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
2001-05-15
2004-04-13
Rotman, Alan L. (Department: 1625)
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...
C528S051000, C528S068000, C560S169000, C560S125000, C560S335000
Reexamination Certificate
active
06720400
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to an improved process for the preparation of polyisocyanates with a biuret structure by continuous reaction of excess amounts of organic diisocyanates having exclusively aliphatically and/or cycloaliphatically bound isocyanate groups with organic diamines having exclusively aliphatically and/or cycloaliphatically bound primary amino groups at elevated temperatures in the presence of acids. The polyisocyanates thus prepared are characterised by high stability and good dilutability.
The preparation of aliphatic polyisocyanates with biuret structures has been known since 1958 (DE-A 1 101 394). Possible production processes are described in a review article (Laas et al., J. prakt. Chem. 336, 1994, 185-200) which discusses the advantages and disadvantages of each particular process.
In principle, two processes are distinguished: firstly, the so-called water processes in which the diisocyanates are reacted with water to form ureas and subsequently biurets, and secondly, the so-called diisocyanate/diamine processes in which urea is prepared directly from isocyanate and amine, followed by a biuret reaction. For both processes, as explained in the review article cited above (Laas et al.), numerous variants have been developed and described. In these processes the reaction of hexamethylene diisocyanate (HDI) to HDI biurets is of greatest industrial importance. The biurets are initially in the dissolved form in excess diisocyanate and are separated from excess diisocyanate by distillation and/or extraction and isolated as low-monomer biuret polyisocyanates. Both processes have undergone constant further development and improvement.
Biuret polyisocyanates prepared by water processes are usually characterized by good monomer stability, i.e. stability towards reverse cleavage to free diisocyanates, good dilutability, i.e. stability of dilute solutions towards cloudiness and precipitation under the action of moisture, and outstanding color numbers in view of the relatively mild reaction conditions during preparation. In the biuret formation reactions by the water process, however, by their very principle, a part of the isocyanate groups contained in the reaction mixture is always converted to amino groups by reaction with a biuret forming agent. As the isocyanate groups thus consumed were originally prepared by phosgenation of amino groups, this procedure is less economical. Moreover, the gaseous or liquid by-products such as, carbon dioxide, carbon monoxide, carbonyl sulfide, olefins or nitriles cannot be recycled and have to be disposed of.
Advantages of the refined diisocyanate/diamine processes as described, e.g., in EP-A 277353 (believed to correspond to U.S. Pat. No. 4,837,359) are little or no by-product formation, and no conversion/loss of isocyanate groups to amino groups. A certain disadvantage of biuret polyisocyanates prepared in this way is their slightly reduced monomer stability and reduced dilution stability, with the possibility of slight cloudiness and even precipitates occurring if high dilutions are prepared (<40% solids).
Acid catalysis in biuret polyisocyanate preparation according to the water process catalysis has been known for a relatively long time. More recent research which was published after the publication of Laas et al., J. prakt. Chem. 1994, is described in EP-A 716080 (believed to correspond to U.S. Pat. No. 5,641,851), WO 97/03044 (believed to correspond to U.S. Pat. No. 6,066,759) and DE-A 19633404. EP-A 716080 discloses that the addition of OH acid compounds such as, e.g., dialkyl phosphates, suppresses the formation of insoluble urea during the biuret forming reaction of aliphatic diisocyanates with water. DE-A 19633404, teaches that the diisocyanates are reacted in special mixing components with a high shear action. The document also mentions acid (dialkyl phosphate)-catalyzed reactions in those examples where water or tert.-butanol, optionally in mixture with diamine, are used as reactants. Examples of this application (Ex. 1, Table 1 and Ex. 2, Table 2) with HDI and HDA were carried out without acid catalysis using the special mixing components.
An object of the present invention is to continuously prepare polyisocyanates with a biuret structure with improved properties while retaining the simple (economically most advantageous) diisocyanate/diamine process. An additional object of the invention is, in particular, to prepare biuret polyisocyanates with improved monomer stability and optimum dilutability in organic solvents by such a continuous process without the occurrence of cloudiness or precipitation. Moreover, polyisocyanates with a biuret structure prepared according to the invention should exhibit little sensitivity to moisture and should have low color numbers. It should be possible to dispense with the need to use special mixing apparatus to produce high shear forces.
Surprisingly, as has now been found, it is possible to prepare, in a continuous process, high-quality polyisocyanates with a biuret structure based on organic diisocyanates having exclusively aliphatically and/or cycloaliphatically bound isocyanate groups and organic diamines having exclusively aliphatically and/or cycloaliphatically bound primary amino groups with improved properties and without the use of special mixing apparatus if the starting materials are caused to react with one another at temperatures above 170° C. with the addition of acids.
This finding is extremely surprising since the use of OH acids in diisocyanate/diamine direct processes led one to assume that, prior to biuret formation proper, the OH acid is neutralized by the amine used and thus becomes ineffective. Moreover, it was to be assumed that the OH acid is attacked by the isocyanate and withdrawn at least partially from the reaction by conversion to the anhydride. In the above-mentioned water processes, this process of becoming ineffective is not a problem because the acid can be re-formed repeatedly by the addition of water. Consequently, it was utterly unexpected that the addition of acids in the simple (economically attractive) diisocyanate/diamine process would bring a series of important advantages:
the monomer stability of the biuret polyisocyanates produced can be markedly improved;
the sensitivity of the biuret polyisocyanates produced towards damp solvents can be decidedly reduced;
the required reaction temperature of the reaction of diisocyanate with diamine can be reduced without prolonging the reaction time and without the intermediate occurrence of cloudiness (polyureas), which results in a considerable energy saving.
SUMMARY OF THE INVENTION
The invention relates to a process for the continuous preparation of polyisocyanates with a biuret structure by continuously reacting excess amounts of organic diisocyanates having exclusively aliphatically and/or cycloaliphatically bound isocyanate groups with organic diamines having exclusively aliphatically and/or cycloaliphatically bound primary amino groups at temperatures above 170° C. and adding acid during the reaction.
DETAILED DESCRIPTION OF THE INVENTION
The starting materials for the process according to the invention are organic diisocyanates having exclusively aliphatically and/or cycloaliphatically bound isocyanate groups and a molecular weight below 300. Examples of such diisocyanates include 1,4-diisocyanatobutane, 1,6-diisocyanatohexane (hexamethylene diisocyanate, HDI), 1,6-diisocyanato-2,2,4-trimethylhexane and/or 1,6-diisocyanato-2,4,4-trimethylhexane, 1,4-and/or 1,5-diisocyanatohexane, 2,6-diisocyanatohexanoic acid ethyl ester, 1,12-diisocyanatododecane, 1,4-diisocyanatocyclohexane, 2,4- and/or 2,6-diisocyanato-1-methylcyclohexane, 1-isocyanato-3,3,5-trimethyl-5-isocyanatomethylcyclohexane (isophorone diisocyanate, IPDI), 1,3- and/or 1,4-bis-(isocyanatomethyl)cyclohexane, 4,4′-diisocyanatodicyclohexylmethane or 6-isocyanatohexanoic acid-2-isocyanatoethyl ester. Any mixtures of such diisocyanates may also be used. 1,6-diisocyanatohexane is preferred.
Further sta
Halpaap Reinhard
Mager Dieter
Mertes Harald
Oeckl Siegfried
Bayer Aktiengesellschaft
Gil Joseph C.
Matz Gary F.
Oh Taylor V
Rotman Alan L.
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