JPH05154907A - Biaxially orientated themoplastic resin film - Google Patents

Abstract

PURPOSE:To provide biaxially orientated thermoplastic resin film, by which the falling of particles off base film in the production process of magnetic recording medium is suppressed and consequently drop-out is reduced. CONSTITUTION:In the biaxially orientated thermoplastic resin film concerned, at least the ratio (sigma/h) of the standard deviation (sigma) of the heights of projections on one surface of the film to the average height (h) of the projections is 0.5 or less and, further, the ratio (h/d) of the average height (h) of the projections to the average diameter (d) of projections is 0.17 or less.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a biaxially oriented thermoplastic resin film, and further to a biaxially oriented thermoplastic resin film having a laminated film structure suitable as a base film for magnetic recording media.

[0002]

2. Description of the Related Art As a biaxially oriented thermoplastic resin film having improved surface properties, a film in which a thermoplastic resin contains substantially spherical silica particles derived from colloidal silica is known (for example, JP-A-59-171
623). In such a biaxially oriented thermoplastic resin film, it is possible to improve the handling property and the running property by forming protrusions on the film surface by the contained silica particles and lowering the friction coefficient of the surface.

However, in the biaxially oriented thermoplastic resin film as described above, since the contained silica particles are randomly distributed over the entire thickness direction of the film, the height of protrusions formed on the film surface is also non-uniform. Will be things. If the height of the protrusions on the film surface is uneven, it is easy to scrape high-height protrusions, and
For example, as the process speed of magnetic layer coating and calendering in magnetic recording media applications increases, scratches are caused by the contacting rolls, or scrapes adhere to the film surface, resulting in DO (dropout) during recording and reproduction. Problems such as sticking up occur. When the projection density on the film surface is low, the effect of improving the slip property of the film surface is low, and the effect of improving the handling property and the running property cannot be obtained as expected.

Further, in magnetic recording media applications, biaxially oriented thermoplastics having a laminated structure with front and back slipperiness, such that the side on which the magnetic layer is provided is made smooth and the opposite side is provided with irregularities to ensure running performance. Resin films are known (for example, JP-A-50-33805).

However, even in the above-mentioned film, various obstacles occur due to the unevenness of the protrusion height,
In particular, when the smoothness of the magnetic surface is required, as is the case with metal tapes for high image quality these days, coarse protrusions on the running surface side during the curing process during tape manufacturing transfer to the magnetic surface, or magnetic properties during the calendar process. A phenomenon such as pushing up to the surface side occurs, and any of them adversely affects the electromagnetic conversion characteristics.

As a means for solving the above-mentioned problems, high-density and uniform-height projections are formed on at least one surface of the biaxially oriented thermoplastic resin film to obtain good handling property and running property. , A film having a surface scratch-proof property is known (Japanese Patent Laid-Open No. 2-77431).
Publication). In such a film, due to the high density and uniform height of the protrusions formed on the surface, it is possible to significantly reduce the damage to the magnetic surface such as the transfer of coarse protrusions in the curing process and the thrusting in the calendering process. Therefore, it is suitable as a base film for a magnetic medium which has high image quality and high recording density.

[0007]

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention
The biaxially oriented thermoplastic resin film disclosed in Japanese Patent No. 31 is a film having a laminated structure, and at least one side of
By providing an ultra-thin layer having a film thickness equal to or smaller than the particle diameter, it is possible to increase the density of the projections to be formed and to make the height uniform.

However, in the above-mentioned biaxially oriented thermoplastic resin film, particles are added in a high concentration in the vicinity of the surface thereof, and the thermoplastic resin layer containing the particles is very thin. I'm worried.

In recent years, magnetic recording media, especially video tapes, are required to have higher recording density and longer recording time, and the tapes are also becoming thinner. Along with this, a thinner base film is required, and higher elastic modulus and higher stiffness are required. In the case of a biaxially oriented thermoplastic resin film, in order to satisfy this requirement, a means for increasing the draw ratio and strengthening the molecular orientation is generally taken. However, in the conventional film to which the inert particles are added, the amount of voids generated near the particles also increases as the draw ratio increases. By increasing the amount of voids, the adhesiveness between the inert particles and the thermoplastic resin is reduced, when the film surface comes into contact with a metal roll or the like in the tape manufacturing process, stress is applied to the protrusions present on the film surface, The projections are broken, and the particles easily fall off the film surface.

