The invention is directed to laminated glazing comprising two glas s sheets laminated by means of at least two thermoplastic interlayers wherein at least one surface of one of the interlayers is provided with a bird protection pattern in between the two thermoplastic interlayers and wherein at least one thermoplastic interlayer comprises a polyvinyl acetal .

Window strikes represent one of the greatest threat s to birds because window glazing is not perceived as a barrier to the bird . Ef fort has been made to develop bird-safe glazing by trans forming window glas s into a barrier that birds will see and avoid . Such glas s usually has bird protection patterns , i . e . vi sual markers , acros s the surface of the glazing to distort the reflections of surrounding elements . Such patterns are generally printed directly onto the surface of one of the glas s sheet s , e . g . by enamel printing . However, such printing techniques are not very flexible and rather expensive in the production proces s . Additionally, they can lead to a reduction in the quality of the glas s as enamel printing requires high temperatures .

Laminated glazing usually consist s of two glas s sheets laminated by means of thermoplastic interlayer films . Such f ilms are often made from plastici ser-containing polyvinyl acetal s like polyvinyl butyral (PVB) .

Thus , modification of the surface of the thermoplastic interlayer with a bird-protection pattern and subsequent lamination between two glas s sheets would also be a pos sible solution . However, it has now been found by the present inventors that this approach has various disadvantages . A bird-protection pattern printed or coated onto the surface of the interlayer using an ink, can interfere with the glas s surface and thus , lead to problems with the adhes ion of the interlayer to the glas s . This can impede the safety of the laminated glazing .

Additionally, it has been surprisingly found that the optical quality, especially in terms of a sharp boarder of the individual object s making up the bird protection pattern, is reduced when the patterns is in direct contact to the glas s surface . This decrease in optical quality will inevitably lead to a lower economic value of the windows produced .

The problem addres sed by the present invention was therefore to provide a laminated glas s compri sing a bird protection pattern with improved stability, improved optical quality, improved duration and/or improved proces sibility . These and other problems have been solved by the present invention .

Accordingly, a f irst aspect of the present invention concerns a laminated glazing for reducing or preventing bird collision compri sing at least two glas s sheets and at least a first and a second thermoplastic interlayer, characterized in that at least one surface of the first thermoplastic interlayer i s provided with a bird protection pattern facing the second thermoplastic interlayer and wherein the first thermoplastic interlayer compri ses a polyvinyl acetal . Preferably, the bird protection pattern is printed or coated onto the at least one surface of the first thermoplastic interlayer .

In other words , the bird-protection pattern is sandwiched between the first and the second thermoplastic interlayer and thus , the pattern is not in direct contact with a glas s surface of one of the two glas s sheet s . This feature highly improves the adhesion of the interlayer to the glas s sheets and thus , ensures the safety of the laminated glazing . Furthermore , the optical quality of the individual features of the pattern is highly improved . Additionally, fading or deterioration of the pattern f rom an exposure to sunlight can be reduced by using a UV-blocking agents present in the two interlayer f ilms on both sides of the pattern .

Also preferably, the bird protection pattern has a transparency for light in the range from 380 to 750 nm of les s than 5% . In this embodiment , the bird protection pattern can have any colour . However, it is preferably black or grey .

Alternatively, the bird protection pattern has a transparency for light in the range f rom 380 to 750 nm of more than 50% and compri ses a UV absorber or a UV reflective agent .

Unlike humans , many birds are tetrachromatic and can see light in the UV range . Thus , the bird protection pattern can also be present on the first thermoplastic interlayer by means of a UV absorbing or UV reflecting agent . These patterns can then be seen by the birds but are being conceived as clear to the human eye .

Examples of suitable UV reflecting agents are tin or titanium oxide . They may be deposited onto the surface of the first thermoplastic interlayer by any conventional thin film deposition, coating or printing technique .

Examples of suitable UV absorbers include benzotriazole-based compounds , benzophenone-based compounds , triaz ine-based compounds , benzoate-based compounds , malonic ester-based compounds , or oxalic anilide-based compounds .

