1. Field of the Invention
The present invention relates to a method for manufacturing a molding body having a groove or grooves thereon, on which at least one groove is formed by turning.
2. Description of the Related Art
Generally, there are molding bodies having a predetermined groove or grooves thereon, such as an inserted plate having grooves thereon that is installed inside a mold in order to form a cylindrical lens having grooves formed on a convex surface or a concave surface thereof along its circumferential direction, or to form a prism sheet for use in a backlight device of a liquid crystal display. As a method of manufacturing a molding body having grooves thereon, such as the above-mentioned inserted plate, there has been known a method to rotate a sheet-like workpiece which is wound around a jig in substantially solid cylindrical shape, and a plurality of substantially V-shaped grooves (defined by a shape of an outer edge of a tip) that extend along a circumferential direction of the workpiece are formed substantially in parallel each other by bringing the tip into contact with an outer peripheral face of the workpiece, as disclosed in JP-A-2001-315001.
In such a method of manufacturing a molding body having grooves thereon, v-shaped slope faces of the respective grooves are normally formed to be the same in angle. However, recently, it has been requested that these slope faces of the grooves be formed with different angles respectively, as desired. In order to satisfy the above-mentioned request, there have been considered two methods as follows.
In one method, a tip C1, having a narrow width and having a rake face C11 with a sharply pointed end, is used as shown in FIGS. 7A and 7B. In this method, by tracing slope faces of virtual grooves Di′ at a front end of the tip C1, the angles of the slope faces of the respective grooves Di can be formed into different angles as desired, as shown in FIG. 7C.
In a second method, as shown in FIG. 8A, a tip C2 of which the rake face C21 has a somewhat larger front end angle α (see FIG. 8B), is inclined with the front end thereof fixed as an anchor point so that a base end portion of the rake face C21 approaches a workpiece W. Accordingly, the angle of the slope faces of the groove Di can be changed as desired. In this method, because by inclining the tip C2, the cross-sectional shape of the groove Di at a predetermined position (for example, the front end position of the tip C2) is formed as if the front end shape of the tip C2 at the predetermined position is projected into the workpiece W, as shown in FIGS. 8B and 8C, so that the angle of the slope face of the groove Di can be changed as desired.
However, the first method has a disadvantage that the slope faces of the groove Di are formed by the sharply pointed front end of the tip C1, which brings difficulties in obtaining a good surface roughness. In the second method, a good surface roughness can be obtained since the groove Di is cut by using side edges of the tip C2. However, in order to incline the tip C2 with the front end thereof fixed as the center, the front end of the tip C2 must agree accurately with the rotation center of a jig that rotatably supports the tip C2, and this center-positioning work is extremely tedious. Particularly, in forming a diffractive element, the rotation center of the jig and the front end of the tip C2 have to agree with each other within an error range of 100 nm or less, which is substantially impossible.
Thus, it has been needed to provide a method of manufacturing a molding body having a groove or grooves thereon, which enables slope faces of grooves to be formed with good surface roughness and enables angles of slope faces of grooves to be changed easily.