Patent Publication Number: US-2004057793-A1

Title: Method for accelerating the drying rate of road marking compositions

Description:
FIELD OF INVENTION  
       [0001] The present invention relates to a process whereby the drying rate of road marking compositions is accelerated. More specifically, the present invention is a process whereby the drying rate of thermosetting and of solvent-based paint road marking compositions are accelerated by admixing such compositions with heated ceramic beads.  
       BACKGROUND OF THE INVENTION  
       [0002] Paved surfaces such as concrete and asphalt roads are commonly marked with stripes to visually denote road edges, vehicular lanes and stop lines. In the past, such pavement markings have comprised paint-like colored mixtures. For example, see U.S. Pat. No. 3,297,617 which discloses a coating slurry for use as a road marking material that may contain various pigments.  
       [0003] In U.S. Pat. No. 4,856,931 the colored paint road marking material additionally contains glass beads that have been scattered on the paint stripe while the paint is still tacky. The glass beads enhance the visibility of the road marking at night.  
       [0004] Numerous patents describe various solvent-based paint pavement marking compositions. For example, see U.S. Pat. Nos. 2,268,537; 2,330,843; RE 28,531; etc. Glass beads are used in these systems for the same purpose as described above. The beads are also applied to the paint surface while it is still semi-wet or tacky.  
       [0005] Because the above-mentioned solvent-based compositions contain volatile components, they are environmentally undesirable. A more acceptable stabilized aqueous dispersion paint useful for road marking purposes is disclosed in U.S. Pat. No. 2,879,171. It may contain glass beads as well.  
       [0006] Many of the prior art solvent-based paints used in road marking applications lack sufficient durability to offer any practical application in high traffic areas. Additionally, solvent-based paint road marking systems typically cure (or dry) when the solvent evaporates. The amount of time for this to occur depends on the type of solvent used and the amount of solvent in the composition. However, drying times of from 15 to 60 minutes are not unusual, which means that the road surfaces marked with such materials must be protected from traffic for relatively long periods.  
       [0007] The durability of pavement marking materials has been greatly improved in the past few years through the use of the non-solvent containing thermosetting (compositions that typically contain two or more liquid components that, when mixed, chemically react to cure (or dry) into a solid mass) or thermoplastic (compositions that are solid at ambient temperatures, but, when heated, liquify and are applied as heated liquids, which reform into solids when cool) polymers. For example, see U.S. Pat. No. 5,128,203.  
       [0008] Conventional thermosetting polymer-based pavement marking materials include alkyd-based compositions. Such compositions disadvantageously cure (dry) slowly. They also contain molecules that are susceptible to degradation, i.e., they have poor road life. Further, they contain solvents or drying oils (in order to obtain compositions that can be sprayed), which, as is the case for solvent-based paint road marking compositions are environmentally unacceptable. Finally, they have a tendency to change color, e.g., they yellow, on exposure to sunlight.  
       [0009] In addition to the above-mentioned alkyd-based systems, epoxide, and isocyanates in combination with polyamines or polyols have been utilized in a two part liquid system to provide polyepoxy, polyurea or polyurethane marking compositions.  
       [0010] While the epoxide art is very broad and encompasses adhesives, castings, potting compounds, etc., it is believed that the following references are illustrative of this art as it applies to the field of pavement marking materials: U.S. Pat. Nos. 4,088,633; 3,793,247; 3,658,728; 3,558,558; 3,468,830; 3,102,823; 2,943,953; etc.  
       [0011] While durability is improved with these abrasion-resistant molecules and color changes are minor, the handling of epoxide and isocyanate materials is challenging because of their moisture sensitivity and toxicity.  
       [0012] More recently, acrylate-based coating compositions have been employed in road marking applications. They provide a balance of stability and rapid cure (even at low temperature) but require the use of relatively low molecular weight ethylene-unsaturated compounds that have significant vapor pressure. They are therefore difficult to handle at high ambient temperatures.  
