JP5390355B2 - Optical deflection device - Google Patents

Description

  The present invention relates to an optical deflection apparatus that performs optical deflection that changes the traveling direction of light.

  As a light distribution switching technique in a vehicle headlight or the like, it has been proposed to use a liquid crystal optical element.

  Patent Document 1 discloses a technique for performing light deflection using a liquid crystal cell in which a prism is formed on one inner surface of a pair of substrates. The light traveling direction is changed by switching the voltage off state and the voltage on state to change the refractive index of the liquid crystal layer. However, in the technique disclosed in Patent Document 1, only one of the two polarization components of which the polarization directions of the incident light to the liquid crystal cell are orthogonal to each other is deflected.

  Patent Document 2 discloses a technique for deflecting both polarization components by using two liquid crystal cells prepared for each polarization direction.

  A technique capable of deflecting both polarization components of incident light with a single liquid crystal cell is desired.

JP 2006-147377 A JP 2009-26641 A

  An object of the present invention is to provide an optical deflecting device capable of performing light deflection for changing the traveling direction of light with respect to both polarization components orthogonal to incident light with a single liquid crystal cell.

According to one aspect of the present invention, a liquid crystal layer having a positive dielectric anisotropy and having a chiral agent added thereto, first and second transparent substrates that are arranged to face each other and sandwich the liquid crystal layer, First and second transparent electrodes formed on the liquid crystal layer side above the first and second transparent substrates, respectively, for applying a voltage to the liquid crystal layer, and one of the first and second transparent substrates of the liquid crystal layer side formed above the prism layer, and a first and second vertical alignment before SL formed in the liquid crystal layer side above the transparent substrate film, the liquid crystal layer, the voltage-off It shows the focal conic state, the light deflecting apparatus according to the homeotropic state by the voltage on is provided by.

  By applying a voltage to the liquid crystal layer, the refractive index of the liquid crystal layer can be changed from the refractive index in the focal conic state to the refractive index in the homeotropic state, thereby changing the light deflection direction by the prism. By using the focal conic state and the homeotropic state, both orthogonal polarization components of incident light from the normal direction of the substrate can be deflected.

FIG. 1 is a cross-sectional view in the thickness direction schematically showing an optical deflection liquid crystal cell according to a first embodiment of the present invention. FIG. 2 is a schematic perspective view of the prism layer and an enlarged view of a cross-sectional shape of the prism. FIG. 3 is a schematic plan view of the prism layer on the glass substrate. FIG. 4 is a photograph of the light deflection liquid crystal cell of the first embodiment when the voltage is on and when the voltage is off. FIG. 5 is a lateral cross-sectional view (top cross-sectional view) schematically showing a lighting device of an application example. 6A and 6B are sketches schematically showing projected images when the voltage is on and when the voltage is off, respectively. FIG. 7 is a cross-sectional view in the thickness direction schematically showing the light deflection liquid crystal cell of the second embodiment.

  First, the structure and manufacturing method of the light deflection liquid crystal cell according to the first embodiment of the present invention will be described.

  FIG. 1 is a cross-sectional view in the thickness direction schematically showing the light deflection liquid crystal cell of the first embodiment. A pair of glass substrates on which a transparent electrode was formed (a glass substrate 1 on which a transparent electrode 2 was formed and a glass substrate 11 on which a transparent electrode 12 was formed) were prepared. The glass substrates 1 and 11 are non-alkali glass, and each has a thickness of 0.7 mm. The transparent electrodes 2 and 12 are indium tin oxide (ITO), and each has a thickness of 150 nm.

  The transparent electrodes 2 and 12 are preferably patterned in a desired planar shape. The ITO film can be patterned by, for example, wet etching using ferric chloride or a method of removing an unnecessary ITO film with a laser.

  A prism layer 3 was formed on the transparent electrode 2 of the glass substrate 1 on one side. The prism layer 3 has a shape in which the prisms 3a are arranged on the base layer 3b. The base layer 3b has a thickness of about 2 μm to 30 μm, for example.

