Multiple glazing with variable scattering by liquid crystals and its method of manufacture

Abstract

A multiple glazing with variable scattering by liquid crystals includes first and second flat float glass sheets sealed on the edge of their internal faces by a sealing joint, in particular made of a given sealing material, in particular essentially organic, first and second electrodes, and a layer of liquid crystals with an average thickness E between 15 and 60 μm inclusive of these values and incorporating spacers. The thickness A of each of the first and second glass sheets is less than or equal to 5.5 mm, and each of the internal faces coated with the first and second electrodes has a dioptric defect score, expressed in millidioptres, of less than 12E/15 where the thickness E of the liquid crystals is in μm.

Claims

1. A multiple glazing with variable scattering by liquid crystals comprising: first and second glass sheets sealed on an edge of their internal faces by a sealing joint; on the internal faces of the first and second glass sheets, first and second electrodes in the form of transparent electrically conductive layers provided with a power supply; and on the first and second electrodes, a layer of liquid crystals adapted to alternate reversibly between a transparent state and a translucent state by application of an alternating electric field, wherein a thickness of each of the first and second glass sheets is less than or equal to 5.5 mm, and wherein each of the internal faces coated with the first and second electrodes has a dioptric defect score, expressed in millidioptres, of less than 12E/15 where the thickness E of the liquid crystals is in μm.

2. The multiple glazing with variable scattering by liquid crystals according to claim 1, wherein for a thickness E of less than 30 μm, the thickness of the first glass sheet and the second glass sheet lies from 3 mm to 5.5 mm, and for a thickness E greater than or equal to 30 μm, the thickness of the first glass sheet and the second glass sheet lies from 2 mm to 5.5 mm.

3. The multiple glazing with variable scattering by liquid crystals according to claim 1, wherein the sealing joint has a width and is interrupted in its width by a plurality of openings each defining lateral joint ends, and wherein for each opening an additional sealing material forms a bridge between the lateral ends of the joint, thus forming material continuity.

4. The multiple glazing with variable scattering by liquid crystals according to claim 3, wherein the sealing joint is interrupted in its width by at least two openings facing a first edge of the glazing and by at least two other openings facing a second edge opposite the first edge.

5. The multiple glazing with variable scattering by liquid crystals according to claim 1, wherein the sealing joint and/or an additional sealing material is essentially organic.

6. The multiple glazing with variable scattering by liquid crystals according to claim 5, wherein the sealing joint and/or the additional sealing material is made of epoxy resin.

7. A method comprising arranging the multiple glazing with variable scattering by liquid crystals according to claim 1 as glazing in vehicles or buildings.

8. A method for producing multiple glazing with variable scattering by liquid crystals according to claim 1, comprising: forming the sealing joint, said forming comprising applying the sealing material on the first glass sheet provided with the first electrode; liquid depositing the layer of liquid crystals with an average thickness E on the first glass sheet provided with the first electrode and optionally on the second glass sheet provided with the second electrode; after forming the sealing joint and depositing the layer of liquid crystals, bringing the first and second glass sheets in contact; and before bringing the first and second glass sheets in contact, forming the plurality of said openings of the sealing joint each defining the lateral ends of the joint.

9. The method for producing multiple glazing with variable scattering by liquid crystals according to claim 8, wherein the sealing joint is interrupted in its width by at least two openings facing a first edge of the glazing and by at least two other openings facing a second edge opposite the first edge, and wherein the assembly of the first and second glass sheets is carried out by calendering, the first and second edges corresponding to the edges in the direction of calendering.

10. The method for producing multiple glazing with variable scattering by liquid crystals according to claim 9, wherein the assembly of the first and second glass sheets is carried out by pressing, wherein the sealing joint is interrupted in its width by at least two openings facing a third edge of the glazing adjacent to the first edge and by at least two other openings facing a fourth edge opposite the third edge.

11. The method for producing multiple glazing with variable scattering by liquid crystals according to claim 8, comprising applying the additional sealing material, forming a bridge between the lateral ends of the joint.

12. The method for producing multiple glazing with variable scattering by liquid crystals according to claim 11, wherein the additional sealing material consists of said sealing material, thus forming material continuity.

13. The method for producing multiple glazing with variable scattering by liquid crystals according to claim 12, wherein the additional sealing material is made of epoxy resin.

