Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
6~
METHOD AND MEANS FOR REPLICATING
CENTRALLY APERTURED VIDEO DISC RECORDS
TECHNICAL FIELD
This invention relates generally to a method
and apparatus for molding a centrally apertured part~
and more particularly concerns a method and apparatus
for in~ection molding a centrally apertured and
spirally tracked record, such as a video dlsc.
EACKGROUND OF THE PRIOR ART
An apparatus for producing in~ection molded
and centrally apertured video discs is shown in U.S.
Patent No. 3,989,436, issued November 2, 1976.
BRIEF SUMMARY OF THE ~NVENTION
The invention is not only useful for ln~ec-
tion molding centrally apertured video disc records, but
is also applicable to the formatlon of in~ection molded
records requiring an accurately positioned centrally
~ placed aperture.
Y In~ certain video disc systems, video informa-
tion is recorded in the form of light scattering or
light reflecting members positioned in a spiral track
on the surface of a centrally apertured record. For
playback, the record is mounted on a rotatable turn-
table having a spindle which engages the record aper-
ture for centerin~, and then relative motion isestablished betl~een the record and a reading assembly.
The reading assembly includes a laser optical system
for generating a laser beam and for directing the laser
beam to impinge upon a spiral track IYhich contalns the
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video information. The optical system includes an
ob~ective lens system which directs the laser beam to
the spiral track and also collects the reflected signal
from the spiral track for transmission to associated
electronic circuitry which translates the detected
reflections into signals suitable for a visual display
by a standard home type television receiver. A system
of the above-mentioned type is described in U. S.
Patent 3,829,622, issued to James E. Elliott and
assigned to the Assignee ~ the present invention.
In such a video disc system, it has been
recognized that, not only the average speed of relative
motion between the implnging laser light beam and the
record must be maintained at a predetermined speed of
- 15 1800 r.p.m., but the cyclical variations about the
average speed must be limited for proper playback.
It is desirable to reduce the cyclical speed variation
to assure that the synchronizing pulses in the recovered
television signal are fairly stable and within the lock-
up range of the deflection circuits ~ the televislon
receiver. The cyclical speed variations are particu-
larly unpleasant when the recorded lnformation is a
color television signal.
One of the sources of cyclical speed variations
- 25 is the record eccentricity. For proper playback of the
video disc, it is important that the replicated record's
center hole is concentric with the spiral groove
center to a~high degree of accuracy. As discussed in
the aforementioned Elliott patent, the time base cor-
3 rection circuitry is useable to achieve correction for
such cyclical speed variations to within the limits of
the time base correcting circuits. More specifically,
a time base correcting circuit has operating limits
itself and can only correct for a certain amount of
error. Therefore, it is preferred to form as perfect
a video disc record as possible during the injection
molding operation.
The concentricity between the center hole of
the record and the record spiral track is particularly
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important when the spiral tracks are spaced a fraction
of a micron from track center to track center, preferably one-
half micron to one micron. The video disc member useable
with the Elliott video disc player has light reflective and
light scattering members positioned in track-like fashion on
the information bearing surface of the video disc member.
These light reflective or light scattering members are pre-
ferably sized to equal one-quarter of a wavelength of the
incident light along the beam axis. More specifically,
typical light scattering structures are more completely de-
scribed in Canadian Patent 1,066,411 of Manfred Jarsen and
entitled -Replication Utilizing a Casting Process--.
In the Elliott system using a laser beam reflection
system for reading the information tracks on the video disc,
lS the video disc must be essentially birefringence free in the
sense that it does not contain impurities embedded in the
plastic material which give a false reflection or light scat-
tering effect to the impinging laser beam. These impurities
could include small particles of matter, left over from the
.20 previous injection cycle, being mixed with the new material
needed in the present cycle. These impurities also induce
stress forces formed within the plastic material during the
injection cycle.
The concentricity of the finished molded video disc
member is required to achieve faithful reproduction of the
video information contained thereon. The center of gravity
must be positioned within ten mils from the center of rotation
of the video disc to limit the vibration due to static im-
balance. The information tracks should be concentric with the
center of rotation within one to two mils for good tracking
and to fall within the time base correction capability
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of the electronic circuitry associated with the Elliott
player. Concentricity of the information tracks with the
center of rotation are achieved, in
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part, by providing a stamper member having means for
allowing expansion of the stamper member within the
video disc cavity in response to the heat assoclated
with the injected plastic material. Concentriclty can
also be damaged during the sprue eJection or aperture
punching steps. The aperture punching step must be
performed without setting up a lateral shear force
which inherently moves a portion of the video disc
further towards or further away from the center of
rotation during the punching operation.
It is an object of the present inventionjto
provide a video disc record without flow lines and
other surface defects in that portion of the record
~ containing the spiral shaped information tracks.
It is a further object of the present inven-
tion to provide a video disc member having a substan-
tially uniform value of birefringence over the entire
surface of the video disc used for recording the video
information tracks.
A still further ob~ect of the present inven-
tion is to provide a platen assembly having means for
allowing the stamper structures to freely expand within
predetermined limits in advance of the in~ected molten
plastic material and the heat created therefrom.
Another ob~ect of the present invention is to
provide an injection molding tool having cooling means
for the platen subassembly.
The production of a video disc record having
uniform values ~ birefringence over the entire in-
3o formation bearing surface of the video disc member is
achieved in part by employing holding means for allow-
ing the video disc stamper members to expand under
the application of heat caused by the injected molded
material; by employing an annular shaped sprue passage
intermediate the principal sprue passage and the video
disc cavity to cause the molten material to flow into
the disc cavity in a manner avoiding stress gradients
within the injected material.
