CN113861465A - Optical polyester film and preparation method thereof - Google Patents

Optical polyester film and preparation method thereof Download PDF

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Publication number
CN113861465A
CN113861465A CN202111148798.0A CN202111148798A CN113861465A CN 113861465 A CN113861465 A CN 113861465A CN 202111148798 A CN202111148798 A CN 202111148798A CN 113861465 A CN113861465 A CN 113861465A
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polyester film
relaxation
optical
optical polyester
film
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CN113861465B (en
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李良彬
张文文
孟令蒲
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Chen Wei
Hefei Zhongke Youcai Technology Co ltd
Li Liangbin
Meng Lingpu
Zhang Wenwen
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University of Science and Technology of China USTC
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    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
    • C08J5/00—Manufacture of articles or shaped materials containing macromolecular substances
    • C08J5/18—Manufacture of films or sheets
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B32—LAYERED PRODUCTS
    • B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
    • B32B27/00—Layered products comprising a layer of synthetic resin
    • B32B27/06—Layered products comprising a layer of synthetic resin as the main or only constituent of a layer, which is next to another layer of the same or of a different material
    • B32B27/08—Layered products comprising a layer of synthetic resin as the main or only constituent of a layer, which is next to another layer of the same or of a different material of synthetic resin
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B32—LAYERED PRODUCTS
    • B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
    • B32B27/00—Layered products comprising a layer of synthetic resin
    • B32B27/18—Layered products comprising a layer of synthetic resin characterised by the use of special additives
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B32—LAYERED PRODUCTS
    • B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
    • B32B27/00—Layered products comprising a layer of synthetic resin
    • B32B27/36—Layered products comprising a layer of synthetic resin comprising polyesters
    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B1/00—Optical elements characterised by the material of which they are made; Optical coatings for optical elements
    • G02B1/04—Optical elements characterised by the material of which they are made; Optical coatings for optical elements made of organic materials, e.g. plastics
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B32—LAYERED PRODUCTS
    • B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
    • B32B2307/00—Properties of the layers or laminate
    • B32B2307/40—Properties of the layers or laminate having particular optical properties
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B32—LAYERED PRODUCTS
    • B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
    • B32B2307/00—Properties of the layers or laminate
    • B32B2307/70—Other properties
    • B32B2307/732—Dimensional properties
    • B32B2307/734—Dimensional stability
    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
    • C08J2367/00—Characterised by the use of polyesters obtained by reactions forming a carboxylic ester link in the main chain; Derivatives of such polymers
    • C08J2367/02—Polyesters derived from dicarboxylic acids and dihydroxy compounds
    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08K—Use of inorganic or non-macromolecular organic substances as compounding ingredients
    • C08K3/00—Use of inorganic substances as compounding ingredients
    • C08K3/34—Silicon-containing compounds
    • C08K3/36—Silica
    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08K—Use of inorganic or non-macromolecular organic substances as compounding ingredients
    • C08K5/00—Use of organic ingredients
    • C08K5/16—Nitrogen-containing compounds
    • C08K5/34—Heterocyclic compounds having nitrogen in the ring
    • C08K5/35—Heterocyclic compounds having nitrogen in the ring having also oxygen in the ring
    • C08K5/357—Six-membered rings

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  • Chemical & Material Sciences (AREA)
  • Manufacturing & Machinery (AREA)
  • Physics & Mathematics (AREA)
  • Engineering & Computer Science (AREA)
  • Materials Engineering (AREA)
  • Optics & Photonics (AREA)
  • General Physics & Mathematics (AREA)
  • Health & Medical Sciences (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • Medicinal Chemistry (AREA)
  • Polymers & Plastics (AREA)
  • Organic Chemistry (AREA)
  • Shaping By String And By Release Of Stress In Plastics And The Like (AREA)
  • Manufacture Of Macromolecular Shaped Articles (AREA)

Abstract

An optical polyester film and a preparation method thereof, wherein, the optical polyester film is prepared from polyester resin; at a preset temperature, the expansion characteristic of the optical polyester film in the first direction is the same as that of the optical polyester film in the second direction; at a predetermined temperatureThe absolute value of the difference between the average linear expansion coefficient of the optical polyester film in the first direction and the average linear expansion coefficient of the optical polyester film in the second direction is 0 to 80 x 10‑8mm/(mm. K); the first direction is a direction perpendicular to the optical slow axis of the optical polyester film in the optical polyester film, and the second direction is the direction of the optical slow axis of the optical polyester film.

