TWI738403B - Retroreflective sheet - Google Patents

Abstract

A retroreflective sheet includes a protective layer, a pressure adhesive resin layer adhered to a license plate of a vehicle, a reflective layer reflecting an incident visible light, a focus resin layer allowing an incident visible light to focus on a surface of the reflective layer, a light collecting layer formed by attaching a plurality of beads on the focus resin layer and transmitting the visible light reflected by the reflective layer to retroreflect the visible light, a first base layer fixing the light collecting layer, an adhesive layer formed on the first base layer, an infrared blocking layer formed on the adhesive layer to reflect and block an infrared light and to selectively transmit the visible light of the incident light from the outside, and a second base layer formed on the infrared blocking layer to prevent the infrared blocking layer from being damaged.

Description

Retroreflective sheeting

The present invention claims priority based on 35 U.S.C. § 119 in Korean Patent Application No. 10-2019-080802 filed with the Korean Intellectual Property Office on July 4, 2019, and the entire contents of which are incorporated herein by reference.

The specific embodiment of the inventive concept disclosed herein relates to a retroreflective sheeting, and more specifically, to a retroreflector that can be used for vehicle license plates.

The retro-reflective sheet is a reflector, which includes a light-collecting layer and a reflective layer that reflects incident light back in the incident direction. The retroreflective sheeting is usually formed in the form of a sheet, processed into the desired shape or pattern on the body surface of the adherend, and attached to the selected part of road signs or uniforms (such as firefighters) by hot pressing or sewing to improve the visibility Sexual and easy to recognize, even in dark environments. Therefore, when attaching retroreflective sheets to clothing worn by people working on roads or dangerous locations, such as environmental health workers, firefighters, police, factory workers, construction site workers, and guards everywhere, The position of the wearer can be confirmed by the surrounding personnel, which is extremely effective for the protection and safety of the wearer.

In addition, retroreflective sheeting can be applied to vehicle license plates. The vehicle license plate becomes dark at night, making it difficult to be easily recognized by other nearby vehicles or pedestrians. Therefore, in order to develop a technology to improve the visibility in the dark hours, retroreflective sheets are applied to the vehicle license plate.

Figure 1 is a cross-sectional view of the retroreflective sheeting of the prior art.

The protective layer 11, the pressure-bonded resin layer 13, the reflective layer 17, the focal resin layer 19, the light-collecting layer 21, and the base layer 23 are stacked to form a retroreflective sheet of advanced technology.

In the above, the protective layer 11 is formed of a release film or paper to prevent the pressure-bonded resin layer 13 from being contaminated.

The pressure-bonding resin layer 13 is a surface-adhesive adhesive, that is, adheres to the surface of the vehicle license plate, and is formed of a resin with strong adhesion to the license plate material (such as aluminum) forming the license plate.

A metal with good reflection characteristics (such as aluminum) is deposited on the pressure bonding resin layer 13 to form a reflection layer 17, which reflects incident light.

The focal resin layer 19 is formed on a surface having a plurality of beads (which form the light-collecting layer 21), so that the light incident through the beads is focused. The focal resin layer 19 is preferably formed of a transparent resin having a thickness of 20 to 40% of the diameter of each bead to prevent light loss.

The light collection layer 21 is formed on the focal resin layer 19 and includes a plurality of beads to focus incident light on the reflective layer 17 and transmit the light reflected from the reflective layer 17 to the outside. In the above, the light collection layer 21 transmits the incident light back to the light source, thereby minimizing the light loss of the reflected light.

The base layer 23 prevents the plurality of beads forming the light collection layer 21 from being damaged or separated due to physical impact (such as friction or collision).

In the above configuration, the reflective layer 17 will retro-reflect the incident light from the light-collecting layer 21 to improve visibility. Therefore, it can be easily recognized even in a dark environment. In addition, the focal resin layer 19 is formed of a transparent resin to focus the light entering through the plurality of beads forming the light-collecting layer 21, thereby preventing light loss.

