JP2003206513A - Retroreflection member and road marking body - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a retroreflection member capable of easily improving, in particular, the visual confirmation property when it rains in addition to the durability without using special glass beads. <P>SOLUTION: This retroreflection member is provided with a reflective basic member and a plurality of transparent composite minute balls buried into the reflective basic member partially. The composite minute ball is composed of a transparent minute ball having refractive index of 1.9 to 2.6 and a transparent material having lower refractive index than that of the transparent minute ball and includes a protection layer covering the whole transparent minute ball uniformly with a fixed thickness. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a retroreflective member. More specifically, the present invention relates to a retroreflective member useful for displaying a road surface wet with water such as rain. The present invention also relates to a road marking body including such a retroreflective member.

[0002]

2. Description of the Related Art As is well known, retroreflective members generally have high visibility and are used for road signs and road markings. A typical retroreflective member includes a reflective element composed of glass transparent microspheres (hereinafter referred to as “glass beads”) and reflects a light ray in a direction parallel to an incident light ray emitted from a light source or the like (ie, Retro-reflection) is made possible.

The above-mentioned retroreflective member is generally classified into a glass bead exposed type and a glass bead embedded type.
An example of a glass bead exposed type retroreflective member is disclosed in Japanese Patent Laid-Open No.
-81794, Japanese Utility Model Publication 6-13229, U.S. Pat. No. 2,440,584 and PCT International Publication No. 00/23655, and 00/2.
No. 3257 pamphlet and No. 01/29587 pamphlet. In the retroreflective members described in these documents, a transparent space layer is provided between the partially exposed glass beads and the reflective layer.

Particularly, Japanese Utility Model Publication No. 6-13229 discloses that
Disclosed is a reflective element in which a transparent space layer (resin layer) and a reflective layer are partially and sequentially coated on individual surfaces of transparent microspheres such as glass beads. Also, US Pat. No. 2,4
No. 40,584 discloses that ordinary glass beads having a refractive index of 1.50 to 1.55 are a transparent coating layer made of a resin having the same refractive index as that of the glass beads (preferably a glass bead having a diameter of 20 to Partially covered (with 40% thickness) is disclosed to improve the angular dependence of retroreflective performance.

Typical glass beads have high hardness and low toughness and are therefore susceptible to fracture or damage. Therefore, if the glass bead exposed type retroreflective member is applied to a road marking object with the glass bead reflecting element described in the above-mentioned document, usually, pebbles or sand scattered on the road are Etc. give a substantial impact to the glass beads through the vehicle. Thus, the road marking body has poor durability and it is difficult to maintain the visibility for a long time.

Further, Japanese Patent Laid-Open No. 10-102444 discloses an oxide photocatalyst particle for the purpose of long-term visibility.
The coating of glass beads with a composite material containing silicone and a water repellent fluororesin is disclosed. However, the above composite material is inferior in transparency, and unless the glass beads are coated with a thickness of about 1 μm or less, the glass bead-embedded retroreflective member does not show effective visibility. Also, with such a thickness, impact on the glass beads is unavoidable. Therefore, although the glass bead-embedded retroreflective member is generally superior in durability to the glass bead-exposed type, such a road marking body of the retroreflective member cannot be expected to have practical durability and has long-term visibility. Have difficulty.

Further, the glass bead exposed type retroreflective member usually reduces the visibility in rainy weather. This is because the glass beads are covered with rainwater and the light rays cannot be efficiently reflected in the direction parallel to the incident light rays. If the glass beads have a relatively high refractive index as disclosed in JP-A-63-123835, it may be possible to prevent the visibility of the glass-bead-exposed retroreflective member from being deteriorated in rainy weather. unknown. It is generally known that when glass beads have a double refractive index with respect to the medium around them, significant retroreflection is observed. For example, if the medium consists of water (with an index of refraction of about 1.3), such glass beads are very special, although the preferred glass beads have an index of refraction of about 2.6.

