JPH05212788A - Biaxially oriented thermoplastic resin laminated film and manufacture thereof - Google Patents

Abstract

PURPOSE:To provide a film which has high S/N and surface durability for a vapor deposition film and keeps an excellent sliding property for both its depositing and traveling surfaces. CONSTITUTION:A biaxially oriented thermoplastic resin laminated film is characterized by the following properties: the surface roughness (Ra) of the one surface (A surface) of the film is within 3nm, and its peak number (RMS-n) is 40 or more; the surface roughness (Ra) of the other surface (B surface) is 3-50nm; the total reflection Raman crystallization indices for both A and B surfaces are 20cm<-1> or less.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a biaxially oriented thermoplastic resin laminated film, a method for producing the same, and a metal thin film type magnetic recording medium using the same.

[0002]

2. Description of the Related Art As a metal thin film type magnetic recording medium, a magnetic recording medium comprising a polyester film and a metal thin film type magnetic layer is known (for example, JP-A-58-682).
No. 25). In addition, as the magnetic recording hardware and software have become higher in performance, the magnetic material of the magnetic recording tape has also been changed to oxide coating, metal coating, and vapor deposition. Along with such changes in magnetic recording, many improvements have been made to the base film of magnetic recording tapes. In a conventional biaxially oriented thermoplastic resin film with two layers, one side has smoothness (related to the high S / N (signal / noise ratio) when used as a magnetic tape) and slipperiness (running property of the magnetic tape). (For example, Japanese Patent Laid-Open No. 2-77431).

[0003]

However, the conventional film as described above has a problem that it is not possible to satisfy the smoothness, the slipperiness and the surface durability on the vapor deposition surface.

The present invention solves the above problems, has a high S / N even when used for a vapor deposition tape, and has a biaxially oriented thermoplastic resin laminated film which has good slipperiness and surface durability on both sides, An object of the present invention is to provide a manufacturing method thereof and a magnetic recording medium using the same.

[0005]

The biaxially oriented thermoplastic resin laminated film of the present invention is a laminated film obtained by coextrusion of at least two layers, and the surface roughness of one surface (A surface) of the film is the center. The line average roughness (Ra) is less than 3 nm, the number of peaks (RMS-n) is 40 or more, the surface roughness (Ra) of the opposite surface (B surface) is 3 to 50 nm, and A Surface total reflection Raman crystallization index is 20c
m ^-1 or less.

Here, the film to be the B side (film B
It is preferable that the thickness (t _B ) and the particle diameter (d _B ) of the inert particles contained in the film B satisfy the following relationship. 0.1 ≦ t _B / d _B ≦ 3

Further, the film to be the A side (referred to as film A) is mainly composed of a thermoplastic resin having a melting point of 40 ° C. or more lower than that of the thermoplastic resin forming the film B, and the inert particles contained therein are Particle size is less than 5 to 50 nm,
It is preferable that the thickness (t _A ) of the film A and the particle diameter (d _A ) of the inert particles contained in the film A satisfy the following relationship. 0.1 ≦ t _A / d _A ≦ 3 Further, the number density of the protrusions existing on the A surface is 8 million / m.
m ² or more and the projection diameter is 40 nm or more and 200 n
It is preferably m or less.

Further, the particle diameter of the inert particles contained in the film B is 50 to 400 nm, the number density of the protrusions present on the B surface is 20 to 5 million / mm ² , and the diameter of the protrusions is 200 nm. It is preferably 1500 nm or less.

In producing such a film, it is preferable to heat it at a temperature not lower than the melting point of the film A and not higher than the melting point of the film B after biaxial stretching.

Further, by using the above-mentioned biaxially oriented thermoplastic resin film as a base material and providing a metal thin film layer on the A surface of the base material, a magnetic recording medium which solves the above problems can be obtained.

The thermoplastic resin constituting the present invention is not particularly limited as long as it has film formability such as polyester, polyolefin, polyamide and polyphenylene sulfide, but is particularly polyester, especially ethylene terephthalate, ethylene-α, β-. Bis (2-chlorophenoxy) ethane-4,4'-dicarboxylate,
It is desirable to have at least one structural unit selected from ethylene-2,6-naphthalate units as a main constituent.

