Patent Description:
Silicone elastomers find wide applicability due to their varied and desirable properties. Silicone elastomers can be prepared from compositions including organopolysiloxanes having alkenyl groups, organohydrogenpolysiloxanes, catalysts and optionally inorganic fillers.

For example, <CIT> relates to silicone elastomer compositions and elastic material for medical devices and medical tubes. This publication discloses elastomer compositions including organopolysiloxanes having alkenyl groups, organohydrogenpolysiloxanes, inorganic fillers and catalysts. The cured products are characterized as having hardness of <NUM> or greater, a breaking elongation of <NUM>% or greater, no yield point and a tensile strength of <NUM> MPa or greater. The tensile strength is particularly preferably from <NUM> to <NUM> MPa. The silicone elastomeric products are disclosed for use in medical tubes, among other uses. <CIT> discloses an optically clear silicone compositions comprising <NUM> parts by weight of at least one polydiorganosiloxane and <NUM> to <NUM> parts by weight of a hydrophobic reinforcing silica filler. It also discloses optically clear cured elastomers useful as lenses or tubing can be prepared from such elastomers. <CIT> discloses a silicone rubber-based hardening composition which can produce a silicone rubber having particular tensile strength and tear strength, a molded article which is made using the silicone rubber-based hardening composition, and a medical tube which is obtained by using the molded article and that the silicone rubber-based hardening composition contains linear organopolysiloxane having a vinyl group (A); linear organohydrogen polysiloxane (B); and silica filler (C) of which the surface is treated with a silane coupling agent having a trimethylsilyl group. <CIT> discloses an addition curable silicone rubber composition having high hardness, elongation, tensile strength, and tear strength is provided. The composition comprises (A) an organopolysiloxane containing at least two alkenyl groups bonded to the silicon atoms at the ends of the molecular chain per molecule and no alkenyl group in the middle of the molecular chain, and having a particular viscosity, (B) a resinous copolymer containing R<NUM>SiO<NUM>/<NUM> and SiO<NUM> units at a particular ratio, and containing a particular amount of vinyl group, (C) an organohydrogenpolysiloxane having at least two SiH groups per molecule, (D) a fumed silica, (E) at least one silica surface treating agent selected from silane and silazane compounds having at least one alkenyl group per molecule, and (F) an addition catalyst. <CIT> discloses an organopolysiloxane composition combining high strength with a particular elongation, which composition comprises a first component, a mixture of two vinyl-containing polysiloxanes or blends of vinyl-containing polysiloxanes, one of which is a high viscosity polysiloxane or a blend of high viscosity polysiloxanes, the other is a low viscosity polysiloxane or a blend of low viscosity vinyl-containing polysiloxanes, a filler and an effective amount of a platinum catalyst. <CIT> discloses an addition curable self-adhesive silicone rubber composition comprising (A) an organopolysiloxane containing at least two alkenyl groups, (B) an organohydrogenpolysiloxane containing at least three SiH groups, (C) another organohydrogenpolysiloxane containing no other reactive groups than SiH groups, and (F) an addition reaction catalyst, with a SiH/alkenyl molar ratio ranging from <NUM> to <NUM>, which is moldable and cures to various metals and organic resins.

However, a continuing need exists for silicone elastomers having appropriate properties for medical device applications, among others.

Advantages of the present disclosure include compositions for forming a silicone elastomer and the silicone elastomers therefrom which have improved characteristics and which can be used for medical devices.

These and other advantages are satisfied, at least in part, by composition for forming a silicone elastomer according to claim <NUM>, the composition comprising: (A) an organopolysiloxane having silicon-bonded alkenyl groups; (B) an organohydrogensiloxane having an average of two or more silicon-bonded hydrogen atoms in the molecule; (C) an inorganic filler; and (D) a filler treatment agent which includes an alkenyl-containing group. While the filler treatment agent having alkenyl groups and inorganic filler can be included in the composition as separate components, a silicone elastomer composition of the present disclosure can advantageously include (C1) an inorganic filler having alkenyl groups instead of or in addition to the inorganic filler and treatment agent as separate components. The compositions can further include (E) a catalytically effective amount of an addition reaction catalyst and/or a curing retarder.

Embodiments include one or more of the following features individually or combined. For example, some embodiments include where the inorganic filler includes fumed silica having a BET specific surface area in a range of about <NUM> square meters per gram or greater, e.g., about <NUM> to <NUM> square meters per gram, which can account for about <NUM> weight % or more of the total quantity of component (C). In other embodiments, the filler treating agent can be a mixture of (D1) an alkenyl-free organosilane, organosilazane, organosilanol, alkoxyorganosilane, or any combination thereof and (D2) an alkenyl-containing organosilane, organosilazane, organosilanol, alkoxyorganosilane, or any combination thereof, e.g., the filler treating agent can be a mixture of (D1) alkenyl-free organosilane or organosilazane and (D2) alkenyl-containing organosilane or organosilazane. In still further embodiments, the weight ratio of D1/D2 is from about <NUM>/<NUM> to about <NUM>/<NUM>.

