GB2090011A

GB2090011A - Electro-optical display element

Info

Publication number: GB2090011A
Application number: GB8135709A
Authority: GB
Original assignee: SWF Spezialfabrik fuer Autozubehoer Gustav Rau GmbH
Current assignee: SWF Auto Electric GmbH
Priority date: 1980-12-24
Filing date: 1981-11-26
Publication date: 1982-06-30
Also published as: GB2090011B; FR2496907A1; FR2496907B1; JPS57135925A; DE3049092A1

Abstract

A cell for an electro-optical display element includes at least one pair of electrically non-conductive plates (20, 21) connected with each other along their edges by a layer (50) of a linear polyester which may be polyalkylene terephthalate and is preferably polyethylene terephthalate and provided with electrically conductive layers (30, 31). At least one of the pates and one of the electrically conductive layers are transparent and between the plates is formed an interspace for receiving a light-controlling colloid-disperse system. <IMAGE>

Description

SPECIFICATION Electro-optical display element This invention relates to a cell for an electrooptical display element, of the kind which includes at least one pair of electrically non-conductive plates connected with each other along their edges and which is provided with electrically conductive layers, and wherein at least one of the plates arid one of the electrically conductive layers are transparent and between the plates is formed an interspace for receiving light-controlling colloiddisperse systems.

Electro-optical display elements are known which include colloid-disperse systems with light controlling qualities. These electo-optical display elements are hereafter called colloidal displays.

The cells for colloidal displays consist preferably of two flat glass plates arranged parallel relative to each other with a very small mutual spacing. These glass plates are provided with thin, transparent, electrically conductive coatings which are connected to a source of current or to a voltage source. The plates are hermetically connected with each other along their edges.

Due to the chemical instability of many colloiddisperse systems, in particular of colloidal suspensions, the usual methods known from the production of cells for liquid crystal displays are not suitable for the production of colloidal displays.

For example, when using plate-connecting means such as glass melting at low temperatures (as, for example, known from German specification AS 21 59 165), sodium ions can diffuse into the colloidal system. With epoxy adhesives, (for example known from the European specification OS 13 875) monomers not compatible with the colloidal system can be dissolved out, thus resulting in a catalytically conditioned decay of a coiloid-disperse system, coagulation of the colloidal particles and changes in the colour of the colloidal display which is therefore unserviceable. The fluor-containing polymers described in US patent specification 3,871,746 as a connecting means for cells of liquid crystal displays require proof against corrosion and thus necessitate expensive machines and form tools as well as extensive safety precautions.

it is an object of the present invention to create a cell for a colloidal display, which cell is chemically and thermally stable, has a high mechanical stability and small spacing tolerances and can be produced simply and economically.

According to the invention in its broadest aspect, an electro-optical display element of the kind referred to is characterised in that the plates are connected by a linear polyester.

Due to their resistance to solvents, their high mechanical stability, their thermal resistance and their indifference to moisture as well as their aging stability, linear polyesters are suitable for the production of colloidal display cells.

In particular, polyalkylene terephthalates especially polyethylene terephthalate have proved to be suitable for this purpose. Polyethylene terephthalate is distinguished by its inert behaviour with respect to the chemical substances normally used in colloidal displays.

It has become obvious that it is especially advantageous from the viewpoint of production and costs to use polyester foils as available on the market, especially polyethylene terephthalate foils.

They are distinguished by an extremely high mechanical and electrical stability, and they are flexible and therefore available unplasticised, whereby the influence of foreign substances on the colloidal system in further reduced.

In the same way also, pulverised or granular types of linear polyesters are suitable for the connection of the colloidal display plates.

In order to achieve and retain a defined spacing between the display cell plates, spacing elements are used which are advantageously arranged in the connecting polyester layer.

Because, during the production process, the cell to be produced can be exposed to increased pressures and temperatures it is necesary that the spacing elements have a greater hardness than the polyester layer between the plates and a higher melting point than the linear polyester used.

Due to the fact that they belong to the thermoplastic group and due to their advantageous thermal qualities, linear polyesters can be used as hot glues. Hot glues are glues which are in solid condition at room temperature and are melted before the gluing process. After the cooling-off process the glue is again in the solid condition. Cells for colloidal displays can be produced in which the plates are connected by hot gluing with a linear polyester.

