KR101353845B1 - Optical sheet having optical pattern layer - Google Patents

Abstract

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical sheet having a structured surface for use in a liquid crystal display, and having a high refractive index coating layer made of a light transmissive polymer material having a high refractive index on a lower surface of the structured resin cured layer. It is possible to compensate for the brightness, ultimately providing a surface-structured optical sheet with improved front brightness while minimizing light loss.

Description

Optical sheet having optical pattern layer

The present invention relates to an optical sheet that can be used in combination of an optical sheet of a backlight unit such as a liquid crystal display device.

As the industrial society develops into an advanced information age, the importance of the electronic display device as a medium for displaying and transmitting various information is increasing day by day. (PDP), a field emission display (FED), and an organic electroluminescent display (EL) have been widely used because of the limitations of the conventional CRT (Cathode Ray Tube) Various flat panel display devices have been replaced. Among such flat panel display devices, in particular, in the case of liquid crystal display devices (LCDs), due to the advantages of thin, light, and low power consumption as a technology-intensive device in which liquid crystal and semiconductor technologies are combined, its structure and manufacturing technology have been researched and developed. In addition to the areas where liquid crystal displays have been widely used, such as notebook computers, desktop computer monitors, and portable personal communication devices (PDAs and mobile phones), large-sized technologies are gradually exceeding their limits. It has been applied as a new display device that can replace CRT, which is synonymous with display, as it has been applied to large-sized TVs.

In the liquid crystal display (LCD) device, since the liquid crystal itself cannot emit light, a separate light source is installed at the rear of the device to adjust the intensity of the passing light through the liquid crystal installed in each pixel to realize contrast. do. Looking more specifically at this,

A liquid crystal display device is a device that controls the transmittance of light by using the electrical properties of the liquid crystal material, and emits light from a light source lamp on the back of the device and passes through various functional prism films or sheets to pass uniformly and directional light through a color filter. In order to realize the colors of red, blue, green (R, G, B), and to control the gradation of each pixel in an electrical manner to implement an image, an indirect light-emitting display device that provides a light source The light emitting device is an important component for determining image quality such as brightness and uniformity of the liquid crystal display device.

A backlight unit (BLU) is widely used as the light emitting device, and the backlight unit sequentially emits light emitted using a light source such as a cold cathode fluorescent lamp (CCFL), a light guide plate, a diffusion sheet, and a prism film. Pass through to reach the liquid crystal panel. Here, the light guide plate transmits the light emitted from the light source to be distributed on the front surface of the flat liquid crystal panel, the diffusion sheet to obtain a uniform light intensity across the entire screen, and the prism film is passed through the diffusion sheet in various directions A light path control function is performed that causes the light beams to be converted within a viewing angle [theta] range suitable for the viewer to recognize the image. In addition, the lower portion of the light guide plate is provided with a reflecting plate for increasing the use efficiency of the light source by allowing the light that is not delivered to the liquid crystal panel to be reflected back out of the path and used.

The present invention relates, in particular, to an optical sheet having an optical structure surface called a prism film. Since the user viewing the screen is mainly in front of the screen, the prism film controls the path of light diffused in various directions through the diffusion sheet. As a result, the front luminance of the display device can be increased to realize a brighter and clearer image.

US Patent Nos. 2,248,638, 4,497,860, US Patent No. 4,805,984, US Patent No. 4,906,070, and Korean Patent Application No. 1986-0009868 present films with special optical structures to increase the brightness of the backlight unit. It is characterized by having a structured surface on one side and vice versa. A structured surface is proposed in which a plurality of isosceles triangular prisms arranged side by side are linearly arranged with a smooth surface at an angle of about 45 degrees.

On the other hand, U.S. Patent No. 4,542,449 has a configuration in which two prism films having a plurality of linearly arranged prism layers are laminated, and each prism array is positioned to be orthogonal or oriented at a predetermined angle. The isosceles prism of is arranged in a linear arrangement, the other side has a smooth surface, the slope of the isosceles prism is arranged with about 90 degrees of two prism films arranged to form an angle of about 45 degrees with the smooth surface, The use has been disclosed to provide a frontal brightness increasing effect together with the polarization function, and it has been proved that the frontal brightness is increased through this arrangement, and is mainly used in such an arrangement.