A first mold-half and a seco~ mold-half are
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reciprocably mounted in the tool. A sprue bushing
having an opening in communication witll an injection
nozzle is secured to the platen. A punch, having an
end portion in registry with the sprue bushing, is
reciprocably mounted relative to the second mold-llalf.
~hen the second mold-half is in a closed location,
(1) the punch end portion and the opening in the sprue
bushing define a sprue passage, and (2) the first and
the second mold halves define an annular cavity sur-
rounding the sprue passage. The annular cavity andthe sprue passage form, respectively, the centrally
apertured part and the sprue when heated material is
injected therein. After partial cooling of the heated
injected material, the first and the second mold halves
move from the closed location to a locatio~ inter-
mediate of the closed location and an open location
while the punch is locked in place to sever the sprue
from the part along the peripheral surface of the punch
end portion. The centering die locator and fixed
center stamper clamp portion of the first mold half,
where the punch end portion enters, serves as a die.
The mold halves are thereafter separated to open the
annular cavity while the sprue is restinæ on the punch
end portion, and while the part is in contact with the
punch end peripheral surface. After the mold nalves
are separated, a sprue ejector member and a part
removal member are actuated to remove, respectively,
the sprue and the part from the punch end portion.
An improved platen assembly is described
having releasable means for centering the stamper and
for holding the stamper in place against the platen
surface. The holding means also includes means for
allowing the stamper to e~pand under the temperature
gradient of the heated plastic injected material.
The stamper expands uniformly in front of the injected
material, as the heated in,~ec~ed material fills the
video disc cavity. The platen assembly further con-
tains a plurality of separate cooling channels for
maintaining the platen at a uniform temperature across
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the surface of the platen.
A center punch is described which accurately
punches a hole in the center of the injected video disc
member. The center punch is held stationary while the fixed
mold half expanding base plate and the moving mold half move
through the punch stroke to an intermediate position set by
a punch stroke limiter device.
An annular shaped sprue passage is formed by the
closing of the first and second mold half members and the
end portion of the punch. The sprue passage comprises a
first section defined by.the sprue bushing itself and a
second section defined by a combination of members including
a portion of the sprue bushing, the end portion of the
punch and portions of the inner centering locators and
clamps.
Cooling apparatus for use in an injection molding
apparatus for molding centrally apertured parts and of the
type employing a molten mixture for injection into a molding
cavity formed by a first mold half and a second mold half
and means for supporting reciprocal motion of said
first mold half and said second mold half for removing the part
from the molding cavity, said cooling apparatus for one of
said mold halves comprising: a first molding member having a
first surface and a second surface, said first surface being
employed as a molding surface by the molding cavity and said
second surface adapted for contact with said one mold half,
a plurality of spiral shaped channels formed in said second
surface, each of said channels having an input and an output;
each of said channels including more than one spiral turn
around said second surface; input means carried by said one
mold half and in registration with said inputs of said spiral
channels for conveying cooling fluid means to said spiral
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shaped channels for cooling said one mold half
to a constant temperature -~across the mold ca~ity during and
immediately after the injection of said molten mixture into
the molding cavity; and output means carried by said one mold
half and in registration with said outputs of said spiral
channels for carrying cooling fluid means from said spiral
shaped channels for cooling said mold half to a constant
temperature across the mold cavity during and immediately after
the injection of said molten mixture into the molding cavity.
A method for cooling an injection molding
apparatus, the apparatus molding centrally apertured parts
by employing a molten mixture for injection into a molding
cavity formed by a first mold half and a second mold half and
means for supporting recipricol motion of said first mold
half and said second mold half for removing the part from the
molding half cavity, the method comprising the steps of:
providing a first molding member having a first surface and a
second surface, said first surface being employed as a
- molding surface by the molding cavity and said second surface
being adapted for contacting said one mold half; forming
a plurality of spiral shaped channels in said second surface,
each of said channels having an input and an output, and
each of said channels including more than one spiral turn
about said second surface; conveying cooling fluid to said
spiral shaped channels via an input means carried by said one
mold half in registration with said inputs of said spiral
channels for cooling said one mold half to a constant temper-
ature across the mold cavity during and immediately after the
injection of said molten mixture into the molding cavity; and
carrying the cooling fluid from said spiral shaped channels via
an output means carried by said one mold half in registration
with the outputs of said spiral channels.
6a
BRIEF DESCRIPTION OF THE DRAWINGS
FIGURE 1 is a cross-sectional v~iew, partly
schematic, taken along the line 1-1 of Figure 7 of an injection
molding apparatus for replicating centrally apertured and
spirally tracked records pursuant to the principles of the
present invention;
FIGURE 2 is a cross-sectional view, similar to
Figure 1, taken along the line 2-2 of Figure 7, of an
injection molding apparatus for replicating centrally
apertured and spirally tracked records pursuant to the
principles of the present invention;
FIGURES 3 through 6 show in schematic form the
sequence of operation executed by the injection molding
apparatus shown in Figures 1 and 2;
FIGURE 7 is a plan view of the moving half shown
in Figure l;
FIGURE 8 is an inverted plan view of the fixed
half of the mold assembly shown in Figure l;
FIGURE 9 is an enlarged sectional view taken
within the circle identified as 9 and as shown in Figure l;
FIGURE 10 is an enlarged sectional view of the
area contained within the circle identifiedas 10 shown in
Figure l;
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FIGURE ll is an enlarged sectional view of the area con-
tained within the circle identified as 11 shown in Figure l;
FIGURE 12 is an enlarged sectional view taken along the
line 12-12 of Figure 1.
FIGURE 13 is a graph showing a changing relationship in
value of birefringence accompanying a changing relationship
in the thickness of a acceptable video disc; and
FIGURE 14 is a graph showing a changing relationship value
of birefringence accompanying a changing relationship in the
thickness of an unacceptable video disc.
