JP2002277867A - Color display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce imprinting phenomenon in comparison with that of conventional devices and to extend an RGB display color reproducing area. SOLUTION: A color display device is provided with: a planar illuminator 10, which has a white light source 11 and radiates light of this white light source like a surface; and a non-light-emitting color image display device 20 which has a three primary color separating means 23 and which receives light emitted from the planar illuminator as illuminating light and separates the illuminating light into the three primary colors, with respect to each of pixels arranged two-dimensionally on a plane, and modulates the transmittance or the reflectance to display an image; and a color-emphasizing filter which has a plurality of laminated double refraction films 30 and at least one polarizing element 40 and emphasizes the main light emission peak of the three primary colors of the white light source.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to a color display device.

[0002]

2. Description of the Related Art In recent years, a color liquid crystal display (hereinafter, also referred to as a color LCD), which is a non-emission type color display device using a liquid crystal instead of a CRT (Cathode Ray Tube), is becoming widespread. As shown in FIG. 33, a general structure of a color LCD is to uniformly illuminate a white light source 11 such as a cold cathode fluorescent tube, the light of the light source 11 and the light reflected by the reflector 12 in a planar manner. Light guide 13, reflector 1
4, a backlight unit 10 including a diffused light condensing film 15, a liquid crystal display element 20 for displaying an image,
Consists of The liquid crystal display element 20 includes a liquid crystal including an incident side polarizing plate 21, an RGB color filter (not shown), a liquid crystal layer (not shown), an alignment film (not shown), and an electrode (not shown). Panel 22 and output-side polarizing plate 29
And White light emitted from the backlight unit 10 as illumination light is converted from non-polarized light to linearly polarized light when passing through the incident-side polarizing plate 21 of the liquid crystal display element 20, and further provided in the liquid crystal panel 22 for each pixel. RGB
The color filters are separated into RGB colors. RG
The incident polarized light separated into the B color has its polarization state modulated in accordance with the arrangement of the liquid crystal molecules electrically controlled for each pixel, and the output side polarizing plate 29 provided on the output surface of the liquid crystal display element 20.
, The ON / OFF display is performed. In many cases, the color filter is located not on the light incident side but on the output side with respect to the liquid crystal layer.

As described above, in a color LCD, color separation is performed by using an RGB color filter. However, the colorant of the color filter is a pigment or a dye, and generally has a high spectral purity because the spectral transmittance is not steep. There is a problem that it is difficult to perform color separation into RGB colors. Therefore, a three-wavelength fluorescent tube using a fluorescent material having a main emission peak in each of the RGB wavelength ranges as a white light source is generally used as a light source.

[0004]

However, with the widespread use of color LCDs, RGB colors having higher purity than before have been required for television applications and the like, and optimization with the conventional configuration is not sufficient. Has a problem in that high performance cannot be obtained. The cause of the decrease in purity at the time of RGB color separation includes the presence of sub-peaks other than the main emission peak in the three-wavelength fluorescent tube, in addition to the color separation performance of the RGB color filter described above.

As a measure for improving the color purity which is an extension of the conventional structure, there is an optimization of the transmission characteristics of the color filter. However, the transmission characteristics are a problem due to the material, and it is difficult to essentially improve the transmission characteristics. Further, although a certain effect can be obtained by improving the optical density of the color filter, the transmittance is reduced, which is not desirable in terms of light use efficiency. On the other hand, it is also possible to suppress the generation of sub-peaks by changing the phosphor composition, but there is a problem of a reduction in luminous efficiency of the main luminescence peak and a reduction in color purity due to the peak shift, and it is difficult to essentially improve it.

As another problem, there is a problem of so-called "reflection" in which a light source existing around the display is reflected on a screen. This is because light that is stronger than the illumination light from the backlight is incident on the screen and is visually recognized by an observer due to specular reflection on the surface of the liquid crystal display element, causing significant display degradation. In an improvement in the conventional configuration, specular reflectivity is reduced by a surface coating or a diffuse reflection treatment.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a color display device capable of expanding a color gamut and reducing reflection as much as possible.

[0008]

SUMMARY OF THE INVENTION A color display device according to the present invention has a white light source, and a flat illuminator for illuminating the white light source in a plane, and a light output from the flat illuminator. A non-emissive color image which receives as illumination light, has three primary color separation means for separating the illumination light into three primary colors for each pixel arranged two-dimensionally, and displays an image by modulating transmittance or reflectance. A display device, comprising: a plurality of laminated birefringent films and at least one polarizing element; and a color enhancement filter for enhancing main emission peaks of three primary colors of the white light source.

The non-emission type color image display device may be a liquid crystal display device having a color filter and a polarizing plate.

The polarizing element is positioned on the white light source side with respect to the plurality of laminated birefringent films, and is 450 to 540 nm in combination with the polarizing plate provided on the light incident side of the liquid crystal display element. It is preferable that absorption ranges exist in the range of 560 to 600 nm, respectively.

Incidentally, the plurality of laminated birefringent films and polarizing elements may be provided between a white light source and a non-light emitting type color image display element.

In this case, the polarizing element is preferably a non-absorbing polarizing plate.

The plurality of laminated birefringent films and polarizing elements may be provided on a display screen of a non-emission type color image display element.

The white light source is preferably a three-wavelength light source.

[0015]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a color display device according to the present invention will be described with reference to the drawings.

First, before describing an embodiment of the present invention,
The basic principle of the present invention will be described.

According to the present invention, a plurality of laminated birefringent retardation films and polarizing elements are used to form RGs necessary for color display.
This is a color display device including an optical element (color enhancement filter) that realizes an optical filter function of transmitting B light and removing other undesired light.

