KR101265105B1 - Biaxial stretched film by polyester for optical film - Google Patents

Abstract

The present invention relates to an optical base film, and more particularly, to a biaxially stretched polyester film coextruded with at least two or more layers, the base layer having a refractive index of 1.6 to 1.7 and coextruded on one or both sides of the base layer. A surface layer having a refractive index of 1.4 to 1.6 and a coating layer made of a resin having a lower refractive index than the surface layer on the surface layer, the base layer does not contain a particulate component, the surface layer and the coating layer are each for high transparency optical Biaxially-stretched polyester film It relates to a polyester film. This film relates to a base film having reduced defects during the manufacturing process and having a total light transmittance of 93% or more.

Base film, total light transmittance, polyester film, PET film

Description

Biaxial stretched film by polyester for optical film

The present invention relates to a biaxially stretched polyester film used for optics and to a biaxially stretched polyester film coextruded with at least two layers.

Optical films started later than general polymer films used in packaging materials, plastic products, automobiles, etc., but with the advancement of LCD-related technology and research on high functionalization of films, the possibility of their use and demand is increasing day by day.

The optical film includes a viewing angle expanding film, an antireflection film, a compensation film, a brightness rising film, and the like, and a polyester film is most commonly used for such an optical film.

Polyester film has excellent physical stability over a wide temperature range from low temperature to high temperature, excellent chemical resistance compared to other polymer resins, and good mechanical strength, surface properties, and uniformity of thickness. As it has applicability, it is applied to capacitors, photo films, labels, pressure-sensitive tapes, decorative laminates, transfer tapes, polarizers and ceramic sheets, and the demand is increasing day by day to meet the trend of high speed and automation. .

The polyester film used in the display field is a base film for touch panels that undergoes a hard coating process through offline coating for use in a liquid crystal display device, a film used for a PDP panel, a diffusion sheet included in a backlight unit, and a prism Base films used in lens sheets, prismatic protective films, and the like, and anti-reflective coating base films for preventing glare caused by external light.

Base films used in such display fields require various characteristics such as process running stability, transparency, scratch resistance, planarity, and light transmittance. The reason why so many requirements are required is that the purpose of the base film in the display field must satisfy the optical specificity.

Planarity, one of the characteristics required for the base film, causes poor slippage due to uneven tension in the production process of the base film when the planarity of the film is poor, resulting in scratch defects on the surface of the film. Because of the non-uniform coating amount, partial coating failure occurs, which acts as a factor that reduces the value of the product.

Scratch resistance can cause problems such as black spots, electrical defects due to uneven distribution of the transparent conductive film, or uneven coating in the post-processing process such as hard coating. Therefore it is a required characteristic. It can also cause optical defects that adversely affect product quality and yield.

These characteristics required for the base film are eventually required to increase the brightness, thermal stability, processing characteristics, etc. in the film. Decreased transparency, scratch resistance, planarity and total light transmittance cause problems of lowering luminance and reliability and lowering yield. This decrease in brightness requires a higher light source in order to obtain the required amount of light, and it is a fatal defect in the base film used in the display field because it requires higher cost of materials and higher power consumption in order to obtain a high light source. .

Therefore, researches on base films have been conducted to improve luminance, and Japanese Patent No. 2006-208993 has a base film and a coating amount, and the coating layer is interposed with a biaxially stretched polyester film, which is a light diffusion layer containing a binder and particles. Japanese Patent No. 2006-163378 discloses a polyester film in which a coating layer containing fine bubbles inside a film and containing a light stabilizer and an antioxidant on the surface of the film is laminated. Japanese Patent No. 1994-059108 No. interpolates the polyester film which provided the unevenness | corrugation in the base film, and laminated | stacked both sides of the base film in the layer containing a light-diffusion agent.

The present invention provides a polyester film having a high total light transmittance in order to improve luminance, which is a requirement for use as a base film used in the display field as described above.

In addition, to provide a total light transmittance as described above, to provide a polyester film with improved coefficient of friction of the film to improve the problem of defects appearing during the manufacturing process or processing of the film.

