Device that can switch between mirror state and image display state

Abstract

To provide a device that is capable of switching between a mirror state and an image display state, with display unevenness eliminated when states change from the mirror state to a transparent state (image display state).SOLUTION: In a device capable of switching between a mirror state and an image display state, a liquid crystal mirror unit 2' is provided on front side of an image display unit 1. The liquid crystal mirror unit 2' includes a VA-type liquid crystal layer 21', transparent electrodes 22, 23 that sandwich the VA-type liquid crystal layer 21', an absorption type polarizing plate 24 that has a transmission axis in a first direction, and that transmits first linearly polarized light and absorbs second linearly polarized light that crosses the first linearly polarized light, and a reflection-type polarizing plate 25 that has a transmission axis in a second direction, and that transmits the second linearly polarized light and reflects the first linearly polarized light. A control circuit 3 raises a drive voltage V between the transparent electrodes of the liquid crystal mirror unit 2' to a prescribed voltage Vmax for placing a vertical orientation-type liquid crystal layer 21' into an ON state from an OFF state going through an initial voltage Vs, by sweeping in a prescribed sweep time Ts.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a device capable of switching between a mirror state and an image display state. The device capable of switching between a mirror state and an image display state is used in a vehicle rearview mirror (see Patent Document 1). [Background technology]

[0002] FIG. 9 is a diagram showing a conventional device capable of switching between a mirror state and an image display state (see Patent Document 2).

[0003] 9, which can switch between a mirror state and an image display, a liquid crystal mirror unit 2 is provided in front of an image display unit 1. The liquid crystal mirror unit 2 includes a twisted nematic (TN) liquid crystal layer 21, a pair of transparent electrodes 22 and 23 sandwiching the TN liquid crystal layer 21, an absorptive polarizer 24 provided on the transparent electrode 22 side and having a horizontal transmission axis that transmits first linearly polarized light and absorbs second linearly polarized light that intersects the first linearly polarized light, and a reflective polarizer 25 provided on the transparent electrode 23 side and having a vertical transmission axis that transmits the second linearly polarized light and reflects the first linearly polarized light. A drive voltage V between the transparent electrodes of the image display unit 1 and the liquid crystal mirror unit 2 is controlled by a control circuit 3, such as a microcomputer.

[0004] FIG. 10 is a timing diagram of the driving voltage V between the transparent electrodes of the liquid crystal mirror unit 2 in FIG.

[0005] As shown in FIG. 10, when the driving voltage V between the transparent electrodes is in the ON state (V=Vmax), the polarization axis of the TN liquid crystal layer 21 does not change. of The first linearly polarized light that has passed through the absorptive polarizer 24 passes through the liquid crystal layer 21 and is reflected by the reflective polarizer 25, and the reflected first linearly polarized light passes through the TN liquid crystal layer 21 and exits the absorptive polarizer 24. In other words, the liquid crystal mirror unit 2 is in a mirror state. In this case, the image display unit 1 is turned off by the control circuit 3.

[0006] On the other hand, when the driving voltage V between the transparent electrodes is in the OFF state (for example, V=0V), the TN polarization axis of the TN liquid crystal layer 21 changes. of Of these, the first linearly polarized light that passes through the absorptive polarizer 24 is changed into second linearly polarized light by the TN liquid crystal layer 21, and the changed second linearly polarized light is then transmitted through the reflective polarizer 25. Similarly, image light from the image display unit 1 passes through the reflective polarizer 25 to become second linearly polarized light, and is then converted into first linearly polarized light by the TN liquid crystal layer 21 before exiting the absorptive polarizer 24. In other words, the liquid crystal mirror unit 2 is in a transparent state. In this case, when the image display unit 1 is turned on by the control circuit 3, the screen display state, for example, a white display state, is displayed. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Patent Publication No. 2021-138195 [Patent Document 2] JP 2003-202565 A (Patent No. 4348061 A) Summary of the Invention [Problem to be solved by the invention]

[0008] In the device shown in FIG. 9 that can switch between a mirror state and an image display state, When a vertically aligned (VA) liquid crystal layer is used instead of the TN liquid crystal layer 21, The following challenges exist:

[0009] In the mirror state shown in Fig. 11, when the driving voltage V between the transparent electrodes is 0 V, the liquid crystal molecules 21a are almost perpendicular to the rubbing direction on the vertical alignment layer, as shown in Fig. 12(A), but the perpendicular direction of the liquid crystal molecules 21a, for example, at a pretilt angle of 89.0°, fluctuates depending on the rubbing lines that are the irregularities on the alignment film surface caused by the rubbing process and the irregularities on the glass substrate (not shown). An example of the state of the device at this time is shown in Fig. 12(A).

