JPH10123309A - Triangular pyramidal cube corner retroerelection sheet - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve an incident angle characteristic and observation angle characteristic by inclining an optical axis by a specific range to direction where the difference between the distance from the vertex of a triangular pyramidal reflection element (element) to the base of a perpendicular and the distance from the intersection point with the base of the element to the base of an element pair is plus. SOLUTION: The inclination of the optical axis is expressed by the angle formed by a segment DF and the perpendicular DE. The inclination direction is plus (+) and the inclination is 5.5 to 10.5 deg. with the element ABCD in the case of q-p>0 when EO=p and FO=q are defined. Namely, the angle between the optical axis and the perpendicular inclines by 5.5 to 10.5 deg. in such a manner that the difference q-p between the distance p from the intersection point of the vertex of the element to the base of the perpendicular and the base to the base copossesed by the element pair and the distance q from the intersection point of the optical axis and base of the element to the base copossesed by the element pair is plus. The average radius of the major radius and minor radius of the inscribing ellipse of the base which is the effective opening of the element with respect to the incident light is 40 to 90μm.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to signs such as road signs and construction signs, license plates for vehicles such as automobiles and motorcycles, clothing and safety materials such as lifesaving equipment, markings for signboards and the like, visible light, and laser. The present invention relates to a triangular pyramid-shaped cube corner retroreflective sheet useful for reflectors of light or ultraviolet light reflective sensors.

More specifically, on a common plane, a triangular pyramid-shaped cube corner retroreflective element having a triangular shape on the bottom surface forming an approximately isosceles triangle shares a base other than the isosceles on the bottom surface. Other retroreflective elements having a bottom surface that is substantially symmetrical with respect to the base to be placed are arranged in a close-packed manner in a pair of elements facing each other, and a perpendicular line from the vertex of the triangular pyramid-shaped reflective element is The distance (p) from the intersection with the bottom surface to the common base of the element pair, and the distance (q) from the intersection of the optical axis of the triangular pyramid-shaped reflective element with the bottom surface and the common base of the element pair. The optical axis is tilted by a specific range in such a direction that the difference (q−p) from
In addition, the present invention relates to a triangular pyramid-shaped cube corner retroreflective sheeting in which the effective opening area of the triangular pyramid-shaped reflective element is in a specific range.

[0003]

2. Description of the Related Art Conventionally, a retroreflective sheet for reflecting incident light toward a light source is well known, and the sheet utilizing the retroreflective property is widely used in the above-mentioned application fields. In particular, a retroreflective sheet utilizing the retroreflection principle of a cube corner retroreflective element, such as a triangular pyramidal cube corner retroreflective element (hereinafter also referred to as a triangular pyramidal reflective element), is a retroreflective sheet using a conventional micro glass ball. The retroreflection efficiency of light is remarkably superior to that of a sheet, and the use thereof is expanding year by year due to its excellent retroreflection performance.

However, the cube-corner retroreflective element has, based on the principle of reflection, the optical axis of the element (the axis at an equal distance from three planes forming the element and having an angle of 90 ° to each other) and the incident light beam. In the range of angles where the angle formed (hereinafter referred to as the incident angle) is small, good retroreflectivity is exhibited (that is, the incident angle characteristics are good), but the retroreflection efficiency is sharply reduced as the incident angle increases (that is, the incident Inferior corner characteristics). In addition, light rays incident on the element surface at an angle less than a critical angle that satisfies the condition of total internal reflection determined by the ratio of the refractive index of the transparent material constituting the cube-corner retroreflective element and the refractive index of air are as follows: A retroreflective sheet using a cube-corner retroreflective element to transmit to the back of the element without total reflection at the interface of the element,
In general, there is a disadvantage that the incident angle characteristics are inferior.

On the other hand, a cube corner retroreflective element
Since the light can be reflected in the direction in which the light is incident over almost the entire surface of the element, the reflected light diverges at a wide angle due to spherical aberration or the like and the retroreflection luminance is increased, as in the case of a micro glass sphere type reflection element. Inconvenience such as lowering does not occur. However, the narrow divergence angle of the retroreflected light is, in practical terms, for example, when light emitted from a headlight of an automobile is retroreflected by a traffic sign, a driver located at a position away from the optical axis of the traffic sign. The inconvenience of being hard to reach the eyes is likely to occur. Such an inconvenience is caused by an angle (hereinafter, referred to as an observation angle) between an incident axis of a light beam and an axis (observation axis) connecting a driver and a reflection point, particularly when the distance between the car and the traffic sign is short. Is particularly remarkable because of an increase in the observation angle characteristic (that is, the observation angle characteristic is inferior).

[0006] Many proposals have been known for such a cube corner retroreflective sheet, particularly a triangular pyramidal cube corner retroreflective sheet, and various improvements have been studied.

For example, US Pat. No. 2,481,757 to Jungersen describes a retroreflective sheet in which various retroreflective elements are mounted on a thin sheet, and a method of manufacturing the sheet. This proposal exemplifies a triangular pyramid-type reflective element having an apex arranged at the center of a base triangle and having no inclination of an optical axis, and an inclined triangular pyramid-type reflective element having a vertex whose position is not arranged at the center of a base triangle. It describes that light is efficiently reflected to an approaching automobile. In addition, the size of the triangular pyramid-shaped reflective element is 1 /
It is described that it is within 10 inches (2540 μm). Further, FIG. 15 of this proposal shows a triangular pyramid-shaped reflecting element pair whose optical axis is inclined in the same direction as that of the present invention (that is, the direction in which the (q−p) becomes plus (+)). As shown in the figure, the inclination angle of the optical axis is estimated to be about 6.5 ° when calculated from the ratio of the length of the long side and the short side of the bottom triangle of the triangular pyramid-shaped reflecting element shown in the figure. .

However, in the above-mentioned proposal of Jungersen, there is no specific disclosure about the extremely small triangular pyramid-shaped reflecting element as shown in the present invention, and it gives excellent observation angle characteristics and incident angle characteristics. For this reason, there is no description or suggestion about the optical axis inclination of the triangular pyramid-shaped reflection element or what range the effective aperture should be.