Usually hot-gluing processes are carried out under increased pressure. This reduces the thickness of many gluing layers. In order to achieve a defined spacing it has proved to be necessary that, when polyester foils are used, the foils have to be one and a half times to twice as thick as the desired spacing.

A desired spacing between the plates can be adhered to by introducing a unitary layer of spacing elements on a polyester foil and pressing them into it.

It is also possible to mix a pulverised or granular substance formed from a linear polyester with spacing elements and extrude them on to foil. This saves the pressing-in of the spacing elements. The foil is matchingly introduced on one of the display plates, the second plate is adjusted thereon and the parts are interconnected under application of increased temperature and increased pressure.

A further hot-gluing process according to the invention for the connection of colloidal display plates by a linear polyester layer can be achieved by using a pulverised and granular substance. For this purpose the substance is mixed with a volatilisable liquid and is introduced on to at least one of the plates, the liquid is completely volatilised and the parts inteconnected under the exertion of an increased temperature and an increased pressure.

An especially reliable connection and sealing of the parts is achieved, when, after the hot-gluing, the cooling off is effected gradually, whereby the contact pressure is retained.

The openings in one of the display plates or in the polyester layer, which openings serve for filling in the colloid-disperse system and for the pressure compensation necessary for this purpose, are thereafter advantageously closed with linear polyester stoppers.

According to the method of the present invention colloidal display cells of any desired dimensions can be produced.

A defined wall spacing in the middle areas of large-area cells can be secured in that layer of linear polyester is also arranged there.

In the same way, colloidal display cells with any number of partitions can be produced bya method in which between the plates to be connected a layer of linear polyester is introduced and then the whole is connected to a unit by hot-gluing.

An embodiment of the invention will now be described by way of example with reference to the accompanying drawings, in which: Fig. 1 is a perspective view of a cell for an electro-optical display element, Fig. 2 a section taken on the line 1I--II of Fig. 1, The colloidal display cells shown in the drawings are of the kind which, for example, as described by the German specification OS 2114 658, works with a suspension of particles in a liquid.

As can be seen from Figs. 1 and 2 the cell of an electro-optical display element 10 known as a colloidal display has two transparent plates 20, 21 which are preferably made of glass, plastics material or another strong, transparent material. The insides of the plates 20, 21 are provided with electrically conductive layers 30, 31, which form area electrodes and which can be connected with a current or voltage source 40 in order to apply excitation potential. The plates 20, 21 are arranged in parallel to each other and, around and alongside their edges, they are firmly connected by a linear polyester layer 50 and form a cell for receiving a colloidal suspension of particles 60 with a light-controlling qualities.

The linear polyester layer 50 includes a unitary layer of spacing elements 70 as shown in Fig. 2.

The spacing elements can consist of glass or quartz balls, inorganic pigments or the like, preferably of non-conducting material. In order to be able to endure the pressure load and temperature rise in the hot-gluing methods to be described the spacing elements 70 must have a greater hardness than the polyester layer 50 and a higher melting point than the linear polyester.

In one of the plates 20, 21 there are openings 80, 81, which are arranged approximately diagonally to each other and close to the edges of the plates 20, 21 and which serve for filling with the colloidal suspension 60 and for the pressure compensation necessary for this purpose. After filling with the suspension the openings 80, 81 are tightly closed by linear polyester stoppers 90, 91.

A colloidal display cell according to the features of the invention can be produced as described below by way of example.

A polyethylene foil, approximately 1 50 ,um thick and available on the market, is dusted with glass balls sieved out according to the diameters of about 100 ym, whereby attention has to be paid to ensure that a unitary layer of granules is generated and that the particles do not overlap.

The glass balls are pressed into the material under the application of a pressure of about 1000 N/cm2. Thereafter, the foil is cut or punched to the desired shape. The cut-out foil is introduced on a glass plate as an adhesive sealing, a further plate is adjusted thereon and the parts are pressed into a frame, so that cannot be displaced any more. Then, in a hot-gluing press for about five minutes, the whole is exposed to a temperature of about 2700C and to a pressure of about 50 N/cm2, with reference to the area of the foil. As a result, the polyethylene terephthalate melts and moistens the glass plate surfaces to the desired extent. The polyethylene terephthalate becomes solid and connects the plates to form a tight cell in the following gradual cooling-off process in which the contact pressure is retained.

Another method according to the invention can, for example, be realised by mixing a granular polyethylene terephthalate, as available on the market, with glass balls and extruding a foil, which will be processed as described above.

