Title of Invention

A STABILIZED LACQUERS AND A PROCESS FOR PRODUCING THE SAME

Abstract

A process for the stabilization of lacquers against the degradation of the polymer material contained in the lacquer caused by atmospheric oxygen, humidity, heat and/or UV light, characterized in that a compound of formula (A) or a mixture consisting of a compound of formula (A) and at least one UV absorber, is added to the lacquer to be stabilized, the concentration of the compound of formula (A) is 0.2 to 5% by weight, preferentially 0.5 to 1.5% by weight, related to the dry content of the lacquers.

Full Text

The present invention relates to a process for the stabihzation of lacquers against the degradation of the polymer material contained in the lacquer due to the effect of atmospheric oxygen, heat and/or UV light. A further object are the lacquers themselves, stabilized in this manner. In lacquers, the influences of atmospheric oxygen, humidity and, above all, UV light lead to degradation of the polymer material contained in the lacquer. This manifests itself, for example, in cracking, loss of gloss, changes in color shading, delamination and formation of blistering. The use of the appropriate stabilizers to delay such processes in lacquers is known. Known lacquer compositions therefore often contain a mixture of a UV absorber and a sterically hindered amine (HALS: hindered amine light stabilizer). It is known that these compounds of the HALS type react as radical traps and are therefore generally used to stabilize polymer substrates. It has now been found that a specific, sterically hindered amine of the formula (A) set out below, that is photoreactive and absorbs UV light, is particularly well suited as a light stabilizer for lacquers, in particularly automobile lacquers, alone or in combination with UV absorbers or mixtures of various UV absorbers. The object of the invention is thus the use of the piperidine compound of the following formula (A) (hereinafter referred to as HALS A) to increase the light stability of lacquers. A further embodiment of the invention relates to the use of a mixture consisting of this photoreactive, UV light-absorbing piperidine compound and at least one UV absorber selected from the group consisting of 2-hydroxyphenylbenztriazoles (1), 2-hydroxyphenyltriazines (2), 2-hydroxybenzophenones (3), oxalanilides (4) and cinnamic acid derivatives (5), as light stabilizer in lacquers. wherein in the compounds of formula (la) Ri is hydrogen, alkyl with 1 to 24 carbon atoms, in particularly alkyl with 1 to 20 carbon atoms such as methyl, ethyl, propyl, butyl, hexyl, octyl, nonyl, dodecyl, tetracyl, hexadecyl, octadecyl, nonadecyl and eicosyl as well as corresponding branched isomers, or phenylalkyl with 1 to 4 carbon atoms in the alkyl portion, particularly benzyl, R2 is hydrogen, halogen, particularly chlorine and bromine, alkyl with 1 to 18 carbon atoms or phenylalkyl with 1 to 4 carbon atoms in the alkyl portion, in particularly benzyl, a-methylbenzyl, cumyl, R3 is hydrogen, chlorine or alkyl with 1 to 4 carbon atoms, particularly methyl, butyl, where at least one of the radicals Ri and R2 is different from hydrogen, wherein in the compounds of formula (lb) T is hydrogen or alkyl with 1 to 6 carbon atoms, particularly methyl and butyl, Ti is hydrogen, chlorine or alkyl with 1 to 4 carbon atoms, in particularly methyl, n is 1 or 2, T2 when n is 1, is chlorine or a radical of the formula -OT3, and when n is 2, a radical of the formula -O-T9-O-, where T3 is hydrogen, alkyl with 1 to 18 carbon atoms optionally substituted by 1 to 3 hydroxyl groups, alkyl with 3 to 18 carbon atoms interrupted once or several times by -O- that is optionally substituted by hydroxyl, alkenyl with 2 to 18 carbon atoms (suitable alkenyl radicals may be deduced from the alkyl radicals listed in the definitions of Ri) optionally substituted by hydroxyl, phenylalkyl with 1 to 4 carbon atoms in the alkyl portion, in particularly benzyl, phenylethyl, cumyl, a-methylbenzyl, or a radical of the formula -CH2CH(OH)-T7, T7 is hydrogen, alkyl with 1 to 18 carbon atoms or phenyl, T9 is alkylene with 2 to 8 carbon atoms, alkenylen with 4 to 8 carbon atoms, cyclohexylen or alkylene with 2 to 18 carbon atoms interrupted once or several times by -0-, where it is also being possible for the alkylene or alkenylen radicals to be branched. wherein is 1 or 2, represents an integer from 1 to 3, independently from one another represent hydrogen, hydroxyl, halogen methyl, alkyl with 1 to 12 carbon atoms, alkoxy with 1 to 18 carbon atoms or halogen, when u is 1, represents alkyl with 1 to 18 carbon atoms, alkyl with 1 to 12 carbon atoms substituted by hydroxyl, alkoxy with 1 to 18 carbon atoms, halogen, by -COOH, -COOYg, -CONH2, -CONHY9, -CONY9Y10, -CN