Another aspect of the present disclosure includes methods of preparing a silicone elastomer. The methods include curing a silicone elastomer composition of the present disclosure and can include compression, transfer or injection molding the composition and/or dip or spray coating the composition on to a substrate and curing the composition to form a cured silicone elastomer.

The silicone elastomer of the present invention has (i) a Shore-A hardness of from about <NUM> to about <NUM> as measured in accordance with ASTM D2240 using a type A durometer hardness tester; (ii) a breaking elongation of at least about <NUM>% as measured in accordance with ASTM D412; and (iii) a tensile strength as measured in accordance with ASTM D412 of at least about <NUM> MPa.

In an embodiment of the present disclosure, the silicone elastomer is prepared from the silicone elastomer compositions described herein.

Another aspect of the present disclosure includes medical devices that incorporate the silicone elastomer of the present disclosure. Such medical devices include, for example, a tissue expander, a gastric restriction or gastric balloon, a drug delivery reservoir or dispensing device, a prosthetic device such as a breast implant. As a prosthetic device, the silicone elastomer of the present disclosure can be included as a shell or a component of a shell of the device. Such devices typically also include a filler, such as a silicone gel, a water containing medium such as an aqueous solution, e.g., saline, a composite, a gas such as air, etc..

Additional advantages of the present invention will become readily apparent to those skilled in this art from the following detailed description, wherein only the preferred embodiment of the invention is shown and described, simply by way of illustration of the best mode contemplated of carrying out the invention. As will be realized, the invention is capable of other and different embodiments, and its several details are capable of modifications in various obvious respects, all without departing from the invention.

The present disclosure relates to an addition-curable silicone elastomer composition according to claim <NUM> that can be cured to a silicone elastomer product. The cured silicone elastomer can have appropriate properties for use in an implantable or non-implantable medical device, for example. In addition, the present disclosure advantageously relates to a molded cured product of said silicone elastomer composition as part of a medical device, such as a breast implant, medical balloon or medical tube.

The silicone elastomer composition of the present disclosure can be cured to a product having a hardness, as measured in accordance with ASTM D2240 using a type A durometer hardness tester (hereinafter referred to as "Shore-A hardness" or "hardness"), of from about <NUM> to about <NUM>, having a breaking elongation of <NUM>% or greater and able to avoid the risk of breakage when formed into a shape due to exhibiting excellent tensile strength of more than <NUM> MPa. The silicone elastomer can also have good tearing strength, which is particularly useful for forming a medical pump tube or an implantable or non-implantable medical device as well as low modulus (low stress over a large range of strain values), low tensile set, favorable compression set, and low hysteresis. Such properties are advantageous when using the silicone elastomer as part of various medical devices, for example.

In one aspect of the present disclosure, a silicone elastomer composition includes: (A) an organopolysiloxane having silicon-bonded alkenyl groups; (B) an organohydrogensiloxane having an average of two or more silicon-bonded hydrogen atoms in the molecule; (C) an inorganic filler; and (D) at least one, and preferably a mixture of, filler treatment agents. The composition can further include (E) a catalytically effective amount of an addition reaction catalyst or the catalyst can be provided to the composition including components (A) through (D) at a later time. When the composition includes the catalyst (E), it is preferable to further include a curing retarder (i.e., inhibitor).

It was surprisingly discovered that including a filler treatment agent having alkenyl groups, e.g., vinyl groups, in a silicone elastomer composition produced a cured silicone elastomer with superior properties. It is believed that a filler treatment agent having alkenyl groups produces an inorganic filler having alkenyl groups which are available for chemically reacting with other components in the composition, such as the organohydrogensiloxane. It is further believed that such an inorganic filler can be chemically incorporated into the polymeric network of the cured silicone elastomer which leads to the improved properties of the product.

While the filler treatment agent having alkenyl groups and inorganic filler can be included in the composition as separate components, a silicone elastomer composition of the present disclosure can include (C1) an inorganic filler having alkenyl groups instead of or in addition to the inorganic filler and treatment agent as separate components. In another aspect of the present disclosure, a silicone elastomer composition includes: (A) an organopolysiloxane having silicon-bonded alkenyl groups; (B) an organohydrogensiloxane having an average of two or more silicon-bonded hydrogen atoms in the molecule; and (C1) inorganic filler having alkenyl groups. The composition can further include (E) a catalytically effective amount of an addition reaction catalyst or the catalyst can be provided to the composition including components (A) through (C1) at a later time. When the composition includes the catalyst (E), it is preferable to further include a curing retarder (i.e., inhibitor).

The (C1) inorganic filler having alkenyl groups can be prepare by combining (C) an inorganic filler with (D) a filler treatment agent, e.g., at least one alkenyl-containing organosilane, organosilazane, organosilanol, alkoxyorganosilane, or any combination thereof. Preferably, (C1) is prepared by combining (C) an inorganic filler with a mixture of treatment agents, which can include: (D1) alkenyl-free organosilane, organosilazane, organosilanol, alkoxyorganosilane, or any combination thereof and (D2) alkenyl-containing organosilane, organosilazane, organosilanol, alkoxyorganosilane, or any combination thereof. In an embodiment of the present disclosure, the inorganic filler includes fumed silica and the filler treating agent includes a mixture of an alkyl silazane and an alkenyl containing silazane and the (C1) inorganic filler having alkenyl groups is prepared from fumed silica and the mixture of filler treating agents.

