JP3243958B2 - Film for magnetic recording media - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a polyester film for a magnetic recording medium, particularly a polyester film for a magnetic recording medium suitable for digital video tape, and more particularly to a polyester film for a magnetic recording medium suitable for vapor deposition type video. It is about.

[0002]

2. Description of the Related Art Digital video tapes require higher density recording than conventional video tapes.
A method such as 147010 is proposed. In addition, the base film particularly requires flatness and defect-free properties, and for example, a method disclosed in Japanese Patent Application Laid-Open No. 58-155940 has been proposed.

[0003]

However, digital video tapes, especially vapor-deposited video tapes, are required to be surface-free. That is, dropouts, which are a kind of electromagnetic conversion characteristics, frequently occur after tapering due to defects on the microprojections on the surface. In particular, as one of the causes of the microprojection defect, there is a group of microprojections made of polyester having a low molecular weight. That is, in the film production process, the low molecular weight polyester is impregnated from the film before the completion of the stretching, and is accumulated on the surface of the production apparatus or the like, becomes a lump and adheres again to the film surface. This is a problem, for example, in low molecular weight substances that are simply precipitated from the inside of the film after the completion of stretching as described in JP-A-58-121128, etc. Easy to cause. In addition, during storage of the film, low-molecular-weight substances of polyester are precipitated on the film surface with the lapse of time, which also causes dropout.

[0004]

In order to solve some of these problems, the present invention has the following arrangement.

A film mainly composed of polyester, which is present on the surface of the film on which the magnetic layer is to be applied;
A magnetic material mainly consisting of a low molecular weight product of the polyester, wherein the number of microprojections having a major axis of 1 μm or more and 10 μm or less and a maximum height h (nm) (A; number / 100 cm ² ) satisfies the following expression. Film for recording media.

H ≧ 0.27 A <50 h> 0.54 A <20 h> 0.81 A <10 h> 1.08 A <2 As the polyester of the present invention, polyethylene terephthalate and polyethylene 2,6-naphthalate, polyethylene α, β-bis (2-chlorophenoxy) ethane 4,4-dicarboxylate, polybutylene terephthalate and the like are used, among which polyethylene terephthalate and polyethylene 2,6-Naphthalate is preferred, and polyethylene-2,6-naphthalate is more preferred. The polyester may be a homopolyester, a copolyester containing less than 20 mol% of another polyester, or a simple mixture of less than 20 mol%.

The polyester film of the present invention is preferably a composite film having two or more layers. That is, the running surface is preferably a sufficiently rough surface for running properties, and the polyester layer on the vapor deposition surface side is preferably a smooth surface for improving electromagnetic conversion characteristics. The sufficiently rough surface of the running surface is a center line surface roughness of 0.005 to 0.0
The surface ranges from 30 μm, preferably from 0.010 to 0.025 μm, and more preferably from 0.015 to 0.020 μm. In the case of a smooth surface having a center line surface roughness of less than 0.005 μm, poor running properties in a cooling can in a film forming step, a coating step of a magnetic layer, and a vapor deposition type video are caused. Further, when the center line surface roughness is larger than 0.030 μm, the running property is good, but in the case of the vapor deposition type video, the contact area to the cooling can is small, the cooling is insufficient, and the deformation and the thermal dimensional change due to heat are caused. So-called "heat loss" occurs.

In order to achieve this surface roughness, it is desirable that the polyester layer on the running surface side contains particles. That is, the particle diameter is in the range of 10 to 1000 nm, more preferably in the range of 50 to 500 nm.
For example, inorganic particles such as silica, calcium carbonate, aluminum oxide, zirconium oxide and titanium oxide, or particles composed of organic polymers such as cross-linked polyvinyl benzene, acrylic particles, cross-linked polystyrene, polyester particles, or other organic polymers on the surface. The above-mentioned organic polymer particles coated, or the inorganic particles whose surface is coated with the above-mentioned organic polymer are exemplified. Regarding the shape of the particles, spherical particles are particularly preferable from the viewpoint of easily controlling the height and shape of the protrusions. In order to make the heights of the projections 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. The content of the particles is 0.01 to 3% by weight, preferably 0.1 to 1% by weight. As a method for incorporating the particles, it may be added before, during or after the polymerization.However, the particles are mixed and dispersed in the form of a slurry with ethylene glycol which is a diol component of the polyester. Is effective. As a method of adjusting the content of particles, a method of diluting a high-concentration master pellet with another chip or pellet at the time of forming a film to a predetermined concentration is effective.

