Patent Description:
Room temperature vulcanizable compositions comprising a polydiorganosiloxane, also referred to as RTV silicones, are well known and used in various applications. The most prominent use is in the area of building and construction, where the RTV silicones are used as sealant, adhesive or coating. Such silicones typically comprise a polydiorganosiloxane having reactive hydroxyl end-groups as the base polymer in combination with a crosslinking agent and optional components such as catalysts, fillers, pigments, dyes, lubricants, plasticizers, adhesion promoters, thickening agents etc. Depending on the reactivity of the components and the desired shelf-life a RTV silicone may be formulated as a single component wherein all ingredients are blended, or as a multi-component formulation wherein different components comprise different (portions of) ingredients and need to be combined before use. The most commonly employed silicone formulations are single component (RTV1) or two-component (RTV2) formulations, which are typically moisture curable and employ a tri- or tetrafunctional silane (or its corresponding siloxane condensation product) as crosslinker.

The ready-to-use moisture-curable silicones are traditionally sold and used with the polydiorganosiloxane and the silane crosslinker pre-condensed in the form of a so-called "prepolymer" or "end-capped" polysiloxane. During production of these moisture-curable silicones, the terminal hydroxyl groups of the polydiorganosiloxane are reacted with the tri- or tetrafunctional silane (or its corresponding siloxane condensation product) crosslinker to form the so-called "prepolymer", which is then capable of curing by cross-linking under the influence of atmospheric moisture. This first reaction step is also referred to as "end-capping", i.e. the addition of a different end group on the reactive polydiorganosiloxane, and the product obtained may thus also be called an "end-capped polymer". Because this step leads to the formation of a "prepolymer", i.e. a compound suitable for further polymerisation, this reaction step is often also referred to as "prepolymerisation". This step prepares the reactive polymer for the subsequent polymerization reaction without itself being a polymerization reaction.

Next, after dispensing the end-capped polysiloxane from its container (e.g. upon application of the silicone to the desired substrate), moisture-curing takes place. The end-capped polymer has two (if the silane crosslinker was trifunctional) or three (if the silane crosslinker was tetrafunctional) remaining reactive groups. Without wishing to be bound by any theory it is believed that moisture from the environment, after application of the silicone paste, hydrolyses these remaining reactive groups into even more reactive silanol groups which in turn form crosslinks with other end-capped polymer chains. Because the cross-linking agent has brought to each end of the original polydiorganosiloxane two or three reactive groups, in this way a three dimensional, cross-linked final structure may be formed.

The commonly employed silane crosslinkers are acidic (e.g. ethyl-tris(acetoxy)silane) or neutrally crosslinking (e.g. methyl-tris(methylethylketoxime) silane) based on the leaving groups which are released during hydrolysis. Acidic crosslinkers are historically the most important group. However, in view of potential substrate deterioration caused by the acid released during crosslinking, suboptimal substrate adhesion, and the often intense and unpleasant odor, more and more systems based on neutral crosslinkers such as oxime silanes are presently being developed.

The most abundant and economically successful oxime silane crosslinker employs methyl ethyl ketoxime (MEKO). However, RTV silicones utilizing MEKO or similar oxime based silane crosslinkers have a number of shortcomings. For example, many known oxime crosslinkers are solid or highly viscous at room temperature or are prone to form solid particles resulting from crystallisation of the oxime leaving group, which complicates manufacturing of the silicone formulation. Importantly, some oxime crosslinker hydrolysis products, such as <NUM>-butanone oxime (generated from MEKO-endcapped siloxane hydrolysis during curing) have been associated with a carcinogenic effect.

In order to be useful in practice, especially when used as a sealant or grouting compound, RTV silicone formulations not only need to have desirable physical properties post-cure but also need to be 'workable', for example by having an appropriate skinning time and exhibiting low or preferably no early cracking behaviour.

The skinning time of a silicone formulation is known as the time from application to the beginning of superficial solidification ('skin formation') and characterizes the time during which it is possible to manipulate the sealant after application (e.g. extrusion from a container). A sufficiently large skinning time is important as in practice a sealant is first applied in a joint and subsequently needs to be 'smoothened' using a detergent-dipped finger or a specific tool.

Early cracking behaviour is known as the (dis)ability of a sealant to withstand deformations in the early stage of sealant curing. Typically sealants with poor early cracking behaviour tend to tear in the joint when deformation of the joint occurs soon after application of the sealant. This can occur in practice in case of a temperature change in joints combining materials with high or different thermal expansion coefficients, or due to (human) manipulation of the joint shortly after application of the sealant, e.g. a person simply stepping in and out of a bathtub which is being sealed can already cause movement of the joint by several mm.

<CIT> discloses a room temperature vulcanizable silicone rubber composition which can be used as caulking material, adhesives, coatings and encapsulating materials amongst others. Example <NUM> discloses a silicone formulation comprising a silanol-terminated polydimethylsiloxane and phenyl substituted tris-functional ketoximino silane crosslinking agent.

<CIT> discloses silanes which are used as intermediates in one-component roomtemperature-curing sealant, adhesive and coating applications among other silicone polymer applications. Example <NUM> discloses a silicone formulation comprising a silanol-terminated polydimethylsiloxane and vinyl tris-(methyl amyl ketoximino) silane.

As will be shown in the appended examples, the present inventors have found that silicone formulations employing known oxime based silane crosslinkers exhibit short skinning time and/or a large early cracking window.

Hence, there exists a need for cross linking agents that can be used in a RTV silicone formulation, especially a sealant formulation, which overcome one or more problems of the prior art.

It is an object of the present invention to provide a silane crosslinker and/or a silicone formulation comprising the crosslinker which is characterized by an increased skinning time and/or reduced early cracking time, for example when compared to a known oxime based silane crosslinker.

It is a further object of the present invention to provide a silane crosslinker and/or a silicone formulation comprising the crosslinker which has a decreased release of carcinogenic compounds and preferably results in a decreased intensity and/or time of malodor upon curing, for example when compared to a known oxime based silane crosslinker.

As is shown in the appended examples, the present inventors have surprisingly discovered that silicone formulations employing an oxime silane crosslinker comprising <NUM>-methyl-<NUM>-heptanone oxime exhibit significantly improved early cracking behaviour and/or skin formation time compared to silicone formulations employing conventional oxime silane crosslinkers. Additionally, the <NUM>-methyl-<NUM>-heptanone oxime released during moisture-curing of the silicone formulation has low volatility and may have reduced or no carcinogenic effects and/or malodor compared to known oxime silane crosslinkers such as MEKO silanes.

