Retroreflective sheet

Abstract

The present invention provides a retroreflective sheet that can retroreflect non-visible light and suppress the reflection of visible light. [Solution] The retroreflective sheet 4 comprises a retroreflective layer 10 that retroreflectively reflects invisible light of a predetermined wavelength, and a visible light absorbing layer 40 that absorbs visible light with a higher absorption rate than the invisible light.

Description

Technical Field

[0001] The present invention relates to a retroreflective sheet.

Background Art

[0002] In the measurement of structures such as tunnels, bridges, roads, and railways, a laser measuring instrument may be used. Patent Document 1 below describes a method for a displacement meter side of a structure using a laser measuring instrument. In this document, the coordinates of targets attached to the wall surface of a tunnel at a predetermined interval are scanned with a 3D laser scanner to measure the displacement of the tunnel.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] A laser measuring instrument that irradiates a target with laser light to measure a structure receives the laser light reflected by the target and maps the position of the target based on the received laser light. Such laser light may be invisible light such as infrared light or ultraviolet light.

[0005] Furthermore, since measurements can be performed efficiently if the target has high reflectivity, it is conceivable to use a retroreflective sheet as a target that reflects light back towards the light source with high reflectivity. However, when a retroreflective sheet is used as a target, it tends to retroreflect not only invisible laser light but also visible light. If light emitted from the headlights of a vehicle is retroreflected, it may give unnecessary warnings to the occupants of the vehicle. Also, even if the light emitted from the headlights of a vehicle is reflected in a way other than retroreflection, it may give unnecessary warnings to people other than the occupants of the vehicle. For this reason, there is a need for a retroreflective sheet that retroreflects invisible light and suppresses the reflection of visible light.

[0006] Therefore, the present invention aims to provide a retroreflective sheet that can retroreflect non-visible light and suppress the reflection of visible light. [Means for solving the problem]

[0007] To achieve the above objective, the retroreflective sheet of the present invention is characterized by comprising a retroreflective layer that retroreflectively reflects invisible light of a predetermined wavelength, and a visible light absorbing layer that absorbs visible light with a higher absorption rate than the invisible light.

[0008] Such retroreflective sheets retroreflect invisible light of a predetermined wavelength through their retroreflective layer. Furthermore, the retroreflective sheet can suppress the reflection of visible light by absorbing visible light.

[0009] Furthermore, it is preferable that at least a portion of the retroreflective layer also serves as the visible light absorbing layer.

[0010] In this case, it becomes unnecessary to laminate a layer solely for absorbing visible light, and the thickness of the retroreflective sheet can be suppressed.

[0011] Furthermore, it is preferable that the material further includes a surface protection layer provided on the side where light is incident to the retroreflective layer and exposed on the surface, and that the surface protection layer also serves as the visible light absorbing layer.

[0012] In this case, the surface protective layer can protect the retroreflective layer from scratches and corrosion, eliminating the need for a layer solely for absorbing visible light, and suppressing an increase in the thickness of the retroreflective sheet compared to the case where a layer solely for absorbing visible light is laminated in addition to the surface protective layer. [Effects of the Invention]

[0013] As described above, the present invention provides a retroreflective sheet that can retroreflect non-visible light and suppress the reflection of visible light. [Brief explanation of the drawing]

[0014] [Figure 1] Figure 1 is a schematic diagram of a measurement system in which the retroreflective sheet of the present invention is used. [Figure 2] Figure 2 is a cross-sectional view of the target. [Figure 3] Figure 3 is a cross-sectional view of the target in the second embodiment. [Figure 4] Figure 4 is a cross-sectional view of the target in the third embodiment. [Modes for carrying out the invention]

[0015] Hereinafter, preferred embodiments of the retroreflective sheet according to the present invention will be described in detail with reference to the drawings. The embodiments illustrated below are for the purpose of facilitating understanding of the present invention and are not intended to limit the interpretation of the present invention. The present invention can be modified and improved within the scope of the claims. Furthermore, the components of the embodiments illustrated below may be combined as appropriate. Note that in the drawings referred to below, the dimensions of each component may be shown differently for the purpose of facilitating understanding. Also, in the drawings, for the sake of readability, reference numerals may be assigned to only some of the similar components, and some reference numerals may be omitted.

