JPH0639128B2 - Biaxially oriented polyester film - Google Patents

Description

TECHNICAL FIELD The present invention relates to a biaxially oriented polyester film having excellent processing characteristics such as slitting property.

(Prior Art) Biaxially oriented polyester film has strength, dimensional stability,
Since it has excellent physical properties such as heat resistance and surface smoothness,
It is used as a base film for magnetic recording media such as audio tapes and video tapes (Japanese Patent Publication No. 55-409).
No. 29).

(Problems to be solved by the invention) However, while the conventional biaxially oriented polyester film is excellent in physical properties such as strength and dimensional stability as described above, for example, slitting a wide roll film during production of the base film. And then divide it into several rolls of narrow width, or to remove the edge of the ear held by the clip of the tenter with a slit, and when manufacturing the magnetic tape, apply a magnetic layer in a wide width state. Slitability is not always good when slitting to the width of a commercially available tape, and film ears are formed on the roll end surface after slitting, fluffing of the cut end, this is scraped, and the dropout of the magnetic tape As a result, the productivity of the base film and the yield of the magnetic tape are reduced. In addition, there is a problem that cutting powder of the film is generated at the time of slitting, which enters the film roll and causes dropout. As the base film is made thinner with the recent miniaturization of video decks and the like, the above-mentioned slitting property tends to be further deteriorated, and its improvement has been desired.

The inventor of the present invention measures the stress-strain curve in the width direction from the idea that the strength in the width direction of the film is related to the slittability of the film, while microscopically, the cutting work of the film is performed between the molecules. It is a cutting operation, and its slit property is measured as the molecular chain length, that is, the intrinsic viscosity of the film is considered to be related to the entanglement of molecules, and as a result, the conventional film has an excessively high intrinsic viscosity, The slit property is poor because the ratio of the breaking strength in the width direction of the film to the stress at 5% elongation is too large. Conversely, limiting these to a certain range improves the slit property, and The present invention has been completed based on the finding that it does not impair practical properties. That is, the present invention is characterized by the intrinsic viscosity of the film and the breaking strength in the width direction of the film,
By limiting the ratio with respect to the% stress at the time of elongation, the conventional problems are solved and a biaxially oriented polyester film having a good slit property is provided.

(Means for Solving the Problems) The biaxially oriented polyester film of the present invention is mainly made of polyethylene terephthalate, has an intrinsic viscosity of 0.55 to 0.60, and has a breaking strength in the width direction and a stress at 5% elongation in the width direction. It is characterized in that the ratio with is 2.20 or less, preferably 2.00 or less.

The polyester of the present invention is a crystalline polyester such as polyethylene terephthalate or polyalkylene naphthalate, and preferably 80 mol% or more of repeating units of ethylene terephthalate. Other copolymerization components include isophthalic acid, p-β-oxyethoxybenzoic acid, 2-6-naphthalenedicarboxylic acid, 4-4 '.
-Dicarboxylic acid components such as dicarboxyl diphenol, 4-4'-dicarboxyl benzophenone, bis (4-carboxylphenol) ethane, adipic acid, sebacic acid, 5-sodium sulfoisophthalic acid, cyclohexane-1,4-dicarboxylic acid , Propylene glycol, butanediol, neopentyl glycol, diethylene glycol, cyclohexanediol, bisphenol A
The ethylene oxide adduct, a glycol component such as polyethylene glycol, polypropylene glycol, polytetramethylene glycol, and the like, an oxycarboxylic acid component such as p-oxybenzoic acid, and the like can be arbitrarily selected. In addition, a small amount of a compound containing an amide bond, a urethane bond, an ether bond, or a carbonate bond can be included as another copolymer component.

As the polyester polymerization method, any polymerization method such as a direct polymerization method in which an aromatic dicarboxylic acid and a glycol are directly reacted and a transesterification reaction in which a dimethyl ester of an aromatic dicarboxylic acid and a glycol are transesterified can be applied. .

Further, the biaxially oriented polyester film, the polyester is melt-extruded by a known method, after sheet formation,
Although it is stretched in the longitudinal-transverse direction or in the transverse-longitudinal biaxial direction and further heat-set, it may be stretched uniaxially or biaxially before the heat-setting treatment.

In addition, the above polyester may contain inactive fine particles acting as a lubricant, if necessary.

