Protective Film

The invention relates to a protective film against harmful substances, especially against gaseous substances towards which an object or device is sensitive, such as oxygen, moisture or other gases contained in the ambient atmosphere; the preparation and use of such a film; objects coated with such a film, such as OLEDs or photochromically coated panes or glasses; and devices comprising objects covered by such a film, such as illumination bodies or OLED-based displays or windows with photochromically coated panes.

Background of the Invention

For the protection of foods and other products, the packaging industry needs films that are impermeable to harmful substances. Their main application is protection against oxygen and water. Other technical products, such as photochromically coated panes or glasses, solar cells, flexible LCDs (liquid crystal displays) and OLEDs (organic light-emitting diodes) are sensitive, inter alia, towards oxygen and water and therefore must be suitably screened therefrom.

Plastic films having barrier properties are known (e.g., EVOH, PVDC from Joachim Nentwig, Kunststoff-Folien, Carl-Hanser-Verlag Mϋnchen 1994) and have perme- abilities of hardly less than 1 cm ³ /m ² -d-bar. This is sufficient for many food applications, but not for the significantly higher demands on photochromically coated panes and glasses, solar cells or even OLEDs. For such applications, so-called ultrabarriers are under development; their functional principle is based on the combination of an inorganic layer with organic hybrid polymers (e.g., ORMOCERs). The inorganic layer is very impermeable a priori, but includes unavoidable breaks which are closed by the hybrid polymers. In addition, there are interactions between the layers which again reduce permeability. With such combination layers, it is hoped that the permeability can be even reduced to the value of 10 ^"6 cm ³ /m ² -d-bar as required for OLEDs. A disadvantage of such layer systems is the fact that the inorganic layer can be prepared only by vapor deposition or sputtering, which are both methods that are relatively expensive and little suitable for industrial mass production.

For packages, it is known that an oxygen-depleting layer that is intended to deplete the oxygen already contained in the packaged product is placed below the barrier. For

example, a plastic multilayer structures comprising an oxygen-barrier layer, an oxygen absorptive layer and a thermoplastic resin layer containing a high silica type zeolite material is known from EP-A-1721737. Said multilayer structures are suitable as packaging material for food and medical and pharmaceutical products. A similar structure is disclosed in US 2006/0170341 as an encapsulating structure for an organic electroluminescence device (OELD). Further, JP-A-07169567 discloses a sealing layer composed of multiple sets of an oxygen absorbing layer and an oxygen barrier layer, wherein the oxygen barrier layer comprises active compounds selected from metallic oxide, nitride and fluoride, and the oxygen barrier layer comprises organic compounds, oxygen absorbing compounds, fluorine compounds and metallic fine powder. However, such layer combinations are not sufficient to effectively reduce the oxygen permeability of the barrier and only have a short-term effect not sufficient for critical applications. An ideal barrier is glass, but due to the risk of breaking, it is little suitable for flexible applications. On the other hand, the permeability Q of a layer for a harmful substance is inversely proportional to the layer thickness are directly proportional to the difference of partial pressures of the harmful substance before and behind the layer. Therefore, a permeability that is lower by several orders of magnitude can hardly be achieved by a higher layer thickness, because the layer would then be impractically thick. Also, a stack of layers reduces the overall permeability only according to the formula

Qoveralf ¹ = Ql ^"1 + Q ₂ ^"1 + ■ ■ ■ + Qn ^"1 , wherein the densest layer alone is hardly worse than the overall stack.

It is the object of the invention to provide a barrier against harmful substances suitable for flexible applications that can be realized inexpensively as a coating on films and other supports.

Summary of the Invention

It has now been found that by superposing a number of suitable layers in such a way that the difference of partial pressures for a harmful substance becomes as low as possible on at least one layer having a good barrier effect for such substance. Such an arrangement drastically reduces the overall permeability to the harmful substance and thus allows much lower layer thicknesses as compared to the prior art and the use of barrier layers which do not yield a sufficient protective effect even at a very high layer thickness.

For the layer structure of a material according to the present invention, the following abbreviations are also used in the following : SU : flexible support; XS: harmful substance against which the film protects, for example, oxygen or moisture; BL: layer having a low permeability to the substance XS (barrier layer); AL: layer which reduces the content of the substance XS in that layer (absorber layer); FL: functional layer; PL: photochromic layer; and MA: XS-sensitive material to be protected.

The local partial pressure of the harmful substance XS can be reduced preferably with absorber layers AS according to the present invention. It has been found particularly preferable to alternately apply barrier layers BL and absorber layers AL on top of one another to a flexible support SU, wherein a barrier layer BL is particularly effective as the (top) layer that faces the medium containing said substance XS.

