JPH07121573B2 - Composite film - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a composite polyester film having excellent smoothness and flatness, which is suitable for a magnetic tape material, particularly for a high-density video tape which has conventionally required a back coat layer. .

[Problems to be Solved by Prior Art and Invention]

In recent years, the demand for video tapes has increased rapidly. With such an increase in users, the grade of the video tape itself has improved, and bigrade and super high grade type video tapes with good image quality have become common. As a tape of this type, the characteristics have been improved by providing a magnetic layer on a flat film surface and a back coat layer for slipping on the opposite surface, but the back coat layer has been conventionally used. There has been a demand for a film that is flat and has satisfactory flatness and slipperiness.

However, until now, various prescriptions have been tried, but in the present situation, no one satisfying sufficiently has been found.

For example, one of the methods that was carried out to make a film that is smooth and smooth without providing a back coat layer is a film in which higher fatty acid is added. Although excellent, it was impossible to put it into practical use because the running property was deteriorated after the magnetic layer was applied.

As a method for obtaining a flat and easily slipping film, a two-layer film in which the surface on the magnetic layer side which is required to have flatness is made flat and the opposite surface which is required to be slippery is roughened is used. , It was proposed to make a film for high density.

However, when using such a film, when the magnetic layer is applied and aged, surface protrusions on the surface with a high degree of roughness are offset by the magnetic surface, and the magnetic surface flattened for high density is also roughened. However, the current situation is that the phenomenon in which the electrical characteristics are deteriorated occurs and the method has not been put to practical use.

Therefore, for a magnetic tape for high density, it is extremely difficult to produce a film satisfying both electric characteristics and running property without a back coat, and its practical application has been demanded.

[Means for solving problems]

The inventors of the present invention have conducted intensive studies to provide a film satisfying such a demand, and as a result, compounded by a coextrusion method, and only a film having a film surface roughness within a specific range has no back coat. The present invention has been completed by finding that the film becomes a satisfactory film when it is used as a video tape.

That is, the gist of the present invention is a biaxially oriented composite film in which at least two layers are laminated by coextrusion, and the center line average roughness (Ra ^A ) of one surface (A side) is 0.002 to 0.015. μm
The center line average roughness (Ra ^B ), the ten-point average roughness (Rz ^B ), and the number of protrusions per 0.1 mm length (m ^B ) on the surface opposite to the A surface (B surface) are respectively It exists in the composite film characterized by satisfy | filling the following and the formula simultaneously.

0.015 ≤ Ra ^B ≤ 0.045 ...... Rz ^B / Ra ^B ≤ 15.0 ...... 10 ≤ m ^B ...... The present invention will be described in detail below.

The composite film in the present invention refers to a film extruded by a coextrusion method in which all layers are comelt extruded from a die and stretched and heat set. A two-layer composite film will be described below as the composite film, but in the present invention, the layer to be composited is not limited to two layers, and may be three or more layers.

In the present invention, the polymer constituting each layer to be composited,
Of the various polyesters, those selected are thermoplastic. Among these, polyethylene terephthalate is the most excellent in terms of polymerization reactivity, film-forming property, film quality performance and economically preferable. In addition, as the raw material polyester, polybutylene terephthalate, polyethylene-2,6-naphthalene dicarboxylate, polybutylene dibenzoate, homopolyester such as polyester of bisphenol A and terephthalic acid or isophthalic acid, or polyethylene terephthalate Homopolyester with ethylene glycol, propylene glycol, butanediol, xylylene glycol, bisphenol A, diethylene glycol, polyethylene glycol as a copolymerization component,
Copolymerized with polytetramethylene glycol, polypropylene glycol, adipic acid, sebacic acid, phthalic acid, isophthalic acid, 2,6-naphthalene dicarboxylic acid, p-oxyethoxybenzoic acid, glycolic acid, and others, polypropylene terephthalate, Polybutylene bibenzoate, polyester of 3,3-bis- (p-oxyphenyl) pentane and terephthalic acid, 2,2-bis (3-
Polyester of methyloxyphenyl) propane and terephthalic acid, 2,2-bis (p-oxyphenyl) pentane and isophthalic acid, polyester of terephthalic acid, copolymerized polyester of ethylene terephthalate and ethylene isophthalate, and sebacate, adipate, etc. Other examples include copolymerized polyester. Needless to say, the raw material polyester is not necessarily limited to these.

