JP6895296B2 - Manufacturing method of liquid crystal display element - Google Patents

Description

The present invention relates to a method for manufacturing a liquid crystal display element.

Ferroelectric liquid crystals are generally used because they have a strong interaction with the electric field applied between the substrates due to the strength of spontaneous polarization of the ferroelectric liquid crystal molecules (hereinafter, simply referred to as liquid crystal molecules). It has an extremely faster response than the nematic liquid crystal display, and exhibits high ability in moving image flicker and image processing speed, which is a problem in today's liquid crystal display elements using the nematic liquid crystal display.

Further, by controlling the substrate spacing (cell gap) to 1 μm or less, the spiral structure characteristic of the ferroelectric liquid crystal disappears, and the liquid crystal molecules are left and right in the substantially vertical direction of the ferroelectric liquid crystal layer, respectively. It stabilizes at a certain angle. By switching between the two directions, the polarization state of the incident light is changed, and whether or not the light is transmitted to the polarizer is determined. In the above-mentioned state, the liquid crystal molecule can control the optical polarization by a very simple driving principle that only turns the driving voltage on and off.

By the way, in an SSFLCD (surface-stabilized ferroelectric liquid crystal display element) having a small cell gap (cell Gap), the control of the cell Gap is an important factor for determining the characteristics, and a predetermined cell Gap is maintained. That is, it is indispensable to realize a high-quality display element to realize the uniformity of the cell Gap in the display element.

One of the characteristics determined by the cell Gap is the amount of birefringence of light due to retardation, that is, the degree of polarization of the incident light emitted through the display element. The degree of polarization of light is one of the factors that determine the brightness and throughput of a display element. Therefore, the non-uniformity of the cell Gap in the display element causes the degree of polarization of the light passing through the display element to become non-uniform, resulting in uneven brightness and uneven throughput of the display element, which significantly deteriorates the display quality. ..

As one of the factors that determine the cell Gap, the liquid crystal injection method and conditions for filling the substrate with the liquid crystal material are important. In general nematic liquid crystal, the inside of the vacuum furnace (chamber) is in a vacuum state, the inside of the cell is in a vacuum state, the liquid crystal is dropped into the injection port, or the injection port is immersed in the liquid crystal, and the liquid crystal is filled in the cell by capillarity. To do. However, in the case of a ferroelectric liquid crystal, since the viscosity of the material is high, it is necessary to heat the liquid crystal so as to make a phase transition to the N phase or the I phase. By heating in a vacuum furnace, it becomes possible to fill the inside of the liquid crystal cell by utilizing the capillary phenomenon.

By the way, a liquid crystal display element having a general SSFLC structure expresses an SmC phase at room temperature, and undergoes a phase transition from SmC⇒SmA⇒N⇒I phase by heating. The phase transition temperature of each phase varies depending on the material, but the SmC phase is about 60 ° C. to 90 ° C., and the transition to the I phase occurs at about 100 to 120 ° C. Generally, a ferroelectric liquid crystal exhibits a high viscosity from the SmC to the N phase and a low viscosity from the N phase to the I phase. Also, even within the same phase, the higher the temperature, the lower the viscosity.

From the above, in order to inject the ferroelectric liquid crystal into the cell, it is necessary to carry out the above heating, but during heating, thermal expansion of the substrate or peripheral members occurs, and cooling causes the phase to become the SmC phase. The liquid crystal injection step may be completed in a non-uniform state of the cell gap due to volume shrinkage of the liquid crystal, the substrate, and peripheral members during the transition.

In order to adjust the cell Gap, a method of creating a pressure difference around the substrate at the time of liquid crystal injection, adjusting the liquid crystal filling amount by the stress due to the pressure difference, or deforming the cell Gap itself to create a uniform cell Gap is described in Patent Document 1. Proposed by 2.

JP 2002-90762 Japanese Patent Application Laid-Open No. 2003-121862

In the method for producing a uniform cell Gap proposed from Patent Documents 1 and 2, when the liquid crystal material used is a highly viscous liquid crystal material such as a ferroelectric liquid crystal, the pressure difference around the substrate It is difficult to obtain a uniform cell Gap because it is difficult for the Gap to be deformed due to the above.

An object of the present invention is to provide a method for manufacturing a liquid crystal display element capable of obtaining a uniform cell gap.

