JP2569471B2 - Method for producing toughened polyester film - Google Patents

Description

The present invention relates to a method for producing a strengthened polyester film.

[Prior Art] As a method for producing a strengthened polyester film, for example, as disclosed in Japanese Patent Publication No. 35-5887,
A method of further stretching a film that has been biaxially stretched is known.

[Problems to be solved by the invention]

Recently, however, it has been desired to increase the redrawing ratio in order to obtain a film with higher strength. However, there is a drawback in that the conventional method cannot perform stable drawing and the product yield is significantly deteriorated. Was.

SUMMARY OF THE INVENTION An object of the present invention is to provide a method for producing a strengthened polyester film which can solve the above-mentioned drawbacks and can stably perform high-magnification redrawing.

[Means for solving the problem]

The present invention relates to a method for producing a film in which an unstretched film is stretched in a longitudinal direction (a film flow direction), then stretched in a transverse direction, and then re-stretched in at least one direction. Is lower than the temperature at the center of the film by 2 ° C or more, and the birefringence in the range of 10 to 150 mm from the gripping position toward the center of the film is 0.05 to
A method for producing a strengthened polyester film, characterized in that the film is stretched in the transverse direction so that the thickness is 0.20 and the average thickness in the range is 3 to 15 times the thickness at the center of the film.

The polyester used in the present invention is not particularly limited as long as it is a thermoplastic polyester obtained by polycondensation of an aromatic dicarboxylic acid (or an ester thereof) and a dioxy compound, but the effect of improving the stretchability according to the present invention is particularly remarkable. Polyethylene terephthalate, polyethylene
α, β-bis (2-chlorophenoxy) ethane-4,4 ′
Rigid polyesters having a glass transition point of 70 ° C. or higher containing dicarboxylate, polyethylene-2,6-naphthalate and the like as main components. Among them, polyethylene-α, β- Polyester containing bis (2-chlorophenoxy) ethane-4,4'-dicarboxylate as a main component.

The polyester used in the present invention may be blended with other polymers as long as the object of the present invention is not impaired, or may be an antioxidant, a heat stabilizer, a surface projection forming agent, a nucleating agent, an ultraviolet absorbing agent. An inorganic or organic additive such as an agent may be added in an amount that is usually added.

Although the melt viscosity of the polyester used in the present invention is not particularly limited, the melt viscosity is 500 to 20,000 poise, and
A range of 0 to 10,000 poise is particularly preferred because stretchability and Young's modulus of the obtained film are further improved.

The following method is effective for stably producing the biaxially stretched film used in the present invention.

The above-mentioned polyester pellets are extruded into a sheet using a known melt extruder, and cooled and solidified to produce an unstretched film.

The unstretched film is stretched 2.5 to 4.0 times, preferably 3.0 to 3.8 times in the longitudinal direction. When the stretching ratio is in the above range, a biaxially stretched film having a portion having a birefringence of 0.05 to 0.20 of 10 to 150 mm is easily obtained. The stretching temperature is Tg-20 ° C to Tg + 35, where Tg is the glass transition point of the polymer.
C. and the stretching speed are preferably in the range of 10 ³ to 10 ⁶ % / min.

Here, the crystallinity of this uniaxially stretched film is 15 to 30%.
This is preferable because a biaxially stretched film having a portion having a birefringence of 0.05 to 0.20 and a width of 10 to 150 mm is more easily obtained.

Next, the uniaxially stretched film is stretched 2.3 to 4.0 times, preferably 2.5 to 3.8 times in the width direction using a stenter. If the draw ratio (maximum width of the stenter / width of the entrance of the stenter) is within the above range, the portion with a birefringence of 0.05 to 0.20 is 10 to 150 mm.
It is easy to obtain a biaxially stretched film having a width and an average thickness of the portion being 3 to 1.5 times the thickness of the center of the film. As for the stretching temperature at this time, when the cold crystallization temperature of the polymer is Tcc, polyester having a difference between Tcc and Tg of less than 45 ° C is Tcc-15 ° C to Tcc + 15 ° C, and the difference between Tcc and Tg is 4 ° C.
The polyester having a temperature of 5 ° C. or more preferably has a range of Tcc−60 ° C. to Tcc.

