Process and apparatus for producing liquid crystal panel

Abstract: A liquid crystal contained in a liquid crystal reservoir (3) is applied to an injection port of a blank liquid crystal panel (1) in a vacuum chamber, and the vacuum chamber is restored to the atmospheric pressure to inject the applied liquid crystal into the liquid crystal panel through the injection port (6). Herein, the liquid crystal, particularly a ferroelectric liquid crystal having a high viscosity, is effectively used for filling the liquid crystal panel with a minimum loss by using a transfer member moving between the liquid crystal reservoir and the liquid crystal panel.

Description: FIELD OF THE INVENTION AND RELATED ART The present invention relates to a process and an apparatus for producing a liquid crystal panel, particularly a process and an apparatus for producing a liquid crystal panel by injecting a ferroelectric liquid crystal into a liquid crystal cell. In a conventional process for filling a liquid crystal panel with a liquid crystal known heretofore as disclosed, e.g., by Japanese Patent Publication (JP-B) Sho. 60-49889, a liquid crystal panel and a liquid crystal reservoir are placed in a pressure-resistant container or chamber, the pressure in the container is reduced, the injection port of the liquid crystal panel is dipped in the liquid crystal reservoir, and then the pressure in the container is restored to the atmospheric pressure to fill the liquid crystal panel with the liquid crystal. However, in case where the above method of liquid crystal injection is used for filling with a ferroelectric liquid crystal material having a higher viscosity than a twisted nematic liquid crystal material, a large amount of the liquid crystal as large as ten times the amount filled in the liquid crystal panel is attached to a portion around the injection port of the liquid crystal panel. Accordingly, a large amount of the liquid crystal is lost and a larger load is required for a troublesome washing step so as to remove the excessive liquid crystal attached to around the injection port. One type of process and apparatus, in which a movable transfer member is employed for filling a liquid crystal panel, is disclosed by JP-A-58 198 023. Another process and apparatus, in which heating means are employed during the filling of a liquid crystal panel, is disclosed by US-A-4 922 972. SUMMARY OF THE INVENTION An object of the present invention is to provide a process and an apparatus which are optimum for producing a liquid crystal panel by injection of a ferroelectric liquid crystal panel through an improvement of such a conventional method of injecting a liquid crystal material into a liquid crystal panel to reduce the loss of liquid crystal material and the load of the washing as a post-step. A method of filling a liquid crystal panel according to the present invention is as claimed in claim 1. An apparatus for filling a liquid crystal panel according to the present invention is as claimed in claim 6. These and other objects, features and advantages of the present invention will become more apparent upon a consideration of the following description of the preferred embodiments of the present invention taken in conjunction with the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a schematic view for illustrating a first embodiment of the process and apparatus for producing a liquid crystal panel according to the present invention. Figure 2 is a schematic view for illustrating a second embodiment of the process and apparatus for producing a liquid crystal panel according to the present invention. Figures 3A - 3C are perspective views each illustrating the shape of a part for transferring a liquid crystal of a transfer member. Figures 4A and 4B are partial enlarged views each showing a part for applying a liquid crystal of a transfer member. DESCRIPTION OF THE PREFERRED EMBODIMENTS In a preferred embodiment of the present invention, a transfer member having a transfer part (end) with a length which is longer than the length of an injection port of a liquid crystal panel and shorter than the face of the liquid crystal panel having the injection port is used. Within a vacuum chamber, the transfer part of the transfer member is dipped in a liquid crystal reservoir, is pulled up from the liquid crystal reservoir to apply the liquid crystal within the liquid crystal reservoir onto the transfer member and is then brought in close proximity to or in contact with the injection port of the liquid crystal panel so as to transfer the liquid crystal to the injection port. As a result, the injection port of the liquid crystal panel can be completely covered by the liquid crystal with minimum attachment of the liquid crystal to an unnecessary part of the liquid