JPH03234739A - Biaxially oriented polyester film - Google Patents

Abstract

PURPOSE:To prepare the title film excellent in flatness, wear resistance, and slipperiness and suitable esp. as a magnetic tape base by forming a polyester contg. ceramic particles having specific properties into a film and biaxially orienting the film. CONSTITUTION:The title film contains 0.01-1.0wt.% thermally conductive ceramic particles having the following properties: an area ratio of circumscribed circle (%) expressed by [(projected area of particle)/(area of the circle circumscribed to particle)]X100 of 60% or higher; a degree of dispersion of particle diameter (%) expressed by [(standard deviation of particle diameter)/(mean particle diameter)]X100 of 30% or lower; a mean particle diameter of 0.01-2.0mum; and a thermal conductivity of 0.01cal/cm.sec. deg.C or higher. As the ceramic having such properties, beta-type silicon carbide and aluminum nitride are pref. in virtue of their high thermal conductivity and low toxicity.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to an oriented polyester film, and particularly to an oriented polyester film that is smooth and has excellent abrasion resistance and slipperiness.

(Prior art) Polyester, represented by polyethylene terephthalate, has excellent physical and chemical properties.Therefore, polyester is used for various fibers and molded products, as well as for magnetic tapes and floppy disks. Polyester is used for a variety of purposes such as film, photography, condensers, packaging, X-ray film, microfilm, etc. When polyester is used for these films, polyester's slipperiness and abrasion resistance This is a major factor that determines the workability of film manufacturing processes and processing steps in various uses, as well as the quality of products in which these films are used.

In particular, when used as a magnetic tape in which a magnetic material is coated on the surface of a polyester film, the following problems will occur if the slipperiness and abrasion resistance of polyester are insufficient.

Since the friction between the coating roll used to apply the magnetic material and the surface of the film increases, the abrasion of the film becomes extremely severe, and wrinkles and scratches are likely to occur on the film surface. Furthermore, if the film feeding speed in the coating and calendering processes is increased in order to increase productivity, the film surface is more likely to be scraped, and when the resulting magnetic tape is used, magnetic recording signal dropouts, or dropouts, are more likely to occur. Become. Furthermore, if the film has insufficient slipperiness and abrasion resistance, problems may occur even after the film is slit (cut in the longitudinal direction) and processed into audio, video or computer tapes. In other words, when a processed tape is pulled out from a reel, cassette, etc., wound up, or otherwise operated, the tape may be worn out, scratched, or distorted due to friction between the guide section, playback head, etc. This may occur. Furthermore, resin powder generated due to tape abrasion, scraping, etc. adheres to the film surface, making dropouts more likely to occur.

Various methods have been proposed to improve the slip properties and abrasion resistance of films. For example, a method is conventionally known in which the contact area between the film and a guide roll or the like is reduced by providing unevenness to the film surface. For example, an internal particle precipitation method (Japanese Patent Publication No. 49-1323
4 and Japanese Patent Publication No. 50-6493, etc.), and an external particle addition method in which inorganic particles insoluble in the polymer used for the film are added during polymerization or before melt extrusion of the polymer (Japanese Patent Application Laid-open No. 51-1989). Publication No. 34272, Japanese Patent Application Publication No. 1978-78953, Japanese Patent Publication No. 55-2
225, Japanese Patent Publication No. 55-41'648, etc.) are known.

The above internal particle precipitation method has the advantage that the particles to be precipitated have good affinity with the polyester, but it is difficult to control the amount and particle size of the particles used. Therefore, it is not possible to precisely adjust the surface morphology of the film,
Moreover, there was a drawback that slipperiness was insufficient. on the other hand,
In the external particle addition method, designing the surface morphology of the film is easier than in the internal particle precipitation method. However, it is difficult to satisfy all of the requirements of surface smoothness, slipperiness, abrasion resistance, and running durability due to the inclusion of coarse particles, secondary agglomeration of particles, poor affinity with polyester, etc. Ta.

Generally, the larger the particle size of the particles in the raw material polymer, the better the slipperiness. However, when used in precision applications such as magnetic tapes, if large particles are mixed in, the particles themselves can cause dropouts and the like.

The occurrence of dropout leads to deterioration of electromagnetic conversion characteristics. Therefore, when used for precision applications, the unevenness on the film surface needs to be as fine as possible.

