Patent Publication Number: US-2023140871-A1

Title: Liquid crystal devices

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of U.S. Pat. Application No. 16/760,586, filed Apr. 30, 2020, which is a U.S. National Phase of International Patent Application No. PCT/EP2018/079921, filed Nov. 1, 2018, which claims priority to Great Britain Patent Application No. 1718268.4, filed Nov. 3, 2017, both of which are incorporated herein by reference in their entireties. 
    
    
     BACKGROUND 
     Some techniques of producing liquid crystal display devices involve combining two liquid crystal (LC) cells in series to improve one or more aspects of the optical output. One conventional technique involves first preparing two LC cells each comprising a LC material contained between two support components and sandwiching a polariser component between the two LC cells. 
     The inventors for the present application have developed a new approach to combining LC cells. 
     There is hereby provided a method of producing a liquid crystal device, comprising: providing an assembly comprising a liquid crystal material contained directly between a polariser component and a first control component including a stack of layers defining electrical control circuitry; and containing further liquid crystal material directly between said polariser component of said assembly and another control component including another stack of layers defining electrical control circuitry. 
     According to one embodiment, containing said further liquid crystal material comprises bringing said assembly to said another control component together via a controlled volume of said further liquid crystal material. 
     According to one embodiment, containing said further liquid crystal material comprises bringing said assembly and said another control component together, and delivering said further liquid crystal material into a space between said assembly and said another control component. 
     According to one embodiment, said polariser component comprises no more than a single component laminated to each side of a polariser element. 
     According to one embodiment, said polariser component comprises two protection films laminated to opposite sides of a polariser element, and alignment layers coated over outer surfaces of said protection films. 
     There is also hereby provided a device comprising liquid crystal material contained directly between a first control component including a stack of layers defining electrical control circuitry and a polariser component, and further liquid crystal material contained directly between said polariser component and another control component including another stack of layers defining further electrical control circuitry. 
     According to one embodiment, said polariser component comprises no more than a single component laminated to each side of a polariser element. 
     According to one embodiment, said polariser component comprises two protection films laminated to opposite sides of a polariser element, and alignment layers coated over outer surfaces of said protection films. 
     There is also hereby provided a polariser component comprising a polariser element, and an alignment layer on at least one side of the polariser element; the alignment layer capable of controlling the director of a LC material interfacing the alignment layer in a LC cell. 
     According to one embodiment, the polariser component comprising alignment layer on both opposite sides of the polariser element. 
     According to one embodiment, the polariser component comprises at least one alignment layer provided over a protection film laminated to said polariser element. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       An embodiment of the present invention is described in detail hereunder, by way of example only, with reference to the accompanying drawings, in which: 
         FIGS.  1 A- 1 C  illustrate a production technique according to an embodiment of the present invention; 
         FIG.  2    illustrates an example of a relationship between the pixels of the two LC cells of a dual LC assembly according to an embodiment of the present invention; 
         FIGS.  3 A- 3 E  illustrate an example of a technique for bringing two flexible components together; and 
         FIG.  4    illustrates an example of a process by which an adhesive layer is released from a carrier. 
     
    
    
     DETAILED DESCRIPTION 
     In one example embodiment, the technique is used for the production of an organic liquid crystal display (OLCD) device, which comprises an organic transistor device (such as an organic thin film transistor (OTFT) device) for the control component. OTFTs comprise an organic semiconductor (such as e.g., an organic polymer or small-molecule semiconductor) for the semiconductor channels. 
     An embodiment of the present invention is described below for the example of using polariser elements comprising iodine crystalline needles in stretched plastic films, but the technique is equally applicable to the use of other kinds of polariser elements. 
     With reference to  FIGS.  1 (A) to  1 (C)  , LC material is contained directly between a first backplane component A and a polariser component B to create a first LC cell assembly D, and then the first LC cell assembly D is itself used as one half of a second LC cell with further LC material contained directly between the polariser component B of the first LC cell assembly D and a second backplane component C to create a second LC cell in optical series with the first LC assembly. 
     In this embodiment, the first backplane component A comprises a support substrate  1 , such as a glass substrate or a plastic support film (e.g., a tri-acetyl cellulose (TAC) film) supporting a stack of layers  2  defining electrical control circuitry for electrically controlling one or more optical properties of a LC material in the first LC cell of the LCD device. For example, the stack of layers  2  may comprise conductor, semiconductor and insulator layers defining an array of pixel electrodes  30  and an array of transistors for controlling the electric potential at each pixel electrode  30 . 
