Surface Marker Strip and Methods for Providing Improved Integrity and Adhesion to Roadways and the Like

The invention will now be described with reference to the accompanying drawings,

FIG. 1 of which is a cross-section through a single ply rubber sheeting prior to embossing the protuberances or ridges;

FIG. 2 is a cross-section through a single ply rubber sheeting after embossing the protuberances or ridges;

FIG. 3 is a cross-section through a double ply rubber sheeting prior to embossing the protuberances or ridges;

FIG. 4 is a cross-section through a double ply rubber sheeting after embossing the protuberances or ridges; and

FIGS. 5 and 6 are cross-sections similar to FIGS. 2 and 4 after the protuberances have been formed and showing retro-reflection glass microsphere distribution on the surfaces.

Referring to the drawings, the base material 1 of the marker strip or tape is shown as comprised of a non-vulcanized rubber mixture in sheet form which lacks memory and is easily deformed because it is soft and exhibits cold flow characteristics. It is comprised of a rubber polymer such as acrylonitrile-butadiene in a non-vulcanized state. In addition reinforcing fibers, a pigment, and other processing aids are also included. An example of a typical formulation is listed in Table I in which the reinforcing fiber is given as wood pulp-like cellulose fibers. Other types of fibers including thermoplastic reinforcing fibers may be used without seriously degrading the deformability characteristic of the sheeting. In accordance with the invention, the bottom portion or layer of this material is left in this un-vulcanized cold-flow non-memory condition, and is attached by adhesive 6 (FIGS. 5 and 6) along the bottom surface to the roadway R. The top portion of the rubber sheeting material comprising the marker strip, however, is to be vulcanized to provide it with memory characteristics. Toward this end, the top layer may be treated as by a shallow layer of peroxide material 1' which penetrates the rubber sheeting to a limited depth depicted by the speckled area of FIGS. 1 and 2. Because of the presence of peroxide or equivalent treatment, this region of the rubber sheeting can be readily cross-linked or vulcanized by the addition of heat. Prior to the heat, it has the same characteristics as the remainder of the sheet; i.e. it is soft, easily deformed and lacks memory. As illustrated in FIG. 2, the sheet of FIG. 1 has been embossed in the top surface with protruding wedges or ridges 3 and then heat is applied immediately thereafter in order to cross-link or vulcanize and harden this ridged top layer that had been permeated with peroxide, imparting to the ridges a permanent memory such that they can maintain shape with cold flow after vehicular depression, while the bottom of the sheeting 1 remains unvulcanized (not cross-linked) and thus deformable and memory-free to provide the necessary shock energy absorption of vehicular traffic and with conformability, to assist the adhesion in securing the marker to the road surface R. The protruding ridges or wedges 3 may be in the form of transversely extending parallel rows, successively longitudinally spaced along the strip, and may be segmented into ridge or wedge blocks, if desired, preferably with a trapezoidal cross-section providing inclined or near-vertical front and rear surfaces 1" for reflecting incident low-angle headlight illumination as described in my aforesaid patents.

FIGS. 3 and 4 illustrate another method of accomplishing the same effect. In this case, the rubber sheeting base material consists of a two-ply laminate comprising a vulcanizable upper layer 2 laminated on top of a non-vulcanizable rubber sheeting layer 1. Layer 2 may contain the same ingredients as layer 1 in addition to vulcanizing agents, such as sulfur (Table II) or other compounds which react with the rubber to cross-link or vulcanize it to completion after the protuberances 3, FIG. 4, have been formed. Once vulcanized, the protuberances or ridges will maintain their shapes because the vulcanization process provides the material with a memory and a degree of surface hardness.

In FIG. 5, the top-embossed surface of FIG. 4 has a retro-reflecting bead-bonding layer 4 convering the entire surface. This layer may be any suitable bead bonding layer such as a vinyl acetate copolymer, a polyurethane, an epoxy or any material which will satisfactorily bond the glass retroreflective microspheres 5 to the structure, curing during the curing of the upper layer of the strip. The bead bonding layer 4 can be applied to the surface either prior to or after the ridges are embossed or otherwise formed. The coating of glass microspheres or beads 5 is applied to this layer 4 prior to solidification of the layer. After vulcanization of the top ridged layer, the beads become secured in a partially embedded manner therein with the beads partially exposed including especially on the inclined or near-vertical front and rear surfaces 1" of the ridges or protuberances facing traffic.