  FIG. 2 is a schematic perspective view of the prism layer 3 and an enlarged view of the cross-sectional shape of the prism 3a. Each prism 3a has a triangular prism shape with apex angles of 75 ° and base angles of 15 ° and 90 °, and a plurality of prisms 3a are arranged in a direction (prism width direction) perpendicular to the prism length direction. The height of the prism 3a is about 5.2 μm, and the length of the base of the prism 3a (prism pitch) is 20 μm.

  A suitable material for the prism layer 3 will be described. On the prism layer 3, a vertical alignment film 4 such as polyimide is formed in a later step. In order to form a highly reliable vertical alignment film, it is desirable to perform heat treatment at a high temperature of about 160 ° C. to 220 ° C. (for example, 180 ° C.). Therefore, a prism material whose characteristics are hardly deteriorated by high-temperature heat treatment is desired.

  The inventor of the present application performed heat treatment at 220 ° C. for 2 hours for a plurality of prism materials, and evaluated the difference in transmittance in the visible light region before and after the heat treatment. As a result, the acrylic ultraviolet (UV) curable resin showed a slight decrease in transmittance on the short wavelength side, but exhibited a transmittance equivalent to that before the heat treatment in almost all visible wavelength regions. Rate) change was found to be less. In the present specification, “there is little change in characteristics (transmittance)” means that the change in characteristics (transmittance) in the visible light region (wavelength 380 nm to 780 nm) is approximately within 2% compared to before heat treatment. Indicates the state.

  The acrylic UV curable resin has not only heat resistance but also excellent adhesion to glass and has a property of being difficult to adhere to metal (good releasability). It was found to be suitable as a material. Epoxy resins are also excellent in heat resistance and are considered to be usable as prism materials. Polyimide can also be used.

  FIG. 3 is a schematic plan view of the prism layer 3 on the glass substrate 1. A method for producing the prism layer 3 will be described. On the transparent electrode 2 of the glass substrate 1, an acrylic UV curable resin 3R is dropped, and a mold in which a mold of the prism layer 3 is formed at a predetermined position (overall size: 80 mm long × 80 mm wide) ) And a thick quartz member or the like was placed on the back side of the glass substrate for reinforcement. The dripping amount of the UV curable resin 3R was adjusted according to the size of the prism (the width of the prism formation region).

After pressing and allowing to stand for 1 minute or longer, the UV curable resin was sufficiently spread, and then the ultraviolet light was irradiated from the back side of the glass substrate 1 to cure the UV curable resin. The irradiation amount of ultraviolet rays was 20 J / cm ² . What is necessary is just to set suitably the irradiation amount of an ultraviolet-ray so that resin may harden | cure. In addition, since ITO absorbs ultraviolet rays, if the film thickness of the transparent electrode is changed, it is necessary to change the ultraviolet irradiation amount. Note that a minute groove for air bleeding may be formed on the prism forming die. Further, the mold and the substrate may be superposed in a vacuum.

  Next, the glass substrate 1 on which the prism layer 3 was formed was washed with a washing machine. Brush cleaning using an alkaline detergent, pure water cleaning, air blowing, UV irradiation, and infrared (IR) drying were sequentially performed. The cleaning method is not limited to this, and high-pressure spray cleaning, plasma cleaning, or the like can also be performed.

  Returning to FIG. 1, the description will be continued. On the transparent electrode 12 of the other glass substrate 11, a vertical alignment film 13 was formed from polyimide or the like. Here, SE-4811 manufactured by Nissan Chemical Industries, Inc. was formed by flexographic printing to a thickness of 80 nm and baked at 180 ° C. for 1.5 hours.

  A vertical alignment film 4 was formed on the prism layer 3 of the glass substrate 1 with polyimide or the like. Here, SE-4811 manufactured by Nissan Chemical Industries, Inc. was formed by flexographic printing to a thickness of 80 nm and baked at 180 ° C. for 1.5 hours. In addition, as a method for forming the vertical alignment films 4 and 13, ink jet, spin coating, slit coating, slit and spin coating, or the like can be used.

