KR100696082B1 - Film for back-light unit of LCD - Google Patents

Abstract

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a film for a backlight unit of an LCD display having excellent heat resistance, and comprising a cellulose acetate butyrate resin together with a polyester resin and an acrylic resin as a binder resin forming a light diffusion layer applied to at least one surface of a base film. It is excellent in stability and exposed to the back light for a long time, so that no heat deformation or warping occurs, so the appearance of the backlight and the change in brightness over time show little performance.

Description

Film for backlight unit of liquid crystal display excellent in heat resistance {Film for back-light unit of LCD}             

1 is a cross-sectional view of a backlight unit of an LCD display,

2 is a cross-sectional view of the light diffusion film constituting the backlight unit of the LCD display.

* Description of the symbols for the main parts of the drawings *

1-Reflective Film 2-Light Guide Plate

3-Light Diffusion Film 4-Prism

5-Prism Protection Film 31-Light Diffusion Layer

32-base film

The present invention relates to a film for a backlight unit of an LCD display, and more particularly, by including a cellulose acetate resin having excellent heat resistance and ultraviolet stability as a binder resin in a light diffusing layer composition applied to at least one surface of a transparent base film as a binder resin. It is related with the film for backlight units excellent in stability.

As the development of display technology is being made innovatively, large screen, low power, and high brightness of LCD display are emerging as the core of future technology in TFT-LCD. In order to cope with such demands, various studies are being conducted on liquid crystal modules and backlight components which are components of TFT-LCDs.

Large screen, low power, and high brightness are being progressed in the backlight unit, but in recent years, attempts to eliminate the backlight unit itself have been made.However, due to the basic characteristics of the LCD, a screen without a separate light source can be formed like an EL element that emits light. Is currently impossible.

1 is a cross-sectional view of the backlight unit of the LCD display. Reflective film 1 for reflecting light from the light source upward, light guide plate 2 for evenly spreading the raised light, light diffusing film 3 for more uniform dispersion of light, and two-stage prism ( 4) and a prism protective film 5.

In particular, the light diffusing film 3 serves to diffuse the light of the transverse light source lamp from one side or the rear of the LCD display in the entire screen and refracts the light into a uniform light in the front direction.

By the way, the intensity of the light emitted from the initial light source is slightly canceled as it passes through the medium as shown in FIG. 1, so that the brightness on the screen we see is only a few hundredth of the original light source.                         

Many attempts have been made to solve this problem. For example, there are methods of increasing the brightness of the light source and reducing the thickness of each medium such as a light guide plate, a reflective film, a prism, and a diffusion plate, but due to the productivity and workability of users, There is a limit to the reduction. Recently, attempts have been made to change the patterning of the light guide plate in various ways.

On the other hand, the light diffusion film serves to spread the light evenly by using particles having good diffusion efficiency, the light diffusion film is a PET film as a base film in general, the composition containing the binder resin and particles on one or both sides thereof Obtained by coating. 2, the light diffusing layer 31 is coated on at least one surface of the base film 32. The same composition is used for the prism protection film, but in the prism protection film, a smaller particle size is used.

In connection with the light diffusing film composition, many attempts have been made for the selection of particles, coating thickness or anti-reflective treatment of back layer coating. Among them, in relation to the selection of particles, organic polymer particles which are transparent and have good diffusion efficiency are used as the particles. Since the polymers are mostly polymerized by emulsion polymerization, the types of particles are limited. In the case of using the inorganic particles, there is no compatibility with the binder resin and no particles having good diffusion effect.

In addition, attempts to increase the brightness by applying an anti-reflective coating on the back side through which light passes are not only difficult because the anti-reflective coating has to be coated with a resin having a refractive index of 1.4 or less at 100 nm level, and the backing layer itself is difficult. When the thin coating, the thickness difference with the light diffusing surface in front of the deep, the curling phenomenon occurs during heat drying, it can not be used.

On the other hand, in recent years, the lifespan of the electronic component itself is also an important factor, and many life-enhancing technologies have been introduced. In the conventional light diffusion film used for the backlight, the heat generated from the rear fluorescent lamp and the backlight itself after a long time has been passed. Thermal deformation is caused by the heat generated at, causing a problem.

