KR100611846B1 - Biaxially oriented polyester film having improved properties and preparation thereof - Google Patents

Abstract

The present invention relates to a biaxially oriented polyester film having excellent physical properties and a method for producing the same, wherein the polyester film before and after the heat treatment satisfies specific conditions, and is prepared according to the present invention. The film is excellent in heat resistance, dimensional stability and smoothness, and can be usefully used for electrical and electronic materials or other industrial films.

Description

Biaxially Oriented Polyester Film With Excellent Physical Properties And Its Preparation {BIAXIALLY ORIENTED POLYESTER FILM HAVING IMPROVED PROPERTIES AND PREPARATION THEREOF}

The present invention relates to a biaxially oriented polyester film having excellent physical properties, in particular excellent in heat resistance, dimensional stability and smoothness, and a method for producing the same.

In general, biaxially oriented polyester films have excellent mechanical properties, heat resistance, moisture resistance, chemical resistance, and the like, and thus are widely used for magnetic, photographic, electrical insulation, electronic circuit boards, transparent conductive circuit boards, and other industrial materials. Is being used. In particular, for electronic circuit boards such as flexible printed circuit boards (FPC) or tape automated bonding (TAB), or for transparent conductive circuit boards such as touch screens or display electrode substrates, a film having extremely low heat shrinkage and excellent smoothness is required. However, since the conventional biaxially oriented polyester film cannot satisfy these required characteristics, a film which is subjected to heat treatment offline to increase dimensional stability is used.

In general methods of heat treating biaxially oriented polyester films, most heat treatments are performed using general polyester films. However, in general polyester films, heat shrinkage and heat resistance are not suitable for heat treatment. Temperature, tension, and processing time conditions of the heat treatment process are inadequate, resulting in high thermal shrinkage or smoothness of the film after heat treatment, which does not meet product quality and customer demand.

Accordingly, it is an object of the present invention to provide a biaxially oriented polyester film which is excellent in heat resistance, dimensional stability and smoothness and can be used stably even at high temperatures.

In order to achieve the above object, in the present invention, in the biaxially oriented polyester film heat-treated, the longitudinal thermal shrinkage (S) measured for the film before heat treatment satisfies the range of the following formula (1), for the film after heat treatment Provided is a film characterized in that the measured longitudinal thermal shrinkage (S ′) satisfies the range of Equation 5:

0.1 × 0.05 × e ^0.0185T ≤ S ≤ 0.05 × e ^0.0185T

0.1 × 0.002 × e ^{0.0265T '} ≤ S´ ≤ 0.002 × e ^0.0265T'

Wherein T and T 'are the heat shrinkage measurement temperatures in the range of 150 to 240 ° C. for the films before and after the heat treatment, respectively, and the heating time at each temperature is 30 minutes below 150 to 200 ° C. and 10 below 200 to 230 ° C. Minutes and 2 minutes at 230-240 degreeC.

Hereinafter, the present invention will be described in more detail.

The heat treated biaxially oriented polyester film of the present invention is characterized in that it has excellent smoothness and dimensional stability even after heat treatment performed at a high temperature by heat treatment at a specific condition with a specific range of heat shrinkage rate before heat treatment.

The biaxially oriented polyester film to be applied to the present invention is composed of a thermoplastic polyester mainly composed of an aromatic dicarboxylic acid component and a glycol component. As the polyester, polyethylene terephthalate or polyethylene naphthalate is particularly preferable.

The polyethylene terephthalate (PET) or polyethylene naphthalate (PEN) resin is prepared by a conventional method, for example, dimethyl terephthalate or dimethyl-2,6-naphthalate and ethylene glycol in a molar ratio of 1: 2. Stabilizers and polycondensation catalysts are added to the reaction product obtained by adding a catalyst containing a metal component such as manganese, potassium, lithium, calcium, magnesium, zinc, or esterification reaction of terephthalic acid or ethylene glycol in case of PET. After the addition, it can be prepared by condensation polymerization at a temperature of 260 to 300 ℃ and high vacuum conditions of 5 to 0.1 Torr.

In the polycondensation reaction, a stabilizer may be a phosphate-based compound such as trimethylene phosphate, and as a condensation polymerization catalyst, a catalyst containing a metal component such as titanium, germanium, tin, antimony, zinc, cobalt, manganese or calcium may be used. The polyester resin produced in this way preferably has an intrinsic viscosity of 0.5 or more.