  Next, a main sealant containing 2 wt% to 5 wt% of a gap control agent was formed on the glass substrate 1 on the prism layer 3 side. As a forming method, screen printing or a dispenser is used. The gap control agent was selected so that the thickness of the liquid crystal layer 15 (from the prism base layer 3b) including the height of the prism 3a was, for example, 10 μm to 20 μm.

  Here, a plastic ball made by Sekisui Chemical having a diameter of 30 μm was selected as a gap control agent, and 4 wt% was added to a sealing agent ES-7500 made by Mitsui Chemicals to make a main sealing agent 16.

  On the other glass substrate 11, Sekisui Chemical plastic balls having a diameter of 17 μm as a gap control agent 14 were dispersed using a dry gap spreader.

  Next, both the glass substrates 1 and 11 were overlapped, and the main sealant was cured by heat treatment in a state where pressure was constantly applied by a press machine or the like. Here, heat treatment was performed at 150 ° C. for 3 hours.

  A liquid crystal layer 15 was formed by vacuum-injecting liquid crystal into the empty cell thus prepared. After liquid crystal injection, an end sealant was applied to the injection port and sealed. After sealing, heat treatment was performed at 120 ° C. for 1 hour to adjust the alignment state of the liquid crystal molecules. In this manner, the light deflection liquid crystal cell of the first example was manufactured. Note that the method for forming the liquid crystal layer is not limited to vacuum injection, and, for example, a One Drop Fill (ODF) method may be used.

  In the examples, a product made by Dainippon Ink & Chemicals, Inc. having a positive dielectric anisotropy Δε (Δn = 0.298) was used as the liquid crystal, and a chiral agent S-811 made by Merck was added. The chiral pitch when the chiral agent was added to the mother liquid crystal at 9.4 wt% was about 1 μm.

  The chiral pitch can be changed by changing the addition concentration of the chiral agent (the lower the addition concentration of the chiral agent, the longer the chiral pitch). Samples having a chiral pitch of 1 μm, 2 μm, 3 μm, 5 μm, and 9 μm were prepared.

  The liquid crystal cell of the example is considered to exhibit a focal conic state in which the helical axis is parallel to the substrate due to the action of the vertical alignment film and the chiral agent when the voltage is off. The degree of light scattering when the voltage was off varied depending on the chiral pitch. When the chiral pitch was 1 μm, weak scattering was exhibited, and when the chiral pitch was 2 μm or more, almost no scattering occurred.

  The helical axis in the focal conic state is parallel to the substrate, but is a vertical alignment that is not subjected to alignment treatment, and therefore the orientation of the helical axis is random in the substrate plane. Therefore, when the voltage is off, the refractive index of the liquid crystal layer viewed from the normal direction of the substrate is an average value (2no + ne) / 3 of the ordinary ray refractive index no and the extraordinary ray refractive index ne of the liquid crystal material used.

  Although this value is very small, the liquid crystal molecules are oriented in a certain direction and have different molecular orientations with respect to the polarized light, but the liquid crystal molecules are different in a very short period (below the wavelength of light). At the level of the director (the magnitude with which the refractive index of light comes out), it is almost averaged and the dependence due to polarization disappears.

  On the other hand, when a sufficient voltage is applied, because of the positive dielectric anisotropy, almost all liquid crystal molecules show a homeotropic state in which they rise in the direction perpendicular to the substrate. Becomes an ordinary ray refractive index no without depending on polarization. The homeotropic state shows a transparent appearance.

  The ordinary light refractive index no of the liquid crystal material of the example is 1.525, and the extraordinary light refractive index ne is 1.823. Therefore, the refractive index of light traveling in the normal direction of the substrate is 1.624 in the liquid crystal layer in the focal conic state when the voltage is off, and 1. in the liquid crystal layer in the homeotropic state when the voltage is on, regardless of the polarization direction. 525 is estimated. The refractive index of the prism material of the example is 1.51.

