Patent Grant
11048123
The present invention relates to a reflective-type liquid crystal display device.
A reflective-type liquid crystal display device is suitable for use in a bright environment. While its application has been widened, including digital devices such as mobile phones, smartphones and tablet devices and digital signage, which are used outdoors, there is a demand for improving the display quality.
For example, Patent Document 1 by the present applicant discloses a reflective-type liquid crystal display device whose light efficiency is improved by using a liquid crystal layer that takes a substantially vertical alignment in the absence of voltage application and takes a twist alignment in the presence or voltage application. The reflective-type liquid crystal display device produces display in a normally black mode. According to Patent Document 1 (Japanese Laid-Open Patent Publication No. 11-142336; Japanese Patent No. 3344554), there is obtained a reflective-type liquid crystal display device whose contrast ratio is 20:1 or more. The disclosure of Patent Document 1 is herein incorporated by reference in its entirety.
As the present inventor studied the reflective-type liquid crystal display device described in Patent Document 1, it was found that the contrast ratio at a diagonal viewing angle (60° viewing angle) was less than 1 in some cases.
The present invention has been made to solve this problem, and an object thereof is to provide a reflective-type liquid crystal display device capable of producing display with a contrast ratio of 1.0 or more at a 60° viewing angle.
An embodiment of the present invention provides a solution as set forth in items below.
[Item 1] A reflective-type liquid crystal display device including:
a first substrate including a light-reflective first electrode;
a second substrate including a light-transmissive second electrode;
a liquid crystal layer that is provided between the first electrode and the second electrode and takes a generally vertical alignment during black display;
a polarizing layer provided on a viewer side of the second substrate; and
a first retardation layer, a second retardation layer and a third retardation layer that are arranged in this order from a side of the polarizing layer,
wherein 40°≤|θ3−2×θ2+2×θ1|≤50°, 130°≤θ3−2×θ2+2×θ1|≤140°, 220°≤|θ3−2×θ2+2×θ1|≤230° or 310°≤|θ3−2×θ2+2×θ1|≤320° is satisfied, where θ1 denotes an angle formed between an absorption axis or a transmission axis of the polarizing layer and a slow axis of the first retardation layer, θ2 an angle formed between the absorption axis or the transmission axis of the polarizing layer and the slow axis of second retardation layer, and θ3 an angle formed between the absorption axis or the transmission axis of the polarizing layer and the slow axis of the third retardation layer.
[Item 2] The reflective-type liquid crystal display device of Item 1, wherein a contrast ratio at a 60° viewing angle is 1.0 or more.
[Item 3] The reflective-type liquid crystal display device of Item 1 or 2, wherein 160°≤θ1≤170°, 90°≤θ2≤100°, 170°≤θ3≤180°; 250°≤θ1≤260°, 180°≤θ2≤190°, 260°≤θ3≤270°; or 340°≤θ1≤350°, 270°≤θ2≤280°, 350°≤θ3≤360° are satisfied which are equivalent to 70°≤θ1≤80°, 0°≤θ2≤10° and 80°≤θ3≤90°.
[Item 4] The reflective-type liquid crystal display device of any one of Items 1 to 3, wherein |θ3 −2×θ2+2×θ1| is 45°, 135°, 225° or 315°.
[Item 5] The reflective-type liquid crystal display device of any one of Items 1 to 4, wherein an in-plane retardation of the first retardation layer is 265 nm or more and 285 nm or less, an in-plane retardation of the second retardation layer is 265 nm or more and 285 nm or less, and an in-plane retardation of the third retardation layer is 130 nm or more and 145 nm or less.
[Item 6] The reflective-type liquid crystal display device of any one of Items 1 to 5, wherein the liquid crystal layer includes a nematic liquid crystal material whose dielectric anisotropy is negative and a chiral agent, and takes a generally vertical alignment in an absence of voltage application and takes a twist alignment or a hybrid alignment in a presence of white voltage application.
[Item 7] The reflective-type liquid crystal display device of any one of Items 1 to 6, wherein where Δn denotes a birefringence of a liquid crystal material of the liquid crystal layer and d denotes a thickness of the liquid crystal layer, Δnd, which is a product between Δn and d, is 160 nm or more and 400 nm or less.
