JPH0592534A - Laminate biaxially oriented polyester film - Google Patents

Abstract

PURPOSE:To manufacture a biaxially oriented polyester laminated film of superior resistance to shaving and superior electromagnetic conversion characteristics under severe magnetic tape manufacturing conditions. CONSTITUTION:A biaxially oriented polyester laminated film composed of polyester containing spindle-shaped calcium carbonate particles of 0.2-8wt.% having the average grain diameter equivalent to area circle of 0.1-2mum, grain diameter ratio (long diameter/short diameter) of 1.5-10 and relative standard deviation of 0.5 or less, and the film is formed by laminating layers of thickness of 0.1-2 times as large as the grain diameter.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a biaxially oriented polyester film, and more specifically, it has fine projections on the film surface and uniform surface roughness, and is excellent in slipperiness, abrasion resistance and scratch resistance. The present invention relates to a laminated biaxially oriented polyester film useful as a base film of a magnetic recording medium.

[0002]

A biaxially oriented polyester film represented by a polyethylene terephthalate film is used as a base film for magnetic recording media such as magnetic tapes and floppy disks because of its excellent physical and chemical properties.

In such a biaxially oriented polyester film, its slipperiness and abrasion resistance are major factors that affect the workability of the film manufacturing process and the working process in each application, and further the quality of the product. ing. If these are insufficient, for example, when a magnetic layer is coated on the surface of a polyester film and used as a magnetic tape, the friction between the coating and the film surface during coating of the magnetic layer is severe, and the abrasion of the film surface due to this is also severe. In that case, wrinkles, scratches, etc. on the film surface occur.

Further, even after slitting the film after coating the magnetic layer and processing it into audio, video or computer tape, etc., it can be pulled out from the reel, cassette or the like.
At the time of winding and other operations, abrasion occurs remarkably with many guide parts, playback heads, etc., and scratches and distortions occur,
Further, as a result of depositing a white powdery substance due to abrasion of the polyester film surface or the like, it often becomes a major cause of loss of magnetic recording signals, that is, dropout.

Generally, in order to improve the slipperiness of a film, a method of reducing the contact area with a guide roll or the like by providing unevenness on the surface of the film is adopted, and it is roughly classified into (i) the raw material polymer. In the production process, a method of precipitating inactive fine particles from the catalyst residue and a method of (ii) adding inactive inorganic fine particles are used. The larger the size of the fine particles in these raw material polymers,
Generally, the improvement in slipperiness is large.

On the other hand, in a magnetic recording medium, particularly a high-density magnetic recording tape or a high-sensitivity floppy disk, the surface of the base film is required to be as flat as possible in order to improve the electromagnetic conversion characteristics. However, if the film surface becomes flat, as described above, the slipperiness of the film deteriorates, causing various troubles.

Therefore, there is a demand for a magnetic recording medium film to satisfy these contradictory characteristics at the same time.

For the purpose of simultaneously satisfying such requirements, there has been proposed a method using a front and back different surface film having one surface flat and the other surface rough so that the surface roughness is different. If a magnetic layer is provided on the flat surface of this film and the rough surface is used as the film running surface, it is possible to have both flatness from the viewpoint of improving electromagnetic conversion characteristics and slipperiness from the viewpoint of film running performance. A better film can be obtained as a recording medium film.

However, these means also have problems to be solved, and it is difficult to meet the demands for higher grade and higher density of the magnetic recording medium as they are.

The problems of the method of roughening the surface using the above-mentioned inert fine particles are considered to be mainly due to the fact that the individual sizes of the fine particles vary and the particle size has a distribution. If this particle size distribution becomes large (wide), coarse protrusions based on large particles will be present on the film surface, which will cause abrasion during processing and also during running as a magnetic tape after processing. It is not desirable because scratches and shavings are generated, resulting in many dropouts and poor electromagnetic conversion characteristics.