  In the liquid crystal cell of the embodiment, when the voltage is off, the refractive index of the liquid crystal layer and that of the prism layer are different from each other. On the other hand, when the voltage is turned on, the refractive indexes of the liquid crystal layer and the prism layer become substantially equal, and the incident light travels straight.

  FIG. 4 shows a photo when the voltage is turned on (upper side) and a photo when the voltage is turned off (lower side) of the light deflecting liquid crystal cell (sample having a chiral pitch of 2 μm) of the first embodiment, and a straight line is drawn through the light deflecting liquid crystal cell. Indicates the state of observation.

  A region indicated by a frame is a portion where a prism is formed and a focal conic state is shown when the voltage is off (an evaluation target portion in the following description). The upper side of this region is a portion where no prism is formed, and the lower side of this region is a portion where a prism is formed but scattered without showing a focal conic state when the voltage is off (vertical). It seems that the regulation by the orientation was weak.)

  When the voltage shown in the upper side of FIG. 4 is on, light is transmitted straight as it is, and a straight line is observed as it is. When the voltage shown in the lower side of FIG. 4 is off, the light is bent at the prism forming portion and the image is shifted laterally. Scattering of the image due to the focal conic state when the voltage is off is seen but slight.

  The light deflecting liquid crystal cell of the first embodiment was combined with a light source to produce an illumination device of an application example assuming a vehicle headlight.

  FIG. 5 is a lateral cross-sectional view (top cross-sectional view) schematically showing a lighting device of an application example. A high intensity discharge (HID) lamp was used as the light source 21. The light beam emitted from the light source 21 is reflected by the elliptical reflector 22 and condensed on the shade 23 disposed at the focal point of the elliptical reflector 22. The light beam that has passed through the shade 23 is converted into substantially parallel light by the lens 24 and enters the light deflection liquid crystal cell 25 of the first embodiment. Light is emitted from the illumination device via the light deflection liquid crystal cell 25. The control device 26 switches the voltage applied to the light deflection liquid crystal cell 25.

  The light deflection liquid crystal cell 25 is set so that the prism length direction is horizontal when viewed from the front of the headlight (with respect to the ground). Further, the prism side is set to be the light source 21 side (note that the light deflection action does not change even if the prism side is opposite to the light source 21).

  Illumination devices of application examples were produced using light deflection liquid crystal cells with chiral pitches of 1 μm, 2 μm, 3 μm, 5 μm, and 9 μm, respectively, and the projected images when the voltage was off and on were observed. First, observation results of a sample with a chiral pitch of 2 μm will be described.

  6A and 6B are sketches schematically showing projected images when the voltage is on and when the voltage is off, respectively. As shown in FIG. 6A, when a sufficient voltage (for example, 20 V) was turned on, a clean cut-off pattern was projected (corresponding to a low beam). Light was not scattered in extra directions such as stray light.

  As shown in FIG. 6B, when the voltage was turned off, the projected image moved approximately 3 ° upward (corresponding to a high beam) while maintaining almost the same size as when the voltage was turned on. The brightness was comparable between the low beam when the voltage was on and the high beam when the voltage was off. No projected image remained when the voltage was turned on, and all the incident light to the light deflecting liquid crystal cell was deflected.

  In the optical deflection liquid crystal cell of the embodiment, the deflection angle is about 3 °, but the deflection angle can be changed by changing the angle of the prism slope (base angle).

  When the voltage is gradually increased, the projected image does not move continuously without changing the size from the image when the voltage is turned off, but spreads up and down slightly in the middle, and a sufficiently high voltage (20 V or higher / AC 150Hz), and finally the image was clearly imaged with the same size. This is because the prism layer is interposed between the transparent electrode on the substrate and the liquid crystal layer, and the prism layer has a different thickness depending on the location, so the voltage (partial pressure) applied to the liquid crystal layer varies depending on the location. This is probably because a refractive index distribution occurs in the plane.

  Note that the direction in which the light deflecting liquid crystal cell is set can be inverted so that the beam is relatively high when the voltage is on and relatively low when the voltage is off. From the viewpoint of fail-safe, it is desirable that the low beam is maintained in the voltage off state.

