FR2791693A1 - Adhesion promoter for silicone composition for use as adhesive coatings and adhesives contains organosilane or non-silicone monomer or polymer in association with epoxy group-containing component - Google Patents

Abstract

An adhesion promoter contains a organosilane or non-silicone monomer or polymer in association with an epoxy group-containing component. A promoter consists of a pair of compounds selected from (1) organosilane (1a), optionally alkoxylated, containing at least one 2-6C alkenyl group per molecule, and monomer or polymer (1b) containing no Si atom and having at least one OH and at least one epoxy group in its structure; (2) non-Si polymer (2a), containing at least one OH group and at least one ethylenic unsaturation, and organosilicon compound (2b) containing at least one epoxy radical; and (3) non-Si monomer or polymer (3a), containing at least one OH group and at least one ethylenic unsaturation, and non-Si monomer or polymer (3b) containing at least one OH group and at least one epoxy group; and optional metal M chelate and/or metallic alkoxide of formula M(OJ)n n = valency of M; J = 1-8C linear or branched alkyl; M = Ti, Zr, Ge, Li, Mn, Fe, Al or Mg. Independent claims are also included for (1) silicone composition of cold-vulcanizable type, comprising (a) at least one polyorganosiloxane, having at least two 2-6C alkenyl groups linked to Si per molecule, (b) at least one polyorganosiloxane, having at least two H atoms linked to Si per molecule, (c) at least one catalyst based on at least one metal from Pt group, and d) adhesion promoter as claimed; and (2) the use of promoter as claimed in preparation of silicone compositions having adhesion properties.

Description

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 The invention relates to novel adhesion promoters useful especially in the silicone field.

It relates to the field of silicone compositions developing adhesion properties. The invention applies in particular to crosslinking compositions by hydrosilylation or cold polyaddition (that is to say at room temperature, but whose crosslinking can be accelerated, eg by heat) and comprising an adhesion promoter according to the invention
The invention is more particularly directed to compositions of this type which are in two-component form, and which crosslink by hydrosilylation or polyaddition to produce a thin-film elastomer, used inter alia as a coating, for example for the protection or mechanical reinforcement of various substrates. for example textile (eg fibrous, woven, knitted or non-woven supports), metal (eg aluminum), plastics (eg epoxy resins). It aims in particular their use for the coating of woven substrates in the manufacture of air bags for the protection of vehicle occupants.

 The invention also relates to compositions of this type which can be used as an adhesive. The silicone composition is intended to be applied to the interface of two solids. The adhesion mechanism results from the crosslinking and curing of the silicone composition comprising the adhesion promoter. It can be applied to the different types of materials mentioned with regard to the coating.

 In these two applications, one of the essential properties of the silicone elastomer is its adhesion to its support.

Various agents or adhesion promoters have been proposed in the past.

 Thus, EP-A-0 681 014 describes a silicone composition, applicable in particular as an "airbag" inner coating and consisting of the mixture consisting of: (1) at least one polyorganosiloxane having, per molecule, at least two alkenyl groups, in C2-C6 bonded to silicon,

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(II) at least one polyorganosiloxane having, per molecule, at least two silicon-bonded hydrogen atoms, (III) a catalytically effective amount of at least one catalyst, composed of at least one platinum group metal, (IV) an adhesion promoter, (V) optionally a filler, preferably a mineral filler, (VI) optionally at least one crosslinking inhibitor, (VII) and optionally at least one polyorganosiloxane resin, - in which the adhesion promoter is constituted exclusively by the at least three-membered combination of the following ingredients: (IV.1) at least one alkoxylated organosilane containing, per molecule, at least one C 2 -C 6 alkenyl group, (IV.2) at least one organosilicon compound comprising at least one epoxy radical, (IV.3) at least one metal chelate M and / or a metal alkoxide of general formula: M (OJ) n, with n = valence of M and J = linear or branched C1-C alkyl C8
M being selected from the group consisting of: Ti, Zr, Ge, Li, Mn, Fe, Al and
Mg.

 The availability of various adhesion promoter means in silicone products in general is an important objective for industry in the sector.

 Thus, the applicant has set itself the objective of proposing new adhesion promoters which make it possible, among other things, to ensure the adhesion properties of silicone elastomers, e. g. those intended for the coating of substrates of the type of those described above or intended to serve as an adhesive.

 Another object of the invention is to provide such adhesion promoters which also make it possible to increase the adhesion properties, external and / or internal, that is to say between constituents of the elastomer for which relates to internal adhesion.

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The subject of the present invention is thus an adhesion promoter comprising a pair of compounds selected from the group consisting of: (i) an organosilane, optionally alkoxylated, containing, per molecule, at least one C 2 -C 6 alkenyl group, a monomer or polymer without a silicon atom having in its structure at least one OH and at least one epoxy group; (2i) - a polymer without silicon, having in its structure at least one OH group and at least one ethylenic unsaturation, - an organosilicon compound comprising at least one epoxy radical; (3i) - a monomer or polymer without silicon, having in its structure at least one OH group and at least one ethylenic unsaturation, - a monomer or polymer without silicon, having in its structure at least one OH group and at least one epoxy group , and optionally a metal M chelate and / or metal alkoxide of general formula: M (OJ) n, with n = valence of M and J = linear or branched C1-C8 alkyl, M being chosen from the group consisting of: Ti, Zr, Ge, Li, Mn, Fe, Al and Mg,
The adhesion promoter thus obtained develops good adhesion properties which can be exploited both inside the elastomer obtained after crosslinking (internal adhesion between constituents) and on the outside (adhesion with a support for example). The preferred applications have been described before.

 The polymers are preferably branched polymers and more particularly hyperbranched polymers. These hyperbranched polymers, which include dendrimers, can be described as highly branched molecules in three dimensions and having a tree structure. Dendrimers have a high degree of symmetry, whereas polymers or macromolecules simply called hyperbranched may have some degree of asymmetry within their structure

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 tree. It can be said that the dendrimers are monodisperse or essentially monodisperse macromolecules or hyperbranched polymers.

The hyperbranched dendritic macromolecules or dendrimers are generally formed of a core or nucleus having one or more reaction sites or functions and a number of branch or generation layers, optionally one or more spacer layers, and a layer of terminal functions. The higher the number of layers, the more ramifications and therefore terminal functions.

 Among the hyperbranched polymers, dendrimers and more particularly polyester-based dendrimers are preferred.

