GB2049973A

GB2049973A - Method of sealing the margins of liquid crystal cells

Info

Publication number: GB2049973A
Application number: GB8013403A
Authority: GB
Original assignee: BBC Brown Boveri AG Switzerland; BBC Brown Boveri France SA
Current assignee: BBC Brown Boveri AG Switzerland; BBC Brown Boveri France SA
Priority date: 1979-04-25
Filing date: 1980-04-23
Publication date: 1980-12-31
Also published as: DE2916722A1

Abstract

In a method of sealing the margins of a liquid crystal cell, after application of the electrodes 4 and liquid crystal orientation layers 3, the two glass plates (1, 2) forming the cell are each provided at their edges with a thermoplastics layer (6) 4-5 mu m thick, preferably by screen printing. Glass beads (5) are embedded in the thermoplastics layers as spacers. The thermoplastics layers are freed of solvents and dried by heating to 180 DEG C. After cooling to 120-125 DEG C, the liquid crystal composition (9) is applied to the lower glass plate. Then the upper glass plate (2) is lowered onto it and the two plates are maintained under pressure and heat to seal the edges. The invention renders possible the sealing of liquid crystal cells at relatively low temperatures. <IMAGE>

Description

SPECIFICATION Method of sealing the margins of liquid crystal cells This invention relates to a method of sealing the margins of liquid crystal cells by means of plastics material.

Liquid crystal incidicating cells generally consist of parallel, plane plates, each provided with a conducting, transparent electrode pattern, the plates being disposed with a spacing of about 10 ym and the gap filled with the liquid crystal composition. This cell is sealed around its edges.

Polarization foils are adhered to the cell at the front and back. When a voltage is applied to selected opposite front and rear electrodes, the interposed liquid crystal layer changes with regard to its optical activity, so that the polarization plane of the light passing through it is rotated, as a result of which, according to the arrangement of the polarization foils with the preferred axes parallel or perpendicular to one another, the addressed pattern appears bright on a dark background or dark on a light background.

Important for the life of liquid crystal cells is, inter alia, the satisfactory sealing at the edges. For this it is known to use glass solder but this requires temperatures of about 5000C and therefore involves difficulties. It is also known to use epoxide resins which harden cold for the sealing; but these contaminate the liquid crystal composition with ions.

In accordance with this invention, there is provided a method of sealing the margins of a liquid crystal cell, comprising providing at least one of the two plates forming the cell with a thermoplastics layer around its edge, which is then baked at an elevated temperature, at least one solid element being provided to form a spacer between the two plates, and then lowering the temperature to a less elevated temperature, supplying liquid crystal composition to an upwardly-facing lower plate, lowering the other plate onto it, pressing the two plates together so that any excess liquid crystal composition is squeezed out and sealing around the edges of the cell is effected by pressure on said edges. This method of sealing liquid crystal indicationg cells does not require high temperatures nor does it contaminate the liquid crystal.

Thus, after applying the electrodes and the liquid crystal orientation layers, either or both of the two plates forming the cell are provided at the edges with layers of thermoplastics preferably 4-5 ym thick, which are then freed of solvents by baking at preferably 1 800 C. After lowering the temperature to 120-1 250C, the liquid crystal composition is applied to the lower plate and the two plates are pressed together, the thermoplastic sealing of the cell being effected by pressure on the edges.

Glass beads with a diameter of about 8 ,um are preferably used as spacers. The diameter of the spacers depends on the gap required between upper and lower glass plate.

The thermoplastics layers are preferably screen printed. The plastics material may comprise a powder of a mixture of polystyrene and polymethylmethacrylate, suspended in spirit. The liquid evaporates and leaves the powder behind as a thermoplastics layer. The last residues of solvent are evaporated by the baking at about 1 800C; in addition, the thermoplastics materials are cross-linked with one another and after prolonged heating forming a thermosetting layer.

