U.S. patent application number 10/750145 was filed with the patent office on 2005-06-30 for process for making a coated optical article free of visible fining lines.
This patent application is currently assigned to Essilor International Compagnie Generale d'Optique. Invention is credited to Adileh, Fadi O., Jiang, Peiqi, Weber, Steven.
Application Number | 20050140033 10/750145 |
Document ID | / |
Family ID | 34701157 |
Filed Date | 2005-06-30 |
United States Patent
Application |
20050140033 |
Kind Code |
A1 |
Jiang, Peiqi ; et
al. |
June 30, 2005 |
Process for making a coated optical article free of visible fining
lines
Abstract
The invention concerns a process for making a coated optical
lens blank free of visible fining lines which comprises: (i)
providing an optical article having at least one fined but
unpolished geometrically defined main face; (ii) providing a mold
part having an internal and external surface; (iii) depositing on
said main face of said optical article or on the internal surface
of the mold part a requisite amount of a liquid curable coating
composition; (iv) moving relatively to each other the optical
article and the mold part to either bring the coating composition
into contact with the main face of the optical article or into
contact with the internal face of the mold part; (v) applying
pressure to the mold part to spread the liquid curable coating
composition on said main face and form a uniform liquid coating
composition layer onto the main face; (vi) curing the liquid
coating composition layer; (vii) withdrawing the mold part; and
(viii) recovering the free of visible fining lines coated optical
article.
Inventors: |
Jiang, Peiqi; (Tarpon
Springs, FL) ; Weber, Steven; (Clearwater, FL)
; Adileh, Fadi O.; (Largo, FL) |
Correspondence
Address: |
FULBRIGHT & JAWORSKI L.L.P.
600 CONGRESS AVE.
SUITE 2400
AUSTIN
TX
78701
US
|
Assignee: |
Essilor International Compagnie
Generale d'Optique
Charenton cedex
FR
|
Family ID: |
34701157 |
Appl. No.: |
10/750145 |
Filed: |
December 31, 2003 |
Current U.S.
Class: |
264/1.7 ;
264/255 |
Current CPC
Class: |
B29K 2995/0026 20130101;
B29C 66/71 20130101; B29C 66/73161 20130101; B29L 2011/0016
20130101; B29D 11/0073 20130101; B29C 43/021 20130101; B29C 66/71
20130101; B29C 2035/0827 20130101; B29C 2043/3649 20130101; B29K
2995/007 20130101; B29C 2043/3652 20130101; B29C 2043/3655
20130101; B29K 2033/12 20130101; B29K 2995/0072 20130101; B29K
2069/00 20130101; B29C 66/71 20130101 |
Class at
Publication: |
264/001.7 ;
264/255 |
International
Class: |
B29D 011/00 |
Claims
1. A process for making a coated optical lens blank free of visible
fining lines which comprises: (i) providing an optical article
having at least one fined but unpolished geometrically defined main
face; (ii) providing a mold part having an internal and external
surface; (iii) depositing on said main face of said optical article
or on the internal surface of the mold part a requisite amount of a
liquid curable coating composition; (iv) moving relatively to each
other the optical article and the mold part to either bring the
coating composition into contact with the main face of the optical
article or into contact with the internal face of the mold part;
(v) applying pressure to the mold part to spread the liquid curable
coating composition on said main face and form a uniform liquid
coating composition layer onto the main face; (vi) curing the
liquid coating composition layer; (vii) withdrawing the mold part;
and (viii) recovering the free of visible fining lines coated
optical article.
2. The process of claim 1, wherein the liquid coating composition
layer is cured under pressure.
3. The process of claim 1, wherein said mold part is rigid and its
internal face inversely replicates said main face of said optical
article.
4. The process of claim 1, wherein said mold part is flexible and
the geometry of its internal face inversely replicates said main
face of said optical article under the pressure applied in step
(v).
5. The process of claim 1, wherein the curable liquid coating
composition is a UV curable composition.
6. The process of claim 1, wherein the mold part is a transparent
wafer.
7. The process of claim 5, wherein the mold part is a UV
transparent wafer.
8. The process of claim 4, wherein the flexible part has a higher
base curvature than the base curvature of the fined and unpolished
optical article to be coated.
9. The process of claim 1, wherein the pressure exerted onto the
mold part ranges from 10 kPa to 350 kPa.
10. The process of claim 1, wherein the pressure exerted onto the
mold part ranges from 30 to 150 kPa.
11. The process of claim 4, wherein the flexible mold part is an
inflatable flexible membrane.
12. The process of claim 4, wherein the flexible mold part has a
thickness of 2 mm or less.
13. The process of claim 4, wherein the flexible mold part is made
of flexible plastic material.
14. The process of claim 4, wherein the flexible plastic material
comprises polycarbonate or poly(methylmethacrylate).
15. The process of claim 1, wherein R.sub.q of the fined but
unpolished geometrically defined main face ranges from 0.01 to 1.5
.mu.m.
16. The process of claim 1, wherein R.sub.q of the fined but
unpolished geometrically defined main face ranges from 0.1 to 1.0
.mu.m.
