WO1997000357A1

WO1997000357A1 - Retroreflective structure and process for producing the same

Info

Publication number: WO1997000357A1
Application number: PCT/US1996/010285
Authority: WO
Inventors: Junichi Saitoh
Original assignee: Minnesota Mining And Manufacturing Company
Priority date: 1995-06-16
Filing date: 1996-06-14
Publication date: 1997-01-03
Also published as: AU6385296A; JP3670343B2; JPH091715A

Abstract

The present invention relates to a retroreflective structure (50) and the process for producing the same. More specifically, it relates to a retroreflective sheeting (10) that is adhered to a flexible support (3), which structure is adhered by a selectively applied adhesive to a surface (4). The selectively applied adhesive is provided so as to include an uncoated portion that forms a vent (6) between the space between the structure and the surface, and the atmosphere. The retroreflective structure according to the present invention does not suffer from bad influences originated especially from the unevenness present on the surface of the article, or water or substances like alkaline substances present on or in the surface.

Description

RETROREFLECTIVE STUCTURE AND PROCESS FOR PRODUCING THE SAME

Technical Field A system for mounting a retroreflective structure on an uneven surface.

Background ofthe Invention

Convention retroreflective sheeting has been used on road sign boards or for structures such as guardrails and traffic cones. This sheeting is adhered to various articles by an adhesive layer to provide retroreflectivity to the articles, which improves nighttime visibility. Such retroreflective sheeting includes, depending on the form ofthe retroreflective element included therein, prism type (cube corner type) retroreflective sheetings, and encapsulated lens type (microspherical lens type) retroreflective sheetings.

Articles to which retroreflective sheeting is adhered are generally flat, such as road sign boards, curved products such as traffic cones, and other articles having relatively smooth surfaces. However, at some dangerous points in roads, such as curved points in freeways and railroad crossing points, retroreflective sheeting is adhered to a surface near that point — generally the wall of a concrete structure ~ so that the danger zone is clearly recognized visually by car drivers or other drivers even at night. This use for retroreflective sheetings is discussed in "Railroad Crossing Notice Fence, For Retroreflective Sheeting Having High Brilliancy," published by East Japan Railway Company, 1991.

Concrete surfaces are typically uneven, however, and ifthe retroreflective sheeting is simply adhered to the concrete surface, the sheeting may crack or become uneven due to the unevenness ofthe surface. As the result, uniform and high reflective brightness cannot be reliably provided. Although the concrete surface may be pretreated by sanding or filling prior to adhering a retroreflective sheeting onto the wall surface, such a process requires labor and time to make the wall surface smooth.

Moreover, sheeting that is adhered to concrete may blister or peel due to the presence of water vapor between the sheeting and the concrete, or due to alkaline substances in the concrete that may penetrate and damage the sheeting.

One conventional method of overcoming the foregoing problems is to bond the retroreflective sheet to an aluminum plate, and affixing the aluminum plate to the concrete wall surface with a fastener. This process, however, requires that the aluminum plate be cut to match the size ofthe wall surface and the retroreflective sheeting. Thus, this process also cannot eliminate the inconvenience of added labor and time. Additionally, since the aluminum plate can fall from the wall surface ifthe fastener becomes loose, this process may be unreliable, and therefore unsafe.

Another way to eliminate the harmful effects of water vapor and alkaline substances on the retroreflective sheeting is to provide a barrier means in the retroreflective sheeting. For example, Japanese Unexamined Patent Publication (Kokai) No. 3-9837 discloses that a plasticizer barrier layer (thickness of about 0.25 to 10 mil) comprising polyester, nylon, polyvinylidene dichloride, ethylene vinyl alcohol, fluoropolymer, and a metal film is provided in a retroreflective sheeting to protect the sheeting from harmful substances such as a plasticizer or a colorant included in the article to which the sheeting is adhered. Further, Japanese Unexamined Patent Publication (Kokai) No. 131589 discloses that a plasticizer transference inhibition film

(thickness of about 10 to 25 μm) preferably comprising polyester resin, acrylic resin, and fluoroplastic is provided between a retroreflective sheeting and an adhesive layer whereby the transference of a plasticizer into the sheeting side is prevented in the case where an article includes a large amount ofthe plasticizer, such as a molded article of vinyl chloride resin.

