U.S. patent application number 10/498744 was filed with the patent office on 2005-06-02 for photochromic coating process.
This patent application is currently assigned to Sola International Holdings Limited. Invention is credited to Chen, Fang, Gieslinski, Bohdan Grzegorz, Lewis, David Andrew, Toh, Huan Kiak, Wong, Kathy Wai Yuen.
Application Number | 20050116381 10/498744 |
Document ID | / |
Family ID | 3833108 |
Filed Date | 2005-06-02 |
United States Patent
Application |
20050116381 |
Kind Code |
A1 |
Wong, Kathy Wai Yuen ; et
al. |
June 2, 2005 |
Photochromic coating process
Abstract
The present invention provides a method for manufacturing a
photochromic article having a photochromic compound containing
layer. The method includes the step of coating a casting face of at
least one mould section with a photochromic host layer. The
photochromic host layer is treated to minimise damage during
subsequent steps, and a mould is then assembled so that it includes
the mould section having the photochromic host layer. The mould is
then filled with a photochromic article monomer composition and the
monomer composition is subsequently cured to form a photochromic
article substrate adhered to the photochromic host layer. The
photochromic compound is introduced into the photochromic host
layer.
Inventors: |
Wong, Kathy Wai Yuen;
(Hallett Cove, AU) ; Lewis, David Andrew; (Marion,
AU) ; Chen, Fang; (Hallett Cove, AU) ;
Gieslinski, Bohdan Grzegorz; (Hallett Cove, AU) ;
Toh, Huan Kiak; (Fullarton, AU) |
Correspondence
Address: |
BURNS DOANE SWECKER & MATHIS L L P
POST OFFICE BOX 1404
ALEXANDRIA
VA
22313-1404
US
|
Assignee: |
Sola International Holdings
Limited
|
Family ID: |
3833108 |
Appl. No.: |
10/498744 |
Filed: |
February 11, 2005 |
PCT Filed: |
December 13, 2002 |
PCT NO: |
PCT/AU02/01691 |
Current U.S.
Class: |
264/236 ;
264/255; 264/265 |
Current CPC
Class: |
B29D 11/0073 20130101;
G02B 5/23 20130101 |
Class at
Publication: |
264/236 ;
264/265; 264/255 |
International
Class: |
B29C 045/14 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 14, 2001 |
AU |
PR 9492 |
Claims
1-45. (canceled)
46. A method for manufacturing a photochromic article, the method
including the steps of: forming a photochromic host layer on the
casting face of at least one mould section, treating the
photochromic host layer to minimise damage during subsequent steps,
filling an assembled mould that includes the mould section having
the photochromic host layer with a substrate monomer composition,
curing the substrate monomer composition to form a solid article
that includes the photochromic host layer, and introducing a
photochromic compound into the photochromic host layer to form the
photochromic article.
47. A method as in claim 46 wherein the photochromic host layer has
a thickness of between 10 and 150 microns.
48. A method as in claim 46 wherein the photochromic host layer has
a thickness of between 25 and 60 microns.
49. A method as in claim 46 wherein the photochromic host layer has
a thickness of between 30 and 50 microns.
50. A method as in claim 47 wherein the photochromic compound is
introduced into the photochromic host layer after the solid article
has been removed from the mould.
51. A method as in claim 46 wherein the photochromic host layer is
at least partially cured and/or solvent is evaporated from the
photochromic host layer in order to minimise damage to the
photochromic host layer during subsequent steps.
52. A method as in claim 50 wherein the photochromic host layer is
at least partially cured to minimise damage during subsequent steps
and it is subsequently completely cured either during or after the
photochromic compound has been introduced into the photochromic
host layer.
53. A method as in claim 46 wherein the photochromic host layer is
formed from a coating monomer composition that forms a relatively
non-polar polymer.
54. A method as in claim 46 wherein the photochromic article is
formed with a photochromic host layer having a Tg of at least
40.degree. Celsius.
55. A method as in claim 46 wherein the photochromic host layer is
formed from a host layer monomer composition that contains any one
or more of: alkylene mono- or poly(meth)acrylates;
poly(alkyleneoxide) mono- or poly(meth)acrylates; urethane mono- or
poly(meth)acrylates and allyl compounds.
56. A method as in claim 55 wherein the poly(alkyleneoxide)
poly(meth)acrylate is a monomer containing a major portion of
nonaethylene glycol dimethacrylate.
57. A method as in claim 55 wherein the poly(alkyleneoxide) poly
(meth)acrylate is a monomer containing a major portion of
quatdecaethylene glycol dimethacrylate.
58. A method as in claim 55 wherein the poly(alkyleneoxide) poly
(meth)acrylate is a polytetramethylene glycol monomer.
59. A method as in claim 46 wherein the photochromic host layer is
formed from a host layer monomer composition that contains an
ethoxylated bisphenol-A dimethacrylate monomer having between 1 and
20 ethoxy groups per molecule.
60. A method as in claim 56 wherein the host layer monomer
composition includes a minor proportion of a hardening monomer that
provides rigidity when cured.
61. A method as in claim 60 wherein the hardening monomer is a
urethane acrylate, an ethoxylated bisphenol-A dimethacrylate
monomer having between 1 and 20 ethoxy groups per molecule or an
isocyanurate based poly(meth)acrylate.
62. A method as in claim 61 wherein the hardening monomer is added
in amount of 1 to 35% by weight of the host layer monomer
composition.
63. A method as in claim 61 wherein the hardening monomer is added
in amount of 5 to 15% by weight of the host layer monomer
composition.
64. A method as in claim 62 wherein the nanoindentation depth of
the photochromic host layer is between about 9000 nm and about 2500
nm.
65. A method as in claim 46 wherein the photochromic article is an
ophthalmic lens.
66. A method for manufacturing a photochromic article, the method
including the steps of: forming a photochromic host layer on the
casting face of at least one mould section, treating the
photochromic host layer to minimise damage during subsequent steps,
applying a barrier layer to the photochromic host layer, filling an
assembled mould that includes the mould section having the
photochromic host layer with a substrate monomer composition,
curing the substrate monomer composition to form a solid article
that includes the photochromic host layer, and introducing a
photochromic compound into the photochromic host layer either
before or after the step of curing the substrate monomer
composition.
67. A method as in claim 66 wherein the barrier layer minimises
penetration of the substrate monomer composition into the
photochromic host layer.
68. A method as in claim 67 wherein the photochromic host layer has
a thickness of between 10 and 150 microns.
69. A method as in claim 67 wherein the photochromic host layer has
a thickness of between 25 and 60 microns.
70. A method as in claim 67 wherein the photochromic host layer has
a thickness of between 30 and 50 microns.
71. A method as in claim 67 wherein the barrier layer is formed by
polymersing a mixture that includes a compound containing double
bonds and a compound containing thiol groups.
72. A method as in claim 67 wherein the barrier layer is formed by
polymersing a mixture that includes a compound containing
isocyanate groups and a compound containing thiol, hydroxy or
aromatic amine groups.
73. A method as in claim 67 wherein the photochromic host layer is
at least partially cured and/or solvent is evaporated from the
photochromic host layer in order to minimise damage to the
photochromic host layer.
