U.S. patent application number 09/569479 was filed with the patent office on 2001-11-08 for formed polyethylene terephthalate polarizing film for incorporation in optical-grade plastic parts.
Invention is credited to Balch, Thomas, Beeloo, Edward A., Evans, Russell E., Yamasakl, Nancy L.S..
Application Number | 20010038438 09/569479 |
Document ID | / |
Family ID | 24275622 |
Filed Date | 2001-11-08 |
United States Patent
Application |
20010038438 |
Kind Code |
A1 |
Beeloo, Edward A. ; et
al. |
November 8, 2001 |
Formed polyethylene terephthalate polarizing film for incorporation
in optical-grade plastic parts
Abstract
An optical-quality plastic part is provided having a PET
polarizing film formed to contour with the optical requirements of
the plastic construct without jeopardizing its optical, mechanical
or cosmetic properties.
Inventors: |
Beeloo, Edward A.;
(Torrance, CA) ; Yamasakl, Nancy L.S.; (Long
Beach, CA) ; Evans, Russell E.; (Chino Hills, CA)
; Balch, Thomas; (Rancho Palos Verdes, CA) |
Correspondence
Address: |
LYON & LYON LLP
633 WEST FIFTH STREET
SUITE 4700
LOS ANGELES
CA
90071
US
|
Family ID: |
24275622 |
Appl. No.: |
09/569479 |
Filed: |
May 12, 2000 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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09569479 |
May 12, 2000 |
|
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09475424 |
Dec 29, 1999 |
|
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6220703 |
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Current U.S.
Class: |
351/159.56 ;
264/1.32; 264/1.34; 264/1.7; 351/159.73 |
Current CPC
Class: |
B29C 51/10 20130101;
G02C 7/12 20130101; B29C 51/428 20130101; B29D 11/00634 20130101;
B29C 2791/007 20130101; B32B 27/36 20130101; B29K 2995/0034
20130101; G02B 5/3033 20130101; B29D 11/00019 20130101; B29D
11/0073 20130101; B29L 2011/0016 20130101 |
Class at
Publication: |
351/162 ;
351/163; 351/165; 264/1.7; 264/1.32; 264/1.34 |
International
Class: |
G02B 003/00; B29D
011/00 |
Claims
What is claimed is:
1. An optical-quality plastic part comprising: an optical-quality
plastic material having a defined contour; and a formed polarizing
film comprising polyethylene terephthalate, wherein the film is
incorporated into the optical-quality plastic material to effect an
optical-quality plastic part.
2. An optical-quality plastic part according to claim 1, wherein
the optical-quality plastic material is comprised of a hard resin
thermoset material.
3. An optical-quality plastic part according to claim 1, wherein
the optical-quality plastic material is comprised of a
thermoplastic material.
4. An optical-quality plastic part according to claim 3, wherein
the thermoplastic material comprises polycarbonate.
5. An optical-quality plastic part according to claim 1, wherein
the formed film is bonded to a pre-existing optical-quality plastic
part.
6. An optical-quality plastic part according to claim 1, wherein
the film further comprises a crystalline o r semi-crystalline
naphthalene dicarboxylic acid polyester.
7. An optical-quality plastic part according to claim 1, wherein
optical properties of the formed film are maintained to pre-formed
optical properties of the film.
8. A method of optical-quality plastic part manufacture comprising
the steps of: forming a heat-sensitive polarizing film to a desired
contour; and incorporating the formed film into an optical-quality
plastic material to effect an optical-quality plastic part.
9. A method of optical-quality plastic part manufacture according
to claim 8, wherein the forming step includes heating only one mold
surface.
10. A method of optical-quality plastic part manufacture according
to claim 8, wherein the forming step is achieved without active
vacuum.
11. A method of optical-quality plastic part manufacture according
to claim 8, wherein the forming step is achieved without
complementary mold surfaces.
12. A method of optical-quality plastic part manufacture according
to claim 8, wherein the forming step includes indirectly warming
the film, applying pressure to conform the film against a mold
surface, then cooling the film to set the shape of the formed
film.
13. A method of optical-quality plastic part manufacture according
to claim 8, wherein the forming step includes heating a mold
surface, bridging the film across the mold surface, allowing the
film to warm indirectly by proximity to the mold surface, applying
pressure to the film to conform it to the mold surface, then
cooling the mold surface before removing the formed film.
14. A method of optical-quality plastic part manufacture according
to claim 13, wherein the mold surface defines a spherical
curve.
15. A method of optical-quality plastic part manufacture according
to claim 13, wherein the mold surface defines a non-spherical
curve.
16. A method of optical-quality plastic part manufacture according
to claim 13, wherein the mold surface defines a combination of
curves that may include spherical curves and aspherical curves.
17. A method of optical-quality plastic part manufacture according
to claim 8, wherein the film is comprised of polyethylene
terephthalate.
18. A method of optical-quality plastic part manufacture according
to claim 17, wherein the film further comprises a crystalline or
semi-crystalline naphthalene dicarboxylic acid polyester.
