JP2016106258A - Retroreflective articles and methods of making the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a retroreflective article made without sealing films and/or metalized cube corners.SOLUTION: A retroreflective article comprises: a retroreflective layer 110 including multiple cube corner elements 112 that collectively form a structured surface 114 that is opposite a major surface; and a sealing layer having a first region and a second region, where the second region is in contact with the structured surface 114 and surrounds the first region to form at least one cell with a certain cell size; and a low refractive index layer 138 between the first region and the structured surface 114 of the retroreflective layer 110, where the first region has a cell size that is less than 1000 microns.SELECTED DRAWING: Figure 1A

Description

  The present disclosure relates generally to retroreflective articles and methods of making such articles.

  The retroreflective material is characterized by the ability to convert light incident on the material back to the light source. Due to this property, retroreflective sheets are used in a wide range of applications for various traffic and personal safety uses. Retroreflective sheeting is commonly used for various articles such as road signs, barricades, license plates, road markings, and marking tapes, and retroreflective tapes for vehicles and clothing.

  Two known types of retroreflective sheeting are optical element sheeting (eg, cube corner sheeting) and microsphere based sheeting. Microsphere-based sheet materials (sometimes referred to as “bead” sheet materials) are typically at least partially embedded in a binder layer and include specular or diffuse reflective materials (eg, pigment particles, metal flakes, Or incident light rays are retroreflected by using a large number of microspheres with a vapor deposition coating or the like). A cube-corner retroreflective sheet (sometimes referred to as a “prism-like” sheet) typically includes a substantially flat first surface and a second structured surface comprising a plurality of geometric structures. A thin transparent layer having three reflective surfaces, part or all of which is configured as a cube corner element.

  Typically, a cube corner element includes three mutually perpendicular optical surfaces that intersect at a single vertex. In general, light incident on the corner cube element from the light source is totally internally reflected from each of the three vertical corner cube optical surfaces and returned to the light source. For example, dirt, water, and adhesive on the optical surface can interfere with total internal reflection (TIR) and lead to a reduction in retroreflective light intensity. For this reason, the air interface is typically protected by a sealing film. However, the sealing film may reduce the overall active area on which retroreflection can occur. Furthermore, the sealing film increases the manufacturing cost. In addition, the sealing process may create a visible pattern on the retroreflective sheeting, which is desirable in many applications where a more uniform appearance is generally preferred, such as use in license plates and / or commercial graphic applications. Absent. Metallized cube corners do not rely on TIR for retroreflected light, but they are generally not white enough for daytime indications (eg, signs). Furthermore, the durability of the metal coating may be insufficient.

  The inventors of the present application have made retroreflective articles without sealing the film and / or metallized cube corners.

  Some embodiments of the retroreflective article of the present disclosure include one or more optically active regions in which incident light is retroreflected by a structured surface, including, for example, cube corner elements, and the incident light is structured. One or more optically inactive regions that are not substantially retroreflected by the surface. The one or more optically active regions include a low refractive index layer or material adjacent to a portion of the structured surface. The one or more optically inert regions include a pressure sensitive adhesive adjacent to a portion of the structured surface. The pressure sensitive adhesive substantially destroys the retroreflectivity of the portion of the structured surface immediately adjacent to it. The low refractive index layer helps maintain retroreflectiveness of adjacent structured surfaces by creating a “barrier” between the structured surface and the pressure sensitive adhesive.

  Some embodiments of the retroreflective article of the present disclosure include a barrier layer between the pressure sensitive adhesive and the low refractive index layer. The barrier layer has sufficient structural integrity and substantially prevents the flow of pressure sensitive adhesive to the low refractive index layer. Exemplary materials for inclusion in the barrier layer include resins, polymeric materials, inks, dyes, and vinyl. In some embodiments, the barrier layer confines the low refractive index material in the low refractive index layer. A low refractive index material is a material having a refractive index of less than 1.3.

  Some embodiments of the present disclosure generally include a retroreflective layer that includes a plurality of cube corner elements that collectively form a structured surface opposite the major surface, and a first region and a second region. A sealing layer, wherein the second region is in contact with the structured surface, the second region surrounds the first region, and forms at least one cell having a cell dimension; A retroreflective article comprising: a low refractive index layer between one region and a structured surface of the retroreflective layer, the first region having a cell dimension of less than 1000 micrometers; About.

  Some embodiments of the present disclosure generally contact the at least a portion of the structured surface with a retroreflective layer that includes a structured surface opposite the major surface and substantially recurs incident light. An encapsulating layer that forms an optically inactive region that does not reflect; and at least one low refractive index that retroreflects incident light and is surrounded by the optically inactive region to form at least one cell. And a low refractive index layer having a cell dimension of 1000 micrometers or less.

  Some embodiments of the present disclosure are generally methods of making a retroreflective article, the method comprising providing a retroreflective layer that includes a structured surface opposite the second major surface; Applying a sealing layer having a first region and a second region, wherein the second region is in contact with the structured surface and surrounds the first region to form at least one cell having a certain cell dimension. And a step of forming a low refractive index layer between the first region and the structured surface of the retroreflective layer, wherein the cell size of the first region is 1000 micrometers or less, Including a method.

The present disclosure may be more fully understood and clarified in view of the following detailed description of various embodiments in connection with the accompanying drawings.
1 is a schematic side view of one exemplary embodiment of a retroreflective article of the present disclosure. FIG. 1 is a schematic side view of one exemplary embodiment of a retroreflective article of the present disclosure. FIG. FIG. 2 is a schematic diagram of one representative intermediate process for making the retroreflective article of FIG. 1. 1 is a schematic diagram of one exemplary embodiment of a retroreflective article of the present disclosure. FIG. Schematic of the pattern used for Examples 11-13. Schematic of the pattern used for Examples 11-13. 1 is a schematic diagram of one exemplary embodiment of a retroreflective article of the present disclosure. FIG. The schematic of the pattern used for Examples 1-6. Plot showing the observation angle versus distance for the left and right headlights of a standard sedan. Plot showing the observation angle versus distance for the left and right headlights of a standard sedan. Schematic of the pattern used for Examples 14-19. Schematic of the pattern used for Examples 14-19.

  FIGS. 1A and 1B show one exemplary embodiment of a retroreflective article 100 facing the viewer 102. The retroreflective article 100 includes a retroreflective layer 110 that includes a plurality of cube corner elements 112 that collectively form a structured surface 114 opposite the major surface 116. The retroreflective layer 110 also includes an overlay layer 118. The pressure sensitive adhesive layer 130 is adjacent to the retroreflective layer 110. The pressure sensitive adhesive layer 130 includes a pressure sensitive adhesive 132, one or more barrier layers 134, and a liner 136. The barrier layer 134 has sufficient structural integrity to prevent the pressure sensitive adhesive 132 from flowing into the low index layer 138 between the structured surface 114 and the barrier layer 134. The barrier layer 134 may be in direct contact with the tip of the cube corner element 112, may be spaced from the tip of the cube corner element 112, or may be pushed slightly into the tip of the cube corner element 112.

  When present, the barrier layer 134 forms a physical “barrier” between the pressure sensitive adhesive 130 and the cube corner element 112. The barrier layer can prevent cube tip or surface wetting by pressure sensitive, either initially during the manufacture of the retroreflective article or over time due to the viscoelastic properties of the adhesive. The layer confined between the pressure sensitive adhesive 130 and the cube corner element 112 is the low index layer 138. The low refractive index layer is therefore surrounded. If a protective layer is applied to it, the low refractive index layer is encapsulated. The encapsulation of the low refractive index layer maintains and / or protects the integrity of the low refractive index layer. The presence of the barrier layer allows the portion of structured surface 114 adjacent to low index layer 138 and / or barrier layer 134 to retroreflect incident light 150. The barrier layer 134 can also prevent the pressure sensitive adhesive 130 from infiltrating the cube sheet material. A pressure sensitive adhesive 130 that does not contact the barrier layer 134 adheres to the cube corner elements, thereby effectively sealing the retroreflective areas and optically forming active areas or cells. The pressure sensitive adhesive 130 also holds the entire retroreflective structure together, thereby eliminating the need for a separate sealing film and sealing process. In some embodiments, the pressure sensitive adhesive is in close proximity to or directly adjacent to the structured surface or cube corner element.

  As shown in FIG. 1B, the light ray 150 incident on the cube corner element 112 adjacent to the low refractive index layer 138 is retroreflected to the viewer 102. For this reason, the region of the retroreflective article 100 that includes the low refractive index layer 138 is optically referred to as the active region. In contrast, a region of the retroreflective article 100 that does not include the low refractive index layer 138 is referred to as an optically inactive region because it does not substantially retroreflect incident light.

  The low refractive index layer 138 comprises a material having a refractive index of 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. Including. Exemplary low refractive index materials include air and low refractive index materials (eg, low refractive index materials described in US patent application Ser. No. 61 / 324,249, incorporated herein by reference).

  In general, any material that prevents the pressure sensitive adhesive from contacting the cube corner element 112 or entering the low index layer 138 may be used in the barrier layer 134. Exemplary materials for use in the barrier layer 134 include resins, polymeric materials, dyes, inks, vinyls, inorganic materials, UV curable polymers, pigments, particles, and beads. The dimensions and spacing of the barrier layer may vary. In some embodiments, the barrier layer may form a pattern on the retroreflective sheet material. In some embodiments, it may be desired to reduce the visibility of the structured pattern. In general, the desired pattern can be generated by a combination of the described techniques, such as letters, words, alphanumeric characters, symbols, or even indicia such as photographs. The pattern can also be a continuous, non-continuous, monotonous, sigmoidal, arbitrarily smoothly changing function, stripe, changing in machine direction, lateral direction, or both, and the pattern can be an image, logo, or Text may be formed and the pattern may include a patterned coating and / or perforations. In some embodiments, the printed area and / or the non-printed area may form a safety mechanism. The pattern may include, for example, irregular patterns, regular patterns, grids, words, graphics, images, lines, and intersecting zones that form cells.