For this reason, the baking operation at 1 800C should only be carried out briefly. The final hardening is effected during the final heat treatment at about 1200 to 1 250C.

An embodiment of this invention will now be described, by way of example only, with reference to the accompanying drawing, the singie figure of which is a cross-section through a liquid crystal cell.

The cell shown in the drawing comprises a lower glass plate 1 and an upper glass plate 2, disposed parallel and spaced apart from one another. On the upper side of the lower glass plate 1 there is disposed a thin-film circuit 7 with active and passive components, which serves to control the image dots. Furthermore, at the two adjacent sides of the glass plates 1,2 there are disposed transparent electrodes 4 and liquid-crystal orientating layers 3. The marginal sealing 6 compises thermoplastic layers applied to both glass plates 1,2 by means of screen printing, to a thickness of 4-5 Clam. Glass beads 5 introduced into the thermoplastic layers serve as spacers.

They determine the gap between the two glass plates 1,2 which receives the liquid crystals 9.

When the glass plates are pressed together, excess liquid crystal composition escapes as drops 8.

The plastics material, which is capable of screen printing and in which the glass beads 5 of about 8 Fm in diameter are embedded, is applied by means of a screen printing mask to the edges of the two glass plates 1,2 over a width of about 1 mm, dried and polymerized at 1800 C. After the plates have cooled to about 120 to 1 250C, the liquid crystal 9 is supplied as drops to the lower glass plate 1. The second plate 2 is slowly lowered onto the first plate 1. Then the cell edges are pressed together and the cell is maintained for about 1 5 minutes at about 1 20 C, still with the edges under pressure. In the course of this, the glass plates approach one another to within the distance of about 8 4m determined by the glass beads 5 and the previously thermoplastic layers acquire thermosetting characteristics. Any air bubbles can be removed by slow parallel displacement of the plates until the two plates are firmly connected to one another.

1. A method of sealing the margins of a liquid crystall cell, comprising providing at least one of the two plates forming the cell with a therrnoplastics layer around its edge, which is then baked at an elevated temperature, at least

