GB2309792A

GB2309792A - Aligning liquid crystals

Info

Publication number: GB2309792A
Application number: GB9623258A
Authority: GB
Inventors: Jong Hyun Kim; Ki Hyuk Yoon; Joung Won Woo; Mi Sook Nam; Yoo Jin Choi
Original assignee: LG Electronics Inc
Current assignee: LG Electronics Inc
Priority date: 1996-02-01
Filing date: 1996-11-07
Publication date: 1997-08-06
Anticipated expiration: 2016-11-07
Also published as: GB9623258D0; KR0182116B1; GB2309792B; KR970062764A; JPH09211456A; DE19637929A1; DE19637929B4; FR2744535A1; JP3860872B2; FR2744535B1

Description

i ' 2309792 1 A METHOD FOR FABRICATING A LIQUID CRYSTAL CEL The present

invention relates to a liquid crystal cell, and more particularly to a method for controlling alignment direction by irradiating of the ultraviolet light on the photopolymeric material coated substrate.

A conventionally used liquid crystal display is mainly a twisted nematic liquid crystal display (referred as TNWD), which has a changeable transmittance at each gray level according to the viewing angle. Especially, while the transmittance is symmetrical in the horizontal direction, the transmittance is asymmetrical in the vertical direction. Therefore, in the vertical direction, the range with inverted image phenomenon is occurred so that the vertical viewing angle becomes very limited.

To overcome said problem, a multi domain TN LC cell such as a two-domain TN LC cell, a domain-divided TN LC cell, and a 4-domain TN LC cell is introduced. In the two-domain TN LC, the viewing angle inversion is through reversed rubbing. The pretilt of each domain is made in the opposite by said reverse-rubbing the alignment layers compensated direction direction j ' 2 consisting of a polyimide. In case of the domain-divided TNW cell, the pixel is formed with two different alignment materials such as, an organic and an inorganic material, so two subpixels have different main viewing angles, thereby, the viewing angle is symmetrically compensated. Furthermore, in the 4-domain TN LC cell, the viewing angle is compensated with a reverse rubbing and a double SiOx oblique evaporation.

However, in manufacturing said multi-domain TN LC cell using rubbing process, the rubbing process causes a dust and/or an electrostatic discharge, so the productivity is reduced and/or the substrate is damaged. The process of manufacturing becomes too complicated because it is comprising the following steps:

the entire alignment layer without any blocking of a domain is rubbed in a first rubbing direction; a photoresist is applied for blocking one domain; then the other domain is rubbed at the reverse direction to said first rubbing direction; finally the photoresist is removed.

Therefore, it is a photo-alignment method that is introduced to reduce the number of steps as well as to prevent the damage of substrate. The photo-alignment is the process in which alignment direction of alignment layer is given by the irradiation of a linearly polarized 1 ' 1 3 ultraviolet light. The alignment layer used in the photo alignment is mainly including PVCN(polyvinyl cinnamate) based polymer. When the photoalignment layer coated on the substrate is irradiated by the ultraviolet, it causes cycloaddition of the cinnamoyl groups of cinnamic acids side chains that belong to different main chains. Thereby, the direction of the photopolymer configuration i.e., the alignment direction of alignment layer is arranged uniformly. However, it is needed to select desired pretilt angle direction between two directions formed by said step. Therefore, referring to the Kobayashi(SID 95, DIGEST 877), after irradiating the linearly polarized UV light, the slanted UV light is irradiated into the layer again to form a uniform pretilt angle.

Accordingly, to control the pretilt direction, double UV light exposure is conducted to determine onedomain LC cell. Therefore, only one-domain LC cell with uniform pretilt angle could be manufactured by said process. To obtain a multi-domain LC cells with reverse pretilt angles, the process is getting complicated. For example, to fabricate two-domain LC cell, eight times irradiation process of uv light as well as photolithography process are needed.

J ' 4 An object of the present invention is to provide a method for controlling the alignment direction of liquid crystal cell using photo alignment process in which alignment direction is determined by the polarized direction of lastly irradiated UV light regradless of the previous one.

In order to achieve the object, a method for controlling the pretilt direction of an alignment layer according to the present invention includes the steps of: irradiating an ultraviolet light an entire alignment layer to determine the alignment direction; irradiating an ultraviolet light in which the polarized direction is different from the previous one, again, so as to form a switched alignment direction which is different from the previous direction.

