Method for preparing an article comprising a silicone foam layer

Abstract

The invention relates to a novel method for preparing an article comprising a silicone foam layer, and to an article comprising a silicone foam layer that can be obtained by the method. According to this method, a silicone composition capable of forming a foam through the release of a gas is deposited between a first textile support T1 and a second textile support T2 on the silicone composition. The silicone foam has a density of 0.2 g / cm3 or less, and the first textile support T1 and the second textile support T2 are gas-permeable.

Description

[0001] DESCRIPTION

[0002] TITLE: Method for preparing an article comprising a layer of silicone foam

[0003] Technical field

[0004] The present invention relates to the technical field of silicone foams. More specifically, the present invention aims to propose a new method for preparing an article comprising a layer of silicone foam.

[0005] State of the prior art

[0006] The term "silicone foam" or "silicone foam" refers to a composition of organopolysiloxanes in the form of foam. Silicone foam materials are known in various fields of application such as thermal and / or acoustic insulation, the production of flexible seals, use as damping elements, etc. These applications utilize the known properties of silicone elastomers such as thermal stability, good mechanical properties and fire resistance. For example, in the automotive field, silicone foam materials can be used in the batteries of electric vehicles and hybrid vehicles ("EV" and "HEV" according to English terminology) to protect the battery cells against thermal runaway.

[0007] Silicone foams are well known in the art and their preparation is described in a number of patents. Patent application WO 2012 / 032231 describes organopolysiloxane compositions for generating a silicone foam having good mechanical properties and a density of less than 0.35 g / cm 3 , and preferably less than 0.25 g / cm 3 Patent application WO 2021 / 014058 describes organopolysiloxane compositions intended to generate, after crosslinking and / or curing, a low density silicone foam, i.e. less than 0.20 g / cm 3, advantageously having good mechanical properties, excellent fire resistance and not releasing toxic fumes during their combustion. Patent application US 2023 / 0287193 A1 also describes a composition intended to generate a silicone foam which comprises an organopolysiloxane containing alkenyl groups, an organopolysiloxane containing SiH groups, a pore-forming agent containing hydroxyl groups and a hydrosilylation catalyst, characterized in that the molar ratio between SiH groups and alkenyl groups is between 5:1 and 15:1, and the molar ratio between SiH groups and hydroxyl groups is between 2:1 and 20:1.

[0008] The silicone foam described in WO 2021 / 014058 is obtained by a foaming reaction that generates hydrogen: in summary, a polyaddition crosslinking composition is used comprising an organopolysiloxane bearing vinyl groups bonded to silicon, an organopolysiloxane containing hydrogen atoms bonded to silicon and water. The water reacts with the hydride-functional organopolysiloxane, thus producing hydrogen gas and a silanol. The silanol then reacts with the hydride-functional organopolysiloxane by a hydrogen condensation reaction, thus generating a second molecule of hydrogen gas, while another polydiorganosiloxane bearing vinyl groups bonded to silicon will simultaneously react by an addition reaction with another hydride-functional polydiorganosiloxane, thus participating in the construction of the silicone foam network.

[0009] Shaping this type of foam represents a technical challenge. Very few prior art documents describe the means and methods for implementing the process for foaming a silicone foam. Document WO 2021 / 014058 describes a standard molding process, in a standard open mold. It has been found that this method of implementation could cause defects in the foam (depressions under the foam block, large bubbles within the foam, etc.). International patent application WO 2023 / 111405 proposes a new process for preparing silicone foam making it possible to obtain low-density foam blocks. This process is particularly suitable for large articles, having a length and width typically between 10 cm and 3 m, and a thickness at least greater than 2 cm, typically between 5 cm and 30 cm, or between 10 cm and 20 cm.

[0010] Low-density silicone foams can also find interesting applications when they are in the form of layers, particularly thin layers, typically less than 5 cm, preferably less than 3 cm. New methods must be developed to enable the manufacture of such articles.

[0011] In 1988, General Electric described in patent application GB 2 192 562 A a flame-retardant fabric consisting of a textile covered with a layer of silicone foam. This article is obtained by depositing on the textile a silicone foam precursor composition whose viscosity is controlled so that the silicone composition partially or completely penetrates the textile. GB 2 192 562 A suggests the use of a waterproof polyolefin film as a backing to control the leakage of hydrogen gas. The use of waterproof films has also been described in international patent application WO 2021 / 176372 A1, which relates to a method for manufacturing silicone foam in the form of a layer. Similarly, patent application EP 3 395 872 A1 describes obtaining a layer of silicone foam by deposition, then foaming and crosslinking of a silicone composition between two base materials A and B which are preferably air-impermeable films.It has been found that the methods described in these publications do not always produce a consistent and good quality foam layer. It has been found that, with low density silicone foams, surface defects can appear, typically blisters and hollows, giving the silicone foam layer an uneven surface appearance.

[0012] The object of the present invention is therefore to propose a new process for preparing silicone foam allowing the manufacture of layers of silicone foam having a regular surface. This process is particularly suitable for silicone foams of low density, preferably less than 0.20 g / cm 3 .

[0013] Summary of the invention

[0014] The present invention therefore relates to a method for preparing an article comprising a layer of silicone foam comprising the following steps: a) preparing a silicone composition capable of forming a foam by releasing a gas; b) depositing said silicone composition on a first textile support T1 by a coating technique so as to obtain a layer whose thickness is less than 10 mm; c) depositing a second textile support T2 on the silicone composition; and d) allowing said silicone composition to foam and crosslink to obtain the layer of silicone foam; in which the silicone foam has a density less than or equal to 0.2 g / cm 3 , and the first textile support T1 and the second textile support T2 are permeable to gases.

[0015] Furthermore, the present invention relates to an article comprising a layer of silicone foam capable of being obtained by the process as defined above, as well as the use of said article, and a battery comprising said article as a protective barrier against thermal runaway.

[0016] Brief description of the figures

[0017] [Fig. 1] shows an experimental removal tool as used in the examples.

[0018] [Fig. 2] is a photograph of the silicone foam layer obtained in the example according to the invention.

