JPH0771819B2 - Biaxially oriented polyethylene terephthalate film - Google Patents

Description

TECHNICAL FIELD The present invention relates to a biaxially oriented polyethylene terephthalate film for magnetic recording media, and more specifically, it is suitable for use mainly as a base material for video tapes. The present invention relates to a biaxially oriented polyethylene terephthalate film.

[Conventional technology]

A biaxially oriented polyethylene terephthalate film having a specified film surface structure, which is particularly suitable as a base material for video tapes (JP-A-61-68727, 61-66627, 60).
-254415, 61-5431, etc.), and
Specific physical properties such as heat shrinkage, Young's modulus, F-5 value (Japanese Patent Laid-Open No. 60-195727, 59-45327, 59-48125, 59-82)
No. 629) is also known.

[Problems to be solved by the invention]

However, the above-mentioned conventional biaxially oriented polyethylene terephthalate film is subjected to a strong shear between the film and a metal roll in a calendar process in the process of making a video tape using the film as a base material for a video tape, and the surface of the film is scraped, resulting in scraped powder. Adheres to the magnetic surface and causes quality defects such as video tape dropout (signal loss). In this sense, there is a strong demand for improvement in the deviation of the film surface, which is a basic problem in designing the surface of the base film.

The present invention relates to a biaxially oriented polyethylene terephthalate film for improving such problems and providing a video tape with less dropout.

[Means for solving problems]

The present invention has a surface abrasion index of 0.1 to 2.0 and a surface protrusion number of 5
60 pieces / mm ² (height 0.54 μm or more), surface average roughness (Ra)
Is 0.01 to 0.03 μm, and the plane orientation coefficient of the crystal (100) plane is 0.03
The main point is a biaxially oriented polyethylene terephthalate film, which is characterized by being 0.11.

The abrasion index of the polyethylene terephthalate (hereinafter referred to as PET) film of the present invention is required to be within the range of 0.1 to 2.0. The value of this abrasion index is a parameter indicating the degree to which the film surface is abraded by running abrasion with a fixed metal roll. When the scraped value is larger than the above range, the scraped white powder adheres to the film surface and is transferred to the applied magnetic layer to cause dropout. The smaller this value, the better the video tape performance. However, in order to reduce the scraping index,
Generally, it is necessary to increase the unevenness of the surface and reduce the coefficient of friction. In this case, the output of the tape is reduced, which is not preferable.

Next, the number of surface protrusions of the PET film of the present invention is 0.54 μm in height.
It is necessary to set the number of protrusions (protrusion density) to 5 to 60 / mm ² , preferably 5 to 40 / mm ² , and more preferably 5 to 20 / mm ² . If the protrusion density is higher than the above range, the protrusion height also increases accordingly, and the S / N ratio of the tape becomes poor, which is not preferable. The protrusion density is 5 /
If it is less than mm ² , defects such as poor running property of the tape are conspicuously unsuitable.

Next, the surface average roughness (Ra) of the PET film of the present invention is 0.01 to
It should be in the range of 0.03 μm, preferably 0.013 to 0.028 μm. If Ra is larger than this range,
When a magnetic layer is coated on this, the video output is reduced.
On the other hand, when Ra is small, when this is used as a video tape, the running property of the video tape deteriorates.

Next, the crystal plane orientation coefficient of the PET film of the present invention is 0.03 to 0.1.
It should be within the range of 1, preferably 0.04 to 0.10. The value of this crystal plane orientation coefficient is (10
This is a parameter that indicates how much the 0) surface is aligned with the film surface. As this becomes smaller, the crystal planes are more aligned with the film surface. When the surface orientation coefficient is larger than the above range, the tape strength becomes weak, the dimensional change becomes large, and image distortion occurs, which is not preferable. If it is smaller than the above range, chips and whiskers are likely to be produced during tape slitting in the tape manufacturing process,
Dropout is likely to occur.

When a video tape is made using the film of the present invention as a base material,
The number of dropouts of the video tape can be reduced, and a high output can be obtained.

The method for producing the film of the present invention is not particularly limited, and any method may be used, but one example of a preferable production method will be described below.

First, as a PET raw material suitable for producing the film of the present invention, terephthalic acid or an ester-forming derivative and ethylene glycol are used to perform transesterification or esterification reaction. When a polyester is subsequently produced by a polycondensation reaction, at any time before the start of the polycondensation, a particulate substance insoluble in the system, for example, a particle size range of 0.3 to 3.0 μm, an average particle size of 0.5 to 1.5 μm, preferably 0.6-1.0 μmφ synthetic calcium carbonate, silica, titanium oxide, magnesium fluoride, etc. were added, and during the polycondensation reaction, particles containing trimethyl phosphate and antimony as a polymerization catalyst as part of the constituents were deposited, and Immediately before the end of the polycondensation reaction, a dispersant such as dodecylbenzenesulfonic acid, polyethylene glycol, ethylene oxide propylene oxide block copolymer or the like, or a plasticizer such as di2-ethylhexyl phthalate, sebacic acid polyester or adipic acid polyester is used. Addition to improve the dispersibility of fine inorganic particles contained in the polymer Let Of course, both the dispersant and the plasticizer may be combined. The particulate matter added to this polymer was 0.
The content of 03-0.08% by weight and the content of dispersant etc. are 0.05-0.20% by weight.

