JP2516100B2 - 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 polyester film such as a magnetic tape having excellent strength in the longitudinal direction and excellent dimensional stability in a heating temperature range around 70 ° C.

[0002]

2. Description of the Related Art Generally, a polyester film typified by polyethylene terephthalate is widely used for magnetic tape applications and electrical applications because of its excellent heat insulating properties, mechanical properties and chemical resistance. For magnetic tapes, especially video tapes, recorded tapes are stored at high temperatures, and heat shrinks due to heat received during repeated playback, causing image distortion (skew distortion), which causes problems. Dimensional stability is required, and it is said that dimensional stability in a temperature range around 70 ° C. is extremely important.

Further, with the recent trend toward smaller and lighter video decks, when a thin base film is required and high strength is required, dimensional stability becomes a very serious problem. Conventionally, in such a high-strength film, dimensional stability is often sacrificed due to its strength, and it is technically difficult to simultaneously satisfy two contradictory properties of strength and dimensional stability. It was

[0004]

The present invention has been made in view of such circumstances, and its purpose is strength and dimensional stability, particularly dimensional stability in a temperature range around 70 ° C. It is intended to provide a biaxially oriented polyester film which simultaneously satisfies two characteristics.

[0005]

In order to solve the above problems, the present inventors have extensively studied the physical properties thereof, and as a result, found that the biaxially oriented polyester having the two characteristics of the present invention has excellent effects. Heading, completed the present invention.

According to the present invention, the biaxial orientation is sequentially performed in the horizontal direction and then in the vertical direction.
The film is at _{F 5} value in the following characteristics or longitudinal direction 15 kg / mm ² 2 or more and a specific gravity of the film A, 975cm ^-1 and 795cm
^When the infrared absorption intensity ratio of ^-1 is B, the C value represented by the formula C = 43.4 AB- (1) is 56.50 or more, and the biaxially oriented polyester film is characterized. (However, F ₅ value is the stress per unit cross-sectional area when the sample is stretched by 5% in the tensile test, and B is the infrared absorption intensity of 975 cm ⁻¹ / 795 cm
^-1 shows the infrared absorption intensity) and its manufacturing method.

The polyester used as the base of the biaxially oriented polyester film used in the present invention is a polyester having ethylene terephthalate as a main repeating unit, and particularly 80% by mole or more of the repeating unit is ethylene terephthalate. .

As a method for producing a polyester using the above-mentioned raw material components, known means such as a direct polymerization method in which a dicarboxylic acid and glycol are directly reacted, a transesterification method in which a diester of dicarboxylic acid and a glycol are transesterified, and the like are appropriately used. Can be adopted. Further, these polyesters may contain inactive inorganic fine particles as needed and in a range that does not significantly affect the electromagnetic conversion characteristics.

The biaxially oriented polyester in the present invention is
It is necessary to satisfy the above two characteristic conditions.
A film having an F ₅ value in the longitudinal direction of 15 kg / mm ² or more is obtained by melt-extruding the polyester obtained as described above according to a conventional method to form a sheet or a film, and then biaxially in the horizontal and vertical directions. It is obtained by heat-treating the film after stretching it, re-stretching it further in the machine direction if necessary. In this case, the F ₅ value is 15 to 25 kg / mm ² , and more preferably 17 to 25 kg / mm ² .

Further, the object of the present invention is the following formula C = 43.4A-B from the relationship between the specific gravity A and the intensity ratio B of the infrared absorption peaks of 975 cm ^-1 and 795 cm ^-1 of the above-mentioned film. .. The C value obtained from (1) must be 56.50 or more. The C value in this case is preferably 57.0.
It is 0 or more, more preferably 57.50 or more. 975
the intensity ratio of the infrared absorption peak cm ^-1 and 795 cm ^-1 are
When an unoriented polyethylene terephthalate sample is heat-treated, it has a linear relationship with the specific gravity, but the above-mentioned strength ratio when a film that has been biaxially oriented in advance is heat-treated loses the linear relationship with the specific gravity. , It is known that even with the same specific gravity, a higher strength ratio is shown (PG Shm
idt, Journal of Polymer Science, Part A, 1, 1271
(1963)).

The inventors of the present invention have paid attention to the above relations and have made earnest studies. As a result, the biaxially oriented film of F ₅ having a high value of 15 kg / mm ² or more is 975 cm ⁻¹ and 795 cm ^−1.
By limiting the infrared absorption peak intensity ratio and specific gravity of the above to a specific range represented by the above formula (1) (that is, limiting the increase in the intensity ratio due to orientation to a certain amount or less), a relatively high temperature near 70 ° C. It could be obtained biaxially oriented film having excellent dimensional stability even at temperature conditions.

