JP2012252345A - Liquid crystal display - Google Patents

Abstract

PROBLEM TO BE SOLVED: To avoid an influence of charged particles accumulated in a liquid crystal layer, without adding a new configuration to a liquid crystal modulation element.SOLUTION: A liquid crystal display comprises: liquid crystal modulation elements 2R, 2G and 2B that individually include a first electrode 103, a second electrode 107, a liquid crystal layer 105 arranged between the first and second electrodes, a first alignment film 104 arranged between the first electrode and the liquid crystal layer, and a second alignment film 106 arranged between the second electrode and the liquid crystal layer; and control means 3 that applies first and second potentials to the first and second electrodes, respectively, so that a mark of an electric field generated in the liquid crystal layer is periodically inverted, in a modulation operation state of the liquid crystal modulation elements. The control means, in states other than the modulation operation state, applies third and fourth potentials to the first and second electrodes, respectively, so that the mark of the electric field generated in the liquid crystal layer is constant, and applies potentials, for which a difference between the third and fourth potentials changes in an in-plane direction of the liquid crystal layer, to the first and second electrodes as the third and fourth potentials.

Description

  The present invention relates to a liquid crystal display device such as a projector using a liquid crystal modulation element.

  The liquid crystal modulation element includes a dielectric difference between a first transparent substrate having a transparent electrode (common electrode) and a second transparent substrate having a transparent electrode (pixel electrode), a wiring, a switching element, and the like forming a pixel. Some have nematic liquid crystal sealed with positive isotropic. This liquid crystal modulation element is called a so-called TN (Twisted Nematic) liquid crystal modulation element in which the major axis of liquid crystal molecules is continuously twisted by 90 ° between two glass substrates, and is used as a transmission type liquid crystal modulation element. . There is also a circuit board using a circuit board having a reflecting mirror, wiring, switching elements and the like instead of the second transparent board. This liquid crystal modulation element is called a so-called VAN (Vertical Arrangement Nematic) liquid crystal modulation element in which the major axis of the liquid crystal molecules is homeotropically aligned substantially perpendicular to the two substrates, and is used as a reflective liquid crystal element. Yes.

  In these liquid crystal modulation elements, in general, an ECB (Electrically Controlled Birefringence) effect is used to control an action of imparting retardation (changing the polarization state) to light waves passing through the liquid crystal layer to form an image.

  In a liquid crystal modulation element that modulates light intensity using such an ECB effect, charged particles (ionic substances) existing in the liquid crystal layer move by applying an electric field to the liquid crystal layer. When the direct current electric field is continuously applied to the liquid crystal layer, the charged particles are attracted to one of the two opposing electrodes. Thereby, even if the voltage applied to the electrode is constant, the electric field applied to the liquid crystal layer is increased or decreased by the charge of the charged particles, and the electric field applied to the liquid crystal layer is substantially attenuated or increased.

  In order to avoid such a phenomenon, a line inversion drive method is generally adopted in which the polarity of the applied electric field is inverted and the polarity is switched at a predetermined cycle such as 60 Hz for each line of the array pixels. In addition, a field inversion drive method is also used in which the polarity of the electric field applied to all of the array pixels is inverted at a predetermined period. By these drive methods, it is possible to prevent the electric field applied to the liquid crystal layer from having a constant polarity, and to prevent ion bias.

  This corresponds to making the effective electric field for the liquid crystal layer always have the same value with respect to the voltage applied to the electrode.

  However, charged particles are also present in the liquid crystal layer and the outer wall material surrounding the liquid crystal layer, and these charged particles drift (move) by driving the liquid crystal particularly in a high temperature environment. These charged particles become a DC electric field component inside the liquid crystal layer, adhere to the alignment film or electrode interface at the interface of the liquid crystal layer, and drift and deposit along the alignment direction of the liquid crystal molecules.

  In addition, in a liquid crystal modulation element having an organic alignment film, in addition to the drift of charged particles caused by driving the liquid crystal in a high temperature environment, light is incident on the liquid crystal modulation element, so that the alignment film, liquid crystal, sealing material, etc. The organic material is decomposed to generate charged particles. These charged particles also become a DC electric field component inside the liquid crystal layer, adhere to the alignment film or electrode interface at the liquid crystal layer interface, and further drift and deposit in the alignment direction of the liquid crystal molecules.

  Then, the effective electric field applied to the liquid crystal is changed by the charged particles deposited in the specific region of the liquid crystal layer, so that desired ECB modulation is not performed and the image quality is deteriorated. For example, uneven brightness is caused in the effective display area of the liquid crystal display element.

  Measures relating to such a problem are disclosed in Patent Documents 1 to 4.

  Patent Document 1 discloses that ions other than those at the time of image display operation cause a phenomenon of image sticking by aligning at least one potential of a pixel electrode and a counter electrode of a liquid crystal cell to a ground level. A method of dissociation from the interface is disclosed.

  Further, in Patent Document 2, an ion trap electrode region is provided in a non-display region of a liquid crystal modulation element, and an ion trap electrode region in a non-display region that does not affect image display by applying a DC voltage to the ion trap electrode. Discloses a method for adsorbing impurity ions.

  In Patent Document 3, a metal film electrode is arranged at a position different from the pixel electrode, and a DC voltage is applied between the metal film electrode and the common electrode to reduce the concentration of mobile ions in the display region. A method for suppressing the flicker phenomenon is disclosed.

