KR101144668B1 - Optical film - Google Patents

Abstract

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

Description

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.

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.

In order to improve the brightness of such an optical film, studies have been conducted, and in Japanese Patent No. 2006-208993, a coating film has a coating amount and a coating layer is 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. 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 provide an optical film having a film roughness of less than 0.5㎛ while improving the total light transmittance.

Specifically, the present invention is to provide an optical film that is less void formation in the film stretching process, the surface adhesion is improved to reduce the occurrence of scratches.

The present invention relates to an optical film, specifically

A base film layer having a refractive index of 1.6 to 1.7;

A surface layer laminated on both sides of the base film layer and having an average particle diameter of 0.1 to 1.0 μm and containing 30 to 1000 ppm of spherical organic silicon beads having silanol (—Si—OH) groups on the surface thereof; And

A coating layer coated with a resin having a refractive index of 1.4 to 1.6 on both surfaces of the surface layer;

It relates to an optical film comprising a.

Specifically, referring to the drawings, the first aspect of the optical film according to the present invention is shown in FIG.

A base film layer 10 having a refractive index of 1.6 to 1.7;

A surface layer 20 laminated on both sides of the base film layer 10 and having an average particle diameter of 0.1 to 1.0 μm and including 30 to 1000 ppm of spherical organic silicon beads having silanol (—Si—OH) groups on the surface thereof; And

A coating layer 30 coated with a resin having a refractive index of 1.4 to 1.6 on both surfaces of the surface layer 20;

It relates to an optical film comprising a.

In addition, if necessary, the surface layer may further improve adhesion to the functional coating layer coated during post-processing while simultaneously controlling the surface of the coating layer hardly and smoothly using a crosslinked resin.

The optical film according to the present invention maintains a high total light transmittance due to the surface of the organic silicon beads while improving the surface structure to reduce defects during the film process and excellent adhesion between the optical film and the post-processing working layer due to the resin coating layer. .

The base film layer 10 of the optical film is preferably a polyester film, more preferably made of a copolymer containing 90 mol% or more of polyethylene terephthalate or polyethylene terephthalate as a main repeating unit. It is good that the refractive index of a film is 1.6-1.7. It is preferable that the base film layer 10 does not contain fine particles, that is, an antiblocking agent, because light transmittance is not impaired.

In addition, it is preferable that the surface layer 20 laminated on both surfaces of the base film layer 10 be laminated by co-extrusion because the process is simple and an excellent film can be produced. At this time, the composition of the resin co-extruded to the surface layer is preferably an organic silicone bead as a polyester resin and an anti-blocking agent.

The polyester resin 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-bisoxyethoxybenzene, bisphenol , Polyoxyethylene glycol, etc. can be used instead.

It is preferable to use spherical organic silicon beads having an antiblocking agent used in the surface layer 20 composed of silanol groups (-Si-OH). Specifically, it is preferable to use an average particle diameter of 0.1 ~ 1.0㎛, the effect is insignificant if the average particle diameter is less than 0.1㎛, if the average particle diameter exceeds 1.0㎛ to form a coarse protrusion on the film surface, It may be good to use a spherical organic silicon beads having an average particle diameter of 0.1 ~ 1.0㎛ because it may cause scratches. In addition, by using an organic silicon bead coated with a silanol group on the surface, it is possible to produce a slurry dispersed without agglomerates during coextrusion, and in the process of stretching the film with good affinity with the polyester resin forming the surface layer 20 Since the void formation is small, the surface adhesion is improved without impairing the light transmittance, so that scratches can be reduced. Therefore, the transmittance of the optical film can be further improved. The content of the organic silicon beads is preferably contained in 30 ~ 1000ppm with respect to the content of the resin used in the surface layer (20).

The coating layer 30 may be formed on one surface or both surfaces of the surface layer, and the coating layer 30 may be formed by applying an aqueous dispersion coating liquid by a method such as bar coating and then drying. The coating layer 30 is preferable because the optical property is excellent when the refractive index is lower than the base film layer 10, and specifically, the refractive index is 1.4 ~ 1.6 can reduce the amount of incident light is reflected from the surface of the optical film as a whole It is preferable because the total light transmittance of the film is increased. In addition, by using an aqueous dispersion coating liquid containing a crosslinkable resin, if necessary, not only the adhesion to the surface 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. If it is above, the viscosity may increase to 20 cps or more, resulting in a decrease in coating properties.

