Reflective sheets are known and use a plurality minute prismatic projections as reflection elements. Such a reflective sheet is a so-called retroreflective sheet which utilizes the good retroreflection properties of the prismatic projections, and the sheet having such prismatic projections is usually called a prismatic reflective sheet. The structure and production of such a reflective sheet are disclosed in US-A-4025159 (corresponding to JP-A-52-110592), US-A-4775219, JP-A-60-100103, JP-A-6-50111, etc.

The prismatic projections are, for example, triangular pyramids, which are called"cube comers". Such prismatic projections are integrally formed with a sheet- form base material to form a prismatic sheet. A resin used to form the prismatic sheet is usually a highly transparent one having a refractive index of 1.4 to 1.7, and examples of such a resin include acrylic resins, epoxy-modified acrylic resins, polycarbonate resins, etc.

To produce a reflective laminate by fixing the prismatic sheet to a substrate, the following method may be used: The prismatic sheet and a seal layer comprising a thermoplastic resin are combined to form a reflective sheet, and then the reflective sheet is adhered and fixed to the surface of the substrate through an adhesive layer comprising an adhesive.

The reflective sheet may be produced as follows: First, the prismatic sheet is laminated over the surface of the seal layer with leaving a specific gap between them, and they are heat embossed from the back surface of the seal layer. The prismatic sheet is placed so that the back surface having the prismatic projections faces the surface of the seal layer. The heat embossing forms the raised ridge elements formed from a part of the seal layer and comprising a thermoplastic resin, and allows the ridge elements in contact with the prismatic sheet.

The ridge elements of the thermoplastic resin function as a kind of a hot-melt adhesive, and the ridge elements and the prismatic sheet are adhered each other, when the ridge elements are cooled while they are in contact with the prismatic sheet. That is, the ridge elements formed are adhered, at one end, to the back surface of the prismatic sheet, and at the other end, to the seal layer. Thus, they separate the prismatic sheet and the seal layer so that the prismatic projections are exposed to the space between the seal layer and the prismatic sheet. The prismatic projections should be exposed in such a way, so that the prismatic projections exhibit the effective reflection, in particular, retroreflection properties. The retroreflective sheet having such a structure is well known. In this connection, the detailed description of the invention and the drawing of above-cited US-A-4025159 may be referred to.

When the prismatic sheet is fixed to the substrate in the production of the reflective laminate by the above series of steps, an adhesive layer of an adhesive should be provided between the back surface of the seal layer and the substrate after the formation of the reflective sheet. That is, the seal layer and the adhesive layer should be provided as discrete layers. For example, a pressure-sensitive adhesive is often used as the adhesive of the adhesive layer, but a seal layer comprising the pressure-sensitive adhesive cannot be used. This is because the ridge elements cannot be formed from the pressure-sensitive adhesive having a high flowability at room temperature (25°C), since the ridge elements function to separate the prismatic sheet and the seal layer as described above.

In addition, the ridge elements are only partly adhered to the prismatic sheet.

Therefore, it is necessary to increase the durability of the adhesion in such a partly adhered structure, since the seal layer and the prismatic layer may be separated in use, if the durability of the adhesion is low. To increase the durability of the partial adhesion, an electron beam-curable composition or a heat-curable composition, the composition of which is optimally designed, should be used as described in the above publications, and the sophisticated technique to design the composition is required to determine the composition of the seal layer.

Furthermore, the durability of the partial adhesion cannot be increased in the absence of the increase of the degree of the adhesion between the ridge elements and the prismatic sheet. Therefore, the production of such a reflective laminate requires a very precise embossing technique.

Alternatively, a prismatic sheet in which raised ridge elements are integrally formed with the sheet is known. For example, such a prismatic sheet is disclosed in

US-A-4025159 (corresponding to JP-A-52-110592), US-A-5946134 (corresponding to JP-A-9-504383), US-A-5882796 (corresponding to JP-A-2000-508088), US-A- 5910858 (corresponding to JP-A-2000-508086), etc.

Such a prismatic sheet having raised ridge elements has a back surface having a plurality of cells each comprising a plurality of prismatic projections and a raised ridge element which surrounds the projections, and a surface opposing to the back surface.

One end of the raised ridge element is integrally bonded to the back surface of the prismatic sheet, while the other end is free. The height of the raised ridge element is larger than that of the prismatic projection. Therefore, when a laminate sheet is formed by adhering the prismatic sheet to another sheet (a bonding sheet or a bonding layer) at the other ends of the raised ridge elements to form a laminate sheet, a reflective sheet comprising such a laminate sheet may be produced.