The present inventors have furthermore found that the improved early cracking behaviour and/or skin formation time may be obtained by employing said oximes as their tri- or tetrafunctional silanes tris(<NUM>-methyl-<NUM>-heptanoneoxime)silane or tetra(<NUM>-methyl-<NUM>-heptanoneoxime)silane as well as when employing <NUM>-methyl-<NUM>-heptanoneoxime as free oxime in combination with any silane or siloxane crosslinker. Without wishing to be bound by any theory, the present inventors believe that the combination of <NUM>-methyl-<NUM>-heptanoneoxime as free oxime with any silane or siloxane crosslinker results in the in-situ formation of a <NUM>-methyl-<NUM>-heptanone oxime silane.

Accordingly, in a first aspect the invention provides a silicone formulation comprising a hydroxy-terminated polydiorganosiloxane and a first crosslinker selected from silanes according to formula (I) and hydrolysis or condensation products thereof:
<CHM>
wherein:.

As will be understood by the skilled person based on the present disclosure, the compound according to formula (I) is an oxime silane crosslinker comprising at least one <NUM>-methyl-<NUM>-heptanone oxime moiety.

In another aspect the present invention provides an oxime silane or siloxane crosslinker selected from silanes according to formula (I) and hydrolysis or condensation products thereof:
<CHM>
wherein:
a, b, c, R<NUM>, R<NUM>, R<NUM> and R<NUM> are as defined herein before.

In another aspect, there is provided a cured silicone elastomer obtainable by curing the silicone formulation as described herein, preferably obtainable by moisture-curing the silicone formulation as described herein.

In another aspect of the invention, there is provided the use of the silicone formulation provided herein, or the cured silicone elastomer provided herein, as a sealant, grouting compound or adhesive, preferably as a sealant.

In another aspect of the invention, various uses of a first crosslinker selected from silanes according to formula (I) and hydrolysis or condensation products thereof as described herein are provided.

In another aspect of the invention there are provided methods for the preparation of the silicone formulations as described herein comprising the steps of:.

Reference is made to substances, components, or ingredients in existence at the time just before first contacted, blended, or mixed with one or more other substances, components, or ingredients in accordance with the present disclosure. A substance, component or ingredient may gain an identity, property, or character through a chemical reaction or transformation during the course of contacting, blending, or mixing if conducted in accordance with this disclosure with the application of common sense and the ordinary skills of an average chemist. Unless otherwise indicated herein, definitions of substances, components, or ingredients and their relative amounts concern the composition as it is prepared at the time of first contacting the ingredients, unless expressly indicated otherwise. For example, it is well known to the skilled person that contacting a hydroxy-terminated polydiorganosiloxane as described herein with a silane crosslinker as described herein may result in end-capping of the polydiorganosiloxane. As explained herein elsewhere, end-capping is typically performed on purpose by blending the polydiorganosiloxane with the crosslinker and optionally a catalyst before addition of the remaining ingredients. Any time the present disclosure references a composition or the preparation of a composition comprising a hydroxy-terminated polydiorganosiloxane, a crosslinker and optionally further ingredients, unless indicated otherwise this expressly includes compositions wherein the hydroxy-terminated polydiorganosiloxane has been end-capped with a crosslinker or with the crosslinker referenced in the composition.

In a first aspect, the invention provides a silicone formulation comprising a hydroxy-terminated polydiorganosiloxane and a first crosslinker selected from silanes according to formula (I) and hydrolysis or condensation products thereof:
<CHM>
wherein:.

In an embodiment, the silicone formulation as defined herein further comprises a catalyst, preferably an organometal catalyst which is present in an amount of <NUM>-<NUM> wt. % (by total weight of the silicone formulation).

As explained herein before and as shown in the examples, the present inventors have found that silicone formulations employing a crosslinker selected from silanes according to formula (I) possess several particular and advantageous properties, such as a reduced or even no early cracking behaviour, increased skin formation time, reduced generation of hazardous (e.g. carcinogenic) compounds or odor during curing.

As is known to the skilled person, silane crosslinkers may be employed as such, or may be (partially) hydrolysed and/or condensed to form corresponding short-chain polysiloxanes. Such hydrolysis and/or condensation often already occurs to some extent due to interaction of the silane crosslinker with trace amounts of water before, during or after preparing the silicone formulation. Hence, it will be understood by the skilled person that the silane crosslinkers described herein may be provided as such or in the form of a hydrolysis or condensation product thereof. In highly preferred embodiments, the first crosslinker selected from silanes according to formula (I) and hydrolysis or condensation products thereof is selected from silanes according to formula (I).

In preferred embodiments according to the invention, the silicone formulation comprising a first crosslinker selected from silanes according to formula (I) and hydrolysis or condensation products thereof as described herein is provided wherein:.

In a particularly preferred embodiment according to the invention, the silicone formulation comprising a first crosslinker selected from silanes according to formula (I) and hydrolysis or condensation products thereof as described herein is provided wherein:.

As will be understood by the skilled person based on the present disclosure, this embodiment corresponds to employing the oximes according to the invention as a trifunctional tris(<NUM>-methyl-<NUM>-heptanoneoxime)silane or as the tetrafunctional tetra(<NUM>-methyl-<NUM>-heptanoneoxime)silane. Furthermore, the inventors have found that using these oximes in the form of their trifunctional methyl silanes (i.e. R<NUM> is methyl) has the additional advantage that the skinning time is increased compared to the corresponding vinyl silanes (i.e. R<NUM> is vinyl) and that the cured silicones are not sticky. The latter is in particular an issue with the corresponding phenyl silanes (i.e. R<NUM> is phenyl) which remain sticky for a long time after curing.

In a highly preferred embodiment according the invention, the silicone formulation comprising a first crosslinker selected from silanes according to formula (I) and hydrolysis or condensation products thereof as described herein is provided wherein the first crosslinker selected from silanes according to formula (I) and hydrolysis or condensation products thereof is a tris(<NUM>-methyl-<NUM>-heptanoneoxime)silane, preferably a tris(<NUM>-methyl-<NUM>-heptanoneoxime)silane selected from the group consisting of methyl tris(<NUM>-methyl-<NUM>-heptanoneoxime)silane, vinyl tris(<NUM>-methyl-<NUM>-heptanoneoxime)silane and phenyl tris(<NUM>-methyl-<NUM>-heptanoneoxime)silane, most preferably methyl tris(<NUM>-methyl-<NUM>-heptanoneoxime)silane.