The pressure-adhesive resin layer 13 in the state where the protective layer 11 is removed is a surface-adhesive adhesive, that is, adheres to the surface of the vehicle license plate, and is formed of a resin with strong adhesion to the license plate material (such as aluminum) forming the license plate.

However, when the license plate on which the retroreflective sheet of advanced technology is applied is photographed by a camera equipped with an infrared lamp at night, the excess light is retroreflected.

Therefore, when a camera equipped with an infrared lamp is used to take pictures of a vehicle license plate attached with a retroreflective sheet at night, there is a problem that it is difficult to recognize the license plate number due to the excessive light being retroreflected.

A specific embodiment of the inventive concept provides a retroreflective sheet that can prevent visibility degradation during the day.

The specific embodiment of the concept of the present invention provides a retroreflective sheet that can easily recognize the license plate number when a camera equipped with an infrared lamp is used to take a picture of a vehicle license plate at night.

According to an exemplary embodiment, a retroreflective sheet includes a protective layer, a pressure-bonded resin layer formed on the protective layer and adhered to a vehicle license plate, a reflective layer formed on the pressure-bonded resin layer and reflecting incident visible light, A focal resin layer formed on the reflective layer and capable of focusing incident visible light on the surface of the reflective layer, by attaching a plurality of beads to the focal resin layer and transmitting the visible light reflected by the reflective layer to reverse the visible light A light collecting layer formed by reflection, a first base layer formed on the light collecting layer and fixing the light collecting layer, an adhesive layer formed on the first base layer, formed on the adhesive layer to reflect and block incident from the outside An infrared blocking layer that selectively transmits visible light to infrared light and a second base layer formed on the infrared blocking layer to prevent damage to the infrared blocking layer.

The focal resin layer is formed of polyurethane, polyester, vinyl resin, acrylic resin, or (meth)acrylate resin, and the thickness is 20 to 40% of the diameter of the bead.

The reflective layer is formed by forming a pair of two thin layers of a low refractive index material and a high refractive index material, which are respectively selected from SiO ₂ , TiO ₂ , ZnS, ZnO, Al ₂ O ₃ , ZrO ₂ , Ta ₂ O ₅ , Nb ₂ O ₅ , CaF ₂ , and Na ₃ AlF ₆ , and repeat the pair N (N is a natural number of 2 or more) times.

The reflective layer is formed by depositing metal of Al, Ag, Cu, Zn, or Sn.

The infrared blocking layer is formed by forming a pair of two thin layers of one of a low refractive index material and a high refractive index material, which are respectively selected from SiO ₂ , TiO ₂ , ZnS, ZnO, Al ₂ O ₃ , ZrO ₂ , and Ta ₂ O _5. Nb ₂ O ₅ , CaF ₂ , and Na ₃ AlF ₆ are formed by repeating the pair N (N is a natural number of 2 or more) times.

The infrared blocking layer is composed of tungsten oxide compound, titanium oxide, zirconium oxide, tantalum oxide, niobium oxide, zinc oxide, indium oxide, indium tin oxide (ITO), tin oxide, antimony tin oxide (ATO), cesium oxide, zinc sulfide , Cerium oxide, and hexaboride.

The second base layer has weather resistance and stretchability, and is coated with transparent polyurethane resin, acrylic resin, polyester resin, PVC, or methacrylate resin to prevent light loss. form.

The concept of the present invention will be described in detail below with reference to the drawings.

Figure 2 is a cross-sectional view of the retroreflective sheeting of the concept of the present invention.

The retroreflective sheet of the concept of the present invention is composed of a protective layer 31, a pressure-adhesive resin layer 33, a reflective layer 37, a focal resin layer 41, a light-collecting layer 43, a first base layer 45, an adhesive layer 47, an infrared blocking layer 49, and a second The base layer 51 is formed.

In the above, the protective layer 31 is formed of a release film or paper to prevent the pressure-bonded resin layer 33 from being contaminated.

