JP2642549B2 - Laminated biaxially oriented polyester film - Google Patents

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 particularly, to uniformity of surface roughness with fine projections on the film surface, and excellent slipping, abrasion resistance and scratch resistance. The present invention relates to a laminated biaxially oriented polyester film useful as a base film for a magnetic recording medium.

[0002]

2. Description of the Related Art Biaxially oriented polyester films represented by polyethylene terephthalate films have been used as base films for magnetic recording media such as magnetic tapes and floppy disks because of their excellent physical and chemical properties.

[0003] In such a biaxially oriented polyester film, its slipperiness and abrasion resistance are major factors that determine the workability of the film manufacturing process and the working process in each application, and the quality of the product quality. ing. If these are insufficient, for example, when a magnetic layer is applied to the surface of a polyester film and used as a magnetic tape, the friction between the coating and the film surface during application of the magnetic layer is severe, and the film surface is also severely worn. In such a case, wrinkles on the film surface, abrasions, etc. occur.

[0004] Even after the film after the application of the magnetic layer is slit and processed into audio, video or computer tape or the like, the film can be pulled out from a reel or cassette or the like.
At the time of hoisting and other operations, wear occurs remarkably with many guide parts, reproduction heads, etc., abrasion, generation of distortion,
Further, as a result of precipitation of a white powdery substance due to abrasion of the polyester film surface or the like, loss of a magnetic recording signal, that is, dropout is often a major cause.

In general, 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 a film surface unevenness is adopted. A method in which inert fine particles are precipitated from the catalyst residue in the production process and a method (ii) in which inert fine particles are added are used. Fine particles in these raw material polymers, the larger the size,
Generally, the improvement in slipperiness is large.

On the other hand, in the case of a magnetic recording medium, especially 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 from the viewpoint of improving the electromagnetic conversion characteristics. However, when the film surface is flat, as described above, the film has poor slipperiness, and causes various troubles.

Therefore, there is a demand for a film for a magnetic recording medium to simultaneously satisfy these contradictory characteristics.

For the purpose of simultaneously satisfying such demands, there has been proposed a method of using a front and back surface different film having different surface roughness such that one surface is flat and the other surface is rough and smooth. When a magnetic layer is provided on the flat surface of the film, and the rough surface is a film running surface, it is possible to have both flatness in terms of improvement of electromagnetic conversion characteristics and slipperiness in terms of film running properties, A film in a better direction can be obtained as a film for a recording medium.

[0009] However, these means also have problems to be solved, and it is difficult to meet the demands for higher-grade, higher-density, etc. magnetic recording media as they are.

[0010] The problem of the above-mentioned method of roughening using inert fine particles is considered to be mainly caused by the fact that the individual particles vary in size and have a distribution in particle diameter. When the particle size distribution becomes large (wide), coarse protrusions based on the large particles are present on the film surface, which may cause shaving during processing, and may also occur during running as a magnetic tape after processing. Undesirably, the number of dropouts increases due to generation of scratches and shavings, and the electromagnetic conversion characteristics deteriorate.

Therefore, in order to improve such a point, a laminated biaxial film formed by laminating, on at least one surface of a biaxially oriented film, a thin layer made of a thermoplastic polymer containing inert spherical particles having a small particle diameter variation. An oriented film has been proposed (JP-A-2-214657). This laminated biaxially oriented film has excellent electromagnetic conversion characteristics, and when used for tapes for video and audio, the rise in friction after repeated running with metal pins and plastic pins is small, and dropout is not increased. Characteristics. But,
In recent years, the speed of the tape manufacturing process has increased, and the conditions of the calender and coater have become severe. In the laminated biaxially oriented film, the spherical particles in the thin layer have fallen off during the process, resulting in an increase in product dropout. A problem has arisen.

[0012]

The present inventors have made intensive studies to solve this problem. As a result, the shape of the particles in the thin layer and the shape of the projections caused by the shape of the particles were solved to solve the problem. The inventors have found that it is important to make the composition suitable, and have reached the present invention.

Accordingly, it is an object of the present invention to provide a magnetic recording medium having a specific projection shape due to the particle shape in the thin layer, having a uniform projection height, having excellent slipperiness and abrasion resistance. An object of the present invention is to provide a laminated biaxially oriented polyester film which is excellent in electromagnetic conversion characteristics when used and can produce a product with little dropout.

[0014]

The present invention has the following configuration to achieve the above object.

At least one surface of the biaxially oriented polyester film has an average particle diameter of 0.1 to 2
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 layer comprising a polyester and a layer having a thickness of 0.1 to 2 times the particle size.

