METHOD FOR FILLING LIQUID CRYSTAL CELLS

Abstract: A method for filling liquid crystal cells includes the steps of advancing complementary preform strips along respective paths that converge to bring the strips into a engaged relationship, filling the nip formed between the two converging preform strips with a liquid crystal material in an amount sufficient to form and maintain an over-supply of liquid crystal material therebetween, and sealing the strips together to form liquid crystal filled cells.

Description: METHOD FOR FILLING LIQUID CRYSTAL CELLS BACKGROUND OF THE INVENTION The present invention relates to the manufacture of liquid crystal cells and more particularly to a contin- uous filling method for liquid crystal cells. Liquid crystal displays have found wide-spread application in consumer and industrial products. The typical liquid crystal display includes a liquid crystal filled cell defined between two plane-parallel plates, usually glass, that are uniformly spaced from one an¬ other by a peripheral spacer/seal. The confronting surfaces of the plates are provided with transparent electrodes formed, for example, in a multi-segment nu¬ meric or alphanumeric pattern. The application of a voltage potential across selected electrodes or elec¬ trode segments locally alters the optical characteris¬ tics of the liquid crystal material to" provide the desi¬ red visual effect. The classic fabrication technique involves pre- paring transparent glass plates with electrodes, and, depending on the type of display being manufactured, alignment layers, polarizers, and a reflector or trans- reflector. The prepared plates are joined together using a spacer/seal that defines the perimeter of the liquid crystal cell and controls the thickness of the liquid crystal layer. One or more fill holes are pro- vided through which the liquid crystal material is in¬ troduced to effect filling with the fill hole or holes plugged to complete the filling procedure. This fabri¬ cation technique can be relatively time consuming and is generally recognized as unsuited for high-speed contin¬ uous fabrication techniques. With the continued wide-spread application of liq¬ uid crystal displays to existing and newly created pro¬ ducts, a need exists for more time and cost effective manufacturing procedures, particularly with regard to cell filling. In one approach, as disclosed in U.S. Patent No. 4,228,574 to Culley et al., two elongated plastic preform strips are each prepared with electrodes and alignment layers. Adhesive seals are deposited onto one of the two strips to define the perimeter of each cell when the strips are joined together. Prior to joining, discrete quantities of liquid crystal material are deposited onto one of the strips in registration with the seals and electrode patterns. Thereafter the two strips are joined to define the liquid crystal filled cells. In the method disclosed in the '574 pat¬ ent, the liquid crystal material is deposited in dis¬ crete quantities in registration with the seal and elec¬ trode pattern of each to-be-formed cell. Any is- registration between the actual position of the liquid crystal material deposited onto the receiving strip and the intended position on the strip and/or errors in the quantity of liquid crystal material dispensed can lead to inadequate cell filling or inclusion of air bubbles in the liquid crystal layer. SUMMARY OF THE INVENTION In view of the above, the present invention pro¬ vides a method, for filling liquid crystal cells by which cell filling is accomplished reliably and by a method well-suited to automatic high-speed production tech¬ niques. In accordance with the present invention, elon¬ gated preform strips are each provided with electrodes and, depending upon the type of display being manufac¬ tured, with alignment layers and other structures to define complementary preform strips which, when joined together, form a complete cell structure. The preform strips are advanced along respective converging paths and brought into an engaged relationship with one an¬ other. The nip or space formed between the converging strips is filled with a liquid crystal material in an amount sufficient to form and maintain an over-supply of liquid crystal material between the preform strips as they advance along their respective converging paths into their engaged relationship. The preform strips are then joined together in a permanent sealed engagement to form a strip-like assembly of filled liquid crystal cells. Maintenance of an over-supply of liquid crystal material at the nip, i.e., a quantity in excess of that required to completely fill the confining gap space of each cell unit, and engagement of the preform strips along their predetermined converging paths in a manner to effect uniform spreading of the liquid crystal material permits exclusion of air that otherwise may be entrapped between the engaged strip-like assembly and the individual cells thereof. The strip assembly is then severed intermediate the filled cells to • provide individual cell units. In one embodiment, the advancing preform strips are passed between spaced, counter-rotating rollers so