The plastics material can also be introduced on to the glass plates in a screen printing process. For this purpose, polyethylene granulates as available on the market are mixed with a volatilisable liquid and glass balls to a paste and this paste is introduced on a glass plate via a template. The liquid is volatilised in a drying stove, another glass plate is put on it and the whole is interconnected in a hot-gluing press as described above.

After filling the display cell with the colloiddisperse system, for example a colloidal suspension, the filling openings are closed with polyethylene terephthalate stoppers in the shape of a cone. The stoppers are secured with a conventionai contact adhesive which can be introduced by means of a hot-gluing pistol. The stoppers can also be secured by a reaction adhesive, for instance, an epoxy adhesive.

The cell elements achieved in such a way are distinguished by excellent chemical and thermal stability, indifference to atmospheric influences, high mechanical stabilty and small spacing tolerances.

Claims

1. A cell for an electro-optical display element, of the kind which includes at least one pair of electrically non-conductive plates connected with each other along their edges and which is provided with electrically conductive layers, and wherein at least one of the plates and one of the electrically conductive layers are transparent and between the plates is formed an interspace for receiving light-controlling colloid-disperse systems, characterised in that the plates (20, 21) are interconnected by a layer (50) of a linear polyester.

2. A cell according to claim 1, characterised in that the linear polyester is a polyalkylene terephthalate.

3. A cell according to claim 2, characterised in that the polyalkylene terephthalate is polyethlene terephthalate.

4. A cell according to any one of claims 1 to 3, characterised in that the cell (10) is provided with at least one opening (80, 81) for filling with the colloid-disperse system, which opening is arranged in the plates (20, 21) and/or in the linear polyester layer (50).

5. A cell according to any one of claims 1 to 4, characterised in that the linear polyester layer (50) between the plates (20, 21) is a foil.

6. A cell according to any one of claims 1 to 4, characterised in that the linear polyester layer (50) between the plates (20, 21) is a pulverised or granular substance of a linear polyester.

7. A cell according to any one of the preceding claims, characterised in that the plates (20, 21) are arranged parallel relative to each other with a defined, very small mutual spacing.

8. A cell according to claim 7, characterised in that spacing elements (70) are arranged between the plates (20, 21).

9. A cell according to claim 8, characterised in that the spacing elements (70) are arranged in the linear polyester layer (50) between the plates (20, 21).

10. A cell according to claim 9, characterised in that the spacing elements (70) have a greater hardness than the linear polyester layer (50) between the plates (20, 21).

11. A cell according to claim 9, characterised in that the spacing elements (70) have a higher melting point than the linear polyester arranged between the plates (20, 21).

12. A method for production of a cell for an electro-optical display element according to claim 1, characterised in that the plates are connected by hot-gluing with a linear polyester.

13. A method for the product of a cell for an electro-optical display element according to claim 12, characterised in that on one of the plates a layer of exactly the same size is introduced, which layer consists of a linear polyester foil which is about one and half times to twice as thick as the desired spacing of the plates, that the second plate is adjusted thereon and that the parts are connected under the application of increased temperature and increased pressure, and wherein the contact pressure is retained during the subsequent period of gradual cooling off.

14. A method of production of a cell for an electro-optical display element according to claim 13, characterised in that, prior to the connection of the plates, a unitary layer of spacing elements is introduced on the layer consisting of a linear polyester foil and pressed into it.

1 5. A method for the production of a cell for an electro-optical display element according to claim 13, characterised in that the foil consisting to a linear polyester layer is produced by extrusion after the spacing elements have been mixed with a pulverised or granular linear polyester substance.

1 6. A method for the production of a cell for an electro-optical display element according to claim 12, characterised in that a pulverised or granular substance of a linear polyester mixed with a volatilisable liquid is introduced on at least one of the plates, the liquid is completely volatilised and the parts are interconnected under exertion of increased temperature and increased pressure, and wherein the contact pressure is retained during the following period of gradual cooling off.

17. A method for the production of a cell for an electro-optical display element according to claim 4 and either of claims 13 or 16, characterised in that after filling in the colloid-disperse system the openings are closed by linear polyester stoppers.

1 8. A cell for an electro-optical display element substantially as described with reference to the accompanying drawings.

1 9. A method of making an electro-optical display element substantially as described with reference to the accompanying drawings.