HK1092223B - Retroreflective sheet and external illumination system - Google Patents

Description

Retroreflective sheet and external illumination type lighting system

Technical Field

The present invention relates to retroreflective sheeting and an externally illuminated lighting system for use in road signs, guide signs, safety guide sign indicator boards, safety indicators, billboards and the like.

Background

Retroreflective (retroreflective) sheets are widely used in various applications such as traffic signs, guide signs, warning signs, traffic control signs, number plates of automobiles, and advertising boards. An example of such a retroreflective sheet includes a so-called enclosed lens type retroreflective sheet in which a surface layer formed of at least 1 layer, high refractive index glass beads, a focusing layer (also referred to as a focusing resin layer), and a metal reflective layer are laminated in this order. Another configuration includes a retroreflective sheet called a capsule lens type, which is formed of a plurality of transparent balls having a reflector provided in a lower hemisphere, a support resin sheet holding the plurality of transparent balls, and a transparent cover film arranged on a surface of the support resin sheet to cover the plurality of transparent balls, and in which a joint portion for supporting the cover film is formed in the support resin sheet. In the case of the capsule lens type, since the direct reflection mirror is formed on the surface of the transparent sphere, the reflection luminance up to a large incident angle at a small observation angle is more excellent than that of the enclosed lens type, and therefore, it is also called a reverse high luminance reflection sheet. An adhesive, a release paper and a release film may be further laminated to the retroreflective sheet. Such a retroreflective sheet can be used as a sign or a signboard by being adhered to a metal substrate such as aluminum, an iron plate, a coated iron plate, or a stainless steel plate, or a substrate such as a Fiber Reinforced Plastic (FRP) or a plastic plate such as hard vinyl chloride. Such retroreflective sheet is useful because it can be recognized in the daytime generally as in the case of a usual sign or signboard, and can retroreflect light correctly in the direction of the light source from which light is projected at night, thereby significantly improving the visibility of the sign, the number plate of an automobile, the signboard, and the like.

The retroreflection performance of such a retroreflective sheet is regulated by the specifications of countries in the world depending on the angle (incident angle) formed by the irradiation axis of the projected light and the normal line of the surface center of the retroreflective sheet and the angle (observation angle) formed by the irradiation axis of the emitted light and the observation axis.

However, japanese industrial standards JIS Z9117 and the standards of all countries in the world require only 2 ° at maximum for observation angles and 50 ° at maximum for incidence angles.

Therefore, it is currently the case that retroreflective sheeting on the market is also produced to fit these specifications. In addition, the markers, the number plates, and the like must have the minimum necessary reflection performance to satisfy the specifications of each country. However, even if these specifications are met, in the market, for example, a road sign that is set at a right angle to a road is effective on a straight road, but when the incident angle exceeds 50 ° at a position where the road is curved, there is a problem that the reflection performance is significantly reduced and the visibility of the sign is extremely low. Even with the number plate, there is a problem that it is difficult to observe the number plate of the preceding vehicle from the vehicle behind because the observation angle is large when the vehicle behind is a driver's seat such as a truck, the observation angle is large when the vehicle ahead is low in number plate position, and the incidence angle is large when the vehicle ahead turns to either the left or right.

It is also said that 18m to 22m are required from the time of feeling a danger until the vehicle stops when the automobile is driven at a speed of 40 km/hour, but safety of the roadside ahead of 22m is confirmed using a retroreflective sheet when the automobile is driven at a speed of 40 km/hour at a distance of 3m from the roadside, and for this reason, the incident angle needs to be about 82 °. Further, since the viewing angle of the conventional retroreflective sheet provided substantially parallel to the road is extremely large, it is not possible to transmit accurate information in the conventional art. For this reason, there is a strong market demand for retroreflective sheeting having excellent wide-angle properties.

As a solution to this problem, for example, in the above-mentioned enclosed lens retroreflective sheeting, patent document 1 below proposes that a resin paint be powder-applied to the upper hemispherical surface of glass microspheres having lower hemispherical portions embedded in a surface resin layer to form a focus resin layer having a uniform thickness. Patent document 2 proposes forming a transparent resin focal layer by superposing a transparent resin film formed in advance to have a uniform thickness on the exposed surface of transparent microspheres half-embedded in a surface resin layer or the like, and heating and softening the transparent resin film to embed and bond the transparent microspheres. Patent document 3 proposes a retroreflective sheet having excellent retroreflective performance with small angle dependence, which is obtained by embedding microspheres having a multilayer structure, which are formed on the surface of transparent microspheres and have a transparent focal layer formed to cover the transparent microspheres substantially concentrically with a substantially constant thickness, in a surface layer and then forming a reflective layer thereon. Patent document 4 proposes a retroreflective sheet-like article comprising a plurality of transparent microspheres embedded in a transparent resin, a focal resin layer, and a light-reflecting layer, wherein the light-reflecting layer on the top and back surfaces of the transparent microspheres is located closer to the transparent microspheres than the focal positions of the transparent microspheres, and the light-reflecting layer on the side and back surfaces of the transparent microspheres is located at the focal positions. Patent document 5 discloses an external illumination type remote lighting system and method, which have become popular as a road sign in recent years. Furthermore, retroreflective sheets having a wide angle such as a wave reflector (manufactured by NTW corporation) and a wide-angle prism retroreflective sheet (VIP grade manufactured by 3M) as an ultra-wide-angle sight-guiding material, which are formed into a wave shape and have a reflective surface using a microprism retroreflective sheet, and a wide-angle prism retroreflective sheet for side display (EV-9010 manufactured by 3M) are also commercially available.

Patent document 1: japanese patent laid-open publication No. 51-128293

Patent document 2: japanese examined patent publication (JP-B) No. 8-27402 (JP-A-59-198402)

Patent document 3: japanese unexamined patent publication No. 8-101304

Patent document 4: JP-A58-8802

Patent document 5: japanese patent No. 2910868 (Japanese patent application laid-open No. Hei 10-506721)

However, in the reflective sheet proposed in patent document 1, it is difficult to form a focal resin layer having a uniform powder thickness on the surface of the microspheres. In addition, the reflective sheet proposed in patent document 2 is difficult to adhere a thin film to the microsphere surface and the surface resin layer in which the microspheres are embedded. In addition, the reflective sheet proposed in patent document 3 is extremely difficult to form a required thickness of the focal layer accurately on the surface of the microsphere. The particle diameters of the microspheres are distributed to some extent, and even if the thickness of the focal layer is formed to match the median particle diameter, an optimum film thickness cannot be obtained on all the microspheres. Therefore, providing a direct reflective layer on each microsphere is far from achieving the reflective properties of a capsule lens retroreflective sheet that all microspheres have the best reflective properties. In addition, there is no description of a device and a method that exhibit reflection performance at a large observation angle. Therefore, as described in these applications, a focus layer having a certain thickness is formed only at the focus forming position, and wide-angle reflection performance at a large incident angle cannot be ensured at a larger observation angle. The aforementioned encapsulated lens retroreflective sheeting may be desirable if sufficiently high reflective performance is obtained at a relatively small viewing angle. Further, patent document 5 discloses a sign illumination system and method in which a retroreflective sheet having a wide observation angle is used as a sign and the sign is illuminated from an illumination light source provided on a roadside far from the sign, but when the conventional capsule lens type retroreflective sheet having a wide observation angle is used in the illumination system, the reflection performance is not sufficient. For example, when the road is a multi-lane road, the brightness of the logo is greatly different between the brightness of the logo confirmed by the automobile driving on the leftmost lane and the brightness of the logo confirmed by the automobile driving on the rightmost lane. That is, there are the following problems: since the vehicle traveling on the leftmost lane observes the light emitted from the external light projector at a small observation angle, the amount of light returned from the emblem is relatively large, and thus it can be clearly seen, but since the observation angle for the vehicle traveling on the rightmost lane is very large, the amount of light returned from the emblem is greatly reduced, and it looks very dark.

Further, since it is difficult to maintain the retroreflective performance when the microprismatic retroreflective sheet comes into contact with light from an oblique direction or a lateral direction, the wave reflector forms the microprismatic retroreflective sheet into a wave shape, and the incident angle of light irradiated from the oblique direction or the lateral direction with respect to the retroreflective sheet is decreased to make the light incident, resulting in an improvement in retroreflective brightness, but the retroreflective sheet itself does not have a wide-angle performance. In addition, since it is extremely difficult to print on the wave reflector by screen printing or the like in order to form the wave shape, there is a problem that necessary information is incorporated into the retroreflective sheet before wave forming and then forming processing is necessary, which causes a problem of cost increase. Further, the inner surface of the wave reflector has large wavy depressions, and when the wave reflector is attached to the side wall of a road, foreign materials such as garbage are stored in the depressions, which causes a problem that the appearance of the film is significantly impaired.

In addition, the aforementioned wide-angle prism-type retroreflective sheeting (VIP) is not designed to irradiate light from an oblique or lateral direction and exhibit retroreflective performance at a relatively large observation angle. For example, at an observation angle of 4 °, an incidence angle of 40 ° or more, there is a problem that retroreflective performance cannot be maintained any more.

In addition, in the case of a wide-angle prism-type retroreflective sheet for side display (EV-9010 manufactured by 3M), when the observation point is located in the transverse direction (display direction) of the sheet, the retroreflective performance can be maintained even at a large observation angle and a large incident angle, but when the observation point is located in the longitudinal direction (vertical direction) of the sheet, there is a problem as follows: if the incident angle exceeds 60 deg., the retroreflection performance is extremely low. When a vehicle is driven, the eyes (i.e., the observation point) of the driver are positioned above the headlamps, and therefore, the incident angle is increased, and if the wide-angle prism-type retroreflective sheet for side display is used for visual guidance, a sufficient retroreflective effect cannot be exerted on the vehicle driver.