  In at least some embodiments, the pressure sensitive adhesive layer includes a first region and a second region. The second region is in direct contact with or in close contact with the structured surface. The first region and the second region have sufficiently different properties to form and separate a low refractive index layer between the pressure sensitive adhesive layer and the structured surface of the retroreflective layer. In some embodiments, the second region comprises a pressure sensitive adhesive and the first region is different in composition from the second region. In some embodiments, the first region and the second region have different polymer forms. In some embodiments, the first region and the second region have different flow characteristics. In some embodiments, the first region and the second region have different viscoelastic properties. In some embodiments, the first region and the second region have different adhesive properties. In some embodiments, the retroreflective article includes a plurality of second regions that form a pattern. In some embodiments, the pattern is one of an irregular pattern, a regular pattern, a grid, a word, a graphic, an image, and a line.

  Exemplary pressure sensitive adhesives for use in the retroreflective articles of the present disclosure include crosslinked and plasticized acrylic pressure sensitive adhesives. Other pressure sensitive adhesives may be used, such as blends of natural or rigid rubber and resin, silicone or other polymer systems with or without adhesives. The definition of pressure sensitive adhesive by PSTC (pressure sensitive tape council) is permanently sticky at room temperature, adheres to various surfaces with light pressure (finger pressure), and has a phase change (from liquid to solid) There is no adhesive.

  Acrylic acid and methacrylic acid ester: The acrylic acid ester is present in the range of about 65 to about 99 parts by weight, preferably about 78 to about 98 parts by weight, and more preferably about 90 to about 98 parts by weight. Useful acrylic esters are selected from the group consisting of first monofunctional acrylate or methacrylate esters of non-tertiary alkyl alcohols (wherein the alkyl group contains from 4 to about 12 carbon atoms), and combinations thereof At least one monomer. Such acrylate or methacrylate esters generally have a glass transition temperature of about −25 ° C. or less as a homopolymer. Larger amounts of this monomer relative to other comonomers allow the PSA to be more tacky at low temperatures.

  Preferred acrylate or methacrylate ester monomers include, but are not limited to, n-butyl acrylate (BA), n-butyl methacrylate, isobutyl acrylate, 2-methylbutyl acrylate, 2-ethylhexyl acrylate, n-octyl acrylate , Isooctyl acrylate (IOA), isooctyl methacrylate, isononyl acrylate, isodecyl acrylate, and mixtures thereof.

  Particularly preferred acrylates include those selected from the group consisting of isooctyl acrylate, n-butyl acrylate, 2-methylbutyl acrylate, 2-ethylhexyl acrylate, and mixtures thereof.

  Polar monomer: A low concentration (typically about 1 to about 10 parts by weight) of polar monomer, such as carboxylic acid, may be used to increase the cohesive strength of the pressure sensitive adhesive. At higher concentrations, these polar monomers tend to reduce sticking, raise the glass transition temperature, and reduce performance at low temperatures.

  Useful copolymerizable acidic monomers include, but are not limited to, those selected from ethylenically unsaturated carboxylic acids, ethylenically unsaturated sulfonic acids, and ethylenically unsaturated phosphonic acids. Examples of such comonomers include the group consisting of acrylic acid (AA), methacrylic acid, itaconic acid, fumaric acid, crotonic acid, citraconic acid, maleic acid, β-carboxyethyl acrylate, sulfoethyl methacrylate, and the like, and mixtures thereof. The thing selected from is mentioned.

  Other useful copolymerizable monomers include (meth) acrylamide, N, N-dialkyl substituted (meth) acrylamide, N-vinyl lactam, and N, N-dialkylaminoalkyl (meth) acrylate, It is not limited to these. Illustrative examples include N, N-dimethyl (meth) acrylamide, N, N-dimethylmethacrylamide, N, N-diethylacrylamide, N, N-diethylmethacrylamide, N, N-dimethylaminoethyl methacrylate, Selected from the group consisting of N, N-dimethylaminopropyl methacrylate, N, N-dimethylaminoethyl acrylate, N, N-dimethylaminopropyl acrylate, N-vinylpyrrolidone, N-vinylcaprolactam, and the like, and mixtures thereof Include, but are not limited to:

  Non-polar ethylenically unsaturated monomers: Non-polar ethylenically unsaturated monomers are those whose homopolymer is measured by the Fedors method (see Polymer Handbook (Bandrup and Immergut)) with a solubility parameter of 10.50 or less and 15 ° C Is a monomer having a Tg greater than. The non-polar nature of this monomer tends to improve surface adhesion due to the low energy of the adhesive. These nonpolar ethylenically unsaturated monomers are selected from alkyl (meth) acrylates, N-alkyl (meth) acrylamides, and combinations thereof. Illustrative examples include 3,3,5-trimethylcyclohexyl acrylate, 3,3,5-trimethylcyclohexyl methacrylate, cyclohexyl acrylate, cyclohexyl methacrylate, isobornyl acrylate, isobornyl methacrylate, N-octyl acrylamide, N-octyl methacryl Examples include, but are not limited to, amides or combinations thereof. Optionally 0 to 25 parts by weight of a non-polar ethylenically unsaturated monomer may be added.

  Tackifiers: Preferred tackifiers include terpene phenol resins, rosins, rosin esters, esters of hydrogenated rosins, synthetic hydrocarbon resins, and combinations thereof. These provide good binding properties on low energy surfaces. Hydrogenated rosin esters and hydrogenated C9 aromatic resins are the most preferred tackifiers due to high levels of “stickiness”, outdoor durability, oxidation resistance, and limited interference after cross-linking of acrylic PSA. is there.

  The tackifier is added at a concentration of about 1 to about 65 parts per 100 parts of the monofunctional acrylate or methacrylate ester of the non-tertiary alkyl alcohol, polar monomer, and non-polar ethylenically unsaturated monomer, and the optional “ "Sticking" can be achieved. Preferably, the tackifier has a softening point of about 65 to about 100 degrees. However, the addition of tackifiers may reduce the shear or cohesive strength of acrylic PSA and increase Tg, which is undesirable for low temperature performance.

  Crosslinking agent: In order to increase the shear or cohesive strength of acrylic pressure sensitive adhesives, crosslinking additives are usually incorporated into PSA. Two main types of crosslinking additives are commonly used. The first crosslinking additive is a thermal crosslinking additive such as a polyfunctional aziridine. An example is 1,1 '-(1,3-phenylenedicarbonyl) -bis- (2-methylaziridine) (CAS number 7652-64-4), referred to herein as "bisamide". Such chemical crosslinkers can be added to the solvent-based PSA after polymerization and activated by heat during oven drying of the coated adhesive.

  In other embodiments, chemical crosslinkers that undergo a crosslinking reaction by free radicals may be used. For example, a reagent such as peroxide functions as a free radical source. When fully heated, these precursors generate radicals that cause a crosslinking reaction of the polymer. A common free radical generating reagent is benzoyl peroxide. Only a small amount of radical generator is required, but generally a higher temperature than that required for the bisamide reagent is required to complete the crosslinking reaction.

  The second type of chemical crosslinker is a photosensitive crosslinker that is activated by high intensity ultraviolet (UV) light. Two common crosslinkers used in hot melt acrylic PSA are benzophenone and 4-acryloxybenzophenone, which can be copolymerized into a PSA polymer. Another photocrosslinker is a triazine that can be later added to the solution polymer and activated by ultraviolet light, such as 2,4-bis (trichloromethyl) -6- (4-methoxy-phenyl) -s-triazine. is there. These crosslinking agents are activated by ultraviolet rays generated from an artificial light source such as a medium pressure mercury lamp or a UV black light.

  Without limitation, methacryloxypropyltrimethoxysilane (available from SILANE ™ A-174, Union Carbide Chemicals and Plastics Co), vinyldimethylethoxysilane, vinylmethyldiethoxysilane, vinyltriethoxysilane, vinyltrimethoxysilane Hydrolyzable free radical copolymerizable crosslinking agents such as monoethylenically unsaturated mono-, di- and trialkoxysilane compounds, including vinyltriphenoxysilane, are also useful crosslinking agents.

  The cross-linking agent is typically present from 0 to about 1 part by weight, based on 100 parts by weight acrylic acid or meth (acrylic) ester, polar monomer, and non-polar ethylenically unsaturated monomer.

  In addition to thermal, moisture, or photocrosslinking agents, crosslinking may be accomplished using high energy electromagnetic radiation such as gamma radiation or electron beam radiation. In this case, a crosslinking agent may not be required.

  Other additives: Since acrylic pressure sensitive adhesives have good oxidative stability, additives such as antioxidants and UV light absorbers are generally not necessary. A small amount of heat stabilizer can be used in the hot melt acrylic PSA to increase the thermal stability during processing.

  Plasticizer: If desired, a low concentration (eg, less than about 10 parts by weight) of a plasticizer may be combined with a tackifier to optimize adhesive release and low temperature performance. The plasticizer that may be added to the adhesive of the present invention can be selected from a wide range of commercially available materials. In each case, the added plasticizer must be compatible with the tackified acrylic PSA used in the formulation. Typical plasticizers include polyoxyethylene aryl ether, dialkyl adipate, 2-ethylhexyl diphenyl phosphate, t-butylphenyl diphenyl phosphate, di (2-ethylhexyl) adipate, toluenesulfonamide, dipropylene glycol dibenzoate, polyethylene Examples include glycol dibenzoate, polyoxypropylene aryl ether, dibutoxyethoxyethyl formal, and dibutoxyethoxyethyl adipate.

