CA2064484C

CA2064484C - Retroreflective sheet

Info

Publication number: CA2064484C
Application number: CA002064484A
Authority: CA
Inventors: William P. Rowland
Original assignee: Reflexite Corp
Current assignee: Reflexite Corp
Priority date: 1991-04-11
Filing date: 1992-03-31
Publication date: 1998-08-11
Anticipated expiration: 2012-03-31
Also published as: GB2254826B; JPH05107406A; JPH087281B2; CA2064484A1; GB9208092D0; FR2675271B1; FR2675271A1; GB2254826A; DE4212203A1

Abstract

A retroflective material retroreflects a white coloration for light beams impinging thereon at night and appears to have the coloration of the underlying support in daylight. This material utilizes retroreflective sheeting having closely spaced microretroreflective formations on one surface, and a transparent adhesive in a pattern over that surface so as to leave the predominant portion of the surface free from adhesive. A transparent backing element is adhered to the sheeting by the adhesive, and it extends in a plane generally above the formations to leave the formations in the predominant surface area exposed to the atmosphere thereabout.
Light rays entering the the other surface of the sheeting and impinging upon the prisms of the predominant surface area are retroreflected by the interface with the atmosphere, and those impinging upon the formations in the area coated by the adhesive pass through the adhesive and the backing for reflection and refraction from the underlying surface, thereby evidencing its color in daylight.

Description

- 206~84 The present invention relates to retroreflective sheeting employing microretroreflective formations to retroreflect light rays impinging thereon at night, and more particularly, to a method for producing such retroreflective sheet material exhibiting a high degree of retroreflectivity and a white coloration at night, and the color of an underlying support in daylight.
Retroreflective sheet material is widely employed for a variety of safety and decorative purposes, and it is particularly useful when the need for night time vlsibility is significant under conditions of low ambient light. In retroreflective materials, light rays impinging upon the front surface are reflected back towards the source of the illumination in a substantially parallel path. In situations where headlights or search lights on boats and aircraft are the only source of illumination, this ability to retroreflect the bulk of the rays falling thereon is especially significant.
Minnesota Mining and Manufacturing Corporation has manufactured retroreflective sheeting utilizing minute glass beads embedded in a matrix of synthetic resin to provide such retroreflection, and these materials have been sold under the trademark SCOTCHLITE. Illustrative of such materials is Bergeson et al United States Letters Patent No. 4,637,950 granted January 20, 1987.
Applicant~s assignee, Reflexite Corporation, has been extensively marketing under the trademark REFLEXITE, 20~448~

reflective sheeting employing microprism formations to produce such retroreflection. Illustrative of such materials is Rowland United States Letters Patent No. 3,689,346 granted September 5, 1972.
Among the applications for such retroreflective materials are the reflective bands seen on posts, barrels, and cones used in traffic control.
It is known that a cube corner prism surrounded by air will retroreflect light incident upon the front surface or base thereof impinging upon and the prism surfaces at an angle greater then a Fresnel angle. However, it is common to coat the prism surfaces with a reflective or specular material such as a vacuum deposited aluminum layer to provide a retroreflective interface. In this manner, adhesive and other backing materials may be deposited about the metallized cube corner prisms to effect lamination to backing sheets and other structures.
However, the use of a metallized aluminum coating on the prism surfaces tends to produce a grey coloration to the observer in ambient light or daylight conditions. In some applications, this grey appearance is considered aesthetically undesirable.
To prevent or minimize the failure of such metallized retroreflective sheet materials incident to penetration of salt or other corrosive materials, or moisture, about the retroreflective formations, it is common to provide a protective backing over the formations and to seal that 206~48~

backing to the retroreflective sheeting in a grid pattern to produce discrete cells containing isolated clusters of retroreflective formations. Illustrative of such grid structures is Bergeson et al U. S. Patent No. 4,637,950 granted January 20, 1987.
In Martin United States Letters Patent No. 4,801,193 granted January 31, 1991, a partially air backed,-partially-metallized microprism sheeting using a grid of adhesive to bond a backing thereto is disclosed and claimed. In that structure, the prisms underlying the grid of adhesive are metallized to effect retroreflection in that area, and the air interface retroreflects the light in the areas between the grid lines. This structure provides a whiter appearance in daylight.
However, some contractors and governmental authorities wish the retroreflective elements placed upon traffic control devices such as barrels and cones to have a uniform coloration in daylight. Some actually remove the retroreflective elements during daylight to avoid the white (or gray) interruptions in the fluorescent orange which is customarily employed for such conical devices.
It is an object of the present invention to provide a novel method for making retroreflective sheeting which during daylight conditions exhibits the underlying color of the substrate upon which placed and which at night exhibits a high degree of retroreflection of light beams impinging thereon.