Next, a cross section of a conventional enclosed lens retroreflective sheet will be described with reference to fig. 8A. The preparation method comprises the following steps: first, a surface layer 10 is formed on a work substrate, then a resin solution for forming a glass ball fixing layer 11 is applied on the surface layer 10, and then dried, and glass balls 13 are scattered on the glass ball fixing layer 11 in a state of remaining viscosity, thereby adhering the glass balls to the glass ball fixing layer 11, then the fixing layer 11 is heated, the fixing layer 11 is thermally cured while the glass balls 13 are settled, and the glass balls 13 are sufficiently fixed, and in the subsequent step, a resin solution for forming a focus layer 12 is applied on the surface of the glass balls 13 and dried. At this time, the glass ball fixing layer 11 is adjusted so that the thickness thereof is 50% to 80% of the particle diameter of the glass ball 13 in a state where the glass ball is sunk. Then, the glass ball is fixed in a state of reaching the surface layer.

Further, the retroreflective sheet of the enclosed lens type, which is constituted by the surface layer 10 and the glass ball fixing layer 11 as the same layer, is also included, and in this case, the glass balls are held in the following state: approximately 60% of the particle size is impregnated into the same layer from the center of the glass sphere. In this case, a method of applying and drying the focal layer resin solution is also used in the same manner as described above.

In this way, the focal layer 12 is formed by applying and drying the focal layer resin solution, and in this case, in order to uniformly apply and dry the focal layer resin solution to the entire surface of the sheet, the film thickness of the focal layer of each glass sphere is adjusted, and only the focal layer having a uniform thickness can be formed on the entire sheet.

When the focal layer resin solution is applied and dried, the focal layer resin solution shrinks in volume, and the shrinkage stress causes the focal layer resin solution to wrap around the inner surface of the glass sphere, thereby forming an ideal concentric circle. The focal layer 12 can be formed to have a uniform thickness at the focal position of the glass sphere, and as shown in fig. 8B, incident light B1 from the front direction is reflected by the metal reflective layer on the inner surface of the focal layer of the glass sphere and retroreflected as reflected light B2 substantially parallel to the incident direction; the incident light c1 from the oblique direction is also retroreflected as reflected light c2 substantially parallel to the incident direction. However, in practice, the fixing layer between the glass spheres is also in contact with the focal layer solution, and in the drying step, the fixing layer also sucks the focal layer solution or the focal layer solution flows in a direction of a low position by gravity. As a result, the focusing layer inhibiting resin forms concentric circles, the inner surface side of the glass sphere becomes thinner, the side surface side becomes thicker, and the focusing layer as shown in fig. 8C is formed.

That is, when the thickness of the focal layer on the inner surface side of the glass sphere is equal to the focal position of the glass sphere, the incident light d1 from the front direction retroreflects as reflected light d2 substantially in parallel with the incident direction, and the incident light c1 from the oblique direction diffuses from the incident direction and retroreflects as reflected light e 2. Therefore, only angles with small incident angles in the range denoted by β in fig. 8c are optimal reflections.

Further, as shown in the reflection sheet proposed in patent document 4 (fig. 8D), if the focus layer is formed so that the light reflected by retroreflection on the side surface side of the glass sphere is reflected as light g2 substantially parallel to the incident light g1, there is a problem that the incident light f1 from the front direction diffuses from the incident direction and retroreflects as reflected light f 2. Therefore, even if the reflection performance can be obtained at a large observation angle, the reflection performance required in the front direction at a relatively small observation angle cannot be achieved by the Japanese Industrial Standard (JIS) and the overseas marking standard value. Therefore, the use is limited, and the present invention cannot be used for general traffic signs, and is difficult to be used for number plates of automobiles, etc., and thus cannot satisfy the market demand in terms of practical use.

As described above, the conventional enclosed-lens retroreflective sheet has a large angle dependency, and cannot sufficiently ensure wide-angle reflection performance at a large observation angle and a large incident angle.

Under such circumstances, there is a strong demand in the market for a retroreflective sheet having wide angle properties that is suitable for the world standards including JIS.

Disclosure of Invention

The present invention has been made to solve the above-described conventional problems, and an object of the present invention is to provide a retroreflective sheet having wide-angle reflectivity that can increase the incident angle and the observation angle. Further, a retroreflective sheet and an external illumination type distance illumination system are provided, which can exhibit high reflection performance when used in the external illumination type distance illumination system as compared with a currently marketed capsule lens type retroreflective sheet having a wide observation angle property.

The retroreflective sheet of the present invention is characterized by comprising: the optical film comprises a surface layer comprising at least 1 layer, a focal layer comprising glass spheres, and a metal reflective layer provided on the inner surface side of the focal layer, wherein the glass spheres are arranged at arbitrary positions in the thickness direction of the focal layer.

The external illumination type lighting system of the present invention is characterized in that: the retroreflective sheeting includes a sign having a sign surface and an external illumination source, wherein the sign surface includes the retroreflective sheet and the distance from the illumination source to the sign surface is in the range of 1m to 100 m.

Drawings

FIG. 1A is a cross-sectional process view of a retroreflective sheeting according to one embodiment of the present invention.

FIG. 1B is a cross-sectional process view of a retroreflective sheeting according to one embodiment of the present invention.

FIG. 1C is a cross-sectional process view of a retroreflective sheeting according to one embodiment of the present invention.

FIG. 1D is a cross-sectional process view of a retroreflective sheeting according to one embodiment of the present invention.

FIG. 1E is a cross-sectional process view of a retroreflective sheeting according to one embodiment of the present invention.

FIG. 1F is a cross-sectional process view of a retroreflective sheeting according to one embodiment of the present invention.

Fig. 2 is a graph showing the measurement curves of the incident angle and the reflection performance when the observation angle is 0.2 ° in examples 1 and 2 of the present invention and comparative examples 1 and 2.

Fig. 3 is a graph showing the measurement curves of the incident angle and the reflection performance when the observation angle is 2.0 ° in examples 1 and 2 of the present invention and comparative examples 1 and 2.

Fig. 4 is a graph showing the measurement curves of the incident angle and the reflection performance when the observation angle is 4.0 ° in examples 1 and 2 of the present invention and comparative examples 1 and 2.

Fig. 5A-C are views of a retroreflective sheet of the present invention applied to printed photographs, which are photographs of viewing the angular dependence of a conventional capsule lens-type high brightness retroreflective sheet and example 2 of the present invention.

Fig. 6A-B are photographs showing the angle dependence of a conventional capsule lens type high brightness retroreflective sheet (HI) and the retroreflective sheet of example 1 (wide angle reflection) of the present invention, assuming that the retroreflective sheet of the present invention is a forward-on indication on a road surface.

Fig. 7 is a diagram illustrating an observation angle and an incident angle of the present invention.

Fig. 8A-D are cross-sectional and explanatory views of a conventional enclosed retroreflective sheet.

Fig. 9 is a graph showing the measurement of the incident angle and the reflection performance when the observation angle is 5 ° in example 1 of the present invention and comparative example 3.

Fig. 10 is a graph showing the measurement of the incident angle and the reflection performance when the observation angle is 35 ° in example 1 of the present invention and comparative example 3.

Fig. 11 is a graph showing the measurement of the incident angle and the reflection performance at an observation angle of 40 ° in example 1 of the present invention and comparative example 3.

Fig. 12 is a diagram illustrating an external illumination system according to an embodiment of the present invention.

Detailed Description

In the present invention, when the retroreflective sheet is viewed in a cross-sectional direction, the height of the glass spheres present in the focal layer is arbitrary. That is, including the glass ball contacting the surface layer and the glass ball not contacting the surface layer, the non-contacting glass balls are also present at positions which are not fixed, respectively. Thus, even if light enters from a wide angle, the light can retroreflect almost in the direction, and the observation angle can be enlarged.

In the present invention, the observation angle is an angle γ shown in fig. 7, and means an angle at which reflected light can be observed. The incident angle is an angle θ shown in fig. 7, and means an angle θ between a perpendicular line perpendicular to the surface of the retroreflective sheet and incident light. In fig. 7, 1 is a surface film, 2 is a focal layer, 3 is a glass sphere, 4 is a metal reflective layer, 5 is an adhesive layer, 6 is a release material, a1 is incident light, and a2 is reflected light.

The glass spheres preferably include a glass sphere group B contacting the surface layer and a glass sphere group a located away from the surface layer. Thus, the glass sphere group a can exhibit retroreflection performance at an observation angle larger than that of the glass sphere group B.

The glass spheres include a glass sphere group B in contact with the surface layer and a glass sphere group a located away from the surface layer, and the reflective layer of the glass sphere group B is preferably formed at a focal point formation position, and the focal point layer of the glass sphere group a is preferably made thinner than the focal point layer of the glass sphere group B. Thus, retroreflection performance can be exhibited at a larger observation angle.

The glass spheres include a glass sphere group B in contact with the surface layer and a glass sphere group a located away from the surface layer, the focal layer formed concentrically on the glass sphere surface of the glass sphere group B has a film thickness that exhibits the highest reflection performance at an observation angle of 0.2 ° and an incidence angle of 5 °, the film thickness of the focal layer of the glass sphere group a is preferably smaller than the film thickness of the focal layer of the glass sphere group B, and the glass sphere group a has retroreflection performance at a larger observation angle than the glass sphere group B.

The ratio of the glass spheres contacting the surface layer is preferably 50 to 90% of all the glass spheres. This makes it possible to satisfy the specifications of various countries in the world represented by JIS Z9117 and to satisfy the reflection performance at a large observation angle of 2 ° or more.

The glass spheres preferably have a refractive index in the range of 2.10 to 2.40, a median particle diameter in the range of 35 to 75 μm, and 80% or more of the glass spheres preferably have a median particle diameter in the range of ± 10 μm. This is preferable because a concentric focal layer can be formed on the glass sphere to obtain desired reflection performance.

The main component of the resin constituting the focal layer is preferably a polyvinyl acetal resin.

