Patent Application
20080200577
The invention relates to radiation-curable formulations which contain adhesion promoters containing phosphoric acid and which in the cured state afford a particular degree of corrosion control for metallic substrates, and to a process for preparing them.
Radiation-curable formulations are known.
Ethylenically unsaturated prepolymers are described for example in P. K. T. Oldring (ed.), “Chemistry and Technology of UV and EB Formulations for Coatings, Inks and Paints”, Vol. II. SITA Technology, London 1991, based for example on epoxy acrylates (pages 31 to 68), urethane acrylates (pages 73 to 123), and melamine acrylates (pages 208 to 214). Formulations of this kind are frequently mentioned in the patent literature as well; by way of example mention may be made of JP 62110779 and EP 947 565.
The coating of metallic substrates poses a particular problem for radiation-curable formulations, since processes of contraction may result in a loss of cohesion. For such substrates it is therefore common to use adhesion promoters containing phosphoric acid. Examples thereof are U.S. Pat. No. 5,128,387 (coating of beer cans) and JP2001172554 (coating of various cans).
On the other hand it is also known that adhesion promoters containing phosphoric acid may have an adverse effect on corrosion resistance.
It was an object, therefore, to find radiation-curable formulations, and a process for preparing them, which on the one hand adhere well to metal but on the other hand also exhibit outstanding corrosion control.
Surprisingly it has been found that the corrosion resistance of coating materials based on radiation-curable formulations which contain adhesion promoters containing phosphoric acid increases drastically on metallic substrates if the formulation in question is first thermally conditioned for a while prior to application.
The present invention provides a radiation-curable formulation composed of
A) radiation-curable resins,
B) radiation-curable reactive diluents,
C) adhesion promoters containing phosphoric acid,
D) optionally photoinitiators,
E) optionally pigments,
F) optionally other adjuvants,
obtained by first thermally conditioning the formulation at a temperature of from 40 to 100° C. for from 30 minutes to 48 hours, prior to application and curing.
In principle it is possible to use all radiation-curable resins. Their preparation is described for example in “Radiation Curing in Polymer Science & Technology, Vol I: Fundamentals and Methods” by J. P. Fouassier, J. F. Rabek, Elsevier Applied Science, London and New York, 1993, Chapter 5, pages 226 to 236, in “Lackharze”, D. Stoye. W. Freitag, Hanser-Verlag, Vienna, 1996, and in EP 0 947 565.
Occupying a special position among radiation-curable resins, and particularly suitable in accordance with the invention, are urethane polyester acrylates, on account of their particularly good mechanical and weather-stability properties. Urethane polyester acrylates are described for example in U.S. Pat. No. 5,719,227.
Especially suitable urethane polyester acrylates are composed of a hydroxyl-containing polyester to which urethane groups and acrylate groups are attached by reaction with polyisocyanates and acrylate-containing alcohols.
Urethane polyester acrylates are prepared from hydroxyl-containing polyesters by reaction with polyisocyanates and with a compound which simultaneously contains at least one alcohol group and at least one polymerizable acrylate group. They contain both urethane groups and terminal acrylate groups.
Hydroxyl-containing polyesters are prepared by polycondensation of suitable dicarboxylic acids and diols. The condensation is accomplished in conventional fashion in an inert gas atmosphere at temperatures from 100 to 260° C., preferably from 130 to 220° C., in the melt or azeotropically, as described for example in Methoden der Organischen Chemie (Houben-Weyl); Volume 14/2, pages 1 to 5, 21 to 23, 40 to 44, Georg Thieme Verlag, Stuttgart, 1963, or in C. R. Martens, Alkyd Resins, pages 51 to 59, Reinhold Plastics Appl. Series, Reinhold Publishing Comp., New York, 1961. The carboxylic acids preferred for the preparation of polyesters may be aliphatic, cycloaliphatic, aromatic and/or heterocyclic in nature and may if desired be substituted by halogen atoms and/or unsaturated. Examples thereof that may be mentioned include the following: succinic, adipic, suberic, azelaic, sebacic, phthalic, terephthalic, isophthalic, trimellitic, pyromellitic, tetrahydrophthalic, hexahydrophthalic, hexahydroterephthalic, dichlorophthalic, tetrachlorophthalic, endomethylenetetrahydrophthalic, glutaric or 1,4-cyclohexanedicarboxylic acid or—where obtainable—their anhydrides or esters. Particular suitability is possessed by isophthalic acid, terephthalic acid, hexahydroterephthalic acid, and 1,4-cyclohexanedicarboxylic acid.
