fully automatic test analyzer-AA-501 type, I / O sensitivity and S / N ratio (signal-noise) are measured at frequencies of 315Hz and 10KHz, and our own standard tape. The results were evaluated as follows.

Input / output sensitivity ○… The output sensitivity is not lower than the input sensitivity.

Δ: The output sensitivity is slightly lower than the input sensitivity, but there is no practical problem.

×: Output sensitivity is lower than input sensitivity and cannot be used.

S / N ratio ◯: No problem as it is comparable to the reference tape for comparison.

Δ: Inferior to the comparative reference tape, but practically no problem.

×: It is inferior to the reference tape for comparison and cannot be used.

As is clear from Table 1, in Example-1, both the pancake winding form as the tape quality and the audio characteristics were good.

Examples-2 to -5 Example-1 is different from Example-1, except that the kind, the average particle size and the addition amount of the lubricant added are as shown in Table 1.
Obtain a film by the same method as above, and further magnetically coat it to 3/20
A magnetic tape was obtained by slitting into inches.

The results of various evaluations are shown in Table 1, and the obtained base film has a pancake winding form as a tape quality,
Both audio characteristics were good.

Comparative Example-1 The unstretched film having a thickness of about 160 μm obtained in Example-1 was preheated to 75 ° C., and then one IR heater having a surface temperature of 900 ° C. from 15 mm above between low speed and high speed rolls. Heated, stretched 3.6 times in the machine direction, then in hot air 1
Stretched 3.9 times in the transverse direction at a temperature of 10 ° C, then 230
Heat treatment was performed at 15 ° C. for 15 seconds to obtain a biaxially oriented film having a thickness of 11 μm.

A magnetic coating material was applied to the obtained biaxially oriented film in the same manner as in Example 1 to obtain a 3/20 inch magnetic recording tape.
The results are shown in Table 2.

This magnetic recording tape has a large residual shrinkage rate, the pancake winding form is poor, and therefore it is difficult to pull out the tape, the tape pulling out coefficient (F) is too large, running trouble occurs during in-cassette, and it cannot be used. It was

Comparative Example-2 A magnetic recording tape was prepared in the same manner as in Comparative Example-1, except that the thickness of the biaxially oriented film in Comparative Example-1 was 7.5 μm. The results are shown in Table 2.

The quality of this tape was further lower than that of Comparative Example-1, the pancake winding form was in an even worse state, running trouble occurred during in-cassette, and it was unusable.

Comparative Examples -3 to -5 A magnetic recording tape was prepared in the same manner as in Comparative Example 1 except that the type, the average particle size and the addition amount of the solvent added to the base film were changed as shown in Table 2.

The results are shown in Table 2. In all cases, the residual shrinkage rate was large, the pancake winding form was poor, and the tape pull-out coefficient was too large, causing trouble during running in the in-cassette and unusable. there were. Further, in Comparative Example-4, the surface roughness of the base film was too rough, and the audio characteristics were poor as well as the shape retention of the pancake.

[Brief description of drawings]

FIG. 1 shows a tape flow of an apparatus for making a pancake of a magnetic recording tape to be used for measuring a tape pulling coefficient (F). 1: Tape roll on the feeding side (original pancake) 2: Capstan roll 3: Pinch roll 4, 6: Free roll 5: Dancer roll 7: Tape roll on the winding side (pancake for sample)

Claims (2)

[Claims] 1. A magnetic recording tape comprising a non-magnetic support of a biaxially oriented polyester film having a magnetic layer formed on one side thereof, wherein the tape has a residual shrinkage ratio of 25 (under a load of 300 g / mm ² ). The residual shrinkage in the longitudinal direction of the tape was 0.005% or less when the temperature was raised from 40 ℃ to 40 ℃, kept at 40 ℃ for 1 hour, and then returned to 25 ℃ by cooling. The longitudinal stiffness is 1.5 g / mm ² or more, and the tape pull-out factor (F) is the following formula (1) 3F15 ... (1) A magnetic recording tape characterized by satisfying: 2. The non-magnetic support has a surface roughness in the range of 0.008 μm to 0.060 μm in terms of center line average roughness (Ra), and the number of protrusions measured by a multiple interference reflection microscope (Tl monochromatic light). (Piece / mm ² ) and height of protrusion (h: μm) 2.0>h> 1.5… 5 pieces / mm ² or less 1.5 ≧ h> 1.0… 10 pieces / mm ² or less 1.0 ≧ h> 0.75… 1-25 Magnetic recording according to claim 1, which is a biaxially oriented polyester film satisfying at least 80 pieces / mm ² 0.75 ≧ h> 0.5 ... 30 to 100 pieces / mm ² 0.5 ≧ h> 0.25 ... 80 pieces / mm ^2. tape.