Glazing unit comprising a variable light scattering system and a pair of absorbing elements

Abstract

The invention relates to a glazing unit comprising a substrate coated with a variable light scattering system switching between a transparent state and a translucent state comprising a scattering layer able to scatter the incident light along scattering angles greater than the critical total internal reflection angle at the interface between the substrate and the air and at least one pair of elements absorbing visible light separated from one another at least by the scattering layer. The invention also relates to the use of said glazing unit as a projection or back-projection screen.

Claims

1. A glazing unit comprising a variable light scattering system switching between a transparent state and a translucent state comprising a scattering layer comprising liquid crystals situated between two electrodes, said variable light scattering system being situated between two substrates carrying said electrodes, wherein: said scattering layer is able to scatter incident light along scattering angles greater than a critical total internal reflection angle at an interface between one of the two substrates and air, and the glazing unit comprises at least one pair of elements absorbing visible light separated from one another at least by the scattering layer.

2. The glazing unit as claimed in claim 1, wherein the glazing unit exhibits an energy absorption greater than 10%.

3. The glazing unit as claimed in claim 1, wherein each element absorbing visible light in the at least one pair of elements is identical.

4. The glazing unit as claimed in claim 1, wherein the at least one pair of elements absorbing visible light are arranged symmetrically with respect to at least one of the variable light scattering system and the scattering layer.

5. The glazing unit as claimed in claim 1, wherein substrates are glass substrates.

6. The glazing unit as claimed in claim 1, wherein the at least one pair of elements absorbing visible light comprise at least one of an absorbing substrate and an absorbing coating.

7. The glazing unit as claimed in claim 1, wherein the at least one pair of elements absorbing visible light comprise at least one absorbing substrate laminated by means of an interlayer spacer to one of the substrates.

8. The glazing unit as claimed in claim 1, wherein the at least one pair of elements absorbing visible light comprises at least one pair of absorbing substrates laminated by means of interlayer spacers to each of the substrates.

9. The glazing unit as claimed in claim 1, wherein at least one of the electrodes comprises a coating absorbing in the visible wavelength range.

10. The glazing unit as claimed in claim 1, wherein the at least one pair of elements absorbing visible light exhibit: a light transmission of at least 50%, and an energy absorption of at least 10%.

11. The glazing unit as claimed in claim 1, wherein the two substrates comprise a first substrate composed of clear glass and a second substrate composed of clear glass, the pair of elements absorbing visible light comprise a first substrate made of tinted glass and a second substrate made of tinted glass, and the glazing unit comprises a multilayer structure having the following layers, in sequential order: the first substrate made of tinted glass, a first lamination interlayer spacer, the first substrate composed of a clear glass, a first one of the two electrodes, the scattering layer, a second one of the two electrodes, the second substrate composed of a clear glass, a second lamination interlayer spacer, the second substrate made of tinted glass.

12. The glazing unit as claimed claim 1, wherein the pair of elements absorbing visible light comprise two substrates made of tinted glass.

Description

EXAMPLE

I. Materials Used

(1) 1. Substrates and Interlayer Spacers

(2) The transparent substrates used are Planilux glass substrates marketed by the company Saint-Gobain. These substrates have a thickness of 4 mm.

(3) The substrates absorbing in the visible are Parsol Bronze glass substrates marketed by the company Saint-Gobain having a thickness of 4 mm, a light transmission of 60% and an energy absorption of 34%.

(4) The coatings absorbing in the visible used, previously deposited onto flat glass substrates of 6 mm in thickness, are as follows: a multilayer comprising a layer based on silver referenced KN 169 at Saint-Gobain exhibiting, when it is deposited onto the substrate, a light transmission TL of 69% and a light absorption of at least 30%, a multilayer comprising a layer based on stainless steel referenced SKN 144 at Saint-Gobain exhibiting, when it is deposited onto the substrate, a light transmission TL of 44% and a light absorption of at least 30%.

(5) These substrates may be laminated by for example using an interlayer spacer of PVB or of EVA.

(6) 2. Variable Light Scattering Systems (SDLV) and Glazing Units

(7) A functional film marketed by the company NSG under the trade name UMU FILM has been used. This film comprises two sheets of PET each carrying an electrode composed of a layer of ITO of around 50 nm and with a resistance of around 100 ohms per square and a layer of liquid crystals of the NCAP type. The assembly consisting of the NCAP layer and of the two electrodes is called SDLVA. According to the information available on this functional film, the layer of liquid crystals is obtained according to NCAP technology and comprises drops of liquid crystals having a diameter of around 5 m.