Further, the reflecting element of Japanese Utility Model Publication No. 6-13229 is manufactured through complicated steps due to its asymmetry and nonuniformity. Further, in order to form a retroreflective member, this reflective element usually needs to be two-dimensionally arranged with the exposed surface of the transparent microspheres facing outward. Otherwise, the retroreflective member cannot arrange the exposed surface of the transparent microspheres in all directions to show effective visibility.

On the other hand, an example of a glass bead-embedded retroreflective member has glass beads coated with a transparent material, as disclosed in Japanese Patent Application Laid-Open No. 50-81794. Generally, the transparent material used here has an index of refraction of about 1.5, which is higher than that of air (approximately 1). Therefore, in order for the glass bead-embedded retroreflective member to exhibit desired retroreflectiveness or visibility regardless of weather, it is usually 2.
It requires very special glass beads with a very high index of 6-3.

[0010]

The present invention, therefore, does not require the use of the special glass beads as described above.
An object of the present invention is to provide a retroreflective member that is easily improved in durability and visibility particularly in rainy weather.

Another object of the present invention is to provide an article in which the excellent features of such a retroreflective member can be utilized.

[0012]

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems, and is made of a reflective base material and a plurality of transparent composites partially embedded in the reflective base material. Microspheres, wherein the composite microspheres are composed of transparent microspheres having a refractive index of 1.9 to 2.6 and a transparent material having a lower refractive index than the transparent microspheres, and have a substantially constant thickness. With a protective layer uniformly covering the entire transparent microspheres,
The retroreflective member is characterized by including.

The present invention also resides in a road sign provided with the retroreflective member of the present invention.

The present invention further resides in a road marking body provided with the retroreflective member of the present invention.

[0015]

BEST MODE FOR CARRYING OUT THE INVENTION The retroreflective member according to the present invention can be implemented in various forms. Hereinafter, the present invention will be described with reference to its preferred embodiments, although not limited thereto.

FIG. 1 is a sectional view showing a preferred embodiment of the retroreflective member according to the present invention. The illustrated retroreflective member 10 has a reflective base material 7 and a plurality of transparent composite microspheres 3 partially embedded in the reflective base material 7. The reflective substrate 7 used here comprises a support 5 and a reflective layer 6 supported thereby. Also,
The transparent composite microspheres 3 are obtained by coating the transparent microspheres (core) 1 having a refractive index of 1.9 to 2.6 and the entire transparent microspheres 1 with a uniform and adjusted film thickness. It is composed of a protective layer 2. The protective layer 2 is made of a transparent material having a refractive index lower than that of the transparent microspheres 1 and has a substantially constant film thickness, so that the entire transparent microspheres 1 are uniformly covered. The configuration of the illustrated retroreflective member 10 can be variously modified within the scope of the present invention, as described in detail below.

The reflective base material, which is one of the main constituent elements of the retroreflective member of the present invention, can be used by selecting an optimum material in consideration of the purpose of use of the retroreflective member and the place of application. . The reflective substrate is generally a material that can be thermally plastically deformed in consideration of processing of the surface of the reflective substrate (for example, formation of protrusions) and good followability with respect to the base. For example, it is preferably formed from natural or synthetic rubber or resin. Suitable substrate materials include, but are not limited to, those listed below, acrylonitrile-butadiene copolymers, neoprene, polyacrylates, natural rubber or styrene-butadiene copolymers, or virgin materials containing at least one of these. For example, vulcanized rubber.

The reflective substrate used in the present invention may be formed of a material curable by heat and / or light, if necessary. Such materials can impart improved durability to the substrate.

The reflective base material can be used in any shape depending on the form of the retroreflective member using the reflective base material.
The reflective substrate is usually used in the form of a sheet,
If necessary, it may be used in the form of a flat plate, a cylinder, a prism, or the like. Therefore, the size of the reflective substrate can be arbitrarily changed depending on such a form.

The surface of the reflective substrate may be flat or may have protrusions in any pattern. For example, when the retroreflective member of the present invention is used for a road marking body or the like, it is preferable to provide a protruding portion for improving visibility.

It is preferable that the protruding portion, which is optionally provided on the surface of the reflective base material, is provided integrally with the base material. In other words, the protruding portion is preferably integrally formed with the base material during the production or processing of the reflective base material, but if necessary, independently of the same or different material as the base material. It may be formed. In the latter case, the protruding portion can be attached to the surface of the base material by using a fixing means such as an adhesive.

