AQUEOUS BINDER DISPERSIONS INTENDED FOR CATHODIC ELECTROCOAT MATERIALS AND COMPRISING A CROSSLINKER BASED ON 2,2-DIMETHYL-1,3-DIOXOLANE-4-METHANOL-BLOCKED POLYISOCYANATES

Abstract

The present invention relates to aqueous binder dispersions for cationic electrocoat materials, comprising as binders amine-modified, hydroxy-functional epoxy resins and comprising as crosslinker at least one fully blocked polyisocyanate blocked at least partly with 2,2-dimethyl-1,3-dioxolane-4-methanol, and also to the use of such cationic electrocoat materials for producing coating systems and to the use of crosslinkers based on polyisocyanates blocked with 2,2-dimethyl-1,3-dioxolane-4-methanol in aqueous binder dispersions.

Claims

1: An aqueous binder dispersion for cathodic electrocoat materials, comprising as binder at least one amine-modified, hydroxy-functional epoxy resin, wherein the binder dispersion comprises as crosslinker at least one fully blocked polyisocyanate blocked at least partly with 2,2-dimethyl-1,3-dioxolane-4-methanol.

2: The aqueous binder dispersion as claimed in claim 1, wherein 50 to 100 mol % of the blocked isocyanate groups in the fully blocked polyisocyanate are blocked with 2,2-dimethyl-1,3-dioxolane-4-methanol.

3: The aqueous binder dispersion as claimed in claim 2, wherein 90 to 100 mol % of the blocked isocyanate groups in the fully blocked polyisocyanate are blocked with 2,2-dimethyl-1,3-dioxolane-4-methanol.

4: The aqueous binder dispersion as claimed in claim 3, wherein 100 mol % of the blocked isocyanate groups in the fully blocked polyisocyanate are blocked with 2,2-dimethyl-1,3-dioxolane-4-methanol.

5: The aqueous binder dispersion as claimed in claim 1, wherein as polyisocyanate an aromatic polyisocyanate is used.

6: The aqueous binder dispersion as claimed in claim 1, wherein as polyisocyanate an oligomeric polyisocyanate is used.

7: The aqueous binder dispersion as claimed in claim 1, wherein the polyisocyanate has an NCO functionality of 2.4 to 4.

8: The aqueous binder dispersion as claimed in claim 1, wherein as crosslinker a polyisocyanate based on 4,4′-diphenylmethane diisocyanate is used.

9: The aqueous binder dispersion as claimed in claim 1, wherein as polyisocyanate an oligomeric 4,4′-diphenylmethane diisocyanate having an NCO functionality of 2.4 to 4 is used.

10: The aqueous binder dispersion as claimed in claim 1, wherein the blocked polyisocyanate is used in an amount of 5 to 50 wt %, based on the binder.

11: The aqueous binder dispersion as claimed in claim 1, wherein the epoxy resin is prepared in the presence of the crosslinker.

12: A process for cathodic electrocoating of an electrically conductive substrate, the process comprising: 1) immersing the electrically conductive substrate into an aqueous electrocoat material which comprises at least one cathodically depositable binder, 2) connecting the electrically conductive substrate as cathode, 3) depositing a film on the electrically conductive substrate with direct current, 4) removing the coated substrate from the electrocoat material, and 5) baking the deposited coating film, wherein the aqueous electrocoat material comprises of an aqueous binder dispersion as claimed in claim 1.

13: The process as claimed in claim 12, wherein the electrically conductive substrate is an automobile body or a part thereof.

14. (canceled)

15: An electrocoat system produced with an aqueous binder dispersion as claimed in claim 1.

16: A multicoat paint system comprising an electrocoat system as claimed in claim 15.

17: The multicoat paint system as claimed in claim 16, which is applied on an automobile body.

18: An electrocoat material comprising an aqueous binder dispersion as claimed in claim 1.

19: An electrocoat system obtained by a process as claimed in claim 12.

20: An electrocoat material obtained by a process as claimed in claim 12.

Description

EXAMPLES

[0070] Methods of Determination:

[0071] Determining the Glass Transition Temperature Tg:

[0072] The glass transition temperature Tg is determined by means of Differential Scanning calorimetry (DSC) in accordance with DIN 53765 (03.1994; Testing of plastics and elastomers—Thermal Analysis—Differential Scanning calorimetry (DSC)) at a heating rate of 10 K/min.

