JP2679234B2 - Method for producing polyester film - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial field of application] The present invention relates to a film made of a substantially amorphous film containing polyethylene terephthalate as a main component, having a high longitudinal draw ratio, excellent thickness uniformity and high strength. The present invention relates to a method for inexpensively producing the biaxially oriented polyester film.

[Prior Art and Problems to be Solved by the Invention] Conventionally, as a method for obtaining a film having high strength in the longitudinal direction, a longitudinal re-longitudinal stretching method in which longitudinal and lateral biaxial stretching is performed, and then longitudinal stretching is performed again Alternatively, after longitudinal stretching in multiple stages, it is cooled to a glass transition temperature or lower, heated again, and re-longitudinal stretched,
Then, a method of transversely stretching is proposed. If the method is adopted, a re-longitudinal stretching device is required, and a large amount of capital investment is required, and the method is not practical because many breaks occur during film formation, and improvement thereof has been demanded.

[Means for Solving the Problems] In view of the above problems, the present inventors have earnestly studied a manufacturing method for obtaining a longitudinal high-strength film that does not require a re-longitudinal stretching device and has few breakages during film formation It was found that a high-strength film can be easily obtained by adopting the longitudinal stretching conditions of No. 3, and completed the present invention.

That is, the gist of the present invention is that a film containing polyethylene terephthalate as a main component in a substantially amorphous state is stretched in the longitudinal direction at a total stretching ratio of 4.0 to 9.0, and then in the transverse direction.
In the method of producing an oriented film by stretching at a draw ratio of 3.5 times or more, the stretching in the machine direction is as follows: (A) a film in an amorphous state is drawn at a draw ratio of 1.2 to 5.0 and a birefringence Δn ₁ of 1.2 × 10 ^-2 The film is longitudinally stretched in one step or multiple steps so as to be 5.0 × 10 ^-2, and (B) the film temperature T ₂ and the birefringence Δn ₂ after longitudinal stretching without cooling the film temperature to a glass transition point or lower.
Is a process for stretching so as to satisfy the following formulas: 95-250 · Δn ₂ ≦ T ₂ ≦ 115-250 · Δn ₂ and 0.080 ≦ Δn ₂ ≦ 0.150.

 Hereinafter, the present invention will be described in detail.

Polyethylene terephthalate (hereinafter abbreviated as PET) used in the present invention is a polyester containing 80 wt% or more of terephthalic acid residues as an acid component and 80 wt% or more of ethylene glycol residues as a glycol component. Therefore, the remaining components may be copolymers or blends with different types of monomers. Also,
The polymer used may contain phosphoric acid, phosphorous acid and esters thereof and inorganic particles (silica, kaolin, calcium carbonate, calcium phosphate, titanium dioxide, etc.) in the polymerization stage, Inorganic particles and the like may be blended.

Next, a method for producing a film will be described. First, the above PET
After sufficiently drying the polymer, it is melt-molded into a sheet through an extruder, a filter, and a die controlled in a temperature range of, for example, 280 to 290 ° C., and cast on a rotating cooling drum to obtain a rapidly solidified film. This rapidly solidified film is substantially in an amorphous state (hereinafter referred to as A film). This A film may be a film laminated by coextrusion.

Next, after preheating A film to 90 ° C or more, Δn ₁
First stretching is performed at a stretching ratio of 1.2 × 10 ^{-2 to} 5.0 × 10 ^-2 (hereinafter, this film is referred to as B-1 film). The first draw ratio in which Δn ₁ falls within the above range is usually 1.2 to 5.0 times, though it depends on the preheating temperature, and can be easily determined by preliminary tests. The Δn _{1 of the} B-1 film is 1.
When it is less than 2 × 10 ^-2 , even if the subsequent steps are optimized, the thickness uniformity is poor and the longitudinal stretching ratio cannot be improved. Also, Δn ₁
Is more than 5.0 × 10 ^-2 , the progress of crystallization in the subsequent steps is remarkable, and breakage frequently occurs during transverse stretching, which is not preferable because stable production conditions cannot be obtained.

The film temperature T ₂ and the birefringence Δn ₂ after longitudinal stretching satisfy the following two equations without cooling the B-1 film obtained below as described above to the glass transition temperature or lower. Second stretching is performed in one stage or in multiple stages (hereinafter, this film is referred to as B-2 film).

95-250 · Δn ₂ ≦ T ₂ ≦ 115-250 · Δn ₂ 0.080 ≦ Δn ₂ ≦ 0.150 If the temperature T ₂ of the film is outside the above range, uneven thickness of the stretched film is not improved.

In the present invention, T ₂ is usually in the range of 70 to 100 ° C. and Δn ₂
Is in the range of 0.080 to 0.150. If the birefringence Δn ₂ of the B-2 film is less than 0.080, it is unsuitable because the thickness unevenness of the stretched film does not improve. If the Δn ₂ exceeds 0.150, the B-2 film is crystallized. Since it proceeds too much, the effect of improving the thickness uniformity is rather weak, and the transverse stretchability deteriorates, which is not preferable. Preferably, 0.100 to 0.150,
More preferably, it is in the range of 0.100 to 0.130.

The second draw ratio is the product of the first draw ratio (total draw ratio)
Is appropriately selected from the range of 4.0 to 9.0 times. If the total draw ratio is less than 4.0 times, a high strength film cannot be obtained. Further, if the total stretching ratio exceeds 9.0 times, breakage frequently occurs during transverse stretching, which is not preferable.

