JPH0685208B2 - Magnetic recording medium - Google Patents

Description

Description: FIELD OF THE INVENTION The present invention relates to a magnetic recording medium, more specifically, a biaxially stretched laminated polyester film having different surface characteristics as a support, and a flat surface formed from an electron beam curable paint. And a magnetic recording medium useful for video tapes, audio tapes, and the like.

2. Description of the Related Art As magnetic recording media based on polyester film, for example, video tapes, audio tapes, computer tapes, floppy discs, etc. are known and widely used.

In recent years, demands for high-density recording and high quality have been increasing in these fields of application, and along with this, the base polyester film has a flat surface and excellent slipperiness.
In addition, the demand for excellent durability and wear resistance is becoming stronger.

Conventionally, a method of adding inorganic particles such as silicon oxide and calcium carbonate to polyester as a method of improving slipperiness, or a method of precipitating fine particles containing calcium, lithium or phosphorus in a polymerization system during synthesis of polyester has been proposed. ing. In either method, when the polyester is formed into a film, protrusions are formed on the film surface due to the fine particles to improve the slipperiness of the film.

However, in the method of improving the slipperiness of the film by the projections by the fine particles as described above, the slipperiness is usually improved as the film surface is roughened, but on the other hand, the magnetic coating is changed due to the roughening. The surface after coating tends to be rough and electromagnetic conversion characteristics tend to deteriorate.

As a measure for solving these contradictory flatness and slipperiness, means for utilizing a composite particle in which a large particle size and a small particle size are combined has been proposed. Since both sides of the film have the same surface property, there is a limit and it is not at a satisfactory level.

Therefore, there have been proposed some front and back different-sided films in which one exposed surface has excellent slipperiness and the other exposed surface is flat, and a laminated film is also used as this means. There is.

However, even if the film surface on which the magnetic coating is applied to the flat and easy-sliding film using this means is flat, if the opposite surface is too rough, the applied magnetic layer surface The unevenness of the rough surface of the film is transferred to the back side,
Unevenness is generated on the surface of the magnetic layer, resulting in loss of flatness.
The electromagnetic conversion characteristics become insufficient.

The mechanism by which the surface roughness of the base film affects the surface roughness of the magnetic layer is that so-called show-through occurs when the coating material is wound up after application and held at a curing temperature of 25 to 80 ° C for 10 to 72 hours. It is believed that the surface roughness is transferred. In order to reduce this show-through development, the video tape with the surface roughness of the base film made as small as possible is
The friction coefficient becomes large, and the running performance becomes extremely poor. Therefore, a back coat layer containing carbon black or calcium carbonate is provided on the base film opposite to the magnetic layer to improve the running property. However, the surface roughness of the back coat layer is also transferred by set-off, and the electromagnetic conversion characteristics are deteriorated as compared with those without the back coat layer.

OBJECT OF THE INVENTION It is an object of the present invention to provide a magnetic recording medium which improves the above-mentioned problems and improves running properties and durability without impairing electromagnetic conversion characteristics.

Constitution / Effect of the Invention The object of the present invention is a biaxially stretched laminated film comprising a film-forming aromatic polyester containing an aromatic dicarboxylic acid as a main acid component and an aliphatic glycol as a main glycol component. Roughness on one exposed surface (A side)
RaA is 0.025 μm or less and 0.010 μm or more, and the number of protrusions is 20 /
The distribution curve showing the relationship between the number of protrusions (y: ke / mm ² ) and the height of protrusions (x: μm) determined in the area of mm ² or more is expressed by the formula (1) log ₁₀ y ＝ －9.8x ＋ 4.4. The curve represented by the formula (2) log ₁₀ y has a projection distribution that does not intersect with the straight line represented by (1) in the range of 2> log ₁₀ y> 1.3, and is larger than the maximum value of the projection distribution curve. ≧ −18x + 3.7 (2) and a projection height (x) of 0.87 μm or more gives a slippery surface substantially free of the other surface of the laminated film. (B side) surface roughness RaB is 0.010μ
In the distribution curve showing the relationship between the number of protrusions (y: number of protrusions / mm ² ) and the height of protrusions (x: μm), which is less than m and the number of protrusions is 20 / mm ² or more, the protrusion distribution The part of the curve that is larger than the maximum value intersects with the formula (3) log ₁₀ y = -18x + 3.7 (3), and the protrusion height (x) is substantially not more than 0.13 μm. Giving a flat surface, the laminated film is 70 ℃
The heat shrinkage in the longitudinal direction when heat-treated for 1 hour under no load was 0.1% or less, and an electron beam-curable magnetic coating was applied on the B side of the laminated film to form a magnetic layer. Is achieved by a magnetic recording medium.

