KR20040072423A - front filter of Plasma Display Panel - Google Patents

Abstract

PURPOSE: A front filter for a plasma display panel is provided to improve a light/darkness contrast ratio and a brightness of PDP in result of having a photo shutter function changed by an electric field. CONSTITUTION: A front filter for a plasma display panel comprises an adhesive(20) added with a dye on a tempered glass(10), a photo shutter(60) deposited successively with an ITO(64)/Electrical Optical(EO)/ITO on the adhesive, an EMI shielding layer formed with a mesh(30) or an Ag/ITO(30') on the photo shutter, an anti-reflection(AR) coating film(50) formed at a both side of the most outside, two electrode surfaces formed between the PDP panel and the EMI shielding layer and applying an electric field, and a polymer dispersed liquid crystal(PDLC)(62) formed between the two electrode surfaces and doped with the dye changing a photo property by an electric field applied at an electrode.

Description

Front filter of plasma display panel

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a plasma display panel. More particularly, the present invention relates to a front surface filter that can improve light characteristics by adding a property to transmit or block light according to an electric field applied from the outside.

Plasma Display Panels (PDPs) driven at high voltages of 100V require front filters having various functions on the front side of the panel to realize high quality video.

The function of the front filter is to firstly protect the panel from external shocks, secondly, to block electromagnetic waves emitted from the panel due to high-voltage driving, and thirdly, to block near-infrared rays to prevent the remote control from malfunctioning. Optical characteristics such as;

PDP front filters currently on the market have a structure that attaches layers to perform the functions of the aforementioned filters on both sides of tempered glass, and the front filter has a metal mesh type and Ag / ITO depending on the type of electromagnetic shielding material used. Are divided into types.

Figure 1 (a) (b) is a view showing the structure of the PDP front filter according to the prior art, Figure 1 (a) is a view showing a metal mesh type front filter, Figure 1 (b) Ag / ITO front filter The figure which shows.

As shown in FIG. 1 (b), when the Ag / ITO multilayer thin film is used, it has not only an electromagnetic wave blocking function but also a near infrared ray blocking function. As shown in FIG. A separate layer is required for the blocking function.

In addition, a dye film that absorbs a specific wavelength is formed between the tempered glass and the metal mesh or Ag / ITO. That is, color purity improvement and color temperature correction are performed using a specially designed dye combination to improve optical characteristics.

Finally, an anti-reflection coating film is attached or deposited on both upper layers.

Due to the complex structure of the front filter and the dye that absorbs light of a specific wavelength to improve the optical properties, most of the filters have a light transmittance of 40 to 55% despite the improvement of the optical properties.

The low light transmittance of these filters causes the PDP brightness to drop, causing a decrease in luminous efficiency. However, if the transmittance of the filter is increased, the contrast contrast of the bright room is lowered due to the strong external light scattering of the PDP itself, making it difficult to realize high quality video.

The front filter for a plasma display panel according to the related art described above has the following problems.

Increasing the transmittance of the filter increases the brightness of the PDP but decreases the contrast contrast ratio, while decreasing the transmittance increases the brightness contrast ratio but decreases the luminance. As described above, the conventional front filter has a disadvantage in that the luminance and contrast ratio cannot be improved at the same time.

Accordingly, the present invention has been made to solve the above problems, and an object thereof is to provide an operation concept of a new front filter which improves PDP brightness and does not lower the clear black and white contrast ratio.

Another object of the present invention is to propose a dye-doped Polymer Dispersed Liquid Crystal (PDLC) as an example of a material or system that can be used in a new front filter and to reveal its requirements.

It is another object of the present invention to provide a manufacturing process of a front filter using a dye-doped PDLC.