The components of the silicone elastomer composition of the present disclosure are in amounts of about (A) <NUM> parts by weight of an organopolysiloxane having a molecular weight such that the number-average degree of polymerization is <NUM>,<NUM> or greater and having silicon-bonded alkenyl groups; (B) <NUM> to <NUM> parts of an organohydrogensiloxane having an average of two or more silicon-bonded hydrogen atoms in the molecule; (C) about <NUM> to about <NUM> parts by weight of an inorganic filler; and (D) <NUM> to <NUM> parts of a filler treatment agent which includes an alkenyl-containing organosilane or organosilazane. Alternatively, a silicone elastomer composition can include <NUM> parts of component (A); about <NUM> to about <NUM> parts of component (B); and about <NUM> to about <NUM> parts of an inorganic filler having alkenyl groups (C1). The parts by weight of the composition for components (A), (B), (C), (C1) and (D) refer to the parts by weight relative to component (A). The composition can further include (E) a catalytically effective amount of an addition reaction catalyst and/or a curing retarder.

In an embodiment of the present disclosure, a silicone elastomer composition includes: (A) <NUM> parts by weight of an organopolysiloxane having silicon-bonded alkenyl groups, preferably component (A) exhibits a raw rubber state or gum state at room temperature and has a number-average degree of polymerization of <NUM>,<NUM> or greater based on the number average molecular weight in terms of polystyrene equivalent as measured by gel permeation chromatography (GPC), and an average of two or more silicon-bonded alkenyl groups on the organopolysiloxane and an alkenyl group content of less than <NUM> weight %; (B) <NUM> to <NUM> parts of an organohydrogensiloxane having an average of two or more silicon-bonded hydrogen atoms in the molecule; (C) <NUM> to <NUM> parts by weight of an inorganic filler; and (D) <NUM> to <NUM> parts of a filler treatment agent which includes a mixture of (D1) an alkenyl-free organosilane, organosilazane, organosilanol, alkoxyorganosilane, or any combination thereof and (D2) an alkenyl-containing organosilane, organosilazane, organosilanol, alkoxyorganosilane, or any combination thereof; and (E) a catalytically effective amount of an addition reaction catalyst, e.g., about <NUM> to about <NUM> parts of an addition reaction catalyst such as platinum based upon the weight ratio of elemental metal to all other components combined.

In another embodiment of the present disclosure, a silicone elastomer composition includes: (A) <NUM> parts by weight of an organopolysiloxane having silicon-bonded alkenyl groups; (B) <NUM> to <NUM> parts of an organohydrogensiloxane having an average of two or more silicon-bonded hydrogen atoms in the molecule; and (C1) <NUM> to <NUM> parts of inorganic filler having alkenyl groups.

The compositions of the present disclosure include a component (A), which makes-up the largest amount by weight of the composition. As such, component (A) can be a characterizing component that realizes the physical properties of the composition. In an embodiment of the disclosure, component (A) is an organopolysiloxane which exhibits a raw rubber state or gum state at room temperature, contains silicon-bonded alkenyl groups, and has a low content of silicon-bonded alkenyl groups.

Component (A) is an organopolysiloxane which has a number-average degree of polymerization of <NUM>,<NUM> or greater based on the number-average molecular weight in terms of standard polystyrene equivalent as measured by gel permeation chromatography (GPC) (hereinafter referred to as "number-average degree of polymerization"), and which exhibits a raw rubber state or gum state at room temperature. Moreover, it is possible and preferable to reduce the concentrations of low molecular weight siloxanes from these components (A) in advance by using a publicly known means such as stripping.

The organopolysiloxane can include siloxane units having hydrocarbon groups R, (e.g., -SiOR<NUM>-) where each R can be the same or different and are substituted or unsubstituted monovalent hydrocarbon groups. Such R groups can have from <NUM> to <NUM> carbons, and preferably from <NUM> to <NUM> carbons.

Examples of the substituted or unsubstituted monovalent hydrocarbon groups bonded to silicon atoms represented by R include alkyl groups such as methyl groups, ethyl groups, propyl groups, isopropyl groups, butyl groups, isobutyl groups, tert-butyl groups, pentyl groups, neopentyl groups, hexyl groups, cyclohexyl groups, octyl groups, nonyl groups and decyl groups; aryl groups such as phenyl groups, tolyl groups, xylyl groups and naphthyl groups; aralkyl groups such as benzyl groups, phenylethyl groups and phenylpropyl groups; alkenyl groups such as vinyl groups, allyl groups, propenyl groups, isopropenyl groups, butenyl groups, hexenyl groups, cyclohexenyl groups and octenyl groups; groups obtained by substituting some or all of the hydrogen atoms in the aforementioned groups with halogen atoms such as fluorine atoms, bromine atoms and chlorine atoms, cyano groups and the like, such as chloromethyl groups, chloropropyl groups, bromoethyl groups, trifluoropropyl groups and cyanoethyl groups, but it is preferable for <NUM>% or more of the R groups to be methyl groups.

