Road structure – process – or apparatus – Process
Reexamination Certificate
2000-05-26
2002-07-02
Hartmann, Gary S. (Department: 3673)
Road structure, process, or apparatus
Process
C427S137000
Reexamination Certificate
active
06413011
ABSTRACT:
The present invention relates to a method for producing fast-drying multi-component waterborne coating compositions, particularly traffic paints or road markings. The invention also relates to the compositions of fast-drying multi-component waterborne coatings, particularly traffic paints or road markings. Used herein, the term “multi-component” refers to traffic paints having two or more components applied to a substrate in one or more steps.
One of the many important features of coatings in general, and road markings or traffic paints in particular, 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 the period of disruption to road traffic during application of the paint to road surfaces, and subsequent drying. The trend is to demand shorter and shorter disruptions of traffic flow, meeting this demand by using fast-drying paint. Used herein, the terms “coating” and “paint” will be used interchangeably and referred to as a general class including traffic paints and road markings. In addition, the terms “traffic paint” and “road marking” are used interchangeably herein.
Solvent-based fast-drying coatings are based on organic polymeric resins (also frequently called binders) dissolved, suspended or otherwise dispersed in relatively low boiling organic solvents. Low-boiling volatile 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 volatile organic solvents into the environment, spreading of the paint formulation tends to expose the 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 coatings or paints while retaining fast-drying properties and/or characteristics.
More environmentally friendly coating use water based, i.e., waterborne, rather than solvent based polymers or resins. Coating formulations, both solvent based and waterborne, include binder polymers. The term binder polymer used herein refers to polymers that are included in the coating composition and that augment or participate in film formation and in the composition of the resultant film. Binder polymers typically have 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 (Tgs) as low as −40° C. Used herein, “Tg” is an abbreviation for glass transition temperature. The glass transition temperature, Tg, of a polymer is the temperature at which a polymer transitions from a rigid, glassy state at temperatures below Tg to a fluid or rubbery state at temperatures above Tg. The Tg of a polymer is typically measured by differential scanning calorimetry (DSC) using the mid-point in the heat flow versus temperature transition as the Tg value. A typical heating rate for the DSC measurement is 20° C. per minute.
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 waterborne paints or coatings 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 coatings are applied. A waterborne paint 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;) traffic markings. Long drying times severely limit the desirability of using waterborne paints, particularly traffic paints and road marking paints because of longer traffic disruptions.
In an attempt to produce waterborne coating compositions with shorter drying times, i.e., “fast-drying” coatings, methods utilizing salt, or acid, or combinations thereof to induce coagulation have been devised, as have pH sensitive binder systems.
EP-B-0,409,459 discloses an aqueous coating composition including an anionically stabilized emulsion polymer having Tg no lower than 0° C., a polyamine functional polymer, and a volatile base in an amount such that the composition has a pH where substantially all of the polyamine functional polymer is in a non-ionic state, and wherein more than 50% by weight of the polyamine functional polymer will be soluble at pH values of 5 to 7 on evaporation of the volatile base. In the non-ionic state (i.e., deprotonated), polyamine interaction with the anionically stabilized emulsion and any other anionic ingredients which may be present in the composition is eliminated. The volatile base must be volatile enough to be released under air drying conditions. In the absence of the volatile base, the protonated amine moieties interact with the anionic ingredients to destabilize the coating composition. U.S. Pat. Nos. 5,804,627, 5,824,734, and U.S. Pat. No. 5,922,398 all disclose coating compositions having latent instability that may be triggered by adjustment of some property such as pH.
U.S. Pat. No. 5,947,632 discloses waterborne coating compositions including a number of general categories of materials including talc, hollow sphere polymer, a solid polymer (e.g., ion exchange resin beads in acid, sodium or potassium form) and inorganic compounds (e.g., inorganic superabsorbent gel, Sumica gel). These materials share the characteristic that they speed the drying of coatings when applied either in the same first step with the waterborne binder, or in a subsequent step. U.S. Pat. No. 5,947,632 also discloses incorporation of glass beads into the waterborne coating compositions. Glass beads impart retro-reflective characteristics to traffic paints and traffic markings, and can also serve as fillers for coating compositions. Other additives such as anti-skid material are also disclosed
As used herein, the term “absorber” refers to the general class of materials that includes hollow sphere polymer, ion exchange resin beads (e.g., in acid form, in base form, in salt form, in partially neutralized form, or in mixed salt form), absorbent inorganic compounds (e.g., inorganic superabsorbent gel, Sumica gel), including talc, molecular sieves, non-porous carbonaceous materials, porous carbonaceous materials, and superabsorbent polymers (abbreviated SAP or SAPs herein).
The coating compositions of U.S. Pat. No. 5,947,632 do provide shorter drying times. These compositions are based on aqueous binder compositions that are defined herein as “fast-drying aqueous binder compositions”. These “fast-drying aqueous binder compositions” include specially modified binder polymers. Such binder polymers may be of a single type in which the polymer chains bear one or more kinds of specialized functionality designed to provide destabilization of the coating composition upon application to a substrate. Alternatively, the binder polymers may be of more than one type, each type bearing a particular kind of specialized functionality. In both of these cases, binder polymer that bears no such specialized functionality may also be present. For example, a typical fast-drying aqueous binder composition may include: a film forming binder polymer that bears no functionality designed to accelerate drying rate; one or more polymers bearing such functionality capable of inducing destabilization of the composition; and other ingredients designed to interact with the polymers bearing such functionality to bring about destabilization and, hence, accelerated drying upon application to a substrate. In a more specific example, a film forming polymer may be stabilized in water by an anionic surfactant. Tha
Hermes Ann Robertson
Sanfilippo Angelo
Schall Donald Craig
Sobczak Jeffrey Joseph
Hartmann Gary S.
Rohm and Haas Company
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