IL25049A

IL25049A - Light-transmitting solid materials

Info

Publication number: IL25049A
Application number: IL6625049A
Authority: IL
Original assignee: Glaverbel
Priority date: 1965-03-23
Filing date: 1966-01-25
Publication date: 1969-07-30
Also published as: AT283627B; FI46719B; US3591248A; DE1596808A1; LU49672A1; GB1152691A; CH456062A; BE676679A; AT286522B; LU49816A1; ES322234A1; FI46719C; NL6603622A

Description

C O H E N Z E D E K & S P I S B A C H E G D. PAT E NT AT TO R N EYS 24, LE VON TIN ST R ., P. O. B. 1169 T E L - A V I V N T S & D E S I G N S O R D I N A N C E SPECIFICATION LIGHT-'-DHANSKITTING SOLID MATERIALS LAVEBBSL, a Belgian Socie¾e Anonyme , of 166, chaussee de la Hulpe , atermael - Boitsf otJb, Belgium, (formerly of 7 Avenue Louise, Bruxellfts 5, Belgium.); EBY DECLARE the nature of this invention and in what manner the same is to be performed to be particularly described and ascertained in and by the following statement: The present invention relates to... light-transmitting solid. materials particularly. lass, and to articles incorporating such. materials .

In various uses of light-transmitting materials i sheet form, coloured materials ..are often used . with a view to protecting persons. or objects against...light, or heat radiation of a., nature or intensity which .is harmful or inconvenient.. The use of dark, blue screens by arc-welders and .the glazing of window frames of" building^, with grey-coloured glass to avoid excessive exposure of the interior to the sun are examples of this practise. By virtue of the absorption of radiant energy, these coloured materials become heated and the degree of this heating is often objectionably high when they are exposed to thermal radiation. For example, some coloured glazings are liable to break or to cause damage to a frame as a result of unequal expansion of the glass and frame, or heating of the frame by conduction. It is also evident that the heating of glass as a result of energy absorption is detrimental to the efficiency with which the glass can afford protection against heat radiation, since heat stored in the glass becomes re-radiated..

The basic feature of the present invention is the employment in conjunction with a layer of light-transmitting radiant heat absorbing material, of a light-transmitting laye capable of reflecting radiant heat rays. If the radiant heat reflecting layer is present between the said radiant heat absorbing layer and a source of heat and light radiation the incident thermal radiation so that the other said layer is shielded therefrom.

The term "layer" as used above and hereafter in this specification is used broadly to denote both self-supporting layers or sheets and coating layers, i.e., layers applied to form coatings on sheets. Reference has already been made to the injurious effects which may result from the excessive exposure of coloured light-transmitting glass sheets to heat radiation. Some types of light-transmitting coating layers can also be adversely affected by radiant heat rays: e.g., some phototropic coating layers as applied to window panes to reduce transparency to light under conditions of strong "sunlight, function less efficiently when exposed to appreciable thermal radiation, due to the fact that the radiation is absorbed by the layer to such an extent as to cause an increase in its temperature. This radiant heat absorbing property may be temporarily acquired by the phototropic layer during certain conditions of use, e.g., when the layer is exposed to intense sunlight, and provision can be made by means of the present invention for shielding such a layer from at least the major part of the thermal radiation.

The light-transmitting radiant heat reflecting layer (which will occasionally hereafter be referred to as "the protecting layer" to distinguish it from the layer which has or acquires radiant heat absorbing properties and which will occa iDnally bo referred to as "the layer to be protected") may itself be a layer which temporarily acquires its heat layer may be a layer which becomes radiant heat reflecting during use, e.g., due to the layer being associated with means for creating or intensifying an electric field across such layer when circumstances require its normal transparency to electromagnetic radiation to be reduced.

The invention can be applied in the manufacture of sheet materials comprising a single light-transmitting sheet with radiant heat absorbing properties and coated with one or more light-transmitting protecting layers, and in the manufacture of laminates, e.g., laminates comprising two or more light-transmitting sheets bonded together, and one or more coating layers applied between such sheets or on the outer face of one or each of them.

However the invention is concerned not only with sheet materials as such, but also with articles, e.g., windows, incorporating a light-transmitting layer which has or under certain conditions acquires radiant heat absorbing properties and is protected by a protecting layer which is, or becomes under such conditions, radiant heat reflecting. In such manufactured articles, e.g., multiple glazed units, there may be separate light-transmitting sheets held, e.g. in a frame, in spaced facing relationship and one sheet or a coating layer thereon may serve to protect the other sheet or a coating layer thereon against thermal radiation.

Having regard to the foregoing possibilities, the present invention includes any light-transmitting material or article comprising (a) a light-transmitting layer which has or which is liable under the action of sufficiently acquire radiant heat absorbing properties , and (b) a light-transmitting layer which is radiant heat reflecting or is capable of being temporarily rendered radiant heat reflecting and which is disposed so that it can shield layer (a) from radiant heat rays.

In describing the light-transmit ing layer (a) as a layer having or capable of acquiring radiant heat absorbing properties we mean that its composition is, or under the action of heat radiation or of intense light becomes such that it is capable of absorbing a significant proportion of radiant heat rays from the sun. In referring to layer (b) as one which is radiant heat reflecting or which can be temporarily rendered radiant heat reflecting we do not of course mean that it has necessarily to be capable of reflecting all radiant heat rays from any given source.

On the other hand the said layer must be capable of reflecting a significant proportion of incident thermal rays j, and not just an incidental proportion such as may be reflected by the protected layer (a) itself. It is obviously desirable for the inherent or acquired radiant heat reflecting properties of layer (b) to be as good as possible, and in general layer (b) should be capable of reflecting at least the major part of thermal radiation from the sun.

By way of further explanation, in referring to the use of layers' which possess or acquire radiant heat absorbing or reflecting properties as the case may be, we do not of course exclude layers which normally possess such property but which possess it in greater degree under certain or an electric field „ If the material or article incorporates a protecting layer at only one side of a layer or layers to he protected then of course care must be taken when the material or article is used to ensure that the protecting layer is located between the layer or layers to be protected and the source of potentially harmful thermal radiation.

The primary intended field of use of the invention is the field of windows comprising a transparent pane or panes which or one at least of which is coloured and/or bears a phototropic layer which acquires colouration or a deeper colouration when exposed to strong sunlight. Such windows Eire often used when it is desired to shield the interior of a building from strong sunlight. The advantage of providing a phototropic layer is that the layer can be constituted so as not materially to reduce the transparency of the window to light when the prevailing da^/iight is weak.

A material or article according to the invention may incorporate one or more light-transmitting sheets of plastics composition, e. ., of "Perspex" (Trade Mark), "Plexiglass" (Trade Mark), acetate or acrylic resins- and vinyl resins, and such sheet or sheets may be rigid or flexible. However the invention is more particularly concerned with materials and articles comprising sheet glass.

In spheres of use of coloured light-transmitting materials in which the degree of colouration has hitherto been selected not only with a view to the required light filtration, but also with a view to reducing the amount of transmitted thermal radiation, the invention has the advantage of ermittin a reater freedom of choice s re rd the colour of the material. As the coloured material is at least to some extent relieved of its function of affording protection against thermal radiation, the colour can in any given case be less intense or more pleasing.

By using a radiant heat reflecting coating layer in association with a light-transmitting sheet having a dominant tint complementary to that of the light transmitted by such layer in daylight, a material can be prepared which has a neutral tint or a tint approaching neutral. .

Such a material is of potential value for glazing buildings in which it is desirable for objects to be seen in their natural colours, e.g., for buildings in which textile materials for decorative or clothing purposes are exhibited.

When carrying out the invention with a view to achieving the result just referred to it is recommended to use as the coloured sheet a soda-lime glass containing as colouring agent at least one of the following: Fe^O^, CoO , NiO, MnO, Se.

These colouring agents can be used individually or in combinations of two or more. The use of a single said colouring agent will only permit, in general, the realisation of an imperfect neutral transmission. However by combining two or more said agents and appropriately choosing their proportions, it is possible to achieve an excellent neutral transmission. The choice of one or another compositions should in any given case depend on the purpose which the material or article is to serve.

Preferably, the said colouring agents are used (whether individually or in combinations of two or more) in the from 0.01 to 0.15% from 0.0001 to 0.01 NiO from 0.02 to 0.05% MnO from 0.01- to 0.5% Se from 0.005 to 0.03%.

In any case in whic a coating layer is to be applied, the composition of the layer must be selected to ensure adequate adherence to the surface by which it is borne, and so that it can form a thin film which will not be impaired by exposure to the intended conditions of use.

For forming an inherently radiant heat reflecting film, while any substance which has these properties and has the requisite radiant heat reflecting properties can be used, it is in general preferred to use a metal or metal-containing film. Such films generally show good u^fcra-violet and infra- red ray-reflecting properties. Also compounds of various metalloids can be used. Oxide coatings have the advantage that they are in general very resistant to abrasion.

A metal which is very appropriate for forming film on glass is gold. A preferred metal oxide for forming a radiant heat reflecting film is titanium oxide which is easy to deposit a.nd adheres very well to glass surfaces.

It is recommended to employ for the formation of a radiant hcat-reflecting coating layer, a material of which the refractive index is different from and preferably higher than that of the material on which the layer is deposited so as to promote good reflection of radiant heat rays both at the exposed surface and at the bottom surface of the layer. Titanium dioxide has a high refractive index, appreciably in also recommended that the optical thickness of a said transparent radiant heat reflecting film have a value equal to a quarter of one of the wavelengths of the thermal radiation to which the material is to be exposed or equal to an odd number multiple of such a value; this ensures a very strong reflection of rays of which the wavelength is equal or close to such one wavelength so that the thermal rays will be reflected more strongly than that light rays.

An example of a laminate according to the invention is one comprising two light-transmitting sheets, e.g., of glass, one or each of which sheets may be coloured, glued or soldered together. Preferably a radiant-heat-reflecting film is sandwiched between the sheets so as to be physically protected thereby. The sheets can be bonded together, e.g., by means of an inter-layer of a plastics material, e.g., polyvinylbutyral, or soldered together, e.g., at the margins of the sheets. If both sheets are coloured, then unless a protecting heat reflecting layer is borne on the outside of one of them, the composition of one of the sheets will in general have to be of a composition such that it does not absorb thermal radiation to any appreciable extent. When employing two sheets, the colour of one of them can, e.g., be selected for varying the general tint of the laminate material in a predetermined manner or for selectively absorbing radiation of a particular spectral region.

One disadvantage of a material comprising a transparent of coloured material, is that such material reduces the intensity of the transmitted light by a substantially constant proportion irrespective of the intensity of the incident light. This disadvantage manifests itself particularly if the material is used for windows of buildings located in regions where periods of strong sunlight alternate with periods of feeble sunlight or of o sunlight; during these last periods the level of illumination can become so poor in the interior that the use of artificial light becomes necessary. This use of artificial light would not be necessary if the building were furnished with ordinary windows « For such situations, light t ansmitting materials or windows according to the invention and comprising at least one phototropic layer, are preferably used. By using such a layer it is possible to form a light-transmitting material which when used in windows maintains the illumination level in the interior of the building at a substantially constant level, regardless of changes in the sunlight intensity exterior to the building, A said phototropic layer may bo composed for the purpose of reducing the light transparency of the material when the daylight intensity is high, this layer being shielded by a radiant heat reflecting layer from thermal radiation which might reduce the efficiency of such phototropic layer, or may be composed for the purpose of reflecting a proportion of incident light and much of the thermal radiation on occasions of such high daylight intensity. In any case the transformation of the properties of the phototropic layer of the exterior sunlight, For example a piototropic layer may be composed of a material which when exposed to sufficient light or heat? reversibly crystallises to more or less extent so that its coefficient of reflection is modified. One such material is calcium butyrate incorporated in an agar binder. If such a phototropic layer is used on a coloured light transmitting shee , any heating of the coloured sheet directly participates in increasing the reflecting property of the phototropic layer.

As another example a protecting layer may be in the form of a thin metallic or semi-conductive layer of which the radiation reflecting property is varied by application of an electric field,. The intensity of this field may itself be controlled by siuilight through the agency of a photoelectric cell; or by a thermostatic cell.

As yet another example, a material or article accordin to the invention may comprise a phototropic substance of -which the light transmission varies automatically under the action of variations in the intensity of incident light Co . - so as to afford an illumination level in the interior a room which is substantially constant. Such a phototropic: substance may be provided, e.g0, between two sheets of gla-s or plastics material or may be in the form of a thin transparent coating layer or film which is applied to a sheet of glass or other light-transmitting material (which may be colour].ess) and of which the nature and thickness are chosen in order to preserve a sufficient interior illumination level during periods of feeble sunlight, transmission during periods of strong sunlight. The transformation of the light transmitting properties of such a phototropic layer may occur, e.g., under the action of variations in the intensity of the incident sunlight or under the action of such heat rays as penetrate to such layer through a protecting radiant heat reflecting layer.

Phototropic layers with variable light transmission include layers of organic phototropic substances, for example substances which pass reversibly from sol to gel state with accompanying change of transparency or of colour under the action of heat radiation. Such substances are for example: polyvinyl methyl ether, alkaline earth metal salts of polyacrylic acid, and polymerised polyvinyl partial acetals or cetals having the ether oxygen atoms associated with water or hydrated salts. A material or article according to the invention may equally well comprise a phototropic layer comprising a compound or compounds which reversibly dissociates under the action of light, one of the elements ofdissociation becoming_.absorbed reversibly on a support and subsequently released when the exciting light radiation is reduced or terminated while the other element restricts the passage of visible light and heat rays. Such compounds are for example light-sensitive halogenides to which are added catalysts such as copper halogenides, cadmium halogenides or nickel halogenides.

Several embodiments of the invention, selected by way of example, will now be described with reference to the accompanying drawings in which: Fig. 1 is a cross-section of part of a protective glazing; Pig. 2 is a cross-section of part of another protective glazing; Fig, 3 is a perspective view, partly in section, of part of the protective glazing shown in Fig„ 2; Fig., 4 is a cross-section of part of another form of protective glazing; Fig. 5 is a cross-section of part of another type of protective glazing.

The glazing show in Fig. 1 comprises a coloured glass sheet 1 coated on one side with a transparent radiant heat reflecting film 2. The coloured glass of which sheet 1 is made is for instance an athemianous soda-lime glass containing a high proportion of iron oxide which gives it a blue-green tint. The film 2 is made of titanium dioxide deposited by one of the known processes, for instance by hydrol sing titanium chloride. As the refractive index of this oxide is rather high, an appreciable fraction of the heat and light radiation is reflected at the outer face of the film 2 and at the glass film interface. In order to reflect a high proportion of the heat energy, the interference phenomena are made use of by giving the oxide film an optical thickness which is equal to a quarter or an odd number multiple of a quarter of a wavelength selected in the infrared band. By this means, the radiation of which the wavelength is equal or near to the selected wavelength is more intensively reflected. The selected wavelength lies normally between 1 and 1.2 ? which corresponds with a region The product which, has just bean described can advantageously be used for glazing buildings. It is inexpensive and affords a high standard of thermal comfort as well as protecting the eyes against sun glare.

The glazing shown in Figs. 2 and 3 includes a sheet 3 of blue glass of which the colouration is due in part to the presence of OoO in the glass composition; a sheet 4 made of transparent glass is glued to sheet 3 by an intervening layer 5 of polyvinylbutyral, A silver film 6 which is sufficiently thin for it to pass an appreciable fraction of the incident ' light , is deposited on the sheet 4. Such a glazing' is particularly suitable for the inspection windows in furnaces and for welders' spectacles and helmets. The glazing is orientated in use so that the radiation reaches the film 6 before reaching the sheet 3.

Referring now to Fig,, 4, the glazing here shown comprises a sheet of grey-coloured glass 7, covered with a thin gold film 3 and assembled with another glass sheet 9 by means of a metal strip 10 which is soldered to copper bands 11 and 12 deposited on the edges of sheets 7 and 9. The free space 13 left between sheets 7 and 9 is filled with a dry gas.

Such a product is of particular interest for glazing dwelling houses; it combines the advantages of double glazing with advantages afforded by the invention. It is well known that gold deposited in a thin layer, reflects heat radiation more intensely than light and it is possible to predetermine the quantity of light transmitted by appropriate choice of the composition of the grey coloured glass 7. Besides, this sheet 7 may bjave a dominant tint which is complementary to that of the film 8 so as to transmit to the interior of the premises a light of which the colour is approximately neutral. Although the sheet 9 aj^ be made of colourless glass, it is equally possible to use for this sheet a glass whic is slightly coloured and of which the tint is complementary to that of the film 8 or which (assuming that sheet 9 is disposed to the outside of sheet 7) is chosen to harmonize particularly well with the rest of the structure in which the glazing is used; the sheet 9 heats only to a small degree because its colouration and consequently its absorption are not very intense. As another example , a glazing formed as shown in Pi . 4 may comprise a colourless glass sheet 7 bearing a transparent gold film, and a coloured glass sheet 9 nd. the assembly may be installed so that the radiation roaches sheet 7 first and then sheet 9. The sheet 9 may have a dominant tint complementary to that of the film 8 so that the assembly transmits light of a colour which approaches or is substantially neutral. The gold film 8 has a grey-green colour viewed by transmitted daylight, and a coloured glass sheet 9 having a dominant tint nearly complementary to such film is one constituted by a soda-lime glass of conventiona! composition to which however has been added 0,0065% of CoO. The double glazed unit thus realised has a transmission of the order of 40 for the waves between 400 and 600 u, and a transmission of about 33 between 600 and 750 x.

A dominant tint substantially complementary to that of containing 0.0065^ of cobalt oxide and 0.0133 of aelenium. The double glazing unit thus formed has an almost uniform transmission in the visible range the transmitted light having good colour neutrality. It is equally possible to obtain a good neutrality of light transmission by using a coloured glass prepared by adding to a soda-lime batch of ordinary composition, a mixture of NiO and CoO, a mixture of and NiO, a mixture of Fe^^ and CoO or a mixture of CoO, Pe2°3 and Ni0* Referring now to Fig. , this glazing comprises a sheet 14 of grey coloured glass assembled with another glass sheet 15 by means of a strip 10 and bands 11, 12 in a manner similar to that used in the embodiment shown in Fig. 4. A film 16 of titanium oxide is deposited on the face 17 situated on the outer side of the protective glazing and facing the source of radiation. As is the case for the sheet 9 of the protective glazing shown in Fig. 4, the glass sheet 15 may be uncoloured or coloured. The disposition of the radiant heat reflecting film in the manner shown in Fig. has the advantage over that shown in Fig. 4 that both glass sheets are protected by the film 16 so that the colour of sheet 15 is more open to choice.

It should be mentioned that when a transparent film such as film 8 or 16 is applied to a colourless sheet it is easier to check the properties of the film than when it is applied on a coloured sheet.

Very many other glazings can be prepared ..according to the invention. The following description, which also refers to the accompanying drawings, outlines two examples of layer with, variable reflectance or transmission.

The glaring according to the first of these examples has a structure as is represented in Fig, 1 of the accompanying drawings. The glass of sheet 1 is in this case constituted by an athermanous soda-lirae glass containing between 1 and ?o of PeOc Instead of the film 2 four successive layers are applied to the sheet 1, viz: a first layer of silver of 100 Angstroms thickness; a second layer of SiO 2 microns thick; a third layer of S O^ of 3 microns thickness and containing selenium in a proportion such that the ratio between the selenium and tin atoms is 1 = 100; and a last layer of silver of 100 Angstroms thickness. These different films are applied successively on the athermanous glass sheet 1 by the technique of evaporation under vacuum. In the final composite structure, the layer of S O constitutes a layer with variable reflection. When the glazing is in use, the · reflection of this layer is caused to vary by varying the potential of an electric field applied .across the SnO layer between the two silver layers which constitute electrodes and the tension between which is controlled by a photoelectric cell. The SiO layer constitutes an insu.lating layer preventing the passage of current through In the final installation tho photoelectric cell is placed so that it is exposed to the prevailing daylight. When the sunlight is feeble f the film reflects only a little of the visible light and of the heat radiation. The athermanous glass sheet can absorb the very feeble intensity risk of "breakage of the glass under these conditions.

On the other hand, when the sunlight is very strong, the photoelectric cell causes the application of a potential between the two silver electrodes and the resulting electric field confers a good radiant heat reflecting property on the SnO^ layer. In fact the infrared radiation is totally reflected or nearly so, as is also a small part of the visible light. The athermanous glass sheet can absorb any small residual amount of heat radiation not reflected by the SnO^ film, without thereby becoming unduly heated.

The glazing according to the second of the said examples has a structure as represented by Fig. 5 of the accompanying drawing. The first glass sheet 15 is in this case a colourless sheet and bears a film of gold of 150 Angstromcs thickness. This film reflects the heat rays very intensely. The thickness of this film is such that even in periods of feeble sunlight, the level of illumination in the interior of a room furnished with such a window remains sufficient. In place of the uncoated glass sheet 14, a sheet of soda-lime glass coated with a transparent layer, 200 Angstroms in thickness, comprising a mixture of 50 of AgCl and $Q?/° of AgBr is used. This silver halide layer is coated over with a layer of SiO 5,000 Angstoms thick, and the latter layer is coated over with a protective impermeable calcium silicate layer.

In periods of feeble sunlight, it is only the gold film on sheet 15 irtiich plays an active part in reducing the intensity of the transmitted light. The silver halide photo- As the sunlight increases, the gold film continues to reflect the same proportion of the incident radiation and effectively reflects most of the radiation in the infrared region. Under the action of light, the silver chloride and silver bromide decompose and the bromine and chlorine liberated are adsorbed reversibly by the layer of'SiO.

Consequently the assembly becomes more opaque and stops a greater part of the visible radiation and the residue of the heat radiation, while transmitting radiation of a grey colour. The level of illumination in the room is maintained substantially constant at a comfortable level, whilst the heat radiation is conveniently excluded.

Claims

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1. A light transmitting material or article comprising (a) a light transmitting layer which has or which is liable under the action of sufficiently intense incident light or heat radiation, temporarily to acquire, radiant heat absorbing properties, and (b) a light transmitting layer which is radiant heat reflecting or is capable of being temporarily rendered heat reflecting and which is disposed so that it can shield said layer (a) from radiant heat rays.

2. A material or article according to claim 1 and comprising as^layer (a) a coloured light transmitting sheet with radiant heat absorbing properties Λ

3. A material or article according to claim 2 and comprising as layer (b) a coating layer borne by a light transmitting sheet,

4. A material or article according to claims 2 and 3 wherein layer (b) is a coating layer borne by a coloured light transmitting sheet constituting layer (a).

5. A material or article according to any preceding claim wherein layers (a) and (b) are transparent.

6. A material or article according to claim 1 and comprising as layer (a) a light transmitting coating layer which is borne by a light transmitting sheet.

7. A material or article according to claim 6 wherein layer (a) is coloured.

8. A material or article according to claim 7 wherein c ou sufficiently intense incident light or heat radiation.

9. A material or article according to claim 6 and com- . prising as layer, (a): a colourless or substantially ;colourless layer which acquires colouration when exposed to sufficiently intense incident light or heat radiation.

10. A material or article according to any of claims 6 to 9 and comprising as layer (b) a coating layer borne by a light transmitting sheet.

11. A material or article according to claim 3. 4 or 10 wherein layer (b) comprises a metal, or a metal*- or metalloid-containing compound.

12. A material or article according to claim 10 or 11 wherein layer (b) comprises an oxide.

13. A material or article according to any preceding claim wherein layer (b) is sandwiched between electrodes which are connected to means for establishing an electric field between said electrodes, and wherein said layer (b) can be rendered radiant heat reflecting or more radiant hea,t reflecting by establishing a said field.

14. A material or article according to claim 13 wherein the tension between said electrodes is controlled by a photoelectric cell.

15. A material or article according to any of claims 3, 4 and 10 to 12 wherein the light transmitting sheet bearing layer (b) has a refractive index different from the refractive index of the substance composing said layer (b).

16. A material or article according to claim 15 wherein is larger than the refractive index of the substance forming said sheet bearing this layer.

17. A material or article according to any preceding claim and comprising as layer (b) a film of titanium dioxide,

18. material or article according to any preceding claim wherein layer (a) is formed by a glass sheet.

19. A materia,! or article according to any preceding claim which comprises a coloured sheet as layer (a) and a coloured coating layer as layer (b) and wherein said coloured sheet has a dominant tint complementary or substantially complementary to that of said layer (b) .

20. . A material or article according to claim 19 wherein said coloured sheet forming layer (a) is constituted by a soda-lime glass containing as colouring agent one or more of the following: ^e^,,, OoC, NiO, MnO, Se.

21. A material or article according to claim 20 wherein the or each said oxide colouring agent in said soda-lime glass is present in a proportion as indicated in the following table for the oxide in question: Pe 0_ from 0.01 to 0.15% GoQ from 0.0001 to 0.01 Ή±0 from 0.02 to 0.0 MnO from 0.01 to 0.5% Se from 0,005 to 0.03%»

22. „ A material or article according to any preceding claim comprising two light transmitting sheets as well as a light transmitting coating layer which constitutes layer (b)c.

23. A material or article according to claim 22, wherein said layer (b) is located between said sheets.

24. A material or article according to claim 22 or 23 wherein one of said sheets is coloured and the ot jr is ' J - colourless or substantially colourless.

25. A material or article according to claim 24 wherein layer (b) is a coating layer which is borne by said colourless or substantially colourless sheet.

26. A material or article according to claim 22 or 23 10 wherein both said sheets are coloured.

27. * A material or article according to claim 26 wherein layer (b) is a coating layer and is borne by one of said coloured sheets.

28. , A material or article' according to claim 26 or 27 15 wherein the colours of the coloured sheets are differen .

29. A material or article (which may be a window), according to any of claims 22 to.28 wherein said two light transmitting sheets are held in spaced relationshi »

30. A material or article according to claim 1 and 20 substantially as herein described with reference to any of the figures in the accompanying drawings. k m THIS 20th day of January, 1966. OOW 2EDBK & SPI3R4CH P.O.BOX 1169, TEL-AVI? Attorneys .for Applicants