In a state where the protective layer 31 is removed from the manufactured retroreflective sheet, the pressure adheres to the resin layer 33 to adhere to the surface of the vehicle license plate (not shown). Therefore, the pressure-adhesive resin layer 33 is formed of a resin with strong adhesion to the license plate material (such as aluminum) forming the license plate. In this way, the pressure-bonding resin layer 33 is formed of, for example, an acrylic adhesive, a silicone adhesive, or a rubber adhesive, and is formed by gravure printing, screen printing, flexographic printing, offset printing, slit coating, Or a comma coating method, which is coated to a thickness of about 30 to 100 microns.

The reflective layer 37 is composed of two or more layers selected from the group consisting of SiO ₂ , TiO ₂ , ZnS, ZnO, Al ₂ O ₃ , ZrO ₂ , Ta ₂ O ₅ , Nb ₂ O ₅ , CaF _{2 on the pressure-adhesive resin layer 33} , Formed by multiple thin layers of _{Na 3} AlF _{6 materials. For example, two thin layers of low refractive index material SiO 2} and high refractive index material TiO ₂ each having a thickness of about 500 to 3000 angstroms form a pair, and are repeated N (N is a natural number of 2 or more) times, and have about A total thickness of 4000 to 20000 Angstroms. The reflective layer 37 is composed of two or more layers selected from among SiO ₂ , TiO ₂ , ZnS, ZnO, Al ₂ O ₃ , ZrO ₂ , Ta ₂ O ₅ , Nb ₂ O ₅ , CaF ₂ , and Na ₃ AlF ₆ A plurality of thin layers of materials are formed, and for example, by deposition methods, such as vacuum evaporation, chemical vapor deposition (CVD), sputtering, plasma enhanced chemical vapor deposition (PECVD), or ion beam, interlaced formation of SiO ₂ thin layers The _second thin layer of TiO 2 thin layer.

In the above, the SiO ₂ thin layer and the TiO ₂ thin layer included in the reflective layer 37 become transparent in a thin layer state, and the transparency thereof increases as the thickness of each layer decreases. Therefore, it prevents the visibility of the vehicle license plate to which the reflective layer 37 is applied from deteriorating during the day.

In addition, SiO ₂ has a low refractive index of about 1.46, and TiO ₂ has a high refractive index of about 2.3. In the above, the _two thin layers of the low refractive index SiO 2 thin layer and the high refractive index TiO ₂ thin layer form a pair, and are repeatedly stacked N (N is a natural number of 2 or more) times to form the reflective layer 37, which reflects Visible light and transmit infrared light.

In addition, the concept of the present invention can deposit metals such as Al, Ag, Cu, Zn, or Sn, which have excellent light reflection characteristics, to form the reflective layer 37.

The focal resin layer 41 is formed on the reflective layer 37, and the light incident through the beads included in the light-collecting layer 43 is focused on the surface of the reflective layer 37, thereby preventing the brightness of the reflected light from decreasing. The focal resin layer 41 is preferably formed of a transparent resin, such as polyurethane, polyester, vinyl resin, acrylic resin, or (meth)acrylate resin, to prevent light loss and have a thickness of various 20 to 40% of the diameter of the beads.

The light collection layer 43 is dispersedly formed so that a plurality of beads are layered on the focal resin layer 41. In the above, the light-collecting layer 43 focuses the light incident on a plurality of beads, which are formed of glass, transparent non-glass ceramics, or transparent synthetic resin, and have a diameter of about 20 to 200 microns.

The first base layer 45 is formed on the light collection layer 43. The first base layer 45 is used to fix the beads included in the light-collecting layer 43, and is made of polyurethane resin, acrylic resin, polyester resin, PVC, or (meth)acrylate resin. It is formed and coated to a thickness of about 20 to 100 microns by a method such as gravure printing, screen printing, flexographic printing, offset printing, slit coating, or doctor blade coating.

The subsequent layer 47 is an adhesive or pressure adhesive on the first base layer 45, and is coated by a method such as gravure printing, screen printing, flexographic printing, offset printing, slit coating, or doctor blade coating. The pressure adhesive can use acrylic adhesive, silicone adhesive, or rubber adhesive, and the adhesive can be used together with the following: polyurethane, polyester, acrylic, epoxy , Ethylene, acetate, TPU, or TPE.

