KR101200408B1 - Liquid crystal display using phosphor - Google Patents

Abstract

The present invention consists of a blue LED, a dichroic reflective filter positioned on a substrate, a fluorescent film provided thereon, a reflective partition wall for scattering light generated from the fluorescent film to the front, and a color filter provided thereon. The light from the blue LED passes through the substrate, through a dichroic reflective filter installed on the substrate, and excites the phosphor contained in the fluorescent film. Since most of the light converted from the phosphor passes through the color filter, the light loss corresponding to two thirds of the incident light generated when the light from the conventional white LED passes through the color filter can be greatly reduced. Of the light emitted from the phosphor, the light emitted backward is reflected back by the dichroic reflecting filter, thereby reducing the decrease in front emission efficiency. The reflective partition wall serves to return the light generated from the phosphor to the front side by using scattering phenomena rather than forwarding due to total internal reflection.

Description

Liquid crystal display using phosphors {LIQUID CRYSTAL DISPLAY USING PHOSPHOR}

The present invention relates to a liquid crystal panel and a liquid crystal display device, and more particularly, to a liquid crystal panel and a display device which can improve the panel transmittance of light irradiated from a light source to obtain a clear light image and increased light utilization. It is about.

In the liquid crystal panel using the conventional LED backlight unit, light emitted from the white LED 101 passes through the color filter 102 to implement red, green, and blue light as shown in FIG. 1. However, in this method, since the color filter 206 is made of an absorption type pigment, only one third of the light emitted from the white LED passes through the panel and the remaining two thirds are absorbed. For example, two-thirds of incident light is lost because the red pixel absorbs blue and green light and passes only red light. This is the main cause of reducing the light efficiency of the liquid crystal panel, and in order to realize the display screen of the same brightness, the light output of the LED backlight unit must be further increased, not only increases the electric energy consumption but also increases the number of LEDs or LEDs. Difficulties in heat dissipation and price increases due to improved performance. Efforts to improve electro-optical characteristics such as viewing angle, contrast ratio, and response speed have been actively conducted. At the same time, researches for reducing power consumption and optical loss of liquid crystals have been actively conducted in various forms.

An object of the present invention is to provide a liquid crystal panel having a high light conversion efficiency including a fluorescent film and a dichroic reflection filter and a liquid crystal display device including the same.

In order to achieve the above object of the present invention, a liquid crystal panel transparent substrate for transmitting the primary light emitted from the light source; A fluorescent film comprising a phosphor which is excited by the primary light transmitted through the transparent substrate and emits secondary light equal to or different from the wavelength of the primary light; And a dichroic reflection filter disposed between the transparent substrate and the fluorescent film, wherein the dichroic reflection filter transmits light of a resonant wavelength of the dichroic reflection filter of secondary light emitted from the fluorescent film and transmits light of the remaining wavelength. The light is reflected, and the phosphors are separated by partitions provided inside the phosphor film without red, green, and blue phosphors mixed in one space.

The liquid crystal panel may further include a color filter disposed on the fluorescent film to improve purity of red light, green light, and blue light, which are secondary light emitted from the fluorescent film.

If blue light is used as the light source, the fluorescent film may not include a blue phosphor.

The dichroic reflective filter may be formed by alternately stacking a plurality of thin films of materials having different refractive indices.

In addition, the present invention is the liquid crystal panel; And a backlight unit disposed behind the liquid crystal panel and emitting the primary light.

The backlight unit may include a light source emitting blue light.

The light source may be an LED emitting blue light.

Finally, the backlight unit may further include a prism sheet for orienting the light such that the primary light emitted from the light source is incident perpendicularly to the transparent substrate.

The liquid crystal panel according to the present invention has the advantage that the light loss is significantly reduced compared to the prior art since most of the light excited and converted in the fluorescent film is passed through the color filter to the front of the panel. In addition, among the light emitted from the fluorescent film, the light emitted to the rear of the panel is reflected by a dichroic reflective filter disposed behind the fluorescent film and is emitted toward the front of the panel, and the light irradiated in parallel with the fluorescent film is As reflected by the partition wall and emitted toward the front side of the panel, the panel front radiation efficiency is increased, and thus the effect of increasing light utilization is more pronounced.

1 is a conceptual diagram for explaining a liquid crystal display used in the prior art.
2 is a conceptual diagram illustrating a liquid crystal panel, a liquid crystal display, and a traveling direction of light according to an exemplary embodiment of the present invention.
3 is a conceptual diagram illustrating a liquid crystal panel and a liquid crystal display according to an exemplary embodiment of the present invention.
4 is a conceptual diagram illustrating a dichroic reflection filter using a Fabry-Faro resonator structure.
Figure 5 shows the reflectance and transmittance graph of the filter using a Fabry-Faro resonator.
6 shows a reflectance graph of the dichroic reflection filter using a multilayer thin film.