  Various polymer film substrates composed of various thermosetting or thermoplastic polymers are suitable for use as the overlay and body layers. The body layer may be a single layer film or a multilayer film. Specific examples of the polymer that may be used for the body layer film of the flexible retroreflective article include (1) poly (chlorotrifluoroethylene), poly (tetrafluoroethylene-co-hexafluoropyropylene), poly (tetrafluoro Fluorinated polymers such as ethylene-co-perfluoro (alkyl) vinyl ether), poly (vinylidene fluoride-co-hexafluoropropylene); (2) poly (ethylene-co-methacrylic acid) with sodium or zinc ions E.g. I. such as SURLYN-8920 brand and SURLYN-9910 brand available from duPont Nemours (Wilmington, Del); (3) low density polyethylene; linear low density polyethylene; and very low density polyethylene Low density polyethylenes; plasticized vinyl halide polymers such as plasticized poly (vinyl chloride); (4) poly (ethylene-co-acrylic acid) “EAA”, poly (ethylene-co-methacrylic acid) “ Polyethylene copolymers containing acid functional polymers such as "EMA", poly (ethylene-co-maleic acid), and poly (ethylene-co-fumaric acid); alkyl groups are methyl, ethyl, propyl, etc., or CH3 (CH2) n-, where n is 0-12. Acrylic functional polymers such as those present, and poly (ethylene - co - vinyl acetate) "EVA"; and (5) (for example) aliphatic polyurethanes; and the like. The body layer is preferably an olefin polymer material, generally containing at least 50% by weight of alkylene having 2 to 8 carbon atoms, most commonly ethylene and propylene are used. Other body layers include, for example, poly (ethylene naphthalate), polycarbonate, poly (meth) acrylate (eg, polymethyl methacrylate or “PMMA”), polyolefins (eg, polypropylene or “PP”), polyesters ( For example, polyethylene terephthalate “PET”), polyamides, polyimides, phenol resins, cellulose diacetate, cellulose triacetate, polystyrene, styrene-acrylonitrile copolymers, cyclic olefin copolymers, epoxy resins and the like.

  Exemplary liners for use in the retroreflective articles of the present disclosure include paper and silicone coated materials including plastics, such as polymer films. The liner substrate may be a single layer or multiple layers. Specific examples include polyester (eg, polyethylene terephthalate), polyethylene, polypropylene (including cast and biaxially oriented polypropylene), and paper (including clay-coated paper, polyethylene-coated paper, or polyethylene-coated poly (ethylene terephthalate)). Is mentioned.

  In some embodiments, such as in retroreflective article 100, cube corner element 112 is in the form of a tetrahedron or pyramid. The dihedral angle between any two facets can vary depending on the properties desired for the application. In some embodiments (including one shown in FIGS. 1A and 1B), the angle between any two facets is 90 degrees. In such embodiments, the facets are substantially perpendicular to each other (like room corners) and the optical elements may be referred to as cube corners. Alternatively, the dihedral angle between adjacent facet angles can deviate from 90 ° as described in US Pat. No. 4,775,219, which is hereby incorporated by reference in its entirety. Alternatively, the optical element in the retroreflective article may be a truncated cube corner. The optical element may be a complete cube, a truncated cube, or a (PG) cube of a preferred shape as described in US Pat. No. 7,422,334, which is hereby incorporated by reference in its entirety. . Each retroreflective optical element includes an axis of symmetry that makes an angle equal to the facet. In some embodiments, the axis of symmetry is perpendicular to the bottom surface or the front surface. In some embodiments, the axis of symmetry is not perpendicular to the bottom surface or front surface, and the apex or optical element is as described in US Pat. No. 4,588,258, which is hereby incorporated by reference in its entirety. It may be diagonal. The retroreflective layer 110 of FIGS. 1A and 1B is shown with an overlay layer 118 and no land layer or land portion. A land layer can be defined as a continuous layer of material that is coextensive with a cube corner element and is composed of the same material. This structure may be desirable for flexible embodiments. Those skilled in the art will appreciate that the retroreflective layer 110 may include a land layer or land portion.

  As schematically illustrated in FIG. 2, one method of making at least a portion of the retroreflective article of the present disclosure includes placing a barrier layer material 134 on the pressure sensitive adhesive material 132, and then And laminating the resulting pressure sensitive adhesive layer 130 on the retroreflective layer 110. The pressure sensitive adhesive layer 130 may be formed by various methods including, but not limited to, the following representative methods. In one exemplary embodiment, the material forming the barrier layer is printed on the pressure sensitive adhesive. The printing method may be a non-contact method, for example printing using an inkjet printer. The printing method may be a contact printing method, for example flexographic printing. In other exemplary embodiments, the material forming the barrier layer is printed on the flat release surface, for example using an ink jet or screen printing method, and then subsequently on the pressure sensitive adhesive from the flat release surface. Is transcribed. In another exemplary embodiment, the material forming the barrier layer is flood coated onto a microstructured adhesive surface (eg, a conformable liner manufactured by 3M Company (St. Paul, MN)). The barrier layer material is then transferred from the microstructured liner to the pressure sensitive adhesive, for example by lamination. The retroreflective article may then optionally be adhesively bonded to a substrate (eg, an aluminum substrate) to form, for example, a license plate or sign.

  3 and 5 illustrate some alternative exemplary retroreflective articles of the present disclosure. Specifically, FIGS. 3 and 5 show a retroreflective article that includes a structured sealing layer. In some embodiments, the sealing layer comprises at least one of, for example, a thermoplastic polymer, a crosslinkable material, and a radiation curable material. In some embodiments, the sealing layer includes an adhesive, such as a heat activated adhesive and / or a pressure sensitive adhesive. These structures are characterized by having an embossed, replicated, or similarly formed sealing layer laminated to the back of the retroreflective layer. The sealing layer may be a pressure sensitive adhesive, a heat activated adhesive, or other material that can be formed using replication, hot embossing, embossed replication, and the like.

  FIG. 3 is a schematic diagram of one exemplary embodiment of a retroreflective article 300 facing the viewer 302. The retroreflective article 300 includes a retroreflective layer 310 that includes a plurality of cube corner elements 312 that collectively form a structured surface 314 that is opposite the major surface 316. The retroreflective layer 310 also includes an overlay layer 318. Although the retroreflective layer 310 is shown as a flexible substrate without a land layer or land portion, as noted above, the retroreflective layer 310 includes any type of land layer and / or optical element. obtain. The structured adhesive layer 330 is adjacent to the retroreflective layer 310. The structured adhesive layer 330 includes raised areas of adhesive (areas that are raised relative to surrounding areas) in a closed pattern (eg, a hexagonal array, etc.). The structured adhesive layer includes a structured adhesive liner 340 and a hot melt adhesive layer 350. Structured adhesive layer 330 defines a low index layer 338 that retains the retroreflective properties of structured surface 314 when bonded to retroreflective layer 310. More specifically, the presence of the low index layer 338 allows the portion of the structured surface 314 adjacent to the low index layer 338 to retroreflect the incident light 150. Thus, the portions of the retroreflective article 300 that include cube corner elements 312 adjacent to the low index layer 338 are optically active in that they retroreflect incident light. In contrast, portions of the retroreflective article 300 having portions of the structured adhesive layer 330 adjacent to the cube corner elements 312 are optically inert in that they do not substantially retroreflect incident light. is there. The portion of the structured adhesive layer 330 that does not contact the structured surface 314 adheres to the cube corner element 312, thereby effectively sealing the retroreflective regions and forming optically active regions or cells. The structured adhesive layer 330 also holds the entire retroreflective structure together, thereby eliminating the need for a separate sealing layer and sealing process. In the embodiment shown in FIG. 3, retroreflective article 300 is adhesively bonded to aluminum substrate 360 to form a license plate.

  The structured adhesive layer can be formed in several different ways. The structured adhesive layer may include multiple layers formed simultaneously, for example, or may be made through a repeated coating process. One exemplary method optionally begins with a flat film of adhesive on the carrier web. The adhesive is sandwiched between a flat roll and a roll with the desired relief pattern. By applying temperature and pressure, the relief pattern is transferred to the adhesive. The second exemplary method requires a castable or extrudable adhesive material. The adhesive film is made by extruding the material onto a roll with the required relief pattern. When the adhesive material is removed from the roll, it retains the relief pattern associated with the roll. The structured adhesive layer is then laminated to the retroreflective layer.

  In an alternative embodiment, the structured adhesive layer may comprise, for example, a material that is not adhesive but is coated with an adhesive on the tip of the structure.

  A typical method of making such a retroreflective article 400 begins with a flat non-adhesive film such as polyethylene. The polyethylene film is sandwiched between a flat roll and a roll with the required relief pattern. By applying temperature and pressure, the relief pattern is transferred to the polyethylene film. The adhesive is then transferred to the top of the replicated film using, for example, kiss coating or other suitable method. The structured liner coated with adhesive is then laminated to the retroreflector.

  Regardless of which manufacturing method is used, the structured adhesive layer is then bonded to the retroreflective layer by sandwiching the two films together in a nip composed of two flat rolls. With the addition of temperature and pressure, the films adhere and bond, creating air pockets that retain the retroreflective properties of the cube corner elements.

  Optionally, the first region or non-raised portion of the adhesive serves to reduce the creep of the sealing leg of the structured adhesive layer, as well as the cube corner element during processing or use. Minimize harmful grounding effects by the bottom of the well on top. FIG. 5 shows a retroreflective article 500 where the barrier layer 580 is confined to the bottom of the structured adhesive layer, but the barrier layer 580 substantially provides adhesion of the sealing leg to the retroreflective layer 310. As long as it is not reduced, it can be anywhere in the well.