The biaxially stretched laminated polyester film used as the base film in the present invention is a laminated film having a layer providing a slippery surface and a layer providing a flat surface.

The layer providing the easy-sliding surface (A-side) has a surface roughness RaA of 0.025 μm or less and 0.010 μm or more as film surface characteristics, and does not substantially include protrusions having a protrusion height (x) of 0.87 μm or more. , And the distribution curve showing the relationship between the number of protrusions (y: number / mm ² ) and the height of protrusions (x: μm) determined in the area where the number of protrusions is 20 / mm ² or more is as shown in the following formula (1) log ₁₀ y = −9.8x + 4.4 (1) The straight line represented by 2> log ₁₀ y> 1.3 has a protrusion distribution that does not intersect in the range, and the curve of the portion larger than the maximum value of the protrusion distribution curve is as follows. Equation (2) log ₁₀ y ≥ -18x + 3.7 (2) The characteristic is in the range. This surface roughness RaA is 0.0
When it is larger than 25 μm, the surface of the base film is too rough, and even if the magnetic surface is mirror-finished in the coating process of the magnetic powder, the magnetic surface is not sufficiently flattened, so that the electromagnetic conversion characteristics are deteriorated, which is preferable. Absent. Further, if RaA is smaller than 0.010 μm, the running property is deteriorated, which is not preferable. The preferable surface roughness RaA is 0.020 μm or less and 0.0125 μm or more.

Furthermore, the distribution curve showing the relationship between the number of protrusions (y) and the height (x) of the protrusions obtained in the region where the number of protrusions is 20 / mm ² or more is a straight line represented by the above formula (1) and a 2> If it intersects in the range of log ₁₀ y> 1.3, the flatness of the magnetic surface will be impaired and the electromagnetic conversion characteristics will be deteriorated, which is not preferable, and projections may be scraped off during the tape processing process, especially the calendar process, and the tape may be used repeatedly At times, abrasion is not preferable because the friction coefficient rises and the abrasion powder adheres to the tape surface to increase dropout. Furthermore, if the curve of the portion larger than the maximum value of the above distribution curve is not within the range of the above formula (2), the film surface becomes too flat, and the friction coefficient (μk) after repeating 200 times is 0.1.
It is difficult to satisfy the range of 5 to 0.35, which is not preferable. In the above distribution curve, the curve on the side exceeding the maximum value preferably satisfies the range of −18x + 3.7 ≦ log ₁₀ y ≦ −9.8x + 4.4 (however, log ₁₀ y> 1.3). Furthermore, if the film surface has protrusions of 0.87 μm or more, the running property of the tape is improved, but this is not preferable because it causes scraping of the protrusions in the processing step and causes the dropout.

Furthermore, the layer that provides a flat surface (B surface) in the laminated polyester film of the present invention has film surface characteristics having a surface roughness RaB of less than 0.010 μm and a protrusion having a protrusion height (x) of 0.13 μm or more. No, and the number of protrusions is 20
In the distribution curve showing the relationship between the number of projections (y: ke / mm ² ) and the height of projections (x: μm) obtained in the area of at least ² mm / mm ² , the curve of the portion larger than the maximum value of the projection distribution curve is Equation (3) log ₁₀ y = -18x + 3.7 (3) It has a characteristic that intersects with (3). This surface roughness RaB is 0.010
If it is larger than 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. Further, in the distribution curve showing the relationship between the number of protrusions (y) and the height (x) of the protrusions obtained in the region where the number of protrusions is 20 / mm ² or more, the curve of the portion larger than the maximum value of the protrusion distribution curve is If it does not intersect with the above formula (3) or if there are protrusions with a protrusion height of 0.13 μm or more, the magnetic surface will not be flattened due to the film surface being too rough, and the electromagnetic conversion characteristics will deteriorate, resulting in a high-quality product. It is not preferable because the characteristics required for the magnetic recording tape of 1 cannot be maintained.

