Apparatus capable of switching between mirror state and image display state

Abstract

In a device capable of switching between a mirror state and image display, a liquid crystal mirror unit (2 ') is provided on the front side of an image display unit (1). The liquid crystal mirror unit (2 ') has: a VA-type liquid crystal layer (21'); transparent electrodes (22, 23) that sandwich the VA-type liquid crystal layer (21 '); an absorption-type polarizer (24) that has a transmission axis (TX1) in the first direction, transmits the first linearly polarized light, and absorbs second linearly polarized light that intersects the first linearly polarized light; and a reflective polarizer (25) that has a transmission axis (TX2) in the second direction, transmits the second linearly polarized light, and reflects the first linearly polarized light. The control circuit (3) increases the drive voltage (VD) between transparent electrodes of the liquid crystal mirror unit (2 ') by scanning for a predetermined scanning time (Ts) from a state in which the vertical alignment liquid crystal layer (21') is turned off to a predetermined voltage (Vmax) at which the vertical alignment liquid crystal layer (21 ') is turned on via the initial voltage (Vs).

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 for a vehicle interior mirror (see: Patent Document 1). Background Art

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

[0003] exist Fig. 9 In a device capable of switching mirror states and displaying images, a liquid crystal mirror unit 2 is provided on the front side of an image display unit 1. The liquid crystal mirror unit 2 has: a twisted nematic (TN) liquid crystal layer 21; a pair of transparent electrodes 22 and 23 sandwiching the TN liquid crystal layer 21; an absorption-type polarizing plate 24, which is provided on the transparent electrode 22 side and has a horizontal transmission axis TX1 to transmit a first linear polarized light and absorb a second linear polarized light that crosses the first linear polarized light; and a reflection-type polarizing plate 25, which is provided on the transparent electrode 23 side and has a vertical transmission axis TX2 to transmit the second linear polarized light and reflect the first linear polarized light. A driving voltage V between the transparent electrodes of the image display unit 1 and the liquid crystal mirror unit 2 is D It is controlled by a control circuit 3 such as a microcomputer.

[0004] Fig.10 yes Fig. 9 The driving voltage V between the transparent electrodes of the liquid crystal mirror unit 2 D Timing diagram of .

[0005] like Fig.10 As shown, the driving voltage V between the transparent electrodes D In the on state (V D =Vmax), the polarization axis of the TN type liquid crystal layer 21 does not change, so the first linear polarized light that has passed through the absorption type polarizer 24 in the external light EL passes through the liquid crystal layer 21 and is reflected by the reflection type polarizer 25, and then the reflected first linear polarized light passes through the TN type liquid crystal layer 21 and is emitted from the absorption type polarizer 24. That is, the liquid crystal mirror unit 2 is in the mirror state S1. In addition, in this case, the image display unit 1 is turned off by the control circuit 3.

[0006] On the other hand, the driving voltage V D In the disconnected state (for example, V D=0V), the TN-type polarization axis of the TN-type liquid crystal layer 21 changes, so that the first linear polarization light in the external light EL that has passed through the absorption type polarizer 24 is changed into the second linear polarization light through the TN-type liquid crystal layer 21, and then the changed second linear polarization light passes through the reflection type polarizer 25. Similarly, the image light IL passes through the reflection type polarizer 25 from the image display unit 1 to become the second linear polarization light, is converted into the first linear polarization light through the TN-type liquid crystal layer 21, and is emitted from the absorption type polarizer 24. That is, the liquid crystal mirror unit 2 is in the transparent state S2. In addition, in this case, if the image display unit 1 is turned on by the control circuit 3, it becomes a screen display state, such as a white display state.

[0007] Prior art literature

[0008] Patent Literature

[0009] Patent Document 1: Japanese Patent Application Publication No. 2021-138195

[0010] Patent Document 2: Japanese Patent Application Publication No. 2003-202565 (Patent No. 4348061) Summary of the invention

[0011] Problems to be solved by the invention

[0012] exist Fig. 9 In the device capable of switching between the mirror state and the image display state shown above, when a vertical alignment (VA) type liquid crystal layer is used instead of the TN type liquid crystal layer 21, the following problems arise.

[0013] exist Fig.11 In the mirror state, when the driving voltage V D When it is 0V, Fig.12 As shown in the mirror state S1 of (A), the liquid crystal molecules 21a are approximately perpendicular to the rubbing line L in the rubbing treatment direction on the vertical alignment layer, but the vertical direction of the liquid crystal molecules 21a, for example, the pretilt angle 89.0°, is swung by the unevenness generated on the alignment film surface during the rubbing treatment, i.e., the rubbing line L and the unevenness of the glass substrate not shown. An example of the mirror state S1 of the device at this time is as follows Fig.13 As shown in (A).

