JPH081769A - Polyester film and production thereof - Google Patents

Abstract

PURPOSE:To obtain running properties without lowering electromagnetic conversion characteristics and to reduce dropout and the abrasion of a head by setting the number of projections/number of particles and the area ratio of projection parts on at least one surface to specific values. CONSTITUTION:The number of projections/number of particles (NR) on at least one surface is set to 5 or more and the area ratio of the projection parts thereon is set to 0.001 - below 5%. In order to enhance electromagnetic conversion characteristics, it is pref. that the surface provided with projections is as smooth as possible and the center line average roughness Ra of the surface is 15nm or less and the value of a ratio Rt/Ra of the max. height Rt of the surface and Ra is 15.0 or less. The surface temp. of a polyester film is held to a temp. range from temp. lower than the crystallization temp. on cooling of polyester A by 70 deg.C to the crystallization temp. for 0.5-20sec and the film is cooled to the glass transition temp. of polyester A or lower to be biaxially stretched to form desired surface projections.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a polyester film and a method for producing the same, and more particularly to a polyester film having fine projections formed on its surface and a method for producing the same.

[0002]

2. Description of the Related Art Polyester films are widely used for various purposes. With the increase in processing speed of polyester film processing, such as printing in packaging applications, magnetic layer application in magnetic recording media applications, or thermal transfer layer application in thermal transfer applications, polyester films are even better. Surface properties such as excellent running property and wear resistance are being demanded. It is known that it is effective to uniformly form fine protrusions on the film surface in order to obtain good runnability.

A polyester film containing substantially spherical silica particles derived from colloidal silica in order to form fine projections on the film surface is known (for example, JP-A-59-171623). . Also,
A polyester film in which a thin layer containing particles for forming surface protrusions is laminated on a base layer is also known (for example, JP-A-2-77431).

[0004]

For example, when a polyester film is used as a support for a magnetic recording medium, a magnetic layer provided on the support has recently been required to have a very high level of electromagnetic conversion characteristics. It is desired to minimize the spacing loss with the magnetic head.
Therefore, the support also needs to be very smooth. The friction coefficient must be reduced while maintaining such ultimate smoothness. One means for satisfying the contradictory requirements of smoothness and friction reduction is to disperse ultra-fine projections on an ultra-smooth support.
When such ultrafine protrusions are formed using inert particles, there are the following major problems.

That is, since it is very difficult to disperse the particles, coarse projections are often generated, which easily causes deterioration of electromagnetic conversion characteristics, dropout, and wear of the head. In addition, voids are large in these coarse protrusions and are easily scraped. When such scraping occurs, scraped powder can also cause dropout.

An object of the present invention is to provide a polyester film having desired fine projections formed on the surface thereof by utilizing the crystallization of polyester essentially without depending on the contained particles, and a method for producing the same. Has a uniform surface protrusion with high strength, good scratch resistance, and can obtain a high level of electromagnetic conversion characteristics especially when used as a magnetic recording medium, and the surface of the magnetic layer. A polyester film capable of reducing the friction coefficient of

[0007]

The polyester film of the present invention for this purpose is a biaxially oriented polyester film containing polyester A as a main component, and the number of projections on the surface and the number of projections on at least one surface of the polyester film. The number of protrusions / number of particles (NR), which is the ratio of the number of particles contained in the surface layer forming the surface, is 5 or more, and the area ratio of the protrusions on the surface is 0.001% or more and less than 5% ( It is preferably 0.01% or more and less than 5%, more preferably 0.1% or more and less than 5%).

If the value of NR is less than 5, the projections on the surface are easily broken, and if the projections are broken, the fragments are likely to damage the film. Further, if the area ratio of the protrusions is less than 0.001%, the coefficient of friction of the film surface is too high, and stable running properties and transportability of the film cannot be obtained. Further, if the area ratio of the protrusions is 5% or more, the probability that coarse protrusions will occur increases. When the number of protrusions / the number of particles (NR) and the area ratio of the protrusions are within the above ranges, it is possible to reduce friction without impairing the smoothness of the film surface. Further, it is possible to reduce the possibility that the protrusions are scraped off by the minute protrusions of the contact partner, and since there are no coarse protrusions, the amount of scraped powder is reduced, resulting in less head wear and less magnetic dropout.