When a protrusion is provided on the surface of the reflective substrate,
In order to expose the microspheres from the horizontal plane of water to improve the retroreflectivity when wet, a plurality of protruding portions can be provided in various arrangement patterns. A suitable layout pattern for the protrusions is multiple stripes, multiple circular blocks,
It may be a plurality of rectangular blocks or a combination thereof. Further, other shapes may be arbitrarily combined as long as they do not adversely affect the effects of the present invention.

The size of each protrusion is not particularly limited and can be widely changed. The height of the protrusions from the surface of the base material is usually about 0.
It is preferably in the range of 5 to 2.0 mm. If the height of the protrusion is less than about 0.5 mm, the retroreflective efficiency of the composite microspheres fixed to the surface is significantly reduced, and conversely, the height of the protrusion exceeds about 2.0 mm. In this case, there are inconveniences such as an increase in the material cost of the base material.

In the retroreflective member of the present invention, the reflective base material preferably has a support and a reflective layer provided between the support and the composite microspheres. However, the reflective substrate may be composed of only the reflective layer as long as it does not adversely affect the effects of the present invention when used alone.

As described above, the support is preferably composed of acrylonitrile-butadiene polymer, neoprene, polyacrylate, natural rubber, unvulcanized rubber containing at least one styrene-butadiene polymer, and the like. This is because these support materials have appropriate flexibility and can impart viscoelasticity to the reflective substrate. Due to this viscoelasticity, for example, when the retroreflective member of the present invention is used as a road marking body or the like, the force and pressure of vehicle road traffic can be absorbed without generating an internal force that tends to remove the marking body from the road. Further, in the case of a road marking object, when there is a traffic of a car or a pedestrian, that is, when a pedestrian traffics in a direction perpendicular to the flow direction of the marking object, the protruding portion becomes inconspicuous. Therefore, there is an effect that the visibility is further improved only in the portion where the gap of the protruding portion is eliminated.

The reflective layer for fixing the composite microspheres preferably comprises a resin material and a pigment dispersed therein. Here, the resin material functions as a binder and is made of a thermoplastic or thermosetting polymer binder. Such a binder is, for example, a vinyl-based thermoplastic resin, a polyurethane resin, or an epoxy-based resin. Also, the pigment is preferably a white pigment, such as titanium oxide. In addition to the function as a white colorant, the particles of titanium oxide provide the reflective layer with an efficient reflective function. As a result, when the light of the headlight of the vehicle is incident on the road marking object, it can be retroreflected with a wide viewing angle and reach the driver. Therefore, the particles of titanium oxide can provide the road marking body with higher visibility. The pigment used here is not limited to the above-mentioned titanium oxide. Other useful pigments include pearlescent pigments, specular reflectors such as aluminum powder or flakes, chrome lead pigments and the like. Further, other pigments used for coloring pavement markings can be used, if necessary. Incidentally, regarding the details of the reflective layer, if necessary, for example, JP-A-2-3860.
See Publication No. 5.

In addition to the above-mentioned support and reflective layer, the reflective substrate may optionally have other elements commonly used in retroreflective members. Suitable substrate constituents include, for example, an adhesive layer provided on the back surface of the support.

The composite microspheres, which are another main component of the retroreflective member of the present invention and which are fixed by the reflective base material and greatly contribute to the retroreflective characteristics, durability and the like of the present invention, are as described above. In addition to having transparent microspheres as a core, the entire surface of the core is covered with a transparent material having a lower refractive index than the core as a protective layer.

The transparent microspheres as the core are for exhibiting a high level of retroreflectivity in the retroreflective member of the present invention, and can be formed from various transparent materials. Suitable microspheres are glass beads, plastic beads, glass-ceramic beads and the like, with glass beads being particularly useful.

The refractive index of transparent microspheres is usually 1.9 to.
It is in the range of 2.6, and particularly preferably in the range of 2.0 to 2.4. If the refractive index of the transparent microspheres is less than 1.9, the desired retroreflection efficiency cannot be obtained.
On the other hand, if it exceeds 2.6, the protective layer has to be thin,
The protective layer tends to fail to function effectively.

