Classifications

• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08F—MACROMOLECULAR COMPOUNDS OBTAINED BY REACTIONS ONLY INVOLVING CARBON-TO-CARBON UNSATURATED BONDS
  • C08F283/00—Macromolecular compounds obtained by polymerising monomers on to polymers provided for in subclass C08G
  • C08F283/10—Macromolecular compounds obtained by polymerising monomers on to polymers provided for in subclass C08G on to polymers containing more than one epoxy radical per molecule
• • C—CHEMISTRY; METALLURGY
  • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
  • C09D—COATING COMPOSITIONS, e.g. PAINTS, VARNISHES OR LACQUERS; FILLING PASTES; CHEMICAL PAINT OR INK REMOVERS; INKS; CORRECTING FLUIDS; WOODSTAINS; PASTES OR SOLIDS FOR COLOURING OR PRINTING; USE OF MATERIALS THEREFOR
  • C09D4/00—Coating compositions, e.g. paints, varnishes or lacquers, based on organic non-macromolecular compounds having at least one polymerisable carbon-to-carbon unsaturated bond ; Coating compositions, based on monomers of macromolecular compounds of groups C09D183/00 - C09D183/16
  • C09D4/06—Organic non-macromolecular compounds having at least one polymerisable carbon-to-carbon unsaturated bond in combination with a macromolecular compound other than an unsaturated polymer of groups C09D159/00 - C09D187/00

Definitions

• Aqueous coating agent process for its preparation and its use for coating cans
• the invention relates to an aqueous coating agent obtained from an epoxy resin, partially containing carboxyl group-containing ethylenically unsaturated monomers, a peroxide initiator, a crosslinking agent, a neutralizing agent, organic solvents and, if appropriate, other conventional additives, such as plasticizers, stabilizers, wetting agents , Dispersing aids, catalysts and pigments. -
• High molecular epoxy resins are particularly suitable for sheet metal interior protective lacquers. Phenol formaldehyde, melamine and urea resins, for example, serve as crosslinkers.
• Such solvent-based coating compositions contain a solvent content of mostly between 70 and 60% due to the given application viscosity. If - like in the painting of two-part beverage cans - it is necessary to work with spray paint applications, the result is usually a further increase in the solvent content, which results in severe pollution from solvent emissions.
• aqueous coating systems lie in a significantly reduced solvent emission.
• the application of aqueous synthetic resin dispersions by means of electrocoating is particularly advantageous, since with this method an almost 100% paint yield and a further reduction increased emission of solvents can be achieved.
• the coating of various can geometries is possible due to the effect of encompassing electrical varnishes, whereby, in contrast to the coating application, a uniform layer thickness and thus also good edge coverage are achieved by spray application.
• the electrocoating process offers the best conditions for process automation, as a result of which this process offers additional savings in addition to the reduced material requirement.
• electrocoating can be used for both anionic and cationic binder systems.
• the interior protective lacquers must comply with strict food law regulations.
• such coatings must be constant when stored in contact with the predominantly acidic to neutral contents. Taking these requirements into account, the anodic electrocoating is fundamentally more advantageous than the cathodic variant, since the 5 cathodically deposited films mostly contain amine groups and can therefore result in weaknesses in contact with acidic fillings.
• a carboxyl functionality is usually introduced for the production of anionically dissolved synthetic resins.
• the epoxy resin as described for example in US Pat. No. 3,862,914, can be converted into a carboxyl-functional polymer by reaction with polycarboxylic acid anhydrides.
• Systems of this type in which polycarboxylic acids are bound to polymers via half-ester functions, are extremely susceptible to hydrolysis, as a result of which the corresponding aqueous dispersions of such polymers have an insufficient shelf life (ETTurpin, J. Paint Technol., Vol. 47, No. 602, page 40, 1975).
• a "hydrolytically stable connection of the Carboxylfunktiona ⁇ diversity at the epoxy resin according to the US-PS 3,960,795 through the reaction of epoxy with para-hydroxy benzoic acid esters are achieved with the formation of an ether bond, followed by hydrolysis of the benzoic acid ester with release of the carboxylic functionality.
• the disadvantage This method consists in that, in particular, the high molecular epoxy resins required for internal protective coating lacquers cannot be functionalized with carboxyl groups to the extent necessary for an aqueous dispersion because of their low content of epoxy groups.
• US Pat. No. 4,247,439 and European Patent Nos. 6334 and 6336 disclose hydrolysis-stable aqueous can protective lacquers which are obtained from esterification products of epoxy resins with carboxyl-functional polyacrylate resins. Hydrolysis-stable aqueous interior protective lacquers are also known from US Pat. No. 4,212,781 and US Pat. No. 4,308,185.
