MXPA99006161A - Use of silicone compositions cross-linkable by cationic process under uv radiation and of an onium borate type photoinitiator for coating flat joints, particularly cylinder head gaskets - Google Patents

Abstract

The invention concerns the use of cross-linkable silicone compositions for fast, economical and simple impregnation and/or varnishing of flat joints (e.g. cylinder head gaskets). More precisely it concerns the use of silicone compositions cross-linkable under UV radiation, by cationic process, and in the presence of specific photoinitiators selected among onium borates or organometallic complexes, of which the borate counter-anions contain at least a boron bound to at least a substituted phenyl (Me, F). The silicone liquid precursor is a polydimethylsiloxane (PDMS) substituted by cross-linking functional groups, by cationic process (Gfp) under UV of the epoxy or vinyloxy type. These Gfp are present at the rate of 0.15 to 2.0 pr kg of PDMS. The invention also concerns the method for impregnating/varnishing flat joints (e.g. cylinder head gaskets) using the specific PDMS composition + photoinitiator of borate type as well as the treated joints and the composition themselves.

Description

USE OF RIVETABLE SILICONE COMPOSITIONS THROUGH CATIÓNIC PROCESS, UNDER UV RADIATION AND A PHOTOINICIADOR OF TYPE BORATO DE ONIO, FOR COATINGS OF FLAT JOINTS, MAINLY OF CYLINDER HEAD PACKINGS DESCRIPTION OF THE INVENTION The domain of the present invention is that of the silicone compositions based on organofunctional polyorganosiloxane (POS) crosslinkable by cationic route, under the effect of an oxidation obtained by means of light radiations, preferably UV, and / or by means of a beam of electrons and / or by means of thermal energy. More precisely, the invention relates to the use of such compositions for the treatment of joints or flat joints, mainly for impregnating or varnishing the gaskets or joints of the gasket (cylinder head) of the combustion engines. In particular, it is intended to perform, with the aid of these compositions crosslinkable by cationic process under UV radiation, for example, impregnations of joints or flat joints (cylinder head or cylinder head gaskets), and / or of anti-adhesive coatings in the block / motorcycle / cylinder head interface of thermal engines, said interface preferably being the union of a cylinder head with itself. The silicone compositions which can be used for this purpose were not silicone compositions crosslinkable by cationic route under UV radiation. The operation of a combustion engine requires a strong cohesion of the fixed parts, an intimate lubrication of the moving parts and an efficient cooling of the block-motor assembly. The cylinder head gasket plays a double role; This ensures the cohesion of the removable cylinder-motor / cylinder head assembly as well as the tightness or tightness of the cross-circulations of cooling liquid (water added by glycol and alkaline agents), oil and gas in the course of combustion. Cylinder head gaskets can be very elaborate composite materials comprising a metal core in finely perforated sheet metal, a cardboard (preferably without asbestos) composed of organic fibers and mineral fillers, fire ring crimpers that open on the chamber of explosion, a platform of silicone elastomer to circumscribe possible leaks on the surface. The cylinder head joints or joints are also simply formed of one or more metal sheets optionally coated with an elastomeric NBR rubber coating or fluorinated elastomer of the Viton type (see, for example, Japanese Patent JPA-A-082 09 113). In general, the joints or joints of the cylinder head suffer prior to their use, two types of treatment with the help of silicones: 1 an impregnation treatment intended to fill the empty spaces in order to waterproof the cardboard and improve its thermal resistance, as well as a varnish treatment designed to reduce the coefficient of friction of the joint and induce a good anti-adhesion. In addition to these treatments, a silicone elastomer platform is also deposited by screen printing on the head gaskets. The impregnation of the head gaskets by crosslinked silicones is recommended in the case where the support is porous. This makes it possible to ensure the tightness against the different operating fluids of the engine (oils, gasolines, fuel, cooling liquid, combustion gas). The impregnation provides, on the other hand, in the joint, a certain compressibility, which is necessary at the time of the crushing that it suffers at the time of tightening the cylinder head gasket. When disassembling the cylinder head, the gasket must rise very easily without adhering to the surfaces of the cylinder head. It is therefore imperative that the two faces of the joint are antiadhesive, and this is one of the essential roles of the varnishing by the crosslinked silicone compositions. The varnishing with silicone participates in the tightness or tightness, but also in the protection of the joint against eventual degradation during engine operation (mechanical constraint: shearing and / or thermal shock: heating / cooling). The impregnators and varnishes classically used are compositions composed of oils or resins of silicones of low viscosity, which include the functional groups SiOH or SiH ((US Patent No. 4,720,316; European Patent EP-A-272,382), SiVinils (German Patent DE-A-3, 731, 032; U.S. Patent No. 4,499,135), or mixtures of a silicone oil or resin including SiH functional groups and a silicone oil or resin including Si-vinyl functional groups (German Patent DE-A-3, 718, 559; EP-A-471, 979; German Patent DE-A-3, 544, 740), capable of cross-linking at elevated temperature (generally above 100 ° C) in the presence of a metal catalyst such as tin salts, titanium, platinum or a peroxide. The compositions based on oils or silicone resins include functional groups SiOH, SiH, Si-vinyl or S iH / S i-vini, which generally have at least one of the following drawbacks: the mixture constituted by the silicone matrix and the catalyst is unstable at room temperature (especially in the absence of the solvent), this instability being translated into an increase in viscosity, even in a gelation of the impregnation or varnishing bath, which necessitates a frequent replacement of the impregnation bath or varnishing or a two-stage treatment; for example, US Patent No. US-A-4,720,316 and European Patent EP-A-272,382 teach the operation of the catalyst at the time of manufacture of the cardboard, and then the impregnation of the dry cardboard with a silicone oil with SiH groups.; it is often necessary to disperse the silicone + catalyst mixture in an organic solvent in order to increase the stability and decrease the viscosity of said mixture; This results in inconveniences linked to the use of solvents (toxicity, provide safety devices, solvent recycling ...). - the resale price of raw materials is high, mainly in the case of oils or vinylated resins optionally associated with oils or resins with SiH functional groups, and with a platinum catalyst; these mixtures can be very stable at room temperature, mainly in the presence of a platinum inhibitor, but are expensive due to the operation of vinylated resins or oils. In the search for a new silicone composition for the treatment of head gasket gaskets, which aims to perfect the previously known compositions considered (RHONE-POULENC French patent application on head gasket gaskets No. 2,697,532 ), it has been proposed to use a silicone composition crosslinkable by hydrosilylation and containing a POS a,? - diOH, a post with a SiH portion of the PMHS type as well as ethynylcyclohexanol, the latter compound allowing the formation of resins with a silanol functional group; the SiH / SiOH proportion of the POS in question is of the order of 10/1 to 30/1, the composition also comprising a polyaddition catalyst of the Kars tedt type. Even if a composition of this type effectively provides improvements, on the plane of stability, reactivity and flexibility of use, there is no less that adequate crosslinking to that type of composition includes a temperature-controlled heating stage. high (160 ° C) for 5 to 10 minutes. A stage of this type is particularly penalizing in terms of the productivity of an industrial process of treatment in the coating of cylinder head gaskets with the aid of silicones. For example, it may be necessary in this way to resort to the use of sophisticated and expensive apparatus, such as long heating tunnels.

