WO2008153595A1

WO2008153595A1 - A novel photochromic article and a process for making a novel photochromic article

Info

Publication number: WO2008153595A1
Application number: PCT/US2007/086176
Authority: WO
Inventors: Ronald C. Wiand
Original assignee: Softlight, Inc.
Priority date: 2007-05-29
Filing date: 2007-11-30
Publication date: 2008-12-18

Abstract

A process for making a photochromic article such as a lens by reacting a liquid reaction composition confined in a mold to an intermediate state of hardness; freeing the composition from the mold and subjecting the composition to a further curing step to substantially fully react the reaction composition and form a solid article; then contacting the solid article with a photochromic moiety to imbibe the photochromic moiety in at least a surface portion of the article.

Description

A NOVEL PHOTOCHROMIC ARTICLE AND A PROCESS FOR MAKING A NOVEL PHOTOCHROMIC ARTICLE

Field of the Invention

The present invention relates to photochromic articles including optical articles such as lenses for ophthalmic or piano sunglasses, and to the preparation of photochromic articles such as lenses for ophthalmic or piano sunglasses from organic reaction compositions.

Background of the Invention

Photochromic articles such as lenses generally comprise a photochromic moiety which undergoes a reversible color change when exposed to light of a certain wavelength particularly in the UV and visible ranges of the electromagnetic spectrum. Photochromic lenses may be prepared by imbibing a transparent polymeric lens with a photochromic moiety such as described in U.S. Pat. Nos. 4,286,957 September 1, 1981 to LeNaour- Sene and 5,130,353 July 14, 1992 to Fischer et al. or by casting a polymeric lens with an incorporated photochromic moiety as described in U.S. Pat. No. 4,851,471, July 25, 1989 to Maltman et al. The classes of known photochromic moieties include naphthopyrans and fulgides, spirooxazine chromenes and others.

One problem often encountered by users of photochromic lenses is that the development of color (activation) may not be rapid when the article is exposed to direct sun light and more importantly, that the reverse process (fade) is not rapid on moving indoors out of sunlight. It is believed that the photochromic moiety requires localized free volume to change between activated and inactivated states. In any event, it would be desirable to have an improved photochromic lens which rapidly changes between activated and inactivated conditions. Accordingly, the present invention provides an improved process for manufacture of a photochromic polymeric article such as a lens. The process of the invention includes partly curing a liquid reaction composition to form a solid article with improved ability to change between activated and inactivated states. Further understanding of the present invention will be had from the following disclosure taken in conjunction with the appended claims.

Summary of the Invention

The process of the present invention generally includes casting of the liquid reaction composition using a suitable mold. The photochromic article is typically a shaped article such as a lens. The process of the present invention comprises the steps of providing a liquid polymerizable reaction composition in a mold; subjecting the liquid reaction composition to a first curing step to provide a solid article of intermediate hardness; removing the solid article of intermediate hardness from the mold and subjecting the solid article of intermediate hardness to a second curing step to complete the curing of the article while allowing the article to expand or cure free of the mold or other restraint and to increase the hardness of the article; and then contacting the fully cured solid article with a photochromic substance to thereby provide a polymeric article imbibed with the photochromic substance. The present invention also includes the product made by the process of this invention.

The degree of curing which takes place prior to removal of the solid article from the mold will depend on the type of article and its intended application. The first curing step will generally provide a solid shaped article which preferably has sufficient integrity to allow it to maintain its shape during the additional curing step. Where the article is cast using a mold it is preferred that the first curing step provides sufficient hardness to allow the article to be removed from the mold without being deformed. The hardness of the intermediate product will typically be governed by the mechanical handling required for the second curing stage. The final hardness will depend on the intended use of the product. In the case of lens materials the photochromic article will typically be cured to allow the lens to be worked for example by cutting and polishing for use in spectacles or other optical applications after imbibing with a photochromic moiety. It is preferred to cut or "edge" the lens before the second curing step to relieve stress around the edge of the lens which might otherwise lead to cracks in the lens.

The first and second curing steps may be conducted by peroxide, thermal curing, radiation curing or a combination thereof. The method of carrying out the first curing step or second curing step is chosen to ensure that the first curing step does not obtain a full cure before the article is removed from the mold. In a particularly preferred embodiment of the present invention, both the first and second steps of curing are carried out by peroxide curing of the reaction composition with heat. In this embodiment the reaction composition will typically include peroxide polymerization initiator and the composition is heated to a temperature to provide curing in the presence of the peroxide polymerization initiator. The further curing step will typically be at a temperature which is higher than the first intermediate curing step.

Detailed Description of the Invention

In accordance with the present invention, an article is made by curing, i.e., reacting a liquid reaction composition or mixture comprised of a primary, cross-linkable organic prepolymer and a secondary, non-crosslinkable organic prepolymer to form a solid substrate having a polymeric matrix which is then imbibed with a photochromic moiety to provide an article having photochromic properties. The polymeric matrix is provided by conduncting the reaction in two steps: first in a mold and second free of the mold. The second step is conducted free of the mold to allow the substrate to expand or react without confinement during the second step to enhance open structure in the substrate for improved diffusion and later operation of the photochromic moiety between activated and inactivated states.

