JPH07240021A - Biaxially oriented polyester film - Google Patents

Abstract

PURPOSE:To obtain a biaxially oriented polyester film which has excellent flatness, chipping resistance, slittability and easy slipperiness and is adequate mainly for a magnetic recording medium base. CONSTITUTION:Spherical inert particles having a volume averaged grain size of 0.1 to 1.0mum, volume averaged grain size larger than twice the number averaged grain size, a grain size ratio (major diameter/minor diameter) of 1.0 to 1.2 and a relative standard deviation of over 0.5 are incorporated at 0.01 to 5wt.% into polyester.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a biaxially oriented polyester film, and more specifically, it contains spherical inert particles having a specific particle size distribution, and has flatness, abrasion resistance, slitting property,
The present invention relates to a biaxially oriented polyester film which is excellent in slipperiness and is particularly useful as a magnetic recording medium base film.

[0002]

2. Description of the Related Art Today, a polyester film mainly composed of polyethylene terephthalate is widely used as a base film of a magnetic recording medium, and it is still improved in order to achieve high density and high quality. Is being continued.

In a magnetic recording medium, particularly a high-density magnetic recording tape or a high-sensitivity floppy disk, the surface of the base film is required to be as flat as possible from the viewpoint of improving electromagnetic conversion characteristics. However, when the film surface becomes flat, the slipperiness of the film deteriorates,
It causes various troubles. In recent years,
As the magnetic recording system becomes more compact and the tape running system becomes more and more severe, the magnetic tape is required to have abrasion resistance such as a fixing pin. Further, at the time of slitting, which is the final step of the magnetic tape manufacturing process, chips are generated from the cross section of the film, which causes an increase in dropout during magnetic recording. Therefore, a film for a magnetic recording medium is required to satisfy these contradictory characteristics at the same time.

For the purpose of satisfying the above requirements at the same time, a method of using particles having a small relative standard deviation as a lubricant has been proposed. (JP-A-63-1
However, even with such a known method,
In reality, it is difficult to satisfy all the above problems.

[0005]

The biaxially oriented polyester film of the present invention for this purpose comprises:
The volume average particle diameter is 0.1 to 1.0 μm, the particle diameter ratio (major axis / minor axis) is 1.0 to 1.2, and the volume average particle diameter is more than twice the number average particle diameter, And the relative standard deviation is 0.5
More than 0.01 to 5% by weight of spherical inert particles.

The polyester in the present invention is not particularly limited, but ethylene terephthalate, ethylene α, β-bis (2-chlorophenoxy) ethane-4,4
It is particularly preferable when at least one structural unit selected from'-dicarboxylate and ethylene 2,6-naphthalate units is the main constituent. Of these, polyesters containing ethylene terephthalate as a main constituent are particularly preferable. In addition, within the range which does not inhibit the present invention, 2
One or more polyesters may be mixed, or a copolymerized polymer may be used.

The volume average particle diameter of the spherical inert particles used as the lubricant in the present invention is 0.1 to 1.0 μm, preferably 0.1 to 0.8 μm, more preferably 0.1 to 0.
It is 6 μm. If the volume average particle size of the particles is too small, friction increases and the running characteristics of a video tape deteriorate. Further, if it becomes large, the electromagnetic conversion characteristics of a magnetic recording medium represented by a video tape will become poor. The particle size ratio (major axis / minor axis) of the particles is 1.0 to
It is 1.2, preferably 1.0 to 1.1, and more preferably 1.0 to 1.05. When the particle size ratio becomes too large, voids are easily formed around the particles,
When a video tape is used, it is not preferable because the abrasion resistance is deteriorated during running.

The relative standard deviation, which is a measure of the spread of the particle size distribution of the particles, needs to exceed 0.5, preferably exceeds 0.6, and more preferably exceeds 0.7. It is a thing. The upper limit is not particularly defined, but it is preferably 3 or less in order to keep the waviness of the film surface in a good condition.

The relative standard deviation referred to here is represented by the following equation (1) as a ratio of the standard deviation obtained in number unit from the area-equivalent diameter of particles and the number average diameter.

[0010]

[Equation 1] When spherical inert particles having a relative standard deviation of more than 0.5 are used, the slit property, particularly the continuous slit property is improved, and the slit blade is used for a long time at the time of the final step of the magnetic tape manufacturing process such as video tape. Even if you do not change it, the amount of chips generated from the cross section of the film is extremely small,
Further, the swelling of the cross section of the end portion of the film is reduced. The manifestation of this effect is brought about by the extremely small wear of the slit blade in this step.

