KR20050072949A - Prism sheet for backlight unit, backlight unit and liquid crystal display using the same - Google Patents

Abstract

The present invention provides a backlight comprising a transparent substrate, a prism portion having a plurality of acid portions disposed on the substrate and having a triangular cross-sectional shape arranged in parallel, and an adhesive layer disposed under the substrate, the backlight being integrated with the light guide plate by the adhesive layer. By providing a prism sheet for a unit and a backlight unit using the same, it is possible to improve luminance and improve productivity at the same time while improving luminance in a liquid crystal display device.

Description

Prism sheet for backlight unit, backlight unit and liquid crystal display using the same {Prism sheet for backlight unit, backlight unit and liquid crystal display using the same}

The present invention relates to a prism sheet for a backlight unit integrated into a light guide plate by an adhesive layer, and a backlight unit and a liquid crystal display (LCD) using the same.

A liquid crystal display (LCD) is a kind of light that displays numbers or images by generating contrast by injecting liquid crystals, which are intermediates between solid and liquid, between two thin glass plates and changing the arrangement of liquid crystal molecules by the voltage difference between the electrodes on the upper and lower glass plates. It is a device using a switch phenomenon. The passive matrix method and the active matrix method are classified according to the driving method. The passive matrix method includes TN (Twisted Nematic) and STN (Super Twisted Nematic) methods, and the active matrix method includes TFT (Thin Film Transistor) method. LCDs are widely used in electronic products such as electronic clocks, electronic calculators, liquid crystal TVs, and notebook PCs, and speed displays and driving systems for automobiles and aircrafts.

The advantages of such LCDs are low power consumption (1/3 of CRT), low operating voltage, and light and thin processability. On the other hand, the LCD has a narrow viewing angle, difficult to implement a large screen, and low temperature operation.

As a core component of the LCD, there is a backlight unit, which is used as a dimming device for evenly transmitting light to the entire TFT-LCD panel and displays an image with transmitted light.

Unlike the CRT (Cathode Ray Tube), PDP (Plasma Display Panel), and FED (Field Emission Display), the screen display by LCD cannot be used without a light source because the liquid crystal display device itself is non-luminescent. An apparatus that functions as a light source and uniformly irradiates an information display surface is a backlight unit.

Since the backlight unit is used as a light source for a monitor TFT-LCD and a notebook, a function that needs to emit the brightest light with the minimum power is required. In addition, the backlight unit should play a role of changing the light emitted from the light source to the surface light by maintaining the same brightness to every corner of the LCD surface.

The components of the backlight unit include a lamp as a light source, a reflector reflecting the light emitted from the lamp, a light guide plate for transmitting light, a mold frame for tying components together, and sheets for improving brightness and viewing angle.

The backlight unit is a direct method of directly dimming the front surface of the panel by arranging a light source on one side of the panel, and an edge for reflecting / diffusing light on a light guide plate and a reflective sheet by disposing a light source on one side or multiple sides of the panel. ) Is divided into (or side light). Recently, a side light method in which a light source is disposed on at least one side of a liquid crystal display device has been widely used for manufacturing a small electronic device by reducing the weight and thickness of a backlight unit.

Most of the backlight units currently used are light guide panels (LGPs) using a cathode fluorescent lamp (especially a cold cathode fluorescent lamp (CCFL)) as a light source 1 as shown in FIG. 1. 3), a light diffusion sheet 4, a prism sheet 5 and a protective sheet 6 are sequentially disposed toward the light emitting surface thereof, and a reflecting plate 2 is included on the opposite side of the light emitting surface.

On the back surface of the light guide plate 3, a dot pattern of paint is formed, which is to allow the light incident from the light source on the side to be evenly emitted to any position on the screen. The light scattering printing pattern formed on the back surface of the light guide plate 3 may be a pseudo light source. The light rays emitted from the light source 1 are diffusely reflected by the dot pattern on the rear surface of the light guide plate 3 and are emitted forward from the front surface of the light guide plate 3.

The reflecting plate 2 is located at the rear of the light guide plate 3 and serves to reflect light rays coming from the light source 1 to the front side. Silver is coated on base materials such as stainless steel, copper, aluminum, and polyethylene terephthalate (PET) to increase reflectivity, and titanium coating is applied to prevent deformation due to endothermic long time even if heat is generated minutely.