The methods for firmly bonding the raised ridge elements of the prismatic sheet to the bonding layer disclosed in the above publications include a method using an electron beam-curable resin or a thermosetting resin, and an ultrasonic welding method.

In such a case, after the production of the laminate sheet comprising the prismatic sheet and the bonding layer, the laminate sheet is adhered to the substrate with an adhesive layer which is distinct from the bonding layer to finish the reflective laminate.

The above publications do not describe the production of the reflective laminate by adhering the prismatic sheet with the raised ridge elements directly to the substrate.

Prior art reflective laminate are produced by first forming a reflective sheet comprising a prismatic sheet, and adhering the reflective sheet to a substrate. However, it has been required to reduce the costs of the whole reflective laminate in these years.

To satisfy such requirement, the steps from the production of the prismatic sheet to the finish of the reflective laminate should be made more efficient. Thus, the present inventor has made researches on the structure of the reflective laminate, with which the prismatic sheet can be bonded to the substrate with ease in a relatively short time using no special equipment such as an electron-beam irradiation apparatus, so that the prismatic projections are exposed to the space in order that they exhibit the reflection properties, in particular, retroreflection properties, effectively, and such a bonding process can be carried out manually. That is, the present inventor has made extensive study within the framework that the provision of such a structure of the reflective laminate can satisfy the above-described various requirements, and thus completed the present invention.

SUMMARY Accordingly, the present invention provides a reflective laminate with which a prismatic sheet can be bonded to a substrate with ease in a relatively short time, and which can be produced using no special equipment. To solve the above problems, the present invention provides a reflective laminate comprising (I) a prismatic sheet which has a back surface having a plurality of cells each comprising a plurality of prismatic projections and a raised ridge element surrounding said prismatic projections, and a surface opposing to said back surface, and which can reflect light incident on said surface with said prismatic projections, (II) a substrate having a surface facing said prismatic sheet, and (III) a bonding layer having an adhesive layer fixed to said surface of the substrate, wherein said raised ridge element is integrally bonded, at its one end, to said back surface of the prismatic sheet, and adhered, at its the other end, to said adhesive layer of the bonding layer, and separates said prismatic sheet and said bonding layer so that said prismatic projections are exposed to a space between said bonding layer and said prismatic sheet characterized in that said adhesive layer of the bonding layer comprises a self-adherent polymer.

BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a cross sectional view of the reflective laminate of the present invention.

Fig. 2 is a plan view of the reflective laminate of the present invention.

Fig. 3 is a cross sectional view of another reflective laminate constructed in accordance with the present invention.

Fig. 4 is a cross sectional view of another reflective laminate constructed in accordance with the present invention.

Fig. 5 is a cross sectional view of another reflective laminate constructed in accordance with the present invention.

DETAILED DESCRIPTION In the reflective laminate of the present invention, a prismatic sheet having raised ridge elements is used as a prismatic sheet, the bonding layer comprises the adhesive layer containing a self-adherent polymer, and the adhesive layer is adhered to the raised ridge elements of the prismatic sheet. Therefore, the prismatic sheet can be bonded to the substrate with ease in a relatively short time, and thus the reflective laminate can be produced using no special equipment. That is, the reflective laminate

can be produced by placing the bonding layer on the surface of the substrate, laminating the prismatic sheet to the surface of the bonding layer with the back surface of the prismatic sheet facing the bonding layer, and pressing the prismatic sheet to the bonding layer to press adhering the raised ridge elements to the bonding layer. With such a method, the prismatic sheet can be bonded to the substrate while the prismatic projections being exposed to the space, so that the projections can exhibit their reflection properties, in particular, the retroreflective properties, and such a method can be carried out manually.

In the structure of the laminate according to the present invention, the adhesion surface of the adhesive layer constitutes the surface of the bonding layer. That is, (1) the bonding layer consists of the adhesive layer, or (2) the bonding layer consists of an adhesive laminate comprising the bonding layer and the adhesive layer provided on the outermost surface of the bonding layer. When the raised ridge elements and the bonding layer are thermally press adhered while applying heat during the press adhesion process, the bonding strength (the peel strength between the prismatic sheet and the bonding layer) can be effectively increased.

