KR101781206B1 - Microlens optical sheet, and backlight unit and liquid crystal display using same - Google Patents

Abstract

The present invention relates to an optical sheet having improved hiding power and viewing angle characteristics, and a backlight unit and a liquid crystal display using the same, the optical sheet comprising: (1) a transparent substrate; (2) a diffusion sheet which is disposed on one surface of the transparent substrate and integrally includes a plurality of hemispherical microlens protrusions; (3) a resin layer containing beads filled in the valleys between the microlens protrusions of the diffusion sheet; And (4) a resin layer containing a filler, which is located on the other surface of the transparent substrate, wherein the micro lens protrusion occupies 50 to 90% of the total surface area of the diffusion sheet, and the resin layer containing the bead is a binder resin 100 to 100 parts by weight of the beads and 30 to 180 parts by weight of the beads and is filled at a height of 10 to 80% of the height from the bottom of the valleys to the top of the convexes of the microlenses, and the beads have an average particle diameter of 0.5 to 5 탆 , The bead and the binder resin have refractive indices in the range of 1.41 to 1.59 and the difference between the two refractive index values is 0.02 or more. The micro lens optical sheet of the present invention can provide excellent hiding power and viewing angle characteristics, And liquid crystal display devices.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention [0001] The present invention relates to a micro-lens optical sheet, and a backlight unit and a liquid-

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a micro-lens optical sheet that provides excellent hiding power and viewing angle characteristics by improving the light utilization efficiency and diffusing function by improving light utilization efficiency, and a backlight unit and a liquid crystal display device using the same.

BACKGROUND ART [0002] Liquid crystal displays (LCDs) have been gradually expanded in accordance with the development of information society environments and technologies, and many models of liquid crystal display devices have been introduced. In accordance with this trend, the specifications required are becoming increasingly strict. In recent years, features such as light weight, thinness, and low power consumption are required. In recent years, in recent years, the number of the lamps used in the backlight unit is reduced, the number of diffusion sheets constituting the optical sheet is reduced, and the gap between the lamp and the light guide plate is reduced to reduce the thickness.

With the reduction of the number of the lamps and the simplification of the diffusion sheet, the necessity of the optical sheet having the excellent hiding power and excellent viewing angle characteristic capable of concealing the lamp luminance line and the light guide plate pattern, More and more.

The micro-lens sheet is an optical member having a plurality of hemispherical protrusions made of a photocurable resin, which is located on one side of a transparent substrate, and is used in a backlight unit which is an illumination device for a liquid crystal display. The microlens optical sheet functions to condense and diffuse the light emitted from the lamp to the upper portion of the light guide plate to widen the luminance characteristic and the wide viewing angle of the emission surface.

1A is a perspective view showing a conventional micro-lens optical sheet, and a sectional view (A) - (B) thereof is shown in FIG. 1B. 1A and 1B, the microlens diffusing sheet includes a plurality of microlens protrusions 110 formed on one side of the support 120 and formed at random. The cross-section 113 of the micro-lens protrusion 110 has a substantially hemispherical shape when viewed from the front. A resin layer of a thin film containing a fine pillar 112 is located on the other surface of the support 120 to prevent adhesion between the interfaces and to provide antistatic properties to suppress foreign matter adhesion. In the microlens diffusion sheet, a plurality of microlens protrusions 110 are irregularly distributed, and the microlens protrusions 110 and the valleys 111 alternate with each other. The microlens diffusing sheet structured as described above refracts light incident on the support 120 through the microlens protrusions 110. More specifically, light incident at a low angle diffuses toward the side along the first path L1. The light incident in the vertical direction to the support part 120 causes total reflection along the second path L2 to circulate or pass through the microlens protrusion 110 as it is, thereby contributing to improvement of the front brightness. On the other hand, the light incident on the valleys 111 is not refracted or totally reflected and travels to the third path L3, which has a problem in that it does not contribute to improvement of luminance by condensing or improvement of viewing angle characteristics by diffusion.