In the case of the above-mentioned biaxially oriented thermoplastic resin film, since the projections are formed at a high density on the surface, the stress received by contact with a metal roll or the like is dispersed by the numerous projections to absorb the shock. Although the effect is excellent, when the pressure force with the roll is working in the surface direction of the film, or depending on the surface morphology of the metal roll,
A phenomenon occurs in which stress concentrates on individual protrusions. In such a situation, the particles are unevenly distributed in the surface layer, so that the breakage of the protrusions and the dropout of the particles occur relatively easily, which becomes more remarkable as the stretching ratio is increased. The particles that have fallen off the film surface become a deposit and reattach to the running film surface, transfer to the magnetic surface side during winding, and cause an increase in dropout after tape formation.

The present invention starts from the above-mentioned known technique, and by optimizing the resin and particle formulation of the coating layer and the film forming conditions, it is possible to maintain high electromagnetic conversion characteristics and excellent runnability, Biaxially oriented thermoplastic resin that has sufficient strength in the longitudinal and width directions of the film to suppress dropout of particles from the film surface by increasing the protrusion strength and to enable the production of extremely thin tapes with high recording density. An object is to provide a resin film.

[0012]

The biaxially oriented thermoplastic resin film of the present invention for this purpose has a ratio (σ) of the standard deviation σ of the projection height of at least one surface and the average projection height h.
/ H) is 0.5 or less, and the ratio (h / d) of the average protrusion height h of the surface to the average protrusion diameter d is 0.17 or less.

The above-mentioned film preferably contains a thermoplastic resin B and an inert particle having an average particle diameter of 0.05 to 1.0 μm as main components on at least one surface of a layer (A layer) containing the thermoplastic resin A as a main component. Is a biaxially oriented thermoplastic resin film in which the layer (B layer) is laminated, the content of the particles in the B layer is 0.5 to 20% by weight, and the average particle diameter is 1.0 of the B layer thickness. ~ 1
It consists of what is 0.0 times.

Further, in this film, the sum of F-5 values in the longitudinal direction and the width direction is preferably 28 kg / mm ² or more.

Further, in the above film, the average protrusion height on the surface of layer B before heat setting treatment is h ₁ , the average protrusion diameter is d ₁ , the standard deviation of protrusion height is σ ₁ , and the layer B after heat setting treatment is the average protrusion height of the surface h _2, the average projection diameter d _2, if the standard deviation of the projection height was set to sigma _2, a heat treatment under a condition satisfying the relationship of formula (1) to (3) It is manufactured by applying. h ₂ <h ₁ (1) σ ₂ / h ₂ <σ ₁ / h ₁ (2) h ₂ / d ₂ <h ₁ / d ₁ (3)

The biaxially oriented thermoplastic resin film according to the present invention preferably has a laminated film construction, and at least one surface thereof is provided with projections having a uniform height and a comparatively gentle shape to manufacture a magnetic recording medium. It is possible to remarkably improve the ease of falling of particles due to projection breakage (projection strength) without impairing the scratch resistance (scratch resistance) of the film surface.

A crystalline polymer is desirable as the thermoplastic resin A used in the support layer A constituting the film, and particularly, the crystallization parameter ΔTcg is 20 ° C. to 100 ° C.
When the temperature is in the range of ° C, the scratch resistance is good, which is desirable. Specific examples thereof include polyester, polyamide, polyphenylene sulfide, polyolefin and the like, but polyester is preferably used. In addition, as the polyester, at least one structural unit selected from ethylene terephthalate, ethylene α, β-bis (2-chlorophenoxy) ethane-4,4′-dicarboxylate, and ethylene 2,6-naphthalate units is the main component. When it is used as a constituent component, scratch resistance becomes particularly good, which is desirable. However, other components may be copolymerized within a range that does not impair the present invention and a range that does not impair the desired crystallinity, preferably within 5 mol%. Further, other polymers may be blended within a range not impairing the object of the present invention, and additives such as an antioxidant, a lubricant, a heat stabilizer, an antistatic agent, an ultraviolet absorber and a light shielding agent. May be added to the extent that is usually added.

