The present invention relates to a retioreflective function member which causes the incoming light to reflect toward a light source, and a retroreflective unit in which the retroreflective function members are laminated. More particularly, the present invention is directed to devices such as delineators of a guardrail on a highway, studs, signs used for marine salvage which are required to be visibly confirmed both at long and short distances.
There is a micro-glass sphere type retroreflective function member and a cube corner type retroreflective function member in a retroreflective function member.
Known for providing the micro-glass sphere type retroreflective function member are technology whereby glass beads are mixed with road traffic paint with the help of the glass beads' (lens) own retroreflective ability, a reflective cloth in which one surface of base cloth is provided with a paint layer containing glass beads semi-embedded in the paint layer, or a reflective sheet in which one surface of a transparent resin plate in which glass beads are embedded is provided with an adhesive layer (refer to Non-Patent Document 1).
Conventional technology is also known in which a lateral surface of the reflective sheet disclosed in the Non-Patent Document 1 is provided with a refractive element and non-slip particles (refer to Patent Document 1).
Another conventional technology is also known in which a glass sphere in which the refractive index is higher the nearer the center, is used to correct the spherical aberrations, thereby heightening the contribution rate to retroreflection (refer to Patent Document 2).
On the other hand, known for providing the cube corner type retroreflective function member is conventional technology in which the surface of a protective film forming a microscopic space is provided with a cube corner type retroreflective element (refer to Patent Document 3).
Further, as an improved version of the cube corner type retroreflective function member, conventional technology is known in which incident rays are retroreflected by a triangular pyramidal type reflective surface consisting of three surfaces which intersect at right angles (refer to Patent Document 4).
Still further, another conventional technology is known in which a device is fixed to a guard rail member and adapted to fall down when coming in contact with a vehicle body, thereby expanding the area of the effective retroreflective surface (refer to Patent Document 5).
[Non-Patent Document 1] Pages 168 -171 of a dictionary of glass (issued on Sep. 20, 1985 by Asakura Bookstore);
[Patent Document 1) Japanese Unexamined Patent Publication No. Hei 11-508653 (508653/1999),
[Patent Document 2] Japanese Unexamined Patent Publication No. 2000-075115
[Patent Document 3] Description of Japanese Unexamined Patent Publication No. Hei 8-234006 (234006/1996) in [0003]-[0005]
[Patent Document 4] International Application No. WO98-18028
[Patent Document 5] Japanese Unexamined Patent Publication No. 2002-146729
As to each type of reflective performance of the conventional technology, the reflective brightness of the enclosed lens type (bead resin embedded type) reflective sheet is about 100 cd/1 xm2, the reflective brightness of a capsule lens type reflective sheet is about 300 cd/1 xm2, and the reflective brightness of the cube corner type (prism lens type) reflective sheet is about 900 cd/1 xm2. The prism lens type reflective sheet is the best reflective material among the current products.
In the conventional technology, to calculate the retroreflective efficiency of the enclosed lens type reflective sheet, a retroreflective state diagram of the enclosed lens type reflective sheet is shown in
As shown in
As shown in the Non-Patent Document, a focus position of the glass bead of which the refractive index is 1.5 can conduct the retroreflection most efficiently by bringing the reflective surface to a position where it is 1.38 times as long as the hemisphere (R) of the bead. In this connection, in case of the glass bead of which the refractive index is 1.93, it is most efficient to make the bead surface the reflective surface.
In this manner, the enclosed lens type reflective sheet is provided to bring the reflective surface to a position where it is about 1.38 times as long as the bead's hemisphere (R). However, the focus position varies with the incident height angle of light (an angle relative to the center of the glass bead) as shown in
When a calculation is made on condition that only light with an incident height angle between 0° and 30° retroreflects as shown in the retroreflective state diagram of
retroreflectance of the glass bead=cross-sectional area corresponding to the incident angle of 30°/cross-sectional area of the glass bead=πR2×sin 302/2=0.25
where the reflective efficiency is about 25 %.
Then, non-uniformity of the glass bead in particle diameter affects the reflective efficiency. In order to obtain adequate retroreflection, it is necessary to adapt a reflective film to a focus position of each bead in the particle diameter. Accordingly, it is desirable that the particle diameter of the bead be constant and the beads which have been well sorted within the limits of 50-100 μm are used. However, it is considered that the reflective efficiency is reduced by about 22% due to the non-uniformity of the particle diameter compared with using the beads of which the particle diameters are the same and ideal.