In addition, the temperature of the clip must be Tg + 100 ° C or less, and the temperature of a portion within a range of 10mm from the clip holding position toward the center must be lower than the film center by 2 ° C, preferably 4 ° C, more preferably 10 ° C or more. . The stretching speed is preferably in the range of 10 ³ to 10 ⁵ % / min.

Next, the biaxially stretched film is relaxed in the width direction at a temperature in the range of 120 to 180 ° C. by 3 to 30% with respect to the original length, while being 0.5 mm apart.
After heat treatment for ~ 120 seconds, the part with birefringence of 0.05 ~ 0.20 becomes 10 ~ 1
50mm, and the average thickness of the part is 3mm at the center of the film.
It is easier to obtain a biaxially stretched film of up to 15 times.

Here, the biaxially stretched film has a birefringence of 0.05 to less from the clip holding position of the edge toward the center of the film.
A part in the range of 0.20 is 10 to 150 mm width, preferably 15 to 100 mm
It must have a width, more preferably a width of 20 to 80 mm. If the width of the portion is smaller than the above range, the stretchability when re-stretching the portion is not preferable, which is not preferable. On the other hand, if the width of the portion is wider than the above range, the width of the obtained strengthened film is reduced, and the production yield is undesirably reduced.

The average thickness obtained by continuously measuring the thickness in the above-mentioned range of birefringence is 3% of the thickness at the center of the film.
~ 15 times, preferably 3.5 ~ 12 times, more preferably 4 ~ 1
Must be 0 times. If this value is smaller or larger than the above range, the stretchability in the case of re-stretching becomes unfavorable because it becomes poor.

If the longitudinal refractive index ratio of the part of 5 mm from the edge gripping position of the edge of the biaxially stretched film toward the film center is in the range of 1.03 to 1.08 and the density index is in the range of 0.01 to 0.04. Is preferable because the stretchability of the film becomes even better.

In order to make the above description easy to understand, a description will be given with reference to the drawings schematically showing the gripping state of the clip.

FIG. 1 is a plan view of a state in which a clip is gripping a film, 1 is a clip, 4 is a film, and is a center of the film, especially a center in the width direction of the film.

FIG. 2 is a sectional view taken along the line AA 'in FIG.
Is the clip gripping position, W is the width of the portion where the birefringence is 0.05 to 0.20, and it is essential in the present invention that W is 10 to 150 mm. In addition, l ₀ is the thickness of the film center, W
It is essential in the present invention that the average thickness of the part having the width of 3 is ₃ to 15 times l0.

Next, the biaxially stretched film is stretched again in at least one of the longitudinal direction and the width direction. At this time, it is preferable that the stretching ratio α in the longitudinal direction and the stretching ratio β in the width direction satisfy the following expression, because the stretchability of the re-stretching is further improved.

2.2 ≦ α ² + β ² ≦ 8.0 For example, when re-extending only in the longitudinal direction, β
= 1.

The stretching temperature at this time is 120-200 ° C, and the stretching speed is 10
A range of ³ to 10 ⁶ % / min is preferred.

Next, if necessary, the re-stretched biaxially stretched film can be re-heat treated. The heat treatment conditions in this case are not particularly limited, but the temperature is 180 to 260 ° C., preferably 200 to 2 ° C.
A temperature of 40 ° C. for a time of 0.5 to 120 seconds, preferably 1.0 to 60 seconds is suitable from the viewpoint of the Young's modulus of the obtained film.

[Action]

As described above, the present invention specifies the physical properties of the edge of the biaxially stretched film in the vicinity of the clip holding position of the edge, so that the edge of the biaxially stretched film is less likely to break during re-stretching, and the following excellent effects are obtained. It is obtained.