Examples of suitable polyols include monoethylene glycol, 1,2- and 1,3-propylene glycol, 1,4- and 2,3-butylene glycol, di-β-hydroxyethylbutanediol, 1,5-pentanediol, 1,6-hexanediol, 1,8-octanediol, decanediol, dodecanediol, neopentyl glycol, cyclohexanediol, 3(4),8(9)-bis(hydroxymethyl)tricyclo[5.2.1.02,6]decane (Dicidol), 1,4-bis(hydroxymethyl)cyclohexane, 2,2-bis(4-hydroxycyclohexyl)propane, 2,2-bis[4-(β-hydroxyethoxy)phenyl]propane, 2-methylpropane-1,3-diol, 2-methylpentane-1,5-diol, 2,2,4(2,4,4)-trimethylhexane-1,6-diol, glycerol, trimethylolpropane, trimethylolethane, hexane-1,2,6-triol, butane-1,2,4-triol, tris(β-hydroxyethyl) isocyanurate, pentaerythritol, mannitol, and sorbitol, and also diethylene glycol, triethylene glycol, tetraethylene glycol, dipropylene glycol, polypropylene glycols, polybutylene glycols, xylylene glycol, and neopentyl glycol hydroxypivalate. Preference is given to monoethylene glycol, neopentyl glycol, Dicidol, cyclohexanedimethanol, trimethylolpropane, and glycerol.
Polyesters prepared in this way have an OH number of from 15 to 750 mg KOH/g. Mixtures of polyesters can also be used.
Polyisocyanates used for preparing urethane polyester acrylates are diisocyanates of aliphatic, (cyclo)aliphatic or cycloaliphatic structure. Representative examples of the polyisocyanates are 2-methylpentamethylene 1,5-diisocyanate, hexamethylene diisocyanate, trimethylhexamethylene 1,6-diisocyanate, in particular the 2,2,4 isomer and the 2,4,4 isomer, and technical mixtures of both isomers, 4,4′-methylenebis(cyclohexyl isocyanate), norbornane diisocyanate, and 3,3,5-trimethyl-1-isocyanato-3-isocyanatomethylcyclohexane (IPDI). Likewise highly suitable are polyisocyanates obtainable by reacting polyisocyanates with themselves via isocyanate groups, such as isocyanurates; which come about through reaction of three isocyanate groups. The polyisocyanates may likewise contain biuret or allophanate groups. IPDI is especially suitable.
Examples of suitable polymerizable compounds having at least one free OH group and a polymerizable acrylate group include hydroxyethyl acrylate (HEA), hydroxypropyl acrylate, hydroxybutyl acrylate, and glyceryl diacrylate. Particular suitability is possessed by hydroxyethyl acrylate (HEA).
To prepare the urethane polyester acrylate from the amorphous, OH-containing polyesters, polyisocyanates, and the acrylate-containing component, the polyisocyanate is introduced first of all, admixed with DBTL as catalyst and IONOL CP (Shell) as polymerization inhibitor, and the polyester is added in an NCO:OH ratio of from 2.5 to 1.5:1. Thereafter the acrylate-containing component, hydroxyethyl acrylate for example, is added to the reaction product in a residual-NCO:OH ratio of from 1.0 to 1.1:1, and the reaction is taken to completion at 40 to 120° C., to give an NCO content of below 0.1%. It is also possible to subject a polyisocyanate, IPDI for example, to preliminary reaction with the acrylate-containing component, and to add this NCO-containing precursor to the hydroxyl-containing polyester.