The biaxially oriented polyester film is melt-extruded from the polyethylene terephthalate or polyethylene naphthalate resin by a T-die method to form an unstretched sheet, and then sequentially or simultaneously biaxially stretched in the longitudinal and transverse directions. It can be prepared by heat setting and cooling.

In the present invention, the stretching step is 2.5 to 3.8 times, preferably at a temperature of 30 ° C higher than the glass transition temperature (Tg) to the glass transition temperature of the unstretched sheet, preferably 10 to 20 ° C higher than the glass transition temperature. Longitudinally stretched from 2.8 to 3.5 times, and 3.3 to 4.5 times, preferably 3.5 to 4.3 times, at a temperature of 20 to 60 ° C. higher than the glass transition temperature of the unstretched sheet, preferably 20 to 50 ° C. higher than the glass transition temperature. It is preferably carried out by transverse stretching.

If the longitudinal stretching temperature is lower than the glass transition temperature of the unstretched sheet, whitening occurs in the sheet, the fracture is severe, and the heat shrinkage is high. If the stretching temperature is higher than 30 ° C., the adhesion to the stretching roll is severe. Stretching patterns may occur, or the orientation may be degraded due to relaxation of the oriented polymer chains, resulting in uneven thickness. In addition, when the longitudinal stretching ratio is less than 2.5 times, the orientation of the polymer chain is insufficient, so that the strength, heat resistance, durability, etc. of the film are deteriorated, or the stretching pattern is generated due to uneven stretching, or the thermal shrinkage ratio and thickness deviation are large. On the other hand, when the longitudinal draw ratio exceeds 3.8 times, the longitudinal heat shrinkage rate of the raw film becomes high, so that it is difficult to obtain a desired heat shrinkage rate after heat treatment of the film off-line.

On the other hand, when the lateral stretching temperature is lower than the glass transition temperature of the sheet by more than 20 ° C, the breakage becomes severe, the heat shrinkage rate increases, the bowing increases, and the deviation of the lateral heat shrinkage rate increases, and 60 ° C above the glass transition temperature. If too high, the degree of orientation drops due to the relaxation of the polymer chain, and the thickness in the transverse direction becomes uneven. In addition, when the transverse stretching ratio is less than 3.3 times, the orientation of the polymer chain is insufficient as in the longitudinal stretching, resulting in poor strength, heat resistance and durability of the film, incomplete stretching, resulting in an increase in thickness variation, and a transverse stretching ratio of 4.5. It is not good to exceed the ship because the lateral heat shrinkage rate increases and the breakage becomes severe and the process becomes unstable.

In the present invention, the heat setting step is an in-line process, it is preferably carried out at 220 to 260 ℃, preferably 230 to 250 ℃. When the heat setting temperature is less than 220 ℃ heat treatment effect is insufficient to increase the thermal shrinkage of the film, when it exceeds 260 ℃ is not good because the smoothness of the film is lowered and the thickness deviation is increased.

In the present invention, the cooling step is preferably performed at 100 to 200 ℃. If the cooling temperature is less than 100 ℃ or higher than 200 ℃ high temperature film is quenched or insufficient cooling causes wrinkles in the film.

The biaxially oriented polyester film prepared as above preferably has a thickness of 12 to 250 μm or less.

Such a polyester film according to the present invention has a longitudinal heat shrinkage rate (S) of the following Equation 1, thereby obtaining a very low heat shrinkage rate and excellent smoothness after a high temperature heat treatment later offline:

Equation 1

0.1 × 0.05 × e ^0.0185T ≤ S ≤ 0.05 × e ^0.0185T

Where T is the heat shrinkage measurement temperature in the range of 150 to 240 ° C. for the film before heat treatment, and the heating time (t) is 30 minutes (150 ° C. ≦ T <200 ° C.), 10 minutes (200 ° C. ≦) depending on the temperature conditions. T <230 ° C.) or 2 minutes (230 ° C. ≦ T ≦ 240 ° C.).