A preferred embodiment of the present invention is a method for making a photochromic lens. In accordance with this method, a mold is prepared by filling it with a liquid reaction composition of the present invention. Curing of the prepolymer reaction mixture of primary and secondary prepolymers is carried out by heating or otherwise initiating curing as is conventional in the art and disclosed, for example, in United States Patent No. 5,882,556 March 16, 1999 to Perrott et al, the disclosure of which is specifically incorporated by reference herein. The pre -polymer reaction mixture is allowed to react to a intermediate state of hardness, i.e., the mixture is substantially a solid lens; the lens is released from the mold and subjected to further curing to obtain a substantially cured lens.

The substrate is then ready to receive the desired photochromic moiety. Photochromic molecules can be infused or permeated into the entire lens or into a surface layer portion of the lens by contacting the surface with a solution of photochromic molecules. Of course, the photochromic moiety can be brought into contact with a surface or surfaces of the substrate to accomplish its permeation therein by various methods including, but not limited to, coating a solution containing the photochromic moiety onto the surface of the substrate, applying a layer of polymeric film having the photochromic moiety dissolved or suspended therein to the surface of the substrate and then heating the film near to but below the melting point of the photochromic moiety for a time sufficient to incorporate the photochromic moiety into the surface layer, or any of the methods for incorporating photochromic compounds into a surface of a host material disclosed in United States Patent No. 5,066,818 November 19, 1991 to Gemert et al. for "Photochromic Naphtopyran Compounds" the disclosure of which is specifically incorporated by reference herein.

The reaction mixture comprises a primary prepolymer or monomer reactant with cross-linkable moieties, such as an allyl diglycol carbonate monomer, and a secondary prepolymer or monomer reactant which is without cross-linkable moieties, but which is soluble or dispersible in the reaction mixture. A suitable secondary reactant is an ethoxylated nonylphenol acrylate monomer. The secondary reactant polymerizes during the simultaneous polymerization of the primary reactant but without crosslinking and is believed to interfere with the cross-linking of the primary reactant to thereby enhance an open structure in the resulting polymeric matrix. Thus, the polymeric matrix is porous and readily accepts diffusion of a photochromic moiety therein. In a preferred embodiment of the present invention, the substrate is an optical lens which has a photochromic moiety imbibed or otherwise put into at least part of the porous structure of the polymeric matrix.

As used herein, the term primary pre -polymer includes monomeric moieties as well as oligomers, dimers, etc. so long as the moiety is polymerizable and cross-links during polymerization. The primary pre-polymer is polymerized and cross-linked simultaneously with a secondary pre-polymer to form a polymeric substrate. Suitable primary pre -polymers are well known and may be ultraviolet cross-linkable pre- polymers, radiation cross-linkable pre -polymers or thermally cross-linkable pre- polymers. Initiation of polymerization and/or cross-linking may be by peroxide, ultraviolet or electron beam radiation, or heat or a combination thereof.

More specifically, in accordance with the method of the present invention, a substrate, preferably a lens, is made by the steps of:

providing a liquid reaction composition comprising a primary cross- linkable pre-polymer and a secondary non-crosslinkable pre-polymer confined in a mold;

polymerizing said primary and secondary pre -polymers to form a polymeric matrix substrate of an intermediate hardness;

freeing the polymeric matrix substrate of intermediate hardness from the mold;

further curing the polymeric matrix substrate to a state of increased hardness free of physical constraint; and infusing an effective amount of a photochromic moiety into at least a surface region of said polymeric matrix.

Primary Pre -polymer

For an optical quality lens, the reaction mixture comprises an optical quality primary prepolymer which is a polymerizable monomer and/or pre -polymer having an index of refraction between 1.440 and 1.90. Suitable primary pre-polymers for use in making lenses are liquid and must be placed in a desired lens mold before initiation of polymerization. Examples of suitable primary pre-polymers include monomers, homopolymers and copolymers of polyol(allyl carbonate) monomers, homopolymers and copolymers of polyfunctional acrylate monomers, polyacrylates, poly(alkylacrylates) such as poly(methylmethacrylate), cellulose acetate, cellulose triacetate, cellulose acetate propionate, cellulose acetate butyrate, poly(vinyl acetate), poly( vinyl alcohol), poly(vinyl chloride), poly(vinylidene chloride), polyurethanes, polycarbonates, poly(ethylene- terephthalate), polystyrene, copoly(styrene-methylmethacralate), copoly(styrene- acrylonitdrile), poly(vinylbutyral), and homopolymers and copolymers of diallylidene pentaerythritol, such as copolymers with polyol(allyl carbonate) monomers, e.g. diethylene glycol bis(allyl carbonate), and acrylate monomers. Transparent copolymers and blends of the transparent polymers are suitable as matrix materials. A preferred primary pre-polymer is diethlene glycol bis allyl carbonate, (CR-39) monomer.

The polymerizable monomer may be selected from any suitable type, e.g. methacrylates, acrylates, vinyls, vinyl ethers, allylic, aromatic olefins, ethers, polythiols, ADC, epoxies and the like and mixtures thereof. A diacrylate or dimethacrylate monomer is preferred. The diacrylate or dimethacrylate monomer may be a polyoxyalkylene glycol diacrylate or dimethacrylate, for example a polyethylene glycol dimethacrylate with an average molecular weight of approximately 600.