This resin is colorless and transparent, and is excellent in pigment dispersibility, adhesion to titanium oxide glass, toughness and flexibility, and good in solubility in organic solvents, and has a functional group capable of undergoing a crosslinking reaction, and thus is suitable.

The polyvinyl acetal resin is preferably a polyvinyl butyral resin having a polymerization degree of 500 to 1500. This makes it possible to adjust the viscosity to an appropriate solid content.

The polyvinyl alcohol unit of the polyvinyl butyral resin is preferably 17 to 23 wt%. Thus, the curing speed of the curing agent can be appropriately adjusted.

The glass transition temperature (Tg) of the polyvinyl butyral resin is preferably 60 to 80 ℃. This is preferable because the focal layer can be formed concentrically on the glass spherical surface.

Preferably, the polyvinyl butyral resin is a layer insoluble in a solvent in which a hydroxyl group in a polyvinyl alcohol unit of the polyvinyl butyral resin is crosslinked with an amino resin and the focal layer is immersed in toluene for 1 minute, xylene for 1 minute, and methanol for 10 minutes. Thus, printing can be performed using screen printing inks or the like containing various organic solvents, and moreover, since the retroreflective sheet exhibits gasoline resistance when used in vehicles or the like, the retroreflective sheet can be practically used as an appropriate retroreflective sheet.

The weight of the resin of the focal layer and the mixing ratio of the glass spheres are preferably such that the weight of the glass spheres is 1.5 to 3.7 per unit weight of the resin. Thereby, sufficient reflection performance can be ensured.

The focus layer preferably contains a non-silicon defoaming agent in an amount of 0.01 to 3.0% by weight based on the weight of the focus layer resin. This is preferable because the defoaming effect can be exhibited and the adhesion to the metal reflective film is not reduced.

The non-silicon defoaming agent is preferably an alkyl vinyl ether copolymer. This is preferable because a sufficient defoaming effect can be obtained.

In order to meet the marking specifications of the lens-enclosed retroreflective sheeting in various countries around the world, the retroreflective sheeting of the present invention can maintain the 1 st order reflection performance specified in JIS Z9117, and further, preferably has the following reflection performance in each color, in order to ensure effective visibility at night even at an observation angle of 4 ° which is about 2 times as large as that of conventional products and at an incident angle of more than 50 °.

The white retroreflective sheeting preferably has a reflection performance of 0.75 or more at an observation angle of 2 ° and an incidence angle of 70 °, and has a wide-angle reflection performance of 0.50 or more at an observation angle of 4 ° and an incidence angle of 70 °.

The yellow retroreflective sheeting preferably has a reflection performance of 0.50 or more at an observation angle of 2 ° and an incidence angle of 70 °, and has a wide-angle reflection performance of 0.35 or more at an observation angle of 4 ° and an incidence angle of 70 °.

The red retroreflective sheeting preferably has a reflection performance of 0.15 or more at an observation angle of 2 ° and an incidence angle of 70 °, and has a wide-angle reflection performance of 0.10 or more at an observation angle of 4 ° and an incidence angle of 70 °.

The orange retroreflective sheeting preferably has a reflection performance of 0.17 or more at an observation angle of 2 ° and an incidence angle of 70 °, and has a wide-angle reflection performance of 0.11 or more at an observation angle of 4 ° and an incidence angle of 70 °.

The green retroreflective sheeting preferably has a reflection performance of 0.11 or more at an observation angle of 2 ° and an incidence angle of 70 °, and has a wide-angle reflection performance of 0.08 or more at an observation angle of 4 ° and an incidence angle of 70 °.

The blue retroreflective sheeting preferably has a reflection performance of 0.04 or more at an observation angle of 2 ° and an incidence angle of 70 °, and has a wide-angle reflection performance of 0.03 or more at an observation angle of 4 ° and an incidence angle of 70 °.

The retroreflective sheet of the present invention is useful for various applications such as traffic signs, guide signs, warning signs, traffic control signs, automobile license plates, advertising display panels, and printed photographs. As a particularly useful example, the retroreflective sheet is useful for indicating high visibility through the ultra-wide angle retroreflective performance in road side indication using the ultra-wide angle retroreflective performance, guardrail line indication such as a guardrail or a protective tunnel, curb indication, tunnel interior indication, tunnel door interior indication, a mark for a vehicle, a station name, a place of stay indication, a residence indication, a side surface of an automatic vending machine, a front display, a snow pole indication, wind protection, a snow fence line indication, a railway track interior indication, a security sign, a fence indication for construction, a building construction plan indication, a sound absorbing panel, a sound proof panel indication, a sight line guidance indication, a river, a shoreline water level indication, a road surface indication, or the like.

Further, the retroreflective sheet of the present invention has a larger reflection performance at a larger observation angle, specifically, at angles of 5 °, 35 °, 40 °, and the like, as compared with the currently marketed capsule-lens retroreflective sheet and the capsule-lens retroreflective sheet having a wide observation angle characteristic. Therefore, in recent years, the led has become popular as a road sign, and is also used for an external illumination type remote lighting system of a sign board.

According to the invention, the reflection performance of each retro-reflective glass ball is adjusted to distinguish the glass ball group which has the function of maintaining the reflection performance at a smaller observation angle until a larger incidence angle; and a group of glass spheres having reflection performance at a larger observation angle and a larger incident angle, and the respective performances are borne, thereby obtaining a retroreflective sheet having high practicality and maintaining an ultra-wide angle performance.

That is, in order to secure the retroreflection performance at the above-mentioned large incident angle, the biggest problem is: in order to form the focus layer in a concentric manner with the glass sphere while keeping the thickness of the focus layer constant, it is necessary to accurately form the focus layer in the focus forming position of the glass sphere in order to comply with the world standard.

In order to ensure the reflection performance at an observation angle larger than that specified by the world standard and at a larger incident angle, the focal layer thickness must be made constant and formed concentrically with the glass sphere as described above, and in order to obtain the reflection performance at a larger observation angle, the focal layer thickness must be formed slightly thinner on the glass sphere than at the focal point formation position of the glass sphere.

As described above, it was found that a retroreflective sheet having a super-wide angle that satisfies the strong demand of the market can be completed by including 2 kinds of glass sphere groups that perform the above-described functions on the same focal layer.

On the other hand, the formation of the focal layer in the conventional retroreflective sheet production process can be performed as follows: half of the glass spheres are embedded in the surface layer, or half of the glass spheres are embedded in a glass sphere fixing layer provided on the surface layer, and the focal layer resin solution is applied and dried from above. At this time, the focus layer resin solution flows down from the upper surface of the glass sphere along the glass sphere on the side surface, and a spherical focus layer is formed on the hemispherical surface of the glass sphere where the hemisphere is approximately exposed from the surface layer or the glass sphere fixing layer.

However, the focal layer resin solution flowing down from the exposed hemispherical surface, that is, the vertex side of the glass sphere is deposited on the surface layer in which the glass sphere is buried or the fixed layer of the glass sphere, the focal layer film thickness on the side surface side of the glass sphere becomes thick, and the film thickness originally required for forming the focal point forming position of the glass sphere is limited to a very small portion in the vicinity of the vertex of the glass sphere.

Therefore, the present inventors have studied how to form a focal layer concentrically with a glass sphere while keeping the thickness of the focal layer constant, and as a result, have found that a resin solution flowing down from the side surface of the glass sphere is deposited from the bottom side of the glass sphere when the focal layer is formed without burying the glass sphere in a surface layer, so that formation of a concentric focal layer from the apex of the glass sphere is not hindered, and that the surface area of the focal layer formed concentrically along the glass sphere is significantly larger than that of the conventional focal layer.

That is, the following conclusions can be drawn: it is useful to form the concentric focal layer by dispersing glass spheres in a focal layer resin solution and directly applying the glass spheres to the surface layer.

In order to form such a concentric focal layer, the following requirements may be applied. First, the resin that can be used as the focus layer is a resin having a polyurethane resin, a polyvinyl acetal resin, an acrylic resin, or a polyester resin as a raw material polymer component, and a curing agent such as an amino resin, an epoxy resin, a polyisocyanate, or a blocked polyisocyanate is preferably mixed and used as a thermosetting resin. Particularly preferred is a polyvinyl acetal resin which is colorless and transparent, has excellent pigment dispersibility, has excellent adhesion to titanium oxide glass, has high strength and excellent flexibility, has good solubility in organic solvents, has a functional group, and can undergo a crosslinking reaction.

The viscosity of the resin solution to be applied, drying conditions, the polymerization degree of the resin, the solid content of the resin solution, the weight ratio of the solid content of the resin to the glass beads, the functional group and the amount thereof of the resin, a curing agent and a curing catalyst which react with the functional group, and the like have a large influence, and the detailed conditions thereof will be described later.

Next, a method of distinguishing a group of glass spheres that function to maintain the reflection performance at a small observation angle up to a large incident angle; and a group of glass spheres that function to maintain reflection performance at a larger observation angle up to a larger incident angle, and that assume the respective performances.