The film of the present invention contains the above-mentioned composition as a main component, but may be blended with other polymers within a range not impairing the object of the present invention, or may be an antioxidant, a heat stabilizer and a lubricant. Inorganic or organic additives such as UV absorbers and nucleating agents may be added.

The film of the present invention is a film in which the above composition is biaxially oriented, and the refractive index ratio in the thickness direction showing the degree of the orientation is not particularly limited, but, for example, ethylene terephthalate is a main component. In the case of polyester, when the range is 0.935 to 0.970, S /
N, slipperiness, and surface durability are further improved, which is particularly desirable.

In the film of the present invention, the surface roughness of the A side is less than 3 nm in center line average roughness (Ra). More preferably 0.3 to 2.5 nm, and even more preferably 0.5 to
It is preferably 1.5 nm. If it is less than this range, the slipperiness and surface durability will deteriorate, and if it is more than this range, S
/ N decreases, which is not preferable. Further, the surface roughness (Ra) of the B side is 3 to 50 nm. More preferably 8
It is desirable that the thickness is -40 nm, more preferably 12-30 nm. If it is less than this range, the slipperiness deteriorates,
If it is larger than this range, the output characteristics become poor, which is not preferable. Further, if RMS-n is less than 40, the slipperiness of the A surface is deteriorated, which is not preferable.

The surface total reflection Raman crystallization index of plane A is 2
When it is 0 cm ^-1 or less, the durability is further improved and the handling property is also improved.

In the film of the present invention, the relationship of 0.1 ≦ t _B / d _B ≦ 3 is established between the thickness (t _B ) of the film B and the particle size (d _B ) contained in the film B. Preferably. More preferably 0.
It is 2 or more and 2 or less, and more preferably 0.5 or more and 1.5 or less. If it is less than this range, the slipperiness is deteriorated, which is not preferable. If it is larger than this range, the output characteristics become poor, which is not preferable.

In the film of the present invention, the main component of the film A is a thermoplastic resin having a melting point of 40 ° C. or more lower than that of the thermoplastic resin constituting the film B, and the inert particles contained therein have a particle size of 5 to 5. It is preferably less than 50 nm, more preferably 10 to 40 nm, and further preferably 15 to 30 nm. If it is smaller than this range, the slipperiness and surface durability are deteriorated, and if it is larger than this range, the S / N is lowered, which is not preferable. The number density of the protrusions present on the A surface is preferably 8 million pieces / mm ² or more, and more preferably 12 million pieces / mm ²
The above is more preferable, and it is more preferable that the number is 15 million pieces / mm ² or more. If it is less than this range, the slipperiness and surface durability are deteriorated, which is not preferable. The projection diameter is preferably 40 nm or more and 200 nm or less, more preferably 60 nm or more and 160 nm or less, and further preferably 80 nm or more and 130 nm or less. If it is smaller than this range, the slipperiness and surface durability are deteriorated, and if it is larger than this range, the S / N is lowered, which is not preferable. Further, the addition amount of the inert particles contained in the film A is 0.
It is preferably from 05 to 5% by weight, more preferably from 0.1 to 4% by weight, and further preferably from 0.25 to 3% by weight. If it is smaller than this range, the slipperiness and surface durability are deteriorated, and if it is larger than this range, the S / N is lowered, which is not preferable. Further, the film of the present invention is film A
(T _A ) and the particle diameter (d _A ) of the inert particles contained in the film A preferably satisfy the following relationship. 0.1 ≦ t _A / d _A ≦ 3 If it is smaller than this range, the slipperiness and surface durability are deteriorated, and if it is larger than this range, the output characteristics become unfavorable. further,
It is preferable to use a copolymerized thermoplastic resin as the thermoplastic resin forming the film A because a high S / N can be obtained.

