KR102493926B1 - Liquid crystal display - Google Patents

Abstract

An embodiment of the present invention relates to a liquid crystal display capable of preventing a contrast ratio from being lowered even when a light diffusing polarizer is applied. A liquid crystal display device according to an embodiment of the present invention includes a display panel and a backlight unit for irradiating light to the display panel. The display panel includes a lower substrate to which a lower polarizer is attached, an upper substrate to which an upper polarizer is attached, and a liquid crystal layer between the lower and upper substrates. The lower polarizer includes a coated polarizer and a light diffusing polarizer. The coated polarization layer is disposed on one side of the lower substrate facing the backlight unit. The light-diffusing polarizer is provided with a polarization layer disposed below the coated polarization layer and a diffusion layer disposed below the polarization layer and diffusing light from the backlight unit.

Description

Liquid Crystal Display {LIQUID CRYSTAL DISPLAY}

An embodiment of the present invention relates to a liquid crystal display device.

As the information society develops, demands for display devices for displaying images are increasing in various forms. Accordingly, recently, various flat panel display devices such as a liquid crystal display (LCD), a plasma display panel (PDP), and an organic light emitting diode display device have been utilized. . Among flat panel display devices, a liquid crystal display device displays an image by modulating light incident from a backlight unit by controlling an electric field applied to a liquid crystal layer.

Specifically, the liquid crystal display device includes a display panel and a backlight unit radiating light to the display panel. The display panel includes a lower substrate, an upper substrate, and a liquid crystal layer between the lower substrate and the upper substrate. A lower polarizing plate is attached to the lower substrate, and an upper polarizing plate is attached to the upper substrate. The light absorption axis of the lower polarizer and the light absorption axis of the upper polarizer cross each other. For example, when the light absorption axis of the lower polarizer is in the x-axis direction, the light absorption axis of the upper polarizer may be in the y-axis direction. The liquid crystal layer controls the liquid crystal molecules to adjust the phase of light incident from the backlight unit through the lower polarizer. Therefore, the degree to which light incident from the backlight unit through the lower polarizing plate passes through the upper polarizing plate may be adjusted according to how the liquid crystal layer controls the phase of light.

The backlight unit includes light sources, a light guide plate, and optical sheets. The backlight unit converts light from the light sources into a uniform surface light source through the light guide plate and the optical sheets and radiates the light to the display panel.

Recently, a polarizing plate having a function of a diffusion sheet for diffusing incident light among optical sheets to increase luminance (hereinafter, referred to as a "light diffusing polarizing plate") is applied to a liquid crystal display device. However, since the recently proposed light-diffusing polarizer has a low degree of polarization, when it is applied to a liquid crystal display, black luminance is increased and a contrast ratio (CR) is lowered. Contrast ratio is defined as black luminance compared to white luminance.

Embodiments of the present invention provide a liquid crystal display capable of preventing a contrast ratio from being lowered even when a light-diffusing polarizer is applied.

A liquid crystal display device according to an embodiment of the present invention includes a display panel and a backlight unit for irradiating light to the display panel. The display panel includes a lower substrate to which a lower polarizer is attached, an upper substrate to which an upper polarizer is attached, and a liquid crystal layer between the lower and upper substrates. The lower polarizer includes a coated polarizer and a light diffusing polarizer. The coated polarization layer is disposed on one side of the lower substrate facing the backlight unit. The light-diffusing polarizer is provided with a polarization layer disposed below the coated polarization layer and a diffusion layer disposed below the polarization layer and diffusing light from the backlight unit.

In an embodiment of the present invention, the lower polarizer includes a coated polarizer as well as a light diffusive polarizer, the light absorption axis of the light diffusive polarizer is formed differently from the light absorption axis of the coated polarizer, and the light transmission axis of the polarizer is It is formed the same as the light transmission axis of the coated polarization layer. As a result, in the embodiment of the present invention, since the coated polarizing layer can absorb some of the light not absorbed by the polarizing layer of the light diffusing polarizing plate, the degree of polarization of the light diffusing polarizing plate is reduced by using the coated polarizing layer. It is possible to prevent an increase in black luminance due to Therefore, the embodiment of the present invention can prevent the contrast ratio from being lowered.

1 is a perspective view showing a liquid crystal display according to an embodiment of the present invention;
2 is an exploded perspective view of the liquid crystal display of FIG. 1;
Figure 3 is a cross-sectional view showing II' of Figure 1;
4 is a side view showing only a lower substrate, an upper substrate, a lower polarizing plate, and an upper polarizing plate of the liquid crystal display according to the first embodiment of the present invention;
5 is a side view showing details of a polarizing layer and an upper polarizing plate of the light diffusing polarizing plate of FIG. 4;
6a to 6c are tables showing the change in contrast ratio according to the degree of polarization when the light transmittance of the coated polarization layer of FIG. 4 is 40%, 60%, and 65%.
7 is a table showing a change in contrast ratio according to a change in the thickness of a coated polarization layer.
8 is a table showing a change in contrast ratio according to polarization degree when the light transmittance of the coated polarization layer is 50% when the coated polarization layer is an O-type polarization layer.
9 is a side view showing only a lower substrate, an upper substrate, a lower polarizing plate, and an upper polarizing plate of a liquid crystal display according to a second embodiment of the present invention;
10A to 10C are tables showing changes in contrast ratio according to polarization degree when the light transmittance of the upper polarizer is 40%, 60%, and 65%.