[0019] [Fig. 3] is a photograph of the silicone foam layer obtained in the comparative example.

[0020] Detailed description of the invention

[0021] Unless otherwise indicated, all viscosities of the silicone oils discussed in this disclosure correspond to a dynamic viscosity quantity at 25°C known as “Newtonian”, i.e. the dynamic viscosity which is measured, in a manner known per se, with a Brookfield viscometer at a shear rate gradient sufficiently low so that the measured viscosity is independent of the rate gradient.

[0022] The present invention relates to a method for preparing an article comprising a layer of silicone foam. This method comprises a first step (a) which consists of preparing a silicone composition capable of forming a foam by releasing a gas. Such compositions are known in the literature.

[0023] According to a preferred embodiment, the silicone composition capable of forming a silicone foam is a composition crosslinking by poly addition and which generates hydrogen during the foaming reaction. According to this preferred embodiment, said silicone composition comprises:

[0024] - at least one organopolysiloxane A having, per molecule, at least two C2-C12 alkenyl groups linked to silicon,

[0025] - at least one organopolysiloxane B having, per molecule, at least two SiH units,

[0026] - a catalytically effective amount of at least one hydrosilylation catalyst C, and

[0027] - at least one pore-forming agent D comprising a hydroxyl group.

[0028] In the following section regarding the description of organopolysiloxane A, the following nomenclature has been used to represent the siloxyl units:

[0029] M: siloxyl unit R SiO ,

[0030] M V1 : siloxyl unit chosen from YRkSiOi / and Y2R 'S iO 1 / 2,

[0031] D: siloxyl unit R SiCY / z.

[0032] D V1 : siloxyl unit chosen from YzSiCY / z and YR'SiCY / z.

[0033] T: siloxyl unit R'SiOs / z,

[0034] Q: siloxyl unit SiC>4 / 2, with Y and R 1 such that: Y represents a C2-C12 alkenyl group, preferably a vinyl group; R 1 represents a monovalent hydrocarbon group having from 1 to 12 carbon atoms, preferably chosen from alkyl groups having from 1 to 8 carbon atoms such as methyl, ethyl, propyl groups, cycloalkyl groups having from 3 to 8 carbon atoms and aryl groups having from 6 to 12 carbon atoms.

[0035] As examples of terminal motifs M and M V1 , we can cite the trimethylsiloxy, dimethylphenylsiloxy, dimethylvinylsiloxy or dimethylhexenylsiloxy groups.

[0036] As examples of patterns D and D V1 , we can cite the dimethylsiloxy, methylphenylsiloxy, methylvinylsiloxy, methylbutenylsiloxy, methylhexenylsiloxy, methyldecenylsiloxy or methyldecadienylsiloxy groups.

[0037] Examples of T units include the methylsiloxy group.

[0038] The organopolysiloxane A having, per molecule, at least two C2-C12 alkenyl groups bonded to silicon, may preferably have a linear structure. By “linear structure” is meant a structure which does not contain, or substantially does not contain, siloxy units T and / or Q.

[0039] The linear organopolysiloxane A having, per molecule, at least two C2-C12 alkenyl groups linked to silicon, may preferably consist essentially of siloxyl units chosen from M, M V1 , D, D V1, and combinations thereof. Organopolysiloxane A having, per molecule, at least two alkenyl groups, C2-C12 linked to silicon, may preferably be a linear organopolysiloxane formed:

[0040] - at least two siloxyl units of the following formula: Y a R 1 bSiO<4 a b) / 2 in which Y represents a C2-C12 alkenyl group, preferably a vinyl group; R 1 represents a monovalent hydrocarbon group having from 1 to 12 carbon atoms, preferably selected from alkyl groups having from 1 to 8 carbon atoms such as methyl, ethyl, propyl groups, cycloalkyl groups having from 3 to 8 carbon atoms and aryl groups having from 6 to 12 carbon atoms; a = 1 or 2, b = 0, 1 or 2 and the sum a+b = 2 or 3, and

[0041] - possibly patterns of the following formula: R 1 c SiO<4 C ) / 2 in which R 1has the same meaning as above and c = 2 or 3.

[0042] It is understood in the above formulas that, if several R groups 1 are present, they can be the same or different from each other.

[0043] Preferably, said organopolysiloxanes A are oils with a dynamic viscosity of between 100 mPa.s and 100,000 mPa.s, preferably between 100 mPa.s and 80,000 mPa.s, and more preferably between 1,000 mPa.s and 50,000 mPa.s.

[0044] Examples of linear organopolysiloxanes which may be an organopolysiloxane A according to the invention are:

[0045] - a poly(dimethylsiloxane) with dimethylvinylsilyl ends;

[0046] - a poly(dimethylsiloxane-co-methylphenylsiloxane) with dimethylvinylsilyl ends;

[0047] - a poly(dimethylsiloxane-co-methylvinylsiloxane) with dimethylvinylsilyl ends; and

[0048] - a poly(dimethylsiloxane-co-methylvinylsiloxane) with trimethylsilyl ends.

[0049] Preferably, the organopolysiloxane A contains terminal dimethylvinylsilyl units and even more preferably the organopolysiloxane A is a poly(dimethylsiloxane) with dimethylvinylsilyl ends.

[0050] Preferably, the organopolysiloxane compound A has a mass content of alkenyl units of between 0.001% and 30%, preferably between 0.01% and 10%, preferably between 0.02% and 5% (mass % of alkenyl units, based on the total weight of the organopolysiloxane A).

[0051] The silicone composition preferably comprises from 40% to 85% by weight of organopolysiloxane A, even more preferably from 50% to 70% by weight of organopolysiloxane A.

[0052] According to one embodiment, the silicone composition comprises less than 2% by weight, preferably does not comprise, branched organopolysiloxanes or resins comprising C2-C12 alkenyl units.

