RETROREFLECTIVE SHEETING COMPRISING A DIVERGENCE ENHANCING LAYER

FIELD OF THE INVENTION

This invention relates generally, as indicated, to retroreflective sheeting and, more particularly, to retroreflective sheeting comprising a layer having a front light- receiving surface and a rear surface with an array of retroreflective elements formed therein.

BACKGROUND OF THE INVENTION

Retroreflective sheeting is used in highway safety applications to reflect light from a vehicle's headlights back to the eyes of the driver. Retroreflective sheeting typically comprises a transparent layer having a front light-receiving surface and a rear surface with an array of retroreflective elements formed thereon. When incident light reaches the front light-receiving surface, it passes therethrough, impinges on the retroreflective elements, and reflects back out through the front surface at a two- dimensional retroreflective pattern. The divergence range of a retroreflective array is the range of angles for which this pattern is relatively intense so as to be useful for its intended purpose. It is usually preferable for retroreflective sheeting to produce a pattern of retroreflected light with sufficient intensity over a divergence range of at least 1° and preferably 3° or more.

An intentional aberration in one or more retroreflective elements can positively affect (e.g., broaden without introducing undesirable diffraction) the divergence range of an overall array. Historically, aberrations in retroreflective arrays have stemmed from the geometries introduced into the master plate during ruling, these ruled geometries then being transferred to copies/clusters and eventually to the production tool which is used to form the retroreflective sheeting. (See e.g., US3712706, US4775219, US4938563, US 6015214, US2003/007815A1 , etc.). US 6871966 each discloses a method of introducing aberration-producing geometries by controlled working of the second "non-arrayed" surface of the master substrate aftertooling or by similar controlled working of copy substrates made from

the master substrate. (This patent is assigned to the assignee of the present invention and its entire disclosure is hereby incorporated by reference.)

SUMMARY OF THE INVENTION The present invention provides retroreflective sheeting having a broad divergence range due, at least in part, to a divergence-enhancing layer having localized aberration regions. The invention allows the same expensive tooling to be used to fabricate a plurality of similar retroreflecting layers because different divergence-enhancing layers can be used to create sheeting products of different divergences for different applications. Additionally or alternatively, the divergence- enhancing layer can be used in conjunction with aberrated retroreflective elements to further improve divergence to a degree perhaps not possible with only aberrated retroreflective elements.

More particularly, the present invention provides retroreflective sheeting comprising a retroreflecting layer, which has an array of retroreflective elements (e.g., cube corner elements) formed thereon, and a divergence-enhancing layer. The divergence-enhancing layer is positioned in front of the retroreflecting layer and has localized aberration regions which change the divergence of light traveling therethrough. The placement of the localized aberration regions relative to the retroreflective elements results in the sheeting having a broad divergence range (e.g., at least about 1 ° and preferably about 3° or more).

The divergence-enhancing layer can comprise a substrate and a plurality of lenses carried by the substrate. The size of the lenses can be comparable to the size of the retroreflective elements whereby, if the retroreflective elements are microcubes and/or micro-optical elements, the lenses can be microlenses. The lenses can occupy only the localized regions whereby their presence (as opposed absence) creates the aberration(s). Alternatively, the lenses can be provided in an array (e.g., a tight two-dimensional array) that covers the localized aberration regions and regions outside thereof. If such an array of lenses is provided, the lenses within the localized aberration regions can have different optical parameters and/or different spacial distribution than the lenses in the outside regions to thereby create the aberration(s).

These and other features of the retroreflective sheeting are fully described and particularly pointed out in the claims. The following description and drawings set forth in detail certain illustrative embodiments of the retroreflective sheeting which are indicative of but a few of the various ways in which the principles of the invention may be employed.

DRAWINGS

Figures 1A - 1 F are side views of retroreflective sheeting according to the present invention.

Figure 2 is a rear view of a retroreflecting layer of the sheeting, this layer including an array of retroreflective elements.

Figure 2A is a close-up rear view of a retroreflective element. Figure 3 is a front and isolated view of a divergence-enhancing layer having localized aberration regions according to one embodiment of the invention.

Figure 3A is a close-up partial side view of the divergence-enhancing layer shown in Figure 3, this view showing the absence of lenses outside the localized aberration regions.

Figure 3B is a close-up partial side view of the divergence-enhancing layer shown in Figure 3, the view showing the presence of lenses within the localized aberration regions. Figure 4 is a front and isolated view of a divergence-enhancing layer having localized aberration regions according to another embodiment of the invention.

