Silicone Foam Preparation Method

Abstract

The present invention relates to a novel method for preparing silicone foams, ideal for manufacturing articles in the construction, transport, electrical insulation or household appliances sectors, in particular as upholstery material for seats in the transport sector, which method comprises the steps of (a) preparing a silicone composition capable of forming a foam by release of gas, (b) introducing said silicone composition into a closed mould, and (c) crosslinking and / or curing said silicone composition to obtain a silicone foam, the walls of the mould being permeable to gas at least during all or part of the step of crosslinking and / or curing said silicone composition.

Description

[Technical Field]

[0001] The present invention relates to the technical field of silicone foams, and more particularly to a novel method for preparing silicone foams. [Background technology]

[0002] The expressions "silicone foam" or "silicone foam" designate organopolysiloxane compositions in the form of foam. Silicone foam materials are known for various applications, such as thermal and / or acoustic insulation, the manufacture of soft seals, and use as vibration-damping elements. These applications utilize the known properties of silicone elastomers, such as thermal stability, good mechanical properties, and flame resistance.

[0003] The transportation industry in particular is seeking silicone foams that have low density yet maintain excellent mechanical properties, heat resistance, and fire resistance.

[0004] Silicone foams are well known in the prior art and their preparation is described in a number of patents. In particular, patent application WO 2021 / 014058 describes silicone foams which, after crosslinking and / or curing, advantageously have good mechanical properties, excellent fire resistance, do not emit toxic gases during combustion, and have a low density, i.e., 0.20 g / cm. 3 Organopolysiloxane compositions are described that are intended to produce silicone foams of less than 1000 kJ / g.

[0005] The silicone foam described in WO 2021 / 014058 is obtained by a hydrogen-generating blowing reaction. In summary, a polyaddition-crosslinking composition is used, comprising an organopolysiloxane having silicon-bonded vinyl groups, an organopolysiloxane containing silicon-bonded hydrogen atoms, and water. The water reacts with the organopolysiloxane containing hydride functional groups to generate gaseous hydrogen and silanol. The silanol then reacts with the organopolysiloxane containing hydride functional groups via a hydrogen condensation reaction, thereby generating a second molecule of gaseous hydrogen, while another polydiorganosiloxane containing silicon-bonded vinyl groups simultaneously reacts with another polydiorganosiloxane containing hydride functional groups via an addition reaction, thereby participating in the construction of the silicone foam network.

[0006] It has been observed that when foaming is carried out in a standard open mold, the foam can exhibit significant defects, particularly depressions under the foam blocks, large air bubbles within the foam itself, etc. Such defects are unacceptable for industrial-scale production of silicone foam articles.

[0007] In the prior art, there are few documents describing the means and methods for carrying out the process of expanding silicone foam.

[0008] European Patent Application EP 0 495 566, published in 1992, describes a method for preparing silicone foams, in which a precursor foam composition is introduced into a closed and sealed mold having a volume at least 10% less than the volume the foam would occupy in an open mold. According to the inventors of this application, foaming under suppressed conditions can improve the flame resistance of the foam. However, a post-crosslinking step of thermal annealing in the mold for several hours appears to be necessary. In addition, the density of the resulting foam is systematically higher in closed molds than in open molds. However, in the transportation industry, it is preferable to obtain low-density silicone foams.

[0009] Japanese Patent Application JP2004-123836 describes a method for producing silicone foam in a closed mold under reduced pressure. According to this document, this method can be used to obtain uniform silicone foam with a desired density. However, this method is complicated to implement, and mold sealing control is very important. Since hydrogen is a gas that easily spreads in the air, sealing cannot be guaranteed.

[0010] Patent application US2011 / 0074061A1 describes a method for molding a silicone elastomer sponge, preferably in the form of a tube. According to this method, a silicone composition is introduced into a closed mold and crosslinked, and then the gas present in the mold cavity is released before the mold is opened. This intermediate degassing step prevents damage to the molded object, such as breakage or tearing, when it is removed from the mold. However, this degassing step is performed only after the silicone composition has crosslinked. Therefore, it cannot affect defects that appear in the object during crosslinking. In addition, as is clear from the embodiment described in US2011 / 0074061A1, the hole used for gas release is located at the small end of the tube and cannot be used to prevent deformations on essential surfaces of the tube, such as the inner or outer surface.

[0011] Although there are other documents in the prior art relating to methods for molding foams (e.g., US Pat. No. 3,431,331), they relate to polyurethane foams, which, compared to silicone foams, not only have a completely different crosslinking chemistry, but also different foaming reactions, gases released during expansion, kinetics of crosslinking and foaming, etc.

[0012] Therefore, the improved foaming methods described in the prior art cannot be used to easily produce low density silicone foams.

[0013] The object of the present invention is therefore to propose a novel method for preparing silicone foam that can be used to obtain blocks of foam with low density and without major defects in terms of shape. Advantageously, this method for preparing silicone foam is easy to carry out and does not require an annealing step. Summary of the Invention

[0014] Accordingly, the present invention provides a method for preparing a silicone foam, comprising the following steps: a) preparing a silicone composition capable of forming a foam by releasing a gas; b) introducing the silicone composition into a closed mold; and c) crosslinking and / or curing the silicone composition to obtain a silicone foam. Including, The method for preparing a silicone foam further relates to a method for preparing a silicone foam, wherein the walls of the mold are permeable to gases at least during all or part of the step for crosslinking and / or curing the silicone composition.

