JPH0516224A - Biaxially oriented polyester film - Google Patents

Abstract

PURPOSE:To provide a film having excellent resistance to abrasion and excellent runnability. CONSTITUTION:This biaxially orientated polyester film has a form of an aggregate of primary particles whose mean diameter is 5 to 40nm, contains 0.1 to 0.8wt.% of theta (theta) type aluminum oxide whose mean particle diameter is 50 to 400nm, and has 950kg/mm<2> or more in the sum of Young's moduli measured in the longitudinal and lateral directions of the film.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a polyester film having excellent abrasion resistance and running properties. More specifically, the present invention relates to a polyester film particularly suitable as a base material for magnetic recording media.

[0002]

BACKGROUND OF THE INVENTION Polyester films are widely used as industrial materials because of their excellent physical and chemical properties. In particular, the biaxially oriented polyethylene terephthalate film is excellent in cost and performance and is widely used in various applications such as a base film of a magnetic recording medium and a capacitor dielectric.

However, in recent years, abrasion resistance has become a problem in films for magnetic recording media, which have remarkably increased elongation. For example, when the film comes into contact with the metal pin at a high speed, friction and wear between the film and the metal pin are increased, so that the film is scratched and abrasion powder is generated. This phenomenon is remarkable especially in a film having high strength.

The inventors of the present invention have made extensive studies as to the improvement of the wear resistance property, and as a result, previously found JP-A-1-306220.
In the publications, etc., a method was proposed in which, for example, aluminum oxide particles having a high Mohs hard carbon content were blended with the film. Regarding film characteristics by blending aluminum oxide particles, JP-A-2-129230 and JP-A-3-6.
According to Japanese Patent No. 238, delta (δ) type and gamma (γ) type aluminum oxide particles exhibit excellent effects. Further, JP-A-2-185533 describes that an aggregate of beta (β) type, γ type or δ type aluminum oxide particles is used. According to the same publication, alpha (α) type is used. , Chi (χ) type, eta (η)
Type and theta (θ) type aluminum oxide particles are described as having poor abrasion resistance of the film.

[0005]

Means for Solving the Problems In view of the above problems, the inventors of the present invention have made earnest studies on the causal relationship between θ-type aluminum oxide and film physical properties and characteristics. The present inventors have completed the present invention by finding that the use of a specific agglomerate of aluminum makes it possible to obtain excellent wear resistance properties and, in addition, to exert an effect in improving the running property.

That is, the gist of the present invention is that the average particle size is 5
Is in the form of an aggregate of primary particles having a particle size of ˜40 nm and an average particle size of 50˜400 nm, and theta (θ) type aluminum oxide is contained in an amount of 0.1 to 0.8% by weight, and the length and width thereof are The biaxially oriented polyester film is characterized in that the sum of Young's moduli in the directions is 950 kg / mm ² or more.

The present invention will be described in more detail below. The polyester referred to in the present invention refers to a polyester obtained by using terephthalic acid or its ester and ethylene glycol as a main starting material, but may contain other third component. In this case, examples of the dicarboxylic acid component include one or two of isophthalic acid, phthalic acid, 2,6-naphthalenedicarboxylic acid, adipic acid, sebacic acid, and an oxycarboxylic acid component (for example, p-oxyethoxybenzoic acid). The above can be used.
As the glycol component, one kind or two or more kinds of diethylene glycol, propylene glycol, butanediol, 1,4-cyclohexanedimethanol, neopentyl glycol and the like can be used. In any case, the polyester of the present invention means a repeating structural unit of 8
Refers to a polyester in which 0% or more is an ethylene terephthalate unit.