Component (A) is an organopolysiloxane which has a number-average degree of polymerization of <NUM>,<NUM> or greater, has an average of two or more silicon-bonded alkenyl groups, and exhibits a raw rubber state or gum state at room temperature. In terms of the structure of this component, the content of silicon-bonded alkenyl groups is determined according to the degree of polymerization and the presence/absence of branches on the main chain, but component (A) is preferably a straight chain or partially branched organopolysiloxane in which the alkenyl group content is from <NUM> to <NUM> weight %, and more preferably a straight chain organopolysiloxane having an average of two or more silicon-bonded alkenyl groups at both molecular termini.

In an aspect of the present disclosure, the structure of component (A) is such that the molecular termini are capped by triorganosiloxy groups having silicon-bonded alkenyl groups and the main chain has a straight chain structure comprising repeating diorganosiloxane units, but may be a partially branched chain structure. The molecular weight of component (A) is such that the number-average degree of polymerization is <NUM>,<NUM> or greater (from <NUM>,<NUM> to <NUM>,<NUM>) and component (A) exhibits in a raw rubber state or gum state, and the number-average degree of polymerization is preferably <NUM>,<NUM> or greater (from <NUM>,<NUM> to <NUM>,<NUM>). If the number-average degree of polymerization is less than the aforementioned lower limit, it is difficult to obtain a satisfactory rubbery feeling, the surface may become sticky or tacky.

The organopolysiloxane of component (B) is a crosslinking agent for the present composition, and is an organopolysiloxane having an average of two or more silicon-bonded hydrogen atoms in the molecule. The bonding sites of the silicon-bonded hydrogen atoms in component (B) are not particularly limited, and may be molecular termini, or pendant to (along) the molecular chains or molecular termini and pendant to the molecular chains. In addition, examples of silicon-bonded groups other than hydrogen atoms in component (B) include monovalent hydrocarbon groups, for example, alkyl groups such as methyl groups, ethyl groups, propyl groups, butyl groups, pentyl groups and hexyl groups; cycloalkyl groups such as cyclopentyl groups and cyclohexyl groups; aryl groups such as phenyl groups, tolyl groups and xylyl groups; aralkyl groups such as benzyl groups and phenethyl groups; halogenated alkyl groups such as <NUM>,<NUM>,<NUM>-trifluoropropyl groups and <NUM>-chloropropyl groups; alkenyl groups such as vinyl groups, allyl groups, propenyl groups, isopropenyl groups, butenyl groups, hexenyl groups, cyclohexenyl groups and octenyl groups;, with alkyl groups and aryl groups being preferred and methyl groups and phenyl groups being particularly preferred.

The molecular structure of component (B) is not limited, and may be, for example, straight chain, branched chain, straight chain having some branches, cyclic, dendritic (dendrimer-like) or resin-like. Component (B) may be a homopolymer having these molecular structures, a copolymer comprising these molecular structures or a mixture thereof.

The viscosity of component (B) is not limited, but the viscosity at <NUM> (as measured using a rotational viscometer and the like) is preferably from <NUM> to <NUM>,<NUM> mPa - s, more preferably from <NUM> to <NUM>,<NUM> mPa - s, and particularly preferably from <NUM> to <NUM>,<NUM> mPa - s.

Examples of this type of component (B) include methylhydrogenpolysiloxanes capped at both molecular termini with trimethylsiloxy groups, copolymers of dimethylsiloxane and methyl hydrogen siloxane capped at both molecular termini with trimethylsiloxy groups, dimethylpolysiloxane capped at both molecular termini with dimethylhydrogensiloxy groups, methylhydrogenpolysiloxanes capped at both molecular termini with dimethylhydrogensiloxy groups, copolymers of dimethylsiloxane and methyl hydrogen siloxane capped at both molecular termini with dimethylhydrogensiloxy groups, cyclic methylhydrogenpolysiloxanes, organosiloxanes comprising siloxane units represented by the formula (CH<NUM>)<NUM>SiO<NUM>/<NUM>, siloxane units represented by the formula (CH<NUM>)<NUM>HSiO<NUM>/<NUM> and siloxane units represented by the formula SiO<NUM>/<NUM>, tetra(dimethylhydrogensiloxy)silanes and methyltri(dimethylhydrogensiloxy)silanes.

In the present composition, the content of component (B) is from <NUM> to <NUM> parts by weight per <NUM> parts by weight of component (A), and is preferably such that the amount of silicon-bonded hydrogen atoms in component (B) is from <NUM> to <NUM> moles, more preferably from <NUM> to <NUM> moles, and particularly preferably from <NUM> to <NUM> moles, per <NUM> mole of silicon-bonded alkenyl groups in component (A). This is because if the content of component (B) is less than the lower limit of the above-mentioned range, crosslinking is inadequate, the hardness of the obtained cured silicone elastomer product is insufficient, the surface may become sticky or tacky. Meanwhile, if the content of component (B) exceeds the upper limit of the above-mentioned range, hydrogen gas is generated from the obtained cured silicone elastomer product, foaming occurs in a molded product, and it may be difficult to release a molded product from a mold.