The support layer A need not contain particles, but 0.001 to 0.5 weight of particles having an average particle size of 0.01 to 2 μm, preferably 0.02 to 0.5 μm. %, Preferably 0.005 to 0.3% by weight, is preferable because not only the coefficient of friction and scratch resistance are further improved, but also the winding shape of the film is improved. The type of the inert particles contained in the support layer A is not particularly limited, but substantially spherical silica particles derived from colloidal silica, particles of a crosslinked polymer, calcium carbonate, titanium dioxide, zirconia, alumina, alumina. One kind or a plurality of kinds of silicates may be used in combination, and it is particularly preferable to use one that is preferably used for the covering layer B described later.

On at least one surface of the support layer A,
A cover layer B is provided. As the thermoplastic resin B forming the covering layer B, polyester is desirable. Further, in order to achieve the present invention, the thermoplastic resin B needs to have a melting point lower than that of the thermoplastic resin A constituting the support layer A. The melting point difference between the two is preferably 10 to 100 ° C., more preferably 20 to 50 ° C. from the viewpoint of performance or manufacturing process.

To achieve the object of the present invention, the thermoplastic resin B is preferably composed of a copolymerized polyester containing ethylene terephthalate units and other ester components. Examples of the acid component used for the other ester component include adipic acid, sebacic acid, phthalic acid, isophthalic acid and 2,6-naphthalene dicarboxylic acid, and examples of the diol component include diethylene glycol, propylene glycol and 1,4-cyclohexane. Dimethanol or the like is used. However, homopolyesters such as polybutylene terephthalate and polybutylene naphthalate may be used as long as they satisfy a predetermined melting point difference.

The inert particles contained in the covering layer B are preferably spherical particles, and the particle diameter ratio (major axis / minor axis of particles) in the film is preferably 1.0 to 1.3. Further, it is desirable to use those having a uniform particle size because the effect of suppressing particle dropout and the scratch resistance are improved. For this reason, it is desired that the inert particles in the covering layer B of the present invention have a relative standard deviation in the film of 0.6 or less, preferably 0.5 or less.

The type of the inert particles in the covering layer B is not particularly limited, but in order to satisfy the above preferable particle characteristics, substantially spherical silica particles derived from colloidal silica and particles formed by a crosslinked polymer ( For example, it is desirable to use polydivinylbenzene). Further, in the case of spherical silica derived from colloidal silica, the scratch resistance is further improved in the case of substantially spherical silica produced by the alkoxide method and having a low sodium content, which is desirable. However, other particles such as calcium carbonate, titanium dioxide, zirconia, and alumina can be sufficiently used by appropriately controlling the thickness of the covering layer and the average particle diameter.

The size of the inert particles is such that the average particle diameter in the covering layer B is 1.0 to 10.0 times, preferably 1.2 to 5.0 times the thickness of the covering layer B, More preferably 1.5-3.
It is necessary that the range is 0 times. When the average particle diameter / B layer thickness ratio is smaller than the above range, the friction coefficient and scratch resistance are poor, and when the average particle diameter / B layer thickness ratio is larger, dropout of particles increases and dropout increases, and S / N (signal / noise) is increased. Ratio) becomes defective.

The average particle diameter of the inert particles in the layer B is 0.05 to 1.0 μm, preferably 0.2 to 0.45 μm.
When it is in the range of m, the friction coefficient, scratch resistance, and particle fall-off suppressing effect are particularly good, which is desirable.

The content of the inert particles in the B layer is 0.
It should be 5 to 20% by weight, preferably 1 to 15% by weight, more preferably 2 to 10% by weight. If the content of the inert particles is less than the above range, not only the coefficient of friction and scratch resistance become poor, but also the number of projections is small, so that stress is likely to be concentrated on each projection and particles are likely to fall off. On the other hand, when it is larger than the above range, coarse projections are generated due to agglomerated particles, which causes a decrease in S / N after tape formation and an increase in dropout.