[0014] Then, when the driving voltage V D When it rises sharply from 0V to Vmax, Fig.12As shown in (B), the liquid crystal molecules 21a in the vertical direction will sway. Therefore, under the reflux phenomenon in which a part of the liquid crystal molecules 21a moves in a direction different from the direction specified by the rubbing treatment due to the strong electric field, these liquid crystal molecules tilt unevenly in different directions, and a region of the transparent state S2I of the liquid crystal molecules 21b will be generated. The transparent state S2I of the device at this time is as shown in FIG. Fig.13 As shown in (B), it can be seen that uneven display occurs. The interval of uneven display is about 30mm, and its duration is about 1 second. Then, after a few seconds, for example 1 second, the display is finally as shown in FIG. Fig.12 As shown in (B), the liquid crystal molecules 21c are in the transparent state S2II, and the arrangement direction is determined by the friction. Fig.13 In addition, Fig.13 (B) The transparent state S2I and Fig.13 The image displayed in the transparent state S2II of (C) is a white image in which the entire surface is set to white in order to facilitate confirmation of display unevenness.

[0015] Means for solving problems

[0016] In order to solve the above-mentioned problems, a device capable of switching between a mirror state and an image display state is provided, comprising: an image display unit for emitting image light; a liquid crystal mirror unit disposed on the light emitting 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 comprises: a vertical alignment type liquid crystal layer; a first transparent electrode disposed on the side of the vertical alignment type liquid crystal layer opposite to the image display unit; a second transparent electrode disposed on the side of the vertical alignment type liquid crystal layer close to the image display unit; an absorbing polarizer disposed on the first transparent electrode opposite to the side of the vertical alignment type liquid crystal layer close to the image display unit; The control circuit increases the driving voltage between the transparent electrodes of the liquid crystal mirror unit by scanning from a state in which the vertical alignment type liquid crystal layer is turned off via an initial voltage to a predetermined voltage in which the vertical alignment type liquid crystal layer is turned on at a predetermined scanning time.

[0017] Effects of the Invention

[0018] According to the present invention, the driving voltage between the transparent electrodes is scanned and increased from a state in which the vertically aligned liquid crystal layer is turned off via an initial voltage to a predetermined voltage in which the vertically aligned liquid crystal layer is turned on within a predetermined scanning time, thereby generating a transition state between the turned-off state and the turned-on state. As a result, the liquid crystal molecules of the vertically aligned liquid crystal layer are evenly tilted in the same direction, thereby eliminating display unevenness. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 It is a diagram showing an embodiment of a device capable of switching a mirror state and an image display state according to the present invention.

[0020] Figure 2 yes Figure 1 Detailed cross-sectional view of a liquid crystal mirror unit.

[0021] Figure 3 yes Figure 1 Timing diagram of the driving voltage between the transparent electrodes of the liquid crystal mirror unit.

[0022] Figure 4 It is used to illustrate Figure 3 Flow chart of a method for setting a driving voltage between transparent electrodes.

[0023] Figure 5 It is shown Figure 4 A graph of the transparent electrode driving voltage / transmittance characteristics used in the transparent electrode saturation driving voltage setting step 401 is shown.

[0024] Figure 6 yes Figure 4 The transparent electrode initial driving voltage setting table used in step 402.

[0025] Figure 7 yes Figure 4 The table used in the scan time setting step 403.

[0026] Figure 8 It is shown Figure 3 A timing diagram showing an example of changing the driving voltage between transparent electrodes.

[0027] Fig. 9 This is a diagram showing a conventional device capable of switching between a mirror state and an image display state.

[0028] Fig.10 It is shown Fig. 9 Timing diagram of the driving voltage between transparent electrodes.

[0029] Fig.11 It shows that Fig. 9 When the liquid crystal layer is set to vertical alignment (VA) type Fig. 9 Timing diagram of the inter-electrode driving voltage.

[0030] Fig.12 It is explained in Fig. 9 A diagram illustrating the problems encountered when a vertically aligned (VA) liquid crystal layer is used in a conventional device capable of switching an image display state between a mirror state and a transparent state, wherein (A) shows liquid crystal molecules in a mirror state, and (B) shows liquid crystal molecules during a transition from a mirror state to a transparent state.

