JP3123693B2 - Retroreflective sheet - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a road sign, a construction sign,
The present invention relates to a retroreflective sheet useful for use as a license plate for vehicles such as automobiles and motorcycles, clothing, and safety materials such as lifesaving tools, and marking for signboards and the like.

[0002]

2. Description of the Related Art Conventionally, a retroreflective sheet for retroreflecting light toward a light source is well known. By utilizing the retroreflective property, the sheet can be used for road signs, construction signs, vehicle license plates, and the like. It is widely used in the fields of materials for safety, display marking of signboards and the like.

[0003] Retroreflective sheets are roughly classified into five types according to the difference in structure for obtaining the retroreflective properties.

One type is described in, for example, Japanese Patent Publication No. 48-28837, in which a microsphere such as a glass bead is used as a lens, and a transparent resin layer and a metal vapor-deposited film are provided on the back of the microsphere. A light-reflective layer is disposed such that the light-reflective layer is substantially at the focal position of the microsphere lens, and the microsphere is embedded with another transparent resin of the same or different kind, which is generally called an encapsulated lens type. It is a retroreflective sheet.

[0005] One is described in, for example, Japanese Patent Publication No. 61-13561, in which a microsphere such as a glass bead is used as a lens in the same manner as described above, and a metal deposition film is directly formed on the back of the microsphere. Etc., and the microspheres are half-buried in the resin fixing layer so as to embed the light reflection layer, and a protective film is formed on the top of the microspheres so that the air layer is encapsulated. It is a retroreflective sheet generally called a capsule lens type.

Further, for example, as described in JP-A-57-189839, the protective film of the capsule lens type retroreflective sheet is not provided, that is, the protective film is provided on the back of a microsphere lens such as a glass bead. This is a retroreflective sheet generally called an open lens type in which a metal vapor deposition film is directly provided, and the microspheres are only half-buried in a resin fixing layer so as to embed a layer of the metal vapor deposition film.

[0007] Still another one is, for example, as described in JP-B-61-13561, which is similar to that described above, and is provided on the back surface of a top film having a cube corner shape which geometrically satisfies the retroreflection condition. This is a retroreflective sheet generally called a capsule cube corner type in which a covering sheet is arranged so that an air layer is closed in a capsule shape.

Still another is that, similarly to the above, a top film having a cube corner shape which geometrically satisfies the retroreflection condition, and a light reflection layer such as a metal deposition film is directly provided on the back surface of the cube corner shape. This is a retroreflective sheet provided, generally called a metallized cube corner type.

These five types of retroreflective sheets are widely used in the above-mentioned application fields by utilizing their respective characteristics.

[0010]

However, these conventional retroreflective sheets have various problems as described below.

First, an encapsulated lens type, a capsule lens type,
In a retroreflective sheet of the type that reflects light using a light reflective layer such as a metal vapor-deposited film such as an open lens type or even a metallized cube corner type retroreflective sheet, the light reflective layer inevitably exhibits a metallic color. In the case where the layer containing the retroreflective element on the light reflecting layer is a chromatic or achromatic light transmissive layer, a retroreflective sheet excellent in whiteness and chroma cannot be obtained. That is. Also, for the capsule lens type retroreflective sheet, a complicated process for enclosing air in a capsule shape is inevitable.

In a capsule cube corner type retroreflective sheet, light is totally reflected by utilizing a large difference in refractive index between a cube corner-shaped resin layer which is a retroreflective element and an air layer existing on the back surface thereof. Therefore, there is no problem that a retroreflective sheet having excellent whiteness and chroma as described above cannot be obtained, but a complicated process for enclosing air in a capsule shape is inevitable as in the case of a capsule lens type retroreflective sheet. .

In addition, these conventional retroreflective sheets usually have at least 4
The sheet is composed of layers, in many cases 6 to 7 layers, and more layers, and the production of the sheet is inevitable.

Accordingly, it is an object of the present invention to provide a retroreflective sheet which has excellent whiteness and chroma and can be manufactured by a very simple process.