The reaction composition may include a polymerisable comonomer. The polymerisable comonomer(s) may be selected to improve the properties and/or processability of the cross-linkable polymeric casting composition. The polymerisble comonomer may be a low viscosity comonomer. The comonomer may be selected from one or more of aromatic olefins, polymerisable bisphenol monomers capable of forming a homopolymer having a high refractive index of more than 1.55, urethane monomers having 2 to 6 terminal acrylic or methacrylic groups, and thiodiacrylate or dimethacrylate monomers. The most preferred comonomers are diallyl terephthalate, diallyl isophthalate, and polyethylene glycol monomethylacrylate.

The reaction composition may and preferably will include an aromatic olefin. The aromatic olefins may be selected from styrene, divinyl benzene and 3,9-divinyl-2,4,8,10- tetraoxaspiro [5.5] undecane (DTU). The aromatic olefins may be present in amounts of approximately 5 to 50% by weight.

The reaction composition preferably includes one or more monomers selected from the group of a) polyoxyalkylene glycol diacrylate or dimethylacrylate; b) bis- ethylenically unsaturated bisphenol monomer; c) urethane acrylate or methacrylate monomers having 2 to six unsaturated terminal groups selected from acrylate and methacrylate; d) cross linking monomers containing at least three unsaturated groups selected from allyl, acrylate and methacrylate; and e) a polyol allyl carbonate monomers generally containing two to 5 allyl carbonate groups.

The reaction composition may comprise a) a polyoxyalkylene diacrylate or dimethacrylate; b) bis ethylenically unsaturated bisphenol monomerc); c) optionally an urethane acrylate monomer having from 2 to 6 terminal unsaturated groups; and d) optionally a cross linking agent such as a polyol substituted with at least three acrylate groups.

Other preferred reaction compositions containing a primary prepolymer aare disclosed in U.S. Pat. Nos. 4,912,185, march 27, 1990 to Toh and 5,373,033 December 13, 1994 to Toh et al. the disclosures of both of which patents are hereby specifically incorporated by reference herein.. The polyoxy alkylene glycol diacrylate or dimethacrylate compound according to the present invention may include ethylene oxide or propylene oxide repeating units in its backbone. A polyethylene glycol dimethacrylate is preferred. One suitable material is that sold under the trade name NK ESTER 9G by Shin Nakamura. Alternatively, an NK Ester 6G, 4G or 14G may be used.

The polyoxy alkylene glycol diacrylate or dimethacrylate component may be present in amounts of from approximately 20% by weight to 80% by weight based on the total weight of the casting composition.

The high index bisphenol monomer component in the cross-linkable casting composition may be selected from: dimethacrylate and diacrylate esters of bisphenol A; dimethacrylate and diacrylate esters of 4,4'bishydroxyethoxy-bisphenol A and the like. The high index bisphenol monomer may be present in amounts of from approximately 20 to 75% by weight, preferably 30 to 70% by weight, based on the total weight of the composition.

The reaction composition may include a urethane monomer having 2 to 6 terminal acrylic and/or methacrylic groups. Suitable materials falling within this definition include materials supplied under the trade names U-4H, U-4HA and U-6HA by Shin Nakamura. The urethane monomer may be present in amounts of from approximately 0% to approximately 35% by weight, preferably 5% by weight, based on the total weight of the composition.

Secondary Pre-polvmer

As used herein, the term "secondary" pre -polymer includes monomeric moieties as well as oligomers, dimers, etc. so long as the moiety is polymerizable and does not cross-link during polymerization. The secondary pre -polymer is polymerized and cross- linked simultaneously with the primary pre -polymer to form the desired polymeric substrate. Suitable secondary pre-polymers are well known and may be ultraviolet initiated pre -polymers, radiation initiated pre -polymers or thermally initiated pre- polymers. Thus, initiation of polymerization may be by ultraviolet or electron beam radiation or heat or a combination thereof. Preferred secondary pre -polymers include ethoxylated nonylphenol acrylates such as SR-504 (molecular weight 450) from Sartomer, Exton PA, ethoxylated bisphenol A diacrylate (molecular weight 512) and propoxylated neopentyl glycol diacrylate (molecular weight 328). Generally speaking it has been found that suitable secondary pre-polymers have a molecular weight of from about 220 to about 1660. It has also been found that the secondary pre -polymer should have a glass transition temperature of from about -20 to about 112 degrees Centigrade, a refractive index of from about 1.440 to about 1.55 and a specific gravity of from about 1.10 to about 1.40 grams per cubic centimeter. For an optical quality lens, the present method requires that the secondary pre -polymer have an index of refraction between 1.45 and 1.90 and, of course, the secondary pre-polymer must be soluble or dispersible in the primary pre-polymer.

Additional Ingredients

It is contemplated that the reaction mixture of the present invention will comprise a major amount of primary pre-polymer and a minor amount of secondary pre-polymer. It is also contemplated that the reaction mixture may comprise other components as is conventional in the art. For example, a suitable reaction mixture may include a polymerization initiator, a cross-linking agent, a UV absorber or HALS, or other additives conventionally used in the manufacture of lenses. Suitable initiators, cross- linking agents, additives and other lens materials for use in the present invention are disclosed in United States Patent No. 5,882,556, March 16, 1999 to Perrott et al. which is specifically incorporated by reference herein.