Even if the alignment layer material such as a PVCN-F or polysiloxane based materials is exposed to the linearly polarized ultraviolet light in several times at the different polarized direction each other, the alignment direction formed on the alignment layer is determined regarding to the lastly irradiated ultraviolet light regardless of the previous irradiated ultraviolet lights.

When the alignment direction is determined, the pretilt angle e has two directions which are degenerated on the alignment layer as showing FIG.1. Then if the LC is injected, one of the pretilt angles formed on the substrate with symmetrical status is selected by flowing effect of liquid crystal material. Accordingly, to control the pretilt direction, the LC injection is conducted after forming the pretilt angle with irradiating the ultraviolet light.

To manufacture LC cell in the same way mentioned above, the pretilt angles Which is in the same alignment direction and in the symmetrical direction, are determined by irradiating the linearly polarized ultraviolet light on both upper and lower substrates formed with an alignment layer, one pretilt direction is selected between the degenerated pretilt directions by the flowing effect of LC. Then, the ultraviolet light which has different polarized direction than the determined polarized direction on a substrate, is irradiated to the substrate so that it can be obtained that the alignment direction of the TNLCD is different.

Further, to obtain muti-domain LC cell, some domains of the LC cell which have already set up an alignment direction are blocked with mask such as a photoreist, then the ultraviolet light of which the 6 polarized direction is perpendicular to previous one, is irradiated again, then the mask is removed.

For a better understanding of the present invention embodiments will now be described by way of exampler with reference to the accompanying drawings, in which:

FIG.1 is showing two pretilt angles degenerated by photo alignment.

FIG.2 is a drawing showing the ultraviolet irradiating device to control the alignment direction according to the present invention.

FIG.3 is a graph showing the relationship between the birefringence and the irradiation time.

FIG.4 is showing the alignment direction when the linearly polarized ultraviolet is radiated the alignment layer.

FIG.5a is showing the LC cell in which the alignment direction is previously determined according to the method of controlling liquid crystal cell by irradiating ultraviolet light on the photopolymeric material coated substrate of the present invention.

FIG.5b is a sectional view of FIG 5a according to the method of controlling liquid crystal cell by irradiating ultraviolet light on the photopolymeric 7 material coated substrate of the present invention.

FIG.5c is a view showing that the pretilt direction is determined by the flowing effect in this present invention.

FIG.5d is showing the direction of the LC injection in this present invention.

FIG.Se is showing the LC cell in which the pretilt direction is determined according to the method of controlling liquid crystal cell of irradiating ultraviolet light on the photopolymeric material coated substrate according to the present invention.

FIG.5f is showing the TNW cell is formed by irradiating the ultraviolet to the LC cell determined on the alignment direction.

FIG.6 is showing the other embodiment of the method of controlling liquid crystal cell according to the present invention.

FIG.2 is showing a device for irradiating the ultraviolet to form the LC cell according to the present invention, 7, referring number, is the alignment layer 8 coated with PVCN-F (polyvinyl Eluorocinnamate). Sa id alignment layer 7 is formed by the way which said PVCN-F is spin-coating on the substrate coated with ITO(indium tin oxide). Then the ultraviolet from a lamp 2 which is linearly polarized when it passes through a polarizer 5, is irradiated to the alignment layer 7, and wherein the lamp 3 used is Mercury lamp having a wave length equal to or less than 365nm. When the ultraviolet from the lamp 3 is irradiated the substrate coated with PVCN-F, the pretilt angle of the alignment layer is depending upon the irradiation energy. Furthermore, it is possible to use polysiloxane based materials instead of PVCN-F as a alignment layer, in this time, the pretilt angle of the alignment layer is changeable according to the irradiation energy of the ultraviolet light.

Polysiloxane cinnamate, one of the polysiloxane based materials, and PVCN-F have following structural formulas PVCN-F CHz C11z 1 0 c - CII = Cfi-GF 0 9 n = 300-6,000 which can be prepared by the reaction of polyvinyl alcohol(here: PVA) and 4-Elouro cinnamic acid.