Incidentally, the polyester constituting each of these layers, as appropriate, a stabilizer, a colorant, an antistatic agent, or the like, or even if each layer is subjected to the treatment,
There is no problem if the obtained film has the requirements of the present invention.

In the present invention, the flat surface of the surface of the film is
The surface, and the easy-to-slip surface that is the opposite surface are abbreviated as surface B.

In the present invention, the surface roughness of the surface ^A needs to have a center line average roughness (Ra ^A ) in the range of 0.002 to 0.015 μm, preferably 0.006 to 0.015 μm, and more preferably 0.
It is in the range of 008 to 0.015 μm. When Ra ^A is less than 0.002 μm, it is no longer possible to give good running properties to the magnetic tape, while when Ra ^A exceeds 0.015 μm, A
When a magnetic layer is provided on the surface, the characteristics are deteriorated, which is not preferable. In addition, it is preferable that the number of coarse protrusions on the surface A is as small as possible.

On the other hand, surface B has a center line average roughness (Ra ^B ) of 0.015 to 0.045μ.
It is necessary to be in the range of m, preferably 0.020 to
The thickness is 0.045 μm, more preferably 0.025 to 0.045 μm. When Ra ^B is less than 0.015 μm, the slipperiness after forming into a magnetic tape is unsatisfactory and unsuitable. A film having Ra ^B of more than 0.045 μm is not suitable because it is largely transferred to the magnetic layer after being formed into a magnetic tape and the output as a magnetic tape is reduced.

The B side of the film of the present invention has ten-point average roughness (Rz ^B ), Ra ^B
It is necessary that the ratio Rz ^B / Ra ^B with the ratio is 15.0 or less.

Here, when the value of Rz ^B / Ra ^B exceeds 15.0, coarse protrusions increase,
It is not preferable because it is transferred to the A side and roughens the magnetic surface. The value of Rz ^B / Ra ^B is preferably 12.0 or less, more preferably 10.0 or less.

The B side of the film of the present invention is required to further have 10 or more protrusions (m ^B ) per 0.1 mm length. When m ^B is less than 10, the number of protrusions is small, the lubricity is insufficient, and at the same time, the protrusions are easily transferred to the magnetic layer surface, which is unsuitable.

In addition, the friction coefficient of the film B of the present invention after coating the magnetic layer on the surface A on the surface B after 50 times of multiple running is preferably 0.20 or less, more preferably 0.18 or less, and particularly preferably 0.15 or less.

On the other hand, the number of coarse protrusions of 1.08 μm or more on the B side is 25 cm ²
The number is preferably 100 or less, more preferably 50 or less, and particularly preferably 30 or less. If the number of coarse projections is more than 100, the dropout increases due to transfer to the magnetic surface, and it cannot be used.

In order to provide such surface roughness, the particles to be contained in the A layer, that is, the layer on the smooth surface (A surface) side, should be particles that are used in current high-grade and super high-grade video tapes. preferable.

That is, it is suitable to add 0.01 to 1% by weight, preferably 0.05 to 0.5% by weight, and more preferably 0.1 to 0.5% by weight of particles having an average particle size of 0.1 to 5 μm, preferably 0.3 to 2 μm. In this case, the particles are preferably composed mainly of internal particles as described above, but any form of internal particles alone, external particles alone, or a combination thereof can be adopted. In addition, it may be a bimodal system of large particles and small particles, even in that case, the inner particles alone as small particles,
External particles alone, or may be any combination thereof, also as large particles internal particles alone, external particles alone,
Alternatively, any combination of these may be used. When using a bimodal system, small particles with a particle size of 0.3-1.5 μm should be 0.
01 to 1% by weight, preferably 0.1 to 0.5% by weight, large particles are
0.01 with a particle size of 1.0-5 μm, preferably 1.0-2 μm
It is preferable that the content is 0.1 to 0.1% by weight.

On the other hand, the B layer, that is, the layer on the side of the easy sliding surface (B surface) may use any particles as long as the projections have a uniform height and a large number of particles, but the best one is , Carbon black, titanium oxide, and spherical silica. A combination system of carbon black and other uniform particles is also preferable. As particles to be used in combination, particles having a uniform particle size and a nearly spherical shape such as silica particles and titanium oxide particles are preferable.

