JP2002192609A - Manufacturing method of biaxially oriented polyester film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide the manufacturing method of a biaxially oriented polyester film, excellent in the stability of size and reduced in the physical property difference of widthwise direction. SOLUTION: The manufacturing method of the biaxially oriented polyester film is characterized in heating the end part of the film immediately before the orientation in the lengthwise direction of the same.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a biaxially stretched polyester film having at least excellent dimensional stability and a small difference in physical properties in the width direction.

[0002]

2. Description of the Related Art Biaxially stretched polyester films are widely used as base materials for magnetic recording, electronic and electric materials, and various packaging materials because of their excellent mechanical strength and thermal dimensional stability. .

[0003] Generally, a biaxially stretched polyester film is stretched in the longitudinal direction by using a difference in roll speed by passing between a plurality of rolls having different speeds, and then stretched in the width direction by a tenter type transverse stretching machine. It is manufactured by a sequential biaxial stretching method in which heat setting is performed.

However, it is extremely difficult to make the physical properties of the product film in the width direction uniform by the conventional manufacturing method. The reason is that both ends of the film are gripped by clips in the transverse stretching device in the stretching process, and the longitudinal stretching stress generated by the widthwise stretching and the shrinkage stress generated by heat, and the shrinkage stress generated by the heat fixing process Is restrained at the edge of the film by a clip which is a gripping means, whereas the central portion of the film is less affected by the gripping means and has a weaker binding force, and is gripped by the clip due to the above-described stress. This is because the center portion of the film is delayed with respect to the edge. And, in the case where the stretching in the width direction and the heat setting are continuously performed by the same transverse stretching device, if a straight line is drawn along the width direction on the surface of the film before entering the transverse stretching device, the straight line becomes the transverse stretching. The film is deformed in the apparatus and deforms into a convex shape in the region at the beginning of the stretching process with respect to the traveling direction of the film. Furthermore, in the region of the heat-setting step, the concave deformation reaches a maximum value, and the curve passes through the subsequent transverse stretching device without changing the curve, and the concave deformation remains in the film exiting the transverse stretching device.
This phenomenon is called a bowing phenomenon, which causes the physical properties of the film to be non-uniform in the width direction. Due to the bowing phenomenon, the film at both ends in the width direction has an orientation main axis inclined with respect to the longitudinal direction, and the angle of the orientation main axis tends to differ in the width direction. As a result, for example, the difference in the physical property value in the ± 45 ° direction from the vertical direction of the heat shrinkage differs in the width direction of the film. The bowing phenomenon causes troubles such as printing pitch deviation, unevenness, curling, meandering, and the like in a printing laminating process, a bag making process, and the like, for example, in packaging applications.

More specifically, as a conventional technique for providing a cooling step between stretching in the width direction and heat setting, Japanese Patent Publication No.
Japanese Patent Laid-Open No. 11774 proposes a manufacturing method in which a relaxation step at 20 ° C. to 150 ° C. is interposed between the stretching in the width direction and the heat setting step, and a substantial cooling step is provided. However, the length of this cooling step is not described at all,
The effect of suppressing the Boeing phenomenon is completely unknown.

Further, as a technique for suppressing or eliminating the bowing phenomenon, Japanese Patent Application Laid-Open No. 50-73978 proposes a method for producing a film in which a nip roll group is provided between a stretching step and a heat fixing step. However, in this technique, since the temperature of the intermediate zone where the nip roll is installed is equal to or higher than the glass transition point, the rigidity of the film at the nip point is low, so that the improvement effect is small.

Japanese Patent Publication No. Sho 63-24459 proposes a process of forcibly advancing only a narrow area near the center by a nip roll while gripping both ends of the film after the transverse stretching. However, in this technique, it is necessary to install the nip roll in a high-temperature region in the horizontal stretching device, it is necessary to cool the roll and its peripheral devices, and since the film is at a high temperature, there is a possibility that the roll may be damaged, so that practical use is not possible. In terms of size.

