GB2445821A

GB2445821A - Silicone rubber compositions comprising extenders/plasticisers

Info

Publication number: GB2445821A
Application number: GB0719682A
Authority: GB
Inventors: Tommy Detemmerman; Robert Andrew Drake; Jary David Jensen; Jean Willieme
Original assignee: Dow Corning Corp
Current assignee: Dow Silicones Corp
Priority date: 2006-10-10
Filing date: 2007-10-09
Publication date: 2008-07-23
Also published as: GB0719682D0

Abstract

A method of preparing a silicone rubber composition comprising the steps of blending: <SL> <LI>a) A pre-prepared organopolysiloxane polymer of the formula R(3-n)R<1>nSiO[(R2SiO)x(RR<1>SiO)y]SiR(3-n)R<1>n wherein each R is the same or different and is an alkyl group containing 1 -6 carbon atoms, a substituted alkyl group containing 1 to 6 carbon atoms or a phenyl group; R<1> is an alkyl group an unsaturated organic group or -OH; n is zero or 1, x is an integer and y is zero or an integer and the sum of x + y is equal to a value of from 200 to 20,000; <LI>b) a filler; <LI>c) a curing component sufficient to cure the composition; <LI>d) an unreactive organic or siloxane based plasticiser and/or an unreactive organic extender. </SL> Preferred plasticisers include phosphate esters, polyisobutylenes, fatty acid esters, polyalkylbenzenes and trimethylsiloxy-terminated polydimethylsiloxanes. Suitable fillers include treated kaolin and silica.

Description

PREPARATION OF SILICONE RUBBER COMPOSITIONS

(0001] This invention is concerned with the use of extenders in organosiloxane based rubber compositions.

2] The use of organosiloxane based compositions which cure to elastomenc solids at either room temperature in the presence of moisture or with application of heat are well documented. Typically those compositions which cure at room temperature in the presence of moisture are obtained by mixing a polydiorganosiloxane polymer or the like having reactive terminal groups, with a suitable silane (or siloxane) based cross-linking agent in the presence of one or more fillers (where required) and a curing catalyst. These compositions are typically either prepared in the form of one-part compositions curable upon exposure to atmospheric moisture at room temperature or two part compositions curable upon mixing at room temperature and pressure conditions and are generally used as silicone sealants.

(0003] It has become common practice in the formulation of silicone based compositions used as room temperature cure sealants, to include additives which serve to "extend" and/or "plasticise" silicone sealant compositions by blending the or each extending compound (henceforth referred to as an "extender") and/or plasticising compound (henceforth referred to as a "plasticiser") with the pre-prepared polymer and other ingredients of the composition. Details of the extenders currently used in sealant formulations are described in the applicants prior application No GB 2424898 which was published after the priority date of this application. Contents of which are incorporated herein by reference.

(0004] An extender (sometimes also referred to as a process aid or secondary plasticiser) is used to dilute the sealant composition and basically make the sealant more economically competitive without substantially negatively affecting the properties of the sealant formulation. The introduction of one or more extenders into a silicone sealant composition not only reduces the overall cost of the product but can also affect the properties of resulting uncured and/or cured silicone sealants. The addition of extenders can, to a degree, positively effect the rheology, adhesion and clarity properties of a silicone sealant and can cause an increase in elongation at break and a reduction in hardness of the cured product both of which can significantly enhance the lifetime of the cured sealant provided the extender is not lost from the cured sealant by, for example, evaporation or exudation.

(0005] A plasticiser (otherwise referred to as a primary plasticiser) is added to a silicone sealant composition to provide properties within the final polymer based product to increase the flexibility and toughness of the final polymer composition. This is generally achieved by reduction of the glass transition temperature (T9) of the cured polymer composition thereby generally, in the case of sealants for example, enhancing the elasticity of the sealant which 1 C in turn enables movement capabilities in a joint formed by a silicone sealant with a significant decrease in the likelihood of fracture of the bond formed between sealant and substrate when a sealant is applied thereto and cured. Plasticisers are typically used to also reduce the modulus of the sealant formulation. Plasticisers may reduce the overall unit cost of a sealant but that is not their main intended use and indeed some plasticisers are expensive and could increase the unit cost of a sealant formulation in which they are used. Plasticisers tend to be generally less volatile than extenders and are typically introduced into the polymer composition in the form of liquids or low melting point solids (which become miscible liquids during processing.

2 C (0006] Whilst the use of such extenders and plasticisers have been considered to have benefits for use in sealant type applications there use for other types of organopolysiloxane compositions is considered by those skilled in the art to provide no benefit and indeed to negate the benefits provided by such compositions. One such application is in relation silicone rubber applications.

(0007] In the case of silicone rubber compositions, the molecular structure of the organosiloxane polymer generally has a degree of polymerization (dp) in the range of from to 20,000. This dp range includes polymers which are thick, flowable liquids which are incorporated into silicone rubber compositions commonly known In the industry as "liquid 3C silicone rubbers" (LSRs) as well as those that have a stiff, gum-like consistency, commonly known in the industry as high consistency silicone rubbers (HCRs). Generally, these stiff gum-like polymers have a dp above about 1500 and have a Williams plasticity number (ASTM D926) in the range of from about 30 to 250. The plasticity number, as used herein, is defined as the thickness in millimetres x 100 of a cylindrical test specimen 2 cubic cm in volume and approximately 10 mm in height after the specimen has been subjected to a compressive load of 49 Newtons for three minutes at 25 C. Liquid silicone rubbers are made from polymers that are thick flowable liquids which can be pumped through a die without e.g. the use of a screw-type extruder. The polymers that are thick flowable liquids have a dp below about 1500 and have a viscosity of between about 200 to 100,000 mPas at25 C.

