Patent Description:
Transparent surfaces, especially glass facades of buildings or automotive glazing are more and more subject to functionalization. The main fields of interest are transparent sun control, lighting and displaying of information. In the automotive market illumination of transparent glass surfaces is of particular interest.

<CIT> describes a device for illuminating an automotive sunroof. However, the structure of the device described therein is rather complex and leads to an increased thickness of the sunroof part. This thickness increase unavoidably leads to a reduction of the headspace of the driver and to an increase of the vehicle weight.

<CIT> describes illuminable glazing for an automotive sunroof comprising a light guiding layer made with light scattering particles embedded therein or with a physically modified surface.

<CIT> discloses a chromatic stratified glass structure comprising two glass sheets; and an adhesive transparent polymeric layer sandwiched between the two glass sheets, wherein the face of one of said two glass sheets facing the adhesive polymeric layer is coated with a nanoparticle-loaded paint as a Rayleigh-like diffusing interlayer for visible light which preferentially scatters short- wavelength components of impinging light with respect to long-wavelength components of impinging light, or wherein the adhesive polymeric layer itself is coated with said nanoparticle- loaded paint. Said adhesive polymeric layer is made of EVA or PVB.

However, there is still a need for improved illuminable glazing. Therefore, one objective of the present invention is a laminated glazing with improved production costs, raw material costs and/or an improved environmental footprint. Another objective of the present invention is to provide laminated glazing with improved characteristics like an improved thermal stability, improved optical properties like an improved haze, transparency and/or transmissibility, and/or improved design features.

Accordingly, the present invention provides a laminated glazing comprising two sheets of glass (<NUM>,<NUM>) and at least one polymer interlayer film (<NUM>), as well as a further polymer interlayer film (102A) comprising polyvinyl butyral and at least <NUM> % by weight of a plasticizer before lamination, between the two sheets of glass characterized in that a functional layer (<NUM>) comprising light scattering particles is applied to at least one surface of the polymer interlayer film (<NUM>), wherein the polymer interlayer film (<NUM>) comprises polyvinyl butyral and optionally a plasticizer W, wherein the content of plasticizer W in the polymer interlayer film (<NUM>) before lamination is equal to or less than <NUM>%. Furthermore, the polymer interlayer film (<NUM>) has a thickness of equal to or more than <NUM> microns , to equal to or less than <NUM> microns before lamination.

One advantage of using a polyvinyl butyral (PVB) polymer interlayer film (<NUM>) with very little or no plasticizer is the possibility to generate a film with a particularly smooth surface and thus a better, homogeneous print image on the smooth side. Also, the polyvinyl butyral material used for film <NUM> is naturally very compatible with the standard PVB interlayers used in the glass industry. Furthermore, the a plasticizer-free and therefore stiff PVB film <NUM> can be printed on using new, more economical roll-to-roll processes such as flexographic printing. This is not possible with glass or soft PVB films.

Preferably, the polymer interlayer film (<NUM>) also comprises homo- or copolymers of (meth)acrylates, poly(vinyl) acetals, ionomers like ethylene methacrylic acid copolymers, nitro cellulose, polystyrenes, thermoplastic polyurethane, polycarbonates, polyvinyl chloride, polyolefines like polyethylene or polypropylene, polyethylene terephthalate, ethylene-vinyl acetate or mixtures thereof.

The light scattering particle are typically applied to the at least one surface of the polymer interlayer film (<NUM>) by means of a coating or printing process. In case of printing, they can be applied via techniques that are commonly known in the printing industry such as offset printing, rotogravure printing, flexography, screen-printing and inkjet printing.

The thickness of the functional layer (<NUM>) is preferably <NUM> to <NUM>, more preferably <NUM> to <NUM> before lamination.