[0016] (First Embodiment) Figure 1 is a schematic diagram of a measurement system in which the retroreflective sheet of this embodiment is used. As shown in Figure 1, the measurement system 1 mainly comprises a target 2 and a laser measuring instrument 3.

[0017] In the example shown in Figure 1, the measurement system 1 comprises multiple targets 2. Each target 2 is attached at predetermined intervals to the wall surface W of a tunnel, which is an example of a structure. The targets 2 in the example shown in Figure 1 include markers M for alignment.

[0018] The laser measuring instrument 3 is installed at a predetermined distance from the target 2. In this example, the laser measuring instrument 3 is installed on the road surface away from the wall W. The laser measuring instrument 3 irradiates the target 2 with laser light L and receives the laser light L reflected from the target 2. The laser measuring instrument 3 measures the distance between the laser measuring instrument 3 and the target 2 from the timing of the emission of the laser light L and the timing of the reception of the reflected laser light L. Furthermore, if the laser measuring instrument 3 is a 3D laser measuring instrument such as LiDAR (Light Detection And Ranging), the laser measuring instrument 3 measures the distance between the laser measuring instrument 3 and the target 2, and the position of the target 2 relative to the laser measuring instrument 3.

[0019] The wavelength of the laser light L is invisible light of a predetermined wavelength. In this specification, the wavelength of visible light is 380 nm or more and less than 780 nm. Therefore, the predetermined wavelength is, for example, the near-infrared region with a wavelength of 780 nm or more and less than 2500 nm. When the predetermined wavelength is in the near-infrared region, it is more preferable that the wavelength is 800 nm or more and less than 1600 nm from the viewpoint of suppressing absorption of the laser light L by water molecules in the air. Alternatively, the predetermined wavelength is, for example, the ultraviolet region with a wavelength of less than 380 nm. It is preferable that the wavelength is 200 nm or more from the viewpoint of suppressing absorption of the laser light L by oxygen molecules and water molecules in the air. When the predetermined wavelength is in the ultraviolet region, it is more preferable that the wavelength is 280 nm or more and less than 380 nm, and even more preferable that it is 315 nm or more and less than 380 nm, from the viewpoint of safety.

[0020] Figure 2 is a cross-sectional view of the target 2. As shown in Figure 2, the target 2 includes a retroreflective sheet 4 and an adhesive layer 9.

[0021] The retroreflective sheet 4 retroreflects the laser light L of non-visible light of a predetermined wavelength, and the reflection of visible light is suppressed more than that of the laser light L. Therefore, when the laser light L and visible light of the same power are incident on the retroreflective sheet 4, the power of the reflected light is greater for the laser light L than for the visible light. Note that reflection includes retroreflection.

[0022] The retroreflective sheet 4 of the present embodiment is a cube corner type retroreflective sheet, and mainly includes a surface protective layer 30, a printing layer 20, a visible light absorption layer 40, and a retroreflective layer 10.

[0023] The retroreflective layer 10 includes a retroreflective element layer 11 having a plurality of cube corner type retroreflective elements 111, a holding body layer 12, and a reflective layer 13.

[0024] The holding body layer 12 holds the retroreflective element layer 11, and the retroreflective element layer 11 is provided on one side of the holding body layer 12. In this example, the holding body layer 12 and the retroreflective element 111 are made of the same resin and are integrated by resin molding. Note that the holding body layer 12 and the retroreflective element 111 may be made of different resins. The retroreflective element layer 11 is formed by arranging a plurality of retroreflective elements 111 in a planar manner. It is preferable that the polyhedral retroreflective elements 111 such as triangular pyramid type or full cube type are provided in the retroreflective element layer 11 in a close-packed manner. By providing the retroreflective elements 111 in this way, the retroreflective elements 111 can be arranged without gaps, and the reflection efficiency of the retroreflective layer 10 can be increased.