In the present invention, the particle diameter of the inert particles contained in the film B is preferably 50 to 400 nm, more preferably 60 to 350 nm, further preferably 100 to 300 nm. If it is less than this range, the slipperiness is deteriorated, which is not preferable.
If it is larger than this range, the output characteristics become poor, which is not preferable. The addition amount is preferably 0.1 to 10% by weight, more preferably 0.5 to 7% by weight, and further preferably 1 to 5% by weight. Also,
The number density of protrusions on the B side is 200,000 / mm ² or more 5
Preferably 00 at thousands / mm ² or less, more preferably 500,000 / mm ² or more 4,000,000 / mm ² or less,
More preferably 1 million pieces / mm ² or more and 3 million pieces /
It is desirable that it is not more than mm ² . If it is smaller than this range, the slip property deteriorates, and if it is larger than this range, the output characteristics deteriorate. The protrusion diameter is preferably 200 nm or more and 1500 nm or less, more preferably 250 nm or more and 1200 nm or less, and further preferably 300 nm or more 1.
It is preferably 000 nm or less. If it is smaller than this range, the slip property deteriorates, and if it is larger than this range, the output characteristics deteriorate.

In order to obtain the film of the present invention, in the production thereof, after biaxial stretching, the melting point of the film A is not less than the melting point of the film B and not more than the melting point of the film B, more preferably not less than the melting point of the film A + 10 ° C. and the melting point of the film B. It is desirable to perform the heat treatment at −10 ° C. or lower, more preferably at a melting point of film A + 15 ° C. or higher and a melting point of film B −15 ° C. or lower.

The film of the present invention has at least a two-layer laminated constitution of the above-mentioned film A and film B, but a C layer is provided between the film A and the film B, and A / C / B is used.
It may be a layer film. In this case, the central C layer may not contain the inert particles, but particles having the same particle size as the particles contained in the film A may be added to the same amount.

The effect of the biaxially oriented thermoplastic resin laminated film obtained by the present invention is remarkable in a vapor deposition film, particularly a three-layer vapor deposition film.

The type of the inert particles used in the present invention is not particularly limited, but examples thereof include substantially spherical silica particles derived from colloidal silica, particles of a crosslinked polymer (eg, crosslinked polystyrene), and the like. In particular, the temperature at the time of 10% weight loss (thermogravimetric analyzer under nitrogen, Shimadzu TG-
Measured using 30M. Temperature rising rate of 20 ° C / min) is 380 ° C
In the case of crosslinked polymer particles having a high degree of crosslinking up to the above, durability is further improved, which is particularly desirable. In the case of spherical silica derived from colloidal silica, the durability is further improved in the case of substantially spherical silica produced by the alkoxide method and having a low sodium content, which is particularly desirable.

Next, the method for producing the film of the present invention and the magnetic recording medium using the film as a base material will be described. First, as a method of incorporating the inert particles into the thermoplastic resin A, B or C, a method in which the inert particles are made into a slurry of ethylene glycol and kneaded into the thermoplastic resin using a vent type twin-screw kneading extruder is used. It is extremely effective for obtaining a base film having a relationship between the thickness and the average particle diameter and the content within the range of the present invention without stretching breakage. As a method for adjusting the content of particles, a high-concentration master is prepared by the above method, and the content of particles is adjusted by diluting it with a thermoplastic resin that does not substantially contain inert particles during film formation. The method is effective.

Next, the pellets of the thermoplastic resin A, B or C containing a predetermined amount of inert particles are dried, if necessary, and then supplied to a known extruder for melt lamination, and a sheet is cut from a slit-shaped die. It is extruded into a shape and cooled and solidified on a casting roll to form an unstretched film. That is, for the A / B two-layer structure, two extruders, a two-layer manifold or a merging block are used to laminate the thermoplastic resins A and B, a two-layer sheet is extruded from the die, and cooled by a casting roll. To make an unstretched film. In this case, the method of installing a static mixer and a gear pump in the polymer flow path of the thermoplastic resin A does not cause stretching breakage, and the relationship between the thickness and the average particle diameter within the range of the present invention, the content,
It is effective in obtaining a film having a surface layer particle concentration ratio within a desired range. Further, it is extremely effective to use a rectangular feed block as the merging block. Also, A / C
In the case of the / B configuration, three extruders are used in the same manner, a three-layer manifold or a merging block is used to laminate the thermoplastic resins A, C, and B, and a three-layer sheet is extruded from the die, Cool on a casting roll to make an unstretched film.

