Addition-crosslinkable liquid silicone rubber composition with low total volatile content

Abstract

The present invention relates to a cured silicone rubber composition having a toluene-soluble content, wherein the toluene-soluble content in the GPC measurement using polystyrene as a standard has a main peak eluted before the extracting solvent peak corresponding to a number average molecular weight of more than 1500 Dalton, and a weight loss measured according to BfR of less than 0.5 wt.-%, wherein the composition is obtained by curing a hydrosilylation curable silicone rubber composition.

Description

[0001] ADDITION-CROSSLINKABLE LIQUID SILICONE RUBBER COMPOSITION WITH LOW TOTAL VOLATILE CONTENT

[0002] Field of the invention

[0003] This invention relates to new curable liquid silicone rubber (LSR) compositions with low volatile content, in particular to a cured silicone rubber composition with a low volatile content, a curable silicone rubber composition, a process for the manufacture of the cured silicone rubber composition, the use of the silicone rubber composition for the manufacture of cured articles, an article comprising such cured silicone rubber composition, and a process for the manufacture of the curable silicone rubber composition.

[0004] Background / State of the art

[0005] Silicone rubbers are widely used in a variety of fields while taking advantage of their heat resistance, low temperature resistance, and electric properties. It is known in the art that since siloxane polymers for forming silicone rubbers are prepared through equilibration reaction of siloxane oligomers with the aid of acid or alkali, they always contain, independently of whether the degree of polymerization (DOP), i.e. the number of silicon atoms per molecule is high or low, considerable amounts of cyclic siloxanes having a DOP of up to 20, called low-molecular- weight siloxanes, and being free of reactive groups such as SiH and alkenyl functional groups in the molecule, called non-functional siloxanes. As also known in the art, the low-molecular- weight siloxanes will volatilize from the cured rubber not only in high temperature atmosphere, but also slightly in room temperature conditions and deposit on the surroundings, giving rise to various problems such as haze or turbidity evolution, adhesion interference, and hydrophobic surface. While the low-molecular weight siloxanes may be substantially reduced by post-curing the cured rubber at high temperature, the rubber which is used in a sealed state or as a part to be combined with a less heat resistant resin has the problem of prohibited exposure to high temperature. While the low-molecular-weight siloxanes may be removed by volatilization at high temperature under reduced pressure, complete removal is difficult, with some siloxanes being left at a level around 1% by weight or a lower level of about 0.5% by weight (about 5,000 ppm).

[0006] The demand for low volatile liquid silicon rubber has been addressed in the art.

[0007] JP-A H03- 157474 discloses an addition reaction-curable silicone rubber adhesive in which the content of low-molecular-weight siloxanes having a vapor pressure of at least 10 mmHg at 200°C is up to 500 ppm, and JP-B H06-054405 describes a fixing roller in which the content of low-molecular-weight siloxanes having a DOP of 20 or less is up to 0.75% by weight. JP-A H04-311764 also discloses a method for preparing a siloxane polymer having a low content of low-molecular-weight siloxanes through the chain extending step using a polymer having SiH functional groups at both ends of the molecular chain. In the description of H04-311764, it is disclosed in a general manner that as fillers those obtained by subjecting their surfaces to hydrophobic treatment with cyclic organopolysiloxane, hexamethyldisilazane, or the like may be used. In the Examples of the application, however, dry silica is used without hydrophobic treatment by such compounds and / or water. JP-A2008-255227 discusses unique problems of low-molecular-weight siloxanes having a hydrogen atom directly bonded to a silicon atom (or SiH functional group) and discloses a composition having a reduced content of low-molecular- weight siloxanes. JP6428591 (EP 3388488 A1 and US 2018346722 A1) discloses an addition- curable silicone rubber in which the content of non-functional and SiH functional low-molecular- weight siloxanes having a DOP of up to 10 is reduced, and the content of Si — OH functional low-molecular-weight silanes and siloxanes having a DOP of up to 10 is reduced to or below 0.3% by weight based on the total composition. In said patent application, it is disclosed in the description in a general manner that water may be added for surface treatment without further specifying the amounts to be applied or the effects thereof. In the Examples 1-4 of the invention of that application, the weight ratio of water to the surface treating agent HMDZ is from 33 weight-% to 63 weight-%.

[0008] Summary of the invention

[0009] The invention addresses the increasing demand for post cure free / low volatile LSR grades. Regarding the weight loss of cured silicone rubber, Chapter 15 Silicone in Recommendations on Food Contact Materials by BfR (Bundesinstitut fur Risikobewertung) prescribes the guideline indicating a weight loss of up to 0.5% by weight upon heating at 200°C / 4 hours.

[0010] An object of the invention is to provide an addition-curable silicone rubber composition which cures into a cured product or silicone rubber from which low-molecular weight siloxane components will volatilize only extremely small quantities, which eliminates problems such as mold fouling, haze or turbidity evolution, adhesion interference, and hydrophobic surface caused by deposition of the volatilized low-molecular-weight siloxanes on the surroundings. Such silicone rubber compositions may find safe use as infant goods such as bottle teats and baby dummies, kitchen goods such as cake molds, gaskets for water plumbing, and medical and health care tools such as dialyzers, and a silicone rubber.

[0011] Another object of the invention is to provide an addition-curable silicone rubber composition which cures into a cured product or silicone rubber with a maximum weight loss of 0.5% according to the BfR even without post curing. The present invention thus relates to a cured silicone rubber composition having a toluene- soluble content, wherein the toluene-soluble content in the GPC measurement using polystyrene as a standard has a main peak eluted before the extracting solvent peak corresponding to a number average molecular weight of more than 1500 Dalton, preferably more than 1600 Dalton, more preferably more than 1700 Dalton, more preferably more than 1800 Dalton, and a weight loss measured according to BfR of less than 0.5 wt.-%, preferably less than 0.45 wt.-%, more preferably of less than 0.4 wt.-%, even more preferably of less than 0.35 wt.-%, and still more preferably of less than 0.30 wt.-%, wherein the composition is obtained by curing a curable silicone rubber composition, wherein the curable silicone rubber composition comprises:

[0012] (A) one or more organopolysiloxanes having at least two silicon-bonded aliphatic unsaturated groups per molecule,

[0013] (B) one or more organohydrogenpolysiloxanes having at least two silicon-bonded hydrogen atoms per molecule,

[0014] (C) one or more reinforcing fillers,

[0015] (D) one or more hydrosilylation catalysts,

[0016] (E) optionally one or more additives.

[0017] The invention further relates to a curable silicone rubber composition, a process for the manufacture of the cured silicone rubber composition, the use of the curable silicone rubber composition for the manufacture of cured articles, an article comprising the cured rubber composition, and a process for the manufacture of the curable silicone rubber composition, all of them addressing the problems described above.

[0018] Detailed description of the invention

[0019] In a first aspect, the invention relates to a cured silicone rubber composition wherein the composition is obtained by curing a curable silicone rubber composition, wherein the curable silicone rubber composition comprises:

[0020] (A) one or more organopolysiloxanes having at least two silicon-bonded aliphatic unsaturated groups per molecule,

[0021] (B) one or more organohydrogenpolysiloxanes having at least two silicon-bonded hydrogen atoms per molecule,

[0022] (C) one or more reinforcing fillers,

[0023] (D) one or more hydrosilylation catalysts,

[0024] (E) optionally one or more additives. In a preferred embodiment, the cured silicone rubber composition is a cured silicone rubber composition having a toluene-soluble content, wherein the toluene-soluble content in the GPC measurement using polystyrene as a standard has a main peak eluted before the extracting solvent peak corresponding to a number average molecular weight of more than 1500 Dalton, preferably more than 1600 Dalton, more preferably more than 1700 Dalton, more preferably more than 1800 Dalton, and a weight loss measured according to BfR of less than 0.5 wt.-%, preferably less than 0.45 wt.-%, more preferably of less than 0.4 wt.-%, , even more preferably of less than 0,35 wt.-%, and still more preferably of less than 0,30 wt.-%, wherein the composition is obtained by curing a curable silicone rubber composition, wherein the curable silicone rubber composition comprises:

[0025] (A) one or more organopolysiloxanes having at least two silicon-bonded aliphatic unsaturated groups per molecule,

[0026] (B) one or more organohydrogenpolysiloxanes having at least two silicon-bonded hydrogen atoms per molecule,

[0027] (C) one or more reinforcing fillers,

[0028] (D) one or more hydrosilylation catalysts,

[0029] (E) optionally one or more additives.

[0030] The present invention relates to a cured silicone rubber composition. While silicone rubbers obtained by all types of curing, including addition curing, condensation curing and peroxide curing are comprised by the scope of the invention, the invention primarily refers to hydrosilylation-curing polyorganosiloxane compositions and / or silane compositions, i.e. to compositions in which the curing of the composition is effected by a hydrosilylation reaction of at least one compound containing one or more Si-H groups to at least one compound containing one or more unsaturated C-C bonds via an addition reaction of said groups. In the present invention, the hydrosilylation reaction takes place between

[0031] (A) one or more organopolysiloxanes having at least two silicon-bonded aliphatic unsaturated groups per molecule, and

[0032] (B) one or more organohydrogenpolysiloxanes having at least two silicon-bonded hydrogen atoms per molecule, wherein the reaction is catalysed by

[0033] (D) one or more hydrosilylation catalysts.

[0034] Preferably, the cured silicone rubber composition of the present invention is characterized in that it has a toluene-soluble content in the GPC measurement using polystyrene as a standard has a main peak eluted before the extracting solvent peak corresponding to a number average molecular weight of more than 1500 Dalton. As defined herein, the main peak in GPC measurement is the highest intensity peak before the solvent elution obtained in a GPC measurement of the extract obtained by extracting the cured silicone rubber material with toluene. Between curing and extraction, the cured silicone rubber material is not submitted to any post-curing treatment involving prolonged heating or decompression under reduced pressure.

[0035] In order to perform the GPC measurement, the cured silicone rubber is cut to small cubes having an edge length of about 2 mm. The cut cured silicone rubber sample is then immersed in the five-fold amount by mass of toluene and shaken at room temperature (25 °C) for one day (24 hours), then 2 g of the toluene solution extract are dried on an inert base, e.g. a metal plate, at open air in a draft chamber at room temperature (25°C) for about 6 hours, then the remaining residue is heated and further dried at 120 ° C for 30 minutes in a ventilated oven. The weight of the residue is measured and the content in wt.-% is calculated (residue (g) / 2 g x 100). If the toluene-soluble content in the toluene solution extract obtained as described above is more than 0.5 wt.-%, then the toluene solution extract was diluted with toluene to adjust the toluene-soluble content to 0.5% prior to performing the GPC analysis, and if the toluene-soluble content of the toluene solution extract is less than 0.5%, the GPC measurement is performed on the sample as it is. This examination of the sample is made in order to obtain reproducible results by avoiding the saturation of the GPC and too high GPC peak intensities. 20 microliters of the toluene solution extract, which depending on its content determined as described above is further diluted or taken at it is, are injected into the column SHIMAZU GPC-80M X 2 of the GPC equipment SHIMAZU LC Solution. The detector used is an Rl (refractive index) detector, and the eluent used is toluene with a flow rate of 1.0 ml / min at 40°C. The standard used for calibration is polystyrene.

[0036] Specifically, the following polystyrene standards provided by Tosoh Bioscience are used to obtain a calibration curve for the subsequent GPC analysis of the extract:

[0037] From the resulting GPC chromatogram, the number average molecular weight (Mn) is calculated based on the retention time of the main peak eluted before the elution of the extracting solvent peak, i.e. the peak with the highest intensity eluted before the toluene peak, using the software of the GPC device, which is “Shimazu LC solution version 1.21 SP1”.

[0038] Preferably, the main peak determined as described above corresponds to a number average molecular weight of more than 1600 Dalton, more preferably of more than 1700 Dalton, and even more preferably of more than 1800 Dalton.

[0039] The cured silicone rubber composition of the present invention is further preferably characterized by having a weight loss measured according to BfR (Bundesinstitut fur Risikobewertung (BfR, Federal Institute for Risk Assessment) of less than 0.5 wt.-%.

[0040] As stated above, it is desirable to provide an addition-curable silicone rubber composition which cures into a cured product or silicone rubber from which low-molecular weight siloxane components will volatilize only in extremely small quantities, as this eliminates problems such as mold fouling, haze or turbidity evolution, adhesion interference, and hydrophobic surface caused by deposition of the volatilized low-molecular-weight siloxanes on the surroundings. Such compositions can find safe use as infant goods such as bottle teats and baby dummies, kitchen goods such as cake molds, gaskets for water plumbing, and medical and health care tools such as dialyzers, and a silicone rubber, and thus an addition-curable silicone rubber composition which cures into a cured product or silicone rubber with a maximum weight loss of less than 0.5% according to the BfR even without post curing is provided.

[0041] Regarding the weight loss of cured silicone rubber, in “Chapter 15: Silicone” of the publication “Recommendations on Food Contact Materials” by BfR (Bundesinstitut fur Risikobewertung) as of 01.06.2020 it is prescribed under “III. Silicone elastomers (Silicone rubbers)” that the silicone elastomers must release no more than 0.5 % volatile organic components. In the corresponding protocol “Determination of volatile compounds in consumer goods made of silicone” as of March 2022 (“Bestimmung von fluchtigen Verbindungen in Bedarfsgegenstanden aus Silikon”, Stand: 03 / 2022), which hereby is incorporated by reference, a precise protocol for the determination of the release of volatiles from silicone consumer goods is provided. The “weight loss measured according to BfR of less than 0.5 wt- %” refers to a weight loss of less than 0.5 wt.-% which has been determined according to said protocol. The protocol requires that the sample is pre-dried at 100 °C for 60 minutes in a drying oven in order to remove absorbed water before the sample is heated to 200 °C for 4 hours in a drying oven in order to remove the volatiles. Subsequently, the loss of weight is determined by weighing the sample and comparison with the weight of the sample after pre-drying. In order to obtain reliable results, three experiments are performed in order to determine the result as the average of the individual measurements.

[0042] The curable silicone rubber composition from which the cured silicone rubber composition according to the invention is obtained by curing said curable composition comprises

[0043] (A) one or more organopolysiloxanes having at least two silicon-bonded aliphatic unsaturated groups per molecule,

[0044] (B) one or more organohydrogenpolysiloxanes having at least two silicon-bonded hydrogen atoms per molecule,

[0045] (C) one or more reinforcing fillers,

[0046] (D) one or more hydrosilylation catalysts,

[0047] (E) optionally one or more additives.

[0048] Therein, the components (A) to (E) are further characterized as follows:

[0049] Component (A)

[0050] According to the invention, the curable silicone rubber composition comprises one or more organopolysiloxanes (A) having at least two silicon-bonded aliphatic unsaturated groups per molecule, for example those disclosed in US 3,096,303 or US 5,500,148 A (examples).

[0051] Suitable compounds (A) can be described by the general formula (I),

[0052] [MaDbTcQd]m (I) wherein the formula (I) represents the ratios of the siloxy units M, D, T and Q, which can be distributed blockwise or randomly in the polymer chain. Within a polysiloxane chain each siloxane unit can be identical or different, and preferably a = 1-10 b = 0 -12000 c = 0 - 50 d = 0 - 1 m = 1- 5000.