 For example, it is possible to use a hyperbranched polyester with alkenyl (ethylenic) functions obtainable from a polymer having at least one carboxyl group and m hydroxyl groups, m being an integer greater than or equal to 3, such that especially 3,4, 5,6, 8,10, 16 or 32. The prepolymer is the condensation product obtained from at least one monomer selected from the group consisting of di-, tri- and poly-hydroxyfunctional monocarboxylic acids. having from 2 to 18 carbon atoms. The condensation product obtained constitutes the prepolymer or may be used as an intermediate condensation product in the context of additional chain extension carried out by the addition of at least one monohydroxyfunctional monocarboxylic acid or an internal ether thereof, namely a lactone having 2 to 24 carbon atoms. The optional addition of a monohydroxyfunctional monocarboxylic acid is carried out by esterification with a molar ratio intermediate condensation product on monohydroxyfunctional monocarboxylic acid of between 1: 1 and at least 1: m. The prepolymer, ie the condensation product with or without additional chain extension, is functionalized (alkenyl functions) by the addition of at least one monomer or polymer having at least one allylic or acrylic unsaturation. The addition is carried out at a molar ratio of prepolymer to allyl or acrylic compound of between 1: 1 and at least 1: m, which leads to the production of a hyperbranched polyester with alkenyl functions having at least one allylic unsaturation or acrylic. For more details, a person skilled in the art can refer to WO-A-97 23 539.

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 It is also possible to use, for example, a hyperbranched polyester with epoxy functions obtainable from a prepolymer having at least one carboxylic group and m hydroxyl groups, m being an integer greater than or equal to 3, such as in particular 3. , 4, 5.6, 8.10, 16.32. The prepolymer is a condensation product obtained by a condensation reaction from at least one monomer selected from the group consisting of di-, tri- and polyhydroxyfunctional monocarboxylic acids having from 2 to 18 carbon atoms. The condensation product obtained constitutes the prepolymer or may be used as an intermediate condensation product for additional chain extension, this elongation being carried out by adding at least one monohydroxyfunctional monocarboxylic acid or an internal ether of this acid, namely a lactone. having 2 to 24 carbon atoms. The optional addition of a monohydroxyfunctional monocarboxylic acid is carried out by esterification at a molar ratio of intermediate condensation product on monohydroxyfunctional monocarboxylic acid of between 1: 1 and at least 1: m. The prepolymer, namely the condensation product with or without chain extension, is functionalized (epoxy functions) by: - reaction between at least one hydroxyl group of the prepolymer and at least one monomeric or polymeric compound having at least one epoxy group. Suitable compounds are, for example, haloalkyl oxiranes, preferably halomethyl oxiranes such as epichlorohydrin. The reaction is carried out at a prepolymer to monomer or polymer compound molar ratio of from 1: 1 to at least 1: m.

or by addition of at least one unsaturated compound having at least one oxidizable unsaturation, this unsaturation being epoxidized by the use of an oxidizing agent, the addition being carried out at a molar ratio of prepolymer to unsaturated compound of between 1: 1 and1: m.

 For more details, those skilled in the art can refer to WO-A-97 23 538.

 Those skilled in the art will also be able to refer to the documents WO-A-96 12 754, WO-A-97 45474 and the book dendrimers, Club CRIN Hétérochimie, Association ECRIN 1998, 32, bd de Vaugirard 75015 PARIS.

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 Particularly suitable dendritic polymers are those sold by the company PERSTORP, for example under the name G2 and Boltorn U1 for the dendrimers with allyl functions and Boltorn E1 for the epoxy dendrimers.

 The monomers are preferably linear or branched monomers.

 The monomers with unsaturated functional groups may be mono or polyhydric alcohols containing unsaturated ethylenic groups and containing one or more oxygenated heteroatoms. Aliphatic mono or polyhydric alcohols with ether functions are particularly suitable. Among them may be mentioned the following: glycerol monoallyl ether, glycerol diallyl ether, trimethylol ethane monoallyl ether, trimethylol ethane diallyl ether, trimethylolpropane monoallyl ether, trimethylolpropane diallyl ether, pentaerythritol monoallyl ether, pentaerythritol diallyl ether, pentaerythritol triallyl ether and mixtures thereof.

 Also suitable are allyl ethers of monosaccharides or itols (in English sugar alcohols), such as glycosides, galactosides, talitol, mannitol, dulcitol, iditol, sorbitol, arabinitol, xylitol and mixtures thereof. They can also be combined with the aliphatic alcohols mentioned above.

 The preferred monomers are: - trimethylolpropane monoallylether (CAS 682-11-1).

triallylpentaerythritol (CAS 1471-17-6) or pentaerythritol triallyl ether.

 The epoxidized monomers are preferably epoxy alcohols or glycidols having the two required functional groups, namely the epoxy or oxyran configuration and the hydroxyl group. Mention may in particular be made of the following compounds: 2,3-epoxy-1-propanol or glycidol, 2,3-epoxybutanol, 3,4-epoxypentanol, 2,3,4,5-diepoxyhexanol, 2-methyl-3,4 epoxybutanol, 1-2-epoxyhexanol-8, and mixtures thereof. Those skilled in the art will be able to refer to US-A-3,005,832 and US-A-3,041,356 for the description and the preparation of such compounds.

 Epoxy phenols can also be used. For example, polyglycidyl ethers of dihydrophenols such as bisphenol-A or 2,2-bis (4-hydroxyphenol) propane may be mentioned. Advantageously, a person skilled in the art can refer, for example, to US Pat. No. 3,062,840 describing a particular class of epoxy phenols. These are epoxy substituted polynuclear polyhydric phenols, comprising an epoxyalkyl chain in which a carbon atom is

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 connected to two hydroxyphenyl substituents. As examples of such bisphenols, mention may be made of the following compounds: 1,2-epoxy-3,3-bis (hydroxyphenyl) butane, 1,2-epoxy-3,3-bis (hydroxy-phenyl) hexane, 1,2 epoxy-4,4bis (hydroxyphenyl) pentane, 1,2-epoxy-3,3-bis (dihydroxyphenyl) propane, 1,2-epoxy-3,3-bis (o-cresyl) propane, 1,2-epoxy -3,3-bis (dihydroxyphenyl) butane, and mixtures thereof. They can also be combined with epoxy alcohols.