Description

Optical polyester film and preparation method thereof
Technical Field
The invention relates to the field of optical display, in particular to an optical polyester film and a preparation method thereof.
Background
As a mainstream technology of a current flat panel display, a Liquid Crystal Display (LCD) and an Organic Light Emitting Display (OLED) have a core component formed by laminating various functional polymer films. Among the various polymer films involved are polyester films, polycarbonate films, polyvinyl alcohol films, cellulose triacetate films, polymethyl methacrylate films, and the like, wherein the polyester films are widely used in the display field owing to their excellent processability and optical and mechanical properties and low cost. However, there are still some problems in the current use, such as when the polyester film is laminated or laminated between the components, the temperature sometimes rises rapidly, which causes the original inherent dimensional change and deviation of optical properties, resulting in assembly and optical display problems. In addition, when the mylar is enclosed in a display panel, the mylar is used at a high temperature even when the display panel is used in a mobile phone, a car, a monitor, or the like, and unevenness in brightness or darkness of a display screen occurs.
Disclosure of Invention
In view of the above, the main object of the present invention is to provide an optical polyester film and a method for preparing the same, which are intended to at least partially solve at least one of the above-mentioned technical problems.
In order to achieve the above object, as one aspect of the present invention, there is provided an optical polyester film, wherein the optical polyester film is formed of a polyester resin; at a preset temperature, the thermal expansion characteristic of the optical polyester film in the first direction is the same as that of the optical polyester film in the second direction; under a preset temperature, the absolute value of the difference value between the average linear expansion coefficient of the optical polyester film in the first direction and the average linear expansion coefficient of the optical polyester film in the second direction is 0-80 multiplied by 10-8mm/(mm. K); the first direction is a direction perpendicular to the optical slow axis of the optical polyester film in the optical polyester film, and the second direction is the direction of the optical slow axis of the optical polyester film.
According to the embodiment of the invention, the preset temperature is-30-70 ℃.
According to the embodiment of the present invention, the average linear expansion coefficient of the optical polyester film in the first direction is 100 x 10 or less-8mm/(mm·K)。
According to the embodiment of the present invention, the average linear expansion coefficient of the optical polyester film in the second direction is 100X 10 or less-8mm/(mm·K)。
According to the embodiment of the invention, the thermal shrinkage rate of the optical polyester film in the first direction is less than or equal to 5 percent;
according to the embodiment of the present invention, the thermal shrinkage rate of the optical polyester film in the second direction is 5% or less.
According to the embodiment of the present invention, the thickness of the optical polyester film is 30 μm to 300 μm.
According to an embodiment of the present invention, there is also provided a method for producing an optical polyester film, for producing the optical polyester film of any one of claims 1 to 5, including: carrying out melt extrusion on polyester resin to obtain a cast sheet; stretching the cast sheet in a first direction to obtain a first stretched film; stretching the first stretched film in a second direction, and simultaneously performing first relaxation treatment on the first stretched film in the first direction to obtain a second stretched film; and (3) performing heat treatment on the second stretched film, and simultaneously performing second relaxation treatment on the second stretched film in a second direction to obtain the optical polyester film.
According to an embodiment of the present invention, the method of preparing an optical polyester film further comprises: the second stretched film is subjected to a heat treatment while the second stretched film is subjected to a third relaxation treatment in the first direction.
According to the embodiment of the invention, the relaxation amount of the first relaxation treatment is 0.1 to 25%
According to the embodiment of the present invention, the relaxation amount of the second relaxation treatment is 1 to 15%.
According to an embodiment of the present invention, the amount of relaxation in the third relaxation treatment is 0 to 5%.
According to the embodiment of the present invention, the relaxation amount of the third relaxation treatment is equal to or less than the relaxation amount of the second relaxation treatment.
According to the embodiment of the present invention, the temperature at which the cast sheet is stretched in the first direction is Tg to Tg +20 ℃, Tg being the glass transition temperature of the polyester resin.
The temperature of the heat treatment is Tm-50-Tm, and Tm is the melting temperature of the polyester resin.
According to the embodiment of the invention, the first stretching ratio of the first stretching is 1-3.
According to the embodiment of the invention, the second stretching ratio of the first stretching is 2.8-5.5.
According to the technical scheme, the optical polyester film and the preparation method thereof have the following effects or one of the effects:
according to the optical polyester film and the preparation method thereof, the difference value of the average linear expansion coefficients of the polyester film in the second direction and the first direction is limited within a certain range by controlling the average linear expansion coefficients of the polyester film in the second direction and the first direction, so that the dimensional change and the optical performance deviation caused by the dimensional change after the optical polyester film is subjected to rapid temperature rise can be effectively avoided.
