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
1995-05-01
2002-05-21
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...
C528S058000, C252S182200, C252S182210, C252S182220, C560S025000, C560S026000, C560S027000, C560S115000, C560S132000, C560S158000, C560S159000
Reexamination Certificate
active
06392001
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a new process for the production of light-colored, light-stable (cyclo)aliphatic allophanate polyisocyanates and to the use of the polyisocyanates obtained by this process as a synthesis component for the production of polyurethanes.
2. Description of the Prior Art
Processes for the production of polyisocyanates containing allophanate groups are described in GB-PS 994,890, U.S. Pat. No. 3,769,318, EP-B 0,000,016, EP-B 0,000,194 and EP-A-0,303,150.
According to GB-PS 994,890, polyisocyanates containing urethane groups are obtained by reacting simple monohydric or polyhydric alcohols with organic polyisocyanates, more particularly diisocyanates, by heating for several hours at elevated temperatures respectively in the presence of catalysts, such as metal carboxylates, metal chelates or tertiary amines. These urethane polyisocyanates are then reacted with further quantities of organic polyisocyanates, preferably diisocyanates, until the isocyanate content calculated for complete reaction of the urethane groups has been reached. According to the British patent, the exact constitution of the reaction products cannot be stated with any certainty. It is concluded from the measured NCO contents of the reaction mixtures or rather the end products isolated therefrom that the reaction products are essentially allophanate polyisocyanates.
As shown in a Comparison Example, strongly colored products are obtained when the reaction is carried out purely thermally in accordance with GB-PS 994,890. According to
13
C-NMR spectroscopy, the products obtained contain not only allophanate polyisocyanates, but also considerable quantities of uretdione, urea and biuret polyisocyanates (which are formed by secondary reactions such as dimerization and biuretization), and also unreacted urethanes. This can be explained by the fact that, when the reaction is terminated at the NCO content calculated for complete allophanatization, one urethane group remains behind unreacted in the reaction mixture for every NCO group reacted off by secondary reaction.
The catalysts described in GB-PS 994,890, such as metal carboxylates, metal chelates and tertiary amines, have long been known as dimerization and/or trimerization catalysts for isocyanates, so that the occurrence of such secondary reactions to a considerable extent during the reaction of urethane groups with isocyanates to form allophanates, as shown in Comparison Examples 3 and 4, is entirely understandable. It is not apparent from the patent specification what conditions and/or catalysts are necessary to produce pure allophanate polyisocyanates. Nor is it apparent what conditions are necessary to obtain light-colored, light-stable products.
The problem of producing allophanate polyisocyanates which are not accompanied by dimeric or trimeric polyisocyanates is addressed in U.S. Pat. No. 3,769,318. According to this patent, allophanate polyisocyanates containing at least one aromatically bound isocyanate group are prepared by reaction of N-substituted carbamic acid esters with isocyanates in the presence of alkylating sulfuric acid or sulfonic acid esters. According to one particular variant, this process is carried out in the presence of certain metal compounds. In the long list of such compounds, the specification mentions, inter alia, tin(II) octoate, although this salt is not used in any of the examples. Accordingly, there is nothing in this prior publication to suggest that the tin compounds according to the present invention described hereinafter should be selected from the long list of suitable metal compounds for the production of purely (cyclo)aliphatic allophanate polyisocyanates.
EP-B 0,000,016 and EP-A 0,303,150 describe the purely thermal reaction of urethanes with organic polyisocyanates to form allophanate polyisocyanates. As can be seen from Comparison Example 1, however, purely thermal reactions of urethanes and isocyanates lead to a considerable extent to secondary reactions and to discoloration of the products.
EP-B 0,000,194 describes a process for the production of allophanate polyisocyanates containing aliphatically and/or cycloaliphatically bound isocyanate groups in which compounds containing urethane groups are reacted with polyisocyanates containing aliphatically and/or cycloaliphatically bound isocyanate groups in the presence of strong acids. Although the presence of strong acids, such as hydrogen chloride, largely suppresses secondary reactions, such as trimerization and biuretization, the products obtained are discolored and tend to darken in color during prolonged storage (Comparison Example 2).
Accordingly, the cited prior art does not suggest how high-quality and, in particular, light-stable, (cyclo)aliphatic allophanate polyisocyanates could be obtained. However, since such polyisocyanates would be expected to be valuable starting materials for the production of light-stable polyurethane lacquers, an object of the present invention is to provide a process for the production of such allophanate polyisocyanates.
Surprisingly, this object may be achieved by carrying out the reaction between aliphatic or cycloaliphatic polyisocyanates and compounds containing urethane groups in the presence of certain tin compounds described in detail hereinafter. The products obtained by the process according to the invention are distinguished by a low color value, high light stability and color stability and, in addition, by comparatively low viscosity. They are also valuable starting materials for the production of polyurethanes, in particular polyurethane coatings.
SUMMARY OF THE INVENTION
The present invention relates to a process for the production of polyisocyanates containing allophanate groups and having aliphatically and/or cycloaliphatically bound isocyanate groups by reacting organic compounds containing urethane groups with organic polyisocyanates containing aliphatically and/or cycloaliphatically bound isocyanate groups in the presence of tin compounds.
The present invention also relates to the use of these polyisocyanates as a synthesis component for the production of polyurethane, more particularly as a crosslinking resin, which may optionally be blocked, for two-component polyurethane lacquers.
DETAILED DESCRIPTION OF THE INVENTION
Starting materials for the process according to the invention are (i) organic compounds containing urethane groups and (ii) organic polyisocyanates containing aliphatically and/or cycloaliphatically bound isocyanate groups.
The compounds containing urethane groups to be used in the process according to the invention are any optionally isocyanate-containing compounds which contain from 1 to 70% by weight and preferably from 1 to 40% by weight of urethane groups (expressed as CHNO
2
, molecular weight 59) and which, apart from the urethane groups, preferably contain no other H-active, isocyanate-reactive groups. The compounds containing urethane groups may optionally contain isocyanate groups. Suitable compounds include urethane-containing compounds which have been obtained by the reaction of amines containing primary amino groups with chloroformic acid esters. However, the compounds containing urethane groups are preferably reaction products of isocyanates, more particularly polyisocyanates, with organic hydroxyl compounds, i.e. alcohols or phenols, preferably alcohols.
In a preferred embodiment of the process according to the invention the urethane starting materials are prepared in situ from phenols or alcohols and excess quantities of aliphatic or cycloaliphatic polyisocyanates. The reaction mixture obtained in this reaction contains the second main component of the process according to the invention, i.e., the aliphatic or cycloaliphatic polyisocyanate, which was used in excess in the preparation of the urethane.
Preferred compounds containing urethane groups to be used as starting materials in the process according to the invention include those corresponding to the general formula:
wherein
A is the residue obtained
Halpaap Reinhard
Mertes Harald
Pedain Josef
Gorr Rachel
Roy Thomas W.
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