JPH0649780B2 - Biaxially oriented thermoplastic resin film - Google Patents

Description

TECHNICAL FIELD The present invention relates to a biaxially oriented thermoplastic resin film, a magnetic recording medium using the same, and a heat-sensitive transfer material.

[Prior Art] As a biaxially oriented thermoplastic resin film, a film in which inert inorganic particles are contained in polyester is known (for example, JP-A-59-171623). As a magnetic recording medium or a heat-sensitive transfer material, one having a magnetic layer or a heat-sensitive transfer layer provided on at least one surface of a polyester film is known (for example, JP-A-59-20322).
8 and JP-A-62-95289).

[Problems to be Solved by the Invention] However, the conventional biaxially oriented thermoplastic resin film described above,
Along with the increase in process speed of film processing processes such as packaging process, magnetic layer application and calender process in magnetic media, the defect that the surface of the film is scratched by a contacting roll has recently become a problem. It has become to. In addition, recently, the conventional magnetic recording medium and heat-sensitive transfer material described above have a problem that the front surface and the back surface thereof are scratched due to severer operating conditions.

It is an object of the present invention to solve such problems and provide a film, a magnetic recording medium, and a heat-sensitive transfer material that are not scratched even when running at high speed (hereinafter referred to as good scratch resistance).

[Means for Solving the Problems] The present invention provides (1) a film containing a crude product composed of a thermoplastic resin and inert particles as a main component, and having a depth of at least 3000 nm from at least one surface of the film. In the concentration distribution curve of the measured inactive particles, the depth (distance from the surface) Anm at which the particle concentration is 10 times the surface layer particle concentration value and the depth Bnm (B> A) at which the particle concentration is the same as the surface layer particle concentration value )
The present invention relates to a biaxially oriented thermoplastic resin film, a magnetic recording medium and a heat-sensitive transfer material using the biaxially oriented thermoplastic resin film, which satisfy the following expressions (i) and (ii).

10 ≦ BA−1500 (i) 5 ≦ A ≦ 500 (ii) The thermoplastic resin in the present invention is not particularly limited, and polyester, polyamide, polyolefin, polyphenylene sulfide, etc. can be used. However, polyester, especially ethylene terephthalate, ethylene α, β-
Particle concentration composition of the present invention in the case of polyester having at least one structural unit selected from bis (2-chlorophenoxy) ethane-4,4'-dicarboxylate and ethylene 2,6-naphthalate units as a main constituent This is desirable because the effect of the above becomes more remarkable.

The inert particles in the present invention have a sphericity of 1.6 or less, preferably 1.5 or less, and more preferably 1.3 or less because scratch resistance is further improved, which is particularly preferable. The type of the inert particles is not particularly limited, but substantially spherical silica derived from colloidal silica, tungsten oxide, and 10% weight loss temperature are organic polymer particles having a temperature of 350 ° C. or higher, the scratch resistance is further improved. It is particularly desirable because it becomes good. The average particle size of the particles is not particularly limited, and the preferable range varies depending on the type, but the average particle size is c
(Nm), the scratch resistance is further improved when the relationship with (BA) in the above formula (i) satisfies the following formula (a), preferably (b). When the particle size is 10 to 500 nm, particularly 30 to 450 nm, scratch resistance is further improved, which is particularly desirable.

1.0 ≦ c / (BA) ≦ 3.5 ··· (a) 1.3 ≦ c / (BA) ≦ 3.0 ··· (b) The film of the present invention comprises the above composition as a main component. However, other types of polymers may be blended within a range that does not impair the object of the present invention, and inorganic or organic additives such as antioxidants, heat stabilizers, lubricants, UV absorbers and nucleating agents. May be added to the extent that is usually added. Further, in addition to the inert particles, it may contain internally precipitated particles. The internally deposited particles in the present invention are particles formed by binding at least one compound of calcium compound, magnesium compound and lithium compound added at the time of polyester polymerization and the polyester constituent component. The internally precipitated particles of the present invention may contain elemental phosphorus and a trace amount of other metal components, such as zinc, cobalt, antimony, germanium, and titanium, within a range that does not impair the object of the present invention. Good.

The film of the present invention is a film in which the above composition is biaxially oriented. An unstretched film is not preferable because it has poor slipperiness and abrasion resistance. The degree of biaxial orientation is not particularly limited, but scratch resistance is further improved when the film or Young's modulus indicating the degree of molecular orientation is 350 Kg / mm ² , preferably 400 Kg / mm ² or more in both the longitudinal and axial directions. Therefore, it is particularly desirable.