Component (C) is an inorganic filler, which imparts the silicone elastomer with strength, among other properties. The filler is not limited so long as the filler imparts the silicone elastomer with hardness and permanent elongation, as described below. It is possible to use one or more types of inorganic filler, and component (C) can be a reinforcing filler such as a silica fine powder or fumed titanium oxide; a non-reinforcing filler such as diatomaceous earth, an aluminosilicate, iron oxide, zinc oxide or calcium carbonate; or a thermally conductive filler such as aluminum oxide or boron nitride. A silica fine powder can be a dry type silica such as fumed silica or a synthetic silica such as a wet type silica, and preferably has a specific surface area, as measured using the BET method, of about <NUM> square meters per gram or greater, and more preferably from <NUM> to <NUM> square meters per gram such as from about <NUM> to <NUM> square meters per gram, such as from about <NUM> to about <NUM> square meters per gram. In an embodiment of the present disclosure, the inorganic filler includes fumed silica which accounts for at least <NUM> weight % of the total quantity of component (C), e.g. the inorganic filler includes <NUM> weight % or more, <NUM> weight % or more of the total quantity of component (C).

In addition, the compounded amount of the inorganic filler of component (C) is from <NUM> to <NUM> parts by weight, and preferably from <NUM> to <NUM> parts by weight, per <NUM> parts by weight of component (A). It is difficult to achieve satisfactory hardness or physical strength if the compounded amount is less than the aforementioned lower limit, and elasticity deteriorates, tensile strength and breaking elongation in particular deteriorate, and the composition may not be suitable for use as a medical device if the compounded amount exceeds the aforementioned upper limit.

The inorganic filler of component (C) (for example, fumed silica) can be used without further modification, but can also be treated in advance with a surface treatment agent, such as component (D), to form an inorganic filler having alkenyl groups. Examples of surface treatment agents are provided below for component (D).

Component (D) is a surface treatment agent for the inorganic filler which includes an alkenyl-containing group. Examples of such a filler treatment agent include an alkenyl-containing organosilane, organosilazane, organosilanol, alkoxyorganosilane, or any combination thereof. In one aspect of the present disclosure, the filler treatment agent, component (D), is a mixture of (D1) alkenyl-free organosilane, organosilazane, organosilanol, alkoxyorganosilane, or any combination thereof and (D2) alkenyl-containing organosilane, organosilazane, organosilanol, alkoxyorganosilane, or any combination thereof, e.g., a mixture of (D1) alkenyl-free organosilane or organosilazane and (D2) alkenyl-containing organosilane or organosilazane. For example, the filler treating agent can include a mixture of D1 an organosilane or organosilazane including alkyl, aryl, haloalkyl or haloaryl groups and <NUM> weight % alkenyl functional groups, e.g., a silane, chlorosilane, silazane, an alkyl substituted silane, chlorosilane, silazane, and (D2) an organosilane or organosilazane including alkenyl functional groups or both (i) alkyl (e.g., C<NUM>-<NUM> alkyl), aryl, haloalkyl or haloaryl and (ii) alkenyl functional groups, e.g., a C<NUM>-<NUM> alkyl, aryl, haloalkyl or haloaryl and vinyl substituted silane or silazane. The mixture can include a weight ratio of D1/D2 of from about <NUM>/<NUM> to about <NUM>/<NUM> and preferably from about <NUM>/<NUM> to about <NUM>/<NUM>, e.g., from about <NUM>/<NUM> to about <NUM>/<NUM>. In an embodiment of the present disclosure, D1 and D2 have a parts by weight ratio (D1:D2) of from about <NUM>:<NUM> to about <NUM>:<NUM>.

As explained above, it is believed that the alkenyl groups formed on the inorganic filler can chemically react, e.g., to form covalent bonds, with other components in the composition to form a chemically bound filler incorporated in the cured silicone elastomer. The structure or "architecture" of other parts of this network is also a consideration and includes the polymer-to-polymer crosslinking and non-covalent polymer-to-silica interactions (primarily surface wetting and hydrogen bonding) in addition to the covalent polymer-to-silica bonds. The balance of these factors provides the ultimate and desired properties of the silicone elastomer of the present disclosure. As shown in the examples below, compositions that included a filler treatment agent with alkenyl groups (Examples <NUM>-<NUM>) provided superior tensile strength over a comparable example that included a filler treatment agent but without alkenyl groups (Comparative Example <NUM>).

The addition reaction catalyst of component (E) is a catalyst used to facilitate curing of the present composition, and may be a platinum-based catalyst, a palladium-based catalyst, a rhodium-based catalyst and the like. A platinum metal-type catalyst is particularly preferred.

Examples of component (E) include platinum-based catalysts, for example, platinum fine powders, platinum black, chloroplatinic acid, platinum tetrachloride, alcohol-modified chloroplatinic acid, olefin complexes of platinum, alkenylsiloxane complexes of platinum, carbonyl complexes of platinum, carbene complexes of platinum, platinum on finely divided solid supports such as silica, powdered thermoplastic organic resins and silicone resins containing these platinum-based catalysts; rhodium-based catalysts, palladium based catalysts, other transition metal based catalysts.

