EP2571944A1

EP2571944A1 - Method for producing a coating composition having reversible color shade change properties, for rendering substrates uv-absorbing

Info

Publication number: EP2571944A1
Application number: EP11741091A
Authority: EP
Inventors: Peter Graf
Original assignee: Graf Thorsten
Current assignee: Graf Thorsten
Priority date: 2010-05-21
Filing date: 2011-05-20
Publication date: 2013-03-27
Also published as: DE102010022219A1; WO2011144354A1

Abstract

The invention relates to a method for producing a coating composition having reversible color shade change properties, for rendering polymer paint-based substrates UV-absorbing. According to said method, a solvent (A, B) is first mixed with an acrylate-based binder (C). A photochromic dye (H) is then added to the solution (A, B, C). The paint produced this way is applied to the substrate and cures.

Description

A method of making a reversible hue change coating composition for the UV light absorbing equipment of substrates

Description:

The invention relates to a process for preparing a reversible hue change coating composition for the UV light absorbing equipment of substrates.

Such coating compositions with reversible color change are used, for example, to darken transparent surfaces such as windows, glazings, plastic surfaces, films, spectacle lenses, etc. in a targeted manner under UV irradiation. For this purpose, the prior art proposes according to DE 10 2005 042 002 A1 a correspondingly constructed multifunctional layer, which represents a significant contribution to the development of safety. This is especially true in the case that transparent sun visors are equipped with a suitably designed coating composition. The ability to reversibly change hue makes the coating composition able to provide unrestricted daytime and nighttime visibility. Only in the case of solar radiation and in this context additionally existing UV light, the desired darkening takes place.

In addition, a coating has become known from WO 03/018696 A1, which absorbs UV light. The coating in question is used to equip bottles for the storage of drinks (beer). In this case, as a UV-sensitive additive, inorganic oxide materials selected from the group consisting of zinc oxides, titanium dioxides, etc., function.

The present coating compositions and associated methods can not be completely satisfactory. On the one hand, special preparatory measures are required to make the substrate to be coated suitable for application of the coating composition. On the other hand, the coated substrates are often of their mechanical properties disappointing. This is especially true when the coated substrate is to be deformed, for example, in a downstream processing step. Because such procedures often lead to the applied coating composition flaking off, showing cracks or otherwise being damaged. - Here the invention aims to provide a total remedy.

The invention is based on the technical problem of providing such a method for producing a coating composition and a coating composition applied in this way to a substrate, by means of which the UV-absorbing equipment of the relevant substrate can be easily, permanently and inexpensively succeed and at the same time the possibility of subsequent processing of the coated substrate is opened.

To solve this technical problem, a process for the preparation of a reversible shade change coating composition for the UV light-absorbing finish of substrates based on a polymeric paint is characterized by the following process steps:

a solvent (A, B) is coated with an acrylate-based binder (C)

offset;

- The solution (A, B, C) is added to a photochromic dye (H);

- The paint thus prepared is applied to the substrate

and hardens.

The solvent (A, B) prepared in the first process step is generally an alcohol-based organic solvent (A, B). These may be alkanols, ie a group of substances derived from alkanes. In addition, in the case of the solvent (A, B), the invention recommends recourse to a solvent mixture of different alcohols. In this connection, a first solvent (A) based on acetone and a second solvent (B) based on a polyhydric alkanol have proven to be particularly favorable. The first solvent (A) based on acetone provides in particular for the dissolution of the subsequently introduced binder (C). On the other hand, that represents second solvent (B) based on a polyhydric alkanol, primarily to ensure that the photochromic dye (H) added to the solution (A, B, C) undergoes a solution. In addition, with the aid of the polyhydric alkanol, a particularly stable dispersion of the photochromic dye (H) usually added in powder form in the solution is made available.

It should be understood, of course, and overall that both solvents mentioned (A, B) are miscible with each other. In addition, polyhydric alkanols (second solvent B) regularly have a hygroscopic character, so that any water present in the solution (A, B, C) is bound and does not or not practically affect the production of the polymeric varnish.

In detail, the first alcoholic solvent (A) based on acetone may advantageously be diacetone alcohol (DAA). As a second solvent (B) based on the polyhydric alkanol recourse to 1, 2-propanediol is recommended. Both solvents mentioned (A, B) can be easily mixed with each other and ensure on the one hand for a perfect dissolution of the introduced into the mixture binder (C) based on acrylate and on the other hand ensure that the subsequently added photochromic dye (H) is also properly dissolved or a total stable dispersion of the photochromic dye (H) is carried out in the solution.

Furthermore, the following solvents A and B are used according to the invention, which are selected from the group comprising acetone, ethanol, ethyl acetate, ethylene glycol, tetrahydrofuran, methylene chloride, methanol, dioxane, butyl acetate, isopropanol.