In the polyester film of the present invention, the surface on which the projections are provided is preferably as smooth as possible in order to improve the electromagnetic conversion characteristics, and the center line average roughness R
It is preferable that a is 15 nm or less, and more preferably 10 nm or less. In addition, the value of the ratio Rt / Ra of the maximum surface height Rt and Ra is 1 as an index of the presence or absence of coarse protrusions.
It is preferably 5.0 or less, more preferably 10
It is the following.

In the polyester film of the present invention, the projections on the surface are preferably projections mainly caused by crystals. That is, the protrusions on the surface are formed by utilizing the crystallization of polyester A itself. Therefore, the problem of void generation when particles are added is substantially eliminated, and protrusions with high strength that are difficult to break are formed.

Particles may be supplementarily added for the purpose of further reducing friction, facilitating the cutting of the film, and the like. In this case as well, the number of projections on the surface and the number of particles contained are The ratio of the number of protrusions / the number of particles (NR) is 5
It is necessary to do above. When NR is less than 5, the ratio of protrusions formed by the contained particles increases, and the ratio of protrusions that are easily broken due to void formation increases, so that dropout of the protrusions increases and dropout increases. Alternatively, the dropped projections may be accumulated and solidified, which may scratch the film surface.

The formation of surface protrusions utilizing the crystallization of polyester A as described above is performed as follows.

In producing a biaxially oriented film containing polyester A as a main component, at least one surface of the unstretched film is heat treated, and then the unstretched film is biaxially stretched to form a desired surface protrusion. It

By first heat-treating the unstretched film, crystallization of the surface of the unstretched film is promoted,
A large number of fine crystals are formed. This unstretched film is biaxially stretched, the film is biaxially oriented to achieve the target strength of the film itself, and due to the difference in hardness between the crystal and the other part, the uniform crystal resulting from the fine crystals is obtained. Fine surface protrusions are formed.

Whether the surface protrusions are made of fine crystals of polyester A is determined by etching under the subject protrusions in an appropriate solvent in the film thickness direction to form the protrusions. When the substance remains as an insoluble substance, it is treated as particles added from the outside or particles precipitated internally (I). When there is substantially nothing that remains as an insoluble matter, it can be inferred that the substance that forms the protrusion is a fine crystal (II). Examples of the solvent include phenol / carbon tetrachloride (weight ratio: 6 /
The mixed solvent of 4) is preferably used. The frequency of I and the frequency of II when the visual field is set to about 1 mm ² is obtained by this method, and the value of I / (I + II) is preferably 70% or more. However, the method for determining whether or not the surface protrusions are made of fine crystals of polyester A is not limited to the above method, and an appropriate method can be selected.

In the present invention, the type of polyester A is not particularly limited, but the crystallization parameter ΔTcg is 70.
℃ or less, preferably 65 ℃ or less, more preferably 60 ℃
The following is desirable. If the crystallization parameter ΔTcg is larger than 70 ° C., it is difficult to obtain the surface protrusions targeted by the present invention. Even if it is obtained, the scratch resistance of the film surface is likely to be inferior.

In the present invention, the type of polyester A is not particularly limited, but ethylene terephthalate, ethylene α, β-bis (2-chlorophenoxy) ethane-
It is particularly preferable when at least one structural unit selected from 4,4-dicarboxylate and ethylene naphthalate units is the main constituent. Of these, polyesters containing ethylene terephthalate as a main constituent are particularly preferable. In addition, within a range not hindering the object of the present invention,
Two or more kinds of polyesters may be mixed, or a copolymerized polymer may be used. Further, it is desirable that the polyester A contains substantially no particles.

In the polymerization of polyester A, it is preferable to use antimony trioxide as a polymerization catalyst, and acetate as the metal compound as the transesterification catalyst in order to reduce ΔTcg and enhance the effect of the crystal nucleating agent. The acetate salt is not particularly limited, but it is particularly preferable to use a magnesium compound in order to achieve the object of the present invention.
Further, it is preferable to use phosphonate as the phosphorus compound added during the polymerization of PET. However, the method for producing the polyester A is not limited to the above. Increasing the amount of catalyst added to increase the nucleating agent effect is not preferable because it causes precipitation of internal particles and increases haze.

The polyester film of the present invention may be used as a single layer of a biaxially oriented film containing polyester A as a main component, or as a laminated film laminated on at least one side of a film containing polyester B as a main component. You may be asked.

The type of polyester B is not particularly limited. Polyester B preferably contains no particles, but may contain them.