Thus, when used as a film for precision applications, it is necessary to satisfy two contradictory characteristics.

As a means to satisfy these two characteristics, that is, to improve the slipperiness and to make the surface unevenness finer, inert inorganic particles of different particle sizes (large particle size particles and small particle size particles) are used. ) has been proposed.
-78953, Japanese Patent Publication No. 55-40929, USP 3821156, USP 38848
No. 70, etc.). However, since the large particles used in these methods have a relatively large particle size, the surface smoothness is insufficient and coarse protrusions are likely to be formed on the film surface. The formed coarse protrusions cause dropouts, and furthermore, since inert inorganic particles generally have poor affinity with polyester, when blended with polyester, the polyester polymer becomes poorly dispersed in the matrix. Therefore, agglomerates with large particle sizes are formed, which causes dropouts and the like. Even if inorganic particles that have excellent dispersibility in the polymer matrix are used, the affinity of the inorganic particles for polyester is weak, so polyester to which inorganic particles are added will cause the unstretched film of the polyester to be biaxially oriented. If an external force is applied during this process, voids may be formed, resulting in a decrease in transparency and a decrease in the abrasion resistance of the film surface.

In order to improve the affinity between inert inorganic particles and polyester, in Japanese Patent Publication No. 58-23414, etc., inert inorganic particles are produced by a coupling reaction between a silane compound or a titanate compound, etc., and inert inorganic particles. A method of surface treatment has been proposed.

However, the adhesion of the interface between the inorganic particles and the polymer surface-treated by this method is still not sufficient, and no satisfactory effect has been achieved in terms of improving the abrasion resistance of the film.

(Problems to be Solved by the Invention) The present invention solves the above-mentioned conventional problems, and its purpose is to provide wear-resistant and The purpose of the present invention is to provide a high-quality oriented polyester film with excellent slip properties.

(Means for solving the problem) The biaxially oriented polyester film of the present invention has the following formula (1)
The area with respect to the circumscribed circle expressed by
The polyester used in the present invention contains 0.01 to 1.0% by weight of thermally conductive ceramic fine particles having a temperature of 0.01 to 2.0 μm and an average particle size of 0.01 to 2.0 μm. It is a crystalline polyester that is a terephthalate. The content of ethylene terephthalate is not particularly limited, but is preferably 80 mol% or more. Other copolymer components contained in the polyester of the present invention include:
The following dicarboxylic acid components and glycol components are mentioned. As the dicarboxylic acid component, isophthalic acid, p-β
Oxyethoxybenzoic acid, 2,6-naphthalene dicarboxylic acid, 4,4°-dicarboxyldiphenyl, 4.4'
Dicarboxylbenzophenone, bis(4-carboxylphenyl)ethane, adipic acid, sebacic acid, 5-sodium sulfoisophthalic acid, cyclohexane-1,4
- dicarboxylic acids, etc. As a glycol component,
Examples include propylene glycol, butanediol, neopentyl glycol, diethylene glycol, cyclohexane dimetatool, ethylene oxide adduct of bisphenol A, polyethylene glycol, polypropylene glycol, and polytetramethylene glycol. In addition, oxycarboxylic acid components such as p-oxybenzoic acid may also be used. Further, as other copolymer components, compounds containing small amounts of amide bonds, urethane bonds, ether bonds, carbonate bonds, etc. may be included.

As methods for producing such polyesters, either the so-called transesterification method in which dimethyl ester of aromatic dicarboxylic acid and glycol are transesterified, or the direct polymerization method in which aromatic dicarboxylic acid and glycol are directly reacted can be applied. It's okay. Further, both batch-type and continuous-type production methods can be applied. In the above transesterification method, the transesterification catalyst is not particularly limited. Conventionally known transesterification catalysts can be used. In the direct polymerization method, amines and quaternary polymers are used as inhibitors to suppress the by-product of diethylene glycol
Grade ammonium salts and the like may also be used.

The average particle diameter of the thermally conductive ceramic fine particles used in the present invention is 0.01 to 2.0 μm. Preferably 0.1-1
．． 5 μm, more preferably 0.3 to 1.2 μm
It is. If the average particle size is less than 0.01 μm, the resulting film will have insufficient slipperiness. Average particle size is 2.0μm
If it exceeds , the surface smoothness will be insufficient.