It thus appears that these compositions of silicones crosslinkable by means of polyadheses ion, and used for the coating of cylinder head gaskets, still do not provide a completely satisfactory solution to the problem of carrying out impregnation and silicone treatment of the head gaskets, which respond to the specifications of anti-adhesion and compressibility, in the same way as to the demands of productivity and profitability for large-scale productions. The French patent application No. 2, 722, 203 is related to the application of a crosslinkable fluorosilicone coating on a cylinder head gasket. A coating of this type is obtained from a silicone composition crosslinkable under the effect of heat, UV radiation, or electron beam, by hydrosilylation. This composition comprises a vinylated fluorosilicone, a POS carrying portions SiH, a hydrosilylation catalyst with platinum, a condensation catalyst of the peroxide type and optionally a solvent of the halogenated solvent type, ester, acetone, etc. The support on which this composition is capable of being applied is preferably described as silicone in nature. This coating is more specifically intended to reduce the impermeability to oil of the head gaskets. It is a relatively thick coating: from 0.1 to 10 mm, which is characterized by a relatively long time of crosslinking, of several minutes, and which can not prevent a heat activation for crosslinking, even in cases where the UV radiation. This known coating is therefore not satisfactory as regards the requirements related to large-scale industrial production. On the other hand, the fact that the crosslinking of this fluorosilicone composition is based on a SiH / SiVi hydrosilylation mechanism, imposes stability problems. U.S. Patent No. 5,260,348 also describes a silicone composition crosslinkable under UV radiation, according to a condensation mechanism. A composition of this type is useful for the preparation of non-stick coating ("release coating") mainly for cylinder head gaskets. This composition comprises a POS a, γ-diOH of the polydimethylsiloxane or polydifluoroalkylsiloxane type, a crosslinking agent of the methyl or et triacetoxysilane or methyla tribenzoxy ilane type, and a photoinitiator formed by an onium (iodonium) salt where the opposite ion is BF4 ~ or SbF6 ~. These silicone compositions crosslinkable under UV radiation by condensation, can not prevent a complementary thermal activation to obtain reasonable crosslinking durations. It is that this in itself complicates the industrial process. The most functional counter ion for cross-linking under UV radiation is SbF6 ~, but the major drawback of being toxic is to date. It is therefore necessary to state that in the current state of the art, there is no crosslinkable silicone composition perfectly adapted to the requirements of the specific application, such as impregnation and / or coating. flat joints and in particular cylinder head gaskets. The expected specifications for the impregnation and varnishing of cylinder head gaskets, which are mainly sealing or sealing, compressibility, anti-adhesion, stability, ease of use and preparation, are not met by the known crosslinkable silicone compositions. nowadays. In this state of knowledge, one of the essential objectives of the present invention is to update a crosslinkable silicone composition for the impregnation and varnishing of flat joints, mainly of cylinder head gaskets, which remedy the deficiencies of the prior art, and in particular that offer a process of application and preparation / crosslinking of the silicone coating, which is fast, that does not need sophisticated equipment, nor of high temperatures and that allows to obtain a coating of sufficiently non-stick coating and endowed with mechanical properties convenient. Another essential objective of the present invention is to find a crosslinkable silicone composition for impregnating and / or varnishing flat joints, mainly cylinder head gaskets, which is stable to storage, economical and which does not involve toxic solvents. Another object of the present invention is to provide a method of coating a flat gasket, mainly of a cylinder head gasket, by means of impregnation and / or varnishing, with the help of a crosslinkable silicone composition, this procedure must be easy to put into operation, be economical, fast to drive in a silicone cylinder head gasket, which is non-stick and what functions in its environment of use. Another essential objective of the present invention is to provide a flat gasket, and in particular a cylinder head gasket which is coated and / or impregnated with a crosslinked, non-stick and compressible silicone, having all the expected and previously mentioned specifications of "processability" material and of intrinsic qualities of the material Once these objectives have been set, the applicant has the merit of finding, after numerous studies and experiments, that, in a totally surprising and unexpected way, it is convenient to select the crosslinkable silicone compositions by cationic process, preferably under activation by ultraviolet radiation, in which the initiator is an onium borate and / or a borate of organometallic salts having, in particular, a borate counter-ion of a totally specific nature, mainly comprising a boron atom linked to at least one phenyl radical replaced by at least one electroatra group In addition to this advantageous selection of the initiator, the Applicant has isolated a class of POS carriers of organofunctional bridging groups (Gfp), crosslinkable by cationic route, for example of the epoxide or vinyl ether type, in which GfP groups are present in an amount of at least 0.01 equivalent per kg of POS. It is in this way that the present invention relates to the use: • for the realization of impregnations and / or non-stick coatings, put into operation in the motor block / cylinder head interface of the motors, and applied on these flat joints, mainly the head gaskets, • compositions based on at least one polyorganosiloxane (POS) that can be crosslinked cationically, preferably under ultraviolet radiation, and an effective catalytic amount of at least one initiating salt (PA), said use is characterized in that i) the initiator salt (PA) is formed by at least one onium borate of an element of groups 15 to 17 of the periodic classification [Chem. & Eng. News, vol. 63, No. 5, 26 of February 4, 1985] or an organometallic complex of an element of groups 4 to 10 of the periodic classification (same reference), - the ca th ion ion of said borate is chosen from: 1) -onium salts of the formula (I): [(R1) pA- (R2) m] + (I) formula in which: • A represents an element of the groups to 17, such as for example iodine, sulfur, selenium phosphorus or nitrogen, • R 1 represents a carbocyclic or heterocyclic aryl radical of 6 to 20 carbon atoms, said heterocyclic radical, such as heteroelements, containing nitrogen or sulfur, • R 2 represents R 1 or a linear or branched alkyl or alkenyl radical of 1 to 30 carbon atoms; said radicals R1 and R2 are optionally substituted with an alkoxy group of 1 to 25 carbon atoms, alkyl of 1 to 25 carbon atoms, nitro, chlorine, bromine, cyano, carboxyl, ester or mercapto, • n is an integer which it goes from 1 to + 1, where v is the valence of element A, • m is an integer that goes from 0 to av -1 with n + m = v + 1, 2) -oxoiso thiochromanium salts described in the application WO 90/11303, mainly the sulfonium salt of 2-ethyl-4-oxoisothiochromanium or 2-dodecyl-4-oxoisothiochromanium; 3) -sulfonium salts in which the cationic entity comprises: -3.1 at least one polysulfonium species of the formula III.1. wherein: - the symbols Ar1, which may be identical or different from each other, each represent a monovalent radical phenyl or naphthyl, optionally substituted with one or more radicals chosen from: a linear or branched alkyl radical of 1 to 12 atoms carbon, preferably 1 to 6 carbon atoms, a linear or branched alkoxy radical of 1 to 12 carbon atoms, preferably 1 to 6 carbon atoms, a halogen atom, an -OH group, a group - COOH, a ter-COO-alkyl group wherein the alkyl part is a linear or branched residue of 1 to 12 carbon atoms, preferably of 1 to 6 carbon atoms, and a group of formula Y4-Ar2 where the symbols Y4 and Ar2, have the same meanings given below, the symbols Ar2, which may be identical or different from each other or with Ar1, each represent a monovalent radical phenyl or naphthyl, optionally substituted with one or more radicals chosen from: a linear alkyl radical or branched from 1 to 12 carbon atoms, preferably from 1 to 6 carbon atoms, a linear or branched alkoxy radical of 1 to 12 carbon atoms, preferably 1 to 6 carbon atoms, a halogen atom, an -OH group, a -COOH group, an es-ter-COO-alkyl group wherein the alkyl part is a linear or branched residue of 1 to 12 carbon atoms, preferably 1 to 6 carbon atoms, preferably 1 to 6 carbon atoms, the symbols Ar3, which may be identical or different from each other, each represent a divalent phenylene or naphthylene radical, optionally substituted with one or more radicals chosen from: a linear or branched alkyl radical of 1 to 12 carbon atoms carbon, preferably 1 to 6 carbon atoms, a linear or branched alkoxy radical of 1 to 12 carbon atoms, preferably 1 to 6 carbon atoms, a halogen atom, an -OH group, a -COOH group , a group is ter-COO-alkyl where the alkyl part is a linear or branched acid of 1 to 12 carbon atoms, preferably of 1 to 6 carbon atoms, t is an integer equal to 0 or 1, with the supplementary conditions according to which: + when t = 0, the symbol And it is then a monovalent radical Y1 that represents the group of formula: + Y1 S ArJ Ar ' where the symbols Ar1 and Ar2 have the meanings given above, + when t = 1: on the one hand, the symbol Y is then a divalent radical that has the meanings Y ' And following: a group of formula: + S r 'where the symbol Ar- possesses the meanings given above, • Y3: a simple valence bond, Y4: a divalent residue chosen from: O C II O 0 a linear or branched alkylene residue of 1 to 12 carbon atoms, preferably 1 to 6 carbon atoms, and a residue of the formula Si (CH 3) 20,? on the other hand, in the case only where the symbol Y represents Y3 or Y4, the radicals Ar1 and Ar2 (terminals) possess, in addition to the meanings given above, the possibility of being linked to each other by the remainder Y 'consisting of Y'1 a 'simple valence bond or in Y'2 a divalent residue chosen from the residues cited by the definition of Y4, which is installed between the carbon atoms, opposite, located on each aromatic cycle in the ortho position with relation to the carbon atom directly linked to the S + cation; 3.2 and / or at least one monosulfonium species having a single cationic center S + per mole of cation, and consisting in most cases of the species of the formula: + Ar1 S-AR1 (III.2. in which Ar1 and Ar2 have the meanings given above with respect to formula (III.1), including the possibility of linking directly between them only one of the radicals Ar1 to Ar2 according to the manner indicated above, with regard to the definition of the supplementary condition in force when t = 1 in the formula (II), using the remainder Y '; 4) - the organometallic salts of the formula (IV): (L1L2L3M) + q (IV) formula in which: • M represents a metal from group 4 to 10, mainly iron, manganese, chromium, cobalt, • L1 represents 1 ligand bound to the metal M by p-electrons, ligand chosen from the α3-alkyl, α-5-cyclopentadienyl and 7-cycloheptatrienyl ligands and the α6-aromatic compounds chosen from the optionally substituted β6-benzene ligands and the compounds having from 2 to 4 condensed cycles, each cycle being capable of contributing to the valence layer of the metal M with 3 to 8 electrons p, • L2 represents a ligand linked to the metal M by p-electrons, ligand chosen from the ligands? -cycloheptatrienyl and the 6-aromatic compounds chosen from the optionally substituted β6-benzene ligands and the compounds having from 2 to 4 condensed cycles, each cycle being capable of contributing to the valence layer of metal M with 6 or 7 electrons p. • L3 represents from 0 to 3 identical or different ligands linked to the metal M by electron s, ligand or ligands chosen between CO and N02 +; the total electronic charge q of the complex to which L1, L2 and L3 contribute and the ionic charge of metal M, is positive and equal to 1 or 2; the borate anionic entity has by formula: [BXa Rb] "formula in which: a and b are integers that go, for a from 0 to 3, and for b from 1 to 4 with a + b = 4, the symbols X represent: * a halogen atom (chlorine, fluorine) with a = 0 to 3, * an OH functional group with a = 0 to 2, the symbols R are identical or different and represent: a phenyl radical substituted with at least an electrically entraining group such as for example OCF3, CF3, N02, CN and / or by at least 2 halogen atoms (more particularly fluorine), when this cationic entity is an onium of an element of groups 15 to 17, * > a phenyl radical substituted by at least one element or an electrically active group, in particular a halogen atom (more particularly fluorine), CF3, OCF3, N02, CN, and in that the cationic entity is an organometallic complex of an element of groups 4 to 10 , * > an aryl radical containing at least two aromatic nuclei such as, for example, bifen ilo, naphthyl, optionally substituted with at least one element or an electron withdrawing group, mainly a halogen atom (more particularly fluorine), OCF3, CF3, N02, CN, whatever the cationic entity; (2i) the POS includes at least one monomer and / or an oligomer and / or a selected polymer: - among the compounds comprising at least one functional cross-linking group (organ) via cationic (GfP) bridge of heterocyclic nature which has one or more electrons atoms such as oxygen, sulfur, nitrogen and phosphorus, - and / or among those which include at least ethylenically unsaturated GfP and substituted with at least one electrowinning atom that increases the alkalinity of the p-system, the epoxidized POS and / or carriers of vinyl ether groups are particularly preferred, in the manner of Gfp, and (3i) the GfP are present, at a rate (expressed in equivalents per kg of POS) of at least 0.01, preferably at least 0.10, and more preferably still at a ratio of 0.15 to 2.00. The present invention thus proceeds from an advantageous, novel and inventive selection of a particular class of silicone compositions crosslinkable by cationic route - preferably under ultraviolet radiation - which is singled out with the nature of its (photo) initiator of the borate type of onium or borate of organometallic salts with a borate counterion of the borophenyl genus substituted with electron-withdrawing groups, for example fluorinated, as well as by a particular POS having an appropriate cup of functional GfP bridging functional groups. A selection of this type gives access to any of a number of interesting advantages, namely mainly: the excellent stability ('container life') of the composition, the evolution of the viscosity of the latter remains weak despite the presence of initiator for several days, even several months after the completion of the composition so that it is stored protected from light; a very good reactivity at room temperature; - a low sale price due to the low cost of raw materials and the simplicity of the application / crosslinking process, for impregnation and / or varnishing; a good flexibility of use, of the reactivity, stability, viscosity as well as the coefficient of friction of the varnish of the impregnator or of the non-crosslinked varnish, which can be easily modulated, to a large extent, by modifying: V the molar mass of the oil carrier POS of GfP, V the concentration of the initiator V as well as the molar ratio Gfp / POS; a coating process for impregnation and / or varnishing, simple to put into operation, fast, that does not need sophisticated and expensive equipment, and that is therefore fine, productive and profitable; - an absence of resorting to toxic products in the composition. It should also be noted that the varnishes or impregnations obtained on the flat joints, in particular on the head gaskets, have a beautiful appearance (absence of bubbles) and satisfy the required qualities of non-adhesion, tightness or tightness and compressibility. On the other hand, the varnish and / or the impregnated crosslinker have good mechanical properties, an abrasion resistance as well as a thermal resistance, a resistance to oils and more generally a resistance to aggressive products such as cooling liquid , totally satisfactory. According to a preferred arrangement of the invention, the POS put into operation has Gfp of the epoxide and / or vinyl ether type and is selected from among the POS which are: - either linear or substantially linear, and consisting of portions of the formula (V), terminated by portions of the formula (VI), - or cyclic and consisting of portions of the formula (V): R1 RJ Si- (V) -Yes -O- (VI) R1 formulas in which: the symbols R1 are similar or different and represent: either a linear or branched alkyl radical of 1 to 6 carbon atoms, optionally substituted, advantageously with one or two halogens, the optionally substituted alkyl radicals are: methyl, ethyl, propyl, octyl and 3, 3, 3-trifluoropropyl, or a cycloalkyl radical of 5 to 8 carbon atoms, optionally substituted, - or an aryl or aralkyl radical, optionally substituted: principally by halogens and / or alkoxyls, the phenyl, xylyl, tolyl and dichlorophenyl radicals which are more particularly selected, and, more preferably still, at least 60 mol% of the radicals R1 are methyl, • the symbols Z are similar or different and represent: either the radical R1, or a Gfp group corresponding to an epoxide residue or vinyl ester bonded to silicon by means of a divalent radical containing, advantageously, 2 to 20 carbon atoms including, optionally, a heteroatom, at least one of the symbols Z corresponds to a group Gfp. As examples of organofunctional groups, Gfp of the epoxy type, those of the following formulas can be mentioned: In the case of Gfp organophunic groups of the vinyl ether type, there may be mentioned, for example, those contained in the following formulas: - (CH2) 3-0-CH = CH2; - (CH 3) 2"-R") -CH = CH 2 - (CH 2) 3- CH = CH-R 5 with R 4 = linear or branched alkylene of 1 to 12 carbon atoms, optionally substituted, or arylene, preferably phenylene, optionally substituted, preferably by one to three alkyl groups of 1 to 6 carbon atoms; with Rs = linear or branched alkyl of 1 to carbon atoms. The POS used has a 'viscosity'? (expressed in mPa.s at 25 ° C) where the value can vary considerably according to the application conditions and the nature of the joints to be treated. In the case of the treatment of an already coated joint or the placement of a small thickness of coating, a POS having a low viscosity between:? 200 and 3000, and - preferably 300 and 2000, - > • and more preferably still between 400 and 900. In the case of the treatment of an uncoated gasket or the placement of a larger coating thickness, a POS having a higher viscosity between: - a higher value will advantageously be used. of 3000 and 10000, - > preferably: a value greater than 3000 and 6000, - and more preferably still: a higher value of 3000 and 5000. These viscosity values refer both to the linear POS and to the cyclic POS susceptible to be operated in accordance with the use according to the invention. The dynamic viscosity at 25 ° C, of all the silicone polymers considered here, can be measured with the help of a viscometer BROOKFIELD, according to the standard AFNOR NFT 76 102 of February 1972. The viscosity that is in question in the present description, is the dynamic viscosity at 25 ° C, called "Ne toniana", ie the dynamic viscosity that is measured , in a manner known per se, to a shear viscosity gradient sufficiently small so that the measured viscosity is independent of the velocity gradient. According to the invention, it is perfectly considerable to operate a mixture of different products with portions of formula (V) and (VI), as defined above (linear and / or cyclic). Preferred polyorganosiloxanes with epoxy or vinyloxy functional groups are described mainly in German Patent DE-A-4,009,889; European Patents EP-A-0, 396, 130; EP-A-0,355,381; EP-A-0, 105, 341; French Patents FR-A-2,110,115; FR-A-2, 526, 800. The polyorganosiloxanes with epoxy functional groups can be prepared by hydrosilylation reaction between the oils with Si-H portions and epoxy-functional compounds, such as for example the 4-vinyl cyclohexenoxide, allyl glycidyl ether. Polyorganosiloxanes with vinyloxy functional groups can be prepared by hydrosilylation reaction between oils with Si-H portions and compounds with vinyloxy functional groups, such as for example allyl vinyl ether, allyl-vinyl oxyethoxy benzene. In the case of the initiator, which in practice is a photoinitiator (PA) since the activation of the crosslinking is preferably carried out under UV radiation, it is preferable to put into operation according to the invention, a PA that includes a borate anionic entity selected from the following group: [B (C6F5) 4] "[B (C6H4CF3) 4]" [B (C6H3 (CF3) 2) 4] ~ [(CSF5) 2BF2] ' [CsF5BF3r [B (C6H3F2) 4r, [B (C6F4OCF3) 4]] and their mixtures In the case of the cationic entity of the photoinitiator, the following are distinguished: - 1) the onium salts of formula (I) - 2) the salts of oxoisothiochromanium of formula (II) 3) the mono- and / or polysulfonium salts of the formula (III.1) and / or (III.2) 4) the organometallic salts of the formula (IV). The first counter-ions of type 1) are described in numerous documents mainly in U.S. Patent Nos. US-A-4, 026, 705, US-A-4,032,673, US-A-4, 069, 056, US-A -4, 136, 102, US-A-4,173,476. Among these, the following cations will be of more particular privilege: [(f) 2I] + [C8H17-0-fIf] + [(f-CH3) 2I] + [C? 2H25-fIf] + [(CßH? -7 -Of) 2I] + [(C8H17-0-fIf)] + [(f) 3S] + [(f) 2-Sf-0-C8H17] + [CH3-fIf-CH (CH3) 2] + [fSfS (f) 2] + [(C12H25-F) 2I] + [CH3-fIf-0C2H5] + In the case of the second family of cationic entities of formula (ti) and of the oxoisothiochromanium type, this preferably comprises cations corresponding to the structure Say it is defined on page 14 of International Application WO-A-90/11303 and has the formula (II): where the radical R has the meaning given in this application WO with respect to the symbol R1; - a cationic entity of this type which is advantageously preferred is that where Rb represents an alkyl radical, linear or branched, of 1 to 20 carbon atoms. Particularly suitable salts of oxoisothiochromanium are the sulfonium salt of 2-ethyl-4-oxoisothiochromanium or 2-dodecyl-4-oxoisothiochromanium.

