JP2008026781A - Liquid crystal display - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a liquid crystal display wherein deterioration of a visual field angle is improved without deteriorating display characteristics of a front surface with a simple structure. <P>SOLUTION: In the liquid crystal display 100 provided with a backlight unit 20, a linearly polarized light separating layer 11 separating incident light into transmission light and reflection light of linearly polarized light, a first polarizing plate 13, a liquid crystal cell 15 comprising a pair of substrates 15a and 15b disposed opposite to each other and having a transparent electrode on at least one inner surface thereof and a liquid crystal layer 15b interposed between the substrates 15a and 15b and a second polarizing plate 17 in this order, a retardation layer 12 having birefringence having positive or negative uniaxiality to an optical axis in a direction vertical to a transmission axis of the first polarizing plate 13 is provided between the linearly polarized light separating layer 11 and the first polarizing plate 13. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a liquid crystal display device with improved viewing angle degradation.

  Compared with a display device using a conventional cathode ray tube (CRT), the liquid crystal display device has features such as low power consumption, low voltage operation, light weight, and thinness. It is rapidly spreading as a display device. However, it has been pointed out that the liquid crystal display device has a problem in that the contrast and chromaticity differ from the original display characteristics depending on the viewing angle (the angle dependence of such display characteristics is hereinafter referred to as viewing angle deterioration).

  The reason why the viewing angle is deteriorated in this manner is that the liquid crystal display device performs display using a polarizing plate and a liquid crystal cell. The polarizing plate has a characteristic of transmitting only light of a specific polarization plane. For this reason, the transmission axis and absorption axis of the polarizing plate must maintain a certain angular relationship with respect to the polarization plane (FIG. 1 (a)). . However, when viewed from an oblique direction, this relationship is lost (FIG. 1B), and unexpected light is emitted (light leakage). In addition, the amount of change in the polarization plane of light varies depending on the angle of the liquid crystal cell itself, which can cause light leakage.

  Therefore, in the conventional technique, a retardation film is disposed between the light source side polarizing plate and the viewer side polarizing plate, and the angle relationship with the absorption axis of the polarizing plate is maintained by appropriately bending the polarization plane. However, it is difficult to sufficiently suppress the viewing angle deterioration with a certain film. This is because the appropriate phase difference value varies depending on the angle of the observer and the wavelength to be compensated.

  As an example, consider compensation for a polarizing plate. FIG. 2A shows the relationship of black luminance at an azimuth angle of 45 ° with respect to the polarizing plate with only the polarizing plate, and FIG. 2B shows the relationship of black luminance with an elevation angle of 60 ° with respect to the polarizing plate with only the polarizing plate. Show. When viewed obliquely, the orthogonal relationship between the transmission axis and the absorption axis of the polarizing plate is broken (FIG. 1 (b)), and the black luminance increases (light leakage) as the elevation angle increases in the vicinity of an azimuth angle of 45 ° (in perspective).

  Accordingly, when the polarizing plate is viewed in an XYZ orthogonal coordinate system, a liquid crystal cell is formed by combining a Positive A-Plate film in which nx> ny = nz and a Positive C-Plate in which nx = ny <nz as a relationship of refractive indexes in respective directions. Considering the case of being arranged inside, the relationship of black luminance at an azimuth angle of 45 ° is as shown in FIG. 3A, and the relationship of black luminance at an elevation angle of 60 ° is as shown in FIG. Thus, even if the elevation angle is increased as shown in FIG. 3, the black luminance does not increase as compared with FIG. That is, the light leakage is improved.

  However, various problems arise when the retardation film is arranged inside the polarizing plate in this way. For example, providing two retardation layers increases the cost. Further, the haze of the retardation film is also a problem. Furthermore, by disposing a film having haze between the polarizing plates, the plane of polarization is broken, and light leakage occurs from both the front and the diagonal.

  The problem of misalignment is also serious. The retardation film must maintain a right-angle or parallel relationship with the polarizing plate. If the positive A-plate is shifted by 0.5 ° from the angle of the polarizing plate, the front black luminance is 1 .4 times. That is, when viewed from the front, the black display state is blurred. Therefore, high accuracy is required for the bonding of the film and the polarizing plate in order to prevent the problem caused by the misalignment. In addition, even if the bonding is successful, the optical axis distribution is included in the retardation film by about 0.5 °, so the use of the retardation film increases the black luminance as viewed from the front. There's a problem.