Therefore, the invention relates to

(1) a protective film for reducing the exposure to a substance XS, comprising a flexible support and layers applied thereto in the following order: a) a layer having a low permeability to said substance XS (barrier layer BL); b) a layer which reduces the content of free substance XS in this layer (absorber layer AL); and c) another layer having a low permeability to said substance XS (barrier layer

BL).; (2) a preferred embodiment of the protective film (1) which comprises the structure (AL-BL-)n, wherein n is > 2 and wherein one of the barrier or absorber layers may serve as the support;

(3) a preferred embodiment of the protective film (1) or (2), wherein said substance XS is oxygen; (4) a process for the preparation of the protective film of (1) to (3) above, which comprises applying at least one layer by a continuous casting process;

(5) the use of a protective film of (1) above or as prepared according to (4) above as a protective film for OLEDs, solar cells or photochromic layers;

(6) an object coated with a protective film of (1) to (3) above or as prepared according to (2) above; and

(7) a device containing an object of (6) above.

In the following, the invention is described in an exemplary manner for oxygen as the harmful substance, but the user skilled in the art is able to transfer it to any other substances, such as harmful gases or moisture, with correspondingly modified reagents. Detailed Description of the invention

The minimum configuration of the protective film of (1) of the invention is:

SU - BL - AL - BL or BL - AL - BL, wherein one of the BL or AL layers in the latter case is the support. In the preferred embodiments of the present invention shown in the following, in which a support is explicitly described, such support may also instead be one of the other layers mentioned or one of the BL or AL layers may serve as the support.

During use, the protective film is applied to the material MA to be protected in a way as gas-tight as possible, which results in the following structure, for example: MA - SU - BL - AL - BL or SU - BL - AL - BL - MA.

The latter structure has the advantage of being protected mechanically at the same time by the support being provided outermost. During use, the protective films mentioned in the following are respectively suitable for both arrangements of materi- als. In addition, the material MA may optionally be provided with the protective film on more than one side.

In an advantageous embodiment of the protective film (1) to (3) of the present invention has the following structure:

SU - BL - AL - BL - AL - BL For such layer stacks, it has been found within the scope of the present invention that they screen the material (bulk) MA under the protective film against the substance XS clearly better than the barrier layers alone would.

In a preferred embodiment of the invention, if a functional layer FL within the layer composite is to be protected from the substance XS, layer sequences such as SU - BL - AL - BL - FL - BL - AL - BL

are advantageous. For the case of an integrated functional layer FL to be protected as described here, the protective film according to the present invention may be the ready-to-use film itself with a function determined by FL. This film can be either used as such or applied to any desired material. If the support is impermeable to XS are if it is applied to a material that is impermeable to XS, the following layer structure may also be suitable:

SU - FL - BL - AL - BL.

If a functional layer FL sensitive towards XS is to be integrated in the protective film according to the invention, it is advantageous to place it within the layer structure in such a way that it experiences the lowest possible exposure to the substance XS. The person skilled in the art can readily find such a structure using the present description and usual experimentation.

The same applies generally to layer structure variants other than those explicitly stated here, to which the present invention is not limited. Within the scope of the present invention, "impermeable to XS" means that the thus designated material in the desired design, especially in the desired layer thickness, is so little permeable to XS that there is no or at most an acceptable degree of adverse influence on MA by XS during the sought service life of MA. As materials which are impermeable to XS, for example, glass, metals, semiconductors, oxides, ceramics or plastic materials with a correspondingly low permeability to XS are suitable. Such materials are frequently available as flexible supports as well.

In the case where the support faces towards the side from which the exposure to XS occurs (for example, towards the ambient air), the following structure is advantageous if the layer stack is applied with the side facing away from the support to a material impermeable to XS:

SU - BL - AL - BL - FL.

An example of an oxygen-sensitive functional layer FL is a photochromic layer PL.

In an advantageous embodiment of the present invention, the protective layer additionally comprises further pairs of barrier layer/absorber layer provided on top of one another, wherein a few pairs, especially 1 to 6 further pairs, already can achieve significant advantages, but improvements may also be observed with a number of

pairs significantly higher than 6. Thus, an example of a preferred protective film according to the present invention with a total of 3 such pairs (AL - BL) may have the following structure: (SU - BL - AL - BL - AL - BL - AL - BL). The protective effect is significantly improved by the described division into more than one pair of barrier layer/absorber layer as compared to one pair of the same overall layer thickness and the same ingredients. As described above, the structure may advantageously be combined also with functional layers FL integrated into the protective film as well as with any further layers.

The protective film according to the present invention can be one-sided or two-sided with respect to the support, wherein the coating of the support on the two sides may be different in the two-sided case. The protective film may contain, for example, at least one functional layer on one side of the support or on both sides. A two-sided protective film could have the following structure, for example: (BL - AL - BL - SU -

BL - AL - BL). Despite the higher production expenditure, such a structure could suggest itself if a very good planarity is required, since the symmetric structure compensates for the tensile forces applied by the coating to the support. In this case too, a functional layer may be advantageously integrated into the protective film.

