Note: Descriptions are shown in the official language in which they were submitted.
7~
MEq~IO~ AND MEANS FOR REPLICATIN~
CENTRALLY APERTURED VIDEO DISC RECORDS
TECHNICAL FIEID
Thls lnvenkion relates generally to a method
and apparatus for molding a centrally apertured part;
and more particularly concerns a method and apparatus
~or injection molding a centrally apertured and
spirally tracked record, such as a video disc.
BACKGROUND OF T~E PRIOR ART
An apparatus ~or produc-Lng injection molded
and centrally aperturecl video dlscs is shown in U.S.
Patent No. 3~989~436, issued November 2, 1976.
BRIEF SUMMARY OF THE INVENTION
The lnvention is not only use~ul for inJec-
tion molding centrally apertured vldeo disc recordsg butis also applicable to the ~ormation o~ in~ection molded
records requiring an accurately positioned centrally
placed aperture.
In certain video disc systems, video ln~orma-
tion is recorded in the ~orm of light scattering orlight reflecting members positioned in a spiral track
on the sur~ace o~ a centrally apertured record. For
~ playback, the record is mounted on a rotatable turn-
-~ table havin~ a spindle which engages the record aper- -
ture for~centering, and then relative motion ls
e~tablished between the record and a reading assembly.
The reading assembly includes a laser optlcal system
for generating a laser beam and ~or directing the laser
beam to impinge upon a splral track which contains the
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video lnformation. The optical system includes an
objective lens system which directs the laser beam ko
the spiral track and also collects the reflected slgnal
from the spiral krack ~or transmisslo~ to associated
electron-lc circu~try which translates the detected
re~lectlons into s-lg~als suitable ~or a visual display
by a standard home type television receiver. A system
o~ the above-ment:Loned kype is described in U. S.
Patenk 3,829,622~ issued to James E. Elliott and
ass-Lgned to the Assignee ~ the present lnventlon.
In such a video disc system, it has been
recogniæed that, not only the average speed of relative
motion between khe impinging laser lighk beam and the
record must be maintained at a predetermined speed of
1800 r.p.m., but the cyclical variations about the
average speed must be limited ~or proper playback.
It is desirable to reduce the cyclical speed variation
to assure that the synchronizing pulses in the reco-~ered
television signal are fairly stable and within the lock-
up range o~ the de~lection circuits ~ the televisionreceiver. The cyclical speed variakions are particu-
larly unpleasant when the recorde~ in~ormation is a
color television sLgnal.
One of the sources o~ cyclical speed variations
is the record eccentricityO For proper playback of the
video discg it is important that the replLcated record's
center hole is concentrlc wlth the spiral groove
center to a high degree of accuracy. As discussed ln
the a~orementioned Elliott patent~ the time base cor-
3 rection circultry is useable to achie~e correctlon forsuch cycllcal speed variations to within the limlts o~
the time base correcting circuits. More specifically,
a time base correcting c^lrcuit has operaking limits
itself and can only correct ~or a certain amount of
error. ~herefore, it is preferred to form as perfect
video disc record as possible during the injection
molding operation.
The concentricity bekween the center hole of
the record and khe record spiral trac~ is particularly
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important when the spiral tracks are spaced a fraction
of a micron from track center to track center~ prefer-
ably one-half micron to one micron. The video disc
member useable with the Elliott video disc player has
light reflective and light scaktering members positioned
in track-like fashion on the information bearing sur-
face of the video disc member. These light reflective
or light scatterlng members are preferably sized to
equal one-quarter of a wavelength of the incident
light along the beam axis. More speclfically, typical
light scattering structure~ are more completely de-_
scribed in Canadian Patent 1,066,411 of Manfred Jarsen,
entitled ~'Replication utilizing a casting Process".
~~ In the Elliott system using a laser beam
re~lection system for reading the information tracks
on the video disc, the video disc must be essentially
birefringence free in the ~ense that it does not
contain impurities embedded in the plastic material
which give a false reflection or light scattering
effect to the impinging laser beam. These lmpuritles
could include small particles of matter, left over
from the previous in~ection cycle, being mixed with
the new material needed in the present cycle~ These
impuritles also induce stress forces formed withln
the plastic material durlng the lnJection cycle.
