Information recording discs

Information recording discs comprise a disc substrate having a recording layer on one side thereof, one hub having an insertion portion to be inserted into a center hole of the disc substrate and a flange portion to cover the disc substrate in the vicinity of the center hole, at least an apex of the insertion portion being composed of a magnetic material, the hub being inserted into the center hole so that the flange portion is positioned on the recording layer side of the disc substrate, and an adhesive layer is provided between the flange portion and the disc substrate. By this construction, a portion of the hub which protrudes from the back surface of the disc substrate, facing toward the spindle of a turn table can be altered in dimension and/or the diameter of the protrusion portion of the hub can be made smaller than that of the center hole of the disc substrate. Thus, the hub has a large degree of freedom of shape and can have a structure fitted to the shape of a turn table, while still providing a large adhesive surface between the hub and the disc substrate for strength.

FIELD OF THE INVENTION 
This invention relates to information recording discs which are used as 
optical discs and the like and particularly to information recording discs 
which are clamped by a magnet clamping system. 
BACKGROUND OF THE INVENTION 
Information recording discs to perform storing and reading information by 
converging rays of light such as laser beam and the like on recording 
layers of the discs are known, said information recording discs being 
prepared by laminating at least two plastic disc substrates, each having a 
recording layer on one surface thereof, directly or via spacers with 
adhesives so that the recording layers face toward each other. A magnet 
clamping system is one of clamping systems for clamping such information 
recording discs of the type referred to above. 
In the accompanying drawings, FIG. 4 is a sectional view of an information 
recording disc, showing the state wherein the disc is going to be clamped 
by a conventional magnet clamping system, for example, such as disclosed 
in Japanese Patent L-O-P Publn. No. 167663/1987. 
In FIG. 4, 1 is an information recording disc, which is so assembled that 
two transparent plastic disc substrates 2 are laminated together via an 
inner peripheral spacer 4 and an outer peripheral spacer (not shown) so 
that recording layers 3 face toward each other, hubs 6 are fitted 
individually from above and below to a center hole 5 of the two disc 
substrates 2 and bonded with adhesive layers 7 to the top and bottom 
surfaces of the laminated disc substrate. The information recording disc 1 
thus assembled is contained in a cartridge 8 and fitted onto a turntable 9 
to effect storing and reading of information. In the turntable 9, it is so 
designed that a concavity 10 equipped with a magnet 11 and a yoke 12 is 
provided so as to attract and set the hubs 6 on the turntable 9 and said 
hubs 6 are positioned in inserting a spindle 13 into center holes of the 
hubs 6, thereby setting and holding the information recording disc 1 on 
the turntable 9. 
The information recording disc 1 set on the turntable 9 in the manner now 
described is rotated, and information is stored in or read from the 
recording layers 3 by irradiation from the bottom with a laser beam or the 
like through the laminated disc substrate 2. 
The information recording disc 1 comprises two disc substrates 2 laminated 
together, each having a recording layer, and is assembled and used in the 
manner as illustrated above. When an amount of information to be recorded 
is small, however, it is taken into consideration that the information is 
stored or read by means of an information recording disc comprising one 
disc substrate having a recording layer, said information recording disc 
being used for storing or reading information likewise after containing it 
in the cartridge 8. 
FIG. 5 is a sectional view of a conventional single substrate type 
information recording disc which is one of the two parts obtained by 
simply dividing the information recording disc of FIG. 4 into two halves. 
That is, this information recording disc 1 is assembled by inserting an 
insertion portion 6a of a hub 6 having a flange portion 6b into a center 
hole of a disc substrate 2 having a recording layer 3 from the side 
opposite to the recording layer 3, and bonding the disc substrate 2 with 
an adhesive layer 7 to the flange portion 6b. In the same manner as in the 
case of the information recording disc of FIG. 4, the information 
recording disc 1 of FIG. 5 is used likewise for storing or reading 
information after inserting the hub 6 into a concavity 10 equipped with a 
magnet 11 and a yoke 12 of a turntable 9 to attract the hub 6 thereto, and 
inserting a spindle 13 into a center hole 14 of the hub 6 to position and 
set the information recording disc on the turntable 9. 