[0025] When using the retroreflective element layer 11 including the polyhedral retroreflective element 111, the length of one side of the retroreflective element 111 is preferably 0.1 mm or more. By the length of one side of the retroreflective element 111 being 0.1 mm or more, the diffusion of the laser light L retroreflected from the retroreflective sheet 4 is suppressed, and the laser light L can be more reliably retroreflected in a desired direction.

[0026] The retaining layer 12 and the retroreflective element 111 are preferably made of a material that has excellent transmittance of light of a predetermined wavelength of laser light L. Examples of such materials include polycarbonate resins, vinyl chloride resins, vinylidene fluoride resins, acrylic resins, epoxy resins, styrene resins, polyester resins, fluororesins, polyethylene resins, olefin resins, cellulose resins, and urethane resins.

[0027] The reflective layer 13 is a layer provided on the surface of the retroreflective element 111 opposite to the holder layer 12, and is a layer for reflecting laser light L. This reflective layer 13 is made of a metal with excellent reflective properties, such as aluminum, silver, copper, or nickel. Alternatively, the reflective layer 13 is made of a dielectric multilayer film that efficiently reflects laser light L. These metals and dielectric multilayer films are provided by means such as vacuum deposition or sputtering. The maximum thickness of the reflective layer 13 is, for example, 0.1 μm.

[0028] The visible light absorbing layer 40 is made of a resin containing a material with a higher visible light absorption rate than the laser light L. Therefore, the visible light transmittance of the visible light absorbing layer 40 is lower than the transmittance of the laser light L. As an example of the resin constituting the visible light absorbing layer 40, a resin similar to the resin constituting the retroreflective element 111 can be used. As an example of a material with a higher visible light absorption rate than the laser light L, if the predetermined wavelength is in the infrared region, examples include anthraquinone dyes, perinone dyes, perylene dyes, methine dyes, phthalocyanine dyes, coumarin dyes, etc. If the predetermined wavelength is in the ultraviolet region, examples include anthraquinone dyes, nitroso dyes, cyanine dyes, phthalocyanine dyes, coumarin dyes, azo dyes, and benzophenone dyes. From the viewpoint of easily adjusting the visible light absorption rate, it is preferable to include at least one anthraquinone dye or a phthalocyanine dye.

[0029] As a material with a higher visible light absorption rate than laser light L, resins containing fluorescent dyes that absorb visible light and emit near-infrared or ultraviolet light can also be used. Examples of such fluorescent dyes include compounds having an absorption maximum wavelength in the visible light region and an emission maximum wavelength in the near-infrared region, as described in Japanese Patent Application Publication No. 2023-128931.

[0030] The printed layer 20 is printed on the side of the visible light absorption layer 40 opposite to the retroreflective element layer 11, and is a layer in which the transmission of visible light is suppressed. Therefore, the pattern formed by the printed layer 20 is visible. In addition, the transmission of laser light L may be suppressed, or it may be transmitted. The pattern is not particularly limited, but in this embodiment, the printed layer 20 forms the marker M shown in Figure 1. The printed layer 20 in this embodiment is formed by printing. The printing method is not particularly limited, but examples include gravure printing, screen printing, flexographic printing, and inkjet printing. The maximum thickness of the printed layer 20 is, for example, 10 μm.

[0031] Examples of materials for the printed layer 20 include resin components and colorants. In addition to resin components and colorants, various additives such as plasticizers, defoamers, leveling agents, light stabilizers, heat stabilizers, and crosslinking agents may be added as needed.

[0032] The resin component of the printing layer 20 is not particularly limited as long as it suppresses the transmission of visible light, but examples include melamine resin, epoxy resin, urethane resin, vinyl resin, polyester resin, alkyd resin, and acrylic resin, which have excellent dispersibility and stability of colorants, solubility in solvents, weather resistance, printability, and adhesion to the film. These may be materials polymerized individually or materials copolymerized by combining two or more of these.

[0033] The coloring agent for the printing layer 20 is not particularly limited, but examples include pigments and dyes of colors produced by mixing pigments and dyes such as black, red, green, and blue. Furthermore, the printing layer 20 may use a coloring agent with a higher visible light absorption rate than the laser light L. Examples of such coloring agents include those containing anthraquinone-based dyes and phthalocyanine-based dyes.

