JPH08147672A - Film for magnetic recording medium - Google Patents

Abstract

PURPOSE: To obtain a polyethylene-2,6-naphthalate film for digital video tapes which shows superior running properties, good abrasion resistance at projections thereof and also superior properties without defects at the surface thereof. CONSTITUTION: This is a film for magnetic recording media mainly comprising polyethylene-2,6-naphthalate, containing organic high-molecular particles of an average particle size of 10-500nm and/or inorganic particles processed at the surfaces thereof through an organic high-molecular treatment. The ratio of the average height of surface projections and the average size of the particles is 1/6-1/2 at least at one surface of the medium. Moreover, a surface roughness RaA on a center line of one face (A side) is 5-30nm and a surface roughness RaB on a center line of the other face (B side) is 10nm or smaller.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a film for a magnetic recording medium, and more particularly to a film for a magnetic recording medium which is preferably used for digital video tape.

[0002]

2. Description of the Related Art Digital video tape requires higher density recording than conventional video tape.
Methods such as the 6453 publication have been proposed. The base film is particularly required to have flatness and defect-free property, and for example, JP-A-58-155940 has been proposed. In particular, in recent years, tapes have tended to have a long time, and it has been desired to make the base film thinner and have higher elasticity. Therefore, as a material for the base film, it has high elasticity and heat resistance. An excellent polyethylene-2,6-naphthalate has been attracting attention, and it has been proposed as a film for the digital tape (Japanese Patent Publication No. 5-59813).

[0003]

However, there are the following problems when the above means is used for polyethylene-2,6-naphthalate. First, inorganic particles such as silica and calcium carbonate are generally added to the polymer in order to impart the running property, but polyethylene-2,6-naphthalate has a polyethylene terephthalate-based affinity with inorganic substances. However, there are problems that particles are likely to fall off, and dropouts frequently occur after tape formation. For the same reason, the protrusion becomes steep, and the problem on the magnetic surface side is head scraping.The problem on the running surface side is the transfer of dents to the magnetic surface side and the cooling cam in the case of vapor deposition tape. There is a problem such as thermal deformation of the film due to a decrease in the contact area with the film, and so-called "heat loss". Further, in the digital video tape, compared with the conventional video tape, the defect-free surface is particularly required, so that the surface properties of the conventional video base film and general-purpose video base film are not so good. It cannot be used for digital video tape.

[0004]

In order to solve such a problem, the present invention has the following constitution.

That is, mainly polyethylene-2,6-
A film for a magnetic recording medium comprising a naphthalate, containing organic polymer particles having an average particle diameter of 10 to 500 nm and / or inorganic particles having a surface treated with an organic polymer,
The ratio of the average height of the surface projections to the average diameter of the particles on at least one surface is in the range of 1/6 to 1/2, and the center line surface roughness RaA of one surface (A surface) is 5 to 30 nm. , The center line surface roughness RaB of the other surface (B surface) is 10 n
The present invention relates to a film for a magnetic recording medium, which is characterized by being m or less.

The film of the present invention is mainly composed of polyethylene-2,6-naphthalate. "Mainly" here
Means that the content of polyethylene-2,6-naphthalate is 80 mol% or more. The above-mentioned polyethylene-2,6
The naphthalate may be a homopolyester,
Further, other polyesters such as polyethylene terephthalate, polyethylene α, β-bis (2-chlorophenoxy) ethane 4,4-dicarboxylate, polybutylene terephthalate, etc. in a proportion of less than 20 mol% are used. It may be polyester, and the above components may be 20 mol%.
It may be a mixture simply mixed at a ratio less than.

The film of the present invention is preferably a composite film comprising at least two layers of A layer and B layer. Here, the A layer means A of the two outermost layers of the film.
Refers to the layers that form the surface. The surface A is preferably a running surface and needs to be a sufficiently rough surface for imparting running performance. On the other hand, the B layer means B out of the two outermost layers of the film.
Refers to the layers that form the surface. The surface B is preferably a magnetic surface and needs to be a smooth surface in order to improve the electromagnetic conversion characteristics. The sufficiently rough surface of the surface A is a surface having a center line surface roughness of 5 to 30 nm, preferably 10 to 20 nm. If the center line surface roughness is less than 5 nm, a smooth surface is not preferable because it causes poor runnability in a film forming process, a magnetic layer coating process, and a cooling can in the case of a vapor deposition video. Further, when the center line surface roughness is larger than 30 nm, the runnability is good, but in the case of vapor deposition video, the contact area with the cooling can is small, cooling is insufficient, and deformation and thermal dimensional change due to heat increase. This is not preferable because so-called "heat loss" occurs.