  As described above, an attempt to solve the viewing angle deterioration by disposing the retardation film between the polarizing plates may deteriorate the front display performance. Therefore, an attempt to solve the viewing angle deterioration outside the polarizing plate has been proposed. For example, in Patent Document 1, a pixel-size partition is arranged outside the viewer-side polarizing plate of the liquid crystal display device, and light leaking from an oblique direction is cut, so that the display characteristics in the black display on the front side are impaired by a single film. The viewing angle degradation is improved without any problems. However, there are problems that the processing cost for making the partition is high, and that the light component that cannot be transmitted by the partition is generated, and thus the front luminance in the white display state is lowered.

JP 58-215687 A

  The present invention has been made in view of the above problems in the prior art, and an object of the present invention is to provide a liquid crystal display device that improves the viewing angle deterioration with a simple structure without deteriorating the front display characteristics.

  The present invention provided to solve the above-described problems includes a backlight unit, a linearly polarized light separating layer that separates incident light into linearly polarized transmitted light and reflected light, a first polarizing plate, and at least disposed oppositely. A liquid crystal display device comprising a liquid crystal cell comprising a pair of substrates having a transparent electrode on one inner surface and a liquid crystal layer sandwiched between the substrates, and a second polarizing plate in this order, wherein the linearly polarized light separation A retardation layer having a positive uniaxial or negative uniaxial birefringence about the optical axis perpendicular to the transmission axis of the first polarizing plate is provided between the layer and the first polarizing plate. A liquid crystal display device characterized in that (claim 1).

Here, in the invention of claim 1, the retardation layer preferably has a retardation Rth in the film thickness direction defined by the following formula of 550 nm or more and 1100 nm or less.
Rth = | {(nx−ny) / 2−nz} × (retardation layer thickness) |
(Here, nx and ny are parallel to the transmission axis of the first polarizing plate and are in the direction perpendicular to the plane of the retardation layer, and nz is the transmission axis of the first polarizing plate. (It is the refractive index in the thickness direction of the retardation layer perpendicular to the direction.)

  The present invention provided to solve the above-described problems includes a backlight unit, a linearly polarized light separating layer that separates incident light into linearly polarized transmitted light and reflected light, a first polarizing plate, and at least disposed oppositely. A liquid crystal display device comprising a liquid crystal cell comprising a pair of substrates having a transparent electrode on one inner surface and a liquid crystal layer sandwiched between the substrates, and a second polarizing plate in this order, wherein the linearly polarized light separation A retardation layer having a positive uniaxial or negative uniaxial birefringence about the optical axis parallel to the transmission axis of the first polarizing plate is provided between the layer and the first polarizing plate. A liquid crystal display device characterized in that (claim 3).

Here, in the invention of claim 3, the retardation layer preferably has an in-plane retardation Ro defined by the following formula of 210 nm or more and 350 nm or less.
Ro = | (nx−ny) × (retardation layer film thickness) |
(Here, nx and ny are refractive indexes in a direction parallel to the transmission axis of the first polarizing plate and perpendicular to the plane of the retardation layer.)

  The present invention provided to solve the above-described problems includes a backlight unit, a linearly polarized light separating layer that separates incident light into linearly polarized transmitted light and reflected light, a first polarizing plate, and at least disposed oppositely. A liquid crystal display device comprising a liquid crystal cell comprising a pair of substrates having a transparent electrode on one inner surface and a liquid crystal layer sandwiched between the substrates, and a second polarizing plate in this order, wherein the linearly polarized light separation A retardation layer having biaxial birefringence about the optical axis perpendicular to and parallel to the transmission axis of the first polarizing plate is provided between the layer and the first polarizing plate. (5).

Here, in the invention of claim 5, the retardation layer has a thickness direction retardation Rth defined by the following formula of 550 nm or more and 1100 nm or less, and an in-plane retardation Ro of 210 nm or more and 350 nm. The following is preferable.
Rth = | {(nx−ny) / 2−nz} × (retardation layer thickness) |
Ro = | (nx−ny) × (retardation layer film thickness) |
(Here, nx and ny are parallel to the transmission axis of the first polarizing plate and are in the direction perpendicular to the plane of the retardation layer, and nz is the transmission axis of the first polarizing plate. (It is the refractive index in the thickness direction of the retardation layer perpendicular to the direction.)