The functional layer (<NUM>) preferably comprises the light scattering particles and at least one matrix material. Suitable matrix materials include polymers in which the light scattering particles can be homogenously dispersed without decomposition. Preferably, the matrix material comprises homo- or copolymers of (meth)acrylate, methyl methacrylate, poly(vinyl) acetal, nitro cellulose, polystyrene, poly vinyl alcohol, polyurethane, poly carbonate and polyvinyl chloride. Most preferably, the matrix material is polyvinyl butyral.

Further components might be present in the functional layer (<NUM> ). Examples of further components include co-resins, solvents, UV absorber, UV-stabilizer, cross-linker, curing agents, accelerants, photo-initiators, surfactants, stabilizers, filler, thixotropic modifiers and plasticizers.

Light scattering materials known in the art can be employed. Preferably, the light scattering particles are chosen from the group consisting of TiO<NUM>, ZnO, Al<NUM>O<NUM>, ZrO<NUM>, PbSO<NUM>, BaSO<NUM>, CaCO<NUM>, glass, polymers and mixtures thereof. The light scattering particles can be used as solid or hollow beads or fibres.

Preferably, the light scattering particles are present in the functional layer (<NUM>) in an amount of <NUM> to <NUM> % by weight, more preferred <NUM> to <NUM> % by weight, most preferably <NUM> to <NUM> % by weight.

Also preferably, the light scattering particles have a median particle size D50 by volume determined by the laser diffraction method according to DIN <NUM> of equal to or more than <NUM>, more preferably <NUM>, <NUM> or <NUM>. Also preferably they are equal to or less than <NUM>, more preferably <NUM> and most preferably <NUM>. Preferably, the median particle size by volume determined by the laser diffraction method according to DIN <NUM> is equal to or more than <NUM> and equal to or less than <NUM>.

Preferably, the light scattering particles are present in the functional layer (<NUM>) in form of a concentration gradient, i.e. concentration of functional particles in the functional layer (<NUM>) varies depending on the distance to the light source. More preferably, the concentration of light scattering particles in the functional layer (<NUM>) increases with an increasing distance to the nearest light source.

In one embodiment, the laminated glass according to the present invention is used as glazing in an automobile. Preferably, the second glass sheet (<NUM>) is facing the outside of the vehicle. Also preferably, the laminated glazing of the present invention is used for a sunroof. In that case, second glass sheet (<NUM>) may be tinted in order to reduce the solar energy which is transmitted through the laminate into the vehicle and thus may show increased absorption. Such highly light-absorptive sheets are particularly unsuited as optical waveguides.

Preferably, the functional layer (<NUM>) completely covers the at least one surface of the polymer interlayer film (<NUM>).

Also preferably, the functional layer (<NUM>) covers only part of the polymer interlayer film (<NUM>). Thus, the functional film (<NUM>) can be applied in form of a pattern and illumination in form of certain pattern can be achieved, which is not possible in case the light scattering particles are evenly dispensed in the laminate. Thus, preferably, the functional film (<NUM>) covers equal to or less than <NUM>%, <NUM>%, <NUM>% and most preferably less than <NUM>% of the at least one surface of the polymer interlayer film (<NUM>). This embodiment is especially useful for informative and/or decorative glazing for aircrafts, trains or ships and for use in the construction area, especially for shop windows, elevators or facade glazing.

The thickness of the functional layer (<NUM>) is preferably from <NUM> to <NUM>, more preferably, from <NUM> to <NUM>, most preferably from <NUM> to <NUM> as measured by IR microscopy.

In the present invention optically transparent means completely optically transparent as well as semi-transparent. Hence, optically transparent means that at least <NUM>% of the initial light passes through the device comprising layer (<NUM>), even more preferred is <NUM> to <NUM>%, and even more preferred is <NUM> to <NUM>%. The transparency (light transmission) is determined as light transmission TL (<NUM> to <NUM>) based on DIN EN <NUM> on a test laminate using two standard panes of clear glass.