The self-adherent polymer in the bonding layer is preferably crosslinked. The crosslinked self-adherent polymer can increase the cohesive force of the adhesive layer without deteriorating the adhesion properties of the adhesive layer to the raised ridge elements, and also the pressure resistance of the adhesive layer. With such function, the direct contact of the raised ridge elements to the substrate surface through the bonding layer can be prevented when the prismatic sheet is press adhered to the bonding layer. If the raised ridge elements are in direct contact to the substrate surface through the bonding layer, the peel strength between the bonding layer and the prismatic layer may decrease and thus the durability of the bond between the prismatic layer and the bonding layer tends to decrease. The decrease of the bond durability may cause the peeling (pop-off) of the prismatic sheet from the bonding layer during the use of the reflective laminate. The increase of the pressure resistance of the adhesive layer allows the prismatic sheet to be press adhered to the bonding layer with a sufficiently large force (pressure), effectively increases the adhesion force (peel strength) between the raised ridge elements and the bonding layer, and makes it easy to increase the durability of the bond between the prismatic sheet and the bonding layer.

When the bonding layer further has a support comprising a polymer and the adhesive layer is fixed to the support, the pressure resistance of the whole bonding layer can be effectively increased. Thus, the use of the polymer support also makes it

possible to press adhere the prismatic sheet to the bonding layer with a sufficiently large force, and increases the durability of the bond between the prismatic sheet and the bonding layer. In view of the effective increase of the pressure resistance of the bonding layer as a whole, a foam sheet is preferably used as the polymer support.

Furthermore, when the adhesive layer of the bonding layer contains a crystalline polymer in addition to the self-adherent polymer, the pressure resistance of the adhesive layer can also be effectively increased. In addition to this effect, the crystalline polymer can impart the heat press adhesion properties (heat-sensitive adhesion properties) to the adhesive layer and decrease the tack of the adhesion surface of the adhesive layer.

When the whole thickness of the bonding layer is 20 um or more, the penetration of the raised ridge elements through the bonding layer can be effectively prevented when the prismatic sheet is adhered to the adhesive layer. In view of the prevention of the penetration of the raised ridge elements, the upper limit of the thickness of the bonding layer is not limited, but the thickness of the bonding layer usually does not exceed 1,000 um. If the thickness of the bonding layer is too large, the adhesive layer of the bonding layer may be in contact with the prismatic projections depending on the press adhering conditions or the height of the raised ridge elements, when the prismatic layer is adhered to the bonding layer, and thus the reflection properties tend to deteriorate.

The reflective laminate of the present invention is preferably used as a retroreflective sign, when the substrate is a sign substrate, and the prismatic projections comprise cube corner prisms. Since the adhesive layer which adheres the raised ridge elements comprises the self-adherent polymer in the reflective laminate of the present invention, the adhesive failure, such as the crack of the adhesive layer, hardly occurs even if an impact is applied to the laminate. Thus, such a sign is suitably used as a retroreflective sign which is provided on the roadside, airport, construction site, etc.

In the reflective laminate of the present invention, the prismatic sheet (1) and the substrate (2) are bonded through the bonding layer (3) as shown in Figs. 1 and 2.

The prismatic sheet (1) has, on its back surface, a plurality of prismatic projections (11), and raised ridge elements (12) each surrounding the respective prismatic region (10) in which the prismatic projections (11) are provided. A plurality of the prismatic projections (11) provided in one prismatic region (10) and the raised ridge element (12) surrounding the prismatic region (10) constitute one cell (13). As shown in the figure, a plurality of the cells (13) are provided on the back surface (14) of

the prismatic sheet so that they are adjacent to each other through the raised ridge element. Usually, the surface (15), which is opposed to the back surface (14) of the prismatic sheet, is a light-incident surface through which outside light impinges. The light which enters through the surface (15) can be reflected by the prismatic projections (11) like the conventional prism type reflective sheets.

The substrate (2) is provided with its surface (21) facing the prismatic sheet (1), and the bonding layer (3) is fixed to the surface (21) of the substrate. The bonding layer (3) may be a single layer consisting of the adhesive layer as shown in Fig. 1, or a laminate comprising a support having the adhesive layer thereon. The adhesive laminate is usually fixed to the substrate through another adhesive layer provided on the back surface of the substrate. As such an adhesive laminate, a double-coated adhesive sheet (or tape) is preferably used from the viewpoint of the easy bonding process.

The raised ridge element (12) of the prismatic sheet is integrally bonded at its one end (121) to the back surface of the prismatic sheet, and adhered at the other end (122) to the adhesive layer (the bonding layer 3 itself being the adhesive layer in the embodiment shown in the figures). The raised ridge element (12) separates the prismatic sheet (1) and the bonding layer (3) so that the prismatic projections (11) are exposed to the space between the bonding layer (3) and the back surface (14) of the prismatic sheet. For example, the height of the raised ridge element measured from the sheet surface (15) (the distance from the sheet surface (15) to the other end (122) ) is larger than the height of the prismatic projections (the distance from the sheet surface (15) to the apexes (111)).