〔The invention's effect〕

According to the production method of the present invention, when re-stretching a biaxially stretched film in at least one direction, even if the re-drawing ratio is increased, the film is hardly broken, and a film having a high Young's modulus can be produced stably with a high yield. It becomes possible. The resulting film is useful for magnetic tape bases and capacitors.

[Measurement and evaluation methods]

(1) Stretchability A re-stretching film-forming operation is performed continuously for 48 hours. The film is good in stretchability when the film tears during that time is in the range of 0 to 1 time, and is stretched when tears occur 2 or more times. It was judged as poor sex.

(2) Refractive index Using a sodium D line (wavelength: 589 nm) as a light source, the refractive index was measured using an Atsube refractometer. Use methylene iodide or a sulfur-methylene iodide solution as the mounting solution.
It was measured at 65 ° C. and 65% RH.

(3) Birefringence The refractive index in the longitudinal direction and the width direction of the sample was measured by the above-mentioned method, and the sample was defined as birefringence with a difference of (longitudinal direction-width direction).

(4) Longitudinal refractive index ratio The longitudinal refractive index (A) of the sample and the longitudinal direction of a non-oriented (amorphous) film made by quenching into 10 ° C water after melt-pressing by the method of (2) above. Index of refraction (B
Was measured, and A / B was taken as the longitudinal refractive index ratio.

(5) Density and density index Using a density gradient tube composed of carbon tetrachloride and n-heptane, the density of the sample (referred to as ρ) and a non-oriented (amorphous) film made by quenching in water at 10 ° C after melt pressing. (Ρ ₀ ) was measured, and ρ−ρ ₀ was used as the density index. The measurement was performed at 25 ° C. The crystallinity was calculated from the density.

(6) Melt viscosity Using a Shimadzu Koka type flow tester, 290 ° C, shear rate 2
It was measured at 00 sec ^-1 .

(7) Young's modulus of film Measured at 25 ° C. and 65% RH using an Instron type tensile tester according to the method specified in ASTM-D-882.

(8) Glass transition point Tg Cold crystallization temperature Tcc Measured using a DSC (differential scanning calorimeter) type II manufactured by PerkinElmer. The measurement conditions of the DSC are as follows. That is, 10 mg of a sample polymer is set in a DSC apparatus, melted at a temperature of (melting point + 30 ° C.) for 5 minutes, and then rapidly cooled in liquid nitrogen. The quenched sample is heated at a rate of 10 ° C./min, and the glass transition point Tg is detected. The temperature is further increased and the crystallization temperature from the glassy state is reached.
And

〔Example〕

Examples of the present invention will be described below, but the present invention is not limited to these examples.

Examples 1-2, Comparative Examples 1-3 Polyethylene α, β-bis (2-chlorophenoxy)
A pellet of ethane 4,4'-dicarboxylate (melt viscosity: 2600 poise) was dried under reduced pressure (3 Torr) at 180 ° C. for 3 hours. This is supplied to an extruder (screw diameter: 40 mmφ),
The film was melt-extruded at 300 ° C into a sheet, wound around a casting drum with a surface temperature of 20 ° C by an electrostatic application casting method, cooled and solidified, and an unstretched film having a thickness of about 105 μm at the center of the film was produced. The unstretched film is stretched at a stretching temperature of 115.
The film was stretched 3.4 times in the longitudinal direction at ° C. The stretching was performed by a difference in peripheral speed between two sets of rolls, and the stretching speed was 10,000% / min. Using this uniaxially stretched film with a stenter,
The film was stretched 3.8 times in the width direction at a stretching speed of 2000% / min. The stretching temperature was 130 ° C. However, the clip temperature is 50 ° C, and the temperature in the area of 10 mm from the clip gripper toward the center is 115 ° C.
A hot air shut-off plate and a clip cooling water device were provided in the stenter so that the temperature became ℃. Further, the biaxially stretched film was heat-treated at 160 ° C. for 10 seconds while relaxing in the width direction by 5% of the original length.