The binder (C) is one based on acrylate. This may be added as a powdery substance to the solution or solvent (A, B) described above in detail. In order to accelerate at this point the solution of the powdered binder (C) in the solvent or the mixture of the two solvents described (A, B), it is recommended that the solvent (A, B) with the introduced powdered binder (C. ) too mix, for example, by the solvent (A, B) is processed with the binder (C) in a stirred tank. In this case, a so-called toothed disk has proved to be particularly favorable as a stirring body. In addition, it is recommended to heat the solvent (A, B) or the solvent mixture.

Since the two solvents (A, B) described in detail above are those with a boiling point in the range of about 150 ° C. to 200 ° C., the heating is limited to values of well below 100 ° C. In addition, a warming in the steam is recommended, which is particularly gentle and avoids local overheating. That is, before or during the addition of the acrylate-based binder (C), the solvent (A, B) or the solvent mixture is heated. The heating generally takes place in a water bath. In this case, temperatures of well below 100 ° C are usually set, usually even below 80 ° C. In fact, a temperature of about 60 ° C for the water bath and thus the solvent (A, B) has proven to be particularly favorable and for the desired solution of the binder (C) and then the photochromic dye (H) as completely sufficient.

The invention recommends a powdery adhesive, for example methacrylate adhesive or a binder based on methacrylate, as binder (C) based on acrylate. This binder (C) provides the subsequent curing of the paint produced on the substrate primarily for the desired polymerization.

In addition, according to the invention as binder (C) one or more of the (co) polymers used from the group comprising polymethyl methacrylate, co-poly (butyl acrylate-styrene 45:55), polycarbonate, cellulose triacetate, polybutyl methacrylate, polyester, polyurethane, polyamides , Copolymers of vinylidene chloride and acrylic esters, acrylonitrile copolymers and mixtures of (meth) acrylic-modified polymers with reactive solvents such as hexanediol diacrylate or trimethylolpropane triacrylate.

In addition, one or more additives (D, E, F, G) can be added to the solution (A, B, C) or the solvent (A, B) with the incorporated acrylate-based binder (C), but these are not obligatory are. In detail, the addition of an additive (D), which increases the surface tension of the prepared solution (A, B, C) and consequently also of the varnish produced therefrom. This additive (D) may be a silicon-based inorganic polymer or a silicone, respectively. The reduction of the surface tension of the solution (A, B, C) is carried out purely physically with the aid of the relevant additive (D). The described reduction of the surface tension is of importance insofar as the polymeric varnish produced in this way can be applied to different substrates. By reducing the surface tension with the aid of the additive described (D), it is possible to apply the paint to the substrate in question in a particularly comprehensive manner and to counteract any inclinations of the paint for "islanding" or cohesion. In detail, siloxanes have been found to be suitable additives (D) in this connection.

Mostly a polydimethylsiloxane is used, which may also be modified by polyether. Said siloxane is particularly suitable for the desired purpose in that it is colorless, transparent and chemically inert and non-toxic. As a result, the produced polymeric varnish is only positively provided by the additive (D) in question with respect to its wetting ability when applied to the desired substrate, without fear of any adverse effects. In addition, the described additive (D) for reducing the surface tension prevents any foaming on stirring the solution (A, B, C) or upon stirring the binder (C) and / or the photochromic dye (H).

As a further additive (E), a dispersant can be used, which is advantageously added to the solution before the addition of the photochromic dye (H). This additive (E) or dispersant is based on a polyacrylate. In detail, a silicone-modified polyacrylate is used as the relevant additive (E). These are special plastics, namely polymeric esters of acrylic acid and of acrylic acid derivatives with alcohols. These are used in the context of the invention as a dispersant, thus ensuring in the preparation of the desired solution that it comes to optimal mixing of the individual immiscible phases respectively substances respectively the individual phases are stabilized. Specifically, the additive provides (E) or the additive (E) based primarily on polyacrylates and used primarily as a dispersant, for the particles of the photochromic dye (H) subsequently introduced into the solution (A, B, C) to be incorporated into the liquid without fail, or herein experience stable flooding. This ensures a uniform distribution of the particles or pigments of the subsequently introduced photochromic dye (H) in the solution.

In addition, the additive (E) acting as a dispersing agent and additionally described above additionally ensures that the surface wetting on the substrate is improved in addition to the surface tension-reducing additive (D). Furthermore, the dispersant-acting additive (E) ensures that the polymeric paint applied to the substrate has excellent surface finish and smoothness. As a result, its overall weather resistance and water resistance is improved and, for example, a film equipped herewith can be easily removed from a substrate, for example a glass pane. The release properties of a film coated with the lacquer according to the invention from the relevant glass pane are thus positively influenced because a particularly smooth and non-porous surface of the applied coating composition with high gloss is made available by the described additive (E), which acts as a dispersant.