The concentricity of the ~inished molded
video disc member ls required to achieve f'aithful
reproduct-lon of the video il~formation contained there-
on. The center of graYity must be posltioned withln
ten mils from the center of rotat:Lon o~ the video disc
to limit the vibration due to static imbalanceO The
information tracks should be concentric with the center
o~ rotation within one to two mils for good tracking
and to fall within the time base correction capability
o~ the electronic cirGuitry associated wlth the
Elliott player. Concentricity of the information
tracks with the center of rotation are achie~edg in
,
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part~ by prov-Lding a stamper member having means ~or
allowing expansion of 'che stamper member w-Lth-Ln the
video disc cavity in response to the heat assoclated
with the injected plastic material. Concentricity can
also be da~aged during the sprue e~ection or aperture
punch-ln~ steps. The aperture punching step must be
performed without set~ing up a lateral shear force
which lnherently moves a portion of the v-ldeo disc
further towards or further away f'rom the center of
rotation during the punchlng operatlon.
lt is an ob~ect of the present invention to
provide a video disc record without flow lines and
other s~rface de~ects in ~hat portion of the record
contalning the spiral shaped -lnformation tracks.
It ls 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 v~deo disc used ~or recordlng the video
information traclcs.
A still further ob~ect of the present lnven-
tion is to provide a platen assembly having means ~or
allowing the stamper structures to freely expand within
predetermined limits in advance o~ the inJected molten
plastic material and the heat created therefromO
Another obJect o~ the present invention is to
provide an inJection molding tool having cooling means
for the platen subassembly.
The productlon of a video disc record having
unifor~ values ~ b-Lrefringence over the entire in-
3o formation bearing surface of the video disc member is
achleved ln part by employing holdin~ means for allow-
lng the v-ideo disc stamper members to ~xpand under
the application o~ heat caused by the lnjected molded
material; by employing an annular shaped sprue passage
lntermediate the principal sprue passage and the video
dLsc cavity to cause the molten material to flow into
the di~c cavity in a manner avoiding stress gradlents
~ithln the ln~ected material.
A f':Lrst mold~hal~ and a seco~ mold-half are
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reciproca~,ly mounted in the to~l. A sprue bushin~
having an opening in communication with an injection
nozzle is secured to the platen. A punch, having an
end portion in registr~ with the sprue bushing~ is
rec-lprocably mourted relative to the second mold-half.
~hen the second molcl-hal~ is in a closed locationJ
(1) the punch end portion and the opening in the sprue
bushing define a sprue passage~ ancl (2) the first and
the second mold halves de~ine an annular cavity sur-
rounding the sprue passage. The annular cavlty andthe sprue passage rorm3 respectively~ the centrally
apertured part and the sprue when heated material is
in~ected therein. ~ter partial cooling o~ the heated
lnjected materlalg the ~`irst and the second mold halves
move from the closed location to a location inter-
mediate of the closed locatlon and an open location
whlle ~he punch is locked in place to sever the sprue
from the part along the peripheral sur~ace o~ the punch
end portion. The centering die locator and iixed
center stamper clamp portion of the first mold half,
where the punch end portion enters9 serves as a dieO
The mold halves are therea~ter separated to open the
annular cavity while the sprue is resting on the punch
end portion, and while the part is in contact with the
punch end peripheral sur~ace. ~ter the mold halves
are separated, a sprue ejector member and a part
removal member are actuated to remove, respectlvely3
the sprue and the part ~rom the punch end portion.
An improved platen assembly is described
3o having releasable means ~or centering the stamper and
~or holding the stamper in place against the platen
sur~ace. The holding means also includes means ~or
allowing the stamper to expand under the temperature
gradient o~` the heated plastic inàected mater-lalO
The stamper expands uni~ormly in ~ront of the injected
material, as the heated injected material ~ills the
video disc cavityO The platen assembly ~urther con-
tains a plurallty o~ s~parate cooling channels ~or
maintain-lng the platen at a uniform temperature across
'3 ~
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 statlonary while the fixed mold half
expanding ~ase 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
de~ined 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 centeriny locators and clamps.
In accordance with one broad aspect, the invention
relates to an injection molding apparatus for molding centrally
apertured parts, said apparatus comprising: a port for receiving
molten material, an annular cavity formed by first and second
mold halves into which the molten material is injected, and an
injection gate positioned intermediate said port and sai~
cavity, said injection gate including a disc shaped passage
whose height decreases with increasing radius such that the
molten material flows thereacross at a substantially constant
rate.
BRIEF DESCRIPTION OE' THE DR~INGS
FIGURE 1 is a cross-seckional view, partly schematic,
taken along the line 1-1 of Figure 7 of an injectlon molding
apparatus ror replicating centrally apertured and spirally
tracked records pursuant to the principles of the present
invention;
FIG~-RE 2 is a cross-sectional view, similar to Figure 1,
7~
~t.s.~ 3
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 oE 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 identified as 10 shown in Figure l;
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FI'~U~E 11 is an enlarged sectlonal view of
the area con~alned within the circle ldentif~led as 11
shown in Figure 19
FIGURE 12 ~s an enlarged sectional view taken
along the llne 12-]2 o~ Ftgure 1.