At this time, almost all of the emitted light is emitted in a direction deviating greatly from the vertical direction of the light guide plate 3 by the light rays emitted from the light source 1, and since the distribution thereof is remarkably deflected, it is usually from the vertical direction of the light guide plate 3. A user observing a panel typically sees a very dark liquid crystal display.

In order to solve this drawback, it is proposed to arrange a light control sheet on the front surface of the light guide plate. In Japanese Patent Laid-Open No. 3-78701, a light control sheet containing an inorganic or organic light diffusing agent in a transparent glass or plastic sheet is provided. Japanese Patent Laid-Open No. 62-291618 discloses the use of a light control sheet having a fine and random roughness of roughness (Ra) of 100 to 150 µm by matt or embossing the entire surface of the transparent plastic.

Another kind of light control sheet is disclosed in a number of patents, such as US Pat. No. 4906070, US Pat. No. 5,068,93, and includes a prism sheet 5 having a structural surface in which a plurality of triangular shapes are arranged in parallel. The prism sheet 5 is an optical function sheet in which a plurality of small prisms are arranged in parallel on one surface, and the light incident on the prism is refracted or reflected.

On the other hand, Japanese Patent Laid-Open No. 2-257188 and Japanese Patent Laid-Open No. 7-141908 describe a backlight structure having a structure in which a prism is laminated on a light diffusion sheet. The structure of the conventional backlight is made by stacking the light diffusing sheet and the prism sheet into separate sheets and then laminating each other. This process is complicated in the manufacturing process and cannot achieve the desired optical properties. There is also a manufacturing method of forming a prism directly on the light guide plate, but this process still has a limitation in the size of the screen due to the limitation of the manufacturing process.

SUMMARY OF THE INVENTION The present invention has been made in an effort to provide a prism sheet integrated with a light guide plate by an adhesive layer, and a backlight unit and a liquid crystal display device having excellent brightness characteristics by using the same.

In order to achieve the above technical problem, the present invention includes a transparent substrate, a prism portion having a plurality of acid portions arranged on the substrate and a triangular cross-sectional shape is arranged in parallel, an adhesive layer located under the substrate, the adhesive layer A prism sheet for a backlight unit integrated in a light guide plate is provided.

In order to achieve the above another technical problem, the prism sheet for the backlight unit; A light source for generating light; A light guide plate including beads and converting light generated from the light source into a surface light source; It provides a backlight unit formed on the lower portion of the light guide plate to reflect the light traveling toward the lower surface and the side of the light guide plate toward the upper surface, the prism sheet is integrated into the light guide plate by the adhesive layer.

In order to achieve the above another technical problem, a liquid crystal display using the backlight unit is provided.

Hereinafter, the present invention will be described in more detail.

Figure 2 schematically shows the structure of a prism sheet according to a preferred embodiment of the present invention. According to FIG. 2, the prism sheet has a prism in which a primer layer 14 is selectively formed on the transparent substrate 13, and a plurality of protrusions (called “mountains”) having a triangular cross-sectional shape are arranged in parallel on the prism sheet 13. The part 15 is positioned, and the adhesive layer 12 is positioned below the substrate 13, and has a structure integrated with the light guide plate 11 laminated under the adhesive layer 12.

The prism portion 15 uses a photocurable resin to form a prism sheet in which a plurality of acid portions having a triangular or similar shape in cross section are arranged in parallel. It is preferable that height is 15-35 micrometers, and the angle (theta) is 70-110 degrees in the peak part of a prism part. In this case, the luminance is sharply deteriorated when it is out of the range of the height and angle of the peak, which is not preferable.

The active energy ray curable resin for forming a three-dimensional pattern layer like the prism portion 15 provided in the prism sheet according to the present invention is not particularly limited as long as it is cured with active energy rays such as ultraviolet rays and electron beams. For example, (meth) acrylate type resins, such as polyester, epoxy resin, polyester (meth) acrylate, epoxy (meth) acrylate, and urethane (meth) acrylate, etc. are mentioned. Especially, (meth) acrylate type resin is especially preferable from a viewpoint of an optical characteristic. As the active energy ray curable composition used for such a cured resin, polyhydric acrylate and / or polymethacrylate (hereinafter referred to as polyvalent (meth) acrylate), monoacrylate and / or It is preferable to have monomethacrylate (hereinafter, referred to as mono (meth) acrylate) and a photopolymerization initiator based on an active energy ray as a main component. As typical polyvalent (meth) acrylate, polyol poly (meth) acrylate, polyester poly (meth) acrylate, epoxy poly (meth) acrylate, urethane (meth) acrylate, etc. are mentioned. These are used alone or as a mixture of two or more kinds. Moreover, as mono (meth) acrylate, a monoalcohol mono (meth) acrylic acid ester, the mono (meth) acrylic acid ester of a polyol, etc. are mentioned, In the latter case, when using a metal type, the influence of a free hydroxyl group is used. In order to reduce the mold release difficulty with the metal mold considered to be, it is good to use in small quantities. Moreover, when using a metal mold | die, since it has high polarity also about (meth) acrylic acid and its metal salt, it is good to use it in small quantities.