The PET raw material made in this way is sufficiently vacuum dried in the usual way, then this is fed to an extruder and melt-extruded, the molten polymer is passed through, it is molded into a sheet with a spinneret, and wrapped around a cooling drum. An unstretched sheet is made by cooling and solidifying. The unstretched sheet is stretched at a temperature of 85 to 100 ° C., both edges of the sheet are held by clips, and the longitudinal interval of the clips is expanded to 3.0 to 3.8 times the original interval, and the film is stretched in the longitudinal direction. Then, while holding both edges of the film with the clips, it is introduced into the next hot air heating zone and the hot air temperature is set to 90 to 130 ° C, and the widthwise interval between the opposing clips is set to 3.0 to 3.8 of the original width. The film is stretched in the width direction by doubling. In order to increase the areal magnification of the film, it is guided to the next simultaneous biaxial stretching zone and the stretching temperature is set to 105.
~ 155 ℃, again 1.05 ~ longitudinal direction width direction at the same time again
Stretch 1.30 times. Increasing the surface magnification by re-stretching has the effect of reducing the aggregated particles in the polymer. Then, this film is led to the heat treatment zone, 190 ~ 220 ℃
For 1 to 10 seconds. In this heat treatment zone, the film is relaxed in the longitudinal and width directions by 0.5 to 5%, and then the film is led out of the oven. The film is cooled as it leaves the oven, and when it exits the oven, the temperature of the film has cooled to about room temperature.

On the surface of the thus obtained biaxially oriented PET film, inorganic particles added as an external additive, and further, internal particles composed of a polymerization residue form minute protrusions. The average diameter of the internal particles in the polymer is 0.1-0.8 μm (maximum diameter 1.5-3.0
μm) and the average diameter of the inorganic particles is 0.3-1.5 μm (maximum diameter 2.2
It is preferable that the distribution has two peaks (.about.3.5 μm). In addition,
Large decrease in crystallization temperature of PET when externally added inorganic particles are blended with PET, for example, ΔTcg of 50 to 70 ° C
Is preferable for improving surface abrasion.

The film of the present invention is extremely excellent as a base material for video tapes. After applying an anchor coating agent on one side of this film, a magnetic coating is dried on it and then applied so as to have a thickness of 3 to 5 μm, and subjected to orientation treatment in a magnetic field, followed by drying and super calendar treatment. , Slit this to the required tape width (eg 1/2 inch width) and roll it up to make a so-called pancake. By winding an appropriate length of this pancake on a reel and storing it in a cassette, a video tape containing a cassette that can be put to practical use can be obtained.

[Measurement method of characteristics and confirmation of effect]

The method of measuring each characteristic and the method of evaluating the effect used in the present invention are summarized below.

(1) Scraping index A tape having a width of 1/2 inch and a length of 127 cm is cut into a loop, and the tape is run using a tape running tester manufactured by Yokohama System Research Institute. If a metal fixed pin (SUS, 0.2S finish, diameter 8mmφ) is used for the friction cylinder in the system, the film surface will be scraped and worn due to running of the film. The driving conditions are as follows.

Ambient temperature / humidity: 40 ℃, 80RH% Initial load: 25g Friction cylinder contact angle: 180 degrees Travel speed: 3.3cm / sec Number of travels: 100 times The surface of the friction cylinder pin after running test was scraped by abrasion. Objects appear white and spotted. Attach cellophane tape to this and transfer it to remove the scraped object from the pin, and attach it to the slide glass. A slide glass attached to this was placed on the negative setting part of the enlarger, and the state of the burned and scraped material was enlarged (14 times) on the photographic paper to facilitate quantification. The total area of the shavings that appeared white on the photographic paper was determined using an image processor (Image Analyzing Computer, "Contimet" 720, manufactured by Cambridge Instruments) and expressed in mm ² (A).

