JPS5914721B2 - retroreflective material - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to retroreflective signs, markings, etc., and particularly to a reflective material that uses glass beads with a low refractive index and yet has a high retroreflective ability.

Retroreflective materials, so-called retroreflectors or reflective sheets, consist of a single layer of glass beads in close relationship to each other, with the glass beads either fully or partially embedded within a layer of binder. They are classified into two types: embedded type and exposed type, depending on how embedded they are in the body. As shown in Fig. 1, in the glass bead-embedded reflective material, the entire glass bead 1 is normally embedded in a single layer in close proximity to each other in a thin film-like transparent resin 2, and the glass beads 1 are placed under the transparent resin 2. It has a structure in which a light reflecting film 3 is attached to the end face of a focusing resin 2a having an optical thickness 5 determined based on the diameter and refractive index of the glass beads 1 and the refractive index of the resin 2. Reference numeral 4 denotes a pasting adhesive applied to the back surface of the light reflecting film 3, and a release paper 5 is pasted to the top surface thereof.

In this case, since the refractive index of resin is generally around 1.5, glass beads 1 with a refractive index of 2.15 or more are used in order to make the focusing resin 2a as thin as possible by 10 mm. Note that the reflected path of the light beam in this embedded reflective material is shown by the incident light beam l and the reflected light beam l' in FIG. On the other hand, in the glass bead exposed type reflective material, as shown in FIG. A light reflecting film 3 is provided on the surface of the resin 1 embedded in the resin 2. The reflected path of the 20 rays projected onto the exposed surface of the glass bead 1 is indicated by the incident ray l and the reflected ray l'. The refractive index of the glass beads used in this exposed reflective material is usually adjusted to 1.9 to 2.0. This means that when using glass beads exposed in the air, the highest retroreflection brightness is glass 2.
This is because it has been confirmed both theoretically and through actual measurements that this can be obtained when the refractive index of the 5 beads is between 1.9 and 2.0. A disadvantage of conventional retroreflective materials such as those described above is that glass beads with a high refractive index must be used.

For glasses with a refractive index exceeding 1.9, PbO, TiO2,
Preparations containing large amounts of heavy metal oxides such as BaO, Bi2O3 must be melted. Furthermore, since oxides necessary for vitrification, such as SiO2 and B2O3, lower the refractive index, it is necessary to reduce their content as much as possible. These melts, which contain a large amount of heavy metal oxides and have an extremely small amount of vitrifying oxides, rapidly become opaque during cooling, so they must be shaped into glass beads using a special method. Moreover, the raw materials are expensive, they severely corrode the refractories of the melting furnace, and they also generate large amounts of toxic gas. Furthermore, since the density of glass is twice or more than that of ordinary glass, the price of glass beads per unit volume has become extremely high. The present invention uses glass beads with a refractive index of less than 1.9, but has the same retroreflection brightness as when using glass beads with a refractive index of 1.9 or 2.15 or more. It provides materials.

Glass beads with a refractive index of 1.9 to 2.0 focus incident light onto the rear end face of the bead.

However, with glass beads having a refractive index of less than 1.9, the focal point of the incident light beam is further rearward than the rear end surface of the beads. In order to connect the focal point outside the circumferential surface of the bead at the same position as the glass bead with a refractive index of 1.9, that is, on the rear end surface of the bead, the radius of the front half of the bead must be made smaller than the radius of the rear half. Bye. For this purpose, spherical glass beads are embedded in resin in advance so that half of their circumferential surface is exposed, and the entire beads are immersed in a dissolving solution such as dilute hydrofluoric acid for the required time. are dissolved and removed in approximately concentric spherical shapes to obtain glass beads having a desired shape. The thickness of the front half of the bead to be dissolved and removed varies depending on the refractive index of the glass beads, but it is determined by the diameter of the bead (1.03-0.55n, where n is the refractive index of the bead).
) to (1.010.50n) times is found to be optimal. That is, for example, a refractive index of 1.
In 0.1 mm diameter glass beads with 50
The thickness to be removed of the front half is 0.0205 to 0.02
Preferably it is 6mm. Note that the front half here does not necessarily mean the entire one side of the glass bead bordering on the equatorial plane of the bead, but just the majority of the part that protrudes into the air from the resin binding the beads. It is. The thickness of the glass beads to be dissolved and removed is determined from (1.03-0.55n) to (1.01n) of the diameter of the glass beads.
The reason for limiting the range to 0.50n) times will be explained below.

