The invention relates to a method for producing a cylindrical buff having a smooth abrasive surface.
It is well known art to burnish the surface of a work for removing the protruding particles or high spots from the surface by using cylindrical buff which is driven to rotate and urged against the surface of the work. The work is for example, optical disc such as compact disc (CD) or Laser disk (LD.)
FIG. 8 shows a prior art of burnishing apparatus for burnishing optical disc such as compact disc 1. A cylindrical buff 7 is rotated by a drive shaft 6 which is connected to a drive source (not shown), an abrasive surface 7a of the buff 7 burnishes a reading surface of a compact disc 1. U.S. Pat. No. 5,524,313, applicant and assignee are same with the present application, discloses the burnishing apparatus of this type. U.S. Pat. No. 3,943,666, assigned to Dysan Corporation also discloses the burnishing apparatus of this type.
Typically, the buff 7 is produced by the steps of blanking the sheet material 8 to form a circular buff material 9 as shown in FIG. 9, and stacking a plurality of circular buff material 9 to form cylindrical shaped buff. This art is briefly disclosed in the above-mentioned U.S. Pat. No. 5,524,313. A cut edge or surface 9a of the circular buff material 9 corresponds to the abrasive surface 7a of the buff 7. Reference numeral 9b denotes a hole to penetrate therethrough the drive shaft 6.
FIG. 10 is a cross sectional view which shows schematically the cross section of the compact disc 1. In FIG. 10, the compact disc 1 has a laser-penetratable layer 2 made of synthetic resin. The layer 2 includes the lower surface on which the digital date is recorded as small pits 5. The pits 5 are formed as a spiral. Under the layer 2 is formed a laser-reflectable layer 3 which is made of a aluminum metallic film, for example. In turn under the layer 3 is formed a support layer 4. The layer 4 includes the lower surface on which an information for explaining the contents recorded in the disc 1, for example title of the music, is to be printed.
A reading head (not shown) includes a beam eject element and beam receive element. The beam eject element ejects the laser beam toward the laser-penetratable layer 2 and the beam receive element receives the beam which is reflected by the laser-reflectable layer 3. It has been recognized that the reading head sometimes skip or jump data to be reading due to the damages on the disc laser-penetratable layer2. It has been also recognized that the damages on the layer 2 sometimes let the disc un-readable in the excessive case. To remove such damages, the buff 7 is used to grind or burnish the reading surface of the laser-penetratable layer 2 as described above referring FIG. 8. Apparatus for burnishing or polishing to remove the damages on the disc is also disclosed in U.S. Pat. No. 5,099,618, U.S. Pat. No. 4,179,852. U.S. Pat. No. 4,586,296 and Japanese Unexamined Patent Publication No. 4-372785.
The sheet material 8 is for example, woven cloth with threads, namely warp and weft. Such sheet material 8 made of cloth inclines to transform or deform during the blanking process due to the lack of rigidity, whereby the cut surface 9a of the circular buff material 9 tends to slant as shown in FIGS. 11A and 11B.
The stacking or assembling process of the circular buff material 9 sometimes results in irregular abrasive surface 7a. An example is shown in FIG. 12A where the irregular surface is formed because the centers of the circular buff materials 9 are not aligned. Another example is shown in FIG. 12B where the irregular surface is formed because the circular buff material 9 is transformed due to the pressing force during the assembling process, which press is forged along the length of the buff 7.
The buff 7 having the irregular abrasive surface with projected portions 7b as shown in FIGS. 12A, 12B and 13 will make the scratches, corresponding to the projected portions 7b, on the surface of the disc.