KR19990028473A - High entry angle retro-reflective products with spherical refractive elements - Google Patents

Abstract

Retroreflective product 80 provides effective retroreflective luminosity at very high entry angles 82 as well as at low entry angles 60 and under wet conditions. The article includes a spherical refractive element 60 having a refractive index greater than 1.35 and less than 1.75 adhered to a cover 66 film of an enclosed-lensoidal retroreflective base sheet.

Description

High entry angle retro-reflective products with spherical refractive elements

Road signs, such as the centerline and outer lanes of the roadway, are important for visually guiding motorists. Road marking materials are used as traffic control signs for many purposes, such as short lane lane stripes on roads, stop lines, pedestrian road signs at intersections, and the like. A common form of road marking product is an adhesive-backed tape that is attached to the road surface at the desired location and length. The upper surface of the tape has a selected color and typical retroreflective properties.

Currently, many flat road signs typically rely on exposed-lens optical systems, which are reflective such as titanium dioxide (TiO ₂ ) or lead chromate (PbCrO ₄ ) as a retroreflector mechanism. Transparent microspheres partially embedded in a binder layer containing pigment particles. In use, the light from the headlights of the vehicle enters the microspheres and is refracted to reach the reflective pigments. Some of the light typically returns to the vehicle along the original path of entry, making it visible to the driver. The amount of refraction and concentration of these microspheres depends in part on the maintenance of a low index of refraction at the air interface of the exposed portion of the microspheres. In rainy conditions, the microspheres are wetted with water, reducing the ability of the light to refract and consequently decrease the retroreflective function.

One solution to this problem is raised road markings in which retroreflective elements appear somewhat vertical. U.S. Pat. Nos. 4,388,359 to Ethen et al. And 4,988,555 and 4,988,541 to Hedblom disclose road signs with projections having exposed-lens retroreflective elements on their sides.

It is also known to use sealed-lens retroreflective structures on road markings. Typically, such structures are used as spot guides enhanced by continuous paint or tape labels. See US Patent No. 5,277,513 to Flanagan et al. And US Patent No. 5,340,231 to Steeeer et al. Closed-lens retroreflective sheets with flat cover films (sometimes also referred to as cover sheets, top sheets, top films, etc.) have been constructed as a means to improve wet retroreflectivity. McGrath, US Pat. No. 4,025,159, of which encapsulated-lens retroreflective products are disclosed, and US Pat. See, e.

Crone US Pat. No. 4,145,112 discloses a series of short-range permeable layers having a base retroreflective layer at the bottom and a longitudinally extending top surface soft edge surface at the front and back (formed for the anticipated light source to be reflected), respectively. A product comprising a light-directing layer consisting of protrusions of is disclosed. The front edge surfaces are arranged to intersect (ie, relatively vertically) with the expected path of high incidence angle light, so the front edge surfaces transmit rather than reflect a large amount of incident light from the approaching vehicle. The back edge surface reflects light transmitted through the front edge surface into the passageway within a predetermined angular range for retroreflection by the retroreflective element, and also directs the light retroreflected by the retroreflective element toward the light source. It is arranged to reflect back through the surface. In order to maintain proper retroreflection, precise morphological relationships of the upwardly extending edge surfaces of the front and rear surfaces of each projection must be established and maintained. In addition, there is a tendency for the flexibility of such sheets to decrease due to the protrusions extending in the longitudinal direction. Wyckoff, US Pat. No. 4,236,788, discloses a related type of road marking strip, with two sides of transverse prism passing downward internal reflections from one side into the base sheet and into the space between successive prisms. Is applied to provide the refraction of the into the base sheet from the other side. As in the product disclosed in US Pat. No. 4,145,112, maintaining a precise morphological relationship between the two upward faces of the prism is essential.

Wykov's U. S. Patent No. 3,920, 346 discloses a serrated cover strip comprising a protrusion with a curved edge and comprising an upwardly disposed retroreflective member embedded in the protrusion. It is known that the curved edges of the raised projections reduce the loss of incident light so that the indicia emits light by the light incident on the marker strip over a wide angle. In addition, since the retro-reflective member disposed upward on the protrusion is incorporated, the angle of light entering or entering from the approaching vehicle is narrowed, and the product can enable more effective retro-reflection.

Eigenmann, US Pat. No. 4,072,403, discloses a retroreflective assembly that is particularly useful in situations where retroreflection is required in rainy weather. The assembly disclosed above includes a transparent globule with a single layer of transparent microspheres in a portion of the globule and a reflective layer disposed behind the microspheres. A retroreflective assembly, often referred to as a "globulb / microsphere retroreflective assembly", is located on the top surface of the road markings where the retroreflection of light at high incidence angles is enhanced by the assembly. Bradshaw, US Pat. No. 5,268,789, discloses an improved globule / microsphere retroreflective assembly and an improved method for making such an assembly.

European Patent No. 385746 B1 to Kobayashi et al. Includes a layer of large glass microspheres embedded on top of a retroreflective buried-lensed base sheet. These retroreflective road signs are known to be particularly useful in rainy weather because large glass microspheres are partially exposed to air. However, the disclosed road sign is limited to use microspheres as a light collecting source. Moreover, the road markings are known to increase the retroreflectivity of the base sheet at entry angles between only 60 ° and 80 °. It is known in the art that high entry angles greater than approximately 85 ° are more common in road marking applications. Moreover, the reference discloses that large glass microspheres with refractive indices less than 1.75 are not suitable for the present invention.

Currently available road markings sometimes only retroreflect effectively for a narrower range of angles of incidence than desired. In addition, currently available road signs are not as effective retroreflectors as desired for some applications. For example, currently available flat road markings that rely on microspheres partially embedded in the layer containing pigment particles are most readily visible at distances of less than 80 meters. At longer distances, the retroreflected luminous intensity decreases due to the relatively larger entrance angle of the incident light and limited retroreflective efficiency. In addition to retroreflectivity at low, high incidence angles in general, flat road signs are particularly difficult to see in rainy weather. The elevated road markings have better wet reflectivity because the rainwater will flow out of the raised portions. However, snow removal often occurs as a problem on roads with raised road signs because snow plows tend to be caught on raised projections and to remove signs from the road surface.