Drawings
FIG. 1 is a temperature-deformation rate curve of a film obtained by thermomechanical analysis (TMA) in example 1 of the present invention;
FIG. 2 is an enlarged view of the portion of FIG. 1 at a temperature of 10-100 ℃.
Detailed Description
In order that the objects, technical solutions and advantages of the present invention will become more apparent, the present invention will be further described in detail with reference to the accompanying drawings in conjunction with the following specific embodiments.
According to an embodiment of the present invention, there is provided an optical polyester film, wherein the optical polyester film is formed of a polyester resin; the thermal expansion characteristic of the optical polyester film in the first direction is the same as the thermal expansion characteristic of the optical polyester film in the second direction at a preset temperature, and the absolute value of the difference between the average linear expansion coefficient (thermal expansion coefficient) of the optical polyester film in the first direction and the average linear expansion coefficient of the optical polyester film in the second direction is 0-80 multiplied by 10 at the preset temperature-8mm/(mm. K); the first direction is a direction perpendicular to the optical slow axis of the optical polyester film (perpendicular optical axis direction, MD direction)In the longitudinal direction) and the second direction is the direction of the optical slow axis of the optical polyester film (optical axis direction, TD direction, transverse direction).
In order to ensure the dimensional stability and optical performance of the optical polyester film under the condition of rapid heating, the absolute value of the difference between the thermal expansion coefficient of the optical polyester film in the first direction and the thermal expansion coefficient of the optical polyester film in the second direction is controlled to be (0-80) multiplied by 10-8mm/(mm. K); when the value is larger than 80X 10-8mm/(mm. K), the difference in the deformation of the optical polyester film due to expansion thereof is too large during heating due to the difference in the coefficients of expansion of the optical polyester film in different directions, thereby causing distortion in the optical properties of the optical polyester film, and the absolute value of the difference between the coefficient of thermal expansion of the optical polyester film in the first direction and the coefficient of thermal expansion of the optical polyester film in the second direction is further preferably 60X 10-8mm/(mm·K)。
It should be emphasized that the absolute value of the difference between the first and second directions of the optical polyester film is limited in the present invention, but according to the idea of the present invention, the difference of the thermal expansion coefficients in any two different directions with respect to the optical axis of the optical polyester film should be limited to be not higher than 80 × 10-8mm/(mm. K). The coefficient of thermal expansion can be measured using a thermomechanical analysis (TMA) method.
According to the embodiment of the invention, the preset temperature is-30-70 ℃. The preset temperature is further selected to be-30 to 50 ℃. It is emphasized that the expansion in the present invention generally includes three cases of the optical polyester film becoming larger, unchanged and smaller in size due to heat. The expansion characteristic specifically means that when the optical polyester film is heated, the dimension of the optical polyester film is simultaneously increased in the first direction and the second direction, and the optical polyester film is not changed in dimension or is reduced in dimension.
According to the embodiment of the present invention, the thermal expansion coefficient of the optical polyester film in the first direction is 100 x 10 or less-8mm/(mm. K); the thermal expansion coefficient of the optical polyester film in the second direction is less than or equal to 100 multiplied by 10-8mm/(mm. K). When it is higher than this value, although the distortion of the optical properties of the optical polyester film is not theoretically affected, a large geometric scale occursVariations in dimensions also cause difficulties in assembly and increased effectiveness during use. The thermal expansion coefficient of the optical polyester film in the first direction and the thermal expansion coefficient of the optical polyester film in the second direction are further selected to be 70 x 10 or less-8mm/(mm·K)。
According to the embodiment of the invention, the thermal shrinkage rate of the optical polyester film in the first direction is less than or equal to 5 percent; the thermal shrinkage rate of the optical polyester film in the second direction is less than or equal to 5 percent.
According to the embodiment of the present invention, the thickness of the optical polyester film is 30 μm to 300 μm. From the application angle, the thickness of the optical polyester film should be controlled to be 30-300 um, when the thickness is lower than 30um, the uniformity of the microstructure in the optical polyester film is difficult to control, so that the difference of thermal performance in each direction in the plane of the optical polyester film is increased, and when the thickness is larger than 300um, the thinning of the display panel is not facilitated in the practical use.
According to the embodiment of the present invention, the difference between the refractive index of the optical polyester film in the second direction and the refractive index of the optical polyester film in the first direction is 0.01 to 0.2, and more preferably 0.03 to 0.15. When the amount is less than 0.01, the effect of optical distortion of the optical polyester film during use is amplified, which affects display performance, and when the amount is more than 0.2, the optical polyester film causes great difficulty in processing and increases the thermal expansion coefficients in the first direction and the second direction.