Further, the biaxially stretched laminated polyester film has the above-mentioned film surface characteristics and has a heat shrinkage ratio of 0.1% in the machine direction when heat-treated at 70 ° C. for 1 hour under no load.
It must have the following characteristics: Heat shrinkage rate is 0.1%
If it exceeds the range, the heat shrinkage rate after forming the magnetic tape is high, and the skew characteristic is deteriorated, which is not preferable. Especially when the electron beam curable magnetic coating material of the present invention is applied, since the curing treatment is not performed for a long time after application, the heat shrinkage of the base film directly affects the heat shrinkage of the magnetic tape. When the value is high, the skiing characteristics are deteriorated.

Further, in the present invention, an electron beam curable magnetic coating material is applied on the flat surface (B surface) of the above-mentioned base film to form a magnetic layer. Due to the formation of this magnetic layer, even if the surface roughness of the opposite surface (A surface) of the base film is large, the surface property of the magnetic layer does not deteriorate due to show-through, and the electromagnetic conversion characteristics are good without providing the back coat layer. Moreover, it is possible to obtain a magnetic recording medium having good running properties.

As the electron beam curable self-painting paint, those used in this field can be used, and a magnetic powder and an electron beam curable binder are used as basic components, and if desired, a lubricant, a dispersion aid,
Other components such as abrasives and antistatic agents are included.

As the magnetic powder, for example, ferromagnetic γ-Fe ₂ O ₃ , Co-containing γ-
Fe ₂ O _3, metallic iron, Fe-Co, Fe-Ni , Fe-Co-Ni, Fe-Co-B, Fe
Powders such as -Co-Cr-B can be mentioned.

The binder is not particularly limited as long as it is a compound having an electron beam curable unsaturated double bond. For example, a compound or a prepolymer having a functional group such as an acryloyl group, an acrylamide group, an allyl group or a vinylthioether group ( For example, unsaturated polyester) is preferable.

Examples of the dispersion aid include lecithin or oleic acid,
Higher fatty acids such as palmitic acid are preferred.

Examples of the abrasive include α-alumina, α-Fe ₂ O ₃ , chromium oxide and the like. As the antistatic agent, for example, Ketchin Black EC, Black Pearl L and the like can be mentioned.

Various kneaders can be used for kneading and dispersing the magnetic paint. For example, three roll mill, attritor, high speed stone mill, ball mill, agitator mill, pebble mill,
A sand grinder, a high-speed mixer, a homomix line flow, a homogenizer, a high-frequency wave disperser, a high-speed impeller disperser, a disper, a pressure kneader, etc. may be used alone or in combination.

The aromatic polyester in the present invention is a polyester having an aromatic dicarboxylic acid as a main acid component and an aliphatic glycol as a main glycol component. Such polyesters are substantially linear and have film forming properties, especially film formation by melt molding. Examples of the aromatic dicarboxylic acid include terephthalic acid, naphthalene dicarboxylic acid, isophthalic acid, diphenoxyethane dicarboxylic acid, diphenyl carboxylic acid, diphenyl ether dicarboxylic acid, diphenyl sulfone dicarboxylic acid, diphenyl ketone dicarboxylic acid, anthracene. A dicarboxylic acid etc. can be mentioned. Examples of the aliphatic glycol include ethylene glycol, trimethylene glycol, tetramethylene glycol, pentamethylene glycol,
Examples thereof include polymethylene glycol having 2 to 10 carbon atoms such as hexamethylene glycol and decamethylene glycol, and alicyclic diols such as cyclohexanedimethanol.

In the present invention, as the aromatic polyester, one having alkylene terephthalate and / or alkylene naphthalate as a main constituent is preferably used.

Among such polyesters, for example, polyethylene terephthalate and polyethylene naphthalate are of course used. For example, 80 mol% or more of all dicarboxylic acid components are terephthalic acid and / or naphthalene dicarboxylic acid, and 80 mol% or more of all glycol components are ethylene glycol. Are particularly preferred. In that case, less than 20 mol% of dicarboxylic acid in total acid formation can be the above-mentioned aromatic dicarboxylic acids, and aliphatic dicarboxylic acids such as adipic acid and sebacic acid; and fats such as cyclohexane-1,4-dicarboxylic acid. It can be a cyclic dicarboxylic acid or the like. Also, up to 20 mol% of the total glycol component can be the above glycols other than ethylene glycol, or, for example, hydroquinone, resorcinol, 2,2-bis (4
-Aromatic diol such as hydroxyphenyl) propane; Aliphatic diol containing aromatic such as 1,4-dihydroxymethylbenzene; Polyalkylene glycol (polyoxyalkylene glycol) such as polyethylene glycol, polypropylene glycol, polytetramethylene glycol And so on.