  Furthermore, in Patent Document 4, an ion trap electrode provided independently of a transparent electrode is provided on opposing surfaces provided on two electrode substrates in the vicinity of a liquid crystal sealing port, and a voltage is applied to the ion trap electrode. Thus, a method for trapping ionic impurities is disclosed.

As described above, it is possible to improve the quality of image display by controlling the charged particles inside the liquid crystal modulation element by controlling the voltage from the outside.
JP-A-2005-55562 JP-A-8-201830 Japanese Patent Laid-Open No. 11-38389 JP-A-5-323336

  However, in the method disclosed in Patent Document 1, since it is necessary to provide a switching unit for dropping the counter electrode to the ground level inside the circuit of the liquid crystal modulation element, the manufacturing process of the liquid crystal modulation element increases. Further, if the counter electrode is simply set to the ground level, the force for peeling off the ions attached to the alignment film and the electrode interface is weaker than the Coulomb force, and the effect is low.

  In addition, in the methods disclosed in Patent Documents 2 to 4, since an ion trap electrode that attracts ions to the non-display area is newly provided, the number of manufacturing steps is also increased. Moreover, although the ion impurity is attracted by the Coulomb force, the Coulomb force is inversely proportional to the square of the distance, and therefore, ions generated at a position away from the ion trap electrode cannot be attracted efficiently.

  The present invention provides a liquid crystal display device capable of avoiding the influence of the accumulation of charged particles in a liquid crystal layer without adding a new switching unit, ion trap electrode, or the like to the liquid crystal modulation element.

A liquid crystal display device according to one aspect of the present invention includes a first electrode, a second electrode, a liquid crystal layer disposed between the first electrode and the second electrode, and a gap between the first electrode and the liquid crystal layer. A liquid crystal modulation element including a first alignment film disposed on the second electrode and a second alignment film disposed between the second electrode and the liquid crystal layer, and an electric field generated in the liquid crystal layer in a modulation operation state of the liquid crystal modulation element And a control means for applying first and second potentials to the first and second electrodes, respectively, so that the sign is periodically inverted. The control means applies the third and fourth potentials to the first and second electrodes, respectively, so that the sign of the electric field generated in the liquid crystal layer is constant in a state other than the modulation operation state. As the fourth potential, the first and second electrodes are provided with a potential at which the difference between the third and fourth potentials changes in the in-plane direction of the liquid crystal layer.

  According to the present invention, the third and fourth potentials are applied to the electrodes to which the first and second potentials are applied in the modulation operation state, so that they adhere to the interface between the liquid crystal layer and the alignment film, Deposited charged particles can be forced to dissociate or diffuse from the interface. For this reason, it is possible to suppress degradation in image quality due to the influence of charged particles without adding a new switching unit, ion trap electrode, or the like to the liquid crystal modulation element.

1 is a diagram illustrating a configuration of a liquid crystal projector that is Embodiments 1 to 4 and Reference Example 1 of the present invention. FIG. Sectional drawing of the liquid crystal panel used in Examples 1-4 and Reference Example 1. FIG. The figure explaining the pretilt direction of the vertical alignment mode in the said liquid crystal panel. Sectional drawing which shows the charged particle deposited in the liquid crystal panel in the reference example 1. FIG. In the reference example 1, the figure seen from the glass substrate side which shows the charged particle deposited in the liquid crystal panel. The figure explaining the applied voltage to the counter electrode for making a chargeable particle float in Reference Example 1. FIG. The figure explaining the applied voltage to the counter electrode for making a chargeable particle float in Reference Example 1. FIG. The figure explaining the charged particle which floated by the applied voltage control in the reference example 1. FIG. The figure explaining the alternating current drive of the liquid crystal panel in an Example and a reference example. FIG. 3 is a view for explaining an in-plane distribution given to a reflective pixel electrode layer in order to diffuse charged particles deposited in Example 1. FIG. 11 is a diagram for explaining a voltage applied to the counter electrode in a region 124 in FIG. 10 in Example 1. FIG. 11 is a diagram for explaining a voltage applied to a counter electrode in a region 122 in FIG. 10 in Example 1. FIG. 11 is a diagram for explaining a voltage applied to a counter electrode in a region 123 in FIG. 10 in Example 1. The figure explaining the applied voltage to the counter electrode for diffusing the deposited charged particle in Example 1. FIG. In Example 1, the figure which shows the state which diffused the deposited charged particle. FIG. 11 is a diagram for explaining a voltage applied to a counter electrode in a region 124 in FIG. 10 in Example 2. FIG. 11 is a diagram for explaining a voltage applied to a counter electrode in a region 122 in FIG. 10 in Example 2. FIG. 11 is a diagram for explaining a voltage applied to a counter electrode in a region 123 in FIG. 10 in Example 2. 9 is a flowchart showing the operation of a liquid crystal projector in Example 4. 9 is a flowchart showing the operation of a liquid crystal projector in Example 4.

Hereinafter, preferred embodiments and reference examples of the present invention will be described with reference to the drawings.
[Reference Example 1]

  FIG. 1 shows a configuration of a liquid crystal projector (image projection apparatus) as a liquid crystal display apparatus which is a reference example 1 of the present invention.