(0008] DE3342026 describes a process for making a silicone sealant composition involving the physical blending of a portion of pre-formed organosilicone polymer together with some or all of the plasticiser. The physical blending of polymer and plasticiser is 1 C exemplified in the examples using an alpha omega dihydroxypolydimethylsiloxane having a viscosity of merely about 80 000mPa.s at 20 C thereby avoiding the problems which the present inventors have addressed and which would be encountered using such a physical blending process for high viscosity polymers wherein such a blending process would involve very expensive mixing equipment for long time periods of time to obtain anything like a suitable blend rendering such a process economically unviable and most likely not provide a suitable blend.

9] In accordance with the present invention there is provided a method of preparing a silicone rubber composition comprising the steps of blending (a) A pre-prepared organopolysiloxane polymer of the formula RRmflSiO[(R2SiO)x(RRIsio)y]siR(3fl)R1fl (1) wherein each R is the same or different and is an alkyl group containing 1-6 carbon atoms, a substituted alkyl group containing 1 to 6 carbon atoms or a phenyl group; R1 is an alkyl group an unsaturated organic group or -OH; n is zero or 1, x is an integer and y is zero or an integer and the sum of x + y is equal to a value of from 200 to 20,000 (b) a filler (c) a curing component sufficient to cure the composition (d) an unreactive organic or siloxane based plasticiser and/or an unreactive organic extender (0010] The concept of "comprising" where used herein is used in its widest sense to mean and to encompass the notions of "include" and "consist of'.

1] The ingredients may be blended in any order but preferably either the polymer (a) and filler (b) are mixed into a base prior to introduction of the plasticiser and/or extender (d) or the polymer (a) and plasticiser and/or extender (d) are mixed together prior to the introduction of the filler (b). Alternatively, the polymer (a), filler (b) and plasticiser and/or extender (d) may be intermixed together. Subsequent to any of the above three alternatives the cure package is introduced.

(0012] The process can be carried out either batchwise or continuously on any suitable mixers. In case of a polycondensation, generated water can either be removed by chemical drying using e.g. hydrolysable silanes like methyltrimethoxysilane or by physical separation using evaporation, coalescing or centrifuging techniques.

(0013] The present invention additionally provides a method for producing an extended silicone rubber elastomer by producing the composition as hereinbefore described and then curing the composition in the presence of moisture or heat as required.

(0014] Component (a) used in the preparation in accordance with the present invention has the formula R(a.fl)R1flSiO[(R2SiO)x(RR1SiO)y]SiR(3fl)R1fl (1) Each R is the same or different and is an alkyl group containing 1-6 carbon atoms, such as methyl, ethyl, propyl, isopropyl or butyl groups, a substituted alkyl group containing 1 to 6 carbon atoms, an aryl group such as a phenyl group or an alkylaryl group.

(0015] For the purpose of this application "Substituted" means one or more hydrogen atoms in a hydrocarbon group has been replaced with another substituent. Examples of such substituents include, but are not limited to, halogen atoms such as chlorine, fluorine, bromine, and iodine; halogen atom containing groups such as chloromethyl, 3,3,3-trifluoroalkyl groups such as trifluoroethyl, perfluoroalkyl groups, and nonafi uorotiexyl; oxygen atoms; oxygen atom containing groups such as (meth)acrylic and carboxyl; nitrogen atoms; nitrogen atom containing groups such as amino-functional groups, amido-functional groups, and cyano-functional groups; sulphur atoms; and sulphur atom containing groups such as mercapto groups.

(0016] Each R1 group may be the same or different and preferably is an unsaturated organic group containing from 2 to 6 carbon atoms such as alkenyl groups, alkynyl groups, acrylate groups and br alkylacrylate groups. Alkenyl groups are most preferred.

Representative, non-limiting examples of such alkenyl groups are shown by the following structures; H2C=CH-, H2C=CHCH2-, H2C=C(CH3)CHr, H2C=CHCH2CH2-, 1 C H2C=CHCH2CH2CH2-, and H2C=CHCH2CH2CH2CH2-. Vinyl groups are particularly preferred. Representative, non-limiting examples of alkynyl groups are shown by the following structures; HCEC-, HCECCH2-, HCCC(CH3) -, HCCC(CH3)2 -, HC!CC(CH3)2CH2-. At least some R1 groups may be replaced with -OH groups. If present -OH groups are preferably terminally situated. Preferably each component (a) contains at least one, preferably 2 or more unsaturated groups per molecule. The value of n can be zero or I but most preferably the value of each n is 1.

7] Preferably when each n is zero y is equal to at least 2. The sum of x + y is equal to a value of from 200 to 20,000 preferably 200 to 10 000 more preferably between 500 and 6000.

(0018] Representative polysiloxane polymers include high molecular weight gums with the formula Me2 ViSiO[(Me2SiO)x(MeViSiO) yJSiMe2 Vi and/or high molecular weight gums of the formula Me2ViSi(Me2SiO)XSiMe2Vi wherein Me represents the methyl group, Vi represents the vinyl group CH2=CH-, and the value of x + y is at least 1800.