[0053] In the following section regarding the description of organopolysiloxane B, the following nomenclature has been used to represent the siloxyl units:

[0054] M: siloxyl unit R 2 3SiOi / 2,

[0055] M': siloxyl motif R 2 2HSiOi / 2,

[0056] D: siloxyl unit R 2 2SiC>2 / 2, D': siloxyl unit R 2 HSiC>2 / 2,

[0057] T: siloxyl unit R 2 SiC>3 / 2,

[0058] Q: siloxyl unit SiC>4 / 2, with R 2 representing a monovalent radical having from 1 to 12 carbon atoms.

[0059] Organopolysiloxane B is an organopolysiloxane having, per molecule, at least two SiH units. It is therefore an organohydrogenopolysiloxane compound. Preferably, organopolysiloxane B comprises at least three SiH units.

[0060] The organopolysiloxane B may advantageously be an organopolysiloxane comprising at least two, preferably at least three, siloxyl units of the following formula: HdR 2 e SiO<4 of) / 2 in which R 2 represents a monovalent radical having from 1 to 12 carbon atoms, d = 1 or 2, e = 0, 1 or 2 and d+e = 1, 2 or 3; and optionally other units of the following formula: R 2 fSiO<4 f) / 2 in which R 2 has the same meaning as above, and f = 0, 1, 2, or 3.

[0061] It is understood that, if several R groups 2 are present in the above formulas, they can be identical or different from each other. Preferably, R 2may represent a monovalent radical selected from the group consisting of alkyl groups having 1 to 8 carbon atoms, optionally substituted by at least one halogen atom such as chlorine or fluorine, cycloalkyl groups having 3 to 8 carbon atoms and aryl groups having 6 to 12 carbon atoms. R 2 may advantageously be selected from the group consisting of methyl, ethyl, propyl, 3,3,3-trifluoropropyl, xylyl, tolyl and phenyl.

[0062] The symbol d is preferably equal to 1.

[0063] Organopolysiloxane B may have a linear, branched, or cyclic structure. The degree of polymerization is preferably greater than or equal to 2. Generally, it is less than 5000. Preferably, the viscosity of organopolysiloxane B is between 1 mPa.s and 5000 mPa.s, more preferably between 1 mPa.s and 2000 mPa.s, and even more preferably between 5 mPa.s and 1000 mPa.s.

[0064] When they are linear or cyclic polymers, these essentially consist of siloxyl units chosen from M, M', D, D', and combinations thereof. Examples of organohydrogenpolysiloxanes which may be organopolysiloxanes B according to the invention are:

[0065] - a poly(dimethylsiloxane) with hydrogenodimethylsilyl ends;

[0066] - a poly(dimethylsiloxane-co-methylhydrogensiloxane) with trimethylsilyl ends;

[0067] - a poly(dimethylsiloxane-co-methylhydrogensiloxane) with hydrogenodimethylsilyl ends;

[0068] - a poly(methylhydrogensiloxane) with trimethylsilyl ends; and

[0069] - a cyclic poly(methylhydrogensiloxane).

[0070] When the organohydrogenpolysiloxane B has a branched structure, it is preferably chosen from the group consisting of silicone resins of the following formulae: - M'Q where the hydrogen atoms linked to silicon atoms are carried by the M groups;

[0071] - MM'Q where the hydrogen atoms linked to silicon atoms are carried by part of the M motifs;

[0072] - MD'Q where the hydrogen atoms linked to silicon atoms are carried by the D groups;

[0073] - MDD'Q where the hydrogen atoms linked to silicon atoms are carried by part of the D groups;

[0074] - MM'TQ where the hydrogen atoms linked to silicon atoms are carried by part of the M motifs;

[0075] - MM'DD'Q where the hydrogen atoms linked to silicon atoms are carried by part of the M and D motifs;

[0076] - and their mixtures.

[0077] Preferably, the organopolysiloxane B has a mass content of hydrogenosilyl Si-H functions of between 0.2% and 91%, more preferably between 3% and 80% and even more preferably between 15% and 70%.

[0078] Advantageously, the molar ratio of the hydrogenosilyl functions Si-H of the organopolysiloxanes B to the alkene functions of the organopolysiloxanes A is between 5 and 100, preferably between 10 and 90, more preferably between 15 and 65, and even more preferably between 20 and 55.

[0079] The silicone composition according to the invention preferably comprises from 1% to 20% by weight, and more preferably from 3% to 15% by weight, of organopolysiloxane B.

[0080] The hydrosilylation catalyst C may in particular be chosen from platinum and rhodium compounds but also from silicon compounds such as those described in patent applications WO 2015 / 004396 and WO 2015 / 004397, germanium compounds such as those described in patent applications WO 2016 / 075414, nickel, cobalt or iron complexes such as those described in patent applications WO 2016 / 071651, WO 2016 / 071652, WO 2016 / 071654

[0081] WO 2018 / 115601, WO 2019 / 008279, WO 2019 / 138194, WO 2023 / 031524 and WO 2023 / 031525, or manganese complexes such as those described in applications WO 2023 / 139322 and WO 2024 / 146993. Catalyst C is preferably a compound derived from at least one metal belonging to the platinum group. These catalysts are well known. In particular, it is possible to use the complexes of platinum and an organic product described in US patents 3,159,601, US 3,159,602, US 3,220,972 and European patents EP 0.057.459, EP 0.188.978 and EP 0.190.530, or the complexes of platinum and vinyl organosiloxanes described in US patents 3,419,593, US 3,715,334, US 3,377,432 and US 3,814,730.

[0082] Alternatively, a hydrosilylation photocatalyst may be used. Such a catalyst may be activated by irradiation, preferably by UV irradiation. A platinum-based photocatalyst may be selected, for example, from: platinum bis(acetylacetonate), platinum trimethyl(acetylacetonate), platinum trimethyl(2,4-pentanedione), platinum trimethyl(3,5-heptanedione), platinum trimethyl(methyl acetoacetate), platinum bis(2,4-pentanedione), platinum bis(2,4-hexanedione), platinum bis(2,4-heptanedione), platinum bis(3,5-heptanedione) and platinum bis(1-phenyl-1,3-butanedione).

[0083] Preferably, catalyst C is a compound derived from platinum. In this case, the weight quantity of catalyst C, calculated as the weight of platinum metal, is generally between 2 ppm and 400 ppm by mass, preferably between 5 ppm and 200 ppm, based on the total weight of the silicone composition.

