Coating processes – With post-treatment of coating or coating material – Heating or drying
Reexamination Certificate
2001-08-28
2003-04-08
Cameron, Erma (Department: 1762)
Coating processes
With post-treatment of coating or coating material
Heating or drying
C528S045000
Reexamination Certificate
active
06544592
ABSTRACT:
The present invention relates to an aqueous dispersion of a crosslinkable polyurethane obtained by chain extension of a polyurethane prepolymer with a compound containing hydrazone functions having the general formula:
wherein
Q
1
and Q
2
is a hydrazone functional group of formula (2), H or R
1
R and R
1
in formula (1) is an organic group which has no reactivity towards the hydrazone function,
R
2
and R
3
is an organic group which has no reactivity towards the hydrazone functions, with the proviso that at least one of the groups Q
1
or Q
2
in formula (1) is of formula (2) It relates to a process for the preparation of said polyurethane dispersion, to a process for the preparation of a crosslinked film or a coated substrate and to the obtained crosslinked film or coated substrate.
INTRODUCTION
It is well known that the performance and properties of coatings or films of aqueous polyurethane dispersions can be increased by the incorporation of crosslinkable groups in the polymer backbone and crosslinking of said polymers with relevant crosslinkers. For application onto temperature sensitive substrates, such as leather and artificial leather, the low-temperature baking types are of special interest. An overview of low baking type cross-linking for polyurethane dispersions is presented in EP-507407. This application describes further an improved crosslinking system in which carboxylic acid functional polymers are crosslinked by carbodiimide functional oligomers or polymers containing additional reactive functional groups, which contribute to the crosslinking.
An alternative crosslinking system is described in U.S. Pat. No. 4,598,121, which comprises the incorporation of a hydrazide functional chain extender in a polyurethane and crosslinking of the polyurethane with formaldehyde.
Since the use of formaldehyde type crosslinkers are expected to cause environmental problems, other types of compounds which are reactive towards the hydrazide function became of interest as crosslinkers, such as isocyanate functional, ketone functional or epoxide functional compounds. Research has shown that, because of the reactivity of these groups towards the hydrazide function, especially of the isocyanate functional compounds, the potlife of the hydrazide functional polyurethane together with the crosslinkers was limited. Moreover, it appeared that the polyurethane dispersions containing hydrazide functions became yellow in stability tests.
We now developed a new aqueous dispersion of a cross-linkable polyurethane in which a product containing blocked reactive sites is incorporated in the polymer chain. The obtained aqueous polyurethane dispersion combined with a relevant crosslinker is suitable for the preparation of a crosslinked film or of a crosslinked coating onto a substrate.
DESCRIPTION OF THE INVENTION
The present invention provides an aqueous dispersion of a crosslinkable polyurethane obtained by chain extension and/or chain terminating of an isocyanate functional polyurethane prepolymer with a compound which contains hydrazone functions having as the general formula:
wherein
Q
1
and Q
2
is a hydrazone functional group of formula (2), H, or R
1
R and R
1
in formula (1) is an organic group which has no reactivity towards the hydrazone function,
R
2
and R
3
in formula (2) is an organic group which has no reactivity towards the hydrazone function,
x has a value from 1 to 10, and is preferably from 1 to 4 with the proviso that at least one of the groups Q
1
or Q
2
is of formula (2).
In an aqueous solution at pH above 7 the hydrazone function is stable, but at lower pH, or during drying at elevated temperatures the hydrazone function in the polyurethane reacts with water under formation of a ketone and a hydrazide function of formula
The resulting product which contains hydrazide functions can be crosslinked and/or chain extended by a polyisocyanate, a polyketone or a polyepoxy functional material.
Since the product of formula (1) is used as a chain extender and/or chain terminating group for isocyanate functional polyurethane prepolymers at least one of the groups Q must be a hydrogen. The invention therefore includes the aqueous dispersion of a polyurethane which contains as chain extender or chain terminating group a hydrazone functional compound of formula (1), wherein at least one of the groups groups Q
1
or Q
2
is H.
It appeared that under aqueous conditions only the NH or NH
2
function of the product of formula (1) reacts with a isocyanate functional material under formation of a urea function, while the hydrazone function remains intact. In the presence of only one hydrogen reactive amine in formula (1) the isocyanate functional material is just capped.
More preferably the product of formula (1) contains two or more hydrogen reactive amine functions and it can chain extend and/or crosslink a polyisocyanate functional material to obtain an aqueous dispersion of a polyurethane containing hydrazone functions. Accordingly the present invention relates to an aqueous dispersion of a polyurethane which preferably contains as chain-extender a hydrazone functional product, which contains at least two hydrogen functional amino groups.
Usually the product of general formula (1) which is used as chain extender in the aqueous polyurethane dispersion is prepared by reacting a hydrazide functional compound of formula
wherein
P
1
and P
2
is a hydrazide functional group of formula (3) or is H, or is R
1
,
R and R
1
, and x are as in formula (1)
with the proviso that at least one of the groups p
1
or p
2
has formula (3)
with an equimolar amount of a ketone functional compound of formula
wherein R
2
and R
3
are as in formula (2).
The hydrazide functional compound is prepared from a polyamine by a method as described in U.S. Pat. No. 4,598,121. The polyamine has the structure conform formula (4) in which the hydrazide functional group P was originally hydrogen. According to this method the polyamine is first reacted with an alkyl-acrylate whereafter the obtained alkyl aminopropionate functional compound is reacted with hydrazine.
The hydrazide functional compound is a hydrazide functional alkylamine, a cycloalkylamine, an arylamine, an alkylpolyamine, a cycloalkylpolyamine, an arylpolyamine, an alkylamino-cycloalkylamine, a polyalkoxyamine, a polyalkoxypolyamine, an aminoalkylamine, an amino-poly(alkylamine).
The preferred hydrazide functional compound can be selected from a hydrazide functional 5-amino-1,3,3-trimethylcyclohexanemethylamine, methylpentanediamine, diaminohexane, 3,3′-dimethyl-4,4′-diaminodiyclo-hexylmethane, 4,4′-diamino-dicyclohexylmethane, a polyoxypropylenediamine with a molecular weight of around 230, 400, or 2000, a polyoxyethylenediamine with a molecular weight of around 600, 900, 2000, 4000 or 6000, a polyalkoxyethyleneamine with a molecular weight of around 600, 1000, 2000, a polyoxypropylenetriamine with a molecular weight of around 470, a long chain alkylamine with a mean molecular weight from 140 to 550, a (long chain alkyl)-aminopropylamine with a mean molecular weight from 280 to 360.
The ketone which is used for the blocking of the hydrazide function in the preparation of the product of formula (1) is prefarably acetone or butyl ketone.
The product of formula (1) is a polyamine which is modified by replacing an N—H function by a N-hydrazone function. The number of hydrazone functions can be varied from 0.1-1 equimolar amount regarding to the NH-functions in the polyamine.
Furthermore the invention relates to the process for the preparation of the aqueous dispersion of a crosslinkable polyurethane containing hydrazone functions comprising:
dispersion of an isocyanate functional polyurethane prepolymer in water, optionally in the presence of neutralizing agents and/or surfactants
chain extension of the prepolymer with a hydrazone functional product containing at least two hydrogen functional amino groups, optionally in the presence of a surfactant, during or after the dispersion in water.
The isocyanate functional polyurethane prepo
Hesselmans Laurentius Cornelius Josephus
Van Den Goorbergh Johanna Antonia Maria
Cameron Erma
Myers Jeffrey D.
Stahl International B.V.
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