The biaxially stretched film thus obtained has a birefringence of 0.05 from the edge of the clip to the center of the film.
The width of the part in the range of .about.0.20 is 35 mm, and the average value of the thickness of this part is 65 μm.
It was doubled (Table 1 and Example 1).

In addition, various biaxially stretched films were produced by changing the film production conditions (Table 1, Example 2, Comparative Examples 1 to 3).

These films are stretched at a stretching temperature of 190 ° C in the longitudinal direction for 1.8
It was stretched twice. This stretching was performed by a difference in peripheral speed between two sets of rolls, and the stretching speed was 50,000% / min.

As shown in Table 1, the stretchability at this time was good when the production method was within the scope of the present invention (Examples 1 and 2).
A high-strength film with a high Young's modulus was produced stably. However, when the production method was outside the present invention, the stretchability was poor and stable production was not possible (Comparative Examples 1 to 4).
3).

Examples 3-4, Comparative Examples 4-6 Pellet of polyethylene terephthalate (melt viscosity: 1
(700 poise) was dried under reduced pressure (3 Torr) at 180 ° C. for 3 hours. This is supplied to an extruder (screw diameter: 40 mmφ),
The film was melt-extruded at 0 ° C into a sheet, wound around a casting drum having a surface temperature of 20 ° C by the electrostatic application casting method, cooled and solidified, and an unstretched film having a thickness of about 105 μm at the center of the film was produced.

This unstretched film is stretched at a stretching temperature of 80 ° C.
It was stretched twice. The stretching was performed by a difference in peripheral speed between two sets of rolls, and the stretching speed was 10,000% / min. The uniaxially stretched film was stretched 3.8 times in the width direction using a stenter at a stretching speed of 2000% / min. The stretching temperature was 90 ° C.
However, a hot air cut-off plate and a clip cooling water device were installed in the stenter so that the clip temperature was 50 ° C and the temperature in the area of 10 mm from the clip gripping position to the center of the stenter was 80 ° C. Further, the biaxially stretched film was heat-treated at 120 ° C. for 10 seconds while relaxing in the width direction by 5% of the original length.

The biaxially stretched film thus obtained has a birefringence of 0.05 from the edge of the clip to the center of the film.
The width of the part in the range of ~ 0.20 is 20 mm, and the average thickness of this part is 50 µm.
It was doubled (Table 2 and Example 3).

Further, various biaxially stretched films were produced by changing the film production conditions (Table 2, Example 4, Comparative Examples 4 to 6).

These films were stretched 1.5 times simultaneously in the longitudinal and width directions at a stretching temperature of 150 ° C. using a simultaneous biaxial tenter.

As shown in Table 2, the stretchability at this time was good when the production method was within the scope of the present invention (Examples 3 and 4).
A high-strength film with a high Young's modulus was produced stably. However, when the production method was outside the present invention, the stretchability was poor and stable production was not possible (Comparative Examples 4 to 5).
6).

[Brief description of the drawings]

FIG. 1 is a plan view showing a state in which the clip is gripping the film, and FIG. 2 is a sectional view taken along the line AA 'in FIG.
The numbers and symbols in the figure are as follows. 1: clip, 2: clip support, 3: clip upper holding plate,
4: Film: film center portion: clip gripping position, W: width of the portion of the birefringence 0.05 to 0.20, l _0: the thickness of the film center portion.

 ──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-55-37370 (JP, A) JP-A-55-34937 (JP, A) JP-A-58-224723 (JP, A) 35817 (JP, U)

Claims (1)

(57) [Claims] An unstretched film is stretched in the machine direction, stretched in the transverse direction, and then re-stretched in at least one direction. Temperature lower than 2 ° C and move 10 to 15 from the gripping position toward the center of the film.
Strengthened polyester characterized in that it has a birefringence of 0.05 to 0.20 in a range of 0 mm and is stretched in the transverse direction so that the average thickness in the range is 3 to 15 times the thickness of the center of the film. Film manufacturing method.