Therefore, for the purpose of improving such a point, a biaxially laminated film obtained by laminating a thin layer of a thermoplastic polymer containing inert spherical particles having a small variation in particle size on at least one surface of the biaxially oriented film. An oriented film has been proposed (JP-A-2-214657). This laminated biaxially oriented film has excellent electromagnetic conversion characteristics and is good in terms of slipperiness and little increase in friction after repeated running with metal pins and plastic pins when used as a tape for video and audio, and no increase in dropout. Shows the characteristic. But,
In recent years, as the speed of tape manufacturing process has become faster, the conditions of calendar and coater have become stricter, and in the above-mentioned laminated biaxially oriented film, spherical particles in a thin layer fall off in the process, resulting in many product dropouts. A problem has arisen.

[0012]

DISCLOSURE OF THE INVENTION The inventors of the present invention have conducted extensive studies to solve this problem, and as a result, to solve this problem, the particle shape in the thin layer and the projection shape resulting from the particle shape were investigated. They have found that it is essential to make the material suitable, and have reached the present invention.

Therefore, the object of the present invention is to have a specific projection shape due to the particle shape in the thin layer and to make the projection heights uniform, and to be excellent in slipperiness and abrasion resistance, and for magnetic recording media. It is an object of the present invention to provide a laminated biaxially oriented polyester film which is excellent in electromagnetic conversion characteristics when used and can be manufactured with a small dropout.

[0014]

In order to achieve the above-mentioned object, the present invention has the following constitution.

The biaxially oriented polyester film has an average area-equivalent diameter of 0.1 to 2 on at least one surface.
0.2 to 8% by weight of spindle-shaped calcium carbonate particles having a particle size ratio (major axis / minor axis) of 1.5 to 10 and a relative standard deviation represented by the following formula of 0.5 or less. A laminated biaxially oriented polyester film comprising a polyester containing therein and having a layer thickness of 0.1 to 2 times the particle size.

[0016]

[Equation 2]

The polyester in the present invention is a polyester having an aromatic dicarboxylic acid as a main acid component and an aliphatic glycol as a main glycol component. Such polyesters are substantially linear and have film-forming properties, especially film-forming by melt molding. Examples of the aromatic dicarboxylic acid include terephthalic acid, naphthalene dicarboxylic acid, isophthalic acid, diphenoxyethane dicarboxylic acid, diphenyl dicarboxylic acid, diphenyl ether dicarboxylic acid, diphenyl sulfone dicarboxylic acid, diphenyl ketone dicarboxylic acid and anthracene dicarboxylic acid. You can Examples of the aliphatic glycol include polymethylene glycol having 2 to 10 carbon atoms such as ethylene glycol, trimethylene glycol, tetramethylene glycol, pentamethylene glycol, hexamethylene glycol and decamethylene glycol, and alicyclic compounds such as cyclohexanedimethanol. Examples thereof include diols.

In the present invention, as the polyester, for example, one having alkylene terephthalate and / or alkylene naphthalate as a main constituent is preferably used.

Among such polyesters, not only polyethylene terephthalate and polyethylene-2,6-naphthalate but, for example, terephthalic acid and / or 2,6-naphthalenedicarboxylic acid account for 80 mol% or more of the total dicarboxylic acid component, 80 of all glycol components
Copolymers in which more than mol% is ethylene glycol are preferred. 20 mol% or less of the total acid component can be the above aromatic dicarboxylic acids other than terephthalic acid and / or 2,6-naphthalenedicarboxylic acid, and aliphatic dicarboxylic acids such as adipic acid and sebacic acid. An alicyclic dicarboxylic acid such as cyclohexane-1,4-dicarboxylic acid can be used. Further, 20 mol% or less of the total glycol component may be the above-mentioned glycol other than ethylene glycol, or an aromatic diol such as hydroquinone, resorcin, 2,2-bis (4-hydroxyphenyl) propane, etc .; 1 An aliphatic diol having an aromatic ring such as 1,4-dihydroxydimethylbenzene; a polyalkylene glycol (polyoxyalkylene glycol) such as polyethylene glycol, polypropylene glycol, polytetramethylene glycol and the like can also be used.

The polyester of the present invention includes
Aromatic oxyacids such as hydroxybenzoic acid, ω-
Also included are those in which a component derived from an oxycarboxylic acid such as an aliphatic oxyacid such as hydroxycaproic acid is copolymerized or bonded at 20 mol% or less based on the total amount of the dicarboxylic acid component and the oxycarboxylic acid component.

