JPH07118078B2 - Magnetic recording medium - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a coating type magnetic recording medium.

[Prior Art] As a coating-type magnetic recording medium, there is known a magnetic recording medium in which a coating-type magnetic layer is provided on a polyester film (for example, JP-A-60-66319).

[Problems to be Solved by the Invention] In a magnetic recording medium, since the S / N (signal / noise ratio is higher and the higher the quality, the better the image quality) in high density recording, the surface of the magnetic layer is further smoothed. There is. But,
When the surface of the magnetic layer becomes smooth, the friction coefficient during running becomes large and its durability becomes poor, and there is a problem that the S / N decreases greatly due to repeated running during use. If you try to improve the durability by roughening the surface of the magnetic layer
I had a dilemma that the S / N would be low. The present invention solves this problem, and has a high S / N and S
An object of the present invention is to provide a magnetic recording medium with a small decrease in / N.

[Means for Solving the Problems] The present invention is a magnetic recording medium having a coating type magnetic layer provided on at least one surface of a substrate film, wherein the peak number (SPc) of the irregularities on the surface of the magnetic layer is 100. The magnetic recording medium described above is characterized by having a 10-point average roughness SRz of 500 nm or less.

In the present invention, the thermoplastic resin constituting the base film is not particularly limited to polyester, polyolefin, polyamide, polyphenylene sulfide, etc., but particularly polyester, especially ethylene terephthalate, ethylene α, β-bis (2-chloro) Phenoxy) ethane-4,
When at least one structural unit selected from 4'-dicarboxylate and ethylene 2,6-naphthalate units is the main constituent, the running property is further improved, which is desirable.

Further, when the above-mentioned substrate film has the following characteristics, it is extremely effective for obtaining the magnetic layer surface of the present invention, and the S / N can be further increased and the S / N reduction can be further reduced. So desirable. That is, the base film has a thickness of 0.005 to 3 μm, preferably 0.01 to 2 μm, and more preferably 0.03 to 0.8 μ, whose main component is thermoplastic resin A and particles on at least one surface layer.
A biaxially oriented thermoplastic resin film having a film layer A of m (the surface of the A layer is a characteristic surface), wherein the average particle size of the particles contained in the film layer A is 0 of the thickness of the film layer A. .
1 to 10 times, preferably 0.4 to 5 times, more preferably 1.1
~ 3 times, the content of the particles is 1 to 30% by weight, preferably 2
When the content is from 20 to 20% by weight, more preferably from 3 to 15% by weight, the base film is a biaxially oriented thermoplastic resin film, and the average height of surface protrusions on at least one surface (characteristic surface) of the film is particles in the film. 1/4 or more of the average particle size, preferably 1 / 3.5 or more, more preferably 1/3 or more, and,
When the number of protrusions is 10,000 / mm ² or more, preferably 50,000 / mm ² or more, more preferably 100,000 / mm ² or more, the substrate film is a biaxially oriented thermoplastic resin film, On at least one surface (characteristic surface), the number of protrusions having a height of 1/3 or less of the average particle diameter of the particles in the film is 70% or less of the total number of protrusions, preferably 65% or less, more preferably 60% or less. When the base film is a biaxially oriented thermoplastic resin film, the relative standard deviation of the surface projection height distribution of at least one surface (characteristic surface) is 0.60 or less, preferably 0.55 or less, more preferably 0.50 or less In some cases, the base film is a biaxially oriented thermoplastic resin film, and the F5 value in the longitudinal direction thereof is 15 kg / mm ² or more, preferably 18
This is the case of kg / mm ² or more.

