KR20150077993A - Transparent biaxially oriented polyester film and preparation method thereof - Google Patents

Abstract

The present invention relates to a transparent biaxially-oriented polyester film and a preparation method thereof. The present invention comprises polyester resin including a diol component containing 90 mol% or more of 1,4-cyclohexane methanol and a dicarboxylic acid component containing 90 mol% or more of a terephthalic acid and has a heat shrinkage rate of 3% or less in both longitudinal and transverse directions after being maintained at 150°C for 30 minutes and a strength and elongation retention rate of 50% or more after 72 hours at 120°C and 1.2 atm. The biaxially-oriented polyester film of the present invention is transparent and has excellent hydrolysis resistance, thereby being usefully used for sunlight, electrical insulation, and retort packaging.

Description

TRANSPARENT BIAXIALLY ORIENTED POLYESTER FILM AND PREPARATION METHOD THEREOF FIELD OF THE INVENTION The present invention relates to a transparent biaxially stretched polyester film,

The present invention relates to a biaxially stretched polyester film which is transparent and excellent in hydrolysis resistance and suitable for packaging for solar cells, electric insulation and retort, and a method for producing the same.

Relatively long durability up to several years is required under the application temperature of about 78 캜 which is the vitrification temperature region of polyethylene terephthalate (PET), which is a polyester, for the electric insulation application field or the film for the rear laminate of the solar cell module. Under these conditions, the hydrolysis tendency of the polyester is very important for its durability in the field of application.

In this connection, it has long been known that the hydrolysis rate can be lowered when the carboxyl end group content (CEG content) of the polyester is low. However, in order to produce a polyester having a low carboxyl end group content, (US Patent No. 3,051, 212).

On the other hand, poly (1,4-cyclohexanedimethylene terephthalate) (PCT) derived from 1,4-cyclohexane dimethanol (CHDM) is known as a hydrolytically stable polyester, but has high brittleness It is not actually used in the production of a biaxially stretched film.

Accordingly, the present inventors have found that poly (1,4-cyclohexanedimethylene terephthalate) (PCT) can be obtained by forming a polyester biaxially stretched film composed of 1,4-cyclohexane dimethanol (CHDM) The inventors of the present invention discovered that the film had a high crystallization speed and thus the stretching resistance of the film was greatly improved by controlling the stretching conditions during the production of the film.

U.S. Patent No. 3,051,212

Accordingly, an object of the present invention is to provide a biaxially stretched polyester film suitable for packaging for photovoltaic, electric insulation and retort, which is transparent and excellent in hydrolysis resistance, and a method for producing the same.

In order to achieve the above object,

A polyester resin comprising a diol component containing 90 mol% or more of 1,4-cyclohexane dimethanol and a dicarboxylic acid component containing 90 mol% or more of terephthalic acid,

The biaxially stretched polyester film has a heat shrinkage ratio of 3% or less in both longitudinal and transverse directions after holding at 150 캜 for 30 minutes, and a tenacity retention ratio of 50% or more after 72 hours at 120 캜 and 1.2 atm.

The present invention also relates to a process for producing a sheet by melt extruding and cooling a polyester resin comprising a diol component containing 90 mol% or more of 1,4-cyclohexane dimethanol and a dicarboxylic acid component containing 90 mol% or more of terephthalic acid And biaxially stretching the sheet in the machine direction and the transverse direction, followed by heat fixation. The present invention also provides a method for producing the above biaxially stretched polyester film.

The present invention also provides a solar cell module comprising the biaxially stretched polyester film.

The present invention also provides an electrically insulating product comprising the biaxially stretched polyester film.

The present invention also provides a retort article comprising the biaxially stretched polyester film.

The biaxially stretched polyester film of the present invention exhibits excellent resistance to hydrolysis, such as being able to maintain excellent inherent film properties even when exposed to high temperatures and humidity for a long period of time, and also exhibits excellent electrical insulation, And thus can be usefully used for solar cells, electrical insulating films, and retort packaging films.