74. A method as in claim 73 wherein the photochromic compound is
introduced into the photochromic host layer after the solid article
has been removed from the mould.
75. A method as in claim 67 wherein the photochromic host layer is
formed from a host layer monomer composition that contains any one
or more of: alkylene mono- or poly(meth)acrylates;
poly(alkyleneoxide) mono- or poly(meth)acrylates; urethane mono- or
poly(meth)acrylates; and allyl compounds.
76. A method as in claim 75 wherein the poly(alkyleneoxide)
poly(meth)acrylate is a monomer containing a major portion of
nonaethylene glycol dimethacrylate.
77. A method as in claim 75 wherein the poly(alkyleneoxide)
di(meth)acrylate is a monomer containing a major portion of
quatdecaethylene glycol dimethacrylate.
78. A method as in claim 75 wherein the poly(alkyleneoxide)
di(meth)acrylate is a polytetramethylene glycol monomer.
79. A method as in claim 67 wherein the photochromic host layer is
formed from a coating monomer composition that contains an
ethoxylated bisphenol-A dimethacrylate monomer having between 1 and
20 ethoxy groups per molecule.
80. A photochromic article prepared by the method of claim 46.
81. A method for manufacturing a photochromic article wherein
physical and/or chemical properties of a photochromic host layer
can be adjusted to alter the transition time of photochromic
compounds contained in that layer, the method including the step of
adjusting one or more of the polarity and/or the local rigidity of
the photochromic host layer to either increase or decrease the
transition time of the photochromic compounds.
82. A method as in claim 81 wherein the transition time of the
photochromic compound is controlled by including a hardening
monomer in the photochromic host layer.
83. A method as in claim 82 wherein the hardening monomer is a
urethane acrylate, an ethoxylated bisphenol-A dimethacrylate
monomer having between 1 and 20 ethoxy groups per molecule or an
isocyanurate based poly(meth)acrylate.
84. A method as in claim 83 wherein the urethane acrylate is U-4HA
or U-6HA.
85. A method as in claim 84 wherein the photochromic host layer is
formed from a coating monomer composition that contains
nonaethyleneglycol dimethacrylate.
86. A method as in claim 84 wherein the hardening monomer is
present in an amount of 1 to 35%.
87. A method as in claim 84 wherein the hardening monomer is
present in an amount of 5 to 15%.
Description
FIELD OF THE INVENTION
[0001] The present invention relates to methods for manufacturing
photochromic articles that have host layers including photochromic
compounds. In one specific form, the invention relates to a method
for manufacturing plastic ophthalmic lenses with a host layer
including a photochromic compound.
[0002] The present invention also relates to processes for
adjusting the transition times of photochromic compounds contained
in host layers of photochromic articles.
BACKGROUND OF THE INVENTION
[0003] Photochromic articles that incorporate photochromic
compounds have been known for some time. In particular, many
ophthalmic lenses contain photochromic compounds so that when they
are exposed to light of a particular wavelength, such as actinic
radiation (sunlight), the compound changes from a transparent
ground state to a coloured activated state in which the lens is
able to filter out at least some of the incident light. The
transition from the ground state to the activated state is
reversible. Therefore, whilst the photochromic compounds remain
exposed to incident light, they remain in the activated state.
However, once the source of light is removed, the compounds relax
to the ground state in which they are colourless or minimally
coloured.
[0004] Ophthalmic lenses having a photochromic capacity have been
found to be particularly suitable for glasses so that in artificial
light the lenses remain transparent, but as a wearer moves into
sunlight the lenses darken and reduce the amount of transmitted
light. Such lenses are typically formed by including a photochromic
compound within the substrate of the lens or on a surface of the
lens.
[0005] The advent and widespread adoption of ophthalmic lenses
formed from plastic materials has meant that new processes have had
to be developed to permit photochromic compounds to be used.
Typically this is done either by imbibing a photochromic compound
directly into the lens substrate, or by coating the lens with a
layer containing a photochromic compound.
[0006] However, with some known methods of introducing photochromic
compounds into plastic articles such as ophthalmic lenses it is
difficult to control the extent to which the photochromic compound
passes into the article substrate, and/or it is difficult to
incorporate sufficient of the photochromic compound into the
article substrate or the coating. In addition, some article
substrates provide a hostile environment for photochromic compounds
because they constrain the transition of the compound from the
ground to the activated state and/or they cause fatigue in the
photochromic compound.
[0007] Additionally, there is a need to provide photochromic
ophthalmic lenses in which the transition time between the coloured
activated state and the transparent ground state is as short as
possible so that the photochromic article reacts as rapidly as
possible to any change in lighting conditions.
SUMMARY OF THE INVENTION
[0008] The present invention provides a method for manufacturing a
photochromic article, the method including the steps of:
[0009] forming a photochromic host layer on the casting face of at
least one mould section,
[0010] treating the photochromic host layer to minimise damage
during subsequent steps,
[0011] filling an assembled mould that includes the mould section
having the photochromic host layer with a substrate monomer
composition,
[0012] curing the substrate monomer composition to form a solid
article that includes the photochromic host layer, and
[0013] introducing a photochromic compound into the photochromic
host layer to form the photochromic article.
[0014] The present invention also provides photochromic articles,
and especially photochromic ophthalmic lenses, that are formed
using the method of the present invention.
[0015] For discussion purposes, reference will be made to
photochromic articles in the form of plastic ophthalmic lenses in
the further description of the invention. However the methods of
the present invention are not to be taken as being limited to that
particular application and it is envisaged that the methods can be
used to produce a variety of plastic articles that include
photochromic compounds.
[0016] The `photochromic host layer` of the present invention is a
coating layer that is capable of hosting photochromic compounds.
Generally, the `photochromic host layer` will not have any
photochromic properties until photochromic compounds have been
introduced into the host layer.
[0017] In one specific form of the invention, both the photochromic
host layer and cured substrate monomer composition are polymers,
however, the polymers are preferably different and the photochromic
host layer is preferably more readily imbibable with photochromic
compound than is the cured substrate monomer composition.
[0018] The photochromic host layer is preferably between about 10
microns and about 150 microns in thickness. The host layer may be
formed by coating the casting face with a solution of host layer
monomer or with neat liquid host layer monomer using any of the
techniques that are used for that purpose in the art, such as dip
coating, spin coating, flow coating and spray coating.
[0019] Preferably, the casting face is coated by spin coating a
neat host layer monomer solution, or in the case of a relatively
viscous monomer, a solution of host layer monomer in a suitable
solvent. Spin coating may be preferred to other coating techniques
because spin coating generally provides more control over the
coverage of the casting face, and the thickness and uniformity of
the thickness of the host layer can also be controlled. For this
reason, the viscosity of the host layer monomer solution may affect
the coating process. For example, non-viscous monomers (less than
about 10 cp) will generally not provide a photochromic host layer
that is of 10 to 150 micron thickness. Similarly, very viscous
monomers may provide a photochromic host layer that is too thick,
although in that instance the viscosity can be reduced using an
appropriate solvent. In one example the casting face of the mould
section may be spin coated at less than 1000 rpm with a host layer
monomer composition having a viscosity of about 80 cp.