Particularly when used for magnetic tape, the particles cause dropouts and the like. The amount of such thermally conductive ceramic fine particles added is 0.01 of the total weight of the film.
~1.0% by weight. Preferably 0.05-0.50
% by weight, particularly preferably from 0.10 to 0.30% by weight. If it is less than 0.0% by weight, slipperiness is insufficient. 1
．． If it exceeds 0% by weight, the surface smoothness will be insufficient.

In particular, when used for magnetic tape, the number of coarse particles that cause dropouts and the like increases.

The uniformity of the particle shape and particle size of the thermally conductive ceramic fine particles can be one of the factors for improving slipperiness, surface smoothness, etc. Therefore, regarding the particle shape, considering the necessity of precisely adjusting the surface morphology of the film, evaluation using the conventionally used volume shape coefficient alone is insufficient. In the present invention, in order to quantitatively understand the particle shape, the particle shape is defined as the ratio of the projected cross-sectional area of the particle to the area of a circle circumscribing the projected diagram of the particle, that is, the area ratio (%) to the circumscribed circle.
(formula (1)).

The area ratio with respect to the circumscribed circle defined by formula (1) is 100%
The closer it gets to , the more spherical the particle shape becomes. The area ratio of the thermally conductive ceramic fine particles used in the present invention to the circumscribed circle is 60% or more, preferably 65% or more, and more preferably 70% or more. A film using thermally conductive ceramic fine particles having an area ratio of less than 60% with respect to the circumscribed circle is not preferable because slipperiness becomes insufficient. In addition, regarding the uniformity of particle size, the inventors have found through studies that the closer the particle size distribution is to monodisperse, the more uniform the height and shape of the protrusions formed on the film surface will be. . Based on this knowledge, the uniformity of particle size is defined by the ratio of the standard deviation of individual particle sizes to the average particle size, that is, the degree of variation in particle size (Equation (2)).

The degree of variation in particle size of the thermally conductive ceramic fine particles defined by formula (2) is 30% or less, preferably 25% or less,
More preferably, it is 20% or less. When the degree of variation in particle size exceeds 30%, the shape of the protrusions on the film surface becomes irregular.

The thermal conductivity of the thermally conductive ceramic fine particles used in the present invention is 0.01 cal/cm-sec. This requirement is an important requirement for improving the abrasion resistance of the film. The reason for this is not clear, but it may be because the heat conduction from the particles to the polymer near the particles is large when the film is heated and stretched, which suppresses the crystallization of the polymer near the particles, or because the fluidity of the polymer around the particles This is thought to be because the internal strain at the particle-polymer interface was reduced and the voids became smaller. Thermal conductivity is O.01ca
Such an effect cannot be obtained with ceramic fine particles having a ratio of less than l/c+yrsec1.

Ceramic fine particles having a thermal conductivity of 0°01 cal/cm-sec·°C or higher include beryllia, silicon carbide, aluminum nitride, titania, spinel, alumina, magnesia, boron nitride, and the like.

Among the currently commercially available products that satisfy the conditions of the present invention, that is, an average particle size of 0.01 to 2.0 μm with a spherical shape and a particle size distribution close to monodisperse, the products have high thermal conductivity (thermal conductivity of 0.01 μm). 0
5 cal/cm-sec.)'J6 and toxicity, β-type silicon carbide or aluminum nitride is preferable.

As a method for adding such thermally conductive ceramic fine particles to polyester, there is a method in which the ceramic fine particles are added in the form of a slurry during polyester polymerization. As the solvent for the slurry of ceramic fine particles, it is preferable to use ethylene glycol alone, but other solvents such as water and alcohols may be mixed as long as the amount is 50% by weight or less. When dispersing ceramic fine particles into a slurry, the ceramic fine particles are uniformly dispersed so that they remain as original primary particles as much as possible without agglomeration.

In particular, it is particularly preferable to substantially eliminate particles of 5 μm or more in the slurry from the viewpoint of reducing coarse protrusions. The method of dispersing the thermally conductive ceramic fine particles during slurry preparation is not particularly limited. Any method such as a rotary high-speed stirring method, a high-pressure homogeneous dispersion method, an ultrasonic dispersion method, or a combination of these methods may be employed. Furthermore, in order to obtain particles with a predetermined average particle size, treatments such as crushing, classification, and filtration may be employed.