dans laquelle : - R1, R2, R3 sont des radicaux hydrogénés ou hydrocarbonés identiques ou différents entre eux et représentent, de préférence, l'hydrogène, un alkyle linéaire ou ramifié en C1-C4 ou un phényle éventuellement substitué par au moins un alkyle en C1-C3, - U est un alkylène linéaire ou ramifié en Ci - C4, ou un groupement divalent de formule -CO-O-alkylène- où le reste alkylène est un alkyle linéaire ou ramifié en C1-C4 et la valence libre de droite (en gras) est reliée au Si - R4 et R5 sont des radicaux identiques ou différents et représentent un alkyle en C1 - C4 linéaire ou ramifié, - a = 0 à 2, de préférence 0 ou 1 et plus préférentiellement encore 0 - b=Ooul. Preferably, when it is present, the alkoxylated organosilane of the promoter (4) is more particularly selected from the products of the following general formula (I):

in which: R1, R2, R3 are hydrogenated or hydrocarbon radicals that are identical to or different from each other and preferably represent hydrogen, a linear or branched C1-C4 alkyl or a phenyl optionally substituted by at least one alkyl group; C1-C3, - U is a linear or branched C1-C4 alkylene, or a divalent group of formula -CO-O-alkylene- where the alkylene residue is a linear or branched C1-C4 alkyl and the free valence of right (in bold) is connected to Si - R4 and R5 are identical or different radicals and represent a linear or branched C1 - C4 alkyl, - a = 0 to 2, preferably 0 or 1 and even more preferably 0 - b = Ooul.

 Vinyltrimethoxysilane (VTMO) and γ-methacryloxypropyltrimethoxysilane (MEMO) may be mentioned in particular.

 With regard to the organosilicon epoxy compound, it is preferred, when present, to choose it

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dans laquelle : # R6 est un radical alkyle linéaire ou ramifié en C1 - C4, # R7 est un radical alkyle linéaire ou ramifié, # c est égal à 0,1, 2 ou 3, de préférence à 0 ou 1 et, plus préférentiellement encore à 0, # X est

avec A E et D qui sont des radicaux identiques ou différents choisis parmi les alkyles en C1-C4 linéaires ou ramifiés, # d qui est égal à 0 ou 1, A R8, R9, R10 qui sont des radicaux identiques ou différents représentant l'hydrogène ou un alkyle linéaire ou ramifié en
C1-C4, l'hydrogène étant plus particulièrement préféré,
A R8 et R9 ou R10 pouvant alternativement constituer ensemble et avec les deux carbones porteurs de l'époxy, un cycle alkyle ayant de 5 à 7 chaînons, - among the products satisfying the following general formula (II):

in which: # R6 is a linear or branched C1-C4 alkyl radical, # R7 is a linear or branched alkyl radical, #c is equal to 0.1, 2 or 3, preferably 0 or 1 and, more preferably still at 0, # X is

with AE and D which are identical or different radicals chosen from linear or branched C1-C4 alkyls, # d which is equal to 0 or 1, A R8, R9, R10 which are identical or different radicals representing hydrogen or a linear or branched alkyl in
C1-C4, hydrogen being more particularly preferred,
R 8 and R 9 or R 10 may alternatively constitute, together with the two epoxy-bearing carbons, an alkyl ring having from 5 to 7 members,

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dans laquelle : # X est le radical tel que défini ci-dessus pour la formule (II) # G est un groupe hydrocarboné monovalent, exempt d'action défavorable sur l'activité du catalyseur et choisi, de préférence, parmi les groupes alkyles ayant de 1 à 8 atomes de carbone inclus, éventuellement substitués par au moins un atome d'halogène, avantageusement, parmi les groupes méthyle, éthyle, propyle et 3,3,3- trifluoropropyle et ainsi que parmi les groupes aryles et, avantageusement, parmi les radicaux xylyle et tolyle et phényle, # p =1 ou 2, # q = 0,1 ou 2, . p + q = 1, 2 ou 3, et (2i) éventuellement au moins un motif siloxyle de formule (V) :

dans laquelle G a la même signification que ci-dessus et r a une valeur comprise entre 0 et 3, par exemple entre 1 et 3. or among the products consisting of epoxyfunctional polydiorganosiloxanes comprising: (i) at least one siloxyl unit of formula (IV):

in which: # X is the radical as defined above for the formula (II) # G is a monovalent hydrocarbon group, which has no adverse effect on the activity of the catalyst and is preferably selected from alkyl groups having from 1 to 8 carbon atoms inclusive, optionally substituted by at least one halogen atom, advantageously from methyl, ethyl, propyl and 3,3,3-trifluoropropyl and also from aryl groups and, advantageously, from xylyl and tolyl and phenyl radicals, # p = 1 or 2, # q = 0.1 or 2,. p + q = 1, 2 or 3, and (2i) optionally at least one siloxyl unit of formula (V):

in which G has the same meaning as above and r a value between 0 and 3, for example between 1 and 3.

 These compounds are preferably epoxyalkoxymonosilanes.

 By way of example of such compounds, mention may be made of: 3-glycidoxypropyltrimethoxysilane (GLYMO) or 3,4-epoxycyclohexylethyltrimethoxysilane.

 With respect to the chelate or aloxide type compound, it may consist of or comprise a metal chelate. The metal M chosen may thus comprise one or more ligands such as those derived in particular from a beta-diketone, such as, for example, acetylacetone. This compound may consist

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 still in, or include, a metal alkoxide having the formula M (OJ) n defined above wherein the alkoxy radicals are for example the n-propoxy and n-butoxy radicals. Note that in this formula, one or more alkoxy radicals OJ may be replaced by one or more constituent ligands of a chelate, such as for example an acetylacetonate ligand.

 Preferred compounds are those in which the metal M is selected from the following list: Ti, Zr, Ge, Mn, Al.

 Note that titanium is more particularly preferred.

 Concrete examples of suitable compounds are those in the structure of which the metal M is selected from the list: Ti, Zr, Ge, Mn, and Al and is associated with: - a chelate: to ligands of acetylacetonate type - being an alkoxide: to n-propoxy or n-butoxy radicals.

 Quantitatively, it can be specified that the weight proportions between the various constituents of the adhesion promoter, expressed in percentages by weight relative to the total of the three, are the following: unsaturated compound 10% - epoxy compound <90% - Chelate, alkoxide, silicate, polysilicate: from 0 to 25%.

 Adhesion promoters of types (i) and (2i) are preferred.

 The most preferred adhesion promoters are those of the type (2i) comprising an alkenyl-functional dendrimer, an epoxy-functional organosilicon compound and a metal chelate and / or alkoxide. The organosilicon compound is then preferably GLYMO or else 3,4-epoxycyclohexylethyltrimethoxysilane.

 Other types of promoters of interest are those which follow: - VTMO or MEMO + epoxy dendrimer + chelate or metal alkoxide - alkenyl dendrimer + epoxy dendrimer + optionally chelate or metal alkoxide or ethyl silicate.