[0020] Preferably, the casting face for a front optical lens
surface is coated with the photochromic host layer. Preferably
also, substantially all of the casting face is coated with the
photochromic host layer. Further, it is also preferable for the
photochromic host layer to be applied with a relatively uniform
thickness across the casting face.
[0021] Ideally, the photochromic host layer is applied so that it
replicates the mould surface from which the lens is to be made and
thereby provides an optical surface having the desired surface
configuration that is substantially free from surface aberrations
that may arise due to non-uniformity of the thickness of the
photochromic host layer, flow marks and coating build up.
[0022] After the casting face has been coated with the monomeric
photochromic host layer composition, the layer is treated to
prevent damage during subsequent steps. This treatment may include
at least partially curing the host layer, or alternatively,
evaporating solvent from the host layer. If the host layer includes
a solvent, the solvent removal preferably occurs either in concert
with the partial curing or as a separate process that is conducted
prior to the partial curing. Solvent removal may be achieved by air
drying or by the use of infra-red radiation, microwave radiation or
heat.
[0023] The treatment step preferably prevents damage such as
lifting, delamination, dissolution and/or excessive swelling of the
photochromic host layer. However, the photochromic host layer
monomer is preferably only partially cured so that there is some
interpenetration of the photochromic host layer composition with
the substrate monomer composition to allow good adherence between
the photochromic host layer and the substrate in the moulded
article. Additionally, intermixing between the substrate monomer
composition and the photochromic host layer may provide a diffuse
interface of 2 to 5 microns thickness between the host layer and
the article substrate which may reduce or eliminate interference
patterns.
[0024] Additionally, it may be preferable to partially cure the
photochromic host layer and to complete the cure either during or
after the photochromic compound has been introduced into the host
layer. In this way, it is thought that the photochromic compounds
are able to diffuse into the host layer and create space within the
host layer before it is fully cured. Once the photochromic host
layer is fully cured, it may be too hard for the photochromic
compounds to penetrate sufficiently.
[0025] Optionally, in cases where the substrate monomer composition
forms a substrate that is not imbibable with photochromic compounds
it may be necessary to apply a barrier layer to the photochromic
host layer before the mould is filled with the substrate monomer
composition so that the barrier layer minimises interpenetration of
the substrate monomer into the photochromic host layer.
Interpenetration or breakthrough of the substrate monomer
composition into the host layer in that case could affect the
properties of the photochromic host layer and hence the transition
time of the photochromic compound. A barrier layer may also prevent
penetration of photochromic compounds into the article substrate.
However, preferably the barrier layer does not substantially affect
adherence between the photochromic host layer and the lens
substrate. For example, barrier layers may be formed from a thin
layer of highly cross linked polymeric material. Suitable barrier
layers may be formed by polymerising a composition that includes a
compound containing double bonds and a compound containing thiol
groups. Alternatively, the barrier layer may be formed by
polymerising a composition that includes a compound containing
isocyanate groups and a compound containing thiol, hydroxy,
aromatic amine or other nucleophilic groups.
[0026] The use of a barrier layer may article substrates that are
not normally imbibable with photochromic compound to be used.
Examples of such substrate materials include highly crosslinked
polymers such as MR-6, MR-7, MR-8, MR-10, CR-39 and episulfides.
Typically, these polymers are too rigid to be readily imbibable
with photochromic compounds and as a consequence they are
traditionally difficult to use on photochromic articles. Also, some
of these polymers have a high sulphur content which can
detrimentally affect the life of the photochromic compound.
However, the application of a barrier layer and/or the minimisation
of mixing of the substrate monomer composition with the
photochromic host layer means that impact of the substrate monomer
composition on the imbibability of photochromic compounds into the
photochromic host layer is reduced.
[0027] Photochromic compounds can be attacked by the substrate
monomer composition during curing by reaction with the
polymerisation initiator, reaction with the catalyst or an additive
in the monomer formulation and by reaction with a component of the
substrate monomer composition (such as an isocyanate).
Additionally, over time, the dye can suffer from excessive fatigue
if the monomer composition has significant sulphur content.
[0028] The use of a barrier layer overcomes these issues by
preventing the interpenetration of the monomer composition into the
photochromic host layer.
[0029] Since the barrier layer is preferably thin and cured in a
rapid manner, interpenetration of the barrier layer can be
minimised. This then affords the opportunity to introduce the
photochromic compound into the photochromic host layer before
coating the photochromic host layer onto the mould surface or at
sometime after the initial coating but before filling the moulds
with monomer composition and ensure that (i) any initiators in the
monomer composition will not destroy the photochromic compound, and
(ii) excessive dye fatigue caused by the interpenetration of
photochromic dye hostile monomer compositions into the photochromic
host layer is minimised.
[0030] Preferably, the composition of the host layer is selected to
provide an environment in which the effect of the host layer on the
transition of the photochromic compound between the activated and
the ground states is minimised. In this way, the transition time of
the photochromic compound between the ground and activated states
may also be optimised. Clearly, the more rapid the transition
between ground and activated states, the more rapid the lightening
or darkening of the photochromic article when moving out of or into
sunlight.
[0031] Without intending to be bound by theory, it is thought that
under normal conditions, photochromic compounds reach a steady
state that is a balance between the number of photons incident upon
the photochromic host layer, and the number of photochromic
compound molecules in the activated state. To overcome the steady
state, the present inventors believe that it is favourable to have
a higher number of photochromic compound molecules in the host
layer so that more of the incident photons are consumed and the
steady state is shifted in favour of the photochromic compound
molecules being in the activated state. Using the method of the
present invention it is possible to form photochromic host layers
having a thickness that allows sufficient photochromic compound
molecules to be incorporated into the layer to beneficially affect
transition times.
[0032] Additionally, the present inventors also believe that there
is a depth in a photochromic host layer beyond which light of an
activating wavelength (usually about 395 nm) does not penetrate and
therefore any photochromic compound molecules beyond this depth
will not be activated. Accordingly, to minimise the transition
time, the photochromic host layer preferably has a thickness of
between 10 and 150 microns, more preferably 25 to 60 microns, and
most preferably about 30 to 50 microns.
[0033] The composition of the photochromic host layer may also
affect the transition time of the photochromic compounds in the
host layer. Thus, the local rigidity of the host layer surrounding
the photochromic compound molecules, and/or the polarity of the
photochromic host layer in the vicinity of the photochromic
compound molecules may affect the transition time. Specifically, it
is thought that a relatively polar photochromic host layer
stabilises the activated state (which is likely to be ionic) of the
photochromic compound molecules and ultimately increases the
activated to ground state transition times. Accordingly, a
relatively non-polar photochromic host layer may contribute to fast
transition times, whereas a relatively polar photochromic host
layer may contribute to slow transition times.
[0034] Similarly, the rigidity of the photochromic host layer in
the vicinity of the photochromic compound molecules may also affect
the transition time. Specifically, it is thought that a relatively
rigid local environment slows the transition of the photochromic
compound molecules by limiting flexibility and room for the
molecule to enter the activated state. Conversely, a relatively
non-rigid or `soft` local environment is thought to allow
sufficient flexibility and room for the photochromic compound
molecules to move into the activated state.
