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
2003-02-04
2004-10-12
Lipman, Bernard (Department: 1713)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Mixing of two or more solid polymers; mixing of solid...
C524S512000
Reexamination Certificate
active
06803413
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to waterborne thermosetting compositions that contain copolymers of vinyl monomers. More specifically, the present invention is directed to waterborne thermosetting compositions that contain functional copolymers containing isobutylene type monomers.
2. Description of Related Art
Reducing the environmental impact of coating compositions, in particular that associated with emissions into the air of volatile organics during their use, has been an area of ongoing investigation and development in recent years. Accordingly, interest in high solids waterborne coatings has been increasingly due, in part, to their inherently low volatile organic content (VOC), which significantly reduces air emissions during the application process. While both thermoplastic and thermoset coating compositions are commercially available, thermoset coatings are typically more desirable because of their superior physical properties, e.g., hardness and solvent resistance.
Low VOC coatings are particularly desirable in the automotive original equipment manufacture (OEM) market due to the relatively large volume of coatings that are used. However, in addition to the requirement of low VOC levels, automotive manufacturers have very strict performance requirements of the coatings that are used. For example, automotive OEM clear top coats are typically required to have a combination of good exterior durability, acid etch and water spot resistance, and excellent gloss and appearance. While liquid top coats containing, for example, capped polyisocyanate and polyol components, can provide such properties, they have the undesirable drawback of higher VOC levels relative to higher solids liquid coatings or powder coatings, which have essentially zero VOC levels.
Functional polymers used in coating compositions are typically random copolymers that include functional group-containing acrylic and/or methacrylic monomers. Such a functional copolymer will contain a mixture of polymer molecules having varying individual functional equivalent weights and polymer chain structures. In such a copolymer, the functional 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 polymer molecules may actually be free of functionality.
In a thermosetting composition, the formation of a three-dimensional crosslinked network is dependent on the functional 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 finally formed thermoset coating.
Many patents express the potential for using isobutylene-containing polymers in coating compositions. For example, U.S. Pat. No. 6,114,489 to Vicari et al. discloses a coating composition that includes a functional acrylic resin binder; a co-reactant capable of reacting with the functionality of the acrylic binder; a degasser; and a hyperbranched polyester flow and leveling agent. Isobutylene is suggested as a potential co-monomer for use in the acrylic binder as part of a long list of monomers. U.S. Pat. No. 5,552,487 to Clark et al. discloses powder coating compositions that include a copolymer having a reactive functionality and a suitable crosslinking agent capable of reaction with the reactive functionality of the copolymer. The copolymer is a made by copolymerizing functional monomers with other monomers, isobutylene being one among many listed as potential co-monomers. Although only two are referenced herein, of the many patents that express the possibility of using isobutylene-type co-monomers, none actually shows or discloses a working example of such a copolymer.
The fact that no examples of isobutylene-type monomer-containing copolymers in coating compositions can be found is most likely due to the generally non-reactive nature of isobutylene with acrylic and methacrylic monomers. Reactivity ratios for monomers can be calculated using the Alfrey-Price Q-e values (Robert Z. Greenley, Polymer Handbook, Fourth Edition, Brandrup, Immergut and Gulke, editors, Wiley & Sons, New York, N.Y., pp. 309-319 (1999)). The calculations may be carried out using the formulas I and II:
r
1
=(
Q
1
/Q
2
)exp{−
e
1
(
e
1
−e
2
)} I
r
2
=(
Q
2
/Q
1
)exp{−
e
2
(
e
2
−e
1
)} II
where r
1
and r
2
are the respective reactivity ratios of monomers 1 and 2, and Q
1
and Q
2
and e
1
and e
2
are the respective reactivity and polarity values for the respective monomers (Odian,
Principals of Polymerization
, 3
rd
Ed., Wiley-Interscience, New York, N.Y., Chapter 6, pp. 452-467 and 489-491 (1991)). Table 1 shows the calculated reactivity ratios of selected monomers with isobutylene:
TABLE 1
Monomer
r
1
(isobutylene)
r
2
Methyl acrylate
0.10
13.67
Glycidyl methacrylate
0.08
34.17
Methacrylic acid
0.09
39.71
As one skilled in the art of polymer chemistry can appreciate, when r
1
is near zero and r
2
has a value of 10 or more, monomer 2 is reactive toward both monomers and monomer 1 is reactive toward neither monomer. In other words, it is extremely difficult to prepare copolymers having significant amounts of both monomers. It is not surprising then that no examples can be found of coating compositions that include isobutylene-type monomer-containing copolymers, because the monomers do not tend to copolymerize.
In some cases, it is observed that monomers that do not readily homopolymerize are able to undergo rapid copolymerization reactions with each other. The most typical situation occurs when a strong electron donating monomer is mixed with a strong electron accepting monomer from which a regular alternating copolymer results after free radical initiation. Maleic anhydride is a widely used example of a strong electron accepting monomer. Styrene and vinyl ethers are typical examples of electron donating monomers. Systems, such as maleic anhydride—styrene, are known to form charge transfer complexes, which tend to place the monomers in alternating sequence prior to initiation. The application of the free radical initiator “ties” the ordered monomers together to form an alternating copolymer (Cowie, Alternating Copolymers, Plenum, N.Y. (1985)).
U.S. Pat. Nos. 2,378,629 to Hanford and 4,151,336 to Sackman et al. disclose that even when a moderately electron donating monomer, such as diisobutylene, is copolymerized with a strong electron acceptor monomer, such as maleic anhydride, an alternating copolymer results.
When a moderately electron donating monomer, such as isobutylene, is copolymerized with a moderately electron accepting monomer, such as an acrylic ester, poor incorporation of the electron donating monomer results. For example, free radical copolymerization of isobutylene (IB) and acrylic monomers has resulted in copolymers that contain at no more than 20-30% of IB and have low molecular weights because of the degradative chain transfer of IB. Examples of such copolymerizations of IB are disclosed by U.S. Pat. No. 2,411,599 to Sparks et al. and U.S. Pat. No. 2,531,196 to Brubaker et al.
Conjugated monomers, such as acrylic esters and acrylonitrile, have been shown to react with monomers such as propylene, isobutylene, and styrene, in the presence of Lewis acids, such as alkylaluminum halides, to give 1:1 alternating copolymers. The alternating copolymers were obtained when the concentration ratio of the Lewis acids to the acrylic esters was 0.9 and the concentration of IB was greater than the concentration of the acrylic esters (Hirooka et al, J. Polym. Sci. Polym. Chem., 11, 1281 (1973)). The metal halides
Coleridge Edward R.
Grolemund Mary E.
Martin Roxalana L.
Tucker Mark A.
Lipman Bernard
PPG Industries Onio, Inc.
Uhl William J.
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