[0053] These indices should represent the average polymerisation degree Pnbased on the average number molecular mass Mn.

[0054] The polymer (A) is selected from the group of polyorganosiloxanes having at least two silicon- bonded aliphatic unsaturated groups per molecule, which can undergo hydrosilylation reactions with hydrogen siloxanes to form silicon-carbon bonds. The polymer (A) or mixtures thereof comprise groups selected from

[0055] M = R’aSiOiQ, or M*

[0056] D=R’2SiO2 / 2, or D*

[0057] T = R’SiC>3 / 2, or T*

[0058] Q = SiO4 / 2, divalent R2’-groups, wherein M* = R1’PR’3-PSiOi / 2, D* = R1’qR’2-qSiO2 / 2, T* = R1’SiC>3 / 2, wherein P = 1-3, q = 1-2.

[0059] R’ is preferably selected from n-, iso, or tertiary Ci-Cso-alkyl, alkoxyalkyl, Cs-Cso-cyclic alkyl, or Ce-Cso-aryl, alkylaryl, which groups can be substituted by one or more O-, N-, S- or F-atom, e.g. ethers or amides or poly(C2-C4)-alkylene ethers with up to 1000 alkylene oxy units.

[0060] Examples of said monovalent residues R’ in component (A) include hydrocarbon groups and halohydrocarbon groups.

[0061] Examples of suitable monovalent hydrocarbon radicals include alkyl radicals, preferably such as CH3-, CH3CH2-, (CH3)2CH-, CsHn- and C H2I-, cycloaliphatic radicals, such as cyclohexylethyl, aryl radicals, such as phenyl, tolyl, xylyl, aralkyl radicals, such as benzyl and 2-phenylethyl. Preferable monovalent halohydrocarbon radicals have the formula CnF2n+iCH2CH2- wherein n has a value of from 1 to 10, such as, for example, CF3CH2CH2-, C4F9CH2CH2-, C6Fi3CH2CH2-,

[0062] C2F5-0(CF2-CF2-0)I-IOCF2-, F[CF(CF3) -CF2-O]I-5- (CF2)0-2-, C3F7-OCF(CF3)- and C3F7- OCF(CF3) -CF2-OCF(CF3)-.

[0063] Preferred groups for R’ are methyl, phenyl, 3,3,3-trifluoropropyl.

[0064] R1’ is selected from unsaturated groups, comprising C=C-group-containing groups (alkenyl groups), e.g.: n-, iso-, tertiary- or cyclic- C2-C3o-alkenyl, Ce-Cso-cycloalkenyl, C8-C30 - alkenylaryl, cycloalkenylalkyl, vinyl, allyl, methallyl, 3-butenyl, 5-hexenyl, 7-octenyl, ethyliden- norbornyl, styryl, vinylphenylethyl, norbornenyl-ethyl, limonenyl, substituted by one or more O- or F-atoms, e.g. ethers, amides or C2-C4-polyethers with up to 1000 polyether units. The alkenyl radicals are preferable attached to terminal silicon atoms, the olefin function is preferably at the end of the alkenyl group of the higher alkenyl radicals, because of the more ready availability of the alpha-, omega-dienes used to prepare the alkenylsiloxanes.

[0065] Preferred groups for R1’ are vinyl, allyl, 5-hexenyl. R2’ represents divalent hydrocarbon residues, and R2’ includes for example divalent aliphatic or aromatic n-, iso-, tertiary- or cyclo-Ci-Cu-alkylene, arylene or alkylenearyl groups which brigde siloxy units. Their content does not exceed 30 mol-% of all siloxy units. Preferred examples of suitable divalent hydrocarbon groups R2include any alkylene residue, preferably such as -CH2-, -CH2CH2-, -CH2(CH3)CH-, -(CH2)4-, -CH2CH(CH3)CH2-, -(CH2)6-, -(CH2)8- and -(CH2)i8-; cycloalkylene radical, such as cyclohexylene; arylene radicals, such as phenylene, xylene and combinations of hydrocarbon radicals, such as benzylene, i.e. -CH2CH2-C6H4- CH2CH2-, -C6H4CH2-. Preferred groups are alpha, omega-ethylene, alpha, omega-hexylene or 1 ,4-phenylene.

[0066] Examples of suitable divalent halohydrocarbon radicals R2’ include any divalent hydrocarbon group wherein one or more hydrogen atoms have been replaced by halogen, such as fluorine, chlorine or bromine. Preferable divalent halohydrocarbon residues have the formula -CH2CH2(CF2)I-IOCH2CH2- such as for example, -CH2CH2CF2CF2CH2CH2- or other examples of suitable divalent hydrocarbon ether radicals and halohydrocarbon ether radicals including -CH2CH2OCH2CH2-, -CebU-O-CebU-, -CH2CH2CF2OCF2CH2CH2-, and -CH2CH2OCH2CH2CH2-.

[0067] Such polymers containing R’, R1’ and / or R2’ radicals are polyorganosiloxanes, e.g. alkenyl- dimethylsiloxy or trimethylsiloxy terminated polydimethylsiloxanes, which can contain other siloxane units than alkenylmethylsiloxy groups and dimethylsiloxy groups, such as poly- (dimethyl-co-diphenyl)siloxanes.

[0068] Broadly stated component (A) of the compositions of this invention can be any polyorganosilicone compound containing two or more silicon atoms linked by oxygen and / or divalent groups R2’ wherein the silicon is bonded to 0 to 3 monovalent groups per silicon atom, with the proviso that the organosilicon compound contains at least two silicon-bonded unsaturated hydrocarbon residues. This component has measurable viscosity of less than 100 kPa.s at a shear rate of D=10 s-1at 20 °C.

[0069] The siloxane units with radicals R’ and / or R1’ can be equal or different for each silicon atom. In a preferred embodiment the structure of component (A) is represented by the general formulas (la) to (lb), shown below.

[0070] A preferred polyorganosiloxane component (A) for the composition of this invention is a substantially linear polyorganosiloxane (A1) having the formula (la) or (le) to (li). The expression “substantially linear” includes polyorganosiloxanes that contain not more than 0.2 mol-% (trace amounts) of siloxy units of the type T or Q. This means the polymer (A) is preferably a linear, flowable fluid or gum (A1) with a Newton like viscosity but not solid at 20 (la) (A1) )bix SiR’s-pRp1’ (lb), wherein b = > 0 - 12000 b1 = > 0 -12000 b1x = 0 -1000 b1 + b1x = > 0 - 12000 p= 0 to 3 q= 1 to 2, with the proviso, that there are at least two silicon-bonded aliphatic unsaturated groups per molecule.

[0071] Preferred groups for R’ are methyl, phenyl, 3,3,3-trifluoropropyl. Preferred groups for R1’ are vinyl, hex- 5-enyl and cyclohexenyl-2-ethyl.

[0072] The average polymerization degrees Pn or 'b' etc. is based on Mnas average number mol mass in the range of up to 12000, the preferred range is 500 to 5000. The viscosity of such polymers is in the range of 10 to 100,000,000 mPa.s at 20 °C at a shear rate of D=10 s’1, the preferred range is about 200 to 10,000,000 mPa.s. Such a viscosity at 20 °C for the component (A) is suitable for the application of the manufacturing of broad variety of products such as molded or extruded shaped rubber parts with liquid silicone rubbers and high viscous rubbers, curable 'Formed-in-Place'- sealants well as coatings of substrates.

[0073] In the group of alkenyl comprising siloxanes (A), it is preferred to select so-called vinyl rich polymers (A2) as component (A) or to add them in addition to other compounds (A) in order to modify mechanical properties.

[0074] The polymers (A2) are selected either from the group consisting of polymers of the formulas (lb) to (Id) or (Ih) to (li), i.e. linear polyorganosiloxanes having additional alkenyl side groups, or from branched polyorganosiloxanes having a higher concentration of T- and Q-groups than the previous types.

[0075] Me3SiO(Me2SiO)bi(MeViSiO)bixSiMe3 (Ic), and ViMe2SiO(Me2SiO)bi(MeViSiO)bixSiMe2Vi (Id), wherein Vi= vinyl.

[0076] The preferred value of b1x is less than 0.5 * b1 or zero. If b1x is not zero then it is preferably between 0.0003*b1 to 0.25*b1 , preferably 0.0015*b1 to 0.15*b1. b1 is as defined above. Other preferred structures according to the formulas (le) to (li) achieve suitable viscosities as defined later on and describe polymers applicable without any solvent for a viscosity adjustment. The range of subindices defines a range of the possible average polymerization degrees Pn.

[0077] VipMe3-pSiO(Me2SiO)io-i2ooo SiMe3-pVip (I e)

[0078] PhMeViSiO(Me2SiO) 10-12000 SiPhMeVi (I f),

[0079] VipMe3-pSiO(Me2SiO)io-i2ooo (MeViSiO)i-25oo SiMe3-p Vip (I g),

[0080] Me3SiO(Me2SiO) -i2ooo (MeViSiO)i-25ooSiMe3 (I h),

[0081] PhMeViSiO(Me2SiO) -i2ooo (MePhSiO)i-wooSiPhMeVi (I i) and wherein

[0082] Ph= phenyl, p= 0 to 3, preferred p=1.

[0083] In a preferred embodiment the polymer component (A) is a mixture of polymers of the formula (la) and of the formula (lb) or (Ih), whereby (lb) has an alkenyl content of 1 to 50 mol-% in a ratio in that the alkenyl content of mixture of (A1) and (A2) is below 2 mol-%.

[0084] Another class of preferred polymers are branched polyorganosiloxanes (A2) having a high concentration of SiMe(3-P)(alkenyl)pgroups with distinct cure rates. Such structures are especially used in release coating applications. Branched polymers are described e.g. in US 5,616,672 and are preferably selected from those of the formula (I) wherein the polyorganosiloxane (A2) comprising alkenyl groups has more than 0.2 mol-% of T=R’SiC>3 / 2 or Q=SiC>4 / 2-units.

[0085] Preferably the branched vinyl-rich polymers have a range of D : T > 10 : 1 , preferably > 33 : 1 and / or respectively (Malkenyl: Q) = 0.6 - 4 : 1.

[0086] All these polymers can be prepared by any of the conventional methods for preparing triorganosiloxane-terminated polydiorganosiloxanes. For example, a proper ratio of the appropriate hydrolyzable silanes, e.g., vinyldimethylchlorosilane and dimethyldichlorosilane, may be co-hydrolyzed and condensed or alternatively an appropriate 1 ,3- divinyltetraorganodisiloxane, e.g., symmetrical divinyldimethyldiphenylsiloxane or divinyltetramethylsiloxane, which furnishes the endgroups of the polydiorganosiloxane, may be equilibrated with an appropriate dipolyorganosiloxane, e.g., octamethylcyclotetrasiloxane, in the presence of an acidic or basic catalyst. Regardless of the method of preparation of polydiorganosiloxane (A), there is usually coproduced a varying quantity of volatile, cyclic polydiorganosiloxanes.

[0087] The viscosities of the polydiorganosiloxanes (A) defined above for the purposes of this invention, refer preferably to the portion of the polyorganosiloxane essentially free of cyclic polydiorganosiloxanes (less than 1 wt.%, preferably 0.5 wt.% measured for 1 h 150 °C 20 mbar). This essentially cyclic free portion can be prepared by stripping the polydiorgano- siloxane at 150 °C for at least 1 hours to yield a polymer residue of this type. This residue will be essentially free of cyclic material with the exception of trace quantities of macrocyclic polydiorganosiloxanes (molecular weight > 518 g / mol) which are non-volatile as defined above.

[0088] The average polymerization degree Pnof the polymer (A) measured by GPC measurement versus polystyrene standard based on the average number mol weight Mnis preferably in the range of > 10 to 1500, the more preferred range is 40 to 6000. The viscosities of such polymers are in the range of 10 to 200 Pa.s at 25 °C at a shear rate of D=10 s-1. The value for Pnor the index 'b' in the above formula (la) is such that the linear polyorganosiloxane (A) has a viscosity at 25 °C, of at least 10 mPa.s. Preferably the range of the viscosity is from about 40 mPa.s to 185 Pa.s and, most preferably from 100 mPa.s to 170 Pa.s. Said viscosity corresponds approximately to the values of the average Pn, indicated by ' b' or 'b1+b1x'.

[0089] The concentration of the functional unsaturated groups is in the range of 50 mol-% to 0.033 mol-% (mol-% of alkenyl-functionalized Si-atoms per total of Si-atoms), i.e. in case of polydimethylsiloxanes about preferably 0.002 to 12 mmol SiR17g, more preferred 0.004 - 3 mmol SiR17g. Preferably, therein R1’ represents a vinyl group, i.e. the unsaturated group is a vinyl group.

[0090] Said siloxane units can be combined in any molecular arrangement such as linear, branched, cyclic and combinations thereof, to provide polyorganosiloxanes (A1) and (A2) that are useful as component (A). In a preferred embodiment the hydrosilylation-curable composition is solvent-less (less than 1 wt.-% volatiles).

[0091] The alkenyl content of the components (A) can be determined here by way of1H NMR - see A.L. Smith (ed.): The Analytical Chemistry of Silicones, J. Wiley & Sons 1991 Vol. 112 pp. 356 et seq. in Chemical Analysis ed. by J.D. Winefordner.

[0092] According to the invention, particularly preferred polyorganosiloxanes having at least two silicon-bonded aliphatic unsaturated groups are

[0093] - dimethylvinylsilyl-terminated polydimethylsiloxanes of the general average composition of MVi2Dm, wherein m is in the range of from 200 to 1500, preferably 300 to 1300, more preferably 400 to 1100, even more preferably 450 to 1000,

[0094] - dimethylvinylsiloxy-terminated poly(dimethylsiloxane- co-methylvinylsiloxane) of the general average composition MVi2DnDVi0, wherein n is in the range of from 100 to 1000, preferably 200 to 900, more preferably 300 to 800, and even more preferably 400 to 700, and o is independently in the range of from 10 to 120, preferably in the range of 15 to 90, more preferably in the range of 20 to 70, even more preferably in the range of 25 to 50.

[0095] The curable silicone rubber composition comprises component B), that is, one or more organohydrogensiloxanes having at least two silicon-bonded hydrogen atoms per molecule. The component (B) is from the group consisting of polyorganosiloxanes having at least 2 SiH groups in average, which can react with aliphatic unsaturated groups of the polymers (A) and crosslink both polymers to an elastomeric network. In order to get a more elastomeric behaviour rather than a gel it is preferred that at least 30 mol.-% of the component (A) or (B) should preferably have a functionality of reactive groups of 3 or more (number of Si-alkenyl groups per total of Si atoms for (A) and number of SiH-groups per total of Si atoms for (B)). The component (B) is selected from the group of SiH-containing polyorganosiloxanes. Suitably component (B) is composed of siloxane units selected from the groups M= R’3SiOi / 2, MH=R’2YSiOi / 2, D=R’2SiC>2 / 2, DH=R’YSiC>2 / 2, T=R’SiC>3 / 2, TH=YSiC>3 / 2, SiC>4 / 2, wherein R’ is as defined above and Y = R1’ and / or H, with the proviso that there are in average at least two SiH-groups per molecule.