  Reference numeral 3 denotes a liquid crystal panel driver as control means, which converts image information input from an image supply device 50 such as a personal computer, a DVD player, or a TV tuner into red, green and blue panel drive signals. Each panel drive signal is input to a red liquid crystal panel 2R, a green liquid crystal panel 2G, and a blue liquid crystal panel 2B, which are reflective liquid crystal modulation elements. As a result, the three liquid crystal panels 2R, 2G, and 2B are driven independently of each other. The liquid crystal panels 2R, 2G, and 2B modulate light (color-separated light) from an illumination optical system, which will be described later, by a modulation operation according to the panel drive signal. Thus, an image corresponding to each color component of the image information input from the image supply device 50 is displayed.

  Reference numeral 1 denotes an illumination optical system. A top view is shown on the left side of the frame in the figure, and a side view thereof is shown on the right side. The illumination optical system 1 includes a light source lamp, a parabolic reflector, a fly-eye lens, a polarization conversion element, a condenser lens, and the like, and emits illumination light as linearly polarized light (S-polarized light) having a uniform polarization direction.

  The illumination light from the illumination optical system 1 is incident on a dichroic mirror 30 that reflects magenta and transmits green. The magenta color component of the illumination light is reflected by the dichroic mirror and passes through the blue cross color polarizer 34 that gives half-wave retardation to the blue polarized light. This generates blue linearly polarized light (P-polarized light) whose polarization direction is parallel to the paper surface of the figure and red linearly polarized light (S-polarized light) whose polarization direction is the direction perpendicular to the paper surface of the figure. Is done.

  The blue P-polarized light enters the first polarization beam splitter 33, passes through the polarization separation film, and is guided to the blue liquid crystal panel 2B. The red S-polarized light is reflected by the polarization separation film of the first polarization beam splitter 33 and guided to the red liquid crystal panel 2R.

  On the other hand, the green linearly polarized light (S-polarized light) transmitted through the dichroic mirror 30 passes through the dummy glass 36 for correcting the optical path length, and then enters the second polarizing beam splitter 31. The green S-polarized light is reflected by the polarization separation film and guided to the green liquid crystal panel 2G.

  In this way, the red, green, and blue liquid crystal panels 2R, 2G, and 2B are illuminated by the illumination light.

  The light incident on each liquid crystal panel is provided with polarization retardation according to the modulation state of the pixels arranged in each liquid crystal panel, and is reflected and emitted by the liquid crystal panel. Of the reflected light, the polarization component having the same polarization direction as that of the illumination light traces the optical path of the illumination light in the reverse direction and returns to the illumination optical system 1 side.

  In addition, a polarization component (modulated light) having a polarization direction orthogonal to the polarization direction of the illumination light in the reflected light proceeds as follows. The modulated light from the red liquid crystal panel 2 </ b> R that is P-polarized light passes through the polarization separation film of the first polarization beam splitter 33. Next, the light is transmitted through a red cross color polarizer 35 that gives half-wave retardation to red polarized light to be S-polarized light. Then, the red S-polarized light is incident on the third polarization beam splitter 32, reflected by the polarization separation film, and guided to the projection lens 4.

  The modulated light from the blue liquid crystal panel 2B, which is S-polarized light, is reflected by the polarization separation film of the first polarization beam splitter 33, passes through the red cross color polarizer 35 without being subjected to retardation, and passes through the third polarization beam. The light enters the splitter 32. The blue S-polarized light is reflected by the polarization separation film of the third polarization beam splitter 32 and guided to the projection lens 4.

  The modulated light by the green liquid crystal panel 2G that is P-polarized light is transmitted through the polarization separation film of the second polarization beam splitter 31, and is transmitted through the dummy glass 37 for correcting the optical path length, and the third polarization beam splitter. 32 is incident. The green P-polarized light passes through the polarization separation film of the third polarization beam splitter 32 and is guided to the projection lens 4.

  The three colors of modulated light thus synthesized are projected by the projection lens 4 onto the light diffusion screen 5 which is the projection surface. Thereby, a full color image is displayed.

  The liquid crystal panel 2R for red, the liquid crystal panel 2G for green, and the liquid crystal panel 2B for blue used in the present embodiment are vertical alignment mode (for example, VAN type) reflective liquid crystal modulation elements.

  FIG. 2 shows a cross-sectional structure common to the red liquid crystal panel 2R, the green liquid crystal panel 2G, and the blue liquid crystal panel 2B. In order from the light incident side, 101 is an AR coating film, and 102 is a glass substrate. Reference numeral 103 denotes a transparent electrode film (first electrode) formed of ITO or the like formed on the glass substrate 102. Reference numeral 104 denotes a first alignment film disposed between the transparent electrode film 103 and a liquid crystal layer described later. Reference numeral 105 denotes a liquid crystal layer disposed between the first alignment film 104 and the second alignment film 106. Reference numeral 107 denotes a reflective pixel electrode layer (second electrode) which is disposed to face the transparent electrode film 103 and is formed of a metal such as aluminum. Reference numeral 108 denotes a Si substrate on which the reflective pixel electrode layer 107 is formed. The transparent electrode film 103 and the reflective pixel electrode layer 107 may be collectively referred to as an electrode layer hereinafter.

  FIG. 9 shows an effective electric field generated in the liquid crystal layer 105 by controlling the voltage applied to the electrode layers 103 and 107 by the liquid crystal panel driver 3 in the modulation operation state (liquid crystal driving state) for image display. The horizontal axis represents time, and the vertical axis represents the effective electric field (potential difference) of the liquid crystal layer 105. The liquid crystal panel driver 3 stores a computer program therein, and controls the voltage applied to the electrode layers 103 and 107 according to the program.