Then, an area of the glass bead of the reflective sheet per unit area affects the reflective efficiency. Assuming that the focal distance is 1.38R and the glass beads are filled by an ideal molding, the area ratio of the glass bead of the reflective sheet per unit area is πR2/(2×1.38R)2=0.4. It is therefore considered that the reflective efficiency is further reduced by about 40%.
The above results are summarized as follows: 0.25×0.22×0.4=0.022 It is to be noted that an extremely low reflective efficiency of about 2.2% is obtained.
If the reflective efficiency of the enclosed lens type reflective sheet is about 2.2%, it is considered that the reflective efficiency of the capsule lens type reflective sheet is about 6.6% and that of the prism lens type reflective sheet is about 20%, judging from the value of the retroreflective brightness.
The cube corner type reflective sheet has an excellent retroreflective efficiency in that the incident angle for retroreflection is extremely limited, but in a specific range, 20% of the incident light retroreflects within the scope of ±1.5°.
However, assuming that the cube corner type reflective sheet is used as a visual guide sign (a delineator) for a guard rail in a highway, all of the retroreflective light of ±1.5° does not enter the eyes of a driver, but only a part thereof.
The angle (an observation angle) between the driver's eyes and the reflector is 0.716°. Then, the relationship between toric rays of light in the direction of the observation angle of 0.716° and the driver's eyes is such that 6cm of both eyes' width exists at the upper portion of the toric ring of 0.716° as shown in FIGS. 24(a) and (b). With this, the angle of light directed from the reflector toward the driver's eyes is found in accordance with the formula:
6/(2×3.14×50)×360°=6.8°=±3.4°
This is shown in
Of course, the light rays with the observation angle of 0.716° among the light rays with the observation angles of 0°-1.5° reflected from this section finally become the effective light which enter the eyes of the driver who is 40 m away from the reflector. The area ratio of the triangle relative to a gross area of the circular reflector in this case can be found as follows:
6.8°/360°=0.0189
where the area ratio is only 1.89%.
In this manner, the extent of the ratio of the light rays reflected in the direction of the position of the driver's eyes among the retroreflected light rays is very important. Namely, it is considered that the retroreflective properties are proportional to the value obtained by multiplying the retroreflective efficiency by the ratio of light reflected in the direction of the driver's eyes. Although the distance between the driver's eyes and the reflector is set 40 m in
On the one hand, a reflective material provided with more excellent retroreflective properties is required. Specifically, a delineator of which the diameter is 70 mm or more is generally used above a guardrail as a visual guide sign for a guardrail on a highway. However, to improve the visibility and landscape of the guardrail during night driving, it is necessary to install the visual guide sign (delineator) on a depressed portion at the center of the guardrail.
To meet such requirements, various companies are trying to develop a thin visual guide sign (delineator) in which the cube corner type reflective member is incorporated. However, as far as performance is concerned, their prototype models are still in such a state that the driver “cannot see at all” the delineator 400 m ahead or he “can manage to see” it 100 m-300 m ahead. In this manner, to be adopted on the highway, it is required for the delineator to be upgraded so that it has a performance of more than 10 times regarding the reflective properties at a long distance.
The ultimate cause of deficiency in performance at a long distance is that the reflective section is extremely small in area. The area of the reflective section of the cube corner type delineator which is now used above the guardrail can be defined as follows: π/4×10×10=78.5 cm2
where the diameter is 100 mm. On the contrary, in the case where the visual guide sign (delineator) is installed at the depressed portion of the guardrail, about 20 mm is only allowed for the thickness of the visual guide sign so that it does not project toward the road side and about 100 mm for the width. In this manner, an allowable area of the reflective section can be defined as follows:
1.2×9.0=10.8 cm2 Accordingly, the area becomes about 1/7 of a φ100 type delineator.
As a result, the retroreflective brightness becomes insufficient and only such a structure as shown in the Patent Document 5 can be made available.
It is therefore an object of the present invention to provide an excellent retroreflective member at a low price which can be installed in a narrow space such as that for a guardrail on a highway and which has a performance gain ratio of more than 10 times, at a long distance (e.g., 300-400 m), as high as a cube corner type reflective sheet which has the highest retroreflective performance of conventional products.
To attain the above-mentioned object, according to the present invention, a retroreflective function member comprising a flat plate-shaped transparent body made of acrylic resin and the like is provided, in which the front surface is an incident and outgoing surface, the rear surface is a reflective surface provided with aluminum deposition and the like, the upper and lower surfaces are flat surfaces, and at least one surface of both side surfaces is a flat reflective surface, wherein the front surface projects forward to have a cylindrical shape (i.e., the shape in which a column is axially cut) when seen from the side and at least one surface of the rear surface and both side surfaces is a bow shape or an inverse bow shape.