       [0013] While the road marking paints and thermosetting compositions are usually applied by spraying, in the case of the above polymer-based thermoplastic systems, a mobile extruder allows the molten material to be applied directly to the pavement surface where it gradually cools and hardens.  
       [0014] In a more exotic method, a flame-spray apparatus is used for application of a road marking material that is a polyamide condensation product, i.e., it is produced by condensing a polyamine and a polycarboxylic acid).  
       [0015] Just as in the solvent-based systems, night visibility of the thermoplastic or thermosetting materials is also improved by using glass beads. The preferred method for incorporating these glass beads is simply to drop them into the molten or liquid material after it is applied to the road and before it “drys” (cures or hardens by cooling). See for example U.S. Pat. No. 3,849,351 cited above. In one case heated glass beads have been sprayed in a reapplication process onto a thermoplastic road marking material that has lost its reflectivity because of traffic wear. See U.S. Pat. No. 5,039,557.  
       [0016] A large variety of patents disclose pavement marking tapes (U.S. Pat. Nos. 4,937,127; 5,053,253; 5,124,178; etc.) that typically includes a base sheet and an upper polymer-comprising sheet. Glass beads are imbedded in the polymer before it is cured. In use, the tape is fixed to the road surface with an adhesive.  
       [0017] While tapes are easy to handle and apply to road surfaces, they are noted for problems associated with adhesion to such surface. As such, they tend to move and even detach from the road surface.  
       [0018] Thus there exists a continuing need in the art for pavement marking compositions that can easily and safely be applied and handled without the need for expensive and unusual equipment and that can cure (dry) relatively quickly even at ambient temperatures. There also remains a need for road making compositions that are durable and can withstand high density traffic conditions.  
       SUMMARY OF THE INVENTION  
       [0019] A method for accelerating the drying rate of a ceramic bead-containing thermosetting road marking composition admixture when deposited onto a road surface is described. The method comprising heating ceramic beads to a temperature from about 100° to about 500° F. The heated ceramic beads are then admixing with a liquid thermosetting road marking composition, forming a substantially homogeneous admixture, before depositing the admixture of heated ceramic beads and thermosetting road marking composition onto said road surface. The substantially homogeneous admixture is then deposited on the road surface where it drys at an accelerated rate. 
     
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
     [0020] The above and further advantageous of the invention may be better understood by referring to the following description of the preferred embodiments of the present invention in conjunction with the accompanying drawings, in which:  
     [0021]FIG. 1 shows the percent decrease in time for initiation of the cure for admixed beads and epoxy resin versus Bead Type #1 glass bead concentration where the glass beads are at the temperatures of 150° F., 250° F. and 350 F°.  
     [0022]FIG. 2 shows the percent decrease in time for termination of the cure for admixed beads and epoxy resin versus Bead Type #1 glass bead concentration where the glass beads are at the temperatures of 150° F., 250° F. and 350 F°.  
     [0023]FIG. 3 shows the percent decrease in time for initiation of the cure for admixed beads and epoxy resin versus Bead Type #2 glass bead concentration where the glass beads are at the temperatures of 150° F., 250° F. and 350 F°.  
     [0024]FIG. 4 shows the percent decrease in time for termination of the cure for admixed beads and epoxy resin versus Bead Type #2 glass bead concentration where the glass beads are at the temperatures of 150° F., 250° F. and 350 F°.  
     [0025]FIG. 5 shows the percent decrease in time for initiation of the cure for admixed beads and epoxy resin versus Bead Type #3 glass bead concentration where the glass beads are at the temperatures of 150° F., 250° F. and 350 F°.  
     [0026]FIG. 6 shows the percent decrease in time for termination of the cure for admixed beads and epoxy resin versus Bead Type #3 glass bead concentration where the glass beads are at the temperatures of 150° F., 250° F. and 350 F°. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
     [0027] While a wide variety of ceramic (typically inorganic) materials and sizes of such materials can be used in the method and composition of the present invention, it is required that these materials be able to withstand heating to a temperature of from about 100° F. to about 500° F., preferably from about 150° F. to about 450° F., most preferably from about 250° F. to about 350° F. before being admixed with the thermosetting epoxide resin composition.  
