Pavement marking composition

Details Pavement marking composition Pavement marking composition

2001-06-13

2003-02-18

Short, Patricia A. (Department: 1712)

Synthetic resins or natural rubbers -- part of the class 520 ser

Synthetic resins

Mixing of two or more solid polymers; mixing of solid...

C525S452000, C525S454000, C525S920000, C523S172000, C427S137000

Reexamination Certificate

active

06521718

ABSTRACT:

FIELD OF THE INVENTION
This invention relates to compositions comprising polymeric binder and optional reflective elements for use in marking trafficable surfaces.
BACKGROUND OF THE INVENTION
Various striping or marking compositions have been used on roads, highways, parking lots, and recreational trails for many years. Such compositions are typically used to form stripes, bars, and other markings for the delineation of lanes, crosswalks, parking spaces, symbols, legends, and the like. The compositions are often applied by spray coating (i.e., painting) a pavement surface.
Conventional liquid pavement marking compositions include alkyd-based compositions and epoxy-based compositions. Such compositions typically dry slowly and contain chemical linkages (e.g., ester linkages) that are susceptible to degradation (e.g., by hydrolysis), leading to poor weatherability upon application to pavement surfaces. The compositions also typically require the rise of organic solvents or drying oils (in order to obtain sprayable viscosities) or the use of drying accelerators, which can lead to discoloration.
In addition to alkyd- and epoxy-based compositions, isocyanates plus polyethers or polyamines have been utilized as two-part compositions to provide polyurethane- or polyurea-based pavement markings. Such compositions have provided improvements in drying times, weatherability, and resistance to discoloration (relative to alkyd- and epoxy-based compositions), but require the handling of moisture sensitive, potentially hazardous isocyanates.
Numerous other pavement marking compositions have been developed to get faster drying times by using heated application of materials to road surfaces. Also, waterborne coatings based on acrylic lattices and epoxy resin emulsions have been suggested for use in pavement marking. Such compositions have the advantages of low volatile organic content and one-part coating application but are not yet sufficiently durable for long term road presence and retained reflectivity performance. The former also require the use of
Acrylate-based coating compositions have provided a balance of stability and fast cure (even at low temperatures) but have required the use of low molecular weight, ethylenically unsaturated compounds that have significant vapor pressures and are thus somewhat difficult to handle at higher ambient temperatures. Preformed pavement marking sheets or tapes have been used for their ease of handling but often exhibit adhesion problems, especially at road intersections.
Thus, there exists a continuing need in the art for pavement marking compositions that can be easily and safely handled and applied without the need for expensive equipment, that can be quickly cured even at ambient temperatures, and that are durable under a wide range of weather and use conditions.
SUMMARY OF THE INVENTION
Briefly, in one aspect, this invention provides a pavement marking composition comprising (a) a polyfunctional ethylenically unsaturated polymer selected from the group consisting of polyfunctional ethylenically unsaturated polyurethanes, polyureas, polythiocarbamates, polythiocarbamateurethanes, polythiocarbamateureas, and polyurethaneureas comprising at least one chain extender-derived segment and at least one polycarbonate, polyether, or polyester segment; and (b) at least one ethylenically unsaturated monomer. (As used herein, the term “chain extender” refers to a polyfunctional, molecular weight increasing co-reactant.) Preferably, the polyfunctional polymer comprises a least one polycarbonate or polyester segment, and the ethylenically unsaturated monomer is a (meth)acryloyl-functional monomer having a molecular weight greater than about 150. Most preferably, the composition further (comprises a curing system, filler, pigment, and/or reflective elements.
Relative to known liquid pavement marking compositions, the pavement marking composition of the invention provides durably bondable pavement markings that surprisingly exhibit both improved cold impact (snow plow) resistance and improved wear resistance, even though these characteristics are generally difficult to simultaneously achieve and/or enhance. The composition can easily applied (e.g., by hand using a trowel or a drawbox or by spraying), without the need for expensive and/or bulky heating equipment, and cures in a reasonable amount of time at any of a wide range of commonly-encountered temperatures. Furthermore, since the composition does not contain either solvent or reactive isocyanate (nor, in preferred embodiments, low molecular weight monomer), it can be safely handled with reduced inhalation risk and environmental hazard.
In other aspects, this invention also provides a pavement Marking comprising the cured pavement marking composition of the invention, a trafficable surface bearing the pavement marking, and a process for marking or for applying a pavement marking.
DETAILED DESCRIPTION OF THE INVENTION
Polyfunctional ethylenically unsaturated polymers suitable for use in the composition of the invention are those polyfunctional ethylenically unsaturated polyurethanes, polyureas, polythiocarbamates, polythiocarbamateurethanes, polythiocarbamateureas, and polyurethaneureas that comprise at least one chain extender-derived segment and at least one polycarbonate, polyether, or polyester segment. The polymers can be prepared by the reaction of at least one polyisocyanate; at least one hydroxyl-, thio-, or secondary amino-polyfunctional polycarbonate, polyether, or polyester; at least one isocyanate-reactive polyfunctional chain extender; and at least one ethylenically unsaturated monomer heaving additional functionality, e.g., hydroxyl or amine, that is reactive with isocyanate.
Useful polyisocyanates include aliphatic, alicyclic, and aromatic diisocyanates, and mixtures thereof. A number of such diisocyanates are commercially available. Representative examples of suitable diisocyanates include hexamethylene diisocyanate (HDT), trimethyl hexamethylene diisocyanate (TMHDI), m- and p-tetramethylxylene diisocyanate (TMXDI), diphenylmethane diisocyanate (MDT), napthalene diisocyanate (NDI), phenylene diisocyanate, isophorone diisocyanate (IPDI), toluene diisocyanate (TDI), bis(4-isocyanatocyclohexyl) methane (H
12
MDI), and the like, and mixtures thereof. Useful polyisocyanates also include derivatives of the above-listed monomeric polyisocyanates. These derivatives include, but are not limited to, polyisocyanates containing biuret groups, such as the biuret adduct of hexamethylene diisocyanate (HDI) available from Bayer Corp., Pittsburgh, Pa. under the trade designation Desmodur™ N-100, polyisocyanates containing isocyanurate groups, such as that available from Bayer Corp., Pittsburgh, Pa. under the trade designation Desmodur™ N-3300, as well as polyisocyanates containing urethane groups, uretdione groups, carbodiimide groups, allophonate groups, and the like. If desired, small amounts of one or more polyisocyanates having three or more isocyanate groups can be added to effect a degree of crosslinking. Preferred polyisocyanates include aliphatic diisocyanates and derivatives thereof, with IPDI being most preferred.
Useful polycarbonates, polyethers, and polyesters include those which have an equivalent weight in the range of about. 250 to about 5000 (preferably from about 400 to about 2,500 more preferably from about 500 to about 1,500) and which have an average secondary amino-, thio-, and/or hydroxyl-functionality of about 2.0 to about 3.0 (preferably of about 2.0 to about 2.8, more preferably of about 2.0 to about 2.5). A number of such functional polymers are commercially available. Diols are preferred due to their availability, low cost, and stability. Representative examples of polymers that are useful (when functionalized in the foregoing manner) include aliphatic polycarbonates such as polyestercarbonates and polyethercarbonates; polyethers such as polyethylene glycol, polypropylene glycol, polybutylene glycol, and polytetrahydrofuran; polyesters such as polycaprolactones, polybutylene adipate,

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