In the aromatic polyester used in the present invention, a component derived from an oxycarboxylic acid such as an aromatic oxyacid such as hydroxybenzoic acid; an aliphatic oxyacid such as ω-hydroxycaproic acid, a dicarboxylic acid component and a Those containing 20 mol% or less based on the total amount of the oxycarboxylic acid component are also included. Further, in the aromatic polyester in the present invention, a tricarboxylic or polyfunctional polycarboxylic acid or polyhydroxy compound such as trimellitic acid, in an amount in a range substantially linear, for example, an amount of 2 mol% or less based on the total acid component, The thing which copolymerized the ventaerythritol is also included.

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

The aromatic polyester has an intrinsic viscosity of about 0 measured at 35 ° C as a solution in o-chlorophenol.
Those of 4 to about 0.9 are preferred.

In the present invention, the polyester film layer forming one surface (A surface: easy sliding surface) exposed contains inorganic fine particles such as calcium carbonate, silicon oxide, kaolin, titanium oxide or phosphorus as inert particles. Those containing fine particles are included.

The other surface exposed in the present invention (B surface: flat surface)
It is preferable that the polyester film layer forming the film contains inorganic fine particles such as silicon oxide and titanium oxide to the extent that flatness is not impaired, but the inorganic fine particles may not be included.

The thickness constitution of the laminated film in the present invention is not particularly limited, but the easily slippery surface (A side) has a layer thickness of 2 μm after biaxial stretching in order to maximize the effect of the contained inert particles. It is preferably at least 3 μm, more preferably at least 4 μm. If the thickness of the easy-slip layer is too thin, protrusions, particularly protrusions due to fine particles, are less likely to appear, resulting in poor running properties and scratch resistance. Further, in order to maintain the flatness of the layer providing the flat surface (B surface), the layer thickness after biaxial stretching is preferably 3 μm or more, more preferably 4 μm or more, and particularly 5 μm or more. Is preferred. If the thickness of the flat layer is too thin, the flatness is impaired due to the influence of the inert particles in the easy-slip layer, which is not preferable.

The laminated film of the present invention is a film having a multi-layer structure of two or more layers, but a two-layer structure is particularly preferable. In the case of a laminated film having three or more layers, the outermost layer is the above-mentioned surface A, B.
In the case of the polyester film layer (1), the intermediate layer may be any polymer layer.

The laminated film of the present invention can be manufactured by a conventionally accumulated method for manufacturing a laminated film. For example, the polyester layer forming the surface A and the polyester layer forming the surface B can be laminated in a melted state or a cooled and solidified state. More specifically, for example, coextrusion /
It can be manufactured by a method such as extrusion coating. The film laminated by the above-mentioned method is sequentially biaxially stretched or simultaneously biaxially stretched by a method according to the conventional accumulated biaxially stretched film production method, and further heat treated. At that time, the film surface characteristics are changed depending on the shape, particle size, amount and the like of the inert particles, and also depending on the stretching conditions, and therefore are appropriately selected from the conventional stretching conditions.

For example, the stretching temperature is such that the first stage stretching temperature (for example, the longitudinal stretching temperature: T ₁ ) is in the range of (Tg-10) to (Tg + 45) ° C (however, T
g is the glass transition temperature of the polyester) and the second stretching temperature (for example, the transverse stretching temperature: T ₂ ) is (T ₁ +15) to (T ₁
It is recommended to select from the range of +40) ℃. The stretching ratio may be selected from a range in which the stretching ratio in the uniaxial direction is 2.5 or more, particularly 3 or more, and the area ratio is 8 or more, particularly 10 or more.

Furthermore, the heat setting temperature is 180-250 ℃, 200-230 ℃
It is good to select from the range. The longitudinal stretching temperature is (Tg + 25) ° C or higher, the longitudinal stretching speed is 1500% / sec or less,
It is preferably 900% / second or less.

The magnetic recording medium according to the present invention has excellent characteristics, especially for high-grade magnetic tapes, without using a back coat layer.

EXAMPLES Hereinafter, the present invention will be further described with reference to examples.