For the avoidance of doubt, the light transmission is measured in an area of the test laminate which comprises the functional layer (<NUM>) and is compared to an area which does not comprise the functional layer (in the same laminate or, if the functional layer (<NUM>) completely covers the surface of the polymer interlayer film (<NUM>), on a test laminate prepared without the functional film (<NUM>) using the same type of film).

In order to avoid haze in the polymer interlayer films (<NUM>) and (102A), the amount of chloride ions and/or nitrate ions and/or sulphate ions in any of the different layers may be reduced. The chloride content can thus be less than <NUM> ppm, preferably less than <NUM> ppm, and in particular less than <NUM> ppm. Most preferably, the chloride content is less than <NUM> ppm. The nitrate content may be less than <NUM> ppm, preferably less than <NUM> ppm, and in particular less than <NUM> ppm. Most preferably, the nitrate content is less than <NUM> ppm. Again optionally, the sulphate content may be less than <NUM> ppm, preferably less than <NUM> ppm, and in particular less than <NUM> ppm, most preferably less than <NUM> ppm.

Also preferably, the polymer interlayer film (<NUM>) comprises polyvinyl butyral and a plasticizer W, wherein the content of plasticizer W in the polymer interlayer film (<NUM>) before lamination is equal to or less than <NUM>%. More preferably less than <NUM>%, more preferably less than <NUM>% or <NUM>% and more preferably less than <NUM>% or more preferably, the polymer interlayer film is free of any added plasticizer.

The term "before lamination" shall denote the state of the film before it is brought into contact with any of the other components of the present laminated glazing.

In case of polyvinyl butyral, the films are generally produced by extrusion with use of a cast-film line or in the form of a blown film. Here, a surface roughness may also be produced by controlled melt fracture or with the cast-film method additionally by use of a structured chill roll and/or structure back roll. Preferably, the at least one surface of polymer interlayer film (<NUM>) has a roughness Rz of equal to or less than <NUM> before lamination measured in accordance with EN ISO <NUM>. The polymer interlayer film (<NUM>) used in accordance with the invention preferably has a one-sided surface structure with a roughness Rz of less than <NUM>, preferably from <NUM> to <NUM>, more preferably Rz from <NUM> to <NUM>. This smooth surface ensures that light scattering particles can be applied to the surface of polymer interlayer film (<NUM>) in a very homogenous manner leading to a high quality optical pattern of the illuminated glazing. The other surface of the polymer interlayer film may have roughness as described above.

However, regular lamination interlayers made from polyvinyl butyral typically have a rougher surface to ensure proper de-airing during the lamination process. The roughness of such films typically range from an Rz value of <NUM> to <NUM>. Thus, the other surface of the polymer interlayer film may have roughness as of <NUM> to <NUM>, preferably <NUM> to <NUM>, more preferably <NUM> to <NUM>.

The polymer interlayer film (<NUM>) has a thickness of equal to or more than <NUM> to equal to or less than <NUM> before lamination, more preferably <NUM> to <NUM>, most preferably <NUM> to <NUM>, also preferably <NUM> to <NUM> and at specifically <NUM> to <NUM>. This range of thickness does not include additional coating on the film. It is especially preferred for these thin polymer interlayer films to have the low or no content of plasticizer or even no plasticizer as described earlier to avoid sticking issues and to exhibit the required rigidity to print on and handle such thin films.

The further polymer interlayer film (102A) comprises polyvinyl butyral. Preferably, at least one surface of the further polymer interlayer film (102A) has a roughness Rz of <NUM> to <NUM>, more preferably, <NUM> to <NUM>, and most preferably <NUM> to <NUM> before lamination measured in accordance with EN ISO <NUM>. Also preferably, the other surface has a roughness Rz of <NUM> to <NUM>, more preferably, <NUM> to <NUM>, and most preferably <NUM> to <NUM> before lamination measured in accordance with EN ISO <NUM>.

