WO2014099486A1

WO2014099486A1 - Photoluminescent retroreflective articles

Info

Publication number: WO2014099486A1
Application number: PCT/US2013/074095
Authority: WO
Inventors: John A. Worrell; Marc D. Radcliffe
Original assignee: 3M Innovative Properties Company
Priority date: 2012-12-21
Filing date: 2013-12-10
Publication date: 2014-06-26

Abstract

A photoluminescent retroreflective article includes a retroreflective layer including multiple cube corner elements that collectively form a structured surface that is opposite a major surface and a conforming layer having a first region and a second region wherein the second region is in intimate contact with the structured surface and the first region forming a low refractive index layer between the conforming layer and the structured surface of the retroreflective layer. The conforming layer is separated from the structured surface at the first region by a barrier layer. A photoluminescent layer is disposed on the conforming layer.

Description

PHOTOLUMINESCENT RETROREFLECTIVE ARTICLES

Background

[0001] Retroreflective materials are characterized by the ability to redirect light incident on the material back toward the originating light source. This property has led to the widespread use of retroreflective sheeting for a variety of traffic and personal safety uses. Retroreflective sheeting is commonly employed in a variety of articles, for example, road signs, barricades, license plates, pavement markers and marking tape, as well as retroreflective tapes for vehicles and clothing.

[0002] Two known types of retroreflective sheeting are optical element sheeting (e.g., cube corner sheeting) and microsphere-based sheeting. Microsphere-based sheeting, sometimes referred to as "beaded" sheeting, employs a multitude of microspheres typically at least partially embedded in a binder layer and having associated specular or diffuse reflecting materials (e.g., pigment particles, metal flakes or vapor coats, etc.) to retroreflect incident light. Cube corner retroreflective sheeting, sometimes referred to as "prismatic" sheeting, typically comprises a thin transparent layer having a substantially planar first surface and a second structured surface comprising a plurality of geometric structures, some or all of which include three reflective faces configured as a cube corner element.

[0003] A cube corner element can include three mutually perpendicular optical faces that intersect at a single apex. Generally, light that is incident on a corner cube element from a light source is totally internally reflected from each of the three perpendicular cube corner optical faces and is redirected back toward the light source.

[0004] Luminescent dyes and pigments are utilized in the preparation of signs and other articles where visibility in dark conditions is required. Chemiluminescent and/or photoluminescent materials may be used. The luminous material may be attached to exits, stairways, fire extinguishers, and so on to guide a person in the event of a power failure. While this is effective immediately after loss of power occurs, the luminescence of such materials decreases rapidly and may be substantially gone in a relatively short time. These photoluminescent films are known and are commercially used to provide signage that warns, cautions, and provides other messages conveying safety information. Frequently, these films are combined with an adhesive to form a photoluminescent tape. Sometimes also characterized as "Glow-in-the-Dark", "luminous", or "luminescent", these films or tapes are based on materials that absorb photons and emit visible light [0005] There is a need to provide a signage article that combines the properties of retroreflectivity and luminescence. An article having such properties would be highly visible when there is a light source available to impinge upon its surface in a "front-lit" condition and would also be visible in conditions of complete or near-complete darkness.

Summary [0006] The present disclosure relates to photoluminescent retroreflective articles. In particular, the present disclosure relates to photoluminescent retroreflective articles where the retroreflective elements do not substantially interfere with the charging and emission of the photoluminescent element. [0007] In a first aspect of the disclosure, a photoluminescent retroreflective article includes a photoluminescent retroreflective article including a retroreflective layer having multiple cube corner elements that collectively form a structured surface that is opposite a major surface and a conforming layer having a first region and a second region wherein the second region is in intimate contact with the structured surface and the first region forming a low refractive index layer between the conforming layer and the structured surface of the retroreflective layer and the conforming layer is separated from the structured surface at the first region by a barrier layer. A photoluminescent layer is disposed on the conforming layer and the conforming layer separates the photoluminescent layer and the retroreflective layer. [0008] In one or more embodiments, the conforming layer transmits excitation light to the photoluminescent layer and the conforming layer transmits emission light from the photoluminescent layer. In one or more embodiments, the barrier layer transmits excitation light to the photoluminescent layer and the barrier layer transmits emission light from the photoluminescent layer. In one or more embodiments, the low refractive index layer includes air. In one or more embodiments, the conforming layer includes a pressure sensitive adhesive. In one or more embodiments, a light reflective layer is disposed on the photoluminescent layer. The photoluminescent layer separates the light reflective layer from the conforming layer. In one or more embodiments, an adhesive layer is disposed on the light reflective layer. The light reflective layer separating the adhesive layer from the photoluminescent layer. In one or more embodiments, a releasable liner is disposed on the adhesive layer. In one or more embodiments, the conforming layer is index matched to the retroreflective layer.