Means for achieving the same purpose and function as those of the optical element according to the present invention are described in Japanese Patent Application Laid-Open No. 5-17862.
As described in Japanese Unexamined Patent Application Publication No. 3 (1993) -301, a method of providing a colored filter that absorbs a specific undesired wavelength range, a dichroic mirror for color separation / synthesis of a projection type display device, and a dielectric material frequently used in a prism and the like. A method using a multilayer film is known. However, in the former method, it is difficult to obtain a steep transmittance curve similarly to the color filter, and it is difficult to perform efficient selective light transmission filtering. The latter method can obtain a steep transmittance curve, but requires multi-layer deposition by vapor deposition or sputtering, and it is difficult and expensive to increase the area. Also,
Because the wavelength shift of the interference region occurs due to the oblique incidence of light,
It is not suitable for a direct-view display that also requires visibility from an oblique direction.

Further, the wavelength selection region of the optical element used in these conventional systems does not have polarization selectivity with respect to vertical incidence of light. Therefore, the color LC which is a polarization utilizing device
In D, it is effective to use an optical filter having polarization selectivity as in the present invention.

On the other hand, as a similar conventional example using the polarization selectivity, as shown in JP-A-3-256020, by providing a polarizing plate and a 1/4 phase difference film on a display screen, ambient light can be reduced. There is known an example in which the reflection of light is reduced and the display contrast in a bright place is improved. However, in this conventional example, only the display polarized light and the ambient light are separated over the entire visible region, and there is no wavelength selectivity. Therefore, as described below, there is no function of improving the RGB color separation function and widening the display reproduction range.

A general method for obtaining a specific transmittance characteristic using a laminated birefringent retardation film and a polarizing element is as follows.
For example, I. Solc (J. Opt. Soc. Amer
ica Vol. 55 (1965), p621-62
5. ) And S.I. E. FIG. Harris (ibid., Vol. 54)
(1964), p1267-1279. ). The following relationship exists between the optical parameters and the transmittance characteristics of the birefringent retardation film. That is, the wavelength profile of the transmittance is determined by the angle of the phase axis of the laminated retardation film and the polarization axis angle of the polarizing element, and the transmission characteristic is wavelength-shifted by changing the retardation value of the retardation film (strictly). Is shifted with respect to the reciprocal of the wavelength, so that the transmission characteristics are extended in the long wavelength region and are compressed in the short wavelength region.) When the number of layers increases, the transmission characteristics become steep.

Using these design techniques, G. D. Sh
Arp et al. have proposed an RGB color separation color filter (see US Pat. No. 5,751,384).
U.S. Pat. No. 5,929,946 clearly discloses a configuration of a transmission filter for removing a boundary region of RGB wavelengths. However, the former is R
A transmission filter having a function of transmitting only a specific wavelength range among the three primary colors of GB. Even if these filters are laminated, for example, any one of the RGB wavelength ranges is lost. No properties are obtained.

The latter is obtained by applying the above-described design method (TYPEI) for the narrow band filter of Solc by inverting the sign of the phase angle between the former stage and the latter stage of the stacked layers to make the interference range higher. It is something that can be done. S
27 (a) and 27 (b) show conceptual designs of olc and Sharp, respectively. As described below, the above-described design method does not match the main emission wavelength peak of the currently used three-wavelength light source, and cannot achieve the object.

In order to clarify the reason specifically,
First, FIG. 3 of US Pat. No. 5,929,946 is disclosed.
8, 39 (hereinafter referred to as Sharp's design) will be clarified while being compared with the Solc's design method. 28 (a) and 28 (b) show the design value of Sharp (FIG. 28 (b)) and the design value of Solc (FIG. 28 (a)) which is a prototype of the design value of Sharp. FIG. 29 shows a PC as a birefringent wavelength film.
FIG. 9 shows transmittance characteristics of a filter sandwiched between ideal polarizing plates (transmission axis transmittance: 1.0, polarization degree: 100%) when (polycarbonate) is used. Solc's filter is called "Folded Filter".
r)), and when ρ = 45 ° / N when the birefringent film layer is an N layer, the angle of the first layer is defined as the angle between the polarization transmission axis and the fast axis. .rho., the second layer is obtained as -.rho. In this case, the birefringence of the birefringent film is Δn (=
n _e -n _o), the retardation wavelength lambda _C = [Delta] n, which is defined from the retardation value [Delta] n · d of the film thickness as d
By setting N = 3 with two layers of (λ _C ) × d = 440 nm as one unit, ρ = 15 °, and FIG.
The configuration shown in FIG. Incidentally, n _e is the extraordinary ray refraction index, n _o is the ordinary index of refraction. The retardation wavelength λ _C is the wavelength at which the maximum value of the transmittance chromatic dispersion curve obtained when the birefringent retardation film is arranged between the orthogonal Nicols and the phase axis direction is set at 45 ° to the polarization axis. Measured as 1/2.

On the other hand, in the design of Sharp, the basic configuration of Solc, ρ / −ρ / ρ, is a two-stage of the former stage, the former stage and the latter stage with the sign inverted, and the connecting part between the former stage and the latter stage is partially changed. The configuration is as follows. That is, a composite ρ / −ρ / ρ of the former stage of ρ / −ρ / ρ and the latter stage of −ρ / ρ / −ρ
Replace the central part ρ / −ρ of / −ρ / ρ / −ρ with 0 °,
It can be seen that ρ / −ρ / 0 ° / ρ / −ρ. By adopting this configuration, the transmittance characteristic of the Solc filter is folded, and a “W” -shaped transmittance characteristic is obtained. That is, as schematically shown in FIGS. 27A and 27B, it can be understood that the two absorption wavelengths at 500 to 600 nm are not independent but are values uniquely determined from one design.