polysiloxane cinnamate 1 Z can f rom Z Si (CHz,) 0' CH - CH 0- X be selected from the group consisting of OH, CH3 or mixtures thereof, m = 10-100, 1 = 1-11, L = 0 or 1, K = 0 or 1, X, Xl, X2, Y = H, F, Cl, CN, CF3, CnH2n+ l or OCnH2n+l wherein n can be from 1 to 10, or from mixtures thereof; polysiloxane cinnamate II z L 0 Xp7 _j 2 Z - Si (CH2)i C - CH = CH 0 X xl - can be selected from the group consisting of OH, CH3 or from mixtures thereof, - Y K Y K from mixtures thereof, m 10-100, L 0 or 1, K 0 or 1, X, X1f X2, Y = H, F, Cl, CN, CF.,, C,H1,1, or 0C.H2o. 1 wherein n can be from 1 to 10, or from mixtures thereof; FIG.3 is a graph of the birefringence(-An) when the ultraviolet has been irradiated said alignment layer by changing the alignment direction from 0 to 90, or from 90 to 0, wherein the vertical line refers birefringence(- An), and the horizontal line refers the irradiation time of ultraviolet light. According to the graph, the birefringence An of which the polarization direction is 0, is larger than that of 90, the longer the ultraviolet light is, the smaller the birefringence(An) toward to each polarized direction. Referring to the graph, the birefringence is depending upon the lastly polarized direction of the ultraviolet irradiated to the alignment layer, that is, the alignment direction is determined by the polarized direction of the ultraviolet light that is irradiated only for the lastly time other than previous ultraviolet light.

11 Referring to FIG.4, if the ultraviolet light is irradiated with changing the polarized direction, only alignment direction responding the lastly irradiating ultraviolet light is remained on the alignment layer 7. In said drawing, the vector E refers the electric field of light, that is, the polarized direction, the arrow refers the alignment direction.

FIG.5a-FIG.5f are illustrating the first FIG.Sa shows anale embodiment of the present invention. ol regarding between alignment direction of the upper layer 10 and of the lower layer 11 determined by the irradiating the polarized ultraviolet light, and in FIG.5b shows that the pretilt angles el, e2 are degenerated with two directions. Then, when the LC is injected into between an upper and a lower layer, the pretilt angles el, e2 are tilted with the LC injection direction, so the pretilt angles are selected as shown in FIG.5c. In FIG.5d, if the first area is with the angle between -900and 900 with respect to the alignment direction of the upper layer 10, and if the second area is with the angle between -90" and 9W' with respect to the alignment direction of the lower layer 11, the LC is injected into the common area which is overlapped between said two areas. In addition, FIG. 5e is a drawing 1 12 showing the LC cell formed by said method, and the angle 01 between the alignment direction of the upper layer 10 and that of the lower layer 11 is directed to the LC injection direction.

When the upper layer of LC formed by said method is irradiated with the linearly polarized ultraviolet in different polarized direction than the previous irradiation, the alignment direction is determined according to the polarized direction of the ultraviolet irradiating at that time, regardless of the polarized direction previous. If the polarized direction of UV light into the upper layer 10 is shifted to form perepndicular between alignment direction of upper layer 10 and that of lower layer 11, the alignment direction of the upper layer 10 will be shifted but that of lower layer 11 will be fixed. Therefore, it is possible to obtain the TN LC cell of FIG.5f in which the alignment direction of the upper layer 10 is perpendicular to that of the lower layer 11.

FIG. 6 is illustrating the second embodiment of the present invention. FIG.6a shows the LC cell which has an angle 02 between the alignment direction of the upper layer 10 and that of the lower layer 11 determined by irradiating the polarized ultraviolet. Then, when the LC is injected such as the direction of the first 1.

13 embodiment, alignment directions of the upper layer 10 and lower layer 11 are directed to the injection direction having angle 02, owing to the injection effect, as shown in FIG.6b. The ultraviolet is irradiated for the alignment direction of the upper layer 10 to be perpendicular to that of the lower layer 11 by shifting the polarized direction of the ultraviolet as showing FIG.6c. Therefore, when LC injected into TN cell, the TN LC cell in which LC molecules is twisted between upper layer 10 and the lower layer 11, can be obtained.

After blocking the first domain of upper layer 10 with a mask such as a photoresist, the ultraviolet light is irradiated to the second domain of upper layer 10 in different direction than with the first domain of upper layer 10. Then, the cell is turned back, the first domain of lower layer 11 is blocked with a mask such as a photoresist, and the ultraviolet light is irradiated to the second domain of lower layer 11 in different direction than with the first domain of lower layer 11. The photoresist used both subatrates is removed, as a result, it is obained that twodomain LC cell has the first domain and the second domain which have different alignment directions each other.