If the support has a relatively high permeability to the harmful substance XS, it is preferred to contain at least one barrier and/or absorber layer on the backside. In the case of a support having a relatively high oxygen permeability and/or a high oxygen content after production, it has been found advantageous in addition if the support is coated on at least one side with an absorber layer, for example, according to the following layer structures: (SU - AL - BL - AL - BL), (AL - SU - BL - AL - BL) or (AL - SU - AL - BL - AL - BL). This has been found preferably even if the side of the support is otherwise barred towards oxygen, for example, by adhering the support to a gypsum plate. The mechanism of this is not known either, but by hindsight it is assumed that the harmful substance XS can diffuse in laterally through free cutting edges of the support and migrate through the support.

With respect to its barrier effect, the film according to the invention meets even high requirements and, for example, as an oxygen protection film, it is at least comparable with materials in which an oxygen barrier layer was expensively applied by vapor deposition, and is often more robust against mechanical loads.

In addition to the barrier effect, a barrier layer according to the present invention may simultaneously exhibit an absorber effect as well as any other effects, and in addition to the absorber effect, an absorber layer according to the present invention may simultaneously exhibit a barrier effect as well as any other effects. The individual layers of the film according to the invention can be applied by usual methods, such as laminating or casting methods. Preferably, at least one layer having a barrier and/or absorption effect is not applied by a vapor deposition technique, and more preferably none of the barrier and/or absorption layers is applied by a vapor deposition technique, and even more preferably, no layer is applied by a vapor deposition technique.

Suitable casting methods include all known methods for the liquid coating of materials, for example, knife casting. However, it has been found particularly preferred to use as the support a flexible film which is sufficiently stable for the casting method and to subject it to continuous casting, for which, especially when more than one layer is present, a multiple casting system, especially a cascade or curtain casting machine is preferred with which the multilayered material is produced, especially in one machine run (multiple casting). Surprisingly, the stability of the material prepared by continuous casting towards the usual simple application methods, such as knife coating or brushing, is significantly improved. In multilayered materials, a further significant improvement is to be observed by the simultaneous application of several layers (multiple casting) as compared to several successive individual castings. Without knowing the underlying mechanism, this could be due to the uniformity of the layers which is possible with such casting methods, whereby there are no weak points in the barrier and/or absorber effect. What also speaks in favor of this theory is the fact that the stability of the protective film could be further improved within the scope of the present invention by the known measures for improving the casting quality, such as optimization of the rheological properties of the casting solutions and/or the careful degassing thereof.

Each of the layers mentioned may be single layers or multiple layers. Within the scope of the present invention, a "barrier layer" BL preferably means a layer that has a permeability coefficient, P, to the harmful substance of smaller than 0.1, preferably smaller than 0.01. A definition of the permeability coefficient P and its values for the case that the harmful substance XS is oxygen for numerous polymers

can be found in the Polymer Handbook, 4 ^th edition, J. Brandrup, E. H . Immergut and E. A. Grulke, John Wiley & Sons, Inc. New York, pages VI/543 ff. Suitable examples are stated in Table 1, and the permeability coefficient as mentioned therein is in units of cm ³ (273.15 K; 1.013 • 10 ⁵ Pa) • cm / (cm ² • s • Pa).

Table 1

The barrier layers are preferably cast from a solution, especially aqueous solution, or applied in the form of dispersions. The barrier polymers may contain additives such as plasticizers, wetting agents and/or anti-ageing agents. Suitable plasticizers include, for example, tricresyl phosphate, dibutyl phthalate, tributyl citrate or sebacic ester alone or as a mixture.

As barrier polymers, those polyvinyl alcohols which have a degree of hydrolysis of about 99% such as Elvanol T-66 (DuPont) are particularly preferred.

Within the scope of the present invention, "absorber or absorption layer" AS preferably means a layer which is capable of permanently binding a harmful substance XS, such as molecular oxygen, and thus reducing the partial pressure of the substance XS in the layer. Thus, the substance XS present in the layer or diffusing into the layer is trapped within the layer as completely as possible, and the content of free substance in the layer is correspondingly reduced. Said trapping of the substance XS may be effected either physically, for example, by adsorption, or chemically, for example, by chemisorption or other chemical reactions, such as reduction. Within the scope of the present invention, all means with which the harmful substance XS is trapped are referred to as harmful substance scavengers in the following and as oxygen scavengers in the case of oxygen as the substance XS.

As the absorber layer AL, especially for oxygen, matrix materials such as PVOH or gelatin in which absorbing substances are embedded are suitable, in particular. Examples thereof include L-ascorbic acid, isoascorbic acid, L-ascorbates, isoascor- bates, ascorbyl palmitate and stearate, tocopherols (alpha-, gamma-, delta- tocopherol), gallates (propyl, octyl, dodecyl), butylhydroxyanisole (BHA), butylhy- droxytoluene (BHT). Due to the castable matrices, such layers can also be applied on an industrial scale. Alternatively, oxygen-depleting copolymers may also be employed; they can be applied, for example, in the form of one- or two-component paints. If harmful substances other than oxygen are to be absorbed, such as moisture (water vapor), then the person skilled in the art can easily find suitable materials and employ them according to the present invention.