Further, in the polyester of the present invention,
Amounts in a range that is substantially linear, eg, 2 based on total acid component.
It also includes a copolymerized polycarboxylic acid or polyhydroxy compound having a functionality of 3 or more, such as trimellitic acid and pentaerythritol, in an amount of not more than mol%.

The above polyester is known per se and can be produced by a method known per se.

The above polyester preferably has an intrinsic viscosity of about 0.4 to about 0.9 measured at 35 ° C. as a solution in o-chlorophenol.

The laminated biaxially oriented polyester film of the present invention comprises at least two layers. The two layers of polyester may be the same or different, but the same is preferred.

In the present invention, the polyester layer forming at least one side of the laminated biaxially oriented polyester film has an average particle diameter corresponding to an area circle of 0.1 to 2 μm,
It is necessary to contain 0.2 to 8% by weight of spindle-shaped calcium carbonate particles having a particle size ratio (major axis / minor axis) of 1.5 to 10 and a relative standard deviation of 0.5 or less. If the average particle size is less than 0.1 μm, the height of protrusions is insufficient,
This is not preferable because the slipperiness of the film is insufficient. On the other hand, if the average particle size exceeds 2 μm, the surface of the film becomes too rough, and the roughness of the film is transferred to the magnetic surface during the production of a magnetic recording medium, which deteriorates the electromagnetic conversion characteristics, which is not preferable. A more preferable average particle size is 0.2 to 1.2 μm. On the other hand, when the particle size ratio of the particles is less than 1.5, the particles do not exhibit stress relaxation in the stretching direction of the film, voids are likely to occur around the particles, or the projections formed are too sharp, resulting in a tape. There is a problem that particles are likely to fall off during the manufacturing process, which is not preferable. On the other hand, when the particle size ratio exceeds 10, the slipperiness of the film is deteriorated and shavings are easily generated, which is not preferable. Furthermore, the relative standard deviation of the particle size of the particles is 0.5 or less, more preferably 0.4 or less. If the relative standard deviation exceeds 0.5, the heights of the protrusions become uneven, shavings are easily generated, and the electromagnetic conversion characteristics are deteriorated when used for a magnetic recording medium, which is not preferable. Furthermore, the addition amount is 0.2% by weight.
When it is less than the above range, the number of projections formed on the film surface of the layer becomes insufficient and the slipperiness is insufficient, which is not preferable. On the other hand, if the amount added is more than 8% by weight, the particles are significantly overlapped in the layer, resulting in uneven projections formed on the film surface, which is not preferable. The preferable addition amount range is 0.3 to 5% by weight, and the more preferable addition amount range is 0.4 to 3% by weight.

Examples of the method for producing the spindle-shaped calcium carbonate used in the present invention include a carbon dioxide gas blowing method, a salt metathesis method, and a method in which calcium chloride and sodium hydrogen carbonate are reacted in the presence of ammonia. For example, carbon dioxide gas is blown into the calcium hydroxide slurry, and after adding a water-soluble polysaccharide or a sulfate to the slurry at a carbonation rate of 60 to 70%, carbon dioxide is added until the carbonation rate becomes substantially 100%. However, the method is not limited to the manufacturing method as long as the spindle-shaped calcium carbonate satisfies the above conditions.

Examples of the crystal form of the spindle-shaped calcium carbonate include calcite, aragonite, vaterite, etc. Among these, vaterite calcium carbonate is more preferably used.

The surface of these spindle-shaped calcium carbonates may be modified with various surface treatment agents. The surface treatment agent used for the purpose of improving the affinity with ethylene glycol or polyester is generally applied in an amount of 5% by weight or less based on the particles, and examples thereof include silane coupling agents and titanium cups. Examples thereof include ring agents and polyacrylic acid.

In the present invention, in addition to the above-mentioned spindle-shaped calcium carbonate particles, other inert particles can be contained within a range that does not impair the characteristics of the spindle-shaped calcium carbonate particles. However, when the amount of the inert particles other than the spindle-shaped calcium carbonate particles is large, the abrasion resistance is deteriorated, which is not preferable. From this meaning, the amount of the other inert particles is preferably 25% by weight or less, particularly preferably 10% by weight, based on the total amount of the particles.
It is less than or equal to weight%.