Figure 4A is a close-up partial side view of the divergence-enhancing layer shown in Figure 4, the view showing lenses occupying areas outside the localized aberration regions. Figure 4B is a close-up partial side view of the divergence-enhancing layer shown in Figure 4, the view showing lenses within the localized aberration regions that have different optical parameters than the lenses outside of the localized aberration regions.

Figure 5 is a front and isolated view of a divergence-enhancing layer having localized aberration regions according to a further embodiment of the invention.

Figure 5A is a close-up partial side view of the divergence-enhancing layer shown in Figure 5, this view showing lenses that occupy areas outside the localized aberration regions.

Figure 5B is a close-up partial side view of the divergence-enhancing layer shown in Figure 5, this view showing lenses within the localized aberration regions that have a different spatial distribution than the lenses outside the localized aberration regions.

DETAILED DESCRIPTION Referring now to the drawings, and initially to Figures 1A- 1 F, retroreflective sheeting 10 according to the present invention is shown. The retroreflective sheeting 10 comprises a retroreflecting layer 12 and a divergence-enhancing layer 14. The sheeting 10 can be used in highway safety applications to reflect light from a vehicle's headlights back to the eyes of the driver in a two-dimensional retroreflective pattern. The range of angles for which this pattern is sufficiently intense is the divergence range of the retroreflective sheeting 10.

The sheeting 10 can include other layers such as, for example, a color layer 16, a reflection-aiding layer 18, a backing layer 20, an adhesive layer 22, and/or removable release layer 24. The color layer 16 will usually be a transparent colored layer providing a color quality to the retroreflected light. The reflection-aiding layer 18 can be a metallized film, granular silica particles, or any other acceptably reflective material. The backing layer 20 can serve as a space-filler behind the layers 12/18 and/or as a carrier for the adhesive layer 22 and, to this end, can comprise a paper, plastic, metal, or other substrate which performs these functions. The adhesive layer 22 is used for attachment to the mounting surface of the end product and can comprise a pressure-sensitive or heat-activated adhesive. The removable release layer 24 can be provided to cover the adhesive layer 22 during pre-mounting stages and can comprise a paper or plastic film with a suitable release coating.

The divergence-enhancing layer 14 is positioned in front of the retroreflecting layer 12. For example, the divergence-enhancing layer 14 can be positioned directly in front of the retroreflecting layer 12 ( Figures 1A - 1C) and, if so, can be laminated directly to the layer 12 (Figure 1A), adhered to the layer 12 by an optical adhesive

26 (Figure 1 B), or incorporated-integrated into the retroreflecting layer 12 during its fabrication. Alternatively, an intermediate layer (e.g., the color layer 16) can be positioned between the retroreflecting layer 12 and the divergence-enhancing layer 14 (Figures 1D - 1 F). In the latter case, the divergence-enhancing layer 14 can be laminated directly to the intermediate layer (Figure 1 D), adhered to the intermediate layer by an optical adhesive 26 (Figure 1 E), or incorporated-integrated into the intermediate layer during its fabrication (Figure 1F).

The retroreflecting layer 12 comprises a front light-receiving surface 30 and a rear surface 32 on which a plurality of retroreflective elements 34 are formed. As is best seen by referring additionally to Figure 2 (and Figure 2A), the retroreflective elements 34 can comprise cube corner elements. If so, each retroreflective element 34 has three mutually perpendicular faces 36 that meet an apex 38 and that intersect with each other at dihedral edges 40. (In a geometrically perfect cube corner element, the dihedral angles would each be exactly 90°.) The cube area of each retroreflective element 34 can be about 1 mm ² or less and, if so, the elements 34 can be considered microcubes (or, more generally, micro-optical elements). The retroreflecting layer 12 can be made of any suitable thermoplastic material which is compatible with desired manufacturing methods {e.g., acrylic, vinyl, polycarbonate, etc.). As is best seen by referring to Figures 3 - 5, which show the divergence- enhancing layer isolated from the other layers of the retroreflective sheeting 10, this layer 14 comprises localized aberration regions 42 which change the divergence of light traveling therethrough. The placement of the regions 42, and/or the divergence-changing qualities, of each region 42 can be the same or varied (e.g., patterned or semi-random). In either or any case, this placement and/or these qualities cause the retroreflective sheeting 10 to have a broader divergence range than it would without the divergence-enhancing layer 14. For example, if the retroreflective elements 34 are geometrically perfect (or almost geometrically perfect), the retroreflecting layer 12 be optically capable of providing a divergence range of about 0° to 0.5°. With the divergence-enhancing layer 14, the retroreflected light can have sufficient intensity over a much wider range of observation angles (e.g., at least 1 ° and preferably 3° or more). Preferably, the total retroreflectance of the layer 12 is substantially preserved (i.e., the sheeting 10 still

provides a total retroreflectance that is at least 90%, at least 94% and/or at least 98% of the total retroreflectance of the layer 12).