With this structure, it is possible to obtain a retroreflective function member which has retroreflective properties more than 10 times as high as the conventional products at a long distance (300-400 m).
A working principle of the retroreflective function member with the above structure will now be described. First, as shown in
Now, the relationship between the radius R1 of curvature of the front surface 6 and the radius R2 of curvature of the rear surface 7 is 1.5≦R2/R1≦2.5, preferably 1.7≦R2/R1<2.0. If R2/R1 (H1) is below 1.5, the extent (spread) of light flux of the reflected light in the vertical direction becomes too large. If R2/R1 is approximately 2.0, the light flux of the reflected light in the vertical direction is reduced to the fullest extent. On the contrary, if R2/R1 is above 2.5, the extent of the light flux of the reflected light in the vertical direction becomes too large.
When taking this into consideration, as shown in Table 1, to make the reducing angle in the vertical direction 1.5° which is suitable for a short distance (25-50 m), H1=1.71. To make the reducing angle in the vertical direction 0.3° which is suitable for a long distance (300-400 m), H1=1.95. Particularly, when taking very short distances and very long distances into consideration, 1.5≦H1≦2,5.
As shown in
By causing the center of the radius of curvature of the front surface when viewed from the side to coincide with or to be situated at the rear of, the center of the radius of curvature of the rear surface on the center line when viewed from the side, it is possible to widen the angle of the incident light in the front surface which can retroreflect.
Further, it is desirable that the center of the curvature radius R3 of the rear surface when viewed from the top be situated between the central axis of the incident light and an extension of the reflective side surface. With this structure, there is a point that retroreflects 100% on the reflected surface of the rear surface.
It is also desirable that the thickness of the retroreflective function member when viewed from the side be provided in such a manner that an angle (θ1) between the incident light from the horizontal direction and the line passing through the center of curvature radius of the front surface is within 30°. When the thickness of the retroreflective function member is larger than the above, the extent of the light flux of the reflected light in the vertical direction becomes large to increase the dead wood.
As shown in
Further, a retroreflective unit according to the present invention comprises a lens unit formed by laminating a plurality of retroreflective function members in the vertical direction with the front surface and the side surface aligned. In case of the lamination layer, the front surface becomes lenticular (a series of shapes formed by axially cutting a column).
By selecting laminated retroreflective function members having different retroreflective properties, for example, by increasing the number of lens bodies used for a long distance, it is possible to drastically improve the visibility at a long distance of 300-400 m in night driving.
Even though the distance between the retroreflective function member and a vehicle changes in accordance with the running of the vehicle, the efficiency of the unit itself improves because optimum conditions can be attained for any of the retroreflective function members.
The above and other objects, features and advantages of the present invention will become more apparent from the following description when taken in conjunction with the accompanying drawings.
FIGS. 6(a)-(c) are plan views of the retroreflective unit in which the lens bodies are incorporated;
Preferred embodiments of the present invention will now be described with reference to the accompanying drawings.
A retroreflective function member 1 is formed by injection molding the transparent acrylic resin and is substantially plate-shaped, in which the upper surface 2, the lower surface 3, and right and left side surfaces 4 and 5 are formed flat. The front surface 6 is the incident (incoming) and outgoing surface, the rear surface 7 is aluminum-deposited to serve as a reflected surface, and the outside of the rear surface 7 is protected by a resin 8.
The side of the retroreflective function member 1 is not particularly limited, but the width is about 10-20 mm, the thickness is about 2.5-6 mm, and the length is about 15-30 mm.
The front surface 6 projects forward to have a cylindrical shape when viewed from the side and the rear surface 7 projects backwards to have a convex aspheric surface (i.e., a bow shape) viewed from the top. As shown in
As shown in
In this connection, when the retroreflective function member 1 is designed in such a manner that θ2 is 0.1°, the reflecting light is reduced to within ±0.3° in the horizontal direction around the light axis.
The rear surface 7 projects backwards to have a bow shape when viewed from the top, but as shown in
Further, it is desirable that the thickness of the retroreflective function member when viewed from the side be provided in such a manner that the angle (θ1: refer to
Referring to the side surfaces 4 and 5, the side surface 4 contributing to retroreflection is made flat, but the side surface 5 is provided partly with a notch 5a for easy positioning in the case where the lens body is incorporated in the casing as a unit or for easily locking other members.
Further, in the embodiment as shown in (b), the center of the curvature radius (R1) of the front surface coincides, on the center line, with the center of the curvature radius (R2) of the rear surface 7 when viewed from the side. However, as shown in (c), by locating the center of the curvature radius (R1) of the front surface 6 at the rear of the center of the curvature radius (R2) of the rear surface 7, namely by overlapping them on the center line when viewed from the side, it is possible to widen the retroreflectable incident angle in the vertical direction.
