KR100699098B1 - Biaxially oriented polyester film having improved isotropic property of heat shrinkage and preparation thereof - Google Patents

Abstract

The present invention relates to a biaxially oriented polyester film with improved heat shrink isotropy, wherein both longitudinal heat shrinkage (S _MD ) and lateral heat shrinkage (S _TD ) when heated at 230 ° C. for 5 minutes without load. The heat treatment film according to the invention, characterized in that the range of 0.1 to 1%, and the heat shrink isotropic index (S _I = S _MD / S _TD ) is in the range of 0.5 to 2 by heat treatment in a heating furnace provided with a series of nip rolls It can be manufactured, and 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 Improved Heat Shrinkage Isotropy and Its Manufacturing Method {BIAXIALLY ORIENTED POLYESTER FILM HAVING IMPROVED ISOTROPIC PROPERTY OF HEAT SHRINKAGE AND PREPARATION THEREOF}

1 schematically shows an apparatus for performing a heat treatment process of a biaxially oriented polyester film according to the present invention,

Figure 2a is a detailed view showing the angle (θ) of the nip roll running direction with respect to the traveling direction of the biaxially oriented polyester film,

2B illustrates a state in which both ends of the exit-oriented polyester film are supported by the nip rolls.

3 is a detailed view showing the lateral distance between nip rolls supporting both ends of the biaxially oriented polyester film.

<Description of Major Symbols in Drawing>

1: hot air nozzle or infrared heater 2: heating furnace

3: nip roll 4: biaxially oriented polyester film

5: guide roll 6: tension detection roll

7: unwinding roll 8: winding roll

The present invention relates to a biaxially oriented polyester film with improved heat shrink isotropy.

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, in the case of electronic printed circuit boards such as flexible printed circuit boards (FPC), tape automated bonding (TAB), automotive seat sensors, or transparent conductive circuit boards such as touch screens or display electrode substrates, thermal contraction rate Although this extremely low and excellent smoothness film is required, conventional biaxially oriented polyester films cannot satisfy these required characteristics, and thus films having high dimensional stability by heat treatment offline have been used.

In the conventional methods of heat treating a biaxially oriented polyester film, in most cases, the film is transported in the longitudinal direction without any transverse restraint and passed through a high temperature heating furnace to reduce the stress in the film. It is reducing heat shrinkage at high temperature. However, in this case, tension does not act at all in the transverse direction of the film, whereas tension inevitably acts in the longitudinal direction for the transport of the film. There is a problem that the smoothness is lowered, the difference in the lateral thermal contraction rate and the longitudinal thermal contraction rate of the heat-treated film is severely generated to increase the anisotropy of the thermal contraction rate. In particular, when the anisotropy of thermal contraction rate is large, shrinkage occurs unevenly when the film is used at a high temperature, and thus it is difficult to be used for applications requiring high precision, such as flexible circuit boards, seating sensors, and display electrode substrates.

Accordingly, it is an object of the present invention to provide a biaxially oriented polyester film having a high thermal contraction isotropy due to a small difference between these two values while having a low thermal contraction rate in the longitudinal and transverse directions.

In order to achieve the above object, in the present invention, in the biaxially oriented polyester film heat-treated, the longitudinal heat shrinkage (S _MD ) and the lateral heat shrinkage when heated for 5 minutes at 230 ℃ no-load after heat treatment Both (S _TD ) is in the range of 0.1 to 1%, and the heat shrink isotropic index (S _I = S _MD / S _TD ) is in the range of 0.5 to 2 to provide a biaxially oriented polyester film.

In addition, the present invention provides a method for producing the biaxially oriented polyester film, characterized in that the heat treatment is performed by passing both ends of the biaxially oriented polyester film between a series of nip rolls installed in the advancing direction of the film inside the heating furnace. .

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

The present invention increases the smoothness of the film by applying tension in the transverse direction of the film during the heat treatment of the biaxially oriented polyester film, and improves the thermal contraction isotropy of the film by reducing the thermal shrinkage in the longitudinal and transverse directions and the difference between the two. It is characterized by.

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 make an unstretched sheet, and then sequentially or simultaneously biaxially stretched in the longitudinal and transverse directions, and then heated. It can be prepared by fixing 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 thermal contraction rate is high, the variation of the transverse thermal shrinkage rate is severe, and the glass transition temperature is higher than 60 ° C. In this case, due to the relaxation of the polymer chains, the degree of orientation drops 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.

In order to use the biaxially oriented polyester film fabric for a substrate such as an electronic circuit, the heat treatment is performed by an offline process after the cooling step. In the present invention, a series of nip rolls are used to impart tension in the transverse direction of the film. It is done.

