KR100707731B1 - Light Diffusion Film for Liquid Crystal Display Backlight Unit - Google Patents

Abstract

The present invention is a LCD display made by applying a back layer containing cellulose acetate butyrate on the back side of a plastic support film in a light diffusion film for a backlight unit of an LCD display made by applying a light diffusion layer containing a resin and particles on a plastic support film. The present invention relates to a light diffusing film for a backlight unit, which has excellent coating properties and high heat resistance, and does not cause color fading without thermal deformation caused by back light.

Description

Light diffusion film for liquid crystal display backlight unit {Film for LCD back light unit}             

1 schematically shows a cross section of a light diffusing film according to the present invention.

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

100-Light Diffusion Film 11-Light Diffusion Layer

12-Base Film 13-Back Layer

The present invention relates to a light diffusing film for a backlight unit of an LCD display, and more particularly, a thermal coating by a back light coated with a back coating layer containing cellulose acetate butyrate having heat resistance and excellent coating performance. It is related with the light-diffusion film which can prevent fading.

Recently, as the use of LCD displays has been expanded from notebook computer monitors to large desktop computer monitors and TV monitors, large screens, low power consumption, and high brightness are required. Among the problems addressing these demands, the most important is the large screen, low power, and high brightness of the backlight unit that makes the light source of the LCD display.

In the backlight unit, the light diffusing film plays a role of diffusing the light of the lateral light source lamp on one side or the back of the LCD display to the entire screen and refracting the light into a uniform light in the front direction. Since the light diffusing film is in a position directly in contact with the light source of the lamp, it should be stable to heat generated when the light source is On. The plastic film support is thermally contracted by the repeated process of generating and dissipating heat by the light source, and by the heat contraction, deformation is applied to the light diffusing film fixed to a predetermined frame, thereby increasing the central portion of the light diffusing film, thereby providing uniform light diffusion. The overtransmission does not occur, resulting in partial non-uniform light transmission degradation of the pattern on the LCD display screen. In addition, the adhesive force with the light diffusion layer applied on the plastic support is separated, and as time passes, the plastic support and the light diffusion layer are separated, so that uniform light diffusion and light transmission do not occur, thereby decreasing the brightness of the LCD display screen.

In addition, the light diffusing film is manufactured by applying a light diffusing agent to the transparent resin to perform the role of light diffusion, because the light diffusing agent and the resin is discolored by the ultraviolet light emitted from the light source lamp discolored by ultraviolet light It was necessary to prevent them.

The conventional manufacturing process of the light diffusion film is applied by adding an additive to prevent such a heat resistance and fading discoloration to ultraviolet light, but the effect of the heat stabilizer or ultraviolet stabilizer used as an additive is not permanent, so that its effect over time Decreases. In addition, the compatibility with the resin used over time is reduced and protrudes to the surface, the dots or patterns appear on the screen of the LCD display. In addition, the wear resistance of the light diffusing layer containing the light diffusing agent is reduced by the use of the additive so that the light diffusing layer comes off by friction with the light guide plate.

In addition, in order to obtain a uniform LCD display screen, the light diffusing agent layer coating liquid must be uniformly dispersed before applying the light diffusing layer to the plastic support. When using an additive such as a heat stabilizer or an ultraviolet stabilizer, When the coating liquid is impaired and the uniformity of the coating liquid is decreased and the amount of the additive is increased, the compatibility with the coating liquid is reduced, so that the additive is precipitated or the resin of the coating liquid is agglomerated.

Therefore, the inventors of the present invention, while trying to solve the problems of the thermal deformation and fading prevention methods of the conventional light diffusion film, as a result of using a high heat-resistant cellulose derivative for the back coating, has excellent coating properties and high heat resistance The present invention was completed by knowing that no fading occurs without thermal deformation caused by the backlight.

Accordingly, an object of the present invention is to provide a light diffusion film capable of preventing heat deformation and discoloration caused by back light by synthesizing cellulose derivative having excellent heat resistance and excellent film forming ability, and using the same as a back layer. have.

The light diffusing film of the present invention for achieving the above object is characterized by having a structure in which a back coating layer made of cellulose acetate butyrate is laminated on a plastic support.

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

The schematic structure of the light diffusion film for a backlight unit used in the LCD display obtained according to the present invention is as shown in FIG.

As shown in FIG. 1, the light diffusing film 100 of the present invention has a structure in which a light diffusing layer 11 is coated on one surface of a plastic film support 12, and a rear layer 13 is stacked on a rear surface thereof.

