Note: Descriptions are shown in the official language in which they were submitted.
PHN. 10.943
The invention relates to an optically readable
storage disc which comprises:
- a flat transparent substrate with flat sides and a
cixcular periphery,
- a recording layer which can be modified locally by means
of a radiation beam and which is situated on a flat side
of the substrate,
- a cover disc which is secured to the substrate by annular
means with interposed adhesive means such as a layer of
adhesive, so as to be spaced from at least that part of
the recording layer near the periphery and in such a
manner that a sealed space is enclosed between the sub-
strate and the cover disc, and
- protective circumferential means which form part of the
1~ annular means and which have.a circumference with an
outer diameter which is larger than that of the sub-
strate.
Such a storage disc is disclosed in, for example,
Japanese Patent Application JP-PA 57-74842 (Patents Ab-
~tracts of Japan), Vol. 6, No. 156 (P-135)(1034), August
198~. The known storage disc comprises two flat disc
members and annular means formed by concentric inner and
outer annular spacers which are interposed between said
~isc m~mbers near a centre hole and near the outer circum-
~5 exence respectively of the storage disc to.affix saiddisc members to each other by means of an adhesive. The
outer.annular spacer comprises protective circumferential
means in the form of a cylindrical mounting ring which
extends transversely of the interposed portion and between
which the two said flat disc members are mounted.
Optical storage discs have a very high informa-
tion storage capacity. For example, a storage disc having a
PHN. 10.943 2
diameter of 30 cm can store approximately one giga-bit of
information on each recording side. Once the storage disc
has been provided with information the value of the stor-
age disc is no longer equal to the price of a blank storage
disc but rather depends on the importance of the informa-
tion stored on it. Loss of recorded information may have
serious conse~uences.
In optical storage discs the substrate should be
o a high optical quality. Moreover, the substrate should
comply with some other requirements depending on the
radiation-sensitive material used. Currently, substrates
of hard glass (see U.S.-PS 4,074,282) or of a high-
~uality plastics such as polymethylmetacrylate or poly-
carbonate are often used. Both said hard-glass substrates
and said plastics substrates are susceptible to damage by
forces acting on the outer rim, in the plane of the sub-
strate or impact forces. However, the storage disc is not
unlikely to be subjected to such impact forces, for
example if the storage disc inadvertently slips out of the
hands o the user or if during handling the storage disc
strikes against objects in its proximity. Moreover,
allowance must be made for the fact that storage discs of
the type discussed here are usually intended for filing
~urposes, which means that a service life of at least 10
~5 y~ars is required. During this long period the storage
disc may have to be handled many times.
Despite the pressure of the mounting ring the
known storage disc is not protected ade~uately against
damage by external forces impinging on, for example, the
outer rim and caused by falling or shocks, not even if the
storage disc is accommodated in a cassette. This is
because the impact forces are transmitted directly to the
disc members via the cylindrical mounting ring in which
they are mounted.
~he likelihood of damage to the storage disc is
not always minimized by accommodating the storage disc in
P~N 1O943 3 ~ 23-Ol-85
a cassette. This is because the cassette itself has also a
certain mass. If the cassette is readily deformable the
impact load exerted on the rim of the stora~e disc may be
even larger than in the absence of a cassette. However,
the cassette does provide satisfactory protection against
damage due to forces which ac~ perpendicularly to the plane
of the storage disc.
Another disadvantage of the known storage disc is
that it may happen that the substrate fractures when the
storage disc is subjected to a thermal cycle This is be-
cause at its circumference the glass substrate is mounted
in the cylindrical mounting ring which will not expand to
the ~ame e~tent as the substrate during said thermal cycle.
~or e~ample, if the mounting ring is made of a metal1 this
may result in the periphery of the substrate being sub~
jected to substantial faces.
The invention aims at solving this problem of the
known storage disc and to this end it is characterized in
that between the circumference of the substrate and cir-
cumferential means a space is formed which is substantial-
ly free of intermediate means which in the case of de-
formation of the periphery of the circumferential means
can transmit to the periphery of the substrate a force
which is directed to the centre of the substrate and which
has such a magnitude that it can damage the substrate.