[0034] The surface protection layer 30 is the layer on the side of the retroreflective sheet 4 where light is incident from the outside. The surface protection layer 30 is a layer that transmits at least laser light L and protects the printed layer 20 and the retroreflective layer 10. The surface protection layer 30 is a layer provided on the side of the retroreflective layer 10 opposite to the retroreflective element layer 11, and the printed layer 20 is sandwiched between the retroreflective layer 10 and the surface protection layer 30. Examples of materials for this surface protection layer 30 include the same materials as those used for the retaining layer 12 and the retroreflective element 111. Note that the surface protection layer 30 is the layer on the side of the retroreflective sheet 4 where light is incident from the outside.

[0035] An adhesive layer 9 is provided on the side of the retroreflective sheet 4 opposite to the surface protective layer 30. In this embodiment, the adhesive layer 9 is laminated on the surface of the reflective layer 13 opposite to the retroreflective element layer 11. Examples of materials for the adhesive layer 9 include acrylic resin, epoxy resin, phenolic resin, vinyl acetate resin, nitrile rubber resin, and silicone rubber resin. The maximum thickness of the adhesive layer 9 is, for example, 70 μm.

[0036] If target 2 is not attached, a release sheet (not shown) is laminated on the side of the adhesive layer 9 opposite to the retroreflective sheet 4 side, preventing dust and other debris from adhering to the adhesive layer 9.

[0037] As shown in Figure 2, when laser light L is incident on the retroreflective sheet 4 from the surface protective layer 30 side, the laser light L, being invisible light of a predetermined wavelength, passes through the surface protective layer 30, the visible light absorption layer 40, and the retaining layer 12, and is retroreflected by being reflected multiple times at the interface between the retroreflective element 111 and the reflective layer 13. The retroreflected laser light L passes through the retaining layer 12, the visible light absorption layer 40, and the surface protective layer 30 and is emitted from the retroreflective sheet 4. On the other hand, visible light incident on the retroreflective sheet 4 from the surface protective layer 30 is absorbed in the visible light absorption layer 40 with a higher absorption rate than the laser light L. Furthermore, even if some of the visible light passes through the visible light absorption layer 40 and is retroreflected by the retroreflective element 111, the retroreflected visible light is again absorbed in the visible light absorption layer 40 with a higher absorption rate than the laser light L. Therefore, when laser light L and visible light of the same power are incident on the retroreflective sheet 4, the energy of the emitted light is less for the visible light than for the laser light L.

[0038] In the example shown in Figure 2, the visible light absorbing layer 40 is provided between the retroreflective layer 10 and the surface protection layer 30. However, the visible light absorbing layer 40 may be provided in other positions as long as it is located on the optical path of light incident on the retroreflective sheet 4. For example, if the holder layer 12 and the retroreflective element layer 11 are separate components, the visible light absorbing layer 40 may be provided between the holder layer 12 and the retroreflective element layer 11. Also, the visible light absorbing layer 40 may be provided on the side opposite to the retroreflective layer 10 from the surface protection layer 30. However, since the surface protection layer 30 is intended to protect the retroreflective sheet 4, it is preferable that the surface protection layer 30 be exposed, and therefore, it is preferable that the visible light absorbing layer 40 be provided on the side of the retroreflective element layer 11 from the surface protection layer 30.

[0039] Furthermore, some layers of the retroreflective layer 10 may also serve as the visible light absorbing layer 40. That is, at least one of the holder layer 12 and the retroreflective element layer 11 may also serve as the visible light absorbing layer 40. Alternatively, the surface protective layer 30 may also serve as the visible light absorbing layer 40. In these cases, the layer that serves as the visible light absorbing layer 40 contains a material with a higher visible light absorption rate than the laser light L.