Here, the kind of the thermoplastic resin A in the above case is not particularly limited, but a crystalline thermoplastic resin such as polyester, polyolefin, polyamide, polyphenylene sulfide, among others, polyester, polyphenylene sulfide,
Particularly, polyester is preferably used. Among the polyesters, ethylene terephthalate, ethylene α, β-bis (2-chlorophenoxy) ethane-4,4 ′
A polymer having at least one structural unit selected from dicarboxylate and ethylene 2,6-naphthalate units as a main constituent is desirable for obtaining the surface morphology within the scope of the present invention. The crystallinity here means that it is not so-called amorphous, and quantitatively, it is a differential scanning calorimeter (DSC).
The melting point is detected by thermal analysis at a temperature rising rate of 10 ° C./min., And the crystallization parameter ΔTcg is preferably 150 ° C. or less. Furthermore, when the heat of fusion (change in enthalpy of fusion) measured by a differential scanning calorimeter shows a crystallinity of 7.5 cal / g or more, the S / N becomes even better, which is highly desirable.

In addition, the particles in the film layer A are not particularly limited, but in the case of spherical particles having a particle size ratio (major axis / minor axis of particles) of 1.0 to 1.3, the magnetic layer surface morphology of the present invention is easily obtained, and ,
It is desirable because the S / N can be made higher and the S / N reduction can be made smaller.

The relative standard deviation of the particles in the film layer A is 0.6 or less,
A ratio of 0.5 or less is preferable because the surface morphology of the magnetic layer of the present invention can be easily obtained, and the S / N can be further increased and the S / N reduction can be further reduced.

Examples of the types of particles include substantially spherical silica particles derived from colloidal silica and particles formed by a crosslinked polymer (for example, crosslinked polystyrene, silicone, polyimide, etc.) in order to satisfy the above desired characteristics, but are not limited to these. However, other particles, for example, titanium dioxide, alumina, calcium carbonate, kaolinite, and other conventionally known particles can be used by devising the film forming method.

Particle size is not particularly limited, but average particle size (diameter)
Of 5 to 2000 nm, particularly 10 to 1500 nm, and more preferably 10 to 500 nm, the magnetic layer surface morphology of the present invention is easily obtained, and S /
It is desirable because N can be made higher and S / N reduction can be made smaller.

Further, in the thermoplastic resin portion other than the film layer A, within a range not hindering the present invention, preferably within a range of 1% by weight or less,
Particles larger than the particles of the film layer A, particles of the same size, particles of a small size, or a mixture thereof may be contained.

Further, the base film of the present invention has a composition comprising a thermoplastic resin and particles as a main component, but may be blended with various polymers within a range not impairing the object of the present invention, and an antioxidant, Organic additives such as heat stabilizers, lubricants, and ultraviolet absorbers may be added to the extent that they are usually added.

Further, the total reflection Raman crystallization index of the characteristic surface of the substrate film constituting the present invention (the surface of the film layer A, or the surface whose surface morphology has the specific characteristics defined in the present invention) is 20 cm ^-1.
The magnetic layer surface morphology of the present invention is easily obtained in the following cases,
Further, it is desirable because the S / N can be further increased and the S / N reduction can be further reduced.

The surface layer particle concentration ratio measured by the secondary ion mass spectrum of the above-mentioned characteristic surface of the substrate film constituting the present invention is not particularly limited, but the surface layer particle concentration ratio is 1/10 or less, particularly
When it is 1/50 or less, the running property and the output property are further improved, which is particularly desirable. This surface layer particle concentration ratio is not obtained by the conventional coating method or coating / stretching method, and by setting the surface layer particle concentration ratio within this range, the magnetic layer surface morphology of the present invention can be easily obtained, and Higher S / N and smaller S / N reduction are desirable,
Further, the abrasion resistance of the film surface is improved, and troubles due to particles falling off in the film forming process, the magnetic layer coating process and the processing process such as calendering are greatly improved.

The present invention is a magnetic recording medium comprising a coating type magnetic layer provided on at least one surface of the above biaxially oriented thermoplastic resin film. The magnetic powder used is not particularly limited, but iron oxide, chromium oxide, oxides such as Co-adhered iron oxide, or metals or alloys such as Fe, Co, Fe-Co, Fe-Co-Ni, and Co-Ni. , Alloys of these with Al, Cr, Si, etc. are used, but in particular, a simple metal (including an alloy) that is not substantially an oxide, that is, the magnetic layer of the present invention when the magnetic layer is a metal coating type. It is desirable because the surface morphology can be easily obtained, the S / N can be further increased, and the S / N reduction can be further reduced.