There has been a need for low profile retroreflective products that continuously exhibit high retroreflective luminosity at high incidence angles and maintain effective retroreflective luminosity at high incidence angles even when wet. As used herein, “low profile” refers to a product that is low enough to withstand minimal damage to the product from impacts from the snow plow after one winter. There is also a need for retroreflective products that exhibit an effective retroreflective response over a wide range of entry angles for use on vertical surfaces such as guard rails, Jersey barriers and the like.

The present invention relates to retroreflective articles that exhibit high retroreflective luminosity at high and low entrance angles and under wet conditions and methods of making such products. This product is very suitable for use as road marking or as a vertical barrier or delineator marker.

The present invention will be further described with reference to the drawings.

1 is a perspective view of a conventionally known road sign with a light-inducing layer disposed over a base retroreflective layer.

FIG. 2 is a sectional view of the road marking shown in FIG. 1; FIG.

3 is a perspective view of a retroreflective product according to the present invention;

4 is a cross-sectional view of another retroreflective product.

Ideally not adapted to accumulation, these figures are illustrative only and not restrictive.

The present invention is novel and preferably low profile, with improved retroreflectivity at very high entrance angles (more than 88 °) where road signs are observed, bright retroreflection at low entrance angles, and better than typical road signs at wet conditions. Provides retroreflective products that combine much greater retroreflectivity. The present invention also provides a novel method for producing such retroreflective products.

In short, the product according to the invention comprises an enclosed-lense retroreflective base sheet and an array of refractive elements on the front surface of the base sheet. The base sheet includes an array of retroreflective elements underneath a continuous transparent cover layer overlying it. Spherical refracting elements are disposed relative to the retroreflective base sheet such that light incident at a high entry angle to the array of refracting elements is refracted and refracted to be transmitted to the base sheet and back reflected by the base sheet. Unlike the spherical refractive elements disclosed in US Pat. Nos. 4,145,112 and 4,236,788, the front and back sides of the spherical refractive elements of the article according to the present invention do not need to have precise shapes that are interrelated to achieve effective retroreflection. Unlike in European Patent No. 385746 B1, the refractive element is not limited to glass microspheres with a refractive index of 1.75 to 2. As a result, retroreflective products according to the invention can be produced very easily and inexpensively. As described herein, the refractive element can be rounded or have a relatively straight profile. The retroreflective article according to the invention redirects the light entering the high entrance angle to the base sheet using refraction in front of the refractive elements. As a result, the product according to the invention provides surprisingly bright retroreflective and surprisingly durable.

Retroreflective products according to the invention are particularly suitable for applications in which light enters a high entrance angle greater than approximately 85 °, for example in the form of road markings. Such applications include applications in which incident light can be incident in any direction, such as road signs and horizontal signs. Examples describing such horizontal signs include legends and signals located on the floor of a parking lot, and arrows and lane signs located on the floor of an intersection to indicate that they are usually handicaped parking areas. In addition, the retroreflective products according to the invention are also very suitable for use in vertical surfaces such as guardrails, building walls lined in alleys, Jersey barriers, bridge abutments, and especially at high angles of incidence. Suitable. The advantage of retroreflective products according to the invention is that, in addition to showing enhanced retroreflective luminosity at high incidence, retroreflective products also exhibit high retroreflective luminosity even at low entry angles within 30 ° to 40 ° where the label is often observed. Is the point. Accordingly, the product according to the invention is particularly suitable for use in walls and barriers and other applications where vehicles are installed along highways that approach structures at a wide range of angles where effective retroreflective brightness is required. For example, the first roadway may be a vertical barrier installed substantially parallel to a portion thereof, and the second roadway may intersect the first roadway. If the surface of the barrier is provided with a seat according to the invention, effective retroreflection is provided for vehicles approaching the barrier on both roads, thereby increasing safety. Retroreflective products according to the invention are used, for example, in a curved format wrapped around traffic cones and barrels or wrapped in curved guard rails and the like, thus providing an excellent degree of entry of the product. angularity provides excellent retroreflective brightness over substantially the entire visible area.

Unlike exposed-lensed retroreflective sheets that do not reflect back when wet, retroreflective products according to the present invention have wet retroreflective properties. This means that the product according to the invention is retroreflective in the early morning when dew is collected in the product, or in similar conditions, when the rainwater is drained but the product is not yet dry. In addition, in road marking applications, the surface of the spherical refracting element is raised so that the water flows easily and the product continues to maintain wet retroreflection. Yet, the profile of the raised surface is relatively low, allowing retroreflective products to maintain their utility even in areas where snow plows are used.

In brief summary, the method according to the invention provides a retroreflective base sheet comprising (1) an array of retroreflective elements and a cover layer; (2) attaching or forming an array of spherical refracting elements on the cover layer, the spherical refracting elements being retroreflected by the base sheet and refracted by the product so that light entering the array is refracted to be transmitted through the base sheet; It is arranged relative to the base sheet to be further refracted by the spherical refracting elements retroreflectively.

The process of making retroreflective products according to the invention is very easy compared to the conventional process for producing retroreflective products comprising a light-inducing layer and a retroreflective base sheet. In conventional retroreflective products, such as those disclosed in US Pat. Nos. 4,145,112 and 4,236,788, the light-inducing layer must be carefully formed. In contrast, the refractive element according to the invention can be randomly positioned and have a random shape on the retroreflective base sheet if desired. In addition, the refractive element according to the present invention is very smallly affected from impact and abrasion by road transport, which tends to twist the light-induced layer of conventional retroreflective products, which maintains the precise shape of the retroreflective This is not important for implementation. After all, since the maintenance of precise geometry is not important, softer and more adaptable materials can be selected, thereby increasing the ability of the road markings according to the invention to remain on the roadway.

The retroreflective sheet according to the present invention provides a novel optical system that increases the retroreflective property of the base sheet at high entrance angles without compromising retroreflectivity at all other entrance angles. As used herein, "high entry angle" means an angle greater than approximately 85 ° (an explanation of the term is provided at the end of the present specification). The product according to the invention can be used for horizontal applications such as road signs since it can reflect light back at high entrance angles. Sheets according to the invention also have good angularity and good front retroreflective luminosity, so they can be used in vertical applications such as indicators and barrier markings. "Front" brightness typically exhibits a low entry angle from 0 ° to approximately 30 ° to 40 °.