The present invention is a biaxially stretched polyester film coextruded at least two or more layers, a base layer having a refractive index of 1.6 to 1.7, a surface layer having a refractive index of 1.4 to 1.6 and coextruded on one or both surfaces of the base layer and an upper portion of the surface layer. It has a coating layer made of a resin having a lower refractive index than the surface layer, the base layer does not contain a particulate component, the surface layer and the coating layer relates to a biaxially stretched polyester film for high transparency optics, each containing fine particles.

The biaxially stretched polyester film for high transparency optics according to the present invention can reduce the occurrence of defects during the manufacturing process, it can provide an optical base film having a total light transmittance of 93% or more.

The polyester film according to the present invention has improved surface structure while maintaining high total light transmittance due to the fine particles of the surface layer, thereby reducing defects in the film process, and adhesive strength between the substrate layer and the post-working layer due to the crosslinked resin coating layer. It is excellent and more suitable for use as an optical base film.

The manufacturing method of the biaxially stretched polyester film for high transparency optics of this invention is

a) co-extrusion of a base layer having a refractive index of 1.6 to 1.7 with 30 to 500 ppm of fine particles on one or both surfaces thereof, and a surface layer having a refractive index of 1.4 to 1.6;

b) stretching in the machine direction (MD) at a temperature above the glass transition temperature (T _g ) of the coextruded film;

c) 80 to 90% by weight of a resin binder having a refractive index of 1.35 to 1.55, 1 to 5% by weight of fine particles having an average particle diameter of 20 to 300nm, and additives 1 to 5 on the surface of the film layer drawn in the machine direction (MD). Applying a coating liquid in the form of an aqueous acid solution having a solid content of 2 to 10 wt%, the remainder including water;

d) stretching the film coated with the coating solution in a vertical width direction (TD) perpendicular to the machine direction at a temperature of 20 to 30 ° C. higher than the machine direction draw temperature; And

e) heat setting;

.

Hereinafter, the present invention will be described more specifically.

Referring to the drawings, the first embodiment of the present invention, as shown in Figure 1, the refractive index is 1.6 ~ 1.7, and the refractive index is 1.4 ~ on both sides of the base layer 10 The surface layer 20, which is 1.6, is coextruded and has a coating layer 30 made of a resin having a lower refractive index than the surface layer. The substrate layer 10 does not include a particulate component, and the surface layer 20 and the coating layer 30 each contain particulates.

The fine particles of the surface layer 20 may be any one selected from silica sol having an average particle diameter of 20 to 300 nm, and amorphous silica particles having an average particle diameter of 1.0 to 3.0 μm, or a mixture thereof. The content is preferably 30 to 500 ppm. The coating layer 30 is 80 to 90% by weight of the resin binder having a refractive index of 1.35 to 1.55, 1 to 5% by weight of the fine particles having an average particle diameter of 20 to 300nm, 1 to 5% by weight of the additive and the rest includes water, and the solid content A coating liquid in the form of this aqueous solution of 2-10% by weight is used.

The base layer 10 and the surface layer 20 is a polyester resin or a copolymer thereof, and the coating layer 30 is made of a resin selected from polyacrylate, polyurethane, and polyester resin.

At this time, any one of the coating layer may further include any one or a mixture of two or more selected from an antistatic agent, UV stabilizer, waterproofing agent, slip agent, thermal stabilizer.

In addition, in the second embodiment of the present invention, as shown in FIG. 2, the base layer 10 having a refractive index of 1.6 to 1.7, and the surface layer 20 having a refractive index of 1.4 to 1.6 on both surfaces of the base layer 10. This is coextruded and has a coating layer 10 made of a resin having a lower refractive index than the surface layer on either side of the surface layer 20. The substrate layer 10 does not include a particulate component, and the surface layer 20 and the coating layer 30 each contain particulates.

In addition, in the third embodiment of the present invention, as shown in FIG. 3, the base layer 10 having a refractive index of 1.6 to 1.7 and the surface layer 20 having a refractive index of 1.4 to 1.6 on one surface of the base layer 10. This is coextruded, and has a coating layer 10 made of a resin having a lower refractive index than the surface layer on the surface layer 20. The substrate layer 10 does not include a particulate component, and the surface layer 20 and the coating layer 30 each contain particulates.