In these filters, a birefringent filter
The fast axis angle of the system gives the transmittance profile, but the retardation
Birefringence determined by the solution value Δn · d and the birefringent material
The chromatic dispersion of Δn determines the peak wavelength of the filter. S
According to olc, the transmittance profile of the filter is ω =
Expressed as the sum of cosine functions of ω defined by 2π · Δn · d / λ
And the peak wavelength λ₀Is ω₀= 2π · K (K = 0.5,
1.5, 2.5,...), That is, Δn₀・
d / λ₀= 0.5,1.5,2.5, ...
Can be Where Δn₀= Δn (λ₀). FIG.
At λ _C= 440nm PC (Polycarbonate)
The thickness of 545 from its birefringence wavelength dispersion characteristic.
In nm, Δn · d = 409 nm. And 2
The film thickness d is doubled by treating the layer as one unit.
409 nm x 2/545 nm
= 1.5, the peak wavelength is 545 nm.
Is shown. The transmittance characteristic shown in FIG.₀Noseki
FIG. 30 shows a characteristic diagram expressed as numbers.

From the above discussion, the number of retardation films and the direction of the fast axis are essential design parameters that determine the transmittance profile of the filter, and the retardation wavelength λ
It can be seen that _C and the wavelength dispersion Δn (λ) of the retardation film are additional design parameters that determine the peak wavelength λ ₀ , the half width of the peak, and the like.

Using the results of the above examination, Sharp
Can be shown that this design does not meet this purpose. The main emission peak of a three-wavelength fluorescent tube is 435 n for B (blue).
m (the emission line of mercury (Hg) is 435 nm, the main emission peak of the phosphor is 445 nm), and G (green) is 543.
nm, R (red) is 610 nm, and λ ₀ = 543 nm
It is. In order to make the emission wavelengths of B and R into the transmission range, FIG.
From ω / ω ₀ > 1.2 at λ = 435 nm, λ = 6
At 10 nm, ω / ω ₀ <0.8 must be satisfied. ω / ω ₀ = (Δn (λ) · λ ₀ ) / (Δn ₀ ·
λ), Δn (λ) at λ = 435 nm
/ Δn ₀ > 0.96, λ = 610 nm, Δn
It is necessary that (λ) / Δn ₀ <0.90.

Here, FIG. 31 shows the birefringence wavelength dispersion of various birefringent film materials as Δn (λ) / Δn ₀ together with the above conditions. As is clear from FIG. 31, a birefringent film material of high wavelength dispersion such that the main emission peak of R is in the transmission region, that is, 6 for a birefringence value of 543 nm.
It is difficult to select a material having a value of 10 nm of 0.90, and even if such a birefringent material is obtained, there is a possibility that the value will greatly deviate from the optimum value at the main emission peak of B. Is high.

FIG. 32 shows a transmittance characteristic and a light emission characteristic 101 of a three-wavelength fluorescent tube when a Sharp filter configuration is realized by using the birefringent film material shown in FIG. FIG.
As can be seen from FIG. 2, even when a Sharp filter is made of such a birefringent film material, the transmittance at the main emission peak wavelength of R of 610 nm is greatly reduced.
A decrease in light use efficiency and a shift in white balance occur, indicating that the purpose of the present invention is not met.

In order to obtain transmission characteristics that meet the purpose of the present invention, it is desirable to design according to the following guidelines. That is, two regions between the RGB three wavelength peaks, B
-Lamination is performed so as to combine filters that have absorption regions in the G wavelength region and the GR wavelength region, respectively, and transmit all the light in the other wavelength regions (see FIGS. 10A and 10B). For example, in FIG. 10A, a filter 120 having transmission characteristics in the BG wavelength region and a filter 122 having transmission characteristics in the GR wavelength region are laminated so as to be combined.
In (b), a filter 124 having transmission characteristics in the BG wavelength region and a filter 126 having transmission characteristics in the GR wavelength region are laminated so as to be combined. The transmittance shape of such an absorption filter is based on a narrow band filter (also called a notch filter) proposed by Solc et al.
3A and 3B, the filters 120, 122, 1
26 and a trapezoidal filter, for example, in FIG. In particular, as will be described later, in a commonly used three-wavelength fluorescent tube material, since the BG wavelength range is wide and the GR wavelength range is narrow, for example, FIG.
As shown in (b), it is preferable that the former is composed of a trapezoidal filter and the latter is composed of a narrow band filter.

Among the specific means for realizing the above filter, a method for designing a narrow band filter is based on the method disclosed by Solc et al. For example, FIGS. 11A, 11B, and 11C show design examples in which “foldable” filters are arranged between parallel Nicols as designs 1 to 9. The value is an angle with respect to the transmission polarization axis in each layer of the birefringent film. Assuming that the number of birefringent retardation films is N, the parameters ρ and α that determine the fast axis direction are determined so as to satisfy N · ρ + (N−1) ² · α / 4 = 45 ° (1). α is an auxiliary parameter for determining the filter shape, and is arbitrary, but is shown as α = 0 °, 1 °, and ρ for each N as a design example. N is the number of birefringent film layers and is an odd number. The larger the N, the smoother the side peak of the filter, but N = 3 to 9 is appropriate in practice.

Using the fast axis angle shown in FIG. 11, the retardation wavelength of the birefringent retardation film is taken into consideration so that the absorption peak comes between the main emission peaks of the three-wavelength fluorescent tube and the wavelength dispersion of the birefringence Δn. By providing λ _C , the object of the present invention can be achieved. 12, 13, and 14
The configuration of each design example, G among three band, so that a peak wavelength between R main emission peak is located, the retardation wavelength lambda _C is lambda _{C =} 820 nm of the PC (the polycarbonate) as the birefringent retardation film It is a transmittance profile at the time of using. As can be seen from FIGS. 12, 13 and 14, N = 7 or 9, and α = 0 to 1 ° are optimal parameter values. 12, 13, and 14, reference numeral 101 is a graph showing the emission spectrum spectral characteristics of the three-wavelength cold cathode fluorescent tube.