The reflective laminate of the present invention may be produced by a method comprising the steps of providing the bonding layer (3) on the surface (21) of the substrate, laminating the prismatic sheet on the bonding layer (3) with the back surface (14) of the prismatic sheet facing the boding layer (3), and pressing the prismatic sheet (1) against the bonding layer (3) to press adhere the raised ridge element (12) to the bonding layer (3).

The pressure in the pressing (press adhering) step is usually from 50 g/cm2 to 50 kg/cm2 (from about 5 kPa to 4.9 MPa). When the adhesive layer of the boding layer is heat-sensitive, the laminate is heated in the pressing step, and then cooled to finish the adhesion. In such a case, a heating temperature depends on the activation temperature of the adhesive layer and the level of the heat resistance of the components of the reflective laminate, and is usually from 50 to 200°C.

For the reasons described above, it is preferable to prevent the direct contact of the raised ridge elements to the surface of the substrate through the bonding layer.

However, the tip end portion of the raised ridge element (12) may be embedded in the shallow part of the bonding layer (3).

The raised ridge element (12) is integrally bonded to the prismatic sheet (1), when the latter is produced. For example, the prismatic sheet may be produced by integral molding comprising supplying a mold with a cavity having the same shape, size and arrangement as those of the prismatic projections (11) and the raised ridge elements (12), pouring a resin in the liquid state in the cavity and solidifying the resin which is in contact with the mold. The solidification of the resin may be carried out by cooling of the resin melt, curing of a curable resin, etc. When the resin is solidified with allowing the sheet-form support in contact with the liquid-state resin, the support, the raised ridge elements and the prismatic projections are bonded. Furthermore, the prismatic sheet may be produced by a contact molding method comprising supplying a resin sheet as a raw material of the prismatic sheet, and pressing the mold having the cavity described above.

When the reflective laminate is used outdoors, a protective layer is preferably provided on the surface (15) of the prismatic sheet. As the protective layer, a transparent polymer sheet comprising a UV absorber may be used.

The reflective laminate may have a structure shown in Fig. 3. The reflective laminate of this Figure comprises the raised ridge elements (52) bonded to the prismatic sheet (5), and the prismatic projections (51), like the laminate of Fig. 1. Different from Fig. 1, in the laminate of Fig. 3, the raised ridge elements (52) have an adhesive, and function also as an adhesive layer.

In this embodiment, the raised ridge elements (52) have the adhesive layer (523) on the tip ends (521) opposing to the bonding ends (521) of the elements (52). The prismatic sheet (5) is fixed to the substrate (2) through the adhesive layer (523) like the embodiment shown in Fig. 1. That is, the raised ridge elements are bonded to the back surface of the prismatic sheet at the one ends and adhered to the substrate at the other ends (tip ends), and separate the prismatic sheet and the substrate so that the prismatic projections are exposed to the space between the substrate and the prismatic sheet.

The adhesive layer (523) may be applied to the tip ends of the raised ridge elements with a roll coater, etc. The prismatic sheet having the raised ridge elements is inserted between an application roll and a nip roll under a suitable pressure, and the adhesive comprising a self-adherent polymer is applied only to the tip ends of the

raised ridge elements. After the application of the adhesive layer, a liner may be laminated on the adhesive layer to protect the adhesive layer until the prismatic sheet is fixed to the substrate.

The protective sheet (59) is provided on the surface of the prismatic sheet. The protective sheet (59) may be laminated on the surface of the prismatic sheet before the prismatic sheet is fixed to the substrate.

The reflective laminate may have a structure shown in Fig. 4. In the embodiment of this Figure, the raised ridge elements, which are bonded to the back surface of the prismatic sheet (6), are made of an adhesive, and thus the raised ridge elements themselves function as an adhesive layer. That is, the raised ridge elements (62) are bonded to the back surface of the prismatic sheet at their one ends and adhered to the substrate (2) at the other ends, and separate the prismatic sheet (6) and the substrate (2) so that the prismatic projections (61) are exposed to the space (46) between the substrate and the prismatic sheet.