The manufacturing method of the liquid crystal display device having a liquid crystal into the gap between the bonded a pair of substrates with each other, and heating the steps of injecting the liquid crystal into the gap, the liquid crystal injected into the gap in the first temperature A step of deforming the gap by applying a suction force by vacuum adsorption to the outer surface of at least one of the pair of substrates while the liquid crystal injected into the gap is heated to the first temperature. The liquid crystal is shrunk by cooling the liquid crystal injected into the gap from the first temperature to the second temperature while the attractive force is applied to the outer surface of at least one of the substrates. It is a method of manufacturing a liquid crystal display element having a step of making the gap uniform by force.

In the step of deforming the gap, the suction force may be a method of manufacturing a liquid crystal display element in which the suction force is applied to only one of the pair of substrates.

The suction force may be the same as the method for manufacturing a liquid crystal display element during heating and cooling.

According to the present invention, since the cell Gap can be made uniform, it is possible to prevent problems such as uneven brightness in the display area. Since the present invention can be applied even after the liquid crystal injection is completed, for example, when a liquid crystal cell having a non-uniform cell gap is manufactured due to a defect in the liquid crystal injection process, the defect can be corrected and the yield can be reduced. It can be expected to improve.

Cross-sectional view of the embodiment of the present invention (Example 1) Cross-sectional view of the embodiment of the present invention (Example 1) Cross-sectional view of the embodiment of the present invention (Example 2) Cross-sectional view of the embodiment of the present invention (Example 2) Cross-sectional view of the embodiment of the present invention (Example 2)

In the present invention, for example, in a liquid crystal cell using a highly viscous ferroelectric liquid crystal, when the cell Gap is deformed due to a pressure difference around the substrate, the liquid crystal injected into the liquid crystal cell is heated to reduce the viscosity. It is characterized by letting it. Since the cell Gap is difficult to deform when the liquid crystal has a high viscosity, it is necessary to heat the liquid crystal to reduce the viscosity in order to efficiently deform the cell Gap. Specifically, when the liquid crystal is a ferroelectric liquid crystal, the desired effect can be obtained by heating the liquid crystal to a temperature at which the N phase or the I phase appears.

Further, the present invention is characterized in that the liquid crystal injected into the liquid crystal cell is cooled to increase the viscosity while the cell Gap is deformed by the above-mentioned pressure difference. Even if the desired cell Gap is obtained by the pressure difference while the liquid crystal is heated, when the pressure difference is released in that state, the cell Gap is non-uniform due to the influence of atmospheric pressure or the like due to the low viscosity of the liquid crystal. It is assumed that the state will return to the state, and that the cell Gap will change due to the volume contraction of the liquid crystal when the temperature of the liquid crystal drops. Therefore, the cell Gap obtained by the pressure difference is maintained and finally. In order to make the cell Gap uniform, it is necessary to cool the liquid crystal while maintaining the pressure difference. Specifically, when the liquid crystal is a ferroelectric liquid crystal, a desired effect can be obtained by cooling the liquid crystal to a temperature at which it becomes the SmC phase while maintaining the pressure difference and then releasing the pressure difference.

The adjustment of the cell Gap by this method can be performed in the liquid crystal cell at the time of liquid crystal injection or the liquid crystal cell in which the liquid crystal injection is completed. Specific examples are as follows.

Hereinafter, a first embodiment (Example 1) for carrying out the present invention will be described. FIG. 1 is a cross-sectional view of a embodiment of the present invention and shows a part of a manufacturing process. In the step shown in FIG. 1, first, a gap (for example, a gap (for example, silicon and glass, respectively) formed by bonding the pair of substrates 101 and 103 (for example, silicon and glass, respectively) to each other via a substantially frame-shaped sealing material (which may include a spacer) is formed. The liquid crystal 102 made of a ferroelectric liquid crystal is injected into the cell Gap) through an injection port provided in a part of the sealing material, and the liquid crystal cell before the injection port is sealed with the sealing material, which is a liquid crystal cell of the substrate 103. A liquid crystal cell in which the cell Gap is in a non-uniform state due to distortion or the like is installed on the suction plate 105. Specifically, of the pair of substrates 101 and 102, the substrate 101 is installed so as to be in close contact with or close to the suction hole 107 provided with the vacuum line 106 on one side. The position and shape of the suction hole 107 are appropriately determined depending on the state of the cell Gap, but since the non-uniformity of the cell Gap usually tends to occur concentrically around the center of the cell, it faces the center of the cell. It is conceivable to arrange a concentric conical suction hole 107 at the position.

