JP3931201B2 - Reflective / transmissive color liquid crystal display - Google Patents

Description

  The present invention relates to a reflective / transmissive color liquid crystal display device having a reflective function and a transmissive function, and more particularly to a reflective / transmissive color liquid crystal display device that places importance on transmissive display. The reflective / transmissive color liquid crystal display device is a color liquid crystal display device that performs reflective display using external light incident from the outside when the ambient environment is bright, and performs transmissive display using backlight when the ambient environment is dark. is there. The liquid crystal display device of the present invention is used for OA equipment such as a word processor and a personal computer, portable information equipment such as an electronic notebook, or a camera-integrated VTR equipped with a liquid crystal monitor.

  The reflection / transmission dual-use color liquid crystal display device is widely used as a display for portable devices and the like because of its low power consumption and transmissive display using a backlight, which can be used in any environment.

  In a conventional reflective / transmissive color liquid crystal display device, a color filter is laminated on a reflective film formed on a back substrate for performing color display, and the reflective film is partially for light transmission. The reflection film having the opening is used as a reflection / transmission reflection film.

  Here, the color filter and the reflective film are formed in the liquid crystal panel in order to prevent display color saturation from being reduced due to parallax due to the substrate thickness, and the color filter having a high transmittance is used to increase the brightness at the time of reflection. .

  Other semi-transparent reflective films include aluminum and silver metal thinned into a half mirror, or metal is patterned by etching, and the remaining metal is used for reflection, and the metal is removed. There are ones that use such portions for transmission, and others that use interference by laminating dielectrics having different refractive indexes.

  The above liquid crystal display device is disclosed in, for example, Patent Document 1 (Japanese Patent Laid-Open No. 11-052366). In this publication, a color filter is laminated on a reflective film formed on a back substrate, and the reflective film has a light transmission aperture in a part of the part facing the pixel of the color filter as the reflective film. Is adopted.

Further, in Patent Document 2 (Japanese Patent Laid-Open No. 11-183892), an opening is provided in the color filter provided on the front substrate, and a reflective film is provided on the inner surface of the rear substrate at a position corresponding to the opening of the color filter. Furthermore, a liquid crystal display element in which a transflective plate is provided on the back side has been proposed. As a result, during reflective display, colored light that has been transmitted through a portion other than the color filter aperture and reflected by the transflective reflector, and high-luminance non-colored light that has been transmitted through the color filter aperture and reflected by the reflective film Light can display high-luminance color pixels, and during transmissive display, only colored light that has passed through portions other than the openings of the color filter can be emitted to the front of the device to display color pixels with high contrast. It has been shown.
Japanese Patent Laid-Open No. 11-052366 Japanese Patent Laid-Open No. 11-183892

  However, in the liquid crystal display device described in Patent Document 1, when a high transmittance color filter is used to increase the brightness at the time of reflection, the color saturation is high because the color filter passes twice during the reflective display. However, there is a problem that the color saturation of the display is greatly reduced because it passes through the color filter only once during the transmissive display, and the color filter of high saturation (low transmittance) is intended to increase the display color saturation during the transmissive display. However, there is a problem that the brightness at the time of reflection is greatly reduced, and the visibility is remarkably lowered.

  Furthermore, in the liquid crystal display element described in Patent Document 2, it is necessary to prepare two reflective films. Further, at the time of reflective display, the reflective film provided on the inner surface of the rear substrate and the half provided on the back side are provided. Since two reflected lights from the transmissive reflector are used, there is a problem that the color purity is lowered due to the influence of parallax due to the presence of the rear substrate.

  Therefore, the present invention provides a transmissive display while maintaining the brightness contrast in the reflective display without increasing the number of manufacturing steps in the reflective / transmissive color liquid crystal display device, particularly the reflective / transmissive dual-use color liquid crystal display device that emphasizes transmissive display. It is to improve display color saturation at the time.

  In order to solve the above-described problems, a reflective / transmissive color liquid crystal display device according to the present invention includes a first substrate and a second substrate facing each other, and a liquid crystal layer interposed between the first substrate and the second substrate. And a reflective film formed on the second substrate on the liquid crystal layer side, and a color filter formed on the reflective film, and the light incident from the first substrate side is A reflection / transmission dual-use color liquid crystal display in which a plurality of pixel regions each having a reflection region that reflects toward one substrate and a transmission region that transmits light incident from the second substrate toward the first substrate are formed in a matrix. In the apparatus, the color filter has an opening in the reflection region.