DETAILED DESCRIPTION OF THE INVENTION
. . _
Referring to Figures l and 2, there is shown a tool 10
for use in combination with a standard injection molding
machine, such as the 375 ton model manufactured by the Stokes
Division of Penwalt Mfg. Co. The tool 10 is used for re-
plicating a centrally apertured video disc record, and com-
prises a fixed mold half (first mold half) 12 and a moving
mold half (second mold half) 14. The fixed mold half 12 com-
prises a fixed mold fixed base plate 16 which is attached to
the fixed frame member of a standard molding machine (not
shown) and a fixed mold half expanding base plate 18. The
base plate 16 carries in integral attachment therewith a
plurality of major guide and support pins, one of which is
shown at 20. A fixed mold half major guide and sup~ort pin bushing
is shown at 22 for reciprocally mounting the base plate 18
with the base plate 16 during the punching step. The punch-
ing step is defined in part by the reciprocal movement of the
expanding base plate 18 with reference to the fixed base plate
16.
The moving mold half 14 comprises a moving mold half car-
rier plate 30, a moving mold half spacer plate 32 and a moving
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mold half fixed base plate 34. The moving mold half fixed
base plate 34 is attached to the frame of a standard injec-
tion molding machine (not shown). The spacer plate 32 is
attached to the fixed base plate 34 by a plurality of moving
mold half spacer plate bolts, one of which is shown at 36.
The bolts 36 are countersunk within the spacer plate 32 and
are uniformly spaced around the periphery of the spacer plate
32 for firmly attaching it to the fixed base plate 34.
The base plate 34 is additionally attached to the carrier
plate 30 by a plurality of moving mold half clamp bolts, one
of which is shown at 38. Each-of the clamp bolts 38 passes
through the spacer plate 32 as indicated by the dotted lines
at 40 and are threadably attached to the carrier plate 30 as
indicated by the dotted lines shown at 42. The clamp bolts
38 are uniformly spaced about the periphery of the base plate
to securely fasten together the carrier plate 30, the spacer
plate 32 and the base plate 34. Each of the bolts 38 is
countersunk within the base plate 34 to provide a smooth
contact surface 43 to the plate 34.
A moving mold half major support pin bushing is shown at
44 carried by the carrier plate 30. The support pin 20 is
positioned within the bushing 44 and provides reciprocal move-
ment between the fixed mold half fixed base plate 16 and the
carrier plate 30 during the punching operation. The support
pin 20 also provides conjunctive movement between the fixed
mold half expanding base plate 18 and the moving mold half
carrier plate 30 during the punching operation. With the
completion of the punching operation, the support pins 20 are
fully withdrawn from the bushings 44 during the remaining
portion of the opening step. At the fully opened position,
the support pins are spaced from the moving stamper 144 to
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the same extent as the primary punch plate assembly stroke
limiter 90 is shown spaced from the expanding base plate 18
in Figure 5.
A punch plate assembly 50 comprises a punch
plate assembly clamp plate 52 and a punch plate assembly
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g
support plate 54. The punch plate assembly 50 is
carried within the moving mold half fixed base plate 34
and is reciprocally mounted therewith by a plurality of
punch plate assembly guide pins integrally attached to
the base plate 34. One of the punch plate assembly
guide pins is shown at 55. A punch plate assembly
clamp plate bushing is shown at 56 and a punch plate
assembly support plate bushing is shown at 58. The
guide pins 55 extend through the plates 52 and 54.
10 The plates 52 and 54 are reciprocally mounted upon the
pins 55 by the bushings 56 and 5~, respectively.
The guide pins 55 extend into the moving mold
half carrier plate 30, as shown by the dotted lines 60.
A plurality of moving mold half carrier
15 support bars 64 are attached to the base plate 34 by
individual bolts, one of which is shown at 66. The
- support bars 64 extend through openings in the plates
52 and 54 as indicated oy the dotted llnes at 72 and
74J respectively.
The support bars 64 provide added support to
the back surface 76 of the carrier plate 30 during the
inJection of the molten material into the video disc
cavity.
Referring to Figure 2, a punch plate stop bar
25 is shown at 77 positioned intermediate the punch plate
assembly support plate 54 and the fixed base plate 34.
- The stop bar is attached to the base plate 34 by a
plurality of punch plate stop bar bolts, one of which
is shown at 7~. The stop bar 77 is circular in cross
section. ~ portion of the bar is shown at both the
left and right hand portion of Figure 2. The stop bar
77 adds rigidity to the tool allowing it to withstand
the full force of the closing force of the main ram
associated with the injection molding machine. In
35 this capacity, it cooperates with the side members 34a
of the fixed base plate 34 in withstanding the ram
pressure during the closing and closed portion of the
molding operation. ~hile the stop bar 77 is described
as circular in cross section, it can also be a single
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plate. If a single plate configuration is usedJ a
number of such plates are disposed around the periphery
of the base plate 34 so that the combined effect of
the single member 77 is to uniformly separate the sup-
port plate 54 from the base plate 34.
The punch plate assembly support plate 54 isintegràlly attached to the punch plate assembly clamp
plate 52 by a plurality of support plate to clamp plate
bolts, one of which is shown at 80. Disassembly of the
clamp plate 52 from the support plate 54 allows assem-
bly of a plurallty of primary punch plate assembly
stroke limiters, one of which is shown at 90, to be
positioned within an opening 92 carried by the clamp
plate 52. Each primary stroke limiter rests at an
interface 94 with the support plate 54. The stroke
limiter 90 extends through openings 96 and 98 carried
by the carrier plate 30 and the base ~ate 18. The
stroke limiter is ln engagement with the base plate
16 at an interface identified as 100.
