Stock material or miscellaneous articles – Circular sheet or circular blank
Reexamination Certificate
2001-02-06
2002-12-31
Mulvaney, Elizabeth (Department: 1774)
Stock material or miscellaneous articles
Circular sheet or circular blank
C428S064400
Reexamination Certificate
active
06500512
ABSTRACT:
FIELD OF THE INVENTION
This invention relates generally to optical disc manufacturing and more particularly, to the manufacture of multilayer optical discs.
BACKGROUND OF THE INVENTION
Multilayer discs are now being produced that are an assembly of two discs, each with its own data layer of grooves or pits representing recorded and stored data or information. Referring to
FIG. 5
, a composite disc
18
is formed of a first, bottom disc
20
normally having a first, lower, sputtered semi-reflective data layer or surface
22
. A read laser either focuses on the first surface
22
or, alternatively, penetrates through the first surface
22
and focuses on a second, data layer or surface
24
on a second, top disc
26
. The distance between the two surfaces or focal planes
22
,
24
is made up of a transparent bonding layer
28
joining the two discs
20
,
26
together. Industry DVD specifications require that the transparent bonding layer be in the range of from 40 microns to 70 microns. Other specifications may be required to comply with other specific formats.
The composite disc
18
is formed from two discs that are normally manufactured using an injection molding process. An ultraviolet, curable, liquid resin, for example, lacquer, that functions as an adhesive is first deposited on a lower rotating disc
20
. Upon striking the rotating disc surface
22
, the resin spreads across the disc surface
22
toward the inner centerhole
30
and the outer disc circumference
32
. However, the resin that first contacts the disc surface
22
will have experienced substantial spreading as the last of the resin is deposited on the surface
22
of the disc
20
. Thus, before the final resin deposited spreads, the first resin deposited may reach and spill over the inner hole
30
and/or the outer circumference
32
of the disc
20
. Any resin that does spill off of the disc
20
must somehow be handled and contained which adds cost to the process in terms of machine design, maintenance and the cost of the resin.
The construction of the composite disc
18
continues by placing the other disc
26
on top of the resin coating on the upper surface
22
of the first disc
20
, thereby forming the multilayer disc
18
. The multilayer disc assembly
18
with the uncured resin layer therebetween is subjected to a high speed spinning process to achieve a desired thickness of the intermediate laquer layer. After the spinning process, the resin is cured; and the multilayer disc construction process is complete.
The above spinning process presents several challenges with respect to consistently manufacturing a high quality multilayer disc. First, the spinning process has no process feedback and thus, is not subject to precise control from one disc to another. Further, the forces created by the spinning create a nonuniform resin thickness profile across the resin layer. The resin thickness profile changes from a thinner layer close to the centerhole
30
of the multilayer disc
18
to a thicker layer near its outer circumference
32
. The nonuniform resin layer between the discs
20
,
26
does not permit a true noise-free replay of the disc.
To hold the thickness of the resin layer within specifications, the resin layer of a finished multilayer disc is measured at many different locations. Those measurements are statistically processed, and the spinning process is adjusted over a period of time, as required, to maintain the resin layer within desired thickness specifications. Many manufacturing environments strive for a thickness specification that is more strict than the about 40-70 microns thickness required by the industry specification. And, the known manufacturing processes can lead to the production of out-of-specification discs while the spinning process is being tuned to hold the resin layer thickness within specification.
Thus, the current multilayer disc bonding process presents several opportunities for improvement. First, there is no real-time control of the thickness of the resin bonding layer between the discs. Second, since the resin is continuously deposited over a single rotation, the first resin deposited reaches the inner hole and the outer edge sooner than the later deposited resin. Third, control over the thickness of the resin layer is further complicated because both of the discs are flat; and therefore, the resin flows freely in all directions and may flow into the inner hole and/or over the outer edge of the disc.
Consequently, there is a need for an improved process for joining two optical discs to form a multilayer disc with an intermediate bonding fluid layer that has a more predictable thickness profile.
SUMMARY OF THE INVENTION
The present invention provides an improved optical disc for use in a multilayer disc that provides a consistently high quality noise-free playback of data on the disc. Further, in the manufacture of a multilayer optical disc, the improved optical disc of the present invention can be adhered to another optical disc with a bonding layer thickness that is reliably and repeatably maintained within specification. Therefore, multilayer optical discs are manufactured with a minimum of scrap and thus, manufacturing costs are reduced. Further, the repeatably consistent bonding layer thickness provided by the present invention has the advantage of being able to consistently read data through the bonding layer.
According to the principles of the present invention and in accordance with the described embodiment, the invention provides an optical disc for use in the manufacture of a multilayer optical disc. The optical disc has a first side with a data layer and at least one projection extending outward from the first side. The projection separates the first side from another optical disc used in the manufacture of the multilayer optical disc. The projection is effective to maintain a known and constant bonding layer separation between this optical disc and another optical disc bonded thereto in the manufacture of the multilayer optical disc. Maintaining a repeatably consistent bonding layer improves the consistency of the reading of data from the disc.
In one aspect of the invention, the projection is comprised of a first projection located between a center hole and the data layer and a second projection located between the data layer and an outer circumferential edge of the optical disc. In another aspect of the invention, the first and second projections extend outward from the first side a distance of about 40-70 microns. The use of two projections radially separated on the first side of the optical disc provides a better control over the consistency of the thickness of the bonding layer. In addition, the inner projection substantially stops the migration of air from the centerhole into the bonding layer during a spinning process. Thus, the present invention provides a more consistent and pure bonding layer thickness across the whole diameter of the resulting multilayer optical disc. Such consistency further improves the noise-free readability of data from the optical disc.
In another embodiment, the present invention provides a multilayer optical disc having a first optical disc with a first side and a second optical disc with a first side facing the first side of the first optical disc. An adhesive extends between the first sides of the first and second optical discs, thereby bonding the first and second optical discs together to form the multilayer optical disc. A spacing bridge is located between, and contacts, the first sides of the first and second optical discs. The spacing apparatus separates the first and second optical discs by a distance that is substantially equal to a desired thickness of the adhesive. Again, the multilayer optical disc has a more consistent bonding layer thickness across its whole diameter which further improves the noise-free readability of data from the multilayer optical disc.
In another embodiment, the present invention provides a method of making a multilayer optical disc by first, applying a bonding agent to a first
Fite Barry
Russell Robert Lowell
Mulvaney Elizabeth
Sony Corporation
Wood Herron & Evans L.L.P.
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