PHOTOLUMINESCENT RETROREFLECTIVE SHEETING

Abstract: A photoluminescent retroreflective sheeting (10) for use in structures when a power outage occurs. Guidance systems are made from this sheeting to mark exits and escape routes as well as possible hazards and safety devices. The novel sheeting includes photoluminescent (14) properties that glow in the dark as well as retroreflective (12) properties that retroreflect light incident upon the same sheet such that only one sheet has to be used rather than individual sheets with separate properties.

Description: DESCRIPTION PHOTOLUMINESCENT RETROREFLECTIVE SHEETING TECHNICAL FIELD The invention relates generally to a photoluminescent retroreflective sheet material for use as a guide marker and which has particular utility in buildings when a power outage occurs. Specifically, the present invention relates to a photoluminescent retroreflective sheeting combining both photoluminescent and retroreflective properties in a single product to be used to form a marker system to help indicate exits, doorways, hazards, OSHA markings, pipe markings, high voltage areas, fire hoses and extinguishers and the like, when it is dark in the building, perhaps when caused by a power outage. BACKGROUND OF THE INVENTION The term "building" as used throughout this application is intended to include any structure such as an aircraft, boat or other moveable and non-moveable conventional structures. It is well known that within buildings at night or especially when the power has been lost, it is difficult to find ones way along the necessary corridors to the building exits. Similarly, in some emergencies, the location of important fixtures such as fire alarms, extinguishers, shut-off valves and the like are difficult to find. In the prior art, a photoluminescent material is utilized as a guide for such purposes. The luminous material is attached to doorways, hallways, and the like, so that in the event of a power outage, the photoluminescent material will glow in the dark and guide a person to an exit or along a prescribed path. Of course, it is only useful to those individuals in the building that have adjusted their eyes to the darkness. Further, the luminescence produced is significantly lost within the first 20 minutes of an "outage." This makes it virtually useless to anyone entering the building after a short period of time. The present invention overcomes the disadvantages of the prior art by providing a single sheeting material having both photoluminescent and retroreflective properties. The sheeting should exhibit the same photoluminescent properties as the current product being used, and it has significant retroreflective properties. Thus it is an important object of the present invention to provide a photoluminescent retroreflective sheet material that is designed to provide both photoluminescence and retroreflection of light. It is also an object of the present invention to provide a photoluminescent retroreflective sheeting in which a phosphorescent pigment is added to the retroreflective layer. It is a further object of the present invention to provide a photoluminescent retroreflective sheet in which the retroreflective layer has cube corner retroreflectors embossed on the backside thereof and covered by a predetermined pattern of hydrophobic silica. A backcoating contains the phosphorescent pigment and is in contact with the retroreflective layer in areas of the pattern not covered by the hydrophobic silica. It is yet another object of the present invention to provide a photoluminescent reflective sheet which has a transparent flexible film with retroreflective cube corners formed on the reverse surface thereof and a clear adhesive with phosphorescent pigment screen-printed in a pattern and cured on the cube corners. It is believed that the present invention may be utilized with retroreflector sheeting produced in a variety of ways but will be particularly useful with that retroreflective sheeting described and claimed in U.S. Patent No. 4,618,518, issued October 21, 1986, to Robert M. Pricone, et al. and assigned to applicants 1 assignee, the disclosure of which is incorporated by reference. Others forms and methods of producing retroreflective sheeting include those of "casting" cube corner elements, such as disclosed in Rowland U.S. Patents 3,810,804, issued May 14, 1974; 3,684,348, issued August 15, 1972; and 3,689,346, issued September 15, 1972. Useful apparatus for embossing a film to provide cube corner retroreflective elements is disclosed in Pricone, et al. U.S. 4,601,861, issued July 22, 1986, commonly assigned. Other techniques for compression or sequential embossing are disclosed in Rowland U.S. 4,244,683, dated January 13, 1981. Efforts have been made in the past to utilize fluorescent pigmented materials in conjunction with retroreflective sheet materials of the cube corner type. However, such use of fluorescent