As a further additive (F) for the solution (A, B, C), the invention recommends the optional addition of a so-called light stabilizer (F). Such a light stabilizer is essentially used to stabilize the paint produced in terms of its photosensitivity and also to provide a durable upgrade against weathering. Here, acrylate-based additives (F), for example acrylic resins or even polyurethanes, have proven to be particularly favorable. In general, the resins in question ensure that the coating remains durable and firm after it has hardened. In addition, a good appearance, a good gloss and a high weather resistance is observed. In this context, one- and two-component polyurethanes can be used. The acrylates or acrylic resins can be designed to cure photoinitiated, in which the radical polymerization is thus carried out by UV or visible light. Also, thermosetting acrylic resins are conceivable and can be used.

The photochromic dye incorporated into the solution (H) is one which reacts to UV light irradiation with a reversible color change. The UV light is present predominantly as part of the sunlight, but can also provide in the context of so-called black light for the described reversible change in hue. In fact, the UV light impinging on the photochromic dye alters the chemical structure of the particular dye and thus its absorption behavior.

As a rule, the photochromic dye (H) as powder or plastic granules of the solution (A, B, C) is added. In order to allow at this point a desired homogeneous mixture and suspension of the pigments in the solution, the addition of the photochromic dye (H) is carried out with simultaneous stirring of the relevant solution (A, B, C). In addition, the additive (E) which acts as a dispersant and which is prepared on the basis of a particularly silicone-modified polyacrylate and ensures a uniform distribution of the individual pigments in the solution, is advantageously present in the solution.

The photochromic dyes (H) in question are available in various shades, so that the color of the coating composition or of the polymeric coating produced in this way can be adjusted individually. The effect of photochromism on both inorganic and organic compounds is observed. This manifests itself in a visible or ultraviolet light caused reversible conversion of the corresponding substance into another, which differs from the starting compound by its color (its absorption spectrum). The so-called reverse reaction is triggered by light of different wavelengths or by heat. It can be spontaneous. This has long been known, for which reference is made, for example, to "Römpp, Chemielexikon, Stuttgart / New York, 1991, Volume 4, page 3403". In the context of DE 196 43 773 A1, the use of UV-sensitive photochromic spirooxazine compounds is described. Such compounds can also be used within the scope of the invention as photochromic dyes. In the case of organic photochromic dyes, it is known that they become fatigued over time and in particular are destroyed by oxidation. In this connection, the so-called number of cycles is known as an important parameter with the aid of which photochromic dyes (H) or also compounds produced therefrom are characterized. For example, the Zso value indicates after how many staining / decolorization cycles the initial absorbance value has decreased by half.

The inventively provided photochromic dye (H) is selected from the group comprising benzopyrans, naphthopyrans, fluorenopyrans, spiropyranes, spirooxazines, spirodihydroindolizines, chromenes, azo compounds, anils, polycyclic quinones, viologens, diarylethenes, triarylmethanes, fulgides, fulgimides.

In particular, according to the invention the following photochromic dyes come into consideration: in the 2,2-position aromatic or heteroaromatic substituted

[2H] -naphtho (1,2-b) -pyrane; correspondingly substituted in the 3,3-position

[3H] -naphtho (2, 1 -b) -pyrane;

lndeno [2,1-f] naphtho [1,2-b] pyridine derivatives;

Spiro-9-fluoreno [1,2-b] pyridine derivatives;

3,13-diphenyl-3- (4-diphenylaminophenyl) -13-hydroxy-6-methoxy-indeno [2, 1-f] -naphtho [1,2-b] pyran; 3- (2,5-dimethylphenyl) -3- (4-diphenylaminophenyl) -13-hydroxy-6-methoxy-3-phenylindeno [2,1-f] naphtho [1,2-b] pyran;

13- (2,5-dimethylphenyl) -3- (4-diphenylaminophenyl) -13-hydroxy-3-phenylindeno [2,1-f] naphtho [1,2-b] pyran;

Spiro-9-fluoreno-13 '- [3- (4-dimethylaminophenyl) -6-methoxy-3-phenylindeno [2,1-f] naphtho [1,2-b] pyran];

Spiro-9-fluoreno-13 '- [3- (4-dimethylaminophenyl) -3-phenylindeno [2, 1-f] naphtho [1,2-b] pyran];

Spiro-9-fluoreno-13 '- [3- (4-diphenylaminophenyl) -6-methoxy-3-phenyl-indeno [2,1-f] naphtho [1,2-b] pyran]; Spiro-9-fluoreno-13 '- [3- (4-diphenylaminophenyl) -3-phenylindeno [2, 1-f] naphtho [1,2-b] pyran];

Spiro-9-fluoreno-13 3- [4- (N-morpholinyl) phenyl] -6-methoxy-3-phenylindeno [2,1-f] naphtho [1,2-b] pyran};

Spiro-9-fluoreno-13 '- {3- [4- (N -monomolinyl) phenyl] -3-phenylindeno [2, 1-f] naphtho [1,2-b] pyran};