As regards the cationic entities 3), it will be specified that the cationic polysulfonium entity preferably comprises a species or a mixture of species of the formula (III.1) in which: the radicals Ar1, identical or different from each other, represent each a phenyl radical, optionally substituted with a linear or branched alkyl radical of 1 to 4 carbon atoms or with * the group of the formula: - the radicals Ar, identical or different from each other and with Ar1, each represent an eadical phenyl, optionally substituted with a linear or branched alkyl radical of 1 to 4 'carbon' atoms, - the radicals Ar3 each represent a radical unsubstituted para-phenylene, - t equals 0 or 1, with the supplementary conditions according to which: + when t = 0, Y = Y1 -S + Kr- Ar 'where the radicals Ar1 and Ar2 have the preferred meanings given above in the present paragraph; + when t = 1:? on the one hand, Y = Y2 to Y4 with: + S Ar 'where the radical Ar2 has the preferred meaning given above in the present paragraph, and "a valence bond, Yq -O- Y? On the other hand, when Y = Y3 or Y4 and when it is desired then to put into operation the radicals Ar1 and Ar2 (terminals) linked to each other, a Y 'link consisting of a valence bond or the O residue is installed. The monosulfonium species, when they exist, that fall within the framework of this preferential modality, are species of formula III.2 in which the symbols Ar1 and Ar2 have the preferred meanings indicated above in the preceding paragraph, including, when these radicals are directly linked together by a residue Y ', the installation of a valence bond or the residue O. As examples of cationic sulfonium entities, there may be more particularly cited: • the mixtures, in variable quantities, of the species 5_ + 2_ + eventually 3_, • the mixtures, in variable quantities, of the species 5 with the species 10 of the formula: lfi The borate anionic entity is preferably chosen from the anions of the formula [BXaRb] ~ in which: the symbols X represent a fluorine atom, the symbols R, identical or different, represent a phenyl radical substituted with at least one electron withdrawing group chosen from OCF3, CF3, NO2 and CN and / or by at least two fluorine atoms. Advantageously, the borate anionic entity of the formula [BXaRb] ~ is chosen from the following anions: [B (C6F5) 4] - [B (C6H4CF3) 4r [B. { C6H3 (CF3) 2} 4] "1 '3' 5 ' [(C6F5) 2BF2] "[B (C6F4OCF3) 4]" [B (C6H3F2) 4] - 2 '4' 6 ' The new polysulfonium borates which will be put into operation most preferably are the salts formed by the association of the following cations and anions: Caión Anión 5 1 '5 3' 5 4 'mixtures 5_ + 10 1' mixtures 5_ + 1_0 3 'mixtures 5 + 10 4' These polysulfonium borates can be prepared by exchange reaction between a salt of the cationic entity (halide, such as, for example, chloride, iodide) with an alkali metal salt (sodium, lithium, potassium) of the anionic entity. The operating conditions (respective amounts of reagents, choice of solvents, duration, temperature, agitation) are at the discretion of the person skilled in the art; these should allow the desired polysulfonium borate to be recovered under the solid form, by filtering the formed precipitate or in the oily form by extraction with the aid of an appropriate solvent. The operation modalities of halide synthesis of the cationic entities of the formula (III.1) are mainly described in: 'Polymer Bulletin (Berlin)', vol 14, pages 279-286 (1985) and North American Patent No. US-A-4, 400, 541. According to an alternative concerning to the preparation of polysulfonium borates, the latter can be prepared directly by reaction between a diarylsulphoxide and a diarylsulfide according to the teaching described in: * J. Org. Chem. ", Vol. 55, pages 4222-4225 ( 1990). These novel polysulfonium borates can be put into operation, as they are obtained at the exit of their preparation process, for example under the solid or liquid form or in solution in an appropriate solvent, in monomer / oligomer / polymer compositions that are intended to be polymerized and / or cross-linked by cationic process and under activation, for example with ultraviolet radiation. The monosulfonium species (III.2) where the previous question has existed, can be in particular the coproducts that are formed at the time of the preparation of the polysulfonium cations, and where the presence can be more or less avoided. Up to 99%, more in general up to 90% and still more in general up to 50 mol% (of cation) of the polysulfonium species of the formula (III.1) can be replaced with monosulfonium species (III .2). Regarding the fourth type of cationic entity, this is described in U.S. Patent Nos. US-A-4, 973, 722, US-A-4,992,572, European Patent Applications EP-A-203,829, EP-A-323,584 and EP-A-354, 181. The most suitable organometallic salts used in practice are mainly: - (5-cyclopentadienyl) (6-toluene) Fe + - (5-cyclopentadienyl) (6-methyl-1-naphthalene) Fe + ( 5-cyclopentadienyl) (? 6-cumene) Fe + the bis (? 6-mesitylene) Fe + - the bis (? 6 -benzene) Cr + It is deduced from this process that the preferred photoinitiators according to the invention are those that respond to the following formulas: [(f) 2I] +, [B (C6F5) 4] - [C8H17-0-fIf] +, [B (C6F5) 4r [C12H25-fIf] +, [B (C6F5) 4r [B (C6F5) 4] - [B (C6F5) "[(F) 3S] +, [B (C6F5) 4] - [(f) 2S-f-0-C8H17] +, [B (C6H4CF3) 4]" [(C2H25-f) 2I] +, [B (C6F5) 4] "[(f) 3S] +, [B (C6F4OCF3) 4]" [(f-CH3) 2I] +, [B (C6F5) 4 ] "[(f-CH3) 2I] +, [B (C6F4OCF3) 4]" • (? 5-cyclopentadienyl) (? 6-toluene) Fe +, [B (C6F5)] ~ (? -cyclopentadienyl) (? d -metil-l-naf talen) F e +, [B (C6F5) 4r (? 5-cyclopentadienyl) (? 6-cumene) Fe +, [B (C6F5) 4- As another literary reference to define the borates of onium 1) and 2) and the borates of the organometallic salts 4), selected as photoinitiators in the context of the use of cylinder head gaskets according to the invention, the entire content can be cited of European Patent Applications Nos. 0,562,897 and 0,562,922. This content is integrally incorporated by reference in the present description. The initiator salts of type 1) and 2) put into operation in the context of use according to the present invention can be prepared by exchange reaction between a salt of the cationic entity (halide, such as, for example, chloride, iodide, hexafluorophosphate). , tetrafluoroborate, tosylate) with an alkali metal salt (sodium, lithium, potassium) of the anionic entity. The operating conditions (mainly respective amounts of reagents, choice of solvents, duration, temperature, agitation) are at the choice of the person skilled in the art; these must allow recovering the initiating salt sought, under the solid form by filtering the formed precipitate, or in the oily form by extraction with the aid of an appropriate solvent. The alkali metal salts of the anionic entity can be prepared in a known manner, by exchange reaction between a halogenoborated compound and an organometallic compound (for example magnesium, lithium, tin) including the desired hydrocarbon groups, in a stoichiometric amount, followed optionally of a hydrolysis with the aid of an aqueous solution of alkali metal halide; this type of synthesis is for example described in 'J. of organometallic Chemistry ", Vol. 178, pp. 1-4, 1979; 'J.A.'C.S." 82, 1960, 5298; 'Anal. Chem. Acta "44, 1969, 175-183; U.S. Patent No. US-A-4, 139, 681 and German Patent DE-A-2, 091, 367; 'Zh. Org. Khim", Vol. 25, No. 5, pages 1099-1102, May 1989. The mode of operation of the salts of the cationic entity 4) of the formula (IV) is described mainly in D. ASTRUC, Tetrahedron Letters, 36, p. 3437 (1973); D. ASTRUC, Bull. Soc. Chim. Fr, 1-2, p. 228 (1976); D. ASTRUC, Bull. Soc. Chim. Fr, 11-12, p. 2571 (1975); D. ASTRUC, CR Acad. HE. Paris, series C, 272, p. 1337 (1971); A. N. NESMEYANOV and collaborators, Izves, Akad, Nauk SSSR, ser. Khim., 7, p. 1524 (1969); A.N. NESMEYANOV et al., Dokl. Akad. Nausk SSR, 160 (6), p. 1327 (1965); A.N. NESMEYANOV et al., Dokl. Akad. Nausk SSSR, 149 (3), p. 615 (1963). In practice, the initiators of the use according to the invention are prepared in a very simple manner by dissolving the onium borate or the organometallic complex, preferably onium, occurring under the solid form (powder) in a solvent. According to an alternative embodiment with respect to onium borate, the latter can be prepared directly in the solvent, from a salt (for example chloride) of the cation (iodonium) and a salt (for example potassium) of the borate anion . Preferably, it is provided, according to the use according to the invention, that the initiator (PA) is used in solution in an organic solvent, preferably chosen from the proton donor solvents and more preferably still from the following group: isopropyl alcohol , benzyl alcohol, diacetone alcohol, esters of hydroxylated carboxylic acid, such as butyl lactate, and mixtures thereof. It should be pointed out that by an effective catalytic amount of PA, it is understood, in the sense of the invention, that there is sufficient amount to initiate crosslinking. To the extent that in practice, as indicated above, the photoinitiator is advantageously dissolved in a polar solvent, in such quantity that its title for the solution obtained is between 1 and 50% by weight, preferably between 10 and 30% by weight, and more preferably still between 15 and 25% by weight. According to an advantageous embodiment of the use of the invention, the incorporation of PA in solution of the composition comprising the POS with molar proportion in given GfP, is done at a ratio of 0.1 to 10% by weight of solution in relation to the final mixture, preferably 0.5 to 5% by weight, and more preferably of the order of 1% by weight. Among the borate-type photoinitiator (s) 1) to 4), the initiator system may comprise, according to an advantageous variant, at least one photosensitizer selected from (poly) aromatic, optionally metallic, and heterocyclic products, and preference in the list of following products: phenothiazine, tetracene, perylene, anthracene, diphenyl-9, 10-anthracene, thioxanthone, benzophenone, acetophenone, xanthone, fluorenone, anthraquinone, 9,10-dimethylanthracene, 2-ethyl-9, 10- dimethyloxyanthracene, 2,6-dimethylnaphthalene, 2,5-diphenyl-1,3,4-oxadiazole, xantopinacol, 1,2-benzanthracene, 9-nitro-anthracene, and mixtures thereof. According to a variant of the use according to the invention, the crosslinking inhibitors, preferably chosen from the alkali products, can be put into operation, and more preferably still between the alkali products of the aminated type, for example of the type of those which consist of a silicone on which is grafted at least one amino group, preferably tertiary. It is possible to resort to other known additives in this type of application of the crosslinkable silicone compositions, under UV radiation by cationic route. Examples of these other additives will be given later in a part of the present description, in relation to the compositions.