materials was intended to provide a combination of day/night visibility in highway signs. One example is that found in Rowland U.S. Patent 3,830,682, issued August 20, 1974. However, in such uses, unlike phosphors, the flourescent material would not continue to glow or provide light under "darkened" conditions but instead is illuminated by the light of certain wave lengths, so as to provide some "daylight" visibility to highway signs. The present invention utilizes a phosphorescent pigmentation in conjunction with retroreflective sheet material in a manner which does not materially impede the retroreflective capability of the sign when illuminated either under normal lighting conditions, such as in a building and under hallway lighting lights, nor does it impede the "dark" or night light retroreflective capability when illuminated by a flashlight or other temporary light source. SUMMARY OF THE INVENTION The present invention relates to a photoluminescent retroreflective sheeting material, which, in one embodiment, comprises a first layer of transparent retroreflective film having a front face and a plurality of. cube corner retroreflective elements formed on at least a portion of the reverse or rear face to retroreflect light impinging upon the front face; a second layer of clear adhesive is screen-printed in a pattern and cured on the formed cube corner elements; a third layer of opaque film is adhered to the second layer to form air cells; an adhesive fourth layer is applied to the third layer for attaching the sheet material to a substrate surface; and a release liner is normally secured to the adhesive layer to prevent inadvertent contact of the adhesive layer with a surface. A phosphorescent pigment is contained in at least one of the first, second, third or fourth layers to cause the sheet to glow in the dark. In a second embodiment the second layer is comprised of hydrophobic silica which eliminates the "air cell". Other embodiments are disclosed and claimed. BRIEF DESCRIPTION OF THE DRAWINGS These and other objects of the present invention will be more fully understood when taken in conjunction with the following detailed description and the attached drawings in which like numerals represent like elements and in which: FIG. 1 is a first embodiment that illustrates a cross sectional view of photoluminescent retroreflective sheeting of the present invention in which clear adhesive with a phosphorescent pigment is screen printed in a pattern on the retroreflective cube corners formed on the rear surface of a transparent film; FIG. 2 is a cross-sectional view of a second embodiment of the present invention in which the retroreflective layer of film has the cube corners embossed on the rear surface thereof and a hydrophobic silica pattern is applied on the embossed surfaces; a backcoating with phosphorescent pigment is applied over the hydrophobic silica and is in contact with the otherwise exposed retroreflective cube corner elements; FIG. 3 is a cross-sectional view of a third embodiment of the present invention in which the retroreflective layer has the cube corner reflectors on one side thereof and which layer also contains the phosphorescent pigment for enabling the sheet to be seen when not illuminated by an external source. An adhesive layer is applied over the hydrophobic silica layer and exposed cuber corner elements, and a release liner is added to prevent accidental contact of the adhesive with a substrate surface; FIG. 4 is a cross-sectional view of yet another embodiment of the present invention, in which the retroreflective layer contains the phosphorescent pigment; the hydrophobic silica is screened in a pattern over the embossed cube corner retroreflectors on the retroreflective layer; a white backcoating is applied to the silica layer and to the exposed cube corner elements, an adhesive layer is added and a release liner is applied to prevent the adhesive from accidentally touching a surface; FIG. 5 is a flow diagram of a process for making one embodiment of the present invention; FIG. 6 is a flow chart illustrating the process for making the invention illustrated in FIG. 2 of the present invention; FIG. 7 is a flow chart illustrating the process for making the embodiment of FIG. 3 of the drawings; FIG. 8 is a schematic drawing of the flow chart for making the photoluminescent retroreflective sheeting of the FIG. 4 embodiment; and FIG. 9 is a cross-sectional view of another embodiment of the invention in which the phosphorescent pigment is utilized with "beaded sheeting" containing microspheres to provide retroreflectivity. DETAILED DESCRIPTION OF THE DRAWINGS A preferred embodiment of the present photoluminescent retroreflective sheeting is illustrated in cross-section in FIG. 1. The sheet comprises a first layer of transparent retroreflective film 12 that is formed generally in accordance with the method and apparatus disclosed in the aforesaid