When harmful substance scavengers are used that are insoluble in the respective casting solution, they are introduced in the form of dispersions. For preparing the dispersions, the harmful substance scavenger is dispersed in an aqueous polymer solution in a known manner by means of a dispersing device using wetting agents or dispersing agents. This method is advantageous in particular to enable aqueous casting solutions, which are preferred for all layers according to the present invention that are applied by a casting method because they place less of a load on the environment as compared to organic solutions and do not require any explosion protection measures. When organic soluble harmful substance scavengers are used, the compounds are dissolved, for example, in a high-boiling solvent (oil former, permanent solvent), and the solution is emulsified into an aqueous polymer solution using an emulsifying device. Conveniently, emulsification aids, such as emulsifiers, or low-boiling water- insoluble solvents which are evaporated off during the emulsification process are used. Examples of water-soluble polymers include polyvinyl alcohol, gelatin, poly- acrylamides, polyvinylpyrrolidone, polyvinylimidazole, hydroxyethylcellulose, cellulose, polyoxazolinones, polyallylamine, polyacrylic acids or copolymers or mixtures of such polymers. Examples of high-boiling solvents include tricresyl phosphate, tritoluyl phosphate, dibutyl phthalate, N,N-diethyldodecanamide, N,N- dibutyldodecanamide, tris(2-ethylhexyl) phosphate, acetyltributyl citrate, 2,4-di- tert-pentylphenol, 2-(2-butoxyethoxy)ethyl acetate and 1,4-cyclohexyldi- methylenebis(2-ethylhexanoate). As examples of auxiliary solvents, ethyl acetate or diethyl carbonate may be mentioned.

Another possibility of introduction when water-soluble polymers are used is to use the water-insoluble harmful substance scavenger together with a polymer dispersion or a polymer latex in a finely dispersed form. This technique is known under the designation of "charging of latexes" and is described, for example, in DE-A- 2541274, US 4,199,363, DE-A- 2541230, US 4,247,625 and EP-A-049399.

When water-soluble harmful substance scavengers are used, they are dissolved in water together with an aqueous binder solution or binder dispersion, followed by casting into a layer and drying. As binders, there may be used, for example, PVA, gelatin, polyvinylimidazole, polyvinylpyrrolidone, substituted celluloses, polyacrylic acids, polyacrylamide and mixtures thereof.

Prior to casting, the thus obtained dispersions, emulsions or solutions can be admixed in the known manner with wetting agents for casting, biocides, thickening agents or other additives in order to improve the casting quality and stability.

As harmful substance scavengers, any compounds are suitable which are capable of binding or converting a substance (XS), such as molecular oxygen, especially adsorbents, oxidants (not in the case of oxygen) and reducing agents. The harmful substance scavengers may be introduced directly in their reactive form, but activatable harmful substance scavengers are more preferred. By the activation, it can be avoided that the harmful substance scavenger is already partially consumed in the preparation process of the photochromic material. Suitable activation reactions can be triggered by, for example, light, heat or chemical additives. Any reactions can be applied that are suitable for releasing a compound acting as a harmful substance scavenger, especially the cleavage of camouflaged harmful substance scavengers. Suitable oxygen scavengers are, for example, the compounds stated in US 5,350,622, US 5,211,875, US 6,287,481, WO 94/12590 and especially in US 6,942,821, columns 7 to 10.

Examples of oxygen scavengers according to the present invention include, alone or in a mixture, organic oxygen scavengers, for example, unsaturated hydrocarbons, both high and low molecular weight, in combination with transition metal compounds, ascorbic acid, ascorbates, isoascorbic acid, isoascorbates, ascorbyl palmitate, gallic acid and its salts, tocopherol, hydroquinone, catechol, resorcinols, dibutylhydroxy- toluene, dibutylhydroxyanisole, pyrogallol, rongalite, sorbose, glucose, lignins, sulfites, tannin, ascorbates in combination with transition metal catalysts, thiosulfite, mercaptopropionic acid, thiosulfate, bisulfite, hydrogensulfite, dithionate, dithionite, hyposulfite, sulfide, tin compounds, hydroxylamine, hydrazine, phosphine compounds, iron-based oxygen scavengers, such as iron powder, activated iron, iron oxide or iron salts, polymeric oxygen scavengers, such as oxidation-reduction resins and polymeric metal complexes, oxygen adsorbers, such as zeolites and active charcoal, or mixtures of the mentioned oxygen scavengers. Preferred phosphine compounds include triphenylphosphine, tri-p-tolylphosphine, diphenylmethyl- phosphine, diphenylethylphosphine, diphenylpropylphosphine, dimethylphenyl- phosphines, diethylphenylphosphine, dipropylphenylphosphine, divinylphenyl-

phosphine, divinyl-p-methoxyphenylphosphine, divinyl-p-bromophenylphosphine, divinyl-p-tolylphosphine, diallylphenylphosphine, diallyl-p-methoxyphenylphos- phine, diallyl-p-bromophenylphosphine and diallyl-p-tolylphosphine. Triphenyl- phosphine is particularly preferred. Preferred ascorbates and phenolic oxygen scavengers are described, for example, in US 5,977,212, column 5, lines 15-67.