1 and 2 show conventionally known retroreflective products disclosed in US Pat. No. 4,145,112, wherein product 10 includes internal reflective protrusions 16, underlying retroreflective base sheet 14, and below Light-inducing layer 12 with an optical conformance layer 18. Typically, such products further comprise an adhesive layer (not shown) on the underside of the adaptation layer 18, whereby the product will adhere to the desired surface, such as a road surface (not shown). As discussed above, the high reflection angle light is redirected to the base sheet 14 by the internal reflections at the protrusions 16 and then the light reflected back by the base sheet 14 is redirected to the light source by the internal reflections. . Layer 12 is shown to be adhered to base sheet 14 by an intermediate adhesive layer 13. The base sheet 14 has a series of cube corner retroreflective elements 20 at the back of the main layer 22 and a mesh providing a boundary to the cube corner elements 20 required for retroreflective properties. An encapsulation film 24 encapsulated in the main layer 22 by an interconnecting bond 26 of a network is provided.

I. General structure of the product according to the invention

The retroreflective product according to the invention is shown in FIG. The road sign 30 may include an array 32 of retroreflective base sheets 32 with light refracting elements 34 on its top surface, any adaptation layer 36 underneath the base sheet 32, and an adaptation layer ( 36) an optical adhesive layer 38 underneath.

Other types of retroreflective sheets may be used as the base sheet 32. Typically, retroreflective base sheets themselves provide sufficient retroreflectivity, for example at very high entrance angles of 86 ° to 89 °. However, the use of such a base sheet in a composite article according to the invention results in a very good retroreflective function at both high and low entrance angles.

Spherical refracting elements 34 are attached to a relatively flat front of the retroreflective base sheet, for example partially embedded. Because of this arrangement, these spherical refracting elements usually capture specularly reflected light at high entrance angles. The captured light is refracted by the spherical refracting element to enter the base sheet 32, back reflected by the base sheet 32, and refracted again to be directed towards the light source.

At least some of the retroreflective products according to the invention, such as refractive elements and / or one or more elements of the base sheet, comprise pigments. Examples of common pigments are white, sulfur, and red, but other pigments as desired may be used.

In addition, a high abrasion and / or contamination resistant coating is applied thinly to the top surface of the retroreflective product to protect the retroreflective product from traffic wear and contamination accumulation. The coating is preferably light transmissive and does not reduce the skid resistance of the article according to the invention.

Another retroreflective product according to the invention is shown in FIG. The road sign 80 includes refractive elements 60, anti-skid particles 62, high angle retroreflective base sheet 82, optional adaptation layer 74, optional adhesive layer 76, and Optional liner 78. The base sheet 82 has a retroreflective element 68 embedded in a transparent polymer matrix 65, a specular coat 70, an adhesive layer 72, and a spherical refractive element 60 protruding from the base sheet 82. The cover layer 66 is further included.

II. Retroreflective base sheet

The retroreflective base sheet used in the present invention preferably has a good angle; That is, the base sheet still has substantial retroreflectivity at relatively high entrance angles of approximately 80 ° or more. The entire layer of components of the retroreflective base sheet are preferably glued together in all types of weather conditions under repeated impact and shear stresses as a result of road traffic passing over the sheet in the case of road marking applications. In addition, the sheet used in the present invention has inherent wet retroreflection because the critical components of the optical system are enclosed in the sheet and are not exposed to water.

The retroreflective base sheet used herein includes a relatively flat cover layer on its front face. The cover layer protects the components underneath the base sheet and may be single or multiple layers. The cover layer is typically a polymer, but may be other light transmissive material if desired. They can be chosen to make the most of the unique properties of the sheets individually. The spherical refractive element can be attached to the base sheet by embedding in either a cover layer adhered to the front side of the cover layer or an additional layer attached to the front side of the cover layer.

Other types of retroreflective base sheets can be used in the present invention. Examples of retroreflective base sheets that may be used in the present invention include, but are not limited to, buried-lensoidal retroreflective sheets and capsule-lensoidal retroreflective sheets (ie, both microsphere types and cube corner types). .

Exemplary capsule-lensed sheets include a microsphere-based retroreflective sheet comprising a layer of a single layer of transparent microspheres partially embedded in a binder layer having a reflective layer on the backside (or buried) portion. An air interface is provided by a cover layer disposed in front of the microspheres. Sheets of the cube corner type with a single layer cube corner retroreflective element with an air interface protected by an encapsulation layer can also optionally be used. Cube corner type materials may also be used in which the cube corner elements are covered with a mirrored reflective metal layer. In a cube corner type sheet, the cover layer may be an integral part of the cube corner or may be an independent film. McGrath, US Pat. No. 4,025,159, discloses some microsphere type and cube corner type capsule-lensular retroreflective sheets that can be used herein.

Exemplary buried-lensed sheets comprise a microsphere-base comprising (1) a single layer of transparent microspheres whose front and back surfaces are embedded in a transparent matrix and (2) a reflective layer disposed from the rear surface of the microspheres at a predetermined distance. Retroreflective sheeting. As used herein, the term cover layer refers to any layer in front of the microspheres. Bailey, US Pat. No. 4,505,967, discloses a buried-lensoidal retroreflective sheet which is particularly suitable for use according to the present invention. Examples of cube-corner, buried-lens sheets include a single layer of cube-corner whose front and back surfaces are embedded in a polymer matrix and a reflective layer which is mirror-coated or cured on the surface of the cube-corner. It is known in the art that curing of a cube-corner sheet increases the degree of entry of the sheet.

Typically, embedded-lens retroreflective sheets are preferred over capsule-lenticular retroreflective sheets when used as road markings. The solid state structure of the buried-lensed sheet is believed to be more durable when traffic conditions are applied because it does not contain internal voids like the capsule-lensed sheet. Landfill-lensed retroreflective sheets are useful for highly durable and stretchable commercial forms. They are useful in embodiments that provide an effective and bright retroreflective function at higher entry angles than is possible in many capsule-lensed systems. Moreover, in many landfill-lensed sheets the retroreflective layer is aluminum and aluminum adaptation layers are commonly used in road marking materials. This similarity minimizes the possibility of certain corrosion problems that can occur if other metals are used.

