ANTI-SKINNING AGENT FOR COATING COMPOSITIONS

Abstract: The invention pertains to a coating composition containing at least one compound of general formula (I) and/or at least one compound of formula (II) as anti-skinning agent, wherein X, Y, R1-R4, and n have the meaning defined below. These compounds are especially suitable for use as anti-skinning agent for air-drying coating compositions.

Description: ANTI-SKINNING AGENT FOR COATING COMPOSITIONS The invention pertains to a coating composition containing at least one compound of the general formula and/or at least one compound of the formula Xc Υ , -N (R 4 ) n as anti-skinning agent, wherein X, Y, R 1 -R 4 , and n have the meaning defined below. These compounds are particularly suitable for use as anti-skinning agent for air-drying coating compositions. Air-drying coatings harden under the influence of atmospheric oxygen. Without appropriate precautions, these coatings, when they come into contact with oxygen - e.g. from the air - unstirred, will form a skin on their surfaces. Since air-drying is an irreversible cross-linking process, this skinning generally cannot be cancelled even by renewed thorough mixing of the coating composition and this cross-linked top paint film will be useless for further processing. In order to enable coating compositions to be stored for a considerable period of time in packings with air present above or to enable opened up barrels - in which the air present above will inevitably increase as a result of the removal of coating material - to remain storage stable for a certain period of time, substances are added to the coating compositions which eliminate this skinning. These substances are known as anti-skinning agents. Similar phenomena are also known from primers and coatings which are exposed and subject to prolonged atmospheric action, e.g. dipping primers with a long turn over. Also in such covering or coating compositions use is made of anti-skinning agents. They are further used in fillers. The properties profile of anti-skinning agents requires that skinning be avoided, yet they must not have a negative effect on the actual hardening of the coating following application. A widely used anti-skinning agent is butanonoxim, which is also marketed under the trade designations Aconox M, Metoxim 100, Ascinin R, Borchinox M2, Exkin 2, etc.. / OH N This substance was assigned a new value in the MAK Values List for 1997. While in the EC Safety Specification Sheet butanonoxim is classified as Xi (irritating) as before and not yet identified as carcinogenic, nevertheless, in the MAK and BAT Values Lists for 1997 of the German Society for the Advancement of Scientific Research it appears in Group III A2, which lists substances which are unmistakably carcinogenic in animal experiments, more particularly under test conditions which are infectious to humans. In the 1997 supplement on butanonoxim the following statements with regard to the carcinogenicity of ketoxims are found: 5.6.2 Genotoxicity in vivo „After intraperitoneal administration of butanonoxim (2,24 mmoles/kg KG) to male F344-rats the formation in the liver was proved of DNA-modification DX1, RNA-modifications RX1 and RX2 as ^ well as an increased formation of 8- oxoguanine in DNA and RNA." „The formation of the nucleic acid modifications DX1 and 8-aminoguanosine and an increased formation of 8-oxoguanine in DNA a RNA were also demonstrated after application of the ketoxims acetonoxim, 3-pentanonoxim, 4- heptanonoxim, cyclopentanonoxim, and cyclohexanonoxim " 2 Working mechanism „The hepatocarcinogenicity of the butanonoxim observed in two studies is probably a general feature of the ketoxims, since acetonoxim and cyclo- pentanonoxim also led to an increased incidence of liver tumors in male rats." Moreover, the carcinogenic effect of butanonoxim presumably should not be attributed to the individual substance but to a metabolic process, which shows the entire group of ketoxims to be critical. From the patent literature some few examples of other anti-skinning agents are known. In US 3,346,523 of Esso Research and Engineering Co. and US 3,701 ,781 of Cincinnati Milacron Chemicals, Inc., however, again compounds with oxim groups are described. DE 3418988 of BASF AG describes the use of α-hydroxyketones such as hydro xyacetone. Given these facts, the use of ketoxims as anti-skinning agent appears to be critical. For that reason a search was made for a suitable alternative which is not a ketoxim, which is unobjectionable from a toxicological point of view, and which in terms of properties profile is comparable with butanonoxim. Surprisingly, the above-mentioned objective was met by means of a coating composition comprising one or more compounds of the general formula wherein Ri and R 2 may be the same or different and represent a C C 6 alkyl group and/or one or more compounds of the general formula wherein X and Y represent either a carbon atom and a nitrogen atom or a nitrogen atom and a carbon atom, R 3 is hydrogen or an alkyl group, R 4 , or when n is greater