[0084] Preferably, catalyst C is a Karstedt platinum.

[0085] The pore-forming agent D comprising a hydroxy group Ic may be chosen from the group consisting of water, polyols, monofunctional alcohols, organosilanes containing at least one silanol group, organosiloxanes containing at least one silanol group, and mixtures thereof.

[0086] According to a preferred embodiment, the pore-forming agent D is water. The water may be added directly into the silicone composition. Alternatively, the water may be introduced in the form of an aqueous emulsion, for example a direct oil-in-water silicone emulsion or a reverse water-in-oil silicone emulsion comprising a silicone oil phase, an aqueous phase and a stabilizer. According to one embodiment, the water is introduced via an emulsion of silicone oil in water with a water content of the order of 60% by weight. When the water is introduced into the silicone composition via an emulsion, the dispersion of the water in the silicone composition and its storage stability are improved.

[0087] According to another embodiment, the pore-forming agent D is a polyol. Preferably, it is an organic polyol having from 3 to 12 carbon atoms and comprising at least 2 hydroxyl groups per molecule. The polyol may be linear or branched, and it may optionally comprise one or more aromatic rings. Examples that may be mentioned are saturated polyhydric alcohols having at least 2 hydroxyl groups per molecule, such as those described in US 4,871,781. Examples of polyols that can be used as a pore-forming agent according to the invention are:

[0088] - diols, for example 1,2-ethanediol, 2,3-propanediol, 1,3-propanediol, 1,4-butanediol, 1,5-pentanediol and 1,6-hexanediol;

[0089] - triols, for example 1,2,3-propanetriol and 2,2-bis-hydroxymethyl-butanol;

[0090] - tetritols, for example erythritol and pentaerythritol;

[0091] - pentitols, for example arabitol, xylitol, and methylpentitol;

[0092] - hexitols, for example mannitol and sorbitol; and

[0093] - cycloaliphatic polyols, for example cyclohexanediols, cyclohexanetriols, and inositol.

[0094] According to another embodiment, the pore-forming agent D is a monofunctional alcohol. Preferably, it is an organic alcohol having from 1 to 12 carbon atoms and comprising a single hydroxyl group per molecule. The alcohol may be linear or branched, and it may optionally comprise one or more aromatic rings. Examples of monofunctional alcohols that can be used as a pore-forming agent according to the invention are methanol, ethanol, n-propanol, isopropanol, n-butanol, 2-butanol, tert-butanol, n-octanol, benzyl alcohol, and mixtures thereof.

[0095] According to yet another embodiment, the pore-forming agent D is an organosilane containing one or more silanol groups. These compounds may for example be represented by the following formula (1) or formula (2):

[0096] (1) (R 3 )3SiOH

[0097] (2) (R 3 )2Si(OH)2in which R 3 represents a monovalent radical selected from the group consisting of alkyl groups having 1 to 8 carbon atoms, optionally substituted by at least one halogen atom such as chlorine or fluorine, cycloalkyl groups having 3 to 10 carbon atoms and aryl groups having 6 to 12 carbon atoms.

[0098] It is understood that, if several R groups 3 are present in the above formulas, they can be the same or different from each other.

[0099] Examples of organosilanes containing one or more silanol groups that can be used as a blowing agent according to the invention are (CHs^SiOH, (CôHsjSiOH, (CHsXCôtLXSiOH and (C6H5)2Si(OH)2.

[0100] According to yet another embodiment, the pore-forming agent D is an organosiloxane containing one or more silanol groups. Preferably, it may be an organopolysiloxane compound formed:

[0101] - at least one siloxyl unit of the following formula: R 3 g (OH)hSiO(4 g h) / 2 in which R 3 has the same meaning as above; g - 0, 1 or 2, h = 1 or 2, and the sum g+h = 1, 2 or 3, and

[0102] - possibly patterns of the following formula: R 3 iSiO<4 i) / 2in which R 3 has the same meaning as above and i = 0, 1, 2 or 3.

[0103] The silicone composition according to the invention preferably comprises from 0.3% to 2.5% by weight, and more preferably from 0.5% to 1.5% by weight, of pore-forming agent D.

[0104] The silicone composition may further comprise other compounds, in particular:

[0105] - at least one mineral filler, in particular silica, quartz, or a mixture of these;

[0106] - at least one thermal resistance and / or fire resistance additive;

[0107] - at least one diorganopolysiloxane gum;

[0108] - a diorganopolysiloxane oil blocked at each end of its chain by a triorganosiloxy unit whose organic radicals linked to the silicon atoms are chosen from alkyl radicals having from 1 to 8 carbon atoms;

[0109] - a crosslinking inhibitor;

[0110] - a coloring base;

[0111] - optionally other fillers. According to a preferred embodiment, the silicone composition comprises a mineral filler, which is preferably a combustion silica or a precipitation silica. The silica-type mineral fillers preferably have a specific surface area, measured according to BET methods, of at least 10 m 2 / g, in particular between 50 m 2 / g and 400 m 2 / g, preferably greater than 70 m 2 / g, an average primary particle size of less than 0.1 pm (micrometer) and an apparent density of less than 200 g / liter. Very preferably, the mineral filler is a combustion silica with a specific surface area of ​​between 10 m 2 / g and 300 m 2 / g.

[0112] The silica-type mineral fillers, preferably hydrophilic, may be incorporated as such into the silicone composition or may optionally be treated with a compatibilizing agent. According to a variant, these silicas may optionally be treated with one or more organosilicon compounds, for example organosilane or organosilazane, usually used for this purpose. These compounds include methylpolysiloxanes such as hexamethyldisiloxane, octamethylcyclotrisiloxane, methylpolysilazanes such as hexamethyldisilazane, hexamethylcyclotrisilazane, tetramethyldivinyldisilazane, chlorosilanes such as dimethyldichlorosilane, trimethylchlorosilane, methylvinyldichlorosilane, dimethylvinylchlorosilane, alkoxysilanes such as dimethyldimethoxy silane, dimethylvinylethoxy silane, trimethylmethoxysilane.These compounds can be used alone or in a mixture (see French patents FR 1 126 884, FR 1 136 885, FR 1 236 505 and English patent GB 1 024 234). According to a preferred embodiment, the silica is treated during mixing with all or part of the organopolysiloxane A according to an in-situ process. According to an advantageous embodiment, the silica is treated with one or more hexaorganodisilazanes. Even more preferably, the silica is treated with hexamethyldisilazane alone or in a mixture with divinyltetramethyldisilazane.

