KR101195428B1 - Polyester film for optical film - Google Patents

Abstract

The present invention relates to a biaxially stretched polyester film for optics, specifically including crosslinked organic particles, while maintaining a high total light transmittance, the surface structure is improved to reduce defects during the film process, the post-processing by the coating layer The present invention relates to a high-transparence biaxially oriented polyester film suitable for use as an optical base film due to excellent adhesion between working layers and a method of manufacturing the same.

Description

Polyester film for high transparency optics {Polyester film for optical film}

The present invention relates to an optical film, and relates to an optical film having a total light transmittance of 90% or more, a haze of 1.0% or less, and a film surface roughness (Rz) of less than 0.5 µm.

Optical films started later than general polymer films used in packaging materials, household goods, automobiles, etc., but as the development of LCD-related technology and the advancement of films have been conducted, the possibility of their use and demand are 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 condenser, photo film, label, pressure-sensitive tape, decorative laminate, transfer tape, polarizer and ceramic sheet, 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 liquid crystal display devices, 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 film is poor in planarity, which causes scratch defects on the surface of the film. Since the coating amount is non-uniform in the process, partial coating defects occur, which acts as a factor in degrading the value of the product.

Scratch resistance may cause black spots, which are electrical defects due to coating irregularities on the transparent conductive film, or problems such as coating unevenness in the post-processing process, such as hard coating, when scratches occur on the base film. It is therefore 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. The lowering of transparency, scratch resistance, planarity and total light transmittance causes problems of lowering of luminance and reliability and lowering of 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. .

Accordingly, base film studies have been conducted to improve luminance, and Japanese Laid-Open Patent Publication No. 2006-208993 has a base film and a coating amount, and the coating layer includes a biaxially stretched polyester film which is a light diffusion layer containing a binder and particles. Japanese Laid-Open Patent Publication 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. 059108 discloses a polyester film in which irregularities are formed on a base film and laminated on both sides of the base film in a layer containing a light diffusing agent.

However, there are problems such as voids in the process of stretching these films.

The present invention is to improve the overall light transmittance to improve the brightness, which is a requirement of the base film used in the display field as described above, the optical friction coefficient of the change is small, so that the occurrence of defects due to scratches during the machining process is reduced To provide a polyester film.

The present invention relates to a biaxially drawn coextruded polyester film for high transparency optics.

Polyester base layer not containing inorganic particles;

An outer layer which is coextruded and laminated on at least one surface of the base layer, and contains 30 to 1000 ppm of spherical organic particles having a particle diameter of 0.1 to 1.0 μm with respect to a polyester content;

A coating layer coated on one surface of the outer layer by applying an aqueous dispersion coating solution containing a resin having a lower refractive index than the polyester used in the outer layer;

It relates to a biaxially drawn co-extruded polyester film for high transparency optics, including a total light transmittance of 90% or more, haze of 1.0% or less, and a film surface roughness (Rz) of less than 0.5 μm.

Also,

a) A resin composition containing 30 to 1000 ppm of polyester resin (A) not containing inorganic particles, polyester resin and crosslinked spherical organic particles having a heat resistance temperature of 300 ° C. or higher and a particle diameter of 0.1 to 1.0 μm (B) Melting) and co-extrusion through a die consisting of B / A / B;

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

c) applying and coating an aqueous dispersion coating solution containing a resin having a lower refractive index than the polyester resin used in the resin composition (B) and an inorganic filler;

d) stretching in the widthwise direction TD perpendicular to the machine direction above the stretch temperature in the machine direction; And

e) heat setting;

It relates to a method for producing a biaxially stretched polyester film for high transparency optics comprising a.

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 coextruded outer layer, thereby reducing defects during the film process, and having excellent adhesion during post-processing due to the crosslinked resin coating layer. It is more suitable for use as a base film.

Hereinafter, the present invention will be described more specifically.