Hereinafter, the present invention will be described in more detail with reference to the drawings and examples. However, the following description and examples are provided to enhance the understanding of the present invention, and the scope of the present invention is not limited by the following contents. In addition, those skilled in the art to which the present invention pertains can easily make simple design changes or structural changes to the present invention without departing from the scope of the present invention. In addition, in describing the present invention, when it is determined that the detailed description of related known functions or components may unnecessarily obscure the gist of the present invention, the detailed description and the detailed illustration will be omitted. In this regard, the liquid crystal panel of the present invention is provided with a conventional liquid crystal layer, but the description and illustration of the liquid crystal layer are omitted.

The present invention is a transparent substrate 203 for transmitting the primary light emitted from the light source 201; A fluorescent film 205 including a phosphor which is excited by the primary light transmitted through the transparent substrate 203 and emits secondary light having a wavelength equal to or different from that of the primary light; And a dichroic reflection filter 204 disposed between the transparent substrate 203 and the fluorescent film 205.

2 is a schematic cross-sectional view of a liquid crystal panel according to an exemplary embodiment of the present invention.

The substrate 203 is used as a substrate of the liquid crystal panel. The light emitted from the light source 201 is preferably made of a transparent material so that the light can be emitted to the entire surface of the substrate 203. In general, it is preferable to use a synthetic resin of glass or transparent material.

The fluorescent film 205 includes a phosphor, which is excited by primary light transmitted through the substrate 203 to emit light of red (R), green (G), and blue (B). Red, green, and blue fluorescent light emitting materials.

Secondary light emitted from the phosphor in the fluorescent film 205 is emitted in all directions. Since the light efficiency decreases when the amount of light emitted to the rear of the panel increases during the secondary light, the present invention provides a dichroic reflective filter between the fluorescent film 205 and the transparent substrate 203 so that the secondary light is emitted toward the front side of the panel. 204 was placed.

In one embodiment of the liquid crystal panel according to the present invention, the dichroic filter 204 reflects light having a wavelength different from the wavelength of the incident primary light among the secondary lights, and reflects the same wavelength as the primary light. The light having a role to selectively transmit. Accordingly, the light emitted to the rear of the panel among the secondary light emitted from the fluorescent film 205 is reflected by the dichroic reflection filter 204 disposed behind the fluorescent film 205 and is emitted toward the front of the panel.

The dichroic reflective filter 204 is formed by alternately stacking a thin film of a material having a low refractive index and a material having a low refractive index. Its selective light transmission function can be achieved by high reflectance due to the multilayer film interference phenomenon. Materials with low refractive index are metals or metal oxides, for example MgF ₂ or SiO ₂ The material having a high refractive index is a metal or a metal oxide, for example, Ag, TiO ₂ , Ti ₂ O ₃ , Ta ₂ O ₃ and the like, but is not limited thereto. The thickness of each thin film may be determined according to the design in the range of 1/8 to 1/2 of the wavelength of the transmitted light.

According to one embodiment of the present invention, the dichroic reflective filter 204 has a structure in which a plurality of dielectric thin films having different refractive indices are stacked. In this case, the dichroic reflection filter 204 has a multi-layer film interference phenomenon caused by a mirror surface having a much higher reflectance than that of metal. Such a dichroic reflection filter is also called an edge filter in the optical field, and may be designed such that the reflectance rapidly changes around a specific wavelength depending on the design.

According to the exemplary embodiment of the present invention, the dichroic reflection filter 204 freely selectively transmits / reflects light in an arbitrary wavelength range according to the structure of the dielectric thin film constituting the dichroic reflection filter 204 to improve light utilization. To make it possible. For example, when the primary light incident on the liquid crystal panel is blue light, the dichroic reflection filter 204 may be designed to transmit blue light but reflect green light and red light. Accordingly, the light emitted from the rear of the panel among the green light and the red light emitted from the fluorescent film 205 is reflected by the dichroic reflective filter 204 and exits in front of the panel. In this way, the dichroic reflecting filter can increase the light efficiency of the phosphor.

4 is a schematic diagram of a dichroic reflective filter 204 used in a liquid crystal panel according to an embodiment of the present invention.

The dichroic reflective filter 204 of FIG. 4 uses a thin film and has a Fabry-Perot resonator structure. The dichroic reflective filter 204 is a glass substrate 301, silver (Ag) layer 302, SiO ₂ The spacer layer 303 and the silver layer 302 are sequentially stacked, which is a dichroic reflection filter 204 that transmits only the resonant wavelength with respect to the blue light wavelength and reflects light of the remaining wavelength.