[0113] The silica may optionally be predispersed in a silicone oil, so as to obtain a suspension. It is particularly preferred to use a suspension of treated combustion silica, in particular with hexamethyldisilazane, in a polyorganosiloxane oil, in particular vinylated.

[0114] The silicone composition according to the invention preferably comprises at least 3% by weight, and more preferably from 3% to 14% by weight, of silica.

[0115] Alternatively or in addition, the silicone composition according to the invention may also contain at least one other mineral filler which is quartz. Preferably, a ground natural quartz with an average particle size of less than 10 microns is used. The quartz may optionally be treated to improve its compatibility with organopolysiloxanes.

[0116] The silicone composition according to the invention preferably comprises at least 6% by weight, and more preferably from 6% to 25% by weight, of quartz.

[0117] According to a preferred embodiment, the silicone composition contains a mixture of silica and quartz, with a mass ratio between quartz and silica preferably between 0.5 and 4, more preferably between 1 and 3.6, even more preferably between 1.5 and 3.2, and even more advantageously between 1.5 and 2.8.

[0118] Other mineral fillers may be considered, including bulking fillers, such as diatomaceous earth, calcium carbonate and / or kaolin.

[0119] The silicone composition may optionally comprise at least one thermal resistance and / or fire resistance additive. These thermal resistance and / or fire resistance additives are well known to those skilled in the art. It may advantageously be chosen from the group consisting of: salts, oxides and hydroxides of metals such as iron, titanium, aluminum, nickel and copper; salts, hydroxides and oxides of rare earths such as cerium and lanthanum; organophosphorus compounds; platinum derivatives; carbon black; and calcium, aluminum and / or potassium silicates such as, for example, mica and wollastonite. Mention may also be made of hydrated mineral fillers, oxides or carbonates of calcium, magnesium or aluminum, such as magnesium hydroxide Mg(OH)2, aluminum hydroxide A1(OH)3, hydromagnesite of empirical formula Mg5(CO3)4(OH)2.4H2O, and calcium hydroxide.According to another embodiment, hollow glass microspheres can be added to the silicone composition.

[0120] The silicone composition according to the invention preferably comprises from 0.4% to 5% by weight of thermal resistance and / or fire resistance additive.

[0121] The silicone composition may optionally comprise at least one diorganopolysiloxane gum. Diorganopolysiloxane gums are linear polymers of high molecular weight with a viscosity greater than 1000 Pa.s at 25°C, preferably greater than 2000 Pa.s and whose diorganopolysiloxane chain is essentially made up of units of formula R2SiO 2 / 2and blocked at each end by units of formula R3S i O i / 2, the radical R represents an alkyl radical having from 1 to 8 carbon atoms or an alkenyl radical having from 2 to 6 carbon atoms. The presence, along the diorganopolysiloxane chain, of small quantities of units other than R2SiO2 / 2, for example RSiC>3 / 2 and / or SiC>4 / 2 units, is however not excluded in the proportion of at most 2% relative to the number of R2SiO2 / 2 units. Preferably, the diorganopolysiloxane gums comprise at least two C2-Ci2 alkenyl groups linked to silicon. Advantageously, the diorganopolysiloxane gum has a mass content of vinyl units greater than 0.3%, preferably greater than 0.5%, more preferably between 0.5% and 6%, even more preferably between 0.5% and 4%, and even more preferably between 1% and 3.5%.

[0122] According to one embodiment, the silicone composition according to the invention may optionally comprise a crosslinking inhibitor. The function of the inhibitor is to slow down the hydrosilylation reaction. The crosslinking inhibitor may be chosen from the following compounds:

[0123] - an organopolysiloxane, advantageously cyclic, and substituted by at least one alkenyl, tetramethylvinyltetrasiloxane being particularly preferred,

[0124] - pyridine, - organic phosphines and phosphites,

[0125] - unsaturated amides,

[0126] - alkylated maleates, and

[0127] - acetylenic alcohols.

[0128] Preferably, the crosslinking inhibitor is an acetylenic alcohol of formula (R 4 )(R 5 )C(OH)- C=CH, in which:

[0129] - R 4 is a linear or branched alkyl radical, or a phenyl radical,

[0130] - R 5 is a hydrogen atom, a linear or branched alkyl radical, or a phenyl radical,

[0131] - the R radicals 4 , R 5 and the carbon atom located alpha to the triple bond which can possibly form a cycle, and

[0132] - the total number of carbon atoms contained in R 4 and R 5 being at least 5, preferably 9 to 20.

[0133] Said alcohols are preferably chosen from those having a boiling point above 250°C. Examples which may be mentioned are the following products which are commercially available: 1-ethynyl-1-cyclohexanol, methyl-3-dodecyne-1-ol-3, trimethyl-3,7,1-dodecyne-1-ol-3, diphenyl-1,1-propyne-2-ol-1, ethyl-3-ethyl-6-nonyne-1-ol-3 and methyl-3-pentadecyne-1-ol-3. Preferably, the crosslinking inhibitor is 1-ethynyl-1-cyclohexanol.

[0134] The presence of the inhibitor may or may not be necessary depending on the silicone composition and the process used. If necessary, such a crosslinking inhibitor may typically be present at a maximum of 3000 ppm, preferably at a maximum of 100 ppm to 2000 ppm relative to the total weight of the silicone composition.

[0135] According to one embodiment, the silicone composition according to the present invention may optionally comprise other additives traditionally used in this technical field by those skilled in the art, for example an adhesion promoter, a colorant, a fire retardant, a rheological agent such as a thixotropic agent, etc.