  The structured adhesive layer of FIGS. 3-5 can include, for example, a thermoplastic polymer, a thermoactive adhesive, such as an acid as described in US Pat. No. 7,611,251, which is incorporated herein by reference in its entirety. May include EVA / acrylate or anhydride / acrylate modified EVA, such as Bynel 3101. The structured adhesive layer of FIGS. 3-5 can include, for example, acrylic PSA, or any other embossable material with adhesive properties that adhere to corner cube elements. The interface between the encapsulating film layer and the (eg, cube corner) microstructured layer typically includes a surface treatment that promotes adhesion. Various adhesion enhancing surface treatments are well known, such as mechanical roughening, chemical treatment, corona treatment (in an inert gas such as air or nitrogen) (eg, US 2006/0003178). A1)), plasma treatment, flame treatment, and actinic radiation.

The retroreflective coefficient _RA of the present disclosure, sometimes referred to as the retroreflective properties of the retroreflective article, may be varied depending on the properties desired for the application. In some embodiments, _{R A} is compliant with ASTM D4956-07e1 standards orientation angle of 0 degrees and 90 degrees. In some embodiments, when measured at an observation angle of 0.2 degrees and an incident angle of +5 degrees according to the ASTM E-810 test method or CIE 54.2; 2001 test method, R _A is about 5 cd / The range is from (lux · m ² ) to about 1500 cd / (lux · m ² ). In some embodiments, for example, in embodiments where retroreflective articles are used in traffic control signs, line-of-sight signs, or barricades, in accordance with ASTM E-810 test method or CIE 54.2; the incident angle of 2 degrees observation angle and +5 degrees, _{R a} is at least about ^{330cd / (lux · m 2)} , or at least about ^{500cd / (lux · m 2)} , or at least about 700cd / (lux · ^m 2) It is. In some embodiments, for example in automotive applications, R _A is at least about 60 cd at 0.2 degree observation angle and +5 degree incidence angle according to ASTM E-810 test method or CIE 54.2; 2001 test method. / (lux · ^m 2), or at least about ^{100cd / (lux · m 2)} , or at least about ^{80cd / (lux · m 2)} .

Other methods of measuring these unique optical properties of the sheet material of the present application, include the measurement of partial retroreflective (Fractional retroreflectance) R _T. Partial retroreflection (R _T ) is another parameter useful for characterizing retroreflectivity. R _T (which is described in detail in ASTM E808-01) is part of the unidirectional flux that illuminates the retroreflector, which is the maximum, at an observation angle smaller than what is called α _max . Accepted. Therefore, _RT represents the portion of light that returns within the aforementioned maximum observation angle, α _max . In scheme that matches the ASTM E808-01, _{R T} can be calculated as follows.

Where α is the observation angle (expressed in radians), γ is the display angle (also expressed in radians), β is the incident angle, and R _a is candela per lux per square meter. It is the conventional retroreflection coefficient expressed in units. For the purposes of this application, _RT is referred to as fractional partial retroreflection, and% _RT is referred to as percentage partial retroreflection, i.e.,% _RT = _RT * 100%. It is. In either case, the partial retroreflection is unitless. As an aid to the image in understanding the observation angle of the retroreflective sheet material, the partial retroreflection can be plotted as a function of the maximum observation angle, α _max . Such a plot is referred to herein as an R _T -α _max curve, or% R _T -α _max curve.

Another useful parameter that characterizes retroreflection is R _T Slope, which can be defined as the change in R _{T with} respect to small changes or increments in the maximum observation angle Δα _max . The associated parameter,% R _T Slope, can be defined as the change in% R _{T with} respect to a small change in the maximum observation angle, Δα _max . Therefore, R _T Slope (ie,% R _T Slope) represents the slope of the R _T -α _max curve (ie,% R _T -α _max curve), that is, the rate of change. At separate data points, these quantities are calculated by calculating the difference in R _T (ie,% R _T ) for two different observation angles α _max as well as the maximum observation angle expressed in radians, Δα It can be estimated by dividing by the increment in _max . When Δα _max is expressed in radians, R _T Slope (ie,% R _T Slope) is the rate of change per radian. Alternatively, as used herein, when Δα _max is expressed in degrees, R _T Slope (ie,% R _T Slope) is the rate of change per degree in the observation angle.

The above equation for R _T is the integral of the retroreflective coefficient _{RA with other} coefficients over the entire display angle (from γ = −π to + π) and over the range of observation angles (α = 0 to α _max ). including. When processing separate data points, this integration can be performed using R _A measured at separate observation angle α _max values (0.1 degrees) separated by increments Δα _max .

  In at least some embodiments of the present disclosure, the structured surface is about 5% or more, 8% or more, 10% or more, 12% or more, 15% or more for visible light incident at an incident angle of -4 degrees. It presents a certain return light. In at least some of the embodiments of the present disclosure, the structured surface of the retroreflective article can be about 40 cd / (lux · m 2) or greater, 50 cd / ( lux · m2) or more, 60 cd / (lux · m2) or more, 70 cd / (lux · m2) or more, and 80 cd / (lux · m2) or more.

  By appropriate selection of barrier layer material, dimensions, and / or spacing, the retroreflective article of the present disclosure has a more uniform appearance than can be obtained with conventional retroreflective articles that include a sealing layer. Have. Furthermore, the retroreflective articles of the present disclosure do not include or require the use of a sealing layer, reducing their cost.

  For example, embodiments that include a sealing structure of the type shown in FIGS. 3 and 5 have some additional specific benefits. For example, the sealing legs can be made small enough so that they do not adversely affect the aesthetics of the design or design printed on the surface of the retroreflective article or structure. Furthermore, these methods of sealing do not substantially change the angled distribution of light retroreflected from the bare retroreflective layer. These methods also allow the sealing of any shape and color leg to be made. Thus, a retroreflective article having a white appearance can be formed similar to an article with an anti-moire effect and / or a safety mechanism. Finally, the manufacturing process is simplified because the vapor coating step is removed from the process.

  Furthermore, the retroreflective articles of the present disclosure have improved performance when compared to bead sheet materials. Prismatic sheet materials are generally known to retroreflect a higher percentage of incident light toward the source when compared to glass bead-based sheet materials. (See, for example, “Driver-Focused Design of Retroreflective Sheeting for Traffic Signs,” Kennes Smith, 87th Annual Meeting of Trans. 13). When retroreflected light is correctly positioned with respect to the observation angle, a product with excellent brightness and performance is obtained.

  The microencapsulated cell geometries, shapes, dimensions, and structures may be uniform across the sheet material or may vary in a controlled manner. In a cell array, changes such as size, shape, and cell width are intended for slight variations in appearance at close distances (20 feet (6.09 m) or less, and preferably 5 feet (1.52 m) or less). May be used to automatically capture. Such variations can be due to accidental defects (contamination, coating defects, etc.) that can be randomly distributed in the sheet material, or alternatively to periodic structures in the mold or product (eg scale-up or weld lines). It can have the effect of hiding what can be attributed.

The micro-sealed prismatic sheet material is particularly suitable for applications such as license plates and graphics. Prismatic sheet material, when replaced with glass beads sheet material, much lower production costs, reduced cycle time, in particular to provide benefits such as deleting wastes containing solvent and CO _2. Furthermore, the prismatic structures return significantly increased light when compared to glass bead retroreflectors. Proper design also allows this light to be preferably placed at a particularly important observation angle (eg 1.0-4.0 degrees) on the license plate. Finally, the microencapsulated sheet material provides a bright whiteness and a uniform appearance at the close viewing distance required for these product applications.

The sealing cell can be characterized by cell size dimensions and sealing cell leg, or line width. The cell dimensions of 3M HIP and 3M flexible prismatic products are approximately 0.143 inches and 0.195 inches (0.36 cm and 0.49 cm), respectively. The width of the sealing leg of the same sample is about 0.018 inch and 0.025 inch (0.05 cm and 0.06 cm), respectively. Another way to characterize characteristic cell dimensions is to divide the cell area by the length of the perimeter. This characteristic cell dimension D _c can be useful when compared to different cell shapes. These relatively large sealed cell dimensions are perfectly suitable for the applications in which they are normally employed. However, the non-uniform appearance of retroreflective sheeting with these cell dimensions is evident when viewed nearby (eg, a few feet away, or in a mobile or demo in an office). However, the actual distance that this retroreflective sheeting is used is much greater. For example, important sign distances (based on factors such as distances seen first and last, sign placement, and obstruction and visibility) are about 50-150 m for signs placed on the right shoulder. These important distances represent the area where the driver actually gets information from the high speed sign. Individual sealed cells are generally not visible at these critical distances based on vision thresholds.

  At a distance of 1 foot, the normal vision of the human eye is about 0.0035 inches (88.9 micrometers). This means that if you have alternating black and white lines that were all about 89 micrometers wide, it appears to most people as a solid gray. (See, for example, http://www.ndted.org/EducationResources/CommunityCollege/PenetranTest/Introduction/visualalacity.htm). Alternatively, the 20/20 vision is about 1/16 inch at the visual acuity of −20 feet required to distinguish two points separated by one arc (0.009 m, 0.16 inches). 6) (See, eg, http://en.wikipedia.org/wiki/Visual_acity#Visual_acity_expression). Thus, for an approximately expected minimum viewing distance of about 2 feet (0.61 m), any shape below about 180 micrometers cannot be resolved. Sheet material with distinct geometries below this level appears uniform to the human eye.

  The alphanumeric characters used in the license plate are relatively small compared to many road sign applications. For example, a character height and stroke width (alphanumeric thickness) of 0.35 inches (0.89 cm) of about 2.75 inches (6.99 cm) is common in the United States. Similarly, a character height of about 3.0 inches (7.62 cm) and a stroke width of 0.45 inches (1.14 cm) are common in the United States. Under ideal conditions, the vision limit for black over white is about 0.0035 inches (0.029 cm / m) per distance foot, as described above. Thus, the stroke width on the United States plate is about 0.35 inches (0.89 cm), and then the maximum distance at which they can be seen is about 100 feet (30.5 m). The contrast ratio between the alphanumeric characters and the background may be reduced by factors such as picking up dirt or graphic design (moving away from black letters on a white background). In such a situation, the maximum distance for reading the plate is further reduced. Realistic changes such as poor lighting, moving vehicles, bad weather, and poor visual acuity further and significantly reduce the maximum visibility distance. Thus, common in the license plate market is to specifically examine plate visibility at critical license plate distances in the range of about 50-125 feet (15.2-38.1 m). A particularly important observation angle is roughly in the range of about 1.0 to about 4.0 degrees, as plotted in FIGS. 7A and 7B. In large vehicles such as SUVs or large trucks, the driver's eyes are farther from the headlights when compared to standard sedans. Thus, in the same scenario, the observation angle is even larger for larger vehicles.