The magnetic powder can be made into a magnetic coating using various binders, but in general, thermosetting resin-based binders and radiation-curable binders are preferable, and other additives such as dispersants, lubricants, and antistatic agents are used according to a conventional method. You may use. For example, a binder made of vinyl chloride / vinyl acetate / vinyl alcohol copolymer, polyurethane prepolymer and polyisocyanate can be used.

The thickness of the magnetic layer is not particularly limited, but it is easy to obtain the surface morphology of the magnetic layer of the present invention by setting it in the range of 0.5 to 5 μm, and the S / N can be further increased and the S / N reduction can be further reduced. desirable.

Peak count of the surface of the magnetic layer of the magnetic recording medium of the present invention
SPc is 100 or more, preferably 150 or more, more preferably 2
It must be at least 00. If the SPc is smaller than the above range, the S / N ratio will decrease due to repeated running and the durability will be poor, such being undesirable. The upper limit of SPc is not particularly limited, but usually about 5000 is a manufacturing limit.

The SRz of the surface of the magnetic layer is 500 nm or less, preferably 400 nm.
Hereafter, it is necessary that the thickness be 200 nm or less. When SRz is larger than the above range, the S / N is lowered, the image quality is deteriorated, and the S / N deterioration is apt to be large, which is not preferable. The lower limit of SRz is not particularly limited, but usually about 5 nm is the manufacturing limit.

Further, in the magnetic recording medium of the present invention, when the magnetic layer has only one surface, the opposite side may be subjected to so-called back coating treatment. The thickness of the back coat layer in this case is 0.1 ~
1.5 μm, average surface roughness Ra is 5-200 nm, preferably 10-
A range of 100 nm is desirable because the surface morphology of the magnetic layer of the present invention can be easily obtained, the S / N can be further increased, and the S / N reduction can be further reduced.

Next, a method of manufacturing the magnetic recording medium of the present invention will be described.

First, a method for producing a biaxially oriented thermoplastic resin film having a characteristic surface, which is desirable for a substrate, will be described.

As a method of incorporating particles into a thermoplastic resin, a method of adding the particles to a thermoplastic resin by using ethylene glycol slurry as a slurry or using a vent-type twin-screw kneading extruder without stretching breakage, It is extremely effective in obtaining the base film desired in the present invention.

As a method of adjusting the content of particles, a method of preparing a high-concentration master by the above method and diluting it with a thermoplastic resin that does not substantially contain particles during film formation is a method of adjusting the content of particles. It is valid.

Next, the pellets of the thermoplastic resin A containing particles are dried, if necessary, and then supplied to a known melt laminating extruder, extruded into a sheet from a slit die, and cooled and solidified on a casting roll. And the thickness of the A layer is A
Make an unstretched film that is 0.8 to 80 times the average particle size of the particles contained in the layer. That is, using two or three extruders, a two- or three-layer manifold or a merging block, thermoplastic resins A and B are laminated, two or three-layer sheets are extruded from a die, and cooled by a casting roll. Make an unstretched film. In this case, a method of installing a static mixer and a gear pump in the polymer channel of the thermoplastic resin A is extremely effective for obtaining a base film which is desirable for the present invention without stretching breakage.

Further, it is extremely effective to use a feed block having a rectangular confluent section as the confluent block in order to obtain the base film desired in the present invention.

In the above description, A / B and A / B / A were mainly described as the configuration (a characteristic surface is the layer A surface), but in the case of the configuration of A / B / C, 3
Similarly, using a three-stage extruder or a three-layer manifold or confluent block, the thermoplastic resins A, B, and C are laminated, the three-layer sheet is extruded from the die, cooled by a casting roll, and unstretched. Make a film. In any case, A, B, and C may be the same thermoplastic resin or different (the surfaces of the A and C layers are characteristic surfaces).