  According to the present invention, light that is not expected by reducing the transmittance of oblique light without impairing the front display performance by the retardation layer provided between the linearly polarized light separating layer and the first polarizing plate. Can be reduced. In particular, leakage light can be cut off in the black display state.

The configuration of the liquid crystal display device according to the present invention will be described below.
FIG. 4 is a cross-sectional view showing the configuration of the liquid crystal display device according to the present invention.
The liquid crystal display device 100 includes a backlight unit 20, a linearly polarized light separating layer 11 that separates incident light into linearly polarized transmitted light and reflected light, a first polarizing plate 13, and at least one inner surface disposed to face each other. A liquid crystal cell 15 composed of a pair of substrates 15a and 15c having transparent electrodes and a liquid crystal layer 15b sandwiched between the substrates 15a and 15c, and a second polarizing plate 17 are arranged in this order, and linearly polarized light A retardation layer 12 having a predetermined birefringence is provided between the separation layer 11 and the first polarizing plate 13. In addition, retardation plates 14 and 16 may be provided between the first polarizing plate 13 and the substrate 15a and between the substrate 15c and the second polarizing plate 17, respectively.

  Here, the linearly polarized light separating layer 11 may be a known linearly polarized light separating element. For example, natural light is separated into reflected and transmitted light composed of linearly polarized light by a Brewster angle through a multilayer film with a dielectric thin film superimposed, or a multilayer film with a birefringent dielectric thin film superimposed Any suitable light can be used such as natural light separated into reflected light and transmitted light made of linearly polarized light. In FIG. 4, the linearly polarized light separating layer 11 transmits linearly polarized light (P wave) having a P-polarized component, and reflects linearly polarized light (S wave) having an S-polarized component.

  The retardation layer 12 forms the basis of the present invention, and a part of the linearly polarized light incident obliquely from the linearly polarized light separating layer 11 is made a different straight line without impairing the display characteristics viewed from the front of the liquid crystal display device 100. It is changed to polarized light. In FIG. 4, the retardation layer 12 changes a part of light (all P wave components) incident obliquely from the linearly polarized light separating layer 11 to S waves. In order to realize this, the retardation layer 12 may be any one of the following three forms, for example.

(Embodiment 1) The retardation layer 12 exhibits positive uniaxial (nx = ny <nz) or negative uniaxial (nx = ny> nz) birefringence with respect to the film thickness direction of the first polarizing plate 13. That is, it has positive uniaxial or negative uniaxial birefringence about the optical axis perpendicular to the transmission axis of the first polarizing plate 13. As the retardation layer 12, a layer having a larger retardation value as the incident angle (outgoing angle) becomes larger is preferable. This is because when viewed from the front of the liquid crystal display device 100, the display characteristics do not change so much, and when viewed from an oblique direction, the light leakage component is reduced according to the angle to produce a desired display color.

In this case, the retardation layer 12 preferably has a retardation Rth in the film thickness direction defined by the following formula (1) of 550 nm or more and 1100 nm or less.
Rth = | {(nx−ny) / 2−nz} × (retardation layer film thickness) | (1)
(Here, nx and ny are parallel to the transmission axis of the first polarizing plate 13 and are in the direction perpendicular to the plane of the retardation layer, and nz is the transmission axis of the first polarizing plate 13. (It is the refractive index in the thickness direction of the retardation layer perpendicular to the direction.)

(Mode 2) The retardation layer 12 exhibits positive uniaxial (nx> ny = nz) or negative uniaxial (nx <ny = nz) birefringence with respect to the in-plane direction of the first polarizing plate 13. That is, it has positive uniaxial or negative uniaxial birefringence about the optical axis parallel to the transmission axis of the first polarizing plate 13.

In this case, the retardation layer 12 preferably has an in-plane retardation Ro defined by the following formula (2) of 210 nm or more and 350 nm or less.
Ro = | (nx−ny) × (retardation layer film thickness) | (2)
(Here, nx and ny are refractive indexes in a direction parallel to the transmission axis of the first polarizing plate and perpendicular to the plane of the retardation layer.)

