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Патент USA US2409959

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‘
0a, 22, 1946.,
H, G, ROGERS ET AL
‘ METHOD OF MOLDING_ PRISMS
Filed April 16, 1943
2,409,958
Patented Oct. 22, 194-6
2,469,958
UNITED’ STATES PATENT OFFICE
2,409,958 .
METHOD OF MOLDING PRISMS
‘Howard G. Rogers, Wellesley Hills, Mass, and ‘
Dexter P. Cooper, J13, Washington, D. C., as
si'gnors to Polaroid Corporation, Cambridge,
Mass., a corporation of Delaware
Application April 16, 1943, Serial No. 483,308
13 Claims.
1
This invention relates to the formation of rigid
elements from organic plastics and resins and
more particularly to methods of hardening poly
merizab-le materials ina mold to accurately im
part a desired shape thereto.
One object of the present'invention is to pro
vide a novel method of molding an optical ele
ment, such as a prism, from a polymerizable
(CI. 18—58)
2
prisms from styrene, a suitable mold I0 is pro
vided comprising a plurality of optically ?at
plates H, preferably of ‘glass, a separate plate
de?ning each of ‘the prism faces. Plates II are
so arranged that the edges thereof are not in
contact with one another, being separated by at
least the amount of shrinkage expected during
the hardening stage of polymerization. An end
material, as for example styrene, cyclohexyl
plate 12 abutsplates l l to close off one end of the
methacrylate or methyl methacrylate, whereby 10 mold and said plates are bonded together and
the deleterious effects of shrinkage‘during hard
rigidly held in position by a ‘suitable cement I3.
em'ng are/greatly minimized.
The latter’is of a type that can be readily removed
Further object-sof the invention are the provi
or separated from plates“ and i2, as by fusion
sion of a-novel method of hardening a plastic in
or by beingmechanically scraped or pried there
a mold which consists in ‘freeing the mold ele
from, the removal being ‘desired to the extent of
ments for relative movement after a preliminary
not inhibiting free movement of said plates rela
hardening of the plastic, and the inclusion in said
tive to each other. Preferred materials for the
method of novel steps ‘for automatically freeing
cement are Belmont alloy 255 or Wood’s metal.
said elements in the desired manner.
The moldable material which is preferably a
The aboveand other objects and novel features 20 partially ‘polymerized styrene or cyclohexyl
of the invention will more fully appear from the
'methacrylate monomer solution, is poured into
following detailed description when the same is
the open end of ‘said mold 10, and the mold‘and
read in connection with the accompanying draw
the contents thereof are then‘baked, or otherwise
ing. It is to be expressly understood, however,
treated, in order to advance the polymerization
that the drawing is for purposes of illustration 25 of the solution unti1 ‘a substantially rigid product
only and is ‘not ‘intended as a de?nition of the
is obtained. For styrene the initial baking ‘pref
limits of ‘the invention, reference being primarily
‘erably is carried out at temperatures between 25
had for this latter purpose to the appended
and 40'degrees C. for from one to two days, de
claims.
pending on thev size of the product being molded.
30
In the drawing, wherein like reference char
Larger‘masses of material are baked at the lower
acters refer to ‘like parts throughout the several
temperatures for a longer time. Excessive bak
views:
ing during this ?rst stage of hardening’ has been
Figure l is a perspective view'of a molding ap.
paratus ‘for carrying out the method of the in
determined to have no undesirable effects on the
?nished‘ product and accordingly the baking is
t
continued until a hardened product is assured.
Fig. 2 is a perspective view showing said ap
'At the completion of the initial baking, cement
paratus in a later stage of the process.
v‘i73‘is removed from plates H and i2 without af- '
The formation in molds of accurately surfaced
footing the ‘bond between plates H and the sur
optical elements, such as prisms, from organic
faces de?ned thereby. Plates H are thus
resins and plastics, has involved the development 40 adhesively retained in full'contact with the faces
of molding methods whereby suitable compensa
of the‘hardened product but are free-to move with
tion is made for the shrinkage which occurs when
said faces upon contraction of said ‘product.
polymerization of the resin or plastic is advanced
Thereafter the 'mold walls and the product are
vention; ‘and
through the hardening stage. The shrinkage
subjected to further heating, preferably at a
tends to causethe hardened product to pull away 45 higher temperature than the initial heating, as
from the mold surfaces, creating surface irregu
for example between 80 degrees and 90 degrees C.,
larities and internal ‘strains and destroying the
for approximately 24 ‘hours. This second- baking
homogeneity of the product. According to the
relieves ‘internal strains in the product by ‘per
‘present invention these undesirable effects of
mitting contraction thereof and advances poly
shrinkage are substantially minimized, if not 50 merization to substantial completion, ‘themol'd ‘
avoided, by carrying out the hardening of the
walls II_I serving to’maintainthe surfaces optically ,
plastic in two stages, and-by suitably freeing the
mold ‘elements for movement during the ?nal
stage.
