KR20040017023A - Biaxially oriented polyethylenenaphthalate film for an electric insulation and method for the preparation thereof - Google Patents

Abstract

PURPOSE: Provided is a bi-axially oriented polyethylene naphthalate film having excellent heat resistance, dimension stability, hydrolysis resistance and mechanical properties suitable to be used as a heat insulating material. CONSTITUTION: The bi-axially oriented polyethylene naphthalate film satisfies the following: (1) the refraction index is 1.760-1.780 at the machine direction and the cross-machine direction, respectively, and the difference of the refraction index values at both directions is 0.01 or less; (2) the residual break elongation at machine direction is 50% or more, after treating for 75 hours in the atmosphere of 130 deg.C and relative humidity of 100%; and (3) the shrinkage(%) is less than 0.7% after standing for 30 minutes at 150 deg.C at the machine direction and the cross-machine direction, respectively.

Description

Biaxially Oriented Polyethylenenaphthalate Film for Electrical Insulation and Manufacturing Method Thereof {BIAXIALLY ORIENTED POLYETHYLENENAPHTHALATE FILM FOR AN ELECTRIC INSULATION AND METHOD FOR THE PREPARATION THEREOF}

The present invention relates to a biaxially oriented polyethylene naphthalate film for electrical insulation and a method for manufacturing the same. Specifically, the biaxial orientation useful as an electrical insulation film is excellent in heat resistance, dimensional stability, hydrolysis resistance, and mechanical properties under high temperature and high humidity conditions. It relates to a polyethylene naphthalate film and a method of manufacturing the same.

In general, polyethylene naphthalate film has excellent mechanical properties, heat resistance, moisture resistance, and chemical resistance compared to polyethylene terephthalate film, and thus is widely used as a magnetic, photographic, electrical insulation, and industrial material in place of polyethylene terephthalate film. It is used. Particularly, polyethylene naphthalate film has excellent heat resistance and dimensional stability at high temperature, so it is flexible printed circuit, flexible flat cable, membrane touch switch, and condenser. It is widely used for electrical insulation and industrial materials such as heat-resistant adhesive tapes, transformers and motors.

Among the various applications, a study on a polyethylene naphthalate film suitable as an electrical insulation film has been proposed. For example, Japanese Patent Laid-Open No. 62-93991 has a low thermal shrinkage at high temperature and a residual fracture elongation after a long heat treatment. An excellent polyethylene naphthalate film for flexible printed wiring is disclosed. However, the document does not disclose a specific method for achieving the desired thermal shrinkage rate and minimum residual elongation, and the film has a problem that the physical properties of the film is sharply degraded when used for a long time under high temperature and high humidity conditions.

In addition, Japanese Patent Laid-Open No. 7-211149 discloses a polyethylene naphthalate insulating film for flexible flat cable, in which a problem in which curl occurs in the wiring by controlling the tanδ value through heat treatment is improved, but this film also has a high temperature. And when it is used for a long time under high humidity conditions, there is a problem that the property decreases and is not suitable as an insulating material.

In addition, many studies on the electrical insulation polyethylene naphthalate film has been proposed, but the electrical insulation material excellent in heat resistance and hydrolysis resistance that can be used for a long time under the harsh conditions of high temperature and high humidity, such as automotive engine room or dashboard It has not been announced yet.

Accordingly, an object of the present invention is to provide an electrical insulation polyethylene naphthalate film and a method for manufacturing the same, which can maintain excellent heat resistance, dimensional stability, hydrolysis resistance, and mechanical properties even in long-term use under severe conditions of high temperature and high humidity. .

In order to achieve the above object, in the present invention, (1) the refractive index in the longitudinal and transverse directions are respectively 1.760 to 1.780, the difference between the two values is 0.01 or less, and (2) 75 in 130 ℃ and 100% relative humidity atmosphere The biaxially oriented polyethylene naphthalate film which satisfy | fills that the longitudinal residual elongation after time process is 50% or more, and (3) longitudinal and lateral shrinkage after 30-minute hold | maintain at 150 degreeC is respectively less than 0.7%.

The present invention also provides a method for producing a biaxially oriented polyethylene naphthalate film by stretching, heat-treating and cooling a melt-extruded polyethylene naphthalate unstretched sheet, wherein the unstretched sheet is 30 or less than the glass transition temperature or glass transition temperature of the sheet. The longitudinal stretching at a high temperature of 3.5 to 4.2 times at a high temperature, the transverse stretching at a temperature of 3.7 to 4.3 times at a temperature of 10 to 30 ℃ higher than the glass transition temperature of the sheet, and the heat treatment at 200 to 250 ℃ It provides a method for producing a biaxially oriented polyethylene naphthalate film having a.