Here, the wavelength dispersion characteristics of the birefringent material are taken into consideration.
While controlling the absorption peak wavelength to the desired wavelength.
Dation wavelength λ_CState the specific method of determining
You. Absorption peak wavelength for "foldable" filters
λ₀Is K = Δn₀・ D / λ₀= 0.5, 1.5, 2.5,... (2) Where Δn₀Is the peak wavelength λ₀To
Birefringence, ie Δn ₀= Δn (λ₀). Main building
In the example, K = 1.5, λ₀= 580nm,
Δn₀D = 870 nm.

On the other hand, the dispersion curve of the birefringence Δn is represented by, for example, Δn (λ) = (A · λ ² + B) / (λ ² −C ² ) (3) It can be represented using C. Since the film thickness d is obtained from the equations (2) and (3), the cubic equation λ _C ³ −A · d · λ _C is obtained from the definition of the retardation wavelength λ _C = Δn (λ _C ) × d (4) By solving ²⁻ C ² · λ _C −d · B = 0 (5), the retardation wavelength λ _C can be obtained.

FIG. 15 shows that the birefringence at 550 nm is 1
As the wavelength dispersion parameter for each birefringent material,
Tables show respective retardation wavelengths λ _C obtained when λ ₀ = 580 nm (wavelength dispersion characteristics of each birefringent material are shown in FIG. 31). FIG. 16 shows the results of Design Example 4 for each birefringent material. As described above, even if a birefringent material having any wavelength dispersion characteristics is used, it is possible to obtain an optimum filter characteristic by configuring a filter according to the above procedure. In FIG. 16, reference numeral 101 is a graph showing the emission spectrum spectral characteristics of the three-wavelength cold cathode fluorescent tube.

Next, as another example of forming a narrow band filter, a "fan-shaped filter (Fan
17 (a), (b), and (c) show design examples in which “Filter” is arranged as designs 10 to 18. Similarly to FIG. 11, the fast axis angle parameters ρ and α are determined from equation (1). Here, the polarizing plate transmission axis was set to 0 ° on the first layer (No. 1) side and 90 ° on the Nth layer side. The “fan type” filter has a wider absorption peak half-value width than the “folding type” filter, so that it is convenient to use it as an absorption filter between B and G. The condition of the peak wavelength λ ₀ in the “fan type” filter is as follows: K = Δn ₀ · d / λ ₀ = 1, 2, 3,. Therefore, if K = 1, the peak wavelength λ ₀ becomes the retardation wavelength λ _C from the equation (4), and the desired absorption peak wavelength may be used as the retardation wavelength regardless of the birefringent material. Assuming that λ ₀ = λ _C = 480 nm,
Design Examples 10 to 1 when PC is used as the birefringent material
The filter characteristics of No. 8 are shown in FIGS. 18, 19 and 20. FIG. 21 shows the filter characteristics of Design Example 14 for each birefringent material. From FIGS. 18, 19, and 20, it can be seen that N = 5 or 7 is the optimum number of films. In FIGS. 18, 19, and 20, reference numeral 101 denotes
5 is a graph showing emission spectrum spectral characteristics of a three-wavelength cold cathode fluorescent tube.

As an absorption filter between the BG main emission peaks, a trapezoidal filter which can take a wider wavelength range than the above-mentioned notch filter is more suitable. For the steepness of the filter, a rectangular filter is more preferable than a trapezoidal filter. However, if a rectangular filter is to be composed of a limited number of birefringent retardation films, fringe will occur in the transmission region, so that it is practical. Is suitable to use a trapezoidal filter.

The specific procedure for designing a trapezoidal filter is as follows. First, a transmittance curve for ω defined by ω = 2π · Δn · d / λ (7) is determined. Where the trapezoidal function has a Fourier series

(Equation 1) Was used. Here, d ₀ and Δd are parameters for determining the trapezoidal shape, and m is a finite Fourier series of 1 to N. N is the number of birefringent retardation films and takes an odd number. FIG. 22 shows an example of the curve of the equation (8) with respect to ω.
(8) Since a trapezoidal convex function on the equation ^{(9), | D (ω) | 2} = 1-T (ω) to become (10) | D (ω) | 2 is an object of the present invention Represents a trapezoidal absorption filter characteristic that conforms to.

Next, the peak wavelength λ ₀ and the shape parameter d are taken into consideration while considering the birefringence wavelength dispersion characteristics of the birefringent material used.
₀ and Δd may be determined. From FIG. 22 and equation (7), the peak wavelength is given by K = Δn ₀ · d / λ ₀ = 1, 2, 3,. By selecting an appropriate value of K and obtaining the retardation wavelength λ _C from the peak wavelength λ ₀ by the above-described method, a desired trapezoidal absorption filter curve can be designed. K = 2, peak wavelength λ ₀ = 480 n
FIGS. 23 to 26 show examples in which the BG absorption filter is designed with the birefringent material having the birefringence characteristic shown in FIG. 15 as m. From these characteristics, it can be seen that desired filter characteristics can be obtained with N = 3 or 5 sheets. 23 to 26 also show the fast axis direction of each layer of the birefringent retardation film and the transmission polarization axis direction of the output side polarizing plate (analyzer). These values are shown with the polarization transmission axis azimuth of the incident-side polarizing plate as 0 °. The value of each fast axis azimuth is obtained from the coefficient values C _{0 to} C _{N of} (8) expressed by the equation (9).