The B side of the film of the present invention is preferably a smooth side for improving the electromagnetic conversion characteristics. In addition, the smooth surface of the surface B is a surface having a center line roughness of 10 nm or less, preferably 5 nm or less. If the center line surface roughness is 10 nm or more, the electromagnetic conversion characteristics deteriorate.

As long as the smoothness is not impaired, the particles to be contained in the polyester on the running surface, the content and the addition method can be applied to the layer on the vapor deposition surface side. In order to improve the runnability, a coating formed by applying an aqueous coating solution comprising the following water-soluble polymer or fine particles, or both, to one or both of the running surface and the deposition surface of the film is formed. May be. At that time, the surface deposited after the coating film formation had a center line surface roughness of 0.010 μm or less in terms of the surface roughness, and the running surface had a center line surface roughness of not more than 0.10 μm.
It is preferable that the surface be in the range of 005 to 0.030 μm. The water-soluble polymer has a molecular weight of 10,000 to 20.
100,000 and preferably 100,000 to 1,000,000 are used. Such water-soluble polymers include polyvinyl alcohol-
, Tragacanth, gum arabic, casein, gelatin methylcellulose, hydroxyethylcellulose, carboxymethylcellulose and the like can be applied.

The fine particles present in the coating film and on the coating film surface of the present invention have a particle size 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, cross-linked polyvinyl benzene, acrylic resin particles, and particles obtained by laminating a component that adheres to a film on the particle surface. 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 a water-soluble polyester, a silane coupling agent, a titanium coupling agent, a wax, and a mixture thereof.

The surface of the film of the present invention on the side on which the magnetic layer is provided must be highly defect-free. That is, the diameter of the low molecular weight product of the polyester, which is present on the surface of the film on which the magnetic layer is provided, is 1 μm to 10 μm.
m or less and the number of microprojections having a height h (nm) (A;
100 cm ² ) must satisfy the following equation.

H ≧ 0.27 A <50 h> 0.54 A <20 h> 0.81 A <10 h> 1.08 A <2 Here, a group of microprojections made of a low molecular weight polyester is defined as , Each of which is not more than 10 μm away from the closest microprojection. That is,
When a certain microprojection is separated from the nearest microprojection of the nearest microprojection by more than 10 μm, the former microprojection is another microprojection not included in the latter microprojection group. For example, in the case of the small projection group in FIG. 1, the number is counted as three. In a digital video tape, in terms of many disadvantages exceeding the range of the above equation, there are many dropouts, which are one of the electromagnetic conversion characteristics, and cannot be used for the present invention at all. More preferably, the number of microprojections mainly having a diameter of 1 μm or more and 10 μm or less and a height h (nm) (A;
cm ² ) must satisfy the following expression.

H ≧ 0.27 A <20 h> 0.54 A <10 h> 0.81 A <5 h> 1.08 A <1 In order to achieve the above object, the production apparatus, especially the magnetic properties of the film, A preferred method is to periodically clean equipment that contacts the surface on which the layer is to be provided. Further, the surface of the obtained film on the side on which the magnetic layer is provided may be mechanically or chemically treated to remove the minute projections. For example, corona discharge treatment,
Surface cleaning with a solvent such as chloroform, acetone and the like can be mentioned.

In the film of the present invention, it is desirable that the amount of the low molecular weight product of the polyester deposited on the surface of the film after 48 hours at 50 ° C. is 0.2 mg / m ² or less. That is, when the amount of the low molecular weight product of the polyester deposited on the surface of the film exceeds 0.2 mg / m ² ,
When the film is stored, low-molecular-weight substances of the precipitated polyester become projections due to aging and cause dropout. Preferably, after 48 hours at 50 ° C., the amount of the low molecular weight product of the polyester deposited on the surface of the film is 0.1%.
mg / m ² or less, more preferably 0.05 mg / m ² or less.