 The subject of the present invention is also the silicone compositions of the type of those that can be cold vulcanized (EVF), comprising: (1) at least one polyorganosiloxane having, per molecule, at least two alkenyl groups, in C 2 -C 6 bonded to silicon,

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 (2) at least one polyorganosiloxane having, per molecule, at least two silicon-bonded hydrogen atoms, (3) a catalytically effective amount of at least one catalyst, based on at least one platinum group metal (4) an adhesion promoter according to the invention, (5) optionally a filler, (6) optionally a polyorganosiloxane described as an extender and having hydrogen functional terminal siloxyl units, (7) optionally a neutralizing agent, (8) ) optionally a crosslinking inhibitor and / or other (s) used in the type of composition referred to, (9) optionally a polyorganosiloxane resin.

 The person skilled in the art knows that when component (1) has 2 alkenyl groups per molecule, component (2) must have at least 3 hydrogen atoms per molecule. Conversely, when component (2) has 2 hydrogen atoms per molecule, component (1) has at least 3 alkenyl groups per molecule.

 Advantageously, the adhesion promoter is present in a proportion of 0.1 to 10, preferably 0.5 to 5 and even more preferably 1 to 3% by weight relative to all the constituents of the composition.

The polyorganosiloxane (1) is by weight one of the essential constituents of the composition according to the invention. Advantageously, it is a product comprising (i) siloxyl units of formula:
TaZb SiO4 - (a + b)
2 (1.1) wherein: - T is an alkenyl group, preferably vinyl or allyl, - Z is a monovalent hydrocarbon group, which has no adverse effect on the activity of the catalyst and is preferably selected from alkyl groups having from 1 to 8 carbon atoms inclusive, optionally substituted by at least one halogen atom, advantageously from methyl groups,

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dans laquelle Z a la même signification que ci-dessus et c a une valeur comprise entre 0 et 3, de préférence entre 2 et 3. ethyl, propyl and 3,3,3-trifluoropropyl and as well as among the aryl groups and, advantageously, among the radicals xylyl, tolyl and phenyl, a is 1 or 2, b is 0,1 or 2 and a + b is included between 1 and 3, preferably between 2 and 3, and (2i) optionally other siloxyl units of formula:

in which Z has the same meaning as above and ca a value between 0 and 3, preferably between 2 and 3.

 It is advantageous for this polydiorganosiloxane to have a viscosity of between 100 and 200,000 mPa.s. It is preferably 500 to 5000 mPa.s in the case where a reinforcing filler is used, in particular a reinforcing filler treated in situ. In the absence of such a charge, it preferably becomes between 10,000 and 200,000 mPa.s.

 Of course, in case of mixing of several oils (1) of different viscosity, the viscosity of the mixture is taken into account.

 All the viscosities referred to herein correspond to a dynamic viscosity quantity which is measured, in a manner known per se, at 25 C.

 The polyorganosiloxane (1) may be formed solely of units of formula (1.1) or may further contain units of formula (1.2).

 Z is generally selected from methyl, ethyl and phenyl, 60 mol% (or by number) at least Z radicals being methyl radicals.

 Examples of siloxyl units of formula (1.1) are the vinyldimethylsiloxyl unit, the vinylphenylmethylsiloxyl unit, the vinylmethylsiloxyl unit and the vinylsiloxyl unit.

 Examples of siloxyl units of formula (I.2) are SiO4 / 2, dimethylsiloxyl, methylphenylsiloxyl, diphenylsiloxyl, methylsiloxyl and phenylsiloxyl units.

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 Examples of polyorganosiloxanes (1) are linear and cyclic compounds such as: dimethylvinylsilyl-terminated dimethylpolysiloxanes, trimethylsilyl-terminated (methylvinyl) (dimethyl) polysiloxane copolymers, dimethylvinylsilyl-terminated (methylvinyl) (dimethyl) polysiloxane copolymers; cyclic methylvinylpolysiloxanes.

dans laquelle :
L est un groupe hydrocarboné monovalent, exempt d'action défavorable sur l'activité du catalyseur et choisi, de préférence, parmi les groupes alkyles ayant de 1 à 8 atomes de carbone inclus, éventuellement substitués par au moins un atome d'halogène, avantageusement, parmi les groupes méthyle, éthyle, propyle et 3,3,3-trifluoropropyle et ainsi que parmi les groupes aryles et, avantageusement, parmi les radicaux xylyle, tolyle et phényle, d est 1 ou 2, e est 0,1 ou 2, d + e a une valeur comprise entre 1 et 3, de préférence entre 2 et 3, et (2i) éventuellement des autres motifs siloxyles de formule moyenne (2.2) :

dans laquelle L a la même signification que ci-dessus et g a une valeur comprise entre 0 et 3, de préférence entre 2 et 3. The polyorganosiloxane (2) is preferably of the type of those comprising (i) siloxyl units of formula (2.1):

in which :
L is a monovalent hydrocarbon group, which has no adverse effect on the activity of the catalyst and is preferably chosen from alkyl groups having from 1 to 8 carbon atoms inclusive, optionally substituted with at least one halogen atom, advantageously among the methyl, ethyl, propyl and 3,3,3-trifluoropropyl groups and, as well as among the aryl groups and, advantageously, among the xylyl, tolyl and phenyl radicals, d is 1 or 2, e is 0,1 or 2; , d + ea a value between 1 and 3, preferably between 2 and 3, and (2i) optionally other siloxyl units of average formula (2.2):

wherein L has the same meaning as above and g has a value between 0 and 3, preferably between 2 and 3.

 The dynamic viscosity of this polyorganosiloxane (2) is at least 10 mPa.s and preferably is between 20 and 1000 mPa.s.

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 The polyorganosiloxane (2) may be formed solely of units of formula (2.1) or may further comprise units of formula (2.2).

 The polyorganosiloxane (2) may have a cyclic or network branched linear structure.

 Group L has the same meaning as group Z above.

Examples of units of formula (2.1) are: H (CH 3) 2 SiO 1/2, HCH 3 SiO 2/2, H (C 6 H 5) SiO 2/2
The examples of units of formula (2.2) are the same as those given above for the units of formula (1.2).

 Examples of polyorganosiloxane (2) are linear and cyclic compounds such as: - dimethylpolysiloxanes with hydrogenodimethylsilyl ends, - trimethylsilyl-endblocked (dimethyl) (hydrogenomethyl) polysiloxane copolymers, - (dimethyl) (hydrogenomethyl) polysiloxane-patterned copolymers with hydrogenodimethylsilyl ends, - trimethylsilyl-terminated hydrogenomethylpolysiloxanes, - cyclic hydrogenomethylpolysiloxanes.