17. The process of claim 1, wherein the optical article is made of
polycarbonate.
18. The process of claim 13, wherein said main face of the optical
article has a R.sub.q of about 0.5 .mu.m.
19. The process of claim 1, wherein the optical article is made of
diethylene glycol bis-allylcarbonate, polycarbonate,
polythiourethane or episulfide material.
20. The process of claim 19, wherein said main face of the optical
article has a surface roughness S.sub.q of about 1.0 .mu.m.
21. The process of claim 1, wherein the cured coating has a
thickness of 1 to 50 .mu.m.
22. The process of claim 1, wherein the cured coating has a
thickness of 1 to 25 .mu.m.
23. The process of claim 22, wherein the cured coating has a
thickness of 1 to 10 .mu.m
24. The process of claim 23, wherein the cured coating has a
thickness of 1 to 5 .mu.m.
25. The process of claim 24, wherein the refractive index
difference between the lens blank and the cured coating is up to
0.1.
26. The process of claim 1, wherein the coating composition is an
anti-abrasive hard coating composition.
27. The process of claim 1, wherein the said main face of the lens
blank is the back face of the lens blank.
28. The-process of claim 1, wherein the lens blank is a tinted lens
blank.
29. The process of claim 1, further comprising applying an
anti-reflective coating directly onto the cured coating.
30. The process of claim 1, wherein said optical article is a lens
or lens blank.
31. The process of claim 1, wherein said optical article is a
transparent lens mold.
32. The process of claim 30, wherein said optical article is a
tinted lens or lens blank.
33. The process of claim 31, wherein said lens mold is a glass
mold.
34. The process of claim 30, wherein the said main face of the lens
or lens blank is the back face of the lens or lens blank.
35. The process of claim 1, further comprising applying an
anti-reflective coating directly onto the cured coating.
36. A process for making a coated article whose main surface has a
surface state corresponding to a polished stated which comprises:
(i) providing an article having at least one fined but unpolished
geometrically defined main face; (ii) providing a mold part having
an internal and external surface; (iii) depositing on said main
face of said article or on the internal surface of the mold part a
requisite amount of a liquid curable coating composition; (iv)
moving relatively to each other the article and the mold part to
either bring the coating composition into contact with the main
face of the article or into contact with the internal face of the
mold part; (v) applying pressure to the mold part to spread the
liquid curable coating composition on said main face and form a
uniform liquid coating composition layer onto the main face of the
article; (vi) curing the liquid composition layer; (vii)
withdrawing the mold part; and (viii) recovering the coating
article having a surface state corresponding to a polished
state.
37. The process according to claim 36, wherein the surface of the
coated article has a R.sub.q under 0.01 .mu.m.
38. The process according to claim 37, wherein the coated article
is a lens mold.
39. The process according to claim 38, wherein the lens mold is not
transparent.
40. The process of claim 1, wherein the mold part is precoated by a
release coating and/or protective coating.
41. The process of claim 1, wherein the mold part has a
microstructure or a pattern to be duplicated in the lens blank
coating.
42. The process of claim 36, wherein the mold part is precoated by
a release coating and/or protective coating.
43. The process of claim 36, wherein the mold part has a
microstructure or a pattern to be duplicated in the lens blank
coating.
Description
BACKGROUND OF THE INVENTION
[0001] The present invention relates to a process for making a
coated optical article, in particular an ophthalmic lens, a lens
blank or a lens mold, free of visible fining lines, and in
particular for directly forming a functional coating, such as an
anti-abrasion hard coating, onto a fined but unpolished main face
of an optical article, whereby no fining lines are visible when the
coated lens blank is illuminated with an arc lamp. This process may
be designated as "press coating process".
[0002] The main faces of an ophthalmic lens blank, such as a lens
blank made of a transparent plastic material, are classically
subjected to a surface mechanical treatment.
[0003] This mechanical treatment comprises a group of operations
leading to the production of a lens blank whose main faces are
perfectly polished and have the desired curvatures (optical
powers).
[0004] The mechanical treatment typically comprises three
successive steps grinding, fine grinding (also called fining) and
polishing.
[0005] Grinding is a mechanical processing step intended to create
the curvature on the face of the lens blank.
[0006] Fine grinding (fining), performed after grinding further
changes the geometry of the treated face of the lens blank but can
lead to a translucent lens blank whose treated face still shows
significant surface roughness. Typically, the Rq of the fined face
is above 0.01 .mu.m, and preferably ranges from 0.05 to 1.5 .mu.m,
more preferably from 0.1 to 1.0 .mu.m.
[0007] Finally, the polishing, a relatively long mechanical
processing step, which does not change the geometry of the treated
face, removes the remaining roughness as far as possible to give
the final transparent lens blank. Typically, the surface roughness
Rq of the polished face of the lens blank ranges under 0.01 .mu.m,
preferably around 0.05 .mu.m.
[0008] Following the mechanical treatment, functional coatings such
as primer coating, impact-resistant coating, anti-abrasion hard
coating, anti-reflective coating and top coat are classically
deposited on the mechanically treated main face of the lens
blank.