Next, this unstretched film is biaxially stretched to be biaxially oriented. As a stretching method, a sequential biaxial stretching method or a simultaneous biaxial stretching method can be used. However, a sequential biaxial stretching method of first stretching in the longitudinal direction and then in the width direction is used, and the stretching in the longitudinal direction is divided into three or more steps, and the total longitudinal stretching ratio is 3.0 to 6.5 times. The method is effective for obtaining a film having a relationship between the thickness and the average particle size and the content within the range of the present invention. The lengthwise stretching temperature differs depending on the type of thermoplastic resin and cannot be generally stated, but usually the first stage is set to 50 to 130 ° C. and the second stage and subsequent stages are made higher than that. The unevenness is effective for obtaining a film having a surface layer particle concentration ratio within the desirable range of the present invention. The longitudinal stretching speed is preferably in the range of 5000 to 50000% / min. As a stretching method in the width direction, a method using a stenter is generally used. The stretching ratio is appropriately in the range of 3.0 to 5.0 times. The stretching speed in the width direction is 1000 to
It is preferable that the temperature is 20000% / min and the temperature is 80 to 160 ° C.

Next, this stretched film is heat-treated. After stretching in the width direction, it is also possible to perform stretching in the longitudinal direction and width direction again without performing heat treatment, and then perform heat treatment.

Next, a metal thin film to be a magnetic layer is formed on this film. The method of forming the magnetic layer can be performed by a known method. For example, it is preferable to form a metal thin film of iron, cobalt-nickel or its alloy by vacuum deposition, ion plating, sputtering or the like directly on the base material film or through an underlying thin film of aluminum, titanium, chromium or the like.

[Method of measuring characteristics and method of evaluating effects]
The method for measuring the characteristic value and the method for evaluating the effect of the present invention are as follows. (1) Average particle size of particles Polyester is removed from the film by a plasma low temperature ashing method to expose the particles. The processing conditions are selected such that polyester is incinerated but particles are not damaged.
This is observed with a scanning electron microscope (SEM), and the image of the particles is processed with an image analyzer. The following numerical processing is performed when the number of particles is changed to 5,000 or more by changing the observation location, and the number average diameter D thus obtained is taken as the average particle diameter. D = ΣDi / N Here, Di is the equivalent circle diameter of particles, and N is the number of particles.

(2) Protrusion Diameter and Protrusion Density Using SEM manufactured by Akashi Seisakusho Co., Ltd., the film surface was photographed at about tens of thousands of times, depending on the grain size, and the protrusion diameter was measured for 200 particles. Then, the average is taken as the projection diameter. Further, 20 fields of view were photographed at a lower magnification than this, and the projection density was converted from the average number of projections present in each field.

(3) Content of Particles A solvent in which polyester is dissolved but not particles is selected is selected, the particles are centrifuged from the polyester, and the ratio (% by weight) to the total weight of the particles is taken as the particle content.
In some cases, the combined use of infrared spectroscopy is also effective.

(4) Surface roughness parameters Ra (center line average roughness), Rt (maximum height), RMS-n (number of peaks) Measured using a high precision step measuring instrument ET-10 manufactured by Kosaka Laboratory did. The conditions are as follows, and the average value of 20 measurements was taken.・ Stylus tip radius: 0.5 μm ・ Stylus load: 5 mg ・ Measurement length: 0.5 mm ・ Cutoff value: 0.008 mm

(5) The S / N film was obliquely vapor-deposited by a high frequency sputtering method using a cobalt-nickel alloy (Ni 20 wt%) in the presence of a slight amount of oxygen in a vacuum vapor deposition machine to form a vapor deposition layer having a thickness of μm. Then, the tape width was slit and the pancake of a vapor deposition tape was created. A length of 250 m from this pancake was incorporated into a VTR cassette to obtain a VTR cassette tape. Using a home-use VTR on this tape, use a TV test waveform generator (TG7 / U706) manufactured by Shibasoku to produce 100
% Chroma signal is recorded, and chroma S / from the reproduced signal is recorded by Shiba Soku color video noise measuring device (925D / 1).
N was measured, and this chroma S / N was compared with a commercially available 8 mm video tape (120-minute ME), and a value higher than 1.0 dB was determined as S / N good, and a value less than that was determined as S / N defective. ..