Further polymer interlayer film (102A) may be any plasticized PVB film known in the art, i.e. it may contain a single plasticiser as well as mixtures of plasticisers, before lamination, at least <NUM> % by weight, such as <NUM> to <NUM> % by weight, preferably <NUM> to <NUM> % by weight and in particular <NUM> - <NUM> % by weight plasticiser (s).

Suitable plasticizers include one or more compounds selected from the following groups:.

Particularly preferred are <NUM>,<NUM>-cyclohexane dicarboxylic acid diisononyl ester (DINCH) or triethylene glycol-bis-<NUM>-ethyl hexanoate (3GO or 3G8).

In addition, polymer interlayer films (<NUM>) and (102A) may contain further additives, such as residual quantities of water, UV absorber, antioxidants, adhesion regulators, optical brighteners or fluorescent additives, stabilisers, colorants, processing aids, inorganic or organic nanoparticles, pyrogenic silicic acid and/or surface active substances.

Alternatively, the polymer interlayer film (<NUM>) and/or the further polymer interlayer film comprise less than <NUM> % by weight, more preferably no UV absorber to avoid color shift in the visible light.

The thickness of the further polymer interlayer film (102A) before lamination is preferably <NUM> to <NUM>, more preferably <NUM> to <NUM>, more preferably <NUM> - <NUM> and most preferably <NUM> to <NUM>.

It is especially preferred to use polymer interlayer films (<NUM>) and (102A) that have at least one rougher surface and orientate them in a manner that the rougher surface is in contact with the glass sheets (<NUM>,<NUM>) in order to allow sufficient de-airing in the lamination process.

Depending on the location where the final glazing is used, e.g. in case of an automotive sunroof, the second glass sheet (<NUM>), which faces the sun, may often be tinted in order to reduce the solar energy which is transmitted through the laminate into the vehicle. Thus, an optical separation layer (<NUM>) may be used between the optionally tinted glass sheet (<NUM>) and the light source in order to reduce the amounts of the light which enters glass sheet (<NUM>), where it would be absorbed and lost for the purpose of illumination.

Accordingly, another embodiment of the present invention concerns a laminated glazing comprising, in that order, a first sheet of glass (<NUM>), a further polymer interlayer film (102A), a functional layer (<NUM>), a polymer interlayer film (<NUM>), and an optical separation layer (<NUM>), and a second sheet of glass (<NUM>).

The optical separation layer (<NUM>) may consist of any medium which is capable of preventing major amounts of light entering glass sheet (<NUM>). As regular lamination interlayers have a similar refractive index as the clear glass sheets (<NUM>,<NUM>) these are not well suited as optical separation layer (<NUM>). Hence, the refractive index of the optical separation layer (<NUM>) has to be significantly lower. The lower the refractive index of optical separation layer (<NUM>), the more efficient the light guiding and the lighting will be. Suited materials show sufficient adhesion, cohesion and mechanical strength to enable a firm bond between the neighbouring layers (<NUM>) and (<NUM>). Suitable material include a polymer or inorganic materials or composites of these. Furthermore, the low refractive index layer may consist of a nanoscale, porous material, which enables to incorporate low refractive index fluids in its pores.

In another configuration, the low refractive index layer can also be chosen to be a simple gap filled by air or another gas in a similar fashion as is the case in common insulating glass units. In another embodiment, the gap may be chosen to be left unfilled, thus providing a vacuum in a similar fashion as for vacuum insulating glasses. In this latter case, the gap needs to be held open and prevented from collapsing by tiny spacers in form of printed on dots which preferably are made from a non-transparent, preferably white material.

Inherent part of the final application is the light source (<NUM>), which provides the light which is coupled into the light guiding layers (<NUM>) and (<NUM>) via an optical connector (<NUM>). The optical connector (<NUM>), which is a transparent, optically clear material with low light absorption, may form a permanent bond between the light source (<NUM>) and the light guiding layers (<NUM>) and (<NUM>), e.g. by means of physical and/or chemical curing, optical clear adhesive. Alternatively, by a positive-fit or force-fit connection. The latter options allows for an improved maintainability, e.g. change of the light source (<NUM>). Materials which are suited for positive-fit or force-fit materials are optically clear polymers, especially elastomers. The light source (<NUM>) may be any conventional light source, preferably it is an LED light source.

