Patent ID: 7906193

Claim:
A retroreflective sheet, comprising: plural retroreflective elements; a resin support sheet; a transparent cover film disposed on a surface side of the resin support sheet; and a pressure-sensitive adhesive layer formed on a rear face side of the resin support sheet, wherein the retroreflective elements are held in at least one of the resin support sheet and the cover film, the resin support sheet and the cover film are connected to each other by heat press emboss forming from the rear face side of the resin support sheet so as to form a connection part, a groove of the connection part is formed on the rear face side of the resin support sheet, the groove is filled with a part of the pressure-sensitive adhesive layer and a filing factor of the pressure-sensitive adhesive layer in the groove is 50% or more, a residual rate of the pressure-sensitive adhesive layer ranges between 10% and 50% inclusive, a fall time of the pressure-sensitive adhesive layer ranges between 10 hours and 150 hours inclusive, the pressure-sensitive adhesive layer is formed of a rubber-based resin or an acrylic resin; where the filling factor (%)=[(A−B)÷A]×100, the letter A denotes an area of the groove per unit area of the retroreflective sheet, and the letter B denotes an area of an opening gap formed on an interface between the groove and the pressure-sensitive adhesive layer per unit area of the retroreflective sheet, and where the residual rate (%)=(a residual displacement ÷an initial displacement)×100, the initial displacement represents a displacement (mm) between a flat plate and the retroreflective sheet measured by a Yamamoto's cohesion tester, which occurs after 5 minutes from steps of: pressing the retroreflective sheet with a size of 10 mm×5 mm onto the mirror-surfaced flat plate of a SUS304 steel plate specified by JISG 4305 with a width of 5 mm, using a pressing device specified by JIS Z 0237; adding loads of 17 g respectively to both ends of the retroreflective sheet via strings immediately after the pressing; and further applying a measurement load of 200 g to one of the loads, the residual displacement represents a displacement occurring between the flat plate and the retroreflective sheet after 10 minutes from removal of the load of 200 g, and the fall time represents a fall time of the retroreflective sheet with a load of 9.8 N imposed in a holding power test at 40° C. in accordance with a JISZ0237 holding power test.