The infrared blocking layer 49 is composed of two or more layers selected from SiO ₂ , TiO ₂ , ZnS, ZnO, Al ₂ O ₃ , ZrO ₂ , Ta ₂ O ₅ , Nb ₂ O ₅ , CaF ₂ , and Na ₃ AlF ₆ Formed by multiple thin layers of the material. _{For example, two thin layers of low refractive index material SiO 2} and high refractive index material TiO ₂ each having a thickness of about 500 to 3000 angstroms form a pair, and are repeated N (N is a natural number of 2 or more) times to have about 4000 To a total thickness of 20000 Angstroms. Therefore, the infrared blocking layer 49 causes the infrared light (including near-infrared light) of the incident light to be reflected to the outside, and is blocked and does not enter the light-collecting layer 43. In the above, the infrared blocking layer 49 is composed of two or more layers selected from SiO ₂ , TiO ₂ , ZnS, ZnO, Al ₂ O ₃ , ZrO ₂ , Ta ₂ O ₅ , Nb ₂ O ₅ , CaF ₂ , and Na ₃ AlF ₆ is formed by multiple thin layers of material, and for example, by deposition methods such as vacuum evaporation, chemical vapor deposition (CVD), sputtering, plasma enhanced chemical vapor deposition (PECVD), or ion beam, staggered formation _Two thin layers of SiO 2 thin layer and TiO ₂ thin layer.

_{The SiO 2} thin layer and the TiO ₂ thin layer included in the infrared blocking layer 49 become transparent in a thin layer state, and the transparency thereof increases as the thickness of each layer decreases. Therefore, it prevents the visibility of the vehicle license plate to which the infrared blocking layer 49 is applied from deteriorating during the day.

In addition, SiO ₂ has a low refractive index of about 1.46, and TiO ₂ has a high refractive index of about 2.3. In the above, the _two thin layers of the low refractive index SiO 2 thin layer and the high refractive index TiO ₂ thin layer form a pair, and are repeatedly stacked N (N is a natural number of 2 or more) times to form the infrared blocking layer 49, which Reflects and blocks infrared light (including near-infrared light) of incident light and transmits visible light.

In addition, in the concept of the present invention, _two thin layers of a low refractive index SiO 2 thin layer and a high refractive index TiO ₂ thin layer can form a pair, and be stacked repeatedly N (N is a natural number of 2 or more) times. Infrared blocking layer 49.

In addition, in the concept of the present invention, the infrared blocking layer 49 can be made of tungsten oxide compound, titanium oxide, zirconium oxide, tantalum oxide, niobium oxide, zinc oxide, indium oxide, indium tin oxide (ITO), tin oxide, antimony tin oxide (ATO ), cesium oxide, zinc sulfide, cerium oxide, and hexaboride. The infrared blocking layer 49 absorbs and blocks infrared light (including near-infrared light).

At the same time, when shooting with a camera equipped with an infrared lamp at night, most of the light is emitted in the form of infrared light, and a small amount of light is emitted in the form of visible light. That is, the infrared lamp installed on the camera does not completely block visible light, and emits a small amount of visible light along with the infrared light.

When the light emitted from the infrared lamp mounted on the camera enters the infrared blocking layer 49, the infrared light is selectively reflected or absorbed, but the visible light is transmitted.

3 is a diagram showing the optical characteristics of the infrared blocking layer 49, in which _two thin layers of a low refractive index SiO 2 thin layer and a high refractive index TiO ₂ thin layer form a pair, and are stacked twice. In this drawing, the solid line represents the transmission characteristic, and the dashed line represents the reflection characteristic.

