JPH0773876B2 - Isotropic polyester film - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial field of application> The present invention relates to an isotropic polyester film, more specifically, a dimensional change and its in-plane anisotropy are extremely small, and a magnetic layer coating particularly for magnetic disk applications. The present invention relates to an isotropic biaxially oriented polyester that gives excellent processability during processing.

<Prior Art> Biaxially oriented polyester film has excellent properties.
It is used for various industrial applications, but especially for magnetic disks, film capacitors, photoengraving, FPC, membrane switches, etc., mechanical properties in the film plane,
An isotropic film is desired in which dimensional changes such as temperature and humidity expansion coefficient and thermal shrinkage are balanced in both the vertical and horizontal directions. Therefore, as an improvement measure for the isotropic property, it has been proposed to reduce the bowing phenomenon in the film forming process to reduce the in-plane anisotropy of the temperature expansion coefficient to some extent to achieve the isotropic property.
For example, there are JP-A-57-87331, JP-A-59-139131, JP-A-1-150521, and JP-A-1-165423.

<Problems to be Solved by the Invention> However, the films obtained by these conventional techniques still have a large heat shrinkage ratio or are not sufficiently isotropic.
Further, these do not take into consideration the isotropic deformation that the film undergoes during the processing process.

<Means for Solving the Problems> An object of the present invention is to provide a biaxially oriented polyester film capable of ensuring excellent isotropy, particularly when subjected to post-processing after heat treatment.

The present invention has an in-plane dimensional change rate of ± 0.02% or less when held at a temperature of 60 ° C and a humidity of 80% for 72 hours, and an in-plane dimensional change rate when held at a temperature of 105 ° C for 30 minutes. Is less than 0.5% and its in-plane anisotropy is ± 0.1%
It is an isotropic biaxially oriented polyester film characterized by the following.

The polyester in the present invention is a polyester having an aromatic dicarboxylic acid as a main acid component and an aliphatic glycol as a main glycol component. Such polyesters are substantially linear and have film forming properties, especially film formation by melt molding. Examples of the aromatic dicarboxylic acid include terephthalic acid, naphthalenedicarboxylic acid, isophthalic acid, diphenoxyethanedicarboxylic acid, diphenyldicarboxylic acid, diphenyletherdicarboxylic acid, diphenylsulfonedicarboxylic acid, diphenylketonedicarboxylic acid and anthracenedicarboxylic acid. You can Examples of the aliphatic glycol include polymethylene glycol having 2 to 10 carbon atoms such as ethylene glycol, trimethylene glycol, tetramethylene glycol, pentamethylene glycol, hexamethylene glycol and decamethylene glycol, and alicyclic compounds such as cyclohexanedimethanol. Examples thereof include diols.

In the present invention, as the polyester, for example, one having alkylene terephthalate and / or alkylene naphthalate as a main constituent component is preferably used.

Among such polyesters, for example, polyethylene terephthalate, polyethylene-2,6-naphthalate, of course, for example, 80 mol% or more of the total dicarboxylic acid component is terephthalic acid and / or 2,6-naphthalenedicarboxylic acid, and the total glycol component. A copolymer having 80 mol% or more of ethylene glycol is preferable. 20 mol% or less of the total acid component of the dicarboxylic acid may be the above aromatic dicarboxylic acid other than terephthalic acid and / or 2,6-naphthalenedicarboxylic acid, or a fatty acid such as adipic acid or sebacic acid. Group dicarboxylic acids; alicyclic dicarboxylic acids such as cyclohexane-1,4-dicarboxylic acid and the like. Further, 20 mol% or less of the total glycol component may be the above-mentioned glycol other than ethylene glycol, or an aromatic diol such as hydroquinone, resorcin, or 2,2-bis (4-hydroxyphenyl) propane; Aliphatic diols containing aromatic rings such as 4,4-dihydroxymethylbenzene; polyethylene glycol, polypropylene glycol. It may also be a polyalkylene glycol (polyoxyalkylene glycol) such as polytetramethylene glycol.

