JP4547509B2 - Light diffusion sheet for backlight unit - Google Patents

Description

  The present invention relates to a light diffusion sheet for a backlight unit used for a backlight unit of an LCD, and more particularly, to light used for a thin film transistor liquid crystal display (TFT-LCD) or a super twisted nematic liquid crystal display (STN-LCD). A light diffusing sheet for a backlight unit, which is a diffusing sheet, which induces uniform surface light through linear light emitted from a cold cathode fluorescent lamp located on the side or rear surface of the display, thereby obtaining a bright light image It is about.

  In general, light diffusion sheets for LCD backlights are light guide plates used in small car navigation systems, mobile phones, PDAs, digital cameras, portable TVs, camcorders, medium and large notebooks and pancons, and desktop monitors. Non-uniform light emitted from a light guide plate in a WEDGE-type backlight unit characterized in that a linear lamp is installed in one cross section and a SIDE-type backlight unit in which one or more lamps are installed and used Is switched to uniform light centered on the front direction of the backlight unit, and a direct type used in TVs and some large monitors, that is, a large number of cold cathode fluorescent lamps or flat lamps on the back of the backlight. Even in the case of installation, it diffuses the light that is visually recognized linearly, and the center of the uniform front direction Of performed functions of surface light, the distribution center of the light from the role of switching the front direction, resulting in Effect of increasing the luminance in the front direction.

  In such a function of the light diffusion sheet for LCD backlight, in order to perform a shielding function and a diffusion function, and to improve luminance, transparent organic resin particles or inorganic resin particles are made transparent on a transparent resin film. A method of coating as a resin binder has been developed (Japanese Patent Laid-Open No. 7-174909, Korean Patent Publication No. 2000-0027862, Korean Patent Publication No. 1998-0020430).

However, the conventional techniques as described above do not satisfy the bright line shielding performance required for backlights that are becoming thinner because resin particles are coated on a transparent resin film.
JP 7-174909 A Korean Patent Publication No. 2000-0027862 Korean Patent Publication No. 1998-0020430

  The present invention has been devised in order to solve the above-mentioned problems, and the object of the present invention is to replace the conventional transparent resin film with an organic diffusing agent to reduce turbidity. Providing a light diffusing sheet for backlight units that uses the raised internal diffusion film as a base material to maximize light refraction and scattering, improve the diffusion function, and improve the bright line shielding power It is to be.

  The above and other objects and advantages of the present invention will be apparent from the embodiments of the present specification and the accompanying drawings.

  The light diffusing sheet for a backlight unit according to the present invention for achieving the above object is an internal diffusion film in which an organic diffusing agent is distributed in a transparent base film, and has a haze of 40 to 95% and a transmittance of 50 to 95%. And an optical diffusion layer coated with a binder resin and transparent resin particles on at least one surface of the internal diffusion film.

  Desirably, the transparent resin particles are one kind of monodisperse particles having a particle size distribution of 80% or more within ± 20% of the average particle size and particles having an average particle size smaller than the monodisperse particles. It is characterized by being mixed particles as described above.

  More preferably, the particles having a small average particle diameter are two or more kinds of particles having a maximum average particle diameter of 3 μm to 7 μm and 1 μm to 3 μm, respectively.

  More desirably, the maximum average particle size of the monodisperse particles is 10 μm to 50 μm.

  More preferably, the difference between the refractive index of the binder resin and the refractive index of the transparent substrate film is 0.22 or less, and the refractive index of the binder resin is higher than the refractive index of the transparent substrate film. It is small.

  As described above, according to the light diffusing sheet according to the present invention, by using an internal diffusion film in which an organic diffusing agent is added to the inside of the base material, the light refraction and scattering properties are maximized, and the diffusion function is improved. There is an effect that it is possible to provide an excellent light diffusion sheet such as having a high bright line shielding power.

  Therefore, the light diffusing sheet according to the present invention is useful for manufacturing a slim BLU that requires high shielding performance.

  Hereinafter, embodiments of the present invention will be described in more detail with reference to the drawings. However, these embodiments are for illustrating specific examples of the present invention, and the scope of the present invention is not limited to these embodiments. Will be obvious to those of ordinary skill in the art.

  FIG. 1 is an end view of a light diffusion sheet for a backlight unit using an internal diffusion film according to an embodiment of the present invention, and FIG. 2 is a plan view of FIG.