As a result of various studies on retroreflective sheets having various configurations, the present inventors have found that a resin layer having a plurality of recesses smaller than the number of retroreflective elements on the surface is used as a back layer of the retroreflective element. It has been found that the above problem can be solved by enclosing a low refractive index gas such as air between the light transmitting layer and the light transmitting layer including the retroreflective element.

Thus, according to the present invention, a light transmissive layer including a retroreflective element and a resin back layer having a plurality of recesses smaller than the number of retroreflective elements on the surface are provided with a large number of recesses on the surface of the back layer. A retroreflective sheet characterized by being laminated while maintaining a state, a light transmissive layer including a retroreflective element, and a resin back layer having a surface with a plurality of recesses smaller than the retroreflective element Are laminated on the surface of the back layer while maintaining a state of a large number of dents, wherein a resin back layer in which dents are formed in advance, and a light-transmitting layer And a method of manufacturing a retroreflective sheeting, characterized in that:

Hereinafter, the present invention will be described in more detail with reference to the cross-sectional views of the retroreflective sheet shown in FIGS.

In the retroreflective sheet of the present invention, the upper layer comprises a light transmitting layer containing a retroreflective element. The light transmissive layer is not particularly limited as long as it does not have a light reflective layer such as a light non-transmissive metal vapor-deposited film.

For example, in the case of a cube corner type retroreflective sheet as shown in FIG. 1, the light transmitting layer (1)
Is a sheet-shaped material having transparency and a cube corner shape provided on one surface.

In the case of an encapsulated lens type retroreflective sheet as shown in FIG. 2, the light-transmitting layer (1 ') is made of, for example, microspheres (11) such as glass beads used as a lens. Almost hemispherical surface of the sphere (11) is buried, and the adjacent resin back layer
A focusing layer (12) provided on the surface of (3) so that the focus of the microsphere lens comes, and a fixing layer (13) for embedding the remaining hemisphere of the microsphere (11) and fixing the microsphere. ) And a coating layer (14) laminated on the outer surface of the fixing layer.

In the case of an open lens type retroreflective sheet as shown in FIG. 3, the light transmissive layer (1 ") is composed of a layer of microspheres (11) such as glass beads used as a lens. ing.

Furthermore, in the case of a capsule lens type retroreflective sheet as shown in FIG. 4, the light transmitting layer (1 "')
Are microspheres (1
1), a coating layer (14) provided via an air layer (16) above the microspheres (11) in which a substantially hemispherical surface is embedded in an adjacent resin back layer (3), and the resin back layer It is composed of a mesh-like connecting part tissue (15) for joining the microsphere (11) and the air layer (16) by encapsulating the microsphere (11) and the coating layer (14).

Of these, the light transmissive layer used in the retroreflective sheet of the present invention has a relatively easy total reflection condition, a high retroreflective efficiency, and a simple and relatively simple structure. It is most preferable to use a light-transmitting layer including a cube-corner retroreflective element because it can be manufactured in a simple process.

When a light-transmitting layer including an open lens type retroreflective element is used, a retroreflective sheet having a simple structure and which can be manufactured by a relatively simple process can be obtained. Dust easily accumulates on the surface, and has a quality defect such as a decrease in retroreflection performance in rainy weather.

In any case, in the present invention, since the layer containing the retroreflective element is made light-transmitting without using a dull metal layer such as a metal vapor-deposited film in the layer containing the retroreflective element, the obtained retroreflection It is possible to make the non-woven sheet excellent in whiteness and saturation.

The light transmittance of the light-transmitting layer is usually designed so that the total light transmittance is 20% or more, preferably 35% or more, more preferably 50% or more. 20 total light transmittance
% Or more, preferable retroreflection performance can be obtained.

A light-transmitting layer (1) containing a retroreflective element,
On the back side of (1 ′), (1 ″) or (1 ″ ′), a resin back layer (3) having a large number of depressions on the surface is provided with a large number of depressions (2) in the back layer.
The layers are stacked while maintaining the state.

In the present invention, part or all of the light that has passed through the light-transmitting layer is partially or entirely separated from the transparent material constituting the portion of the light-transmitting layer that is in contact with the depression, and from the depression (2) of the resin back layer (3). )
Due to the large difference in the refractive index from the gas contained inside,
It is totally reflected at this transparent material / enclosed gas interface. That is,
The gas in the cavity (2) of the back layer (3) plays an important role in the light reflection function.

