KR20210086572A - Retro-reflection sheet with improved visibility and durability and auto number plate including the same sheet - Google Patents

Abstract

The present invention relates to a retro-reflection sheet with improved visibility and durability and an auto number plate including the same, and specifically, to a retro-reflection sheet that can adjust the whiteness and retro-reflection performance, thereby having excellent daytime visibility and nighttime visibility and improved durability, and an auto number plate including the same. The retro-reflection sheet comprises a base optical layer, a lower layer, and an upper layer.

Description

Retroreflective sheet with improved visibility and durability and license plate for vehicle including same {RETRO-REFLECTION SHEET WITH IMPROVED VISIBILITY AND DURABILITY AND AUTO NUMBER PLATE INCLUDING THE SAME SHEET}

The present invention relates to a retroreflective sheet with improved visibility and durability, and a license plate for a vehicle including the same, and specifically, whiteness and retroreflective performance can be adjusted, and thus both daytime visibility and nighttime visibility are excellent, and durability is improved. It relates to a reflective sheet and a license plate for a vehicle including the same.

The retroreflection function in the retroreflection sheet has a feature that allows light coming from the outside to return in the direction in which the light entered by a structured surface such as a corner cube. In such a retroreflection implementation method, there is a method of using total reflection with an air layer by forming a sealing layer on a structured surface, or a method of using a specular reflection by forming a metal layer on the structured surface.

Retroreflective sheets used for attaching road signs, safety signs, license plates, dials, etc. that require a clear or bright background are not suitable because of the dark color of the metal layer when a deposited metal layer is formed on the structured surface. When the sealing layer is formed, it is mainly used because it is bright and clear.

However, the conventional retroreflective sheet has a problem in that the line width and pitch size of the sealing pattern of the sealing layer are large, so that the sealing pattern is visually recognized when observed from a close distance, and there is a problem in terms of aesthetics. There was a problem that was not suitable for use such as advertisement boards) or various vehicle license plates.

In addition, in the case of retroreflective sheets attached to various dial plates such as vehicle license plates, sufficient whiteness is required for the background color around the letters in order to improve the visual visibility of the letters during the daytime, but due to insufficient whiteness, the dial containing numbers during the daytime There was a problem of low visibility with the naked eye.

In addition, in the case of a license plate photographing device such as a parking lot camera or a speed camera, when irradiating light such as infrared light on a license plate with a retro-reflective sheet for shooting, the retroreflected light from the license plate is too intense, so the photographed picture is too bright. There was a problem that it was difficult to identify the license plate by being photographed.

In this case, the license plate requires a technology to effectively control the high retroreflection performance implemented by the corner cube, the air layer, and the sealing layer to implement the appropriate retroreflection performance, but there is considerable difficulty.

Meanwhile, among the above problems, efforts have been made to improve the visual recognition problem of the sealing pattern. However, in the case of Figure 1b, due to problems such as deformation or discoloration of the resin, dye, pigment, etc. constituting the barrier layer 22 during high-temperature and high-pressure sealing, it is not suitable for forming the sealing layer 21 at high temperature and high pressure. Rather, there is a problem that the corner cube layer 11 and the sealing layer 21 are easily separated after the sealing layer is formed. Even when sealing is performed using pressure-sensitive adhesive instead of high-temperature and high-pressure sealing, the sheet is separated due to the limitation of adhesive strength outdoors for a long period of time, resulting in a durability problem.

Therefore, due to the limitations of the physical properties of the material (resin, polymer material, dye, pigment, etc.) forming the barrier layer and the problem of not having sufficient adhesion of the adhesive to the corner cube pattern, the durability is poor and the sheet is easily opened or torn There was a problem with losing. In addition, there was a complicated problem in the manufacturing process according to the formation of the barrier layer.

Currently, there is a need to develop a technology that can overcome these problems.

KR 10-2017-0018114 A

The present invention has been devised to solve the above problems, and the problem to be solved is that the sealing pattern is not observed with the naked eye and the whiteness is increased to improve the visibility, and by adjusting the retroreflection performance of the license plate photographing device. An object of the present invention is to provide a retroreflective sheet capable of improving camera visibility and enhancing durability when used in an outdoor environment, and a license plate for a vehicle including the same.

In order to solve the above problems, the present invention provides a base optical layer provided with a pattern of a plurality of retroreflective optical elements on a lower surface;

a lower layer coupled to the lower surface of the base optical layer and including a low refractive region made of a low refractive material having a lower refractive index than that of the base optical layer, and a sealing material for sealing side surfaces and lower surfaces of the low refractive region; and

An upper layer coupled to the upper surface of the base optical layer and including a printed pattern that partially blocks light transmission; including,

The low refractive region is in contact with the lower surface of the base optical layer and is partitioned in a predetermined pattern, and the sealing material seals the side and lower surfaces of the low refractive region and is attached to the lower surface of the base optical layer from the side of the low refractive region become,

It provides a retroreflective sheet, characterized in that at least a portion of the print pattern is formed in an area corresponding to at least a portion of the low refractive index area.

In a preferred embodiment of the present invention, the low refractive material may be air.

In a preferred embodiment of the present invention, the retroreflective optical element may be a corner-cube structure.

In a preferred embodiment of the present invention, the low refractive region may occupy an area of 5% to 30% of the lower layer.

In a preferred embodiment of the present invention, an area that is not blocked by the print pattern among the areas corresponding to the low refractive index region may be 0.5% to 15% of the total area of the retroreflective sheet.

In a preferred embodiment of the present invention, the area in which the sealing material is attached to the lower surface of the base optical layer may be 70% to 95% of the total area of the retroreflective sheet.

In a preferred embodiment of the present invention, in the sealing material, a sealing line is linearly attached to the lower surface of the base optical layer along the side surface of the low refractive region, and the sealing material is attached to the lower surface of the base optical layer. The line width may have a width of 100 μm to 2000 μm.

In a preferred embodiment of the present invention, the retroreflective sheet, characterized in that the low refractive region is divided and sealed in a repeating pattern of a triangular, square or hexagonal shape.

In a preferred embodiment of the present invention, the print pattern may be a linear or regular or irregular wavy pattern printed at intervals of 100 μm to 2,000 μm in one direction.

In a preferred embodiment of the present invention, the print pattern of the upper layer and the pattern of the low refractive region of the lower layer may satisfy the following relational expression (1).

[Relational Expression 1]

은 상기 하부층의 저굴절 영역 패턴의 임의의 일방향으로의 평균 반복 주기를 나타내고,

는

과 같은 방향으로의 상기 상부층 인쇄 패턴의 평균 반복 주기를 나타낸다.In the above relation 1,

represents the average repetition period in any one direction of the low-refractive region pattern of the lower layer,

is

and represents the average repetition period of the upper layer printed pattern in the same direction.

In a preferred embodiment of the present invention, the upper layer may include two or more printed patterns arranged in different directions.

In a preferred embodiment of the present invention, the printed pattern may be printed using a paint containing one or more additives selected from _{titanium dioxide (TiO 2} ) and silicon dioxide (SiO _{2 ).}

In a preferred embodiment of the present invention, the upper layer is located above the printed pattern, the protective layer to protect the printed pattern from the outside; and

and an adhesive layer formed on the lower surface of the protective layer and bonding the protective layer and the upper surface of the base optical layer.