  On the other hand, from the viewpoint of avoiding the influence of scattering at the time of turning off and producing a clear cut-off pattern, it is desirable to use a low beam when the voltage is on.

  Next, the difference due to the chiral pitch in the projected state will be described. At a chiral pitch of 1 μm, weak scattering was seen in the voltage off state. By applying voltage, the projected image moved, the transparency of the liquid crystal cell increased, and the cut-off pattern of the projected image became clear.

  When the chiral pitch was 3 μm or more, a portion where the projected image was not partially bent was seen with the voltage off. Such a portion was very small when the chiral pitch was 3 μm, but increased when the chiral pitch was 5 μm, and when the chiral pitch was 9 μm, the area of the unbent portion was larger. In these liquid crystal cells, the portion where the image was bent moved by voltage application, but the portion where the image was not bent did not move even when voltage was applied.

  The longer the chiral pitch, that is, the lower the concentration of the chiral agent, the wider the portion where the image is not bent. Therefore, the following causes of this phenomenon are presumed. It is considered that the longer the chiral pitch, the less the force with which the chiral agent twists the direction of the liquid crystal molecules, and the easier the liquid crystal molecules are vertically aligned even in the voltage off state. That is, the portion where the image is not bent is already in a homeotropic state when the voltage is turned off, and it is presumed that the alignment state does not change even when a voltage is applied.

  From the viewpoint of good light deflection in the voltage off state, the chiral pitch is preferably 1 μm and 2 μm, 3 μm is acceptable, 5 μm indicates a partial failure, 9 μm is impossible, and the longer the chiral pitch, It can be said that it is difficult to deflect light when off. On the other hand, from the viewpoint of scattering in a voltage-off state, weak scattering occurs when the chiral pitch is 1 μm, almost no scattering occurs at 2 μm or more, and it can be said that the shorter the chiral pitch, the larger the scattering. Therefore, when these results are put together, it can be said that the chiral pitch is preferably 1 μm or more and less than 5 μm, more preferably 1 μm or more and 3 μm or less.

  As described above, the prism layer is provided inside the liquid crystal cell, and the refractive index of the liquid crystal layer is changed by changing the refractive index of the liquid crystal layer by switching the focal conic state and the homeotropic state with a voltage. Made to work. By using the focal conic state and the homeotropic state, light deflection can be performed regardless of the polarization direction of incident light from the normal direction of the substrate.

  As an application example, an illumination device that deflects light in the vertical direction has been described. However, the deflection direction can be changed by changing the prism length direction. For example, when light deflection in the left-right direction is desired, the light deflection liquid crystal cell may be set so that the prism length direction is perpendicular to the headlight (when viewed from the ground).

  In addition, the light deflection liquid crystal cell of an Example can be applied to various illuminating devices besides the vehicle headlight. In addition to HID, a light emitting diode (LED), a field emission (FE) light source, a fluorescent lamp, or the like can be used as the light source.

  Next, the light deflection liquid crystal cell of the second embodiment will be described.

  FIG. 7 is a cross-sectional view in the thickness direction schematically showing the light deflection liquid crystal cell of the second embodiment. Hereinafter, differences from the first embodiment will be described. In the second embodiment, the transparent electrode is not formed on the glass substrate 31 on the prism layer 3 side, and the prism layer 3 is formed directly on the glass substrate 31. The prism layer 3 can be formed in the same manner as in the first embodiment.

In the second embodiment, the transparent electrode 32 is formed above the prism layer 3 (on the liquid crystal layer side). First, the glass substrate 31 on which the prism layer 3 is formed is cleaned in the same manner as in the first embodiment. In order to improve the adhesion of the transparent electrode 32 (ITO film), a SiO ₂ film 33 can be formed on the prism layer 3. For example, the SiO ₂ film 33 is formed to a thickness of 50 nm by sputtering (AC discharge) at a substrate temperature of 80 ° C.

