KR20060095050A - Polyester film having excellent optic properties - Google Patents

Abstract

The present invention relates to a polyester film having excellent optical properties, and according to the present invention, one or both sides of a biaxially stretched polyester base film containing no inorganic particles, including inorganic particles, is easily bonded to a photocurable acrylic resin. The polyester film coated with the water-soluble polymer primer layer having excellent properties has excellent optical properties such as total light transmittance, low haze, and excellent adhesion and running property to the photocurable coating layer. It can be usefully used for manufacturing a display device.

Description

Polyester film with excellent optical properties {POLYESTER FILM HAVING EXCELLENT OPTIC PROPERTIES}

The present invention relates to a polyester film having excellent optical properties and a method of manufacturing the same.

Recently, plastic film is widely used as a component of display devices such as LCD and PDP. Among them, polyester film is used when optical transparency is required, and polyimide film is mainly used when durability and heat resistance are required. . In particular, the biaxially stretched polyester film has excellent dimensional stability, thickness uniformity, and optical transparency, so that the use range is widely used for various industrial materials as well as display devices.

When the biaxially stretched polyester film is used for optical purposes, it is used after various post-treatment treatments such as prism lens, anti-reflection layer, or hard coating layer, as necessary, rather than using polyester alone. Curable acrylic resins are used. However, since a general polyester film has a weak adhesiveness to such an ultraviolet curable resin, a method of improving the adhesive strength by coating a primer layer using an acrylic or urethane resin having easy adhesiveness in preparing a polyester to compensate for this problem. This is being studied (US 4,571,363; US 6,187,524; and Korean Patent Publication No. 2003-15868).

However, conventional polyester films have a disadvantage of impairing optical transparency even if the primers used do not have sufficient adhesiveness or have sufficient adhesiveness. In particular, in the case of a biaxially stretched polyester film, the refractive index has a high refractive index. The transmittance is lower than 90%, there is a problem such that the particles contained in the film to improve the running performance to lower the light transmittance or increase the haze and optical defects due to particle aggregation.

Accordingly, an object of the present invention is to provide an optical polyester film having high light transmittance, low reflectance and excellent adhesion to a photocurable resin to be post-processed, as well as excellent runability and dimensional stability in a post-processing process.

According to the above object, the present invention provides a polyester film for optics comprising a biaxially stretched polyester base film and a water-soluble polymer primer layer comprising an acrylic-ester copolymer resin and inorganic particles coated on one or both sides thereof. do.

Hereinafter, the present invention will be described in detail.

The optical polyester film of the present invention is one surface of a polyester base film biaxially stretched to a thickness of 25 to 350 µm, preferably 50 to 250 µm, without including inorganic particles to be contained for improving runability. It is characterized by having a structure coated on both sides, a water-soluble polymer primer layer containing an acrylic-ester copolymer resin and inorganic particles.

First, the polyester substrate of the optical film according to the present invention comprises a polyester resin in which polyhydric organic acid components and aliphatic glycols are polycondensed according to a conventional method, wherein the organic acid components are isophthalic acid, phthalic acid, terephthalic acid, 2,6 Naphthalenedicarboxylic acid, adipic acid, sebacic acid and oxycarboxylic acid may be used, and aliphatic glycols include ethylene glycol, propylene glycol, butanediol, 1,4-cyclohexanedimethanol, neopentyl glycol, diethylene glycol and 1,4-cyclodimethanol and the like can be used. The polyester may also be in the form of a copolymer containing a third acid or glycol component in addition to the organic acid and aliphatic glycol. Two or more kinds of the organic acid and the aliphatic glycol may be mixed together. Representative examples of the polyester include polyethylene terephthalate (PET) and polyethylene-2,6-naphthalenedicarboxylate (PEN). The polyester resin thus obtained may have an intrinsic viscosity of 0.40 to 0.90, preferably 0.45 to 0.80, more preferably 0.50 to 0.70. In this case, when the resin has an intrinsic viscosity of 0.40 or less, the film may break, and 0.90 If it is above, a manufacturing cost will rise.

