JPH082592B2 - Biaxially oriented polyethylene terephthalate film with good slitting property - Google Patents

Description

TECHNICAL FIELD The present invention relates to a biaxially oriented polyethylene terephthalate film having a good slit property, and more specifically, it is mainly a magnetic recording medium (magnetic tape, floppy disk, video). The present invention relates to a biaxially oriented polyethylene terephthalate film exhibiting a good slitting property when used as a base material for disks and the like.

[Prior Art] As a biaxially oriented polyethylene terephthalate film having a good slitting property, one having an average refractive index in a specific range, a slightly low degree of plane orientation, and a limited number of protrusions on the surface is known ( JP-A-58-23323).

[Problems to be Solved by the Invention] However, the above-mentioned conventional film has a good slitting property in the sense that the cut edge is less likely to rise when slitting the film, which is different from the slitting property in the present invention. It is a thing. The good slitting property in the present invention means a film or a film having a magnetic layer on the film, which is less likely to produce whiskers or powder from a cut edge when slitting at high speed. If a large amount of beard or powder is produced during slitting, these will adhere to the magnetic layer and cause quality defects such as dropout (signal loss). Therefore, improvement of the slitting property in this sense is strongly desired. An object of the present invention is to provide a biaxially oriented polyethylene terephthalate film which is excellent in slitting property in the sense that whiskers and powders do not easily come out.

[Means for Solving Problems] In the present invention, film impact strength Fi (kg · cm / mm ² ), tear strength Ft (g / mm) are Ft ≦ −14.8Fi + 1067, Fi ≧ 20 and Ft ≧ The main point is a biaxially oriented polyethylene terephthalate film having a good slitting property, which is in the range of 400.

First, the present invention polyethylene terephthalate (hereinafter PET
The impact strength Fi (kg · cm / mm ² ) and tear strength Ft (g / mm) of the film must satisfy Ft ≦ −14.8Fi + 1067. If the inequality is not satisfied, a beard is likely to occur during slitting, which is not preferable.

Next, Fi must be 20 or higher and Ft must be 400 or higher. If any of these is removed, the film becomes brittle, easily broken, and easily torn, which is not practically preferable.

The PET of the PET film of the present invention may contain a diethylene glycol component in an amount of 0.2 to 2.0% by weight. Further, it is desirable that the intrinsic viscosity of PET (measured in orthochlorophenol at 25 ° C.) is within the range of 0.58 to 0.65, preferably 0.61 to 0.64 dl / g.

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, a PET raw material suitable for producing the film of the present invention, during the polycondensation reaction, fine particles insoluble in the system are added, and during the polycondensation reaction, one or more of alkali metal or alkaline earth metal is a constituent component. It is produced by precipitating a part of particles (so-called precipitated particles). More specifically, transesterification or esterification reaction of terephthalic acid or its ester-forming derivative with ethylene glycol is carried out, followed by a polycondensation reaction to produce a polyester. At this point, particulate matter insoluble in the system (specific surface area
5 m ² / g or more is preferable), and further, during the polycondensation reaction, particles having one or more of alkali metal or alkaline earth metal as a part of the constituent components are precipitated. The method of incorporating diethylene glycol in the PET raw material can be achieved by adding a desired amount of diethylene glycol to the above ethylene glycol.

The PET raw material made in this way is sufficiently vacuum dried according to the usual method, supplied to an extruder and melt-extruded, the molten polymer is filtered, formed into a sheet with a die, and wound around a cooling drum to cool. An unstretched sheet is made by solidifying. This unstretched sheet is stretched 3 to 5 times in the longitudinal direction of the film at a glass transition temperature or higher. After that, the stretching temperature is raised little by little while stretching in the width direction in multiple stages. In the first stretching in the width direction, the stretching temperature is set to a relatively low temperature of 85 to 95 ° C, and the film is stretched 2.0 to 2.3 times. In the second width stretching, the temperature is raised to 96 to 105 ° C and the stretching is performed 1.3 to 1.7 times. The third stretching is performed at a temperature of 101 to 110 ° C. and stretching 1.1 to 1.5 times. In this way, by stretching in multiple stages, a stable fine structure in which molecules are well arranged in the width direction of the film can be obtained. If necessary, the stretching in the width direction may be repeated three times or more to further align the molecules in the width direction. However, it is necessary to take care so that the molecular orientation in the width direction is not excessively increased and conversely the mechanical properties in the longitudinal direction of the film are deteriorated.