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

According to the first aspect of the present invention, the longitudinal and transverse refractive indices of the polyethylene naphthalate film are in the range of 1.760 to 1.780, preferably 1.765 to 1.775, respectively, to have excellent hydrolysis resistance and uniform longitudinal and transverse physical properties. Adjust When the longitudinal refractive index of the film is less than 1.760, the polymer chain is insufficient in orientation so that the film is inferior in heat resistance and hydrolysis resistance. When it exceeds 1.780, the film has excellent heat resistance and hydrolysis resistance, but the longitudinal heat shrinkage of the film is high. Lamination occurs badly, and workability is poor. In addition, when the lateral refractive index of the film is less than 1.760, the orientation of the polymer chains is insufficient, so that the strength and heat resistance of the film are inferior. When the transverse refractive index of the film is greater than 1.780, the lateral thermal shrinkage becomes high and the fracture becomes severe, resulting in unstable processes. At this time, in order to balance the longitudinal and transverse properties of the film, the difference between the longitudinal and transverse refractive index values should be less than 0.01. When this value is larger than 0.01, it is not good because the difference of physical properties, such as intensity | strength, elongation, heat contraction rate, etc. between a longitudinal direction and a lateral direction becomes large.

In addition, the polyethylene naphthalate film having excellent hydrolysis resistance provided by the present invention has a residual residual elongation of 50% or more, preferably 60% or more after processing the film for 75 hours at 130 ° C. and 100% relative humidity atmosphere. If the value is less than 50%, the mechanical properties such as strength, elongation, break strength, and flexibility are greatly reduced by hydrolysis of the polymer chain when used for a long time in a high temperature and high humidity environment. Is not suitable as an electrically insulating material because it may occur.

The thermal contraction rate of the film according to the present invention is suitably 0.7% or less, preferably 0.5% or less in each of the longitudinal direction and the transverse direction after being left for 30 minutes in a 150 ° C unloaded state. When the film's thermal shrinkage exceeds 0.7%, the dimensional change is greatly generated during processing such as heating, thermocompression, soldering, etc., making it difficult to form fine circuits or surface mounting of parts, and in some cases, short circuits of formed circuits occur. Not good.

According to the second aspect of the present invention, by controlling the film forming conditions such as the stretching temperature, the stretching ratio and the heat setting temperature in the longitudinal and transverse directions as appropriate within the above-mentioned range, the desired refractive index, residual elongation at break and thermal shrinkage are achieved. A biaxially oriented polyethylene naphthalate film can be manufactured.

Polyethylenenaphthalate used in the present invention is ethylene-2,6-naphthalate as the main repeating unit, and is produced by the following conventional method.

Dimethyl-2,6-naphthalate and ethylene glycol are used in a molar ratio of 1: 2, and a transesterification reaction is carried out by adding a catalyst containing a metal component such as manganese, potassium, lithium, calcium, magnesium, and zinc. The same functional derivatives as dimethyl-2,6-naphthalate include dimethyl-1,2-naphthalate, dimethyl-1,5-naphthalate, dimethyl-1,6-naphthalate, dimethyl-1,7-naphthalate, Dimethyl-1,8-naphthalate, dimethyl-2,3-naphthalate, dimethyl-2,7-naphthalate and the like can be used. In addition, diols that can be used in addition to ethylene glycol include polyethylene glycol, 1,3-propylene glycol, 1,2-propylene glycol, 2,2-diethyl-1,3-propanediol, 2,2-dimethyl-1 , 3-propanediol, 1,3-butanediol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, 1,3-cyclohexanedimethanol, 1,4-cyclodimethanol, and the like have.

After the end of the transesterification reaction and before starting the condensation polymerization reaction, a stabilizer and a condensation polymerization catalyst dispersed in ethylene glycol are added. As the stabilizer, a phosphate-based compound such as trimethylene phosphate, and a catalyst containing a metal component such as titanium, germanium, tin, antimony, zinc, cobalt, manganese, calcium or the like can be used.

The polycondensation reaction proceeds at a temperature of 260 to 300 ° C. and high vacuum conditions of 0.1 to 5 Torr, and the ultimate viscosity of the polyethylene naphthalate resin thus produced is preferably 0.5 or more. In addition, in view of the handleability and processability of the film, the polyethylene naphthalate resin preferably contains organic or inorganic fine particles having an average particle diameter of 0.05 to 5 µm in an amount of 0.05 to 0.5% by weight. The fine particles may be selected from at least one of wet, dry silica, colloidal silica, and calcium carbonate, such as amorphous, plate, spherical, and the like, and are preferably dispersed in ethylene glycol and added before the start of the polycondensation reaction.

If necessary, a mixture of polyethylene naphthalate and other polyesters or a copolymer containing ethylene naphthalate as the main structural unit may be used within the scope of not impairing the effects of the present invention.