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

First, the polyester pellets on the magnetic surface side and the running surface side are separated, and at least one of the polyester pellets is made of an inorganic particle and / or an organic polymer particle having an average particle diameter of 10 to 1000 nm and / or an organic particle. 0.01% of inorganic particles coated with a polymer film
３3% by weight and thoroughly dried. Thereafter, the polyester pellets on the magnetic surface side are melted, filtered through a filter having a filtration accuracy of less than 4 μm, and the polyester pellets on the running surface side are laminated with the polymer thus melted. Extrude as an object. Known methods are applied to the particle addition method, the melting method, the extrusion method, and the lamination method at this time. The obtained sheet-like material is stretched in one direction in the longitudinal direction or width direction of the film, and then stretched in a direction perpendicular to the direction to be biaxially oriented. In the case of further strengthening, after the stretching is completed, the film is further stretched in the longitudinal direction and the width direction. When a film is provided on the film, the sheet-like material from the die or the sheet-like material is stretched in one direction, and then the water-soluble polymer and / or fine particles are coated on at least one surface thereof. An aqueous solution consisting of
Thereafter, it is biaxially oriented. After the stretching is completed, the film is heat-treated in a temperature range of 180 to 250 ° C. for 5 seconds or more with the both ends of the film being gripped, and finally cut into a predetermined width to obtain a product. If necessary, the surface of the obtained film is subjected to corona discharge treatment or surface washing with a solvent such as chloroform or acetone to remove projections due to low molecular weight substances on the surface.

In order to obtain a magnetic recording medium, a magnetic material is applied by coating a polymer binder containing a magnetic material powder on the surface of the film or by evaporating a magnetic metal such as cobalt under reduced pressure. After applying a surface treatment or the like, the product is cut into a predetermined width and assembled into a cassette or the like to obtain a product. The tape obtained in this way is particularly suitable for digital applications.

[0019]

[Method of measuring characteristics] The characteristic values of the present invention are based on the following measuring methods and evaluation criteria. Surface roughness (Ra) The surface roughness (Ra) was measured using a high-precision thin film step measuring device ET-10 manufactured by Kosaka Laboratory. The conditions were as follows, and the value was determined as the average value of 20 measurements.・ Stylus tip radius: 0.5 μm ・ Stylus load: 5 mg ・ Measurement length: 1 mm ・ Cut-off value: 0.08 mm The definition of Ra is, for example, “Method for measuring and evaluating surface roughness” by Jiro Nara ( Comprehensive Technology Center, 1983). Regarding the number of microprojections due to polyester low molecular weight products Regarding the number of microprojections due to polyester low molecular weight products,
Observation was made with a microscope at 50 cm ² or more, and the height of the projections was determined by a multiple interference method, and the number was converted to the number per 100 cm ² . In addition, when judging whether or not it was a polyester low molecular weight product, chloroform was dropped on the projection and when the projection group disappeared, it was judged as a polyester low molecular weight product. Temporal change of precipitation of polyester low molecular weight substance A 30 cm square film is heated in an oven at 50 ° C. for 24 hours, and then the film surface is extracted with ethyl alcohol for 5 minutes. The extracted solution was diluted to a predetermined concentration, quantified by an ultraviolet absorption method, and converted to an amount per 1 m ² . Judgment of heat loss Regarding heat loss, electron beam evaporation of 0.1 μm cobalt was conducted in a vacuum of 1 × 10 ⁻⁵ Torr along a cooling can at 20 ° C., and the film was observed for 10 m in the longitudinal direction. Then, the degree of deformation such as swelling or dent due to heat was determined.・ No deformation after vapor deposition ◎ ・ Partial deformation △ (Bulge and dent) ・ The whole surface is significantly deformed × (Bulge and dent, and holes due to heat) For dropout measurement The cobalt-deposited film obtained as described above was slit into 、 inch, and a signal of 4.4 MHz was recorded at normal speed using an NV-3700 type video deck manufactured by Matsushita Electric Industrial Co., Ltd. Okura Industry
15μsec with a drop-out counter manufactured by
The number of dropouts at 20 dB is measured for 20 minutes,
It was converted to the number of dropouts per minute (pieces / minute).