Advantages and features of the present invention, and methods of achieving them, will become clear with reference to the detailed description of the following embodiments taken in conjunction with the accompanying drawings. However, the present invention is not limited to the embodiments disclosed below, but will be implemented in various different forms, only these embodiments make the disclosure of the present invention complete, and common knowledge in the art to which the present invention belongs. It is provided to fully inform the holder of the scope of the invention, and the present invention is only defined by the scope of the claims.

The shapes, sizes, ratios, angles, numbers, etc. disclosed in the drawings for explaining the embodiments of the present invention are illustrative, so the present invention is not limited to the details shown. Like reference numbers designate like elements throughout the specification. In addition, in describing the present invention, if it is determined that a detailed description of related known technologies may unnecessarily obscure the subject matter of the present invention, the detailed description will be omitted.

When 'includes', 'has', 'consists', etc. mentioned in this specification is used, other parts may be added unless 'only' is used. In the case where a component is expressed in the singular, the case including the plural is included unless otherwise explicitly stated.

In interpreting the components, even if there is no separate explicit description, it is interpreted as including the error range.

In the case of a description of a positional relationship, for example, 'on top of', 'on top of', 'at the bottom of', 'next to', etc. Or, unless 'directly' is used, one or more other parts may be located between the two parts.

In the case of a description of a temporal relationship, for example, 'immediately' or 'directly' when a temporal precedence relationship is described in terms of 'after', 'following', 'next to', 'before', etc. It can also include non-continuous cases unless is used.

Although first, second, etc. are used to describe various components, these components are not limited by these terms. These terms are only used to distinguish one component from another. Therefore, the first component mentioned below may also be the second component within the technical spirit of the present invention.

"X-axis direction", "Y-axis direction", and "Z-axis direction" should not be interpreted only as a geometric relationship in which the relationship between each other is made upright, and may be broader within the range in which the configuration of the present invention can function functionally. It can mean having a direction.

The term “at least one” should be understood to include all possible combinations from one or more related items. For example, "at least one of the first item, the second item, and the third item" means not only the first item, the second item, or the third item, respectively, but also two of the first item, the second item, and the third item. It may mean a combination of all items that can be presented from one or more.

Each feature of the various embodiments of the present invention can be partially or entirely combined or combined with each other, technically various interlocking and driving are possible, and each embodiment can be implemented independently of each other or can be implemented together in a related relationship. may be

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings.

1 is a perspective view showing a liquid crystal display according to an embodiment of the present invention. 2 is an exploded perspective view of the liquid crystal display of FIG. 1; 3 is a cross-sectional view showing II' of FIG. 1; 1 to 3 , a liquid crystal display device according to an embodiment of the present invention includes a display panel 100, a driving circuit unit for driving the display panel 100, a backlight unit 300, and a case member. .

The display panel 100 includes a lower substrate 110 , an upper substrate 120 , and a liquid crystal layer interposed between the lower substrate 110 and the upper substrate 120 . The lower substrate 110 and the upper substrate 120 may be formed of glass or plastic.

The size of the lower substrate 110 may be larger than that of the upper substrate 120 . For this reason, the source flexible film 220 may be attached to one edge of the upper surface of the lower substrate 110 that is not covered by the upper substrate 120 . An upper surface of the lower substrate 110 corresponds to a surface facing the upper substrate 120 .

Signal lines and pixels are provided on the upper surface of the lower substrate 110 of the display panel 100 . The signal lines may include data lines and gate lines crossing each other, a common line for supplying a common voltage to common electrodes, and gate control signal lines supplied as control signals to the gate driving circuit. Pixels may be disposed at intersections of the data lines and the gate lines. Each of the pixels includes a thin film transistor (TFT), a pixel electrode, and a common electrode. The thin film transistor supplies the data voltage of the data line to the pixel electrode in response to the gate signal of the gate line. The liquid crystal of the liquid crystal layer is driven by an electric field generated by a potential difference between the data voltage supplied to the pixel electrode and the common voltage supplied to the common electrode, and thus the transmission amount of light incident from the backlight unit can be adjusted.

A black matrix and color filters may be provided on the lower surface of the upper substrate 120 of the display panel 100 . A lower surface of the upper substrate 120 corresponds to a surface facing the lower substrate 110 . However, when the display panel 100 is formed using a color filter on TFT array (COT) method, the black matrix and color filters may be provided on the upper surface of the lower substrate 110 . The common electrode is provided on the lower surface of the upper substrate 120 in vertical electric field driving methods such as TN (Twisted Nematic) mode and VA (Vertical Alignment) mode, and in IPS (In Plane Switching) mode and FFS (Fringe Field Switching) mode and It may be provided on the upper surface of the lower substrate 110 in the same horizontal electric field driving method. In addition, an alignment layer for setting a pretilt angle of liquid crystal may be formed on the upper surface of the lower substrate 110 and the lower surface of the upper substrate 120 of the display panel 100 . In this case, the alignment layer may be formed through a rubbing process.