Pricone U.S. patent No. 4,486,363. However, as noted, other methods of forming a film with cube corner retroreflector elements (or spherical retroreflectors) may be used. In the preferred form, the film 12 is approximately 0.006-0.008 inches thick and has a plurality of retroreflective corner cube elements 13 embossed on the rear side thereof. It also has a layer of clear adhesive 14 containing a phosphorescent pigment screened in a preselected pattern over certain of the cube corner elements 13 so as to leave spaces or cells 22. One such adhesive 14 may be that known as Flexcrill GP-2, sold by Air Products, Inc., and applied by screen printing. This is a water based acryclic. The adhesive 14 contains a phosphorescent pigment which may be of a type known as P-1000, sold by Hanovia, a division of Conrad, Inc. of Newark, N.J. and which is commercially available. Other phosphorescent pigments may be used. The pigment may be batch mixed with the adhesive so as to constitute about 30% by weight thereof. Other adhesives that may prove satisfactory would be drawn from unpigmented acrylics; urethanes; UV curable 100% solids; the criteria being that the adhesive bond between the resin layer and back layer be flexible and be readily applied. The transparent retroreflective film 12 with the clear adhesive 14 and containing the phosphorescent pigment therein is then cured by heating or, if appropriate, and if UV curable, then curing can be accelerated. After curing, an opaque layer of material 16, (such as polyester, PVC, or Mylar) , is then applied over the transparent clear adhesive 14 with the phosphorescent pigment, to complete the "air" cells 22. The air cells permit retroreflectivity to be achieved, as is known in the art. Preferably, this layer 16 will be of a white color to enhance the brightness of the phosphorescent effect, but other colors or metallized films may be used. An adhesive fourth layer 18 then may be applied to the white layer 16, enabling the sheeting material to be attached to a surface. A release liner 20 is applied to the adhesive layer 18 to prevent inadvertent contact of the adhesive with a surface until the user is ready to install the sheeting. In the embodiment of FIG. 1, the retroreflective cells 22 allow the transparent film 12 to be retroreflective and reflect light impinging upon the front surface. The clear adhesive 14 with the phosphorescent pigment allows the strip to glow in the dark so that it can be followed by an individual. Thus, such sheeting can be used to form guidance systems that mark exits, doorways, hazards and the like in the case of a power outage. When the photoluminescent property of the sheets fail then the retroreflective cube corner elements will retroreflect incident light, such as from a flashlight or the like carried by service individuals such as police, fire or utility department officials. In FIG. 2, the sheeting 24 could be formed of a retroreflective layer of transparent flexible film 26 with cube corner retroreflective elements 27 formed on the reverse side thereof by embossing, to reflect incident light thereon. A hydrophobic silica layer 28 is screen printed in a pattern over the cube corner retroreflective cells 27. A clear water-based backcoating 30 is then placed over the hydrophobic silica 28. The backcoating contains the phosphorescent pigment. A white pigment adhesive 32 is laminated to the backcoating 30 for attaching the sheet to a surface. White pigment is used to enhance reflectivity as well as brightness of the phosphorescent material. A release liner 34 is laminated to the adhesive to prevent the adhesive 32 from inadvertently contacting a surface until the user is ready. In the embodiment illustrated in FIG. 3, the retroreflective layer 38 also includes the phosphorescent pigment therein. The hydrophobic silica 42 is then screened on the cube corners 40 in a predetermined pattern and a white pigmented adhesive 44 is coated over the hydrophobic silica pattern. Again, a release liner 46 is laminated to the adhesive 44 to prevent the sheet from inadvertently sticking to a surface until the user is ready for it. Other advantageous uses of the present invention with respect to retroreflective sheeting of other kinds, such as metallizing over some or all of the reflector elements, also will be recognized. Thus, for example, retroreflective sheeting material is disclosed and Martin U.S. Patent 4,801,193 may be provided with the phosphorescent pigmentation advantageously employed in the present invention. In the embodiment illustrated in FIG. 4, the sheet 48 is again formed of a transparent flexible film 50 that has retroreflective cube corner elements 52 formed on the reverse side thereof and which contains the phosphorescent pigment described earlier. Again, a hydrophobic silica 54 is screened on the cube corners of the translucent reflective flexible film 50 in a predetermined pattern. A white