Note: Descriptions are shown in the official language in which they were submitted.
~24396
PHN 8897
The invention relates to a method of manufact-
uring an optically readable information disk, in which
a transparent plastics information carrier comprising
a radiation-reflecting optical structure on one side
is provided, on the side of the optical structure, with
a cover plate connected thereto by means of an adhes-
iv~ .
Such a method is known from Netherlands PatentApplication 72 ll 999 in the name of Applicants laid
open to public inspection on March 5, 1974.
The disadvantage of the known method is that
there is a real chance that the optically readable
information disks manufactured according to the method
: will show defects or deviations in the optical struc-
ture in the long run, so that the quality of the stored
information, for example, video information or audio
information, is reduced.
A11 the optical readable information disks
manufactured so far from a plastic synthetic resin
have the above disadvantage. It has therefore been
~ endeavoured to improve this, special search having
:~ been made for special compositions of synthetic resins
showing the desired great stability for longer periods
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P~-TN.8897
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of time and in varying cllmatological conditions. In
this connection it is to be noted that very stringent
requirements have to be imposed on the stability o~
a plastics information disk in view of the great fine-
ness of the information structure. ~s stated also in
the above Patent Application, said structure usually
consists of radiation-reflecting areas, arranged in
tracks, of very small diMensions, in the order of mag-
nitude of 1/u. These areas are, for example, small
blocks and intermediate areas situated in one plane,
the coefficient of reflection of the blocks dif`fering
from that of the intermediate areas. The optical struc-
ture preferably consists of small blocks and inter-
mediate areas having the same coefficients of reflec-
tion, the blocks and intermediate areas being situ-
ated at different levels Thus a crenellated struc-
~ ture of the information track is obtained with a dif-
I ference in height between the blocks and the inter-
mediate areas of` approximately 0.5/u. The inf`ormation
track may be spiral-like or be constructed f`rom con-
centric circles.
The radiation-reflectlng optical structure is
read in reflection by meaus of a focused light beam, in
particular laser light.
Plastics information d:isks having a unilateral
reflecting optical structure can be mass-produced while
using matrices. Various methods may be used, for example
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~24396
PHN 8897
a pressing process described inter alia in our
Canadian Patent 998,173 which issued on October 5,
1976. Another known method is an injection mould-
ing process or a moulding process. German Offen-
legungsschrift 23 43 020, for example, discloses a
moulding process in which a liquid polyurethane
resin with a polyester substrate thereon is provided
on a matrix of silicone rubber. After curing of the
urethane resin, the substrate with the cured poly-
urethane layer connected thereto is removed from the
matrix surface. Another method of manufacturing is
the so-called printing process, in which a thermo-
plastic foil is provided with the desired optical
structure by a treatment with a rotating matrix which
is provided, for example, on a roller.
The resulting information disks are then
provided, on the side of the optical structure, with
a radiation-reflecting layer, for example, a layer
of metal or a layer of a selenide dielectric. A
suitable radiation-reflecting layer is or example,
a layer of aluminium,silver or gold provided by vap-
our deposition or by electroless plating. In order
to protect the radiation-reflecting layer from chem-
ical and mechanical attack, a protective layer of
plastics is provided hereon. This usually is a layer
of lacquer, but according to the above Canadian Patent
998,173, it may alternatively be a thin sheet or foil
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4396
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provided with an adhesive.
Another known method of manufacturing information
disks provided unilaterally with a reflecting optical
structure starts from a substrate in disk form on
which a reflective layer is vapour-deposited via an
apertured mask. So in this method no matrix is used.
i Instead Or a vapour deposition process, an etching
process rnay a]ternatively be used~ in which a layer of
photoresist provided on a metal layer is exposed to
light v;a a mask and is developed, after which the
exposed parts of the metal layer are etched away.
These latter methods are considered to be less suitable
for series manufacture.
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It has also been tried to remove the above dis-
advantage of reduction in quality of the-optical struc-
- ture by making such improvements in the manufacturing
technique that the pressure load and thermal load
exerted on the synthetic resin are minimum. It has been
suggested, for example~ in the pressing process and
the printing process, to heat only the uppermost layer
of the synthetio resin in which the in~ormation structure
is to be provided.
. IIowever, all these attempts have failed to pro-
duce an optimal re~sult. Applicants have invented a
method o~ manufacturing optically readable information
disks which does not show the above disadvantage.
More in particular the present invention relates
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to a method of the kind mentioned in the preamble which
t
is characterized in that the cover plate is a flat~
, stiffening, heat-conducting plate manufac-tured from
inorganic material and connected to the information
carrier throughout its surface.
~ This characterizing measure in the method accor-
1~l ding to the invention is based on the following
insight gained by Applicants.
