JP2611413B2 - Method for producing high-strength polyester film - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for stably producing a polyethylene terephthalate film having high mechanical strength in the longitudinal direction (longitudinal direction) and low shrinkage.

[Problems to be Solved by the Related Art and the Invention] Conventionally, as a method of producing a film having high mechanical strength in the longitudinal direction, a method of longitudinally stretching a biaxially stretched film stretched in the longitudinal-horizontal biaxial directions again. It has been known.

However, the mechanical strength of the film manufactured by such a conventional method, that is, the F-5 value is usually about 20 kg / mm ² , and it is difficult to stably manufacture a film having an F-5 value of more than 20 kg / mm ^2. Met. For example, in Japanese Patent Application Laid-Open No. 58-118220, a method for producing a high-strength film employing specific stretching conditions has been proposed. There were many breaks, and it was still difficult to commercialize.

[Means for Solving the Problems] In view of the above problems, the present inventors have conducted intensive studies,
The present inventors have found that a high-strength film can be easily produced by employing the novel stretching method, and have completed the present invention.

That is, the gist of the present invention is to provide a substantially amorphous film containing polyethylene terephthalate as a main component, in a longitudinal direction so that the birefringence of the film is 1.0 × 10 ^{−3 to} 2.5 × 10 ^−2. The film is stretched in one step or multiple steps at ~ 4.0 times, and without cooling the film temperature below the glass transition point, the birefringence of the film is 3.0 × 10 ^{-2 to} 8.0 × 10 ^-2 so as to be 1.1 × 10 ^−2.
Was longitudinally stretched in a single stage or multiple stages to 3.5 times, the film temperature _{(95-250 · Δn 1) ~ (} 130-250 · Δn 1) ℃ range (however, after [Delta] n ₁ is the longitudinal stretching, transverse direction (Showing the birefringence of the film before stretching)), longitudinal stretching so that Δn ₁ is 0.060 to 0.150, and then transverse stretching at 2.5 to 4.5 times, the product of each longitudinal and transverse stretching ratio is 18 times or more The present invention is directed to a method for producing a high-strength polyester film, wherein the film is longitudinally stretched again.

 Hereinafter, the present invention will be described in detail.

Polyethylene terephthalate (hereinafter abbreviated as PET) used in the present invention is a polyester containing at least 80% by weight of a terephthalic acid residue as an acid component and at least 80% by weight of an ethylene glycol residue as a glycol component. 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, the A film is usually preheated sufficiently to 100 ° C. or higher, and then subjected to a first stretching at a stretching ratio such that the birefringence Δn is 1.0 to 10 ^{−3 to} 2.5 × 10 ⁻² (hereinafter, this film is referred to as B- 1 film). The first stretch ratio at which Δn falls within the above range is 1.2 to 4.0 times, depending on the preheating temperature, and can be easily determined by a preliminary test. Δn of B-1 film
However, when it is less than 1.0 × 10 ⁻³ , even if the subsequent steps are optimized, the thickness uniformity is poor and the improvement in the longitudinal stretching ratio cannot be expected. On the other hand, if it exceeds 2.5 × 10 ⁻² , the progress of crystallization in the subsequent step is remarkable, and breakage during transverse stretching frequently occurs, and stable production conditions cannot be obtained. Δn of B-1 film
Is preferably in the range of 1.0 × 10 ^{−3 to} 1.0 × 10 ⁻² .

The number of stretching steps in the first stretching may be one, but of course two
Multi-stage stretching of more than one stage may be used. The number of steps for performing the first stretching depends on the intended first stretching ratio, but is usually 1 to 4
Steps, preferably 1 to 3 steps. Each stretching start point of the first stretching is preferably constituted by a driven non-adhesive roll and a non-adhesive nip roll, and it is preferable that the film does not fall below the glass transition temperature during the first stretching.

Without cooling the B-1 film obtained as described above to a glass transition temperature or lower, the birefringence is 3.0
The stretch ratio as × a 10 ^-2 to 8.0 × 10 ^-2 adjusted in the range of 1.1 to 3.5, the second stretched in one stage or multiple stages (hereinafter, referred to as the film and B-2 film). At this time, the temperature of the film is usually in the range of 100 to 130 ° C.

