Note: Descriptions are shown in the official language in which they were submitted.
,r~ .
The presen-t invention refers to a production process
oE lenses and optical means made of polyrnerizable synthetic
resins, through a continuous compensation casting.
In the last decades the technological world has been
paying attention to the research after molding methods based
on the mold polymerization of one or more monomers, likely to
produce solids provided with special characteristics.
The optical industry has been engaging in such a
direction to produce lenses or ot;her optical means: in practice,
the various technologies aim at overcoming the obstacles occur-
ring during the polymerization process, such as:
- physico-chemical characteristics of the product, correlated
to the theoretically optimal polymer,
- physico-chemical characteristics of the product, correlated
to the polymer obtained;
- shape of the product.
These technologies have been directed, in particular,
towards the casting of thermohardening polymers, as the latter
offer physico-chemical characteristics and other advantages
better suited, when used as optical means, f.i. lenses, than
the thermoplastic polymers. By now, entered into general use is
the diethyleneglycol-bis-allyl-carbonate ~and its copolymers) ~-
having the formula:
. ~CH2--CH2-0-CO--O-CH2-CH = CH2 "
~i ~ O\
;`! CH2--cH2--O-cO-O--cH2-cH = CH2
.
better known under the trade-mark CR-39. The latter with the
addition of a catalyzer (or better said, of a free-radicals
starterl, polymerizes to an homopolymer or to a copolymer.
The preferred starter is the isopropyl-dicarbonate-
peroxide having the formula:
CH , CH~
3 -CH-0-C0-0-0-C0-0-CH
CH3/ 3 ~ ;
~ ' ,
known as I.P.P.. The latter infacts, allows the polymerization
to run at a lower temperature and wi.thin shorter cycles, when
compared to the benzoyl-peroxide or to other peroxides, which
also may be used. In practice the casting methods of a lens
made of CR-39 or its copolymers, include the introduction o~
catalyzed monomer/s, in the fluid state, or prepolymerized up
to the syrupy state, between two g].ass lenses, kept together
by means of a spring, and kept at a given distance from each
other, through a T section gasket. The gasket distancer may
be shaped according to the curvature of both lenses, to secure
tightness and separation, or to the same end it may become
elastically deformed. The catalyzed monomer, added as a fluid
in the molds thus formed, solidifies at the end of a thermic or
radiating cycle, producing strong tridimensional shrinkings
(14% in the case of the CR-39 homopolymer). Thus a further
function of the spring is to contihuously squeeze the distancer
of the lenses forming the mold, until the fluid reaches the
intermediate gel state, to avoid the leakage of fluid monomer
from the mold. On the other hand, after the gel phase has
been reached, the pressure of the spring, shall straïn the
thermoplastic or elastic distancer, to facilitate the adherence
mould/polymer. Such a strain may be considered as a squeezing
of the distancer or as an expansion of the gasket.
The mold/polymer adherence is required to avoid
possible breakages of the polymer or of the mold, due to the
strong tensions wh.ich occur when the polymer shrinks, and to
avoid, at least on the usable surface of the polymer, air
: infiltrations which, by hindering the polymerization, would
cause irreparable damages to the product.
The lenses thus obtained, made of CR-39j or its
copolymers, may present faulty perimeters, due to air bubbles.
Air leakages, even after the gel phase is ended, may cause air
- 2 - .
3~.q3
bubbles and cavities, or the formation of a perimetrical soft
polymer stripe, or a possible chemical reactivity between the
gasket material and the catalyzed monomer. A feature co~non
to all processes is, any how, an appreciable reduction of the
diameter of a lens made of CR-39 and its copolymers, with respect
to the diameter of the lenses forming the mold. This is due
to following reasons:
(A) the internal mold cavity is reduced by the space occupied
by the sealing gasket, acting as distancer.
0 (B) the tridimensional shrinkage of the polyrner involves also
the perimetrical stripe, thus further reducing the diameter
of the product, particularly in the case of negative or
diverging lenses.
(C) possible perimetrical faults (air bubbles, air suctions
and a stripe of soft polymer) equally reduce the usable
diameter by the affected depth.
These faults generally occur in the perimetrical
stripe, as by now it is generally preferred to position the
molds with their concave side upwards. Whereas the positioning
of the molds with their convex side upwards, would originate
the same faults at the center of the polymeric lenses, thus
rendering the lenses worthless. Concavity and convexity are
referred to the external side of the molds.