Next, this unstretched film is biaxially stretched and biaxially oriented. As the stretching method, a known biaxial stretching method or a simultaneous biaxial stretching method, which is performed in the order of longitudinal → horizontal or lateral → vertical, can be used. The stretching conditions cannot be generally stated depending on the type of thermoplastic resin, but it is desirable that the product of the longitudinal ratio and the lateral ratio is 8 times or more as the stretching ratio. It is effective in optimizing and biaxially orienting polymer molecules near the characteristic surface, and obtaining desired mechanical properties of the entire film. The fact that the polymer molecules in the vicinity of the characteristic surface are biaxially oriented means that this film has a coating method or coating
This is a point greatly different from the film produced by the stretching method, and the surface morphology of the magnetic layer of the present invention is easily obtained, and S /
N is higher and S / N lowering can be further reduced, which is desirable. Also, the abrasion resistance of the film surface is improved, and troubles due to particles falling off during the film forming process, magnetic layer coating, calendering, and other processing processes are greatly reduced. It is what is done.

Further, a method of re-stretching the biaxially oriented film in at least one direction is effective for obtaining desired mechanical properties. Then, this stretched film is
It is preferable to carry out the reaction in the temperature range of -100 ° C for 0.5 to 60 seconds.

Next, a predetermined magnetic layer is applied to this base film. The method of applying the magnetic layer can be carried out by a known method, but the method of applying with a gravure roll or giesa is easy to obtain the magnetic layer surface morphology of the present invention, and the S / N is higher and the S / N is higher. This is desirable because the reduction can be further reduced.

The temperature of the drying step after coating is preferably 90 to 120 ° C.

Further, the calendering step, using a polyamide-based resin or a polyester-based resin for the elastic roll, it is easy to obtain the magnetic layer surface morphology of the present invention to be carried out in the temperature range of 25 to 90 ° C., and the S / N is further increased. , S / N can be further reduced, which is desirable. The pressure during calendar is 100-500kg / c
The range of m is desirable because the surface morphology of the magnetic layer of the present invention can be easily obtained, the S / N can be further increased, and the S / N reduction can be further reduced.

Next, the raw material coated with the magnetic layer is wound and cured in the form of a roll to cure the magnetic layer. Cure temperature condition is 40 ~
The range of 100 ° C. is preferable because the surface morphology of the magnetic layer of the present invention can be easily obtained, the S / N can be further increased, and the S / N reduction can be further reduced.

Although the surface of the magnetic layer of the present invention can be obtained by finely adjusting the production conditions of such a magnetic recording medium, the magnetic recording medium produced under the following conditions using the preferred base film described in the present invention is a magnetic layer of the present invention. The surface morphology is easily obtained, the S / N is further increased, and the S / N reduction can be further reduced, which is particularly desirable.

In other words, (a) When the magnetic layer is applied to the characteristic surface of the base film (including the case where a pretreatment such as undercoating is applied to the characteristic surface, etc.): Both sides of the base film have a characteristic surface and a coated surface. The characteristic surface and the opposite surface correspond to the normal surface.-Calendar temperature: 75 to 90 ° C-Calendar pressure: 170 to 500 kg / cm-Cure temperature: 40 to 70 ° C (2) Apply the magnetic layer on the opposite side of the characteristic surface of the base film. Case: Normal surface of the base film corresponds to the characteristic surface, and the opposite surface corresponds to the characteristic surface.-Calendar temperature: 20-80 ° C-Calendar pressure: 100-300kg / cm-Cure temperature: 55-90 ° C Furthermore, this magnetic recording medium The original fabric (wide width) is slit to obtain a magnetic recording medium. Further, the magnetism when the back coat is provided on the side opposite to the magnetic layer is not particularly limited, and may be before coating the magnetic layer, before calendering, after calendering or before curing, or after curing.

[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) Average particle size of particles The thermoplastic resin is removed from the film surface by a plasma low temperature ashing method to 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 scanning electron microscope (SEM), and the image of the particles is processed with an image analyzer. The following numerical processing is performed when the number of particles is 5,000 or more while changing the observation location, and the number average diameter D thus obtained is taken as the average particle diameter.

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

(2) Particle size ratio This is the ratio of (average value of major axis) / (average value of minor axis) of individual particles 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 number of particles.