[0136] According to one embodiment, the silicone composition according to the present invention may contain a low level of volatile organic compounds, typically less than 100 pgC / g, preferably less than 70 pgC / g, or even less than 50 pgC / g. For this, the organopolysiloxane compounds used in the composition according to the present invention may preferably be chosen from compounds themselves containing a low level of volatile organic compounds.

[0137] According to one embodiment, the silicone composition comprises (by weight relative to the total weight of the silicone composition): a. from 40% to 85% by weight of at least one organopolysiloxane A having, per molecule, at least two C2-C12 alkenyl groups bonded to silicon, b. from 1% to 20% by weight of at least one organopolysiloxane B having, per molecule, at least two SiH units and preferably at least three SiH units, c. from 2 ppm to 400 ppm by weight of a hydrosilylation catalyst C chosen from platinum compounds (quantity calculated by weight of platinum metal), d. from 0.3% to 2.5% by weight of a pore-forming agent D, e. at least 3% by weight of a combustion silica whose specific surface area is between 10 m 2 / g and 300 m 2 / g, f. at least 6% by weight of ground quartz, and g. from 0.4% to 5% by weight of at least one thermal resistance and / or fire resistance additive.

[0138] According to another embodiment, the silicone composition comprises (by weight relative to the total weight of the silicone composition): a. from 40% to 85% by weight of at least one organopolysiloxane A having, per molecule, at least two C2-C12 alkenyl groups bonded to silicon, b. from 1% to 20% by weight of at least one organopolysiloxane B having, per molecule, at least two SiH units and preferably at least three SiH units, c. from 2 ppm to 400 ppm by weight of a hydrosilylation catalyst C chosen from platinum compounds (quantity calculated by weight of platinum metal), d. from 0.3% to 2.5% by weight of a pore-forming agent D, e. from 3% to 14% by weight of a combustion silica whose specific surface area is between 50 m 2 / g and 300 m 2 / g, f. from 6% to 25% by weight of a ground quartz, g. from 0.4% to 5% by weight of at least one fire resistance additive, h. from 0 to 3000 ppm by weight of a crosslinking inhibitor, and i. from 0 to 4% by weight of a diorganopolysiloxane gum comprising at least two C2-C12 alkenyl groups bonded to silicon.

[0139] Although the polyaddition crosslinking composition as described above is the preferred embodiment of the silicone foam according to the present invention, other silicone compositions capable of forming a foam are entirely conceivable, insofar as the composition releases a gas allowing the foaming phenomenon. According to one embodiment, the silicone composition contains a pore-forming agent which expands the material under the action of heat by decomposition with release of gas, in particular the case of azo-type derivatives, for example azodicarbonamide, which will allow the release of nitrogen, carbon dioxide and ammonia. According to another embodiment, the silicone composition contains a pore-forming agent which expands the material under the action of heat by phase change, typically liquid to gas, in particular the case of solvents with a low boiling point.

[0140] According to one embodiment, the silicone composition according to the invention can be prepared from a two-component (or multi-component) system characterized in that it is presented in two (or more) distinct parts intended to be mixed to form said silicone composition. In particular, in the case of the preferred silicone compositions as described above, the silicone composition can be prepared from a two-component system characterized in that one of the parts comprises catalyst C and does not comprise organopolysiloxane B, while the other part comprises organopolysiloxane B and does not comprise catalyst C. Other multi-component systems can be provided to improve the storage life and / or optimize the viscosity of each of the components.For example, the silicone composition according to the invention can be prepared from a three-component system characterized in that it is presented in three distinct parts intended to be mixed to form said silicone composition.

[0141] The mixing of the parts of said two-component (or multi-component) system can typically take place at a temperature close to room temperature, i.e. between 10°C and 40°C. An increase in the temperature of the silicone composition is sometimes observed during this mixing depending on the type of mixer and the shear applied. If it is desired to accelerate the foaming and crosslinking of the silicone foam, the mixing can be carried out at a higher temperature, advantageously between 40°C and 70°C. It is important to have a good mixing quality to obtain a homogeneous silicone foam with good mechanical properties.

[0142] The method according to the present invention further comprises a step (b) consisting of depositing said silicone composition on a first textile support T1 and a step (c) consisting of depositing a second textile support T2 on the silicone composition. The silicone composition is thus sandwiched between the first textile support T1 and the second textile support T2.

[0143] The coating may be total or partial, that is to say that the deposition of the silicone composition may be carried out on the entire surface of the first textile support T1 or on one or more parts of this surface.

[0144] The first textile support T1 and the second textile support T2 may be identical or different, preferably identical. The first textile support T1 and the second textile support T2 are gas-permeable. Preferably, it is a flexible material, typically a fibrous material. Said fibrous material may be of natural, artificial and / or synthetic origin. It may be a woven, knitted or non-woven fibrous material. When it is a woven or knitted fibrous support, i.e. a fabric or a knit, the yarns are advantageously based on thermoplastic polymer.Examples of suitable thermoplastic (co)polymers that may be mentioned include: polyolefins, polyesters, polyalkylene oxides, polyoxyalkylenes, polyhaloalkylenes, poly(alkylene phthalate or terephthalate), poly(phenyl or phenylene), poly(phenylene oxide or sulfide), polyvinyl acetates, polyvinyl alcohols, polyvinyl halides, polyvinylidene halides, polyvinyl nitriles, polyamides, polyimides, polycarbonates, polysiloxanes, acrylic or methacrylic acid polymers, polyacrylates or methacrylates, natural polymers such as cellulose and its derivatives, synthetic elastomers, or thermoplastic copolymers comprising at least one monomer identical to any of the monomers included in the aforementioned polymers, as well as mixtures and / or alloys of all these (co)polymers.The use of natural fibers such as cotton, wool, hemp and linen is also possible. When the fibrous material is made of thermoplastic polymer, it is preferably made of polyester, such as polyethylene terephthalate (PET), polypropylene terephthalate (PPT), polybutylene terephthalate (PBT), their copolymers and blends, or polyamide such as polyamide 6, polyamide 6.6, polyamide 4, polyamide 1.1, polyamide 1.2, polyamides 4-6, 6-10, 6-12, 6-36, 12-12, their copolymers and blends.