A second aspect of the present invention is a process for the production of a laminated glazing as described above comprising a step wherein the functional film (<NUM>) is applied to the polymer interlayer film (<NUM>) by means of a printing or coating process. The glass sheets (<NUM>,<NUM>) and the various interlayer films can be laminated by any known lamination technique known in the art.

For forming the functional layer (<NUM>) a printing ink, consisting of <NUM> % by weight titanium dioxide (as light scattering particles) with a particle size D50 of <NUM> determined by laser diffraction method according to DIN <NUM>, <NUM> % by weight of poly(methyl methacrylate) (PMMA) (as matrix material) and <NUM> % by weight of <NUM>-butoxyethanol acetate and <NUM> % by weight of cyclohexanone (as sacrificial solvents), was chosen.

A polyvinyl butyral interlayer with a thickness of <NUM> containing no added plasticizer was used. This substrate had a side A with a roughness Rz of <NUM> and a side B with a roughness Rz of <NUM>. The functional layer was applied to the side B of the interlayer by screen printing using the above described printing ink. A screen with <NUM> threads/cm and a thread diameter of <NUM> was used. The screen was previously treated with a photoemulsion which was partially cured to form the desired printing pattern of a rectangle measuring <NUM> x <NUM>. The printed ink was dried for <NUM> minutes at room temperature. The printed substrate was then placed on a regular sheet of float glass with a thickness of <NUM> so that the unprinted side A was in direct contact with the glass. On top of the printed side B of the substrate a regular, plasticized polyvinyl butyral interlayer <NUM>, Trosifol® UltraClear available from Kuraray Europe GmbH) was placed. On top of this second interlayer a second sheet of regular float glass with a thickness of <NUM> was placed. All layers were A4 sized and were fixed in above described sequence by applying adhesive tapes to the outer glass sheets. In an vacuum bag this stack was then pre-laminated by applying a vacuum at room temperature for <NUM> minutes, followed by a vacuum at <NUM> for another <NUM> minutes. After pre-lamination the pre-laminate was autoclaved in an autoclave at <NUM> and a pressure of <NUM> bar for <NUM> minutes.

Due to the low roughness of side B of the first polyvinyl butyral interlayer, a homogeneous illumination of the printed region was obtained as compared to laminates which had been made with printed, standard lamination interlayers like Trosifol® UltraClear from Kuraray Europe GmbH with a higher roughness. Furthermore, a high visible light transmission (TL) (<NUM> to <NUM>) measured according to DIN EN <NUM> was achieved in the printed region of the laminate:.

A polyvinyl butyral interlayer with a thickness of <NUM> and no added plasticizer is used. This substrate has a side A with a roughness Rz of <NUM> and a side B with a roughness Rz of <NUM>. The functional layer is applied to the side B of the substrate by screen printing using the above described printing ink. A screen which has <NUM> threads/cm and a thread diameter of <NUM> is used. The screen is previously treated with an photoemulsion which is partially cured to form the desired printing pattern of rectangle measuring <NUM> x <NUM>. The printed ink is dried for <NUM> minutes at room temperature. The printed substrate is then placed on a sheet of low-iron glass with a thickness of <NUM> so that the unprinted side A is in direct contact with the glass. On top of the printed side B of the substrate a regular, plasticized polyvinyl butyral interlayer (thickness: <NUM>, Trosifol® UltraClear available from Kuraray Europe GmbH) is placed. On top of this thicker interlayer a <NUM> thick tinted glass sheet having a visible light transmission TL (<NUM> to <NUM>) of <NUM>% measured according to DIN EN <NUM> is placed. The tinted glass sheet has a regular side A and a side B which faces interlayer and is coated with a low refractive index coating having an refractive index of <NUM>.