than 1 , each R-i group, which may be the same or different, is an alkyl, alkenyl, aralkyl, aryl, alkylaryl, amine or group, wherein R 5 represents a d-C alkyl group and n is greater than or equal to 0 and less than or equal to 3. Preferably, air-drying coating compositions are concerned. It was established that compounds of formula (I) and/or (II) used according to the invention showed a good anti-skinning effect comparable to that of butanonoxim, without the air drying of the film being negatively affected. Surprisingly, as a side effect there is a clear reduction of the yellowish tinge otherwise common in air-drying coatings - both in the wet and the dry phase. So far as is apparent from toxicological data collections such as the MAK and BAT Values Lists, the compounds of formulae (I) and (II) show no objectionable toxicological effects as compared with butanonoxim. The term coating composition according to the invention is to be interpreted very broadly. For instance, it concerns varnishes, priming coats, filling pastes, glazes, emulsions. The compounds of formula (I) and/or (II) used according to the invention are especially suitable for use in all air-drying systems. The coating compositions according to the invention preferably are solvent- based air-drying coatings and/or house paints. However, they may also be formulated as a water-dilutable or water-borne system. By house paints is meant the group of pigmented and unpigmented surface coating compositions which is used in priming or reconditioning coats for coating doors, windows, floors, equipment objects, and the like. They appear in the form of glazes, clear lacquers, priming coats - including fillers - precoats, and finishes and are used for coating substrates common in construction such as wood, metal, synthetic material, but also stone and mineral surfaces (e.g. concrete, ceramic material). Preferably, the coating compositions according to the invention are alkyd based. A preferred coating composition is a house paint, e.g. an alkyd paint, which contains acetylacetone as the compound of the general formula (I) and no compound of the general formula (II). Furthermore, the use of acetylacetone by itself as the compound of general formula I without a compound of formula II as anti-skinning agent in coating compositions is an advantageous embodiment of the present invention. Especially good results, however, can be obtained by using at least one compound of general formula (I), more particularly acetylacetone, together with at least one compound of general formula (II). The compound of the general formula concerns 1 ,3-diketones, wherein R-i and R 2 may be the same or different and a C C 6 alkyl group, preferably a Cι-C 4 alkyl group. Ri and R 2 may be, e.g., a methyl, ethyl, n-propyl, i-propyl, n-butyl, sec-butyl, tert.-butyl, pentyl or hexyl group. Preferably, Ri and R 2 each are a methyl group, i.e. acetylacetone. The compound of general formula / X^γ R 3 — N -— (R 4 ) n concerns a heterocycle in which X and Y represent either a carbon atom and a nitrogen atom or a nitrogen atom and a carbon atom, R 3 is hydrogen or an alkyl group, preferably a C C 4 alkyl group, R , or when n is greater than 1 , each R 4 group, which may be the same or different, is an alkyl, alkenyl, aralkyl, aryl, alkylaryl, amine or group, wherein R 5 is a C C 4 alkyl group and n is greater than or equal to 0 and less than or equal to 3. The alkyl group for R 3 may be an alkyl group with C Cι 5 carbon atoms, preferably with C C 4 carbon atoms. For the alkyls with d-C 4 carbon atoms suitable for use for R 3 reference may be had to the groups mentioned earlier for Ri and R 2 . R 3 being hydrogen or methyl is especially preferred. The alkyl group for R4 may be an alkyl group with 1-15 carbon atoms, preferably with 1-4 carbon atoms. Examples of alkyl groups suitable for use are decyl, octyl, heptyl, hexyl, pentyl, and the CrC 4 alkyl groups mentioned earlier for Ri and R 2 . The alkenyl groups may be alkenyl groups with 2-15 carbon atoms, preferably 2-4 carbon atoms. Examples of alkenyl groups suitable for use are ethenyl, propenyl (e.g. 1-propenyl or 2-propenyl), and butenyl. The aralkyl groups may be aralkyl groups with 7-15 carbon atoms. One example is phenylethyl. The aryl groups may be aryl groups with 6-14 carbon atoms such as phenyl, naphthyl, and anthryl. The alkylaryl groups, e.g. with 7-15 carbon atoms, may be, e.g., ethylphenyl. The amine groups employed may be primary, secondary, and tertiary amines. As substituents on the amine are considered, e.g., alkyl, aryl, aralkyl or alkylaryl groups. For specific examples of these groups reference may be had to the aforementioned examples for R 4 . For examples of the C C 4 alkyl groups for R 5 reference may be had to the groups mentioned for R-i and R 2 . The number n substituents R 4 present on heterocycle (II) is 3 at the most, but can also be 0. The present substituents R 4 may all be the same or different. A preferably used compound of formula (I) is acetylacetone. As compound of formula (II) preferably compounds