[0145] Textile supports Tl and T2 can have a weight between 120 g / m 2 and 900 g / m 2 , preferably between 150 g / m 2 and 300 g / m 2. In the case of a woven textile, the textile supports Tl and T2 can also be defined by their texture, corresponding to a number of warp and weft threads per centimeter, and by the title of the thread used expressed in dtex (abbreviation of decitex), corresponding to the mass in grams of ten thousand meters of this thread. We can thus cite such fabrics, in particular in polyamide or polyester, having a texture of between 10x10 and 21x21 threads / cm, for example fabrics of 200 to 500 dtex.

[0146] The porosity of the textile support can be assessed according to ISO 9237.

[0147] Preferably, the quantity of silicone composition deposited on a first textile support T1 is determined so as to obtain a layer, before foaming and crosslinking, the thickness of which may be between 1 mm and 10 mm, preferably between 1.5 mm and 5 mm.

[0148] As a technique for depositing the silicone composition, we can cite for example the coating techniques carried out by doctor blade, in particular by doctor blade on cylinder and doctor blade on belt, or by padding, that is to say by squeezing between two rollers, or by licking roller, rotating frame, reverse roll or transfer, by spraying, or by curtain coating.

[0149] The deposition of the second textile support T2 can be done simultaneously or after the deposition of the silicone composition on the first textile support TL. According to a preferred embodiment, step (c) of deposition of the second textile support T2 is done simultaneously with step (b) of deposition of the silicone composition on the first textile support TL. In this case, a single coating device can be used to carry out these two steps simultaneously. Typically, the second textile support T2 can be arranged between the silicone composition and the doctor blade. However, any other embodiment is possible, and several devices can be arranged in series to ensure the deposition of these different elements.

[0150] According to a preferred embodiment, the silicone composition is deposited between the two textile supports T1 and T2.

[0151] According to a preferred embodiment, the method according to the present invention is a continuous method.

[0152] A continuous process advantageously makes it possible to obtain a regular article and to achieve high production rates. The process according to the present invention finally comprises a step (d) consisting of allowing said silicone composition to foam and crosslink to obtain the silicone foam. This step (d) can have a variable duration depending in particular on the silicone composition and the temperature of step (b). Generally, a silicone foam with good properties is obtained after a few minutes depending on the temperature and the concentration of catalyst and inhibitor in the silicone composition.

[0153] The silicone composition can foam and crosslink without external intervention if the reactivity between the parts brought into contact beforehand is sufficient.

[0154] It is possible to thermally activate the crosslinking reaction. The means for thermal activation of crosslinking are conventionally ovens (for example tunnel ovens), heated laminating rollers, or infrared sources. This thermal activation can be supplemented by actinic activation and / or by electron bombardment. The crosslinking temperature can be higher than 120°C, without exceeding the degradation temperature of the support, preferably between 160°C and 200°C.

[0155] However, since the foaming and crosslinking reaction can cause hydrogen release, the silicone foam manufacturing process can preferably be carried out at atmospheric pressure and room temperature. The room temperature is generally between 15°C and 40°C, typically around 25°C. In addition to safety reasons, carrying out the process at atmospheric pressure and / or room temperature is a significant advantage in terms of technological simplification and implementation costs. To avoid risks associated with hydrogen release during the process, the entire silicone foam manufacturing process can be carried out under air or nitrogen scavenging.

[0156] Alternatively, the foaming and crosslinking reaction can be activated by irradiation, for example by UV. For this, the person skilled in the art will be able to choose a photo-activatable hydrosilylation catalyst, and possibly appropriate photosensitization additives.

[0157] After foaming and crosslinking, the final thickness of the silicone foam layer may be less than 30 mm, preferably between 2 mm and 25 mm, more preferably between 4 mm and 20 mm.

[0158] After foaming and crosslinking, a layer of silicone foam is obtained between the two textile supports T1 and T2.

[0159] The method according to the present invention may optionally comprise an additional step (e) consisting of removing the first textile support T1 and / or the second textile support T2. If the removal of one or more textile supports is envisaged, the textile support(s) T1 and / or T2 may advantageously be chosen so that the removal is easy. For this, the textile support is chosen from materials adhering little or not at all to the silicone foam after its crosslinking, preferably polyester. Alternatively, the textile support may be surface-treated to improve its non-adhesion to the silicone foam, for example with a fluorocarbon coating. To facilitate the removal of the textile support(s) T1 and / or T2, a person skilled in the art may choose the appropriate moment so that the adhesion of the silicone foam to the support is minimal and so that the crosslinking of the silicone foam is sufficient.

[0160] The method according to the present invention may optionally comprise an additional step (f) consisting of annealing the article comprising a layer of silicone foam obtained in step (d) (or optionally (e)). This optional annealing step may consist of a heat treatment lasting from 1 to several hours, preferably from 1 to 4 hours, at a temperature between 50°C and 200°C, preferably between 100°C and 150°C. It may make it possible to improve, if necessary, the fire resistance and the mechanical properties of the silicone foam. However, this step is not essential, and a method for preparing an article comprising a layer of silicone foam according to the invention will be preferred, characterized in that it does not comprise an additional annealing step.

[0161] Another subject of the present invention is an article comprising a layer of silicone foam obtained by the process as defined above.

[0162] The silicone foam layer obtained by the process which is the subject of the present invention advantageously has a density of less than 0.20 g / cm 3 , more preferably less than 0.17 g / cm 3 , even more preferably less than 0.15 g / cm 3 It is visually uniform with a homogeneous distribution of bubble sizes within the foam and does not contain large bubbles with a diameter greater than or equal to 2 mm.

[0163] The silicone foam layer preferably has a low thickness. Its thickness may preferably be less than 30 mm, more preferably between 2 mm and 25 mm, even more preferably between 4 mm and 20 mm, and even more preferably between 4 mm and 10 mm.