(0019] Component (b) in the method in accordance with the present invention contains one or more finely divided, reinforcing fillers such as high surface area fumed and precipitated silicas and to a degree calcium carbonate or additional non-reinforcing fillers such as crushed quartz, diatomaceous earths, barium sulphate, iron oxide, titanium dioxide and carbon black, talc, wollastonite. Other fillers which might be used alone or in addition to the above include aluminite, calcium sulphate (anhydrite), gypsum, calcium sulphate, magnesium carbonate, clays such as kaolin, aluminium trihydroxide, magnesium hydroxide (bwcite), graphite, copper carbonate, e.g. malachite, nickel carbonate, e.g. zarachite, barium carbonate, e.g. witherite and/or strontium carbonate e.g. strontianite (0020] Other fillers which may be used include Aluminium oxide, silicates from the group consisting of olivine group; garnet group; aluminosilicates; ring silicates; chain silicates; and sheet silicates. The olivine group comprises silicate minerals, such as but not limited to, forstente and Mg2SiO4. The garnet group comprises ground silicate minerals, such as but not limited to, pyrope; Mg3A12Si3O12; grossular; and Ca2Al2Si3O12. Aluninosilicates comprise ground silicate minerals, such as but not limited to, sillimanite; Al2SiO5; mullite; 1 C 3Al2O3.2SiO2; kyanite; and Al2SiO5 The ring silicates group comprises silicate minerals, such as but not limited to, cordiente and Al3(Mg,Fe)2[Si4AlO18]. The chain silicates group comprises ground silicate minerals, such as but not limited to, wollastonite and Ca[Si03J.

(0021] The sheet silicates group comprises silicate minerals, such as but not limited to, mica; K2AI 14[Si6A12O20](OH)4; pyrophyllite; Al4[Si8020](OH)4; talc; Mg6[Si8020](OH)4; serpentine for example, asbestos; Kaolinite; A14[Si4010](OH)8; and vermiculite.

(0022] Preferably the filler(s) (b) are surface treated to render them hydrophobic to ease 2 C their incorporation into the polymer. Such a surface treatment of the filler(s) may be performed, for example with a fatty acid or a fatty acid ester such as a stearate, or with organosilanes, organosiloxanes, or organosilazanes hexaalkyl disilazane or short chain siloxane diols to render the filler(s) hydrophobic. Hydrophobic fillers are easier to handle and obtain a homogeneous mixture with the other composition components. The surface treatment of the fillers makes the ground silicate minerals easily wetted by the silicone polymer. These surface modified fillers do not clump, and can be homogeneously incorporated into the silicone polymer. This results in improved room temperature mechanical properties of the uncured compositions. Furthermore, the surface treated fillers give a lower conductivity than untreated or raw material. 3C

(0023] The proportion of such fillers When employed will depend on the properties desired in the elastomer-forming composition and the cured elastomer. Usually the filler content of the composition will reside within the range from about 5 to about 150 parts by weight per parts by weight of the polymer (a) excluding any extender portion, if present.

4] Any suitable curing agent may be introduced into the composition prepared in accordance with the present invention. The catalyst agent utilised is typically determined by the intended cure reaction pathway and/or the reactive groups on the polymer to be cured. One family of curing agents which may be used herein include organic peroxides such as dialkyl peroxides, diphenyl peroxides, benzoyl peroxide, 1,4-dichlorobenzoyl peroxide, 2,4-dichlorobenzoyl peroxide, di-t-butyl peroxide, d icu myl peroxide, tertiary butyl- perbenzoate, monochlorobenzoyl peroxide, ditertiary-butyl peroxide, 2,5-bis-(tertiarybutyl- peroxy)-2,5-dimethylhexane, tertiary-butyl-trimethyl peroxide, tertiary-butyl-tertiary-butyl- 1 C tertiary-triphenyl peroxide, 1,1 -bis(t-butylperoxy)-3,3,5-trjmethylcyclohexane, and t-butyl perbenzoate. The most suitable peroxide based curing agents are benzoyl peroxide, 2,4-dichlorobenzoyl peroxide, di-t-butyl peroxide, and dicumyl peroxide. Such organic peroxides are used at up to 10 parts per 100 parts of the combination of polymer, filler and optional additives. Preferably between 0.2 and 2 parts of peroxide are used.

(0025] The present compositions can also be cured and/or cross-linked by a hydrosilylation reaction catalyst in combination with an organohydrogensiloxane as the curing agent instead of an organic peroxide, providing a majority of polymer molecules which contain at least two unsaturated groups suitable for cross-linking with the 2C organohydrogensiloxane. These groups are typically alkenyl groups, most preferably vinyl groups. To effect curing of the present composition, the organohydrogensiloxane must contain more than two silicon bonded hydrogen atoms per molecule. The organohydrogensiloxane can contain, for example, from about 4-20 silicon atoms per molecule, and have a viscosity of up to about 10 Pa.s at 25 C. The silicon-bonded organic groups present in the organohydrogensiloxane can include substituted and unsubstituted alkyl groups of 1-4 carbon atoms that are otherwise free of ethylenic or acetylenic unsaturation.

6] Preferably the hydrosilylation catalyst chosen may comprise any suitable 3C hydrosilylation catalyst such as a platinum group metal based catalyst selected from a platinum, rhodium, iridium, palladium or ruthenium catalyst.