     In this embodiment, the first backplane component A additionally comprises a colour filter array  4  applied to the support substrate  1  and including sets of red, green and blue filters, each aligned with a respective pixel electrode  30  of the pixel electrode array of the first backplane component A. An upper surface of the first backplane component A (outer surface at the opposite side of the pixel electrode array to the support substrate  1 ) is constituted by an alignment coating  6  which controls the director (which represents the direction of preferred orientation of the liquid crystal molecules), of local liquid crystal material of the first LC cell (and thus, together with the alignment coating  16  on the other side of the LC material  24  of the first LC cell, the transmittance of the first LC cell), in the absence of an electric field applied via the electrical control circuitry. The alignment coating  6  may, for example, comprise a thin polymer coating (e.g., a thin polyimide coating) rubbed in a single direction with a cloth. 
     In this embodiment, the polariser component B comprises a polariser element  8  sandwiched between two plastic protection films  10 ,  12  (e.g., two TAC films). In this embodiment, the polariser element  8  constitutes a stretched polyvinylalcohol (PVA) film coated (before stretching) with iodine crystalline needles, the PVA polymer chains being aligned substantially unidirectionally, and the iodine needles being aligned substantially parallel to the PVA polymer chains. The above-mentioned protection films  10 ,  12  are then laminated to opposite surfaces of the polariser element  8  using adhesive. 
     Both opposing, outer surfaces of the polariser component B are constituted by alignment coatings  14 ,  16  of the kind described above for the first backplane component A. 
     Depending on the type of LCD device, the polariser component B may additionally comprise one or more conductor films to function as one or more common conductor planes. For some types of LCD devices, such as in-plane-switching (IPS) and fringe-field-switching devices (FFS) devices, the polariser component B does not comprise any common conductor plane; the electrical field for controlling the director of the LC material is generated between conductor elements within the backplane component A. 
     A first LC cell is created by containing a liquid crystal material  24  between the alignment coating  6  at the upper surface of the first backplane component A and an alignment coating  16  at an outer surface of the polariser component B. Spacer elements (not shown) are used to ensure a substantially uniform thickness of LC material across the whole array of pixel electrodes of the first backplane component A. The spacer elements may be separate to both the first backplane component A and polariser component B (e.g., spacer balls) or may form an integral part of one or more of the first backplane component A and polariser component B. 
     Containing (sandwiching) the LC material between the first backplane component A and polariser component B may, for example, be achieved by (a) bringing the two components A, B together via adhesive/sealant material in selected locations (either according to a linear process involving simultaneously compressing the whole of the two components together while both in a flat configuration, or according to a roller lamination process in which successive portions of the two components are brought together and compressed together in turn using one or more pressure rollers) and then delivering the LC material into one or more spaces (created by the spacer elements) between the two components A, B by e.g. a vacuum technique; or (b) applying LC material to one of the two components A, B either before during the process of bringing the two components A, B together (either by the linear or roller lamination process mentioned above) via adhesive/sealant material in selected locations, by which the applied LC material is forcibly spread substantially uniformly over at least the area of the pixel electrode array of the first backplane component A. 
     As discussed below, in addition to providing a first LC cell, the resulting LC cell assembly D also provides one half of a second LC cell in optical series with the first LC cell. 
     A second backplane component C also comprises a support substrate  18 , such as a glass substrate or plastic support film (e.g., a tri-acetyl cellulose (TAC) film) supporting a stack of layers  20  defining electrical control circuitry for electrically controlling one or more optical properties of a LC material  26  in the second LC cell of the dual cell display device. For example, the stack of layers may comprise one or more conductor, semiconductor and insulator layers defining an array of pixel electrodes  30  and an array of transistors for controlling the electric potential at each pixel electrode  30  substantially independently of the electric potential at any other pixel electrode. 
     Unlike the first backplane component A, the second backplane component C does not comprise a colour filter array in this embodiment. An upper surface of the second backplane component C (outer surface at opposite side of the pixel electrode array to the support substrate) is constituted by an alignment coating  22  of the kind already described above for the first backplane component A and the polariser component B. 