of the formula are used, wherein R4 and n are as defined above. The use of 3,5-dimethyl- pyrazole as compound of formula (II) or (III) is quite especially preferred. The compounds of formula (I) and formula (II), respectively, can be included in the coating composition as anti-skinning agent by themselves. Moreover, in each case only one compound of the formula in question or several compounds of the formula in question may be used. Preferably, however, in the coating compso according to the invention use is made of at least one compound of general formula (I) and at least one compound of formula (II). Further examples of compounds of general formula (II) are pyrazole, 3- methylpyrazole, 1 ,4-dimethyipyrazole, imidazole, 1-methylimidazole, 2-methyl- imidazole, 4-methylimidazole, 2-ethylimidazole, 1 ,2-dimethylimidazole, 2-ethyl- 4-methylimidazole, N-(3-aminopropyl)imidazole, and ethyl-(3-aminopyrazole-4- carboxylate). In addition to the especially preferred compound 3,5-dimethyl- pyrazole, the compounds imidazole and 1 ,2-dimethylimidazole also have preference. It was found that a combination of acetylacetone and 3,5-dimethylpyrazole is especially advantageous. Slight colour changes in the wet film, which may occur when using single components, are avoided by the combination, as in that case the effects offset each other. However, also in the case of single components the shift in colour disappears after 1-2 days when the applied film has hardened. Surprisingly, it is especially through this combination that also the yellowish tinge common with air-drying coatings is clearly reduced, both in the wet and the dry phase. Preferably, all things considered, the compounds of formula (I) and formula (II) are used in the coating composition together in an amount of 0,1 to 5 wt.%, more preferably 0,5 to 3 wt.%, calculated on the coating composition. In so far as acetylacetone is present, the proportion thereof, calculated on the overall quantity of coating material, preferably is 0,05 to 2 wt.%, especially preferably 0,25 to 1 wt.%. The coating composition according to the invention may contain siccatives, for instance the naphthanate salt or octoate salt of cobalt, manganese, nickel, vanadium, zirconium or molybdenum. The following examples elucidate the invention. While in these embodiments solid components are always used as a solution, it is possible - when a coating material is dispersed through a sand mill, ball mill or three-roll mill - to add the solid to the material to be ground and also grind it. In this way it is possible to economise on optional additional solvent. Examples Unless indicated otherwise, all % and parts data refers to weight percentages and parts by weight. High-gloss white test coating composition without anti-skinning agent 68 parts of a long oil soya alkyd (AN 8-13, OH no. about 60-70, SC 65% in white spirit) were dissolved together with 25 parts of titanium dioxide (rutile type), 1 part of bentonite paste (25% in white spirit), and 1 part of soya lecithin until a grain size of less than 10 μm was achieved. Next, the mixture was supplemented with 0,5 part of a 6% cobalt octoate solution and set to a processing viscosity of 5,5-6,0 dPa-s with at most 4,5 parts of white spirit. Test coating compositions with anti-skinning agent For the determination the above-described high-gloss white test coating composition was mixed with the different anti-skinning agents in different variations of quantities and mixed thoroughly with an impeller. To evaluate the surface drying a 100 μm application of each of the thus obtained test compositions was made on lined paper and the surface drying was assigned a value after 4 and 8 hours in accordance with DIN 53230. About 200 ml of the different test coating compositions were stored in a PE beaker at room temperature, exposed, and the skinning after 24 hours was evaluated in accordance with DIN 53230. The results are listed in the Table below. Each time the above-described test coating composition without further additives was also assigned a value as a blank test sample. Results: Notes: 1) Surface drying grades of 0-5; 0 stand for dust-free dry, 5 stands for wet trends are evaluated with + (better, - 0) or - (poorer, → 5) 2) Surface drying grades of 0-5; 0 stands for no skin, 1 stands for incipient skinning at the edges, 2 stands for incipient skinning, 3 stands for fine continuous skin, 4 stands for skin, 5 stands for strong skin trends are evaluated with + (better, - 0) or - (poorer, → 5) 3) The solid compounds of formula II were dissolved in a mixture of Solvesso 150 and methoxypropanol. The solvent was not taken into account in the determination of the amount calculated on 100 parts of test coating composition. It was found that by using the compounds of formula I and/or II, more particularly by using acetylacetone and 3,5-dimethylpyrazole, an anti-skinning effect comparable with that of butanonoxim can be achieved, without the drying properties of the thus prepared coating compositions being adversely affected. It was found that a combination