(Operation) The biaxially oriented polyester film of the present invention exhibits excellent slit properties and can sufficiently satisfy other practical properties. However, if the intrinsic viscosity of the film is less than 0.55, the film becomes brittle and easily breaks during film production, while if it exceeds 0.60, the viscosity of the film becomes excessive and the slit property deteriorates. . On the other hand, when the ratio of the breaking strength in the width direction to the stress at 5% elongation is larger than 2.20, the slits of the film become fuzzy or so-called ears during slitting, and when slitting after coating the magnetic layer. The shaving powder of the film is generated in the film, which easily causes the dropout. This is because local yield elongation occurs when the film is cut with a cutter blade, and it occurs because the cut end face of the film is finely discontinuously stretched or the film is finely shredded. It is considered to be one. When the ratio of the breaking strength to the stress at elongation of 5% is 2.20 or less, particularly 2.00 or less, the above local yield elongation does not occur and good slitting property can be obtained.

In order to reduce the ratio of the breaking strength in the width direction of the film to the stress at 5% elongation in the width direction to 2.20 or less, it is effective to reduce the intrinsic viscosity of the film, but as described above, The intrinsic viscosity of the film should be 0.55 or higher. A film with an intrinsic viscosity of 0.55 to 0.60 has an intrinsic viscosity of 0.
65-0.56 polymer pellets in the temperature range of 275-310 ° C, preferably 2 pellets with an intrinsic viscosity of 0.62-0.57.
Obtained by melt extrusion in the temperature range of 85 to 295 ° C. Regarding stretching, it is preferable to direct the molecules in the length direction rather than the width direction of the film in order to make the above ratio 2.20 or less. When transversely and longitudinally biaxially stretching, the above ratio can be set to 2.20 or less by appropriately selecting the intrinsic viscosity of the film within the range of 0.55 to 0.60. When stretching in the longitudinal and transverse directions, the temperature of the transverse stretching is kept within the temperature of the longitudinal stretching plus 20 ° C, and the intrinsic viscosity of the film is set within the range of 0.58 to 0.55 so that the above ratio is 2.20 or less. Can be Further, strengthening the heat setting treatment after stretching of the film is also effective in reducing the above ratio, and when a film having an intrinsic viscosity of 0.58 to 0.60 is formed by longitudinal and transverse stretching, the temperature of transverse stretching The above ratio can be set to 2.20 or less by suppressing the temperature within the longitudinal stretching temperature plus 15 ° C. or less and heat-treating the stretched film at a temperature of 200 to 230 ° C. for 2 seconds or more.
Further, it is very effective to perform the re-longitudinal stretching after the biaxial stretching, in order to reduce the above-mentioned ratio, and a good slit property can be obtained. These methods are preferable as a method for producing a biaxially oriented film having an intrinsic viscosity of 0.55 to 0.60 in the present invention, a ratio of breaking strength in the width direction and stress at 5% elongation in the width direction of 2.20 or less, but not particularly limited. It is not something that will be done.

Next, prior to describing the examples of the present invention, a method for measuring the breaking strength, the stress at 5% elongation, the slittability and the intrinsic viscosity will be described.

(1) Breaking strength, stress at 5% elongation Tensilon UTM-II-500 manufactured by Toyo Baldwin Co., Ltd.
Using a mold, the temperature was 23 ° C. and the relative humidity was 65%. The rupture strength is the stress at the time of rupture of a sample when a tensile test is performed (the tensile load at rupture divided by the cross-sectional area of the sample before the test), and the stress at 5% elongation is 5% elongation of the sample. This means the stress at each time, and the film was cut into a rectangle of 10 mm in the length direction and 150 mm in the width direction to make a sample piece, and the inter-chaak distance was 1 between the check racks of the above tester.
It is the value obtained by mounting it so that it becomes 00 mm and conducting a tensile test at a tensile rate of 100% / min.

(2) Slitting property Slitting property is determined by slitting a biaxially oriented polyester film and winding it, and judging by the state of the end surface of the roll. When the end surface of the roll is visually observed, there is no fluffing or wrinkling, and it is 1 , The following 4 ranks were ranked.

(3) Intrinsic viscosity of film Measured in a mixed solution of tetrachloroethane / phenol at a weight ratio of 6/4 under the condition of 30 ° C.