Such a prism film discharges a large amount of light sources emitted from the backlight unit to the front to increase the brightness, and thus, the luminance of the prism film may be higher than that of the conventional backlight unit without installing additional light sources.

That is, the light source emitted to the front from the backlight unit is recycled back to the backlight unit through two total reflection processes in the prism layer, and the light source emitted in a direction other than the front from the backlight unit is refracted from the prism layer to be discharged to the front. .

In general, the total amount of light emitted from the backlight unit is about 60%, and about 35% of the total amount of light emitted from the backlight unit is about 30% to 70 °. Therefore, the amount of light corresponding to 60% emitted to the front from the backlight unit is totally reflected from the prism film and the amount of light corresponding to 35% emitted to the side is refracted from the prism film and emitted to the front.

Here, the totally reflected light source has a light loss while frequently passing through different air layers, transparent substrate layers, and prism layers. This is because most of the light sources of the backlight unit is totally reflected, so that the loss in terms of light efficiency. The light returned by total reflection may have another light loss depending on the reflection material inside the backlight unit. Therefore, there is a problem to improve the internal reflectance of the backlight unit.

Therefore, in order to improve the efficiency of the light source recycled and lost in the prism film, the transmittance of the incident surface of the prism film should be improved, and the light source emitted from the backlight unit should be directed so that it can be discharged without total reflection in the prism layer.

When the two prism films are used alternately, the smooth surface of the prism film disposed on the top and the vertices of the prism structure of the prism film disposed on the bottom are in contact with each other. The prism film may also be located on top of the light diffusing film. The light diffusing film is a light base material with protruding particles, the surface hardness of which is weak as pencil hardness HB. Therefore, when the smooth surface of the prism film and the protruding particles of the light diffusing film are in contact with each other, because the surface strength of the smooth surface of the prism film is weak, the contact portion is damaged by being pressed by a light substrate having a relatively high surface hardness. At this time, there is room for light interference such as wetout phenomenon, which is an optical interference effect caused by damaged parts besides physical damage, and Newton's ring in a rainbow band shape caused by light interference. There is a problem that directly affects the uniformity and sharpness of the.

In addition, the conventional prism film has a regular arrangement of prisms, leaving room for optical interference images such as Moire phenomenon, in which a wave pattern is generated as an interference effect when combined with a regular arrangement of liquid crystal pixels. This is a physical phenomenon that cannot be avoided in a structure in which regularity overlaps.

Recognizing the above problems, the Applicant maximizes the light efficiency so that light is emitted even in the total reflection of the prism film, thereby minimizing the light loss to provide a uniform light source and increase the use efficiency of the light source, It prevents damage to the structure of the prism layer due to vibration and friction and damage to the back surface of the prism film, and prevents adhesion of foreign substances due to the friction static electricity. Patent registration No. 554518). Here, the transparent substrate layer; A prism layer formed of a light transmissive material on one surface of the transparent substrate layer and having a plurality of three-dimensional structures repeatedly formed thereon; And a bottom layer formed of a light transmissive polymer material on the rear surface of the transparent substrate layer, wherein the prism layer has the highest refractive index and the bottom layer has the lowest refractive index, and the bottom layer includes particles to control the optical path. It improves the front brightness and maximizes the light efficiency so that light is emitted even in the total reflection area of the prism film, thereby minimizing the light loss to provide a uniform light source and increase the utilization efficiency of the light source. In order to prevent the damage of the prism layer structure due to the vibration and friction and the damage of the back surface of the prism film and to reduce the contact surface, foreign matter adhesion due to the friction static electricity was prevented.

According to one embodiment of the present invention, when the refractive index of the prism layer, that is, the surface-cured resin cured layer is increased, the refractive index of the surface-cured resin cured layer is lowered to further improve the amount of totally reflected light. Resin cured layer whose surface is structured by condensing light more in the front direction by placing a high refractive index layer under the resin cured layer whose surface is structured to minimize the loss of light by minimizing total reflection and thereby compensate for the frontal brightness. It is an object of the present invention to provide an optical sheet having a surface structured so as to narrow the angle of the emitted light passing through it.