According to an embodiment of the present invention, it is possible to provide a reflective-type liquid crystal display device capable of producing display with a contrast ratio of 1.0 or more at a 60° viewing angle. Note that a 60° viewing angle refers to a viewing angle such that the polar angle from the normal to the display surface is 60°.
A reflective-type liquid crystal display device according to an embodiment of the present invention will now be described with reference to the drawings, but the present invention is not limited to the embodiment described below.
The polarizing layer 42 is a linear polarizing layer and absorbs linearly-polarized light that is parallel to the absorption axis (perpendicular to the transmission axis) PA. The liquid crystal layer LC is sealed and held by a seal 11 between the first substrate 10 and the second substrate 20. The first substrate 10 and the second substrate 20 are insulative substrates, and may each be a glass substrate or a plastic substrate, for example. At least the second substrate 20 is transparent. Note that the first substrate 10 and the second substrate 20 may each be a flexible substrate.
The liquid crystal layer LC of the reflective-type liquid crystal display device 100 takes a generally vertical alignment during black display. That is, while the reflective-type liquid crystal display device 100 may be either a normally black mode (e.g., a VA mode) or a normally white mode (e.g., a TN mode), a normally black mode where black display is produced in the absence of voltage application will be illustrated below.
The liquid crystal layer LC includes a chiral nematic liquid crystal material whose dielectric anisotropy Δε is negative, for example. A chiral nematic liquid crystal material includes a nematic liquid crystal material whose dielectric anisotropy Δε is negative and a chiral agent. The liquid crystal layer LC takes a generally vertical alignment (see the left portion of the liquid crystal layer LC of
As shown in
Subjecting both of the vertical alignment films 16 and 26 to an alignment treatment gives a liquid crystal layer LC that takes a twist alignment, and subjecting only one of the films to an alignment treatment gives a liquid crystal layer LC that takes a hybrid alignment. They result in reflective-type liquid crystal display devices that produce display in a VATN mode and a VAHAN mode, respectively. The substrate to be subjected to an alignment treatment when producing a reflective-type liquid crystal display device of a VAHAN mode may be either substrate, but when it is subjected to a rubbing treatment, it is preferably the substrate for which the step on the surface of the alignment film is smaller. The present invention is not limited to a vertical alignment but may be of a TN mode where horizontal alignment films are arranged on both substrates, and both of the alignment films are subjected to a rubbing treatment to obtain a cell in which a liquid crystal having a positive dielectric anisotropy is arranged.
The polarizing layer 42, the first retardation layer 44, the second retardation layer 45 and the third retardation layer 46 refer to optical layers that have the respective functions. Although not shown in the figure, in addition to these optical layers, a protection layer (e.g., a TAC layer) and/or an adhesive layer (including a pressure sensitive adhesive layer) are arranged between these optical layers. Herein, for the sake of simplicity, the protection layer and/or the adhesive layer are ignored. Where the protection layer and/or the adhesive layer have a retardation, these layers and the retardation layers as a whole can be made to be equivalent to the first retardation layer 44, the second retardation layer 45 and the third retardation layer 46.
Typically, 40°≤|θ3−2×θ2+2×θ1|≤50°, 130°≤|θ3 −2×θ2+2×θ1|≤140°, 220°≤|θ3−2×θ2+2×θ1|≤230°, 310°≤|θ3−2×θ2+2×θ1|≤320° are satisfied, where θ1 denotes the angle formed between the absorption axis of the polarizing layer 42 and the slow axis of the first retardation layer 44, θ2 the angle formed between the absorption axis of the polarizing layer 42 and the slow axis of the second retardation layer 45, and θ3 the angle formed between the absorption axis of the polarizing layer 42 and the slow axis of the third retardation layer 46. Particularly, it is preferred that |θ3−2×θ2+2×θ1| is 45°, 135°, 225° or 315°. That is, for the relationship 40°≤|θ3−2×θ2+2×θ1|≤50°, the relationship is optically equivalent even when 90°, 180° or 270° is added to the angles. Note that when the value of |θ3−2×θ2+2×θ1| is 360° or more, 360° is subtracted from the value to obtain a value of 0° or more and less than 360°. Although the absorption axis of the polarizing layer 42 is herein used as the reference, the same relationship holds when the transmission axis is used as the reference.