[0009] Avoiding the cumbersome polishing step of the main face of
the lens blank prior forming a functional coating on the main face
of the lens blank would thus be a definitive advantage for both
economy and environment.
[0010] U.S. Pat. No. 4,417,790 and international patent application
WO 01/67139 disclose spin or dip coating a fined but unpolished
main face of a lens. The coating thickness is at least more than 10
times higher than the surface roughness of the fined main face and
in WO 01/67139 application the difference of value of the
refractive indexes between the lens material and the coating
material shall be less than 0.01. Although the resulting coating
lens becomes transparent using such a coating thickness or
refractive index matching, the fining lines on the lens main face,
i.e. the lines resulting from the fine grinding processing step,
remain visible in particular when the coated lens is illuminated by
an arc lamp.
[0011] U.S. Pat. No. 6,562,466 discloses a process for transferring
a coating onto a main face of a lens blank which comprises
depositing a requisite amount of a curable glue on a main face of a
lens blank, bringing a coating born by a flexible support in
contact with the curable glue, applying a pressure to the flexible
support to spread the glue and form a uniform layer of glue on the
main face of the lens, curing the glue and withdrawing the support,
whereby one recovers a lens blank having the coating adhering to
the main face of the lens blank.
[0012] Although coated lens blank free of visible fining lines may
be obtained with the above coating transfer process, the thickness
of the final coating including the cured glue layer and the
transferred coating is typically of 25 .mu.m or more and the
transferred coating comprises several layers of different
chemistry.
[0013] Applicant has now found that it is possible to make a coated
optical article, especially a lens blank, free of visible fining
lines in which the coated main face of the article is merely fine
grinded but not polished and even though the coating is a thin
coating, for example has a thickness of 10 .mu.m or less, and/or
the refractive index difference between the coating and the
article, in particular a lens blank, is high, for example is up to
0.05, even 0.1 or more.
[0014] Other classical spin, dip or flow coating cannot lead to an
article free of visible fining lines when the article is
illuminated by an arc lamp.
SUMMARY OF THE INVENTION
[0015] This is an object of the invention to provide a process for
making a an optical article free of visible fining lines, in which
the coating is directly formed on a fined but unpolished main
surface of the article;
[0016] It is a further object of the invention to provide a process
as defined above in which the coating has a thickness of 50 .mu.m
or less;
[0017] It is also an additional object of the invention to provide
a process as defined above in which the difference in the
refractive index values between the coating and the lens blank may
be up to 0.1 and more.
[0018] In accordance with the above objects and those that will be
mentioned and will become apparent below, the process for making a
coated optical article free of visible fining lines according to
the invention comprises:
[0019] (i) providing an optical article having at last one fined
but unpolished geometrically defined main face;
[0020] (ii) providing a mold part having an internal and an
external surface;
[0021] (iii) depositing on said main face of said optical article
or on the internal surface of the mold part a requisite amount of a
liquid curable coating composition;
[0022] (iv) moving relatively to each other the optical article and
the mold part to either bring the coating composition into contact
with the main face of the optical article or into contact with the
internal surface of the mold part;
[0023] (v) applying pressure to the mold part to spread the liquid
curable coating composition on said main face and form a uniform
layer of the liquid coating composition onto the main face;
[0024] (vi) curing the liquid coating composition layer;
[0025] (vii) withdrawing the mold part; and
[0026] (viii) recovering a free of visible fining lines coated
optical article.
[0027] Preferably, the pressure is maintained during the curing
step.
[0028] By a requisite amount of liquid curable coating composition
one means at least a sufficient amount for forming a final coating
covering the entire surface area of the main face to be coated.
[0029] The present invention also concerns a process for making a
coated article whose main surface has a surface state corresponding
to a polished stated which comprises:
[0030] (i) providing an article having at least one fined but
unpolished geometrically defined main face;
[0031] (ii) providing a mold part having an internal and external
surface;
[0032] (iii) depositing on said main face of said article or on the
internal surface of the mold part a requisite amount of a liquid
curable coating composition;
[0033] (iv) moving relatively to each other the article and the
mold part to either bring the coating composition into contact with
the main face of the article or into contact wit the internal face
of the mold part;
[0034] (v) applying pressure to the mold part to spread the liquid
curable coating composition on said main face and form a uniform
liquid coating composition layer onto the main face of the
article;
[0035] (vi) curing the liquid composition layer;
[0036] (vii) withdrawing the mold part and
[0037] (viii) recovering the coating article having a surface state
corresponding to a polished state.
[0038] The following description will be made referring in most of
the cases to a lens blank.
[0039] The lens blank for use in the present process may be made of
any transparent plastic material typically used for making optical
lenses and in particular ophthalmic lenses. Among the preferred
plastic materials there may be cited diethylene glycol bis-allyl
carbonate (such as CR 39.RTM. from PPG INDUSTRIES), polycarbonates
(PC), polyurethanes, polythiourethanes, poly(meth)acrylates and
polyepisulfide based polymer and copolymers.