A plurality of secondary punch plate assembly
stroke limiters are carried by the punch plate assembly
clamp plate 52. One of the stroke limiters is shown
at 102 attached to the plate 52 by a bolt 104. In
Figure 1, an end surface 106 of the secondary punch
plate assembly 102 is shown spaced from the under-
surface 107 of the carrier plate 30 by the distance
indicated by a line 108. This distance 108 represents
the distance to be traveled by the carrier plate 30
from the 4pen position to the intermediate position, as
described in greater detail with reference to Figures 4
and 5.
The fixed mold half fixed base plate ~
carries a sprue bushing at 110 held in place by a
sprue bushing lock ring 112. The sprue bushing 110
has an opening 114 ~hich communicates at one end 115
with an injection no~.zle 116 of the injection ~olding
machine and at another end 117 with the video disc
cavity.
The fixed mold half expanding base plate 18
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carries a fixed platen 120 attached thereto by a number
of bolts, one o~ which is shown at 122. The fixed
platen 120 carrles a fixed stamper 124 held against the
fixed platen 120 at its inner radius by a centering
die locator and fixed center stamper clamp 126, and
held at its outer radius by a fixed outer stamper ring
clamp 128. The clamp 126 is held in place by a center
clamp retaining bolt 130 which passes through the fixed
mold half expanding base plate 18 and the fixed platen
120. The fixed outer stamper ring clamp is shown in
greater detail in Figure 10. The relationship between
the fixed center stamper clamp 126 and the fixed
stamper 124 is shown in greater detail with reference
to Figure 9.
The moving mold half carrier plate 30 carries
a moving platen 140 attached thereto by a number of
bolts, one of which is shown at 142. The moving platen
. 140 carries a moving stamper 144 held against the
platen 140 at its inner radius by a centering punch
locator and moving center stamper clamp 146 and at its
outer radius by a moving outer stamper ring clamp 148.
~ oth outer ring clamps 128 and 148 can be
effectively held in place by bolts countersunk in their
respective platens 120 and 140 and extending through
the platens into the rings 128 and 148. The bolts
would provide a fixed connection ~hile the configura-
tion schematically shown to the left edge of the
platens 120 and 140 provide a releasable connection.
~ he moving platen 140 is releasably attached
to the movin~ mold half carrier plate 30 by a center
clamp locking assembly 150. The assembly 150 can also
comprise a number of bolts which would bolt the clamp
146 to the platen 140 as does the assembly 150. The
bolts replacing the assembly 150 are countersunk with-
in the carrier plate 30 in a manner similar to the
positioning o~ the bolt 142.
A sprue ejector pin 155 has a sprue ejector
pin base nut 158 resting against a piston 159 of an
air cylinder 160. A center hole punch 162 comprlses a
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vertical center hole forming punch member 164 and a
horizontal center hole forming punch member 166 having
a punch end peripheral surface 167. A center hole
punch adjusting nut 168 is attached to the bottom end
170 of the vertical punch member 164 and rests against
the surface 94 of the punch plate assembly support
plate 54. The horizontal punch member 166 of the
center hole punch 162 carries an undercut 173, as
best seen in Figure 5, on an interior surface 174
which forms a portion of the sprue region. During
injection of the molten plastic material, some sprue
material fills the undercut region. During separation
of the fixed mold half expanding base plate 18 from
the moving mold half carrier plate 30, the plastic in
the undercut region holds the sprue 175 to the punch
- 162. The centrally apertured part is shown at 175a.
~ The air cylinder 160 is bolted to a surface
180 of the assembly support plate 54 by bolts 182. As
a design consideration, the cylinder 160 fits within
an opening defined by a surface 184 carried by the
base plate 34. An air intake passage into the cylinder
160 is schematically shown at 186 while an exhaust port
is æhematically shown at 188.
Referring generally to Figures 3 through 6,
the operation of the injection mold apparatus is de-
scribed. Schematic representations are shown illus-
trating basic movements provided by the standard
injection molding machine, previously identified,
which cooperates with the remaining elements of the
tool 10 to provide the molding apparatus of the present
invention. These basic steps form a portion of the
method of the present invention and the basic machine
elements which perform these movements also form a
portion of the injection molding apparatus of the pre-
sent invention. These basic movements and apparatusprovided by and contained ~thin a standard injection
moldin6 machine is schematically shown with reference
to Fi~ure 3.
The injection molding apparatus is shown in
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the closed position in Figure 3. This closed position
is de~ined in part with the end surface 100 of the
primary punch plate assembly stroke limiter 90 in
contact with the fixed mold half fi~ed base plate 16.
The secondary punch plate assembly stroke limiter 102
is spaced a distance 108 from the surface 76 of the
moving mold half carrier plate 30. The ejector pin
156 is in its retracted position. The horizontal
portion 166 of the punch assembly 162 is in its re-
tracted position. An end surface 1~9 of the punchassembly 162 and the opening 114 of the sprue bushing
110 defines the sprue passage. The first and second
mold halves define an annular cauity surrounding the
sprue passage. The annular cavity and the sprue
passage form, respectively, a centrally apertured part
175a and a sprue 175 when heated material is in~ected
therein.
A first selectively actuated means 190 causes
motion of the second mold half 14 betl~een a closed
location (Figs. 1 and 3) and the open locations (Figs.
5 and 6). The first selectively actuated means com-
prises a piston 191 (Fig. 3) riding in a cylinder 192.
