Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – At least one aryl ring which is part of a fused or bridged...
Reexamination Certificate
2002-06-03
2003-06-24
Sergent, Rabon (Department: 1711)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
At least one aryl ring which is part of a fused or bridged...
C252S182200, C252S182210, C524S839000, C528S045000, C528S067000, C560S125000, C560S170000, C564S032000, C564S057000, C564S123000, C564S192000
Reexamination Certificate
active
06583216
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to blocked polyisocyanate cross-linking agents and their use in one-component stoving lacquers, in particular in solvent-containing or predominantly water-based plastics coatings having a soft-feel effect.
The use of CH-acid esters as isocyanate blocking agents is prior art; cf. the work reported by S. Petersen in Liebigs Ann. Chem. 562 (1949) page 205 et seq. An advantage of these blocking agents, for example, diethyl malonate or ethyl acetoacetate, is the low stoving range of 80° C. to 120° C. for producing the coatings. Moreover, unlike other blocking agents, they produce no harmful substances.
Disadvantages of these blocking agents are firstly the increased tendency of the coatings to yellow during the stoving process and secondly the tendency of the blocked polyisocyanate cross-linking agents to crystallise. For example, a polyisocyanate based on 1,6-diisocyanatohexane (HDI) and blocked with diethyl malonate, despite a considerable quantity of solvent, solidifies after a few days to form a glass-like composition, which can, however, be carefully melted again.
Accordingly, methods of averting these disadvantages have also been published in the patent literature. In DE-A 19 748 587 it is proposed that, instead of exclusively diethyl malonate, a mixture of diethyl/diisopropyl malonate be used for the blocking. In this way the tendency to crystallise is counteracted.
DE-A 19 813 352 describes the incorporation of formaldehyde for the same purpose. Furthermore, the incorporated formaldehyde as well as the content of certain hydrazides and HALS amines prevent the development of a distinct thermal yellowing of the stoving lacquer. It has been found, however, that in the case of certain polyisocyanates the method of DE-A 19 813 352 is inadequate to prevent opacity and precipitation (see comparison examples 2 and 3).
The object of the invention is to prepare polyisocyanate cross-linking agents blocked with CH-acid esters in such a way as to ensure that the cross-linking agents are stable in storage and that as little thermal yellowing as possible occurs in the coatings. This object was achievable with the blocked polyisocyanate cross-linking agents according to the invention.
SUMMARY OF THE INVENTION
The invention provides blocked polyisocyanate cross-linking agents which are dissolved in a solvent (mixture) and have a content of blocked isocyanate groups of from 5 to 20%, preferably 8 to 14%, and contain
100
equivalent. %
NCO groups of an aliphatic and/or
cycloaliphatic polyisocyanate,
80-95
equivalent. %
of a CH-acid ester blocking agent,
5-20
equivalent. %
of NH
2
groups of an aliphatic/cycloaliphatic
diamine and
5-50
mol. %
of formaldehyde in incorporated form.
The invention finally also provides the use of the blocked polyisocyanate cross-linking agents according to the invention for curing organic polyhydroxyl compounds in polyurethane stoving lacquers in solvent-containing phase or in aqueous phase. These are used, for example, in automobiles, for plastics coatings having a soft-feel effect.
DETAILED DESCRIPTION OF THE INVENTION
Besides the above-mentioned components which are essential to the invention, the blocked polyisocyanate cross-linking agents according to the invention may also contain hydrazides and HALS amines as additives which provide resistance to thermal yellowing, as described in EP-A 829 500 or DE-A 19 856 968.
In addition, the blocked polyisocyanate cross-linking agents according to the invention further contain 5 to 50 wt. %, preferably 15 to 30 wt. %, of solvents. Solvents which exhibit a tendency to be miscible in water are preferred, such as, for example, 1-methoxy-2-propyl acetate, isobutanol, butyl glycol, N-methylpyrrolidone, butyl diglycol or butyl diglycol acetate.
The blocked polyisocyanate cross-linking agents according to the invention are
non-crystallising, clear products which are stable in storage
curing components which react with themselves and also with OH components at 80° C. to 120° C.
coreactants for both solvent-based and water-based OH components.