(Example) Polyethylene terephthalate pellets having an intrinsic viscosity of 0.60 were sufficiently dried, then fed to an extruder and melt-extruded at a temperature of 280 ° C, which was cooled and solidified at a temperature of 30 ° C to give a thickness of 16
An unoriented film of 0μ was obtained, and the unoriented film was stretched 3.7 times in the transverse direction at a temperature of 90 ° C., then stretched 3.6 times in the longitudinal direction at a temperature of 95 ° C., and further heated at 220 ° C. for 3 seconds. The biaxially oriented polyester film of Example 1 was obtained by performing fixing treatment, cooling and winding.

The unoriented film of Example 1 was longitudinally oriented at a temperature of 90 ° C.
The biaxially oriented polyester film of Example 2 was obtained by subjecting it to 7-fold stretching, subsequently stretching at a temperature of 95 ° C. in the transverse direction by 3.6 times, and further subjecting it to heat setting treatment at 235 ° C. for 7 seconds.

A biaxially oriented polyester film of Comparative Example 1 was obtained in the same manner as in Example 1 except that polyethylene terephthalate pellets having an intrinsic viscosity of 0.70 were used in Example 1.

A biaxially oriented polyester film of Comparative Example 2 was obtained in the same manner as in Example 1 except that the melt extrusion temperature was changed to 310 ° C. However, many breakages occurred during production, and productivity was extremely poor.

In Example 2, the heat setting treatment temperature after stretching was 190 ° C.
A biaxially oriented polyester film of Comparative Example 3 was obtained in the same manner as in Example 2 except that the above was changed to.

An unoriented film obtained in the same manner as in Example 1 was stretched 3.7 times in the transverse direction at a temperature of 90 ° C., then stretched 3.6 times in the longitudinal direction at a temperature of 95 ° C., and then at a temperature of 120 ° C. in the longitudinal direction.
The film was re-stretched 1.1 times, further heat-set at 220 ° C. for 3 seconds, cooled and wound to obtain a biaxially oriented polyester film of Example 3.

The intrinsic viscosity, properties and slit properties of the biaxially oriented polyester films of Examples 1 to 3 and Comparative Examples 1 to 3 are shown in the table below. However, TS (TD) in the table indicates the breaking strength in the width direction, F5 (TD) indicates the stress at 5% elongation in the width direction, and F5 (MD) indicates the stress at 5% elongation in the length direction.

As is clear from the above table, the intrinsic viscosity and the ratio TS (TD) / F5 (TD) of the breaking strength in the width direction and the stress at 5% elongation satisfy the conditions of the present invention. Example 3
Had a good slitting property and did not cause any trouble during production, but Comparative Example 1 has an intrinsic viscosity and a ratio TS.
Since both (TD) / F5 (TD) are excessively large, the slitting property is the worst, and Comparative Example 2 has an inherent viscosity that is too low, so that the slitting property is good but the productivity is extremely poor.
Since (TD) / F5 (TD) was too large, the slit property was poor.

Further, in Example 2 above, the stretching ratio in the length direction was
A biaxially oriented polyester film of Comparative Example 4 was produced in the same manner as in Example 2 except that the stretching ratio in the width direction was set to 3.6 times and the stretching ratio in the width direction was set to 3.8 times. Later, and because the draw ratio in the width direction is larger than that in the length direction, TS (TD) / F5 (TD) was too large at 2.37, and the productivity was good, but the slitability was 2
Fell to.

(Effects of the Invention) The biaxially oriented polyester film of the present invention limits the intrinsic viscosity of the film to the range of 0.55 to 0.60, and limits the ratio of the breaking strength in the width direction to the stress at 5% elongation to 2.20 or less. Therefore, it is possible to improve the slitting property without lowering the productivity, and no fluffing occurs on the end surface of the roll obtained by winding after slitting, and therefore the dropout when used as a magnetic recording medium Decreased,
The yield is improved. Moreover, the pellets can be produced by adjusting the intrinsic viscosity of the pellets, the melt extrusion temperature, and the processing conditions from stretching to heat setting, and there is no need to prepare special equipment or use special raw materials.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Katsuro Kuze 10-24 Toyo-cho, Tsuruga City, Fukui Prefecture Toyobo Co., Ltd. General Research Laboratory Tsuruga Branch Office (56) Reference JP-A-53-138477 (JP, A) )

Claims (1)

[Claims] 1. A biaxially oriented film mainly composed of polyethylene terephthalate, wherein the film has an intrinsic viscosity of 0.55 to 0.60, a breaking strength in the width direction and a breaking strength in the width direction of 5
A biaxially oriented polyester film having a ratio with a stress at% elongation of 2.20 or less.