A connecting rod 193 connects the piston 191 to the
base plate 34. Pressurized fluid is admitted into the
cylinder 192 through a fluid valve 194 to move the
second mold half 14 from the closed location (Figs. 1
and 3) to the open location (Figs. 5 and 6). Pressur-
ized fluid is admitted into the cylinder 192 through a
fluid valve 195 to move the second mold half 14 from
the open location (Figs. 5 and 6) to the closed loca-
tion (Figs. 1 and 3).
When the first and the second mold halves 12
and 14 are in the closed location (Figs. 1 and 3)/ (a)
an end portion 189 of the punch 162 and the sprue bush-
ing opening 114 define a sprue passage and (b) the firstand second mold halves define an annular cavity sur-
rounding the sprue passage. The annular cavity and
the sprue passage form, respectively, a centrally
apertured part 175a and a sprue 175 ~hen heated
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material is in~ected therein.
A second selectively actuated means causes
motion of the first mold half 12 with the second mold
half 14 in response to the motion of the second mold
half from the closed location (Figs. 1 ~ 3) to a loca- -
tion which is intermediate (Fig. 4) of the closed
location and an open location (Figs. 5 & 6) whereby
the annular cavlty remains closed whlle the flrst and
second mold halves move from the closed location to
the intermediate locatlon The second selectively
actuated means comprises a latching means 197 com-
prising a fixed base plate 216 attached to the fixed
mold half expanding base plate 18 by a plurality of
bolts 218. A first latch member 220 is bolted to the
!~ 15 fixed mold half rixed base plate 16 by a plurality of
bolts 222. A second latch member 224 is bolted to
the moving mold half carrier plate 30 by a plurality
of bolts 226. I~hile this latch is a standard latch,
its mode of operation has been specifically incorpor-
ated into the present invention and as such it repre-
sents an integral operatin~ mechanism within the inven-
tive combination. This latch mechanism is a standard
commercially available latch identified as the "~iffy
latch" Model LL-201 manufactured by the Detroit Mold
and Engineering Company.
~ riefly stated, the method of operation of
the latch ctanters around a horizontal disposed plvoting
latch member 230 having a pivot pin 232 having a sur-
face 234 which engages latching surfaces carried by
each latch member 220 and 224. In the views, it shows
the surface 234 and the latching surfaces of the member~
220 and 224 are all represented by the line 234 since
all these members are shol~n from the top view The
length of the pivot pin indicated by the length of the
line 234 represents the extent to which the first
latch member 220 can move away from and with relation
to the second latch member 224, while the latch re-
mains in the latclled condition. This distance is
represented b~- tile length of the line 235 shown in
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Figure 4. The latching means 197 functions to hold
the fixed mold half expanding base plate lo against
the moving mold half carrier plate 30 while ~oth last
identified members move a distance indicated by the
length of the line 235 shown in Figure 4.
Figure 4 shows the pivot pin 232 ln its fully
extended p~sition at the instant the first latch member
220 has moved the full distance with relation to the
second latch member 224. The latch mechanism 197
keeps the annular cavity closed while the first and
second mold halves move from the closed location to
the intermediate location.
Referring back to Figure 3~ an expanding base
stroke ]imiter comprises a plurality of bolts, one of
which is shown at 240. The bolt 240 has a shank por-
tion 2~2 fitting within an opening 244 carried by the
fixed mold half fixed base plate 16. A head member
245, carrying a shoulder 246, is integrally connected
to the shank member 242. The stroke limiter 240 is
threadingly engaged with the expanding base plate 18
as shown at 248. A plurality of such stroke limiters
240 are provided around the periphery of the base
plate 16 and function to llmit the movement to the
fixed base plate 16 with relation to the expanding
base plate 18 during the rotation of the pivot latch
member 230 during the movement of the tool from its
closed ~sition shown in Figure 3 to its intermediate
position shown withln Figure 4.
Third selectively actuated means 250 locks
3o the punch assembly 50 in place while the first and
second mold halves 12 and 14 move from the closed
location (Figs. 1 ~ 3) to the intermediate location
(Fi~. 4)~ at which position the sprue 175 is fully
severed from the part 175a by the peripheral surface
167 of the punch end portion 166. h portion of the
sprue bushing where the punch end portion 166 enters
serves as a die. Third selectively actuated means
250 comprises a piStOIl 252 riding in a cylinder 254.
A con2lecting rod 256 connects the piston 252 to the
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punch plate assembly support plate 54 through an open-
ing in the base plate 34 defined by a surface 257.
Pressurized fluid or air is admitted to the cylinder
254 through valve 258 to lock the punch plate assembly
5 support plate 54 in contact with the base plate 16 at
interface 100 while the first and second mold halves
12 and 14 move from the closed location (~igs. 1 & 3)
to the intermediate location (Fig. 4). After the second
mold half 14 reaches the intermediate location (Fig.
4), the punch plate assembly support plate 54 moves in
conjunction with the second mold half 14 from the
intermediate location (Fig. 4) to the open location
(Figs. 5 & 6). This is accomplished by opening the
valve at 258 and thus reducing the pressure holding
piston 252 against the punch plate assembly support
- plate 54 alone or in conjunction with the admission of
pressurized fluid or air through valve 260 to drive
piston 252 back to its retracted position.