The coating layer B contains a composition comprising the above-mentioned thermoplastic resin B and inert particles as a main component, but other types of polymers may be blended within a range not impairing the object of the present invention. Further, antioxidants, heat stabilizers, lubricants, antistatic agents, ultraviolet absorbers, light-shielding agents and the like may be added to the extent that they are usually added.

The support layer A and the coating layer B as described above are laminated by coextrusion, molded into a sheet and then biaxially stretched to obtain a biaxially oriented thermoplastic resin. The lamination by coextrusion in the present invention means that the thermoplastic resin B containing particles and the thermoplastic resin A are extruded by different extruders, respectively, and laminated before discharging the laminated sheet from the die. This lamination may be performed in a die for molding and discharging into a sheet (for example, a manifold), but as described above, since the laminated film layer is extremely thin, it is performed in a polymer tube before being introduced into the die. Preferably. Particularly, it is particularly preferable to form the laminated portion in the polymer tube in a rectangular shape because the laminated portion can be uniformly laminated in the width direction.
The molten polymer laminated in the rectangular laminated part in the polymer pipe is
It is widened to a predetermined width in the sheet width direction by a manifold in the die, discharged into a sheet form from the die, and then biaxially stretched. Therefore, even if the laminated film after biaxial orientation is extremely thin, since the particle-containing polymer is laminated in a considerable thickness in the polymer tube rectangular laminated portion, it can be laminated easily and accurately.

The desirable film in the present invention is obtained by laminating the coating layer B on at least one surface of the support layer A by coextrusion as described above, forming a sheet, and then biaxially stretching the biaxially oriented thermoplastic resin. It is a resin film. An object of the present invention is not only to make the height of the protrusions formed on the surface of the B layer uniform, but to increase the overall wear resistance by controlling the shape itself.
The present inventors have found that it is difficult to achieve the intended purpose only by controlling the height of protrusions as has been done conventionally, and found the solution by optimizing the shape of each protrusion.

That is, the projections formed on the surface of the coating layer B of the biaxially oriented thermoplastic resin film of the present invention have a ratio (σ / h) of the standard deviation σ of the heights and the average projection height h. In addition to satisfying 0.5 or less, the ratio (h / d) of the average protrusion height h and the average protrusion diameter d is 0.17 or less, preferably 0.05 or more and 0.17 or less. σ
When / h is more than 0.5, the uniformity of the height of the protrusions is insufficient, the scratch resistance and the calendering resistance are insufficient, and the smoothness of the magnetic surface is stronger. The S / N ratio may be insufficient for high-grade metal tape applications that are required these days. Further, even if σ / h is 0.5 or less, if h / d is larger than 0.17, the shape of the protrusions is steep, and the film surface has a steep shape. The impact stress applied to the projections on the film surface due to the collision with the projections becomes large, and the projections are easily broken. On the other hand, if h / d becomes too small, the coefficient of friction and scratch resistance become insufficient, so h / d is preferably in the above range.

In order to produce a biaxially oriented thermoplastic resin film satisfying the above conditions, the coating layer B and the support layer A having the above-mentioned composition are coextruded, biaxially stretched and then heat-treated. When performing the fixing treatment, the heat fixing treatment needs to be performed under the following conditions. That is, the heat setting treatment temperature _TH is (melting point of thermoplastic resin B) < _TH <(melting point of thermoplastic resin A) preferably (melting point of thermoplastic resin B + 10 ° C.) < _TH <(thermoplastic resin A (Melting point of −20 ° C.). Further, it is desirable that the heat setting treatment time is at least 2 seconds or more in the above temperature range in order to obtain a sufficient effect. When T _H is below the above temperature range, re-melting of the resin constituting the B layer and rearrangement of particles in the B layer do not occur, and the desired projection shape cannot be obtained, and the heat of the entire film is not obtained. The contraction rate is adversely affected. On the other hand, when T _H is above the above temperature range, the mechanical properties of the film become remarkably insufficient, and any of them cannot be used.

Further, when the heat-setting treatment is performed, the standard deviation of the height of the protrusions in a desired range can be set by setting the conditions regarding the protrusions before and after the treatment to satisfy the expressions (1) to (3).
The average protrusion height and average protrusion diameter can be obtained more easily and reliably.