19. A method of optical-quality plastic part manufacture according
to claim 8, wherein the forming step includes heating a mold
surface to 80-145.degree. C., bridging the film across the mold
surface to indirectly warm the film, applying pressure of 10-50 psi
to the film to conform it to the mold surface, then cooling the
mold surface to 70-85.degree. C. before removing the formed
film.
20. A method of optical-quality plastic part manufacture according
to claim 8, wherein the film is bonded at or near a surface of the
optical-quality plastic material.
21. A method of forming a heat-sensitive polarizing film comprising
the steps of: indirectly warming a heat-sensitive polarizing film;
applying pressure to conform the film against a mold surface;
cooling the film to set the shape of the formed film.
22. A method of forming a heat-sensitive polarizing film according
to claim 21, wherein the film is indirectly warmed by heating a
mold surface.
23. A method of forming a heat-sensitive polarizing film according
to claim 21, wherein the film is cooled by cooling the mold
surface.
24. A method of forming a heat-sensitive polarizing film according
to claim 21, wherein the film is bridged across a heated mold
surface to indirectly warm the film by proximity.
25. A method of forming a heat-sensitive polarizing film according
to claim 21, wherein non-vacuum action pressure is applied to the
film to conform it to the mold surface.
26. A method of forming a heat-sensitive polarizing film according
to claim 21, wherein wherein the mold surface defines a spherical
curve.
27. A method of optical-quality plastic part manufacture according
to claim 26, wherein the mold surface defines a non-spherical
curve.
28. A method of optical-quality plastic part manufacture according
to claim 21, wherein the film is comprised of polyethylene
terephthalate.
29. A method of forming a heat-sensitive polarizing film according
to claim 21, wherein the film is indirectly warmed by heating a
mold surface to 80-145.degree. C. and bridging the film across the
mold surface.
30. A method of forming a heat-sensitive polarizing film according
to claim 29, wherein pressure of 10-50 psi is applied to the film
to conform it against the mold surface.
31. A method of forming a heat-sensitive polarizing film according
to claim 30, wherein the film is cooled by cooling the mold surface
to 70-85.degree. C. before removing the formed film.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] This is a continuation-in-part of application Ser. No.
09/475,424, filed Dec. 29, 1999, hereby incorporated by reference
as if fully set forth herein.
BACKGROUND OF THE INVENTION
[0002] The field of the present invention relates to the use of
formed polyethylene terephthalate (PET) polarizer film in
optical-quality plastic parts.
[0003] A variety of polarizing films is known to exist.
Conventional polarizing films, however, have not been comprised of
PET. This fact is primarily due to PET's inert properties. The use
of PET polarizing films in optical-quality polarized parts, as
disclosed in the parent application, is therefore a unique
innovation. Moreover, as disclosed in the parent application, such
polarized parts can include ophthalmic lenses (semi-finished or
finished prescription or non-prescription blanks, lenses, goggles,
visors, shields), polarized facemasks or shields, and polarized
display devices or windows that require low haze.
[0004] Two requirements should be met for all such optical
applications: (1) controlled and reproducible curving of the
polarizing film to accommodate the contour of the optical parts;
and (2) controlled positioning of the polarizer film in the
optical-plastic construct.
[0005] Much of the formed film manufactured for ophthalmic lenses
is laminated, that is, a thin material with the desired optical or
mechanical properties (polarization, optical density, color,
resistance to breakage, etc.) is sandwiched between two additional
layers of plastic for easier handling. These sheets are often
joined by adhesives but may be chemically bonded. Lamination
techniques with adhesives or by thermal heating are well-known
(e.g., Plastics Engineering Handbook, pp. 492ff, The Society of
Plastics Industry, Inc. NY, 1960). U.S. Pat. Nos. 5,286,419 and
5,051,309, which are incorporated by reference as if fully set
forth herein, discuss heating and forming such laminates of one or
more support layers in combination with polarizers.
[0006] The problem with lamination is that under stress, the joined
layers may delaminate, leaving defects that compromise either the
appearance or integrity of the final product. Therefore, techniques
have also been developed to form free-standing film into desired
shapes.
[0007] Free-standing film techniques commonly involve heating the
film directly to a softening point so that pressure, vacuum, or a
combination of both can be used to force the film into a molded
shape. A distinct problem with applying these techniques to common
polarizer film (e.g., polyvinyl alcohol (PVA)) is that the high
heat needed to soften the film sufficiently to slump into the
mold's shape damages the optical and/or mechanical properties of
the film. Accordingly, improvements in polarizer films or forming
techniques are desirable.
[0008] As disclosed in the parent application, polarized film
comprised of PET such as that described in U.S. Pat. No. 5,059,356,
which is incorporated by reference as if fully set forth herein,
has several advantages over PVA, including affordability,
significantly better heat, moisture, and solvent resistance, and
good mechanical stability.
