GB2085465A - Afterglowing transparent material and a process for its manufacture - Google Patents

Abstract

An afterglowing transparent material is produced by the vulcanisation and cross-linking of a mixture containing 65-80 parts by weight of a silicone rubber, 0.5-1 part by weight of a cross-linking agent, 15-30 parts by weight of an after- glowing or luminous powder and 2 to 5 parts by weight of silicone oil or a silicone rubber base polymer, optionally with additives such as organic silane and highly active silica. The material is preferably moulded in the form of wall cladding elements with a thickness of 1 to 5 mm and may be used for signs or emergency lighting. The silicone rubber may a polysiloxane and silicic acid and the phosphors ZnS or CdS. According to whether the composition is hot or cold vulcanising, the silicone oil may be a vinyl alkoxy silane or methyl triacetyl silane.

Description

SPECIFICATION Afterglowing transparent fabric and a process for its manufacture The invention concerns an afterglowing transparent fabric and a process for its manufacture. The fabric is to be produced particularly in the form of wall facing or cladding elements in a thickness of 1 to 5 mm.

The phenomenon of luminescence is generally known and is also exploited practically in various fields, e.g. in the production of tubular discharge lamps and television screens. A body luminesces when under the effect of a non-thermal excitation it emits light. The emission of light may be maintained after the disappearance of the source of excitation, i.e.

the body afterglows. Shorter afterglowing is designated as fluorescence while longer afterglowing is designated as phosphorescence, (see Miiszaki Lexikon Akadémia Kiad6, Budapest 1 972 Volume 2), (Technical Encyclopaedia, Academic Press, Budapest 1972). According to the type of excitation one distinguishes between electro-luminescence, photoluminescence bio-luminescence and galvanoluminescence.

The designation of afterglowing "light" powders collects together a group of materials which under the effect of electronic or electromagnetic radiation emit light and, even after the disappearance of the exciting source of radiation, afterglow for a certain time. These "light" powders are, in the main, inorganic compounds. This property is particularly strongly marked in the sulphides of alkaline earth metals when they contain traces of salts of heavy metals. Other compounds containing a small amount of foreign atoms as activators exhibit afterglow, e.g. zinc sulphide, cadmium sulphide, gallium arsenide etc.

In addition to the already mentioned discharge and electron tubes, other areas of use of the "light" powder include luminous paints, e.g. for marking air-raid shelters.

In the technology of safety lighting and protection against accidents, there is a definite need for working materials, especially surface cladding or panel elements which by virtue of accumulating natural or artificial light may on cessation of illumination afford emergency lighting for a predetermined length of time; which have suitable rigidity, are self-supporting, and relatively inexpensive and which may be manfactured in a simple manner. At present no working material is known which can completely satisfy all these demands.

The present invention seeks to satisfy the said demands and to provide an afterglowing transparent flat surface fabric; the fabric according to the invention is produced from: 65 to 80 parts by weight of silicone rubber 0.5-1 parts by weight of a cross-linking agent 15-30 parts by weight of long-afterglowing "light" powder (luminous powder), 2-5 parts by weight of silicone oil and/or a silicone rubber base polymer, and optionally additives, such as 0.1-2 parts by weight of an organic silane and optionally 3-40 parts by weight of active silica.

Preferably the fabric or material contains as luminous powder zinc sulphide activated with copper in a hexagonal crystal structure. In a preferred embodiment of the surface fabric according to the invention, the fabric is manufactured from colourless transparent components, with the exception of the luminous powder. The surface material or fabric according to the invention may be provided on one side thereof with a self-adhering coating or with a light-reflecting layer. The'specific amount or quantity of the luminous powder calculated on the surface of the fabric amounts to about 1 00-2,1 00 g/m2, preferably 200-1500 g/m2.

According to another aspect of the invention, there is provided a process for the manufacture of an afterglowing transparent surface or flat fabric, wherein: 65-80 parts by weight of silicone rubber, 0.5-1 parts by weight of a cross-linking agent, 15-30 parts by weight of an afterglowing luminous powder, 2-5 parts by weight of silicone oil and/or a silicone rubber base polymer, and optionally additives, are homogenised together, the mixture is shaped and vulcanised, in given cases with the aid of heat and/or pressure. Expediently, the luminous powder used in the process is zinc sulphide activated with copper, in a hexagonal crystal structure.

Zinc sulphide provides a greenish-yellow light.

To achieve other colours, other luminous powders may, however, by used, e.g. cadmium sulphide. It is possible, and in many cases advantageous, to mix together different luminous powders. For instance, by making mixtures containing differing ratios of zinc sulphide and cadmium sulphide many shades or transitions between greenish-yellow and brick- red may be achieved.

Both hot-vulcanisable and cold-vulcanisable silicone rubber types may be used. For instance, mixtures of dimethylpolysiloxane and highly active silicic acid are commercially available. It is important that the siloxane should not contain, besides the highly dispersed silicic acid, further fillers or pigments, because these would degrade the transparency and the light-absorptivity and emissivity.

The single inactive filling material in the flat material according to the invention is the luminous powder itself.

As cross-linking agent organic peroxides are preferred, e.g. 2,4-dichlorobenzoylperoxide, benzoylperoxide, dicumylperoxide etc.

The silicone oil or silicone rubber prepolymer has a preferred viscosity of 200-60,000 cP. In the case of hot-vulcanising rubber types, vinyltriethoxysilane or vinyl (methoxy-ethoxy)-silane may be used, whereas for cold-vulcanising types, methyltriacetylsilane is preferred. The silicone oil or prepolymer act as dispersing agents in the preparation of the raw or basic mixture.