FIGURE 13 is a graph showlng a changing rela-
tionshlp in value of birefrlngence accompanying a
changing relationship in the t;hickness of an accept-
able video discg and
FI~URE lLI -ls a graph showing a changing rela-
tionship in value of b-Lrefringence accompanying a
changing relationship in the thickness of an un-
acceptable v-ldeo disc~
DET~ILED DESCRIPTION OF THE _~E TION
Ref'erring to Figures land 27 there is shown
a tool 10 for use in combination with a standard in-
jection molding machine, such as the 375 ton model
manufactured by the Stokes Division o~ Penwalt M~g.
Co. The tool 10 is used for replicating a centrally
apertured video disc recordg and comprises a fixed
mold half (first mold half) 12 and a movi.ng mold half
(second mold half) 14~ The fixed mold half 12 com-
prises a fixed mold f-lxed base plate 16 which is
attached to the fixed ~rame member of a standard mold-
ing machine (not shown) and a fixed mold half expandingbase plate 18. The base plate 16 carrles in integral
attachment therewith a plurality of maJor guide and
support pins9 one of which is shown at 20. A fixed
mold half ma~or guide and support pin bushing is shown
at 22 for reclprocally mounting the base plate 18
with the base ~ate 16 during the punching step. The
punching step is defined in part by the reciprocal
movement of the expanding base plate 18 with re~erence
to the fixed base plate 16.
The moving mold half 14 comprises a moving
mold half carrler plate 309 a moving mold half spacer
plate 32 and a moving mold half fixed base plate 34.
The moving mold half fixed base plate 34 is attached
to t~e ~rame of a standard in~ection molding machine
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(not shown). The spacer plate 32 is attached to the
fixed base plate 34 by a plurality of moving mold half
spacer plate ~olts~ one o~ which is shown at 360 The
bolts 36 are countersunk wlthin the spacer plate 32
and are uniformly spaced around the periphery of the
spacer plate 32 for f-lrmly attaching it to the fixed
base plate 34.
~ he base plate 34 is additionally attached to
the carrier plate 30 by a plural-.Lty of moving mold
hal~ clamp bolts, one of WhiC~l 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 indi-
cated by the dotted lines shown at 42. The clamp bolts
15 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 cr the bolts ~8 is countersunk within the base
plate 34 to provide a smooth contact surface 43 to the
20 plate 34.
A moving mold half major support pin bushing
is shown at 44 carr-led by the carrier plate 30. The
support pin 20 is positioned within the bushing 44 and
provides reciprocal movement bet~een the fixed mold
25 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 withdral~n from the bushings
44 during the remaining portion of the opening step.
At the full~ opened position, the support pins are
spaced from the moving stamper 144 to the same extent
35 as the prlmary pnnch plate assembly stroke limiter 90
is shown spaced from the eY~panding 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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_9_
support plate 54. The punch plate assembly 50 is
carried within the moving mold half fixed 'base pla.te 3
and is reciprocally mounted therewith by a plurality of
punch plate assembly guide pins integrally a~'cached to
the base plate 3~. One o~ the punch plate assembly
guide pins .Ls shown at 55. A punch plate assembly
clamp plate 'bushirlg is shown at 56 and a punch plate
assembly support plate bushing is shown at 58. The
~uide p-lns 55 e~Ytend through the plates 52 and 54.
10 The plates 52 and 5ll are reciprocally mounted upon the
pins 55 by the 'bushi.ngs 56 and 5~, respectively.
The guide pins 55 extend into the moving mold
half carrier plate 303 as shown by -the dotted lines 60.
A plurality o~ moving mold half carr-ler
support bars 6~ are attached to the base plate 34 by
lndiv-ldual bolts~ one o~ which is shown at 66. The
support bars 64 extend through openings in the plates
52 and 54 as ind-Lcated by the dotted lines at 72 and
74g respectively.
The support bars 6~ 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.
Re~'erring to Figure 2; a punch plate stop bar
is shown at 77 positioned -lntermedlate the punch plate
assembl~ support plate 54 and the fixed base plate 34.
The stop bar is attached to the base ~ate 34 by a
plurality of punch plate stop bar bOltsg one of which
ls shown at 78. The s-top bar 77 is c-~rcular in cross
section. A 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
assoclated with the inJection molding machine. In
this capacity~ it cooperates with the side members 34a
of the fixed base plate 34 ln withstanding the ram
pressure during the closing and closed ~ortion of the
molding operatlon. While the stop bar 77 is described
as clrcular in cross section~ it can also be a single
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plate~ If 3. single plate con~iguratlon ~, used, a
number of such plates are disposed around the per-1pher~J
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 isintegrally attached to the pllnch plate assembly clamp
plate 52 by a plurality of support plate to clamp plate
bolts~ one of whLch is shown at 80. Disassembly of the
clamp plate 52 from the support plate 54 allows assem-
bly of a plurality of primary punch plate assembly
stroke llmiters~ one of which :Ls shown at 90, to be
positioned within an openlng 92 carried by the clamp
plate 52. Each primary stroke limlter rests at an
inter~ace 94 with the support plate 54. The stroke
limlter 90 extends through openings 96 and 98 carrled
by the carrler plate 30 and the base plate 18. The
stroke limiter is in engagement with the base plate
16 at an interface ldent-lfied as 100.