[0073] Determining the NCO Content:

[0074] The NCO content is determined quantitatively by reacting the NCO groups (isocyanates) with an excess of dibutylamine to give urea derivatives and then back-titrating the excess amine with HCl. The NCO content indicates the isocyanate content in wt % and can be converted into the NCO equivalent weight, which indicates the number of grams of substance containing one mole of NCO groups.

[0075] Determining the Solids Content:

[0076] Approximately 2 g of sample are weighed out into an aluminum boat which has been dried beforehand, and the sample and boat are dried in a drying cabinet at 130° C. for an hour, cooled in a desiccator, and then reweighed. The residue (i.e., nonvolatile fraction) corresponds to the solids fraction or solids content. If the solids content has been determined in a procedure different from this, time and temperature are reported accordingly, in parentheses, for example.

[0077] Determining the Binder Fraction:

[0078] The binder fraction in each case is the fraction of the coating material that is soluble in tetrahydrofuran (THF) prior to crosslinking. For its determination, a small sample is dissolved in 50 to 100 times the amount of THF, insoluble constituents are removed by filtration, and subsequently the solids content is determined in line with the description above.

[0079] Determining the OH Number and the Acid Number or Acid Content:

[0080] The acid number (AN) is determined according to DIN 53402 and the OH number (hydroxyl number) according to DIN 53240. The acid number can be converted into the acid content.

[0081] MEQ Acid and MEQ Base

[0082] The MEQ (milli-equivalent) figure indicates the number of milliequivalents of acids or bases that are present in 100 g of the nonvolatile fraction (solids) of a coating material or binder. For the determination, the weighed-out sample (2 to 5 g, based on binder) is admixed with a suitable solvent, such as methoxypropanol or butyl glycol, and titrated with potassium hydroxide solution for the MEQ acid figure and with hydrochloric acid for the MEQ base figure. Details can be found in DIN EN ISO 15880.

[0083] Epoxide Equivalent Weight:

[0084] The determination of the epoxide equivalent weight serves for determining the amount of epoxidically bonded oxygen in epoxy-functional polymers. The epoxide equivalent weight is understood to be the amount of epoxy resin in g that contains 16 g of epoxidically bonded oxygen, i.e., 1 mol of epoxy groups. The resin is dissolved in a mixture of dichloromethane and acetic acid. The solution is admixed with N-cetyl-N,N,N-trimethylammonium bromide and is titrated with perchloric acid in glacial acetic acid, using crystal violet as indicator. Reaction of the bromide salt with perchloric acid produces hydrogen bromide (HBr), which is added onto the molecule with opening of the oxirane ring. Each mole of epoxy function requires 1 mol of perchloric acid. If the reaction has proceeded to completion, the indicator, finally, becomes protonated by excess protons, and there is a color change to green via blue. Details can be found in DIN EN ISO 7142 and DIN 16945.

[0085] Determining the Average Particle Size:

[0086] The average size of the particles of binder in the binder dispersions is measured using the Zetasizer Nano S90 photon correlation spectrometer from Malvern, UK. The parameter evaluated is the “volume mean”.

[0087] Crosslinker 1:

[0088] Preparation of a Crosslinker for an Electrocoating Composition

[0089] A reactor equipped with a stirrer, reflux condenser, internal thermometer, and inert gas inlet is charged with 1053.5 g of 2,3-O-isopropylidene glycerol (2,2-dimethyl-1,3-dioxolane-4-methanol, Solketal®; Glaconchemie GmbH, D-06217 Merseburg) under a nitrogen atmosphere. 1.4 g of dibutyltin dilaurate are added, the mixture is heated to 50° C., and 878.4 g of isomers and higher-functionality oligomers based on 4,4′-diphenylmethane diisocyanate with an NCO equivalent weight of 135 g/eq (Lupranat M20S, BASF; NCO functionality about 2.7; amount of 2,2′- and 2,4′-diphenylmethane diisocyanate below 5%) are added dropwise at a rate such that the product temperature remains below 70° C. Toward the end of the addition, the temperature is allowed to rise to 100° C. and subsequently this temperature is maintained for a further 90 minutes. At the subsequent check, NCO groups are no longer detectable. Cooling is commenced and the product is diluted by addition of 175.0 g of Pluriol C 1651 (dibutoxyethoxyformal, manufacturer: BASF SE) and 66.7 g of ethanol, followed by cooling to 65° C. The solids content is 80%.