Japanese Patent Publication No. Sho 62-43856 proposes a technique in which a film immediately after transverse stretching is cooled to a temperature not higher than the glass transition point, and then heat-fixed in multiple stages to simultaneously stretch in the width direction with heat fixing. I have. However, in this technique, the bowing phenomenon is less likely to be suppressed in the cooling step, or because the bowing phenomenon is likely to occur again in the heat setting, or in addition to the cooling step, a complicated step of multi-stage heat fixing and redrawing is required. Has become. Therefore, there is a concern that it may be difficult to stably control the atmospheric humidity and the film temperature in the horizontal stretching apparatus for a long time. In addition, this technology is also
As in JP-A-5-11774, the length of the cooling step is not described.

Japanese Patent Application Laid-Open No. 1-165423 proposes a technique in which a film after stretching in the width direction is cooled to a temperature not higher than the stretching temperature in the width direction, and then stretched again in the width direction while increasing the temperature in multiple stages. However, with this technology,
As in the case of JP-A-43856, it may be because the effect of suppressing the bowing phenomenon in the cooling step is small, or because the bowing is likely to occur in the heat fixing step, or in addition to the cooling step, the step of performing heat fixing in multiple stages and re-stretching. And a complicated process. For this reason, there is a concern that it may be difficult to stably control the ambient temperature and the film temperature in the horizontal stretching apparatus for a long time. Further, it is described that the cooling temperature is preferably equal to or higher than the glass transition point and equal to or lower than the stretching temperature. However, when the length of the cooling step or the temperature of the cooling step is equal to or higher than the glass transition point, there is a fear that the effect of suppressing the bowing phenomenon is small, and it is presumed that the above complicated steps have to be adopted. You.

Japanese Patent Publication Nos. Hei 25-25694 and Hei 1-262569 propose a technique in which the running direction of a film is reversed to perform transverse stretching and heat fixing.
However, in this technique, it is necessary to take up the film once in order to reverse the running direction of the film, and there is a problem that productivity is limited because of the online manufacturing method.

Furthermore, Japanese Patent Application Laid-Open No. 32-183327 discloses that, after longitudinal stretching, when the film is transversely stretched by a transverse stretching device and heat-fixed,
A technique has been proposed in which a preheating step of setting a temperature between a glass transition point and a heat setting temperature only at a side end portion between a horizontal stretching step and a heat setting step is performed. However, in this technique, since it is necessary to control the temperature of the preheating step while providing a temperature gradient in the width direction, there is a concern that it may be difficult to control the film temperature for a long time. In the embodiment of this technique, since the length of the preheating step is as short as half of the film width, it is presumed that the effect of suppressing the bowing phenomenon is small.

Further, Japanese Patent Publication No. 2-44976 discloses that
A heat treatment method has been proposed in which the heat setting step is divided into two stages, and a temperature distribution is imparted in the film width direction in the second stage. However, although this technique is effective in suppressing the bowing phenomenon that occurs in the heat treatment step, it does not have the effect of suppressing the bowing phenomenon that occurs in the stretching step, and it is estimated that the effect of suppressing the bowing phenomenon finally obtained is small. .

[0013] Further, in order to solve this problem, a device relating to a width stretching method and a heat fixing method has been proposed, but it is not sufficient. (JP-A-1-150521, JP-A-57
-87331)

On the other hand, in the conventional method for producing a biaxially stretched polyester film in the longitudinal direction, the film is stretched in a longitudinal direction by preheating the film to a temperature near its softening temperature and intersecting the film moving direction between rolls having different speeds. A method is known in which a film is stretched in the longitudinal direction by utilizing a difference in speed of a roll while heating a film to a stretching temperature by a near-infrared heater arranged in the above.

When the film is stretched in the longitudinal direction using the above-mentioned conventional technique, a difference in physical properties occurs between the center and the end of the film in the width direction. Further, the biaxially stretched polyester film obtained by stretching the film in the width direction is in the center. The difference in physical properties at the edges was enlarged, and there was a problem that the films at the edges had distortion in physical properties such as heat shrinkage. In particular, in a large-scale process (for example, an actual production machine), the above-mentioned problem was remarkable.

