KR19990057623A - Method for producing biaxially stretched polyester film - Google Patents

Abstract

The present invention is carried out by dividing the melt-extruded plate-like film successively biaxially stretched to produce a biaxially stretched polyester film, divided into three stages of longitudinal stretching, but immediately after the third and transverse stretching in the longitudinal direction and 5 However, by providing a three-dimensional birefringence system at three points in the width direction immediately after the heat-setting part, the process conditions are checked in real time, and then fed back to provide a manufacturing method of the biaxially stretched polyester film characterized in that the process conditions are continuously controlled. According to the present invention, it is possible to reduce the variation of the mechanical properties in the width direction through the real-time measurement of the orientation, and ultimately to improve the quality uniformity of the final product, and to improve the productivity by reducing the breaking rate and the defective rate. .

Description

Method for producing biaxially stretched polyester film

The present invention relates to a method for producing a biaxial stretching polyester film, and more particularly, in the production of a polyester film by successive biaxial stretching by a tenter method, in the longitudinal stretching process, the longitudinal stretching portion and the heat-extracting part The 3D birefringence system is installed at the 3 points in the width direction immediately after the opening and the 5 stage heat-setting, and the orientation is measured in real time, and the process conditions are adjusted based on this to suppress bowing phenomenon occurring in the stretching process. A method for producing a biaxially stretched polyester film having uniform physical properties in the width direction.

Polyester films are widely used as substrates for packaging, magnetic recording media, labels, capacitors, and photographic films because of their excellent electrical, mechanical, and thermal properties and good processing properties.

In general, polyester film is melt-extruded by an extruder to successively stretch the cast film in the machine direction (MD) and transverse direction (TD) to cause molecular orientation, and then heated to a temperature higher than the stretching temperature By crystallization to stabilize heat shrinkage.

As a conventional method for producing a polyester film, a cooling roll is provided between a transverse stretching portion of a tenter and a heat-exiting part to cool to a temperature below the glass transition temperature (70 to 80 ° C.) of the biaxially stretched polyester film. There is a manufacturing method (Domestic Patent Publication No. 97-10077). Specifically, in this method, the transversely stretched film in the tenter's transverse stretching process has the length of the cooling zone in the tenter greater than the length of the heat-setting zone, and the maximum temperature of the heat-setting zone is 50 ° C or more higher than the transverse stretching temperature. The length of the area should be less than half of the total tenter length. However, this method has a limit to vary the amount of bowing distortion in a thermal manner by providing a cooling zone below the glass transition temperature.

Another method (Korean Patent Publication No. 96-37255) is a thermoplastic in a longitudinal drawing machine including a plurality of pre-rolls and a plurality of cooling rolls in a step of melting, extruding and cooling a polyester resin chip to produce a thermoplastic sheet. Stretching the resin sheet in the longitudinal direction and the method of stretching by maintaining the temperature of the first cooling roll of the plurality of cooling rolls 30 to 50 ℃ lower than the transition temperature of the resin. Films produced by this method have reduced neck-in, and thus have uniform physical properties in the transverse direction. However, in the case of producing the polyester film by this method, since the longitudinally oriented crystals are laterally aligned faster than the amorphous chain during the lateral stretching of the continuous process, the tension applied to the film immediately after the cooling immediately before stretching is shown in FIG. 3. As shown, a phenomenon occurs that is the lowest in the center and increases toward the end. In proportion to this, a deviation occurs in the transverse mechanical properties from the center to the end. This difference in physical properties impairs the appearance of the final product and thus becomes a barrier to lowering the value of the product.

It is therefore an object of the present invention to provide a method for producing a biaxially stretched polyester film having uniform mechanical properties in the width direction to overcome the problems of the prior art as described above.

That is, in the present invention, the longitudinally stretched and lateral stretched melt-extruded plate-like film to produce a biaxially stretched polyester film, the longitudinal stretching process is carried out in three stages, but the third stretching portion in the longitudinal direction and the transverse stretching portion Providing a method for producing a biaxially stretched polyester film, characterized in that a three-dimensional birefringence system is installed at three points in the width direction immediately after the drawing to check process conditions in real time, and then feedback the same to continuously control the process conditions. It is.

1 is a schematic diagram of a polyester film three-stage longitudinal stretching apparatus of the present invention,

Figure 2 is a schematic diagram showing the installation position of the three-dimensional birefringence system in the longitudinal stretching process of the present invention,

3 is a diagram illustrating the distribution of the force in the width direction in the lateral stretching step.

* Description of the symbols for the main parts of the drawings *

V1, V2, V3 and V4: speed of nip rolls

BR1, BR2, BR3 and BR4: birefringence system

BR1-1, BR1-2, BR1-3: birefringence meter installed at three points in the width direction

Hereinafter, the present invention will be described in more detail with reference to the accompanying drawings.