In order to achieve this surface roughness, it is preferable that the layer A contains particles. That is, the particle size is 10
It is in the range of 500 nm, preferably 50 to 400 nm, more preferably 50 to 300 nm, and examples of the material include particles made of organic polymers such as crosslinked polyvinylbenzene, acrylic particles, crosslinked polystyrene, and polyester particles, or other materials on the surface. The above-mentioned organic polymer particles that have been subjected to various treatments such as coating with an organic polymer, or inorganic particles that have been subjected to various treatments such as coating the surface with the above-mentioned organic polymer, such as titanium oxide, aluminum oxide, zirconium oxide, carbonic acid Examples thereof include calcium and colloidal silica. That is, since polyethylene-2,6-naphthalate has a poorer affinity for inorganic particles than polyethylene terephthalate, organic polymer particles or organic polymers having high affinity for polyethylene-2,6-naphthalate are used. It is necessary to use inorganic particles whose surface has been treated with molecules. Regarding the shape of the particles, spherical particles are particularly preferable from the viewpoint of easily controlling the height of the projections and the shape of the projections. Further, in order to make the heights of the protrusions formed on the film surface uniform, it is particularly preferable that the particle size distribution of the particles is 0.5 or less in relative standard deviation. It is particularly preferable that the particles are so-called heat resistant polymer particles that are less likely to be deformed or thermally deteriorated by heat during polymer melting or heat during a film forming process. Here, the heat resistant polymer particles refer to polymer particles whose temperature at which 10% weight loss occurs in thermogravimetric analysis is 350 ° C. or higher, more preferably 380 ° C. or higher.

For the projections on the surface of the film, the ratio of the average height of the projections to the average diameter of the particles must be within a specific range. That is, when the height of the protrusions is higher than the average diameter of the particles, the protrusions become steep, and the portion buried in the polymer becomes small, so that the film forming step, the magnetic layer coating step and the magnetic layer vapor deposition step are performed. This is because they easily fall off due to friction with the roll at the time. Specifically, the ratio of the average height of the protrusions to the average diameter of the particles needs to be 1/6 to 1/2. The ratio of the average height of the protrusions to the average diameter of the particles is preferably 1/4 to 1/2, more preferably 1/3 to 2/5. When the ratio of the average height of the protrusions to the average diameter of the particles is less than 1/6, the protrusions are not sufficient to give the running property, which is not preferable. On the other hand, when it is larger than 1/2, the particles are easily separated by friction due to a roll or the like, which is not preferable.

The content of the particles is preferably 0.001 to
It is 3% by weight, more preferably 0.01 to 1% by weight.
As a method of incorporating the particles, before polymerization, during polymerization,
It may be added after polymerization, but it is effective to add it by mixing and dispersing it in the form of slurry with ethylene glycol, which is the diol component of polyester. As a method of adjusting the content of particles, a method of diluting a high-concentration master pellet with other chips or pellets at the time of film formation to a predetermined concentration is effective.

The surface roughness of the B side of the film of the present invention is a center line surface roughness, and it is necessary that the surface roughness is 10 nm or less, preferably 5 nm or less. The surface roughness of surface B is 1 in terms of center line roughness.
If the surface is rougher than 0 nm, the electromagnetic conversion characteristics are deteriorated when the magnetic layer is provided, which is not preferable.

As long as the smoothness is not impaired, B
Particles may be added to the layer. In that case, the particles to be contained in the layer A, the content and the addition method may be applied,
Further, other particles, content and addition method may be used. In order to improve the running property, a coating film is formed by applying an aqueous coating liquid comprising the following water-soluble polymer and / or fine particles on either or both of A-side and B-side of the film. May be. In that case, regarding the surface roughness after forming the coating film, the surface B has a centerline surface roughness of 10 nm or less, and the surface A has a centerline surface roughness of 5 to 30 nm.
Must be in terms of range.

The above water-soluble polymer has a molecular weight of 1
Those having a viscosity of 10,000 to 2,000,000, preferably 100,000 to 1,000,000 are used. Examples of such water-soluble polymers include polyvinyl alcohol, tragacanth gum, gum arabic, casein,
Gelatin methyl cellulose, hydroxyethyl cellulose
, Carboxymethyl cellulose and the like can be applied.

