GB2333885A

GB2333885A - Optical data storage carrier protection apparatus

Info

Publication number: GB2333885A
Application number: GB9802149A
Authority: GB
Inventors: Trevor Burroughs
Original assignee: Optidisc International Ltd
Current assignee: Optidisc International Ltd
Priority date: 1998-01-30
Filing date: 1998-01-30
Publication date: 1999-08-04
Also published as: WO1999039340A1; GB9802149D0; AU2432399A

Abstract

Protection apparatus comprising a protective sheet or film (1) dimensioned to overlie a region comprising at least part of a surface of the optical data storage carrier (e.g. CD, CD-ROM etc.), the protective sheet being fastenable to the optical data storage carrier by way of at least one adhesive track (5) provided with one or more apertures (6) extending through the adhesive and permitting air to escape from said region. When the CD has a first annular area surrounding the centre hole and a second annular area surrounding the first annular area and when the surface of one of these areas is raised relative to the other a first and a second annular protective film are placed over the first and second annular areas respectively. The annular protective films do not overlap and each have means of attachment to their respective surfaces.

Description

OPTICAL DATA STORAGE CARRIER PROTECTION APPARATUS The present invention relates to apparatus for providing protection to optical data storage carriers, such as discs (such as CDs and CD ROMS) bearing digital data and referred to hereinafter generally as CDs.

CDs generally comprise a discoidal clear substrate of good quality polycarbonate material, bearing optically recorded digital data and are intended to be optically interrogated in order to recover the data recorded on or in the substrate.

CDs and other optical data storage carriers are generally durable but can be susceptible to minute scratches and other surface damage which can easily exceed in size the typical dimensions of strings of recorded data characters. There are, of course, quite sophisticated error recovery procedures incorporated into the electronic systems of most units intended to retrieve and/or reproduce the recorded data from such devices, but there are limits to the capabilities of such systems, and they can be defeated by damage which is extensive and/or of certain types. For example, with CDs, damage running arcuately along the recorded tracks is generally much more serious than similarly extensive damage running radially across the tracks. It is therefore desirable to provide a film-like member that can be applied to new carriers to protect their surfaces from damage.

Protective sheet systems for optical data storage carriers 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 protective sheet to an optical disc. The adhesive rings are arranged so that they do not obscure the data portion of the optical disc. A problem associated with the above systems is that, when the protective sheet is being applied, irregular cohesion, which is difficult to control, tends to occur between localised areas of the protective sheet and the underlying surface. Accordingly, air bubbles are likely to become trapped between the protective sheet and the optical disc which will have an adverse effect on the reading of data from the optical disc.

Further, because the protective sheet is anchored between the two rings of adhesive, it is likely to stretch and distort in response to dimensional changes to the disc arising, for example, due to thermal expansion and/or contraction of the optical disc. Such dimensional changes may occur, for example, locally, whilst the optical data storage carrier is being read by a laser, and/or generally, due to its being stored or read in a warm environment, such as a closed compartment within which the optical data storage carrier is rotated at high speed, as in a CD player. Such distortion of the protective sheet caused by heating will impair the correct reading of data from the disc.

It is an object of the present invention to provide apparatus for providing protection to an optical data storage carrier which seeks to alleviate the problems associated with the prior art discussed above.

In a first aspect of the invention there is provided protection apparatus for an optical data storage carrier, said protection apparatus comprising a protective sheet dimensioned to overlie a region comprising at least part of a surface of the optical data storage carrier; the protective sheet being fastenable to the optical data storage carrier by way of at least one adhesive track provided with one or more apertures extending through the adhesive and permitting air to escape from said region. The apertures aid the application of the protective sheet by helping to eradicate the entrapment of air bubbles when the protective sheet is applied. If continuous tracks of adhesive are present after part of the protective sheet has been applied to the optical data storage carrier then air entrapment can occur and it is more difficult to apply the rest of the protective sheet without creating creases and bubbles. The apertures in the adhesive track of this embodiment allow the air to escape and the likelihood of the formation of bubbles is reduced.

Preferably, the adhesive track is provided in the form of a ring and thus mirrors the discoidal shape of commonly used optical data storage carriers. Thus it is possible for the adhesive track to be present without covering information recorded on the readable face of the optical data storage carrier unnecessarily and distorting readability.

In preferred embodiments, the ring is provided at substantially an outer and/or inner circumference of the data-carrying surface of the optical data storage carrier.

If the ring is provided at substantially the outer and/or inner circumference of the data-carrying surface of the optical data storage carrier, it does not interfere with the reading by laser of the data carried in that area.