Microsphere-based buried-lensoidal optical systems (based on microspheres) utilize the light refraction and concentration effects of the microspheres to refract the light refracted by the reflecting member after being reflected and returned to its light source. The degree of refraction and thus the optimal placement of the specular reflector depends on the relative index of refraction of the cover layer on the microspheres, the microspheres, and the spacing layer (if any) between the microspheres and the reflector member. For example, when used as a cover layer and gap layer material having an index of refraction of approximately 1.5, microspheres with a refractive index of 2.25 will focus light at a distance of approximately 0.44 times the diameter behind the microspheres. Preferably, the thickness of the spacer layer is similar to this so that light is concentrated on the specular reflector. Any slight deflection from this precise optical relationship tends to reduce the retroreflectivity of the base sheet. Therefore, the cover layer is preferably kept firmly attached to the microsphere layer, and the microspheres are preferably positioned stably in the matrix, and any layer that must pass through in order for the light to be reflected back is distorted. It is desirable that there is no at all. In addition, the specular reflector, which is typically vapor deposited aluminum, is preferably maintained as a substantially continuous, cracking free or corrosion free layer. The interfacial-mirror layer interface is preferably smooth and free of wrinkles. Although very small changes do not result in noticeable loss of luminosity, minute changes can severely affect these precise relationships. If even a very small change in such an optical relationship occurs, the result is that the retroreflective function of the base sheet and, therefore, a predetermined product manufactured using the base sheet is degraded. Certain retroreflective sheets manufactured using these precise optical relationships can withstand the impact and shear stresses of repeated traffic combined with sunlight, rain, road oil, road sand, road salt, and vehicle exhaust. It is surprising that there is.

When light enters a buried-lenticular retroreflective sheet at high entrance angles and passes through the microspheres, the light is directed to the side of the microspheres rather than the rear, as occurs when light is incident in a somewhat vertical manner at low incidence. There is a tendency to concentrate. Therefore, it is important to maintain proper spacing between the microspheres and the reflective layer. As will be appreciated by those skilled in the art, the thickness of the gap coat layer can be controlled in part by the manufacturing method. If the spacer layers tend to be hemispherical, ie concentric to the backside of the microspheres, optimal spacing for various entrance angles can be achieved. Bailey's US Pat. No. 4,505,967 discloses a buried-lens retroreflective sheet suitable for use herein, and details the relationship between the shape of the spacer layer and the retroreflective reaction of the sheet. 3M SCOTCHLITE Brand Reflective License Plate Sheeting 3750 is an example illustrating a commercial retroreflective sheet that can be used in the present invention.

Because road markings are exposed to large amounts of traffic in some applications, the durability of the light-transparent cover layer disposed in front of the retroreflective element is important. The cover layer is preferably substantially continuous. The composition of the cover layer should be chosen to provide a strong bond to the spherical refractive element.

It is preferable that a cover layer is a thermoplastic polymer. Examples of suitable thermoplastic polymers for use according to the invention include polyurethane, ethylene methacrylate (Ethylene Methacrylic Acid, EMAA), ethylene acrylic acid (EAA), ionically crosslink Polyethylene acid copolymers composed of EMAA or EAA. Aliphatic polyurethanes are the preferred materials because they are high in impact resistance, low temperature elasticity, color, clarity, wear resistance, and strength to be bonded to the desired base sheet cover layer. The cover layer is also preferably resistant to contamination accumulation, clean, stretchable to match the rod surface, incorporating inorganic anti skid particles, and not significantly changing color during use.

If desired, the spherical refractive element can be treated with a material to further increase the bond to the cover layer.

III. Refractive elements

According to the invention, an array of spherical refractive elements is attached to the cover layer of the base retroreflective sheet. As used herein, an array means a plurality of refractive elements regardless of whether the elements are arranged in a regular pattern or randomly. The elements are typically discontinuous (isolated).

The required properties of the spherical refractive element include high transparency and shiny scratch-resistant surfaces. The transparency of the element is important because the incident light is reduced to the minimum and transmitted through the element so that most of the light is reflected back to the light source. The surface of the element is preferably scratch-resistant so that the surface remains glossy and the light is not scattered by the scratch. The element should preferably have a hardness sufficient to withstand the planarization effect of traffic and should not significantly soften at temperatures below 75 ° C. (170 ° F.). Preferably, at least some elements have a Shore D Hardness of at least 45. In addition, the element should be free of cracks in traffic impacts at temperatures between −40 ° C. and 75 ° C. (-40 ° F. to 170 ° F.). The urea is also preferably adhered well to the retroreflective base sheet, and is also preferably oil-resistant, dirt-resistant, and moisture resistant. Another desired or desirable property of the element includes low color and low cost.

The spherical refractive element applied to the base retroreflective sheet according to the invention may be one of glass, ceramic, or polymer. The choice is based, in part, on the desired properties of the resulting product, such as abrasion resistance, weather resistance and the like.

Examples of thermosetting or thermoplastic polymers suitable for use as spherical refractive elements include polycarbonates, acrylics, polyurethanes, polyvinyl chloride, and ethylene methacrylic polyolefin copolymers such as polyethylene acid copolymers composed of acid, EMMA), ethylene acrylic acid (EAA), ionically crosslinked EMAA or EAA. Aliphatic polyurethanes are preferred materials because they have high impact resistance, flexibility at low temperatures, color, clarity, wear resistance, and strength to be bonded to the desired base sheet cover layer. to be.

The spherical refractive element preferably has a refractive index greater than 1.35 and less than 1.75, and more preferably has a value between about 1.4 and 1.7. Unlike European Patent No. 385746 B1 to Kobayashi et al., A high refractive index is not necessary to carry out the present invention because the retroreflective base sheet has a good degree of angle; That is, the retroreflectivity of the base sheet is still substantial at relatively high entrance angles of approximately 80 ° or more. In general, large glass microspheres (ie, microspheres close to 2 mm in diameter) with high refractive index (approximately 2 or more) are difficult to manufacture and are expensive.