  Typical retroreflective articles include, for example, retroreflective sheeting, retroreflective signs (eg, traffic control signs, road signs, highway signs, road signs, etc.), license plates, line-of-sight signs, barricades, individuals Safety products, graphic sheet materials, safety vests, vehicle graphics, and display signs.

  The following examples describe some exemplary structures of various embodiments of retroreflective articles and methods of making the retroreflective articles described in this disclosure. The following examples are for purposes of illustration and are not intended to limit the scope of the present disclosure.

Preparation of the retroreflective layer:
The overlay film is ethylene acrylic acid (EAA) (Trademark “Primacor 3440”, commercially available from Dow Company (Midland, MI) as a 0.01 mil (4 mil) thick film, approximately 53 inches wide). And pellets of EAA were prepared by CW Brabender Instruments Inc. (South Hackensack, Inc.), and 0.05 mm (0.002 inch) thick corona-treated polyethylene terephthalate (PET) carrier. NJ) was fed into a 1.9 cm (3/4 inch) single screw extruder, the extruder temperature profile of 140 ° C. (284 ° F.) to 175 ° C. (347 °). F) The melting temperature is about 75 ° C. (347 ° F.) As the molten resin exits the extruder, it passes through a horizontal die (trademark “Ultraflex-40” commercially available from Extension Dies Industries LLC (Chippewa Falls, Wis.)). The PET carrier moved at about 36 meters / minute (120 ft / minute) and the resulting melt overlay film on the PET carrier was between the rubber roll and the cooled steel backup roll. The EAA surface was corona treated with an energy of 1.5 J / cm ² .

  The cube corner structure had 3 sets of intersecting grooves with a pitch of 81.3 micrometers (0.0032 inches) or major groove spacing. The intersecting grooves formed cube corner base triangles including 61, 61, and 58 degree angles, resulting in cube corner element heights of 37.6 micrometers (0.00148 inches). The main groove spacing is defined as the groove spacing between the grooves forming the two 61 degree base angles of the base triangle.

  25% by weight bisphenol A epoxy diacrylate, 12% by weight dimethylaminoethyl acrylate (“DMAEA”), 38% by weight TMPTA (trimethylpropane), available under the trade name “Ebecryl 3720” from Cytek (Woodland Park, NJ) A cube corner microstructure was prepared using a resin composition formed by mixing (triacrylate) and 25% by weight of 1,6-HDDA (hexanediol diacrylate). The formulation had 0.5 pph TPO (2,4,6-trimethylbenzoyldiphenylphosphine oxide) photoinitiator.

  This resin composition was cast at 25 fpm (7.6 m / min) at room temperature onto a metal mold heated to 77 ° C. (170 ° F.). The resin composition fills the cavity of the mold cube corner microstructure through a rubber nip roller with a gap, set to minimize the amount of resin on the land area of the mold, and the mold The amount of resin on the land area was minimized. The retroreflective layer was made by contacting a corona-treated EAA film / PET carrier with a resin cube corner microstructure. Cube corner microstructure resin is available from 12 Fusion D UV lamps (Fusion Systems, Rockville, MD) set at 600 W / inch (236.2 W / cm) by PET carrier / EAA film on mold ). A dichroic filter was used in front of the UV lamp to minimize IR heating of the structure. When the curing process was completed and the retroreflective layer was removed from the mold, the cube corner microstructure was irradiated by a Fusion D UV lamp operating at 50% and post-cured by UV irradiation. The retroreflective layer was passed through an oven set at 127 ° C. (260 ° F.) to relax the stress in the film.

(Examples 1 to 15):
The structured layer was prepared by making the structure on the substrate layer. In some embodiments, the structure was made by selectively applying a barrier material (material for use in the barrier layer) on the substrate layer (eg, pattern printing, pattern coating). Alternatively, the barrier material was applied over the release layer, followed by lamination of the release layer containing the barrier material to the substrate. In some embodiments, the structured layer was prepared by applying a pattern onto the substrate layer using a mold. In some embodiments, the substrate layer is an adhesive layer. The retroreflective optical structure was prepared by laminating a structured layer to the retroreflective layer, where the barrier material contacted the cube corner microstructure.

Comparative Examples A1 and A2:
The retroreflective layer was prepared as described above except that a different lot of material was used.

(Examples 1 to 5):
A radiation polymerizable pressure sensitive adhesive (PSA) was prepared as described in US Pat. No. 5,804,610 (Hamer), incorporated herein by reference. The PSA composition is commercially available from 95 parts by weight isooctyl acrylate (IOA), 5 parts by weight acrylic acid (AA), 0.15 parts by weight Irgacure 651 (Ciba Corporation, currently BASF Company (NJ). ), 0.10 parts by weight of 4-acryloyl-oxy-benzophenone (ABP), 0.05 parts by weight of isooctyl thioglycolate (IOTG), and 0.4 parts by weight of Irganox 1076 (commercially available from Ciba Corporation). It was made by mixing. The PSA composition is placed in an approximately 10 cm x 5 cm package made from an ethylene vinyl acetate copolymer (commercially available from Pliant Corporation (Dallas, TX) under the trademark "VA-24"). And heat sealed. The PSA composition was then polymerized. After polymerization, the PSA composition is mixed with 10% TiO ₂ pigment, generally as described in US Pat. No. 5,804,610 and about 4 inches × 6 inches (10.2 cm × 15.2 cm) Cast onto a silicone release liner at a thickness of 27 grains (11.3 mg / cm ² ). The PSA film was then subjected to a radiation crosslinking process.

  The barrier material was selectively printed on the PSA film using a UV inkjet printer (commercially available from Mimaki (Suwanee, GA) under the trademark “Mimaki JF-1631”). A yellow inkjet ink (commercially available from Makiki) was used as the barrier material. The printer was implemented using 8 unidirectional printings with a resolution of 600 × 600 dpi (236.2 × 236.2 dpcm) with the lamp set to “High”. The ink level was set at 100% or 300% ink laydown. A printing pattern was used that included dots arranged in the shape of a rhomboid parallelogram, with each dot centered at the apex of the parallelogram, as shown schematically in FIG. The radius of the dot is in the range of 400 to 600 μm, the distance between the centers of horizontally adjacent dots is “S” (pitch), and the distance between the centers of vertically adjacent dots is “S” / 2. It was. “S” was in the range of 1418-2127 μm. The width of the print pattern was calculated by subtracting 2R from the pitch value. The coverage area (% area) was calculated based on the relative amount of the printed area and the unprinted area. Details on the patterns used to make the printed adhesive layers 1-5 are shown in Table 1 below.

  The retroreflective optical structures (Examples 1-5) are made by laminating printed adhesive layers 1-5 on the retroreflective layer using a roll laminator with a hand pressure setting of 40 psi (276 kPa). Prepared, where the barrier layer was in contact with the cube corner microstructure of the retroreflective layer.

The retroreflectivity (R _A ) of the samples prepared as described in Examples 1-5 was measured at observation angles of 0.2, 1.0 and 2.0 degrees, an incident angle of -4 degrees, and an orientation of 0 degrees. It was done. Retroreflective of the retroreflective layer (ie, before the printed adhesive layer is laminated to the cube corner microstructure) (“initial”) and retroreflective of the retroreflective optical structure (ie, printed adhesive) ("Laminated") is measured and is shown in Table 2 below.

  The formation of the optically active area was determined by the number and / or dimensions of the barrier film printed on the PSA film. A high coverage area (eg, multiple and / or large area barrier materials printed on a PSA film) results in the creation of a higher percentage of optically active areas, thus increasing retroreflectivity.

(Example 6):
The PSA composition was prepared as described in Examples 1-5 except that the monomer ratio was 90/10 IOA / AA and no TiO ₂ was used. The PSA composition was cast as a film at a thickness of 0.8 grains / inch ² (7.95 mg / cm ² ).

  The printed adhesive layer 6 was prepared by printing the barrier material on the PSA film using a square grid pattern, where each square was 500 × 500 μm. The pitch (distance between the centers of adjacent squares) was 700 μm. The distance (width) between each square was 200 μm. The ratio of pitch to width was 3.5. The ink level was 300%. The area coverage (% area) was calculated based on the dimensions of the sample and the printed pattern and corresponded to 51%.

  A retroreflective optical structure (Example 6) was prepared by laminating the printed adhesive layer 6 to the retroreflective layer as described in Examples 1-5.

  The retroreflectivity was measured at an observation angle of 0.2 degrees, an incident angle of -4 degrees, and directions of 0 and 90 degrees and is shown in Table 3 below.

(Example 7):
The barrier material was printed on the silicone coated release layer of Examples 1-5 using a UV inkjet printer and yellow inkjet ink. The ink jet used was 100%. The dot pattern described in Examples 1-5 is used and is shown schematically in FIG. The printed release layer 7 was prepared using the print pattern detailed in Table 4 below.

  The printed release layer 7 was prepared by laminating the printed release layer 7 on a PSA film prepared as described in Examples 1-5. A retroreflective optical structure (Example 7) was prepared by laminating a printed adhesive layer 7 to the retroreflective layer.

  The retroreflectivity was measured in directions of observation angles of 0.2 degrees, 1 degree, and 2 degrees, incident angle of -4 degrees, and 0 degrees, and is shown in Table 5 below.