In the present invention, at least one side of the unstretched film is heat treated and then biaxially stretched. Here, the unstretched film refers to a state immediately after being extruded from the die and before being solidified by cooling, to a film slightly stretched (up to about 2 times) in the uniaxial direction. The purpose of this heat treatment is to increase the crystallinity of the film surface before stretching to a preferable crystallinity, and as a treatment method,
There is a method of gradually cooling a film having a high temperature immediately after extrusion to crystallize it, a method of reheating a film once cooled and solidified to crystallize it, and a method of heat-treating it in a state of being slightly stretched in a uniaxial direction.

Further, a more detailed example of the method for producing the polyester film of the present invention will be described.

In the process of cooling the melt-extruded film containing polyester as the main component on the surface of the cooling roll, the glass transition temperature Tg of the polyester A or more and the melting temperature T
A temperature of 100 ° C. higher than m (Tm + 100 ° C.) or less, the unstretched film is heat-treated from the opposite surface in contact with the cooling roll, and then the unstretched film is biaxially stretched to form a desired surface protrusion. Therefore, it is preferable.
More preferably, the temperature is 20 ° C. higher than Tg (Tg + 20
℃) and higher than Tm by 80 ℃ (Tm + 80
C.) or lower, more preferably 40 ° C. higher than Tg (Tg + 40 ° C.) or higher and Tm or lower. As a method of heat-treating the unstretched film from the surface opposite to the one in contact with the cooling roll, hot air or radiant heat from an infrared heater can be used, but it is not limited to this method.

The surface roughness of the cooling roll surface is 0.2.
When it is S or more and 10 S or less, the crystallinity of the film surface before stretching can be increased to a desired crystallinity, which is preferable. More preferably, the surface roughness of the surface of the cooling roll is 0.3 S or more and 8 S or less. When the surface roughness of the roll surface is less than 0.2 S, the unstretched film tends to stick to the cooling roll. If the surface roughness exceeds 10 S, desired surface protrusions may not be formed or the film may slip on the cooling roll.

In the present invention, when heat-treating an unstretched film that has been cooled and solidified, the surface (or surface layer) temperature of at least one surface thereof is 20 ° C. lower than the cold crystallization temperature Tcc of polyester A (Tcc-20 ° C.) or more. And 40 ° C. higher than the temperature falling crystallization temperature Tmc (Tmc + 40 ° C.)
In the following, heat treatment is performed so as to be maintained for 0.5 to 100 seconds, and thereafter, Tg or more and 20 ° C higher than Tcc (Tcc +
By biaxially stretching at a temperature of 20 ° C. or less, desired surface protrusions are formed, which is preferable. More preferably,
0.5 to 50 seconds at Tcc or more and Tmc or less, more preferably 0.5 to 2 at Tcc or more and Tmc or less.
The heat treatment is such that it is held for 0 seconds.

The following manufacturing conditions are also possible. Unstretched film is finely stretched uniaxially and has birefringence of 0.5 × 1
0 ^-3 to 50 x 10 ^-3, and then the surface (or surface layer) temperature of at least one side of the slightly stretched film is 20 ° C lower than the cold crystallization temperature Tcc of polyester A (Tcc-20.
C.) and a temperature lower than the crystallization temperature Tmc by 40.degree. C. or less (Tmc + 40.degree. C.) or less so as to be maintained for 0.3 to 50 seconds, and then Tg or more and 20.degree. C. from Tcc.
By biaxially stretching at a high (Tcc + 20 ° C.) or lower temperature, desired surface protrusions are formed, which is preferable. More preferably, Tcc or more and Tmc or less, 0.5
˜20 seconds, more preferably, a heat treatment that is maintained at 10 ° C. higher than Tcc (Tcc + 10 ° C.) or higher and 20 ° C. lower than Tmc (Tmc−20 ° C.) or lower for 0.5 to 15 seconds.

As for the heat treatment method, a method of heat treatment by wrapping around a heating roll, a method of hot air treatment from the side opposite to the roll which is in contact with the roll in the state wound around the roll, or a side opposite to contact with the roll in the state of being wound around the roll There is a method of heat treatment with an infrared heater, a method of heat treatment with an infrared heater between rolls, a method of heating with a stenter, etc., but the method is not particularly limited to these.

In the present invention, the temperature of at least one surface (or surface layer) of the melt-extruded film containing polyester as the main component is set to the temperature-lowering crystallization temperature Tm of polyester A.
When the temperature is 70 ° C. lower than C (Tmc-70 ° C.) or higher and the temperature-lowering crystallization temperature Tmc of the polyester A is lower,
It is preferable to hold for 20 seconds, then cool to a glass transition temperature Tg or lower, and then biaxially stretch the unstretched film to form a desired surface protrusion.