In a highly preferred embodiment according the invention, the silicone formulation comprising a first crosslinker selected from silanes according to formula (I) and hydrolysis or condensation products thereof as described herein is provided wherein the first crosslinker selected from silanes according to formula (I) and hydrolysis or condensation products thereof is tetra(<NUM>-methyl-<NUM>-heptanoneoxime)silane.

As will be understood by the skilled person based on the present disclosure, this embodiment corresponds to employing <NUM>-methyl-<NUM>-heptanone as free oxime in combination with a silane or siloxane crosslinker. Without wishing to be bound by any theory, the present inventors believe that the combination of <NUM>-methyl-<NUM>-heptanone as free oxime with a silane or siloxane crosslinker results in the in-situ formation of a <NUM>-methyl-<NUM>-heptanone oxime silane or siloxane.

The present inventors have found that the combination of <NUM>-methyl-<NUM>-heptanone as free oxime with an oxime silane or siloxane crosslinker is particularly advantageous. As is shown in the examples, the combination with <NUM>-pentanonoxime silanes (also referred to as methylpropyl-ketoximosilanes) has been found to be most preferred, resulting in a silicone formulation which has a longer skinning time, improved early cracking properties, and improved mechanical properties (Elasticity modulus, elongation at break and/or shore A hardness). Hence in preferred embodiments according to the invention, the silicone formulation comprising a first crosslinker selected from silanes according to formula (I) and hydrolysis or condensation products thereof as described herein is provided wherein.

In preferred embodiments according to the invention, the silicone formulation comprising a first crosslinker selected from silanes according to formula (I) and hydrolysis or condensation products thereof as described herein is provided wherein the total amount of silanes according to formula (I) and hydrolysis or condensation products thereof is in the range of <NUM> to <NUM> wt. % (by total weight of the silicone formulation), preferably in the range of <NUM> to <NUM> wt. %, more preferably in the range of <NUM>-<NUM> wt.

In highly preferred embodiments according to the invention, the silicone formulation as described herein is provided wherein the hydroxy-terminated polydiorganosiloxane is at least partially end-capped with the first crosslinker.

The silicone formulations according to the invention may comprise one or more additional crosslinking agents. In some embodiments of the invention, the silicone formulation comprising a first crosslinker selected from silanes according to formula (I) and hydrolysis or condensation products thereof described herein is provided further comprising a second silane or siloxane crosslinker.

In preferred embodiments of the invention, the silicone formulation comprising a first crosslinker selected from silanes according to formula (I) and hydrolysis or condensation products thereof described herein is provided further comprising a second silane or siloxane crosslinker selected from silanes according to formula (II) and hydrolysis or condensation products thereof:
<CHM>
wherein.

As will be appreciated by those skilled in the art, the second silane or siloxane crosslinker selected from silanes according to formula (II) and hydrolysis or condensation products thereof is different from the first crosslinker selected from silanes according to formula (I) and hydrolysis or condensation products thereof.

As will be shown in the appended examples, the present inventors have found that the combination of a first crosslinker selected from silanes according to formula (I) and hydrolysis or condensation products thereof as described herein with a second silane or siloxane crosslinker selected from tris-(methylpropylketoximo)methylsilane, tris-(methylpropylketoximo)vinylsilane, and tris-(methylpropylketoximo)phenylsilane, in particular tris-(methylpropylketoximo)methylsilane is especially advantageous and allows the provision of a formulation having sufficiently long skinning time, little or no early cracking and good mechanical properties. Similar formulations employing conventional crosslinkers such as methyl tris(acetone oximo)silane or methyl tris(methyl ethyl ketoximo)silane as second silane or siloxane crosslinker were found to have inferior properties, in particular in relation to the skinning time and/or the mechanical properties and/or to require larger amounts of the first crosslinker to exhibit satisfactory properties.

In embodiments according to the invention, the silicone formulation comprising a first crosslinker selected from silanes according to formula (I) and hydrolysis or condensation products thereof described herein is provided further comprising a second silane or siloxane crosslinker selected from silanes according to formula (II) and hydrolysis or condensation products thereof wherein the silane according to formula (II) is selected from the group consisting of methyltrimethoxysilane, chloromethyltrimethoxysilane, ethyltrimethoxysilane, propyltrimethoxysilane, vinyltrimethoxysilane, methyltriethoxysilane, vinyltriethoxysilane, phenyltriethoxysilane, methyltripropoxysilane, phenyltripropoxysilane, tetramethoxysilane, tetraethoxysilane, tetra-n-propoxysilane, tetra-n-butoxysilane, <NUM>-aminoethyl-<NUM>-aminopropyltrimethoxysilane, <NUM>-aminoethyl-<NUM>-aminopropyltriethoxysilane, N-phenylaminomethyltrimethoxysilane, <NUM>-glycidyloxypropyltrimethoxysilane, bis-(N-methylacetamido)methylethoxysilane, tris-(methylethylketoximo)methylsilane, tris-(methylethylketoximo)vinylsilane, tris-(methylethylketoximo)phenylsilane, tris-(methylpropylketoximo)methylsilane, tris-(methylpropylketoximo)vinylsilane, tris-(methylpropylketoximo)phenylsilane, N,N-bis-(triethoxysilylpropyl)amine, N,N-bis-(trimethoxysilylpropyl)amine, <NUM>,<NUM>-bis-(triethoxysilyl) ethane and combinations thereof, preferably selecteed from the group consisting of tris-(methylpropylketoximo)methylsilane, tris-(methylpropylketoximo)vinylsilane, and tris-(methylpropylketoximo)phenylsilane, most preferably selected from the group consisting of tris-(methylpropylketoximo)methylsilane.

In highly preferred embodiments of the invention, the silicone formulation described herein is provided comprising a first crosslinker selected from silanes according to formula (I) as described herein and hydrolysis or condensation products thereof and a second silane or siloxane crosslinker according to formula (II) as described herein, wherein the weight ratio of the second crosslinker to the first crosslinker is in the range of <NUM> to <NUM>, preferably in the range of <NUM> to <NUM>, more preferably within the range of <NUM> to <NUM>, most preferably within the range of <NUM> to <NUM>.

In highly preferred embodiments of the invention, the silicone formulation described herein is provided comprising a first crosslinker selected from silanes according to formula (I) as described herein and hydrolysis or condensation products thereof and a second silane or siloxane crosslinker selected from silanes according to formula (II) as described herein and hydrolysis or condensation products thereof, wherein the weight ratio of the second crosslinker to the first crosslinker is in the range of <NUM> to <NUM>, preferably in the range of <NUM> to <NUM>, more preferably within the range of <NUM> to <NUM>, most preferably within the range of <NUM> to <NUM>; and wherein the total amount of silane or siloxane crosslinkers is within the range of <NUM>-<NUM> wt. % (by total weight of the silicone formulation), preferably within the range of <NUM>-<NUM> wt. %, most preferably within the range of <NUM>-<NUM> wt.