 The ratio of the number of silicon-bonded hydrogen atoms in the polyorganosiloxane (2) to the total number of alkenyl unsaturated groups of the polyorganosiloxane (1) is between 1 and 5, preferably between 1 and 2.

 The catalysts (3) are also well known. The platinum and rhodium compounds are preferably used. In particular, platinum complexes and an organic product described in US-A-3 159 601, US-A-3 159 602, US-A-3,220,972 and European patents can be used. A-0 057 459, EP-A-0 188 978 and EP-A-0 190 530, the complexes of platinum and vinyl organosiloxanes described in US-A-3,419,593, US-A-3,715,334. , US-A-3,377,432 and US-A-3,814,730. The generally preferred catalyst is platinum-based. In this case, the amount by weight of catalyst (3), calculated by weight of platinum-metal, is generally between 2 and 400 ppm, preferably between 5 and 50 ppm based on the total weight of the polyorganosiloxanes (1) and (2). ).

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 Advantageously, the silicone composition according to the invention may further comprise at least one retarder of the addition reaction or crosslinking inhibitor (8), chosen from the following compounds: polyorganosiloxanes substituted with at least one alkenyl which may be present optionally under cyclic form, tetramethylvinyltetrasiloxane being particularly preferred, - pyridine - phosphines and organic phosphites, - unsaturated amides - alkylated maleates - and acetylenic alcohols.

formule dans laquelle, - R' est un radical alkyle linéaire ou ramifié, ou un radical phényle ; - R" est H ou un radical alkyle linéaire ou ramifié, ou un radical phényle ; les radicaux R', R" et l'atome de carbone situé en a de la triple liaison pouvant éventuellement former un cycle ; le nombre total d'atomes de carbone contenu dans R' et R" étant d'au moins 5, de préférence de 9 à 20. These acetylenic alcohols (see FR-B-1,528,464 and FR-A-2,372,874), which form part of the preferred hydrosilylation reaction heat blockers, have the formula:

formula in which - R 'is a linear or branched alkyl radical, or a phenyl radical; - R "is H or a linear or branched alkyl radical, or a phenyl radical, the radicals R ', R" and the carbon atom located at a of the triple bond possibly forming a ring; the total number of carbon atoms contained in R 'and R "being at least 5, preferably 9 to 20.

 Said alcohols are preferably chosen from those having a boiling point greater than 250 ° C. Examples that may be mentioned include: ethynyl-1-cyclohexanol-1; 3-methyl-1-dodecyn-3-ol; trimethyl-3,7,11-dodecyn-1-ol-3; 1,1-diphenylpropyne-2-ol-1; 3-ethyl-6-ethyl nonyne-1-ol-3; 2-methyl-3-butyneol-2; 3-methylpentadecyn-1-ol-3.

 These α-acetylenic alcohols are commercial products.

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 Such a retarder is present at a maximum of 5000 ppm, preferably at 100 to 2000 ppm relative to the total weight of the organopolysiloxanes (1) and (2).

 The filler (5) may be a reinforcing or non-reinforcing filler, or a combination of both, depending on the desired properties.

 The reinforcing filler is preferably a siliceous filler.

 The reinforcing siliceous fillers are chosen from colloidal silicas, silica powders for combustion and precipitation, or mixtures thereof.

 These powders have an average particle size generally close to or less than 0.1 m and a BET specific surface area greater than 50 m 2 / g, preferably between 50 and 400 m 2 / g, especially between 150 and 350 m 2 / g.

 Among the non-reinforcing fillers of complement include diatomaceous earths, calcium carbonate, crushed quartz and zirconium oxide or crushed zirconia. These fillers have a particle size generally of between 0.001 and 300 m and a BET surface area of less than 100 m 2 / g.

 Other additional fillers are, for example, carbon black, titanium dioxide, aluminum oxide, hydrated alumina, expanded vermiculite, unexpanded vermiculite, zinc oxide, mica, talc. , iron oxide, barium sulphate and slaked lime.

 Other additional fillers may be microspherical fillers.

 The reinforcing silicas may be incorporated preferably as they are or after having been treated with organosilicon compounds usually used for this purpose. Among these compounds, there are methylpolysiloxanes such as hexamethyldisiloxane, octamethylcyclotetrasiloxane, methylpolysilazanes such as hexamethyldisilazane, hexamethylcyclotrisilazane, chlorosilanes such as dimethyldichlorosilane, trimethylchlorosilane, methylvinyldichlorosilane, dimethylvinylchlorosilane, alkoxysilanes such as dimethyldimethoxysilane, dimethylvinylethoxysilane,

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 trimethylmethoxysilane. During this treatment, the silanes can increase their starting weight up to a level of 20%, preferably about 10%.

 Preferably, the siliceous filler is treated in situ.

 By in situ treatment of the siliceous filler is preferably meant the bringing together of the filler and the compatibilizing agent in the presence of at least a portion of polyorganosiloxane silicone oil (1). In a particularly preferred manner, the procedure is as described in WO-A-98 58997 to which the skilled person can refer for more details. In a particularly preferred manner, this consists essentially in introducing compatibilizer (AC) in two stages in the preparation medium: # firstly, before and / or substantially simultaneously with the bringing together of at least one part of the silicone oil used with at least a portion of the siliceous filler used, this introduction of AC (portion 1) occurring in one or more times and corresponding to a proportion of less than or equal to 8%, preferably at 5% and more preferably at 3% by dry weight relative to the total charge; # and secondly (portion 2), after this introduction of silicone oil / charge.

The compatibilizing agent of the portion 1 is thus chosen from molecules that satisfy at least two criteria: - exhibit a strong interaction with the silica at its hydrogen bonds with itself, and with the surrounding silicone oil - it itself, or its degradation products, easily removed from the final mixture by heating under vacuum or in a gaseous stream, and the low molecular weight compounds are therefore preferred,
By globally equivalent amount is meant the respect of the order of magnitude of the molar amounts of AC with respect to the hydrogen bonds.

 The agent of the portion 1 may be for example: a silazane, preferably a disilazane, or their mixtures, hexamethyldisilazane (HMDZ) being the preferred silazane and may be combined with divinyltetramethyldisilazane - a hydroxylated siloxane di- or preferably monofunctional

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 an amine such as ammonia or a low molecular weight alkylamine such as diethylamine, a low molecular weight organic acid such as formic or acetic acid, and is preferably used in the presence of water.

 The compatibilizing agents of the portion 2 can be chosen from the different silazanes and disilazanes encountered above, taken alone or in mixtures with each other, preferably from disilazanes, hexamethyldisilazane, with or without divinyltetramethyldisilazane, being particularly preferred.