[0096] The polymer (B) can be formally described by the ratios of the general formula (II), [Ma2Db2Tc2Qd2]m2 (II) wherein the siloxy units M, D, T and Q are as defined above including the possible SiH- containing M, D, T groups MH=R’YSiOi / 2, DH=R’YSiC>2 / 2, and TH=YSiC>3 / 2, with the proviso that are in average at least two SiH-groups per molecule. Also possible is that part of the siloxy groups are alkenyl siloxy groups, as long as there are at least in average two SiH-groups per molecule. The siloxy units can be distributed blockwise or randomly in the polymer chain. Within a polysiloxane chain each siloxane unit can be identical or different and preferably a2 = 1-10 b2 = 0-1000 c2 = 0-50 d2 = 0-1 m2 = 1-2000

[0097] The afore-mentioned indices should represent the average polymerisation degree Pnbased on the average number molecular mass Mn.

[0098] The range for M-, D-, T- and Q-units present in the molecule can cover nearly all values representing fluids, flowable polymer, liquid and solid resins. It is preferred to use liquid silanes or liquid linear, cyclic or branched siloxanes comprising optionally remaining Ci-Cs-alkoxy or Si-hydroxy groups remaining from the synthesis. These compounds can have a low molecular weight or are condensation products, which can be partially hydrolysed, as well as siloxanes polymerized via an equilibration or condensation under the assistance of acidic catalysts.

[0099] The siloxane units with radicals R’ or Y can be equal or different for each silicon atom.

[0100] The preferred structures of reactive polyorganosiloxanes for component (B) in the compositions of this invention are silanes or condensed silanes / siloxanes of formula (Ila) to (Hd).

[0101] The preferred structure composed with these units are selected from

[0102] YrR’3-rSiO(R’2SiO)z(R’YSiO)vSiR’3-rYr(Ila)

[0103] YrMe3-rSiO(Me2SiO)z(MeYSiO)vSiMe3-rYr(lib)

[0104] Me3SiO(MeYSiO)vSiMe3(lie)

[0105] [YR’SiO]w(lid) z = O to 1000 v = O to 100 z+v = 1 to 1000 w= 3 to 9 r= 0 or 1 , and structures of the formula

[0106] {[YSiO3 / 2] [9’OI / 2]n2} m2 (He)

[0107] {[SiO4 / 2}] [R9’Ol / 2]n2 [ ’2YSiOl / 2] 0,01-10 [YSiO3 / 2 ]o-5O [R’YSiO2 / 2] 0-1000 }m2 (Ilf) wherein

[0108] R9’OI / 2is an alkoxy residue at the silicon atom

[0109] R’ is defined above, n2= 0.001 to 3 a2 = 0.01- 10 b2 = 0-1000 c2 = 0- 50 m2 = 1 to 2000

[0110] Y= hydrogen or R1'

[0111] R9’ is hydrogen, n-, iso-, tertiary- or cyclo- Ci-C2s-alkyl, such as methyl, ethyl, propyl, alkanoyl, such acyl, aryl, -N=CHR, such as butanonoxime, alkenyl, such as propenyl, which groups R9’ may be substituted by one or more halogen atoms or pseudohalogen groups, like cyano groups. The preferred groups for Y are hydrogen, and by definition each compound of the component (B) bears two or more silicon-bonded hydrogen atoms.

[0112] One preferred embodiment of the compounds of class (lie) and (Ilf) is provided by way of example by monomeric to polymeric compounds which can be described via the formula [(Me2HSiOo.5)kSi04 / 2]m2 wherein index k can have integer or decimal values from 0.01 to (2*m2+2). Such liquid or resinous molecules can contain significant concentrations of SiOH- and / or (Ci-Ce)-alkoxy-Si groups of up to 10 mol-% related to the silicon atoms.

[0113] The indices z and v for the other types of preferred compounds with the formulas (Ila) to (He) are in the range of 0-1000 defined as average Pnbased on the number average mol mass Mnmeasured by GPC versus a polystyrene standard.

[0114] Other examples of preferred suitable compounds for component (B) in the compositions of this invention include HMe2SiO(Me2SiO)zSiMe2H, Me3SiO-(MeHSiO)v-SiMe3, (MeHSiO)3-6, Si(OSiMe2H)4, MeSi(OSiMe2H)3. HMe2SiO(Me2SiO)zi(MePhSiO)z2(MeHSiO)vSiMe2H, wherein z1+z2 = z, and z and v are as defined above.

[0115] The component (B) can be used as a single component of one polyorganosiloxane polymer or mixtures thereof. In another embodiment it is preferred to use mixtures of formula (lib) and (lie). If the increase of the cure rate is required, it is preferred to use some organopolysiloxanes (B) having HMe2SiOo,s- units to adjust the cure rate to shorter times.

[0116] The molecular weight of component (B) is smaller; the functionality in (B) per molecule is higher when compared to component (A).

[0117] If it is necessary to still further increase the cure rate, this can be achieved by way of example via an increase of the molar ratio of SiH to Si-alkenyl, or an increased amount of catalyst (D), or an increase in the proportion of polyorganosiloxanes (B) which contain HMe2SiOo.s units. Thus preferred components (B) include HMe2SiOo.5(MH groups), in order to provide faster curing rates.

[0118] In a further preferred embodiment, the component (B) is selected from the group according to formula (Ila) which consist of a component (B1) such as YR’2SiO(R’2SiO)z(R’YSiO)vSiR’2Y or formula (He) having a functionality of Y of 3 or more, and a component (B2) having a functionality of Y of 2 in average such as YR’2SiO(R’2SiO)zSiR’2Y, wherein Y, R’ and z are as defined above.

[0119] If (B1) and (B2) are used together, the preferred ratio of functionality SiH of (B1) to (B2) is from more than 0 to 70 mol-%, and more preferably from 30 to 100 mol-% of (B2), based on the combined amount of SiH functional groups of (B1) and (B2) components. The molecular weight for the component (B) is not critical; however, it is preferred such that the polyorganosiloxane component (B) has a viscosity at 25 °C up from 3 to 10,000 mPa.s in the case of R’= methyl. The viscosity depends upon the kind of the R’ and Y substituents, and the ratio of the units M, D, T and Q as well as the mol weight. For polyorganosiloxanes containing only methyl groups as R group the range of the mol weights expressed as Mnis between 136 and 100,000 g / mol.

[0120] It is preferred to use liquid siloxanes with a low molecular weight, i.e. smaller than 1 ,000,000 g / mol, preferably smaller than 75,000 g / mol in case of polydimethylmethylhydrogensiloxanes. The siloxane units with radicals R’ or Y can be equal or different for each silicon atom. Each molecule can bear one or more groups independently.

[0121] The crosslinker (B1) should have at least more than 2 reactive groups Y per molecule whereas the chain extender (B2) has a functionality Y of 2 in average per molecule.

[0122] The concentration of the reactive group Y, in particular of H, is in the range of 0.2 to 100 mol- % Y groups related to Si atoms, i.e. for polydimethyl-methylhydrogensiloxane preferably about 0.1 -17 mmol SiY / g, the preferred range is 0.15 to 16 mmol / g.

[0123] In one preferred embodiment a mixture of compounds having formula (lie) or (lid) are used together with (Ila) and / or (lib), where z= 0, R’= methyl and the SiH concentration is preferably >7-17 mmol SiH / g and in the second compound of (B) the index z > 0 wherein the SiH concentration has values of preferably 0.2 to 7 mmol SiH / g.

[0124] It is preferred to use compounds of formula (Ila) and / or (lib) wherein R’= aryl, in particular phenyl, if adherence onto other substrates such as thermoplastic substrates has to be achieved.

[0125] The SiH-content in the present invention is determined by way of1H-NMR, see A.L. Smith (ed.): The Analytical Chemistry of Silicones, J. Wiley & Sons 1991 Vol. 112 pp. 356 et seq. in Chemical Analysis ed. by J.D. Winefordner.

[0126] The ratio of the crosslinker (B) to polymer (A) necessary for getting an elastomeric network, i.e. a non-sticky surface can be calculated by the ratio of reactive SiH groups in (B) and aliphatic unsaturated groups in (A). It is preferred to have an excess of reactive groups (B) : (A) of 0.7 to 20 : 1 , preferably 1.2 to 6 : 1 , more preferably 1.5 to 4 : 1 in order to ensure a certain level of multifunctional structures in the cured elastomeric network.

[0127] According to the invention, particularly preferred polyorganosiloxanes having in average at least two SiH groups are

[0128] - hydride terminated poly(dimethylsiloxane)s of the general average composition MH2Da, wherein a is in the range of from 5 to 100, preferably from 8 to 80, more preferably in the range from 10 to 50, even more preferably in the range from 12 to 40, even more preferably in the range from 13 to 25;

[0129] - trimethylsilyl-terminated poly(dimethylsiloxane-co- methylhydrogensiloxane)s of the general average composition IVhDbDHc , wherein b is in the range of from 10 to 50, preferably 12 to 40, more preferably 14 to 40, even more preferably 15 to 30, and c is independently in the range of from 2 to 50, preferably 4 to 40, more preferably 6 to 40, even more preferably 8 to 30;

[0130] - a resin type with a general average composition of MHdxQx, wherein d is in the range of 1.1 to 2.5, preferably in the range of 1 .2 to 2.2, more preferably in the range of 1 .3 to 2.1 , and even more preferably in the range of 1 .5 to 2.0, for example an average composition of MHuxQx;

[0131] - trimethylsilyl-terminated polymethylhydrogensiloxanes with a general average composition of IVhDHe, wherein e is in the range of from 5 to 100, preferably 10 to 80, more preferably 15 to 60, even more preferably 20 to 40; or trimethylsilyl-terminated poly(dimethylsiloxane-co-diphenylsiloxane-co- methylhydrogensiloxane)s with a general average composition M2D(Ph2)fDHgDh, wherein f is in the range of from 1 to 50, preferably 2 to 40, more preferably 3 to 25, even more preferably from 5 to 15, g is independently in the range from 2 to 50, preferably 6 to 40, more preferably 12 to 30, and h is in the range of from 1 to 50, preferably 2 to 40, more preferably 3 to 25, even more preferably from 5 to 15.

[0132] The group “DH” according to the invention is MeHSiC>2 / 2, thus falling under the more general term DH=R’YSiC>2 / 2 as defined above.

[0133] The curable silicone rubber composition according to the invention comprises at least one reinforcing filler C) which is preferably selected from at least one silica filler (C1), preferably a surface-treated silica (CT). As defined herein, a reinforcing filler is a filler having a BET of 50 or more m2 / g, in particular from 50 to 500 m2 / g, preferably measured according to DIN-ISO 9277 with nitrogen.

[0134] Preferably the reinforcing filler C) is a silica filler (C1) which is selected from the group of fumed silica and precipitated silica, having a BET from 50 to 500 m2 / g preferably measured according to DIN-ISO 9277 with nitrogen. Most preferably, the reinforcing filler C) is a silica filler selected from a surface-treated filler.

[0135] Preferably the surface treatment of the silica filler can be done though reaction with hydrophobes selected from the group of disilazanes, silylamines, silanols, bis(polyorganosiloxanyl)amine of the formula [RaRbRcSi (Osi(Me)2)t]2NH where Rais methyl, ethyl, or phenyl; Rbis methyl or ethyl, Rcis vinyl or allyl; and t is an integer of from 2 to 12 inclusive, trimethylsilanol, trimethylchlorosilane, trimethylethoxysilane, triorganosilyloxyacylates, such as vinyldimethylacetoxysilane, triorganosilylamines, such as trimethylsilylisopropylamine, trimethylsilylethylamine, dimethylphenylsilylpropylamine and vinyldimethylsilylbutylamine, triorganosilylaminooxy compounds, such as diethylaminooxytrimethylsilane and diethylaminooxydimethylphenylsilane, and additionally hexamethyldisiloxane, 1 ,3-divinyltetramethyldisiloxane, 1 ,3-diphenyltetramethyldisiloxane and 1 ,3-diphenyltetramethyldisilazane.

[0136] Other examples of organosilicon compounds for surface treatment are dimethyldichlorosilane, dimethyldiethoxysilane, dimethyldimethoxysilane, diphenyldiethoxysilane, vinylmethyldimethoxysilane, methyltriethoxysilane, octamethylcyclotetrasiloxane and / or dimethylpolysiloxanes having from 2 to 12 siloxane units per molecule and containing a hydroxyl group bonded to Si in each of the terminal units.

[0137] Most preferably the reinforcing filler C) is at least one silica filler surface-treated with at least one silazane, preferably an organosilazane, e.g. of the formula R Si-[NH-SiRd,2]n-NH-SiRd,3 (with n being > 0) and Rd’ being an organic group, preferably selected from methyl and / or vinyl. Most preferred are divinyltetramethyldisilazane and hexamethyldisilazane and a mixture thereof.

[0138] In a particular preferred embodiment, the silica filler is subjected to an extended surface treatment with one or more organosilazanes, which may include a single step treatment for an extended period of time, such as at least 2 or 3 hours, or a multiple step surface-treatment.

[0139] In a particular preferred embodiment, the surface-treated silica filler (CT) is prepared by the surface-treatment of silica in a two-step process comprising subsequent reaction of said silica with at least two charges of silazanes. Preferably the at least one silica filler is a surface- treated silica filler (CT), which is obtained by the following steps: a) providing a mixture comprising the components (A), (B) and at least one silica filler (C1), b) adding at least one silazane having at least one alkenyl group and at least one silazane which does not have alkenyl groups to said mixture, c) heating to at least 100°C for at least 1 h, d) removal of the volatiles, and e) further adding at least one silazane which preferably does not have alkenyl groups, f) heating to at least 100°C for at least 1 h, and g) removal of the volatiles.

[0140] Preferred silica fillers are preferably those known as reinforcing silicas, which also permit the production of elastomers having sufficient transparency for irradiation. Preferred are reinforcing silicas, in particular those increasing the strength. Examples are silicas whose BET surface areas are from 50 to 400 m2 / g, preferably 80 to 350 m2 / g preferably measured according to DIN-ISO 9277 with nitrogen, in particular, fumed or precipitated silicas. Preferably, these fillers are surface-hydrophobicized. The amount of reinforcing filler C) is preferably from 5 to 100 parts by weight, more preferably from 8 to 90 parts by weight, even more preferably from 10 to 80 parts by weight, even more preferably from 15 to 70 parts by weight based on 100 parts by weight of the total amount of component (A).

[0141] Fillers whose BET surface areas are above 50 m2 / g permit production of silicone elastomers with improved properties. In view of strength and transparency, fumed silicas are preferred, and even more preferred silicas are, for example, Aerosil® 200, 300, HDK® N20 or T30, Cab- O-Sil® MS7 or HS5, i.e. silicas having more than 200 m2 / g BET surface area. As BET surface area rises, the transparency of the silicone mixtures in which these materials are present also rises. Examples of trade names of the materials known as precipitated silicas, or wet silicas, are Vulkasil®VN3, or FK 160 from Evonik (formerly Degussa), or Nipsil® LP from Nippon Silica K.K. and others.

[0142] It is preferred to use silica fillers having BET-surface areas of 50 m2 / g or more, preferably having a BET-surface of at least 150 m2 / g. Such compositions can be also photo-activated if desired due to sufficient transparency.