[0009] In a second aspect of the disclosure, a method of forming a photoluminescent retroreflective article, includes providing a retroreflective layer including multiple cube corner elements that collectively form a structured surface and disposing one or more discontinuous barrier layers adjacent to the structured surface. Then the method includes placing a conforming layer adjacent to the one or more discontinuous barrier layers and structured surface and positioning a photoluminescent layer on the conforming layer so that the conforming layer separates the photoluminescent layer from the structured surface.

[0010] In one or more embodiments the method includes transmitting excitation light through the conforming layer layers to excite the photoluminescent layer. In one or more embodiments the method includes transmitting photoluminescent layer emission light through the conforming layer and structured surface. In one or more embodiments the method includes transmitting excitation light through the discontinuous barrier layers to excite the photoluminescent layer. In one or more embodiments the method includes comprising transmitting photoluminescent layer emission light through the discontinuous barrier layers and structured surface and conforming layer. In one or more embodiments the disposing step forms and maintains a low refractive index layer between the structured surface and the conforming layer. In one or more embodiments the low refractive index layer includes air. In one or more embodiments the method includes forming or printing the one or more discontinuous barrier layers onto the conforming layer.

[0011] These and various other features and advantages will be apparent from a reading of the following detailed description.

Brief Description of Drawings [0012] The disclosure may be more completely understood in consideration of the following detailed description of various embodiments of the disclosure in connection with the accompanying drawings, in which: [0013] FIG. 1 is a schematic side view of an exemplary embodiment of a photoluminescent retroreflective article.

[0014] The figures are not necessarily to scale. Like numbers used in the figures refer to like components. However, it will be understood that the use of a number to refer to a component in a given figure is not intended to limit the component in another figure labeled with the same number.

Detailed Description

[0015] In the following description, reference is made to the accompanying set of drawings that form a part hereof and in which are shown by way of illustration several specific embodiments. It is to be understood that other embodiments are contemplated and may be made without departing from the scope or spirit of the present disclosure. The following detailed description, therefore, is not to be taken in a limiting sense. [0016] Unless otherwise indicated, all numbers expressing feature sizes, amounts, and physical properties used in the specification and claims are to be understood as being modified in all instances by the term "about." Accordingly, unless indicated to the contrary, the numerical parameters set forth in the foregoing specification and attached claims are approximations that can vary depending upon the desired properties sought to be obtained by those skilled in the art utilizing the teachings disclosed herein.

[0017] As used in this specification and the appended claims, the singular forms "a", "an", and "the" encompass embodiments having plural referents, unless the content clearly dictates otherwise. As used in this specification and the appended claims, the term "or" is generally employed in its sense including "and/or" unless the content clearly dictates otherwise.

[0018] Spatially related terms, including but not limited to, "lower," "upper," "beneath," "below," "above," and "on top," if used herein, are utilized for ease of description to describe spatial relationships of an element(s) to another. Such spatially related terms encompass different orientations of the device in use or operation in addition to the particular orientations depicted in the figures and described herein. For example, if a cell depicted in the figures is turned over or flipped over, portions previously described as below or beneath other elements would then be above those other elements. [0019] As used herein, when an element, component or layer for example is described as forming a "coincident interface" with, or being "on", "connected to," "coupled with", "in contact with", "separating" or "adjacent" another element, component or layer, it can be directly on, directly connected to, directly coupled with, in direct contact with, or intervening elements, components or layers may be on, connected, coupled or in contact with or separating the particular element, component or layer, for example. When an element, component or layer for example is referred to as being "directly on," "directly connected to," "directly coupled with," or "directly in contact with" another element, there are no intervening elements, components or layers for example.