[0090] Binder Dispersion 1:

[0091] Preparation of a Low-Solvent Aqueous Binder Dispersion Comprising a Cathodically Depositable Synthetic Resin Having Primary Amino Groups and Hydroxyl Groups, and the Crosslinker 1.

[0092] A laboratory reactor heated with heat transfer oil and equipped with stirrer, reflux condenser, thermometer, and inert gas inlet tube is charged with 961.2 parts of a commercial epoxy resin based on bisphenol A with an epoxide equivalent weight (EEW) of 186 g/eq, 63.9 parts of phenol, 52.4 parts of dodecylphenol, 218.9 parts of bisphenol A, and 68.4 parts by xylene, and this initial charge is heated to 130° C. with stirring and with nitrogen introduced. When 125° C. have been reached, 2.6 parts of N,N-dimethylbenzylamine are added. An exothermic reaction ensues, with the temperature rising to 146° C. After the temperature has dropped to 137° C., a further 1.2 parts of N,N-dimethylbenzylamine are added. The temperature is allowed to fall further and is held at 130° C. until the epoxide equivalent weight (EEW) has reached 870 g/eq (about 3 hours).

[0093] Then, with cooling, 967.1 parts of the crosslinker from example 1 and also 31.8 parts of butyl glycol and 198.6 parts of isobutanol are added. When the temperature has dropped to 96° C., 71.3 parts of a 70% strength solution of the bismethylisobutyl diketimine of diethylenetriamine in methyl isobutyl ketone (MIBK) and also 79.2 parts of N-methylethanolamine are added. 30 minutes later, when the temperature has risen to 100° C., 19.3 parts of N,N-dimethylaminopropylamine are added. 20 minutes later, the batch is cooled to 80° C., during which it is diluted with 152.4 parts of Loxanol PL 5060 (BASF SE) and 100 parts of phenoxypropanol, and discharged.

[0094] Subsequently, 2105.4 parts of the resin mixture are introduced in a separate dispersing vessel into a mixture of 1118.9 parts of fully demineralized water and 69.2 parts of 88% strength lactic acid, with stirring. When the mixture has become homogeneous, it is slowly diluted with a further 1903.2 parts of fully demineralized water.

[0095] This gives an aqueous cationic dispersion which is subsequently freed from its volatile solvents by means of azeotropic vacuum distillation at 40° C., with the organic distillate being replaced by fully demineralized water. Filtration over K 900 plate filters (from Seitz) gives a dispersion having the following characteristics: [0096] Solids content: 32.4% [0097] Base content: 0.687 meq/g resin solids*) [0098] Acid content: 0.328 meq/g resin solids*) [0099] Mean particle size: 98 nm**) [0100] Sedimentation stability: no sediment after 2 months' storage time at room temperature *) milliequivalents/gram resin solids**) measured using Zetasizer Nano S90 photon correlation spectrometer from Malvern

[0101] Crosslinker 2:

[0102] Preparation of a Comparative Crosslinker

[0103] The crosslinker from EP 0961797 B1 (page 6 lines 43-52) is used. A reactor equipped with a stirrer, reflux condenser, internal thermometer, and inert gas inlet is charged with 1084 g of isomers and higher-functional oligomers based on 4,4′-diphenylmethane diisocyanate with an NCO equivalent weight of 135 g/eq (Lupranat M20S, BASF; NCO functionality about 2.7; amount of 2,2′- and 2,4′-diphenylmethane diisocyanate below 5%) under a nitrogen atmosphere. 2 g of dibutyltin laurate are added and 1314 g of butyl diglycol are added dropwise at a rate such that the product temperature remains below 70° C. It may be necessary to carry out cooling. After the end of the addition, the temperature is maintained at 70° C. for a further 120 minutes. At the subsequent check, NCO groups are no longer detectable. Cooling takes place to 65° C.

[0104] The solids content is >97%.

[0105] Binder Dispersion 2 (Comparative):

[0106] Preparation of the Low-Solvent Aqueous Binder Dispersion Comprising a Cathodically Depositable Synthetic Resin and Crosslinker 2 as a Comparative.