Typically, a portion of each refractive element will be exposed over the cover layer with the remaining portion embedded in the cover layer. For example, approximately 10 to 70 percent of the diameter of the element will typically be embedded. It would be desirable to expose approximately 30 to 70 percent of each spherical refractive element diameter. More preferably, approximately 40 to 60 percent of each spherical refractive element diameter will be embedded. The spherical refractive element is preferably buried between approximately 70 ° and 90 ° so that most of the light incident on the product is refracted and enters the retroreflective base sheet. According to the invention, the retroreflective brightness of the article according to the invention at an entrance angle of at least 89 °, typically at least 85 °, is higher than the retroreflective light of only one base sheet. Typically, the spherical refractive element preferably has a diameter in the range of about 0.5 to 4.0 mm, more preferably about 1 to 2 mm in diameter.

The elements disclosed in U.S. Patent No. 4,145,112 to Crohn and U.S. Patent No. 4,236,788 to Wykov require a second side of the element that is directed relative to the first side and has the property of reflecting light to the base sheet. In contrast, refractive elements according to the invention typically rely on refraction at a single surface (ie, frontal). Accordingly, it is not necessary to form the first and second surfaces so as to realize retroreflectivity on the second surface, and the second surface does not need to have a reflective property such as gloss. Typically, the properties required for reflection are more stringent than those required for refraction. Consequently, the product disclosed in this reference is not known to utilize a base sheet capable of retroreflecting high-incidence light as was preferably used in the present invention.

The spacing between the spherical refracting elements may be uniform, or the elements may be randomly placed. Spacing of elements smaller than the optimal spacing can be used in applications where optimal brightness is not needed. This characteristic of random refraction element placement allows for simplified and inexpensive manufacturing. However, in the present invention, the uniform arrangement of a particular pattern is advantageous because the elements can be placed in a specific position where each element does not shade the other elements. The majority of incident light is captured in this way by the element to maximize the retroreflective brightness in the geometry of the road markings. For example, the spherical refracting elements are spaced apart to allow greater surface contact of the vehicle tire by the spacing between the light refracting elements including the protruding slide control particles while minimizing the shadowing of adjacent elements at the expected entry angle. The surface area occupied by the refractive elements is preferably less than 50 percent of the base sheet for maximum adaptation of the product according to the invention to roads, guard rails, or other structures. More preferably, the surface area covered by the refractive element is less than 25 percent.

The entire product according to the invention, including the spherical refractive element, can be protected using a protective coating. Such coatings have the advantage of providing wear and / or contamination resistance. Examples of protective coating compositions include, but are not limited to, ceramer coatings or crosslinked aqueous polyurethane coatings.

As used herein, "ceramer" refers to a fluid consisting of surface-modified colloidal silica particles dispersed in a free-radical polymerizable organic liquid. Advantages of the coating include excellent resistance to moisture, light, and heat; Resistance to wear; Chemical erosion and resistance to automotive engine oil and carbon black (such as tire black); Desired optical performance such as transparency; Good adhesion to spherical refractive elements; And the ability to withstand external conditions with good flexibility. In a first step, a ceramic precursor coating composition is applied to the surface of the retroreflective article, preferably the top surface of the refractive element and the portion of the base sheet not covered by the refractive element. The coating composition may comprise approximately 20 weight percent (wt%) to 80 wt% ethylenically unsaturated monomers; About 10 wt% to 50 wt% of acrylic functional colloidal silica; Approximately 5 wt% to 40 wt% N, N-disubstituted acrylamide monomer, or N-substituted-N-vinyl-amide monomer; The percentage is a weight percentage of the total weight of the coating. The composition is then cured to form a light-transmitting ceramic coating herein, that is wear-resistant. The ceramic composition may be applied by any of the methods known in the art, including spraying, rolling, dip coating, or knife coating. Assignee's pending US application 08/444076, filed May 19, 1995, incorporated herein by reference only, discloses the use of ceramers on road markings and retroreflective sheets.

Examples of crosslinked polyurethane protective coatings suitable for use in the present invention include NEOREZ R-960 brand polyurethane resins (all commercially available from Geneca Resin, Wilmington, Mass.) Crosslinked with a crosslinker of the CX100 brand. It is composed. As will be appreciated by those skilled in the art, other aqueous systems and crosslinkers may be used to formulate the protective coating.

IV. Manufacturing method

The method according to the invention comprises the steps of (1) providing a retroreflective base sheet comprising an array of reflective elements and a cover layer, and (2) adhering or forming an array of spherical refractive elements over the cover layer, The spherical refracting element is arranged such that light incident on the array at a high entrance angle is refracted to be transmitted through the base sheet, retroreflected by the base sheet, and further refracted by the spherical refractive element to be retroreflected by the product. Place it against the base sheet.

In a typical assembly process for making road markings, a base sheet (such as 3M SCOTCHLITE brand reflective license plate sheet 3750) is applied to an aluminum adaptation layer. As a result, the spherical refractive element will be attached to the cover layer of the base sheet by embedding it in the cover layer or additional layer.

Typically, the spherical refractive element has a greater resistance to movement when embedded deeper. In addition, when at least 50 percent of the diameter is buried, contamination and debris (which reduces the retroreflective function of the product) are less likely to accumulate than when buried shallower.

In the assembly process, anti skid particles are typically added at the same time as attaching the refractive element to the base sheet. In addition, depending on where the dye is needed in the particles, dyes such as dyes and / or pigments can be introduced at a suitable time during the assembly process.

The components of the particles according to the invention underneath the retroreflective base sheet are preferably selected to suit the desired application. For example, scrim adhesives (ie, polymer scrim saturated with adhesive) add additional strength to the retroreflective product in addition to the selected adhesive properties. Suitable adaptation layers, adhesive layers, reinforcement layers and the like can be preselected by those skilled in the art.

V. Dyes

Several methods can be used to add the dye to the selected portion or to the entire retroreflective product. In road marking applications, examples of preferred dyes include white, sulfur, red, and blue among others. The dye may be light transmissive or opaque as desired.

Typically, when the dye is placed in the optical path, it is desirable that the dye is light transmissive so that there is no undesirable reduction in retroreflective function. However, in some cases, it is understood that opaque dyes are preferably used in place to reduce retroreflective light but provide some other desired effect, such as more vivid overall color or appearance.