In the conventional single substrate type information recording disc as 
mentioned above, however, there were problems because the flange portion 
6b of the hub 6 is positioned at the side of the disc substrate 2 opposite 
the recording layer 3, in a case wherein a clamping area 15 on the 
concavity 10 of the turntable 9 is small in diameter, the diameter of the 
flange portion 6b becomes small and an adhesive surface thereof also 
become small, and in a case wherein the diameter of the clamping area 15 
is the same as, or smaller than, that of the center hole 5, the flange 
portion 6b disappears, so adhesion of the disc substrate 2 to the hub 6 is 
attained only at the edge face of the insertion portion 6a, thus in either 
case the adhesion strength between the disc substrate 2 and the hub 6 
decreases. Further, there was a similar problem when the clamping area 
formed on the concavity 10 of the turntable 9 is shallow, and when no 
concavity 10 is present at all in the clamping area 15, that is, when the 
back surface of the hub 6 and that of the disc substrate 2 are on the same 
level, there was also the problem that the disc substrate 2 is bonded to 
the hub 6 only at the edge face thereof. 
OBJECT OF THE INVENTION 
The present invention is intended to solve the above-mentioned problems, 
and an object of the invention is to provide information recording discs 
on which an adhesion surface between a hub and a disc substrate can be 
made large and thereby increase the adhesion strength therebetween even 
when the diameter and depth of the clamping area of a turntable are 
designed to be made small. 
Further, an object of the invention is to provide information recording 
discs on which the attached portion of a hub to a disc substrate can be 
made large or small without being restricted by the shape of the clamping 
area of a turntable. 
SUMMARY OF THE INVENTION 
The present invention is directed to an information recording disc 
comprising one disc substrate having a center hole and a recording layer 
on one side thereof, one hub having an insertion portion inserted into the 
center hole of said disc substrate and a flange portion covering a part of 
said disc substrate in the vicinity of said center hole, at least the 
lower portion of said insertion portion opposite the flange portion being 
composed of a magnetic material and said hub being fitted into said center 
hole so that said flange portion is positioned on the recording layer side 
of said disc substrate, and an adhesive layer formed between said hub and 
disc substrate. 
The present invention also relates to an information recording disc 
comprising one disc substrate having a center hole and a recording layer 
on one side thereof; and one hub having a flange portion covering the disc 
substrate in the vicinity of said center hole, at least a portion of said 
hub being composed of a magnetic material and said hub being attached to 
the disc substrate by means of the flange portion so that said flange 
portion is positioned on the recording layer side of said disc substrate.

DETAILED DESCRIPTION OF THE INVENTION 
Materials which may be used for forming the disc substrate may be any 
materials as long as they are transparent and include glass and 
transparent thermoplastic resins such as polycarbonates, polymethyl 
methacrylates and polyolefins. Preferred resins are copolymers of ethylene 
and cycloolefins represented by the following formulas (I) or (II), and 
preferred copolymers are those having the ethylene content of 40-85 mol %, 
preferably 50-80 mol %. Particularly preferred resins for forming the disc 
substrate include cycloolefin type random copolymer compositions 
comprising components (A) a cycloolefin type random copolymer comprising 
an ethylene component and a cycloolefin component represented by the 
following general formula (I) or (II), said copolymer having an intrinsic 
viscosity [.eta.] of 0.05-10 dl/g as measured in decalin at 135.degree. C. 
and a softening temperature (TMA) of at least 70.degree. C., and (B) a 
cycloolefin type random copolymer comprising an ethylene component and a 
cycloolefin component represented by the following general formula [I] or 
[II], said copolymer having an intrinsic viscosity [.eta.] of 0.01-5 dl/g 
as measured in decalin at 135.degree. C. and a softening temperature (TMA) 
of less than 70.degree. C., the weight ratio of said component 
(A)/component (B) being 100/0.1 to 100/10. Preferably, the component (A) 
contains 40-85 mol %, preferably 50-75 mol % of ethylene, and the 
component (B) contains 60-98 mol %, preferably 60-95 mol % of ethylene. 
##STR1## 
wherein n and m are each zero or a positive integer, l is an integer of 3 
or more, R.sup.1 to R.sup.10 each represent hydrogen atom, halogen atom or 
hydrocarbon radical. 
The hubs may be those made of any materials as long as at least the lower 
portion of an insertion portion of said hubs opposite the flange is 
composed of a magnetic material. Magnetic materials as used in the present 
invention means a magnetic material itself or a composite of a magnetic 
material and other materials. The magnetic materials include concretely 
(1) magnetic metals, (2) magnetic material-blended plastics and (3) 
plastics having fitted a magnetic metal to the lower portion of the 
insertion portion thereof. From the standpoint of strength and attraction 
force, preferred hubs are those made of (1) magnetic metals. The hub is 
attached to the disc substrate by means of the flange portion of the hub. 
For example, the hub may be attached by placing the flange portion in a 
concave portion formed on the surface of the disc substrate and forming 
projection(s) on the side surface of the concave portion, which project(s) 
above the flange portion. The projection can be formed by ultrasonic 
welding technique. 