The film is then guided to the heat treatment zone, 190-2
Heat treatment at 20 ° C for 2-10 seconds. In this heat treatment zone, it is preferable to provide relaxation of 1 to 8% of the original length in both the longitudinal direction and the width direction. Heat treated film 80-120
The biaxially oriented PET film of the present invention can be obtained by guiding the film to an intermediate cooling zone at 0 ° C., cooling it to some extent, and then gradually cooling it to room temperature.

[Uses] The biaxially oriented PET film thus obtained is provided with a magnetic layer on one or both sides thereof, so that various magnetic recording media, for example, video tape, audio tape,
It is processed into floppy disks and used. The magnetic layer may be formed by applying a magnetic powder together with a binder, or may be formed by thinning a ferromagnetic material by vacuum deposition, sputtering, ion plating or plating. The film of the present invention can be used for the above-mentioned various magnetic recording media, but is particularly effective for videotape applications.

With video tape, if a lot of whiskers and powder are generated on the end surface when slitting this, not only will dropouts increase, but these whiskers and powder may also cause clogging of the magnetic head. The film of the present invention is particularly effective.

As described above, the main use of the film of the present invention is for magnetic recording media, especially for video tapes, but other uses, such as graphics, stamping foils, electrical insulating materials, dielectrics for capacitors, packaging, etc. But
It can be effectively used in applications where the slit property is a problem.

[Operation] The present invention optimizes the impact resistance and tear strength of the biaxially oriented PET film, so that, particularly during slitting,
The inventors have found that when a slit is made with a magnetic layer placed on this film, it is difficult for whiskers and powder to come out. The slit is a destruction phenomenon in which the film or the film and the magnetic layer are cut together, and it is very difficult to clearly analyze the relationship between such destruction and the film characteristics. However, since this breaking phenomenon and the breaking characteristics of the film itself are closely related to each other, it is considered that it was possible to contribute to the improvement of the slitting property by specifying the impact characteristics and tearing characteristics of the film. .

[Characteristic measuring method and effect evaluating method] (1). Evaluation of Slitting Property A 14.5 μm-thick PET film is coated on one side with a magnetic coating solution having the following composition so that the film thickness will be 3 μm after drying.

(Parts by weight) Polyester polyurethane resin 35 Vinyl chloride / maleic acid copolymer 30 α-alumina 15 Carbon black 3 Oleic acid 5 Aluminum stearate 4 Triisocyanate compound 22 Ferromagnetic metal powder 300 Butyl acetate 300 Methyl isobutyl ketone 300 After coating, direct current After orientation treatment in a magnetic field and drying, calendering is performed. This sheet is slit into 1/2 inch width with a shear cutter to make a video tape.
The slit location by the shear cutter is visually observed, and the degree of generation of mustache and powder is evaluated in the following five grades.

Slit property A: generation of mustache and powder is extremely small.

 〃 B: There are few.

 〃 C: 〃 Normal level.

 〃 D: 〃 Somewhat.

 〃 E: There are many.

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

(2) Film impact resistance (Charpy impact strength) Using a Charpy impact tester manufactured by Toyo Seiki Seisakusho according to the method specified in ASTM-D-256, the film's Charpy impact strength (unit: kg · cm / mm ² ) Was measured. In ASTM, the strength is displayed in kg · cm, but here, the value obtained by dividing by the cross-sectional area of the film is taken as the film impact strength. The impact strength of the film was determined when the film was set horizontally between two fulcrums in the longitudinal direction.

(3) Tear strength The tear strength was measured according to JIS P8116-1976.
However, in this case, in order to accurately determine the tear strength of one film, a light load tear tester shown in the Plastic Testing Handbook (published by Nikkan Kogyo Shimbun Co., Ltd., edited by Plastic Standard Test Method Study Group) was used. 50.8 (longitudinal direction)
A film sample of × 63.5 (width direction) was sampled, a 12.7 mm cut was made in the width direction at a right angle at the center of both grips along the longitudinal direction, and the tearing force (g) for the remaining 50.8 mm was obtained. . This value was divided by the film thickness to obtain tear strength.