More preferably, the UV absorber is a benzotriazole-based UV absorber such as 2- ( α, ω-methyl-2-hydroxyphenyl ) benzotriazole, 2- [ 2-hydroxy-3 , 5-bis ( α, ω -dimethylbenzyl ) phenyl ] -2H-benzotriazole, 2- ( 3 , 5-di-t-butyl-2-hydroxyphenyl ) benzotriazole, 2- ( 5-chloro-2- benzot riazolyl ) - 6-tert-butyl-p-cresol , 2- ( 3-t-butyl-5-methyl-2- hydroxyphenyl) -5-chlorobenzotriazole, 2- (3, 5-di-t-butyl-5- methyl-2-hydroxyphenyl ) -5-chlorobenzotriazole, 2- (3, 5-di-t-amyl- 2-hydroxyphenyl ) benzotriazole, and 2- (2 ' -hydroxy-5 ' -t- octylphenyl ) benzotriazole; or a hindered amine-based UV absorber such as 2 , 2 , 6 , 6-tetramethyl-4-piperidylbenzoate, bis (2, 2,6, 6- tetramethyl-4-piperidyl ) sebacate, bis (1, 2, 2, 6, 6-pentamethyl-4- piperidyl) -2- (3, 5-di-t-butyl-4-hydroxybenzyl ) -2-n- butylmalonate, and 4- (3- (3, 5-di-t-butyl-4- hydroxyphenyl ) propionyloxy) -1- (2- (3- (3, 5-di-t-butyl-4- hydroxyphenyl ) propionyloxy) ethyl) -2, 2, 6, 6- tetramethylpiperidine ; or a benzoate-based UV absorber such as 2, 4-di-t-butylphenyl-3, 5-di-t-butyl-4-hydroxybenzoate, and hexadecyl-3, 5-di-t-butyl-4-hydroxybenzoate . Most preferably, the UV absorber has a hydroxyphenyl benzotriazole structural unit. Especially preferred is 2- (2H-benzotriazol-2-yl ) -4 , 6-bis ( 1- methyl-l-phenylethyl ) phenol .

The transparency for light in the range from 380 to 750 nm is measured according to JIS R 3106.

The bird protection pattern can have any shape or motif. Preferably, the bird protection pattern comprises a plurality of separate elements such as dots, lines or grids. More preferably, the separate elements have a main dimension of 1 mm to 10 mm. Most preferably, the bird protection pattern is a dot pattern.

Surprisingly, it has also been found that laminated glazing with a low yellowness index db of the laminated glazing in the areas not comprising the bird protection pattern, i.e. in the areas where no coating or printing is present and the laminated glazing appears transparent, give especially advantageous results in terms of bird deterrence. It is believed that these highly clear areas increase the contrast to the printed/coated areas on the first interlayer and thus, the latter can more easily be detected by the birds . Accordingly, a preferred embodiment of the invention concerns a laminated glazing wherein the yellowness index db of the laminated glazing in the areas not comprising the bird protection pattern is less than 3, preferably less than 2.5, more preferably less than 2 and particularly preferably less than 1.0.

The yellowness is determined by the transmission of the film according to EN 410 at 430 nm on a ColorQuest XE in the Hunterlab 2 ° / C setting.

Preferably, the thickness of the first and the second thermoplastic interlayer is independently 450 - 2500 μm, more preferably 600 - 1000 μm, and most preferably 700 - 900 μm.

Alternatively, one of the thermoplastic interlayers can have a much lower thickness if the other one has a thickness as described hereabove . In this embodiment, the thinner thermoplastic interlayer is less than 100 μm, preferably 10 - 100 μm, more preferably 15 - 75 μm, most preferably 20 - 50 μm and specifically around 25 μm.

Preferably, both the first and the second thermoplastic interlayers contains a polyvinyl acetal .

The films can contain polyvinyl acetals, each having a different polyvinyl alcohol content, degree of acetalization, residual acetate content, ethylene proportion, molecular weight and/or different chain lengths of the aldehyde of the acetal groups.

In particular, the aldehydes used for the production of the polyvinyl acetals can be linear or branched (that is to say of the "n" or "iso" type) containing 2 to 10 carbon atoms, which leads to corresponding linear or branched acetal groups . The polyvinyl acetals are referred to accordingly as "polyvinyl (iso) acetals" or "polyvinyl (n) acetals".

Especially preferred is polyvinyl butyral .

The polyvinyl acetals used have a proportion of polyvinyl acetate groups of 0.1 to 20 mol %, preferably 0.5 to 3 mol %, or 5 to 8 mol % .

The polyvinyl alcohol content of the polyvinyl acetals may be between 6 - 26 % by weight, 8 - 24 % by weight, 10 - 22 % by weight, 12 - 21 % by weight, 14 - 20 % by weight, 16 - 19 % by weight and preferably between 16 and 21 % by weight or 10 - 16 % by weight .

The vinyl alcohol content and vinyl acetate content of the polyvinyl acetal are determined in accordance with DIN ISO 3681 (Acetate content) and DIN ISO 53240 (PVA content) .

Preferably, the first and the second thermoplastic interlayer contain at least 16 % by weight, such as 16.1 - 36.0 % by weight, preferably 22.0 - 32.0 % by weight and in particular 26.0 - 30.0 % by weight plasticiser.

Alternatively, one the two interlayer films may contain less than 18 % by weight (such as 17.9 % by weight) , less than 12 % by weight, less than 8 % by weight, less than 6 % by weight, less than 4 % by weight, less than 3 % by weight, less than 2 % by weight, less than 1 % by weight or even no plasticiser (0.0 % by weight) if the other interlayer contains substantial amounts of plasticizer in the ranges given hereabove .