Although there are various heat treatment methods as described above, one of these methods can be carried out in the film forming process to obtain a target surface morphology. Two or more of them may be used in combination and carried out in the film forming process of the film.

The use of the film of the present invention is not particularly limited, but a base film for a magnetic recording medium, particularly a coating type high-grade metal tape which requires smoothness of the film surface,
It is preferably used as a base film of a metal thin film type magnetic recording medium. For thermal transfer such as ink ribbon, O
It can also be used for heat-sensitive transfer such as HP, graphics, packaging, etc.

[Physical property measuring method and effect evaluating method] The characteristic value measuring method and effect evaluating method of the present invention are as follows.

(1) Number of projections on film surface, projection height, relative standard deviation of projection height 2 Scanning electron microscope [E]
SM-3200, manufactured by Elionix Co., Ltd. and a cross-section measurement device [PMS-1, manufactured by Elionix Co., Ltd.] are used to perform image processing on the measured values of the height of protrusions when the height of the flat surface of the film is 0. It is sent to an apparatus [IBAS2000, manufactured by Carl Zeiss Co., Ltd.] and a film surface projection image is reconstructed on the image processing apparatus. Next, the highest value among the individual projections obtained by binarizing the projections in this surface projection image is set as the projection height of the projection, and this is calculated for each projection. This measurement was repeated 500 times at different places, and the number of protrusions was 10 nm or more, and the number of protrusions and the average protrusion height were determined. Moreover, the standard deviation of the height distribution was calculated based on the individual projection height data. The value obtained by dividing the obtained standard deviation by the average value of the above heights was taken as the relative standard deviation. The magnification of the scanning electron microscope is selected to be 1000 to 8000 times. In some cases, the high-precision optical interference type 3
Even if the number information such as height information and peak count obtained by a three-dimensional surface analyzer (TOPO-3D manufactured by WYKO, objective lens: 40 to 200 times, use of a high precision camera is effective) is read into the value of the SEM. good. Regarding the number of protrusions, in order to capture the protrusions three-dimensionally, the film was tilted by 82.5 °, and a photograph was taken with an electron microscope (SEM) at a magnification of 10,000 to 500,000, and 100 fields of view were measured. The number of protrusions may be converted from the value per 1 mm ² .

(2) Number of Particles Contained in Surface Layer In the present invention, the surface layer means a portion from the film surface to a depth of 3D. Here, 3D means the average particle diameter D × 3 of the particles contained in the film. The term "particles" as used herein means that when the cross section of a film is observed with a TEM, the particles observed in the thickness direction are those having an average protrusion height greater than or equal to the average protrusion height obtained by the above method. But particles smaller than that are not considered as particles.

A transmission electron microscope (TE
The number of particles existing in a portion from the surface to a depth of 3D may be observed in 500 visual fields at a magnification of 3000 to 10000 and converted into 1 mm ² by observing with M).

(3) Average Particle Size of Particles Polyester is removed from the film by a plasma ashing method to expose the particles. The processing conditions are such that the polymer is incinerated but the particles are not damaged as much as possible. The particles are observed with a scanning electron microscope (SEM), and the particle image is processed with an image analyzer. The magnification of SEM is approximately 2000 to 10,000 times, and the visual field in one measurement is appropriately selected from approximately 10 to 50 μm on each side. The volume average diameter d is obtained by the following formula from the volume fraction with the particle diameter when the number of particles is 5000 or more by changing the observation location.

D = Σdi · Nvi Here, di is the particle size and Nvi is the volume fraction thereof.

When the particles are organic particles or the like and are significantly damaged by the plasma low temperature ashing method, the following method may be used.

The cross section of the film was examined with a transmission electron microscope.
Observe at 3,000 to 100,000 times. The section thickness of the TEM is set to about 100 nm, the location is changed and 500 or more visual fields are measured, and the volume average diameter d is obtained from the above formula.

(4) Content of particles After adding 1.0 liter of o-chlorophenol to 100 g of polyester and heating at 120 ° C. for 3 hours, using an ultracentrifuge 55P-72 manufactured by Hitachi Koki Co., Ltd., 30,000 rp
Centrifugation for 40 minutes at m
Vacuum dry with. When a dissolution peak corresponding to polyester is observed when the fine particles are measured with a scanning kinetic calorimeter, o-chlorophenol is added to the fine particles, and after heating and cooling, centrifugation is performed again. When no melting peak is observed, the fine particles are designated as precipitated particles. Usually, two centrifugation operations are sufficient. The ratio of the weight of the particles thus separated to the total weight was determined and used as the content of the particles.