The light transmissive dye may enhance the day and night colors of the product according to the invention. As in other road marking applications, it is important for the driver to determine colored signs, for example between yellow and white signs. One method of achieving nighttime color involves placing a translucent colored material in the path of the light beam.

In one way, color is realized using colored base sheets. For example, in Fig. 4, the light transmissive matrix 65 may be made of a desired color such as yellow. In the capsule-lenticular cube-corner type base sheet, the cube-corner itself can be colored. Another method is to use a colored cover layer if necessary. For example, the product according to the invention can be made to comprise a transmissive yellow, red or blue colored top film. In addition, colored refractive elements can be used. If a transparent colored top film is used in connection with a transparent colored refractive element, the result is a highly effective colored retroreflective product. Instead, a translucent colored layer can be printed on the cover layer of the base sheet. A colorless top film can be applied on top of the printed base sheet. This method has the advantage of embedding the colored layer to enhance its durability. In addition, multiple patterns of a pattern may be added by printing to form the desired symbol or legend.

Typically, opaque dyes are used mainly to enhance the daylight of the product according to the invention, and are preferably placed outside the path of the light rays so as not to reduce the retroreflective function. Thus, the gray colored base sheet initially due to the aluminum reflective layer can be changed to the desired color by the addition of an opaque dye. For example, one method of making a colored product is to apply a white opaque segment on the product of the invention or use an opaque spherical refractive element. These particular segments and opaque elements increase the true color of the sheet when used in small amounts, even if they do not retroreflect incident light. Optionally, between the spherical refractive elements, pellets of white colored resin are applied to the cover layer and melted by heating to adhere to the cover layer.

In addition, segments colored in the desired color may be applied to a portion of the light refracting element as well as the base sheet, despite some reduction in retroreflective response. For example, a method of manufacturing a colored retroreflective product includes the following steps of (1) providing a retroreflective base sheet comprising an array of retroreflective elements and a cover layer, (2) laminating an adaptation layer on the bottom of the base sheet ( V) adhering an array of spherical refractive elements to the cover layer of the base sheet, (4) debossing the upper refractive element to yield a relatively flat upper surface, (5) coloring Applying the layer to the top surface, and (6) embossing the base sheet such that the spherical refractive element protrudes from the base sheet.

As used herein, "debossing" is contrary to embossing, ie, making the textured surface relatively flat. As used herein, the refractive element projecting from the top surface of the original base sheet is pressed so that the element is relatively horizontal with the base sheet. One method of debossing includes supplying the adhered adaptive layer to the base sheet and refracting the element through a series of rollers. For example, the refractive element is in contact with the steel roll, while the adaptation layer is in contact with the rubber roll, which can deform under the lamination pressure. Pressure is applied to press the refractive element into the adaptation layer. After debossing, the top surface of the sheet need not be completely smooth. Some surface topography is allowed. It is preferable that the resulting surface of the base sheet is as nearly as parallel to the refractive element as possible. After debossing, the colored layer is applied to parts of the base sheet, parts of the refractive element, and anti skid particles by conventional techniques.

The opaque colored layer may be further moved to selected portions of the base sheet before adding the spherical refractive elements. For example, a method of manufacturing a colored retroreflective article may comprise the following steps: (1) providing a retroreflective base comprising an array of reflective elements and a thermoplastic cover layer, and (2) routinely yielding a partially printed base sheet. Providing a discontinuous thermosetting polymer to the cover layer of the pattern, (3) heating the partially printed base sheet to soften the cover layer, (4) while the cover layer is softened and the spherical refractive element is the base sheet Precipitating the spherical refractive element on the partially printed base sheet so as to adhere to it; (5) melting the refractive element, and (6) cooling. Portions of the thermosetting polymer can contain the desired dye. For example, in one embodiment, the total area of the base sheet may be printed with a thermoset colored layer except for the areas that are bonded to the cover sheet, ie to the cover sheet. In other embodiments, the light transmissive thermoset polymer may be printed to enclose the refractive element in a defined radius. The balance of the sheet can be printed with another thermosetting polymer, for example colored white. The area just below the refractive element is not printed. Since it is possible for light rays to enter the base sheet outside the base of the refractive element, the region of the light transmissive polymer surrounding the refractive element still allows the light to enter the base sheet and be reflected back by the base sheet. This same method has the advantage of positioning the refractive element in a defined manner to increase the optical efficiency of the product while minimizing the amount of refractive element used for cost efficiency.

The composition of the colored layer should be resistant to solvents, abrasion by traffic, and ultraviolet light. For example, certain dye solutions include 78 wt% NEOREZ R960 brand water-based urethane resins (Massachusetts, Wilmington, Geneca Resin acid), 19 wt% WW3000 brand titanium dioxide dispersions (Pennsylvania, Fairy Hill, Hucotech Limited acid), and 3 wt% CX100 crosslinkers. (Mt. Genca Resin, Wilmington, Mass.). It will be apparent to those skilled in the art that other colored layer compositions may be used.

It will be apparent to those skilled in the art to use combinations of opaque dyes and light transmissive dyes. For example, a translucent colored spherical refractive element located in the light path can be used with an opaque colored layer located outside the light path. In this way, the product can have effective day and night colors. Thus, any of the combined opaque and light transmissive colored systems can be used.

VI. Anti-skid particles

Anti skid particles are a common component of many road marking products that increase the sliding resistance of road markings and have been widely used in the art. Anti skid particles may be located anywhere on the surface of the product in contact with the tire of the vehicle.

Typically, the anti skid particles can be randomly sprayed onto the cover film of the base sheet while in the softened state. Anti skid particles may also be located in the refractive element as deliberate parts. It is recognized that anti skid particles may preferentially precipitate near the zenith of the refractive element. For example, a web of base sheet with refractive elements thereon can be kiss-coated with a binder composition. Kiss-coating is such that the composition is preferably coated only on the upper portion of the refractive element; That is, the coating method means that the solution "kisses" only the top of the refractive element. This process is done by controlling the gap between the coating rolls and maintaining the web so that only the top of the spherical refractive element is in contact with the coating composition. While the composition retains moisture, large amounts of anti skid particles are sprayed onto the web. Since the remaining base sheet is dry, the particles adhere only to the wet area. Excess anti skid particles are vibrated to separate from the web. Thereafter, the web is sent through a series of ovens to dry, cure, or solidify the wet binder composition. As a result, the anti skid particles are selectively fixed in the upper region of the refractive element to provide anti skid resistance.