[0040] If at least one of the retaining layer 12, the retroreflective element layer 11, and the surface protection layer 30 also functions as the visible light absorbing layer 40, the visible light absorbing layer 40 shown in Figure 2 may be omitted. In this case, the lamination of a layer solely for absorbing visible light is unnecessary, and the retroreflective sheet 4 can be simplified. Furthermore, since the lamination of a layer solely for absorbing visible light can be omitted, the total thickness of the retroreflective sheet 4 can be reduced, the flexibility of the sheet may be improved, and adhesion to curved substrates may be improved. When at least one of the retaining layer 12 and the retroreflective element layer 11 also functions as the visible light absorbing layer 40, the visible light absorbing layer 40 is provided inside the retroreflective sheet 4, so even if the surface protection layer 30 is scratched, a decrease in visible light absorption performance can be suppressed. Furthermore, when the retroreflective element layer 11 also functions as the visible light absorbing layer 40, light is reflected multiple times within the retroreflective element 111 as it propagates. Compared to when another layer of the same thickness is the visible light absorbing layer, this allows for a longer optical path and greater absorption of visible light.

[0041] When the retaining layer 12, the retroreflective element layer 11, and the surface protective layer 30 do not also serve as visible light absorbing layers, and a visible light absorbing layer 40 is laminated as shown in Figure 2, it may be possible to fully utilize the performance of each layer.

[0042] The visible light absorbing layer has a minimum absorption value in one of the visible light wavelength ranges (380 nm to less than 780 nm) from the viewpoint of improving visibility to observers in dark places such as at night or inside tunnels, and it is preferable that this minimum absorption value is 85% or less, more preferably 75% or less, and even more preferably 65% ​​or less. Furthermore, from the viewpoint of further suppressing unnecessary attention to people, it is preferable that this minimum absorption value is 40% or more, more preferably 45% or more, and even more preferably 50% or more.

[0043] From the viewpoint of more efficiently measuring structures, the visible light absorbing layer preferably has an absorption rate of 20% or less in the near-infrared wavelength range (780 nm to 2500 nm) or the ultraviolet wavelength range (less than 380 nm), more preferably 10% or less, and even more preferably 5% or less.

[0044] The absorption of the visible light absorption layer in the visible light and laser light L wavelength ranges can be measured using a general method with a spectrophotometer.

[0045] Furthermore, in addition to the above configuration, the retroreflective sheet 4 may have a configuration in which the reflective layer 13 suppresses the reflection of visible light more than the laser light L. In this case, the reflective layer 13 is, for example, a dichroic mirror and is composed of a dielectric multilayer film. Specifically, a dielectric with a low refractive index and a dielectric with a high refractive index are stacked with a thickness that is a multiple of 1 / 4 of the wavelength of the laser light L. Examples of dielectrics with a low refractive index include silicon dioxide, and examples of materials with a high refractive index include titanium oxide, zirconium oxide, tantalum pentoxide, titanium monoxide, and cerium oxide. In this case, the reflective layer 13 can reflect the laser light L and transmit visible light.

[0046] In this case, even if visible light passes through the visible light absorption layer 40, the visible light also passes through the reflective layer 13. In other words, visible light passes through the reflective layer 13 with a higher transmittance than the laser light L. Therefore, the power of the visible light emitted from the retroreflective sheet 4 can be reduced.

[0047] (Second Embodiment) Next, a second embodiment of the present invention will be described. Note that, unless otherwise specified and denoted by the same reference numerals, redundant descriptions of components identical or equivalent to those in the first embodiment will be omitted.

[0048] Figure 3 is a cross-sectional view of target 2 in the embodiment. As shown in Figure 3, target 2 in this embodiment differs from target 2 in the first embodiment in that the retroreflective sheet 4 is a micro-spherical retroreflective sheet.

[0049] The retroreflective sheet 4 in this embodiment differs from the retroreflective sheet 4 of the first embodiment in that the retroreflective layer 10 has a retaining layer 12, a microsphere layer 15, a focal-forming layer 16, and a reflective layer 13.

[0050] The microsphere layer 15 consists of a plurality of microspheres 151 arranged on a generally planar surface. The microspheres 151 are made of a light-transmitting material, such as glass or resin. Examples of such resins include (meth)acrylic acid esters, styrene compounds, vinyl esters, carbonate esters, and polycarbonate. The particle size of the microspheres is, for example, about 50 μm. Approximately half of each microsphere 151 is held in the retaining layer 12. Therefore, a portion of each microsphere 151 is embedded in and held in the retaining layer 12.