(3) Relative standard deviation of particle size Standard deviation σ (= {Σ (Di-
D) ² / N} ^1/2 ) was divided by the average diameter D to express (σ / D).

(4) Content of particles A solvent that dissolves the thermoplastic resin and does not dissolve the particles is selected, the particles are centrifuged from the thermoplastic resin, and the ratio (% by weight) to the total weight of the particles is defined as the particle content.

(5) Crystallization parameter ΔTcg, heat of fusion It was measured using a differential scanning calorimeter (DSC). The DSC measurement conditions are as follows. That is, 10 mg of a sample is set in a DSC apparatus, melted at a temperature of 300 ° C. for 5 minutes, and then 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. When the temperature rises further, the crystallization exothermic peak temperature from the glass state is reached and the cold crystallization temperature Tcc
And 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.

(6) F5 value In accordance with the method specified in JIS-Z-1702, using an Instron type tensile tester, 25 ℃, 65% RH
It was measured at.

(7) Total reflection Raman crystallization index The total reflection Raman spectrum was measured, and the half-value width of 1730 cm ^-1 , which is the stretching vibration of the carbonyl group, was used as the total reflection Raman crystallization index of the surface. The measurement conditions are as follows. However, the measurement depth was about 500 to 1,000Å from the surface.

Light source Argon ion laser (5,145Å) Setting the sample Press the film surface to the total reflection prism so that the laser polarization direction (S polarization) and the film longitudinal direction are parallel, and the incident angle of the laser to the prism (the film thickness direction) The angle) was 60 °.

Detector PM: RCA31034 / Photon Counting System (Hamamatsu C123
0) (supply 1,600V) Measuring condition SLIT 1,000μm LASER 100mW GATE TIME 1.0sec SCAN SPEED 12cm ^-1 / min SAMPLING INTERVAL 0.2cm ^-1 REPEAT TIME 6 (8) Surface molecular orientation (refractive index) Sodium D line (589nm) ) Was used as a light source, and an Abbe refractometer was used for measurement. Methylene iodide was used as the mount solution, and measurement was performed at 25 ° C. and 65% RH. The biaxial orientation of the polymer is such that the absolute value of (N1-N2) is 0.07 or less, and N3 / when the refractive indices in the longitudinal direction, the width direction, and the thickness direction are N1, N2, and N3.
One of the criteria is that [(N1 + N2) / 2] is 0.95 or less. Further, the refractive index may be measured using a laser type refractometer. Further, when the measurement is difficult by this method, the total reflection laser Raman method can be used. Ramanor manufactured by Jobin-Yvon is used for the measurement of laser total reflection Raman.
The total reflection Raman spectrum was measured by the U-1000 Raman system. For example, in the case of polyethylene terephthalate, it was 1615 cm ^-1 (skeleton vibration of benzene ring) and 1730 cm.
Polarization measurement ratio of ^-1 (stretching vibration of carbonyl group) band intensity ratio (YY / XX ratio, etc. where YY: laser polarization direction is Y
That is, Raman light detection parallel to Y and XX: Raman light detection parallel to X where X is the polarization direction of the laser) correspond to the molecular orientation. The biaxial orientation of the polymer is the parameter obtained from Raman measurement in the longitudinal direction,
It can be determined from the absolute value, the difference, etc. by converting it into the refractive index in the width direction. The measurement conditions in this case are as follows.

Light source Argon ion laser (5145Å) Sample setting The film surface was pressed onto a total reflection prism, and the angle of incidence of the laser on the prism (angle with the film thickness direction) was 60 °.

Detector PM: RCA31034 / Photon Counting System (Hamamatsu C123
0) (supply 1600V) Measurement condition SLIT 1000μm LASER 100mW GATE TIME 1.0sec SCAN SPEED 12cm ^-1 / min SAMPLING INTERVAL 0.2cm ^-1 REPEAT TIME 6 (9) Surface particle concentration ratio Using secondary ion mass spectrum (SIMS) The concentration ratio of the element having the highest concentration among the elements originating from the particles in the film and the carbon element of the thermoplastic resin is taken as the particle concentration, and the analysis in the thickness direction is performed. The ratio of the particle concentration A at the outermost surface particle concentration (point at the depth of 0) measured by SIMS and the maximum concentration B obtained by continuing the analysis in the depth direction, A / B was defined as the surface layer particle concentration ratio. The measuring device and conditions are as follows.