The systems for preparation of the non-stick coating, by crosslinking a film of a silicone composition, by exposure to ultraviolet radiation, and by means of crosslinking mechanisms of the cationic chain reaction type, are known, as shown mainly by the applications European Patent Nos. 0,562,897 and 0,562,922 discussed above. But he would never have imagined until after exploiting such systems or such compositions for the coating (impregnation / varnishing) of flat joints, mainly of head gaskets, selecting POS that have specific rates of Gfp crosslinking, epoxy type or vinyl ether, for example. The advantages of these systems are: - little or no solvents. It is a small pollution and a low cost. - a fast crosslinking where a high possibility results. a weak heating from which arises a possibility to enlarge the spectrum of considerable supports. a small energy consumption that induces a substantial economy. a methodological simplicity and on the plane of the device, which limits the cost of the necessary industrial investments. In the case where it is used as a varnish, the silicone composition selected according to the invention is applied to a support formed by a flat gasket, mainly a cylinder head gasket, made airtight or sealed by impregnation with the aid of a silicone and / or coated with a layer of silicone elastomer designed to form, for example, the sealing platform. Thus, according to a variant of the invention, the receiving support of the silicone coating, obtained by cationic crosslinking, is a flat gasket, mainly a cylinder head gasket: ° which is previously impregnated with at least one gasket material. sealing or sealing formed by at least one crosslinked polymer, preferably by at least one silicone resin, and / or which is previously coated with at least one layer of at least one elastomer, preferably selected from cross-linked silicone elastomers or not and their mixtures. In other words, varnishing with the help of the selected silicone composition can be carried out directly on the bare surface of the flat joint, mainly on the cylinder head gasket, whatever its nature, or on the flat gasket, mainly the gasket. head gasket impregnated with a cross-linked silicone resin of the condensation or polyaddition type, or on a flat gasket, mainly a cylinder head gasket impregnated with a cross-linked silicone resin and covered with a cross-linked or non-formed silicone elastomer, for example, the board platforms. The coating according to the invention can therefore be applied on any metal support, composite (kevlar, graphite) silicone elastomer, fluorinated elastomer of the viton type or NBR elastomer. Advantageously, the flat seal varnish, mainly the cylinder head gasket formed by the coating obtained by crosslinking by the cationic route, is single layer or multi-layer and has a thickness comprised between 1 and 100 μm - preferably between 5 and 50 μm and more preferably still between 10 and 20 μm. According to another of these aspects, the present invention relates to a method of carrying out impregnation (s) and / or anti-adhesive coating (s) at the engine block / cylinder head interface on the supports constituted by flat gaskets, mainly head gaskets, characterized in that it consists essentially of putting into operation a crosslinkable composition under the effect of ultraviolet radiation and possibly under the effect of heat, said composition and the support being those as defined above. The present invention also relates to a flat gasket, mainly a cylinder head gasket., characterized in that it is impregnated and / or coated by a matrix obtained by cationic crosslinking according to the use as defined above and / or to the process as defined above. Also within the scope of the invention, any cationic crosslinkable silicone composition is included, characterized in that it is intended to make the impregnations and / or the anti-adhesive coatings on flat joints, mainly cylinder head gaskets, and because it comprises: at least one POS with groups Gfp as defined above, - at least one initiator, preferably a photoinitiator, (PA) of a type of onium borate as defined above, at least one PA solvent as defined above, - and at least an additive chosen from those generally used in treatments aimed at making hermetic or watertight and adherent the cylinder head / engine block interface, and in particular flat gaskets, mainly such as head gaskets. The various additives suitable for the final application considered, namely the flat gaskets and mainly the cylinder head gaskets are, for example, one or more crosslinking inhibitors, preferably chosen from the alkali products, and more preferably still from the alkali metal products of the present invention. aminated type, for example of the type consisting of a silicone on which is grafted at least one amino group, preferably tertiary or of the type of those comprising a piperidinyl residue optionally substituted with alkyl. The compositions according to the invention may also include: adhesion modulators (resins or silicone linear polymers including, for example, vinyl, epoxy, vinyl ether, alcohol functional groups), such as those disclosed in European Patent Application No. 0,738,769; • one or several photosensitizers of the type mentioned above, • one or more fillers, such as, for example, mineral fillers, such as synthetic fibers (polymers) or natural crushed, calcium carbonate, talc, clay fibers, titanium dioxide, precipitation or combustion silica; • one or more accelerators of the polymerization and / or crosslinking preferably chosen from the hydroxylated carboxylic acid esters liquid at room temperature (23 ° C); • one or more thixotropic agents; • and their mixtures.