The biaxially stretched polyester film according to the present invention comprises a polyester resin containing a diol component containing 90 mol% or more of 1,4-cyclohexane dimethanol (CHDM) and a dicarboxylic acid component containing 90 mol% or more of terephthalic acid And the heat shrinkage rate after keeping at 150 占 폚 for 30 minutes is 3% or less in both the longitudinal direction (longitudinal direction or machine direction, MD) and the transverse direction (width direction, TD), and after 72 hours at 120 占 폚 and 1.2 atm, And a retention ratio of 50% or more.

The polyester resin used in the present invention is obtained by transesterifying a diol component and a dicarboxylic acid component and then polymerizing. The diol component is at least 90 mol%, preferably at least 98 mol%, more preferably at least 99 mol% Mol% or more CHDM. The higher the CHDM ratio, the higher the hydrolysis resistance.

Specific examples of usable diol components include ethylene glycol, 1,3-propanediol, 1,2-octanediol, 1,3-octanediol, 2,3-butanediol, 1,3- , 1,5-pentanediol, 2,2-dimethyl-1,3-propanediol (neopentyl glycol), 2-butyl- Pentanediol, 2,4-diethyl-1,5-pentanediol, 3-methyl-1,5-pentanediol, 1,1-dimethyl-1,5-pentanediol and mixtures thereof .

Further, the dicarboxylic acid component includes terephthalic acid in an amount of 90 mol% or more, and aromatic dicarboxylic acids such as dimethyl terephthalic acid, isophthalic acid, naphthalene dicarboxylic acid and orthophthalic acid; Aliphatic dicarboxylic acids such as adipic acid, azelaic acid, sebacic acid and decanedicarboxylic acid; Alicyclic dicarboxylic acid; And their esterified products can be used alone or in combination of two or more. In order to slow down the crystallization rate at this time, preferably 10 mol% or less of isophthalic acid can be used.

Thus, the polyester resin used in the present invention contains 1,4-cyclohexanedimethylene terephthalate as the main repeating unit, has an intrinsic viscosity (at 25 캜) of 0.6 to 1.2 for filming, and has a viscosity of 30,000 to 50,000 g / mol, in particular from 30,000 to 40,000 g / mol.

In polyester, defects are mostly due to decomposition of polyester chains due to hydrolysis, and even at the minimum chain length, film brittleness is so large that they can no longer withstand mechanical deformation such as elongation or bending. Therefore, as a method for slowing the decomposition rate, it is possible to greatly enhance the resistance to the decomposition rate by giving orientation to the molecular chains by controlling the stretching conditions, that is, the stretching speed and the stretching ratio.

In relation to the stretching conditions, in the present invention, biaxial stretching in both the longitudinal direction and the transverse direction is performed, preferably, the product of the longitudinal direction and the transverse direction stretching ratio (MD x TD) is 4 to 16, preferably 7 to 14 , More preferably from 8 to 12, and the longitudinal stretching speed may be from 22 to 500 m / min, preferably from 25 to 400 m / min.

At this time, when the longitudinal stretching speed is 22 m / min or more, the desired orientation property can be maintained in the present invention, and the transverse stretching speed depends on the longitudinal stretching condition since crystallization is imparted depending on the longitudinal stretching speed and the stretching ratio.

The polyester film of the present invention can be produced by a conventional method of producing a sheet by melt extrusion and cooling of the polyester resin of the specific composition and then biaxially stretching the unoriented sheet in the longitudinal and transverse directions have.

The melt extrusion is preferably carried out at a temperature of Tm + 30 to Tm + 60 占 폚. If the temperature of the extruder is less than Tm + 30 ° C during melt extrusion, the melt will not melt smoothly, resulting in an increase in the viscosity of the extrudate, resulting in poor productivity. On the contrary, if the temperature exceeds Tm + 60 ° C, the molecular weight of the resin decreases due to depolymerization due to thermal decomposition, A problem may arise. The cooling is preferably carried out at a temperature of 30 ° C or lower, more preferably 15 to 30 ° C.