‘
In the ‘fabrication, for example ‘of triangular
smooth during contraction.
V
‘
At the completion of the second stage of hard
ening, plates I I and 12 may bev removed from the
hardened product byiim'mersing the mold and the
t
2,409,958
-
4
3
formed prism into a water bath maintained at
the same temperature as that at which said sec
ond stage of hardening was carried out, said bath
containing a surface active agent, such as “Aero
sol O. T.” A one-percent solution of “Aerosol”
has proved satisfactory.
Unless the removal of the cement is carried
out at .the temperature of the initial bake or at a
2. The method of fabricating an optical ele
ment which comprises rigidly securing together a
plurality of mold parts to form a; mold having
the contour of said element, said parts being
spaced from one another so as to permit move
ment thereof towards one another upon removal
'of the securing means, introducing a flowable
partially polymerized polymerizable mass into
said mold, which mass, in its hardened, partially
mold walls from the molded product may take 10 polymerized condition, adheres to said mold and
which is adapted, upon substantially complete
place during said removal. To avoid this occur}
rence, it is preferable to select cement Hi from’ ' polymerization, to form a transparent, inherent
ly rigid mass, heating the mold and the contents
the class of fusible materials having their melt
ing points between the temperatures at which the
thereof until the latter harden to produce a hard
partially polymerized material to which the mold
initial and final stages of the hardening are car
parts adhere, releasing the mold parts from one
ried out. A preferred cement of this type is
another without affecting the engagement be
Wood’s metal, which has a melting point of 67
higher temperature, undesirable separation of the
degrees C. and which produces a good bond be
tween said parts and the surfaces of the hardened
product de?ned by said parts, and advancing the
tween plates il and 62 when solid. By utilizing
a cement of this character, the second baking 20 polymerization of said product to produce a
transparent, inherently rigid mass with the mold
fuses/the cement and automatically releases the
mold walls for relative movement.
parts secured thereto.
While it is preferable to effect the second stage
’ 3. The method of fabricating an optical ele
ment which comprises rigidly securing together a
of hardening at the higher temperature, it is to
plurality of mold parts to form a mold having
be understood that the temperature of the sec
ondbake may be carried out at the same temper
the contour of said element, said parts being
spaced from one another so as to permit move
ature as the ?rst.
ment thereof towards one another upon removal
' There is thus provided a novel method of
of the securing means, introducing a flowable
forming optical or other elements having highly
accurate surfaces by casting the latter in molds,
novel steps'being taken to obviate the effects of
‘_ shrinkage on the molded product. There is also
provided a novel method of securing together the
elements of a mold structure whereby said ele
polymerizable mass into said mold, which mass, in
_ its hardened, partially polymerized condition, ad
heres to said moldyand which is adapted, upon
substantially complete polymerization, to produce
a transparent, inherently'rigid mass,_advancing
35 the polymerization of said flowable mass to pro
duce a hard, partially polymerized material to
other at a desired point in the molding process.
Since certain changes in carrying out the above
which the mold parts adhere, releasing the mold
parts from one another without affecting the
'method may be made without departing from its
scope, it is intended that all matter contained in
engagement vbetween said parts and thesurfaces
the above description or shown in the accom 40 of the hardened product de?ned by said parts,
panying drawing shall be interpreted as illus
advancing the polymerization of said mass to
ments are automatically released from one an
trative and not in a limiting sense. 'For example,
it is to be expressly understood that the method
‘comprehended by the invention could be utilized
to fabricate lenses or prismatic members other
than triangular.
substantial completion to produce a transparent,
inherently rigid mass-with said parts attached
to the molded product, and removing said parts
from said product.
a
- ‘
>
4. The ‘method of fabricating an optical ele
' It is also to be imderstood that the following
ment which comprises rigidly securing together
claims are intended to cover all the generic and
speci?c features of the invention herein de
a plurality of mold parts to form a mold having
the contour of said element by means of an ad
scribedjand all statements of the scope of the in- .
'vention which, as a matter of language, might be
said to fall therebetween.