Specific examples of commercially available additives include Q 1301 —from Wako, Tinuvin 765/292, Tinuvin 770 from Ciba-Geigy, Amicure DBU, Amicure BDMA, Uvecryl 115 from Radcure and DABCO. Typically levels of their use are from 0.01% to 0.5% and preferably 0.02% to 0.1% by weight.

The extent of polymerization which occurs before removing the article from the mold may be measured by the percentage of double bond conversion. The change in percentage conversion of the liquid reaction composition between the article of intermediate hardness is (i.e., the change brought about by the further curing step) is typically in the range of from 5 to 30% and preferably 10 to 20%. The article is most preferably released from the mold as a polymer having a double bond conversion of from 70 to 85% (preferably 77 to 83%) and the further curing provides a double bond conversion of at least 88% preferably at least 90% more preferably 92% and most preferably from 92 to 94%.

There are a number of known curing methods which may be used for the first curing step and second curing step. The appropriate technique may depend on the components of the reaction composition and the required properties. Radiation polymerization, for example by electron beam or ultraviolet radiation, may be used. Where curing is produced by ultraviolet radiation the composition may include one or more compounds for initiating polymerization in the presence of UV light or otherwise sensitizing the composition to produce initiation in UV light.

Preferably both the first and second curing steps are carried out by peroxide curing with heat with the second step being carried out at a higher temperature than the first step. The curing steps are preferably conducted at a temperature in the range of from 25° to 135° C. In a preferred embodiment of the invention, the liquid reaction composition comprises a free radical peroxide initiator and the first curing step includes subjecting the liquid polymerizable composition to heating and the second curing step comprises further heating the article of intermediate hardness consuming the residual peroxide initiator in the final curing step.

Examples of UV initiators which may be used in the preferred embodiment include benzophenone, benzoin ethers, dimethoxy-. alpha. -phenylacetophenone, diethoxyacetophenone , . alpha. -hydroxy- . alpha. , . alpha, -dialkylacetophenones , acylphosphine oxides, salts of organic carboxylates and sulfonates, cyclic photoinitiators such as cyclic benzoin ethers and benzil ketones, Michlers ketones, ketocoumarins and combinations thereof. The preferred UV photosensitisers are selected from acylphosphine oxides, benzoin ethers and mixtures thereof. A specific example of preferred UV initiators are 2,4,6-trimethylbenzoyidiphenylphosphine oxide (available under the trade name LUCIRTN TPO) and methylphenylglyoxylate (Vircure 55), bis(2,4,6- trimethylbenzoyl)-phenyl-phosphine oxide (Irgacure 819); l-bis(2,6-dimethoxybenzoyl)- 2,4,4-trimethylpentyl phosphine oxide and mixtures thereof.

The amount of UV initiator used in the polymerizable composition cure system is normally less than that used to fully cure the lens composition by itself. Typically, the amount can be halved, or even less. It may be less than 0.5% where a thermal initiator is also used. The presence of thermal initiator for the further cure step can compensate for an amount of UV initiator to provide the desired final hardness.

In one embodiment the liquid reaction composition includes at least one free radical peroxide polymerization initiator. Alternatively, the composition may include a relatively low temperature thermal initiator and a relatively high temperature thermal initiator and the first curing step will include heating the composition to a temperature sufficient to cause sufficient curing to an intermediate state of hardness and insufficient to provide significant initiation of the high temperature initiator, if present, and the further curing step involves heating the article to a temperature higher than the first curing step to complete the curing step or activate the relatively high temperature initiator. Where thermal initiators are used to provide initiation of polymerization in each stage of the curing process they may be chosen together with the appropriate temperature for each stage, to enable a solid article of the required intermediate hardness to be isolated and contacted with the photochromic substance. For example, a first thermal initiator having a relatively short half life at a temperature in the range of 40° to 68° C. may be used together with a second thermal initiator having a relatively long half life in the range of 68° to 120° C. The second thermal initiator may for example have a 1 hour half life temperature of greater than 120° C. Alternatively, a single free radical initiator may be used that is reacted throughout the required thermal curing processes.

Examples of thermal polymerization initiators which may be used in the first curing step may be selected from the group consisting of azo radical initiators such as AIBN (azodiisobutyronitrile), dialkyl peroxide radical initiators such as 1,1-di- (butylperoxy-3,3,5-trimethyl cyclohexane, alkyl perester radical initiator such as TBPEH (t-butyl per-2-ethylhexanoate), diacyl peroxide radical initiator such as benzoyl peroxide, peroxy dicarbonate radical initiator such as ethyl hexyl percarbonate, ketone peroxide initiator such as methyl ethyl ketone peroxide, bis(t-butyl peroxide)diisopropylbenzene, t- butylperbenzoate, t-butyl peroxy neodecanoate a and combinations of two or more thereof.

An example of a free radical peroxide initiator would be IPP, diisoproypyl peroxydicarbonate.

In one embodiment the polymerizable composition contains a UV initiator and a thermal polymerization initiator. In this embodiment the method includes partially curing the composition to a predetermined intermediate hardness by UV polymerization in the presence of a thermal polymerization initiator; the partly cured composition after mold release is heated to start the second stage thermal polymerization initiator to produce the hardened photochromic article. The thermal polymerization initiator preferably remains essentially unreacted during the photo-polymerization stage.