  That is, the reflective / transmissive color liquid crystal display device of the present invention (hereinafter also simply referred to as “liquid crystal display device”) is provided so that the opening of the color filter is located in the reflective region in one pixel, It is provided so as not to overlap the transmission region.

  In the liquid crystal display device of the present invention, during transmissive display using a light source provided on the back surface of the liquid crystal display device, the light transmitted through the transmissive region is emitted through the color filter, so that a bright display that satisfies display color saturation is achieved. Is obtained. At this time, desired characteristics can be obtained by adjusting the luminance of the light source, the area and shape of the transmissive region on the second substrate, and the saturation, transmittance, or film thickness of the color filter.

  The transmissive region is usually a region where no reflective film is formed, but the thickness of the reflective film is reduced so that light from the light source provided on the back surface of the liquid crystal display device has a transmittance of 90% or more, preferably 95. A region that transmits at% or more is also included in the transmission region. In addition, the reflection region is not only a region where the light from the first substrate side (observer side) is totally reflected (reflectance 100%), but also a part of the light from the first substrate side is transmitted, and the reflectance 90 %, More preferably 95% or more.

  At the time of reflective display using outside light, light incident from the front (observer side) of the liquid crystal display device passes through the color filter or the opening of the color filter and is reflected by the reflective region of the reflective film. Since the light passes through the opening of the color filter and is emitted, it becomes a composite outgoing light of the colored outgoing light and the colored outgoing light, and a bright display is obtained. At this time, it is possible to adjust the brightness and saturation of the emitted light by adjusting the characteristics of the color filter and the area and shape of the opening of the color filter as appropriate. In addition, by increasing the color filter opening, it is possible to employ a color filter with high color purity.

  In the liquid crystal display device of the present invention, it is preferable that the color filter has a plurality of openings in the reflection region. Thereby, at the time of reflective display, since the emitted light which is not colored is dispersed in one pixel and emitted to the first substrate side, bright areas in one pixel are dispersed, and visibility is improved.

  In the liquid crystal display device of the present invention, it is preferable that the reflective film is a diffuse reflective film having a concavo-convex shape on the surface on the liquid crystal layer side. Thereby, at the time of reflective display, the reflected light by the reflective film is diffused and transmitted through the color filter and emitted to the first substrate side, so that the brightness and saturation of the synthesized emitted light are homogenized in one pixel, Visibility is improved.

  In the liquid crystal display device of the present invention, the area ratio of the transmissive region to the pixel region is 10% to 50%, and the area ratio of the region where the opening is formed to the reflective region is 5% to 30%. The following is preferable. As a result, it is possible to realize a reflection / transmission type color liquid crystal display device that can satisfy actual use during reflection display and transmission display. Specifically, by setting the area ratio of the region where the reflective film is not formed (transmission region) to 10% or more, the brightness at the time of transmissive display can be secured, and by setting the area ratio to 50% or less, Brightness is secured. On the other hand, when the aperture ratio of the color filter is 5% or more, the brightness during the reflective display is ensured, and when it is 30% or less, the color area during the reflective display is secured and the color difference can be determined. It becomes. Here, the aperture ratio of the color filter is expressed as a relative ratio to the area of the reflective region in order to perform evaluation during reflective display. This is because the size of the color filter opening greatly affects the reflective display.

  In this specification, an area of the liquid crystal display device corresponding to a “pixel” that is a minimum unit of display is referred to as a “pixel area”. In a color liquid crystal display device, “pixels” of R, G, and B correspond to one “picture element”. In the simple matrix liquid crystal display device, each region where a column electrode provided in a stripe shape and a row electrode provided so as to be orthogonal to the column electrode intersect each other defines a pixel region. In an active matrix liquid crystal display device, a pixel region is defined by a pixel electrode and a counter electrode facing the pixel electrode. In the configuration in which the black matrix is provided, strictly speaking, among the regions to which a voltage is applied according to the state to be displayed, the region corresponding to the opening of the black matrix corresponds to the pixel region.

  In the liquid crystal display device of the present invention, it is preferable that a transparent resin having a transmittance of 90% or more is filled in the opening of the color filter. As a result, the step of the color filter opening is eliminated, so that the rise of the liquid crystal molecules in the vicinity of the color filter opening becomes uniform, and the contrast (particularly, the contrast during reflection) is improved. On the surface of the color filter, a flattening film made of an acrylic resin or the like is laminated in order to flatten the unevenness on the surface of the color filter. Therefore, when the opening of the color filter is shallow, the opening is filled with the planarizing film. However, when the color filter has a deep opening, the step in the opening is not eliminated by the planarization film unless the transparent resin is filled in the opening, and the step remains. Particularly in the STN liquid crystal, the presence of a step due to the opening of the color filter may cause a serious problem that the rise of liquid crystal molecules in the pixel becomes non-uniform and the contrast during reflection display is lowered.