[0143] The reinforcing filler C) may be subject of any suitable conventional surface-treatment with suitable surface-treatment agents belonging to hydrophobizing treatment with a suitable hydrophobizing agent, dispersing treatment with suitable dispersing agents, which influence the interaction of the filler with the silicone polymer, e.g. influence thickening action. The surface treatment of the fillers is preferably a hydrophobation with silanes or with siloxanes. It can by way of example take place in situ via addition of silazanes, such as hexamethyldisilazane and / or 1 ,3-divinyltetramethyldisilazane, with addition of water, and 'in- situ '-hydrophobation is preferred. It can also take place with other familiar filler-treatment agents, such as polyorganosiloxanediols whose chain lengths are from 2 to 50 siloxane units and which bear unsaturated organic radicals, with the aim of providing reactive sites for the crosslinking reaction.

[0144] Examples of commercially available silicas pre-hydrophobized with various silanes are: Aerosil® R 972, R 974, R 976, or R 812, or, for example, HDK 2000 or H30 Examples of trade names for materials known as hydrophobized precipitated silicas or wet silicas are e.g. Sipernat D10 or D15 from Evonik (formerly Degussa).

[0145] Rheological properties, i.e. technical processing properties, of the non-cured silicone rubber mixtures can be influenced by the selection of the type of the filler, its amount, and the nature of hydrophobization. Component (D)

[0146] The curable silicone rubber composition further mandatorily comprises one or more hydrosilylation catalysts, i.e. at least one compound capable of catalyzing the addition of Si-H bonds across unsaturated bonds, in particular unsaturated C-C bonds. While main group metal-based catalysts and non-metal catalysts are explicitly included, the vast majority of hydrosilylation catalysts in the art are transition metal-based hydrosilylation catalysts, wherein the catalysts based on the platinum group metals ruthenium, rhodium, palladium, osmium, iridium, and platinum and on iron, cobalt and nickel, in particular platinum, are preferred according to the invention.

[0147] Component D) is preferably selected from the group of organometal compounds, salts or metals, having the ability to catalyze hydrosilylation wherein the metal is preferably selected from transition metals, more preferably from the group of Ni, Ir, Rh, Ru, Os, Pd and Pt compounds as taught in US 3,159,601 ; US 3,159,662; US 3,419,593; US 3,715,334; US 3,775,452 and US 3,814,730. Most preferred are platinum compounds.

[0148] Preferably the metal catalyst D) is selected from hydrosilylation catalysts comprising at least one metal selected from the group consisting of platinum, rhodium, palladium, ruthenium and iridium.

[0149] The catalyst component D) for the hydrosilylation reaction of the inventive composition is a compound which facilitates the reaction of the silicon-bonded hydrogen atoms of component (B) with the silicon-bonded olefinic hydrocarbon substituents of component (A). Preferably, the metal or organometal compound is generally based on a platinum group metal. Without wishing to be bound by theory, it is believed that the catalyst (D) includes complexes with sigma- and pi-bonded carbon ligands as well as ligands with S-, N, or P atoms, metal colloids or salts of the afore mentioned metals. The catalyst can be present on a carrier such as silica gel or powdered charcoal, bearing the metal, or a compound or complex of that metal. Preferably, the metal catalyst of component (D) is any platinum complex compound.

[0150] A typical platinum containing catalyst component in the silicone rubber compositions of this invention is any form of platinum (0), (II) or (IV) compounds, which are able to form complexes. Preferred complexes are Pt-(O)-alkenyl complexes, such as alkenyl, cycloalkenyl, or alkenylsiloxane complexes, in particular vinylsiloxane complexes, because of their easy dispersibility in polyorganosiloxane compositions.

[0151] A particularly useful form of the platinum complexes are the Pt(0)-complexes with aliphatically unsaturated organosilicon compounds, such as a 1 ,3-divinyltetramethyldisiloxane (Vinyl-M2 or Karstedt catalyst: as disclosed by e.g. US 3,419,593 incorporated herein by reference. Further especially preferred are cyclohexene-Pt, cyclooctadiene-Pt and tetravinyltetramethyl-tetracyclosiloxane (Vinyl-D4)-Pt, e.g. Ashby’s catalyst, a Pt(O) complex in tetramethyltetravinylcyclotetrasiloxane with the empirical formula Pt[(C3HeSiO)4]x.

[0152] Most preferred catalyst component D) is a Pt° complex with tetramethyl- tetravinylcyclotetrasiloxane that contains about 1 to 3 wt.-% Pt, preferably 2 wt.-% Pt, in particular, Ashby’s catalyst.

[0153] Also preferably is a so-called Lamoreaux catalyst, which is a platinum (II) complex compound, obtained from chloroplatinic acid hexahydrate and octyl alcohol (as described for example in US 3,197,432 or US 3,220,972). Pt(O) or Pt(ll) catalysts are preferred, with preference to Ashby and Lamoreaux platinum catalysts.

[0154] The amount of platinum-containing catalyst component that is used in the compositions of this invention is not narrowly limited as long as there is a sufficient amount to accelerate the hydrosilylation between (A) and (B) at the desired temperature in the required time in the presence of all other ingredients of the composition according to the invention. The exact necessary amount of said catalyst component will depend upon the particular catalyst, the amount of other inhibiting compounds and the SiH to olefin ratio and is not easily predictable. However, for platinum catalysts said amount can be as low as possible due to cost reasons. Preferably, one should add more than one part by weight of platinum for every one million parts by weight of the organosilicon components (A) and (B) to ensure curing in the presence of other undefined inhibiting traces. For the compositions of this invention, the amount of platinum containing catalyst component to be applied is preferably sufficient when from 0.01 to 300 ppm are provided, preferably from 0.5 to 200 ppm, more preferably 1 to 100 ppm, even more preferred 2 to 60 ppm, and especially preferred from 3 to 40 ppm by weight of platinum per weight of polyorganosiloxane components (A) plus (B). Preferably, said amount is at least 4 ppm platinum by weight per sum of (A) and (B). In case the one or more hydrosilylation catalysts are based on one or more other metals than platinum, or hydrosilylation catalysts other than platinum catalysts are present in addition to platinum catalysts, the amount of the metal based hydrosilylation catalyst (D) to be applied is preferably sufficient when from 0.01 to 300 ppm are provided, preferably from 0.5 to 200 ppm, more preferably 1 to 100 ppm, even more preferably 2 to 60 ppm, and especially preferred from 3 to 40 ppm by weight of catalyst metal(s) relative to the weight of the combined amounts of the components (A) and (B).

[0155] The hydrosilylation catalyst can also be selected from the group of catalysts capable of being photoactivated. These photo-activatable catalysts preferably contain at least one metal selected from the group composed of Pt, Pd, Rh, Co, Ni, Ir or Ru. The catalysts capable of being photoactivated preferably comprise platinum compounds. Catalyst capable of being photo-activatable is preferably selected among organometallic compounds, i.e. comprise carbon-containing ligands, or salts thereof. In a preferred embodiment, a photoactive catalyst (D) has metal carbon bonds, including sigma- and pi-bonds. Preferably, a catalyst capable of being photo-activated (D) is an organometallic complex compound having at least one metal carbon sigma bond, still more preferably a platinum complex compound having preferably one or more sigma-bonded alkyl and / or aryl group, preferably alkyl group(s). Sigma-bonded ligands include in particular, sigma-bonded organic groups, preferably sigma-bonded Ci-Ce-alkyl, more preferably sigma-bonded methyl groups, sigma-bonded aryl groups, like phenyl, Si and O substituted sigma bonded alkyl or aryl groups, such as triorganosilylalkyl groups, sigma- bonded silyl groups, like trialkyl silyl groups. Most preferred photo-activatable catalysts include r|5-(optionally substituted)-cyclopentadienyl platinum complex compounds having sigma- bonded ligands, preferably sigma-bonded alkyl ligands.

[0156] Further catalysts capable of being photoactivated include (r|-diolefin)-(sigma-aryl)-platinum complexes (see e.g. US 4,530,879).

[0157] The catalyst capable of being photoactivated can be used as such or supported on a carrier. Examples of catalysts capable of being photo-activated include r|-diolefin-o-aryl-platinum complexes, such as disclosed in US 4,530,879, EP 122008, EP 146307 (corresponding to US 4,510,094 and the prior art documents cited therein), or US 2003 / 0199603, and also platinum compounds whose reactivity can be controlled by way of for example using azodicarboxylic esters, as disclosed in US 4,640,939 or diketonates.

[0158] Platinum compounds capable of being photo-activated that can be used are moreover those selected from the group having ligands selected from diketones, e.g. benzoylacetones or acetylenedicarboxylic esters, and platinum catalysts embedded into photodegradable organic resins. Other Pt-catalysts are mentioned by way of example in US 3,715,334 or US 3,419,593, EP 1 672 031 A1 and Lewis, Colborn, Grade, Bryant, Sumpter, and Scott in Organometallics, 1995, 14, 2202-2213, all incorporated by reference here.

[0159] Catalysts (D) capable of being photo-activated can also be formed in-situ in the silicone composition to be shaped, by using Pt(0)-olefin complexes and adding appropriate photo- activatable ligands thereto. The catalysts capable of being photo-activated that can be used here are, however, not restricted to these above-mentioned examples.

[0160] The most preferred catalyst capable of being photo-activated to be used in the process of the invention are (r|5-cyclopentadienyl)-trimethyl-platinum, (r|5-cyclopentadienyl)-triphenyl- platinum complexes, in particular, (r|5-methylcyclopentadienyl)-trimethyl-platinum.

[0161] The amount of the catalyst capable of being photo-activatable is preferably 1 to 500 ppm relative to the weight of the combined amounts of the components (A) and (B), and is further preferably in the same lower range as defined for the heat-activatable hydrosilylation catalysts mentioned above.

[0162] The most preferred curable silicone rubber composition according to the invention comprises a hydrosilylation catalyst (D) comprising platinum.

[0163] Component (E)

[0164] The curable silicone rubber composition according to the invention further comprises optionally one or more additives (E), preferably up to 50 parts by weight based on the overall weight of the component A) being 100 parts.

[0165] The additive (E) is different from any of the other components (A), (B), (C) and (D) as defined herein, and is preferably selected from the group consisting of low compression set additives, surface-treating agents, lubricating oils, oil bleeding agents, hydrosilylation inhibitors etc.

[0166] The compositions according to the invention may also comprise, by way of example, stabilizers, solvents, fillers, pigments or process aids added to achieve better process properties for the inventive silicone rubber composition (A) to (D).

[0167] In general, the additives may serve the tuning of the processing time, the starting behavior and the curing rate of the curable composition, as well as the tuning of the properties of the cured silicone rubber composition obtained by curing such curable silicone rubber composition comprising the components (A) to (E).

[0168] The compositions according to the invention may contain an appropriate amount of one or more inhibitors. Inhibitors for the platinum group metal catalysts are well known in the organosilicon art. Examples of various classes of such metal catalyst inhibitors include unsaturated organic compounds such as ethylenically or aromatically unsaturated amides, US 4,337,332; acetylenic compounds, US 3,445,420 and US 4,347,346; ethylenically unsaturated isocyanates, US 3,882,083; olefinic siloxanes, US 3,989,667; unsaturated hydrocarbon diesters, US 4,256,870, US 4,476,166 and US 4,562,096, and conjugated eneynes. US 4,465,818 and US 4,472,563; other organic compounds such as hydroperoxides, US 4,061 ,609; ketones, US 3,418,731 ; sulfoxides, amines, nitriles, US. 3,344,111 ; diaziridines, US 4,043,977; and various salts, such as US 3,461 ,185, phosphorous compounds preferably excluded. Examples thereof include the acetylenic alcohols of US 3,445,420, such as ethynylcyclohexanol and methylbutynol, 3,5-dimethyl-1-hexyn-3-ol and 3-Methyl-1-dodecin-3- ol, the unsaturated carboxylic esters of US 4,256,870, such as diallylmaleate and dimethyl maleate; and the maleates and fumarates of US 4,562,096 and US 4,774.111 , such as diethyl fumarate, diallyl fumarate and bis-(methoxyisopropyl)maleate. The half esters and amides of US 4,533,575; and the inhibitor mixtures of US 4,476,166 would also be expected to behave similarly. Further classes of inhibitors are trialkylcyanurates, organic hydroperoxides such as cumol hydroperoxide, tert-butyl hydroperoxide and pinnae hydroperoxide, organic peroxides, organic sulfoxides, phosphanes, triazoles and oximes. The above-mentioned patents relating to inhibitors for platinum group metal-containing catalysts are incorporated herein by reference.

[0169] If the compositions of the present invention optionally comprise solvents, these solvents are usual organic solvents in the range of less than 20 wt.-%, preferably less than 10 wt.-% and most less than 5 wt.-% related to the overall weight of the components (A) to (D). Appropriate reactive solvents can be selected from the group of olefinic hydrocarbons such as alphaolefins, e.g. C8-C25-alpha-olefins, preferably Ci4-C2o-alpha-olefins, or evaporable siloxanes having a molecular weight below 518 g / mol without alkenyl or SiH groups. Mixtures of alphaolefins can also be used.

[0170] Other additives falling under definition of component (E) are selected from the group of heat stabilizers, coloring compounds or pigments, antioxidants, biocides, fungicides, such as Preventol®, Katon®, Dowicil®, non-reinforcing fillers, anti-mist additives as disclosed in US 6,586,535 or US 2003 / 0134043, anchorage additives, slipping agents as disclosed in EP 819735 A1 and further auxiliary components typical for silicone release compositions.

[0171] Fillers used as additives include by way of example all of the fine-particle fillers, i.e. those having particles smaller than 100 pm (sieve residue), i.e. preferably composed of particles smaller than this value. These fillers are non-reinforcing fillers, i.e. fillers with a BET surface of less than 50 m2 / g such as quartz, diatomaceous earth, calcium silicate, zirconium silicate, talcum, kaoline, zeolites, metal oxide powders, such as aluminum, titanium, iron, or zinc oxides and mixed oxides thereof, respectively, barium sulfate, calcium carbonate, gypsum, silicon nitride, silicon carbide, boron nitride, glass or polymer powders, such as polyacrylonitrile powder.

[0172] Preferred are mineral fillers, such as silicates, carbonates, nitrides, oxides, carbon blacks, or silicas being fumed or precipitated silica, wherein these are preferably fillers which are specifically surface-hydrophobized here. Surface-treated fillers having low BET-values are preferred because the ability to build up shear thinning effects is reduced. The preferred surface treatment can be achieved with polyorganosiloxanediols, polyorganosiloxanes, alkoxy- or chlorosilanes, which allows a certain concentration of fillers having lowest degree of thickening properties and shear thinning.

[0173] Another class of fillers serving as non-transparent non-reinforcing fillers are powdered quartz, diatomaceous earths, powdered crystobalites, micas, aluminum oxides, aluminum hydroxides, oxides and salts of Fe, Mn, Ti, Zn, Zr, chalks, or carbon blacks, whose BET-surface areas are from 0.3 to below 50 m2 / g.

[0174] These fillers are available under variety of trade names, examples being Sicron®, Min-U-Sil®, Dicalite®, Crystallite® and serve as matting agents.