Further, the polyester film of the present invention refers to a biaxially oriented polyester film using such polyester as a starting material, and a known method can be used for its production. For example, usually 2
After melt extruding into a sheet at 70 to 320 ° C., 40 to
Cooled and solidified at 80 ° C to form an amorphous sheet, then
Biaxial stretching in the transverse direction or simultaneous stretching, 160-
A method such as heat treatment at 250 ° C. (for example, Japanese Patent Publication No. 30-5
The method described in Japanese Patent No. 639) can be used. When stretching in the machine direction and the transverse direction, each may be stretched in one stage, or may be stretched in multiple stages or a heat treatment section for relaxing orientation may be provided between the multi-stage stretches, if necessary. In addition, the biaxially stretched shape may be stretched again before being subjected to the heat treatment step of the next step. This re-stretching can be carried out in any of the longitudinal and lateral directions, or in both directions.

One of the features of the present invention is the particle size and morphology of the aluminum oxide particles incorporated in the polyester film. That is, in the present invention, aggregate particles obtained by appropriately aggregating fine primary particles are used. To obtain a high-strength film, it is necessary to strongly orient the film during film formation, but in this case, particles often fall off from the film surface and abrasion powder is prominently produced. However, in the case of agglomerated particles, because the stretching stress during film formation is dispersed appropriately,
The particles are unlikely to come off, and the film surface is provided with comparatively gentle protrusions, which provides favorable friction and wear characteristics different from those of a single particle.

One of the advantages of using the agglomerated particles of theta-type aluminum oxide of the present invention is that the friction coefficient can be kept low even after repeated running under high temperature and high humidity. In order to keep the handling workability of the film favorable, it is essential to reduce the friction coefficient thereof. However, according to the knowledge of the present inventors, when a single particle is used, it can be repeatedly run. , Its value gradually increases. However, when the aggregate particles of the present invention are used, this property is improved and the practicality is further improved.

The size of the aggregate is 50 to 400 nm,
It is preferably 70 to 300 nm. If this value is less than 50 nm, when the film contacts the metal pin, the abrasion resistance of the film becomes slightly inferior, and the friction coefficient after repeated running also increases. In addition, this value is 400
If the thickness exceeds nm, the surface of the magnetic layer that comes into contact with the film will be scratched, resulting in poor electromagnetic characteristics.

In the present invention, the average particle size of the primary particles constituting such an aggregate is 5 to 40 nm. This value is 5
When it is less than nm, the aggregate often has an extremely strong bond, and the bond is hardly broken even by stretching stress, and it becomes difficult to obtain the effect peculiar to the present invention. Further, if this value exceeds 40 nm, the aggregate particles are separated and fall off to deteriorate the electromagnetic characteristics.

As described above, in the present invention, certain specific agglomerated particles are used, but the effect is exhibited in the case of so-called high strength film. That is, even in the film forming method described above, the effect is particularly remarkable when the particles are strongly oriented in the longitudinal and transverse directions, that is, when a strong stretching stress acts on the internal particles. Specifically, the sum of Young's modulus in the machine direction and the transverse direction of the film of the present invention is 95.
It is 0 kg / mm ² or more, preferably 1000 kg / mm ² , and more preferably 1100 kg / mm ² or more in both length and width.

The θ-type aluminum oxide used in the present invention can be obtained, for example, by heating and firing boehmite, vialite or gibbsite at about 880 to 1150 ° C. in air or in vacuum. By selecting the conditions at the time of production, for example, the type and crystallinity of the starting material, the particle size, the purity or the atmosphere and temperature at the time of heating, the speed,
It is possible to obtain the primary particle sizes of 5-40 nm required according to the invention, but these often form aggregates of more than 1 μm. The aggregate having an appropriate particle size used in the present invention can be easily obtained by, for example, pulverizing such a coarse aggregate.

For the pulverizing process, for example, a rod mill, a ball mill, a vibrating rod mill, a vibrating ball mill, a pan mill,
A roller mill, impact mill, agitation mill, fluid energy mill, etc. can be used. If necessary, ultrasonic dispersion treatment may be carried out, but if the degree of the dispersion is strong, primary particles or a state close to the primary particles will be dispersed. In the present invention, treatments such as classification and filtration may be used together.