[0015] Furthermore, the present invention relates to articles made from silicone foam obtainable by the method defined above, as well as to the use of a closed mould, the walls of which are permeable to gas, for the manufacture of silicone foam. [Brief explanation of the drawings]

[0016] [Figure 1] 1 shows one embodiment of a mold according to the present invention. [Figure 2] 2A, 2B, 2C and 2D show four embodiments of the wall of a mold according to the invention. [Figure 3] 1 is a photograph of a block of silicone foam obtained according to a comparative example. [Figure 4] 1 is a photograph of a mold used in an example according to the present invention. [Figure 5] 1 is a photograph of a block of silicone foam obtained according to an example according to the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0017] Unless otherwise indicated, all of the viscosities of the silicone oils considered in this disclosure correspond to values ​​of dynamic viscosity at 25° C., termed "Newtonian", i.e. values ​​of dynamic viscosity measured using a Brookfield viscometer in a manner known per se, at shear rate gradients sufficiently low that the measured viscosity is independent of the shear rate gradient.

[0018] The present invention relates to a method for preparing a silicone foam, which method comprises a first step (a) consisting of preparing a silicone composition capable of forming a foam by releasing a gas. Compositions of this type are known in the literature.

[0019] According to a preferred embodiment, the silicone composition capable of forming a silicone foam is a composition that crosslinks by polyaddition and generates hydrogen upon foaming. According to this preferred embodiment, the silicone composition comprises: At least two C2-C bonded to silicon per molecule 12 at least one organopolysiloxane A containing alkenyl groups; at least one organopolysiloxane B having at least two SiH motifs per molecule, a catalytically effective amount of at least one hydrosilylation catalyst C, and at least one pore-forming agent D containing hydroxyl groups Includes:

[0020] At least two C2-C bonded to silicon per molecule 12 The organopolysiloxane A having alkenyl groups is preferably The following formula: Y a R 1 b SiO (4-a-b) / 2 and Y is C2 to C12 represents an alkenyl group, preferably a vinyl group; R 1 represents a monovalent hydrocarbon group containing 1 to 12 carbon atoms, preferably selected from alkyl groups containing 1 to 8 carbon atoms, such as methyl, ethyl, propyl, etc., cycloalkyl groups containing 3 to 8 carbon atoms, and aryl groups containing 6 to 12 carbon atoms; at least two siloxy motifs, where a=1 or 2 and b=0, 1 or 2, and the sum a+b=2 or 3, and Optionally, a compound of the formula: 1 c SiO (4-c) / 2 a motif having R 1 has the same meaning as above, and c=2 or 3, The organopolysiloxane may be a linear organopolysiloxane formed by the following formula:

[0021] In the above formula, some R 1 It is to be understood that when groups are present they may be the same or different from one another.

[0022] Preferably, the organopolysiloxane A is an oil having a dynamic viscosity of 100 mPa·s to 100,000 mPa·s, preferably 100 mPa·s to 80,000 mPa·s, and more preferably 1,000 mPa·s to 50,000 mPa·s.

[0023] At least two C2-C bonded to silicon per molecule 12 The linear organopolysiloxane A containing alkenyl groups preferably has a siloxy motif R 1 2SiO 2 / 2 , Y.R. 1 SiO 2 / 2 and Y2SiO 2 / 2 a siloxy motif "D" selected from the group consisting of: 1 2SiO 1 / 2 , Y2R 1 SiO 1 / 2 and R 1 3SiO 1 / 2The symbols Y and R may essentially consist of a terminal siloxy motif "M" selected from the group consisting of 1 is as described above.

[0024] Examples of terminal motifs "M" that may be mentioned are the trimethylsiloxy, dimethylphenylsiloxy, dimethylvinylsiloxy or dimethylhexenylsiloxy groups.

[0025] Examples of motif "D" that may be mentioned are the dimethylsiloxy, methylphenylsiloxy, methylvinylsiloxy, methylbutenylsiloxy, methylhexenylsiloxy, methyldecenylsiloxy or methyldecadienylsiloxy radicals.

[0026] Examples of linear organopolysiloxanes that can form organopolysiloxane A according to the invention are: · Poly(dimethylsiloxane) with dimethylvinylsilyl end groups; · Poly(dimethylsiloxane-co-methylphenylsiloxane) with dimethylvinylsilyl end groups; Poly(dimethylsiloxane-co-methylvinylsiloxane) with dimethylvinylsilyl end groups; and Poly(dimethylsiloxane-co-methylvinylsiloxane) with trimethylsilyl end groups is.

[0027] Preferably, organopolysiloxane A contains terminal dimethylvinylsilyl motifs, more preferably organopolysiloxane A is a poly(dimethylsiloxane) having dimethylvinylsilyl end groups.

[0028] Preferably, organopolysiloxane compound A has an alkenyl motif content by weight of 0.001% to 30%, preferably 0.01% to 10%, preferably 0.02% to 5%.

[0029] The silicone composition preferably comprises 40% to 80% by weight of organopolysiloxane A, more preferably 50% to 70% by weight of organopolysiloxane A. According to one embodiment, the silicone composition comprises C2 to C 12 It does not contain branched organopolysiloxanes or resins containing alkenyl motifs.