In the preferred embodiment, the divergence-enhancing layer 14 comprises a substrate 44 and a plurality of lenses 46 carried the substrate 44. The substrate 44 can be made from a transmissive material (e.g., glass, plastic) that is capable of supporting the lenses 46 and/or that is compatible with the fabrication of the lenses 46 thereon. The lens structure can be made by energy modification, chemical coating, or extrusion of the substrate 44 or a coating thereon, by the integration of glass beads into the substrate 44 or a sub-level thereof, by differentiated dispersions inside the substrate 44 or a film applied thereto, and/or by the incorporation of soluble and insoluble species into the substrate 44.

The lenses 46 each have a geometry (e.g., hemispherical or cylindrical, concave or convex, etc.) and given optical parameters (e.g., radii of curvature, conic constants, focal points, aspheric coefficients, etc.). If the lenses 46 are arranged in a tight two-dimensional array (see e.g., Figures 4 and 5), this array itself will have certain optical parameters dictated by the optical parameters of each lenses 46 and the spacial distribution of the lenses 46 within the array. In the preferred embodiment, the size of the lenses 46 is comparable to the size of the retroreflective elements 34 whereby, if the elements 34 are microcubes, the lenses 46 will be microlenses (i.e., a lens having a diameter, or other analogous dimension, that is less than 1 mm).

The lenses 46 can be present only in the localized regions 42 whereby their presence creates the aberration in contrast to the non-lense regions of the layer 14. (Figures 3, 3A and 3B.) Alternatively, the lenses 46 can be provided in an array 48, preferably a tight two-dimensional array, which can (or cannot) correspond to the array 32 of the retroreflective elements 34. (Figures 4 and 5.) If an array of lenses 46 is provided, the individual lenses 46 in the localized regions 42 can have a shape corresponding to optical parameters which differ from those of the lenses 46 outside the localized regions 42 to thereby provide the desired aberration(s). (Figures 4A and 4B.) Additionally or alternatively, the spacial distribution of the lenses 46 within the localized regions 42 can differ from the spacial distribution of the lenses 46 in outside regions to thereby provide the desired aberration(s). (Figure 5A and 5B.)

(To insure that the shape and spacial differences were visible for comparison, these features may have been greatly exaggerated in the drawings.)

Other lense arrangements and/or other techniques for providing different diffusion qualities within the localized areas 42 are certainly possible with, and contemplated by, the present invention. For an example, the lenses 46 could be provided in multiple levels, which are aligned or offset from each other, to provide the desired aberration(s). For another example, the localized regions 42 could have different material characteristics (e.g., by injection of a structure-changing substance into this area) or could have different profiles (e.g., slanted, sloped, recessed, or projected) to provide the desired aberration(s). Such different material characteristics and/or profiles could be used instead of, or in addition to, the lenses 46.

The present invention allows the same retroreflecting layer 12 (and thus the same expensive tooling) to be used to fabricate a plurality of similar retroreflecting layers 12 and then different divergence-enhancing layers 14 used to create sheeting products of different divergences for different applications. This feature can eliminate the need to customize tooling to provide aberrations in the retroreflecting element 34 themselves. That being said, the use of the divergence-enhancing layer 14 with already aberrated retroreflective elements 34 is certainly possible with and contemplated by, the present invention. In certain retroreflecting situations, an optimum divergence range may be accomplished by the combination of aberrated retroreflective elements and the localized aberration regions 42 on the divergence- enhancing layer 14. In such situations, the localized aberration regions 42 can be aligned with aberrated retroreflective elements and/or aligned with non-aberrated retroreflective elements depending upon what provides the desired divergence.

One may now appreciate that the present invention provides retroreflective sheeting 10 having a broad divergence range due, at least in part, to the divergence- enhancing layer 14. Although the retroreflective sheeting 10 has been shown and described with respect to certain preferred embodiments, it is obvious that equivalent and obvious alterations and modifications will occur to others skilled in the art upon the reading and understanding of this specification. The present invention includes all such alterations and modifications and is limited only by the scope of the following claims.