KR101051147B1 - Light Diffusion Film - Google Patents

Abstract

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to light diffusing films used in various display devices, including a polyester film containing diffused particles, having a haze of 60 to 90%, and a total light transmittance of 70 to 97%. .

Light Diffusion Film, Diffusion Particles, Polyester Film

Description

Light Diffusion Film {Diffusion film}

The present invention relates to a light diffusing film used in various display devices.

The light diffusion film is used in backlight units of various display devices, and serves to induce uniform light diffusion while transmitting light emitted from a light source.

One of the most important factors for light diffusion film is total light transmittance. This is because the higher the total light transmittance, the higher the transmittance of the light irradiated from the light source, and the more suitable for use for optics.

However, the higher the haze of the film, the smaller the amount of light is dispersed and transmitted in the film by the small particles present in the film, so the overall total light transmittance is lowered.

In Korean Patent Publication No. 2006-0015105 and Korean Patent Publication No. 2007-0098413, a high transparency polyester film is used as a base film, and light is formed on one side or both sides of the polyester film to form a diffusion layer containing beads. It is interposed with a diffusion film.

That is, the conventional light diffusing film uses expensive, high-transparent polyester film because the light is dispersed in the film by the small particles as the haze increases, so that a high-transparent polyester film is used, and a diffusion layer containing beads is formed in the polyester film. In order to induce light diffusion, a method of increasing total light transmittance was used.

On the other hand, as the use of various display devices becomes popular, the demand for a method of increasing the price competitiveness by lowering the manufacturing cost of each display is increasing.

However, since the conventional light diffusing film uses a highly transparent polyester film as a base film, the manufacturing method is complicated to have a high transparency of the polyester film, and a complicated manufacturing process has a problem of causing an increase in manufacturing cost.

The present invention provides an inexpensive light diffusion film having a high total light transmittance.

In order to solve the above problems, the present invention includes a polyester film containing the diffusion particles, the haze is 60 to 90%, and provides a light diffusion film having a total light transmittance of 70 to 97%.

The polyester film used in the light-diffusion film according to the present invention is not particularly limited, but it is preferable to use a polyethylene terephthalate (PET) film in consideration of the thermal stability and physical properties of the film.

The PET film 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 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 diffusion particles contained in the polyester film is not limited as long as the diffusion particles used in the light diffusion film, and examples thereof include hard calcium carbonate (CaO), silica (SiO ₂ ), barium sulfate (BaSO ₄ ), and sodium oxide ( Inorganic particles such as NaO ₂ ), sodium sulfate (Na ₂ SO ₄ ), kaolin, kaolin, and talc; Alternatively, crosslinked acrylic resins such as silicone resins, crosslinked divinylbenzene polymethacrylates and crosslinked polymethacrylates and crosslinked polystyrene resins, benzoguanamine-formaldehyde resins, benzoguanamine-melamine-formaldehyde resins and melamine-form Organic particles, such as an aldehyde resin, are mentioned.

The use of silica as an inorganic particle is more suitable for the scattering and ease of manufacture of the film, and the use of silicone resin as the organic particle is suitable for application for ease of product selection, thermal stability, transparency and dispersion of aqueous solution. Do.

In the case where the average particle diameter of the diffusion particles is an inorganic particle, it is preferable to use particles of 0.5 to 5 μm. When the average particle diameter of the inorganic particles is in the above range, it is good to improve the problem of coagulation of resin and the problem of inferior concealability, and not only the transmittance is lowered but also the absorption loss of absorbing light in the ultraviolet region. Good to reduce.

The content of the inorganic particles is preferably used in 1,000 ~ 7.000ppm with respect to the polyester film. If the content of the inorganic particles is more than 1,000ppm with respect to the polyester film, it is effective to increase the scattering of light, and if the content of the inorganic particles is less than 7,000ppm with respect to the polyester film, the content of the inorganic particles is increased to increase the manufacturing cost. Good to solve.

In addition, in the case where the average particle diameter of the diffusion particles is organic particles, it is preferable to use diffusion particles of 1 to 10 µm. This can minimize the problem that the scattering effect falls, it can be excluded that the film is not manufactured by maintaining the film forming properties.

The diffused particles are contained in the polyester film using a polymerization method which is added during the polymerization process of the polyester chip, or a compounding method which is added before extrusion of the polyester chip containing no diffused particles and extruded.

The light diffusing film according to the present invention is prepared by stretching the coextruded polyester sheet.

The light diffusing film according to the present invention has a coating layer on one or both sides of the polyester film containing the diffusion particles, the coating layer is selected from poly (meth) acrylate-based resin, polyurethane-based resin, and polyester-based resin Using a coating layer containing any one or more. The coating layer is prepared alone or in a mixture using an acrylate, urethane, ester-based emulsion as a binder polymer.

The coating layer has an effect of increasing the total light transmittance of the light diffusion film by forming a coating layer having a refractive index different from that of the polyester film.