1 (a) and (b) are views showing the structure of a PDP front filter according to the prior art

Figure 2 (a) (b) is a schematic diagram of a plasma display driving method according to the prior art

3 is a view showing the structure of a front filter for a plasma display panel according to the present invention;

Figure 4 (a) (b) is a view showing a structure of a dye-doped PDLC surrounded by a polymer solidified liquid crystal in the front filter according to the present invention

5 (a) (b) are schematic diagrams of a plasma display driving and optical shutter operation method according to the present invention;

* Explanation of symbols for main parts of the drawings

10 tempered glass 20 pigmented additives

30: metal mesh 30 ': Ag / ITO

40: adhesive 50: antireflective coating film (AR)

60: optical shutter 62: pigment-doped PDLC

64: ITO 70: polymer

80: liquid crystal 90: pigment

Features of the front filter for a plasma display panel according to the present invention for achieving the above object is an adhesive with a pigment added on the tempered glass, an optical shutter sequentially deposited on the adhesive by ITO / EO / ITO, In the front filter for a plasma display (PDP) panel consisting of an EMI shielding window formed of a mesh or Ag / ITO on the optical shutter, and an anti-reflective coating film (AR) formed on the outermost both sides, the PDP panel and the EMI shielding layer And two dye-doped PDLCs formed between the two electrode surfaces capable of applying an electric field and the optical properties of the two electrode surfaces formed between the two electrode surfaces and applied to the electrodes.

At this time, the dye-doped PDLC is hundreds Can be enough It is preferable to have a reaction rate of.

In addition, it is preferable that the optical properties vary by the electric field in a state in which light is transmitted and in a state in which light is blocked.

In addition, the dye-doped PDLC is preferably composed of at least one of a nematic liquid crystal, a ferroelectric liquid crystal (ferroelectric liquid crystal).

In addition, the nematic liquid crystal and the ferroelectric liquid crystal preferably form liquid crystal droplets of several hundreds or tens of nm.

Other objects, features and advantages of the present invention will become apparent from the following detailed description of embodiments taken in conjunction with the accompanying drawings.

A preferred embodiment of the front filter for a plasma display panel according to the present invention will be described with reference to the accompanying drawings.

3 is a view showing the structure of a front filter for a plasma display panel according to the present invention.

As shown in FIG. 3, the optical shutter 20 sequentially deposited with pigments on the tempered glass 10 and ITO 64 / EO 62 / ITO 64 on the adhesive 20. 60, an EMI shielding layer 30 (30 ') formed of a mesh or Ag / ITO on the optical shutter 60, and an antireflective coating (AR) 50 on both outermost surfaces.

At this time, the electrical optical (EO) material 62 is hundreds Up to 1 degree It has a reaction rate of.

The driving principle of the video of the plasma display panel configured as described above is as follows.

In one second, a 60-frame still picture signal is input to the PDP. In other words, one frame still image is implemented on the panel for a time of 1/60 = 16.6 ms (milli-second).

At this time, the present invention can be easily applied to the ADS (Address Display Separated) method in which the time between the syringes and the desired screen is displayed among the PDP driving methods.

The ADS method also has various configuration methods of subfields (SF) forming one frame according to the gradation representation method, and the present invention will be described based on the most popular Fujistu method.

In the Fujistu method, as shown in FIG. 2, one frame is composed of eight subfields (SFs), each of which has a reset period for removing an electric charge generated in the PDP cell from the previous SF to an initial state and an input. It consists of an address cycle for generating charges in each cell in accordance with the signal, and a sustain cycle for emitting light by applying a high voltage driving signal to all cells at the same time.

On the other hand, the time of each cycle of each SF is defined as a time of 300 ~ 400 sec for the reset period, 600 seconds for the address period.

In this case, the reset period and the address period each take the same time, whereas in the case of the sustain period, according to the bit order of each SF Has a time ratio.

During the address period, the charge is charged to the cell with the input signal 1 (or on), and the cell with 0 (or off) is not charged.

Accordingly, due to the nonlinear characteristics of the plasma, the voltage value for discharging is lower in the charged cell. Therefore, when the sustain signal is input to all the cells at a voltage slightly higher than this threshold voltage, the discharged cell is discharged. This happens and the light is emitted, but the cells that do not emit light.

In this way, by selecting SFs having different emission times in one frame, 256 gray levels of each cell can be represented.

One of the optical characteristics of the PDP panel is the contrast ratio.

This means the ratio of the brightness when a signal of 0 is input and the brightness when a signal of 255 is input.

According to the actual measurement conditions, the contrast ratio is the contrast contrast ratio and darkroom contrast ratio.

Dark-room contrast ratio is measured under the condition that the external lighting is completely blocked. When inputting a signal of 0, some light is emitted due to the driving characteristics of the PDP panel, thereby limiting the contrast ratio.

That is, unwanted light is emitted in the process of eliminating the charge charged in the reset and address periods.