[0051] The focus-forming layer 16 covers the surface of each microsphere 151 that is not held by the retaining layer 12. The focus-forming layer 16 is made of a light-transmitting resin layer with a refractive index lower than that of the microspheres 151, and has a thickness such that light transmitted through the microspheres 151 is focused onto the surface of the focus-forming layer 16 opposite to the microsphere layer 15 side. Examples of materials constituting the focus-forming layer 16 include acrylic resin, alkyd resin, fluororesin, polyvinyl chloride resin, polyester resin, urethane resin, polycarbonate resin, and butyral resin, either alone or in combination. However, from the viewpoint of weather resistance, coating suitability, and thermal stability, the material constituting the focus-forming layer 16 is preferably acrylic resin.

[0052] A reflective layer 13 is provided on the surface of the focal-forming layer 16 opposite to the microsphere layer 15. Therefore, the reflective layer 13 is located at a position where light transmitted through the microspheres 151 is focused. The reflective layer 13 is a layer that reflects the light transmitted through the microspheres 151.

[0053] As shown in Figure 3, when laser light L is incident on the retroreflective sheet 4 from the surface protective layer 30 side, the laser light L passes through the surface protective layer 30, the visible light absorption layer 40, the retaining layer 12, the microspheres 151, and the focus-forming layer 16, focuses onto the reflection layer 13, and is reflected by the reflection layer 13. Subsequently, the laser light L passes through the focus-forming layer 16, the microspheres 151, the retaining layer 12, the visible light absorption layer 40, and the surface protective layer 30 and is emitted from the retroreflective sheet 4. In this way, the laser light L incident on the retroreflective sheet 4 is retroreflective. On the other hand, visible light incident on the retroreflective sheet 4 from the surface protective layer 30 is absorbed in the visible light absorption layer 40 with a higher absorption rate than the laser light L. Furthermore, even if some of the visible light passes through the visible light absorption layer 40 and is retroreflective, the retroreflective visible light is absorbed in the visible light absorption layer 40 with a higher absorption rate than the laser light L. Therefore, when laser light L and visible light of the same power are incident on the retroreflective sheet 4, the energy of the emitted visible light will be less than the energy of the laser light L.

[0054] In the example shown in Figure 3, the visible light absorbing layer 40 is provided between the retroreflective layer 10 and the surface protective layer 30. However, the visible light absorbing layer 40 may be provided in other locations as long as it is located on the optical path of the light incident on the retroreflective sheet 4. For example, similar to the first embodiment, the visible light absorbing layer 40 may be provided on the side opposite to the retroreflective layer 10 from the surface protective layer 30.

[0055] Furthermore, similar to the first embodiment, some layers of the retroreflective layer 10 may also serve as the visible light absorbing layer 40. That is, in this embodiment, at least one of the retaining layer 12, the microsphere layer 15, and the focus-forming layer 16 may also serve as the visible light absorbing layer 40. Alternatively, the surface protective layer 30 may also serve as the visible light absorbing layer 40. In these cases, the layer that serves as the visible light absorbing layer 40 contains a material with a higher visible light absorption rate than the laser light L. Therefore, when the microsphere layer 15 also serves as the visible light absorbing layer 40, the microspheres 151 are made of resin.

[0056] If at least one of the retaining layer 12, the microsphere layer 15, the focus-forming layer 16, and the surface protection layer 30 also functions as the visible light absorption layer 40, the visible light absorption layer 40 shown in Figure 3 may be omitted. In this case, the lamination of a layer solely for absorbing visible light is unnecessary, and the retroreflective sheet 4 can be simplified. Furthermore, since the lamination of a layer solely for absorbing visible light can be omitted, the total thickness of the retroreflective sheet 4 can be reduced, the flexibility of the sheet can be improved, and adhesion to curved substrates can be improved. When at least one of the retaining layer 12, the microsphere layer 15, and the focus-forming layer 16 also functions as the visible light absorption layer 40, the visible light absorption layer is provided inside the retroreflective sheet 4, so even if the surface protection layer 30 is scratched, a decrease in visible light absorption performance can be suppressed. In addition, when the microsphere layer 15 also functions as the visible light absorption layer 40, the retroreflective light always passes through the microsphere layer 15, so the visible light absorption efficiency can be improved.