(5) Crystallization parameter ΔTcg This was measured using a Perkin-Elmer DSC (differential scanning calorimeter) type II. The measurement conditions of DSC are as follows. That is, 10 mg of the sample was set in the DSC device, and 3
After melting for 5 minutes at a temperature of 00 ° C., it is quenched in liquid nitrogen. The temperature of this quenched sample is raised at 10 ° C./min, and the glass transition point Tg is detected. The temperature is further raised, and the difference (Tcc-Tg) between Tcc and Tg, which is the cold crystallization temperature Tcc based on the crystallization exothermic peak temperature from the glass state, is used as the crystallization parameter ΔTc.
Define as g. The crystallization exothermic peak temperature from the glass state was taken as the cold crystallization temperature Tcc, the endothermic peak temperature due to crystal melting was taken as the melting temperature Tm, and similarly the crystallization exothermic peak temperature at the time of falling was taken as the lowered crystallization temperature Tmc. The difference between Tcc and Tg (Tcc-Tg) is taken as the crystallization parameter ΔTcg
Is defined.

(6) Surface roughness parameters Ra and Rt The surface roughness parameters Ra and Rt were measured using a high precision thin film step measuring instrument ET-10 manufactured by Kosaka Laboratory. The conditions are as follows, and the average value of 20 measurements was used as the value.

-Stylus tip radius: 0.5 μm-Stylus load: 5 mg-Measuring length: 1 mm-Cutoff: 0.08 mm-Stylus speed: 4 μm / sec The definition of Rt and Ra is, for example, Jiro Nara It is described in the book "Measurement and Evaluation Method of Surface Roughness" (General Technology Center, 1983).

(7) Birefringence The refractive index nMD in the longitudinal direction and the refractive index nTD in the width direction of the uniaxially oriented film were measured using an Abbe refractometer, and defined by the difference between these values, that is, | nMD-nTD | . The light source was sodium D line (wavelength 589 nm), and the mount solution was methylene iodide at 25 ° C. and 65% RH.

(8) Film temperature A radiation thermometer, a contact type surface thermometer, or a thermolabel was attached to the film for measurement. The film temperature in the molten state is measured by a radiation thermometer,
Alternatively, the measurement was performed by inserting a thermocouple into the molten film.

(9) Output characteristics (C / N) A vapor deposition layer of a cobalt-nickel alloy (Ni 20% by weight) was formed on the surface of the A layer of the film of the present invention by using a continuous vacuum vapor deposition apparatus in the presence of a trace amount of oxygen. Was formed (thickness: 20
0 nm). Then, a carbon protective film is formed on the surface of the vapor-deposited layer and a back coat layer is formed on the opposite surface by a known method, and then 8 m
A pancake was prepared by slitting to a width of m. Then, a length of 200 m from this pancake was incorporated into a cassette to form a cassette tape.

On this tape, a commercially available Hi8 VTR (S
7MHz using ONY EV-BS3000)
The C / N of ± 1 MHz was measured.

This C / N was compared with a commercially available video tape for Hi8 (ME for 120 minutes), and it was determined that it was +3 dB or more: excellent +1 to +3 dB: good +1 dB or less: poor.

(10) Tape magnetic surface runnability Using the tape running tester, the above-mentioned tape having a width of 8 mm was subjected to a metal guide pin (material: SUS, surface roughness: 0. 1 s) was run with the magnetic surface in contact (running speed 3.3 cm / min, running tension 20 g, wrapping angle 60 degrees). The friction coefficient after 100 times of repeated running was measured, and it was determined to be less than 0.2: excellent 0.2 or more and less than 0.3: good 0.3 or more: poor.

(11) Head wear The above tape of 8 mm width was repeatedly rewound 100 times under the conditions of 40 ° C. and 80% RH using the Hi-8 VTR, and the state of the head was changed to Lasertec Co., Ltd. Manufactured, and observed using a laser microscope. When the wear amount of the head was less than 1 μm as compared with that before running, those having a wear amount of 1 to 3 μm were judged to be good and those having a wear amount of 3 μm or more were judged to be defective.