In the present invention, the base layer 10 is not limited if the polyester film used in a conventional base film, but 90 mol% of polyethylene terephthalate (PET, polyethylene terephthalate) or ethylene terephthalate as the main repeating unit It is made of a copolymer containing above and the refractive index of the film is preferably 1.6 to 1.7.

The said polyethylene terephthalate is obtained by condensation polymerization of the acid component which has dicarboxylic acid as a main component, and the glycol component which has alkyl glycol as a main component. Terephthalic acid or its alkyl ester or phenyl ester is mainly used as the dicarboxylic acid, but a part thereof is transferred, such as isophthalic acid, oxyethoxy benzoic acid, adipic acid, sebacic acid, 5-sodium sulfoisophthalic acid, and the like. It can be used in place of a functional carboxylic acid or its esterifying derivative. As the glycol component, ethylene glycol is the main object, but a part thereof is neopentyl glycol, propylene glycol, trimethylene glycol, 1,4-cyclohexanediol, 1,4-cyclohexanedimethanol, 1,4- It may be used instead of bisoxyethoxybenzene, bisphenol, polyoxyethylene glycol, or may be used in combination with a monofunctional compound or trifunctional compound if the content is small.

The present invention is formed by co-extruding the surface layer 20 having a refractive index of 1.4 to 1.6 on one or both surfaces of the base layer 10 having a refractive index of 1.6 to 1.7. The coextruded surface layer 20 may be made of a polyethylene terephthalate copolymer containing 50 to 85 mol% of ethylene terephthalate repeating units. The polyethylene terephthalate copolymer is obtained by condensation polymerization of an acid component containing dicarboxylic acid as a main component and a glycol component containing alkyl glycol as a main component. Terephthalic acid or its alkyl ester or phenyl ester is mainly used as the dicarboxylic acid, but a part thereof is transferred, such as isophthalic acid, oxyethoxy benzoic acid, adipic acid, sebacic acid, and 5-sodium sulfoisophthalic acid. It can be used in place of a functional carboxylic acid or an ester forming derivative thereof. As the glycol component, ethylene glycol is the main object, but a part thereof is neopentyl glycol, propylene glycol, trimethylene glycol, 1,4-cyclohexanediol, 1,4-cyclohexanedimethanol, 1,4- It may be used in place of bisoxyethoxybenzene, bisphenol, polyoxyethylene glycol, and may be used in combination with a monofunctional or trifunctional compound if the content is small.

In the surface layer 20 of the present invention, it is preferable that the antiblocking agent contains fine particles of colloidal or chain silica (SiO ₂ ). The fine particles used are as follows. Silica sol having an average particle diameter of 20 to 300 nm and amorphous silica particles having an average particle diameter of 1 to 3.0 µm are preferably used alone or in combination. The fine particle concentration in the surface layer 20 is preferable because it expresses antiblocking property in a range in which 30 to 500 ppm does not lower the total light transmittance of the film.

If the average particle diameter of the silica sol is less than 20nm, not only does not help runability and scratch resistance in the base film, but also does not affect the effect of fine particles, and also agglomeration of the resin may occur, and if the average particle diameter of the silica sol is 300 nm or more, It is preferable to use a silica sol having an average particle diameter of 20 nm to 300 nm because it may cause scratches due to formation and dropping of coarse protrusions on the surface of the film.

In addition, if the average particle diameter of the amorphous silica particles is less than 1㎛ protruding effect is small, the friction coefficient is difficult to improve, if more than 3㎛ coarse projections may be formed.

At least one surface of the coating layer 30 is made of a polyester film composed of the base layer 10 and at least one surface layer 20 and the refractive index of the coating layer 30 is lower than the refractive index of the surface layer 20 and 1.35 to 1.55. To be The above configuration increases the total light transmittance of the entire film, because the light loss can be suppressed by reducing the amount of light reflected from the surface of the film and making the transmission possible. This suppression of light loss can increase the brightness after processing of the final post-processing product, such as diffusion film and prism film.

The coating layer 30 is 80 to 90% by weight of the resin binder having a refractive index of 1.35 to 1.55, 1 to 5% by weight of the fine particles having an average particle diameter of 20 to 300nm, 1 to 5% by weight of the additives, and the rest thereof include water. The solid content is 2 to 10% by weight based on the weight of the coating liquid, the viscosity of the coating liquid is preferably 20cps or less.