5 is a 20 nm silver layer on top of a glass substrate, 260 nm SiO _2. The reflectance curve R and the transmittance curve T of the dichroic reflection filter 204 in which the spacer layer and the 20 nm silver layer were sequentially deposited are shown. According to this, it can be seen that the filter shows about 80% transmittance near the 460 nm wavelength and reflects the remaining wavelength.

In addition, according to the exemplary embodiment of the present invention, the TiO ₂ and SiO ₂ thin films are sequentially stacked to include a dichroic reflection filter 204 for passing light of the blue wavelength band and reflecting light of the remaining wavelength band. FIG. 6 shows a graph of reflectance change when TiO ₂ and SiO ₂ thin films are sequentially stacked on a glass substrate. In the graph of FIG. 6, 1.5p represents a reflectance change curve of a dichroic reflective filter stacked in the order of TiO ₂ / SiO ₂ / TiO _{2 on} the glass substrate, and 2.5p represents TiO ₂ / SiO ₂ / TiO on the glass substrate. The reflectance change curve of the dichroic reflection filter formed by laminating in order of ₂ / SiO ₂ / TiO ₂ is shown. In the two dichroic reflection filters, the thickness of SiO ₂ was set to 108 nm and the thickness of TiO ₂ was set to 60 nm. It can be seen that both curves have a very small reflectance near 460 nm and a very high reflectance in the green wavelength region and the red wavelength region.

In the recent liquid crystal display device, a LED blue light source is generally used as the light source 201, and the LED blue light emits a wavelength of 405 nm to 460 nm band, and the wavelength band corresponds to a phosphor contained in the fluorescent film 205. They are excited to emit red, green, and blue light, respectively. Thus, the structure of the illustrated dichroic reflection filter 204 can effectively increase the light utilization rate in the liquid crystal display device using the LED blue light.

The liquid crystal panel according to the present invention is characterized in that the fluorescent barrier 205 is provided with a reflective partition wall 207 so that red, blue and green phosphors are not mixed but separated from each other (see FIG. 2). The phosphors may be separated from each other in the phosphor film 205 so as to correspond to the positions of the red, green, and blue subpixels of each pixel of the liquid crystal panel, which is achieved by providing the reflective barrier wall 207. In this case, a plurality of reflective barrier ribs 207 are formed in the fluorescent film 205 to divide the fluorescent film 205 in the vertical direction with respect to the fluorescent film 205 to separate the spaces so as to correspond to the respective sub-pixels, and to separate the respective ones. R, G, and B phosphors are separated to correspond to the R, G, and B positions of the subpixels in the space.

If blue light having a band of about 460 nm is used as the light source, the blue phosphor does not need to be used, and thus, the blue pixel position may be used as the transparent layer in the fluorescent film 205. In this case, since there is no light loss by the phosphor, the efficiency is further improved.

The reflective partition wall 207 prevents the secondary light emitted from the phosphor in the fluorescent film 205 from propagating in parallel to the surface of the substrate 203 by total internal reflection and allows the secondary light to be irradiated toward the front surface of the panel ( 2). Since the average refractive index of the synthetic resin or the phosphor used as the material of the fluorescent film 205 is about 2.0, the total internal reflection angle is 30 ° accordingly. That is, since the vertex angle of the escape cone is 60 °, the light incident on the interface at an angle greater than this travels parallel to the substrate 203. Therefore, when the refractive index is 2.0, about 80% of light is trapped in the fluorescent film 205 by total internal reflection. Therefore, the reflective partition wall 207 structure extracts the secondary light trapped in the fluorescent film 205 by the total internal reflection in the vertical direction with respect to the panel surface to be irradiated toward the front surface of the panel.

The reflective barrier rib 207 is preferably made of a metal material such as silver or aluminum and a ceramic material having high reflectance. The thickness of the reflective barrier rib 207 is preferably about 1% to 10% thicker than the thickness of the fluorescent film 205.

According to an embodiment of the present invention, the liquid crystal panel of the present invention may include a color filter 206 in front of the fluorescent film 205. The light generated by the fluorescent film 205 passes through the color filter 206 and is converted into light having high color purity.

In addition, the present invention is the liquid crystal panel; And a backlight unit disposed behind the liquid crystal panel and including a light source 201 to which the primary light is radiated.

2 schematically illustrates a liquid crystal display of the present invention.

Preferably, the light source 201 emits blue light, and more preferably, emits blue light. In addition, the backlight unit may further include a prism sheet 202 for changing the direction of the light so that the primary light emitted from the light source 201 is incident perpendicularly to the transparent substrate 203.

Primary light emitted from the light source 201 passes through the prism sheet 202 and is incident to the liquid crystal panel.