7
ing spaced‘from one another so as to- permit
movement thereof towards one another upon re
What is claimed is:
'
_
,
hesive having a low melting point, said parts be
moval of the adhesive, introducing a flowable
'1. The method of fabricating an optical ele
polymerizable mass into-said mold, which mass,
ment which comprises rigidly securing together
in its hardened, partially polymerized condition,
adheres to said mold and which is adapted upon
substantially. complete polymerization, to form
a plurality of mold parts to form a mold having
the contour of said element, said parts being
spaced from one another so as to permit move
ment thereof toward one another upon removal
of the securing means, introducing a ?owable
polymerizable mass into said mold, which mass,
a transparent, inherently rigid mass, advancing
the polymerization of said ?owable mass through
its hardening stage at temperatures below the
melting point of said adhesive, to produce a
,inits hardened, partially polymerized condition,
hard partially polymerized material to which the
adheres to said mold and which is adapted, upon
substantially complete polymerization, to form a
mold parts adhere, releasingrthe mold parts from _
one another without affecting the engagement
between said parts and the surfaces of the hard
transparent, inherently rigid mass, advancing
the polymerization of said ?ow'able mass to pro
duce a hard partially polymerized material to
which the mold parts adhere, releasing the mold
parts from. one another without affecting the
ened product de?ned by said parts by fusing said
adhesive, and advancing the polymerization of
said mass tosubstantia-l completion'to produce
engagement between said parts and’ the surfaces
of the hardened product de?ned by said parts,
and advancing the polymerization of’ said mass
to substantial completion to produce a transpar
ent, inherently rigid mass with‘ said, partsjat
parts attached to the molded product.
ment which comprisesrigidly securing together
tached, to the, molded product;
hesirerharing a 10W meltinepoint. said parts he
_ _
a transparent, inherently rigid mass with said
5. The method of fabricating an optical-ele
a plurality of mold parts to formra mold having
the contour of said element by means of an ad
2,409,958
5
ing spaced from one another ‘so as to ‘permit
“movement thereof towards one another upon re
moval ‘of the adhesive, introducing a ‘fiowable
polymerizable mass into said mold,'which mass,
in its hardened, partially polymerized condition,
adheres to said mold and which is adapted,'upon
substantially complete polymerization,‘ to produce
6
of the securing means, introducing a 'flowable
partially polymerized polymerizable mass into
said mold, which mass, in its hardened,.partially
polymerized condition, adheres to said'plates and
which is adapted, upon ‘substantially icomplete
polymerization, to produce a‘transparent, inher
ently rigid mass, advancing the polymerizationsof
a transparent, inherently rigid mass, advancing
said flowable mass to produce a hard partially
the‘ polymerization of said ?owable mass through
polymerized material to ‘which the mold parts ad
its hardening stage at temperatures below the 10 here, releasing the plates from one another with
melting point of said adhesive to produce a, hard
out affecting the surface engagement "between
partially polymerized material to which the-mold
said plates and the surface of the hardened mass
parts adhere, releasing thev mold parts from ‘one
de?ned thereby, advancing the polymerization of
another without aifecting the engagement be
said mass until substantial completion to produce
a transparent, inherently rigid mass without‘ re
tween said parts and the surfaces of the hardened
product de?ned by said parts by fusing ‘said ad
moving said plates, and removing said plates
hesive, and advancing the polymerization of said
from said mass by immersing said mass and-‘said
plates in a bath containing a surface ‘active
‘mass to substantial completion to produce a
‘ transparent, inherently rigid mass with said parts
attached to the molded product at a temperature
above the melting point of saidadhesive.
agent.
-
9. The method of fabricating a prism which
comprises rigidly securing together-a plurality of
comprises rigidly securing together a plurality
separated, optically ?at plates to form a mold of
the desired prismatic shape, said plates being
of separated, optically flat plates to form a mold
spaced from one another so as to permit move
6. The method of fabricating a prism which
of the desired prismatic shape, said plates being 25 ment thereof towards one another upon removal
spaced from one another so as to permit'move
ment thereof towards one another upon removal
of the securing means, introducing a ilowable
of the securing means, introducing a 'liowable
prises cementing together with a fusible cement
a plurality of separated, optically flat plates to
form a mold wherein each of said plates de?nes
a side of said prism, said plates being spaced from
of separated optically ?at glass plates so as to
have the ?at surfaces of the latter de?ne said
prism, said plates being spaced from one an
other so as to permit movement thereof towards
one another upon removal of the securing means,
partially polymerized polymerizable mass into
said mold, which mass, in its hardened, partially
partially polymerized polymerizable mass into
polymerized condition, adheres to said plates and
said mold, which mass, in its hardened, partially 30 which is adapted, upon substantially complete
polymerization, to produce a transparent inher
polymerized conditionadheres to said plates and
which is adapted, upon substantially complete
ently rigid mass, heating the mold and the con
polymerization, to produce a transparent, inher
tents thereof until the latter harden to produce
a hard partially polymerized material to which
ently rigid mass, advancing the polymerization of
the mold parts adhere, releasing the plates from
said flowable mass to produce a hard partially
polymerized material to which the mold parts
one another without affecting the surface en
gagement between said plates and the surfaces
adhere, releasing the plates from one another
without affecting the surface engagement between
of the hardened mass de?ned thereby, and re
heating the hardened prism with the plates se
said plates and the surface of the hardened mass
de?ned thereby, and advancing the polymeriza 40 cured to the surfaces thereof to substantially
complete the polymerization to produce a trans
tion of said mass until substantial completion to
parent, inherently rigid mass.
produce a transparent, inherently rigid mass
without removing said plates.