In a preferred embodiment of the present invention, the area in which the sealing material is attached to the lower surface of the base optical layer may be formed to be larger than the area in which the low refractive region is in contact with the lower surface of the base optical layer.

In addition, the present invention provides a license plate for a vehicle including the retroreflective sheet described above in order to solve the above problems.

The retroreflective sheet according to the present invention improves the color of the sheet and improves the whiteness to increase the visual visibility during the day and at night for the license plate letter to which the retroreflective sheet of the present invention is attached.

In addition, the present invention makes it possible to secure an appearance suitable for graphics, advertising boards (indoor/outdoor), and vehicle license plate applications by making the sealing pattern structure of the retroreflective sheet, which has been previously visually recognized, not visually recognized.

In addition, by varying the optical profile according to the method of composing the finely divided print pattern, the retroreflection performance suitable for the required use (ultra-high brightness, high brightness, etc., automobile, road, advertisement, printing, etc., depending on the performance) can be adjusted and implemented. can

By adjusting the retroreflection performance, the visibility of shooting for the license plate letters by the night camera is increased.

In addition, as the white sealing material seals the fine low-refractive region and adheres to the optical element wider than the low-refractive region, the overall adhesive strength is strengthened due to the increase of the bonding area, thereby improving the sheet durability and improving the whiteness of the sheet.

In addition, it is possible to secure a beautiful surface appearance by solving the previous problem that the low refractive area pattern of the lower layer is visually recognized at a short distance by the combination between the low refractive area and the wide sealing pattern of the lower layer and the printed pattern of the upper layer, and in particular, retroreflective performance can be lowered according to the required level to prevent light blur and improve the visibility of characters such as cameras at night.

1A is a view schematically showing a layered structure of a retroreflective sheet according to a preferred embodiment of the present invention.
Figure 1b is a view schematically showing the layered structure of the retroreflective sheet according to the prior art.
Figure 2a is a photograph taken of a vehicle license plate to which a retroreflective sheet according to the prior art is applied.
Figures 2b and 2c is a photograph of a license plate for a vehicle to which a retroreflective seat according to an embodiment of the present invention is applied.
3A to 3B are plan photos taken by enlarging the lower layer coupled to the base optical layer of the retroreflective sheet according to an embodiment of the present invention.
3c to 3e are plan photos taken by magnifying the print pattern of the upper layer of the retroreflective sheet according to an embodiment of the present invention.
4 is a view for explaining a reference indicating the arrangement angle of the print pattern in the retroreflective sheet according to an embodiment of the present invention.
5A is a diagram schematically illustrating a printed pattern linearly disposed on an upper layer of a retroreflective sheet according to an embodiment of the present invention.
5B is a view schematically showing a printed pattern having a grid pattern disposed in two different directions on the retroreflective sheet upper layer according to an embodiment of the present invention.
5C is a diagram schematically illustrating a print pattern disposed in a wavy shape on an upper layer of a retroreflective sheet according to an embodiment of the present invention.
5D is a diagram schematically illustrating a printed pattern arranged in a dotted line on the upper layer of the retroreflective sheet according to an embodiment of the present invention.
5E is a diagram schematically illustrating a printed pattern in which dotted and linear patterns are disposed in two different directions on an upper layer of a retroreflective sheet according to an embodiment of the present invention.
6A and 6B are plan photos taken by magnifying the retroreflective sheet according to an embodiment of the present invention at the print pattern position of the upper layer.
7A is a view schematically illustrating a situation in which the daytime visibility of a license plate to which a retroreflective sheet is applied is a problem.
7B is a view schematically showing a situation in which the night visibility of the license plate to which the retroreflective sheet is applied is a problem.
7C is a diagram schematically illustrating a reflection principle of a retroreflective sheet according to an embodiment of the present invention.
8 is a perspective view schematically showing the structure of a retroreflective sheet according to the present invention.
9 is a diagram illustrating a CIE L*a*b* color space.
10A is a photograph taken of the result of performing an immersion test on the retroreflective sheet according to the present invention.
10B is a photograph taken of the result of performing an immersion test on the retroreflective sheet according to the prior art.

Prior to the detailed description of the present invention, first, it is intended to define the meaning of the terms used herein.

In the present specification, "upper surface" means a surface in a direction from the base optical layer toward the upper layer, and "lower surface" means a surface in a direction from the base optical layer toward the lower layer.

In the present specification, the term "average repetition period" means that when a predetermined shape is formed in a repeated pattern, the length of the shape repeated 10 times in an arbitrary direction is measured and averaged in that direction of one repeating unit. indicates the length.

Hereinafter, the present invention will be described in more detail.

As described above, the conventional retroreflective sheet has a problem in day and night visibility and a problem in photographing visibility of a license plate photographing device, and when applied outdoors, there is a problem such as peeling occurs due to poor durability.

Hereinafter, in the present invention, a base optical layer provided with a pattern of a plurality of retroreflective optical elements on a lower surface; a lower layer coupled to the lower surface of the base optical layer and including a low refractive region made of a low refractive material having a lower refractive index than that of the base optical layer, and a sealing material for sealing side surfaces and lower surfaces of the low refractive region; and an upper layer coupled to the upper surface of the base optical layer and including a printed pattern that partially blocks light transmission, wherein the low refractive area is in contact with the lower surface of the base optical layer and is partitioned into a predetermined pattern. and wherein the sealing material is attached to the lower surface of the base optical layer from the side of the low refractive region, and at least a part of the printed pattern is retroreflection, characterized in that it is formed in a region corresponding to at least a part of the low refractive region A sheet was provided to solve this problem.

The retroreflective sheet of the present invention effectively controls the retroreflectance of the retroreflective sheet by stacking a lower layer having a sealed low refractive region and an upper layer including a printed pattern that partially blocks retroreflection on the lower and upper parts of the retroreflective sheet, and There is an advantage of improving daytime visibility and nighttime visibility.

Hereinafter, each configuration will be described in detail in order. Prior to the description of each configuration, each configuration of the present invention will be schematically described with reference to the accompanying drawings.

1A is a view schematically showing a layered structure of a retroreflective sheet according to a preferred embodiment of the present invention.

Referring to Figure 1a, the retroreflective sheet according to the present invention consists of a base optical layer 100, an upper layer 200 and a lower layer 300, the upper layer 200 and the lower layer 300 is the base optical layer ( 100) is coupled to the upper and lower surfaces.

A plurality of retroreflective optical elements 110 are formed on a lower surface of the base optical layer 100 . 1A shows a corner cube pattern.

Light is incident from the outside of the upper layer 200, passes through the upper layer 200 and the base optical layer 100, causes total reflection in the retroreflective optical element 110, and is returned, and in the process, in the 180° direction of the incident light will go back

A lower layer 300 is provided on the lower surface of the base optical layer 100 , and the lower layer 300 includes a low refractive region 311 and a sealing material 320 which are partitioned having a predetermined shape. The sealing material 320 is located on the side and lower surfaces of the low refractive region 311 to seal each section of the low refractive region and divides them so as not to be connected to each other, and the base optical layer ( 100) is attached to the lower surface 110 . Similarly, the low refractive region 311 is in contact with the lower surface 110 of the base optical layer 100 .