crystal panel. Then, the vacuum chamber is restored to the atmospheric pressure to inject the liquid crystal into the liquid crystal panel. If the temperatures of the respective members are controlled, the above-mentioned transfer step can be further stabilized. The transfer member, the injection port of the liquid crystal panel and the liquid crystal reservoir are heated so as to provide a temperature T₁ for the liquid crystal in the liquid crystal reservoir, a temperature T₂ for the transfer member and a temperature T₃ for the injection port of the liquid crystal panel, satisfying the relationship of: T₁ ≧ T₃ > T₂. The above temperature relationship is desirable for the following reasons. A ferroelectric liquid crystal generally has a high viscosity, so that it is desirable to utilize a temperature difference between two members in transferring or applying the liquid crystal to control the movement of the liquid crystal. Firstly, a step of transferring a liquid crystal in a liquid crystal reservoir to a transfer member is explained. A liquid crystal material is generally a mixture comprising many mesomorphic compounds, so that it is necessary to prevent a change or localization in composition within the liquid crystal reservoir. For this reason, it is desirable to heat the liquid crystal reservoir to an elevated temperature to lower the viscosity of the liquid crystal in the reservoir. In case of transferring the liquid crystal to the transfer member, it is possible to transfer the liquid crystal in a necessary minimum amount if the relationship of T₁ ≧ T₂ is satisfied between the temperature T₁ of the liquid crystal reservoir and the temperature T₂ of the transfer member. If a condition of T₁ < T₂ stands reversely, an excessive amount of liquid crystal is transferred to the transfer member, so that it becomes necessary to effect a cleaning of the transfer member or the liquid crystal is liable to drop during the movement of the transfer member. Next, a step of applying the liquid crystal to the liquid crystal panel from the transfer member is explained. It is desired that as large a proportion as possible of the liquid crystal transferred to the transfer member is applied to the liquid crystal panel. This is because, if a large amount of the liquid crystal remains attached to the transfer member, a cleaning operation can be required for removing the liquid crystal prior to a subsequent transfer cycle. Further, unless the injection port of the liquid crystal panel is completely covered with the liquid crystal, the injection of the liquid crystal fails. For the above reason, it is desired that a relationship of T₃ > T₂ is satisfied between T₂ and the temperature T₃ of the injection port of the liquid crystal panel. Under a higher injection temperature, i.e., a higher T₃, it is possible to prevent the invasion of air bubbles at a higher degree because of a lower viscosity, so that a higher T₃ is generally preferred. Too high T₃ however leads to a problem of dropping of the liquid crystal from the liquid crystal panel. Therefore, it is desired that the upper limit of T₃ is set to T₁ to satisfy the relation of T₁ ≧ T₃. Consequently, it is desirable to set T₁, T₂ and T₃ so as to satisfy the relationship of T₁ ≧ T₃ > T₂. In the case where the present invention is applied to a ferroelectric liquid crystal material, it is desired to control the temperatures T₁, T₂ and T₃ corresponding to the phase transition temperatures of the ferroelectric liquid crystal. The ferroelectric liquid crystal can be selected from a large scope without particular restriction. For example, (1) if a ferroelectric liquid crystal has a phase transition series of Crystal SmC* SmA Ch. Iso. (SmC*: chiral smectic phase, SmA: smectic A phase, Ch.: cholesteric phase, Iso.: isotropic phase), or a series of Crystal SmC* Ch. Iso., it is preferred to effect a temperature control so as to satisfy a relationship of T₁ ≧ T₃ ≧ (cholesteric phase temperature) > T₂, and (2) if a ferroelectric liquid crystal has a phase transition series of Crystal SmC* SmA Iso. or Crystal Sm3 SmC* Iso. (Sm3: a smectic phase (un-identified)), it is preferred to effect a temperature control so as to satisfy a relationship of T₁ ≧ T₃ ≧ (isotropic phase temperature) > T₂. Consequently, it is preferred to effect a temperature control so as to satisfy a relationship of T₁ ≧ T₃ ≧ (a temperature providing a higher temperature phase than SmC*) > T₂. This is because a ferroelectric liquid crystal does not generally show a substantial fluidity and is not suitable for transfer and application in SmC* phase or in a lower temperature phase than SmC*. Such a temperature control can be effected by a heater, a thermistor and/or a temperature controller. The transfer member may preferably have an end