In the present invention, the base layer is not limited if the polyester resin is used, but a polyethylene terephthalate (PET (Polyethylenete terephthalate)) or ethylene terephthalate is composed of a copolymer containing 90 mol% or more in the main repeating unit of the film It is good that refractive index is 1.6-1.7.

Polyethylene terephthalate 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, 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 mainly used, but a part thereof is propylene glycol, trimethylene glycol, 1,4-cyclohexanediol, 1,4-cyclohexanedimethanol, 1,4-bisoxyethoxy It can also be used by replacing it with benzene, bisphenol, and polyoxyethylene glycol, and if it is a small content, you may use together a monofunctional compound or a trifunctional compound.

The present invention forms a coextrusion outer layer that adds an antiblocking agent to both sides of the substrate layer having a refractive index of 1.6 to 1.7 and to which the antiblocking agent that inhibits light transmittance is not added. The outer layer laminated on both surfaces of the substrate layer is preferably laminated by co-extrusion because the process is simple and an excellent film can be produced.

The outer layer to be coextruded is preferably made of polyethylene terephthalate and copolymers thereof containing 80 mol% or more 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, 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 mainly used, but a part thereof is propylene glycol, trimethylene glycol, 1,4-cyclohexanediol, 1,4-cyclohexanedimethanol, 1,4-bisoxyethoxy It can also be used by replacing it with benzene, bisphenol, and polyoxyethylene glycol, and if it is a small content, you may use together a monofunctional compound or a trifunctional compound.

The outer layer of the present invention preferably contains spherical organic particles prepared by highly crosslinking the polymer resin as fine particles of the antiblocking agent. The spherical organic particles used are observed with an electron microscope 3000 times magnification, and the average particle size is 0.1-1.0 μm when measured, and the concentration of fine particles in the outer layer is preferably 30-1000 ppm relative to the weight of the outer layer A. In this case, as the crosslinkable polymer resin constituting the spherical organic particles, an acrylic polymer, a styrene polymer, or the like may be used.

Although the components of the spherical organic particles are polymer resins, they are highly crosslinked and have excellent heat resistance. As a result, heat resistance measured by measuring 10% of the heat loss generated under nitrogen flow using a thermogravimetric analyzer (TGA) is evaluated to be 300 ° C. or more. It is preferable to use this. If the heat resistance is less than 300 ° C, the polymer resin constituting the spherical organic particles is thermally decomposed to destroy the shape and properties of the particles, making it difficult to obtain a target transparent film and a film having good surface antiblocking properties.

If the average particle diameter of the spherical organic particles is less than 0.1 μm, not only does not contribute to the running and scratch resistance of the base film, but also does not have the effect of fine particles, and may also cause aggregation of the resin, and the average particle diameter of the spherical organic particles is 1.0. If the thickness is larger than the above-mentioned thickness, spherical protrusions may be formed on the surface and scratches may occur due to dropping, so that spherical organic particles having an average particle diameter of 0.1 to 1.0 μm may be used.

In addition, the surface layer of the spherical organic particles has a surface treatment component which improves affinity with the polyester resin and reduces the refractive index difference, so that it is easy to make a slurry well dispersed without aggregates on the ethylene glycol solution and dispersed in the polyester resin. With good affinity at, there is little void formation during film stretching and light scattering is suppressed, thereby preventing light transmission and producing a film having excellent transparency.

A coating layer may be formed on one surface of the outer layer, and the coating layer may be formed by applying an aqueous dispersion coating solution by a method such as bar coating and then drying. The coating layer is preferable because the optical properties are excellent when the refractive index is lower than the base layer is excellent, specifically, the refractive index of 1.4 ~ 1.6 can reduce the amount of incident light is reflected from the surface of the optical film, so the total light transmittance of the entire film is increased desirable. In addition, by using an aqueous dispersion coating solution containing a crosslinkable resin, if necessary, not only the adhesion to the outer layer is improved, but also the smoothness is increased, and the adhesion to the functional coating layer to be coated on the upper part of the optical film in post processing is further improved. Can be. The functional coating layer coated during the post-processing may include an antiglare coating layer, a slip layer, an anti slip layer, and the like.