Further, it is necessary that the volume average particle diameter of the particles is larger than twice the number average particle diameter, preferably 2.5.
It is desirable to be more than double. The relative standard deviation is 0.
When the volume average particle diameter is smaller than twice the number average particle diameter, the particles having a volume average particle diameter larger than the volume average particle diameter are substantially present, resulting in poor flatness when used as a video tape. The electromagnetic conversion characteristics of the recording medium become poor. When the volume average particle diameter is larger than twice the number average particle diameter, the contact area between the background of the film and the guide pin in the running system can be reduced, which is advantageous in terms of slipperiness, and further the guide pin can be used. Especially, the abrasion resistance with the fixing pin becomes extremely good.

The content of the particles is required to be 0.01 to 5% by weight, preferably 0.05 to 2% by weight, more preferably 0.1 to 1% by weight, based on the polyester. Is preferred. Content of the particles is 0.01
If it is less than 10% by weight, friction will increase and the running characteristics will deteriorate when used as a video tape. On the other hand, if it is more than 5% by weight, the electromagnetic conversion characteristics of the magnetic recording medium represented by a video tape will be poor. The inert particles in the present invention are not particularly limited as long as they are particles satisfying the above-mentioned requirements, but inorganic oxide spherical particles (for example, spherical silica particles, spherical titania particles, spherical zirconia particles, spherical alumina particles, etc.) Preferred examples include resin spherical particles (for example, spherical silicon resin particles, spherical crosslinked polystyrene particles, etc.). These may be used alone or in combination of two or more. Such inert particles are not limited by the manufacturing method and other factors.

For example, the spherical silica particles can be synthesized by an ion exchange method using water glass (sodium silicate aqueous solution) as a starting material, a hydrolysis method using an alkoxy silicate as a starting material, and the like. In particular, in order to improve the slitting property, which is one of the objects of the present invention, synthetic silica starting from water glass is more preferable, and further, 20 wt% ethylene glycol slurry of the spherical silica particles at 25 ° C. A refractive index of 1.430, and preferably 1.435 or more, is more preferable because not only the occurrence of voids around the particles in the polyester is reduced but also the effect of improving the slit property becomes remarkable.

Further, the method for obtaining the inert particles satisfying the particle size distribution of the above-mentioned requirements may be a method in which the time and conditions for particle synthesis are changed. Alternatively, a method of removing coarse particles may be used. Further, the centrifugal classification method is also very effective.

In the film of the present invention, a different polymer may be blended within a range not impairing the object of the present invention, and an antioxidant, a heat stabilizer, a lubricant, an ultraviolet absorber, a light shield. Organic additives such as agents and antistatic agents may be added to the extent that they are usually added.

Next, the method for producing the film of the present invention will be described. First, the method of incorporating the particles into the polyester is not particularly limited, but it is generally preferable to add a slurry of the particles during the production of the polyester. As the addition method and the addition timing, conventionally known methods and timings can be used, but the addition method is preferably a method of adding as a slurry of glycol which is a raw material for synthesizing the polyester. The slurry concentration at this time is SiO
_{The amount of 2} % by weight is preferably 0.5 to 40% by weight, and more preferably 1 to 20% by weight because the particle dispersibility in polyester is improved. Further, the water content in the glycol of the slurry at the time of addition is 1% by weight.
It is preferable that the amount is 0.5% by weight or less, because the particle dispersibility in the polyester is improved. The addition time may be arbitrary, and it may be added at the time of charging the monomer, at the time of transesterification reaction, or before and after it. Further, the slurry of the particles may be added and dispersed by using a uniaxial or biaxial vent type extruder or the like after polymer production.

Next, the polyester pellets obtained by the above method are mixed at a predetermined ratio, dried, and then fed to a known melt extruder, extruded into a sheet from a slit die, and cast on a casting roll. An unstretched film is prepared by cooling and solidifying. In this case, the method of installing a static mixer and a gear pump in the polymer channel is effective.