[0031] Fig.13 It is shown Fig.11 Photos of display examples of the mirror state, transparent state S2I and transparent state S2II. DETAILED DESCRIPTION

[0032] Figure 1 It is a diagram showing an embodiment of a device capable of switching a mirror state and an image display state according to the present invention.

[0033] exist Figure 1 In the embodiment, a liquid crystal mirror unit 2' is provided to replace Fig. 9 In the liquid crystal mirror cell 2 ′, a vertical alignment (VA) type liquid crystal layer 21 ′ is provided instead of a twisted nematic (TN) type liquid crystal layer 21 .

[0034] Figure 2 yes Figure 1 Detailed cross-sectional view of a liquid crystal mirror unit 2'.

[0035] like Figure 2 As shown, as the upper structure, an upper glass substrate 26, a transparent electrode 22, an insulating layer 27, and an upper vertical alignment layer 28 are provided, and as the lower structure, a lower glass substrate 29, a transparent electrode 23, an insulating layer 30, and a lower vertical alignment layer 31 are provided, and a vertical alignment type liquid crystal layer 21' is supported by the insulating layers 27, 30, and the insulating layer 31 and the spacer 32. In addition, the transparent electrodes 22 and 23 are electrically insulated by the insulating layers 27, 30, and 31, and the interval is maintained by the spacer 32. An absorption type polarizer 24 is provided on the outer side of the upper glass substrate 26 via an optical compensation plate 33, and on the other hand, a reflection type polarizer 25 is provided on the outer side of the lower glass substrate 29. In addition, the opposing surfaces of the upper vertical alignment layer 28 and the lower vertical alignment layer 31 are rubbed, for example, in an anti-parallel direction.

[0036] Figure 3 yes Figure 1 The driving voltage V between the transparent electrodes of the liquid crystal mirror unit 2' D Timing diagram of .

[0037] exist Figure 3 In the transparent electrode driving voltage V DThe rise of the saturated driving voltage Vmax from the mirror state S1 to the transparent state S2 via the initial driving voltage Vs is scanned straightly in the transition state S3 of the scanning time Ts. In this case, as described later, the saturated driving voltage Vmax, the initial driving voltage Vs, and the scanning time Ts are set to values ​​that do not cause display unevenness.

[0038] The driving voltage V between the transparent electrodes at time t0 to t1 D When the level is low, the direction of polarized light passing through the VA type liquid crystal layer 21' does not change. Therefore, the first linear polarized light passing through the absorptive polarizer 24 in the external light EL passes through the VA type liquid crystal layer 21' and is reflected by the reflective polarizer 25, and the reflected first linear polarized light passes through the VA type liquid crystal layer 21' and is emitted from the absorptive polarizer 24. That is, the liquid crystal mirror unit 2' is in the mirror state S1. In addition, in this case, the image display unit 1 is turned off by the control circuit 3.

[0039] Next, from time t1 to t2, the driving voltage V between the transparent electrodes D Scanning starts from Vs and rises to Vmax. At this time, the long axis of the liquid crystal molecules in the VA type liquid crystal layer 21' changes slowly. At this time, the long axis of the liquid crystal molecules in the entire TN type liquid crystal layer 21' becomes the friction treatment direction, and the liquid crystal molecules tilted in different directions due to the swing are also oriented along the orientation of the surrounding liquid crystal molecules. That is, the liquid crystal molecules in the VA type liquid crystal layer 21' move from the vertical direction to the friction treatment direction and tilt. Therefore, in the transition state S3 of the device switching from the mirror state S1 to the transparent state S2, no uneven display will occur. Finally, at time t2, the driving voltage V between the transparent electrodes DWhen Vmax is reached, the change of the long axis of the liquid crystal molecules of the VA type liquid crystal layer 21' ends. As a result, the polarization direction of the first linear polarized light transmitted through the absorption type polarizer 24 in the external light EL is changed by the VA type liquid crystal layer 21', and the polarized light with changed direction is transmitted through the reflection type polarizer 25. Similarly, the image light from the image display unit 1 is transmitted through the reflection type polarizer 25 to become the second linear polarized light, the polarization state of the second linear polarized light is changed by the VA type liquid crystal layer 21', and the second linear polarized light is emitted from the absorption type polarizer 24. That is, the liquid crystal mirror unit 2 is in the transparent state S2. In addition, in this case, when the image display unit 1 is turned on, it becomes an image display state, such as a white display state. Here, when a chiral material with a d / p of about 0.25 is added to the liquid crystal layer, the liquid crystal molecules at Vmax generate a chirality of about 90 degrees between the transparent electrodes 22 and 23, and show the same optical rotation as the TN type liquid crystal layer. In this case, by setting the absorptive polarizer 24 and the reflective polarizer 25 in a cross Nicol arrangement, the external light EL passes through the absorptive polarizer 24 to become the first linear polarized light, and is converted into the second linear polarized light by the VA liquid crystal layer 21'. In addition, the image light IL passes through the reflective polarizer 25 to become the second linear polarized light, and is converted into the first linear polarized light by the VA liquid crystal layer 21'.