(0027] Platinum based hydrosilylation catalysts are illustrated by the following; chloroplatinic acid, alcohol modified chloroplatinic acids, olefin complexes of chloroplatinic acid, complexes of ch loroplatin Ic acid and divinyltetramethyldisi loxane, fine platinum particles adsorbed on carbon carriers, platinum supported on metal oxide carriers such as Pt(A1203), platinum black, platinum acetylacetonate, platinum(divinyltetramethyldisi loxane), platinous halides exemplified by PtCl2, PtCl4, Pt(CN)2, complexes of platinous halides with unsaturated compounds exemplified by ethylene, propylene, and organovinylsiloxanes, styrene hexamethyldiplatinum, Such noble metal catalysts are described in US Patent 3,923,705, incorporated herein by reference to show platinum based catalysts. One preferred platinum based catalyst is Karstedt's catalyst, which is described in Karstedt's US Patents 3,715,334 and 3,814,730, incorporated herein by reference. Karstedt's catalyst is a platinum divinyl tetramethyl disiloxane complex typically containing one weight percent of platinum in a solvent such as toluene. Another preferred platinum based catalyst is a reaction product of chloroplatinic acid and an organosilicon compound containing terminal aliphatic unsaturation. It is described in US Patent 3,419,593, incorporated herein by reference.

Another preferred platinum based catalyst is a neutralized complex of platinous chloride and divinyl tetraniethyl disiloxane, for example as described in US Patent 5,175,325.

(0028] Ruthenium catalysts such as RhCI3(Bu2S)3 and ruthenium carbonyl compounds such as ruthenium 1,1,1-trifluoroacetylacetonate, ruthenium acetylacetonate and triruthinlum dodecacarbonyl or a ruthenium 1,3-ketoenolate may alternatively be used.

(0029] Other hydrosilylation catalysts suitable for use in the present invention include for example rhodium catalysts such as [Rh(O2CCH3)2]2, Rh(O2CCH3)3, Rh2(C8H1502)4, Rh(C5H702)3, Rh(C5H702)(CO)2, Rh(CO)[Ph3P](C5H702), RhX43[(R3)2S]3, (R23P)2Rh(CO)X4, (R23P)2Rh(CO)H, Rh2X42Y24, HaRhbolefincCld, Rh (O(CO)R3)(OH) where X4 is hydrogen, chlorine, bromine or iodine, Y2 is an alkyl group, such as methyl or ethyl, GO, C8H14 or 0.5 C8H12, R3 is an alkyl radical, cycloalkyl radical or aryl radical and R2 is an alkyl radical an aryl radical or an oxygen substituted radical, a is 0 or 1, b is 1 or 2, c is a whole number from 1 to 4 inclusive and d is 2,3 or 4, n is 0 or 1. Any suitable iridium catalysts such as lr(OOCCH3)3, lr(C5H702)3, [lr(Z4)(En)2J2, or (Ir(Z4)(Dien)]2, where Z4 is chlorine, bromine, iodine, or alkoxy, En is an olefin and Dien is cyclooctadiene may also be used.

(0030] The hydrosilylation catalyst may be added to the present composition in an amount equivalent to as little as 0.001 part by weight of elemental platinum group metal, per one million parts (ppm) of the composition. Preferably, the concentration of the hydrosilylation catalyst in the composition is that capable of providing the equivalent of at least 1 part per million of elemental platinum group metal. A catalyst concentration providing the equivalent of about 3-50 parts per million of elemental platinum group metal is generally the amount preferred.

(0031] Preferably component (d) may comprise any suitable organic extender and/or siloxane or organic plasticiser. Mineral oil extenders and plasticisers are however particularly preferred. Examples include linear or branched mono unsaturated hydrocarbons such as linear or branched alkenes or mixtures thereof containing at least 12, ic e.g. from 12 to 25 carbon atoms; and/or mineral oil fractions comprising linear (e.g. n-paraffinic) mineral oils, branched (iso-paraffinic) mineral oils, cyclic (referred in some prior art as naphthenic) mineral oils and mixtures thereof. Preferably the hydrocarbons utilised comprise at least 10, preferably at least 12 and most preferably greater than 20 carbon atoms per molecule.

2] Other preferred mineral oil extenders include alkylcycloaliphatic compounds, alkybenzenes including polyalkylbenzenes which are unreactive with the polymer.

(0033] Any suitable mixture of mineral oil fractions may be utilised as the extender in the 2C present invention but high molecular weight extenders (e.g. >220) are particularly preferred.

Examples include:-

alkylcyclohexanes (molecular weight > 220); paraffinic hydrocarbons and mixtures thereof containing from I to 99%, preferably from 15 to 80% n-paraffinic and/or isoparaffinic hydrocarbons (linear branched paraffinic) and I to 99%, preferably 85 to 20% cyclic hydrocarbons (naphthenic) and a maximum of 3%, preferably a maximum of 1% aromatic carbon atoms. The cyclic paraffinic hydrocarbons (naphthenics) may contain cyclic and/or polycyclic hydrocarbons. Any suitable mixture of mineral oil fractions may be used, e.g. mixtures containing 3C (i) 60 to 80% paraffinic and 20 to 40% naphthenic and a maximum of 1% aromatic carbon atoms; (ii) 30-50 %, preferably 35 to 45% naphthenic and 70 to 50% paraffinic and or isoparaffinic oils;

C

(iii) hydrocarbon fluids containing more than 60 wt.% naphthenics, at least 20 wt.% polycyclic naphthenics and an ASTM D-86 boiling point of greater than 235 C; (iv) hydrocarbon fluid having greater than 40 parts by weight naphthenic hydrocarbons and less than 60 parts by weight paraffinic and/or isoparaflinic hydrocarbons based on 100 parts by weight of hydrocarbons.