The prism sheet 202 serves to increase the front luminance by orienting light emitted from the light source 201 in a direction perpendicular to the liquid crystal panel surface to be incident on the panel. In this case, the amount of light of the LED incident to the phosphor is increased to increase the overall light efficiency. In particular, when the light source 201 is LED blue light, the light irradiated from the LED light source is Lambertian, and the half width is about 60 degrees. On the other hand, the dichroic reflective filter 204 made of a multi-layered thin film varies in accordance with the angle of incidence, while passing vertically incident blue light, but may reflect blue light when the angle of incidence is 50 ° or more. Accordingly, in the case of the blue LED light source, the light efficiency is lowered because the blue LED light source does not pass through the dichroic reflection filter 204 and is reflected. Therefore, in order to prevent this, especially when using a blue LED as the light source 201, it is preferable to provide the prism sheet 202 between the transparent substrates 203. As shown in FIG.

According to the exemplary embodiment of the present invention, the liquid crystal panel may be formed in a shape in which the prism sheet 202 is integral with the liquid crystal panel by interviewing the rear portion of the substrate 203 (FIG. 3).

The movement path of the light according to the embodiment of the liquid crystal panel and the liquid crystal display according to the present invention is as follows. First, the primary light irradiated from the light source 201 is oriented in a direction perpendicular to the panel surface of the liquid crystal panel while passing through the prism sheet 202. Primary light passing through the prism sheet is incident to the liquid crystal panel. The incident primary light passes through the transparent substrate 203 and the dichroic reflection filter 204 to reach the fluorescent film 205. The primary light excites the phosphor in the fluorescent film 205 to generate secondary light. The light emitted behind the panel during the secondary light is reflected by the dichroic reflection filter 204 disposed between the transparent substrate 203 and the fluorescent film 205 and is emitted back to the front of the panel. On the other hand, the light propagated in parallel to the panel surface in the fluorescent film 205 is reflected by the reflective partition wall 207 provided in the fluorescent film 205 is emitted to the front of the panel. Since the light emitted from the fluorescent film 205 passes through the color filter 206 disposed in front of the fluorescent film 205, the purity of the light color is improved. Since the secondary light converted from the phosphor mostly passes through the color filter 206, the light loss corresponding to two thirds of the incident light generated when the light from the conventional white LED passes through the color filter 206 is large. Can be reduced. Although energy loss due to a stoke shift occurring in the phosphor may occur even when a white light LED is used as a light source, the liquid crystal panel according to the present invention has a wavelength in which incident primary light is close to the color filter 206 for each pixel. The energy efficiency of the entire panel is remarkably improved as compared with the conventional liquid crystal panel because it is converted into.

101 ... White LED 102 ... Board
103 ... color filter
201 ... light source 202 ... prism sheet
203 ... transparent substrate 204 ... dichroic reflective filter
205 ... fluorescent film 206 ... color filter
207 ... reflective bulkhead
301 ... glass substrate 302 ... silver layer
303 ... SiO ₂ spacer layer

Claims (8)

In a liquid crystal panel provided with a normal liquid crystal layer,
A transparent substrate that transmits primary light emitted from a light source and supports the liquid crystal layer;
A fluorescent film comprising a phosphor which is excited by the primary light transmitted through the transparent substrate and the liquid crystal layer and emits secondary light equal to or different from the wavelength of the primary light; And
A dichroic reflective filter disposed between the transparent substrate and the fluorescent film;
And,
The dichroic reflection filter is to transmit the light of the resonant wavelength of the dichroic reflection filter of the secondary light emitted from the fluorescent film and to reflect the light of the remaining wavelength,
The phosphors are separated by barrier ribs provided inside the phosphor film without red, green, and blue phosphors mixed in one space.
The partition wall is a liquid crystal panel comprising a reflector to reflect the secondary light emitted from the phosphor to be irradiated in the front direction of the liquid crystal panel. The method of claim 1,
The liquid crystal panel further comprises a color filter disposed above the fluorescent film to improve the purity of the red light, the green light, and the blue light, which are the secondary light emitted from the fluorescent film. The method according to claim 1 or 2,
When blue light is used as the light source, the fluorescent film does not include a blue phosphor. The method according to claim 1 or 2,
The dichroic reflective filter is a liquid crystal panel formed by alternately stacking a plurality of layers of materials having different refractive indices. The liquid crystal panel according to claim 1 or 2; And a backlight unit disposed behind the liquid crystal panel and emitting the primary light. The method of claim 5,
The backlight unit includes a light source for emitting blue light. The method of claim 5,
And the light source is an LED emitting blue light. The method of claim 5,
And the backlight unit further comprises a prism sheet for orienting the light such that the primary light emitted from the light source is incident on the transparent substrate vertically.

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