The biaxially oriented polyethylene naphthalate film of the present invention, after making an unstretched sheet melt-extruded from the above polyethylene naphthalate resin by the T-die method or the like, and sequentially or simultaneously biaxially stretching in the longitudinal and transverse directions And heat treatment and cooling. At this time, the sheet is stretched longitudinally at 3.5 to 4.2 times, preferably 3.7 to 4.0 times, at a temperature of 30 ° C. higher than the glass transition temperature or the glass transition temperature of the sheet, preferably 10 to 20 ° C. higher than the glass transition temperature. Stretching transversely is 3.7 to 4.3 times, preferably 3.9 to 4.1 times at a temperature of 10 to 30 DEG C higher than the glass transition temperature.

When the longitudinal stretching temperature is lower than the glass transition temperature of the sheet, whitening occurs in the sheet, the fracture becomes more severe, and the heat shrinkage rate is higher. Patterning occurs, or the orientation of polymer chains is loosened, resulting in poor orientation and uneven thickness. In addition, when the longitudinal draw ratio is less than 3.5 times, the orientation of the polymer chain is insufficient, resulting in poor film strength, heat resistance, durability, etc., and when the longitudinal draw ratio exceeds 4.2 times, the longitudinal thermal shrinkage is high and delamination is performed. It's not good because it gets worse.

When the lateral stretching temperature is lower than 10 ° C below the glass transition temperature of the sheet, the fracture is severe, the heat shrinkage rate is increased, the bowing increases, and the lateral property deviation is increased, and the glass transition temperature is higher than 30 ° C. Due to loosening of the polymer chains, the degree of orientation drops and the thickness in the transverse direction becomes uneven. In addition, when the transverse draw ratio is less than 3.7 times, the orientation of the polymer chain is insufficient as in the longitudinal stretch, resulting in poor film strength, heat resistance and durability, and when the transverse draw ratio exceeds 4.3 times, the transverse thermal shrinkage rate increases and breaks. This is not good because it gets worse and the process becomes unstable.

Then, according to the method of the present invention, the heat treatment at 200 to 250 ℃, preferably 220 to 240 ℃, when the heat treatment temperature is less than 200 ℃ heat treatment effect is insufficient to increase the thermal shrinkage of the film, when it exceeds 250 ℃ The crystallinity and thickness deviation of the film will increase.

As needed, you may surface-treat various films, a corona discharge treatment, etc. to a film in the range which does not impair the effect of this invention.

Polyethylene naphthalate film prepared according to the present invention can be designed in a suitable thickness depending on the application, but usually has a thickness in the range of 25 to 125㎛.

The biaxially oriented polyethylene naphthalate film according to the present invention can maintain excellent heat resistance, dimensional stability, hydrolysis resistance and mechanical properties even in long-term use under severe conditions of high temperature and high humidity, flexible printed wiring, flexible flat cable, It can be very usefully used as a film for electrical insulation in products such as membrane contact switches, condensers, heat resistant adhesive tapes, transformers, motors and automobile parts.

Hereinafter, the present invention will be described in more detail based on the following examples. However, the following examples are not intended to limit the present invention, but are not limited thereto. Various performance evaluations of the films prepared in Examples and Comparative Examples of the present invention were performed by the following methods.

1) Thermal Shrinkage

The film specimen having a length of 200 mm and a width of 10 mm was placed in an air circulation oven at 150 ° C. under no load and heat-treated for 30 minutes. After removing the specimen from the oven and leaving it at room temperature for 2 hours, the change in length was measured, and thermal contraction rate (%) was calculated according to Equation 1 below.

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

2) refractive index

The longitudinal and transverse refractive indices of the film were measured using an ABBE refractometer and sodium D-ray (589 nm) as a light source.

3) Residual rupture elongation (hydrolysis resistance)

Five specimens 200 mm long and 15 mm wide were taken with respect to the longitudinal direction of the film. After the specimen was treated for 75 hours in a 100% relative humidity atmosphere at 130 ° C. using an autoclave, the specimen was taken out and left at room temperature for 2 hours. Tensile elongation (%) of the specimen was measured before and after the treatment using an Instron tensile tester at a sample length of 50 mm and a tensile speed of 200 mm / minute, and the average value of each was determined. The residual elongation at break (%) was calculated according to the following Equation 2 from the average value of the elongation at break.

4) strength

Five specimens 200 mm long and 15 mm wide were taken with respect to the longitudinal direction of the film. After the specimen was treated for 75 hours in a 100% relative humidity atmosphere at 130 ° C. using an autoclave, the specimen was taken out and left at room temperature for 2 hours. Using an MIT type tester, the average number of refractive indices of the five treated specimens was measured and classified into A, B, and C according to the number of times.