Suitable plasticisers can be selected from the following groups :

- esters of polyvalent aliphatic or aromatic acids, for example dialkyl adipates, such as dihexyl adipate, dioctyl adipate, hexyl cyclohexyl adipate, mixtures of heptyl adipates and nonyl adipates, diisononyl adipate, heptyl nonyl adipate, and esters of adipic acid with cycloaliphatic ester alcohols or ester alcohols containing ether compounds, dialkyl sebacates, such as dibutyl sebacate, and also esters of sebacic acid with cycloaliphatic ester alcohols or ester alcohols containing ether compounds, esters of phthalic acid, such as butyl benzyl phthalate or bis-2-butoxyethyl phthalate.

- esters or ethers of polyvalent aliphatic or aromatic alcohols or oligo ether glycols with one or more unbranched or branched aliphatic or aromatic substituents, for example esters of glycerol, diglycols, triglycols or tetraglycols with linear or branched aliphatic or cycloaliphatic carboxylic acids; Examples of the latter group include diethylene glycol-bis- (2-ethyl hexanoate) , triethylene glycol-bis- ( 2-ethyl hexanoate) , triethylene glycol-bis- (2-ethyl butanoate) , tetraethylene glycol-bis-n-heptanoate, triethylene glycol- bis-n-heptanoate, triethylene glycol-bis-n-hexanoate, tetraethylene glycol dimethyl ether and/or dipropylene glycol benzoate

- phosphates with aliphatic or aromatic ester alcohols, such as tris (2-ethylhexyl) phosphate (TOF) , triethyl phosphate, diphenyl-2-ethylhexyl phosphate, and/or tricresyl phosphate

- esters of citric acid, succinic acid and/or fumaric acid.

In addition, the films may contain further additives, such as residual quantities of water, antioxidants, adhesion regulators, optical brighteners or fluorescent additives, stabilisers, colorants, processing aids, organic nanoparticles, pyrogenic silicic acid and/or surface active substances . In particular, the films may comprise 0.001 to 0.1 % by weight of alkaline salts and/or alkaline earth salts of carboxylic acids as adhesion regulators . The films may further contain one or more of the UV absorbers described above in the bulk of the material in addition to or instead of the UV absorber used for forming the bird protection pattern on the surface of the interlayer.

The laminated glazing of the invention can be used for a variety of architectural applications, including windows, structural architectural panels in buildings or stadiums, decorative architectural panels, indoor or outdoor stairs or platforms, pavement or sidewalk skylights, balustrades, curtain walls, flooring, balconies, support columns, skylights and privacy screens .

In a second aspect, the present invention concerns a glass window comprising the laminated glazing according to the present invention and further comprising a third glass sheet separated by air from the first glass sheet or the second glass sheet. Such glass windows are generally used for improved thermal and/or noise insulation purposes .

The present invention also relates to a method for producing the glass laminates described above.

The first and the second thermoplastic interlayer can be any conventional polyvinyl butyral sheet, e.g. the Trosifol® range of products commercially available from Kuraray Europe GmbH, e.g. in a thickness of 0.76 mm.

The bird protection pattern can be coated or printed onto at least one surface of the first thermoplastic interlayer. The printed or coated layer usually contains an inorganic or organic pigment, which should not dissolve in the polymer matrix. Suitable pigments include carbon black , iron oxides , polyaniline, perylenes or spinel pigments are used . The pigments may be dispersed in a carrier fluid like water, alcohol or mixtures of alcohol and water . Furthermore, binders like polyvinyl alcohol , polyvinyl butyral , polyvinylpyrrolidone , polyacrylates , polyurethanes or poly styrene-acrylate may be present . Such printing compositions are referred to as "printing inks" or simple "inks" hereinafter .

Water-based printing inks are preferred over printing inks based on organic solvents since they do not swell or dis solve the films and/or lead to f ilm defect s .

The printing inks can be applied via techniques that are commonly known in the printing industry such as of f set printing, rotogravure printing, f lexography, and s creen-printing, followed usually by a drying step .

The dry-film thicknes s of the printed parts is 1 - 50 μm depending on the printing technique and the opacity required . Usually, the dry-film thicknes s is 10 - 30 μm . The total dry-film thicknes ses can be achieved by overlaying several ink-layers from sequential steps of printing or coating .

Subsequently, the laminated glazing can be prepared by combining the first and the second thermoplastic interlayer such that the bird protection pattern is in touch with a main surface of the second thermoplastic interlayer followed by lamination of the thus prepared interlayer stack between two glas s sheets .

Vacuum laminators can be used . These consist of a chamber that can be heated and evacuated, in which laminated glaz ing can be laminated within 30 - 60 minutes . Reduced pres sures from 0 . 01 to 300 mbar and temperatures from 100 to 200 °C, in particular 130

- 160 °C, have proven their worth in practice.