Preferably, respective rings are provided just outside the inner and outer circumferences of the data-carrying area of the discoidal optical data storage carrier and the apertures in the inner ring are angularly misaligned with the apertures in the outer ring. This ensures that sufficient adhesive anchoring of the protective sheet is provided at all angular positions around the optical data storage carrier and reduces the risk of strain-induced local radial slippage of the protective sheet relative to the optical data storage carrier. This misalignment of the apertures in the inner and outer rings may include precise interleaving of said apertures.

Conveniently, the adhesive is formed of a tacky, elastic material. The elastic material allows movement which compensates for any stretching which could occur, for example, by heating during storage and/or playing of the carrier.

Localised heating may occur whilst the optical data storage carrier is being read by a laser and more general heating may occur when the carrier is exposed to heat during storage or is read in a warm environment, such as a closed compartment within which the optical data storage carrier is rotated at high speed, such as in a CD player.

Preferably, the protective sheet is formed of a material that is transparent to the laser light used to read the data recorded on the carrier. The use of such a transparent material when applied to the readable face of the optical data storage carrier helps to reduce distortion of the laser light and therefore enhance the quality of the data read from the disc. If the sheet is generally transparent, then it can be applied to the non-readable face of the optical data storage carrier, whilst still permitting any preprinted design on the said face to be seen after application of the protective sheet.

In preferred embodiments, the transparent material has a similar refractive index to that of the optical data storage carrier. Where the transparent material has a similar refractive index to that of the optical data storage carrier, optical losses, associated for example with distortion of the laser beam during reading, are minimised.

The adhesive tracks may each be made of any convenient adhesive, or one track may be adhesive and the other treated to render it cohesively adherent to the protected surface. In the latter event, it is preferred that the outer track be cohesively adherent to the surface, as this provides strong central location of the protective film to the record carrier whilst the cohesive bond at the outer edges of the film can shear to accommodate dimensional changes of the carrier.

Moreover, it is possible with this configuration for the user to smooth out ripples in the film that may occur during its application to the carrier or in use.

In preferred embodiments, at least one of the tracks (adhesive or cohesive) by means of which the film is rendered adherent to the carrier comprises an optical couplant. Where a track comprises an optical couplant then it can, if necessary, overlie part of the data-carrying area of the optical data storage carrier.

Those skilled in the art will be aware that, in the case of CDs, a circular area, coaxially surrounding the centre hole (which has a diameter of 15mm) and extending to a diameter of some 33mm, is raised relative to the remainder of the CD surface, and that there is a precise thickness relationship between this raised area and the rest of the CD which is critical, inter alia, to the maintenance of a set distance between the surface of the CD in its data-carrying area and a lens through which the laser beam impinges thereon, in order to maintain a set focal distance for the lens.

This has implications for protective film systems, principally because, if the protective film is applied only over the datacarrying area of the CD, the laser focussing, derived from the "virgin" raised area of the CD, will be incorrect.

If, on the other hand, the film is made to extend over both the data-carrying area and the raised area, it will not generally or reliably conform to the topography of the disc surface and, in particular, will tend to depart from this topography in the vicinity of the 33mm diameter circular step formed at the junction of the raised area and the remainder of the CD including its data-carrying surface. Unfortunately, the critical start-point of the recorded data usually occurs at or near this very location, and if that start-point cannot be found, through laser defocus or other optical problems attributable to the failure of the film to conform to the surface topography of the disc, the disc is rendered unreadable. A further problem can arise also, in that the protective film may directly contact the laser lens in the vicinity of the start-point, since the film is higher than it should be as a result of its non-conformity with the surface topography of the CD, and such contact may damage the lens and/or the film.

According to the invention from another aspect, therefore, there is provided a protective film system for a CD having a centre hole, a first area annularly surrounding the centre hole, and a second, data-carrying, area annularly surrounding the first area; the surface of one of said areas being raised relative to that of the other, the system comprising first and second annular protective films, each dimensioned and configured to overlie at least a substantial part of a respective one of said first and second areas but not to extend beyond it, and means for securing each said film to the surface of its respective area.

This other aspect, which is believed to be inventive in its own right and can be used together with or separately from any of the arrangements previously described herein, provides means to overcome the problems outlined in the two immediately preceding paragraphs and, in a preferred embodiment, separate annular protective films of substantially identical thickness are applied to the aforementioned raised area and to the remainder of the CD respectively.

Examples of the present invention will now be described, by way of illustration only, with reference to the figures accompanying the specification.

Figure 1 shows an aerial view of the adhesive side of the protective sheet; Figure 2 shows an exploded cross-section of both the optical storage device and the protective sheet before application; and Figure 3 shows a cross-sectional view of a system in acordance with another aspect of the invention.