face having a length L₂ for applying a liquid crystal to the injection port of the liquid crystal panel satisfying the relationship of L₃ ≦ L₂ ≦ L₁ with respect to the liquid crystal panel which has a face including the injection port and having a length L₁ and has the injection port having a length L₃. This is because, in case of L₁ < L₂, the liquid crystal attached to one or both sides is not applied to the liquid crystal panel but remains on the transfer member, thus resulting in difficulties such that it drips or requires a cleaning step and an unnecessary amount of liquid crystal is attached to a side face of the liquid crystal panel. On the other hand, in case of L₂ < L₃, the injection port of the liquid crystal panel is not sufficiently covered with the applied liquid crystal, thus allowing air bubbles to enter the liquid crystal panel. Figures 3A - 3C respectively show some shapes of a part 8 (Figure 3A) or parts 8 (Figure 3B and 3C) carrying and applying a liquid crystal of the transfer member 5 and particularly embodiments of the parts 8 (Figures 3B and 3C) for simultaneously transferring the liquid crystal to a plurality of liquid crystal panels held in a cassette. Figures 4A and 4B are partially enlarged illustrations of two type of concavities formed at the top of a part 8 for transferring a liquid crystal for illustrating the operation of the part 8 corresponding to one shown in Figure 3B. The end face of a liquid crystal panel having an injection port is formed by bonding a pair of glass or plastic substrates after alignment at their ends which have been optionally formed by cutting. Particularly, in the case where the end face is formed by cut ends, for example, an injection port is positioned inward from utmost ends of the substrates, and it is preferred that the part 8 carrying and applying the liquid crystal of the transfer member is concave as shown in Figures 4A and 4B. Such a concavity has a function of automatically aligning the end face of the liquid crystal panel at the time of applying the liquid crystal to the liquid crystal panel. The concavity also has a function of effectively retaining the liquid crystal to prevent the liquid crystal from dripping. The shapes of the transfer member and the end face thereof for transferring the liquid crystal are not restricted to those specifically shown in the drawings. The pressure within the vacuum chamber after evacuation and for the liquid crystal transfer operation may desirably be 1.0x10⁻³ torr or below, preferably 1.0x10⁻⁵ torr or below. As described above, according to the present invention, the injection of a liquid crystal into a liquid crystal panel is effectively carried out with minimum loss of the liquid crystal and alleviation of the load of washing of the liquid crystal as a post-treatment, and also the injection of a ferroelectric liquid crystal having a high viscosity can also be effected easily. Hereinbelow, the present invention will be explained with specific examples. Example 1 Figure 1 is a schematic view of an embodiment of the apparatus for producing a liquid crystal panel according to the present invention. Referring to Figure 1, the apparatus includes, within a vacuum chamber 2, a liquid crystal panel 1 having at least one injection port 6, a liquid crystal reservoir 3 containing a liquid crystal 4, and a transfer member 5 which is moved between the liquid crystal reservoir 3 and the liquid crystal panel 1 for carrying a portion of the liquid crystal 4 in the liquid crystal reservoir 3 and applying the carried portion of the liquid crystal to the injection port 6 of the liquid crystal panel. In this instance, the liquid crystal panel 1 is formed to have an end face having a length L₁ and including the injection port 6 having a length L₃, and the transfer member 5 is constituted to include an end face having a length L₂ for applying the liquid crystal to the injection port of the liquid crystal panel, satisfying the relationship of L₃ ≦ L₂ ≦ L₁. In a specific example, these lengths were set to L₁ = 275 mm, L₂ = 100 mm, and L₃ = 60 mm. The liquid crystal 4 was a ferroelectric liquid crystal ("CS-1014", available from Chisso K.K.) showing the following phase transition series: The temperature T₁ of the liquid crystal 4 in the liquid crystal reservoir 3, the temperature T₂ of the transfer member 5 and the temperature T₃ at the injection port of the liquid crystal panel 1 were set to T₁ = 90 °C, T₂ = 25 °C, and T₃ = 75 °C. The transfer member 5 was formed to have liquid crystal application parts 8 shown in Figure 3C and having a concavity as shown in Figure 4B. In preparation of a liquid crystal panel by using the above-mentioned apparatus, an exhaust system 7 conductively connected to a vacuum chamber 2 is first operated to evacuate the