[0009] Also, US Pat.
In the specification of U.S. Pat. No. 3,712,706, the shape of the triangle on the bottom surface is a regular triangle on a thin sheet. A reflective sheet is described.
According to this proposal, the reflective surface of the element is subjected to a vapor deposition treatment with a metal such as aluminum, for example, and is mirror-reflected, so that the retroreflection efficiency is reduced due to an increase in the incident angle, or at an angle exceeding the total internal reflection condition. Attempts have been made to improve the above-mentioned problem that incident light passes through the interface of the element and does not retroreflect.

However, in the above-mentioned proposal of Stam, since the specular reflection principle is employed as a means for improving the wide-angle property, the obtained retroreflective sheet has a darkened appearance or aluminum which is employed in the mirror surface layer. Metals such as silver are oxidized during use by water and air,
Problems such as a tendency to cause a decrease in reflection luminance are likely to occur. In addition, the proposal does not disclose any means for improving the wide-angle property by tilting the optical axis.

Further EP by Hoopman
In Japanese Patent No. 137,736, an inclined triangular pyramid-type reflecting element in which the shape of a triangle on the bottom is an isosceles triangle is arranged on a thin sheet so that the bottom is in a close-packed shape on a common surface. A retroreflective sheet is described. The inclination of the optical axis of the triangular pyramid-shaped reflecting element described in this proposal is opposite to the direction of inclination of the optical axis of the triangular pyramid-shaped reflecting element of the present invention [that is, (q-p) is minus (-).
And the inclination angle is about 7 to 13 °.

[0012] However, in the above Hoopman proposal,
It is not specified what size of the triangular pyramid-shaped reflective element provides excellent wide-angle characteristics. According to the wide-angle simulation by the light tracking method used in the present invention described later, the incident angle characteristics of the negatively inclined triangular pyramid-shaped reflecting element show a sharp luminance change particularly when the incident angle is in the range of 5 to 10 °. It turned out to show. This incident angle range is not preferable because it is a range in which it is desired that a change in luminance is particularly small in practical use.

Further, also in US Pat. No. 5,138,488 to Szczech, an inclined triangular pyramid-type reflecting element having a triangular bottom surface having an isosceles triangle shape on a thin sheet similarly has a common bottom surface. It describes a retroreflective sheet that is arranged in a closely packed manner on a surface. Also in this proposal, the inclination of the optical axis of the triangular pyramid-shaped reflecting element is inclined in the direction of a side shared by the two triangular pyramid-shaped reflecting elements facing each other, and the inclination angle is about 2 degrees.゜ 5 °, and the size of the element is specified to be 25 μm to 100 μm.

Further, EP Patent No. 548, corresponding to the above-mentioned patent,
In Japanese Patent Publication No. 280, the direction of the inclination includes a common side of the two elements forming a pair, and the distance between a plane perpendicular to the common plane and the vertex of the element, the optical axis of the element intersects the common plane. It is described that the distance between the point and the perpendicular plane is not equal, the inclination is about 2 to 5 °, and the size of the element is 25 μm to 100 μm.

As noted above, Stetch EP Patent 548,
In Japanese Patent Publication No. 280, the inclination of the optical axis is in the range of about 2 to 5 degrees in which the (q-p) includes both plus (+) and minus (-). However, in the examples of the U.S. Patent and EP Patent Publications to Schetch, the optical axis tilts (α) are 8.2 °, 9.2 ° and 4.3 °, and the element height (h) is 87.
Only a triangular pyramid-shaped reflective element of 5 μm is disclosed.

In these embodiments, in order to improve the wide-angle property of the triangular pyramid-shaped reflecting element, the vertical angle of the element is slightly deviated from its theoretical value of 90 °. However, in this method, the divergence of light is reflected as, for example, a group of six divided light beams, and the reflection luminance of light at different rotation angles depends on from which direction of the element the reflected light is observed. Changes, which is not preferable in practical use.

[0017]

Next, a technical problem desired for a retroreflective sheet and a problem of a triangular pyramidal cube corner retroreflective sheet using a triangular pyramidal reflective element will be described.

In general, the basic performance desired for a retroreflective sheet is high luminance, that is, high reflection luminance typified by the reflection luminance of light incident from the front of the sheet, and wide-angle characteristics. As for the characteristics, three characteristics of the observation angle characteristic, the incident angle characteristic, and the rotation angle characteristic are required.

Usually, it is said that the retroreflective brightness from the front of the triangular pyramid-shaped cube corner retroreflective sheet is two to three times higher than that of the micro-glass sphere retroreflective sheet. The reason is that the latter is a glass ball generally used for a micro glass ball type retroreflective sheet, the optical imperfection as a lens element, the spherical aberration or the reflectance of the metal reflecting surface provided on the reflecting surface. While the retroreflection efficiency is likely to decrease due to its lowness, etc., in the case of the cube corner type retroreflection element used for the former,
It is said that a relatively accurate optical element can be formed.

The first wide angle property is an observation angle characteristic. When the retroreflective sheet is used for various signs such as traffic signs, for example, the light source and the observer are usually not at the same position, so that stronger light reaches the observer located away from the incident optical axis. There is a need to. For that purpose, it is necessary that the decrease in the reflection luminance is small even when the observation angle is increased.

The bundle of light reflected by the retroreflective sheet needs to spread to some extent and reach an observer at a position off the incident optical axis. In order to do so, it is necessary to design so that the reflected light spreads at a slight angle (divergence angle). This is achieved by changing the 90 ° theoretical vertical angle formed by the three surfaces forming the cube-corner retroreflective element with each other, or by slightly bending the reflective surface of the element. In view of the relative position between the headlights and the driver of a vehicle such as a large truck, the observation angle is usually about 2 ° at maximum, so the divergence angle is controlled at an angle slightly exceeding this maximum observation angle. It should be.

The second wide angle property is an incident angle characteristic. For example, when a car is approaching a traffic sign, the angle of incidence of the headlight emitted from the car on the sign gradually increases, and accordingly, the brightness of the light reaching the observer driver gradually increases. Decrease. In order for the sign to maintain sufficient brightness even when the driver approaches the sign,
Requires excellent incident angle characteristics.