     [0028] It should be noted that, as is amply illustrated in the FIGS.  1  thru  6 , the temperature at which the heated ceramic materials are admixed with the epoxy resin is critical for ensuring the maximum cure rate, i.e., the maximum rate of drying. The Figures show both time to initiation of the epoxy resin cure and time to termination of the epoxy resin cure. These parameters are important since they demonstrate the time required before a stripe of the material bear traffic after being applied to a pavement. Thus, and referring to these Figures, by adding heated glass beads to an epoxy resin system where the glass beads are at temperatures of 150° F. and below, the initiation time (FIGS. 1, 3 and  5 ) and the termination time (FIGS. 2, 4 and  6 ) for epoxy curing are not appreciably changed from that of the epoxy system that has no heated ceramic material added it. Compare the 150° F. line in each of these figures to the base or 0% change line which represents the epoxy system without heated glass beads. However, when such ceramic materials are added at 250° F. and at 350° F., the initiation time and termination time are dramatically diminished. While a further enhancement in drying rate (decrease in initiation and termination time) can be expected at even higher temperatures then those shown in the FIGS.  1  thru  6 , it should be noted that admixing ceramic materials with the epoxy resin systems where such ceramic materials are heated up to or over the flash point of the epoxy system is not advisable and can result in severe thermal degradation and/or in combustion of the organics in the epoxy mixture. Of course, the flash point of the epoxy varies from epoxy system to epoxy system depending of the components used in the formulation. It is also a requirement of the present invention that such ceramic materials not cause any appreciable degradation of the chemical components of the road marking materials.  
     [0029] The ceramic materials of use in the present invention may be any shape, such as flakes, pebbles, sand, particles of aluminum oxide, zirconium or glass. Particles of glass are preferred, particularly spherical glass beads that have a sieve size of from about 10 to about 250 (U.S. Sieve Series Sieves). Such glass beads may be those conventionally ones manufactured such as quartz, soda lime, borosilicate, phosphosilicate, aluminosilicate and aluminoborate glasses. Especially preferred are spherical soda lime glass beads having a diameter of about 0.18 mm. Such glass beads may also contain doping materials, e.g., the lanthanide elements, which allow them to fluoresce or photoluminesce in the proper lighting condition. See for example U.S. Pat. No. 3,459,673 incorporated herein by reference as one method used for the manufacture of such glasses.  
     [0030] These ceramic materials are typically used in the compositions of the present invention at concentrations as high as 2 parts ceramic to 1 part epoxy resin, although lesser ratios, e.g, 1:1 to 0.10:1 may also be used.  
     [0031] One component of the thermosetting epoxy resin of use in the present invention is an epoxide polymer. Such polymer is typically a polyether manufactured by the condensation of epichlorohydrin with the a polyhydric phenol, e.g., when the phenol is diphenylpropane, the epoxide formed is  
                 
 
     [0032] Briefly, the reaction of the oxirane ring of epichlorohydrin with the polyhydric alcohol has been studied extensively and is well understood. The ring readily opens when attacked by a compound having available unbonded electrons, such as the oxygen atom in the polyhydric phenol. The ring opening of this first reaction causes formation of a chain that terminates in an oxirane ring, i.e., the C 2 H 4 O group, resulting in a second and subsequent further ring opening reactions and chain extension. Without more, a typical epichlorohydrin diphenylpropane reaction produces a chain where x in the above formula is about 15.  
     [0033] When the compound attacking the oxirane ring not only is an oxygen atom in the polyhydric phenol as described above, but also is that from a primary or secondary amine, a further transformation occurs. Obviously, chain extension can occur with the first proton being removed from the primary or secondary amine or from the —OH group of the polyhydric phenol. However, because there remains an active site on the primary amine, the chain extended polymer can continue to react at the amine site resulting in a cross-link. Thus, when primary amines are added to a low molecular weight polyether formed from epichlorohydrin and a polyhydric phenol both chain extension and cross-linking occurs and a polyether\amine copolymer is formed. In such a case, the amine additive acts as a hardener or co-reactive. Such amine hardener or co-reactant is a second component of the thermosetting epoxy resin of the present invention.  