(12) Laminate Thickness Using a transmission electron microscope (H-600 manufactured by Hitachi), the film cross section was subjected to an ultrathin section method (R) at an acceleration voltage of 100 kV.
uO ₄ staining), the interface is captured, and the laminated thickness is determined. The magnification is usually selected according to the laminated thickness to be judged, and is not particularly limited, but 10,000 to 100,000 times is suitable.

(13) A high-definition image analysis is applied to the measurement of the area ratio of the protrusions.
"PIAS-IV" as a high resolution personal image analysis system
(Manufactured by Pias Co., Ltd.), an optical microscope "Meta" manufactured by Leitz
loplan ”was used.

(A) Plate-prepared film A sample is vapor-deposited with aluminum (thickness: 500 to 800 angstroms) and attached to a slide glass to give a plate-shaped plate.

(B) Adjustment Method and Measurement Conditions The objective lens of the optical microscope is set to 80 times, a reflection method is used for microscopic observation, and the image is captured on a high-resolution monitor of an image analyzer. At this time, the observation magnification on the monitor becomes 3900 times. When inputting an image, it is a black-and-white image and is performed under the condition that a green filter is applied. The input image is binarized and the brightness is converted.
The brightness value representing the density level at this time is set to 175. Before setting, the brightness of the diaphragm of the optical microscope is adjusted so that the average brightness value when measuring the mirror surface as a blank value is 154 in advance. The mirror surface used was the glossy surface used in the objective micrometer (reflection type) manufactured by Nikon Corporation.

(C) Measurement The sum of the pixel numbers of the individual protrusions obtained by binarizing the protrusion image is measured, and the total pixel number of the measurement visual field is divided to obtain the area ratio of the protrusion portion by the following equation. . The total number of pixels per field of view is about 2 million, and the measurement area at this time is 0.0064 mm ²
And change the place and repeat this 10 times. In addition,
The diameter of the projection is 0.11 μm or more when defined as an equivalent circle.

[0055]

(Equation 1)

[0056]

EXAMPLES Next, the present invention will be explained based on examples.

Example Polyester A was polyethylene terephthalate polymerized by a conventional method (polymerization catalyst: magnesium acetate 0.1
0% by weight, antimony trioxide 0.03% by weight, dimethyl phenylphosphonate as a phosphorus compound 0.35% by weight
Was used. ) Was used (intrinsic viscosity: 0.60, melting point: 2)
58 ° C).

As the polyester B, polyethylene terephthalate polymerized by a conventional method using 0.06% by weight of magnesium acetate, 0.008% by weight of antimony trioxide and 0.02% by weight of trimethyl phosphate was used (intrinsic viscosity : 0.62, melting point: 259 ° C).

Example 1 Polyester A pellets were dried at 180 ° C. for 3 hours,
Melt extrusion at 290 ° C. using a known extruder,
Using an electrostatically applied casting method, the film was wound on a casting drum having a surface temperature of 30 ° C., cooled and solidified to prepare an unstretched film. The surface temperature of this unstretched film is 1
Heat treatment was performed for 12 seconds using a known Teflon roll at 40 ° C.

After the heat treatment, the film was stretched at a temperature of 90 ° C. by 3.4 times in the longitudinal direction, and further, using a known stenter, at a stretching rate of 2000% / min, at 95 ° C., a width of 3.5. The film was double-stretched and further heat-treated at 210 ° C. for 5 seconds under a constant length to obtain a biaxially oriented film having a thickness of 10 μm.

Example 2 Polyester A pellets and polyester B pellets were mixed in a ratio of 1: 9, and the mixed pellets were mixed at 180 ° C.
After being dried for 3 hours at 290 ° C., it is melt-extruded using a known extruder, and is wound on a casting drum having a surface temperature of 30 ° C. by an electrostatic cast method, cooled, solidified, and unstretched. I made a film. This unstretched film was heat-treated for 8 seconds using a known Teflon roll having a surface temperature of 140 ° C.

After the heat treatment, the film was stretched at a temperature of 90 ° C. by a factor of 3.4 in the longitudinal direction, and further, using a known stenter, at a stretching speed of 2000% / min, at 95 ° C., a width of 3.5. The film was double-stretched and further heat-treated at 210 ° C. for 5 seconds under a constant length to obtain a biaxially oriented film having a thickness of 10 μm.