As shown in fig. 1A, glass spheres 3 are put into a focal layer resin solution 2, and the glass spheres are uniformly dispersed and applied to a surface layer 1 with sufficient stirring. Then, the coating solution is left at room temperature for a certain period of time to remove or break the bubbles mixed in the coating solution. Thereafter, the solvent is volatilized in the heat drying step, and at this time, the glass beads 3 are also settled toward the surface layer 1 (fig. 1B). Specifically, a focus layer resin solution containing glass beads 3 is applied to the surface layer 1 to a predetermined thickness using a knife coater, a comma coater (comma coater), a curtain coater, or the like. As shown in fig. 1B, the coated resin film (hereinafter, also referred to as "WET film") has glass beads 3 randomly (irregularly) distributed in the thickness direction, and when heated, the glass beads in the vicinity of the surface layer 1 settle in the surface layer direction. As shown in fig. 1C, when 50 to 90 wt%, preferably 55 to 85 wt%, and more preferably 60 to 80 wt% of all the glass spheres come into contact with the surface layer 1, the glass spheres are preferably fixed by curing the focus layer resin in order to prevent the glass spheres from settling. The glass spheres 3b in contact with the surface layer 1 mainly serve to maintain the observation angle from 0.2 ° to 2 ° and the incidence angle from 5 ° to less than 90 °. The effect of the reflective properties of (c). In addition, the remaining glass spheres 3a not in contact with the surface layer 1 mainly play a role of maintaining the reflection performance of a larger observation angle from 2 ° to 4 ° and an incidence angle from 5 ° to less than 90 °. As a method of adjusting the thickness of the focal layer at this time, it is also possible to apply a focal layer resin solution in a thin layer so as to be overlapped and applied to the glass spheres 3b in contact with the surface layer 1 so as to have an optimum thickness of the focal layer film that exhibits the highest reflection performance at an observation angle of 0.2 ° and an incidence angle of 5 °, but it is more preferable to set the initial WET film thickness in advance so as to have an optimum thickness of the focal layer film on the glass spheres 3 b.

The focal layer resin solution is volatilized together with the solvent in the drying and curing step, and the focal layer 2 can be formed concentrically by causing volume shrinkage in a state of wrapping the glass spheres 3 at the positions having the glass spheres. As a result, the region where the thickness of the focal layer is uniform becomes an angle α of fig. 1C, which is wider than β of fig. 8C.

The film thickness L1 of the focal layer 2 formed on the glass spheres 3b in contact with the surface layer 1 becomes thicker, and the film thickness L2 of the glass spheres 3a not in contact with the surface layer 1 becomes thinner as the distance from the surface layer 1 increases. The film thickness becomes thin, and the glass sphere has wide-angle reflection performance even at a larger observation angle. By continuously containing these various glass spheres, a wide-angle performance with good balance can be obtained.

The WET film thickness is preferably adjusted to 3.5 to 5.5 times, preferably 3.7 to 5.3 times, and more preferably 4 to 5 times the particle diameter of the glass spheres.

If the WET film thickness is less than 3.5 times, the time for adjusting the glass balls in contact with the surface layer to 50 to 90 wt% is too short, and it is difficult to control the positions of the glass ball groups B and a for distinguishing the reflection performance. If the amount exceeds 5.5 times, the time for adjusting the glass spheres in contact with the surface layer to 50 to 90 wt% becomes too long, the viscosity of the resin excessively increases, and formation of concentric focal layers on the glass spheres is inhibited, which is not preferable.

In order to obtain an optimum focal layer film thickness by the WET film thickness, the solid content of the resin solution is preferably 15 to 25 wt%, preferably 16 to 24 wt%, and more preferably 17 to 23 wt%. If the amount is less than 15 wt%, it is difficult to form a focus layer concentrically on the glass sphere, which is not preferable; if the amount exceeds 25% by weight, fine adjustment of the thickness of the focal layer becomes difficult, and it becomes difficult to control the reflection performance.

The glass beads used in this case are preferably those having titanium oxide as a main component and a refractive index of 2.10 to 2.40, preferably 2.15 to 2.35, and more preferably 2.20 to 2.30. The median particle diameter of the glass spheres is more suitably from 35 μm to 75 μm, preferably from 40 μm to 70 μm. When the thickness is less than 35 μm, desired reflection performance cannot be obtained, and when the thickness exceeds 75 μm, it is difficult to form a concentric focal layer on the glass sphere, which is not preferable.

The resin viscosity at the time of coating is preferably 500 to 3000 mPas, more preferably 700 to 2800 mPas, and still more preferably 900 to 2600 mPas. When the viscosity is less than 500 mPas, the dropping speed of the glass beads dispersed in the resin solution of the focal layer becomes too high, and it becomes difficult to control the positions of the glass beads. Further, the resin flowing from the apex to the side surface of the glass sphere also becomes too fast, and the resin deposited on the bottom side (surface layer side) of the glass sphere becomes too much, which is not preferable because the resin is prevented from being formed concentrically on the glass sphere. When the viscosity exceeds 3000 mPas, the time taken for the glass spheres to reach the surface layer becomes excessively long, and the viscosity of the resin solution increases, so that the glass spheres do not reach the surface layer, and the bubbles in the resin solution are not removed, which is not preferable.

The polymerization degree of the polyvinyl butyral resin suitable for the solid content and viscosity of the resin solution is preferably 500 to 1500, preferably 600 to 1400, and more preferably 700 to 1300. If the polymerization degree is less than 500, the solid content of the resin solution becomes too high, and the adjustment of the film thickness becomes difficult; if the amount exceeds 1500, the solid content becomes too low, and it becomes difficult to form the solid content concentrically, which is not preferable.

Further, the polyvinyl alcohol unit of the aforementioned polyvinyl butyral resin is 17 to 23 wt%, which is suitable in adjusting the curing speed with the curing agent.

In this case, the curing agent which undergoes a crosslinking reaction with the hydroxyl group in the polyvinyl alcohol unit may be an amino resin, an epoxy resin, a polyisocyanate, a blocked polyisocyanate, or the like, and a mixed solvent of an alcohol solvent and an aromatic solvent is mainly used as a solvent for dissolving the polyvinyl butyral resin, and when the alcohol solvent is used, the use of the polyisocyanate and the blocked polyisocyanate is not preferable because the reactivity is inhibited, and an amino resin is preferable. After the curing reaction, the retroreflective sheet can be suitably used because it is not dissolved when immersed in toluene for 1 minute, xylene for 1 minute, or methanol for 10 minutes, and can be printed with screen printing inks containing various organic solvents, or the like, and further exhibits gasoline resistance when used in vehicles or the like.

The glass transition temperature (Tg) of the polyvinyl butyral resin is preferably 60 to 80 ℃, and if it is less than 60 ℃, heat resistance becomes too low when forming a focal layer on a glass sphere, and the resin flows and cannot be formed concentrically, which is not preferable. When the Tg value exceeds 80 ℃, the heat resistance becomes too high, and the fluidity of the resin during heat drying is poor, so that it is difficult to form a concentric focal layer on the glass spheres, which is not preferable.

The mixing ratio of the weight of the resin solid content and the weight of the glass spheres in the focal layer resin solution in which the glass spheres are dispersed is preferably 1.5 to 3.7, more preferably 1.7 to 3.5, and even more preferably 1.9 to 3.2, based on the weight of the resin per unit weight. If less than 1.5, sufficient reflection performance cannot be ensured, so this is not preferable; if the amount exceeds 3.7, the space between the beads disappears, and it becomes difficult to control the position of the glass beads for discriminating the reflection performance of the glass beads in a well-balanced manner, which is not preferable.

In addition, when mixing glass beads into the resin solution, for example, the air to be mixed is mixed as bubbles, and after applying the resin solution to the surface layer, in order to eliminate the bubbles in a short time, it is preferable to add an antifoaming agent, and it is preferable to use a non-silicon antifoaming agent in a subsequent step so as not to hinder adhesion to the metal reflective layer to be provided, and it is more preferable to add 0.01 to 3.0 wt% of the resin weight. Among the above-mentioned non-silicon defoaming agents, an alkyl vinyl ether copolymer is preferably used, and particularly if the alkyl vinyl ether copolymer is added in an amount of 0.02 to 2.0% by weight based on the weight of the resin, a sufficient defoaming effect can be obtained, and adhesion to the metal reflective layer is not impaired, which is more preferable.

The steps subsequent to fig. 1C are the same as the conventional steps. First, as shown in fig. 1D, a metal reflective layer 4 of aluminum or the like is formed on the surface of the focal layer 2 along the focal layer 2. Next, as shown in fig. 1E, a retroreflective sheet was obtained by forming an adhesive layer 5 on a release material 6, pressing the adhesive layer onto a metal reflective layer 4, and performing an integration process (fig. 1F).

The retroreflective sheet thus produced is formed of a surface layer, a focal layer containing glass spheres and a metal reflective layer formed on the surface opposite to the surface layer of the focal layer, and the glass spheres obtained by the present invention are composed of a group of glass spheres which function to maintain retroreflective performance at a small observation angle up to a large incident angle; and glass spheres that maintain retroreflective performance at higher viewing angles up to higher entrance angles, and retroreflective sheeting having ultra-wide angle retroreflective performance is produced.

The retroreflective sheet of the present invention is produced by adding glass spheres to a resin solution for a focal layer, sufficiently stirring the mixture to uniformly disperse the glass spheres, and applying the mixture to a surface layer. Then, the coating solution is left at room temperature for a certain period of time to remove or break the bubbles mixed in the coating solution. In the subsequent drying step, the solvent is volatilized, and at this time, the glass beads are also deposited on the surface layer.

When 50-90% of the glass balls are in contact with the surface layer, the focus layer is cured to fix the glass balls and prevent the glass balls from moving during heating. Further comprising: a metal reflective layer is formed on the focal layer, and a pressure-sensitive adhesive layer and a release material are laminated on the metal reflective layer.