The method for producing a biaxially stretched polyester film according to the present invention is as follows. First, the polyester raw material in the intrinsic viscosity range of 0.5 to 0.8 g / dl is sufficiently dried, then transferred to an extruder, heated, melted and mixed at a temperature of 280 to 290 ° C., filtered in a filter, and quantified by a gear pump to obtain a gap. Extrude through an adjustable slit die. Subsequently, the molten polymer is quenched on a rotating cooled casting drum maintained at a temperature below the glass transition temperature to prepare an unstretched sheet. At this time, it is preferable to adhere the sheet to the grounded drum according to the electrostatic bonding method. The sheet is in a randomly oriented state in which moderate isotropic strength is imparted to the polymer chain appropriately and its thickness is preferably 300 μm or less.

The unstretched sheet thus obtained was passed through a preheat roll group maintained at 80 to 100 ° C. and stretched in the longitudinal direction (MD) in three stages by two or more continuous nip rolls [V1 to V4]. (See FIG. 1). Each successive nip roll rotates at a speed faster than the speed of the immediately preceding roll, and stretching is performed by the speed difference between the low speed roll and the high speed roll (V1 <V2 <V3 <V4).

In this longitudinal stretching step, longitudinal stretching is performed 3.5 times to 5.5 times the original length, the distance between the total stretching sections is 100 to 500 mm, and the stretching temperature is performed at 110 to 130 ° C. Specifically, as illustrated in FIG. 1, the draw ratio of the first stage longitudinal stretching process is 1.2 to 2.0 times, the stretching temperature is 110 to 130 ° C., and the draw ratio of the second stage longitudinal stretching process that is the diagonal stretching process between the vertices of the roll is 1.4 to 3 times, the stretching temperature is 110 to 130 ℃, the draw ratio of the third stage longitudinal stretching process is 2.0 to 3.0 times.

The present invention is carried out by dividing the longitudinal stretching process into three stages in order to improve the deviation of the mechanical properties between the central portion and both ends of the width direction of the full width film, but immediately after the third stretching portion in the longitudinal direction and the transverse stretching portion (BR1). ) And the three-dimensional birefringence system at three points in the width direction immediately after the five-stage opening and closing (BR2), and check the process status in real time, and then feed it back to adjust the process conditions to the width direction of the film. It is characterized by making anisotropy uniform.

In the present invention, the position where the birefringence system is installed is not particularly limited. Preferably, one position is provided at the center portion, and it is preferable to install at the portion close to both ends where the physical property deviation in the width direction occurs most severely. Preferably, as shown in Figure 2, when the total width is set to 100% it is good to install at three points 10%, 50%, 90% from the left.

The film longitudinally stretched in the above-described manner is once cooled to below the glass transition temperature and then preheated to 95-120 ° C. in a tenter and stretched in the transverse direction at 3 to 5 times the original width in the transverse stretching area. The mechanical properties of this biaxially stretched film are anisotropic with increased force in the film plane.

Subsequently, the biaxially stretched film is heat-treated for 1 to 30 seconds at a temperature range of 160 to 230 ° C., more specifically, 180 to 210 ° C. in the heat setting region of the same tenter, and the first stage is 160 to 180 ° C. , The second and third stages are controlled between 200-230 ℃ and the fourth and fifth stages between 160-205 ℃, and the birefringence meter BR2 is installed in the same direction as BR1 at the position immediately after the five-stage opening and closing. Anisotropy is measured in real time. In this heat setting process, the degree of crystallinity is greatly increased to improve strength, dimensional safety, and the like, and if necessary, the stretched film is relaxed 0.5 to 10% in the transverse direction during the heat treatment or rolls only after the heat treatment to satisfy specific required properties. It is possible to relax 0.05 to 3% in the longitudinal or transverse direction before winding up.

The heat treated film is then cooled to room temperature in order to frozen-in the microstructure, exiting the tenter, trimming the end gripped with grips and winding up in a mill roll. The mill roll is hung on a slitter and cut to the required length and width.

The birefringence (Birefringence) used in the present invention is measured by the intensity of light absorbed after parallel light is incident on the optical axis while rotating the optical plane about the optical axis, that is, the phase difference of optical light in two directions. It is a method of evaluating orientation three-dimensionally by the difference of refractive index. This method measures the basic properties of the film and the degree of bowing distortion from each other's relations, using ① anisotropy, ② 3D birefringence, orientation angle, and ③ plane orientation and phase difference as the important measurement items. Thus, when a difference in physical properties in the width direction of the film is detected, it can be immediately alleviated. The above measuring method is applicable to magnetic base films, shrink films, optical function films, and other general purpose films.

Conventional cooling roll control method wastes a lot of time to feed back the process conditions and causes many defects between sampling cycles, but the film produced by the present invention can be obtained by confirming the orientation of the film in real time in the orientation. The factor can be minimized.

In producing the biaxially stretched polyester film according to the present invention, both the tenter method and the blown film method are possible, but the tenter method is more practical and suitable. In addition, as the opacity increases, the surface orientation tends to be negative, and a film with high transparency shows relatively higher accuracy than a low film. Therefore, the present invention is more suitable for films having a haze of 5 or less in the tenter film and having high transparency.