The particle size (diameter) of the transparent microspheres can be widely varied depending on the desired function and effect, but is usually in the range of about 50 to 200 μm on average, and particularly 100 to It is preferably in the range of 200 μm. If the particle size of the transparent microspheres is smaller than 50 μm, the retroreflection efficiency is significantly reduced. On the contrary, when the particle size of the transparent microspheres is larger than 200 μm, for example, when the retroreflective member of the present invention is used as a road marking, it is greatly impacted by a running vehicle and peeled off from the surface of the reflective base material. , It becomes easy to fall off.

The transparent microspheres may be composed only of glass beads, plastic beads or other beads. Suitable transparent microspheres can have an additive such as titanium oxide or barium titanate to effectively improve the refractive index.

As described above, the protective layer covering the entire surface of the core is made of a transparent material having a refractive index lower than that of the transparent microspheres. The refractive index of such transparent materials is typically about 1.
It is preferably in the range of 34 to 1.75. If the refractive index of the transparent material is less than 1.34, the protective layer must be thin, and if it exceeds 1.75, the desired retroreflective effect cannot be obtained. To do.

The transparent material used for forming the protective layer preferably has toughness in addition to the above-mentioned refractive index.

The transparent material capable of satisfying the above-mentioned refractive index and toughness includes various materials, but resin materials such as urethane resin, acrylic resin and epoxy resin are preferable. If necessary, these resin materials may be mixed and used. A urethane resin is particularly useful for forming the protective layer.

The protective layer is usually formed of the above-mentioned transparent material alone, but it is preferable to include an optional filler in order to improve the retroreflection efficiency. The filler used here is usually used in the form of particles, and may be inorganic particles, organic particles, or a mixture of these particles. Although not limited to those listed below, suitable inorganic particles include, for example, colloidal silica, silicon dioxide, aluminum oxide, and
Suitable organic particles are, for example, polymethylmethacrylate and the like.

The protective layer is usually coated on the surface of the core with the transparent material as described above (containing a filler if necessary) at the same time as or after the formation of the core made of transparent microspheres by a conventional thin film forming method. Thus, it can be advantageously formed. In that case, the film thickness of the protective layer can be changed within a wide range according to desired effects and the like. Although the thickness of the protective layer is usually determined by the size of the transparent microspheres, the particle size of the transparent microspheres is 5 as described above.
When it is in the range of 0 to 200 μm, it is in the range of about 5 to 50 μm, preferably in the range of about 10 to 30 μm. If the thickness of the protective layer is less than 5 μm, the function as a protective layer will be lost, and on the contrary 50 μm
If it exceeds m, there is a problem that it takes time to form a film.

When the transparent microspheres of the core and the transparent material of the protective layer have a refractive index of 2.26 and 1.50, respectively, the thickness of the protective layer is substantially 13 times the radius of the transparent microspheres.
It is preferably about 22%. This is because in such a range, a significant improvement in retroreflection efficiency can be achieved. Further, under such conditions, the optimum value of the film thickness of the protective layer that maximizes the retroreflective efficiency in water is about 15% of the radius of the transparent microspheres.

The composite microspheres are usually used in uniform sizes, that is, only those of approximately the same size are used.
If desired, the size may be varied, that is, two or more types of composite microspheres may be used in any combination. Furthermore, in combination with the composite microspheres as described above, conventional microspheres may be additionally used in the field of retroreflective members.

The microspheres that can be additionally used provide retroreflectivity to the road markings and other articles, especially when water is not adhered, and thus visibility is obtained even in fine weather. It is used for the purpose of making it possible and solving the problem of surface friction from a road marking body and the like, and is preferably made of glass beads. The refractive index of the transparent microspheres is preferably at least 1.
It is 5 or more. If the refractive index of the transparent microspheres is less than 1.5, the above effects cannot be sufficiently obtained. The refractive index of the additional transparent microspheres is particularly preferably in the range of 1.5 to 2.0 from the viewpoint of easy availability.