[0010] Next, when the driving voltage V between the transparent electrodes rises sharply from 0 V to Vmax,12 As shown in (B) of Figure 13, the liquid crystal molecules 21a in the vertical direction are fluctuating, and a strong electric field causes some of the liquid crystal molecules 21a to move in a direction different from that determined by the rubbing process, resulting in a backflow phenomenon in which the liquid crystal molecules 21a are tilted unevenly in different directions, creating areas of liquid crystal molecules 21b (transparent state I). The transparent state I of the device at this time is shown in (B) of Figure 13, and it can be seen that display irregularities have occurred. The intervals between the display irregularities are about 30 mm, and their duration is about 1 second. Furthermore, after a few seconds, for example 1 second, have passed, finally, As shown in Figure 12(B), liquid crystal molecule 21c (Transparent State II) This results in the alignment direction defined by rubbing. The transparent state II of the device at this time is shown in FIG. 13(C). of (B) Transparent state I and Fig. 13 of The image displayed in the transparent state II of (C) is entirely white so that display irregularities can be easily confirmed. [Means for solving the problem]

[0011] In order to solve the above-mentioned problems, there is provided a device capable of switching between a mirror state and an image display state, which includes an image display unit for emitting image light, a liquid crystal mirror unit provided on the light emission side of the image display unit, and a control circuit for controlling the image display unit and the liquid crystal mirror unit, wherein the liquid crystal mirror unit includes a vertical alignment type liquid crystal layer, a first transparent electrode provided on the side of the vertical alignment type liquid crystal layer opposite to the image display unit, a second transparent electrode provided on the side of the vertical alignment type liquid crystal layer opposite to the image display unit, and a second transparent electrode provided on the side of the first transparent electrode opposite to the vertical alignment type liquid crystal layer. and a reflective polarizer disposed on the opposite side of the second transparent electrode from the vertical alignment type liquid crystal layer, the reflective polarizer having a second transmission axis perpendicular to the first transmission axis and transmitting the second linearly polarized light and reflecting the first linearly polarized light. The control circuit sweeps and increases the drive voltage between the first and second transparent electrodes of the liquid crystal mirror unit from an off state to an initial voltage, and then to a predetermined voltage that turns the vertical alignment type liquid crystal layer on, in a predetermined sweep time. The predetermined voltage is the saturation voltage of the driving voltage between the first and second transparent electrodes when the light transmittance of the liquid crystal mirror unit is saturated, the initial voltage is 40% or less of the saturation voltage, and the sweep time is 70 ms or more and 1000 ms or less. It is something. [Effects of the Invention]

[0012] According to the present invention, the driving voltage between the transparent electrodes is swept and raised over a predetermined sweep time from the OFF state of the vertical alignment type liquid crystal layer to an initial voltage, and then to a predetermined voltage that turns the vertical alignment type liquid crystal layer ON. As a result, a transient state occurs between the OFF state and the ON state, and as a result, the liquid crystal molecules in the vertical light distribution type liquid crystal layer tilt uniformly in the same direction, eliminating display unevenness. [Brief explanation of the drawings]

[0013] [Figure 1] 1 is a diagram showing an embodiment of a device according to the present invention that can switch between a mirror state and an image display state; [Figure 2] FIG. 2 is a detailed cross-sectional view of the liquid crystal mirror unit of FIG. [Figure 3] 2 is a timing diagram of the driving voltage between the transparent electrodes of the liquid crystal mirror unit of FIG. 1. FIG. [Figure 4] 4 is a flowchart for explaining a method for setting a driving voltage between the transparent electrodes in FIG. 3. [Figure 5] 5 is a graph showing the inter-transparent electrode driving voltage / light transmittance characteristics used in step 401 of setting the inter-transparent electrode saturation driving voltage in FIG. 4. [Figure 6] 5 is a table used in step 402 of setting the initial driving voltage of the transparent electrode in FIG. 4. [Figure 7] 5 is a table used in the sweep time setting step 403 in FIG. 4. [Figure 8] 4 is a timing chart showing a modified example of the driving voltage between the transparent electrodes in FIG. 3. FIG. [Figure 9] FIG. 1 is a diagram showing a conventional device that can be switched between a mirror state and an image display state. [Figure 10] 10 is a timing diagram showing the driving voltage between the transparent electrodes in FIG. [Figure 11] 10 is a timing chart showing the inter-electrode drive voltage in FIG. 9 when the liquid crystal layer in FIG. 9 is of a vertical alignment (VA) type. [Figure 12]This figure explains the issues that arise when a vertically aligned (VA) liquid crystal layer is used in the conventional device shown in Figure 9 that can switch between a mirror state and an image display state. (A) shows the liquid crystal molecules in the mirror state, and (B) shows the liquid crystal molecules during the transition from the mirror state to the transparent state. [Figure 13] 12A and 12B are photographs showing display examples of the mirror state, the transparent state I, and the transparent state II in FIG. 11. DETAILED DESCRIPTION OF THE INVENTION