In Applicants' opinion, the reduced quality of
the in~ormation disk is mainly the result of micro-
¦ structured ~orces, l.e. forces which act on a very small
;t~ surface part of the information disk and which are re-
i~ leased upon rs_ading the disk by means of laser light.
j~ The laser light beam focused on-the optical
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$ ~ 15 structure of the information disk will traverse the
~ transparent synthetic resin without noteworthy loss
`~ of light energy and will then be reflected by the ra-
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dlation-reflecting layer. Dependent on the coefficient
6~ ~ of reflection of the reflecting layer used, - generally
1~ 20 a metal layer - more or less light energy will be
3~ absorbed by the reflecting layer. The absorbed light
.
~ ~ energy is converted into thermal energy; as a result
1 ~ ~
of this the temperature of the layer will rise locally,
which in turn produces a local heating of the part of
the optical structure engaging the reflecting layer.
Many internal stresses are present in the part of the
informatlon carrier comprising the optical structure.
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`~Z4396
PHN 8897
In connection herewith it is to be noted that in the
above-described manufacture of plastics information
carriers which are provided unilaterally with an opt-
ical structure, a thermal load and a pressure load
are exerted on the thermoplastic material to be pro-
cessed. This is the more prominent in a pressing or
printing process, in which the optical structure is
provided in a heated thermoplastic synthetic resin
under pressure and by means of a matrix. Cooling is
~ 10 then carried out, the internal stresses introduced
; into the material under the influence of pressure and
heat being frozen-in. Such internal stresses occur
frequently in particular in that part of the synthe-
tic resin where the deformation is maximum, in other
words in or near the optical structure.
Internal stresses are present even in the
information carriers manufactured according to methods
of manufacturing plastics information carriers in
which no elevated pressure or high temperature is
used. In this connection, reference is made to our
Canadian Patent Application 288,224 which was filed
on October 5, 1977. The process described in sald
Application starts from a liquid lacquer which can
be cured with light, for example U.V.-light and which
is spread over the information-carrying surface of a
metal matrix. A transparent plastics sheet is then
provided over the lacquer, after which the lacquer is
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PHN.8897
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~124396
exposed to light via the plastics sheet, cured and
finally the assembly of plastics sheet and the infor-
mation-carrying cured lacquer layer connected thereto
is removed from the matrix surface.
The plastics information carrier thus manufac-
tured also shows internal stresses, especially in the
plastics sheet which, during the manufacture thereof,
for example, by means of an extrusion process, has also
been subjected to a pressure and thermal treatment.
As already stated hereinbefore, a very local
heating of the plastics information carrier in or near
the optical structure takes place when the information
disk is exposed to laser light. The heated surface
area is very small, in the order of magnitude of
1~ microns. The stresses present in the heated part of the
information carrier will be released and the forces
resulting herefrom will produce a deformation, however
small in dimension. In view of the detail fineness of
the optical structure, this results 1n errors in the
stored information to be read.
By using a heat-conducting plate according to
the present in~en$ion, upon irradiating the optical
~; ; structure with laser light, the energy absorbed by the
reflecting Iayer will flow for the greater part to
~ ~ 2~ the heat-conducting plate so that no noteworthy rise of
;~ temperature will occur a-t the area of the irradiated
surface. The information carrier and in particular the
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PHN.8897
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~Z4396
optical structure thereof will hence not be heated, so
that no internal stresses are released.
In addition to the above-described micro-struc-
tured ~orces, macro-structured ~orces also occur which
are operative over a larger surface of the plastics
~, information carrier. These are in particular forces
which, in ~pplicants' opinion, are the result of a uni-
lateral absorption or release of moisture by the in-
s formation carrier and which result in warping of the
information carrier. A comparatively small extent of
j warping over a large surface area of the plate will
I as a rule not exert a direct influence on the in~ormation
-1 to be read, since the objective which focus~s the
¦ laser light can keep the gradually ~arying distance
1~ ~ to the optical structure within the depth of focus which
j is a ~èw microns, if desired by a compensating gradual
~ displacement of the objective. In the case in which the
:;J
~ carrier warps considerably over a smaller distance,
,~ ~ the objective can no longer follow-the varying position
¦ 20 Or ~the optical structure upon reading and the in~ormation
carrier is no longer optically readable.
The flat, stif~ening, heat-conducting plate used
; ~ according to the invention can receive the above-
mentioned forces without de~ormation o~ the plate
~5 occurring. An information disk manufactured according
to the invention will not warp.
The method according to the invention produces
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.~ PIIN,8897
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¦I good results in particular if the flat, stiffening,
¦ heat-conducting plate used is a metal plate or a
glass plate in a thickness of 0.2-2 mm. Owing to -
s the very good thermal conductivity and in addition
the e~cellent thermal capacity~ a plate is to be
z preferred which is manufactured from metal, such as
nickel,steel or aluminium.