The aforementioned surface layer is formed of at least 1 coating layer and/or resin sheet. In the case of a resin sheet, at least 1 coating layer is preferably formed thereon. Examples of the material of the surface layer include a fluoroolefin copolymer having a reactive functional group, a polyester resin, an alkyd resin, a polyurethane resin, a vinyl resin, and an acrylic polymer having a reactive functional group. The coating layer is preferably a composition containing these resins as a matrix resin component and a curing agent and/or a curing catalyst such as an amino resin, an epoxy resin, a polyisocyanate, or a blocked polyisocyanate. Specifically, for example, when the surface layer is a polyethylene terephthalate film, a resin solution for a focal layer in which the glass spheres are dispersed may be applied to a biaxially oriented polyethylene terephthalate film subjected to an easy adhesion treatment such as corona discharge treatment or resin coating to form a focal layer containing glass spheres; further, after a metal reflective layer is formed on the entire inner surface of the focal layer, and a release material having a pressure-sensitive adhesive laminated thereon is bonded, a composition containing a fluoroolefin copolymer having a reactive functional group, a polyester resin, an alkyd resin, a polyurethane resin, a vinyl resin, or an acrylic polymer having a reactive functional group as a matrix resin component, and a curing agent and/or a curing catalyst such as an amino resin, an epoxy resin, a polyisocyanate, or a blocked polyisocyanate may be mixed with the base resin component to form a second surface layer in a subsequent step. When the fluoroolefin copolymer is used as the second surface layer, it is preferable that an image-forming resin layer containing 0 to 20 wt% of a low molecular weight compound having a molecular weight of about 1300 or less is formed between the fluoroolefin copolymer and the biaxially oriented polyethylene terephthalate film, since the sublimation dye can be heated by sublimation dyeing to permeate the sublimation dye into the image-forming resin layer from the second surface layer and color the image-forming resin layer, and the dye from the image-forming resin layer can be prevented from bleeding. In this case, when the biaxially oriented polyethylene terephthalate film is heated at 150 ℃ for 30 minutes, the sublimation dye is sublimated if the shrinkage rate in the film curling direction is 1.0% or less, and wrinkles and streaks occurring at a heating temperature of 150 ℃ to 190 ℃ at which the sublimation dye penetrates into the image-forming resin layer and is colored can be suppressed, and thus, the biaxially oriented polyethylene terephthalate film is suitable.

If necessary, an ultraviolet absorber, a light stabilizer, and an antioxidant may be added to the composition for forming the surface layer and the composition for forming the image-forming resin layer, or a combination thereof may be added to the compositions. As such an ultraviolet absorber, known ultraviolet absorbers can be used, and as a representative ultraviolet absorber, benzophenones, benzotriazoles, cyanoacrylates, salicylates, oxalic anilides and the like can be used, as a light stabilizer, hindered amine compounds and the like can be used, and as an antioxidant, known compounds such as hindered phenol compounds, amine antioxidants, sulfur antioxidants and the like can be used. However, if a low molecular weight compound-based ultraviolet absorber, light stabilizer or antioxidant is used, phase separation from the transparent resin causes phase generation and bleeding, and the sublimable coloring agent sublimes and penetrates into the image forming resin layer, so that problems such as a volatilization phenomenon during heat treatment are conspicuously caused.

In contrast to the above method, the resin solution containing the resin composition for a surface layer and various ultraviolet absorbers, light stabilizers, antioxidants and the like may be mixed with the various curing agents and/or curing catalysts, coated on a biaxially oriented polyethylene terephthalate film which is not subjected to an easy-adhesion treatment, heated and dried to produce a surface layer, and the resin solution for a focal layer in which the glass spheres are dispersed may be coated to form a focal layer. In this case, after the final lamination step of the adhesive and the release material is completed, the biaxially oriented polyethylene terephthalate film is peeled off to complete the retroreflective sheet of the present invention.

If necessary, the synthetic resin for the surface layer may be laminated and coated on the easily adhesive polyethylene terephthalate film, and after heating and drying, the resin solution for the focal layer in which the glass spheres are dispersed may be coated on the surface layer. In this case, the biaxially oriented polyethylene terephthalate subjected to the easy adhesion treatment is not peeled off, but remains as a part of the surface layer on the final product.

Since the use of the fluoroolefin copolymer composition as the resin composition for the surface resin layer can improve the hydrophobicity, the contact angle between the surface layer and a water droplet adhering to the surface layer becomes large during rain, and the water droplet approaches a perfect sphere due to the surface tension. In this case, the light beam incident on the surface of the retroreflective sheet is refracted when passing through the water droplet, and the light beam enters the retroreflective sheet at a smaller incident angle with respect to the incident angle on the surface of the retroreflective sheet before entering the water droplet. Because of this effect, the use of the fluoroolefin copolymer composition as the resin composition for the surface resin layer is preferable because the reflection luminance value in the rainy weather becomes higher than that in the sunny weather when light rays having a relatively large incident angle are projected onto the surface of the retroreflective sheet. In particular, in rainy weather, since traffic accidents increase, the effect of preventing the traffic accidents from occurring is also improved, and therefore, the present invention is more preferable.

The surface layer used in the present invention is coated with a resin solution for a focal layer in which glass spheres are dispersed, and the resin solution is heated and dried to deposit 50 to 90 wt% of the glass spheres until the glass spheres come into contact with the surface layer, and the glass spheres are prevented from depositing at a position in contact with the surface layer so that the glass spheres that first come into contact with the surface layer do not further deposit into the surface layer, with a difference in time between the glass spheres depositing on the surface layer.

For this reason, it is needless to say that the focal layer is solidified to suppress the sedimentation of the glass spheres as a necessary condition, and as described above, since a time difference is generated by the sedimentation of the glass spheres, in order to prevent the glass spheres which have reached the surface layer initially from further sinking, the surface layer must have a resistance to prevent the glass spheres from sinking. The 1 st property required for the resistance is that the surface layer is in contact with the solvent of the solution for the focal layer without being dissolved, and that the surface layer has the following requirements: softening at a temperature at which the resin for the focal layer is dried and cured, and the glass spheres do not sink into the heat resistance of the surface layer.

If the glass spheres are further sunk into the surface layer, the respective positions of the glass spheres, which are responsible for 50 to 90 wt% of the reflection performance at a relatively small observation angle, are shifted, and the desired reflection performance cannot be achieved. The present inventors have made various studies and, as a result, have confirmed that the desired reflection performance can be achieved and the focal layer can be formed concentrically with the glass spheres if the amount of the glass spheres sinking into the surface layer is controlled to 10% or less of the particle diameter of the glass spheres.

Examples of the resin constituting the pressure-sensitive adhesive layer of the present invention include rubber-based resins such as acrylic resins, natural rubbers, and synthetic rubbers. In particular, as the acrylic resin, a polymer acrylic resin containing at least 1 of an acrylic copolymer and an acrylic prepolymer as main components or a modified acrylic resin obtained by further adding a thickener and a monomer imparting cohesive force to the acrylic resin is suitable.

Further, by using a clear paint containing no pigment or dye as a paint for forming each layer of the retroreflective sheet of the present invention, it is possible to obtain an uncolored retroreflective sheet, and by using a colored paint containing a pigment or dye as a paint for forming each layer, it is also possible to obtain a colored retroreflective sheet. As the pigment used for preparing the colored coating material, known pigments such as organic pigments such as phthalocyanine blue, phthalocyanine green, quinacridone red, hansa yellow and picene orange (Perinone orange) and inorganic pigments such as iron oxide red, iron oxide yellow, titanium white and cobalt blue can be used.

The metal reflective layer may be formed of a metal having a thickness of 5 to 200nm, preferably 10 to 100nm, depending on the metal used. When the thickness of the metal reflective layer is less than 5nm, the concealing property of the metal reflective layer is insufficient and the metal reflective layer cannot be used as a reflective layer, and conversely, when the thickness exceeds 200nm, cracks are likely to occur in the metal reflective layer and the cost is high, which is not preferable. The method for providing the metal reflective layer is not particularly limited, and a commonly used vapor deposition method, sputtering method, transfer method, plasma method, or the like can be used. In particular, from the viewpoint of operability, a vapor deposition method or a sputtering method is preferably used. The metal used for forming the metal reflective layer is also not particularly limited, and examples thereof include metals such as aluminum, gold, silver, copper, nickel, chromium, magnesium, and zinc, and among them, aluminum, chromium, and nickel are particularly preferable in view of workability, easiness of forming the metal reflective layer, durability of light reflection efficiency, and the like. The metal reflective layer may be formed of an alloy of 2 or more kinds of metals.

The drying conditions after coating the coating material for forming the surface layer and the focal layer including the glass spheres are determined depending on the type of the matrix resin used as a coating material, the type of the reactive functional group in the matrix resin, the type of the curing agent, the type and the amount of the curing catalyst added, and the type of the solvent, and thus a desired state is appropriately determined.

Fig. 12 shows a suitable embodiment of the invention arranged on a conventional highway. In the drawing, T1 and T2 denote 1 st and 2 nd traffic lanes, S1 is a side road (e.g., right side road), and E is a roadside. In addition, W is the width of the mark 30. The marking surface is an ultra-wide angle retroreflective sheeting of the present invention. The illumination source 20 is suitably arranged on the roadside with a light emitting illuminator 20a mounted on top of the illumination source 20 emitting reflected light. X is the height from the ground to the bottom of the marking surface, Y is the height of the marking surface itself on the ground, L is the horizontal distance between the illumination source 20 and the road marking 30, and H is the height of the light-emitting illuminator 20a of the illumination source 20 to the ground. The broken line indicates the path of light emitted from light-emitting luminaire 20a facing road sign 30. The optical path forms incident angles θ 1, θ 2, θ 3, θ 4 at respective vertexes a, B, C, D of the road sign 30. The road markings 30 are preferably substantially at right angles to the traffic lanes T1, T2.

The distance from the illumination source to the marking surface in the external illumination type illumination system of the present invention is in the range of 1m to 100 m. In order to effectively utilize the amount of light from the illumination source and reduce the running cost, it is preferable to set the illumination source closer to the marking surface, and within the above range, the distance at which effective reflection performance can be obtained is set in consideration of the incident angle, the observation angle, the size of the marking dimension, and the installation height of the marking surface.

The illumination source emits light incident on the marking surface at an incident angle in a range of 0 ° to 50 ° with respect to the marking surface, and when the standard light a having a color temperature of 2,856K is incident on the marking surface at an incident angle of 35 °, the illumination source preferably has a reflection performance of 0.07 or more at an observation angle of 35 °. Wherein the incident angle is an angle formed by an irradiation axis of the projected light and a normal line of a surface center of the retroreflective sheet; the observation angle is an angle formed by an irradiation axis and an observation axis of the projected light; the reflection property is a coefficient calculated by the following numerical expression.