Generally, the retroreflection efficiency decreases as the incident angle increases. This is because, in order to satisfy the principle of three-sided reflection, which is the principle of retroreflection of a cube-corner retroreflective element, the incident angle is relatively close to 0 °, that is, light enters the retroreflective sheet surface at an angle close to perpendicular. It is necessary that when the incident angle increases, the light does not reach the second or third element surface to be reflected next, and the light escapes out of the element to reduce the efficiency of retroreflection. It is. Also,
As the incident angle increases, the condition of total internal reflection is not satisfied, and light is transmitted through the reflection surface of the element. As a method of improving the above-mentioned problem, a method of increasing the retroreflection efficiency in the tilted direction by slightly tilting the optical axis of the cube corner retroreflective element in various directions is generally adopted.

The third wide-angle characteristic is a rotation angle characteristic. As a phenomenon peculiar to the cube corner retroreflective element, there is a property that the retroreflective luminance changes depending on from which direction of the retroreflective sheet light enters. For this reason, when attaching the retroreflective sheet to the sign, there is a complicated problem that the sheet must be managed and attached in a certain direction. In the micro glass ball type retroreflective sheet, this problem does not occur because the reflective element has a rotating body shape.

The rotation angle characteristic remarkably occurs particularly in the case of a triangular pyramid type reflection element. As a method for improving this, a method of dividing the triangular pyramidal reflective element assembly surface into certain sections and changing the direction of the assembly surface has been adopted (US Pat. No. 4,243,618). In this method, the rotation angle incident on the element differs for each section, and the reflection luminance changes accordingly. Therefore, when viewed from a long distance, the rotation angle characteristics are averaged and the rotation angle characteristics are made uniform. The compartments can be seen quite clearly from the surface of the retroreflective sheet, causing problems such as a reduction in the design of the sheet appearance and a decrease in the strength of joints between the compartments.

The above-mentioned improvement of the incident angle characteristic can be achieved by the above-described principle of tilting the optical axis. The range of the incident angle at this time is determined from the geometrical positional relationship between the position of the ordinary traffic sign and the car.For example, the range of the incident angle specified in the Japanese Industrial Standard is up to 30 °. Stipulated. Therefore, it is necessary that the incident angle characteristic of the retroreflective sheet used as a traffic sign does not significantly decrease the incident angle characteristic up to the range of the incident angle of 30 °.

Further, when the retroreflective sheet is used for various signs such as traffic signs, for example, the position of the light source and the observer are usually not the same. Stronger light needs to reach. For that purpose, the light reflected by the retroreflective sheet must have a certain spread and reach the observer located at a position off the incident optical axis.
It must be designed so that the reflected light spreads at a slight angle (divergence angle). Thus, a desirable retroreflective sheet is required to maintain a high level without a significant decrease in observation angle characteristics within a maximum range of 3 ° specified in Japanese Industrial Standards, for example.

The present inventors have found that the relationship between the above-mentioned incident angle characteristics and observation angle characteristics and the optical axis tilt angle can be analyzed by a computer simulation using an optical tracing method.
Analysis by this method shows that the optical axis is
For example, the direction opposite to the direction described in the above-mentioned Hoopman's proposal, that is, the distance from the intersection of the vertical line descended from the vertex of the triangular pyramid-shaped reflective element to the bottom surface and the bottom surface to the shared base of the element pair The difference (q−p) between (p) and the distance (q) from the intersection between the optical axis of the triangular pyramid-shaped reflecting element and the bottom surface to the base shared by the pair of elements is positive (+). In a specific direction, it is preferable to incline by an angle in a specific range, and by setting the area of an effective opening capable of retroreflecting light from the bottom surface serving as an opening of the element to a specific range, That the incident angle characteristics and observation angle characteristics of the triangular pyramidal cube-corner retroreflective sheet can be significantly improved, and based on this knowledge, a prototype triangular pyramidal cube-corner retroreflective sheet was actually produced, Make sure Thus, the present invention has been completed.

[0029]

According to the present invention, a triangular pyramidal cube-corner retroreflective element having a bottom surface on a common plane (XX ') is provided.
X ') protrudes to one side of the triangular pyramid-shaped reflecting element, and the bottom surface of the triangular pyramid-shaped reflecting element has a substantially isosceles triangular shape. Another retroreflective element having a bottom surface which is substantially symmetrical with respect to the shared base is arranged in a close-packed manner on the common plane (XX ') by forming a pair of elements facing each other. In a triangular pyramid-shaped cube corner retroreflective sheeting in which the optical axes of these element pairs are tilted in opposite directions to each other, a perpendicular line descending from the vertex of the triangular pyramid-shaped reflecting element to the bottom surface and the The distance (p) from the intersection with the bottom surface to the common base of the element pair, and the distance (q) from the intersection of the optical axis of the triangular pyramid-shaped reflective element and the bottom surface to the common base of the element pair. Between the optical axis and the perpendicular in such a direction that the difference (q−p) The angle of inclination is 5.5 to 10.5 °, preferably 6.5 to 9.5 °, and serves as an effective opening of the triangular pyramid-shaped reflective element with respect to incident light. Long radius (a) and short radius (b)
The geometric mean radius of the (sometimes called the mean radius of the effective aperture)

[0030]

(Equation 2)

It is an object of the present invention to provide a triangular pyramid-shaped cube corner retroreflective sheet having a thickness of 40 to 90 μm.

Hereinafter, the present invention will be described in detail with reference to the drawings.

FIG. 1 shows a triangular pyramidal cube corner retroreflective element group according to the present invention when the bottom surface, which is an opening for incident light, is directed downward and the vertex of the triangular pyramidal reflective element is directed upward. FIG. 2 is a plan view, FIG. 2 is an enlarged plan view of a pair of triangular pyramidal reflective elements surrounded by a dotted line in the triangular pyramidal reflective element group, and FIG. 3 is a side view thereof. FIG. 4 is an enlarged plan view of a triangular pyramidal cube-corner retroreflective element according to the related art, and FIG. 5 is a side view thereof.