Each layer will be described in more detail as follows.

(1) light diffusing layers (11)

The light diffusing layer scatters and reflects the incident light, diffuses light, diffuses light, and transmits a lot of light at the same time.

The composition of the light diffusion layer contains a resin and particles.

Therefore, the light diffusion layer uses a resin having good adhesion with the plastic support 12 and good compatibility with the particles that play a role of light diffusion. The main resins are unsaturated polyester, methyl methacrylate, ethyl methacrylate, Isobutyl methacrylate, normal butyl methacrylate, normal butyl methyl methacrylate, acrylic acid, methacrylic acid, hydroxyethyl methacrylate, hydroxypropyl methacrylate, hydroxyethyl acrylate, acrylamide, methirol Acrylamide, urethane, epoxy, melamine, etc., such as acrylamide, glycidyl methacrylate, ethyl acrylate, isobutyl acrylate, normal butyl acrylate, 2-ethylhexyl acrylate polymer, copolymer or terpolymer Can be used. Here, in order to improve heat resistance, abrasion resistance, and adhesiveness, a hardening agent is added and the film of resin is hardened and used.

Of these, preferred resins preferably have high light transmittance, and it is preferable to use a resin that can increase the light diffusion effect even with a small amount due to a large difference in refractive index with the particles depending on the type of particles used.

On the other hand, as the particles that act as a light diffusion, there can be used a variety of organic and inorganic particles to increase the light transmittance and diffusion while having a difference in refractive index with ordinary resin.

Examples of representative particles include methyl methacrylate, ethyl methacrylate, isobutyl methacrylate, normal butyl methacrylate, normal butyl methyl methacrylate, acrylic acid, methacrylic acid, hydroxyethyl methacrylate, hydroxy Propyl methacrylate, hydroxyethyl acrylate, acrylamide, metyrol acrylamide, glycidyl methacrylate, ethyl acrylate, isobutyl acrylate, normal butyl acrylate, 2-ethylhexyl acrylate polymer, air It is a multilayer formed by coating different types of monomers on the layer after forming olefinic particles such as acrylic, polyethylene, polystyrene and polypropylene, copolymers of acryl and olefin, and homopolymer such as copolymers or terpolymers. Organic particles such as component particles; Examples of the inorganic particles include silicon oxide, aluminum oxide, titanium oxide, zirconium oxide, magnesium fluoride and the like.

The particle | grains used are 20-30 micrometers which is the thickness of a coating film, and small particles of 1-20 micrometers may be used.

In addition, in order to increase light diffusion efficiency, particles having different particle sizes may be mixed and used.

In addition, it is possible to increase the light diffusion rate by mixing two or more kinds of particles having a difference in refractive index rather than using a single type of particles.In addition, when the light diffusion efficiency is increased to two types having similar refractive indices but only different sizes. There is also.

These particles have different light transmittances and light diffusion rates depending on the ratios contained in the resin. In order to show a high light transmittance and light diffusion rate, the ratio of particles contained in the resin is 10 by weight ratio when the thickness of the coating film is 20-30 μm. It is preferred to be at least% by weight, and more preferably a higher particle content is required. However, when the content of the particles is increased or the difference in the refractive index of the particles is large, the light transmittance is lowered, and the dispersion of the particles when the particle-containing resin solution is prepared, there is a problem that a uniform solution is impossible. Therefore, it is advantageous for the production of the light diffusion layer uniformly dispersed so that the content of particles in the resin does not exceed 60% by weight.

In addition to the resins and particles as described above, an antistatic agent may be used to impart contamination resistance to prevent generation of dust or impurities that may occur when manufacturing a backlight unit using a light diffusing film.

As the antistatic agent, various kinds of quaternary amines, anionics, cationics, nonionics, fluorides, and the like can be used.As the amount of the antistatic agent increases, the antistatic property is high, but the wear resistance is low and there is a risk of precipitation if used for a long time. It is good to use it with 10 weight part or less with respect to 100 weight part of resin, Preferably it is 5 weight part or less.

In addition, in the light diffusion layer composition, since the particles or the antistatic agents must be uniformly dispersed together with the resin to make the light diffusion layer having high light diffusion efficiency, a dispersant for a uniform crude liquid may be used.