As the resin having a refractive index in the above range, polyacrylate, polyurethane, polyester and the like can be used, and if necessary, a crosslinking agent for crosslinking and a conventional additive can be used. As the crosslinking agent, polyisocyanates, tertiary amines and the like can be used. The coating liquid for forming the coating layer is preferably a water-dispersible emulsion, the solid content of the coating liquid is 2 to 10% by weight, the viscosity is preferably 20 cps 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 it is above, the viscosity may increase to 20 cps or more, resulting in a decrease in coating properties.

Since the optical film according to the present invention has improved antiblocking property by spherical organic particles added to the coextrusion outer layer, the defects due to slip and adhesion can be minimized in the manufacturing process and the processing process, thereby improving the quality of the optical film. In addition, the cross-linked resin coating layer is excellent in the adhesion between the post-working layer is more suitable for use as an optical base film.

The optical film according to the present invention may provide an optical film having a total light transmittance of 90% or more, a haze of 1.0% or less, and a film surface roughness (Rz) of less than 0.5 μm.

Hereinafter, the present invention will be described in more detail with reference to Examples and Comparative Examples, which are not intended to limit the present invention. The method of measuring the physical properties shown in the following Examples and Comparative Examples is as follows.

-Particle heat resistance temperature measurement: In a thermogravimetric analyzer (TGA), the sample was placed under nitrogen stream and heated to elevated temperature to measure a temperature of up to 10%.

Film total light transmittance and haze measurement: The total light transmittance was measured using a Nippon Denshoku 300A.

-Measurement of particle size of organic particles: The particle size was measured on a scale of 3000 times magnification using an electron microscope.

-Film surface roughness measurement: Two-dimensional surface roughness of at least five film surfaces was measured using a surface roughness meter of KOSAKA, Japan, and evaluated as five measured mean values of 10 point average surface roughness Rz values.

Friction Coefficient Measurement: Measurement was performed based on ASTM D 1894 using Friction Tester TR manufactured by Toyoseiki, Japan.

-Film defect measurement: The black antireflection sheet was placed under a fluorescent lamp in a dark room, and the number of the films was measured by observing shiny or optically distinguished defects observed under the reflected light. If necessary, the detected defects were observed under a microscope to reconfirm the type of defects and their presence. (Judgement criteria: ◎: less than 1 / m2, ○: 1 ~ 3 / m2, △: 3 ~ 10 / m2, ×: more than 10 / m2)

Example 1

In order to prepare the base layer, a polyethylene terephthalate chip having water removed to 100 ppm or less was prepared.

In order to prepare the outer layer, polyethylene terephthalate obtained by dispersing and polymerizing 400 ppm of highly crosslinked spherical organic particles in which 50 parts of ethylene glycol and an average particle diameter of 0.5 μm (electron microscopy) of the acrylic polymer resin were added to 100 parts by weight of terephthalic acid. The chip was dried to prepare moisture of 100 ppm or less.

In order to prepare the coating layer, 1.44 wt% of an acrylic binder having a refractive index of 1.44, 44 wt% of a solid content, 0.1 wt% of a silicone wetting agent (Dow Corning, polyester siloxane copolymer), and a colloidal silica particle having an average particle diameter of 0.4 nm After the weight% was added to water, the mixture was stirred for 3 hours to prepare a coating solution (1) having a content of 4.35 wt% of a final solid content and a viscosity of 12 cps.

The prepared polyethylene terephthalate chip (A) for the base layer and the polyethylene terephthalate chip (B) for the outer layer were injected into each melt extruder and melted, followed by three layers of B / A / B (thickness ratio of 5: 90: 5). Extruded into a feed block capable of manufacturing a structure, and then quenched and solidified with a casting drum having a surface temperature of 20 ℃ to prepare a polyethylene terephthalate sheet having a thickness of 2000㎛ formed with an outer layer (B) on both sides of the base layer (A). .

