Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Mixing of two or more solid polymers; mixing of solid...
Reexamination Certificate
1999-10-22
2002-05-21
Sellers, Robert E. L. (Department: 1712)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Mixing of two or more solid polymers; mixing of solid...
C252S183110, C525S531000, C525S532000, C526S214000, C526S224000
Reexamination Certificate
active
06391983
ABSTRACT:
The present invention relates to the manufacture of plastic optical articles such as video discs and ophthalmic lenses.
The most widely used plastic ophthalmic lens material is polymerised diethylene glycol bis (allyl carbonate). This polymer has proved a satisfactory material for the manufacture of ophthalmic lenses because of a combination of features, including excellent transmission, resistance to discolouration, high strength and high impact resistance. The material has a reasonable abrasion resistance and can be coated to improve that resistance.
Lenses formed from polymers including divinyl benzene are generally brittle and have a high yellowness index.
In Australian Patent Application 81216/87, the entire disclosure of which is incorporated herein by reference, applicant describes a cross-linkable casting composition including at least polyoxyalkylene glycol diacrylate or dimethacrylate and at least one poly functional unsaturated cross-linking agent. Whilst the lenses produced from the prior art compositions provide advances in the art, difficulties may be encountered in certain applications. For example, difficulties may be encountered in some patients in fitting lenses made from such compositions. Eye discomfort, including eye fatigue problems, may be encountered. Moreover, such lenses have been found to be cosmetically unattractive.
Japanese Patent Application 63-309509 to Showa Denko KK discloses the formation of a prepolymer of divinyl benzene and a polythiol compound which may be used in the formation of optical materials with high refractive indexes.
Japanese Patent Application 63-19498 to Mitsubishi Gas discloses a high refractive index composition of divinyl benzene and a thiol compound. However optical lenses produced thereby may exhibit unacceptable strain characteristics and cure times.
However, there remains a need in the prior art for optical articles of very high refractive indexes, very low densities and excellent colour, that still retain excellent mechanical properties.
Accordingly, it is an object of the present invention to overcome, or at least alleviate, one or more of the difficulties related to the prior art.
Accordingly, the present invention provides a cross-linkable polymeric casting composition including an effective amount of
an aromatic di- or poly-vinyl monomer;
a polythiol compound; and
an epoxide strain reducing agent.
The inclusion of the strain reducing agent provides a reduction in strain evident in optical articles produced therefrom, together with a significant decrease in cure time, e.g. from approximately 24 hours to approximately 1 to 6 hours.
The aromatic di- or poly-vinyl monomer may be a di- or tri-olefin monomer. An aromatic divinyl monomer is preferred. The aromatic divinyl monomer may be selected from divinyl benzene, divinyl naphthene or derivatives thereof. Divinyl benzene is preferred. Other aromatic monomers may be included as discussed below.
The aromatic di- or poly-vinyl monomer may preferably be present in amounts of from approximately 35 to 85% by weight, more preferably approximately 40 to 60% by weight, based on the total weight of the casting composition.
The di- or polythiol compound may be of any suitable type. A di-, tri- or tetra polythiol compound may be used. A tri- or tetra-polythiol is preferred. The thiol may be selected from one or more of the following:
The polythiol is preferably pentaerythritol tetrakis (3-mercapto propionate) (PTMP) or trimethylolpropane tris (3-mercaptopropionate) (TTMP).
The thiol compound may preferably be present in amounts of from approximately 15 to 60% by weight, more preferably approximately 30 to 50% by weight, based on the total weight of the casting composition.
The strain reducing agent may be a cure modifier. The strain reducing agent may be an epoxidised monomer or oligomer. The strain reducing agent should exhibit optical transparency, in use. The epoxidised monomer or oligomer may fall into one or more of the following classes: internal, terminal, mono-functional, di-functional, tri-functional, tetra-functional, aliphatic, aromatic, cyclic, structurally simple, structurally complex, esters, ethers, amines. A diepoxy monomer or oligomer is preferred. An epoxidised soybean material may be used. The epoxidised monomer or oligomer may be selected from one or more of the following
The strain reducing agent may be present in amounts of from approximately 0.001% to 10% by weight, preferably approximately 0.01% to 1%, more preferably approximately 0.5% to 0.4% by weight, based on the total weight of the casting composition. Where the strain reducing agent is an epoxy monomer, epoxy groups may be present in a concentration of at least approximately 0.001 moles, preferably 0.002 moles, per 100 grams of other monomers. The maximum concentration allowable in the formulation is dictated by the amount of dilution that is allowed. For a typical formulation including 48% divinyl benzene, 42% PTMP and 10% 9G, it is preferred that the concentration of epoxy groups be kept below 0.01 moles per 100 grams of monomer.
Whilst we do not wish to be restricted by theory, it is postulated that a number of competing reactions are involved in the polymerisation of the casting composition. The strain reducing agent may function as a polymerisation rate modifier. The strain reducing agent may function as a polymerisation inhibitor of unwanted sub-reactions.
The crosslinkable polymeric casting composition according to the present invention may be utilised in the preparation of an optical article. The optical article may be characterised by being thinner and/or lighter than known prior art articles whilst retaining good abrasion resistance and impact resistance. The optical article may exhibit a high to very high refractive index, excellent colour and low density. Surprisingly, the polymeric article may also exhibit a very low Yellowness Index and may minimise or eliminate problems of strain exhibited in prior art formulations.
By the term “high refractive index”, as used herein, we mean a polymer having a refractive index of at least approximately 1.55, preferably 1.57. By the term “very high refractive index” as used herein, we mean a polymer having a refractive index of approximately 1.59 or above, preferably 1.60 or above.
By “low density”, as used herein, we mean a density in the range of approximately 1.15 to 1.25 g cm
−3
.
The cross-linkable polymeric casting composition may optionally further include a polymerisable comonomer.
The polymerisable comonomer may be selected to improve the properties and/or processability of the cross-linkable polymeric casting composition. The polymerisable comonomer may be an unsaturated comonomer. The polymerisable comonomer may be selected from any suitable type, e.g. methacrylates, acrylates, vinyls, vinyl ethers, allyls, urethanes, unsaturated epoxides, and the like.
The polymerisable comonomer may preferably be selected from one or more of vinyls, allylics, polyoxyalkylene glycol di-, tri-, tetra- and higher acrylates or methacrylates, 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, high rigidity acrylates or methacrylates, fluorene diacrylates or dimethacrylates, and thiodiacrylate or dimethacrylate monomers.
Where a vinyl comonomer is included, the vinyl comonomer may be selected from styrene, substituted styrenes, 3,9-divinyl-2,4,8,10-tetraoxaspiro[5.5]undecane (DTU), and mixtures thereof. The vinyl comonomers may be present in amounts of from approximately 1 to 40% by weight, preferably approximately 5 to 30% by weight, based on the total weight of the casting composition.
Where a thiodiacrylate or dimethacrylate is included, the thiodiacrylate or dimethacrylates may be selected from bis(4-methacryloylthioethyl)sulfide (BMTES) and bis(4-methacryloylthiophenyl)sulfide (BMTS). The thiodiacrylate or dimethacrylate may be present in amounts of from approximately 1 to 40% by weight, preferably appr
Bateman Ian Roger
Diggins David Robert
Kloubek Helena
Toh Huan Kiak
Sellers Robert E. L.
Sola International Holdings Ltd.
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