UV polymerization may be conducted in a known manner by passing the composition through a UV exposure line or a number of UV exposure lines. The extent of cure may be controlled to provide the desired hardness by controlling the amount of UV initiator together with the radiation dose. In another preferred aspect of the present invention the reaction composition may further include at least one poly-functional unsaturated cross-linking agent. The polyfunctional unsaturated cross-linking agent according to the present invention may be a tri- or tetra-functional vinyl, an acrylic or methacrylic monomer. The cross-linking agent may be a short chain monomer for example trimethylol propane trimethacrylate, pentaerythritol triacrylate or tetracrylate, or the like. Other polyfunctional cross-linking agents which may be used include NK Ester TMPT, NK Ester A-TMPT, NK Ester A- TMM-3, NK Ester A-TMMT, di -trimethylol propane tetraacrylate, trimethylolpropane triacrylate, pentaerylthritrol tetramethacrylate, dipentaerythritol monohydroxypenta acrylate, pentaerylthritol triacrylate, ethoxylated trimethylolpropane triacrylate, ethoxylated trimethylolpropane trimethacrylate.

The polyfunctional unsaturated cross-linking agent may be present in amounts of from approximately 5 to 45% by weight, preferably approximately 30 to 40% by weight based on the total weight of the casting composition.

The article of an intermediate state of hardness may be subject to an intermediate thermal treatment stage prior to the final curing cycle. This thermal treatment may take place at the end of the first curing step or beginning of the further curing step. Where a photo-initiator is used the intermediate thermal treatment is particularly useful in reacting any remaining photo-generated radicals. However, one skilled in the art would realize that when using a free radical initiator the additional curing stage is only to enhance the mechanical properties of the article before or after mold release. The intermediate treatment stage will use a temperature less than required in the further curing step and when a thermal initiator is used in the further curing step the intermediate thermal treatment stage will generally be at a temperature less than required to actuate the initiator. Preferably the intermediate thermal treatment stage is at a temperature in the range of 60 to 135. degree. C. and more preferably 60 to 7O.degree. C.

One skilled in the art will appreciate that a commercially important reaction composition can be made of a major component, allyl diglycol carbonate monomer known in the trade as CR-39 a product of PPG. Still more than 50% of all photochromic eyeglass lenses are made using a 1.499 index of refraction monomer. The focus of this invention is a 1.499 index of refraction lens. However, much of the disclosure herein deals with all refractive indices from 1.499 to 1.70.

The photochromic material is incorporated by bringing it into contact with the surface of the substrate and subjecting it to heat to cause thermal transfer into the substrate. An example of a suitable method for incorporation of the photochromic material is described in U.S. Pat. No. 4,286,957 the contents of which are specifically incorporated by reference herein.

A useful imbibition temperature is about 135. degree. C, which is preferably above the glass transition temperature of the lens material, thereby promoting the diffusion process of the photochromic dye into the lens material. A typical time for this imbibition process is about 1 hours to about 6 hours

The reaction composition may further include a co-reactant including a polythiol.

Further examples of a liquid reaction compositions suitable for use in the invention are high index/high ABBE No. compositions of U.S. Pat. No. 6,166,158.

Any suitable photochromic moiety may be imbibed or diffused into the polymeric matrix resulting from polymerization of the reaction mixture. Suitable photochromic moieties are well-known in the art and include photochromic moieties selected from the group consisting of anthraquinones, naphtopyrans, phhalocyanines, spiro-oxazines, chromenes, pyrans including spiro-pyrans and fulgides photochromic moieties. Suitable photochromic moieties include but are not limited to those disclosed in United States Patents Nos. 5,882,556 March 16, 1999 to Perrott et al. which patent is specifically incorporated by reference herein. In addition to photochromic molecules, it is contemplated that other moieties such as a non-photochromic dye or UV stabilizers and antioxidants may be imbibed or diffused into the polymeric substrate. The photochromic substance may be chosen from a range of known chemical classes anthraquinones, phthalocyanines, spiro-oxazines chromenes, pyrans and fulgides. Naphthopyrans and oxazines are preferred. Specific examples of photochromic substances are disclosed in WO95/10790, U.S. Pat. No. 5,763,511, WO98/16863 and U.S. Pat. No. 6,022,497.

The photochromic substance may be applied to the surface of the substrate as a solution in a suitable solvent or carrier. The solvent or carrier may then be removed, for example by evaporation, to provide a layer of photochromic material on the surface into which the photochromic material is to be imbibed.

Without wishing to be bound by theory, it is believed that the surprising improvement in the rate of activation and rate of fading when the photochromic materials are introduced to a cured polymer substrate may be due to an increased localized free volume. These localized free volumes are created during the unrestrained mold free curing while the article subjected to an extended curing after mold release. Futher, the interlatice structure developed by a mold free curing tends to develop bond angles greater than 90 degrees which allows for less molecular friction of the photochromic molecules as they reorient themselves during activation and deactivation. As these photochromic substances are incorporated into polymers, especially highly crosslinked polymers, the rate of activation and fading become dependent on the "free volume" of the lens. In the conventional crosslink lens the crosslink density for a lens increases, there is less volume to allow the dye to change configuration and hence, the activation and fade kinetics are slower than in a high free volume state. In the process of the invention we have found that imbibing an article of intermediate hardness with the photochromic substance allows the high free volume of resin contacting the molecules of photochromic material to be maintained while the lens is fully cured. Typically, there is a relationship between the activation and fade kinetics, such that the fade kinetics may be 3-10 times longer (preferably 5 to 10 times) than the activation kinetics. Another unexpected result of the present invention is the increase in the modulus of elasticity of the fully cured article which increases substrate flexibility. Unexpectedly, by adding the photochromic dye to the substrate after final curing, two aspects are gained: (1) a substrate of greater flexibility, and (2) the photochromic dyes fit themselves into an opening that is more comforming to their physical geometry, reducing molecular fiction and allowing for greater photochromic efficiency and thereby more rapid response to uv light.