In the polyester of the present invention, a component derived from an oxycarboxylic acid such as an aromatic oxyacid such as hydroxybenzoic acid; an aliphatic oxyacid such as ω-hydroxycaproic acid, a dicarboxylic acid component and an oxycarboxylic acid component. Those which are copolymerized or bonded at 20 mol% or less based on the total amount of

Further, in the polyester of the present invention, a polycarboxylic acid or polyhydroxy compound having a functionality of 3 or more, such as trimellitic acid or penta, is used in an amount in a substantially linear range, for example, an amount of 2 mol% or less based on all acid components. A copolymer of erythritol and the like is also included.

The polyester is known per se and can be produced by a method known per se.

The polyester has an intrinsic viscosity of about 0.4 to 0.8 when measured at 35 ° C. as a solution in o-chlorophenol.
Are preferred.

The polyester film in the present invention is required to have an in-plane dimensional change rate of ± 0.02% or less when kept for 72 hours under the conditions of a temperature of 60 ° C. and a humidity of 80%. A film having an in-plane dimensional change rate of more than ± 0.02% is not preferable because, for example, when a high-quality magnetic disk is manufactured using the film, the dimensional change is large under the usage environment of the disk and a track deviation problem occurs. .

In the process of coating the magnetic layer on the surface of the polyester film, the magnetic layer is usually coated, dried, calendered, cured,
Distortion removal processing or the like is performed. Usually 60 to 12 in these treatments
In some cases, the temperature of the polyester film is higher than the glass transition point (Tg) of the polyester because it includes heat treatment at about 0 ° C., and the film is often thermally deformed. When the heat shrinkage in the film surface is large or the in-plane anisotropy is large, the flatness is remarkably impaired due to the illegal shrinkage. And due to the distortion of the magnetic disk,
The adhesion with the head is deteriorated, the functionality as a magnetic disk is lost, and the product yield is reduced. In addition, in order to recover this flatness, it is necessary to add a process such as a strain removing process that hinders productivity.

The polyester film according to the present invention has the above-described in-plane dimensional change rate characteristics and at the same time at 105 ° C. for 30 minutes in order to eliminate problems in the magnetic layer coating process and further improve productivity. It is necessary that the in-plane dimensional change rate when kept is 0.5% or less, preferably 0.3% or less, and the in-plane dimensional change rate anisotropy is within ± 0.1%. As a result, the product yield can be improved, and the most preferable characteristics can be obtained for high-end magnetic disk use as the final product.

The polyester film having such characteristics is, for example, melt-extruded polyester and then rapidly solidified to be an unstretched film, and when the unstretched film is uniaxially stretched in the machine direction and then stretched in the transverse direction, in a transverse stretching region in multiple stages. The temperature is raised, the temperature of the former stage of stretching is set to Tg to Tg + 50 ° C, and the latter stage of stretching is stretched in the range of Tc-30 ° C to Tc + 10 ° C with respect to the next heat setting temperature Tc, and the temperature Tc is set to Tm ( Polyester melting point) -90 ° C to Tm-20 ° C, heat set while extending in the horizontal direction by 5 to 20%, then once the film is cooled to Tg + 30 ° C or less, then heated without restraining the horizontal direction. It can be manufactured by subjecting it to a relaxation treatment in the lateral direction (width direction) and the longitudinal direction. The conditions for this relaxation treatment vary depending on the stretching ratio in the biaxial direction, but for example, in the case of a polyethylene terephthalate film stretched 3.6 times in the biaxial direction, it is heated and floated at 140 ° C. with a heating gas under low tension, for example. It is recommended to relax in both axial directions with a tension of 5 kg / cm ^{2 for} 1 to 5 seconds.

<Examples> Hereinafter, the present invention will be further described based on Examples. The film characteristics were measured by the following method.

[Dimensional change rate of film] A sample with a width of 10 mm and a length of 150 mm is cut out along the measuring direction, marked points are provided in the vicinity of both ends in the longitudinal direction of the sample, and the distance between the marked points is measured before processing. It is left for a predetermined time at the free end in an oven adjusted to the temperature and humidity. After taking this out and adjusting it at room temperature, the gauge length is measured again to obtain the dimensional change rate. Regarding the in-plane anisotropy of the film, samples are cut out from the original film at intervals of 10 ° over 180 °, the dimensional change rate is measured using these samples, and the maximum and minimum values are obtained.