The amount of A) in the formulation varies from 5% to 95% by weight, preferably from 10% to 70% by weight.
Radiation-curable reactive diluents B) and their preparation are described for example in “Radiation Curing in Polymer Science & Technology, Vol I: Fundamentals and Methods” by J. P. Fouassier, J. F. Rabek, Elsevier Applied Science, London and New York, 1993, Chapter 5, pages 237 to 240. Generally speaking they are acrylate- or methacrylate-containing substances which are liquid at room temperature and hence able to lower the overall viscosity of the formulation. Examples of such products are hexanediol diacrylate, isobornyl acrylate, hydroxypropyl methacrylate, dipropylene glycol diacrylate, tripropylene glycol diacrylate, trimethylolpropane formal monoacrylate, trimethylenepropane triacrylate, tetrahydrofurfuryl acrylate, phenoxyethyl acrylate, lauryl acrylate, pentaerythrityl tetraacrylate, and also urethanized reactive diluents such as Ebecryl 1039 (UCB), and others. Examples of manufacturers of such products include UCB, Sartomer, BASF, Rahn, Akzo, and others. The amount of B) in the formulation is from 5% to 90% by weight. Additionally suitable are other liquid components which are capable of undergoing reaction as well under conditions of free-radical polymerization, examples including vinyl ethers or allyl ethers.
Adhesion promoters C) for radiation-curable formulations for metallic substrates are composed in general of reaction products (esters, for example) of phosphoric acid and alcohol-functionalized acrylates. While the three phosphoric acid groups are responsible for direct adhesion to the metal, the acrylate groups ensure integration with the matrix of the coating. Products of this kind are also described in WO 01/98413, in JP 08231564, and in JP 06313127.
Typical commercial products are Ebecryl 169 and 170 from UCB, Alditol Vxl 6219 from Vianova, CD 9050 and CD 9052 from Sartomer, Sipomer PAM-100, Sipomer PAM-200 and Sipomer PAM-300 from Rhodia, and Genorad 40 from Rahn. The amount of B) in the formulation is from 0.1% to 10% by weight.
Photoinitiators D) and their preparation are described for example in “Radiation Curing in Polymer Science & Technology, Vol II: Photoinitiating Systems” by J. P. Fouassier, J. F. Rabek, Elsevier Applied Science, London and New York, 1993. An example of a photoinitiators manufacturer is Ciba, and they can be present in amounts of from 0.2% to 10% by weight.
Suitable pigments E) in radiation-curable formulations are described for example in “Radiation Curing in Polymer Science & Technology, Vol IV: Practical Aspects and Application” by J. P. Fouassier, J. F. Rabek, Elsevier Applied Science, London and New York, 1993, Chapter 5, pages 87 to 105, and they can be present in amounts of from 1% to 40% by weight. Examples of anticorrosion pigments are found for example in Pigment+Füllstoff Tabellen, O. Lückert, Vincentz Verlag, Hanover, 6th edition 2002. The following may be mentioned by way of example: Shieldex C 303 (Grace Davison) and Halox Coil X 100, Halox Coil X 200, and Halox CW 491 (Erbslöh), Heucophos SAPP (Heubach), K-White TC 720 (Tayca), and Hombicor (Sachtleben). Of course, simple inorganic salts are also suitable, such as zinc phosphate.
Adjuvants F) for radiation-curable formulations are available in various compositions and for a variety of purposes, examples including flow control agents, matting agents, devolatilizers, and others.
Some of them are described in the brochure “SELECTED DEGUSSA PRODUCTS FOR RADIATION CURING AND PRINTING INKS”, published by Tego Coating & Ink Additives, Essen, 2003. Another manufacturer of such products, for example, is Byk. The amount of F) varies from 0.01% to 5% by weight, if present.