20S~48 1 It is also an object to provide such a novel retroreflective sheet material which may be readily fabricated and which is durable and resistant to the elements.
Another object of the present invention is to provide a traffic control device or the like using such retroeflective material.
It has now been found that the foregoing and related -objects may be readily attained by use of retroreflective sheeting which is formed with microretroreflective formations closely spaced about one surface thereof. These~formations are configured to retroreflect light entering the other surface of the sheeting and impinging upon the inner surface of the formations. A transparent adhesive is deposited in a pattern over the prism surface of the sheeting, and the pattern leaves the predominant portion of this surface free from adhesive. A transparent backing element is adhered to this surface by the adhesive, and it extends in a plane generally above the formations and spaced from predominant surface area of the formations to leave the formations in the predominant surface area exposed to the atmosphere thereabout.
As a result, light rays entering the the other surface of the sheeting and impinging upon the prisms in the predominant surface area are retroreflected by the interface with the atmosphere thereabout, and those impinging upon the formations in the area coated by the adhesive pass through the adhesive and backing, and will be reflected by the surface of a substrate upon which the sheeting is mounted.

206~8~

Preferably, the adhesive is applied in a grid pattern, and the retroreflective formations are microprisms.
Desirably, the retroreflective sheeting and the backing element are fabricated from synthetic resin.
In use of the sheeting, it is mounted upon a support having a coloration whereby light rays passing through the backing element produce that apparent coloration in the sheeting. The backing element is adhesively engaged upon the support.
Usually, the support is a traffic control member, and the sheeting is formed into a band which is adhesively engaged thereon.
Figure 1 is an elevational view of a traffic cone to which has been applied a retroreflective band embodying the present invention;
Figure 2 is a plan view of a block of reflective sheeting prior to forming into the frustro-conical configuration of the band of Figure 1;
Figure 3 is an elevational view of the band formed from the block of Figure 2;
Figure 4 is a fragmentary plan view of the grid pattern of adhesive applied to the microprism surface of the retroreflective material used in Figures 1-3;
Figure 5 is a fragmentary sectional view of the sheet material of Figure 2 drawn to a generally enlarged scale;
Figure 6 is a fragmentary sectional view to a greatly enlarged scale of the reflective band and cone in Figure l; -and 206448~