10. The method of forming a prism which
'7. The method of forming a prism which com
comprises rigidly securing together a plurality
one another so as to permit movement thereof
towards one another upon removal of the ce 50 introducing a plastic mass comprising a mon
ment, introducing a ?owable partially polymer
ized polymerizable mass into said mold, which
mass, in its hardened, partially polymerized con
dition, adheres to said plates and which is
adapted, upon substantially complete polymeri
zation, to produce a transparent, inherently rigid
mass, advancing the polymerization of said flow
omer into said mold, which mass in its hardened,
partially polymerized condition, adheres to said
plates and which is adapted, upon substantially
complete polymerization, to produce a transpar
ent, inherently rigid mass, heating the mold and
the contents thereof to produce a hard partially
polymerized material to which the mold parts
able mass at a temperature below the melting
adhere, releasing said plates for free movement
relative to each other without disturbing the ad
point of said cement to produce a hard partially
polymerized material to which the mold parts ad 60 hesion between said plates and the hardened
mass, heating the mass with said plates attached
here, removing the cement from said plates with
thereto for a substantial period of time to pro
out alfecting the surface engagement between
duce a transparent, inherently rigid mass, and
said plates and the surfaces of the hardened
removing said plates at a temperature corre
mass de?ned thereby by fusing said cement, and
advancing the polymerization of said mass for a 65 sponding to the temperature at which the ?nal
substantial time and at a temperature above the
melting point of said cement to produce a trans
heating is carried out.
_
11. The method of forming a prism which
parent, inherently rigid mass without removing
comprises securing together a plurality of sep
said plates.
arated glass plates by means of a fusible cement
8. The method of fabricating a prism which 70 ‘to form a mold of the desired prismatic shape,
comprises rigidly securing together a plurality of
said plates being spaced from one another so as
separated, optically ?at plates to form a mold of
to permit movement thereof towards one another
the desired prismatic shape, said plates being
upon removal of the cement, introducing a ?uid
spaced from one another so as to permit move
solution comprising monomeric plastic material
ment thereof towards one another upon removal 75 into said mold, which solution in its hardened,
2,409,958
7
'8
partially polymerized condition, adheres to said
and continuing the baking at the latter tempera
plates and which is adapted, upon substantially
complete polymerization, to form a transparent,
inherently rigid mass, heating the mold at a
temperature below the melting point of said ce
ment to harden the solution to produce a hard
ture until substantial completion of the poly
merization of the mass within said mold to pro
duce a transparent, inherently rigid mass.
13. The‘ method of forming a prism which
consists in securing'together a plurality of sep
arated glass plates by means, of a fusible ce
partially polymerized material to which the mold
adheres, raising the heating temperature to a
ment having a melting point between 40 degrees
point above the melting point of said cement,
and 80 degrees C., said plates being spaced from
and maintaining the latter temperature to effect 10 one another so as to permit movementthereof,
a substantial completion of the polymerization of
the molded plastic to produce a transparent, in
herently rigid mass.
12. The method of forming a prism which
consists in securing together a plurality of sep
arated glass plates by means of a fusible ce»
ment having, a melting point between 40 degrees
and 80 degrees 0., said plates being spaced from
one another so as to permit movement thereof
towards one another upon removal of the ce
ment, introducing a ?uid mass comprising es
sentially styrene into said mold, which mass, in
its hardened, partially polymerized condition, ad~
heres to said platesvand which is adapted, upon
substantially complete polymerization, to'fo-rm a
towards one another upon removal of the ce
ment, introducing a ?uid mass comprising es
sentially‘styrene into said mold, which mass, in
its hardened, partially polymerized conditiomad
heres to said plates and which is adapted, upon
substantially complete polymerization to form a
transparent, inherently rigid mass, baking the
mold and the contents thereof at a temperature
of 25 to 40 degrees C. for over 24 hours to pro
duce a hard, partially polymerized material to
which the mold parts adhere, and then raising
the baking temperature to 80 to 90 degrees C.
and continuing the baking at the latter temper
ature until substantial completion of the poly-v
transparent, inherently rigid mass, baking the
merization of the mass within said mold to pro
duce a transparent, inherently rigid mass, and
mold and the contents thereof at a temperature
removing said plates from said mass by immers
of 25 to 40 degrees C_ for over 24 hours to pro
duce a hard, partially polymerized material to
ing said mass and said plates in a bath contain
ing a surface active agent.
which the mold parts adhere, and then raising
the baking temperature to 80 to 90 degrees C.
HOWARD G. ROGERS.
DEXTER P. COOPER, JR.
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