and/or -OCOYn, alkyl with 4 to 20 carbon atoms interrupted by one or several oxygen atoms and optionally substituted by hydroxyl or alkoxy with 1 to 12 carbon atoms, alkenyl with 3 to 6 carbon atoms, glycidyl, phenylalkyl with 1 to 5 carbon atoms in the alkyl portion unsubstituted or substituted by hydroxyl, chlorine and/or methyl, -COY12 or -SO2Y13 or when u is 2, is alkylene with 2 to 16 carbon atoms, alkenylen with 4 to 12 carbon atoms, xylylen, alkylene with 3 to 20 carbon atoms interrupted by one or several -O- and/or substituted by hydroxyl, -CH2CH-(OH)CH2-0-Yi5-OCH2CH(OH)CH2, or -(CH2)m-C02-Yi8-OCO(CH2)m, where m is 1, 2 or 3, represents alkyl with 1 to 18 carbon atoms, alkenyl with 3 to 18 carbon atoms, alkyl with 3 to 20 carbon atoms interrupted by one or several oxygen atoms and/or substituted by hydroxyl; glycidyl or phenylalkyl with 1 to 5 carbon atoms in the alkyl portion, Y9 and Yio independently from one another represent alkyl with 1 to 12 carbon atoms, alkoxyalkyl with 3 to 12 carbon atoms, dialkylaminoalkyl with 4 to 16 carbon atoms or cycloalkyl with 5 to 12 carbon atoms, Yii represents alkyl with 1 to 18 carbon atoms, alkenyl with 2 to 18 carbon atoms or phenyl, Y12 represents alkyl with 1 to 18 carbon atoms, alkenyl with 2 to 18 carbon atoms, phenyl, alkoxy with 1 to 12 carbon atoms, phenoxy, alkylamino with 1 to 12 carbon atoms or phenyiamino, Yi3 represents alkyl with 1 to 18 carbon atoms, phenyl, alkylphenyl with 1 to 8 carbon atoms in the alkyl radical, Yi5 represents alkylene with 2 to 20 carbon atoms, phenylene or a -phenylene-M-phenylene group, where M is -0-, -S-, -SO2-, -CH2- or -C(CH3)2-, and Yig is alkylene with 2 to 10 carbon atoms or alkylene with 4 to 20 carbon atoms interrupted once or several times by oxygen. wherein X is an integer from 1 to 3, y is 1 or 2, L independently of one another is H, alkyl with 1 to 20 carbon atoms, hydroxyl or alkoxy with 1 to 20 carbon atoms. In this case, the substituents L are preferably in ortho- and/or para-position. Examples of alkyl-, alkoxy-, phenylalkyl, alkylene-, alkenylene-, alkoxyalkyl- and cycloalkyl radicals as well as alkylthio-, oxaalkylene or azoalkylene radicals in the compounds of formulae (2), (3), (4) and (5) can be derived from the above remarks. wherein n is an integer from 1-4 Ui is H, alkyl, hydroxy, alkoxy, NH2, NH alkyl, N-dialkyl U2 is H, alkyl, aryl, aryl substituted by alkyl, alkoxy aryl, p-hydroxy aryl, p-amino aryl U3 is H, CN, COOUfi U4 for n = 1 is Ci-C2oalkyl (n, iso, cyclo), possibly interrupted by 1 or several oxygen atoms for n = 2 is Ci-Caoalkylene (n, iso, cyclo), possibly interrupted by 1 or several oxygen atoms for n = 3 is a radical of a triol, such as trimethylolpropane, trihydroxypropane for n = 4 is a radical of a tetraol, such as pentaerythritol U5 is hydrogen or a substituent such as Ui, preferably alkoxy U6 is Ci-Caoalkyl (n, iso, cyclo). The UV absorbers of the formulae (la), (lb), (2), (3), (4) and (5) are known per se and described together with their preparation in EP-A-0 323 408, EP-A-0 057 160, EP 0 434 608, US-A-4 619 956, DE-A-3 135 810, GB-A-1 336 391 and EP-A-0 322 557. UV absorbers that correspond to the formulae UVA-1 to UVA-11 below are particularly preferred. The present invention also relates to a process for the stabilization of lacquers against the degradation of the polymer material contained in the lacquer caused by the effect of heat and light, characterized in that a piperidine compound of the formula A or a mixture consisting of this piperidine compound and at least one UV absorber selected from the group consisting of 2-hydroxyphenylbenztriazoles, 2-hydroxyphenyltriazines, 2-hydroxybenzophenones, oxalanilides and cinnamic acid derivatives in an amount sufficient for stabilization in solid or dissolved form is added to the lacquers to be stabilized and worked into the lacquers or lacquer compositions in methods known per se. The total amount of light stabilizer to be selected and the mixing ratio of HALS A to UV absorber depends on the nature of the lacquer composition and on the requirements for its stability. As a rule, the total amount of light stabilizer is between 0.2 to 5% by weight, preferentially 0.5 to 1.5% by weight, related to the dry content of the lacquer. The mixing ratio of HALS A to UV absorber depends on the nature of the lacquer, the stability required and the nature of the UV absorber used. It can therefore vary between 10:1 to 1:10. Typical mixing ratios lie between 4:1 to 1:4, preferentially 3:1 to 1:3. In polyurethane lacquers, for example, a mixture according to the invention consisting of 2 parts of the piperidine compound of formula A and 1 part UV absorber is recommended, whereas a mixing ratio of HALS A to UV absorber of 1 to 3 