By performing the appropriate heat setting treatment as described above, the thermomechanical properties of the entire film are not impaired,
It is possible to obtain a film in the form of protrusions that satisfies the intended purpose. That is, the re-melting of the thermoplastic resin forming the B layer causes rearrangement of the contained inactive particles.
The rearrangement here means that the inert particles contained in the B layer are B
By controlling the position in the vicinity of the interface between the layer and the supporting layer A, the distribution in the thickness direction of the particles in the B layer becomes sharper. Therefore, the height of the protrusions becomes more uniform, the height itself decreases, and the shape of the protrusions becomes broader than that before the heat setting treatment.

Further, by remelting the thermoplastic resin constituting the B layer, the voids existing in the vicinity of the inert particles in the B layer after the biaxial stretching are extinguished at once, and as a result, the protrusion strength is remarkably improved. The effect is also recognized. This effect is particularly effective in the recent biaxially oriented film in which the stretching ratio is increased to increase the mechanical strength.

As described above, in the biaxially oriented thermoplastic resin film of the present invention, the support layer A bears the original mechanical strength, elastic modulus and heat shrinkage ratio of the film, and the coating layer B provides the conventional base film for magnetic media. It was developed to solve various problems that the company had. In order that the biaxially oriented thermoplastic resin film of the present invention exerts its characteristics, the thickness of the coating layer B is 10% or less, preferably 5% or less, more preferably 3% or less of the thickness of the entire film. The overall balance of performance will be excellent.

Next, the method for producing the biaxially oriented thermoplastic resin film of the present invention will be described more specifically. First, as a method of incorporating particles into the thermoplastic resins A and B,
Either after the polymerization, during the polymerization or before the polymerization may be used, but a method of kneading the polymer with a vent type twin-screw extruder is effective for obtaining the surface morphology within the scope of the present invention. Further, as a method of adjusting the content of particles, a high-concentration master is prepared by the above method, and the content of particles is adjusted by diluting it with a thermoplastic resin that does not substantially contain particles during film formation. The method is effective to obtain a surface morphology film within the scope of the present invention.

Thus, the pellets A of the thermoplastic resin A containing substantially no particles or containing particles are sufficiently dried and then fed to a known melt extruder at a temperature not lower than the melting point and not higher than the decomposition point of the thermoplastic resin. The thermoplastic resin B containing the other particles melted is supplied to the laminating apparatus as described above, extruded into a sheet form from a slit die, and cooled and solidified on a casting roll to produce an unstretched film. That is, these polymers are laminated using two or three extruders, a merging block or a die for two or three layers. When using the confluence block method, it is possible to stabilize the film having a surface morphology within the scope of the present invention by keeping the laminated portion rectangular as described above, without unevenness in the width direction,
It is effective for industrial production.

Next, the multilayer unstretched film is biaxially stretched and biaxially oriented. The method of biaxial stretching is simultaneous biaxial stretching,
Although it may be any of sequential biaxial stretching, in the case of a sequential biaxial stretching method of stretching in the longitudinal direction and the width direction in order, a film having a surface morphology within the scope of the present invention is stably produced without any unevenness in the width direction and industrially produced. It is effective to do. In the case of sequential biaxial stretching, stretching in the longitudinal direction is divided into two stages, particularly three or more stages, and 40 to 40
A method of performing 3 to 6 times in the range of 150 ° C. and a stretching rate of 1000 to 50000% / min is effective for obtaining a film having a surface morphology within the range of the present invention. Stretching temperature and speed in the width direction are 80 to 170 ° C. and 1000 to 20000.
A range of% / min is preferred. The draw ratio is preferably 3 to 10 times. Further, in order to further increase the mechanical strength, elastic modulus, etc. of the film, the film can be re-stretched in at least one of the longitudinal direction and the width direction. In any case, it is desirable to provide a very thin layer containing particles and then perform stretching at an area stretching ratio (longitudinal direction ratio × width direction ratio) of 9 times or more.

