GB2279799A

GB2279799A - Shield for optical data storage medium

Info

Publication number: GB2279799A
Application number: GB9411821A
Authority: GB
Inventors: Trevor Alan Burroughs
Original assignee: Individual
Current assignee: Individual
Priority date: 1993-06-11
Filing date: 1994-06-13
Publication date: 1995-01-11
Anticipated expiration: 2014-06-13
Also published as: GB2279799B; GB9411821D0

Abstract

A shield assembly for an optical data storage device 60 comprises a planar transparent shield 30, 50 dimensioned to overlie the read surface of an optical data storage device. The shield has a uniform coating of fluid adhesion means on the surface thereof to be attached to said device in use. The adhesion means has a refractive index compatible with the refractive index of said device. <IMAGE>

Description

SHIELD FOR OPTICAL DATA STORAGE MEDIUM The present invention relates to optical data storage media such as compact discs and, in particular, to a shield assembly for protecting at least the data surface of such data storage media. The invention also relates to a method of repairing minor surface defects and blemishes in optical data storage media.

Optical data storage media are becoming increasingly commonplace in everyday life. They are generally planar devices and have a substrate of clear plastics material or glass on which a surface formation of data "pits" is provided.

The pitted surface is coated with a layer of diffused metal, such as aluminium, which serves to reflect incident light passing through the substrate from its opposing face. Data is generally read by a laser shone through the clear plastics material or glass, the incident light being distorted by the data pits and then reflected from the mirrored surfaces to be read by a pick-up.

Damage to the read surface, that is to say the surface through which the laser reads the data pits, will result in distortion of the laser beam, causing errors in the reading of data. Similarly, damage to the reflective surface will result in a loss of reflectivity and loss of data, which will also lead to errors in reading of the data. Any loss of laser light through dispersal as it passes through the substrate material reduces laser intensity and may also cause read errors. In addition, non-planarity or imbalance of the data storage medium may cause laser distortion resulting in read errors, for instance due to wobbling of a compact disc in a playback apparatus.

Protective shields for optical data storage devices are known, for example as described in United States Patent No.

4,879,710. This patent discloses an optical disc protector comprising a transparent annular protective sheet provided with radially inner and outer rings of adhesive for securing the sheet to an optical disc. The adhesive rings are arranged so that they do not obscure the data portion of the disc. Such an arrangement suffers from the drawback that air is likely to become trapped between the surface of the disc and the protective sheet. As a result, the laser executes different refraction pathways as it passes through different regions of the disc/shield combination, leading to read errors at the pick-up.

In another protective arrangement known from United States Patent No. 4,736,966, an optical data storage device such as a data card is provided with a plurality of peelable transparent protective layers. When a layer becomes too severely scratched for efficient reading of data, it is removed by peeling. This approach has a number of disadvantages.

Firstly, the data is obscured at the outset by the number of layers interposed between the read surface and the pick-up.

This problem is exacerbated if the optical data storage device is intended for recording as well as playback, since the signal to be recorded will be attenuated by the interposed protective layers. Further attenuation occurs on reading, so the playback signal may be very weak and severely distorted. Another disadvantage is that the removal of successive layers by peeling leaves a residue of adhesive which needs to be cleaned away prior to playback. The very act of cleaning may damage the next layer of protective film.

In European Patent Application No. 0 375 298 A2, a protective shield for an optical disc is described which is designed to stripped from the disc immediately prior to the recording of data thereon by laser irradiation. The shield thus serves to protect the disc in the post-manufacture phase, during storage, transport and purchase by an end user. Such shields are formulated with anti-static properties to minimise attraction of air-borne dust particles. This ensures that the data is recorded on a "clean" disc. However, no provision is made for protecting the disc after recording.

European Patent Application No. 0 300 733 A1 describes a heat-shrinkable shield for optical data storage devices. One of the drawbacks of this arrangement is that specialist equipment is required to ensure even application of heat to the shield to effect shrinkage thereof around the device to be protected. Temperature control is also important to prevent damage to the substrate. This arrangement is therefore unsuitable for use by non-experts.

In British Patent Application No. 2 217 507 A, annular protective shields are disclosed for attachment to compact discs through the intermediary of a transparent or translucent gum. A special apparatus is also disclosed for applying the shields to compact discs. The shields are shown attached to the non-read surfaces of discs, since the applicant believes that the non-read surface is particularly vulnerable to damage by virtue of having only a relatively thin protective layer of u.v.-curable lacquer. Whilst there are undoubtedly some grounds for this belief, the document does not address the problem of protecting the read surface of optical data storage devices from accidental damage.

It is therefore an object of the present invention to provide means for protecting the data reading surface of an optical data storage device from accidental damage. It is also an object of the present invention to provide a method of repairing minor surface defects and blemishes in such devices.