FIGS. 6(a)-(c) show a plan view of a retroreflective unit in which the lens body of the above shape is incorporated. The lens body as shown in
In the retroreflective unit as shown in
Only one lens body 1 is shown in
In the retroreflective unit as shown in
In the retroreflective unit as shown in
Specific design examples are shown in Table 2, in which eight types of lens bodies of A-C″ types of which the reducing angles in the vertical direction are 0.3°, 0.6°, 1.5° and the reducing angles in the horizontal direction are 0.065°, 0.129°, 0.258°, 0.6°, and 1.5° were made, and the values of R1, R2, R3, and T are shown in Table 3.
As one example of the visual guide sign (delineator) in which the above lens bodies are combined, comparative calculations were made for the conventional products regarding the performance (i.e., corneal lighting intensity) using A type (3 pieces), A′ type (1 piece), B type (2 pieces), B″ type (2 pieces), C type (8 pieces), and C″(2 pieces). As shown in Table 4, a slim, high-performance visual guide sign (delineator) having a performance gain ratio of 10.1 times at a distance of 100 m, 13.5 times at a distance of 200 m, 21.2 times at a distance of 300 m, 19.6 times at a distance of 400 m as high as conventional products is available.
The rear surface 7 projects backwards to have a cylindrical shape when viewed from the side, but it is linear when viewed from the top. Instead, the side surface 4 laterally projects to have a curved surface (R4=2500-24000 mm).
In this molding equipment, by bringing the parting line of the metal mold to an intersection point between the front surface 6 and the side surface 4 of the lens body 1, an intersection point between the front surface 6 and the side surface 5, and an intersection point between the rear surface 7 and the side surface 5, the parting line is removed from the side surface 4 and the rear surface, and the intersection point between the side surface 4 and the rear surface 7 which most affects the retroreflective function. In particular, when the parting line comes to the intersection point between the side surface 4 and the rear surface 7, an angle between the side surface 4 and the rear surface 7 is considered to slightly change each shot. As seen in this embodiment, if the intersection point between the side surface 4 and the rear surface 7 is formed in advance within the metal mold 21, it is possible to obtain a lens body which excels in dimensional accuracy. The fixed metal mold 23 for forming the side surface 5 which does not contribute to the retroreflection is provided with a runner 24.
Injection molding equipment for molding the lens unit 11 comprises two metal molds 21 and 22. By bringing the parting line of these metal molds to an intersection point between the front surface 6 and the side surface 4 of the lens unit 11 and an intersection point between the rear surface 7 and the side surface 5, the parting line is removed from a location which affects the retroreflective function as described above.
Each lens unit 11 is formed by laminating four lens bodies 1 and a front surface of adjacent lens units 11 is arranged to be alternated based on the axis line in the front and back direction. Specifically, an angle of +35° is formed between the front surface of three (3) lens units 11 among six (6) lens units 11 and the axis line in the front and back direction, while an angle of −35° is formed between the front surface of three (3) remaining lens units 11 and the axis line in the front and back direction.
In this manner, it is possible to retroreflect the incident light from a large range by changing the direction of the adjacent lens units 11.
The embodiment as shown in
Although specific forms of embodiments of the present invention have been described above by, for example, applying the retroreflective function member (retroreflective unit) to the visual guide sign (delineator) to be mounted on the guardrail on the highway and the studs, it is to be noted that the present invention is not limited to the embodiments described above. For example, the present invention can be widely applied to the members such as signs for marine salvage which are required to be visible from a long distance.
A retroreflective function member according to the present invention can attain reflective performance (properties) of at a long distance more than 10 times (300-400 m) as high as a cube corner type retroreflective function member which is considered to be the most excellent in retroreflective efficiency among the conventional retroreflective function members.
In this manner, even though the retroreflective function member is installed in an extremely limited area such as a depressed section of a guardrail on the side surface, it is possible to fully exhibit the retroreflective function.
Further, studs using the retroreflective function member according to the present invention are highly visible from a long distance, and the retroreflective efficiency is high in comparison with studs in which conventional reflectors are incorporated. Since a driving source such as a solar battery is not required, this is also advantageous in cost.
Number | Date | Country | Kind |
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2002-367519 | Dec 2002 | JP | national |
2003-123463 | Apr 2003 | JP | national |
Filing Document | Filing Date | Country | Kind | 371c Date |
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PCT/JP03/16361 | 12/19/2003 | WO | 3/17/2006 |