[0009] The present inventors recognized that an optical-quality
plastic part utilizing PET film might offer advantages over an
optical construct utilizing a conventional polarizer such as PVA
film if the inert PET film could be reliably incorporated into the
optical construct. Thus, a suitable method to form the PET
polarizer film and properly position the film within the construct
is desired.
[0010] Polyethylene terephthalate is widely used to form plastic
bottles via blow molding. Blow molding, however, is not suitable
for forming polarized PET film. In blow molding, melted PET
material is extruded as a tube that is then sealed at one end and
expanded into a cooled outer mold shape by forcing air or other
gases into the interior of the hot plastic tube. First, an enclosed
shape such as this is not suitable for most optical constructs,
which normally have open, curved shapes. Secondly, and more
importantly, this common technique requires melting the PET, which
would negate the polarizing effect of this film.
[0011] A similar loss of the polarizing effect of the PET film
would result if another common technique, vacuum forming of hot or
molten material, was used. In addition, vacuum forming requires
vias in the mold to remove entrapped air. Such vias cause
unacceptable marks on the polarizer film, resulting in optical
distortion on the final parts.
[0012] Alternatively, the PET film may be curved or formed by
techniques commonly known to those skilled in the art as described
in, for example, U.S. Pat. Nos. 5,641,372 and 5,434,707, which
disclosures are hereby incorporated by reference as if fully set
forth herein. In particular, U.S. Pat. No. 5,641,372 describes the
use of vacuum and liquid pressure to force a heated sheet of
material against the molding surface, whereas U.S. Pat. No.
5,434,707 describes forming a laminated part under heat and
pressures in the range of 250-300 psi.
[0013] Such techniques used to form conventional polarizer
laminates or free-standing PVA films are not appropriate for
forming PET polarizer films. In particular, the PET polarizer film
has a thickness of .about.100.mu.. Laminates have a minimum
thickness of 0.6 mm, which is a significantly larger mass for heat
transfer. In addition, the laminate construction (of protective
thermoplastic layers on each side of the polarizer film) means that
the polarizer will experience less heat than the outer protective
layers. This construction means that the polarizing property of the
sandwiched film is less likely to be compromised than in a
free-standing PET film. On the other extreme, the free-standing
polyvinyl alcohol films are commonly only about 30.mu. thick, and
have much less elasticity than the PET polarizer film. Hence, these
thinner, weaker films can be forced out of shape more readily than
the PET polarizer film.
[0014] Accordingly, an improved method of forming a polarizer film
into a curved shape to accommodate the contour of the typical
optical application, and then reliably incorporate the formed film
into an optical-quality plastic part without degrading the optical
and/or mechanical properties of the film is desired.
SUMMARY OF THE INVENTION
[0015] The preferred embodiments relate to an optical-quality
plastic part having a PET polarizing film formed to a curved shape
suitable for the optical application, and to a method of reliably
positioning the film relative to surfaces of the optical construct.
In addition, the optical performance and cosmetic quality of the
formed film is preferably maintained at the high level required for
optical-quality constructs such as ophthalmic lenses and displays.
Various other embodiments may utilize some but not all of the above
elements, or may include additional refinements, while obtaining
the benefit of an optical-quality plastic part utilizing PET
film.
BRIEF DESCRIPTION OF THE DRAWINGS
[0016] The various objects, features, and advantages of the present
inventions may be better understood by examining the Detailed
Description of the Preferred Embodiments found below, together with
the appended figures, wherein:
[0017] FIG. 1 is a flowchart illustrating the general forming
process for PET polarizer film according to a preferred
embodiment;
[0018] FIG. 2 illustrates an exemplary forming apparatus with
heating and cooling coils for effecting a curved film piece;
[0019] FIG. 2a is a detailed view of the sealing surface shown in
FIG. 2;
[0020] FIG. 2b is a detailed view of the combination
heating/cooling coil shown in FIG. 2;
[0021] FIG. 2c is a detailed view of the molding surface shown in
FIG. 2; and
[0022] FIG. 3 illustrates another exemplary forming apparatus with
electrical heater and separate cooling coils for effecting a curved
film piece.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0023] The preferred embodiments will now be described with respect
to the drawings. To facilitate the description, any numeral
identifying an element in one figure will represent the same
element when used in any other figure.
[0024] As disclosed in the parent application, the optical-quality
plastic substrate (e.g., lens substrate) may comprise a thermoset
material or a thermoplastic material. With respect to thermoset
materials, the preferred materials comprise polymers from
diethylene glycol bis (allyl carbonate) or diallyl diglycol
carbonate, such as CR-39.RTM. from PPG Industries, Inc., or Akzo
Nobel brand NS205. The optical-quality plastic substrate may
comprise other thermoset materials such as polymers of 1,3 butylene
glycol dimethacrylate, acrylonitrile, allyl methacrylate,
ethoxymethyl methacrylate, ethylene glycol dimethacrylate,
polyethylene glycol dimethacrylate; ally esters; co-polymers of
allyl esters with styrene or vinyl type monomers, such as diallyl
maleate, diallyl phthalate, methallyl methacrylate, etc.; and high
index copolymers containing, e.g., vinyl functionality,
isocyanates, urethanes, sulfur-containing aromatic vinyl compounds,
and bromine-containing aromatic acrylic compounds.
