MXPA99002380A - Hydroxipival acid pliisocianate acid reticulants and blocked with dimetilpira - Google Patents

Abstract

The present invention relates to: The invention relates to aqueous polyisocyanate crosslinkers blocked with pyrazole ring compounds, to their preparation and to their use as a component of clear lacquers or primers in automotive lacquering.

Description

Aqueous Polyisocyanate Crosslinkers with Hydroxypropic Acid and Blotted with Dimethylpyrazole Description of the invention: The invention relates to aqueous polyisocyanate crosslinkers blocked with pyrazoic ring compounds, their preparation and their use as a component of clearcoats or primers in automotive lacquering. Pyrazoles, for example 3, 5-dimethylpyrazole, belong to the few isocyanate blocking agents which, in the aqueous phase, are stable on the one hand and, on the other, allow the formation of reactive crosslinking agents. For example, an aliphatic polyisocyanate blocked with 3, 5-dimethylpyrazole is already crosslinked under baking conditions of 30 minutes / 120 to 130 ° C, whereas a polyisocyanate blocked with butanone oxime needs 30 minutes / 140 ° C. Aqueous polyisocyanate crosslinkers blocked with pyrazoles are described in WO 97/12924, the hydrophilization of these crosslinking agents being limited to polyhydroxycarboxylic acids. Hydrophilization by the simplest insertion of onohydroxycarboxylic acids is not mentioned. From EP-A 576 952 and EP-A 566 953 it is known to use hydroxypivalic acid and blocked polyisocyanates with e-caprolactam, diethyl malonate, ethyl acetoacetate, oximes, for the preparation of mixtures of water-dispersible polyisocyanates. EP-A 802 210 also discloses aqueous polyisocyanate crosslinkers with a 3,5-dimethylpyrazole blocking. The hydrophilization of these crosslinking agents is, however, carried out by nonionic poly (ethylene oxide) chains. However, it has been indicated that lacquers based on these crosslinking agents with polyethylene oxide have a permanent hydrophilization and therefore do not exceed the salt spray test. Therefore, these lacquers have insufficient corrosion resistance for the automotive industry. It is the object of the invention to avoid the drawbacks mentioned and to provide an aqueous polyisocyanate crosslinker with good reactivity, simple synthesis and good corrosion resistance. This task has been achieved with the polyisocyanate crosslinking agents according to the invention. The invention relates to blocked polyisocyanates which are aqueous or water-dilutable, consisting of a) 100% equivalents of a polyisocyanate component, b) 60 to 85% equivalents of a compound with pyrazole ring as a blocking agent, c) 15 to 40% in equivalents of a monohydroxycarboxylic acid as a hydrophilizing agent and optionally d) 0 to 15% equivalents of a difunctional chain elonator component carrying OH and / or NH2 groups, the quantitative relationships of the coctants being chosen so that the equivalent ratio of NCO groups of component a) to groups reactive towards isocyanates of components b), c) and d) is between 1: 0.8 and 1: 1.2. Another object of the invention is a process for the preparation of the polyisocyanate crosslinking agents.

The preparation of the polyisocyanate crosslinking agents according to the invention is carried out stepwise, with the polyisocyanate component a) and optionally from 5 to 10% by weight, based on solid matter, of a solvent miscible with water, for example N-methylpyrrolidone and reacting it in a first reaction step at approx. 80 ° C approx. 50% by weight of the NCO groups present with the pyrazole blocking agent and integrating in another reaction step the hydroxypivalic acid and finally reacting the rest of the NCO groups still present with more pyrazolic blocking agent, using 100% in equivalents of NCO groups of component a) approximately 100% equivalents of reactive groups of components b) and c) and then with a sufficient amount of neutralizing agent, to obtain a stable dispersion, the carboxyl groups, in whole or in part, in carboxylate groups. The invention also relates to the use of the water-soluble or water-dilutable blocked polyisocyanates in combination with water-soluble and / or water-dispersible polyhydroxy compounds for the production of aqueous stoving lacquers in the oven., if necessary, contain adjuvants and additives common to coatings technology. The polyisocyanates a) which give rise to the blocked polyisocyanates according to the invention are lacquer polyisocyanates known per se with aliphatic or cycloaliphatically bound isocyanate groups and an isocyanate content of 7 to 30, preferably 12 to 25% by weight. In particular, the known lacquer polyisocyanates based on 1,6-diisocyanatohexane (HDI), l-isocyanate-3, 3, 5-trimethyl-5-isocyanatomethyl-cyclohexane (PDI) and / or bis- (4) are considered. -isocyanatocyclohexyl) -methane (H12MDI) containing biuret, isocyanurate and / or uretdione groups. In addition, polyisocyanates or short chain NCO prepolymers based on aromatic diisocyanates, such as, for example, diisocyanatotoluene (TDI) or 4,4'-diisocyanatodiphenylmethane, can also be used.