Recently, a variety of microlens diffusion sheets have been developed in which the light converging function and the diffusion function are improved. For example, Korean Patent Laid-Open No. 10-2009-0035373 discloses an optical sheet in which convex lens shapes and concave lens-shaped patterns are irregularly formed on one surface of a supporting substrate; Korean Patent Laid-Open No. 10-2008-0092729 discloses an optical sheet in which a light diffusion layer, a prism sheet and a plurality of bead-containing coating layers are sequentially formed on one surface of a support substrate; Korean Patent Laid-Open No. 10-2008-0090636 discloses an optical sheet in which main micro-lens shapes and sub-microlens-shaped patterns of different sizes are spaced apart from each other on one surface of a supporting substrate. Korean Patent Laid-Open Nos. 10-2010-0032767 and 10-2011-0079255 disclose a microlens diffusing sheet having a plurality of convex portions (microlens patterns) and having an embossing pattern or irregular portion between convex portions and convex portions, .

However, the conventional micro-lens diffusion sheet has a problem in that it can not exhibit satisfactory physical properties in view of hiding power and viewing angle characteristics when applied to a backlight unit.

Korea Patent Publication No. 10-2009-0035373 Korean Patent Publication No. 10-2008-0092729 Korean Patent Publication No. 10-2008-0090636 Korean Patent Publication No. 10-2010-0032767 Korean Patent Publication No. 10-2011-0079255

Accordingly, an object of the present invention is to provide a micro-lens optical sheet capable of providing excellent hiding power and viewing angle characteristics by improving the light utilization efficiency and diffusing function by improving light utilization efficiency, and a backlight unit and a liquid crystal display will be.

In order to achieve the above object,

(1) a transparent substrate;

(2) a diffusion sheet, positioned on one surface of the transparent substrate, including a plurality of hemispherical micro-lens protrusions;

(3) a resin layer containing beads filled in the valleys between the microlens protrusions of the diffusion sheet; And

(4) a resin layer containing a filler, which is located on the other surface of the transparent substrate,

The micro lens protrusion occupies 50 to 90% of the total surface area of the diffusion sheet,

Wherein the resin layer containing the beads comprises 100 parts by weight of a binder resin and 30 to 180 parts by weight of a plurality of beads and is filled at a height of 10 to 80% of the height from the bottom of the valleys to the top of the micro-

Wherein the beads have an average particle diameter of 0.5 to 5 mu m,

Wherein the beads and the binder resin each have a refractive index in the range of 1.41 to 1.59, and the difference between the two refractive index values is 0.02 or more.

The microlens optical sheet of the present invention can provide an excellent hiding power and an excellent viewing angle characteristic that can effectively hide the lamp luminance line and the light guide plate pattern while improving the luminance required for the conventional optical film, And can be usefully used for display devices. This makes it unnecessary to use two or more diffuser sheets (i.e., by reducing (simplifying) the lamination structure of the diffusion sheet), contributing to the cost reduction of the backlight unit.

FIG. 1A is a perspective view showing the surface shape of a conventional micro-lens optical sheet, and FIG. 1B is a cross section ((A) - (B)) thereof.
FIG. 2A is a perspective view showing the surface shape of the micro-lens optical sheet of the present invention, and FIG. 2B is a cross section ((A) - (B)) thereof.
FIG. 3A is a scanning electron microscope (SEM) image of the micro-lens optical sheet of the present invention, and FIG. 3B is an SEM image of the cross section thereof.

The microlens optical sheet according to the present invention comprises a bead-containing resin layer filled in a trough portion between microlens protrusions, wherein 100 parts by weight of a binder resin and 30 to 180 parts by weight of beads having an average particle diameter of 0.5 to 5 mu m (Having a refractive index in the range of 1.41 to 1.59 and a difference in refractive index of 0.02 or more) between 10% and 80% of the height from the bottom of the bone site to the top of the micro lens projection, The diffusion function is enhanced to provide improved viewing angle characteristics and concealment characteristics.

FIG. 2A is a perspective view of the micro-lens optical sheet of the present invention, and FIG. 2B is a cross-sectional view (A) - (B) thereof.

