JP3077835B2 - Biaxially oriented polyester film - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a biaxially oriented thermoplastic resin film having a good winding shape, and particularly to a film used as a base material of a magnetic recording medium (magnetic tape, floppy disk, video disk, etc.). The present invention relates to a biaxially oriented polyester film exhibiting good rollability.

[0002]

2. Description of the Related Art As a biaxially oriented polyester film having a good winding shape, a film having a limited particle diameter of a fine particle to be added and a height of projection of the film is known (for example, JP-A-1-48836).

[0003]

The above-mentioned conventional film is biaxially stretched longitudinally and laterally, heat-treated, wound around an intermediate spool, slit into a product width in a slitter process, and wound around the intermediate spool. In the period during which the film is formed, distortion caused in the film forming process causes a tightening due to a change in shrinkage with the lapse of time, resulting in a defect in the wound shape. Although it can be alleviated to some extent by adjusting the conditions of the slitting process (surface pressure, tension, etc.), it is difficult to completely eliminate these defects on the winding shape. In particular, when the intermediate spool storage period is longer than half a day, there is a disadvantage that the deterioration of the winding form rapidly increases. Further, in order to make the slit speed follow the film forming speed, it is necessary to increase the slit speed. However, this tends to increase the defect rate of the winding property of the product after the slit.

[0004] Furthermore, even if the product is slit into a good roll, if the distortion received in the film forming process is too large, the roll of rolled product after the slit is tightened due to shrinkage and changes over time, thereby causing the flat surface of the film. It causes poor sex.
This causes quality defects such as uneven coating and wrinkles of the magnetic layer in a later processing step. In particular, in recent years, there has been an increasing demand for high-density recording (long-time recording), high performance, and miniaturization of magnetic tapes, and base films have better characteristics such as being thinner, stronger, and smoother. Is required. In particular, by making the base film thinner and stronger, the amount of deformation strain received in the film forming process is increased, and the influence of the tightening caused by a change in shrinkage with time is increased. For this reason, there is a strong demand for improvement in roll formability.

[0005] The present invention includes a purpose of tight turns of the intermediate spool is reduced, flatness in a later step, hardly de drawbacks such as wrinkles, providing superior biaxially oriented polyester film in winding shape of I do.

[0006]

According to the present invention, there is provided a biaxially oriented polyester film having a thickness d (μm) in a biaxially stretched polyester film.
m), the stress relaxation rate Sr and 70 in the longitudinal direction of the film.
The thermal shrinkage σ (%) at ° C. is expressed by the following formulas (1), (2) and (3): 13.3d (Sr−0.725) ≧ 85.5σ (1) 5 ≦ d ≦ 15 (2) σ> 0 (3) and the coefficient of friction μ between one side of the film and the other side.
s is 0.2 or more and 1.0 or less.

In the film of the present invention, first, the thickness d (μm) of a polyester film, for example, a polyethylene terephthalate (hereinafter abbreviated as PET) film, the stress relaxation rate Sr in the film longitudinal direction, and the film longitudinal direction at 70 ° C. The heat shrinkage σ (%) is the above (1)
Equation, that is, 13.3d (Sr−0.725) ≧ 85.5
satisfies σ. If the inequality is not satisfied, the winding becomes tight due to shrinkage with the lapse of time during the storage period of the intermediate spool and the product, which tends to cause winding defects such as flatness and wrinkles, which is not preferable. Here, d and σ are in the ranges of the above equations (2) and (3).

Next, the friction coefficient μs is 0.2 or more, 1.0
Or less, preferably 0.3 or more and 0.8 or less. Outside this range, the slip between the films is too good or too bad, and unless the surface pressure and tension in the slitting step are increased considerably, a good rolled shape cannot be obtained, which is not practically preferable.

The PET film of the present invention includes diol components such as diethylene glycol, propylene glycol, polyethylene glycol and 1,4-cyclohexanedimethanol, adipic acid, sebacic acid, isophthalic acid, and 2,6-naphthalenedicarboxylic acid. , A dicarboxylic acid component such as sodium sulfoisophthalic acid, and a copolymerization component such as P-oxyethoxybenzoic acid in an amount of 0.2 to 5.0.
% By weight. Further, the intrinsic viscosity of PET (measured in ortho-chlorophenol at 25 ° C.) is 0.1.
55 to 0.70, preferably 0.57 to 0.66 dl /
Those within the range of g are desirable.