After the sealing gasket has been removed, the opening
of the mold is carried out by lntroducing a wedge into the slot
previously occupied by the distancer, and using it as a lever
between the two glass lenses, which normally adhere to the ~ i
polymer. The polymeric lens thus extracted is complete, so
~ar as the surfaces are concerned, but sharply tensioned due
to the shrinkage. To achiéve its structural distension, the
lens has then to be submitted to a thermic treatment~
This treatment, or temper distension, is currently
- 3 -
.,
~ 3
applied to all mold plastic materials, to the glass, and tometals. The duration of the treatment, to obtain the c1esired
effect, depends upon the temperature, related to the s-tate of
tension exis-ting in the product and to the grade of polymeriza-
tion of the polymer.
The above disclosure aims to provide a preliminary
information on the prior art related to the polymerization
process. It is a summary of experimental researches, carried
out by the author, and of documents deriving from patents.
Among the latter the following ones are mentioned: US-PS
2.403.112/US-PS 2.464.062/ US~PS 3.171.869/UP-PS 3.038.210/-
US-PS 2.964.501/ FR-PS 2.171.073/FR-PS 1.541.889/FR-PS
1.204.627!E'R-PS 1.462.519 DE-PS 1.062.003/GB-PS 1.402.573.
The present invention takes into consideration the
numerous disadvantages of a technical and/or of an economical
nature, which occur in the production of lenses or optical
means made of CR-39 and its copolymers. The present process
studies, plans and solves the problem of producing lenses or
optical means made of CR-39 and its copolymers, in a completely
new manner, with reference to:
- the chemical basic preparation of the components;
- the ways and the means of polymerization
- the shape of the articles, obtainable without any reduction
- the possible unification of the polymerization cycles, for
all given thicknesses ~.
- the obtention of a polymer foreseen according special
adsorption and transmission requirements of the electro- -
magnetic energy.
In particular the present invention provides a poly-
meri~ation process.for producingr by way of molding and con-
tinuous compensation, lenses and optical means, from a p~lymer-
izable thermohardening plastics material, said process comprising
: _ 4 _
~ - .
/5~
the steps oE:
- forming a tubuIar sleeve of a plast.ic material
substantially indeformable, said plas-tic material being
: chemically compatible with said polymerizable material and
thermically stable at the temperature of polymerization,
- positioning mold halveswithin said sleeve at
the required distance from each other, so that they define,
. with the lateral wall of khe sleeve, a cavity having a diameter
equal to that of the mold halves, the position of each mold half
with respect to the sleeve being only kept by friction of the
` mold half rim, over the sleeve wall,
;l - forming outside of said cavlty a compensation re-
servoir communicating with said cavity through at least a pre-
formed passage way,
- introducing into the cavity, through said preformed
passage way, catalysed polymerizable thermohardening plastics
. material until said cavity is completely filled and said compen- ~:.
sation reservoir is partially filled,
: ~ - submitting said mold to homogeneous heating to :
thereby cause a passage of polymerizable material in excess
from the cavity of the mold, into the compensation reservoir,
during the state of expansion of the polymerizable material,
and a passage in the opposite dlrection during the subsequent
stage of shrinkage of:the polymerizable material, until the `
, ~ .
gel stage lS reached,
- continuing the heating of the mold.until the poly-
merization of the polymerizable~material is completed, the final
; shrinkage of t:he latter, from the beginning of the gel stage,
being only compensated through the approaching of the mold halves
to each other,
~ - removlng the two mold halves from the lens thus
.~ obtained when the polymerization of the polymerizable material
? ~L35~13
has been completed.
In accordance with -the present invention,
catalysed polymerizable material may be submitted to a
thermic cycle o 15 hours with a gradual thermic increase
of from about +40C to 110C.
In the present invention, it is considered as
obvious, to extend to all monomers, copolymers of the same,
catalyzers or starters, likely to be used, the total or
partial series of the claims, when th same reasoning,
methods and devices, are ~~~~ ~~~
_ . .. . ... _ .. . .. __ ... _ _ __ .. . ~ . .. . .
~-31. 3rS~
applied to solve the same problems or to attain the same aims,
and when the same results are obtained, even if only partial ones.