If the concentration of the solid content is less than 2% by weight, the amount of wet coating should be increased to obtain the desired thickness of the coating layer, and a large amount of energy is required to dry it, which may increase the manufacturing cost of the base film and the concentration of the solid content is 10% by weight If exceeded, the viscosity may be increased to 20 cps or more, resulting in a decrease in coating properties.

As the binder resin, an acrylic resin, an emulsion binder having a urethane-based functional group, or the like can be used.

The use of the fine particles can form irregularities on the surface of the coating layer to adjust the coefficient of friction of the film, improve the hardness of the coating layer to improve the wear characteristics, and also by the difference in refractive index between the layers constituting the film using organic particles It can also be used to increase the diffusivity to induce an increase in total light transmittance. The fine particles used are not particularly limited as long as the fine particles are usually used for plastic films. Examples thereof include colloidal silica having an average particle diameter of 20 to 300 nm, hard calcium carbonate (CaO), silica (SiO ₂ ) sol, and barium sulfate (BaSO _4). ), Crosslinked acrylics such as sodium oxide (NaO ₂ ), sodium sulfate (Na ₂ SO ₄ ), kaolin, kaolin, talc, antiblocking inorganic particles, silicone resin, crosslinked divinylbenzenepolymethacrylate, crosslinked polymethacrylate Organic particles such as resins and crosslinked polystyrene resins, benzoguanamine-formaldehyde resins, benzoguanamine-melamine-formaldehyde resins, melamine-formaldehyde resins and the like. Of these, colloidal silica and silica sol have been commercialized to nano size, and are excellent in thermal stability, which is good for use as fine particles. And it is most suitable to apply, since it is excellent in transparency compared with other microparticles | fine-particles, and is excellent in aqueous solution dispersibility.

As the fine particles, fine particles having an average particle diameter of 20 to 300 nm are used. When the average particle size of the fine particles is 20 nm or less, it does not help runability and scratch resistance in the base film, and does not have an effect of adding fine particles, and may also cause agglomeration of resin, and when the average particle size of the fine particles is 300 nm or more, the film It is preferable to use fine particles having an average particle diameter of 20 to 300 nm since scratches may be generated by formation and dropping of coarse protrusions on the surface.

As other additives, curing agents, antioxidants, quick-drying agents, wetting agents and the like can be used. Using these additives in the range of 1 to 5% by weight is possible to express physical properties without inhibiting the physical properties of other components.

Such additives are not limited to those types as long as they are commonly used in the art. Specifically, for example, melamine-based or the like may be used as the curing agent, phenol-based compounds may be used as the antioxidant, isopropyl alcohol or the like may be used as the quick-drying agent, and silicone-based surfactants may be used as the wetting agent. It is possible.

The polyester film of the present invention further includes at least one component selected from an antistatic agent, an ultraviolet stabilizer, a waterproofing agent, a slipping agent, and a thermal stabilizer on at least one side of the coating layer, if necessary, when the coating layer 30 is coated on both sides. can do.

The antistatic agent is used to prevent adhesion of foreign matters, such as dust, to the base film to reduce adhesion by foreign matter in the post-processing process, and any antistatic agent used for a conventional base film is not limited to its use. Typical examples of the antistatic agent to be used include quaternary ammonium salts such as butyloxyethyl hydroxyethyl orthodecyloxy ammonium salt, bishydroxydecylpropyl ammonium salt and hydroxybutyl dodecyloxybutyl ethylammonium salt, and silver, gold and copper Metal particles, such as aluminum, platinum, nickel, chromium, lead, cobalt, rhodium, ruthenium, tin, iridium, palladium, titanium, or the like, include, but are not limited to, metal antistatic agents.

UV stabilizers are used to absorb ultraviolet rays to prevent decomposition of the coating layer by light, and any UV stabilizer used in a conventional base film is not limited. Representative examples of ultraviolet stabilizers to be used include ultraviolet absorbers such as benzophenone series, benzotriazole series, resorcinol monobenzoate series, salicylate series, hydroxyate series, and formamidine series, hindered amine ultraviolet stabilizers, and the like. A noester ultraviolet stabilizer may be used, but is not limited thereto.