(Mode 3) The retardation layer 12 has biaxial birefringence (different in nx, ny, and nz) about the optical axis in the direction perpendicular to and parallel to the transmission axis of the first polarizing plate 13. And

  In this case, the retardation layer 12 has a retardation Rth in the film thickness direction defined by the formulas (1) and (2) of 550 nm or more and 1100 nm or less, and an in-plane retardation Ro of 210 nm or more. It is preferable that it is 350 nm or less.

  In addition, what kind of phase difference layer 12 should just be suitably selected from a conventionally well-known thing. For example, polycarbonate, polyester, polyimide, polyethersulfone, polysulfone, polystyrene, polyvinyl alcohol, polyarylate, polyvinyl chloride, polyvinylidene chloride, polyacryl, polyamide, epoxy, Examples thereof include stretched films made of cellulose, polyolefins such as polyethylene and polypropylene, and films obtained by aligning and curing liquid crystalline molecules.

  In particular, the liquid crystalline film is preferable because the adjustment of the retardations Rth and Ro is achieved by adjusting the thickness of the retardation layer 12.

  The first polarizing plate 13 and the second polarizing plate 17 are arranged on both sides of the liquid crystal cell 15 and are arranged so that their transmission axes (polarization axes) are substantially orthogonal to each other. The first polarizing plate 13 is arranged so that the transmission axis direction thereof is aligned with the axial direction of linearly polarized light (P wave in FIG. 4) transmitted through the linearly polarized light separating layer 11.

  As the 1st polarizing plate 13 and the 2nd polarizing plate 17, a thing with a high degree of polarization, especially 95% or more, and especially 99% or more can be used preferably. Incidentally, as a polarizing plate with a high degree of polarization, for example, a film of a hydrophilic polymer such as polyvinyl alcohol, partially formalized polyvinyl alcohol, or ethylene / vinyl acetate copolymer partially saponified, iodine and / or dichroism. Examples thereof include an absorbing polarizing film obtained by adsorbing a dye and subjected to a stretching treatment. Moreover, you may have a protective film in the one side or both sides of this polarizing film.

  The liquid crystal cell 15 is not particularly limited as long as it functions as a liquid crystal shutter, and a usable one is appropriately used. In the present invention, linearly polarized light (P wave in FIG. 4) is incident on the liquid crystal cell 15 for display, and for example, twisted nematic liquid crystal or super twisted nematic liquid crystal can be preferably used as the liquid crystal layer 15b. A guest-host liquid crystal or a ferroelectric liquid crystal in which a base liquid crystal or a dichroic dye is dispersed in the liquid crystal may be used. Further, the driving method of the liquid crystal is not particularly limited.

  The retardation plates 14 and 16 are intended to improve visibility by compensating for the wavelength dependence of birefringence, etc., and may be appropriately used depending on the wavelength region and the like. What is necessary is just to use.

  The backlight unit 20 may be a conventionally known light source for a liquid crystal display device, and may be an illumination device that serves as a surface light source such as a sidelight or an EL lamp using a light guide plate.

  In the liquid crystal display device 100, of the P waves emitted from the linearly polarized light separating layer 11, the light incident on and emitted from the front surface of the backlight unit 20 to the linearly polarized light separating layer 11 is reflected on the polarization plane of the retardation layer 12. No change occurs and the display characteristics are not impaired when viewed from the front of the liquid crystal display device 100.

On the other hand, the light L ₀ incident on the linearly polarized light separating layer 11 obliquely becomes light L ₁ emitted obliquely as a P wave by the linearly polarized light separating layer 11. Subsequently, the polarization plane of the light L ₁ is changed by the phase difference layer 12, and the light L ₁ becomes light L ₂ in which the P wave component is reduced and the S wave component is increased. Thereafter, the light L ₂ is incident on the first polarizing plate 13, but only the P wave component of the light L ₂ is transmitted through the first polarizing plate 13. Therefore, the intensity of light transmitted through the first polarizing plate 13 can be reduced by the amount of the S wave component of the light L ₂ as compared with the conventional case (in the case where the phase difference layer 12 is not provided), and finally recognized by the viewer. It is possible to reduce light leakage. In addition, it can be said that the viewing angle is further improved by using the phase difference layer 12 so that the obliquely incident component is not emitted as light leakage.

