Colour liquid crystal electro-optical device and method of manufacturing the same

Abstract: A coloured liquid crystal electro-optical device comprises a pair of electrodes (2,7), a colour filter (3) on at least one of the electrodes and an orientation layer (5) disposed on the colour filter. A protective layer (4) is disposed between the orientation layer and the colour filter.

Description: This invention relates to colour liquid crystal electro-optical devices, for example, display devices, and to methods of manufacturing the same. Figure 2 illustrates a multi-colour liquid crystal display device having electrodeposited colour filters. A transparent substrate 10 is made of glass. Electrodes 11 consisting of a transparent conductive film are formed on the substrate and patterned in the shape of numerals or characters. A colour filter 12 is formed by electrodepositing an electrodepositable polymer and a pigment. The colour filters 12 are of the same shape as the electrodes 11 on which they are deposited. An orientation film 13 is formed by printing, spin coating or dipping a polyimide solution. A transparent second electrode 4 is formed on a transparent second substrate 15. Liquid crystal material 16 is sandwiched between the two substrates 10,15 to form a liquid crystal cell. When a voltage is applied across the liquid crystal cell and the cell is observed when interposed between a polariser and an analyser, the colours of the colour filters can be seen in the portions of the liquid crystal cell which are in a transmission mode while the remainder of the liquid crystal cell appears black because it does not permit the transmission of light. Thus the display device produces a multi-colour liquid crystal display for displaying the colours of the colour filters using the liquid crystal material as an optical shutter. Conventionally, the orientation film is formed by a polyimide layer having its surface rubbed with, for example, a cloth in a predetermined direction so that the orientation film orients the molecules of the liquid crystal material in the predetermined direction. Polyester-melamine resins, acryl-melamine are also known as materials for the electrodeposited colour filters. When the polyimide orientation film is formed on a colour filter of a synthetic polymer, the polyimide film itself has poor adhesion to the colour filter. In addition, thermophysical behaviour of the polyimide film is different from that of the filter material. For these reasons, stress imposed at the interface between the polyimide film and the filter is likely to be relatively great, so that the reliability of orienting power of the polyimide orientation film is much reduced and the orienting power is lost within about 100 hours when the orientation film is left standing at a temperature of 80°C. EP-A-0122168 discloses a colour liquid crystal electro-optical device comprising a pair of substrates arranged substantially parallel and mutually opposed, liquid crystal material confined between the substrates, electrodes deposited on the inward facing surfaces of the substrate, a colour filter deposited on one of the electrodes, a polyimide protective layer deposited on the colour filter and an orientation layer of silane formed over the polyimide protective layer. One method of producing colour filters by electrodeposition is disclosed in US-A-4522691. This method affords an effective means capable of easily producing high precision colour filters. The present invention seeks to provide an improved colour liquid crystal electro-optical device having reliable orientation characteristics, and electrodeposited colour filters with high adhesion and high orientation characteristics. According to the present invention, a colour liquid crystal electro-optical display device comprises transparent electrodes deposited on the inward facing surfaces of two spaced substrates arranged substantially parallel and mutually opposed, a colour filter deposited on at least one electrode, a polymer protective layer deposited on the colour filter, an orientation layer formed over the polymer protective layer and liquid crystal material confined between the substrates, characterised in that the polymer protective layer contains an epoxy group, thereby providing high adhesion between the colour filter and the orientation layer and protecting the orientation layer from stress imposed at the interface therebetween. The colour filter may be an electrodeposited colour filter. The colour filter may thus be formed by electrodeposition from a solution containing an electro-depositable polymer and pigments dispersed therein. Preferably, the electrodepositable polymer contains a polyester resin and a melamine resin or an acryl resin and a melamine resin. The orientation layer may be selected from at least one of a polyimide polymer, a polyimide polymer and a cellulosic polymer. In one embodiment, colour filters of different colours are on different electrodes. According to another aspect of the present invention, there is provided a method of manufacturing a colour liquid crystal electro-optical device, including the steps of depositing at least one electrode on each of two substrates, depositing a colour filter on the electrode or electrodes of at least one substrate, depositing a polymer protective layer on the colour filter, forming an orientation layer on the colour filter, and confining a liquid crystal material between the substrates, characterised in that the