[0175] Some very special fillers can be used as matting agent, agent for increasing the mechanical modulus, or anti-blocking agent; these filler are selected from the group of spherical or fiber shaped thermoplastic powders or fibres such as PTFE-powders, PTFE-emulsions or polyamide, polyurethane or silsesquioxanes powders, thermoplastic fibers cured silicone elastomers or resins und are used if present in amounts of up to 10 weight parts related to 100 weight parts of (A). Tradenames are Teflon® emulsions, Nylon®^powders, Tospearl®, Acemat®, Twaron®, Kevlar®, Dralon®, Diolen® etc.

[0176] This type of filler, especially if the particles have a spherical shape, can preferably be used as anti-blocking agents in the release layer and can give an especially soft touch and low friction properties of the rubber surfaces.

[0177] Another class of additives are stabilizers, such as heat stabilizers which can be selected from the group of metal compounds, organic or inorganic salts, complexes of Ce, Fe, La, Mn, Ti and Zr.

[0178] Levelling agents, mold release agents are selected from the group consisting of polyethersiloxanes, polyols, polyethers, polyhalides, fatty alcohol or fluoroalkyl derivatives.

[0179] Another class of important additives (E) are adhesion promotors, which can either be incorporated in the composition (A) to (D) or applied in an appropriate form as primer applied prior onto the substrate foreseen for getting adhered to the rubber composition under curing. Adhesion promotors are preferably selected from the group of alkoxysilanes, their condensation product alkoxysiloxanes bearing further organofunctional groups linked over Si- C-bonds, in particular epoxyalkyl, acryloxyalkyl, methacryloxyalkyl, NCO-alkyl, aminoalkyl, urethanealkyl, alkenyl which further can bear SiH groups. In line with this, the alkoxy silane serving as an adhesion promoter may further comprise an additional functional group that can interact with groups on a substrate, e.g. a plastic substrate. Thus, the alkoxy silane may further comprise a group such as, without being limited thereto, an epoxide, an ester, or an anhydride. Preferably, the ester is an ester of fumaric acid, succinic acid, or maleic acid. Also preferably, the anhydride is succinic anhydride, and the at least one alkoxy silane may comprise an ester or an anhydride group. The alkoxy silane may be selected from the group comprising glycidoxypropyl trimethoxy silane, bis(3-trimethoxysilylpropyl) fumarate, and (3- triethoxysilyl)propyl succinic anhydride. The adhesion promoters applied may also include at least two alkoxy silanes, and preferably they include at least two alkoxy silanes further comprising an additional functional group. The alkoxy silanes applied as adhesion promoters may also be selected from bis(3- trimethoxysilylpropyl) fumarate and / or (3-triethoxysilyl)propyl succinic anhydride.

[0180] Such silanes / siloxanes can be combined with condensation catalyst selected from the group of organometal compounds of Ca, Zr, Zn, Sn, Al or Ti and / or polycyclic aromatic compounds having reactive groups such as alkenyl substituted aromatic biphenyl ethers, esters. The effects of adhesion can be further improved by the addition of selected compounds of component (B), e.g. incorporated by reference US 4,082,726, US 5,438,094; US 5,405,896; US 5,536,803; US 5,877,256; US 6,602,551 ; EP 581504 A; and EP 875536.

[0181] Silanes which may be comprised by the composition as component (E) can be also selected of the group of silanes such as of the general formulae:

[0182] R‘eR1‘fSi(OR9‘)(4-e-f)

[0183] R‘eR1‘fSi(NR9‘2)(4-e-f) wherein R’, R1’ is as defined above, R9’ is hydrogen, n-, iso-, tertiary- or cyclo- Ci-C2s-alkyl, such as methyl, ethyl, propyl, alkanoyl, such acyl, aryl, -N=CHR, such as butanonoxime, alkenyl, such as propenyl, which groups R9’ may be substituted by one or more halogen atoms, pseudohalogen groups, like cyano, and e = 0 - 3 f = 1 - 4, and e + f = 4;

[0184] (R9’O)(3-g-h)(R1’g)(R’h)Si-R2’-Si(R’h)(R1’g)(OR9’)(3-h-g), (R9’2N)(3-g-h)(R1’g)(R’h)Si-R2’-Si(R’h)(R1’g)(NR9’2)(3-h-g), wherein R’, R1’, R2’ and R9’ are as defined above, and g = 1-3, h = 0-2, and g + h = 3.

[0185] The auxiliary additive (E) may include in particular: - low compression set additives, such as acetylene alcohols having the formula: H-C=C-R”- OH, wherein R” is a divalent organic group, preferably a cyclic saturated or unsaturated hydrocarbyl group such as cyclohexane-diyl, fluorene-diyl, e.g. 1-ethynyl-1 -cyclohexanol ("ECH"), 9-ethynyl-fluorenol, and the like, preferably ECH and 9-ethynyl-9-fluorenol, most preferably ECH (these compounds act also as hydrosilylation inhibitors),

[0186] - curing retardant or flame retardants such as a triazole compound selected e.g. from the group consisting of 1 ,2,3-triazole, 1 ,2, 4, -triazole, benzotriazole, 1-methyl-1 ,2,3-triazole, 1-phenyl-

[0187] 1.2.3-triazole, 4-methyl-2-phenyl-1 ,2,3-triazole, 1-benzyl-1 ,2,3-triazole, 4- hydroxy- 1 ,2,3- triazole, 1-amino-1 ,2,3-triazole, 1-benzamido-4-methyl-1 ,2,3-triazole, 1-amino-4,5-diphenyl- 1 ,2, 3, -triazole, 1 ,2,3-triazole-4-aldehyde, 4-cyano-1 ,2,3-triazole, 1-methyl-1 ,2,4-triazole, 1 ,3- diphenyl-1 ,2,4-triazole, 5-amino-3-methyl-1 ,2,4-triazole, 3-mercapto-1 ,2,4-triazole, 1-phenyl-

[0188] 1.2.4-triazole-5-one, 1-phenylurazole, 1 -methylbenzotriazole, 5,6-dimethylbenzotriazole, 2- phenylbenzotriazole, 1 -hydroxybenzotriazole and methyl 1 -benzotriazolecarboxylate, a metal salt, carbon black, phthalocyanine compounds or metal derivatives of said compound where said metal is selected from the group consisting of copper, nickel, cobalt, iron, chromium, zinc, platinum, palladium, vanadium,

[0189] - surface-treating agents,

[0190] - lubricating oils,

[0191] - oil bleeding agents,

[0192] - hydrosilylation inhibitors,

[0193] - coloring agents or pigments, such as inorganic pigments, metal oxides and organic dyes,

[0194] - adhesion promoters,

[0195] - stabilizers, such as heat stabilizers,

[0196] - non-reinforcing fillers, such as quartz powder and diatomaceous earth, calcium carbonate,

[0197] - dispersants,

[0198] - flow improvers,

[0199] - plasticizers,

[0200] - slip agents,

[0201] - toughening agents,

[0202] - conductive stability improvers, such as carbon black or graphite, and

[0203] - foam forming additives, e.g. alcohols,

[0204] - anti-oxidants,

[0205] - thixotropic agents,

[0206] - foam stabilizers,

[0207] - ultraviolet stabilizers, and

[0208] - water, which may be used in the preparation of the curable silicone rubber compositions. In a preferred embodiment of the invention the curable silicone rubber composition comprises at least one hydrosilylation inhibitor, preferably 1-ethynyl-1 -cyclohexanol ("ECH").

[0209] In a preferred embodiment of the invention, the curable silicone rubber composition comprises at least one coloring agent or pigment. Such coloring agents or pigment are not colourless, and may include inorganic pigments, and organic dyes. In this respect, the curable silicone rubber composition according to the invention can be in particular provided as a colourless curable silicone rubber composition, i.e. which does not comprise any coloring agent or pigment. From such colourless curable silicone rubber compositions according to the invention, colored curable silicone rubber compositions can be easily obtained by mixing the colourless curable silicone rubber compositions according to the invention with at least one coloring agent or pigment or colored metal oxides such as red iron oxide etc. That is, a colourless curable silicone rubber composition of the invention may serve as a basic composition for obtaining various types of colored curable silicone rubber compositions according to the invention.

[0210] In an embodiment according to the invention, the component (A) is an alkenyl terminated polyorganosiloxane having a viscosity in the range of 5 and 200 Pa.s at 20°C and a shear rate of 10 s'1measured according to DIN 53019.

[0211] Preferred alkenyl-terminated polyorganosiloxanes (A) displaying a viscosity falling into the above-cited range are polyorganosiloxanes of the formula MVi2DnDVi0, wherein n is in the range of from 100 to 1500, preferably 200 to 1400, more preferably 300 to 1400, and even more preferably 400 to 1400, and o is independently in the range of from 0 to 120, preferably in the range of 5 to 90, more preferably in the range of 10 to 70, even more preferably in the range of 25 to 50, or of the formula MVi2Dm, wherein m is in the range of from 200 to 1500, preferably 300 to 1300, more preferably 400 to 1100, even more preferably 450 to 1000.

[0212] According to the invention, the viscosity of the alkenyl terminated polyorganosiloxanes (A) is preferably in the range of 5 to 200, more preferably in the range of 5 to 190, and even more preferably in the range of 5 to 180 Pa.s at 20°C and a shear rate of 10 s-1(DIN 53019).

[0213] In a further embodiment according to the invention, the component (B) has a viscosity in the range of 10 to 1000 mPa.s at 20°C, preferably 15 to 800 mPa.s, more preferably 20 to 600 mPa.s, even more preferably 30 to 400 mPa.s measured with a falling sphere viscosimeter according to DIN 53015 (ball 3). Preferred organohydrogenpolysiloxanes having at least two silicon-bonded hydrogen atoms per molecule (B) falling into the above-cited range are displayed by the formulas

[0214] YrR’3-rSiO(R’2SiO)z(R’YSiO)vSiR’3-rYr(ll’a)

[0215] YrMe3-rSiO(Me2SiO)z(MeYSiO)vSiMe3-rYr(ll’b)

[0216] [YR’SiO]w(ll’d) z = O to 1000 v = O to 100 z+v = 1 to 1000 w= 3 to 9 r= 0 or 1 , and structures of the formula

[0217] {[YSiO3 / 2] [R9’OI / 2]n2} m2 (He)

[0218] {[SiO4 / 2}] [R9’Ol / 2]n2 [R’2YSiOl / 2] 0,01-10 [YSiO3 / 2 ]o-5O [R’YSiO2 / 2] 0-1000 }m2 (I lf) wherein

[0219] R9’OI / 2is an alkoxy residue at the silicon atom

[0220] R’ is defined above, n2= 0.001 to 3 a2 = 0.01- 10 b2 = 0-1000 c2 = 0- 50 m2 = 1 to 2000

[0221] Y= hydrogen

[0222] R9’ is hydrogen, n-, iso-, tertiary- or cyclo- Ci-C2s-alkyl, such as methyl, ethyl, propyl, alkanoyl, such acyl, aryl, -N=CHR, such as butanonoxime, alkenyl, such as propenyl, which groups R9’ may be substituted by one or more halogen atoms, pseudohalogen groups, like cyano.

[0223] Specifically preferred component (B) compounds are crosslinkers of the formula M(DH)O2Dn2M type or MHI,7XQX type where n2 is from 5 to 100, preferably 7 to 80, more preferably 8 to 60 and o2 is from 2 to 100, preferably 3 to 80, more preferably 4 to 60. Some chain extenders are also preferred, like compounds of the formula MH2Dn3 where n3 is from 5 to 300, preferably from 7 to 250 and more preferably from 10 to 230.

[0224] According to the invention, it is further preferred that the viscosity of the component (B) as defined above is in the range of 10 to 1000 mPa.s at 20°C measured according to DIN 53015 (ball 3), more preferably in the range of 15 to 800 mPa.s, and even more preferably in the range of 15 to 700 mPa.s . In still a further embodiment according to the invention, the component (C) is a reinforcing filler selected from silicas (C1), preferably selected from the group consisting of fumed silicas and precipitated silicas, more preferably selected from fumed silicas.

[0225] As defined above, according to the invention any filler having a BET surface of 50 or more than 50 m2 / g measured according to DIN-ISO 9277 with nitrogen, preferably more than 50 m2 / g measured according to DIN-ISO 9277 with nitrogen is considered a reinforcing filler. The silicas (C1) can be fumed silicas or precipitated silicas, which may be either untreated or preferably surface-treated silicas.

[0226] In an embodiment according to the invention, the component (D) is selected from the group of platinum compounds.

[0227] Preferred platinum compounds acting as hydrosilylation catalysts (D) are Pt-(O)-alkenyl complexes, such alkenyl, cycloalkenyl, alkenylsiloxane such vinylsiloxane, because of its easy dispersibility in polyorganosiloxane compositions.

[0228] A particularly useful form of the platinum complexes are the Pt(0)-complexes with aliphatically unsaturated organosilicon compound such as a 1 ,3-divinyltetramethyldisiloxane (Vinyl-M2 or Karstedt catalyst: as disclosed by e.g. US 3,419,593 incorporated herein by reference. Further especially preferred are cyclohexene-Pt, cyclooctadiene-Pt and tetravinyltetramethyl-tetracyclosiloxane (Vinyl-D4)-Pt, e.g. Ashby’s catalyst, a Pt(O) complex in tetramethyltetravinylcyclotetrasiloxane with the empirical formula Pt[(C3HeSiO)4]x.

[0229] Most preferred catalyst component D) is a Pt° complex with tetramethyl- tetravinylcyclotetrasiloxane, typically in a solution of methylvinylcyclosiloxanes, in particular of tetramethyl-tetravinylcyclotetrasiloxane, that contains about 1 to 3 wt% Pt, preferably 2 wt% Pt, in particular, Ashby’s catalyst.

[0230] Also preferably is a so-called Lamoreaux catalyst, which is a platinum (II) complex compound, obtained from chloroplatinic acid hexahydrate and octyl alcohol (as described for example in US 3,197,432 or US 3,220,972). The amount of the platinum compound hydrosilylation catalyst (D) by weight platinum per weight of polysiloxane components (A) and (B) according to this embodiment is preferably in the range of 0.01 to 600 ppm, more preferably 1 to 500 ppm, still more preferably in the range of 2 to 200 ppm, even more preferably 3 to 100 ppm, even further preferably 4 to 60 ppm, most preferably in the range of 5 to 40 ppm.

[0231] In an embodiment according to the invention, the component (E) is an additive selected from the group consisting of

[0232] - curing inhibitors, preferably one or more acetylenic compounds,

[0233] - additional fillers or pigments, preferably carbon black and / or titanium dioxide,

[0234] - heat stabilizers, and

[0235] - oil bleeding additives.

[0236] Preferred curing inhibitors according to the embodiment may be selected from the group consisting of benzotriazole, maleic or fumaric diester, acetylenic compounds and polymethylvinylcyclosiloxanes having three to six methylvinylsiloxane units per molecule. Examples of vinylsiloxane-based inhibitors are 1 ,1 ,3,3-tetramethyl-1 ,3-divinylsiloxane and vinyl-containing poly-, oligo- and disiloxanes. Examples of inhibitors based on unsaturated dicarboxylic acids are fumaric diesters or maleic diesters such as bis(2-methoxyisopropyl) maleate for example Therein, acetylenic compounds, for example acetylenic alcohol, 2-methyl- 3-butyn-2-ol and / or 1-ethynyl-2-cyclohexanol 3,5-dimethyl-1-hexyn-3-ol and 3-methyl-1- pentyn-3-ol are particularly preferred.