The invention will now be described with reference to the following examples. It is to be understood that the examples are provided by way of illustration of the invention and that they are in no way limiting to the scope of the invention.

Example 1

94.0 grams of allyl diglycol carbonate monomer (Great Lakes NG ADC 1.499) is poured into a glass beaker. Then 2.0 grams of ethoxylated (4) nonyl phenol acrylate (Sartomer SR-504) is added to the NG material and stirred for 30 minutes at 24 C. Then 2.0 Grams of a free radical peroxide initiator (diisoproypyl peroxydicarbonate, "IPP") is added and the mixture is prepolymerized by stirring and allowing the temperature of the mixture to rise to 50 C. The temperature is then cooled to 24 C and is a liquid prepolymerized mixture.

A lens mold is assembled by using an EVA gasket as an outer support for the glass front and back of the mold. The prepolymerized mixture is poured into the lens mold which is put into a convection curing oven and heated through a heating profile that has a maximum temperature of 67 C which is reached in about 23 hours. The heating profile is: room temperature to 37⁰C 35 minutes

37⁰C to 4O⁰C 35 minutes maintain at 4O⁰C 180 minutes

4O⁰C to 45⁰C 390 minutes

45⁰C to 5O⁰C 240 minutes

5O⁰C to 6O⁰C 360 minutes

6O⁰C to 67⁰C 168 minutes

At 67 C the lens is cured to an intermediate hardness and is removed from the mold and the outside diameter of the lens is removed by turning. Then the lens is washed and placed back into the convection curing oven at room temperature to complete the curing of the lens. The temperature in the oven is raised to 120° C over 10 minutes and held at 12O⁰C for 90 minutes. The oven is allowed to cool to room temperature and then the lens is removed from the oven. The lens is then imbibed with a photochromic dye, Midnight Grey from Keystone Aniline (Chicago, IL). The lens exhibits a rapid activation and unexpectedly an extremely fast deactivation rate when placed in and out of sunlight. The lens also shows reduced mechanical properties throughout its cross-section as compared to a conventional CR-39 (a registered trademark of PPG Industries, Inc.) lens but is strong enough to pass an FDA Drop ball test and all lens fabrication requirements. The lens is ground and polished to a -1.25 spherical power, edged and inserted into an eyeglass frame. The lens is worn in and out of Sunlight for several days and the photochromic effect works well through-out the trial.

Example 2

98.0 Grams of Great Lakes NG ADC 1.499 (allyl diglycol carbonate monomer) is poured into a glass beaker. Then 2.0 grams of Sartomer SR-504 (ethoxylated (4) nonyl phenol acrylate) and 2.0 grams of Sartomer SR-340 (2- phenoxyethyl methacrylate) are added to the NG material and stirred for 30 minutes at 24 C. Then 2.4% by weight of IPP (diisoproypyl peroxydicarbonate) is added and the mixture is prepolymerized by stirring and allowing the temperature of the mixture to rise to 50 C. The mixture is then cooled to 24⁰C and is a liquid prepolymerized mixture.

A lens mold is assembled by using an EVA gasket as an outer support for the glass front and back of the mold. The liquid prepolymerized mixture is poured into the lens mold which is put into a convection curing oven and heated through a heating profile as set forth in example 1 that has a maximum temperature of 67 C which is reached in about 23 hours. At 67 C, the lens is cured cure to an intermediate hardness and is removed from the mold. The outside diameter of the lens is removed by turning. The lens is washed and then placed back into the convection curing oven to complete the curing of the lens following the procedure of Example 1.

The lens is then imbibed with a photochromic dye, Graphite Grey from Keystone Aniline (Chicago, IL). The lens shows a rapid activation and unexpectedly a extremely fast deactivation rate when placed in and out of sunlight. The lens also shows reduced mechanical properties throughout its cross-section as compared to a conventional CR-39 (a registered trademark of PPG Industries, Inc.) lens but is strong enough to pass an FDA Drop ball test and all lens fabrication requirements. The lens is ground and polished to a - 1.25 spherical power, edged and inserted into an eyeglass frame. The lens is worn in and out of Sunlight for several days and the photochromic effect works well through-out the trial.

Example 3

94.0 grams of Great Lakes NG ADC 1.499 monomer (allyl diglycol carbonate monomer) is poured into a first glass beaker. Then 2.0 grams of Sartomer SR-504 (ethoxylated (4) nonyl phenol acrylate) and 2.0 grams of Sartomer SR-340 (2- phenoxy ethyl methacrylate) is poured into a first glass beaker and stirred for 30 minutes at 24 C. Then 25.0 grams of the mixture in the first beaker is poured into a second glass beaker and 0.500 grams of IPP (diisoproypyl peroxydicarbonate) is added to the mixture in the second beaker while stirrin ¹gB.^• The mixture in the second beaker is stirred while the temperature is allowed to rise to 50 C and then the mixture is cooled to 24 C. The mixture in the second beaker is then combined with the 75.0 grams of mixture in the first beaker along with 1.5 Grams of IPP and mixed for 30 minutes while controlling the temperature at 24⁰C to provide a prepolymerized liquid mixture.