     [0034] Other materials may be also be present, e.g., adhesion promoters, such as trimethoxysilane, triethoxysilane, etc., organic or inorganic fillers, pigments, etc. Reflective fillers, in addition to the heated ceramic materials, which include reflective materials, may also be added in the process of the present invention.  
     [0035] The curable polyether (or epoxide) to which the amine hardener is added is referred to in various ways. It some cases it may be called an epoxide resin, when in fact it is a prepolymer illustrated by the polyether shown above. As already noted, it is this prepolymer that is capable of being “cured” or chain extended and cross-linked with the addition of a composition comprising a primary amine.  
     [0036] In order to effectively produce a road marking composition in accordance with the method of the present invention it is first necessary to intimately blend the above discussed curable epoxide resin and the amine curing agent, i.e., the hardener (preferably in the liquid form) immediately before admixture with the heated ceramic beads. Typical ratios of resin to hardener are from about 3.0 parts of epoxide to about 1.0 part or hardener. However, depending on the rate of hardening (cure rate) desired, ratios of 2.0 to 1.0 or 1.0 to 1.0 may be used. It is preferable to have the epoxide and the hardener at a temperature above ambient to enhance the cure rate of the final combination when on the pavement surface, typically about 70° to about 200° F. The temperature of the components also controls the viscosity of each of the components before and during their mixing. An ideal viscosity for premixed epoxide resin and amine hardener are in the range of 6,000 to 9,000 cps at about 125° F.  
     [0037] It should be understood that the epoxide resin and the amine co-reactive are used as 100% solids, i.e., there are no volatile solvents or carriers present.  
     [0038] Thus, the method of the present involves:  
     [0039] a—supplying to a point prior to the application upon the pavement surface the aforementioned heated curable epoxy resin;  
     [0040] b—supplying to a point prior to the application to the pavement surface the aforementioned heated curing agent;  
     [0041] c—supplying to a point prior to the application to the pavement surface the aforementioned heated ceramic beads  
     [0042] wherein an intimately, i.e., substantially homogeneous, mixture of the heated curable epoxy resin, the heated amine curing agent and the heated ceramic beads occurs;  
     [0043] d—applying the intimately mixed components a, b and c to the pavement surface; and  
     [0044] e—permitting the intimately mixed components to cure in situ on the pavement surface.  
     [0045] As briefly discussed herein, heated ceramic beads are intimately mixed with the heated epoxy resin and heated amine curing agent before application to the pavement surface, i.e., they may be premixed as by simple addition with stirring or they may be admixed by directing a sprayed stream of heated ceramic material into a sprayed stream of a heated epoxy resin (with hardener). In this manner, the ceramic beads and cured epoxide form a substantially homogeneous mixture prior to being placed (by hot spraying or by extrusion of the hot admixture) on the surface of the pavement. The ceramic beads are firmly held in place in the cured resin matrix and are exposed as the road surface wears. This is particularly advantageous in a further embodiment of the present invention, wherein retroreflective materials are applied (for example by sprinkling) onto the surface of the epoxide admixture as an over coating before the epoxy is fully cured. These top-coated retroreflective materials (such illustrated by glass beads) eventually are removed thru traffic wear resulting in the exposure of the ceramic materials that are contained in the cured resin matrix.  
     [0046] It should be noted that when heated ceramic materials are projected, e.g. by spraying, onto the epoxy road marking material after it is applied to the pavement surface, no accelerated cure takes place (see Table 2).  
     [0047] Objects and advantages of this invention are further illustrated in the following Examples, but the particular materials and amounts recited in these Examples as well as process conditions and other details should not be construed to unduly limit the scope of this invention.  