The content of component (E) in the present composition is a catalytic quantity, but is more specifically an amount where the quantity of a platinum group metal in component (E) is from <NUM> to <NUM>,<NUM> ppm by weight, and preferably from <NUM> to <NUM> ppm by weight, relative to the total quantity of component (A). This is because the obtained silicone elastomer composition is not sufficiently cured if the content of component (E) is less than the lower limit of the above-mentioned range and the curing speed of the obtained silicone elastomer composition is not significantly improved even if the content of component (E) is greater than the upper limit of the above-mentioned range.

The silicone elastomer composition according to the present disclosure can contain the above-mentioned components (A) to (E), but may also contain (F) an inert solvent.

It is particularly preferable for component (F) to be used where the end-use product requires a lower viscosity, as is the case for spray or dip-coating the composition on to a substrate, e.g., a medical device. Component (F) is an optional component that may be compounded if necessary, and the compounded amount thereof is greater than <NUM> parts by weight, and preferably from <NUM> to <NUM>,<NUM> parts by weight, per <NUM> parts by weight of component (A).

The addition-curable silicone elastomer composition according to the present disclosure may contain a curing retarder in order to adjust the curing speed or pot life. Examples of curing retarders include alcohol derivatives having carbon-carbon triple bonds, such as <NUM>-methyl-<NUM>-butyn-<NUM>-ol, <NUM>,<NUM>-dimethyl-<NUM>-hexyn-<NUM>-ol, phenylbutynol and <NUM>-ethynyl-<NUM>-cyclohexanol; ene-yne compounds such as <NUM>-methyl-<NUM>-penten-<NUM>-yne and <NUM>,<NUM>-dimethyl-<NUM>-hexen-<NUM>-yne; alkenyl group-containing low molecular weight siloxanes such as tetramethyltetravinylcyclotetrasiloxane and tetramethyltetrahexenylcyclotetrasiloxane; and alkyne-containing silanes such as methyl-tris(<NUM>-methyl-<NUM> -butyne-<NUM>-oxy)silane and vinyl-tris(<NUM>-methyl-<NUM> -butyne-<NUM>-oxy)silane.

The compounded amount of the curing retarder may be selected as appropriate according to the usage method, molding method and the like of the addition-curable silicone elastomer composition. A commonly used compounded amount is from <NUM> to <NUM> weight % relative to the total mass of the composition.

The addition-curable silicone elastomer composition according to the present disclosure may contain carbon black such as acetylene black, furnace black or channel black as long as the properties of the elastomer are not impaired. In addition, the addition-curable silicone elastomer composition according to the present disclosure may, if necessary, contain additives such as pigments (coloring agents such as red iron oxide and organic pigments, titanium dioxide and the like), heat-resistant agents, flame retardants, internal release agents, plasticizers, non-functional silicone oils and the like). Moreover, examples of internal release agents include higher fatty acid salts such as calcium stearate. Moreover, it is particularly preferable to use additives such as heat-resistant agents and flame retardants when the addition-curable silicone elastomer composition according to the present disclosure is used as a medical tube in an environment that is exposed to high temperatures, such as in heat sterilization or in a thermocouple.

The silicone elastomer composition of the present disclosure can be readily prepared by homogeneously mixing components (A) through (E) together along with any optional ingredients. Mixing the components and ingredients can be achieved by any conventional means such as a Morehouse Cowles mixer, a two roll mill or a kneader mixer.

The method for molding or curing the addition-curable silicone elastomer composition according to the present disclosure may be a commonly used method, but the molding method is preferably an injection molding method, a compression or transfer molding method, an extrusion molding method (including hot air vulcanization), a dip molding method, a spray molding method, or a rotary molding method. In addition, curing conditions such as the curing temperature and the curing time are not particularly limited, and good curing is generally carried out at a temperature from room temperature to <NUM>. From the perspective of industrial production of an elastic material for a medical device such as a medical tube, it is possible to use heat curing conditions of from <NUM> to <NUM> for a period of from <NUM> seconds to <NUM> minutes, and preferably from <NUM> to <NUM> for a period of from <NUM> seconds to <NUM> minutes. In addition, by press curing (compression molding) the addition-curable silicone elastomer composition according to the present disclosure at <NUM> for <NUM> minutes, as described below, an elastic material for a medical device can exhibit appropriate hardness and permanent elongation characteristics, but it is also possible to cure the composition by means of a stepwise vulcanization (step curing) process, such as carrying out primary vulcanization and then carrying out secondary vulcanization. In such cases, however, the cycle time required for production may be increased and productivity may decrease.

Specifically, the addition-curable silicone elastomer composition according to the present disclosure can be cured in a single step at the above-mentioned temperatures. Furthermore, characteristics such as permanent elongation may be further improved by step curing in which the composition is first heated to a temperature from room temperature to <NUM>, and preferably from <NUM> to <NUM>, and then heated to from <NUM> to <NUM>, and preferably from <NUM> to <NUM>. In addition, in order to remove small quantities or trace quantities of volatile components and further improve characteristics such as permanent elongation, it is preferable to carry out secondary vulcanization (heat aging) at from <NUM> to <NUM> for a period of from <NUM> minutes to <NUM> hours following completion of the curing.