MO~OMER - The diethyleneglycol-bis-allyl~carbonate, or CR-39,
is to be found on the market at a high purity grade i.e. about
99,150%. Gas chromatographic analysis indicates the presence
of allyl-carbonate and of a not well identified su~stance.
(Fig. 1).
During the colur~ separation perormed on occasion
of the a.m. analysis, it was stated that the impurities are
more volatile i.e. have shorter retention times than the
monomer. An experimental series was then carried out to
eliminate the impurities and it was discovered the following:
- the allyl carbonate is eliminated when the monomer is
submitted to a warming up at a temperatuxe of 50-90C;
- this elimination is possibly due to a partial polymerization
of the allyl carbonate as it may be analytically stated by
observing the area referring to the a.m. unidentified product
- the latter may, as a consequence, be considered as a polymer
of the allyl carbonate.
The above was confirmed during the warming up of the
monomer, carried out on purpose o~ a longer time span, at a
temperature of 90C, in static tanks. As the elimination
of the àllyl carbonate was partially suppressed, due to the
tanks staticity, the analysis of the monomer revealed an
appreciable increase of the polymer, caused by the allyl
carbonate. These facts having been ascertained, a depurating
system of the monomer was set up, as indicated in following
example:
EXAMPLE NR. 1
The monomer CR-39 was gradually warmed up, at tempera-
tures in the range of 50-90C.
The partial elimination of the allyl carbonate obtained
-- 5
.
, ~ ~. , .
`'~ ' ~ 1 3r5~
at all the a.m. temperatures was obviously related to the
ratios: time - temperature - quantity treated.
In practice at a lower temperature, a longer duration
of the operation was required; whereas at higher temperature
corresponded a shorter duration of the treatment.-Thus for
instance:
- Quantity of the treated monomer CR-39: 1 Liter;
- Average thermic value: 70C during four hours ~ the warming
up *ime and the time of the gradual cooling down to room
temperature.
- Strength of the monomer, before treatment: 99,158 (Fiy. 1).
- Strength of the monomer, after treatment: 99,484 (Fig. 2).
EXAMPLE NR.2
Through gradual warming up of the monomer CR-39, at
temperatures in the range of 50-90C, under active stirring,
to homogenize the fluid and accelerate the elimination of allyl
carbonate, the latter was partially eliminated according to the
ratio time - temperature - quantity treated, (as in example
N 1). Thus for instance:
- Quantity of the treated monomer CR-39. 1 Liter,
- Average thermic value: 70C during 4 hours ~ the warming up
time and the time of the graduai cooling down to room
tem~erature;
- Strength of the monomer, before treatment: 99,158. (Fig. 1).
- Strength of the monomer after treatment: 99,713. (Fig. 3).
EXAMPLE NR 3.
Through warming up of the monomer CR-39, according
to the conditions described in the Example N. 1, but carrying
out the operations under vacuum, we obtained:
- Quantity of the treated monomer CR-39: 1 liter; -~
- Average thermic value: 70C during 4 hours ~ the warming up
time and the time of the gradual cooling down to room
- 6 -
. ~ . :
r~i~3 1~ 3
tempera-ture,
~ Strength of the monomer before -treatment: 99,158 (Fig. 1).
- Strength of the monomer after treatment: 99,686. (Fig. ~).
EXAMPLE NR. 4
Through warming up of the monomer CR-39, according
to the conditions described in the Example N 2, but carrying
out the operation under vacuum, we obtained;
- Quantity of the treated monomer CR-39: 1 liter,
- Average thermic vaLue: 70C during 4 hours + the warming up
time and the time of the gradual cooling down to room
temperature;
- Strength of the monorner before treatment: 99,158. (Fig. 1).
- Strength of the monomer after treatment: 100%. (Fig. 5).
EXAMPLE NR 5
Through warming up of the monomer according to the
conditions described in the Examples N 1,2,3 and 4 the total
dehydratation of the monomer, was also obtained. Spectropho-
tometric analysis, in the visible field from 400 to 700 nm,
give for the thus depurated monomer CR-39, outstanding linearity
and transmission.
STARTER - As a generally accepted rule the isopropyl-dicar-
bonate-pero~ide, known under the commercial name of I~P.P.,
is added to monomer CR-39, in a percentage of 3%. This
percentage has been adopted in all processes, though a higher
or a lower percentage may be adopted, for special purpose.
Even if the I.P.P. of the commerce, may be considered
as pure, being an industry product difficult to be synthetized
and handled, it contains in practice spurs of water and free
chlorine ions.