As will be understood by the skilled person based on the present disclosure, in case the first crosslinker selected from silanes according to formula (I) and hydrolysis or condensation products thereof is prepared in situ by combining <NUM>-methyl-<NUM>-heptanone as free oxime in combination with a silane or siloxane crosslinker, the silicone formulation will inevitably comprise a second silane or siloxane crosslinker (i.e. the unreacted portion of the silane or siloxane crosslinker used to generate the silane according to formula (I)).

In highly preferred embodiments according to the invention, the silicone formulation described herein is provided comprising a first crosslinker selected from silanes according to formula (I) as described herein and hydrolysis or condensation products thereof and a second silane or siloxane crosslinker selected from silanes according to formula (II) as described herein and hydrolysis or condensation products thereof, wherein the hydroxy-terminated polydiorganosiloxane is at least partially end-capped with the first crosslinker and the second crosslinker. More preferably, substantially all terminal hydroxy groups of the polydiorganosiloxane have been end-capped with the first crosslinker or the second crosslinker.

As explained herein before, the present inventors have found that the improved early cracking behaviour and/or skin formation time may also be obtained by employing <NUM>-methyl-<NUM>-heptanone as free oxime in combination with any silane or siloxane crosslinker. Without wishing to be bound by any theory, the present inventors believe that the combination of <NUM>-methyl-<NUM>-heptanoneoxime as free oxime with any silane or siloxane crosslinker results in the in-situ formation of a <NUM>-methyl-<NUM>-heptanone oxime bearing silane.

According to the invention, the hydroxy-terminated polydiorganosiloxane included in the silicone formulations described herein may be any linear or branched polydiorganosiloxane conventionally used in silicone formulations and is not particularly limited.

In embodiments according to the invention, the hydroxy-terminated polydiorganosiloxane comprises repeating diorganosiloxane units having the structure [-SiRaRb-O-]n wherein n is such that the dynamic viscosity at <NUM> of the resulting polymer is in the range of <NUM> and <NUM> mPa s and wherein Ra and Rb are independently selected from the group consisting of methyl, ethyl, propyl, butyl, phenyl, methylphenyl, ethylphenyl, vinyl, ally, cyclohexyl, tolyl, isopropyl chloropropyl, <NUM>,<NUM>,<NUM>-trifluoropropyl, chlorophenyl, beta-(perfluorobutyl)ethyl and chlorocyclohexyl, preferably Ra and Rb are independently selected from the group consisting of methyl, ethyl, phenyl, vinyl or <NUM>,<NUM>,<NUM>-trifluoropropyl, most preferably Ra and Rb are methyl.

In preferred embodiments of the invention, the hydroxy-terminated polydiorganosiloxane is a hydroxy-terminated polydialkylsiloxane, preferably hydroxy-terminated polydimethylsiloxane.

In preferred embodiments of the invention the hydroxy-terminated polydiorganosiloxane has a dynamic viscosity at <NUM> of at least <NUM> mPa s, preferably at least <NUM> mPa s, more preferably at least <NUM> mPa·s.

In preferred embodiments of the invention the hydroxy-terminated polydiorganosiloxane has a dynamic viscosity at <NUM> of less than <NUM> mPa s, preferably less than <NUM> mPa s, more preferably less than <NUM> mPa s.

Hence, in highly preferred embodiments of the invention the hydroxy-terminated polydiorganosiloxane is a hydroxy-terminated polydialkylsiloxane, preferably a hydroxy-terminated polydimethylsiloxane, having a dynamic viscosity at <NUM> within the range of <NUM>-<NUM> mPa s, more preferably <NUM>-<NUM> mPa s, most preferably <NUM>-<NUM> mPa s.

The determination of the dynamic viscosity of polysiloxanes is known to the skilled person. A preferred method to determine the dynamic viscosity of the hydroxy-terminated polydiorganosiloxane is in accordance with DIN53019-<NUM>(<NUM>).

In preferred embodiments of the invention the hydroxy-terminated polydiorganosiloxane as described herein is present in an amount of more than <NUM> wt. % (by total weight of the silicone formulation), preferably more than <NUM> wt. %, more preferably more than <NUM> wt.

In embodiments of the invention the total amount of any hydroxy-terminated polydiorganosiloxanes present in the formulation is within the range of <NUM>-<NUM> wt. % (by total weight of the silicone formulation), preferably <NUM>-<NUM> wt. %, more preferably <NUM>-<NUM> wt.

According to the invention, the silicone formulations described herein may further comprise a catalyst. In a very preferred embodiment, the catalyst is an organometal catalyst which is present in an amount of <NUM>-<NUM> wt. % (by total weight of the silicone formulation). The catalyst may be any catalyst conventionally used in silicone formulations, such as organic bases, metal complexes, amines and/or carbenes and is not particularly limited.

Examples of suitable organic bases are guanidine or amidines, such as C<NUM>-C<NUM> alkyl amidines.

Examples of suitable metal complexes, preferably organometal complexes, are metal complexes wherein the metal is selected from the group consisting of Al, Bi, Co, Fe, Ga, La, Mn, Pb, Pd, Pt, Rh, Sc, Sn, Sr, Ti, TI, Y, Zn, and Zr, more preferably wherein the metal is selected from the group consisting of Ti(IV), Sn(II), Sn(IV), Bi(III), Zn(ll) and Zr(IV). Suitable complexing groups include for example alkyl groups, such as C<NUM>-C<NUM> alkyl groups, and carboxylates, such as C<NUM>-C<NUM> carboxylates.

Examples of suitable amines include secondary amines and tertiary amines, such as diazabicyclo-undecenes.

Suitable catalysts are e.g. the catalysts which are available under the brand name TIB KAT®, such as types <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM> and <NUM> from the company TIB Chemicals AG.