A plurality of~ secondary punch plate assembly
stroke llmlters are carried by ~he 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 lg an end surface 106 of the secondary punch
plate assembly 102 Ls shown spaced ~rom the under-
surface 107 of the carrier plate 30 b~ the distance
indlcated by a llne 108. This distance 108 represents
the distance to be traveled by the carrler plate 30
from the open posit:Lon to the intermed-late posit-Lon, as
described in greater detail with ref'erence to Figures 4
and 5.
The f'ixed mold half fl~ed base plate ~
carries a sprue bushing at 110 held in place by a
sprue bushing lock ring 112. ~he sprue bushing 110
has an open-lng 114 which communicates at one end 115
wlth an inJection nozzle 116 of the injection moldlng
machine and at another end 117 with the video disc
c~vit~.
The fixed mold half expanding base plate I8
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,
,
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~ J ~J~'~3
carrles a fixed pla~en 1~0 attached thereto by a nu.rnber
o~ bolts, one of whi.ch is s'nown at 122. The ixed
platen 120 carries a fixed stamper ~24 held against the
fixed platen 1~0 at its inner radius by a centering
die locator and fixed center stamper clamp 126, and
held at lts outer radius by a flxed outer stamper ring
clamp 128. The clamp 126 -ls held ln place by a center
clamp retaining bolt 130 which passes through the fixed
mold hal~ expanding base plate 18 and the fixed platen
120. The flxed outer stamper ring clamp is shown in
greater detail in Figure 10. The relationship between
the ~ixed center stamper clamp 126 and the fixed
stamper 124 is shown ln greater detail with reference
to ~igure 9O
The moving mold half carrier plate 30 carries
a moving platen 140 attached thereto by a number o~
bolts, one of which is shown at 142. The moving platen
140 carries a moving stamper 144 held against the
platen 140 at lts inner radius by a centering punch
locator and moving center stamper clamp 146 and at lts
outer radius by a moving outer stamper ring clamp 148.
Both outer ring clamps 128 and 148 can be
effeckively held ln place by bolts countersunk in their
respectlve platens 120 and 140 and extending through
the platens into the rings 128 and 148. The bolts
would provide a ~ixed connection while the con~igura-
tion schematically shown to the left edge of the
platens 120 and 140 provide a releasable connection.
The moving platen 140 is releasably attached
to the moving 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 of the bolt 142.
A sprue ejec'cor pin 156 has a sprue e~ector
pin base nut 158 resting against a piston 159 of an
air cyl~nùer 160. ~ center hole punch 162 compr~ses a
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12-
vertical center hole forming punch member 164 and a
horizontal center hole forming punch member 1~6 havlng
a punch end peripheral surface 167. A center hole
punch adjusting nut 168 is attached to the bottom end
170 of the ver~ical punch member 164 and rests aga:inst
the surface 9~ of the punch plate assembly support
plate 5L~. The horizontal puncll mem~er 166 of the
center hole punch 16~ carr~es an undercut 173; as
best seen in ~`lgure 5~ on an lnterior surface 174
whlch f`orms a portlon of the sprue region. During
inJection of the molten plas~ic material, some sprue
material fills the undercut region. During separation
of the ~ixed mold half expandlng base plate 18 from
the movlng mold half carrier plate 30, the plastic in
the undercut reglon holds the sprue 175 to the punch
162. The centrall~ apertured part ls shown at 175a.
The alr cylinder 160 is bolted to a surface
180 of the assembly support plate 51~ by bolts 182. As
a design conslderation, the cylinder 160 fits within
an openlng deflned by a surface 184 carrled b~ the
base plate 3~. An alr intake passage lnto the cyllnder
160 is schematlcally shown at 1~6 whlle an exhaust port
- is s~hemat-lcally shown at 188.
Referring generally to Figures 3 through 6~
the operation of the injection mold apparatus is de-
scrlbed. Schematic representations are shown illus-
trating basic movements provided by the standard
injection molding machineg previously identified~
whlch cooperates with the remaining elements of the
tool 10 to provide the molding apparatus of the present
invention. These basic steps form a poxtion of the
method of the present lnvention and the basic machine
elements which perform these movements also ~orm a
portion of the injection molding apparatus of the pre-
Isent invention. These basic movements and apparatusprovided b~J and contained ~thin a standard injection
molding machine is schematically shown with re~erence
to Flgure 3.