The raised ridge elements (62), that is, the adhesive layer in the form of the raised ridge elements, may formed on the back surface of the prismatic sheet by applying a paint (containing an adhesive) with screen printing or with an applicator which can apply the paint in a pattern form such as a roll coater, a gravure coater, etc. so that the raised ridge elements surround the prismatic projections. Alternatively, the adhesive layer in the form of the raised ridge elements is provided on the surface of the substrate, and then the prismatic sheet having no raised ridge elements is adhered to the substrate.

The protective film (69) may be laminated on the surface of the prismatic sheet before or after fixing the prismatic sheet to the substrate.

As one modification of the embodiment of Fig. 4, the reflective laminate of the present invention can have a structure shown in Fig. 5. In the embodiment of this Figure, the laminate has the adhesive layer (72) in the form of the raised ridge elements on the back surface of the prismatic sheet (7) like the embodiment of Fig. 4. In the embodiment of Fig. 5, the substrate (20) has the raised parts (201) bonded to the substrate, and the adhesive layer (72) is provided on the tip ends (201E), and the prismatic sheet and the substrate (20) are adhered through the adhesive layer in the form of the raised ridge elements. That is, the raised ridge elements (72) comprising the adhesive are bonded to the back surface of the prismatic sheet (7) at their one ends and adhered to the raised parts (201) of the substrate (20) at the other ends, and separate

the prismatic sheet (7) and the substrate (20) so that the prismatic projections (71) are exposed to the space (47) between the substrate (20) and the prismatic sheet (7).

The reflective laminate of Fig. 5 may be produced by forming the raised parts (201) on the surface of the substrate (20), forming the adhesive layer (72) in the form of the raised ridge elements on the tip ends (201E) of the raised parts using a paint- transfer type applicator such as a roll coater, and then laminating the prismatic sheet (7) having the protective sheet (79).

As described above, the adhesive layer of the bonding layer contains a self- adherent polymer. The self-adherent polymer means a polymer which is tacky at room temperature (about 25°C).

Examples of the self-adherent polymer include acrylic polymers, nitrile- butadiene copolymers (e. g. NBR, etc. ), styrene-butadiene copolymers (e. g. SBR, etc.), amorphous polyurethane, silicone polymers, etc. The self-adherent polymers may be used independently or in admixture of two or more.

Preferably, the self-adherent polymer has a crosslinkable functional group in the molecule so that it is crosslinkable. Examples of the crosslinkable functional group include (a) photocrosslinkable functional groups such as an unsaturated double bond, aromatic ketone structures, etc. and (b) crosslinkable functional groups such as a hydroxyl group, a carboxyl group, etc. In addition to these crosslinkable functional groups, the self-adherent polymer preferably has an alkyl group having 4 to 8 carbon atoms and/or an aryl group as well as a polar group other than the above crosslinkable functional groups.

The aryl group means a functional group having an aromatic ring such as a benzene ring in its chemical structure. Examples of the aromatic group include a phenyl group, a phenoxy group, a benzyl group, a benzoyl group, a naphthyl group, a biphenyl group, etc. Preferable examples of the polar group include nitrogen- containing functional groups such as a nitrile group, a pyridyl group, an di-alkyl substituted amino group, etc.

The number of carbon atoms in the alkyl group is preferably 6 or less, namely 4, 5 or 6.

The proportion of the monomeric units having the above alkyl group and/or the aryl group (repeating units derived from monomers having the alkyl group or the aryl group respectively) in the self-adherent polymer is usually from 60 to 99 mole %, preferably from 70 to 98 mole %.

One example of the self-adherent polymer to be used in the present invention is an acrylic polymer prepared by copolymerizing a monomer mixture containing (i) an acrylate monomer having 4 to 8 carbon atoms in the molecule and/or an acrylate with an aryl group in the molecule, and (ii) a (meth) acrylate having a crosslinkable functional group.

Examples of the monomer (i) include n-butyl acrylate, isobutyl acrylate, 2- methylbutyl acrylate, 2-ethylhexyl acrylate, isooctyl acrylate, phenoxyethyl (meth) acrylate, phenoxypropyl (meth) acrylate, etc. Examples of the monomer (ii) include (meth) acrylic acid, fumaric acid, itaconic acid, 2-hydroxyethyl (meth) acrylate, 2-hydroxylpropyl (meth) acrylate, hydroxy-3-phenoxypropyl (meth) acrylate, etc.

When a (meth) acrylate monomer having a functional group derived from an aromatic compound as the photocrosslinkable group is used, the monomer (ii) may be omitted. Examples of the photocrosslinkable group derived from the aromatic compound include those derived from benzophenone, vinylbenzene, benzalacetophenone, cinnamylidene, coumarin, stilbene, styrylpyridine, a- phenyhnaleimide, anthracene, etc.