Next, a hot plate (not shown) installed under the adsorption plate 105 heats the liquid crystal cell together with the adsorption plate 105 to reduce the viscosity of the liquid crystal 102. The heating temperature is, for example, the temperature at which the liquid crystal 102 undergoes a phase transition to the N phase or the I phase. As a heating method, the adsorption plate 105 and the liquid crystal cell may be arranged in a chamber capable of heat treatment, and the heat treatment may be performed by a furnace.

FIG. 2 is a cross-sectional view of the embodiment of the present invention and shows a part of the manufacturing process. The step shown in FIG. 2 is a step following the step shown in FIG. 1, and in this step, stress due to a pressure difference is applied to the outer surface of the liquid crystal cell sufficiently heated in the previous step to deform the cell Gap. Specifically, the outer surface of the liquid crystal cell is evacuated from the vacuum line 106 installed through the suction plate 105 in the direction of the arrow in the drawing through the suction hole 107, and the substrate 101 is sucked onto the suction plate 105. The pressure due to evacuation causes the substrate 101 to warp so as to be convex downward, resulting in a change in the cell Gap. This Gap change does not occur in the SmC phase with high viscosity of the liquid crystal 102, but occurs in a state of phase transition to the N phase or I phase with low viscosity. As a result, the cell Gap is in a uniform state or a state close to it.

Since this Gap change occurs only during heating of the liquid crystal cell (N phase or I phase) and while vacuuming from the suction hole 107, a vacuum from the suction hole 107 is maintained in order to maintain the change in the cell Gap. Cool the liquid crystal cell while maintaining the pull. It is desirable that the degree of evacuation at the time of slow cooling is the same as the degree of evacuation immediately before that, but the degree of evacuation may be different from that. The slow cooling of the liquid crystal cell is performed, for example, by stopping the heating by the heater and naturally cooling the liquid crystal, and by releasing the evacuation when the liquid crystal 102 becomes the highly viscous SmC phase, the liquid crystal of the highly viscous SmC phase. 102 does not flow out of the cell, stays in the cell, and the state in which the cell Gap is changed is maintained even after the evacuation is released. The volume of the liquid crystal 102 shrinks as the temperature decreases, and the stress is also applied to the liquid crystal cell, so that the cell Gap is finally brought into a uniform state. The cell Gap may be in a uniform state at least in a portion corresponding to the display area of the image, and may not be in a completely uniform state but in a state as uniform as normally required for a product. .. After the cell Gap is in a uniform state, the injection port of the liquid crystal 102 provided in a part of the sealing material 104 is sealed with a sealing material. The inlet may be sealed before or after the suction hole 107 is evacuated.

The temperature at which the ferroelectric liquid crystal reaches the N phase or the I phase depends on the material, but is generally around 100 ° C. to 120 ° C. The SmC phase is also about 60 ° C. to 90 ° C., although it depends on the material. Therefore, regarding the heat treatment of the step shown in FIG. 1, heat treatment is performed at about 100 ° C. to 120 ° C. in order to reach the N phase or the I phase, and after the start of evacuation of the step shown in FIG. It is desirable to perform cooling while maintaining evacuation to a temperature of about ° C. or lower (for example, room temperature).

The vacuum pressure of the vacuum line 106 and the hole diameter of the suction hole 107 are appropriately determined according to the cell outer shape and the degree of Gap non-uniformity, but the hole diameter of the suction hole 107 (the hole diameter of the portion in contact with the liquid crystal cell). Is preferably about 1/3 to 1/2 of the outer diameter of the cell, and the vacuum pressure of the vacuum line 106 is preferably about 30 KPa to 50 Kpa.

As described above, in this embodiment, it is possible to create an optimum cell Gap at a stage after the liquid crystal injection into the cell Gap is once completed.

Hereinafter, a second embodiment of the present invention (Example 2) will be described. FIG. 3 is a cross-sectional view of the embodiment of the present invention and shows a part of the manufacturing process. In the step shown in FIG. 3, first, a suction plate 105 provided with a suction hole 107 is installed in the vacuum furnace, and a liquid crystal cell before liquid crystal injection is placed on the suction plate 105. In this state, the center of the substrate 101 of the liquid crystal cell faces the suction hole 107 of the suction plate 105 and is in close contact with or close to the suction hole 107. The suction hole 107 is a concentric conical through hole, and is connected to a vacuum line on the tip side having a small diameter thereof.