According to an embodiment of the present invention, there is also provided a method for preparing an optical polyester film, for preparing the optical polyester film described above, including: steps S1-S4.
Step S1: the polyester resin is used for melt extrusion to obtain a cast sheet. The polyester film in step S1 can be obtained from any polyester resin, and the kind of the polyester resin is not particularly limited, and for example, polyethylene terephthalate, polypropylene terephthalate, polybutylene terephthalate, polyethylene naphthalate, polyethylene terephthalate, and other copolymerization components such as polyethylene terephthalate-1, 4-cyclohexanedimethanol ester can be cited. The polyester resin has high light transmittance, excellent thermal property and mechanical property, particularly the polyethylene terephthalate has comprehensive optical, thermal and mechanical properties, is easy to control crystallization, has lower cost and is easy to realize industrialization. In addition, additives such as ultraviolet absorbers, slipping agents, opening agents, and the like may be added to the polyester resin in appropriate amounts.
The method of melt-extruding the polyester resin to obtain a cast sheet may include: the polyester resin may be melt-extruded by a conventional method, for example, by drying the polyester resin, feeding the dried polyester resin into an extruder, melt-extruding the dried polyester resin at 250 to 280 ℃ and forming a cast sheet on a chill roll through a die.
Step S2: the cast sheet is stretched in a first direction to obtain a first stretched film.
Step S3: the first stretched film is stretched in the second direction, and at the same time, the first stretched film is subjected to a first relaxation treatment in the first direction, to obtain a second stretched film. Further optionally, the first relaxation treatment of the first stretched film in the first direction is completed at the same time as the stretching of the first stretched film in the second direction is completed.
Step S4: and (3) performing heat treatment on the second stretched casting sheet, and performing second relaxation treatment on the second stretched casting sheet in a second direction to obtain the optical polyester film.
According to an embodiment of the present invention, the temperature at which the cast sheet is stretched in the first direction in step S2 is Tg +20 ℃, Tg being the glass transition temperature of the polyester resin; the first stretch ratio is 1 to 3.
According to the embodiment of the present invention, the second stretching ratio in the step S3 is 2.8 to 5.5, and the relaxation amount in the first relaxation treatment is 0.1 to 25%, and more preferably 2 to 15%.
According to the embodiment of the invention, the relaxation amount of the second relaxation treatment in the step S4 is 1-15%. The relaxation process refers to an action of reducing the effective length or width of the film. For example, a 5% relaxation amount is a reduction in the effective length of the film to 95% of the original length before the relaxation treatment. The temperature of the heat treatment is Tm-50-Tm, and Tm is the melting temperature of the polyester resin.
According to the embodiment of the present invention, the second stretched film is subjected to a heat treatment while being subjected to a third relaxation treatment in the first direction, the amount of relaxation of the third relaxation treatment being 0 to 5%.
According to the embodiment of the present invention, the relaxation amount of the third relaxation treatment is equal to or less than the relaxation amount of the second relaxation treatment.
The technical solutions of the present invention are further described in detail below with reference to specific examples and drawings, it should be understood that the following examples are only illustrative of the present invention and are not intended to limit the present invention.
Example 1
Selecting polyethylene terephthalate (PET) slices with the intrinsic viscosity of 0.7dl/g, adding 0.8 mass percent of (2, 2' - (1, 4-phenylene) bis (4H-3, 1-benzoxazine-4-one) ultraviolet absorbent, drying, feeding into a double-screw mixing extruder, extruding for 5min at 280 ℃, and granulating to obtain the core layer PET master batch containing the ultraviolet absorbent.
Selecting PET slices with the intrinsic viscosity of 0.7dl/g, adding silicon dioxide particles with the concentration fraction of 8000ppm and the granularity of 2 mu m, and fully and physically mixing uniformly to prepare the PET master batch for the surface layer containing the tapping machine.
Drying 20 parts by mass of core layer PET master batch and 100 parts by mass of PET slices with the intrinsic viscosity of 0.67dl/g at 160 ℃ to enable the water content to be less than 100ppm, putting the core layer PET master batch and the PET slices into a single-screw extruder, setting the temperature of a feeding section to be 265 ℃, the temperature of a compression section to be 275 ℃, the temperature of a homogenizing section to be 275 ℃, setting the temperature of a neck mold to be 275 ℃, and adjusting the rotating speed of a screw and the rotating speed of a metering pump to enable the pressure after the pump to be stabilized at 1.2 MPa.