Referring to Figure 4, the tool 10 is in its
intermediate ~sition. The intermediate position is
defined, in partJ as that position l~herein the shoulder
246 of the expanding base stroke limiter 240 ls in
contact with the fixed mold half fixed base plate 16
at the interface identified as 246. The first latch
member 220 has retracted from the second latch member
224 by a distance indicated by the line 235 and the
pivot pin 232 has rotated in the direction indicated by
an arrowhead 270 to its maximum latched position just
prior to bpening. The connecting rod 256 of the third
selectively actuated means 250 bears against the sur-
face 1 80 of the punch plate assembly support plate 54
maintaining contact of the primary punch plate assembly
stroke limiter 90 with the fixed mold half fixed base
plate 16 at the interface lO0. With the third selec-
35 tively actuated means 250 maintaining contact ofthelimiter 90 with the base plate 16 and holding the
punch assembly 162 stationary with relation to the
sprue bushing llO, the fixed mold half expandin~ base
plate 18 and the moving mold half carrier plate 30
JL ~ 2 ~ 4 ~ ~
-17-
move in the direction indlcated by an arrow 272 under
the admission of fluid by the valve 194 intothe cylinder
192 of the first actuated means 190. A punching actlon
occurs between the horizontal portion 166 of the punch
162 and the centering die locator and fixed center
stamper clamp 126 for severing the sprue 175 from the
part 175a, An annular disposed portion 274 o~ the part
175a remains attached to the sprue 175. The portion
274 is that part positioned between and in contact
with the end surface 1~9 of the punch 162 and the end
surface 299 of the sprue bushing 110. The sprue 175
is held by its undercut 173 to the punch end surface
189 and the part 175a is resting on the punch end peri-
pheral surface 167. It should be noted at this point
that the main parting line indicated at 278 between
~ the expanding base plate 18 and the carrier plate 30
illustrates that the two plates are still firmly held
together by the second selectively actuated means 197.
When the combined movement Or the expanding
base plate 18 and the carrier plate 30 is such that
surface 76 of the carrier plate 30 contacts surface
106 of the secondary punch plate stroke limiter 102,
and when surface 24S of the stroke limiter 240 contacts
fixed base plate 16, the latching means 197 opens.
The expanding base stroke limiter 240 stops the move-
ment of the base plate 16. The actuating means con-
tinues to open the cavity by continuing movement of the
second mold half 14 including the punch assembly 50
to the open position shown in Figure 5.
3 Figure 5 shows the mold injection tool 10 in
its open position. In the open pOSition the shoulder
246 of the expanding base stroke limiter 240 is in
contact with the fixed mo~d half fixed base plate 16
at the interface identified by numeral 246. The pri-
mary punch plate stroke limiter 90 is fully withdrawn
from the base plate 18. The latching member 230 is
fully rotated in the direction indicated by the arrow
270 such that the pivot pin 232 is disengaged from
both the upper latch member 220 and the lower latch
~L~244~8
-18-
member 224 A latching surface 2~0 of the first latch
member 220 is shown in its disengaged position from
the pivot pin 232. A latching sur~ace 282 of the second
latching member 224 is shown in its disengaged positi~
from the latching surface 234 ~ the latching means
197. The sprue 175 is attached to the end of the
e~ector pin 156 and carries an annular protuberance
at 284 which corresponds to the undercut 173. During
the in~ection of the molten material into the sprue
passage and the annular cavity, theprotuberance 284
was formed in the undercut 173.
The piston 159 of the air cylinder 160 is
shown in its extended position whereby the ejector
pin is moved forward carrying the sprue 175 and its
annular part 274 free of the end 189 of the punch 162.
The piston 159 is caused to move its forward position
by admission of pressurized fluid through the valve
186.
With the sprue 175 separated from the part
175a, the next function to be performed is the removal
of the sprue from the end of the ejector pin 156.
Referring to Figure 6, the tool 10 is shown
in the fully open position and the e~ector pin 156 is
shown in its retracted position. The retracted posi-
tion is caused by the admission of fluid into the valve188 for moving the piston to its second retracted
position as shown in Figure 6. In the movement of the
ejector pin 156 back to its retracted position in the
direction as shown by the arrow 286, the protuberance
at 284 engages the surface 189 of the punch for separ-
ating the sprue from the ejector pin 156 as shown in
Figure 6.
Referring to Figure 9, there is shown an
expanded view of that portion of Figure 1 shown within
circle 9. The fixed platen is shown at 120 having
the fixed stamper 124 held thereto by a finger 126a of
the centering die and rixed center stamper clamp 126.
~ le moving platen is shown at 140 having the
moving stamper 144 held thereto by a finger 146a of
4~68
(,
-19-
the centering punch locator and moving center stamper
clamp 1~6. T,le sprue bushing 110 is shown having its
,; lower end 117 positioned in proximity to the ejector
pin 156. The horizontal punch member 166 is shown
5 having the undercut 173 positioned in the inner surface
174. Assuming that the cavity defined by the members
just above described is filled with hardened plastic
material injected during the injection cycle of the
injection molding machine, the sprue is shown at 175,
the annular portion 274 is shown attached integrally
formed with the sprue 175. The protuberance 284 is
also shown in integral ~ormation with the sprue 175.
It has been found that the design of the sprue
passage, including an annular shaped gate passage 298
positioned intermediate the sprue opening 114 and a
video disc cavity 306 formed between stampers 124 and
144, should possess a configuration such that the
inJected material advances across the stamper surface
at a uniform rate. In order to achieve this desired
20 ef~ect, the annular shaped gate passage 298 assumes
a unique rorm comprising a plurality of annularly
shaped passage sections and each section has an entry
region and an exit region. The exit region of one
section corresponds to the entry passage of the follow-
25 ing section.
The first annular section is formed betweenan end surface 299 of the sprue bushlng 110 and an
end surface 189 of the punch 166 as indicated by the
bracket 300. Each of the surfaces 299 and 189 lie
at an angle (f three percent with the horizontal. Sur-
face 299 lies three percent above the horizontal and
line 189 lies three percent below the horizontal. The
entry region of this first sectlon 300 is at llOa.
The exit section is at llOb. The distance between
surfaces 299 and 189 at the exit region equals the
thickness of the cavity 306. ~y observation, the
entrance section betweell 110~ and 165a is thicker than
the exit region between points llOb and 166b. This
means that a pressure dir~orential exists between
~2446~
(
--20--
regions llOa and 1 lOb .
