KR100313684B1 - Magnetic recording media - Google Patents

Abstract

An object of the present invention is to provide a magnetic recording medium having high S / N ratio and durability.

The present invention provides a magnetic recording medium comprising a base film and a magnetic layer formed on at least a cross section of the base film, wherein the magnetic layer has a center of the concave maximum depth of the surface of the magnetic layer above the center plane. It has an irregular surface larger than the maximum height of the peak above the magnetic layer surface from the plane.

The magnetic recording medium of the present invention exhibits a high S / N ratio even though the magnetic layer has an irregular surface, and the durability of the recording medium is good, so that the S / N ratio can be kept high even if the recording medium is repeatedly used.

Description

Magnetic recording media

The present invention relates to a magnetic recording medium.

More specifically, the present invention relates to a magnetic recording medium of a type in which a magnetic layer is applied on a base film.

A magnetic recording medium of the type in which the magnetic layer is applied on the base film (hereinafter referred to as "coated magnetic recording medium") is known.

As the coated magnetic recording medium, a magnetic recording medium consisting of a magnetic layer coated on a polyester film and a film is known, for example, disclosed in US Patent No. 4,684,546.

In the conventional coated magnetic recording medium, the S / N ratio (signal-to-noise ratio) is determined by the high density recording (the higher the S / N ratio, the better the quality of recording information such as a recording image when the recording medium is videotaped). It is made as smooth as possible to promote.

However, when the surface of the magnetic layer is smooth, the coefficient of friction becomes large when the magnetic recording medium travels.

Since the high coefficient of friction damages the recording medium more severely, the durability of the magnetic recording medium having such a smooth surface magnetic layer is low, so that the high S / N ratio is greatly lowered when the magnetic recording medium is repeatedly used.

On the other hand, roughening the surface of the magnetic layer to enhance durability lowers the S / N ratio.

Thus, the enhancement effect of the S / N ratio weakens the durability of the recording medium and creates defects.

Accordingly, it is an object of the present invention to provide a magnetic recording medium having both high S / N ratio and durability.

The present inventors found that if the surface of the magnetic layer is irregular and the concave maximum depth of the surface of the magnetic layer from the center plane is greater than the maximum height of the projection peak from the center plane to the surface of the magnetic layer, the magnetic recording medium exhibits a high S / N ratio. The durability of the recording medium is also good.

That is, in the present invention, in a magnetic recording medium in which a magnetic layer is formed on at least one surface of a base film and the base film, the magnetic layer has an irregular surface and the concave maximum depth of the surface of the magnetic layer from the center plane is the center thereof. A magnetic recording medium is provided which is larger than the maximum height of the peak on the surface of the magnetic layer from the plane.

The magnetic recording medium of the present invention exhibits a high S / N ratio even though the magnetic layer has an irregular surface, whereas the recording medium is excellent in durability, and maintains a high S / N ratio even when the recording medium is repeatedly used.

As described above, the magnetic recording medium of the present invention is composed of a base film and a magnetic layer formed thereon.

The base film is preferably a thermoplastic resin film, more preferably a biaxially oriented thermoplastic resin film.

Although not limited, polyesters, polyolefins, polyamides and polyphenylene sulfides are preferable as the thermoplastic resin.

Of these, at least one structural unit selected from ethylene terephthalate units, ethylene α, β-bis (2-chlorophenoxy) ethane-4, 4′-dicarmoxylate units, and ethylene 2,6-naphthalate units The thermoplastic resin film containing as a main component is particularly preferable because of its excellent running property of the recording medium.

A magnetic layer is formed on the base film by coating.

The main feature of the magnetic recording medium of the present invention is the shape of the surface of the magnetic layer.

In particular, the magnetic layer surface is irregular.

The maximum depth of the concave (hereinafter referred to as "SRv") on the surface of the magnetic layer (hereinafter referred to as "SRv") is greater than the maximum height of the pits (hereinafter also referred to as "SRp") on the same surface (hereinafter also referred to as "concave-subject"). Bigger

Even if the surface of the magnetic layer is irregular, the inventors have found that if the surface has a concave-subject shape, the S / N ratio of the recording medium is high and the S / N ratio is not greatly reduced even if the recording medium is used repeatedly.

If SRp is larger than SRv (this shape feature is referred to as "protrusion-subject" hereinafter), it is difficult to satisfy high S / N ratio and high durability at the same time.

In the specification and appended claims of the present invention, SRa, SPc and SRz as well as SRp and SRv, which will be detailed below, are measured with a three-dimensional surface roughness meter unless otherwise specified.

It is desirable that the SRv of the magnetic layer surface be at least 10 nm larger than SRp, more preferably at least 15 nm and most preferably at least 20 nm because of the higher durability (smaller reduction) of higher S / N ratio and S / N ratio. Because it is obtained.