By having the constitution described above, the addition-curable silicone elastomer composition according to the present disclosure is characterized by providing a cured product having a hardness, as measured in accordance with ASTM D2240 using a type A durometer hardness tester (Shore-A hardness), of from about <NUM> to about <NUM>. The Shore-A hardness is preferably from <NUM> to <NUM>. If the hardness falls outside the aforementioned range, the strength and flexibility of the cured product may be insufficient and the cured product may not be suitable for use as a medical device.

Furthermore, the cured product of the addition-curable silicone elastomer composition according to the present disclosure has a tensile strength, as specified in ASTM D412, of about <NUM> MPa or greater, more preferably from about <NUM> to about <NUM> MPa, and particularly preferably from about <NUM> to about <NUM> MPa.

In addition, from the perspective of strength as an elastic material for a medical device, the cured product has a breaking elongation, as specified in ASTM D412, of about <NUM>% or greater, and preferably from about <NUM> to about <NUM>,<NUM>%. Moreover, the breaking elongation is preferably from about <NUM> to about <NUM>,<NUM>% when the aforementioned hardness is from <NUM> to <NUM>, and more preferably from about <NUM> to about <NUM>,<NUM>% when the aforementioned hardness is from about <NUM> to about <NUM>.

Physical properties such as the above-mentioned hardness, breaking elongation, and tensile strength are physical properties that are achieved as a direct result of the constitution of the addition-curable silicone elastomer composition according to the present disclosure, and especially as a result of using the prescribed components (A), (B), (C) and (D) or (A), (B) and (C1). Furthermore, from the perspective of use as an elastic material for a medical device such as a medical tube, the addition-curable silicone elastomer composition according to the present disclosure has a <NUM>% modulus (M100), as measured in accordance with ASTM D412, of from <NUM> to <NUM> MPa, and particularly preferably from <NUM> to <NUM> MPa, following press curing at <NUM> for <NUM> minutes.

Similarly, from the perspectives of strength and service life as an elastic material for a medical device, the addition-curable silicone elastomer composition according to the present disclosure preferably has a tearing strength, as measured in accordance with ASTM D684 using a crescent mold, of <NUM> kN/m or more, and especially from <NUM> to <NUM> kN/m.

Another aspect of the present disclosure includes medical devices that incorporate the silicone elastomers of the present disclosure. The silicone elastomer of the present disclosure can be a component part of a medical device that functions as a tissue expander, a gastric restriction or gastric balloon, an artificial urethral sphincter, a drug delivery reservoir or dispensing device, a prosthetic device such as a breast implant, a testicular prosthesis, a penile prosthesis, a calf prosthesis, a buttocks prosthesis, a vitreous body prosthesis in the eye, an inflatable facial prosthesis. The silicone elastomer of the present disclosure can also be used as a component of an implantable mechanical device such as a valve, finger joint or toe joint. The silicone elastomer of the present disclosure can be a coating or part thereof for a medical device such as a stent, housing for electronic device such as a pacemaker, or a mechanical device such as a pressure transducer or strain gauge or on a catheter, or as a drain or pump tubing.

As a prosthetic device, the silicone elastomer of the present disclosure can be included as a shell or a component of a shell of the device. Such devices typically also include a filler, such as a silicone gel, a water containing medium such as an aqueous solution, e.g., saline, a composite, a gas such as air. The shell typically envelopes the filler and can further include components to seal the filler in the shell such as patches, valves or sealants to establish a continuous barrier to contain the filler material. In an embodiment, a medical device comprises an outer shell including the silicone elastomer of the present disclosure, e.g., a prosthetic such as a breast implant. The medical device, e.g., prosthetic such as a breast implant, can further include a filler material, e.g., a silicone gel or a water containing medium such as saline.

The following examples are intended to further illustrate certain preferred embodiments of the invention and are not limiting in nature. Those skilled in the art will recognize, or be able to ascertain, using no more than routine experimentation, numerous equivalents to the specific substances and procedures described herein.

Measurement of number-average molecular weight and average degree of polymerization. In the Examples and the like, the average degree of polymerization of an organopolysiloxane is the number-average degree of polymerization, based on the number-average molecular weight relative to polystyrene equivalent as measured by gel permeation chromatography (GPC) using an analytical apparatus described below, and was measured under the following conditions: Measurement temperature: <NUM> (column oven temperature); Sample: <NUM> weight % toluene solution of organopolysiloxane; Detector: Refractive index detector; Polymer for calibration curve: Standard polystyrene.

GPC separations were performed on an Agilent <NUM> Infinity HPLC system with refractive index (RI) detector and ChemStation software. Two Phenomenex Phenogel fixed pore GPC columns (<NUM> x <NUM>) were connected in series: Injector - Phenogel <NUM>,000A - Phenogel 500A - Detector. The mobile phase was toluene at a flow rate of <NUM>/minute. Columns were maintained at a temperature of 35C.