  As shown in FIG. 1, the internal diffusion film 2 is composed of an organic diffusing agent 1 and a transparent substrate film 1 '. In the formation of the internal light diffusion layer by the organic diffusing agent (1), the optical function is determined by the shape of the lens formed by the organic diffusing agent (1) or the shape of the bend. The greater the lens shape or the bent shape, the better the shielding function and diffusion function of the internal diffusion film.

  In the internal diffusion film 2, the transparent base film 1 ′ includes, as a thermoplastic resin, polyethylene terephthalate, polyethylene-2, 6-naphthalate and the like, a copolymer containing these as a main component, or a mixture of these resins. Further, the organic diffusing agent 1 is a polyolefin resin such as polyethylene, polypropylene, polymethylpentene, a copolymer containing these as a main component, or a mixture of these resins as a thermoplastic resin. Resins are desirable.

  Here, as the transparent substrate film 1 ′, a biaxially stretched polyethylene terephthalate film is most desirable. The main purpose of this biaxially stretched polyethylene terephthalate film is that it is excellent in mechanical strength, heat resistance, transparency, flatness, and the like. There is an advantage that the performance can be demonstrated.

  On the other hand, in the light diffusion layer (5) formed on one surface of the internal diffusion film, in order to increase the surface area of the surface lens, it is desirable to use large particles having an average particle diameter of 7 microns or more. It is desirable to use particles (hereinafter referred to as “monodispersed particles”) having an average particle size of not less than 50 microns and not more than 50 microns and having a particle size distribution of 80% within ± 20% of the average particle size.

  For such a particle size distribution, a method of measuring the particle size using light scattering can be used by a particle size distribution measuring device LS PARTICLEIZE ANALYZER (manufactured by Coulter). In particular, in the backlight unit by direct type LAMP method used for televisions with a plurality of lamps arranged on the rear surface to increase the amount of light emitted, the role of improving the brightness by maximizing the diffusion function and eliminating the bright line of the lamp Light that passes straight without being refracted or scattered by the light diffusing agent creates bright lines and degrades the light quality.

  Therefore, by using an internal diffusion film with an organic diffusing agent added to the inside of the base film, the diffusibility is maximized and the surface area of the surface lens is increased to increase the diffusion function and shielding power, thereby increasing the brightness. In order to obtain the effect of increase, the larger the maximum average particle diameter of the transparent spherical organic particles 3a on the surface, the more advantageous. The monodisperse particles of 7 microns or more, more preferably 10 microns or more and 50 microns or less are desirable. . When particles having an average particle diameter of 50 microns or more are used, wet coating is difficult and dispersion of the coating solution is difficult. The resin particles applied to the surface for maximizing the shielding function are one or more kinds of particles (3b or 3c) smaller than the particles having the maximum average particle diameter, preferably two or more kinds of particles (3b, 3c). ) Is desirable.

  In a preferred embodiment, the maximum average particle size of the two small particles is preferably 3 μm to 7 μm, 1 μm to 3 μm, respectively.

  As the light diffusing agent used in the light diffusing layer 5, spherical transparent particles are suitable. As the transparent particles, organic particles such as acrylic particles, styrene particles, and silicon particles, synthetic silica, glass beads, diamond and the like are used. Inorganic particles may be used, and these light diffusing agents may be used alone or in admixture of two or more.

  The binder resin used for the light diffusing layer (5) of the light diffusing film must be transparent, such as acrylic, urethane, epoxy, vinyl, polymethyl methacrylate or methacrylate ester copolymer, You may use individually or in mixture of 2 or more types from resin, such as a polyester type and a polyamide type. The refractive index of the transparent binder resin must be a value that has a difference from the refractive index of the transparent base film 1 'of 0.22 or less and smaller than the refractive index of the transparent base film 1'. When the refractive index of the binder resin is larger than the refractive index of the transparent substrate film 1 ′, in the traveling direction of light from the transparent resin layer to the light diffusion layer, at the boundary surface between the light diffusion layer and the transparent substrate film 1 ′, Reflection is more than light transmission, and the light transmittance is reduced. In addition, when the difference in refractive index is 0.22 or more, light refraction and scattering increase at the boundary surface between the light diffusion layer 5 and the transparent base film 1 ′, and a high luminance can be obtained. Manufacturing becomes difficult.