The lower polarizing plate 140 is disposed on the lower surface of the lower substrate 110 of the display panel 100 , and the upper polarizing plate 150 is disposed on the upper surface of the upper substrate 120 . The lower polarizing plate 140 may be formed to have a smaller size than the lower substrate 110 , and the upper polarizing plate 150 may be formed to have a smaller size than the upper substrate 120 . A detailed description of the lower polarizer 140 and the upper polarizer 150 will be described in conjunction with FIGS. 4 and 5 .

The driving circuit unit includes a gate driving circuit, source driving circuits 210, source flexible films 220, a circuit board 230, and a light source driving unit 240.

The gate driving circuit supplies gate signals to gate lines of the lower substrate 110 . The gate driving circuit may be directly formed on the upper surface of the lower substrate 110 in a gate driver in panel (GIP) method. Alternatively, when the gate driving circuit is implemented as a driving chip, it may be mounted on a gate flexible film in a COF (chip on film) method, and the gate flexible films are a lower substrate that is not covered by the upper substrate 120. It can be attached to the edge of the upper surface of (110).

The source driving circuits 210 supply data voltages to data lines of the lower substrate 110 . When each of the source driving circuits 210 is implemented as a driving chip, it may be mounted on the source flexible film 220 in a COF (chip on film) method. Alternatively, the source driving circuits 210 may be bonded to the upper surface of the lower substrate 110 using a chip on glass (COG) method or a chip on plastic (COP) method. The source flexible films 220 may be attached to one edge of the upper surface of the lower substrate 110 that is not covered by the upper substrate 120 and to the circuit board 230 . The circuit board 230 may be implemented as a printed circuit board.

The light source driving unit 240 includes a light source driving circuit 241 and a light source circuit board 242 . The light source driving circuit 240 supplies driving currents to the light sources 310 to emit light. The light source driving circuit 240 may be mounted on the light source circuit board 242 . Alternatively, the light source driving circuit 240 may be mounted on the circuit board 230, in which case the light source circuit board 242 may be omitted.

The driving circuit unit may further include a timing control circuit and a control circuit board on which the timing control circuit is mounted. In this case, the control circuit board may be connected to the circuit board 230 through a predetermined flexible cable.

The backlight unit 300 includes light sources 310 , a light source circuit board 320 , a light guide plate 330 , a reflective sheet 340 , optical sheets 350 , and the like. The backlight unit 300 converts the light from the light sources 310 into a uniform surface light source through the light guide plate 320 and the optical sheets 350 and radiates the light to the display panel 100 .

The light sources 310 may be implemented as light emitting diodes. The light sources 310 are disposed on at least one side of the light guide plate 320 to emit light to the side of the light guide plate 320 . The light sources 310 are mounted on the light source circuit board 320 and are turned on and off by receiving driving current from the light source driving circuit 241 . The light source circuit board 320 is connected to the light source driver 240 .

The light guide plate 320 converts light from the light sources 310 into a surface light source and radiates the light to the display panel 100 . The reflective sheet 340 is disposed on the lower surface of the light guide plate 330 to reflect light from the light guide plate 330 downward toward the light guide plate 330 toward the light guide plate 330 .

Optical sheets 350 may be disposed between the light guide plate 330 and the display panel 100 . That is, optical sheets 350 may be disposed below the display panel 100 , and light guide plates 330 may be disposed below the optical sheets 350 . The optical sheets 350 may include one or more diffusion sheets. Alternatively, the optical sheets 350 may further include one or more prism sheets in addition to one or more diffusion sheets.

In FIGS. 2 and 3 , it has been described that the backlight unit 300 is implemented as an edge type, but it is not limited thereto and it should be noted that it may be implemented as a direct type. When the backlight unit 300 is implemented as a direct type, a diffusion plate may be provided instead of the light guide plate 320, and light sources 310 are provided under the diffusion plate to emit light through the diffusion plate.

The case member includes a bottom cover 410 , a support frame 420 , and a top case 430 .

The bottom cover 410 is made of metal with a square frame and covers the side and bottom surfaces of the backlight unit 300 as shown in FIG. 3 . The bottom cover 410 may be made of high-strength steel, for example, electro-galvanized steel (EGI), stainless (SUS), galvalume (SGLC), aluminum-plated steel (aka ALCOSTA), tin-plated steel (SPTE), etc. can be made with

The support frame 420 supports the lower surface of the lower substrate 110 of the display panel 100 . The support frame 420 is also referred to as a guide panel or a guide frame. The support frame 420 may be fixed by being coupled with the bottom cover 410 by a fixing member. The support frame 420 may be made of a square frame in which glass fibers are mixed in a synthetic resin such as polycarbonate, plastic, or made of stainless steel (Steel Use Stainless, SUS). Meanwhile, in order to protect the lower substrate 110 of the display panel 100 from being impacted by the support frame 420, as shown in FIG. 3, a buffer member 421 is provided between the lower substrate 110 and the support frame 420. can be provided.

The top case 430 covers the edge of the display panel 100 , the top and side surfaces of the guide frame 420 , and the side surface of the bottom cover 410 . The top case 430 may be made of electro-galvanized steel (EGI) or stainless steel (SUS). The top case 430 may be fixed to the support frame 420 with hooks or screws. Meanwhile, in order to protect the upper substrate 110 of the display panel 100 from being impacted by the top case 430, a buffer member 421 is provided between the lower substrate 110 and the top case 430 as shown in FIG. can be provided.