Components. The components used in the Examples and Comparative Example, as reported in Table <NUM> below, were as follows: (A) Organopolysiloxane <NUM> (gum-like state) Dimethylsiloxane capped at both molecular termini with vinyldimethylsilyl groups (number-average degree of polymerization: <NUM>,<NUM>) (Commercially available from NuSil catalogue No. MED-<NUM>); (B) Organohydrogenpolysiloxane Copolymer of dimethylsiloxane and methyl hydrogen siloxane capped at both molecular termini with trimethylsilyl groups (viscosity: <NUM> mPa-s, Si-H content: <NUM> mmol Si-H/gram, <NUM>% methylhydrogen units per molecule. (Commercially available from NuSil catalogue No. XL-<NUM>); (C) Fumed silica having a BET specific surface area of <NUM> square meters per gram, purchased from Cabot Corporation; (D1) hexamethyldisilazane, available from multiple sources including Sigma Aldrich, which acted as a filler treating agent containing alkyl (methyl) groups and <NUM> weight % alkenyl functional groups on an organosilane; (D2) symmetrical-tetramethyldivinyldisilazane, available from multiple sources including Sigma Aldrich, which acted as a filler treating agent containing both alkyl (methyl) and alkenyl (vinyl) functional groups on an organosilane; (E) Addition reaction catalyst Platinum-<NUM>,<NUM>-divinyl-,<NUM>,<NUM>,<NUM>-tetramethyldisiloxane complex. (The amount of elemental platinum used in the composition was <NUM> parts per million by weight relative to the total silicone elastomer composition. ); (F) xylenes which acted as a medium to disperse the components of the composition. The curing retarder was <NUM>-ethynyl-<NUM>-cyclohexanol.

The components listed in Table <NUM> are in weight percent.

Sample preparation and curing conditions. For Examples <NUM> to <NUM> and Comparative Example <NUM>, components A, C and D reported in Table <NUM> were combined in a mixer with constant agitation at a temperature of <NUM> for a minimum of <NUM> minutes and then subjected to vacuum at a temperature of <NUM> for a minimum of <NUM> hours. After cooling this "base" compound was split into two parts. Component E was added to the first part on a two-roll mill to produce Part A. Component B and cure retarder were added to the second part on a two-roll mill to produce Part B. Part A and Part B were homogeneously mixed on a two roll mill and then press vulcanized at <NUM> for <NUM> minutes to obtain samples having thicknesses of about <NUM>. For Example <NUM>, which is an example of a dispersion composition including xylenes (component (F)), the components reported in Table <NUM> were mixed as above and then Part A and Part B were separately dispersed in xylenes. Part A and Part B dispersions were mixed and cast into a non-stick mold, and the mixture was cured to give an elastomer slab of <NUM> thickness in a class-A oven with the following ramp cure schedule:.

Example <NUM> is an example of using a silicone elastomer composition in the form of a dispersion or solution to produce a coated medical device (especially medical implant shells) by dip or spray coating the composition onto the device and then curing.

The following physical properties of the cured silicone elastomeric products of Examples <NUM> to <NUM> and Comparative Example <NUM> were measured in the following manner.

As shown in Table <NUM>, the compositions of Examples <NUM> to <NUM> were cured to form silicone elastomers which had hardness of from <NUM> to <NUM>, high breaking elongation of greater than <NUM>,<NUM>% and high tensile strength of greater than <NUM> MPa. Example <NUM> provided a silicone elastomer which had a hardness of <NUM>, a high breaking elongation of over <NUM>% and had high tensile strength of greater than <NUM> MPa. Such silicone elastomers can be prepared by a dip- or spray-coated process and suitable for medical devices (especially medical implant shells).

As shown in Table <NUM>, Comparative Example <NUM> had inferior tensile strength (less than <NUM> MPa) and inferior hardness (less than <NUM>). Comparative Example #<NUM> demonstrates that leaving out a filler treatment agent having alkenyl groups in the composition results in a silicone elastomer with significantly worse properties despite the fact that a filler treatment agent was included in the composition. This Comparative Example demonstrates the significance of the filler treatment agent having alkenyl groups.

Claim 1:
A silicone elastomer obtainable by a process comprising:
(<NUM>) forming a composition comprising:
(A) <NUM> parts of an organopolysiloxane having a molecular weight such that the number-average degree of polymerization is <NUM>,<NUM> or greater and having alkenyl radicals;
(B) <NUM> to <NUM> parts of an organohydrogensiloxane having an average of two or more silicon-bonded hydrogen atoms in the molecule;
(C) <NUM> to <NUM> parts of an inorganic filler; and
(D) <NUM> to <NUM> parts of a filler treatment agent which includes an alkenyl-containing group;
wherein the parts by weight refer to the parts by weight relative to component (A) and
(<NUM>) curing the composition to form the silicone elastomer having:
(i) a Shore-A hardness of from about <NUM> to about <NUM> as measured in accordance with ASTM D2240 using a type A durometer hardness tester;
(ii) a breaking elongation of at least about <NUM>% as measured in accordance with ASTM D412; and
(iii) a tensile strength as measured in accordance with ASTM D412 of at least <NUM> MPa.