The PET master batch for the surface layer with the mass fraction of 20 percent and the PET slices with the mass fraction of 80 percent and the intrinsic viscosity of 0.67dl/g are put into a double-screw extrusion auxiliary machine, the temperature of a melting extrusion section is set to be gradually increased from 260 ℃ to 270 ℃, and the temperature of a melt conveying section and a die head is set to be 272 ℃. And (3) pressing three layers of melt (the thickness ratio is 12: 76: 12) flowing out of the neck ring die on a cooling roller in an electrostatic adhesion mode for quenching, wherein the temperature of the cooling roller is constant at 30 ℃, obtaining an amorphous casting sheet, and obtaining the casting sheet with the thickness not obtained by adjusting the extrusion amount.
With the cast sheet described above, first stretching was performed in the first direction (the optical axis direction perpendicular thereto, the machine direction, the MD direction) at 85 ℃ at a first stretching ratio (longitudinal stretching ratio) of 2.6, and then second stretching was performed in the second direction (the optical axis direction, the transverse direction, the TD direction) at 105 ℃ at a second stretching ratio (transverse stretching ratio) of 4.8, first relaxation was performed in the machine direction while stretching in the transverse direction, the relaxation amount of the first relaxation was 6%, and then heat treatment was performed at 230 ℃, while performing second relaxation in the TD direction, and third relaxation in the MD direction. The second relaxation amount was 12% and the third relaxation amount was 3%, and a 75um thick biaxially-oriented polyester film (BOPET film), i.e., an optical polyester film to be produced, was obtained. The properties of the BOPET film (film for short) were tested and filled in table 1.
Test of thermal shrinkage:
5 square BOPET film samples of 120mm by 120mm area were taken and marked with mutually perpendicular 100mm by 100mm marks in the middle of the BOPET film samples in the longitudinal and transverse directions. Placing them in a constant temperature oven at (150 + -1) ° C, keeping for 30min, and taking out. After cooling to ambient temperature, the lengths of the machine and transverse direction gauge lines were measured, and the heat shrinkage in the MD and TD directions of BOPET film samples of different thicknesses was calculated using the following formula, the arithmetic mean of the results being taken:
Figure BDA0003284492490000071
L0is the initial length of the film sample, i.e. the length of the film before it is placed in the oven at constant temperature, L150Is the length of the film sample after heat treatment. I.e. the heat shrinkage is equal to the amount of deformation/initial length.
And (3) judging the display effect: a display observation device is configured, a white LED is used as a light source, and two polaroids with mutually vertical light absorption axes are arranged above the light source. The film after the thermal shrinkage test is arranged between two polaroids in an observation display device in a direction of 45 degrees of the optical axis direction of the film and the absorption axis of the polaroid to observe whether the display is uniform or not:
very good: all the observation angles of all the positions of the film are uniform
O: few locations are slightly uneven;
x: there is a great unevenness.
FIG. 1 is a temperature-deformation rate curve of a film obtained by thermomechanical analysis (TMA) in example 1 of the present invention; FIG. 2 is an enlarged view of the portion of FIG. 1 at a temperature of 10-100 ℃.
As shown in FIGS. 1 and 2, the optical polyester film prepared in this example has a small deformation rate at-30 to 70 ℃ and a gentle change in deformation rate with an increase in temperature.
Example 2
As in the production method of the cast sheet in example 1, the cast sheet was subjected to first stretching in the machine direction at 85 ℃ at a machine direction stretching ratio of 2.6, and then to second stretching in the transverse direction at 105 ℃ at a transverse stretching ratio of 4.8, first relaxation was performed in the machine direction while stretching in the transverse direction, the relaxation amount of the first relaxation being 10%, and then to heat treatment at 230 ℃ while performing second relaxation in the TD direction, and third relaxation in the MD direction. The second relaxed relaxation amount was 12% and the third relaxed relaxation amount was 3%, resulting in a BOPET film having a thickness of 75 um. The properties of the films were tested and filled in table 1.
Example 3
As in the production method of the cast sheet in example 1, the cast sheet was subjected to first stretching in the machine direction at 85 ℃ at a machine direction stretching ratio of 2.6, and then to second stretching in the transverse direction at 105 ℃ at a transverse stretching ratio of 4.8, and first relaxation was performed in the machine direction while stretching in the transverse direction, the relaxation amount of the first relaxation being 6%, and then to heat treatment at 230 ℃, the heat treatment while performing second relaxation in the TD direction, and third relaxation in the MD direction. The second relaxation amount was 12% and the third relaxation amount was 3%, to obtain a BOPET film having a thickness of 100 um. The properties of the films were tested and filled in table 1.