It is an object of the present invention to provide an optical sheet whose surface is increased in front brightness while minimizing light loss.

In one embodiment of the present invention; And a resin cured layer formed on one surface of the transparent substrate layer and comprising a photopolymerizable material and having a plurality of three-dimensional structures arranged to have a structured surface thereof, wherein the transparent substrate layer and the resin cured layer It is formed between, and provides a surface-structured optical sheet, characterized in that made of a light-transmitting material and having a high refractive index coating layer having a higher refractive index than the transparent base layer and the resin cured layer.

The optical sheet having a structured surface according to the embodiment of the present invention may be formed on the rear surface of the transparent substrate layer, and may further include a bottom layer made of a light transmissive material.

In this case, the bottom layer may have a smaller refractive index than the transparent base layer.

Preferably, the bottom layer may have a refractive index of 1.40 to 1.49.

In the surface-structured optical sheet according to the present invention, the light transmissive material may be any one or more selected from acrylic resins, urethane resins, epoxy resins, and melamine resins.

In the surface-structured optical sheet according to the present invention, the three-dimensional structure may be a triangular, polygonal, semi-circular or semi-elliptic polyhedron shape, or the cross-section is a triangular, polygonal, semi-circular or semi-elliptic columnar shape.

In the optical sheet structured surface according to the present invention, including organic or inorganic particles, the particles may be formed to protrude on the surface.

In the optical sheet structured surface according to the present invention, the bottom layer may further include an antistatic agent.

According to the present invention, the optical sheet having a high refractive index coating layer having a high refractive index under the structure of the resin cured layer having a lower refractive index than the conventional structure can reduce the total reflection light, thereby minimizing the amount of light loss and entering the prism layer. By adjusting the angle of incidence of the light to increase the front brightness to compensate for the front brightness, it is possible to provide an optical sheet with improved front brightness while minimizing light loss.

Hereinafter, the present invention will be described in detail.

The optical sheet according to the present invention is formed of a light transmissive material having a higher refractive index than the transparent base layer or the resin hardened layer, instead of forming the resin hardened layer having a surface having a total reflection and refractive function on one surface of the transparent base layer. It has a structure in which a high refractive index coating layer is formed. That is, a high refractive coating layer is formed on the transparent substrate layer, and a resin cured layer having a surface structured on the high refractive coating layer is formed. As another example, a bottom layer may be further formed on the other side of the transparent base layer.

In the above and the following description, "surface structured" means that a plurality of three-dimensional structure is formed to have a surface having a pattern, the three-dimensional structure here is not limited, the cross-section is triangular, polygon , Semi-circular or semi-elliptic polyhedron shape or cross section may be triangular, polygonal, semi-circular or semi-elliptic columnar.

As the transparent base layer, a polyethylene terephthalate film, a polycarbonate film, a polypropylene film, a polyethylene film, a polystyrene film, or a polyepoxy film may be used, and mainly a polyethylene terephthalate film and a polycarbonate film are used. The transparent substrate layer may have a thickness of 10 to 1000 μm, and particularly 25 to 600 μm may be advantageous in that mechanical strength and thermal stability, flexibility, or loss of transmitted light may be prevented.

In general, an optical sheet having a resin cured layer having a structured surface has a resin cured layer having a higher refractive index than a transparent base layer on one surface of the transparent base layer. In this case, the front luminance is improved but the amount of total reflection is increased. Is increased. The larger the refractive index of the material constituting the resin cured layer, the greater the critical angle at which total reflection occurs.In this case, when light is incident at an angle smaller than the critical angle, the light is emitted at a larger angle even though it is incident at the same angle of incidence. In this case, the larger the refractive index of the material constituting the prism film is discharged at a smaller angle. That is, the higher the refractive index of the material constituting the optical sheet including the resin cured layer having a structured surface, the narrower the light emission angle is to the front direction, which is preferable to the brightness enhancement side of the front surface, but the total amount of light is more reflected. This results in weight loss. In addition, most of the light sources incident at an angle close to the vertical of 45 dB or less with respect to the vertical axis of the prism structure are totally reflected by the prism and returned.