The waterproofing agent is used to prevent the surface film of moisture from increasing as the moisture absorption increases as the moisture absorption increases, and if the waterproofing agent is commonly used in the base film, the use thereof is not limited. Representative waterproofing agents can be used as waterproofing agents such as fluorine-containing compounds such as perfluoroalkyl acrylates and silicone compounds.

The slip agent is used to increase the release property of the base film and to suppress defects by the post-processing process, and colloidal silica, organosilicon polymer, or derivatives thereof may be used, but any conventional slip agent used for the base film may be limited. Do not leave.

The heat stabilizer can be used to obtain a uniform thickness sheet by electrostatic application on the rotating cooling roll during the processing of the base film, or a heat stabilizer used for the purpose of preventing oxidation during the heat treatment section and remanufactured chips in the coating composition. If it is a heat stabilizer such as phosphoric acid or a phosphorus compound that is commonly used, there is no particular restriction on its use.

The polyester film according to the present invention has improved surface structure while maintaining high total light transmittance due to the fine particles of the surface layer, thereby reducing the occurrence of defects in the film process, and excellent adhesion between the base film and the post-processing working layer due to the coating layer. It is more suitable for use as a base film.

The polyester film according to the present invention has a higher total light transmittance of 1 to 5% than the base film without the coating layer, and minimizes defects caused by slip and adhesion in the manufacturing process and the processing process, thereby improving the quality of the optical film. It has a high cross-linked resin coating layer, so it is more suitable for use as an optical base film because it has excellent adhesion between the base film and the post-working layer.

Hereinafter, the present invention will be described in detail with reference to the following examples. However, the present invention is not limited to the following examples.

The method of measuring the physical properties shown in the following Examples and Comparative Examples is as follows.

1. Measurement of total light transmittance of the film: The total light transmittance was measured using a Nippon Denshoku 300A.

2. Film refractive index measurement: The refractive index was measured at room temperature using an ABE refractometer (ATAGO).

3. Permeability and Haze Measurement: A Nippon Denshoku 300A meter was used and measured according to ASTM D-1003.

4. Friction Coefficient Measurement: A friction coefficient measuring instrument manufactured by Toyoseiki, Japan, was used and measured according to ASTM D-1434.

5. Film defects: A fluorescent lamp was turned on in a dark room and the size and frequency of the defects reflected by the naked eye reflected on the film with the film placed on the antireflective black sheet underneath were checked. (Circle) and the case where there are no defects were made into (circle) and the case of 1-5 were made into (circle), and the case of 6-10 was made into (triangle | delta) and the case with more than 10.

Example 1 Preparation of Double-coated Base Film After Co-Extrusion

3 hours after adding 4 g of an acrylic binder with a refractive index of 1.44, 0.1 g of a silicone wetting agent (polyester siloxane copolymer of TEGO), 0.1 g of 200 nm colloidal silica particles, and 0.15 g of a melamine curing agent (DIC) in water By stirring, a coating liquid having a solid content of 4.35% and a viscosity of 12 cps (25 ° C.) was prepared.

The chip composition of the base layer was polymerized by mixing 100 mol% of terephthalic acid and 100 mol% of ethylene glycol, preparing polyethylene terephthalate chip (CHIP) without adding particles, and putting it in a drier and drying at 180 ° C. for 8 hours. The moisture content in the chip was lowered below 100 ppm.

The chip composition of the surface layer was polymerized by adding 100 mol% of dimethyl terephthalate, 75 mol% of ethylene glycol and 25 mol% of neopentyl glycol, and 50ppm of amorphous silica particles having an average particle diameter of 1.4 µm (Coulter counter method) and an average particle diameter of 200 nm. 50 ppm of silica sol particles (Coulter counter method) were polymerized together to prepare a Copolyester Chip (CHIP), which was placed in a dryer and dried at 180 ° C. for 8 hours to lower the water content of the chip to 100 ppm or less. .

The polyethylene terephthalate chip from which moisture was removed was placed in the main extruder (B) and melt-extruded, and then connected by a feed block to form an A / B / A three-layer structure. (A) was melt extruded and connected to the feed block.