The technique of using a barrier layer or film may not be effective ifthe sheeting is used on an uneven surface. For example, when the surface is made of concrete, the harmful alkaline substances and water in the concrete is retained in the space between the uneven surface ofthe concrete and the undersurface ofthe retroreflective sheeting. The retention or the penetration into the sheeting of such substances may cause blistering or deterioration ofthe retroreflective sheeting. Also, such conventional retroreflective sheetings can crack, and may not be evenly bonded to the concrete surface, which may prevent the sheeting from providing uniform and high retroreflective brightness.

In view ofthe disadvantages ofthe prior art, it is desirable to provide a retroreflective structure which does not suffer from the bad effects caused by an uneven surface or by the retention of water or alkaline substances that may be present in a concrete surface. Further, it is desirable to provide a simple method for producing and affixing a retroreflective structure.

Summary ofthe Invention

In one aspect ofthe present invention, there is provided a retroreflective structure comprising a retroreflective sheeting having a retroreflective element and an flexible support adhered to the back portion ofthe retroreflective sheeting. The flexible support also bears an adhesive portion selectively applied to a surface ofthe support opposed to the retroreflective sheeting, such that a space is formed to provide a vent to the atmosphere. The vent enables potentially harmful elements such as water vapor and alkaline substances to escape to the atmosphere when the structure is applied to a surface.

Also provided in accordance with the present invention is a process for producing a retroreflective structure, comprising the steps of providing a retroreflective sheeting having a retroreflective element; adhering a first major surface of a flexible support to the retroreflective sheeting; and selectively applying an adhesive onto a second major surface ofthe flexible support, to provide an uncoated portion that, when the retroreflective structure is applied to a surface, provides a vent between the second major surface and the atmosphere

In another aspect ofthe present invention, there is also provided a process for producing a retroreflective structure comprising a retroreflective sheeting having a retroreflective element and an article which fixedly supports the back portion of the retroreflective sheeting through an adhesion means, wherein the process comprises the steps of adhering a flexible support ofthe adhesion means through an adhesive layer comprising a first adhesive onto the back portion ofthe retroreflective sheeting; cutting the resulting composite ofthe sheeting and support in conformity with the configuration and size ofthe article to obtain a composite piece having a suitable size; and selectively applying an adhesive onto the surface, opposed to the retroreflective sheeting so that the resulting space formed between the surface ofthe article and the surface ofthe flexible support is communicable through a vent constituting a part ofthe space with an external atmosphere.

In the practice ofthe present invention, a retroreflective sheeting can have a structure generally used in this technical field and, therefore, can be produced according to a conventional method. Specifically, a retroreflective element can be constructed by including a prism, glass microspherical lens, and the like. Accordingly, the retroreflective sheeting can be a prism type retroreflective sheeting, an encapsulated type retroreflective sheeting, an enclosed lens type retroreflective sheeting, and an exposed lens type retroreflective sheeting, or the like. These retroreflective sheetings are commercially available. For example, the prism type retroreflective sheeting is available from Minnesota Mining and Manufacturing Company (3M Company) of St. Paul, Minnesota under the designation 3970 G.

An adhesion means for fixedly supporting a retroreflective sheeting at the back portion, opposed to its retroreflective surface, with an article comprises an adhesive layer comprising a first adhesive and a flexible support carrying the adhesive layer. The supports used herein preferably can fit various shapes of articles and has an adequate flexibility for appropriately adhering a retroreflective sheeting to the article.

Further, the thickness ofthe support is preferably at least one wherein the surface unevenness ofthe article which is to be a base does not cause problems. The support is preferably plastic film having a thickness of preferably 200 to 5000 μm.

On the surface ofthe flexible support opposite the retroreflective sheeting, an adhesive portion is selectively applied. The formation ofthe adhesive portion referred herein is not particularly limited as long as a space is formed by the surface ofthe article, the adhesive portion and the surface bearing the adhesive portion ofthe support, a vent is formed with at least a portion ofthe space, and the space is communicable through this vent with an extemal atmosphere. The adhesive portion can be formed by using, preferably, at least one stripe-like adhesive layer, that is, coating the adhesive layer in the form of at least one stripe (band) onto a support in an optional pattem.

An article used in combination with a retroreflective sheeting is not particularly limited. The retroreflective structure ofthe present invention, however, would be able to produce noticeable effects when an article having an uneven surface, for example, an article made of concrete is chosen as an article.