  Hereinafter, the example which implemented the present invention and checked the effect is explained. In this embodiment, in order to eliminate the influence of the liquid crystal cell and clarify the effect of the present invention, the liquid crystal cell 15 and the retardation plates 14 and 16 are excluded from the configuration of the liquid crystal display device 100 shown in FIG. Then, a model comprising a linearly polarized light separating layer 11, a retardation layer 12, and polarizing plates 13 and 17 as shown in FIG. It should be noted that the viewing angle improvement effect shown in the present embodiment can be expressed in the liquid crystal display device 100 as well.

(Example 1)
In the present embodiment, among those shown in the form 1 as the form of the retardation layer 12, those having positive uniaxial birefringence about the optical axis perpendicular to the transmission axis of the first polarizing plate 13 are used. Using. Specifically, nx and ny are parallel to the transmission axis of the first polarizing plate 13 and perpendicular to the direction of the retardation layer, and nz is the transmission axis of the first polarizing plate 13. When the refractive index in the thickness direction of the retardation layer is perpendicular to the above, there is a relationship of nx = ny <nz, and the refraction of nx = ny = 1.5 and nz = 1.6375 at a wavelength of 550 nm. Positive-C plates with a rate were used.

  Here, by changing each refractive index nx, ny, nz and film thickness of the retardation layer 12, the retardation Rth in the film thickness direction defined by the equation (1) is changed in the range of 0 to 1650 nm, The maximum value of black luminance at an elevation angle of 60 ° in each case was determined. The results are shown in Table 1.

  As a result, it was found that when the retardation Rth in the film thickness direction is 1500 nm or less, the viewing angle is improved in any case. Furthermore, it was found that Rth = 550 to 1100 nm is an appropriate retardation value. In addition, since the retardation layer 12 is disposed outside the first polarizing plate 13 in this embodiment, the display quality viewed from the front is not impaired due to haze, axial misalignment, or the like.

  In the present embodiment, the retardation layer 12 has a negative uniaxial birefringence about the optical axis perpendicular to the transmission axis of the first polarizing plate 13, for example, a relationship of nx = ny> nz. When using a Negative-C plate with the same results as in Table 1. When Rth = | {(nx−ny) / 2−nz} × (retardation layer film thickness) | is defined, the positive and negative values of {(nx−ny) / 2−nz} are reversed. However, the value of Rth is the same. Therefore, the relationship between Rth and the maximum value of black luminance in Table 1 is the same.

(Example 2)
In the present embodiment, among those shown in the form 2 as the form of the retardation layer 12, those having positive uniaxial birefringence about the optical axis parallel to the transmission axis of the first polarizing plate 13 are used. Using. Specifically, nx and ny are parallel to the transmission axis of the first polarizing plate 13 and perpendicular to the direction of the retardation layer, and nz is the transmission axis of the first polarizing plate 13. When the refractive index in the thickness direction of the retardation layer is perpendicular to the above, there is a relationship of nx> ny = nz, and refraction of nx = 1.6375 and ny = nz = 1.5 at a wavelength of 550 nm. Positive-A plates with rates were used.

  Here, by changing each refractive index nx, ny, nz and film thickness of the retardation layer 12, the in-plane retardation Ro defined by the formula (2) is changed in the range of 0 to 560 nm, respectively. In this case, the maximum value of black luminance at an elevation angle of 60 ° was obtained. The results are shown in Table 2.

  As a result, it was found that when the in-plane retardation Ro was 560 nm or less, the viewing angle was improved in any case. Further, it was found that Ro = 210 to 350 nm is an appropriate retardation value. In addition, since the retardation layer 12 is disposed outside the first polarizing plate 13 in this embodiment, the display quality viewed from the front is not impaired due to haze, axial misalignment, or the like.

  In this embodiment, the retardation layer 12 has negative uniaxial birefringence about the optical axis parallel to the transmission axis of the first polarizing plate 13, for example, a relationship of nx <ny = nz. When using a Negative-A plate with the same results as in Table 2. When Ro = | (nx−ny) × (retardation layer film thickness) | is defined, the value of (nx−ny) is reversed between positive and negative, but the value of Ro is the same. Therefore, the relationship between Rth and the maximum value of black luminance in Table 2 is the same.