[0030] Organopolysiloxane B is an organopolysiloxane having at least two SiH motifs per molecule. It is therefore an organohydrogenopolysiloxane. Preferably, compound B contains at least three SiH motifs.

[0031] The organopolysiloxane B advantageously has the following formula: H d R 2 e SiO (4-d-e) / 2 (where R 2 represents a monovalent radical containing 1 to 12 carbon atoms, d=1 or 2, e=0, 1 or 2, d+e=1, 2 or 3), and optionally at least two, preferably at least three siloxy motifs having the following formula: R 2 f SiO (4-f) / 2 (where R 2 has the same meaning as above, and f=0, 1, 2 or 3).

[0032] In the above formula, several R 2 It should be understood that when groups are present, they may be the same or different from one another.

[0033] Preferably, R 2 R may represent a monovalent group selected from the group consisting of alkyl groups containing 1 to 8 carbon atoms, which may be substituted with at least one halogen atom, such as chlorine or fluorine, cycloalkyl groups containing 3 to 8 carbon atoms, and aryl groups containing 6 to 12 carbon atoms. 2may advantageously be selected from the group constituted by methyl, ethyl, propyl, 3,3,3-trifluoropropyl, xylyl, tolyl and phenyl.

[0034] The symbol d is preferably equal to one.

[0035] Organopolysiloxane B may have a linear, branched, or cyclic structure. The degree of polymerization is preferably 2 or greater. Generally, it is less than 5000. Preferably, the viscosity of organopolysiloxane B is in the range of 1 mPa·s to 5000 mPa·s, more preferably in the range of 1 mPa·s to 2000 mPa·s, and even more preferably in the range of 5 mPa·s to 1000 mPa·s.

[0036] In the case of linear polymers, they essentially consist of motif R 2 2SiO 2 / 2 and R 2 HSiO 2 / 2 The siloxy motif "D" and the motif R are selected from 2 3SiO 1 / 2 and R 2 2HSiO 1 / 2 and a terminal siloxy motif "M" selected from the group consisting of: 2 has the same meaning as above.

[0037] Examples of organohydrogenopolysiloxanes which can be compound B according to the invention are: · Poly(dimethylsiloxane) with hydrogenodimethylsilyl end groups; · Poly(dimethylsiloxane-co-methylhydrogenosiloxane) with trimethylsilyl end groups; · Poly(dimethylsiloxane-co-methylhydrogenosiloxane) with hydrogenodimethylsilyl end groups; Poly(methylhydrogenosiloxane) with trimethylsilyl end groups; and Cyclic poly(methylhydrogenosiloxane) is.

[0038] If the organohydrogenopolysiloxane B has a branched structure, it is preferably chosen from the group constituted by the silicone resins having the following formula: ·M'Q, where the hydrogen atom bonded to the silicon atom is carried by the M group; ·MM'Q, where the hydrogen atom bonded to the silicon atom is part of the motif M; ·MD'Q, where the hydrogen atom bonded to the silicon atom is carried by a D group; ·MDD'Q, where the hydrogen atom bonded to the silicon atom is part of the D group; ·MM'TQ, where the hydrogen atom bonded to the silicon atom is part of the motif M; ·MM'DD'Q, where the hydrogen atom bonded to the silicon atom is part of the motifs M and D; and mixtures thereof, where M = formula R 2 3SiO 1 / 2 and M'=a siloxy motif having the formula R 2 2HSiO 1 / 2 and D=a siloxy motif having the formula R 2 2SiO 2 / 2 and D'=a siloxy motif having the formula R 2 HSiO 2 / 2 and T=a siloxy motif having the formula R 2 3SiO 1 / 2 and Q=a siloxy motif having the formula SiO 4 / 2 where R is a siloxy motif having 2 has the same meaning as above.

[0039] Preferably, organopolysiloxane B has a content by weight of hydrogenosilyl functional groups Si—H of 0.2% to 91%, more preferably 3% to 80%, even more preferably 15% to 70%.

[0040] Advantageously, the molar ratio of the hydrogenosilyl functional groups Si—H of organopolysiloxane B to the alkene functional groups of organopolysiloxane 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.

[0041] The silicone composition according to the present invention preferably contains organopolysiloxane B in an amount of 1 to 20% by weight, more preferably 3 to 15% by weight.

[0042] The hydrosilylation catalyst C can be selected in particular from platinum and rhodium compounds, but also from silicones such as those described in patent applications WO2015 / 004396 and WO2015 / 004397, germanium compounds such as those described in patent applications WO2016 / 075414, or nickel, cobalt, or iron complexes such as those described in patent applications WO2016 / 071651, WO2016 / 071652, and WO2016 / 071654. Catalyst C is preferably a compound derived from at least one metal belonging to the platinum group. These catalysts are well known. In particular, complexes of platinum with organic products as described in patents US 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, complexes of platinum with vinylorganosiloxanes as described in patents US 3,419,593, US 3,715,334, US 3,377,432 and US 3,814,730 can be used.

[0043] Preferably, catalyst C is a compound derived from platinum. In this case, the amount by weight of catalyst C is calculated as the weight of metallic platinum and is generally 2 ppm to 400 ppm by weight, and preferably 5 ppm to 200 ppm by weight, relative to the total weight of the silicone composition.