The afterglowing surface material or fabric according to the invention will be produced in per se known methods employed customarily in the plastics and rubber industries. The homogenisation of the compounds takes place in roller mills or in a Banbury mixer at temperatures which prevent a "start" of the mixture.

The mixture may be shaped in the usual manner under pressure for instance in a multistage press and pre-vulcanised at temperatures of 11 0-1 40'C. The already solidified, no longer flowing product is then taken from the press and in order to remove traces of plasticiser and decomposition products, is freely vulcanised for a longer time at 1 80-250 C.

More modern processes of higher productivity are injection-moulding and extrusion. In these processes, the operating temperatures are higher and therefore the throughput times are correspondingly shorter. At temperatures between 1 80 and 250"C, the working material according to the invention may be extruded as endless strips or sheets at rates between 3-1 5 m/s, depending on the thickness. Where the working material according to the invention is provided on one side with a self-adhering layer, then the non-adhesive paper side of this layer may serve as a separation paper when the extruded sheet or strip is wound up into rolls.

The invention will be described more particularly by way of a preferred but non-limiting example.

Example A mixture consisting of 40 parts by weight of dimethylpolysiloxane, 35 parts by weight of highly dispersed silicic acid and 0.75 parts by weight of 2,4-dichlorobenzoylperoxide is homogenised in the cold state (1 5-35 C) for 10-15 minutes in a roller mill. Then, 20 parts by weight of zinc sulphide activated with copper are worked into the mixture, also in the cold state. The uniform distribution of the luminous powder indicates the attainment of homogeneity. The mixture is then placed in a vulcanising mould and is vulcanised in a multi-stage press at a pressure of 20-120 kp/cm2 and at a temperature of 1 10-140 C for 1 5 minutes, these parameters depending on the size of the mould.This pre-vulcanisation is then followed by a separation of the press and the semi-vulcanised product is taken from the mould and is then freely vulcanised for another 4 hours, at 230"C, in order to remove decomposition products and also to achieve complete cross-linking.

The afterglowing transparent material according to the invention is resilient, (elastic), corrosion-resistant, can be subjected to temperatures between - 30 and + 300"C and produces a smooth workable surface cladding.

The surface material accumulates a significant.

portion of the light to which it is exposed.

After disappearance of the effect of light, the surface remains, in dependence upon the intensity and duration of the illumination, afterglowing or self-illuminated for a considerable length of time. For instance, after half an hour of illumination with 30 lux the surface material emits light for at least 30 minutes after the disappearance of the source of light at an intensity which in most cases is sufficient for the continuation or termination of the previous activity or for the repair of the original source of light. Although the light provided by the material gets steadily weaker, the human eye nevertheless partially compensates this reduction of intensity by accommodation.

Suitable light-absorbing symbols may be arranged on the afterglowing surface whereby in spaces provided with wall-cladding made of the material according to the invention safety instructions and signs may be applied, e.g. for emergency exits, fire extinguishers, telephones. Such an emergency lighting is needed for instance in mining, in underground transport systems, and in certain buildings etc.

Nevertheless, the use of the material according to the invention is not restricted to the field of safety technology. For instance, the applicability of the invention also extends to self-adhering special effect wall hangings, or wall tilings measuring 1 5 X 1 5 cms which are washable and afterglowing, in decorating or dressing display windows, in the field of advertising etc.

Claims (14)

1. Afterglowing transparent surface material produced by vulcanisation of a mixture including 65-80 parts by weight of a silicone rubber 0.5-1 parts by weight of a cross-linking agent 15-30 parts by weight of an afterglowing luminous powder, 2-5 parts by weight of a silicone oil or a silicone rubber base polymer, and optionally additives such as organic silane and highly active silica, by cross-linking.

2. Material according to claim 1, wherein the luminous powder in copper-activated zincsulphide in a hexagonal crystal structure.

3. Material according to claim 1 or claim 2, wherein with the exception of the luminous powder, all the components are colourless and transparent.

4. Material according to any preceding claim, wherein the material is provided with a self-adhesive coating on one side thereof.

5. Material according to any one of claims 1 to 3, wherein one side of the material is provided with a light-reflecting layer.

6. Material according to any preceding claim, wherein the material contains, calculated on its surface area, luminous powder in the specific quantity of 100-2,100 g/m2, preferably 200-1500 g/m2.

7. A material according to claim 1, substantially as herein described with reference to the example.

8. A process for the production of an afterglowing transparent surface material wherein: 65-80 parts by weight of a silicone rubber, 0.5-1 parts by weight of a cross-linking agent, 15-30 parts by weight of a luminous powder, and 2-5 parts by weight of silicone oil and/or a silicone rubber base polymer, and optionally additives, are homogenised together, shaped and vulcanised, optionally under the effect of heat and/or pressure.

9. A process according to claim 8, wherein the luminous powder is copper-activated zinc-sulphide of a hexagonal crystal structure.

1 0. A process according to claim 8 or claim 9, wherein the cross-linking agent is an organic peroxide.

11. A process according to any of claims 8 to 10, wherein a prepolymer with a viscosity of 200-60,000 cP is used as the silicone rubber base polymer.

1 2. A process according to any one of claims 8 to 11, wherein a hot-vulcanisable silicone rubber starting material is used, the homogeneous mass is first prevulcanised in a mould under pressure and at a temperature of 110-140"C and then fully vulcanised by free vulcanisation at 1 80-250'C.

1 3. A process according to any of claims 8 to 12, wherein the mass or mixture is shaped in an extruder.

14. A process according to claim 8, substantially as herein described with reference to the example.

1 5. An afterglowing transparent material whenever produced by the process claimed in any of claims 8 to 14.