vacuum chamber 2 and the inside of the liquid crystal panel 1 contained therein. During the exhaustion step, the liquid crystal 4 in the liquid crystal reservoir 3 is heated by a heater 8 for the liquid crystal reservoir to a temperature (T₁ = 90 °C) for providing an isotropic phase, the end face having the injection port 6 of the liquid crystal panel 1 is heated by a heater 14 for the liquid crystal panel to a temperature (T₃ = 75 °C) providing the cholesteric phase of the liquid crystal, and the transfer member 5 is heated to a temperature (T₂ = 25 °C) by a heater 11 for the transfer member. After a sufficient degree of evacuation to a pressure (e.g., 3x10⁻⁵ torr) within the vacuum chamber 2, the transfer member 5 is partly dipped in and then pulled out of the liquid crystal reservoir 3 to carry a portion of the liquid crystal 4. Then, the transfer member 5 is turned up side-down so as to direct the dipped end upward and then further moved upward to contact the injection port 6 of the liquid crystal panel 1, so that the injection port 6 is completely covered by the carried and transferred portion of the liquid crystal 4. Then, the vacuum chamber 2 is restored to the atmospheric pressure to effectively inject the liquid crystal inside the liquid crystal panel 1. In this way, in a specific example, the attachment of the liquid crystal to an unnecessary part other than the injection port 6 was minimized. The heat generation from the heater 8 for the liquid crystal reservoir, the heater 11 for the transfer member and the heater 14 for the liquid crystal panel was controlled by annexed thermistors 9, 12 and 15, respectively, and a temperature controller 10. Example 2 Figure 2 is a schematic view of another embodiment of the apparatus for producing a liquid crystal panel according to the present invention. In Figure 2, like parts are denoted by like references numerals as used in Figure 1. More specifically, Figure 2 shows an embodiment of the apparatus wherein a transfer member 5a after dipping for carrying a portion of a liquid crystal 4 within the liquid crystal reservoir 3 is moved to the injection port 6 of the liquid crystal panel 1 for transfer of the liquid crystal without turning or rotation thereof. In this example, as the transfer member 5 is not turned or rotated after dipping, the relative positions or directions of the liquid crystal reservoir, and the liquid crystal panel are different from those in Example 1. However, other structures or members and operation thereof are similar to those in Example 1. In Figure 2, the heaters, thermistors and temperature controller are omitted from showing. In a specific example according to this example, the liquid crystal panel was also effectively filled with the liquid crystal. Comparative Example 1 Liquid crystal panels were prepared similarly as in Example 1 except that L₁, L₂ and L₃ were set to L₃ < L₁ < L₂. Because of the relation of L₁ < L₂, a portion of the liquid crystal carried on the transfer member and not transferred to a liquid crystal panel remained at both ends of the transfer member. As a result, after several times of the repetitive transfer operation, the liquid crystal was caused to drip, so that a cleaning of the transfer member and inner parts of the vacuum chamber was necessary. Further, as a part of the liquid crystal was attached to side faces of liquid crystal panels, it was also necessary to clean the liquid crystal panels. Comparative Example 2 Liquid crystal panels were prepared in the same manner as in Example 2 except that the temperatures were set to T₂ = 40 °C and T₃ = 30 °C (T₂ > T₃ unlike T₂ < T₃ in Example 2). As the temperature T₂ of the transfer member was higher than the temperature T₃ at the injection port of the liquid crystal panel, about a half of the liquid crystal carried by the transfer member remained thereon without being applied to the injection port of the liquid crystal panel. Because of a little shortage of the liquid crystal applied to the injection port, air bubbles were introduced into the liquid crystal panels at the time of restoration of the atmospheric pressure within the vacuum chamber, so that some liquid crystal panels were not practically acceptable. A liquid crystal contained in a liquid crystal reservoir is applied to an injection port of a blank liquid crystal panel in a vacuum chamber, and the vacuum chamber is restored to the atmospheric pressure to inject the applied liquid crystal into the liquid crystal panel through the injection port. Herein, the liquid crystal, particularly a ferroelectric liquid crystal having a high viscosity, is effectively used for filling the liquid crystal panel with a minimum loss by using a transfer member moving between the liquid crystal reservoir and the liquid crystal panel.