[0044] Preferably, catalyst C is a Karstedt platinum catalyst.

[0045] The hydroxyl-containing pore former D can be selected 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.

[0046] According to a preferred embodiment, pore-forming agent D is water.Water can be directly added to silicone composition.Alternatively, water can be introduced in the form of aqueous emulsion, for example, a normal oil-in-water silicone emulsion or an inverse water-in-oil silicone emulsion, which comprises a continuous oily silicone phase, an aqueous phase and a stabilizer.According to one embodiment, water is introduced through an emulsion of silicone oil in water, and the amount of water is about 60% by weight.When water is introduced into silicone composition through emulsion, the dispersion of water in silicone composition and its storage stability are improved.

[0047] According to another embodiment, the pore former D is a polyol. Preferably, it is an organic polyol containing 3 to 12 carbon atoms and at least two hydroxyl groups per molecule. The polyol may be linear or branched and may optionally contain one or more aromatic rings. Examples that may be mentioned are saturated polyhydric alcohols containing at least two hydroxyl groups per molecule, such as those described in US Pat. No. 4,871,781. Examples of polyols that can be used as pore formers according to the invention are: Diols, such as 1,2-ethanediol, 2,3-propanediol, 1,3-propanediol, 1,4-butanediol, 1,5-pentanediol and 1,6-hexanediol; Triols, such as 1,2,3-propanetriol and 2,2-bis-hydroxymethyl-butanol; Tetritols, such as erythritol and pentaerythritol; Pentitols, such as arabitol, xylitol, and methylpentitol; hexitols, such as mannitol and sorbitol; and Cycloaliphatic polyols, such as cyclohexanediol, cyclohexanetriol, and inositol is.

[0048] According to another embodiment, the pore-forming agent D is a monofunctional alcohol. Preferably, it is an organic alcohol containing 1 to 12 carbon atoms and a single hydroxyl group per molecule. The alcohol may be linear or branched, and it may optionally contain one or more aromatic rings. Examples of monofunctional alcohols that can be used as pore-forming agents according to the invention are methanol, ethanol, n-propanol, isopropanol, n-butanol, 2-butanol, tert-butanol, n-octanol, benzyl alcohol, and mixtures thereof.

[0049] According to yet another embodiment, the pore-forming agent D is an organosilane containing one or more silanol groups. These compounds can be represented, for example, by the following formula (1) or formula (2): (1)(R 3 )3SiOH (2)(R 3 )2Si(OH)2, where R 3 represents a monovalent group selected from the group consisting of alkyl groups containing 1 to 8 carbon atoms, which may be substituted with at least one halogen atom, such as chlorine or fluorine, cycloalkyl groups containing 3 to 10 carbon atoms, and aryl groups containing 6 to 12 carbon atoms.

[0050] In the above formula, several R 3 It should be understood that when present, they may be the same as or different from one another.

[0051] Examples of organosilanes containing one or more silanol groups that can be used as pore formers according to the present invention are (CH3)3SiOH, (C6H5)SiOH, (CH3)(C6H5)2SiOH and (C6H5)2Si(OH)2.

[0052] According to yet another embodiment, the pore-forming agent D is an organosiloxane containing one or more silanol groups. Preferably, it is The following formula: R 3 g (OH) h SiO (4-g-h) / 2 At least one siloxy motif having 3 has the same meaning as above, g=0, 1 or 2, h=1 or 2, and the sum of g+h=1, 2 or 3), Optionally, a compound of the formula: 3 i SiO (4-i) / 2 A motif having 3 has the same meaning as above, where i=0, 1, 2 or 3) The organopolysiloxane compound may be formed by

[0053] The silicone composition may further comprise other ingredients, in particular at least one inorganic filler, in particular silica, quartz, or a mixture thereof; at least one heat- and / or fire-resistant additive; at least one diorganopolysiloxane gum; diorganopolysiloxane oils, the chain of which is blocked at each end by a triorganosiloxy motif in which the organic radicals bonded to the silicon atom are selected from alkyl radicals containing 1 to 8 carbon atoms; · Cross-linking inhibitors; Base color Optionally, other fillers may include:

[0054] According to a preferred embodiment, the silicone composition comprises an inorganic filler, which is preferably fumed silica or precipitated silica. The silica-type inorganic filler preferably has a specific surface area, measured according to the BET method, of at least 50 m 2 / g, especially 50m 2 / g~400m 2 / g, preferably 70m 2 / g, an average primary particle size of less than 0.1 μm (micrometer) and an apparent density of less than 200 g / l. Highly preferably, the inorganic filler has a specific surface area of ​​100 m 2 / g~300m 2 / g of fumed silica.

[0055] The silica-type inorganic fillers are preferably hydrophilic and can be incorporated directly into the silicone composition, or can be optionally treated with a compatibilizer.In a variation, these silicas can be optionally treated with one or more organosilicon compounds commonly used in this application, such as organosilanes or organosilazanes.These compounds include methylpolysiloxanes, such as hexamethyldisiloxane, octamethylcyclotetrasiloxane, etc.; methylpolysilazanes, such as hexamethyldisilazane, hexamethylcyclotrisilazane, tetramethyldivinyldisilazane, etc.; chlorosilanes, such as dimethyldichlorosilane, trimethylchlorosilane, methylvinyldichlorosilane, dimethylvinylchlorosilane, etc.; alkoxysilanes, such as dimethyldimethoxysilane, dimethylvinylethoxysilane, trimethylmethoxysilane, etc. These compounds may be used alone or in mixtures (see, for example, French Patents FR1126884, FR1136885, FR1236505 and British Patent GB1024234). According to a preferred embodiment, the silica is treated in situ while being mixed with all or part of the organopolysiloxane A. According to one advantageous embodiment, the silica is treated with one or more hexaorganodisilazanes. More preferably, the silica is treated with hexamethyldisilazane alone or in a mixture with divinyltetramethyldisilazane.