[Examples] The present invention will be described with reference to the following examples and comparative examples.
The present invention is not limited to these examples.

Example 1 100 parts by weight of dimethyl terephthalate, 69 parts by weight of ethylene glycol, 0.5 parts by weight of diethylene glycol, and 0.09 parts by weight of calcium acetate as a catalyst were subjected to a transesterification reaction by a conventional method, and the product was antimony trioxide. 0.03 part by weight, lithium acetate 0.3 part by weight, trimethyl phosphate 0.2 part by weight and silicon dioxide fine powder (specific surface area 1
80m ² / g) and polymerize by a conventional method to obtain an intrinsic viscosity of 0.
635 polymer pellets were obtained. This pellet at 180 ℃, 8
After vacuum-drying for a period of time, it is supplied to an extruder, melt-extruded at 280 ° C, and discharged from a T-shaped die through a gear pump and a filter into a sheet.
An unstretched sheet was prepared by winding around a 40 ° C. cooling drum and cooling and solidifying.

During this cooling, in order to improve the adhesion between the molten sheet and the drum surface, a wire electrode is placed on the molten sheet side, and a DC voltage of 8 KV is applied thereto so that the molten sheet adheres well to the drum. did.

This unstretched sheet was stretched 3.5 times in the longitudinal direction at 85 ° C., then the stretched sheet was guided to a stenter, both ends of the sheet were held by clips, and stretched in the width direction 2.0 times at 90 ° C.
This sheet is guided to the second stenter zone, re-stretched 1.5 times in the width direction at 96 ° C, and then 105 times in the third stenter zone.
The film was further stretched in the width direction by 1.3 times at ℃.

Then, without cooling this film, it is introduced into the heat treatment zone as it is, and heat-fixed at 205 ° C. for 2 seconds, followed by 2% in the longitudinal direction and 3% in the width direction (for each original length) at the same temperature. After relaxing, tension heat fixing again for 5 seconds at the same temperature, and then introducing it directly to an intermediate cooling chamber at 100 ° C, where it is subjected to intermediate cooling, and then at the exit, 1
% Relaxation was given, and the mixture was gradually cooled to room temperature and wound up to obtain a biaxially oriented PET film having a thickness of 14.5 μm. The film had an intrinsic viscosity of 0.61 dl / g, impact strength of 25 kg · cm / mm ² , and tear strength of 500 g / mm. Using this film as a base material, a video tape was produced by the method described above, and the slitting property when slitting this was evaluated. As a result, the occurrence of whiskers and powder was extremely small and the slitting property was A.

Examples 2 to 11 and Comparative Examples 1 to 9 Under the conditions of Example 1, the amount of additives during polymerization, the stretching temperature, the stretching ratio, the heat setting temperature, and the degree of relaxation during heat setting are variously changed. By doing so, samples having different values of impact strength and tear strength were prepared. The results of evaluating the slit property of these films are shown together in FIG. From these results, it can be seen that the film having the characteristic values within the range of the present invention is excellent in the slit property.

In the drawing, the symbols ⊚, ◯, □, Δ and × correspond to the slit characteristics A, B, C, D and E, respectively.

EFFECTS OF THE INVENTION The present invention improves the slitting property of a film, particularly the slitting property of a video tape provided with a magnetic layer on the film, by optimizing the impact resistance and tear strength of the biaxially oriented PET film. The effect of doing is.

The characteristic that whiskers and powders do not easily come out at the time of slitting is effective for reducing the dropout of the video tape and preventing the clogging of the magnetic head. In that sense, the film of the present invention is particularly useful as a base material for video tapes.

[Brief description of drawings]

FIG. 1 is a diagram showing the evaluation results of the samples of Examples and Comparative Examples. The vertical axis represents tear strength, and the horizontal axis represents impact strength.
⊚, ∘, □, Δ, and × represent the quality of the slit property.

Claims (1)

[Claims] 1. A film impact strength Fi (kg · cm / mm ² ) and tear strength Ft (g / mm) are in the range of Ft ≦ −14.8Fi + 1067, Fi ≧ 20 and Ft ≧ 400. A biaxially oriented polyethylene terephthalate film with good slitting properties.