The particle size of the additional transparent microspheres can be widely changed depending on the desired action and effect, but it is usually preferable to be in the range of about 20 to 100 μm on average. If the particle size of the transparent microspheres is smaller than 20 μm, the slip resistance value decreases. On the other hand, when the particle size of the transparent microspheres is larger than 100 μm, the transparent microspheres are easily separated from the surface of the reflective base material by an impact from a running automobile and easily fall off.

In addition, the additional transparent microspheres have a Mohs hardness of at least 6.5, preferably about 7 to 12, in order to prevent the additional microspheres from being damaged by the traffic of automobiles or pedestrians. It is preferable. If the hardness of the transparent microspheres is less than the above lower limit, not only damage cannot be avoided, but also slip resistance cannot be imparted to the surface of the road marking body or the like.

The composite microspheres are used by being partially embedded in the surface of the reflective base material in order to fully exert the effect. The depth at the time of burying is not particularly limited as long as the desired effect is obtained and the substrate is not easily detached during use. The embedding rate of the composite microspheres is usually in the range of about 40-60% of the particle size, preferably in the range of about 45-55%.

Similarly, the composite microspheres can be embedded in the surface of the base material in various patterns depending on the desired retroreflectivity. That is, the composite microspheres may be wholly or partially densely embedded in the surface of the base material, or may be coarsely embedded. The composite microspheres can be embedded roughly or densely, but usually about 10 to 400 g
The density is preferably / m ² . When the distribution density of the composite microspheres is less than about 10 g / m ² , the retroreflective efficiency is reduced. On the contrary, when it exceeds about 400 g / m ² , inhibition of retroreflection due to the shadow of the composite microspheres occurs. . In addition, in the case where the reflective base material has a protruding portion on its surface, the composite microspheres may be embedded only in the protruding portion, otherwise, between the protruding portions arranged adjacent to each other. That is, it may be selectively embedded in the valley portion of the protruding portion. Further, the transparent microspheres may be provided on the side surface of the protruding portion in addition to the valley portion of the protruding portion.

In the retroreflective member of the present invention, the composite microspheres are formed such that a transparent material (protective layer) having a low refractive index is uniformly formed around a microsphere (core) having a high refractive index such as glass beads. Since it is constructed by coating, it can be designed to have a retroreflective performance in water that is comparable to beads having a higher refractive index than glass beads. This is because when the protective layer having a low refractive index is formed concentrically on the surface of the core microsphere having a high refractive index, the protective layer has an effect of increasing the refraction angle of incident light. Hereinafter, this will be described with reference to FIGS. 2 and 3.

FIG. 2 is a partially enlarged view of the retroreflective member shown in FIG. 1. This optical system was used for theoretical calculation of retroreflective efficiency. As an example, let us consider the retroreflective performance in water of a composite microsphere 3 composed of a transparent microsphere (core) 1 having a refractive index of 2.26 and a protective layer 2 covering the transparent microsphere 1 having a refractive index of 1.5.
Incident light L ₁ is incident on the composite microsphere 3 as shown in the figure,
After being reflected by the wall surface of the protective layer 2, it is emitted from the composite microsphere 3 in the direction of arrow L ₂ . Here, when the film thickness of the protective layer 2 is less than the ideal range, the bending angle of most of the incident light L ₁ is 1
It does not reach 80 ° (retroreflection). On the contrary, if the thickness of the protective layer 2 is too large, the bending angle exceeds 180 °, and the retroreflection efficiency (the ratio of the light retroreflected to the light incident on the composite microsphere 3) decreases. Therefore, it is necessary to optimize the film thickness of the protective layer according to the refractive index of the core microspheres and the protective layer. Core microspheres with a refractive index of 2.26 and a refractive index of 1.5
In the case of composite microspheres consisting of the protective layer of, the thickness of the protective layer is
About 15% of the radius of the core microspheres is desirable.