[0056] The silica may optionally be pre-dispersed in silicone oil in such a way that a suspension is obtained. In particular, it is preferred to use a suspension of treated fumed silica, in particular fumed silica treated with hexamethyldisilazane, in a polyorganosiloxane oil, in particular a vinylated polyorganosiloxane oil.

[0057] Alternatively or additionally, the silicone composition according to the present invention may also contain at least one other inorganic filler, which is quartz. It is preferably natural quartz powder with an average particle size distribution of less than 10 microns. The quartz may optionally be treated to improve its compatibility with the organopolysiloxane.

[0058] According to a preferred embodiment, the silicone composition contains a mixture of silica and quartz, wherein the weight ratio between quartz and silica is 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.

[0059] Other inorganic fillers may be envisaged, in particular bulking fillers such as diatomaceous earth, calcium carbonate and / or kaolin.

[0060] The silicone composition may optionally contain at least one heat-resistant and / or fire-resistant additive. These heat-resistant and / or fire-resistant additives are well known to those skilled in the art. They may be advantageously selected 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 earth metals such as cerium and lanthanum; organic phosphorus compounds; platinum derivatives; carbon black; and silicates of calcium, aluminum, and / or potassium, such as mica and wollastonite. Hydrated inorganic fillers, oxides, or carbonates of calcium, magnesium, or aluminum, such as magnesium hydroxide Mg(OH)2, aluminum hydroxide Al(OH)3, hydromagnesite having the empirical formula Mg5(CO3)4(OH)2·4H2O, and calcium hydroxide, may also be mentioned. According to another embodiment, hollow glass microspheres can be added to the silicone composition.

[0061] The silicone composition may optionally contain at least one diorganopolysiloxane gum, which is a linear polymer with a high molecular weight and a viscosity at 25°C of greater than 1000 Pa·s, preferably greater than 2000 Pa·s, whose diorganopolysiloxane chains are essentially of the formula RSiO 2 / 2 Each terminus is composed of a motif having the formula RSiO 1 / 2 where the R group represents an alkyl group containing 1 to 8 carbon atoms or an alkenyl group containing 2 to 6 carbon atoms. However, along the length of the diorganopolysiloxane chain, there are small amounts of RSiO 2 / 2 Motifs other than RSiO 3 / 2 and / or SiO 4 / 2 The motif is R2SiO 2 / 2 It is not excluded that the diorganopolysiloxane gum has a maximum proportion of 2% of the number of motifs. Preferably, the diorganopolysiloxane gum has at least two silicon-bonded C2-C 12 Advantageously, the diorganopolysiloxane gum has a vinyl motif content by weight of 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%.

[0062] If the silicone composition comprises a crosslinking inhibitor (or addition reaction inhibitor), this may be selected from the following compounds: organopolysiloxanes, advantageously cyclic and substituted by at least one alkenyl, particularly preferably tetramethylvinyltetrasiloxane, pyridine, phosphines and organic phosphites, unsaturated amides, alkylated maleates, and acetylenic alcohols, such as 1-ethynyl-1-cyclohexanol, 3-methyl-1-dodecin-3-ol, 3,7,11-trimethyl-1-dodecin-3-ol, 1,1-diphenyl-2-propyn-1-ol, 3-ethyl-6-ethyl-1-nonyn-3-ol, and 3-methyl-1-pentadecin-3-ol.

[0063] According to one embodiment, the silicone composition comprises (by weight based on the total weight of the silicone composition): a. 40 wt% to 80 wt% of at least two C2 to C3 groups bonded to silicon per molecule 12 at least one organopolysiloxane A containing alkenyl groups; b. 1% to 20% of at least one organopolysiloxane B having at least two SiH motifs per molecule, preferably at least three SiH motifs; c. 2 ppm to 400 ppm by weight of a hydrosilylation catalyst C selected from platinum compounds (amount calculated by weight of platinum metal); d. 0.3 wt% to 2.5 wt% of a pore-forming agent D; e. At least 3% by weight of a material with a specific surface area of ​​100 m 2 / g~300m 2 / g fumed silica, f. at least 6% by weight of at least one inorganic filler that is quartz powder; and g. 0.4% to 5% by weight of at least one heat-resistant and / or fire-resistant additive Includes:

[0064] According to another embodiment, the silicone composition comprises (by weight based on the total weight of the silicone composition): a. 40 wt% to 80 wt% of at least two C2 to C3 groups bonded to silicon per molecule 12 at least one organopolysiloxane A containing alkenyl groups; b. 1% to 20% by weight of at least one organopolysiloxane B having at least two SiH motifs per molecule, preferably at least three SiH motifs; c. 2 ppm to 400 ppm by weight of a hydrosilylation catalyst C selected from platinum compounds (amount calculated by weight of platinum metal); d. 0.3 wt% to 2.5 wt% of a pore-forming agent D; e.3% to 14% by weight of a specific surface area of ​​100m 2 / g~300m 2 / g of at least one inorganic filler which is fumed silica; f. 6% to 25% by weight of at least one inorganic filler that is quartz powder; g. 0.4 wt.% to 5 wt.% of at least one fire-resistant additive; h. 0 to 3000 ppm by weight of a cross-linking inhibitor, and i. 0 to 4 wt. % of at least two C2 to C3 bonded to silicon 12 Alkenyl-containing diorganopolysiloxane gum Includes:

[0065] Although the composition crosslinked by polyaddition as described above is a preferred embodiment for the silicone foam according to the present invention, other silicone compositions capable of forming bubbles are entirely conceivable as long as they release a gas that enables the foaming phenomenon. According to one embodiment, the silicone composition contains a pore-forming agent that expands the material by decomposing under the action of heat and releasing a gas, particularly in the case of azo-type derivatives such as azodicarbonamide, which allow the release of nitrogen, carbon dioxide, and ammonia. According to another embodiment, the silicone composition contains a pore-forming agent that expands the material by changing phase under the action of heat, typically from liquid to gas, this being the case in particular in the case of low-boiling point solvents.

[0066] According to one embodiment, the silicone composition according to the present invention can be prepared from a two-component (or multi-component) system characterized by two (or more) separate parts intended to be mixed to form the aforementioned silicone composition. In particular, in the case of a preferred silicone composition, such as that described above, the silicone composition can be prepared from a two-component system, one of which contains catalyst C but not organopolysiloxane B, and the other of which contains organopolysiloxane B but not catalyst C. Other multi-component systems can be provided to improve shelf life and / or optimize the viscosity of each component. As an example, the silicone composition according to the present invention can be prepared from a three-component system characterized by three separate parts intended to be mixed to form the aforementioned silicone composition.

[0067] The mixing of the parts of the aforementioned two-component (or multi-component) system may typically be carried out at temperatures close to room temperature, i.e., between 10°C and 40°C. Depending on the type of mixer and the shear applied, an increase in the temperature of the silicone composition may be observed during this mixing. If crosslinking or curing of the silicone foam is to be accelerated, the mixing may be carried out at a higher temperature, preferably between 40°C and 70°C.

[0068] Good mixing is important to obtain a homogeneous silicone foam with good mechanical properties.

[0069] Furthermore, the method according to the invention comprises a step (b) consisting of introducing the aforementioned silicone composition prepared during step (a) into a closed mold.

[0070] The closed mold defines a hollow volume corresponding to the shape of the article to be molded. The mold can have a simple geometric shape, such as a parallelepiped as shown in Figure 1, or a complex shape corresponding to the use of the molded article, such as a shape corresponding to an ergonomically shaped seat.

[0071] The dimensions of the mold can be selected by the user depending on the article to be molded. The method is particularly suitable for large articles, typically 10 cm to 3 m in length and width, and at least 2 cm thick, typically 5 cm to 30 cm or 10 cm to 20 cm.

[0072] Preferably, the bottom and top walls of the mold define the maximum surface of the molded article, while the side walls define the thickness of the molded article.

[0073] According to a first embodiment shown in Figure 1, the mold (1) is composed of side walls (2) (four side walls are shown here), a bottom wall (3), and a cover (4). The cover (4) constitutes the top wall of the mold (1). The bottom wall (3) is provided with legs (5) that serve to support the mold. The cover (4) is preferably removable. When carrying out step (b) of the method according to the invention, a silicone composition can be poured or injected into the mold (1), and then the cover (4) can be fixed to the side walls, thereby defining a closed hollow volume.

[0074] According to another embodiment (not shown), the mold may be constituted by two half-molds which, when assembled, define a closed hollow volume. When carrying out step (b) of the method according to the invention, the silicone composition may typically be injected into the closed hollow volume defined by the assembled two half-molds.

[0075] The closed mold used in the present invention is characterized by walls that are permeable to gases at least during all or part of the aforementioned crosslinking and / or curing process of the silicone composition. Preferably, all of the walls of the mold according to the present invention are permeable to gases. As used in the present invention, the term "permeable to gases" refers to the ability of the material in question to pass through the gas generated during the reaction for foaming the silicone composition according to the present invention.

[0076] According to one embodiment, all of the walls of the mold are made of the same material or materials, all of which are permeable to gases at least during all or part of the aforementioned process of crosslinking and / or curing of the silicone composition.

[0077] According to another embodiment, the permeability of the mold is not uniform. As an example, it is possible to envision an embodiment in which certain walls of the mold, typically the bottom wall (3) and the cover (4) in Figure 1, are permeable to gases during all or part of the aforementioned crosslinking and / or curing process of the silicone composition, while the side wall (2) has low or no permeability to gases during all or part of the aforementioned crosslinking and / or curing process of the silicone composition.

[0078] Furthermore, the walls must be sufficiently rigid to ensure the mechanical strength of the mold and must be able to accommodate the silicone composition in liquid form prior to the crosslinking and / or curing reaction of the silicone composition. Thus, the walls of the mold according to the present invention are permeable to gases at least during all or part of the crosslinking and / or curing process of said silicone composition; Impermeable to silicone compositions prior to the crosslinking and / or curing reaction; ·Sufficiently rigid to ensure the mechanical strength of the mold.