[0107] The same procedure is operated as for the binder dispersion 1 example. Now, instead of the crosslinker 1, 797.6 parts of the crosslinker 2 (corresponding in terms of solids content to the amount of crosslinker 1 in the binder dispersion 1 example) are used.

[0108] Following removal of the volatile solvents by azeotropic vacuum distillation at 40° C., the product is diluted with fully demineralized water to a target solids content of 32%.

[0109] Filtration over K 900 plate filters (from Seitz) gives a dispersion having the following characteristics: [0110] Solids content: 32.2% [0111] Base content: 0.684 meq/g resin solids*) [0112] Acid content: 0.323 meq/g resin solids*) [0113] Mean particle size: 110 nm**) [0114] Sedimentation stability: no sediment after 2 months' storage time at room temperature *) milliequivalents/gram resin solids**) measured using Zetasizer Nano S90 photon correlation spectrometer from Malvern

[0115] Production of a Grinding Resin A

[0116] Grinding resin A from EP 0961797 (page 9 lines 17-21) is used. A reactor equipped with stirring mechanism, internal thermometer, nitrogen inlet, and water separator with reflux condenser is charged with 30.29 parts of an epoxy resin based on bisphenol A and having an epoxide equivalent weight (EEW) of 188 g/eq, 9.18 parts of bisphenol A, 7.04 parts of dodecylphenol, and 2.37 parts of butyl glycol. This initial charge is heated to 110° C., 1.85 parts of xylene are added, and the xylene is distilled off again under a gentle vacuum together with possible traces of water. Then 0.07 part of triphenylphosphine is added and the mixture is heated to 130° C. After exothermic heat production to 150° C., reaction is allowed to continue at 130° C. for one hour more. The EEW of the reaction mixture is at that point 860 g/eq. It is cooled, during which 9.91 parts of butyl glycol and 17.88 parts of a polypropylene glycol diglycidyl ether of EEW 333 g/eq (DER 732, Dow Chemicals) are added. At 90° C., 4.23 parts of 2,2′-aminoethoxyethanol (H.sub.2N—CH.sub.2—CH.sub.2—O—CH.sub.2—CH.sub.2—OH) and, 10 minutes later, 1.37 parts of N,N-dimethylaminopropylamine are added. After a brief exotherm, the reaction mixture is maintained at 90° C. for 2 hours more, until the viscosity remains constant, and is then diluted with 17.66 parts of butyl glycol. The resin has a solids content of 69.8% and a viscosity of 5.5 dPas (measured on a 40% resin solution diluted with propylene glycol monomethyl ether (Solvenon PM, BASF), on a cone/plate viscometer at 23° C.). For greater ease of handling, the resin is additionally neutralized and diluted with 2.82 parts of glacial acetic acid and 13.84 parts of fully demineralized water. This reduces the original solids content to 60%.

[0117] Production of Aqueous Pigment Pastes

[0118] In analogy to the process described in EP 0505445 B1 (page 10 lines 35-42), aqueous pigment pastes are produced from the starting materials listed in table 1 below. First of all, deionized water and the grinding resin A are premixed. Then the remaining constituents are added, in accordance with the quantity figures in table 1, and the mixture is mixed for 30 minutes on a high-speed dissolver stirring mechanism. The mixture is subsequently dispersed to a Hegmann fineness of less than 12 on a small laboratory mill for 1 to 1.5 hours. The quantities given are weight fractions.

TABLE-US-00001 TABLE 1 Pigment pastes Pigment paste A Pigment paste B Grinding resin A 40 40 Fully demineralized water 10.5 9.4 DBTO moist (85% form) 3.6 Bismuth subnitrate 6 Carbon black 0.5 0.5 Aluminum silicate 8 8 Titanium dioxide* 35.2 33.1 Deuteron MK-F6** 2.2 3 *TI-PURE R900, DuPont **Polyurea, Deuteron

[0119] Electrocoating Materials A and B:

[0120] Inventive and Comparative Example of an Inventive and a Conventional Cathodic Electrocoat Material

[0121] In order to produce a conventional and the inventive cathodic electrocoat material, binder dispersions 1 and 2 and aqueous pigment paste A are combined with fully demineralized water in the quantities (weight fractions) indicated in table 2. The procedure here is to introduce the binder dispersion first and to dilute it with fully demineralized water. Then, with stirring, the pigment paste is introduced. This gives the inventive electrocoat material A and also the conventional electrocoat material B.