 The silicic reinforcing filler represents from 10 to 50% by weight of the suspension obtained. In practice, this load is of the order of 10%.

 Advantageously, the proportion of compatibilizer introduced in a first step is at most equal to 8% of the reinforcing filler (and for example between 1 and 3% of the reinforcing filler, preferably between 1 and 2%). Furthermore, it can be stated that the total amount of AC agent is preferably between 5 and 30% of the silicic filler, preferably between 10 and 20%.

 Alternatively, it is possible to use the compatibilization methods of the prior art providing for early treatment with silazane (eg FR-A-2320324) or late treatment (eg EP-A-462 032), while knowing, however, that according to the silicas used, their use will generally not make it possible to obtain the best results in terms of mechanical properties, in particular extensibility, obtained by a two-stage treatment in accordance with the invention.

 In the case where the in situ treatment leads to a basic pH, a neutralizer (7) such as, for example, weak acids (e.g., acetic acid and buffered phosphoric acid) can be added. It will be noted that this neutralization may advantageously be obtained by the incorporation of acidic fillers such as crushed quartz.

 The microsphere fillers are preferably expandable organic microspheres comprising, as is known per se, a polymer wall enclosing a liquid or a gas. These microspheres are expanded by heating them beyond the softening point of the polymer

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 and at a temperature sufficient to vaporize the liquid or suitably expand the gas, which may be for example an alkane such as isobutane or isopentane. The wall may consist, as is known per se, of polymers or copolymers, for example prepared from monomers vinyl chloride, vinylidene chloride, acrylonitrile, methyl methacrylate or styrene or mixtures of polymers and / or copolymers, for example in particular acrylonitrile / methacrylonitrile copolymer, acrylonitrile / vinylidene chloride copolymer. See especially US-A-3,615,972.

 They can be incorporated into the composition, either in the expanded state or before their expansion, which can be induced, by appropriate heating, during the crosslinking of the composition.

 It may be advantageous for the microspheres to be surface-treated, as is known per se, to promote their dispersion in the composition; it may be especially expansible or expanded microspheres having an inorganic coating, for example silica or metal salts or hydroxides such as Ca, Mg, Ba, Fe, Zn, Ni, Mn, as described for example in EP-A A-486 080, or else carbonates, for example calcium carbonate.

 As a preferred example, the microspheres sold under the name Dualité by UCB-chemicals are used.

 Before their expansion, the microspheres will preferably have a diameter of between 3 and 50 m, more particularly between 5 and 30 m.

 We will also seek a diameter after expansion (in situ or original) including between 10 and 150, especially between 20 and 100 m.

 These microspheres will be present in particular in a proportion of 1 to 30% by weight, preferably 2 to 10% and more preferably more than 3 or 4%, by weight relative to the total composition.

 The polyaddition composition may also comprise an extender polyorganosiloxane (6) having, per molecule, two siloxyl groups carrying a hydrogen bonded hydrogen atom. These lengthening polyorganosiloxanes are well known to those skilled in the art.

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avec . R identiques ou différents entre eux et correspondant à un groupement alkyle linéaire ou ramifié en Ci-Ce et/ou aryle substitué ou non, R étant préférentiellement CH3. The lengthening polyorganosiloxane (6) has terminal siloxy units

with. R identical or different from each other and corresponding to a linear or branched C 1 -C 6 alkyl and / or substituted or unsubstituted aryl group, R being preferentially CH 3.

 It should be noted that the rest of the molecule is a polydiorganosiloxane, preferably a polydimethylsiloxane.

 By way of example, mention may be made of poly (dimethylsiloxy) - [alpha], # - (dimethylhydrogensiloxy).

 According to a particular embodiment of the invention, the silicone composition associates a reinforcing filler (5) treated in situ, preferably according to WO-A-98 58997, and an extender polyorganosiloxane (6). In such a composition, if the alkoxylated organosilane is present, b is preferably 1. This type of composition is particularly useful for the coating of substrates, especially fibrous substrates, for example for the production of airbags.

 The composition according to the invention may comprise, in addition, at least one polyorganosiloxane resin (9) comprising at least one alkenyl residue in its structure, and this resin has a weight content of alkenyl group (s) of between 0, 1 and 20% by weight and, preferably, between 0.2 and 10% by weight.

 These resins are branched organopolysiloxane oligomers or polymers well known and commercially available. They are in the form of solutions, preferably siloxanes. They have, in their structure, at least two different units chosen from those of formula R3SiO0.5 (motil M) 1, R2SiO (unit D) 1, RSiO1.5 (unit T) and SiO2 (unit Q), one at least one of these patterns being a T or Q pattern.

 The radials R are identical or different and are chosen from linear or branched C1-C6 alkyl radicals, C2C4 alkenyl radicals, phenyl, 3,3,3-trifluoropropyl. For example, as

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 R alkyl radicals, methyl, ethyl, isopropyl, tert-butyl and hexyl radicals, and R alkenyl radicals, vinyl radicals.

 It should be understood that in the resins (9) of the aforementioned type, a portion of the radicals R are alkenyl radicals.

 Examples of oligomers or branched organopolysiloxane polymers that may be mentioned include MQ resins, MDQ resins, TD resins and MDT resins, the alkenyl functions that may be carried by the M, D and / or T units. resins which are particularly suitable include vinylated MDQ resins having a weight content of vinyl group of between 0.2 and 10% by weight.

 This compound (9) has the particular function of increasing the mechanical strength of the elastomer, e. g. silicone elastomer coating, as well as its adhesion, e. g. in the context of the coating of the faces of a synthetic fabric (for example polyamide), for example in the manufacture of airbags. When present, this structural resin is advantageously present in a concentration of between 10 and 70% by weight relative to all the constituents of the composition, preferably between 30 and 60% by weight and, more preferably still between 40 and 60% by weight.

 In a particularly preferred manner, the polyorganosiloxane resin (9) will comprise at least 2% by weight of SiO 2 units (Q units), in particular from 4 to 14%, preferably from 5% to 12%.

 The incorporation of these resins allows, if desired, to dispense with charge and in particular reinforcing siliceous filler. The interest is then to be able to apply very thin layers of elastomer, with for example a deposited weight of less than or equal to 30 g / m2.