[0040] Next, refer to Figure 4 illustrate Figure 3 The setting of the saturation driving voltage Vmax between transparent electrodes, the initial driving voltage Vs between transparent electrodes and the scanning time Ts.

[0041] First, in step 401, the saturation driving voltage Vmax between transparent electrodes is set. The saturation driving voltage Vmax between transparent electrodes is set by measuring the driving voltage / transmittance (VT) characteristics between transparent electrodes of the liquid crystal mirror unit 2'. Figure 1 The VT characteristics of the liquid crystal mirror unit 2' are obtained. Figure 5 According to the VT characteristics shown. Figure 5 The saturation driving voltage Vmax between transparent electrodes for saturating the transmittance T is 10.5 V, and the saturated transmittance Tmax at this time is 40.1%. In addition, the transmittance T=100% is the transmittance obtained without the liquid crystal mirror unit 2' in the measurement system.

[0042] Next, in step 402, the initial driving voltage Vs between the transparent electrodes is set. Since the display unevenness is observed at intervals of about 30 mm, the appearance of the display unevenness in the transition state from V = Vs to V = Vmax = 10.5 V is visually confirmed using a small display with a display area of ​​260 mm × 470 mm and a room mirror with a display area of ​​60 mm × 260 mm. Figure 6 The result shown. At this time, the scanning time Ts is fixed at 100ms. As a result, in order to avoid uneven display, the initial driving voltage Vs between the transparent electrodes is Vs=0~4.2V, that is, Vs=0~0.4Vmax. According to the above, if Vs is set to above 4.4V (above 0.42·Vmax), the liquid crystal molecules will tilt in an uneven direction due to the backflow effect, thereby causing uneven display. On the contrary, if Vs is set to below 4.2V (below 0.4·Vmax), the liquid crystal molecules will not produce the backflow effect but tilt in the same direction, thereby suppressing the occurrence of uneven display. That is, the initial driving voltage Vs is preferably less than 40% of the saturation driving voltage Vmax.

[0043] Next, in step 403, the scanning time Ts is set. Vs = 4V, Vmax = 10.5V are fixed, and the scanning time Ts is changed from 10 to 200ms. When the appearance of the display unevenness in the transition state from V = Vs = 4V to V = Vmax = 10.5V is visually judged using a small display with a display area of ​​260mm × 470mm and a room mirror with a display area of ​​60mm × 260mm, the result is Figure 7 The result shown. As a result, in order to avoid uneven display, the scanning time Ts is 70 to 200 ms. That is, since Vmax is applied before the liquid crystal molecules tilt when the scanning time Ts is set to 60 ms or less, the liquid crystal molecules tilt in an uneven direction due to the backflow effect, resulting in uneven display. In contrast, since Vmax is applied after the liquid crystal molecules tilt when the scanning time Ts is set to 70 ms or more, the liquid crystal molecules tilt evenly in the same direction, thereby suppressing the occurrence of uneven display. That is, when the scanning time Ts is more than 70 ms, the backflow effect does not occur. In addition, the response speed of the liquid crystal molecules depends on the temperature, which is about 50 ms at 25°C and about 5000 ms at -30°C. Therefore, considering the temperature, the scanning time Ts is set to 70 ms to 1000 ms. Considering the practicality of switching between the reflector state and the image display state while suppressing the backflow phenomenon, the scanning time Ts is preferably 70 to 200 ms, and more preferably 70 ms.

[0044] The larger the pixel size, the easier it is to visually observe the display unevenness caused by the backflow effect. In the case of the embodiment of the present invention, the interval of the display unevenness is about 30 mm, which can be visually recognized, so the present invention can obtain good results without unevenness in the liquid crystal mirror unit 2' with a pixel size of 30 mm or more. In addition, for the pixel size in the device that can switch the mirror state S1 and the image display state S2, a size equal to the display area can be applied. For example, it is confirmed that the function is performed by a 260mm×470mm element. In the present invention, the display unevenness visually recognized by using a larger pixel size is solved. The larger pixel size refers to the case where the pixel size is 30mm or more applied to the device that can switch the mirror state S1 and the image display state S2.