The film of the present invention has a depth (distance from the surface) Anm at which the particle concentration is 10 times the surface layer particle concentration value in the concentration distribution curve of the inert particles measured from at least one surface of the film to a depth of 3000 nm and the surface layer. Depth Bnm (B> A, that is, B is A
It is necessary that the relationship of (deeper point) satisfies the following expression (i), preferably (i ′), and more preferably (i ″).

10 ≦ BA ≦ 1500 (i) 30 ≦ BA ≦ 1300 (i ′) 50 ≦ BA ≦ 1000 (i ″) BA on at least one side of the film Is preferably in the above range because the scratch resistance is good. The depth is A
In the deeper region, if there is no point having the same particle concentration as the surface layer particle concentration within 3000 nm, B = 300
0 nm.

The film of the present invention has a depth (distance from the surface) Anm at which the particle concentration is 10 times the surface layer particle concentration value in the concentration distribution curve of the inert particles measured from at least one surface of the film to a depth of 3000 nm. It is necessary to satisfy the formula (ii), preferably (ii '), and more preferably (ii'').

5 ≦ A ≦ 500 (ii) 5 ≦ A ≦ 250 (ii ′) 10 ≦ A ≦ 100 (ii ″) The depth at which the particle concentration is 10 times the surface layer particle concentration value. (Distance from the surface) If Anm is smaller or larger than the above range, scratch resistance becomes poor, which is not preferable.

Since the film of the present invention has a ratio of 10-point average roughness Rz and maximum height Rt, Rz / Rt, of the surface satisfying the above-mentioned particle concentration distribution structure, scratch resistance is further improved when Rz / Rt is 0.85 or more. Especially desirable.

The film of the present invention is more scratch resistant when the ratio of the center line average roughness Ra to the maximum height Rt of the surface satisfying the above-mentioned particle concentration distribution configuration, Rt / Ra is 9.0 or less, particularly 8.0 or less. It is particularly desirable because it becomes even better.

Further, Rt / Rp, which is the ratio of the center line depth Rp and the maximum height Rt of the surface satisfying the above particle concentration distribution configuration, is 1.4 to 2.
When it is 0, particularly 1.6 to 2.0, scratch resistance is further improved, which is particularly desirable.

The film of the present invention has a center protrusion spacing Sm of 6 μm or less, preferably 4.5 μm, on the surface satisfying the above particle concentration distribution configuration.
When it is m or less, scratch resistance is further improved, which is particularly desirable.

The film of the present invention is particularly preferable because the scratch resistance is further improved when the height of the central protrusion on the surface satisfying the above particle concentration distribution constitution is in the range of 10 to 200 nm.

The film of the present invention has a content of a low molecular component content (such as a cyclic trimer in polyester) in the range of 2000 nm from the surface satisfying the above-mentioned particle concentration distribution constitution of 0.6.
When the content is less than or equal to 5% by weight, preferably less than or equal to 0.5% by weight, scratch resistance is further improved, which is particularly desirable.

In the film of the present invention, the oxygen permeability coefficient up to the depth of B in the above formula (i) on the surface of the surface satisfying the above particle concentration distribution constitution is 40 cc / m ² · when converted to a thickness of 15 μm.
24 hours atm or less, preferably 300 cc / m ²
In the case of 24 hours · atm, scratch resistance is further improved, which is particularly desirable.

The type of the magnetic layer of the magnetic recording medium of the present invention is not particularly limited, and a known magnetic material, that is, γ-iron oxide, Co-containing γ-iron oxide, chromium dioxide, iron, cobalt, or an alloy thereof is used. , But especially iron, cobalt,
Alternatively, the effect of the present invention is particularly obtained in the case of a so-called metal coating type consisting of those alloys and an organic binder, and a metal thin film type magnetic layer formed by a method such as vapor deposition or sputtering substantially without using an organic binder. It is particularly desirable because it becomes remarkable. The type of binder is not limited, and vinyl chloride / vinyl acetate copolymer, polyvinyl butyral, polyurethane, etc. can be used. The back coat layer may or may not be present, but when the back coat layer is provided, those mainly containing known binders such as vinyl chloride, vinyl acetate, vinyl alcohol and copolymers thereof, and polyurethane cellulose derivatives can be used. .

The thickness of the magnetic layer is not particularly limited, but it is particularly desirable when the thickness is 3 μm or less because the effect of the present invention becomes particularly remarkable.