  As a method of diluting and applying the light diffusing agent and the organic resin binder to a transparent base film, a normal wet coating method such as a knife coating method, a gravure transfer coating method, or a reverse roll coating method should be used. Can do.

  At this time, if the coating thickness does not exceed 150% of the particles having the maximum average particle size, the desired effect of a uniform coated surface can be obtained.

  If the coating thickness exceeds 150% of the particles having the maximum average particle diameter, the luminance may decrease due to the excessive amount of particles per unit area.

  The back surface of the light diffusion layer formed on one surface of such an internal diffusion film is provided with a slip property, and the hardness is increased to prevent the occurrence of scratches during cutting and assembling work, thereby preventing the entry of foreign matters. Therefore, a coating layer having an antistatic function can be formed.

  Examples of the present invention and comparative examples will be described below. In the compositions of the coating liquids of the following examples and comparative examples, the parts by weight indicating the weight of each component are parts by weight based on 100 parts by weight of the total coating liquid composition.

Example 1
On one surface of an internal diffusion film (QE 31-125 μm, Haze: 92, Transmission: 90, manufactured by Toray Industries, Inc.), a light diffusion sheet was manufactured using a microgravure with a coating liquid having the following composition.
Composition of coating liquid- Binder resin (Ai Chemical Co., Ltd .: A-811): 18.2 parts by weight-Curing agent (Ai Chemical Co., Ltd .: DN980S): 1.8 parts by weight-Synthetic resin particles (Made by Soken Chemical Co., Ltd .: MX) −1500 monodisperse average particle size 15 μm): 18.1 parts by weight Synthetic resin particles (manufactured by Soken Chemical Co., Ltd .: MX-500 monodisperse average particle size 5 μm): 5.0 parts by weight methylethylketone: 28.3 parts by weight -Toluene: 28.3 parts by weight

(Example 2)
On one surface of an internal diffusion film (QE 32-125 μm, Haze: 40, Transmission: 92, manufactured by Toray Industries, Inc.), a light diffusion sheet was manufactured using a microgravure with a coating liquid having the following composition.
Composition of coating solution- Binder resin (Ai Chemical Co., Ltd .: A-811): 18.2 parts by weight-Curing agent: (Ai Chemical Co., Ltd .: DN980S) 1.8 parts by weight-Synthetic resin particles (Made by Soken Chemical Co., Ltd .: MX) −1500 monodisperse average particle size 15 μm): 18.1 parts by weight Synthetic resin particles (manufactured by Soken Chemical Co., Ltd .: MX-500 monodisperse average particle size 5 μm): 5.0 parts by weight methylethylketone: 28.3 parts by weight -Toluene: 28.3 parts by weight

Example 3
On one surface of an internal diffusion film (PY-2-110 μm, Haze: 85, Transmission: 90, manufactured by Toray Industries, Inc.), a light diffusion sheet was manufactured using a microgravure with a coating liquid having the following composition.
Composition of coating liquid- Binder resin (Ai Chemical Co., Ltd .: A-811): 24.5 parts by weight-Curing agent (Ai Chemical Co., Ltd .: DN980S): 2.5 parts by weight-Synthetic resin particles (Made by Soken Chemical Co., Ltd .: MX) −1500H monodisperse average particle size 15 μm): 14.0 parts by weight Synthetic resin particles (manufactured by Soken Chemical Co., Ltd .: MX-500 monodisperse average particle size 5 μm): 5.9 parts by weight Methyl ethyl ketone: 29.3 parts by weight -Toluene: 29.3 parts by weight

Example 4
On one surface of an internal diffusion film (PY-3-110 μm, Haze: 93, Transmission: 68, manufactured by Toray Industries, Inc.), a light diffusion sheet was manufactured using a microgravure with a coating liquid having the following composition.
Composition of coating liquid- Binder resin (Ai Chemical Co., Ltd .: A-811): 24.5 parts by weight-Curing agent (Ai Chemical Co., Ltd .: DN980S): 2.5 parts by weight-Synthetic resin particles (Made by Soken Chemical Co., Ltd .: MX) −1500H monodisperse average particle size 15 μm): 14.0 parts by weight Synthetic resin particles (manufactured by Soken Chemical Co., Ltd .: MX-500 monodisperse average particle size 5 μm): 5.9 parts by weight Methyl ethyl ketone: 29.3 parts by weight -Toluene: 29.3 parts by weight