(MDI).

However, the polyisocyanates based on HDI or H12MDI having isocyanurate groups are especially preferred as component a). As the blocking component, 1H-pyrazoles, such as, for example, pyrazole, 3-methyl-pyrazole or 3, 5-dimethylpyrazole. 3, 5-dimethylpyrazole is preferred, which is, for example, easily accessible by condensation of hydrazine hydrate with acetylacetone. As a hydrophilizing component c), onohydroxycarboxylic acids carrying one or two methyl groups in position are preferably considered. Especially preferred is hydroxypivalic acid or hydroxymethyldimethylacetic acid (2-hydroxymethyl-2-methylpropionic acid), optionally in the presence of small amounts of other hydrophilizing reagents, such as, for example, from 0.01 to 0.1% in weight of functional OH hydrophilic polyethers or polyhydroxycarboxylic acids. As the difunctional chain elonator component c) diamines, diols and also hydroxyamines of a molecular weight range from 32 to 300 are considered. Examples are hydrazine, ethylenediamine, isophorone diamine, isophoronediamine biscetimine and methyl isobutyl ketone, 1,4-dihydroxybutane, ethanolamine, N-methylethanolamine, hydroxyethylethylendia ina, the adduct of 2 mol of propylene carbonate and 1 mol of hydrazine of formula Suitable neutralizing agents are, for example, dimethylethanolamine, methyldiethanolamine, triethylamine, N-ethylmorpholine or 2-amino-2-methylpropanol. To prepare an aqueous solution or dispersion, the aforementioned hot solution of component a) blocked and hydrophilized with hot distilled water is mixed and stirred. To prepare a dissolved organic crosslinker, dilutable in water and storage stable at room temperature, the above mixture must be diluted with more solvent to reduce its viscosity. The polyisocyanate crosslinking agents according to the invention have the following advantages: Polyisocyanate components a) with high functionalization (functionalization 3-4) can also be prepared relatively without problems. - The baking conditions are already in 30 minutes between 120 and 130 ° C. - The thermo yellowing is clearly lower than in the polyisocyanate crosslinkers that are blocked with butanone oxime. The simplest synthesis and the improved anticorrosion effect (salt spray test) are demonstrated by the following Examples. Example Example 1 In this example according to the invention, 75% of the equivalents of the NCO groups present and 25% of the equivalents hydrophilized with hydroxypivalic acid are blocked with dimethylpyrazole. Formulation: 200.0 g (1.0 equiv of a lacquer polyisocyanate based on 1,6-diisocyanatohexane (HDI) containing isocyanurate groups with an NCO content of approximately 21%, a viscosity at 23 ° C of approx. 3.000 Pas and a functionalization of about 3.5 72.0 g (0.75 equiv.) 3, 5-Dimethylpyrazole 29.5 g (0.25 equiv.) Hydroxypivalic acid 22.2 g (0.25 equiv.) Di ethylethanolamine 30.0 g N-Methylpyrrolidone 422 , 3 g Water 776.9 0 (0.925 equiv.) Blocked NCO groups Solids content: (301.5 g) 38.9% Viscosity (23 ° C): approx.2.000 Pas NCO content blocked: 4.0 % 1 Equivalent of groups NCO block. : 1050 g Embodiment: Polyisocyanate, N-methylpyrrolidine and a partial amount of 48 g (0.5 mol) of dimethylpyrazole were reacted for ca. 5 h at 85 ° C until an NCO content in the range of 7.5 to 7.7% was measured. After this, crystalline hydroxypivalic acid was added and stirred for ca. 2h 30 in to approx. 65 ° C, until an NCO content of 3.4% resulted. Then the remaining amount of solid dimethylpyrazole (24 g / 0.25 mol) was added, stirred for ca. 30 min at 65 ° C and the absence of free NCO groups was determined by IR spectroscopy. It was then neutralized by stirring by adding dimethylethanolamine to the reaction mixture, hot water was added drop at 70 ° C (demineralized) and a bright blue dispersion (almost a solution) of a blocked polyisocyanate crosslinker was obtained. The blocked NCO content reached 4%, its equivalent of NCO blocked 1,050 g. Example 2 (Comparative Example) This example will show that it is difficult to prepare, with a dihydroxycarboxylic acid such as dimethylolpropionic acid and a polyisocyanate with high functionalization (F of at least 3.5) according to Example 1, a polyisocyanate crosslinking agent dispersible in water stable to the storage.