In FIG. 6, the retroreflection characteristics of glass beads obtained by dissolving and removing the front D hemisphere of glass beads having a diameter D into concentric spheres having a thickness t are expressed by the following general formula.

1: Angle of ray incidence on glass beads S: Angle of reflection with respect to the incident ray In the above general formula, D-1, t-0, Nl. 9 and D-
1, t-0, n-2.0, the reflection angle S for an incident angle of 110 to 900 is calculated and graphed, and the refractive index is 1.
The retroreflection characteristics of true spherical glass beads of 9 and 2,0 are obtained.

That is, among glass beads, those with a refractive index of 1.9 to 2.0 have the highest retroreflection brightness,
This shows the spread of the retroreflected light. Next, for glass beads with a refractive index of less than 1.9, the thickness t to be dissolved and removed is such that the retroreflection characteristic graph falls between the two retroreflection characteristic graphs with refractive indexes of 1.9 and 2.0. Determine the value of

Therefore, the refractive index n-1.5, 1.55, 1.6, 1.65
, 1.7, 1.75, 1.8, 1.85 and t-0.02
, 0.04, 0.06, . Obtain the characteristic graph. From this result, a graph (Figure 7) showing the relationship between the refractive index of the glass beads and the thickness to be dissolved and removed is obtained, and the thickness t corresponding to the area 11 between the straight line 9 and the other straight line 10 in this figure is obtained. All you have to do is dissolve and remove it. That is, by analyzing the graph in FIG. 7, the thickness to be melted and removed of glass beads with a refractive index of n is the diameter of the glass beads (1.
03-0.55n) to (1.01-0.50n) times. Glass beads with a refractive index n less than 1.9 function exactly like glass beads with a refractive index of 1.9 when a thickness equal to (1.03-0.55n) times their diameter is removed. In other words, the incident light is focused exactly on the rear surface of the bead. The thickness to be removed is (1.03-
If it is less than 0.55n), the incident light will be focused outside the beads, making it impossible to obtain high brightness.

Next, if a thickness equal to (1.01-0.50n) times the diameter of the beads is removed, they function exactly like glass beads with a refractive index of 2.0. In other words, the incident light is focused exactly on the rear surface of the bead. The thickness to be removed is (1.0
If it exceeds 1-0.50n) times, the incident light will be focused inside the beads and high brightness will not be obtained. The present invention is a retroreflective material using glass beads formed based on the above, and an example thereof will be explained with reference to FIG.

Glass beads 1' have a refractive index of less than 1.9.
The exposed surface of the bead 1 is embedded in the transparent resin 2 in a single layer in close proximity to each other and approximately half of its circumferential surface is exposed. (1.010.50n) times the thickness is dissolved and removed, and the exposed side is formed with a smaller radius than the resin layer side, and a light reflecting film 3 is provided on the resin layer side surface of the glass beads v. There is. In the retroreflective material configured in this way, the light beam projected onto the exposed surface of the glass bead 1' is focused on the rear end surface of the bead 1'', so it has a refractive index of 1.9 or 2.15 or more. It is easily understood from the above description that the same retroreflection brightness as that obtained when using glass beads having the following properties can be obtained.Next, the method for manufacturing the retroreflection material of the present invention will be described with reference to Examples.

Example 1 Diameter 0.04-0.07 mm with refractive index 1.50
Transparent glass beads are temporarily glued onto the top of a piece of kraft paper that has been previously coated with polyethylene.

When performing this temporary bonding, the polyethylene coated paper is passed with the coated side outward over the surface of a heated drum to ensure sufficient tackiness of the polyethylene.
At the same time, a heated adhesive polyethylene coating comes into contact with a large number of glass beads placed on the underside of the drum. In this way, the glass beads are uniformly deposited in a single layer on the surface of the polyethylene coated paper.