[0025] With respect to thermoplastic materials, the preferred
materials comprise polycarbonate (PC) resin such as that sold by
Bayer, Inc. of Pittsburgh, Pa. under their trademarks Makrolon.RTM.
DPI-1821 or 1815, or Lexan.RTM. OQ2720 manufactured by General
Electric. The optical-quality plastic substrate may comprise other
thermoplastic materials such as polysulfones, polyethersulfones,
polyamides, polystyrenes; and mixtures of PC and polyurethanes,
polyesters, polysulfones, polystyrenes, amorphous polyolefins, and
acrylics.
[0026] The PET film is preferably of very high optical quality to
match ophthalmic standards, such as Developmental Film 99-04
distributed by R&S Enterprises of Yokohama, Japan with a
polarizing efficiency of at least 96.3% and a transmission average
(400-700 nm) of 14-18%. The present inventors currently prefer the
un-annealed form to the standard annealed form of Developmental
Film 99-04 distributed by R&S Enterprises. The PET film may
further comprise a crystalline or semi-crystalline naphthalene
dicarboxylic acid, such as polyethylene naphthalate polyester or a
copolymer derived from ethylene glycol, naphthalene dicarboxylic
acid, and some other acids such as terephthalate.
[0027] While the preferred embodiments utilize PET film, the
following disclosed forming techniques are also applicable to other
heat-sensitive polymer films, or for PET films that may contain
other heat-sensitive additives. Such additives could include
organic dyes or colorants, photochromic agents, and ultraviolet,
infrared, or selective visible light absorbers.
[0028] The following disclosed forming techniques, as exemplified
in FIG. 1, realize a more reliable, optical-quality part compared
to conventional techniques that are complicated and likely to
damage the optical and/or mechanical properties of the polarizing
film.
[0029] As illustrated in FIG. 1, contrary to conventional
techniques of film forming, with the preferred embodiments, the
film is not actively heated before being placed in contact with the
molding surface. Thus, less degradation occurs for two reasons:
first, the film is not subjected to excessive heat that causes
burning or discoloration of the film; and secondly, the film is not
heated such that it undergoes unsupported stretch that mis-aligns
the polarizer. Preservation of both these characteristics is ideal
to the usefulness of this product.
[0030] Turning in detail to FIG. 1, this PET film forming flow
chart illustrates forming PET film at the lowest preferred settings
10 beginning with the step of "heat lower mold to about 80 to
90.degree. C" 12. Advantageously step 12 involves heating a single
mold surface for shaping the film. Thus, step 12 is an improvement
over conventional PET forming techniques, such as the blow-forming
technique discussed above. This is typically because that technique
require the expense and added care of mated forming surfaces, and
in any event would likely compromise the film's polarization
characteristic. In step 12, the single mold surface is heated to a
temperature above the glass transition of the PET polarizing film
(69.degree. C.), but significantly lower than the film's melting
point (.about.250.degree. C.). The preferred mold temperature,
identified experimentally, is approximately 135.degree. C., but
temperatures as low as about 80-90.degree. C. can be used
successfully. As the temperature of the mold is increased further
(>145.degree. C.), this extra heating will burn, discolor, or
mis-shape the film.
[0031] The next step in FIG. 1 illustrates the step of "turn off
heater; place piece of PET film across lower mold surface" 14. In
step 14, the heater is turned off, and the PET polarizing film is
bridged across the edges that define the limits of the mold's
surface. The mold may comprise spherical, cylindrical, or compound
curves that combine such shapes as spherical, cylindrical, and
toric elements.
[0032] For example, an aspherical shape is often desired for a
particular optical application. In fact, the aspherical shape is
typically used for progressive ophthalmic lenses. To effect this
shape for such an optical application, one requires a mold wherein
the spherical radius of curvature for the main viewing region can
be .about.84 mm, but can change over a distance of less than 15 mm
to achieve a spherical radius of only 47 mm for increased lens
power in the reading zone. The embodiments of the present invention
allow controlled forming of the film to this type of contoured
application without compromising the film's optical properties by
introducing folds, wrinkles, or other physical defects in the film,
or losing the required polarization.
[0033] Referring to FIG. 1, the next step of "lower sealing surface
to mold surface to hold PET film; warm for approximately 30 secs"
16 involves a sealing surface that is pressed behind the PET
polarizer film to hold at least the edges of the film against the
desired mold surface, or against a sealing or gasket material on
its edges. The sealing surface behind the film need not be
conformal to the final shape, or contact the PET film except at the
general location of the edges of the mold surface. For simplicity,
it may be flat or shaped in any convenient manner that holds the
film against the edges of the mold. A solid part, such as a flat
metal sheet or a soft, deformable plastic, may be used. Preferably,
the sealing surface should also be adapted to hold the film
stationary against these edges when moderate pressure is
applied.
