The present invention relates to a multilayer film suitably used for liquid crystal devices such as liquid crystal display devices or liquid crystal aberration compensating elements.
As is well known, liquid crystal display devices include a direct viewing-type liquid crystal display used for a liquid crystal television, a cellular phone and the like, and a projection-type liquid crystal display device used for a projection television, a liquid crystal projector and the like.
The direct viewing-type liquid crystal display device contains a liquid crystal display element fabricated by forming various wirings or elements on a substrate such as sheet glass, laying two kinds of substrates to face each other, that is, a color filter substrate (hereinafter referred to as a “CF substrate”) having printed thereon R (red), G (green) and B (blue) dyes in a three-color array and a TFT array substrate (hereinafter referred to as a “TFT substrate”) having formed thereon TFT for controlling the liquid crystal, and enclosing a liquid crystal therebetween. Such liquid crystal display elements include a transmission type and a reflection type, and in the case of a transmission type, a light source unit (backlight) is disposed on the back surface of the liquid crystal display element, whereas in the case of a reflection type, a light source unit is not required and for reflecting the incident light, the TFT substrate surface is made to work as a reflecting surface. In either case, the CF substrate uses a transparent electrically-conductive film such as ITO as the electrode so as to transmit light. Furthermore, in order for preventing liquid crystals from being disorderly disposed to deteriorate the image quality, an orientation film such as organic resin film or silicon oxide film is formed on a surface of the CF substrate or TFT substrate which comes into contact with the liquid crystal, and the orientation film of the CF substrate or the orientation film of the TFT substrate of a transmission-type liquid crystal element is formed of a transparent material so as to transmit light.
The projection-type liquid crystal display device usually contains three liquid crystal display elements, dichroic mirrors, a light source unit and a prism. A light emitted from the light source unit is split into light's three primary colors by dichroic mirrors, and these colors pass through respective liquid crystal display elements, then combined by a prism and projected on a screen.
As for the liquid crystal display element used in the projection-type liquid crystal display device, a reflection-type liquid crystal display element called LCOS (Liquid Crystal On Silicon, see, for example, Patent Document 1) or a transmission-type liquid crystal display element called HTPS (High Temperature Poly-Silicon) is attracting attention because of their high display image quality and high possibility of low-cost production.
As illustrated in
Further, as is well known, a liquid crystal aberration compensating element is used for an optical pickup device or the like and, as illustrated in
Patent Document 1: unexamined published Japanese patent application: JP-A-2002-296568
Patent Document 2: unexamined published Japanese patent application: JP-A-2001-100174
Incidentally, one of important problems in recent years is to show a projected image or a screen as bright as possible for the liquid crystal display device or to increase the transmittance for the liquid crystal aberration compensating element.
An increase in the amount of outgoing light from the liquid crystal display element is a theme more important for a projection-type liquid crystal display device displaying an enlarged and projected image than for a direct viewing-type liquid crystal display device. In combination with this, increasing the contrast is also an important theme.
As for the measure for increasing the amount of outgoing light from the liquid crystal display element and for increasing the contrast, in the reflection-type liquid crystal display element 20 described in Patent Document 1, as illustrated in
Also, in the liquid crystal aberration compensating element of Patent Document 2, great reflection occurs between the glass substrate and the ITO film or between the ITO film and the orientation film, and this gives rise to a problem that the transmittance decreases.
The present invention has been made in view of these circumstances and an object of the present invention is to provide a multilayer film that can make large the amount of outgoing light from a liquid crystal device such as liquid crystal display element and liquid crystal aberration compensating element and, at the same time, can realize a high contract in a liquid crystal display element.
The multilayer film of the present invention, which has been devised for attaining the object above, is a multilayer film which is formed on an inner side of a transparent substrate (for example, when applied to a liquid crystal display element or a liquid crystal aberration compensating element, the side having a liquid crystal layer) and contains a transparent electrically-conductive film and an orientation film, in which an antireflection film is formed at least either between the transparent substrate and the transparent electrically-conductive film or between the transparent electrically-conductive film and the orientation film.
That is, since the present invention has the above-described construction, reflection of visible light on the inner surface of a transparent substrate of a liquid crystal display element, a liquid crystal aberration compensating element or the like can be suppressed. For example, in this case, the maximum reflectance at 400 to 700 nm can be suppressed to 2% or less. When this multilayer film is applied to a liquid crystal device such as liquid crystal display element (e.g., HTPS, LCOS) or liquid crystal aberration compensating element, reflection on both surfaces of a transparent substrate is reduced, so that the amount of outgoing light of a liquid crystal display element, a liquid crystal aberration compensating element or the like can be increased and the contrast of a liquid crystal display element can be made high.
In the construction above, an antireflection film is preferably provided both between the transparent substrate and the transparent electrically-conductive film and between the transparent electrically-conductive film and the orientation film. In this case, reflection of visible light on the inner surface of the transparent substrate can be more successfully suppressed. In particular, in the case where low resistance electrical conductivity is required as in HTPS and a transparent electrically-conductive film having a geometric thickness of 50 to 200 nm is therefore provided, it is preferable to form the antireflection film both between the transparent substrate and the transparent electrically-conductive film and between the transparent electrically-conductive film and the orientation film, because the effect of suppressing reflection of visible light on the inner surface of the transparent substrate can be increased.
In the construction above, the antireflection film is preferably a stacked film of a low refractive index layer and a high refractive index layer. The low refractive index layer is suitably formed of a material having a refractive index of 1.6 or less, such as SiO2 or fluoride (e.g., MgF2), and the high refractive index layer is suitably formed of a material having a refractive index of 2.0 or more, such as Nb2O5, TiO2, Ta2O5, HfO2 and ZrO2.