[0012] and in this way F ₅ value is 15 kg / mm ² or more and C value determined from the relationship between the intensity ratio and the specific gravity of the infrared absorption peak of 975cm ^-1 and 795 cm ^-1 is in the above specific range The reason why the limited film of the present invention exhibits excellent dimensional stability in the temperature range of about 70 ° C. is unknown, but the intensity ratio and specific gravity of infrared absorption peaks at 975 cm ⁻¹ and 795 cm ⁻¹ are in the above specific range. In the film limited to the above, the amount of the strained amorphous region in the film is limited to a certain amount or less, and the crystal portion that can limit the movement of the amorphous region in the temperature range of about 70 ° C. It exists, and it is speculated that the movement of the amorphous region is sufficiently suppressed at around 70 ° C., and good dimensional stability is exhibited.

The method for producing the biaxially oriented polyester film satisfying the above-mentioned required characteristics is not particularly limited as long as the object is achieved, but the most general method will be described below. A raw polyester is melted according to a conventional method, and a non-oriented polyester extruded into a sheet is molded at a glass transition temperature or higher.
The film is biaxially stretched sequentially in the lateral direction and then in the longitudinal direction, and re-stretched monoaxially or biaxially as necessary. The stretching temperature is 80 to 130 ° C., preferably 90 to 120 ° C.
It is 6.0, preferably 3.5 to 5.5. Next, the stretched polyester film is heat-fixed with a tenter. The heat setting temperature is 150 to 235 ° C. in the case of polyethylene terephthalate, preferably 180 to 230 ° C.
Therefore, the treatment time is preferably 1 to 10 seconds. Next, the heat-treated film as described above is subjected to relaxation heat treatment at 80 to 150 ° C. As for the relaxation heat treatment method, any method may be used as long as it gradually relaxes the moving speed of the clip holding the film in the tenter to relax in the film flow direction and a method of providing a speed difference between the heating roll and the cooling roll each having a nip roll. The method of can also be used. Relaxation temperature as preferred relaxed condition 9 0-12
0 ° C, relaxation rate 0.2-2%, preferably relaxation time 1
Within seconds. The thickness of the polyester film thus obtained is usually 5 to 20 μm.

As described above, according to the present invention, horizontal / vertical sequential 2
After axial orientation and heat setting , at a relatively low temperature, that is, 80 to 150
By applying a low rate of relaxation treatment at ° C., it can also be expressed excellent dimensional stability in a temperature range of a vicinity of 70 ° C. while maintaining the strength of the film. The biaxially oriented polyester of the present invention has a very high dimensional stability with a heat shrinkage ratio of about 0.05% or less in a heating temperature range of 70 ° C.

[0015]

The present invention will be described in more detail with reference to the following examples, but the present invention is not limited by these examples. In addition, the measuring method of each physical property of the film shown in the following Example is as follows.

(1) Dimensional stability at 70 ° C. A sample to be measured which has a size of 50 mm (length) × 4 mm (width) and whose longitudinal direction coincides with the longitudinal direction of the film is vacuumed. RMA-made TMA-300
A 0 type thermomechanical tester was used to measure the heat distortion curve of the film under constant load (9.4 g) at 70 ° C. in the deformation mode, and after the sample atmosphere reached 70 ° C. (necessary for about 30 minutes) 1 The amount of deformation generated over time was calculated and divided by the original length to obtain the amount of heat shrinkage per hour.

(2) F ₅ value Tensilon UTM-II-500 manufactured by Toyo Baldwin Co., Ltd.
It was measured using a mold under the conditions of 23 ° C. and 65% RH.
F ₅ value here means 5% of the sample when a tensile test is performed.
It means the stress per unit area when stretched. The F ₅ value is
It is a value obtained by cutting the film to be measured into a rectangle of 150 mm in the longitudinal direction and 10 mm in the width direction (direction perpendicular to the longitudinal direction), and performing a tensile test at a tensile speed of 1.00% / min with a chuck distance of 100 mm.

(3) Specific gravity Using a density gradient tube with a mixed solution of n-heptane and carbon tetrachloride, the density was measured under the conditions of 25 ° C. and 65% RH,
This was taken as the specific gravity.

