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Патент USA US2406401

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Aug. 27, 1946.
2,406,401 '
Filed Sept. 2, 1942 ‘
,FtlG. 2
. . V, .
v v. v .
Patented Aug. 27’, 1946
’ 2,406,401\RJ.-.
John H. Richardson, Needham, Mass‘, assignor to '
> Polaroid‘ Corporation, Cambridge, Mass., al‘cor
poration of'Delaware.
' Alwl'ication September 2, 1942, Serial No.‘ 457,933.;
This invention relates to an'improved mold for —' ‘K of suitable" molds has presented ’ a problem, of
use in the manufacture of optical elements
considerable .di?lcult'y? One ‘of the main elements
formed-of polymerized synthetic plastics, resins,
and like materials.
jofv cost'in the production of such devices'is the
cost of'thernold, particularly where attempts are ‘i
An object of the invention'is to provide a mold
made to produce, directly from the mold, optical
of the character described comprising a plurality '
of elements having optically smooth surfaces for
molding the light-transmitting faces'of a plastic
optical element and a cement forrsimult'aneously
positioning said elements, sealing/the joints be
elements of. uniform ‘optical properties .7 and with
optically smoothlight-transmitting surfaces. It‘
tween said elements, and "for forming those ‘walls '1 ~‘
of .the mold which are not intended to mold light
trans'mitting faces‘of the molded element.
Other objects of the invention are the provision
of a mold of the character described in which
the cement employed is a water-soluble cement;
in which the cement employed‘ is a metal or
metallic alloy which may be applied in ?uid con
the. cost of such molded products is to be kept
low ‘it‘is essential that "the" ‘molds be of a type
which can be repeatedly reused, and it ishighly
desirable that all ,thev'elements‘ and materials
comprising the "moldyv including the. elements
forming‘ the‘molding faces “ and the adhesive or
cement employed insealing these elements, be
.15 reclaimable and readily prepared for’subseque'nt
dition to the molding elements, which sets up
' ' ' In‘the manufactuer of molded joptical . elements
"from synthetic ‘plastic ‘or ‘resinous .materials ‘the
plastic material is ordinarily introduced into the ‘
little or no strain therein as it hardens or solidi 20 mold. in a. monomeric or'partially polymerized
?es, which remains solid at temperatures em- * i" ‘condition, and polymerization is then, carried
ployed in the polymerization of a plastic optical
element in the mold but, which softens and fuses
forward within the mold until it is substantially
at temperatures not greatlyin excess thereof; the
found particularly suitable in the production of
complete. , Plastic materials which have ‘been
provision of a cement or bonding material which
such ‘molded optical ‘ elements are .cyclohexyl
provides an airtight seal; the provision of a mold ' *
methacrylate, styrene; methyl methacrylate,‘ and
of the character described in which a plurality
of mold walls are formed of the cement; the
provision of a mold for optical wedges in which
all molding faces except‘the two principal optical 30
similar materials.
With materials of this class
maintained not greatly in excess of 90 degrees C.
This invention is directed primarily tothe pro
surfaces are formed of the cement; and the pro
vision of molds of the character described in
vision of a mold for optical elements of the type
of optical wedges or thin prisms wherein only two
which all of the elements forming the mold; in
faces of the mold element are employed as light
cluding the cement and the elements providing
transmitting faces, and where the ends of the
the optically smooth surfaces of the mold, may 35 element are, in the shape of relatively long, nar
be repeatedly reused.
row wedges. It has been found that with molds
Other objects of the invention will in part be
of this type satisfactory results can be obtained
obvious and will in par-t appear hereinafter.
at considerable saving in cost by forming the
The invention accordingly comprises the prod
ends of the mold of thesame material used to
uct possessing the features, properties and rela 40 cement together the two walls of the mold which
tion of elements which will be exempli?ed in the
form the light-transmitting faces of the molded
following detailed disclosure and the scope of
element. These mold walls may preferably com
the application of which will be indicated in the
prise plates of glass having optically smooth
For a fuller understanding of the invention 45 molding surfaces. They may be mounted in
position with the edges forming the apex of the
reference should be had to the following detailed
wedge or narrow prism in close contact and with
description, taken in connection with the accom
panying drawing, in which:
removable wedge elements positioned adjacent
the ends of the glass plates. This mounting may
Figure 1 is a side elevation partly in section
along the line l——| in Fig. 2 showing a mold 60 be accomplished in any suitable jig or ?xture. A
suitable cement may then be applied to the apex
constituting one embodiment of the invention;
of the mold and along both ends so as to‘com
pletely cover the removable wedges holding the
Fig. 2 is a section along the line 2--2 in Fig. 1.
glass plates in position. When the cement has y'
_With the development of plastic optical devices
such as prisms, lenses and the like, the provision 65 dried or hardened the wedges may be removed
suitable‘ molding material and having optically
and the moldthen filled with the partially poly
smooth molding surfaces are illustrated at l0.