The polyisocyanate cross-linking agents according to the invention may be prepared as follows:
The polyisocyanate component, optionally with a little solvent, for example, 1-methoxy-2-propyl acetate (MPA), is initially introduced at approximately 50° C.; the CH-acid ester, for example, malonic ester, is added thereto as a mixture with approximately 2 to 3% of a 30% Na methylate solution and the reaction is allowed to proceed at 60° C. to 90° C. until the calculated NCO content has been attained. Then the calculated quantity of diamine, for example, 1-amino-3,3,5-trimethyl-5-aminomethylcyclohexane (IPDA), dissolved in additional MPA, is added thereto and the reaction continued at approximately 50° C. to 70° C., so that NCO groups are no longer detectable. Thereafter, at 40° C. to 50° C., the clear solution of paraformaldehyde and about 10%, based on paraformaldehyde, of a 30% Na methylate solution as base and isobutanol are added to the batch, which is then stirred for 1 to 2 hours at 40° C. to 50° C., as a result of which the formaldehyde is chemically bound (the incorporated form). The detectable amounts of free formaldehyde are only less than 0.1%. For the special embodiment of the cross-linking agents according to the invention, in particular for light-coloured coatings, at this stage of the batch the stabilisers which provide resistance to thermal yellowing, for example, the above-mentioned addition product of 2 mol propylene carbonate and 1 mol hydrazine, and the HALS amine Tinuvin 770 DF® (Ciba Speciality) can be stirred in. In order to adjust the required viscosity to within a range of <10000 mPas, the batch is diluted with further alcohol, for example, isobutanol and/or butyl glycol, and finally made slightly acid (pH 5.0-6.9) with 0.5 to 2.5%, based on the batch, of dibutyl phosphate.
The polyisocyanates constituting the blocked polyisocyanate cross-linking agents according to the invention are known coating polyisocyanates having aliphatically and/or cycloaliphatically bonded isocyanate groups and an isocyanate content of 7 to 30 wt. %, preferably 12 to 25 wt. %.
Polyisocyanates preferably used are known per se coating polyisocyanates based on 1,6-diisocyanatohexane (HDI), 1-isocyanato-3,3,5-trimethyl-5-isocyanatomethylcyclohexane (IPDI) and/or bis(4-isocyanatocyclohexyl)methane (H
12
MDI or Desmodur W®/Bayer AG) having biuret, isocyanurate, urethane, allophanate and/or uretdione groups. The asymmetrically trimerised (that is, in addition to isocyanurate also having iminooxadiazindione groups) coating polyisocyanates based on 1,6-diisocyanatohexane, of the type described, for example, in EP-A 798 299, can also be used as polyisocyanate components.
Polyisocyanates based on other isocyanates can also be used, such as, for example, diisocyanatobutane-1,4,2,4- or 2,6-diisocyanato-1-methylcyclohexane, 2,5- and/or 2,6-bis(isocyanato)norbomane, 3- and/or 4-isocyanatomethyl-1-methyl-cyclohexane, 1,4-bis(2-isocyanatoprop-2-yl)benzene, 1,3-diisocyanatomethylbenzene, 1,3- or 1,4-bis(isocyanatomethyl)cyclohexane.
The most preferred polyisocyanate components are polyisocyanates based on 1-6 diisocyanatohexane which contain isocyanurate groups.
Suitable blocking agents are CH-acid esters, for example, diethyl malonate or ethyl acetoacetate and/or their methyl, isopropyl, isobutyl or tertiary butyl derivatives. Diethyl malonate is preferred.
The diamine component incorporated in the cross-linking agents according to the invention has the task of reacting mildly with the NCO groups still remaining after the NCO-blocking reaction and thereby contributing to the enlargement of the molecules. In this way 5 to 20 equivalent. %, preferably 7 to 10 equivalent. %, of NCO groups are reacted by diamine extension and a possible tendency to crystallise is prevented. Aliphatic and cycloaliphatic diamines are suitable. Examples which may be mentioned are ethylenediamine and propylenediamine, 4,4′-diaminodicyclohexylmethane and 1,4-diaminocyc
Klippert Uwe
Kobusch Claus
König Eberhard
Küttner Wolfram
Bayer Aktiengesellschaft
Gil Joseph C.
Roy Thomas W.
Sergent Rabon
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