(0034] Preferably the mineral oil based extender or mixture thereof comprises at least one of the following parameters:-

C

(i) a molecular weight of greater than 150, most preferably greater than 200; (ii) an initial boiling point equal to or greater than 230 C (according to ASTM D 86).

(iii) a viscosity density constant value of less than or equal to 0.9; (according to ASTM 2501) (iv) an average of at least 12 carbon atoms per molecule, most preferably 12 to carbon atoms per molecule; (v) an aniline point equal to or greater than 70 C, most preferably the aniline point is from 80 to 110 C (according to ASTM 0 611); 2 C (vi) a naphthenlc content of from 20 to 70% by weight of the extender and a mineral oil based extender has a paraffinic content of from 30 to 80% by weight of the extender according to ASTM D 3238); (vii) a pour point of from -50 to 60 C (according to ASIM D 97); (viii) a kinematic viscosity of from I to 20 cSt at 40 C (according to ASTM D 445) (ix) a specific gravity of from 0.7 to 1.1 (according to ASTM D1298); (x) a refractive index of from 1.1 to 1.8.at 20 C (according to ASTM D 1218) (xi) a density at 15 C of greater than 700kg/rn3 (according to ASTM D4052) and/or (xii) a flash point of greater than 100 C, more preferably greater than 110 C (according to ASTM D 93) (xiii) a saybolt colour of at least +30 (according to ASTM 0 156) (xiv) a water content of less than or equal to 25Oppm (xv) a Sulphur content of less than 2.5ppm (according to ASTM D 4927) [0035] Other organic extenders (d) may include for the sake of example, alkylbenzene compounds suitable for use include heavy alkylate alkylbenzene or an alkylcycloaliphatic compound. Examples of alkyl substituted aryl compounds useful as extenders and/or plasticisers are compounds which have aryl groups, especially benzene substituted by alkyl and possibly other substituents, and a molecular weight of at least 200. Examples of such extenders as described in US Patent No. 4,312,801, the content of which is incorporated herein by reference. These compounds can be represented by general formula (2), (3), (4) and (5) 1 C (0036] The alkylbenzene compounds suitable for use include heavy alkylate alkylbenzene or an alkylcycloaliphatic compound. Examples of alkyl substituted aryl compounds useful as extenders and/or plasticisers are compounds which have aryl groups, especially benzene substituted by alkyl and possibly other substituents, and a molecular weight of at least 200. Examples of such extenders as described in US Patent No. 4,312,801, the content of which is incorporated herein by reference. These compounds can be represented by general formula (2), (3), (4) and (5) R1l R7 R1 R8 R9 (2) R H -(CH2)-cH R7 (3) 2C (4) R6 R12 : (CH2))J R9 R15 (5) where R6 is an alkyl chain of from 1 to 30 carbon atoms, each of R7 through to R16 is independently selected from hydrogen, alkyl, alkenyl, alkynyl, halogen, haloalkyl, nitrile, amine, amide, an ether such as an alkyl ether or an ester such as an alkyl ester group, and n is an integer of from I to 25.

(0037] In particular, the extender used in accordance with the process of the present invention is of formula (2) where each of R7, R8, R9, R1 and R11 is hydrogen and R6 is a C10-C13 alkyl group. A particularly useful source of such compounds are the so-called "heavy alkylates", which are recoverable from oil refineries after oil distillation. Generally distillation takes place at temperatures in the range of from 230 to 330 C, and the heavy alkylates are present in the fraction remaining after the lighter fractions have been distilled off.

(0038] Examples of alkylcycloaliphatic compounds are substituted cyclohexanes with a molecular weight in excess of 220. Examples of such compounds are described in EP 0842974, the content of which is incorporated herein by reference. Such compounds may be represented by general formula (6).

QT R19 (6)

where R17 is a straight or branched alkyl group of from I to 25 carbon atoms, and R18 and R19 are independently selected from hydrogen or a C125 straight or branched chain alkyl group.

(0039] In one embodiment of the present invention the extender and/or plasticiser (d) may 1C comprise a suitable non-mineral based natural oil or a mixture thereof, i.e. those derived from animals, seeds and nuts and not from mineral oils (i.e. not from petroleum or petroleum based oils) such as for example almond oil, avocado oil, beef tallow, borrage oil, butterfat, canola oil, cardanol, cashew nut oil, cashew nutshell liquid, castor oil, citrus seed oil, cocoa butter, coconut oil, cod liver oil, corn oil, cottonseed oil, cuphea oil, evening primrose oil, hemp oil, jojoba oil, lard, linseed oil, macadamia oil, menhaden oil, oat oil, olive oil, palm kernel oil, palm oil, peanut oil, poppy seed oil, rapeseed oil, rice bran oil, safflower oil, safflower oil (high oleic), sesame oil, soybean oil, sunflower oil, sunflower oil (high oleic), tall oil, tea tree oil, turkey red oil, walnut oil, perilla oil, dehydrated castor oils, apricot oil, pine nut oil, kukul nut oil, amazon nut oil almond oil, babasu oil, argan oil, black 2C cumin oil, bearberry oil, calophyllum oil, camelina oil, carrot oil, carthamus oil, cucurbita oil, daisy oil, grape seed oil, foraha oil, jojoba oil, queensland oil, onoethera oil, ricinus oil, tamanu oil, tucuma oil, fish oils such as pilchard, sardine and herring oils. The extender may alternatively comprise mixtures of the above and/or derivatives of one or more of the above.