Likewise, soluble dyes, oxidation inhibitors and / or any other material that does not interfere with the catalytic activity of the photoinitiator and that do not absorb in the wavelength range chosen for photoactivation, can be added to the composition or posts in operation within the framework of the process according to the invention. These compositions according to the invention are prepared, without distinction, before (even long before) or immediately before use. It should be noted that these compositions are particularly stable to storage and offer, according to the process of the invention, fast crosslinking kinetics. In addition, its non-crosslinked state, before exposure to activation light radiation, offers great facilities for handling, application or placement on flat joints, mainly such as head gaskets. The method according to the invention which makes it possible to make flat joints, mainly non-adhesive cylinder head gaskets, consists in applying an amount of the composition of the invention, generally comprised between 2.5 and 250 g per m2 of surface, to harden and to crosslink the composition with energy input where at least a part, preferably the whole, is provided by ultraviolet radiation. The ultraviolet radiation used has a wavelength comprised between 200 and 400 nanometers, preferably between 254 and 360 nanometers. The duration of the irradiation can be short and this is generally less than 1 second, and is of the order of a few hundredths of a second for the very small thicknesses of coatings. The crosslinking performed is excellent, even in the absence of any heating. Of course, the coupling of the photoactivation to a thermoactivation, for example by heating between 25 and 100 ° C, is not excluded from the invention. Of course, the hardening time can be regulated, mainly by the number of UV lamps used, by the duration of exposure to UV light and by the distance between the composition and the UV lamp. The amounts of the compositions deposited on the supports are variable and are staggered, more frequently, between 2.5 and 250 g / m2 of treated surface. These quantities depend on the nature of the supports and the non-stick properties sought. These are more frequently comprised between 10 and 50 g / m2 for the non-porous supports. The following examples are given by way of illustration and can not be considered as limiting the domain and spirit of the invention.

EXAMPLES I. Raw Materials 1.1 The functionalized polyorganosiloxanes (UV RESIN) put into operation are the (1,2-epoxy-4-yl-cyclohexyl) -polydimethylsiloxanes of the formula: -.

Several POSs having different proportions of epoxy are prepared. This synthesis is carried out in the following way: The siliconized oil put into operation is a polydimethylhydrogenosiloxane (PDMS) of the following simplified formula: M2 D'a Db Me Me Me I M Me SiO; D Yes 0 D '= Yes -0 I Me H ? The VCMX Marketed by UNION CARBIDE. - > The catalyst = Karstedt Pt at 10% Pt in divinyltetramethyldisiloxane; this catalyst can be used according to the need in a mixture with a Pt inhibiting agent consisting of thiodiethanol. - »Resin A21 is an AMBERLI exchange resin.

? METHODOLOGY Phase I: PHASE OF HIDROSILILATION load 1/3 silicone oil SiH under N2 atmosphere (first part) - load the VCMX under agitation - load the catalyst; Pt of karstedt to 10% - heat slowly up to 60 ° C under N2 - load the second part of the silicone oil keeping? = 60-80 ° C (duration of introduction: 0.5 to 1 hour) - maintain up to TTSÍH% maximum (residual SiH <300 ppm) PHASE II: ELIMINATION OF Pt - load resin A2 1 (crushed, dry) - maintain 60-80 ° C until obtaining the maximum discoloration of the medium (duration >; 10 hours to get < 100 Hazen) filter to remove the ion exchange resin PHASE III: ELIMINATION OF LIGHT MATERIALS - vacuum devolatilize: 120/125 ° C to 5 mmHg under N2 purge to remove the siliconized oligomers and the excess VCMX - effect a final clearance to eliminate the possible micro-gels formed during the previous stage. The final polymer yield recovered = 90% Weight data The POS A, B, C, D, E obtained in this way are defined in the following table: 1. The initiator (hereinafter referred to as PA photoinitiator) is an onium borate: the tetrakis (pentafluorophenyl) borate of ditolylodiconium of the formula: The cation of this onium borate is prepared according to the general methodology described in European Patent Applications Nos. 0,562,922 and 0,562,897. Regarding the borate anionic entity, proceed as follows: Bromopentafluorobenzene (21.3 g, * "• 0.086 mol) and isopropyl ether are charged, under an inert atmosphere, in a 500 ml. mechanical agitation, with a coolant and with an addition funnel. The mixture is stirred and cooled to -78 ° C with the aid of an acetone + dry ice bath. The n-butyl lithium in hexane solution (1.6 M, 52.3 ml, 0.97 eq) is charged in the addition funnel, then added in about 10 minutes. The mixture is then left for 30 minutes under stirring at a temperature of -78 ° C. The addition funnel is replaced with an addition funnel containing boron trichloride in hexane solution (1.0 M, 19 ml). The boron trichloride is added in 15 minutes, then the reaction mixture is left for 30 minutes under stirring at the temperature of -78 ° C. The temperature is immediately allowed to reach the mixture in about 1 hour. A saturated aqueous solution of potassium chloride (100 ml) is then added. The mixture is then biphasic and homogeneous. The isopropyl ether is distilled. The KB (C6F5) 4 precipitates at the end of the distillation. This is recovered by filtration, then washed with a saturated solution of potassium chloride (100 ml) before being dried under vacuum at the temperature of 35 ° C. In this way a product is obtained that titrates 97% of the expected product, with a yield of 99%. The solvents used are isopropyl alcohol, butyl lactate, diacetone alcohol esters or mixtures thereof. The photoinitiator system is prepared by the solubilization of onium borate (eventually completed with a part of epoxidized PDMS to be put into operation), in solvent. 11. The general mode of operation followed is as follows: at 100 parts by weight of epoxidized PDMS, - x parts by weight of a solution of onium borate in a solvent (titre 18% by weight) are added by hand stirring for 30 minutes. minutes III. Material III.1 Type of UV lamp: FUSIÓN technology SYSTEM® F450 (Société FUSIÓN) Total power of the lamp: 120 Watts The emitter of the UV lamp is composed of a transparent quartz tube filled with mercury. The UV radiation is carried out by excitation of the emitter with microwaves and magnets that in this way cause the evaporation of the mercury and the emission of UV: UV Fusion system.

III .2 Characteristics of the UV bank: The UV bank carpet can reach a maximum sliding speed of the order of 52 m / minute. The speed of this bank is adjustable according to the needs of the user or the nature of the product to be reticulated. 111. 3 Meyer Bar: To deposit a film of thin thickness on the joints, a Meyer bar is placed. This bar contains the length of its rod with rays that allow, after the application of the resin, to obtain the desired thickness. The deposit is made automatically with the help of an electric motor with which it is possible to vary the speed of passage of the bar on the joint. 111.4 Cylinder head gaskets: The tests have been carried out on traditional 'Soft' joints (cardboard joints) that come from the group 'Payen' or 'joint Meillor.' These cardboard joints are made up of an agglomerate of composite fibers (generally based on KEVLAR). walled and grafted onto a metal lattice.

EXAMPLE Influence of the photoinitiator ratio on the Shore A hardness of the resin obtained by crosslinking under UV radiation a POS A functionalized with epoxy The POS used is the POS A. The PA is dissolved at a rate of 18% by weight in butyl lactate. The POS contains an inhibitor whose function is to increase the "container life" of the resin, which is present up to 50 ppm in the POS In all the examples, this inhibitor is constituted by a tertiary amine marketed under the brand name TINUVIN 765 by the company CIBA GEIGY (1, 2, 2, 6, 6, 6-pentamethyl-4-piperidyl derivative.) The methodology used is that described in the preamble of the examples, measurements of Shore A Hardness have been made at different proportions of photoinitiator solution, 1%, 1.5%, 2%, 2.5% and 3% (resin with inhibitor and photoinitiator in butyl lactate) Two reproducibility tests have been carried out (trials 1 and 2).

The reference is formed by a two-component, polyaddition resin (part A and part B mixed at 50/50 by weight). Part A consists of a vinyl silicone oil and a platinum catalyst (2.5% vinyl groups and 45 parts per million platinum). Part B consists of a mixture of different vinylated or hydrogenated silicone oils and a polymerization retarder consisting of ethynylcyclohexanol (1.5% of the vinyl groups and 20% of the polymethylhydroxy-siloxane group).