Since the polyester is weak in adhesion to the ultraviolet curable resin used in the post-processing treatment, a water-soluble polymer aqueous dispersion is applied as a primer layer on the polyester film to compensate for this. In general, the primer layer is suitable to use an acrylic or urethane-based resin excellent in adhesion to the ultraviolet curing post-processing layer, but these have a problem of poor adhesion to the polyester substrate, in the present invention, An acrylic-ester copolymer having both adhesiveness and adhesion to a polyester film as a base material is used for the primer layer, and in order to prevent the haze from rising due to an increase in the coating amount of the primer layer, in particular, As a copolymer, a colloidal acrylic-ester copolymer colloidal resin having a refractive index of 1.55 or less and having self-emulsifying property may have little or no effect on the haze of the entire film.

In addition, according to the present invention, the water-soluble polymer primer layer may contain an inorganic particle having a relatively small difference in refractive index with an acrylic-ester copolymer colloid resin, thereby ensuring runability, and the inorganic particle may be 10 to 200 nm, preferably 50. Silica particles may be preferably used, for example, having a particle size in the range from 150 nm to 150 nm.

In addition, the water-soluble polymer primer layer of the present invention may further include an isocyanate, epoxy or melamine-based curing agent to improve durability and solvent resistance.

On the other hand, the water-soluble polymer primer layer of the present invention is coated with a thickness and refractive index is appropriately adjusted to improve the light transmittance of the polyester film and reduce the surface reflection, wherein the refractive index of the primer layer is the refractive index of the polyester film as a substrate It is desirable to bring it closer to the geometric mean value of the refractive index, but such primers are difficult to make in water dispersion and poor adhesion to the photocurable layer and the polyester film. Therefore, the refractive index of the water-soluble polymer primer layer of the present invention is to be 1.45 to 1.55, wherein less than 1.45 is usually impossible to manufacture, less than 1.55 is less light transmittance improvement effect.

In addition, since the thickness of the primer layer is preferably to be 100 to 200 nm based on the visible light wavelength 550 nm in consideration of the ideal 1/4 of the transmitted light wavelength, for this purpose the dry solid content The primer layer is applied in the range of 0.1 to 0.2 g / ㎡ on the basis of, wherein the coating amount is less than 0.1 g / ㎡ or more than 0.2 g / ㎡ inferior light transmittance improvement effect, especially in the case of more than 0.2 g / ㎡ Sticking property is increased, driving performance is very poor and easy to pick up.

According to the present invention, the polyester film coated with the primer layer by adjusting the refractive index and the coating amount is very excellent in the total light transmittance of 92 to 96%. In addition, even if the polyester film as the substrate does not include various inorganic particles, which are usually added for improving the running property, the running property is secured, and thus it is not necessary to add such inorganic particles to the base material. Therefore, the injected inorganic particles are less likely to cause problems such as deterioration of optical properties of the film or aggregation of the inorganic particles, it is possible to lower the haze level of the polyester film to 1.0 or less.

The polyester optical film of the present invention is a biaxially stretched polyester by melting, extruding, cooling and solidifying a polyester resin obtained by condensation polymerization of an organic acid and an aliphatic glycol in a conventional manner to obtain an unstretched sheet, and then biaxially stretching it. After obtaining a film, it can be manufactured by apply | coating the composition for water-soluble polymer primer layer formation to one or both surfaces of this film.

As described above, the polyester resin of the present invention may be prepared by polycondensation of a polyvalent organic acid component and an aliphatic glycol, or may be made of a copolymer containing a third component in addition to the organic acid and aliphatic glycol, In order to improve the intrinsic viscosity, it may be prepared using a method such as solid phase polymerization.