In Figure 1 an annular protective sheet 1 has an outer circumference 2 of diameter slightly smaller than that of a discoidal optical data storage carrier (not shown), such as a CD, with which it is intended to be used. The protective sheet has an inner circumference 3 bounding a central excised section 4. The central excised section 4 has, in this example, a diameter slightly larger than that a central hole in the optical data storage carrier. The diameter of the central hole of a CD is conventionally 15mm. The protective sheet 1 must be sufficiently smaller in overall diameter than the optical data storage carrier so that when the protective sheet 1 is applied to the optical data storage carrier its outer circumference 2 does not extend beyond the circumference of the optical data storage carrier. Likewise the central excised section 4 must be sufficiently larger than the central hole in the optical data storage carrier so that overlapping of the inner circumference does not occur. It is important to keep the inner circumference of the central hole in the optical data storage carrier as the manufacturer intended because it is utilised in reproduction equipment to centralise and grip the disc during playback.

The protective sheet 1 has, in this example, an adhesive track running around the outer and/or inner circumferences 2 and 3. The adhesive track is in the form of predetermined amounts of adhesive 5 provided at regular intervals around the outer and/or inner circumference of the protective sheet. In between the adhesive 5 apertures 6 exist which allow air to escape and reduce the likelihood of permanent entrapment of air bubbles. The adhesive track may thus be regarded as crenellate.

In another embodiment the inner circumference of the protective sheet 3 may comprise a continuous track of adhesive while the outer circumference 2 may be crenellate as described in Figure 1 (i.e. the adhesive is present at intervals).

In yet a further embodiment, the outer circumference of the protective sheet 2 may comprise a continuous track of adhesive while the inner circumference 3 may be crenellate as described in Figure 1 (i.e. the adhesive is present at intervals).

In a preferred embodiment, the apertures 6 are provided in both adhesive tracks at the inner and outer circumferences 2 and 3. The apertures 6 in the adhesive tracks at the inner circumference 3 are angularly interleaved with those in the adhesive tracks at the outer circumference 2. This ensures that adhesive anchoring of the protective sheet 1 is provided at substantially all angular positions around the optical data storage carrier and reduces the risk of strain-induced local slippage of the protective sheet 1 relative to the optical data storage carrier (not shown). The interleaving need not, however, be precise, and any substantial degree of angular misalignment between the apertures 6 in the two adhesive tracks at the inner and outer circumferences 2 and 3 will materially assist in this respect.

In any of the foregoing examples, the crenellation of the adhesive need not be regular along the respective tracks, although it is preferred that the crenellation be controlled within predetermined limits, determined by the application and by the materials used for the film and the record carrier, to avoid the formation of apertures 6 of circumferential dimensions too large for proper anchoring of the film or too small to permit the egress of trapped air.

Moreover, in any event, it will be appreciated from what has been said earlier that it is preferable to make allowance for the fact that use is made of the circular area, coaxially surrounding the centre hole (which has a diameter of 15mm) and extending to a diameter of some 33mm, which is raised relative to the remainder of the CD surface, in the maintenance of a set distance between the surface of the CD in its datacarrying area and a lens through which the laser beam impinges thereon, in order to maintain a set focal distance for the lens.

If a single annular film is made to extend over both the datacarrying area and the raised area of the CD, it will, as aforesaid, tend to depart from the surface topography of the disc in the vicinity of the 33mm diameter circular step formed at the junction of the raised area and the remainder of the CD including its data-carrying surface. Since the critical start-point of the recorded data usually occurs at or near the very location of that circular step, any laser defocussing or other optical problems attributable to the failure of the film to conform to the surface topography of the disc at that location may render the disc is unreadable. Moreover, since (at the location of the step) the film is higher than it should be, as a result of its non-conformity with the surface topography of the CD, it may contact the laser's lens, and such contact may damage the lens and/or the film. Such damage may also be caused if, as aforesaid, the protective film should, in operation, separate from the carrier's surface and move up to contact the laser's lens.

It is thus preferred, in any system where a protective film is used in relation to a CD, to provide separate annular protective films of substantially identical thickness for the aforementioned raised area and for the remainder of the CD respectively, as shown in Figure 3. It is preferred, though not essential, that at least the film associated with the remainder of the CD (i.e. the part including the data-carrying area of the CD) be securable to the CD's surface by crenellate adhesive tracks taking any of the forms described hereinbefore. It is to be noted however that the provision of separate films for the two areas of the CD's surface is regarded as inventive of itself and is not dependent on the nature of the attachment of the films to the surface of the CD.

The film associated with the raised area of the CD can of course be secured by tracks of adhesive which may be annular, radial or of any other convenient form and which may or may not be crenellate, or the entire film may be coated with adhesive. Alternatively it may, in its entirety or in selected regions or tracks thereof, be secured by cohesion to the raised area of the CD. Further, combinations of cohesion and adhesion can be used if desired.