Specifically, the micro lens optical sheet according to the present invention

(A) forming a diffusion sheet including a plurality of hemispherical microlens protrusions 210 on one surface of a transparent substrate 220;

(B) applying a resin composition containing a filler (212) to the other surface of the transparent substrate (220) to form a filler-containing resin layer; And

(C) applying a resin composition containing beads 211 to the surface of the diffusion sheet formed in the step (A) to fill the bead-containing resin layer in the valleys between the microlens protrusions 210

≪ / RTI >

The components of the micro-lens optical sheet of the present invention will be described in more detail as follows.

Transparent substrate

The transparent substrate to be used in the present invention is mainly a transparent plastic and should have good adhesion to the binder resin and transmittance of light incident from the back surface should be 90% or more, and the surface smoothness should be uniform, do. The thickness of the transparent substrate is preferably 50 to 300 占 퐉. When the thickness is more than 50 占 퐉, the handling property in the manufacturing process is favorable. When the thickness is 300 占 퐉 or less, the structure of the LCD module becomes thinner.

Specific examples of materials suitable for the transparent substrate include polyether sulfone (PES), polyacrylate (PAR), polyetherimide (PEI), polyethylene naphthalate (PEN), polyethylene terephthalate polyethyleneterephthalate (PET), polyphenylene sulfide (PPS), polyallylate, polyimide, polycarbonate (PC), cellulose triacetate (TAC), cellulose acetate propionate acetate propionate, CAP) and mixtures thereof. Particularly preferred is polyethylene terephthalate (PET).

Diffusion sheet

In the present invention, the diffusion sheet formed on the transparent substrate includes a plurality of hemispherical microlens protrusions at 50 to 90% of the total surface area of the sheet, and may be made of a photo-curable resin. The microlens protrusions have randomly different diameters within a range of about 10 to 100 占 퐉, preferably 50 to 90 占 퐉, and these microlens protrusions provide an effect of improving the condensing and diffusing function. The microlens protrusions may be made of the same material as the diffusion sheet or may be different materials, and preferably the same material, and may be integrally formed.

The photocurable resin constituting the diffusion sheet is not particularly limited as long as it is curable with active energy rays such as ultraviolet rays and electron beams. Specific examples thereof include polyesters; Epoxy resin; (Meth) acrylate resins such as polyester (meth) acrylate, epoxy (meth) acrylate and urethane (meth) acrylate; And mixtures thereof. Among them, a (meth) acrylate resin is particularly preferable from the viewpoint of optical characteristics. It is preferable that the photocurable resin has a refractive index in the range of 1.41 to 1.59. When the refractive index of the resin after curing is 1.41 or more, reduction of the light diffusion effect and deterioration of the hiding power due to increase of the total light transmittance can be prevented. It is possible to prevent a decrease in luminance due to a decrease in total light transmittance. The photocurable resin composition is preferably coated on a semi-spherical concave pattern roll or a belt-shaped pattern sheet and a transparent substrate to a thickness of 5 to 50 탆, Depending on the thickness.

The bead-containing resin layer

In the present invention, the bead-containing resin layer coated on the surface of the diffusion sheet and filled in the bone between the microlens protrusions is filled at a height of 10 to 80% of the height from the bottom of the bone site to the top of the micro lens protrusion. When the filling height is 10% or more, an additional diffusion function can be expected. When the filling height is 80% or less, the decrease in the light condensing function of the microlens is suppressed, and the luminance required as the optical sheet can be achieved.

The bead-containing resin layer according to the present invention may include a plurality of beads and a binder resin, preferably 100 parts by weight of the binder resin and 30 to 180 parts by weight of the beads, more preferably 50 to 150 parts by weight can do.