     The second LC cell is created by containing a liquid crystal material  26  between the alignment coating  22  at the upper surface of the second backplane component C and an alignment coating at the outer surface of the first LC cell assembly D (remaining outer surface of the polariser component B in situ in the first LC cell assembly D). Spacer elements (of the kind described above for the first LC cell assembly) are used to ensure a substantially uniform thickness of LC material  26  across the whole array of pixel electrodes  32  of the second backplane component C. As with the first LC cell assembly D, containing the LC material  26   between the second backplane component C and the polariser component B (in situ in the first LC cell assembly D) may, for example, be achieved by (a) bringing the first LC cell assembly D and second backplane component C together via adhesive/sealant material in selected locations (either according to a linear process involving simultaneously compressing the whole of the two components together while both in a flat configuration, or according to a roller lamination process in which successive portions of the two components are brought together and compressed together in turn using one or more pressure rollers), and then delivering the LC material into one or more spaces (created by the spacer elements) between the first LC cell assembly D and the second backplane component C by, e.g., a vacuum technique; or (b) applying LC material to one or both of the first LC cell assembly D and the second backplane component C either before or during the process of bringing the two components together (either according to the linear or roller lamination processes mentioned above) via adhesive/sealant material in selected locations. 
     When creating the second LC cell, a conventional alignment technique is used to align the pixel electrode array of the first backplane component A (in the first LC cell assembly D) to the pixel electrode array of the second backplane component C. In one example illustrated in  FIG.  2   , the second backplane component C (without the colour filter array) is designed to have less and larger pixels than the first backplane component (including the colour filter array), with each pixel  32  of the second backplane component C occupying the combined area of a respective set of red, blue and green pixels  30  of the first backplane component A, and overlapping (extending laterally beyond) the respective set of red, blue and green pixels  30  of the first backplane component A by a substantially equal amount in both the orthogonal x and y directions.  FIG.  2    only shows a small number of pixels, but an LCD device will typically comprise a large number of pixels. 
     After creating the second LC cell, further polariser components (not shown) are applied to the outer surfaces of the dual cell assembly E. Each of the further polariser components may comprise a polariser element of the kind described above for the middle polariser component B laminated on both sides to protection films of the kind described above for the middle polariser component B. According to one variation, the outer polariser components could form a part of the two backplane components prior to assembling the two LC cells, and polariser components may be used as the support substrates  1 ,  18  of the two backplanes. 
     Further components may be applied to one or both outer surfaces of the dual cell assembly E, such as, e.g., a pair of transparent encapsulation films to protect the dual cell assembly E against air species such as oxygen and moisture, and a backlight component. 
     In this embodiment, the second backplane component is used as a brightness modulator to modulate the amount of light that can be emitted from the display screen independently for each set of three RGB sub-pixels, and thereby achieve optical display outputs with higher contrast ratios. 
     The technique described above facilitates the production of dual LC cell displays that (i) are less affected by the shadow image phenomenon known as parallax; (ii) exhibit less image defects and uniformity problems known as mura; (iii) allow a wide range of viewing angles. 
     The above-described technique may involve bringing together flexible components (e.g., (i) the kind of backplane component described above comprising a plastic support film as the support substrate or a first cell assembly including such a backplane component, and (ii) the kind of polariser component described above) that are susceptible to distortion upon heating and cooling; and the technique may involve temporarily adhering said components to relatively rigid carriers (e.g., glass plates) for the assembly process, and later releasing the assembly from the carriers. 
     One example of a linear process for compressing together flexible components via spacer structures using rigid carriers is described in UK Patent Application No. 1608279.4 and International Patent Application No. PCT/EP2017/061319, from which content is reproduced below. 
     With reference to  FIGS.  3 A- 3 E , a first flexible component  48  is releasably secured to a rigid carrier  44  via an adhesive element  46 , whose strength of adhesion to both the rigid carrier  44  and the flexible component is sufficiently high during processing of the assembly to resist excessive thermal expansion of the flexible component  48 , but which either is (i) not too high to prevent peeling of the adhesive element  46  away from at least the assembly after processing or (ii) can be reduced after processing of the assembly to facilitate release of the adhesive element  46  from at least the assembly. For example, this adhesive element  46  may be a single layer of pressure-sensitive adhesive, or a single layer of adhesive whose adhesion strength to one or more of the first flexible component  48  and rigid carrier  44  can be reduced by increasing temperature (heat release), by reducing temperature (cold release) or by exposure to UV radiation (UV release). The adhesive element  46  may also comprise two layers of adhesive on opposite sides of a support film, which two layers may, for example, comprise any combination of a pressure-sensitive adhesive, a heat release adhesive, cold release adhesive and UV release adhesive. 