Therefore, it is essential that the resin back layer (3) has a number of depressions (2) on the surface, and the light-transmitting layers (1), (1 '), (1 ") of the back layer. Alternatively, the ratio of the surface area occupied by the depression (2) on the surface relative to the total surface area of the surface in contact with (1 "') is 20 to 95%, preferably 40 to 93%, and more preferably 50 to 90%. It is good. If the surface of the back layer (3) has no dents and the back layer and the light-transmitting layer are laminated in a state of being in close contact with each other, favorable light reflectivity cannot be obtained.
When the proportion is 95% or less, favorable adhesiveness to the light transmitting layer is easily obtained.

The retroreflective sheet of the present invention is a light-transmitting layer that includes a retroreflective element and does not include a light-impermeable light-reflecting layer.
(1), (1 '), (1 ") or (1"') can be easily manufactured simply by laminating and bonding the resin back layer (3). Conventional capsule lens type retroreflection There is an advantage that a complicated process for air entrapment is not required at all, unlike a flexible sheet or a capsule cube corner type retroreflective sheet.

The light transmitting layer can be easily manufactured by using a conventionally known method. For example, the light transmissive layer (1) can be manufactured by subjecting a transparent resin film to cube corner molding by means such as heating embossing.

For example, the light-transmitting layer (1 ') can be manufactured by a known technique described in JP-B-48-28837, except that a metal vapor-deposited film is not provided. A multilayer resin layer is formed by applying and drying a resin solution on the base material, and a refractive index of about 2.0 is set so that the surface of the resin back layer (3) is exactly at the focal position of the glass bead lens.
It can be manufactured by enclosing glass beads (11) of about ~ 2.7 in a resin layer in a state of being substantially monolayer and arranged over the entire surface.

For example, the light-transmitting layer (1 ") is a layer of a microsphere lens such as a glass bead, and is directly formed on the resin back layer (3) by a microsphere such as a glass bead having a refractive index of about 1.9. The lens can be manufactured by embedding and fixing a substantially hemispherical surface of the lens.

The resin used to form the light-transmitting layer is not particularly limited, but is usually an acrylic resin, a urethane resin, a fluorine resin,
Polyester-based resin, vinyl chloride-based resin, polycarbonate-based resin, polyarylate-based resin, silicone-based resin, polyolefin-based resin, ionomer resin, etc. are used alone or in a mixed system, and are particularly excellent in transparency, weather resistance, etc. Acrylic resins, urethane resins, fluorine resins, polycarbonate resins and the like are preferably used.

In the light-transmitting layer, the material forming the portion in contact with the resin back layer (3) should have a refractive index as high as possible without impairing the retroreflective characteristics in order to further enhance the total reflection characteristics. It is preferable to select a material, and if possible, a material having a refractive index of 1.5 times, more preferably, 1.7 times or more the refractive index of the gas in the depression is good.

A coloring agent may be added to the resin layer used to form the light-transmitting layer as long as the total light transmittance is not significantly impaired.
Additives such as an ultraviolet absorber, a light stabilizer, a heat stabilizer, an antioxidant, and a fungicide may be added.

On the back surface of the light transmitting layer, a resin back layer (3) having a large number of depressions (2) on its surface is laminated while maintaining the state of the depressions.

The depression (2) is a light-transmitting layer, a resin back layer (3)
May be formed by foaming using a foaming agent or the like contained in the back layer.However, in order to more reliably form a recess at the interface with the light-transmitting layer, foaming may be performed in advance. It is preferable to form a material having a depression formed by such means as described above, or a material having a depression formed by means such as embossing or the like bonded to a light transmitting layer.

The resin used to form the resin back layer (3) is not particularly limited, but is usually an acrylic resin, a urethane resin, a fluorine resin, a polyester resin, a vinyl chloride resin, Polycarbonate resin, polyarylate resin, silicone resin, polyolefin resin, ionomer resin, etc. are used alone or in a mixed system. Among them, acrylic resin, silicone resin, urethane resin, etc. which are excellent in workability etc. Is preferably used.