Coefficient of retroreflection R' ═ I/ES.A

R': coefficient of retroreflection

ES: illuminance (1x) on a plane perpendicular to the incident light among the incident lights at the center of the test piece

A: surface area (m) of test piece²)

I: the luminance (Cd) in the observation axis direction of the test piece was calculated from the following equation.

I＝Er·d²

Wherein, Er: illuminance on the light receptor (1x)

d: distance (m) between center of test piece surface and light receiver

When the standard light a having a color temperature of 2,856K is externally irradiated onto the label surface, the reflection performance at an observation angle of 5 ° and an incident angle of 50 ° is preferably 0.5 or more, and the reflection performance at an observation angle of 40 ° and an incident angle of 50 ° is preferably 0.055 or more.

In this way, since the reflection performance is excellent at both a larger incident angle and a larger observation angle, the illumination source can be installed closer to each other, the light amount of the illumination source can be reduced, and the maintenance cost can be reduced, which is preferable.

As described above, the retroreflective sheet of the present invention can exhibit high retroreflection even when light is incident from a wide angle position, and can enlarge the observation angle. Furthermore, the retroreflective performance of the marking standard of the enclosed-lens retroreflective sheet that is suitable for the world is ensured, and sufficient retroreflective performance can be maintained even at an incident angle of more than 50 ° specified in the standard. That is, by including a glass sphere group in the same focal layer to maintain sufficient retroreflection performance at an incidence angle of 2 ° or less and more than 50 ° at an observation angle; and a group of glass spheres that maintain retroreflection performance at an incidence angle greater than 50 ° and greater than 2 ° of an observation angle specified in the specification, wherein the group of glass spheres that each function is used separately, and wide-angle retroreflection performance can be maintained even at an incidence angle greater than 50 ° and greater than 4 ° which is about 2 times as large as the observation angle of the existing product. When used in an external illumination system, the retroreflective sheeting exhibits high reflectivity as compared with conventional capsule lens retroreflective sheeting having a wide observation angle.

Examples

The present invention will be described below with reference to examples. The following examples employ the previously described procedures of FIGS. 1A-F. The numerical values of "part" and "%" indicating the mixing ratio in examples mean part by weight or% by weight, unless otherwise specified.

The methods of the measurement tests performed in examples and comparative examples are as follows.

(1) Reflection performance

The reflection properties were measured by a method for measuring the reflection properties according to JIS Z9117 using a color luminance meter (manufactured by Topcon corporation). The reflection performance was measured by combining various observation angles and incidence angles.

(2) Method for determining the proportion of glass spheres in contact with the No. 1 surface layer

The cross-sectional structure of the sheet was analyzed using an ultra-deep shape measuring microscope (manufactured by Keyence corporation) or an optical microscope (manufactured by Nikon corporation), and the ratio of the glass sphere group a to the glass sphere group B was measured.

(example 1)

A glass-sphere-dispersed resin solution described below as a focal layer was applied to an annealed biaxially oriented polyethylene terephthalate Film (trade name MX534 manufactured by Teijin DuPont Film Co., Ltd., shrinkage rate in the Film curling direction when heated at 150 ℃ for 30 minutes was 0.3%, Film thickness was 97 μm) used as a first surface layer.

(1) Polyvinyl butyral resin solution: 75.0 parts (degree of polymerization: 680, 23% by weight of polyvinyl alcohol units, glass transition temperature 66 ℃, 21% solids, n-butanol/toluene 1: 1)

(2) Super Beckamine J-820-60: 3.3 parts (butylated melamine resin, solid content 60%, manufactured by Dainippon ink chemical industries, Ltd.)

(3) Beckamine P-198: 0.2 part (curing accelerator, acid value 400, manufactured by Dainippon ink chemical industries, Ltd.)

(4) BYK-053: 0.5 part (alkyl vinyl ether copolymer, antifoaming agent, BYK Chemie Japan Co., Ltd.)

(5) Polysider W-360-ELS: 7.0 parts (manufactured by Dainippon ink chemical industries, Ltd., Polymer plasticizer)

(6) Toluene: 7.6 parts of

(7) N-butanol: 7.6 parts of

(8) Glass ball: 68.0 parts (90% or more of particles having a median diameter of 50 μm or within a range of. + -. 10 μm, and a refractive index of 2.25. + -. 0.05)

The viscosity of the mixed resin (excluding glass spheres) coating was 1900mPa · s.

The WET film thickness is adjusted, and the glass ball dispersion resin solution is coated on the first surface layer, so that a focus layer is formed on the focus position (the dry film thickness from the top of the glass ball is about 13-14 μm) of the glass ball contacting the first surface layer.

Thereafter, the resin was dried at room temperature for about 5 minutes, and in the subsequent steps, the resin was dried at 100 ℃ for 5 minutes and then heated at 140 ℃ for 10 minutes to cure the focal layer resin.

Next, aluminum was used as a metal reflective layer, and the metal reflective layer was attached to the focal layer by vacuum evaporation so that the film thickness became 80 nm.

A mixed solution of 100 parts by weight of acrylic adhesive Finetack SPS-1016 (manufactured by Dainippon ink chemical industries, Ltd.) and 1 part by weight of crosslinking agent DN-750-45 (manufactured by Dainippon ink chemical industries, Ltd.) was applied to the silicon-coated surface of a separately prepared silicon-coated release paper, and dried at 100 ℃ for 5 minutes to prepare an adhesive layer having a thickness of 50 μm.

Next, the adhesive layer surface and the metal reflective layer surface are bonded to each other to form a final product. At this time, the glass sphere in contact with the first surface layer was about 67%.

Before forming the metal layer, the intermediate product was immersed in toluene for 1 minute, xylene for 1 minute, and methanol for 10 minutes in various solutions, and thus the focal layer was not dissolved.

(example 2)

A biaxially oriented polyethylene terephthalate Film (trade name MX534 manufactured by TeijinnDuPont Film Co., Ltd., the shrinkage rate in the Film curling direction when heated at 150 ℃ for 30 minutes was 0.3%, and the Film thickness was 97 μm) which had been annealed was coated with the following glass bead resin dispersion solution.

(1) Polyvinyl butyral resin solution: 98.0 parts (degree of polymerization: 1100, polyvinyl alcohol unit 18 wt%, glass transition temperature 76 ℃, solid content 16%, n-butanol/toluene 1: 1)

(2) Beckamine P-196-M: 3.0 parts (butylated Urea resin, solid content 60%, manufactured by Dainippon ink chemical industries, Ltd.)

(3) Beckamine P-198: 0.1 part (curing accelerator, acid value 400, manufactured by Dainippon ink chemical industries, Ltd.)

(4) BYK-053: 0.5 part (alkyl vinyl ether copolymer, antifoaming agent, BYK Chemie Japan Co., Ltd.)

(5) PolysiderW-360-ELS: 2.0 part (manufactured by Dainippon ink chemical industries Co., Ltd., Polymer plasticizer)

(6) DIDP: 2.0 parts (phthalate, plasticizer)

(7) Toluene: 8.0 parts of

(8) N-butanol: 8.0 parts of

(9) Glass ball: 60.0 parts (90% or more of particles having a median diameter of 50 μm or + -10 μm, and a refractive index of 2.25 + -0.05)

The viscosity of the mixed resin (excluding glass spheres) was 1100mPa · s when applied.

The WET film thickness was adjusted in the same manner as in example 1, and the above glass bead-dispersed resin solution was applied to the surface layer so that a focal layer was formed at the focal position of the glass beads in contact with the first surface layer.

Thereafter, the resin layer was dried at room temperature for 3 minutes, and in the subsequent steps, the resin layer was dried at 100 ℃ for 3 minutes and then heated at 150 ℃ for 5 minutes to cure the focal resin layer.

Next, aluminum was used as a metal reflective layer, and the metal reflective layer was attached to the focal layer by vacuum evaporation so that the film thickness became 80 nm.

A mixed solution of 100 parts by weight of acrylic pressure-sensitive adhesive Finet ack SPS-1016 (manufactured by Dainippon ink chemical industries, Ltd.) and 1 part by weight of crosslinking agent DN-750-45 (manufactured by Dainippon ink chemical industries, Ltd.) was applied to a silicon-coated surface of a separately prepared silicon-coated release Film (manufactured by Teijin DuPont Film, trade name A-31, shrinkage in the Film curling direction when heated at 150 ℃ for 30 minutes was 0.4%), and dried at 100 ℃ for 5 minutes to produce a pressure-sensitive adhesive layer having a thickness of 50 μm.

Next, the adhesive layer surface and the metal reflective layer surface are bonded together.

Then, the following resin composition was applied to the first surface layer so that the dry film thickness became about 30 μm, and the resultant was dried by heating at about 140 ℃ for about 10 minutes to obtain an image-forming resin layer.

A mixed example of the resin composition is that Burnock D6-439 (manufactured by Dainippon ink chemical industries, alkyd resin, solid content hydroxyl value 140, non-volatile content 80%) is about 100 parts, Bumock DN-980 (manufactured by Dainippon ink chemical industries, polyisocyanate prepolymer, non-volatile content 75%) as a curing agent is about 82 parts, Tinuvin900 (manufactured by Ciba-Geigy Chemicals, ultraviolet absorber) is about 1 part, Tinuvin 292 (manufactured by Ciba-Geigy Chemicals, antioxidant) is about 1 part. The low-molecular-weight compound having a molecular weight of 1300 or less contained in the obtained image-forming resin layer is less than 5%.

Further, the following resin composition was applied onto the image forming resin layer so that the dry film thickness was about 20 μm, and the resultant was dried by heating at about 140 ℃ for about 10 minutes to obtain a second surface layer.