Next, this stretched film is heat-set.
The heat setting treatment condition in this case is loosening in the width direction, fine stretching, or under a fixed length. As described above, the heat setting treatment temperature ( _TH ) is set to (thermoplastic resin B Melting point) < _TH <(melting point of thermoplastic resin A) Preferably, (melting point of thermoplastic resin B + 10 ° C.) < _TH <(melting point of thermoplastic resin A−20 ° C.) is required. 14 for polyester
It is effective to obtain a biaxially oriented film having surface properties and mechanical properties within the scope of the present invention at 0 to 260 ° C., preferably 170 to 250 ° C., more preferably 200 to 240 ° C. for a minimum of 2 seconds or more. .. In addition, it is preferable to use microwave heating together with the heat setting treatment because a film having a surface morphology within the scope of the present invention can be easily obtained.

The feature of the production method of the film of the present invention is that after providing an extremely thin layer containing high concentration particles, the film is biaxially stretched, and after the coating layer becomes a single particle layer, it is heated at an appropriate temperature. By fixing treatment to make the height of the protrusions more uniform, to make the protrusion shape broader, and to eliminate voids that occurred during stretching, in the film forming process, after uniaxially stretching the film, coating etc. The film of the present invention is far inferior to the performance of the film of the present invention in the method of subjecting the film of the present invention to stretching, or a laminated film produced by coating a biaxially stretched film, and the film of the present invention is also excellent in cost.

[Physical Property Measuring Method and Effect Evaluation Method] The characteristic value measuring method and effect evaluating method of the present invention are as follows. (1) Average particle size of particles The thermoplastic resin is removed from the film surface by a plasma low temperature ashing method (for example, PR-503 type manufactured by Yamato Scientific Co., Ltd.),
Expose the particles. The treatment conditions are selected such that the thermoplastic resin is incinerated but the particles are not damaged. This is observed with a SEM (scanning electron microscope), and an image of the particles (light and shade of light generated by the particles) is analyzed by an image analyzer (for example, QTM90 manufactured by Cambridge Instruments).
0), the number of particles is measured, and the number of particles is changed, and the following numerical processing is performed when the number of particles is 5000 or more. The average diameter D thus obtained is taken as the average particle diameter. D = ΣDi / N Here, Di is the equivalent circle diameter of the particles, and N is the number.

(2) Content of Particles A solvent in which the thermoplastic resin is dissolved and the particles are not dissolved is selected, the particles are centrifuged from the thermoplastic resin, and the content of the particles is determined by the ratio (% by weight) to the total weight of the particles. And
In some cases, the combined use of infrared spectroscopy is also effective.

(3) Crystallization parameter ΔTcg, melting point T
m Perkin Elmer DSC (Differential Scanning Calorimeter) II
It was measured using a mold. The measurement conditions of DSC are as follows. That is, 10 mg of the sample is set in the DSC device,
After melting for 5 minutes at a temperature of 300 ° C., it is rapidly cooled 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 melting peak temperature was set to the melting point Tm. Further, the difference between Tcc and Tg (Tcc-Tg) is defined as the crystallization parameter ΔTcg.

(4) F-5 value A film cut into a width of 10 mm was set in a tensile tester so that the length between chucks was 100 mm, and the film was cut under the conditions of a pulling speed of 20 mm / min and a temperature of 25 ° C.
The strength corresponding to% elongation was measured.

(5) Average diameter of surface protrusions, average height, and standard deviation of height distribution 2 scanning electron microscope [ESM-3200, manufactured by Elionix Co., Ltd.] and cross-section measuring device [PMS-1] ，
Elionix Co., Ltd.] sends the measured value of the height of the projection when scanning is performed with the height of the flat surface of the film as 0, and sends it to the image processing device [IBAS2000, Carl Zeiss Co., Ltd.]. To reconstruct the film surface projection image. Next, the equivalent circle diameter is obtained from the area of each protrusion obtained by binarizing the protrusion portion in this surface protrusion image, and this is made the protrusion diameter. Further, 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 to determine the number of projections, and the average value of the diameters of all the measured projections was defined as the average projection diameter d, and the average value of the heights was defined as the average projection height h. Then, h / d was obtained as a parameter representing the shape of the protrusion. In addition, the standard deviation σ of the height distribution was obtained based on the height data of each protrusion. The value obtained by dividing the obtained standard deviation σ by the average value h of the heights was defined as the relative standard deviation σ / h. The magnification of the scanning electron microscope is selected to be 1000 to 8000 times. Depending on the case, a high-precision optical interference type three-dimensional surface analyzer (TOPO-3D manufactured by WYKO, objective lens:
The height information obtained by using a high resolution camera (40 to 200 times, effective use of a high resolution camera) may be read as the value of the SEM and used.