(0040] A wide variety of derivates are available. These include transesterified natural vegetable oils, boiled natural oils such as boiled linseed oil, blown natural oils and stand natural oils. An example of a suitable transesterified natural vegetable oil is known as biodiesel oil, the transesterification product produced by reacting mechanically extracted natural vegetable oils from seeds, such as rape, with methanol in the presence of a sodium hydroxide or potassium hydroxide catalyst to produce a range of esters dependent on the feed utilised. Examples might include for example methyloleate (CH3(CH2)7CH=CH(CH2)7C02CH3).

(0041] Stand oils which are also known as thermally polymerised or heat polymerised oils and are produced at elevated temperatures in the absence of air. The oil polymerises by cross-linking across the double bonds which are naturally present in the oil. The bonds are of the carbon-carbon type. Stand oils are pale coloured and low in acidity. They can be produced with a wider range of viscosities than blown oils and are more stable in viscosity. In general, stand oils are produced from linseed oil and soya bean oil

but can also be 1 C manufactured based on other oils.

2] Blown oils which are also known as oxidised, thickened and oxidatively polymerised oils and are produced at elevated temperatures by blowing air through the oil.

Again the oil polymerises by cross-linking across the double bonds but in this case there are oxygen molecules incorporated into the cross-linking bond. Peroxide, hydroperoxide and hydroxyl groups are also present. Blown oils may be produced from a wider range of oils than stand oils. In general, blown oils are darker in colour and have a higher acidity when compared to stand oils.

(0043] Most preferably the extender comprises a mineral oil fraction or a natural oil or a derivative of the latter.

(0044] The amount of extender/plasticiser which may be included in the composition will depend upon factors such as the end use of the polymer prepared in accordance with the process in accordance with the present invention, the physical characteristics, e.g. molecular weight, of the extender/plasticiser(s) concerned etc. Products of the process in accordance with the present invention may contain from 5%w/w up to 70%wlw extender/plasticiser (based on the combined weight of polymer and extender/plasticiser(s)) depending upon these factors. In general however, the higher the molecular weight of the extender/plasticiser(s), the less will be tolerated in the composition. Suitable polymer products comprise from I O-50%w/w of a extender/plasticiser(s) whereas 20-40%w/w will be more preferred when the extender/plasticiser is a heavy alkylate. The extender/plasticiser content will typically be determined by the intended end use of the product prepared.

(0045] The composition in accordance with the present invention provides the user with formulations suitable for silicone rubber formulations.

(0046] Other ingredients which may be included in the compositions include but are not restricted to co-catalysts for accelerating the cure of the composition such as metal salts of carboxylic acids and amines; Adhesion promoters, pigments, Heat stabilizers, Flame retardants, UV stabilizers, Chain extenders, cure modifiers, electrically and/or heat conductive fillers, Fungicides and/or biocides and the like (which may suitably by present in an amount of from 0 to 0.3% by weight), water scavengers, (typically the same compounds as those used as cross-linkers or silazanes). It will be appreciated that some of the additives are included in more than one list of additives. Such additives would then have the ability to function in all the different ways referred to.

7] The rheological additives include silicone organic co-polymers such as those described in EP 0802233 based on polyols of polyethers or polyesters; non-ionic surfactants selected from the group consisting of polyethylene glycol, polypropylene glycol, ethoxylated castor oil, oleic acid ethoxylate, alkylphenol ethoxylates, copolymers or ethylene oxide (E0) and propylene oxide (P0), and silicone polyether copolymers; as well as silicone glycols. For some systems rheological additives, particularly copolymers of ethylene oxide (EO) and propylene oxide (P0), and silicone polyether copolymers may enhance the adhesion of the sealant to substrates, particularly plastic substrates.

8] Heat stabilizers may include Iron oxides and carbon blacks, Iron carboxylate salts, cerium hydrate, barium zirconate, cerium and zirconium octoates, and porphyrins.

9] Flame retardants may include for example, carbon black, hydrated aluminium hydroxide, and silicates such as wollastonite, platinum and platinum compounds.

(0050] Electrically conductive fillers may include carbon black, metal particles such as silver particles any suitable, electrically conductive metal oxide fillers such as titanium oxide powder whose surface has been treated with tin and/or antimony, potassium titanate powder whose surface has been treated with tin and/or antimony, tin oxide whose surface has been treated with antimony, and zinc oxide whose surface has been treated with aluminium.

(0051] Thermally conductive fillers may include metal particles such as powders, flakes and colloidal silver, copper, nickel, platinum, gold aluminium and titanium, metal oxides, particularly aluminium oxide (Al203) and beryllium oxide (BeO);magnesium oxide, zinc oxide, zirconium oxide; Ceramic fillers such as tungsten monocarbide, silicon carbide and aluminium nitride, boron nitride and diamond.

(0052] Optional additives for a silicone rubber composition may comprise one or more of the following rheology modifiers, pigments, colouring agents, anti-adhesive agents, heat stabilisers, blowing agents, flame retardants, electrically and/or thermally conductive fillers, and desiccants, each of which are preferably as hereinbefore described.

(0053] Other optional ingredients which may be incorporated in the composition of a silicone rubber include handling agents, peroxide cure co-agents, acid acceptors, and UV stabilisers.