[0016]

(Equation 2)

The polyester in the present invention is a polyester containing 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, naphthalenedicarboxylic 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. Can be. As the aliphatic glycol, for example, a polymethylene glycol having 2 to 10 carbon atoms such as ethylene glycol, trimethylene glycol, tetramethylene glycol, pentamethylene glycol, hexamethylene glycol, decamethylene glycol or the like, or an alicyclic group such as cyclohexanedimethanol. Diols and the like can be mentioned.

In the present invention, as the polyester, those containing, for example, alkylene terephthalate and / or alkylene naphthalate as a main component are preferably used.

Of these polyesters, in particular, polyethylene terephthalate and polyethylene-2,6-naphthalate, for example, terephthalic acid and / or 2,6-naphthalenedicarboxylic acid account for at least 80 mol% of all dicarboxylic acid components, 80 of all glycol components
A copolymer in which at least mol% is ethylene glycol is preferred. At that time, not more than 20 mol% of the total acid component can be the above-mentioned aromatic dicarboxylic acids other than terephthalic acid and / or 2,6-naphthalenedicarboxylic acid, and also aliphatic dicarboxylic acids such as adipic acid and sebacic acid. An alicyclic dicarboxylic acid such as cyclohexane-1,4-dicarboxylic acid; Further, 20 mol% or less of the total glycol component can be the above-mentioned glycol other than ethylene glycol, or an aromatic diol such as hydroquinone, resorcinol, 2,2-bis (4-hydroxyphenyl) propane; Aliphatic diols having an aromatic ring such as 1,4-dihydroxydimethylbenzene; and polyalkylene glycols (polyoxyalkylene glycols) such as polyethylene glycol, polypropylene glycol, and polytetramethylene glycol.

Further, the polyester in the present invention includes:
For example, aromatic oxyacids such as hydroxybenzoic acid, ω-
Also included are those which copolymerize or combine a component derived from an oxycarboxylic acid such as an aliphatic oxyacid such as hydroxycaproic acid at 20 mol% or less based on the total amount of the dicarboxylic acid component and the oxycarboxylic acid component.

Further, the polyester in the present invention includes:
An amount in the range that is substantially linear, for example, 2 for the total acid component
Also included are those obtained by copolymerizing a tri- or higher functional polycarboxylic acid or polyhydroxy compound such as trimellitic acid or pentaerythritol in an amount of not more than mol%.

The above polyesters are known per se and can be produced by a method known per se.

As the above-mentioned polyester, those having an intrinsic viscosity of about 0.4 to about 0.9 measured at 35 ° C. as a solution in o-chlorophenol are preferred.

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 are preferably the same.

In the present invention, the polyester layer forming at least one surface of the laminated biaxially oriented polyester film has an average diameter of an area circle equivalent diameter of 0.1 to 2 μm,
It is necessary to contain 0.2 to 8% by weight of spindle 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 projection height is insufficient,
The film has insufficient slipperiness, which is not preferable. On the other hand, if the average particle size exceeds 2 μm, the surface of the film becomes too rough, and when the magnetic recording medium is manufactured, the roughness of the film is transferred to the magnetic surface, and the electromagnetic conversion characteristics deteriorate, which is not preferable. A more preferred average particle size is 0.2 to 1.2 μm. Further, when the particle size ratio of the particles is less than 1.5, the particles do not exhibit stress relaxation in the film stretching direction, so that voids are easily generated around the particles, or the formed projections are too sharp, and the tape is formed. There is a problem that particles easily fall off during the production process, which is not preferable. On the other hand, if the particle size ratio exceeds 10, the slipperiness of the film decreases, and shaving powder is 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 projections become irregular, shavings are likely to be generated, and electromagnetic conversion characteristics when used for a magnetic recording medium are undesirably reduced. 0.2% by weight
If the thickness is less than the above range, the number of projections formed on the film surface of the layer becomes insufficient, and the slipperiness becomes insufficient, which is not preferable. On the other hand, when the addition amount is more than 8% by weight, the particles are remarkably overlapped in the layer, and as a result, projections formed on the film surface are not uniform, which is not preferable. A preferable addition amount range is 0.3 to 5% by weight, and a more preferable addition amount range is 0.4 to 3% by weight.

Examples of the method for producing spindle-shaped calcium carbonate used in the present invention include a method of blowing carbon dioxide gas, a method of double decomposition of salt, and a method of reacting calcium chloride and sodium hydrogen carbonate in the presence of ammonia. For example, a carbon dioxide gas is blown into a calcium hydroxide slurry, a water-soluble polysaccharide or a sulfate is added to the slurry at a carbonation rate of 60 to 70%, and then the carbonation rate is reduced to substantially 100%. However, as long as it is a spindle-shaped calcium carbonate satisfying the above conditions, the production method is not limited.

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

These spindle-shaped calcium carbonates may have their surfaces 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. Examples of the surface treatment agent include a silane coupling agent and a titanium cup. A ring agent, polyacrylic acid, and the like can be given.