[0035] Accordingly, to provide for a photochromic article that has
a fast transition time, the photochromic host layer is preferably
relatively soft (when polymerised). For the purposes of the present
invention, a `relatively soft` polymer may have a glass transition
temperature (Tg) of less than about room temperature.
[0036] However, in use, it may be found that such a photochromic
host layer is physically vulnerable, and in particular is easily
abraded because of its softness, and therefore the selection of a
material for use in the photochromic host layer will generally also
have to take into account physical parameters that favour a higher
Tg. In practice, a `relatively soft` photochromic host layer may be
formed from any monomer that forms a polymer having a Tg that is
about 40 deg C. or higher.
[0037] It may be possible to quantify the softness of the
photochromic host layer and correlate this with the transition time
of a lens. Thus, the surface hardness of the photochromic host
layer of the photochromic article may be used as a guide to the
transition times expected. The hardness of the photochromic host
layer may be measured using a nanoindenter.
[0038] By way of example, suitable photochromic host layer monomers
may be selected from any one or more of the list including:
alkylene di(meth)acrylates, such as decanediol diacrylate;
poly(alkyleneoxide) di(meth)acrylates such as A200 (polyethylene
glycol 200 diacrylate), A400 (polyethylene glycol 400 diacrylate),
A600 (polyethylene glycol 600 diacrylate), APG-200 (tripropylene
glycol diacrylate), APG-400 (polypropylene glycol 400 diacrylate),
14G, 9G and 4G; urethane(meth)acrylates such as U-4HA and U-6HA;
and allyl compounds such as DAIP.
[0039] Particularly preferred photochromic host layer monomers are
nonaethylene glycol dimethacrylate containing compositions such as
9G, quatdecaethylene glycol dimethacrylate containing compositions
such as 14G, polytetramethylene glycol and ethoxylated bisphenol-A
dimethacrylate (having between 1 and 20 ethoxy groups per
molecule). The photochromic host layer monomer may also be a
mixture of any two or more of the listed photochromic host layer
monomers. As used herein, the term (meth)acrylate is used to denote
either an acrylate or a methacrylate group. Thus, a
di(meth)acrylate monomer may contain one acrylate and one
methacrylate groups or two methacrylate groups.
[0040] Using the methods of the present invention, it is possible
to prepare lenses that have transition times that are significantly
faster than commercially available photochromic lenses that are
known to the present inventors. As a result, there may be some
instances where the transition times are too fast and it may be
either necessary or preferred to suppress the transition time. For
instance, on occasions in which a wearer moves from shadow to light
and back to shadow, it may be preferable for the lenses not to
react rapidly to the change in light, but rather for the transition
to be buffered somewhat so that the lenses do not undergo a series
of rapid transitions.
[0041] Using the methods described herein it is possible to tune or
selectively adjust the transition time of a photochromic compound
in a photochromic host layer. As discussed previously, the rigidity
of the photochromic host layer in the vicinity of the photochromic
compound molecules may affect the transition time, and it is
thought that a relatively rigid local environment slows the
transition of the photochromic compound molecules by limiting
flexibility and room for the molecule to enter the activated state.
Similarly, for reasons discussed earlier a relatively polar
environment in the vicinity of the photochromic compound molecules
may slow the transition times.
[0042] Accordingly, the present invention also provides a method
for manufacturing a photochromic article wherein physical and/or
chemical properties of a photochromic host layer can be adjusted to
alter the transition time of photochromic compounds contained in
that layer, the method including the step of adjusting one or more
of the polarity and/or the local rigidity of the photochromic host
layer to either increase or decrease the transition time of the
photochromic compounds.
[0043] It will be appreciated that, until the method of the present
invention was discovered, it was not possible to achieve transition
times that were sufficiently fast that one would need to
deliberately slow them down. However, the separation of the
photochromic compound environment from the optical and mechanical
properties of the lens substrate, such fast transition times have
been achieved with the present invention. It is also possible that
other methods may ultimately be discovered that provide lenses
having very fast transition times. Accordingly, the method of
adjusting the transition time discussed herein may also be used in
lenses having fast transition times that are produced using method
other than the methods described herein.
[0044] For the purposes of the present invention, the photochromic
host layer monomer may also be a mixture of any two or more
photochromic host layer monomers wherein the photochromic host
layer includes a major proportion of a soft polymer, such as an
ethyleneglycol dimethacrylate such as 9G, that is modified with a
minor proportion of a hardening monomer to provide some rigidity
when cured. In particular, hardening monomers such as relatively
rigid urethane acrylates (eg. U-4HA or U-6HA), ethoxylated
bisphenol-A dimethacrylate monomer having between 1 and 20 ethoxy
groups per molecule or isocyanurate based poly(meth)acrylate
monomers may be added in amount of 1 to 35%, and preferably 5 to
15%, to 9G to form a photochromic host layer in which the
transition time of the photochromic compound in the coating is
slowed or suppressed by the addition of the urethane acrylate.
DETAILED DESCRIPTION OF THE INVENTION
[0045] The basic in-mould coating process that forms part of the
method of the present invention is preferably similar to the one
described in International patent application PCT/AU00/01152, which
is incorporated herein by reference solely for the purpose of
exemplifying in-mould coating processes.
[0046] Briefly, the in-mould coating process typically involves
coating the mould section casting face with the photochromic host
layer monomer composition as a neat monomer solution.
Alternatively, the monomer solution may be in a suitable solvent
such as methyl acetate or methylene chloride. The photochromic host
layer monomer composition may be applied by a variety of techniques
including spraying, dipping, brushing, flow coating, spin coating
and the like. However, spin coating is preferred. The photochromic
host layer monomer composition may then be partially cured, for
example by UV initiated partial polymerisation. The degree of
polymerisation may be controlled as described in
PCT/AU00/01152.
[0047] The moulds used in the manufacture of lenses from polymeric
materials are generally made from glass or metal and typically have
first and second mould sections which are mounted in a gasket to
form the front and back optical surfaces on the lenses. At least
one of the mould sections has a surface that forms a finished
optical surface. Depending upon the particular application, a
permanent or semi-permanent treatment may be applied to facilitate
mould release.
[0048] After coating the mould section with the photochromic host
layer composition and partial curing and/or solvent removal, the
mould pieces are fitted together to form a mould cavity that is
coated with the photochromic host layer in a partially cured form.
Plastics forming substrate monomer is then poured into the mould
and the plastic is cured in the usual way. The moulded lens is
finally removed from the mould to provide the lens coated with the
photochromic host layer.
[0049] For ease of polymerisation, the photochromic host layer
monomers preferably contain an alkene moiety that is able to
undergo free radical polymerisation. Acrylate or methacrylate
moieties are particularly suitable for this purpose.
[0050] Curing or partial curing of the photochromic host layer may
be initiated using suitable polymerisation initiators, including
any of the suitable thermal and/or chemical initiators known in the
art, and the degree of polymerisation may be controlled by
selecting an appropriate amount of initiator, as is described in
PCT/AU00/01152. For photochromic host layer monomers that undergo
free radical polymerisation, suitable initiators are compounds that
liberate or generate a free-radical on addition of energy. Such
initiators include peroxy, azo, and redox systems each of which are
well known and are described in polymerisation art.