Primary ion species: O ₂ ⁺ Primary ion acceleration voltage: 12KV Primary ion current: 200nA Raster area: 400μm □ Analysis area: Gate 30% Measuring vacuum degree: 6.0 × 10 ^-9 Torr E-GUN: 0.5KV-3.0 A (10) Surface projection height, height analysis, number 2 Detector scanning electron microscope [ESM-3200, Elionix Co., Ltd.] and cross-section measuring device [PMS-1, Elionix Co., Ltd.] In, the height of the flat surface of the film surface was scanned as 0 and the measured height of the projection was sent to the image processing device [IBAS2000, Carl Zeiss Co., Ltd.] and the film surface projection image was re-displayed on the image processing device. To construct. 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 set as 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 to determine the number of protrusions, and the average value of the heights of all the measured protrusions was taken as the average height. In addition, the standard deviation of the height distribution was calculated based on the height data of each protrusion. The relative standard deviation is the value obtained by dividing this standard deviation by the average height. The magnification of the scanning electron microscope is selected to be a value between 1000 and 8000 times. Depending on the case, a high-precision optical interference type three-dimensional surface analyzer (TOPO-3D manufactured by WYKO, objective lens: 40 to 200)
Height information obtained by using a double high-resolution camera is effective) may be used instead of the SEM value.

(11) Surface morphology of magnetic layer Non-contact surface roughness meter HIPOS (Model ET-30HK) from Kosaka Laboratory
Was used to measure the three-dimensional roughness. The conditions are as follows, and the average value of 20 measurements was taken as the value.

・ Vertical magnification: 20,000 times ・ Horizontal magnification: 500 times ・ Cutoff: 0.08 mm ・ Feeding pitch: 0.5 μm ・ Measuring length: 500 μm ・ Measuring area: 0.0194 mm ²・ Scanning speed: 100 μm / sec ・ HYST: ± 5 nm average The surface roughness SRz is the average roughness of 10 points obtained by the above measurement, and the number of peaks SPc is the number of peaks when the number of peaks protruding from the bottom across the central plane ± 5 nm region is counted as one, that is, HYST: Peak number at ± 5 nm,
It is converted to 0.1 mm ² .

(12) Surface roughness parameter Ra of back coat Measured using a surface roughness meter. The conditions are as follows, and the average value of 20 measurements was taken as the value.

・ Stylus tip radius: 0.5μm ・ Stylus load: 5mg ・ Measuring length: 1mm. Cut-off value: 0.08mm (13) Laminated thickness of base film Due to the highest concentration of particles in the film in the depth range of 3000nm from the surface layer using the secondary ion mass spectrometer (SIMS) The concentration ratio (M ⁺ / C ⁺ ) of the element to be used and the carbon element of polyester is used as the particle concentration, and the analysis in the thickness direction from the surface to a depth of 3000 nm is performed. 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 desirable film forming the present invention, the particle concentration, which once reached the maximum value, usually starts to decrease again. Based on this concentration distribution curve, the depth at which the surface layer particle concentration becomes 1/2 of the maximum value of (the depth is deeper than the maximum value) was obtained and used as the stack thickness. The conditions are as follows.

Measuring instrument Secondary ion mass spectrometer (SIMS) A-DIDA3000 manufactured by ATOMIKA, West Germany Measuring conditions Primary ion species: O ₂ ⁺ Primary ion accelerating voltage: 12KV Primary ion current: 200nA Raster area: 400μm □ Analysis area: Gate 30% Measurement vacuum degree: 5.0 × 10 ^-9 Torr E-GUN: 0.5KV-3.0A In addition, it is difficult to measure with SIMS when the most contained particles in the depth range from the surface layer to 3000 nm are organic polymer particles. Therefore, while etching from the surface, the depth profile similar to the above may be measured by XPS (X-ray photoelectron spectroscopy), IR (infrared spectroscopy), etc. to obtain the laminated thickness, or the cross section by an electron microscope or the like. It is also possible to recognize the interface from the state of change in particle concentration and the difference in contrast by observation to determine the layer thickness.