When the back coat layer is provided, the thickness is not particularly limited, but is 0.05 to 2.5 μm, particularly 0.1 to 1.5 μm.
In this case, scratch resistance is further improved, which is particularly desirable.

The heat-sensitive transfer layer of the heat-sensitive transfer material of the present invention is not particularly limited,
A known one can be used, but basically, a coloring agent,
It is a composition comprising a binder. As the colorant, dyes, organic and / or inorganic pigments can be used. Known binders such as carnauba wax can be used as the binder.

Next, a method for producing the film of the present invention will be described.

First, as a method of incorporating inert particles into a predetermined thermoplastic resin, it may be added before polymerization, during polymerization, or after polymerization, but in the case of polyester, it is mixed and dispersed in the form of a slurry with a diol component in the case of polyester. The method of adding at least is effective in satisfying the particle concentration distribution constitution of the present invention. Also. As a method of adjusting the content of particles, a method of diluting a high concentration master polymer at the time of film formation is used, and the melt viscosity of the master polymer is higher than that of the thermoplastic resin, preferably 500 poise or more. Higher,
Moreover, it is effective to satisfy the particle concentration distribution constitution of the present invention that the cohesive energy density is made smaller than that of the thermoplastic resin which is diluted by adjusting the components of the master polymer.

Thus after drying the pellets of the thermoplastic resin containing a predetermined amount of inert particles, if necessary, supplied to a known melt extruder, extruded into a sheet from a slit die,
An unstretched film is prepared by cooling and solidifying on a casting roll. In this case, using a known film forming apparatus for laminated sheets (for example, 2 or 3 extruders, 2 or 3 layer manifolds, etc.), a two- or three-layer structure made of the same or different thermoplastic resin is not formed. The stretched film has a film thickness d (n of at least one surface as a biaxially oriented film.
m) and the average particle diameter c (n) of the inert particles contained in the layer
m) is 0.1 ≦ d / c ≦ 1.5 and the film thickness of the layer is 0.03 to 0.5 μm, which is extremely sufficient to satisfy the particle concentration distribution structure of the present invention. It is valid. Further, setting the particle content of the layer to 3 to 45% by weight is extremely effective for satisfying the particle concentration distribution constitution of the present invention. Further, it is preferable that the melt viscosity of the thermoplastic resin used for the layer (surface layer) is set to be 500 poise, preferably about 1000 poise, higher than the melt viscosity of the thermoplastic resin of the other layer in contact with the layer. It is extremely effective in satisfying the distribution structure. Further, a method of installing a static mixer and a gear pump in the polymer flow path of the thermoplastic resin of the layer is extremely effective in satisfying the particle concentration distribution constitution of the present invention without stretching breakage. In order to satisfy the particle concentration distribution constitution of the present invention, the crystallization parameter ΔTcg of the thermoplastic resin of the layer is set to be smaller than ΔTcg of the thermoplastic resin of the other layer in contact with it, preferably 10 ° C. or more. It is extremely effective.

Next, this unstretched film is biaxially stretched and biaxially oriented. As a stretching method, a sequential biaxial stretching method or a simultaneous biaxial stretching method can be used. However, using a sequential biaxial stretching method in which stretching in the longitudinal direction first and then in the width direction is performed first,
Stretching in the longitudinal direction is performed from the glass transition point of the thermoplastic resin by 10
1000 to 10 in the range of 10 ° C to 10 ° C lower temperature
The method of carrying out at a relatively low drawing speed of 000% / min is extremely effective for satisfying the particle concentration distribution constitution of the present invention. The stretching method in the width direction is 1 at a high glass transition point of the thermoplastic resin of the core layer at a high humidity of 50% RH or more.
The method of stretching in the range of 0 ° C. lower temperature to 30 ° C. higher than the glass transition point is extremely effective for satisfying the particle concentration distribution constitution of the present invention. It is effective for satisfying the particle concentration distribution constitution of the present invention that the stretching speed in the width direction is 1000 to 20000% / min and is higher than the stretching speed in the longitudinal direction. The stretching ratio is preferably 3 to 5 times in both the longitudinal and width directions. Next, the stretched film is heat-treated, and a known method can be used. Even in a film having a single-layer structure, the melt viscosity and cohesive energy density of the particle master polymer are adjusted, a gear pump is introduced into the polymer particle passage, a static mixer is introduced, the stretching conditions are strictly adjusted, or the melt film formation is performed. Although it is possible to satisfy the particle concentration distribution constitution, there are problems such as stable production and reproducibility, which is not industrially preferable.