  The transparent resin only needs to have a higher transmittance than the color filter. However, in order to ensure the brightness at the time of transmissive display, it is better that the transmittance is high. Even when a pigment for color tone correction is mixed in the transparent resin, the transmittance is 90% or more, preferably 95% or more. It is desirable to ensure.

  According to the configuration of the present invention, the reflective film having the opening and the color filter having the opening are provided on one substrate so that each opening is located in a different region in one pixel. The liquid crystal display device of the present invention can be obtained without increasing the number of conventional processes.

  Furthermore, in the liquid crystal display device of the present invention, at the time of transmissive display using the light source provided on the back surface of the liquid crystal display device, the light transmitted through the opening of the reflective film is emitted through the color filter, thereby displaying color saturation. A bright display that satisfies the above can be obtained.

  At the time of reflective display using outside light, light incident from the front of the liquid crystal display device passes through the color filter or the color filter opening, is reflected by the reflection area of the reflective film, and passes again through the color filter or the color filter opening. Therefore, it becomes a combined outgoing light of the outgoing light without coloring and the colored outgoing light, and a bright display is obtained.

  Furthermore, it is possible to adjust the brightness and saturation of the emitted light by adjusting the characteristics of the color filter and the area and shape of the color filter opening as appropriate, so a color filter with high color purity should be adopted. Is also possible.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. In the following embodiments, a simple matrix drive type STN liquid crystal display device is taken as an example of the liquid crystal display device, but the reflection / transmission dual-use color liquid crystal display device of the present invention is a TFT (Thin Film Trasistor) or MIM (Metal). It can also be applied to an active matrix color liquid crystal display device using a switching element such as -Insulator-Metal).

  FIG. 1 is a diagram schematically showing a reflective / transmissive color liquid crystal display device according to this embodiment. The reflective / transmissive dual-use color liquid crystal display device of the present embodiment includes an upper polarizing plate 1, a first retardation plate 2, a second retardation plate 3, an upper substrate 4 and a transparent plate from the viewer side (upper side in FIG. 1). Display electrode 5a, alignment film 7a, STN liquid crystal layer 8, alignment film 7b, transparent display electrode 5b, overcoat layer 9, color filter 10, reflection film 11, lower substrate 12, third retardation plate 13, lower The side polarizing plate 14, the light guide plate 151, and the backlight 161 are stacked in this order. Note that the upper substrate 4 and the lower substrate 12 are bonded to each other via the seal resin 6 to form the STN liquid crystal layer 8.

  In the liquid crystal display device of the present embodiment, the reflection region that reflects the light incident from the upper substrate 4 side to the upper substrate 4 side by the reflective film 11 and the light incident from the lower substrate 12 side are transmitted to the upper substrate 4 side. A plurality of pixel regions each having a transmission region to be formed are formed in a matrix.

  FIG. 2 is a cross-sectional view of the color filter 10 and the reflective film 11 showing the positional relationship between the reflective region Re and the transmissive region Tr and the opening of the color filter. Here, a pixel region having a reflection region Re and a transmission region Tr is formed in each of red (R), green (G), and blue (B) pixels, and a plurality of openings 10a are provided in the color filter 10 of each pixel. Each opening 10a of the color filter 10 is provided in the reflection region.

  In the present embodiment, the transmissive region Tr is formed by forming the transmissive through hole portion 11a on the reflective film 11 covering one surface of the lower substrate 12 by using the photolithography method. It can also be expressed as an opening (light transmission region) 11a of the reflective film 11. Therefore, the liquid crystal display device of this embodiment has the liquid crystal layer 8 sandwiched between the pair of substrates 4 and 12, and the color filter 10 and the opening (light transmission region) 11 a in the pixel region serving as a display unit. A reflective / transmissive color liquid crystal display device having a reflective film 11 having an opening 10a of the color filter 10 is provided in a region of the reflective film 11 other than the opening (light transmission region) 11a. It can also be expressed as a reflection / transmission dual-use color liquid crystal display device.

  FIG. 3 is a plan view showing the reflective film 11 used in this embodiment, and shows the reflective film 11 in each pixel region of red (R), green (G), and blue (B). The reflective film 11 is formed by depositing 1000 mm (100 nm) of aluminum on the lower substrate 12, and a through-hole portion 11a for transmission is formed by patterning the aluminum film using a photolithography method.