Figure 7 is a diagrammatic view of the band and cone of Figure 6 showing light rays impinging thereon.
Turning first to Figure 1, a conventional traffic cone generally designated by the numeral 10 has adhesively bonded about its periphery a frustro-conical band 12 of retroreflective sheeting. Conventionally, such traffic cones 10 are formed from synthetic resin and are providéd with a fluorescent orange coloration so as to make them highly visible in daylight, and they are molded with a base 16 for stability and a frustro-conical hollow body 18.
As seen in Figures 2 and 3, an arcuate strip or block 20 of reflective material is formed into a band 12 with overlapping end portions 22 which are secured together by rivets 44. Other means of fastening the overlapping end portions 22 may also be employed such as adhesive bonding and sonic welding.
Turning next to Figure 5 therein is illustrated a fragmentary and greatly enlarged sectional view of the retroreflective material of Figure 2 showing the microprisms 22 which are formed on the rear surface of a planar surfaced body portion 24. The microprisms 22 are closely spaced and can be described as cube corner formations. Further details concerning the structure and operation of such microprisms may be found in Rowland United States Letters Patent No. 3,684,348 granted August 15, 1972. These microprisms 22 or cube corner formations may have a side edge dimension of up to 0.025 inch, but the preferred structures use edge dimensions of not more than 0.010 inch, and most desirably on the order of 0.004-0.008 inch. The body portion 24 of the sheeting will generally have a thickness from the outer surface to the base of the prisms on the order of 0.002-0.030 inch and preferably about 0.003-0.010 inch depending upon the method of fabrication, the resins, and the characteristics desired for the retroreflective sheeting.
A particular advantageous method for making such retroreflective sheeting is described and claimed in Rowland United States Letters Patent No. 3,689,346 granted September 5, 1972 in which the cube corner formation~ are cast in a cooperatively configured mold and are bonded to sheeting which is applied thereover to provide a composite structure in which the cube corner formations project from the one surface of the sheetinq.
Another method for fabricating such microprism sheeting is shown in Rowland United States Patent No. 4,244,683 granted January 13, 1981 in which the cube corner formations are produced by embossing a length of sheeting in suitable embossing apparatus with precisely formed molds in a manner which avoids entrapment of air.
It is customary to provide a backinq element or sheet 26 behind the microprisms 22 so as to protect them and to provide a smooth surface for application of the structure to support surfaces. To effect lamination of such a backing sheet to the retroreflective sheeting, adhesive 28 is employed.
As seen in Figure 4, the microprism surface of the retroreflective sheeting is therein diagrammatically 206~L484 illustrated as having a adhesive 28 applied thereto in a grid-like pattern. As a result, only limited number of microprisms 22 are coated with the adhesive 28, and the predominant portion of surface area is free from adhesive 28.
The backing sheeting 26 extends in a plane spaced above the prisms 22. As a result, the bulk of the surface area of the microprisms 22 is surrounded by air or other atmosphere.
In this embodiment, the front surface of the body 24 has a protective coating 34 of a lacquer containing ultraviolet ray absorbers. On the opposite surface of the backing sheet 26 is a pressure sensitive adhesive coating 30. Superposed on this adhesive coating 30 is a release coating or film 32, and this is removed to adhere the retroreflective material to the surface of a support.
Turning now to Figure 6, it can be seen that the backing sheet 26 is shown as bonded by the adhesive 30 to the cone 10.
When adhesives are employed, it is known that the adhesives tend to wet the surface of the microprisms and this destroys the air interface and eliminates their ability to retroreflect.
In daylight, the entire cone 10 evidences the fluorescent orange coloration albeit with some variations in the area of the band 12. At night, an observer positioned adjacent the source of a light beam incident upon the cone 10 observes a bright white band 12 on the cone 10 as it retroreflects the light towards that source.

As seen in Figure 7, a light ray 50 entering through the front surface of the body portion of the retroreflective sheeting 12 (not shown) impinges upon the adhesively coated surface of the microprism 22 and passes through the adhesive coating 28 and backing sheet 26 and the adhesive 30 to the surface of the substrate 10 from which it is reflected and scattered upwardly and outwardly of the sheeting in various paths. As a result, these reflected and scattered light rays will evidence the coloration of the substrate.
The light ray 52 enters into the body of the sheeting 24, and impinges upon the leftward surface of the prism 22. It is reflected to the rightward prism surface and then reflected outwardly in a parallel path. At night, when the surface is receiving light rays from a source near the observer, the eye will see these retroreflected light rays and the sheeting will have a bright white coloration.
Moreover, during daylight hours, light rays incident upon the front surface are coming in large amounts from various directions. The light ray 54 is incident upon the front surface at a steep angle of more than 30~ from the perpendicular and strikes the uncoated surface of the prism 20 at a steep angle which is greater than the Fresnel angle. As a result, it passes outwardly of the prism 22 through the air space and through the backing sheeting 26 and adhesive 30 to the surface of the substrate 10 where it is reflected and scattered. Thus, some light rays impinging upon the uncoated prisms will be colored when reflected.

": .