(Equation 2) In represented by the electric field response function C (ω), D coefficients _A 0 _{to A} N of the _(ω), B 0 ~B _N look, values of these coefficients derived by Harris et al. And the fast axis azimuth relationship Required from. For example, the transmission polarization axis azimuth of the output side polarizing plate is θ.
_{If p}

(Equation 3) It is represented as

As described above, in order to solve the problem of removing the undesired components other than the main emission peak of the three-wavelength fluorescent tube and expanding the color reproduction range, the object of the present invention has been proposed. It is difficult to solve the problem with the filters that have been used, and the structure of a new color enhancement filter that solves the problem and the specific design method thereof are shown, and further, the structure of a new color display device using the same is proposed. Things. Hereinafter, the configuration of the novel color display device proposed in the present invention will be described.

Among the constituent elements of the present invention, it is desirable to use a retardation film made of PC (polycarbonate) or PVA (polyvinyl alcohol) as the birefringent retardation film, but it is preferable to use PSF (polysulfone) or PMMA.
Even if other materials such as (polymethyl methacrylate) are used, equivalent characteristics can be realized by changing the retardation value in consideration of the wavelength dispersion of birefringence. In addition, in consideration of the visibility from an oblique direction, it is preferable to use a three-dimensional compensation film (biaxial retardation film) whose retardation value is less likely to change as compared with a uniaxial retardation film even at oblique incidence. As the three-dimensional compensation film, for example, NRZ series manufactured by Nitto Denko Corporation can be used.

As the polarizing element, a normal iodine-based or dye-based polarizing plate (for example, Nitto Denko NPF-1425DU or Polatechno KN series) can be used. In this case, a non-absorbing polarizing plate is desirable in terms of light use efficiency. This is because the light component absorbed by the absorption axis of the polarizing plate can be used recursively. The condition of the non-absorbing polarizing plate is required to be a linear polarizer.
For example, DBEF of Sumitomo 3M, which forms a dielectric multilayer film by laminating birefringent polymers, and DRPF-H, which is a non-absorbing polarizing element based on anisotropic diffuse reflection, can be used to separate polarized light. The principle of doing this does not matter. However, Merc
k's TransMax and Nitto Denko's PCF300
In the case of a non-absorbing polarizing element utilizing the circular polarization selectivity of a cholesteric liquid crystal polymer as in the above, a quarter-wave film for converting the output circularly polarized light into linearly polarized light is disposed between the birefringent retardation film layer and the polarizing plate. It is necessary to add an additional element (in some products, a 1/4 wavelength film is added to the non-absorbing polarizing element to emit linearly polarized light). Alternatively, it is necessary to design the lamination parameters of the birefringent layer so that the transmittance characteristic satisfies the specification with the circularly polarized light as the incident polarized light. The higher the degree of polarization of the polarizing element is, the more desirable it is. However, a desired effect can be sufficiently obtained even by using a polarizing element having a degree of polarization of 90% or less, such as the above-described non-absorbing polarizing element.

The positions of the birefringent retardation film layer and the polarizing element are provided on the light source and the liquid crystal display element, or on the front (observation surface) side of the liquid crystal display element. In the former arrangement, for example, the polarizing element may be disposed between the light source and the light guide, and the birefringent retardation film layer may be disposed between the light guide and the liquid crystal display element. Is preferable in that the degree of polarization is maintained. Similarly, it is desirable that the exit surface of the birefringent retardation film and the incident-side polarizing plate of the liquid crystal display element are also in close contact.

As a white light source, in a color LCD,
Use commonly used three-wavelength cold cathode fluorescent tubes
Is desirable. As a fluorescent material, 61 is used as a phosphor for R.
Y having an emission peak of 0 nm₂O₃: Eu₃₊For G
CeMg having an emission peak at 543 nm as a phosphor
Al₁₁O₁₉: Tb³⁺, LaPO₄: Ce³⁺, T
b³⁺, La₂O₃・ 0.2SiO₂・ 0.9P
₂O₅: Ce³⁺, Tb³⁺435 as a phosphor for B
Ba having an emission peak at ~ 452 nm₃MgSi₂O
₈: Eu²⁺, CaWO₄: Pb²⁺, BaMg₂Al
₁₆O₂₇: Eu²⁺, (Sr, Ca)₁₀(PO₄)
₆Cl₂: Eu²⁺, 3 (Sr, Ca, Ba) ₃(PO
₄)₂: Eu²⁺, (Sr, Ca, Ba)₁₀(P
O₄)₆Cl₂・ NB₂O₃: Eu²⁺Using
However, in phosphor materials other than those described above,
Phosphor material whose main emission peak falls within the range described above
It is clear that any material can be used in the present invention.
You. The form of the flat light source is a white light source just below the liquid crystal display element.
Even with a so-called direct type structure in which color light sources are
Even with a side light type structure with a light guide under the child
both are fine.

Hereinafter, embodiments of the present invention will be described. However, the configuration of the present invention is not limited to that described in the embodiment, and the configuration described in this embodiment can be used in various combinations.