In FIGS. 2 to 5, △ BAC and △ B′A
C is a bottom surface of the triangular pyramid-shaped cube corner retroreflective element and has a substantially isosceles triangle shape in which sides BA and BC and B'A and B'C are almost equal to each other.
And △ B′AC are arranged in a close-packed manner on a common plane (XX ′), and serve as openings of the triangular pyramid-shaped reflection element for incident light. In addition, the triangular pyramid type reflection element ABC
D shares one base AC other than the isosceles of the bottom surface △ BAC having the shape of the substantially isosceles triangle, and the shared base A
It forms an element pair facing each other with another retroreflective element AB'CD 'having a bottom surface △ B'AC which is substantially symmetrical with respect to C, and has the element pair ABCD and AB'CD'. The optical axes (straight lines including the line segments DF and D'F ') are inclined in opposite directions as indicated by arrows. Also, the element pair protrudes on one side of the common plane (XX ′), and as is clear from FIG. 1, all other element pairs similarly have the common plane (XX ′). ) Protrudes to one side.

The vertex D of the triangular pyramid-shaped reflecting element ABCD
A point of intersection with the bottom surface △ BAC on a common plane (XX ′) with a perpendicular line lowered from the bottom to the bottom surface is E, and the element ABC
The optical axis of D (the three △ DBA, △ DBC, and △ D, which pass through the vertex D of the triangular pyramidal reflective element ABCD and form the element)
A straight line equidistant from each plane of the DAC) and the bottom surface {BA
Assuming that an intersection with C is F, points E and F are calculated from the apex angle B of the bottom surface △ BAC to the respective bottom surfaces △ BAC and △ B ′ of the element pair.
It lies on a vertical line extending down to the bottom AC shared by the AC, and this vertical line passes through the midpoint O of the bottom AC.

The inclination angle of the optical axis is represented by the angle formed by a line segment DF on the optical axis and a perpendicular line DE extending downward from the vertex to the bottom surface. , F
When O = q, the case of qp> 0 is expressed as plus (+), and the case of qp <0 is expressed as minus (-). Triangular pyramidal cube corner retroreflective element A used in triangular pyramidal cube corner retroreflective sheeting of the present invention
In the BCD, the direction of the inclination is plus (+) and the inclination angle is 5.5 to 10.5 ° as is clear from FIG. On the other hand, the direction of inclination of the triangular pyramid-shaped reflecting element according to the prior art shown in FIGS. 4 and 5 is minus (-).

Next, in the present invention, a computer simulation of an optical tracing method used for analyzing the relationship between the incident angle characteristic and the observation angle characteristic and the optical axis inclination angle and the inclination direction will be described with reference to FIG. I do.

In FIG. 6, 1 is a retroreflective sheet, 2 is a reference center point of the sheet 1, 3 is a reference axis perpendicular to the light incident surface of the retroreflective sheet 1, and 4 is a light source 6 and a reference center point 2. The light incident axis 5 is an observation axis connecting the reference center point 2 and the observer 7, and 9 is an evaluation surface installed with the light source as the center.

In the light tracing method, a retroreflective sheet 1 in which desired triangular pyramid-type reflecting elements are arranged in a close-packed shape on a plane is assumed, and is installed at an arbitrary position on the sheet 1 at a predetermined incident angle. Light is emitted from the light source 6 to cause retroreflection in geometrical optics. Further, the light is spread based on the diffraction effect of the Fraunhofer, which is inversely proportional to the opening area of the triangular pyramid-shaped reflection element, based on the theory of diffraction. In this way, the light that has been retroreflected with the spread is evaluated by the evaluation screen 9.
Projected above to determine how light is retroreflected. Such calculation operation is repeated tens of thousands of times, and the light intensity distribution 8 of the reflected light is drawn on the evaluation screen.

Next, the area of the effective aperture used to determine the diffraction effect of Fraunhofer will be described. In general, in the case of a triangular pyramid-shaped reflection element, for example, light incident on a portion near each apex angle of the base triangle cannot be reflected at all three interfaces due to its structure, and is transmitted through the element or one. Alternatively, the light is reflected at two interfaces and exits the element in a direction different from the direction of retroreflection. As described above, in the triangular pyramid-shaped reflection element, the entire area of the bottom surface does not always serve as an effective opening for retroreflection. Therefore, the effective aperture here means that light incident from the bottom surface of the triangular pyramid-shaped reflecting element is totally reflected at three interfaces forming the triangular pyramid-shaped reflecting element, so that the light source direction is parallel to the incident optical axis. Refers to the effective portion of the aperture that can reflect the light, that is, can retroreflect.

According to the Fraunhofer diffraction theory, the primary diffraction angle θ at the circular aperture is given by the following equation (1), where λ is the light wavelength and r is the aperture radius: sin θ = 1.22λ / (2r) (1) It is known that as the opening area decreases, the spread of light due to the diffraction effect increases. Although a diffraction effect equal to or higher than the second-order diffraction is also conceivable, the spread of light at that time is very small and can be ignored.

The radius of the opening of the regular triangular pyramid-shaped reflecting element is the intersection of the bottom surface of the triangular pyramid-shaped reflecting element and the optical axis.
Can be approximated as the radius of a circle inscribed in the equilateral triangle on the bottom. In addition, the effective aperture of the inclined triangular pyramid-shaped reflective element having a substantially isosceles triangle whose optical axis is inclined at the bottom is the circular aperture of the regular triangular pyramid-shaped reflective element having the same major axis, when viewed from an oblique direction. It can be approximated as an elliptical opening. At this time, the values of the opening radius for obtaining the primary diffraction angle include the major radius (a) and the minor radius (b) of the ellipse.
Geometric mean radius of

[0043]

(Equation 3)

Can be adopted. Such an inscribed ellipse has the largest area among countless inscribed ellipses inscribed in the isosceles triangle on the bottom surface.