Although this embodiment includes the twodomained LC cell which formed by shifting the polarized 14 direction and being irradiated of the ultraviolet light, after blocking the first domain of the substrate with a mask, it is possible to use the other mask which is changed in terms of the shape and size, and it is also possible to obtain the multi-domain LC cell such as 4domain by irradiating the ultraviolet light repeatedly. It is easy to determine the alignment direction because the alignment direction of an alignment layer is determined by the last irradiating the ultraviolet light, and it is also possible to make LC cell desired alignment direction by irradiating the ultraviolet light again after the injection of LC. Also, the multi- domain LC cell in which each domain has a different alignment direction is easily fabricated by irradiating the ultraviolet light using a mask.

It is to be understood that the form of the prevent invention herein show and described is to be taken as a preferred example of the same and that various application may be resorted to without departing from the spirit of the prevent invention or the scope of the subjoined claims.

1,

Claims

1. A method for fabricating a liquid crystal cell comprising the steps of: irradiating an alignment layer of said liquid crystal cell with a first polarized light to impart a first alignment direction in said alignment layer; and irradiating said alignment layer with a second polarized light to impart a second alignment direction in said alignment layer which is different than said first alignment direction.

2. A method for fabricating a liquid crystal cell in accordance with claim 1, wherein said alignment layer includes polyvinylfluorocinnamate.

3. A method for fabricating a liquid crystal cell in accordance with claim 1, wherein said alignment layer includes polysiloxane based materials.

4. A method for fabricating a liquid crystal cell comprising the steps of: irradiating a first alignment layer of said liquid crystal cell with a first polarized ultraviolet light to set a first alignment direction in said first 16 alignment layer; irradiating a second alignment layer of said liquid crystal cell with a second polarized ultraviolet light to set a second alignment direction in said second alignment layer; and irradiating one of said first and sec6nd alignment layers with a third polarized ultraviolet light to change one of said first and second alignment directions.

5. A method for fabricating a liquid crystal cell in accordance with claim 4, wherein said first and second alignment layers include polyvinylfluorocinnamate.

6. A method for fabricating a liquid crystal cell in accordance with claim 4, wherein said first and second alignment layers include polysiloxane based materials.

7. A method for fabricating a liquid crystal cell in accordance with claim 4, further comprising a step of injecting liquid crystal material between said first and second alignment layers after said first and second alignment directions have been set.

17 8. A method for fabricating a liquid crystal cell in accordance with claim 4, further comprising a step of injecting liquid crystal material between said first and second alignment layers after said step of irradiating one of said first and second alignment layers with the third polarized ultraviolet light.

9. A method for fabricating a liquid crystal cell comprising the steps of: irradiating a first alignment layer of said liquid crystal cell with a first polarized ultraviolet light to set a first alignment direction in said first alignment layer; irradiating a second alignment layer of said liquid crystal cell with a second polarized ultraviolet light to set a second alignment direction in said second alignment layer; blocking a part of said first alignment layer with a mask; irradiating a first alignment layer of said liquid crystal cell with a third polarized ultraviolet light to set a third alignment direction in said first alignment layer; blocking a part of said second alignment layer with a mask; 18 irradiating a second alignment layer of said liquid crystal cell with a fourth polarized ultraviolet light to set a fourth alignment direction in said second alignment layer; removing said mask.

10. A method for fabricating a liquid crystal cell in accordance with claim 9, wherein said first and second alignment layers include polyvinylfluorocinnamate.

11. A method for fabricating a liquid crystal cell in accordance with claim 9, wherein said first and second alignment layers includes polysiloxane based materials.

12. A method for fabricating a liquid crystal cell in accordance with claim 9, further comprising a step of injecting liquid crystal material between said first and second alignment layers after said first and second alignment directions have been set.

j ' 19 13. A method for fabricating a liquid crystal cell comprising providing an alignment layer including polyvinylfluorocinnamate or polysiloxane based materials, and irradiating the alignment layer with polarised light, the alignment direction being determined by the polarisation direction of only the last irradiated light.

14. A method for fabricating a liquid crystal cell substantially as hereinbefore described with reference to and/or as illustrated in any one of or any combination of Figs. 2, 3, 4, 5a - 5f, and 6a - 6f of the accompanying drawings.

is. A liquid crystal cell substrate having an alignment layer comprising polyvinylfluorocinnamate or polysiloxane based materials.

16. A liquid crystal cell substrate substantially as hereinbefore described with reference to and/or as illustrated in any one of or any combination of Figs. 2, 3, 4, Sa - 5f, and 6a - 6f of the accompanying drawings.