[0045] Figure 8 It is shown Figure 3 The driving voltage V between the transparent electrodes D A timing diagram of an example of a change.

[0046] like Figure 8 As shown in (A), the driving voltage V between transparent electrodes during the scanning time Ts D The process can be performed in a multi-step process with two or more steps. D The output is digital, so the structure of the control circuit 3 can be simplified. In addition, since the liquid crystal molecules respond according to the effective value of the input signal, Figure 8 As shown in (B), the driving voltage V between transparent electrodes within the scanning time Ts can be D Set as a pulse width modulation (PWM) waveform. At this time, the on-duty ratio increases with time. In this case, the structure of the control circuit 3 can also be simplified. In addition, the driving voltage V is linearly scanned between the transparent electrodes. D In this case, analog processing is required, so the control circuit 3 becomes complicated.

[0047] In addition, the image display unit in the above-mentioned embodiment is, for example, a liquid crystal display device or an organic electroluminescent display device.

[0048] In addition, the present invention can be applied to any modifications within the obvious range of the above-mentioned embodiment.

[0049] Possibility of industrial application

[0050] The device of the present invention can be used for vehicle-mounted smart interior mirrors, residential mirror displays, digital signage, etc.

[0051] Description of Reference Numerals

[0052] 1: Image display unit

[0053] 2, 2': Liquid crystal mirror unit

[0054] 21: TN type liquid crystal layer

[0055] 21': VA type liquid crystal layer

[0056] 22, 23: Transparent electrode

[0057] 24: Absorbing polarizer with a first transmission axis for linearly polarized light

[0058] 25: Reflective polarizer with a second transmission axis for linearly polarized light

[0059] 26: Upper glass substrate

[0060] 27: Insulation layer

[0061] 28: Upper vertical orientation layer

[0062] 29: Lower glass substrate

[0063] 30: Insulation layer

[0064] 31: Bottom vertical alignment layer

[0065] 32: Spacer

[0066] 33: Optical compensation plate

Claims

1. A device capable of switching a mirror state and an image display state, comprising: an image display unit (1) for emitting image light (IL); a liquid crystal mirror unit (2') arranged on the light emission side of the image display unit (1); and a control circuit (3) for controlling the image display unit (1) and the liquid crystal mirror unit (2'), wherein: The liquid crystal mirror unit (2') comprises: A vertically aligned liquid crystal layer (21'); A first transparent electrode (22) disposed on a side of the vertical alignment type liquid crystal layer opposite to the image display unit (1); A second transparent electrode (23) disposed on the side of the vertically aligned liquid crystal layer (21') close to the image display unit (1); an absorbing polarizer (24) disposed on the side of the first transparent electrode (22) opposite to the vertically aligned liquid crystal layer (21'), having a first transmission axis (TX1), allowing first linear polarized light to pass through and absorbing second linear polarized light that crosses the first linear polarized light; as well as A reflective polarizing plate (25) is arranged on the side of the second transparent electrode (23) opposite to the vertically aligned liquid crystal layer (21'), has a second transmission axis (TX2) orthogonal to the first transmission axis (TX1), transmits the second linearly polarized light, and reflects the first linearly polarized light. The control circuit (3) increases the driving voltage (V) between the first transparent electrode (22) and the second transparent electrode (23) of the liquid crystal mirror unit (2'). D ) is scanned and raised from a state in which the vertically aligned liquid crystal layer (21') is turned off via an initial voltage (Vs) to a predetermined voltage in which the vertically aligned liquid crystal layer (21') is turned on within a predetermined scanning time (Ts).

2. The device according to claim 1, wherein: The specified voltage is the driving voltage (V) between the first transparent electrode (22) and the second transparent electrode (23) when the light transmittance (T) of the liquid crystal mirror unit (2') reaches saturation. D )’s saturation voltage (Vmax).

3. The device according to claim 1, wherein: The scan from the initial voltage (Vs) to the predetermined voltage is a straight line.

4. The device according to claim 1, wherein: The scanning from the initial voltage (Vs) to the predetermined voltage is a multi-step scanning of two or more steps.

5. The device according to claim 1, wherein: In the scanning from the initial voltage (Vs) to the prescribed voltage, the pulse width is modulated, and the closer to the application of the prescribed voltage, the larger the on-duty ratio of each pulse.

6. The device according to claim 2, wherein: The initial voltage (Vs) is less than 40% of the saturation voltage (Vmax).

7. The device according to claim 1, wherein: The scanning time (Ts) is greater than or equal to 70 ms and less than or equal to 1000 ms.

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