  In the following description, the voltage applied to each electrode or liquid crystal layer means a potential (potential difference from the ground) with respect to a ground (0 V) not shown. In addition, the center value of the AC potential applied to the reflective pixel electrode layer 107 is referred to as a center potential.

  A voltage (electric field) applied to the reflection electrode side end of the liquid crystal layer 105 through the reflection pixel electrode layer 107 is an alternating voltage (solid line) V2 having a specific period α, and the liquid crystal layer is formed through the transparent electrode film 103. A voltage (electric field) applied to the transparent electrode side end portion 105 is a DC voltage (broken line) V1. At this time, the DC voltage applied to the transparent electrode film 103 corresponds to the first potential, and the AC voltage applied to the reflective pixel electrode layer 107 corresponds to the second potential.

  The effective electric field generated in the liquid crystal layer 105 is an AC electric field that is generated according to the difference between the AC voltage V2 and the DC voltage V1, and that the positive electric field PV and the negative electric field NV are alternately switched at a specific period α. That is, the potential difference generated in the liquid crystal layer 105 periodically changes between positive and negative. In other words, a potential (potential difference) is applied to both electrodes so that the sign of the electric field generated in the liquid crystal layer is periodically inverted (changes periodically between positive and negative). In the modulation operation state (image display state) of the liquid crystal modulation element, the control of the voltage (potential, electric field) as described above is performed.

  Here, the specific period α is 1/120 second in the NTSC system and 1/100 second in the PAL system, and corresponds to a period of one field. One frame image is displayed in two field periods (1/60 seconds or 1/50 seconds). However, the specific period α may correspond to a display period of one frame image.

  Further, the positive electric field PV and the negative electric field NV are caused by a voltage drop (electric field) applied to the electrode layers 103 and 107, a voltage drop due to the resistance of the alignment films 104 and 106, and charges trapped by the alignment films (electrons). And the minute voltage (electric field) generated by the electric charges of the holes) is superimposed.

  FIG. 3 shows the red liquid crystal panel 2R, the green liquid crystal panel 2G, and the blue liquid crystal panel 2B as viewed from the glass substrate 102 side. Reference numeral 110 denotes a director direction (pretilt direction) of liquid crystal molecules aligned by the first alignment film 104. Reference numeral 111 denotes a director direction (pretilt direction) of liquid crystal molecules aligned by the second alignment film 106. Reference numeral 112 denotes an effective display area of the liquid crystal panel. Both the director directions 110 and 111 are inclined by several degrees with respect to the normal line of the alignment film surface, and the directions in which they are inclined are opposite to each other.

  Orientation processing is performed in a direction of about 45 degrees with respect to the short side 112a and the long side direction 112b of the effective display area 112.

  In the projector, the temperature of the liquid crystal panels 2R, 2G, and 2B rises due to light irradiation from a high-intensity lamp, and is controlled to be about 40 degrees under a normal temperature operating environment. However, when the projector is used for a long period of time, the liquid crystal panels 2R, 2G, and 2B are in a heated state (high temperature state) for a long period of time, and the liquid crystal molecules are driven for image display, causing the following problems. Arise.

  Charged particles 113 are present in the vicinity of the interface between the sealing material, which is an organic substance in the liquid crystal layer 105 and its surroundings, the first alignment film 104, the second alignment film 106, and the electrode layers 103 and 107. As shown in FIGS. 4 and 5, the charged particles 113 travel in the director direction of the liquid crystal molecules along the interface with the second alignment film 106 on the reflective pixel electrode layer 107 side, as shown in FIGS. The effective display area 112 is deposited in a diagonal area on the second alignment film 106 side. The charge of the chargeable particles 113 here is a negative sign charge. 4 is a cross-sectional view of the liquid crystal panel, and FIG. 5 is a view of the liquid crystal panel viewed from the glass substrate 102 side.

  The effective electric field generated in the liquid crystal layer 105 is changed by the charged particles 113 deposited at the interface between the second alignment film 106 and the liquid crystal layer 105 as described above. As a result, the quality of the image of the area where charged particles are deposited is degraded.

  In this reference example, in order to float the charged particles 113 deposited in this way from the interface of the second alignment film 106 and the diagonal region of the effective display region 112, the liquid crystal panel driver 3 applies them to the electrode layers 103 and 107. The applied voltage is controlled. This applied voltage control is performed in a state other than the modulation operation state of the projector (hereinafter referred to as a non-modulation operation state), that is, in a state in which the above-described AC electric field is not generated in the liquid crystal layer 105 (first and In a state where the second potential is not applied).

  First, as shown in FIG. 6, in order to float the deposited charged particles 113 inside the liquid crystal layer 105, a positive voltage (third potential) is applied to the transparent electrode film 103, and a negative voltage is applied to the reflective pixel electrode layer 107. (The fourth potential) is applied. Here, the voltage applied to the reflective pixel electrode layer 107 may not be negative. Specifically, when the voltage applied to the reflective pixel electrode layer 107 and the voltage applied to the transparent electrode film 103 are compared, the voltage applied to the reflective pixel electrode layer 107 is a relatively negative voltage (with the same sign). Voltage). That is, it is sufficient that the voltage applied to the reflective pixel electrode layer 107 is lower than the voltage applied to the transparent electrode film 103 (if it is a minus side). Of course, both the voltage applied to the reflective pixel electrode layer 107 and the voltage applied to the transparent electrode film 103 can be positive voltages, both can be negative voltages, one can be positive, and the other can be positive. As long as the above-described conditions are satisfied. This is the same in the embodiments described later.