that the complementary surfaces of the converging strips confront and engage one another in the nip defined be- tween the spaced rollers. The liquid crystal material is deposited into the nip defined between the two con¬ verging strips in an amount sufficient to create and maintain a "flooded nip", or over-supply of liquid crys¬ tal material between the confronting surfaces of the strips, to assure reliable filling of the liquid crystal cells as the strips pass between and through the rollers. A principal objective of the present invention, therefore, is the provision of a method for filling liquid crystal cells that is highly effective and well- suited for automatic, high-speed production techniques. Other objects and further scope of applicability of the present invention will become apparent from the detailed description to follow, taken in conjuction with the accompanying drawings, in which like parts are desig- nated by like reference characters. BRIEF DESCRIPTION OF THE DRAWING Fig. 1 illustrates, in schematic form, process machinery for filling liquid crystal cells in accordance with the present invention; Fig. 2 illustrates,, in cross-section, first and second starting strips suited for use with the process machinery of Fig. 1; Fig. 2A illustrates, in cross-section, first and second starting strips also suitable for use with the process machinery of Fig. 1; Fig. 3 illustrates a partial view of one of the .starting strips of Fig.2A with spacers and an adhesive seal applied; Fig. 3A is detail isometric view of a spacer for maintaining spacing between the two starter strips of Fig. 2A; Fig. 4 illustrates a modification of the process machinery of Fig. 1. Fig. 5 is an isometric view of process machinery for filling liquid crystal cells in accordance with the present invention; and Fig. 6 is a side elevation view of the process machinery of Fig. 5. DESCRIPTION OF THE PREFERRED EMBODIMENTS In accordance with the present invention, liquid crystal cells are filled and formed in an efficient manner by forming flexible starting strips and proces- sing the strips using the process machinery of Fig. 1. As shown therein, first and second strips S and S' are advanced along respective processing paths and subjected to modification, as explained more fully below, to de¬ fine complementary preform strips P and P' which form completed liquid crystal cells when assembled together. As shown in Fig. 2, the first and second starting strips S and S' can each include a substrate 10 and 10', respectively, formed from a flexible, substantially transparent polymeric material, such as polyethylene terephthalate or other polyester, polyether sulfone, a polycarbonate, a cellulose ester, or the like. The thickness of the substrates 10 and 10* is not particu¬ larly critical, although the substrates should be suf¬ ficiently thick to impart adequate mechanical strength to the final product. In accordance with one liquid crystal display manufactured in accordance with the invention, the substrates 10 and 10' are seven (7) mils thick (about 0.175 mm.) and approximately 16 cm. wide. The substrates 10 and 10' are respectively treated to include electrode layers 12 and 12' . The electrode layers 12 and 12* typically include a pattern of sub¬ stantially transparent conductive material such as an indium oxide, indium-tin oxide, or the like that is initially deposited as a uniform layer onto the sub- strate surface by one of a variety of known techniques, including vapor deposition, sputtering, and like. The conductive layers 12 and 12' are formed into a desired electrode pattern by selective photo-resist etching techniques as is known in the art. The particular pat- tern formed depends upon the end use of the display, although multi-segment numeric and alpha numeric pat- terns and row and column matrix type patterns are typi¬ cal. The starting strips S and S* illustrated in Fig. 2 are well suited for the manufacture of simple displays. Where more sophisticated field effect type displays are manufactured, the starting strips S and S* can include, as shown in Fig.. 2A, alignment layers 14 and 14' and a reflective or transreflective layer 16 on one of the two strips. The alignment layers 14 and 14' are typically a known material such as polyvinyl alcohol, a polyamide, polyvinylidene chloride, a fluorinated polymer or a polyimide and can be rubbed or buffed in a selected direction to establish a preferential orientation for the liquid crystal molecules adjacent each layer. The thickness of the alignment layers 14 and 14' is not critical although they must be thick enough to achieve the desired liquid crystal alignment effect. In gen¬ eral, a thickness of 500 to 1500 angstroms is suffi¬ cient. Depending on the type of liquid crystal cell manu- factured, the starting strips S and S' can also include appropriately aligned polarizing layers, various pro¬ tective coatings, anti-reflection coatings, and adhesive layers. As shown in Fig. 1, the starting strips S and S', such as those illustrated in. Fig. 2A, are advanced along respective paths through below described processing "stations to define preform strips P and P' that-are brought