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 increased, the abrasion resistance deteriorates, which is not preferable. In this sense, 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.
% By weight or less.

Examples of such inert particles include (1) silicon dioxide (including hydrate, diatomaceous earth, silica sand, quartz, etc.);
(2) alumina; (3) silicate containing at least 30% by weight of SiO ₂ (for example, amorphous or crystalline clay mineral,
Aluminosilicate (including calcined and hydrated products), hot asbestos, zircon, fly ash, etc.); (4) Mg, Zn,
Oxides of Zr and Ti; (5) sulfates of Ca and Ba; (6) phosphates of Li, Ba and Ca (including monohydrogen and dihydrogen salts); (7) Li, Na (8); terephthalates of Ca, Ba, Zn, and Mn; (9) Mg, Ca, Ba, Zn, Cd, Pb, Sr,
(10) Ba, titanates of Mn, Fe, Co, and Ni;
(11) carbon (eg, carbon black, graphite, etc.); (12) glass (eg, glass powder, glass beads, etc.); (13) Mg carbonate; (14) Ca carbonate ( (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 the polyester containing the spindle-shaped calcium carbonate particles. The other film layers constituting the laminated biaxially oriented polyester film may or may not contain inert particles. However, when the inert particles are contained, the particle size and the amount of the inert particles should be selected so that the projection 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 must 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 size, the contained particles are likely to fall off, which is not preferable. On the other hand, if it exceeds twice the particle size, the particles contained in the layer tend to overlap, and the height of the projections formed on the film surface is not uniform, which is not preferable.
The preferred layer thickness is 0.2 to the average particle size of the contained particles.
The layer thickness is preferably 1.5 times, more preferably 0.3 to 1.0 times the average particle size 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 produced by a conventionally accumulated method for producing 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 or a cooled and solidified state of polyester can be used. More specifically, it can be manufactured by a method such as coextrusion / extrusion lamination.

The film laminated by the above-mentioned method can be further made according to the conventional method of manufacturing a biaxially oriented film, and can be made into a biaxially oriented film. For example, polyester is melted and co-extruded at a temperature of melting point (Tm: ° C.) to (Tm + 70) ° C. to have an intrinsic viscosity of 0.35
A laminated unstretched film of 0.9 dl / g was obtained, and the laminated unstretched film was uniaxially (longitudinal or transverse) (Tg-1).
0) to (Tg + 70) ° C. (however, Tg: glass transition temperature of polyester) at a magnification of 2.5 to 5.0 times, and then in a direction perpendicular to the above-mentioned stretching direction (the first-stage stretching is the longitudinal direction). In the case, the second stretching is in the transverse direction).
It can be manufactured by stretching at a temperature of (° C.) − (Tg + 70) ° C. at a magnification 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 either simultaneous biaxial stretching or sequential biaxial stretching.

Further, the biaxially oriented film is (Tg + 7
0) It can be heat-set at a temperature of from 0 ° C. to Tm (° C.).
For example, a polyethylene terephthalate film is preferably heat-set at 190 to 230 ° C. The heat fixing 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 and has less roughened magnetic surface when used as a magnetic recording medium, and has excellent electromagnetic conversion characteristics, as compared with the conventional one. It has excellent slipperiness and can withstand severe use conditions in the tape manufacturing process.

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

1) From powder The powder is scattered so that individual particles do not overlap as much as possible on an electron microscope sample table, and a gold thin film deposition layer is formed on this surface with a thickness of 200 to 300 Å by a gold sputtering apparatus. Formed, and, for example, 100
Observation is performed at a magnification of 00 to 30,000, and the major axis, minor axis, and area circle equivalent diameter of at least 100 particles are determined using Luzex 500 manufactured by Nippon Regulator Co., Ltd. Then, the average particle size and the particle size ratio are calculated from these values.

2) From particles in the film A small piece of the sample film was fixed on a sample stage for a scanning electron microscope, and a sputtering device (JFC-
The film surface is subjected to ion etching under the following conditions using a 1100 type ion etching apparatus). The conditions were as follows: the sample was placed in a bell jar, the degree of vacuum was raised to a vacuum state of about 10 ⁻³ Torr, the voltage was 0.25 kV, and the current was 1
Perform ion etching at 2.5 mA for about 10 minutes. Further, the film surface is subjected to gold sputtering by the same apparatus, observed at a magnification of 10,000 to 30,000 times with a scanning electron microscope, and the average particle diameter and the particle diameter ratio are calculated in the same manner as in 1). (2) Film surface flatness Ra (center line average roughness) is measured according to JIS B0601. 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
Under a condition of 7 g, a chart (film surface roughness curve) is drawn, a portion of the measured length L is extracted from the obtained film surface roughness curve in the direction of the center line, and the center line of the extracted portion is defined as the X axis. When the roughness curve is represented by Y = f (x) with the direction of the vertical 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, when the reference length is set to 0.25 mm, 8
The number is measured, and Ra is expressed as an average value of five pieces excluding three pieces from the larger value. (3) Film surface roughness PV1 / 1 Using a stylus-type surface roughness meter, enlarge the surface 50 times in the reference length direction and 50,000 times in the surface roughness direction, write the surface roughness on a chart, Of the straight lines parallel to the average line of the portion extracted by 1.0 mm in length, those that pass through the first peak from the highest and the bottom of the first valley from the deep are selected.
The value obtained by dividing the interval between the straight lines by the vertical magnification is expressed in units of microns (μm), and the average value of ten PV values is expressed. (4) Affinity The periphery of particles in the film (surface) is exposed according to the method of (1) -2), and the major axis and major axis of at least 50 fine particles are measured. The number average value of the void ratio expressed by the formula: This number average is displayed according to the following criteria.