 According to another of its aspects, the present invention relates to a two-component precursor system of this preferred silicone composition described above. Such a precursor system is in two distinct parts A and B, intended to be mixed to form the composition, one of these parts A or B comprising the catalyst (3) and a single species (1) or (2) of polyorganosiloxane. Another characteristic of this precursor system is that its part A or B containing the polyorganosiloxane (2) is free of chelate or metal alkoxide compounds of the promoter (4) and that its

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 Part A or B including the unsaturated compound of the promoter (4) does not include the catalyst (3); when present, the in situ treated filler (5) is present in the part (s) A and B which contain the polyorganosiloxane (1).

 The determination and optimization of the two parts A and B to avoid bringing together in one of the parties species capable of reacting together, are part of the normal capabilities of the skilled person.

 Once the parts A and B are mixed together, they form a ready-to-use silicone composition, which can be applied to the support by any suitable coating means (for example scrapes, rolls, screen printing, etc.). ). Although the crosslinking can be carried out under cold conditions (that is to say at a temperature close to the ambient temperature close to 20 ° C.), the compounds according to the invention are crosslinked by appropriate means, in particular by thermal means and / or by electromagnetic radiation (accelerated electron radiation or "electron beam"), and / or infrared radiation.

 The subject of the invention is also the use of the adhesion promoter according to the invention in the preparation of silicone compositions, in particular those that can be used for coating various substrates such as those described above and / or for adhesive use. .

 According to a first preferred embodiment of the invention, the silicone compositions comprising the above promoter may be used, in particular for coating or coating, woven, knitted or non-woven fibrous supports, and, preferably, woven, knitted supports. or nonwovens made of conventional or technical synthetic fibers, advantageously polyester or polyamide and glass fabrics.

 The invention relates more particularly to the coating or coating of at least one of the faces (inner and / or outer) of the flexible support material (polyamide fabric for example) useful for the manufacture by sewing air bags for personal protection of occupants of vehicles, in case of shock.

 According to a second preferred embodiment, the compositions according to the invention can also be used as adhesive, especially textile, metal or plastic parts.

 The present invention also relates to the use of these compositions or their precursor systems as described above, for the

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 coating or coating fibrous supports as described above or for adhesion.

 Finally, the adhesion promoters can also be used in the heat-curable silicone compositions known under the name EVC and in particular those crosslinking by polyaddition or peroxide EVC.

 The invention also relates to the use of the monomers and polymers described above for the production of adhesion promoters and for the preparation of silicone compositions.

 The invention will now be described in more detail using embodiments and as non-limiting examples.

EXAMPLES The tested polymer is an ester-type dendritic polymer. It is characterized by: # a star-shaped 4-branch star # level 2 generation # an allylic feature * allyl functionality level: 2.06 mmol / g
14.4 mole allyl / mole G2 * residual functionality hydroxyl residual functionality rate OH: 0.11 mmol / g
0.8 mole hydroxy / mole G2
This dendritic polymer hereinafter named G2 is accessible from the company PERSTORP.

EXAMPLE 1 REFERENCE COMPOSITION 1
It is a two-component silicone composition whose composition is particularly suitable for bonding.

 A suspension called premix is first prepared by mixing in a reactor at ambient temperature:

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 51.7 parts of resin of MMViDDViQ structure containing 0.9% by weight of vinyl groups (Vi) and consisting of: 21% by weight of (CH 3) 3 SiO 0.5 units; 0.2% by weight of (CH3) 2ViSiO0.5 units; 67.8% by weight of (CH 3) 2 SiO 3 units; 3% by weight of (CH 3) ViSiO units; 8% by weight of SiO 2 units.

15 parts by weight of a polydimethylsiloxane (PDMS) blocked with (CH 3) 2 ViSiOo 5 units having a viscosity of 10,000 mPa.s and containing
0.005 SiVi functions per 100 g of oil - 33.3 parts by weight of a crushed silica with an average particle size of about 2 m.

This premix serves for the preparation of parts A and B of the two-component
Part A of two-component
In a reactor at ambient temperature, 99.3 parts by weight of premix are mixed with 0.7 part by weight of butyl orthotitanate, 0.004 parts by weight of platinum metal in the form of a metal complex known under the name of Karstedt catalyst
Part B of two-component
In a reactor at ambient temperature, 90.3 parts by weight of premix are mixed with 4.52 parts by weight of a poly (dimethyl) (hydrogen methyl) siloxane blocked with (CH 3) 2 HSiO 0.5 units having a viscosity. of 25 mPa.s and containing in total 0.7 SiH function per 100 g of oil - 0.04 parts by weight of EthynylCycloHexanol - 1.8 parts by weight of vinyltrimethoxy silane (VTMO) - 1.8 parts by weight of 3-glycidoxypropyltrimethoxysilane (GLYMO) - 0.2 parts by weight of a coloring base.

 The two-component is obtained by mixing 100 parts of A n 1 and 100 parts of B n 1 at room temperature.

 The composition C1 is thus obtained.

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EXAMPLE 2 REFERENCE COMPOSITION 2
This is the previous two-component silicone composition from which the unsaturated silane of the adhesion promoter has been removed.

 The same suspension called the premix and the same part A as described in Example 1 are used.

Part A of bicomponent n 2 It is part A of bicomponent n 1 Part B of bicomponent n 2 In a reactor at ambient temperature: 90.3 parts by weight of premix are mixed with 4.52 parts by weight of one part poly (dimethyl) (hydrogenomethyl) siloxane blocked with (CH 3) 2 HSiO 0.5 units having a viscosity of 25 mPa.s and containing in total 0.7 SiH function per 100 g of oil.

0.04 part by weight of EthylnylCycloHexanol - 1.8 part by weight of 3-glycidoxypropyltrimethoxysilane (GLYMO) - 0.2 part by weight of a coloring base
The two-component is obtained by mixing at room temperature 100 parts of A n 2 and 100 parts of B n 2. The composition is thus obtained.
C2.

EXAMPLE 3: COMPOSITION ACCORDING TO THE INVENTION
The composition is that of the reference two-component silicone preparation to which the dendritic polymer has been added.

 The same suspension called the premix and the same part A as described in Example 1 are used.

Part A of two-component
It is the part A of the bicomponent n 1

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Part B of two-component
In a reactor at ambient temperature, 90.3 parts by weight of premix are mixed with 4.52 parts by weight of a poly (dimethyl) (hydrogen methyl) siloxane blocked with (CH 3) 2 HSiO 0.5 units having a viscosity of 25 mPa.s and containing in total 0.7 SiH function per 100g of oil - 0.04 part by weight of EthynylCycloHexanol - 3.6 parts by weight of the dentritic polymer with allylic functions (G2) - 1.8 parts by weight weight of 3-glycidoxypropyltrimethoxysilane (GLYMO) - 0.2 parts by weight of a coloring base.