This applies in particular to an aluminium plate
in a thickness of 0.3 to 1.3 mm.
In a further favourable embodiment of the method
according to the invention the side of the flat plate
remote from the information carrier is provided with a
second transparent plastics information carrier com-
prising a unilateral radiation-reflecting optical struc-
- ture, the said side of the flat plate being connected
throughout its surface to the radiation-reflecting op-
; tical structure of the information carrier by means of
an adhesive.
This results in an information disk carrying
information on two sides which compri9es the double
quantity of information, or~ in other words, has a double
playing time. Moreover the further advantage is ob-
tained that there is a fair chance that the macro-
structured forces which may occur in the information
carriers situated on both sides of the flat plate, com~
pensate each other at least partly. In this connection
it is noted that life tests under ext:reme atmospheric
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10-10-1977
~L124396
circumstances have demonstra-ted that such an information
s carrier remains entirely flat if herein a comparatively
thin aluminium plate of 0.5 mm is used.
The adhesive used in the method according to
the invention is of a conventional type, for example,
a two-components adhesive. In an advantageous embodi-
ment a radiation-curable lacquer is used, for example,
an ultraviol0t-curable lacquer on the basis of acrylic
acid. The thin liquid lacquer can easily be provided
on one of the surfaces to be connected, for example by
i means of a spraying process or a cen-trifuging process,
`l~ that is to say, either on the informa-tion-carrying sur-
face of the information carrier, or on the flat,
stiffening, heat-conducting plate. A rapid curing of the
;, 15 laquer is possible by exposure via the transparent in-
,~ ,
~ formation carrier. It has been found that the radiation-
Y~ reflecting layer which reflects in particular in the
infrared region, still passes sufficient shortwave light,
~`~ for example ultraviolet light.
; ~ 20 ` If desired, the flat, stif~ening, heat-conduc-
i~ ~ ting plate used may be provided with reinforcement ribs
on the sids remote from the in~ormation carrier. An
; ~ information carrier and a plate may also be used which
both have a central aperture so that the resulting
` ~ ~
information disk has a central aperture.
The invention will now be described in greater
detail with reference to the drawing, in which: -
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Figure 1 is a cross sectional view of a plastics
information carrier used in the method5
Figure 2 is a cross-sectional view of an in~or-
. mation carrier obtained according to the invention, and
Figure 3 is a cross-sectional view of another
embodiment of an informatlon disk obtained according to
the invention,
Reference numeral 1 in Figure 1 denotes a trans-
parent plastics information carrier comprising an op-
I . tical structure 2 on one side. Information carrier 1
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~J 10 with optical structure 2 has a thickness of approximate-
`. ly 1 mm and is manufactured from transparent polyvinyl
chloride/acetate copolymer according to a known pressi.ng
.process. The optical structure is crenellated and consists
of small blocks 3 with intermediate-areas 4 the dimen-
¦~ 15 sions of which lie in the order of magnitude of 1/u.
, ~ Optical structure 2 is covered with a vapour deposited
~J, radiation-reflecting aluminium làyer 5, approximately
~! 300 ~ thick
1 ~ .
~ ~ On the side o~ optical structure 2~ the informa-
¦~ 20 tion carrier 1 is provided with a 0.5 mm thick aluminium
.~ .plate 6 (Fig~ure 2) while using a layer of adhesive, not
~ : shown, for example, a two-components adhesive.
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The resulting information disk is shown in
,~ Figur.e 2. The disk is read optically and in re~lection
:. .
¦~ 25 by mean: o~ laser light in the direction denoted by an
~ arrow.
.
Re~erenoe numeral 7 in Figure 3 denotes a 0.5 mm
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PHN.8897
10-10-1977
~;24396
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thick aluminium plate provided on both sides with
plastics information carriers, referenced 8 and 9,
, respectively. Information carr:iers 8 and 9 correspond
i to that shown in Figure 1 and are provided on one
' 5 side with an optical structure 10, 11 covered by a
vapour-deposited aluminium layer, not shown. Infor-
mation carriers 8, 9 are connected to plate 7 on the
side o~ the optical strueture 10, 11 by means of an
adhesive, not shown. The information disk shown in
~igure 3 is read bilaterally in the direction denoted
by arrows.
; The thickness (appro~imately 1 rnm) of the plas-
tics information earriers 1(Figures 1, 2) and 8, 9 (~i-
~, gure 3) is amply suffieient to keep dust particles or
seratches possibly present on the ~surface beyond the
~¦~ depth of focus of the ob~ective, not sho~, which
focuses the reading beam on the optical structures 2
igures 1, 2) and 10, 11 (Figure 3~).
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