[0079] Several embodiments can be envisioned by those skilled in the art.

[0080] In a first embodiment, the wall of the mold according to the present invention is made of a hard material that ensures the mechanical strength of the mold, is permeable to gases, and is impermeable to liquids. Such an embodiment is shown, for example, in FIG. 2A, where the wall (6a) is made of a material having an inner surface (7) and an outer surface (8). This material is permeable to gases but impermeable to liquids. In addition, this material is sufficiently hard to ensure the mechanical strength of the mold. As an example, it can be a microporous composite material or a microporous plastic material, such as microporous PET.

[0081] In a second embodiment, the walls of the mold according to the invention are composed of two adjacent materials: one rigid outer material, e.g., a screen or perforated plate, ensuring the mechanical strength of the mold, and the other inner material, which is permeable to gases and impermeable to liquids. This type of embodiment is shown, by way of example, in FIGS. 2B and 2C, where the walls (6b) / (6c) are composed of a first material (9) / (12) defining the interior of the mold and a second material (10) / (13) defining the exterior of the mold. Both the first and second materials are permeable to gases. The second material (10) / (13) ensures the mechanical support function of the mold, while the first material (9) / (12) ensures impermeability to liquids. The second material (10) / (13) is rigid and ensures the mechanical strength of the mold. To ensure gas permeability, the second material (10) is provided with perforations (11), as can be seen in FIG. 2B. The total surface area of ​​the perforations can represent at least 30%, more preferably at least 40%, and even more preferably at least 50% of the total surface area of ​​the second material (10). The second material (10) can be made of metal, such as steel or aluminum, of rigid plastic, typically PET, polypropylene, or indeed polycarbonate, or of a composite material. In FIG. 2C, the second material (13) is a screen or metal or plastic mesh. The first material (9) / (12) preferably adjoins the second material (10) / (13) and has the function of ensuring that its wall is impermeable to liquids. Preferably, it is a soft material, typically a fibrous material. The aforementioned fibrous material can be of natural, artificial, and / or synthetic origin. It can be a woven, knitted, or nonwoven fibrous material. If it is a woven or knitted textile substrate, ie a fabric or knitted fabric, its filaments are advantageously based on a thermoplastic polymer.Examples of suitable thermoplastic polymers or copolymers that may be mentioned are polyolefins, polyesters, alkylene polyoxides, polyoxyalkylenes, polyhalogenoalkylenes, poly(alkylene phthalates or terephthalates), poly(phenyl or phenylene), poly(oxide or phenylene sulfide), polyvinyl acetate, polyvinyl alcohol, polyvinyl halides, polyvinylidene halides, polyvinyl nitrile, polyamides, polyimides, polycarbonates, polysiloxanes, acrylic or methacrylic acid polymers, polyacrylates or methacrylates, natural polymers such as cellulose and its derivatives, synthetic polymers such as synthetic elastomers, or thermoplastic copolymers comprising at least one monomer which is identical to any one of the monomers contained in the above-mentioned polymers, as well as mixtures and / or alloys of all these polymers or copolymers. If the fiber material is made from a thermoplastic polymer, it is preferably made from polyesters, such as polyethylene terephthalate (PET), polypropylene terephthalate (PPT), polybutylene terephthalate (PBT), etc., copolymers and blends thereof, or from polyamides, such as polyamide 6, polyamide 6.6, polyamide 4, polyamide 1.1, polyamide 1.2, polyamide 4·6, 6·10, 6·12, 6·36, 12·12, etc., copolymers and blends thereof.

[0082] According to a third embodiment, the wall of the mold according to the invention comprises: a rigid outer material for ensuring the mechanical strength of the mold, with vents for ensuring permeability to gases; Removable device that ensures impermeability of the wall to liquids It is composed of:

[0083] The one or more vent holes may be spaced apart to allow gas to be released uniformly against the mold wall. Their size and number can be adapted depending on the amount of gas generated during crosslinking and / or curing of the silicone composition. Preferably, the one or more vent holes may be located in the bottom wall of the mold, and optionally, in the top wall of the mold, which preferably defines the largest surface of the molded article.

[0084] An embodiment of this type is shown in FIG. 2D, where, for example, the wall (14) is made of a hard material that ensures the mechanical strength of the mold and is provided with a vent hole (15) that ensures permeability to gases. To ensure impermeability to liquids, the wall is provided with a plug (16) that fits into the vent hole (15). The plug (16) is placed in the vent hole (15) when the silicone composition is introduced into the mold in liquid form. Once the crosslinking and / or curing reaction begins, the silicone composition reaches a gel point, beyond which it is no longer fluid enough to pass through the wall. From this moment on, the plug (16) is removed to allow gas to escape for the remainder of the crosslinking and / or curing reaction. Alternatively, a removable device that ensures the wall's impermeability to liquids can be a removable panel, an outer impermeable adhesive film, etc.

[0085] The method according to the present invention finally comprises step (c) of crosslinking and / or curing the silicone composition to obtain a silicone foam. The duration of this step (c) may vary depending on the silicone composition and the temperature of step (b). Generally, a silicone foam with good properties is obtained after a few minutes or hours, depending on the temperature and the concentration of catalyst and inhibitor in the silicone composition.