• the generic US Pat. No. 4,212,781 discloses resin mixtures which are dispersible in an aqueous, basic medium and are obtained by copolymerization of partially carboxyl-containing ethylenically unsaturated monomers in the presence of an aliphatic or aromatic 1,2-diepoxide resin using at least 3% by weight.
• the resin mixtures known from US Pat. No. 4,212,781 can be crosslinked with aminoplast resins. They are particularly suitable for spray painting beverage receptacles.
• DE-OS 34 46 178 discloses water-thinnable compositions for coating metal cans, the polymer present in the composition consisting of a reaction product of acrylic monomers, a high molecular weight epoxy resin, a phenol formaldehyde resin and a radical initiator.
• aqueous systems known from the prior art are mainly used for spray painting two-part aluminum beverage cans. They have the disadvantage that they are based on problematic surfaces, e.g. stretched-deep-drawn beverage cans made of tinplate, offer inadequate surface protection.
• the object of the present invention was to provide an aqueous coating agent for the coating of metal cans, wherein the coating compositions should be universally replaceable, ie the coating compositions should be suitable for coating cans made of aluminum, tinplate and made of otherwise specially surface-treated steel.
• the coating of two-part beverage cans is contemplated so that 1 but also to the coating of preserve cans, which must be resistant to a wide range of products even under sterilization conditions.
• the new coating systems should also offer adequate surface protection on problematic substrates.
• the problematic substrates to be considered are, for example, drawn-deep-drawn tinplate cans with a small tin coating, the surface of which is known to consist of iron, little free tin 0 and various iron-tin alloys.
• the aqueous dispersions should in particular be stable on storage and they should be easy to pigment. Coating agents produced from this should be able to be applied perfectly by means of spray painting and also anodic electro-painting. in the
• the binders In the case of electrocoating, the binders have to be closed under the influence of the electrode reactions on the can connected as anode. '• paint film coagulate having a highest possible Q Filmwi- resistor. All coating agent components, such as crosslinking agents, auxiliaries and possibly pigments, must be separated in the ratio in which they are also present in the dispersion. In most systems of the prior art, the process enters 5 on problem in that the neutral cross-linking agent is not deposited to the extent as it is present in the aqueous persion discontinuously.
• the electrocoat materials should allow coating times of between about 0.5 and 30 seconds, taking into account the conditions of industrial can production. Under these conditions, the c film layer thicknesses typical for sheet metal packaging between about 4 and 10 ⁇ m must be able to be produced. To do this, the wet film resistance must be at least 10 J ⁇ cm " .
• the wrap-around of the electrocoat should be so well developed that even decorated can geometries can be coated with a pore-tight lacquer film of constant layer thickness. Furthermore, the current-voltage characteristics of the electro-dipping materials have to be matched to practically usable electrode geometries.
• the deposited wet films should be sufficiently hydrophobic to enable the cans to be rinsed with the usual rinsing media, such as distilled water, drinking water, ultrafiltrate, and to prevent redissolving in the electro-immersion material.
• the usual rinsing media such as distilled water, drinking water, ultrafiltrate, and to prevent redissolving in the electro-immersion material.
• the baked-on paint films should at least achieve or exceed the level of properties of conventional interior can protective lacquers with regard to freedom from pores, filling material resistance, sheet adhesion, hardness, elasticity and taste neutrality.
• the residual monomer content of the binders may have to be kept as low as possible by means of suitable production processes.
• Pasteurization or sterilization resistance of baked paint films against various test solutions - in the simplest case against water - is important.
• the object on which the present invention is based is achieved by the aqueous coating agent of the type mentioned at the outset, which is characterized in that the coating agent is based on a binder a) which is obtainable from
• polyester polycarboxylic acids with an average molecular weight of 500 to 5000 and an acid number of 30 to 150
• C 10 to 50% by weight of ethylenically unsaturated monomers, 10 to 50% by weight of the monomers containing carboxyl groups
• Polyglycidyl ethers of bisphenol A with an average molecular weight of 500 to 20,000 are preferably used as component A).
• suitable epoxy resins are glycidyl polyethers, e.g. are sold under the trademark Epikote 1001, 1004, 1007 and 1009.
• the epoxy resins (component A) advantageously have an average molecular weight of at least 3000 g / mol.