[0020] The present disclosure relates to photoluminescent retroreflective articles. In particular, the present disclosure relates to photoluminescent retroreflective articles where the

retroreflective elements do not substantially interfere with the charging and emission of the photoluminescent element. While the present disclosure is not so limited, an appreciation of various aspects of the disclosure will be gained through a discussion of the examples provided below.

[0021] FIG. 1 is schematic side view of an exemplary embodiment of a photoluminescent retroreflective article 100 that faces viewer 102. Photoluminescent retroreflective article 100 includes a retroreflective layer 110 including multiple cube corner elements 112 that collectively form a structured surface 114 opposite a major surface 116. The specific photoluminescent retroreflective article 100 shown in FIG. 1 includes an overlay layer 118 (also referred to as a top film), but those of skill will appreciate that some embodiments do not include an overlay layer. One or more barrier layers 134 are positioned between retroreflective layer 110 and conforming layer 132. Barrier layers 134 form a physical "barrier" between cube corner elements 112 and conforming layer 132. Barrier layers 134 are discrete and discontinuous elements. Barrier layer 134 can directly contact or be spaced apart from or can push slightly into the tips of cube corner elements 112. A photoluminescent layer 135 is disposed on the conforming layer 132. The conforming layer 132 separates one or both of barrier layer 134 and cube corner elements 112 from the photoluminescent layer 135. Barrier layer 134 can directly contact or be spaced apart from the photoluminescent layer 135. [0022] In general, any material that prevents the conforming layer material from contacting cube corner elements 112 or flowing or creeping into low refractive index area 138 can be used to form the barrier layer. The portions of structured surface 112 that are adjacent to low refractive index area 138, which is created, in part, by barrier layers 134, are typically retroreflective. Exemplary materials for use in barrier layer 134 include resins, polymeric materials, dyes, inks (including color-shifting inks), vinyl, inorganic materials, UV-curable polymers, multi-layer optical films (including, for example, color-shifting multi-layer optical films), pigments, particles, and beads. The size and spacing of the one or more barrier layers can be varied. In many embodiments, the barrier layer 134 can be formed of any material that transmits excitation light to the photo luminescent layer 135 and transmits emission light from the photo luminescent layer 135.

[0023] In some embodiments, the barrier layers may form a pattern on the retroreflective sheeting. In some embodiments, one may wish to reduce the visibility of the pattern on the sheeting. This can be accomplished, for example, by using barrier layers that are relatively small and difficult to resolve at a specific distance. In general, any desired pattern can be generated by combinations of the described techniques, including, for example, indicia such as letters, words, alphanumerics, symbols, graphics, logos, or pictures. The patterns can also be continuous, discontinuous, monotonic, dotted, serpentine, any smoothly varying function, stripes, varying in the machine direction, the transverse direction, or both; the pattern can form an image, logo, or text, and the pattern can include patterned coatings and/or perforations. The pattern can include, for example, an irregular pattern, a regular pattern, a grid, words, graphics, images lines, and intersecting zones that form cells. [0024] A low refractive index area 138 is positioned between (1) one or both of barrier layer 134 and conforming layer 132 and (2) cube corner elements 112. The low refractive index area 138 facilitates total internal reflection such that light that is incident on cube corner elements 112 adjacent to a low refractive index area 138 is retroreflected. A light ray incident on a cube corner element 112 that is adjacent to low refractive index layer 138 is retroreflected back to viewer 102. For this reason, an area of retroreflective article 100 that includes low refractive index layer 138 can be referred to as an optically active area. In contrast, an area of

retroreflective article 100 that does not include low refractive index layer 138 can be referred to as an optically inactive area because it does not substantially retroreflect incident light. As used herein, the term "optically inactive area" refers to an area that is at least 50% less optically active (e.g., retroreflective) than an optically active area. In some embodiments, the optically inactive area is at least 40%> less optically active, or at least 30%> less optically active, or at least 20%> less optically active, or at least 10% less optically active, or at least at least 5% less optically active than an optically active area.