The acrylic polymer may be prepared by copolymerizing the monomer mixture containing the monomers in the specific ratio with a conventional method such as bulk polymerization, solution polymerization, suspension polymerization, emulsion polymerization, etc.

The glass transition temperature Tg of the self-adherent polymer is usually from - 50 to 10°C, preferably from-40 to 5°C, particularly preferably from-30 to 0°C. The molecular weight of the self-adherent polymer may be in a range such that the specific adhesion force is achieved, and the weight average molecular weight is usually from 10,000 to 1,000, 000. Like the conventional pressure-sensitive adhesives, a tackifier may be used in combination with the self-adherent polymer.

As described above, the self-adherent polymer is preferably crosslinked. For example, when the crosslinkable functional group is a carboxyl group, a bisamide crosslinking agent, an epoxy resin, an isocyanate compound, etc. are preferably used as the thermal crosslinking agents. When such a crosslinking agent is used, the proportion of the crosslinking component in the whole weight of the adhesive composition is usually from 0.01 to 20 wt. %, preferably from 0.05 to 10 wt. %.

The adhesive composition comprising the self-adherent polymer may be prepared by uniformly mixing the raw materials by a conventional mixing method. For example, the self-adherent polymer, the crosslinking agent, a solvent, and other

optional additives are mixed with a mixing apparatus such as a homomixer, a planetary mixer, etc. to uniformly dissolve or disperse the components to prepare the liquid composition.

Alternatively, a monomer mixture containing a monomer, which forms the self- adherent polymer through polymerization, and a crosslinking agent monomer can be used as the liquid composition described above. When the monomer mixture is used, preferably, the composition comprising the monomer mixture is applied on an adherent such as the substrate, and then UV rays or electron beams are irradiated to the applied composition to polymerize (or polymerize and crosslink) the monomers to form the adhesive layer.

One example of the additive is a crystalline polymer. The crystalline polymer can impart the heat-sensitive adhesion properties or thermal peeling-easy properties to the adhesive layer. The thermal peeling-easy property means that an adhesive can be peeled from an adherent when the adhesive is heated to a specific temperature (equal to or higher than the melting point of the crystalline polymer) so that the peel strength is lowered to a value smaller than that prior to heating. As the crystalline polymer, polyester, polyol, polyurethane, etc. may be used.

When the crystalline polymer and the self-adherent polymer have good compatibility each other at a temperature higher than the melting point of the crystalline polymer, the thermal peeling-easy properties can be further improved, and the tack of the adhesion surface of the adhesive layer can be decreased. An example of the combination of the two polymers with good compatibility is a combination of the self-adherent polymer having the aryl group in the molecule and the crystalline polymer comprising the repeating units of the alkylene group having 4 to 6 carbon atoms. Examples of such a crystalline polymer include polycaprolactone, polycaprolactone base polyurethane, polytetramethylene glycol ether, etc.

When such a crystalline polymer is used, the proportion of the crystalline polymer in the whole adhesive composition is usually from 3 to 50 wt. %, preferably from 4 to 45 wt. %.

The components of the bonding layer are not limited insofar as the bonding layer has the adhesive layer which is adhered to the raised ridge elements. For example, the bonding layer preferably comprises a double-coated adhesive tape having a polymer support, or a film-form adhesive comprising the adhesive composition (which may be referred to as a film-adhesive).

The double-coated adhesive tape consists of a support and adhesive layers provided on the both surfaces of the support. The support may be a plastic film, a foam sheet, a nonwoven fabric, etc. The thickness of the support may be appropriately selected so that the thickness of the whole bonding layer is in a suitable range, and is usually from 30 to 950 pm, preferably from 35 to 850 p. m. The thickness of the adhesive layers of the double-coated adhesive tape is not limited. The thickness of each adhesive layer is usually form 5 to 200 um, preferably from 10 to 100 um.

The support is preferably the foam sheet from the viewpoint of the effective improvement of the pressure resistance of the whole bonding layer as described above.

The foam sheet comprises a matrix phase of a polymer and a bubble phase. The polymer of the matrix phase may be an organic polymer such as an acrylic polymer, polyvinyl chloride, polystyrene, polyurethane, a butyl rubber, neoprene, etc. The bubble phase may comprise closed cells, open cells, or a mixture thereof. The density of the foam sheet is usually from 0.30 to 0.90 g/cm3.