Although there is no critical upper limit of the difference between SRv and SRp (SRv-SRp), it is difficult to produce a magnetic layer with (SRv-SRp) over 300nm.

The ratio of the SRv to the average surface roughness of the magnetic layer surface (hereinafter referred to as "SRa"), ie SRv / SRa, is preferably 10 or less, preferably 8 or less because of the higher S / N ratio and S / N. This is because a smaller reduction in the ratio is obtained.

The peak number on the surface of the magnetic layer preferably has a peak across the range of -5 nm to 5 nm from the center plane of the surface of the magnetic layer in the thickness direction of 100 / 0.1 mm ² or more, more preferably 150 / 0.1 mm ² or more, and 200 / 0.1 More than mm ² is more preferred because higher S / N ratios and smaller reductions in S / N ratios are obtained.

More specifically, the peak number is the number of protrusions per 0.1 mm ² , and the protrusions start to rise from the point of -5 nm or less of the center plane of the magnetic layer surface to the point of +5 nm or more of the center plane of the magnetic layer surface.

The above values of -5 nm and +5 nm are distances from the center plane of the magnetic layer surface in the thickness direction of the magnetic layer.

The average surface roughness of the surface of the magnetic layer is preferably 3-45 nm, more preferably 10-30 nm, because higher S / N ratios and smaller decreases in S / N ratios can be obtained.

The magnetic layer surface preferably has a 10-point average roughness (hereinafter referred to as "SRz") of 30-450 nm, more preferably 50-300 nm, with a higher reduction in S / N ratio and smaller S / N ratio. Because you can get.

The magnetic powder contained in the magnetic layer is not limited, but oxides such as iron oxide, chromium oxide or Co-coated iron oxide: metals or alloys such as Fe, Co, Fe-Co, Fe-Co-Ni or Co-Ni, these irons or alloys And alloys with Al, Cr, Si, and the like.

Since the magnetic powder of iron or alloy is practically easy to obtain the shape characteristic of the surface of the magnetic layer, it is preferable that it does not contain an oxide, so that higher S / N ratio and smaller reduction of S / N ratio can be obtained. have.

In order to make the magnetic coating solution applied on the base film forming the magnetic layer, a binder type may be mixed with the magnetic powder.

Although not limited, the binder is preferably a thermosetting resin binder or a radiation curable resin binder.

As a dispersant and other additives, additives such as a dispersant, a lubricant and an antistatic agent may be mixed with the magnetic coating solution according to the conventional method.

For example, a binder made of vinyl chloride / vinyl acetate / vinylylcopolymer, polyurethane prepolymer, polyisocyanate, or the like can be used.

In addition, the thickness of the magnetic layer is not particularly limited, but 0.5-5 탆 is preferable, but the above-described morphological features of the surface of the magnetic layer are easily obtained, and a higher reduction in S / N ratio and smaller S / N ratio can be obtained.

As will be detailed later, a preferred manufacturing process of the magnetic recording medium of the present invention is that the magnetic medium is wound on a roll after application of the magnetic layer and before curing of the magnetic layer, so that curing of the magnetic layer is performed in a roll state.

In this manufacturing process, the above-mentioned concave-subject surface shape of the magnetic layer is divided by the surface shape of the base film surface. When the recording medium is wound on a roll, the surface is in contact with the surface of the magnetic layer, so that the surface is opposite the base film. Is on the side.

Therefore, the surface form of the base film, the surface opposite to the magnetic layer is important, preferably the characteristic surface form (the surface of the base film having a characteristic surface form is referred to as "surface characteristics of the base film" or simply "surface features" Is referred to as ".

More specifically, if the base film is one of the following (i)-(iv), the morphological characteristics of the surface of the magnetic layer can be easily obtained, so that higher S / N ratio and smaller reduction of S / N ratio can be obtained. .

(Iii) The base film is a biaxially oriented thermoplastic resin film, and the film is composed of particles having an average particle size of 0.1-10 times the thickness of the thermoplastic resin A and the layer A, and preferably 0.3-5 times the thickness, 0.005- It has a layer A of 3 micrometers, preferably 0.01-2 micrometers, and content of said particle | grains in the layer A is 0.1-30% of the total amount of layer A, Preferably it is 0.2-20%.

In this case, layer A is formed on the base film side opposite to the magnetic layer.

(Ii) the base film is a biaxially oriented thermoplastic resin film, the film contains particles and has projections on its surface, the average height of these projections being at least 1/4 of the average particle size of the particles, preferably 1 / It is 3.5 or more, More preferably, it is 1/3 or more and stone number is 10,000 / mm <^2> or more, More preferably, it is 20,000 / mm <^2> .