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

First, a PET raw material suitable for producing the film of the present invention is prepared by adding fine particles insoluble in the system during the polycondensation reaction, and further adding one or more alkali metals or alkaline earth metals during the polycondensation reaction. It is manufactured by precipitating particles (so-called precipitated particles) as a part of the constituent components. More specifically, an ester exchange reaction or esterification reaction between terephthalic acid or an ester-forming derivative thereof and ethylene glycol is performed, and a polycondensation reaction is subsequently performed to produce a polyester. At this time, a particulate matter insoluble in the system (preferably having a specific surface area of 5 m ² / g or more) is added, and at least one of an alkali metal or an alkaline earth metal is used as a component during the polycondensation reaction. This is a production method for depositing particles. The method for incorporating diethylene glycol into the PET raw material can be achieved by adding a desired amount of diethylene glycol to the above ethylene glycol. In addition, when the film was stretched, fine particles, catalyst residue or anti-coloring agent, which caused film surface projections, were added from the so-called intrinsic particles or external components formed by reacting with the polyester monomer or oligomer. Inert particles or the like may be included.

The PET raw material thus produced is sufficiently vacuum-dried in accordance with a conventional method, supplied to an extruder and melt-extruded, and the molten polymer is filtered, discharged into a sheet with a die, and wound around a cooling drum. The unstretched sheet is made by attaching and cooling and solidifying. Further, using a composite extruder, a PET raw material containing 0.3 to 10% by weight of fine particles which cause film surface projections is applied to one or both sides of the base in an amount of 1 to 20%.
% Uncompressed sheet may be used. Unstretched sheet in the longitudinal direction at a temperature of 90 to 125 ° C.
Stretched 3.5 times, and then at a temperature of 75 to 95 ° C for 1.0 to
Stretch 5.0 times in the longitudinal direction. Thereafter, the temperature is 85 ° C.-1
Stretch 3.0 to 4.5 times in the width direction at 00 ° C. The heat-strengthened type which is further stretched in the longitudinal direction and the width direction before the heat treatment may be used, and the total stretching area ratio (longitudinal stretching ratio × widthwise stretching ratio) is 14 to 30 times, preferably 16 to 25 times. This is preferable for obtaining a film that is small and hard to receive distortion in the film forming process and tightness of winding of the intermediate spool and the product roll.

Next, the film is guided to a heat treatment zone and subjected to heat treatment. If the heat treatment temperature is too high, the crystallinity inside the film is increased, but the molecular chains in the amorphous part are loosened, and the creep resistance of the film becomes poor. On the other hand, if the heat treatment temperature is too low, the crystallinity becomes small, so that the amorphous chains are liable to flow deformation, and the creep resistance is poor. In the case of the present invention, the crystal size in the direction of the polyethylene terephthalate (100) plane is 35 to 6 in terms of the mechanical toughness of the film.
Preferably, the heat treatment is performed at a temperature of 140 to 220C, preferably 180 to 210C for 2 to 10 seconds. In this heat treatment zone, it may be relaxed in the width direction by 1 to 8%, but it is preferable that the longitudinal direction is in a tension state. The heat-treated film is cooled from the heat treatment temperature to room temperature, and this cooling condition has a great effect on the characteristics of the film, particularly, the rate of change in shrinkage of the intermediate spool over time. From the heat treatment temperature, the film may be cooled in a tension state up to 120 ° C., but in the cooling to 120 to 70 ° C., the transfer speed of the parallel holding rolls is gradually reduced from the transfer speed of the film holding roll on the tenter side, and the longitudinal direction is reduced. Perform a multi-stage relaxation process of ~ 4.0% in the direction. The relaxation time is preferably 1 second or more. The balance and width direction tensilized type film can be heat-shrinked to the extent that it is not affected by tightness by one-step relaxation, but it is necessary to increase the relaxation rate in one step, resulting in poor flatness of the film. In this respect, a multi-stage relaxation treatment is preferred. Furthermore, the longitudinal tensilized type and the strengthened type film with a large stretching surface magnification have a large amount of deformation strain received in the film forming process, have a large flatness defect in the single-stage relaxation process, and have a flat surface unless the multi-stage relaxation process. A film that satisfies both the properties and the heat shrinkage to such an extent that the tightness of the winding is not affected cannot be obtained.