FIG. 3 is a graph showing the results of geometrical optics analysis of the relationship between the refractive index of the protective layer, the maximum retroreflective efficiency, and the film thickness of the protective layer that gives the maximum refractive index to the composite microspheres as described above. . In the figure, curve I represents the thickness of the protective layer, and curve II represents the maximum retroreflection efficiency. The retroreflection efficiency here is the ratio of the total incident light (parallel light) whose bending angle is included in the range of 180 ± 1.5 °. As can be seen from the curve of FIG. 3, in the region where the refractive index of the protective layer is smaller than that of the core microspheres, the maximum retroreflecting efficiency of the protective layer shows a high value, which means that the refractive index of the protective layer is It is about 4 to 4.5 times that of 2.26 (optically equivalent to the core microspheres). Although not shown, when the refractive index of the protective layer exceeds that of the core microspheres, the retroreflection efficiency of the protective layer is lower than that when the refractive index of the protective layer is 2.26. Further, the film thickness of the protective layer that gives the maximum retroreflective efficiency increases as the refractive index of the protective layer increases.

The retroreflective member of the present invention can be manufactured simply and easily without suffering a decrease in yield. For example, composite microspheres used for retroreflective members are
The structure is spherically symmetric because the protective layer uniformly and completely covers the transparent microspheres of the core. Therefore, a large amount of transparent microspheres can be uniformly coated at one time. Also,
Since the obtained composite microspheres have spherical symmetry, a large number of composite microspheres are scattered on the reflective layer, and they are partially buried,
Even after the intended retroreflective member is formed, all the composite microspheres are oriented in the same direction, and therefore, it is possible to simply and easily manufacture a retroreflective member having high retroreflective performance as in the past. it can.

The retroreflective member of the present invention can be manufactured according to various techniques. As a preferable example, the retroreflective member can be manufactured according to the following steps. (1) A step of forming a reflective base material from a thermally plastically deformable material, (2) preparing a molding die having a plurality of openings penetrating through, and forming composite microspheres on at least one surface of the molding die. Coating step, and (3) pressing the composite microsphere application surface of the molding die against one surface of the reflective base material to allow a part of the base material to enter the opening of the molding die, Transferring the sphere to the reflective substrate.

In step (1), a commercially available material can usually be used as the reflective substrate.

For the composite microspheres used in the step (2), for example, a coating solution for forming a protective layer is prepared, and the coating solution is thinly and uniformly applied on the surface of the transparent microspheres to be the core. It can be manufactured by coating. Spray coating can be advantageously used for coating, but other conventional coating methods may be used if necessary.

Further, the transfer of the composite microspheres in the step (3) is performed, for example, by using a molding die in which a plurality of cylindrical openings are penetrated, and therefore circular openings are exposed on both the upper surface and the lower surface. It can be carried out.

The retroreflective member of the present invention can be provided in various forms depending on its use. For example, when it is used as a road sign, it is in the form of a cylinder, prism, plate, or the like, and when it is used as a road marking, it is in the form of a sheet such as a square or a rectangle. If necessary, the retroreflective member may be provided in a spherical shape, a triangular prism shape, a conical shape, or the like.

Further, the retroreflective member can be arbitrarily changed in size as well as in its form. As an example, if a retroreflective member is used as a sheet-shaped road marking body, the width is about 1 cm from a small thing of about 10 cm in length and width.
Various dimensions can be adopted, depending on the purpose of use, from 0 to 50 cm × length of about 2 to 10 m or larger.

The retroreflective member of the present invention can be advantageously used in various fields by utilizing its excellent durability, good visibility in rainy weather, and excellent retroreflectivity. Suitable uses of the retroreflective member include, but are not limited to, those listed below, road signs,
For example, a road marking object.

For example, when the retroreflective member of the present invention is used for a road marking body, it can be applied in various patterns to a predetermined portion of the road surface depending on the mounting location and desired effect. Since the pavement marking body is usually used as a marking line, that is, as a center line, a sidewalk display mark, a direction indicating mark, or a regulation indicating mark, it can have a pattern suitable for the intended use. Generally, it is preferable that the road marking body is provided so as to exhibit a linear pattern when seen in a plan view. The linear pattern may be, for example, a straight line, a broken line, or a combination thereof.