[0034] The film may be pressed directly against the edges of the
molding surface or separated by a sealing or gasket material.
Similarly, the sealing surface may directly contact the film, or be
separated from it by gaskets, o-rings, or other sealing media.
Thus, the sealing surface should be adapted to secure the film in
place, withstand mild additional pressure, direct this added force
relatively evenly against the film, and not cause distortion of the
film in the final working area.
[0035] Once the film has been sealed against the edges of the mold,
this closed environment is allowed to warm with the residual heat
of the mold. Such warming currently requires approximately thirty
seconds, as shown in step 16.
[0036] FIG. 1 illustrates the active forming step of "apply molding
pressure of about 50 psi for approximately 15 secs" 18 after the
sealing and warming step 16. In active forming step 18, added
pressure is applied through or via movement of the sealing surface
behind the PET film to conform the film to the mold surface. One
preferred method of applying this pressure is to introduce air or
other pressurized gases through the sealing surface onto the back
of the film. This pressure can be directed through a single channel
in a metal backing plate or multiple channels in a porous backing
plate. Alternately, the pressure may be applied indirectly if a
deformable sealing surface is used. With a deformable sealing
surface, pressurized gases may be directed at the sealing material,
which then changes its distance from the film and creates an
indirect pressure wave to press the film against the mold.
[0037] In active forming step 18, the preferred pressure range is
approximately 10-20 psi, and most preferably the range is
approximately 15-20 psi. Pressures in the range of 5-50 psi may be
used. Pressures in the upper portion of this range are preferred if
lower molding temperatures are employed. At higher pressures,
unacceptable wrinkling may occur at the sealing surface or sealing
gasket. In addition, higher pressures may cause wrinkling or
distortion in the main molding surface because they do not allow
the film to adapt to the forming surface evenly.
[0038] In the disclosed forming embodiments, the pressure may be
applied from approximately 15-45 seconds, depending on the mold
shape. The slightly longer forming times are used for deeper or
more complicated (non-spherical) mold shapes. As shown in step 18,
pressure at about 50 psi is applied for approximately 15 seconds,
but it should be noted that other pressures as discussed are
contemplated by the current invention.
[0039] Advantageously, with the forming embodiments disclosed
herein, active vacuum is not used to either remove the trapped
gases or draw the film against the molding surface. This
improvement simplifies the production process and the forming
equipment requirements, and avoids any deformations caused by
actively drawing the film against vacuum ports. Nonetheless, if a
vacuum assist is desired, vent hole(s) or channel(s) may optionally
be incorporated into a film forming apparatus.
[0040] After the short forming time of step 18, FIG. 1 illustrates
the next step is "open cooling valves; cool mold to about
70.degree. C." 20. Step 20 describes another preferred stage in the
process: cooling the mold. With the forming techniques disclosed
herein, as noted above, only the forming mold has been heated,
while the rest of the forming equipment remains at approximately
room temperature. This advantage also simplifies production
requirements and ensures that the PET film is not overheated in the
forming process. Therefore, at step 20 it is preferred that only
the forming mold surface is actively cooled. An alternate
embodiment may include additional cooling in the upper sealing
surface, for faster, albeit indirect, heat transfer.
[0041] In step 20, the mold is cooled preferably to about
70-85.degree. C., and most preferably to about 75.degree. C. As
FIG. 1 illustrates the lowest settings, step 20 shows the mold may
be cooled to about 70.degree. C. This short cooling step in the
mold allows the film to further "set" into its new shape. If it is
removed at the mold temperature, the film may not replicate the
mold surface sufficiently for reproducible optical constructs.
There is also a tendency for the film to adhere to the mold while
it is still warm.
[0042] With the preferred embodiments, the molding surface is the
active element for heating and cooling the film. Contrary to
conventional forming techniques, which normally maintain the
molding surface at a low temperature to simply freeze the hot
(melted) material in place, the preferred embodiments
advantageously allow the polarized PET film to be formed without
protective thermoplastic sheets, without destroying the optical
properties of the film, and without causing heat damage to the film
that degrades its mechanical integrity.
[0043] The final step in the exemplified forming process
illustrated in FIG. 1 is "close cooling valves; turn off forming
pressure, raise seal; remove formed wafer; turn on heater" 22. Step
22 ends the pressure and cooling cycle, and removes the sealing
surface so that the formed film can be taken from the molding
apparatus. At this point, one may begin the forming cycle with
another piece of film, as indicated by the connection back to step
12.