The fine particles present in the coating film and on the surface of the coating film of the present invention have a particle diameter of 5 nm or more and a height of 100 nm or less, preferably 50 nm or less. Examples of such fine particles include colloidal silica, aluminum oxide, zirconium oxide, titanium oxide, crosslinked polyvinylbenzene, acrylic resin particles, and particles obtained by laminating a component that adheres to a film on the surface of the particles. Here, the height refers to the maximum height of the fine particles present on the coating film surface from the coating film forming surface (the surface of the polyester film), and the value is 100 nm or less.

As long as the effects of the present invention are not impaired,
The coating film may contain other components. Examples of such other components include water-soluble polyester, silane coupling agent, titanium coupling agent, wax and the like, and mixtures thereof. The surface of the film of the present invention on which the magnetic layer is provided needs to be highly defect-free. That is, on the B side (magnetic surface) of the film, the height h (n
The number of coarse protrusions (A; number / 100 cm ² ) of m) satisfies the following formula.

H ≧ 270 A <500 h> 540 A <100 h> 810 A <30 h> 1080 A <10 In digital video tape, in terms of many defects exceeding this range, one of the electromagnetic conversion characteristics is considered. There are many dropouts, which cannot be used for the purpose of the present invention.

In order to satisfy the above formula, the polyethylene-2,6-naphthalate polymer on the magnetic surface side is passed through a filter having a predetermined filtration accuracy in a molten state, and coarse foreign matters existing in the polymer are passed through. Is preferred. Here, the filtration accuracy is defined as the particle size of the particles just captured on the 95% filter when the particles are dispersed in a polymer or a solvent and passed through the filter. Naturally, the smaller the value of this filtration accuracy, the smaller the foreign matter can be removed. The filtration accuracy of the filter of the present invention is less than 4000 nm, preferably 2000.
It is less than nm, and more preferably 1500 nm or less.
In addition, there is also a method of using a clean polymer having few coarse foreign substances at the polymer polymerization stage due to the absence of surface defects. The layer on the traveling surface side may or may not adopt the above method.

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

First, the polyethylene-2,6-naphthalate pellets on the magnetic surface side and the running surface side are separated, and the polyethylene-2,6-naphthalate pellets on at least one side are formed into organic particles having an average particle size of 10 to 500 nm. 0.001 to 3% by weight of polymer particles and / or inorganic particles whose surface is coated with an organic polymer film are added, and each is sufficiently dried. Then, the polyethylene-2,6-naphthalate pellets on the magnetic surface side were melted,
After filtering with a filter having a filtration accuracy of less than 4000 nm, polyethylene-2,6-naphthalate pellets on the running surface side are laminated with a melted polymer, and extruded as a sheet-like material from a die. Particle addition method at this time,
Known methods are applied to the melting method, the extrusion method and the lamination method. The obtained sheet-like material is stretched in one direction in the longitudinal direction or the width direction of the film, and then stretched in a direction perpendicular to the direction to orient in the biaxial direction. In the case of further strengthening, after the stretching is finished, the film is further stretched in the longitudinal direction and width direction of the film. When a coating film is provided on the film, a sheet-like material from the die or
After the sheet-like material is stretched in one direction, an aqueous solution containing a water-soluble polymer and / or fine particles is applied to at least one surface thereof, dried, and then biaxially oriented. After the stretching, the film is heat-treated for 5 seconds or more in a temperature range of 180 to 250 ° C. while holding both ends of the film, and finally cut into a predetermined width to obtain a product. In order to obtain a magnetic recording medium, a magnetic substance is applied to the surface of the film by applying a polymer binder containing a magnetic substance powder or a method of depositing a magnetic metal such as cobalt under reduced pressure, and the surface treatment is performed. After cutting, etc., the product is cut into a predetermined width and incorporated into a cassette or the like to make a product.

The tape thus obtained is particularly suitable for digital applications.

[Measurement Method of Characteristic] The characteristic value of the present invention is based on the following measuring method and evaluation criteria.

(1) Protrusion height A vertical cross section of the obtained film was measured by an electron microscope at 1200.
A photograph was taken at a magnification of 0 times, and the height of the protrusion was determined as the vertical distance from the film plane to the apex of the protrusion, and an average value of 100 of them was determined.

(2) Surface Roughness (Ra) The surface roughness was measured using a high precision thin film step measuring instrument ET-10 manufactured by Kosaka Laboratory. The conditions are as follows, and the average value of 20 measurements was used as the value.