The low refractive region 311 is made of a material having a lower refractive index than the material of the base optical layer 100, so that the incident light from the base optical layer 100 toward the lower layer 300 is totally reflected at the interface between the two layers. make it easy On the other hand, the sealing material 320 preferably has a higher refractive index than that of the low refractive material. Therefore, in the portion in which the sealing material 320 is in contact with the lower surface 110 of the base optical layer 100 , the total reflection does not occur sufficiently compared to the portion in which the base optical layer 100 is in contact with the low refractive region 311 . The sealing material may have the same or similar refractive index as that of the base optical layer so that the retroreflectivity is mostly lost in the portion in contact with the sealing material of the base optical layer. To this end, the sealing material may mainly include a material of the base optical layer.

In this specification, the area in which the low refractive region 311 contacts the lower surface 110 of the base optical layer 100 is referred to as an 'effective area', and since retroreflectivity occurs in this effective area, it becomes an active region.

The upper layer 200 includes a printed pattern 210 that partially blocks transmission of incident or reflected light. Therefore, when both incident light and reflected light are considered, retroreflection is applied to an area excluding the area covered by the printed pattern 210. can only happen against

The upper layer 200 may be adhered to the base optical layer 110 by an adhesive layer 220 .

In addition, Figure 8 is a schematic perspective view of the layered structure of the retroreflective sheet according to an embodiment of the present invention. In FIG. 8 , the base optical layer 100 and the lower layer 300 are spaced apart so that the structure can be easily recognized. In reality, the two are in contact.

Referring to FIG. 8 , a low refractive region 311 in which the lower layer 300 is separated from other adjacent low refractive regions 311 by the sealing material 320 and partitioned in a predetermined repeated pattern can be confirmed. An effective area in contact with the low refractive region 311 and the base optical layer 100 is partially covered by the printed pattern 210 of the upper layer 200 . Due to this, the retroreflected light in the effective area is partially blocked in the portion covered by the printed pattern 210 of the upper layer 200 , and the remaining retroreflected light is emitted to the outside through the portion not covered.

1. Base optical layer

The base optical layer 100 forms a skeleton of the retroreflective sheet, and has a retroreflective optical element 110 on one surface to cause a retroreflection phenomenon. In addition, it is preferable to use a material with high transparency. In addition, in order to protect the pattern of the retroreflective optical element 110 formed on one surface, impact resistance, heat resistance, and flexibility are required, and a sheet having excellent workability is used.

As described above, the base optical layer may have an integrated structure in which one surface is molded with a retroreflective optical element through a single sheet, but unlike this, the base optical layer has a transparent base optical layer and a retroreflective optical element 110 provided on its lower surface. may be respectively formed of different materials.

Various thermosetting and thermoplastic materials are suitable for the material of the base optical layer. Preferably, the base optical layer is polycarbonate (PC), polyethylene terephthalate (PET), polymethyl methacrylate, polyurethane (polyurethane) and polyvinylchloride (PVC) It may be a film manufactured using one or more materials selected from among. Preferably, the material of the base optical layer may be at least one selected from polycarbonate, polymethyl methacrylate, and polyvinyl chloride. However, the material is not limited thereto, and a person skilled in the art may select a film having impact resistance, heat resistance and flexibility among those used as a transparent film in the art, and excellent processability.

In addition, if necessary, a copolymer of two or more of the above resins may be used or two or more layers may be included.

The light transmittance of the base optical layer may be preferably 85% to 95%, preferably 90% to 95%.

In addition, the base optical layer may preferably have a thickness of 80㎛ to 300㎛. If the thickness of the base optical layer is less than 80㎛, there is a risk that the durability between each layer of the retroreflective sheet is lowered, on the contrary, when the thickness of the base optical layer exceeds 300㎛, the thickness of the base optical layer is too thick As the light transmittance is lowered, there is a problem in that the appearance such as visibility and aesthetics is lowered.

In addition, a UV blocking agent may be added to the base optical layer to prevent discoloration of the film by ultraviolet (ultraviolet ray, UV), and UV according to the method of forming the retroreflective optical element (UV imprinting, hot stamping, etc.) The content of the blocking agent can be adjusted.

The UV blocking agent may be used in an appropriate amount by selecting an appropriate one to meet the purpose of the present invention among those generally used in the art.

The base optical layer 100 according to the present invention may have a retroreflective optical element 110 on one surface thereof. The retroreflective optical element 110 may be a microsphere or a corner cube structure, preferably a corner cube structure. The retroreflective optical element 110 totally reflects the incident light so that the direction of the reflected light can be returned to 180° of the direction of the incident light.

The retroreflective optical element 110 is formed on the lower surface of the base optical layer, and by causing total reflection at the interface with the low refractive region 311 coupled to the lower surface of the base optical layer, excellent retroreflective efficiency can be achieved. have.

The corner cube structure may have a triangular pyramid-shaped pattern in which three surfaces are at right angles to each other. In this case, as the difference in refractive index between the corner cube forming the triangular pyramid and the low refractive region 311 adjacent thereto increases, total reflection may occur more easily.

The corner cube structures are arranged in a plane direction to form a corner cube pattern.

The pattern of the retroreflective optical element 110 formed on the lower surface of the base optical layer may have a thickness of 30 μm to 120 μm, preferably 40 μm to 80 μm.

In addition, the retroreflective optical element 110 may be made of the same material as the base optical layer, or the material may be different according to a pattern forming method of the retroreflective optical element.

When the optical element is formed of another material, it may be formed by coating the lower surface of the base optical layer with another material.

The corner cube pattern in which the retroreflective optical element 110 is arranged may be preferably manufactured by UV imprinting or hot stamping. Such a manufacturing method is generally known in the field of retroreflective sheets, and those skilled in the art can perform it through a known method.

In particular, when the retroreflective optical element 110 is formed by UV imprinting, it is important to control the UV transmittance in the UV-A, UV-B, and UV-C regions so that a sufficient amount of light can be irradiated for UV curing to proceed. .

The choice of material for the corner cube pattern varies according to a method of forming the pattern.

When the corner cube pattern is formed by UV imprinting, it is preferable to use a urethane or urethane acrylic resin having a refractive index of 1.48 or more in order to realize retroreflective performance, and an isocyanate-based curing agent may be used. In addition, it is preferable to select a photoinitiator that acts on a wavelength corresponding to the ultraviolet transmission wavelength of the base optical layer.

When the corner cube pattern layer is formed by hot stamping, it is preferable that the melt flow index (MI) is 5 g/10 min to 30 g/10 min. In addition, a pattern may be formed using a polycarbonate resin having a high refractive index of about 1.58.

Preferably, the polycarbonate film can improve weather resistance by adding a UV stabilizer or absorber to block the UV region as much as possible.

2. lower layer

A lower layer 300 is coupled to a lower surface of the base optical layer 100 , that is, a lower surface of the retroreflective optical element 110 , and the lower layer 300 includes a low refractive region 311 and a sealing material 320 .

The low-refractive region 311 is made of a low-refractive material having a lower refractive index than the pattern of the retro-reflective optical element 110, so that light incident from the upper surface of the retro-reflective sheet is formed between the retro-reflective optical element 110 and the low-refractive region ( 311) serves to facilitate total reflection at the interface. Therefore, there is an advantage that the reflected light of retroreflection has less optical loss compared to the incident light.