TABLE-US-00002 TABLE 2 Inventive and conventional electrocoat materials Inventive Conventional electrocoating electrocoating Batch formula bath A bath B Binder dispersion 1 2356.6 Binder dispersion 2 2371.2 Fully demineralized water 1865.1 1850.5 Pigment paste A 578.3 578.3 Total: 4800.0 4800.0

[0122] The electrocoating baths are aged with stirring at room temperature for 3 days. The coating films are deposited over 2 minutes at 220-270 volts deposition voltage and 350 volts breakdown voltage (bath temperature 32° C.) onto cathodically connected, zinc-phosphatized steel test panels without a Cr(VI) rinse in the pretreatment process.

TABLE-US-00003 TABLE 3 Bath characteristics (pH levels, conductivities, solids contents) of the inventive E-coat materials E-coat material B E-coat material A (comparative) pH 6.1 6.0 Conductivity (mS/cm) 1.37 1.39 Solids content (30 20.9 21.6 minutes at 180° C.)

[0123] The deposited films are rinsed with deionized water and baked at 175° C. (substrate temperature) for 15 minutes (also at 160° C. for the determination of glass transition temperature Tg as a measure of crosslinking).

TABLE-US-00004 TABLE 4 Film properties and glass transition temperatures Tg of the resulting E-coat systems A and B E-coat system B E-coat system A (comparative) Film thickness (μm) 20.1 20.8 Leveling very good very good Glass transition 79 72 temperature Tg (160° C.) Glass transition 82 81 temperature Tg (175° C.)

[0124] The 72° C. Tg glass transition temperature of the comparative paint system B on 160° C. baking shows as yet incomplete crosslinking by comparison with the 81° C. Tg at 175° C. baking. In contrast, the 79° C. Tg on 160° C. baking shows the inventive E-coat system A to be almost at the end state (Tg=82° C. on 175° C. baking). Even at 160° C., the crosslinking density for coating system A has developed further than in the case of the comparative coating system B, and therefore exhibits improved underbake security in comparison to the prior art.

[0125] Binder Dispersion 3

[0126] Preparation of a Low-Solvent Aqueous Binder Dispersion Comprising a Cathodically Depositable Synthetic Resin with Hydroxyl Groups, but without Primary Amino Groups, and Comprising the Crosslinker 1.

[0127] A binder dispersion is prepared in accordance with EP 0 961 797 B1:

[0128] A laboratory reactor heated with heat transfer oil and equipped with stirrer, reflux condenser, thermometer and inert gas inlet tube is charged with 1211.5 parts of a commercial epoxy resin based on bisphenol A with an epoxide equivalent weight (EEW) of 186 g/eq, 95.7 parts of phenol, 47.5 parts of n-butoxypropanol, and 278.5 parts of bisphenol A, and this initial charge is heated to 127° C. under nitrogen. With stirring, 1.6 parts of triphenylphosphine are added, whereupon there is an exothermic reaction and the temperature climbs to 170° C. The mixture is cooled again to 130° C. and then the epoxide content is checked. The EEW of 521 g/eq indicates that all of the phenolic OH groups have reacted. Then 158.9 parts of Pluriol P 900 (polypropylene glycol MW 900, BASF) are added with simultaneous cooling. 5 minutes later, with further cooling, at 120° C., 117.7 parts of diethanolamine are added. As soon as the temperature has fallen to 100° C. (30 minutes) after a brief exotherm (Tmax 127° C.), 57.2 parts of N,N-dimethylaminopropylamine are added. After a brief exotherm (Tmax 145° C.), the batch is allowed to continue reacting at 130° C. for 2 hours until the viscosity remains constant (1280 mPas, Brookfield CAP 200+ viscometer, at 23° C., CAP 03 cone, 5000 1/s, 51% in Solvenon PM (BASF)). Subsequently with simultaneous cooling, 1031.5 parts of crosslinker 1 are added, and the product is discharged at 105° C.