• polyester polycarboxylic acids used as component B) are prepared in accordance with the conditions known to the person skilled in the art for polyesterification reactions. These are known polycondensates 1 from aromatic and / or aliphatic dicarboxylic acids, aromatic dicarboxylic acid anhydrides, aromatic tricarboxylic acid anhydrides, aromatic tetracarboxylic acid anhydrides and dianhydrides and aliphatic
• Preferred starting compounds for the polyester polycarboxylic acids are terephthalic acid, isophthalic acid, trimellitic acid, trimellitic anhydride, adipic acid, sebacic acid, aliphatic monools with 4 to 20 carbon atoms, 2,2-dimethyl-1,3-propanediol, ethylene glycol, diethylene glycol, Trimethylolpropane, glycerin, pentaerythritol.
• the polyester polycarboxylic acids B) lg preferably have an average molecular weight of 1000 to 3000 and an acid number of 50 to 100.
• polyester polycarboxylic acid component B is that as the polyol component for the preparation of the polyester polycarbonate
• esters diols and / or glycidyl esters of monocarboxylic acids can be used.
• Hydroxypivalic acid neopentylglycol ester may be mentioned as an example of suitable ester diols.
• a suitable commercially available glycidyl ester of monocarboxylic acids is the glycidyl ester
• polyester polycarboxylic acids produced using ester diols and / or glycidyl esters of monocarboxylic acids have acid numbers in the range
• the ethylenically unsaturated monomers used as component C) consist of 10 to 50% by weight of monomers containing carboxyl groups.
• carboxyl group-containing monomers are acrylic acid and methacrylic acid. Furthermore, non-functionalized monomers, such as styrene, vinyl toluene and undomethylstyrene.
• (meth) acrylic esters having 1 to 20 carbon atoms in the alcohol radical preference is given to using (meth) acrylic esters having 1 to 20 carbon atoms in the alcohol radical, it also being possible to use hydroxyl-functional monomers.
• these are ethyl acrylate, propyl acrylate, isopropyl acrylate, butyl acrylate, isobutyl acrylate, t-butyl acrylate, pentyl acrylate, decyl acrylate, lauryl acrylate, methyl methacrylate, butyl methacrylate, isobutyl methacrylate, hexyl methacrylate, methacrylate, methacrylate, methacrylate, methacrylate, methacrylate, methacrylate, , Hydroxypropyl acrylate, hydroxibutyl acrylate, hydroxyethyl ethacrylate, hydroxypropyl methacrylate and hydroxibutyl methacrylate
• the ethylenically unsaturated monomers of component C) preferably consist of
• y 0 to 50 wt .-%, preferably 20 to 40 wt .-%, non-functionalized monomers and
• Component C) has an acid number in the range from 30 to 150, preferably in the range from 50 to 100.
• the binder a) is preferably obtained from 35 to 60% by weight of A), 10 to 35% by weight of B) and 15 to 30% by weight of C), the sum of A), B) and C) Is 100% by weight.
• Peroxide initiators are preferably used, at least 2.6% by weight, particularly preferably at least 3% by weight, based on the total weight of the ethylenically unsaturated monomers.
• Phenolic resin can be used as long as it has the methylol functionality required for reactivity.
• Preferred phenolic resins are reaction products of alkali
• Phenol, substituted phenols and bisphenol A Phenol, substituted phenols and bisphenol A with
• Methylol group linked either ortho or para to the aromatic ring is
• Phenolic resins of the resol type are preferably used which are based on bisphenol A and contain more than one methylol group per phenyl ring.
• Suitable aminoplast resins are available on the market, for example, under the trademark Cymel.
• a suitable aminoplast resin is, for example, hexamethoxymethylmelamine.
• the coating agent contains 1 to 7% by weight, preferably 2 to 5% by weight, of ammonia and / or amines as neutralizing agent.
• the coating agent is dispersible in water.
• Triethylamine and / or dimethylethanolamine are preferably used as neutralizing agents.
• the aqueous coating compositions according to the invention further contain 20 to 60% by weight of organic solvents. When using the aqueous coating compositions as anodic electrocoating materials, care must be taken that the organic solvents have a positive effect on the effectiveness of the anodic deposition and the course of the coating film.
• Low volatility cosolvents are preferably used, such as monoalcohols with 4 to 18 carbon atoms, glycol ethers, such as 10 ethylene glycol monoethyl ether and its higher homologs with 5 to 20 carbon atoms or corresponding ethers of 1,2- and 1,3-propanediol.