By preparing a master chip containing a high concentration of thermally conductive ceramic particles and blending it with polyester (bright resin) that does not contain the ceramic particles, the concentration of the ceramic particles can be diluted to an appropriate concentration. It may be adjusted to

An unstretched film is produced from the polyester containing thermally conductive ceramic fine particles as described above by an appropriate method such as an extrusion method. This is stretched appropriately depending on the purpose to obtain a biaxially oriented polyester film.

Note that other inert inorganic particles may be added to the polyester matrix as long as they do not interfere with the effects of the thermally conductive ceramic fine particles.

(Example) Examples of the present invention will be described below. In Examples and Comparative Examples, all parts are by weight unless otherwise specified. The average particle diameter, area ratio and degree of dispersion with respect to the circumscribed circle of the fine particles used in the present invention are determined as follows (a) to (
It was determined by method C). Furthermore, the obtained films were evaluated by methods (d) to (g).

(a) Average particle size of fine particles The particles are sufficiently dispersed in a slurry using ethylene glycol as a solvent. The particle size distribution in the obtained slurry was measured using a light transmission type centrifugal sedimentation type particle size distribution analyzer (SA-CPa).
Measurement is performed using a model manufactured by Shimadzu Corporation. The cumulative value is 50
% is defined as the average particle diameter.

(b) Observe and photograph the area ratio particles with respect to the circumscribed circle using a scanning electron microscope (Hitachi S-510 model), and enlarge and copy this.Furthermore, trace is performed and randomly correspond to 200 particles. The image is painted black. From this trace image, the projected cross-sectional area of each particle is measured using an image analysis device (Luzex Model 500 manufactured by Reco Co., Ltd.). The area of a circle circumscribing those particles is calculated, and the area ratio is determined using equation (1).

(C) Degree of dispersion of particle size, etc.) Using the trace image obtained in (C), the Feret diameter in the horizontal direction is measured using an image analyzer (Luzex Model 500 manufactured by Reco Co., Ltd.). Let the average value of Feret's diameter be the average particle diameter in equation (2). The degree of variation in particle diameter is calculated using the following formula.

(The powder of medium thermal conductivity ceramic fine particles was measured by the unsteady hot wire method after hot press molding. The unit of thermal conductivity is cal/
cm-sec·t.

(e) Surface smoothness (TAR) of the film
8K) under the following measurement conditions over one measuring length.

Needle radius: 2 μm Load: 30 ■ Cutoff value + 0.25 law Measurement direction: Measurement data in the height direction is measured every 2 μm in the longitudinal direction of the film, with a quantization width of 0, 00
It is imported into an external storage device at 312 μm.

A series of such measurements are carried out 150 times continuously at intervals of 2 μm in the transverse direction of the film, that is, over a width of 0.3 mm in the transverse direction of the film.

The measurement data in the height direction at each position (longitudinal direction, transverse direction) is h (i, j) [i=1 to 50 [L, j=
1 to 150], the value obtained by calculating the following formula is μ
The value expressed in m units is TAR (Three Dimensional Average Roughness).

(f) Slip property of film According to ASTM-D-1894-63, the coefficient of static friction between films is measured using a thread type slip tester under environmental conditions of 23° C. and 65% RH.

(0 Wear resistance A film slit to a width of 12.5 mm is brought into contact with a commercially available razor and run at a speed of 60 m/min. After running for 10 m, the amount of white powder adhering to the razor is determined in 3 stages as follows. Evaluate by ranking.

○... Almost no white powder generated △... Much white powder generated ×... Very much white powder generated (b) Number of coarse particles in the film Cover with two films with a small amount 28 between the glasses
After melt pressing at 0°C and quenching, observation was made using a phase contrast microscope. Next, the image analysis device Luzex 500
(manufactured by Nippon Regulator), and in the obtained particle image, the number of particles with a maximum length of 5 μm or more (number per measurement area of 4.8 mm) is counted, and depending on the number of particles, the following Evaluate by ranking.

X ・---51 pieces or more / 4.8mm '×～△・・
・・21~50 pieces/4.8mm '△ -----11
~20 pieces/4.8mm "Δ~○...4~10 pieces/4.8mm 20...0~3 pieces/4.8m
Example 1 Using a continuous esterification reactor consisting of a two-stage complete mixing tank equipped with a stirring device, a condenser, a raw material inlet, and a product outlet, esterification was carried out in the first esterification reactor of the device. A slurry of ethylene glycol of TPA in which the molar ratio of ethylene glycol to terephthalic acid (TPA) in the system is 1.7 and contains 289 ppm of antimony trioxide per unit of TPA as antimony atoms is continuously added to the system where the reaction product is present. provided.