[0044] After the film has been formed utilizing the disclosed
embodiments exemplified by the flow chart of FIG. 1, the film may
be subjected to surface treatments, as disclosed in the parent
application and related continuation-in-part application entitled
"Treated Polyethylene Terephthalate Polarizing Films For Improved
Adhesion In Optical Parts," filed May 10, 2000, which is hereby
incorporated by reference as if fully set forth herein. Such
disclosed surface treatments advantageously allow this inert PET
polarizing film to integrally bond to common optical-grade plastic
materials, including thermosets, thermoplastics, and
reaction-injection molding materials for realizing a variety of
optical-quality plastic parts. Additionally, these methods may
allow the formed film to be incorporated with existing optical
plastic constructs by adhesive lamination, or binding to an outer
surface of the part, or between surfaces of a multi-layered
part.
[0045] An additional refinement for thermoset or reaction-injection
molded mixtures is to use the molding apparatus described in
application Ser. No. 09/447,445, filed Nov. 22, 1999, hereby
incorporated by reference as if fully set forth herein. The molding
apparatus disclosed therein allows for more precise positioning of
the film within the optical-quality plastic construct, and better
controlled introduction of liquid monomer(s) around both sides of
the film.
I. OVERVIEW OF THE EXAMPLES
[0046] The preferred embodiments for forming and using formed PET
polarizer film are more particularly described in the following
examples that are intended as illustrations only since
modifications and variations within the scope of the general
disclosure will be apparent to those skilled in the art.
[0047] Examples 1-5 demonstrate the use of the disclosed forming
techniques relative to one application and particularly the
production of thermoplastic ophthalmic lenses. Example 3
demonstrates the limitations inherent in using existing laminate
polarizer technology for non-spherically curved optical parts, in
contrast to the advantages of the preferred embodiments as
discussed in Examples 4 and 5.
[0048] FIG. 2 illustrates an exemplary forming apparatus 50 with
heating and cooling coils for effecting a curved film piece.
Utilized in Example 1, this polymer film-forming apparatus 50
comprises a concave (uniform or contoured in shape), heatable mold
surface 52 with a through-gas vent hole 54 for allowing egress of
air trapped between the film 56 and the mold surface 52. Although
shown as a single hole 54, this means to allow egress of gases as
the film is pressed to the mold 52 may take the form of minute
hole(s) in the mold or minute channel(s) at the edge of the mold 52
to allow escape of entrapped gases between the materials. Thus,
additional vent holes may be added, and if desired, active vacuum
can be used to remove entrapped air. Advantageously, additional
vents and vacuum were not employed in any of the disclosed
Examples.
[0049] To reduce marking of the film during forming, the vent hole
54 pierces the molding surface with a very small (preferably
<0.001") hole. This vent hole may be enlarged behind the molding
surface 52 for optional use with vacuum. The molding surface 52 and
vent hole 54 are shown in greater detail in FIG. 2c.
[0050] A sealing surface 58 is placed over the film 56 either
directly or preferably slightly separated by use of a gasket,
o-ring or other buffer material indicated as sealing o-ring 60. The
sealing surface 58, as best seen in FIG. 2a, may be a solid, flat
metal plate with a groove 67 to retain the sealing o-ring 60 in its
position at the edge of the molding surface 52. This sealing o-ring
60 may be positioned on the curve of the molding surface 52, on the
edge of the molding surface 52, or sealing surface 58 can be made
larger such that sealing occurs on a flat area surrounding the
curve of the mold 52 (see FIG. 2).
[0051] An air ram 62 or other suitable device may provide pressure
to hold the sealing o-ring 60 securely against the film 56.
Alternately, the sealing surface 58 may be an impermeable but
deformable material that will either contact the film 56 under
pressure to force it against the molding surface 52, or transmit a
pressure wave against the film 56 to direct it toward surface
52.
[0052] A combination heating/cooling coil 64 may heat the molding
surface 52. This coil 64 is shown in greater detail in FIG. 2b.
Heated and cooled oil may be circulated through coil 64. Other
materials (liquid, solid or gaseous) with good thermal conductivity
can be used to provide heating and cooling of the molding surface
52.
[0053] The film 56 (either flat or previously curved) is inserted
as shown to bridge across the molding surface 52. If the optional
vacuum were used, it can be applied to draw the film onto the
molding surface 52. In the disclosed Examples, only air (or other
gas) pressure was applied to the opposite side of the film 56
through the gas pressure port 66 of sealing surface 58. The
additional gas pressure in the closed environment defined by the
molding surface 52 and the sealing surface 58 forced the film 56
against the molding surface 52. The film 56 is then cooled under
pressure. The result is a film 56 with the shape and contours of
the concave molding surface 52.
A. Example 1
[0054] As noted above, Example 1 utilized the forming apparatus 50
illustrated in FIG. 2. In this Example, the molding apparatus 50
was equipped with a molding surface 52 curved to a spherical,
concave shape with a radius of 124.7 mm (4.25 diopters, referenced
to a refractive index of 1.53). Heating and cooling were supplied
from hot (160.degree. C.) and cold (21.degree. C.) oil reservoirs
through the combination coil 64.
[0055] The molding surface 52 was heated to a temperature of
143.degree. C. The sealing surface 58, equipped with a sealing
o-ring 60 and the molding surface 52, were then pneumatically
separated and a piece of flat PET polarizer film 56 bridged across
the molding surface 52. The sealing surface 58 and o-ring 60 were
then lowered via air ram 62 pressure of 40 psi onto the film 56 to
form an airtight seal.