14. A multiple glazing comprising: first and second glass sheets each having a face sealed on an edge thereof by a sealing joint; first and second electrodes arranged respectively on the face of the first and second glass sheets, each of the first and second electrodes including an electrically conductive layer provided with a power supply; a layer of liquid crystals arranged on the first and second electrodes and adapted to alternate reversibly between a transparent state and a translucent state when an alternating electric field is applied, wherein a thickness of each of the first and second glass sheets is less than or equal to 5.5 mm, and wherein each of the faces coated, respectively, with the first and second electrodes has a dioptric defect score, expressed in millidioptres, of less than 12E/15 where the thickness E of the liquid crystals is in μm.

Description

(1) Other details and features of the invention will become apparent from the following detailed description, which is provided with reference to the appended drawings in which:

(2) FIG. 1 (already described) represents a schematic sectional view of reference multiple glazing with variable scattering by liquid crystals, not according to the invention,

(3) FIG. 2 represents a schematic sectional view of multiple glazing with variable scattering by liquid crystals in a first embodiment according to the invention,

(4) FIG. 3 shows the layout diagram of the measurement of the dioptric defect score,

(5) FIG. 4 shows the principle of the formation of an umbrascopic image on a screen on the basis of a planarity profile Y(x) of the glass,

(6) FIG. 5 shows an example of a local illumination profile E(x) and an average illumination profile E0(x),

(7) FIG. 6 represents a schematic view from below of multiple glazing with variable scattering by liquid crystals according to the invention, showing in particular the sealing joint and the openings,

(8) FIG. 6bis represents a schematic plan view of the multiple glazing with variable scattering by liquid crystals, showing in particular the sealing joint and the openings, in a variant of FIG. 6,

(9) FIG. 7 represents a schematic plan view of the manufacture of the multiple glazing with variable scattering by liquid crystals according to the invention, showing in particular the sealing joint and the openings.

(10) The exemplary embodiment represented in FIG. 2 shows the design of the liquid-crystal multiple glazing according to the invention in a first embodiment.

(11) On two sheets of float glass 1 and 1′, electrically conductive layers 3, 4 with a thickness of about 20 to 400 nm, having external surfaces 21, 31 and made for example of indium tin oxide (ITO), are arranged on the internal faces 11, 21. The ITO layers have an electrical sheet resistance of between 5 Ω/□ and 300 Ω/□. Instead of layers made of ITO, other layers of electrically conductive oxide or layers of silver whose sheet resistance is comparable may also be used for the same purpose.

(12) The layer 5 of liquid crystals, which may have a thickness of about 15 to 60 μm, is placed between the electrode layers 3 and 4.

(13) The layer 5 of liquid crystals contains spherical spacers. The spacers 6 consist of a transparent hard polymer. For example, the product from Sekisui Chemical Co., Ltd, known by the designation “Micropearl SP” has proven highly suitable as a spacer.

(14) In order to ensure uniformity of the thickness E of the liquid-crystal layer 5 and thus ensure the optical performance of the glazing with liquid crystals, glass panes 1, 1′ with their electrodes 3, 4 are each selected with a dioptric defect score according to the invention, which score is measured by umbrascopy in reflection.

(15) The basic principle is associated with the geometrical optics. The diagram of the layout is represented in FIG. 3.

(16) From a very thin source, such as a projector 100, a light flux is projected onto the face of the glass sheet 11 (coated or not with the electrode) intended to be the internal face. A projected image is observed on a screen 300 after reflection from the internal face 11 of the glass sheet. This image is acquired by a digital camera 200 in order to be processed. The reflection from the second face 12 is neutralized by using a wetted black fabric which is placed behind the glass pane 1 and on which the glass is bonded by capillary effect.

(17) FIG. 4 indicates the principle of the formation of an umbrascopic image on the screen 300 on the basis of a planarity profile Y(x) of the glass. A concave region on the glass pane (convergent defect) causes concentration of the incident reflected light 110 and therefore local over-illumination on the screen 300. A complex region on the glass (divergent defect) causes spreading of the incident reflected light 120 and therefore local under-illumination on the screen 300.

(18) FIG. 5 shows an example of a local illumination profile E(x) and an average illumination profile E0(x).

(19) When the local illumination E(x) is equal to the average illumination E0(x), the contrast is zero and consequently Y″(x)=0 and the optical power is zero.