Spiro-9-fluoreno-13 '- {6-methoxy-3-phenyl-3 -> - (N-piperidinylphenyl) -indeno] - 1-naphtho [1,2-b] pyran};

Spiro-9-fluoreno-13 3-phenyl-3- [4- (N-piperidinyl) phenyl] indeno [2,1-f] naphtho [1,2-b] pyran};

3- (4-diphenylaminophenyl) -3- (2-fluorophenyl) -3H-naphtho [2,1-b] pyran;

3- (4-dimethylaminophenyl) -3- (2-fluorophenyl) -3H-naphtho [2,1-b] pyran;

3- (2-fluorophenyl) -3- [4- (N-morpholinyl) phenyl] -3H-naphtho [2,1-b] pyran;

3- (2-fluorophenyl) -3- [4- (N-piperidinyl) phenyl] -3H-naphtho [2, 1-b] pyran;

3- (4-dimethylaminophenyl) -6- (N-morpholinyl) -3-phenyl-3H-naphtho [2, 1-b] pyran;

6- (N-ynyl Morpho!) -3- [4- (N-morpholinyl) phenyl] -3-phenyl-3H-naphtho [2,1-b] pyran;

6- (N-Morpholinyl) -3-phenyl-3- [4- (N -piperidinyl) phenyl] -3H-naphtho [2,1-b] pyran;

6- (N-morpholinyl) -3-phenyl-3- [4- (N-pyrrolidinyl) phenyl] -3H-naphtho [2,1-b] pyran;

3-phenyl-3- (2-fluorophenyl) -3H-naphtho [2,1-b] pyran;

6- (NMo-holinyl) -3,3-diphenyl-3H-naphtho [2,1-b] pyran and

6- (N-Morpholinyl) -3- (4-methoxyphenyl) -3-phenyl-3H-naphtho [2,1-b] pyran.

In a preferred embodiment of the present invention, the photochromic dyes used are spirofluorenopyrans of the formula (PF-I):

wherein R ^{1 is} a substituent selected from the group A consisting of (C ₁ to C ₆ ) alkyl, (C ₁ to C ₆ ) alkoxy, phenyl, bromine, chlorine and fluorine; R ² , R ³ , R ^{4 are} independent are the same or different and represent a substituent selected from the group A 'consisting of hydrogen and the substituents of the group A, or (R ¹ together with R ² ) and / or (R ³ together with R ⁴ ) independently represent an unsubstituted, mono- or disubstituted benzo or pyrido ring, the substituents of which are selected from group A; G including the spiro carbon atom represents a 5- to 8-membered ring to which at least one aromatic or heteroaromatic ring system is fused, the ring system (s) being selected from the group E consisting of benzene, naphthalene, phenanthrene, pyridine, Quinoline, furan, thiophene, pyrrole, benzofuran, benzothiophene, indole and carbazole, which in turn may have one or two substituents selected from group A; and B, B 'are independently selected from the following groups a), b), c) or d), with

a) phenyl or naphthyl, which are unsubstituted, mono-, di- and trisubstituted; or b) the heterocycles pyridyl, furanyl, benzofuranyl, thienyl, benzothienyl and julolidinyl, which are unsubstituted, monosubstituted or disubstituted; where the substituent (s) of the aryl or heteroaryl groups in a) and

b) from a group F, consisting of hydroxy, amino, mono- (Ci to Ce) - alkylamino, di (Ci to C6) -alkylamino, mono- or disubstituted mono- and diphenylamino on the phenyl ring, piperidinyl, N -substituted piperazinyl, pyrrolidinyl, imidazolidinyl, pyrazolidinyl, indolinyl, morpholinyl, carbazolyl, mono-, di- and disubstituted pyrryl, (Ci to C ₆ ) -alkyl, (Ci to C ₆ ) - alkoxy, bromine, chlorine and fluorine are selected wherein the substituent (s) on the aromatic and heteroaromatic are selected from the group consisting of (C ₁ to C ₆ ) alkyl, (C ₁ to C ₆ ) alkoxy, bromine, chlorine and fluorine; or

c) the groups with the following structure pictures:

wherein Y and Z are independently selected from the group O, S, CH, CH ₂ , NRN and the nitrogen substituents RN is selected from the group consisting of (C ₁ to C ₆ ) alkyl, (C ₁ to C ₆ ) acyl, phenyl and hydrogen are selected and the substituents R ⁵ are selected from the group A and hydroxy, where m = 0, 1 or 2, and R ⁶ and R ^{7 are} independently hydrogen and / or (Ci to Ce) alkyl; or

d) B and together un- B ', mono- or disubstituted fluoren-9-ylidene or constitute a saturated hydrocarbon, the C3 to Ci2-spiro monocyclic, C ₇ - to Ci2-spiro-bicyclic and / or C ₇ - to C ₂ -spiro-tricyclic, wherein the fluorine substituents are selected from group A.