backcoating 56 as described earlier is coated over the hydrophobic silica 54. An adhesive layer 58 is laminated to the white backcoating 56 and a release liner 60 is laminated to the adhesive 58 to prevent the adhesive from inadvertently contacting a surface before the user desires. The method of application and composition of the hydrophobic silica, backcoating and adhesive as discussed herein may be as disclosed in the aforesaid Pricone et al. U.S. Patent No. 4,618,518. A process for forming the photoluminescent retroreflective sheeting shown in FIG. 1 is illustrated in FIG. 5. The transparent flexible film may be extruded and have retroreflective cube corner elements embossed or cast on the reverse side thereof at step 64. At step 68, a clear adhesive containing a phosphorescent pigment is screen printed in a predetermined pattern on the cube corner elements on the reverse or rear side of the flexible film. At step 70, the adhesive is cured and at step 72 an opaque film, preferably white, is adhered to the adhesive to form air cells. At step 74, an adhesive layer is added to the film and at step 76 a release layer is laminated to the adhesive layer to prevent the adhesive - from adhering to a surface prior to the time it is needed. Fig. 6 illustrates the process steps for forming the invention of FIG. 2. Again, in step 1, the transparent flexible film is extruded. At step 80 retroreflective cube corners are formed on the reverse side by casting or embossing. At step 82, hydrophobic silica is screen printed in a pattern over the cube corner elements. At step 84, the silica is coated with a clear water-based backcoating containing the phosphorescent pigment. A white (or other color) pigmented adhesive is applied to the silica coating at step 86 and a release layer is laminated to the pigmented adhesive at step 88 to prevent the adhesive from inadvertently sticking to a surface. FIG. 7 is a flow chart of the process for forming the photoluminescent retroreflective sheeting illustrated in FIG. 3. As can be seen in FIG. 7, the flexible film is extruded and contains the phosphorescent pigment which glows in the dark. The retroreflective cube corner elements are then embossed on the reverse side of the extruded flexible film at step 92. Hydrophobic silica is then screen printed on the cube corners in a predetermined pattern at step 94. A water-based backcoating adhesive is applied to the hydrophobic silica at step 96. Finally, a release liner is laminated to the adhesive at step 98 to prevent the product from sticking to a surface inadvertently. The flow chart of FIG. 8 discloses the method of making the sheeting sample illustrated in FIG. 4. Again, at step 100, the flexible film containing the phosphorescent pigment is extruded. In step 102 the reverse side of the sheet is embossed with the cube corner elements. In step 104, the hydrophobic silica is coated with a pigmented water-based backcoating, preferably white. At step 108 the layer of adhesive is applied to the backcoating and in step 110 a release liner is laminated to the adhesive. Again, such liner is used to prevent the adhesive from inadvertently sticking to a surface before it is intended to be used. Since the present film is primarily to be used indoors, additional overlays or other ultraviolet inhibitors which help prevent deterioration of outdoor retroreflective sheeting may not be necessary, further reducing the processing cost. FIG. 9 discloses a sample microsphere beaded type sheet material 130 employing the present invention. The beaded sheeting 130 may be of the type produced by 3M Corporation and sold under the trademark Scotchlite®. It is believed such material is made in accordance with various 3M patents such as Nos. 2,407,680 and 4,511,210. In this embodiment the sheeting comprises a layer of monosphere beads 135 and a transparent layer of resin below which may be a specially reflecting surface 136. The phosphorescent pigment 134 may be employed in an overlay over the beads, or in the binder layer 137 in which the beads are embedded. In the case of so-called high intensity beaded sheets, the phosphorescent pigment may be incorporated into the cell walls. A layer of adhesive 138 and a release liner 139 also may be used. It will be appreciated from the foregoing that the present invention provides significant advantages for safety purposes in that dual functions can be obtained while utilizing sheeting having a high degree of retroreflectivity and photoluminescence while minimizing the amount of material required for each such purpose. While the invention has been described in connection with a preferred embodiment, it is not intended to limit the scope of the invention to the particular form set forth, but, on the contrary, it is intended to cover such alternatives, modifications, and equivalents as may be included within the spirit and scope of the invention as defined by the appended claims.