AMENDMENTS TO THE CLAIMS HAVE BEEN FILED AS FOLLOWS:

-10 A method for fabricating a liquid crystal cell comprising the steps of:

irradiating an alignment layer of said liquid crystal cell with a first polarized light to impart a first alignment direction in said alignment layer; and irradiating again said alignment layer with a second polarized light having a different polarized direction from that of said first polarized light so as to determine a second alignment direction in said alignment layer, the second alignment direction being changed from the first alignment direction by the irradiation of the second polarized light, the second alignment direction being directed in the different direction than said first alignment direction.

2. A method for fabricating a liquid crystal cell in accordance with claim 1, wherein sa id alignment layer includes polyvinylfluorocinnamate.

A method for fabricating a liquid crystal cell in accordance with claim 1, wherein said alignment layer includes polysiloxane based materials.

4. A method for fabricating a liquid crystal cell comprising the steps of irradiating a first alignment layer of said liquid crystal cell with a first polarized ultraviolet light to set a first alignment direction in said first 2-1 alignment layer; irradiating a second alignment layer of said liquid crystal cell with a second polarized ultraviolet light to set a second alignment direction in said second alignment layer; and irradiating one of said first and sec6nd alignment layers with a third polarized ultraviolet light to change one of said first and second alignment directions.

5. A method for fabricating a liquid crystal cell in.accordance with claim 4, wherein said first and second alignment layers include polyvinylfluorocinnamate.

7. A method for fabricating a liquid crystal cell in accordance with claim 4, further comprising a step of injecting liquid crystal material between said.first and second alignment layers after said first and second alignment directions have been set.

2-2- 8. A method for fabricating a liquid crystal cell in accordance with claim 4, further comprising a step of injecting liquid crystal material between said f irst and sec ond alignment layers after said step of irradiating one of said first and second alignment layers with the third polarized ultraviolet light.

steps of:

9. A method for fabricating a liquid crustal cell comprising the irradiating a first alignment layer of said liquid crystal cell with a first polarized ultraviolet light to set a first alignment direction in said first alignment layer, said first alignment layer including a first region and a second region; irradiating a second alignment layer of said liquid crystal cell with a second polarized ultraviolet light to set a second alignment direction in said second alignment layer, said second alignment layer including a third region and a fourth region; irradiating again said first region of said first alignment layer with a third polarized ultraviolet light having a different polarized direction from that of said first polarized ultraviolet light so as to determine a third alignment direction, said third alignment direction being changed from said first alignment direction by the irradiation of the third polarized ultraviolet light; and irradiating again said third region of said second alignment layer with a fourth polarized ultraviolet light having a different polarization di rection from that of said second polarized ultraviolet light so as to determine a fourth C 2, alignment direction, said fourth alignment direction being changed from said second alignment direction by the irradiation of said fourth polarized ultraviolet light.

10. A method for fabricating a liquid crystal cell in accordance with claim 9, wherein said first and second alignment layers include polyvinylfluarocinnamate.

1 Z 4- 13. A method for fabricating a liquid crystal cell comprising providing an alignment layer including polyvinylfluorocinnamate or polysiloxane based materials, and irradiating the alignment layer with polarised light, the alignment direction being determined by the polarization direction of only the last irradiated light.

14. A method of manufacturing a liquid crystal cell comprising: irradiating an alignment layer with a first polarised ultraviolet light to set a first alignment direction in said alignment layer, said alignment layer including a first region and a second region; providing a mask on said alignment layer to block said second region; irradiating the entire alignment layer with a second polarized ultraviolet light having a different polarized direction from that of said first polarized ultraviolet light so as to impart a second alignment direction to said first region, said second alignment direction being changed from said first alignment direction by the irradiation of the second polarized ultraviolet light; and removing the mask.

A method according to claim 14, wherein the alignment layer includes polyvinylfluorocinnamate.

16. A method according to claim 14, wherein the alignment layer includes polysiloxane based materials.

17. A method for fabricating a liquid crystal cell substantially as hereinbefore described with reference to and/or as illustrated in any one of or any combination of Figs. 2, 3, 4, 5a - 5f, and 6a - 6f of the accompanying drawings.

26 18. A liquid crystal cell substrate substantially as hereinbefore described with reference to and/or as illustrated in any one of or any combination of Figs. 2, 3, 4, 5a - 5f, and 6a - 6f of the accompanying drawings.