The sealing material 320 serves to seal the low-refractive region 311 so that the low-refractive region 311 is partitioned in a predetermined pattern to maintain a divided shape, and has the greatest effect on the durability of the retroreflective sheet according to the present invention. go crazy

The lower surface of the sealing material 320 may further include a lower adhesive layer and a release film, which is a necessary configuration when the retroreflective sheet is attached to an article in the form of a sticker.

The low refractive region 311 is divided by a sealing material 312 that divides the low refractive region 311 into a repeated pattern having a predetermined shape. Accordingly, total reflection occurs at the interface between the low refractive region 311 and the retroreflective optical element 110 so that retroreflected light is strong, and there is no or small difference in refractive index at the interface between the retroreflective optical element 110 and the sealing material 312 . It has a characteristic that there is no retroreflected light or very weak by preventing total reflection from occurring well.

The low refractive region 311 may be an air layer. The refractive index of air is 1.0003, which is almost the same as vacuum, so it is the most suitable low-refractive material for inducing total reflection.

The low refractive region 311 is sealed in a predetermined shape by the sealing material 320, and the shape is maintained. The low refractive region 311 may form a repeating pattern of a triangle, a rectangle, a rhombus, or a hexagon. In this case, the sealing material may have a linear shape forming an edge or a side in the shape formed by the low refractive area, respectively. That is, a sealing material disposed between the low refractive regions and attached to the lower surface of the base optical layer is referred to as a sealing line 312 . And a portion of the sealing material 320 sealing the lower surface of the low refractive index region is referred to as a sealing cover (313).

Preferably, the sealing line 312 forming the side of the low refractive region 311 may have a linear shape with a line width of 100 μm to 2000 μm, more preferably 200 μm to 1000 μm.

The low refractive region 311 may have a width of 100 μm to 1,500 μm. For example, when the low-refractive region 311 has a square or triangular shape, one side may have a length of 100 μm to 1,500 μm, and in the case of a rhombus, hexagon or octagonal shape, the inner maximum diagonal length is 100 μm to 1,500 μm can be The low refractive region 311 may have a more preferable width of 200 μm to 1,000 μm.

If the sealing line 312 on the side of the low refractive region 311 has a line width of less than 100 μm, the sealing of the low refractive region 311 is not properly performed, and there is a problem in that durability may be weakened due to weakening of adhesive force. In addition, on the contrary, when the line width of the sealing line 312 exceeds 2000 μm, there is a problem in that the retroreflection performance is too deteriorated.

Next, the sealing material 320 will be described.

The sealing material 320 layer is preferably formed by a hot melt adhesive method, and the material is preferably ethylene vinyl acetate, polyamide, polyurethane, or polyester. may include.

The sealing material 320 layer may be formed as a single layer of the resin or may be manufactured by coating on a substrate such as PET. It is preferable to use a polyester series because heat resistance suitable for a high-temperature hot melt process is required, and properties capable of bonding with the pattern of the UV-curable imprinting retroreflective optical element 110 formed on the lower surface of the base optical layer are required. .

In addition, additives such as titanium dioxide (TiO2) and silicon dioxide (SiO2) may be used for the sealing material 320 to improve whiteness.

The additive used at this time is preferably added as nano-sized particles, and in this case, a milling process may be added for smooth dispersion.

The sealing material 320 may have a thickness of preferably 30 μm to 35 μm. If the thickness of the sealing material 320 is less than 30 μm, the durability of the sealing material 320 is weak, so that the retroreflective sheet is easily damaged due to immersion and inflow of foreign substances, and there is a fear that moisture may penetrate. In addition, when the thickness of the sealing material 320 exceeds 35 μm, the thickness of the retroreflective sheet is too thick, so that the sealing material easily penetrates into the low refractive index region during high temperature and high pressure sealing. In addition, when the thickness of the retroreflective sheet becomes too thick, the difference between the inner radius of curvature and the outer radius of curvature increases when bent, so there is a problem in that durability is weakened, such as delamination between layers.

The lower layer 300 is formed by bonding the sealing line 312 to the retroreflective optical element 110 pattern on the lower surface of the base optical layer as a barrier rib between the low refractive region patterns at high temperature and high pressure to form the retroreflective optical element 110 . ) and the low-refractive region 311 to prevent foreign substances (water, dust, etc.) from entering, thereby maintaining retroreflective performance, and increasing the adhesive area between the retroreflective optical element 110 and the sealing wire 312 . can improve durability. In particular, the retroreflective sheet used outdoors must be able to prevent snow or rainwater from flowing into the interface between the retroreflective optical element 110 and the low refractive area 311, and for this purpose, the immersion test and strength against adhesion High standards are required, and the present invention satisfactorily meets these standards.

In the case of the conventional retroreflective sheet, in a situation in which the area of the low refractive region is large when viewed from a short distance, the pattern is visually recognized due to the difference in retroreflective performance in the corresponding region due to the difference in refractive index between the sealing material and the low refractive region. In the present invention, the low refractive region area is increased by making the sealing line 312 on the side of the low refractive region 311 to have a line width of 100 μm to 2000 μm and the width of the low refractive region 311 to be 100 μm to 1500 μm. The effect that the pattern as described above is not visually recognized by the naked eye is further increased.

Since the sealing line 312 suppresses light reflection, it is also referred to as a reflection control pattern, and the sealing material is also referred to as a reflection suppression layer.

Figure 2a is a car license plate to which a retroreflective seat according to the prior art is applied, and Figures 2b and 2c are car license plates to which a retroreflective seat is applied according to an embodiment of the present invention.

As shown in FIGS. 3A and 3B , an optically inactive region is induced in the sealing line 312 , and an optically active region (retroreflective region) is induced in the low refractive region 311 .

Preferably, the area of the region where the sealing line 312 is attached to the lower surface of the base optical layer 100 may occupy 70% to 95% of the total area of the retroreflective sheet. That is, in the retroreflective sheet according to the present invention, the active area, which is the effective area of the low refractive region, may be 5% to 30%.

In this way, by widely attaching the sealing wire 312 to the lower surface of the base optical layer 100, it is possible to reduce the total amount of retroreflected light by inducing a significant part of the loss of retroreflected light. will improve

In addition, by performing sealing and bonding of the sealing material widely, the retroreflective sheet of the present invention can make the sealing of the low refractive region 311 strong, and has strong resistance to penetration of moisture or foreign substances in a harsh outdoor environment and retroreflection. The durability of the sheet can be improved.

Although it has been mentioned that the area of the region where the sealing line 312 is attached to the lower surface of the base optical layer 100 may occupy 70% to 95% of the total retroreflective sheet area, if the upper layer printed pattern 210 is When the area to be covered is sufficiently wide, the area where the sealing line 312 is attached to the base optical layer 100 may occupy at least 50% of the area of the retroreflective sheet.

Figure 2a is a car license plate to which a retroreflective seat according to the prior art is applied, and Figures 2b and 2c are car license plates to which a retroreflective seat is applied according to an embodiment of the present invention.

Referring to FIG. 2A , the region in which retroreflection occurs throughout the sheet (the part shown in a dark color of the background) and the region in which retroreflection does not occur well (the white line dividing the part shown in the dark color) are easily recognized with the naked eye. Able to know.

2b and 2c, it can be seen that the pattern as described above is not easily seen with the naked eye by applying the retroreflective sheet according to the present invention.