The invention also provides a process for preparing radiation-curable formulations with enhanced corrosion control on metal substrates, which comprises obtaining a mixture composed of
A) radiation-curable resins,
B) radiation-curable reactive diluents,
C) adhesion promoters containing phosphoric acid,
D) optionally photoinitiators,
E) optionally pigments,
F) optionally other adjuvants,
by first thermally conditioning this mixture at a temperature of from 40 to 100° C. for from 30 minutes to 48 hours, prior to application and curing.
All of the ingredients (or parts thereof) are mixed intimately with one another in a suitable mixing assembly (e.g., stirred tank, Dispermat, static mixer, extruder or flow tube).
The mixing temperature can be from room temperature (20° C.), to 140° C., but generally does not exceed 80° C., and is preferably from 20 to 60° C.
Thermal conditioning may take place either in the whole formulation or else in constituents of said formulation necessarily containing the adhesion promoter containing phosphoric acid. Thermal conditioning constitutes storage at a temperature of from 40 to 100° C. for from 30 minutes to 48 hours. From 40 to 60° C. for from 2 to 8 hours is preferred. From 40 to 50° C. for from 4 to 8 hours is particularly preferred.
As is customary for powder coating materials, in the case of solid formulations the mixture is also ground and sieved prior to application.
Application may take place by the techniques that are known in coatings technology, examples being knifecoating, roller coating, spraying or injecting.
A particularly suitable metallic substrate is steel, with all of the various pretreatment methods, but also aluminum and other alloys provided with a coating for reasons of corrosion control.
Curing is accomplished in the presence of photoinitiators under a UV lamp, or in the absence of photoinitiators under electron beams. The properties of the cured coatings are almost identical irrespective of the curing method.
UV curing and UV lamps are described for example in “Radiation Curing in Polymer Science & Technology, Vol I: Fundamentals and Methods” by J. P. Fouassier, J. F. Rabek, Elsevier Applied Science, London and New York, 1993, Chapter 8, pages 453 to 503.
Electron beam curing and EBC sources are described for example in “Radiation Curing in Polymer Science & Technology, Vol I: Fundamentals and Methods” by J. P. Fouassier, J. F. Rabek, Elsevier Applied Science, London and New York, 1993, Chapter 4, pages 193 to 225, and in Chapter 9, pages 503 to 555.
The invention is elucidated below with reference to examples, but without being thereby restricted.
2626 g of adipic acid (acid component) and 2661 g of butanediol (alcohol component) were admixed with 0.2 percent by mass of n-butyltin trioctoate and this mixture was heated to 190° C., under nitrogen and with stirring, in an apparatus provided with a distillation column. Over the course of elimination of water, this temperature was slowly raised to 230° C. When about 98% of the theoretical amount of water had been removed by distillation, the product was cooled and found to have an OH number of 252 mg KOH/g. The acid number was 0.6 mg KOH/g.
37.3 g of the polyester (P) were melted and this melt was added in portions with vigorous stirring and at 80° C. to a mixture of 38.4 g of IPDI, 0.2 g of IONOL CP, and 0.1 g of DBTL. After 10 minutes' reaction, additionally, 24.0 g of hydroxyethyl acrylate were added dropwise. After a further 30 minutes' stirring the NCO content was below 0.1% and the hot reaction mixture was cooled.
The urethane acrylate (BAB) was stirred together well with the other formulation ingredients. In the case of pigmented systems, in addition, the batch was dispersed in a Dispermat at 9000 rpm for 20 minutes. This was followed, in the case of the inventive experiments, by thermal conditioning in a drying oven (at 50° C. for 8 hours). Finally, the ready-to-use formulation was applied by knifecoating (40 μm film thickness) to steel panels (Q-Panel, R 36) and subsequently cured under a UV lamp (UV, Minicure, mercury vapor lamp, 80 W/cm, Tecnigraf) or under an electron beam source (EBC, Energy Sciences).
It is clearly apparent that the thermally conditioned formulations ensure substantially greater corrosion control.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10 2005 031 271.3 | Jul 2005 | DE | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/EP2006/062286 | 5/12/2006 | WO | 00 | 12/26/2007 |