[0051] Included among the free-radical initiators are the
conventional heat activated initiators such as organic peroxides
and organic hydroperoxides. Examples of these initiators are
benzoyl peroxide, tertiary-butyl perbenzoate, cumene hydroperoxide,
azo-bis(isobutyronitril- e) and the like.
[0052] The preferred initiators for the photochromic host layer are
photopolymerisation initiators. Included among such initiators are
acyloin and derivatives thereof, such as benzoin, benzoin methyl
ether, benzoin ethyl ether, benzoin isopropyl ether, benzoin
isobutyl ether, and .alpha.-methylbenzoin; diketones such as benzil
and diacetyl, etc.; organic sulfides such as diphenyl monosulfide,
diphenyl disulfide, decyl phenyl sulfide, and tetramethylthiuram
monosulfide; S-acyl dithiocarbamates, such as
S-benzoyl-N,N-dimethyldithiocarbmate; phenones such as
acetophenone, .alpha.,.alpha.,.alpha.-tribromacetophenone,.alpha.-
,.alpha.-diethoxyacetophenone,
alpha.,.alpha.-dimethoxy-.alpha.-phenylacet- ophenone,
o-nitro-.alpha.,.alpha.,.alpha.-tribromacetophenone, benzophenone,
and p,p'-bis(dimethylamino)benzophenone; aromatic iodonium and
aromatic sulfonium salts, sulfonyl halides such as
p-toluenesulfonyl chloride, 1-naphthalenesulfonyl chloride,
2-naphthalenesulfonyl chloride, 1,3-benzenedisulfonyl chloride,
2,4-dinitrobenzenesulfonyl bromide, and p-acetamidobenzenesulfonyl
chloride.
[0053] When the photochromic host layer is to be cured or partially
cured using a radical polymerisation initiator, the mould coating
and curing steps are beneficially conducted in an environment
containing minimal oxygen so as to minimise oxygen inhibition of
polymerisation. The amount of polymerisation initiator used and the
conditions of polymerisation will be readily determined by those
skilled in the art, or can easily be determined empirically.
Throughout this specification, reference to the partial curing of
the photochromic host layer is to be understood to mean reference
to at least partially curing the photochromic host layer, and also
encompasses the possibility of complete curing of the photochromic
host layer, if this is required.
[0054] Once the photochromic host layer has been cured to a desired
level, the mould is preferably assembled and filled with the
substrate monomer composition to provide the solid lens substrate.
Optionally, a barrier layer is applied to the host layer before the
mould is assembled. The substrate monomer composition for forming
the lens may be any of the thermosetting materials known in the art
for that purpose. Preferably, the lens substrate material is
capable of solidifying to form a room-temperature stable, optically
clear lens. Examples of thermosetting materials that may be used
include allyl diglycol carbonate monomer (also known commercially
as CR-39), acrylate monomers, and acrylate oligomers,
thiourethanes, combinations of multifunctional thiols with
acrylates, etc. SPECTRALITE.TM. (a trade mark of Sola International
Inc) is particularly preferred because it is rapidly cured by
photopolymerisation and therefore the monomer composition in a
liquid form is in contact with the partially cured photochromic
host layer for the minimum amount of time possible. In this way,
diffusion of the monomer composition into the photochromic host
layer, and vice versa, can be controlled.
[0055] Once the mould is filled, the substrate monomer composition
is hardened using any suitable technique. For example, allyl
diglycol carbonate may be hardened by subjecting it to heat in the
range of 35.degree. C. to 90.degree. C. for up to 24 hours in an
oven or in a series of waterbaths, according to a predetermined
schedule in the presence of a suitable polymerisation agent. Once
hardened, the cast lens is removed from the mould.
[0056] Optionally, the photochromic host layer may be post-reacted
after the cast lens has been removed form the mould to ensure
essentially complete curing of the photochromic host layer.
However, the photochromic host layer is preferably not completely
cured until after the photochromic compound has been
introduced.
[0057] After the cast lens has been removed from the mould, and
optionally post-reacted, the photochromic compound is introduced
into the lens, preferably by being imbibed with a solution
containing the photochromic compound. Suitable imbibition methods
are disclosed in U.S. Pat. No. 5,882,556, which is incorporated
herein by reference solely for the purpose of providing suitable
methods. However, the photochromic compounds may also be
incorporated into the lens by permeation or other transfer methods
known to those skilled in the art.
[0058] Various classes of photochromic compounds are known and have
been used in applications in which a sunlight-induced reversible
colour change or darkening is desired. The most widely described
classes of photochromic compounds are oxazines, pyrans and
fulgides. Typically, the photochromic compounds have a visible
lambda max of from 400 nm to 700 nm.
[0059] Examples of preferred photochromic compounds may be selected
from the group consisting of:
[0060]
1,3-dihydrospiro[2H-anthra[2,3-d]imidazole-2,1'-cyclohexane]-5,10-d-
ione;
[0061]
1,3-dihydrospiro[2H-anthra[2,3-d]imidazole-2,1'-cyclohexane]-6,11-d-
ione;
[0062]
1,3-dihydro-4-(phenylthio)spiro[2H-anthra-1',2-diimidazole-2,1'-cyc-
lohexane-6,11-dione;
[0063]
1,3-dihydrospiro[2-H-anthra[1,2-d]imidazole-2,1'-cycloheptane]-6,11-
-dione-1,3,3-trimethylspiroindole-2,3'-[3H]naphtho[2,1-b]-1,4-oxazine]
[0064] 2-methyl-3,3'-spiro-bi-[3H-naphtho[2,1-bipyran](2-Me);
[0065]
2-phenyl-3-methyl-7-methoxy-8'-nitrospiro[4H]-1-benzopyran-4,3'-[3H-
]-naphtho[2,1-b]pyran;
[0066] spiro[2H-1-benzopyran-2,9'-xanthene];
[0067]
8-methoxy-1',3'-dimethylspiro(2H-1-benzopyran-2,2'-(1H)-quinoline;
[0068] 2,2'-spiro-bi-[2H-1-benzopyran];
[0069]
5'-amino-1',3',3'-trimethylspiro[2H-1-benzopyran-2,2'-indoline;
[0070]
ethyl-.beta.-methyl-.beta.-(3',3'-dimethyl-6-nitrospiro(2H-1-benzop-
yran-2,2'-indolin-1'-yl)-propenoate;
[0071]
(1,3-propanediyl)bis[3',3'-dimethyl-6-nitrospiro[2H-1-benzopyran-2,-
2'-indoline];
[0072]
3,3'-dimethyl-6-nitrospiro[2H-1-benzopyrao-2,2'-benzoxazoline];
[0073]
6'-methylthio-3,3'-dimethyl-8-methoxy-6-nitrospiro[2H-1-benzopyran--
2,2'-benzothiozoline];
[0074]
(1,2-ethanediyl)bis[8-methoxy-3-methyl-6-nitrospiro[2H-1-benzopyran-
-2,2'-benzothiozoline];
[0075]
N-N'-bis(3,3'-dimethyl-6-nitrospiro[2H-1-benzopyran-2,2'(3'H)-benzo-
thioazol-6'-yl)decanediamide];
[0076]
alpha.-(2,5-dimethyl-3-furyl)ethylidene(Z)-ethylidenesuccinicanhydr-
ide;
[0077]
.alpha.-(2,5-dimethyl-3-furyl)-.alpha.',.delta.-dimethylfulgide;
[0078] 2,5-diphenyl-4-(2'-chlorophenyl)imidazole;
[0079] (2',4'-dinitrophenyl)methyl]-1H-benzimidazole;
[0080]
N-N-diethyl-2-phenyl-2H-phenanthro[9,10-d]imidazol-2-amine;
[0081] 2-nitro-3-aminofluoren
2-amino-4-(2'-furanyl)-6H-1,3-thiazine-6-thi- one.