  Further, the effect of the present invention can be obtained even when the retardation layer 12 is not limited to the one having biaxial birefringence as in the first and second embodiments but is biaxial (differs in nx, ny, and nz). It is done.

It is a figure explaining the light leakage at the time of seeing a liquid crystal display device from diagonally. It is a figure which shows the black luminance distribution in the case of only a polarizing plate. It is a figure which shows a black luminance distribution at the time of combining a polarizing plate and two phase difference plates. It is sectional drawing which shows the structure of the liquid crystal display device which concerns on this invention. It is sectional drawing which shows the structure of the evaluation model used in the Example.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1a, 1b ... Polarizing plate, 11 ... Linearly polarized light separation layer, 12 ... Retardation layer, 13 ... 1st polarizing plate, 14, 16 ... Retardation plate, 15 ... Liquid crystal cell, 15a, 5c ... substrate, 15b ... liquid crystal layer, 17 ... second polarizing plate, 20 ... backlight unit, 100 ... liquid crystal display device

Claims (6)

A backlight unit; a linearly polarized light separating layer that separates incident light into linearly polarized transmitted light and reflected light; a first polarizing plate; a pair of substrates having transparent electrodes on at least one inner surface disposed oppositely; A liquid crystal display device comprising a liquid crystal cell comprising a liquid crystal layer sandwiched between substrates and a second polarizing plate in this order,
A position having positive uniaxial or negative uniaxial birefringence about the optical axis perpendicular to the transmission axis of the first polarizing plate between the linearly polarized light separating layer and the first polarizing plate. A liquid crystal display device comprising a retardation layer. 2. The liquid crystal display device according to claim 1, wherein the retardation layer has a retardation Rth in a film thickness direction defined by the following formula of 550 nm or more and 1100 nm or less.
Rth = | {(nx−ny) / 2−nz} × (retardation layer thickness) |
(Here, nx and ny are parallel to the transmission axis of the first polarizing plate and are in the direction perpendicular to the plane of the retardation layer, and nz is the transmission axis of the first polarizing plate. (It is the refractive index in the thickness direction of the retardation layer perpendicular to the direction.) A backlight unit; a linearly polarized light separating layer that separates incident light into linearly polarized transmitted light and reflected light; a first polarizing plate; a pair of substrates having transparent electrodes on at least one inner surface disposed oppositely; A liquid crystal display device comprising a liquid crystal cell comprising a liquid crystal layer sandwiched between substrates and a second polarizing plate in this order,
A position having positive uniaxial or negative uniaxial birefringence with respect to the optical axis parallel to the transmission axis of the first polarizing plate between the linearly polarized light separating layer and the first polarizing plate. A liquid crystal display device comprising a retardation layer. The liquid crystal display device according to claim 3, wherein the retardation layer has an in-plane retardation Ro defined by the following formula of 210 nm or more and 350 nm or less.
Ro = | (nx−ny) × (retardation layer film thickness) |
(Here, nx and ny are refractive indexes in a direction parallel to the transmission axis of the first polarizing plate and perpendicular to the plane of the retardation layer.) A backlight unit; a linearly polarized light separating layer that separates incident light into linearly polarized transmitted light and reflected light; a first polarizing plate; a pair of substrates having transparent electrodes on at least one inner surface disposed oppositely; A liquid crystal display device comprising a liquid crystal cell comprising a liquid crystal layer sandwiched between substrates and a second polarizing plate in this order,
A retardation layer having biaxial birefringence about the optical axis perpendicular to and parallel to the transmission axis of the first polarizing plate between the linearly polarized light separating layer and the first polarizing plate. A liquid crystal display device comprising: The retardation layer has a retardation Rth in the film thickness direction defined by the following formula of 550 nm or more and 1100 nm or less, and an in-plane retardation Ro of 210 nm or more and 350 nm or less. 5. A liquid crystal display device according to 5.
Rth = | {(nx−ny) / 2−nz} × (retardation layer thickness) |
Ro = | (nx−ny) × (retardation layer film thickness) |
(Here, nx and ny are parallel to the transmission axis of the first polarizing plate and are in the direction perpendicular to the plane of the retardation layer, and nz is the transmission axis of the first polarizing plate. (It is the refractive index in the thickness direction of the retardation layer perpendicular to the direction.)

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