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
2001-05-04
2002-10-15
Acquah, Samuel A. (Department: 1711)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Mixing of two or more solid polymers; mixing of solid...
C525S437000, C528S059000, C528S080000, C528S083000, C528S405000, C528S423000, C428S402000
Reexamination Certificate
active
06465582
ABSTRACT:
This invention relates to multi-functional oxazoline compounds and more particularly to surface coating compositions containing these compounds as crosslinkers.
Thermoset surface coatings containing crosslinkers and coreactants are well known. The chemical structure of the crosslinker composition influences the end-use application of the coating, such as the bake temperature and time for curing. For example, small, highly functional molecules are desirable crosslinkers in liquid coatings since high solvent levels to reduce viscosity are avoided—i.e. the coatings can have high solids and low viscosity thereby keeping VOC levels and the energy required to evaporate solvent low to minimize environmental pollution. Small crosslinker molecules in powder coatings improve melt rheology prior to curing—i.e. after spraying the powder coating on the substrate and prior to gelation at elevated temperature, the small solid crosslinker molecules readily melt and flow thereby directly contributing to an attractive appearance of the final powder coating. In chemically designing such crosslinkers, the balance between cost and performance is also a factor. Desirable commercial properties of the coating include UV insensitivity, good adhesion to metal and other coating substrates and the absence of volatile emissions such as water or organics during cure. The latter is especially important in powder coatings to avoid disrupting the finished powder film coating.
SUMMARY OF THE INVENTION
New molecules have been designed which usefully satisfy the foregoing requirements for crosslinkers in surface coating compositions.
Accordingly, a principal object of this invention is to provide low molecular weight (less than 1000) molecules having multi-functional sites available to participate in reactions with other chemical components.
Another object is to provide such polyfunctional molecules in which such multi-functional sites are particularly capable of crosslinking carboxyl functional coreactants of coating compositions.
An additional object is to provide cured coatings having high crosslink density and a balance of performance properties which includes resistance to UV exposure for outdoor applications.
A specific object is to provide multi-functional molecules which are particularly designed for crosslinking use in powder coating formulations.
Other objects will in part be obvious and will in part appear from the following description and claims.
These and other objects are accomplished by providing a compound of the formula:
where n is 4 or 6; R
1
is a tetravalent or hexavalent group of the formula:
where R
2
is H or C
1
to C
6
linear or branched alkyl; R
3
is selected from: (CH
2
)
x
and its branched isomers where x is 1 to 20; —C
6
H
10
—; and
and R
4
and R
5
are each H or CH
3
.
Also provided is a curable coating composition containing a carboxyl-functional coreactant polymer such as polyester and the polyoxazoline compound of formula (1) above as crosslinker wherein during curing the rings of the oxazoline groups react with the carboxyl functionality of the coreactant by ring opening.
DETAILED DESCRIPTION OF THE INVENTION
Polyoxazoline compounds of formula (1) are formed by reactively coupling iminodialkylnitriles (e.g. 3,3
1
-iminodipropionitrile (IDPN) with a difunctional or trifunctional aliphatic polycarboxylic acid or polycarboxylic acid derivatives such as adipoyl chloride as coupling agents which react with the imino group (secondary amine) of the iminodialkylnitrile forming polyfunctional (i.e. tetra or hexa) nitrile intermediates which, in a subsequent step, are converted to tetra or hexa-substituted polyoxazolines by reacting each nitrile group with a monoethanolamine group. The iminodialkylnitrile intermediate may be obtained commercially or prepared as just noted. IDPN is synthesized from readily available raw materials by reacting 2 moles of acrylonitrile (AN) or methyl or dimethyl substituted acrylonitrile with ammonia according to the following reaction (using unsubstituted AN):
IDPN prepared by this reaction is described in Example 1, Part A of U.S. Pat. No. 3,444,137 to Higginbottom et al. The iminodialkylnitrile intermediate is of formula
where R
2
is selected from H (i.e. IDPN) or C
1
to C
6
linear or branched alkyl.
The coupling agent for reaction with the reactive H of the imino group of the iminodialkylnitrile intermediate is aliphatic di or tri carboxylic acid or di or tri acid derivative thereof of the formula
where Y
1
and Y
2
are each selected from hydroxyl (i.e. the diacid) and halogen which includes fluorine, chlorine and bromine with chlorine being a preferred halogen (i.e. the acid chloride derivative) Y
1
and Y
2
react with the imino hydrogen in the coupling reaction forming H
2
O or H-halogen—e.g. HCl. R
3
of the coupling agent is selected from (CH
2
)
x
and its branched isomers where x is 1 to 20;
The latter group is based on 1,3,6-hexanetricarboxylic acid.
The final step in synthesizing polyoxazoline compounds of formula (1) is the reaction of ethanolamine with the iminodialkylnitrile intermediate product of the coupling reaction described above. In this reaction each CN group of the intermediate is converted to an oxazoline group of the formula within the brackets in (1). For example, tetraoxazoline of formula (1) from one mole of tetranitrile intermediate (from IDPN and adipoyl chloride) and 4 moles of ethanolamine is formed according to the following reaction:
The polyoxazoline compounds of the invention are usable as crosslinkers in liquid and powder coating compositions. They are highly functional from the presence of 4 or 6 oxazoline rings reactive toward carboxyl groups of a coreactant by ring opening of the oxazoline groups. Such polyoxazolines of the invention are high purity, crystalline compounds having a sharp melting point to facilitate incorporation into powder coating systems. For liquid coatings, the crosslinker usable in powders is dissolved in an appropriate solvent known to skilled coating artisans. Oxazoline functionality is achieved in such non-polymeric compounds with relatively low (e.g. 450-1000) molecular weight by choice of the coupling agent in the coupling reaction to define the backbone structure of the compounds (R
1
in formula (1)). High molecular weight polyoxazolines are less desirable as crosslinkers because they increase solution viscosity of liquid applied coatings or melt viscosity of powder coatings. The former affects VOC and the latter affects appearance. Moreover, the invention polyoxazolines are aliphatic (as opposed to aromatic) compounds to provide UV stability and avoid degradation of the coatings in outdoor applications.
The species of polyoxazoline crosslinkers of the invention with methyl substituents on the oxazoline rings (R
4
and R
5
in formula (1) are CH
3
) are less reactive in the curing reaction than those with unsubstituted rings (R
4
and R
5
are H). This change of reactivity with constituents on the rings can be exploited in formulating powder coatings of different reactivities; e.g. use the less reactive methyl substituted oxazoline species in formulations with bake temperatures greater than about 150° C. whereas the more reactive unsubstituted species would be used with formulations for low and high temperature cure applications. The less reactive substituted species can be used over a broader range of processing conditions without premature reaction.
In forming a surface coating from the curable coating composition of the invention, the carboxyl group of a carboxyl-functional coreactant reacts with and opens an oxazoline ring of the polyoxazoline crosslinker to form an ester-amide crosslink structure in the cured coating. This addition reaction importantly avoids liberating any byproducts (including disfavored volatiles) and is illustrated by the following reaction where R
1
is defined as in formula (1) and R is the backbone of the coreactant.
The oxazoline-containing crosslinker has no strong hydrogen bonding sites present which desirably contributes to low melt viscos
Gurge Ronald M.
Higginbottom Harold P.
Yuan Ping
Acquah Samuel A.
Howrey Simon Arnold & White L.L.P.
Solutia Inc.
LandOfFree
Polyoxazoline compounds and their use in surface coating... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Polyoxazoline compounds and their use in surface coating..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Polyoxazoline compounds and their use in surface coating... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2948539