In preferred embodiments of the invention the silicone formulations described herein are provided further comprising a catalyst which is an organometal catalyst wherein the metal is selected from the group consisting of Al, Bi, Co, Fe, Ga, La, Mn, Pb, Pd, Pt, Rh, Sc, Sn, Sr, Ti, TI, Y, Zn, and Zr, more preferably comprising a catalyst which is an organotin compound, more preferably an organotin compound selected from the group consisting of dimethyltin di-<NUM>-ethylhexanoate, dimethyltin dilaurate, di-n-butyltin diacetate, di-n-butyltin di-<NUM>-ethylhexanoate, din-butyltin dicaprylate, di-n-butyltin di-<NUM>,<NUM>-dimethyloctanoate, di-n-butyltin dilaurate, di-n-butyltin distearate, di-n-butyltin dimaleate, di-n-butyltin dioleate, di-n-octyltin di-<NUM>-ethylhexanoate, di-n-octytin di-<NUM>,<NUM>-dimethyloctanoate, di-n-octyltin dimaleate, di-n-octyltin dilaurate, di-n-butyltin oxide, and di-n-octyltin oxide, most preferably di-n-octyltin oxide.

In preferred embodiments of the invention, the silicone formulations described herein are provided further comprising a catalyst as described herein, preferably an organometal catalyst as described herein wherein the catalyst is present in an amount of more than <NUM> wt. % (by total weight of the silicone formulation), preferably more than <NUM> wt. %, more preferably more than <NUM> wt.

In preferred embodiments of the invention, the silicone formulations described herein are provided further comprising a catalyst as described herein wherein the catalyst is present in an amount of less than <NUM> wt. % (by total weight of the silicone formulation), preferably less than <NUM> wt. %, more preferably less than <NUM> wt.

In preferred embodiments of the invention, the silicone formulations described herein are provided further comprising a catalyst as described herein wherein the catalyst is present in an amount within the range of <NUM>-<NUM> wt. % (by total weight of the silicone formulation), preferably within the range of <NUM>-<NUM> wt. %, more preferably within the range of <NUM>-<NUM> wt.

In accordance with the invention, the total combined amount of metal catalysts present is less than <NUM> wt. % (by total weight of the silicone formulation), preferably less than <NUM> wt.

According to the invention, the silicone formulations described herein may further comprise a filler. The filler may be any filler conventionally used in silicone formulations and is not particularly limited. As used herein, the term filler is meant to encompass reinforcing fillers (e.g. fumed silica, precipitated calcium carbonate or carbon black) as well as non-reinforcing fillers (e.g. ground calcium carbonate). Fillers may also function as rheology modifiers and vice versa (e.g. fumed silica).

In accordance with preferred embodiments of the invention, the silicone formulations described herein are provided further comprising a filler which is also a thickening agent. A preferred filler which is also a thickening agent is silica, also called silicic acid. Silicic acid is a weak acid derived from silicon dioxide, SiOz, having as general formula SiO<NUM>. nH<NUM>O, whereby n may differ. Silicic acid is preferred because it bonds/interacts with the backbone of the polymer, bringing a significant enhancement of the physical and mechanical properties of the final product. The inventors have found that various forms of silica may be used as thickener, but fumed silica (also called "pyrogenic silica") is preferred because of its superior effect on mechanical properties of the final cured product (such as the tear strength). Suitable fillers which function as thickening agent are e.g. available as HDK® V15, V15A, N20, H13L, H15, H18 from the company Wacker, as Cabosil® L-<NUM>, LM-<NUM>, M-<NUM>, TS-<NUM>, TS-<NUM> from the company Cabott, as Aerosil® <NUM>, <NUM>, <NUM>, R972, R974 from Evonik.

In preferred embodiments of the invention, the silicone formulations described herein are provided further comprising a filler selected from the group consisting of mineral fillers, metal oxide fillers, fly ash, bottom ash, carbon black, and combinations thereof, preferably selected from the group consisting of: chalk, calcium hydroxide; natural, ground or precipitated calcium carbonates; dolomites; fumed silica; carbon black; calcined kaolins; boehmite; clay; talc; aluminium silicates; magnesium aluminium silicates; zirconium silicates; finely ground quartz; finely ground cristobalite; diatomaceous earth; mica; iron oxides; titanium oxides; zirconium oxide and combinations thereof, more preferably selected from the group consisting of chalk, dolomite, fumed silica and combinations thereof.

The filler may be surface modified. Surface modification of fillers is known to the skilled person. Preferred surface modifications include surface treatment with a fatty acid (e.g. stearic acid) or a silane (e.g. an alkoxysilane). The filler may be a reinforcing filler which has a BET surface area of <NUM> to <NUM><NUM>/g, preferably <NUM> to <NUM><NUM>/g, more preferably <NUM> to <NUM><NUM>/g. The filler may be a non-reinforcing filler or semi-reinforcing filler, which has a BET surface area of <NUM> to <NUM><NUM>/g, preferably <NUM> to <NUM><NUM>/g, more preferably <NUM> to <NUM><NUM>/g.

In preferred embodiments of the invention the silicone formulations described herein are provided further comprising a filler as described herein wherein the filler is present in an amount of more than <NUM> wt. % (by total weight of the silicone formulation), preferably more than <NUM> wt. %, more preferably more than <NUM> wt.

In preferred embodiments of the invention the silicone formulations described herein are provided further comprising a filler as described herein wherein the filler is present in an amount of less than <NUM> wt. % (by total weight of the silicone formulation), preferably less than <NUM> wt. %, more preferably less than <NUM> wt.

In preferred embodiments of the invention the silicone formulations described herein are provided further comprising a filler as described herein wherein the filler is present in an amount within the range of <NUM>-<NUM> wt. % (by total weight of the silicone formulation), preferably within the range of <NUM>-<NUM> wt. %, more preferably within the range of <NUM>-<NUM> wt.

In other preferred embodiments of the invention, the silicone formulations described herein further comprise <NUM>-<NUM> wt. % (by total weight of the silicone formulation), preferably within the range of <NUM>-<NUM> wt. %, more preferably within the range of <NUM>-<NUM> wt. % of a filler selected from the group consisting of mineral fillers, metal oxide fillers, fly ash, bottom ash, carbon black, and combinations thereof, preferably selected from the group consisting of: calcium hydroxide; natural, ground or precipitated calcium carbonates; dolomites; fumed silica; carbon black; calcined kaolins; boehmite; clay; talc aluminium silicates; magnesium aluminium silicates; zirconium silicates; finely ground quartz; finely ground cristobalite; diatomaceous earth; mica; iron oxides; titanium oxides; zirconium oxide, more preferably selected from the group consisting of dolomite and fumed silica.

In accordance with the invention, the total combined amount of fillers present is less than <NUM> wt. % (by total weight of the silicone formulation), preferably less than <NUM> wt.

According to the invention, the silicone formulations described herein may further comprise an adhesion promotor. The adhesion promotor may be any adhesion promotor conventionally used in silicone formulations and is not particularly limited.