together and filled at a filling station FS. The starting strip S is first passed through a buffing station 100 that includes a buffing roll 100a and a cooperating strip support 100b so as to buff or rub the alignment layer 14 of the starting strip S in a preferred orientation, for example, in a direction par¬ allel to the longitudinal axis of the strip. In a sim- ilar manner, the starting strip S 1 is passed through another buffing station 100' that includes a buffing roll 100a' and cooperating strip support 100b 1 which are designed to buff or rub the alignment layer 14* in a preferred direction, usually orthogonal to the orien¬ tation of the complementary alignment layer 14. Where 5 polarizer layers are incorporated into the starting strips, the plane of polarization of th * e polarizers are aligned parallel or perpendicular to the preferential " orientation of the respective alignment layer. Upon completion of the preferential buffing of the 10 alignment layers 14 and 14', the strip S' is advanced directly to the filling station FS around guide roller G while the strip S is advanced through a spacer appli¬ cation station 102. The spacer application station 102 includes a gravure cylinder 102a and a cooperating strip ^-5 support 102b. The gravure cylinder 102a applies post¬ like spacers 18 to the strip S. As shown in the detail of Fig. 3A, each spacer 18 has a height dimension 'h*, generally between 5 and 50 microns with a preferred dimension between 8 and 12 microns, and an approximately 20 75 micron diameter dimension 'd' . The height 'h' is selected to control and maintain the spacing between the two strips S and S' of the assembled display and thus maintain a uniform liquid crystal layer thickness. The spacers 18 are applied in a uniform pattern along the 25 entire length of the strip S and on the side of the strip S that confronts the strip S' when the two strips are assembled. In one liquid crystal cell manufactured in accordance with the present invention, the spacers 18 are applied in a regular row and column matrix with a 30 1000 micron center-to-center spacing. Also, the spacers 18 need not be formed as cylinders as shown in Fig. 3A and can b ' formed as frusto-conical 'dots' or the like. The spacers 18 can be formed from a hot-melt polymer such as polyamide or from a radiation-polymerizable material 35. such as UV-curable acrylate. For example, polymeric spacer elements can be deposited by gravure or screen printing and simply cooled, as in the case of hot-melt polymer, or subηected to .ι curing (polymerization) step, as in thecase of UV-curable acrylate. When spacers 18 are desirably formed from radiation-polymerizable ma¬ terial, the material is deposited on the strip S and the strip is advanced through a curing station 104 where curing is effected to permanently form the spacers 18. As an alternate to the disclosed spacers 18, the liquid crystal material of the manufactured display can be mixed with polymeric rods, spheres or fibers having a diameter or other body dimension sufficient to maintain the desired spacing between the strips S and S'. After formation of spacers 18, the strip S is ad¬ vanced through an adhesive seal application station 106 that includes a gravure cylinder 106a and cooperating strip support 106b. An adhesive material is deposited onto the strip S to define a perimeter seal 20 for the liquid crystal cell. In one preferred liquid crystal display manufactured using the method of the present in¬ vention, as shown in Fig. 3, the adhesive seal 20 patterns are generally rectuangular, having length 'X' and width 'Y 1 dimensions of 9 and 15 cm., respectively, and a seal- ing-surface width approximately 9 to 12 mm. wide. The ad¬ hesive seals 20 are preferably spaced from one another 7 to 9 cm. as they are applied to strip S. The adhesive ma¬ terial is preferably a heat-activatable solvent-base polyes- ter or vinyl polymer, or mixture thereof, applied by the gravure cylinder 106a directly onto and between the previously applied spacers 18 of the strip S. If de¬ sired, the gravure cylinder 102a that applies the spacers 18 can be appropriately patterned to omit the spacers in the area to be occupied by the adhesive seals 20. * As can be appreciated, the starting strips S and S' thus form complementary preform strips P and P' that can be assembled to form the completed liquid crystal cells. As shown in Fig. 1, the preform strip P is guided by a guide roller Gl and the preform strip P' is guided by a guide roller Gl ' along respective converging paths to and into the filling station FS. The filling station FS includes first and second opposed and counter rotat- ing squeeze rollers G2 and G2 1 that are spaced apart from one another by a selected distance that is suf¬ ficient to force the confronting surfaces of the preform strips P and P-' into engagement with one another as they pass through the rollers G2 and G2'. A liquid crystal dispensing station 108 is located. just above the inter-roller nip and includes a dispensing nozzle N connected to a reservior 108a by a conduit 108b. Flow control valving (not shown) is provided to control the flow .of liquid crystal material