In a retroreflective sheeting having an enclosed retroreflective element, when light of running cars, etc. (for example, light from a headlight) is irradiated thereto, for example, at night time, almost reflective light beam is retumed so that drivers can readily recognize the presence ofthe sheeting.

Further in the retroreflective structure equipped with this retroreflective sheeting, since an adhesion means comprises a flexible support such as plastic film, are prevented the formation of cracks on the retroreflective surface ofthe retroreflective sheeting which is adhered on the surface of an article having an unevenness surface such as a concrete wall and surface defects such as unevenness due to unevenness ofthe article surface, and, further, a uniform and high reflective brightness can be provided throughout the surface ofthe article after adhering the retroreflective sheeting thereto. Still further, an adhesive portion present between a film support and a wall surface is equipped so as to form a space having a vent communicated with an extemal atmosphere, and, therefore, it can be prevented that water and substances like alkaline substances, etc. are retained between the retroreflective sheeting and the article and are penetrated into the retroreflective sheeting and it can be further prevented that blistering ofthe retroreflective sheeting is caused thereby and the peeling ofthe retroreflective sheeting due to such blistering is caused. Preferable embodiments ofthe present invention will be described in detail below by referring to the accompanied drawings. It should be understood, however, that the present invention is not restricted to the illustrated embodiments.

Brief Description ofthe Drawings

Figure 1 illustrates a cross-sectional view of an embodiment of a retroreflective stmcture according to the present invention;

Figure 2 illustrates a cross-sectional view of another embodiment of a retroreflective stmcture according to the present invention; Figure 3 illustrates a perspective view of an embodiment of a retroreflective stmcture according to the present invention;

Figure 4 illustrates an bottom view of one embodiment of a patterned adhesive portion formed in a retroreflective stmcture according to the present invention; Figure 5 illustrates a bottom view of another embodiment of a patterned adhesive portion formed in a retroreflective stmcture according to the present invention;

Figure 6 illustrates a bottom view of another embodiment of a patterned adhesive portion formed in a retroreflective stmcture according to the present invention; Figure 7 illustrates a bottom view of another embodiment of a patterned adhesive portion formed in a retroreflective stmcture according to the present invention; Figure 8 illustrates a bottom view of another embodiment of a patterned adhesive portion formed in a retroreflective stmcture according to the present invention; Figure 9 illustrates a bottom view of another embodiment of a patterned adhesive portion formed in a retroreflective stmcture according to the present invention; and Figure 10 illustrates a bottom view of another embodiment of a patterned adhesive portion formed in a retroreflective stmcture according to the present invention; and

Figure 11 illustrates a bottom view of another embodiment of a patterned adhesive portion formed in a retroreflective stmcture according to the present invention. Detailed Description ofthe Invention

Figure 1 represents an example ofthe retroreflective stmcture according to the present invention wherein a prism type retroreflective sheeting is used in combination with an article made of concrete as an article. As shown in this figure, the retroreflective stmcture 50 comprises a retroreflective sheeting 10 and an article 5 which fixedly supports the back portion ofthe retroreflective sheeting through an adhesion means including an adhesive layer 2, a flexible support 3 and an adhesive portion 4. In this example, as the flexible support 3, a plastic film is used and, as can be seen from the drawing, as the article 5, a concrete wall having an uneven surface is illustrated. A space 6 is present between the plastic film 3 and the concrete wall 5 and the space, as explained by the perspective view of Figure 3, communicates through a vent 7 with an extemal atmosphere. Thus, water vapor and other undesirable substances may be vented to the atmosphere to prevent damage to the retroreflective stmcture.

The retroreflective sheeting 10 is a prism type retroreflective sheeting, one type of which is available from 3M Company under the designation 3970 G. Altematively, an enclosed lens type retroreflective sheeting ofthe type shown in Figure 2 and explained below can be used. Other types of retroreflective sheeting, such as encapsulated lens type retroreflective sheetings and exposed lens type retroreflective sheeting can also be used.