(Example 5)
On one surface of an internal diffusion film (PY-4-110 μm, Haze: 93, Transmission: 57, manufactured by Toray Industries, Inc.), a light diffusion sheet was manufactured using a microgravure with a coating liquid having the following composition.
Composition of coating liquid- Binder resin (Ai Chemical Co., Ltd .: A-811): 24.5 parts by weight-Curing agent (Ai Chemical Co., Ltd .: DN980S): 2.5 parts by weight-Synthetic resin particles (Made by Soken Chemical Co., Ltd .: MX) −1500H monodisperse average particle size 15 μm): 14.0 parts by weight Synthetic resin particles (manufactured by Soken Chemical Co., Ltd .: MX-500 monodisperse average particle size 5 μm): 5.9 parts by weight Methyl ethyl ketone: 29.3 parts by weight -Toluene: 29.3 parts by weight

(Comparative Example 1)
A coating solution similar to that of Example 1 was applied to one surface of a transparent resin film (XU42, 188 μm, manufactured by Toray Sehan Co., Ltd.) instead of an internal diffusion film, to produce a light diffusion sheet.

(Comparative Example 2)
A coating solution similar to that in Example 3 was applied to one surface of a transparent resin film (XU42, 188 μm manufactured by Toray Sehan Co., Ltd.) instead of an internal diffusion film, to produce a light diffusion sheet.

(Experimental example)
Experimental Example 1: Evaluation of haze (HAZE) An experiment was conducted to evaluate the haze (HAZE) of the light diffusion sheets produced in Examples 1 to 5 and Comparative Examples 1 and 2. Measurement was performed based on ASTM D-1003, and a model 1000 manufactured by Nippon Denshoku Industries Co., Ltd. was used as the measuring instrument.

Experimental Example 2: Evaluation of shielding power An experiment for evaluating the shielding power of the light diffusing sheets produced in Examples 1 to 5 and Comparative Examples 1 and 2 was performed. Using a Topcon BM-7 equipment, the front luminance on the backlight assembly was measured at an equal interval of 30 points, and defined as Equation 1 and digitized.

  From Table 1, as in Examples 1 to 5, the light diffusion sheet produced using an internal diffusion film with an organic diffusing agent added as a base material is a transparent resin film as in Comparative Examples 1 and 2. It can be seen that it has an excellent shielding power as compared with the light diffusion sheet produced. In addition, as in Examples 1 to 5, it can be seen that an internal diffusion film having a high internal haze and a low transmittance can implement an excellent shielding power.

  The above-described embodiments are for specifically illustrating the present invention, and do not limit the scope of rights of the present invention. In addition, it will be understood that all modifications and variations of the present invention are considered to be within the scope of the present invention.

1 is an end view of a light diffusion sheet for a backlight unit using an internal diffusion film according to an embodiment of the present invention. It is a top view of FIG.

Explanation of symbols

1: Organic diffusing agent 1 ': Transparent substrate film 2: Internal diffusion film 3a: Monodispersed resin particles 3b, 3c: Resin particles 4: Binder resin 5: Light diffusion layer

Claims (5)

In the light diffusion sheet for the backlight unit,
As the internal diffusion film (2) in which the organic diffusion agent (1) is distributed in the transparent base film (1 ′), the internal diffusion film (2) having optical characteristics of haze 40 to 95% and transmittance 57 to 68 %. )When,
At least one surface on the inner diffusion film (2), the binder resin (4) and more applied light diffusing layer on a transparent resin particles child and (5), characterized in that it comprises a light backlight unit Diffusion sheet. The transparent resin particles, particles in which the particles having a monodispersed particle size distribution is present more than 80% ± 20% of the average particle diameter, a small average particle diameter than the monodisperse particles are for mixed The light diffusion sheet for a backlight unit according to claim 1, wherein The maximum average particle size of the particles having a small average particle size characterized in that it is a 3μm~7μ m, a backlight unit for light diffusion sheet according to claim 2.   The light diffusion sheet for a backlight unit according to claim 1, wherein the maximum average particle diameter of the monodisperse particles is 10 μm to 50 μm. The difference between the refractive index of the binder resin (4) and the refractive index of the transparent substrate film (1 ′) is 0.22 or less,
The backlight unit according to any one of claims 1 to 4, wherein the refractive index of the binder resin (4) is smaller than the refractive index of the transparent base film (1 '). Light diffusion sheet for use.

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