The beads may be organic polymeric beads comprising a material selected from the group consisting of hard acrylate, polystyrene, nylon, soft acrylate, and silicon. Of these, hard acrylates having good solvent resistance and easy dispersion are preferable. The beads are preferably spherical, and may have an average particle diameter of 0.5 to 5 μm, preferably 0.8 to 3 μm. When the average particle diameter is 0.5 μm or more, the beads are dispersed evenly when mixed with the resin, It is possible to fill the trough portion between the microlens protrusions when the thickness is 5 mu m or less, and the condensing function of the microlens can be improved.

The binder resin serves to fix the beads to the diffusion sheet, and commonly used thermosetting resins and UV curing resins can be used. A suitable binder resin is an acrylic, urethane, epoxy, vinyl, polyester, polyamide resin or a mixture thereof, which is easy to be coated because of high transparency and excellent light transmittance and easy viscosity control. Specific examples thereof include (meth) acrylate resin, unsaturated polyester resin, polyester (meth) acrylate resin, silicone urethane (meth) acrylate resin, silicone polyester (meth) acrylate resin, fluorourethane Late resins and mixtures thereof. Preferably, acrylic resins capable of realizing excellent coating properties, mechanical properties, adhesive strength, durability and the like can be used. Specific examples thereof include methyl methacrylate, methacrylate, ethyl acrylate, butyl acrylate, aryl acrylate, hexyl acrylate, isopropyl A homopolymer having repeating units of methacrylic, benzyl acryl, vinyl acryl, 2-methoxyethyl acryl or styrene, or a copolymer obtained by copolymerizing the above two or more components may be used.

The bead and the binder resin have refractive indices in the range of 1.41 to 1.59, respectively, and the difference in the two refractive index values should be 0.02 or more.

As described above, 100 parts by weight of a binder resin and 30 to 180 parts by weight of a plurality of beads are mixed with a solvent and stirred, and the obtained resin composition is coated on the surface of a diffusion sheet and dried. When the resin is a UV curable resin, To form a desired bead-containing resin layer.

The filler-containing resin layer

In the present invention, the filler-containing resin layer formed on the opposite side of the diffusion sheet-forming surface of the transparent substrate is an anti-blocking layer, and may be an inorganic particle such as silica having a particle size of 0.1 to 50 탆 or an organic crosslinked particle And a binder resin. As the binder resin, those exemplified as the binder resin constituting the coating layer of the diffusion sheet may be used, but the present invention is not limited thereto.

If desired, various applications can be applied to prevent and / or prevent a decrease in brightness or to further improve the viewing angle and concealment characteristics. As the thickness of the coating layer formed on the diffusion sheet changes, the luminance and the viewing angle / concealment characteristics change in inverse proportion to each other. For example, as the thickness of the coating layer increases, the luminance decreases and the viewing angle / concealment characteristics are improved. Further, it is possible to suppress the decrease in luminance and improve the viewing angle / hiding property according to the composition of the beads and the binder resin constituting the coating layer. Also, as the size of the bead particle decreases, the viewing angle / concealment characteristic is improved, and the diffusion effect can be maximized by using the difference between the bead refractive index and the resin refractive index. In addition, air bubbles having a size of several tens nm to several micrometers, for example, 10 to 10,000 nm, may be formed in the coating layer to improve the internal diffusion effect.

The backlight unit manufactured using the optical sheet according to the present invention is also included in the scope of the present invention. That is, the present invention provides a backlight unit comprising at least one light source for providing light, and a micro-lens optical sheet of the present invention located adjacent to the light source.

The present invention also provides a liquid crystal display device including a liquid crystal panel and a backlight unit disposed on the rear surface of the liquid crystal panel and illuminating the liquid crystal panel of the present invention.

As described above, the micro-lens optical sheet of the present invention can provide an excellent hiding power and excellent viewing angle characteristics that can improve the brightness required for the conventional optical film and can effectively hide the lamp luminance line and the light guide plate pattern, And further can be usefully used in liquid crystal display devices. This makes it unnecessary to use two or more diffuser sheets (i.e., by reducing (simplifying) the lamination structure of the diffusion sheet), contributing to the cost reduction of the backlight unit.

Hereinafter, the present invention will be described in more detail with reference to the following examples. However, the following examples are intended to illustrate the present invention, but the scope of the present invention is not limited thereto.