The above may be observed from the infrared spectro-
photometric ana:Lysis (Fig. 6)~ To start a series of tests
aiming at ascertaining the influence of the chlorine ions on
-- 7 --
, .,; . . . . ~ ,. . .
the polymerization, in the frame of the present invention, the
isopropyl-dicarbonate-peroxide was synthetized through reaction
between sodium peroxide and isopropyl-chloroformiate, (previously
purified up to 99,99%). The product obtained was used, after
1,2,3,4,5 water leachings. Each leaching produced an appreciable
reduction of the chlorine ions. By polymerizing the monomer
CR-39, with the addition of 3% of isopropyl~dicarbonate-peraxide
(obtained from the a.m. repetitive leachings), according to a
gradual thermic cycle of 15 hours, from +40C to fllooc~ we
obtained:
- after 1 leaching only: a frankly yellow polymer,
- after 2 leachings: a yellow polymer,
- after 3 leachings: a pale yellow polymer,
- after 4 leachings: a straw-yellow polymer,
- after 5 leachings: 2 colourless polymer.
It was thus ascertained that the yellowing of the ;
polymer depends upon an higher content of chlorine ions.
On the other hand, when leaching with water the
isopropyl-dicarbonate~peroxide, we separated a lighter fraction
of the same product partially degraded, due to deoxygenation.
To obtain an isopropyl-dicarbonate-peroxide, with
the highest grade of purity from free chlorine ions, and
degraded deoxygenated fractions, we followed the following line
of operations.
EXAMPLE NR ~
In a bain-marie, cooled to +9C we melted 100gr, of
commercial I.P.P. having a point of fusion of -~ 8C. We added
H20 cooled to ~ 9C , into which some drops of pyridin had
been solved. After stirring and decanting, the phases were
separated.
We then washed twice, with H20, the isopropyl-di-
carbonate-peroxide and carefully separated, together with the
- 8
3~
water, the ligh-ter fraction of the isopropyl-dicarbonate-
peroxide, corresponding to the partially degraded or deoxy-
genated product. At this point a purified I.P.P. had been
obtained. (Fig. 7).
EXAMPLE NR. 7
When the I.P.P., purified according to the above
described method (Example N 6), was frozen again and after-
wards brought to melting, we observed a me]ting point of -~ 9C
(instead ~ 8C of the starting material).
EXAMPLE NR. 8
Two test samples prepared with the same CR-39 monomer,
catalyzed under the same polymerization conditions , respectively
with the addition of 3% of
- Commercial I.P.P., and
- I.P.P. depurated according to the method described in
Example N 6 above;
showed following differences, at 53C, after 4 hours of gradual
induced warming up from 40.
- in the test sample added with commercial I.P.P. the monomer
was present in the polymer in a percentage of 52%; and
- in the test sample added with I.P.P., depurated according
to the described method, the monomer was present in the
polymer, in a percentage of 34%.
In other words, the use of depurated I.P.P. (when
compared with that of commercial I.P.P.) causes a higher
catalytic activity, likely to allow to obtain a given polymeric
value, with:
- reduced percentages of the starter,
- shorter times of reaction, and
- lower temperatures.
Furthermore the test sample, obtained from purified
I.P.P., was perfectly colourless.
g
', ' ' . : '`
~3~ 3
ADDITIVES The addition to the monomers of additives which
absorb the U.V. radiation, allow the protection of polymers
from the degr~dation caused by the said radiation.
As the U.V. absorbers are not easily soluble, follow~
ing drawbacks may be observed in the polymer according to the
quality and quantity o~ the absorber used:
- optical distortion (diffraction and dispersion), due to the
unsatisfactory distribution of the absorbers, within the
monomer,
- yellow green yellow, orange yellow colour of the product,
- transmission intererence in th,e visible electromagnetic ~ield.
With reference to the present invention we selected
as absorber the 2 - (2-hydroxy-5-methyl-phenyl) benzo-triazole.
To establish the optimal quantity of said U.V. absorber, to be
added to the monomer CR-39, with respect to the interferences
likely to be caused in the polymer by said addition, so far
as the transmission of the visible light is concerned, and
the solution methods.