The retroreflective sheeting 10 of Figure 1 comprises a substantially flat retroreflective surface 11 as one surface, a prism 1 having many substantially triangular pyramid shaped portions 12 located on one surface, and a binding layer 14 adhered to the portions 12 so as to provide an air layer 13 adjacent the exposed side ofthe portions

12. The thickness ofthe retroreflective sheeting 10 is not particularly limited, but is generally about 100 to 500 μm.

When the retroreflective sheeting 10 is an enclosed lens type (microspherical lens type) retroreflective sheeting, it can have the constmction as shown in Figure 2 in accordance with the retroreflective sheeting described in the above¬ mentioned Japanese Unexamined Patent Publication (Kokai) No. 5-131589. That is, in the case ofthe retroreflective sheeting shown in the drawing, 20, 21, 22 and 23 represent a transparent top film, a transparent binding layer, a transparent supporting layer and a microspherical lens, respectively. The microspherical lens 23 can be constmcted by transparent glass microspheres. The supporting layer 22 includes a reflective member (not shown) arranged at a predetermined distance from the microspherical lens 23.

The adhesion means for adhering the retroreflective sheeting 10 to a concrete wall 5 comprises a plastic film 3, an adhesive layer 2 adhering the retroreflective sheeting 10 on one main surface 31 ofthe film 3 and an adhesive portion

4 forming a space 6 having a vent 7 (shown in Figure 3) provided between another main surface 32 ofthe film 3 and the concrete wall 5 and communicating with an extemal atmosphere. The adhesive layer 2 may be ofthe pressure-sensitive adhesive type already applied to many commercially available retroreflective sheetings. Altematively, a desired adhesive layer can be provided by coating an adhesive on a surface ofthe sheeting.

In the retroreflective stmcture according to the present invention, the plastic film used as a portion ofthe adhesion means prevents the retroreflective surface ofthe retroreflective sheeting adhered to the surface of an article having an uneven surface from forming cracks. It also attenuates the effects of surface defects such as unevenness, and prevents water vapor and alkaline substances from penetrating into the retroreflective sheeting. The plastic film can be more easily cut and applied than can the aluminum sheetings of conventional stmctures. Furthermore, the final stmcture thus formed is lightweight.

Any suitable plastic films can be used as long as they have a sufficient mechanical strength. Preferred plastic films comprise a polymer having superior impact resistance, such as polyester, polyvinyl chloride, polyolefin, polycarbonate or polyvinylidene fluoride. Polystyrene films or acrylic films comprising a modifier such as elastomer, mbber, and having an improved impact resistance also can be used. A preferred plastic film is polyester, which has excellent tensile strength or tear strength and chemical resistance, so that the generation of surface defects and the penetration of a substance present inside an article into a retroreflective sheeting can be prevented. This film is also excellent in the heat shrinkage resistance and, therefore, can prevent a retroreflective sheeting from peeling off together with the film from an article, which may be caused by the shrinkage ofthe film with increase in the extemal temperature. Specifically, such polyester film are available from the I.C.I. Japan CO. Ltd. under the designation "MERINEX NO. 339," and from Toyobo Co. Ltd. under the designation "CRISPER."

In place ofthe polyester films described above, a polyester film having an improved gas barrier property also can be used. This film is advantageous because it further prevents a volatile substance present inside an article from penetrating into a retroreflective sheeting. One such polyester film includes polyethylene isophthalate copolymer.

The thickness ofthe plastic film, although it can be widely varied depending upon factors such as the type of retroreflective sheeting 10 or the material of the underlying article, is preferably 200 to 5000 μm, and more preferably 250 to 2000 μm. When the thickness ofthe film is less than 200 μm, the strength sometimes can be insufficient for eliminating the influence from the uneven surface on the retroreflective surface. When the thickness ofthe film is more than 5000 μm, the film is more difficult to flex to fit the unevenness ofthe surface or to a curved surface, and thus it may be difficult to adhere the retroreflective sheeting to the article.

The tensile strength of a plastic film used is preferably 500 to 3000 kgf?cm², and more preferably 1500 to 2500 kgf/cm². When the tensile strength ofthe film is too low, the adhesion of a retroreflective sheeting to the plastic film is liable to be difficult. When it is too high, a retroreflective sheeting that becomes partially peeled off from an article can become wholly peeled off more easily. The plastic film can be either a transparent film or a colored film, and is preferably white. This is because the white-colored film, when used together with a light-transmissive prism type retroreflective sheeting, can prevent the appearance from deteriorating and prevent the reflective brightness from lowering. The degree of whiteness is preferably 80 to 90 in terms of brilliance in Y value. Such white plastic film can be formed from a material comprising a polymer and a white pigment. As the white pigment, inorganic powder such as calcium carbonate, barium sulfate, titanium dichloride or silica can be used.