(First Embodiment) A first embodiment of the present invention will be described. FIG. 1 is a diagram schematically showing the configuration of the color display device of the present embodiment. The color display device of this embodiment includes a white light source 11 such as a cold cathode fluorescent tube, a light guide 13 for uniformly illuminating the light of the light source 11 and the light reflected by the reflector 12 in a planar manner, and a reflector 14 , A backlight unit 10 composed of a diffusion condensing film (BEF manufactured by Sumitomo 3M) and a diffusion sheet (not shown), a liquid crystal display element 20 for displaying an image, a birefringent retardation film layer 30, and a non-absorbing material Polarizing plate (Sumitomo 3
M DBEF) 40. The liquid crystal display element 20 includes an incident-side polarizing plate 21 and R
It has a GB color filter 23, a liquid crystal layer 25, a liquid crystal panel 22 including an alignment film and electrodes 24 and 26, and an output-side polarizing plate 29. White light emitted from the backlight unit 10 as illumination light is supplied to the non-absorbing polarizing plate 4.
When passing through 0, the light is converted from non-polarized light to linearly polarized light, and enters the birefringent retardation film layer 30. Non-absorbing polarizing plate 4
The light component that does not pass through 0 is reflected to the side of the diffuse light-condensing film 15, and is depolarized by diffuse reflection at each interface of the reflector 14, the light guide 13, the diffuse light-condensing film 15, and a diffusion sheet (not shown). Recursively non-absorbing polarizing plate 40
Incident on. The linearly polarized light that has entered the birefringent retardation film 30 is phase-modulated for each wavelength, and when passing through the incident-side polarizing plate 21 of the liquid crystal display element 20, an undesired light component contained in the white light source 11 is absorbed. As described above, only the main emission peak component is incident on the liquid crystal panel 22, and
2 are separated into respective RGB colors by RGB color filters 23 provided for each pixel. The incident polarized light separated into RGB colors has its polarization state modulated in accordance with the arrangement of the liquid crystal molecules electrically controlled for each pixel, and passes through the exit side polarizing plate 29 provided on the exit surface of the liquid crystal display element 20. As a result, ON / OFF display is performed. In many cases, the color filter is located not on the light incident side but on the output side with respect to the liquid crystal layer.

FIG. 2 shows the spectral characteristics 102, 103, and 10 of the RGB color filters provided in the liquid crystal display panel 22.
4 shows emission spectra 101 of four- and three-wavelength cold cathode fluorescent tubes. In the conventional color display device shown in FIG. 33, the RGB color gamut 110 shown in FIG. 7 is determined from both the spectral characteristics of FIG. 2 and the retardation of the liquid crystal layer 25 in the liquid crystal panel 22. FIG. 7 is a u′v ′ chromaticity diagram, and reference numeral 109 denotes an RGB color gamut in the color display device of the present invention.

On the other hand, in the present embodiment, the birefringent retardation film layer 30 and the non-absorbing polarizing plate 40 constituting the color enhancing filter are provided between the backlight 10 and the incident side polarizing plate 21 of the liquid crystal display element 20. Is provided. FIG. 3 shows the optical arrangement of the birefringent retardation film layer 30, the non-absorbing polarizing plate 40, and the incident side polarizing plate 21 of the liquid crystal display device 20. The birefringent retardation film layer 30 was composed of a total of 12 layers, and a biaxial compensation film NRZ series manufactured by Nitto Denko was used. These are composed of a five-layer birefringent retardation film layer having a retardation of 850 nm and a seven-layer birefringent retardation film layer having a retardation of 820 nm. The former is the main emission peak BG of a three-wavelength cold cathode fluorescent tube.
The latter is arranged for the purpose of a sub-peak absorption filter between GRs. The main emission peaks of the three-wavelength cold cathode fluorescent tube are B: 435 nm, G: 543 nm, and R: 610 nm. Since the BG emission peak wavelength interval is rather wide, the absorption filter between BGs is trapezoidal, and the absorption filter between GRs is notch. Each was designed as a filter (see FIG. 10B). FIG. 4 shows design values obtained by realizing each absorption filter between ideal polarizing plates having a polarization degree of 100%. Each retardation value was determined in consideration of the wavelength dispersion of birefringence. In FIG. 4, reference numeral 101 denotes a graph showing the emission spectrum spectral characteristics of the three-wavelength cold cathode tube, reference numeral 105 denotes a graph showing the transmittance characteristics of the BG absorption filter, and reference numeral 106 denotes the transmission of the GR absorption filter. It is a graph which shows a rate characteristic.

The design values shown in FIG. 3 were compared with actual non-absorbing polarizers (D
BEF), incident-side polarizing plate (Nitto Denko EG1425DU)
FIG. 5 shows the transmittance characteristic 107 when the above configuration is adopted. Each RG
It can be seen that the transmission characteristic of transmitting the B main emission peak and absorbing the sub-peak between the main emission peaks has been realized. FIG. 6 shows the emission spectrum after passing through this filter. It can be seen that the sub-peaks indicated by arrows in the figure are removed, and that the light illuminating the liquid crystal panel 20 has only the main emission spectrum with excellent color purity. That is, the color enhancement filter according to the present embodiment is configured to enhance the main emission peaks of the three primary colors of the white light source 11.

As described above, according to the present embodiment, it is possible to reduce the sub-peak of the three-wavelength cold cathode fluorescent tube which is a white light source. The color gamut 109 when RGB display is performed using the RGB color filters having the characteristics shown in FIG.
Is shown in FIG. Color gamut 110 of conventional color display device
It can be seen that the RGB color gamut has been increased as compared with.

Further, when comparing the light use efficiency in the present embodiment with the conventional example, by using the non-absorbing polarizing plate 40 as the incident side polarizing plate of the birefringent retardation film layer 30, the incident side polarizing plate of the liquid crystal panel 20 is used. The undesired polarized light component absorbed by the plate is reflected to the backlight unit 10 side, and becomes a desired polarized light component transmitted through the incident-side polarizing plate by depolarization at the time of diffuse reflection at each interface of the backlight such as the reflection sheet 14 and retroreflection. Because of the conversion, the effective luminous flux is about 1.6
Increase by a factor of two. Since the main light emission peak transmission efficiency of the birefringent retardation film layer 30 is about 80%, the final illumination efficiency is 1.28 times the conventional one. Therefore, by using this embodiment, the lighting efficiency is equal to or higher than the conventional configuration,
The color gamut can be increased without changing the configurations of the liquid crystal display element 20 and the backlight unit 10.