     A second flexible component  412  is releasably secured to another rigid carrier  416  via a dual-sided adhesive unit  14  comprising a support film  414   b  supporting a layer of heat-release adhesive  414   c  adjacent to the carrier  416  and a second layer of adhesive  414   a  adjacent to the flexible component  412 . In this example, the second layer of adhesive  414   a  is one whose strength of adhesion to the second flexible component  412  is sufficiently high during processing of the assembly to resist excessive thermal expansion of the assembly, but which either (i) is not too high to prevent peeling of the adhesive element away from the assembly after processing, or (ii) can be reduced after processing of the assembly to facilitate release of the adhesive element  414   a  from the assembly. The second layer of adhesive  414   a  may, for example, comprise (a) a pressure-sensitive adhesive, (b) a layer of heat-release adhesive having a higher release temperature than the first layer of adhesive  414   c , (c) a layer of cold-release adhesive, or (d) a layer of UV-release adhesive. 
     In this example, at least one of the flexible components  48 ,  412  is provided with a heat-curable adhesive for securing the two flexible components together. The two flexible components  48 ,  412  are then aligned to one another (e.g., means of alignment marks included as part of the second flexible component and observable from above via the optically transparent carrier (e.g., glass)  44 , optically transparent adhesive element  46 , and optically transparent first flexible component  48 ) and mechanically compressed together ( FIG.  3 B ) between the carriers  44 ,  416  via spacer structures  410 . While under mechanical compression, the assembly (and carriers  44 ,  416 ) is uniformly heated in an oven (so as to establish a zero temperature gradient across the assembly) under conditions at which the adhesive between the two flexible components  48 ,  412  of the assembly becomes completely cured. Whether or not the adhesive between the two flexible components is completely cured can, for example, be determined by subjecting the assembly to a peel strength test and comparing the measured peel strength against a known or pre-determined maximum peel strength for the specific adhesive being used. Also, where the uncured form of the adhesive has a damaging effect on, e.g., liquid crystal material to be contained within the assembly between the two flexible components, the existence of uncured adhesive (i.e., a failure to completely cure the adhesive) manifests itself as a degradation in the performance of the liquid crystal display device. 
     This heating may involve raising the temperature of the oven in a series of steps and maintaining the oven at each step temperature for a respective period of time. The heating required to cure the adhesive involves raising the temperature of the assembly to a temperature where crinkling of the plastic support films within the assembly tends to occur, but as discussed below, the pressure at which the assembly is mechanically compressed between the carriers is sufficiently high to substantially prevent any significant crinkling. 
     After sufficient heating has been performed to completely cure the adhesive between the two flexible components  48 ,  412 , the temperature of the oven is reduced and the assembly and carriers inside the oven are allowed to cool, while continuing to mechanically compress the assembly between the two carriers to prevent crinkling of the plastic films during the cooling process. In this example, the adhesives used for the adhesive element  46  (between the first flexible component and the rigid carrier  4 ) and the adhesive used for adhesive layer  414   a  all retain their strength of adhesion to the assembly/carrier during the heating process to completely cure the adhesive between the two flexible components  48 ,  412 . On the other hand, the heat-release adhesive for adhesive layer  414   c  is a material at which gas is generated during the process of heating the assembly to cure the adhesive between the two flexible components  48 ,  412 . As described below with reference to  FIG.  4   , the generated gas forms pockets of gas  420  at the interface of the adhesive layer  414   c  with the rigid carrier  416 , and the formation of these gas pockets  420  serves to partially reduce the strength of adhesion between the adhesive layer  414   c  and the carrier  416 . The pressure at which the assembly is compressed between the two carriers  44 ,  416  is both (i) sufficiently low to retain the gas generated in the adhesive layer  414   c  as pockets of gas  420  at the interface between the adhesive layer  414   c  and the carrier  416  (i.e., to prevent gas generated within the adhesive layer  414   c  from being expelled laterally out from between the adhesive layer  414   c  and the carrier  416 , but (ii) sufficiently high to prevent crinkling (distortion out of the plane) of the plastic support films within the assembly during the process of heating the assembly to cure the adhesive between the two flexible components. 