[0082] Optionally, a mixture of two or more of the photochromic
compounds may be imbibed into the photochromic host layer. By using
appropriate mixtures of photochromic compounds, it is possible to
obtain specific activated colours such as a near neutral grey or
brown.
[0083] It has been found that by using the method of the present
invention and using conventional photochromic compounds, it is
possible to form a lens in which the transition time for transition
from the ground state to the activated state, or vice versa, is
rapid. By way of example, the time for photochromic compounds to
reach 50% of equilibirm intensity (t.sub.1/2(activation)) in the
fastest commercially available lens known to the inventors is about
25 seconds, whereas the t.sub.1/2(activation) for a lens formed
according to the present invention has been measured at about 10
seconds.
[0084] The method of the present invention may also include the
step of applying subsequent layers over the photochromic host
layer. For example, after the photochromic host layer has been
imbibed with photochromic compound, it may be overcoated with an
abrasion resistant layer. The over coat may be applied using any of
the techniques that are used for that purpose in the art, including
dip coating, spin coating, flow coating and spray coating.
Optionally, the over coat may be a permeable layer and may be
applied by in-mould coating so that the photochromic compound can
be imbibed into the cast lens through the over coat. The over coat
is preferably thin and preferably has a thickness in the range 0.8
to 10 microns, and most preferably 1 to 5 microns.
[0085] The method of the present invention may also be used to form
a lens having a multi-layer coating with different amounts of
photochromic compounds in each layer. In this way, a photochromic
gradient may be formed in the coating. Thus, a first photochromic
host layer may be applied using the process of the present
invention. Subsequently, further photochromic host layers may be
applied using any of the traditional coating techniques in the art
or by applying a second layer over a partially cured first layer
using the in-mould coating processes described herein. The
subsequent layer may then be imbibed with a photochromic compound.
The thickness of each of the photochromic host layers may be
different so that different amounts of photochromic compound can be
introduced into each layer. Alternatively, the rate of diffusion or
imbibition may be controlled so that different amounts of compound
are introduced into each layer.
[0086] The method of the present invention is thus capable of
producing a photochromic article in the form of a lens having a
photochromic coating on one or more of its optical surfaces.
Optionally, the lens may also have an abrasion resistant
coating.
DESCRIPTION OF EXAMPLES OF THE INVENTION
[0087] Examples of materials and methods for use with the processes
of the present invention will now be provided. In providing these
examples, it is to be understood that the specific nature of the
following description is not to limit the generality of the above
description.
[0088] In the examples, the following abbreviations are used.
[0089] NS110: bisphenol A ethoxylated dimethacrylate
[0090] 9G and 14G: polyethylene glycol dimethacrylate
[0091] DATP: diallyl terephthalate
[0092] PTMG: polytetramethylene glycol diacrylate
[0093] U6HA: urethane monomer have 2-6 terminal acrylic or
methacrylic groups
[0094] Irgacure 651: 2,2-dimethoxy-2-phenyl acetophenone
[0095] Terpinolene: 4-isopropylidene-1-methyl-cyclohexene
[0096] DHBP: 2,5-dimethylhexane-2,5-ditertbutylperoxide
[0097] NK Ester A-9200: tris(2-hydroxy ethyl)isocyanurate di and
tri acrylate (45%--di/55% tri functional (mono);
[0098] NK Ester A-400: polyethylene glycol diacrylate
[0099] Lucirin TPO: (Diphenyl(2,4,6-trimethylbenzoyl)phosphine
oxide)
[0100] GST: 1,2-bis(2-mercaptoethylthio)-3-mercaptopropane
[0101] Type S: bis(2-mercaptoethyl) sulphide dimethacrylate
[0102] TAIC: triallyl isocyanurate
[0103] Vicure 55: methyl phenyl glyoxylate
[0104] 4G: tetraethylene glycol dimethacrylate*
[0105] 9G: nonaethylene glycol dimethacrylate*
[0106] 14G: quatdecaethylene glycol dimethacrylate*
[0107] * As is known, the polyethylene glycol dimethacrylates may
be supplied as a mixture containg a range of ethylene chain
lengths, but with the named compound in the majority.
Example 1
[0108] Table 1 shows a typical formulation that is used in the
method of the present invention to produce ophthalmic lenses. A
solution of the formulation was stirred for about an hour to allow
complete dissolution of all components before degassing under
vacuum for 30 mins. To obtain the in-mould coating, the solution
was spin-coated onto the casting face with spinning speed at
approximately 870 rpm. The coating was then UV cured (line speed=5
ft/min) and the mould sections were subsequently set into gaskets.
The coated mould was then filled with the lens monomer composition
and UV cured using two passes (one front and one back) at a line
speed of 3.5 ft/min. The cured lenses were then imbibed for
incorporation of photochromic compounds. The imbibition method was
the same as that disclosed in U.S. Pat. No. 5,882,556.
[0109] TEM results showed that a coating with at least 20 .mu.m
thickness could be achieved.
1 TABLE 1 Components Amount (wt %) Photochromic host layer monomer
(9G) 100 UV 5411 0.025 Tinuvin 765 0.05 Blue dye 0.03 Irgacure 651
(photoinitiator) 5.0.sup.A .sup.AThe range of initiator of may be
2-5 wt %.
[0110] Table 2 shows the photopic intensity, t.sub.1/2
(activation), the t.sub.1/2 (fade), t.sub.1/2 (fade) which is the
equilibrium intensity reached after 15 minutes of continuous
radiation, the time for the photochromic compounds to reach 50% of
equilibrium intensity, the time for the photochromic compounds to
fade back to 50% of equilibrium intensity and the time for the
photochromic compounds to fade back to 25% of equilibrium
intensity, respectively. It can be seen that the times achieved
with lenses formed using the method of the present invention are
much shorter than for a commercially available lens (Velocity.TM.
which is available from SOLA International Inc. and is a cast lens
which is later imbibed after curing).