A magnetic recording medium can be obtained by forming a magnetic layer on at least one surface of the above biaxially oriented film. That is, it can be manufactured by a method in which a coating material containing a magnetic material is applied, dried and then calendered, or a method in which a magnetic metal thin film is formed by vapor deposition or sputtering. If necessary, the back coat layer is formed by applying a solution having a predetermined composition,
Dried and done. The back coat layer may be formed before the magnetic layer is formed, after the magnetic layer is formed, before the calender treatment, after the calender treatment, or after the curing step.

The heat-sensitive transfer material is produced by hot-melt coating a predetermined heat-sensitive transfer agent on one side of the biaxially oriented thermoplastic resin film, or by dispersing or dissolving it in a solvent, and applying this coating solution. There is no limit.

EFFECTS OF THE INVENTION The present invention provides a film that is not damaged even when running at a high speed and a material composed of the film, because the particle concentration distribution structure on at least one surface of the film is in a special state.

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

(1) Inert particle concentration distribution (depth profile) By using a secondary ion mass spectrometer (SIMS), the element derived from the highest concentration of particles in the film in the depth range of 3000 nm from the surface layer The concentration ratio (M ⁺ / C ⁺ ) of the carbon element of the thermoplastic resin is used as the particle concentration, and the analysis in the thickness direction is performed from the surface to a depth of 3000 nm. In the surface layer, the particle concentration is low due to the interface of the surface, and the particle concentration increases as the distance from the surface increases. In the case of the film of the present invention, the particle concentration once reaching the maximum value starts to decrease again. Based on this concentration distribution curve, a point A (distance from the surface) showing a particle concentration 10 times the surface layer particle concentration, and a point B (a point B where the particle concentration once increased decreases to the same value as the surface layer particle concentration) (Distance from the surface). Naturally, B is deeper than A. The conditions are as follows.

(1) Measuring instrument Secondary ion mass spectrometer (SIMS) A-DIDA3000 manufactured by ATOMIKA, West Germany (2) Measuring conditions Primary ion species: O ₂ ⁺ Primary ion acceleration voltage: 12KV Primary ion current: 200nA Raster region : 400 μm □ Analysis area: 30% gate Measurement degree of vacuum: 5.0 × 10 ^-9 Torr E-GUN: 0.5 KV-3.0 A It should be noted that the most contained particles in the range of depth 3000 nm from the surface layer are organically high. In the case of molecular particles, it is difficult to measure with SIMS, so using the etching method from the surface or the section method,
The depth profile similar to the above is measured by XPS (X-ray photoelectron spectroscopy), IR (infrared spectroscopy), etc., and the depths of A and B are obtained.

(2) Average particle size of particles The thermoplastic resin is removed from the film by a plasma low temperature ashing method (for example, PR-503 type manufactured by Yamato Scientific Co., Ltd.) to expose the particles. The processing conditions are selected such that polyester is incinerated but particles are not damaged. This is SE
Observe with M (scanning electron microscope), connect the image of the particles (light and shade of light produced by the particles) to an image analyzer (for example, QTM900 made by Cambridge Instruments), change the observation point and the number of particles is 5000 or more. The number average diameter D obtained by the treatment is used as the average particle diameter.

D = ΣDi / N Here, Di is the equivalent circle diameter of the particles, and N is the number.

(3) Content of particles A solvent is selected which dissolves the thermoplastic resin but not the particles, and the particles are centrifuged from the polyester, and the ratio (% by weight) to the total weight of the particles is taken as the particle content.
In some cases, the combined use of infrared spectroscopy is also effective.

(4) Crystallization parameter ΔTcg It was measured using a DSC (Differential Scanning Calorimeter) II type manufactured by Perkin Elmer. The measurement conditions of DSC are as follows. That is, 10 mg of the sample was set in the DSC device, and 3
After melting for 5 minutes at a temperature of 00 ° C., it is quenched in liquid nitrogen. The temperature of this quenched sample is raised at 10 ° C./min, and the glass transition point Tg is detected. The temperature was further raised and the crystallization exothermic peak temperature from the glass state was set as the cold crystallization temperature Tcc. The temperature was further raised and the heat of fusion was determined from the melting peak. Here, the difference between Tcc and Tg (Tcc-Tg) is defined as the crystallization parameter ΔTcg.