• 15 tel are produced in a process which is characterized in that the epoxy resin A) is first reacted at 80 to 200 ° C, preferably at 120 to 180 ° C, using catalysts with the polyester polycarboxylic acid component B), so that minimum
• peroxidic initiators which preferably give benzoyloxy and / or phenyl radicals, is radically polymerized, in a third process step the product obtained is neutralized with component c) 0, the organic solvent d ), the crosslinking agent b) and, if appropriate, other customary additives are admixed and the coating agent is dispersed in water.
• the reaction 5 of the epoxy resin with polyester polycarboxylic acids which takes place in the first process step is catalyzed with amines, preferably with tertiary amines.
• the implementation takes place in such a way that at least at least 80% of the oxirane rings are converted into ⁇ -hydroxyester groups.
• the ethylenically unsaturated monomers of component C), some of which contain carboxyl groups, are subjected to a radical polymerization reaction in the presence of the ⁇ -hydroxy ester generated in the first process step.
• the radical polymerization is initiated by at least 2% by weight, based on the total weight of the monomers, of peroxidic initiators which preferably give benzoyloxy and / or phenyl radicals. At least 2.6% by weight, particularly preferably at least 3% by weight, of initiators are preferably used. Of course, good results are also achieved if high proportions of initiators, e.g. 8 to 10% by weight can be used, but this is not recommended for economic reasons.
• Peroxidic initiators which decompose to form benzoyloxy and / or phenyl radicals are primarily used. Of course, it is also possible to use other initiators if they lead to equivalent radical conditions.
• Dibenzoyl peroxide and / or tert are preferred.
• Other possible initiators are tert.
• the proportion of residual monomers is advantageously kept to less than 0.2%, based on the sum of a) to d), by initiator replenishment and / or by extending the initiator feed.
• the polymer obtained is neutralized in a third process step. to make the coating agent water-dispersible.
• the low-volatility cosolvents d) necessary for the production of a well-running anodically deposited film, the phenoplast resins or aminoplast resins b) serving as crosslinking agents and further additives, for example those customary in electrocoating, are mixed into the system. Finally, the system is dispersed in water.
• a preferred embodiment of the process according to the invention is that after the radical polymerization, precondensation with the crosslinking agent b) is already carried out. In this way it is achieved that the crosslinking agent b) is deposited to the same extent in an electrocoating as is present in the aqueous coating agent.
• the mixture obtained before the dispersion in water can be used as a compensating varnish in that the aqueous dispersion is not prepared until the binder is used in the electrocoating material.
• a preferred embodiment of the process according to the invention consists in that the organic solvent d) is already used as the solvent for the esterification of the epoxy resin A) and the polyester polycarboxylic acids B) which is carried out as the first process step.
• aqueous coating compositions according to the invention are advantageously used for the anodic electrocoating of cans and half-cans. Of course, they can also be used for spray painting cans.
• the cans are immersed in an aqueous bath based on the coating agents according to the invention described above and switched as an anode. A film is deposited on the cans by means of direct current, the substrate is removed from the bath, and the film is hardened by baking.
• the final hardening of the paint film takes place during spray painting and also during electrodeposition by baking.
• aqueous coating compositions according to the invention are suitable for coating cans which can consist of different materials and can have a wide variety of can geometries. This is how cans made of aluminum and tinplate, e.g. coated and deep-drawn two-part beverage cans equally well coated with the coating agents according to the invention. Furthermore, cans made from surface-pretreated steel sheet can also be coated excellently.
• aqueous coating agents described above are also excellently suitable for coating stretched-tefle drawn or otherwise deep-drawn cans which are subjected to a sterilization load in order to preserve the contents.
• the can half parts mentioned are hulls and lids which are used for the production of cans.
• the anodic coating of the can half-parts proves to be particularly advantageous if the hulls are welded and the lids are present as tear-open lids.
• the aqueous coating compositions according to the invention are stable in storage and they can be applied perfectly by means of anodic electrocoating.
• the baked lacquer films obtained have a good property level with regard to pore purity, filling material resistance, sheet metal adhesion, hardness, elasticity and taste neutrality.
• the binder combinations used enable good pigment wetting.
• Propylene glycol monophenyl ether heated to 140 C. After adding 2 g of N, N-dimethylbenzylamine, 950 g of the polyester polycarboxylic acid prepared under 1.2 are run in and at the same time the solvent (2-butanone) is distilled off. The mixture is kept at 160 C for 3 hours. The acid number is then 37 mg KOH / g and the viscosity (a 30% solution in butyl glycol at 23 ° C) is 380 mPa.s. 3. Preparation of binder solutions from the epoxy resins prepared under 2.
• 25 electrodeposition coating can be used.