[0040] The plastic material may optionally contain one ore more
photochromic material. Also, the lens blank material may be
tinted.
[0041] At least one main face of the lens blank to be coated using
the process of the invention has been fined but unpolished.
Typically, such a fined but unpolished main face will have a
R.sub.q of 0.05 to 1.5 .mu.m, preferably of 0.1 to 1.0 .mu.m. When
the lens blank is made of diethylene glycol bis-allyl carbonate
polymer, the surface roughness R.sub.q of the fined but unpolished
main face is generally about 1.0 .mu.m, whereas when the lens blank
is made of polycarbonate, the surface roughness of the fined but
unpolished main face is generally about 0.5 .mu.m.
[0042] The lens blank and generally any article that can be treated
by the process of the invention may also be a fined but not
polished lens blank which has been previously coated by
conventional coating processes such as spin coating, flow coating
and spray coating.
[0043] Indeed, as explained previously, such a conventional coating
process is not able to suppress fining lines visible by arc lamp
illumination.
[0044] The process of the invention will be particularly preferred
for lenses which have been coated, using conventional processes,
with a thin coating film of less than 5 .mu.m, preferably less than
2 .mu.m.
[0045] Preferably, the process of the invention is used for coating
fined but unpolished lens blanks.
[0046] The lens blank can be a lens having one or both of its main
faces surfaced or casted to the required geometry (a lens having
only one of its main faces or casted to the required geometry is
called a semi-finished lens).
[0047] Preferably, the lens blank has a first face conferring
progressive power and a second face conferring non-progressive
power, but of spherical or torical shape onto which coating
application according to the invention process is preferably
performed. Preferably, the progressive face is the front face of
the blank. However, if the progressive face is on the back face of
the lens or lens blank, it is possible to apply the coating on the
back face using the process of the invention.
[0048] The lens blank can also be a semi-finished lens wherein one
face of the lens, preferably the front face of the lens has
previously been treated with an appropriate coating
(anti-reflective, hard coat, etc.) and the remaining face,
preferably the rear face, of the lens is coated using the process
of the invention. The lens blank can be a polarized lens.
[0049] The lens blank can be pre-treated before applying the
process of the invention.
[0050] The pre-treatment can be physical, for example a plasma
treatment, or chemical, for example a solvent treatment or a NaOH
treatment.
[0051] Preferably, the fined and unpolished coated main face of the
lens blank is the back concave main face of the lens.
[0052] However, the front convex main face or both main faces of
the lens blank can be fined and unpolished and directly coated
using the process of the invention.
[0053] The curable liquid coating composition can be any well known
curable liquid coating composition typically used for forming
functional coatings in the optical lens field, such as in
particular primer coating compositions (improving adhesion of
subsequent coating onto the lens blank), impact-resistant coating
compositions, and anti-abrasive hard coating compositions.
[0054] Preferred impact-resistant and primer coating compositions
are polyurethane latex or acrylic latex compositions.
[0055] Preferred anti-abrasion hard coating compositions comprise a
hydrolyzate of one or more epoxysilane(s) and one or more inorganic
filler(s) such as colloidal silica.
[0056] The curable liquid coating compositions can be thermally
cured or cured through light irradiation, in particular UV
irradiation or both. Preferably, the curable liquid coating
compositions are UV curable coating compositions and in particular
UV curable anti-abrasion hard coating compositions.
[0057] After application and cure of the coating composition
according to the process of the invention, the resulting cured
coating has generally a thickness ranging from 1 to 50 .mu.m,
preferably from 1 to 25 .mu.m and more preferably from 1 to 10
.mu.m, typically of about 5 .mu.m.
[0058] Preferably, R.sub.q of the coated face of the optical
article is under 0.01 .mu.m.
[0059] The curable liquid coating composition is preferably
deposited onto the fined and unpolished main face of the lens blank
in the form of a drop in the centre of the face or of several drops
on different points of the main face.
[0060] The amount of curable liquid coating composition must be
sufficient to at least fill up the grooves of the surface roughness
and form a uniform layer on the entire surface area of the main
face.
[0061] The mold part may be rigid and its internal face inversely
replicates said main face of the optical article.
[0062] The mold part may be flexible and its internal face
inversely replicates said main face of the optical article under
the pressure applied in step (v).
[0063] The pressurizing flexible mold part can be a flexible wafer,
preferably having higher base curvature than the curvature of the
fined and unpolished lens blank to be coated, especially when the
back side of the lens blank is to be coated.
[0064] The flexible wafer can be made of any appropriate material,
preferably of a flexible plastic material, especially a
thermoplastic material and in particular of polycarbonate.
[0065] The working surface of the flexible wafer i.e. the surface
of the wafer in contact with the curable liquid coating composition
may have a relief organized according to a pattern, in other words,
may be microstructured and may confer to the final lens an optical
surface having the properties imparted by the microstructure (for
example antireflective properties).
[0066] Different techniques for obtaining a microstructured mold
part are disclosed in WO99/29494.