Examples of such inert particles include (1) silicon dioxide (including hydrate, diatomaceous earth, silica sand, quartz, etc.);
(2) Alumina; (3) Silicate containing 30% by weight or more of SiO ₂ (eg, amorphous or crystalline clay mineral,
Aluminosilicate (including calcined products and hydrates), hot asbestos, zircon, fly ash, etc .; (4) Mg, Zn,
Zr and Ti oxides; (5) Ca and Ba sulfates; (6) Li, Ba, and Ca phosphates (including monohydrogen and dihydrogen salts); (7) Li, Na , And benzoate of K; (8); terephthalate of Ca, Ba, Zn, and Mn; (9) Mg, Ca, Ba, Zn, Cd, Pb, Sr,
Mn, Fe, Co, and Ni titanates; (10) Ba,
And Pb chromate; (11) carbon (eg carbon black, graphite etc.); (12) glass (eg glass powder, glass beads etc.); (13) Mg carbonate; (14) Ca carbonate ( However, except spindle-shaped ones); (15) Fluorite;
(16) ZnS; and (17) heat-resistant polymer particles (for example, silicone resin particles, crosslinked acrylic particles, crosslinked polystyrene particles, crosslinked polyester particles, Teflon particles, polyimide particles, melamine resin particles, etc.); ..

The laminated biaxially oriented polyester film of the present invention has a laminated structure of two or more layers, and at least one of the outermost layers is made of polyester containing the spindle-shaped calcium carbonate particles. The other film layers constituting this laminated biaxially oriented polyester film may or may not contain the inert particles. However, when the inert particles are contained, the particle size and the addition amount of the inert particles should be selected so that the protrusion height is low and flat with respect to the surface property of the layer containing the spindle-shaped calcium carbonate particles. preferable.

In the laminated biaxially oriented polyester film, the thickness of the film layer containing the spindle-shaped calcium carbonate particles is required to be 0.1 to 2 times the average particle diameter of the spindle-shaped calcium carbonate particles contained. .. If the thickness of the layer is less than 0.1 times the particle diameter, the particles contained therein are likely to fall off, which is not preferable. On the other hand, if the particle size exceeds twice the particle size, the particles contained in the layer are likely to overlap with each other, and the height of protrusions formed on the film surface becomes uneven, which is not preferable.
The preferable layer thickness is 0.2 to the average particle size of the contained particles.
1.5 times, more preferably the layer thickness is 0.3 to 1.0 times the average particle diameter of the contained particles.

The laminated biaxially oriented polyester film of the present invention can be obtained by a conventionally known method or a method accumulated in the art. For example, it can be obtained by first producing a laminated unoriented film and then biaxially orienting the film. This laminated non-oriented film can be manufactured by a conventionally accumulated manufacturing method of a laminated film. For example, a method of laminating a film layer forming a surface and a film layer forming a core layer in a molten state of polyester or in a state of being cooled and solidified can be used. More specifically, it can be produced by a method such as coextrusion / extrusion lamination.

The film laminated by the above-mentioned method can be made into a biaxially oriented film by further carrying out according to the conventionally accumulated manufacturing method of the biaxially oriented film. For example, polyester is melted and coextruded at a temperature of melting point (Tm: ° C.) to (Tm + 70) ° C. and an intrinsic viscosity of 0.35 to
A laminated unstretched film of 0.9 dl / g was obtained, and the laminated unstretched film was uniaxially (longitudinal or lateral) (Tg-1
0 to (Tg + 70) ° C. (however, Tg: glass transition temperature of polyester) is stretched at a draw ratio of 2.5 to 5.0, and then in the direction perpendicular to the stretching direction (the first stage stretching is in the longitudinal direction). In the case, the second stage stretching is in the transverse direction)
It can be produced by stretching at a temperature of (° C)-(Tg + 70) ° C at a draw ratio of 2.5 to 5.0 times. In this case, the area stretching ratio is preferably 9 to 22 times, more preferably 12 to 22 times. The stretching means may be simultaneous biaxial stretching or sequential biaxial stretching.