(5) Average height of surface protrusions 2 detector scanning electron microscope [ESM-3200,
Elionix Co., Ltd.] and cross-section measuring device [PMS-1,
Elionix Co., Ltd.], the measurement value of the height of the projection when scanning is performed with the height of the flat surface of the film as 0, and the measured value of the height of the projection is image processing apparatus [IBAS2000, Carl Zeiss Co., Ltd.
Manufactured] to reconstruct the film surface projection image on the image processing device. Next, the equivalent circle diameter is calculated from the area of each protrusion obtained by binarizing the protrusion portion in this surface protrusion image, and this is made the average diameter of the protrusion. In addition, the highest value among the binarized individual projection portions is set as the height of the projection, and this is obtained for each projection. This measurement was repeated 500 times at different places, and the height distribution of the measured protrusions was regarded as a normal distribution and approximated by the least squares method. The scanning electron microscope has a magnification of 1000-80.
Select a value between 00 times.

(6) Center line average surface roughness Ra, 10-point average roughness Rz,
The center line depth Rp, the maximum height Rt, and the protrusion spacing Sm were measured using a high precision thin film step measuring instrument ET-10 manufactured by Kosaka Laboratory. The conditions are as follows, and the average value of 20 measurements was used as the value.

・ Stylus tip radius: 0.5 μm ・ Stylus load: 5 mg ・ Measurement length: 1 mm ・ Cutoff value: 0.08 mm Note that Ra, Rp, Rt, and Sm are defined by, for example, Jiro Nara "Surface roughness". "Measurement and evaluation method" (General Technology Center, 1983).

(7) Young's modulus According to the method specified in JIS-Z-1702,
25 using an Instron type tensile tester
It was measured at 65 ° C. and 65% RH.

(8) Melt viscosity 290 ℃, shear rate 20 using high flow tester
It was measured at ⁰ sec ^-1 .

(9) Sphericity This is the ratio of the average value of the major axis / the average value of the minor axis of each particle in the measurement of (1) above.

That is, it is calculated by the following formula.

Major axis = ΣD1i / N Minor axis = ΣD2i / N D1i and D2i are the major axis (maximum diameter) and minor axis (shortest diameter) of each particle, and N is the total number.

(10) Relative standard deviation of particle size Standard deviation calculated from individual projection diameter Di, average diameter D, and total number N of particles measured by the method of (1) above Was divided by the average diameter D (σ / D).

(11) Content of low-molecular component Sample polymer in a predetermined depth range was crushed, and a Soxhlet extractor was used.
Extract time. The low molecular weight component was defined as the ratio (% by weight) of the weight of the extract obtained by evaporating chloroform to the weight of the original sample.

(12) Scratch resistance At a temperature of 20 ° C. and a relative humidity of 60%, a thermal transfer ribbon slitted into a tape-shaped film (or magnetic recording medium) of 1/2 inch width on a guide pin with an outer diameter of 6 mmφ or a tape of 8 mm width. Angle θ = π / 2 (ra
d), tension T1 = 200 g, aluminum film was vapor-deposited on the film surface after running 30 times at a speed of 1000 m / min, and the number of scratches, the size of the width, and the generation state of white powder were observed by a differential interference microscope. . Scratch resistance: 4 with no scratches and almost no white powder, scratch resistance: 3, scratches with less than 3 scratches and 3-10 scratches Scratch resistance: 2 for which there is a large amount of white powder and scratches: 2; there is a large width with 10 or more scratches; It was determined. If the scratch resistance is 4 or 3, it can be used practically without any problem.

[Examples] The present invention will be described based on Examples.

Examples 1 to 5 and Comparative Examples 1 to 4 Silica particles derived from colloidal silica having different average particle diameters, polyethylene terephthalate containing divinylbenzene / styrene copolymer crosslinked particles, polyethylene 2, 6
-Adjusted naphthalate (change melt viscosity). This master polymer and polyethylene terephthalate (melt viscosity: 1500 poise) or polyethylene 2,6-naphthalate (melt viscosity: 40) containing substantially no inert particles.
00 poise was mixed to obtain a predetermined particle concentration (thermoplastic resin A). The thermoplastic resin A and various thermoplastic resins (B) are supplied to the extruder 1 and the extruder 2, respectively, at 290 ° C.
Were melted, and these polymers were combined and laminated, wound around a casting drum having a surface temperature of 30 ° C. by an electrostatically applied cast method, and cooled and solidified to form an unstretched film having a three-layer structure. The total thickness and the thickness of the thermoplastic resin A layer were adjusted by adjusting the discharge rate of each extruder. This unstretched film was stretched 4.0 times in the longitudinal direction while changing the temperature.
This stretching is performed by the peripheral speed difference between the two sets of rolls, and the stretching speed is 2
It was 000% / min. This uniaxially stretched film was stretched 4.5 times in the width direction by changing the stretching speed and humidity atmosphere using a stenter, and then heat-treated at 200 ° C. for 5 seconds under a fixed length, and biaxially oriented with a total thickness of 15 μm. A laminated film was obtained. The parameters of the present invention for these films are as shown in Table 1, and when the parameters of the present invention were within the range, the scratch resistance was good as shown in Table 1,
Otherwise, a film satisfying scratch resistance could not be obtained.