  FIG. 7 shows applied voltages 103 a and 107 a for both electrode layers 103 and 107. As can be seen from FIG. 7, the applied voltage (fourth potential) 107a to the reflective pixel electrode layer 107 is a negative voltage with respect to the applied voltage (third potential) 103a to the transparent electrode film 103. The applied voltages 103a and 107a to the electrode layers 103 and 107 are constant DC voltages that do not change with time. However, the constant voltage mentioned here includes not only a voltage that does not vary at all, but also a voltage that varies only within a range that can be regarded as the same voltage due to a variation in power supply voltage, a control error, or the like. This is the same in other embodiments described later.

  As a result, a negative DC electric field that does not periodically change between positive and negative is generated in the liquid crystal layer 105. Note that the strength of the DC electric field may vary within a range in which the DC electric field is applied to the liquid crystal layer 105 so as not to periodically change between positive and negative. That is, the voltage (potential) of both electrodes may change, but it is desirable that the sign of the voltage (potential) of the other electrode with respect to the voltage (potential) of one electrode does not change. In other words, a potential (potential difference) is applied to both electrodes so that the sign of the electric field generated in the liquid crystal layer is constant (so that it is constant as it is positive or constant as it is negative). In a state other than the modulation operation state of the liquid crystal modulation element (image non-display state, device activation, sleep state, device termination operation, etc.), the control of the voltage (potential, electric field) as described above is performed by the control means.

  In addition, the voltage applied to the transparent electrode film 103 and the reflective pixel electrode layer 107 is the in-plane direction of the liquid crystal layer 105, that is, the direction orthogonal to the thickness direction (the in-display direction of the liquid crystal panel or the in-modulation plane direction). The same). However, the voltage applied to the liquid crystal layer in the region where charged particles are deposited is increased (the potential difference between both electrodes is increased), and the voltage is applied to the liquid crystal layer in the region where other charged particles are deposited in a small amount. The voltage may be lowered.

  Such applied voltage control is performed for a predetermined time in the non-modulation operation state. Accordingly, the negatively charged particles 113 attached or deposited on the interface between the liquid crystal layer 105 and the second alignment film 106 as shown in FIG. 8 are repelled by the Coulomb force with respect to the negative voltage applied to the reflective pixel electrode layer 107. It is dissociated from the interface and floats inside the liquid crystal layer 105 by force.

  Here, the predetermined time is a period until most (for example, 70% or more) or all of the deposited charged particles 113 are separated from the interface of the second alignment film 106 and float inside the liquid crystal layer 105. Is the time.

  In addition, as described above, the sign of the voltage applied to the reflective pixel electrode layer 107 on the second alignment film side where the charged particles 113 are deposited on the interface with the liquid crystal layer 105 is the sign of the charged particles 113. Same negative.

  According to this reference example, the charged particles 113 deposited at the interface between the liquid crystal layer 105 and the second alignment film 106 are dissociated from the interface and suspended in the liquid crystal layer. As a result, it is possible to suppress deterioration in image quality due to the influence of the accumulated charged particles 113.

  In this reference example, the case where the negatively charged particles 113 deposited on the interface between the liquid crystal layer 105 and the second alignment film 106 are dissociated from the interface has been described. However, the liquid crystal layer 105 and the first alignment film 104 are described. There is a possibility that positively charged particles are deposited on the interface. Also in this case, by performing the same applied voltage control as described above, the charged particles can be dissociated from the interface and suspended. In this case, the sign of the voltage applied to the transparent electrode film 103 on the first alignment film 104 side on which positive charged particles are deposited at the interface with the liquid crystal layer 105 may be the same as the sign of the charged particles. .

  As described in the first reference example, the negatively charged particles 113 may be converted into a diagonal region in one diagonal direction of the effective display region 112 of the liquid crystal layer 105 on the second alignment film 106 side by using the projector for a long time. Deposits in the vicinity.

  In this embodiment, the charged particles 113 are attracted in a diagonal direction different from the diagonal direction in which the charged particles 113 are deposited, and the charged particles 113 are diffused (moved). In the present embodiment, the same reference numerals as those in the reference example 1 are assigned to components common to the reference example 1. This is the same in other embodiments described later.

  Also in this embodiment, the voltage applied to the transparent electrode film 103 and the reflective pixel electrode layer 107 is controlled so that the AC electric field described with reference to FIG. This is the same in other embodiments described later.

  On the other hand, in the non-modulation operation state, the difference in voltage applied to the transparent electrode film 103 and the reflective pixel electrode layer 107 in the in-plane direction of the liquid crystal layer 105 (potential difference between electrodes) changes, that is, the distribution is changed. A voltage is applied to hold. Specifically, the voltage applied to the transparent electrode film 103 and the reflective pixel electrode layer 107 is controlled so that a larger interelectrode potential difference is generated in a region where more charged particles in the liquid crystal layer 105 are deposited. . Such applied voltage control is performed for a predetermined time.

  FIG. 10 shows a voltage distribution in the effective display area 112 applied to the reflective pixel electrode layer 107. A region 122 where the applied voltage is large is shown bright (in white), is shown as a region 123 that becomes dark (becomes gray) as the applied voltage is reduced, and a region 124 where the applied voltage is 0 is shown in black. Further, the pixel effective area of the reflective pixel electrode layer 107 corresponding to the effective display area 112 is indicated by a thick line 125.