should, for example, be used for lacquers on the basis of hardenable acrylic resins to achieve the results according to the invention. The individual components of the synergistic mixture can be added individually or as a mixture to the corresponding lacquer compositions. In the case of the two layer lacquers, the addition may be to the bottom layer and/or top layer. The top layer preferentially contains the light stabilizer according to the invention. The conventional additional additives may also be added to the lacquer compositions without thereby impairing the protective effect of the light stabilizer used according to the invention. The light stabilizer according to the invention is preferentially used in powder form, liquid form or in liquid formulations which can be rapidly and accurately volumetrically metered into liquid lacquer systems. The lacquer compositions according to the invention may comprise any desired type of lacquers, e.g. pigmented or unpigmented lacquers or metallic effect lacquers. They may contain an organic solvent or be solvent-free or be aqueous lacquers. Examples of lacquers with special binding agents are the following: 1. Lacquers based on cold-crosslinkable or hot-crosslinkable alkyd-, acrylate, polyester-, epoxy- or melamine resins or mixtures of such resins, optionally with the addition of an acid hardening catalyst; 2. Two-component polyurethane lacquers based on hydroxyl group-containing acrylate-, polyester- or poly ether resins and aliphatic or aromatic polyisocyanates; Single-component polyurethane lacquers based on masked polyisocyanates that are demasked during stoving.; Two-component lacquers based on (poly)ketimines and aliphatic or aromatic polyisocyanates; Two-component lacquers based on (poly)ketiniines and an unsaturated acrylate resin or a polyacetoacetate resin or a methylacrylamido-glykolatemethylester; Two-component lacquers based on carboxyl- or amino group-containing polyacrylates and polyepoxides; Two-component lacquers based on anhydride group-containing acrylate resins and a polyhydroxy- or polyamino component; Two-component lacquers based on (poly)oxazolidines and anhydride group-containing acrylate resins or unsaturated acrylate resins or aliphatic or aromatic polyisocyanates. Two-component lacquers based on unsaturated polyacrylates and polymalonates. Thermoplastic polyacrylate lacquers based on thermoplastic acrylate resins or co-reacting acrylate resins in combination with etherified melamine resins. Lacquer systems based on siloxane-modified acrylate resins. Lacquer systems based on fluoro-modified acrylate resins. The lacquers may also be radiation hardenable lacquers. In this case, the binding agent consists of monomeric or oligomeric compounds that contain ethylenic double bonds and that pass into a cross-linked high molecular form on radiation with actinic light or with electron radiation. A mixture of such compounds is generally involved here. The lacquers may be applied as single-layer or twin-layer lacquers, the stabilizers according to the invention preferentially being added to the unpigmented top layer. The lacquers can be applied to the substrates (metal, plastic, wood, etc.) using conventional processes, for example by brushing, spraying, casting, dipping or electrophoresis. The compositions according to the invention are particularly preferred as lacquers for motor vehicles. Appropriate lacquer systems and binding agents are, for example, described in US-A-4 314 933, 4 344 876, 4 426 471, 4 426 472 and 4 429 077. The present invention also relates to lacquer films that are obtainable by application to a surface and hardening. Another object of the invention are lacquers light-stabilized with the compound HALS A or with a mixture consisting of HALS A and LTV absorbers. Accordingly the present invention provides a process for the stabilization of lacquers against the degradation of the polymer material contained in the lacquer caused by atmospheric oxygen, humidity, heat and/or UV light, characterized in that a compound of formula (A) or a mixture consisting of a compound of formula (A) and at least one UV absorber, is added to the lacquer to be stabiUzed, the concentration of the compound of formula (A) is 0.2 to 5% by weight, preferentially 0.5 to L5% by weight, related to the dry content of the lacquers. The following examples describe the invention, all proportions and percentages being parts by weight and percents by weight unless indicated to the contrary. The light stabilizer according to the invention are worked tel quel into the resin components in the amounts set out in the following tables (% pure light stabilizer, i.e. active substance, in each case related to the solid constituents of the lacquer, i.e. resin and hardener). Hardener B is worked into this mixture. Examples 1 - 4 are carried out in a 2-component high-solid polyurethane lacquer (2K HS-PUR-lacquer). Both the resin component, FQ 95-0104, and also the hardening component SC 29-0160, are obtainable from BASF. The clear coat is adjusted to spraying viscosity with xylene and sprayed onto a prepared substrate (coil coat-coated aluminium sheeting, silver-metallic base coat [aqueous, moondust silver XSC 2431 WCA, BoUig u. Kemper]), flashed off approx. 