Accordingly, the present inventors have recognized that the selection of the transparent substrate used in the light diffusing film has a limit, and as a result of using the resin constituting the light diffusing layer with a binder having excellent heat resistance, the problem of thermal deformation as described above does not occur. The present invention has been completed.

Therefore, an object of the present invention is excellent heat resistance and UV stability, no heat deformation and distortion even when exposed to the back light for a long time, the light diffusion for the backlight unit of the LCD display with little change over time with the appearance of the backlight and luminance over time To provide the film.

The light diffusing film for the backlight unit of the LCD display of the present invention for achieving the above object is obtained by coating a crude liquid containing a binder resin, organic particles and additives on at least one side of the transparent base film, wherein the binder resin is a polyester It is characterized by including 100 weight part of tere resin, 30-200 weight part of acrylic resin, and 1-100 weight part of cellulose acetate butyrate resins.

The present invention will be described in more detail as follows.

The present invention relates to a film for a backlight unit obtained by coating a crude liquid (hereinafter referred to as a light diffusion layer) containing a binder, organic particles and an additive on at least one side of a transparent base film.

Looking at the configuration of the film in detail as follows, the schematic cross section is shown in FIG.

(1) transparent base film

As the transparent base film, any transparent support surface can be used, and specific examples thereof include polycarbonate, polypropylene, polyethylene terephthalate, polyethylene, and epoxy, but mainly polyethylene terephthalate is used.

In recent years, polyethylene naphthalate having an ultraviolet blocking effect has been used without adding a UV stabilizer to the light diffusion layer, but since it is expensive, it has not been commercialized. Such a transparent base film should have adhesion to the resin used and should not affect the light diffusing layer due to its high light transmittance within itself, and the surface smoothness should be uniform so that there is no variation in luminance.

As for the thickness of a transparent base film, 50-200 micrometers, Preferably 75-150 micrometers is suitable. Only within this thickness range can the processability, handling, and heat resistance of the film be achieved.

(2) light diffusion layer

The light diffusion layer scatters, reflects, and refracts the incident light to diffuse the light, and at the same time, transmits the light through the light guide plate to spread the light evenly throughout the LCD screen. Therefore, the light diffusion layer uses a resin having good adhesion with the transparent base film and good compatibility with particles that play a role of light diffusion.

Preferred binder resins include unsaturated polyesters, methyl methacrylate, ethyl methacrylate, isobutyl methacrylate, normal butyl methacrylate, normal butyl methyl methacrylate, acrylic acid, methacrylic acid and hydroxyethyl methacrylate. Acrylate, hydroxypropyl methacrylate, hydroxyethyl acrylate, acrylamide, methrol acrylate, glycidyl methacrylate, ethyl acrylate, isobutyl acrylate, normal butyl acrylate, 2-ethylhexyl acryl Acrylic type, urethane type, epoxy type, melamine type resin, such as a latex polymer, a copolymer, or a terpolymer, etc. are mentioned.

In order to improve heat resistance, abrasion resistance, and adhesiveness, these are used by hardening the film of resin using a hardening | curing agent.

In particular, the binder resin preferably has a high light transmittance, and an adhesive force with the base film is important.

As the base film, polyethylene terephthalate having good mechanical properties and optical properties is mainly used as described above, but in order to have good adhesion with the base film, it is preferable to use a polyester resin having a similar structure.

However, the polyester resin has an excellent adhesive strength with the base material compared to other resins, while the surface hardness is low due to the unsaturated properties of the resin.

Therefore, when the polyester resin is used alone, the hardness of the light diffusion layer is less than 1H, which causes a lot of scratches when the backlight is mounted or coated, resulting in damage to the appearance of the film.

Therefore, in the present invention, the acrylic resin having excellent hardness is mixed to 30 to 200 parts by weight with respect to 100 parts by weight of the polyester resin so that the surface hardness is about 1H to 2H.

If the acrylic resin is less than 30 parts by weight with respect to 100 parts by weight of the polyester resin, the surface hardness is less than 1H and there is no effect of improving the hardness. If the acrylic resin is used in excess of 200 parts by weight, the surface hardness of the light diffusion layer is about 3H. When the hardness of the light diffusion layer is 1H to 2H, the workability and other fairness is good, but when the level is about 3H, the surface of the light guide plate on the back surface is not preferable.