  As can be seen from FIG. 10, in the diagonal direction A in which the charged particles 113 are deposited, the inter-electrode potential difference is constant, and the inter-electrode potential difference on the diagonal line in the diagonal direction A and in the vicinity thereof is zero. . On the other hand, in the other diagonal direction B, the change in the interelectrode potential difference is increased, and the interelectrode potential difference is increased as it is closer to the diagonal region.

  Note that the region 122 is a region where the charged particles 113 are deposited most, and corresponds to a first region. Further, the region 123 and the region 124 correspond to a second region with respect to the region 122. Further, the region 123 and the region 124 correspond to a first region and a second region, respectively.

  In the present embodiment, as shown in FIGS. 11 to 13, applied voltages (third and fourth potentials) to both electrode layers 103 and 107 are set.

  FIG. 11 shows the applied voltage in the region 124 in FIG. The applied voltage 103b to the transparent electrode film 103 and the applied voltage 107b to the reflective pixel electrode layer 107 are both constant DC voltages that do not change with time. In addition, the applied voltages 103b and 107b coincide with each other, and the potential difference between the electrodes is zero.

  Note that the term “match” includes not only a case where there is a complete match but also a case where there is a difference only within a range that can be regarded as a match due to a control error or the like. This is the same in other embodiments described later.

  FIG. 12 shows an applied voltage in the region 122 in FIG. The applied voltage 107 b to the reflective pixel electrode layer 107 is an alternating voltage, and the minimum value of the alternating voltage matches the applied voltage 103 b to the transparent electrode film 103. The applied voltage 103b to the transparent electrode film 103 is a DC voltage.

  Such applied voltage control is positive for the reflective pixel electrode layer 107 corresponding to the time integral value (indicated by a dotted line) of the applied voltage 107b to the reflective pixel electrode layer 107 with respect to the transparent electrode film 103. This is equivalent to applying a DC voltage.

  FIG. 13 shows the applied voltage in the region 123 in FIG. Similar to the region 122, the applied voltage 107b to the reflective pixel electrode layer 107 is an alternating voltage, and the minimum value of the alternating voltage matches the applied voltage 103b to the transparent electrode film 103. The applied voltage 103b to the transparent electrode film 103 is a DC voltage. However, the maximum value of the AC voltage applied to the reflective pixel electrode layer 107 is lower than the maximum value of the AC voltage applied to the reflective pixel electrode layer 107 in the region 122.

  Such applied voltage control is positive for the reflective pixel electrode layer 107 corresponding to the time integral value (indicated by a dotted line) of the applied voltage 107b to the reflective pixel electrode layer 107 with respect to the transparent electrode film 103. This is equivalent to applying a DC voltage.

  As a result, a larger inter-electrode potential difference 120 than that of the region 123 is given to the region 122, and a higher DC voltage is applied.

  FIG. 14 shows a cross-sectional structure of the liquid crystal panel. This figure shows the sign of the voltage applied to the liquid crystal layer 105 in the regions 122 and 123 excluding the region 124 where the applied voltage of the liquid crystal layer 105 is 0 among the regions 122, 123 and 124. As described above, the applied voltage 107b of the reflective pixel electrode layer 107 is a positive voltage with respect to the applied voltage 103b of the transparent electrode film 103, and the positive DC current that does not periodically change between positive and negative also in the liquid crystal layer 105. A world arises.

  The sign of the voltage applied to the reflective pixel electrode layer 107 on the second alignment film side where the charged particles 113 are deposited at the interface with the liquid crystal layer 105 is positive, which is different from the sign of the charged particles 113. However, the applied voltage 107b to the reflective pixel electrode layer 107 increases toward a diagonal region in the diagonal direction B different from the diagonal direction A in which the charged particles 113 are deposited.

  Therefore, the negatively charged particles 113 deposited in the diagonal direction A at the interface of the second alignment film 106 are attracted in the diagonal direction B by the Coulomb force as shown in FIG. Spread.

  The predetermined time described in the present embodiment is a time until most (for example, 70%) or all of the charged particles 113 deposited in the diagonal direction A diffuse in the other diagonal direction B. .

  In this way, by diffusing the charged particles 113 deposited in a specific diagonal direction, it is possible to suppress deterioration in image quality due to the influence of the deposition of the charged particles 113.

  As described in the first embodiment, the negatively charged particles 113 are diagonally aligned in one diagonal direction of the effective display region 112 of the liquid crystal layer 105 on the second alignment film 106 side by using the projector for a long time. Deposits in the vicinity.

  In the present embodiment, as in the first embodiment, in the non-modulation operation state, the charged particles 113 are attracted in a diagonal direction different from the diagonal direction in which the charged particles 113 are deposited, and the charged particles 113 are diffused. . Specifically, as described with reference to FIG. 10 in Example 1, the difference in voltage applied to the transparent electrode film 103 and the reflective pixel electrode layer 107 in the in-plane direction of the liquid crystal layer 105 ( A voltage is applied so that the potential difference between the electrodes changes. Specifically, the voltage applied to the transparent electrode film 103 and the reflective pixel electrode layer 107 is controlled so that a larger interelectrode potential difference is generated in a region where more charged particles in the liquid crystal layer 105 are deposited. . Such applied voltage control is performed for a predetermined time.

  16 to 18 show voltages applied to both electrode layers 103 and 107 during the predetermined time in this example.

  FIG. 16 shows the applied voltage in the region 124 in FIG. The applied voltage 103b to the transparent electrode film 103 and the applied voltage 107b to the reflective pixel electrode layer 107 are both constant DC voltages that do not change with time. In addition, the applied voltages 103b and 107b coincide with each other, and the applied voltage of the liquid crystal layer 105 is zero.