[0056] The PET film 56 was allowed to warm for 60 seconds in this
closed environment. After the warming period, air was admitted at
20 psi pressure through the gas pressure port 66. This pressure was
applied for 30 seconds. The valves (not shown) directing the flow
of oil for heat transfer were then switched from heating to
cooling, and the formed film 56 allowed to cool under pressure to
74.degree. C. The forming pressure was then released, the sealing
surface 58 raised, and the formed PET film 56 removed.
[0057] At this point, the heat transfer valves could be switched to
allow heating oil to re-enter the apparatus 50 and prepare for the
next forming cycle. Total cycle time with this technique was
.about.10 minutes, due primarily to time required to heat and cool
the common thermal transfer lines of coil 64.
[0058] The curve of the formed PET polarizer film 56 was evaluated
by comparison with a 4.25 diopter template. The formed film 56
matched the curve very well. The formed film 56 was of the same
cosmetic quality as the flat film, and polarization was equivalent.
This formed film 56 was cut to shape, and successfully injection
molded with optical-grade PC resin to yield a light polarizing lens
with good optical qualities.
B. Example 2
[0059] For improved cycle time, alternate methods of heating and
cooling a forming apparatus were investigated. FIG. 3 illustrates
an example of another, improved, exemplary forming apparatus 80,
similar in respects to apparatus 50, but with electrical heater 82
and separate cooling coils 84 for effecting a curved film piece. As
shown in FIG. 3, the molding surface 86 is heated using an
electrical heater 82 and cooled with a closed loop system via
separate cooling coils 84. In this instance, the coolant was oil
and maintained by a chiller at 13.degree. C.; other coolants can be
employed. A thermocouple gauge 88 may be used to monitor the
system's temperature.
[0060] The forming apparatus 80 as shown in FIG. 3 was equipped
with a molding surface 86 curved to a spherical, concave shape with
a radius of 64.24 mm (8.25 diopters, referenced to a refractive
index of 1.53).
[0061] The power transformer of the electrical heater 82 was set to
100% and heated until the thermocouple 88 indicated 140.degree. C.
A piece of flat PET polarizer film 90 was bridged across the
molding surface 86. Sealing surface 92 and o-ring 94 were then
lowered via air ram pressure of 40 psi onto the film 90 to form an
airtight seal. The heater 82 transformer was turned off, and the
PET film 90 allowed to warm in this ambient, closed condition for
45 seconds. After the initial warming period, air pressure was
admitted at 20 psi through the gas pressure port 96. The apparatus
80 was maintained at 135.degree. C. at this pressure for 30
seconds. The cooling valves (not shown) were then opened to admit
chilled oil into the coils 84, and the formed film 90 allowed to
cool under pressure until a temperature of 74.degree. C. was
achieved. The forming pressure was then released, the sealing
surface 92 raised, and the formed PET film 90 removed.
[0062] At this point, the cooling valves may be closed, the
transformer restarted, and the next forming cycle begun. With the
apparatus of FIG. 3, the cycle time has been reduced to less than 6
minutes. Further cycle time improvements are probable with other
heating/cooling systems.
[0063] The curve of the formed PET polarizer film 90 was evaluated
by comparison with an 8.25 diopter template. The formed film 90
matched the curve very well. The formed film 90 was of the same
cosmetic quality as the flat film, and polarization was equivalent.
This formed film 90 was cut to shape, and successfully injection
molded with optical-grade PC resin to yield a light polarizing lens
with good optical qualities.
C. Overview of Examples 3, 4, and 5
[0064] Examples 3, 4 and 5 compare standard thermoplastic polarizer
molding technology for non-spherical optical parts with the
embodiments of the present invention.
[0065] Often, optical designs require non-spherical surfaces. One
example in the ophthalmic industry is progressive lens designs.
Such lenses have a range of spherical and/or aspherical curves
blended over an area not larger than 80 mm. For instance, a common
progressive lens design, denoted a 6-200, is approximated by a
spherical radius of curvature of about 84.8 mm (6.25 diopters of
power at a reference refractive index of 1.53) in the distance
portion of the lens surface that transitions over a distance of
less than 15 mm to a radius of curvature in the reading zone of
approximately 64 mm. These curvatures are blended in aspherical
combinations to soften the contours of the final lens.
i. Comparative Example 3
[0066] A commercially available 6.25 diopter PC/polarizer film/PC
laminate curved wafer (0.8 mm thick) was obtained. The curve was
confirmed by comparison to a 6.25 diopter template. This polarizer
wafer was positioned in the cavity of a standard thermoplastic
injection-molding machine equipped with a concave insert molding
surface contoured to a 6-200 design. Optical-grade PC was admitted
at standard injection-molding temperatures and pressures to form a
6-200 lens incorporating this polarizer wafer.