Example 3 A laminated film having an A / B / A three-layer structure was prepared. Pellets of polyesters A and B dried at 180 ° C. for 3 hours were respectively fed to two extruders, melted at 290 ° C., merged and laminated in a rectangular confluent block (feed block) for three layers, and statically mixed. By using an electric cast method, it is wound on a casting drum having a surface temperature of 30 ° C., cooled and solidified,
An unstretched film was made. This unstretched film was subjected to 12 using a known Teflon roll having a surface temperature of 140 ° C.
Heat treatment was performed for a second.

Thereafter, a total thickness of 1 is obtained by the same process as in Example 1.
A 0 μm biaxially oriented laminated film was obtained. The layer A had a laminated thickness of 0.7 μm on each side. However, in Example 3, the stretching ratio was set to 4.0 times in the longitudinal direction and the width direction, respectively.

Example 4 A laminated film having an A / B / A three-layer structure was prepared by using the mixed pellets used in Example 2 instead of the polyester A in Example 3. However, the heat treatment of the unstretched film was performed for 10 seconds using a well-known Teflon roll having a surface temperature of 130 ° C.

Thereafter, a total thickness of 1 is obtained by the same process as in Example 1.
A 0 μm biaxially oriented laminated film was obtained. The layer A had a laminated thickness of 0.7 μm on each side. However, the stretching ratio was 4.0 times in the longitudinal direction and the width direction.

Example 5 In the same manner as in Example 3, except that polyester A and B were mixed in a weight ratio of 5:95 instead of polyester A, a biaxially oriented laminated film having a total thickness of 10 μm was prepared in the same process as in Example 3. Got The layer A has a laminated thickness of 0.
It was 6 μm. However, in Example 5, the stretching ratio was set to 4.0 times in the longitudinal direction and the width direction, respectively.

Example 6, Comparative Examples 1 and 2 An ethylene glycol slurry containing silica particles derived from colloidal silica having an average particle size of 0.03 μm was prepared, and the ethylene glycol slurry was heat treated at 190 ° C. for 2 hours, Polyester terephthalate pellets containing 0.5 to 1.0 wt% of the particles were prepared by transesterification with dimethyl terephthalate and polycondensation (polymerization catalyst: magnesium acetate 0.10 wt%, antimony trioxide 0). 0.03 wt% and trimethyl phosphate 0.026 wt% were used as phosphorus compounds). This pellet is designated as polyester C.

In Example 3, polyester A and polyester C were mixed in the following proportions instead of polyester A, and a biaxially oriented laminated film having a total thickness of 10 μm was obtained in the same manner as in Example 3. The laminated thickness of the layer A was 0.6 μm on each side. However, the stretching ratio was 4.0 times in the longitudinal direction and the width direction.

Example 6: Polyester A: C = 99.
9: 0.1 Comparative Example 1: Polyester A: C = 99: 1 Comparative Example 2: Polyester A: C = 95: 5 Comparative Example 3 Using polyester B only, the same process as in Example 1 was performed to obtain a thickness of 10 μm. A biaxially oriented film of was obtained.

Example 7 As in Example 3, pellets of polyesters A and B dried at 180 ° C. for 3 hours were fed to two extruders, respectively, and melted at 290 ° C. to form a rectangular layer for three layers. In a confluence block (feed block), confluent lamination is performed, and the film is wound on a casting drum having a surface temperature of 30 ° C. by using an electrostatically applied casting method, and a surface opposite to the drum is blown with hot air of 330 ° C. to form a film drum. The surface on the opposite side was kept at 150 to 180 ° C. for 4 seconds, then cooled and solidified to prepare an unstretched film. This unstretched film is heated to a temperature of 90
At a temperature of 95 ° C. at a stretching rate of 2000% / min, using a known stenter.
The film was stretched 3.5 times in the width direction and further heat-treated at 210 ° C. for 5 seconds under a constant length to obtain a biaxially oriented film having a thickness of 10 μm.

Example 8 Pellets of polyesters A and B dried at 180 ° C. for 3 hours in the same manner as in Example 3 were fed to two extruders, respectively, melted at 290 ° C., and merged into a rectangular shape for three layers. Using a block (feed block), the layers were combined and laminated, and by an electrostatic cast method, they were wound on a casting drum having a surface temperature of 30 ° C., cooled and solidified to prepare an unstretched film. The unstretched film was stretched uniaxially by 1.8 times and then heat-treated for 10 seconds using a known Teflon roll having a surface temperature of 140 ° C. Furthermore, at a temperature of 90 ° C., it is stretched 2.0 times in the longitudinal direction, and further, using a known stenter, at a stretching speed of 2000% / min, at 95 ° C., it is stretched 3.5 times in the width direction, and then a fixed length is obtained. It was heat-treated at 210 ° C. for 5 seconds under the conditions described above to obtain a biaxially oriented film having a thickness of 10 μm.