Contrast contrast is measured under bright light, similar to the conditions of watching TV in real life. In this case, the light of the illumination is reflected by the panel to increase the brightness of the arm.

Attaching a conventional front filter to a PDP panel allows the external light to pass through the filter twice when reflected by the panel. Therefore, if the filter transmittance is 50%, the effect of external light is 1/4 compared to the case without the filter. Is reduced to (1/2 x 1/2).

On the other hand, the amount of light on the panel is reduced by 1/2, so the contrast ratio That's about twice the panel.

Dark contrast contrast ratios, on the other hand, remain unchanged because both light and dark stem at the same rate.

In the present invention, as shown in FIG. 3, the function of the optical shutter layer 60 whose optical characteristics are changed by an external electric field applied to the existing front filter is implemented by the dye-doped PDLC 62.

The optical shutter layer 60 has a PDLC layer 62 doped with pigments between transparent substrates on which Indium Tin Oxide (ITO) 64, which is a transparent electrode material for applying an electric field, is positioned.

The location of the optical shutter layer 60 may be located above or below the tempered glass 10, which must be located between the PDP panel and the EMI shielding layer (mesh or Ag / ITO) 30, 30 ′. .

In some cases, the EMI blocking layers 30 and 30 'may be one electrode of the EO material (the other side of the panel).

This can simplify the structure of the front filter.

Figure 4 (a) (b) is a view showing a structure of a dye-doped PDLC surrounded by a polymer solidified liquid crystal in the front filter according to the present invention.

The basic structure, principle, and manufacturing method are similar to PDLC (Polymer Dispersed Liquid Crystal).

That is, the liquid crystal 80 and the monomer / polymer or polymer 70 are mixed homogeneously or inhomogeneously, and then a phase separation or encapsulation method is performed. Is produced by.

From the beginning, when a 1-dimensional dye having a similar structure is added to the liquid crystal, it becomes a dye-doped PDLC 62.

In this case, when the polymer 70 is used, the dye 90 is easily mixed with the liquid crystal 80, but when the monomer is used, the dye 90 may be mixed with the monomer, so the selection of an appropriate dye 90 is required. do.

In addition, if no electric field is applied to the PDLC 62, liquid crystal droplets are arbitrarily arranged as shown in FIG. In this case, light scatters due to the difference in refractive index between the liquid crystal 80 having the optical anisotropy and the polymer 70.

When an electric field is applied to the PDLC 62, liquid crystal droplets are arranged in one direction as shown in FIG.

4 (b) shows a case where the anisotropy of the liquid crystal dielectric constant is positive.

In this case, the PDLC 62 selects a material such that the refractive index of the vertical component of the liquid crystal is the same as that of the polymer 70, and thus light does not pass through the difference in refractive index.

In addition, the dye 90 of the pigment-doped PDLC 62 has a structure similar to that of the liquid crystal 80 and is surrounded by the liquid crystal 80 to move together with the liquid crystal 80. When the electric field becomes the length direction of the pigment 90, light is emitted. When the silver is absorbed by the dye 90 and becomes vertical, absorption is minimized.

Therefore, the dye-doped PDLC 62 is arbitrarily arranged like the liquid crystal 80 to absorb incident light or scattered light when an electric field is not applied as shown in FIG.

In the dye-doped PDLC 62, when the electric field is applied as shown in FIG. 4 (b), absorption is minimized since the dye 90 is arranged in the direction of light propagation.

As described above, in the present invention, the dye-doped PDLC 62 having a change in transmittance depending on the electric field is used as the optical shutter material 60.

That is, when an electric field is applied, the transmittance is maximum, and when the electric field is 0, the transmittance is minimum.

The operation of the optical shutter 60 including the dye-doped PDLC 62 is related to the PDP driving process.

That is, as shown in FIG. 5, the screen information is displayed on the PDP during a sustain period. In this period, the optical shutter 60 is transmitted by applying a voltage to the pigment-doped PDLC 62 and the screen information appears. During the reset period and the address period, the voltage is set to 0 to minimize the transmittance of the optical shutter 60.

This minimizes the emission of unwanted light generated in the PDP panel during the reset / address period, thereby lowering the black luminance in the dark room and improving the dark gray level without deteriorating the white luminance.