4 is a side view showing only the lower substrate, the upper substrate, the lower polarizing plate, and the upper polarizing plate of the liquid crystal display according to the first embodiment of the present invention. In FIG. 4 , only the lower substrate 110 , the upper substrate 120 , the lower polarizing plate 140 , and the upper polarizing plate 150 of the display panel 100 are illustrated for convenience of description.

Referring to FIG. 4 , the lower polarizer 140 includes a coated polarizer 141 and a light diffusing polarizer 142 . The coated polarization layer 141 is disposed on the lower surface of the lower substrate 110 to face the backlight unit 300 .

The coated polarization layer 141 may be formed by being coated on the lower surface of the lower substrate 110 and then cured by heat or ultraviolet rays. That is, since the coated polarization layer 141 is directly formed on the lower surface of the lower substrate 110, the coated polarization layer 141 and the lower substrate 110 are between the coated polarization layer 141 and the lower substrate 110. ) does not require a separate adhesive or adhesive film to adhere.

Specifically, the coated polarization layer 141 is formed by applying a material including polyimide, discotic liquid crystals, and dyes on the lower surface of the lower substrate 110, and curing by heat. Alternatively, it may be formed by UV curing. When the coated polarization layer 141 includes discotic liquid crystal, it may have characteristics of an E-type polarizer. On the other hand, when the coated polarization layer 141 is formed using a material containing rod type liquid crystals instead of discotic liquid crystals, it may have characteristics of an O-type polarizer. . The E-type polarizer has the advantage of being thinner than the O-type polarizer.

The coated polarization layer 141 preferably has a degree of polarization of 45% or more. The degree of polarization may be defined as in Equation 1.

In Equation 1, P is the degree of polarization, T1 is the parallel transmittance obtained when a pair of polarizers are placed in a state in which absorption axes are parallel, and T2 is obtained when a pair of polarizers are placed in a state in which absorption axes are orthogonal to each other. Represents the orthogonal transmittance. A detailed description of the degree of polarization of the coated polarization layer 141 will be described later in connection with FIGS. 6A to 6C.

The coated polarization layer 141 is preferably formed to a thickness of 5 μm or less. This is because the white luminance of the liquid crystal display device is higher as the thickness of the coated polarization layer 141 is thinner. A detailed description of the thickness of the coated polarization layer 141 will be described later with reference to FIG. 7 .

The coated polarization layer 141 may be formed of either an E-type polarization layer or an O-type polarization layer, but is preferably formed of an E-type polarization layer. When the coated polarization layer 141 is formed of an E-type polarization layer, an optical axis of the coated polarization layer 141 may be aligned with a rubbing axis of the alignment layer. The reason why it is preferable that the coated polarization layer 141 is formed of an E-type polarization layer will be described later in conjunction with FIG. 8 .

The light-diffusing polarizer 142 includes a polarization layer 142a having a polarization function and a diffusion layer 142b having a diffusion function.

As shown in FIG. 5 , the polarization layer 142a may include a polarization film 1100 and a tri-acetate cellulose (TAC) film 1200 . The polarizing film 1100 may be a polyvinyl alcohol (PVA) film. The polarizing film 1100 may be manufactured by stretching a polyvinyl alcohol film in one direction and then adsorbing iodine (I) or a dichroic dye. The polarizing film 1100 has an absorption axis in a stretching direction and a transmission axis in a direction perpendicular to the absorption axis. That is, the polarization film 1100 may be a linear polarizer that emits only linearly polarized light in a direction parallel to a transmission axis among incident light.

The TAC film 1200 may be provided on the upper surface of the polarizing film 1100 . The TAC film 1200 preferably has durability so as to maintain the mechanical strength, heat resistance, and moisture resistance of the polarizing film 1100 . The TAC film 1200 preferably has non-optical properties so that the properties of light transmitted through the polarizing film 1100 are not changed.

The light absorption axis of the polarization layer 142a is the same as that of the coated polarization layer 141 . Due to this, the coated polarization layer 141 may absorb some light not absorbed by the polarization layer 142a of the light diffusing polarizer 142 . As a result, since the embodiment of the present invention can prevent an increase in black luminance due to a decrease in the polarization degree of the light diffusing polarizer 142 by using the coated polarization layer 141, it is possible to prevent a decrease in contrast ratio. . The contrast ratio represents black luminance against white luminance, white luminance represents luminance when the liquid crystal display expresses the peak white gray level, and black luminance represents the luminance when the liquid crystal display expresses the peak black gray level. represents the luminance when expressing .

The diffusion layer 142b of the light diffusing polarizer 142 diffuses light incident from the backlight unit 300 . The polarization layer 142a of the light diffusing polarizer 142 may be disposed below the coated polarization layer 141, and the diffusion layer 142b may be disposed below the polarization layer 142a. Since the light diffusing polarizing plate 142 is not formed by curing after coating like the coated polarizing layer 141 , an adhesive or adhesive film is required to adhere to the coated polarizing layer 141 . For example, the TAC film 1200 and the coated polarization layer 141 may be adhered using an adhesive or an adhesive film.