Next, this unstretched film is biaxially stretched,
It is biaxially oriented. As a stretching method, a sequential biaxial stretching method or a simultaneous biaxial stretching method can be used. However,
A method in which a sequential biaxial stretching method of first stretching in the longitudinal direction and then in the width direction is used, stretching in the longitudinal direction is divided into three or more stages, and the total longitudinal stretching ratio is 3.5 to 6.5 times is Particularly preferred. The stretching temperature in the longitudinal direction varies depending on the type of polyester and cannot be generally stated, but the first stage is usually 50 to 1
It is effective to set the temperature to 30 ° C. and raise the temperature from the second stage onward. The longitudinal stretching speed is 5000 to 50000% /
The range of minutes is preferred. As a stretching method in the width direction, a method using a stenter is generally used. Draw ratio is 3.0-
A range of 5.0 times is appropriate. Width direction stretching speed is 100
The range of 0 to 20000% / min and the temperature of 80 to 160 ° C are suitable. Next, this stretched film is heat-treated. The heat treatment temperature in this case is 170 to 220 ° C., especially 180 to 2
The temperature is preferably 00 ° C. and the time is 0.2 to 20 seconds.

The polyester film obtained by the above method is particularly useful as a base film of a magnetic recording medium and is sufficient as a base film of a high-density magnetic recording medium corresponding to the recent digital magnetic recording. Is. For example, for consumer use, S-VH
S, W-VHS, Hi-Eight 8 mm, DCC (Digital Compact Cassette), DAT (Digital Audio Tape), etc. can be mentioned. For business use, for digital format (D1, D2, D3, Digital Betacam, etc.), for HDTV, DCT. (Digital component technology) For tape, data storage, etc.

In addition, for packaging, printer ribbon,
It is also useful as a film for graphics and printing.

[0021]

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. The film evaluation method is as follows.

(1) Particle Size Ratio of Spherical Silica Particles Polyester is removed from the film by a plasma low temperature ashing method to expose the particles. The processing conditions are selected such that polyester is incinerated but particles are not damaged.
Scanning electron microscope (ESM32 manufactured by Elionix Co., Ltd.)
00) and the image of the particles is processed with an image analyzer (IBAS2000 manufactured by Carl Zeiss).

In this measurement, the major axis / minor axis ratio of the individual particles shown in the following formula is obtained, and the particle size ratio "average value of major axis / minor axis" is calculated from these values.

Length / minor diameter ratio of individual particles = D1 / D2 Here, D1 represents a major diameter (maximum diameter), and D2 represents a minor diameter (minimum diameter).

Particle size ratio = Σ (D1i / D2i) / N D1i and D2i are the major axis (maximum diameter) and minor axis (minimum diameter) of each individual particle, and N is the number of counted particles.

(2) Number average diameter of particles, relative standard deviation For each of the particles counted in the measurement in (1) above, the area equivalent circle diameter was determined, and the number of particles was changed to 5,000 or more and the following numerical values were obtained. By performing the treatment, the number average diameter D is obtained by the following formula.

D = ΣDi / N where Di is the equivalent circle diameter of the particles, and N is the number of counted particles.

Then, a standard deviation σ (= {Σ (Di-D) ² / N} calculated from Di, the number average diameter D, and the number N of particles is used.
^The value obtained by dividing ^0.5 ) by the number average diameter D (σ / D) was taken as the relative standard deviation.

(3) Volume average diameter of particles For the particles counted in the measurement of the above (2), the volume average diameter V is obtained from the following formula.

V = (ΣDi ³ / N) ^1/3 Here, Di is the equivalent circle diameter of the particles, and N is the number of counted particles.

(4) Content of Particles A solvent in which polyester is dissolved and particles are not dissolved is selected, the particles are centrifuged from the solvent, and the amount of particles is calculated as a ratio (% by weight) to the whole.

(5) Three-dimensional surface roughness (SRa) Three-dimensional fine shape measuring instrument (Model ET-30H of Kosaka Laboratory)
K) and three-dimensional surface roughness analysis system (model MARM
EC-3D) was used to measure the three-dimensional surface roughness (center plane average roughness). The conditions are as follows, and the average value of 20 measurements was taken as the value.