The pattern of the low-refractive region 311 may be manufactured and formed in a roll-to-roll method using a sealing roll capable of implementing a fine pattern, and the temperature is adjusted to prevent problems such as water immersion and foreign matter inflow and improve durability. It can be prepared at a high temperature of 170 °C to 195 °C, preferably 180 °C to 185 °C. At this time, if the temperature is less than 170 degrees, the durability of the sealing may be reduced, and problems such as adhesion and water immersion may occur. If the temperature is higher than 195 degrees, the sheet may expand due to heat and a wave phenomenon may occur. The wall 312 may become too thick, resulting in reduced reflective performance.

In addition, when the retroreflective sheet is applied to a specific article as the sealing material, micro-sized titanium oxide (TiO ₂ ) particles may be used to improve whiteness of the sheet.

In addition, preferably, the present invention may further include an external adhesive layer and a release film on the lower surface of the lower layer (300). It can be applied and applied to various articles in the form of a sticker, including an external adhesive layer and a release film.

A urethane-based pressure-sensitive adhesive may be used for the external adhesive layer, and preferably, a curing agent and a polymerization initiator for thermal curing may be used.

The thickness of the outer adhesive layer is preferably 40 μm to 80 μm. If the thickness of the outer adhesive layer is less than 40㎛, the adhesive force may not be sufficient. Conversely, when the thickness of the outer adhesive layer is greater than 80 μm, when the retroreflective sheet is bent, the difference between the radius of curvature of the inner and the outer side becomes large and there may be a problem in durability such as peeling.

When the external adhesive layer is used for outdoor structures such as retroreflective sheets for roads, a holding force of a certain level or more is required to prevent product drop-off and separation.

In addition, in a specific product such as a car license plate, titanium dioxide (TiO ₂ ) may be added to the adhesive composition of the external adhesive layer in the range of 5 wt% to 15 wt% as needed to improve whiteness.

The release film serves to protect the outer adhesive layer from the bottom of the product and is releasably attached to the external adhesive layer.

As the release film, silicone release-treated PET, paper release paper, OPP film, CPP film, etc. may be used depending on the type of product to which the retroreflective sheet is to be applied.

3. upper floor

The retroreflective sheet according to the present invention further includes an upper layer 200 on the upper surface of the base optical layer 100 . The upper layer 200 is formed on an area corresponding to at least a portion of the effective area of the lower layer 300 and includes a printed pattern 210 that blocks transmission of incident or reflected light.

The print pattern is also called a fine division pattern because a plurality of fine lines that block light are divided and arranged, and since the light transmission is controlled by this principle, it is also called a light transmission control pattern.

The print pattern 210 may satisfy Relation 1 below in relation to the pattern of the low refractive region 311 of the lower layer 300 .

[Relational Expression 1]

은 상기 하부층의 저굴절 영역 패턴의 임의의 일방향으로의 평균 반복 주기를 나타내고,

는

과 같은 방향으로의 상기 상부층 인쇄 패턴의 평균 반복 주기를 나타낸다.In the above relation 1,

represents the average repetition period in any one direction of the low-refractive region pattern of the lower layer,

is

and represents the average repetition period of the upper layer printed pattern in the same direction.

In other words, when a straight line is drawn in any one direction on the retroreflective sheet, the repetition period of the pattern of the low refractive region 311 of the lower layer 300 in the same direction as the average of the period in which the print pattern 210 is repeated 10 times The average of may satisfy the above conditions.

That is, when the difference in the period of the two patterns is within the range as described above, the wavelength of the moire pattern generated by the period mismatch of the two patterns is generated with a wavelength that is difficult to recognize with the naked eye, so that the appearance of the retroreflective sheet is not impaired. It is not easy to have a difference smaller than the above level due to the occurrence of technical errors.

5A is a diagram schematically illustrating a print pattern linearly printed on a retroreflective sheet according to an embodiment of the present invention.

Referring to FIG. 5A , a linear print pattern having a width of D is spaced apart with an interval of d therebetween, and the print pattern has a period of L. The average of 10 consecutive patterns of L _{represents L 2} in Relation 1 above. Since L ₂ is not necessarily L, but is for an arbitrary direction, it may be a period for a line drawn in a diagonal direction.

The print pattern 210 is a finely divided pattern and has an opaque characteristic, so it has a pattern for controlling light transmission, blocks some incident light and reflected light, and serves to adjust the retroreflective ability of the retroreflective sheet. To be precise, it reduces the retroreflection ability and prevents characters or pictures printed on the retroreflection sheet from being blocked by the strong retroreflection light, thereby increasing visibility at night, such as when shooting with intermittent cameras.

When the retroreflective sheet is used for a vehicle license plate, etc., a high whiteness of the background color of the license plate is required. In ^{order to improve the whiteness (L *} a ^* b ^* ) of the retroreflective sheet, a white pigment and It is better to include the same material. The material of the print pattern 210 is preferably a material that does not deteriorate due to high temperature or light. The print pattern 210 may be expressed as a simple image, a symbol, or a character through a finely divided pattern design.

By including the print pattern (fine division pattern) as described above, the previous problem that the pattern of the low refractive region 311 of the lower layer is visually recognized at a short distance is solved, which after performing fine sealing to make the pattern of the lower layer more fine than before When overlapped with the printed pattern 210 of the upper layer 200, it is further finely divided by the overlapping pattern and is not visually recognized, thereby having a beautiful surface appearance (see FIGS. 3c, 3e, 6a, and 6b). ).

More specifically, the retroreflective sheet that does not include the printing pattern as described above has an appearance as shown in FIG. 3B . It can be seen that retroreflection from the low refractive region 312 forms an optically active region, and a portion where retroreflection is suppressed by the sealing line 312 forms an optically inactive region. However, such a sealing line visually recognized by the naked eye greatly impairs the appearance of the retroreflective sheet.

The printed pattern having a constant pattern as shown in FIG. 5A can further reduce the area of the optically active region by more finely dividing the sealing pattern of a large size visually recognized as such, and thus FIGS. 3C, 6A and 3C , 6A and FIG. As shown in 6b, it is possible to greatly improve the appearance of the retroreflective sheet as it greatly reduces the area of the retroreflection portion due to the low refractive index region, thereby making it difficult to visually recognize the pattern.

A paint may be used to form a printing pattern, and the paint may include a thermosetting paint or a UV curable paint.

The upper layer 200 may further include an overlay layer of a transparent material for protection of the retroreflective sheet on the upper surface of the printed pattern 210, and the printed pattern 210 is on the lower surface of the overlay layer. can be formed. Without being limited to this position, the printed pattern 210 may be formed on the upper surface of the base optical layer 100 on which light is incident.

Transmission of retroreflected light is suppressed due to the print pattern 210, and the area of the print pattern 210 where retroreflection does not occur can be adjusted by adjusting the size, spacing and direction of the print pattern 210. and, thereby, the retroreflective performance of the retroreflective sheet can be adjusted.

In order to prevent discoloration due to ultraviolet rays, a paint having light resistance is used for the print pattern 210 .

In order to control the height of the printing pattern, the solid content is adjusted using a solvent such as isopropyl alcohol (IPA), methyl ethyl ketone (MEK), and toluene.