Accordingly, ring system G, with the addition of the spiro carbon atom, represents a 5-membered to 8-membered ring. At least one aromatic or heteroaromatic ring system is fused to this ring. According to the invention, the annelated ring system (s) may independently of one another be selected from the group consisting of benzene, naphthalene, phenanthrene, pyridine, quinoline, furan, thiophene, pyrrole, benzofuran, benzothiophene, indole and carbazole. Of course, the ring systems may be both unsubstituted and mono- or disubstituted, with the substituent (s) selected from group A as defined above.

In the present invention, C3 to C12 spiro-monocyclic is understood to mean a 3-membered to 12-membered ring known to the person skilled in the art. Orbis ci-spiro-bicyclic systems, which may be present according to the invention, belong to the knowledge of the person skilled in the art. Examples include Norbornan, norbornene, 2,5-norbornadiene, Norcaran and Pinan called. A known spirotricyclic system useful in the invention is, for example, adamantane.

In another preferred embodiment of the present invention, the photochromic dyes used are spirofluorenopyrans of the formula (PF-II): wherein R ¹ to R ⁴ , B and B 'are as defined above; X is either a single bond or is selected from the group consisting of -O-, -S-, - (CR ² ) n-, -D = D- or -L-L-, n 1, 2 or 3 is, D, D 'is N or CR, L, L' is O, S, NR, CHR or CR ² , and R is H, (C to C) alkyl or phenyl, and wherein L and L 'are not both O or simultaneously S can be; and C and C are independently selected from the group E defined above, each of which may have one or two substituents selected from the group A.

When X in the present invention description is referred to as a "single bond", it means that there is an immediate link between the ring systems C and C to be linked, for. no other atom should serve as bridging.

According to a further preferred embodiment of the invention, X represents a single bond, wherein the two existing ring systems C and C are bridged by a further linkage in ortho.ortho'-position to the first linkage.

Such bridging includes any means known to those skilled in the art to join the two ring systems C and C, such as heteroatoms such as oxygen or sulfur, saturated or unsaturated C 2 to C 5 carbon chains, or the like. For example, the further linkage in ortho, ortho'-position can lead to a 4,5-phenanthryl-spiro compound, wherein the spiro compounds according to the invention can then have the following general structure (PF-III):

It may also be advantageous if, in the spiro compounds B and B 'according to the invention, they are selected independently of one another from the group a) or d). B and B 'are particularly preferably independently of one another mono- or monosubstituted phenyl or naphthyl, where the substituent is in each case selected from group F as defined above. In the photochromic spiro compounds according to the invention, B and B 'may also be the same substituents.

According to a further preferred embodiment of the invention, C and C independently of one another are unsubstituted or monosubstituted phenyl or naphthyl, the substituent in each case being selected from group A. Also, C and C may represent the same substituents.

Advantageous properties are possessed by the following photochromic spirofluorenopyrans according to the invention:

1) spiro-S-fluorene-IS'- .S-diphenyl-ö-methoxy-indenophenyl-naphthoil-b-pyran];

2) spiro-9-fluorene-13 '- [6-methoxy-3- (4-methoxyphenyl) -3-phenylindeno [2,1-f] naphtho [1,2-b] pyran];

3) spiro-9-xanthene-13 '- [6-methoxy-3- (4-methoxyphenyl) -3-phenyl-indeno [2, 1-f] -naphtho [1,2-b] pyran];

4) spiro-9-fluorene-13 '- [3,3-bis (4-methoxyphenyl) -6-methoxy-indeno [2,1-f] naphtho [1,2-b] pyran];

5) spiro-9-xanthene-13 ^, - [3,3-bis (4-methoxyphenyl) -6-methoxy-indeno [2, 1-f] -naphtho [1,2-b] pyran]; 6) spiro-9- (9-O-dihydroanthracene) -13,3,3-bis (4-methoxyphenyl) -6-methoxy-indeno [2,1-f] naphtho [1,2-b] pyran];

7) spiro-9-fluorene-13 6-memoxy-3- [4- (N -monomolinyl) phenyl] -3-phenyl-indeno [2,1-f] -naphtho [1,2-b] pyran};

8) spiro-9-fluorene-13 ^, - [3- (4-dimethylaminophenyl) -6-methoxy-3-phenyl-indeno [2, 1-f] -naphtho [1,2-b] pyran];

9) spiro-9-fluorene-13 3- (4-diphenylaminophenyl) -6-methoxy-3-phenyl-indeno [2, 1-f] -naphtho [1,2-b-pyran];

10) spiro-9-fluorene-13 '- [3,3-bis (4-methoxyphenyl) indeno [2, 1-f] naphtho [1,2-b] pyran];

11) spiro-9-fluorene-13 ^, - {3- [4- (N -monominyl) phenyl] -3-phenylindeno [2,1-f] naphtho [1,2-b] pyran};

12) spiro-9-fluoren-1 1 ^, - [3,3-bis (4-methoxyphenyl) -5-bromo-fluoro [2,1-b] pyran]; or

13) spiro-9-fluorene-13,3,3-bis (4-methoxyphenyl) -5-bromo-benzo [1] fluoreno [2,1-b] pyran].