The average particle size and content of such particles is preferably 0.01 to
It is preferable that the content of 10 μm, more preferably 0.01 to 5 μm, be contained in 0.01 to 10% by weight, further preferably 0.1 to 5% by weight.

In the present invention, when the difference in surface roughness between the A surface and the B surface is relatively large, the large particles on the easy sliding surface (B surface) side are smooth (A surface) in the process of compounding by coextrusion. It affects the surface roughness on the (Surface) side and may cause the generation of coarse protrusions on the A surface. Therefore, the limiting viscosity on the smooth surface (A surface) side is
It is preferable to increase the intrinsic viscosity on the (surface) side.

Further, in order to eliminate the above factors, the thickness ratio of the A layer and the B layer, that is, the value of (A layer thickness) / (B layer thickness) is preferably in the range of 1 to 50, more preferably 2 to 50. The range is 45, particularly preferably 4 to 20.

Next, the method for producing the oriented polyester film of the present invention will be specifically described, but the film of the present invention is not limited to the following production examples.

A polyester raw material containing particles mainly containing internal particles (for forming A layer) and a polyester raw material containing particles mainly containing external particles (for forming B layer) are separately dried, and separate extruders are used. Extruded by using a feed block type co-extrusion device and then compounded in front of the die and then formed into two layers in the same die, or by a multi-manifold type co-extrusion apparatus to laminate two layers in the die. It is made into an integral composite and is cooled and solidified on a casting drum to produce a two-layer unstretched polyester sheet. At this time, it is preferable to adopt a known casting method such as an electrostatic contact method.

The sheet thus obtained is then stretched in the machine direction. The stretching temperature is 75 to 150 ° C., and the stretching is performed in one stage or multiple stages,
It is stretched 2.0 to 9.0 times so that the birefringence Δn after longitudinal stretching is preferably 0.045 to 0.150. In this case, in particular, the birefringence Δn after longitudinal stretching is controlled to be 0.045 to 0.080 so that the orientation is kept low, so that after biaxial stretching, projections and depressions are formed around the protrusions as nuclei to form irregularities. It is a very effective method for improving the flat slipperiness of the film.

The longitudinally stretched film thus obtained is then transversely stretched at 85 to 150 ° C. to obtain a biaxially stretched film. At this time, in order to improve the adhesiveness between the film and the magnetic layer, it is a very preferable method to apply a water-soluble resin or emulsion to the smooth surface (A surface) before transverse stretching and then subject it to stretching.

The biaxially stretched film obtained by the transverse stretching is heat-fixed after re-stretching in the longitudinal and / or transverse directions as necessary. At the time of heat fixing, processing such as tentering and relaxation in the width direction may be performed depending on the required characteristics. Further, the temperature may be fixed in two or more steps by repeating the temperature rising and cooling.

Further, it is possible to provide an intermediate layer between the A layer and the B layer as long as the gist of the present invention is not exceeded.

〔Example〕

Hereinafter, the present invention will be described in more detail with reference to Examples and Comparative Examples, but the present invention is not limited to these Examples.

The methods for measuring or evaluating the film properties in Examples and Comparative Examples are as follows.

Further, in the following, "part" means "part by weight".

(1) Surface roughness (center line average roughness Ra, ten-point average roughness R
z) According to the method described in JIS B 0601-1976. For the measurement, a surface roughness measuring machine model SE-3F manufactured by Kosaka Laboratory was used. Stylus diameter 2μ
m, stylus pressure 30 mg, cutoff value 0.08 mm, measuring length 2.5 mm
The center line average roughness was measured under the conditions of.

The ten-point average roughness was measured at 12 points, the maximum value and the minimum value were cut, and the average value of 10 points was shown.

(2) Number of protrusions per 0.1 mm length (m) Using the Kosaka thin film step gauge ET-10, vertical magnification of 20,000 times and horizontal magnification of 5
It was measured with a stylus diameter of 0.5μ at 10,000 times, and the number of convex protrusions per 5 cm was counted.