At this time, the coating layer and the polyester film is preferably a refractive index difference of 0.05 or more, for example, can illustrate a range of about 0.05 ~ 0.3. If the difference between the refractive index of the coating layer and the polyester film is less than 0.05, the amount of light reflected from the surface is increased, the total light transmittance is lowered and the luminance is reduced when the final optical sheet is made. And the larger the difference is, the total light transmittance increases. Therefore, the coating layer is good to improve the total light transmittance when the refractive index difference with the polyester film is 0.05 or more.

In order to improve the total light transmittance, the thickness of the coating layer is preferably 0.03 to 0.15 μm. If the thickness of the coating layer is 0.03㎛ or more, the coating layer is thin, so that the problem of increasing the total light transmittance does not occur effectively.If the thickness of the coating layer is 0.15㎛ or less, the viscosity rises, causing coating unevenness, resulting in optical defects. It is good to improve the problem of drying inside the tenter, the problem of the slip characteristics being lowered, the winding characteristics being lowered, and the problem of causing the quality increase when the recycled raw material is made as thick as the thickness becomes.

The coating layer used in the invention can be applied using a coating method such as gravure coating method, gas coating method, wire bar coating method, spray coating method, air knife coating method, impregnation coating method, etc. After stretching to (MD), the coating liquid is applied, and after the transverse direction (TD) stretching is carried out by tenter stretching above the longitudinal stretching temperature, the in-line coating method of manufacturing a coated film by heat setting is used. good.

The light diffusion film according to the present invention may further include at least one component selected from an antistatic agent, an ultraviolet stabilizer, a fluorescent brightener, a slip agent, and a thermal stabilizer.

Antistatic agent is used to prevent adhesion of foreign matters such as dust to base film and to reduce adhesion decrease by foreign matter in post-processing process. If antistatic agent is used for ordinary light diffusion film, its use is not limited. . Representative examples of the antistatic agent used include quaternary ammonium salts such as butyloxyethyl hydroxyethyl orthodecyloxy ammonium salt, bishydroxydecylpropyl ammonium salt, hydroxybutyl dodecyloxybutyl ethyl ammonium salt, silver, gold, 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 and the like.

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

Fluorescent whitening agent absorbs the light of ultraviolet rays (330 ~ 380nm) to emit light to the short wavelength side of the visible light, which can lead to an increase in the total light transmittance. Fluorescent whitening agent is not limited to the use of the fluorescent whitening agent used in the conventional light diffusing film that can lead to the improvement of the total light transmittance.

The slip agent is used to increase the releasability of the light diffusing film and to suppress defects caused by the post-processing process, and colloidal silica, organosilicon polymer, or derivatives thereof can be used, but any slip agent used in the light diffusing film can be used. There is no limit.

The heat stabilizer can be used to obtain a sheet with uniform thickness by electrostatic application method on the rotary cooling roll during processing of the light diffusion film, or a heat stabilizer used for the purpose of preventing oxidation during the manufacturing of heat treatment section and regenerated chip on the coating composition. If it is a heat stabilizer such as phosphoric acid or a phosphorus compound commonly used, there is no particular restriction on its use.

The light diffusing film according to the present invention is used for general light diffusing film but is particularly suitable for use in a backlight unit (BLU) for LCD.

LCD backlight unit is composed of reflective film, light source, diffuser plate, diffuser film, prism film, image diffuser film and DBEF.

The light diffusion film according to the present invention is used as the lower diffusion film and the upper diffusion film, and the lower diffusion film preferably has a more uniform scattering effect between the diffusion plate and the prism film. It is preferable to use a light diffusion film, and in the case of an image diffusion film, it is preferable to use a light diffusion film having a haze of 30% to 60%, which is easier to go straight between the prism film and the DBEF.

The light diffusing film according to the present invention has a coating layer while increasing the competitiveness of manufacturing cost by using a polyester film containing diffusion particles, which is relatively inexpensive compared to the conventional light diffusing film using a highly transparent polyester film. It is more suitable for use as an optical film, and has a high total light transmittance.

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.

1. Measurement of Average Particle Size of Particles: The average particle diameter was measured using a laser diffraction particle size measuring instrument (Beckman, Coulter LS13 320);

2. Haze measurement: Haze measurement was measured by ASTM D1003, it was calculated by the following equation using Nippon Denshoku 300A.

Haze (%) = (total scattered light / total transmitted light) × 100;

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

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

Example 1

After transesterification of 100 g of terephthalic acid, 45 g of ethylene glycol and 0.384 g of antimony trioxide, the silica particles dispersed in ethylene glycol (average particle diameter: 3 µm) were 10,000 ppm with respect to the polyethylene terephthalate (hereinafter 'PET'). Polyethylene terephthalate chip A was obtained by adding so as to perform a condensation polymerization reaction.

