Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – From reactant having at least one -n=c=x group as well as...
Reexamination Certificate
2001-12-11
2003-02-04
Gorr, Rachel (Department: 1711)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
From reactant having at least one -n=c=x group as well as...
C528S073000, C544S067000, C544S222000, C252S182200, C252S182210
Reexamination Certificate
active
06515097
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to new blocked isocyanates based on 1,6-hexamethylene diisocyanate (HDI) and their preparation and use.
DESCRIPTION OF THE PRIOR ART
The preparation and use of blocked polyisocyanates has been known for a long time. In this procedure the free NCO groups of polyisocyanates are (temporarily) deactivated in order to arrive at products which can preferably be employed in formulations to be processed as one component (cf. D. A. Wicks and Z. W. Wicks Jr., Progr. Org. Coatings, vol. 36, 1999, p. 148 et seq. and literature cited therein). Blocked polyisocyanate hardeners based on polyisocyanates prepared from oligomeric HDI derivatives, for example, trimers (isocyanurates), have been widely introduced.
Alcohols have proved suitable as blocking agents in numerous uses (cf. also Y. Huang, G. Chu, M. Nieh and F. N. Jones, J. Coat. Techn., vol. 67, 1995, p. 33-40 and literature cited therein). However, products based on HDI derivatives are treated only on the margin in the literature reference cited above (cf. loc. cit., p. 37, line 1, this is a methanol-blocked Desmodur® N 3300 from Mobay). The use of specific high-boiling alcohols, such as 1- and 2-octanol (I. de Aguirree and J. Collot, Bull. Soc. Chim. Belg., vol. 98, 1989, 19); furfuryl alcohol (EP-A 206 071), benzyl alcohol (H. Ulrich and D. Gilmore, Urethane Chem. Appl., ACS Symp. Series # 172, ACS Washington D.C., 1981, p. 519); and cyclohexanol (EP-A 21 014) is mentioned more often.
It is a disadvantage in this connection that the blocking of HDI isocyanurate trimers with simple alcohols, such as methanol, ethanol, n-and iso-propanol etc., leads to products which have an unsatisfactory resistance to crystallization in conventional paint solvents, such as n-butyl acetate (BuAc), 2-methoxypropyl acetate (MPA), xylene (X), solvent naphtha (SN 100) etc., at room temperature (22±2° C.). After preparation of the blocked polyisocyanate hardener, a thickening of the solution is observed, sometimes with somewhat of a delay in time, resulting after a few days in complete solidification or in partial gelling of the previously clear, liquid mixture.
The tendency of alcohol-blocked HDI isocyanurate trimers to crystallize intensifies at high concentrations of the alcohol-blocked polyisocyanate in the above-mentioned paint solvents, and when the HDI isocyanurate polyisocyanate contains high contents of the “ideal structure” of the HDI trimer, 2,4,6-tris(6-isocyanatohexyl)-2,4,6-triazine-1,3,5-trione. This indicates that the reaction products of 2,4,6-tris(6-isocyanatohexyl)-2,4,6-triazine-1,3,5-trione with three equivalents of alcohol have the greatest tendency to crystallize, while an increasing “contamination” of the latter with alcohol-blocked higher molecular weight isocyanurate polyisocyanates (pentamers, heptamers etc.) reduces the tendency of the overall mixture to crystallize. Such effects are often encountered in organic chemistry. However, it is impossible to predict the content down to which the constituents which tend to crystallize must be depleted in order to arrive at products which are stable towards crystallization.
An object of the present invention is to provide HDI polyisocyanates which are blocked with simple alcohols and which have a significantly improved resistance towards crystallization compared with the known HDI isocyanurate polyisocyanates blocked with simple alcohols, while maintaining or improving the other advantageous technology properties of blocked HDI isocyanurate polyisocyanates.
Surprisingly, it has been possible to achieve this object by using HDI polyisocyanates which contain a portion of iminooxadiazinedione groups (asymmetric trimers, AST; HDI-AST polyisocyanates).