Figure 1 schematically shows an apparatus for carrying out the heat treatment process of the film according to the present invention, the film 4 is a hot air nozzle or by a releasing roll 7, tension detection roll 6 and the guide roll (5) After passing through the heating furnace 2 including the infrared heater 1 and the nip roll 3, it is wound by the winding roll 8 by the guide roll 5 '. 2A shows the angle θ of the nip roll traveling direction with respect to the traveling direction of the biaxially oriented polyester film, and FIG. 2B shows a state in which both ends of the exiting oriented polyester film are supported by the nip rolls. Shows the lateral distance between the nip rolls 3 which support both ends of the film 4.

According to the present invention, a series of nip rolls (3) capable of angle adjustment in the interior of the heating furnace (2) is installed at both ends of the film in the advancing direction of the film so that the film end passes between the upper roll and the lower roll so that the film is transverse Tension can be added in the direction. The heating method of the heating furnace 2 may be either an infrared radiation or an air circulation heating method, and both methods may be used in parallel.

In the present invention, the series of nip rolls used for tensioning the film in the transverse direction is installed at an angle so that the traveling direction of each of the nip rolls has an angle of 0.5 to 5 ° in the traveling direction of the film, as shown in FIG. 2A. It is preferable. If the installation angle (θ) of each nip roll supporting both ends of the film is less than 0.5 °, it is not good because it is difficult to give tension in the transverse direction of the film and the film may come off from the nip roll during traveling, and if it is larger than 5 ° It is not good because excessive tension is applied in the lateral direction so that the lateral thermal contraction rate is increased, and the film is excessively tensioned in the lateral direction so that lateral wrinkles occur or the smoothness is lowered.

In addition, the series of nip rolls inside the furnace 2 is preferably installed to have a relaxation rate (R) value defined by Equation 1 in the range of -2 to 2%.

Relaxation rate (R) = [(L _i -L _o ) / L _i ] × 100 (%)

Where L _i and L _o are each as shown in FIG. 3, when the film enters and exits the nip roll (ie, the film at the first and last nip roll position in the direction of film travel in a series of nip rolls). It is the lateral distance between the nip rolls in which both ends are located.

When the relaxation rate is less than -2%, the film is excessively stretched in the transverse direction to increase the transverse thermal contraction rate, which is not good because the transverse wrinkles occur or the smoothness is lowered. It is not good because it lacks the longitudinal wrinkles and the anisotropy of the longitudinal and transverse thermal shrinkage becomes severe.

On the other hand, during the off-line heat treatment of the polyester fabric film, the maximum reaching temperature (T _max ) of the film is 200 to 240 ° C., and the holding time (t _max ) of the film at the highest reaching temperature is 5 to 30 seconds and the tension in the film traveling direction. It is preferable that (F) satisfy | fills the conditions of 0.1-2 kgf / cm <2>.

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 240 ° C, the heat shrinkage rate of the film after heat treatment is low and excellent in thermal stability, but since more heat than necessary is applied to the film, the deformation of the film increases and the smoothness is lowered. When it is low, the smoothness of the film is increased, but the heat shrinkage rate after heat treatment is increased 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, and the higher the thermal shrinkage rate, longer than 30 seconds At this time, the progress of the film is slowed down and the productivity is lowered, and oligomer generation on the film surface increases, which is not good.

When the tension (F) applied to the film is less than 0.1 kgf / ㎠, the film is stretched in the heating furnace of high temperature, the smoothness decreases, the running of the film is poor, and the meandering occurs. When the tension is greater than 2 kgf / ㎠ In the heat treatment process, the film is not sufficiently relaxed, so that the stress remains in the film, which is not good because the shrinkage rate of the heat-treated film is increased, or the longitudinal wrinkles in the film worsen the smoothness.

The biaxially oriented polyester film heat-treated under the above conditions according to the present invention has a longitudinal thermal shrinkage (S _MD ) and a transverse thermal shrinkage (S _MD ) of 0.1 to 1% when heated at 230 ° C. for 5 minutes under no load. _TD ) and an isotropic index (S _I = S _MD / S _TD ) of 0.5 to 2. If the heat shrinkage ratio (S _MD or S _TD ) is greater than 1%, the dimensional deformation is severe. Therefore, it is not suitable as an electric and electronic film material requiring high precision when used at a high temperature, and when smaller than 0.1%, the draw ratio at the time of biaxial stretching Since it is necessary to significantly lower the temperature or excessively increase the heat treatment temperature in the off line, the orientation of the film is insufficient, so that the heat resistance is poor or the appearance is poor due to the thermal deformation of the film. In addition, when the isotropic index (S _I ) is out of the above range, the variation in the longitudinal shrinkage rate and the transverse shrinkage rate is so large that the difference in shrinkage occurs badly when used at high temperature, which is not good. In particular, when mounting electronic components at high temperatures such as flexible circuit boards, the isotropy of the longitudinal and transverse dimensional deformation is important. It is important.