Examples of photochromic dyes which are particularly advantageous in the context of the present invention are the following dyes of the formula (PF-IV) and in particular the following dyes of the formula (PF-V):

It has now been found that the polymeric coating prepared by the process of the invention significantly improves the stability of such photochromic dyes (H) or generally photochromic materials, including those based on organic. In fact, even after two years of intense and alternating irradiation with UV light, no significant changes in the absorption behavior are observed.

The resistance of photochromic materials is usually given by the Z ₅ o value. The Z ₅ o value corresponds to the number of switching cycles at which the maximum photochromic absorption coefficient in the visible wavelength range (ie in the range from 380 to 780 nm) drops to half of its initial value. In this case, the term switching cycle designates a transition of the photochromic material from low to increased absorption induced by electromagnetic radiation, in particular by UV light, and the return to the initial state, after switching off the exciting radiation.

With the coating according to the invention coated transparent polymeric substrates have cyclic irradiation with daylight or with light from a wavelength band of 280 to 780 nm Z ₅ o value greater than 8000, preferably greater than 10,000, especially greater than 15,000 and more preferably greater than 20,000.

It is additionally of particular importance that the solution (A, B, C) additionally a UV absorber (G) is added as a further additive (G), which on the one hand prevents the present in the finished paint photochromic dyes (H) are not decomposed by light and UV light in particular and on the other hand lets enough UV light through to provide with the help of the embedded photochromic dye (H) for the desired reversible hue change , The UV absorber (G) optionally added to the solution thus ensures stabilization of the solution or of the paint produced. As UV absorbers (G) so-called sunscreen filter substances are used. The UV absorbers (G) used in the context of the invention are generally those based on triazine. In fact, triazines are a class of chemical compounds whose basic structure is an aromatic heterocycle. As a rule, a 1, 3,5-triazine compound is used, in which the heterocycle or six-membered ring consists of three alternately arranged carbon and nitrogen atoms. The ability of such triazine compounds to be able to react to ultraviolet radiation has long been known, for which reference is made, by way of example only, to DE 1 184 761. Herein, the use of triazine compounds to protect higher molecular weight organic compounds against ultraviolet radiation is described. In detail, the invention recommends the use of a special UV absorber or a specific 1, 3, 5-triazine compound. In fact, for example, a liquid or powdered hydroxyphenyl-triazine (HPT) UV absorber can be used. This has a high stability, a pronounced environmental resistance and is particularly suitable in connection with the use of the previously described photochromic dyes (H).

The paint according to the invention is coated on polymeric substrates and on glass. As polymeric substrates there are preferably used sheets or sheets of polymers such as polycarbonate, polyethylene terephthalate, polymethyl methacrylate, polyvinyl chloride, polyvinyl butyral and / or mixtures thereof, optionally containing 0 to 15% by weight of additive based on the total weight of the substrate material.

The substrates are coated by means of flooding or dipping, by spraying, knife coating, screen printing, curtain casting, dip or spin coating. The paint of the invention is suitable for the coating of large-area substrates, such as film webs. The invention comprises substrates coated with the lacquer according to the invention and having an area of from 1 to 100 mm ² , from 0.01 to 1.0 m ² , from 1 to 100 m ² , from 100 to 1000 m ² , from 1000 to 10000 m ² and from 10,000 to 100,000 m ² . Due to the good processing properties of the paint according to the invention, there is no size limitation with regard to the size of the coated substrates. In particular, film webs can be coated in the roll-to-roll process with the paint according to the invention.

The lacquer according to the invention has a very good adhesion to polymeric substrates.

Substrates coated with the lacquer according to the invention can be hot-formed at temperatures of up to 150 ° C., preferably up to 170 ° C. and in particular up to 190 ° C. Preferably, the deformation is carried out by deep drawing. Accordingly, the invention comprises coated, planar or three-dimensionally contoured substrates or shaped bodies with the lacquer according to the invention.

Coated and hot-shaped polymeric substrates coated with the coating according to the invention are characterized in that the coating is virtually free of cracks and spalling. The surface density of defects detectable by optical film inspection systems or scanners with a maximum lateral dimension of greater than or equal to 1 μm is less than 10 m ^"2 , preferably less than 5 m ^{" 2} , in particular less than 1 m ^"2 , and particularly preferably less than 0, 1 m ^"2 . The above defect densities are measured on substrates coated with the lacquer according to the invention and on substrates coated with the lacquer according to the invention and hot-formed. embodiment

First, a solvent (A, B) is prepared as a solvent mixture of diacetone alcohol and 1, 2-propanediol. In this case, about 40% by weight of the solvent (A) or of the diacetone alcohol is mixed with about 44% by weight of the solvent (B) or 1,2-propanediol in the example. The solvent mixture is heated in a water bath to about 60 ° C. Subsequently, a binder (C), in the specific example, methyl methacrylate, added, in an amount of about 11 wt .-%. This is done with constant stirring of the thus prepared solution (A, B, C) with a stirring body. The stirring body may be a toothed disk. This has in the example case a diameter of 70 mm and rotates at about 4000 to 5000 revolutions / min. The stirring is carried out for about one hour.