Examples of the dispersant include acrylic emulsions, modified silicones, polydimethylsiloxanes, and fluorides. The amount of the dispersant is preferably used in a small amount so that the light transmittance is high and the surface is not precipitated after the coating film is formed. Preferably it is used within 5 weight part with respect to 100 weight part of resin.

Additives of such a light diffusion layer should be used within a range that does not degrade the light transmittance of the basic resin.

Although the light-diffusion crude liquid obtained in this way is apply | coated on a plastic support body using a comma knife, the thickness of a coating film is 20-30 micrometers.

(2) plastic support (12)

Polyethylene terephthalate is mainly used as the plastic support that can be used in the present invention. Recently, polyethylene naphthalate having an ultraviolet blocking effect is used without adding an ultraviolet stabilizer to the light diffusion layer.

Such plastic supports should have adhesion to the resin used and should not affect the light diffusing layer due to their high light transmittance within them.

50-200 micrometers is suitable for the thickness of a plastic support body, Preferably it is 75-150 micrometers.

(3) back layer (13)

In the present invention, the rear layer 13 positioned on the rear side of the plastic support provides slipability to increase workability when the light diffusing film is mounted on the backlight unit, and also has antistatic properties to stabilize it from dust and contaminants. It plays a role of preventing thermal deformation or fading due to light.

The resins used for the back layer are mainly unsaturated polyesters, methyl methacrylate, ethyl methacrylate, isobutyl methacrylate, normal butyl methacrylate, normal butyl methyl methacrylate, acrylic acid, methacrylic acid, hydroxy Ethyl methacrylate, hydroxypropyl methacrylate, hydroxyethyl acrylate, acrylamide, methrol acrylamide, glycidyl methacrylate, ethyl acrylate, isobutyl acrylate, normal butyl acrylate, 2-ethyl Acrylic, urethane, epoxy, melamine, etc., such as hexyl acrylate polymer, copolymer or terpolymer may be used.

However, their drawback is that the heat resistance is weak due to heat deformation after a long time due to the back light to form an irregular screen on the LCD screen.

Therefore, the present invention uses a cellulose derivative having heat resistance and good coating property to form a rigid coating film on the plastic support. Specifically, the heat resistant cellulose derivatives include esterified compounds of cellulose such as cellulose acetate butyrate, cellulose acetate propionate, cellulose propionate and cellulose acetate. Such cellulose derivatives are easy to synthesize and can easily form a coating film with a plastic support due to intramolecular ester groups.

Among them, cellulose acetate, cellulose propionate, and mixed-substituted cellulose acetate propionate, in which only an acetyl group and a propion group are substituted alone, are difficult to control the degree of substitution and are difficult to coat because of solvent resistance, and the resulting substituents become cloudy when the coating is formed. There is a disadvantage that damages the appearance.

Thus, the preferred cellulose derivative is cellulose acetate butyrate.

Cellulose derivatives vary in glass transition temperature according to esterification degree and viscosity, and the number of hydroxyl groups per four anhydroglucose units. The content of acetyl groups in cellulose acetate butyrate is preferably 1.0 to 80%, more preferably 2.0 to It is necessary to have 20%. The content of butyl group is preferably 10 to 90%, more preferably 20 to 40% by weight, and in this case, the glass transition temperature of cellulose acetate butyrate is about 110 to 160 ° C, and it is preferable to maintain this temperature range. .

If the temperature is higher than this temperature, the heat resistance is excellent, but the film strength is weak. If the temperature is lower than this temperature, the heat resistance is insufficient, resulting in thermal deformation caused by the backlight. The degree of substitution of the acetyl group is also controlled by the content of the substituted butyl group. The degree of substitution of the butyl group and the acetyl group is not more than 60% in total. It is the butyl group that has a greater influence on the glass transition temperature. If the content is more than 40%, the glass transition temperature is 110 ° C. or lower. If the content is less than 10%, the glass transition temperature is 160 ° C. or higher. This is hard to use bad.

The preparation of cellulose acetate butyrate involves mixing a certain amount of butyric acid and acetic anhydride in cellulose, and acting a sulfuric acid catalyst to form dope cellulose triester, which is then hydrolyzed in a water-acid mixture, The content of the substituents in the range required by the present invention.

The gelling or fibrous component of the remaining solution is filtered and water is added to the filtrate to produce cellulose acetate butyrate.

After washing with water and drying to prepare a cellulose acetate butyrate in powder form.