(Example 8):
The barrier material is a white UV crosslinkable screen printing ink (commercially available from 3M Company (St. Pal, MN) under the trademark “9808 Series”) screen printed on a silicone coated release layer (A (Using Accu-Print Printer available from WT World Trade, Inc. (Chicago, IL)). Using a 380 mesh screen, the dot printing patterns of Examples 1-5 were used to make the barrier material. A printed release layer 8 was prepared using the print patterns of Examples 1-5.

After screen printing, the barrier material was cured using a UV curing station made by the American Ultraviolet Company (Murray Hill, NJ), set at 226 mJ / cm ² and run at 50 fpm (15.24 m / min). It was.

  The printed release layer 8 was prepared by laminating the printed release layer 8 on a PSA film. The retroreflective optical structure 8 was prepared by laminating the printed adhesive layer 8 on the retroreflective layer.

(Example 9):
The structured layer was prepared using embossing rolls as generally described in US Pat. No. 6,254,675 (Mikami), incorporated herein by reference. As shown in FIG. 4a of US Pat. No. 6,254,675, the embossing roll has a truncated quadrangular column having an exposed surface and a second disposed on the exposed surface of the first pyramid. And machined with a laser to provide a pattern having a quadrangular prism. This structure had a pitch of 200 μm, a height of 15 μm, and a width of 25 μm, as generally described in Example 6 of US Pat. No. 6,254,675. A polyethylene-coated paper release liner having a silicone coating on polyethylene, such as those available from Rexam or Innocoat, is embossed between a heated rubber roll and an embossing roll and comprises a ridge A microstructured liner was made. The rubber roll was heated to a temperature of 110 ° C., and the release liner was heated to a surface temperature of 110 ° C. before entering between the rubber roll and the embossing roll. The release liner was moved to about half of the embossing roll and then moved to a cooling can to cool the liner.

  The coating composition consisted of a vinyl solution having 10% solids, and a vinyl resin (commercially available from Dow Chemical (Midland, MI) under the name “UCAR VYHH”) was dissolved in methyl ethyl ketone (MEK). The coating composition was coated on the structured layer to form a coated release layer 9. The line speed was 5 fpm (1.52 m / min), the pump flow rate was 5 mL / min, and the coating was dried in an oven set at 170 ° F. (77 ° C.).

  The printed release layer 9 was prepared by laminating the coated release layer 9 to a PSA film prepared as described in Example 6. A retroreflective optical structure (Example 9) was prepared by laminating a printed adhesive layer 9 to the retroreflective layer.

  Retroreflectivity was measured in directions of observation angles 0.2, 1 and 2 degrees, incident angles -4 degrees, and 0 and 90 degrees. Retroreflectivity was reported in Table 6 below as an average of reflectivity in the 0 and 90 degree directions.

(Examples 10 to 13)
The following description was used to prepare Examples 10-13: a laser ablation system generally described in US Pat. No. 6,285,001 (Fleming), incorporated herein by reference, was used. Then, a predetermined pattern was applied to the polymer film. The laser ablation system includes a KrF excimer laser that emits a beam at a wavelength of 248 nm, a patterned mask manufactured using standard semiconductor lithography mask technology, and an image of a pattern of light on the substrate through the mask. It was comprised from the imaging lens which projects. A substrate composed of a 5 mil (0.13 mm) thick polyimide layer was attached to the copper layer. The substrate was exposed to patterned radiation and the resulting structure in the polyimide layer comprised a pattern of hexagonal channels as shown in FIG. Each hexagon was 0.731 mm wide and 0.832 mm long. The width of the channel, i.e., the distance between adjacent walls of adjacent hexagons is 0.212 mm (width d), and the distance between the center of one hexagon and the center of the adjacent hexagon is As shown in 4A, it was 0.943 mm (pitch D).

After cutting the pattern, a stripping process was applied to the substrate by first depositing silicon containing the film by plasma deposition and subsequently coating the fluorochemical composition. Plasma deposition was performed with a commercially available reactive ion etcher (model 3032 available from Plasmatherm), consisting of a 26 inch (66 cm) powered electrode and a central gas pump. The substrate was placed on a powered electrode and treated with oxygen plasma by flowing a standard 500 cm ³ / min oxygen gas and 1000 watts of plasma power for 30 seconds. After the oxygen plasma treatment, silicon containing diamond-glazed glass film was deposited by flowing tetramethylsilane gas at a standard flow rate of 150 cm ³ / min and at a flow rate of standard 500 cm ³ / min for 10 seconds. After deposition of the diamond-glazed glass film, the substrate was exposed to oxygen plasma for 60 seconds at a standard flow rate of 500 cm ³ / min. The fluorochemical composition (commercially available under the trade designation “EGC-1720” from 3M Company (St. Paul, MN)) is then used to manually dip the substrate into the solution followed by drying it Applied by The substrate was then heated at 120 ° C. for 15 minutes.

Comparative Examples B1 and B2:
The retroreflective layer was prepared as described in Comparative Examples A1 and A2.

(Example 10):
A sealing layer comprising a two-layer structure of acid / acrylate-modified ethylene vinyl acetate (EVA) polymer (commercially available from Dow Corning (Michigan, USA) under the trademark “Bynel 3101”) was prepared by coextrusion; Here, the first layer was transparent and the second layer was colored by the addition of TiO _{2 as} a coextrusion column. 20 wt% of 80/20 pellets _TiO 2 / EVA Bynel 3101 mixed with blend is fed into the extruder molding, it is cast as a white film with a thickness of 0.005 cm (2 mil) on a PET carrier. The transparent layer (ie without TiO ₂ ) was cast as a film with a thickness of 0.002 cm (1 mil) and corona treated with an energy of about 1 J / cm ² .

  On the sealing layer by pressing the transparent Bynell side of the aforementioned multilayer film on a patterned polyimide layer for 3 minutes in a hot press (model “PW-220H” available from IHI Corporation, Houston, TX) A structure was fabricated. The embossing temperature at the top and bottom of the press was about 230 ° F. (110 ° C.) and the embossing pressure was 10 psi (69 kPa).

  The structured sealing layer is then laminated to the retroreflective layer and comprises a transparent film adjacent to the cube corner microstructure to form a retroreflective optical structure. A hot press (model “N-800” from HIX Corporation (Pittsburg, KS)) was used for 30 seconds at a lamination temperature of about 200 ° F. (93 ° C.) and a pressure of 30 psi (207 kPa).

(Example 11):
The sealing layer was prepared as described in Example 10, except that the structured sealing layer was coated on the retroreflective layer using a low refractive index coating material.

Low refractive index coating compositions are non-surface treated alkali reinforced dispersions of M-5 silica (Trademark “Cabo-Sperse PG002” from Cabot (Bellerica, Mass.)) And polyvinyl alcohol (PVA) (trademark from Kuraray USA). Prepared by using “Poval 235”. The silica is characterized by its low surface area, which is typically about 80-120 m ² / g. 150 g 7.2% solids PVA solution in water in a 1000 mL plastic beaker, 2.0 g non-ionic surfactant (commercially available under the trademark “Tergitol Min-Foam 1X” from Dow Chemical Company (Midland, Michigan) And 1 mL of concentrated NH ₄ OH solution was added. This solution was mixed at low shear using an air-driven overhead laboratory mixer operating at low speed. Silica dispersion (216 g, 20 wt% in water) was added to the solution followed by 130 g of deionized water. This mixture was allowed to mix for about 15 minutes. This mixture, containing 1 part PVA to 4 parts silica on a dry weight basis, is then transferred to a 1 L round bottom flask and placed on a rotary evaporator at a temperature of about 40 ° C. and 600 mm Hg (79.9 kPa) vacuum. Arranged. The final solid content of the low refractive index coating composition was adjusted to 5% using deionized water.

  The low refractive index coating composition was coated on the structured surface of the sealing layer using a knife coater. The knife was set to provide zero land in the coating, i.e. excess silica was removed from the sealing layer. The sealing layer was placed in an oven at 50 ° C. for 10 minutes before being laminated to the cube corner microstructure.

  Retroreflectivity was measured in directions of observation angles 0.2, 1 and 2 degrees, incident angles -4 degrees, and 0 and 90 degrees. Retroreflectivity was reported in Table 7 below as the average reflectivity in the 0 and 90 degree directions.

(Example 12):
A PSA film was prepared as described in Example 6. The structured adhesive film was obtained by pressing the adhesive film against the polyimide layer as described in Example 10.

  The retroreflective optical structure was prepared by laminating a structured adhesive film to the retroreflective layer, where the structured adhesive contacted the cube corner microstructure. Lamination occurred at room temperature using a hand roller.

(Example 13):
A structured adhesive film was prepared as described in Example 12, except that the low refractive index coating composition of Example 11 was coated onto the structured adhesive. Retroreflective optical structures are prepared by laminating a coated structured adhesive film to a retroreflective layer at room temperature using a hand roller, where the adhesive surface of the film contacts the cube corner microstructure. did.

  Retroreflectivity was measured at an observation angle of 0.2 degrees, an incident angle of -4 degrees, and directions of 0 and 90 degrees. The retroreflectivity was reported in Table 8 below as the average reflectivity in the 0 and 90 degree directions.

Comparative Example C:
A sealed prismatic retroreflective sheeting material marketed under the trademark “Diamond Grade 3910” by 3M Company (St. Paul, MN) was obtained.

Comparative Example D:
A retroreflective sheeting of beads marketed by the 3M Company under the trademark “License Plate Sheeting Series 4770” was obtained.

Comparative Example E
A sealing layer prepared as described in Example 10 was obtained.