In order to improve this point more efficiently, the surface should reduce the amount of total reflection light generated in the structured resin cured layer, in which it may be advantageous to slightly lower the refractive index of the resin cured layer, the refractive index of the resin cured layer Compensate the front brightness by lowering. In this case, it is possible to satisfy two disposition characteristics such as minimizing light loss and improving front brightness. To this end, the present invention provides a high refractive index coating layer having a higher refractive index on the transparent substrate layer as compared to the transparent substrate layer or the prism layer, and in this case, even if the refractive index of the surface-structured resin cured layer is lowered to a certain level, Luminance can be satisfied.

Thus, when the high refractive coating layer is placed between the resin cured layer and the transparent substrate layer, even though the refractive index of the resin cured layer is the same or smaller than that of the transparent base layer, the light passing through the transparent base layer is simply collected and sent from the high refractive coating layer, thereby providing a transparent base layer. As compared with the case where a low refractive index resin cured layer is formed on the front surface, the front brightness can be improved, and as the refractive index of the resin hardened layer is lowered, total light reflected can be reduced to minimize light loss.

The high refractive coating layer may be made of a light-transmitting material forming a bottom layer, which will be described later, having good adhesion with a transparent substrate layer, and examples thereof include unsaturated polyester, methyl methacrylate, ethyl methacrylate, and isobutyl methacrylate. Normal butyl methacrylate, normal butyl methyl methacrylate, acrylic acid, methacrylic acid, hydroxyethyl methacrylate, hydroxypropyl methacrylate, hydroxyethyl acrylate, fluorene group-containing (meth) acrylate, Acrylic type, such as a homopolymer of acrylamide, metyrol acrylamide, glycidyl methacrylate, ethyl acrylate, isobutyl acrylate, normal butyl acrylate, 2-ethylhexyl acrylate, a copolymer thereof, or a terpolymer Resins, urethane resins, epoxy resins, melamine resins and the like.

In the optical sheet according to the present invention, the surface-structured resin cured layer may have a higher refractive index than the transparent base layer, but may satisfy an appropriate luminance even when the refractive index is the same or smaller than that of the transparent base layer. As the material constituting the resin-cured layer having a structured surface, a polymer resin including an ultraviolet curable resin or a thermosetting resin is used. For example, an unsaturated fatty acid ester, an aromatic vinyl compound, an unsaturated fatty acid and its derivatives, an unsaturated dibasic acid ( unsaturated dibasic acid) and derivatives thereof, and vinyl cyanide compounds such as methacrylonitrile.

Meanwhile, the bottom layer, which may be formed on the rear surface of the transparent substrate layer, may be formed of a material having a smaller refractive index than the transparent substrate layer, which may reduce the reflection loss at the interface of the light incident on the optical sheet in the air. May be advantageous.

The resin used for the bottom layer is a resin having good adhesion with the transparent base layer and having good compatibility with the particles that may be included in the bottom layer, that is, the particles are uniformly dispersed in the resin and separated or precipitated. You can use something that does not look handsome.

As an additional method for minimizing light loss in the present invention, the refractive index of the bottom layer may be the lowest. According to the Fresnel law represented by the following equation, a part of light incident perpendicularly to the interface of different media is reflected and passed through. can not do. The amount of reflected light increases gradually as the difference in refractive index of different media increases.

Where R is reflection loss, n ₁ : medium 1 _, n ₂ : medium 2

For example, the light incident on the transparent film having a refractive index of 1.5 in air generates 4% reflection loss at the interface. However, when a layer having a refractive index of 1.45 is formed on the transparent film having a refractive index of 1.5, light generates 3.4% reflection loss at the interface. Therefore, the bottom layer serves to reduce the reflection loss of the light by reducing the difference in the refractive index of the interface of the medium to improve the overall transmittance.