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.

In addition, anti-blocking properties are improved by spherical organic silicon beads added to the surface layer during co-extrusion, thereby minimizing defects due to slip and adhesion in the manufacturing process and the processing process, thereby improving the quality of the optical film.

In addition, it is more suitable for use as an optical film because it is excellent in adhesion to the functional coating layer is post-processed by a coating layer made of crosslinked resin.

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

2) Organic silicon bead particle size measurement: The particle size was measured on a scale of 3000 times magnification using an electron microscope.

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

4) Friction Coefficient Measurement: Measured according to ASTM D 1894 using Friction Tester TR manufactured by Toyoseiki, Japan.

5) Film defect measurement: The black antireflective sheet was placed under the fluorescent lamp in the 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

Fabrication of Double-coated Base Film after Co-Extrusion

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

In order to prepare the surface layer, 300 ppm of spherical organosilicon beads having a silanol (-Si-OH) group on the surface of 100 parts by weight of terephthalic acid were ethylene glycol 50 intermediate parts, an average particle diameter of 0.8 µm (electron microscope measurement). The polyethylene terephthalate chip obtained by dispersing and superposing | polymerizing was dried and prepared so that moisture might be 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 the final solid content and a viscosity of 12 cps.

The prepared polyethylene terephthalate chip for the base film layer and the polyethylene terephthalate chip for the surface layer are injected into each melt extruder and melted, and a three-layer structure of B / A / B (thickness ratio of 5: 90: 5) can be prepared. Extruded into a feed block, 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 a surface layer (B) on both sides of the base film 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 was coated on both sides by a bar coating method, and then stretched 3.5 times in a transverse direction (TD) through preheating and drying at 140 ° C. Thereafter, heat treatment was performed at 235 ° C. in a 5-stage tenter, and thermally fixed at 10 ° C. in the longitudinal and transverse directions at 200 ° C. to prepare a 188 μm biaxially oriented film coated on one surface.

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

[Example 2]

Manufactured in the same manner as in Example 1 except that the coating layer (1) prepared in Example 1 was applied to one surface of the coating layer, and the coating solution (2) prepared as follows was applied to the opposite side.

The coating solution 2 was prepared by adding 10 wt% of a urethane binder having a refractive index of 1.52, 0.2 wt% of a silicone wetting agent (Dow Corning Co., Ltd., a polyester siloxane copolymer), and 0.15 wt% of colloidal silica particles having an average particle diameter of 140 nm. After stirring for 3 hours to prepare a coating solution (2) having a total solid content of 4.35% and a viscosity of 14 cps.

Comparative Example 1

The polyethylene terephthalate chip from which moisture was removed was placed in an extruder, melt-extruded, and then quenched and solidified with a casting drum having a surface temperature of 20 ° C. to prepare a polyethylene terephthalate sheet having a thickness of 2000 μm. 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

Prepared in the same manner as in Example 1, the silicon beads used for the surface layer was used to 300ppm silicon beads having an average particle diameter of 0.8㎛ untreated.

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

[Table 1]

As shown in the table, it was found that the optical film according to the present invention had 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. However, in the case of Comparative Example 1 without a coating layer, it was found that the haze was high and the transmittance was low. In Comparative Example 2 using silicon beads not surface-treated with silanol groups, it was found that the film defects were severe and the coefficient of friction and haze were increased.

1 is a cross-sectional view showing a lamination example of an optical film according to the present invention.

Description of the main parts of the drawing-

10: base film layer

20: surface layer

30: coating layer

Claims (4)

A base film layer having a refractive index of 1.6 to 1.7; A surface layer laminated on both sides of the base film layer and having an average particle diameter of 0.1 to 1.0 μm and a surface of 30 to 1000 ppm of spherical organic silicon beads made of silanol (-Si-OH); And A coating layer coated with a resin having a refractive index of 1.4 to 1.6 on both surfaces of the surface layer; Optical film comprising a. The method of claim 1, The base film layer and the surface layer is an optical film made of a polyester resin. 3. The method of claim 2, The coating layer is an optical film coated using a water dispersion coating liquid containing any one selected from polyacrylate, polyurethane, polyester. The method according to any one of claims 1 to 3, The optical film is an optical film having 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.

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