Further, the biaxially oriented film has (Tg + 7
It can be heat-set at a temperature of 0) ° C to Tm (° C).
For example, polyethylene terephthalate film is preferably heat set at 190 to 230 ° C. The heat setting time is, for example, 1 to 60 seconds. The laminated biaxially oriented polyester film of the present invention does not have high protrusions on the film surface as compared with the conventional one, and rarely roughens the magnetic surface when used as a magnetic recording medium, and has excellent electromagnetic conversion characteristics, It has excellent slidability and can withstand the harsh conditions of use in the tape manufacturing process.

Various physical properties and characteristics in the present invention are measured and defined as follows. (1) The area circle equivalent diameter of the spindle-shaped calcium carbonate particles, the particle diameter ratio, etc. The following methods are available for measuring the particle area circle equivalent diameter, particle diameter ratio, etc. 1) When obtaining the average particle diameter, particle diameter ratio, etc. of the area circle equivalent diameter from the powder 2) When obtaining the average particle diameter, particle diameter ratio, etc. of the area average circle diameter of the particles in the film.

1) From powders The powders are scattered on an electron microscope sample stand so that the individual particles do not overlap as much as possible, and a gold thin film deposition layer is formed on the surface of the gold sputtering device at a thickness of 200 to 300 angstroms. Formed, scanning electron microscope, for example, 100
Observing at a magnification of 00 to 30000 and using Luzex 500 manufactured by Nippon Regulator Co., Ltd., the major axis, the minor axis, and the area equivalent circle diameter of at least 100 particles are determined. Then, the average particle diameter and the particle diameter ratio are calculated from these values.

2) In the case of particles in the film A small piece of the sample film is fixed on a sample stand for a scanning electron microscope, and a sputtering device (JFC-made by JEOL Ltd.) is used.
The film surface is subjected to ion etching treatment under the following conditions using a 1100 type ion etching apparatus). The condition is that the sample is placed in a bell jar, the degree of vacuum is raised to a vacuum state of about 10 ^-3 Torr, the voltage is 0.25 kV and the current is 1
Ion etching is performed at 2.5 mA for about 10 minutes. Further, the film surface is subjected to gold sputtering with the same apparatus and observed with a scanning electron microscope at 10,000 to 30,000 times, and the average particle diameter and particle diameter ratio are calculated in the same manner as 1). (2) Flatness of film surface Ra (center line average roughness) is measured according to JIS B 0601. Using a stylus type surface roughness meter (SURFCOM3B) manufactured by Tokyo Seimitsu Co., Ltd., the radius of the needle is 2 μm and the load is 0.0
A chart (film surface roughness curve) is applied under the condition of 7 g, a portion of the measurement length L is extracted from the obtained film surface roughness curve in the direction of its center line, and the center line of this extracted portion is taken as the X axis. When the roughness curve Y = f (x) is expressed with the direction of longitudinal magnification as the Y axis, the value (Ra: μm) given by the following equation is defined as the flatness of the film surface.

[0039]

[Equation 3]

In the present invention, the reference length is 0.25 mm and 8
Ra is expressed as an average value of 5 pieces obtained by measuring 3 pieces from the largest value. (3) Film surface roughness PV1 / 1 Using a stylus-type surface roughness meter, expand the surface roughness to 50 times in the reference length direction and 50000 times in the surface roughness direction and write the surface roughness on the chart. Of the straight lines parallel to the average line of the portion extracted by 1.0 mm in length, select the one that goes through the first mountain from the highest and the first valley from the deep, and select this 2
A value obtained by dividing the distance between the straight lines by the vertical magnification is expressed in units of microns (μm), and is expressed as an average value of 10 PV values. (4) Affinity According to the method of (1) -2), the periphery of particles in the film (surface) is exposed, the major axis of at least 50 fine particles and the major axis of voids are measured, and the following formula: void ratio = major axis of void / Determine the number average value of the void ratio represented by the major axis of the fine particles. This number average value is displayed according to the following criteria.

Grade 1: 1 ≤ void ratio <1.5 (that is, voids do not exist or are extremely small) Grade 2: 1.5 ≤ void ratio <2.0 Grade 3: 2.0 ≤ 〃 <3. 04 grade: 3.0 ≦ 〃 <4.0 (2) Blade abrasion resistance The following measurement is performed using the apparatus shown in FIG. Figure 1
Among them, 1 is an unwind reel, 2 is a tension controller, 3, 5, 6 and 8 are free rollers, 4 is a tension detector, 7 is a blade (blade for industrial razor tester made by US GKI), and 9 is a guide roller. Denoted at 10 are take-up reels, respectively.