[0164] The article comprising a layer of silicone foam according to the invention may advantageously be in the form of a sheet or a mat, the thickness of which is significantly less than the length and the width. The dimensions of such an article may typically be:

[0165] - thickness: between 2 mm and 30 mm;

[0166] - width: between 50 cm and 3 m;

[0167] - length: between 50 cm and 10 m if the manufacturing process is discontinuous, and greater than 10 m if the manufacturing process is continuous.

[0168] The sheets or mats thus obtained can be rolled up.

[0169] Advantageously, the silicone foam layer according to the invention does not have any surface defects. The surface of the silicone foam layer is soft and regular. According to a first embodiment, the article according to the invention comprises the silicone foam layer and the two textile supports T1 and T2. According to a second embodiment, the article according to the invention comprises the silicone foam layer and a single textile support T1 or T2. In this case, one of the two textile supports T1 or T2 will have been removed according to the optional step (e). According to a third embodiment, the article according to the invention comprises the silicone foam layer but does not comprise either the textile support T1 or the textile support T2. In this case, the two textile supports T1 and T2 will have been removed according to the optional step (e).

[0170] The thermal resistance and fire resistance properties of the silicone foam obtained by the process which is the subject of the present invention are excellent, due to the nature of the silicone composition used. The foam advantageously does not release toxic fumes during combustion. In addition, silicone foams are known for their excellent thermal insulation properties.

[0171] The advantages presented above therefore make the article comprising a layer of silicone foam according to the invention a material particularly suitable for use in heat management in many industries, in particular in electronics and in the automotive industry. The present invention also relates to the use of the article which is the subject of the present invention as a thermal barrier, in particular as a protective barrier against thermal runaway, and very particularly as a thermal barrier in battery modules. The present invention also relates to a battery, preferably an electric vehicle or hybrid vehicle battery, comprising the article which is the subject of the present invention as a protective barrier against thermal runaway.

[0172] Other details or advantages of the invention will appear more clearly from the examples given below for information purposes only.

[0173] Examples

[0174] A silicone composition, capable of forming a foam and crosslinking by polyaddition, was prepared by mixing at room temperature the compounds described in Table 1 below:

[0175] [Table 1]

[0176] Example according to the invention:

[0177] An experimental removal tool as shown in Figure 1 was used. A height-adjustable scraper equipped with a knife (3) (knife angle to the plane ~ 45°) was used. The distance between the lower edge of the scraper and the knife was set at 2 mm.

[0178] Two 24 cm x 24 cm polyester textile sheets (1 and 2) (PET Loomstate, 470 dtex, 20x20 thread count) were joined by their short edge. The silicone composition obtained after mixing (4) was deposited, still liquid, at the junction of the two sheets (1 and 2). Once the deposition was complete, the upper sheet was folded over the liquid, then the assembly of the two sheets and the liquid was moved under the doctor blade at approximately 6 m / min.

[0179] Once this step is completed, the assembly consisting of the silicone composition (4) sandwiched between the two textile supports (1 and 2) was laid flat and left for 45 minutes at 23°C. The two textile supports (1 and 2) were removed. The foam layer obtained has a uniform thickness of 5 mm and a density of 0.2 g / cm 3 . As can be seen in Figure 2, the foam layer obtained according to the present invention does not have any surface defect.

[0180] Comparative example:

[0181] The method was repeated using two waterproof polyester films (Toray PET film 120 μm thick) instead of the textile sheets. The resulting foam layer also has a thickness of 5 mm and a density of 0.2 g / cm 3 . However, as can be seen in Figure 3, the resulting foam layer has defects on the upper part of the foam film, highlighted in the photo by the circles.

Claims

CLAIMS 1. A method for preparing an article comprising a layer of silicone foam comprising the following steps: a) preparing a silicone composition capable of forming a foam by releasing a gas; b) depositing said silicone composition on a first textile support T1 by a coating technique so as to obtain a layer whose thickness is less than 10 mm; c) depositing a second textile support T2 on the silicone composition; and d) allowing said silicone composition to foam and crosslink to obtain the layer of silicone foam; wherein the silicone foam has a density less than or equal to 0.2 g / cm 3 , and the first textile support T1 and the second textile support T2 are permeable to gases.

2. The method of claim 1, wherein said silicone composition comprises: - at least one organopolysiloxane A having, per molecule, at least two C2-C12 alkenyl groups linked to silicon, - at least one organopolysiloxane B having, per molecule, at least two SiH units, - a catalytically effective amount of at least one hydrosilylation catalyst C, and - at least one pore-forming agent D comprising a hydroxyl group.

3. Method according to either of claims 1 or 2, in which step (c) of depositing the second textile support T2 is carried out simultaneously with step (b) of depositing the silicone composition on the first textile support T1.

4. Method according to any one of claims 1 to 3, in which the coating technique of step (b) is chosen from coating techniques carried out by doctor blade, in particular by doctor blade on cylinder and doctor blade on belt, by padding, that is to say by squeezing between two rollers, by licking roller, rotating frame, reverse roller or transfer, by spraying, and by curtain coating.

5. A method according to any one of claims 1 to 4, wherein said method of preparing an article is a continuous method.

6. Method according to any one of claims 1 to 5, in which, after foaming and crosslinking, the final thickness of the silicone foam layer is less than 30 mm, preferably between 2 mm and 25 mm, more preferably between 4 mm and 20 mm.

7. Method according to any one of claims 1 to 6, wherein said method comprises an additional step (e) consisting of removing the first textile support T1 and / or the second textile support T2.

8. Article comprising a layer of silicone foam obtained by the process as defined in any one of claims 1 to 7.

9. Article according to claim 8, wherein said article comprises the silicone foam layer and the two textile supports T1 and T2.

10. Article according to claim 8, wherein said article comprises the silicone foam layer but does not comprise either the textile support T1 or the textile support T2.

11. Use of the article according to any one of claims 8 to 10 as a thermal barrier, in particular as a protective barrier against thermal runaway, and very particularly as a thermal barrier in battery modules.

12. Battery, preferably an electric vehicle or hybrid vehicle battery, comprising the article according to any one of claims 8 to 10 as a protective barrier against thermal runaway.

Images