Various physical properties and characteristics in the present invention are measured and defined as follows.

(1) Average particle size of inert solid particles Shimadzu CP-50 Centrifuyugur Particle
Size Analyzer (Centrifugal Particle Size An
alyser). From the cumulative curve of each particle size calculated based on the obtained centrifugal sedimentation curve and its abundance, the particle size corresponding to 50 mass percent was read, and this value was taken as the average particle size. (See "Particle size measurement technology" published by Nikkan Kogyo Shimbun, 1975, pp. 242-247).

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

In the present invention, 8 pieces are measured with a reference length of 0.25 mm, and 3 pieces are removed from the one with the larger value (3) Protrusion distribution measuring method Using a three-dimensional roughness meter (SE-3OK) of Kosaka Laboratory Needle diameter 2 μm
R, needle pressure 30 mg, measurement length 1 mm sampling pitch 2 μm, cutoff 0.25 mm, vertical magnification 20,000 times, horizontal magnification 200
Under the condition that the number of scans is 150 and the number of scans is 150, the profile of protrusions on the film surface is imaged three-dimensionally (three-dimensionally).

When the profile is cut in a plane perpendicular to the film thickness direction, the plane where the total cross-sectional area of the profile of each projection is 70% of the area of the film measurement area is the reference level (0 level). ), And y is the number of projections cut when cut on a plane parallel to the plane of the reference level and separated by a distance x in the height direction of the projections. By sequentially increasing or decreasing x, reading the number of y at that time, and plotting it on a graph, a projection distribution curve is drawn.

(4) Frictional coefficient of film (μk) It was measured as follows using the apparatus shown in FIG. In Fig. 2, 1 is an unwind reel, 2 is a tension controller, 3, 5, 6, 8, 9, and 11 are free rollers, 4 is a tension detector (inlet), 7 is a stainless steel SUS 304 fixed A bar (outer diameter 5 mmφ), 10 is a tension detector (outlet), 12 is a guide roller, and 13 is a take-up reel.

The film cut into 1/2 inch width in an environment of temperature 20 ° C and humidity 60% is fixed to 7 fixed rods (surface roughness 0.3 μm). Contact at (152 °) and move at a speed of 200 cm per minute (friction)
Let When the tension controller 2 is adjusted so that the entrance tension T ₁ is 35g, the exit tension (Ti
After the film has run 90 m, it is detected by the exit tension detector and the running friction coefficient μk is calculated by the following formula.

(5) Electromagnetic conversion characteristics of magnetic coating tape Using a commercial VTR for home use, 50% white level signal (100% white level signal is peak; two; peak voltage is 0.714 volt) and 100% chroma level signal The weighted signal is recorded, and the reproduced signal is recorded by a shibasoku noise meter: Type 92
5 R is used for measurement. The definition of chroma S / N is as follows according to the definition of Shibasoku.

Here, ES (p-p) is the peak-to-peak voltage difference (p-p) of the reproduced signal of the white level signal.

ES (p-p) = 0.714V (p-p) EN (rms) is the square root value of the peak voltage of the reproduction signal of the chroma level signal.

(6) Dropout A magnetic coating tape (1/2 inch width) was counted with a commercially available dropout counter (for example, Shibasoku VH01BZ type) for 5 μsec × 10 dB, and the number of counts per minute was calculated.

(7) Scratch judgment Magnetic coating tape (1/2 inch width) above (4)
20cm / se by using the friction coefficient measuring device of No. 1 so that the base film surface of the tape contacts the fixed rod at an angle of 152 °.
The thickness of the scratch on the surface of the 1/2 inch width base film after running 10 m at c speed and repeating this 50 times,
The following five levels of judgment were made by integrating the depth and number.

<5-level judgment> ◎ No scratches are found on the 1/2 inch width base film.

○ There is almost no scratch on the 1/2 inch width base film.

△ Scratches are found on the 1/2 inch width base film. (Several) X-inch width base film has a large number of thick scratches X X 1 / 2-inch width base film has a large number of thick and deep scratches (8) Squeeze After heat-treating the videotape recorded at 20 ° C under normal humidity for 1 hour at 70 ° C, play it again under normal temperature and normal humidity, and read the shift amount at the head switching point.