The roll having the transfer pattern on the periphery is usually made of metal such as aluminum, brass, steel, or synthetic resin such as silicone resin, polyurethane resin, epoxy resin, ABS resin, fluorine resin, polymethylfetene resin, or Ni electroforming method. And the like are used. The pattern suitable for a light control sheet is formed in the roll surface, and it is preferable to plate chromium (Cr) etc. on it.

In the prism sheet according to the present invention, the adhesive layer 12 formed for adhesion to the light guide plate 11 is formed of a polymer having light transparency. As the light transmissive polymer, an acrylic polymer, a fluorine polymer, a vinyl chloride polymer, an olefin polymer, a styrene polymer, a polyurethane, a polyester, a silicone polymer, or the like can be used. The coating thickness of the adhesive layer 12 is preferably set to a thickness of 10 to 100 μm in consideration of the adhesive strength to the light guide plate 11. If the thickness of the adhesive layer 12 is less than 10 μm, the adhesive force may not be sufficiently exhibited. If the thickness of the adhesive layer 12 is greater than 100 μm, the adhesive layer 12 is not preferable because of the influence on the decrease in luminance. The coating method of the adhesive layer 12 may be any method that can be commonly used in the field of the present invention, but preferably, a roll coating method using gravure roll, reverse gravure roll, micro gravure roll, etc. , Bar coating method using a die coating or the like, coating method using an air knife can be used.

The transparent base material 13 is not particularly limited as long as it is a material that transmits active energy such as ultraviolet rays, visible rays, and electron beams. Specifically, for example, sheets and films of transparent resins such as flexible polyester resins, acrylic resins, polycarbonate resins, vinyl chloride resins, and polymethacrylamide resins are preferable. Particularly, polyester resins such as polymethyl methacrylate, polymethyl acrylate and polyvinylidene fluoride-based resins, polycarbonate-based resins and polyethylene terephthalate, which have lower refractive index and surface reflectance than the pattern portion It is preferable. As for the film thickness of this transparent base material 13, 100-150 micrometers is suitable.

The primer layer 14 serves to facilitate adhesion of the photocurable resin to the transparent substrate 12, and should be excellent in adhesion with the transparent substrate 12, and examples thereof include polyurethane resins, and the like. Water-soluble polyurethanes are preferred. In addition, the thickness of the primer layer 14 is suitably 0.001-1 micrometer. If the thickness is less than 0.001 μm, the coating property is poor, while if the thickness is more than 1 μm, the adhesive force with the laminate or the polymer resin to be coated may be deteriorated.

The light guide plate 11 is formed of a plastic plate having a transmittance of 20 to 60% containing a light diffusing agent. This light transmittance can be controlled by the content of the light diffusing agent. In the present invention, a transparent spherical bead was used as the light diffusing agent, and inorganic and organic beads are used. Examples of inorganic beads include silica, zirconia, and glass, and organic beads include urethane resin, acrylic resin, and vinyl chloride resin. There is this. The content of the beads is preferably 1 to 10 parts by weight based on 100 parts by weight of the resin forming the light guide plate. At this time, when the content of the beads is out of the range of less than 1 part by weight, light diffusion is not sufficient, resulting in streaks due to the difference in brightness of the light. The particle diameter of the beads suitable for the invention is 0.1 to 50 μm, in particular 0.1 to 20 μm. The particle diameter of the beads affects the light diffusing function. The smaller beads have a larger light diffusing function, and the larger beads have a higher light transmittance, resulting in an increase in luminance. In this case, when the particle diameter of the beads is less than 0.1 μm, the luminance decreases, and when it exceeds 50 μm, it is not preferable because of insufficient light diffusion.

As the resin of the light guide plate 11, a resin such as a transparent acrylic resin, a polycarbonate resin, or the like may be used. The thickness of the light guide plate is suitably 500 to 5000 m. In this case, when the thickness is outside the thickness range of the light guide plate, the luminance is lowered, which is not preferable.