(3) Number of Coarse Protrusions Aluminum was vapor-deposited on the film surface, and the number was measured using a two-beam interference microscope. The number of interference fringes of the third order or higher at the measurement wavelength of 0.54 μm is converted and shown per 25 cm ² .

(4) Dynamic friction coefficient with metal (F / Me-μd) Fixed hard chrome-plated metal roll (diameter 6mmφ)
The film is contacted at a wrap angle of 135 °, a load of 53 g is applied to one end and it is run at a speed of 1 m / min, and the resistance force (T ₁ (g)) of the other end is measured. The coefficient of friction inside was determined. The measurement was performed at a temperature of 23 ° C. and a humidity of 50%.
The sample used had a width of 10 mm and a length of 300 mm.

(5) Characteristic evaluation after magnetic tape formation Magnetic layer formation (magnetic tape formation) First, a magnetic layer was applied to a polyester film by a conventional method. That is, 250 parts of γ-Fe ₂ O ₃ , polyurethane 40 parts, nitrocellulose 15 parts, vinyl chloride / vinyl acetate copolymer 20 parts, lecithin 7 parts, methyl ethyl ketone 250 parts and butyl acetate 270 parts were mixed and kneaded in a ball mill for 24 hours. , 14 parts of polyisocyanate compound was added to make a magnetic paint, and the dry thickness was 6μ.
Was applied to the film.

Then, while the coating material was not sufficiently dried, the coating material was magnetically oriented by a conventional method, and thereafter, the coating material was opened and dried and cured. The magnetic tape thus obtained was subjected to a super calender treatment and slit into a 1/2 inch width to form a tape.

The following magnetic tape characteristics of the video tape obtained by the above method were evaluated at a constant speed using an NV-3700 type video deck manufactured by Matsushita Electric Industrial Co., Ltd.

(I) Electromagnetic conversion characteristics (VTR head output) The VTR head output at a measurement frequency of 4 MHz with a synchroscope was measured and evaluated in four levels.

(Ii) Playback a videotape recording a signal with a dropout number of 4,4 MHz, and use a dropout counter manufactured by Okura Industry Co., Ltd.
The measurement was carried out for 0 minutes, and the good ones were marked with ◯ and the bad ones were marked with x.

(Iii) Magnetic tape The diamagnetic surface was run multiple times and anti-mammo tape was wound on a winder and rubbed against a metal guide roll installed in the middle to run back and forth at high speed. 50 at this time
The measurement was performed by setting the Masatsu coefficient at the 50th round to be μ50. Further, the amount of white powder generated at this time was measured, and the mammow resistance was ranked as follows.

Rank 1st grade Good 2nd grade Normal 3rd grade Electricity 4th grade Very poor Example 1 <Manufacture of polyester raw material> Raw material 1 100 parts of dimethyl terephthalate, 70 ethylene glycol
Parts, lithium acetate 0.19 parts and calcium acetate-hydrate 0.09
Part of the mixture was placed in a reactor, heated and heated to distill off methanol to carry out a transesterification reaction. The reaction start time is 15
The temperature was set to 0 ° C., and 4 hours after the reaction was started, the temperature reached 235 ° C., and the transesterification reaction was substantially completed.

Then, an ethylene glycol solution mixed with 0.19 parts of triethyl phosphate and 0.03 parts of phosphoric acid was added, and 0.045 parts of antimony trioxide was further added, followed by carrying out a polymerization reaction according to a conventional method.

That is, the temperature of the reaction system after the addition of antimony trioxide was gradually reduced by atmospheric pressure to finally reach 1 mmHg. After 4 hours, the pressure in the system was returned to normal pressure, and polyester chips were used as raw material 1.

The intrinsic viscosity at this time was 0.65.

Raw material 2 100 parts dimethyl terephthalate and 6 ethylene glycol
0 parts, 0.095 parts of calcium acetate monohydrate as a transesterification catalyst, 0.04 parts of antimony trioxide as a polymerization catalyst,
Ethyl acid phosphate (0.069 parts) was added as a polymerization stabilizer, and a polymerization reaction was carried out by a conventional method to obtain a polyethylene terephthalate copolymer. This polymer was taken out in a cut shape and cut into chips (raw material 2). The intrinsic viscosity at this time was 0.65.