Referring to the figure, usually infrared lamps emit light with a wavelength in the range of 700 to 900 nm, and the infrared blocking layer 49 transmits 60 to 100% of the visible light with a wavelength in the range of 400 to 700 nm, and reflects or absorbs 60 to 80 % Of 700 to 900 nanometers of infrared light (including near-infrared light) and block infrared light. Therefore, when the light emitted from the infrared lamp mounted on the camera enters the light collection layer 43, the infrared blocking layer 49 reflects or absorbs infrared light (including near-infrared light) to block and prevent infrared light (including near-infrared light) from entering In the light collection layer 43, visible light is simultaneously transmitted.

Table 1 shows the infrared blocking rate. In the above, the reflective layer 37 of the concept of the present invention transmits about 60% of the infrared light (including near-infrared light) of the incident light, and only reflects about 40%. In the above, the infrared blocking layer 49 reflects or absorbs about 80% of infrared light (including near-infrared light) and blocks infrared light (including near-infrared light), and the reflective layer 37 transmits about 60% of infrared light (including near-infrared light) . Therefore, when the reflective layer 37 and the infrared blocking layer 49 are used, about 88% of the infrared light (including near-infrared light) of the incident light can be blocked.

The second base layer 51 is formed on the infrared blocking layer 49 to prevent the infrared blocking layer 49 from being damaged due to external physical impact (such as friction or collision). In addition, the second base layer 51 should not only have weather resistance and stretchability without damaging the infrared resistance. The blocking layer 49 should also be transparent to prevent the loss of visible light incident on the light-collecting layer 43. Therefore, the second base layer 51 is formed of polyurethane resin, acrylic resin, polyester resin, PVC, or (meth)acrylate resin, and is formed by gravure printing, screen printing, and flexographic printing. The method of printing, lithography, slit coating, or doctor blade coating is applied to a thickness of about 20-100 microns.

In the above structure, the protective layer 31 is removed and the pressure-adhesive resin layer 33 is pressurized to adhere to the license plate on which the license plate number is formed, and the retroreflective sheet is applied to the vehicle license plate. In the above, the low-refractive-index SiO ₂ thin layer and the high-refractive TiO ₂ thin layer included in the infrared blocking layer 49 are transparent, which prevents the vehicle license plate to which the retroreflective sheet is applied from deteriorating during the day.

In addition, the infrared blocking layer 49 reflects and absorbs infrared light among the light emitted from the infrared lamp mounted on the camera, so that visible light is incident on the light-collecting layer 43. The incident visible light is condensed by the light collecting layer 43 and the focal resin layer 41, and is focused on the surface of the reflective layer 37. In addition, the reflective layer 37 reflects the visible light focused on its surface, and the visible light reflected by the reflective layer 37 is retro-reflected through the light-collecting layer 45 to the camera. The visible light incident through the light-collecting layer 45 is focused by the focal resin layer 41 on the surface of the reflective layer 37 and is reflected to prevent the loss of visible light that passes through the light-collecting layer 45 to the camera from retroreflecting.

In the above, when shooting with a camera equipped with an infrared lamp at night, most of the light is emitted in the form of infrared light, and a small amount of light is emitted in the form of visible light. Therefore, in the retroreflective sheeting of the concept of the present invention, the infrared blocking layer 49 reflects and absorbs infrared light from the light emitted by the infrared lamp without retroreflecting it, and transmits only a small amount of visible light and is reflected by the reflective layer 37 and the light collection. Layer 43 is retroreflective. Therefore, the vehicle license plate attached by the retroreflective sheet is photographed at night by a camera equipped with an infrared lamp, so that the license plate number can be easily recognized.

In addition, although the infrared blocking layer 49 does not block all infrared light and allows a small amount of infrared light to enter, the reflective layer 37 is formed of a SiO ₂ thin layer and a TiO ₂ thin layer, which are stacked to transmit a small amount of the infrared light. Further improve the effect of removing infrared light.

Therefore, when a camera equipped with an infrared lamp is used to take a picture of a vehicle license plate at night, the concept of the present invention can easily recognize the license plate number while preventing visibility degradation during the day.