The in~ection moldlng apparatus is shown in
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the closed position -Ln Figure 3. This closed posi~lon
is de~lned ln part with the end surface 100 of the
primary punch plate assembly stroke limiter 90 in
contact with khe fixed molcl half fi~ed base plate 16.
The secondary punch plate assembly stroke limiter 102
ls spaced a distance 108 ~rom the surface 76 of the
moving mold half carrier plate 30. The ejector pin
156 is in its retracted position. The horizontal
port~on 166 of the punch assembly 162 is ~n its re-
tracted poslt-lon. An end surface 189 of the punch
assembly 162 and the opening 114 of the sprue bushlng
110 derines the sprue passage~ The first and second
mold halves define an annular cavity surrounding the
sprue passage. The annular cavity and the sprue
passage form, respectlvely, a centrally apertured part
175a and a sprue 175 when heated material is inJected
therein.
A flrst selectively actuated means 190 causes
motlon of ~he second mold half 14 between 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) rldlng ln a cylinder 192.
A connectlng rod 193 connects the plston ~1 to the
base plate 3L~. Pressurlzed fluid is admitted into the
cylinder 192 through a fluid valve 194 to move the
second mold half 14 ~rom the closed location (Figs. 1
and 3) to the open location (F-lgs. 5 and 6). Pressur-
ized fluid ls admitted -lnto the cylinder 192 through a
fluid valve 195 to move the second mold hal~ 14 from
the open locat~on (~igs. 5 and 6) to the closed loca-
t-lon (Flgs. 1 and 3).
When the first and the second mold halves 12
and 14 are ln the closed locatlon (Flgs~ 1 and 3), ~a)
an end portion 189 o~ the punch 162 and the sprue bush-
ing openlng 114 de~lne a sprue passage and (b) the flrstand second mold halves de~lne an annular cavity sur-
rounding the sprue passage. The annular cavity and
the sprue passage form, respectlvely3 a centrally
apertured part 175a and a sprue 175 when heated
J'~ ~'3
-14-
makerial is injected therein.
A second selectively actuated means causes
motion of the :~irst mo].d half 12 with the second mold
hal~ in response to the motion of the second mold
half from the closed location (Flgs. 1 ~ 3) to a loca-
tion wllich ls interrnediate (Fig. 4) of khe closed
location and an open locatlon (~-Lgs. 5 ~ 6) whereby
the an~ular cavi.l,y remains closed while the firsk and
second mold halves move f'rom the closed location to
the intermedlate location. The second selectively
actuated means comprlses a latching means 197 com-
prislng a fixed base pla'ce 216 attached to the fixed
mold half expanding base plate 18 by a plurality of
bolts 218. ~ firsk latch member 220 is bolted to the
fixed mold half flxed base plate 16 by a plurallty of
bolts 222. A second latch member 22~ is bolted to
the moving mold hal~ carr-Ler plate 30 by a pluralikcy
of bolts 226. While this latch is a standard lateh,
lts mode of opera'cion has been specifically ineorpor-
ated into the present invention and as such it repre-
sents an integral operating mechanism within the inven-
tive combination. This latch mechanlsm is a standard
eommeroially available lateh identified as the "~iffy
lateh" Model LL-201 manufactured by the De~roit Mold
and Engineering Company.
Briefly stated, the method of operakion of
the lateh e~nters around a horizontal d~sposed pivoting
lateh member 230 having a pivot pin 232 having a sur-
faee 234 whieh engages latehing s~rfaces earried by
eaeh lakceh member 220 and 224. In the views9 it shows
the surfaee 234 and the la'cching surfaees of the member~
220 and 224 are all represented by 'che line 23~ sinee
all these members are shown lrom the 'cop view. The
len~th of the pivot pin indicated by the length of the
llne 23l~ represents the extent to whlch the first
lateh member 220 ean move away from and wlkh relatlon
to the seeond la'cch member 22~, whlle the lateh re-
mains in the la'cched eondltion. Thls dlstanee ls
represented by the len~th of the line 235 shown ~n
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Figure 4. The latching means 197 functions to hold
the ~ixed mold halr expandin~ base plate ~ against
the movir~ mold half carrier plate 30 while both last
-ldentified members move a distance lndlcated by the
length o~ the line 235 shown in Figure 4
~ igure 4 shows the pivot pin 232 in its fully
extended ~sition at the instant the first latch member
220 has moved the full d~stance 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 expandlng base
stroke limiter comprises a plurality of bolts~ one of
which is shown at 240, The bolt 240 has a shank por-
tion 21~2 fitting within an opening 244 carried by the
fixed mold half fixed base plate 16. A head member
245, carrying a shoulder 246, is ~ntegrally connected
to the shank member 242. The stroke limiter 240 is
threadingly enga~ed with the expanding base plate 18
as shown at 24~. A plurality of such stroke limiters
240 are provided around the periphery of the base
plate 16 and function to limit the movement to khe
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
(Fig. 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. A portion of the
sprue bushing ~here the punch end portion 166 enters
; serves as Q die. Third selectively actuated means
250 comprises a piston 252 riding in a cylinder 254.
connecting rod 256 connects the piston 252 to the
-~6-
punch plate assernbly support plate 54 thrGugh an open-
ing ln the base plate 34 deflned by a surface 257.