The biaxially oriented PET film thus obtained has good flatness, a small rate of change in shrinkage over time during storage of the intermediate spool, and prevents deterioration in flatness and winding appearance such as streaks due to tightening of the winding. can do.

[Method of Measuring Characteristics] The characteristic values of the present invention are measured by the following methods. (1) Heat shrinkage σ A film is sampled from a film that has passed 24 hours or more after film formation (end of intermediate spool winding) so that the size is 300 mm × 10 mm and the longitudinal direction of the film matches the longitudinal direction of the film. The sample to be measured was allowed to stand in an atmosphere of 23 ° C. and 60% RH for 30 minutes. Under the atmosphere, two marks were made at intervals of about 200 mm in the longitudinal direction of the film, and a linear scale measuring machine was used. The interval between the marks is measured, and the measured value is A. Next, the sample to be measured is allowed to stand in an atmosphere of 70 ° C. for 48 hours in a tension-free state, then cooled for 1 hour in an atmosphere of 23 ° C. and 60% RH, adjusted to a humidity, and marked with the mark previously attached. The interval is measured, and the measured value is B.
From the above measured values, the heat shrinkage is determined by the following equation. σ = 100 (AB) / A

(2) Stress relaxation rate Sr A long sample slit to a width of 10 mm (the longitudinal direction of the sample coincides with the longitudinal direction of the film) is fixed to a Tensilon tensile tester at a test length of 100 mm, and a stress corresponding to 10 kg / mm ^2. With (F _O ) applied, fixed length was fixed and stress relaxation was measured. One minute later, the stress was measured. From the above measured values, the stress relaxation rate is obtained by the following equation. Sr = F / F _O

(3) Coefficient of friction μs Using a slip tester manufactured by Toray Industries, Inc. manufactured according to ASTM-D1894-63, load 200 g, contact area 63.5 × 63.5 mm, moving speed 150 mm /
The friction coefficient μs between the drum surface (D) and the non-drum surface (ND) of the film was measured under the conditions of minutes.

(4) Crystal Size When a diffraction peak is observed by a reflection method using an X-ray diffractometer while changing the incident angle of X-rays in the width direction of the film, the diffraction peak at about 13 ° C. Diffraction crystal (10
0) The crystal size D (Å) in the plane direction was calculated according to the following equation. D = λ / (B−b) cos θ where B: half width of diffraction peak, b = 0.12, λ:
Kα ray wavelength of Cu (1.5418 °), θ: diffraction angle of peak.

(5) Rollability The film is slit into a width of 500 mm and a length of 5000 m.
Film roll. The film roll was visually inspected for deviation of the end face, vertical wrinkles of the film, pressing marks, and flatness.
Rollability when no end face deviation, vertical wrinkles, press marks, and flatness defects are present: 5. Roll form when end face deviation is less than 0.1 mm and no vertical wrinkles, push marks, and flatness defects. Properties: 4, when the end face deviation is less than 0.2 mm and vertical wrinkles, press marks and slight defects in flatness are slightly observed. Winding property: 3, when the end face deviation is 0.2 mm or more and vertical wrinkles, press marks. The case where the defect of flatness was slightly observed was determined as roll formability: 2, and the other cases were determined as roll formability: 1.