(Second Embodiment) FIG. 8 shows the configuration of a color display device according to a second embodiment of the present invention. In the present embodiment, the backlight unit 10A has a direct-type structure in which a plurality of cold cathode fluorescent tubes 11 are disposed immediately below the liquid crystal display element 20, and constitutes a color enhancement filter.
The birefringent retardation film layer 30 and the absorptive polarizing plate 42 are arranged above the liquid crystal display element 20. There is no direct relationship between the arrangement order of the birefringent retardation film layer 30 and the absorptive polarizing plate 42 and the structure of the backlight unit 10A, and a cold cathode fluorescent tube is arranged on the side as in the first embodiment. A side light structure may be used at all. The color emphasizing filter according to this embodiment also has a configuration in which the main light emission peaks of the three primary colors of the white light source 11 are emphasized, as in the case of the first embodiment.

In the present embodiment, since the birefringent film layer 30 and the polarizing plate 42 constituting the color enhancement filter are arranged at the upper part of the screen, these birefringent film layers 3
The 0 and the polarizing plate 42 also function as an anti-reflection layer that reduces the reflection of ambient light, that is, effectively reduces the reflection of illumination light from the observation side of the liquid crystal display element 20. This functions as an RGB color emphasizing filter for transmitted light, and for the reflected light reflected at the interface of the liquid crystal display element 20, due to the polarization conversion effect of the birefringent retardation film layer 30, the uppermost portion This is due to the effect that the reflected light is absorbed by the polarizing plate 42.

In the structure of this embodiment, since the polarizing plate 42 is a normal absorptive polarizing plate, the transmittance is 70%.
%, But transmits only the wavelength components of the phosphor, which is the illumination light, and absorbs the other wavelength components, effectively reflecting the surrounding environment light onto the display screen. Thus, the effective contrast can be significantly improved.

Note that the color reproduction range can be widened in the second embodiment as in the first embodiment.

(Third Embodiment) FIG. 9 shows a configuration of a color display device according to a third embodiment of the present invention. The color display device according to the present embodiment is the same as the color display device according to the first embodiment, except that the birefringent retardation film layer 30 and the non-absorbing polarizing plate 40 constituting a color enhancement filter are formed as a white light source. 11 and the light guide 13. By adopting the configuration of the present embodiment, it is possible to reduce the required area of the birefringent retardation film layer 30 having a relatively large number of laminations and reduce the thickness of the color display device. The essential polarizing plate 40 is arranged between the white light source 11 and the birefringent retardation film layer 30. The color emphasizing filter according to this embodiment also has a configuration in which the main light emission peaks of the three primary colors of the white light source 11 are emphasized, as in the case of the first embodiment. In the present embodiment, in addition to the birefringent retardation film layer 30 and the non-absorbing polarizing plate 40, the polarizing plate 44, the light guide 13 and the liquid crystal are disposed between the birefringent retardation film layer 30 and the light guide 13. Display element 20
A non-absorbing polarizing plate 46 and a non-absorbing polarizing plate 46
波長 wavelength film 60 is provided between the
Is further provided.

In this embodiment, the non-absorbing polarizing plate 40 is arranged to improve the illumination efficiency. However, a general absorbing polarizing plate may be used except for the efficiency. In the case of the non-absorbing polarizing plate 40, the reflected unwanted polarized light is depolarized by the retroreflection by the fluorescent tube 11 and the reflector 12, and the transmission efficiency is improved. The polarizing plate 44 provided between the birefringent retardation film layer 30 and the light guide 13, and the non-absorbing polarizing plate 46 between the light guide 13 and the liquid crystal display element 20 are not essential, but are not required. Since the degree of polarization is reduced during light emission and emission, it is a member that is desirably installed from the viewpoint of maintaining characteristics. The former polarizing plate 44 secures the transmittance characteristics of the absorption filter, and the latter polarizing plate 46 reduces absorption in the polarizing plate 21 of the liquid crystal panel 20 due to a decrease in the degree of polarization when the backlight is emitted. Things.

A desirable output polarization direction in which the degree of polarization is preserved when light is guided in the light guide is such that the plane of polarization is horizontal or vertical to the bottom surface of the light guide. Therefore, the illumination light is efficiently emitted while maintaining the degree of polarization when there is a polarization plane in the horizontal (0 °) or vertical (90 °) direction with respect to the screen. In general, the orientation of the polarizing plate of the liquid crystal display element 20 is arranged in the direction of 45 ° in view of the problem of the viewing angle. Coincidence) and the liquid crystal display element 20
The polarizing plate 21 has a function of converting the plane of polarization to a desired direction by arranging the fast axis in the direction that divides the direction of the polarized light transmission axis of the polarizing plate 21 into two.

Therefore, when the transmission axis direction of the incident-side polarizing plate is horizontal or perpendicular to the screen, or when the polarization depolarization in the light guide is large and the illumination efficiency does not depend on the non-absorbing polarizing plate direction, etc. The half-wave film 60 is not required.

A plurality of half-wave films 60 may be used to reduce the wavelength dispersion. For example, when two sheets are used, the exit polarization direction of the illumination light and the transmission axis direction of the polarizing plate of the liquid crystal display element 20 are divided into four, and each is divided by 1 /.
It is good to arrange in the directions of 4, 3/4.

In the third embodiment, similarly to the first embodiment, the color gamut can be widened and the reflection can be reduced as much as possible.

[0063]

As described above, according to the present invention, RG
The B color reproduction range can be widened and the reflection can be reduced.

[Brief description of the drawings]

FIG. 1 is a diagram showing a configuration of a first embodiment of a color display device according to the present invention.

FIG. 2 is a diagram showing an emission spectrum of a light source and a spectral characteristic of an RGB color filter in the first embodiment and a conventional example.