Results: Table 1 Aná1 is is The Shore A Hardness is virtually identical regardless of the composition of the UV +% photoinitiator resin mixture. This is distributed in a hardness range between 74 to 80. This is slightly higher than the hardness of the reference resin. These results, thus obtained, prove that the resin possesses the same level of crosslinking, whatever the concentration of PA.

EXAMPLE 2: Determination of Kónig Hardness 2. 1"INFLUENCE OF THE SLIDING SPEED OF THE UV BANK ON THE KONIG HARDNESS OF THE RESIN WITH INHIBITOR AT DIFFERENT PERCENTAGES OF PHOTOINICITER (BUTYL LACTATE) The aim of this study is to control, thanks to the Kónig hardness, the evolution of the crosslinking of type A UV resin as a function of the exposure hardness to UV irradiation and the proportion of added photoinitiator. The coating has been made with a Meyer No. 3 bar (deposited thickness of approximately 20 μm) on paper. The resin, once crosslinked at different sliding speeds, is then subjected to the Kónig Pendulum.

Results POS resin with 50 ppm of inhibitor constituted by TINUVIN. = > Aná 1 i s i s: After analysis of the table concerning the Kónig hardness of the UV resin (with inhibitor) at different proportions of photoinitiator (butyl lactate) as a function of the speed of the UV bank, it is found that the crosslinking takes place in all cases , whatever the percentage of photoinitiator and the speed, even for a small proportion of photoinitiator and a maximum speed on the UV bank. The Kónig hardness values regardless of the percentage of photoinitiator and the UV bank speed are between 19.6 and 29.4. It would seem, however, that the 1% mixture has a better crosslinking rate than the other mixtures, and despite the variation in the sliding speed of the bank. 2. 2. EVOLUTION IN THE TIME OF THE KONIG HARDNESS OF THE RESIN A (WITH INHIBITOR) AND OF THE REFINEMENT RESIN ON A METAL PLATE (STEEL) COVERED BY ONE SIDE OF A PROMOTER OF ADHERENCE A metal plate is coated on one side, by an adhesion promoter or primary (isopropyl titanate 4% in isopropyl alcohol) previously defatted. Next, the resin (resin A and reference resin) is deposited on each face and subsequently the evolution of the Kdnig hardness is controlled five days after the application.

Results: = > Analysis : The Kónig hardness of the reference resin is higher than that of the resin A. But its value remains unchanged in the course of time, after five days at room temperature. The adhesion promoter improves the hardness in the case of the reference resin. As for the resin A, the adhesion promoter decreases the Kónig hardness. The hardness of Resin A increases after five days at room temperature. EXAMPLE 3: Control of anti-adhesion of UV resin = > Principle: ASTM F 607-84 standard test The anti-adhesion test is carried out using an extensometer. A small thickness of POS A resin film thanks to a Meyer bar is applied to each face of a pre-impregnated soft (or matched) joint. This resinous film with the oily appearance is then cross-linked with a passage under the UV bench where the sliding speed of the carpet is 2.8 m / minute, in order to ensure that the cross-linking is complete. In the case of the reference resin, the joint, after coating with the Meyer bar, is placed inside a graduated oven at a temperature of 150 ° C for about 5 to 10 minutes. After the varnishing of the joint, the joint is cut out in the punching machine to form two disc-shaped circular discs (0 50 mm) that include on each of these faces the non-stick varnish. Each disc is placed between two G5 cast iron supports. With the help of a press, a pressure of 10 Mpa is exerted on the supports that contain the circular joint, to be placed in the conditions of tightening of the head gaskets at the moment of the assembly of the engine. The pressure of 10 Pa is made by closing or tightening the bolts located at the ends of the press, with the help of a key that has a dynamometer. Next, the set of presses containing the samples of the varnished discs is subjected to a temperature of 130 ° C for 72 hours.

After a lapse of 72 hours under the stove at 130 ° C, the presses are removed from the stove and left for a day at room temperature in order to cool down. These are then disassembled in order to recover the supports that enclose the circular joints. These supports are embedded in the jaws adapted to the extensometer where the paper will measure the breaking force (in Newtons) that is exerted to separate the two supports that imprison the joint. In fact, the varnish resin deposited on the joint can, after having suffered a temperature of 130 ° C and a pressure of 10 MPa for 72 hours, stop the interactions with the material of the supports, that is to say, or adhere to the supports . If the extensometer indicates a high breaking force, this means that the varnish adheres to the support and that the anti-adherence of the resin is weak. It happens, however, that the supports detach automatically during the disassembly of the press after the obligatory step in the stove at 130 ° C for 72 hours. This spontaneous detachment of the previously varnished joint comes from the excellent non-stick property of the silicone resin that has served the coating. The adhesion of the board is totally negligible. It will therefore be accepted that the breaking force, resulting from the separation of two supports that enclose the joint, is null and that the non-stick capacity of the resin is considerable. At the end of the break in the extensometer, each support, which has been used for the closing or tightening of the joint, is analyzed by the operator to estimate the percentage of resin that remains anchored. This percentage can be expressed in percent of cohesive or adhesive break. 100% cohesive rupture means that the joint has both adhered on the supports and that which is detached, dividing into two parts that remain linked to their initial contact support. 0% cohesive rupture corresponds to a perfect anti-adhesion of the resin on the supports, and no trace of the resin remains on the support after the rupture with the extensometer. = > Results: Tested resin = UV type A resin with TINUVIN inhibitor (50 ppm) and reference resin Coating: Meyer No. 3 bar, thickness of approximately 15-20 μm UV crosslinking: 1 step under UV bank, speed = 10% ( 2.8 m / minute) Crosslinking = Reference resin: 10-15 minutes a 150 ° C with an elevation in constant temperature from 70 ° C to 150 ° C.

Table 4 Table 4 (continued) Aná1 i s i s If reference is made to Table 4 which groups together the anti-adhesion test values of the type A UV resin and the reference resin, it turns out that the UV resin retains approximately the same anti-adhesion capacity, independently of the proportion of the photoinitiator (value average breaking force between 498 and 360 N). This anti-adhesion is comparable to that of the reference resin (mean value of the force until the breaking of 393 N). The anti-adherence of the reference resin is in the same order of magnitude of the UV resin.

CONCLUSION Type A UV resin (resin with TINUVIN inhibitor, photoinitiator diluted in butyl lactate) has the same mechanical properties as the reference resin. The anti-adhesion test has shown that the percentage of adhesive breakage would be close to 100% for the reference resin and that this is between 70% and 90%, as regards the UV resin, despite a force up to the equivalent break.

EXAMPLE 4: Influence of the presence of inhibitor and the chemical nature of the diluent used for the photoinitiator on the anti-adhesion 4. 1 UV Resin of type A: = > Principle: In order to know what would be the influences of the inhibitor and the diluent on the anti-adhesion, a series of four mixtures (NRNC, NRAC, ARNC, ARAC) of a proportion in photoinitiator solution of 2%, has been submitted to the anti-adhesion test.

Results: see Table 5 Resins V Resin tested: Resin A (idem to Examples 1 to 3) described in 1.1 V Reference resin: (idem to Examples 1 to 3) described in Example 1. Inhibitor: TINUVIN (idem to Examples 1 to 3) . Coating: Mayer bar No. 3, thickness of approximately 15-20 μm UV crosslinking: 1 step under UV bank, speed = 10% (2.8 m / minute) Crosslinking: Reference resin: 10-15 minutes at 150 ° C with a constant rise in temperature from 70 ° C to 150 ° C.

Table 5 O NRNC = UV Resin with 50 ppm of inhibitor and photoinitiator diluted in butyl lactate OR NRAC = UV Resin with 50 ppm of inhibitor and photoinitiator diluted in IPA = isopropyl alcohol = > ARNC = UV Resin without inhibitor and photoinitiator diluted in butyl lactate «• ARAC = UV Resin without inhibitor and photoinitiator diluted in IPA Note: Regarding the two tests of the resin ARNC and to the second test of the resin (NRAC), the supports of cast iron G5 that include the board, are separated simply after the dismantling of the press, after having been submitted to the stove at a temperature of 130 ° C. It is considered that the force until the rupture is null and that the constraint until the rupture is approximately equal to 0.

Aná1 i s i s The influence of the inhibitor on the anti-adherence of the varnish is remarkable. The UV resins that do not contain inhibitor (ARNC, ARAC) have almost no breaking force, and it is not necessary to impose the anti-adhesion test on the supports that include the varnished joint. Thus, during the dismantling of the press, the joint has no adhesion to the supports. The UV, ARNC and ARAC resins, comparatively to the reference resin (strength to rupture equivalent to 387.5 N), have a superior non-sticking property. The UV resins without inhibitor (ARNC and ARAC) have a 100% adhesive break (90% adhesive break for the reference resin). These 100% adhesive breaks, UVC RNA and ARAC resins prove that the latter do not adhere to the G5 cast iron supports, and have an excellent pre-stress behavior exerted by the anti-adhesion test. 4. 2 UV Resin type E: Example 4.1 is reproduced at the exit of resin E described in 1.1. An ARAC type mixture having a 1% photoinitiator solution ratio has been subjected to the anti-adhesion test. = > Results: force to rupture in N: 0 constraint to rupture in MPa close to 0 type of rupture: 100% adhesive.

EXAMPLE 5: Control of the dynamic viscosity of UV resins (NRNC, NRAC, ARNC, ARAC) at 2% ratio of photoinitiator solution The objective of this experiment is to evaluate the dynamic viscosities of each UV resin in a period of three days and follow its evolution. This in order to appreciate the 'container life' of each resin studied. = > Results: Table 6 = > NRNC = UV Resin with 50 ppm of inhibitor and photoinitiator diluted in butyl lactate OR NRAC = UV Resin with 50 ppm of inhibitor and photoinitiator diluted in IPA < t ARNC = Type A UV Resin without inhibitor and photoinitiator diluted in butyl lactate ARAC = UV Resin without inhibitor and photoinitiator diluted in IPA The inhibitor used is the same as the aforementioned TINUVIN.