(Iii) The base film is a biaxially oriented thermoplastic resin film, the film containing particles having projections having a surface projection and having a height equal to or less than one third of the average particle diameter of the projections, preferably 70% or less of the projection number. Is 65% or less.

In this case, the surface as described above is formed at least on the base film side opposite to the magnetic layer.

(Iii) The base film is a biaxially oriented thermoplastic resin film, which has projections on the surface, and the ratio of the maximum height to the average height of the projections is 1.1-3, preferably 1.1 to 2.5.

In this case, the surface with protrusions is formed at least on the opposite side to the magnetic layer.

In the above case, the characteristic surface in (ii)-(iii) is at least on the base film side opposite to the magnetic layer.

In this way, the base film may be a monolayer film having a surface shape characteristic on both surfaces of the magnetic layer or only on one surface thereof, or having a film having a characteristic surface shape bonded on the opposite side of the magnetic layer or on both sides of the base film ( It may be a laminated film as shown in (iii).

The thickness of the magnetic layer applied on the base film is greater than the height of the protrusion on the characteristic surface of the base film, and although the magnetic layer is formed on the protrusion-main character characteristic surface of the base film, the applied magnetic layer is not made of the protrusion-maintenance, Although the magnetic layer is formed on the protruding-subject characteristic surface of the base film, it is not disturbed by the opposite effect.

In this way, as described above, the base film may have characteristic surfaces on both sides thereof.

In the case of having a characteristic surface on both sides of the base film, a magnetic layer may be formed on both sides of the surface.

In the above case (iii), preferred examples of the thermoplastic resin A include crystalline thermoplastic resins such as polyesters, polyolefins, and polyamides, particularly crystalline polyesters.

Among the crystalline polyesters, selected from the group consisting of ethylene terephthalate units, ethylene α, β-bis (2-chlorophenoxy) ethane-4,4'-dicarboxylate units, and ethylene 2,6-naphthalate units It is particularly preferable to have at least one structural unit as a main component, since the surface form of the magnetic layer defined in the present invention is easy to obtain.

Here, "crystalline" means that the film is not "amorphous".

More specifically, "crystalline" means that the melting point can be analyzed by thermal analysis using a differential scanning calorimeter at a heating rate of 10 ° C / min.

Preferably, the crystallization parameter Tcg is at most 150 ° C.

Moreover, since running | running property becomes more favorable when heat of fusion shows crystallinity of 7.5 mW / g or more, it is especially preferable.

The above-described form of the surface of the magnetic layer when the particles contained in the base film for forming the characteristic surface of the base film are spherical, that is, when the particle size ratio (long diameter of the particles / short diameter of the particles) of the particles is 1.0-1.3. It is preferable because it is easy to obtain, the S / N ratio is higher, and the decrease in the S / N ratio can be reduced.

These particles are preferably, but are not limited to, substantially spherical silica particles resulting from colloidal silica, or crosslinked polymer particles (eg crosslinked polystyrene, silicone or polyimide).

Particles such as titanium oxide, alumina, calcium carbonate, kaolinite or the like commonly used in this field may also be used if the film forming conditions are appropriately selected.

The particles have an easily obtained surface morphology of the above-described magnetic layer when the average particle size (diameter) of 5-2000 nm, in particular 10-1500 nm, and even 10-1000 nm, is higher and the ratio is lowered, and the S / N ratio is lowered. It is preferable because it can be made smaller.

When the characteristic surface of the base film has a total crystallinity index of only 2-20 cm ^-1 or less, the above-described magnetic layer surface form is easily obtained, the S / N ratio is higher, and the decrease in the S / N ratio is further reduced. It is preferable because it can be made small.

As for the characteristic surface of a base film, 1/10 or less are preferable, and 1/50 or less of the surface particle density | concentration ratio measured by secondary ion mass spectrum (SIMS) is more preferable.

If the surface particle concentration ratio is within this range, the above-described surface form of the magnetic layer is easy to be obtained, the S / N ratio is higher, and the decrease in S / N ratio can be made smaller.

In addition, running and output characteristics are improved.

In addition, the corrosion resistance of the film surface is improved, and troubles caused by the dropping of particles are greatly improved in the processing steps such as the film forming step, the magnetic layer coating and the calendar step.

In the case where the base film is a laminated film, the layer forming the feature surface thereof preferably contains particles in an amount of 1% by weight or less.

In this case, the particles may be particles or mixtures of approximately the same size as those contained in the layer forming the feature surface or having a particle size larger or smaller than that contained in the layer forming the feature surface.

In the base film of the magnetic recording medium of the present invention, not only ordinary organic additives such as antioxidants, heat stabilizers, lubricants, UV absorbers, etc., but also other copolymers may be mixed in an amount that will not adversely affect the advantageous effects of the present invention.