(8) The SDLVB comprises a PDLC layer obtained by phase separation induced by UV radical polymerization using the mixture of liquid crystals marketed by the company Merck under the reference MDA-00-3506 and a photopolymerizable composition in the presence of a spacer. The photopolymerizable composition is obtained based on the product MXM 035 marketed by Nematel. This product in two parts A and B comprises: a mixture of two acrylate monomers, ethylhexyl acrylate and hexanediol diacrylate and of acrylate oligomers (part B), a mercaptan (part A), a photoinitiator for its UV polymerization (part A).

(9) The spacers are beads marketed under the trade name Sekisui Micropearl of 15 m in mean diameter.

(10) The SDLVB is placed between two glass substrates. In order to obtain the glazing units incorporating the SDLVB, the following steps are carried out: a layer of ITO of around 50 nm and with a resistance of around 100 ohms per square is deposited by a magnetron process onto a Planilux or Parsol glass substrate so as to form an electrode carrier substrate, a seal using an acrylate adhesive bond is applied around the edge of the glass substrate, the precursor composition of the PDLC layer comprising the photopolymerizable composition, the mixture of liquid crystals and the spacers is deposited onto an electrode carried by a substrate, a second substrate coated with an electrode is deposited onto the first substrate with the two conducting layers of the electrodes face-to-face and separated by the layer of precursor composition of the PDLC layer, the two glass sheets are pressed together, the whole assembly is exposed to UV radiation.

(11) TABLE-US-00001 Scattering Layer SDLVA SDLVB Technology NCAP PDLC Type of liquid crystals Nematic Nematic Mean dimensions of the drops (m) 5 0.74 Nature of the polymer Not specified acrylate Proportions of mixture of liquid crystals Not specified 50-55% Thickness of the layer Not specified 15 m

II. Description of the Glazing Units

(12) TABLE-US-00002 Multilayer Comp. 1 Inv. 0 Inv. 1 Inv. 2 Inv. 3 Inv. 4 Substrate/ Planilux Parsol KN169 SKN144 Layer Interlayer EVA PVB PVB PVB spacer Substrate/ PET Planilux Planilux Parsol Planilux Planilux Layer SDLV SDLVA SDLVB SDLVB SDLVB SDLVB SDLVB substrate PET Planilux Planilux Parsol Planilux Planilux Interlayer EVA PVB PVB PVB spacer Substrate/ Planilux Parsol KN169 SKN144 layer TL % 75% 84.8% 36.3% 37.3% 48% 19%

III. Determination of the Scattering Indicators in Transmission

(13) FIGS. 3 and 4 respectively show the scattering indicators of the glazing units Inv.0 and Comp.1 incorporating the variable light scattering systems SDLVB and SDLVA. These indicators show, as a function of the scattering angle in the range between 90 and 90, the intensity of the transmitted light (normalized between 0 and 1). These profiles have been measured using the test bench REFLET marketed by the company STIL.

(14) FIG. 3 corresponds to the scattering indicator of a glazing unit developed by SAINT-GOBAIN (Inv. 0) comprising the SDLVB placed between two Planilux glass sheets themselves laminated between two Parsol glass sheets. The scattering indicator in transmission for the glazing unit Inv. 0 exhibits: a sharp peak in the center corresponding to the least deflected part of the rays, a bell curve underneath the peak corresponding to the major part of the rays scattered at large angles.

(15) Thus, the whole angular range is explored, and rays emerge from the substrate with angles going up to 90. It is therefore observed that, for the glazing unit Inv.0 comprising a layer scattering the incident light along scattering angles greater than the critical total internal reflection angle at the interface between the substrate and the air (c is around 40), a part of the rays cannot get out owing to the total internal reflection.

(16) FIG. 4 corresponds to the scattering indicator of the glazing unit Comp. 1 comprising the SDLVA system included between sheets of PET, the whole assembly being laminated between two Planilux glass sheets. The scattering indicator in transmission for the glazing unit comp. 1 is much more pointed. The rays do not go beyond 40 in air. This means that the scattered rays for the scattering layer arrive at the glass/air interface with a maximum incident angle of 25 corresponding to an angle of incidence lower than the critical total internal reflection angle at the interface between the substrate and the air of around 40. The phenomenon of diffuse reflection is not observed for these glazing units but the hiding ability is reduced.

IV. Evaluation of the Quality of the Screens

(17) 1. Assessment of the Visual Aspect in the ON State

(18) The improvement of the visual aspect in the ON state (transparent) of the glazing units has been assessed. A panel of several persons has visually assessed the diffuse reflection of several glazing units corresponding to the presence or otherwise of a white fogging or bright halo. These glazing units are observed at an angle in the range between 50 and 60. The panel has assigned for each glazing unit an assessment indicator chosen from amongst: presence of a marked white fogging indicating a strong diffuse reflection, 0 slight white fogging indicating a weak diffuse reflection, + absence of white fogging indicating the absence of visible diffuse reflection.