The Operations were carried out as follows:
EXAMPLE NR. 9
We obtained a highly satisfactory solution and
distribution of 2 (2 hydroxy-5-methyl-phenyl) benzotriazole,
in the percentage of 0,0125% in the purified monomer CR-39,
(or catalyzed with I.P.P.) by inducing to the container,
ultrasonic frequencies in the range of 20-70 KHertz. The
selected percentage of 0,0125% of 2.(2.hydroxy-5-methyl--
phenyl) benzotriazole caused in the polymer CR-39, on test
samples of 4 mm of thickness, a good U.V. absorption and an ~`
almost linear transmission in the visible field. (Fig. 8).
EXAMPLE NR. 10
With the use of ultrasounds we obtained the perfect
solution and distribution of 2(2-hydroxy- -5-methyl-phenyl)
-- 10 --
benzotriazole in the monomer CR~39, both pure or catalyzed
with I~P.P., in the selected percentage of 0,0100%. The latter
percentage of additive originated in the polymer spectra close
to what has been described in Example N 9, on test samples of
6 mm of thickness.
EXAMPLE NR~ 11
With the use of ultrasounds, it was possible to obtain
the perfect solution and distribution of 2(2-hydroxy-5-methyl-
phenyl) benzotriazole, in the monomer CR-39, both pure or
catalyzed with I.P.P., in the selected percentage of 0,0150%.
The spectra thus originated in the polymer were close to those
described in Example N 9, on test samples of 2 mm of thickness.
EXA~PLE NR. 12
With the use of ultrasounds it was possible to obtain
the perfect solution and distribution of a very high percentage
of 2(2~hydroxy-5-methyl-phenyl) benzotriazole, with respect
to those described in the Examples N 9,10 and 11 above, both
in the pure monomer or catalyzed with I.P.P. or with benzoyl-
peroxide. It was thus possible to obtain the preparation of
easily tested concentrates, which later on were diluted in the
desired percentage, in large quantities of pure of catalyzedmonomer.
EXAMPLE NR. 13
CATALYSIS- Under mechanical stirring we mixed:
- CR-39 monomer, depurated and dehydrated as indicated in
Examples N 1,2,3 and 4 above, wlth
- 3% of I.P.P. depurated as in Example N 6 above, and
- 0,0125% of 2(2~hydroxy-5-methyl-phenyl) benzotriazole, as
in Examples N 9 and 12 above,
the whole being filtèred, under decompression.
EXAMPLE NR. 14
Through ultrasonic induction we mixed:
-- 11 _
,. :.
.
3L.31.3,5~ 3
- CR-39 monomer, purified and dehydrated as indicated in
Examples N 1,2,3 and ~ above, with
- 3% of I.P.P. depurated as in Exa~ple N 6 above, and
- 0,0125 of 2(2-hydroxy-5-methyl-phenyl) benzotriazole, as in
Examples N 9 and 12 above,
the whole being filtered under decompression.
EXAMPLE NR. 15
With CR-39 monomer, catalyzed and with the addition
of additive, as indicated in the Examples N 13 and 1~ above,
and submitted to a thermical cycle of polymerization, we
obtained practically colourless transparent polymers. The
latter, if compared with polymers obtained through a current
preparation showed a quicker and more uniform polymerization
cycle, with reference to the reactive saturation within a time
X, for thermical cycles Y and thickness Z. Furthermore said
polymers showed outstanding physico--chemical characteristics,
as observed through thermic differential calorimetric analysis,
and tests of chemical inertia.
It may be observed that the methods described in the
examples above are an improvement or a variant of the techni-
ques already followed up to now, whereas the proportions of
the components correspond to values which may be modified,
even though following the same techniques. ;;
The Author, in describing the invention in detail,
aims at leading towards the same claims, the combination of
the various techniques, proportions and/or the share of
individual components.
PRINCIPLE OF CONTINUOUS MOLDS COMPENSATION- The shrinkage of
CR-39 polymer and its copolymers, causes - as a rule - the
need of introducing devices, of an empirical nature to eliminate
all possible drawbacks. Generally the polymerization has been
carried out with variable thermical cycles, according to the
- 12 _
~ 3~
thickness of the polymer. Other devices refer to the ways
of assembling the molds and/or to intermediate manipulations.
As a rule, with the increase in the thickness of the
polymer the duration of the thermic cycles was extended, even
to the outmost; the molds filled with the catalyzed monomer
were kept at a low temperature (about -~ 40C) for a long span
of time, to slow down the reaction's speed and to reduce, so
far as possible, the ~egative effects of the shrinkage of the
polymers.