VII. Example

Retroreflective products according to the invention can be advantageously used in a number of different applications, in particular where light is incident at high entrance angles. In particular, the product is very suitable for use as a road sign or level sign. Because of the high retroreflectivity at both high and low entering angles, the product is suitable for vertical applications such as jersey barriers or guard rails; Curved surface applications such as traffic barrels, tubes, and cones; Vehicle surface; And other applications where an exceptionally effective angle of entry of the product would be advantageous. For example, in many embodiments of the sheet according to the present invention, effective retroreflection can be provided over the full entrance angle of 0 ° to almost 90 °. As a result, when the sheet is wrapped around an object such as a telephone pole or barrel, the entire surface of the sheet in the line of sight may include a portion of the surface of the object that is curved away from the viewer to provide effective retroreflection. As a result, the area of retroreflection increases to provide a more visible label, thereby increasing stability. In addition, a single sign, such as a guard rail, a barrier barrier, or a strip on a wall, parallel to the first road and perpendicular to the second road crossing the first road on the opposite side of the first road, is the first and second roads. It is possible to provide drivers of both vehicles a very bright and effective retroreflective response that is visible.

Another advantage according to the present invention is that retroreflective products are identifiable in various orientations. This omnidirectional feature makes the present invention particularly suitable for applications that signal horizontally when a vehicle approaches a plurality of angles, intersection signs, and the like.

This is particularly beneficial for the horizontal signal because the coloring of this sheet is easy. The transparent color layer can be printed on the sheet in a graphic pattern such that the retroreflected light has a coloration and pattern that are almost identical to that seen in daytime viewing. Such a print is particularly advantageous if the ink is printed under the top film layer so that it is protected from road wear by both the element and the transparent solid cover over it in succession. This feature is particularly important because the ink normally used is thin and quickly wears out when exposed and left unattended.

The material according to the invention can itself be wound in the form of a roll. The protrusion formed by the element is not substantially enough to prevent winding.

VIII. Yes

The invention is further illustrated by the following illustrative examples which are not for purposes of limitation.

Wet retroreflective

Wet retroreflectivity of retroreflective sheets is measured using LTL 2000 (available from Delta Lite and Optics, Ringley, Denmark), which measures retroreflected luminosity at an entry angle of 88.76 ° and an observation angle of 1.05 °. . Such a form is similar to that experienced by a driver of a normal vehicle 30 meters from the retroreflective road sign. The sheet was first placed horizontally on the test area and then submerged in a solution of tap water and 0.1 weight percent AJAX brand dishwashing soap. The solution was flushed and then photometric measured within approximately 10 seconds. Soap was added to the water to increase the surface humidification of the sheet. Soap also better mimics the effects of rain after retroreflective road markings have been maintained on the road for a period of time, exposed to the sun, abrasive grit and sand, and increased humidification due to the action of contamination accumulation.

Example 1

Thermoplastic polyethylene methacrylic acid copolymer resin (NUCREL brand 699, sold by DuPont) was extruded into polyethylene terephthalate (PET) to yield a 0.25 mm thick EMAA cover film.

A high angular base sheet (3M SCOTCHLITE brand reflective license plate sheet 3750, "3750 sheet") was prepared in the following manner. It was primed with a water-based polyethylene acrylic acid solution (available from ADCON brand 50T4983, Morton Chemical Coporation, Sibruck, New Hampshire) by a conventional scriber coating technique using a 150 line square gravure pattern. The solution was applied to the front of a 3750 sheet, such as a reflective surface, and dried in a forced air convention oven at 93 ° C. (200 ° F.) for 1 minute to yield a primed 3750 sheet.

EMAA cover films were hot laminated to 3750 sheets primed in nips produced by hot cans and rubber rolls under the following conditions. The PET carrier of the EMAA cover film was contacted with a hot can heated to 150 ° C. (300 ° F.); EMAA films were exposed to the atmosphere. The primed sheet with the reflective surface exposed was in contact with the rubber roll. The two films were contacted with each other in the nip, thus laminating the EMAA film to primed 3750 sheets to yield a composite sheet. Both hot cans and rubber rolls were spun at a surface speed of 6.1 m (meters) / m (minutes) (20 ft / m).

On the composite sheet, the PET carrier was removed from the EMAA film. The liner on the 3750 sheet was also separated to expose the pressure sensitive adhesive (PSA) accompanying the 3750. A 0.075 mm (0.003 in) aluminum foil (1145-O single roll foil, sold by A. J. Oster Foil Inc.) was laminated to PSA.

Glass microspheres (A135 glass beads, sold by Potter's Braze) having a diameter of approximately 1.5 mm and a refractive index of 1.5 were sprayed onto the foil-laminated composite sheet. The whole product was heated in an oven at 205 ° C. (400 ° F.) for 2 minutes. Melting of the glass microspheres did not occur. The microspheres were embedded into the EMAA cover layer through the effect of gravity. EMAA resins also wicked up around the microspheres due to capillary action. Approximately 83,000 beads were used per square meter of sheet.

Wet retroreflective luminosity, in millicella (mcd) / lux (lx) / square meter (m ² ), was measured as described above under “wet retroreflective”. In this example, wet soft emissivity was measured between 700 and 800 mcd / lx / m ² . When dry, the sample had a retroreflective intensity of 840-960 mcd / lx / m ² .

Terms

The following definitions are used herein when discussing the geometry of retroreflections:

The "reference axis" is a line perpendicular to the retroreflective lens at the point where light enters.

An “incidence axis” is an axis formed by the path of incident light from a headlight of a light source, such as a vehicle, to a point of incidence on a product.

The "entrance axis" (often referred to as "incidence angle", or β) is the angle between the reference axis and the incident axis.

An "observation axis" is an axis formed by a path of retroreflected light from a point of incidence on a product to a viewpoint, such as the eyes of a vehicle driver.