(6) Sliding property: Measured using a slip tester according to ASTM-D-1894B-63. Less than 0.7 is judged as good for A side, and 0.7 or more is judged as bad, and 0.5 is judged for B side.
Less than was judged to be good and less than 0.5 was judged to be bad.

(7) Surface Durability A film slit into a tape having a width of 1/2 inch was placed on a guide pin (surface roughness: Ra of 100 nm) using a tape running tester. Run (travel speed 1,00
0m / min, 10 passes, winding angle: 60 °, running tension: 65g). At this time, the scratches in the film were observed with a microscope, and it was judged that scratches having a width of 2.5 μm or more were excellent when less than 2 per tape width, good when 2 or more and less than 10 were good, and bad when 10 or more. .. Good is desirable, but good is practically usable.

(8) Thickness of Laminated Resin Layer Using a secondary ion mass spectrometer (SIMS), the element derived from the highest density particle among the particles in the film having a depth of 3000 nm from the surface is identified. The carbon element concentration ratio (M ⁺ / C ⁺ ) of the polyester is used as the particle concentration, and analysis is performed in the thickness direction from the surface to a depth of 3000 nm. In the surface layer, the particle concentration is low due to the interface of the surface, and the particle concentration increases as it enters from the surface. In the case of the film of the present invention, the particle concentration once reaching the maximum value starts to decrease again. Based on this concentration distribution curve, the depth at which the surface layer particle concentration becomes ½ of the maximum value (this depth is deeper than the maximum value) was determined and used as the laminated thickness. The conditions are as follows. Measuring device Secondary ion mass spectrometer (SIMS) West Germany, ATOMIKA, A-DIDA3000 Measuring conditions Primary ion species: O ₂ ⁺ Primary ion accelerating voltage: 12KV Primary ion current: 200nA Raster area: 400μm □ Analysis area : Gate 30% Measured vacuum degree: 6.0 × 10 ^-9 Torr E-GUN: 0.5KV-3.0A In addition, when the most contained particles in the range of depth 3000 nm from the surface are organic polymer particles Since it is difficult to measure with SIMS, the depth profile similar to the above may be measured by XPS (X-ray photoelectron spectroscopy), IR (infrared spectroscopy), etc. while etching from the surface to obtain the laminated thickness. By observing the cross section using an electron microscope, etc., the interface is recognized from the difference in particle concentration and the difference in contrast due to the difference in polymer, and the layer thickness is determined. And it can also be. Furthermore, after peeling the laminated polymer, the laminated thickness can be obtained by using a thin film step measuring machine.

[0036]

EXAMPLES The present invention will be described based on Examples and Comparative Examples. Examples 1 to 6 and Comparative Examples 1 to 7 Ethylene glycol slurries containing specified amounts of crosslinked polystyrene particles having different average particle diameters and silica particles derived from colloidal silica were prepared. After heat treatment for an hour, it undergoes transesterification reaction with a mixture of dimethyl terephthalate or dimethyl isophthalate, dimethyl terephthalate, polycondensation,
Polyethylene terephthalate containing the particles (hereinafter P
Abbreviated as ET) pellets A, B, and C were prepared. At this time,
The polycondensation time was adjusted so that the intrinsic viscosity was 0.65.

Each of these polymers was dried under reduced pressure (3 Torr) at 180 ° C. for 6 hours, then supplied to three extruders and melted at 280 ° C., and these polymers were combined and laminated by a combining block (feed block). The film was wound around a casting drum having a surface temperature of 30 ° C. by using the electrostatically applied casting method and cooled and solidified to prepare a laminated unstretched film.
At this time, for the thickness adjustment, the thickness of each layer was adjusted by using a gear pump for the A layer and the B layer, and the total thickness was adjusted by adjusting the discharge amount of the C layer extruder.