• the result is a 58% binder solution, which can be used directly as a compensating varnish for the anodic electrodeposition after adding basic neutralizing agent.
• Example 3 2352 g of the epoxy ester prepared under 2.1 are placed in a four-necked flask equipped with a stirrer, thermometer, reflux condenser and two feed tanks. For this purpose, at 140 ° C., a mixture of 130 g of acrylic acid, 160 g of styrene and 190 g of butyl acrylate is simultaneously added from the first feed tank and a solution of 13.4 g of tert from the second feed tank. Butyl perbenzoate in 40 g butyl glycol. The monomers are metered in over 2 hours and the initiator over 3 hours. After the end of the polymerization, 190 g of a highly methylolated
• Bisphenol A formaldehyde resin precondensed at 90 C for 2 hours.
• the high molecular epoxy resin used under 2. is reacted with a monocarboxylic acid with trimellitic anhydride after esterification of the glycidyl residues.
• a monomer mixture is polymerized in the presence of a highly molecular epoxy resin, but in the absence of a polyester component.
• 1120 g of a high molecular weight epoxy resin based on bisphenol A with an epoxide equivalent weight of 3400 are dissolved in 570 g of butylglycol and 850 g of n-butanol and at 140 ° C. with 44 g of dimethylolpropionic acid and 1.5 g of N, N -Diethylbenzylamine reacted until the acid number has fallen below 3 mg KOH / g. To do this . within 2 hours at 120 C a mixture of 175 g methacrylic acid, 130 g styrene, 5 g 2-ethylhexyl methacrylate and 28 g benzoyl peroxide (75%).
• the advertising precondensed 160 g of a highly methylolated bisphenol A-formaldehyde resin at 90 C for 2 hours with the approach _>.
• the result is a 50% binder solution with a viscosity (30% in butylglycol) of 0.8 Pa.s and an acid number of 90 mg KOH / g.
• the binder solutions of Examples 1, 2, 3, 4 and Comparative Examples 1 and 2 are neutralized with amine according to the information in Table 1, slowly dispersed in deionized water with vigorous stirring and adjusted to a solids content of 12%.
• the properties and characteristics of the resulting dispersions are summarized in Table 1.
• the binder dispersion E does not have sufficient storage stability at room temperature. After a month, the binder is largely coagulated and the dispersion is destroyed. In contrast, dispersions A, B, C, D and F are free of sediment even after 6 months of storage at room temperature.
• An unpainted, two-part beverage can made of tinplate is held at the edge of the flange with an electrically conductive clamp, filled with the binder dispersion A and completely immersed in a conductive vessel with a diameter of 20 cm which is insulated from the earth and which has also previously been used the electrocoat has been filled.
• the positive pole of a direct current voltage source is connected to the socket and the negative pole to the outer vessel.
• the coating takes place using an auxiliary cathode in the interior of the can.
• the inside and outside of the can is completely covered with a thin clear lacquer film which is pore-tight. Measured values cf. Table 2.
• Example Example Example 5 game 6 game 7 game 8 game 9 equals to the same example 3 example 4
• the coating is carried out analogously to 5.1 and 5.2.
• the can is completely covered with a white lacquer film.
• the coating is carried out analogously to 5.1 or 5.2.
• the can is completely covered on the inside and outside with a thin, pore-tight clear lacquer film. Table 2.
• the coating is carried out analogously to 5.1 or 5.2.
• the inside and outside of the can is completely covered with a thin, pore-tight clear lacquer film. Table 2.
• the coating is carried out analogously to Examples 4-9.
• the can is coated on the inside and outside with a matt clear lacquer film which is not pore-tight and has surface defects. Measured values cf. Table 2.
• the coating is carried out as previously described.
• the inside and outside of the can is covered with a matt clear lacquer film that is not porous and has surface defects. Measured values cf. Table 2.
• the deposited and baked-on lacquer films show in all examples no odor, taste or color impairment in relation to water as filling material. Similar results are achieved if, instead of a two-part beverage can made of tinplate, one made of aluminum is used.
• the inside of a two-part beverage can made of tinplate is spray-coated with the anionic binder dispersion A. 65 bar is selected as the spray pressure.
• the painting is 2 min. baked at 210 C in a convection oven.
• the result is a coat of lacquer of 220 mg dry / 0.33 can.
• the lacquer film is clear and glossy and has a porosity (enamel rater) of 0.8 mA.
• the other technical lacquer properties correspond to those of Examples 5 to 9 in Table 2.

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• Chemical & Material Sciences (AREA)
• Organic Chemistry (AREA)
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• 1986
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