Pressurlzed fluid or a-lr is admitted to the cylinder
254 through valve 258 to lock the punch plate assembly
support plate 54 in contact with the base plate ~ at
interface 100 while the flrst and second mold halves
12 and 14 move from the closed location (Figs. 1 ~ 3)
to the lntermediate locatlon (Fig. 4). After the second
mold half 14 reaches the intermed:late location (Flg.
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 locatlon
(Figs. 5 & 6). This is accomplished by opening the
valve at 258 and thus reduclng the pressure holding
piskon 252 against the punch plate assembly support
plake 54 alone or in conjunction with the admission of
pressurized fluid or air through valve 260 to drive
p:lston 252 back to lts retracted position.
Referring to Flgure 49 the tool 10 is in its
intermedlate ~sition. The intermediate positi.on is
defined, in part~ as that position wherein the shoulder
246 of the expanding base stroke limiter 240 is in
contact with the f-lxed mold half fixed base plate 16
at the interface identified as 246. The first latch
-, 25 member 220 has retracted from the second latch member
224 by a dlstance indicated by the line 235 and the
pivot pin 232 has rotated in the direction lndlcated by
an arrowhead 270 to its maximum latched position JUSt
prlor to opening. The connectlng rod 256 of khe third
selectively actuated means 250 bears against the sur-
face 180 of the punch plate assembly support plate 54
malntaining contact of the primary punch plate assembly
stroke llmiter 90 with the fixed mold half fixed base
plate 16 at the interface 100. With the third selec-
tively actuated means 250 maintaining contact ofthelim~ter 90 with the base p ate 16 and holding the
punch assembly 162 stationary with relation to the
sprue bushing 1109 the fixed mold half expanding base
plate 18 and the moving mold half carr-ler plate 30
-17-
move in the direction indicated by an arrow 272 under
tile admission o~ fluid by the valve 194 intothe cylincler
192 o~ the first actuated means 190. A punchlng action
occurs between tne 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 of the part
175a remains attached to the sprue 175. The portion
274 ls that part positioned between and in contact
with the end surface 189 of the punch 162 and the end
sur~ace 299 o~ the sprue bushing 110. The sprue 175
is held by its u~dercut 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 a-~ this point
that the main par~ing line indicated at 27~ 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.
~len the combined movement of the expanding
base plate 18 and the carrier plate 30 is such that
surface 76 of the carrler plate 30 contacts surface
106 of the secondary punch plate stroke limiter 102~
and when surface 245 of the stroke limiter 240 contacts
fixed base plate 159 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 ln
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 flxed 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 pivo~ pin 232 is di~engaged ~rom
both the upper latch member 220 ancl the lower latch
~'s'',
-18-
member 224~ A latching surface 280 of the first latch
member 220 is shown in its disengaged position from
the pivot pin 232. A latching surface 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. Durlng
the injection of the molten material into the sprue
passage and the annular cavity~ theprotuberance 284
was formed ln the undercut 173.
The plston 159 of the air cylinder 160 ls
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 ~orward posltion
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 F-Lgure 6~ the tool 10 is shown
in the fully open position and the ejector pin 155 is
shown in its retracted position. The retracted posi-
tion is caused by 'che 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
e~ector pin 156 back to its retracted posltion in the
direction as shown b~ the arrow 286~ the procuberance
at 284 engages the surface 189 o~ the punch ~or separ-
ating the sprue from the ejector pin 156 as shown in
Figure 6.
Referring to Figure 9, there is shown an
expanded vlew of that portion of Figure 1 shown within
circle 9. The fixed pla'cen is shown at 120 having
the fixed s'camper 124 held thereto by a finger 126a of
the centering die and flxed center stamper clamp 126.
The moving platen is shown at 140 havlng the
moving stamper 144 held thereto b~ a flnger 146a of
the cenkerin~, punch locakor and moving center stamper
clamp 1l~6~ The sprue bushing 110 is s'nown having its
lower end 117 posit-ioned in prOx:~mlt~J to the ejector
pln 156. The horizontal punch member 166 is shown
5 having the undercut 173 positloned in the inner surface
17L~. Assuming that the cavity de~inecl by the members
Just above describecl is ~illed wlth hardened plastic
mater:lal injected during the in~ection cycle o~ the
lnJectlon molding machine, the sprue is shown at 175
19 the annular port-Lon 274 is shown attached integrally
~ormed with the sprue 175. The protuberance 284 is
also shown in integral formation wlth the sprue 175.