[0067] When using this flexible wafer, it is only necessary to
provide the wafer with a surface the geometry of which conforms to
the general shape of the optical surface of the lens blank onto
which the coating is to be applied, either a concave or convex
shape, but it is not necessary that this surface strictly
corresponds to the geometry of the lens blank surface to be coated.
Thus, the same flexible wafer can be used for applying coatings
onto lens blanks having surfaces of different specific geometries.
Generally, the flexible wafer has two parallel main surfaces and
consequently has an even thickness.
[0068] Flexible wafers typically have a thickness of 0.2 to 5 mm,
preferably of 0.3 to 5 mm. More preferably, the flexible wafer is
made of polycarbonate, and in this case the thickness is from 0.5
to 1 mm.
[0069] Preferably, the flexible wafers are light transparent, in
particular the UV light, thus permitting UV curing of the coating
composition.
[0070] According to the invention, a pressure is exerted on the
external surface of the wafer (i.e. the surface of the wafer which
is not in contact with the coating composition) and is preferably
substantially maintained at least up to the gelling of the
composition. Maintaining the pressure can be effected through the
use of an inflatable membrane placed on the external surface of the
wafer.
[0071] The applied pressure usually ranges from 10 to 350 kPa (3.5
kgf/cm.sup.2), and preferably from 30 to 150 kPa, even better 30 to
100 kPa.
[0072] As previously mentioned, pressurization of the flexible
wafer may be effected using an inflatable membrane.
[0073] The inflatable membrane can be made of any elastomeric
material which can be sufficiently deformed by pressurization with
appropriate fluid for urging the flexible wafer against the lens or
lens blank in conformity with he surface geometry of the lens or
the lens blank.
[0074] Typically, the inflatable membrane has a thickness ranging
from 0.50 mm to 5.0 mm and an elongation of 100 to 800%, and a
durometer 10 to 100 Shore A.
[0075] If the coating composition is thermally cured, then the
material of the inflatable membrane shall be selected to bear the
curing temperature.
[0076] If the coating composition is UV cured, then a transparent
material shall be selected, for example a transparent silicone
rubber or other transparent rubbers or latexes: the UV light is
preferably irradiated from the mold part side.
[0077] The pressure applied to the mold part by the inflatable
membrane typically ranges from 10 kPa to 150 kPa and will depend on
the lens or lens blank and flexible wafer sizes and curvatures. Of
course, the pressure needs to be maintained onto the flexible wafer
and the lens or lens blank until the coating composition is
sufficiently cured so that enough adhesion of the coating to the
lens or lens blank is obtained.
[0078] The flexible part of the process of the invention may be the
inflatable membrane itself described above, in particular an
inflatable membrane of an air accumulator apparatus. In that case,
of course, no flexible wafer is used.
[0079] Similar pressures as with a flexible wafer are used with the
inflatable membrane.
[0080] Either the wafer or the inflatable membrane can be
pre-coated, for example with a release coating, to exhibit good
optical surface for keeping optical grade of the coated lens
blank.
[0081] As for the flexible wafer, the inflatable membrane may
comprise in its surface contacting the coating composition a
micro-structure or pattern that will be duplicated in the lens
blank coating during the coating process.
[0082] The final coated lens blanks obtained by the process of the
invention have very good optical quality and they have no visible
fining lines under arc lamp illumination.
BRIEF DESCRIPTION OF THE DRAWINGS
[0083] The foregoing and other objects, features and advantages of
the present invention will become readily apparent to those skilled
in the art from a reading of the detailed description hereafter
when considered in conjunction with the accompanying drawings
wherein:
[0084] FIGS. 1A and 1B are schematic views of the main steps of a
first embodiment of the process of the invention for forming a
coating onto fined but unpolished main face of a lens blank, using
a flexible wafer as the flexible part; and
[0085] FIGS. 2A and 2B are schematic views of the main steps of a
second embodiment of the process of the invention using directly
the inflatable membrane of an air accumulator apparatus as the
flexible part.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
[0086] FIGS. 1A and 1B are schematic views of an embodiment of the
process of the invention in which the coating is performed through
a flexible wafer urged against the lens blank fined and unpolished
main face using an inflatable membrane apparatus.
[0087] FIG. 1A shows the lens blank 1, flexible wafer 4 and
inflatable membrane 14 before pressurization and inflatation of the
membrane, whereas FIG. 1B shows the same after pressurization and
inflatation of the membrane 14.
[0088] Although, the following description will be made in
connection with UV curing of the liquid coating composition,
similar apparatus and process can be used with a thermally curable
coating composition.
[0089] Referring to FIG. 1A, a lens blank 1, for example a toric
lens blank, is placed in a lens blank support 2 with its fine but
unpolished geometrically defined main face la facing outwardly.
[0090] A drop of UV curable liquid coating composition 3 is
deposited at the center of the geometrically defined main face 1a
of the lens blank 1.
[0091] A thin flexible wafer 4, for example a spheric wafer, is
placed on the coating composition.
[0092] The whole assembly is then placed in front of the membrane
14 of an inflatable membrane apparatus 10.