Claims: A method of filling a liquid crystal panel (1) comprising the steps of placing, within a vacuum environment, an unfilled liquid crystal panel (1) having an injection port (6), and a liquid crystal reservoir (3) containing a liquid crystal (4) material, causing a transfer member (5) moving between said crystal reservoir (3) and said liquid crystal panel (1) to carry a portion of said liquid crystal material (4) from said liquid crystal reservoir (3), applying said liquid crystal material (4) carried on said transfer member (5) to said injection port (6) of said crystal panel (1), placing said injection port (6) of said liquid panel (1) within an environment of a pressure higher than that of said vacuum environment to inject said liquid crystal material (4) into said liquid panel (1), and cooling said liquid crystal panel (1) to an operating temperature, characterized in that said liquid crystal material (4) is a chiral smectic liquid crystal material showing a successive phase transition series of isotropic phase, cholesteric phase, smectic A phase, chiral smectic phase and crystal phase upon temperature decrease, and the temperature, T₁, of said liquid crystal material (4) in said reservoir (3) is maintained at a temperature corresponding to the isotropic phase or cholesteric phase of said liquid crystal material, the temperature, T₂, of said transfer member (5) is maintained at a temperature corresponding to a smectic phase of said liquid crystal material, and the temperature, T₃, of said injection port (3) at the time of injection is maintained at a temperature corresponding to the cholesteric phase of said liquid crystal material, so as to satisfy a relationship of T₁ ≧ T₃ > T₂. A method according to claim 1, wherein the temperatures are controlled to satisfy a relationship of T₁ > T₃ > T₂. A method according to claims 1 or 2, wherein said transfer member (5) has a face (8) having a length, L₂, between the length, L₃, of said injection port (6) and the length, L₁, of a face of said crystal panel (1) so as to satisfy the relation L₁ ≧ L₂ ≧ L₃. A method according to any preceding claim, wherein said transfer member (5) comprises a concave portion for receiving said liquid crystal material (4). A method according to any preceding claim, wherein the pressure of said liquid crystal material injection which is higher than that of said vacuum environment is atmospheric pressure. An apparatus for filling a liquid crystal panel with a chiral smectic liquid crystal material showing a successive phase transition series of isotropic phase, cholesteric phase, smectic A phase, chiral smectic phase and crystal phase upon temperature decrease, comprising a vacuum chamber (2) for receiving a liquid crystal panel (1) having an injection port (6) for injecting a liquid crystal material (4) into said panel (1) , a liquid crystal reservoir (3) disposed in said vacuum chamber (2) and containing said liquid crystal material (4), a transfer member (5) provided in said vacuum chamber (2), said transfer member being movable between said liquid crystal reservoir (3) and said injection port (6) so as to transfer and apply a portion of said liquid crystal material (4) contained in said reservoir (3) to said injection port (6), and means (7) for establishing a reduced pressure in said vacuum chamber and, after the application of said liquid crystal material (4) to said injection port (6), for increasing the pressure within said vacuum chamber so as to inject said liquid crystal material into said panel (1) owing to a pressure difference, wherein said apparatus further comprises control means (10) for individually controlling the temperature, T₁, of said liquid crystal material (4) in said reservoir (3), the temperature, T₂, of said transfer member (5), and the temperature, T₃, of said injection port (3) so that T₁ is a temperature corresponding to the isotropic phase or cholesteric phase of said liquid crystal material, T₂ is a temperature corresponding to a smectic phase of said liquid crystal material, and T₃ at the time of injection is a temperature corresponding to the cholesteric phase of said liquid crystal material, satisfying a relationship of T₁ ≧ T₃ > T₂. An apparatus according to claim 6, wherein the temperatures are controlled to satisfy a relationship of T₁ > T₃ > T₂. An apparatus according to claim 6 or 7, wherein said transfer member (5) has a face (8) having a length, L₂, between the length, L₃, of said injection port (6) and the length, L₁, of a face of said crystal panel (1) so as to satisfy the relation L₁ ≧ L₂ ≧ L₃. An apparatus according to any of claims 6 to 8, wherein said transfer member (5) comprises a concave portion for receiving said liquid crystal material (4). An apparatus according to any of claims 6 to 9, wherein the pressure of said liquid crystal material injection which is higher than that of said vacuum environment is atmospheric pressure.

Inventors: YOSHIHARA SATOSHI C O CANON KA, YOSHIHARA, SATOSHI, C/O CANON KABUSHIKI KAISHA
Applicants: CANON KK, CANON KABUSHIKI KAISHA
Application year: 1991
Main classification: G02F1
IPC codes: G02F1