As previously indicated, the microprism sheeting may be formed by casting prisms upon a film serving as a body, or by embossing a preformed sheeting, or by casting both body and prisms concurrently. Generally, the resins employed for the microprism sheeting are cross linked thermoplastic formulations, and desirably these resins provide flexibility, light stability, and good weathering characteristics. In some instances, the front face of the retroreflective sheeting may be provided with a protective coating such as by application of a lacquer or other coating material containing ultraviolet ray absorbers to a thickness of 0.0002-0.0005 inch. Suitable resins for the retroreflective sheeting include vinyl chloride polymers, polycarbonates, methyl methacrylate polymers, polyesters, polyurethanes and acrylated urethanes.
The backing sheet will also be a flexible, durable polymeric material. Suitable resins include polyethylene, polypropylene, polyesters, polyurethanes, acrylated polyurethanes and ethylene/vinyl acetate copolymers.
Generally, flexible materials of polyethylene and its copolymers are preferred.
The specific transparent adhesive utilized in the process of the present invention will depend upon the process employed and whether pressure-sensitive or heat activated adhesive characteristics are desired, and the mode of application. In the preferred techniques, the coating material is a pressure-sensitive adhesive. Preferred adhesives include ethylene-propylene block elastomeric copolymers systems in solvent carriers and acrylic-based adhesives in solvent systems. Other adhesives may also be employed including clear silicones and polyesters. Water based systems may also be employed, although sometimes requiring drying time before further processing. Specific examples of suitable adhesive systems are a ethylene/propylene block copolymer adhe6ive sold - by Pierce and Stevens under the trademark KRAYTON-G, and an acrylic based adhesive system sold by Coating Science under the trademark UV405.
The adhesive coating is conveniently applied in a grid-like pattern by means of a modified gravure-type roll.
However, sprayinq through a mask and other coating methods may also be employed to provide the limited area pattern.
It is also possible to apply the adhesive pattern to the backing film before lamination albeit with less control over the pattern after lamination due to the tendency for the adhesive to "flow" under the laminating pressure.
The adhesive layer on the opposite surface of the backing sheet for mounting the reflective sheeting to a substrate should be continuous to provide the desired passage of light rays to the substrate, and it may be applied by spraying, roller coating, gravure coating and the like. It may be preapplied to the backing sheeting together with its release coating or film.
The step of adhering the backing sheet to the retroreflective sheeting may simply involve passing the adhesive coated retroreflective sheeting through the nip of a 20~484 pair of rolls together with a backing sheet to apply the necessary pressure to effect adhesion. If a heat activatable adhesive is employed, the retroreflective sheeting may be subjected to preheating prior to passage through the rolls, or the rolls may be heated to achieve the necessary activation.
Although the invention has been shown as applicable to reflective traffic cones, the bands may also be ~sed with -barrels, posts and other structures which utilize a reflective band about their periphery.
Exemplary of the efficacy of the present invention is the following example.
EXAMPLE ONE
Utilizing the method generally illustrated and described in Rowland United States Patent No. 3,689,346, microprisms having a height o~ 0.0028 inch and a spacing of 0.006 inch on center are cast upon a polyester film having a thickness of 0.002 inch. The resin employed for the prisms is an acrylated epoxy oligomer modified with monofunctional and trifunctional acrylic monomers.
The surface of the sheeting opposite that having the microprisms is coated to a depth of 0.0003 inch with an acrylic lacquer containing an ultraviolet absorber sold by Ciba-Gergy under the trademark Tenuvin 328.
The prism bearing surface of the sheeting is then imprinted by a modified gravure roll with a grid pattern to deposit a pressure sensitive, ever-tacky ethylene/propylene block copolymer adhesive sold by Pierce and Stevens under the trademark ~RAYTON-G. The grid has a spacing of 1/4 inch between lines and the lines have a thickness of approximately 0.04 inch, and the adhesive covers about 40 percent of the surface area to a depth greater than the height of the prisms.
The sheeting is passed through the nip of a pair of pressure rollers together with a polyethylene backing sheet of 0.001 inch thickness to effect lamination thereto, and the ~acking sheet has a coating of acrylic pressure sensitive, ever-tacky adhesive sold by Coating Science under the trademark UV405, and a water-soluble release coating thereon.
The resulting sheet material is found to exhibit excellent weathering characteristics is a weatherometer, excellent retroreflective characteristics, and desirable orange coloration in daylight when bonded to a fluorescent orange traffic cone.
Thus, it can be seen from the foregoing detailed description and attached drawings that the process of the present invention provides a novel retroreflective microprism sheet material exhibiting in daytime the coloration of the underlying substrate and excellent nighttime retroreflectivity. The method for making the sheeting is relatively simple and economical, and it produces material exhibiting reasonably long life.

. .