(14) S / N of magnetic recording medium An 8mm VTR tape was built by incorporating the magnetic recording medium into a VTR cassette. Using a VTR for home use on this tape, 100% chroma signal was recorded by a TV test waveform generator (TG7 / U706) made by Shibasoku, and from the reproduced signal, chroma S was made by a color video noise measuring instrument made by Shibasoku (925D / 1). / N was measured.

Comparing this chroma S / N with commercially available Ni8 tape (8 mm VTR tape for high band, Hi8MP120 made by SONY), S / N is 1
It was judged that the S / N was good when it was higher than dB, and the S / N was poor when it was less than 1 dB.

(15) Durability of magnetic surface The above tape was reproduced 1,000 times under the condition of 40 ° C and 80% RH using SONY Hi8VTR, and after repeating rewinding, the above S / N was measured again and the S / N declined. It was determined that the durability was good when it was less than 1 dB compared to that before running, and the durability was poor when it was 1 dB or more.

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

Examples 1 to 10 and Comparative Examples 1 to 6 Ethylene glycol slurries containing cross-linked polystyrene particles having different average particle diameters and spherical silica particles derived from colloidal silica were prepared, transesterified with dimethyl terephthalate, and polycondensed. , Polyethylene terephthalate containing 1 to 35% by weight of the particles (hereinafter abbreviated as PET)
Pellets were made (thermoplastic resin A). Further, PET containing 0.2% by weight of spherical silica particles (average diameter 0.2 μm) derived from colloidal silica was produced by a conventional method, and was designated as a thermoplastic resin B.

Each of these polymers was dried under reduced pressure at 180 ° C for 6 hours (3To
rr), and then the thermoplastic resin B is supplied to the extruder 1 at 310 ° C.
Melt, and then the thermoplastic resin A is supplied to the extruder 2 and melted at 280 ° C., these polymers are combined and laminated in a confluent block, and a surface temperature of 30 ° C. is obtained by using an electrostatically applied casting method.
It was wound around a casting drum of No. 1 and cooled and solidified to make a laminated unstretched film. At this time, the discharge amount of each extruder was adjusted to adjust the total thickness and the thickness of the thermoplastic resin A layer.

This unstretched film was stretched 4.0 times in the longitudinal direction at a temperature of 80 ° C. This stretching was carried out in three 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 2,000% / min using a stenter, and then re-stretched 1.6 times in the longitudinal direction, and then stretched at a constant length to 190 times.
Heat treatment was performed at 5 ° C. for 5 seconds to obtain a biaxially oriented laminated film having a total thickness of 7 μm. Further, 0.2% by weight of spherical silica having a diameter of 0.2 μm and 0.05% by weight of spherical silica having a diameter of 0.6 μm are prepared by a known method.
A biaxially oriented monolayer film having a total thickness of 7 μm containing Further, a biaxially oriented monolayer film containing 6% by weight of spherical silica having a diameter of 0.3 μm in the entire film was obtained.

A magnetic coating was applied to these films using a gravure roll on the surface (characteristic surface) on the layer A side. The magnetic paint was prepared as follows.

・ Fe 100 parts Average particle size Length: 0.3 μm Needle ratio: 10/1 Coercive force 2000 Oe ・ Polyurethane resin 15 parts ・ Vinyl chloride / vinyl acetate copolymer 5 parts ・ Nitrocellulose resin 5 parts ・ Oxidation Aluminum powder 3 parts Average particle size: 0.3 μm ・ Carbon black 1 part ・ Lecithin 2 parts ・ Methyl ethyl ketone 100 parts ・ Methyl isobutyl ketone 100 parts ・ Toluene 100 parts ・ Stearic acid 2 parts After mixing and dispersing the above composition in a ball mill for 48 hours The kneaded product obtained by adding 6 parts of the curing agent was filtered with a filter to prepare a magnetic coating liquid, which was coated on the film, magnetically oriented, dried at 110 ° C., and further a small test calender device (steel). Roll / nylon roll (5 steps), temperature and linear pressure are changed, calendered, rolled into a roll, temperature is changed in the range of 10 to 150 ° C, curing is applied for 48 hours, and coating type It was got distracted recording medium.

