Coating processes – Direct application of electrical – magnetic – wave – or... – Electrostatic charge – field – or force utilized
Reexamination Certificate
2001-06-29
2002-11-12
Wilson, D. R. (Department: 1713)
Coating processes
Direct application of electrical, magnetic, wave, or...
Electrostatic charge, field, or force utilized
C427S472000, C427S384000, C427S388200, C427S386000, C524S901000, C524S505000, C524S548000
Reexamination Certificate
active
06479109
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to thermosetting compositions comprised of active hydrogen-containing polymers which contain onium salt groups, and curing agents therefor which are reactive with the active hydrogen groups of the polymer. The active hydrogen-containing polymers are prepared by atom transfer radical polymerization, and have well defined polymer chain structures, molecular weights and molecular weight distributions. The invention also relates to methods of electrocoating conductive substrates and to substrates electrocoated by such methods.
BACKGROUND OF THE INVENTION
Electrodeposition as a coating application method involves deposition of a film-forming composition onto a conductive substrate under the influence of an applied electrical potential. Electrodeposition has become increasingly important in the coatings industry because, by comparison with non-electrophoretic coating means, electrodeposition offers increased paint utilization, improved corrosion protection and low environmental contamination.
Initially, electrodeposition was conducted with the workpiece being coated serving as the anode. This was familiarly referred to as anionic electrodeposition. However, in 1972, cationic electrodeposition was introduced commercially. Since that time, cationic electrodeposition has steadily gained in popularity and today is by far the most prevalent method of electrodeposition. Throughout the world, more than 80 percent of all motor vehicles produced are given a primer coating by cationic electrodeposition.
Electrodepositable coating compositions comprising active hydrogen-containing polymers which contain onium salt groups are known and have been developed for use, inter alia, in electrodepositable automotive OEM primer coatings. Such electrodepositable coating compositions typically comprise a crosslinking agent having at least two functional groups that are reactive with active hydrogen groups, and an active hydrogen-containing polymer which contains onium salt groups. The polymers used in such electrodepositable coating compositions are typically prepared by condensation reactions or by conventional, i.e., non-living, radical polymerization methods, which provide little control over molecular weight, molecular weight distribution and polymer chain structure.
Many physical properties, e.g., viscosity, of a given polymer can be directly related to its molecular weight. Higher molecular weights are typically associated with, for example, higher glass transition temperature (Tg) values and viscosities.
The physical properties of a polymer having a broad molecular weight distribution, e.g., having a polydispersity index (PDI) in excess of 2.5, can be characterized as an average of the individual physical properties of and indeterminate interactions between the various polymeric species that comprise it. As such, the physical properties of polymers having broad molecular weight distributions can be variable and hard to control.
The polymer chain structure, or architecture, of a polymer can be described as the sequence of monomer residues along the polymer back bone or chain. An active hydrogen containing polymer containing onium salt groups prepared by standard radical polymerization techniques will contain a mixture of polymer molecules having, for example, varying individual hydroxyl and onium salt group equivalent weights and varying polymer chain structures. In such a copolymer, the onium salt groups and the hydroxyl groups are located randomly along the polymer chain. Moreover, the number of functional groups is not divided equally among the polymer molecules, such that some fraction of the polymer molecules may actually be free of onium salt groups and/or hydroxyl groups.
In any thermosetting composition, the formation of a three-dimensional crosslinked network is dependent upon the functional equivalent weight, e.g. hydroxyl equivalent weight, as well as the architecture of the individual polymer molecules that comprise it. Polymer molecules having little or no reactive functionality (or having functional groups that are unlikely to participate in crosslinking reactions due to their locations along the polymer chain) will contribute little or nothing to the formation of the three-dimensional crosslinked network, resulting in decreased crosslink density and less than optimum physical properties of the resultant cured film.
An electrodepositable coating composition is comprised of a resinous phase dispersed in an aqueous medium. Polymer molecules of the resinous phase typically contain an ionic species, e.g. onium salt groups, to facilitate dispersion of the polymer in the aqueous medium. Polymer fractions having few or no ionic groups will be difficult to disperse in the aqueous medium, resulting in poorer stability of the electrodeposition bath and poorer appearance of the resultant electrodeposited coating.
The continued development of new and improved electrodepositable coating compositions which provide stable electrodeposition baths and a combination of favorable coating performance properties is desirable. In particular, it would be desirable to develop thermosetting compositions that comprise active hydrogen-containing polymers which contain onium salt groups, the polymer having well-defined molecular weights and tailored polymer chain structure, and narrow molecular weight distributions, for example, PDI values less than 2.5. Such compositions would have efficient dispersibility and a combination of favorable performance properties, particularly in electrodepositable coatings applications.
U.S. Pat. Nos. 5,789,487 and 5,763,548 and International Patent Publication WO 97/18247 describe a radical polymerization process referred to as “atom transfer radical polymerization” (ATRP). The ATRP process is described as a living radical polymerization that results in the formation of polymers having predictable molecular weight and molecular weight distribution. The ATRP process of these publications is also described as providing highly uniform products having controlled structure (i.e., controllable topology, composition, etc.). These patent publications also describe polymers prepared by ATRP, which are useful in a wide variety of applications, for example, in paints and coatings.
SUMMARY OF THE INVENTION
In accordance with the present invention, provided is a thermosetting composition comprising a resinous phase dispersed in an aqueous medium, the resinous phase comprised of the following components:
(a) an ungelled active hydrogen group-containing polymer prepared by atom transfer radical polymerization in the presence of an initiator having at least one radically transferable group, wherein the polymer contains at least one of the following polymer chain structures:
—[—(G)
j
—(M)
k
—(A)
l
—]
x
—; (I)
—[—(G)
j
—(A)
l
—(M)
k
—]
x
—; (II)
—[—(A)
l
—(G)
j
—(M)
k
—]
x
—; (III)
—[—(M)
k
—(A)
l
—(G)
j
—]
x
—; (IV)
—[—(M)
k
—(G)
j
—(A)
l
—]
x
—; (V)
—[—(A)
l
—(M)
k
—(G)
j
—]
x
—; (VI)
—[—[—(M)
k
—(A)
l
—]
q
—(G)
j
—]
x
—; (VII)
—[—[—(M)
k
—(G)
j
—]
q
—(A)
l
—]
x
—; (VIII)
—[—[—(A)
l
—(M)
k
—]
q
—(G)
j
—]
x
—; (IX)
or
—[—[—(G)
j
—(M)
k
—]
q
—(A)
l
—]
x
—; (X)
where j, k, l, q and x, each are independently selected for each structure such that the polymer has a number average molecular weight of at least 250, as determined by gel permeation chromatography using a polystyrene standard; G is a residue of at least one ethylenically unsaturated radically polymerizable monomer, said residue containing onium salt groups; A is a residue of at least one ethylenically unsaturated radically polymerizable monomer, said residue containing active hydrogen groups and being free of onium salt groups; and M is a residue of at least one ethylenically unsaturated radically polymerizable monomer and is different
Anderson Linda K.
Coca Simion
McCollum Gregory J.
Uhl William J.
Wilson D. R.
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