One surface of the polyester film of the present invention by corona discharge treatment or inline coating in order to impart surface properties such as adhesion, peeling property, antistatic property, and active activity required for various uses of the polyester film of the present invention. Alternatively, functionality may be imparted or layers may be formed on both surfaces. The biaxially stretched polyester film produced by the present invention can be used in various applications, but is particularly suitable for packaging and porcelain use.

Hereinafter, the present invention will be described in more detail with reference to Examples, but the present invention is not limited by the following Examples.

Example 1

The sufficiently dried polyester chip was melt extruded at 280 ° C. and cooled and solidified on a casting drum using an electrostatic bonding method to prepare an unstretched sheet, which was preheated, three-stage longitudinal stretch, transverse stretch and heat set to prepare a biaxially stretched film. . At this time, the longitudinal drawing process has a total draw ratio of 3.5 to 5.0 times, a drawing temperature of 110 to 130 ° C., a drawing ratio of 1.2 to 2.0 times of drawing, and a drawing temperature of 110 to 130 ° C., and a draw ratio of 1.4 to 3 times. The second stage longitudinal stretching process, which is the diagonal stretching process between the vertices of the rolls, and the third stage longitudinal stretching process having the stretching temperature of 110 to 130 ° C. and the stretching ratio of 2.0 to 3.0 times were carried out continuously. At this time, as shown in Figs. 1 and 2, the width direction becomes 10%, 50%, 90% from the left when the total width of the third longitudinal stretching portion and immediately after the transverse stretching portion BR1 is 100%. A three-dimensional birefringence system was installed at three points BR1-1, BR1-2, and BR1-3 to make the anisotropy uniform in real time.

The heat setting region was carried out in a temperature range of 180 to 210 ℃, the first stage is 160 to 180 ℃, the second and third stages were controlled between 200 to 230 ℃, the fourth and fifth stages 160 to 205 ℃. At this time, a three-dimensional birefringence system was installed at the position (BR2) immediately after the five-stage heat-setting section, which is the third region of the heat setting, to measure the lateral anisotropy in real time.

The heat-set film was cooled, trimmed, and wound to prepare a biaxially stretched polyester film, and the mechanical properties thereof were evaluated. The results are shown in Table 1 below.

Comparative Example 1

A biaxially stretched polyester film was prepared in the same manner as in Example 1 except that the position of the three-dimensional birefringence system was changed to immediately after preheating and transverse stretching (BR3), and the physical properties thereof were measured and the results are shown in Table 1 together. It was.

Comparative Example 2

Except for changing the position of the three-dimensional birefringence system immediately after preheating (BR4) to prepare a biaxially stretched polyester film in the same manner as in Example 1 and measured the physical properties and the results are shown in Table 1 together.

Left end Center Right end Breaking Strength (㎏ / ㎠) Elongation at Break (㎏ / ㎠) n Breaking Strength (㎏ / ㎠) Elongation at Break (㎏ / ㎠) n Breaking Strength (㎏ / ㎠) Elongation at Break (㎏ / ㎠) n MD TD MD TD MD TD MD TD MD TD MD TD MD TD MT TD MD TD Example 1 26 25 125 124 1.684 1.671 27 26 133 134 1.741 1.748 25.5 25 130 133 1.679 1.689 Comparative Example 1 26 25 122 121 1.674 1.712 27 25 130 131 1.681 1.692 26 25 129 130 1.673 1.708 Comparative Example 2 27 24 123 123 1.657 1.687 28 25 131 131 1.694 1.677 26 24 128 129 1.585 1.614

[Measurement Method]

* Break strength and elongation at break were measured according to ASTM D882.

According to the present invention, it is possible to reduce the variation of mechanical properties in the width direction through real-time measurement of the orientation, and thus can improve the quality uniformity of the final product, and furthermore, it is effective in terms of quality improvement and reduction of defective rate. In addition to the above-mentioned applications, it is possible to apply a wide range of applications such as setting of drawing conditions and feedback on the influence of the process speed.

Claims (3)

In manufacturing biaxially stretched polyester film by sequentially biaxially stretching the melt-extruded plate film, the longitudinal stretching process is divided into three stages, but after the third longitudinal stretching section and the transverse stretching section, and the five-stage heat-opening section. A method for manufacturing a biaxially stretched polyester film, comprising: installing a three-dimensional birefringence system at three points in the width direction immediately after checking a process situation in real time, and then controlling the process conditions by feeding back the process conditions. The method of claim 1, wherein the three-step longitudinal drawing process is performed under the condition that the total drawing ratio of the longitudinal drawing process is 3.5 to 5.5 times, the total drawing section distance is 100 to 500 mm and the drawing temperature is 110 to 130 ° C. Method for producing a biaxially stretched polyester film, characterized in that. According to claim 1, wherein the heat-setting region is carried out in the range of 160 to 230 ℃, the first stage is 160 to 180 ℃, the second and third stage 200 to 230 ℃, the fourth and fifth stage is between 160 to 205 ℃ Method for producing a biaxially stretched polyester film characterized in that the heat setting by controlling.