Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Mixing of two or more solid polymers; mixing of solid...
Reexamination Certificate
1999-04-09
2001-09-11
Lovering, Richard D. (Department: 1712)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Mixing of two or more solid polymers; mixing of solid...
C252S182200, C523S428000, C524S901000, C525S124000, C525S458000
Reexamination Certificate
active
06288176
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a novel agent for blocking polyisocyanates. The present invention also relates to novel blocked polyisocyanates produced with the aid of the novel agent. Last but not least, the invention relates to novel coating compositions comprising the novel blocked polyisocyanates.
Here and below, the term “blocking” denotes the reversible reaction of isocyanate groups with appropriate compounds, such as hydroxyfunctional compounds, for example, to form groups which when heated release the blocking agent and the isocyanate groups. The latter are then available again for crosslinking reactions in the coating compositions. The reversal of blocking is also widely known as deblocking.
On grounds of energy, cost and a process regime which does not subject the object to be coated—a car body, for instance—to excessive thermal loading the aim is to use fully blocked polyisocyanates which effect complete crosslinking of the coating compositions at comparatively low temperatures, i.e., at or below 150° C., and in a comparatively short time, i.e., during 10 to 30 minutes.
Patents EP-A-0 206 071 and U.S. Pat. No. 5,086,090 disclose for this purpose blocking the polyisocyanates with furfuryl alcohol. However, the polyisocyanates blocked with this agent have an extremely great tendency to crystallize, which in electrodeposition coating materials in particular is manifested to disadvantage by the formation of unwanted precipitates after just a short time of standing. This occurs in particular with fully blocked diphenylmethane diisocyanates, which are used with preference in electrodeposition coating materials on account of their advantageous technological properties: in particular, their yellowing stability.
The disadvantageous great tendency to crystallize can be countered to a certain degree by subjecting the polyisocyanates to only partial blocking with furfuryl alcohol in a first stage before carrying out full blocking of the resultant partially blocked polyisocyanate with trimethylolpropane in a second stage. A disadvantage of this conventional process is the additional step, which requires additional expenditure on monitoring, time and energy. Furthermore, trimethylolpropane is a solid and must be added either as a melt or as a powder, either option being comparatively laborious.
It is an object of the present invention to provide a novel, furfuryl alcohol-based blocking agent which permits the simple, elegant and full blocking of polyisocyanates in one stage and results in novel fully blocked polyisocyanates having a very small tendency to crystallize and a comparatively low deblocking temperature. A further object of the present invention is to provide novel coating compositions, especially electrodeposition coating materials, which no longer have the disadvantages of the prior art but instead exhibit no unwanted precipitation even on long times of standing, lend themselves to thermal crosslinking at comparatively low temperatures, and result in coatings having an outstanding profile of performance properties and, in particular, no yellowing tendency.
SUMMARY OF THE INVENTION
Accordingly, a novel agent has been found for the single-stage full blocking of polyisocyanates, which consists of or comprises a mixture A) of at least two alcohols, the alcohol mixture A) comprising
a) furfuryl alcohol or substituted furfuryl alcohols in an amount corresponding to from 60 to 90, in particular from 65 to 85, mol % of hydroxyl groups, based on the total amount of hydroxyl groups in components a) and b), and
b) at least one monoalcohol in an amount corresponding to at least 2 mol % of hydroxyl groups, based on the total amount of hydroxyl groups in components a) and b).
DETAILED DESCRIPTION OF THE INVENTION
In the text below the novel agent for the single-stage full blocking of polyisocyanates is referred to for short as “blocking agent of the invention”.
Accordingly, the novel single-stage process for the full blocking of polyisocyanates is referred to as “process of the invention”.
In the light of the prior art it was surprising that the achievement of the object on which the present invention is based could be achieved with the aid of the blocking agent of the invention and process of the invention. This is all the more surprising in view of the fact that conventional blocking processes for polyisocyanates, which aim to reduce the crystallization tendency of fully blocked polyisocyanates, especially diphenylmethane diisocyanates, always involve a plurality of stages and are comparatively complex. In this context reference may be made by way of example to patents U.S. Pat. No. 5,410,001 or EP-B-0 536 166, which describe such processes.
The essential constituent of the blocking agent of the invention is the alcohol mixture A). In addition to furfuryl alcohol and/or substituted furfuryl alcohols a) it comprises at least one further monoalcohol b), or consists of these components a) and b).
Examples of suitable substituted furfuryl alcohols to be used in accordance with the invention are those which, on the ring and/or on the methylene carbon, carry groups which do not react with isocyanate groups and so do not disrupt the blocking and crosslinking. Examples of suitable groups of this kind are alkyl, aryl, alkylaryl and/or arylalkyl groups and/or halogen atoms.
In accordance with the invention it is of advantage to use furfuryl alcohol.
Where the alcohol mixture A) which is essential to the invention consists of components a) and b) it is of advantage in accordance with the invention for the monoalcohol or monoalcohols b) to have a molecular weight >163 g/mol. Although for specific purposes it is possible to use monoalcohols b) having lower molecular weights, the advantageous effects of the present invention may then in some circumstances be established reliably only after the alcohol mixture A) has been optimized by means of routine experiments.
Examples of suitable monoalcohols b) with a molecular weight >163 g/mol are monoalkyl ethers of oligomeric polyalkylene glycols, especially the monomethyl, monoethyl, monopropyl, monobutyl and/or monopentyl ethers of tri-, tetra-, penta- and/or hexaethylene glycol, -propylene glycol and/or -butylene glycol.
The alcohol mixture A) which is essential to the invention comprises component a) in an amount corresponding to from 60 to 90 mol % of hydroxyl groups, based on components a) and b). Although it is possible to use smaller amounts of component a), the deblocking temperature of the blocked polyisocyanates and thus the crosslinking temperature of the corresponding coating compositions may in that case rise again. If higher amounts of component b) are used it may no longer be possible to control the crystallization tendency of the resulting blocked polyisocyanates in the desired manner. Therefore, the stated range of amounts is an optimum within which the advantages of the invention are reliably established. Within this range, that from 65 to 85 mol % should be highlighted, since alcohol mixtures A) comprising that amount of component a) give particularly outstanding results.
The alcohol mixture A) which is essential to the invention comprises component b) in an amount which corresponds to at least 2 mol % of hydroxyl groups, based on the total amount of hydroxyl groups in components a) and b).
In the variant of the blocking agent of the invention that is described above, in which the alcohol mixture A) consists of components a) and b), component b) is present therein in an amount corresponding to from 10 to 40 and, in particular, from 15 to 35 mol %.
In a further, advantageous variant of the blocking agent of the invention and of the process of the invention the alcohol mixture A) which is essential to the invention comprises not only components a) and b) but also at least one aliphatic polyol c) which is of low molecular mass and has a functionality of three and/or more.
Examples of suitable components c) to be used in accordance with the invention are glycerol, trimethylolethane, trimethylolpropa
Grempels Ingeborg
Hsieh Bing
Johannpoetter Oliver
Jouck Walter
Kathmann Walburga
BASF Coatings AG
Lovering Richard D.
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