Fluoronate K-703 (weight average molecular weight 40000, hydroxyl value in solid state 72, and nonvolatile content of about 60%, manufactured by Dainippon chemical industries, Ltd.) was used as the fluororesin, Burnock DN-950 was used as the curing agent, Tinuvin900 was used as the ultraviolet absorber, and Tinuvin 292 was used as the antioxidant. The resin composition for the second surface layer in this example 2 was mixed in such a ratio that Fluoronate K-703 was about 100 parts, BurnockDN-950 was about 25 parts, Tinuvin900 was about 1 part, DICTON WHITE A-5260 (titanium oxide, solid content 75%) was about 15 parts, and Tinuvin 292 was about 1 part.

The retroreflective sheet having a super-wide angle property thus produced is preferably such that a sublimable coloring agent penetrates into the image-forming resin layer from the second surface layer by heating by a sublimation coloring method to thereby color the sheet, and the penetration of the dye from the image-forming resin layer is preferably carried out in a 2000-hour test in accordance with the light irradiation accelerated weather resistance test specified in JIS Z9117, whereby the dye does not cause bleeding.

Additionally, in the retroreflective sheeting made in example 2, the glass spheres contacting the first surface layer were about 78%.

Before forming the metal reflective layer, the intermediate product was immersed in toluene for 1 minute, xylene for 1 minute, and methanol for 10 minutes, so that the focal layer was not dissolved.

Comparative example 1

A resin composition for surface layer was prepared from 100 parts of Bekkolite M-6401-50 (polyester resin, manufactured by Dainippon ink chemical industries Co., Ltd.), 20 parts of Super Beckamine J-820-60 and 1 part of Beckamine P-198.

The composition was coated on a support film so that the dry film thickness became 50 μm, and dried at 140 ℃ for 5 minutes, thereby obtaining a surface layer.

Next, the resin composition for a glass bead fixing layer was adjusted with 100 parts of Bekkolite M-6401-50, 10 parts of Super Beckamine J-820-60 and 0.5 part of Beckamine P-198. The composition was applied to the surface layer so that the dry film thickness was about 70% of the particle diameter of the glass spheres, dried at room temperature to volatilize the solvent, embedded in the glass spheres, and dried at 140 ℃ for 5 minutes. The glass beads used are high-refractive-index glass beads containing titanium oxide as a main component, having a refractive index of 2.23 and a particle diameter of about 55 to 65 μm. The glass beads are embedded as shown in fig. 8A.

Next, a resin composition for a focus layer was adjusted from a urethane resin, 100 parts of Bumock L8-974 (manufactured by Dainippon ink chemical industries, Ltd.), and 10 parts of Super Beckamine J-820-60.

The resin composition was applied so that the dry film thickness of the focal layer laminated on the inner surface apex of the glass sphere was about 15 μm, dried at 100 ℃ for 10 minutes, and then dried by heating at 140 ℃ for 10 minutes.

Next, aluminum was used as a metal reflective layer, and the metal reflective layer was attached to the focal layer by vacuum deposition so that the film thickness became 60nm, thereby producing a retroreflective sheet having the structure of fig. 8C.

A mixed solution of 100 parts by weight of acrylic adhesive Finetack SPS-1016 (manufactured by Dainippon ink chemical industries, Ltd.) and 1 part by weight of crosslinking agent DN-750-45 (manufactured by Dainippon ink chemical industries, Ltd.) was applied to the silicon-coated surface of a separately prepared silicon-coated release paper, and dried at 100 ℃ for 5 minutes to prepare an adhesive layer having a thickness of 35 μm.

After the adhesive layer surface and the metal reflective layer surface were bonded, the support film was peeled off to obtain a conventional enclosed-lens retroreflective sheet.

Comparative example 2

In comparative example 1, the resin composition for the focal layer was applied so that the dry film thickness of the focal layer laminated at the apex of the inner surface of the glass sphere was about 15 μm, whereas in comparative example 2, the aforementioned about 15 μm was set to about 12 μm, to improve the reflection performance at a large observation angle. The rest is the same as in comparative example 1.

This structure corresponds to the enclosed-lens wide-angle retroreflective sheet of patent document 4.

The measurement results of the observation angle and the incidence angle of the retroreflective sheet manufactured as described above and the 1 st order reflection performance defined in JISZ9117 are shown in table 1.

However, table 1 does not describe the reflection performance at observation angles of 20' (0.33 °), and incidence angles of 5 °, 30 °, and 40 °, and the reflection performance is 65, 53, and 42 for the retroreflective sheet of example 1, and 77, 65, and 51 for example 2. The grade 1 reflection properties specified in JIS Z9117 were 50, 24 and 9.0, respectively, and the retroreflective sheets of examples 1 and 2 met the grade 1 reflection properties specified in JIS Z9117.

Comparative example 3

Further, a commercially available capsule lens type retroreflective sheet having a wide observation angle property (HV-8100 white, high-brightness wide-angle retroreflective sheet manufactured by 3M) used in the marker illumination system of patent document 5 was used as comparative example 3, and the retroreflective performance was compared with that of the retroreflective sheet of example 1 of the present invention. The values are shown in Table 2.

The irradiation light in tables 1 to 2 is standard light A having a color temperature of 2,856K.

(example 3)

A glass sphere dispersion resin solution for a focal layer was produced in the same manner as in example 1. Next, in order to produce yellow, red, orange, green, and blue retroreflective sheeting, the following coloring materials were mixed into the focusing layer glass bead dispersion resin solutions having different colors.

(1) Yellow focal layer glass sphere dispersion resin solution: 0.2g of a 20% solution of AWB-CP201 orange (manufactured by Nikko Bics: pigment concentration 40%) in toluene/n-butanol (1/1), 3.5g of a 20% solution of AWB-CP310 yellow (manufactured by Nikko Bics: pigment concentration 50%) in toluene/n-butanol (1/1)

(2) Red focal layer glass sphere dispersion resin solution: 5.5g of a 20% solution of AWB-CP102 red (manufactured by Nikko Bics: pigment concentration 50%) in toluene/n-butanol (1/1)

(3) Orange focus layer glass sphere dispersion resin solution: 4.9g of a 20% solution of AWB-CP201 orange (manufactured by Nikko Bics: pigment concentration 40%) in toluene/n-butanol (1/1)

(4) Green focus layer glass sphere dispersion resin solution: 0.5g of a 20% solution of AWB-CP310 yellow (manufactured by Nikko Bics: pigment concentration 50%) in toluene/n-butanol (1/1), 8.0g of a 20% solution of AWB-CP400 green (manufactured by Nikko Bics: pigment concentration 50%) in toluene/n-butanol (1/1)

(5) Resin solution for blue focus layer glass sphere dispersion: 0.14g of a 20% solution of AWB-CP102 red (manufactured by Nikko Bics: pigment concentration 50%) in toluene/n-butanol (1/1), 7.5g of a 20% solution of AWB-CP650 blue (manufactured by Nikko Bics: pigment concentration 45%) in toluene/n-butanol (1/1)

Retroreflective sheeting of each color was produced in the same manner as in example 1 using the focal layer glass sphere dispersion resin solution for each color produced above. The reflection properties at this time are shown in table 3.

The color of these reflective sheets was measured according to the measurement method defined in table 2 of JIS Z9117, and all the colors were within the range of chromaticity coordinates defined in table 2 of JIS Z91174 (1).

TABLE 1

Observation angle	Angle of incidence	JIS specification grade 1	Example 1	Example 2	Comparative example 1	Comparative example 2
							0.2°	+5°	70	88	110	104	30
+30°	30	66	85	55	17
						+40°		10	-	-	-	-
+50°	-	34	42	9.5	13
						+70°		-	7.1	8.5	0.4	3.0
+80°	-	0.9	1.1	0.01	0.4
						2.0°		+5°	5.0	8.4	6.8	7.2	4.8
+30°	2.5	6.6	5.3	5.6	4.6
							+40°	1.5	-	-	-	-
+50°	-	5.5	4.4	2.6	5.0
							+70°	-	1.4	1.1	0.6	1.8
+80°	-	0.5	0.4	0.04	0.3
							4.0°	+5°	-	3.8	2.2	2.4	1.6
+30°	-	3.1	2.0	2.3	1.5
						+50°		-	2.6	1.7	1.3	1.4
+70°	-	1.1	0.8	0.2	0.8
						+80°		-	0.3	0.2	0.01	0.2

TABLE 2

Observation angle	Angle of incidence	JIS specification grade 1	Example 1	Comparative example 3
					5°	+5°	-	1.386	0.867
+30°	-	1.099	0.545
				+40°		-	1.017	0.391
+50°	-	0.974	0.267
				35°		+5°	-	0.189	0.133
+30°	-	0.144	0.094
					+40°	-	0.100	0.074
+50°	-	0.069	0.047
					40°	+5°	-	0.154	0.121
+30°	-	0.123	0.104
				+40°		-	0.091	0.089
+50°	-	0.069	0.047

The data in tables 1 and 2 are graphed as shown in FIGS. 2 to 4 and FIGS. 9 to 11. Fig. 2 is a measurement curve of the incident angle and the reflection performance at an observation angle of 0.2 °, fig. 3 is a measurement curve of the incident angle and the reflection performance at an observation angle of 2.0 °, and fig. 4 is a measurement curve of the incident angle and the reflection performance at an observation angle of 4.0 °. Fig. 9 is a measurement curve of the incident angle and the reflection performance at an observation angle of 5 °, fig. 10 is a measurement curve of the incident angle and the reflection performance at an observation angle of 35 °, and fig. 11 is a measurement curve of the incident angle and the reflection performance at an observation angle of 40 °.

As shown in table 1 and fig. 2 to 4, the retroreflective sheet of examples 1 to 2 of the present invention can exhibit high retroreflection even when light enters from a wide angle position, and can enlarge the observation angle. Further, the retroreflective sheet has retroreflective performance conforming to the marking standard of a worldwide enclosed-lens retroreflective sheet. That is, it can be confirmed that: a glass sphere group which can maintain sufficient retroreflection performance at an incident angle of 2 ° or less and more than 50 ° as an observation angle determined in specifications is included in the same focal layer; and glass ball groups that function to maintain retroreflection performance at an observation angle greater than 2 ° and an incidence angle greater than 50 °, and thus the glass ball groups that function to separate each other are used, so that wide-angle retroreflection performance can be maintained even at an observation angle 4 ° greater than about 2 times greater and an incidence angle greater than 50 ° as compared with existing products.