(20) When the local illumination E(x) is greater than the average illumination E0(x), the contrast is negative and Y″(x)<0. A convergent defect is therefore involved, which corresponds to a concavity on the glass pane.

(21) When the local illumination E(x) is less than the average illumination E0(x), the contrast is positive and Y″(x)>0. A divergent defect is therefore involved, which corresponds to a convexity on the glass pane.

(22) Knowing that the planarity variations are more significant in the direction of the overall width, in order to explain the operating principle of the apparatus we will consider a planarity profile in the plane perpendicular to the casting direction and perpendicular to the surface of the glass. It can be shown on the basis of the laws of geometrical optics and conservation of energy that there is a relationship between the illumination E(x) measured on the screen corresponding to an abscissa point x on the glass pane and the profile Y(x) of the surface of the glass pane.

(23) Certain geometrical simplifications made on the basis of the following aspects: the layout is in quasi-normal reflection and the source is considered to be a point source, give the following relationship:

(24) $\frac{d^{2}Y\left(x\right)}{d{x}^2}=\frac{1}{D}\left(\frac{E_0}{E\left(x\right)}-1\right)$
with: Y(x): profile of the glass pane D: the glass pane—screen distance E.sub.0: average illumination at x (that which would be obtained without a planarity defect)

(25) Let the optical reflection power ORP (in dioptres) be:

(26) $ORP=2\times \frac{d^{2}Y\left(x\right)}{d{x}^2}\approx 2\times \frac{C\left(x\right)}{D}$
with the contrast C(x) such that

(27) $C\left(x\right)=\frac{E_0-E\left(x\right)}{E\left(x\right)}.$

(28) The contrast corresponds to the visual perception of the “linearity” (here in dashes because a profile rather than a surface is being considered) observed on the umbrascopic image projected onto the screen.

(29) Processing software calculates the contrast, and therefore the optical reflection power ORP, for each pixel of the image.

(30) The dioptric defect score (in millidioptres) reflects the homogeneity of the optical powers and is in fact the standard deviation σ of the distribution of the optical reflection powers over the internal face, defined by the relationship:

(31) $\sigma =\sqrt{\stackrel{\_}{{\left(O.P.r^2\right)}_{i,j}}-{\stackrel{\_}{\left(O.P.r\right)}}_{i,j}^2}$
with

(32) (O,P,r.sup.2).sub.i,j: mean square of the optical powers over the entire internal face

(33) (O,P,r).sub.i,j.sup.2: square of the mean of the optical powers over the entire internal face.

(34) The score must be less than 12 E/15 in order to ensure a sufficient optical quality in transmission, that is to say a good homogeneity of the light transmission in the “off” state.

(35) By way of example, for a thickness E of 15 μm with a standard float line having a capacity of 600 tonnes/day with a raw glass width of 3.5 m: the score of the 2.1 mm glass is less than 22 mdt, the score of the 3 mm glass is less than 11 mdt, the score of the 4 mm glass is less than 8 mdt.

(36) Furthermore, it is also possible to use known compounds for the layer of liquid crystals, for example the compounds described in Document U.S. Pat. No. 5,691,795. The liquid-crystal compound from Merck Co., Ltd, marketed under the brand name “Cyanobiphenyl Nematic Liquid Crystal E-31 LV” has also proven particularly suitable. In the case of this embodiment, this product is mixed in a ratio of 10:2 with a chiral substance, for example 4-cyano-4′-(2-methyl)butylbiphenyl, and this mixture is mixed in a ratio of 10:0.3 with a monomer, for example 4,4′-bisacryloylbiphenyl, and with a UV initiator, for example benzoin methyl ether. The mixture prepared in this way is applied onto one of the coated glass sheets. After curing of the layer of liquid crystals by irradiation with a UV light, a polymer network is formed in which the liquid crystals are incorporated.

(37) As a variant, the layer of liquid crystals does not contain a stabilizing polymer but consists only of the compound comprising liquid crystals and spacers. The compound comprising liquid crystals is therefore applied as such without a monomer additive, with a thickness of from 3 to 20 μm onto one of the glass sheets 1, 1′. Compounds for liquid-crystal layers of this type are described, for example, in Document U.S. Pat. No. 3,963,324.

(38) For the layer of liquid crystals, it is possible to use PDLCs such as the compounds 4-((4-ethyl-2,6-difluorophenyl)-ethinyl)-4′ -propylbiphenyl and 2-fluoro-4, 4′-bis (trans-4-propylcyclohexyl)-biphenyl, for example marketed by the company Merck under the reference MDA-00-3506.