A: 500 or more times

B: 50 or more times and less than 500 times

C: less than 50 times

Example 1

Dimethyl-2,6-naphthalate and ethylene glycol were mixed in a 1 to 2 molar ratio, and 0.05% by weight of manganese acetate tetrahydrate was added thereto to carry out transesterification with methanol. 0.1 and 0.2 wt% of wet silica having an average particle diameter of 3 µm and colloidal silica having 0.1 µm, respectively, were added to the reaction mixture as inert fine particles, 0.05 wt% of trimethylene phosphate as a stabilizer and 0.04 wt% of a condensation catalyst. after the addition of antimony trioxide, and subjected to polycondensation to obtain a polyethylene naphthalate resin (T _g = 123 ℃). The obtained resin was dried at 180 ° C. for 6 hours, and then melt-extruded at 290 ° C. to obtain an unstretched sheet, which was stretched 3.8 times in a longitudinal direction at 135 ° C. and 4.1 times in a transverse direction at 145 ° C. Then, heat-treated at 230 ° C. for 20 seconds and cooled to prepare a biaxially oriented polyethylene naphthalate film having a thickness of 75 μm.

The refractive index, residual breaking elongation, thermal shrinkage and break strength of the prepared film were measured and shown in Table 1 below.

Examples 2-7 and Comparative Examples 1-7

A biaxially oriented polyethylene naphthalate film was produced in the same manner as in Example 1, except that the thickness, longitudinal or transverse stretching conditions (temperature or stretching ratio), or heat setting temperature of the film were changed as shown in Table 1 below. It was.

The refractive index, residual breaking elongation, thermal shrinkage and break strength of the prepared film were measured and shown in Table 1 below.

From Table 1, it can be seen that the films of Examples 1 to 7 according to the present invention have a refractive index, a residual breaking elongation and a thermal contraction rate within a desired range, and also have excellent cut strength. However, in Comparative Examples 1 to 3 having a low longitudinal refractive index, properties such as elongation at break and fracture strength are not good, and variations in thermal shrinkage in the longitudinal and transverse directions occur, and in the case of Comparative Example 4 having a high longitudinal refractive index. In this case, the residual fracture elongation and the rupture strength are excellent, but the longitudinal thermal contraction rate is increased, so that the variation in the longitudinal and transverse thermal contraction rates occurs, and in Comparative Examples 5 to 7, the residual fracture elongation is high or low. The fracture strength was good, but there were severe variations in the thermal shrinkage in the longitudinal and transverse directions.

As can be seen from the above experimental results, the biaxially oriented polyethylene naphthalate film according to the present invention has a refractive index, residual elongation at break, and thermal shrinkage in a desired range, and thus excellent heat resistance even in long-term use under severe conditions of high temperature and high humidity. , Dimensional stability, hydrolysis resistance and mechanical properties can be maintained, so it can be usefully used as an electrical insulation material.

Claims (7)

(1) the refractive indices in the longitudinal and transverse directions were 1.760 to 1.780, respectively, and the difference between the two values was 0.01 or less, and (2) the longitudinal residual elongation at break after 75 hours treatment at 130 ° C. and 100% relative humidity. It is% or more and (3) Biaxially-oriented polyethylene naphthalate film which satisfy | fills that the longitudinal and lateral shrinkage rate after hold | maintaining at 150 degreeC for 30 minutes is less than 0.7%, respectively. The method of claim 1, It has a thickness of 25-125 micrometers, Biaxially-oriented polyethylene naphthalate film. In the method for producing a biaxially oriented polyethylene naphthalate film by stretching, heat-treating and cooling the melt-extruded polyethylene naphthalate unstretched sheet, the unstretched sheet is 3.5 at a temperature of 30 ° C. higher than the glass transition temperature or glass transition temperature of the sheet. The biaxially oriented polyethylene naphthalate of claim 1, characterized by being longitudinally stretched to -4.2 times, transversely stretched to 3.7 to 4.3 times at a temperature of 10 to 30 占 폚 higher than the glass transition temperature of the sheet, and heat-treated at 200 to 250 占 폚. Method for producing a film. The method of claim 3, wherein Longitudinal drawing is carried out at a draw ratio of 3.7 to 4.0 times at a temperature of 10 to 20 ° C. higher than the glass transition temperature of the sheet. The method of claim 3, wherein The transverse stretching is carried out at a draw ratio of 3.9 to 4.1 times. An article in which the biaxially oriented polyethylene naphthalate film of claim 1 is used as an electrical insulation material. The method of claim 6, Flexible printed wiring, flexible flat cable, membrane contact switch, condenser, heat-resistant adhesive tape, transformer, motor or automotive parts.