In preferred embodiments of the invention, the silicone formulations described herein are provided further comprising an organosilane adhesion promotor selected from the group consisting of aminosilanes, alkoxysilanes and epoxysilanes, preferably selected from the group consisting of aminoalkyltrialkoxysilanes, aminoalkylalkyldialkoxysilanes, bis(alkyltrialkoxysilyl)amines, tris(alkyltrialkoxysilyl)amines, tris(alkyltrialkoxysilyl)cyanuarates, tris (alkyl-trialkoxy-silyl)isocyanuarates, alkoxy terminated polydimethylsiloxanes comprising aminoalkyl sidegroups (such as ethoxy terminated (<NUM>-aminopropyl)(methyl)polysiloxane)), hydroxy-terminated polydimethylsiloxane end-capped with N-(<NUM>-trimethoxysilyl) propyl cyclohexane amine, condensation products of any of the recited silanes, and combinations thereof. Preferably the alkyl group is a C<NUM>-C<NUM> alkyl and the alkoxy group is a C<NUM>-C<NUM> alkoxy.

In highly preferred embodiments of the invention, the silicone formulations described herein are provided further comprising an adhesion promotor which is selected from the group consisting of <NUM>-aminopropyl triethoxy silane, <NUM>-aminopropyl trimethoxy silane, N-(<NUM>-aminoethyl)-<NUM>-aminopropyl trimethoxy silane, <NUM>-(<NUM>-amino¬ethylamino)propyl triacetoxy silane, N-(<NUM>-trimethoxysilylpropyl) diethylene-triamine, bis-(<NUM>-methoxysilylpropyl)-amine, amino ethylaminopropyl methyl dimethoxy silane, N-(<NUM>-aminoethyl)-<NUM>-aminopropyl dimethoxy methyl silane, N-(n-butyl)-<NUM>-aminopropyl trimethoxy silane, N-(n-butyl)-<NUM>-aminopropyl trimethoxy silane, <NUM>-aminopropyl methyl diethoxy silane, amino ethyl amino trimethoxy silane, <NUM>-glycidoxypropyl trimethoxy silane, <NUM>-glycidoxypropyl triethoxy silane, gamma-ureidopropyl trimethoxy-silane, <NUM>-aminopropyl (methyl) silsesquioxanes and combinations thereof.

Suitable adhesion promoters may e.g. be found in the families of products that are offered as Geniosil® from the company Wacker, as Silquest® from Momentive Performance Materials, and as Dynasylan® from Evonik.

In preferred embodiments of the invention, the silicone formulations described herein are provided further comprising an adhesion promotor as described herein wherein the adhesion promotor is present in an amount of more than <NUM> wt. % (by total weight of the silicone formulation), preferably more than <NUM> wt. %, more preferably more than <NUM> wt.

In preferred embodiments of the invention, the silicone formulations described herein are provided further comprising an adhesion promotor as described herein wherein the adhesion promotor is present in an amount of less than <NUM> wt. % (by total weight of the silicone formulation), preferably less than <NUM> wt. %, more preferably less than <NUM> wt.

In preferred embodiments of the invention, the silicone formulations described herein are provided further comprising an adhesion promotor as described herein wherein the adhesion promotor is present in an amount within the range of <NUM>-<NUM> wt. % (by total weight of the silicone formulation), preferably within the range of <NUM>-<NUM> wt. %, more preferably within the range of <NUM>-<NUM> wt.

In accordance with the invention, the total combined amount of adhesion promotors present is less than <NUM> wt. % (by total weight of the silicone formulation), preferably less than <NUM> wt.

According to the invention, the silicone formulations described herein may further comprise a plasticiser. The plasticiser may be any plasticiser conventionally used in silicone formulations and is not particularly limited. Preferred plasticizers are silicon oils, which may be partially or completely replaced by C<NUM>-C<NUM> hydrocarbons.

Hence, in preferred embodiments of the invention, the silicone formulations described herein are provided further comprising a plasticizer which is a linear or branched polydialkylsiloxane which contains two or less hydrolyzable Si-O bonds, preferably a plasticizer which is a trialkylsilyl-terminated polydialkylsiloxane, preferably a trimethylsilyl-terminated polydimethylsiloxane. Said linear or branched polydialkylsiloxane preferably has a dynamic viscosity at <NUM> in the range of <NUM>-<NUM> mPa s, preferably a viscosity in the range of <NUM>-<NUM> mPa·s.

In preferred embodiments of the invention, the silicone formulations described herein are provided further comprising a hydrocarbon plasticizer consisting of one or more C<NUM>-C<NUM> hydrocarbons, preferably consisting of one or more C<NUM>-C<NUM> hydrocarbons. Preferably said hydrocarbon plasticizer comprses <10wt. % (by total weight of hydrocarbon plasticizer) aromatics, preferably less than <NUM> wt. % aromatics.

Such products are, for example, offered as Exxsol® D60, D80, D100, D120, or D140, or as Isopar® H, J, K, L, M, N, or V from the company ExxonMobil Chemical, or Ketrul® D100, Hydroseal® G232H, G240H, G3H , G250H, G270H, G400H, G310H, G315H, G340H from the company Total, or Shellsol® D60, D80, D100 from the company Shell, Pilot® <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM> from the company Petrochem Carless, or Nyflex® <NUM>, <NUM>, <NUM> from the company Nynas.

In embodiments of the invention, the silicone formulations described herein are provided further comprising a plasticizer which is an alkyl endcapped poly(alkylene)glycol, preferably C<NUM>-C<NUM> endcapped polyethylene or polypropylene glycol.

In preferred embodiments of the invention, the silicone formulations described herein are provided further comprising a plasticizer as described herein wherein the plasticizer is present in an amount of more than <NUM> wt. % (by total weight of the silicone formulation), preferably more than <NUM> wt. %, more preferably more than <NUM> wt.

In preferred embodiments of the invention, the silicone formulations described herein are provided further comprising a plasticizer as described herein wherein the plasticizer is present in an amount of less than <NUM> wt. % (by total weight of the silicone formulation), preferably less than <NUM> wt. %, more preferably less than <NUM> wt.

In preferred embodiments of the invention, the silicone formulations described herein are provided further comprising a plasticizer as described herein wherein the plasticizer is present in an amount within the range of <NUM>-<NUM> wt. % (by total weight of the silicone formulation), preferably within the range of <NUM>-<NUM> wt. %, more preferably within the range of <NUM>-<NUM> wt. % by total weight of the silicone formulation.