Claims: CLAIMS 1. Photoluminescent retroreflective sheeting comprising: (a) a first layer of film having front and rear surfaces; (b) a second layer of retroreflecting elements juxtaposed with said rear surface to retroreflect light impinging on said front surface of said first layer; (c) a third layer overlying said rear surface and adhered thereto in a pattern over portions of said rear surface while being essentially out of contact with portions of said retroreflecting elements, so as to define a pattern of cells containing said retroreflecting elements; (d) an adhesive fourth layer applied to said third layer to adhere said sheeting to an underlying associated surface; and (e) a phosphorescent pigment contained within one or more of said first, second, third or fourth layers to cause said sheet material to glow in the dark. 2. The sheeting of Claim 1, and further including a layer of hydrophobic silica disposed within said cells. 3. The sheeting of Claim 2, in which said third layer is a clear adhesive. 4. The sheeting of Claim 3, in which said phosphorescent pigment is provided in said clear layer. 5. The sheeting of Claim 1, and further including a fifth opaque layer disposed between said third layer and said fourth layer. 6. The sheeting of Claim 5, wherein said opaque fifth layer is white. 7. The sheeting of Claim 1, wherein said film of said first layer is generally transparent and in which the retroreflecting elements of said second layer are comprised of cube corner elements integrally formed on said rear surface of said first layer. 8. The sheeting of Claim 7, in which said phosphorescent pigment is provided in said first layer. 9. The sheeting of Claim 8, in which said film is flexible and said cube corner retroreflecting elements are formed by embossing. 10. The sheeting of Claim 1, in which said retroreflective elements constitute cube corner retroreflective elements formed by casting against said first layer. 11. The sheeting of Claim 1, in which at least a portion of said retroreflecting elements are metalized and said adhesive layer is applied to portions of said metalized surfaces. 12. The sheeting of Claim 1, wherein said retroreflective elements comprise a matrix of microshperea beads. 13. In a cube corner retroreflective sheeting comprising a relatively transparent and flexible film having a plurality of cube corner retroreflective elements on the rear surface thereof and having one or more additional layers of backcoating or metallizing and adhesive applied thereto, the improvement consisting of a phosphorescent pigment within one or more of said layers so that said sheeting will glow in the dark for a limited time. 14. A photoluminescent retroreflective sheeting comprising: a first layer of retroreflective film having a first side and a pattern of cube corner retroreflector elements formed on the reverse side to retroreflect light when illuminated by a light source; a second layer of clear adhesive screen printed in a pattern and cured on said cube corner elements; a third layer of film adhered to the printed pattern and otherwise spaced from said uncoated cube corner elements; an adhesive layer formed on said film for attaching the sheet to a surface; a release liner removably secured to the adhesive layer to prevent inadvertent contact of the adhesive layer with a surface; and a phosphorescent pigment contained in at least one of said first, second or third layers to cause the sheeting to glow in the dark, and coloration pigmentation contained within one or more layers disposed behind said layer containing said phosphorescent pigment. 15. The photoluminescent retroreflective sheeting as in claim 14, wherein said phosphorescent pigment is in said second layer of clear adhesive. 16. The photoluminescent retroreflective sheeting as in claim 14, wherein said phosphorescent pigment is in said first layer of retroreflective film. 17. The photoluminescent retroreflective sheeting as in claim 14, wherein the screen-printed pattern of adhesive creates air cells that are sealed by the pigmented film layer. 18. Photoluminescent retroreflective sheeting comprising: a transparent film having cube corner retroreflectors embossed on the reverse side thereof for retroreflecting light incident on said film; a layer of hydrophobic silica screen printed in a pattern on the cube corner elements; a clear back coating containing phosphorescent pigment formed over the hydrophobic silica layer and the exposed cube corner elements to cause the sheeting to glow in the dark; an adhesive secured to the back coating for attaching the sheet to a surface. 