The upper polarizer 150 is disposed on the upper surface of the upper substrate 120 . The upper polarizing plate 150 may be attached to the upper surface of the upper substrate 120 using an adhesive or an adhesive film.

The upper polarizing plate 150 may include a polarizing film 1300 and a TAC film 1400 as shown in FIG. 5 . The polarizing film 1300 may be a polyvinyl alcohol (PVA) film. The polarizing film 1300 may be manufactured by stretching a polyvinyl alcohol film in one direction and then adsorbing iodine (I) or a dichroic dye. The polarizing film 1300 has an absorption axis in a stretching direction and a transmission axis in a direction perpendicular to the absorption axis. That is, the polarization film 1300 may be a linear polarizer that emits only linearly polarized light in a direction parallel to a transmission axis among incident light.

The TAC film 1400 may be provided on the lower surface of the polarizing film 1300 . The TAC film 1400 preferably has durability so as to maintain mechanical strength, heat resistance, and moisture resistance of the polarizing film 1300 . The TAC film 1400 preferably has non-optical properties so that the properties of light transmitted through the polarizing film 1300 are not changed. For example, the TAC film 1400 and the upper substrate 150 may be bonded using an adhesive or an adhesive film.

As described above, in the embodiment of the present invention, the lower polarizer 140 includes not only the light diffusive polarizer 142 but also the coated polarization layer 141, and the polarization layer 142a of the light diffusive polarizer 142. ) is formed to be the same as the light absorption axis of the coated polarization layer 141 . As a result, in the embodiment of the present invention, since the coated polarization layer 141 can absorb some of the light not absorbed by the polarization layer 142a of the light diffusing polarizer 142, the coated polarization layer 141 An increase in black luminance due to a decrease in polarization degree of the light-diffusing polarizer 142 can be prevented by using . Therefore, the embodiment of the present invention can prevent the contrast ratio from being lowered.

Meanwhile, in order to optimally adjust the black luminance, white luminance, and contrast ratio of the liquid crystal display, the polarization degree, thickness, and light transmittance of the coated polarization layer 141 must be adjusted within appropriate ranges. Hereinafter, polarization degree, thickness, and light transmittance of the coated polarization layer 141 will be described in detail with reference to FIGS. 6A to 6C and FIG. 7 .

6A to 6C are tables showing the change in contrast ratio according to the degree of polarization when the light transmittance of the coated polarization layer of FIG. 4 is 40%, 60%, and 65%. 6A to 6C , light transmittance (%), polarization degree (%), and thickness (μm) indicate light transmittance, polarization degree, and thickness of the coated polarization layer 141 . In FIGS. 6A to 6C , CR (%) represents the contrast ratio of the liquid crystal display of FIG. 4 . In FIGS. 6A to 6C , “Pol” indicates the linear polarizer of FIG. 5 , “One Pol” indicates the light diffusing polarizer 142 of FIG. 4 , and “CP” indicates the coated polarization layer 141 of FIG. 4 . indicate In addition, the coated polarization layer 141 in FIGS. 6A to 6C corresponds to an E-type polarization layer.

In the case of the prior art using a linear polarizer (Pol) as the upper polarizer 150 and a light-diffusing polarizer (One Pol) as the lower polarizer 140, as shown in FIGS. 6A to 6C, the contrast ratio (CR (%)) is very low at 8,991:1.

In FIG. 6A, the inventors of the present invention apply a linear polarizer (Pol) as the upper polarizer 150 and apply a polarizing layer (CP) coated with the lower polarizer 140 and a light diffusing polarizer (One Pol) in a liquid crystal display device. , The light transmittance of the coated polarization layer 141 was fixed at 40%, and the polarization degree was varied from 40% to 99% while the thickness was fixed at 1 μm, and the contrast ratio (CR (%)) of the liquid crystal display was measured. . In this case, the contrast ratio (CR (%)) tends to increase as the degree of polarization increases. For example, when the polarization degree of the coated polarization layer (CP) is 40%, the contrast ratio (CR (%)) is 18,355:1, and when the polarization degree is 95%, the contrast ratio (CR (%)) increases to 69,167:1 do. In addition, there is almost no difference in the contrast ratio (CR (%)) when the degree of polarization is 95% and 99%.

In FIG. 6B, the light transmittance of the coated polarization layer 141 is fixed at 60% and the polarization degree is varied from 40% to 65% while the thickness is fixed at 1 μm, and the contrast ratio (CR (%)) of the liquid crystal display is measured. In this case, when the polarization degree of the coated polarization layer (CP) is 40%, the contrast ratio (CR (%)) is 18,358: 1, and when the polarization degree is 65%, the contrast ratio (CR (%)) increases to 30,321: 1 .

In FIG. 6C, the light transmittance of the coated polarization layer 141 is fixed at 65% and the polarization degree is changed from 40% to 50% while the thickness is fixed at 1 μm, and the contrast ratio (CR (%)) of the liquid crystal display is measured. In this case, when the polarization degree of the coated polarization layer (CP) is 40%, the contrast ratio (CR (%)) is 18,358: 1, and when the polarization degree is 65%, the contrast ratio (CR (%)) increases to 22,215: 1 .