polymer protective layer contains an epoxy group, adheres the orientation layer to the colour filter and protects the orientation layer from stress imposed at the interface between. The invention is illustrated, merely by way of example, in the accompanying drawings, in which:- Figure 1 is a longitudinal sectional view of a multi-colour liquid crystal display device according to the present invention; and Figure 2 is a longitudinal sectional view of a known multi-colour liquid crystal display device. Although the mechanism of degradation of orienting power of an orientation film has not been sufficiently clarified, the following mechanism may be assumed. One mechanism is the peeling of the orientation film from the substrate and the peeled portion cannot exert any controlling power on liquid crystal molecules so that orientation power is disturbed. Another mechanism is where energy having directivity to the surface of the orientation film that is provided by rubbing or the like cannot be kept due to subsequent thermal energy or the like and is offset by the latter. More definitely, the directivity is lost if the rearrangement of the molecules or the surface shape such as phase transition or melting occurs due to the thermal energy. If such a mechanism is to be applied to the orientation film provided on the colour filter, one of the problems is adhesion between the orientation film and the colour filter and the other is the stress between them. Although it is not clear to which of these two mechanisms of degradation of the orienting power in the actual electrodeposited filter belongs, a method has now been found of disposing a protective film on the electrodeposited filter, which protective film has high adhesion to both the colour filter and the orientation film, as effective means for solving either of these problems. As a result of intensive studies, it has also now been found that a polymer containing an epoxy group is effective as a material for the protective layer. The present invention will now be described in further detail with reference to the following Examples. EXAMPLE 1 Figure 1 illustrates an example of a multi-colour liquid crystal display device produced by a method according to the present invention. Transparent electrodes 2 made of tin oxide were patterned and formed on a transparent glass substrate 1. This substrate was immersed in an electrodeposition solution having the following composition: ELECTRODEPOSITION SOLUTION polyester resin 6.5 parts melamine resin 1.5 parts ethyl cellosolve 2.0 parts water 88.0 parts red pigment 2.0 parts A positive voltage was applied between the electrodes to be coloured red, while a negative voltage was applied to an opposed electrode. The substrate was removed from the electrodeposition solution, washed with water and then baked (or cured) at 200°C for about 30 minutes to form a red filter. Electrodeposition solutions were prepared by replacing the red pigment in the electrodeposition solution described above by a green pigment and a blue pigment, respectively, and green and blue filters were likewise formed sequentially on other selected electrodes. A multi-colour filter 3 of red, green and blue was obtained. A film was formed on this filter by spin coating from a solution having the following composition and was heated and cured at 200°C for one hour to obtain a protective layer 4: polyamide resin 2.5 parts epoxy resin ("Shell Epikote" No 1002) 2.5 parts xylenol 95.0 parts This protective layer was coated with a 10 wt % cyclohexanone solution of a polyimide of the following formula by spin coating: Baking was carried out at 200°C for one hour, and the surface was rubbed with a cotton cloth in a predetermined direction to obtain an orientation layer 5. Thereafter, a second transparent electrode 7 was disposed on a second glass substrate 6 and a further orientation film 8 was formed on the electrode 7 and rubbed similarly. This substrate was bonded to the opposed substrate 1 and liquid crystal material 9 was confined between them to prepare a multicolour liquid crystal display device. When the display device was left standing at a temperature of 80°C, the orientation state of the orientation layer remained excellent even after the passage of 1,000 hours and degradation of the orientation state could scarcely be observed. COMPARATIVE EXAMPLE 1 A multi-colour liquid crystal display device was produced in the same manner as in Example 1 except that the composition of the protective layer coating solution was changed as follows: polyamide resin 2.5 parts benzoguanamine resin 2.5 parts xylene 95.0 parts When the resulting multi-colour liquid crystal display device was left standing at a temperature of 80°C, the orientation state almost completely disappeared after 300 hours. COMPARATIVE EXAMPLE 2 A multi-colour liquid crystal display device was produced in the same way as in Example 1 except that the protective layer of Example 1 was not used. When the resulting display device was left standing at a temperature of 80°C, the orientation state almost completely disappeared after the passage of 250 hours. EXAMPLE 2 The protective layer in Example 1 was formed by spin coating of a 10 wt % ethyl cellosolve acetate solution of an epoxy modified acrylic resin and baking at 200°C for one hour. Thereafter, the same steps were employed as those of Example 1 to produce a multi-colour liquid crystal display device, and substantially similar effects as in Example 1 were