Example 1 [Method for producing polymer for film] 100 parts by weight of dimethyl terephthalate and 70 parts by weight of ethylene glycol were used, and 0.015 was added to dimethyl terephthalate.
Mol% manganese acetate and 0.010 mol% sodium acetate were added, and transesterification was performed at 150 to 250 ° C while distilling methanol. At that time, an ethylene glycol slurry (concentration: 10%) of calcium carbonate particles, which had been adjusted in advance, was added.

After completion of the transesterification reaction, 0.015 mol% of trimethyl phosphate heated and refluxed in the presence of ethylene glycol was added to dimethyl terephthalate. Furthermore, antimony trioxide was added to dimethyl terephthalate in an amount of 0.030 mol%
After the addition, the polycondensation reaction was performed under a high vacuum of 1 Torr or less.
After completion of the polycondensation reaction, the polymer was cooled with water and cut to obtain polyethylene terephthalate pellets containing calcium carbonate particles dispersed therein (hereinafter referred to as polyester I).

The transesterification reaction and polycondensation reaction are carried out in the same manner as above except that the ethylene glycol slurry of titanium dioxide particles prepared in advance is added instead of the ethylene glycol slurry of calcium carbonate particles to disperse the titanium dioxide particles. A polyethylene terephthalate pellet was obtained [hereinafter referred to as polyester II].

Next, in the production method of polyester I, a transesterification reaction and a polycondensation reaction were performed without adding inert particles to obtain polyethylene terephthalate pellets to which external inert particles were not added [hereinafter referred to as polyester III].

[Film formation]

Polyester I, Polyester II, and Polyester III
Are mixed so that the content of calcium carbonate particles is 0.30% by weight and the content of titanium dioxide particles is 0.15% by weight to obtain a blend A, and polyester II and polyester III are mixed in a content of 0.25% by weight of titanium dioxide particles. To obtain a blend B. Then, the blended product B is further blended so that the blended product A is a layer forming the A side.
Is supplied to separate extruders of the film forming machine so that the layer B forms the B side, and the polyester layer forming the A side extrudes from the die so that the thickness of the polyester layer occupies 60% of the laminated film thickness. An unstretched film of 200 μm was obtained.

This unstretched film is stretched at a longitudinal stretching temperature of 115 ° C and a longitudinal stretching ratio of 3.7.
2 times, a transverse stretching temperature of 120 ° C., a transverse stretching ratio of 3.8 times, sequential biaxial stretching was performed, and heat treatment was performed at 225 ° C. Further, this heat-treated biaxially oriented polyester film was heated at a temperature of 120 ° C. and a tension of 30 kg /
The longitudinal relaxation treatment was performed under the condition of cm ² (film cross-sectional area).
The film thickness obtained was 14 μm.

The characteristics of the laminated polyester film thus obtained are shown in Table-1, and the distribution of the irregularities on the film surface is shown as curve A in Fig. 1.

The symbol A means the A-side and the symbol B means the B-side.

On the other hand, the following composition: ferromagnetic Co deposited γ-Fo ₂ O ₃ 100 parts by weight Oleic acid 1 part by weight Nitrocellulose 5 parts by weight Polyurethane resin having acrylic group in the molecule 20 parts by weight Carbon black 3 parts by weight Stearic acid 1 part by weight α-alumina 5 parts by weight EK-toluene-cyclohexane 250 parts by weight Pressurized kneader Using an agitator mill and kneading and dispersing for 3 hours, a magnetic coating material was prepared.

The obtained magnetic coating material was passed through a filter having an average pore size of 1 μm.

This magnetic paint was applied on the B side of the film by a reverse roll coater, then oriented, dried, mirror-finished and irradiated with an electron beam of 4 Mrad under a nitrogen stream to cure it. Magnetic layer thickness 5
A magnetic tape of μm was obtained.

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

This tape had improved electromagnetic conversion characteristics as compared with the standard tape, and was good in running property and scratch resistance without providing a back coat.

Example 2 A biaxially stretched laminated film was produced in the same manner as in Example 1 except that the composition of the blend A was changed, and a magnetic tape was obtained in the same manner. The results are shown in Table-1 and Figure-1.

Similar to Example 1, this magnetic tape also had good electromagnetic conversion characteristics and running properties.

Comparative Examples 1 to 3 Magnetic tapes were obtained in the same manner as in Example 1 except that the composition of the blend A or B was changed. The results are shown in Table-1 and Figure-1.