[0025] Low refractive index layer 138 includes a material that has a refractive index that is less than about 1.30, less than about 1.25, less than about 1.2, less than about 1.15, less than about 1.10, or less than about 1.05. In general, any material that prevents the conforming layer material from contacting cube corner elements 112 or flowing or creeping into low refractive index area 138 can be used as the low refractive index material. In some embodiments, barrier layer 134 has sufficient structural integrity to prevent conforming layer 132 from flowing into a low refractive index area 138. In such embodiments, low refractive index area may include, for example, a gas (e.g., air, nitrogen, argon, and the like). In other embodiments, low refractive index area includes a solid or liquid substance that can flow into or be pressed into or onto cube corner elements 112. Exemplary materials include, for example, ultra-low index coatings (those described in PCT Patent Application No. PCT/US2010/031290), and other highly porous materials.

[0026] The portions of conforming layer 132 that are adjacent to or in contact or direct contact with cube corner elements 112 form optically inactive (e.g., non-retroreflective) areas or cells. The conforming layer 132 can be formed of any material that transmits excitation light to the photoluminescent layer 135 and transmits emission light from the photoluminescent layer 135. In many embodiments, a light reflective layer 137 is disposed on the photoluminescent layer 135. The photoluminescent layer 135 can separate the light reflective layer 137 from the conforming layer 132. In many embodiments, the light reflective layer 137 has a white color. In these embodiments, the photoluminescent layer 135 can have adhesive properties to adhere to the light reflective layer 137 or a separate adhesive layer (not shown) can adhere the light reflective layer 137 to the photoluminescent layer 135. In some embodiments an pressure sensitive adhesive layer (not shown) on an exterior surface of the light reflective layer 137 and an optional release liner (not shown) can be disposed on the pressure sensitive adhesive layer to protect the pressure sensitive adhesive layer until the photo luminescent retroreflective article 100 is prepared for mounting to a substrate.

[0027] In some embodiments, conforming layer 132 is an adhesive. Exemplary adhesives include those described in PCT Patent Application No. PCT/US2010/031290. Where the conforming layer is an adhesive, the conforming layer may assist in holding the entire photo luminescent retroreflective construction together and/or the viscoelastic nature of barrier layers 134 may prevent wetting of cube tips or surfaces either initially during fabrication of the photoluminescent retroreflective article or over time.

[0028] In some embodiments, conforming layer 132 is a pressure sensitive adhesive. The PSTC (pressure sensitive tape council) definition of a pressure sensitive adhesive is an adhesive that is permanently tacky at room temperature which adheres to a variety of surfaces with light pressure (finger pressure) with no phase change (liquid to solid). While most adhesives (e.g., hot melt adhesives) require both heat and pressure to conform, pressure sensitive adhesives typically only require pressure to conform. Exemplary pressure sensitive adhesives include those described in U.S. Patent No. 6,677,030. Barrier layers 134 may also prevent the pressure sensitive adhesive from wetting out the cube corner sheeting. [0029] The conforming layer 132 can be formed in a variety of ways including but not limited to the following exemplary methods. In one exemplary embodiment, the material(s) forming the barrier layer is printed onto the conforming layer and/or the cube corner elements. The method of printing can be a non-contact method such as, for example, printing using an inkjet printer. The method of printing can be a contact printing method such as, for example, flexographic printing. In another exemplary embodiment, the material(s) forming the barrier layer is printed onto a flat release surface using, for example, an inkjet or screen printing method, and are then subsequently transferred from the flat release surface onto the conforming layer and/or cube corner elements. In another exemplary embodiment, the material(s) forming the barrier layer are flood coated onto a microstructured surface. The barrier layer material is subsequently transferred from the microstructured surface to the conforming layer by, for example, lamination. The structured surface is removed after lamination to provide a conforming layer with barrier layers that is laminated to a retroreflective layer to make the retroreflective article. The retroreflective article can then be adhesively bonded to the photolummescent layer 135 to form the photolummescent retroreflective article 100.