Examples of the double-coated adhesive tape having the foam sheet are Acrylic Foam Tapee and Scotch° VHB adhesive tape (both available from 3M Company, St.

Paul, Minnesota).

The film-form adhesive has no support and consists of the self-supporting adhesive layer. As the self-supporting adhesive layer, for example, an adhesive layer containing the crosslinked self-adherent polymer and the crystalline polymer may be used. The film-form adhesive is usually supplied in the form of a laminate with a liner.

Thus, one adhesion surface of the film-form adhesive is adhered to the substrate to form the substrate having the bonding layer, and then the liner is peeled off to expose the other adhesion surface prior to adhering to the prismatic sheet. Thereafter, the raised ridge elements are adhered to the other adherent surface exposed.

The adhesive layer may be formed by applying the adhesive composition to a material and drying (or curing) it. For example, the adhesive composition is applied to the substrate or the liner to form the adhesive layer comprising the coated film of the composition. The application means may be any conventional one such as a knife coater, a roll coater, a die coater, a bar coater, etc. When the adhesive composition contains an organic solvent, the applied composition is usually dried at a temperature of 60 to 180°C. The drying time is usually from several ten seconds to several minutes.

The bonding layer may be light-transmissive as a whole, or the support of the adhesive layer and/or the double-coated tape may be colored white or other color to

make it opaque. For example, a pigment may be added to the adhesive layer and/or the support of the double-coated adhesive tape to color it.

The bonding layer may be substantially permanently fixed to the substrate and/or the prismatic sheet, or it may be removably adhered to the substrate and/or the prismatic sheet by bonding the bonding layer to the substrate or the prismatic layer using the film-form adhesive comprising the thermal-peeling easy adhesive composition described above, and optionally heating the reflective laminate (or the bonding layer). In particular, when the bonding layer can be thermally peeled from the substrate, the substrate is easily reused or recycled.

The prismatic sheet may be produced by a production method described in the patent publications cited above. A resin used to form the prismatic sheet is usually a highly transparent one having a refractive index of 1.4 to 1.7, and examples of such a resin include acrylic resins, epoxy-modified acrylic resins, polycarbonate, etc. The total light transmittance of such a resin is usually at least 70 %, preferably at least 80 %, particularly preferably at least 90 %.

The shape, size and arrangement of the prismatic projections of the prismatic sheet used in the present invention may be the same as those used conventionally (see US-A-4,775, 219, etc. ). Also, the shape, size and arrangement of the raised ridge element may be the same as those used conventionally (see US-A-5,946, 134, etc.).

For example, when the reflective laminate is used as the retroreflective sign, the preferred shape of the prismatic projection is a triangular pyramid, which is called a "cube corner". In the preferred cube corner (triangular pyramid element), one side of the bottom triangle has a length of 0.1 to 0.3 mm, and the height is 25 to 500 um. The bottom triangle is usually an equilateral triangle or an isosceles triangle, although it may be a scalene triangle having slightly different side lengths.

The area of one minute cell surrounded with the raised ridge element is usually from 3 to 40 mm, preferably from 5 to 30 mm2. The proportion of the total area of the raised ridge elements in relation to the whole area of the back surface of the prismatic sheet is usually from 10 to 50 %, preferably from 15 to 40 %.

The sheet-form base part of the prismatic sheet (the part except the raised ridge elements and the prismatic projections) is called a land. The thickness of the land is usually from 50 to 500 pm, preferably from 70 to 300 u. m. The height of the prismatic projection measured from the bonding surface of the land is usually from 20 to 400 u. m, preferably from 50 to 300 um. The height of the raised ridge element measured from

the bonding surface of the land is usually from 100 to 700 u. m, preferably from 150 to 600 urn.

The material of the substrate is not limited, and is usually a metal plate or a plastic plate. The metal plate may be a stainless or aluminum plate. The plastic plate is preferably a relatively hard one, and for example a plate of polycarbonate, polyimide, an acrylic resin polyethylene, polypropylene, etc.

The thickness of the substrate is usually from 250 llm to 10 mm, but not limited to such a thickness insofar as the effects of the present invention are not impaired. The area of the surface of the substrate to be bonded to the prismatic sheet is usually from 40 to 2,000 cm2, but not limited to such a thickness insofar as the effects of the present invention are not impaired.

Example 1 This example used an aluminum substrate (an aluminum plate available from HEIWA Metal Co., Ltd. ; 30 mm x 150 mm x 1 mm thickness), and a film-form adhesive as a bonding layer.