Example 1 Polyethylene terephthalate was melt extruded and then rapidly cooled and solidified to obtain an unstretched film, which was then longitudinally stretched 3.6 times. The longitudinally stretched film obtained is subjected to a tenter and heated in multiple stages in the transverse stretching zone, that is, the front stage temperature is 100 ° C and the rear stage temperature is 1 ° C.
The film was transversely stretched 3.6 times while changing from 70 ° C to 220 ° C, and heat-set at 215 ° C while being extended by 15% in the transverse direction (width direction) in the heat-setting zone. Then, after the heat setting film is once cooled to 100 ° C or less, it is heated with air without restraining the width direction.
It was subjected to a heating floatation treatment at 140 ° C., and was subjected to a relaxation treatment in a biaxial direction (width direction and longitudinal direction) at a tension of 5 kg / cm ^{2 for} 1 to 5 seconds.

The properties of the obtained polyester film are shown in Table 1.

This film has a sufficiently low dimensional change rate in an environment of 60 ° C, 80% humidity and 72 hours, and has a low heat absorption at 105 ° C for 30 minutes, and the heat absorption in the width direction from the center to the edge of the film. The in-plane anisotropy is small, and the flatness during processing is extremely good,
There is no curl distortion and no distortion removal process is required.

Comparative Example 1 When the longitudinally stretched film of Example 1 was transversely stretched by a factor of 3.6, the stretching was carried out at one step temperature, that is, at a temperature of 100 ° C., and the film was heat-set at 210 ° C. without stretching in the width direction and wound as it was. .

The properties of the obtained polyester film are shown in Table 1.

This film is poor in flatness during processing, has a poor product yield due to curling, and requires a strain removing step.

Comparative Example 2 When the longitudinally stretched film of Example 1 was transversely stretched by a factor of 3.6, the stretching temperature was set to 100 ° C. in one step, and heat setting was performed at 215 ° C., and 0.8% was limited in the width direction in the latter half of the heat setting zone. Heat treatment was performed at 180 ° C. while applying shrinkage. Next, this film was subjected to a relaxation treatment in a width direction and a longitudinal direction at a running tension of 5 kg / cm ² by heating and floating treatment with air at 140 ° C. continuously with the heat setting zone.

The properties of the obtained polyester film are shown in Table 1.

In the center of this film, the heat absorption value at 105 ° C for 30 minutes is almost balanced with the maximum value / minimum value: 0.21% / 0.17%, but the orientation angle at the edge of the film is due to the bowing phenomenon due to the bowing phenomenon. The distortion is large, the in-plane orientation becomes anisotropic, and the maximum / minimum heat absorption value is 0.45% / 0.12%, which is anisotropy and the width yield of the product is greatly reduced.

<Effects of the Invention> The polyester film of the present invention is excellent in dimensional stability and isotropy under wet heat conditions and further under dry heat conditions, and is particularly excellent in flatness in magnetic disk production, product yield, and strain relief process. The feature is that it is unnecessary. This polyester film is particularly useful in the production of high quality magnetic disks.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Masami Etchu 3-37-19 Oyama, Sagamihara City, Kanagawa Prefecture, Sagamihara Research Center, Teijin Limited (56) Reference JP-A-2-22038 (JP, A) JP-A-1-204723 (JP, A) JP-A 1-204722 (JP, A) JP-A-63-288735 (JP, A) JP-A-62-124926 (JP, A) JP-A-62-84424 (JP, A)

Claims (1)

[Claims] 1. A in-plane dimensional change rate of ± 0.02% or less when kept at a temperature of 60 ° C. and a humidity of 80% for 72 hours, and an in-plane dimensional change when kept at a temperature of 105 ° C. for 30 minutes. The average value of the rates is 0.5% or less and the in-plane anisotropy is ± 0.1.
% Or less, isotropic biaxially oriented polyester film.