[0093] The inflatable membrane apparatus 10 comprises a fluid
accumulator 11, for example an air accumulator provided with fluid
port 12, for example an air port connected to a pressurized fluid
source (not represented) for introducing pressurized fluid within
the accumulator and also evacuating pressurized fluid from the
accumulator. The upper face of the accumulator 10 comprises a light
transparent portion 13, for example a UV transparent quartz glass
portion, whereas the lower face of the accumulator 10 comprises a
transparent inflatable membrane 14 in register with the transparent
quartz glass 13.
[0094] As shown in FIG. 1A, the apparatus 10 further comprises a
guiding means 15 for laterally guiding the inflatable membrane 14
during inflatation thereof. More specifically, this guiding means
comprises a trunconical part or funnel 15 projecting outwardly from
the lower face of the accumulator 10 and whose greater base is
obturated by the inflatable membrane 14 and whose smaller base is a
circular opening having a diameter at least equal to the base
diameter of the flexible wafer 4 but preferably slightly larger (up
to 5 mm larger).
[0095] Typically, the funnel height will range from 10 to 50 mm,
preferably 10 to 25 mm, and will have a taper of 10 to 90.degree.,
preferably 30 to 50.degree..
[0096] Finally, a light source, for example a UV light source 16 is
placed behind the accumulator 10 in front of the transparent quartz
plate 13.
[0097] Generally, the assembly comprising the lens blank holder 2,
the lens blank 1, the coating composition drop 3 and the flexible
wafer 4 is placed so that the rim of the flexible wafer 4 be within
the plan of the rim of the smaller base opening of funnel 15 or
separated therefrom by a distance up to 50 mm, preferably up to 20
mm.
[0098] As shown in FIG. 1B, a pressurized fluid, such as
pressurized air, is introduced into the accumulator 11 from an
external source (not represented) through entrance 12. The pressure
increase within the accumulator, inflates the inflatable membrane
14 and, thanks to the membrane guiding means 15, the membrane 14
uniformly urges the flexible wafer 4 against the lens blank 1,
while uniformly spreading the coating composition 3.
[0099] The coating composition is then UV-cured.
[0100] After completion of the curing step, the lens blank 1 is
disassembled from the holder 2 and the flexible wafer 4 is removed
to recover a lens blank 1 whose geometrically defined surface 1a is
provided with a coating.
[0101] Of course, in case of a thermal curing process, light source
and transparent portion of the upper face of the accumulator are
not needed.
[0102] In this case also, the inflatable membrane needs not to be
transparent. Otherwise, the apparatus remains the same.
[0103] FIGS. 2A and 2B are schematic views of another embodiment of
the process in which the inflatable membrane 14 of the apparatus 10
is directly used as the flexible part for uniformly spreading the
UV curable liquid coating composition 3 on the fined but unpolished
main face 1a of the lens blank 1.
[0104] Otherwise, the coating process proceeds in a similar manner
as disclosed in connection with FIGS. 1A and 1B.
[0105] In the description and the following examples the surface
roughness Sq of the fined but unpolished main face of the lens
blank is as follows:
[0106] S.sub.q: Quadratic mean of the deviations from the mean 1 Sq
= 1 NM x = 1 N y = 1 M Z x , y 2
[0107] Computes the efficient value for the amplitudes of the
surfaces (RMS). This parameter is included in the EUR 15178 EN
report (Commission of the European Communities) Stout et A1 1993:
The development of methods for the characterisation of roughness in
three dimensions.
[0108] The roughness (S.sub.q) is measured by P-10 Long Scan of
KLA-Tencor.
[0109] The measurement condition was under 2 .mu.m tip 1 mg force
10 scans 500 .mu.m long 2000 data points.
[0110] In the description and the following examples, 2 R q = 1 N n
= 1 N ( Zn ) 2
[0111] Rq is determined as follows:
[0112] A TAYLOR HOBSON FTS (Form Talysurf Series 2)
profilometer/roughness measuring system is advantageously used to
determined the root-mean-square profile height Rq (2DRq) of the
surface (also referred as roughness Rq before).
[0113] The system includes a laser head (product reference
112/2033-541, for example) and a 70 mm long feeler (product
reference 112/1836) having a 2 mm radius spherical/conical
head.
[0114] The system measures a two-dimensional profile in the chosen
section plane to obtain a curve Z=f(x). In this example the profile
is acquired over a distance of 20 mm.
[0115] Various surface characteristics can be extracted from this
profile, in particular its shape, undulation and roughness.
[0116] Accordingly, to determine Rq, the profile is subject to two
different processes, namely shape extraction and filtering, which
corresponds to mean line extraction.
[0117] The various steps for determining a parameter Rq of this
kind are as follows:
[0118] acquisition of the profile Z=f(x),
[0119] shape extraction,
[0120] filtering (mean line extraction), and
[0121] determination of parameter R.sub.q.
[0122] The profile acquisition step consists in moving the stylus
of the aforementioned system over the surface of the lens in
question, to store the altitudes Z of the surface as a function of
the displacement x.