Therefore, since most of the light sources that play the role of total reflection in the development of the high-performance prism film is applied to the Fresnel law, the synergistic effect is increased by increasing the transmittance by reducing the interface reflection loss caused by the introduction of the bottom layer.

Considering that the refractive index of the polyethylene terephthalate film, which is typically used as a transparent substrate layer, is 1.49, the bottom layer may be a resin having a refractive index lower than 1.49, but may be 1.40 to 1.49 in consideration of surface hardness and quality effects. have.

In addition, the bottom layer may use a resin that is stronger than polyester or polycarbonate to increase surface hardness, thereby preventing excessive adhesion to the underlying mineral substrate, thereby preventing the wet-out and Newton's rings from occurring.

The bottom layer may include organic or inorganic particles, and the particles may protrude to the surface to make the incident surface have a non-horizontal interface, and at the same time add the function of light diffusion, Reduces the surface damage that may occur during separation, transfer, or assembly during sheeting or storage by reducing the contact area of the opposing surface or other stacked optical sheets in the process equipment during loading or storage or assembling the optical sheet with other components. It can prevent. In addition, when a plurality of optical sheets are overlapped, damage to the bottom layer due to the surface portion of the optical structure of the prism layer in contact with the bottom of the bottom layer may be prevented. In other words, by contacting the peak portion of the optical structure surface of the prism layer and the protrusions at the bottom of the bottom layer, the contact area between the optical sheets is reduced, and the buffering effect by the particles is enabled, so that Damage or surface damage of the bottom layer can be prevented.

Representative types of particles that may be included in the bottom layer may be spherical, non-spherical, triangular pyramid, cube, polygonal particles. The more the interface perpendicular to the incident surface of the optical sheet is preferable, in order to discharge the light of the front having the greatest amount of light in the backlight unit out of the prism layer without frequent total reflection. Therefore, in order to have many vertical interfaces, cube particles may be used. However, when using the particles of the cube is difficult to be disposed due to the irregular shape by the particles during the production of the prism film, there is a disadvantage that may damage the lower film due to the sharp shape. On the other hand, since spherical particles exist at an infinite tangent at the same time on the surface and maintain point contact at the time of contact with the surface, it is preferable to use the spherical particles.

In this case, it may be advantageous in terms of structural and optical uniformity that the spherical particles have a monodisperse size distribution.

In addition, it may be advantageous that a certain amount of empty region exists between the particles and the particles rather than a structure in which a plurality of particles are locally agglomerated or layers of other particles are superimposed on a layer in which the particles are arranged. The size of the particles may vary depending on the thickness of the designed bottom layer, and may be 0.1-20 μm in size.

The organic particles in the particles include methyl methacrylate, acrylic acid, methacrylic acid, hydroxyethyl methacrylate, hydroxypropyl methacrylate, acrylamide, metyrol acrylate amide, glycidyl methacrylate, ethyl acrylate. Of acrylic particles of isobutyl acrylate, normal butyl acrylate, 2-ethylhexyl acrylate homopolymer or copolymer and olefinic particles such as polyethylene, polystyrene and polypropylene, copolymer particles of acryl and olefinic copolymer and homopolymer The multi-layered multi-component type particle | grains made after forming particle | grains and covered with the monomer of another kind on the layer are mentioned, As an inorganic particle, silicon oxide, aluminum oxide, titanium oxide, zirconium oxide, magnesium fluoride, etc. can be used. Such organic and inorganic particles are merely exemplary and are not limited to the particles of the organic or inorganic materials listed above, and may be replaced by other known materials as long as the main object of the present invention can be achieved. Obviously, such material change is also within the scope of the technical idea of the present invention.

On the other hand, by including an antistatic agent in addition to the binder in the bottom layer-forming resin of the present invention can eliminate the static electricity caused by the friction to prevent the defect is attached. Antistatic agents that can be used at this time include quaternary amines, anionics, cationics, nonionics and fluorides.

Hereinafter, the present invention will be described in more detail with reference to Examples, but the scope of the present invention is not limited to the following Examples.