  In the present embodiment, the area of the through hole portion 11a on the lower substrate 12 is set to 30% with respect to the area on the lower substrate 12 in the pixel region. The area ratio of the through-hole portion 11a is not limited to this embodiment, and is preferably 10% or more and 50% or less. When the area ratio of the through-hole portion 11a is less than 10%, the use of transmitted light is small and the screen during transmissive display becomes dark. When the area ratio exceeds 50%, the reflective display screen is dark even in the transmissive display-oriented type and the visibility problem is low. I get out.

  For example, an electrodeposition method can be used to manufacture the color filter 10 having the opening 10a. An example of the manufacturing process of the color filter 10 by the electrodeposition method will be described. An electrodeposition ITO film (electrode) is formed on the reflective film 11. An opening that penetrates the electrodeposition ITO film in the thickness direction is formed at a position corresponding to the formation region of the opening 10a of the color filter 10 by photolithography. After the resist is formed on the electrodeposition ITO film, the resist in the pixel region of the color to be electrodeposited is removed. The electrodeposition ITO film is energized, and the color filter material of the color to be electrodeposited is electrodeposited on the exposed electrodeposition ITO film. At this time, since the color filter material is not electrodeposited in the region of the opening of the electrodeposited ITO film, the opening 10 a is formed in the color filter 10. After removing the resist, a new resist is formed on the electrodeposition ITO film. The resist in the pixel region of the other color that is the electrodeposition target is removed. In the same manner, the color filters 10 of other colors are formed.

  In the present embodiment, the electrodeposition method is used for manufacturing the color filter 10, but in addition to the electrodeposition method, a general method for manufacturing a color filter such as a pigment dispersion method, a printing method, a dyeing method, or the like is used to open the aperture. You may create the color filter 10 which has the part 10a.

  FIG. 4 is a plan view showing the reflective film 11, the electrodeposition ITO film, and the color filter 10. The left side of FIG. 4 is a plan view of one pixel, and shows a state in which a plurality of slit-like ITO film removal portions are formed by depositing and patterning an electrodeposition ITO film on the reflective film 11. The center of FIG. 4 shows a state in which the color filter (CF) of each pixel of red (R) green (G) blue (B) is electrodeposited on the electrodeposition ITO film. The right side of FIG. 4 shows a state in which pixels of red (R), green (G), and blue (B) are arranged in a matrix. As shown in FIG. 4R> 4, in the present embodiment, the through hole portion 11a of the reflective film 11 is formed at a substantially central portion of one pixel region. In addition, in each pixel of the color filter 11, four parallel opening portions 10 a extending in the column direction are formed in two upper and lower stages with the through hole portion 11 a of the reflective film 11 interposed therebetween. Since the color filter 10 has a plurality of openings 10a in the reflection region Re, emission light without coloring is dispersed in one pixel and emitted to the upper substrate 4 side during reflection display. Therefore, bright areas in one pixel are dispersed, and visibility is improved.

  The optimum ratio of the opening area of each of the reflective film 11 and the color filter 10 will be described. Hereinafter, the ratio of the aperture of the reflective film is defined as “the ratio of the area of the aperture of the reflective film to the area of one pixel region”, and the ratio of the aperture of the color filter is defined as Each area ratio is defined. The areas of one pixel, the opening of the reflection film, and the opening of the color filter are defined when the respective regions are viewed from the normal direction of the substrate surface, in other words, in a plane parallel to the substrate surface. Area.

  A liquid crystal display device was produced in which the ratio of the reflective film opening to one pixel and the ratio of the color filter opening to the reflective part were changed, and the optical characteristics during reflective display and transmissive display were measured. The results are shown in FIGS.

  FIG. 5 is a graph showing the color reproducibility at the time of reflective display when the color filter aperture ratio is changed, and shows the relationship between the color filter aperture ratio and the color area at the time of reflective display. The color area is an index of color reproducibility and is defined as follows. It can be said that the larger the color area, the better the color reproducibility.

  Color area = Area of triangle connecting RGB chromaticity coordinates × 1000 In the measurement shown in FIG. 5, a reflection film having a reflection film opening ratio of 40% is used, and a color filter having a Y value of 40 is used. .

  FIG. 6 is a graph showing the reflectance when the color filter opening ratio is changed. In the measurement shown in FIG. 6, as in the measurement of FIG. 5, a reflection film having a reflection film opening ratio of 40% is used, and a color filter having a Y value of 40 is used.