The print pattern (finely divided pattern) may be formed within a range that preferably covers 50% to 90% of the area of the retroreflective sheet. If less than 50% of the area of the retroreflective sheet is covered, the retroreflected light is too strong, so there may be a problem that characters printed on the retroreflective sheet are not properly recognized at night. Conversely, if the area exceeds 90% The retroreflected light may be too weak to perform the role of the retroreflective sheet properly.

In addition, at least a portion of the print pattern 210 may be formed on an effective area. That is, at least a portion of the print pattern 210 is formed on an area corresponding to the low refractive area 311 , thereby further lowering the retroreflective performance, thereby preventing light blur in night camera visibility. Visibility and the like can be improved.

As one of the print patterns 210 , as shown in FIGS. 5A to 5B , the print pattern 210 may be formed in various types of patterns such as straight lines, curves, lattice structures, wave designs, and random designs. The width (D) of the printed pattern lines is 0.1 mm to 2.0 mm, preferably 0.1 mm to 1.0 mm, more preferably 0.2 mm to 0.4 mm, and the spacing (d) between the printed pattern lines 210 is 0.1 mm to 2.0 mm, preferably 0.1 mm to 1.0 mm, more preferably 0.1 mm to 0.4 mm.

As another example of the print pattern 210 , as shown in FIG. 5E , the print pattern 210 may have a form in which two types of print patterns 210 arranged in two or more different directions are overlapped.

In addition, the thickness of the print pattern 210 may be in a range of 1 μm to 25 μm, preferably 3 μm to 20 μm, and more preferably 5 μm to 15 μm.

When the width (D) of the printed pattern 210 is less than 0.1 mm, there is a problem in that the height of the pattern is collapsed and the uniformity of the pattern is lowered. Conversely, when the width (D) of the line of the print pattern 210 exceeds 2.0 mm, recursive Since the effective area where reflection occurs is too small, it is difficult to implement a desired appropriate retroreflectance.

When the spacing (d) between the lines of the print pattern 210 is less than 0.1 mm, the uniformity of the pattern is lowered and the effective area is covered by the collapsed pattern line, so that the retroreflective performance is not properly implemented, and the print pattern 210 If the distance between lines exceeds 2.0mm, the effective area is exposed too much to the front, making it difficult to implement low retroreflective performance.

In addition, the print pattern 210 serves to increase the whiteness of the product, and a blind effect can be expected by the pattern height and directionality. This blind effect plays a role in improving license plate visibility by being brightly recognized from the front during the day when manufacturing a car film-type license plate. That is, by reducing the light that is introduced or reflected in the lateral direction of the license plate, the number plate characters are blocked from spreading, thereby increasing the character visibility of the license plate.

In addition, at night, the bright light of the camera flash irradiated from a higher position than the car blocks some of the inflow into the license plate, thereby preventing the retroreflective sheet of the license plate from being too brightly colored, and improving the camera recognition rate. It is possible to increase the character photographing properties of the license plate at night (see Fig. 7c).

On the other hand, it is good to prevent pattern interference such as moiré, that the printing pattern of the upper layer is arranged differently from the traveling direction of the pattern of the low refractive index region or the sealing line pattern of the lower layer. More preferably, when viewed from a plane in a state of being stacked with each other, the moving direction of the printed pattern of the upper layer is staggered to the moving direction of the pattern of the low refractive region of the lower layer or the sealing line pattern at an angle of 30 to 60 degrees. .

7A and 7B are diagrams schematically illustrating a situation in which a license plate to which a retroreflective seat is applied according to a preferred embodiment of the present invention is observed by an observer in day and night situations.

Referring to Figure 7a, the daytime visibility of the retroreflective sheet used for the license plate is independent of the retroreflective performance, so it is usually determined according to the whiteness of the license plate background so that the contrast with the characters printed in black can be clear. Able to know.

Referring to Figure 7b, since the visibility of the night camera of the retroreflective sheet used in the license plate is determined according to the retroreflective performance of the incident light generated from the camera flash, the control of the retroreflective performance by the printing pattern is a major factor.

In the retroreflective sheet according to the present invention, the upper layer is formed on the lower surface of the protective layer and the protective layer that is positioned above the printed pattern to protect the printed pattern from the outside and the protective layer and the base optical layer. and an adhesive layer for adhering the upper surface.

For the overlay layer according to the invention, thermosetting and thermoplastic materials are suitable. The thermosetting or thermoplastic material is polycarbonate (polycarbonate), polyethylene naphthalate (polyethylene naphthalate), polyethylene terephthalate (polyethylene terephthalate), polyester (polyester), polyamide (polyamide), polystyrene (polystyrene), polymethyl methacrylate (polymethyl methacrylate), polyurethane (polyurethane), polyvinyl chloride (PVC), polyethylene (polyethylene), polypropylene (polypropylene), and polyvinylidene fluoride (polyfluorovinylidene), polyvinyl fluoride (polyfluorovinyl) It includes one or more selected, preferably polyethylene terephthalate, polyvinyl chloride, etc. may be selectively used.

In addition, a copolymer resin may be used as needed, and may include a co-extruded sheet base material manufactured by laminating two or more sheets during the extrusion process of manufacturing the sheet.

The overlay layer preferably has a thickness of 30 μm to 100 μm, more preferably a thickness of 40 μm to 60 μm. The overlay layer is preferably used without discoloration of the film itself due to sunlight or heat. Depending on the use of the product, a flexible or rigid film may be selectively used. A flexible film is desirable for applications that are attached to curved surfaces or are curved, such as license plates.

In order to improve the weather resistance of the overlay layer, one or more of benzotriazole-based, hindered amine-based, benzophenone-based, and salicylate-based compounds may be used as additives. contained within and manufactured.

The overlay layer formed on the lower surface of the printed pattern may be coupled to the upper surface of the base optical layer 100 by an adhesive. That is, the upper layer 200 may further include an adhesive layer 220 . The adhesive layer 220 may be formed from a transparent pressure-sensitive adhesive composition including a urethane or urethane-acrylic adhesive resin including monofunctional and polyfunctional functional groups and an isocyanate-based curing agent.

The adhesive layer 220 may have a thickness of 10 μm to 30 μm.

The adhesive layer 220 has a function of bonding the upper layer 200 to the base optical layer 100 .

Through this, the upper layer 200 and the lower layer 300 are integrated to form a retroreflective sheet. The adhesive layer 220 may be used as a pressure sensitive adhesive, and is optically transparent, with little effect on retroreflective performance. The adhesive layer 220 has good physical properties so that pores are not formed due to the thickness of the printed pattern 210 during adhesion.

On the other hand, although it has been described that the printed pattern 210 may be formed on the lower surface of the overlay, as an example of another structure, the print pattern may be printed on the lower surface of the adhesive layer, or the printed pattern is on the upper surface of the base optical layer. It may be printed, and in this case, the printed pattern 210 can be positioned between the adhesive and the base optical layer when the overlay layer and the base optical layer 100 are adhered by the adhesive.

If the retroreflective sheet according to the present invention is applied to a vehicle license plate as an example, it may satisfy the following license plate background color conditions based on KS A 0067 L*a*b* color system.