In accordance with the invention, the total combined amount of plasticizers present is less than <NUM> wt. % (by total weight of the silicone formulation), preferably less than <NUM> wt.

As will be understood by the skilled person, the silicone formulations described herein may comprise further ingredients (such as biocides, pigments, etc.) and the combined amount of all ingredients employed in the silicone formulations is <NUM> wt. % (by total weight of the silicone formulation).

In preferred embodiments according to the invention the silicone formulations described herein are provided wherein the total combined amount of any silane or siloxane crosslinker present is in the range of <NUM> to <NUM> wt. % (by total weight of the silicone formulation), preferably in the range of <NUM> to <NUM> wt. %, more preferably in the range of <NUM>-<NUM> wt.

In highly preferred embodiments according to the invention, the formulations provided herein are room temperature (e.g. <NUM>) vulcanizable, preferably under the influence of moisture and thus moisture-curable. In even more preferred embodiments according to the invention, the formulations provided herein are moisture-curable, one component room temperature vulcanizable (RTV1) silicone sealant formulations.

As will be appreciated by the skilled person, the silicone formulations described herein may be provided as one or multi-component (e.g. two-component) systems. The silicone formulations described herein are preferably one component systems.

In the event that the silicone formulations described herein are provided as a multi-component system, it is to be understood that the relative amounts of the ingredients as defined throughout the present disclosure are calculated based on the total formulation as if the different components were combined.

The present inventors have found that while silane or siloxane crosslinkers comprising at least one vinyl group (e.g. tris(alkoxy)vinylsilane or tris(alkoxime)vinylsilane) may be employed to improve the early cracking behaviour of known oxime silane or siloxane crosslinkers, the silicone formulation of the present invention require less or even no silane or siloxane crosslinkers comprising at least one vinyl group in order to be free of early cracking. The compositions of the present invention thus not only increase skinning time, improve early cracking behaviour and improve one or more mechanical properties as explained herein elsewhere, they also allow a reduced amount of silane or siloxane crosslinkers comprising at least one vinyl group to be used, resulting additional advantages, such as a cost reduction, and reduced or no gelling during end-capping (which is a typical issue with vinyl silanes). Hence, in preferred embodiments of the invention, the silicone formulations described herein are provided comprising less than <NUM> wt. % silane or siloxane crosslinkers comprising at least one vinyl group (by total weight of the silicone formulation), preferably less than <NUM> wt. %, more preferably less than <NUM> wt. In a highly preferred embodiment the silicone formulation is substantially free of a vinyl substituted silane or siloxane crosslinker. Similarly, the use of phenyl silanes can be avoided, such that in preferred embodiments of the invention the silicone formulations described herein are provided comprising less than <NUM> wt. % silane or siloxane crosslinkers comprising at least one phenyl group (by total weight of the silicone formulation), preferably less than <NUM> wt. %, more preferably less than <NUM> wt. In a highly preferred embodiment the silicone formulation is substantially free of a phenyl substituted silane or siloxane crosslinker. Preferably, the silicone formulations described herein are provided with low vinyl substituted silane or siloxane crosslinker and low phenyl substituted silane or siloxane crosslinker.

Furthermore, according to preferred embodiments of the invention, the silicone formulations described herein are provided having one or both of the following characteristics:.

In accordance with the invention, the skinning time is determined according to the following method, performed at room temperature (about <NUM>) and about <NUM>% Relative humidity:.

In accordance with the invention the early cracking time is determined according to the following method, performed at room temperature (about <NUM>) and about <NUM>% Relative humidity:.

If no ruptures or cracks visible to the naked eye are formed in the bending line after <NUM> minutes of testing, the system is considered to display no early cracking.

As explained throughout the disclosure, the present inventors have found that the particular silanes comprising <NUM>-methyl-<NUM>-heptanone oxime are useful as crosslinking agent in silicone formulations, especially silicone sealant formulations. Hence, in another aspect the present invention provides an oxime silane or siloxane crosslinker selected from silanes according to formula (I) and hydrolysis or condensation products thereof:
<CHM>
wherein:.

In preferred embodiments according to the invention, the oxime silane or siloxane crosslinker selected from silanes according to formula (I) and hydrolysis or condensation products thereof is provided wherein:.

In highly preferred embodiments according to the invention, the oxime silane or siloxane crosslinker selected from silanes according to formula (I) and hydrolysis or condensation products thereof is provided wherein:.

Hence, in highly preferred embodiments according to the invention, the oxime silane or siloxane crosslinker selected from silanes according to formula (I) and hydrolysis or condensation products thereof, preferably selected from silanes according to formula (I) is provided wherein the silane according to formula (I) is a tris(<NUM>-methyl-<NUM>-heptanoneoxime)silane, preferably methyl tris(<NUM>-methyl-<NUM>-heptanoneoxime)silane, vinyl tris(<NUM>-methyl-<NUM>-heptanoneoxime)silane or phenyl tris(<NUM>-methyl-<NUM>-heptanoneoxime)silane, most preferably methyl tris(<NUM>-methyl-<NUM>-heptanoneoxime)silane.

In more preferred embodiments according to the invention, the oxime silane or siloxane crosslinker selected from silanes according to formula (I) and hydrolysis or condensation products thereof is provided wherein:.

In a further aspect of the invention, there is provided a cured silicone formulation obtainable by curing a silicone formulation as described herein, preferably by moisture-curing a silicone formulation as described herein. In a preferred embodiment of the invention there is provided a cured silicone formulation obtainable by curing a silicone formulation as described herein at a temperature within the range of <NUM>-<NUM>, preferably by moisture-curing a silicone formulation as described herein at a temperature within the range of <NUM>-<NUM>.

In preferred embodiments according to the invention, there is provided a cured silicone formulation as described herein which has one, two, three or four of the following characteristics:.

wherein the elastic modulus, tensile strength and elongation at break are determined in accordance with DIN53504 (<NUM>-<NUM>) using a film thickness of <NUM> cured for <NUM> week at room temperature (<NUM>) and the shore A hardness is determined in accordance with ISO868 (<NUM>) using a film thickness of <NUM>.

In a further aspect of the invention, there is provided the use of the silicone formulation as described herein, or the cured silicone formulation as described herein, as a sealant, grouting compound or adhesive, preferably as a sealant.

In a further aspect of the invention, there is provided the use of a first crosslinker selected from silanes according to formula (I) and hydrolysis or condensation products thereof as described herein, to improve early cracking behaviour and/or to increase skin formation time of a silicone formulation.

The invention also provides the use of a crosslinker selected from silanes according to formula (I) and hydrolysis or condensation products thereof as described herein, to reduce the amount of vinyl silane employed in a silicone formulation.