All layers are A4 sized and are fixed in the above described sequence by applying adhesive tapes to the outer glass sheets. In an vacuum bag this stack is then pre-laminated by applying a vacuum at room temperature for <NUM> minutes, followed by a vacuum at <NUM> for another <NUM> minutes. After pre-lamination the pre-laminate is autoclaved in an autoclave at <NUM> and a pressure of <NUM> bar for <NUM> minutes.

Even within such laminate which comprises a highly absorptive tinted glass sheet <NUM> the functional layer <NUM> can be illuminated sufficiently, as the low refractive index coating <NUM> optically separates the tinted glass sheet <NUM> from the light guide layers <NUM>,<NUM>,<NUM> and 102A.

A <NUM> wide, plasticizer-free polyvinyl butyral film with a thickness of <NUM> and a surface roughness of <NUM> on its top side and <NUM> on its bottom side was doubled with <NUM> thick OPP carrier film on the bottom side. The OPP carrier film was wound-in without application of heat to form a temporary unit with the thin PVB to stabilize the web in the printing step and prevent any contamination or ink transfer to the unprinted side of the PVB and was essentially held together by electrostatic force. The PVB side of the temporary bi-lam was printed-on in a flexographic press using an water based ink essentially containing a poly-urethane binder, <NUM>% of TiO<NUM>, ink additives and water as the suspension liquid. An EPDM printing sleeve with a continuous dot pattern (<NUM> dot diameter, <NUM> inter-dot distance in horizontal and vertical direction) was used as the printing master. An anilox roller with an ink transfer volume of <NUM>/m<NUM> was chosen and the film was printed at a speed of <NUM>/min and wound to a roll. The resulting dry layer thickness of the ink was in the range of <NUM>. A <NUM> × <NUM> glass/glass laminate with the light diffusing interlayer and a standard PVB interlayer was constructed in the following way: <NUM> Planiclear® glass of above dimension was prepared by washing it dust free, the OPP carrier film was carefully removed and the <NUM> printed PVB was positioned on the first glass with the printed side facing upwards and the <NUM> rough bottom side contacting the glass surface. TROSIFOL® NR <NUM> was placed on top of the printed PVB and the assembly was completed with the second glass. Lamination was done using standard rubber bag and the same overall process conditions from above. The resulting laminate did hardly show any visual haze upon inspection (the dots being practically invisible when the laminate is inspected under normal illumination). An LED bar was attached to one edge of the laminate and when lit up, the according light colour couples out and the dot pattern appears to be illuminated.

Above laminate was compared to a region of a laminate of identical construction, except that in that region, a non-printed <NUM> film was used instead of the dot-printed film.

Visible light transmission TL and Haze were measured according to ISO <NUM> and ASTM D1003. The results indicate that despite the good light diffusing properties, the light diffusing print on a thin PVB only slightly reduces TL and only slightly increases visible haze:.

Claim 1:
Laminated glazing comprising two sheets of glass (<NUM>,<NUM>) and at least one polymer interlayer film (<NUM>) and a further polymer interlayer film (102A) between the two sheets of glass characterized in that a functional layer (<NUM>) comprising light scattering particles is applied to at least one surface of the polymer interlayer film (<NUM>), wherein the polymer interlayer film (<NUM>) comprises polyvinyl butyral and optionally a plasticizer W, wherein the content of plasticizer W in the polymer interlayer film (<NUM>) before lamination is equal to or less than <NUM>% and wherein the polymer interlayer film (<NUM>) has a thickness of equal to or more than <NUM> to equal to or less than <NUM> before lamination and wherein the further polymer interlayer film (102A) comprises polyvinyl butyral and before lamination, at least <NUM> % by weight of a plasticiser.