A polyethylene terephthalate having a thickness of 2000 μm by quenching and solidifying a molten resin formed at A / B / A (layer composition ratio 5% / 90% / 5%) through a feed block and a die with a casting drum having a surface temperature of 20 ° C. A sheet was obtained. The obtained polyethylene terephthalate sheet was stretched 3.5 times in the longitudinal direction at a temperature of T _g or more, that is, 110 ° C., and then cooled to room temperature, and then coated on both sides by a bar coating method. Thereafter, the film is preheated and dried at 130 ° C., which is higher than the longitudinal drawing, and stretched 3.5 times in the transverse direction (TD) and heat treated at 230 ° C. in a heat treatment zone of five or more tenters, and then the film is cooled at 200 ° C. in a cooling zone. The biaxially stretched film coated on both sides was prepared by heat setting by relaxing 10% in the longitudinal and transverse directions at the following temperature.

Physical properties of the prepared film were measured by the above method, and the results are shown in Table 1 below.

Example 2 Preparation of Double-coated Base Film with Different Refractive Index after Co-Extrusion

4 g of an acrylic binder having a refractive index of 1.44, 0.1 g of a silicone wetting agent, 0.1 g of a 200 nm colloidal silica particle, and 0.15 g of a melamine-based curing agent (DIC) were added to water, followed by stirring for 3 hours to obtain a solid content of 4.35%, Coating solution 1 having a viscosity of 12 cps was prepared.

4 g of a urethane binder having a refractive index of 1.52, 0.1 g of a silicone wetting agent, 0.1 g of a 200 nm colloidal silica particle, and 0.15 g of a melamine curing agent (DIC) were added to water, followed by stirring for 3 hours to obtain a solid content of 4.35% and viscosity. A coating solution 2 of 14 cps was prepared.

The chip composition of the base layer was polymerized by adjusting the molar ratio of 100 mol% of terephthalic acid and 100 mol% of ethylene glycol, preparing a polyethylene terephthalate chip (CHIP) to which no particles were added, putting it in a drier and drying at 180 ° C. for 8 hours. The moisture content in the interior was lowered below 100 ppm.

The chip composition of the surface layer was polymerized by adding 100 mol% of dimethyl terephthalate, 75 mol% of ethylene glycol and 25 mol% of neopentyl glycol, and 50ppm of amorphous silica particles having an average particle diameter of 1.4 µm (Coulter counter method) and an average particle diameter of 200 nm. Copolymer polyester (Co-PET) chips (CHIP) are prepared by polymerizing together 50 ppm of silica sol particles (Cooler counter method), and placed in a dryer and dried at 180 ° C. for 8 hours to reduce the water content of the chip to 100 ppm or less. It was.

The polyethylene terephthalate chip from which moisture was removed was placed in the main extruder (B) and melt-extruded, and then connected by a feed block to form an A / B / A three-layer structure. (A) was melt extruded and connected to the feed block.

A polyethylene terephthalate having a thickness of 2000 μm by quenching and solidifying a molten resin formed at A / B / A (layer composition ratio 5% / 90% / 5%) through a feed block and a die with a casting drum having a surface temperature of 20 ° C. A sheet was obtained. After the obtained polyethylene terephthalate sheet was stretched 3.5 times in the longitudinal direction at a temperature of T _g or more, that is, 110 ° C., and then cooled to room temperature, the coating liquid 1 prepared was coated on one side by a bar coating method, and then the coating liquid on the other side. 2 was coated. Thereafter, the film is preheated and dried at 130 ° C., which is higher than the longitudinal draw, and stretched 3.5 times in the transverse direction (TD) and heat treated at 230 ° C. in a heat treatment zone of at least five stages of tenter, and then the film is cooled at 200 ° C. in a cooling zone. The biaxially stretched film coated on both sides was prepared by heat setting by relaxing 10% in the longitudinal and transverse directions at the following temperature.

Physical properties of the prepared film were measured by the above method, and the results are shown in Table 1 below.

[Example 3]

A film was prepared in the same manner as in Example 1, but the coating liquid was applied to only one surface as shown in FIG. 2.

Physical properties of the prepared film were measured by the above method, and the results are shown in Table 1 below.

Example 4

A film was prepared in the same manner as in Example 1, but as shown in FIG. 3, the surface layer and the coating layer were formed on only one surface.