In order to bond the plastic film to a retroreflective sheeting, an adhesive layer is provided. The adhesive layer can be formed by using a known adhesive. For example, it can be formed by coating an adhesive comprising an adhesion material such as acrylic resin, epoxy resin, polyurethane resin, polyvinyl chloride resin, silicone resin, or natural or synthetic mbber on a retroreflective sheeting and/or a plastic film according to a conventional coating technique. The adhesive is preferably an acrylic adhesive, especially preferably, an acrylic pressure-sensitive adhesive. These adhesives have a desirable adhesion property to a plastic film such as a polyester film. The acrylic pressure-sensitive adhesives having a desirable adhesion property especially to polyester films mainly comprise a copolymer of isooctyl acrylate and acrylic acid. The thickness ofthe adhesive layer can be widely varied depending upon various factors. The thickness is generally 30 to 120 μm.

An adhesive portion is used to bond the retroreflective sheeting/plastic film composite to the uneven surface, and is described with reference to Figure 1 and other succeeding drawings. Figures 1 and 3 illustrate that an adhesive portion 4 is provided between a plastic film 3 and a concrete wall 5 as an article so as to form a space 6 having a vent 7 communicating with the extemal atmosphere. Thus, substances such as water vapor and the like can be emitted to the atmosphere without remaining between a retroreflective sheeting and the article. Thus, the potential for blistering of the retroreflective sheeting caused by a gas remaining between the retroreflective sheeting and for the article, and for the article peeling away from the retroreflective sheeting due to such blistering, is reduced. Although substances may remain in space 6, they typically cannot penetrate into the retroreflective sheeting to damage the retroreflective sheeting.

The adhesive portion 5 and the space 6 can be selectively applied in the pattem shown in Figure 4. That is, on the main surface 32 opposite the surface to which a retroreflective sheeting is adhered, an adhesive portion is provided in the form of band 41 along the four sides ofthe surface 32. The adhesive portion comprises an adhesive stripe and an adhesive spot 42 provided substantially at the center ofthe surface 32. As shown in Figure 4, in three co ers 34 an adhesive 41 in the form of stripe is coated so as to leave a gap where the ends ofthe adhesive do not contact with each other. In the fourth comer 33, no adhesive is coated so as to provide a vent 7. The gaps in comers 34 may become clogged with the adhesive when the film is adhered to the article, but the uncoated portion 33 cannot become clogged when the film 3 is adhered, to provide an adequate width for forming the vent 7.

The thickness ofthe coating in the band-shaped adhesive portion 41 and the spot adhesive portion 42 is generally within the range of 1 to 20 mm, preferably, in the range of 5 to 15 mm. When the thickness ofthe coating ofthe adhesive is less, there may be insufficient adhesive to prevent the retroreflective sheeting from blistering and peeling. When the thickness is greater, rainwater or dust can enter the space, and thus cause blistering or peeling ofthe retroreflective sheeting.

When multiple films 3 are used, they should be adhered to an article in such a manner that the side 3 A on which the uncoated portion 33 is provided does not face another film 3. For example, when the plural pieces of film 3 are adhered in parallel, the arrangement shown in Figure 5 should be used. That is, the side 3 A on which is provided the uncoated portion 33 functioning as a vent is not adjacent to any sides of other film 3. Further, when four pieces of film 3 are arranged, the configuration can be as shown in Figure 6, where the uncoated portion 33 provided on the side 3 A of each film 3 is arranged so as to face away from other films 3. Figure 7 illustrates a suitable configuration for still greater numbers of films 3. Eight pieces of films 3(A) to 3(D) are arranged to surround the film 3(C) arranged in the center. Each uncoated portion 33 constitutes a vent when each film is adhered to an article, and the uncoated portion 33 of films 3(A) and 3(D) provide vents to the atmosphere as in other embodiments. The uncoated portion 33(a) of film 3(B) communicates with the uncoated portion 33(b) ofthe adjacent film 3(C), and the uncoated portion 33(c) ofthe same film communicates with the uncoated portion 33(d) ofthe adjacent film 3(C) having the same constmction as that ofthe film 3(C). Because each vent formed with each uncoated portion 33(a) to 33(d) communicates with each other, these vents can communicate with an extemal atmosphere through the vent formed with the uncoated portion 33(e) ofthe film 3(C).

