Alignment film for liquid crystal and method for production thereof

Abstract: An alignment film for liquid crystal formed by monomolecular film comprising silane-type compounds with a linear hydrocarbon chain and method for production of said film, as well as liquid crystal display units utilizing said film and method for production of said display unit are disclosed.

Description: BACKGROUND OF THE INVENTION FIELD OF THE INVENTION This invention relates to the alignment film for liquid crystals usable for planar display panels which display television picture images and computer picture images and method for production thereof. RELATED ART STATEMENT Liquid crystal display units such as color liquid crystal display panels have conventionally been produced by sealing liquid crystal between two substrates formed of a matrix of counter electrodes through an alignment film for liquid crystal formed by coating polyvinyl alcohol or polyimide using a spinner. These units, as shown in Figure 2, are produced by precoating poly(vinyl alcohol) or polyimide using a spinner in an insulating manner onto the respective electrodes of the first glass substrate (31) with a thin-film transistor (hereinafter abbreviated as TFT) array (33) with a picture element electrode (32), and the second glass substrate (34) formed of multiple red, blue, and green color filters (35) and a common transparent electrode (36) on top of the aforementioned color filters, forming an alignment film for liquid crystal (37) by rubbing, then assembling them facing each other by electrode side on either side of the spacer (38) using the adhesive (39); the twist nematic (hereinafter abbreviated as TN) liquid crystal (40), etc., is then inserted, forming a panel structure; polarizing plates (41, 42) are then installed on the front and back sides of the panel, and the TFT is operated while irradiating with the back light (43) so that the color picture image is displayed in the arrow direction A. However, the conventional production of an alignment film for liquid crystal involves dissolving polyvinyl alcohol or polyimide in an organic solvent, then forming a film using rotating coating methods, then finally rubbing it with a felt cloth; therefore, it was difficult to achieve uniform coating of the alignment film for liquid crystal panels with large surface areas, e.g., 14-inch display; further, rotating coating methods resulted in films up to several 5 µm thick, causing a large defect in performance of display panels such as ferroelectric liquid crystal requiring alignment films for liquid crystal with a thickness of approximately 1,000 Angstroms. EP-A-0 286 539 discloses the use of organosilane-type compounds for forming an alignment film for liquid crystals. According to said document octadecyl-trietoxysilane, dimethyl-octadecyl-aminopropyl-silane and mixtures obtained by mixing one of the above compounds with N-methyl-aminotrimethoxysilane or dimetoxy-methyl-chlorosilane are particularly preferred for forming the alignment film. Further, US-A-3,854,793 discloses the use of a monolayer of a silane coupling material which forms a chemical bond with a substrate as an alignment film for a liquid crystal. In this document N,N-dimethyl-N-octadecyl-3-aminopropyl-trimetoxysilyl-chlorid is identified as a particularly preferred compound for forming the alignment film. Further, GB-2 194 792 A discloses a method for the orientation of the liquid crystals on substrate surfaces wherein a matrix is applied onto the substrate surface as orientation layer, to the functional groups of which matrix thermotropic liquid crystals are bound, partly before the application onto the substrate surface. For forming this matrix it is proposed in said document to use organosilanes of the general formula X n SiR 4-n , wherein X represents a hydrolysable group (halogen, alkoxy group, etc.) and R represents an organo functional residue. OBJECT AND SUMMARY OF THE INVENTION The purpose of this invention is to provide a substrate with a highly efficient, uniform, yet thin alignment film for liquid crystal as defined in claim 1 and method for production thereof as defined in claim 2. In conducting various tests to achieve the above-mentioned purpose, the inventors found that a film with superior uniformity in coating and a thickness of approximately 10 - 30 Angstroms could be achieved by mixing a chlorosilane-type surfactant bonded with a liquid crystal molecule of the type of the molecules to be aligned and adsorbing the mixture onto a substrate, to thereby cause chemical bonding between the silicon in said surfactant and the surface of said substrate. Liquid crystal display units using alignment films for liquid crystal formed related with this invention have characteristics well suited to the production of large scale display panels. BRIEF EXPLANATION OF THE DRAWINGS Figure 1 shows a cross sectional view of a liquid crystal display unit using the alignment film for liquid crystal of this invention; Figure 2 shows a cross sectional view of a liquid crystal display unit using the conventional alignment film for liquid crystal; Figure 3 shows the FTIR spectrum of an alignment film formed by adsorption method and an alignment film formed by conventional spin-coat method. The numbers and codes used in the figures are described below: 11 ... first electrode group; 13 ... first substrate; 15 ... second electrode group; 16 ... second substrate; 17 ... alignment film for liquid crystal; 20 ... liquid crystal; 21 ... polarizer; 22 ... polarizer; 23 ... back light; A ... direction of picture image; 31 ... first glass substrate; 32 ... picture element electrode; 33 ... TET array; 34 ... second glass substrate; 35 ... color filter; 36 ... common