Further, if the spread of light beyond the second-order diffraction is neglected, the light intensity distribution is calculated by using the radius of the opening as a median function.
It can be obtained as an expression including the following Bessel function. The spread of the reflected light from each of the triangular pyramid-shaped reflecting elements obtained in this way is obtained for all the triangular pyramid-shaped reflecting elements on the retroreflective sheet, and the intensity distribution integrated on the evaluation screen is calculated. It can be calculated as a bundle of light. Therefore, since the integrated intensity distribution is a superposition of light rays that have been diffusely reflected due to the diffraction effect of a large number of triangular pyramid-shaped reflecting elements, it differs from the first-order diffraction angle simply obtained from diffraction theory. I have.

When the apex angle of the triangular pyramid type reflection element is exactly 90 °, the integrated intensity distribution becomes a gentle mountain shape spreading around the light incident axis, and as the incident angle increases, the peak shape of the mountain increases. Height decreases. An observation axis 5 connecting the observer 7 standing on the evaluation screen and the reference center point 2 of the sheet;
The light intensity at the observation angle formed by the incident axis 4 matches the integrated intensity at the position where the observer stands. In this manner, given the inclination angle of the optical axis of the triangular pyramid-shaped reflecting element and the geometric mean radius of the inscribed ellipse, it is possible to obtain the angle characteristic between the observation angle and the incident angle of the reflecting sheet, that is, the wide-angle property. It is possible.

Based on this light tracing method, the retroreflective sheet 1
By installing a triangular pyramid-shaped reflection element having various optical axis inclination angles on the above, a change in retroreflection behavior due to the optical axis inclination is required. Also, by changing the installation position of the light source 6 and moving the incident axis 4 with respect to the reference axis 3 of the sheet to change the incident angle, the incident angle characteristics of the installed triangular pyramid-type reflection element can be obtained. Further, the observation angle characteristics include the light intensity distribution 8 drawn on the evaluation screen 9, the observation point 7, and the light source 6.
Can be obtained as a relationship with the distance.

FIG. 7 shows a retroreflective sheet provided with a regular triangular pyramid-shaped reflective element (average radius of an effective aperture of about 70.7 μm) having no optical axis inclination and having an element height of 100 μm, obtained by the above-mentioned optical tracking method. 2 shows the relationship between the observation angle, the incident angle, and the relative reflection luminance. FIG. 8 shows the observation of a retroreflective sheet provided with a triangular pyramid-shaped reflective element (average radius of an effective aperture of about 72.9 μm) having an optical axis inclination of plus (+) 8 ° and an element height of 100 μm. The relationship between angle, incident angle, and relative reflection luminance is shown. The relationship between the observation angle, the incident angle, and the relative reflection luminance according to the light tracing method shown in FIGS. 7 and 8 was measured by actually forming a retroreflection sheet having a triangular pyramid-shaped reflection element having such a shape. It was found that the behavior agreed well with the behavior of those who did.

FIG. 9 shows the inclination of the optical axis obtained by the above-mentioned optical tracing method for various triangular pyramidal reflective elements in which the height of the element is 80 μm and the inclination angle of the optical axis is changed from −14 to + 14 °. Corner-
The relationship between the incident angle and the relative reflection luminance is shown. At a small incident angle, the reflection luminance gradually decreases as the inclination of the optical axis increases in the plus or minus direction. Regarding the relationship between the tilt angle of the optical axis, the incident angle and the reflection luminance, in the case of a triangular pyramidal reflection element having a small inclination of the optical axis, for example, in the range of 0 to ± 4 °, the reflection luminance sharply increases as the incident angle increases. Decrease. In the case of a triangular pyramid-shaped reflecting element inclined at least 4 ° in the negative direction, the luminance sharply decreases between the incident angles of 5 ° and 15 °, and the luminance decreases slowly at incident angles larger than this. . On the other hand, in the case of a triangular pyramid-shaped reflecting element having an incident angle of 6 ° or more in the positive direction, the incident angle is in the range of 5 to 25 °, and particularly in the case of a triangular pyramid-shaped reflecting element inclined of 8 ° or more, the incident angle is 5 to 35 °. It can be seen that in the range of, the reflection luminance decreases gradually (hereinafter also referred to as flat incident angle characteristics). This phenomenon occurs because, for example, considering that the retro-reflective sheet used as a traffic sign must maintain a flat incident angle characteristic up to an incident angle of 30 °, a positively inclined element has a negatively inclined element. The device is more practical than the device described in the above, and particularly shows that the triangular pyramid-shaped reflection device of the present invention having an optical axis inclination angle in the above range is excellent.

As is apparent from the above, the inclination angle of the triangular pyramid-shaped reflecting element is positive in (q-p) and 5.5 to 10.5.
゜, preferably 6.5 to 9.5 ゜. When the inclination angle is within the above range, a flat incident angle characteristic can be obtained and a retroreflective sheeting excellent in practicality can be obtained. On the other hand, when the inclination angle is less than the lower limit, the incident angle characteristic is small. Cannot be sufficiently improved, and a relatively sharp decrease in luminance is observed with an increase in the incident angle, which is not preferable. On the other hand, when the inclination angle exceeds the upper limit, a flat incidence angle characteristic can be obtained, but the brightness in the front direction near the incidence angle of 0 ° is significantly reduced, and the shape of the triangular pyramid-shaped reflecting element is reduced. When the retroreflective sheet is molded and processed, defects such as a decrease in resin filling property and poor releasability from a molding die are liable to occur. When the shape of the type reflective element is significantly deformed and elongated, the change in reflected luminance with respect to the incident direction of light, that is,
It is not preferable because there is a problem that a retroreflective sheet excellent in practicality cannot be obtained because the rotation angle characteristic is too low.