In a first aspect, the invention is a shield assembly for an optical data storage device, said assembly comprising a planar transparent shield dimensioned to overlie the read surface of an optical data storage device, said shield having a uniform coating of fluid adhesion means on the surface thereof to be attached to said device in use, wherein said adhesion means has a refractive index compatible with the refractive index of said device.

Advantageously, the refractive index of the adhesion means is chosen to be as close as possible to that of the optical data storage device to which the shield is to be attached.

Preferably, the refractive index of the adhesion means differs by no more than +10% and most preferably by no more than +5% from the refractive index of the surface of the optical data storage device to which it is attached in use.

An especially preferred form of adhesion means is a blend containing silicone oil and inert fillers, such as the formulation sold under the Registered Trade Mark "Rhodorsil" by Rhone-Poulenc. Rhodorsil Paste 4 has been found particularly suitable for attaching protective shields to compact music discs.

In this respect, the adhesion means may be regarded as an optical couplant which facilitates comprehensive joining between the shield and the laser read surface of the optical data storage device. There is no air or other contaminant between the two. The optical couplant can be adhesive or cohesive in its action, and is preferably peelable to allow removal of the shield should this prove necessary. A shield may need to be removed, for example, if it becomes damaged and needs to be replaced with another.

Since optical data storage devices are often formed with a plastics substrate such as polycarbonate or acrylic resins, it is particularly advantageous to form the shield from the same material. This ensures good optical matching between the shield, the adhesion means and the optical data storage device to which the shield is attached.

A shield may also be attached to the non-read surface of an optical data storage device to ensure that its protection is comprehensive. Preferably, a shield attached to the nonread surface is arranged such that indicia provided on the nonread surface are still visible when the shield is in place.

The shield or shields may be retained in place by rim means extending around the periphery of the optical data storage device. Preferably, the rim means have reflective surfaces on the radially-inwardly directed portions thereof to reflect dispersed laser light back into the device and thereby minimise losses and reduce data read errors.

The rim means may be provided as a pair of interengageable parts which snap together, one being applied in the direction of a first side (face) of an optical data storage device and the other being applied, in the opposite direction, from the other side of the device. The two rim portions are releasably engaged so that they can be separated to allow removal of shield members if required.

Advantageously, the rim means are dimensioned to allow their use with magazines of optical data storage devices with automatic changing apparatus, for example multi-disc CD players. Such rims must be sufficiently robust that they are capable of withstanding the handling forces encountered in the automatic changing apparatus whilst retaining the shield or shields in place.

In optical data storage devices which are rotated at high velocity during playback, the rim means may perform a secondary function in preventing extrusion of the adhesion means from the outer extremity of the shield.

The rim means may be integrally formed with a respective shield member, or may be separate therefrom. The rim means may be secured to a respective shield member by welding or some other form of permanent bonding. If the rim means is metal, the reflective radially-inwardly directed surface may simply be the bright finish of the metal itself.

In a second aspect, the invention provides a method of repairing minor surface defects and blemishes in optical data storage devices, the method comprising the steps of: (a) applying a uniform coating of fluid adhesion means to one face of a planar transparent shield member, said fluid adhesion means having a refractive index compatible with that of the optical data storage device to be repaired; (b) placing the coated face of said shield member over the damaged surface of the optical data storage device; (c) squeezing any air from between the shield and the device, and (d) allowing the adhesion means to flow into the damaged regions of the surface of said device.

This is possible because the fluid adhesion means is of a nature which allows it to be moulded slightly. As described above in relation to the first aspect of the invention, the adhesion means behaves as an optical couplant between the material of the shield and the substrate of the optical data storage device. The ideal optical couplant is a non-setting clear silicone paste with relatively high viscosity such as Rhodorsil (RTM) Paste 4 described earlier.

The method defined above is capable of curing minor surface defects for as long as the shield remains in place.

The adhesion means flows into scratches and like surface blemishes to leave a surface which is readable by incident laser without losing focus. If the shield is removed, however, the damage will become apparent again once the surface is cleaned. A more permanent optical couplant could be selected which would remain in place after removal of the shield and after cleaning.

The invention will now be described by way of example with reference to the drawings, in which: Figure 1 is a view from below of one embodiment of the invention, showing an upper rim and a shield member; Figure 2 is a view from above of the arrangement depicted in Figure 1; Figure 3 is a view from above of a lower rim and shield in accordance with the invention; Figure 4 is a view from below of the arrangement shown in Figure 3; Figure 5 is an exploded side view of upper and lower rims and shields prior to their attachment to an optical data storage device; Figure 6 is a side view in cross-section of the components shown in Figure 5 after assembly, and Figure 7 is a close-up view of the arrangement depicted in Figure 6, showing detail of the cooperating rims.

Referring now to Figures 1 and 2, these views show the bottom and top views, respectively of an upper rim 20 and shield 30 for use with a laser-readable compact disc (not shown). The upper shield 30 has a central cut-out 31 to accommodate a central boss of the compact disc. Typically, the diameter of the cut-out 31 is arranged to be larger than the diameter of the central boss of the compact disc because the internal rim region of such bosses is utilised in reproduction equipment to centralise and grip the disc during playback.