L*: 85 or more

ΔE: 3 or less (Meaning: ΔE is the distance from the point where a* and b* are reference 0 to the measured point)

By satisfying the above conditions, daytime and nighttime visibility may be improved with high brightness and high whiteness. When L* is 85 or more, it has a bright brightness, and when ΔE of a* and b* is 3 or less, it has a white color close to an achromatic color, and thus bright whiteness can be realized.

The L*, a*, b*, and ΔE symbols will be described with reference to FIG. 9 , wherein the L* value represents the brightness (brightness) a*, the b* value represents the chromaticity, and the ΔE value represents the color difference. L* = 0 indicates black, and L* = 100 indicates white. a* indicates which side is biased toward red or green. If a* is negative, it is a color biased toward green, and if a* is positive, it is a color biased toward red/violet. b* stands for yellow and blue. If b* is negative, it is blue; if b* is positive, it is yellow. In addition, ΔE refers to the color difference, and a* and b* are the distance values from a certain reference coordinate point to the measured coordinate point. That is, an error is expressed as a three-dimensional distance between the positions of two colors in a spherical color space. If the coordinate distances of two colors are far from each other in three dimensions, there is a large color difference, and if there is little difference in the coordinate distances, the same color is recognized.

In addition, the retroreflective sheet according to the present invention may have a reflection performance of 3 cd/lx·m2 to 12 cd/lx·m2 measured by the PR-3000 equipment at an incident angle of 5° and an observation angle of 0.2°. If the reflective performance is less than 3 cd/lx ㎡, the retroreflective performance may be weak and it may not function as a retroreflective sheet. Distinguishing power of characters printed on the reflective sheet is weakened due to light bleed, and there is a fear that the visibility of the night camera may deteriorate.

Hereinafter, the present invention will be described in more detail with reference to examples. However, it should be understood that the configuration of the present invention is not limited to the examples to be described later, and the following examples are merely examples to help the understanding of the present invention.

<Example>

Example 1

The base optical layer was formed by forming a corner cube structure pattern with a retroreflective optical element on the lower surface through a UV imprinting process on a base optical layer made of polyvinyl chloride having a thickness of 100 μm. The lower layer was formed by pressing a sealing film made of a polyester material in a hot-melt manner at a temperature of 185° C. to form a low-refractive region pattern in a rhombus lattice shape so that the corner cube structure pattern could be in contact with the low-refractive material.

In the low refractive region, a long diagonal line connecting opposite vertices in the rhombus shape has an average length of 445 μm, and a short diagonal has an average length of 443 μm, the line width of the sealing material is 450 μm on average, and the thickness of the sealing material is It was formed with an average of 30 µm.

An external adhesive layer was formed on the lower surface of the sealing layer by using a pressure-sensitive adhesive composition containing 15% by weight of white toner.

An upper layer was formed on the upper surface of the base optical layer by the following method.

A parallel line-shaped printed pattern having a pattern width of 0.35 mm and a distance between the patterns of 0.2 mm was formed on the lower surface of the 50 μm thick and polyvinyl chloride overlay layer. At this time, the print pattern was printed using a paint containing titanium dioxide (TiO2).

Thereafter, a pressure-sensitive adhesive was coated on the lower surface of the overlay layer on which the print pattern was printed, and an adhesive layer was formed.

The upper layer and the lower layer bonded to the base optical layer were combined by a laminating process. It was laminated so that the adhesive layer of the upper layer and the upper surface of the base optical layer were combined. A retroreflective sheet was obtained by bonding.

Example 2

A retroreflective sheet was prepared in the same manner as in Example 1, except that the pattern width was adjusted to 0.3 mm and the distance between the patterns was adjusted to 0.1 mm in the printed pattern.

Example 3

A retroreflective sheet was prepared in the same manner as in Example 1.

Comparative Example 1

The base optical layer was formed by forming a corner cube structure pattern with a retroreflective optical element on the lower surface through a UV imprinting process on a base optical layer made of a polycarbonate material having a thickness of 125 μm. The lower layer was formed by pressing a sealing film made of a polyester material in a hot melt method at a temperature of 185° C. to form a low-refractive region pattern in the shape of a rhombus lattice so that the low-refractive material could be in contact with the corner cube structure pattern.

The low-refractive region is a size visually recognized in the prior art, and a long diagonal line connecting opposite vertices in a rhombus has an average length of 5200 μm, and a short diagonal has an average length of 4220 μm, and the line width of the sealing material is an average It was 450 μm and the thickness of the sealing material was formed to be 30 μm on average.

An external adhesive layer was formed on the lower surface of the sealing material using a transparent pressure-sensitive adhesive composition.

Comparative Example 2

It was prepared in the same manner as in Comparative Example 1.

Experimental Example 1: Evaluation of whiteness and retroreflectance

The whiteness and retroreflectance of the retroreflective sheets according to Examples 1 and 2 and Comparative Example 1 were respectively compared and shown in Table 1 below. In addition, the retroreflectance by the effective area ratio of the optically active area to the lower layer and the ratio of the non-blocking area to the upper layer of each retroreflective sheet is shown in Table 2.

As an embodiment, the whiteness for the background color of the license plate is shown based on the CIE L*a*b* color system of FIG. 9, and CIE L*a*b* is a value measured using CM2500 equipment (KONICA MINOLTA) , The retroreflectance is a value measured using PR-3000 equipment (Pymax) at an incident angle of 5.0˚ and an observation angle of 0.2˚, and has a unit of cd/lx·m2.

Each evaluation is performed once (A) with the base optical layer alone, once (B) for the sheet combining the base optical layer with the lower layer, and once (C) for the completed retroreflective sheet including the upper layer. Results are shown separately.

division reference value
(background color) A B C result Example 1 reflectivity
(0.2 ˚ / 5.0 ˚ ) 3 to 12 311 31.4 10.5 fitness L* 85 or more 66.6 79.23 89.01 fitness a* △E 0 3 or less -1.55 -3.54 -2.64 2.64 fitness b* 0 -10.3 -0.86 0.16 Example 2 reflectivity
(0.2 ˚ / 5.0 ˚ ) 3 to 12 305 29.0 6.7 fitness L* 85 or more 66.9 78.91 89.78 fitness a* △E 0 3 or less -1.58 -3.82 -2.41 2.41 fitness b* 0 -9.93 -0.93 -0.07 Comparative Example 1 reflectivity
(0.2 ˚ / 5.0 ˚ ) 3 to 12 307 199.6 incongruity L* 85 or more 58.5 73.4 a* △E 0 3 or less -1.4 -1.29 1.76 b* 0 2.43 1.19

(Reflectance unit: cd/lx ㎡, L*: Brightness, a* b*: Chromaticity, △E: Color difference)

Referring to Table 1, in Examples 1 and 2, it can be seen that the brightness L* significantly increased from 66.6 and 66.9 to 89.01 and 89.78, respectively, after each combination of the base optical layer, the upper layer, and the lower layer. In Comparative Example 1, it was found that L* was 73.4 and the brightness was low.

In addition, in Examples 1 and 2, it was confirmed that the reflectance (retroreflective performance) was greatly limited in the upper layer and the lower layer, respectively, due to the reduction of the effective area by the sealing material and the partial blocking of the retroreflection by the printing pattern. However, in the case of Comparative Example 1, it was found that the reflectance was remarkably high because the upper layer was not combined.