Since the concave-substrate surface shape of the magnetic layer is separated by another method that is not used to impart the concave-substrate shape as described later, the surface shape of the base film opposite the magnetic layer, the magnetic layer having the concave-substrate shape is the base film. It may be formed on both sides of.

Such magnetic recording media having magnetic layers on both sides of the base film are also within the scope of the present invention.

Moreover, a magnetic recording medium having a magnetic layer having a concave-subject surface shape and a smooth magnetic layer on the opposite side of the base film are also within the scope of the present invention.

When the magnetic layer is formed only on one side of the base film, the conventional so-called backcoat treatment may be performed on the surface opposite to the magnetic layer.

The thickness of the backcoat layer is preferably 0.1-1.5 μm, more preferably 0.2-0.8 μm, and the average surface roughness Ra of the back code layer is preferably 5-200 nm, more preferably 5-100 nm and 5-50 nm. More preferred, in this case the above-mentioned surface morphology of the magnetic layer is easy to obtain, the S / N ratio is higher, and the reduction in S / N ratio can be less.

A preferred manufacturing process of the magnetic recording medium of the present invention will be described in detail.

However, the manufacturing process of the magnetic recording medium of the present invention is not limited to the process to be described above.

Firstly, a preferred process for producing a bonded substrate film having one or two feature surfaces will be described in detail.

As described above, the preferred base film includes particles therein.

The particles can be mixed with the thermoplastic resin by mixing the particles with ethylene glycol to form ethylene glycol, slurry.

The polyester containing particle | grains can be obtained by using the ethylene glycol slurry containing particle | grains for copolymerization with an acid component.

Instead, the particles may be mixed into the thermoplastic resin using a two-side kneading extruder.

These methods are preferred because in this case they are suitable films as base films that do not break when the stretched state is obtained.

The content of the particles can be preferably adjusted by diluting the master polymer containing the particles at high density and diluting the thermoplastic resin and the master polymer during the film forming step to adjust the density of the particles in the mixed polymer to the desired value. .

The thermoplastic resin A containing the appropriate particle density thus obtained is made into pellets by a conventional method and dried when necessary.

The pellets of thermoplastic resin A are fed to a conventional melt lamination extrusion device and extracted from the die in the form of slits to form a sheet and solidified on a casting roll. This extraction step is two or three extruders, two or three layers. It is carried out using a manifold or confluence block and the sheet of two or three layers of the thermoplastic resin A and the thermoplastic resin A film is extruded under lamination conditions and the lamination sheet is cooled in a casting roll to solidify the lamination sheet, thereby disorienting it. A laminated film is obtained.

In this case, the thickness of the layer A made of the thermoplastic resin A (which will form the feature surface of the base film) is adjusted to obtain a thickness of 0.8-80 times the average particle diameter contained in the thermoplastic resin A.

In this extraction step, it is preferable to provide a conventional static mixer or gear pump in the polymer flow path of the thermoplastic resin A in order to obtain a suitable base film which does not break upon stretching.

A peered block having a rectangular cross section as the joining block is preferable for obtaining a desired base film.

In the above-described method, a laminated film of mainly A / B or A / B / A structure (layer A outer surface is a feature surface) is produced. A laminated film having an A / B / C structure may also be prepared in a similar manner.

That is, using a generation of extruders and three layers of manifolds or confluence blocks, thermoplastics A, B and C are laminated and the three layers of sheet are extracted from the detention.

In this case, the thermoplastics A, B and C may be the same or different (the surfaces of layers A and C are characteristic surfaces).

The non-oriented film thus obtained is biaxially stretched to biaxially align the film.

In addition to the conventional simultaneous biaxial stretching method, a conventional sequential stretching method which is sequentially performed in the longitudinal direction and the transverse direction or the transverse direction and the longitudinal direction for stretching the film is used.

Although the desired stretching conditions vary depending on the thermoplastic resin constituting the film, the ratio of aspect ratios and aspect ratios should be greater than 8 in order to create a desirable relationship between particle size and thickness of lamination A to optimize the surface morphology of the feature surface. It is desirable to adjust the draw ratio.

Moreover, by using such draw ratios, the polymer molecules adjacent to the feature plane are biaxially oriented and the entire film has the desired mechanical properties.

The polymer molecules adjacent to the feature surface are biaxially oriented and the feature cannot be obtained by conventional application methods or application-stretching methods.

The advantage of the biaxial orientation of the polymer molecules in close proximity to the feature plane makes the surface morphology of the magnetic layer defined in the present invention easier to obtain, the higher the S / N ratio, and the smaller the reduction in the S / N ratio.