Primary: 1 ≦ void ratio <1.5 (ie, no void or very small) Secondary: 1.5 ≦ void ratio <2.0 Tertiary: 2.0 ≦≦ <3. Grade 04: 3.0 ≦ 〃 <4.0 (2) Blade Sharpness Measured using the device shown in FIG. 1 as follows. FIG.
Among them, 1 is an unwinding reel, 2 is a tension controller, 3, 5, 6, and 8 are free rollers, 4 is a tension detector, 7 is a blade (a blade for an industrial razor testing machine manufactured by GKI, USA), and 9 is a guide roller. Reference numerals 10 and 10 respectively indicate take-up reels.

A sample film slit to a 1/2 inch width was run at 100 m at a running speed of 100 m / min and a tension of 50 g at a running speed of 100 m / min so as to strike the blade blade at an angle of 6 degrees. To 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 calender or a die coater in the magnetic tape manufacturing process. <Judgment> ◎: The width of the shaving powder adhering to the blade tip is less than 0.5 mm ○: The width of the shaving powder adhering to the blade tip is 0.5 mm or more and less than 1.0 mm △: The shaving powder adhering to the blade tip Width 1.0 mm or more and less than 2.0 mm ×: The width of the shaving powder adhering to the blade tip 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 and Comparative Examples 1 to 3 Dimethyl terephthalate and ethylene glycol, manganese acetate as a transesterification catalyst, antimony trioxide as a polymerization catalyst,
Phosphorous acid is added as a stabilizer, and the additive particles shown in Table 1 are further added as a lubricant, and polymerized by a conventional method to obtain polyethylene terephthalate for the A layer and the B layer having an intrinsic viscosity (orthochlorophenol, 35 ° C) of 0.62. Obtained.

Next, the polyethylene terephthalate for the A layer and the B layer was dried at 170 ° C. for 3 hours, and then supplied to separate extruders of a co-extrusion film forming machine, where the thickness ratio of the A layer and the B layer was 3:97. An unstretched film was obtained by co-extrusion from a two-layer die.

The unstretched film thus obtained is preheated at 75 ° C., and is further moved between low-speed and high-speed rolls by 15 mm.
The film was heated by one IR heater having a surface temperature of 900 ° C. from above and stretched 4.0 times, quenched, and subsequently supplied to a stenter, and stretched 3.9 times horizontally 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. Table 1 also shows the properties of the laminated biaxially oriented polyester film thus obtained.

[0048]

[Table 1]

As is clear from Table 1, although the layer according to the present invention had a surface roughness Ra of the layer A (rough surface layer) almost equal to that shown in the comparative example, the PV1 /
1 Value is low. In other words, it can be seen that there are few high protrusions and a uniform protrusion shape. As a result, when used for 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, the affinity of the particles added to the layer A is good, and it can be seen that the projections have excellent resistance to falling off in the tape manufacturing process. Further, the blade has good shaving properties, and it can be seen that the blade can withstand severe tape manufacturing conditions.

It should be noted that there is no practical problem if the blade shaving property is determined to be at or above the レ ベ ル level. However, if it is at or below the △ level, there is a concern that a 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 having excellent abrasion resistance and the most excellent electromagnetic conversion characteristics even under severe magnetic tape production conditions.

[Brief description of the drawings]

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

[Explanation of symbols]

 DESCRIPTION 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

──────────────────────────────────────────────────続 き Continuation of the front page (51) Int.Cl. ⁶ Identification number Agency reference number FI Technical display location B29L 7:00 9:00 (56) References JP-A-3-246033 (JP, A) JP JP-A-5-84821 (JP, A) JP-A-2-214657 (JP, A) JP-A-2-29437 (JP, A)

Claims (1)

(57) [Claims] An at least one surface of a biaxially oriented polyester film has an average particle diameter equivalent to an area circle of 0.1 to 2
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 layer comprising a polyester and a layer having a thickness of 0.1 to 2 times the particle size. (Equation 1)