SUMMARY OF THE INVENTION
The present invention relates to blocked polyisocyanates which are the reaction product of polyisocyanate resins prepared from HDI and containing iminooxadiazinedione groups in an amount of at least 20 mol %, based on the total moles of iminooxadiazinedione and isocyanurate groups, with alcohols of formula (I)
ROH (I),
wherein
R represents aliphatic, straight chain or branched, optionally cyclic, optionally substituted (O—R
1
, NR
1
2
), C
1
-C
6
radicals, preferably C
1
-C
4
radicals, and
R
1
has the same meaning as R.
The present invention also relates to a process for the preparation of blocked polyisocyanates by reacting polyisocyanate resins prepared from HDI and containing iminooxadiazinedione groups in an amount of at least 20 mol %, preferably at least 30 mol %, based on the total moles of iminooxadiazinedione and isocyanurate groups, with alcohols of formula (I).
The present invention finally relates to the use of the blocked HDI polyisocyanates according to the invention and containing iminooxadiazinedione groups for the preparation of polyurethane plastics and coatings, preferably for coating substrates.
DETAILED DESCRIPTION OF THE INVENTION
The preparation of HDI-AST polyisocyanates is described, for example, in EP-A 798 299. The use of HDI-AST polyisocyanates for the preparation of blocked polyisocyanates is disclosed in EP-A 947 531, p. 3, I. 23-25. However, EP-A 947 531 provides polyisocyanates which are blocked with malonic esters and are stabilized with formaldehyde against thermal yellowing. Alcohol-blocked polyisocyanates are not dealt with in EP-A 947 531. Furthermore, polyisocyanates which are based exclusively on HDI are not preferred as starting components for the preparation of the blocked polyisocyanate claimed in EP-A 947 531, as mentioned explicitly in loc. cit. p. 3, I. 26-28.
The previous publications of the prior art lack any indication that the combination of “alcohol+HDI-AST polyisocyanates” could lead to products with advantageous properties. The expert cannot deduce generally from the previous publications of the prior art that the resistance of blocked HDI-AST polyisocyanates towards crystallization differs in any manner from their counterparts based purely on isocyanurate (symmetric trimers). Only the generally lower viscosity of AST-PIC compared with their symmetric counterparts is known from the literature (Proc. XXIVth Fatipec Conference, Jun. 8-11, 1998, Interlaken, Switzerland, vol. D. pp. 131-145). There is no “lower viscosity of the non-blocked hardener—better stability of the blocked form to crystallization” connection. It is generally known that with increasing “contamination” of organic substances a lowering in melting point as a rule occurs, but whether and how long such mixtures are stable towards crystallization is completely uncertain and always requires experimental trials in the individual case.
The blocked HDI-AST polyisocyanates according to the invention can be prepared in an industrially simple manner by reaction of the HDI-AST polyisocyanates with alcohols. Pure alcohols or mixtures can be used in this reaction. Suitable alcohols for the blocking reaction are all, optionally substituted (—O—R
1
, —NR
1
2
; R
1
=straight chain or branched C
1
-C
4
-alkyl), linear, branched, or cycloaliphatic C
1
-C
6
alcohols. Examples of said alcohols are methanol, ethanol, methoxyethanol (ethylene glycol monomethyl ether), ethoxyethanol (ethylene glycol monoethyl ether), dimethylaminoethanol, diethylaminoethanol, propanol (any isomer), methoxy propanol (any isomer), ethoxy propanol (any isomer), dimethylaminopropanol (any isomer), diethylaminopropanol (any isomer), butanol (any isomer), pentanol (any isomer), and hexanol (any isomer). Preferred alcohols are methanol, ethanol, n- and iso-propanol and methoxypropanol isomers.
It is irrelevant whether or not the alcohols used as the blocking agent are employed in exactly the stoichiometric ratio, based on the free NCO groups of the HDI-AST polyisocyanates. A small excess of alcohol is usually employed: however, a certain deficit of alcohol is also tolerated, since the free NCO groups of the polyisocyanates can react to a small extent beyond the pure NCO—OH reaction in side reactions, e.g. to form allophanates. The NCO—OH molar ratio in the b
Baumbach Beate
Füssel Christian
Richter Frank
Bayer Aktiengesellschaft
Gil Joseph C.
Gorr Rachel
Roy Thomas W.
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