In addition to the above two binder resin compositions, in the present invention, cellulose acetate butyrate having a glass transition temperature of 130 ° C. to 150 ° C. is used in an amount of 1 to 100 parts by weight based on 100 parts by weight of the polyester resin.

The reason is that the coating layer formed by mixing two kinds of acrylic resin and polyester resin is weak in heat resistance and has a disadvantage in that an irregular image is formed on the screen due to distortion and generation of heat deformation when exposed for a long time by back light. Therefore, it is preferable to use the cellulose derivative which can form a hard coating film in the base film which has heat resistance, but has good coating property.

As the heat resistant cellulose derivative, cellulose ester compounds such as cellulose acetate butyrate, cellulose acetate propionate, cellulose propionate, cellulose acetate and the like are mainly used. This is because the coating film is easily formed with the base substrate film.

Of these, cellulose acetate, cellulose propionate, and mixed-substituted cellulose acetate propionate, each of which is substituted with each acetyl group and propion group alone, are difficult to be substituted and are difficult to coat due to solvent resistance, and are compatible with the acrylic resin and polyester resin. This lack of the resulting substituents are cloudy when forming the coating film has a disadvantage of damaging the appearance of the coating. Therefore, most preferably, the cellulose acetate butyrate is mixed with an acrylic resin and a polyester resin in a predetermined range to form a light diffusion layer coating film.

The cellulose derivatives have different glass transition temperatures depending on the degree of esterification, viscosity, and the number of hydroxyl groups per four anhydrous glycosides. The content of acetyl groups in cellulose acetate butyrate is preferably 1.0 to 80%, more preferably 2.0 to 20. It is necessary to have a%. The content of the butyl group is 10 to 90%, preferably 20 to 40%. In this case, the glass transition temperature of the cellulose acetate butyrate becomes 130 to 150 ° C, so that the desired heat resistance can be maintained. The degree of substitution of the acetyl group is controlled by the content of the substituted butyl group. The content of the butyl group and the acetyl group is not more than 60% in total. The ester group which has a greater influence on the glass transition temperature of cellulose acetate butyrate is a butyl group having a higher molecular weight. If the content is less than 20%, the glass transition temperature is 130 ° C. or lower, and thus there is no heat and UV stabilizing effect, and more than 40%. The surface glass transition temperature is very high above 160 ° C., but the film properties deteriorate.

The method for preparing cellulose acetate butyrate is a mixture of butyric acid and acetic anhydride in cellulose, and a sulfuric acid catalyst is added thereto to form a cellulose triacetate in a dope state, where the dope is hydrolyzed in a water-acid mixture. The content of substituents in the desired range is indicated. The gelling or fibrous component of the remaining solution is filtered and water is added to the filtered solution to form cellulose acetate butyrate. After washing with water and drying it can be prepared in the form of powder cellulose acetate butyrate.

The content of the substituted acetyl group thus prepared is 2.0 to 20%, the substituted butyl group is 20 to 40%, and the cellulose acetate resin, polyester resin and acrylic resin having a glass transition temperature of 130 to 150 ° C. Transparent spherical organic particles are dispersed in the mixed three-component transparent binder resin and coated on the base film to prepare a light diffusion film.

At this time, the particles used may have a variety of organic and inorganic particles in order to increase the light transmittance and diffusivity while having a difference in refractive index with ordinary resin.

Representative particles that can be used include methyl methacrylate, ethyl methacrylate, isobutyl methacrylate, normal butyl methacrylate, normal butyl methyl methacrylate, acrylic acid, methacrylic acid and hydroxyethyl methacrylate. , Hydroxypropyl methacrylate, hydroxyethyl acrylate, acrylamide, metyrol acrylamide, glycidyl methacrylate, ethyl acrylate, isobutyl acrylate, normal butyl acrylate, 2-ethylhexyl acrylate polymer Olefinic particles such as acrylic, polyethylene, polystyrene, polypropylene, copolymers of acrylic and olefins, homopolymers such as copolymers or terpolymers, and then covered with other monomers on the layer Organic particles, such as a multilayer multicomponent particle | grain, are mentioned.

As the inorganic particles, silicon oxide, aluminum oxide, titanium oxide, zirconium oxide, magnesium fluoride and the like can be used.