Figure 1 shows a rim edge 21 which slightly overlies the outer periphery of the shield 30, and a rim lip 22. The rim lip 22 should be regarded as extending outwards from the plane of the drawing and is only shown here schematically as a circle surrounding the rim edge 21.

Figure 2 merely shows the rim edge 21 from above. In this view, the rim lip is not visible but may be regarded as projecting from beneath the plane of the drawing.

Figures 3 and 4 are similar views to Figures 1 and 2, except that they show top and bottom views, respectively of a lower rim 40 and shield 50 for use with the laser-readable compact disc. Like its upper counterpart, the lower shield 50 has a central cut-out 51 to accommodate the central boss of the compact disc. For the reasons given above, the diameter of cut-out 51 is larger than the diameter of central boss of the compact disc.

In Figure 3, a rim edge 41 is shown slightly overlying the outer periphery of the shield 50. Rim 40 has a rim lip 42 shown here schematically as a circle surrounding the rim edge 41. This lip 42 should be regarded as extending outwards from the plane of the drawing. In Figure 4, rim lip 42 is not visible.

Figure 5 is an exploded view of the upper 20 and lower 40 rims and their respective shield members 30 and 50, prior to attachment to a compact disc 60.

In practice, one of the upper or lower assemblies would be selected for attachment to a first surface of the compact disc 60. Any air bubbles which are trapped between the first surface of the disc and the shield which is attached first are squeezed out by stroking the shield gently in a radially outward motion. Conveniently, the rim members are provided with minute channels at their edges through which trapped air can be expelled.3 Such channels are not shown in the drawings.

When the attachment of the first assembly to the first side of the disc is complete, the second assembly is offered up to the second face of the disc and the above process of air bubble removal is repeated. The respective rim portions are releasably clipped together to form a unitary retaining mechanism for the upper and lower shields.

The fully assembled arrangement is shown in cross-section in Figure 6. Compact disc 60 is securely sandwiched between upper and lower shield members 30 and 50 by the intermediary of fluid adhesion means such as the silicone preparations described previously.

Figure 7 is a close-up view of the interengaging rim members. In this view, the rim members are clearly shown as separate entities from their associated shield members.

However, as mentioned above, the rim members may be integrally formed with the shield members or may be permanently bonded thereto such as by welding.

Although the invention has been particularly described with reference to one embodiment in which both sides of a compact disc are shielded,, it will be understood by persons skilled in the art that various modifications are possible without departing from the scope of the claims which follow.

Claims

1. A shield assembly for an optical data storage device, said assembly comprising a planar transparent shield dimensioned to overlie the read surface of an optical data storage device, said shield having a uniform coating of fluid adhesion means on the surface thereof to be attached to said device in use, wherein said adhesion means has a refractive index compatible with the refractive index of said device.

2. A shield assembly as claimed in claim 1 wherein the refractive index of the adhesion means differs by no more than +10% from the refractive index of the surface of the optical data storage device to which it is attached in use.

3. A shield assembly as claimed in claim 1 or claim 2 wherein the refractive index of the adhesion means differs by no more than +5t from the refractive index of the surface of the optical data storage device to which it is attached in use.

4. A shield assembly as claimed in any preceding claim wherein the adhesion means is a blend containing silicone oil and inert fillers.

5. A shield assembly as claimed in any preceding claim wherein the adhesion means is cohesive in its action.

6. A shield assembly as claimed in any preceding claim wherein the adhesion means is peelable to facilitate removal of the shield.

7. A shield assembly as claimed in any preceding claim wherein a shield is also attached to the non-read surface of the optical data storage device.

8. A shield assembly as claimed in any preceding claim wherein the or each shield is made from the same material as the substrate of the optical data storage device.

9. A shield assembly as claimed in any preceding claim wherein the or each shield is retained in place by rim means extending around the periphery of the optical data storage device.

10. A shield assembly as claimed in claim 9 wherein the rim means have reflective surfaces on the radially-inwardly directed portions thereof to serving reflect dispersed light back into the device.

11. A shield assembly as claimed in claim 9 or claim 10 wherein the rim means are a pair of releasably engageable parts which snap together.

12. A shield assembly as claimed in any one of claims 9 to 11 wherein the rim means are provided with minute channels at their edges through which trapped air can be expelled.

13. A method of repairing minor surface defects and blemishes in optical data storage devices, the method comprising the steps of: (a) applying a uniform coating of fluid adhesion means to one face of a planar transparent shield member, said fluid adhesion means having a refractive index compatible with that of the optical data storage device to be repaired; (b) placing the coated face of said shield member over the damaged surface of the optical data storage device; (c) squeezing any air from between the shield and the device, and (d) allowing the adhesion means to flow into the damaged regions of the surface of said device.

14. A shield assembly for an optical data storage device substantially as herein described with reference to the drawings.