The stretching temperature is preferably in the range of Tg + 5 to Tg + 50 deg. C, and the lower the Tg, the better the stretchability, but the breakage may occur. In particular, in order to improve the brittleness, a stretching temperature range of Tg + 10 to Tg + 40 deg. C is preferable.

After initiating the heat setting, the film relaxes in the longitudinal and / or transverse direction, and the heat setting temperature range is preferably 200 to 260 ° C.

The thus-produced polyester film of the present invention may have a thickness of 12 to 400 탆. In addition, the polyester film of the present invention may contain various additives such as ordinary electrostatic charge applying agents, antistatic agents, ultraviolet ray blocking agents, antiblocking agents and other inorganic lubricating agents within the range not impairing the effects of the present invention.

The polyester film of the present invention has a heat shrinkage rate of 3% or less in both the longitudinal direction (longitudinal direction or machine direction, MD) and the transverse direction (width direction, TD) after holding at 150 캜 for 30 minutes, The retention rate of strength is 50% or more after time.

In addition, the polyester film of the present invention may have a transmittance of 88% or more at a wavelength of 400 to 700 nm and an intrinsic viscosity (IV) retention ratio of 70% or more after 72 hours at 120 ° C. and 1.2 atm.

As described above, the biaxially stretched polyester film of the present invention exhibits excellent resistance to hydrolysis, such as being able to maintain excellent inherent film properties even when exposed to high temperatures and humidity for a long period of time, Heat resistance and make-up, and thus can be usefully used for solar light, electrical insulation, and retort packaging films.

Accordingly, the present invention provides a solar cell module, an electric insulation product, and a retort product including the biaxially stretched polyester film.

Hereinafter, the present invention will be described in more detail with reference to preferred embodiments for better understanding of the present invention. However, the following examples are intended to illustrate the present invention, but the scope of the present invention is not limited to or by the following examples.

Example 1

100 moles of 1,4-cyclohexane dimethanol (CHDM) and 100 moles of terephthalic acid were placed in an autoclave equipped with a stirrer and a distillation tower, and manganese acetate as an ester exchange reaction catalyst was added in an amount of 0.1% by weight of terephthalic acid, The transesterification reaction was carried out at 290 ° C. After completion of the ester exchange reaction, 0.001% by weight of Ti was added as a polymerization catalyst, and the mixture was stirred for 10 minutes. Subsequently, the reaction product was transferred to a second reactor equipped with a vacuum apparatus and then polymerized at 300 ° C for 180 minutes to obtain poly (1,4-cyclohexanedimethylene terephthalate) (IV) having an IV of 0.80 and a weight average molecular weight of 35,000 PCT) resin.

The produced PCT resin was melt-extruded through an extruder at 280 캜, and then adhered to a cooling roll cooled to 20 캜 to obtain an unoriented sheet. The sheet thus obtained was immediately heated to 60 DEG C and stretched 2.9 times and 3.4 times in the longitudinal direction and in the transverse direction at 110 DEG C, respectively, wherein the longitudinal and transverse stretching speeds were 29 m / min and 28 m / Min.

Then, the stretched sheet was heat set at 240 캜 to prepare a PCT biaxially stretched film having a thickness of 50 탆.

Examples 2 and 3, and Comparative Examples 3 and 4

Except that the longitudinal and transverse stretch ratios and the longitudinal stretch rates were changed as described in the following Table 1 while using the PCT resin produced by the method similar to that of Example 1, The same process was carried out to prepare a PCT biaxially oriented film.