2TABLE 2 Lens Photopic/ photochromic 15 mins t.sub.1/2 (activation)
t.sub.1/2 (fade) t.sub.3/4 (fade) host layer activation (s) (s) (s)
Commercially 0.738 23 60 140 available photochromic lens 9G 0.525
11 33 80 14G 0.56 10 34 80 PTMG 0.645 11 34 --
Example 2
[0111] Further coating and lens compositions are provided in Table
3. In each case, the lens was produced using the method described
in example 1. This example demonstrates the use of a different lens
substrate composition to example 1. In particular the lens
substrate in this example is hostile to photochromic compounds in
that the polymer is highly cross linked which tends to slow down
the activation and fading of the photochromic compound and it is
also relatively high in sulphur which tends to degrade photochromic
compounds.
3 TABLE 3 Amount (wt %) Material for photochromic host layer 14G 66
NS110 34 Vicure 55 5 Leveling agent BYK 371 1 Tinuvin 765 0.05 UV
5411 0.1 Lens substrate composition Triphenyl phosphine 0.05
Lucirin TPO 0.5 TAIC 47.54 GST 52.46 DHBP 0.1
[0112] Host layer: Spin speed 600 rpm, UV cure at 4.5 ft/min
[0113] Substrate is cured: 3.5 ft/min 2 times (one front and one
back) with a V lamp
Example 3
[0114] Further coating and lens compositions are provided in Table
4. In each case, the lens was produced using the method described
in example 1.
4 TABLE 4 Amount (wt %) Material for photochromic host layer 14G 70
NS110 30 Vicure 55 3 Leveling agent BYK 371 0.1 Substrate
composition Type S 75 GST 25 DHBP 0.1 Irgacure 819 0.9
[0115] UV cure of substrate is 3 ft/min, 2 times (one front and one
back); V lamp
[0116] Refractive Index=1.62
[0117] Abbe=37
Examples 4 to 9
[0118] Table 5 shows further formulations that were used in the
process of the present invention. In the table, the quantities of
material are given in wt % and the coatings were applied as for
Example 1.
5TABLE 5 Irgacure Example 9G 14G U6HA DATP PTMG 651 4 95 0 5 0 0 5
5 90 0 10 0 0 5 6 90 0 0 10 0 5 7 0 100 0 0 0 5 8 100 0 0 0 0 5 9 0
0 0 0 100 5
[0119] Table 6 shows the results of the photochromic performance of
the lenses of Examples 4 to 9. In the table the steel wool abrasion
test data refers to lenses that were coated with a standard
siloxane hard coat and cured before abrasion testing.
6TABLE 6 t.sub.1/2 t.sub.1/2 Nano- (activation) (fading) Optical
indentation Steel Wool Example (S) (S) density depth (nm) Abrasion
4 12 35 0.519 6200 Fail 5 23 42 0.607 3890 Pass 6 13 39 0.551 6243
Fail 7 10 34 0.559 10000 Fail 8 11 34 0.523 7423 Fail 9 11 34 0.645
15200 Fail
Examples 10 to 14
Measurement of Photochromic Performance
[0120] We have found that the nanoindentation depth of a coated
lens provides an indication of the activation half life or the
photochromic performance of a coated lens. As previously discussed,
a relatively non-rigid or `soft` local environment in the
photochromic host layer is thought to allow sufficient flexibility
and room for the photochromic compound molecules to move into the
activated state. This is thought to lead to an increase in
photochromic performance.
[0121] In Examples 10 to 14 the Barcol hardness of monolithic
lenses was correlated with the nanoindentation depth of the
monolithic lenses. The Barcol hardness is a macro-indentation
method that provides information about the softness of a lens at
about 100 micron depth in the lens. In contrast, measurement of the
nanoindentation depth is only sensitive to the top 1 to 20 microns
of the lens.
[0122] It has previously been shown that the Barcol hardness of a
lens can be correlated with the photochromic performance of the
lens (see International patent application WO0172851).
[0123] We have found that there is a correlation between the
nanoindentation depth and the Barcol hardness of a cast lens. If a
monolithic lens is cast using the coating material there is a good
correlation between the nanoindentation depth of the cast lens and
the Barcol hardness of the cast lens. This is because a cast lens
has the same composition where the Barcol hardness is being
measured as it does at the top layer where the nanoindentation
depth is measured. Measurement of the Barcol hardness of lenses
that are formed using the method of the present invention therefore
only provides hardness values of the lens substrate monomer and not
the photochromic host layer.
[0124] We were able to show that the photochromic performance is
correlated to nanoindentation depth. The nanoindentation depth of
lenses having the compositions shown in Table 7 was measured using
a UMIS 2000 which is available through the Division of Applied
Physics of CSIRO Australia. Different indenter tips may be used,
but a half spherical tip of radius 5 micron was generally used. The
experiments were performed using a force controlled method where
the indentation curves as a function of applied force up to a
determined maximum force (for example 10 mN) were studied. The
nanoindentation depth, photochromic performance and abrasion
resistance for the coated lenses are provided in Table 8. The
abrasion resistance data shown in Table 8 refers to a lens that has
been coated with a standard siloxane hard coat and cured prior to
abrasion testing.
7 TABLE 7 Irgacure Example 14G NS110 651 10 88 12 0.5 11 82 18 0.5
12 70 30 0.5 13 68 32 0.5 14 66 34 0.5
[0125]
8TABLE 8 t.sub.1/2 t.sub.1/2 Nano- Steel Wool (activation) (fading)
Optical indentation abrasion Example (S) (S) Density depth (nm)
resistance 10 12 40 0.613 8880 Fail 11 13 42 0.599 8145 Fail 12 15
46 0.604 5738 Pass 13 17 51 0.598 4822 Pass 14 17 54 0.617 4081
Pass
[0126] As the data in Table 8 shows, as the nanoindentation depth
decreases the photochromic performance of the lens becomes slower.
FIG. 1 shows the correlation between nanoindentation depth and
darkening times.
[0127] This data indicates that the optimal nanoindentation depth
of a lens of the present invention, given that it should have
reasonable abrasion resistance and fast photochromics, may be
between 9000 nm to 2500 nm.
[0128] We also found that the nanoindentation depth may also give
an indication of the abrasion resistance of a hard coated lens. It
has been found that the abrasion resistance of a hard coated lens
is dependent to some degree on the material onto which the hard
coating is applied. Generally, the softer the photochromic host
layer the poorer the abrasion resistance of the lens even after it
has been over coated with a conventional hard coat.
Example 15
Multiple Layer Coatings
[0129] It may be thought that the thicker a `soft` coating such as
the photochromic host layer is, the worse the abrasion resistance
of the coating. However, we found that the abrasion resistance was
somewhat independent of the thickness of the photochromic host
layer. This suggested that it may be possible to apply multiple
layers of coating without reducing the subsequent abrasion
resistance of the lens. Table 9 describes different curing and
coating conditions used for a 64% 14G, 36% NS110, 0.5% Irgacure 651
(photointitator), 0.12% terpinolene and 0.1% DHBP lens and provides
the measured nanoindentation depths and abrasion ratios.