[0016]

SUMMARY OF THE INVENTION The present invention has been made in order to solve the above-mentioned problems, and it is intended to reduce the bowing phenomenon so that the film at the center and at the end of a biaxially stretched film stretched in the width direction. It is an object of the present invention to provide a method for producing a biaxially stretched polyester film having a small difference in gender and a small distortion of the film at the end.

[0017]

Means for Solving the Problems The inventors of the present invention have made intensive studies to solve the above-mentioned problems, and as a result, have reached the present invention. That is, the method for producing a biaxially stretched polyester film of the present invention is a method for producing a biaxially stretched polyester film, which comprises heating the film end just before stretching in the longitudinal direction. In this case, the thickness is
It is preferable to heat a position in the width direction that is 1.1 times or more.

In this case, in addition, 30 to 10 before the stretching point
It is preferable to heat the 00 mm position with a hot air fan.

Further, in this case, it is preferable to cool the heated position of the uniaxially stretched film immediately after stretching in the longitudinal direction with a cool air fan.

[0020]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail.

The polyester used in the present invention includes polyethylene terephthalate, polybutylene terephthalate,
Polyesters such as polyethylene naphthalate, and mixtures or copolymerized polyesters thereof may be used. As the polyester, a polyester composition containing additives such as an organic or inorganic lubricant, an antioxidant, a heat stabilizer, an ultraviolet absorber, and an antistatic agent is used as long as the effects of the present invention are not impaired in addition to the above polyester. be able to.

The polyester of the present invention is supplied to a well-known melt extruder represented by an extruder, and is heated and melted at a temperature not lower than the softening point of the polyester. The melted composition is extruded from a slit die such as a T die, adhered on a cooling roll, and cooled and solidified to obtain a substantially non-oriented polyester film. By supplying the substantially non-oriented polyester film between a plurality of rolls,
A uniaxially stretched film continuously stretched in the longitudinal direction is obtained.
That is, a plurality of rolls set to low peripheral speed rotation (hereinafter referred to as
The film is passed through a set of rolls set to a high peripheral speed rotation, and the film is stretched in the longitudinal direction by applying tension to the film by a speed difference between the respective roll groups.

At this time, the end of the film is heated just before the stretching section between the last roll of the roll group set to the low peripheral speed rotation and the first roll of the roll group set to the high peripheral speed rotation. Provide means. The position and width at which the means for heating the edge of the film are arranged are such that the thickness of the edge of the non-oriented film is larger than the thickness of the central portion so that the film can be easily gripped by the clip in the transverse stretching step. The position and width corresponding to the part where it is located is suitable. At this time, it is preferable to heat a position where the thickness is 1.1 times or more of the center. further,
It is preferable to heat 1.3 times or more positions. The reason for this is that the temperature is less likely to increase in a portion thicker than the center. The means for heating the edge of the film may be located on one or both sides of the front and back surfaces of the film.

Various heat sources such as hot air, a roll, a near-infrared heater, and a far-infrared heater can be used as the means for heating the film edge. Further, a shielding plate may be provided at the center of a long heater capable of heating the entire film in the width direction. The method of the present invention, when stretching a substantially unoriented polyester film in the longitudinal direction,
Preferably, the uniaxially stretched film after stretching in the longitudinal direction has a heat shrinkage stress in the longitudinal direction of 6.0 N / mm ² or less in the entire width and a difference in heat shrinkage stress in the longitudinal direction in the width direction of 10% or less. At this time, the effect of suppressing the bowing phenomenon of the biaxially stretched film after the uniaxially stretched film is stretched in the width direction and thermally fixed is large. The heating of the film edge is preferably performed so that the film temperature is higher by 1 to 10 ° C. than the center. The reason for this is that by making the temperature higher than the central portion, it is possible to reduce the difference in the width direction of the heat shrinkage stress in the longitudinal direction of the film after uniaxial stretching.

The method of the present invention may be either one-stage stretching or multi-stage stretching in which two or more stages are stretched in the longitudinal direction. However, it is effective when used in a one-stage stretching method having a large difference in physical properties in the width direction. .