With further regard to the film associated with the raised area of the CD, it will be appreciated that this film does not overlie any of the recorded data and performs a purely mechanical function so it can, if desired, be made opaque or strongly coloured, or may bear logos and the like.

In general, in all of the embodiments disclosed herein, there can be advantage in omitting one or more of the tracks of adhesive and providing instead for the film to be cohesively secured to the surface of the record carrier. In particular, the track at the outer circumference 2 may be replaced with cohesive bonding, either by the provision of a corresponding area of treatment of the film or by making the film itself of a material that exhibits a sufficient degree of cohesive bonding to the carrier surface such that it resists forces, such as the centrifugal forces generated during playing of a CD, tending to lift the film from the surface. This problem requires particular attention where a single film, adherent to both the raised portion and the recorded portion of a CD, is used. In operation, i.e. when the CD is being played, the centrifugal forces tend to lift the film off of the disc surface near the outer diameter 2 as the film attempts to adopt a flat surface profile. This is still more significant where the CD is used in the CD-ROM drive of a computer, as it is typical for such drives to operate at many times the standard speed used for audio applications.

Figure 2 shows a protective sheet 1 in a position ready to be applied to the readable face 8 of the optical data storage carrier 7. An additional sheet may be applied to the nonreadable face 9 for further protection. It will be appreciated, however, that any such further sheet may be secured in any desired manner to the face 9, as it has no significant optical function to perform, and may also have opaque or strongly coloured regions and/or logos if desired, though users may prefer not to obscure or confuse the existing labelling which of course is usually viewable from the face 9. Where a manufacturer of CDs chooses to incorporate the application of such a protective film into the manufacturing process, however, it may be more convenient for the labelling information to be applied to the protective film rather than to the reverse side of the CD itself.

In a further embodiment of the invention, a conformable, but non-tacky, silicone couplant of refractive index close to that of the carrier itself is interposed between the protective film and the optical record carrier, at least where the film overlies the data-carrying area of the carrier. This provides a capability for repair, as well as protection, of carriers, since the silicone couplant is capable of flowing into scratches or other imperfections at the surface of the carrier. The film can be secured to the carrier in any convenient manner, including any of the ways described herein or the rim-based systems described in GB-2 279 799 B or WO-9 625 928 A.

Claims

Claims 1. Protection apparatus for an optical data storage carrier, said protection apparatus comprising a protective sheet dimensioned to overlie a region comprising at least part of a surface of the optical data storage carrier, the protective sheet being fastenable to the optical data storage carrier by way of at least one adhesive track provided with one or more apertures extending through the adhesive and permitting air to escape from said region.
2. Protection apparatus according to claim 1, wherein the carrier is discoidal and the at least one adhesive track is provided in the form of a ring.
3. Protection apparatus according to claim 2, wherein the ring is provided at substantially an outer and/or inner circumference of the data-carrying area of said optical data storage carrier.
4. Protection apparatus according to claim 3, wherein respective rings are provided at substantially the inner and outer circumferences of the data-carrying area of said discoidal optical data storage carrier and the apertures in the inner ring are angularly misaligned with the apertures in the outer ring.
5. Protection apparatus according to claim 4 wherein the apertures in the inner ring are precisely interleaved with the apertures in the outer ring.
6. Protection apparatus according to any preceding claim, wherein the adhesive is formed of a tacky, elastic material.
7. Protection apparatus according to any preceding claim, wherein the protective sheet is formed of a transparent material.
8. Protection apparatus according to claim 7, wherein the transparent material has a similar refractive index to that of the optical data storage carrier.
9. Protection apparatus according to any preceding claim wherein the at least one adhesive track is complemented by another track at which the sheet is cohesively adherent to the carrier surface.
10. Protection apparatus according to any preceding claim, wherein the at least one adhesive track comprises an optical couplant.
11. Protection apparatus according to any preceding claim, wherein the carrier is a CD having an annular raised area, coaxially surrounding its centre hole, and a data-carrying area annularly surrounding the raised area, wherein said sheet is applied to the data-carrying area, and wherein a further sheet, of substantially the same thickness as said first-mentioned sheet, is applied to said raised area.
12. Protection apparatus according to any preceding claim, wherein a non-tacky silicone couplant material, of refractive index substantially equalling that of said carrier and capable of filling, at least in part, surface defects in the surface of said carrier, is interposed in said region between said sheet and said at least part of the surface of said carrier.
13. Protection apparatus substantially as hereinbefore described with reference to the accompanying drawings.
14. A protective film system for a CD having a centre hole, a first area annularly surrounding the centre hole, and a second, data-carrying, area annularly surrounding the first area; the surface of one of said areas being raised relative to that of the other, the system comprising first and second annular protective films, each dimensioned and configured to overlie at least a substantial part of a respective one of said first and second areas but not to extend beyond it, and means for securing each said film to the surface of its respective area.