When the temperature of the film is lower than 100 ° C., the unevenness of the thickness of the stretched film is not improved. On the other hand, when the temperature exceeds 130 ° C., crystallization of the film proceeds, or the film surface is roughened,
It is not suitable because the lateral stretching property is deteriorated. Further, if the birefringence of the B-2 film is less than 3.0 × 10 ^−2, it is inappropriate because the thickness unevenness of the stretched film is not improved, and the birefringence of the B-2 film is 8.0 × 10 ⁻² . If it exceeds, the crystallization of the B-2 film proceeds excessively, and the effect of improving the uniformity of the thickness is rather weak, and the lateral stretchability is deteriorated. Preferably, it is in the range of 3.0 × 10 ^{-2 to} 6.0 × 10 ^-2 , more preferably 4.0 × 10 ^{-2 to} 5.5 × 10 ^-2 . The average refractive index () of the film thus obtained is 1.570-1.600.
Is preferably within the range. If it is less than 1.570, uniformity of the thickness cannot be obtained even if it is longitudinally stretched in the next step, which is not preferable. On the other hand, when it exceeds 1.600, the transverse stretchability is extremely deteriorated, which is not preferable.

The B-2 film thus obtained has a film temperature in the range of (95-250 · Δn ₁ ) to (130-250 · Δn ₁ ) ° C, preferably (105-250 · Δn ₁ ) to (120-Δn ₁ ). 250 ・ Δ
n ₁ ) ° C. (where Δn ₁ indicates the birefringence after stretching in the longitudinal direction of the film and before stretching in the transverse direction)
n ₁ is the third stretched in the longitudinal direction at the magnification becomes 0.060 to 0.150 (hereinafter, referred to as the film and B-3 film).

If Δn ₁ is less than 0.060, breakage occurs frequently during transverse stretching. On the other hand, if Δn ₁ exceeds 1.150, the film is likely to break during longitudinal stretching again, and it becomes difficult to collect the product. If the stretching temperature of the third stretching is outside the above-mentioned temperature range, the thickness unevenness worsens, which is not preferable.

B-3 film stretched longitudinally under the above conditions
By stretching by 2.5 to 4.5 times, a biaxially stretched film (hereinafter, this film is referred to as C film) is obtained.
The temperature at the time of transverse stretching is usually in the range of 90 to 150 ° C, preferably in the range of 100 to 130 ° C.

The obtained C film may be subjected to a heat treatment at 110 to 220 ° C. if necessary, and then longitudinally stretched again so that the product of each longitudinal and transverse stretching ratio becomes 18 times or more to obtain the high-strength polyester film of the present invention. . Re-longitudinal stretching in the present invention is 110
Preferably, the film is stretched 1.05 to 2.0 times at a film temperature of 200 ° C. If the stretching ratio is less than 1.05, a high-strength film cannot be obtained, and if it exceeds 2.0 times, the film breaks frequently, which is not preferable. The obtained film may be heat-treated at 130 to 250 ° C, but if necessary, may be subjected to re-lateral stretching before the heat treatment.

The high-strength film thus obtained has high productivity,
It has excellent film properties such as thickness uniformity, dimensional stability, lubricity and transparency, and can be applied to various known film applications. That is, it is suitable not only as a base film for a magnetic recording medium such as a magnetic tape and a base film for an electric insulator such as a capacitor but also as a packaging film.

The method of the present invention is particularly preferably 0.5 μm to 50 μm
Applied in the production of films of thickness. It is also preferable to improve the film properties by performing various surface treatments in the steps of the present method as necessary.

EXAMPLES Hereinafter, the present invention will be described in more detail with reference to Examples, but the present invention is not limited to the following Examples as long as the gist of the present invention is not exceeded.

 The method for evaluating the characteristics of the film is as follows.

(1) F ₅ value Co. INTESCO Ltd., tensile tester in Tesco model 20
Using a type 01, cut in the vertical direction of the film in a room adjusted to a temperature of 23 ° C and a humidity of 50% RH, length 50mm, width 15
The sample film of mm pulled at a rate of 50 mm / min in the longitudinal direction, the strength at 5% elongation was F ₅ value.

(2) Heat Shrinkage (%) The heat shrinkage was performed in a 100 ° C. atmosphere for 30 minutes in a tensionless state, and the length of the sample before and after the heat treatment was measured.