Within the frame of the present invention we ound
; a satisfactory solution to the problem through a continuous
molds compensation, wherein the catalyzed monomer i9 likely
to fill the cavities, formed during the polymerization, due
to the shrinkage of the polymer. The above is possible as the
CR-39 monomer, and its copolymers, with addition of peroxide
or percarbonate as catalyzer, pol~merize only partially and,
in any case very slowly, in the presence of air, and rema1n
in a fluld state for a long span of time.
We assembled as follows, molds for the casting of
optical lenses.
,
EXAMP1E NR. 16
Two or more glass lenses, were introduced and brought
to slide down within a tubular stripe of polyethilene (or of
a different material, which would not react with the catalyzed
monomer). me diameter of the tube was kept within such
dimensions as to originate sliding elasticity or friction,
and -to allow the positioning of the lenses at the desired
dlstance from each other. Thus one or more cavities were
created by the lenses' curvature. (Fig. 9 wherein 1 = tubular
stripe; 2 = lenses; 3 = cavity).
EXAMPLE NR. 17
Two or more glass lenses were introduced and brought
- 13 -
~13~ f~ L3
-to slide down within a tubular s-tripe, as in the Example ~. 16
above, of such a diameter to originate s:Liding elasticity or
friction. Beforehand we had introduced or created in the
tubular stripe a distancer having a desired length and a
minimum thickness, to cause the interruption of the sliding
of the lenses. (Fig. 10 wherein: 1 - tubular stripe' 2 =
lenses; 3 ~ cavity; 4 = distancer).
EXAMPLE NR. 18
Two or more glass lenses were slided down a tubular
stripe, as in Example N 16 above, the diameter of the tube
being about the~same as that of the lenses. A distancer had
been introduced or casted beforehand in the tube, as in Example
N 17 above.
EXAMPLE NR. 19
The molds prepared according to Examples N 16,17 and
18 above, were filled with CR-39 monomer, catalyzed according
to Examples N 13 and 14 above, and positioned with their
convex side upwards. The catalyzed monomer was added in the
perimetrical channel, partially formed from the surface of
the higher situated lens, and partially from the internal wall
of the tube. (Fig. 11 and Fig. 12, wherein: 1 = tube, 2 =
lenses; 5 = catalyzed monomer).
EXAMPLE NR. 20
The molds prepared according to Examples N 16, 17
and 18 above, were filled with CR-39 monomer, catalyzed accord-
ing to Examples N 13 and 14 above, and positioned with their
concave side upwards. Catalyzed monomer was added in the
internal cavity of the higher situated lens, up to reach
the internal walI of the tube. (Fig~ 13 and Fig. 14, wherein:
1 = tube; 2 = lenses; 5 = catalyzed monomer).
EXAMPLE NR. 21
The molds prepared according to Examples N 16, 17
_ 14 -
~3 ~ ~
and 18 above, were ~illed wi-th CR--39 monomer, catalyzed accord-
ing to Examples N 13 and 14 above, and positioned horizontally,
according to Examples N 19 and 20 above. The tubular stripes
were provided with, or formed as, a receptacle communicating
with the internal cavity of the molds. The receptacle was
also filled with the catalyzed monomer~ Said receptacle had
been made by totally or partially covering the perimeter of
the tube inside and/or outside. (Fig. 15 and Fig. 16, wherein:
1 = tube, 2 = lenses; 5 - catalyzed monomer; 6 = receptacle).
EXAMPLE NR. 22
The molds prepared according to Examples N 16, 17
and 18 above, were filled with CR-39 monomer, catalyzed
according to Examples N~ 13 and 14 above, and positioned
vertically. The external tubular stripes were provided with,
or formed as, a receFtacle communicating with the internal
cavity of the molds. Said receptacle was aLso filled with the
catalyzed monomer. (Fig. 17, wherein: 1 = tubular strip,
2 = lenses; 5 = catalyzed monomer, 6 - receptacle).