In many cases it will be preferred if the space between
the periphery of the substrate and the circumferential
means is completely void. In the case of deformation of
the circumferential means this ensures that no forces at
30 nll c~n be e~erted on the periphery of the substrate.
However, it is also conceivable that said space is filled
with a readily deformable material.
If the outer wall of the protective rim of the
storage disc in accordance with the invention is subjected
35 to shocks these are not transmitted to the periphery of
the substrate but, via the annular means, to a flat side
of the substrate, namely by shear stresses in the adhesive
~2~L~L7~
PHN. 10.943 4
means between the substrate and the annular means. Adhe-
sive means such as layers of adhesive, as is known, can
withstand shear stresses comparatively well. Since the
annular means are very rigid in the plane in which they
are situated, the faces exerted on the substrate via the
adhesive means will be distributed over the entire area
or at least a part of the area covered by the adhesive
means.
An embodiment of the invention is characterized
in that said annular means and circumferential means to-
gether constitute a flat ring having an outer diameter
which is larger than that of the substrate. This embodi-
ment has several advantages. The combination of annular
means and protective circumferential means has the sim-
plest shape, namely that of a flat ring. The mass of thesemeans is minimal, which ma~ be important in order to mini-
mize the mass inertia and the mass eccentricity of a
rapidly rotating storage disc. There are no portions which
project from the flat side of the substrate which should
2~ face the optical write unit of an apparatus. Thus, contact
between the circumferential means on a rotating storage
disc and the write unit is precluded.
However, it is also possible to employ a combina-
~ion of annular means and circumferential means having a
~5 cross-section in the form of, for example, a letter T
lyin~ on its side, as in the known storage disc, or a
letter L lying on its side. Through plastic deformation
the additional portions then formed on the outer wall of
the circumferential means may contribute substantially to
the absorption of impact energy, in particular if this
impact face acts at an angle to the substrate.
Storage discs which are not accommodated in
cassettes may be employed for simple applications. Then,
but also in other cases, it may be advantageous to use an
embodiment of the invention which is characterized in that
the protective circumferential means are provided with
portions which extend around the outer circumference of
7~
PHN 10943 5
the storage disc and over the flat side of said disc situ-
ated opposite the annular means. As a result of this the
movement of the optical devices with which the storage
disc cooperates may be obstructed but this is no-t neces-
sarily always so, in particular if the associated appar-
atus is constructed to allow for the said shape of the cir-
cumferential means. In the above embodiment the circum-
ferential means of the storage disc also provides some pro-
tection if the storage disc is dropped in a direction
1~ perpendicular to its surface. It also protects the sub-
strate surface against scratching when the storage disc is
laid down.
If the storage disc is of a type in which the cover
is made of a different material than the substrate, for
e~ample as described in N.V. Philips' Gloeilampenfabrieken
Canadian Patent Applications 4~6,584 and 446,58S, which
were filed on February 2, 1984 and which issued as Canadian
Patents 1,211,558 and 1,211,559 on Sept. 16, 1986, it may
be advantageous to use a further embodiment of the inven-
2~ tion in which the cover has a larger outer diameter thanthe substrate and in which the portion of the cover which
projects from the substrate serves as the protective cir-
cumferential means. In the optically readable storage
discs in accordance with the Applicant's previous ~ppli-
~5 ~ations the cover is made of, for example, a thin aluminium
sheet material. Such a material is particularly suitable
~r ~bsorbin~ local shocks because it has a comparatively
low resistance to plastic deformation and can thus absorb
the impact energy.
Embodiments of the invention will now be described
in more detail, by way of example, with reference to the
drawing, in which:
Figure 1 is a perspective view, partly sectional
view, of a storage disc which is a first embodiment of the
invention,
Figure 2 is a similar view of a second embodimentof the invention,
7~
PHN 109~3 6
Figure 3 is a similar view of a third embodiment
of the invention, and
Figure 4 is a similar view of a fourth embodiment
of the invention.