[0057] Furthermore, in this embodiment as well, the retroreflective sheet 4 may have a configuration in which the reflective layer 13 suppresses the reflection of visible light more than the laser light L, in addition to the above configuration of this embodiment. In this case, the configuration of the reflective layer 13 is the same as the configuration in the first embodiment when the reflective layer 13 suppresses the reflection of visible light more than the laser light L. Therefore, the reflective layer 13 transmits visible light and reflects the laser light L.

[0058] In this case, even if visible light passes through the visible light absorbing layer 40, the visible light passes through the reflective layer 13 with a higher transmittance than the laser light L. Therefore, the power of the visible light emitted from the retroreflective sheet 4 can be reduced.

[0059] (Third embodiment) Next, a third embodiment of the present invention will be described. Note that, unless otherwise specified and denoted by the same reference numerals, redundant descriptions of components identical or equivalent to those in the first embodiment will be omitted.

[0060] Figure 4 is a cross-sectional view of target 2 in this embodiment. As shown in Figure 4, target 2 in this embodiment differs from target 2 in the first embodiment in that the retroreflective sheet 4 is a capsule-shaped retroreflective sheet.

[0061] The retroreflective sheet 4 in this embodiment differs from the retroreflective sheet 4 of the first embodiment in that the retroreflective layer 10 does not include a reflective layer 13, but rather includes a binder layer 70.

[0062] The binder layer 70 has a main body portion 71 which is a layered portion, and a plurality of columnar support portions 72 which are columnar portions. The support portions 72 extend in the planar direction of the main body portion 71, with one end connected to the main body portion 71 and the other end connected to some of the retroreflective elements 111 of the retroreflective element layer 11. As a result, a space AR is formed between the main body portion 71 and the other portion of the retroreflective elements 111, and the other portion of the retroreflective elements 111 are in contact with the space AR. The thickness of the space AR in the stacking direction is, for example, 20 to 100 μm.

[0063] Preferably, the main body 71 and the support column 72 are made of the same material and formed integrally. However, the main body 71 and the support column 72 may be made of different materials. The binder layer 70 is made of the same material as the retroreflective element 111, for example. For example, the binder layer 70 may be made of amorphous polyester. Preferably, the support column 72 is made of a material with a lower refractive index than the retroreflective element 111. In this case, light can be reflected at the interface between the retroreflective element 111 and the support column 72.

[0064] As shown in Figure 4, when laser light L is incident on the retroreflective sheet 4 from the surface protective layer 30 side, the laser light L passes through the surface protective layer 30, the visible light absorption layer 40, and the retaining layer 12, and is retroreflected by being reflected multiple times at the interface between the retroreflective element 111 and the space AR. The retroreflected laser light L passes through the retaining layer 12 and the surface protective layer 30 and is emitted from the retroreflective sheet 4. On the other hand, visible light incident on the retroreflective sheet 4 from the surface protective layer 30 is absorbed in the visible light absorption layer 40 with a higher absorption rate than the laser light L. Furthermore, even if some of the visible light passes through the visible light absorption layer 40 and is retroreflected, the retroreflected visible light is absorbed in the visible light absorption layer 40 with a higher absorption rate than the laser light L. Therefore, when laser light L and visible light of the same power are incident on the retroreflective sheet 4, the energy of the emitted visible light will be less than the energy of the laser light L. Furthermore, if the refractive index of the support column 72 is lower than that of the retroreflective element 111 with respect to the wavelength of the laser light L, as described above, this is preferable because the laser light L can be retroreflected multiple times at the interface between the retroreflective element 111 and the support column 72.