. merized or monomeric plastic.
They are bonded together and held in position
The cement employed is preferably one which
by the cement l2, which it will be noted not only .1
seals the apex of the mold but forms as well the
two-ends thereof. In the drawings the base of Y '
“may be applied in a molten or liquid condition,"
and which sets quickly when dried or cooled. It
_ is preferably.lonelwhichw-provides an; aiiitightseal
the mold is shown as.,uncovered.‘ Under these
circumstances it will be understood that the mold
is held, during the polymerization of the plastic
and which sets" up?little, or no strain- in theglass
molding elements.
Examples of suitable fusible metals for use
the practice of the present invention are the al
loys known as Wood’smetal and Rose’s' Ynietall
therein, with its apex down; It will of course
understood that the base may also be coV- 7
Any other suitable cement may be employed p'ro- '
cred: either by a cover plate or by anextension
vided it fuses at a temperature above-but not;
greatly above the temperatures employed in ef
- of the cement forming the end walls.
Since certain changes may be made in the \
fecting polymerization of the plastic introduced
into the mold. A fusible cement having a melt
above product and ‘different embodiments of- the
invention couldbe made without departing from
ing point slightly in excess of 90 degrees C. is ‘ ‘ "its scope, it is intended that all matter contained,
.inthe above description or shown in the accom
Such a cement may be poured around. :
panying drawing shall be interpreted as illustra
, the mold joints withoutginjury to the glass mold
elements and may be readily removed from the 20 tive and not in a5limiting sense.’ .
7 preferred.
mold?by melting thejj cement at .a temperature
, , ltis also to be understood that ‘the following
which does not injure the molded plastic. , A ce- '
claims are intended toacover all the-genericand
ment of this type which is particularlyfuseful in
speci?c features of the inventionvherein described,
the present invention islthe ‘material sold com
and all statements of the scope of the invention
mercially as Behnont Brand No. 255 low melting 25 which, as a matter ofv language, might be said
to, fall therebetween.
valloy solder, an alloy of bismuth and lead. in the
proportionsof substantially’ ?vevparts of bismuth
-'.What is claimed» Y 1
_, _
1. A mold for use in the formation of ayprism
to fourparts of lead. This material has little‘if
of polymerized synthetic-plastic material, com
anyexpansion ,or'contraction at the temperature
at IWhich'it solidi?es, and therefore setsup no so prising, in combination, aplurality of angularly
strain in the glass molding elements. _
v .
positioned optically smooth mold walls of glass ‘
which are
for molding the light-transmitting surfaces of said
useful 'in the present. invention are a mixture .‘of
sodium silicate with a suitable ?ller, such asv wood
prism, and a cementcomprising a low melting
' _ .7 Examples of suitablesoluble cements
point, fusible metallic alloy rigidly bonding said
flour, pumice,‘or the like, and the refractory wa 35 walls together andforming a, plurality of addi
ter-soluble cement sold underthe trade vname
“InsaluteL’? ‘Either of these cements may be ap
plied in fluid condition, rapidly dried, and‘re
tional mold walls.-
2.’A mold for use in the formation of ;a prism
vof polymerized synthetic plastic material com
prising, in combination, a pair of angularly posi
moved , fromv the mold. after polymerization g 'of
.the vplastic therein has been completed by im 40 tionedv optically smooth mold walls of glass for
moldingthelight-transmitting surfaces of said
‘ mersing the mold in water, in
I which either cement
_ The drawingsillustrate a mold embodying the
features of the presentinvention. The molding
elements, i..e. the walls made of glass or other
. prism, and’ a fusible metallic alloy rigidly bonding
saidrwalls- together and-‘forming, a pair of end
walls for
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