FIG. 5 is a sublimation coloring method for coloring by allowing a sublimation coloring agent to permeate into the inside of an image-forming resin layer, forming an image, and applying to the case of printing a photograph, the upper photograph "HI" being a conventional capsule lens-type high-brightness retroreflective sheet, and the lower photograph "wide-angle reflection" being the retroreflective sheet of example 2 of the present invention; a is incident light from an angle of 5 DEG to the panel and a photograph taken at an observation angle position of 2 DEG, B is incident light from an angle of 50 DEG to the panel and a photograph taken at an observation angle position of 2 DEG, and C is incident light from an angle of 70 DEG to the panel and a photograph taken at an observation angle position of 2 deg. As is apparent from fig. 5, the example of the present invention can perform high retroreflection even when light is incident from a wide angle position, and can enlarge the observation angle.

Fig. 6 is a view assuming an orientation mark on the road surface, where a is day time, B is night time, the right photograph "HI" is a conventional high-brightness retroreflective sheet of the capsule lens type, and the left photograph "wide-angle retroreflection" is a retroreflective sheet of example 1 of the present invention. The photograph of night B is a photograph taken at an observation angle of 4 ° with incident light at an angle of 70 ° with respect to the road sign. As is apparent from fig. 6, the example (left side) of the present invention can perform high retroreflection even when light is incident from a wide-angle position at night, and can enlarge the observation angle.

In addition, table 2 and fig. 9 to 11 show that the retroreflective sheet of example 1 of the present invention has excellent reflection performance at larger observation angles of 5 °, 35 °, and 40 ° and larger incident angles of 5 °, 30 °, 40 °, and 50 ° compared to commercially available capsule lens type retroreflective sheets having wide observation angle performance. That is, even when used in an external illumination type distance illumination system, it can exhibit very excellent reflection performance as compared with a capsule lens type retroreflective sheet having wide-angle performance which is currently commercially available.

Next, the reflection properties of the retroreflective sheet of example 3 of the present invention are shown in table 3.

[ Table 3]

Observation angle	Angle of incidence	Yellow colour	Red colour	Orange colour	Green colour	Blue color
							0.2°	+5°	62	24	46	26	8.8
+30°	46	16	34	18	5.9
						+40°		35	11	27	13	4.3
+50°	24	8.6	18	9.7	3.6
						+70°		5.0	1.8	3.7	2.1	0.8
+80°	0.6	0.3	0.5	0.2	0.1
						2.0°		+5°	5.9	2.4	4.3	2.6	0.9
+30°	4.8	1.8	3.6	2.0	0.7
							+40°	-	-	-	-	-
+50°	3.7	1.5	2.6	1.6	0.6
							+70°	1.0	0.4	0.8	0.5	0.1
+80°	0.4	0.1	0.3	0.2	0.05
							4.0°	+5°	2.8	1.1	1.9	1.3	0.5
+30°	2.1	0.8	1.6	0.9	0.3
						+50°		1.9	0.7	1.5	0.8	0.3
+70°	0.8	0.3	0.6	0.3	0.1
						+80°		0.2	0.1	0.2	0.1	0.03

As can be seen from table 3, the retroreflective sheet of example 3 of the present invention has a reflection performance exceeding the reference value defined for each color, and it is confirmed that the retroreflective sheet of the present invention can exhibit excellent reflection performance even for a color.

The retroreflective sheet of the present invention can be used for various purposes such as traffic signs, guide signs, warning signs, control signs, automobile number plates, advertising boards, printed photographs, and the like. In addition, it can be used for external illumination type long distance lighting system.

Claims (21)

1. A retroreflective sheeting comprising: the optical element comprises a surface layer composed of at least 1 layer, a focal layer including glass spheres arranged at any position in the thickness direction of the focal layer, and a metal reflective layer provided on the inner surface side of the focal layer along the glass spheres.

2. The retroreflective sheeting of claim 1, wherein the glass spheres comprise a population of glass spheres B in contact with the surface layer and a population of glass spheres A located away from the surface layer, the population of glass spheres A having retroreflective properties at an observation angle greater than the observation angle of the population of glass spheres B.

3. The retroreflective sheet according to claim 1, wherein the glass spheres comprise a group of glass spheres B in contact with the surface layer and a group of glass spheres a at a position away from the surface layer, the metal reflective layer of the group of glass spheres B being formed at a focal point formation position, the focal layer thickness of the group of glass spheres a being thinner than the focal layer thickness of the group of glass spheres B, the group of glass spheres a having retroreflective properties at a relatively larger observation angle than the group of glass spheres B.

4. The retroreflective sheet according to claim 1, wherein the glass spheres comprise a group B of glass spheres in contact with the surface layer and a group a of glass spheres located away from the surface layer, and the focal layer formed concentrically on the surface of the glass spheres of the group B of glass spheres has a film thickness that exhibits the highest reflection performance at an observation angle of 0.2 ° and an incidence angle of 5 °; the thickness of the focal layer of the glass sphere group A is smaller than that of the focal layer of the glass sphere group B, and the glass sphere group A has retroreflection performance at a larger observation angle than the glass sphere group B.

5. The retroreflective sheeting of any of claims 2-4, wherein the proportion of glass spheres contacting the face layer is 50-90 wt.% of all glass spheres.

6. The retroreflective sheeting of any of claims 1-4, wherein the glass spheres have a refractive index of 2.10 to 2.40.

7. The retroreflective sheet according to any one of claims 1 to 4, wherein the glass spheres have a median diameter in the range of 35 μm to 75 μm, and 80% or more of the glass spheres are in the range of (median diameter-10 μm) to (median diameter +10 μm).

8. The retroreflective sheet according to any one of claims 1 to 4, wherein the resin constituting the focal layer is a polyvinyl acetal resin as a main component.

9. The retroreflective sheet according to claim 8, wherein the polyvinyl acetal resin is a polyvinyl butyral resin having a polymerization degree of 500 to 1500.

10. The retroreflective sheeting of claim 9, wherein the polyvinyl alcohol units of polyvinyl butyral are present in an amount of 17 wt% to 23 wt%.

11. The retroreflective sheet of claim 9 or 10, wherein the polyvinyl butyral resin has a glass transition temperature of 60 ℃ to 80 ℃.

12. The retroreflective sheet according to claim 9 or 10, wherein a hydroxyl group in a polyvinyl alcohol unit of the polyvinyl butyral resin is subjected to a crosslinking reaction with an amino resin, and the focal layer is a layer that does not dissolve when immersed in toluene for 1 minute, xylene for 1 minute, or methanol for 10 minutes.

13. The retroreflective sheet according to any one of claims 1 to 4, wherein the focal layer has a resin weight and glass spheres mixed in a ratio of 1.5 to 3.7 in terms of glass sphere weight per unit weight of resin.

14. The retroreflective sheet according to any one of claims 1 to 4, wherein the focusing layer contains a non-silicon defoaming agent in an amount of 0.01 to 3.0% by weight based on the resin of the focusing layer.

15. The retroreflective sheeting of claim 14, wherein the non-silicon defoamer is an alkyl vinyl ether copolymer.

16. The retroreflective sheeting of claim 1, wherein the surface layer contains at least 1 coating layer or at least 1 coating layer formed on the resin sheeting, and the coating layer is a composition obtained by mixing at least 1 resin component selected from the group consisting of fluoroolefin copolymers having a reactive functional group, polyester resins, alkyd resins, polyurethane resins, vinyl resins and acrylic polymers having a reactive functional group, and at least 1 curing agent and/or curing catalyst selected from the group consisting of amino resins, epoxy resins, polyisocyanates and blocked polyisocyanates.

17. The retroreflective sheeting of claim 1, wherein the surface layer comprises at least 1 coating layer or at least 1 coating layer formed on a resin sheeting, the outermost coating layer being a fluoroolefin-based copolymer composition.

18. The retroreflective sheeting of claim 16, wherein the resin component of the coating layer is a fluoroolefin copolymer having reactive functional groups.

19. An external illumination system comprising a sign having a sign face comprising the retroreflective sheet according to any one of claims 1 to 18 and an external illumination source, wherein the distance from the illumination source to the sign face is 1m to 100 m.

20. The illumination system of claim 19, wherein the illumination source emits light incident on the marking surface at an incident angle in a range of 0 ° to 50 ° with respect to the marking surface, and the marking surface has a reflectance of 0.07 or more at an observation angle of 35 ° when the standard light a having a color temperature of 2,856K is incident at an incident angle of 35 °;

wherein the incident angle is an angle formed by an irradiation axis of the projected light and a normal line of a surface center of the retroreflective sheet; the observation angle is an angle formed by an irradiation axis and an observation axis of the projected light; the reflection performance is a coefficient calculated by the following mathematical formula;

coefficient of retroreflection R' ═ I/ES.A

R': coefficient of retroreflection

ES: illuminance in a plane perpendicular to the incident light among the incident lights at the center of the test piece in a unit of 1 ×

A: surface area of test piece, the unit of surface area is m²

I: the luminance in Cd is obtained from the following formula by using a luminance meter for measuring the luminance of a test piece in the direction of the observation axis

I＝Er·d²

Wherein, Er: illuminance on the light receiver in units of 1 ×

d: the distance between the center of the test piece surface and the light receiver is in m.

21. The exterior illumination system according to claim 19, wherein when the standard light a having a color temperature of 2,856K is externally applied to the label surface, the reflectance at an observation angle of 5 ° and an incident angle of 50 ° is 0.5 or more, and the reflectance at an observation angle of 40 ° and an incident angle of 50 ° is 0.055 or more.