Physical properties of the prepared film were measured by the above method, and the results are shown in Table 1 below.

Comparative Example 1 Preparation of Base Film without Coating Layer

In the polyethylene terephthalate polymerization step, a chip obtained by polymerizing a master batch by adding 500 ppm of silica having an average particle diameter of 1.4 μm (Coulter Counter method) and a polyethylene terephthalate chip polymerized without adding particles are mixed into a final chip. Mix to contain 50 ppm of particles. Then, the mixed polyethylene terephthalate chip (CHIP) was put in a drier and dried at 180 ° C. for 8 hours to lower the water content in the chip to 100 ppm or less.

The polyethylene terephthalate chip from which the water was removed was placed in an extruder and melt-extruded, followed by quenching and solidifying with a casting drum having a surface temperature of 20 ° C. to obtain a polyethylene terephthalate sheet having a thickness of 2000 μm. The obtained polyethylene terephthalate sheet was stretched 3.5 times in the machine direction (MD) at a temperature of Tg or more, that is, 110 ° C., cooled to room temperature, then preheated and dried at 140 ° C., higher than the machine direction stretch, and then transversely. The film is stretched 3.5 times more and heat-treated at 230 ° C. in a heat-treatment zone of five or more tenters. Then, in the cooling zone, the film is heat-set by relaxing 10% in the longitudinal and transverse directions at a temperature of 200 ° C. or less, thereby biaxially stretching without a coating layer. A film was prepared.

Physical properties of the prepared film were measured by the above method, and the results are shown in Table 1 below.

Comparative Example 2 Preparation of One Side Coating Base Film

4 g of an acrylic binder having a refractive index of 1.44, 0.1 g of a silicone wetting agent, 0.1 g of a 200 nm colloidal silica particle, and 0.15 g of a melamine-based curing agent (DIC) were added to water, followed by stirring for 3 hours to obtain a solid content of 4.35%, A coating solution having a viscosity of 12 cps was prepared.

In the polyethylene terephthalate polymerization step, a chip obtained by polymerizing a master batch by adding 500 ppm of silica having an average particle diameter of 1.4 μm (Coulter Counter method) and a polyethylene terephthalate chip polymerized without adding particles are mixed into a final chip. Mix to contain 50 ppm of particles. Then, the mixed polyethylene terephthalate chip (CHIP) was put in a drier and dried at 180 ° C. for 8 hours to lower the water content in the chip to 100 ppm or less.

The polyethylene terephthalate chip from which the water was removed was placed in an extruder and melt-extruded, followed by quenching and solidifying with a casting drum having a surface temperature of 20 ° C. to obtain a polyethylene terephthalate sheet having a thickness of 2000 μm. The obtained polyethylene terephthalate sheet was stretched 3.5 times in the machine direction (MD) at a temperature of Tg or more, that is, 110 ° C., then cooled to room temperature, and then coated on one surface by a bar coating method. After preheating and drying at a higher temperature of 140 ° C., the film is stretched 3.5 times more in the transverse direction and heat treated at 230 ° C. in a heat treatment zone of at least five stages of tenter. 10% relaxation in the transverse direction was heat-set to prepare a biaxially stretched film coated on one surface.

Physical properties of the prepared film were measured by the above method, and the results are shown in Table 1 below.

Comparative Example 3 Preparation of Double-coated Coating Particle-Based Film

4 g of an acrylic binder having a refractive index of 1.44, 0.1 g of a silicone wetting agent, 0.1 g of a 200 nm colloidal silica particle, and 0.15 g of a melamine-based curing agent (DIC) were added to water, followed by stirring for 3 hours to obtain a solid content of 4.35%, A coating solution having a viscosity of 12 cps was prepared.