Next, an ITO film having a thickness of 100 nm is formed on the SiO ₂ film 33 by sputtering (AC discharge) at a substrate temperature of 100 ° C., for example, to form the transparent electrode 32. By masking unnecessary portions with a SUS mask, high-temperature heat-resistant tape or the like, an ITO film can be selectively formed on a desired portion. In addition to sputtering, vacuum deposition, ion beam method, chemical vapor deposition (CVD), or the like can be used as a film forming method.

  Next, the glass substrate 31 on which the transparent electrode 32 is formed is washed with a washing machine. For example, brush cleaning using an alkaline detergent, pure water cleaning, air blowing, UV irradiation, and infrared (IR) drying are sequentially performed. The cleaning method is not limited to this, and high-pressure spray cleaning, plasma cleaning, or the like can also be performed.

  Next, the vertical alignment film 4 is formed on the transparent electrode 32 using polyimide or the like. For example, Nissan Chemical Industries SE-4811 is formed by flexographic printing to a thickness of 80 nm and baked at 180 ° C. for 1.5 hours. In addition, as a method for forming the vertical alignment film 4, ink jet, spin coating, slit coating, slit and spin coating, or the like can be used.

  Similar to the first embodiment, the glass substrate 11 on the opposite side has a transparent electrode 12 formed thereon, and a vertical alignment film 13 is formed on the transparent electrode 12. Then, similarly to the first embodiment, the substrates 11 and 31 are overlapped to form an empty cell, and the liquid crystal layer 15 is formed to produce the light deflection liquid crystal cell of the second embodiment.

  The liquid crystal layer 15 is the same as that of the first embodiment, and the focal conic state and the homeotropic state are switched depending on the voltage. In the light deflection liquid crystal cell of the second embodiment in which the prism side transparent electrode is formed above the prism (liquid crystal layer side), light deflection can be performed as in the first embodiment.

  In the second embodiment, no prism layer is interposed between the prism-side transparent electrode and the liquid crystal layer. This is considered to reduce the in-plane distribution of the refractive index due to the in-plane distribution of the prism layer thickness, and when the voltage is continuously changed, the projected image is expected to move without changing the shape. The In addition, a decrease in drive voltage required for moving the projected image is expected.

  Although the present invention has been described with reference to the embodiments, the present invention is not limited thereto. It will be apparent to those skilled in the art that various modifications, improvements, combinations, and the like can be made.

1, 11, 31 Glass substrate 2, 12, 32 Transparent electrode 3 Prism layer 3a Prism 3b Base layer 4, 13 Vertical alignment film 14 Gap control agent 15 Liquid crystal layer 16 Main sealant 33 SiO ₂ film 21 HID lamp 22 Elliptical reflector 23 Shade 24 Lens 25 Light deflection liquid crystal cell 26 Control device

Claims (5)

A liquid crystal layer having a positive dielectric anisotropy and a chiral agent added thereto;
First and second transparent substrates disposed opposite to each other and sandwiching the liquid crystal layer;
First and second transparent electrodes formed on the liquid crystal layer side above the first and second transparent substrates, respectively, for applying a voltage to the liquid crystal layer;
One of the first and second transparent substrates, a prism layer formed above the liquid crystal layer side;
And a vertical alignment film formed before Symbol liquid crystal layer side above the first and second transparent substrates,
The liquid crystal layer, shows a focal conic state by voltage off, the optical deflection apparatus showing the homeotropic state by the voltage on. The light deflection apparatus according to claim 1 , wherein the prism layer is made of an acrylic UV curable resin. Chiral pitch in the liquid crystal layer is, the optical deflecting device of claim 1 or 2 in the range of less than 1 [mu] m 5 [mu] m. Of the first and second transparent electrodes, the prism layer side electrode is formed above the prism layer on the liquid crystal layer side , and the prism layer side substrate has the vertical alignment film on the prism layer. The light deflection apparatus according to claim 1 , wherein the light deflection apparatus is formed on an electrode formed above the liquid crystal layer . Further, the optical deflecting device according to any one of claims 1 to 4 having a light source to be incident light to the liquid crystal layer.