JPH07186351A - Laminated polyester film - Google Patents

Abstract

PURPOSE:To provide a laminated polyester film not damaged in mechanical characteristics, excellent in antistatic properties, easy slip properties and abrasion resistance and having characteristics especially excellent as a material for a magnetic recording medium. CONSTITUTION:A laminated polyester film is a co-extrusion laminated polyester film consisting of at least three layers and the surface resistivity value of at least one outermost layer thereof is 10<9>-10<12>OMEGA and cavities with an average diameter of 0.5-10mum and average depth of 0.2-2.0mum based on the antistatic agent dispersed and contained in the film are provided to the surface.of the outermost layer.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a biaxially oriented laminated polyester film having excellent antistatic properties, slipperiness and abrasion resistance, and particularly having excellent dropout characteristics for magnetic recording media.

[0002]

2. Description of the Related Art Biaxially stretched polyester films have excellent properties such as mechanical strength, dimensional stability, flatness, heat resistance, chemical resistance and transparency. It is used in various applications such as base film for recording media and film for plate making, as well as packaging, but in these film applications, the demand for higher functionality has increased in recent years, and as a result, it has become a base film. On the contrary, it is required to have many excellent functions and characteristics. However, the conventional film has insufficient abrasion resistance, and when, for example, the base material and the film are contacted at a high speed, abrasion powder is often generated, which causes various adverse effects. In addition, the slipperiness is not sufficient and handling workability is difficult. Heretofore, a method of roughening the film surface has been known as one of the effective means for solving these problems, and it has been effective to some extent, but it is still insufficient. That is, in order to achieve such roughening, usually, inorganic or organic fine particles are added to the film to form protrusions on the surface. The presence of the projections contributes to the improvement of the surface characteristics, but on the other hand, when the running conditions of the film become severe, the projections are peeled off to produce a white powdery substance. Further, depending on the degree of surface roughening, there are drawbacks such as deterioration of electromagnetic characteristics after processing for a magnetic recording medium.

In order to improve such a defect, attempts have been made to develop fine depressions on the film surface, which are known to be effective. For example, JP-A-57-669
In Japanese Patent Publication No. 36-36957, by selecting special stretching conditions, depressions having protrusions produced by particles as cores are produced. In Japanese Patent Publication No. 2-57573, an aliphatic polyester is represented. It is described that fine recesses are generated by blending linear polymers. However, the depth of the depression cannot be adjusted by either method, and the deep depression causes a dropout in a magnetic recording medium. On the other hand, the biaxially stretched polyester film is liable to generate static electricity like other plastics, and as a result, the film is easily charged. In general, as an antistatic method for polyester films, a method of kneading an anionic surfactant type low molecular weight compound such as an organic sulfonate, a method of depositing a metal compound, an anionic compound, a cationic compound or a conductive compound. There is known a method of applying the to the surface.
Among them, a method of kneading an anionic surfactant type low molecular weight compound such as an organic sulfonate can form fine depressions on the film surface, but it is difficult to control the depth of the depressions.

[0004]

Means for Solving the Problems As a result of intensive studies on the above improvements, the present inventors have found that a film having a specific constitution has excellent properties, and have completed the present invention. . That is, the gist of the present invention is a coextrusion laminated polyester film comprising at least three layers, wherein the surface resistivity of at least one outermost layer is 10 or less.
⁹ to 10 ¹² Ω and an average diameter of 0.5 to 10 μm based on the antistatic agent dispersed and contained in the film on the outermost layer surface.
The present invention relates to a biaxially oriented laminated polyester film, which is characterized by having pits having an average depth of 0.2 to 2.0 μm.

The present invention will be described in detail below. The polyester that can be used in the present invention includes, for example, 80 structural units.
Polyethylene terephthalate in which mol% or more is ethylene terephthalate, and polyethylene-2,6 in which 80 mol% or more of constitutional units is ethylene-2,6-naphthalate
-Naphthalate, 80 mol% or more of the structural unit is 1,4-
Cyclohexane dimethylene terephthalate poly-
Examples include 1,4-cyclohexanedimethylene terephthalate and the like, as well as polyethylene isophthalate, polybutylene terephthalate and the like. Examples of the copolymerization component other than the above-mentioned superior constituent components include diol components such as diethylene glycol, propylene glycol, neopentyl glycol, polyethylene glycol, polytetramethylene glycol, isophthalic acid,
Dicarboxylic acid components such as 2,7-naphthalenedicarboxylic acid, 5-sodium sulfoisophthalic acid, adipic acid, ageric acid, sebacic acid, and ester-forming derivatives such as oxymonocarboxylic acid can be used.
As the polyester, in addition to a homopolymer or a copolymer, a blend with a small proportion of another resin can be used.