(4) Intensity ratio of infrared absorption peaks at 975 cm ^-1 and 795 cm ^-1 The intensity ratio is measured by the method of Schmidt (Journal of Polymer S
cience, Part A, 1, 1271 (1963)). PERKIN E
Using LMER 983 infrared spectrophotometer, 975 cm ^-1
The absorption height (I ₉₇₅ ) and the absorption intensity (I ₇₉₅ ) at ₇₉₅ cm ^-1 were determined respectively, and I ₉₇₅ / I ₇₉₅ was defined as the intensity ratio.

Example 1 Polyethylene terephthalate was melt extruded by a conventional method, formed into a sheet, stretched in the transverse direction at 95 ° C. by 3.0 times, and subsequently stretched at 105 ° C. in the longitudinal direction by 4.9 times, and further 200 times. A heat setting treatment was performed at 5 ° C. for 5 seconds to obtain a biaxially oriented polyester film having a thickness of 9 μm. This film was relaxed by 0.5% in the longitudinal direction at a film temperature of 100 ° C. for 3 seconds,
After cooling, it was wound up. The characteristics of the obtained film are shown in Table 1. Comparative Example 1 A biaxially oriented polyester film having a thickness of 9 μ was stretched and heat-set in the same manner as in Example 1, and a relaxation treatment was not performed. The characteristics of the obtained film are shown in Table 1.

Example 2 Polyethylene terephthalate was melt-extruded by a conventional method, formed into a sheet, stretched in the transverse direction at 90 ° C. by 3.2 times, and subsequently stretched at 140 ° C. in the longitudinal direction by 5.2 times, and further 225. A heat setting treatment was performed at 5 ° C. for 5 seconds to obtain a biaxially oriented polyester film having a thickness of 9 μ. This film is relaxed 0.9% in the longitudinal direction at a film temperature of 100 ° C. for 3 seconds,
After cooling, it was wound up. The characteristics of the obtained film are shown in Table 1. Comparative Example 2 Stretching was carried out in the same manner as in Example 2, and heat setting treatment was carried out at 195 ° C. for 5 seconds, and the obtained biaxially oriented polyester film having a thickness of 9 μ was longitudinally stretched at 0.
It was relaxed by 3%, cooled, and wound up. The characteristics of the obtained film are shown in Table 1. Comparative Example 3 Example except that the relaxation heat treatment temperature in the longitudinal direction was 200 ° C.
15 μm thick biaxially oriented polyester film similar to
I got the film. The characteristics of the obtained film are shown in Table 1.
It was

[0022]

[Table 1]

From Table 1, since Examples 1 and 2 both satisfy the requirements of the present invention, they have high strength,
Excellent heat shrinkage properties around 70 ° C. In contrast,
Comparative Examples 1 and 2 are 975 cm ⁻¹ and 795 of the formula (1).
Since the value C obtained from the intensity ratio B of the infrared absorption peak of cm ⁻¹ and the specific gravity A does not satisfy the requirements of the present invention, the dimensional stability near 70 ° C. is poor. In addition, Comparative Example 3
Has a low F ₅ value because the relaxation heat treatment temperature is as high as 200 ° C.
Yes.

[0024]

As described above, the biaxially oriented polyester of the present invention has a longitudinal F ₅ of 15 kg / mm ² or more, and has an infrared absorption peak intensity ratio of 975 cm ⁻¹ and 795 cm ^−1. It is obtained by specifying the specific gravity, and it is possible to provide a film having high strength and excellent heat shrinkage properties in the temperature range of around 70 ° C.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Tadashi Okuhira 10-24 Toyo-cho, Tsuruga City, Fukui Prefecture Toyobo Co., Ltd. General Research Laboratory Tsuruga Branch Room (56) Reference JP-A-51-146573 (JP, A) JP-A-49-5177 (JP, A) JP-A-62-170322 (JP, A)

Claims (2)

(57) [Claims] 1. A film which is biaxially oriented in the horizontal direction and then in the vertical direction.
The film has a F ₅ value of 15 kg / mm ² 2 or more in the longitudinal direction and a specific gravity of A and an infrared absorption intensity of 975 cm ⁻¹ / 79.
When the infrared absorption intensity at 5 cm ⁻¹ is B, the C value represented by the formula C = 43.4A-B (1) is 56.50 or more, a biaxially oriented polyester film. (However, F ₅ value indicates the stress per unit cross-sectional area when the sample is stretched 5% in the tensile test.) 2. The non-oriented polyester is biaxially stretched laterally and then longitudinally at a glass transition temperature or higher, then heat set, and then subjected to relaxation heat treatment at 80 to 150 ° C. A method for producing a biaxially oriented polyester film having the characteristics of 1.