It is preferable that the contrast ratio (CR (%)) is 20,000:1 or more in order to look excellent in the image quality of the liquid crystal display. In order to satisfy this, it is preferable that the degree of polarization of the coated polarization layer 141 is 45% or more, as shown in FIGS. 6A to 6C. In particular, since the contrast ratio (CR (%)) increases as the polarization degree of the coated polarization layer 141 increases, in order to manufacture a liquid crystal display having a higher image quality with excellent contrast ratio (CR (%)), the coated polarization layer The degree of polarization of (141) can be increased, and this can be changed within a design changeable range by those skilled in the art.

On the other hand, as can be seen from FIGS. 6A to 6C , the contrast ratio (CR (%)) has no significant relationship with the light transmittance change of the coated polarization layer 141 . However, when the light transmittance of the coated polarization layer 141 is low, white luminance may decrease, so the light transmittance of the coated polarization layer 141 is preferably 45% or more.

As described above, in the embodiment of the present invention, it is preferable to form the polarization degree of the coated polarization layer 141 to 45% or more in order to maintain the contrast ratio (CR (%)) of the liquid crystal display at 20,000: 1 or more. Do. In addition, in the embodiment of the present invention, it is preferable to form the light transmittance of the coated polarization layer 141 to 45% or more in order to prevent the white luminance of the liquid crystal display from being lowered.

7 is a table showing a change in contrast ratio according to a change in thickness of a coated polarization layer. In FIG. 7 , light transmittance (%), polarization degree (%), and thickness (μm) indicate light transmittance, polarization degree, and thickness of the coated polarization layer 141 . In FIG. 7 , W transmittance (%) represents white luminance of the liquid crystal display, and B transmittance (%) represents black luminance of the liquid crystal display. In FIG. 7 , CR (%) represents the contrast ratio of the liquid crystal display of FIG. 4 . In FIG. 7 , “Pol” denotes the linear polarizer of FIG. 5 , “One Pol” denotes the light-diffusing polarizer 142 of FIG. 4 , and “CP” denotes the coated polarization layer 141 of FIG. 4 . In addition, the coated polarization layer 141 in FIG. 7 corresponds to an E-type polarization layer.

The inventors of the present invention, in FIG. 7, a linear polarizer (Pol) is applied as an upper polarizer 150 and a polarization layer (CP) coated with a lower polarizer 140 and a light diffusing polarizer (One Pol) are applied in a liquid crystal display device. , W transmittance (%), B transmittance (%) of the liquid crystal display while changing the thickness from 1 μm to 5 μm with the light transmittance of the coated polarization layer 141 fixed at 50% and the degree of polarization fixed at 72% ), and contrast ratio (CR (%)) were measured. In this case, W transmittance (%) and B transmittance decrease as the thickness of the coated polarization layer 141 increases, but contrast ratio CR (%) increases as the thickness of the coated polarization layer 141 increases. shows a tendency to That is, since the decrease in W transmittance (%) is greater than the decrease in B transmittance (%) as the thickness of the coated polarization layer 141 increases, the contrast ratio CR (%) increases. For example, when the thickness of the coated polarization layer (CP) is 5 μm, since the W transmittance (%) is reduced by 20% compared to the case where the thickness of the coated polarization layer (CP) is 1 μm, the thickness of the coated polarization layer (CP) is preferably 5 μm or less. .

As described above, in the embodiment of the present invention, it is preferable to form the thickness of the coated polarization layer 141 to 5 μm or less when considering the contrast ratio (CR (%)) and W transmittance (%) of the liquid crystal display device. In addition, the thickness of the coated polarization layer CP may be appropriately set in consideration of the contrast ratio (CR (%)) and the W transmittance (%).

8 is a table showing a change in contrast ratio according to polarization degree when the light transmittance of the coated polarization layer is 50% when the coated polarization layer is an O-type polarization layer. In FIG. 8 , light transmittance (%), polarization degree (%), and thickness (μm) indicate light transmittance, polarization degree, and thickness of the coated polarization layer 141 . In FIG. 8 , W transmittance (%) represents white luminance of the liquid crystal display, and B transmittance (%) represents black luminance of the liquid crystal display. In FIG. 8 , CR (%) represents the contrast ratio of the liquid crystal display of FIG. 4 . In FIG. 8 , “Pol” denotes the linear polarizer of FIG. 5 , “One Pol” denotes the light-diffusing polarizer 142 of FIG. 4 , and “CP” denotes the coated polarization layer 141 of FIG. 4 . The coated polarization layer 141 in FIGS. 6A to 6C is an E-type polarization layer, whereas the coated polarization layer 141 in FIG. 8 corresponds to an O-type polarization layer.

As shown in FIG. 8 , in the case of the prior art using a linear polarizer (Pol) as the upper polarizer 150 and a light-diffusing polarizer (One Pol) as the lower polarizer 140, the contrast ratio (CR (%)) is 8,991: 1 is very low.