The prepared polyethylene terephthalate sheet was stretched 3.5 times in the machine direction (MD) at 110 ° C. and then cooled to room temperature. Thereafter, the coating solution 1 is coated on both sides of a polyethylene terephthalate sheet having a thickness of 2000 μm with an outer layer B formed on both sides of the substrate layer A by a bar coating method, and then preheated at 140 ° C. After stretching, the film was stretched 3.5 times in the transverse direction (TD). Thereafter, heat treatment was performed at 235 ° C. in a 5-stage tenter, followed by heat setting at 10 ° C. in the longitudinal and transverse directions at 200 ° C. to prepare a 188 μm biaxially oriented film coated on both sides.

The physical properties of the optical film thus obtained are shown in Table 1 below.

[Example 2]

A film was prepared in the same manner as in Example 1, except that the content of the organic particles used in the outer layer in Example 1 was 200 ppm.

The physical properties of the optical film thus obtained are shown in Table 1 below.

Comparative Example 1

In the polyethylene terephthalate polymerization step, a polyethylene terephthalate chip containing 50 ppm of silica having an average particle diameter of 1.4 μm (Coulter Counter method) is placed in an extruder, melt-extruded, and then rapidly cooled and solidified with a casting drum having a surface temperature of 20 ° C. to 2000 μm. Phosphorus polyethylene terephthalate sheet was prepared. The prepared polyethylene terephthalate sheet was stretched 3.5 times in the machine direction (MD) at 110 ° C. and then cooled to room temperature. Then, the film was stretched 3.5 times in the transverse direction (TD) through preheating and drying at 140 ° C. Thereafter, heat treatment was performed at 235 ° C. in a 5-stage tenter, followed by heat setting at 10 ° C. in the longitudinal and transverse directions at 200 ° C. to prepare an uncoated 188 μm biaxially oriented film.

The physical properties of the optical film thus obtained are shown in Table 1 below.

Comparative Example 2

After stretching in the machine direction in Comparative Example 1, the film was prepared in the same manner as in Comparative Example 1 except that the coating solution (1) of Example 1 was coated on one surface and stretched in the transverse direction.

The physical properties of the optical film thus obtained are shown in Table 1 below.

[Comparative Example 3]

After stretching in the machine direction in Comparative Example 1, the film was prepared in the same manner as in Comparative Example 1 except that the coating solution (1) of Example 1 was coated on both sides and then stretched in the transverse direction.

The physical properties of the optical film thus obtained are shown in Table 1 below.

[Comparative Example 4]

As an organic particle used in the outer layer in Example 1, a film was prepared in the same manner as in Example 1 except that the acrylic polymer resin having an average particle diameter of 2.0 μm (electron microscopy) was used as the highly crosslinked spherical organic particles of 300 ppm. It was.

The physical properties of the optical film thus obtained are shown in Table 1 below.

[Table 1]

Claims (4)

Polyester base layer not containing inorganic particles;
An outer layer which is co-extruded and laminated on at least one surface of the base layer, and contains 30 to 1000 ppm of crosslinked spherical organic particles having a heat resistance temperature of 300 ° C. or more and a particle diameter of 0.1 to 1.0 μm with respect to a polyester content;
A coating layer coated on one surface of the outer layer by applying an aqueous dispersion coating solution containing a resin having a lower refractive index than the polyester used in the outer layer;
It comprises a high light transmittance of 90% or more, haze 1.0% or less, the film surface roughness (Rz) is less than 0.5㎛ polyester film for high optical transparency. The method of claim 1,
The organic particles are a cross-linked acrylate-based resin or a cross-linked styrene-based polyester film for high transparency optics. The method of claim 1,
The coating layer has a refractive index of 1.4 ~ 1.6 polyester film for high transparency optics. The method of claim 1,
The water dispersion coating liquid is a polyacrylate, polyurethane, polyester film for high transparency optics comprising any one resin and inorganic filler selected from polyester.