An "observation angle (often called α)" is the angle between the entry axis and the observation axis.

An "entrance plane" is a plane formed by a reference axis and an incident axis.

An "observation plane" is a plane formed by an observation axis and an incident axis.

Many modifications and variations of the present invention will be possible to those skilled in the art without departing from the scope of the invention.

Claims (35)

(a) a retroreflective base sheet comprising an array of retroreflective elements and a cover layer; And (b) a portion of the light incident on the array of spherical refracting elements is refracted to be transmitted through the base sheet, retroreflected by the base sheet, and further refracted by the refracting element to be retroreflected by a retroreflective article. And an array of spherical refracting elements attached to the front of the base sheet, the spherical refracting elements having a refractive index greater than 1.35 and less than 1.75. The retroreflective article of claim 1, wherein the base sheet comprises at least one of a group consisting of a buried-lensoidal retroreflective seating or a capsule-lensoidal retroreflective seating. The retroreflective article of claim 1, wherein the cover layer comprises a thermoplastic polymer. The retroreflective article of claim 1, wherein the retroreflective brightness of the article at an entry angle greater than 85 ° is greater than the retroreflective brightness of the article without the array of refractive elements. The retroreflective product of claim 1, further comprising anti-skid particles. The retroreflective article of claim 1, wherein at least some of the refractive elements comprise a material selected from the group consisting of glass, ceramic, and polymeric materials. The method of claim 1, wherein at least some of the refractive elements are selected from fluoropolymers, polycarbonates, acrylics, polyesters, polyurethanes, polyvinyl chlorides, polyolefins copolymers, and mixtures thereof. A retroreflective product, characterized in that it comprises a polymeric material selected from the group consisting of: The retroreflective article of claim 1, wherein at least some of the refractive elements comprise a thermoplastic material. The retroreflective article of claim 1, wherein at least a portion of the spherical refracting element comprises a thermoset material. The retroreflective article of claim 1, wherein the spherical refractive element has an average diameter between approximately 0.5 and 4 mm. The retroreflective article of claim 1, wherein the spherical refractive element has an average diameter between approximately 1 and 2 mm. The retroreflective article of claim 1, wherein the spherical refractive element has a refractive index between approximately 1.4 and 1.7. The retroreflective product of claim 1, wherein a portion of the spherical refractive element is embedded in the cover layer. The retroreflective article of claim 13, wherein the portion is between approximately 30 and 70 percent of the diameter of the spherical refractive element. 14. The retroreflective article of claim 13, wherein the portion is between approximately 40 and 60 percent of the diameter of the spherical refractive element. The retroreflective article of claim 1, wherein the spherical refracting elements contact less than 50 percent surface area of the retroreflective base sheet surface area. The retroreflective article of claim 1, wherein the spherical refractive elements contact less than 25 percent of the surface area of the retroreflective base sheet surface area. The retroreflective article of claim 1, wherein the spherical refractive elements are randomly arranged at the front side of the base sheet. The retroreflective article of claim 1, wherein the spherical refractive elements are uniformly arranged on the front side of the base sheet. The retroreflective article of claim 1, wherein the spherical refractive elements are located in a regular pattern on the front side of the base sheet. 2. The base sheet of claim 1, wherein the base sheet comprises a single layer of transparent microspheres, a cover layer embedding the front surface of the microspheres, reflecting means behind the microspheres, and a cover layer disposed in front of the transparent matrix. And a buried-lensoidal retroreflective sheet comprising: the spherical refractive elements are attached to the cover layer. 22. The retroreflective article of claim 21, wherein at least one of said spherical refractive element, said cover layer, and said transparent matrix comprises a dye. The retroreflective article of claim 1, wherein the base sheet further comprises a single layer of cube-corner retroreflective elements. The retroreflective article of claim 1, further comprising a discontinuous pigment containing layer covering an upper portion of at least a portion of the spherical refractive elements and a portion of the cover layer between the spherical refractive elements. The retroreflective product of claim 1, wherein the retroreflective product is applied to a surface on which a motor vehicle runs. The method of claim 1, characterized in that it is applied to vertically placed surfaces selected from the group consisting of guard rails, Jersey barriers, building walls, fences, telephone poles, traffic cones, and vehicle sides. Retroreflective products. 27. The retroreflective article of claim 25, wherein at least a portion of the surface is curved. (a) providing a retroreflective base comprising an array of retroreflective elements and a cover layer; And (b) a portion of the light incident on the array of spherical refracting elements is refracted to be transmitted through the base sheet, retroreflected by the base sheet, and further refracted by the refracting element to be retroreflected by a retroreflective article. Attaching the array of refractive elements having an index of refraction greater than 1.35 and less than 1.75 to the front of the cover layer. 29. The group of claim 28 comprising mixing one or more dyes into the refractive elements, incorporating one or more dyes into the cover layer, or incorporating one or more dyes into a layer formed in the cover layer. A method of making a retroreflective product further comprising one or more steps. (a) providing a retroreflective base sheet having a major surface comprising an array of retroreflective elements and a cover layer; (b) applying an adaptation layer to the major surface of the base sheet; (c) attaching an array of spherical refractive elements having a refractive index greater than 1.35 and less than 1.75 to the cover layer; (d) debossing the spherical refractive element such that a relatively flat top surface is produced; (e) applying a colored layer to the top surface; (f) embossing the base sheet such that the spherical refractive elements protrude from the base sheet. 31. The method of claim 30, wherein the dye comprises a polymer that is resistant to solvents, abrasion by traffic, and ultraviolet light. 33. The method of claim 30, wherein the colored layer comprises an opaque dye. (a) providing a retroreflective base sheet comprising an array of reflective elements and a thermoplastic cover layer; (b) adding a thermoset polymer to a portion of the cover layer; (c) heating the cover layer to soften; (d) depositing spherical refractive elements having a refractive index greater than 1.35 and less than 1.75 to selectively attach to the softened cover layer; (e) cooling the cover layer to cure. 34. The method of claim 33, wherein the layer of thermosetting polymer is light transmissive. 34. The method of claim 33, wherein the thermosetting polymer comprises a dye selected from the group consisting of light transmissive dyes and opaque dyes.