The polyester resin is melt-extruded from an extruder according to a conventional extrusion method, and then cooled and solidified with a chill roll to form an unstretched sheet. The modified polymer, carbide, and other impurities of the polymer generated in the melt extrusion process may cause optical defects, so that the molten polymer is filtered by using a filtration filter having an average particle diameter of 10 μm or less after the melt extrusion process to remove them. It is preferable to further carry out, and in order to reduce the content of impurities and oligomers generated by the degradation of the polymer, the shorter the length of the conduit from melting to extrusion of the molten polymer is shorter. In addition, during cooling after melt extrusion, it is important to evenly cool the melt-extruded polyester sheet by increasing the adhesion between the sheet and the cooling roll in order to improve the planarity of the polyester sheet. Electrostatic applied adhesion method to increase the adhesion between the sheet and the cooling drum by installing an electrode in which DC current flows in a direction perpendicular to the flow and applying static electricity to the sheet, or by uniformly applying liquid to all or part of the surface of the rotary cooling roll. Liquid coating adhesion method to increase the adhesiveness between the and the cooling roll can be used, these two methods can be used in combination in some cases.

The obtained polyester unstretched sheet is stretched simultaneously or sequentially in a traveling direction and a direction perpendicular to the traveling direction, preferably a sequential stretching system in accordance with each direction is used. At this time, in the case where the sheet is stretched simultaneously in the traveling direction and the perpendicular direction of the traveling direction, it is 4 to 50 times, preferably 8 to 36 times, and more preferably 10 to 10 times at 70 to 120 ° C, preferably 80 to 110 ° C. It can be stretched at a draw ratio of about 20 times, and when drawn sequentially, it is 2.5 to 7 times at 70 to 120 ° C., preferably 80 to 110 ° C., preferably using a circumferential speed difference between the rolls or a stenter. After stretching at a draw ratio of about 3 to 6 times, stretching may be performed at a draw ratio of 2 to 6 times, preferably 3 to 5 times, in the direction perpendicular to the traveling direction. After this stretching process, a heat setting and relaxation process may be performed at 170 to 260 ° C. to obtain a final biaxially stretched polyester base film.

A water-soluble polymer aqueous dispersion containing an acrylic-ester copolymer colloidal resin and inorganic particles is applied to the polyester base film to form a primer layer. In this case, immediately before application to improve adhesion between the primer layer and the polyester base film. The base film may be corona treated or may further contain a surfactant in the aqueous dispersion.

As a method of applying the water-soluble polymer aqueous dispersion according to the present invention, commonly known methods such as gravure coating, roll coating, extrusion coating, mayer bar coating, blade coating or air knife coating may be used.

In the optical film manufacturing method of the present invention, when the polyester sheet is sequentially drawn in the advancing direction (longitudinal direction) or perpendicular to the advancing direction (lateral direction) in the stretching step of the base film, the primer layer is formed immediately before the secondary stretching. It is preferable to apply the water-soluble polymer aqueous dispersion, and to dry and harden it with a stenter and to stretch, and more particularly, to perform stretching after applying and drying just before stretching in the transverse direction. The inline coating method has an advantage that the drying speed is high and the additional drying process is not necessary because the temperature in the stent where the film is stretched is high.

Hereinafter, the present invention will be described in detail by way of examples.

However, the following examples are merely to illustrate the invention, but the content of the present invention is not limited to the following examples.

Example 1

The polyester resin (polyethylene terephthalate, SKC) having an intrinsic viscosity of 0.6 was melt extruded at 280 ° C, and then stretched 3.5 times in the advancing direction at 70 to 100 ° C to obtain a polyester sheet. On one side of the obtained polyester sheet, 40 parts by weight of an acrylic-ester copolymer colloidal resin (Japan Pure Chemical Co., Ltd. ET-410, solid content 30%), 2 parts by weight of water-disperse silica particles (monochemical, Snowtex ST-ZL, solid content 40%), A water-soluble polymer dispersion consisting of a mixing ratio of 0.1 parts by weight of surfactant (3M, FC4430, 100% solids) and 57.9 parts by weight of pure water was applied by a gravure coating method as a primer layer, and then 4 times in the direction perpendicular to the traveling direction at 100 to 130 ° C. At the same time, the applied primer layer was dried and cured to obtain a coating thickness of 0.15 g / m 2, and then heat-set at 220 to 240 ° C. to prepare a polyester film having a thickness of 100 μm.