(6) Particle size ratio In the measurement of (1) above, the average value of the major axis of individual particles /
It is the ratio of the average value of the minor axis. That is, it is calculated by the following equation. Major axis = ΣD1i / N Minor axis = ΣD2i / N D1i and D2i are the major axis (maximum diameter) and minor axis (minimum diameter) of each particle, and N is the total number.

(7) Thickness of the coating layer B layer in the laminated film Using a secondary ion mass spectrometer (SIMS), the element and thermoplasticity attributable to the highest concentration of particles in the film The carbon atom concentration ratio (M ⁺ / C ⁺ ) of the resin is used as the particle concentration, and analysis is performed in the depth (thickness) direction from the surface of the coating layer B layer. 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 at the depth [I] starts to decrease again. Based on this concentration distribution curve, the depth at which the maximum particle concentration is 1/2 [II]
(Here, II> I) was defined as the laminated thickness. The measuring device and conditions are as follows. Measuring device Secondary ion mass spectrometer (SIMS) West Germany, ATOMIKA, A-DIDA3000 Measuring conditions Primary ion species: O ₂ ⁺ Primary ion accelerating voltage: 12 kV Primary ion current: 200 nA Raster area: 400 μm □ Analysis area : Gate 30% Measured vacuum degree: 6.0 × 10 ⁹ Torr E-GUN: 0.5 kV-3.0A If the most abundant particles in the film are organic polymer particles, the measurement can be performed by SIMS. Because it ’s difficult
While etching from the surface, the depth profile of the particle concentration is measured by XPS (X-ray photoelectron spectroscopy), IR (infrared spectroscopy) or a confocal microscope, and the layer thickness can be obtained by the same method as above. Good.

(8) Coefficient of friction μk A tape running test machine SFT-700 type (manufactured by Yokohama System Laboratories) was used to slit a film into a tape having a width of 1/2 inch at 25 ° C. and 65% RH atmosphere. The vehicle was run underneath, and the initial friction coefficient was obtained from the following formula. μk = 0.733 log (T ₂ / T ₁ ) where T ₁ is the inlet tension and T ₂ is the outlet tension. The guide diameter is 6 mmφ, the guide material is SUS27 (surface roughness 0.2S), the winding angle is 180 degrees, and the running speed is 3.
It is 3 cm / sec.

(9) Scratch resistance A film slit into a tape having a width of 1/2 inch is run on a guide pin (surface roughness: Ra of 100 nm) using a tape running tester. (Running speed 1
000m / min, 10 passes, winding angle: 60
Degree, running tension: 90 g) At this time, scratches in the film are observed with a microscope, and scratches with a width of 2.5 μm or more are excellent when less than 2 per tape width, excellent when 2 or more and less than 10 are good, 10 or more Was judged to be defective. Good is desirable, but good is practically usable.

(10) Protrusion Breaking Strength A film slit into a tape having a width of 1/2 inch is repeatedly run on a guide pin using a tape running tester. (Guide material: SUS, surface roughness:
0.3S) A load of 200 g is applied to one end of the film, the film is run for 20 passes at a wrapping angle of 90 degrees and a running speed of 3.3 cm / sec, and then the amount of white powder adhering to the guide pins is evaluated. Was observed with a differential interference microscope to evaluate the damage of protrusions and the state of dropout of particles. Magnification 1
Observed in 10 fields of view at a magnification of 000, and the ratio of the locations where the particles fall out relative to the total number of protrusions is excellent (almost no particles are found), good (some particles are found, but the amount of white powder is very small), poor (A large number of particles dropped out and a large amount of white powder adhered) were used for the three-level evaluation.