[0014] FIG. 1 is a diagram showing an embodiment of a device according to the present invention that can switch between a mirror state and an image display state.

[0015] In FIG. 1, a liquid crystal mirror unit 2' is provided instead of the liquid crystal mirror unit 2 in FIG. 9, and in the liquid crystal mirror unit 2', a vertically aligned (VA) liquid crystal layer 21' is provided instead of the twisted nematic (TN) liquid crystal layer 21.

[0016] FIG. 2 is a detailed cross-sectional view of the liquid crystal mirror unit 2' in FIG.

[0017] As shown in FIG. 2, the upper structure includes an upper glass substrate 26, a transparent electrode 22, an insulating layer 27, and an upper vertical alignment layer 28, and the lower structure includes a lower glass substrate 29, a transparent electrode 23, an insulating layer 30, and a lower vertical alignment layer 31. The vertical alignment type liquid crystal layer 21′ is formed by insulating layers 27 and 30. 、 Insulation layer 34 The transparent electrodes 22 and 23 are supported by the insulating layers 27 and 30, and the spacer 32. 34 The upper and lower glass substrates 26 and 29 are electrically insulated from each other by a spacer 32, and the gap between them is maintained by a spacer 32. An absorptive polarizer 24 is provided on the outer side of the upper glass substrate 26 via an optical compensation plate 33, while a reflective polarizer 25 is provided on the outer side of the lower glass substrate 29. Furthermore, the opposing surfaces of the upper and lower vertical alignment layers 28 and 31 are subjected to rubbing treatment, for example, in an antiparallel direction.

[0018] FIG. 3 is a timing diagram of the driving voltage between the transparent electrodes of the liquid crystal mirror unit 2' of FIG.

[0019] 3, the inter-transparent electrode drive voltage V is linearly swept over a sweep time Ts, increasing from the mirror state through an initial drive voltage Vs to a saturation drive voltage Vmax for the transparent state. In this case, as will be described later, the saturation drive voltage Vmax, initial drive voltage Vs, and sweep time Ts are set to values ​​that do not cause display irregularities.

[0020] When the inter-transparent electrode drive voltage V is at a low level from time t0 to t1, the direction of polarization passing through the VA liquid crystal layer 21' does not change. Therefore, the first linearly polarized light of the external light that passes through the absorptive polarizer 24 passes through the VA liquid crystal layer 21' and is reflected by the reflective polarizer 25, and the reflected first linearly polarized light passes through the VA liquid crystal layer 21' and exits the absorptive polarizer 24. In other words, the liquid crystal mirror unit 2' is in a mirror state. In this case, the image display unit 1 is turned off by the control circuit 3.

[0021] Next, from time t1 to t2, the driving voltage V between the transparent electrodes is swept from Vs to rise to Vmax. At this time, the long axis of the liquid crystal molecules in the VA-type liquid crystal layer 21' changes relatively slowly. At this time, the long axis of the liquid crystal molecules in the liquid crystal layer as a whole is in the direction of the rubbing treatment, and the liquid crystal molecules that have been tilted in a different direction due to fluctuations are also oriented in a direction that follows the alignment of the surrounding liquid crystal molecules. In other words, the liquid crystal molecules in the VA-type liquid crystal layer 21' move and tilt from the vertical direction toward the rubbing treatment direction. Therefore, no display unevenness occurs when the device switches from the mirror state to the transparent state. Finally, at time t2, the driving voltage V between the transparent electrodes reaches Vmax, and the liquid crystal molecules in the VA-type liquid crystal layer 21' liquid crystal The change in the molecular long axis ends. As a result, the polarization direction of the first linearly polarized light of the external light that has passed through the absorptive polarizer 24 is changed by the VA liquid crystal layer 21', and the polarized light whose direction has been changed is then passed through the reflective polarizer 25. Similarly, the image light from the image display unit 1 passes through the reflective polarizer 25 and becomes the second linearly polarized light, and its polarization state is changed by the VA liquid crystal layer 21' before it is emitted through the absorptive polarizer 24. In other words, the liquid crystal mirror unit 2’In this case, when the image display unit 1 is turned on, the image display state, for example, the white display state, is achieved. Here, a chiral material is added to the liquid crystal layer at a ratio of about d / p=0.25. (where d is the liquid crystal intermolecular gap, and p is the chiral pitch) When a polarizer is added to the VA liquid crystal layer 21', the liquid crystal molecules below Vmax exhibit a chirality of approximately 90 degrees between the transparent electrodes, exhibiting the same optical rotation as a TN liquid crystal layer. In this case, by arranging the absorptive polarizer 24 and the reflective polarizer 25 in a crossed Nicol configuration, ambient light passes through the absorptive polarizer 24 and becomes the first linearly polarized light, which is then converted to the second linearly polarized light by the VA liquid crystal layer 21'. Furthermore, image light passes through the reflective polarizer 25 and becomes the second linearly polarized light, which is then converted to the first linearly polarized light by the VA liquid crystal layer 21'.