1 hour at room temperature and then stoved at 140 C for 30 minutes (pmt: peak metal temperature). A dry layer thickness of 40-50 ^m clear coat is formed. The samples are subjected to accelerated weathering in a Xenon-Weatherometer (Ci 35, Atlas; CAM 180); the 20° gloss (DIN 67530) is measured and the residual gloss is calculated therefrom in % in relation to the initial value. Examples 5 and 6 are carried out in a 2-component medium solid polyurethane lacquer (2K MS-PUR-lacquer). Both the resin component, 5 K.53.058 and also the hardener component, 8 K.71.037 are available from Akzo Nobel Coatings. The clear coat is adjusted to spraying viscosity with xylene and sprayed onto a prepared substrate (silver metallic base coat [light gray MS 612 VR modified polyester/melamine, solvent containing, Akzo Nobel]), flashed off at room temperature for approximately 1 hour and then stoved at 80°C for 30 minutes (pmt: peak metal temperature). There results a dry layer thickness of 40-45 |im clear coat. In example 5, the samples are subjected to accelerated weathering in a UVCON apparatus (ASTM G53-93: 8 hours light 70°C, 4 hours dark phase / condensation 50°C); the 20° gloss (DIN 67530) is measured and the residual gloss is calculated therefrom in % as compared to the initial value. In addition, the yellowing is measured colorimetrically (b* value measured according to the CIELAB standard and the delta b* value calculated according to the initial value). In example 6, the samples are subjected to accelerated weathering in a Xenon Weatherometer (WOM Ci 65; CAM 7/DIN 53 231A); the 20° gloss (DIN 67530) is measured and the residual gloss in % is calculated therefrom in relation to the initial value. In the comparative examples, the following, non-photoreactive HALS compounds according to the state of the art that do not absorb UV light are used: HALS 1: Tinuvin (RTM) 292, a commercial product from Ciba-Geigy, Switzerland HALS 4: Sanduvor (RTM) 3055, a commercial product from Clariant, Switzerland Numbers 4 and 7 are examples according to the invention. In examples 1 to 3, the samples stabilized with HALS A display greater resistance to weathering than samples that contain the same amount of a non-UV light-absorbing and non-photoreactive HALS. Here it is surprisingly found that the efficiency of the UV light absorbing-HALS A alone is equally good or even better than those of the combinations of UV absorbers and sterically-hindered amines of the state of the art that are neither photoreactive nor absorb UV light when it is used in a concentration corresponding to the combinations. These examples also show the surprising efficiency of the combinations of UV absorbers with the HALS according to the invention. It is also possible to establish a clearly visible improvement in the tendency to yellowing - expressed in the delta b* values - of these combinations (example 5). WE CLAIM 1. A process for the stabilization of lacquers against the degradation of the polymer material contained in the lacquer caused by atmospheric oxygen, humidity, heat and/or UV light, characterized in that a compound of formula (A) or a mixture consisting of a compound of formula (A) and at least one UV absorber, is added to the lacquer to be stabilized, the concentration of the compound of formula (A) is 0.2 to 5% by weight, preferentially 0.5 to 1.5% by weight, related to the dry content of the lacquers. 2. The process for the stabilization of lacquers according to claim 1, wherein the UV absorber is selected from the group consisting of 2-hydroxyphenylbenztriazoles, 2-hydroxyphenyltriazines, 2-hydroxybenzophenones, oxalanilides and cinnamic acid derivatives. 3. The process for the stabilization of lacquers according to claim 1, wherein the ratio of the compound of formula (A) to UV absorber is 10:1 to 1:10, preferred 4:1 to 1:4, particularly preferred 3:1 to 1:3. 4. A stabilized lacquers, in particular automobile lacquers, comprising 0.2 to 5% by weight, preferentially 0.5 to 1.5% by weight of a compound of formula (A) as herein described or a mixture consisting of a compound of formula (A) and at least one UV absorber. 5. A process for the stabilization of lacquers substantially as herein described and exemplified.

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