  From the measurement results shown in FIGS. 5 and 6, it can be seen that as the color filter opening ratio increases, the color area at the time of reflection display decreases, whereas the reflectance increases conversely. From the measurement result of FIG. 5, when the color area at the time of reflection is less than 4, the chromaticity difference between R, G, and B becomes small, and it becomes difficult to distinguish the color difference particularly when multicolor display is performed. Therefore, since it became a blurred display, it turned out that it is not an actual use level. Therefore, the upper limit of the color filter opening ratio is preferably 30% at which the color area is 4.

  Since external light is used during reflection display, the display quality during reflection depends on the brightness of the environment when used. In very bright environments such as outdoors in fine weather, even if the reflectance is about 1%, it is sufficiently recognizable, but in office environments that are considered to be most frequently used on mobile devices, it is darker than outdoors. Therefore, the minimum reflectance necessary for recognizing the display is considered to be about 4%. According to the measurement result of FIG. 6, the color filter opening ratio at which the reflectance is 4% is 5%, so the lower limit of the color filter opening ratio is preferably 5%.

FIG. 7 is a graph showing changes in reflectance and transmittance when the ratio of the opening portions of the reflective film is changed. In the measurement shown in FIG. 7, a color filter having an aperture ratio of 10% and a Y value of 40 was used. The lower limit of the transmittance depends on the luminance level of the back lamp. For example, in a display device for use in a mobile phone, a back lamp that can obtain a light emission luminance of approximately 1000 cd / m ² is used. In an office environment and an environment darker than that, if the luminance at the time of transmission is 10 cd / m ^2, it can be recognized sufficiently. Therefore, in a display device for cellular phones, a reflectance of about 1% is sufficient. According to the result of FIG. 7, the reflectance is 1% when the reflection film opening ratio is 10%. Therefore, the lower limit of the reflection film opening ratio is preferably 10%. As described above, the reflectance should be about 4% when it is assumed to be used in an office environment as described above. According to the result of FIG. 7, the reflectance is 4% when the reflection film opening ratio is 50%. Therefore, the upper limit of the reflection film opening ratio is preferably 50%.

  In the liquid crystal display device of this embodiment, an overcoat layer 9 of acrylic resin is formed on the color filter 10. The overcoat layer 9 is formed to flatten the uneven surface of the color filter 10 and make the rise of liquid crystal molecules uniform. In the case of a liquid crystal display device in which a color filter is provided on one substrate and a reflective film is provided on the other substrate, it is necessary to form an overcoat layer on each of the color filter and the reflective film. On the other hand, since the color filter 10 is laminated on the reflective film 11 in the liquid crystal display device of this embodiment, the overcoat layer 9 only needs to be provided on the color filter 10, and the manufacturing process is simplified. Is done. Even when a diffuse reflection film is used as the reflection film, surface irregularities are eliminated by the overcoat layer 9.

  FIG. 8 is a cross-sectional view schematically showing a lower substrate having a diffuse reflection film. The diffuse reflection film is composed of a transparent resin layer 30 made of an acrylic resin or the like having a smooth uneven surface and a reflection film 11 laminated on the transparent resin layer 30. The transparent resin layer 30 is manufactured by the following process, for example. A photosensitive resin film is formed on the lower substrate 12, and a plurality of openings are formed by photolithography. When the heat treatment is further performed, the surface is deformed by a drooling phenomenon, and the corners of the opening are removed to form a gentle uneven surface. By using a diffuse reflection film as the reflection film, the reflected light from the diffuse reflection film is diffused and transmitted through the color filter 10 and emitted to the upper substrate 4 side at the time of reflective display. The degree is homogenized in one pixel, and visibility is improved. In addition, the reflective film 11 is mirror-formed, and an overcoat film made of a transparent resin in which a light scattering material is dispersed is separately formed on the reflective film 11 as a scattering layer to give a light diffusion function to the liquid crystal display device. Also good.

  When the thickness of the color filter 10 is large, in other words, when the opening 10a of the color filter 10 is deep, the step between the color filter forming portion and the opening 10a becomes large, and the overcoat layer 9 cannot eliminate this step. , Planarization may be insufficient. In particular, in the display device using the STN liquid crystal layer, the rise of the liquid crystal molecules in the vicinity of the color filter opening 10a is delayed due to the presence of the step, and the rise of the liquid crystal molecules becomes uneven in the pixel. There arises a problem that the contrast is lowered.