It has been ~ound that the design of the sprue
passage, including an annular shaped gate passage 298
15 positioned intermediate the sprue opening 114 and a
video disc cavity 306 formed between stampers 12~ and
14~, should possess a conflguratlon such that the
inJected material advances across the stamper sur~ace
at a uniform rate. In order to achieve th-ls desired
20 ef~ect, the annular shaped gate passage 298 assumes
a unique form comprising a plurality o~ annularly
shaped passage sections and each section has an entry
region and an exit region. The exit region o~ one
section corresponds to the entry passage of t~le ~ollow-
25 ing section.
The ~lrst annular sect-lon ls formed between
an end surface 299 o~ the sprue bushing 110 and an
end sur~ace 189 o~ the punch 166 as indi¢ated by the
; bracket 300. Each o~ the surfaces 299 and 189 lie
at an angle ~ three percent with the horizontal. Sur-
~ace 299 lies three percent above the horizontal and
line 189 lies three percent below the horizontal. The
entry region o~ this ~irst section 300 is at llOaO
The e~it section is at llOb. The distance between
~; 3~ sur~aces 299 and 189 at the exit region equals the
thickness o~ the cauity 305. ~y observation~ the
entrance section between llOa and 166a is thicker than
the e~it region hetween points llOh and 166b. This
means that a pressure dif~erential e~ists between
-20-
regions llOa and 110~.
A second annular section i3 formed by a por-
tion of the surface 126b and a portion of a surface
146c ~ the fixed center stamper clamp 12~ and the
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 thlc~ness
of the video disc cavity 306 and are coextensive over
their entire length.
A thlrd annular section of the annularly
shaped gate passage 298 comprises relatively short
portions 12~c and 1~6b of the fixed center stamper
clamp 126 and the moving center stamper clamp 146,
respectively, as indicated by the bracket 304. The
15 entrance region of the third annular section equals
the thickness cf the video disc cavity 306 and the
exit region is considerably smaller than the entrance
region.
A fourth annular section of the annularly
shaped gate passage 29$ 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 ~s an entry nozzle into the video disc cavity
2g 306.
In operatlon, the hot material to be in~ected
into the video disc cavit-; for forming the video disc
record enters the sprue passage 114 as a hot melt and
then spreads out circumferentially around the sprue
30 passage 114 into the annularly shaped gate passage 298
and finally into the video disc cavity 30~ 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 posltion until the
molten plastic solidifies to a certain temperature as
ls more completely discussed with reference to Figures
7 and 8. During the previously descrlbed inJection
cycle, the hot melt enters the entrance region ~
passage 2~v at a gr:eater rate than it can exit the
, ,~..~,
same passage 298 through the section identified b~J
the bracket 305 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 flrst
and second sections 300 and 302 act as a pressure
reservoir and distribution header for the flow of
material to -lnsure 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
information 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 available if the annular gate passage
were not used.
Referring to Figure 13g 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
in~ormation 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 between birefringence of an unacceptable
video disc member having a thickness of plus two to
minus five thousandths of an inch from a nominal value
of forty-four thousandths of an inch over the informa-
tion carrying portion of the video disc surface.
Curve B shows the change in birefringence over the
same region a~ the disc surface. This change in
--22_
birefringence varies from a maximum of twenty-two to a
minimum of two nanometers. It has been found that a
video disc l,~ill only operate when the birefringence
of the video disc is substantially uniform over the
5 playing surface. Referring back to Figure 13, the
information carrying surface cf the video disc lies
between f-lfty-flve millimeters and one hundred and
flfty millimeters wherein the value of birefringence
varies ~rom a maximum of seven to a minimum of two.
10 It has been found by experimental study that the video
disc exhibiting I;he characteristics shown with refer-
ence to Figure 13 is suikable for play on a vldeo disc
player as described in Elliott patent9 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 vie~ cf that portion of Figure 1 shown within
the circle 10. The fixed outer stamper ring clamp is
shown at 128 and the moving olter stamper ring clamp
is shown at 148. The fixed pla~en is shown at 120 of Figure
1 for holding ~he 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. Thls expansion àrea for the :Eixed stamper
124 allo~s the stamper to expand as the heated mater-
ial t5 inJected into the video d-lsc cavity.
The mov-lng 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 rlng clamp 148 a distance as indicated by
the bracket 308. A foot 310 of the flxed 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 brac-
ket 308 in response to the heat from the in~ected
molten material.
,i'~ .
-23-
I,~en the molten plastic is in~ec~ed lnto 'che
video disc cavlt~J, it -Ls important that the v~deo dlsc
have a substantially un-lform thickness across khe pla^~
area o~ the video disc as illustrated in Figure 13.