In a preferred embodiment of the present invention, the photochromic material contains oxygen quenchers and especially singlet oxygen quenchers. The mentioned quenchers may be contained in any layer of the material and also in several layers. Suitable singlet oxygen quenchers are known, for example, from JP-A Nos. 58- 175693, 59-81194, 60-18387, 60-19586, 60-19587, 60-35054, 60-36190, 60- 36191, 60-44554, 60-44555, 60-44389, 60-44390, 60-54892, 60-47069, 63- 209995 and 4-25492, JP-B Nos. 1-38680 and 6-26028, DE-A-350399 and Journal of the Chemical Society of Japan, October 1992, p. 1141. NQ-13 from Hayashibara Biochemical Laboratory, Inc. is an example of a commercially available singlet oxygen quencher.

In a preferred embodiment of the present invention, conjugated polyenes, transition metal complexes, amines including hindered amines (HALS compounds), aminium salts, iminium salts and/or the oxygen quenchers stated in EP 0 486 216 Bl, especially the substances referred to as compounds of formula II-a-2 and R therein, are used as singlet oxygen quenchers.

In an advantageous embodiment of the present invention, the protective film comprises further layers, such as intermediate layers, functional and protective layers, with which the material can be adapted to the desired application. If the film is also to offer protection from light or from substances produced under the action of light, such as singlet oxygen, it has been found preferred for the material to contain at least one UV absorber. Although the UV absorber leads to stability benefits in any layer, i.e., for example, also in the functional, barrier and/or absorber layers as well as in the support, the effect is the more pronounced, the closer it is to the side of the material which is directly exposed to the light, and it is particularly pronounced if it is contained in a separate layer UL which, as the uppermost layer of the protective film, is directly exposed to the light. Such a structure is, for example:

SU - PL - AL - BL - UL, if the protective film is applied to the material to be protected on its support side, and

UL - SU - BL - AL - PL, if the protective film is applied to the material to be protected on its BL side.

As the UV absorbers, any substances which absorb ultraviolet radiation may be used alone or in admixture. UV absorbers suitable therefor and their amounts to be employed can be found out by a person skilled in the art by usual experimentation. Preferably suitable are organic substances, such as triazines (e.g., according to EP-A- 531258), hydroxyphenylbenzothiazoles (e.g., according to EP-A-451813, EP-A- 190003 and EP-A-577122), polymeric UV absorbers (e.g., according to DE-A- 19500441) and inorganic compounds, such as ZnO nanoparticles (e.g., according to DE-A-19832937 and US 6,015,655), as well as the classes of substances as described in DE-A-19746513.

The following UV absorbers are preferred : a) Benzotriazole derivatives:

wherein

R, X are the same or different and represent H or alkyl or alkylaryl; b) dimeric benzotriazole derivatives:

(UV-II)

wherein

R ¹ , R ² are the same or different and represent H, halogen, Ci to Ci ₀ alkyl, C ₅ to Cio cycloalkyl, C ₇ to Ci ₃ aralkyl, C ₆ to Ci ₄ aryl, -OR ⁵ or -(CO)-OR ⁵ ;

R ³ , R ⁴ are the same or different and represent H, Ci to C ₄ alkyl, C ₅ to C ₆ cycloalkyl, benzyl or C ₆ to Ci ₄ aryl;

R ⁵ represents H or Ci to C ₄ alkyl; m is 1, 2 or 3; and n is 1, 2, 3 or 4;

wherein represents the bridge -(CHR ³ ) _p -C(=O)-O-(Y-O) _q -C-(CHR ⁴ ) _p -; p is an integer of from 0 to 3; q is an integer of from 1 to 10;

Y represents -CH ₂ -CH ₂ -, -(CH ₂ ) ₃ -, -(CH ₂ ) ₄ -, -(CH ₂ ) ₅ -, -(CH ₂ ) ₆ - or CH(CH ₃ )- CH ₂ -; and

R ¹ , R ² , R ³ , R ⁴ , m and n have the meanings as stated for formula (UV-III); c) triazine derivatives

(UV-IV)

wherein

R ¹ , R ² , R ³ , R ⁴ independently represent H, alkyl, CN or halogen; and

X represents alkyl; d) triazine derivatives as described in EP1033243; e) dimeric triazine derivatives

wherein

R ¹ , R ² , R ³ , R ⁴ , R ⁵ , R ⁶ , R ⁷ , R ⁸ independently represent H, alkyl, CN or halogen; and

X represents alkyl or -(CH ₂ CH ₂ -O-) _n -C(=O)-; f) diarylcyanoacrylates

wherein

R represents C ₂ alkyl to Cio alkyl or aryl; and of which Uvinul 3035 with R

-C ₂ H ₅ and Uvinul 3039 with R = -CH ₂ CH(C ₂ H ₅ )C ₄ H ₉ are preferred; h) hydroxybenzophenone derivatives