A lens mold is assembled by using an EVA gasket as an outer support for the glass front and back of the mold. The prepolymerized liquid mixture is poured into the lens mold which is then put into a convection curing oven and heated through a heating profile as set forth in Example 1 that has a maximum temperature of 67 C which is reached in about 23 hours. At 67⁰C, the lens is cured to an intermediate hardness and is removed from the mold. The outside diameter of the lens is removed by turning. The lens is washed and then placed back into the convection curing oven to complete the curing of the lens following the procedure of Example 1. The lens is then imbibed with a photochromic dye, Oxford Blue from Keystone Aniline (Chicago, IL). The lens shows a rapid activation and unexpectedly an extremely fast deactivation rate when placed in and out of sunlight. The lens also shows reduced mechanical properties throughout its cross-section as compared to a conventional CR-39 (a registered trademark of PPG Industries, Inc.) lens but is strong enough to pass an FDA Drop ball test and all lens fabrication requirements. The lens is ground and polished to a - 1.25 spherical power, edged and inserted into an eyeglass frame. The lens is worn in and out of Sunlight for several days and the photochromic effect works well through-out the trial.

Example 4

95.0 grams of Great Lakes NG ADC 1.499 monomer (allyl diglycol carbonate monomer) is poured into a glass beaker. Then 5.0 grams of Sartomer SR-504 (ethoxylated (4) nonyl phenol aery late) is added to the NG material and stirred for 30 minutes while maintaining the temperature of the mixture at 24⁰C. Then 2.5 grams of IPP (diisoproypyl peroxydicarbonate) is added and the mixture is prepolymerized while stirring and maintaining the temperature of the mixture at 24⁰C for 12 hours.

A lens mold is assembled by using a tape gasket as an outer support for the glass front and back of a glass mold and the liquid prepolymerized mixture is poured into the lens mold which is put into a convection curing oven and is heated through a heating profile as described in Example 1. At 67⁰C the lens is cured to an intermediate hardness and is removed from the mold. The outside diameter of the lens is removed by turning, the lens is washed and placed back into the convection oven to complete the curing of the lens following the procedures set forth in Example 1.

The lens is then imbibed with a photochromic dye, Midnight grey from Keystone Aniline (Chicago, IL). The lens shows reduced mechanical properties throughout its cross-section as compared to a conventional CR-39 (a registered trademark of PPG Industries, Inc.) lens but is strong enough to pass an FDA Drop ball test and all lens fabrication requirements. The lens is exposed to artificial UV light and exhibits strong color change and has rapid activation and deactivation rates.

Example 5

The procedures of Example 4 are carried out except that the second curing step is carried out by placing the lens in a convection oven at room temperature and then raising the temperature in the oven to 105⁰C in 10 minutes and maintaining the oven temperature at 105⁰C for 90 minutes. Then the oven is allowed to cool down to room temperature and the lens is removed.

The lens is then imbibed with a photochromic dye, Graphite grey from Keystone Aniline (Chicago, IL). The lens shows reduced mechanical properties throughout its cross-section as compared to a conventional CR-39 (a registered trademark of PPG Industries, Inc.) lens but is strong enough to pass an FDA Drop ball test and all lens fabrication requirements. The lens is exposed to artificial UV light and exhibits strong color change and has rapid activation and deactivation rates.

It is to be understood that the invention described hereinabove is susceptible to variations, modifications and/or additions other than those specifically described and that the invention includes all such variations, modifications and/or additions which fall within the spirit and scope of the above description.

Examples 6-9

Four batches are made up of the following (in weight percent):

monomer Formula A Formula B Formula C Formula D

Great Lakes NG 94 94 96 95

SR504 3 3 4 5

SR340 3 3 The monomers are mixed for 3 hours. Then IPP is added to each mixture according to the following table (weight percent) and the mixtures are allowed to pre -polymerize:

Formula A Formula B Formula C Formula D IPP 2.4 2.1 2.1 2.4

The pre-polymerizing mixtures are mixed and allowed to reach 4O⁰C and then are cooled to 6⁰C while continuing mixing overnight.

The prepolymerized mixtures made by the above procedures are then poured into lens molds and the procedures of Example 4 are followed to make photochromic lenses which exhibit excellent photochromic charactistics as in Example 4.

Claims

What is claimed is:

1. A process for manufacture of a photochromic article, such as a lens, comprising: providing a liquid reaction composition confined in a mold; subjecting the liquid reaction composition to a first curing step to provide a solid article having intermediate hardness; freeing the solid article of intermediate hardness from said mold; subjecting the solid article of intermediate hardness to a further second curing step to substantially fully react the reaction composition while allowing the article to expand; then, imbibing a surface portion of the solid article with a photochromic moiety to provide a photochromic article.

2. A process according to claim 1 wherein the solid article of intermediate hardness has a double bond conversion of from about 67% to about 87.3% with reference to the double bonds in the liquid reaction composition.