~hen the thlckness of the video d~sc varies six
thousandths o~ an inc~lg a non-playable disc results as
lllu,strated ln Figure 1~ lhen the thickness of the
video dlsc ls maintained with:Ln two thousandths of an
inch as shown in Flgure 13, a playable disc results.
It has been foun~ that allow-lng the upper stamper 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 ko fill these
areas and does not buckle when subjected to the heat
of the inJected molten plastic material causing a
varlatlon in thickness ~ the vldeo disc member. A
passage 312 allows venting ~ the video dlsc cavity
durlng the in~ection cycle.
The cooling system provided in the instant
-lnvention ls calculated to remove heat from the tool
10 caused b~J the injection o~ molten plastic into the
sprue passage and video disc cavity. Coollng pre-
vents stress imperfectlons in the finished video disc
record. The absence of stress imperfections improves
the birefringence characteristic of the finlshed video
disc record.
The cooling channels will be descrlbed with
reference to Figures 1~ 2~ 7 and 8. Referring
collectively to Figures 1 and 8g a sprue bushing cool-
ing channel is shown at 350 having an entry valve at352 and an exit valve at 35L~. As seen best in Figure 1
the cooling channel 350 is spirall~ shaped and has
four threads per -lnch 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 itsel~ back up the sprue
bushing and exits f'rom the exit valve 354O An 0-ring
is shown at 356 to provide a ~luid tight connection
between the sprue bushing cooling channel 350 and the
, ~ '
.. .
. . . .
.
f~32~
-24-
sprue bushing lock ring 112.
Referring 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 tu m 357a shown in
Figure 8 at the center of the Figure. A flxed platen
inner region cooling channel 3~0 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 of turns before exiting the exit valve 364
f'or providing an inner cooling zone f'or the fixed
platen. A fixed platen intermediate cooling channel
is at 3~0 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 reglon cooling channel
380 has its input valve at 382 and its exit valve at
384. The flxed platen outer region cooling channel
provides a further cooling zone to the ~ixed platen.
Referring to Figures 2 and 7, there is shown
a plurality of cooling zones associated with the
moving mold hal~ 14. A moving platen, punch region
cooling channel is shown at 391 having an input valve
at 393 and an exlt valve at 395. This punch region
cooling channel makes 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
ls shown at 400~ having an input valve at 402 and an
exit valve at 404. The moving platen inner region
cooling channel makes a number ~ turns around the
platen before exiting through the exit valve 404. The
moving platen inner region cooling zone provides a
further cooling zone f'or the moving platen. A moving
-25-
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
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. The moving platen outer
reglon cooling channel provides for the coollng zone
for the moving platen. Any suitable cooling fluidg
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
of cooling channels previously described. A pair of
0-rlngs are provided at 366 and 368 to provide a
fluid tight connection for the ~ixed platen sprue
region cooling channel 357 o~ the fixed mold half 12.
A second pair of 0-rings are provided at 390 and 3~2
20 to provide a fluid tight connection for the plurality
of cooling zones 3609 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 400g 410 and 420 f`ormed
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 Fi~ure 7g the moving platen 140
3o includes a plurality of transvérse cooling channels.
A f'irst moving platen transverse cooling channel is
sho7~n at 440 having its input valve at 442 and -lts eæit
valve at 444. A second moving platen transverse cool-
ing channel ls shown at 446 having its ~put valve at
44~ and its exit valve at 450.
Ref'err~ng to Figure ~g the fi~ed platen 120
includes a plurality of transverse cooling channels.
A first ~ixed platen transverse cooling channel is
sho7~n at 452 having its input valve at 454 and its exit
, ., ~
-2~-
valve ak 455. r~ S econd ~-lxecl platen transverse cool-
lng channel is shown at 45~ havlng its input valve at
L~60 and lts exit valve at L~62.
It is important to note that a high degree Or
concentricity between the record spiral krack and khe
record center hole is obtainecl because both operations,
the formakion of the splrally tracked record and punch-
lng o~ the sprue to de~ine the record center hole, are
perfo~med in a slngle set-up. In the set-up, the -Lnner
sur:~aces on the stamper cooperate wlth the correspond-
lng mating surfaces on the mold to obtain highly accur-
ate poslkioning of the stamper on the mold. The outer
surface of khe skamper is allowed to float as previously
dlscussed with reference to Figure 10. Similarlyg the
punch peripheral surface which defines the record
center hole is very precisely located relative to the
making surfaces on the flxed center stamper clamp 12~.
Slnce both the skamper~ which forms the record spiral
! krack~ and the punch per~pheral surfaceg which defines
the record center holeJ are very carefully aligned with
respect ko the mold, a high degree of concenkricity
between the record spiral track and the record center
hole is obkained~
,
- . . ~ . . .
:' '