(UV-VII)

wherein

A represents H or OH; and

R represents H, alkyl, acyl, -(CH ₂ )n-O-(CH ₂ )n-CH3, -(CH ₂ )n-O-C(=O)-(CH ₂ )n-

CH ₃ ; and n is an integer of from 1 to 20; i) resorcinol derivatives

Ar represents phenyl, naphthyl, alkylphenyl or alkoxyphenyl; and R represents H, alkyl, isoalkyl, cycloalkyl, acyl, -(CH ₂ )n-O-(CH ₂ )n-CH3,

-(CH ₂ ) _n -O-C(=O)-(CH ₂ ) _n -CH ₃ , -C(=O)-(CH ₂ ) _n -CH ₃ or -C(=0)-Ar; und n is an integer of from 1 to 20;

Particularly suitable UV absorbers among the above mentioned classes of substances include, for example, Tinuvin 234, Tinuvin 360, Tinuvin 1577, Uvinul 3030, Chinaas- sorb 81, Tinuvin 329, Tinuvin 350, Uvinul 3035 and Uvinul 3039.

Surprisingly, in the material according to the present invention, it is also possible to apply an anti-scratch layer without deteriorating the protective effect of the film. Rather, this coating, which is preferably applied as an outer layer, can even improve the effect. In particular, an anti-scratch layer has proven beneficial also in terms of the weather resistance of the protective film. As an anti-scratch layer, for example, UV-curable acrylate paints are suitable which are obtainable, inter alia, from Bayer and Cytec and preferably contain nanoparticles, for example, from Clariant or Byk.

If the material according to the present invention is a film coated on one side thereof and intended for being applied to another body, such as a window surface or a semiconductor, the adhesion between the body and the film can be sufficient to enable the bonding in favorable cases. For a more secure application, however, it is generally preferred to provide the film with an adhesive layer (AL) on the desired

side, which advantageously in turn has a covering film. The adhesive layer and film are preferably applied in one step after the casting of the material according to the invention, especially by lamination, but may also be cast directly upon a film already provided with the adhesive layer and the cover layer. It is also possible to use the cover film provided with the adhesive layer itself as a support according to the present invention and to cover it by casting if the thus obtained layer composite including the adhesive layer has sufficient mechanical strength to peel it off from the cover film.

In the case of a window film, after the cover film has been peeled off and the film has been applied to the window pane, the material has the following structure in the order given, for example: glass pane - adhesive - FL - AL - BL - SU - anti-scratch layer - air. In this case, the functional layer may be a photochromic layer PL as described below, for example.

If the film according to the present invention is also to protect from heat, it can be designed in such a way that it absorbs and/or reflects light in the infrared region, especially in the near infrared region, i.e., with wavelengths of larger than 700 nm, preferably between 700 nm and 2000 nm, especially between 700 nm and 1500 nm.

Such absorption and/or reflection may also increase with increasing radiation (ther- mochromicity), but may also be permanent. The absorption or reflection can be achieved by appropriate dyes in the support material or in a layer of the film (IR or

NIR filter), but also, for example, by interference or refraction effects, such as several thin layers having the appropriate layer thickness and different refractive indices.

All the above mentioned layers may not only be applied on one side of the support, but alone or in combination also on the other side of the support, for example, in order to obtain a particularly high protective effect.

In particular, thin films and sheets having a thickness of from 10 to 300 μm, especially from 50 to 150 μm, are suitable as the support. A survey of support materials and auxiliary layers applied to their front and back sides is set forth in Research Disclosure 37254, Part 1 (1995), p. 285, and in Research Disclosure 38957, Part XV (1996), p. 627. Support materials which are particularly suitable for the present invention include cellulose triacetate, polycarbonate, polystyrene, poly(vinyl chloride) and polyesters, such as polyethylene terephthalate (PET) or polyesters of ethylene glycol and naphthalene dicarboxylic acid (PEN).

Preferably, the support and/or at least one layer applied thereto may be electrically conductive, wherein an antistatic effect or an effect as an electrode, for example, for semiconductor elements, such as solar cells or OLEDs, is obtained depending on the degree of conductivity. Suitable additives increasing the conductivity of layers, such as polythiophenes, are known to the person skilled in the art.

Information about binders suitable for the layers according to the present invention may be found in Research Disclosure 37254, Part 2 (1995), p. 286, and Research Disclosure 38957, Part II.A (1996), p. 598.

Hydrophobic components of the layers, such as UV absorbers, stabilizers, oxygen scavengers etc., are preferably dissolved or dispersed in high-boiling organic solvents or introduced using loadable latexes, as described above for oxygen scavengers, for example.

The protective film according to the invention may further contain filter dyes, plasticizers (latexes), biocides, additives for reducing the yellowing and others. Suitable compounds may be found, for example, in Research Disclosure 37254, Part 8 (1995), p. 292, Research Disclosure 37038, Parts IV, V, VI, VII, X, XI and XIII (1995), p. 84ff, and Research Disclosure 38957, Parts VI, VIII, IX and X (1996), p. 607 and 610 ff.

The layers of the protective film according to the invention can be cured, i.e., the binder employed, for example, gelatin or PVA, is cross-linked by suitable chemical processes.