[0050]

EXAMPLES The present invention will be described below based on examples. Examples 1 to 5 and Comparative Examples 1 to 4 Ethylene glycol slurries containing spherical silica particles derived from colloidal silica having different average particle sizes were prepared, and the ethylene glycol slurries were heated at 190 ° C. 1.5.
After heat treatment for a period of time, polycondensation was performed, and pellets of polyethylene terephthalate (hereinafter abbreviated as PET) containing a predetermined amount of particles were prepared by a conventional method. Further, a pellet of polyethylene terephthalate / isophthalate copolyester (hereinafter abbreviated as PET / I) containing substantially no particles was prepared, and a thermoplastic resin B was prepared by blending the above two pellets (isophthalate. Concentration 12 mol). On the other hand, a PET containing substantially no particles was produced by a conventional method and designated as a thermoplastic resin A.
Each of these polymers was dried under reduced pressure (3 Torr) at 180 ° C. for 3 hours and then melted by a separate extruder,
A confluent block having a rectangular laminated portion is confluently laminated before entering the mouthpiece, and is wound around a casting drum having a surface temperature of 45 ° C. by an electrostatic applied casting method to be cooled and solidified, and has a thermoplastic resin B layer on one side. An unstretched film of layer or tri-layer structure was made. At this time, the discharge amount of each extruder was adjusted to adjust the total thickness and the thickness of the coating layer B layer. This unstretched film was stretched 4.5 times in the longitudinal direction at a temperature of 80 ° C. This stretching was carried out in four stages with the difference in peripheral speed between each pair of rolls. This uniaxially stretched film was stretched 4.0 times in the width direction at 100 ° C. at a stretching speed of 2000% / min using a stenter, and heat-set at a predetermined temperature for 5 seconds under a constant length to give a total thickness of 12 μm and a layer B. A biaxially oriented film having a thickness of 0.15 to 1 μm was obtained. The scratch resistance of the coating layer B layer side of this film was evaluated, and the dropout property of particles from the film surface due to the strength of each protrusion was evaluated.

The respective parameters of the base film are as shown in Tables 1 and 2. When these are within the scope of the present invention, the scratch resistance and the protrusion strength are as shown in Tables 1 and 2. , They showed good characteristics, but otherwise they could not be combined.

[0052]

[Table 1]

[0053]

[Table 2]

[0054]

EFFECTS OF THE INVENTION By using the biaxially oriented thermoplastic resin film of the present invention, the generation of shavings due to the loss of particles in the magnetic recording medium manufacturing process, which has been a problem with conventional films, is significantly reduced. It was possible to manufacture a high-performance video tape having a high degree of electromagnetic conversion characteristics with a high drop resistance and a high degree of scratch resistance.

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Claims (4)

[Claims] 1. The ratio (σ / h) of the standard deviation σ of the protrusion heights of at least one surface to the average protrusion height h is 0.5 or less, and the average protrusion height h of the surface and the average protrusion height are 0.5 or less. A biaxially oriented thermoplastic resin film having a ratio (h / d) to the diameter d of 0.17 or less. 2. A layer containing a thermoplastic resin A as a main component (A
Layer) and the thermoplastic resin B on at least one surface thereof and an average particle size of 0.
A layer containing inactive particles of 0.5 to 1.0 μm as a main component (B
A biaxially oriented thermoplastic resin film in which the content of the particles in the B layer is 0.5 to 20% by weight, and the average particle size is 1.0 to 10.0 times the B layer thickness. The biaxially oriented thermoplastic resin film according to claim 1, wherein 3. The sum of F-5 values in the longitudinal direction and the width direction is 28.
The biaxially oriented thermoplastic resin film according to claim 1 or 2, which has a kg / mm ² or more. 4. The average protrusion height on the B layer surface before heat setting treatment is h ₁ , the average protrusion diameter is d ₁ , the standard deviation of the protrusion height is σ ₁ , and the average protrusion on the B layer surface after heat setting treatment. Height is h ₂ ,
When the average projection diameter is d ₂ and the standard deviation of the projection height is σ ₂ , heat setting treatment is performed under conditions satisfying the relationships of the following expressions (1) to (3). 3. The method for producing a biaxially oriented thermoplastic resin film of 3. h ₂ <h ₁ (1) σ ₂ / h ₂ <σ ₁ / h ₁ (2) h ₂ / d ₂ <h ₁ / d ₁ (3)