Example 4
As in the production method of the cast sheet in example 1, the cast sheet was subjected to first stretching in the machine direction at 85 ℃ at a machine direction stretching ratio of 1.5, and then to second stretching in the transverse direction at 105 ℃ at a transverse stretching ratio of 4.8, first relaxation was performed in the machine direction while stretching in the transverse direction, the relaxation amount of the first relaxation being 6%, and then to heat treatment at 230 ℃, second relaxation was performed in the TD while heat treatment, and third relaxation was performed in the MD. The second relaxed relaxation amount was 12%, and the third relaxed relaxation amount was 3% to obtain a BOPET film having a thickness of 75 um. The properties of the films were tested and filled in table 1.
Example 5
In the same manner as in the production method of the cast sheet in example 1, the cast sheet was subjected to first stretching in the machine direction at 85 ℃ at a longitudinal stretching ratio of 2.6, and then to second stretching in the transverse direction at 105 ℃ at a transverse stretching ratio of 5.3, and first relaxation was performed in the machine direction while stretching in the transverse direction, the relaxation amount of the first relaxation being 6%, and then to heat treatment at 230 ℃ while performing second relaxation in the TD direction and third relaxation in the MD direction. The second relaxed relaxation amount was 12% and the third relaxed relaxation amount was 3% to obtain a BOPET film having a thickness of 75 um. The properties of the films were tested and filled in table 1.
Example 6
As in the production method of the cast sheet in example 1, the cast sheet was subjected to first stretching in the machine direction at 85 ℃ at a machine direction stretching ratio of 2.6, and then to second stretching in the transverse direction at 105 ℃ at a transverse stretching ratio of 5.1, and first relaxation was performed in the machine direction while stretching in the transverse direction, the relaxation amount of the first relaxation being 6%, and then to heat treatment at 230 ℃ while performing second relaxation in the TD direction and third relaxation in the MD direction. The second relaxed relaxation amount was 12% and the third relaxed relaxation amount was 3%, resulting in a BOPET film having a thickness of 75 um. The properties of the films were tested and filled in table 1.
Example 7
As in the production method of the cast sheet in example 1, the cast sheet was subjected to first stretching in the machine direction at 85 ℃ at a machine direction stretching ratio of 3.0, and then to second stretching in the transverse direction at 105 ℃ at a transverse stretching ratio of 4.8, first relaxation was performed in the machine direction while stretching in the transverse direction, the relaxation amount of the first relaxation being 6%, and then to heat treatment at 230 ℃ while performing second relaxation in the TD direction, and third relaxation in the MD direction. The second relaxed amount was 12% and the third relaxed amount was 3%, resulting in a BOPET film thickness of 175 um. The properties of the films were tested and filled in table 1.
Example 8
As in the production method of the cast sheet in example 1, the cast sheet was subjected to first stretching in the machine direction at 85 ℃ at a machine direction stretching ratio of 2.6, and then to second stretching in the transverse direction at 105 ℃ at a transverse stretching ratio of 4.8, first relaxation was performed in the machine direction while stretching in the transverse direction, the relaxation amount of the first relaxation being 2%, and then to heat treatment at 230 ℃ while performing second relaxation in the TD direction, and third relaxation in the MD direction. The second relaxed relaxation amount was 12%, and the third relaxed relaxation amount was 3% to obtain a BOPET film having a thickness of 100 um. The properties of the films were tested and filled in table 1.
Example 9
As in the production method of the cast sheet in example 1, the cast sheet was subjected to first stretching in the machine direction at 85 ℃ at a machine direction stretching ratio of 2.6, and then to second stretching in the transverse direction at 105 ℃ at a transverse stretching ratio of 4.8, first relaxation was performed in the machine direction while stretching in the transverse direction, the relaxation amount of the first relaxation was 6%, and then to heat treatment at 230 ℃ while performing second relaxation in the TD direction, and third relaxation in the MD direction. The second relaxed relaxation amount was 12% and the third relaxed relaxation amount was 5%, resulting in a BOPET film having a thickness of 100 um. The properties of the films were tested and filled in table 1.
Example 10
As in the production method of the cast sheet in example 1, the cast sheet was subjected to first stretching in the machine direction at 85 ℃ at a machine direction stretching ratio of 2.6, and then to second stretching in the transverse direction at 105 ℃ at a transverse stretching ratio of 4.8, first relaxation was performed in the machine direction while stretching in the transverse direction, the relaxation amount of the first relaxation was 6%, and then to heat treatment at 230 ℃ while performing second relaxation in the TD direction, and third relaxation in the MD direction. The second relaxed relaxation amount was 9% and the third relaxed relaxation amount was 3%, resulting in a BOPET film having a thickness of 75 um. The properties of the films were tested and filled in table 1.