By the way, it is excellent in the light diffusivity of organic particle | grains compared with inorganic particle | grains, In this invention, organic particle | grains are mainly used, The particle | grains of 1-30 micrometers are used although the particle size changes with thickness of a coating film. In addition, in order to increase light diffusion efficiency, particles of different particle sizes may be mixed and used. Rather than using a single type of particles, a mixture of heterogeneous particles having different refractive indices may be used to increase the light diffusion rate. In addition, the light diffusion efficiency may be increased to a heterogeneous type having a similar refractive index.

These particles have different light transmittances and light diffusion rates depending on the ratio contained in the resin and the coating thickness. In order to show a high light diffusion rate and high brightness, 100 parts by weight of the binder resin may be used at a thickness of 10-20 μm. It is preferable to contain 50-300 weight part of crosslinking particles with respect to it.                     

If the content of the crosslinked particles is less than 50 parts by weight based on 100 parts by weight of the binder resin, the diffusion effect due to light scattering is reduced, and when the content of the particles is increased, the particles are protruded onto the coating surface to reduce the light transmittance and the particle-containing resin. When the solution is prepared, the dispersibility of the particles is inferior, so that a uniform solution is impossible. Therefore, it is advantageous for the production of a uniformly dispersed light diffusion layer so that the particle content in the resin does not exceed 300 parts by weight.

On the other hand, in addition to the binder resin and particles as described above may be used an antistatic agent to impart contamination resistance to prevent dust or impurities that may occur when manufacturing the backlight unit using a light diffusing film. As the antistatic agent, a variety of quaternary amines, anionics, cationics, nonionics, fluorites, etc. can be used, and as the amount thereof is increased, antistatic properties are increased, but wear resistance is low, and there is a risk of precipitation if used for a long time. Therefore, it is preferable to use 10 weight part or less, preferably 5 weight part or less per 100 weight part of resin.

In addition, since the particles or the antistatic agent can be uniformly dispersed in the resin and the solvent to form a light diffusion layer having a high photohomoaddition efficiency, a dispersant may be used for a uniform crude liquid. Examples of the dispersant include acrylic emulsions, modified silicones, polydimethylsiloxanes, and fluorides, and are preferably used in small amounts so as not to precipitate on the surface after forming a coating film. It is preferable to use within 5 weight part with respect to 100 weight part of resin specifically ,.

The light diffusion crude liquid thus prepared is coated on the transparent base film using a comma knife. The thickness of the coating film is preferably 10 to 30 µm.

Hereinafter, the present invention will be described in detail with reference to Examples, but the present invention is not limited by the Examples.

Example 1

100 parts by weight of cellulose is mixed with 80 parts by weight of butyric acid and 50 parts by weight of acetic anhydride, and then 1 part by weight of sulfuric acid catalyst is made to form a dope cellulose triester, and the dope is hydrolyzed in an appropriate amount of water-acid mixture. The gelling or organic components of the remaining solution were filtered and water was added to the filtered solution to form cellulose acetate butyrate. After washing with water and vacuum drying to prepare a cellulose acetate butyrate in the form of a powder of butyl group content 35%, acetyl group content 15%, glass transition temperature of 135 ℃.

Then, 100 parts by weight of a polyester resin (Vylon 200, manufactured by Toyobo), 100 parts by weight of an acrylic resin (A-11, manufactured by Rohm & Haas) and 20 parts by weight of cellulose acetate butyrate prepared above were mixed, followed by methyl ethyl ketone. After diluting 100 parts by weight and 100 parts by weight of toluene and diluting 200 parts by weight of polymethyl methacrylate particles having an average particle diameter of 12 μm, the mixture was dispersed for 1 hour at a rotational speed of 1000 rpm using a ring mill, and then 100 μm of ultra-transparent polyethylene tere At least one surface of the phthalate film (T600, manufactured by Mitsubishi Corporation) was dried using a comma knife and then coated to have a coating thickness of 15 μm.

Example 2

100 parts by weight of cellulose is mixed with 100 parts by weight of butyric acid and 30 parts by weight of acetic anhydride, followed by 1 part by weight of sulfuric acid catalyst to form a dope cellulose triester, and the dope is dissolved in an appropriate amount of water-acid mixture. The gelled or organic components of the remaining solution were filtered off and water was added to the filtered solution to form cellulose acetate butyrate. After washing with water and vacuum drying to prepare a cellulose acetate butyrate in the form of a powder of butyl group content 38%, acetyl group content 5%, glass transition temperature 140 ℃.