EXAMPLE Determination of the polymerization speed of UV resins The objective of this example is to evaluate the polymerization rate of each type of UV resin and to know what proportion of photoinitiator is faster, this with certifying the results obtained previously, and to estimate the highest degree of crosslinking. The polymerization rate is determined with the aid of an apparatus called VNC RAPRA UV (Company RAPRA Ltd). The time is measured where 95% (T95) of the resin is crosslinked. This time will be immediately reported in the graphs. 6. 1 UV Resin Type A: The attached Figure 1 represents the T95 curves = f (proportion in 18% photoinitiator solution) for resin A, varying the composition as indicated hereinafter: = > NRNC = Type A UV Resin with 50 ppm inhibitor and photoinitiator diluted in butyl lactate • or NRAC = Type A UV Resin with 50 ppm inhibitor and photoinitiator diluted in I PA = > ARNC = UV type A resin without photoinitiator inhibitor diluted in butyl lactate OR ARAC = UV type A resin without inhibitor and photoinitiator diluted in IPA 6. 2 UV type A resin; B; C; D; E (see 1.1) The attached Figures 2 to 5 represent the curves RAPRA T95 = f (proportion in 18% photoinitiator solution) for resins A to D according to 1.1 above. The solvent is IPA. This one is not provided with inhibitor. For type E resin, the RAPRA T95 value is 0.8 minutes, with a ratio of 1% photoinitiator solution.

EXAMPLE 7: Proportion for UV Resin oils 7. 1 UV Resin Type A: B Principle: The proportion for the oils allows to verify the harmlessness and the stability of the resin in front of the oils responsible for the lubrication of the engine in the physical conditions (temperatures) and mechanisms imposed by the engine regime. This test is essential to the extent that it allows judging whether a non-stick silicone resin is not degraded and integrally stores its initial properties. The purpose of this test is to verify that the resin possesses the adequate qualities in order to suffer as little as possible the chemical aggressions to which it is confronted and exposed during the operation of an engine. To appreciate the firmness of the oils, a sample of resin of determined mass is placed in the engine oil and subjected to a temperature of 150 ° C for 72 hours. Next, the following parameters are examined: > the difference in mass the variation of the Shore A hardness > the thickness difference When all the experimental data have been collected, the loss or gain of mass, thickness and hardness in percentage (%) is determined. A percentage close to 0%, regardless of the parameter studied (mass, hardness or thickness) confirms an excellent resistance to oils in the simulation conditions of an engine operating in a regular regime (150 ° C).

Results: Resistance to oils has been carried out for type A UV Resins (see 1.1) without inhibitor = AR (0.5%, 1% AC photoinitiator, NC) and with NR inhibitor (1%, 3% photoinitiator) . - NR: UV resin with 50 ppm of AR inhibitor: UV resin without NC inhibitor: photoinitiator diluted in butyl lactate AC: photoinitiator diluted in IPA The photoinitiator, the inhibitor, the. resin A and the reference resin are the same as in Examples 1 to 6. = > The variation in the percentage of the mass of UV Resins NR, AR before and after the resistance to oils at 150 ° C Table 7 Aná1 i s i s After collecting the values of the masses, the reference resin and the resin type A-RNAC 0.5%, the best resistance to the oils is distributed. The A-NR resins have a less good oil resistance while the A-AR resins have a higher oil resistance. The A-NR resins have a tendency to be breakable. The Shore A hardness and the thickness of the A and reference resins are not affected by oil resistance. 7. 2 UV type E resin: Example 7.1 is reproduced at the exit of resin E described in 1.1. An ARAC type mixture that has a 1% photoinitiator solution ratio has been subjected to the oil resistance test.

Results:% M mass (g): + 6.4,% Shore A Hardness: - 2.5 EXAMPLE 8: Resistance to cooling liquid 1. UV Resin Type A: B Principle: The cooling liquid resistance test is comparable to the oil resistance test. The objective of this study is to verify the safety of the UV resin on contact with glycol or with the cooling liquid. The analysis and experimental procedure of the resistance to the cooling liquid is practically analogous to those of the resistance to oils, with the difference that the resinous and reticulated samples are placed inside a 100% stove for 72 hours, in 100 ml of cooling liquid. This test allows placing in the normal operating conditions of an engine and verify that there is degradation of the resin by the glycol.

Results: The resistance to the cooling liquid has been made for the type A resins (see 1.1) without inhibitor = AR (0.5%, 1% of photoinitiator AC, NC) and type A with NR inhibitor (1%; photoinitiator). - NR: UV resin with 50 ppm of AR inhibitor: UV resin without NC inhibitor: photoinitiator diluted in butyl lactate AC: photoinitiator diluted in IPA The photoinitiator, the inhibitor, the resin A and the reference resin are the same as in Examples 1 to 7.

Table 8 Analysis The loss in mass caused by a resistance to the cooling liquid is more important for the resins A-NR than AR. But it is the reference resin that keeps the best resistance to the cooling liquid (% M = - 1.30). The A-AR resins at 0.5% photoinitiator have an excellent resistance to the cooling liquid, comparable to that of the reference resin. After resistance to the cooling liquid, the A-NR resins are brittle and breakable. Shore A thickness and hardness vary a bit. 8. 2 UV type E resin: Example 8.1 has been reproduced from resin E described in 1.1. An ARAC type mixture that has a resistance in 1% photoinitiator solution has been subjected to the cooling liquid resistance test. ß Results:% M of mass (g). - 5% Shore A Hardness: + 8.

EXAMPLE 9: Determination of the level of crosslinking by the extractable rate, (Ext) Principle Evaluation of the influence of a solvent on the chemical structure of the silicone resin, crosslinked. Place a cylindrical specimen of the resin for 72 hours in the solvent taking care to weigh it before. The rate or proportion of extractables corresponds to the percentage of mass of resin extracted by the solvent (methylcyclohexane). If this rate is important, the mass recovered by the solvent is then high. This mass is in direct relation to the degree of cross-linking. Since the extractable rate is more considerable, the cross-linking of the analyzed resin is more mediocre. In effect, a high extractable rate means that the solvent attacks or more easily deteriorates the resin. Inverse, a small rate of extractables corresponds to a consistent level of crosslinking. - Initial M: mass of the resin after crosslinking M inflated: mass of the resin before being absorbed of solvent (72 hours in methylcyclohexane) M ext: mass of resin recovered by the solvent (initial M - final M) - M final: initial mass minus the mass extracted by the solvent (passage to the stove of the mass inflated at 70 ° C for 24 hours).

Removable rate: Ext (initial M - final M) * 100 / M initial.

Resin A (see 1.1), the reference resin, the inhibitor (with NR -50 ppm, without AC), the photoinitiator are the same as for Examples 1 to 8.

• Results: The experimental conditions are the same as in Example 8.

Table 9 Table 9 (continued) Me: average mass in number of interchain connections -% G: inflation rate -% Ext: Extractable rate - NC: solvent butyl lactate - AC: solvent IPA B Analysis: The A-AR resin (RNAC 0.5% RNAC 1% and ARAC 0.5%, ARAC 1%), followed by a 72-hour immersion in methyclocyclohexane, retains the properties and the excellent physical and chemical qualities that allow it to resist the aggression of the solvent. This one has a small extractable rate.

Claims (14)