The biaxially oriented laminated polyester film (hereinafter abbreviated as laminated film) of the present invention is basically a three-layer structure and is laminated by a coextrusion method, and if necessary, two or more inner layers. It is also possible to employ a layer structure of four or more layers as described above. The feature of the laminated film of the present invention is that the film surface specific resistance value of at least one outermost layer is in a specific range, and the shape of fine depressions based on an antistatic agent related thereto is specified. is there. Although the dents on the surface of the film of the present invention may have some bulge at the edges, there are a recessed portion and a special portion as described in JP-A-57-189822 or JP-A-61-217229. Unlike the one having both of them, the depression has substantially no protrusion.

The above surface resistivity value is determined mainly by blending an antistatic agent with the polyester of the substrate. Specifically, a method of adding an antistatic agent to a raw material in a polyester production process, and a method of blending an antistatic agent or a masterbatch containing the antistatic agent in a raw material resin during film formation are preferably used. Examples of the above antistatic agent include sulfonate and phosphate derivatives that are typical ion conductive compounds. The most typical example is a metal salt of alkylsulfonic acid or a metal salt of alkylbenzenesulfonic acid.

The average diameter of the depressions present on the surface of the outermost layer on at least one side of the laminated film of the present invention is 0.5-1.
It is in the range of 0 μm, preferably 1 to 5 μm, and the area fraction thereof is in the range of 5 to 30%, preferably 10 to 20%. If these values are less than the lower limit, the wear resistance is hardly improved, and if it exceeds the upper limit, the surface roughness becomes too large, and when used for a magnetic recording medium, the electromagnetic characteristics are deteriorated. Will end up. The average depth of such depressions is 0.2 to 2.0 μm, preferably 0.5.
Is in the range of 1.0 μm. If this value is less than the lower limit, the slipperiness of the film deteriorates. On the other hand, if it exceeds the upper limit, the dropout characteristic is deteriorated when it is used for a magnetic recording medium. Furthermore, in the present invention, the surface specific resistance value of the surface of the film having the depressions is 10 ⁹
It is important to be in the range of -10 ¹² Ω. When the surface resistivity of the film is less than 10 ⁹ Ω, a large amount of antistatic agent is blended, which adversely affects the mechanical strength of the film, the thermal strength, and the transparency. . The surface solid resistance of the film is 10 ¹² Ω.
If it exceeds, the antistatic function is lacking.

When the slipperiness of the film is insufficient only by the depressions, the film may contain additional particles, precipitated particles, other catalyst residues, etc., if necessary. Furthermore, if necessary, stabilizer, lubricant, cross-linking agent, anti-blocking agent, antioxidant, infrared absorber,
A colorant or the like may be contained. These additives may be contained in either the inner layer or the outer layer as long as they do not exceed the scope of the present invention. The polyester film of the present invention basically has a three-layer structure and is laminated by a coextrusion method. Specifically, co-extrusion is performed using a co-extrusion laminating apparatus such as a feed block or a multi-manifold die while the inner layer and the polyester forming both outer layers are melted. Then, the obtained melted sheet is rapidly cooled to an unshaped unstretched sheet, and then biaxially oriented and heat-treated according to a conventional method. This heat-treatment is usually the ion conductive compound of the antistatic agent on the film surface. It is carried out at a temperature at which it is sufficiently formed. The thickness of each layer of the laminated film can be usually controlled by adjusting the polymer discharge rate by a gear pump. In the present invention, it is preferable to dispose a biaxial kneading machine for dispersing the antistatic agent for at least the outermost layer on one side. The laminated film of the present invention takes advantage of its excellent properties, in the magnetic recording field of video tapes, audio tapes, floppy disks, magnetic cards, etc., in the field of graphic arts such as photography, microfilm, plate making, tracing films, etc. It can be suitably used in the fields of packaging materials, displays, building materials and the like.