EXAMPLE NR. 23
~11 the molds prepared and positioned as indicated
in the Examples above, the cavities of which corresponded to
the shape of every type of lens (vertical, convergent, divergent,
cylindrical, lenticular, bifocal; prismatic etc.) were submitted,
in an oven, to the same thermic cycle of 15 hours (Fig. 18).
me vertical stroke appearing in the cycle, indicates, as it
will be further explained, the moment where the springs were
applied to the molds, i.e. when the gel phase of the monomer
had been completed. The perfectly polymerized lenses thus
obtained, showed finished surfaces and various curves and
thicknesses. Their diameter was practically equal to that of
the glass lenses forming the simple or multiple molds (with
a very low reduction equal, as an average to 0,7 %)~
_ 15 -
. . .
.. q~
It was thus experimentally confirmed how the continu-
ous compensation had operated, according to the ways and means
described in the Examples above, establishing a continuous flow
of polymerizable monomer from the outside into the inside of
the molds, compensating the shrinkages, hindering the suctions
and/or the creation of air bubbles, which would have caused
the separation of the polymer from the mold.
~ he flow from the exterior to the interior had been
made possible by means of preformed passages or through capillar-
ity. The polymers thus obtained had a particularly homogene-
ous aspect.
SELF-POSITIONING SPRING ~ Many CR-39 lenses, available on the
market,~when examined with polarized light, show tensions which
cannot be removed, even submitting the polymers to heat-treat-
ment. In the frame of the present invention we considered the
convenience of applying a pressure on the lenses forming the
mold, after the polymer had reached the gel phase. It was
then decided to introduce a spring, likely to lean on every
kind of curved or plain surface, and to position itself through
homogeneous contact on the whole of the support surface, to
` avoid localized high pressure, likely to cause the breaking
of the molde or of the polymers, or unacceptable pressures
on the polymers themselves.
EXAMPLE NR. 24
We built whlch springs, easily lean on the molds,
by means of the compression of levers 7, 8, causing the elastic
opening of the pressers 9, I0. The latter, consisting of
small saucers 11, 12, shaped as a meniscus, may swing in all
directions around pins 13, 14. Said springs adapt to whichever
molds assembly including curves or various plains and by means
of the swinging of the small plates, allow a perfect adherence,
likely to exert an even pressure, very useful to the production
- 16 -
' ~ '
. ~. ., , , , ;. , ~ .. ~ . .
3~ ~
of regular polymers. (Fig. 19 and Fig. 20).
EXAMPLE NR. 25
Spring3 as in Example N 24 above, but provided with
only one small saucer. (Fig~ 21).
OPENING OF T~E MOLDS - The lens mad.e of C~-39 and its copolymers,
is strongly adherent to the casti:ng mold, thus the separation
from each other is a problem dif~icult to solve, particularly
in the frame of the present invention. In fact, as the diameter
of the polymer obtained, is practically equal to the molds, it
is impossible to achieve a mechanical separation by means of a
wedge or a similar tool. In the frame of the present invention
it was discovered that ultrasounds in the range of 20-70 KHertz,
induced in a tank filled with water, in which the molds had
been immersed, after the polymerization of their content,
caused the separation of the polymers from the molds.
.. EXAMPLE NR. 26
To separate the polymer from the glass lenses, forming
the molds,.the latter were immersed in warm water baths, after
which ultrasonic frequencies in the range of 20-70 KHertz were
induced.
In all cases, after some minutes, the polymer separated
from the molds. The duration of the operation depended upon
the bath tem.perature: it was shorter for an higher temperature
and vice versa.
; EXAMPLE NR. 27
To carry out at the same time the separation of the
polymer obtained from the glass lenses constituting the molds,
and a first washing up of the latter, the molds were immersed
in warm baths of water solution of any type of cleansing
usbstance (such as detergent, detersive, degreasing, emulsify-
ing or saporification agent, solvent, acid or alcaline sub-
stance). In every case, within some minutes from the induction
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to the bath of ultrasonic frequencies, in the range of 20-70
KHertz, the polymer separated from the molds: the relation:
duration of the operation/bath temperature was the same as
indicated in the Example N 26.
From the above it appears evident that the described
process and/or the means object of the present invention, which
allow the production of quality lenses or other optical means,
made of CR-39 and its copolymers, may be directly or indirectly
related to the whole field of applications of casted homo- :
polymers and copolymers with reference to the casting of
whichever product, and the applicability or the selection of a
whichever polymerizable resin. It also clearly appears that
the examples - though referring to specific realizations of the
present invention, cannot be considered as limiting the latter.
: It is underlined that the process as a whole, attains in a
synergistic manner, the advantages obtainable by means of
each described operation or means, with respect to their
individual Euncti~s
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