Subsequently, the inside of the vacuum furnace is evacuated to make the inside of the liquid crystal cell into a vacuum state, and at the same time, the liquid crystal cell is sucked from the suction hole 107 with a higher vacuum, and the substrate 101 of the liquid crystal cell is projected toward the suction hole 107. The cell Gap is temporarily inflated by deforming it so as to be in a state.

FIG. 4 is a cross-sectional view of the embodiment of the present invention and shows a part of the manufacturing process. The step shown in FIG. 4 is a step following the step shown in FIG. 3, and in this step, the liquid crystal cell in the state where the cell Gap is inflated in the previous step is heated, and the liquid crystal 102 made of the ferroelectric liquid crystal is N. The cell Gap is filled through an injection port provided in a part of the sealing material 104 while heating to a temperature at which it becomes a phase or an I phase. As a result, a liquid crystal cell having a convex state on one side at the center is created in a state where the cell Gap is filled with the liquid crystal 102.

FIG. 5 is a cross-sectional view of the embodiment of the present invention and shows a part of the manufacturing process. The step shown in FIG. 5 is a step following the step shown in FIG. 4, and in this step, the liquid crystal cell in which the cell Gap is filled with the liquid crystal 102 in the previous step is placed on the suction plate 105 from the suction hole 107. The liquid crystal 102 is cooled to room temperature while being adsorbed. The degree of vacuum of the suction hole 107 when cooling the liquid crystal cell is preferably the same as the degree of vacuum immediately before that, but may be different. When the liquid crystal cell is cooled, the substrate 101 of the liquid crystal cell deforms to the opposite side against the suction force of the suction hole 107 as the volume of the liquid crystal 102 shrinks, and the cell Gap shrinks. As a result, the cell Gap becomes uniform at room temperature. It becomes a state. After the cell Gap is in a uniform state, the suction hole 107 is released from evacuation, and the injection port of the liquid crystal 102 is sealed with a sealing material. The inlet may be sealed before or after the suction hole 107 is evacuated.

In FIG. 5, after the liquid crystal cell is cooled, the liquid crystal cell is in a flat state as a whole, but when the suction force of the suction hole 107 is large or the like, the liquid crystal cell is cooled as shown in FIG. After that, the liquid crystal cell may become convex toward the suction hole 107 as a whole.

As described above, in this embodiment, it is possible to create an optimum cell Gap at the stage of injecting the liquid crystal into the cell Gap.

In Examples 1 and 2, the pressure inside the suction hole 107 is depressurized to warp the substrate 101 of the liquid crystal cell so as to be convex outward, but by pressurizing the inside of the suction hole 107, the liquid crystal cell substrate 101 is warped. Can also be bent inward on the opposite side. In that case, in order to prevent the entire liquid crystal cell from rising from the suction plate 105, for example, it is desirable to suck the outer peripheral portion of the liquid crystal cell to the suction plate 105 or press it from above.

In Examples 1 and 2, the suction plate 105 is installed only on the substrate 101 side of the liquid crystal cell, but it is also possible to install the adsorption plate 105 on the substrate 103 side and warp the substrate 103.

The present invention is suitable for a liquid crystal display element using a liquid crystal having a low viscosity at a high temperature and a high viscosity at a low temperature, such as a ferroelectric liquid crystal, but is not limited to this, and is also applicable to other liquid crystal display elements using a liquid crystal. It is possible to do.

101 Substrate 102 Liquid crystal 103 Substrate 104 Sealing material 105 Suction plate 106 Vacuum line 107 Suction hole

Claims (3)

In a method for manufacturing a liquid crystal display element having a liquid crystal in a gap between a pair of substrates bonded to each other.
A step of injecting the liquid crystal into the gap,
The step of heating the liquid crystal injected into the gap to the first temperature and
A step of applying a suction force due to a pressure difference to the outer surface of at least one of the pair of substrates while the liquid crystal injected into the gap is heated to the first temperature to deform the gap.
The liquid crystal injected into the gap while the suction force is applied to the outer surface of at least one of the substrates is cooled from the first temperature to the second temperature to contract the liquid crystal and the contraction force. a step of equalizing the gap in,
A method for manufacturing a liquid crystal display element. The liquid crystal display element according to claim 1, wherein in the step of deforming the gap and the step of equalizing the gap , the suction force is applied to only one of the pair of substrates. Production method. The method for manufacturing a liquid crystal display element according to claim 1 or 2, wherein the suction force is the same at the time of heating and at the time of cooling.

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