Claims

1. In a method for producing a retroreflective sheeting which will retroreflect incident light beams at night and which will appear to have the coloration of an underlying colored support in daylight, the steps comprising:
(a) forming retroreflective sheeting having a planar outer surface on a side of said sheeting nearest the incident light beams and cube corner formations with a base and at least three sides meeting at an inwardly directed apex, the formation being closely spaced about an inner surface of the sheeting;
(b) depositing a transparent adhesive in a pattern over all three sides of the formation, said pattern leaving the formations outside of the pattern free from adhesive;
(c) adhering a transparent backing element to said formations by said adhesive, said backing element extending in a plane generally adjacent said formations and parallel to said planar outer surface and being spaced inwardly from said formations to leave air entrapped inwardly between said formations and said backing element in areas outside of the pattern; and (d) adhering an underlying colored support to said backing, whereby incident light beams impinging upon said formations outside of said pattern at an angle less than the Fresnel angle are retroreflected by the interface between the air and the sides of the formations, and those impinging upon the formations in the patterned area pass through said adhesive and backing for reflection and refraction from the underlying support.

2. The method in accordance with Claim 1, wherein said adhesive is applied in a grid pattern.

3. The method in accordance with Claim 1 or 2, wherein said retroreflective formations are cube corner microprisms.

4. The method in accordance with Claim 1, 2 or 3, wherein said retroreflective sheeting and said backing element are fabricated from synthetic resin.

5. The method in accordance with any one of Claims 1 to 4, wherein said backing element is comprised of a highly visible fluorescent material.

6. The method in accordance with Claim 5, wherein said support is a traffic control member and said sheeting is formed into a band which is adhesively engaged thereon.

7. A retroreflective sheet material which will retroreflect incident light beams at night and which will appear to have the coloration of an underlying support in daylight, comprising:
(a) retroreflective sheeting having a multiplicity of closely spaced transparent prism formations on one surface thereof, said formations having a base and at least three sides which meet at an apex;
(b) a pattern of transparent adhesive on the sides of the prisms, one surface covering a portion of the area of said one surface, said pattern leaving the predominant portion of the prism sides free from adhesive; and (c) a transparent backing element adhered by said adhesive to said prism, said backing element extending in a plane generally inwardly of said formations, such that said formations in said predominant surface area are exposed to the atmosphere thereabout, whereby light rays entering the sheet material impinging upon the formations in the adhesive free surface area are retroreflected by the atmospheric interface thereabout, and those impinging upon the adhesively coated area pass through said adhesive and backing element and are reflected therefrom.

8. The retroreflective sheet material in accordance with Claim 7, wherein said adhesive is disposed on said one surface in a grid-like pattern, and wherein said backing element is adhered to said retroreflective sheeting along said grid-like pattern.

9. The retroreflective sheet material in accordance with Claim 8, wherein said formations between the lines of the grid pattern are substantially free from said adhesive and have an atmospheric interface.

10. The retroreflective sheet material in accordance with Claim 7, 8 or 9, wherein said retroreflective formations are microprisms.

11. The retroreflective sheet material in accordance with any one of Claims 7 to 10, wherein said retroreflective sheeting and said backing element are fabricated from synthetic resin.

12. A retroreflecting structure comprising:
(a) an inner base member having a surface coloration;
(b) an outer retroreflective sheet material comprising:
(i) retroreflective sheeting having a multiplicity of closely-spaced transparent prism formations on an inner surface thereof, sides which meet at inwardly extending apices;

(ii) a pattern of transparent adhesive on said sides covering a portion of the area of the prism sides, said pattern leaving the predominant portion of the surface area of the sides of prisms free from adhesive; and (iii) a transparent backing element adhered by said adhesive to said base member, said backing element extending in a plane generally inwardly from said formations, such that said formations in said predominant surface area thereof are exposed to the atmosphere thereabout, whereby light rays entering the sheet material impinging upon the formations in the adhesive free surface area are reflected by the atmospheric interface thereabout, and those impinging upon the adhesively coated area pass through said adhesive and backing element and are reflected by said inner base member.

13. The retroreflective structure in accordance with Claim 12, wherein said adhesive is disposed on said one surface in a grid-like pattern, and wherein said backing element is adhered to said retroreflective sheeting along said grid-like pattern.

14. The retroreflective structure in accordance with Claim 13, wherein said formations between the lines of the grid pattern are substantially free from said adhesive and have an atmospheric interface.

15. The retroreflective sheet material in accordance with Claim 12, 13 or 14, wherein said retroreflective formations are microprisms.

16. The retroreflective sheet material in accordance with any one of Claims 12 to 15, wherein said retroreflective sheeting and said backing element are fabricated from synthetic resin.