[0237] The amounts in which inhibitor is used are preferably in the range from 0.01% to 2% by weight and more preferably in the range from 0.05% to 1.5% by weight based on the total weight of the composition according to the invention.

[0238] The terms “curing inhibitor”, “metal catalyst inhibitor” and hydrosilylation inhibitor” may be used interchangeably herein.

[0239] Additional fillers according to the embodiment are non-reinforcing fillers, i.e. fillers having a BET specific surface area of < 50 m2 / g, for example quartz, calcium carbonate, diatomaceous earth or perlite. Particularly preferred additional non reinforcing fillers are calcium carbonate and diatomaceous earth.

[0240] Preferred heat stabilizers according to the embodiment are iron oxides and carbon blacks, iron carboxylate salts, cerium hydrate, barium zirconate, cerium and zirconium octoates, and porphyrins.

[0241] According to the embodiment, the amount of additional non-reinforcing fillers, if present, is preferably in the range of 1 to 90 parts, more preferably 5 to 50 parts, even more preferably 10 to 30 parts by weight per 100 parts by weight of reinforcing fillers (C), and the amount of heat stabilizers, if present, is in the range of 0.1 to 50 parts, preferably 0.5 to 40 parts, more preferably 1 to 30 parts, and even more preferably in the range of 2 to 20 parts by weight relative to the amount of the polysiloxane component (A) in the composition being 100 parts by weight.

[0242] It is further preferred according to the embodiment that the amount of curing inhibitors, if present, is in the range of 0.1 to 50 parts, preferably 0.5 to 40 parts, more preferably 1 to 30 parts, and even more preferably 2 to 20 parts by weight relative to the amount of the polysiloxane component (A) in the composition being 100 parts by weight.

[0243] The amount of additional additives (E) given in parts by weight refers to the amount of the polysiloxane component (A) in the composition being 100 parts by weight.

[0244] In case several additional additives are comprised by the curable silicone rubber composition, the overall amount of additional additives (E) by weight is 50 parts or less, preferably 30 parts or less, more preferably 1 to 20 parts, and even more preferably 2 to 15 parts by weight relative to the amount of the polysiloxane component (A) in the composition being 100 parts by weight.

[0245] In a further embodiment according to the invention, the addition-curable silicone rubber composition comprises:

[0246] 100 parts by weight of component (A),

[0247] 0.1 to 10 parts by weight of component (B),

[0248] 5 to 100 parts by weight, preferably 15 to 40 parts by weight of component (C),

[0249] 0.01 to 40 ppm by weight of Pt comprised by hydrosilylation catalyst (D) relative to the weight of combined components (A) and (B),

[0250] 0 to 50 parts by weight of component (E).

[0251] The indications refer to the amount of the components (A) to (E) by weight, wherein the amounts of the components (B), (C) and (E) are indicated in weight parts relative to the weight of component (A), and component (D) is indicated in ppm by weight of the Pt metal contained in the hydrosilylation catalyst (D) relative to the combined weight of component (A) and component (B) present in the composition.

[0252] The amounts of the components (A) to (E) may be independently selected from the preferred ranges as described for each of the components in the foregoing embodiments and general description.

[0253] In still a further preferred embodiment according to the invention, the reinforcing filler (C) is selected from surface-treated silicas (CT). As defined herein, surface-treated silicas are any kind of silica that has been submitted to a treatment with a surface-treating agent in order to chemically modify the surface of the silica particles.

[0254] According to the embodiment, the surface-treated silicas are preferably based on fumed silicas.

[0255] Further, according to the embodiment it is preferred that the silica is treated with organosilazanes, silanols, alkoxysilanes, or alkylchlorosilanes.

[0256] Most preferably, the silica is treated with organosilazanes, for example divinyltetramethyldisilazane or hexamethyldisilazane, wherein the surface-treatment is achieved by contacting the silica with such surface treating agent. The surface treatment can take place in the presence or absence of an organic solvent, at a temperature in the range of 20 to 200°C. The amount of surface-treating agent to the untreated silica is preferably in the range of more than 20 wt-% (w / w), wherein it is more preferably in the range of 27 wt-% (w / w), still more preferably in the range of 35 wt-%, and even more preferably in the range of more than 40 wt-%.

[0257] While any kind of silica may be submitted to the surface-treatment as described above according to the embodiment, surface-treated fumed silica and surface-treated precipitated silica are preferred, wherein fumed surface-treated silica is most preferred.

[0258] It is further preferred according to the embodiment that the surface-treated silica is based on a silica having a BET specific surface area in the range of 50 m2 / g to 1000 m2 / g, preferably 50 m2 / g to 800 m2 / g , more preferably 100 m2 / g to 600 m2 / g, even more preferably 150 m2 / g to 500 m2 / g, and most preferably the surface-treated silica is based on a fumed silica having a BET specific surface area in the range of 200 m2 / g to 400 m2 / g.

[0259] The amount of reinforcing filler may account for 3% to 60% by weight of the entire composition according to the invention, 5% to 45% by weight are preferred and 10% to 40% by weight are particularly preferred.

[0260] In a preferred embodiment according to the invention, the reinforcing filler (C) is selected from surface-treated silicas (CT), wherein the surface treatment is carried out with at least one surface treating agent (C3) selected from the group consisting of silanes, such as silanols, alkoxysilanes, cyclic siloxanes, such as the cyclic dimethylsiloxanes D3, D4, D5, D6, in particular D4, short chain polydimethylsiloxanes (PDMS) having a degree of polymerization below 10, i.e. compounds of the general formula MDpiM, wherein p1 is 0 to 7, and silazanes, preferably hexamethyldisilazane (HMDZ) and divinyl tetramethyldisilazane or mixtures thereof. According to the embodiment, the surface-treated silicas may be based on all kinds of silica, preferred on fumed silica and precipitated silica, wherein fumed silica is preferred, and fumed silica having a BET specific surface area in the range of 50 m2 / g to 600 m2 / g is even more preferred, fumed silica having a BET specific surface area in the range of 100 m2 / g to 500 m2 / g is even further preferred, and fumed silica having a BET specific surface area in the range of 200 m2 / g to 400 m2 / g is most preferred.

[0261] The surface treating agent (C3) according to the embodiment may be selected from silanes, for example silanols such as trimethylsilanol, alkoxysilanes such as trimethylethoxysilane, dimethyldiethoxysilane, dimethyldimethoxysilane, diphenyldiethoxysilane, vinylmethyldimethoxysilane, methyltriethoxysilane and silazanes, such as hexamethyldisilazane (HMDZ), divinyl tetramethyldisilazanes, or mixtures thereof.

[0262] The most preferred surface-treating agents according to the embodiment are hexamethyldisilazane (HMDZ) and divinyl tetramethyldisilazane.

[0263] Further preferred according to the embodiment, the surface treating agent is combined with the polyorganosiloxane component (A) and optionally water before it is mixed with a fumed silica for surface treatment.

[0264] In a further preferred embodiment according to the invention, the surface treating agent (C3) is selected from silazanes, more preferably the surface treating agent is hexamethyldisilazane (HMDZ).

[0265] In a still further preferred embodiment according to the invention, the reinforcing filler (C) is a surface-treated silica (CT), which is obtained in the presence of water (C2) and one or more surface treating agents (C3), wherein the weight ratio of water (C2) to the surface treating agents (C3) is less than 25 wt.-%, preferably less than 23 wt.-%.

[0266] The weight ratio of water (C2) to the surface treating agent(s) (C3) in wt.-% is calculated by the equation weight ratio (C2) to (C3) in wt.-% = [m (C2) / m (C3)] * 100, wherein m (C2) is the amount of water (C2) by mass, and m (C3) is the amount of surface treating agent(s) (C3) by mass. According to the embodiment, it is also preferred that the surface-treated silica is based on fumed silica, and that the surface treating agent (C3) is selected from silanes, silanols, cyclic siloxanes such as dimethylcyclosiloxanes D3, D4, D5, D6, in particular D4, short chain polydimethylsiloxanes (PDMS) having a degree of polymerization below 10, i.e. compounds of the general formula MDpiM, wherein p1 is 0 to 7, or from organosilazanes, e.g. of the formula Rd,3Si-[NH-SiRd’2]n-NH-SiRd,3 (with n being > 0) and Rd’ being an organic group, preferably selected from methyl and / or vinyl, most preferably hexamethyldisilazane (HMDZ) or divinyl tetramethyldisilazanes.

[0267] It is further preferred according to the embodiment that when the untreated silica is a fumed silica and the surface treating agent (C3) is an organosilazane.

[0268] It is also preferred according to the embodiment that the weight ratio of water (C2) to the surface treating agents (C3) is less than 25 wt.-%, preferably less than 23 wt.-%, even more preferably less than 21 wt.-%, and still more preferably less than 20 wt.-%. At the same time, it is preferred according to the embodiment that the weight ratio of water (C2) to the surface treating agents (C3) is more than 1 wt.-%, preferably more than 3 wt.-%, and more preferably more than 5 wt.-%.

[0269] In an even further preferred embodiment according to the invention, the reinforcing filler (C) is a surface-treated silica (CT), which is obtained in the presence of water (C2) and the surface treating agent (C3) HMDZ, wherein the weight ratio of water (C2) to the surface treating agent HMDZ (C3) is less than 25 wt.-%, preferably less than 23 wt.-%, more preferably less than 21 wt.-%, and most preferably less than 20 wt.-%.

[0270] According to the embodiment, HMDZ is the only surface treating agent used for obtaining the surface-treated silica (CT).

[0271] In a further preferred embodiment according to the invention, the reinforcing filler (C) is a surface-treated silica (CT), which is obtained in the presence of one or more surface treating agents (C3), wherein the weight ratio of the surface treating agents (C3) to the silica (C1) is more than 20 wt.-%, preferably more than 27 wt.-%, more preferably more than 35 wt.-% (w / w), even more preferably more than 40 wt.-%.

[0272] The weight ratio of the surface treating agents (C3) to the silica (C1) in wt.-% is calculated by the equation weight ratio (C3) to (C1) in wt.-% = [m (C3) / m (C1 )] * 100, wherein m (C3) is the amount of surface treating agent(s) by mass, and m (C1) is the amount of silica (C1) by mass.

[0273] By the ratio of the surface treating agent (C3) to the silica (C1), the degree of functionalisation of the silica particles’ surface can be controlled. According to the embodiment, it is preferred that the silica to be treated with the surface treating agent is selected from fumed silicas, more preferably from fumed silicas having a BET specific surface area of more than 100 m2 / g, more preferably of more than 175 m2 / g, and even more preferably of more than 250 m2 / g.

[0274] It is further preferred that the that the surface treating agent (C3) is silanes, silanols, cyclic siloxanes like dimethylcyclosiloxanes D4, D5, D6, preferably D4 or organosilazanes, e.g. of the formula R Si-[NH-SiRd,2]n-NH-SiRd,3 (with n being > 0) and Rd’ being an organic group, preferably selected from methyl and / or vinyl, most preferably hexamethyldisilazane (HMDZ) or divinyl tetramethyldisilazane.

[0275] According to the embodiment, it is also preferred that the ratio of the of the surface treating agents (C3) to the silica (C1) is 100 wt.-% or less, preferably 80 wt.-% or less, more preferably 70 wt.-% or less, and even more 60 wt.-% or less.

[0276] Another aspect of the invention is directed at a curable silicone rubber composition.

[0277] The curable silicone rubber composition according to the invention comprises:

[0278] (A) one or more organopolysiloxanes having at least two silicon-bonded aliphatic unsaturated groups per molecule,

[0279] (B) one or more organohydrogenpolysiloxanes having at least two silicon-bonded hydrogen atoms per molecule,

[0280] (C) one or more reinforcing surface-treated silicas (CT),

[0281] (D) one or more hydrosilylation catalysts,

[0282] (E) optionally one or more additives, wherein the surface-treated silicas (CT) are prepared by treating one or more silicas (C1) with one or more surface treating agents (C3) and water (C2), wherein the weight ratio of water (C2) to the surface treating agents (C3) is less than 25 wt.-%, preferably less than 23 wt.-%, more preferably less than 21 wt.-%, and most preferably less than 20 wt.-%. Therein, the components (A) to (E) are as defined above in the description of the foregoing embodiments. The curable silicon rubber composition comprising the components (A) to (D) and optionally (E) is the composition from which the above-described cured silicone rubber composition is obtained, wherein the ratio of the surface treating agents and water is defined as cited above. By controlling the ratio of the surface treating agent and water in the surface treating step of the silica filler, a curable composition that can provide a low VOC silicone rubber composition can be obtained.

[0283] According to the embodiment, it is also preferred that the surface-treated silica is based on fumed silica, and that the surface treating agent (C3) is selected from silanes, silanols, cyclic siloxanes such as dimethylcyclosiloxanes D3, D4, D5, D6, more preferably D4, or organosilazanes, e.g. of the formula R Si-[NH-SiRd,2]n-NH-SiRd,3 (with n being > 0) and Rd’ being an organic group, preferably selected from methyl and / or vinyl, most preferably hexamethyldisilazane (HMDZ) or divinyl tetramethyldisilazanes.

[0284] It is further preferred according to the embodiment that when the untreated silica is a fumed silica and the surface treating agent (C3) is an organosilazane.

[0285] It is also preferred that the weight ratio of water (C2) to the surface treating agents (C3) is less than 23 wt.-%, preferably less than 20 wt.-%, even more preferably less than 18 wt.-%, and still more preferably less than 16 wt.-%. At the same time, it is preferred according to the embodiment that the weight ratio of water (C2) to the surface treating agents (C3) is more than 1 wt.-%, preferably more than 3 wt.-%, and more preferably more than 5 wt.-%.

[0286] In a preferred embodiment according to the invention, the surface-treated silicas (CT) are prepared by treating one or more silicas (C1) with the surface treating agent HMDZ (C3) and water (C2), wherein the weight ratio of water (C2) to the surface treating agent (C3) HMDZ is less than 25 wt.-%, preferably less than 23 wt.-%, more preferably less than 21 wt.-%, and most preferably less than 20 wt.-%.

[0287] The silica (C1) is preferably a fumed silica, more preferably a fumed silica having a BET specific surface area of 50 to 800 m2 / g, even more preferably of 100 to 600 m2 / g, and most preferably of 200 to 400 m2 / g.

[0288] In an embodiment according to the invention, the surface-treated silica (CT) is obtained in the presence of one or more surface treating agents (C3), wherein the weight ratio of the surface treating agents (C3) to the silica (C1) is more than 20 wt-%, preferably more than 27 wt.-%, more preferably more than 35 wt.-%, even more preferably more than 40 wt.-%, most preferably equal or more than 44 wt-%.

[0289] Preferably, the surface treating agent (C3) is hexamethyldisilazane or tetramethyldivinylsilazane.