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. SPECIFICATION Method of sealing the margins of liquid crystal cells This invention relates to a method of sealing the margins of liquid crystal cells by means of plastics material. Liquid crystal incidicating cells generally consist of parallel, plane plates, each provided with a conducting, transparent electrode pattern, the plates being disposed with a spacing of about 10 ym and the gap filled with the liquid crystal composition. This cell is sealed around its edges. Polarization foils are adhered to the cell at the front and back. When a voltage is applied to selected opposite front and rear electrodes, the interposed liquid crystal layer changes with regard to its optical activity, so that the polarization plane of the light passing through it is rotated, as a result of which, according to the arrangement of the polarization foils with the preferred axes parallel or perpendicular to one another, the addressed pattern appears bright on a dark background or dark on a light background. Important for the life of liquid crystal cells is, inter alia, the satisfactory sealing at the edges. For this it is known to use glass solder but this requires temperatures of about 5000C and therefore involves difficulties. It is also known to use epoxide resins which harden cold for the sealing; but these contaminate the liquid crystal composition with ions. In accordance with this invention, there is provided a method of sealing the margins of a liquid crystal cell, comprising providing at least one of the two plates forming the cell with a thermoplastics layer around its edge, which is then baked at an elevated temperature, at least one solid element being provided to form a spacer between the two plates, and then lowering the temperature to a less elevated temperature, supplying liquid crystal composition to an upwardly-facing lower plate, lowering the other plate onto it, pressing the two plates together so that any excess liquid crystal composition is squeezed out and sealing around the edges of the cell is effected by pressure on said edges. This method of sealing liquid crystal indicationg cells does not require high temperatures nor does it contaminate the liquid crystal. Thus, after applying the electrodes and the liquid crystal orientation layers, either or both of the two plates forming the cell are provided at the edges with layers of thermoplastics preferably 4-5 ym thick, which are then freed of solvents by baking at preferably 1 800 C. After lowering the temperature to 120-1 250C, the liquid crystal composition is applied to the lower plate and the two plates are pressed together, the thermoplastic sealing of the cell being effected by pressure on the edges. Glass beads with a diameter of about 8 ,um are preferably used as spacers. The diameter of the spacers depends on the gap required between upper and lower glass plate. The thermoplastics layers are preferably screen printed. The plastics material may comprise a powder of a mixture of polystyrene and polymethylmethacrylate, suspended in spirit. The liquid evaporates and leaves the powder behind as a thermoplastics layer. The last residues of solvent are evaporated by the baking at about 1 800C; in addition, the thermoplastics materials are cross-linked with one another and after prolonged heating forming a thermosetting layer. For this reason, the baking operation at 1 800C should only be carried out briefly. The final hardening is effected during the final heat treatment at about 1200 to 1 250C. An embodiment of this invention will now be described, by way of example only, with reference to the accompanying drawing, the singie figure of which is a cross-section through a liquid crystal cell. The cell shown in the drawing comprises a lower glass plate 1 and an upper glass plate 2, disposed parallel and spaced apart from one another. On the upper side of the lower glass plate 1 there is disposed a thin-film circuit 7 with active and passive components, which serves to control the image dots. Furthermore, at the two adjacent sides of the glass plates 1,2 there are disposed transparent electrodes 4 and liquid-crystal orientating layers 3. The marginal sealing 6 compises thermoplastic layers applied to both glass plates 1,2 by means of screen printing, to a thickness of 4-5 Clam. Glass beads 5 introduced into the thermoplastic layers serve as spacers. They determine the gap between the two glass plates 1,2 which receives the liquid crystals 9. When the glass plates are pressed together, excess liquid crystal composition escapes as drops 8. The plastics material, which is capable of screen printing and in which the glass beads 5 of about 8 Fm in diameter are embedded, is applied by means of a screen printing mask to the edges of the two glass plates 1,2 over a width of about 1 mm, dried and polymerized at 1800 C. After the plates have cooled to about 120 to 1 250C, the liquid crystal 9 is supplied as drops to the lower glass plate 1. The second plate 2 is slowly lowered onto the first plate 1. Then the cell edges are pressed together and the cell is maintained for about 1 5 minutes at about 1 20 C, still with the edges under pressure.In the course of this, the glass plates approach one another to within the distance of about 8 4m determined by the glass beads 5 and the previously thermoplastic layers acquire thermosetting characteristics. Any air bubbles can be removed by slow parallel displacement of the plates until the two plates are firmly connected to one another. CLAIMS

1. A method of sealing the margins of a liquid crystall cell, comprising providing at least one of the two plates forming the cell with a therrnoplastics layer around its edge, which is then baked at an elevated temperature, at least one solid element being provided to form a spacer between the two plates, and then lowering the temperature to a less elevated temperature, supplying liquid crystal composition to an upwardly-facing lower plate, lowering the other plate onto it, pressing the two plates together so that any excess liquid crystal composition is squeezed out and sealing around the edges of the cell is effected by pressure on said edges.

2. A method as claimed in claim 1, in which a said thermoplastics layer is applied to both plates to a thickness of 1 5 cm.

3. A method as claimed in claim 1 or 2, in which said baking is effected at 1800 C.

4. A method as claimed in any preceding claim, in which said less elevated temperature is 120-1 250C.

5. A method as claimed in any preceding claim, in which glass beads are used as spacer elements.

6. A method as claimed in any preceding claim, in which the thermoplastic layers are screen printed.

7. A method as claimed in claim 6, in which a mixture of polystyrene and polymethylmethacrylate in spirits is used to screen-print said thermoplastic layers.

8. A method of sealing the margins of a liquid crystal cell, substantially as herein described with reference to the accompanying drawing.

9. A liquid crystal cell having its margins sealed by a method as claimed in any preceding claim.