The uniaxially stretched film obtained by the above method is converted into a biaxially stretched film by using a conventional transverse stretching apparatus for preheating, stretching in the width direction, heat setting, and cooling. At this time, since the oblique difference in the heat shrinkage of the biaxially stretched polyester film is affected by the transverse stretching condition and the heat setting condition, the condition can be appropriately selected by a known method.

[0027]

When a substantially non-oriented polyester film is stretched in the longitudinal direction, a difference is generated in the heat shrinkage stress between the center and the end of the film after uniaxial stretching. By stretching the uniaxially stretched film in the width direction, the difference in physical properties between the center and the end of the biaxially stretched film is enlarged. Therefore, when the film is stretched in the longitudinal direction, by heating the end portion of the film just before the stretching point in the longitudinal direction, the bowing phenomenon of the biaxially stretched film after stretching the uniaxially stretched film in the width direction and thermally fixing the film can be suppressed. At the same time, the difference in the heat shrinkage in the width direction can be reduced, and as a result, the oblique difference in the heat shrinkage can be reduced.

[0028]

Next, the present invention will be described in detail with reference to examples. In addition, the measuring method used for evaluation of an Example and a comparative example is as follows.

1. Heat shrinkage The film at the center of the film and 45% apart from the center on both sides in the width direction (assuming the total width of the film is 100%). ,
After cutting to a length of 200 mm in the length direction and measuring the dimension (L ₀ ) between the marked lines accurately with a scanning microscope,
After placing the film in the oven for 30 minutes and taking out the film from the oven, leave it in an atmosphere of 23 ° C. x 65% RH for 15 minutes or more to reach a balance, then measure the dimension (L ₁ ) between the marked lines Was determined from the following equation. Heat shrinkage (%) = [(L ₀ −L ₁ ) / L ₀ ] × 100

2. Oblique difference in thermal shrinkage ratio 45% in the width direction (assuming the total width of the film as 100%) in the width direction on both sides from the center and the edges, that is, the center, of the film.
The heat shrinkage in the 45 ° and 135 ° directions was measured, and the difference was determined. Measurement sample is 15mm wide x length along the above diagonal direction
Cut to a size of 200mm, put in an oven at 150 ° C for 30 minutes, take out the film from the oven, leave it in an atmosphere of 23 ° C x 65% RH for 15 minutes or more, measure the dimensions, The shrinkage relative to the dimensions was determined. The absolute value of the difference in the shrinkage in each oblique direction was defined as the oblique difference in the heat shrinkage. Problems such as a film having a large difference in thermal shrinkage having a large difference in heat shrinkage tend to curl when exposed to a high temperature.

3. Heat shrinkage stress The film after uniaxial stretching at a position 45% apart from the center and both ends from the center, that is, both sides from the center (assuming the total width of the film is 100%), is placed in an atmosphere of 23 ° C x 65% RH. Then, it was cut to a size of 4 mm in the width direction and 10 mm in the longitudinal direction, and the thickness T (mm) was measured. Seiko Electronics Industries
The heat shrinkage force G (N) was measured by heating at 5 ° C./min while fixing the length by using Model SSC-5200, and the heat shrinkage stress was determined by the following equation. Heat shrinkage stress (N / mm ² ) = G / (4 × T)