If the longitudinal heat shrinkage (S) of the film before heat treatment is greater than the upper limit, the heat shrinkage rate is increased after the film is heat treated, and the heat treatment temperature must be increased to lower the heat shrinkage rate to a desired level. Will not. On the other hand, when the heat shrinkage ratio (S) is smaller than the lower limit, the longitudinal stretching ratio should be lowered to less than 2.5, or the heat setting temperature should be increased to 260 ° C. or higher, so that a stretched pattern due to incomplete stretching and orientation may occur or the thickness deviation may increase. Not preferred.

In addition, the polyester film according to the present invention preferably has a deviation (ΔS) of the longitudinal heat shrinkage ratio before heat treatment in the range of 0.1 to 0.5. When ΔS is greater than 0.5, the film does not run correctly due to the large difference in shrinkage of the film during offline heat treatment, and the heat shrinkage ratio of the film increases even after heat treatment, which is not good, and ΔS is less than 0.1. This is not good because it may need to change the film manufacturing method and affect other properties of the film.

In the present invention, in order to use such a biaxially oriented polyester film fabric for a substrate such as an electronic circuit, after the cooling step, a heat treatment in a conventional high-temperature infrared radiation heating furnace or an air circulation heating furnace as an offline process, wherein the heat treatment conditions, such as The temperature, the holding time at the highest heat treatment temperature, and the tension applied to the film during the heat treatment must satisfy the following specific conditions.

T'-5 ≤ T _max ≤ T '+ 5

5 ≤ t _max ≤ 30

0.1 ≤ F ≤ 2

Where

T 'is the heat shrinkage measurement temperature in the range of 150 to 240 ° C for the film after heat treatment,

T _max is the maximum reaching temperature (℃) during heat treatment,

t _max is the holding time in seconds at the highest reaching temperature,

F is the tension (kgf / cm 2) at the highest reaching temperature.

The maximum temperature T _{max of} the film is the temperature of the film passing through the highest temperature section of the furnace and can be measured with a non-contact infrared radiation thermometer. When the maximum reaching temperature (T _max ) is higher than T '+ 5 ° C, the thermal shrinkage at the predetermined temperature (T') of the film after heat treatment is satisfied, but more than necessary heat is applied to the film, which increases the deformation of the film and decreases the smoothness. When the temperature is lower than T-5 ° C., the smoothness of the film is increased, but thermal shrinkage at a predetermined temperature T of the film after heat treatment may not be satisfied, and thermal stability is deteriorated.

Top of the film reach a temperature (T _max) when the holding time (t _max) is shorter than 5 seconds at the film in a heating furnace not received fully convey the amount of heat since the heat treatment is insufficient, the heat shrinkage ratio is higher. On the other hand, when it is longer than 30 seconds, the film slows down and the productivity decreases. In particular, when the maximum reaching temperature (T _max ) is higher than 200 ° C., oligomer generation is not good because the film surface is increased.

If the tension (F) applied to the film is less than 0.1 kgf / ㎠, the film is stretched in a high temperature heating furnace, and comes into contact with the equipment, causing surface damage or poor driving, resulting in meandering or less smoothness, and greater than 2 kgf / ㎠ In this case, the film is not sufficiently relaxed in the heat treatment process, so that the stress remains in the film, which is not good because the shrinkage of the heat-treated film is increased, or the longitudinal wrinkles in the film worsen the smoothness.

In the film heat-treated under the above conditions according to the present invention, the heat shrinkage rate S ′ measured in the same manner as in the heat shrinkage rate S performed on the film before heat treatment satisfies the condition of Equation 5 below. do:

Equation 5

0.1 × 0.002 × e ^{0.0265T '} ≤ S´ ≤ 0.002 × e ^0.0265T'

Where T 'is the heat shrinkage measurement temperature in the range of 150 to 240 ° C for the film after heat treatment.

The deviation DELTA S 'of the thermal contraction rate S' is in the range of 0.01 to 0.2.

If the longitudinal thermal shrinkage (S ′) of the film after heat treatment is greater than the upper limit, the longitudinal shrinkage is high and the dimensional deformation is severe, so it is not suitable as an electronic and electronic film material requiring high precision when used at high temperatures. In the smaller case, the biaxial draw ratio must be greatly reduced or the heat treatment temperature at the off-line must be greatly increased, so that the orientation of the film is insufficient, resulting in poor heat resistance or poor appearance due to thermal deformation of the film.

In addition, when the thermal shrinkage deviation (ΔS´) is greater than 0.2, when the heat-treated film is used at a high temperature, the shrinkage or deformation is locally changed to cause curvature and the like. It is not suitable as a material, and if it is smaller than 0.01, it is difficult to achieve in reality.