In the various Figures corresponding parts bear
the reference numerals to which the Figure numbers have
been prefixed.
The optically readable storage disc shown in
Figure 1 comprises a transparent substrate 11 having flat
sides 17 and 18 and a circular periphery 19. The flat
side 17 carries a recording layer 12 which can be modified
locally by means of a radiation beam. Spaced from the
r~cording layer 12 a cover disc 13 is secured to the sub-
strate 11 by annular means comprising an annular spacer 16,
so as to form a sealed space 14 enclosed between the sub-
strate and the cover disc. On the circumference of the
storage disc protective circumferential means in the form
of a protective annular rim 15 are arranged for protecting
the substrate 11 against damaging by external forces which
aet in the plane of the storage disc. The combination of
the annular spacer 16 and the protective rim 15 comprises
a con~pletely flat ring with an outer wall 110. Between the
outer wall 110 of the protective rim 15 and the outer cir-
cumferenee 19 of the substrate there are situated no means
whi~h ean transmit forces which act on the outer wall 110
to the eireumferenee 19 of the substrate. The storage disc
shown in Figure 1 is of a type in which the substrate 11
~nd the cover 13 have the same diameter and are secured to
eaeh other by adhesive means at their circumferences by an
interposed annular spacer 16. Near the centre another
annular spacer 17 is interposed. The cover 13 comprises a
transparent substrate which is identical to the substrate
11 and which in the same way as the substrate 11 has been
provided with a recording layer, not shown. As a result of
this a double-sided storage disc is obtained and each of
the two substrates constitutes a cover for the other sub-
strate.
Figure 2 shows a modification of the storage disc
PHN 10943 7
shown in Figure l. On its circumference the protective rim
25 is provided with portions 25A which extend perpendicu-
larly to the annular surface. In Figure 2 these portions
form a cylindrical ring which surrounds the storage disc.
Both the protective rim 15 of the storage disc shown in
Fig. 1 and the protective rim 25 of the storage disc shown
in Fig. 2 have s~mmetrical shapes. This has advantages
with respect to production engineering. Such annular pro-
ducts can be manufactured for example by means of an
impact-e~trusion process employing an annular preform of
butt-welded aluminium wire. The symmetrical shape of the
annular product thus formed minimizes the risk of warping
due to inevitable internal stresses. Another advantage is
that the overall mass distribution of the storage disc re-
mains symmetrical. The cylindrical rim 25A in Fig. 2 hasan overall height which is smaller than the distance be-
tween the outer surfaces of the two substrates 21 and 23.
Therefore, the protective rim will not obstruct the move-
ment of the optical recording and reproducing means of an
apparatus on which the storage disc is to be used. Obvi-
ously the same applies to the protective rim of the storage
disc shown in Fig. 1. In principle, it is possible to give
the protective rim a different circumferential shape which
m~y be symmetrical or asymmetrical. If the cross-sectional
sha~e of the protective rim 25 shown in Fig. 2 is described
~s that of a lying T, alternative shapes may be used in the
form of a lyin~ L,Y,W etc. A protective rim such as the
rim 25A is better capable of absorbing impact energy acting
on the circumference of the storage disc. A part of the
energy can then be absorbed by plastic deformation of the
annular rim. Moreover, owing to the presence of the an-
nular rim, a better protection is obtained against external
impact forces which do not act exactly in the plane of the
storage disc but which are directed obliquely relative to
this plane. External impact forces on the protective rim
15 or the protective rim 25 give rise to shear stresses in
the layers of adhesive between the spacer 16 and 26,
respectively and the respective substrates. In general,
PHN 10943 8
~c~r~
layers of an adhesive are much ~e~E capable of withstand-
ing shèar stresses than tensile stresses, so that in suc`h
cases the layers of adhesive are subjected to comparatively
favourable load. The annular spaces 212 and 213 situated
between the circumference 29 and 214 and the inner wall 25A
may be filled, if desired, with a material which cannot
transmit undesirably large forces.