[0010]

EXAMPLES The present invention will be described in more detail with reference to examples below, but the present invention is not limited to the following examples as long as the gist thereof is not exceeded. In the examples and comparative examples, "parts" and "%" mean "parts by weight" and "% by weight", respectively. Moreover, the measuring method of physical properties (characteristics) and the raw material polyester are as follows. (1) Average Diameter and Standard Deviation of Dimples The surface of the film was observed with an optical microscope or an electron microscope, and the equivalent diameter Xi was calculated by converting the area of the dimples into a circle for 100 arbitrary dimples. The average diameter and the standard deviation value are given by the following equation.

[Equation 1]

[Equation 2] (In the above formula, Xi represents the i-th equivalent diameter, and n is 10
0)

(2) Area fraction of depressions The areas of the depressions were summed to obtain the ratio to the entire surface of the film. (3) Depth of depression The cross section of the film was observed with a transmission electron microscope.
That is, a film sample was embedded in an epoxy resin containing a curing agent and a curing accelerator, and a section having a thickness of about 200 nm was prepared with an ultramicrotome, and used as an observation sample. The obtained sample was photographed with a transmission electron microscope "H-9000 type" manufactured by Hitachi, Ltd. to take a photomicrograph of the cross section of the film, and the depth of the depression was measured.
The acceleration voltage was 300 kV, and the observation magnification was arbitrarily set according to the depth of each depression. The depth was measured at 50 points and averaged to obtain a measured value. (4) Surface specific resistance Yokogawa-Hulette Packard Co., Ltd. concentric electrode 16
008A (trade name) "(inner electrode 50 mm diameter, outer electrode 70 mm diameter), the sample was placed in an atmosphere of 23 ° C and 50% RH, a voltage of 100 V was applied, and after 60 seconds, the company's high resistance meter" 4329A (trade name) "was used to measure the surface resistivity of the sample.

(5) Running stability A film having a width of 12.5 mm was subjected to 100 g of hearing and 100 windings between plastic pins were observed. The winding shape was observed and evaluated according to the following three ranks. ○ (good): No winding disorder at all △ (normal): Edges are slightly uneven × (Poor): Edges are uneven (6) Wear resistance Fixed hard chrome plated metal pin (diameter 6mm ), The film is contacted at a winding angle of 135 °, and the speed is 10 m /
The amount of white powder adhering to the pins was visually classified into the following four ranks by running for 1,000 m at a tension of 200 g. Rank A: No adhesion Rank B: Small amount adhesion Rank C: Small amount (more than Rank B) adhesion Rank D: Large amount adhesion

(7) Measurement of Dropout Number 200 parts of magnetic powder fine powder, 30 parts of polyurethane resin, 10 parts of nitrocellulose, 10 parts of vinyl chloride / vinyl acetate copolymer, 5 parts of styrene, 100 parts of cyclohexanone,
After 300 parts of methyl ethyl ketone and 100 parts of methyl isobutyl ketone were mixed and dispersed in a ball mill for 48 hours, 5 parts of a polyisocyanate compound was added to form a magnetic paint, which was applied to a polyester film and then magnetically oriented before the paint was sufficiently dried and solidified. After that, it was dried to form a magnetic layer having a thickness of 2 μm, and then the coated film was subjected to surface treatment with a super calender and slit into a 1/2 inch width to obtain a video tape. A signal of 4.4 MHz was recorded, a video tape was reproduced, the number of dropouts was measured by a dropout counter manufactured by Okura Industry Co., Ltd. for about 20 minutes, and converted into the number of dropouts per minute.

<Raw Material Polyester> Raw material polyesters used in Examples and Comparative Examples are as follows. (1) Polyester A 0.02% by weight of spherical silica having an average particle size of 0.5 μm, an antistatic agent (sodium alkyl sulfonate, carbon number = 1)
1) 0.5% by weight of polyethylene terephthalate (2) Polyester B 0.02% by weight of spherical silica having an average particle size of 0.5 μm, 0.5% by weight of sodium dodecylbenzenesulfonate,
Polyethylene terephthalate containing (3) Polyester C Polyethylene terephthalate containing substantially no additive (4) Polyester D Polyethylene terephthalate containing 0.3% by weight of spherical silica having an average particle size of 0.5 μm (5) Polyester E Average particle size Polyethylene terephthalate containing 0.1% by weight of 0.3 μm titanium dioxide