The PET chip A and the PET chip without particles were mixed at a weight ratio of 4: 6, and then dried at 180 ° C. for 6 hours to lower the water content in the chip to a level of 100 ppm or less.

The dried PET chip was melt-extruded at 300 ° C., and then quenched and solidified with a casting drum having a surface temperature of 20 ° C. to obtain a PET sheet containing particles having a thickness of 2.3 mm.

The obtained PET sheet was stretched three times in the longitudinal direction (MD) at a temperature of 100 ° C., then stretched three times in the transverse direction (TD) at 120 ° C. and heat-treated at 220 ° C., and then cooled to room temperature in a cooling zone. A PET film containing the diffused particles of μm was obtained.

[Example 2]

Emulsion acrylic binder having a refractive index of 1.44 (copolymer of methyl methacrylate and butyl acrylate, particle size 90 nm, pH 9) 4 g, silicone wetting agent (TEGO, Wet 250) 0.1 g, colloidal silica (Nalco chemical co., 0.2 g of nalco 2329) was added to 95.87 g of water, followed by stirring to prepare a coating solution 1 having a solid concentration of 4.14% and a viscosity of 15 cps.

The PET sheet prepared in Example 1 was stretched three times in the longitudinal direction (MD) at a temperature of 100 ° C., and then cooled to 40 ° C., and then coated on one surface by a bar coating method, followed by sufficiently drying After stretching three times in the transverse direction (TD) at 120 ° C higher than the direction stretching and heat treatment at 230 ° C, the film was cooled to room temperature in a cooling zone to obtain a PET film containing diffused particles coated on one side.

Example 3

Except that the coating layer of Example 2 was coated on both sides instead of one side, using the same method as in Example 2 to obtain a PET film containing the diffusion particles coated on both sides.

Example 4

4 g of an emulsion urethane binder (Superflex 210) with a refractive index of 1.52, 0.1 g of a silicone wetting agent (Wet 250, TEGO), and 0.2 g of colloidal silica (Nalco chemical co., Nalco 2329) are added to 95.87 g of water. Then, the mixture was stirred to prepare a coating solution 2 having a solid content concentration of 4.14% and a viscosity of 15 cps.

Prepared in the same manner as in Example 2, but one side using the coating solution 1 of Example 2, using the prepared coating solution 2 on the opposite side to obtain a PET film containing the diffusion particles formed with different coating layers.

Experimental Example 1

The haze, total light transmittance and surface roughness of each of Examples 1 to 4 and Kolon EverRay LD613 (transparent PET light diffusion film coated with a diffusion layer) were measured, and the results are shown in Table 1 below. The total light transmittance of the Kolon EverRay LD613 was measured by measuring the total light transmittance from the back to the front with the front surface coated with the diffusion layer.

Table 1. Measurement of Properties of Light Diffusion Film

1 is a schematic diagram of a double-side coated light diffusion film according to the present invention.

2 is a schematic view of a conventional light diffusing film.

1. Polyester film 2. Coating layer

3. Diffusion Particle 4. Diffusion Layer

5. Polyester film

Claims (12)

A light-diffusion film comprising a polyester film containing diffusion particles, having a haze of 60 to 90%, and a total light transmittance of 70 to 97%. The method of claim 1, The diffusion particles are any one or more inorganic particles selected from hard calcium carbonate, silica, barium sulfate, sodium oxide, sodium sulfate, kaolin, kaolin and talc; Or a light diffusion film which is at least one organic particle selected from silicone resin, crosslinked acrylic resin and crosslinked polystyrene resin, benzoguanamine-formaldehyde resin, benzoguanamine-melamine-formaldehyde resin and melamine-formaldehyde resin. 3. The method of claim 2, The organic particles are light diffusion film having an average particle diameter of 1 ~ 10㎛. 3. The method of claim 2, The inorganic particles are light diffusion films having an average particle diameter of 0.5 ~ 5㎛. 3. The method of claim 2, The inorganic particles are light diffusion film containing 1,000 ~ 7,000ppm with respect to the polyester film. 3. The method of claim 2, The polyester film containing the diffusion particles is a light diffusion film produced by the stretching method. The method of claim 1, The light diffusing film further comprises a coating layer on one or both sides of the polyester film containing the diffusion particles, the coating layer has a refractive index difference of 0.05 or more with the refractive index of the polyester film. The method of claim 7, wherein The coating layer is a light diffusion film comprising any one or more selected from poly (meth) acrylate-based resin, polyurethane-based resin, and polyester-based resin. The method of claim 8, The coating layer is a light diffusion film having a thickness of 0.03 ~ 0.15㎛ coating layer. The method of claim 7, wherein The coating layer is a light diffusion film coated by an in-line coating method. The method according to claim 1 or 7, The polyester film is a light diffusion film of polyethylene terephthalate (PET) film. A backlight unit (BLU) of a liquid crystal display (LCD) comprising the light diffusing film of claim 1.

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