obtained. EXAMPLE 3 The protective layer in Example 1 was formed by spin coating of a 10 wt % ethyl cellosolve solution of an isocyanate-modified epoxy resin and baking at 200°C for one hour. Thereafter, the same steps were employed as those in Example 1 to produce a multi-colour liquid crystal display device and substantially similar effects as in Example 1 were obtained. EXAMPLE 4 The protective layer in Example 1 was formed by spin coating of a solution having the following composition and baking at 150°C for one hour: epoxy resin (Shell Epikote No. 1002) 2.5 parts phenolic resin 2.5 parts xylenol 95.0 parts Thereafter, a multi-colour liquid crystal display device was produced in the same way as in Example 1 and substantially similar effects as in Example 1 were obtained. Example 5 Transparent electrodes 2 made of tin oxide were patterned and formed on a transparent glass substrate 1. This substrate was immersed in an electrodeposition solution having the following composition: ELECTRODEPOSITION SOLUTION acrylic resin 6.5 parts melamine resin 1.5 parts ethyl cellosolve 2.0 parts water 88.0 parts red pigment 2.0 parts A positive voltage was applied between the electrodes to be coloured red, while a negative voltage was applied to an opposed electrode. The substrate was removed from the solution, washed with water and baked (or cured) at 200°C for about 30 minutes to form a red filter. Electrodeposition solutions were prepared by replacing the red pigment in the electrodeposition solution described above by a green pigment and a blue pigment, respectively, and green and blue filters were likewise formed sequentially on other selected electrodes. A multi-colour filter 3 of red, green and blue was obtained. A film was formed on this filter by spin coating from each of the solutions having the compositions described in Examples 1 to 4 and was heated and cured at 200°C for one hour to obtain a protective layer 4. Thereafter, the same steps were employed as those of Example 1 to produce a multi-colour liquid crystal display device and substantially similar effects as in Examples 1 to 4 were obtained. As described in the foregoing Examples, the present invention provides a protective layer on the electrodeposited colour filter and further provides the orientation layer on the protective layer. This results in multi-colour liquid crystal electro-optical devices having extremely high reliability and long service life. As described above, the present invention can provide such excellent advantages, but it is not possible to determine clearly whether the effects result from good adhesion between the colour filter and the orientation layer or from the protection layer. In fact, the effects may presumably result from the combined effect of both in view of the fact that the protective layer containing the epoxy coupling agent which provides a good effect in the examples has relatively high adhesion with the colour filter or polyamide and has excellent physio-chemical durability.

Claims: A colour liquid crystal electro-optical display device comprising transparent electrodes (2,7) deposited on the inward facing surfaces of two spaced substrates (1,6) arranged substantially parallel and mutually opposed, a colour filter (3) deposited on at least one electrode (2), a polymer protective layer (4) deposited on the colour filter (3), an orientation layer (5) formed over the polymer protective layer (4) and liquid crystal material (9) confined between the substrates (1,6), characterised in that the polymer protective layer (4) contains an epoxy group, thereby providing high adhesion between the colour filter (3) and the orientation layer (5) and protecting the orientation layer (5) from stress imposed at the interface therebetween. A device as claimed in claim 1, characterised in that the colour filter (3) is an electrodeposited colour filter. A device as claimed in claim 2, characterised in that the colour filter (3) is formed by electrodeposition from a solution containing an electro-depositable polymer and pigments dispersed therein. A device as claimed in claim 3, characterised in that the electro-depositable polymer contains a polyester resin and a melamine resin or an acrylic resin and a melamine resin. A device as claimed in any preceding claim, characterised in that the orientation layer (5) is selected from at least one of a polyimide polymer, a polyamide polymer and a cellulosic polymer. A device as claimed in any preceding claim, characterised by colour filters (3) of different colours on different electrodes. A method of manufacturing a colour liquid crystal electro-optical device, including the steps of depositing at least one electrode (2,7) on each of two substrates (1,6) depositing a colour filter (3) on the electrode or electrodes (2) of at least one substrate (1), depositing a polymer protective layer (4) on the colour filter (3), forming an orientation layer (5) on the colour filter (3), and confining liquid crystal material (9) between the substrates (1,6), characterised in that the polymer protective layer (4) contains an epoxy group, adheres the orientation layer (5) to the colour filter (3) and protects the orientation layer (5) from stress imposed at the interface therebetween.

Inventors: KAMAMORI HITOSHI, SUGINOYA MITSURU, TERADA YUMIKO, KAMAMORI, HITOSHI, SUGINOYA, MITSURU, TERADA, YUMIKO
Applicants: SEIKO INSTR INC, SEIKO INSTRUMENTS INC.
Application year: 1987
Main classification: G02F1
IPC codes: G02F1, G02B5