(Examples 1, 2, 3, 4) A polyethylene terephthalate pellet (intrinsic viscosity: 0.62) containing 0.1% by weight of a sufficiently dried inorganic lubricant was supplied to an extruder, melted at 285 ° C., and then melted by a T-die. It was extruded into a film shape, electrostatically contacted with a cooling roll using an electrode to which a high DC voltage was applied, and solidified by cooling to obtain a non-oriented film having a thickness of 200 μm. In order to make it easy to hold the film on the clip in the transverse stretching process, the thickness of the end of the non-oriented film is the same as the thickness of the center.
1.5 times. This non-oriented film is shown in Fig. It was led to a longitudinal stretching device shown in FIG. This apparatus includes low-speed rotating rolls 1a to 1c and high-speed rotating rolls 2a to 2c, and an infrared heater-A is installed between the low-speed rotating roll 1c and the high-speed rotating roll 2a. A hot-air fan heater-B for heating only the end of the film between the near-infrared heater-A and the low-speed rotating roll 1c, and a cooling fan for cooling only the heated end portion on the high-speed rotating roll 2a are provided. The surface temperature of the low-speed rotating rolls 1a to 1c is set to 76 ° C., and the surface temperature of the high-speed rotating rolls 2a to 2c is set to 25 ° C. The output of the near-infrared heater-A is set to 17KW. It is possible to change the temperature of the low-speed rotating roll and the high-speed rotating roll, the output of the near-infrared heater-A, the near-infrared heater-B, and the output of the cooling fan.

After pre-heating the non-oriented sheet with the low-speed rotating rolls 1a to 1c (surface temperature of 76 ° C.), the hot air fan heater-B was used to heat only the end portion thicker than the center. The non-oriented film whose temperature in the width direction is uniform or whose edge is 0 ° C to 7 ° C higher than the center is further heated using a near-infrared heater-A (output 17KW) longer than the film width direction and 3.7 times longer. And cooled with a high-speed rotating roll (surface temperature 25 ° C.) and a cooling fan (temperature 15 ° C.) to obtain a uniaxially stretched film. Table 1 shows the hot air temperature of the hot air fan heater B and the presence or absence of cooling by the cooling fan.

(Comparative Example 1) The same as in Example 1 except that the hot air fan heater B1 and the cooling fan were not operated.

The ease of stretch film formation of these Examples and Comparative Examples was ranked as follows. ；: A film was formed without breaking. Δ: Breaked several times. ×: Breakage occurred frequently.

[0036]

[Table 1]

As can be seen from the examples, when the film is stretched in the longitudinal direction, the film is heated uniaxially so that the difference in heat shrinkage stress between the center and the edge in the width direction is reduced. The difference in physical properties between the center and the end of the biaxially stretched film after stretching could be reduced. Further, the breakage could be reduced by cooling the edge of the film heated immediately before stretching immediately after stretching in the longitudinal direction.

[0038]

According to the present invention, when the film is stretched in the longitudinal direction, the edge of the film is heated just before the stretching point in the longitudinal direction, so that the film at the center and the edge in the width direction after the stretching in the longitudinal direction is stretched. By reducing the difference in physical properties and stretching the uniaxially stretched film in the width direction, a biaxially stretched polyester film having excellent dimensional stability and a small difference in physical properties in the width direction could be produced.

[Brief description of the drawings]

FIG. 1 is a schematic view of a longitudinal uniaxial stretching apparatus for explaining a method for producing a biaxially oriented polyester film of the present invention.

[Explanation of symbols]

 1a Low peripheral speed rotating roll 1b Low peripheral speed rotating roll 1c Low peripheral speed rotating roll 2a High peripheral speed rotating roll 2b High peripheral speed rotating roll 2c High peripheral speed rotating roll 3 Film before longitudinal stretching 4 Film after longitudinal stretching 5 Near infrared heater-A 6 Hot air fan heater-B (end heating means) 7 Cooling fan

Claims (4)

[Claims] 1. A method for producing a biaxially stretched polyester film, comprising heating an end portion of the film immediately before stretching in the longitudinal direction. 2. The method for producing a biaxially stretched polyester film according to claim 1, wherein a position in a width direction having a thickness of 1.1 times or more from a central portion is heated. Production method. 3. The method for producing a biaxially stretched polyester film according to claim 1 or 2, wherein said polyester film has a thickness of from 30 to less than a stretching point.
A method for producing a biaxially stretched polyester film, characterized by heating a position of 1000 mm with a hot air fan. 4. The method for producing a biaxially stretched polyester film according to claim 1, wherein a heated position of the uniaxially stretched film immediately after stretching in the longitudinal direction is cooled by a cool air fan. A method for producing a biaxially stretched polyester film.