Raw material 3 Dimethyl terephthalate 100 parts and ethylene glycol 6
0 parts, 0.095 parts of calcium acetate monohydrate as a transesterification catalyst, 0.04 parts of antimony trioxide as a polymerization catalyst,
Ethyl acid phosphate (0.069 parts) was added as a polymerization stabilizer, and a polymerization reaction was carried out by a conventional method to obtain a polyethylene terephthalate copolymer. This polymer was taken out in a cut shape and cut into chips (raw material 3). The intrinsic viscosity at this time was 0.65.

Raw material 4 In the production of raw material 2, a material obtained by subjecting substantially anatase type titanium dioxide having an average particle diameter of 0.3μ to pre-classification treatment is used.
A polyester raw material (raw material 4) added with 0.3% by weight was manufactured. The intrinsic viscosity at this time was 0.61.

Raw material 5 In the production of raw material 2, spherical silica with an average particle size of 0.78μ.
A polyester raw material (raw material 5) containing 3% by weight was produced. The intrinsic viscosity at this time was also 0.61.

Raw Material 6 Raw Material 2 was dry-blended to a carbon book of 10 wt% and remasterbatched to obtain Raw Material 6.

Raw Material 7 A polyester raw material (raw material 7) was produced by adding 0.4 wt% of kaolin having an average particle size of 1.2 μm to raw material 2.

Raw Material 8 A polyester raw material (raw material 8) was produced by adding 0.2 wt% of siloid having an average particle size of 1.6 μm to raw material 2.

<Polyester film formation> Raw material 1 / raw material 3 = 9 / as a raw material for the layer (A layer) on the smooth surface side
1 (weight ratio, the same hereinafter) (raw material A) was used, and raw material 6 / raw material 3 = 15/85 (raw material B) was used as the raw material of the layer (B layer) on the easy-sliding surface side. Raw material A and raw material B are each dried to 90 mm
An unstretched sheet was produced by extruding through a 5 μm-cut filter through separate melt extruders having a diameter of φ and 60 mmφ, then coextruding into a unit and cooling and solidifying on a flat casting drum. The thickness ratio of the A layer and the B layer was 4: 1.

The obtained unstretched sheet was stretched at 85 ° C. in the longitudinal direction by 2.4 times, and at 92 ° C. by 1.3 times. Then at 110 ° C laterally
After being stretched 3.8 times, it was heat set at 217 ° C. to obtain a biaxially stretched film having a thickness of 15 μm.

Example 2 In Example 1, raw material 6 / raw material 5 = 2/8 as raw material for layer B
A film was obtained in the same manner as in Example 1 except that the above was used.

Example 3 A 15 μm film was obtained in the same manner as in Example 1 except that the raw material 4 alone was used as the raw material for the layer A.

Comparative Example 1 A film having a thickness of 15 μm was obtained in the same manner as in Example 1 except that the thickness ratio of the A layer to the B layer was 1: 4.

Comparative Example 2 Raw material 7: Raw material 8 = 8: 2 as the raw material of the B layer in Example 1.
A film having a thickness of 15 μm was obtained in the same manner as in Example 1 except that the above raw material was used.

Comparative Example 3 A film having a thickness of 15 μm was obtained in the same manner as in Example 1 except that the raw material of the raw material 2 alone was used as the raw material of the layer B.

The properties of the obtained film and the properties after forming the magnetic tape are summarized in Table-1.

[Effect of the Invention] The film of the present invention is a film that satisfies the contradictory characteristics of flatness and easy slippage, and is a novel material that does not require a back coat layer when used in a high-density recording video tape. , Very useful.

Claims (1)

[Claims] 1. A biaxially oriented composite film in which at least two layers are laminated by coextrusion, and the center line average roughness (Ra ^A ) of one surface (A surface) is in the range of 0.002 to 0.015 μm. And the center line average roughness (Ra ^B ) of the surface opposite to the A surface (B surface),
A composite film characterized in that the ten-point average roughness (Rz ^B ) and the number of projections per 0.1 mm length (m ^B ) simultaneously satisfy the following and formula, respectively. 0.015 ≤ Ra ^B ≤ 0.045 ...... Rz ^B / Ra ^B ≤ 15.0 ...... 10 ≤ m ^B ......