-Stylus tip radius: 0.5 μm-Stylus load: 4 mg-Vertical magnification: 50,000 times-Horizontal magnification: 200 times-Cutoff: 0.25 mm-Feeding pitch: 5 μm-Measuring length: 500 μm・ Measurement area: 0.197 mm ²・ Measurement speed: 100 μm / sec (6) Image quality A magnetic coating composition having the following composition is applied to the film by a gravure roll, magnetically oriented, and dried. Furthermore, after calendering at a temperature of 70 ° C and a linear pressure of 200 kg / cm with a small calender device (styrene roll, nylon roll, 5 steps), 7
Cure at 0 ° C. for 48 hours. This raw fabric was slit into 1/2 inch to prepare a pancake. This pancake was incorporated into a VTR cassette to obtain a VTR cassette tape.

(Composition of magnetic paint) Co-containing iron oxide (BET value of 50 m ² / g): 100 parts by weight S-REC A (vinyl chloride / vinyl acetate copolymer manufactured by Sekisui Chemical Co., Ltd.): 10 parts by weight Nopollan 2304 ( Nippon Urethane Polyurethane Elastomer): 10 parts by weight Cotonate L (Nippon Urethane Polyisocyanate): 5 parts by weight Lecithin: 1 part by weight Methyl ethyl ketone: 75 parts by weight Methyl isobutyl ketone: 75 parts by weight Toluene: 75 parts by weight・ Carbon black: 2 parts by weight ・ Lauric acid: 1.5 parts by weight This tape was recorded with 100% chroma signal by a TV test waveform generator (TG7 / U706) made by Shibasoku using a VTR for home use, and shibasoku was reproduced from the reproduced signal. Image quality by measuring chroma S / N with a color noise measuring machine (925D / 1) Was judged. The judgment criteria are as follows, and if the rank is 4 or higher, there is no practical problem.

Judgment rank S / N ratio (image quality) 5 Excellent, extremely good image quality 4 Good, almost no problem 3 Disturbance in image quality 2 Large disturbance in image quality 1 Poor image quality (7) Evaluation of slitting property 10 μm thickness A magnetic coating solution having the following composition is coated on one side of a polyester film so that the film thickness after drying is 3 μm.

[0036] After coating, it is oriented in a DC magnetic field, dried, and then calendered. This sheet is slit into 1/2 inch width with a shear cutter to make a video tape. The degree of occurrence of whiskers and powder is visually classified and evaluated by visually observing the slit portion by the shear cutter.

Slitting property A: Generation of whiskers and powder is extremely small.

〃 B: 〃 few.

〃 C: 〃 Normal level.

〃 D: 〃 Somewhat large.

〃 E: 〃 Many.

(Note) Most of the biaxially oriented polyester films for video tapes currently on the market have a slit property level of C or D.

(8) Evaluation of abrasion resistance As shown in FIG. 1, the film (1/2 inch width) was run for 200 m in an atmosphere of 22 ° C. and 65% RH,
The amount of powder adhering to the metal pins was magnified 10 times with a stereomicroscope and evaluated, and the ranking shown below was performed.

Rank A: Almost no adhesion.

B: 〃 small.

C: 〃 Somewhat large.

D: There are many.

E: Very large.

The traveling speed of the film is 250 m / m.
in. The winding angle with the pin is controlled to 90 °, the tension (T ₁ ) on the inlet side is 200 g, the tension (T ₂ ) on the outlet side is measured, and the dynamic friction coefficient (μk) at the end of traveling is calculated by the following formula. It was measured at. μk = (1 / π) ln (T ₂ / T ₁ ) = 0.318ln
And (T _2/200) Example 1 Dimethyl terephthalate and ethylene glycol, calcium acetate as an ester exchange catalyst, antimony trioxide as a polymerization catalyst, phosphorus acid used as a stabilizer, further the volume average particle diameter of 0.22μm as a lubricant , Number average particle size 0.
0.3 wt% of spherical silica particles synthesized by the water glass method having a particle diameter ratio of 1.05 and a relative standard deviation of 0.63 was added and polymerized by a conventional method to obtain polyethylene terephthalate having an intrinsic viscosity of 0.615. It was

The above polyester was dried, fed to an extruder and melted at 280 ° C. to obtain 2.4 m of the molten polymer.
The film was extruded into a sheet through a slit-shaped die of m and rapidly cooled and solidified with a cooling roll to obtain an unstretched film having a thickness of 160 μm. At this time, the discharge amount of the extruder was adjusted and the thickness was adjusted.

Then, this was placed at 115 ° C. in a longitudinal direction of 3.3.
2 times, 3 times in the transverse direction, 1.6 times in the longitudinal direction again at 150 ° C., and then heat treated at 220 ° C. for 10 seconds to obtain a biaxially oriented film having a thickness of 10 μm.