Even in the bright room, the transmittance is minimal during the reset / address period, and the contribution of the absorption by the pigment 90 is greater than the reflection itself, so that the external light reflection can be lowered, thereby lowering the brightness of black in the bright room. do.

This can contribute to blackening the black state, the biggest issue of PDP.

In order for the optical shutter function of the dye-doped PDLC 62 to work properly, the response time of the PDLC becomes an important factor.

Reset / address time is approximately 0.9 This depends on the PDP drive method and panel size.

In some cases, the address can be set without reset.

When the transmittance is defined as a time difference of 10% to 90% as shown in FIG. 5, the optical shutter 60 has a response time of 0.1 to 0.2. If the optical shutter function can be optimized below, the longer the length, the better the gradation can be obtained by complementing the PDP driving method.

In this case, in the case of the dye-doped PDLC 62, the response time depends on the intensity of the applied electric field, the size of the liquid crystal, the dielectric constant, and the surface action between the liquid crystal polymers. And the electric field Given by In addition, since the response time is inversely proportional to the square of the electric field, the response time can be reduced by reducing the thickness or increasing the voltage.

Therefore, in the case of PDP, since the voltage used is up to 200V, it is possible to increase the magnitude of the voltage applicable to the PDP optical shutter 60, unlike the existing PDLC application, thereby reducing the response time.

Also, if the liquid crystal droplet size is brought to hundreds or tens of nm, the response time is 100 Lowers.

If a part of the ferroelectric liquid crystal is added instead of the nematic liquid crystal, the response time may be lowered.

In addition, the advantage of the pigment-doped PDLC 62 as the optical shutter 60 is that the transmittance in the 'on' state is high as high as 80% in addition to the fast response time.

When the liquid crystal 80 is used, one or two polarizers are used, in which case the maximum transmittance cannot exceed 40%.

Therefore, the use of the polarizing plate contributes to the low black transmittance due to the low 'off' transmittance. However, when considering the decrease in transmittance due to other functions the filter should have, the 'on' 'PDLC with high transmittance is suitable as optical shutter for PDP filter.

The decrease in transmittance in the 'off' state in general PDLC is due to scattering due to the difference in refractive index, which further increases the external light reflection, whereas in the case of the dye-doped PDLC 62, due to the pigment at the time of 'off' Since absorption is added, it is possible to reduce external light reflection, thereby contributing to the improvement of gradation.

In conclusion, it is possible to apply the front filter using the optical shutter 60 to the pigment-doped PDLC 62 to the PDP, and the time when the desired image is actually displayed and the time to write data to the panel are clearly distinguished. Since only 2/3 of the time the image comes out, the rest of the time is to block both the light from the panel and the light incident on the panel by the external light source, thereby improving both dark and gradation.

As described above, the front filter for a plasma display panel according to the present invention includes an optical shutter function in which optical characteristics are changed by an electric field, thereby significantly improving the brightness and contrast of a dark / dark contrast ratio of a PDP panel.

Those skilled in the art will appreciate that various changes and modifications can be made without departing from the spirit of the present invention.

Therefore, the technical scope of the present invention should not be limited to the contents described in the embodiments, but should be defined by the claims.

Claims (5)

An adhesive added with pigment on tempered glass, an optical shutter sequentially deposited on the adhesive in ITO / EO / ITO, an EMI shielding window formed of mesh or Ag / ITO on the optical shutter, and the outermost both sides In the front filter for a plasma display (PDP) panel composed of an antireflective coating film (AR) formed in the Two electrode surfaces formed between the PDP panel and the EMI blocking layer to apply an electric field; And a dye-doped PDLC formed between the two electrode surfaces, the optical properties of which are changed by an electric field applied to the electrode. The method of claim 1, The dye-doped PDLC is hundreds of Can be enough Front filter for plasma display panel, characterized in that having a reaction rate of. The method of claim 1, The optical characteristic of the plasma display panel is changed in a state in which light is transmitted and the light is blocked. The method of claim 1, The dye-doped PDLC is at least one of a nematic liquid crystal, a ferroelectric liquid crystal (ferroelectric liquid crystal) front filter for a plasma display panel. The method of claim 4, wherein The nematic liquid crystal and the ferroelectric liquid crystal have a liquid crystal droplet size of several hundred or tens of nm, the front filter for a plasma display panel.