Suitable curing agents may be found, for example, in Research Disclosure 37254, Part 9 (1995), p. 294, Research Disclosure 37038, Part XII (1995), page 86, and Research Disclosure 38957, Part II. B (1996), p. 599. As a possible embodiment of the present invention, a photochromic material is described which is suitable, for example, as a window film. In such a use, the photochromic layer would otherwise be exposed to weathering unprotected and, in particular, to atmospheric oxygen and atmospheric moisture, and the sensitive photochromic dye would be destroyed quickly thereby. This is effectively prevented by the protective film according to the invention.

Within the scope of the present invention, "photochromic layer" means a layer that contains at least one photochromically reacting pigment or photochromically reacting

dye. Preferably, it is an organic photochromic dye, also briefly referred to as "photo- chromic dye" in the following, or a mixture of two, three, four or more different photochromic dyes. Photochromic dyes are characterized, in particular, by their absorption spectrum in the switched state and in the basic state, it being preferred for the present invention if said photochromic dye will absorb only a little to not at all in the visible light region in its basic state, but in its switched state will absorb as strongly as possible in the visible light region. The switching, i.e., the excitation into the (more strongly) colored state, is preferably effected with radiation having a short wavelength, such as blue or ultraviolet light, for example, light of from 200 to 500 nm, preferably light of from 250 to 450 nm, more preferably light of from 300 to 420 nm, especially from 350 to 420 nm. Preferably, the photochromic dyes according to the present invention are not introduced into inorganic-organic hybrid polymers, so- called ORMOCERs, and preferably are not surrounded by a supramolecular protective coat either. In a preferred embodiment of the present invention, the coloring with said photochromic dye or said mixture of dyes is substantially neutral gray. As a criterion for this, the subjective color sensation of a statistically relevant group of persons is used who evaluate a colored film with the desired coloration in the switched state that covers only half of the window area of a room. The better the color neutrality of the film is evaluated, the more suitable for the present invention is the dye or mixture of dyes contained therein. Only half of the window area is covered in order to prevent color adaptation by the human eye, which corresponds, for example, the state when windows are partially open. It is particularly preferred to select those photochromic dyes which ensure an acceptable neutrality in the test already as a single dye. Such dyes exhibit a higher long-term stability of gray neutrality, whereas discoloration is often to be observed in the course of time for gray-neutral mixtures of dyes.

The photochromic compounds which may be used for the present invention are not specifically limited. Preferably, they can be selected from the class of benzopyrans, spirobenzopyrans, spirobenzoxazines and higher annelated ring systems derived therefrom, in particular, naphthopyrans, spironaphthopyrans, spironaphthoxazines or fluorenopyrans, as well as fulgides and fulgimides. Thus, for example, (2H)- naphtho[l,2-b]pyrans aromatically or heteroaromatically substituted in 2,2-

position, but also (3H)-naphtho[2,l-b>]pyrans correspondingly substituted in 3,3- position, such as the naphthopyrans described in PCT/DE 98/02820 and the indeno[2,l-f]naphtho[l,2-b]pyran derivatives and/or spiro-9-fluoreno[l,2-b]pyran derivatives described in WO 00/05602, can be used.

Further, the pyrans described in US 5,753,146 and EP-A-0562915 as well as photochromic dyes from other classes, for example, oxazines, such as the oxazines described in US 5,753,146, or fulgides may also be used.

Examples of particularly advantageous photochromic dyes within the scope of the present invention include the below mentioned dyes of formula (PF-IV) and especially the below mentioned dyes of formula (PF-V):

The photochromic dyes can be introduced into layers consisting of organic soluble or water-soluble (co)polymers.

For polymers soluble in organic solvents, the photochromic dye is dissolved in an organic solvent together with the polymer, cast and dried. As organic solvents, there may be used, for example, acetone, ethanol, ethyl acetate, tetrahydrofuran, methylene chloride, methanol, dioxan, butyl acetate, isopropanol, toluene or mixtures of such solvents.

As (co)polymers, there may be used, for example, poly(methyl methacrylate), co- poly(butyl acrylate-styrene 45: 55), polycarbonate, cellulose triacetate, polybutyl methacrylate, polyester, polyurethane, polyamides, copolymers of vinylidene chloride and acrylic acid esters as well as acrylonitrile copolymers.

In a particular embodiment, mixtures of (meth)acryl-modified polymers with reactive solvents, such as hexanediol diacrylate or trimethylolpropane triacrylate, may also be used. These solutions are applied and subsequently cured thermally or by means of ultraviolet light or electron beams. Depending on the kind of curing, such solutions contain thermally activatable curing agents, such as peroxides or azo compounds, or ultraviolet-activatable curing agents, such as Darocure ^® or Irgacure ^® compounds. For curing with electron beams, curing agents are not necessarily required.

For improving the stability of the photochromic dyes enclosed in the polymer matrix, further monomers, such as acrylamides, vinylpyridine or vinylimidazole, may be added to the reactive polymers.