In FIG. 1, curve C shows the thing of Comparative Example 1, curve D shows that of Comparative Example 2, and curve E shows that of Comparative Example 3. Further, the symbol A means the characteristic of the A surface, and the symbol B means the characteristic of the B surface.

The average particle diameter of the added particles of Comparative Example 1 was 1.1μ.
In the case of calcium carbonate of m, the runnability was good, but there were high protrusions, poor electromagnetic conversion characteristics, poor calendering, and many dropouts, making it unusable.

Further, when the easy-sliding surface (A surface) in Comparative Example 2 is too flat, the friction coefficient (μk) after repeating 200 times becomes high,
It had poor runnability and poor scratch resistance, and could not be used.

Further, when the flat surface (B surface) in Comparative Example 3 was too rough, the electromagnetic conversion characteristics were insufficient.

Comparative Example 4 A magnetic tape was obtained in the same manner as in Example 1 except that the longitudinal relaxation treatment of the biaxially stretched film was not performed. The results are shown in Table-1. This magnetic tape had a large skew value and could not be used.

Comparative Example 5 100 parts by weight of iron oxide powder having the following composition Co was deposited on the flat surface (B surface) of the laminated polyester film obtained in the same manner as in Example 1 ESREC A (Vinyl chloride-vinyl acetate copolymer manufactured by Sekisui Chemical Co., Ltd.) ) 10 〃 Nitsuporan 2304 (Polyurethane Elastomer made by Nippon Polyurethane) 10 〃 Coronate L (Polyisocyanate made by Nippon Polyurethane) 5 〃 Lecithin 1 part by weight Methyl ethyl ketone 75 〃 Methyl isobutyl ketone 75 〃 Toluene 75 〃 Additive (lubricant, silicone resin) A magnetic powder coating having 0.15 〃 was applied with a gravure roll, the magnetic coating layer was smoothed with a doctor knife, magnetically oriented by a conventional method while the magnetic coating was still dry, and then introduced into an oven for dry curing. Further calendering to make the coated surface uniform and slit to about 5
A 1 / 2-inch wide magnetic coating tape having a magnetic layer of μm was formed.

The characteristics of the magnetic tape thus obtained are shown in Table 1. This magnetic tape is designed for easy sliding of the base film (A
The surface roughness of the surface) was transferred to the surface of the magnetic layer by show-through, and the electromagnetic conversion characteristics were insufficient.

[Brief description of drawings]

FIG. 1 is a diagram showing the relationship between the height (μm) of protrusions on the film surface and the number of protrusions (ke / mm ² ). FIG. 2 is a diagram showing a film flow of the apparatus using the friction coefficient (μk) measurement.

Claims (1)

[Claims] 1. An aromatic dicarboxylic acid as a main acid component,
A biaxially stretched laminated film composed of a film-forming aromatic polyester containing an aliphatic glycol as a main glycol component, wherein one surface (A surface) exposed is a surface roughness.
RaA is 0.025 μm or less and 0.010 μm or more, and the number of protrusions is 20 /
The distribution curve showing the relationship between the number of protrusions (y: ke / mm ² ) and the height of protrusions (x: μm) determined in the area of mm ² or more is expressed by the formula (1) log ₁₀ y ＝ －9.8x ＋ 4.4. ...... (1) has a protrusion distribution that does not intersect with the range of 2> log ₁₀ y> 1.3, and the curve of the portion larger than the maximum value of the protrusion distribution curve is expressed by equation (2) log ₁₀ y ≧ −18x + 3.7 (2) and a protrusion height (x) of 0.87 μm or more gives a slippery surface substantially free of the other surface of the laminated film exposed ( Surface B) has surface roughness RaB of 0.010μ
In the distribution curve showing the relationship between the number of protrusions (y: number of protrusions / mm ² ) and the height of protrusions (x: μm), which is less than m and the number of protrusions is 20 / mm ² or more, the protrusion distribution The part of the curve that is larger than the maximum value intersects with the formula (3) log ₁₀ y = -18x + 3.7 (3), and the protrusion height (x) is substantially not more than 0.13 μm. Giving a flat surface, the laminated film is 70 ℃
The heat shrinkage in the longitudinal direction when heat-treated for 1 hour under no load was 0.1% or less, and an electron beam-curable magnetic coating was applied on the B side of the laminated film to form a magnetic layer. A magnetic recording medium characterized by: