Reflective projection screen comprising a variable light scattering system

Abstract

The invention relates to a glazing used as projection screen operating in reflection, comprising a front face, onto which the image is projected, and a rear face. The glazing comprises a variable light scattering system comprising a functional film capable of switching between a transparent state and a scattering state and a coating comprising at least one mirror layer, said coating being separated from the front face at least by the functional film. The invention also relates to the use of a glazing as projection screen, to a projection system and to a projection method using said glazing.

Claims

1. A glazing comprising a front face and a rear face, wherein said glazing comprises: a variable light scattering system comprising a functional film that includes a liquid crystal material capable of switching between a transparent state and a scattering state, a coating comprising at least one mirror layer, wherein the mirror layer exhibits a thickness of between 50 and 80 nm, said coating being separated from the front face at least by the functional film, and said glazing exhibits: a light transmission LT of less than 20%, a light reflection LR of greater than 25%, wherein the light transmission LT and the light reflection LR are measured according to ISO 9050:2003 with an illuminant D65 and a 20 observer, and the light reflection LR is measured on the front face of said glazing with the liquid crystal material in the transparent state, and the light transmission LT is measured in at least one of the transparent state and the scattering state; and wherein the mirror layer is one of a metallic layer and a layer comprising a metal nitride that includes at least one metal chosen from the group consisting of silver, aluminum, titanium, gold, nickel, chromium, copper, rhodium, platinum, palladium, cobalt, manganese, molybdenum, tungsten, hafnium, niobium, iron and tantalum, including alloys of these.

2. The glazing as claimed in claim 1, wherein the variable light scattering system is electrically controllable and comprises the functional film framed by front and rear electrode-carrying supports, said electrode-carrying supports each comprising at least one electrically conducting layer and being directly in contact with the functional film.

3. The glazing as claimed in claim 2, wherein the mirror layer is the electrically conducting layer of the rear electrode-carrying support.

4. The glazing as claimed in claim 1, wherein at least one of the light transmission LT of said glazing is less than 5% and the light reflection of said glazing is greater than 50%.

5. The glazing as claimed in claim 1, wherein the mirror layer is chosen from the group consisting of a layer of silver, chromium, niobium, niobium nitride, and alloys predominately comprising silver, chromium, iron, or niobium.

6. The glazing as claimed in claim 1, wherein the mirror layer is positioned inside the glazing.

7. The glazing as claimed in claim 1, wherein the glazing comprises, in sequence: a transparent rear substrate made of flat glass, a plastic insert laminated to the transparent rear substrate made of flat glass, the variable light scattering system comprising the functional film including the liquid crystal material, wherein the function film is framed by two electrode-carrying supports, said electrode-carrying supports each comprising an electrode that is directly in contact with the functional film, a plastic insert laminated to a transparent front substrate made of flat glass, and the transparent front substrate made of flat glass.

8. The glazing as claimed in claim 7, wherein the two electrode-carrying supports are each composed of a polyethylene terephthalate sheet covered with an electrically conducting layer of indium tin oxide providing the electrode that is in contact with the functional film.

9. The glazing as claimed in claim 7, wherein the coating comprising at least one mirror layer is deposited on at least one of: an external face of the transparent rear substrate, an internal face of the transparent rear substrate, an external surface of a rear electrode-carrying support, and an internal surface of the rear electrode-carrying support.

10. A method for projection in reflection according to which a projection screen operating in reflection and a projector are available, said method consisting in projecting images, by virtue of the projector, onto the projection screen, said projection screen comprising a glazing as defined in claim 7.

11. The glazing as claimed in claim 7, wherein the plastic insert laminated to the transparent rear substrate made of flat glass and the plastic insert laminated to a transparent front substrate made of flat glass each comprise a plastic selected from the group consisting of ethylene/vinyl acetate (EVA) copolymers and polyvinyl butyral (PVB).

12. The glazing as claimed in claim 1, wherein the glazing comprises: a transparent rear substrate made of flat glass, a plastic insert laminated to the transparent rear substrate made of flat glass, and the variable light scattering system comprising the functional film that includes the liquid crystal material framed by two electrode-carrying supports, said electrode-carrying supports each comprising an electrode that is directly in contact with the functional film.

13. The glazing as claimed in claim 12, wherein the two electrode-carrying supports each comprise a flat float glass sheet.

14. The glazing as claimed in claim 1, wherein the mirror layer is chromium based.

15. The glazing as claimed in claim 1, further comprising at least one of an undercoat layer deposited under the mirror layer and an overcoat layer deposited over the mirror layer.

16. The glazing as claimed in claim 15, wherein the at least one of the undercoat layer and the overcoat layer has a thickness less than 150 nm.

17. A projection system comprising a glazing used as a projection screen and a projector, said glazing comprising a front face, onto which the image is projected, and a rear face, wherein: said glazing comprises: a variable light scattering system comprising a functional film that includes a liquid crystal material capable of switching between a transparent state and a scattering state, a coating comprising at least one mirror layer, wherein the mirror layer exhibits a thickness of between 50 and 80 nm, said coating being separated from the front face at least by the functional film, and said glazing exhibits: a light transmission LT of less than 20%, a light reflection LR of greater than 25%, wherein the light transmission LT and the light reflection LR are measured according to ISO 9050:2003 with an illuminant D65 and a 20 observer, and the light reflection LR is measured on the front face of said glazing with the liquid crystal material in the transparent state, and the light transmission LT is measured in at least one of the transparent state or the scattering state; and wherein the mirror layer is one of a metallic layer and a layer comprising a metal nitride that includes at least one metal chosen from the group consisting of silver, aluminum, titanium, gold, nickel, chromium, copper, rhodium, platinum, palladium, cobalt, manganese, molybdenum, tungsten, hafnium, niobium, iron and tantalum, including alloys of these.

Description

(1) A better understanding of the invention will be obtained on reading the description which will follow, given solely by way of example and made with reference to the appended drawings, in which:

(2) FIG. 1 is a diagrammatic transverse cross section of a projection system according to the invention comprising a projector and a glazing in accordance with an embodiment according to the invention;

(3) FIG. 2 is a diagrammatic transverse cross section of another projection system according to the invention comprising a projector and a glazing in accordance with an embodiment according to the invention;

(4) FIG. 3 comprises photographs.

(5) The drawings are not to scale, for clear representation, as the differences in thickness between the layers having a glass function and the other layers are significant.

(6) FIG. 1 represents a projection system intended to operate in reflection comprising a projector P and a glazing 100. The glazing comprises an electrically controllable variable light scattering system 6 which can switch between a mirror state and a scattering state on the main external face or front face S2. As explained above, the glazing according to the invention exhibits the distinguishing feature of being able to be used as projection screen, i.e. for a spectator on the projector P side, rather than as back-projection screen, i.e. in which the projector is located behind the glazing.

(7) In the OFF state, a scattering face is obtained on the front face S2 and a mirror face is obtained on the rear face S1 of the glazing. In the ON state, two mirror faces are obtained.

(8) The glazing illustrated in FIG. 1 comprises: two front and rear substrates which are glass sheets 1, a mirror layer 2, which was deposited beforehand on the internal face of the sheet 1 or on the external face of the rear laminating insert 3, two plastic inserts 3, a variable light scattering system 6 comprising a functional film 5, capable of switching between a transparent state and a scattering state, framed by two electrode-carrying supports 4, said electrodes being directly in contact with the functional film.

(9) According to this embodiment, the electrode-carrying supports are composed of a PET (polyethylene terephthalate) sheet covered with an electrically conducting layer of ITO (indium tin oxide) framing the functional film.

(10) The laminating inserts make it possible to attach the front and rear substrates with the electrode-carrying supports.

(11) FIG. 2 represents another projection system intended to operate in reflection comprising a projector P and a glazing 100.

(12) The glazing illustrated in FIG. 2 comprises: a transparent rear substrate made of flat glass which is a glass sheet 1, a mirror layer 2, which was deposited beforehand on the internal face of the sheet 1 or on the external face of the rear laminating insert 3, a laminating insert 3, a variable light scattering system 6 comprising a functional film 5 framed by two electrode-carrying supports 4, said electrodes being directly in contact with the functional film.

(13) According to this embodiment, the electrode-carrying supports are composed of two float glass sheets on which are deposited, on the internal faces, an electrically conducting layer with a thickness of approximately 20 to 400 nm made of indium tin oxide (ITO), for example. The ITO layers have a surface electrical resistance of between 5 /square and 300 /square. Instead of the layers made of ITO, it is also possible to use, for the same purpose, other layers of electrically conducting oxide or layers of silver having a comparable surface resistance.

(14) The functional film 5 composed of a layer of liquid crystals can exhibit a thickness of approximately 5 to 60 m. The layer of liquid crystals comprises spherical spacers. The spacers are composed of a hard transparent polymer. By way of example, the product from Sekisui Chemical Co. Ltd, known under the designation Micropearl SP, has proved to be highly suitable as spacer. On the edge, the layer of liquid crystals is sealed by an adhesive seal (not represented) which serves to connect the glass sheets 4 possessing the electrodes in a firm and permanent manner. The adhesive sealant which seals the separate glass sheets 4 over their edges comprises an epoxy resin.

(15) In the initial stage (OFF state), that is to say before the application of an electric voltage, the functional film comprising liquid crystals is translucent, that is to say that it transmits optically but is not transparent. As soon as the current is turned on, the layer of liquid crystals changes, under the action of the alternating electric field, to the transparent state, that is to say that which makes possible viewing through the functional film.

(16) The glazing can be produced by using a method described in detail below. Float glass sheets according to the invention are coated, in an industrial continuous coating plant, in successive chambers, using the magnetic-field assisted reactive cathode sputtering process, by sputtering with an ITO layer having an approximate thickness of 100 nm or with a layer of silver having a thickness of 70 nm.

(17) Two separate glass sheets of equal size and exhibiting the desired dimensions are cut out from a large glass sheet coated in this way and are prepared for the continuation of the treatment.

(18) The layer of liquid crystals, which is mixed with the spacers, is then applied to one of the two glass sheets thus treated. The application of the layer of liquid crystals can be carried out, during an operation known as filling, dropwise using a specific device which makes it possible to adjust with precision the amounts poured in. In another embodiment of the method, the application of the layer of liquid crystals can be carried out by virtue of a screen printing cloth exhibiting a defined mesh size.

(19) The adhesive layer forming the seal is applied directly along the edge of the glass sheet before or after the removal of the layer of liquid crystals. The application of the sealant is noncontinuous or continuous and then followed by creation of the openings (by withdrawal of sealant).

(20) When the two separate glass sheets are subsequently pushed against one another, the adhesive layer is compressed down to the thickness of the layer of liquid crystals.

(21) The calendering and the pressing of the assembly thus formed is subsequently carried out. Optionally, if the layer of liquid crystals comprises a mixture of liquid crystals and monomers, a polymerization stage is then carried out, for example by irradiation with UV light if the monomers used are photopolymerizable.

(22) The stack obtained is subsequently assembled with a substrate coated with a coating comprising a mirror layer. The assembling can be carried out mechanically, by adhesive bonding or by the use of a laminating insert.

(23) The use of the glazing thus defined as projection screen operating in reflection makes it possible to improve the contrast and/or the luminosity and/or the angle of view.

(24) The glazing according to the invention can be used in particular as internal partition between two rooms or in a space in a building. More particularly, the glazing of the invention is of particular use as internal partition of a meeting room for projecting presentations. It is possible to switch between the mirror state and the scattering state making possible the projection. Furthermore, the coating comprising the mirror layer prevents the projected image from appearing by transparency on the main face. This presents a considerable advantage when the projected images are confidential.

(25) The glazing of the invention may also be of particular use in the hotel industry for separating a bathroom and a bedroom. A perfect mirror is obtained on the bathroom side. In the bedroom, in the ON state, a mirror is obtained which structures the space between the bedroom and the bathroom and, in the OFF state, a projection screen, for example for the television, is obtained.

EXAMPLES

I. Materials Used

(26) The variable scattering system (VSS1) comprises two polyethylene terephthalate sheets covered with an ITO layer acting as electrode framing the functional film, that is to say the medium comprising the droplets of liquid crystals. This variable scattering system is currently used in the Priva-Lite glazings from Saint-Gobain Glass. The functional film comprising the liquid emulsion of nematic liquid crystals has a thickness of approximately 10 to 30 m (preferably of 20 to 25 micrometers). The PET sheets have a thickness of approximately 175 m. The two electrodes are composed of ITO (tin-doped indium oxide) with a resistance of approximately 100 ohms per square.

(27) The variable light scattering system (VSS2) exhibits the configuration illustrated in FIG. 2 and comprises in particular two float glass sheets on which are deposited, on the internal faces, an electrically conducting layer with a thickness of approximately 20 to 400 nm made of indium tin oxide (ITO). The layer of liquid crystals has a thickness of 5 to 60 m.

(28) The variable scattering system (VSS3) comprises two float glass sheets. A coating comprising an electrically conducting mirror layer with a thickness of approximately 70 nm, made of silver, is deposited on the internal face of the float glass acting as rear electrode-carrying support. An electrically conducting layer with a thickness of approximately 20 to 400 nm, made of indium tin oxide (ITO), is also deposited on the internal face of the float glass acting as front electrode-carrying support. The layer of liquid crystals has a thickness of 5 to 60 m.

(29) Mention may be made, as additional front or rear substrates which can be used, of the Planilux or Diamant glasses sold by Saint-Gobain, which are flat glasses.

(30) Laminating inserts made of EVA or PVB were also used.

(31) Finally, three rear substrates composed of a glass sheet with a thickness of 6 mm comprising a coating comprising a mirror layer were also used. The characteristics of these substrates are given in the following table. The light reflection values RE.sub.ext and LR.sub.int correspond respectively to the measurement of the light reflection taken on the side of the glazing not comprising the mirror layer and on the side comprising the mirror layer.

(32) TABLE-US-00001 Layer of Cool-Lite Characteristics silver Mirastar ST 120 Esthetic appearance Silver Silver Neutral Nature of the mirror layer Silver Chromium Niobium nitride LT >1 3 20 RE.sub.ext % >42 32 RL.sub.int % (layer side) >37 58 27 T.sub.UV <3 15

II. Examples of Glazings

(33) The glazings of examples 1, 2, 3 and 5 comprise a variable scattering system VSS1 laminated by virtue of laminating inserts between a standard glass of Planilux or Diamant type and a mirror layer glass chosen from a Mirastar glass, a glass comprising a layer of silver or a Cool-Lite glass comprising an ST 120 layer.

(34) Examples 4, 6 and 7 illustrate an embodiment comprising an active mixture of liquid crystals encapsulated between two glasses comprising conductive layers. In example 7, a metallic mirror layer is used as rear electrode of the variable light scattering system.

(35) TABLE-US-00002 Compar- ative ex- Exam- Exam- Exam- Stack ample ple 1 ple 2 ple 3 Rear substrate Yes Yes Yes Yes Mirror layer nature No mirror Mirastar Mirastar ST120 layer Position of the mirror layer on the rear substrate: external face No No Yes No internal face No Yes No Yes Insert Yes Yes Yes Yes VSS 1 1 1 1 Insert Yes Yes Yes Yes Front substrate Yes Yes Yes Yes Exam- Exam- Exam- Exam- Stack ple 4 ple 5 ple 6 ple 7 Rear substrate Yes Yes Yes No Mirror layer nature ST120 Layer Mirastar Layer of Ag of Ag Position of the mirror layer on the rear substrate: external face No No No No internal face Yes Yes Yes No Insert Yes Yes Yes No VSS 2 1 2 3 Insert No Yes No No Front substrate No Yes No No

III. Gains and Angles of View of the Glazings

(36) In a first step, the Bidirectional Reflectance Distribution Function (BRDF) of these different glazings was measured with a Reflet-90 goniophotometer of the Stil S.A. brand. This made it possible to calculate the characteristics, such as the gain and the angle of view of the projection screens on the scattering face (in the OFF state). The results obtained are summarized in the table below.

(37) TABLE-US-00003 Gain Angle of view () Comparative example 0.95 22 Example 1 2.33 33 Example 2 2.25 30 Example 3 1 31 Example 4 0.11 98

(38) The glazing of the comparative example differs from the glazings of examples 1, 2 and 3 in that it does not comprise a mirror layer. The glazings of the invention used as projection screen exhibit an angle of view which is approximately 10 greater than the angle of view obtained with the glazings of the prior art.

(39) The glazing of example 4, produced with a different configuration and in particular with a layer of liquid crystals, makes it possible to obtain greater values for angles of view.

IV. Analysis of the Contrast

(40) In order to test the qualities of the projection screens of the invention when they are used as partition between two rooms, measurements of the contrast carried out under specific conditions of illumination were carried out. These tests make it possible to observe the influence on the contrast of the illumination in the projection room and in a related room.

(41) In this test, when the projection room is not illuminated (dark projector condition), the mean illumination in the room is less than 2 lux.

(42) In order to be placed under illumination conditions of bathroom type, a Datacolor TrueVue 2 booth with a fluorescent tube positioned in the ceiling of the booth and emitting light close to the spectrum of the illuminant D65 was used. From one scattering glazing to the other, the measurement of luminance is always carried out at one and the same point of the image with a Konica-Minolta LS-110 luminance meter. The image projection is carried out with a Canon XEED SX80 video projector (luminosity, 3000 lumens, contrast 900:1).

(43) The arrangement of the elements is as follows. The screens formed by the glazings are attached to the booth. The image is projected over 30 cm*30 cm of glazing. The video projector is located 1.5 m from the screen. The observers and the photographic apparatus are located 2 m from the screen.

(44) The measurements of illumination in the projection room and in the booth used during these tests: Bright room: greater than 200 lux, Dark room: 1 to 2 lux, Bright booth illuminant D65; floor measurement: 850 lux, Bright booth illuminant D65; glazing face measurement: 650 lux.

(45) The measurements of illumination were carried out 2 m from the active glazing on the projection room side: with the dark projector, the illumination in the room is less than 2 lux, with a white image projection, with dark projection room and booth, the illumination is of the order of 10 lux, with a white image projection, with bright booth and dark projection room, the illumination in the projection room is of the order of 10 lux.

(46) In this test, the light originating from the booth always has a low impact on that of the projection room. This result is observed even when use is made of projection screens with a mirror layer exhibiting a light transmission of approximately 20%, which thus transmit more light toward the projection room. The reason for this arises essentially from the fact that the booth simulating the bathroom is small in size (typically 50 cm50 cm50 cm).

(47) This test makes it possible to measure the contrast of the glazing as projection screen. The contrast is defined as the ratio of the luminance measured when the projector displays a white image (Lw) to the luminance measured when the projector displays a dark image (Lb).

(48) The luminance measurements taken on the diffuse screens are given in the table below. In the case of the strongly illuminated environments, it can be seen that the glazing of example 1 is greatly superior in terms of contrast, in comparison with the glazings of the comparative example and with the glazings comprising a mirror layer exhibiting a light transmission of approximately 20% (example 3).

(49) In this table, the term ON means that the light of the room, of the booth or the projector is switched on or the term OFF means that the light of the room, of the booth or the projector is switched off.

(50) TABLE-US-00004 Projection Luminance Projector Booth room (cd/m.sup.2) C = Lw/Lb Projection screen: Comparative example OFF ON OFF 76.5 12.4 ON ON OFF 948 ON OFF OFF 857 519.4 OFF OFF OFF 1.65 OFF ON ON 83.2 11.2 ON ON ON 935 ON OFF ON 864 108.4 OFF OFF ON 7.97 Projection screen: Example 1 OFF ON OFF 9 327.8 ON ON OFF 2950 ON OFF OFF 2960 518.4 OFF OFF OFF 5.71 OFF ON ON 25.6 116.8 ON ON ON 2990 ON OFF ON 2970 134.4 OFF OFF ON 22.1 Projection screen: Example 2 OFF ON OFF 7.92 337.1 ON ON OFF 2670 ON OFF OFF 2670 507.6 OFF OFF OFF 5.26 OFF ON ON 26.1 103.1 ON ON ON 2690 ON OFF ON 2700 115.4 OFF OFF ON 23.4 Projection screen: Example 3 OFF ON OFF 20.6 66.0 ON ON OFF 1360 ON OFF OFF 1340 515.4 OFF OFF OFF 2.6 OFF ON ON 28.4 48.2 ON ON ON 1370 ON OFF ON 1350 133.7 OFF OFF ON 10.1 Projection screen: Example 4 OFF ON OFF 25.9 10.4 ON ON OFF 269 ON OFF OFF 244 488.0 OFF OFF OFF 0.5 OFF ON ON 34.2 8.1 ON ON ON 277 ON OFF ON 252 27.4 OFF OFF ON 9.19

(51) It is found that very good results are obtained for the examples of the invention. The contrast values show virtually no variation for examples 1 and 2.

(52) Example 3 differs from example 1 essentially in that the mirror layer exhibits higher light transmission values. The contrast values are better for example 1. This shows that the lower the light transmission of the mirror layer, the lower the light transmission of the glazing, the better the contrast.

V. Visual Study of the Quality of the Screens

(53) In order to show the superior quality of the glazings used as projection screen of the invention, a panel of 5 people visually assessed the luminosity and the readability when an image is projected onto the front face of the glazings. Each projected image evaluated by the panel has formed the subject of a photograph. These photographs have been combined in FIG. 3.

(54) The panel assigned, for each image projected onto a glazing, an assessment indicator chosen from: fair, + correct, ++ good, +++ excellent. The glazings, evaluation condition and assessment of the panel, and also the reference to the corresponding photograph, are summarized in the table below.

(55) The variable light scattering systems are in the scattering state. The room in which the projection is carried out is dark. In the table below, the terms ON and OFF respectively refer to the bright or dark state of the booth representing a related room.

(56) TABLE-US-00005 Quality of the screen Photo. Glazing Filter State luminosity readability A Comparative No OFF ++ example B Ex. 1 No OFF +++ +++ C Ex. 2 No OFF +++ + D Ex. 3 No OFF ++ +++ F Ex. 1 Yes OFF +++ +++ G Ex. 3 Yes OFF +++ ++ H Ex. 1 Yes ON ++ ++ I Ex. 3 Yes ON ++

(57) Photographs H and I were taken with the light of the booth switched on and the light of the room switched off. However, a filter was then used to prevent saturation of the photographic equipment.

(58) Photographs A, B, C, D, F and G were taken with the light of the booth and the light of the room switched off. Photographs F and G were also taken with a filter in order to be able to carry out a comparison with photographs H and I.

(59) Example 1 can be compared with example 2. These two glazings differ only in the position of the mirror layer. The mirror layer is located, for example 1, inside the glazing on the internal face of the rear substrate whereas, for example 2, the mirror layer is located on the external face of the rear substrate. In the OFF state, the projection of images onto the scattering face clearly shows that the best results are obtained when the mirror layer is located as close as possible to the functional film, that is to say, for example, with a mirror layer of Mirastar type placed inside the glazing. This configuration provides both a good mirror state in the ON state and good quality of the projection screen in the OFF state.

(60) Example 1 can also be compared with example 3. Example 3 differs from example 1 essentially in that the mirror layer exhibits higher light transmission values. The glazing of example 3 exhibits a light transmission value of 17.1%, whereas the glazing of example 1 exhibits a light transmission value of less than 3%. The comparison of photographs F, G, H and I confirms that better results are obtained with a glazing comprising a lower light transmission.