 The two-component is obtained by mixing at room temperature 100 parts of A n 3 and 100 parts of B n 3. The composition C 3 is thus obtained.

PERFORMANCES FOR EXAMPLES 1 TO 3
Adhesive performance is evaluated by a peel test.

 For this, a layer of controlled thickness of the bicomponent is deposited between two substrates and the crosslinking of the two-component is carried out.

 After cooling, the force necessary to cause the separation of the substrates is measured by means of a traction machine equipped with a device for recording the force exerted.

 The substrate S retained for these evaluations is a polyamide 66 fabric of 470 dtex, woven in 18x18 strands.

The following results were recorded: Table 1

<Tb>
<tb> Two-Component <SEP> Substrate <SEP> 1 <SEP> Substrate <SEP> 2 <SEP> Weight <SEP> Strength <SEP> of
<tb> surface <SEP> coat <SEP> N / mm
<tb> g / m2
<tb> C1 <SEP> S <SEP> S <SEP> 120 <SEP> 0.82
<tb> C2 <SEP> S <SEP> S <SEP> 110 <SEP> 0.36
<tb> C3 <SEP> S <SEP> S <SEP> 115 <SEP> 0.78 <SEP>
<Tb>

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EXAMPLE 4
Products tested
The tested products are described below:
Boltorn U1 is a mass dendrimer of about 8000 which carries about 14 allyl functions.

 Boltorn E1 is a mass dendrimer of about 10,500 which carries about 11 epoxy functions.

 Polyol PS50 is an ethoxylated pentaerythritol of mass about 350 which carries 4 hydroxy functions but no unsaturated function (for comparison).

These products are available from PERSTORP
The composition is that of the standard two-component silicone preparation of Example 1 in which one of the promoter silanes was substituted with one of the tested products (dendritic polymers). Type 1 (unsaturated functional) promoter additives replace VTMO; Type 2 promoter additives (epoxy functional) replace GLYMO.

 The same suspension called the premix and the same part A as described in Example 1 are used.

Part A of two components 4 to 7
It is the part A of the bicomponent n 1
Part B of two components 4 to 7
In a reactor at ambient temperature, 90.3 parts by weight of premix are mixed with 4.52 parts by weight of a poly (dimethyl) (hydrogen methyl) siloxane blocked with (CH 3) 2 HSiO 3 units having a viscosity of 25 mPa.s and containing in total 0.7 SiH function per 100g of oil - 0.04 part by weight of EthynylCycloHexanol - 1.8 part by weight of VTMO or one of the type-promoter additives
1 (see Table 2) - 1.8 parts by weight of GLYMO or one of the type 2 promoter additives (see Table 2) - 0.2 parts by weight of a coloring base.

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 The two-component is obtained by mixing at room temperature 100 parts of A n 4 to 7 and 100 parts of B n 4 to 7. The compositions C 4 to C 9 are thus obtained.

PERFORMANCE
The adhesive performance is evaluated as previously by the peel test.

 The surface weights applied are always of the order of 120 g / m2.

The following results were recorded: Table 2:

<Tb>
<tb> Two-Component <SEP> Additive <SEP> 1 <SEP> Additive <SEP> 2 <SEP> Strength <SEP> of <SEP> Coat
<tb> N / mm
<tb> C1 <SEP> VTMO <SEP> GLYMO <SEP> 0.82
<tb> C4 <SEP> U1 <SEP> GLYMO <SEP> 0.52
<tb> C5 <SEP> VTMO <SEP> E1 <SEP> 0.15
<tb> C6 <SEP> PS50 <SEP> GLYMO <SEP> 0
<tb> C7 <SEP> VTMO <SEP> PS50 <SEP> 0
<Tb>
COMMENTS ON THE EXAMPLES
The results presented demonstrate the equivalence of the performances according to the compositions C1 and C3 and the advantage over the composition C2 which does not contain an unsaturated promoter.

 Example 4 demonstrates the ability of polyfunctional dendrimers self-adhesion to the compositions that contain them. The need for dual function of these molecules for this purpose is also observed.

 It is also known that the adhesive power of these compositions is not limited to the field of textile gluing. Thus they also allow bonding on metal, including aluminum and plastics, including epoxy resins.

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 It has also been noted, without being limiting, that the dendrimer G2 introduced into a heat-curable silicone rubber under the action of a peroxide sticks to the mold in which it is shaped. This further demonstrates the potential of these products to confer a self-adhesive character to silicone elastomer compositions.

Claims (8)

1. An adhesion promoter comprising the following couple of compounds: a polymer without silicon, having in its structure at least one OH group and at least one ethylenic unsaturation, - an organosilicon compound comprising at least one epoxy radical; and optionally a metal M chelate and / or metal alkoxide of general formula: M (OJ) n, with n = valence of M and J = linear or branched C1-C8 alkyl, M being chosen from the group consisting of: Zr , Ge, Li, Mn, Fe, Al and Mg, 2. - Adhesion promoter according to claim 1, characterized in that the polymers are selected from the group consisting of branched polymers and hyperbranched polymers. 3. - Adhesion promoter according to claim 2, characterized in that the hyperamified polymers are dendrimers. 4. - Adhesion promoter according to claim 3, characterized in that the dendrimers are based on polyesters. 5. - A silicone composition of the type of those cold vulcanizable, comprising: (1) at least one polyorganosiloxane having, per molecule, at least two alkenyl groups, C 2 -C 6 bonded to silicon, (2) at least one polyorganosiloxane having, molecule, at least two silicon-bonded hydrogen atoms, (3) a catalytically effective amount of at least one catalyst based on at least one platinum-group metal, (4) an adhesion promoter characterized in that it comprises an adhesion promoter according to any one of claims 1 to 4. <Desc / Clms Page number 31> 6. - Composition according to claim 5, characterized in that it further comprises a compound selected from the group consisting of: (5) a filler, (6) a polyorganosiloxane qualified as an extender and having functional siloxyl terminal units hydrogen, (7) a neutralizer, (8) a crosslinking inhibitor, (9) expandable or expandable inorganic hollow microsphere fillers, (10) a polyorganosiloxane resin, and mixtures thereof. 7.- Use of an adhesion promoter according to any one of claims 1 to 4, for the preparation of silicone compositions having adhesion properties. 8. - Use according to claim 7, for the preparation of a silicone composition crosslinking at room temperature by hydrosilylation or polyaddition. 9. - Use according to claim 7 or 8, for the preparation of silicone compositions for coating substrates. 10. - Use according to claim 7 or 8, for the preparation of silicone compositions intended to serve as an adhesive.