[0030] The photolummescent layer 135 can be formed of any useful luminescent material. The photolummescent layer 135 can be prepared using any of the known photolummescent materials known in the art. This layer may itself be a multi-layered construction consisting of a luminescent layer and a carrier layer. The carrier layer, generally a thermoplastic material such as vinyl, is covered with a layer to prevent migration of the luminescent material into the carrier layer. This layer can be made of any suitable material, such as acrylic or methacrylic type resins. The luminescent layer, which may be a vinyl or other suitable thermoplastic having

photolummescent particles dispersed therein, can be positioned or adhesively disposed on the layer. Any of the known photolummescent materials can be incorporated into this

photolummescent layer 135. Photolummescent film is commercially available from 3M

Company (3M) as 3M™ Photolummescent Film 6900 HPPL that provides luminosity that lasts for an extended time after photon excitation in the film ends.

[0031] All references mentioned herein are incorporated by reference.

[0032] Those having skill in the art will appreciate that many changes may be made to the details of the above-described embodiments and implementations without departing from the underlying principles thereof. Further, various modifications and alterations of the present invention will become apparent to those skilled in the art without departing from the spirit and scope of the invention. The scope of the present application should, therefore, be determined only by the following claims.

[0033] Thus, embodiments of the PHOTOLUMINESCENT RETROREFLECTIVE ARTICLES are disclosed. The implementations described above and other implementations are within the scope of the following claims. One skilled in the art will appreciate that the present disclosure can be practiced with embodiments other than those disclosed. The disclosed embodiments are presented for purposes of illustration and not limitation, and the present disclosure is limited only by the claims that follow.

Claims

What is claimed is:

1. A photolummescent retroreflective article, comprising:

a retroreflective layer including multiple cube corner elements that collectively form a structured surface that is opposite a major surface;

a conforming layer having a first region and a second region wherein the second region is in intimate contact with the structured surface and the first region forming a low refractive index layer between the conforming layer and the structured surface of the retroreflective layer and the conforming layer is separated from the structured surface at the first region by a barrier layer;

a photolummescent layer disposed on the conforming layer, the conforming layer separating the photolummescent layer and the retroreflective layer.

2. The photolummescent retroreflective article of claim 1, wherein the conforming layer transmits excitation light to the photolummescent layer and the conforming layer transmits emission light from the photolummescent layer.

3. The photolummescent retroreflective article of claims 1 to 2, wherein the barrier layer transmits excitation light to the photolummescent layer and the barrier layer transmits emission light from the photolummescent layer.

4. The photolummescent retroreflective article of claims 1 to 3, wherein the low refractive index layer includes air.

5. The photolummescent retroreflective article of claims 1 to 4, wherein the conforming layer comprises a pressure sensitive adhesive.

6. The photolummescent retroreflective article of claims 1 to 5, further comprising a light reflective layer disposed on the photolummescent layer, the photolummescent layer separating the light reflective layer from the conforming layer.

7. The photolummescent retroreflective article of claim 6, further comprising an adhesive layer disposed on the light reflective layer, the light reflective layer separating the adhesive layer from the photolummescent layer.

8. The photolummescent retrorenective article of claim 7, further comprising a releasable liner disposed on the adhesive layer.

9. The photolummescent retroreflective article of claims 1 to 8, wherein the conforming layer is index matched to the retroreflective layer.

10. A method of forming a photolummescent retroreflective article, comprising:

providing a retroreflective layer comprising multiple cube corner elements that

collectively form a structured surface;

disposing one or more discontinuous barrier layers adjacent to the structured surface; placing a conforming layer adjacent to the one or more discontinuous barrier layers and structured surface; and

positioning a photolummescent layer to the conforming layer so that the conforming layer separates the photolummescent layer from the structured surface.

11. The method of claim 10, further comprising transmitting excitation light through the conforming layer layers to excite the photolummescent layer.

12. The method of claims 10 to 11, further comprising transmitting photolummescent layer emission light through the conforming layer and structured surface.

13. The method of claims 10 to 12, further comprising transmitting excitation light through the discontinuous barrier layers to excite the photolummescent layer.

14. The method of claims 10 to 13, further comprising transmitting photolummescent layer emission light through the discontinuous barrier layers and structured surface and conforming layer.

15. The method of claims 10 to 14, wherein the disposing step forms and maintains a low refractive index layer between the structured surface and the conforming layer.

16. The method of claim 15, wherein the low refractive index layer includes air.

17. The method of claims 10 to 16, wherein the disposing step includes forming or printing the one or more discontinuous barrier layers onto the conforming layer.