As such, the film heat-treated according to the present invention is excellent in both dimensional stability and smoothness even at a high temperature, it can be very useful as a film for electrical and electronic materials and other industrial film materials.

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

The film specimens having a length of about 200 mm and a width of 10 mm were placed in an air circulating oven maintained at 230 ° C. and heat-treated at no load for 5 minutes. The specimen was taken out of the oven and the length change after leaving for 1 hour at room temperature was measured, and the thermal contraction rate (%) was calculated according to the following equation (2).

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

In the above formula, L is the length of the specimen before heat treatment, and L 'is the length of the specimen after heat treatment.

2) Isotropic Index (S _I )

Isotropic index of the heat-treated film was calculated according to the following equation (3).

S _I = S _MD / S _TD

In the above formula, S _MD and S _TD are longitudinal heat shrinkage and lateral heat shrinkage when the heat-treated film is heated at 230 ° C. for 5 minutes without load.

3) 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.

Examples 1-5

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 then melt-extruded at 280 ° C. to obtain an unstretched sheet. The unstretched sheet was stretched longitudinally at 90 ° C. and transversely at 135 ° C. and then heat set for 15 seconds and then cooled, with the draw ratio and heat set temperature changed as shown in Table 1 below.

The film thus prepared was heat-treated under conditions as shown in Table 1 in an infrared heating furnace, and the thermal shrinkage rate, isotropic index and smoothness of the final film are shown in Table 1 below.

Comparative Examples 1 to 5

The biaxially oriented polyethylene terephthalate film heat-treated in the same manner as in Examples 1 to 5, except that the draw ratio, heat setting temperature and heat treatment conditions in the infrared heating furnace were changed as shown in Table 2 below. It was prepared, and the heat shrink rate, isotropic index and smoothness of the final film is shown in Table 2 below.

Examples 6-10

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 antimony trioxide as a polycondensation catalyst were added, followed by a polycondensation reaction to obtain a polyethylene naphthalate resin. The resin thus obtained was dried at 180 ° C. for 5 hours and then melt-extruded at 285 ° C. to obtain an unstretched sheet. The unstretched sheet was stretched longitudinally at 135 ° C. and transversely at 145 ° C., then heat set for 15 seconds and then cooled, with the draw ratio and heat set temperature changed as shown in Table 1 below.

The film thus prepared was heat-treated under conditions as shown in Table 1 in an infrared heating furnace, and the thermal shrinkage rate, isotropic index and smoothness of the final film are shown in Table 1 below.

Comparative Examples 6 to 10

A biaxially oriented polyethylene naphthalate film heat-treated in the same manner as in Examples 6 to 10, except that the draw ratio and heat-setting temperature of the raw film and the heat treatment conditions in the infrared heating furnace were changed as shown in Table 2 below. It was prepared, and the heat shrinkage rate, isotropic index and smoothness of the final film is shown in Table 2 below.

As can be seen in Tables 1 and 2, the films prepared according to Examples 1 to 10 were excellent in isotropic index and smoothness, whereas the films according to Comparative Examples 1 to 10 were not.

The film according to the present invention is excellent in both isotropic index 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 (8)

In the offline heat-treated biaxially oriented polyester film, both the longitudinal heat shrinkage (S _MD ) and the lateral heat shrinkage (S _TD ) when heated for 5 minutes without heating at 230 ° C. for 5 minutes after offline heat treatment are 0.1 to in the range of 1%, the heat shrinkage isotropic index _{(S I = S MD / S} TD) is a biaxially oriented polyester film, characterized in that in the range of 0.5 to 2. The film according to claim 1, wherein the polyester is polyethylene terephthalate or polyethylene naphthalate. The film of claim 1 having a thickness of 12 to 250 μm or less. A method for producing the biaxially oriented polyester film according to claim 1, wherein both ends of the biaxially oriented polyester film pass through a series of nip rolls installed in the advancing direction of the film inside the heating furnace. 5. The method according to claim 4, wherein the maximum reaching temperature (T _max ) of the film in the heating furnace is 200 to 240 ° C, the holding time (t _max ) of the film at the highest reaching temperature is 5 to 30 seconds, and the tension (F). Heat-treating to 0.1 to 2 kgf / cm 2. The method according to claim 4, wherein the series of nip rolls installed in the furnace is installed at an angle so that the traveling direction of each of the nip rolls has an angle of 0.5 to 5 ° with respect to the traveling direction of the film. The method according to claim 4, wherein the series of nip rolls in the heating section is installed such that the relaxation rate R defined by Equation 1 is -2 to 2%. Equation 1 Relaxation rate (R) = [(L _i -L _o ) / L _i ] × 100 (%) Wherein, L _i and L _o is the lateral distance between each of the first nip roll as the film traveling direction and the nip rolls to the film end portions of the nip rolls in the final position location. The method according to claim 4, wherein the heating furnace is heated by infrared radiation, air circulation or a combination thereof.

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