Measurement of characteristics of the obtained biaxially oriented film
The evaluation results are shown in Table 1 together with those of other examples and comparative examples.

Example 2 As the lubricant in the polyester of Example 1, the volume average particle size is 0.55 μm, the number average particle size is 0.12 μm, and the particle size ratio is 1.0.
5. A biaxially oriented film having a thickness of 10 μm was obtained in the same manner as in Example 1 except that 0.2% by weight of spherical silica particles synthesized by the water glass method with a relative standard deviation of 0.78 was added.

Comparative Example 1 As the lubricant in the polyester of Example 1, the volume average particle size is 0.22 μm, the number average particle size is 0.20 μm, and the particle size ratio is 1.0.
5. A biaxially oriented film having a thickness of 10 μm was obtained in the same manner as in Example 1 except that 0.3% by weight of spherical silica particles synthesized by the water glass method with a relative standard deviation of 0.26 was added.

Comparative Example 2 As the lubricant in the polyester of Example 1, the volume average particle size is 0.55 μm, the number average particle size is 0.53 μm, and the particle size ratio is 1.0.
5, a biaxially oriented film having a thickness of 10 μm was obtained in the same manner as in Example 1 except that 0.2% by weight of spherical silica particles synthesized by the water glass method with a relative standard deviation of 0.04 was added.

Comparative Example 3 As the lubricant in the polyester of Example 1, the volume average particle size is 1.26 μm, the number average particle size is 0.40 μm, and the particle size ratio is 1.5.
A biaxially oriented film having a thickness of 10 μm was obtained in the same manner as in Example 1 except that 0.1% by weight of aggregated silica particles (cyloid) having a relative standard deviation of 0.88 was added.

Comparative Example 4 As the lubricant in the polyester of Example 1, the volume average particle size is 0.30 μm, the number average particle size is 0.25 μm, and the particle size ratio is 1.0.
5, a biaxially oriented film having a thickness of 10 μm was obtained in the same manner as in Example 1 except that 0.3% by weight of spherical silica particles synthesized by the water glass method with a relative standard deviation of 0.58 was added.

Comparative Example 5 As the lubricant in the polyester of Example 1, the volume average particle size is 0.22 μm, the number average particle size is 0.09 μm, and the particle size ratio is 1.0.
5, a biaxially oriented film having a thickness of 10 μm was obtained in the same manner as in Example 1 except that 6.0% by weight of spherical silica particles synthesized by the water glass method with a relative standard deviation of 0.63 was added.

The films of Examples 1 and 2 satisfying the requirements of the present invention are all excellent in flatness, slipperiness, abrasion resistance and slitting property, and are at a level that is highly satisfactory in magnetic tape characteristics.

On the other hand, the films of Comparative Examples 1 to 5 are examples of films containing particles which do not satisfy the requirements of the present invention, but are inferior in abrasion resistance, slit property and magnetic tape property.

[0061]

[Table 1]

[0062]

INDUSTRIAL APPLICABILITY The film of the present invention described above is excellent in flatness, slipperiness, abrasion resistance and slitting property, and reaches a high level in magnetic tape characteristics. It is useful as a base film and has high industrial value.

[Brief description of drawings]

FIG. 1 shows a schematic view of an apparatus for evaluating the abrasion resistance of a film.

[Explanation of symbols]

 1: Unwinding reel 2, 13: Guide roll 3, 4, 6, 8, 10, 11: Free roll 5: Tension detection roll (entrance side) 7: Metal pin 9: Tension detection roll (outgoing side) 12: Nip roll 14: Take-up reel

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI technical display area C08L 67/02 KKF // B29K 67:00 105: 16 B29L 7:00

Claims (3)

[Claims] 1. A polyester having a volume average particle diameter of 0.
1 to 1.0 μm and a particle size ratio (major axis / minor axis) of 1.0
.About.1.2, the volume average particle diameter is more than twice the number average particle diameter, and the relative standard deviation is more than 0.5. Axial oriented polyester film. 2. The biaxially oriented polyester film according to claim 1, wherein the spherical inert particles are spherical silica particles. 3. The biaxially oriented polyester film according to claim 1, wherein the spherical silica particles are particles synthesized by a water glass method.