A second annular section is formed by a por-
tion of the surface 126b and a portion of a surface
1~6c ~ the fixed center stamper clamp 126 and the
g moving center stamper clamp 146. This second region
is indicated by a bracket 302. The surfaces 126b and
146b are spaced apart a distance equal to the thicl~ness
of the video disc cavity 306 and are coextensive over
their entire length.
A third annular section of the annularly
shaped gate passage 298 comprises relatively short
portions 126c and 146b of the fixed center stamper
clamp 126 and the moving center stamper clamp 146,
respectively, as indicated by the bracket 304. The
1~ entrance region of the third annular section equals
the thickness ~ the video disc cavity 306 and the
exit region is considerably smaller than the entrance
region.
A fourth annular section of the annularly
2~ shaped gate passage 298 is formed by a portion 125d
and 146d of the fixed center stamper clamp 126 and the
moving center stamper clamp 146 as indicated by
bracket 305. The exit section of the fourth annular
section is an entry nozzle into the video disc cavity
2g 306.
In operation, the hot material to be injected
into the video disc cavity for forming the video disc
record enters the sprue passage 114 as a hot melt and
then spreads out circumferentially around the sprue
30 passa~e 114 into the annularly shaped gate passage 298
and finally into the video disc cavity 306 until it
reaches the outside dimensions of the cavity as more
fully discussed with reference to Figure 10. The
machine is held in a quiescence position until the
3~, molten plastic solidifies to a certain temperature as
is more completely discussed with reference to Figures
7 and 8. During the previously described injection
cycleJ the hot melt enters the entrance region ~
passage 298 at a greater rate than it can exit the
~.2~
2 1 -
same passage 298 through the section identified by
the bracket 3~5 because the exit aperture from the
fourth annular section 305 is necked down relative to
the entrance section at the first annular section 300.
The third annular section 304 acts as a partial re-
strictor to the flow of molten material. The first
and second sections 300 and 302 act as a pressure
reservoir and distribution header for the flow of
material to insure that an even flow of molten plastic
flows into the video disc 306 with minimum disturbance
to material flow. This control of the molten material
through the restrictor section 304 provides the added
advantage of makillg very round video disc records with
informati`on tracks on the video disc records which
closely approximated perfect circles. This control
in formation of both the round video disc records and
the tracks closely approximating perfect circles
would not be availab].e if the annular gate passage
were not used.
Referring to Figure 13, there is shown a
graph showing the relationship between the thickness
of an acceptable video disc and the birefringence at
a radius from the center of the sprue passage. Curve
A of Figure 13 shows a variation in thickness of plus
or minus two thousandths of an inch from a nominal
value of forty-four thousandths of an inch over the
information carrying portion of the video disc sur-
face. Curve B shows the change in birefringence over
the same region of the disc surface. The change in
birefringence is from two nanometers to seven nano-
meters.
Referring to Figure 14, curve A shows the
relationship betweell birefringence of an unacceptable
video disc men]ber having a thickness of plus two to
minus five thousalldtlls of an inch from a nominal value
of forty-four thousandths of an inch over the informa-
tion carryillg pOl'tiOn of the-video disc surface.
Curve ~ sh~ws the change in birefringence over the
same regioll ~ the disc surface. This change in
68
- 22 -
birefringence varies from a maximum of twenty-two to a
minimum of two nanometers. It has been found that a
video disc will only operate when the birefringence
of the video disc is substantially uniform over the
playing surface. Referring back to Figure 13, the
information carrying surface of the video disc lies
between fifty-five millimeters and one hundred and
fifty millimeters wherein the value of birefringence
varies from a maximum of seven to a minimum of two.
It has been found by experimental study that the video
disc exhibiting the characteristics shown with refer-
ence to Figure 13 is suitable for play on a video disc
player as described in Elliott patent, U.S. Patent No.
3,829,622 where the disc having the characteristics
shown with reference to Figure 14 does not perform
satisfactorily on the same player.
Referring to Figure 10, there is shown the
exploded view of that portion of Figure 1 shown within
the circle 10. The fixed outer stamper ring clamp is
shown at 128 and the moving outer stamper ring clamp
is shown at 148. The fixed platen is shown at 120 of
Figure 1 for holding the fixed stamper 124. The fixed
stamper 124 terminates a distance from the moving fixed
outer stamper ring clamp 128 as indicated by the length
of the bracket 307. This allows the stamper 124 to
expand outwardly until contact is made with the ring
clamp 128. This expansion area for the fixed stamper
124 allows the stamper to expand as the heated mater-
ial is injected into the video disc cavity.
The moving stamper 144 is held to the moving
platen 140 by the moving outer stamper ring clamp 148.
The fixed stamper 144 terminates at a point removed
from the ring clamp 148 a distance as indicated by the
bracket 308. A foot 310 of the fixed outer stamper
ring clamp 128 helps to hold the moving stamper 144
in place yet allow the stamper 144 to expand through
the distance as indicated by the bracket 308 in response
to the heat from the injected molten material.
~2~4~8
-23-
When the molten plastic is injected into the
video disc cavity, it is important that the video disc
have a substantially uniform thickness across the play
area of the video disc as illustrated in Figure 13.
When the thickness of the video disc varies six
thousandths of an inch, a non-playable disc results as
illustrated in Figure 14. When the thickness of the
video disc is maintained within two thousandths of an
inch as shown in Figure 13, a playable disc results.