On the other hand, the run film is subjected to aluminum vapor deposition with a vacuum vapor deposition machine, and when observed with a reflection type differential interference microscope (“Optiphoto” manufactured by Nippon Kogaku), shavings are scattered and adhered to the film surface. The area and number of the shavings were determined using a micrometer with an eyepiece. 1/2 inch width, 15 mm was used as the measurement area, and scrapes of 2.4 μmφ or more were quantified. Large shavings of 26.4μ or more, which are infrequent, caused an error and were excluded from the measurement results. Calculate the area fraction of the scraped product from the distribution result of the scraped product, and calculate the total tape length (127c
It was expressed in mm ² (B) in terms of the area of m). The total of (A) and (B) was taken as the scraping index.

(2) Protrusion Density Using a surface finish microscope manufactured by Nippon Kogaku Co., Ltd., the number of interference fringes of secondary or higher order is counted by the multiple interference method, and this is converted into the number per 1 mm ² of film area and displayed.

The wavelength of light used for measurement is 0.54 μm, and the reflectance of the mirror is 65.
%, The microscope magnification is 200 times.

(3) Surface average roughness The roughness of the film surface was measured using a universal surface shape measuring device (manufactured by Kosaka Laboratory). The measurement method and Ra calculation principle conform to JIS-B0601-1986.

Curve type: Roughness (R) curve Cut-off value: 0.08mm Magnification in height direction: 50,000 times Magnification in measurement plane direction: 100 times Measurement distance: 4mm (measured in film width direction) Number of repeated measurements: 5 to 10 (4) Plane Orientation Coefficient A film having a thickness of about 50 μm is laminated to form a sample for X-ray diffraction, which is placed in a sample holder of an X-ray diffractometer (Geigerflex manufactured by Rigaku Denki Co., Ltd.). The X-ray irradiation angle is changed in a plane perpendicular to the longitudinal direction of the film, and the diffraction intensity is measured by the reflection method. The measurement conditions are as follows.

Time constant: 2 seconds Running speed: 1 degree / minute Divergency Slit: 1.5mmφ Scattering Slit: 1 degree Receiveing Slit: 0.3mm X-ray: Cn anti-Cn-Kα ray (35KV, 15mA, Ni filter) PET crystal 26.0 corresponding to the diffraction angles of the (100) and (110) planes
If the rotation strengths at ° and 22.5 ° are I ₁ and II ₂ , respectively,
The plane orientation coefficient is given by their ratio (I ₁ / II ₂ ).

(5) Production and performance evaluation of video tape The following mixed composition was mixed and dispersed by a ball mill and a sand mill, and then polyisocyanate (“Coronate L” manufactured by Nippon Polyurethane Industry Co., Ltd.) was added in a solid content of 25% by weight. Partly added as magnetic paint.

Co-coated γ-Fe ₂ O ₃ 300 parts by weight Nitrocellulose 35 parts by weight Polyurethane resin 26 parts by weight Carbon black 18 parts by weight Alumina particles 5 parts by weight Myristic acid 7 parts by weight Butyl stearate 1 part by weight Methyl ethyl ketone 220 parts by weight Butyl acetate 530 parts by weight Part On one side of the biaxially oriented PET film, a polyester copolymer is dried and anchor-coated to a thickness of 0.05 μm, and the above magnetic material is applied to this on a dry thickness of 5 μm. , 100 ° C after applying a magnetic field for orientation treatment
Dry with hot air. Then, this is subjected to a super calendar treatment, slit into a width of 1/2 inch to form a video tape, and the video tape is incorporated into a cassette.

The dropout and video output of the video tape thus obtained are measured and the performance is evaluated.

(A) Dropout The dropout evaluation method uses a household VHS method VTR and 4M
A single signal of Hz is recorded, and when the signal is reproduced, the number of times that the signal decreases by 12 dB or more from the average reproduction level for 5 μsec or more is counted per minute.

(B) Video output Using a home VHS VTR, a single 4 MHz signal was recorded and the playback output was measured. In the standard, the one with the smallest output among the respective experimental levels is relatively displayed as OdB.

〔Example〕

The present invention will be shown in the following examples and comparative examples. Needless to say, the present invention is not limited to these examples.

Example 1 [Preparation of ethylene glycol slurry of solid particles and dispersant] Slurry A: synthetic calcium carbonate particles having an average particle size of 0.80 μm
10 parts by weight, 100 parts by weight of ethylene glycol and phosphoric acid
0.4 part was mixed and stirred with a homogenizer to prepare an ethylene glycol slurry of silica particles. To 100 parts by volume of this slurry, 100 parts by volume of glass beads having an average particle diameter of 0.09 mm was added, and a cross blade having a blade diameter of 16 cm was used to rotate at 2 rpm at 3000 rpm.
Stir for hours. After the dispersion was completed, the glass beads were removed by passing through a 400-mesh wire net, and the silica particle slurry obtained by separation was passed through a filter of 3 μ cut. The thus obtained slurry containing synthetic calcium carbonate is used.