Examples 4 to 5 and Comparative Examples 5 to 8 Polyethylene terephthalate and polyethylene-2,6-naphthalate containing spherical silica derived from colloidal silica having different average particle diameters were prepared (melt viscosity change). Polyethylene terephthalate (melt viscosity: 15) containing substantially no inert particles with these master polymers
00 poise) or polyethylene-2,6-naphthalate (melt viscosity: 4000 whises are mixed to obtain a predetermined particle concentration (thermoplastic resin A). This thermoplastic resin A contains 0.1% by weight of spherical silica particles. An unstretched film having a two-layer structure was produced by laminating various thermoplastic resins (B) by changing the stacking thickness, and the unstretched film was stretched 4.0 times in the longitudinal direction while changing the temperature. Was carried out by the peripheral speed difference between the two rolls, and the stretching speed was 2000% / min.
This uniaxially stretched film was stretched 4.5 times in the width direction by changing the stretching speed and humidity atmosphere using a stenter, and then heat-treated at 200 ° C. for 5 seconds under a constant length, and biaxially oriented with a total thickness of 12 μm. A laminated film was obtained. On the thermoplastic resin A surface of these films, a Co / Ni alloy (C
(O / Ni = 75/25 weight ratio) was obliquely vapor-deposited to a thickness of 180 nm (minimum incident angle: 50 °) to form a magnetic thin film.
The following composition was applied to the opposite surface to form a back coat layer having a thickness of 0.5 μm.

(Backcoat composition) -Polyester (Toyobo Byron 200) 80 parts by weight-Nitrocellulose 20 parts by weight-Carbon black 80 parts by weight-Silica particles (average particle diameter 0.01 μm) (50% by weight based on organic binder) -Methylethylketone 200 Parts by weight Toluene 200 parts by weight Cyclohexanone 200 parts by weight The parameters of the present invention of this magnetic tape are as shown in Table 2. When the parameters of the present invention are within the range, the scratch resistance of the magnetic surface is the second. The film was good as shown in the table, but if not, a film satisfying the scratch resistance could not be obtained.

Example 6, Comparative Examples 9 to 12 After corona treatment on one side of the film of Example 1 and the film of Comparative Examples 1 to 4, 30 parts of carnauba wax, 35 parts of paraffin wax, oil black HBB (Orient Chemical Industry) (5 parts of oil-soluble dye), 25 parts of carbon black and 5 parts of lanolin were mixed and hot-melt coated to a thickness of 4 μm to obtain a film for thermal transfer. This film was slit into a width of 8 mm to obtain a thermal transfer ribbon. The parameters of the present invention of this heat-sensitive transfer ribbon are as shown in Table 3, and when the parameters of the present invention are within the range, the scratch resistance of the film surface was good as shown in Table 3, Otherwise, a film satisfying scratch resistance could not be obtained.

Continuation of the front page (51) Int.Cl. ⁵ Identification code Office reference number FI Technical display area B29L 7:00 4F

Claims (4)

[Claims] 1. A film comprising, as a main component, a crude product composed of a thermoplastic resin and inert particles, wherein the concentration distribution curve of the inert particles is measured from at least one surface of the film to a depth of 3000 nm. The depth at which the particle concentration is 10 times the surface layer particle concentration value (distance from the surface) Anm
And the depth Bnm (B
A biaxially oriented thermoplastic resin film, wherein the relation of> A) satisfies the following formulas (i) and (ii). 10 ≦ B−A ≦ 1500 (i) 5 ≦ A ≦ 500 (ii) 2. The biaxially oriented thermoplastic resin film according to claim 1, wherein the sphericity of the inert particles is 1.6 or less. 3. A magnetic recording medium, comprising a magnetic layer provided on at least one surface of the biaxially oriented thermoplastic resin film according to claim 1. 4. A heat-sensitive transfer material comprising a heat-sensitive transfer layer provided on one surface of the biaxially oriented thermoplastic resin film according to claim 1.