  FIG. 17 shows the applied voltage in the region 122 in FIG. Both the applied voltage 107b to the reflective pixel electrode layer 107 and the applied voltage 103b to the transparent electrode film 103 are DC voltages. A higher (positive) DC voltage than the transparent electrode film 103 is applied to the reflective pixel electrode layer 107.

  FIG. 18 shows the applied voltage in the region 123 in FIG. Similar to the region 122, the applied voltage 107b to the reflective pixel electrode layer 107 and the applied voltage 103b to the transparent electrode film 103 are both DC voltages. Further, a higher (positive) DC voltage than that of the transparent electrode film 103 is applied to the reflective pixel electrode layer 107. However, a voltage lower than the DC voltage applied to the reflective pixel electrode layer 107 in the region 122 is applied to the reflective pixel electrode layer 107.

  As a result, a larger inter-electrode potential difference 120 than that of the region 123 is given to the region 122, and a higher DC voltage is applied.

  Also in this example, as described with reference to FIG. 14 in Example 1, in the regions 122 and 123 excluding the region 124, the applied voltage 107b of the reflective pixel electrode layer 107 is compared to the applied voltage 103b of the transparent electrode film 103. Positive voltage. A positive DC electric field that does not periodically change between positive and negative is generated in the liquid crystal layer 105.

  The sign of the voltage applied to the reflective pixel electrode layer 107 on the second alignment film side where the charged particles 113 are deposited at the interface with the liquid crystal layer 105 is positive, which is different from the sign of the charged particles 113. However, as can be seen from FIG. 9, the applied voltage 107 b to the reflective pixel electrode layer 107 increases toward a diagonal region in a diagonal direction B different from the diagonal direction A in which the charged particles 113 are deposited.

  For this reason, the negatively charged particles 113 deposited in the diagonal direction A at the interface of the alignment film 106 are attracted in the diagonal direction B by the Coulomb force, as described with reference to FIG. And diffuses inside the liquid crystal layer 105.

  The predetermined time is a time until most (for example, 70%) or all of the charged particles 113 deposited in the diagonal direction A diffuse in the other diagonal direction B.

  In this way, by diffusing the charged particles 113 deposited in a specific diagonal direction, it is possible to suppress deterioration in image quality due to the influence of the deposition of the charged particles 113.

  In this embodiment, since a DC voltage is applied to the reflective pixel electrode layer 107, the Coulomb force is always applied for a predetermined time as compared with the case where an AC voltage is applied to the reflective pixel electrode layer 107 as in the first embodiment. Thus, the charged particles 113 can be attracted in the diagonal direction B. For this reason, the diffusion effect of the charged particles 113 can be enhanced.

  In the first and second embodiments, the case where the negatively charged particles 113 deposited in the diagonal region on the second alignment film side are diffused has been described. However, the first alignment film 104 side has the diagonal region. Positively charged particles can accumulate. Also in this case, the charged particles can be diffused by controlling the applied voltage in the same manner as in the first and second embodiments. In this case, the sign of the voltage applied to the transparent electrode film 103 on the first alignment film 104 side where positive charged particles are deposited on the interface with the liquid crystal layer 105 is negative, which is different from the sign of the charged particles. Good.

  In Example 3 of the present invention, the first applied voltage control (first control) described in Reference Example 1 (FIGS. 6 to 8) is first performed, and the charge deposited on the interface of the second alignment film 106 is obtained. The conductive particles 113 are suspended in the liquid crystal layer 105 from the interface. Thereafter, the second applied voltage control (second control) described in the first embodiment (FIGS. 10 to 15) or the second embodiment (FIGS. 16 to 18) is performed. That is, the charged particles 113 are attracted in a diagonal direction B different from the diagonal direction A of the effective display region 112 where the charged particles 113 are deposited, and diffused.

  In this way, by sequentially switching the first applied voltage control and the second applied voltage control, the quality of the image due to the influence of the charged particles 113 is compared with the case where only one applied voltage control is performed. Can be more effectively suppressed.

  In addition, the order which performs 1st applied voltage control and 2nd applied voltage control may be reverse to the order mentioned above.

  Next, a liquid crystal projector that is Embodiment 4 of the present invention will be described. Here, a specific operation of the liquid crystal panel driver 3 that performs applied voltage control for dissociation or diffusion of the charged particles 113 described in the first to third embodiments and the reference example 1 is illustrated in a flowchart illustrated in FIG. 19A. It explains using. This operation is executed according to a computer program stored in the liquid crystal panel driver 3.

  In step S301, the liquid crystal panel driver 3 determines whether or not the power switch of the projector is turned on (power ON). If the power is on, the internal timer starts counting in step S302. This timer counts the integrated value (image display integrated time) T of the time during which the projector is in the modulation operation state (image display time), and the current image display time is added to the previous image display integrated time. to add.

  When the power is turned on, the projector enters an image display state (a modulation operation state of the liquid crystal panel), drives the liquid crystal panel by applying voltage control shown in FIG. 9, and displays (projects) an image.

  Next, in step S303, the liquid crystal panel driver 3 determines whether or not the power switch is turned off. If the power is not turned off, this determination is repeated. If the power is turned off, the process proceeds to step S304.