In the case where a stacked film of a low refractive index layer and a high refractive index layer is formed as the antireflection film both between the transparent substrate and the transparent electrically-conductive film and between the transparent electrically-conductive film and the orientation film, the maximum reflectance at 400 to 700 nm can be suppressed to 0.25% or less.
Furthermore, in the construction above, the antireflection film between the orientation film and the transparent electrically-conductive film preferably has a geometric thickness of 10 to 100 nm. In this case, when a voltage is applied between the transparent electrically-conductive film (transparent electrode) and the opposing electrode (a reflection electrode in the case of a reflection-type liquid crystal display element, or a transparent electrode in the case of a transmission-type liquid crystal display element), the voltage (electric field) to be applied to the liquid crystal portion scarcely decreases.
However, in the case of a liquid aberration compensating element, it is preferred to form no antireflection film between the orientation film and the transparent electrically-conductive film. This is because, in the case of a liquid crystal aberration compensating element, the transparent electrically-conductive film needs to be concentrically patterned, so that for forming an antireflection film also between the transparent electrically-conductive film and the orientation film, the element needs to be once transferred from the film-forming step to the patterning step to effect patterning and then returned again to the film-forming step.
Accordingly, the antireflection film between the transparent substrate and the transparent electrically-conductive film is preferably formed to be composed of a stacked film of three or more layers, more preferably four or more layers, because the maximum reflectance can be made low without forming an antireflection film between the transparent electrically-conductive film and the orientation film.
In the construction above, the transparent electrically-conductive film preferably has a geometric thickness of 10 to 200 nm. In this case, the sheet resistance does not become low and, at the same time, the visible light transmittance can be kept high. That is, if the geometric thickness is less than 10 nm, the sheet resistance becomes excessively high, whereas if the geometric thickness exceeds 200 nm, the visible light transmittance decreases, both of which are not preferred. Also, in the case where low resistance electrical conductivity is required as in HTPS, the geometric thickness of the transparent electrically-conductive film is preferably from 50 to 200 nm, but in the case where light transmittance is more important than the low resistance of the transparent electrically-conductive film as in LCOS or liquid crystal aberration compensating element, the geometric thickness of the transparent electrically-conductive film is more preferably from 10 to 20 nm. This is preferred because the visible light transmittance on the short wavelength side does not become decreased. In particular, in the case of a liquid crystal aberration compensating element used in an optical pickup device, the element can advantageously respond to three wavelengths including BD (Blue Laser Disc, wavelength used: 405 nm), CD (Compact Disc, wavelength used: 780 nm) and DVD (Digital Versatile Disc, wavelength used: 658 nm). As the transparent electrically-conductive film, an ITO film, an AZO film, a GZO film and the like are suitably used.
In the construction above, examples of the transparent substrate which can be used include a glass substrate and a plastic substrate, and in view of environmental resistance, heat resistance, light resistance and the like, a glass substrate is preferred.
The multilayer film of the present invention can suppress reflection of visible light on the inner surface of a transparent substrate. When the multilayer film is applied to a liquid crystal device such as liquid crystal display element (e.g., HTPS, LCOS) or liquid crystal aberration compensating element, reflection is reduced on both surfaces of a transparent substrate and therefore, the liquid crystal display element can be assured of a large amount of outgoing light and a high contrast.
Working examples of the multilayer film of the present invention are described in detail below.
Table 1 shows Examples 1 to 5 of the present invention, and Table 2 shows Examples 6 and 7 of the present invention and Comparative Example.
As shown in Tables 1 and 2 and
In Comparative Example, only a transparent electrically-conductive film and an orientation film were formed but an antireflection film was not formed (not illustrated).
As seen from Tables 1 and 2, in all of Examples 1 to 7 of the present invention, the maximum reflectance in the visible light region was as low as 2% or less, and above all, the maximum reflectance in Examples 3 to 6 was 0.25% or less and was particularly low. On the other hand, in Comparative Example, the maximum reflectance in the visible light region was as high as 5%.
Furthermore, the multilayer films in Examples above, particularly the multilayer films in Examples 6 and 7, are usable not only for LCOS or HTPS, but for a liquid crystal aberration compensating element 5 illustrated in
Reflection of transmitted light is suppressed by employing such a structure, so that even when transmitted light interferes inside of the liquid crystal layer (between multilayer films), high transmittance of transmitted light in the use wavelength region (400 to 800 nm) is obtained. In particular, even when an ITO film is used as the transparent electrically-conductive film, the transmittance of transmitted light in the short wavelength region (400 to 660 nm) can be kept high. Therefore, this liquid crystal aberration compensating element 30 is suitable for an optical pickup device not only of CD or DVD but also of BD.
As described above, the multilayer film of the present invention is assured of a low reflectance and a sufficient large amount of outgoing light as well as high contrast and therefore, is suitable for a liquid crystal device such as transmission-type liquid crystal display element (e.g., HTPS or LCOS), reflection-type liquid crystal display element and liquid crystal aberration compensating element.
While the invention has been described in detail and with reference to specific embodiments thereof, it will be apparent to one skilled in the art that various changes and modifications can be made therein without departing from the spirit and scope thereof.
This application is based on Japanese Patent Application (Patent Application No. 2006-233214) filed on Aug. 30, 2006 and Japanese Patent Application (Patent Application No. 2007-047523) filed on Feb. 27, 2007, the entire contents of which are incorporated herein by way of reference. Furthermore, all references cited herein are incorporated by reference herein in their entirety.
Number | Date | Country | Kind |
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2006-233214 | Aug 2006 | JP | national |
2007-047523 | Feb 2007 | JP | national |
Filing Document | Filing Date | Country | Kind | 371c Date |
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PCT/JP2007/066932 | 8/30/2007 | WO | 00 | 2/27/2009 |