At the same time, an ethylene glycol solution of magnesium acetate tetrahydrate was supplied from a supply port different from the TPA ethylene glycol slurry supply port, and each polyester unit contained 110 Mg atoms per polyester unit in the reaction product passing through the reaction vessel.
The mixture was continuously supplied so as to have a concentration of 0 pp, and the reaction was carried out at normal pressure for an average residence time of 4.5 hours and at a temperature of 255°C.

This reaction product was continuously taken out of the system and supplied to the second esterification reactor. 0.5 parts by weight of ethylene glycol and an ethylene glycol solution of trimethyl phosphate based on the polyester unit in the reaction product passing through the second esterification reactor are 64 P atoms.
ppm, an ethylene glycol solution of sodium acetate as Na atom, 10 ppm, and ethylene glycol of aluminum nitride fine particles with an average particle size of 0.81 μm, which has an area ratio of 75% with respect to the circumscribed circle and a particle size variation of 20%. The slurry has a content of the fine particles of 0.
They were continuously supplied from separate supply ports so that the concentration was 20% by weight. After that, the average residence time was 5.0 at normal pressure.
The reaction was carried out at a temperature of 260°C for a period of time.

The obtained esterification reaction product is continuously supplied to a two-stage continuous polycondensation reactor equipped with a stirrer, a condenser, a raw material inlet, and a product outlet for polycondensation, and the intrinsic viscosity is 0. 620 polyester was obtained. The obtained polyester was melt-extruded at 290°C, stretched 3.5 times in the machine direction at 90°C and 3.5 times in the transverse direction at 130°C, and then heat-treated at 220°C to obtain a film with a thickness of 15 μm. Ta. The properties of this film are shown in Table 1.

The film obtained in this example was smooth, had excellent slipperiness and abrasion resistance, and contained extremely few coarse particles.

Comparative Examples 1 to 5 Comparative Examples 1 to 5 were carried out in the same manner as in Example 1, except that one of the requirements for particle properties was outside the regulations of the present invention.

The properties of the obtained film are shown in Table 1.

From Table 1, it can be seen that these films cannot satisfy all of the characteristics of being smooth, having excellent slipperiness and abrasion resistance, and having extremely few coarse particles in the film.

Example 2 The same procedure as Example 1 was carried out except that β-type silicon carbide having the particle characteristics shown in Table 1 was used instead of the aluminum nitride fine particles. Table 1 shows the film properties of the obtained film.

From Table 1, it can be seen that the obtained film has a smooth surface, excellent slipperiness and abrasion resistance, and the number of coarse particles in the film is also extremely small.

Comparative Examples 6 and 7 Comparative Example 6 is the same as Example 2 except that the amount of β-type silicon carbide added and Comparative Example 7 is that the average particle size of β-type silicon carbide is outside the claimed range of the present invention. .

The film properties of the obtained film are shown in Table 1.

As shown in Table 1, the film of Comparative Example 6 was inferior in abrasion resistance and number of coarse particles. Furthermore, the film of Comparative Example 7 had poor slip properties.

(Margin below) (Effects of the invention) In the biaxially oriented polyester film of the present invention, ceramic fine particles having high thermal conductivity within a predetermined particle size range that is close to spherical and has a particle size distribution close to monodisperse are included in the film. distributed in the proportion of

Therefore, this film is smooth, has excellent abrasion resistance and slipperiness, and has extremely low generation of white powder and the number of coarse particles that cause defects such as dropouts.

that's all

Claims (1)

[Claims] 1. The area with respect to the circumscribed circle expressed by the following formula (1) is 60%
above, the degree of variation in particle size expressed by the following formula (2) is 30% or less, the thermal conductivity is 0.01 cal/cm・sec・℃ or more, and the average particle size is 0.01 Biaxially oriented polyester film containing thermally conductive ceramic fine particles of ~2.0 μm in a proportion of 0.01 to 1.0% by weight: Area ratio (%) with respect to the circumscribed circle = (projected cross-sectional area of the particle / circumscribed particle area of the circle) x 100...(1) Particle size dispersion (%) = (standard deviation of particle size/average particle size) x 100...(2)