  FIG. 9 is a graph showing the relationship between the level difference between the color filter portion and the color filter opening and the contrast during reflection display. In measuring the level difference between the color filter portion and the opening portion, in consideration of the flatness of various films formed on the color filter 10, the substrate after the alignment process is completed (in other words, before the upper and lower substrates are bonded together). Used and measured by a palpation meter. Further, using a color filter material having a transmittance of 95% to which only a color tone correction pigment was added, the opening 10a of the color filter 10 was filled with a transparent resin to adjust the level difference.

  In addition, when a color filter is formed using the electrodeposition ITO film | membrane which has an opening part, since transparent resin cannot be electrodeposited to the opening part 10a of the color filter 10, the opening part 10a is used using the resist direct electrodeposition method. Electrodeposit a transparent resin. The resist direct electrodeposition method is a method of patterning a photosensitive resin applied on electrodeposited ITO to partially expose the electrodeposited ITO and forming an electrodeposition color filter on the exposed portion. Using this method, it is possible to form RGB color filters and a transparent resin layer in the opening 10a.

  According to FIG. 9, it can be seen that the reflection contrast improves as the step becomes smaller (that is, as the step approaches zero). Specifically, if the color filter film thickness is larger than the color filter opening film thickness (that is, the film thickness of the transparent resin layer filled in the opening 20), the liquid crystal molecules in the vicinity of the color filter opening 10a When the rising edge is delayed, and conversely, when the color filter opening film thickness becomes larger than the color filter film thickness, the liquid crystal molecules rise quickly in the opening 10a, and as a result, the contrast decreases. Therefore, it is desirable to adjust the film thickness of the transparent resin filled in the opening 10a so as not to cause a step with the color filter forming portion.

  In this embodiment, the opening 10a of the color filter 10 is a through-hole penetrating the color filter 10 in the thickness direction, and the transmittance in the opening 10a is ensured to be 90% or more, preferably 95% or more. If possible, an opening having a depth shorter than the film thickness of the color filter 10 may be used.

  In the liquid crystal display device of this embodiment, transparent display electrodes 5a and 5b are formed on the STN liquid crystal layer 8 side of the upper substrate 4 and the lower substrate 12, respectively. The transparent electrodes 5a and 5b are formed in stripes by depositing and etching ITO (indium tin oxide) on the upper substrate 4 and on the overcoat layer (planarization layer) 9 of the lower substrate 12, respectively. The regions intersecting each other form a matrix pixel electrode. A black matrix may be formed around the pixel with a light-absorbing substance, which improves the light blocking effect and contributes to higher contrast. On the transparent display electrodes 5a and 5b, a polyimide resin is applied by printing and baked to form alignment films 7a and 7b. Further, the alignment films 7a and 7b are rubbed so that the twist angle of the liquid crystal molecules is 240 ° twist.

  After the upper and lower substrates 4 and 12 are bonded to each other with the sealing resin 6, the STN liquid crystal layer 8 is formed by injecting a liquid crystal material with adjusted birefringence Δn and pitch, thereby forming an STN liquid crystal cell. A polycarbonate-stretched first retardation plate 2, second retardation plate 3, and third retardation plate 13 each having a desired dΔn, and a neutral gray upper polarizing plate 1 and a lower polarizing plate 14. The optical axis of each member is attached so as to be in a predetermined direction with respect to the liquid crystal cell. D is the thickness of the retardation plate. Further, a light guide plate 151 and a backlight 161 are provided on the side opposite to the viewer side so that the backlight light is incident on the liquid crystal cell.

  FIG. 10 shows the axial angle of each optical element in the present embodiment. The angle at which the liquid crystal molecules are twisted from the alignment direction 15 on the lower substrate 12 side of the STN liquid crystal layer 8 to the alignment direction 16 on the upper substrate 4 side is set to 240 °. When the clockwise direction is positive and the counterclockwise direction is negative, the angle formed by the upper alignment direction 16 of the liquid crystal molecules with respect to the slow axis 17 of the second retardation plate 3 is 120 °, and the first retardation plate 2 The angle formed by the slow axis 17 of the second retardation plate with respect to the slow axis 18 is 40 °, and the angle formed by the slow axis 18 of the first retardation plate 2 with respect to the absorption axis 19 of the upper polarizing plate 1. 75 °. The angle formed by the slow axis 20 of the third retardation plate 13 with respect to the orientation direction 15 on the lower substrate 12 side is 50 °, and the lower polarizing plate with respect to the slow axis 20 of the third retardation plate 13. The angle formed by the 14 absorption axes 21 is −40 °.

