Coating processes – With post-treatment of coating or coating material – Chemical agent applied to treat coating
Reexamination Certificate
2000-03-30
2002-01-08
Beck, Shrive P. (Department: 1762)
Coating processes
With post-treatment of coating or coating material
Chemical agent applied to treat coating
C427S337000, C427S340000, C524S431000, C524S430000
Reexamination Certificate
active
06337106
ABSTRACT:
This invention relates to a method of producing a two-pack or multi-pack fast-setting waterborne paint composition, particularly a traffic paint, which has a reducing component in one pack and an oxidizing component in the other pack of the two-pack paint composition. The present invention also relates to the two-pack waterborne paint composition produced in accordance with the method.
One of the many important features of coatings, particularly road markings or traffic paints is the speed at which they dry on the surface of a particular substrate after application. For instance, the drying speed of a traffic paint dictates the length of disruptions to road traffic in order to be able to apply the paint and allow the paint to dry properly. The trend is to demand shorter disruptions by using faster-drying (faster-setting) paint.
Conventional fast-drying coatings or paints compositions are based on organic polymeric resins (also called binders) dissolved, suspended or otherwise dispersed in relatively low-boiling organic solvents. Low-boiling organic solvents evaporate rapidly after application of the paint on the road to provide the desired fast drying characteristics of a freshly applied road marking. However, in addition to releasing organic solvents into the environment, this type paint formulation tends to expose the crew to the vapors of the organic solvents. Because of these shortcomings and increasingly stringent mandates from governments and communities, it is highly desirable to develop more environmentally friendly coatings or paints while retaining fast drying properties and/or characteristics.
A more environmentally friendly coating uses water based, i.e. waterborne, rather than organic solvent based polymers or resins (binders). Mainly due to a combination of water's high boiling point, high latent heat of vaporization, high polarity and hydrogen bonding, the drying times of waterborne paints or coatings are generally longer than those exhibited by the organic solvent based coatings.
WO 94/29391 discloses the use of a waterborne paint based on (a) a unique type of aqueous dispersion polymer as described in EP-B-0-322-188 and EP-A-409459, and (b) application of a water-soluble acid to the freshly applied paint. In view of the chemistry involved, it appears to be only useful for acid-coagulatable paint formulations.
U.S. Pat. No. 5,403,393 describes water-based coating compositions which comprise an aqueous anionically stabilized dispersion of water-insoluble polymer prepared by either emulsion polymerization or mechanical emulsification, inorganic pigment dispersed with anionic polymers, salt, or soaps and the propionic acid salt of calcium. The coatings upon application quickly develop resistance to being washed out by inadvertent precipitation.
It has been unexpectedly discovered that a two-pack or multi-pack waterborne quick-drying paint composition, which contains a binder, can be produced by placing a reducing component in one “pack” and an oxidizing component in the other “pack” and then mixing the two packs upon application on a surface of a substrate, or at a suitable time prior to the application. This pair of components is referred to herein as a “redox couple.” The term “two-pack” is used herein to mean, as understood by those skilled in the art, that a paint composition consists of two separate parts or packs, which are combined either during or shortly before application of the paint on the surface. It is also within the scope of the present invention to use a multi-pack composition. The binder may be in either or both packs in a two pack composition, depending on the chemical and physical properties and compatibilities of the binder, the oxidizing component and the reducing component selected. Alternately, the binder may in a third pack in a multi-pack composition.
The present invention can be used in many coating, painting or marking applications. For instance, the invented method and composition can be used for traffic paints, road markings, house paints, maintenance coating for exterior or interior surfaces of buildings, walls, roof, ceiling, and other structures. Other applications include coating metal surfaces of a variety of objects such as signs, boats, cars, etc. All the surfaces may already have one or more layers of existing coating or paint. All the surfaces may also have a primer.
When discussing road markings or traffic paints, the term “road” is used herein as a generic term. It includes any indoor or outdoor solid surface which is or may be exposed to pedestrians, moving vehicles, tractors, other moving objects or aircrafts continuously, constantly or intermittently. Some non-limiting examples of a “road” include highways, streets, driveways, sidewalks, runways, taxiing areas, tarmac areas, parking lots, rooftops, indoor floors (such as in a shopping mall), etc. The surface material may be masonry, tar, asphalt, resins, concrete, cement, stone, stucco, tiles, polymeric materials, wood and combinations thereof. It is also within the scope of the invention to apply such a two or multi-component waterborne coating over another fresh or aged coating or marking already applied on the surface. There also may be a primer on the surface.
The terms “fast drying”, “faster drying”, “rapid setting”, “fast-setting”, “fast drying property”, “increased drying” and “accelerated drying” are used interchangeably herein to mean that a two or multi-component composition prepared and used in accordance with the method of the present invention has a drying time which is shorter than that of a composition used without using the oxidizing component/reducing component composition. Drying speed is typically measured by “dry-through time” in accordance with a standard testing method, ASTM D1640 with the exception that no thumb pressure is used. For the present invention, it is preferred that the dry-through time of the paint or coating composition(s) is one hour or less at 25° C. and 90% RH (relative humidity).
In the present invention, there are several general requirements for both the oxidizing component and the reducing component. First, the oxidizing component and the reducing component must be compatible with other compounds and materials present in the two or multi packs. This compatibility requirement may limit which compound may have to go with the oxidizing component in one pack, and which may have to go with reducing component in the other pack. Second, both components must be relatively stable in the individual packs under storage conditions. This would allow the two separate packs to have reasonable shelf lives prior to use. Third, in order to be useful for as many paint colors as possible, it is preferred that both components and their reaction products are not highly colored. Fourth, the reaction between the oxidizing component and the reducing component should be completed within a relative short period of time, particularly for a fast-drying paint composition. A period of less than five minutes is preferred within the scope of the present invention. Depending on the mode of application, a very short reaction time, 0.1 seconds to 60 seconds, may or may not be preferred because the finished coating or marking may not possess the desired finish and/or other properties.
A characteristic of a suitable reducing component is that they can form ions of a valence state of at least +1, preferably +2 or higher, upon being oxidized. Another preferred characteristic of a suitable reducing component is that they can form, upon being oxidized, ions of a higher positive charge than those, if any, found in the oxidizing component. The reducing components may be organic, inorganic, organometallic or combinations thereof. Examples of a suitable inorganic reducing component include, but are not necessarily limited to, metal-containing compounds such as elemental metal, ferrous compounds, cobaltous compounds, stannous compounds, and mixtures thereof. Some specific reducing components include elemental aluminum, ferrous sulfate, cobaltous chloride, cob
Beck Shrive P.
Crockford Kirsten A.
Rohm and Haas
Vouros James G.
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