4] Handling agents are used to modify the uncured properties of the silicone rubber such as green strength or processability sold under a variety of trade names such as SILASTIC HA-I, HA-2 and HA-3 sold by Dow Corning corporation) [0055] Peroxide cure co-agents are used to modify the properties, such as tensile strength, elongation, hardness, compression set, rebound, adhesion and dynamic flex, of the cured rubber. These may include di-or tn-functional acrylates such as Trimethylolpropane Triacrylate and Ethylene Glycol Dimethacrylate; Triallyl Isocyanurate, Triallyl Cyanurate, Polybutadiene oligomers and the like. Silyl-hydride functional siloxanes may also be used as co-agents to modify the peroxide catalysed cure of siloxane rubbers.

(0056] The acid acceptors may include Magnesium oxide, calcium carbonate, Zinc oxide and the like.

(0057] The ceramifying agents can also be called ash stabilisers and include silicates such as wollastonite.

(0058] As will be discussed below in finer detail, there are a number of possible methods for introducing the organic extender and/or plasticiser into the composition. A particularly preferred method is by introducing the extender and/or plasticiser into the monomer oligomer used in the preparation of polymer (a) and polymerising the polymer in the presence of the extender/plasticiser, thereby eventually forming a "diluted" polymer (a).

(0059] The silicone rubber composition in accordance with this embodiment may be made by any suitable route, for example one preferred route is to merely blend all the ingredients together by for example first making a silicone rubber base by heating a mixture of fumed silica, a treating agent for the silica, the extender/plasticiser and the organopolysiloxane containing polymer of the present invention. The silicone rubber base is removed from the first mixer and transferred to a second mixer where generally about 150 parts by weight of a non-reinforcing or extending filler such as ground quartz is added per 100 parts by weight of the silicone rubber base. Other additives are typically fed to the second mixer such as curing agents, pigments and colouring agents, heat stabilizers, anti-adhesive agents, plasticizers, and adhesion promoters. In a second preferred route the diluted organopolysiloxane containing polymer of the present invention and any desired filler plus any desired treating agent are fed into a reactor and mixed, further additives as described above including cure agents are then fed into the same reactor and further mixed.

(00601 Elastomers prepared from silicone rubber compositions in accordance with the present invention may be used in a wide variety of applications including in the manufacture of for example:-automotive, aviation and aerospace products, babycare products such as teats for bottles, insulators for power and utilities applications, extruded profiles, gaskets and seals for e.g. air water, fuel and oil applications e.g. hoses, keypads, in medical and office equipment such as protective equipment and masks, rollers for e.g. photocopiers, sponges, and wire and cable coating applications.

(0061] The invention will now be described by way of Example.

Examples

(0062] In the following examples all viscosity measurements relating to organopolysiloxane polymers were taken at 25 C.

Example I

3] A Winkworth Z-blade mixer was loaded with 1200g of a 70 durometer polydimethylsi loxane elastomer with approximate composition, * 35 parts by weight dimethylvinyl siloxy terminated dimethyl siloxane gum, having a plasticity of from 55 to 65 mils * 27 parts by weight dimethylvinyl siloxy terminated dimethyl methylvinyl siloxane gum, having a plasticity of from 55 to 65 mils * I parts by weight of hydroxy-terminated dimethyl methylvinyl siloxane having a viscosity of 20 mPa.s at 25 C.

* 5 parts by weight of hydroxy-terminated dimethyl siloxane having a viscosity of about 21 mPa.s at 25 C * 34 parts by weight of fumed silica [0064] This was allowed to mix on its own for several minutes at ambient temperature. A total of 300g of a hydrocarbon extender (Hydrotreated Middle Distillates (Petroleum -Pilot 900, Petrochem Carless)) was then added over the course of several hours (-6hrs). This gave a 20% oil master batch (MBI). 2C

(0065] Further samples were then prepared, on a two roll mill, at different concentrations of extender by introducing varying amounts of the 70 durometer polydimethylsiloxane composition described above (extender free) into MB1. A hydrosilylation curing system was added in the amounts indicated in Table I below. Each resulting sample was cured for 10 minutes at 130 C to give a test sheet which was tested as indicated in Table 1 below

Table I:

Run 1 2 3 4 MB1 parts 100 50 25 0 duro elastomer parts 0 50 75 100 Platinum Vinyl siloxane complex masterbatch in siloxane 0.9 0.9 0.9 0.9 (-0.1% w/w Pt) parts _____ _____ Poly-dimethyl-methylhydrogen-silOxafle copolymer master 5 5 5 5 batch in siloxane (-0.16% wlw SiH as H) parts 1-Ethynyl-1-cyclohexanol master batch in siloxane (10% 2.2 2.2 2.2 2.2 wiw) parts Tensile Strength (ISO 37: 1994 Type 2) (MPa) 7.7 8.8 9.3 9.7 Elongation at Break (ISO 34: 1994 Type 2) (%) 858 765 747 711 Hardness (BS ISO EN 868:2003) (Durometer Shore A) 38. 3 52.1 57.8 65.5 Tear Strength (ASTM 624 -98, Die B) (kNm') 55.8 53.9 52.0 50.8 Density (kg/ms) 1.10 1.14 1.17 1.19 4 7 0 7 [0066] The results show that up to 20% of hydrocarbon can be added as an extender and this can give a silicone rubber with enhanced properties such as elongation at break and tear as well as reduced density which can be useful in reducing the weight of parts. These property enhancements are larger than those observed when a siloxane 200 fluid is used as an extender as shown in comparative example 2 with the added benefit of lower cost due to use of a hydrocarbon extender compared to a siloxane extender.