Comparative Examples F, G and H and Examples 14-19:
The following description was used in the preparation of Comparative Examples F, G, and H, and Examples 14-19: The cube structure had a pitch of 101.6 micrometers (0.004 inches), i.e., the main groove. The retroreflective layer was prepared as described in “Preparing the Retroreflective Layer” except that it had three sets of intersecting grooves with spacing. The intersecting grooves formed cube corner base triangles including angles of 58, 58 and 64 degrees, resulting in a cube corner element height of 49.6 micrometers (0.00195 inches). The main groove spacing is defined as the groove spacing between the grooves forming the two 58 degree base angles of the base triangle.

  Comparative Examples F and G were prepared as described in “Preparation of Retroreflective Layer”, except that the cube corner structures described above were used.

  Comparative Example H was prepared by laminating the retroreflective layers of Comparative Examples F and G to the sealing layer of Example 10.

  The polyimide layer (molds 1-6) except that the pattern shape is the diamond shape shown in FIGS. 8 and 9, and the angle 1 (A1) and the angle 2 (A2) are 20 degrees and 153 degrees, respectively. Was prepared. The dimensional features of molds 1-6 are shown in Table 9 below. The sealed retroreflective sheeting material of Comparative Example C was analyzed and the pitch and line width of the sealed pattern was measured and reported in Table 9 below.

  As generally described in U.S. Pat. Nos. 4,478,769 (Pricone) and 5,156,863 (Pricone), first generation negative molds can be used to place a polyimide layer in a nickel sulfamate bath. It was produced from a polyimide layer (master) by nickel electroforming polyimide. Several additional generations of positive and negative replicas were formed so that the mold was substantially the same shape as the master.

  Structured sealing layers 14-19 were prepared by pressing the sealing layer of Example 10 on molds 1-6 as generally described in Example 10.

  Retroreflective optical structures (Examples 14-19) were prepared by laminating structured sealing layers 14-19 to the retroreflective layer.

Retroreflectivity (R _A ) was measured at directions of observation angles of 0.2, 0.5, 1, 2, 3, and 4 degrees, incident angles of -4 degrees, and 0 and 90 degrees. Retroreflectivity was reported in Table 10 below as the average reflectivity in the 0 and 90 degree directions.

Retroreflectivity (R _A ) is typically measured at separate observation angles and averaged over an annular region between two adjacent measured observation angles. Incremental% RT for a given observation angle is determined by multiplying by the area of the annular region obtained by dividing the average R _A by the cosine of the angle of incidence. The partially retroreflective% RT is the sum of the increment% RT for the observation angle between 0 degrees and the target observation angle (αmax). The partial retroreflective gradient (% RT gradient) for a given observation angle is the incremental% RT divided by the difference between adjacent observation angles. The% RT slope is reported in Table 11 below.

  % RT is calculated and reported in Table 12 below.

  CAP-Y was measured on a colorimetric spectrophotometer (available under the trademark “ColorFlex” from Hunterlab, Reston, Va.). Samples were measured using a white background behind the sample. There is a linear relationship between CAP-Y and% coverage (ie,% area that is retroreflective), and increased% coverage results in reduced CAP-Y. A decrease in the amount of cube corner microstructure that is exposed (ie, a reduced% coverage) results in an increase in whiteness in the structure. A typical CAP-Y value for a license plate sheet is 50 or greater. The CAP-Y values for Comparative Examples C, E, F, and H and Examples 14-19 are shown in Table 13 below.

  As shown in Tables 10, 12, and 13, an increase in the amount of cube corner microstructure exposed (eg, by printing or laminating a structured film on the cube corner structure) results in an observation angle of 2, As seen in the partially retroreflective% RT at 3 and 4 degrees, the amount of light returning will be reduced.

  Another way to characterize the sample dimensions is to use the sealing cell pitch for the line width ratio (D / d). The pitch D is the distance between the minimum repeated pattern shapes in the pattern. It may also be referred to as the sealed cell size or characteristic cell size. The width d is the width of the sealing leg portion. The effects of pitch / width ratio (D / d) on CAP-Y and% RT gradient of 2, 3, 4 degrees are shown in Tables 10, 11, and 13.

  Microencapsulated retroreflective optical structures are particularly useful in providing bright whiteness and a uniform appearance at close viewing distances while providing excellent retroreflective performance. One additional important aspect of the small or micro-encapsulated cell method is that light distribution is achieved when the shape of the encapsulated cell (eg, cell size (D), leg width (d) and total return light) is reduced. Means that it remains relatively unchanged. The encapsulated retroreflective optical structure shows a decrease in the total return light, but the light dispersion profile remains the same.

  As can be appreciated by those skilled in the art, the shape of the sealing cell is not limited to the diamond shape shown in the above examples. For the shape of the sealing cell. Examples include a circle, an ellipse, a triangle, a rectangle, and a parallelogram. Virtually any shape that achieves the characteristic dimensions,% coatings, or pitch / width ideas shown above, or a combination thereof, may be used. The sealed cell may also have a character or image shape, such as “M” or “3M” inverted as a safety feature.

  Any shape parameters used to define the shape of the sealed cell, such as pitch, line width, angle, linearity, etc., are randomly extracted between the sealed cell and the retroreflective sheet material. The effect of moire can be reduced. The shape may be optimized to hide defects in the sheet material as well as in layups or weld lines.

  In addition, the dimensions or pitch P of the cube may affect the brightness when laminated to the sealing layer due to the formation of edge effects during sealing. Two parameters: the actual cell line width (d) and the effective cell line width (def) can be used to help understand the effect of cube dimensions. The actual line width d is the physical width of the material forming the sealing cell leg portion. The effective line width deff is the optical width of the sealing leg portion, and is determined by the size and shape of the cube corner used in the prismatic film on which the sealing layer is laminated. When the sealing layer is laminated to the retroreflective layer, a portion of the sealing leg that overlaps only a portion of the cube corner microstructure darkens the entire cube. This further darkened area creates an effective width that is wider than the actual width. This effect is very dependent on the dimensions of the cube, and the effect is much worse for large cubes.

  The recitation of numerical ranges by endpoints is intended to include any numbers subsumed within that range (ie, a range of 1 to 10 includes, for example, 1, 1.5, 3.33, and 10 is included).

  All references mentioned are incorporated herein by reference.

  It will be apparent to those skilled in the art that many changes can be made in the details of the embodiments and examples described above without departing from the basic principles of the invention. Furthermore, it will be apparent to those skilled in the art that various modifications and variations of the present invention can be made without departing from the spirit and scope of the invention. Accordingly, the scope of the present application is defined only by the following “claims”.

Claims (84)