Next, the improvement of the observation angle characteristic in the present invention will be described. The improvement of the observation angle characteristic can be realized by giving the spread (divergence angle) of the reflected light using the diffraction phenomenon. The distribution of the light spread and the reflection luminance due to the diffraction effect in each of the triangular pyramid-shaped reflection elements can be obtained by the Fraunhofer diffraction theory. The magnitude of the spread is, as shown by the above equation (1), where sin θ is inversely proportional to the radius r of the opening through which the light passes when the primary diffraction angle is θ, and the radius r is an inclined triangular pyramidal reflection. In the case of an element, the geometric mean radius of the major (a) and minor (b) radii of the ellipse with the largest area inscribed in the triangle at the bottom of the element

[0052]

(Equation 4)

Can be approximated as

The preferred range of the observation angle is determined by changing the geometric average radius (average radius of the effective aperture) of the ellipse inscribed in the triangle on the bottom surface of the triangular pyramid-shaped reflecting element by using the above-mentioned light tracing method. It can be set so that a desired light spread is obtained in a range slightly larger than the range of the observation angle specified in the industrial standard. The average radius of the effective opening thus determined in the present invention is 40 to 90 μm
It is necessary to be. In an element having an average radius of less than 40 μm, the spread of light due to the diffraction effect becomes excessively large, and the observation angle characteristics become flat, but the decrease in the reflection luminance near the front is extremely undesirable. Also, the average radius is 90 μm
In a device having a value exceeding the above, the divergence of light due to the diffraction effect is too small, and satisfactory viewing angle characteristics cannot be achieved.

Means for diverging light to improve the observation angle characteristic can be achieved by giving a very small deviation to the apex angle of the triangular pyramid-shaped reflecting element. The light is reflected as a group of light split into books, and the reflected luminance of the light changes at different rotation angles depending on from which direction of the triangular pyramid-shaped reflecting element the reflected light is observed, which is not practically preferable. In the present invention, the deviation of the apex angle of the triangular pyramid-shaped reflecting element may be given in a range where this light splitting can be ignored, but for example, 0.1.
範 囲 should be kept within the limits.

Further, the size of the triangular pyramid-shaped reflecting element is uniquely determined by the height of the triangular pyramid-shaped reflecting element, the shape of the bottom triangle, and the inclination angle of the optical axis. Height h (DE or D 'in FIG. 3)
E ′) is 30 from the viewpoint of a good balance between the front reflection luminance, incident angle characteristics and observation angle characteristics of the obtained retroreflective sheet.
It is preferably between μm and 120 μm.

Next, a preferred structure of the triangular pyramid-shaped cube corner retroreflective sheeting of the present invention will be described with reference to FIG. 10 which is a cross-sectional view of the retroreflective sheet with an opening for incident light facing upward. I do.

In FIG. 10, reference numeral 11 denotes a reflecting element layer in which the triangular pyramid-shaped reflecting elements according to the present invention are arranged in a close-packed manner, 12 denotes a reflecting element holding layer for holding the reflecting element, and 10 denotes light incidence. Direction. The reflective element layer 11 and the reflective element holding layer 12 (hereinafter, sometimes referred to as the reflective element base layer 13) are generally integrated, but separate layers may be laminated.

The above-mentioned reflection element layer 11 and reflection element holding layer 12
Is not particularly limited as long as it satisfies one object of the present invention, that is, flexibility, but is preferably a material having optical transparency and uniformity. Examples of materials that can be used in the present invention include polycarbonate resins, vinyl chloride resins, (meth) acrylic resins, epoxy resins, styrene resins, polyester resins, fluororesins, olefin resins such as polyethylene resins and polypropylene resins, cellulose resins and Examples thereof include urethane resins, and among them, acrylic resins, polycarbonate resins, vinyl chloride resins, and polyurethane resins are particularly preferable.

The method of manufacturing the triangular pyramid-shaped reflecting element according to the present invention is not particularly limited, and the methods disclosed in the above proposals can be used. For example, the following methods can be mentioned. it can.

Using a diamond tool having a tip angle of 70.5288 degrees, grooves each having a crossing angle of 60 ° and a V-shaped cross section were formed by fly cutting from three directions in a repeating pattern on a brass plate. A triangular pyramid with a peak height of 200 μm is formed on an aluminum plate. Using this matrix, a triangular pyramid-shaped reflection element molding die having a shape in which nickel is inverted is formed by electroforming. Then, using this molding die, for example, an acrylic resin sheet (manufactured by Mitsubishi Rayon Co., Ltd.) having a thickness of 300 μm is compression-molded at a molding temperature of 200 ° C. and a molding pressure of 50 kg / cm ² , and is pressed to 30 ° C. After cooling under pressure, the resin sheet is taken out, and an acrylic resin triangular pyramidal cube corner retroreflective element having a triangular pyramidal reflective element having a reflective element layer with a thickness of 200 μm disposed on the surface in the closest density is formed.

The triangular pyramidal cube corner retroreflective sheet according to the present invention includes a surface protective layer 14, a printed layer 15 for transmitting information to an observer, and a reflective element according to the purpose of use and environment of use of the retroreflective sheet. A binder layer 16 for preventing moisture from infiltrating into the back surface of the base layer 13 and forming a sealed sealing structure so as to form an air layer 20 that increases a critical angle that satisfies the condition of total internal reflection; A support layer for supporting the layer 16 to improve the strength of the retroreflective sheet, improve dimensional stability, and prevent moisture and chemicals from entering the back surface
17, and an adhesive layer 18 and a release material layer 19 used for attaching the retroreflective sheet to another structure can be provided.

The same resin as that used for the reflective element base layer 13 can be used for the surface protective layer 14, but an ultraviolet absorber, a light stabilizer, an antioxidant and the like are used for the purpose of improving weather resistance. Each can be used alone or in combination. Further, an organic pigment, an inorganic pigment, a dye and the like can be contained as a coloring agent. The print layer 15 can be provided on the surface protective layer 14 and the reflective element base layer 13, and can be usually provided by means such as gravure printing or screen printing.

As a method of forming the above-mentioned encapsulation / sealing structure, US Pat. No. 3,190,178 (= Japanese Patent Publication No. 40-7787)
No. 4,025,159 (= Japanese Unexamined Patent Publication No. Sho 52)
No. 110592) and the method disclosed in Japanese Utility Model Laid-Open Publication No. 50-28669 can be employed. As the resin usable for the binder layer 16 used for forming the sealed structure, (meth) acrylic resin, polyester Resin, alkyd resin, epoxy resin, etc. can be selected, and as the joining method, a heat fusion resin joining method, a thermosetting resin joining method, an ultraviolet curing resin joining method, an electron beam curing resin joining method, etc. are appropriately adopted. It is possible.