[0020]

【Example】

Example 1, Comparative Example 1 An ethylene glycol slurry containing crosslinked polystyrene particles having different average particle diameters, spherical silica particles derived from colloidal silica, and the like was prepared, and the ethylene glycol slurry was heat-treated at 190 ° C. for 1.5 hours. After polycondensation, a PET master pellet containing 1% by weight of the particles was obtained by a conventional method. This master pellet and PET pellets substantially containing no particles are mixed so that the particle content becomes 0.2% by weight, vacuum-dried at 180 ° C. for 8 hours, and then supplied to an extruder. The mixture was melt-extruded at a temperature of 0 ° C., discharged from a T-type die through a gear pump and a filter into a sheet, wound around a cooling drum, and cooled and solidified to form an unstretched sheet. This unstretched sheet is stretched 1.6 times at 105 ° C. and then 3.1 times at 80 ° C., and then guided to a stenter,
It was stretched 3.95 times in the width direction at 90 ° C. Next, the film is directly guided to a heat treatment zone without cooling, and subjected to a tension heat treatment at 200 ° C. for 3 seconds, followed by 2% in the longitudinal direction and 3% in the width direction (each with respect to the original length) at the same temperature. After relaxation, it is led to an intermediate cooling chamber at 110 ° C, where it is intermediately cooled. After that, between the gripping rolls arranged in parallel from the outlet, a multistage of 2.0% in total in the longitudinal direction while gradually decreasing the relaxation rate. After a relaxation treatment, the film was cooled to room temperature and wound on an intermediate spool to obtain a biaxially oriented PET film having a thickness of 10 μm (Example 1).

P stretched and heat-treated in the same manner as in Example 1
After the ET film was intermediate-cooled at 110 ° C., the film was cooled to room temperature without being relaxed and wound around an intermediate spool to obtain a biaxially oriented PET film having a thickness of 10 μm (Comparative Example 1).

These films are put on an intermediate spool for about 1 hour.
After leaving for 0 hours, the winding tension is 6.5 kg / m and the surface pressure is 40 k.
g / m, slit to 500mm width, length 500
It was a 0 m film roll.

Examples 2-5, Comparative Examples 2-4 Under the conditions of Example 1, during polymerization, the type of particles to be added, the average particle size, the amount added and the stretching temperature, the stretching ratio, the heat treatment temperature, the heat treatment By variously changing the multi-stage relaxation rate between the holding rolls arranged in parallel from the time and the intermediate cooling chamber outlet,
Samples with different characteristics were made. This film was slit under the conditions of Example 1 to obtain a film roll. Tables 1 and 2 summarize the production conditions and evaluation results of these films.
It was shown to. According to Tables 1 and 2, when the film thickness, the stress relaxation rate, the heat shrinkage rate, and the coefficient of friction are within the range of the present invention, a film having good winding properties can be obtained. It turns out that a film cannot be obtained.

[0024]

[Table 1]

[0025]

[Table 2]

[0026]

As described above, according to the present invention, the film thickness d, the stress relaxation rate Sr in the longitudinal direction of the film, the heat shrinkage σ at 70 ° C. satisfy a specific relationship, and the coefficient of friction μs between the front and back surfaces of the film. Has the following excellent effects. (1) In the film manufacturing process, it is possible to prevent the deterioration of the flatness and the occurrence of wrinkles due to the shrinkage of the film in the intermediate spool with the passage of time. Can be provided. (2) In various processing steps (magnetic medium coating, drying, calendering, vacuum deposition, sputtering, etc.), a good processed product can be provided without deteriorating flatness or wrinkling. In particular, even when a thin (10 μm or less) base film is used as a magnetic tape, a film having excellent electromagnetic conversion characteristics can be provided.

──────────────────────────────────────────────────続 き Continuation of the front page (51) Int.Cl. ⁷ Identification code FI C08L 67:02 (56) References JP-A-62-164733 (JP, A) JP-A-61-68727 (JP, A) Kaihei 5-5039 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) B29C 55/00-55/30 C08J 5/18 G11B 5/62-5/858

Claims (1)

(57) [Claims] In a biaxially stretched polyester film, the thickness d (μm) of the film, the stress relaxation rate Sr in the longitudinal direction of the film, and the heat shrinkage σ at 70 ° C.
(%) Satisfies the following formulas (1), (2) and (3): 13.3d (Sr−0.725) ≧ 85.5σ (1) 5 ≦ d ≦ 15 (2) σ> 0 (3) And the coefficient of friction μ between one side of the film and the other side.
A biaxially oriented polyester film, wherein s is 0.2 or more and 1.0 or less.