     EXAMPLES  
     [0048] The following components were used in the Examples:  
     [0049] The epoxy resin system employed in these Examples is—Epoplex LS50 Yellow, which comprises the following:  
                                               % By Weight                                            Epoxy compound, comprising           Diglycidyl ether of Bisphenol A   &lt;60.00       Lead (As lead sulfochromate)   &lt;20.00       Trimethylolpropane Triacrylate   &lt;20.00       Chromium (As lead sulfochromate)   &lt;10.00       Aluminum Silicate, Synthetic   &lt;10.00       Antimony (3+) Oxide   &lt;10.00       Flash Point:   &gt;200° F.       Hardener compounds - Epoplex LS50 B, comprising       4-Nonylphenol, Branched   &lt;50.00       Diethylenetriamine   &lt;30.00       Bisphenol A   &lt;20.00       Manufacturers additive   &lt;20.00       Flash Point:   &gt;236° F.                  
 
     [0050] All glass beads used were soda lime glass CAS# 65997-17-3. Their size is as follows:  
                              Bead Type #1                             Gradation               Sieve Size   % Retained By Weight                                          80   0.0           100   0.0           120   44.7           140   37.0           170   12.2           Pan   6.1                      
 
     [0051]                                                   Gradation               Sieve Size   % Retained By Weight                                        Bead Type #2                              20   0.0            30   10.6            50   72.5           100   15.9           Pan   1.1                 Bead Type #3                             12   0.0           14   0.2           16   11.5           18   64.6           20   22.1           25   0.8           Pan   0.9                        
     [0052] Test Procedure  
     [0053] The components of the epoxy system were heated separately in a 75±5° F. water bath. 20 mL of the epoxy resin and 10 mL of hardener were transferred by syringe into a thermocouple equipped reaction vessel. To this was added, with mixing, heated glass beads in the amount and at the temperature shown in Table 1. Temperature of the mixed components was followed and recorded on a Digital Temperature Controller. Reaction was considered as started when the slope of the temperature of the mixture with respect to time changed by 10° F. The slope of the exotherm start and exotherm end, an indication of the rate of the reaction, was followed visually. The reaction was considered complete (the termination time) when no further exotherm was detected, i.e., when the temperature did not change for at least 3, 10 second measurements.  
     [0054] The following attached Table 1 shows the cure rate of the illustrative epoxy systems admixed with various sized glass beads. The cure initiation and termination is based on the exotherm developed as the components of the system react. All temperatures are in degrees F.  
     [0055] Table 2, attached, is a comparative example showing: the cure rate of a pure epoxy system (epoxy resin plus hardener); the same epoxy system, applied to a substrate as a stripe 12″×4″ and 120 mils in thickness, where 30 grams of heated glass beads are sprayed onto and into the stripe; and the same epoxy system where 30 grams of heated glass beads are admixed in accordance with the present invention and the mixture applied as a 12″×4″ and 120 mil stripe.  
               TABLE 1                          Pure Epoxy (no glass bead added)                             Initiation (sec)   Termination (sec)                       200   300                             Epoxy admixed with glass beads                                 5.0 grams   10.0 grams   15.0 grams                                             Initia-   Termi-   Initia-   Termi-   Initia-   Termi-       Bead   tion   nation   tion   nation   tion   nation       Temperature   (sec)   (sec)   (sec)   (sec)   (sec)   (sec)                                                 Bead Type #1                               150 F.   190   290   200   310   210   320       250 F.   170   270   130   230   120   220       350 F.   130   210   60   170   50   150       Bead Type #2       150 F.   220   310   220   330   220   320       250 F.   180   280   150   240   140   260       350 F.   150   250   90   190   70   160       Bead Type #3       150 F.   220   320   210   300   200   310       250 F.   160   270   140   240   140   240       350 F.   140   230   90   170   70   170                                  
 
     [0056]                           TABLE 2                                   Initiation (sec)   Termination (sec)                                                        Pure Epoxy*   5   8           Heated Bead Spray On**   5.5   8.5           Heated Bead Admix***   2.5   5.5