After dissolving the produced cellulose acetate butyrate by mixing methyl ethyl ketone and toluene, a very small amount of particles are added to give slip property. The particles to be added may be the same as the particles of the light diffusion layer described above.

Here, a very small amount of particles refers to particles of 1 part by weight or less per 100 parts by weight of resin, and any of them should not impair the basic light transmittance.

The rear layer crude liquid thus prepared is coated on the rear surface of the plastic support through gravure coating, in which case the coating thickness is 1 to 10 µm, preferably 2 to 5 µm.

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

In the embodiment of the present invention, the composition of the light diffusion layer is 100 parts by weight of an unsaturated polyester resin, 5 parts by weight of polyisocyanate as a curing agent, 20 parts by weight of a copolymer containing polymethyl methacrylate as a main component, and air containing polystyrene as a main component. It is composed of 10 parts by weight of copolymer, 3 parts by weight of nonionic surfactant as antistatic agent, polydimethylsiloxane and solvent as dispersant, and the composition is dispersed for 2 hours at 10,000 revolutions per minute using a Tego disperser and then in the crude solution for 5 hours. The bubbles were removed and the crude liquid was applied to the polyethylene terephthalate film using a comma knife and dried to prepare a film (hereinafter referred to as film I) in which only the light diffusing layer 11 was applied.

Example 1

80 parts by weight of butyric acid and 50 parts by weight of acetic anhydride are mixed with 100 parts by weight of cellulose, and 1 part by weight of sulfuric acid catalyst is added thereto to form a dope cellulose triester, and the dope is hydrolyzed in a water-acid mixture. The gelling component or the fibrous component in the remaining solution was filtered, and water was added to the filtrate solution to produce cellulose acetate butyrate.

Next, the mixture was washed with water and dried to prepare cellulose acetate butyrate having a butyl group content of 35%, an acetyl group content of 15%, and a glass transition temperature of 135 ° C, and dissolved in 30 parts by weight of methyl ethyl ketone and 70 parts by weight of toluene. A cellulose acetate butyrate resin solution of% was prepared.

After dispersing 2 parts by weight of polystyrene particles in this solution, the film (film I) coated only the light diffusing layer 14 times bar coating and dried for 30 seconds at a hot air oven temperature of 100 ℃ to give a coating content of 3g / ㎡ to 2.8 A back layer of μm was formed.

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, and then 1 part by weight of sulfuric acid catalyst is made to form a dope cellulose triester, and the dope is hydrolyzed in a water-acid mixture. The gelling component or the fibrous component in the remaining solution was filtered, and water was added to the filtrate solution to produce cellulose acetate butyrate.

Next, the mixture was washed with water and dried to prepare cellulose acetate butyrate having a butyl group content of 25%, an acetyl group content of 15%, and a glass transition temperature of 140 ° C., dissolved in 30 parts by weight of methyl ethyl ketone and 70 parts by weight of toluene, and 10%. Cellulose acetate butyrate resin solution was prepared.

After dispersing 2 parts by weight of polystyrene particles in this solution, the film (film I) coated with only the light diffusion layer was subjected to 14 bar coating, dried at hot air oven temperature of 100 ° C. for 30 seconds, and then the coating content was 3g / m 2. A back layer of μm was formed.

Comparative Example 1

100 parts by weight of cellulose is mixed with 120 parts by weight of butyric acid and 20 parts by weight of acetic anhydride, and then 1 part by weight of a sulfuric acid catalyst is made to form a dope cellulose triester, and the dope is hydrolyzed in a water-acid mixture. The gelling component or the fibrous component in the remaining solution was filtered, and water was added to the filtrate solution to produce cellulose acetate butyrate.

Next, the mixture was washed with water and dried to prepare cellulose acetate butyrate having a butyl group content of 45%, an acetyl group content of 5%, and a glass transition temperature of 105 ° C., dissolved in 30 parts by weight of methyl ethyl ketone and 70 parts by weight of toluene, and 10%. Cellulose acetate butyrate resin solution was prepared.

After dispersing 2 parts by weight of polystyrene particles in this solution, the film (film I) coated only the light diffusing layer 14 times bar coating and dried for 30 seconds at a hot air oven temperature of 100 ℃ to give a coating content of 3g / ㎡ to 2.8 A back layer of μm was formed.

Comparative Example 2

100 parts by weight of cellulose is mixed with 20 parts by weight of butyric acid and 80 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 a water-acid mixture. The gelling component or the fibrous component in the remaining solution was filtered, and water was added to the filtrate solution to produce cellulose acetate butyrate.