In this way, the aluminum oxide agglomerated particles used in the present invention can be obtained. In this case, a part of aluminum, for example, less than 20% is Si, Ti, F.
It may be substituted with an element such as e, Na or K. In any case, the effect of the present invention is exhibited when the ratio of the θ-type crystal form is 70% or more. Further, the surface of these particles may be treated with various surface treatment agents such as silane coupling agents and titanium coupling agents.

As a method of blending the aggregate particles with the polyester, a method of adding the particles as an ethylene glycol slurry to the reaction system in the initial stage of polyester production is usually used because it is simple and preferable. Alternatively, a method of directly blending with In the present invention, the content of the aggregate particles in the polyester film is in the range of 0.1 to 0.8% by weight, preferably 0.2 to 0.7% by weight. If the content is less than 0.1% by weight, scratch resistance,
Wear resistance and running performance at high temperature and high humidity are not sufficiently improved. On the other hand, if it exceeds 0.8% by weight, the guide pin made of plastic is often scratched or the surface roughness becomes too large, resulting in a magnetic field. When used as a base film of a recording medium, it may deteriorate electromagnetic characteristics.

As described above, the present invention has surprisingly found that if the θ-type aluminum oxide particles, which have hitherto been considered unsuitable, are used under certain specific conditions, they can exhibit surprisingly excellent properties. However, since the aluminum oxide particles alone often cause insufficient slipperiness of the film and inferior handling workability, it is preferable to use other particles in combination.

One of such particles is so-called precipitated particles. The precipitated particles are those obtained by precipitating a metal compound as fine particles in the polyester production process, and, for example, the presence of an alkali metal or an alkali metal compound before or after a transesterification reaction or an esterification reaction, and a phosphorus compound In the presence or absence thereof, the particles are precipitated as inert fine particles having an average particle size of about 0.1 to 5 μm. In this case, the running property can be particularly improved by making the particles exist in an amount of 0.01 to 1% by weight based on the polyester film.

Another example is so-called additive particles. The additive particles refer to particles externally added to the polyester manufacturing process, specifically, kaolin, talc, carbon, molybdenum sulfide, gypsum, rock salt, calcium carbonate, barium sulfate, lithium fluoride,
Examples thereof include calcium fluoride, zeolite, calcium phosphate, silicon dioxide and titanium dioxide. In this case, the average particle size of these added particles is larger than that of θ-type aluminum oxide, and it is preferable to select from the range of 0.1 to 3 μm and the blending amount with respect to the polyester from the range of 0.01 to 1% by weight. ..

As an example of such added particles, heat-resistant polymer fine powder can be cited. As a typical example in this case, a monovinyl compound having only one aliphatic unsaturated bond in a molecule, as described in JP-B-59-5216, and a divinyl compound in the molecule as a cross-linking agent. A copolymer with a compound having one or more aliphatic unsaturated bonds can be exemplified. More specific examples of this copolymer include monodisperse particles obtained by an emulsion polymerization method as described in JP-A-59-217755.

As the heat-resistant polymer fine powder,
For example, a thermosetting phenol resin, a thermosetting epoxy resin, a thermosetting urea resin, a benzoguanamine resin, or a fine powder of a fluorine-based resin such as polytetrafluoroethylene can be used. In this case, the average particle size of these heat-resistant polymer fine powders is usually 0.1 to 3 μm, and the compounding amount thereof with respect to the polyester film is 0.01 to 1
It is selected from the range of% by weight.

As described above, according to the present invention, a polyethylene terephthalate film suitable for a base film for a magnetic recording medium can be obtained by using a specific aluminum oxide under a specific condition. It can also be applied to a polyethylene-2,6-naphthalate film. In this case, the average particle size is 5
Polyethylene-2 in the form of an agglomerate of primary particles having a size of ˜40 nm and containing 0.1 to 0.8% by weight of θ-type aluminum oxide having an average particle size of 50 to 400 nm;
A 6-naphthalate film, and the sum of its longitudinal and transverse Young's modulus 1250 kg / mm ² or more, preferably 1300 kg / mm ² or more, more preferably 1400
When it is kg / mm ² or more, a desired effect can be enjoyed.