-Stylus tip radius: 0.5 μm-Stylus load: 5 mg-Measurement length: 1 mm-Cutoff value: 0.08 mm The definition of Ra is, for example, Jiro Nara "Measurement / Evaluation of Surface Roughness". Method "(General Technology Center, 1983).

[0025] (3) large protrusions number for the polymer - for contamination number of coarse protrusions due to the medium, and observed 50 cm ² or more by a microscope, the projection height thereof is determined by the multiple interference method, the number to the number per 100 cm ² Converted.

(4) Average Particle Diameter of Contained Particles Particles are observed with an electron microscope, and an image of the particles (light and shade of light produced by the particles) is linked to an image analyzer (for example, QTM900 manufactured by Cambridge Instrumental) and observed. The following numerical processing is performed with the number of particles changed to 5000 or more at different locations, and the number average diameter D obtained thereby is taken as the average particle diameter.

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

(5) Relative Standard Deviation of Contained Particles Standard deviation σ (= calculated from particle diameter Di, average particle diameter D, and total number N of particles measured by the method (4) above.
It is represented by a value (σ / D) obtained by dividing {Σ (Di-D) ² / N} ^1/2 ) by the average particle diameter D.

(6) Content of Content Particles A solvent which does not dissolve the particles is selected to dissolve the film,
The particles are centrifuged, and the particle content is defined as the ratio (% by weight) to the total weight of the particles. In some cases, combined use of infrared spectroscopy is also effective.

(7) Heat Resistant Temperature of Contained Particles TG-30M manufactured by Shimadzu Corporation was used, and the temperature rising rate was 10 ° C. /
Min, and thermogravimetric analysis was performed in nitrogen, and the temperature at the time of 10% weight loss was defined as the thermal decomposition temperature. The sample weight was 5 mg.

(8) Degree of Dropped Particles The film was slit into halves, a load of 20 g was applied to one end of the film, and 180 ° contact was made with a stainless guide pin having a diameter of 5 mm and a mirror-finished surface in one direction. 10m
The extent of the particles dropped off after rubbing and remaining on the guide pin was judged by the following criteria. ◎: No adhesion to guide pin △: Partially adhered ×: Entirely adhered (9) Judgment of heat loss Regarding heat loss, 1 × 10 ^-5 Torr along a cooling can of -20 ° C. Electron beam evaporation of 0.1 μm cobalt in the vacuum of 10 μm in the longitudinal direction of the film.
It was observed and judged by the degree of deformation such as swelling or dent due to heat.

・ No deformation after vapor deposition ◎ ・ Partially deformed △ (with bulges and dents) ・ Significantly deformed on the whole surface × (In addition to bulges, dents and holes due to heat) (10 ) Measurement of dropout The film after cobalt vapor deposition obtained in (9) above is
Slit to 1/2 inch, Matsushita Electric Industrial Co., Ltd. NV-3
A 700-inch video deck records a signal of 4.4 MHz at a constant speed, reproduces the tape, and uses a dropout counter manufactured by Okura Industry Co., Ltd. for 15 μse.
The number of dropouts at c-20 dB was measured for 20 minutes and converted into the number of dropouts per minute (pieces / minute).

EXAMPLES Next, the present invention will be described in more detail based on examples.

(Example 1) Pellet A of polyethylene naphthalate containing substantially no particles was obtained by polymerizing ethylene glycol and dimethyl naphthalate. The pellet A was used as a vapor deposition surface side, and a spherical shape having an average particle size of 0.3 μm and a relative standard deviation of the particle size distribution of 0.4, which was 10
%, A composite film was formed with heat-resistant crosslinked polystyrene particles having a temperature of 390 ° C. and having a content of the particles of 0.2% by weight as a traveling surface side. First, for pellet A, a filtration accuracy of 1000 from the melt extruder.
nm, and the pellet B was filtered from a melt extruder different from the one used for the pellet A with a filter having a filtration accuracy of 5000 nm, and was placed directly above the slit-shaped die. Then, the polymer was laminated in the thickness direction to form an unstretched film. The unstretched film was stretched in the longitudinal direction at 135 ° C. to 4.23 times, then stretched in the transverse direction at 135 ° C. to 4.75 times, and after stretching was stretched to 200 ° C. at 10 ° C. for 10 times. Heat treatment was performed for a second to finally produce a film having a thickness of 6.2 μm.