[0290] In a further embodiment according to the invention, the surface treating agents (C3) are selected from the group consisting of silanes, such as silanols, alkoxysilanes, cyclic siloxanes, such as the cyclic dimethylsiloxanes D3, D4, D5, D6, in particular D4, short chain polydimethylsiloxanes (PDMS) having a degree of polymerization below 10, i.e. compounds of the general formula MDpiM, wherein p1 is 0 to 7, and silazanes, preferably hexamethyldisilazane (HMDZ) and divinyl tetramethyldisilazanes or mixtures thereof, preferably the surface treating agents (C3) are selected from the group consisting of silazanes, such as hexamethyldisilazane and tetramethyldivinylsilazane.

[0291] In still a further embodiment according to the invention, the curable silicone rubber composition comprises:

[0292] 100 parts by weight of component (A),

[0293] 0.1 to 10 parts by weight component (B),

[0294] 5 to 100 parts by weight, preferably 15 to 40 parts by weight component (C),

[0295] 0.01 to 40 ppm by weight of Pt comprised by the hydrosilylation catalyst (D) relative to the weight of combined components (A) and (B),

[0296] 0 to 50 parts by weight component (E).

[0297] Another aspect of the invention relates to a process for the manufacture of a cured rubber composition according to the invention on the basis of the curable silicone rubber compositions according to the invention.

[0298] The process for the manufacture of the cured silicone rubber composition according to the invention comprises subjecting the curable silicone rubber composition according to the invention as described above to a curing step.

[0299] Without being limited thereto, the curable silicone rubber compositions according to the invention are usually curable as soon as the hydrosilylation catalyst (D) and the polyorganosiloxane components (A) and (B) are combined and mixed. Curing is preferably achieved at an elevated curing temperature in the range of 20 to 200°C, preferably 50 to 190°C, 80 to 190, 100 to 180°C. Such compositions, in one aspect, comprise as the main constituents vinyl-containing polysiloxane having a treated or untreated filler therein, a hydrogen-containing polysiloxane and finally a platinum catalyst which can be a solid platinum metal deposited on a solid carrier such as, gamma-alumina or a solubilized platinum complex.

[0300] It is normal in such compositions to package the vinyl polysiloxane (A), the filler (C) and the platinum catalyst (D) in one package and to package the hydrogen-containing polysiloxane (B) in a second package. When the fabricator or user of the material desires to produce a cured silicone elastomer he mixes the two packages fabricates the composition to the desired shape and allows the composition to cure either at room temperature over a period of time or at elevated temperatures in very short periods of time such as, in seconds or minutes.

[0301] The above-described compositions which are sold in two components or packages are usually referred to as room temperature vulcanizable silicone rubber compositions and more specifically, SiH-olefin platinum catalyzed room temperature vulcanizable silicone rubber compositions. It is understood that these types of compositions are cured either at room temperature over a period of time in the range of 0.5 to 24 hours, preferably 1 to 16 hours, more preferably 2 to 12 hours, even more preferably 3 to 8 hours, such as, 1 hour or 12 hours after the two components are mixed together, or over a very short period of time in seconds, e.g. 1 to 60 seconds, or minutes, e.g. 1 to 60 minutes, by heating the composition at temperatures above 100° or above 200° C. The curing step can be done in an injection molding machine, by press curing or in engine oil operating press.

[0302] Accordingly, the curing step preferably comprises a step of submitting the curable composition to an elevated temperature.

[0303] The curing step may also comprise activation of a photo-activatable catalyst by exposing the curable composition to UV irradiation. The photo-activatable catalyst is selected from r|5- (optionally substituted)-cyclopentadienyl platinum complex compounds having sigma-bonded ligands, preferably sigma-bonded alkyl ligands. The UV activation can be done at room temperature of 25° C for a period of time. The irradiation time may typically range from 1 minute (min) to 2 hours, alternatively from 2 min to 1 hour, more preferably 2 min to 30 min. The irradiation can be done using a medium pressure mercury lamp or UV LED lamp.

[0304] The curing conditions, in particular the curing temperature, depend on the specific selection of the components (A) to (D) and the presence of additives (E) such as curing inhibitors, and the desired curing rate.

[0305] It is further preferred that the curing is performed at an elevated temperature as defined above in an injection mould or a press suitable for press-curing.

[0306] The curing time is preferably less than 60 minutes, more preferably less than 30 minutes, even more preferably less than 20 minutes, and further preferably less than 15 minutes. Still another aspect of the invention relates to the use of the curable silicone rubber composition according to the invention for the manufacture of cured articles, preferably selected from infant care articles, food contact articles, automotive articles, and electronic articles.

[0307] An example for the use of the curable silicone rubber composition according to the invention is the manufacture of infant care articles, for example baby nipples, and of food contact articles, such as kitchen ware, for example baking moulds. The curable silicone rubber composition is beneficially used in the provision of cured silicone rubber compositions and articles made thereof which are characterized by their low content of volatiles and leachable low-molecular weight compounds, which makes them safe to use in infant and kitchen goods. The curable composition can also be beneficially used in the production of automotive articles, such as gaskets and spark plug boots, and for electronic articles, such as cable accessories.

[0308] Another aspect of the invention relates to an article comprising the cured silicone rubber composition according to the invention, selected from the group consisting of infant care articles, food contact articles, automotive articles, and electronic articles.

[0309] From the cured article as cited above, low-molecular weight siloxane components will volatilize only in extremely small quantities, which renders the curable composition suitable for infant care articles, such as baby nipples, food contact articles, such as kitchen ware, and also automotive articles, such as gaskets and spark plug boots, and for electronic articles, such as cable accessories.

[0310] Still another aspect of the invention relates to a process for the manufacture of the curable silicone rubber composition according to the invention, comprising the steps of:

[0311] (a) Preparing a silica-silicone rubber base by admixing at least a part of one or more components (A), one or more silicas (C1), one or more surface treating agent (C3) and water (C2) at elevated temperatures (silica surface treatment step),

[0312] (b) optionally adding further one or more components (A) to the silica-silicone rubber base,

[0313] (c) optionally adding one or more components (E),

[0314] (d) adding one or more components (B) and

[0315] (e) adding one or more components (D).

[0316] The steps (a) to (e) can be performed in any order.

[0317] It is, however, preferred to add the component (D) last, as this makes the composition curable and thus initiates curing. It is further preferred according to this embodiment to prepare a two part composition first, i.e. by preparing a part of the composition comprising component (A) but free from component (B) and another part of the composition comprising component (B) but free from (component (A) separately first. Each of the components (C) and (D) and optionally (E) may be added to any of the two parts described before, or to both of them as well.

[0318] Summary of preferred embodiments

[0319] In the following, the preferred embodiments of the invention are summarized:

[0320] 1. A cured silicone rubber composition having a toluene-soluble content, wherein the toluene-soluble content in the GPC measurement using polystyrene as a standard has a main peak eluted before the extracting solvent peak corresponding to a number average molecular weight of more than 1500 Dalton, preferably more than 1600 Dalton, more preferably more than 1700 Dalton, more preferably more than 1800 Dalton, and a weight loss measured according to BfR of less than 0.5 wt.-%, preferably less than 0.45 wt.-%, more preferably of less than 0.4 wt.-%, even more preferably of less than 0,35 wt.-%, and still more preferably of less than 0,30 wt.-%, wherein the composition is obtained by curing a curable silicone rubber composition, wherein the curable silicone rubber composition comprises:

[0321] (A) one or more organopolysiloxanes having at least two silicon-bonded aliphatic unsaturated groups per molecule,

[0322] (B) one or more organohydrogenpolysiloxanes having at least two silicon-bonded hydrogen atoms per molecule,

[0323] (C) one or more reinforcing fillers,

[0324] (D) one or more hydrosilylation catalysts,

[0325] (E) optionally one or more additives.

[0326] 2. A cured silicone rubber composition according to the previous embodiment, wherein component (A) is an alkenyl terminated polyorganosiloxane having a viscosity in the range of 5 and 200 Pa.s at 20°C and a shear rate of 10 s-1measured according to DIN 53019.

[0327] 3. A cured silicone rubber composition according to any of the previous embodiments, wherein component (B) has a viscosity in the range of 10 to 1000 mPa.s at 20°C according to DIN 53015 (ball 3).

[0328] 4. A cured silicone rubber composition according to any of the previous embodiments, wherein component (C) is a reinforcing filler selected from silicas (C1), preferably selected from the group consisting of fumed silicas and precipitated silicas, more preferably selected from fumed silicas.

[0329] 5. A cured silicone rubber composition according to any of the previous embodiments, wherein component (D) is selected from the group of platinum compounds.

[0330] 6. A cured silicone rubber composition according to any of the previous embodiments, wherein component (E) is an additive selected from the group consisting of

[0331] - curing inhibitors, preferably one or more acetylenic compounds,

[0332] - additional fillers or pigments, preferably carbon black and / or titanium dioxide, - heat stabilizers, and

[0333] - oil bleeding additives.

[0334] 7. A cured silicone rubber composition according to any of the previous embodiments, wherein the addition-curable silicone rubber composition comprises:

[0335] 100 parts by weight of component (A),

[0336] 0.1 to 10 parts by weight of component (B),

[0337] 5 to 100 parts by weight, preferably 15 to 40 parts by weight of component (C),

[0338] 0.01 to 40 ppm by weight of Pt comprised by hydrosilylation catalyst (D) relative to the weight of combined components (A) and (B),

[0339] 0 to 50 parts by weight of component (E).

[0340] 8. A cured silicone rubber composition according to any of the previous embodiments, wherein the reinforcing filler (C) is selected from surface-treated silicas (CT).

[0341] 9. A cured silicone rubber composition according to the previous embodiments, wherein the reinforcing filler (C) is selected from surface-treated silicas (CT), wherein the surface treatment is carried out with at least one surface treating agent (C3) selected from the group consisting of silanes, such as silanols, alkoxysilanes, cyclic siloxanes, such as the cyclic dimethylsiloxanes D3, D4, D5, D6, in particular D4, short chain polydimethylsiloxanes (PDMS) having a degree of polymerization below 10, i.e. compounds of the general formula MDpiM, wherein p1 is 0 to 7, and silazanes, preferably hexamethyldisilazane (HMDZ) and divinyl tetramethyldisilazanes or mixtures thereof.

[0342] 10. A cured silicone rubber composition according to the previous embodiments, wherein the surface treating agent (C3) is selected from silazanes, preferably the surface treating agent is hexamethyldisilazane (HMDZ).

[0343] 11. A cured silicone rubber composition according to any of the previous embodiments, wherein the reinforcing filler (C) is a surface-treated silica (CT), which is obtained in the presence of water (C2) and one or more surface treating agents (C3), wherein the weight ratio of water (C2) to the surface treating agents (C3) is less than 25 wt.-%, preferably less than 23 wt.-%.

[0344] 12. A cured silicone rubber composition according to the previous embodiment, wherein the ratio of water (C2) to the surface treating agent (C3) HMDZ is less than 25 wt.-%, preferably less than 23 wt.-%, more preferably less than 21 wt.-%, and most preferably less than 20 wt.- %.

[0345] 13. A cured silicone rubber composition according to any of the previous embodiments, wherein the reinforcing filler (C) is a surface-treated silica (CT), which is obtained in the presence of one or more surface treating agents (C3), wherein the weight ratio of the surface treating agents (C3) to the silica (C1) is more than 20 wt.-%, preferably more than 27 wt.-%, more preferably more than 35 wt.-%, even more preferably more than 40 wt.-%.

[0346] 14. Curable silicone rubber composition comprising:

[0347] (A) one or more organopolysiloxanes having at least two silicon-bonded aliphatic unsaturated groups per molecule,

[0348] (B) one or more organohydrogenpolysiloxanes having at least two silicon-bonded hydrogen atoms per molecule,

[0349] (C) one or more reinforcing surface-treated silicas (C1 ’),

[0350] (D) one or more hydrosilylation catalysts,

[0351] (E) optionally one or more additives, wherein the surface-treated silicas (CT) are prepared by treating one or more silicas (C1) with one or more surface treating agents (C3) and water (C2), wherein the weight ratio of water (C2) to the surface treating agents (C3) is less than 25 wt.-%, preferably less than 23 wt.-%.

[0352] 15. Curable silicone rubber composition according to the previous embodiment, wherein the surface-treated silicas (CT) are prepared by treating one or more silicas (C1) with the surface treating agent HMDZ (C3) and water (C2), and wherein the ratio of water (C2) to the surface treating agent (C3) HMDZ is less than 25 wt.-%, preferably less than 23 wt.-%, more preferably less than 21 wt.-%, and most preferably less than 20 wt.-%.

[0353] 16. Curable silicone rubber composition comprising according to embodiment 14 or 15, wherein the surface-treated silica (CT) is obtained in the presence of one or more surface treating agents (C3), wherein the weight ratio of the surface treating agents (C3) to the silica (C1) is more than 20 % (w / w), preferably more than 27 wt.-%, more preferably more than 35 wt.-% (w / w), even more preferably more than 40 wt.-% (w / w).

[0354] 17. Curable silicone rubber composition according to embodiments 14-16, wherein the surface treating agents (C3) are selected from the group consisting of silanes, such as silanols, alkoxysilanes, cyclic siloxanes, such as the cyclic dimethylsiloxanes D3, D4, D5, D6, in particular D4, short chain polydimethylsiloxanes (PDMS) having a degree of polymerization below 10, i.e. compounds of the general formula MDpiM, wherein p1 is 0 to 7, and silazanes, preferably hexamethyldisilazane (HMDZ) and divinyl tetramethyldisilazanes or mixtures thereof, preferably the surface treating agents (C3) are selected from the group consisting of silazanes, such as hexamethyldisilazane and tetramethyldivinylsilazane.

[0355] 18. Curable silicone rubber composition, according to any of embodiments 14-17 comprising:

[0356] 100 parts by weight of component (A),

[0357] 0.1 to 10 parts by weight component (B),

[0358] 5 to 100 parts by weight, preferably 15 to 40 parts by weight component (C), 0.01 to 40 ppm by weight of Pt comprised by the hydrosilylation catalyst (D) relative to the weight of combined components (A) and (B),

[0359] 0 to 50 parts by weight component (E).

[0360] 19. A process for the manufacture of the cured silicone rubber composition according to any of the previous embodiments 1 to 13, which comprises subjecting the curable silicone rubber composition according to any of embodiments 14 to 18 to a curing step.

[0361] 20. Use of the curable silicone rubber composition according to any of embodiments 14 to 18 for the manufacture of cured articles, preferably selected from infant care articles, food contact articles, automotive articles, and electronic articles.

[0362] 21. An article comprising the cured silicone rubber composition according to any of the previous embodiments 1 to 13, selected from the group consisting of infant care articles, food contact articles, automotive articles, and electronic articles.

[0363] 22. A process for the manufacture of the curable silicone rubber composition according to any of the previous embodiments 14 to 18, comprising the steps of:

[0364] (a) Preparing a silica-silicone rubber base by admixing at least a part of one or more components (A), one or more silicas (C1), one or more surface treating agent (C3) and water (C2) at elevated temperatures (silica surface treatment step),

[0365] (b) Optionally adding further one or more components (A) to the silica-silicone rubber base,

[0366] (c) Optionally adding one or more components (E),

[0367] (d) Adding one or more components (B) and

[0368] (e) Adding one or more components (D).