[0129] 2194.1 parts of the mixture, which is still hot, are dispersed immediately in an initial charge mixture of 1401.9 parts of fully demineralized water and 31.0 parts of 85% strength formic acid, with intensive stirring. Following brief homogenization, dilution takes place with a further 1247.1 parts of fully demineralized water, and the diluted dispersion is filtered over K900 plate filters (from Seitz). Distillative removal of solvents does not take place, since the dispersion is already obtained in a low-solvent form. The characteristics possessed by the dispersion are as follows: [0130] Solids content: 40.5% [0131] Base content: 0.785 meq/g resin solids*) [0132] Acid content: 0.308 meq/g resin solids*) [0133] Mean particle size: 114 nm**) [0134] Sedimentation stability: no sediment after 2 months' storage time at room temperature *) milliequivalents/gram resin solids**) measured with Zetasizer Nano S90 photon correlation spectrometer from Malvern

[0135] Binder Dispersion 4 (Comparative)

[0136] Preparation of a Low-Solvent Aqueous Binder Dispersion Comprising a Cathodically Depositable Synthetic Resin with Hydroxyl Groups, but without Primary Amino Groups, and Comprising the Crosslinker 2.

[0137] The procedure for the binder dispersion 3 example is carried out. Now, however, instead of the 1031.5 parts of crosslinker 1, 1031.5 parts of a preliminary dilution of 916.9 parts of comparative crosslinker 2 and 83.0 parts of Pluriol C 1651 and 31.6 parts of ethanol are added (corresponding in terms of solids content to the amount of crosslinker 1 in the binder dispersion 3 example). The dispersion is discharged then at 105° C., and the procedure is analogous to example 3:

[0138] 2194.1 parts of the mixture, which is still hot, are dispersed in an initial charge mixture of 1401.9 parts of fully demineralized water and 31.0 parts of 85% strength formic acid, with intensive stirring. Following brief homogenization, dilution takes place with a further 1247.1 parts of fully demineralized water, and the diluted dispersion is filtered over K900 plate filters (from Seitz). Distillative removal of solvents does not take place, since the dispersion is already obtained in a low-solvent form. The characteristics possessed by the dispersion are as follows: [0139] Solids content: 40.2% [0140] Base content: 0.761 meq/g resin solids*) [0141] Acid content: 0.309 meq/g resin solids*) [0142] Mean particle size: 120 nm**) [0143] Sedimentation stability: no sediment after 2 months' storage time at room temperature *) milliequivalents/gram resin solids**) measured with Zetasizer Nano S90 photon correlation spectrometer from Malvern

[0144] Electrocoat Materials C and D

[0145] Preparation of Electrocoating Baths C and D and Deposition of Coating Films

[0146] Electrocoating baths are prepared in line with the procedure described for the preparation of electrocoat materials A and B and in accordance with the mass amounts listed in table 5.

TABLE-US-00005 TABLE 5 Electrocoat materials C and D Bath C Bath D Components and fractions: (inventive) (comparative) Binder dispersion 3 2112.0 Binder dispersion 4 2112.0 Fully demineralized water 2401.2 2401.2 Pigment paste B 286.8 286.8 Total 4800 4800

[0147] In accordance with the deposition conditions specified for electrocoat materials A and B, films are produced on cathodically connected, zinc-phosphatized steel test panels without a Cr(VI) rinse in the pretreatment process. These coated panels, after rinsing, are cured in accordance with the baking conditions identified in table 6 (20 minutes at 160° C. or 175° C.), to give films with a thickness of 20 μm.

TABLE-US-00006 TABLE 6 Film properties and glass transition temperatures Tg of the resulting E-coat systems C and D E-coat system D E-coat system C (comparative) Film thickness (μm) 21.2 20.4 Leveling very good very good Glass transition 78 67 temperature Tg (160° C.) Glass transition 81 80 temperature Tg (175° C.)

[0148] The 67° C. Tg glass transition temperature of the comparative paint system D on 160° C. baking shows as yet incomplete crosslinking by comparison with the 80° C. Tg at 175° C. baking. In contrast, the 78° C. Tg on 160° C. baking shows the inventive E-coat system C to be almost at the end state (Tg=81° C. on 175° C. baking). Even at 160° C., the crosslinking density for coating system C has developed further than in the case of the comparative coating system D, and therefore exhibits improved underbake security in comparison to the prior art.