For water-soluble copolymers, the water-insoluble photochromic dyes are introduced in the form of dispersions, emulsions or loaded polymer latexes.

For preparing the dispersions of particles containing the photochromic dyes (dye latexes) as used according to the invention, water is allowed to flow into a solution of the water-insoluble photochromic dyes and the ionomeric product in a water-miscible low-boiling solvent or solvent/water mixture with stirring.

From the dispersion formed, the solvent is separated by distillation or by other suitable separation processes, such as dialysis or ultrafiltration. According to another embodiment, the solution of the water-insoluble photochromic dyes in a water-miscible low-boiling solvent can be combined with the solution of a urethane prepolymer which still contains NCO groups, whereupon the polyaddition is completed in the presence of the dyes. This embodiment can be used to advantage especially when the dyes do not contain any groups reactive towards isocyanate. As water-miscible organic solvents for the preparation of the dispersion, those are suitable that are able to dissolve both the ionomeric products and the photochromic dyes. Examples of such solvents include acetone, tetrahydrofuran, dioxan, isopropa- nol, methanol, ethanol, methyl ethyl ketone, acetonitrile.

The amount of photochromic dye used for the preparation of the dispersion is generally from 2 to 200% by weight, based on ionically modified polymer. Weight ratios of dye to polymer of from 1 : 200 to 1 : 10 are preferred.

This procedure allows to prepare dispersions of dyes having a particle size of below 150 nm. Preferably, the average particle size (diameter) is within a range of from 10 to 100 nm. In contrast, the particles of dispersions prepared with the use of usual oil formers are significantly larger.

In addition to the dye, the latexes may also be loaded with suitable light stabilizers and/or antioxidants, which increases the stability of the photochromic dye. The dye latexes may further be admixed with surface-active compounds.

Preferably, the photochromic layers according to the present invention also contain dye stabilizers. Particularly suitable dye stabilizers are shown below.

Benzofuranone ST- 8

The dye stabilizer ST-IO is commercially available under the trade name Lowinox 22CP46.

In addition, thiomorpholine dioxide stabilizers (singlet oxygen quenchers) as described, for example, in US 5,491,054 and US 5,484,696 as well as silicon- bridged bisphenols as described, for example, in EP 1 191 398 have proven

advantageous within the scope of the present invention. Further, the known antioxidants are preferred as dye stabilizers.

The invention is further explained by the following examples that are, however, not to be construed as limiting the invention. Examples

Example 1 : Layer structure 101 (structure: SU-PU

The photochromic material 101 was prepared as an example of an oxygen-sensitive layer by applying a layer having the following composition at first to a triacetate film having a thickness of 120 μm (SU) by means of a continuously operating casting machine:

Layer 1 (photochromic layer, PL), dry application 10 μm

99.97% by weight of acrylate paint (30% by weight solids) with a solvent mixture of ethyl and butyl acetates of 1 : 1; and 0.03% by weight of dye according to Table 1. Thus, the dye was dissolved in toluene at a concentration of 30 g/l each. In this layer and in the layers mentioned below, the stated weights are respectively based on the dry mass of the stated additives, i.e., without the substances which are volatile upon drying, such as volatile solvents. Subsequently, the material was dried at room temperature in air. Example 2: Layer structure 201 (structure: SU-PL-BL)

The photochromic material 201 was first prepared as described for 101, and thereafter, another layer having the following composition was applied : Layer 2 barrier layer BL), dry application 10 μm

100.00% by weight of polyvinyl alcohol Elvanol T-66 from Dupont (10% by weight), aqueous solution.

The material obtained was again dried at room temperature in air.

Example 3: Layer structure 301 (structure: SU-PL-BL-AL-BL)

The photochromic material 301 was first prepared as described for 201, and thereafter, the following further layers were applied in the following order: Layer 3 (absorber layer AL), dry application 10 μm

100.00% by weight of ascorbic acid (5% by weight), polyvinyl alcohol Elvanol

T-66 from Dupont (10% by weight), aqueous solution; Layer 4 (barrier layer BL), dry application 10 μm

100.00% by weight of polyvinyl alcohol Elvanol T-66 from Dupont (10% by weight), aqueous solution.

The material obtained was again dried at room temperature in air. The photochromic materials were irradiated with the light of a 100 kl_x xenon lamp normalized to daylight, and the percent density reduction of the dye in the switched state was measured. Low percent density reductions correlate with a high stability of the dye in the photochromic layer. A sample exposed until the maximum absorption was reached respectively served as a 100% sample. As a measure of the useful life, the irradiation time after which the optical density in the switched state was reduced to 1/lOth of the initial value was determined. The values of the relative useful life are stated in Table 2 as percent values, wherein the value for layer structure 101 was arbitrarily set at 100%.

Table 2

As can be seen from the Table, although a barrier layer alone also improves the useful life of the photochromic layer significantly, this is not sufficient for critical applications. It is only by the barrier layer stack according to the present invention that a qualitative stability improvement is achieved that offers sufficient protection even for such critical cases.