Next, when the polyethylene is sufficiently dried, the polyethylene is softened and the single layer of beads is embedded to about half the diameter of each bead. The structure is then cooled, for example by blowing room temperature air onto it. The glass beads bound sheet is slowly passed through a shallow and long bath of dilute hydrofluoric acid at a concentration of about 1% and a temperature of about 40° C., and the protruding surfaces of the glass beads are dissolved and removed by a desired thickness. Next, this sheet is washed with water while being passed through a water tank to remove hydrofluoric acid, dissolved residues, etc., and then dried in a drying oven. Next, a methyl methacrylate polymer material for forming a solid plastic film, which has been adjusted to a desired viscosity with a solvent such as toluene or xylene, is thinly and uniformly applied to the upper surface of the protruding beads, dried, and then coated with the polyethylene coated paper. Peel and remove the carrier. In this way, the surfaces of the beads that have not been dissolved and removed are now exposed to the air. Under this condition, aluminum is deposited on the exposed bead surface of this structure until a visually continuous coating is formed, forming a reflective coating on the rear half of the bead. The top surface of this aluminum film is then coated with a methyl methacrylate polymeric material adjusted to the desired viscosity with toluene, xylene, etc. to a thickness sufficient to completely embed the beads and still provide a smooth surface. do. Next, the film covering the bead surface whose surface has been dissolved and removed by a desired thickness is peeled off to obtain the retroreflective material of the present invention. Example 2 The entire body was treated with a silver mirror in advance, with a refractive index of 1.65 and a diameter of 0.
．． 0.06 to 0.08 mu glass beads are dropped onto the methyl methacrylate resin coated to the desired thickness on the top surface of the polyethylene sheet, about half of it is embedded, and once it dries, the beads are bonded to the resin. .

Next, this sheet is slowly passed through a diluted mixture of nitric acid and hydrofluoric acid to remove the deposited film on the protruding glass bead surfaces, and then the glass surface of the beads is dissolved and removed by the desired thickness. . Then, by washing with water and drying, the retroreflective material of the present invention can be obtained. The retroreflective material of the present invention is usually shipped after applying a pasting adhesive 4 to the surface on which glass beads are not sprayed and pasting a release paper 5 on the top surface, as shown in FIG.

Furthermore, in the present invention, in order to protect the part of the glass beads exposed to the air from moisture and dust adhesion and contamination and to obtain stable retroreflection brightness over a long period of time, a transparent film is placed in front of the glass bead spraying surface. This can be achieved by providing

In this case, as shown in FIGS. 4 and 5, a large number of small squares 6 are formed with thin lines made of adhesive on the exposed surface of the glass beads 1' of the sheet, and then a transparent film 7 is placed on top of these.
The transparent film 7 is fixed on the grid lines 6 by covering the transparent film 7 with the transparent film 7. The beads 1a embedded in the adhesive in the square 6 lose their retroreflectivity, but this amount is only 1 to 2% of the total, and most of the other beads 1'
exists in a sealed pocket space 8 surrounded by the transparent film 7 and the squares 6, so that the retroreflection brightness is not impaired in the slightest. As detailed above, the retroreflective material of the present invention can obtain the same retroreflective brightness as when using glass beads with a high refractive index while using glass beads with a low refractive index, and at a relatively low cost. It has enormous industrial value and can be commercialized.

[Brief explanation of the drawing]

Figure 1 is a diagram showing the cross section of a conventional glass bead-embedded reflective material and the path of retroreflection, and Figure 2 is a diagram showing the cross section of an exposed glass bead reflective material and the path of retroreflection of the beam. , FIG. 3 is a cross-sectional view showing an example of the retroreflective material according to the present invention, FIG. 4 is a cross-sectional view showing another example of the retroreflective material according to the present invention, and FIG. 5 is a plan view of FIG. 4. , FIG. 6 is a sectional view showing the retroreflection state of the glass beads of the present invention, and FIG. 7 is a diagram showing the relationship between the refractive index of the glass beads and the thickness to be dissolved and removed. In the figure, 1,1'' are glass beads, 2 is a transparent resin, 2a is a focusing resin, and 3 is a light reflecting film.

Claims (1)

[Claims] 1. In a retroreflective material in which glass beads with a refractive index n of less than 1.9 are exposed and bonded in a single layer in close proximity to each other on the surface of a substrate, the surface of the glass beads on the binding layer side is exposed to light rays. A reflective coating is provided so that the majority of the exposed surface of the glass bead is 1.
03-0.55n) to (1.01-0.50n) times the thickness, and the exposed side has a smaller radius than the binding layer side. reflective material.