Next, the mixture was washed with water and dried to prepare cellulose acetate butyrate having a butyl group content of 9%, an acetyl group content of 38%, and a glass transition temperature of 165 ° C, dissolved in 30 parts by weight of methyl ethyl ketone and 70 parts by weight of toluene, and 10%. A cellulose acetate butyrate resin solution was prepared.

After dispersing 2 parts by weight of polystyrene particles in this solution, the film (film I) coated only the light diffusing layer 14 times bar coating and dried for 30 seconds at a hot air oven temperature of 100 ℃ to give a coating content of 3g / ㎡ to 2.8 A back layer of μm was formed.

 Comparative Example 3

After dispersing 2 parts by weight of polystyrene particles in 100 parts by weight of a polyester resin solution having a glass transition temperature of 60 ° C., the film was coated 14 times with only the light diffusing layer (film I), and at 30 ° C. for 100 seconds at a hot air oven temperature of 100 ° C. After drying, the coating content was 3 g / m 2 to form a back layer of 2.8 μm.

Comparative Example 4

After dispersing 20 parts by weight of polystyrene particles in 100 parts by weight of a polyurethane resin solution having a glass transition temperature of 9 ° C., the film was coated 14 times with a light diffusion layer (film I) and dried at a hot air oven temperature of 100 ° C. for 30 seconds. After the coating content was 3g / ㎡ to form a back layer of 3.0㎛.

The films obtained according to Examples 1 to 2 and Comparative Examples 1 to 4 were evaluated according to the following methods, and the results are shown in Table 1 below.

(1) Coating properties: The adhesive strength with the film and the appearance of the coating film (fish eyes, pinholes and cratering) are evaluated. If there was even one dot, it was defective, and at all, it was good.

(2) Heat resistance characteristics: After leaving the film sample at 23 ° C. and 50% RH × 2 hours, measuring the length to L ₁ , leaving the film sample at 300 ° C. for 1 hour, and then adjusting the length of the sample to L ₂ . The thermal contraction rate was calculated by the formula.

Shrinkage (%) = {(L ₁ -L ₂ ) / L ₁ } × 100

(3) Light resistance: UV light (365 nm) was continuously irradiated with ultraviolet light on the film surface and measured after 15 hours, 50 hours and 100 hours after yellowing and color change by ultraviolet light.

Example Comparative Example One 2 One 2 3 4 Coating property Adhesion Good Good Good Bad Good Good Exterior Good Good Bad Bad Good Good Heat resistance Heat Shrinkage (%) 1.0 1.1 1.6 1.0 1.8 1.5 Light resistance (yellowing and color change) 15 hours Good Good Good Good Good Good 50 hours Good Good usually Good usually Bad 100 hours Good Good Bad Good Bad Bad

From the results of Table 1, when applying the back layer containing the cellulose derivative according to the present invention it can be seen that the coating film forming ability is also excellent, and yellowing or color change by ultraviolet light does not occur, it is also excellent light resistance.

As described in detail above, the light-diffusion film coated with a backing layer including cellulose acetate butyrate having heat resistance and excellent coating film formation ability on the plastic support according to the present invention has excellent coating property and high heat resistance and thus has a high back light. There is no fading without heat deformation caused by.

Claims (5)

In the light diffusion film comprising a resin and particles on a plastic support film and a back diffusion layer on the back of the plastic support film, a light diffusion film for a backlight unit of an LCD display, The back layer is a light diffusion film for a backlight unit of the LCD display, characterized in that it comprises cellulose acetate butyrate. The light diffusion film for a backlight unit of an LCD display according to claim 1, wherein the cellulose acetate butyrate has an acetyl group content of 1.0 to 80% and a butyl group content of 10 to 90%. The light diffusion film for a backlight unit of an LCD display according to claim 1 or 2, wherein the cellulose acetate butyrate has a glass transition temperature of 110 to 160 ° C. The light diffusion film of claim 1, wherein the back layer comprises particles selected from organic particles or inorganic particles. The method of claim 4, wherein the organic particles are selected from acrylic particles, olefin particles, and copolymer particles of acrylic and olefin, and the inorganic particles are selected from silicon oxide, aluminum oxide, titanium oxide, zirconium oxide, and magnesium fluoride. Light diffusion film for a backlight unit of an LCD display, characterized in that selected.

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