Moreover, the corrosion resistance of the film surface is improved, so that problems due to particle dropout during the manufacturing process such as film forming step, magnetic layer coating step or calendar step are greatly reduced.

The biaxially oriented film thus obtained is preferably stretched again in one direction, in which case better mechanical properties can be obtained.

The biaxially oriented film thus prepared is preferably heat set at a temperature range below the melting point of the thermoplastic resin and higher than the melting point of -100 ° C. for 0.5 to 60 seconds.

The magnetic layer is applied on the base film thus prepared.

Application of the magnetic layer can be performed by a conventional method.

Among the conventional methods, a method using gravure or geasa is preferred, in which case it is easy to obtain the surface morphology of the magnetic layer defined in the present invention, and the S / N ratio is higher and the S / N ratio is lowered. It can be made small.

When both sides of the base film are feature surfaces (A / B / A), the magnetic layer can be formed on both sides of the surface, and when only one side of the base film is the feature surface (A / B), the magnetic layers are feature surfaces It is formed on a surface other than that.

The magnetic layer is preferably dried at a temperature of 90-120 ° C.

The film is then subjected to conventional calendar steps.

The calendering step is easy to obtain the surface form of the magnetic layer defined in the present invention when polyamide or polyester resin is used in the elastic roll at a pressure of 100-500 kg / cm at a temperature of 20-80 ° C, and the S / N ratio is more. Higher, the reduction in the S / N ratio can be made lower, which is desirable.

The thus prepared film with the applied magnetic layer is wound on a roll and the magnetic layer is rolled into a roll state.

At this time, the winding tension is 3㎏ / m-20㎏ / m, and when the curing temperature is 40-100 ℃, the surface shape of the magnetic layer limited to the present invention is easily obtained, and the S / N ratio is high and the S / N ratio is high. The reduction is preferable because it can be made smaller.

The original (wide) plate of the magnetic recording medium is slitted to obtain a magnetic recording medium. When the back coat layer is formed on the surface of the base film on the opposite side of the magnetic layer, the time when the back coat layer is applied may be at any time before applying the magnetic layer, before the calendering step, after the calendering step and before the curing step of the magnetic layer or after the curing step of the magnetic layer. .

Most preferably, the application of the backcoat layer is carried out after the curing step of the magnetic layer.

Although by this method, the concave-subject surface morphology of the magnetic layer is separated by the feature surface of the base film, and the concave-subject surface morphology of the magnetic layer is imparted by another method that does not use the feature surface of the base film.

For example, the magnetic layer of the smooth cloth surface may be roller compacted to a surface having a chord of the above-described feature surface of the base film.

For example, a smooth surface can be crimped | bonded by the roll which wound the said base film on the core roll by the magnetic layer.

By this operation, the surface of the smooth magnetic layer is raised to obtain the concave-subject surface defined in the present invention.

Instead, the above-described base film having one feature surface is tightly wound on a roll so as to exhibit a concave-subject surface shape on a surface other than the feature surface.

By applying the magnetic layer on the concave-substrate wrapping surface of the base film, a magnetic layer having a concave-subject surface shape is formed.

The magnetic recording medium of the present invention is useful for various types of recording media such as video tapes, floppy disks, video floppy disks, audio tapes, memory tapes, and the like. In particular, 8 mm video tapes, 8 mm high band video tapes, digital video tapes, It is used for high-density magnetic recording media such as HDTV (high definition TV, high definition TV) and video tape software that is used repeatedly.

The method of measuring the features relating to the present invention and the method of making the effects of the present invention will be described in detail below.

(1) Average particle size

The thermoplastic resin is removed from the film by plasma thermosetting to expose the particles.

By selecting the painting treatment conditions, the thermoplastic resin is sintered but the particles are not damaged.

This exposed particle is observed with a scanning electron microscope (SEM), and the image of the particle is processed with an image analyzer.

The observation point is changed and the following numerical treatment is carried out with the number of particles of 5000 or more, and the average particle size D thus obtained is taken as the average particle size.

D = Σ Di / N

Here, Di is the original sugar diameter of the particle, N is the number of particles.

(2) particle size ratio

The particle size ratio is the ratio of the (longest diameter average value) / (average value of the short diameter) of the individual particles in the above measurement (1).

That is, the average long diameter and average short diameter of the particles are obtained by the following equations, respectively:

Average length = Σ D1 / N

Mean diameter = Σ D2 / N

Here, D1 and D2 are the longest diameter (maximum diameter), the shortest diameter (shortest diameter), and N is the number of particles, respectively.

(3) relative standard deviation of particle size

The relative standard deviation of the particle size is defined as (δ / D), where δ is the standard deviation defined by the equation:

δ = {Σ (Di-D) ² / N} ^1/2

Here Di, D and N mean the same as (1).