[0024]

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 unless it exceeds the gist thereof. In the examples and comparative examples, “part” means “part by weight”. The measuring method used in the present invention is as follows.

(1) Average Particle Size The particle size of the primary particles and aggregates in the film was determined by observing the cross section of the film with a transmission electron microscope.
The average particle diameter was defined as the particle diameter (diameter) at the point where the volume fraction of the equivalent sphere conversion value was 50%. The particle size of the particles in the dry powder and the slurry was measured using a scanning electron microscope.

(2) Wear characteristics The wear characteristics of the metal pin and the plastic pin were evaluated. For this purpose, a magnetic tape was first produced. That is, 200 parts of magnetic fine powder, polyurethane resin 30
Parts, nitrocellulose 10 parts, vinyl chloride-vinyl acetate copolymer 10 parts, lecithin 5 parts, cyclohexanone 10
After mixing and dispersing 0 parts, 100 parts of methyl isobutyl ketone and 300 parts of methyl ethyl ketone in a ball mill for 48 hours, 5 parts of a polyisocyanate compound was added to obtain a magnetic paint, which was applied to a polyester film, before the paint was sufficiently dried and solidified. Magnetically oriented, then dried, 2
A magnetic layer having a thickness of μm was formed. Further, this coated film is surface-treated with a super calendar, and then halved.
It was slit into an inch width to make a video tape.

Next, the magnetic tape obtained was wrapped around a hard chrome-plated metal pin (diameter 6 mm, surface roughness 3S) and angle 1
The base film surface was brought into contact at 35 ° and a tension of 50 g, and was rubbed at a running speed of 4 m / sec. Next, aluminum was vapor-deposited on the rubbing surface of the magnetic tape, the degree of scratches was visually determined, and the wear characteristics with the metal pin were classified into the following 5 ranks. Rank 1 A large amount of scratches, often deep scratches. Rank 2 The amount of scratches is relatively large, and there are some deep scratches. Rank 3 There are relatively few scratches and few deep scratches. Rank 4 Some scratches are observed, but it is a satisfactory level. Rank 5 Almost no scratches.

On the other hand, the base film surface of the magnetic tape is
It was brought into contact with a nylon pin having a diameter of 6 mm subjected to smoothing treatment and rubbed at 4 m / sec. The wear condition of the pin and the generation condition of the white powder after 2,000 m running were observed, and the wear property with the pin made of plastic was classified into the following five ranks. A lot of vertical stripes are generated on Rank 1 pin, and white powder is often attached. A lot of streaks were found on the rank 2 pins, and white powder was relatively large. Rank 3 Shallow lines are observed, but there is little white powder. Rank 4 Some shallow streaks are observed, but there is little white powder. Rank 5 pins are hardly scratched, and the amount of white powder generated is extremely small.

(3) Electromagnetic characteristics After winding up a magnetic tape whose abrasion characteristics were evaluated with a pin made of nylon, the electromagnetic characteristics were measured by NV-Matsushita Electric NV.
It measured using the 3700 type | mold video deck. VTR head output The VTR head output at a measurement frequency of 4 MHz was measured with a synchroscope, the blank was set to 0 decibel, and the relative value was shown in decibel. ○ Number of dropouts A videotape recording a signal of 4.4 MHz was played back, the number of dropouts was measured for about 20 minutes by a dropout counter of Okura Industry Co., Ltd., and converted into the number of dropouts per minute.

(4) Measurement of Friction Coefficient The dynamic friction coefficient of the base film surface of the tape coated with the magnetic layer was measured according to the method of ASTM D-1894.
The measurement was performed 50 times while winding the same tape and repeating the winding. The environment at the time of measurement is 50
C. and relative humidity 80%.

(5) Young's modulus Intesco tensile tester Intesco model 200
Using the 1st type, a sample film having a length of 300 mm and a width of 20 mm was pulled at a strain rate of 10% / min in a room controlled at a temperature of 23 ° and a humidity of 50% RH to obtain a tensile stress-
It was calculated by the following equation using the first linear portion of the strain curve.