[0123] In the shape extraction step, the profile obtained in the
previous step is related to an ideal sphere, i.e. a sphere with
minimum profile differences relative to that sphere. The mode
chosen here is the LS arc mode (best circular arc extraction).
[0124] This provides a curve representative of the characteristics
of the profile of the surface in terms of undulation and
roughness.
[0125] The filtering step retains only defects corresponding to
certain wavelengths. In this example, the aim is to exclude
undulations, a form of defect with wavelengths higher than the
wavelengths of defects due to roughness. Here the filter is of the
Gaussian type and the cut-off used is 0.25 mm.
[0126] R.sub.q is determined from the curve obtained using the
following equation: 3 R q = 1 N n = 1 N ( Zn ) 2
[0127] where Zn is, for each point, the algebraic difference Z
relative to the mean line calculated during filtering.
[0128] The grinding and fining process used in the examples is V-95
grinding followed by fining with a 15 .mu.m pad (from 3M).
[0129] V-95 is a computer controlled grinding machine from LOH
company with 3D disk cutter. The grinding time is about 1 to 2
minutes;
[0130] Haze has been measured by Haze-Gard Plus made by BYK
Gardner;
[0131] Inspection with an arc lamp is carried out by using a BT X
75/LIS // Lamp made by Bulbtronics Inc. the light from the above
lamp is directed towards the lens and the reflected light is
projected on a screen. The image of the lens on the screen is
visually inspected in order to see if there are fining lines.
EXAMPLE 1
[0132] A semi-finished lens SF lens made of dithyleneglycol
bis-allyl carbonate copolymer (CR-39.RTM.) was generated by V-95
and fined with 15 .mu.m pad to a -1.25 power lens (back curvature
5.0 base, diameter 70 mm) without polishing. Fining process is done
with LOH Toro-X-S/SL fining machine using a 15 .mu.m pad made by
3M. The fining time is about 1 to 2 minutes. The lens was then
washed with water and soap and coated with an abrasion-resistant
coating by the process of the invention using a thin flexible wafer
and the inflatable membrane apparatus as described in connection
with the figures.
[0133] 5 drops of the liquid coating composition (0.12 g in total)
are deposited on the fined main face of the lens. The thin flexible
wafer is carefully placed on the liquid coating composition
drops.
[0134] The resulting assembly is then placed in front of the
inflatable membrane of the air accumulator and air is introduced up
to a pressure of 84 kPa (12 Psi) so that the liquid coating
composition is spread out in the entire fined main face of the
lens.
[0135] The coating composition is then UV cured for 30 seconds
using a UV lamp with high intensity 145 mW/cm.sup.2 and wavelength
from 330 to 490 nm. After separation, there is obtained a clear
coating layer on the lens without any visible fine lines by
illumination with an arc lamp.
[0136] UV Curable Liquid Coating Composition, in Weight %:
1 UVR-6110 (3,4-epoxycyclohexyl 13 methyl-3,4-epoxycyclohexane
carboxylate) GE 21 (1,4-butanediol diglycidyl ether) 30.29 HDODA
(hexane diol diacrylate) 10.85 SR-399 (dipentaerythritol
pentaacrylate) 30.36 SR 230 (diethyleneglycol diacrylate) 7.01 IBOA
(isobornyl acrylate) 2.29 UVI 6974 (cationic photoinoitiator) 5.25
IRGACURE 500 (free radical initiator) 0.82 SLF-18 (hydrocarbon base
surfactant) 0.1
[0137] Flexible Wafer:
[0138] A wafer made of polycarbonate with 0.6 mm thick plano sphere
shape having a 5.50 base curve and a 68 mm diameter. The wafer is
made by injection molding and is precoated with a release and
protective coating solution.
EXAMPLE 2
[0139] Example 1 is reproduced except using a liquid coating
composition of refractive index n.sub.D.sup.25=1.532
[0140] This liquid composition has the following formulation, in
weight %:
2 EPON 228 (bisphenol A epoxy resin) 60 GE 21 (1,4-butanediol
diglycidyl ether) 40 IRGACURE 552 (photoinitiator) 4 phr ITX
(sensitizer) 0.2 phr
COMPARATIVE EXAMPLE 1
[0141] Example 1 is reproduced except using spin coating process
and cured by conveyor UV with the same coating solution. The
results showed that even a much thick coating layer on a fining
lens (60.times. Rq of surface roughness) by spin could not cover
the fining mark. The spin coating was done by Headway Spin Coat and
spinning speed was 600 rpm for 12 seconds and 2000 trm for 4
seconds. Thereafter, curing was effected using a Fusion UV conveyor
at 9 mm H bulb, 692 mW/cm.sup.2 at 350 nm.
COMPARATIVE EXAMPLE 2
[0142] Example 1 is reproduced except using high index
(n.sub.D.sup.25=1.57) coating solution. This coating solution has
the following formulation, in weight %:
3 Diethyleneglycol diacrylate 30 Ethoxylated-8 bisphenol A
diacrylate 30 Bis(2-methacryloylthioethyl) sulfide 40 IRGACURE 819
(photoinitiator) 3 phr
EXAMPLE 3
[0143] A PC SF lens was generated by V-95 and fined with 15 .mu.m
pad to -2.00 power lens (back curve=5.0 base) without polishing.
