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
2002-08-14
2004-05-25
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...
C528S045000, C560S330000, C560S347000, C252S182200, C252S182210, C525S123000
Reexamination Certificate
active
06740726
ABSTRACT:
The invention relates to aliphatic polyisocyanates, to a process for preparing them, to coating compositions and adhesives comprising the aliphatic polyisocyanates, and to the use of the polyisocyanates, coating compositions, and adhesives.
Aliphatic polyisocyanates, i.e., isocyanates having more than one, preferably more than two, isocyanate groups per molecule, are known and are used, inter alia, as crosslinkers for preparing polyurethanes suitable as binders for paints. Since reducing the solvent content of paints is an objective with the aim of reducing emissions, it is necessary to have paint constituents of low viscosity in order to maintain a viscosity which is sufficiently low for the application of the paint. Commercial polyisocyanates which meet this condition are generally prepared by oligomerizing difunctional isocyanates, hexamethylene diisocyanate for example. In the course of this preparation, however, some of the isocyanate groups present originally are reacted and are lost to the subsequent crosslinking reaction. Moreover, this preparation process requires two steps to the polyfunctional isocyanate having three or more NCO groups.
Other polyfunctional isocyanates, an example being nonane triisocyanate, are prepared directly from the corresponding polyfunctional amines. Only a few such polyfunctional amines, however, are available on the industrial scale.
Paint systems known at present, such as clearcoats or topcoats, surfacers and primers, or underbody protection compositions for motor vehicles, have the disadvantage that their solids contents cannot be increased ad infinitum. Paint systems of this kind are known from DE 44 07 415, DE 44 07 409 or DE 43 10 414. Raising the solids content of paints in order to reduce solvent emission is, however, a stated aim of the paint industry. The same applies accordingly to adhesives and sealing compounds.
It is an object of the invention to provide new aliphatic polyisocyanates which with two or more NCO groups per molecule are of low viscosity and whose molecule size and number of NCO groups may be varied as desired, and to provide a process for preparing them that requires no further reaction after the NCO groups have been introduced.
It is a further object of the present invention to provide coating compositions and adhesives which as compared with their prior art counterparts have an increased solids content and permit low-emission formulations.
We have found that these objects are achieved firstly by polyisocyanates of the formula I
in which
R and R′ are identical or different alkyl groups having 1-4 carbon atoms and
n is on average from 1.5 to 5,
and secondly by a coating composition or adhesive comprising
a) polyisocyanates of the formula I, which may be present in blocked form, as crosslinkers,
b) if desired, further crosslinkers, and
c) isocyanate-reactive polymers, oligomers and/or low molecular mass compounds, as binders.
Polyisocyanates of the formula I are therefore compounds containing on average from 1.5 to 5 NCO groups, i.e., essentially those representatives which may be referred to as oligomers. The polyisocyanates of the formula I are frequently in the form of homolog mixtures which include representatives where n=1 to about n=10 and are preferably composed essentially of these representatives.
The invention further proposes a process for preparing polyisocyanates of the formula I which comprises reacting a polyamine of the formula II
in which R, R′, and n are as defined above with phosgene, preferably in excess.
The polyamines may be reacted in one stage at elevated temperature (generally from 120 to 170° C.) or, with particular advantage, in two stages, first at relatively low temperatures in the range from −15 to +10° C. (cold phosgenation) and then with an increase to from 130 to 165° C. (hot phosgenation). Particularly good yields are achieved if the amine is first converted to the hydrochloride and then subjected to cold phosgenation at from 50 to 70° C. and to hot phosgenation at from 120 to 170° C. Phosgene is generally used in an excess of from 10 to 30 mol %, so that, normally, substantially all of the primary amino groups are converted to isocyanate groups. It is, however, also possible to use larger phosgene excesses. The excess phosgene can be removed with ease and recycled to the synthesis.
The reaction may be conducted without the addition of inert solvents. In general, however, it is of advantage to operate in an aprotic solvent such as a halogenated, especially chlorinated, aromatic, preferably mononuclear, hydrocarbon such as dichlorobenzene.
The compounds of the formula II are known and are described, for example, in DE-A 196 54 167. They are preferably obtained by catalyzed metathesis reactions of hydrocarbon mixtures comprising cyclopentene, e.g., petroleum fractions, subsequent hydroformylation of the reaction products, and reaction thereafter with ammonia in the presence of hydrogen and a hydrogenation catalyst.
The polyisocyanates obtained are distinguished by particularly low viscosities, which are generally below 400 mPas. They are therefore outstandingly suitable for preparing low-solvent paint base material mixtures.
The present invention also provides for the use of the polyisocyanates of the formula I to prepare coating compositions and adhesives.
The average functionality of the isocyanates used in accordance with the invention is preferably from 1.5 to 5.0 and with particular preference from 1.5 to 3.5.
The polyisocyanates of the formula I may be used as sole crosslinkers or in blends with further crosslinkers. Examples of suitable further crosslinkers are amino resins, compounds or resins containing siloxane groups, compounds or resins containing anhydride groups, polyisocyanates and/or alkoxycarbonylaminotriazines.
The further crosslinkers preferably comprise or consist of other polyisocyanates, different than the polyisocyanates of the formula I. In principle it is possible to use all polyisocyanates that are common in the paints field. Preferred polyisocyanates are those whose isocyanate groups are attached to aliphatic or cycloaliphatic radicals. Examples are tetramethylene diisocyanate, hexamethylene diisocyanate, isophorone diisocyanate, trimethylhexamethylene diisocyanate, dicyclohexylmethane diisocyanate, 1,3-bis(2-isocyanatoprop-2-yl)benzene (TMXDI), 1,4- and 1,3-bis(isocyanatomethyl)cyclohexane, et cetera, and adducts of these polyisocyanates with polyols, and polyisocyanates derived from these polyisocyanates and containing isocyanurate groups and/or biureth groups.
The polyisocyanates of the formula I and the polyisocyanates used as further crosslinkers may be blocked or nonblocked.
Through the choice of the further crosslinkers and also through the use of the polyisocyanates in blocked or nonblocked form it is possible to configure the coating compositions and adhesives of the invention as one-component or two-component systems.
Blocked isocyanates may be employed in both one-component and two-component systems; preferably, they are employed in one-component systems. A general description of the preparation of suitable blocked isocyanates is given, for example, in DE-A 198 09 643. Blocked isocyanates preferably contain both isocyanate groups blocked with a first blocking agent and isocyanate groups blocked with a second blocking agent, the first blocking agent being a dialkyl malonate or a mixture of dialkyl malonates, preferably dialkyl malonates having 1-6 carbon atoms, and the second blocking agent preferably being an alkyl acetoacetate having 1-6 carbon atoms in the alkyl radical or a ketoxime, such as ethyl acetoacetate or methyl ethyl ketoxime. The ratio between the isocyanate groups blocked with the first blocking agent and those blocked with the second blocking agent is preferably between 8.0:2.0 and 6.0:4.0, suitable blocked polyisocyanates being obtainable by reacting the polyisocyanates with a mixture of the first and the second blocking agent or by mixing isocyanates blocked with the first blocking agent w
Henkelmann Jochem
Jung Werner-Alfons
Maas Heiko
Rink Heinz-Peter
Schulz Gerhard
BASF - Aktiengesellschaft
Gorr Rachel
Keil & Weinkauf
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