As shown in the cross-section of FIG. 6, the glass microspheres 7 are embedded in the cross-linked top portion of the rubber sheeting of FIG. 2. This can be accomplished prior to embossing or during the embossing process itself. The glass microspheres 7 are only partially embedded on the near-vertical or inclined faces of the ridges 3, whereas those shown typically at 8 are fully embedded during the embossment. In order to promote adhesion of these microspheres to the product, it has been found that silane is helpful either incorporated with the base material or as a coating on the microspheres or both. The adhesive layer 6, shown in FIGS. 5 and 6, bonds the marker to the road surface R and should exert as little influence as possible on the conformability characteristics of the product to insure good adhesion to the road surface.

The marker strips or tapes of the invention may be formed by the following illustrative methods of construction which provide the ability to maintain the ridged shape and still permit road surface conformability to assist in good adhesion thereto.

The ingredients listed in Table 1 below, were compounded using a lab roll mill and calender to form a sheet approximately 0.050 inch thick by 4 inches wide by several feet long. A squeegee was then used to apply a liquid layer of methanol and t-butyl perbenzoate onto the surface of the sheeting where a limited penetration of the surface with resulting peroxide occured. After drying with warm air for 30 seconds, the sheeting was then passed between a nip roller and a patterned embossing drum to impress a ridged pattern 3 into the top surface of the sheeting. The embossed material was then heated at 350.degree. F. for 3 minutes during which time the upper layer 1' (FIG. 2) of the rubber sheeting impregnated with the peroxide became cross-linked. The surface durometer was measured at 65-70, whereas before treatment with the peroxide it was only 40.

The embossed strip containing the ridged pattern was then positioned beneath a flat sheet of metal and the s wheel of a 11/2 ton pick-up truck which was allowed to stand over this strip for 10 minutes, depressing the ridges. Inspection of the sample showed that the ridges had flattened to approximately 10% of their normal height. After a 10-minute waiting period, it was observed that the strip showed full recovery of the ridges and restoration to original shape. A similar test but without application of the peroxide failed to recover at all when subjected to the wheel loading for as short a time as 15 seconds.

Similar shape recovery or restoration from depression has been observed with actual vehicular travel as well.

The ingredients in TABLE 1 were compounded into sheet form as in EXAMPLE 1 to form two separate sheets 1 and 2 (FIG. 3). The sheet 1 was calendered to a thickness of 0.040 inch. The layer 2, after the addition of precipitated sulfur in the amount of 3% total weight of rubber, was calendered to produce a 0.020 inch thick sheet. The sheets 1 and 2 were then laminated together and impressed with a ridged pattern 3 and heated at 350.degree. F. for 9 minutes during which time the sulfur reacted with the rubber to effect vulcanization of the upper embossed layer 2 (FIG. 4). As in EXAMPLE 1, the strip was subjected to the truck tire weight for 10 minutes and reacted in a similar manner to the previous test, recovering fully after a 10 minute waiting period.

The procedure of EXAMPLE 2 was repeated except that a layer of isocyanate polyol liquid polyurethane such as sold under the trademark "Amershield" of Ameron Company, was applied on top of the sulfur-containing layer and a layer of glass microspheres 5 (FIG. 5) was applied to the liquid polyurethane layer 4 prior to embossing the ridged pattern. After the polyurethane was dry to the touch, the material was embossed and then subjected to 350.degree. F. heat for 9 minutes. The truck tire test results were similar to those of EXAMPLE 1 and the glass microspheres were noted to be unchanged and firmly anchored.

The procedure of EXAMPLE 2 was repeated except that, prior to embossing, the sulfur-containing top surface 2 was given an overcoat of a 20% solution of Dow Corning Z6040 "Silane" in methanol, followed by application of glass microspheres. The treated sheet was then subjected to 350.degree. F. for 30 seconds and then embossed with a ridged pattern. The embossing procedure caused the beads 7 to be partially embedded on the near vertical faces and almost entirely embedded on the horizontal surfaces (FIG. 6). After embossing, the sheet was heated at 350.degree. F. for 9 minutes to complete the vulcanization of the sulfur containing layer. The truck tire test results were similar to those of EXAMPLE 1 and the glass microspheres were observed to be unchanged and securely anchored to the vulcanized rubber.

Further modifications will also occur to those skilled in this art and such are considered to fall within the spirit and scope of the invention as defined in the appended claims.