Portions to which no adhesive is coated (vents) can open in any orientation as long as they can communicate with an extemal atmosphere. However, when the surface of an article is a vertical surface, such as a vertical concrete wall surface, it is preferable that the uncoated portion 33(x) face the side and that the uncoated portion 33(y) face down. The vent formed in such a manner can prevent rainwater and dust penetration.

The uncoated portion need not be provided at a comer of a film, and can be provided in the center ofthe side 3A ofthe film 3 as in the uncoated portion 33(z) shown in Figure 9. The number of vents also is not limited to one per piece of film, and two or more vents could be provided as necessary. The provision of two or more no- coating portions 33 can be effected, for example, as shown in Figures 10 and 11. In these examples, a band-shaped adhesive layers 41 are used in the patte shown in the drawing to provide four (Figure 10) or eight (Figure 11) uncoated portions 33 having a wide width.

An adhesive portion area provided on a plastic film is usually 10% to 90%, preferably 15% to 80%, and more preferably 20% to 50% ofthe entire area ofthe film. When the adhesion area is too small, there can be a danger that the adhesion to a substrate becomes insufficient. When the adhesion area is too large, a space formed between the film and the article has a small volume so that the effect of preventing blister of a retroreflective sheeting and the peeling ofthe retroreflective sheeting due to such a blister is decreased.

For the adhesive used in the adhesive portions, conventional adhesives as in the above-described adhesive layer can be used. The adhesive is, however, preferably epoxy or silicone. These adhesives can readily provide a high adhesion with a smaller adhesion area. Furthermore, when water and substances like alkaline substances are present at the interface between the adhesive portion and an article, they continue to provide excellent adhesion. An exemplary epoxy adhesive comprises a polyamide compound as a hardener. These epoxy adhesives have a desirable adhesion especially both for concrete and polyester films. One such adhesive is "BOND E 250" manufactured by Konishi Bond Co. Ltd. of Japan. An exemplary silicone adhesive comprises modified silicone polymer. One such adhesive is "MPX-1" manufactured by Konishi Bond Co. Ltd. of Japan.

To produce a retroreflective stmcture according to the present invention, the following method may be used. First, a retroreflective sheeting is adhered to one main surface of a plastic film by an adhesive layer. Second, the film having the retroreflective sheeting is cut and processed in conformity with the configuration and size ofthe article to which the sheeting will be applied. Third, an adhesive portion is provided on another main surface ofthe film so as to form an uncoated portion providing a vent communicable with an exte al atmosphere when the film is adhered to the article. Fourth, the film is adhered to the article so that the vent communicates with the extemal atmosphere.

According to this method, the film and the retroreflective sheeting readily can be adhered entirely and uniformly to each other so that the stmcture to which the retroreflective sheeting is adhered can be readily made. Altematively, a film may be adhered to an article by an adhesive portion, and a retroreflective sheeting thereafter thereafter adhered on the film. In this case, however, it is possible that it will be difficult to adhere the film and the retroreflective sheeting uniformly to each other. In the practice ofthe present invention, an article used as a member of a retroreflective stmcture is not particularly limited. As can be readily understood from the description herein above, however, the present invention is suitable when the article is a material made of concrete such as a concrete wall. This is because, as has been previously described, a typical concrete wall surface is highly mgged and includes water and substances like alkaline substances, and the present invention can solve problems derived therefrom.

The degree ofthe unevenness of an article, especially a concrete wall, is usually in the range of 1 to 10 mm, when defined in terms ofthe difference between the maximum height and the maximum depth ofthe surface to be measured. Such difference can be affected by particle size of ballast mixed into concrete. The particle size of ballast is usually within a range of cmshed stone 1505 to 5005 defined JIS A 5005. The particle size defined with "cmshed stone 1505" means that the maximum particle size included in ballast is 15 mm and the minimum particle size is 5 mm. While, the particle size defined with "cmshed stone 5005" means that the maximum particle size included in ballast is 50 mm and the minimum particle size is 5 mm.