A ceramic roll is preferably used as the stretching roll used in the second stretching. Other materials (for example, rubber coated roll and hard chrome plated roll) can be used, but the ceramic roll is superior in terms of roll durability.

The film longitudinally stretched under the above conditions is stretched in the transverse direction from 80 ℃
A biaxially oriented polyester film is obtained by stretching at 130 ° C. 3.5 times or more. Further film is usually 130
Heat treatment at ℃ ~ 250 ℃.

By the novel manufacturing method of the present invention described above, a large amount of a film having high strength and excellent thickness uniformity can be supplied at low cost.

The film thus obtained is applicable to various currently known uses. In other words, it can be applied not only to base films for various magnetic recording media such as magnetic tapes and for electric / electrical interruptions such as capacitors, but also to other films for packaging.

The thickness of the film to which the present invention is applied is not particularly limited, but is preferably in the range of 0.5 to 50 μm.

[Examples] The present invention is described in more detail below with reference to Examples, but the present invention is not limited to these Examples.

 The methods for measuring various physical properties of the present invention are shown below.

(1) F ₅ value (kg / mm ² ) Intesto Model 20 tensile tester Intesco Model 20
Using the 01 type, a sample film having a length of 50 mm and a width of 15 mm was pulled at a speed of 50 mm / min in a room controlled at a temperature of 23 ° C. and a humidity of 50% RH, and the strength at 5% elongation was defined as F ₅ value. .

(2) Thickness unevenness (%) A biaxially stretched film was cut out with a continuous film thickness measuring device (using an electronic micrometer) manufactured by Anritsu Electric Co.,
The length of 5 m was calculated from the following formula.

(3) Birefringence The retardation of the longitudinally stretched film was measured with a polarizing microscope manufactured by Carl Zeiss, and the birefringence (Δ
n) was determined.

Δn = R / d R: Retardation d: Film thickness Example 1 Polyethylene terephthalate chips (intrinsic viscosity 0.62,
0.32% by weight of Al ₂ O ₃ having an average particle size of 0.03 μm and an average particle size
0.5μm calcium carbonate 0.2% by weight) at 180 ℃
After drying for 4.5 hours, extrude from T-die into sheet at 290 ℃
350 mm wide by cooling and solidifying on a rotating drum kept at 40 ° C
An unstretched amorphous film of was obtained. At that time, a known electrostatic adhesion method was used.

The resulting unstretched amorphous film was first stretched in the machine direction at a film temperature of 115 ° C. by a factor of 1.5 and at a film temperature of 103 ° C. at 2.3 by utilizing the circumferential speed difference of multiple nip rolls.
After the double stretching, the film was continuously stretched 1.6 times at a film temperature of 79 ° C. as a second stretching in the longitudinal direction. A ceramic roll was used as the drawing roll.

The birefringence of the film after the first stretching is 2.8 × 10 ^-2 , and the birefringence of the film after the second stretching is 0.112.
Met.

Next, in a tenter, the film was stretched in the transverse direction by 3.6 times at 100 ° C., heat-set at 215 ° C., and a film having a final film thickness of 10 μm was wound up.

Example 2 A stretched film was formed in the same manner as in Example 1 except that the second stretching was performed at 87 ° C. to 1.5 times.

Comparative Example 1 A stretched film was formed in the same manner as in Example 2 except that the second stretch ratio in Example 2 was 1.2.

Comparative Example 2 When the second stretching was carried out at 109 ° C. in Example 1 and the birefringence after longitudinal stretching was set to 0.090, breakage occurred frequently during transverse stretching and a film could not be obtained.

 The results obtained above are summarized in Table 1.

[Effect of the Invention] According to the present invention, a high-strength polyester having excellent thickness uniformity can be easily produced, and high-speed production thereof is also possible, and the industrial value of the present invention is high.

Front Page Continuation (72) Inventor Takatoshi Miki 5-8 Mitsuyacho, Nagahama City, Shiga Prefecture, Product Research Laboratory, DIAFOIL Co., Ltd. (56) References JP-A-60-61233 (JP, A) JP-A-60- 176743 (JP, A)

Claims (3)

(57) [Claims] 1. An oriented film comprising a film of polyethylene terephthalate as a main component in a substantially amorphous state, stretched in the machine direction at a total stretch ratio of 4.0 to 9.0, and then stretched in the transverse direction at 3.5 times or more. In the method for producing, the stretching in the machine direction is performed so that (A) the amorphous film has a stretching ratio of 1.2 to 5.0 and a birefringence Δn ₁ of 1.2 × 10 ^{−2 to} 5.0 × 10 ^−2. (B) The film temperature T ₂ and the birefringence Δn ₂ after longitudinal stretching are the following formula: 95−250 · Δn ₂ ≦, without cooling the film temperature below the glass transition point. A method for producing a polyester film, comprising a step of stretching so as to satisfy T ₂ ≦ 115-250 · Δn ₂ and 0.080 ≦ Δn ₂ ≦ 0.150. 2. A process for producing a polyester film according to claim 1, wherein the [Delta] n ₂ is characterized by satisfying the 0.100 ≦ Δn ₂ ≦ 0.150. 3. The method for producing a polyester film according to claim 1, wherein a ceramic roll is used as the stretching roll in the step (B) according to claim 1.