In the back layer (3), if necessary, a coloring agent, a filler, a crosslinking agent, an ultraviolet absorber, a light stabilizer, a foaming agent, a heat stabilizer, a tackifier, an antioxidant, A large amount of white pigment, such as titanium oxide, may be added for the purpose of adding a fungicide, etc., for the purpose of contacting with the light-transmitting layer, slightly increasing the light reflectivity in the parts other than the depressions, etc. Is also a preferred embodiment.

The method for laminating the light-transmitting layer and the resin back layer (3) is not particularly limited. One or both layers are made to be in an adhesive state, and the laminating is performed using a laminating roll or the like. It can be easily implemented by means such as bonding.

If necessary, when manufacturing the capsule lens type retroreflective sheet as shown in FIG.
The reticulated sheet of the present invention can be manufactured relatively easily by forming a network-like connected portion structure (15) on the surface side of the retroreflective sheet of the present invention and bonding it to a surface-coated film.

Resin back layer of retroreflective sheeting of the present invention
It is also a preferred embodiment that the back surface of (3) is used by bonding an adhesive layer (4), a release paper (5) or the like as necessary.
In this case, by forming the back layer itself as a layer of an adhesive resin, the configuration becomes simpler and an inexpensive retroreflective sheet can be obtained.

[0044]

According to the present invention, a light-transmitting layer (1), (1 '), (1 ") or (1"') containing a retroreflective element and a large number of depressions (2) on the surface are provided. With a configuration in which the resin back layer (3) and the back layer are laminated while leaving a large number of depressions on the surface of the back layer, a retroreflective sheet excellent in whiteness and saturation and inexpensive can be obtained.

[0045]

EXAMPLES The retroreflective sheeting of the present invention will be specifically described below with reference to examples.

Test Methods The test methods were all performed as follows.

(1) Surface area occupied by depression The resin back layer was observed with a microscope from the front side of the retroreflective sheet, photographed, and the area of the depression portion occupying the whole area was measured and expressed in%. .

(2) Hue The values measured according to the color measurement specified in JIS Z-9117 were expressed in L ^* , a ^* , b ^* color system.

(3) Whiteness / Saturation The hue was calculated from the hue by the following formula.

[0050]

(Equation 1)

(4) Reflection Performance The reflection performance of the retroreflective sheet was measured according to the measurement of the reflection performance specified in JIS Z-9117. The angle conditions were an observation angle of 0.2 ° and an incident angle of 5 °.

(5) Total light transmittance tester [Color analyzer TC-1800MK manufactured by Tokyo Denshoku Co., Ltd.]
2), the total light transmittance of the sample was measured. When the total light transmittance greatly changes depending on the direction in which light is transmitted, an average value in two directions is defined as the total light transmittance.

Example 1 A transparent acrylic film containing polymethyl methacrylate as a main component was heated and embossed, and a light having a thickness of about 200 μm having a cube-corner type projection having a side of about 200 μm and a height of about 90 μm on the entire surface of one surface. A permeable layer was obtained. The total light transmittance of the light transmitting layer was 77.5%.

Next, a release paper [EA2P-S manufactured by Lintec Co., Ltd.]
LPE ''), with a thickness of about 100 with many depressions on the surface
μm white foamed polyethylene sheet (L ^* 83.8, a ^* -
0.1, b ^* 0.2) as the core material, and an acrylic colorless and transparent adhesive [Nissetsu PE- manufactured by Nippon Carbide Industry Co., Ltd.]
121 "] to form a resin back layer having a thickness of about 150 μm having a number of depressions on the surface covered with the adhesive layer, and forming the resin back layer into a cube corner type of the light transmitting layer. The retroreflective sheet of the present invention was obtained by sticking to the projection-forming surface.

The obtained sheet has an indented surface area of about 89.
%Met. Further, as shown in Table 1, the obtained retroreflective sheet sufficiently satisfies the object of the present invention, which is excellent in whiteness / chroma and reflection performance.