Dispersant: Dodecylbenzenesulfonic acid 60% by weight and molecular weight
A dispersant is a mixture of 4000 polyethylene glycol 40% by weight.

[Production of PET polymer] To 100 parts by weight of dimethyl terephthalate, 60 parts by weight of ethylene glycol and 0.04 part by weight of manganese acetate were added.
The transesterification reaction was carried out at 0 to 240 ° C. for 4 hours while removing methanol. Then, 0.02 parts by weight of phosphoric acid and 0.03 parts by weight of antimony trioxide were added, and further, after adding slurry A, polycondensation reaction was performed for 3 hours in a high vacuum of 1 mmHg or less, and a dispersant was added immediately before the reaction was completed. Synthetic calcium carbonate particles (average particle size 0.80μ) 0.05% by weight, dispersant 0.13
A PET polymer containing wt% was obtained. The intrinsic viscosity of this polymer was 0.635.

[Production of Film] The obtained polymer pellets were vacuum dried at 180 ° C. for 6 hours, then fed to an extruder and melt-extruded at 285 ° C. to suppress flow fluctuation of the molten polymer through a gear pump, and then 3 μm. After passing through a metal fiber sintered filter capable of capturing 89% by weight or more of the above solids, the solid was introduced into a T-shaped mouthpiece and discharged as a sheet-like melt from the mouthpiece.

This sheet-like melt is wound around a cooling drum with a surface temperature of 60 ° C, and is cooled and solidified while imparting an electrostatic charge to improve the adhesion between the drum and the molten sheet, and an unstretched film with a surface temperature of about 70 ° C. made. This unstretched film is immediately introduced into the hot air circulation zone at 85 ° C, both edges of the film are gripped by the clips, and the longitudinal interval of the clips is expanded to 3.4 times the original width, whereby the film is stretched in the longitudinal direction. Was stretched. Then, while holding both edges of the film with clips, introduce the film into the next hot air circulation zone and set the hot air temperature to 100.
The film was stretched in the width direction by increasing the distance between the opposing clips in the width direction at 3.5 ° C. to 3.5 times the original width. Next, it is led to the simultaneous biaxial stretching zone and the stretching temperature is set to 11
The temperature was raised to 0 ° C., and the film was again stretched 1.15 times in the biaxial direction.
The thus obtained biaxial directions were simultaneously relaxed and then heat treated again at 205 ° C. for 5 seconds under tension. Then, while keeping the tension, it is introduced into a zone of hot air temperature of 120 ° C, cooled to this temperature, and then introduced into a zone of 100 ° C, where 1% of the original length is relaxed in the longitudinal direction, The film was then allowed to cool to room temperature. The thickness of this film was about 15 μm. The film was conveyed with a tension of 2.5 kg / m width and wound on the core while the film winding portion was heated dielectrically by microwave.

A large-diameter film roll wound around 6000 m (rolling hardness 65 °
Shore. (The film temperature inside the roll or about 70 ℃) is put in a room whose temperature is controlled at 70 ℃ and left for 24 hours, then left to cool in a room temperature atmosphere for 24 hours, then rewound on a slitter to rewind the film width. A film product roll of 500 mm (rolling hardness 90 ° shore) was used.

Table 1 shows the properties of the film thus obtained and the properties of the video tape made from this film. From this result, it can be seen that when a film having the characteristics of the present invention is used as a substrate, a video tape having extremely excellent sharpness can be obtained.

Examples 2 and 3 and Comparative Examples 1 to 4 In Example 1, the type and amount of calcium carbonate added to the PET polymer were changed, and further the stretching temperature, stretching ratio and heat setting temperature during film formation were variously changed. By doing so, films having different values of abrasion index, protrusion density, Ra, and plane orientation coefficient were prepared. Table 1 shows the evaluation results of these films. From these results, it is understood that the film having the characteristic value within the range of the present invention is excellent in the video output, the CS / N ratio and the dropout of the video tape having the film as a base material.

[Advantages of the Invention] The present invention uses the film as a base material by optimizing the range of surface abrasion index, protrusion density, surface average roughness (Ra), and crystal plane orientation coefficient of a biaxially oriented PET film. It succeeded in improving the characteristics of the video tape, especially the dropout characteristics. Since these effects are not necessarily limited to video tapes, the film of the present invention can be applied to other tapes such as computer memory tapes and audio tapes.

Claims (1)

[Claims] 1. The surface abrasion index is 0.1 to 2.0, and the number of surface protrusions is 5.
~ 60 pieces / mm ² (height 0.54 μm or more), surface average roughness (R
a) is 0.01 to 0.03 μm, and the plane orientation coefficient of the crystal (100) plane is 0.
A biaxially oriented polyethylene terephthalate film characterized in that it is 03 to 0.11.