Then, 100 parts by weight of a polyester resin (Vylon 200, manufactured by Toyobo), 50 parts by weight of an acrylic resin (A-11, manufactured by Rohm & Haas), and 50 parts by weight of cellulose acetate butyrate prepared above were mixed, followed by methyl ethyl ketone. After diluting 100 parts by weight and 100 parts by weight of toluene and diluting 200 parts by weight of polymethyl methacrylate particles having an average particle diameter of 12 μm, the mixture was dispersed for 1 hour at a rotational speed of 1000 rpm using a ring mill, and then 100 μm of ultra-transparent polyethylene tere At least one surface of the phthalate film (T600, manufactured by Mitsubishi Corporation) was dried using a comma knife and then coated to have a coating thickness of 16 μm.

Comparative Example 1

After diluting 100 parts by weight of methyl ethyl ketone and 100 parts by weight of toluene in 100 parts by weight of polyester resin (Vylon 200, manufactured by Toyobo Co., Ltd.) and 100 parts by weight of acrylic resin (A-11, manufactured by Rohm & Haas), the average particle diameter was 12 μm. 200 parts by weight of polymethyl methacrylate particles were mixed and dispersed at 1000 rpm for 1 hour using a ring mill, followed by drying using a comma knife on at least one surface of a 100 μm ultra-transparent polyethylene terephthalate film (T600, manufactured by Mitsubishi Corporation). The coating thickness was applied so as to be 15 µm.                     

Comparative Example 2

100 parts by weight of cellulose is mixed with 80 parts by weight of butyric acid and 50 parts by weight of acetic anhydride, and then 1 part by weight of sulfuric acid catalyst is made to form a dope cellulose triester, and the dope is hydrolyzed in an appropriate amount of water-acid mixture. The gelling or organic components of the remaining solution were filtered and water was added to the filtered solution to form cellulose acetate butyrate. After washing with water and vacuum drying to prepare a cellulose acetate butyrate in the form of a powder of butyl group content 35%, acetyl group content 15%, glass transition temperature of 135 ℃.

Then, after mixing 100 parts by weight of a polyester resin (Vylon 200, manufactured by Toyobo), 100 parts by weight of an acrylic resin (A-11, manufactured by Rohm & Haas) and 150 parts by weight of cellulose acetate butyrate prepared above, methyl ethyl ketone was mixed. After diluting 100 parts by weight and 100 parts by weight of toluene and diluting 200 parts by weight of polymethyl methacrylate particles having an average particle diameter of 12 μm, the mixture was dispersed for 1 hour at a rotational speed of 1000 rpm using a ring mill, and then 100 μm of ultra-transparent polyethylene tere It dried on at least one surface of the phthalate film (T600, Mitsubishi Corporation) using a comma knife, and apply | coated so that it might become 17 micrometers of coating thicknesses.

Comparative Example 3

100 parts by weight of cellulose is mixed with 80 parts by weight of butyric acid and 50 parts by weight of acetic anhydride, and then 1 part by weight of sulfuric acid catalyst is made to form a dope cellulose triester, and the dope is hydrolyzed in an appropriate amount of water-acid mixture. The gelling or organic components of the remaining solution were filtered and water was added to the filtered solution to produce cellulose acetate butyrate. After washing with water and vacuum drying to prepare a cellulose acetate butyrate in the form of a powder of butyl group content 35%, acetyl group content 15%, glass transition temperature of 135 ℃.

Then, 100 parts by weight of a polyester resin (Vylon 200, manufactured by Toyobo), 20 parts by weight of an acrylic resin (A-11, manufactured by Rohm & Haas), and 20 parts by weight of cellulose acetate butyrate prepared above were mixed, followed by methyl ethyl ketone. After diluting 100 parts by weight and 100 parts by weight of toluene and diluting 200 parts by weight of polymethyl methacrylate particles having an average particle diameter of 12 μm, the mixture was dispersed for 1 hour at a rotational speed of 1000 rpm using a ring mill, and then 100 μm of ultra-transparent polyethylene tere At least one surface of the phthalate film (T600, manufactured by Mitsubishi Corporation) was dried using a comma knife and then coated to have a coating thickness of 15 μm.