3. A process according to claim 2 wherein the solid article of intermediate hardness has a double bond conversion of from about 70% to about 85% with reference to double bonds in the liquid polymeric reaction composition.

4. A process according to claim 1 wherein the liquid reaction composition includes a thermal polymerization initiator for the further curing step and the first curing step includes subjecting the liquid reaction composition to radiation or thermal curing and wherein the further curing step comprises heating the solid article of intermediate hardness to a temperature sufficient to activate the thermal polymerization initiator and to provide thermal polymerization.

5. A process according to claim 4 wherein the further polymerization step is conducted at a temperature in the range of from about 60 to about 18O.degrees. C.

6. A process according to claim 4 wherein in the step of further heating the solid article of intermediate hardness produces further curing using only one peroxide initiator in the reaction mixture.

7. A process according to claim 4 wherein the further polymerization step is conducted at a temperature in the range of from 120 to 15O.degree. C.

8. A process according to claim 1 wherein the liquid reaction composition comprises an organic monomer component comprising at least two unsaturated groups selected from acrylate, methacrylate and allyl groups.

9. A process according to claim 8 wherein the liquid reaction composition includes at least one polyfunctional acrylate and/or polyfunctional methacrylate monomer.

10. A process according to claim 1 wherein the liquid reaction composition includes a network modifier selected from the group consisting of tertiary amines; chain transfer agent; allylic monomers; monounsaturated compounds and mixtures thereof.

11. A process according to claim 10 wherein the network modifier is present in an amount of no more than 10% by weight of the total composition and is selected from tertiary amines, chain transfer agents, allylics and monounsaturated compounds.

12. A process according to claim 10 wherein the network modifier is selected from the group consisting of (a) amine; (b) Michael addition products of amines and monomers comprising one or more acrylate and/or methacrylate groups; (c) hindered amine light stabilizers; (d) transfer agent; and (e) monofunctional acrylates and/or methacrylates comprising a flexible chain of at least four carbon atoms.

13. A process for manufacture of a photochromic article comprising: providing a liquid reaction composition; subjecting the liquid polymerizable composition to a first curing step to provide a solid article of intermediate hardness wherein the solid article of intermediate hardness; releasing the solid article of intermediate hardness from its mold; subjecting the solid article of intermediate hardness to a further curing step to substantially fully react the reaction composition; then contacting the solid article with a photochromic substance; to provide a polymeric article imbibed with the photochromic substance; wherein the liquid reaction composition includes a network modifier selected from the group consisting of N-(loweralkyl)diethanolamines, tri(loweralkyl)amines, and unsaturated tertiary amines.

14. A process according to claim 12 wherein the chain transfer agent is selected from the group consisting of mercaptans, allylic, styrene derivatives, terpinolene and mixtures thereof.

15. A process according to claim 1 wherein the liquid reaction composition includes at least two initiators including a first initiator for activation in the first cure step and a second initiator for activation in the second curing step wherein the second initiator remains substantially unactivated during the first curing step and is activated to provide further curing in a second curing step.

16. A process according to claim 1 wherein the liquid reaction composition includes a photoinitiator for the first curing step and a thermal polymerization initiator for the further curing step and wherein the first curing step includes photopolymerization of the liquid polymerizable composition and the second curing step includes heating the article to a temperature sufficient to activate the thermal polymerization initiator.

17. A process according to claim 16 wherein the photoinitiator include a benzoin ether or acylphosphine oxide.

18. A process for manufacture of a photochromic article comprising: providing a liquid reaction composition; subjecting the liquid polymerizable composition to a first curing step to provide a solid article of intermediate hardness; subjecting the solid article of intermediate hardness to a further curing step to increase the hardness and contacting the solid article with a photochromic substance; provide a polymeric article imbibed with the photochromic substance; and wherein the liquid reaction composition includes at least two thermal polymerization initiators including a first thermal polymerization initiator which is activated at a relatively low temperature and a second thermal polymerization initiator which is activated at a relatively high temperature and wherein the first curing step includes heating the liquid polymerizable composition to a temperature sufficient to activate the first thermal polymerization initiator and insufficient to provide significant activation of the second thermal polymerization initiator and the further curing step includes heating the solid article to a temperature higher than the first curing step and sufficient to activate the second thermal polymerization initiator.

19. A process according to claim 18 wherein the 10 hour half life of said second thermal polymerization initiator is at least 2O.degree. C. greater than the 10 hour half life of said first thermal polymerization initiator.

20. A process according to claim 18 wherein the second thermal polymerization initiator is selected from the group consisting of t-butyl benzoate, dicumyl peroxide, 2,5- dimethyl hexane, 2,5-di-t-butyl peroxide, dibutyl peroxide, cumen hydroperoxide and mixture thereof.

21. An optical article formed by a process according to claim 1.

22. A process for manufacture of a photochromic article comprising: providing a liquid reaction composition; subjecting the liquid reaction composition to a first curing step to provide a solid article of intermediate hardness wherein the article is cast in a mould and the solid article of intermediate hardness has sufficient integrity to be removed from the mould without deforming; subjecting the solid article of intermediate hardness to a further curing step to increase the hardness and then contacting the solid article of intermediate hardness with a photochromic substance; to provide a polymeric article imbibed with the photochromic substance