  In step S304, it is determined whether or not the image display integration time T counted by the timer has reached a predetermined integration time Ta, assuming that the state has shifted to the non-modulation operation state. The predetermined cumulative time Ta is a time when the charged particles 113 deposited on the interface between the liquid crystal layer 105 and the second alignment film 106 and the diagonal area of the effective display area 112 in the liquid crystal panel are expected to affect the image quality. It is set in advance. If the image display integration time T does not reach the predetermined integration time Ta, the process jumps to step S307 to perform predetermined operation end processing of the projector, and then the power is shut off.

  On the other hand, when the image display integration time T reaches the predetermined integration time Ta, the process proceeds to step S305, and the application for dissociation or diffusion of the charged particles 113 described in the first to third embodiments and the reference example 1 is performed. Start voltage control.

  When the applied voltage control described in Embodiments 1 and 2 and Reference Example 1 is performed in Step S305, the applied voltage control is performed for a predetermined time (described in Embodiments 1, 2 and Reference Example 1) in Step S306. For a predetermined time). If it has not been performed for a predetermined time, this determination is repeated. If it has been performed for a predetermined time, the process proceeds to step S307, a predetermined operation end process of the projector is performed, and then the power is shut off.

  In addition, when the applied voltage control described in the third embodiment is performed in step S305, as illustrated in FIG. 19B, for example, the first voltage application control is performed for the predetermined time described in the reference example 1 in step S306a. It is determined whether or not it has been performed (here, referred to as a first predetermined time). If it has not been performed for the first predetermined time, this determination is repeated. If it has been performed for the first predetermined time, the second applied voltage control is started in step S306b. In step S306c, it is determined whether or not the second voltage application control has been performed for the predetermined time described in the first and second embodiments (herein referred to as a second predetermined time). If it has not been performed for the second predetermined time yet, this determination is repeated. If it has been performed for the second predetermined time, the process proceeds to step S307, a predetermined operation end process for the projector is performed, and then the power is shut off.

  In the present embodiment, the case where the applied voltage control described in the first to third embodiments and the reference example 1 is performed in accordance with the elapse of a predetermined image display integration time when the projector is turned off has been described. However, the application voltage control may be performed from the time the projector is turned on until the liquid crystal panel shifts to the modulation operation state. Further, it may be performed at an arbitrary timing according to a user operation. Further, the applied voltage control may be performed each time the projector is turned off or on regardless of the image display integration time.

  Each embodiment described above is only a representative example, and various modifications and changes can be made to each embodiment in carrying out the present invention.

  For example, each of the above embodiments relates to a liquid crystal modulation element in a vertical alignment mode, but the applied voltage control in the above embodiments is suitable for a liquid crystal modulation element of TN, STN, OCB type other than the vertical alignment mode. It may be modified to be applied to these liquid crystal modulation elements. Further, the present invention may be carried out by modifying it into a form suitable for a transmissive liquid crystal modulation element.

101 AR coating film 102 Glass substrate 103 Transparent electrode film 104 First alignment film 105 Liquid crystal layer 106 Second alignment film 107 Reflective pixel electrode layer 108 Si substrates 110 and 111 Director direction of liquid crystal molecules (pretilt direction)
113 charged particles

Claims (5)

A first electrode and a second electrode; a liquid crystal layer disposed between the first electrode and the second electrode; a first liquid disposed between the first electrode and the liquid crystal layer; A liquid crystal modulation element including an alignment film, and a second alignment film disposed between the second electrode and the liquid crystal layer;
Control means for applying first and second potentials to the first and second electrodes, respectively, so that the sign of the electric field generated in the liquid crystal layer is periodically inverted in the modulation operation state of the liquid crystal modulation element. ,
The control means applies third and fourth potentials to the first and second electrodes, respectively, so that a sign of an electric field generated in the liquid crystal layer is constant in a state other than the modulation operation state, A liquid crystal display device, wherein a potential at which a difference between the third and fourth potentials changes in an in-plane direction of the liquid crystal layer is applied to the first and second electrodes as the third and fourth potentials. In the in-plane direction of the liquid crystal layer, a region in which the charged particles in the liquid crystal layer are deposited is a first region, and a region in which the charged particles are less deposited than the first region is a second region. And when
2. The liquid crystal display device according to claim 1, wherein the control means makes the potential difference between the third and fourth potentials in the second region larger than the potential difference in the first region. .   The control means has a sign different from the sign of the charged particles on the electrode on the alignment film side where the charged particles in the liquid crystal layer are deposited at the interface with the liquid crystal layer, of the first and second electrodes. The liquid crystal display device according to claim 1, wherein the third and fourth potentials are applied.   4. The liquid crystal display device according to claim 1, wherein the liquid crystal modulation element is a vertical alignment mode reflective liquid crystal modulation element. A first electrode and a second electrode; a liquid crystal layer disposed between the first electrode and the second electrode; a first liquid disposed between the first electrode and the liquid crystal layer; A liquid crystal modulation element including an alignment film and a second alignment film disposed between the second electrode and the liquid crystal layer; and a sign of an electric field generated in the liquid crystal layer in a modulation operation state of the liquid crystal modulation element In a liquid crystal display device having control means for applying first and second potentials to the first and second electrodes, respectively, so that is periodically inverted,
A program for executing a control step of applying third and fourth potentials to the first and second electrodes, respectively, so that the sign of the electric field generated in the liquid crystal layer is constant in a state other than the modulation operation state. And
The control step includes, as the third and fourth potentials, a step of applying to the first and second electrodes a potential at which a difference between the third and fourth potentials changes in an in-plane direction of the liquid crystal layer. A program characterized by including.