  Each retardation value is set to STN liquid crystal layer 8 (800 nm), first retardation plate 2 (680 nm), second retardation plate 3 (180 nm), and third retardation plate 13 (140 nm). A liquid crystal display device that is in a normally black mode when transmitting is configured.

  In the liquid crystal display device of the present embodiment, the reflective film 11 having the opening 11a and the color filter 10 having the opening 10a are positioned so that the openings 11a and 10a are located in different regions in one pixel. It is provided on the lower substrate 12. This makes it possible to obtain the liquid crystal display device of this embodiment without increasing the number of conventional processes (see the comparative example described later).

  In the case of a liquid crystal display device in which a color filter is provided on one substrate and a reflective film is provided on the other substrate, it is necessary to form an overcoat layer on each of the color filter and the reflective film. On the other hand, since the color filter 10 is laminated on the reflective film 11 in the liquid crystal display device of this embodiment, the overcoat layer 9 only needs to be provided on the color filter 10, and the manufacturing process is simplified. Is done.

  Further, when manufacturing a liquid crystal display device in which a color filter is provided on one substrate and a reflective film is provided on the other substrate, the bonding accuracy is low when the two substrates are bonded. There is a possibility that problems such as the overlapping of both openings may occur. On the other hand, in the liquid crystal display device of this embodiment, the openings of both the color filter and the reflective film are relatively positioned by a highly accurate photolithographic method, so that both the openings are overlapped. Etc. can be prevented.

  In the liquid crystal display device of this embodiment, during transmissive display using a light source (backlight 161) provided on the back surface of the liquid crystal display device, the light transmitted through the opening 11a of the reflective film 11 passes through the color filter 10 and is emitted. As a result, a bright display satisfying the display color saturation can be obtained. By adjusting the brightness of the light source, the area and shape of the opening 11a of the reflective film 11, the saturation, the transmittance, and the film thickness of the color filter 10, a transmissive display with desired characteristics can be obtained.

  At the time of reflective display using external light, the light incident from the front of the liquid crystal display device passes through the color filter 10 or the color filter opening 10a and is reflected by the reflective region portion (region portion other than the opening portion 11a) of the reflective film 11. Then, the light passes through the color filter 10 or the color filter opening 10a again and is emitted. Therefore, it becomes a composite outgoing light of the outgoing light without coloring and the colored outgoing light, and a bright display is obtained. By adjusting the characteristics of the color filter 10 and the area and shape of the color filter opening 10a as appropriate, the brightness and saturation of the emitted light can be adjusted. Further, by increasing the color filter opening 10a, it is possible to employ a color filter with high color purity.

  Further, in the case of a liquid crystal display device in which a color filter is provided on the substrate on the viewer side and a reflective film is provided on the substrate on the back side, the color filter and the reflective film are provided apart via a liquid crystal layer. There is a risk of color mixing. Specifically, for example, when incident light colored by a blue color filter provided on the viewer side substrate is reflected by a reflective film provided on the back side substrate and emitted to the viewer side, It may pass through a green color filter provided on the substrate on the viewer side. In this case, the emitted light is mixed with blue and green and becomes dark, which may reduce the color purity. On the other hand, since the color filter is formed on the reflective film in the liquid crystal display device of the present embodiment, there is no possibility that color mixing occurs during the reflective display and the color purity is not lowered.

(Comparative example)
A comparative example for comparison with the liquid crystal display device of the present embodiment will be described with reference to FIG. Since the reflective / transmissive dual-use color liquid crystal display device of the comparative example is the same as that described in the embodiment except for the color filter and the reflective film, the description of the configuration other than the color filter and the reflective film is omitted.

  As shown in FIG. 11, the reflective film used in the comparative example is formed by forming an aluminum film having a through-hole portion for transmission on a lower substrate (not shown) with a thickness of 1000 mm (100 nm). Has been. The area of the through hole portion is set to be 30% of the pixel. An RGB striped color filter is formed on the electrodeposition electrode.

  Further, in this comparative example, as shown in FIG. 11, the color filter pigments in the reflective film transmission region (here, the reflective film through-hole portion) and the reflective film reflective region (here, the portion other than the through-hole portion of the reflective film). The concentration is changing. In order to manufacture color filters having different pigment concentrations in the transmission region and the reflection region, a resist direct electrodeposition method is used. Using this method, color filters having different pigment concentrations are formed in the transmissive region portion and the reflective region portion for each color.