After cooling the solution (A, B, C) various additives are added, namely the additive (D) for reducing the surface tension, specifically polydimethylsiloxane to 0.3 wt .-%. In addition, another additive (E) is added as a dispersant to the solution with stirring. This is polyacrylate in an amount of about 3 wt .-%.

The solution thus prepared is added with further stirring the mentioned light stabilizer (F). Specifically, this is acrylic resin in an amount of about 0.5 wt .-%. Finally, the solution of UV absorber (G) is added with further stirring, in an amount of about 1 wt .-%. The UV absorber (G) used is hydroxyphenyltriacin in liquid form.

The solution thus prepared (A, B, C, D, E, F, G) is finished with constant stirring after about 1 hour. That is, the paint requires a production time in the specified frame of about 1 hour. Finally, the photochromic dye (H) of the solution or the paint is added. This may be such as has been described in the previously referred to DE 196 43 773 A1. Its amount is 0.2 wt .-%. The photochromic dye (H) is added with continued stirring to the solution (A, B, C, D, E, F, G). The stirring is then continued for about 8 to 12 hours. Thereafter, the lacquer or the coating composition according to the invention is ready and can be stored or applied directly to the desired substrate. Example of use:

The polymeric acrylic varnish prepared in this way and equipped with the photochromic dye (H) is then applied to an associated substrate and cured. The application of the paint, including the photochromic dye (H) or correspondingly acting pigments can be carried out using conventional coating methods. By way of example, the paint can be rolled up, sprayed on, flooded, painted on, etc. By adding the surface tension reducing additive (D), a pretreatment of the substrate surface is generally not necessary because the paint in question hangs everywhere on the surface and distributes it thereon. However, of course, the surface to be treated can be roughened, especially if conventional plastic surfaces are to be coated. In fact, polycarbonate-based (PC) plastic surfaces, as well as those based on PMMA (polymethyl methacrylate), can be easily coated. If necessary, the plastic surfaces can be roughened by corona discharge or other physical methods.

In addition, the coating composition produced according to the invention or the lacquer prepared by the process described can be finished by a further application of lacquer. It is conceivable to apply an additional scratch-resistant lacquer, anti-fogging lacquer, etc., in order to provide a stable surface against external influences.

In each case, a particularly fast switching behavior of the embedded photochromic dye (H) is observed. The process of transmittance change is reversible, that is, the coating composition has a reversible change in hue. In the absence of UV irradiation, the coating composition is transparent and has a transmittance of about 88%. As soon as the varnish is irradiated with UV light, the transmittance drops to values of less than 30% within seconds and on below 30% after one minute. Transmittances of less than 20% are observed after 15 minutes. Depending on the spectral range in which the photochromic dye (H) reacts, the desired absorption spectrum for the reversible color change can be adjusted. Most of the time one will choose the addition of the photochromic dyes (H) so that a suitable absorption in the wavelength range between 400 nm and 750 nm. That is, as soon as UV light strikes the lacquer according to the invention, its transmission in the relevant and relevant spectral range between 400 nm and 750 nm is reduced from originally close to 90% to less than 30% within seconds. As a result, a correspondingly coated substrate reacts directly to solar radiation with the desired change in transmission and discoloration. As soon as the UV radiation is removed, the original transmittance of about 80% and more is reached (again) in a few seconds.

The substrate may basically be any transparent material. It is not only the coating of plastics conceivable, as already described above. Also plastic films or even glass panes can be coated accordingly. It has also been found that even subsequent processing is possible. This applies, for example, for the coating of polycarbonate or PMMA, to which the paint in question can be applied without pretreatment. In addition, the required adhesion and scratch resistance is given without an additional coat of paint. This is true even if the plastic part coated in this way undergoes a subsequent deformation process or deformation in the context of, for example, a deep-drawing process. This circumstance can be attributed to a particularly successful adaptation of the paint according to the invention to the thermal expansion behavior or the expansion behavior of the thus coated plastic.

Measurement results:

Experiments carried out have shown that the switching speed of the photochromic dyes (H) embedded in the lacquer according to the invention does not deviate from the switching speed of the pigments in the untreated state in the sense of transparent / opaque or transparent virtually impermeable. In fact, the lacquer according to the invention was applied as a coating composition in a layer thickness of about 50 μm to 100 μm onto polycarbonate as substrate or carrier material. Before the start of UV irradiation, the transmission was about 88%. The measurements were carried out at room temperature (about 23 ° C). The excitation light for the subsequent UV radiation impinges with a power of about 30 W / dm ² on the thus designed sample.