In place of hydroxypivalic acid as in Example 1, 0.25 equiv., Corresponding to 16.75 g, of di-ethyl-propionic acid was used and worked up according to Example 1. After the last NCO measurement, a melt was obtained. filamentous, very viscous, almost mucilage, which could no longer be dispersed. EXAMPLE 3 (Application example) This example demonstrates the properties of the crosslinking agents according to the invention according to Example 1 in comparison with a polyisocyanate crosslinking agent blocked with commercial butanone oxime customary in clear lacquers.

Transparent lacquer formulation Bayhydrol VP LS 2017R, Bayer AG, 42% hydroxypolyester dispersion 65.06 57.27 1 Equiv. OH = 1899 s Bayhydur BL 5140R, Bayer AG, polyisocyanate blocked with butanone oxime dissolved at 39.5% 32.89 1 Equiv. NCO block = 955 s Crosslinker according to Example 1 _ 31.5 Additol XW 395R, Vianova resin, 0.72 0, 69 leveling effect Surfinol 104 ER, Air Product / 0.72 0.69 Biesterfeld, anti-crater Asua dest. 0.61 10.00 Parts in weight 100.00 100.00 NCO crosslinking blos.:OH = 1: 1 The binders and additives were mixed homogeneously with an agitator and after 2 h was processed Solid matter content «40%« 38% Pouring time cup ISO 5 mm / 23 ° C * 40s «38s Pouring time after lacquer storage for 7 days at 40 ° C« 34s «31s A wet film of" 120"was applied with a commercial dumbbell on glass plates μ and after air removal of 10 min / 23 ° C was baked in an oven with recirculation of air for 30 minutes at 120 ° C Pendular hardness of Konis = 7s < 19s Solubility in 1 minute against toluene, methoxypropyl acetate, ethyl acetate, acetone 5 555 4 355 (0-5, no destroyed film mark) Pendular pendulum hardness with 30 min baking at 140 ° C «32s« 38s Solubility in 1 minute, as before 4 344 4 244 For the salt spray test the lacquer was sprayed with a cup gun on steel sheet and baked for 30 min at 140 ° C Salt spray test, 144h, Wd * 26mm Wd * 10mm DIN 53 167 TWd * = infiltration1 In the previous synopsis it is observed that the lacquer 2 with the crosslinker according to the invention is more reactive than lacquer 1. This is clear due to the higher hardness of the film and the better resistance to the solubility at the lower baking temperature of 120 ° C. At the baking temperature of 140 ° C these relationships are equalized. In any case, lacquer 2 stands out with a lot of lacquer 1 in the salt spray test with an infiltration of only 10 mm.

It is noted that in relation to this date, the best method known to the applicant to carry out the aforementioned invention, is that which is clear from the present description of the invention.

Claims (3)

R E I V I N D I _C A C I O N E S Having described the invention as above, it is declared as property contained in the following:

1. Water-soluble or water-dilutable blocked polyisocyanates, characterized in that they are composed of a) 100% equivalents of a polyisocyanate component, b) 60 to 85% equivalents of a compound with pyrazole ring as a blocking agent, c) 15 to 40% in equivalents of a monohydroxycarboxylic acid as a hydrophilizing agent and optionally d) 0 to 15% equivalents of a difunctional chain elongation component carrying OH and / or NH2 groups, the quantitative relationships of the coctants being chosen so that the ratio in equivalents of NCO groups of component a) to groups reactive towards isocyanates of components b), c) and d) is between 1: 0.8 and 1: 1.2.

2 . Process for the preparation of the polyisocyanate crosslinking agents according to the claim 1, characterized in that polyisocyanate component a) and, where appropriate, 5 to 10% by weight, based on solid matter, of a solvent miscible with water, eg N-methylpyrrolidone and react in a first reaction step at approx. 80 ° C approx. 50% by weight of the NCO groups present with the pyrazole blocking agent and the hydroxypivalic acid is integrated in another reaction step and finally the rest of the NCO groups still present are reacted with more pyrazole blocking agent, using 100%. % equivalents of NCO groups of component a) approximately 100% equivalents of reactive groups of components b) and c) and then are transformed with a sufficient amount of neutralizing agent, to obtain a stable dispersion, the carboxyl groups, total or partially, in carboxylate groups.

3. Use of the water-soluble or water-dilutable blocked polyisocyanates in combination with water-soluble and / or water-dispersible polyhydroxy compounds for the production of aqueous drying lacquers in the furnace which, if appropriate, contain adjuvants and additives customary in coatings technology.