  As a result, it is possible to achieve high saturation of the display color during transmission while maintaining the brightness during reflection. However, since color filters having different transmittances are formed in the transmissive part and the reflective part, the color filter electrodeposition process increases. Specifically, a total of six photolithography steps are required for electrodepositing the reflective color filter and the transmissive color filter for each of RGB. Further, for each color, color filter materials having two types of pigment concentrations are required, which increases the manufacturing cost. On the other hand, in the liquid crystal display device of this embodiment, the color filter can be electrodeposited through one photolithography process for each of RGB. Even if a photolithographic process for providing an opening in the electrodeposited ITO film is added, the color filter can be electrodeposited by a total of four photolithographic processes. In addition, since each color can be electrodeposited with a color filter material having a single pigment concentration, an increase in manufacturing cost can be suppressed.

  In the comparative example, a high transmission color filter (Y = 60) is employed to maintain the brightness at the time of reflection. However, in the liquid crystal display device of the present embodiment, it is not necessary to use a high transmission color filter. For example, in the above-described embodiment, a color filter with Y = 43 is used. FIG. 12 shows the characteristics of the color filters used in the comparative example and the embodiment, respectively. From the results of the chromaticity coordinates shown in FIG. 12, it can be seen that the liquid crystal display device of this embodiment is preferable also in terms of saturation.

  In this embodiment, the reflective film 11 and the color filter 10 are laminated on the lower substrate 12, but the reflective film 11 and the color filter 10 may be laminated on the upper substrate 4. In this embodiment, a liquid crystal display device having a polarizing plate has been described as an example. However, the present invention can also be applied to a guest-host type or polymer dispersion type liquid crystal display device that does not require a polarizing plate. In this embodiment, the case where a full color image is displayed with three colors of red, green, and blue has been described. However, a full color image may be displayed with three colors of magenta, yellow, and cyan. As the upper substrate 4 and the lower substrate 12 of the present embodiment, glass substrates such as float glass and soda glass, and plastic substrates such as polyethersulfone, polycarbonate, epoxy resin, and polyethylene terephthalate can be used. The liquid crystal display device of the present invention may employ a pixel arrangement such as a stripe arrangement, a delta arrangement, a mosaic arrangement, or a square arrangement. In the liquid crystal display device of the present invention, the number of hues of pixels may be 4 or more.

1 is a diagram schematically showing a reflective / transmissive color liquid crystal display device according to an embodiment of the present invention. FIG. 6 is a cross-sectional view of the color filter 10 and the reflective film 11 showing a positional relationship between the reflective region Re and the transmissive region Tr and the opening of the color filter. It is a top view which shows the reflecting film 11 used for embodiment, and has shown the reflecting film 11 in each pixel area | region of red (R) green (G) blue (B). It is a top view which shows the reflective film 11, the electrodeposition ITO film | membrane, and the color filter 11. FIG. It is a graph which shows the color reproducibility at the time of reflective display when changing a color filter opening part ratio. It is a graph which shows a reflectance when a color filter opening part ratio is changed. It is a graph which shows the change of the reflectance and transmittance | permeability when changing a reflective-film opening part ratio. It is sectional drawing which shows typically the lower substrate which has a diffused reflection film. It is a graph which shows the relationship between the level | step difference of a color filter part and a color filter opening part, and the contrast at the time of reflective display. It is a figure which shows the axial angle of each optical element in embodiment. It is sectional drawing which shows the reflective film and color filter of a comparative example. It is a figure which shows the characteristic of the color filter each used by the comparative example and embodiment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Upper polarizing plate 2 1st phase difference plate 3 2nd phase difference plate 4 Upper board | substrate 5a, 5b Transparent display electrode 6 Seal resin 7a, 7b Alignment film 8 STN liquid crystal layer 9 Overcoat layer 10 Color filter 10a Color filter opening part 11 Reflective film 11a Reflective film opening (through hole)
12 Lower substrate 13 Third retardation plate 14 Lower polarizing plate 151 Light guide plate 161 Backlight Re Reflection region Tr Transmission region

Claims (1)

First and second substrates facing each other, an STN liquid crystal layer interposed between the first substrate and the second substrate, and a reflection formed on the second substrate on the STN liquid crystal layer side A film, a color filter formed on the reflective film, and an overcoat layer formed on the color filter, and the light incident from the first substrate side is directed to the first substrate side by the reflective film. A reflection / transmission color liquid crystal display device in which a plurality of pixel regions each having a reflection region to be reflected and a transmission region for transmitting light incident from the second substrate side to the first substrate side are formed in a matrix. ,
The color filter has an opening whose entire circumference is surrounded by the color filter in the reflection region;
A reflective / transmissive color liquid crystal display device in which the reflective region is formed across the transmissive region in one pixel region .

Images