A sample film slit to a width of 1/2 inch was run for 100 m at a tension of 50 g and a running speed of 100 m / min so that the blade edge had an angle of 6 degrees, and was scraped by the amount of shavings adhering to the blade edge. Evaluate.

This evaluation relates to the impact strength of the projections formed on the film surface, and corresponds well to the generation of shavings on a calendar or die coater in the magnetic tape manufacturing process. <Judgment> ◎: Adhesion width of shavings adhering to the blade edge is less than 0.5 mm ◯: Adhesion width of shavings adhering to the blade edge is 0.5 mm or more and less than 1.0 mm △: Adhesion of shavings adhering to the blade edge Width 1.0 mm or more and less than 2.0 mm x: Shavings adhering to blade edge width is 2.0 mm or more

[0044]

EXAMPLES The present invention will be further described below with reference to examples.

[0045]

Examples 1 and 2, Comparative Examples 1 to 3 Dimethyl terephthalate and ethylene glycol, manganese acetate as a transesterification catalyst, and antimony trioxide as a polymerization catalyst,
Phosphorous acid was added as a stabilizer, and the additive particles shown in Table 1 were further added as a lubricant, followed by polymerization by a conventional method to obtain polyethylene terephthalate for layer A and layer B having an intrinsic viscosity of 0.62 (orthochlorophenol, 35 ° C.) of 0.62. Obtained.

Then, the polyethylene terephthalate for the A layer and the B layer were dried at 170 ° C. for 3 hours and then fed to separate extruders of the coextrusion film-forming machine so that the thickness ratio of the A layer and the B layer was 3:97. To obtain an unstretched film by coextrusion from a two-layer die.

The unstretched film thus obtained is preheated at 75 ° C., and further 15 mm between low speed and high speed rolls.
It was heated from above by one IR heater having a surface temperature of 900 ° C., stretched to 4.0 times, rapidly cooled, then supplied to a stenter, and stretched laterally to 3.9 times at 105 ° C. The obtained biaxially oriented film was heat set at a temperature of 205 ° C. for 5 seconds to obtain a laminated biaxially oriented film having a thickness of 10 μm. The properties of the laminated biaxially oriented polyester film thus obtained are also shown in Table 1.

[0048]

[Table 1]

As is apparent from Table 1, the surface roughness Ra of the layer A (rough surface layer) according to the present invention is almost the same as that shown as the comparative example, but PV1 /
1 Value is low. That is, it can be seen that the number of high protrusions is small and the protrusions have a uniform shape. As a result, when used as a magnetic recording medium, the influence of the transfer of the rough surface layer to the magnetic surface on the roughening of the magnetic surface is reduced.

Further, it can be seen that the particles added to the A layer have a good affinity, and the projections have excellent dropout resistance in the tape manufacturing process. Furthermore, the blade has a good sharpness, and it can be understood that it can withstand severe tape manufacturing conditions.

In the determination of blade sharpness, there is no practical concern when the level is ◯ or more, but when the level is less than Δ, coating trouble may occur in the magnetic tape manufacturing process, or dropout may increase.

[0052]

According to the present invention, it is possible to provide a biaxially oriented polyester film which is excellent in abrasion resistance and has the best electromagnetic conversion characteristics even under severe magnetic tape manufacturing conditions.

[Brief description of drawings]

FIG. 1 is a schematic diagram of an apparatus for measuring blade sharpness of a film.

[Explanation of symbols]

 1 Feeding reel 2 Tension controller 3, 5, 6, 8 Free roller 4 Tension detector (entrance) 7 Blade 9 Guide roller 10 Take-up reel

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Claims (1)

[Claims] 1. A biaxially oriented polyester film having an average area-equivalent diameter of 0.1 to 2 on at least one surface.
0.2 to 8% by weight of spindle-shaped calcium carbonate particles having a particle size ratio (major axis / minor axis) of 1.5 to 10 and a relative standard deviation represented by the following formula of 0.5 or less. A laminated biaxially oriented polyester film comprising a polyester containing therein and having a layer thickness of 0.1 to 2 times the particle size. [Equation 1]