(4) content of particles

The film is treated with a solvent in which the thermoplastic resin is dissolved but the particles are not dissolved.

The resultant is centrifuged to separate the particles.

The content of particles is located as the weight ratio of the separated particles to the total weight of the film.

(5) Crystallization parameter ΔTcg, heat of fusion

The differential scanning calorimeter (DSC) measures the crystallization parameter of ΔTcg and the heat of dissolution of the film.

DSC is performed as follows:

10 g of samples are set in a DSC apparatus, melt | dissolve at the temperature of 300 degreeC for 15 minutes, and quench in liquid nitrogen.

The quenched sample was heated to 10 ° C./min to detect the glass transition point Tg.

The temperature is increased again, and the crystallization exothermic peak temperature in the glass state is measured.

The crystallization exothermic peak temperature was taken as the cold crystallization temperature Tcc.

The temperature of the sample is continued and the heat of fusion is determined as the melting peak.

Here, the difference between Tcc and Tg (Tcc-Tg) is defined by the crystallization parameter ΔTcg.

(6) Total Saraman Crystallization Index

The total reflection only spectrum was measured, and the total reflection only crystallization index of the surface was made into the half width of 1730 cm <^{-1> which} is the elastic vibration of a carbonyl group.

The measured part has a depth of 50-100 nm from the surface of the film.

The measurement conditions are as follows:

a) light source

Argon ion laser (514.5 nm)

b) setting of EUT

The surface of the sample film is pressed against the reflective prism as a whole, and the angle of incidence of the laser beam to the prism (angle between the incident laser beam and the thickness direction of the film) is 60 °.

c) detector

PM: RCA 31034 / Photon Counting System (Hamamatsu C 1230) (Supply 1600 V), commercially available from Hamamatsu Photonics, Hamamatsu, Japan

d) measuring conditions

Slit: 1000 ㎛

Laser: 100 mw

Gate Time: 1.0 sec

Scanning speed: 12 cm ^-1 / min

Sampling Interval: 0.2 cm ^-1

Repeat Time: 6

(7) Surface layer particle density ratio

Using the secondary ion mass spectrum (SIMS), the density ratio of the particles to the maximum density between the particles resulting from particles in the film to the density of carbon in the thermoplastic resin, the ratio is defined as the particle density, the film thickness direction It is measured at several points.

The ratio A / B of particle density A at the outermost surface (at depth 0) measured by SIMS (defined as particle density at surface) to the maximum particle density B obtained by analyzing the sample film in the thickness direction of the film is determined by It is defined as density ratio.

Measuring instruments and measuring conditions are as follows.

Primary ion species: O ₂ ⁺

Primary ion acceleration voltage: 12 KV

Primary ion current: 200 nA

Luster area: 400 μm □

Analysis area: Gate 30%

Measuring vacuum degree: 6.0 × 10 ^-9 Torr

E-GUN: 1.5 KV-3.0 A

(8) altitude, altitude analysis, number of surface protrusions

The projection altitude measured by scanning the surface of the film with the planar portion of the surface as a base (elevation 0) in a two-detector scanning electron microscope (ESM-3200, manufactured by Elionix) (IBA 2000). And the image of the surface projection are reconstructed on the image processing apparatus.

Binary projections are binarized in this surface projection image, which is defined as the maximum value of the projections converted into the measured binarization.

This measurement was repeated 500 times by changing the place, and the average value of the altitude was taken as the average elevation of the projections.

In addition, the ratio of the scanning microscope is 1000 to 8000 times.

The average spacing between adjacent protrusions is calculated as the number of protrusions.

In some cases, altitude information obtained using a high-precision optical interpolation three-dimensional surface analysis apparatus (e.g., TOPO-3D manufactured by WYKO; objective lens 40-200 times) is used at the position of the height measured using a scanning microscope.

(9) Surface shape of magnetic layer

Using the non-contact surface roughness meter HIPOSS (Model ET-30HK) of Kosaka Research Institute, the three-dimensional surface roughness, side, and the average surface roughness SRa defined above, the average surface roughness SRz at 10 points, and the maximum height SRp of the peak from the center plane. , The maximum depth SRv and peak number SPc concave from the central plane are measured.

The value to be described in the following Examples was set to a value having an average value of 20 measurements.

The measurement conditions are as follows.

Species magnification: 20,000 times

Lateral magnification: 500 times

Cut Off: 0.08 mm

Feeding Pitch: 0.5 ㎛

Measuring length: 500 ㎛

Measuring area: 0.0194 mm ²

Scanning Speed: 100 ㎛ / sec

(10) Average surface roughness Ra of the backcoat layer

The average surface roughness Ra of the backcoat layer is measured using a surface roughness meter.