≪ Example 1 >

A polyethylene terephthalate film having a thickness of 125 µm was used as the transparent substrate layer, and 90 parts by weight of an acryl polyol containing fluorene group and 10 parts by weight of polyisocyanate were mixed on one surface of the transparent substrate layer and coated using gravure. , And cured by drying at 120 ℃ for 60 seconds to form a high refractive coating layer on one surface of the transparent substrate layer.

Meanwhile, as the photopolymerizable material for forming the prism layer, an ultraviolet curable monomer including a urethane acrylate monomer and a photoinitiator were mixed and coated on a frame having a prism shape, thereby forming a prism layer.

Thereafter, the high refractive index coating layer and the coating layer of the light transmissive material for forming the prism layer are adhered to each other, and the ultraviolet light (Fusion, 300 watts per inch) is irradiated to cure the light transmissive material for forming the prism layer. An optical sheet on which a prism layer was sequentially formed was produced.

The refractive index of each layer constituting the optical sheet is as shown in Table 1 below.

<Example 2>

An optical sheet was manufactured in the same manner as in Example 1, except that the refractive index was 1.54 by adjusting the components and contents of the ultraviolet curable monomers forming the prism layer.

<Example 3>

An optical sheet was manufactured in the same manner as in Example 1, except that the refractive index after curing was adjusted to 1.59 by appropriately adjusting the content of fluorene group-containing acrylate when forming a high refractive coating layer.

<Example 4>

An optical sheet was manufactured in the same manner as in Example 2, except that the refractive index after curing was adjusted to 1.59 by appropriately adjusting the content of fluorene group-containing acrylate when forming a high refractive coating layer.

<Example 5>

A 125-micrometer-thick polyethylene terephthalate film was used as the transparent substrate layer, and 32 wt% of lauryl acrylate, 40 wt% of butyl acrylate, 13.5 wt% of methyl methacrylate, and trifluoro were used as the light-transmitting polymer material for bottom layer formation. The polymer was prepared by mixing 90 parts by weight of an acrylic polyol having an average molecular weight of 50,000 and a refractive index of 1.477 and 10 parts by weight of polyisocyanate by polymerizing with 14.5% by weight of ethyl methacrylate, and forming the bottom transparent layer of the transparent polymer material. Using a gravure coating on one surface of, and dried for 60 seconds at 120 ℃ hardened to form a bottom layer with a refractive index of 2㎛ on one surface of the transparent base layer.

On the other side of the transparent base layer, 90 parts by weight of the acryl polyol containing fluorene group and 10 parts by weight of polyisocyanate were mixed and applied using gravure, dried at 120 ° C. for 60 seconds, and cured. The high refractive index coating layer was formed in.

On the other hand, as a photopolymerizable material for forming a prism layer, a UV curable monomer containing a urethane acrylate monomer and a photoinitiator were mixed and coated on a frame having a prism shape, thereby forming a prism layer.

Thereafter, the high refractive index coating layer and the coating layer of the light-transmissive material for forming the prism layer, and by irradiating ultraviolet light (Fusion, 300 watts per inch) to cure the light-transmissive material for forming the prism layer, the bottom layer, transparent substrate layer, An optical sheet on which a high refractive index layer and a prism layer were sequentially formed was manufactured.

The refractive index of each layer constituting the optical sheet is as shown in Table 1 below.

<Example 6>

An optical sheet was manufactured in the same manner as in Example 5, except that the refractive index was 1.54 by adjusting the components and contents of the ultraviolet curable monomers forming the prism layer.

&Lt; Example 7 >

An optical sheet was manufactured in the same manner as in Example 5, except that the refractive index after curing was adjusted to 1.59 by appropriately adjusting the content of fluorene group-containing acrylate when forming a high refractive coating layer.

&Lt; Example 8 >

An optical sheet was manufactured in the same manner as in Example 6, except that the refractive index after curing was adjusted to 1.59 by appropriately adjusting the content of fluorene group-containing acrylate when forming a high refractive coating layer.

&Lt; Comparative Example 1 &

An optical sheet was manufactured in the same manner as in Example 1, except that the high refractive coating layer was omitted and a prism layer was formed on the transparent substrate layer.