In the following Examples and Comparative Examples, a sheet composed of a diffusion sheet and a bead-containing resin layer coated on its surface was prepared. The haze (%), the total light transmittance (%), the viewing angle luminance Hiding power and appearance were measured as follows.

1. Haze and total light transmittance

Haze meter NDH-2000 manufactured by Nihon Deshoshushi Co., Ltd. was used, and haze and total light transmittance were measured using the following formula.

Haze (%) = diffused light (DT) / transmitted light (TT)

Total transmitted light (TT) = parallel light (PT) + diffused light (DT)

Total light transmittance (%) = Total transmitted light (TT) / Total incident light

2. Hiding power

For the hiding power, the upper sheet of the direct-type CCFL backlight unit was removed, and a comparative evaluation was made using the conventional two-sheet laminated sheet (CH153 + CH403) as a reference. At this time, the CCFL was evaluated according to the five-point method depending on whether or not the line was visually recognized. The degree of clarification of the line sign was set at 5, and the level was concealed so as to be mass-

3. Viewing angle luminance

The luminance of the viewing angle was measured using a backlight unit having the same structure as that of the measurement of the hiding power, and the light receiving unit was measured in a unit of 5 degrees from -85 degrees to +85 degrees in the horizontal direction using the BM7 of Topcon. At this time, the measured value in the case where the light receiving unit is perpendicular to the backlight unit was measured as the front luminance value. In the evaluation of the luminance, comparative evaluation was made using a conventional two-sheet laminated sheet (CH153 + CH403) as a reference, and it was found to be a good level when the brightness was equal to or higher than that of the reference.

4. Appearance

Visually observe the phenomena such as lumps, longitudinal lines, and sand dunes (defective galaxies, sparkling defects, etc.), flow patterns, stains, spots, etc. Respectively .

[Example 1]

100 parts by weight of organic silicone beads (Tospearl 142, Momentive) having an average particle diameter of 2 탆 and a refractive index of 1.42 and 100 parts by weight of a UV curable resin (HR102, SKC Haas) having a solid refractive index of 1.54 were dissolved in a mixed solvent of toluene and cyclohexanone And the solid content concentration was adjusted to 40% to prepare a coating layer composition liquid of the microlens diffusion sheet. This mixed solution was stirred at 1000 rpm for 1 hour in an agitator equipped with a strong motor to obtain a coating composition in which the beads were uniformly dispersed in the UV cured resin solution. The coating composition was applied to the surface of a microlens diffusion sheet (ML13MK, SKC Haas, where the micro lens protrusion occupied 80% of the entire surface area of the diffusion sheet) with wire bar No. 9, and then the solvent was evaporated for 120 seconds in a 100 ° C convection oven. To prepare a sheet by curing the bead-containing resin layer. The bead-containing resin layer was filled at a height of 40% of the height from the bottom of the valleys between the micro-lens protrusions to the top of the protrusions.

A scanning electron microscope (SEM) image of the produced sheet is shown in Fig. 3A, and an SEM image thereof is shown in Fig. 3B.

[Example 2]

A sheet was prepared in the same manner as in Example 1 except that beads were used in an amount of 50 parts by weight.

[Example 3]

A sheet was produced in the same manner as in Example 1 except that beads having an average particle diameter of 1 탆 were used.

[Example 4]

A sheet was prepared in the same manner as in Example 1 except that beads having an average particle diameter of 3 탆 were used.

[Example 5]

A sheet was prepared in the same manner as in Example 1, except that a UV curable resin (RS-4743, Ake Kyokai) having a refractive index of 1.45 and a melamine bead having an average particle diameter of 1 占 퐉 and a refractive index of 1.58 were used.

[Comparative Example 1]

A sheet was prepared in the same manner as in Example 1 except that 20 parts by weight of beads were used.

[Comparative Example 2]

A sheet was prepared in the same manner as in Example 1, except that the beads were used in an amount of 200 parts by weight.