The measurement conditions are as follows:

Tensile tip radius: 0.5 ㎛

Catch load: 5 mg

Measuring length: 1 mm

Cutoff value: 0.08 mm

(11) Lamination thickness of base film

Using the secondary ion mass spectrum (SIMS), the density ratio (M ⁺ / C ⁺ ) of the particles of maximum density between the elements resulting from the particles of the film to the carbon density in the thermoplastic resin is defined as the particle density, It is defined at various points along the film thickness direction.

Regions from the film surface were analyzed from the surface to a depth of 3000 nm.

Because of the interface of the surface layer (ie surface), the temperature of the particles increases low near the surface and deep from the surface.

In a preferred mode of the invention, after the particle concentration reaches its maximum, the particle concentration decreases with depth.

From the obtained concentration analysis curve, the depth at which the particle concentration becomes 1/2 of the maximum value (this point is deeper than the obtained maximum particle density point) is determined to be the laminated thickness of the base film.

Measurement conditions are the same as in (7).

It is difficult to measure in SIMS when the largest particles in the range of 3000 nm from the surface layer are polymer particles.

In this case, the film thickness is measured by X-ray photoelectron spectroscopy (XPS) or infrared spectroscopy (IR) and the like while the film is etched from the surface to determine the laminated thickness of the film.

Instead, the laminated thickness can be obtained by recognizing the interface in the state of change in the cross-section of the film and the change in particle concentration or contrast by electron microscope or the like.

(12) S / N ratio of magnetic recording medium

The magnetic recording medium was set in a cassette to form an 8 mm VTR tape.

On the thus prepared VTR tape, a 100% chroma generator was recorded by a television test waveform generator (Shiba Corporation Co., Ltd. TR 7 / U706).

The chroma S / N ratio of the reproduced signal was measured using a color video noise meter (925D / 1 manufactured by Shiba Soku Co., Ltd.).

The chroma S / N was measured and compared using a commercially available Hi8 tape (8 mm VTR tape for high band, Hi 8MP 120 manufactured by SONY).

When the S / N ratio is 1 dB or more higher than that obtained using the Hi8 tape, the S / N ratio is determined to be good, and when it is 1 dB or less, the S / N ratio is determined to be poor.

(13) durability of magnetic layer

The VTR tape prepared in (11) is repeatedly played and rewound.

The cycle of regeneration-rewinding is repeated 1000 times at 40 ° C., 80% RH.

After this, the S / N ratio was measured.

If the decrease in the S / N ratio is 1 kPa or less after the cycle regeneration, the durability is judged to be good, and if it is 1 kPa or more, the durability is judged to be poor.

The present invention will be described based on examples.

The examples are not limited to this for the purpose of illustration.

Examples 1-16, Comparative Examples 1-10

Ethylene glycol slurry containing spherical silica particles derived from crosslinked polystyrene particles or colloidal silica having different average particle diameters was prepared, and transesterified with dimethyl terephthalate to obtain polycondensation.

By this operation a pellet of polyethylene terephthalate (hereinafter referred to as PET) containing 0.05 to 35% by weight of particles was prepared.

On the other hand, PET containing 0.2% by weight of spherical silica particles (average particle size 0.2 µm) derived from colloidal silica (thermoplastic B) is prepared by a conventional method.

The thermoplastic polymers (A) and (B) were dried under reduced pressure (3 Torr) at 180 ° C. for 8 hours. The thermoplastic resin B was fed to the extruder 1 and melted at 285 ° C.

On the other hand, the thermoplastic resin A was supplied to the extruder 2 and melted at 280 degreeC.

The polymer was laminated using a confluence block and the polymer was extruded under the lamination conditions.

The extrusion sheet is wound around the casting drum at a surface temperature of 30 ° C. by the electrostatic casting method and the film is solidified to obtain a laminated unstretched film.

While controlling the amount of polymer extruded from each extruder, the total thickness of the film as well as the layer A thickness of thermoplastic A was controlled.

This unstretched film was stretched longitudinally at 80 degreeC by the draw ratio of 4 times original length.

This extending | stretching was performed by the speed difference of two sets of rolls.

This stretching was performed in three steps using two sets of rolls.

This uniaxially stretched film was stretched using a stenter at a drawing speed of 2000% / min, 4 times the original length at 100 ° C.

The biaxially stretched film thus obtained was stretched again in the longitudinal direction at a draw ratio of 1.65 times the original length.

The resultant was heat set at a constant length at 190 ° C. for 5 seconds to obtain a biaxially stretched laminated film having a total thickness of 7 μm.