In the present invention, the binder layer 16 can be applied over the entire surface of the support layer 17 or can be selectively provided at the joint with the reflective element layer 11 by a printing method or the like. Examples of the material forming the support layer 17 include a resin forming the retroreflective element layer and a resin that can be formed into a general film, a fiber, a cloth, a metal foil or a plate such as stainless steel or aluminum, or a combination thereof. be able to.

The adhesive layer 18 used for attaching the retroreflective sheet of the present invention to a metal plate, a wooden plate, a glass plate, a plastic plate or the like, and the release material layer 19 for the adhesive may be any known one. You can choose.

[0067]

The present invention will be described in more detail with reference to the following Examples and Comparative Examples. The retroreflection performance was measured by the following method.

Retroreflective Performance Using a “Model (MODEL) 920” manufactured by Advanced Retro Technology, INC as a retroreflective performance measuring instrument, a sample of a 100 mm × 100 mm luminous retroreflective sheet was used. The retroreflective performance of the retroreflective sheet of the sample was measured at incident angles of 5 °, 10 ° and 30 ° and observation angles of 0.20 °, 0.33 ° and 0.50 ° according to JIS Z-9117.

Example 1 On a 100 mm × 100 mm brass plate whose surface was ground flat, the tip angle was 77.89 ° in the first and second directions and 5 in the third direction.
Using a 4.53mm diamond tool, the first direction and the second
Repeat pattern grooves with a V-shaped cross section so that the repetition pitch in the direction is 163.6 μm, the repetition pitch in the third direction is 196.5 μm, and the intersection angle between the first and second directions is 49.22 °. A triangular pyramid-shaped cube corner retroreflective element group having a reflective element height of 80 μm was formed on a brass cast plate by fly cutting. The optical axis tilt angle of this triangular pyramid-shaped reflecting element was + 8 °, and the geometric mean radius of the inscribed ellipse was 58.3 μm.

Using this brass mold, by electroforming,
A mold for molding a concave triangular pyramid-shaped reflective element in which the material was inverted nickel was prepared. Using this molding die, the thickness
A 300 μm polycarbonate resin sheet (trade name “Europin E2000”; manufactured by Mitsubishi Engineering Plastics Co., Ltd.) is compression molded at a molding temperature of 200 ° C. and a molding pressure of 50 kg / cm ² , and then cooled to 30 ° C. under pressure. After that, the resin sheet was taken out, and a retroreflective sheet made of a polycarbonate resin having a triangular pyramid-shaped reflective element having a cube corner prism layer having a thickness of 200 μm disposed on the surface in the closest density was prepared. The retroreflective performance of the obtained retroreflective sheet was measured according to the method described above. Table 1 shows the measurement results.

Comparative Example 1 In Example 1, the tip angle of the diamond cutting tool was 61.98 ° instead of 77.89 ° in the first and second directions, and 86.53 ° instead of 54.53 ° in the third direction. The repetition pitch in the first direction and the second direction is set to 181.2 μm instead of 163.6 μm, and the repetition pitch in the third direction is set to 19
The height of the reflection element is 80 μm in the same manner as in Example 1 except that the intersection angle between the first direction and the second direction is set to 68.85 ° instead of the intersection angle between the first direction and the second direction is set to 160.3 μm instead of 6.5 μm.
A triangular pyramid-shaped cube corner retroreflective element group was formed. The optical axis tilt angle of this triangular pyramid-shaped reflecting element was −8 °, and the geometric mean radius of the inscribed ellipse was 58.2 μm. Hereinafter, a retroreflective sheet made of a polycarbonate resin was prepared in the same manner as in the examples, and the retroreflective performance was measured according to the above-described method. Table 1 shows the measurement results.

Comparative Example 2 In Example 1, the tip angle of the diamond cutting tool was 73.44 ° instead of 77.89 ° in the first and second directions, and 64.53 ° instead of 54.53 ° in the third direction. Instead of the repetition pitch between the first direction and the second direction being 163.64 μm, the repetition pitch in the third direction is 166.9 μm.
The height of the reflective element was 80 μm in the same manner as in Example 1 except that the height was 177.2 μm instead of 196.5 μm, and the angle of intersection between the first and second directions was 56.19 ° instead of 49.22 °.
An m-shaped triangular pyramidal cube corner retroreflective element group was formed. The optical axis tilt angle of this triangular pyramid-shaped reflecting element was + 3 °, and the geometric mean radius of the inscribed ellipse was 56.8 μm. Hereinafter, a retroreflective sheet made of a polycarbonate resin was prepared in the same manner as in the examples, and the retroreflective performance was measured according to the above-described method. Table 1 shows the measurement results.

Comparative Example 3 In Example 1, the tip angle of the diamond cutting tool was 81.02 instead of 77.89 ° in the first direction and the second direction.
The third direction is set to 46.53 ° instead of 54.53 °, the repetition pitch between the first direction and the second direction is set to 166.9 μm instead of 163.64 μm, and the repetition pitch in the third direction is set to
The height of the reflective element was 80 μm in the same manner as in Example 1 except that the height was 220.5 μm instead of 196.5 μm, and the angle of intersection between the first and second directions was 43.11 ° instead of 49.22 °.
An m-shaped triangular pyramidal cube corner retroreflective element group was formed. The optical axis tilt angle of this triangular pyramid-shaped reflecting element was + 12 °, and the geometric mean radius of the inscribed ellipse was 60.8 μm. Hereinafter, a retroreflective sheet made of a polycarbonate resin was prepared in the same manner as in the examples, and the retroreflective performance was measured according to the above-described method. Table 1 shows the measurement results.

Comparative Example 4 In Example 1, the repetition pitch in the first direction and the second direction was 337.5 μm instead of 163.64 μm, and the repetition pitch in the third direction was 405.2 μm instead of 196.5 μm.
Except that the height of the reflecting element was 16
A 5 μm triangular pyramidal cube corner retroreflective element group was formed. The optical axis tilt angle of this triangular pyramid-shaped reflecting element is + 8 °,
The geometric mean radius of the inscribed ellipse was 120.2 μm. Hereinafter, a retroreflective sheet made of a polycarbonate resin was prepared in the same manner as in the examples, and the retroreflective performance was measured according to the above-described method. Table 1 shows the measurement results.