Comparative Example 1

100 moles of ethylene glycol and 100 moles of terephthalic acid were charged into an autoclave equipped with a stirrer and a distillation tower, and manganese acetate as an ester exchange catalyst was added in an amount of 0.001 wt% of terephthalic acid, followed by transesterification at 280 ° C . After completion of the ester exchange reaction, 0.01 wt% of Sb ₂ O ₃ was added as a polymerization catalyst, and the mixture was stirred for 10 minutes. Then, the reaction product was transferred to a second reactor equipped with a vacuum apparatus and then polymerized at 260 ° C for 180 minutes to obtain a polyethylene terephthalate (PET) resin having an IV of 0.71 and a weight average molecular weight of 34,000.

The PET resin thus produced was melt-extruded through an extruder at 265 DEG C and then adhered to a cooling roll cooled to 20 DEG C to obtain an unoriented sheet. The sheets thus obtained were immediately heated to 60 ° C and then drawn at a temperature of 110 ° C in the longitudinal direction and in the transverse direction at 3.4 times and 4.0 times, respectively. The longitudinal and transverse stretching speeds were 34 m / min and 33 m / Min.

The stretched sheet was then heat-set at 220 DEG C to obtain a PET biaxially stretched film having a thickness of 125 mu m.

Comparative Example 2

Except that the PET resin produced by the method similar to that of Comparative Example 1 was used and the longitudinal and transverse stretch ratios and the longitudinal stretch rates were changed as shown in Table 1 below, The same process was performed to prepare a PET biaxially stretched film.

The heat shrinkage, IV, mechanical properties (tensile strength and elongation at break), transmittance and IV after autoclaving were measured for the films prepared in Examples 1 to 3 and Comparative Examples 1 to 4, The rate of change of mechanical properties was measured and is shown in Table 1 below. In this case, the measurement of the physical properties was carried out in the following manner.

[Autoclave treatment]

The film (width X length: 10 cm x 2 cm) was fixed in an autoclave, and the autoclave was filled with 2 liters of water, and the autoclave was closed and heated. The temperature of the autoclave was adjusted to 120 DEG C and the pressure was increased to 1.2 atm and treated for 72 hours. After the set time, the autoclave was turned off automatically. After the outlet valve was opened, the film was taken out and its physical properties were measured.

[Heat shrinkage rate]

Using a 10 cm x 10 cm square film sample, the film was cut so that one edge was parallel to the machine direction (longitudinal direction) and the other edge was perpendicular to the machine direction (transverse direction). The film was kept in an oven at 150 ° C where air was circulated for 30 minutes, and then the sample was taken out, and the longitudinal and transverse heat shrinkage ratios were calculated according to the following equations by measuring the changes in the longitudinal and transverse directions at room temperature.

Heat shrinkage percentage (%) = 100 X (L ₀ -L) / L ₀

Where L ₀ is the length before heat treatment, and L is the length after heat treatment.

[Viscosity]

After dissolving the obtained resin in o-chlorophenol to prepare a 1 wt% solution, its relative viscosity was measured with an Ostwald viscometer at 25 ° C. The measured relative viscosity was determined by comparing the intrinsic viscosity.

ηr: Relative viscosity

B: Correction coefficient of viscosity tube

t _o : Measurement of the Blank Test of OCP (c)

t ₁ : Measured census (sec)

C: 2.4 (integer)

[Mechanical properties (tensile strength and elongation at break)]

Mechanical properties were measured according to DIN EN ISO 527-1-3.

[Transmittance (Transparency)]

The transmittance was measured according to ASTM-D 1003.