The storage disc shown in Fig. 3 is of a different
construction than those shown in ~igs. 1 and 2. The stor-
age disc comprises a single transparen-t substrate 31 pro-
vided with a radiation-sensitive layer 32. The cover 33 is
made of a thin aluminium sheet formed into a shallow hat-
shaped part. The trim of the hat constitutes the annular
means 36 and is affixed to the substrate 31 by means of an
adhesive. The protective circumferential means 35 are
sprung over the edge of the substrate. The centre portion
of the cover 33 is spaced from the recording layer 32, so
that a sealed space 34 is formed between the substrate and
the cover. Optically readable storage discs of this type
~a have been described in the Applicant's afore-mentioned
Canadian Patent Applications 446,58~ and 446,585. The
aluminium sheet material used is thin and is not in direct
contact with the outer wall 39. Thus, impact energy acting
on the circumference of the storage disc will be absorbed
~5 ~ d~formation of the circumferential means. Additional
protection is provided by an elastic ring 315. This has
t}la ~dc~itional advantage that the external surface 318 of
the substrate 31 is protected against scratching when the
stora~e disc s placed with the substrate facing down.
This ~ay happen in particular in the case of storage discs
of a simpler type, for example those intended for use in
perpipheral equipment of small office computers, personal
computers or home computers, when the storage disc is not
accommodated in a cassette. The ring 315 may be made of an
elastomeric material, preferably a material with optimum
damping properties. Specific elastomers such as butyl
rubber have suitable properties in this respect.
Another possibility of providing a storage disc
7~
PHN. 10.943 9
resembling ~hat shown in Fig. 3 with protective circumfer-
ential means is shown in Fig. 4. The storage disc shown
in this Figure is practically identical to that shown in
Fig. 3 except for a modification near the circumference.
The outer edge portion of the cover 44 has not ~een sprung
over the substrate 41.
Various modifications are possible within the
scope of the present invention. It is always preferred to
provide an optimum protection of the circumference of the
substrate by absorbing shocks with the aid of the protec-
tive circumferential means. Care mus-t be taken that the
eireumferential means eannot give rise to thermal stresses
in the substrate. Plastic deformation of the protective
circumferential means is a method of absorbing the energy
of a shock. However, it is essential that substantially no
forces can be transmitted to the circumference the sub-
strate by such a design that a space is formed between the
circumferenee of the substrate and the circumerential means
and that this spaee does not eontain any means which can
~0 transmit undesirably lar~e impact forces. All forces, or
praetieally all forces, are transmitted to a flat side or
to both flat sides of the substrate or substrates. The cir-
eumerential means may be modified by providing slits or
apertures, not shown, so that they may be deformed more
2~ ~asily. Instead of providing eircumferential means having
a eontinuous eircumference, the circumference may thus be
~ivided in a plurality of parts which may each be deformed
~ndividùally. Any resulting remaining deformation of the
proteetive eireumferential means will generally not inter-
fere with further use of the storage disc and is certainlypreferable over damage to the substrate. When neeessary,
it is often possible to restore at least approxima-tely
damaged circumferential means to the original shape. Elas-
tie deformation may provide additional protection. A stor-
age disc which drops on its circumference may bounce backand subsequently eome down in a less undesirable orienta-
tion. Some elastomers such as the afore-mentioned butyl
rubber, are well-known for their damping and eonsequently
PHN 1~43 10
shock-absorbing properties, so that they are suitable for
the present purpose.
The proteetive circumferential means of the stor-
age disc in accordance with the invention may also be used
for balancing the storage disc when neeessary. This poten-
tial use forms the subject of the Applicant's Canadian
Patent Application 473,765 whieh was filed on February 7,
1~85. Locally, small balancing masses may be provided,
which could locally transmit impact forces from the cir-
1~ eumferenee to the substrate. Although this is preferablyprecluded, such a small risk may be acceptable.