[0369] It will be understood that any numerical range recited herein includes all sub-ranges within that range and any combination of the various endpoints of such ranges or sub-ranges, be it described in the examples or anywhere else in the specification.

[0370] It will also be understood herein that any of the components of the invention herein as they are described by any specific genus or species detailed in the examples section of the specification, can be used in one embodiment to define an alternative respective definition of any endpoint of a range elsewhere described in the specification with regard to that component, and can thus, in one non-limiting embodiment, be used to supplant such a range endpoint, elsewhere described.

[0371] It will be further understood that any compound, material or substance which is expressly or implicitly disclosed in the specification and / or recited in a claim as belonging to a group of structurally, compositionally and / or functionally related compounds, materials or substances includes individual representatives of the group and all combinations thereof. While the above description contains many specifics, these specifics should not be construed as limitations on the scope of the invention, but merely as exemplifications of preferred embodiments thereof. Those skilled in the art may envision many other possible variations that are within the scope and spirit of the invention as defined by the claims appended hereto.

[0372] The present invention will be explained in more detail by the examples in the following.

[0373] Examples

[0374] EXAMPLES 1 BC-4BC AND COMPARATIVE EXAMPLES 1 BC AND 2BC (BASE COMPOUND COMPOSITIONS)

[0375] The examples 1 BC to 4 BC and comparative examples 1 BC and 2BC from Table 1 were prepared by mixing together the components of Table 1 in a lab planetary mixing equipment from Company DALTON. First, the vinyl terminated polymer (A) was mixed with HMDZ and water, and then the mixture was mixed in the planetary mixer for 5min under a nitrogen atmosphere with a stream of N2 inert gas of <1 L / min. Then, the silica filler (C1) was added, and the resulting mixture was mixed for 1 h under a nitrogen atmosphere with a stream of N2 inert gas of N2 < 1 L / min, heated to 100 °C within 20 min and mixed at this temperature for further 40 min. Then the mixture was heated to 150°C within 30 minutes and mixed at 150 °C for 30 min under nitrogen atmosphere. After 1 h of further mixing at 150 °C, decompression at a pressure of 10 mm Hg followed. A further portion of the same vinyl terminated polymer (A) was added, the composition was mixed for 15 min at 150°C, followed by decompression at 10 mmHg. The final base compound compositions were cooled down to a temperature below 80

[0376] Table 1 : Formulations of uncured silicone base compositions of Ex 1 BC to 4 BC and Comparative Ex 1 BC and 2 BC

[0377] To 100 weight parts of one of the base compound compositions (Ex 1BC to Ex 4 BC and Comp Ex 1 BC and 2BC) was added a trimethylsilyl-terminated linear poly dimethyl cohydrogenmethyl siloxane (B) with a SiH content of 0.15 mmol / g and a viscosity of 40 mPa.s at 20°C according to DI N 53015 (ball 3), the curing inhibitor ethynylcyclohexanol and the platinum complex as a solution of Pt at 2% in DVi4 to prepare curable silicone compositions of the examples Ex 1SR to Ex 4SR and Comparative Ex 1SR and 2SR as shown in Table 2 below. The examples 1SR to 4SR and Comparative Ex. 1 SR and 2SR were press-cured for 5 min at 165°C, wherein a 40 ton hot press manufactured by Koto Kogyosyo Co., Ltd was used for press curing, and the mold tool was dimensioned 2mm*15cm*15cm.

[0378] After press-curing, no post-curing treatment such as heating was applied to the cured composition of the examples.

[0379] Table 2: Formulations of silicone rubber compositions in Ex 1SR to Ex 4SR, Comp Ex 1SR and 2SR and testing results (Mn and weight loss) of the cured silicone rubber made thereof

[0380] The weight loss test of the cured silicone rubber from Examples 1SR to 4SR and Comparative Ex. 1SR and 2SR was measured according to BfR Regulations:

[0381] Regarding the weight loss of cured silicone rubber, the chapter “XV. Silicone” in “Recommendations on Food Contact Materials” by BfR (Bundesinstitut fur Risikobewertung) as of 01.06.2020 it is prescribed under “III. Silicone elastomers (Silicone rubber), 5.” that the silicone elastomers must release no more than 0.5 % volatile organic components. In the corresponding protocol “Determination of volatile compounds in consumer goods made of silicone” (“Bestimmung von fluchtigen Verbindungen in Bedarfsgegenstanden aus Silikon”, Stand: 03 / 2022) released by the BfR, a precise protocol for the determination of the release of volatiles from silicone consumer goods is provided. The “BfR weight loss” has been determined by heating cut cured silicone sheets at 200°C / 4 hours according to said protocol.

[0382] Determination of viscosity of component (A):

[0383] The viscosity of component (A) at 20°C and a shear rate of 10 s-1has been determined according to DIN 53019.

[0384] Determination of viscosity of component (B):

[0385] The viscosity of component (B) at 20°C has been determined according to DIN 53015 (ball 3).

[0386] The GPC measurement of the toluene extract of the cured silicone rubber sheets from Examples 1SR to 4SR and Comparative examples 1 SR and 2SR has been performed as follows:

[0387] The cured silicone rubber sheets (non-post cure, NPC) from Examples 1SR to 4SR and Comparative Ex.1 SR and 2SR (press cured sheets 2 mm x 15 cm x 15 cm) were cut per hand to small cubes. (2 mm edge length).

[0388] 4 g of the cut cured silicone rubber sample from Examples 1SR to 4SR and Comparative Ex. 1SR and 2 SR were immersed into 20 g of toluene and shaken at room temperature (25°C) for one day (24 hours).

[0389] 2 g of the toluene solution extract were dried on an aluminum dish at open air in a draft chamber at room temperature (25°C) for about 6 hours, then heated and further dried at 120 ° C for 30 minutes in a ventilated oven. The weight of the residue was measured and the content in wt.- % was calculated (residue (g) / 2 g x 100).

[0390] If the toluene-soluble content in the toluene solution extract obtained as described above was more than 0.5 wt.-%, then the toluene solution extract was diluted with toluene to adjust the toluene-soluble content to 0.5% prior to performing the GPC analysis.

[0391] If the toluene-soluble content of the toluene solution extract was less than 0.5%, the GPC measurement was performed on the sample as it was.

[0392] This way of sample preparation is chosen to avoid the saturation of the GPC and too high GPC peak intensities in order to obtain reproducible results.

[0393] 20 microliters of the optionally diluted toluene solution extract were injected into the column SHIMAZU GPC-80M X 2 of the GPC equipment SHIMAZU LC Solution. The detector was Rl (refractive index), the eluent was toluene with a flow rate of 1.0 ml / min at 40°C. The standard used for calibration was polystyrene. Specifically, the polystyrene standards used for GPC calibration were purchased at Tosoh Bioscience and are as follows:

[0394]

[0395] The calibration curve obtained from the polystyrene standards indicated above is displayed in Fig. 3.

[0396] The Shimazu GPC 80M x2 contains 2 Shim-pack -80M columns installed in series.

[0397] The analytical column has the Shimadzu reference code of 228-20810-91. Two columns are installed in series in the device. Each column has a length of 300 mm and an internal diameter (l:D.) of 8 mm. The target molecular weight is 1000- 20 000 000. The packing of the column is USP L21 i.e. rigid, spherical styrene-divinylbenzene copolymer. Its particle size is 10 pm. Its exclusion limit is 4 x 107.

[0398] The guard column is a “Shim-pack GPC-800P “Guard Column; Dimensions (Length x Internal diameter, mm): 10 x 4.6; with the Shimadzu product number: 228-20812-91 , with a pore size of 1000 nm and has a pressure tolerance of 3.5 MPa.

[0399] The guard column is installed between the sample inlet and the two Shim-pack GPC-80M columns of the device.

[0400] From the resulting GPC chromatogram, the molecular weight average in number (Mn) is calculated based on the retention time of the highest intensity peak using the software of the device, which is “Shimazu LC solution version 1.21 SP1”.

[0401] From examples 1 SR to 4 SR we can see that the cured silicone rubber compositions thereof according to the main peak eluted before the extracting solvent peak have a toluene-soluble content having a number average molecular weight Mn value above 1500 in the GPC measurement using polystyrene as a standard, and a weight loss value below 0.5%. For the comparative example SR1, a weight loss above 0.5% and a corresponding Mn value below 1500 was obtained. For the comparative Example SR2, a weight loss above 0.45 % and a Mn value below 1600 Dalton was obtained.

Claims

Claims:

1. A cured silicone rubber composition having a toluene-soluble content, wherein the toluene-soluble content in the GPC measurement using polystyrene as a standard has a main peak eluted before the extracting solvent peak corresponding to a number average molecular weight of more than 1600 Dalton, preferably more than 1700 Dalton, more preferably more than 1800 Dalton, and a weight loss measured according to BfR of less than 0.45 wt.-%, preferably of less than 0.4 wt.-%, wherein the composition is obtained by curing a curable silicone rubber composition, wherein the curable silicone rubber composition comprises:(A) one or more organopolysiloxanes having at least two silicon-bonded aliphatic unsaturated groups per molecule,(B) one or more organohydrogenpolysiloxanes having at least two silicon-bonded hydrogen atoms per molecule,(C) one or more reinforcing fillers,(D) one or more hydrosilylation catalysts,(E) optionally one or more additives, wherein the reinforcing filler (C) is a surface-treated silica (CT), which is obtained in the presence of water (C2) and one or more surface treating agents (C3), wherein the weight ratio of water (C2) to the surface treating agents (C3) is less than 25 wt.-%, preferably less than 23 wt.-%.

2. The cured silicone rubber composition according to the previous claim, wherein component (A) is an alkenyl terminated polyorganosiloxane having a viscosity in the range of5 to 200 Pa.s at 20°C and a shear rate of 10 s-1measured according to DIN 53019, and / or wherein component (B) has a viscosity in the range of 10 to 1000 mPa.s at 20°C measured with a falling sphere viscosimeter according to DIN 53015 (ball 3).

3. The cured silicone rubber composition according to any of the previous claims 1 and 2, wherein the addition-curable silicone rubber composition comprises:100 parts by weight of component (A),0.1 to 10 parts by weight of component (B),5 to 100 parts by weight, preferably 15 to 40 parts by weight of component (C),0.01 to 40 ppm by weight of Pt comprised by hydrosilylation catalyst (D) relative to the weight of combined components (A) and (B),0 to 50 parts by weight of component (E).

4. The cured silicone rubber composition according to any of the previous claims, wherein the reinforcing filler (C) is selected from surface-treated silicas (CT), wherein the surface treatment is carried out with at least one surface treating agent (C3) selected from the group consisting of silanes, such as silanols, alkoxysilanes, cyclic siloxanes, such as the cyclic dimethylsiloxanes D3, D4, D5, D6, in particular D4, short chain polydimethylsiloxanes (PDMS) having a degree of polymerization below 10, i.e. compounds of the general formula MDpiM, wherein p1 is 0 to 7, and silazanes, preferably hexamethyldisilazane (HMDZ) and divinyl tetramethyldisilazanes or mixtures thereof.

5. The cured silicone rubber composition according to any of the previous claims, wherein the ratio of water (C2) to the surface treating agent (C3) HMDZ is less than 25 wt.-%, preferably less than 23 wt.-%, more preferably less than 21 wt.-%, and most preferably less than 20 wt.- %.

6. The cured silicone rubber composition according to any of the previous claims, wherein the reinforcing filler (C) is a surface-treated silica (CT), which is obtained in the presence of one or more surface treating agents (C3), wherein the weight ratio of the surface treating agents (C3) to the silica (C1) is more than 20 wt.-%.

7. The cured silicone rubber composition according to the previous claim, wherein the weight ratio of the surface treating agents (C3) to the silica (C1) is more than 27 wt.-%, preferably more than 35 wt.-%, more preferably more than 40 wt.-%.

8. A curable silicone rubber composition comprising:(A) one or more organopolysiloxanes having at least two silicon-bonded aliphatic unsaturated groups per molecule,(B) one or more organohydrogenpolysiloxanes having at least two silicon-bonded hydrogen atoms per molecule,(C) one or more reinforcing surface-treated silicas (CT),(D) one or more hydrosilylation catalysts,(E) optionally one or more additives, wherein the surface-treated silicas (CT) are prepared by treating one or more silicas (C1) with one or more surface treating agents (C3) and water (C2), wherein the weight ratio of water (C2) to the surface treating agents (C3) is less than 25 wt.-%, preferably less than 23 wt.-%.

9. The curable silicone rubber composition comprising according to claim 8, wherein the surface-treated silica (CT) is obtained in the presence of one or more surface treating agents (C3), wherein the weight ratio of the surface treating agents (C3) to the silica (C1) is more than 20 wt.-%.

10. The curable silicone rubber composition comprising according to previous claim 9, wherein the weight ratio of the surface treating agents (C3) to the silica (C1) is more than 27 wt.-%, preferably more than 35 wt.-%, more preferably more than 40 wt.-%, and most preferably equal or more than 44 wt-%.11 . The curable silicone rubber composition according to any of claims 8 to 10, wherein the surface treating agents (C3) are selected from the group consisting of silanes, such as silanols, alkoxysilanes, cyclic siloxanes, such as the cyclic dimethylsiloxanes D3, D4, D5, D6, in particular D4, short chain polydimethylsiloxanes (PDMS) having a degree of polymerization below 10, i.e. compounds of the general formula MDpiM, wherein p1 is 0 to 7, and silazanes, preferably hexamethyldisilazane (HMDZ) and divinyl tetramethyldisilazanes or mixtures thereof, preferably the surface treating agents (C3) are selected from the group consisting of silazanes, such as hexamethyldisilazane and tetramethyldivinylsilazane.

12. The curable silicone rubber composition, according to any of claims 8 to 11 , comprising: 100 parts by weight of component (A),0.1 to 10 parts by weight component (B),5 to 100 parts by weight, preferably 15 to 40 parts by weight component (C),0.01 to 40 ppm by weight of Pt comprised by the hydrosilylation catalyst (D) relative to the weight of combined components (A) and (B),0 to 50 parts by weight component (E).

13. A process for the manufacture of the cured silicone rubber composition according to any of the previous claims 1 to 7, which comprises subjecting the curable silicone rubber composition according any of claims 8 to 12 to a curing step.

14. Use of the curable silicone rubber composition according to any of claims 8 to 12 for the manufacture of cured articles, preferably selected from infant care articles, food contact articles, automotive articles, and electronic articles.

15. An article comprising the cured silicone rubber composition according to any of the previous claims 1 to 7, selected from the group consisting of infant care articles, food contact articles, automotive articles, and electronic articles.

16. A process for the manufacture of the curable silicone rubber composition according to any of the previous claims 8 to 12, comprising the steps of:(a) Preparing a silica-silicone rubber base by admixing at least a part of one or more components (A), one or more silicas (C 1 ), one or more surface treating agent (C3) and water (C2) at elevated temperatures (silica surface treatment step),(b) optionally adding further one or more components (A) to the silica-silicone rubber base,(c) optionally adding one or more components (E),(d) adding one or more components (B) and(e) adding one or more components (D).

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