FIG. 3 is a diagram showing optical parameters of each optical element according to the first embodiment.

FIG. 4 is a diagram showing design values of an absorption filter according to the first embodiment.

FIG. 5 is a diagram showing transmittance characteristics of the absorption filter in the first embodiment.

FIG. 6 is a diagram showing an emission spectrum after transmission through an absorption filter in the first embodiment.

FIG. 7 is a diagram showing an RGB color gamut of the first embodiment and a conventional example.

FIG. 8 is a diagram showing a configuration of a color display device according to a second embodiment of the present invention.

FIG. 9 is a view showing a configuration of a color display device according to a third embodiment of the present invention.

FIG. 10 is a diagram showing a design concept of an absorption filter according to the present invention.

FIG. 11 is a diagram showing a first filter design example used in the present invention.

FIG. 12 is a characteristic diagram of the filter design example shown in FIG. 11;

FIG. 13 is a characteristic diagram of the filter design example shown in FIG. 11;

FIG. 14 is a characteristic diagram of the filter design example shown in FIG. 11;

FIG. 15 is a table showing wavelength dispersion characteristic parameters of a birefringent material.

FIG. 16 illustrates a filter design example shown in FIG.
FIG. 16 is a filter characteristic diagram of the birefringent material shown in FIG. 15.

FIG. 17 is a table showing a second filter design example used in the present invention.

FIG. 18 is a characteristic diagram of the filter design example shown in FIG.

FIG. 19 is a characteristic diagram of the filter design example shown in FIG.

FIG. 20 is a characteristic diagram of the filter design example shown in FIG.

21 is a diagram illustrating an example of the filter design shown in FIG.
FIG. 16 is a filter characteristic diagram of the birefringent material shown in FIG. 15.

FIG. 22 is a diagram showing basic filter characteristics in a third filter design used in the present invention.

FIG. 23 is a diagram showing a first design example in a third filter design.

FIG. 24 is a diagram showing a second design example in the third filter design.

FIG. 25 is a diagram showing a third design example in the third filter design.

FIG. 26 is a diagram showing a fourth design example in the third filter design.

FIG. 27 is a diagram showing a conventional concept of designing an absorption filter.

FIG. 28 is a diagram showing a design example of a conventional absorption filter.

FIG. 29 is a view showing filter characteristics in the design example of FIG. 28;

FIG. 30 is a diagram showing the filter characteristics of FIG. 29 as a function of ω.

FIG. 31 is a diagram showing wavelength dispersion of birefringence in various birefringent materials and values required for a conventional filter design.

FIG. 32 is a diagram showing filter characteristics when a filter is configured by changing a birefringent material in a conventional absorption filter.

FIG. 33 is a diagram showing a configuration of a conventional color display device.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 10 Back light unit 11 White light source 12 Reflector 13 Light guide 14 Reflector 15 Diffusion condensing film 20 Liquid crystal display element 21 Incident side polarizing plate 22 Liquid crystal panel 23 RGB color filter 24, 26 Alignment film and transparent electrode 25 Liquid crystal layer 29 Emission Side polarizing plate 30 Birefringent retardation film 40, 46 Non-absorbing polarizing plate 42 Absorbing polarizing plate 44 Polarizing plate 60 1/2 wavelength film 101 Emission spectrum spectral characteristic of three-wavelength cold cathode fluorescent tube 102 Blue color filter spectral transmittance Characteristics 103 Green color filter spectral transmittance characteristics 104 Red color filter spectral transmittance characteristics 105 BG absorption filter transmittance characteristics 106 GR absorption filter transmittance characteristics 107 Absorption filter transmittance characteristics in the first embodiment 108 After absorption filter transmission Luminescence Gamut in the color gamut 110 conventional color display device in a color display device of the spectral spectral characteristic 109 present invention

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) G09F 9/00 313 G09F 9/00 313 324 324 F Term (Reference) 2H048 BA02 BB02 BB10 BB22 BB42 2H049 BA01 BA27 BB03 BB43 BB46 BB51 BB62 BC14 BC22 2H091 FA02Y FA08X FA08Z FA11X FA11Z FA41Z LA15 5G435 AA01 AA04 BB12 BB15 CC12 DD12 EE26 EE27 FF05 FF08 GG24 GG26 HH01

Claims (7)

[Claims] 1. A flat illumination device having a white light source, and illuminating the white light source light in a planar manner, receiving light output from the flat illumination device as illumination light, and being arranged in a two-dimensional plane. A non-emission type color image display element for displaying an image by modulating transmittance or reflectivity, and a plurality of laminated birefringent elements having three primary color separation means for separating the illumination light into three primary colors for each pixel. A color display device comprising: a film and at least one polarizing element; and a color enhancement filter for enhancing main emission peaks of three primary colors of the white light source. 2. A color display device according to claim 1, wherein said non-emission type color image display device is a liquid crystal display device having a color filter and a polarizing plate. 3. The polarizing element is located on the white light source side with respect to the plurality of laminated birefringent films, and is 450 nm in combination with the polarizing plate provided on the light incident side of the liquid crystal display element. 3. The color display device according to claim 2, wherein the absorption region exists in a range from the above to 540 nm or less and in a range from 560 nm to 600 nm. 4. The apparatus according to claim 1, wherein said plurality of laminated birefringent films and said polarizing element are provided between said white light source and said non-emission type color image display element. Color display device. 5. The color display device according to claim 4, wherein said polarizing element is a non-absorbing polarizing plate. 6. A color display device according to claim 1, wherein said plurality of laminated birefringent films and said polarizing element are provided on a display screen of said non-emission type color image display element. . 7. The color display device according to claim 1, wherein the white light source is a three-wavelength light source.