transparent electrode; 37 ... alignment liquid crystal film for liquid crystal; 38 ... spacer; 39 ... adhesive; 40 ... twist nematic liquid crystal; 41 ... polarizer; 42 ... polarizer; 43 ... back light; G ... Green filter; B ... Blue filter; R ... Red filter. DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS Chlorosilane-type compounds bonded with ferroelectric liquid crystal such as azomethyne-type, azoxy-type, or ester-type liquid crystal, can be used as a chlorosilane-type surfactant bonded with a liquid crystal molecule. Needless to say, any compound with a group can be used. Preferably, the substrates have a hydrophilic surface and form a bond when reacting with the Si in the above-mentioned compounds. Because the structure of the alignment film for liquid crystal used in this invention is that of direct monomolecular chemisorption of chlorosilane-type surfactants onto the surface of a substrate, it is uniform and thin. Moreover, by using chlorosilane-type surfactant whose molecules are bonded to the liquid crystal molecules, controllability of orientation is further improved. In cases where an alignment film for liquid crystal is formed, through adsorption of only a chlorosilane-type surfactant with long linear hydrocarbon chains having similar alignment properties as a chlorosilane-type surfactant bonded with a liquid crystal molecule, an alignment film for liquid crystal able to orient the aforementioned liquid crystal almost perpendicularly is produced. As an example, Figure 3 shows the spectrum data measured by FTIR spectroscopy of an alignment film produced through adsorption compared to that of an alignment film produced by the conventional spin-coating method. The test compound used here was CH 2 =CH-(CH 2 -) 17 -SiCl 3 ; in the alignment film produced by adsorption (A), the adsorptions of 2930 cm -1 and 2860 cm -1 were clearly split, but in the spin-coated oriented film (B), two adsorption peaks overlapped; thus it was determined that the hydrocarbon chain is oriented almost perpendicularly to the substrate in the adsorbed monomolecular film, but the orientation in the spin-coated film was irregular at the molecular level. As shown in Figure 1, when producing a liquid crystal display unit using a substrate with an alignment film for liquid crystal comprising monomolecular film according to the present invention chlorosilane-type surfactants which can efficiently control the orientation of long molecules dissolved in n-cetane are chemisorbed onto the second substrate (16), on which a matrix has been formed in advance; thereby single layers of monomolecular film for alignment film for liquid crystal (17) are formed onto the surface of the aforementioned substrate through the chemical bonding between the silicone in the aforementioned chlorosilane-type surfactants and the -OH group in the natural oxidization film on the surface of the aforementioned substrate. Next, the aforementioned first substrate (13) is installed facing the second substrate (16) across the spacer (18), and then fixed using adhesive (19). Next, the specified liquid crystal (20) is inserted between the aforementioned first substrate (13) and the second substrate (16). It is then completed by assembling the polarizers (21) and (22). With this type of liquid crystal display unit, a picture image can be displayed in the direction of the arrow (A) by driving various transistors using video signals while irradiating the entire surface with the back light (23). As described above, because the alignment film for liquid crystal used in this invention is structured by the direct monomolecular chemisorption of chlorosilane-type surfactants onto the surface of the substrate, it is efficient, uniform, and thin; further, it has the ability to improve the controlling characteristics of the liquid crystal molecule orientation. Moreover, by using chlorosilane-type surfactants with molecules bonded to the liquid crystal molecules, the controlling characteristics of the orientation is further improved. Also, in liquid crystal display units using the oriented film for liquid crystal used in this invention, the insulating film between the liquid crystal and the electrode is extremely thin; therefore, the energy requirements to drive the liquid crystal display unit can be reduced. Further, because the alignment film produced by the process of this invention, as well as liquid crystal cells using this alignment film, have the ability to line up the molecules with large intramolecular dipoles in a specific direction, extremely large secondary nonlinear optical effects can be generated.

Claims: A substrate with an alignment film (17) for a liquid crystal material (20) consisting of a monomolecular film of chlorosilane-type surfactants bonded with liquid crystal molecules of the type of the molecules of the liquid crystal (20) to be aligned, said monomolecular film being formed on said substrate (16) by chemisorption. A method for the production of an alignment film for liquid crystal material which comprises forming a single layer of a monomolecular film formed through chemisorption of a chlorosilane-type surfactant bonded with a liquid crystal molecule of the type of the molecules of the liquid crystal to be aligned on a surface of a specified substrate on which electrodes are formed by causing the chemical bonding between the silicon in said surf actant and the surface of same substrate directly on the surface of said substrate.

Inventors: MINO NORIHISA, OGAWA KAZUFUMI, TAMARU HIDEHARU, MINO, NORIHISA, OGAWA, KAZUFUMI, TAMARU, HIDEHARU
Applicants: MATSUSHITA ELECTRIC IND CO LTD, MATSUSHITA ELECTRIC INDUSTRIAL CO., LTD.
Application year: 1990
Main classification: G02F1
IPC codes: G02F1