The lens was then washed with soap and water and the same coating
solution as in comparative example 2 is applied as in Example
1.
COMPARATIVE EXAMPLE 3
[0144] Example 3 is reproduced except using the same low index
(n.sub.D.sup.25=1.518) coating solution as in example 1.
COMPARATIVE EXAMPLE 4
[0145] Example 3 is reproduced except using a flow coating method.
Flow coating is similar to dip coating which still cannot cover the
fining lines in arc lamp even though the coating thickness is
higher than 10.times. S.sub.q of surface roughness and the haze
level is low.
[0146] In that example, 5 g of coating liquid was manually smoothly
applied on the fined lens surface and turned around to let the
liquid wet the whole surface. Then, the coating was cured using a
Fusion UV conveyor at 9 mm H bulb, 692 mW/cm.sup.2 at 350 nm.
EXAMPLE 4
[0147] A CR-39.RTM. SF lens was generated by V-95 and fined with 15
.mu.m pad to -1.25 power lens without polishing. The lens was then
tinted in BPI black bath, commercially available, at 95.degree. C.
for 15 min. After that, the tinted CR-39 lens was press coated by
the same method as Ex. 1 with the commercial UV curable coating
solution (HT-1000 from GERBER COBURN Inc.). The obtained lens has
very good uniform color and very good transmission and low haze
level. There is no any fining line seen in arc lamp after press
coating.
EXAMPLE 5
[0148] A CR-39 SF.RTM. lens was generated by V-95 and fined with 15
.mu.m pad to -1.25 lens without polish. After that, it was press
coated by the same method as in example 1 with the commercial UV
curable coating solution (HT-1000 from Gerber Coburn Inc.). The
obtained lens has very good transmission and low haze level. There
is no any fining line seen in arc lamp after press coating. The
lens was then coated with an anti-reflective coating by using BAK
760 vacuum machine. It has the same properties as a commercial hard
multicoated CR-39.RTM. lens made using a polishing step.
4TABLE 1 Coating Surface Haze refractive Lens roughness before
index Coating Thickness Haze after Fining mark Ex. materials Fining
process (Rq) coating n.sub.D.sup.25 process of coating coating in
arc lamp Ex. 1 CR-39 V-95 + 15 .mu.m 0.3787 89.8 1.518 Press -5
.mu.m 0.37 No fining (2 min) [.mu.m] coating Ex. 2 CR-39 V-95 + 15
.mu.m 0.3943 89.8 1.532 Press -5 .mu.m 1.50 No fining (2 min)
[.mu.m] coating Com. 1 CR-39 V-95 + 15 .mu.m 0.3758 89.8 1.518 Spin
-25 .mu.m 0.35 Yes fining (2 min) [.mu.m] coating Com. 2 CR-39 V-95
+ 15 .mu.m 0.3831 89.8 1.57 Press -- 6.70 Yes fining (2 min)
[.mu.m] coating Ex. 3 PC V-95 + 15 .mu.m 0.2089 83.1 1.57 Press --
1.17 No fining (2 min) [.mu.m] coating Com. 3 PC V-95 + 15 .mu.m
0.2181 83.1 1.518 Spin -- 2.40 Yes fining (2 min) [.mu.m] coating
Com. 4 PC V-95 + 15 .mu.m 0.2163 83.1 1.57 Flow >25 .mu.m 1.15
Yes fining (2 min) [.mu.m] coating
[0149] Thickness of coating layers was measured by using
cross-sectioned samples in microscopy of Nikon Optiphot-2 with
600.times. of Epi illumination.
EXAMPLE 6
[0150] Example 1 was reproduced by using a very low viscosity (7
cps) coating solution consisting of, by weight, 89%
diethyleneglycol dimethacrylate and 11%
bis-2-[(meth)acryloylthioethyl]sulfide (BMTES), with 3 phr
photoinitiator/CGI-819 (Irgacure 819 from Ciba-Geigy:
bis(2,4,6-trimethylbenzoyl)-phenylphosphineoxide). The refractive
index n.sub.D (25.degree. C.) of the coating solution was 1.472.
The observed coating thickness after curing is around 1-2
micrometers. There is no fining mark seen in the arc lamp after
press coating although the coating thickness is very thin.
EXAMPLE 7
[0151] A 20 micrometers pad fined but not polished glass mould with
surfaced roughness of Sq=0.58 .mu.m was press coated by the same
method as in example I with the commercial UV curable coating
solution (HT-1000). The obtained glass mould has very good
transmission and low haze level. There is no any fining line seen
in the arc lamp after press coating.
COMPARATIVE EXAMPLE 5
[0152] The same fined but not polished glass mould as in Example 7
was spin coated using Ultra Optics coating machine with HT-1000 UV
curable coating solution. The obtained glass has a lot of fining
lines seen in the arc lamp.
* * * * *