FIG. 4 schematically shows an example in which the retroreflective member of the present invention is used as a road marking body. In the illustrated road marking body 20, a trapezoidal protrusion 12 is provided on the surface of the pavement material 11, and the retroreflective member 10 of the present invention is attached so as to cover the protrusion 12.
The retroreflective member 10 used here is the reflective base material 7 thereof.
The composite microspheres 3 are not arranged on the entire surface of
It is arranged only in the step portion. Also, in the illustrated example,
Although the trapezoidal protrusions 12 are provided on the surface of the pavement material 11, such protrusions may be omitted if unnecessary.

[0058]

EXAMPLES Next, the present invention will be further described with reference to the examples. It should be understood that the present invention is not limited to the examples below. Manufacture of retroreflective member: A urethane resin having a refractive index of about 1.48 (product name "Urethane Dispersion RESAMIN D-6028", manufactured by Dainichiseika) for forming a protective layer.
And colloidal silica (trade name "SNOWTECH
C ", manufactured by Nissan Kagaku Co., Ltd.) was mixed at a weight ratio of 1: 2 to prepare a coating solution. Next, separately prepared refractive index of about 2.26, average particle size of about 60 μm and density of about 4.6 g.
The surface of each glass bead (hereinafter referred to as "tango bead") having a diameter of 1 / cm ³ was carefully coated with the above-mentioned coating solution so that the desired protective layer was uniformly formed on the entire surface of each glass bead. . Here, "tango beads" are titanium oxide (TiO ₂ ) and barium oxide (B).
aO) as a main component, which is glass beads, and is disclosed in Japanese Patent Publication No. 48-31734 (US Pat. No. 3,493,40).
(Corresponding to No. 3)). A wet spray coating device (manufactured by Front Sangyo Co., Ltd.) that employs a spiral flow system is used as the coating device.
The coating conditions were set so that the film thickness of the protective layer was about 15% of the radius of the glass beads. Observation of the surface of the obtained composite microspheres with a scanning electron microscope reveals that each composite microsphere is spherical, and the core microspheres are uniformly and completely covered by a protective layer made of a transparent urethane resin. It was confirmed.

After producing the composite microspheres as described above, a retroreflective member is formed using a mold having a plurality of cylindrical openings penetrating therethrough, thus exposing circular openings on both the upper and lower surfaces. Was manufactured. After the entire mold was wet with water, the composite microspheres produced in the previous step were attached to the surface of the mold and the inside of the opening.

Next, a urethane resin base material containing a white pigment dispersed therein is separately prepared as a base material for about 150.
It was heated to ℃ and melted. Then, the molten base material was applied to an aluminum plate having a thickness of 1 mm prepared in advance with a flat application thickness of about 2 mm.

Subsequently, the surface of the molding die to which the composite microspheres are adhered is brought into close contact with a urethane resin base material to apply pressure, and the protruding part is formed as a base material while protruding a part of the base material from the opening. It was molded integrally. After transferring the composite microspheres to the substrate and then cooling the substrate to room temperature, a desired retroreflective member in which the composite microspheres were partially buried was obtained. Evaluation of visibility: The visibility of the retroreflective member manufactured as described above was evaluated as follows.

At night, the retroreflective member was visually observed by applying a headlight from the inside of an automobile 10 m away from the location where the retroreflective member was placed. This observation was carried out both in fine weather and in rainy weather. Further, the observation in the rain was also performed after promoting the abrasion of the retroreflective member. In addition, the promotion of wear of the retroreflective member is described in the Ministry of Construction Notification No. 13 of July 21, 1989.
According to the accelerated wear test method of No. 22, abrasion of the retroreflective member was repeated by about 4,000 times. As a result of the observation, the retroreflective member could be observed with high visibility both in fine weather and in rainy weather. Even after accelerating the abrasion, the observation result was comparable to that before the abrasion. Therefore, the retroreflective member according to the present invention is
It has become clear that effective retroreflection in rainy weather can be maintained for a long period of time. Durability acceleration test: A durability acceleration test of the retroreflective member manufactured as described above was performed by a sandblast test. The test procedure is as follows: (i) A hollow tube with a diameter of 50 mm and a length of 1 m is erected vertically on a work table with a gap.