Comparative Example 2

An optical sheet was manufactured in the same manner as in Example 2, except that the high refractive index layer was omitted and a prism layer was formed on the transparent substrate layer.

In the measurement of the refractive index, the refractive index of the bottom layer, the high refractive coating layer and the prism layer was cured to a thickness of 25 μm under the photocuring or thermosetting conditions of Examples or Comparative Examples, followed by using a refractometer (model name: 1T, Japan ATAGO ABBE). Measured.

On the other hand, the refractive index of the transparent substrate layer was measured by using a refractometer (model name: 1T, Japan ATAGO ABBE) of the PET film used as the transparent substrate layer of each of the above Examples and Comparative Examples.

Bottom layer Transparent substrate layer High refractive coating layer Resin hardened layer whose surface is structured
(Prism layer) Example 1 - 1.492 1.58 1.53 Example 2 - 1.492 1.58 1.54 Example 3 - 1.492 1.59 1.53 Example 4 - 1.492 1.59 1.54 Example 5 1.482 1.492 1.58 1.53 Example 6 1.482 1.492 1.58 1.54 Example 7 1.482 1.492 1.59 1.53 Example 8 1.482 1.492 1.59 1.54 Comparative Example 1 - 1.492 - 1.53 Comparative Example 2 - 1.492 - 1.54

Luminance was evaluated for the optical sheets obtained according to the above Examples, Reference Examples and Comparative Examples, and the results are shown in Table 2 below.

Specific evaluation method is as follows.

<Luminance evaluation (Cd / ㎡)>

Each optical sheet obtained by the above Examples and Comparative Examples was fixed to a backlight unit for 17-inch liquid crystal display panel (Model: LM170E01, manufactured by Heesung Electronics, Korea), and the luminance meter (Model: BM-7, TOPCON, Japan) was Measure the luminance at any of 13 points, and find the average value.

Brightness (Cd / m2) Example 1 2685 Example 2 2688 Example 3 2690 Example 4 2695 Example 5 2687 Example 6 2690 Example 7 2693 Example 8 2700 Comparative Example 1 2550 Comparative Example 2 2560

From the results in Table 2, it can be seen that the front luminance is improved when a high refractive index coating layer is provided between the transparent base layer and the prism layer according to the present invention. In particular, when the refractive index of the bottom layer is formed to the lowest it can be seen that the front brightness is further improved.

However, it can be seen that it is not preferable to improve the luminance when the resin cured layer having a refractive index that is not very high in forming a resin cured layer having a surface structured directly on the transparent base layer.

Claims (8)

Transparent substrate layer; And a resin cured layer formed on one surface of the transparent substrate layer and made of a photopolymerizable material and having a plurality of three-dimensional structures arranged to have a structured surface thereof. It is formed between the transparent substrate layer and the resin cured layer, and comprises a high refractive coating layer made of a light transmissive material and having a higher refractive index than the transparent substrate layer and the resin cured layer, The high refractive index coating layer is a surface-structured optical sheet, characterized in that the refractive index is 1.58 ~ 1.59. 2. The surface-structured optical sheet according to claim 1, further comprising a bottom layer formed on the back surface of the transparent base layer and made of a light transmissive material. The optical sheet having a structured surface according to claim 2, wherein the bottom layer has a lower refractive index than the transparent base layer. The surface-structured optical sheet according to claim 2 or 3, wherein the bottom layer has a refractive index of 1.40 to 1.49. The surface-structured optical sheet according to claim 1 or 2, wherein the light transmissive material is at least one selected from acrylic resins, urethane resins, epoxy resins, and melamine resins. 3. The surface-structured optical sheet of claim 2, wherein the bottom layer comprises organic or inorganic particles and is formed so that the particles protrude from the surface. The surface-structured optical sheet according to claim 1, wherein the three-dimensional structure has a polyhedron shape whose cross section is triangular, polygonal, semi-circular or semi-elliptical, or a columnar shape whose cross section is triangular, polygonal, semi-circular or semi-elliptic. 3. The surface-structured optical sheet of claim 2, wherein the bottom layer further comprises an antistatic agent.