of acetylacetone and 3,5-dimethylpyrazole was particularly advantageous. Slight colour changes in the wet film, which may occur when using single components, are avoided by the combination, since the effects in that case offset each other. However, also in the case of single components the shift in colour disappears after 1-2 days, when the applied film has hardened. Surprisingly, it is through this combination that the yellowish tinge common with air-drying coatings is also clearly reduced - both in the wet and the dry phase. Compared with the hydroxyacetone known from DE patent specification 3418988 a clearly improved effectiveness is achieved. In addition to the aforesaid examples, three high-gloss white finishes were formulated. The aforesaid recipe items were dissolved for 15 minutes and then subjected to 1 passage through an agitator mill. The grain size subsequently was less than < 10 μm Next, there was supplementing with the following items. Using white spirit the coating compositions ware set to a processing viscosity of 5,0 to 5,5 dPas. The coating compositions were tested on the following points:

Claims: Claims: 1. Coating composition containing one or more compounds of the general formula wherein R-i and R 2 may be the same or different and represent a C C- 6 alkyl group and/or one or more compounds of the general formula R 3 — N ^ -— (R 4 ) n (II) wherein X and Y represent either a carbon atom and a nitrogen atom or a nitrogen atom and a carbon atom, R 3 is hydrogen or an alkyl group, R , or when n is more than 1 , each R 4 group, which may be the same or different, is an alkyl, alkenyl, aralkyl, aryl, alkylaryl, amine or group, wherein R 5 represents a CrC 4 alkyl group and n is greater than or equal to 0 and less than or equal to 3, wherein in the event that no compound of general formula (II) is included and the coating composition at issue is neither an aqueous coating composition nor a house paint, Ri and R 2 are not simultaneously methyl. 2. Coating composition according to claim 1 wherein Ri and R 2 may be the same or different and represent a C C alkyl group and/or R 3 is hydrogen or methyl. 3. Coating composition according to claim 1 or 2 which contains acetylacetone as the compound of formula (I) and/or contains as compound of formula (II) a compound of the general formula wherein R 4 , or when n is greater than 1 , each R 4 group, which may be the same or different, is an alkyl, alkenyl, aralkyl, aryl, alkylaryl, amine or group, wherein R 5 represents a C C 4 alkyl group and n is greater than or equal to 0 and less than or equal to 3. 4. Coating composition according to claim 1 , 2 or 3 containing at least one compound of formula (I) and at least one compound of formula (II). 5. Coating composition according to claim 4 containing a combination of acetylacetone o o and 3,5-dimethylpyrazole 6. Coating composition according to any one of claims 1-5, characterised in that the coating composition is an air-drying coating composition, more particularly an alkyd coating composition. 7. Coating composition according to any one of claims 1-6, characterised in that the coating composition is a house paint. 8. Coating composition according to any one of claims 1-7 wherein the compounds of formula (I) and/or (II) together are included in an amount of 0,1 to 5 wt.%, calculated on the coating composition. 9. Use of one or more compounds of the general formula wherein Ri and R 2 may be the same or different and represent a CrC 6 alkyl group and/or one or more compounds of the general formula R 3 — N χ ^÷- (R 4 ) n (II) wherein X and Y represent either a carbon atom and a nitrogen atom or a nitrogen atom and a carbon atom, R 3 is hydrogen or an alkyl group, R , or when n is more than 1 , each R 4 group, which may be the same or different, is an alkyl, alkenyl, aralkyl, aryl, alkylaryl, amine or group, wherein R 5 represents a CrC 4 alkyl group and n is greater than or equal to 0 and less than or equal to 3, as an anti-skinning agent in coating compositions. 10. Use of one or more compounds of general formula (I) and/or one or more compounds of general formula (II) according to claim 9, wherein use is made of compounds of formula (I) and/or (II) according to any one of claims 2-5 or 8. 11. Use according to either claim 9 or 10 for an air-drying coating composition, more particularly an alkyd coating composition, and/or a house paint. 12. Use of one or more compounds of general formula (I) and/or one or more compounds of general formula (II) according to claims 1-8 for the preparation of a solvent-based coating composition. 13. Use of one or more compounds of general formula (I) and/or one or more compounds of general formula (II) according to claims 1-8 for the preparation of a coating composition with a water-dilutable formulation.

Inventors: FIGGE HANS-JUERGEN, WEBER BODO, FIGGE, HANS-JUERGEN, WEBER, BODO
Applicants: AKZO NOBEL NV, FIGGE HANS JUERGEN, WEBER BODO, AKZO NOBEL N.V., FIGGE, HANS-JUERGEN, WEBER, BODO
Application year: 1999
Main classification: C09D7
IPC codes: C09D7, C09D167