Thus, the film of the present invention having a specific range of heat shrinkage after offline heat treatment is excellent in both dimensional stability and smoothness at high temperature.

Hereinafter, the present invention will be described in more detail with reference to the following examples, but the present invention is not limited thereto, and the heat shrinkage and the smoothness of the films prepared in Examples and Comparative Examples of the present invention were measured by the following method. .

1) Heat Shrinkage

Film specimens of about 200 mm in length and 10 mm in width were placed in an air circulating oven maintained at a specific temperature T _sr (° C.) and heat-treated at no load for a specific time t _sr (min). The specimen was taken out of the oven and measured for a change in length after being left at room temperature for 1 hour to calculate a heat shrinkage percentage (%) according to the following equation (1).

Equation 1

Thermal contraction rate (%) = [(L ₀ -L) / L ₀ ] × 100

In the above formula, L ₀ and L are the lengths of the specimens before and after the heat treatment, respectively, and the heat treatment time t (minute) according to the temperature when measuring the heat shrinkage was as follows:

Heating time (t): 30 minutes (150 ° C ≤ T <200 ° C)

                10 minutes (200 ℃ ≤T <230 ℃)

                 2 minutes (230 ℃ ≤T ≤ 240 ℃)

The thermal shrinkage rate of the five film specimens was measured by the method described above, and then the average value was determined to determine the thermal shrinkage value. The difference between the maximum and minimum values of the heat shrinkage rate measurements was used as the deviation of the heat shrinkage rate.

2) smoothness

The film after heat treatment was spread on a smooth surface, and the film was visually observed and classified as follows.

(Circle): The film is very smooth and there are few wrinkles.

(Triangle | delta): The deformation | transformation and wrinkles generate | occur | produce weakly in a film.

X: The smoothness of the film is very poor and wrinkles are severely generated.

Example 1

Dimethyl terephthalate and ethylene glycol were added in a molar ratio of 1: 2, and manganese acetate tetrahydrate was added thereto by 0.05% by weight to carry out transesterification with methanol being distilled out. To the reaction mixture, 0.05 wt% of trimethylene phosphate as a stabilizer and 0.05 wt% of antimony trioxide as a condensation polymerization catalyst were added, followed by a condensation polymerization reaction to obtain a polyethylene terephthalate resin. The obtained resin was dried at 180 ° C. for 5 hours and melt-extruded at 280 ° C. to obtain an unstretched sheet, which was stretched 3.1 times in a longitudinal direction at 90 ° C., and stretched 3.9 times in a transverse direction at 135 ° C. Next, heat-setting and cooling at 240 ° C. for 15 seconds to give a biaxially oriented polyethylene terephthalate (PET) film having a thickness of 25 μm, the longitudinal thermal shrinkage (S) and its deviation (ΔS) having the values shown in Table 1 below. Got it.

The film was heat-treated so that the maximum reaching temperature (T _max ), the holding time (t _max ) and the tension (F) at the highest achieved temperature were in the infrared heating furnace. Thus, the heat shrinkage average value (S '), the deviation (ΔS') and the smoothness of the final longitudinal direction of the biaxially oriented polyethylene terephthalate film heat-treated as shown in Table 1 below.

Examples 2-4 and Comparative Examples 1-5

The heat treatment was carried out in the same manner as in Example 1, except that the draw ratio, heat setting temperature and heat treatment conditions (T _max , t _max and F) of the raw film were changed as shown in Table 1 below. A biaxially oriented polyethylene terephthalate film was prepared.

Example 5

Dimethyl-2,6-naphthalate and ethylene glycol were added in a molar ratio of 1: 2, and manganese acetate tetrahydrate was added thereto by 0.05% by weight to carry out transesterification with methanol being distilled out. To the reaction mixture, 0.05 wt% of trimethylene phosphate as a stabilizer and 0.05 wt% of antimonytrioxide as a condensation polymerization catalyst were added, followed by a condensation polymerization reaction to obtain a polyethylene naphthalate resin. The obtained resin was dried at 180 ° C. for 5 hours, and then melt-extruded at 285 ° C. to obtain an unstretched sheet, which was stretched 3.2 times in lengthwise direction at 135 ° C., and 3.9 times in transverse direction at 145 ° C. Next, heat-setting and cooling at 245 ° C. for 15 seconds, the thickness was 25 μm, and the biaxially oriented polyethylene naphthalate (PEN) film having a longitudinal heat shrinkage value (S) and a deviation thereof (ΔS) having the values shown in Table 1 below. Got.