The film-form adhesive was"Bonding Film EFA 2001-4U (thickness of 40 um) available from Sumitomo 3M of Japan), which is formed from an adhesive comprising a crystalline polyester and a crosslinked acrylic self-adherent polymer (a heat sensitive adhesive). The both adhesion surfaces of the film-form adhesive were protected with silicone liners.

As a prismatic sheet having ridge elements, a retroreflective prismatic sheet having cube corner prisms as prismatic projections was used. This prismatic sheet was produced from a polycarbonate resin by the integral molding method using a mold, which is disclosed in US-A-5,946, 134. In the production method, a protective layer having a thickness of 50, um was adhered to the surface of the prismatic sheet (the surface of the land). The protective film was a film of polymethyl methacrylate containing a UV absorber.

The sizes of the prismatic sheet were as follows: -Thickness of land: 150 um -Height of prismatic projection: 180 um -Height of raised ridge element: 300 llm (measured on the surface of the prismatic sheet) - Area of one cell (prismatic area): 9 mm2 (measured on the surface of the prismatic sheet)

- Size of prismatic sheet surface: 25 mm x 150 mm (in the horizontal direction) Using the above components, the reflective laminate of the present invention was assembled as follows: Firstly, the surface of the substrate was degreased with a degreasing agent of Sumitomo 3M (FEY-0180). On the degreased surface of the substrate, the film-form adhesive, which had been heated at 95°C for one minute, was placed after exposing one adhesion surface, and press adhered using a hand roll having a weight of 2 kg at room temperature (about 25°C). Then, the other adhesion surface of the film-form adhesive was exposed, and the prismatic sheet was laminated on the other adhesion surface. The laminate was placed in an oven kept at 95°C for 5 minutes while applying a load of 0.088 kgf/cm2 (about 8.6 kPa) to adhere the prismatic sheet and the film-form adhesive (the bonding layer) each other to obtain the reflective laminate of the present invention.

The properties of the reflective laminate obtained in the above step were evaluated as follows: (1) Retroreflectivity The light beam of a flashlight was irradiated on the surface (prismatic sheet surface) of the reflective laminate from a position near the eye of an observer, and the reflected light was observed with an eye. With the comparison with the reflection from the prismatic sheet having the ridge elements alone, when the sheet was observed with the same reflection luminance, the retroreflectivity was ranked OK, while when the observed reflection luminance decreased due to the bonding, the retroreflectivity was ranked NG. With the reflective laminate of the present invention, no defect, which decreases the retroreflectivity, such as the contact of the bonding layer (film-form adhesive) and the prismatic projections was generated, and the retroreflectivity was ranked OK.

(2) Adhesion force The reflective laminate produced in the above step was aged at room temperature (about 20°C) for 24 hours, and subjected to the 90 degree peel strength test at a pulling rate of 300 mm/min. The peeling occurred at the interface between the adhesion surface of the film-form adhesive and the ridge elements, and the peel strength was 29 N/25 mm. This adhesion strength is in a high level such that the laminate can be used as a retroreflective sign.

Example 2 A reflective laminate of this Example was produced in the same manner as in Example 1 except that the prismatic sheet and the substrate were bonded with a double- coated adhesive tape as a bonding layer.

The double-coated adhesive tape used in this Example was Scotche VHB Construction Adhesive Tape Y-4920 having a thickness of 0.4 mm (available from 3M Company). This adhesive tape consisted of a foam sheet of an acrylic polymer as a support and adhesive layers of an acrylic self-adherent polymer formed on the both surfaces of the support. The T type peel strength of this double-coated adhesive tape against an aluminum foil was 22 N/cm. The T type peeling strength is measured by laminating aluminum foils each having a thickness of 130, um on both surfaces of the adhesive tape, press adhering them by reciprocating a steel roll of 10 kg twice, aging the laminate at room temperature for 72 hours and carrying out the T type peel test at a pulling rate of 300 mm/min.

After one adhesion surface of the double-coated adhesive tape was press adhered to the substrate surface in the same manner as in Example 1, the prismatic sheet was laminated on the other adhesion surface of the double-coated adhesive tape, and pressed by reciprocating a roll of 2 kg once at room temperature. Thus, the prismatic sheet and the double-coated adhesive tape were press adhered to obtain the reflective laminate of this Example.

The reflective laminate of this Example was evaluated by the same methods as in Example 1. The retroreflectivity was ranked OK, and the adhesion force (peel strength) was 6 N/25 mm. This adhesion strength is in a high level such that the laminate can be used as a retroreflective sign.