9 TABLE 9 Curing and coating Nanoindentation Steel wool abrasion
conditions depth (nm) ratio 700 rpm 8274 1-pass (UV = 5 ft/min) 285
rpm 6850 1.2-pass (UV = 5 ft/min) 285 rpm, additional -- 1.3-pass 3
ml while spinning (UV = 5 ft/min) 285 rpm, 3 coats 7390 1.1-pass
(UV = 10 ft/min) Note: the ft/min data refers to belt speed upon UV
curing with a V lamp
Examples 16 to 21
Dual Cure Coating
[0130] It may be desirable in some cases to dual cure the
photochromic host layer, where the layer is partially cured before
setting into the lens and after the substrate is cured, the layer
is still not fully converted. This allows the photochromic compound
to diffuse into the photochromic host layer and allows room for the
photochromic compound to move before the layer is cured to full
conversion. This causes the layer to become more rigid during the
imbibition process and hence have better abrasion resistance. Dual
cure coating requires the use of chain transfer agents which may be
selected from mercaptans, allylics, styrene derivatives,
terpinolene and mixtures thereof.
[0131] We have been able to show that it is possible to dual cure
the coating where the initial nanoindentation depth and final
nanoindentation depth are significantly different. Generally, when
terpinolene and a photoinitiator is used, the layer becomes almost
fully converted. When the layer is fully converted, the
nanoindentation depth before imbibition of the photochromic host
layer with photochromic compound is generally higher than after
imbibition. This is thought to be due to relaxation of the UV cured
monomer on the photochromic host layer when the lens is heated up
to imbibition temperature. Thus, it is not usual that the
difference in the nanoindentation depth before and after imbibition
is more than a few hundred nanometres. The differences are
generally around 200 nm to 11000 nm, with the nanoindentation depth
after imbibition lower than before imbibition. The results are
shown in Table 10. All of the formulations of Examples 16 to 21
contained 0.5% BYK 371, and were spin coated at a spinning speed
285 rpm.
10TABLE 10 % Irga- cure % terpin- % UV curing Example 14G NS110 651
olene DHBP conditions 16 60 40 0.1 0.5 0.5 10 ft/min 17 60 40 0.5
0.5 0.5 5 ft/min 18 60 40 0.5 0.5 0.5 25 mm/s 19 60 40 0.5 0.3 0.5
5 ft/min 20 60 40 0.5 0.4 0.4 5 ft/min 21 50 50 0.5 0.5 0.5 5
ft/min
[0132] The nanoindentation depths before and after imbibition are
shown in Table 11. The imbibition conditions were 135-140 degrees
Celsius for four hours.
11TABLE 11 Nanoindentation Nanoindentation depth (before depth
(after Example imbibition) imbibition) 16 16350 5080 17 10000 6950
18 12000 6500 19 6600 5400 20 9830 8200 21 6900 6250
Example 22
Barrier Layers
[0133] After the photochromic host layer is spin coated onto a
mould section and the mould section assembled in a gasket, the
gasket can then be filled with the substrate of choice. In the
present example, Spectralite.TM. was used. However it was found
that it is possible for the photochromic host layer to be
penetrated by the substrate monomer once the two are in contact.
The occurrence or extent of the breakthrough of substrate monomer
into the photochromic host layer is dependent on the degree of cure
of the host layer and the composition of the host layer. Generally,
the harder the resultant host layer the less breakthrough occurs in
the same amount of time. Table 12 shows the effect of
photoinitiator content on the nanoindentation depth and the
photochromic performance of a 9G in-mould coated lens.
[0134] For comparison, a cast lens using 100% 9G is a very soft
lens, whereas Spectralite.TM. is reasonably hard and rigid by
comparison; the nanoindentation depths are 15000 nm and 2000 nm,
respectively.
[0135] As the percentage of photoinitiator increases, the host
layer is better sealed with higher cure and the top layer of the
lens becomes more like pure 9G, which has a darkening time of 9
seconds as a cast lens. Thus the nanoindentation method can be used
(1) as an indicator of whether the host layer had been breakthrough
by the substrate monomers, and (2) to measure how soft the actual
top layer of host layer is.
[0136] Breakthrough of substrate monomer into the photochromic host
layer causes an apparent decrease in the coating thickness which
therefore decreases the volumetric environment for the photochromic
compound. This leads to a harder coating and a decrease in the
total amount of photochromic compound uptake.
[0137] It is also possible that as the host layer gets glassier by
addition of a rigid monomer, the host layer becomes more rigid and
is more difficult for the substrate monomer to breakthrough. Hence
it is expected that there may be an optimum amount of rigid monomer
that may be used in a host layer, particularly in the case of a
monomer which is both rigid and viscous and thus increasing the
thickness of the actual host layer at a particular spin coating
speed.
[0138] The data in Table 12 also shows an increase in OD (optical
density) when breakthrough is minimised by increasing the amount of
photoinitiator in a lens made of 100% 9G monomer.
12TABLE 12 t.sub.1/2 Photoinitiator t.sub.1/2 (fading) Optical
Nanoindentation (wt %) (activation)(s) (s) Density depth (nm) 0.5
42 140 0.399 2000 1.0 14 42 0.547 2693 2.0 11 34 0.523 7974
[0139] Another example of breakthrough occurs with a substrate
composition such as MR-7, which is a thermally cured substrate that
is not imbibable. The MR-7 monomer is low viscosity and takes hours
to reach gelation. Thus the time of contact for the photochromic
host layer and the substrate monomer is very long and the time
involved easily allows breakthrough to occur. When MR-7 is used
depending on the exact composition of the host layer, the resulting
lens is either not imbibable or very slow due to breakthrough.
[0140] Breakthrough can be overcome by using a barrier layer, which
may be a highly crosslinked material or one sufficiently rigid to
prevent penetration of the substrate monomer into the coating.
[0141] Table 13 provides an example of a barrier layer.
13 TABLE 13 Amount (wt %) Materials for coating A9200 30 NK ester A
400 70 Lucirin TPO (phototinitiator) 2 Leveling agent BYK 371 0.6
Materials for barrier layer Pentaerythritol tetrakis-3-mercapto
59.5 propionate Lucirin TPO 0.5 Levelling agent (BYK-371) 0.6
Triallyl isocyanurate 40.5
[0142] The procedure for applying the barrier layer was as follows.
Initially the coating was UV cured (V-globe) @ 3 ft/min. The
barrier layer material was then applied on top of the photochromic
host layer and subsequently UV-cured using the same conditions as
the photochromic host layer cure. The substrate in this example was
MR-7 which is a commercially available monomer with an index of
1.67.
[0143] Table 14 provides details of another barrier layer
composition.
14 TABLE 14 Amount Materials for barrier layer (wt %) Xylene di
isocyanate 52 Di butyl tin chloride (DBTC) 0.1 Levelling agent
(BYK-371) 0.6 4-Mercapto methyl-3,6-di thia-1,8-octane di thiol
48
[0144] This particular barrier layer example is at stoichiometric
ratio for the thiol and isocyanate. This can be altered to suit a
particular requirement for the substrate. In some cases, it may be
desirable to have a non-stoichiometric ratio so there is an excess
of one component such that the reactive functional group may react
with the substrate monomer. The percentage of the DBTC (catalyst)
may also be changed as appropriate.
[0145] Finally, it will be appreciated that other variations and
modifications may be made to the compositions and methods described
herein without departing from the scope of the invention.
* * * * *