(6) Measurement of Crystal Form of Aluminum Oxide Particles PW1700 manufactured by Philips was used for the measurement of crystal form, and Cu was used as a target (X-ray source). The acceleration voltage was 40 KV. . The crystal type of the particles was specified from the obtained diffraction peak.

Example 1 An agglomerate of θ-type aluminum oxide having a primary particle size of 20 nm obtained by heating and firing boehmite was dispersed in ethylene glycol and gradually dispersed by a sand grinder to obtain an average particle size of 70 nm. To obtain an aggregate of.
Next, 100 parts of dimethyl terephthalate, 65 parts of ethylene glycol and 0.09 part of magnesium acetate were placed in a reactor and heated to raise the temperature, and transesterification was carried out while distilling off methanol. About 4 hours after the start of the reaction, the temperature was raised to 230 ° C., and the transesterification reaction was substantially completed. Next, 0.40% by weight of an aluminum oxide aggregate having an average particle size of 70 nm and 0.1% by weight of silicon oxide having an average particle size of 300 nm were added, and further 0.4 part of ethyl acid phosphate and 0.04 part of antimony trioxide were added. Was added and polymerized according to a conventional method to obtain polyethylene terephthalate having an intrinsic viscosity of 0.63.

Next, after drying the obtained polyester,
It was extruded into a sheet form from an extruder at 290 ° C., and an amorphous sheet of 150 μm was obtained by using a so-called electrostatic applied cooling method. Next, this amorphous sheet was stretched 3.8 times in the longitudinal direction and 3.9 times in the transverse direction, and then re-stretched 1.06 times in the longitudinal direction to obtain a biaxial reinforced film having a thickness of 9.5 μm. A stretched polyester film was obtained. The obtained film has a Young's modulus in the longitudinal direction of 620 kg / mm ² and a Young's modulus in the lateral direction of 51.
It was 0 kg / mm ² . The evaluation results of the obtained film are shown in Table 1.

Examples 2 and 3 and Comparative Examples 1 to 4 A biaxially stretched polyester film was obtained in the same manner as in Example 1 except that the composition of the particles contained in the film was changed as shown in Table 1. , The evaluation was done. The results are shown in Table 1.

[0036]

[Table 1]

The films of Examples 1 to 3 satisfying the requirements of the invention are scarcely scratched on contact with metal pins and plastic pins, and finally a magnetic tape having excellent electromagnetic characteristics can be obtained. .. On the other hand, Comparative Example 1 has an average particle size with no aggregation tendency. In this example, 0.3 μm of titanium oxide was used as the main particles, but only a film having poor wear resistance was obtained. In Comparative Example 2, α-Al ₂ O ₃ having an average particle diameter of 0.3 μm and having no aggregation tendency is also used.
However, as in Comparative Example 1, the friction coefficient was gradually increased and the electromagnetic characteristics were inferior.

In Comparative Example 3, the primary particle size and the degree of aggregation are in accordance with the present invention.
Η-Al within the range of₂O ₃Example of using
Is. In this case, wear characteristics are inferior and dropout
To increase. Comparative Example 4 is θ-Al₂O₃Small amount of
This is an example of the case, but the wear characteristics are still poor and the electromagnetic characteristics
Becomes worse.

[0039]

INDUSTRIAL APPLICABILITY The film of the present invention is excellent in abrasion resistance and running property, and can be suitably used for various purposes including a base film of a magnetic recording medium, and its industrial value is high.

Claims (1)

Claim: What is claimed is: 1. Theta (θ) -type aluminum oxide having an average particle size of 5 to 40 nm in the form of an aggregate of primary particles and having an average particle size of 50 to 400 nm. 1-0.8
A biaxially oriented polyester film which is contained by weight and has a sum of Young's moduli in the longitudinal and transverse directions of 950 kg / mm ² or more.