Example 2

7] The same method as for Experiment I was used except that Biodiesel (a mixed fatty acid methyl ester derived from Palm and Sunflower Oil) was used as the extender to prepare MB2. Mixing was more rapid than in the Example I (-2hrs). Samples were prepared as shown in Table 2. Samples were cured for 10 minutes at 130 C to give a test sheet which was tested according to the procedures shown in 2

Table 2:

Run 1 2 3 4 MB2 100 50 25 0 duro elastomer parts 0 50 75 100 Platinum Vinyl siloxane complex masterbatch in siloxane 0.9 0.9 0.9 0.9 (-0.1% w/w Pt) parts _____ Poly-dimethyl-methylhydrogen-siloxane copolymer master 5 5 5 5 batch in siloxane (-0.16% w/w SiH as H) parts 1-Ethynyl-1-cyclohexanol master batch in siloxane (10% 2.2 2.2 2.2 2.2 w/w) parts 2C Tensile Strength (ISO 37:1994 Type 2) (MPa) 8.3 8.7 9.6 9.7 Elongation at Break (ISO 34: 1994 Type 2)(%) 1166 1117 974 711 Hardness (BS ISO EN 868:2003) (Durometer Shore A) 34.5 42.3 53.6 65.5 Tear Strength (ASTM 624 -98, Die B) (kNm') 52.5 54.5 57.3 50.8 Density (kgIm) 1.12 1.16 1.17 1.19 9 2 6 7 (0068] Again an extended rubber can be prepared that shows enhanced properties with the added advantage of utilizing an extender that is derived from a bio-renewable source.

Example 3

(0069] A mixture of 80 parts by weight of a silanot end-blocked polydimethylsiloxane gum, (Mn = 246000, DP -3300) and 20 parts by weight of a trimethylsilyl end-blocked polydimethylsiloxane extender/plasticiser, (Viscosity -60,000mPa.s at 25 C) was prepared 1 C and charged to a Brabender plasticorder mixer. 100 parts. of a methyltrimethoxysilane treated calcined Kaolin was prepared according to methods described in WO 2005/054352 and added to the mixture of polymer and plasticiser and was mixed at 20 rpm for 90 minutes.

(0070] The product was mixed with 2phr of a paste of Dichlorobenzoyl peroxide 50 parts in silicone oil on a two roll mill and cured for 5 minutes at 116 C to give a test sheet which was tested according to the procedures in Table 3. 2].

Table 3

Tensile Strength (ISO 37:1994 Type 2) (MPa) 5.4 Elongation at Break (ISO 34: 1994 Type 2) (%) 154 Hardness (BS ISO EN 868:2003) (Durometer Shore A) 45 Tear Strength (ASTM 624 -98, Die B) (kNm') 12.2

Claims

1. A method of preparing a silicone rubber composition comprising the steps of blending (a) A pre-prepared organopolysiloxane polymer of the formula R(3n)R1nSiOE(R2SiO)x(RR1 SiO)y]SiR(3.n)R1 n (1) wherein each R is the same or different and is an alkyl group containing 1-6 carbon atoms, a substituted alkyl group containing 1 to 6 carbon atoms or a phenyl group; R1 is an alkyl group an unsaturated organic group or -OH: n is zero or 1, x is an integer and y is zero or an integer and the sum of x + y is equal to a value of from 200 to 20,000 (b) a filler (c) a curing component sufficient to cure the composition (d) an unreactive organic or siloxane based plasticiser and/or an unreactive organic extender

2. A method in accordance with claim 1 characterised in that the extender and/or plasticiser is selected from one or more of the group trialkylsilyl terminated polydimethyl siloxane, polyisobutylenes (PIB), phosphate esters, polyalkylbenzenes, linear and/or branched alkylbenzenes esters of aliphatic monocarboxylic acids.

3. A method in accordance with claim 1 wherein the extender is selected from one or more of the group comprising linear or branched mono unsaturated hydrocarbons such as linear or branched alkenes or mixtures thereof containing from 12 to 25 carbon atoms; and/or mineral oil fractions comprising linear (n-paraffinic) mineral oils, branched (iso-paraffinic) mineral oils and/or cyclic (naphthenic) mineral oils and mixtures thereof.

4. A method in accordance with any preceding claim wherein the curing component is an organic peroxide catalyst.

5. A method in accordance with any one of claim 1 to 3 wherein the curing component is a hydrosilylation reaction catalyst in combination with an organohydrogensiloxane.

6. A method in accordance with any preceding claim wherein the filler material comprising one or more finely divided, reinforcing fillers such as high surface area fumed silica, precipitated silica and calcium carbonate, kaolin, crushed quartz, diatomaceous earth, barium sulphate, iron oxide, titanium dioxide, carbon black, talc and/or wollastonite.

7. A method in accordance with any preceding claim wherein n1.

8. A method in accordance with any preceding claim characterised in that the polymer (a) is blended with the filler (b) before the introduction of the extender and/or plasticiser (d).

9. A method in accordance with any one of claims 1 to 7 characterised in that the polymer (a) and extender and/or plasticiser (d) were blended together prior to the

introduction of filler (b)

10. A method in accordance with any one of claims 1 to 7 characterised in that the polymer (a), extender and/or plasticiser (d) and filler (b) are simultaneously intermixed.

11. A silicone rubber composition obtainable by the method in accordance with any preceding claim.

12. A cured silicone elastomer prepared by curing a composition prepared in accordance with any one of claims I to 10.

13. A method as hereinbefore described with reference to the Examples.