19. Photoluminescent retroreflective sheeting comprising: a layer of transparent extruded film embossed on the rear surface with retroreflective cube corner elements that retroreflect light incident on said film; a phosphorescent pigment contained in the extruded film so said layer will be photoluminescent and will glow in the dark; hydrophobic silica screen-printed in a predetermined pattern on the extruded cube corner elements; a white pigmented adhesive formed over the silica pattern and the exposed cube corner elements for attaching the sheet to a surface; and a release liner attached to said adhesive to prevent inadvertent contact of said adhesive with a surface. 20. Photoluminescent retroreflective sheeting comprising: a first layer of transparent thermoplastic film embossed on the rear surface thereof with retroreflective cube corner elements for retroreflecting light; a phosphorescent pigment included in the film to form a photoluminescent composition such that said first layer glows in the dark; hydrophobic silica screen printed on the phosphorescent pigment in a predetermined pattern; a white pigmented water-based back coating formed over the hydrophobic silica pattern; a layer of adhesive attached to the back coating for attaching the sheet to a surface; and a release liner attached to the layer of adhesive to prevent accidental contact of the adhesive with a surface. 21. A method of forming a photoluminescent retroreflective sheeting comprising the steps of: embossing cube corner retroreflector elements on the reverse side of a thin flexible film to form a retroreflective layer that will produce retroreflective illumination upon receiving incident light; screen printing a second layer of clear adhesive in a predetermined pattern on said layer of embossed cube corner elements; curing said second layer; laminating a third layer of film on the printed pattern; applying an adhesive fourth layer to the third film layer for attaching the sheeting to a surface; removably securing a release liner to the adhesive layer to prevent inadvertent contact of the adhesive layer with a surface; and including a phosphorescent pigment in at least one of said first, second or third layers to cause the sheeting to glow in the dark. 22. The method as in claim 21, further including the step of placing the phosphorescent pigment in the second layer of clear adhesive. 23. The method as in claim 21, further comprising the step of placing the phosphorescent pigment in the retroreflective film first layer. 24. The method as in claim 21, further including the step of placing the phosphorescent pigment in the third film layer laminated on the printed pattern. 25. The method as in claim 21, further including the step of creating air cells with the screen-printed adhesive pattern that are sealed by the third film layer. 26. A method of forming a photoluminescent retroreflective sheeting comprising the steps of: embossing cube corner retroreflectors in the reverse side of a transparent flexible film to form a retroreflective layer for retroreflecting incident light; screen-printing a layer of hydrophobic silica in a predetermined pattern on the cube corners; forming a clear water-based back coating containing phosphorescent pigment over the hydrophobic silica layer to cause the sheet to glow in the dark; applying a pigmented adhesive to the back coating for attaching the sheet to a surface; and removably attaching a release liner to the pigmented adhesive to prevent inadvertent contact of the adhesive with a surface. 27. A method of forming a photoluminescent retroreflective sheeting comprising the steps of: phosphorescent pigment containing film to form a photoluminescent film layer that glows in the dark; embossing cube corner retroreflectors on the rear surface of a layer of film for the purpose of retroreflecting incident light; screen printing hydrophobic silica in a pattern on the extruded film cube corners; forming a pigmented adhesive over the silica pattern for attaching the sheet to a surface; and securing a release liner to the pigmented adhesive to prevent inadvertent contact of the adhesive with a surface. 28. A method of forming a photoluminescent retroreflective sheeting comprising the steps of: embossing a layer of extruded transparent thermoplastic film including a phosphorescent pigment with cube corner retroreflector elements on the rear surface thereof for retroreflecting light, and which provides a photoluminescent film layer that glows in the dark; screen-printing a hydrophobic silica on the embossed cube corner retroreflectors in a predetermined pattern; forming a white pigmented water-based back coating over the hydrophobic silica pattern; applying a layer of adhesive to the back coating for attaching the sheet to a surface; and attaching a release liner to the layer of adhesive to prevent accidental contact of the adhesive with a surface.

Inventors: SZOPINSKI ALEX A, ZAMPA DANIEL E, SZOPINSKI, ALEX, A., ZAMPA, DANIEL, E.
Applicants: STIMSONITE CORP, STIMSONITE CORPORATION
Application year: 1993
Main classification: G02B5
IPC codes: B32B37, B32B38, F21K2, G02B5, G09F13, G09F19