The light diffusing films obtained according to Examples 1 to 2 and Comparative Examples 1 to 3 were evaluated by the following methods, and the results are shown in Table 2 below.

1) Coating Adhesion

The adhesive force between the transparent base film and the coating layer was scratched on the surface with a BRAIVE INSTUMENTS 10 × 10 cutter, and then glued with 3M 5413 industrial tape to remove the coating layer. .

2) Heat resistance (long term appearance properties)

The light-diffusion film is placed in the thermal shock absorber THERMOTRON at 80 ° C and 75% humidity for 100 hours, and then mounted in a 14.1-inch backlight unit. If there is any wrinkles, stains, white spots, black spots, scratches, etc. Good '.                     

3) luminance

Cut the light diffusion film to 14.1 inch and mount it directly to 141 × 4-156 (product of Taesan LCD Co., Ltd.), which is 14.1 inch with backlight, and evaluate the brightness of 9 places with Topcon's BM7 luminance meter. (uniformity) was obtained. In addition, after heat treatment was performed for 1000 hours at 80 ° C. and 75% humidity in the thermal shock absorber THERMOTRON, and after 1000 hours in Xenon Arc lamp of Weather-Ometer, the luminance was evaluated.

4) UV stability

After the light-diffusion film was left to stand in a Xenon Arc lamp of weather-meter for 1000 hours, L, a, b, YI (Yellow Index) before standing and L, a, b, YI values after standing were measured.

5) coating layer hardness

It is evaluated by the pencil lead of the pencil hardness meter, and the highest hardness at which scratch does not occur on the surface is taken as the surface hardness of the coating layer.

Example Comparative example One 2 One 2 3 Appearance Coating Adhesion Good Good Good Bad Good Hardness 1 ~ 2H 1 ~ 2H 1 ~ 2H 1 ~ 2H HB Heat resistance Long time appearance Good Good Bad Bad Bad Luminance (cd / cm2) / uniformity After coating 1945/67 1943/68 1945/66 1941/72 1945/67 After thermal shock 1943/68 1942/68 1910/70 1935/72 1943/68 After UV irradiation 1940/65 1942/66 1850/71 1930/72 1940/68 Light-resistant After coating L 92 92 92 92 92 a 0.4 0.3 0.5 0.4 0.6 b 1.2 1.1 1.4 1.2 1.4 YI 1.8 1.7 1.9 1.8 1.9 After thermal shock L 92 92 92 92 92 a 0.3 0.4 0.5 0.5 0.5 b 1.3 1.2 1.8 1.1 1.5 YI 1.9 1.9 3.8 2.0 2.1 After UV irradiation L 92 92 92 92 92 a 0.4 0.4 0.5 0.4 0.5 b 1.3 1.1 1.9 1.2 1.5 YI 2.1 2.0 6.4 2.0 2.3

As described above in detail, according to the present invention, a film obtained by applying a light diffusion layer composition including a polyester resin and an acrylic resin together with a cellulose acetate butyrate resin as a binder resin to at least one side of the base film has excellent heat resistance and UV stability. As it is exposed to the backlight for a long time, there is no heat deformation or distortion, so the appearance of the backlight and the luminance show little performance with time.

Claims (3)

In the film for a backlight unit of a liquid crystal display obtained by coating the crude liquid which mix | blended the binder resin, the organic particle | grains, and the additive on at least one surface of the transparent base film, The binder resin is 100 parts by weight of polyester resin, 30 to 200 parts by weight of acrylic resin and 1 to 100 parts by weight of cellulose acetate butyrate resin, the film for a backlight unit having excellent heat resistance. The film for a backlight unit of a liquid crystal display having excellent heat resistance according to claim 1, wherein the cellulose acetate butyrate resin has a glass transition temperature of 130 to 150 ° C. The backlight of a liquid crystal display having excellent heat resistance according to claim 1 or 2, wherein the cellulose acetate butyrate resin has a content of a substituted acetyl group of 2.0 to 20% and a content of a substituted butyl group of 20 to 40%. Film for the unit.

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