(19) TABLE-US-00003 Assessment indicator Inv. 0 Comp. 1 + Inv. 1 + Inv. 3 + Inv. 4 +

(20) FIG. 2 shows a photograph of the following glazing units (from left to right): Inv. 0, Comp.1 and Inv.2. The diffuse reflection is very visible for the glazing unit Inv.0 comprising a layer scattering the incident light along scattering angles greater than the critical total internal reflection angle at the interface between the substrate and the air and not comprising any absorbing element. In comparison, for the glazing unit according to the invention Inv.1 furthermore comprising two absorbing substrates, the panel does not observe any white fogging and hence no diffuse reflection. The coloring or tint for the glazing unit Inv.1 comes from the fact that the glass PARSOL is colored in addition to simply being absorbing, but this is not necessary and a neutral absorbing glazing unit would produce the same effect.

(21) Finally, by comparing the glazing unit Comp.1 comprising a layer not scattering the incident light along scattering angles greater than the critical total internal reflection angle at the interface between the substrate and the air and the glazing unit of the invention Inv. 1, surprisingly better results are observed in terms of absence of diffuse reflection for the glazing unit according to the invention Inv.1.

(22) The glazing units Inv.3 and Inv.4 respectively comprising a substrate comprising an absorbing coating KN 169 exhibiting a TL of 69% and an absorbing coating SKN 144 exhibiting a TL of 44% have a more neutral tint than the glazing unit Inv.1. The effect of a reduction in the diffuse reflection is still clearly present and effective.

(23) 2. Quantitative Measurement of the Quality of the Transparent State of the Glazing Units

(24) TABLE-US-00004 Voltage: 30 V Voltage: 12 V Inv. 0 Inv. 1 Inv. 0 Inv. 1 Transmission at 0 100% 43% 99% 40% Diffuse reflection at 0 100% 21% 163% 35% Ratio Trans./Diff. Reflection 1.00 2.07 0.61 1.14 at 0 Improvement at 0 0% +107% 39% +14% Diffuse reflection at 30 218% 26% 351% 32% Ratio Trans./Diff. Reflection at 0.46 1.66 0.28 1.24 30 Improvement at 30 0% +263% 39% +171%

(25) The values of transmission and of diffuse reflection have been measured in the ON state by applying voltages of 30 Vrms corresponding to the nominal voltage and of 12 Vrms corresponding to a low voltage ideal for a bathroom, the power being supplied by an AC voltage at 50 Hz. These values of transmission and of diffuse reflection have been measured at 0 and at 30 with respect to the normal to the glazing unit.

(26) In the table, the value of the diffuse reflection and of the transmission of the glazing unit Inv.0 are taken as 100% by convention, the other values thus being normalized to the latter.

(27) The ratio between the light transmission and the light reflection is considered as a figure of merit of the esthetic aspect of the glazing unit. Finally, the improvement is the ratio between this figure of merit with respect to that of the glazing unit Inv.0 at 30 Vrms and hence the improvement with respect to the latter.

(28) At 0, in other words directly facing: for an applied voltage of 30 Vrms, the performance of the glazing unit Inv. 1 is 2 times better than that of the glazing unit Inv. 0, the performance of the glazing unit Inv.1 at 12 V is comparable with or even greater than that of the glazing unit Inv.0 at 30 V.

(29) Going above 30, the performance of the glazing unit Inv.0 falls dramatically with respect to 0. This is not the case for the glazing unit with absorbing glass Inv.1, which maintains a virtually-constant performance between 30 and 0.

(30) Thus, the invention allows both the level of performance of the glazing unit to be maintained while reducing the voltage to 12 V, and this good performance to be maintained including in angle.

(31) 3. Assessment as a Projection Screen

(32) A panel of several persons has visually assessed the diffuse reflection of glazing units corresponding to the presence or otherwise of a white fogging or bright halo when an image is projected in direct projection mode. The projected image evaluated by the panel has been photographed and is the subject of FIGS. 5 and 6 each comparing the direct projection onto a glazing unit according to Inv.0 (on the left) with respect to a glazing unit according to the invention Inv.1 (on the right). For each image projected onto a glazing unit, the panel has assigned an assessment indicator chosen from amongst:

(33) presence of a white fogging or marked halo resulting from a strong diffuse reflection,

(34) 0 slight white fogging corresponding to a low diffuse reflection,

(35) + absence of white fogging corresponding to the absence of any visible diffuse reflection.

(36) TABLE-US-00005 Assessment indicator Inv. 0 Inv. 1 +
Whereas the halo is clearly present for the glazing unit Inv.0 and does not allow an acceptable quality of image to be obtained, the latter is absent in the glazing unit laminated with the absorbing glass Inv.1. On the other hand, it is clear that the overall brightness of the image is reduced. This is of course expected, but the reduction in the halo achieved is much more significant.