This unstretched film was stretched 3.5 times in the longitudinal direction at a temperature of 80 ° C. The stretching was carried out in four stages with the peripheral speed difference between each pair of two rolls. The obtained uniaxially stretched film was stretched in a width direction at a stretching rate of 2,000% / min at 100 ° C. by a factor of 3.6 using a stenter and heat-treated at a predetermined temperature for 5 seconds to give a total thickness of 10 μm. A biaxially oriented laminated film was obtained.

On one side of these films, a cobalt-nickel alloy (Ni
20 wt%) was obliquely vapor-deposited by a high frequency sputtering method to form a 0.2 μm-thick ferromagnetic thin film layer. Then, slitting was performed in the tape width to obtain a metal thin film type magnetic recording medium.

The evaluation results of the obtained film are summarized in Tables 1 and 2. From these, it is understood that when the surface parameter of the film is within the range of the present invention, a film satisfying all of S / N, slipperiness, and surface durability when used as a vapor deposition tape can be obtained.

[0041]

[Table 1]

[0042]

[Table 2]

[0043]

In the present invention, since the biaxially oriented thermoplastic resin laminated film having a specified surface morphology is used, the S / N and surface durability of the vapor deposition tape are higher than those of the conventional thermoplastic film. Thus, a film having the following characteristics and having extremely excellent slipperiness on both the vapor deposition surface and the running surface was obtained. Furthermore, it can be widely used for improving the quality of magnetic recording media in the future.

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Claims (8)

[Claims] 1. A laminated film obtained by coextrusion of at least two layers, wherein the surface roughness of one surface (A surface) of the film is less than 3 nm in center line average roughness (Ra) and the peak number (RMS-). n) is 40 or more, and the opposite surface (B
Surface roughness (Ra) of 3 to 50 nm, and
A biaxially oriented thermoplastic resin laminated film having a surface total reflection Raman crystallization index of A-side of 20 cm ^-1 or less. 2. The biaxial orientation according to claim 1, wherein the thickness (t _B ) of the film to be the B surface (film B) and the particle diameter (d _B ) of the inert particles contained in the film B satisfy the following relationship. Thermoplastic resin laminated film. 0.1 ≦ t _B / d _B ≦ 3 3. A film to be the A surface (film A) is mainly composed of a thermoplastic resin having a melting point of 40 ° C. or more lower than that of the thermoplastic resin constituting the film B, and the particle diameter of the inert particles contained therein. Is less than 5 to 50 nm, and the film A
The biaxially oriented thermoplastic resin laminated film according to claim 1 or 2, wherein the thickness (t _A ) and the particle diameter (d _A ) of the inert particles contained in the film A satisfy the following relationship. 0.1 ≦ t _A / d _A ≦ 3 4. The number density of the protrusions existing on the surface A is 80.
The biaxially oriented thermoplastic resin laminate film according to claim 2 or 3, wherein the number of protrusions is not less than 0,000 / mm ² and the protrusion diameter is not less than 40 nm and not more than 200 nm. 5. The biaxially oriented thermoplastic resin laminated film according to claim 2, wherein the particle diameter of the inert particles contained in the film B is 50 to 400 nm. 6. The number density of the protrusions existing on the B surface is 20.
The biaxially oriented thermoplastic resin laminate film according to any one of claims 1 to 5, wherein the number of protrusions is 10,000 / mm ² or more and 5 million / mm ² or less, and the protrusion diameter is 200 nm or more and 1500 nm or less. 7. A film A which becomes the A surface after biaxial stretching.
7. The method for producing a biaxially oriented thermoplastic resin laminated film according to claim 1, wherein the heat treatment is performed at a temperature not lower than the melting point of the film B and not higher than the melting point of the film B to be the B surface. 8. A magnetic recording medium comprising the biaxially oriented thermoplastic resin laminated film according to claim 1 as a base material, and a metal thin film layer provided on the surface A of the base material.