Example 2

A polyester film was prepared in the same manner as in Example 1, except that the water-soluble polymer dispersion was applied to both sides of the polyester film.

Example 3

40 parts by weight of acrylic-ester copolymer resin (pure Japan, ET530, 30% solids), 2 parts by weight of water-dispersible silica particles (Ilsan Chemical, Snowtex ST-ZL, 40% solids), surfactant (3M, FC4430, 100% solids) ) A polyester film was prepared in the same manner as in Example 1, except that a water-soluble polymer dispersion composed of a mixing ratio of 0.1 part by weight and 57.9 parts by weight of purified water was used.

Example 4

A polyester film was prepared in the same manner as in Example 3, except that the water-soluble polymer dispersion was applied to both sides of the polyester film.

Example 5

48 parts by weight of an acrylic-ester copolymer resin (Japan Pure Chemical Co., AT613, 25% solids), 2 parts by weight of water-dispersed silica particles (Nisan Chemical, Snowtex ST-ZL, 40% solids), surfactant (3M, FC4430, 100% solids) ) A polyester film was prepared in the same manner as in Example 1, except that a water-soluble polymer dispersion composed of a mixing ratio of 0.1 part by weight and 49.9 parts by weight of purified water was used.

Example 6

A polyester film was prepared in the same manner as in Example 5, except that the water-soluble polymer dispersion was applied to both sides of the polyester film.

Comparative Example 1

A polyester film was prepared in the same manner as in Example 1, except that the process of applying the water-soluble polymer dispersion to the polyester sheet was not performed.

Comparative Example 2

As in Example 1, 0.1 wt% of inorganic particles having a size of 2 to 3 μm was added to prepare a polyester resin without applying a water-soluble polymer dispersion to prepare a polyester film under the same conditions.

Comparative Example 3

40 parts by weight of a water-soluble polyester resin (Japan Synthetic Chemistry, WR901, 30% solids), 2 parts by weight of water-dispersible silica particles (Nisan Chemical, Snowtex ST-UP, 20% solids), surfactant (3M, FC4430, 100% solids) ) A polyester film was prepared in the same manner as in Example 1, except that the composition consisting of 0.1 parts by weight and 49.9 parts by weight of purified water was used to form a primer layer.

Comparative Example 4

34.2 parts by weight of water-soluble polyurethane resin (Cheil Industries, F8582D, 35% solids), 2 parts by weight of water-dispersed silica particles (Nisan Chemical, Snowtex ST-UP, 20% solids), surfactant (3M, FC4430, 100% solids) A polyester film was prepared in the same manner as in Example 1, except that the composition consisting of 0.1 parts by weight and 49.9 parts by weight of purified water was used to form a primer layer.

Comparative Example 5

30 parts by weight of a polyacrylate emulsion (Zeneca, Neocryl A1110, 40% solids), 2 parts by weight of water-dispersed silica particles (Nisan Chemical, Snowtex ST-ZL), 0.1 parts by weight of surfactant and 73.9 parts by weight of purified water A polyester film was prepared in the same manner as in Example 1, except that the primer layer was formed.

Comparative Example 6

A polyester film was prepared in the same manner as in Example 1, except that the final coating thickness of the primer layer was 0.05 g / m 2.

Comparative Example 7

A polyester film was prepared in the same manner as in Example 1, except that the final coating thickness of the primer layer was 0.25 g / m 2.

Various film properties were evaluated for the polyester films obtained in Examples 1 to 6 and Comparative Examples 1 to 7, and the evaluation items and the devices used for each evaluation were as follows.