[0067] The optical properties of the formed lens were evaluated
visually and by optical focal length measurements. Visually,
distortion was apparent to the unaided eye along the curve
transitions to the steeper (shorter) radius. Even worse, in some
instances the wafer delaminated from the main body of the lens in
these transition zones. This result is clearly unacceptable to
industry standards. Focal length measurements showed that in the
reading zone, where a radius of 63.3-63.5 mm would be expected from
measurements on the molding insert, only a radius of 65-63.8 mm was
achieved. This comparative Example indicates that the standard
wafer technology is not well adapted to conform to the aspherical
mold shape, or to make a suitable optical product.
ii. Example 4
[0068] The apparatus 80 and method of Example 2 were used except a
6.25 diopter, spherical, concave mold surface 86 was employed.
[0069] The power transformer of the electrical heater 82 was set to
100%, and heated until the thermocouple 88 indicated 140.degree. C.
A piece of flat PET polarizer film 90 was positioned to bridge
across the molding surface 86. The sealing surface 92 and o-ring 94
were then lowered via air ram pressure of 40 psi onto the film 90
to form an airtight seal. The heater 82 transformer was turned off,
and the PET film 90 allowed to warm in this ambient, closed
condition for 30 seconds. After the initial warming period, air
pressure was admitted at 20 psi through the gas pressure port 96.
The apparatus 80 was maintained at 135.degree. C. at this pressure
for 30 seconds. The cooling valves were then opened to admit
chilled oil into the coils 84, and the formed film 90 allowed to
cool under pressure until a temperature of 74.degree. C. was
achieved. The forming pressure was then released, the sealing
surface 92 raised, and the formed PET film 90 removed.
[0070] The curvature of the formed film 90 was confirmed by
comparison to a 6.25 diopter template. This formed polarizer film
90 was cut to size and positioned in the cavity of a standard
thermoplastic injection-molding machine equipped with a concave
insert molding surface contoured to a 6-200 design. Optical-grade
PC was admitted at standard injection-molding temperatures and
pressures to form a 6-200 lens incorporating this polarizer film
90.
[0071] The resulting lens showed no visual distortion along the
transition zones of different radii of curvature. In addition, the
correct optical lensing power was obtained. However, this
spherically shaped film 90 could not cover the additional surface
area present for an aspherical rather than a spherical shape.
Hence, some edge portions of the lens were not covered by the
polarizer film 90. This result suggests that either a larger
diameter is needed, or a non-spherically formed film is more
adaptable to incorporation with non-spherical designs.
[0072] However, a larger diameter of spherically formed film is not
easily accommodated in an injection-molding apparatus. Either the
part will not fit securely in the injection-molding insert, or it
will overlap the edges of the insert, which can keep the
injection-molding cavity from closing properly and thus ruin the
part. While some modification and accommodation is possible,
options of non-spherical formed film are desired for broader
production tolerance. This desire is explored in Example 5.
iii. Example 5
[0073] The apparatus 80 and method of Example 2 were used except an
aspherical concave mold surface 86 was employed. This asymmetrical
mold 86 had the blended contours of a front surface of a 6-200
progressive lens design, as described above in connection with
Example 4.
[0074] The power transformer of the electrical heater 82 was set to
100%, and heated until the thermocouple 88 indicated 140.degree. C.
A piece of flat PET polarizer film 90 was positioned to bridge
across the molding surface 86. The sealing surface 92 and o-ring 94
were then lowered via air ram pressure of 40 psi onto the film 90
to form an airtight seal. The heater 82 transformer was turned off,
and the PET film 90 allowed to warm in this ambient, closed
condition for 45 seconds. After the initial warming period, air
pressure was admitted at 20 psi through the gas pressure port
96.
[0075] The apparatus 80 was maintained at 135.degree. C. at this
pressure for 30 seconds. The cooling valves were then opened to
admit chilled oil into the coils 84, and the formed film 90 allowed
to cool under pressure until a temperature of 74.degree. C. was
achieved. The forming pressure was then released, the sealing
surface 92 raised, and the formed PET film 90 removed.
[0076] The asphericity of the formed film 90 could be visually seen
by looking through the formed film 90 at a square, checkerboard
pattern. The formed film 90 was of the same cosmetic quality as the
flat film, and polarization was equivalent. This formed film 90 was
cut to shape, and successfully injection molded with optical-grade
PC resin to yield a polarized progressive lens with good optical
qualities, including the correct optical power values.
[0077] Accordingly, an optical-quality plastic part comprising PET
polarizer film and methods of its manufacture are disclosed,
wherein the manufacturing process incorporates forming the PET
polarizer film such that it conforms to the required contours of
the optical part without compromising the part's optical and/or
physical properties. While preferred embodiments are disclosed
herein, many variations are possible which remain within the
concept and scope of the invention. Such variations would become
clear to one of ordinary skill in the art after inspection of the
specification and drawings herein. The inventions therefore are not
to be restricted except within the spirit and scope of the appended
claims.
* * * * *