In the present invention, the light guide plate containing the prism sheet and the light diffusing agent are adhered to each other using a roller to integrate the light guide plate and the prism sheet.

The liquid crystal display device may be adopted by being manufactured without any particular limitation as long as it is a method commonly known in the art. That is, the backlight unit including the prism sheet integrated with the light guide plate by the adhesive layer is fixed to the mold frame, and the liquid crystal panel is assembled thereon.

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

<Example>

As described above, a primer layer is formed on the PET film, and as the curable resin, a 25 μm coating of an acrylic adhesive layer is performed on the back surface of a prism sheet manufactured using an acrylic urethane resin to prepare a prism sheet. Beads having a particle diameter of about 0.1 to 2 μm, which are light diffusing agents, are contained in an amount of 3 to 10 parts by weight based on 100 parts by weight of the acrylic resin forming the light guide plate, and are then adhered to the light guide plate having the following light transmittance using a roller. And luminance were measured, respectively.

Comparative Example 1

Using the same apparatus and method as in the above embodiment, the luminance of the light guide plate without the prism portion was measured.

Comparative Example 2

Using the same apparatus and method as in the above embodiment, the prism sheet without the adhesive layer was laminated on the light guide plate to measure luminance.

No. Bead content (100 parts by weight / resin) of the light guide plate Light transmittance (%) Luminance (cd / m ² ) Example One 3 30 2254 2 6 40 2483 3 7.5 45 2626 4 9 50 2712 Comparative Example 1 One 3 30 1393 2 6 40 1570 3 7.5 45 1664 4 9 50 1754 Comparative Example 2 One 3 30 2211 2 6 40 2440 3 7.5 45 2583 4 9 50 2669

According to the luminance measurement results in Table 1, in the case of the embodiment in which the prism sheet was integrated into the light guide plate by the adhesive layer, in the case of Comparative Example 1 without the prism portion on the average, and Comparative Example 2 without the adhesive layer, The result was higher.

As described above, the prism sheet of the present invention is integrated into the light guide plate containing the transparent beads by the adhesive layer located under the transparent substrate, thereby improving luminance and simultaneously improving the large screen and productivity of the liquid crystal display. . In addition, there is no need for a separate fixing device for fixing the light guide plate, the diffusion plate, and the prism sheet, thereby simplifying the manufacturing process.

1 is a schematic view of a cross section of a backlight unit of a liquid crystal display device.

2 is a cross-sectional view of a prism sheet integrated into the light guide plate according to the present invention.

<Explanation of symbols for the main parts of the drawings>

1: light source (cold cathode tube) 2: reflector

3, 11: light guide plate 4: light diffusion sheet

5: prism sheet 6: protective sheet

12: adhesion layer 13: transparent substrate

14 primer layer 15 prism portion

Claims (11)

Transparent substrates; A prism portion disposed on the substrate and arranged in parallel with a plurality of acid portions having a triangular cross-sectional shape; A prism sheet for a backlight unit including an adhesive layer disposed under the substrate, and integrated into the light guide plate by the adhesive layer. The prism sheet for a backlight unit according to claim 1, wherein the adhesive layer has a thickness of 10 to 100 µm and is made of acrylic resin. The prism sheet for a backlight unit according to claim 1, wherein the peak portion of the prism portion has an angle of 70 to 110 ° and a height of 15 to 35 μm. The prism sheet for a backlight unit according to claim 1, wherein a primer layer is formed between the substrate and the prism portion. The prism sheet for a backlight unit according to claim 4, wherein the primer layer has a thickness of 0.001 to 1 µm and is made of a water-soluble polyurethane. A prism sheet for a backlight unit according to any one of claims 1 to 5; A light source for generating light; A light guide plate including beads and converting light generated from the light source into a surface light source; And a reflecting plate formed under the light guide plate to reflect light traveling toward a lower surface and a side of the light guide plate toward an upper surface thereof, wherein the prism sheet is integrated with the light guide plate by an adhesive layer. The backlight unit of claim 6, wherein the light transmittance of the light guide plate is 20 to 60%. The backlight unit of claim 6, wherein the beads have a particle diameter of 0.1 to 50 μm and are organic. The backlight unit according to claim 6, wherein the content of the beads is 1 to 10 parts by weight based on 100 parts by weight of the resin forming the light guide plate. The backlight unit of claim 6, wherein the light guide plate has a thickness of 500 μm to 5000 μm. A liquid crystal display device comprising the backlight unit according to claim 6.