[Comparative Example 3]

A sheet was prepared in the same manner as in Example 1, except that the coating composition was applied to the surface of the microlens diffusing sheet by wire bar No. 6 (filling height of the bead-containing resin layer: 5%).

[Comparative Example 4]

A sheet was prepared in the same manner as in Example 1, except that the coating composition was applied to the surface of the micro-lens diffusion sheet with wire bar No. 12 (filling height of the bead-containing resin layer: 90%).

[Comparative Example 5]

A sheet was prepared in the same manner as in Example 1 except that beads having an average particle size of 7 mu m were used.

[Comparative Example 6]

A sheet was prepared in the same manner as in Example 1 except that beads having an average particle diameter of 0.3 mu m were used.

[Comparative Example 7]

A sheet was prepared in the same manner as in Example 1, except that a UV curable resin (RS-4700, Ake Kyokai) having a refractive index of 1.49 and polymethylmethacrylate (PMMA) beads having an average particle diameter of 2 탆 and a refractive index of 1.49 were used. Respectively.

[Comparative Example 8]

A conventional two-sheet laminated sheet (CH153 + CH403, SKC Haas) was used.

The results of the physical properties of the sheets prepared in Examples 1 to 5 and Comparative Examples 1 to 8 are shown in Table 1 below.

As can be seen from the test results in Table 1, the sheets prepared in Examples 1 to 5 according to the present invention had a haze of 96% or more, a total light transmittance of 66% or less, a luminance characteristic of 99% or more, a hiding power of 2 or more, Respectively.

On the other hand, in Comparative Examples 1 and 2 in which the amount of beads used was out of the range of 30 to 180 parts by weight, hiding power was lowered or bead desorption occurred and dust was generated. In Comparative Examples 3 and 4 in which the filling height of the coated resin layer was out of the range of 10 to 80%, the hiding power was lowered or the luminance was lowered. In Comparative Examples 5 to 6, in which the average particle diameter of the beads was out of the range of 0.5 to 5 占 퐉, the hiding power and appearance deteriorated. In Comparative Example 7 in which the refractive index of the bead and the resin were 1.49, a decrease in hiding power was confirmed.

As described above, when compared with the conventional diffusion sheet combination (Comparative Example 8), the sheets produced in Examples 1 to 5 are equivalent in terms of hiding power (1 to 2 levels) and luminance (99 to 101%) . ≪ / RTI >

Claims (5)

(1) a transparent substrate;
(2) a diffusion sheet, positioned on one surface of the transparent substrate, including a plurality of hemispherical micro-lens protrusions;
(3) a resin layer containing beads filled in the valleys between the microlens protrusions of the diffusion sheet; And
(4) a resin layer containing a filler, which is located on the other surface of the transparent substrate,
The micro lens protrusion occupies 50 to 90% of the total surface area of the diffusion sheet,
Wherein the resin layer containing the beads comprises 100 parts by weight of a binder resin and 50 to 150 parts by weight of a plurality of beads and is filled at a height of 10 to 80% of the height from the bottom of the valleys to the top of the micro-
Wherein the beads have an average particle diameter of 0.8 to 3 mu m,
Wherein the bead and the binder resin each have a refractive index in the range of 1.41 to 1.59, and the difference between the two refractive index values is 0.02 or more.
The method according to claim 1,
Wherein the micro lens protrusions each have a diameter ranging from 10 to 100 mu m. The method according to claim 1,
Wherein the binder resin is at least one selected from the group consisting of a (meth) acrylate resin, an unsaturated polyester resin, a polyester (meth) acrylate resin, a silicone urethane (meth) acrylate resin, a silicone polyester (meth) acrylate resin, Acrylate resins, and mixtures thereof. ≪ RTI ID = 0.0 > 11. < / RTI > The method according to claim 1,
Wherein the bead comprises a material selected from the group consisting of hard acrylate, polystyrene, nylon, soft acrylate, and silicone. The method according to claim 1,
Wherein the resin layer containing the beads has air droplets of 10 to 10,000 nm in size.

Images