The first retardation layer 44 and the second retardation layer 45 are so-called λ/2 plates, and the third retardation layer 46 is a so-called λ/4 plate. A denotes the wavelength of visible light, and the wavelength range of primary visible light is 400 nm or more and 720 nm or less. Therefore, an in-plane retardation (hereinafter referred to simply as retardation) of the first retardation layer 44 and the second retardation layer 45 is 265 nm or more and 285 nm or less, for example, and the retardation of the third retardation layer 46 is 130 nm or more and 145 nm or less, for example. Note that in the present specification, phase difference may be represented by retardation nm).
As described above, the first retardation layer 44, the second retardation layer 45 and the third retardation layer 46 are arranged so that circularly-polarized light is incident upon the liquid crystal layer LC.
As will be described using a simulation example, using these three retardation layers, the reflective-type liquid crystal display device 100 can realize display with desirable viewing angle characteristics where the normal direction CR is 50:1 or more and the 60° viewing angle CR is 1.0 or more.
Illustrated below is a case where only the pretilt direction LP1 of the liquid crystal molecules on the first vertical alignment film 16 is regulated while the pretilt direction LP2 of the second vertical alignment film 26 is not regulated (no alignment treatment is performed), and the result where the product between Δnd of the liquid crystal layer (the birefringence Δn (589 nm) of the liquid crystal material of the liquid crystal layer) and the thickness (referred to also as the cell gap) d of the liquid crystal layer is 276.5 nm will be described. Note that the following result holds true also when the pretilt direction LP2 of the second vertical alignment film 26 is regulated (i.e., a VATN mode).
In
In
Combinations of θ1 and θ2 that are densely-hatched in both of
With the configuration that only includes two retardation layers described in Patent Document 1, the 60° viewing angle CR was as low as 0.75, failing to produce those having the 60° viewing angle CR of 1.0 or more. In contrast, as can be seen from
Table 1 and Table 2 below show the results of calculating the normal direction CR and 60° viewing angle CR for each of the combinations between the phase difference and θ1 of the first retardation layer, the phase difference and θ2 of the second retardation layer, and the phase difference and θ3 of the third retardation layer. In Table 1 and Table 2, o means that the normal direction CR is 50 or more and the 60° viewing angle CR is 2.0 or more, and Δ means that the normal direction CR is 8 or more and less than 50 and the 60° viewing angle CR is 1.0 or more and less than 2.0. That is, with the combinations shown in Table 1 and Table 2, the 60°viewing angle CR can be improved.
As illustrated in Table 1 and Table 2, desirable viewing angle characteristics are realized when the phase differences of the first retardation layer and the second retardation layer are 265 nm or more and 285 nm or less, the phase difference of the third retardation layer is 130 nm or more and 145 nm or less, and θ1, θ2 and θ3 satisfy the relationship 220°≤|θ3−2×θ2+2×θ1|≤230°. If 70°≤θ1≤80°, 0°≤θ2≤10° and 80°≤θ3≤90° are satisfied as with the 64 combinations illustrated in Table 1 and Table 2, the relationship described above is satisfied, thereby realizing desirable viewing angle characteristics.
Thus, desirable viewing angle characteristics can be realized when 160°≤θ1≤70°, 90°≤θ2≤100°, 170°≤θ3≤180°; 250°≤θ1≤260°, 180°≤θ2≤190°, 260°≤θ3≤270°; and 340°≤θ1≤350°, 270°≤θ2≤280°, 350°≤θ3≤360° are satisfied, which are equivalent to 70°≤θ1≤80°, 0°≤θ2≤10° and 80°≤θ3≤90°.
The example of
As can be seen from
The 60° viewing angle CR shown in
This application claims priority to U.S. Provisional Patent Application No. 62/733,244 filed on Sep. 19, 2018, the disclosure of which is incorporated herein by reference.
| Number | Name | Date | Kind |
|---|---|---|---|
| 6108064 | Minoura | Aug 2000 | A |
| 20040223094 | Hamada | Nov 2004 | A1 |
| Number | Date | Country |
|---|---|---|
| 11-142836 | May 1999 | JP |
| Number | Date | Country | |
|---|---|---|---|
| 20200089050 A1 | Mar 2020 | US |
| Number | Date | Country | |
|---|---|---|---|
| 62733244 | Sep 2018 | US |