[0075]

[Table 1]

[0076]

The triangular pyramid-shaped cube corner retroreflective sheeting of the present invention comprises a triangular pyramid-shaped cube corner retroreflective element having a triangular shape on the bottom that forms an approximately isosceles triangle on a common plane. Sharing the base other than the isosceles,
Other retroreflective elements having a bottom surface that is substantially symmetrical with respect to this shared base are arranged in a close-packed manner in an element pair facing each other, and are arranged from the apex of the triangular pyramid type reflective element. The distance (p) from the intersection of the perpendicular to the bottom and the bottom shared by the element pair, and the distance from the intersection of the optical axis of the triangular pyramid-shaped reflective element with the bottom and the bottom shared by the element pair ( The optical axis is inclined by a specific range in such a direction that the difference (q−p) from q) becomes plus, and the effective aperture of the triangular pyramid-shaped reflecting element is in a specific range.

As is clear from the above Examples and Comparative Examples, a retroreflective sheet made of a triangular pyramid-shaped reflecting element having a negative optical axis or a positive optical axis having an inclination smaller than the essential range of the present invention is used. In the range of 5 to 30 degrees of the incident angle, the luminance change is large and the incident angle characteristic is inferior, and even if the inclination angle of the optical axis is plus, the inclination is larger than the essential range of the present invention, the front luminance, that is, the incident angle 5反射 Reflection brightness near the area is too low. Further, even if the inclination angle of the optical axis is within the range of the present invention, if the average radius of the effective aperture of the element is too large, the front luminance becomes sufficiently high but the viewing angle characteristics are completely insufficient. On the other hand, the retroreflective sheet of the present invention shows high reflection luminance in a wide range, and the luminance change is very gentle. Thus, the triangular pyramid-shaped cube corner retroreflective sheet of the present invention, while maintaining the height of its front luminance, by a combination of the above-described components,
This is an excellent retroreflective sheet having significantly improved incidence angle characteristics and observation angle characteristics.

[Brief description of the drawings]

FIG. 1 is a plan view of a triangular pyramidal cube corner retroreflective element according to the present invention, with the bottom surface, which is an opening for incident light, facing downward and the apex of the triangular pyramidal reflective element facing upward; FIG.

FIG. 2 is an enlarged plan view of a pair of triangular pyramid-shaped reflective elements in a triangular pyramid-shaped cube corner retroreflective element group according to the present invention.

FIG. 3 is a side view of a triangular pyramidal cube corner retroreflective element pair according to the present invention.

FIG. 4 is an enlarged plan view of a triangular pyramidal cube corner retroreflective element pair according to the related art.

FIG. 5 is a side view of a triangular pyramidal cube corner retroreflective element pair according to the related art.

FIG. 6 is a diagram for explaining a computer simulation of an optical tracking method used for analyzing a relationship between an incident angle characteristic and an observation angle characteristic of a triangular pyramid-shaped reflection element and an optical axis inclination angle and an inclination direction. FIG.

FIG. 7 is a view showing a state in which the optical axis is not inclined and the height of the element is 100 μm.
3 is a three-dimensional graph showing the relationship between the observation angle, the incident angle, and the relative reflection luminance of the retroreflective sheet provided with the triangular pyramid-shaped reflective element, which is obtained by the optical tracking method.

FIG. 8 is a view showing a viewing angle of a retroreflective sheet according to the present invention provided with a triangular pyramid-shaped reflecting element having an optical axis inclination of + 8 ° and an element height of 100 μm, obtained by an optical tracing method; Angle of incidence-
6 is a three-dimensional graph showing a relationship between relative reflection luminances.

FIG. 9 is a diagram illustrating an inclination angle of an optical axis obtained by an optical tracking method,
5 is a three-dimensional graph showing a relationship between an incident angle and relative reflection luminance.

FIG. 10 is a cross-sectional view showing a preferred structure of a triangular pyramidal cube corner retroreflective sheet of the present invention.

[Explanation of symbols]

 1... Retroreflective sheet 2... Reference center point of retroreflective sheet 1 3... Reference axis perpendicular to light incident surface of retroreflective sheet 1 4. ..A light incident axis 5 connecting the light source 6 and the reference center point 2... An observation axis connecting the reference center point 2 and the viewer 7 6... A light source 7. Observer 8: Intensity distribution of light drawn on evaluation screen 9 9: Evaluation screen 10: Light incident direction 11: Reflecting element Layer 12 Reflective element holding layer 13 Reflective element base layer 14 Surface protective layer 15 Print layer 16 Bonding Material layer 17 Support layer 18 Adhesive layer 19 Release material layer 20 Air layer

Claims (1)

[Claims] 1. A triangular pyramid-shaped cube corner retroreflective element having a bottom surface on a common plane (XX ′) protrudes to one side of the common plane (XX ′). The bottom surface of the triangular pyramid-shaped reflection element has a substantially isosceles triangle shape,
The triangular pyramid-shaped reflection element forms another element pair facing each other with another retroreflection element having a bottom surface that shares one base other than the isosceles of the bottom surface and is substantially symmetric with respect to the shared base. Triangular pyramid-shaped cube corner retroreflection which are arranged in a close-packed manner on the common plane (XX '), and the optical axes of these element pairs are inclined in diametrically opposite directions. In the sheet, the distance (p) from the intersection of the perpendicular line descended from the vertex of the triangular pyramid-shaped reflecting element to the bottom surface and the bottom surface to the base shared by the element pair, and the optical axis of the triangular pyramid-shaped reflecting element The angle between the optical axis and the perpendicular is 5.5 such that the difference (q-p) between the intersection point with the bottom surface and the distance (q) from the common base of the element pair to the base is positive.
The major radius (a) and the minor radius (b) of the ellipse inclining to the bottom surface of the triangular pyramid-shaped reflecting element, which are inclined so as to be about 10.5 ° and serve as an effective opening of the triangular pyramid-shaped reflecting element with respect to incident light. The geometric mean radius of Is a triangular pyramid-shaped cube corner retroreflective sheet having a thickness of 40 to 90 μm.