[0022] Next, the settings of the saturation drive voltage Vmax between the transparent electrodes, the initial drive voltage Vs between the transparent electrodes, and the sweep time Ts in FIG. 3 will be described with reference to FIG.

[0023] First, in step 401, the saturation drive voltage Vmax between the transparent electrodes is set. The saturation drive voltage Vmax between the transparent electrodes is set by measuring the drive voltage between the transparent electrodes / light transmittance (VT) characteristics of the liquid crystal mirror unit 2'. The VT characteristics shown in Figure 5 were obtained for the liquid crystal mirror unit 2' in Figure 1. From Figure 5, the saturation drive voltage Vmax between the transparent electrodes at which the light transmittance T saturates is 10.5 V, and the saturated light transmittance Tmax at this time is 40.1%. Note that light transmittance T = 100% is the transmittance obtained in the measurement system without passing through the liquid crystal mirror unit 2'.

[0024] Next, in step 402, the initial drive voltage Vs between the transparent electrodes is set. Since display irregularities are observed at intervals of approximately 30 mm, we visually inspected the appearance of display irregularities in the transient state from V = Vs to V = Vmax = 10.5 V using a mini display with a display area of ​​260 mm × 470 mm and a rearview mirror with a display area of ​​60 mm × 260 mm. The results shown in Figure 6 were obtained. In this case, the sweep time Ts was fixed at 100 ms. As a result, to prevent display irregularities, the initial drive voltage Vs between the transparent electrodes was Vs = 0 to 4.2 V, i.e., Vs = 0 to 0.4 Vmax. From the above, when Vs is set to 4.4 V or higher (above 0.42 Vmax), the liquid crystal molecules are tilted in non-uniform directions due to backflow, resulting in display irregularities. However, when Vs is set to 4.2 V or lower (below 0.4 Vmax), the liquid crystal molecules are tilted in the same direction without backflow, preventing display irregularities. That is, the initial drive voltage Vs is preferably 40% or less of the saturated drive voltage Vmax.

[0025] Next, in step 403, the sweep time Ts is set. Vs = 4V, Vmax = 10.5V are fixed, and the sweep time Ts is varied from 10 to 200 ms. Visual inspection of the display irregularities during the transition from V = Vs = 4V to V = Vmax = 10.5V was performed using a mini display with a display area of ​​260mm x 470mm and a rearview mirror with a display area of ​​60mm x 260mm. The results shown in Figure 7 were obtained. As a result, the sweep time Ts required to avoid display irregularities was 70 to 200 ms. In other words, if the sweep time Ts is set to 60 ms or less, Vmax is applied before the liquid crystal molecules tilt, causing the liquid crystal molecules to tilt in non-uniform directions due to backflow, resulting in display irregularities. However, if the sweep time Ts is set to 70 ms or more, Vmax is applied after the liquid crystal molecules tilt, causing the liquid crystal molecules to tilt uniformly in the same direction, thereby suppressing display irregularities. In other words, if the sweep time Ts is 70 ms or more, the backflow phenomenon will not occur. The response speed of liquid crystal molecules depends on temperature, being approximately 50 ms at 25°C and approximately 5000 ms at -30°C. Therefore, taking temperature into consideration, the sweep time Ts is set to 70 to 1000 ms. Taking into consideration the practicality of switching between the mirror state and the image display state while suppressing the backflow phenomenon, the sweep time Ts is preferably 70 to 200 ms, and more preferably 70 ms.