[0065] In this embodiment as well, at least one of the retaining layer 12 and the retroreflective element layer 11 may also serve as the visible light absorbing layer 40, similar to the first embodiment. In this embodiment, since the retroreflective layer 10 is made entirely of resin, the entire retroreflective layer 10 may also serve as the visible light absorbing layer 40. In other words, in this embodiment, at least a portion of the retroreflective layer 10 may also serve as the visible light absorbing layer 40. Furthermore, the surface protective layer 30 may also serve as the visible light absorbing layer 40.

[0066] Based on the embodiments described above, the following aspects of the retroreflective sheet 4 of the present invention have been shown. That is, the retroreflective sheet 4 of the present invention comprises a retroreflective layer 10 that retroreflectively reflects invisible light of a predetermined wavelength, and a visible light absorbing layer 40 that absorbs visible light with a higher absorption rate than invisible light.

[0067] Such a retroreflective sheet 4 retroreflects invisible light of a predetermined wavelength, such as laser light L, through its retroreflective layer 10. Furthermore, by absorbing visible light, the retroreflective sheet 4 can suppress the reflection of visible light.

[0068] Furthermore, at least a portion of the retroreflective layer 10 also serves as the visible light absorbing layer 40. In this case, it becomes unnecessary to laminate a layer solely for absorbing visible light, and the thickness of the retroreflective sheet 4 can be suppressed.

[0069] Furthermore, the retroreflective sheet 4 further includes a surface protection layer 30 that is provided on the side where light enters the retroreflective layer 10 and is exposed on the surface, with the surface protection layer 30 also serving as the visible light absorbing layer 40. In this case, the surface protection layer 30 can protect the retroreflective layer 10 from scratches, corrosion, etc., eliminating the need for a layer solely for absorbing visible light, and suppressing an increase in the thickness of the retroreflective sheet 4.

[0070] Although the present invention has been described above with reference to embodiments, the present invention is not limited to these embodiments.

[0071] For example, in the above embodiment, the retroreflective sheet 4 was described as being used on the target 2 of the measurement system 1. However, the retroreflective sheet 4 may be used for purposes other than the target 2. For example, the retroreflective sheet 4 may be attached to window materials such as glass windows or blinds for the purpose of suppressing the rise in room temperature and the incidence of visible light into the room. Also, because it is suitable for reading using infrared cameras or ultraviolet cameras, it may be used as an anti-counterfeiting component. Examples of anti-counterfeiting components include, for example, automobile license plates or identification labels that are marked with anti-counterfeiting identification that can only be read by infrared light. Furthermore, for example, if the predetermined wavelength is in the ultraviolet range, the retroreflective sheet 4 may be used as a reflector for germicidal LEDs, etc.

[0072] For example, in the above embodiment, the retroreflective sheet 4 had a printed layer 20, but the retroreflective sheet 4 of the present invention does not require a printed layer 20.

[0073] Furthermore, the surface protection layer 30 is not mandatory. However, from the viewpoint of achieving high weather resistance, it is preferable that the retroreflective sheet 4 be provided with the surface protection layer 30. [Industrial applicability]

[0074] According to the present invention, a retroreflective sheet is provided that can retroreflect non-visible light and suppress the reflection of visible light, and can be used in fields such as surveying. [Explanation of symbols]

[0075] 1. Measurement System 2. Target 3. Laser measuring instrument 4. Retroreflective sheet 10. Retroreflective layer 11. Retroreflective element layer 111... Retroreflective element 12...Holder layer 13...Reflection layer 15...Microsphere layer 151...microsphere 16...focal formation layer 20...printing layer 30...Surface protective layer 40. Visible light absorption layer

Claims

1. A retroreflective layer that retroreflects invisible light of a predetermined wavelength, A visible light absorbing layer that absorbs visible light with a higher absorption rate than the aforementioned invisible light, Equipped with A retroreflective sheet characterized by the following features.

2. At least a portion of the retroreflective layer also serves as the visible light absorbing layer. The retroreflective sheet according to feature 1.

3. The retroreflective layer is further provided on the side where light is incident and is exposed on the surface, The aforementioned surface protective layer also serves as the visible light absorbing layer. The retroreflective sheet according to feature 1.

Images