(39) On the edge, the layer of liquid crystals is sealed by an adhesive sealing joint 5 which simultaneously serves to firmly and permanently bond the glass sheets 1, 1′.

(40) The adhesive sealing material which seals the separate glass sheets 1 and 1′ on their edges contains an epoxy resin.

(41) As shown in FIG. 6, the sealing joint has a given width L and is interrupted in its width by a plurality of openings 81 to 84, each defining lateral joint ends 71 to 74′.

(42) More precisely, the sealing joint 7 is interrupted in its width by two openings 81 to 82 facing a first edge of the glazing and by two other openings 83, 84 facing a second edge opposite to the first edge, these edges corresponding to the edges of the assembly direction of the glass panes, preferably by calendering.

(43) For each opening, an additional sealing material 7′ forms a bridge between the adjacent lateral ends of the joint, in particular consisting of the said sealing material, thus forming material continuity as shown in FIG. 6bis.

(44) In the initial state (“off” state), that is to say before the application of an electrical voltage, this liquid-crystal glazing 100 is translucent, that is to say it optically transmits but is not transparent. As soon as the current is connected up, the layer of liquid crystals changes under the effect of the alternating electric field into the transparent state, that is to say the state in which viewing is no longer prevented.

(45) The electrically controllable glazing with liquid crystals is produced by using a method described in detail below.

(46) In an industrial installation for continuous coating, by using the method of magnetic field enhanced reactive sputtering, float glass sheets according to the invention are coated in successive sputtering chambers with a layer of ITO having an approximate thickness of 100 nm.

(47) Two separate glass sheets of the same size and having the desired dimensions are cut from a large sheet of glass coated in this way and are prepared for continuation of the processing.

(48) The two separate glass sheets cut to the desired dimensions then firstly undergo a washing operation.

(49) The liquid-crystal layer mixed with the spacers is then applied onto one of the two glass sheets processed in this way. Since the two separate glass sheets are subsequently connected permanently and closely to one another on their edges by a sealing joint, the edge part of the glass sheet 1 is not coated over a width of about 2 to 10 mm.

(50) The coating with the liquid-crystal compound is carried out with the aid of an operation referred to as drop-by-drop filling. In order to carry out the operation, a drop-by-drop pouring apparatus is used which makes it possible to deposit drops of liquid crystals onto a glass substrate, the quantity poured being finely adjustable.

(51) In another embodiment of the method, in order to print the layer of liquid crystals, a screen printing fabric is used with a mesh the width of which is about 20 to 50 μm and the thread diameter of which is about 30 to 50 μm.

(52) The adhesive layer forming the joint 7 is likewise applied directly along the edge of the glass sheet 24 before or after deposition of the layer of liquid crystals. It may have a width of, for example, from 2 to 10 mm.

(53) As shown by FIG. 7, the formation of a plurality of openings 81 to 84 in the sealing joint is provided, with a size and distribution adapted to remove the excess liquid-crystal layer, the openings 81 to 84 each defining two adjacent lateral ends 71 to 74′ of the joint 7.

(54) Furthermore, in order to do this, the application of the sealing material is either discontinuous or is continuous then followed by creation of openings (by removing material 7).

(55) This is followed by application of the additional sealing material 7′ forming a bridge between the lateral ends of the joint 71 to 74′, preferably consisting of the said sealing material, thus forming sealing material continuity.

(56) When the two separate glass sheets have thus been pressed against one another, the adhesive layer 7 is compressed to the thickness E of the layer of liquid crystals.

(57) The openings 81 to 84 therefore serve: to remove the excess liquid-crystal layer, and therefore to better control the layer thickness and thus avoid a loss of optical quality, to degas the layer of liquid crystals in order to avoid the subsequent formation of bubbles in the layer and thus again to avoid a loss of optical quality.

(58) At least two openings are preferably positioned on the front edge of the calendering and at least two openings on the rear edge of the calendering.

(59) The width of the lateral ends is, for example, 10 mm. The more viscous the layer of liquid crystals is, the greater is the number of openings used.

(60) The calendering operation is subsequently carried out, or as a variant the pressing.

(61) If the layer of liquid crystals consists of a mixture of liquid crystals and a monomer, the polymerization operation is then carried out by irradiation with UV light.