The invention also provides the use of a crosslinker selected from silanes according to formula (I) and hydrolysis or condensation products thereof as described herein, to reduce the carcinogenicity of a silicone formulation, preferably while maintaining or improving early cracking behaviour and/or to increase skin formation time.

The invention also provides the use of a crosslinker selected from silanes according to formula (I) and hydrolysis or condensation products thereof as described herein, to reduce the malodor caused by the curing of a silicone formulation, preferably while maintaining or improving early cracking behaviour and/or skin formation time.

In accordance with the preferred embodiments for the crosslinker described herein, the uses described herein preferably concern the use of a tris(<NUM>-methyl-<NUM>-heptanoneoxime)silane, preferably a tris(<NUM>-methyl-<NUM>-heptanoneoxime)silane selected from the group consisting of methyl tris(<NUM>-methyl-<NUM>-heptanoneoxime)silane, vinyl tris(<NUM>-methyl-<NUM>-heptanoneoxime)silane and phenyl tris(<NUM>-methyl-<NUM>-heptanoneoxime)silane, most preferably methyl tris(<NUM>-methyl-<NUM>-heptanoneoxime)silane.

In another aspect of the invention, there are provided methods for the preparation of the silicone formulations as described herein comprising the steps of:.

Combining the ingredients provided in steps (i) and (ii) may be performed by any conventional means, such as by blending, mixing or stirring, preferably under a moisture-free atmosphere. As will be understood by the skilled person, the method is not to be construed as strictly limited to these ingredients. In case the silicone formulation comprises additional ingredients (e.g. catalysts or fillers as discussed herein), step (iii) may include combining any optional further ingredients in order to obtain a silicone formulation as described herein.

The order of combining is not particularly limited. In preferred embodiments, the compounds provided in step (ii. <NUM>) are first combined, thereby forming a crosslinker preblend, which is subsequently combined with the compound provided in step (i) and any other optional further ingredients provided in step (iii).

As is illustrated in the examples, it is preferred that the ingredients provided in steps (i) and (ii) are combined before addition of optional further ingredients such as catalysts, plasticizers, adhesion promotors, etc. This method results in the so-called end-capping of the siloxane base polymer with the crosslinking agent and provides a more efficient curing of the resulting silicone formulation.

In preferred embodiments the method for the preparation of the silicone formulations as described herein further comprises a step of:
(v) packaging the silicone formulation in an airtight container, such as an aluminium foil or plastic tube.

For a proper understanding of this document and its claims, it is to be understood that the verb `to comprise' and its conjugations are used in its non-limiting sense to mean that items following the word are included, but items not specifically mentioned are not excluded. In addition, reference to an element by the indefinite article 'a' or 'an' does not exclude the possibility that more than one of the element is present, unless the context clearly requires that there be one and only one of the elements. The indefinite article 'a' or 'an' thus usually means 'at least one'.

The terms first, second, third and the like in the description and in the claims, are used for distinguishing between similar elements and not necessarily for describing a sequential or chronological order. The terms are interchangeable under appropriate circumstances and the embodiments of the disclosure can operate in other sequences than described or illustrated herein.

Furthermore, the various embodiments, although referred to as 'preferred' are to be construed as exemplary manners in which the invention may be implemented rather than as limiting the scope of the invention.

The invention will be further illustrated by means of the following examples, which are not intended to limit the scope of the invention in any way.

A series of one-component RTV1 moisture curable silicone sealant formulations comprising different oxime crosslinkers were prepared. The effect of the oxime crosslinker on the mechanical properties, the skinning time and the early cracking behaviour of the silicone formulation was evaluated.

The elastic modulus, tensile strength and elongation at break are determined in accordance with DIN53504 (<NUM>-<NUM>) using a film thickness of <NUM> cured for <NUM> week at room temperature (<NUM>) and the shore A hardness is determined in accordance with ISO868 (<NUM>) using a film thickness of <NUM>. The early cracking time and the skinning time were determined according to the methods described herein earlier.

If no tears or cracks visible to the naked eye are formed in the bending line after <NUM> minutes of testing, the system displays no early cracking.

The sealant formulations comprise the following ingredients: hydroxyl-terminated polydimethylsiloxane (PDMS) having a dynamic viscosity at <NUM> of <NUM> mPa s, PDMS silicone oil having a dynamic viscosity at <NUM> of <NUM> mPa s, an oxime crosslinker as detailed in the following tables, hydrophilic fumed silica having a surface area of <NUM><NUM>/g (filler and thixotropic agent), aminopropyl tris methoxy silane (AMMO) (adhesion promotor) and dioctyl tin oxide (DOTO) (catalyst).

The following oxime crosslinkers and oximes were employed:.

The silicone formulations were prepared with a speed mixer using the following mixing steps:.

As shown in the tables below (wherein examples <NUM>-<NUM>, <NUM>-<NUM>, <NUM>, <NUM> are reference examples, not examples according to the invention) the formulations comprising Me(MAKO)<NUM>Si or Me(trem)<NUM>Si have an increased skinning time and show little or no cracking behaviour. It further demonstrated that a combination of Me(MAKO)<NUM>Si and Me(2PO)<NUM>Si, either added separately or as a preblended mixture to the silicone formulation, also results in a silicone formulation having an increased skinning time and/or showing little or no cracking behaviour and additionally has increased shore A hardness compared to Me(MAKO)<NUM>Si alone. Additionally, it was surprisingly found that even when employed as free oxime, a mixture of Me(2PO)<NUM>Si and MAKO results in a silicone formulation having an increased skinning time and/or showing no cracking behaviour. The Maximum tension as mentioned in the following tables is also referred to herein elsewhere as the Tensile strength.

All compounds employed except Me(trem)<NUM>Si are commercially available and were obtained from various chemical suppliers.

Claim 1:
A silicone formulation comprising a hydroxy-terminated polydiorganosiloxane and a first crosslinker selected from silanes according to formula (I) and hydrolysis or condensation products thereof:
<CHM>
wherein
a is <NUM>, <NUM>, <NUM> or <NUM>
b is <NUM> or <NUM>;
c is <NUM>, <NUM>, <NUM> or <NUM>;
a+b+c is <NUM>;
each occurrence of R<NUM> and R<NUM> is individually selected from the group consisting of hydrogen and optionally substituted monovalent hydrocarbon radicals having from <NUM> to <NUM> carbon atoms; and
R<NUM> and R<NUM> are such that each occurrence of R<NUM> is methyl and R<NUM> is hydrogen.