It has been found that allowing the upper sta~per and
the lower stamper to expand in a horizontal direction
as indicated by the brackets 307 and 308, a playable
disc results because the stamper expands to fill these
areas and does not buckle when subjected to the heat
of the injected molten plastic material causing a
variation in thickness of the video disc member. A
passage 312 allows venting ~ the video disc cavity
during the injection cycle.
The cooling system provided in the instant
invention is calculated to remove heat from the tool
10 caused by the injection of molten plastic into the
sprue passage and video disc cavity. Cooling pre-
vents stress imperfections in the finished video disc
record. The absence of stress imperfections improves
the birefringence characteristic of the finished video
disc record.
The cooling channels will be described with
reference to Figures 1, 2, 7 and 8. Referring
collectively to Figures 1 and 8, a sprue bushing cool-
ing channel is shown at 350 having an entry valve at352 and an exit valve at 354. As seen best in Figure 1,
the cooling channel 350 is spirally shaped and has
four threads per inch extending from a position closer
to the end 115 of the sprue passage 114 and extending
down towards the end 117 of the sprue passage 114.
The spiral then reverses itself bac~ up the sprue
bushing and exits from the exit valve 354. An 0-ring
is shown at 356 to provide a fluid tight connection
between the sprue bushing cooling channel 350 and the
~-~.Z4~t;8
-24-
sprue bushing lock ring 112.
Rererring to Figure 8, a fixed platen sprue
region cooling channel is shown at 357 having an
entrance valve at 358 and an exit valve at 359. The
plurality of spiral shaped turns in the cooling channel
357 is represented by a single turn 357a shown in
Figure 8 at the center Or the Figure. A rixed platen
inner region cooling channel 360 is shown having an
entrance valve at 362 and an exit valve at 364. The
entrance point is at the inner radius and spirals out
a plurality Or turns be~ore exiting the exit valve 364
ror providing an inner cooling zone for the fixed
platen. A fixed platen intermediate cooling channel
is at 370 shown having its input valve at 372 and its
exit valve at 374. The intermediate region cooling
channel provides a second cooling zone to the fixed
platen.
A fixed platen outer region cooling channel
380 has its input valve at 382 and its exit valve at
384. The fixed platen outer region cooling channel
provides a further cooling zone to the fixed platen.
Referring to Figures 2 and 7, there is shown
a plurality of cooling zones associated with the
moving mold half 14. A moving platen, punch region
cooling channel is shown at 391 having an input valve
at 393 and an exit valve at 395. This punch region
cooling channel malces one turn around the punch region
as shown at 390a with reference to Figure 2 and then
exits the exit valve at 395. The hottest portion of
the tool 10 is at the sprue and punch region where
the molten material enters from the injection molding
machine.
A moving platen inner region cooling channel
is shown at 400, having an input valve at 402 and an
exit valve at 404. The moving platen inner region
cooling channel mal~es a number of turns around the
platen before exiting through the exit valve 404. me
moving platen innel region cooling zone provides a
further cooling zolle for the moving platen. A moving
~ ~ 2'~46~3
.,.. , ~ '
platen intermediate region cooling channel 410 is
shown having an input valve at 412 and an exit valve
shown at 414. The moving platen intermediate region
cooling channel provides a further cooling zone for
5 the moving platen. A moving platen outer region cool-
ing zone 420 is shown having its ~put valve at 422
and the output valve at 424. ~he moving platen outer
region cooling channel provides for the cooling zone
for the moving platen. Any suitable cooling fluid,
including water, can be utilized in any one or all
cooling zones.
Both the moving platen 140 and the fixed
platen 120 are cored in the manner shown with refer-
ence to Figures 1 and 2 to provide for the plurality
- 15 of cooling channels previously described. A pair of
- 0-rings are provided at 366 and 368 to provide a
fluid tight connection for the fixed p laten sprue
region cooling channel 357 of the fixed mold half 12.
A second pair of 0-rings are provided at 390 and 392
20 to provide a fluid tight connection for the plurality
of cooling zones 360, 370 and 380 formed in the fixed
platen 120. A further set of 0-rings are provided at
394 and 396 to provide a fluid tight connection for
the plurality of cooling zones 400, 410 and 420 formed
25 in the moving platen 140. Another set of 0-rings are
provided at 430 and 432 to provide a fluid tight
connection for the moving platen punch region cooling
channel 391.
Referring to Figure 7, the moving platen 140
30 includes à plurality of transverse cooling channels.
A first moving platen transverse cooling channel is
shown at 440 having its input valve at 442 and its exit
valve at 444. A second moving platen transverse cool-
ing channel is shown at 446 having its i~put valve at
35 448 and its exit valve at 450.
Referring to Figure 8, the fixed platen 120
includes a plurality of tra~isverse cooling channels.
A first fixed platen transverse cooling channel is
shown at 452 having its input valve at 454 and its exit
~.Z~8
-26-
valve at 456. A second fixed platen transverse cool-
ing channel is shown at 458 having its input valve at
460 and its exit valve at 462.
It is important to note that a high degree of
concentricity between the record spiral track and the
record center hole is obtained because both operations,
the formation of the spirally tracked record and punch-
ing of the sprue to define the record center holeg are
performed in a single set-up. In the set-up, the inner
surfaces on the stamper cooperate with the correspond-
ing mating surfaces on the mold to obtain highly accur-
ate positioning of the stamper on the mold. The outer
surface o~ the stamper is allowed to float as previously
discussed with reference to Figure 10. Similarly, the
punch peripheral surface which defines the record
center hole is very precisely located relative to the
mating surfaces on the fixed center stamper clamp 126.
Since both the stamper, which forms the record spiral
track, and the punch peripheral surface, which defines
the record center hole, are very carefully aligned with
respect to the mold~ a high degree of concentricity
between the record spiral track and the record center
hole is obtained.