Therefore, Examples 1 and 2 are remarkably excellent in whiteness, and by limiting the retroreflectance to a reference value range, both daytime visibility and nighttime camera visibility are excellent, and in the case of Comparative Example 1, both whiteness and reflection performance do not meet the required standards It can be said that there is a problem in the visibility at night of the enforcement cameras installed on the market in Korea.

division base optical layer
self-reflectance lower layer
effective area ratio After bonding the lower layer
reflectivity upper layer
non-blocking area
area ratio retro reflective sheet
total reflectance Example 1 311 10.1% 31.4 33.4% 10.5 Example 2 305 9.5% 29 23.1% 6.7 Comparative Example 1 307 65% 199.6 - -

Referring to Table 2, in Example 1, after forming the corner cube pattern on the lower surface of the base optical layer, the lower layer (including the sealing material and the low-refractive region) forming process proceeded under the conditions of line speed 6m/min and 185°C, and the effective area ratio of the optically active area (effective area ratio reflecting manufacturing error) was formed as 10.1%, and the reflectance was obtained as 31.4. In addition to this, 66.6% of the light blocking area (actual blocking area reflecting manufacturing error) was further formed using the upper layer (including a printed pattern with a width of 0.35 mm and an interval of 0.2 mm), and the reflectance was lowered to 10.5. The brightness was 89.01 and the color difference (ΔE) was 2.64, so good daytime visibility and nighttime camera visibility were secured.

In Example 2, after forming a corner cube pattern on the lower surface of the base optical layer, the lower layer (including the sealing material and the low-refractive region) forming process proceeded under the conditions of a line speed of 5 m/min and 185° C. effective area ratio) was 9.5%, and the reflectance was obtained as 29. In addition, 79.6% of the light blocking area (actual blocking area reflecting manufacturing error) was further formed using the upper layer (including a printed pattern with a width of 0.3 mm and an interval of 0.1 mm), and the reflectance was lowered to 6.7. The brightness was 89.78 and the color difference (ΔE) was 2.41, so good daytime and nighttime camera visibility was secured.

Comparative Example 1 was formed with an effective area ratio of an optically active area of 65% by forming a corner cube pattern on the lower surface of the base optical layer and then proceeding with a line speed of 5 m/min and 185° C. As a result, the reflectance had a reflective performance of 199.6 and a brightness of 73.4, which was not suitable for license plates, etc. due to poor visibility of night cameras and visual visibility due to too intense reflective performance and not high brightness.

Experimental Example 2: Comparison of immersion test results

After the retroreflective sheets according to Example 3 and Comparative Example 2 were immersed in water at a temperature of 50° C. for 24 hours, it was observed whether water penetrated into the low refractive index region, and is shown in FIGS. 10A and 10B , respectively.

Referring to FIGS. 10A and 10B , as the retroreflective sheet of the present invention, the retroreflective sheet according to Example 3, in which the lower refractive region of the lower layer is fine, did not cause immersion, and it was found that the durability was good.

However, in the case of the retroreflective sheet of Comparative Example 2 of the prior art, it can be seen that there is a problem in durability due to flooding.

If we compare and explain the reason for this difference in durability,

Comparing the area of one low refractive region of Example 3 and Comparative Example 2,

Since the area of the low refraction area of Comparative Example 2 is much larger than the area of the low refraction area of Example 3, the seal is not densely that much, thereby weakening the durability.

To put this in reverse,

Since the area of the low refraction area of Example 3 is much smaller and finer than the area of the low refraction area of Comparative Example 2, the micro-sealing is densely formed to the extent that the durability is strengthened,

Since Example 3 has an adhesive area that is several times more than that of Comparative Example 2, the overall adhesive force is much stronger. Therefore, the retroreflective sheet according to the present invention has very strong durability.

100: base optical layer
110: corner cube structure, retroreflective optical element
200: upper layer
210: print pattern
220: adhesive layer
300: lower layer
311: low refractive material
312: sealing wire
313: sealing cover
320: sealing material
D: width of print pattern
d: spacing of the print pattern
L: cycle of print pattern

Claims (15)

a base optical layer having a pattern of a plurality of retroreflective optical elements on a lower surface thereof;
a lower layer coupled to the lower surface of the base optical layer and including a low refractive region made of a low refractive material having a lower refractive index than that of the base optical layer and a sealing material for sealing side surfaces and lower surfaces of the low refractive region; and
An upper layer coupled to the upper surface of the base optical layer and including a printed pattern that partially blocks light transmission; including,
The low refractive region is in contact with the lower surface of the base optical layer and is partitioned in a predetermined pattern, and the sealing material seals the side and lower surfaces of the low refractive region and is attached to the lower surface of the base optical layer from the side of the low refractive region become,
The retroreflective sheet, characterized in that at least a portion of the printed pattern is formed in an area corresponding to at least a portion of the low refractive area.
According to claim 1,
The retroreflective sheet, characterized in that the low refractive material is air (air).
According to claim 1,
The retroreflective sheet, characterized in that the retroreflective optical element is a corner cube (corner-cube) structure.
According to claim 1,
The retroreflective sheet, characterized in that the low refractive region occupies an area of 5% to 30% in the lower layer.
5. The method of claim 4,
The retroreflective sheet, characterized in that the region corresponding to the low refractive index region not blocked by the printing pattern is 0.5% to 15% of the total area of the retroreflective sheet.
According to claim 1,
The retroreflective sheet, characterized in that the area where the sealing material is attached to the lower surface of the base optical layer is 70% to 95% of the total area of the retroreflective sheet.
According to claim 1,
In the sealing material, a sealing line is linearly attached to the lower surface of the base optical layer along the side surface of the low refractive region,
The retroreflective sheet, characterized in that the sealing material is attached to the lower surface of the base optical layer has a width of 100 μm to 2000 μm.
According to claim 1,
The retroreflective sheet, characterized in that the low-refractive region is divided and sealed in a repeating pattern of a triangular, quadrangular or hexagonal shape.
According to claim 1,
The print pattern is a retroreflective sheet, characterized in that the pattern is a linear, or regular or irregular wavy pattern printed at intervals of 100㎛ to 2,000㎛ in one direction.
According to claim 1,
A retroreflective sheet, characterized in that the printed pattern of the upper layer and the pattern of the low refractive region of the lower layer satisfy Relational Equation 1 below:
[Relational Expression 1]

In the above relation 1,

represents the average repetition period in any one direction of the low-refractive region pattern of the lower layer,

is

and represents the average repetition period of the upper layer printed pattern in the same direction.
10. The method of claim 9,
The upper layer is a retroreflective sheet, characterized in that it comprises two or more printed patterns arranged in different directions.
According to claim 1,
The print pattern is titanium dioxide (TiO ₂ ) and silicon dioxide (SiO ₂ ) Retroreflective sheet, characterized in that printed using a paint containing one or more additives selected from the group consisting of.
According to claim 1,
The upper layer is
a protective layer positioned above the printed pattern to protect the printed pattern from the outside; and
and an adhesive layer formed on the lower surface of the protective layer and bonding the protective layer and the upper surface of the base optical layer.
According to claim 1,
The retroreflective sheet, characterized in that the area in which the sealing material is attached to the lower surface of the base optical layer is larger than the area in which the low refractive area is in contact with the lower surface of the base optical layer.
A license plate for a vehicle comprising a retroreflective seat according to any one of claims 1 to 14.

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