Beginning with a transmittance of about 88%, transmittances of about 25% are observed after 1 min irradiation with the aforementioned excitation light of wavelength 280 nm. After 15 minutes of exposure, the transmission drops to about 18%. In further measurements it was found that the switching stability did not change even after a period of 2 years and also the absorption behavior remained essentially constant as described above.

The spectral absorption of the samples coated according to the invention was measured by means of a UV-Vis spectrophotometer (Lambda 850 from PerkinElmer Inc.) in a wavelength range from 280 to 780 nm.

In order to determine the Z ₅ o value of the coatings produced by the process according to the invention, a computer-controlled weathering chamber (Suntest XLS + from Atlas Material Testing Technology GmbH) was used. The weathering filter equipped with a daylight filter was operated with light in a spectral band of 300 to 800 nm and an irradiance of 600 W / m ² in a cyclic mode. The cycle time was 4 minutes, the samples coated according to the invention first being irradiated for 2 minutes during one cycle and then the lamp being switched off for a period of 2 minutes. In total, the samples coated according to the invention were exposed to 20,000 weathering cycles of 4 minutes each. After every 1000 cycles, the samples were taken out of the weathering chamber to record 5 absorbance spectra in the wavelength range of 280 to 780 nm with the UV-Vis spectrophotometer. The recording of the 5 absorption spectra was carried out in each case at a time interval of 1 min, during which the sample was exposed to light in the wavelength range of 280 nm during the entire measurement period of 5 min was irradiated to 780 nm. The maximum photochromic absorption in the visible wavelength range (380 to 780 nm) was achieved in less than 5 minutes for all samples. The maximum photochromic absorption in the visible wavelength range measured after 1000, 2000, 3000, ... weathering cycles was compared with their initial value to determine a decrease to less than 50% of the initial value.

The samples coated with the lacquer according to the invention have a Z ₅ o value of greater than 5000 or greater than 8000, preferably greater than 10,000, in particular greater than 15,000 and particularly preferably greater than 20,000.

Since the lacquer according to the invention can be applied to the substrate by conventional coating techniques, practically all geometries of a surface to be coated can be mastered. As a result, completely new applications for sun protection or UV protection can be tapped.

The curing of the paint applied to the substrate takes place either by a so-called air drying over a period of for example 24 hours or by oven drying. In principle, it is also possible to work with an infrared radiation heater, with the aid of which the lacquer already cures within a minute or less at a temperature of approximately 150 ° C. The base materials used to prepare the paint or the realization of the coating composition are overall neither harmful to the environment nor toxic, so that a special environmental compatibility is given.

Claims

claims:

A process for the preparation of a reversible hue change coating composition for the UV light-absorbing finish of polymeric paint-based substrates, comprising the steps of:

1.1) a solvent (A, B) is mixed with an acrylate-based binder (C);

1.2) of the solution (A, B, C), a photochromic dye (H) is added;

1.3) the paint thus prepared is applied to the substrate and cured.

2. The method according to claim 1, characterized in that as solvent (A, B) is used such an alcohol-based.

3. The method according to claim 1 or 2, characterized in that it is the solvent (A, B) is a solvent mixture of different alcohols, such as diacetone alcohol and 1, 2-propanediol, is.

4. The method according to any one of claims 1 to 3, characterized in that the binder (C) based on acrylate, a powdered adhesive, for example, methyl methacrylate adhesive is used.

5. The method according to any one of claims 1 to 4, characterized in that the solution (A, B, C) before adding the photochromic dye (H) at least one additive (D, E, F, G) is added.

6. The method according to claim 5, characterized in that the additive (D) reduces the surface tension of the solution (A, B, C) and consequently also of the varnish produced therefrom.

7. The method according to claim 5 or 6, characterized in that as an additive (D) for reducing the surface tension of an inorganic polymer based on silicon is used.

8. The method according to any one of claims 5 to 7, characterized in that in addition an additive (E) as a dispersant of the solution (A, B, C) is added prior to the addition of the photochromic dye (H).

9. The method according to any one of claims 5 to 8, characterized in that the solution (A, B, C), a light stabilizer (F) is added as a further additive (F).

10. The method according to any one of claims 5 to 9, characterized in that in addition a UV absorber (G) is added as an additive (G).

11. The method according to any one of claims 1 to 10, characterized in that the solution is composed as follows:

11.1) about 70 wt .-% to 90 wt .-% of the solvent (A, B);

11.2) about 5 wt .-% to 15 wt .-% of the binder (C) and

11.3) about 0.5 wt .-% to 2 wt .-% of the photochromic dye (H).