The above-mentioned inventive concept is not limited by the above-mentioned specific embodiments and drawings. It is obvious to those skilled in the art that there can be various substitutions, modifications and changes within the scope of the technical spirit of the concept of the present invention.

11: protective layer 13: Pressure adheres to the resin layer 17: reflective layer 19: Focus resin layer 21: Light collecting layer 23: grassroots 31: protective layer 33: Pressure adheres to the resin layer 37: reflective layer 41: Focus resin layer 43: light collecting layer 45: The first grassroots 47: Next layer 49: infrared blocking layer 51: The second grassroots

The above and other purposes and features become clear from the following description with reference to the following drawings, in which the same symbols in the drawings refer to the same parts, unless otherwise indicated, in which:

Figure 1 is a cross-sectional view of the retroreflective sheeting of advanced technology;

Figure 2 is a cross-sectional view of the retroreflective sheeting of the concept of the present invention; and

Fig. 3 is a diagram showing the optical characteristics of the transparent selective reflective layer of the retroreflective sheeting of the concept of the present invention.

31: protective layer

33: Pressure adheres to the resin layer

37: reflective layer

41: Focus resin layer

43: light collecting layer

45: The first grassroots

47: Next layer

49: infrared blocking layer

51: The second grassroots

Claims (7)

A retroreflective sheet comprising: a protective layer; a pressure-bonded resin layer formed on the protective layer and adhered to a vehicle license plate; a reflective layer formed on the pressure-bonded resin layer and reflecting incident visible light The focal resin layer, which is formed on the reflective layer and can focus incident visible light on the surface of the reflective layer; the light-collecting layer, by attaching a plurality of beads on the focal resin layer, And transmits the visible light reflected by the reflective layer, and is formed by retroreflecting the visible light; the first base layer is formed on the light-collecting layer and fixes the light-collecting layer; the second layer is formed on the On the first base layer; an infrared blocking layer formed on the adhesive layer to reflect/absorb and block infrared light, and selectively transmit visible light of incident light from the outside; and a second base layer formed on the infrared light Above the blocking layer to prevent damage to the infrared blocking layer. The retroreflective sheet of claim 1, wherein the focal resin layer is formed of polyurethane, polyester, vinyl resin, acrylic resin or (meth)acrylate resin, and the thickness is beads 20 to 40% of the diameter. Such as the retroreflective sheet of claim 1, wherein the reflective layer is formed by forming a pair of two thin layers of one of a low refractive index material and a high refractive index material, and repeating the pair of two thin layers N (N is 2 or more) Natural number), wherein the low refractive index material and the high refractive index material are selected from SiO ₂ , TiO ₂ , ZnS, ZnO, Al ₂ O ₃ , ZrO ₂ , Ta ₂ O ₅ , Nb ₂ O ₅ , CaF ₂ or Na ₃ AlF ₆ . The retroreflective sheet of claim 1, wherein the reflective layer is formed by depositing a metal of Al, Ag, Cu, Zn, or Sn. The retroreflective sheet of claim 1, wherein the infrared blocking layer is formed by forming a pair of two thin layers of one of a low refractive index material and a high refractive index material, and repeating the pair of two thin layers N (N is 2 or more Natural number of ), wherein the low refractive index material and the high refractive index material are selected from SiO ₂ , TiO ₂ , ZnS, ZnO, Al ₂ O ₃ , ZrO ₂ , Ta ₂ O ₅ , Nb ₂ O ₅ , CaF ₂ or Na ₃ AlF ₆ . The retroreflective sheet of claim 1, wherein the infrared blocking layer is made of tungsten oxide compound, titanium oxide, zirconium oxide, tantalum oxide, niobium oxide, zinc oxide, indium oxide, indium tin oxide (ITO), tin oxide, antimony oxide It is formed by one of tin (ATO), cesium oxide, zinc sulfide, cerium oxide and hexaboride. The retroreflective sheet of claim 1, wherein the second base layer has weather resistance and stretchability, and is coated with transparent polyurethane resin, acrylic resin, polyester resin, PVC or methacrylic acid (A) Ester resin is formed to prevent light loss.

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