Example 2 A retroreflective sheet was prepared in the same manner as in Example 1 except that a red foamed polyethylene sheet (L ^* 43.2, a ^* 51.9, b ^* 23.5) was used instead of the white foamed polyethylene sheet. I made it. As shown in Table 1, the obtained retroreflective sheet sufficiently satisfies the object of the present invention, which is excellent in whiteness / chroma and reflection performance.

COMPARATIVE EXAMPLE 1 Instead of laminating a foam sheet, aluminum was vapor-deposited to a thickness of about 0.1 μm on the back surface of the light-transmitting layer using a vacuum vapor deposition machine, and an acrylic pressure-sensitive adhesive was laminated on the back surface. A retroreflective sheet was obtained in the same manner as in Example 1. The total light transmittance of the light transmitting layer on which the vapor deposition layer was laminated was 2.4%. The obtained retroreflective sheet is as shown in Table 1,
The object of the present invention having low whiteness and saturation was not achieved.

Comparative Examples 2 and 3 Sabreite 18012 was used as a commercially available retroreflective sheet.
(Comparative Example 2) [Nikka Polymer Co., Ltd. white encapsulated lens type retroreflective sheet], Sabrite 18035 (Comparative Example 3)
The effect was compared using [Red-enclosed lens type retroreflective sheet manufactured by Nikka Polymer Co., Ltd.]. Both were retroreflective sheets of dull hues with poor whiteness and saturation.

[0059]

[Table 1]

[0060]

According to the present invention, since a light reflecting layer exhibiting a metal color such as a metal vapor deposition film is not required at all, the whiteness and the whiteness can be reduced.
A retroreflective sheet having excellent chroma can be obtained.

Particularly, by using a cube corner type retroreflective element, a retroreflective sheet having a very simple structure and excellent in quality characteristics including retroreflective performance can be manufactured by a very simple manufacturing process. be able to.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of a cube-corner retroreflective sheet of one embodiment of the present invention.

FIG. 2 is a sectional view of an encapsulated lens type retroreflective sheet according to another embodiment of the present invention.

FIG. 3 is a cross-sectional view of an open lens type retroreflective sheet according to another embodiment of the present invention.

FIG. 4 is a cross-sectional view of a capsule lens type retroreflective sheet according to another embodiment of the present invention.

[Explanation of symbols]

1 ... Light transmitting layer of cube corner type retroreflective sheet. 2... Depressions in the back resin layer. 3 A resin back layer having a number of depressions. 4 ... Adhesive layer. 5 ... release paper. 1 '... Light-transmitting layer of encapsulated lens type retroreflective sheet. 1 "... Light transmitting layer of open lens type retroreflective sheet. 1"'... Light transmitting layer of capsule lens type retroreflective sheet. 11: Microsphere lens such as glass beads 12: Focus layer 13: Microsphere lens fixed layer 14: Coating film 15: .Mesh-like joint structure 16 ... encapsulated air layer

Claims (7)

(57) [Claims] 1. A light-transmitting layer including a retroreflective element and a resin back layer having a surface having a plurality of recesses smaller than the number of retroreflective elements, while maintaining the state of the plurality of recesses on the surface of the back layer. A retroreflective sheet, characterized in that the sheet is laminated. 2. The recursive method according to claim 1, wherein the ratio of the surface area occupied by the depression on the surface of the resin back layer to the total vote area of the surface in contact with the light transmitting layer is 20 to 95%. Reflective sheet. 3. The retroreflective sheet according to claim 1, wherein the total light transmittance of the light transmitting layer is 20% or more. 4. The retroreflective sheet according to claim 1, wherein said resin back layer is a layer made of an adhesive resin. 5. The retroreflective sheet according to claim 1, wherein said retroreflective element is a cube corner type retroreflective element. 6. A light transmissive layer including a retroreflective element and a surface.
Resin with many recesses smaller than the number of retroreflective elements
The back layer keeps the state of many depressions on the surface
Of a retroreflective sheet characterized by being laminated by
In the manufacturing method, the resin
Recursion characterized by laminating a surface layer and a light transmitting layer
For producing a reflective sheet. 7. A resin back layer in which recesses are formed in advance.
Is a foamed polyethylene sheet covered with an adhesive layer.
The retroreflective sheet according to claim 6, wherein
Production method.