Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Processes of preparing a desired or intentional composition...
Reexamination Certificate
2002-03-11
2004-05-11
Toomer, Cephia D. (Department: 1714)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Processes of preparing a desired or intentional composition...
C106S031040, C427S136000, C427S137000
Reexamination Certificate
active
06734226
ABSTRACT:
The present invention relates to storage-stable fast-drying multi-component aqueous coating compositions and fast-drying coatings made therefrom.
Used herein, the term “multi-component” refers to aqueous coating compositions having two or more components applied to a substrate in one or more steps.
One of the many important features of coating compositions is the speed at which they dry on the surface of a given substrate after application. For instance, the drying speed of a traffic paint dictates the length of the period of disruption to road traffic during application of that paint to road surfaces, and subsequent drying. The trend is to demand shorter and shorter disruptions of traffic flow, and to meet this demand by using faster drying coating compositions.
Solvent-based fast-drying coating compositions are based on organic polymeric binders dissolved, suspended or otherwise dispersed in relatively low-boiling organic solvents. Low-boiling volatile organic solvents evaporate rapidly after application of the coating composition on the road to provide the desired fast drying characteristics of a freshly applied road marking. However, in addition to releasing volatile organic solvents into the environment, this type of paint formulation tends to expose workers to the vapors of the organic solvents. Because of these shortcomings and increasingly stringent environmental mandates from governments and communities, it is highly desirable to develop more environmentally friendly coating compositions while retaining fast drying properties and/or characteristics.
A more environmentally friendly coating composition uses water based, i.e., aqueous, rather than solvent based, polymers or resins. Coating formulations, both solvent based and aqueous, include binders. The terms “binder” and “binder polymer” used herein refer to polymers that are included in the coating composition and that participate in film formation, becoming part of the resultant film. Binder polymers typically have glass transition temperature (Tg) values in the range −10° C. to 70° C. because those having Tg values below −10° C. tend to have poor resistance to dirt pick-up and those having Tg values above 70° C. usually display diminished ability to form films. In certain applications, however, the lower limit for Tg can be even lower than −10° C. For example, the binder polymers used in roof coatings can have glass transition temperatures as low as −40° C. Primarily due to a combination of high boiling point, high latent heat of vaporization, high polarity, and strong hydrogen bonding of water, drying times of the coatings formed by application of an aqueous coating composition to a substrate surface are generally longer than those exhibited by the organic solvent based coatings. The drying time strongly depends on the relative humidity of the atmosphere in which the coating compositions are applied. An aqueous coating composition may take several hours or more to dry in high humidity. The problem of retarded drying rate is especially aggravated for thick film (greater than about 500 &mgr;) coatings. Long drying times severely limit the desirability of using aqueous coating compositions, particularly traffic paints, the drying times of which directly effect the length of traffic disruptions.
U.S. Pat. No. 5,804,627 discloses methods of producing fast drying coatings on the surfaces of substrates. The methods include applying to those surfaces an aqueous coating composition including an anionically stabilized emulsion polymer having a Tg greater than about 0° C., a polyamine functional polymer having from about 20% to about 100% of the monomer units by weight containing an amine group, and an amount of volatile base sufficient to raise the pH of the composition to a point where essentially all of the polyamine functional polymer is in a non-ionic state. During and after application of the aqueous coating composition to the surface of a substrate, the volatile base evaporates with the result that the anionically stabilized polymer particles are destabilized by protonated polyamine functional polymer, thereby accelerating the drying rate of the coating. Although this system affords improvement in drying speeds, more efficient polyamine functional polymers are desired, imparting, for example, equivalent drying speed at reduced levels in coating compositions.
WO 96/22338 discloses a fast drying aqueous coating composition which derives its fast drying characteristic from a mechanism similar to that of U.S. Pat. No. 5,804,627, except that the polyamine functional polymer is poly(ethyleneimine), also referred to herein as PEI. PEI is formed by polymerization of ethylene imine, a highly carcinogenic monomer. The nitrogen content of PEI is higher than that of the other conventional polyamine functional polymers, and this higher nitrogen content offered the promise of higher drying efficiency. Unfortunately, the highly carcinogenic ethylene imine may be present, to some extent, in coating compositions containing PEI, so that such compositions are to be avoided for environmental reasons. Extensive steps must also be taken during manufacture of PEI to prevent exposure of workers to ethylene imine. Moreover, although the promise of PEI in fast drying aqueous coating compositions is that its high level of nitrogen, present as amino groups in the backbone of PEI, will translate into improved drying rates, that promise cannot be fully realized for at least two reasons. First, as the volatile base evaporates from the coating, acidic substances become available to react with the amino groups, yet a significant portion of those backbone amino groups will be less basic and be less accessible to the acidic substances due to the high degree of steric hindrance from adjacent portions of the backbone of the polymer. As a result, the formation of ammonium ions, an essential step in the destabilization of the coating composition, does not occur for all of the amino groups of PEI. Second, and perhaps more importantly, a substantial portion of the ammonium groups that do form from such reaction are not fully accessible for interaction with, and subsequent destabilization of, anionically stabilized emulsion polymers.
We have, surprisingly, found that vinylamine polymers are highly efficient at producing storage stable, fast-drying aqueous coating compositions when those compositions include anionically stabilized binder polymer and volatile base. Unlike the amino groups of PEI, the amino groups of vinylamine polymers are fully available for protonation after evaporation of the volatile amine with the result that vinylamine polymers are more efficient (i.e., give more rapid drying at equal concentrations) than PEI in spite of equal nitrogen content.
One aspect of the present invention relates to a storage stable, fast drying aqueous coating composition, said composition comprising:
(a) an anionically stabilized binder polymer;
(b) a vinylamine polymer having from 20% to 100% by weight of amine functional units, based on total weight of said vinylamine polymer; and
(c) an amount of volatile base sufficient to raise the pH of said composition to a point where essentially all of the amine groups of said vinylamine polymer are in a non-ionic state.
A second aspect of the present invention relates to a coating on the surface of a substrate, said coating comprising:
(a) an anionically stabilized binder polymer; and
(b) a vinylamine polymer having from 20% to 100% by weight of amine functional units, based on total weight of said vinylamine polymer.
A third aspect of the present invention relates to a method of producing a coating on the surface of a substrate, said method comprising the steps of:
(i) applying to said surface a fast drying aqueous coating composition comprising:
(a) an anionically stabilized binder polymer;
(b) a vinylamine polymer having from 20% to 100% by weight of amine functional units, based on total weight of said vinylamine polymer; and
(c) an amount of volatile base sufficient to raise the pH of said
Rohm and Haas Company
Toomer Cephia D.
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