from the nozzle N into the nip. As the two preform strips-P and P' converge toward and engage one another between the rollers G2 and G2' they define a pre-engagement nip. The liquid crystal dispenser 108 is designed to deposit a flow of liquid crystal material LC into the nip defined between the converging strips P " and P* in an amount sufficient to create and maintain an over-supply of liquid crystal material between the preform strips and, accordingly, form and maintain a "flooded nip". The particular liquid crystal material or mixture thereof depends on the end use of the display. The viscosity of the material is selected to assure adequate flow charac¬ teristics within the nip and the temperature of the liquid crystal material can be adjusted to increase or decrease the viscosity as desired. The rate of flow of liquid crystal material from the dispensing nozzle N into the nip will depend upon a number of factors, including the speed that the preform strips P and P' are advanced along their respective paths, the number of cells per unit length of the pre¬ form strips, and the volume of liquid crystal material required for each cell. In general, the flow of liquid crystal material must be sufficient to maintain the desired over-supply of liquid crystal material between the rollers G2 and G2' and maintain the nip in a flooded condition. The liquid crystal material can be introduced into the nip from the dispensing nozzle N in a continu¬ ous manner with the flow increased or decreased as de¬ sired to maintain the desired continuum of liquid crys¬ tal material between the preform strips P and P' as they pass between the counter-rotating rollers G2 and G2' . In the alternative, the liquid crystal material maybe introduced into the nip in discrete quantities or incre¬ ments. For example, the dispenser 108 can be turned on to fill the nip and then turned off. Prior to all the material in the nip being used to fill cells, the dis¬ penser 108 can again be turned on to repeat the procedure. The quantity of the material introduced during each dispensing period depends on the factors mentioned above. The spacing between the two counter-rotating rollers G2 and G2' is selected so that the two preform strips P and P' are brought together in engaging relationship with one another in the flooded nip so that each of the cells is filled on a continuous basis. The spacers 18 maintain inter-strip spacing and thereby control the thickness of the liquid crystal layer. The engaged relationship of the filled cells is maintained as the strips P and P' advance to a lamination station 110 that applies heat to the heat-activated adhesive seals 20 to effect permanent bonding between the two preform strips P and p » . After bonding is accomplished, the joined strip assembly is guided by a 'guide roller G3 to 'a cell cut ¬ off station 112 where the strip assembly is severed transversely between each of the filled cells with the so-severed cells collected in an accumulator station 114. In Fig. 1, the preform strips P and P' are brought together and passed through the two counter-rotating rollers G2 and G2' along a substantially vertical align- ment. As can be well appreciated by those skilled in the art, the preform strips P and P' can be brought together on an other than vertical alignment, such as the substantially horizontal alignment illustrated, in Fig. 4. Process machinery for implementing a modification of the present invention by which one of the preform strips is segmented prior to being placed into engage¬ ment with its complementary preform is shown in Fig. 5 and Fig. 6. The method described below in relationship to Fig. 5 and Fig. 6 is well suited to manufacturing liquid crystal displays of the dot-matrix type in which the conductive electrode patterns of each preform are defined by parallel, closely spaced conductive stripes. The conductive patterns are arranged orthogonal to one another in the assembled display with an addressable picture element (pixel) defined at each intersection of the various conductive stripes. As shown in Fig. 5, a continuous preform strip P is advanced in the direction indicated by the arrow 200 by suitable advancing apparatus (not shown) . The preform P includes an electrode layer 12 defined by a plurality of closely spaced, parallel conductive stripes that are aligned in the direction of travel of the preform P. As described above in connection with Fig. 2A, the preform P includes a substrate and an alignment layer and, depen- ding the structure of the display being manufactured, polarizing, adhesive, protective, and/or anti-reflection layers or coatings. A set of counter-rotating squeeze rollers 202 and 204, one positioned above the other, is provided in a manner similar to the squeeze rollers G2 and G2' of Figs. 1 and 4 with the preform P passing between the rollers. A liquid crystal dispensing nozzle N is positioned above the preform P in advance of the rollers 202 and 204 to apply a liquid crystal material to the preform P as described above. The nozzle N is connected to dis¬ pensing apparatus (not shown in Figs. 5 and 6) of the type described above in relationship to Fig. 