The characteristics of these magnetic recording media are as shown in Tables 1 and 2, and the coating type magnetic recording media satisfying the requirements of the present invention have a high S / N and S after repeated running. Although the / N drop is small and the durability is excellent, it is understood that a magnetic recording medium satisfying the above cannot be obtained if it is not.

Comparative Example 7 On one side of the biaxially oriented single layer film obtained in Comparative Example 4, spherical silica particles having an average particle size of 0.7 μm were dried in a vinyl chloride binder so that the weight of the spherical silica particles became 10% by weight (about 5% by volume). Apply the contained coating liquid by a known method and dry it to a thickness of 1.5μ.
m coating film was formed. Further, a magnetic layer was provided on the coating film to obtain a coating type magnetic recording medium.

The number of peaks and depressions on the magnetic layer surface of the obtained magnetic recording medium (SP
c) is 70 pieces / 0.1 mm ² , 10-point average roughness SRz is 35 nm, S / N of the magnetic recording medium is 0.9 dB, and durability of magnetic surface (after running)
S / N decrease) was 3.5 dB.

[Advantages of the Invention] In the present invention, the surface of the magnetic layer of the magnetic recording medium is significantly changed from the conventional one, and a large number of minute irregularities are formed. As a result, the abrasion resistance can be improved while suppressing the generation of noise. / N
Is high, and a magnetic recording medium having a small S / N reduction after repeated running and excellent durability is obtained, and by using a special substrate film, the surface of the magnetic layer is easily obtained, In addition, the S / N was made higher, and the S / N reduction could be made smaller.

The magnetic recording medium of the present invention is useful for all applications such as video tapes, floppy disks, video floppies, audio tapes, memory tapes, etc.
It is especially useful for high-density magnetic recording media for video, 8 mm high-band video, SVHS video, digital video, HDTV (high definition TV, high-definition television), etc., or video tapes for software that is often used repeatedly.

Claims (7)

[Claims] 1. A magnetic recording medium comprising a coating type magnetic layer provided on at least one side of a substrate film, wherein the number of peaks (SPc) of irregularities on the surface of said magnetic layer is 100 or more and a 10-point average roughness. A magnetic recording medium characterized in that SRz is 500 nm or less. 2. A base film having a thickness of 0.005 to 3 containing a thermoplastic resin A and particles as main components on at least one surface layer of the base film.
A biaxially oriented thermoplastic resin film having a film layer A of μm, wherein the average particle size of the particles contained in the film layer A is 0.1 to 10 times the thickness of the film layer A, and the content of the particles is The magnetic recording medium according to claim 1, wherein the content is 1 to 30% by weight. 3. The base film is a biaxially oriented thermoplastic resin film, the average height of surface protrusions on at least one side of the film is 1/4 or more of the average particle size of the particles in the film, and the number of protrusions. ^2. The magnetic recording medium according to claim 1, wherein the number is 10,000 / mm ² or more. 4. The base film is a biaxially oriented thermoplastic resin film, and the number of protrusions having a height not more than 1/3 of the average particle size of the particles in the film on at least one surface of the film is the total number of protrusions. 70% or less, Claim (1) characterized by the above-mentioned.
The magnetic recording medium described. 5. The magnetic material according to claim 1, wherein the base film is a biaxially oriented thermoplastic resin film, and the relative standard deviation of the surface projection height distribution on at least one surface is 0.6 or less. recoding media. 6. The substrate film is a biaxially oriented thermoplastic resin film, and the F5 value in the longitudinal direction thereof is 15 kg / mm ² or more, (1) to (5). Magnetic recording medium. 7. The magnetic recording medium according to claim 1, wherein the magnetic layer is a metal coating type.