1. The use for carrying out impregnation and / or non-stick coatings, put into operation in the motor block / cylinder head interface of the motors, and applied on flat joints, mainly head gaskets, of compositions based on at least one polyorganosiloxane (POS) crosslinkable cationically and of an effective catalytic amount of at least one initiating salt (PA), said use is characterized in that: i) the initiating salt (PA) is formed by an onium borate of an element of the groups 15 to 17 of the periodic classification [Chem. & Eng. News, vol. 63, No. 5, 26 of February 4, 1985] or of an organometallic complex of an element of groups 4 to 10 of the periodic classification (same reference), - the ca th ion ion of said borate is chosen from: 1) -onium salts of the formula (I): [(R1) "- A- (R) + (I) formula in which: R1 represents a carbocyclic or heterocyclic aryl radical of 6 to 20 carbon atoms, said heterocyclic radical may contain, as heteroelements, nitrogen or sulfur, R2 represents R1 or a linear or branched alkyl or alkenyl radical from 1 'to 30 carbon atoms; said radicals R1 and R2 are optionally substituted with an alkoxy group of 1 to 25 carbon atoms, alkyl of 1 to 25 carbon atoms, nitro, chlorine, bromine, cyano, carboxyl, ester or mercapto, • n is an integer which goes from 1 to + 1, where v is the valence of element A, • m is an integer that goes from 0 to av - 1 with n + m = v + 1, 2) -oxoisothiochromanium salts that have the formula: wherein the radical R6 has an alkyl radical, linear or branched, of 1 to 20 carbon atoms; 3) -sulfonium salts in which the cationic entity comprises: wherein the radical R6 has an alkyl radical, linear or branched, of 1 to 20 carbon atoms; 3) -sulfonium salts in which the cationic entity comprises: -3.1 at least one polysulfonium species of the formula III.1. + + Ar1 S Ar 'Y ArJ - S Ar: (III.1) Ar "Ar 't wherein: - the symbols Ar1, which may be identical or different from each other, each represent a monovalent radical phenyl or naphthyl, optionally substituted with one or more radicals chosen from: a linear or branched alkyl radical of 1 to 12 atoms of carbon, a linear or branched alkoxy radical of 1 to 12 carbon atoms, a halogen atom, an -OH group, a -COOH group, an ester-COO-alkyl group where the alkyl part is a linear or branched residue of 1 to 12 carbon atoms, and a group of formula Y4-Ar2 where the symbols Y4 and Ar2, have the same meanings given below, the symbols Ar2, which may be identical or different from each other or with Ar1, each represent a radical monovalent phenyl or naphthyl, optionally substituted with one or more radicals chosen from: a linear or branched alkyl radical of 1 to 12 carbon atoms, a linear or branched alkoxy radical of 1 to 12 carbon atoms, a halogen atom no, a -OH group, a -COOH group, an ester-COO-alkyl group where the alkyl part is a linear or branched residue of 1 to 12 carbon atoms, the symbols Ar3, which may be identical or different from each other, each represents a divalent radical phenylene or naphthylene, optionally substituted with one or more radicals chosen from: a linear or branched alkyl radical of 1 to 12 carbon atoms, a linear or branched alkoxy radical of 1 to 12 carbon atoms, an atom of halogen, an -OH group, a -COOH group, an ester-COO-alkyl group where the alkyl part is a linear or branched residue of 1 to 12 carbon atoms, t is an integer equal to 0 or 1, with the supplementary conditions according to which: + when t = 0, the symbol Y is then a monovalent radical Y1 representing the group of formula: + Y1 S - Ar1 Ar ' where the symbols Ar1 and Ar2 have the meanings given above, + when t = 1:? on the one hand, the symbol Y is then a divalent radical having the following meanings Y2 to Y4: • Y2: a group of formula: + S - Ar 'where the symbol Ar2 has the meanings given above, • Y3: a link of simple valence, and 'a divalent residue chosen between OR O O a linear or branched alkylene residue of 1 to 12 carbon atoms, and a residue of the formula Si (CH3) 20,? on the other hand, in the case only where the symbol Y represents Y3 or Y4, the radicals Ar1 and Ar2 (terminals) possess, in addition to the meanings given above, the possibility of being linked to each other by the remainder Y 'consisting of Y'1 a simple valence bond or in Y'2 a divalent residue chosen from the residues cited by the definition of Y4, which is installed between the carbon atoms, opposite, located on each aromatic cycle in the ortho position to the carbon atom directly linked to the S + cation; - 3.2 and / or at least one monosulfonium species having a single cationic center S + per mole of cation, and consisting in most cases of the species of formula: + ArJ S - ARJ (III.2) Ar ' in which Ar1 and Ar2 have the meanings given above with respect to formula (III.1), including the possibility of linking directly between them only one of the radicals Ar1 to Ar2 according to the manner indicated above, with regard to the definition of the supplementary condition in force when t = 1 in formula (II), resorting to residue Y '; 4) - the organometallic salts of the formula (IV): (LxL2L3M) + q (IV) formula in which: • M represents a metal of group 4 to 10, chosen from iron, manganese, chromium, cobalt, • L1 represents 1 ligand bonded to metal M by p-electrons, ligand chosen from the α3-alkyl, α-5-cyclopentadienyl and β-cycloheptatrienyl ligands and the α6-aromatic compounds chosen from the optionally substituted β-benzene ligands and the compounds having 2 to 4 condensed cycles, each cycle being capable of contributing to the valence layer of the metal M with 3 to 8 p-electrons, • L2 represents a ligand bound to the metal M by p-electrons, ligand chosen from the ligands? -cycloheptatrienyl and the 5-aromatic compounds chosen from the optionally substituted β6-benzene ligands and the compounds having from 2 to 4 condensed cycles, each cycle being capable of contributing to the valence layer of metal M with 6 or 7 electrons p. • L3 represents from 0 to 3 identical or different ligands linked to the metal M by electron s, ligand or ligands chosen between CO and N02 +; the total electronic charge q of the complex to which L1, L2 and L3 contribute and the ionic charge of metal M, is positive and equal to 1 or 2; The borate ani óni an boon has by formula: [BXa Rb] "formula in which: a and b are integers that go, for a from 0 to 3, and for b from 1 to 4 with a + b = 4, the symbols X represent: • a halogen atom with a = 0 to 3, * a functional group OH with a = 0 to 2, the symbols R are identical or different and represent: * > a phenyl radical substituted with at least one electroattracting group such as for example OCF3, CF3, N02, CN and / or by at least 2 halogen atoms, when this cationic entity is an onium of an element of groups 15 to 17, a phenyl radical substituted by at least one element or an electrically active group, in particular a halogen atom, CF3, OCF3, N02, CN, and in that the cationic entity is an organometallic complex of an element of groups 4 to 10, * > an aryl radical containing at least two aromatic nuclei such as biphenyl, naphthyl, optionally substituted with at least one element or an electroatr group assist such as a halogen atom, OCF3, CF3, N02, CN, whatever the cationic entity; (2i) the POS includes at least one monomer and / or an oligomer and / or a selected polymer: among the compounds comprising at least one functional cross-linking group (organ) via cationic (Gfp) bridge of heterocyclic nature which has one or more atomizing atoms such as oxygen, sulfur, nitrogen and phosphorus, and / or among those that include at least ethylenically unsaturated Gfp and substituted with at least one electrowinning atom that increases the alkalinity of the p system, (3i) the GfPs are present, at a rate (expressed in equivalents per kg of POS) of at least 0.01.

2. The use according to claim 1, characterized in that the POS put into operation has Gfp of the epoxide and / or vinyl ether type and is selected from the POS which are: - > either linear or substantially linear, and consisting of portions of the formula (V), terminated by portions of the formula (VI), - »or cyclic and consisting of portions of the formula (V): R1 R1 Si-O- (v; Z-Si -o- (VI) RJ formulas in which: • the symbols R1 are similar or different and represent: - either a linear or branched alkyl radical of 1 to 6 carbon atoms, optionally substituted, advantageously with one or two halogens, or a cycloalkyl radical of 5 at 8 carbon atoms, optionally substituted, - or an aryl or aralkyl radical, optionally substituted primarily by halogens and / or alkoxyls, • the symbols Z are similar or different and represent: - either the radical R 1, or a group Gfp corresponding to an epoxide residue or vinyl ester bonded to the silicon by means of a divalent radical containing from 2 to 20 carbon atoms including, optionally, a heteroatom, at least one of the symbols Z corresponds to a Gfp group.

3. The use according to claim 1 or 2, characterized in that the POS has a viscosity? (expressed in mPas at 25 ° C) between 200 and 3000.

4. The use according to claim 1 or 2, characterized in that the POS has a viscosity? (expressed in mPas at 25 ° C) between a value greater than 3000 and 10,000.

5. The use according to any of claims 1 to 4, characterized in that the photoinitiator (PA) comprises a borate anionic entity selected from the following group: [B (C6F5) 4] "[B (C6H4CF3) 4]" [B (C6H3 (CF3) 2) 4] ~ [(C5F5) 2BF2] _ [C6F5BF3r [B (C6H3F2) 4] ", [B (C6F4OCF3) 4] ~ and mixtures thereof.

6. The use according to any of claims 1 to 5, characterized in that the cationic PA entity is of the onium type and is chosen from the following entities [(f) 2I] + [C8H17-0-fIf] + [(f -CH3) 2I] + [C12H25-fIf] + [(C8Hi7-0-f) 2I] + [(C3H17-0-fIf)] + [(f) 3S] + [(f) 2-Sf-0- C8H17] + [CH3-fIf-CH (CH3) 2] + [fSfS (f) 2] + [(C12H25-f) 2I] + [CH3-fIf-OC2H5] +

7. Use in accordance with any of the claims 1 to 5, characterized in that the cationic PA entity is an organometallic salt selected from the following group: (? 5-cyclopentadienyl) (? 6-toluene) Fe + (? 5-cyclopentadienyl) (? 6-met il- 1-naphthalene) Fe + the (? 5-cyclopentadienyl) (? 6-cumene) Fe + the bis (? 6-mesi tilene) Fe + the bis (? 6-benzene) Cr +

8. The use according to any of claims 1 to 7, characterized in that the PA is an onium borate and / or a borate of organometallic salts selected from the following group: [(f) 2I] +, [B (C6F5) 4r [C8H? 7-0-fIf] +, [B (C6F5) 4] "[C12H25-fIf] +, [B (C6F5) 4] ~ [( CßH? -7-Of-) 2I] +, [B (C6F5) 4] ~ [C8H17-0-fIf] +, [B (C6F5) 4_ [(F) SS] +, [B (C6F5) 4] ~ [(f) 2S-f-0-C8H? 7] +, [B (C6H4CF3) 4] "[(C2H25-f) 2 I] +, [(f) 3S] +, [B (CSF40CF3) 4 ] "[(f-CH3) 2I] +, [B (C6F5) 4]" [(f-CH3) 2I] +, [B (CdF4OCF3) 4] "(? 5- cyclopent adi eni lo) (? 6 -toluene) Fe +, [B (C6F5) 4r (? -cyclopentadienyl) (? -methyl-1-naphthalene) Fe +, [B (C6F5) 4] _ (? 5- cyclopentane eni lo) (? 6-cumene) Fe +, [B (C6F5) 4 ~

9. The use according to any of claims 1 to 8, characterized in that the initiator (PA) is used in solution in an organic solvent chosen from proton donor solvents.

10. The use according to any of claims 1 to 9, characterized in that the support receiving the silicone coating, obtained by cationic crosslinking, is a flat gasket, mainly a cylinder head gasket: ° which is previously impregnated with at least a sealing or sealing material formed by at least one crosslinked polymer ° and / or which is previously coated by at least one layer of at least one elastomer.

11. The use according to any of claims 1 to 10, characterized in that the coating obtained by cationic crosslinking is single layer or multi-layer, and has a thickness comprised between 1 and 100 μm.

12. The process of carrying out impregnation (s) and / or of anti-adhesive coating (s) in the motor block / engine cylinder interface on supports constituted by flat gaskets, mainly cylinder head gaskets, characterized in that it consists essentially of: ( 1) applying a composition as defined in any one of claims 1 to 11, relating to use: either directly on the bare surface of the flat joint, mainly of the cylinder head gasket, or on the flat gasket, mainly the cylinder head gasket, previously impregnated with at least one sealing or sealing material formed by at least one crosslinked polymer, or else on the flat gasket, mainly the cylinder head gasket, previously coated by at least one layer of at least one elastomer , or on the flat gasket, mainly the cylinder head gasket previously impregnated with at least one sealing material formed by at least one reticulate polymer coated, and previously coated with at least one layer of at least one elastomer; and (2) having the composition crosslinked under the effect of UV radiation and / or under the effect of an electron beam and / or under the effect of thermal energy.

13. The flat gasket, mainly cylinder head gasket, characterized in that it is impregnated and / or coated by a matrix obtained by cationic crosslinking according to the use as defined according to any of claims 1 to 11, and / or to the process according to claim 12.

14. The silicone composition crosslinkable by cationic route, characterized in that it comprises: at least one POS with Gfp groups as defined according to any of claims 1 to 3, at least one initiator, preferably a photoinitiator, (PA) of an onium borate type as defined according to any one of claims 1, 5 to 8. at least one PA solvent as defined in claim 9, and at least one additive selected from those generally used in the treatments designed to make hermetic and non-stick interface cylinder head / engine block, and in particular the flat joints 10 mainly as cylinder head gaskets.