1. The complementary preform P' is advanced along a path that is above and orthognal to the direction of travel the preform P. The preform P' includes an elec¬ trode stripe layer 12' of like construction to the layer 12 of the preform P. Because of the orthognal alignment of the preforms P and P', the electrode stripe patterns 12 and 12' will, of course, be orthogonally aligned in the assembled cell. The preform P'- is advanced in the direction of the arrow 206 by guiding and advancing apparatus (not shown in Figs. 5 and 6) so that one edge of the preform P' is brought into contact with or at least closely adjacent to the roller 202 in a tangential plane as shown in Fig. 6. A severing device 208 is positioned above the peri¬ odically advanced preform P' to sever the preform into segments of selected length. The roller 202 engages the preform segment and carries the segment around its peri¬ phery to apply the segment to the preform P with a rolling motion while the preform P moves in the direction of the arrow 200. The nozzle N functions as described above to place sufficient liquid crystal matetial onto the preform strip P to maintain a flooded nip between the preform segment as it is rolled onto the moving preform strip P. The joined segment and preform strip P pass between and through rollers 202 and 204 to squeeze excess liquid crystal material from the cells. After passing through the squeeze rollers 202 and 204, the joined components are passed onto the laminating station (not shown in Figs. 5 and 6) with processing continued as described above. The method for filling liquid crystal cells as herein described can be effectively utilized for the filling of cells of different structures or configura- tions. In this connection, the method can be used in the fabrication of liquid crystal display articles as described in the commonly assigned application Serial No. (Attorney Docket No. 6783), filed of even date. Thus, it will be appreciated that as a result of the present invention, a highly effective method for filling liquid crystal cells is provided by which the principal objective, among others, is completely ful¬ filled. It will be equally apparent and is contemplated that modifications and/or changes may be made to the illustrated embodiments without departure from the in¬ tention. Accordingly, it is expressly intended that the foregoing description and accompanying drawings are illustrative * of preferred embodiments only, not limit¬ ing, and that the true spirit and scope of the present invention will be determined by reference to the ap¬ pended claims.

Claims: WHAT IS CLAIMED: 1. A method for forming liquid crystal filled cells comprising the steps of: forming first and second flexible strip preforms each having complementary structures thereon which de¬ fine liquid crystal confining cells when joined to¬ gether; advancing said first and second strip preforms along respective paths that converge from a spaced pre- joining relationship to a joined relationship with said complementary structures in registration with one an¬ other; depositing a liquid crystal material in the space between said pre-joined first and second strip preforms in an amount sufficient to form an over-supply of liquid crystal material therebetween to fill the liquid crystal cells defined between said first and second strip pre¬ forms as they advance along their respective converging paths; and sealing said joined and filled liquid crystal cells together. 2. A method for forming liquid crystal filled cells comprising the steps of: forming first and second flexible strip preforms each having spaced complementary structues thereon which form liquid crystal confining cells when joined to¬ gether; advancing said first and second strip preforms along respective paths that converge between a pair of spaced rollers that bring said first and second strip preforms into a joined relationship and to define a nip between said. first and second strip preforms as they advance between said spaced rollers; depositing a liquid crystal material in the nip defined between said first and second strip preforms in an amount sufficient to form an over-supply of liquid crystal material therebetween to fill the liquid crystal cells defined between said first and second strip pre¬ forms as they advance between said rollers; and sealing said joined and filled liquid crystal cells together. 3. The method claimed in claim 1, wherein said forming step comprises applying seal patterns that de¬ fine the perimeter of each cell in a spaced relationship along one of said strip preforms. 4. The method claimed in claim 3, wherein said seal pattern is formed from a heat-activatable material and said sealing step comprises applying heat to said joined strips to cure said heat-activatable material to effect sealing. 5. The method claimed in claim 4, wherein said heat-activatable material is a heat-activatable poly¬ ester, a vinyl polymer, or a mixture thereof. 6. The method claimed in claim 3,.wherein said forming step further comprises forming electrode patterns on said preform strips. 7. The method claimed in claim 1, wherein at least one of said strip preforms is of indeterminate length. 