(1) Total light transmittance: It measured at the wavelength of 550 nm using the haze meter (NDH 5000W by Nippon Denshoko company) according to the measuring method of ASTMD1003.

(2) Visible light reflectance: Measured using a Minolta spectrophotometer CM-3500d, the reference reflectance was based on 550 nm.

(3) Haze: According to the measuring method of ASTM D1003, it measured using the haze meter (Nippon Denshoko company NDH 5000W).

(4) Friction Coefficient: Friction coefficients of the coated surfaces were measured under a 200 g load using a Toyoseki TR friction coefficient measuring device according to the standard measuring method of ASTM D 1894-78.

(5) Refractive index: The refractive index of the primer layer was measured using a refractometer (ARIAS 500, Reichart). The primer layer was applied to a plate having a releasability and dried to form a film having a thickness of about 20 μm, and then separated, and the refractive index was measured.

(6) Adhesion property to photocurable coating layer: A photocurable acrylic resin (SKUCB Co., U117-3) was applied with # 12 Mayer, and a irradiation distance of 20 cm and a speed of 3 m with a 200 mJ / cm2 of mercury lamp. After forming a hard coating layer having a coating thickness of 15 μm under the condition of / min, the adhesiveness was evaluated by the cross-atch method and evaluated according to the following criteria.

 The evaluation items were measured and shown in Table 1 below. In the following table, ○ means that the coating layer is not peeled at all, △ means that some peeling and × are completely peeled.

As a result, as shown in Table 1, the polyester film of the present invention according to the embodiment showed a high total light transmittance and low haze, excellent adhesion to the photocurable coating layer compared to the film according to the comparative example, It can be seen that this excellent and low reflectance is very excellent to use as a substrate for the optical overall.

As described above, the polyester film coated with a water-soluble polymer primer layer having excellent adhesion to the photocurable acrylic resin while including the inorganic particles on the polyester biaxially stretched film containing no inorganic particles according to the present invention is In addition, the optical properties such as excellent runability and total light transmittance, while exhibiting low haze, excellent adhesion to the photocurable coating layer and excellent runability, etc., can be usefully used for manufacturing display devices such as LCD and PDP.

Claims (11)

An optical polyester film comprising a biaxially stretched polyester base film and a water-soluble polymer primer layer comprising an acrylic-ester copolymer resin and inorganic particles coated on one or both sides thereof. The method of claim 1, The base film does not contain an inorganic particle, The optical polyester film characterized by the above-mentioned. The method of claim 1, The polyester film for optics, characterized in that the inorganic particles have a particle size in the range of 10 to 200 nm. The method of claim 3, wherein The polyester film for optics characterized by the inorganic particle being a silica particle. The method according to any one of claims 2 to 4, An optical polyester film, wherein the water-soluble polymer primer layer is formed by applying a water-soluble polymer aqueous dispersion containing a colloidal acrylic-ester copolymer resin and inorganic particles. The method of claim 5, wherein Acrylic-ester copolymer resin is refractive index 1.55 or less, The optical polyester film characterized by the above-mentioned. The method of claim 5, wherein Optical polyester film, characterized in that the coating amount of the water-soluble polymer aqueous dispersion is 0.1 to 0.2 g / ㎡ based on the dry solid content. The method of claim 1, Optical polyester film, characterized in that the refractive index of the water-soluble polymer primer layer is 1.45 to 1.55. The method of claim 1, An optical polyester film, characterized in that the biaxially stretched polyester base film is made of a polyester resin having an intrinsic viscosity of 0.4 to 0.9. The method of claim 1, A polyester film for optics, characterized in that the biaxially stretched polyester base film has a thickness of 25 to 350 µm. The method of claim 10, An optical polyester film, characterized in that the biaxially stretched polyester base film is made of polyethylene terephthalate (PET) and polyethylene naphthalenedicarboxylate (PEN).