The film was heat-treated so that the maximum reaching temperature (T _max ), the holding time (t _max ) and the tension (F) at the highest achieved temperature were in the infrared heating furnace. The heat shrinkage average value (S '), deviation (ΔS') and smoothness of the final longitudinal direction of the biaxially oriented polyethylene naphthalate film heat-treated in this way are shown in Table 1 below.

Examples 6-8 and Comparative Examples 6-9

The heat treatment was performed in the same manner as in Example 2, except that the draw ratio, heat setting temperature and heat treatment conditions (T _max , t _max and F) of the raw film were changed as shown in Table 1 below. A biaxially oriented polyethylene terephthalate film was prepared.

As can be seen in Table 1, the films prepared by Examples 1 to 8 were excellent in smoothness, whereas the films according to Comparative Examples 1 to 9 were not.

Film according to the present invention is excellent in both dimensional stability and smoothness even in the harsh conditions of high temperature, flexible flat panel wiring (FFC), flexible printed circuit board (FPC), membrane contact switch (MTS), seat sensor (seat sensor), TAB It may be usefully used as a film for electrical and electronic materials such as tape automated bonding, chip on film, and other industrial film materials.

Claims (6)

In the heat treated biaxially oriented polyester film, the longitudinal heat shrinkage rate (S) measured for the film before heat treatment satisfies the range of the following formula (1), and the longitudinal heat shrinkage rate (S ′) measured for the film after heat treatment. A film characterized by satisfying the following Equation 5: Equation 1 0.1 × 0.05 × e ^0.0185T ≤ S ≤ 0.05 × e ^0.0185T Equation 5 0.1 × 0.002 × e ^{0.0265T '} ≤ S´ ≤ 0.002 × e ^0.0265T' Wherein T and T 'are the heat shrinkage measurement temperatures in the range of 150 to 240 ° C. for the films before and after the heat treatment, respectively, and the heating time at each temperature is 30 minutes below 150 to 200 ° C. and 10 below 200 to 230 ° C. Minutes and 2 minutes at 230-240 degreeC. The film according to claim 1, wherein the polyester is polyethylene terephthalate or polyethylene naphthalate. The film according to claim 1, wherein the deviation (ΔS) of the thermal contraction rate (S) is in the range of 0.1 to 0.5, and the deviation (ΔS ') of the thermal contraction rate (S') is in the range of 0.01 to 0.2. The film of claim 1 having a thickness of 12 to 250 μm or less. In the method for producing a biaxially oriented polyester film heat-treated by heat-treating the biaxially oriented polyester film, the polyester film before the heat treatment has a longitudinal heat shrinkage (S) that satisfies the range of Equation 1 below, Wherein the film satisfies the following Equations 2 to 4, and the heat treated polyester film has a longitudinal heat shrinkage (S ′) satisfying the range of Equation 5 below: Equation 1 0.1 × 0.05 × e ^0.0185T ≤ S ≤ 0.05 × e ^0.0185T Equation 2 T'-5 ≤ T _max ≤ T '+ 5 Equation 3 5 ≤ t _max ≤ 30 Equation 4 0.1 ≤ F ≤ 2 Equation 5 0.1 × 0.002 × e ^{0.0265T '} ≤ S´ ≤ 0.002 × e ^0.0265T' Where T and T 'are the heat shrinkage measurement temperatures in the range of 150 to 240 ° C. for the films before and after the heat treatment, respectively, and the heating time at each temperature is 30 minutes below 150 to 200 ° C., 10 minutes below 200 to 230 ° C., and 2 minutes at 230-240 degreeC, T _max is the maximum reaching temperature (℃) during heat treatment, t _max is the holding time in seconds at the highest reaching temperature, F is the tension (kgf / cm 2) at the highest reaching temperature. The method according to claim 5, wherein the deviation (ΔS) of the thermal contraction rate (S) is in the range of 0.1 to 0.5, and the deviation (ΔS ') of the thermal contraction rate (S') is in the range of 0.01 to 0.2.