[0026] The larger the pixel size, the easier it is for display irregularities due to the backflow phenomenon to be visually observed. In the case of the embodiment of the present invention, display irregularities are visually observed at intervals of about 30 mm. ×30mm In the above liquid crystal mirror unit 2' Display unevenness In addition, the pixel size of the device that can switch between the mirror state and the image display state can be set to the same size as the display area. For example, a pixel size of 260 mm x 470 mm can be used. Pixel-sized liquid crystal mirror unit In the present invention, the pixel size applied to the device that can switch between the mirror state and the image display state is 30 mm. ×30mm As described above, the display unevenness that is visually noticeable due to the use of a relatively large pixel size is solved.

[0027] FIG. 8 is a timing chart showing a modified example of the driving voltage between the transparent electrodes in FIG.

[0028] As shown in Figure 8(A), the inter-transparent electrode drive voltage V during the sweep time Ts can be multi-stepped with two or more steps. This allows the inter-transparent electrode drive voltage V to be output digitally, simplifying the configuration of the control circuit 3. Furthermore, because liquid crystal molecules respond based on the effective value of the input signal, the inter-transparent electrode drive voltage V during the sweep time Ts can be a pulse-width modulated (PWM) waveform, as shown in Figure 8(B). In this case, the on-duty ratio increases with time. This also simplifies the configuration of the control circuit 3. Note that linearly sweeping the inter-transparent electrode drive voltage V requires analog processing, which complicates the control circuit 3.

[0029] The image display unit in the above-described embodiments is, for example, a liquid crystal display device or an organic electroluminescence display device.

[0030] Furthermore, the present invention can be applied to any modifications within the obvious scope of the above-described embodiments. [Industrial Applicability]

[0031] The device according to the present invention can be used for smart rearview mirrors in cars, mirror displays for homes, digital signage, etc. [Explanation of symbols]

[0032] 1: Image display unit 2, 2': LCD mirror unit 21:TN type liquid crystal layer 21': VA type liquid crystal layer 22, 23: Transparent electrode 24: Absorptive polarizer having a transmission axis of a first linearly polarized light 25: A reflective polarizer having a transmission axis of a second linearly polarized light 26: Upper glass substrate 27: Insulating layer 28: Upper vertical alignment layer 29: Lower glass substrate 30: Insulating layer 31: Lower vertical alignment layer 32: Spacer 33: Optical compensation plate

Claims

1. an image display unit for emitting image light; a liquid crystal mirror unit provided on the light output side of the image display unit; a control circuit for controlling the image display unit and the liquid crystal mirror unit; A device capable of switching between a mirror state and an image display state, comprising: The liquid crystal mirror unit includes: a vertically aligned liquid crystal layer; a first transparent electrode provided on the opposite side of the vertical alignment type liquid crystal layer from the image display unit; a second transparent electrode provided on the image display unit side of the vertical alignment type liquid crystal layer; an absorptive polarizer provided on the opposite side of the first transparent electrode from the vertical alignment type liquid crystal layer, the absorptive polarizer having a first transmission axis, transmitting a first linearly polarized light and absorbing a second linearly polarized light that intersects with the first linearly polarized light; a reflective polarizing plate provided on the opposite side of the second transparent electrode from the vertical alignment type liquid crystal layer, having a second transmission axis perpendicular to the first transmission axis, and transmitting the second linearly polarized light and reflecting the first linearly polarized light; Equipped with the control circuit sweeps and raises the drive voltage between the first and second transparent electrodes of the liquid crystal mirror unit from an OFF state to an initial voltage, and then to a predetermined voltage that turns the vertical alignment type liquid crystal layer ON, in a predetermined sweep time; the predetermined voltage is a saturation voltage of the drive voltage between the first and second transparent electrodes when the light transmittance of the liquid crystal mirror unit is saturated, the initial voltage is 40% or less of the saturation voltage; The sweep time is between 70 ms and 1000 ms.

2. 2. The apparatus of claim 1, wherein the sweep from the initial voltage to the predetermined voltage is linear.

3. 2. The apparatus according to claim 1, wherein the sweep from the initial voltage to the predetermined voltage is multi-stepped in two or more steps.

4. 2. The device according to claim 1, wherein the sweep from the initial voltage to the predetermined voltage is pulse-width modulated, and the on-duty ratio of each pulse increases as the application of the predetermined voltage approaches.

5. The device described in claim 1, wherein the initial voltage is 4.2V or less.

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