Example 11
As in the preparation method of the cast sheet in example 1, the cast sheet was stretched at 85 ℃ in the machine direction at a stretch ratio of 3.0 in the machine direction, and then stretched at 105 ℃ in the transverse direction at a stretch ratio of 3.2 in the transverse direction, relaxed by 1% in the machine direction while being stretched, and then heat-treated at 230 ℃ while being subjected to a second relaxation in the TD direction and a third relaxation in the MD direction. The second relaxed relaxation amount was 4% and the third relaxed relaxation amount was 3%, resulting in a BOPET film having a thickness of 75 um. The properties of the films were tested and filled in table 1.
Example 12
In the same manner as in the production method of the cast sheet in example 1, the cast sheet was subjected to first stretching in the machine direction at 85 ℃ at a machine direction stretching ratio of 2.6, and then to second stretching in the transverse direction at 105 ℃ at a transverse stretching ratio of 4.9, the first relaxation was carried out in the machine direction while stretching in the transverse direction, the relaxation amount of the first relaxation was 7%, and then to heat treatment at 230 ℃, the second relaxation was carried out in the TD direction while heat treating, the relaxation amount of the second relaxation was 12%, and the relaxation was not carried out in the MD direction, to obtain a BOPET film having a thickness of 75 um. The properties of the films were tested and filled in table 1.
Comparative example 1
In the same manner as in the production method of the cast sheet in example 1, the cast sheet was subjected to first stretching at 85 ℃ in the machine direction at a stretching ratio in the machine direction of 2.6, and then to second stretching at 105 ℃ in the transverse direction at a stretching ratio in the transverse direction of 4.8 without relaxation treatment while being stretched in the transverse direction, and then to heat treatment at 230 ℃ without relaxation treatment in the MD and TD directions, to obtain a BOPET film having a thickness of 75 μm. The properties of the films were tested and filled in table 1.
Comparative example 2
In the same manner as in the production method of the cast sheet in example 1, the cast sheet was subjected to first stretching in the machine direction at 85 ℃ at a machine direction stretching ratio of 2.6, then to second stretching in the transverse direction at 105 ℃ at a transverse direction stretching ratio of 4.8, and subjected to first relaxation in the machine direction while being stretched in the transverse direction by 20%, and then to heat treatment at 230 ℃ with third relaxation in the MD direction at the time of heat treatment at a relaxation amount of 3% without relaxation treatment in the TD direction, to obtain a BOPET film having a thickness of 75 um. The properties of the films were tested and filled in table 1.
Comparative example 3
In the same manner as in the production method of the cast sheet in example 1, the cast sheet was subjected to first stretching in the machine direction at 85 ℃ at a machine direction stretching ratio of 1.1, and then to second stretching in the transverse direction at 105 ℃ at a transverse direction stretching ratio of 6.2, and first relaxation was carried out in the machine direction while stretching in the transverse direction, the relaxation amount of the first relaxation being 6%, and then to heat treatment at 230 ℃ without relaxation treatment in the MD and TD, to obtain a BOPET film having a thickness of 100 um. The properties of the films were tested and filled in table 1.
Comparative example 4
In the same manner as in the production method of the cast sheet in example 1, the cast sheet was subjected to first stretching in the machine direction at 85 ℃ with a machine direction stretching ratio of 5.6, and then to second stretching in the transverse direction at 105 ℃ with a transverse direction stretching ratio of 1.3, and first relaxation was carried out in the machine direction while stretching in the transverse direction with a first relaxation amount of 13% and then to heat treatment at 230 ℃, and second relaxation was carried out in the TD direction with a second relaxation amount of 15% without relaxation treatment in the MD direction, to obtain a double-drawn BOPET film having a thickness of 100 um. The properties of the films were tested and filled in table 1.
BOPET film thickness was obtained using micrometer testing (hotte GL 25); the thermal expansion coefficient was measured by a model TMA7100 (Hitachi thermal Analyzer), the sample was cut to 30mm by 3mm in the MD or TD direction, respectively, the preload force was 20g, the initial sample length was 16mm, and the sample was scanned from-30 ℃ to 250 at a temperature increase rate of 5 ℃/min. In the graph (displacement amount/initial length vs temperature graph), a linear fitting is carried out on an almost linear expansion region of-30 ℃ to 70 ℃, and the obtained slope is the average linear expansion coefficient (thermal expansion coefficient) of the temperature region.