[0020]

Next, embodiments of the present invention will be described based on examples. (Example 1) Pellets A of polyethylene naphthalate containing substantially no particles were obtained by polymerization of ethylene glycol and dimethyl naphthalate. The pellet A was used as a vapor deposition surface side. Pellets B having an average particle diameter of 0.3 μm and a spherical crosslinked polystyrene particle having a relative standard deviation of 0.4 in particle size distribution and containing 0.2% by weight of the particle were used. A composite film on the running surface side was formed. First, for pellet A, a metal fiber sintered type filter
The pellet B was filtered from a melt extruder other than the one used for the pellet A with a metal fiber sintered type filter, and the polymer was filtered with a pinol placed directly above the slit base. -Laminated in the thickness direction to make an unstretched film. The unstretched film is stretched 4.23 times at 135 ° C. in the longitudinal direction by a roll stretching method, and then stretched 4.75 times at 135 ° C. in the transverse direction by a stenter. Then, a heat treatment was performed at 200 ° C. for 10 seconds at − to finally produce a 6.2 μm thick film. (Example 2) In Example 2, the method of Example 1 was followed by stretching in the longitudinal direction and then using a metaling bar coater.
Example 1 was repeated except that the following aqueous solution was applied to the deposition surface and the running surface, respectively, and then stretched in the lateral direction by a stenter.
The invention was implemented in the same manner as described above.・ Evaporation 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 Methyl cellulose 0.2% by weight Water-soluble polyester 0.3 % By weight Colloidal silica 0.1% by weight (average particle size: 15 nm) (Example 3) In Example 3, instead of using pellet A, 90 parts by weight of pellet A and the average particle Except for using pellets D obtained by mixing 10 parts by weight of pellets C containing spherical silica particles having a diameter of 0.1 μm and containing 1.0% by weight of the particles, the same method as in Example 2 was used. The present invention has been implemented. (Example 4) In Example 4, the present invention was carried out in the same manner as in Example 2, except that the film surface was washed with chloroform after the film formation was completed. (Example 5) The method of Example 2 was repeated, except that polyethylene terephthalate was used instead of polyethylene naphthalate and stretched 3.00 times at 108 ° C in the longitudinal direction. The present invention was carried out in the same manner as in Example 2 except that the film was stretched 3.75 times at 90 ° C., and the film surface was washed with chloroform after completion of the film formation. (Comparative Example 1) A comparison with the present invention was performed in the same manner as in Example 5 except that the surface roughness of the running surface was Ra = 0.080 μm. (Comparative Example 2) The present invention was carried out in the same manner as in Example 5, except that the film surface was not washed with chloroform after completion of the film formation.

[0021]

[Table 1] ★

[0022]

The film of the present invention uses a composite film of a polyester film and is coated with a slippery surface to provide a film having excellent running properties and good abrasion resistance of the projections. provide. Further, the present invention provides a polyester film suitable for digital video tape with less dropout, by using a composite film having excellent surface defect-freeness.

[Brief description of the drawings]

FIG. 1 shows a micrograph of a group of microprojections made of a polyester low molecular weight substance present on a film of Example 1.

Claims (9)

(57) [Claims] 1. A film mainly composed of a polyester, which is mainly composed of a low molecular weight substance of the polyester and is present on a surface of the film on which a magnetic layer is to be applied, and has a major axis of 1 μm or more and 10 μm or less and a maximum height h ( The film for a magnetic recording medium, wherein the number (A; number / 100 cm ² ) of the microprojection group of (nm) satisfies the following expression. h ≧ 0.27 A <50 h> 0.54 A <20 h> 0.81 A <10 h> 1.08 A <2 2. The number of the microprojections (A; number / 100c)
^{2. The} film for a magnetic recording medium according to claim 1, wherein m ² satisfies the following expression. h ≧ 0.27 A <20 h> 0.54 A <10 h> 0.81 A <5 h> 1.08 A <1 3. The surface of the film has a smooth surface having a center line surface roughness of 0.010 μm or less, and the other surface has a center line surface roughness of 0% or less. .00
The film for a magnetic recording medium according to claim 1, wherein the thickness is 5 to 0.030 μm. 4. The film according to claim 1, wherein said film is mainly polyethylene-
4. The film for a magnetic recording medium according to claim 1, comprising 2,6-naphthalate. 5. The film for a magnetic recording medium according to claim 1, wherein said film comprises at least two layers. 6. The film for a magnetic recording medium according to claim 1, wherein a coating film comprising a water-soluble polymer and / or fine particles is applied to at least one surface of the film. 7. The polyester having a low molecular weight of 0.3 m deposited on the surface of the film after 48 hours at 50 ° C.
The film for a magnetic recording medium according to claim 1, wherein the g / m ^{2 is not} more than g / m ² . 8. The film for a magnetic recording medium according to claim 1, which is used for digital video. 9. The film for a magnetic recording medium according to claim 1, which is used for a vapor deposition type video.