Example 1 Polyesters A and C were used and laminated so as to have an A / C / A layer structure. That is, both outer layers A were kneaded and dispersed by a twin-screw kneader and then laminated in a die, extruded into a sheet form from a die at 290 ° C., and rapidly cooled on a cooling drum to obtain a three-layered non-oriented sheet. The obtained non-oriented sheet was stretched 3.7 times at 85 ° C. in the length direction and 4.0 times at 95 ° C. in the width direction, and then heat-treated at 235 ° C. for 2 seconds to obtain a biaxially oriented laminated polyester film. It was The obtained laminated film had a thickness constitution of 0.5 μm / 14.0 μm / 0.5 μm. This film was further made into a video tape according to the above-mentioned magnetic tape manufacturing method.
The measurement results of the physical properties and characteristics of this laminated film are shown in Table 1 below. The laminated film has good antistatic properties,
It was a preferred laminated film showing abrasion resistance and dropout characteristics.

Example 2 In Example 1, the antistatic agent of polyester A 0.3
A laminated film and a magnetic tape were obtained in the same manner as in Example 1 except that the weight% was used, and the characteristics thereof were evaluated. Example 3 In Example 1, the thickness composition of the laminated flume was 1.0 μm.
A laminated film and a magnetic tape were obtained in the same manner as in Example 1 except that the thickness was /13.0 μm / 1.0 μm, and the characteristics thereof were evaluated. Example 4 In Example 1, the antistatic agent of polyester A 1.0
A laminated film and a magnetic tape were obtained in the same manner as in Example 1 except that the weight% was used, and the characteristics thereof were evaluated.

Comparative Example 1 A biaxially oriented polyester film and a magnetic tape were obtained in the same manner as in Example 1, except that the single layer film of polyester A having a thickness of 15 μm was used. The measurement results of the physical properties and characteristics of the obtained film are shown in Table 2 below.
As shown in Table 1, the depth of the dents on the film surface was deep, and the dropout characteristics deteriorated when used for magnetic recording. Comparative Example 2 In Example 1, using polyesters B and C,
0.5 μm / 14.0 μm in the same manner as in Example 1 except that the layers were laminated in a die so as to have a B / C / B layer structure.
A biaxially oriented polyester film and a magnetic tape having a three-layer structure of m / 0.5 μm were obtained. The measurement results of the physical properties and characteristics of the obtained film are shown in Table 2. The film had no manifestation of depressions on the surface and had poor slipperiness.

Comparative Example 3 In Example 1, polyesters D and C are used,
0.5 μm / 14.0 μm in the same manner as in Example 1 except that the layers were laminated in a die so as to have a D / C / D layer structure.
A biaxially oriented polyester film and a magnetic tape having a three-layer structure of m / 0.5 μm were obtained. The measurement results of the physical properties and characteristics of the obtained film are shown in Table 2. The film had no appearance of depressions on the surface and had poor abrasion resistance. Comparative Example 4 In Example 1, using polyesters E and C,
0.5 μm / 14.0 μm in the same manner as in Example 1 except that the layers were laminated in a die so as to have an E / C / E layer structure.
A biaxially oriented polyester film and a magnetic tape having a three-layer structure of m / 0.5 μm were obtained. The measurement results of the physical properties and characteristics of the obtained film are shown in Table 2. The film had no appearance of dents on the surface and had poor wear resistance.

[0019]

[Table 1]

[0020]

[Table 2]

[0021]

According to the present invention, the film has excellent antistatic properties, slipperiness and abrasion resistance without impairing its mechanical properties.
In particular, a laminated film having excellent properties is provided for a magnetic recording medium, and it can be suitably used in magnetic recording applications, graphic arts and packaging materials, and the industrial value of the present invention is high.

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Claims (1)

[Claims] 1. A coextruded laminated polyester film comprising at least three layers, wherein at least one outermost layer has a surface specific resistance value of 10 ⁹ to 10 ¹² Ω and is dispersed and contained in the film on the surface of the outermost layer. Based on the antistatic agent, the average diameter is 0.5 to 10 μm and the average depth is 0.2 to 2.0.
A biaxially oriented laminated polyester film having a depression of μm.