Further, the flange portion may be fixed to the disc substrate by any 
means, such as ultrasonic welding or adhesives. For example, when the hub 
and the disc substrate are made of thermoplastic resins, the ultrasonic 
welding is applicable for fusion bonding the lower surface of the flange 
portion to the upper surface of the disc substrate in the vicinity of the 
center hole. The adhesives can be used for bonding the flange portion to 
the disc substrate without depending on the materials thereof as well as 
showing sufficient adhesive strength. Adhesives used for bonding the hub 
to the disc substrate are preferably those of epoxy type, particularly 
epoxy resins of ultraviolet-curing type, though any adhesives other than 
those mentioned above are also usable. 
The information recording discs of the present invention may be prepared by 
placing the hub on the disc substrate from the side of the recording layer 
of said disc substrate, and attaching or fixing the flange of the hub, 
which covers the vicinity of the center hole, to the disc substrate by 
such means of ultrasonic welding or adhesives. 
The information recording disc thus prepared is fitted onto a turntable by 
attracting the lower portion of the hub to a magnet of the turntable. In 
that case, the fixed portion of a hub to a disc substrate can be enlarged 
without being restricted by the shape of the clamping area of a turntable. 
When the hub has the insertion portion, the information recording discs of 
the present invention may be prepared by inserting the insertion portion 
of the hub into the center hole of the disc substrate from the side of the 
recording layer of said disc substrate, and bonding the hub to the disc 
substrate by means of ultrasonic welding or the adhesive layer formed 
therebetween. 
The information recording disc thus prepared is fitted onto a turntable by 
attracting the magnetic portion of the insertion portion of the hub to a 
magnet of the turntable. In that case, even when the diameter and depth of 
the clamping area of the turntable are small, the insertion portion of the 
hub can be changed in dimension according to the dimension of the clamping 
area of the turntable, and in that case the bonding strength between the 
hub and the disc substrate can be increased by enlarging the flange 
portion of the hub to enlarge the bonding surface between said flange 
portion and said disc substrate. 
EFFECT OF THE INVENTION 
Since the information recording discs of the present invention have such a 
structure that the insertion portion of the hub is inserted into the 
center hole of the disc substrate so that the flange portion of the hub is 
positioned on the recording layer side of the disc substrate, and the hub 
is bonded to the disc substrate by ultrasonic welding on the adhesive 
layer formed between the flange portion of the hub and the disc substrate, 
the portion of the hub projecting from the surface of the disc substrate 
facing to the spindle side of the turntable can be optionally changed and 
also a diameter of said projection portion of the hub can be made smaller 
than that of the center hole of the disc substrate. As a result, there are 
obtained such effects that the hub has a large degree of freedom of shape 
and can have a structure fitting with the shape of the turntable and, at 
the same time, the bonding surface between the hub and the disc substrate 
can be made large to increase the bonding strength. 
Since the information recording discs of the present invention have such a 
structure that the hub has a flange portion covering said disc substrate 
in the vicinity of said center hole, the flange portion of the hub being 
attached to the disc substrate, and at least a portion of said hub being 
composed of a magnetic material. 
The information recording disc thus prepared is fitted onto a turntable by 
attracting the lower portion of the hub to the magnet of the turntable. In 
that case, the attached portion of the hub to the disc substrate can be 
made larger or smaller without being restricted by the shape of the 
clamping area of a turntable. Further, in cases when the hub has an 
insertion portion opposite to the flange portion, the portion of the hub 
protruding (projecting) from the surface of the disc substrate facing to 
the spindle side of the turntable can be optionally changed and also a 
diameter of said projecting portion of the hub can be made smaller than 
that of the center hole of the disc substrate. On that account, there are 
obtained such effects that the hub has a large degree of freedom of shape. 
The present invention is illustrated below with reference to example given 
in terms of the accompanying drawings, but it should be construed that the 
invention is in no way limited thereto. 
EXAMPLE 
FIGS. 1-3 and 6 are sectional views showing information recording discs 
obtained in separate examples, respectively. In the figures, 1 is an 
information recording disc, and the surface of a disc substrate 2 on which 
a recording layer 3 is formed, is coated with a protective layer 16 made 
of plastics or the like. A hub 6 is fitted in a center hole 5 of the disc 
substrate 2. The hub 6 is made of a magnetic metal, and has an insertion 
portion 6a, a flange portion 6b and a center hole 14 in the center 
thereof. The insertion portion 6a is inserted into the center hole 5 of 
the disc substrate 2, and the flange portion 6b is positioned so as to 
cover the surface of said disc substrate 2 in the vicinity of the center 
hole 5, said surface having the recording layer 3 thereon. 