(Ii) Between the lower end of the hollow tube and the workbench,
A retroreflective member is arranged.

(Iii) The retroreflective member is fixed by inclining it by 45 ° with respect to the lower end of the hollow tube.

(Iv) Alumina abrasive particles (radius 2 to 5 mm) were supplied to the hollow tube from the upper end thereof to 4.5 kg / mi.
Alumina abrasive particles are dropped in the hollow tube at a mass velocity of n (75 g / sec) to give an impact to the retroreflective member.

(V) The retention rate (%) of the retroreflective efficiency shown after the retroreflective member is shocked is measured.

Test results were obtained as plotted by curve IV in FIG. In FIG. 5, the amount (g) of alumina abrasive particles is plotted on the horizontal axis, and the retention rate (%) of retroreflective efficiency is plotted on the horizontal axis. Also, curve III is
It is a test result of the retroreflective member (control) produced without covering a protective layer for comparison. From the test results shown in the figure, in the case of the retroreflective member of this example, the retroreflective luminance half-life is
It can be seen that the increase is about 2-2.5 times that of the control.

[0068]

As described above, according to the present invention, it is possible to provide a retroreflective member having not only durability but also particularly improved visibility in rainy weather without using special glass beads.

Further, according to the present invention, since the composite microspheres have spherical symmetry, the retroreflective member can be manufactured with a high yield by an easy and simple method.

Further, according to the present invention, it is possible to provide a road sign or a road marking body which makes the most of the remarkable features of the retroreflective member of the present invention. In particular, since the composite microspheres coated with a protective layer having high toughness around the core microspheres are fixed to the reflective substrate, excellent resistance to cracking and chipping can be imparted to the composite microspheres, and therefore, Road signs can be used for a long period of time without repair or replacement.

[Brief description of drawings]

FIG. 1 is a sectional view showing a preferred embodiment of a retroreflective member according to the present invention.

FIG. 2 is an enlarged cross-sectional view showing the vicinity of the composite microspheres of the retroreflective member shown in FIG.

FIG. 3 is a graph showing the results of geometrical analysis of the relationship between the refractive index of the protective layer, the maximum retroreflective efficiency, and the film thickness of the protective layer that provides the composite microsphere used in the present invention.

FIG. 4 is a sectional view showing an example in which the retroreflective member of the present invention is used for a road marking body.

FIG. 5 is a graph showing the results of a durability acceleration test conducted on the retroreflective member of the present invention.

[Explanation of symbols]

1 ... Transparent microsphere 2 ... Protective layer 3 ... Composite microsphere 5 ... Support 6 ... Reflective layer 7 ... Reflective substrate 10 ... Retroreflective member 11 ... Pavement 12 ... Projection 20 ... Road marking object

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Norihiro Kasai             Sumitomo 3-8-8 Minami-Hashimoto, Sagamihara City, Kanagawa Prefecture             Within 3M Co., Ltd. F term (reference) 2D064 AA01 BA03 EB26 EB35                 2H042 EA05 EA08 EA12 EA13 EA19                 5C096 AA02 AA15 AA27 AA29 BA03                       BB02 BB34 BB39 CE22 EB05                       FA03 FA07

Claims (5)

[Claims] 1. A reflective base material and a plurality of transparent composite microspheres partially embedded in the reflective base material, wherein the composite microsphere comprises 1.9 to 2.6. A transparent microsphere having a refractive index; and a protective layer made of a transparent material having a refractive index lower than that of the transparent microsphere and uniformly covering the entire transparent microsphere with a substantially constant thickness. A retroreflective member characterized by the above. 2. The retroreflective member according to claim 1, wherein the transparent microspheres have an average diameter of 50 to 200 μm. 3. The retroreflective member according to claim 1 or 2, wherein the transparent material has a refractive index of 1.34-1.75. 4. The reflective substrate according to claim 1, further comprising: a support and a reflective layer provided between the support and the composite microspheres. The retroreflective member as described in 1 above. 5. A road marking body comprising the retroreflective member according to any one of claims 1 to 4.