Furthermore, for comparison, a 7 탆 thick biaxially stretched monolayer film containing 0.2 wt% of spherical silica particles having an average particle size of 0.2 μm and 0.05 wt% of spherical silica particles having an average particle size of 0.6 μm was prepared by a conventional method.

The magnetic coating solution was applied on the surface of the prepared base film on the side opposite to the layer A of the thermoplastic resin A.

The magnetic layer had all the weight parts and the following composition ratio.

Fe (iron)

Average particle size: Length: 0.3 ㎛

Particle Size Ratio: 10/1

Coercive force: 2000 Oe

15 parts of polyurethane resin

5 parts vinyl chloride / vinyl acetate copolymer

Nitrocellulose resin part 5

Aluminum oxide powder part 3

Average particle size: 0.3 m

Carbon black part 1

Lecithin Part 2

100 parts methyl ethyl ketone

100 parts of methyl isobutyl ketone

Toluene 100 parts

Stearic Acid Part 2

The composition was stirred for 48 hours using a ball mill, and 6 parts of curing agents were added thereto.

The resulting mixture was filtered through a filter to prepare a magnetic coating solution.

The magnetic coating solution was applied on the film, self-oriented and dried at 110 ° C.

The resultant was subjected to a calender treatment by using a small test calender device (steel roll / nylon roll, 5-stage) by varying the temperature and linear pressure.

Thereafter, the film was wound on a roll with varying tension, and the magnetic coating solution was cured for 48 hours at various temperatures of 10 to 150 캜 to obtain a magnetic recording medium.

The properties of the magnetic recording medium thus obtained are shown in Table 1-3.

As shown in this table, the magnetic recording medium of the present invention has a high S / N ratio and a small decrease in the S / N ratio due to repeated driving operation, so that durability is good.

On the other hand, none of the magnetic recording medium outside the scope of the present invention similarly satisfies the high S / N ratio and the high durability.

Although the present invention has been described in terms of the preferred embodiments, it is obvious in the art that many variations do not depart from the spirit and scope of the present invention.

Claims (11)

In a magnetic recording medium comprising a base film and a magnetic layer formed on at least one surface of the base film, the magnetic layer is a coated magnetic layer, and the maximum depth of the concave portion on the surface of the magnetic layer is from the center plane. Magnetic recording medium having an irregular surface larger than the maximum height of the projection peak on the surface of the magnetic layer 2. The magnetic recording medium of claim 1, wherein the maximum depth is 10 nm or more larger than the maximum height. The magnetic recording medium of claim 1, wherein a ratio of the maximum depth to the average surface roughness of the surface of the magnetic layer is 10 or less. 2. The magnetic recording medium of claim 1, wherein the number of peaks of the surface of the magnetic layer crossing the region of -5 nm to 5 nm in the thickness direction from the center plane of the surface of the magnetic layer is 100 / 0.1 mm2 or more. 2. The film of claim 1, wherein the base film is a biaxially oriented thermoplastic resin film, and the film has a layer A having a thickness of 0.005 to 3 µm with a thermoplastic resin and particles as main components, and the average particle size contained in the layer. Is 0.1 to 10 times the thickness of the above-described layer A, the content of the above-mentioned particles of the above-mentioned layer A is 0.1 to 30% of the total weight of the above-mentioned layer A, and the above-mentioned layer A is formed at least on the opposite side to the above-mentioned magnetic layer. Magnetic recording medium, characterized in that. The method of claim 1, wherein the base film is a biaxially oriented thermoplastic resin film containing particles and having projections on the surface, wherein the average height of the projections is equal to or larger than l / 4 of the average particle size of the particles. A magnetic recording medium having a projection number of 10,000 / mm 2 or more, wherein the surface having the projections is formed at least on the opposite side to the magnetic layer. The method of claim 1, wherein the base film is a biaxially oriented thermoplastic resin film containing particles and having a projection surface, wherein the number of projections having a height equal to or less than l / 3 of the average particle size of the particles is the total number of projections. 70% or less of said magnetic recording medium, said surface being formed at least on the opposite side to said magnetic layer. The method of claim 1, wherein the base film is a biaxially oriented thermoplastic resin film having projections on the surface, the ratio of the maximum height to the average height of the projections is 1.1 to 3, wherein the projection surface is at least opposite to the magnetic layer. Magnetic recording medium, characterized in that formed. 2. The magnetic recording medium according to claim 1, wherein the base film is a crystallized polyester film having a surface having a total crystallinity index of 20 cm ^-1 or less. The magnetic recording medium according to claim 1, wherein the base film is a biaxially oriented thermoplastic resin film containing particles having a relative standard deviation of a particle size of 0.6 or less. The magnetic recording medium according to claim 1, wherein the base film is a biaxially oriented thermoplastic resin film containing particles having a particle size ratio of 1.0 to 1.3.