In FIG. 8, the inventors of the present invention apply a linear polarizer (Pol) as the upper polarizer 150, and a polarization layer (CP) coated with an O-type polarizer layer and a light diffusing polarizer (One Pol) as the lower polarizer 140. In the applied liquid crystal display, the light transmittance of the coated polarization layer 141 is fixed at 50%, and the polarization degree is changed from 40% to 99% while the thickness is fixed at 1 μm, and the contrast ratio (CR ( %)) was measured. In this case, the contrast ratio (CR (%)) tends to increase as the degree of polarization increases, but the increase in the contrast ratio (CR (%)) is insignificant. For example, when the polarization degree of the coated polarization layer (CP) is 40%, the contrast ratio (CR (%)) is 9,577:1, and when the polarization degree is 99%, the contrast ratio (CR (%)) increases to 10,062:1 do.

As described above, as the degree of polarization increases, the increase in the contrast ratio (CR (%)) is insignificant and the contrast ratio (CR (%)) is not different from that of the prior art. In the case of using the layer-coated polarization layer (CP) and the light diffusing polarizer (One Pol), the conventional problem of lowering the contrast ratio (CR (%)) cannot be solved. Therefore, in an embodiment of the present invention, it is preferable to form the coated polarization layer 141 as an E-type polarization layer rather than an O-type polarization layer.

9 is a side view showing only a lower substrate, an upper substrate, a lower polarizing plate, and an upper polarizing plate of a liquid crystal display according to a second embodiment of the present invention. In FIG. 9 , only the lower substrate 110 , the upper substrate 120 , the lower polarizing plate 140 , and the upper polarizing plate 150 of the display panel 100 are illustrated for convenience of description.

Referring to FIG. 9 , the lower polarizer 140 is disposed under the lower surface of the lower substrate 110 . The lower polarizing plate 140 may be attached to the lower surface of the lower substrate 110 using an adhesive or an adhesive film.

The lower polarizing plate 140 may include the polarizing film 1100 and the TAC film 1200 shown in FIG. 5 . The polarizing film 1100 and the TAC film 1200 are substantially the same as those described in connection with FIGS. 4 and 5 .

The upper polarizing plate 150 includes a coated polarizing layer 151 and a light diffusing polarizing plate 152 . The coated polarization layer 151 is disposed on the upper surface of the upper substrate 120 .

The coated polarization layer 151 may be formed by being applied on the upper surface of the upper substrate 120 and then cured by heat or ultraviolet rays. That is, since the coated polarization layer 151 is directly formed on the upper surface of the upper substrate 120, the coated polarization layer 151 and the upper substrate 120 are interposed between the coated polarization layer 151 and the upper substrate 120. ) does not require a separate adhesive or adhesive film to adhere.

Since the coated polarization layer 151 is substantially the same as the coated polarization layer 141 described in conjunction with FIG. 4 , a detailed description thereof will be omitted.

The light-diffusing polarizer 152 includes a polarization layer 152a having a polarization function and a diffusion layer 152b having a diffusion function.

The polarization layer 152a may include the polarization film 1300 and the TAC film 1400 shown in FIG. 5 . The polarization film 1300 and the TAC film 1400 are substantially the same as those described in connection with FIGS. 4 and 5 .

The light absorption axis of the polarization layer 152a is the same as that of the coated polarization layer 151 . Due to this, the coated polarization layer 151 may absorb some of the light not absorbed by the polarization layer 152a of the light diffusing polarizer 152 .

The diffusion layer 152b of the light diffusing polarizer 152 diffuses light emitted from the display panel 100 . The polarization layer 152a of the light diffusing polarizer 152 may be disposed on the coated polarization layer 151, and the diffusion layer 152b may be disposed on the polarization layer 152a. The light diffusing polarizer 152 may be adhered to the coated polarization layer 151 using an adhesive or an adhesive film. For example, the TAC film 1400 and the coated polarization layer 151 may be adhered using an adhesive or an adhesive film.

Hereinafter, the contrast ratio of the liquid crystal display according to the second embodiment of the present invention will be described in detail in connection with FIGS. 10A to 10C.

10A to 10C are tables showing changes in contrast ratio according to polarization degree when the light transmittance of the upper polarizer is 40%, 60%, and 65%. In FIGS. 10A to 10C , light transmittance (%), polarization degree (%), and thickness (μm) indicate light transmittance, polarization degree, and thickness of the coated polarization layer 151 of FIG. 9 . In FIGS. 10A to 10C , CR (%) represents the contrast ratio of the liquid crystal display of FIG. 9 . In FIGS. 10A to 10C, "Pol" indicates the linear polarizer of FIG. 5, "One Pol" indicates the light diffusing polarizer 152 of FIG. 9, and "CP" indicates the coated polarization layer 151 of FIG. indicate In addition, the coated polarization layer 151 in FIGS. 10A to 10C corresponds to an E-type polarization layer.

In FIG. 10A, the inventors of the present invention apply a linear polarizer (Pol) as the lower polarizer 140 and apply a polarizing layer (CP) coated with the upper polarizer 150 and a light diffusing polarizer (One Pol) in a liquid crystal display device. , The light transmittance of the coated polarization layer 151 was fixed at 40%, and the polarization degree was varied from 40% to 99% while the thickness was fixed at 1 μm, and the contrast ratio (CR (%)) of the liquid crystal display was measured. . In this case, the contrast ratio (CR (%)) tends to increase as the degree of polarization increases, but the increase in the contrast ratio (CR (%)) is insignificant. For example, when the polarization degree of the coated polarization layer (CP) is 40%, the contrast ratio (CR (%)) is 9,577:1, and when the polarization degree is 99%, the contrast ratio (CR (%)) increases to 10,038:1 do.