In FIGS. 1-3, an adhesive layer 7 is formed via the protective layer 16 
between the flange portion 6b and the disc substrate 2, wherein said 
flange portion 6b and said disc substrate 2 are integrally bonded to each. 
In FIG. 1, the insertion portion 6a of the hub 6 protrudes to form a 
protrusion portion 6c having the same diameter as that of the insertion 
portion 6a. 
In FIG. 2, the back surface of the insertion portion 6a of the hub is flush 
with that of the disc substrate 2. 
In FIG. 3, the insertion portion 6a of the hub 6 protrudes to form a 
protrusion portion 6c having a diameter smaller than that of the insertion 
portion 6a. 
The information recording disc 1 having such a structure as mentioned above 
is assembled by inserting the insertion portion 6a into the center hole 5 
so that the flange portion 6b of the hub 6 is positioned on the surface of 
the disc substrate 2, said surface having formed the recording layer 3 
thereon, and filling the adhesive layer 7 in between the flange portion 6b 
of the hub 6 and the protective layer 16 of the disc substrate 2, thereby 
bonding the hub 6 to the disc substrate 2. 
The information recording discs thus assembled are contained in a cartridge 
8 in the same manner as in the case of the information recording disc of 
FIG. 4, the magnetized lower portion of the insertion portion 6a of the 
hub 6 is fitted to a turntable 9 by placing it face to face on a magnet 11 
and a yoke 12 and positioned by inserting a spindle 13 into the center 
hole 14 and, at the same time, the hub 6 is clamped by attracting the 
magnetic portion of the insertion portion 6a of the hub 6 to the magnet 11 
and the yoke 12, whereby information is stored or read. In this case, the 
protrusion portion 6c is clamped by taking it in a clamping area 15 when 
said protrusion portion 6c is formed in the manner as shown in FIG. 1. 
When the clamping area 15 is shallow, the magnetic portion of the 
insertion portion 6a is positioned flush with the disc substrate 2 in the 
manner as shown in FIG. 2, and when the clamping area is small in 
diameter, a diameter of the protrusion portion 6c is made small in the 
manner as shown in FIG. 3. In either case, a dimension of the flange 
portion 6b of the hub 6 remains unchanged and an adhesive area of the 
adhesive layer 7 can be maintained constant, thereby increasing the 
adhesive strength between the hub 6 and the disc substrate 2. 
In FIG. 6, the disc substrate 2 has a concave portion 21 which is formed on 
the surface on which the recording layer 3 is formed. The flange portion 
6b is placed in a concave portion 21 formed in the vicinity of the center 
hole 5 of the disc substrate 2 and, on the side surface of the concave 
portion 21, projections 23 are formed so as to project above the outer 
peripheral of the flange portion 6b. In the information recording disc 1, 
at least the lower portion of an insertion portion 6a of the hub 6 is made 
of a magnetic material such as metal, and the hub 6 may be wholly made of 
the magnetic material. 
The information recording disc 1 having such a structure as mentioned above 
is assembled by placing the flange portion 6b into the concave portion 21, 
so that the insertion portion 6a is inserted into the center hole 5 of the 
disc substrate 2, and partially fusing the upper part of the side surface 
to form the projections 23 projecting above the outer peripheral of the 
flange portion 6b. The flange portion 6b of the hub 6 may be firmly fixed 
or set with clearance to the disc substrate 2. The projections 23 may be 
formed by partially fusing the upper part of the side surface by means of 
ultrasonic welding technique. 
The information recording disc thus assembled may be contained in a 
cartridge 8 in the same manner as in the case of the information recording 
disc of FIG. 4 and can be used by fitting it onto a turntable having a 
spindle and a magnet. When the information recording disc 1 is fitted onto 
the turntable, the spindle of the turntable is inserted into the center 
hole 14 of the hub 6 with the magnet facing toward the lower portion of 
the insertion portion 6b to attract it to clamp the information recording 
disc 1. In that case, the flange portion 6a of the hub 6 of the disc 
substrate 2 can be made larger or smaller without being restricted by the 
shape of the clamping area of a turntable. 
Further, the portion of the insertion portion 6a projecting from the 
surface of the disc substrate 2 which faces toward the a diameter of the 
protruding (projecting) portion of the insertion portion 6a can be made 
smaller than that of the center hole 5 of the disc substrate 2. On that 
account, the hub 6 has a large degree of freedom of shape. 
In this connection, the shape and structure of the disc substrate 2 and hub 
6 can be varied as desired, and the protective layer 16 is not always 
necessary.