Comparative Example 4 Polyesters A and B constituting the surface layer in Example 5 were used.
And calcium carbonate particles having an average particle diameter of 0.4 μm.
1 wt% was added and a biaxially oriented laminated film was obtained in the same manner as in Example 5.

Table 1 shows the characteristics of each film in each of the above Examples and Comparative Examples.

[0075]

[Table 1] As shown in Table 1, the polyester film within the range of the present invention shows excellent performances in C / N, dropout, tape magnetic surface running property, and head wear. It was inferior in any of the above items to the polyester film in the range.

[0076]

In the film of the present invention, by forming high-strength crystalline fine projections on an ultra-smooth surface, deterioration of electromagnetic conversion characteristics is not caused, and even when a magnetic layer is provided, the surface of the magnetic layer is The friction coefficient can be lowered, stable running performance can be obtained, and dropout and head wear can be reduced.

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Claims (11)

[Claims] 1. A biaxially oriented polyester film containing polyester A as a main component, the projections being the ratio of the number of projections on at least one surface of the film to the number of particles contained in the surface layer forming the surface. Number / number of particles (N
R) is 5 or more, and the area ratio of the protrusions on the surface is 0.001% or more and less than 5%, a biaxially oriented polyester film. 2. The polyester film according to claim 1, wherein the protrusions on the surface are protrusions mainly caused by crystals. 3. The polyester film according to claim 1, wherein the crystallization parameter ΔTcg of the polyester A is 70 ° C. or lower. 4. The surface roughness Ra on at least one surface is 15 nm or less, and the ratio R of Ra to Rt is R.
The polyester film according to claim 1, wherein a / Rt is 15.0 or less. 5. A polyester film comprising the polyester film according to claim 1 laminated on at least one side of a film containing polyester B as a main component. 6. The film according to claim 1, wherein at least one surface of the unstretched film is heat-treated, and then the unstretched film is biaxially stretched. 7. In the process of cooling the melt-extruded film containing polyester as the main component on the surface of the chill roll, at a temperature not lower than the glass transition temperature Tg of polyester A and not higher than the melting temperature Tm by 100 ° C. (Tm + 100 ° C.),
7. The method for producing a polyester film according to claim 1, wherein the unstretched film is heat-treated from the opposite surface in contact with the cooling roll, and then the unstretched film is biaxially stretched. . 8. The temperature of at least one surface (or surface layer) of the unstretched film that has been cooled and solidified is polyester A
20 ℃ lower than the cold crystallization temperature of Tcc (Tcc-20
C.) temperature and 40 ° C. higher than the temperature-lowering crystallization temperature Tmc (Tmc + 40 ° C.) or less so as to be maintained for 0.5 to 100 seconds, and then Tg or more and 20 ° C. higher than Tcc (Tcc + 20 ° C.). ) A method for producing a polyester film according to any one of claims 1 to 6, wherein the film is biaxially stretched at a temperature not higher than the temperature. 9. An unstretched film is finely stretched in a uniaxial direction,
The birefringence is 0.5 × 10 ⁻³ to 50 × 10 ^−3, and then the surface (or surface layer) temperature of at least one side of the slightly stretched film is 20 ° C. lower than the cold crystallization temperature Tcc of polyester A (Tcc- 20 ° C.) temperature or more and lowering temperature crystallization temperature T
0.3 below 40 ℃ higher than mc (Tmc + 40 ℃)
Heat treatment to maintain for ~ 50 seconds, then Tg or more,
The method for producing a polyester film according to any one of claims 1 to 6, wherein the film is biaxially stretched at a temperature 20 ° C higher than Tcc (Tcc + 20 ° C) or less. 10. The temperature of at least one surface (or surface layer) of the melt-extruded film containing polyester as a main component is 70 ° C. from the temperature-lowering crystallization temperature Tmc of polyester A.
Lower temperature (Tmc-70 ° C) or higher, and polyester A
0.5 to 20 seconds below the falling crystallization temperature Tmc of
Then, the unstretched film is biaxially stretched after being cooled to a glass transition temperature Tg or lower in two steps, and then the polyester film production method according to any one of claims 1 to 6. 11. The surface roughness of the cooling roll surface is 0.2S.
It is above and 10 S or less, The manufacturing method of the polyester film of Claim 7 characterized by the above-mentioned.