In FIG. 10B, the light transmittance of the coated polarization layer 141 is fixed at 60% and the polarization degree is varied from 40% to 65% while the thickness is fixed at 1 μm, and the contrast ratio (CR (%)) of the liquid crystal display is measured. In this case, when the polarization degree of the coated polarization layer (CP) is 40%, the contrast ratio (CR (%)) is 9,577: 1, and when the polarization degree is 99%, the contrast ratio (CR (%)) increases to 9,819: 1 .

In FIG. 10C, the light transmittance of the coated polarization layer 141 is fixed at 65% and the polarization degree is changed from 40% to 50% while the thickness is fixed at 1 μm, and the contrast ratio (CR (%)) of the liquid crystal display is measured. In this case, when the polarization degree of the coated polarization layer (CP) is 40%, the contrast ratio (CR (%)) is 9,577: 1, and when the polarization degree is 99%, the contrast ratio (CR (%)) increases to 9,682: 1 .

As described above, as the degree of polarization increases, the increase in the contrast ratio (CR (%)) is insignificant, and the contrast ratio (CR (%)) is compared to the conventional contrast ratio (CR (%)) shown in FIGS. 6A to 6C. Since there is no difference, in the case of a liquid crystal display in which a linear polarizer (Pol) is applied as the lower polarizer 140 and a polarization layer (CP) coated with the upper polarizer 150 and a light diffusing polarizer (One Pol) are applied, The problem of the prior art in which the contrast ratio (CR (%)) is lowered cannot be solved. That is, in the embodiment of the present invention, it is preferable to apply a linear polarizer (Pol) as the upper polarizer 150 and apply a coated polarization layer (CP) and a light diffusing polarizer (One Pol) as the lower polarizer 140. .

As described above, in the embodiment of the present invention, the lower polarizer 140 includes not only the light diffusive polarizer 142 but also the coated polarization layer 141, and the polarization layer 142a of the light diffusive polarizer 142. ) is formed to be the same as the light absorption axis of the coated polarization layer 141 . As a result, in the embodiment of the present invention, since the coated polarization layer 141 can absorb some of the light not absorbed by the polarization layer 142a of the light diffusing polarizer 142, the coated polarization layer 141 An increase in black luminance due to a decrease in polarization degree of the light-diffusing polarizer 142 can be prevented by using . Therefore, the embodiment of the present invention can prevent the contrast ratio from being lowered.

Although the embodiments of the present invention have been described in more detail with reference to the accompanying drawings, the present invention is not necessarily limited to these embodiments, and may be variously modified and implemented without departing from the technical spirit of the present invention. . Therefore, the embodiments disclosed in the present invention are not intended to limit the technical idea of the present invention, but to explain, and the scope of the technical idea of the present invention is not limited by these embodiments. Therefore, it should be understood that the embodiments described above are illustrative in all respects and not restrictive. The protection scope of the present invention should be construed according to the scope of the claims, and all technical ideas within the scope equivalent thereto should be construed as being included in the scope of the present invention.

100: display panel 110: lower substrate
120: upper substrate 140: lower polarizer
150: upper polarizer 141: coated polarizer
142: light-diffusing polarizing plate 142a: polarizing layer
142b: diffusion layer 210: source driving circuit
220: source flexible film 230: circuit board
240: light source driving unit 241: light source driving circuit
242: light source circuit board 300: backlight unit
310: light source 320: light source circuit board
330: light guide plate 340: reflective sheet
350: optical sheets 410: bottom cover
420: support frame 430: top case

Claims (8)

a display panel including a lower substrate to which a lower polarizer is attached, an upper substrate to which an upper polarizer is attached, and a liquid crystal layer between the lower substrate and the upper substrate;
a backlight unit irradiating light to the display panel;
a support frame supporting a lower surface of the lower polarizer; and
A buffer member disposed between the lower polarizing plate and the support frame,
The lower polarizer,
a coated polarization layer disposed on one surface of the lower substrate facing the backlight unit; and
A light-diffusing polarizer having a polarization layer disposed below the coated polarization layer and a diffusion layer disposed below the polarization layer and diffusing light from the backlight unit;
The coated polarization layer includes discotic liquid crystal,
The light transmittance of the coated polarization layer is 40%,
The polarization degree of the coated polarization layer is 45% or more and 90% or less,
The thickness of the coated polarization layer is 1um,
When a linear polarizer is applied as the upper polarizer and the coated polarizer and the light-diffusing polarizer are applied as the lower polarizer, the contrast ratio is 20165: 1 or more and 58331: 1 or less. According to claim 1,
A light absorption axis of the coated polarization layer and a light absorption axis of the polarization layer are the same as each other. According to claim 1,
The coated polarizing layer and the light diffusing polarizing plate are bonded with an adhesive or an adhesive film. According to claim 1,
The coated polarization layer is in direct contact with one surface of the lower substrate liquid crystal display. delete delete delete delete

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