     The generation of gas within the adhesive layer  414   c  and the retention of generated gas at the interface of the adhesive layer  414   c  with the carrier  416  can be detected by: performing the heating in a vacuum and monitoring changes in pressure within the vacuum chamber, and/or remotely analysing, by, e.g., spectroscopy, the interface between the adhesive layer  414   c  and the carrier  416 . 
     After cooling the assembly to a temperature at which the plastic support films within the assembly no longer tend to crinkle (during which cooling, the gas pockets  420  continue to be retained at the interface of the adhesive layer  414   c  with the rigid carrier  416 ), mechanical compression of the assembly between the carriers is ended, and the combination of assembly and carriers  44 ,  416  is placed on a hotplate with the carrier  416  adjacent to adhesive layer  414   c  closest to the surface of the hotplate, such that a temperature gradient is established across the combination of adhesive element  414  and assembly. Without mechanically compressing the assembly between the carriers  44 ,  416 , the hotplate is used to raise the temperature of the adhesive layer  414   c  to a temperature at which, in the absence of mechanical compression, the adhesive layer  414   c  thermally expands to an extent sufficient to further reduce the strength of adhesion between the adhesive layer  414   c  and the rigid carrier  416 . This further heating of the adhesive layer  414   c  is done without increasing the temperature of the assembly to a temperature at which significant crinkling of the plastic support films within the assembly tends to occur. In one example, the temperature to which the adhesive layer  414   c  is raised may be above the maximum temperature that it reached during the heating process for curing the adhesive between the two flexible components  48 ,  412 . However, release of the carrier  416  during this second heating stage can also be achieved at lower temperatures. The thermal expansion of the adhesive layer  414  during this second heating stage reduces the strength of adhesion between the adhesive material and the carrier  416  in the areas of contact around the gas pockets  420  at the interface between the carrier  416  and the adhesive layer  414   c ; and this further reduction in the strength of adhesion between the carrier and the adhesive layer  414   c  allows the carrier to be released from the assembly without the application of mechanical force or with the application of only minimal mechanical force ( FIG.  3 C ). 
     The release of one rigid carrier  416  facilitates the peeling of the whole adhesive unit  414  from the assembly ( FIG.  3 D ) and the subsequent peeling of the assembly away from adhesive unit  6  ( FIG.  3 D ). 
     By way of example: an adhesive product acquired from Nitto Denko Corporation and identified by product name RAU-5HD1.SS was used for one of the adhesive units  414  in the technique described above; and an adhesive product acquired from Nitta Corporation and identified by product name CX2325CA3 was used for the other adhesive unit  46  in the technique described above. The adhesive product identified by product name RAU-5HD1.SS comprises a heat-release adhesive and a UV-release adhesive on opposite sides of a flexible support film, and the adhesive product identified by product name CX2325CA3 comprises a cold-release adhesive and a pressure sensitive adhesive supported on opposite sides of a flexible support film. 
     In the above-described example, the adhesive layer  414   c  adjacent to the carrier is the layer whose strength of adhesion to an adjacent element is partially reduced under mechanical compression during the heating process to cure the adhesive between the two carriers, and further reduced (without mechanical compression) after completion of the heating process to cure the adhesive between the two carriers. However, in an alternative example, this layer may be the adhesive layer  414   a  adjacent to the assembly in the adhesive unit  414  (whereby the adhesive unit  414  is first released from the assembly), or this layer may be a single layer of adhesive in contact with both the assembly and the carrier. 
     In the example described above, a heat-curable adhesive is used to secure the two flexible components together, but (a) an adhesive curable by exposure to, e.g., UV radiation (UV-curable adhesive), (b) pressure-sensitive adhesive, or (c) an adhesive curable by laser, are other examples of adhesives that may be used to secure the two flexible components together. Even when the application of heat is not required to secure the two flexible components together, heating the assembly to a temperature at which crinkling of the plastic support films within the assembly tends to occur may be used for other purposes; and the above-described technique is equally useful in such situations. 
     In addition to any modifications explicitly mentioned above, it will be evident to a person skilled in the art that various other modifications of the described embodiment may be made within the scope of the invention. 
     The applicant hereby discloses in isolation each individual feature described herein and any combination of two or more such features, to the extent that such features or combinations are capable of being carried out based on the present specification as a whole in the light of the common general knowledge of a person skilled in the art, irrespective of whether such features or combinations of features solve any problems disclosed herein, and without limitation to the scope of the claims. The applicant indicates that aspects of the present invention may consist of any such individual feature or combination of features.