A retroreflective layer comprising a plurality of cube corner elements that collectively form a structured surface opposite the main surface;
A sealing layer having a first region and a second region, wherein the second region is in contact with the structured surface, the second region surrounds the first region, and has at least one cell size A sealing layer forming a cell;
A low refractive index layer between the first region and the structured surface of the retroreflective layer, wherein the first region has a cell dimension of less than 1000 micrometers. , Retroreflective articles.   The retroreflective article of claim 1, wherein the cell size of the first region is less than 750 micrometers.   The retroreflective article of claim 1, wherein the cell dimension of the first region is less than 500 micrometers.   The retroreflective article of claim 1, wherein the cell size of the first region is less than 250 micrometers.   The retroreflective article of claim 1, wherein the sealing layer comprises one of a pressure sensitive adhesive, a thermoplastic polymer, a thermally active adhesive, an oligomer crosslinkable material, and a radiation curable crosslinkable polymer.   The retroreflective article of claim 1, further comprising a sealing leg that defines the first region.   The retroreflective article according to claim 6, wherein the retroreflective article includes a plurality of cells forming a pattern having a pitch, and the width of the sealing leg portion is larger than 1/5 of the pitch of the pattern. .   The retroreflective article according to claim 6, wherein the retroreflective article includes a plurality of cells forming a pattern having a pitch, and the width of the sealing leg portion is larger than ¼ of the pitch of the pattern. .   The retroreflective article according to claim 6, wherein the retroreflective article includes a plurality of cells forming a pattern having a pitch, and the width of the sealing leg portion is larger than 1/3 of the pitch of the pattern. .   The retroreflective article of claim 1, wherein the retroreflective article exhibits a total light reflection of about 5% or more for visible light incident at an incident angle of −4 degrees.   The retroreflective article of claim 1, wherein the retroreflective article exhibits a total light reflection of about 9% or greater for visible light incident at an incident angle of −4 degrees. The retroreflective article with respect to the incident angle of observation angle and -4 degrees 0.2 degrees, exhibit coefficient of retroreflection _{R A} of about ^{40cd / (lux · m 2)} , retroreflective according to claim 1 Goods. The retroreflective article with respect to the incident angle of observation angle and -4 degrees 0.2 degrees, exhibit coefficient of retroreflection _{R A} of about ^{60cd / (lux · m 2)} , retroreflective according to claim 1 Goods. The retroreflective article with respect to an incident angle of 2.0 degrees observation angle and -4 degrees, exhibit coefficient of retroreflection R _A of at least about 8Cpl, retroreflective article of claim 1. The retroreflective article of claim 1, wherein the retroreflective article exhibits a% _RT gradient greater than or equal to about 3% / degree for an incident angle of −4 degrees and an observation angle of 2 degrees. The retroreflective article with respect to an incident angle of 3.0 degrees observation angle and -4 degrees, exhibit coefficient of retroreflection R _A of at least about 4Cpl, retroreflective article of claim 1. The retroreflective article of claim 1, wherein the retroreflective article exhibits a% _RT gradient greater than or equal to about 1.5% / degree for an incident angle of −4 degrees and an observation angle of 3 degrees.   The retroreflective article of claim 1, wherein less than about 65% of the structured surface is retroreflective.   The retroreflective article of claim 1, wherein less than about 55% of the structured surface is retroreflective.   The retroreflective article of claim 1, wherein less than about 45% of the structured surface is retroreflective.   The retroreflective article of claim 1, wherein the cube corner element is a truncated cube corner element.   The retroreflective article according to claim 1, wherein the sealing layer has a first region and a second region, and the second region is raised with respect to the first region and contacts the structured surface.   23. The retroreflective article of claim 22, wherein the second region forms a plurality of separate cells.   24. The retroreflection of claim 23, wherein each of the plurality of separate cells has a cell shape and a cell size, and at least one of the cell shape and the cell size of at least two different separate cells is not equal. Sex goods.   25. The retroreflective article of claim 24, wherein the unequal cell shape of the cell masks the effects of defects or discontinuities in the sheet material and improves the appearance.   25. The retroreflective article of claim 24, wherein the unequal cells form a safety mechanism.   The retroreflective article of claim 1, wherein CAP-Y is greater than 55. The retroreflective article with respect to the incident angle of observation angle and -4 degrees 0.2 degrees, exhibit coefficient of retroreflection _{R A} of about ^{40cd / (lux · m 2)} , retroreflective according to claim 1 Goods.   The retroreflective article of claim 1, wherein CAP-Y is greater than 60. The retroreflective article with respect to an incident angle of 1.0 degree observation angle and -4 degrees, exhibit coefficient of retroreflection R _A of at least about 20Cpl, retroreflective article of claim 1. The retroreflective article of claim 1, wherein the retroreflective article exhibits a% _RT gradient greater than or equal to about 9% / degree for an incident angle of −4 degrees and an observation angle of 1 degree. The retroreflective article with respect to an incident angle of 2.0 degrees observation angle and -4 degrees, exhibit coefficient of retroreflection R _A of at least about 8Cpl, retroreflective article of claim 1. The retroreflective article of claim 1, wherein the retroreflective article exhibits a% _RT gradient greater than or equal to about 3% / degree for an incident angle of −4 degrees and an observation angle of 2 degrees. The retroreflective article with respect to an incident angle of 3.0 degrees observation angle and -4 degrees, exhibit coefficient of retroreflection R _A of at least about 4Cpl, retroreflective article of claim 1. The retroreflective article of claim 1, wherein the retroreflective article exhibits a% _RT gradient greater than or equal to about 1.5% / degree for an incident angle of −4 degrees and an observation angle of 3 degrees. A retroreflective layer including a structured surface opposite the main surface;
A sealing layer in contact with at least a portion of the structured surface to form an optically inactive region that does not substantially retroreflect incident light;
At least one low refractive index layer retroreflecting incident light and surrounded by the optically inactive region to form at least one cell, the cell dimension being 1000 micrometers or less; A retroreflective article comprising a low refractive index layer.   38. The retroreflective article of claim 36, wherein the cell dimension is less than 750 micrometers.   37. The retroreflective article of claim 36, wherein the cell dimension is less than 500 micrometers.   38. The retroreflective article of claim 36, wherein the cell dimension is less than 250 micrometers.   37. The retroreflective article of claim 36, wherein the sealing layer comprises at least one of a pressure sensitive adhesive, a thermoplastic polymer, a thermally active adhesive, an oligomer crosslinkable material, and a radiation curable crosslinkable polymer. .   37. The retroreflective article of claim 36, further comprising a sealing leg that defines the first region.   The retroreflective article according to claim 41, wherein the retroreflective article includes a plurality of cells forming a pattern having a pitch, and the width of the sealing leg portion is larger than 1/5 of the pitch of the pattern. .   The retroreflective article according to claim 41, wherein the retroreflective article includes a plurality of cells forming a pattern having a pitch, and the width of the sealing leg portion is larger than ¼ of the pitch of the pattern. .   The retroreflective article according to claim 41, wherein the retroreflective article includes a plurality of cells forming a pattern having a pitch, and the width of the sealing leg portion is larger than 1/3 of the pitch of the pattern. Goods.   37. The retroreflective article of claim 36, wherein the retroreflective article exhibits a total light reflection of about 5% or greater for visible light incident at an incident angle of -4 degrees.   37. The retroreflective article of claim 36, wherein the retroreflective article exhibits a total light reflection of about 9% or greater for visible light incident at an incident angle of -4 degrees. The retroreflective article with respect to the incident angle of observation angle and -4 degrees 0.2 degrees, exhibit coefficient of retroreflection _{R A} of about ^{40cd / (lux · m 2)} , retroreflective according to claim 36 Goods. The retroreflective article with respect to the incident angle of observation angle and -4 degrees 0.2 degrees, exhibit coefficient of retroreflection _{R A} of about ^{60cd / (lux · m 2)} , retroreflective according to claim 36 Goods. The retroreflective article with respect to an incident angle of 2.0 degrees observation angle and -4 degrees, exhibit coefficient of retroreflection R _A of at least about 8Cpl, retroreflective article according to claim 36. 37. The retroreflective article of claim 36, wherein the retroreflective article exhibits a% _RT gradient greater than or equal to about 3% / degree for an incident angle of -4 degrees and an observation angle of 2 degrees. The retroreflective article with respect to an incident angle of 3.0 degrees observation angle and -4 degrees, exhibit coefficient of retroreflection R _A of at least about 4Cpl, retroreflective article according to claim 36. 37. The retroreflective article of claim 36, wherein the retroreflective article exhibits a% _RT gradient greater than or equal to about 1.5% / degree for an incident angle of -4 degrees and an observation angle of 3 degrees.   40. The retroreflective article of claim 36, wherein less than about 65% of the structured surface is retroreflective.   40. The retroreflective article of claim 36, wherein less than about 55% of the structured surface is retroreflective.   38. The retroreflective article of claim 36, wherein less than about 45% of the structured surface is retroreflective.   37. The retroreflective article of claim 36, wherein the cube corner element is a truncated cube corner element.   37. The retroreflective article of claim 36, wherein the sealing layer has a first region and a second region, and the second region is raised relative to the first region and contacts the structured surface.   58. The retroreflective article of claim 57, wherein the second region forms a plurality of discrete cells.   59. The retroreflective article of claim 58, wherein each of the plurality of separate cells has a cell shape and a cell size, and at least one of the cell shape and the cell size of at least two different separate cells is not equal. .   60. The retroreflective article of claim 59, wherein the unequal cell shape of the cell masks the effects of defects or discontinuities in the sheet material and improves the appearance.   60. The retroreflective article of claim 59, wherein the unequal cells form a safety mechanism.   37. The retroreflective article of claim 36, wherein CAP-Y is greater than 55. The retroreflective article with respect to the incident angle of observation angle and -4 degrees 0.2 degrees, exhibit coefficient of retroreflection _{R A} of about ^{40cd / (lux · m 2)} , retroreflective according to claim 36 Goods.   37. The retroreflective article of claim 36, wherein CAP-Y is greater than 60. The retroreflective article with respect to an incident angle of 1.0 degree observation angle and -4 degrees, exhibit coefficient of retroreflection R _A of at least about 20Cpl, retroreflective article according to claim 36. 37. The retroreflective article of claim 36, wherein the retroreflective article exhibits a% _RT gradient greater than or equal to about 9% / degree for an incident angle of -4 degrees and an observation angle of 1 degree. The retroreflective article with respect to an incident angle of 2.0 degrees observation angle and -4 degrees, exhibit coefficient of retroreflection R _A of at least about 8Cpl, retroreflective article according to claim 36. 37. The retroreflective article of claim 36, wherein the retroreflective article exhibits a% _RT gradient greater than or equal to about 3% / degree for an incident angle of -4 degrees and an observation angle of 2 degrees. The retroreflective article with respect to an incident angle of 3.0 degrees observation angle and -4 degrees, exhibit coefficient of retroreflection R _A of at least about 4Cpl, retroreflective article according to claim 36. 37. The retroreflective article of claim 36, wherein the retroreflective article exhibits a% _RT gradient greater than or equal to about 1.5% / degree for an incident angle of -4 degrees and an observation angle of 3 degrees. A method of making a retroreflective article,
Providing a retroreflective layer that includes a structured surface opposite the second major surface;
Applying a sealing layer having a first region and a second region, wherein the second region is in contact with the structured surface and surrounds the first region and has at least one cell dimension Forming a cell; and
Forming a low refractive index layer between the first region and the structured surface of the retroreflective layer, wherein the cell size of the first region is 1000 micrometers or less; and Including a method.   72. The method of claim 71, wherein the sealing layer comprises one of a pressure sensitive adhesive, a thermoplastic polymer, a thermally active adhesive, an oligomer crosslinkable material, and a radiation curable crosslinkable polymer.   72. The method of claim 71, further comprising a sealing leg that defines the first region.   74. The retroreflective article according to claim 73, wherein the retroreflective article includes a plurality of cells forming a pattern having a pitch, and the width of the sealing leg portion is greater than 1/5 of the pitch of the pattern. .   74. The retroreflective article according to claim 73, wherein the retroreflective article includes a plurality of cells forming a pattern having a pitch, and the width of the sealing leg portion is greater than ¼ of the pitch of the pattern. .   74. The method of claim 73, wherein the retroreflective article includes a plurality of cells forming a pattern having a pitch, and the width of the sealing leg portion is greater than 1/3 of the pitch of the pattern.   72. The method of claim 71, wherein less than about 65% of the structured surface is retroreflective.   72. The method of claim 71, wherein less than about 55% of the structured surface is retroreflective.   72. The method of claim 71, wherein less than about 45% of the structured surface is retroreflective.   72. The method of claim 71, wherein the sealing layer has a first region and a second region, and the second region is raised relative to the first region and contacts the structured surface.   81. The method of claim 80, wherein the second region forms a plurality of separate cells.   82. The retroreflective of claim 81, wherein each of the plurality of separate cells has a cell shape and a cell size, and at least one of the cell shape and the cell size of at least two different separate cells is not equal. Goods.   83. The retroreflective article of claim 82, wherein the unequal cell shape of the cell masks the effects of defects or discontinuities in the sheet material and improves the appearance.   83. The retroreflective article of claim 82, wherein the unequal cells form a safety mechanism.

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