Polyethylene terephthalate chip (CHIP) to which fine particles were not added was placed in a drier and dried at 180 ° C. for 8 hours to lower the water content in the chip to 100 ppm or less. The polyethylene terephthalate chip from which the water was removed was placed in an extruder and melt-extruded, followed by quenching and solidifying with a casting drum having a surface temperature of 20 ° C. to obtain a polyethylene terephthalate sheet having a thickness of 2000 μm. After the obtained polyethylene terephthalate sheet was stretched 3.5 times in the machine direction (MD) at a temperature of Tg or more, that is, 110 ° C., and then cooled to room temperature, the coating liquid was coated on both sides by a bar coating method, and then machine direction. The film is stretched 3.5 times more in the transverse direction after preheating and drying at 140 ° C, which is higher than the stretching temperature, and heat-treated at 230 ° C in the heat treatment zone of a tenter of five or more stages, and then the film is longitudinally cooled at a temperature of 200 ° C or lower in the cooling zone. And 10% in the transverse direction was relaxed by heat setting to prepare a biaxially stretched film coated on both sides.

Physical properties of the prepared film were measured by the above method, and the results are shown in Table 1 below.

[Table 1]

As shown in the table, it was found that the embodiment according to the present invention has excellent transmittance of 93% or more, and excellent without film defects.

1 shows an example of a biaxially stretched polyester film for high transparency optics used in the present invention.

Figure 2 shows another example of a biaxially stretched polyester film for high transparency optics used in the present invention.

Figure 3 shows another example of a biaxially stretched polyester film for high transparency optics used in the present invention.

Description of the main parts of the drawing

10: base material layer

20: surface layer

30: coating layer

Claims (8)

A biaxially stretched polyester film coextruded with at least two layers, the base layer having a refractive index of 1.6 to 1.7, a surface layer having a refractive index of 1.4 to 1.6 and coextruded on one or both surfaces of the base layer, and a surface layer on top of the surface layer. It has a coating layer made of a resin having a lower refractive index, The base layer does not contain a particulate component, and the surface layer and the coating layer are biaxially stretched polyester film for high transparency optics, each of which contains fine particles. The method of claim 1, The fine particles of the surface layer is a biaxially stretched polyester film for high transparency optics comprising any one or a mixture of 30 to 500ppm of silica sol having an average particle diameter of 20 ~ 300nm, amorphous silica particles having an average particle diameter of 1.0 ~ 3.0㎛. 3. The method of claim 2, The coating layer may include 80 to 90% by weight of a resin binder having a refractive index of 1.35 to 1.55, 1 to 5% by weight of fine particles having an average particle diameter of 20 to 300nm, 1 to 5% by weight of an additive, and a balance of 2 to 3% of solid content. A biaxially stretched polyester film for high transparency optics using a coating liquid in the form of an aqueous 10 wt% aqueous solution. The method of claim 3, The base layer and the surface layer is a polyester resin or a copolymer thereof, the coating layer is a biaxially stretched polyester film for high transparency optics made of a resin selected from polyacrylate, polyurethane, polyester resin. The method according to any one of claims 1 to 4, When the coating layer is formed on both sides, the biaxially stretched polyester film for high transparency optics further comprising any one or a mixture of two or more components selected from antistatic agents, ultraviolet stabilizers, waterproofing agents, slip agents, thermal stabilizers on at least one side of the coating layer. a) co-extrusion of a base layer having a refractive index of 1.6 to 1.7 with 30 to 500 ppm of fine particles on one or both surfaces thereof, and a surface layer having a refractive index of 1.4 to 1.6; b) stretching in the machine direction (MD) at a temperature above the glass transition temperature (T _g ) of the coextruded film; c) 80 to 90% by weight of a resin binder having a refractive index of 1.35 to 1.55, 1 to 5% by weight of fine particles having an average particle diameter of 20 to 300nm, and additives 1 to 5 on the surface of the film layer drawn in the machine direction (MD). Applying a coating liquid in the form of an aqueous acid solution having a solid content of 2 to 10 wt%, the remainder including water; d) stretching the film coated with the coating liquid in a vertical width direction (TD) perpendicular to the machine direction at a temperature of 20 to 30 ° C. higher than the machine direction draw temperature; And e) heat setting; Method for producing a biaxially stretched polyester film for high transparency optics comprising a. The method according to claim 6, The base layer and the surface layer is a polyester resin or a copolymer thereof, the surface layer further comprises a fine particle biaxially stretched polyester film production method. 8. The method of claim 7, The step b) is performed at 80 to 110 ° C, the d) step is performed at 100 to 140 ° C, and the step e) is carried out at 200 to 235 ° C.

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