unit Example Comparative Example One 2 3 One 2 3 4 Suzy PCT PCT PCT PET PET PCT PCT Layer thickness ㎛ 50 50 50 125 50 50 50 Drawing Ratio (Spec X) 2.9X3.4 2.9X3.6 3.0X3.6 3.4X4.0 3.0X3.6 4X5 2.5X3 Longitudinal stretching speed m / min 29 340 360 340 310 400 21 Sheet IV value immediately after manufacture 0.62 0.66 0.67 0.71 0.69 0.66 0.67 Heat shrinkage
(150, 30 minutes) Longitudinal direction % 2.5 1.2 1.1 1.2 / 0.7 1.5 0.8 Lateral direction 0.9 0.3 -0.1 0 0.1 0 The tensile strength Longitudinal direction kgf / mm ² 15 15 13 18 23 11 Lateral direction 17 18 19 23 27 13 Elongation at break Longitudinal direction % 98 106 87 170 120 100 Lateral direction 61 64 51 100 100 72 After autoclave
(72 hr) Seal
burglar Longitudinal direction kgf / mm ² 13.5 11 11.5 9 19 5.6 Lateral direction 15.1 17 13 9.66 18 6.5 Fracture
Elongation Longitudinal direction % 59 69 54 68 22 37 Lateral direction 40 54 32 8 25 29 After autoclave
(72 hr) IV dl / gr 0.59 0.59 0.59 0.23 0.38 0.30 IV Retention Rate
(Initial IV / IV after autoclave) % 95 89 88 32 55 45 Etc Fracture Light transmittance % 90 91 90.9 91 88

From the results shown in Table 1, it can be seen that the films of Examples 1 to 3 according to the present invention have not only excellent heat shrinkage and transmittance but also high IV retention and high strength retention after autoclave treatment. On the other hand, the film of Comparative Examples 1 and 2 using PET resin and the film of Comparative Example 4 in which the stretching speed deviates from the scope of the present invention showed that the IV value and the strength value rapidly decreased after the autoclave treatment at high temperature and high pressure, In case of Comparative Example 3 deviating from the category, breakage occurred in the manufacturing process.

Claims (13)

A polyester resin comprising a diol component containing 90 mol% or more of 1,4-cyclohexane dimethanol and a dicarboxylic acid component containing 90 mol% or more of terephthalic acid,
A biaxially stretched polyester film having a heat shrinkage ratio of 3% or less in both longitudinal and transverse directions after holding at 150 占 폚 for 30 minutes, and a tenacity retention ratio of 50% or more after 72 hours at 120 占 폚 and 1.2 atm. The method according to claim 1,
Wherein the polyester resin comprises at least 98 mol% of 1,4-cyclohexanedimethanol. The method according to claim 1,
Wherein said polyester resin has an intrinsic viscosity (at 25 占 폚) of 0.6 to 1.2 and a weight average molecular weight of 30,000 to 50,000 g / mol. The method according to claim 1,
Wherein the polyester film is biaxially stretched so as to have a product of a longitudinal direction and a transverse direction stretching ratio of 4 to 16. The method according to claim 1,
Wherein the polyester film is biaxially stretched so as to have a longitudinal stretching speed of 22 to 500 m / min. The method according to claim 1,
Wherein the polyester film has a transmittance of 88% or more at a wavelength of 400 to 700 nm. The method according to claim 1,
Wherein the polyester film has an IV retention of 70% or more after 72 hours at 120 캜 and 1.2 atm. A polyester resin containing a diol component containing 90 mol% or more of 1,4-cyclohexane dimethanol and a dicarboxylic acid component containing 90 mol% or more of terephthalic acid is melt-extruded and cooled to produce a sheet, Of the biaxially stretched polyester film according to claim 1, comprising biaxially stretching the film in the longitudinal and transverse directions and fixing the film by heat. 9. The method of claim 8,
Wherein the sheet is biaxially stretched in the machine direction and in the transverse direction so as to have a product of a longitudinal direction and a transverse direction stretching ratio of 4 to 16. 9. The method of claim 8,
And stretching the sheet in the longitudinal direction so as to have a stretching speed of 22 to 500 m / min. A solar cell module comprising a biaxially stretched polyester film according to any one of claims 1 to 7. An electrically insulating article comprising the biaxially stretched polyester film of any one of claims 1 to 7. A retort product comprising a biaxially stretched polyester film of any one of claims 1 to 7.