The present retroreflective stmcture may also be applied to other articles having uneven surfaces, or having substances therein which are easily transferred from the surface to the retroreflective stmcture, such as a mortar wall or an asphalt road surface.

Examples

Retroreflective stmctures having the constmction shown in Figures 1, 3, and 4 were produced and the characteristics thereof were evaluated. As a retroreflective sheeting 10, "3970 G" manufactured by 3M Company was used, as a plastic film 3, "MERINEX No. 339", manufactured by I. C. I. Japan Co., Ltd. (thickness 250 mm, brilliance in Y-value 83, tensile strength in MD direction 1550 kgffcm², tensile strength in TD direction 1750 kgf?cm²), and as an adhesive portion 4, an epoxy adhesive, "Bond E 250" manufactured by Konishi Bond Co., Ltd. were used, respectively and adhered to an article 5, a concrete wall. The method used was to form a film having a retroreflective sheeting, then process the resulting film, thereafter adhering the processed film to an article. As an adhesive layer 2, an acrylic pressure-sensitive adhesive layer previously applied to the retroreflective sheeting 10 was used. A desired retroreflective stmcture could be obtained.

When the stmcture obtained in this example was adhered with the retroreflective sheeting in such a manner as mentioned above, uniform and high reflective brightness throughout the concrete wall could be provided without causing cracks and surface defects such as unevenness on the retroreflective surface ofthe retroreflective sheeting. Further, water and substances like alkaline substances were less likely to be retained between the retroreflective sheeting and the article and the penetration thereof into the retroreflective sheeting was also inhibited. Thus, blistering ofthe retroreflective sheeting which may be caused by such retention or penetration and the peeling ofthe retroreflective sheeting caused thereby could be prevented for a long time. The adhesion procedure according to the above-described method could shorten the time required for effecting the whole operation as compared with the conventional methods.

As can be understood from the detailed explanation provided above, according to the present invention, since an adhesion means comprises a flexible support such as a plastic film, cracks and surface defects such as unevenness on the retroreflective surface ofthe retroreflective sheeting adhered on the surface of an article such as a concrete wall due to unevenness ofthe surface ofthe article are prevented, and uniform and high reflective brightness throughout the article having the retroreflective sheeting adhered thereto can be provided. Further, since an adhesive portion present between a film support and a wall surface is provided so as to form a space having a vent communicated with an extemal atmosphere, retention of water and substances like alkaline substances included in the concrete or the penetration ofthe same into the retroreflective sheeting is prevented and blistering ofthe retroreflective sheeting which may be caused by such retention or penetration and the peeling ofthe retroreflective sheeting caused thereby can be prevented. The adhesion means as described above can be readily cut and processed. Thus the adhesion procedure does not require labor and time and, therefore, complicated procedure which is the defect ofthe prior art can be eliminated.

Claims

CLAIMS:

1. A retroreflective stmcture comprising:

(a) a retroreflective sheeting having a retroreflective element; and (b) a flexible support having first and second major surfaces, the first major surface adhered to the retroreflective sheeting; and

(c) an adhesive portion selectively applied to the second major surface of flexible support, the adhesive disposed so as to provide an uncoated portion that, when the retroreflective stmcture is applied to a surface, provides a vent between the second major surface and the atmosphere.

2. The retroreflective stmcture of claim 1, wherein said support is a plastic film.

3. The retroreflective stmcture of claim 2, wherein said plastic film has a thickness of 200 to 5000 μm.

4. The retroreflective stmcture of claim 1, wherein said adhesive portion comprises at least one stripe.

5. The retroreflective stmcture of claim 1, wherein said surface is a concrete wall.

6. A process for producing a retroreflective stmcture, comprising the steps of:

(a) providing a retroreflective sheeting having a retroreflective element;

(b) adhering a first major surface of a flexible support to the retroreflective sheeting;

(c) selectively applying an adhesive onto a second major surface ofthe flexible support, to provide an uncoated portion that, when the retroreflective stmcture is applied to a surface, provides a vent between the second major surface and the atmosphere.

7. The method of claim 6, wherein the method further includes the step of cutting the retroreflective sheeting/flexible support composite to a suitable size.

8. The method of claim 6, wherein the method further includes the step of applying the retroreflective stmcture to a surface.

9. The method of claim 7, wherein the surface is an uneven concrete surface.