(Example 2) Example 2 is the same as the method of Example 1, except that the following aqueous solutions were applied to the magnetic surface and the running surface using a metalling bar coater after stretching in the longitudinal direction, and thereafter. The present invention was carried out in the same manner as in Example 1 except that the film was stretched in the transverse direction with a stenter.

Magnetic surface Methyl cellulose 0.1% by weight Water-soluble polyester 0.4% by weight Colloidal silica 0.03% by weight (average particle size 18 nm) Running surface Methylcellulose 0.2% by weight Water-soluble polyester 0.3% by weight Colloidal silica 0.1% by weight (average particle size 15 nm) (Example 3) Example 3 is the same as Example 2 except that pellet A is used in an amount of 90 parts by weight. In the same manner as in Example 2, except that the pellet D obtained by mixing 10 parts by weight of the pellet C having an average particle diameter of 100 nm and the content of the spherical silica particle being 1.0% by weight is used. The present invention has been implemented.

Example 4 In Example 4, the method of Example 2 was repeated except that spherical crosslinked polystyrene particles having an average particle size of 300 nm and a relative standard deviation of particle size distribution of 0.4 were used. The present invention was carried out in the same manner as in Example 2, except that the relative standard deviation of the particle size distribution was 0.4 and spherical silica whose surface was coated with acrylic was used.

(Comparative Example 1) In the method of Example 2, instead of using spherical crosslinked polystyrene particles having an average particle size of 300 nm and a relative standard deviation of 0.4, the relative particle size distribution of 300 nm is used. Comparison with the present invention was carried out in the same manner as in Example 2 except that spherical silica having a standard deviation of 0.4 and having no surface coated with an organic polymer was used.

(Comparative Example 2) The method of Example 1 was repeated except that the surface roughness of the running surface was Ra = 80 nm.
A comparison with the present invention was made in the same manner as.

(Comparative Example 3) In the same manner as in Example 2, except that the pellet A is filtered with a filter having a filtration accuracy of 5000 nm instead of being filtered with a filter having a filtration accuracy of 500 nm. A comparison with the present invention was made.

[0041]

[Table 1]

[Table 2]

[0042]

The film of the present invention comprises polyethylene-2,
By using a composite film of 6-naphthalate film, using predetermined particles, and further coating the surface with slipperiness, a film having excellent running property and good abrasion resistance of protrusions can be obtained. provide. Further, a composite film having an excellent defect-free surface provides a polyethylene-2,6-naphthalate film suitable for tapes for digital video with less dropout.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI technical display area C08L 67/02 LNZ // B29K 67:00 105: 16

Claims (8)

[Claims] 1. A magnetic recording medium film mainly composed of polyethylene-2,6-naphthalate, comprising organic polymer particles having an average particle size of 10 to 500 nm and / or inorganic particles having a surface treated with an organic polymer. The ratio of the average height of the surface protrusions to the average diameter of the particles on at least one surface is in the range of 1/6 to 1/2, and one surface (A
The surface of the magnetic recording medium has a centerline surface roughness RaA of 5 to 30 nm and the other surface (B surface) has a centerline surface roughness RaB of 10 nm or less. 2. A composite film comprising at least two layers of an A layer and a B layer, wherein the A layer contains organic polymer particles and / or inorganic particles whose surface is treated with an organic polymer. The film for a magnetic recording medium according to claim 1. 3. The film for a magnetic recording medium according to claim 1, containing 0.001 to 3% by weight of organic polymer particles and / or inorganic particles whose surface is treated with an organic polymer. 4. The organic polymer particles and / or the inorganic particles whose surface is treated with an organic polymer are spherical, and the particle size distribution is 0.5 or less in relative standard deviation. A film for a magnetic recording medium according to. 5. The film for a magnetic recording medium according to claim 1, wherein the organic polymer particles are made of a heat resistant organic polymer. 6. The magnetic recording medium according to claim 1, wherein the number of coarse protrusions (A; number / 100 cm ² ) having a height h (nm) on the B surface satisfies the following formula. the film. h ≧ 270 A <500 h> 540 A <100 h> 810 A <30 h> 1080 A <10 7. A water-soluble polymer and / or at least one surface thereof
Alternatively, the film for a magnetic recording medium according to any one of claims 1 to 6, wherein a layer made of fine particles is provided. 8. The film for a magnetic recording medium according to claim 1, which is used for a digital video tape.