TABLE 1 EXAMPLES AND COMPARATIVE EXAMPLES AND PERFORMANCE TABLE
Figure BDA0003284492490000131
As can be seen from the above table, the optical polyester films prepared by the preparation method of the present invention have low thermal expansion coefficient and thermal expansion coefficient difference, low shrinkage rate and good display effect through the examples 1 to 12. In comparative examples 1 to 4, the MD or TD thermal expansion coefficient is high and the maximum thermal shrinkage of the film is higher than 5%, showing poor effect. In conclusion, the optical polyester film prepared by the preparation method has higher dimensional stability, and can effectively solve the problems of dimensional change and optical distortion of the film under the heating condition.
The optical polyester film provided by the invention can be used for an optical base film or a polaroid supporting film in a backlight module or a display module in a liquid crystal display module.
The above-mentioned embodiments are intended to illustrate the objects, technical solutions and advantages of the present invention in further detail, and it should be understood that the above-mentioned embodiments are only exemplary embodiments of the present invention and are not intended to limit the present invention, and any modifications, equivalents, improvements and the like made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims (10)

1. An optical polyester film, wherein,
the optical polyester film is prepared from polyester resin;
at a preset temperature, the thermal expansion characteristic of the optical polyester film in the first direction is the same as that of the optical polyester film in the second direction;
at the preset temperature, the absolute value of the difference value between the average linear expansion coefficient of the optical polyester film in the first direction and the average linear expansion coefficient of the optical polyester film in the second direction is 0-80 multiplied by 10-8mm/(mm·K)；
The first direction is a direction perpendicular to an optical slow axis of the optical polyester film in the optical polyester film, and the second direction is the direction of the optical slow axis of the optical polyester film.
2. The optical polyester film according to claim 1, wherein the predetermined temperature is-30 to 70 ℃.
3. As in claimThe optical polyester film according to claim 1, wherein the average linear expansion coefficient of the optical polyester film in the first direction is 100X 10 or less-8mm/(mm·K)；
The average linear expansion coefficient of the optical polyester film in the second direction is less than or equal to 100 multiplied by 10-8mm/(mm·K)。
4. The optical polyester film according to claim 1, wherein the thermal shrinkage of the optical polyester film in the first direction is 5% or less;
the thermal shrinkage rate of the optical polyester film in the second direction is less than or equal to 5%.
5. The optical polyester film according to claim 1, wherein the thickness of the optical polyester film is 30 to 300 μm.
6. A method for producing an optical polyester film, for producing the optical polyester film according to any one of claims 1 to 5, comprising:
carrying out melt extrusion on polyester resin to obtain a cast sheet;
performing first stretching on the casting sheet in the first direction to obtain a first stretched film;
performing second stretching on the first stretched film in the second direction, and simultaneously performing first relaxation treatment on the first stretched film in the first direction to obtain a second stretched film;
and carrying out heat treatment on the second stretched film, and simultaneously carrying out second relaxation treatment on the second stretched film in the second direction to obtain the optical polyester film.
7. The method of claim 6, further comprising:
subjecting the second stretched film to a heat treatment while subjecting the second stretched film to a third relaxation treatment in the first direction.
8. The production method according to claim 7, wherein,
the relaxation amount of the first relaxation treatment is 0.1-25%;
the relaxation amount of the second relaxation treatment is 1-15%;
the relaxation amount of the third relaxation treatment is 0-5%;
the relaxation amount of the third relaxation treatment is equal to or less than the relaxation amount of the second relaxation treatment.
9. The production method according to claim 6, wherein the temperature at which the cast sheet is stretched in the first direction is Tg to Tg +20 ℃, Tg being a glass transition temperature of the polyester resin;
the temperature of the heat treatment is Tm-50-Tm, and Tm is the melting temperature of the polyester resin.
10. The production method according to claim 6, wherein a first draw ratio of the first drawing is 1 to 3;
the second stretching ratio of the second stretching is 2.8 to 5.5 times.
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Publication number Priority date Publication date Assignee Title
US20090035596A1 (en) * 2006-01-27 2009-02-05 Fujifilm Corporation Optical film and method for producing the same
JP2012188631A (en) * 2011-03-14 2012-10-04 Fujifilm Corp Polyester film, method for producing the same, back sheet for solar cell, and solar cell module
WO2014209056A1 (en) * 2013-06-27 2014-12-31 코오롱인더스트리 주식회사 Polyester film and method for manufacturing same

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