(3) Thickness unevenness F ⁵ (%) Measured along the longitudinal direction of the biaxially stretched film using a continuous film thickness measuring device manufactured by Anritsu Denki Co., Ltd. (using an electronic micrometer). It was calculated from:

(4) Birefringence Δn, average refractive index n Using an Abbe refractometer manufactured by Atago Optical Co., Ltd., the maximum value n _γ of the refractive index in the plane of the film, the refractive index n _β in a direction perpendicular thereto, and the thickness of the film Measuring the refractive index n _{α in the} direction,
The birefringence and average refractive index were determined from the following formula.

Example 1 Polyethylene terephthalate chip (intrinsic viscosity 0.60,
0.3% by weight of Al ₂ O _{3 having} an average particle diameter of 0.02 μm and an average particle diameter of 0.7 μm
0.3% by weight of calcium carbonate added during polymerization)
Was dried at 180 ° C. for 5 hours, extruded at 285 ° C. in a sheet form from a T-die, and cooled and solidified on a rotating drum maintained at 45 ° C. to obtain an unstretched amorphous film having a width of 350 mm. At that time, a known electrostatic adhesion method was used. The obtained amorphous film is stretched 1.6 times at 112 ° C. as the first stage in the longitudinal direction at the film temperature of 112 ° C. using the multi-stage nip roll peripheral speed difference, and then continuously as the second stage in the longitudinal direction. The film was stretched 3.1 times at a temperature of 110 ° C.

The birefringence of the film after the first stretching is 3.0.
× 10 ^-3 , and the birefringence of the film after the second stretching was 5.2 × 10 ^-2 . Without cooling the film thus obtained below the glass transition temperature, a film temperature of 78
° C and the third stage of longitudinal stretching was performed at 1.53 times. The birefringence of the obtained vertically stretched film was 0.120.

Then stretched 3.8 times in the transverse direction at 102 ° C in a tenter, 130
After heat setting at 125 ° C, the film was further stretched 1.2 times at 125 ° C,
Tensile heat fixing was performed at 0 ° C. to obtain an 8 μm film.

Example 2 An 8 μm film was obtained in the same manner as in Example 1 except that the re-longitudinal stretching ratio was changed to 1.5 times.

Example 3 An 8 μm film was obtained in the same manner as in Example 1 except that the re-longitudinal stretching ratio was changed to 1.7 times.

Example 4 The film after the longitudinal stretching in Example 1 was again heated at 180 ° C. to 1.14.
The film was stretched twice and stretched and heat-set at 200 ° C. to obtain a 7 μm film.

Table 1 summarizes the properties of the obtained films.

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

 ──────────────────────────────────────────────────続 き Continuation of front page (72) Inventor Takatoshi Miki 5-8, Mitsuya-cho, Nagahama-shi, Shiga Prefecture Inside of Product Research Laboratory of Diafoil Co., Ltd. (56) References JP-A-2-175130 (JP, A) JP-A-2-130125 (JP, A) JP-A-63-178143 (JP, A) JP-A-61-167531 (JP, A) JP-A-61-47235 (JP, A) JP-A-60-176743 (JP , A)

Claims (1)

(57) [Claims] 1. A film in a substantially amorphous state containing polyethylene terephthalate as a main component, and a film having a birefringence of from 1.0 × 10 ^{−3 to} 2.5 × 10 ⁻² in a longitudinal direction of 1.2 to 10 × 10 ^−2.
The film is stretched at 4.0 times in one step or multiple steps, and without cooling the film temperature below the glass transition point, at 1.1 to 3.5 times so that the birefringence of the film becomes 3.0 × 10 ^{-2 to} 8.0 × 10 ^-2. The film is stretched longitudinally in one step or multiple steps, and the film temperature is set to (95-250 · Δn
₁ ) to (130−250 · Δn ₁ ) ° C. (however, Δn ₁ indicates the birefringence of the film after stretching in the machine direction and before stretching in the transverse direction) so that Δn ₁ is 0.060 to 0.150. Stretch longitudinally,
A method for producing a high-strength polyester film, comprising: horizontally stretching at 2.5 to 4.5 times, and then vertically stretching again so that the product of each longitudinal and transverse stretching ratio becomes 18 times or more.