8. The method of claim 1 wherein one of said strip preforms is defined by a continuous strip of indeter¬ minate length and the other of said strip preforms is divided into segments of discrete length prior to " join¬ ing with said strip preform of indeterminate length. 9. The method claimed in claim 1, wherein said depositing step comprises continuously depositing a liquid crystal material into the space between said pre- joined first and second strip preforms and adjusting the rate of flow thereof to maintain an over-supply of liq¬ uid crystal material therein. 10. The method claimed in claim 1, wherein said depositing step comprises depositing a liquid crystal aterial into the space between said pre-joined first and second strip preforms on an intermittent basis. 11. The method claimed in claim 1, further com¬ prising the step of: severing said joined first and second strip pre¬ forms between filled and sealed liquid crystal cells. 12. The method claimed in claim 2, wherein said forming step comprises applying seal patterns that de¬ fine the perimeter of each cell in a spaced relationship along one of said strip.preforms. 13. The method claimed in claim 12, wherein said seal pattern is formed from a heat-activatable material and said sealing step comprises applying heat to said joined strips to cure said heat-activatable material to effect sealing. 14. The method claimed in claim 13, wherein said heat-activatable material is a heat-activatable poly¬ ester, a vinyl polymer, or mixture thereof. 15. The method claimed in claim 12, wherein said forming step further comprises: forming electrode patterns on said preform strips. 16. The method claimed in claim 1, wherein at least one of said strip preforms is of indeterminate length. 17. The method of claim 2, wherein one of said strip preforms is defined by a continuous strip of in¬ determinate length and the other of said strip preforms is divided into segments of discrete length prior to joining with said strip preform of indeterminate length. 18. The method claimed in claim .2, wherein said depositing step comprises continuously depositing a liquid crystal material into the nip and adjusting the rate of flow thereof to maintain an over-supply of liq¬ uid crystal material therein. 19. The method claimed in claim 2, wherein said depositing step comprises depositing a liquid crystal material into the nip on an intermittent basis. 20. The method claimed in claim 2, further com¬ prising the step of: severing said joined first and second strip pre¬ forms between -filled and sealed liquid crystal cells. 21. A method for forming liquid crystal filled cells comprising the steps of: forming first and second flexible strip preforms each having complementary structures thereon, which strip preforms define liquid crystal confining cells when. joined together; advancing one of said strip preforms along a path that passes between spaced squeeze roller means, severing the other of said strip preforms into segments and advancing each so-severed segment along a path that converges with the first-mentioned path be¬ tween said spaced squeeze roller means to define a nip between said one strip preform and said advancing seg¬ ments; depositing a liquid crystal material in the nip defined between said one strip preform and said segments in an amount sufficient to form an over-supply of liquid crystal material therebetween to fill the liquid crystal cells defined between said one strip preform and said segments as they advance between said rollers; and sealing said joined and filled liquid crystal cells together. - 22. The method claimed in claim 21, wherein said forming step comprises applying seal patterns that de¬ fine the perimeter of each cell in a spaced relationship along one of said strip preforms. 23. The method claimed in claim 21, wherein said seal pattern is formed from a heat-activatable material and said sealing step comprises applying heat to said joined strips to cure said heat-activatable material to effect sealing. 24. The method claimed in claim 23, wherein said heat-activatable material is a heat-activatable poly¬ ester, a vinyl polymer, or a mixture thereof. 25. The " method claimed in claim 22, wherein said forming step further comprises forming electrode patterns on said preform strips. 26. The method claimed in claim 21, wherein at least one of said strip preforms is of indeterminate length. 27. The method claimed in claim 21, wherein said depositing step comprises continuously depositing a liquid crystal material into the nip and adjusting the rate of flow thereof to maintain an over-supply of liq¬ uid crystal material therein. 28. The method claimed in claim 21, wherein said depositing step comprises depositing a liquid crystal material into the nip on an intermittent basis. 29. The method claimed in claim 21, further com¬ prising the step of: severing said joined first and second strip pre¬ forms between filled and sealed liquid crystal cells.

Inventors: POLIZZOTTO LEONARD, POLIZZOTTO, LEONARD
Applicants: POLAROID CORP, POLAROID CORPORATION
Application year: 1984
Main classification: G02F1
IPC codes: G02F1