[0086] The crosslinking and / or curing of a silicone composition is first characterized by obtaining a gel. The gel point of a composition is defined as the stage at which a liquid begins to have pseudoelastic properties. In the polymer technology field, the gel point can be defined as the inflection point of a viscosity-time curve. In practice, the gel point of a composition can be determined visually by those skilled in the art. Beyond the gel point, the silicone composition continues to crosslink and / or cure to obtain a silicone foam.

[0087] In the method according to the invention, the walls of the mold are preferably permeable to gases after the gel point of the silicone composition described above, before which the walls of the mold may be permeable to gases or impermeable to gases, depending on the mold used.

[0088] According to one embodiment of the present invention, a method for preparing a silicone foam comprises the following steps: a) preparing a silicone composition capable of forming a foam by releasing a gas; b) introducing the silicone composition into a closed mold, the walls of which are made up of two adjacent materials, one being a rigid outer material to ensure the mechanical strength of the mold and permeable to gases, for example a screen or perforated plate to ensure gas permeability, and the other being an inner material that is permeable to gases and impermeable to liquids; c) crosslinking and / or curing the silicone composition to obtain a silicone foam. Includes:

[0089] According to another embodiment of the present invention, a method for preparing a silicone foam comprises the following steps: a) preparing a silicone composition capable of forming a foam by releasing a gas; b) introducing the silicone composition into a closed mold, the walls of which are constituted by a rigid outer material ensuring the mechanical strength and permeability to gases of the mold, and by a removable device ensuring the impermeability of the walls to liquids; c) crosslinking and / or curing the silicone composition to a gel point; c') removing said removable device ensuring impermeability of the walls to liquids; and c'') crosslinking and / or curing the silicone composition to obtain a silicone foam. Includes:

[0090] Advantageously, the entire method for producing silicone foam is carried out under air or nitrogen flushing during the process to avoid the risks associated with hydrogen release. In addition, the method for producing silicone foam is preferably carried out at atmospheric pressure and room temperature to also avoid the risks associated with hydrogen release. Room temperature is generally between 15°C and 40°C, typically about 25°C. In addition to safety considerations, carrying out the method at atmospheric pressure and / or room temperature offers significant advantages in terms of technology simplification and implementation costs.

[0091] The method according to the present invention can optionally include an additional step (d) of annealing the silicone foam obtained in step (c). This optional annealing step can consist of a heat treatment at a temperature of 50°C to 200°C, preferably 100°C to 150°C, for a period of one to several hours, preferably 1 to 4 hours. This can improve the fire resistance and mechanical characteristics of the silicone foam, if necessary. However, this step is not essential, and a method for preparing a silicone foam according to the present invention that does not include an additional annealing step is preferred.

[0092] After crosslinking and / or curing and optional annealing, a silicone foam is obtained, which can be removed from the mold. Advantageously, the material of the mold's inner surface, i.e., the material that comes into contact with the silicone composition before crosslinking and / or curing and then comes into contact with the silicone foam after crosslinking and / or curing (e.g., the material of the inner surface (7) in the first embodiment or the first materials (9) and (12) in the second and third embodiments described above), is selected to allow easy removal from the mold. For this purpose, the material is selected from materials that have little or no adhesion to the silicone foam after crosslinking and / or curing. Preferably, the material of the mold's inner surface is made of polyester. Alternatively, the material may be surface-treated, for example with a fluorocarbon coating, to improve its non-adhesion to the silicone foam.

[0093] The present invention also relates to an article made from the silicone foam obtained by the method defined above. This silicone foam article is advantageously free of major shape defects. In particular, it is free of deformations or dents on the bottom surface. The foam advantageously reproduces the shape previously determined by the hollow volume of the mold used.

[0094] Furthermore, the foam obtained by the process of the present invention advantageously has a low density, preferably less than 0.20 g / mL, more preferably less than 0.17 g / mL, and even more preferably less than 0.14 g / mL, and is visually uniform, with a uniform distribution of cell sizes within the foam and no large cells greater than 2 mm in diameter.

[0095] Finally, due to the nature of the silicone composition used, the silicone foam obtained by the process of the present invention has excellent heat and fire resistance properties. Advantageously, the foam does not emit toxic gases during its combustion.

[0096] The above advantages therefore ensure that the silicone foam obtained by the method of the present invention forms an ideal material for the manufacture of articles in the construction, transportation, electrical insulation or household appliance sectors, more particularly as an upholstery material for seats in the transportation sector, and the silicone foam article is therefore preferably at least one element of a seat in the transportation sector.

[0097] Other details or advantages of the invention will become more apparent from the examples given below, which are given purely by way of reference. [Example]

[0098] A silicone composition capable of forming foam and crosslinking by polyaddition was prepared by mixing the compounds listed in Table 1 below at room temperature.

[0099] [Table 1]

[0100] Comparative Example: The silicone composition obtained after mixing was poured into a parallelepiped mold without a cover, measuring 27 x 17 x 11 cm, with side and bottom walls made of polypropylene (which is impermeable to gas). After 45 minutes at 23°C, the resulting foam was removed. As can be seen in Figure 3, the foam block showed significant deformation, especially at its bottom. The density of the foam was 0.150 g / mL.

[0101] Examples according to the invention: The same silicone composition was poured into a mold according to the invention, consisting of a perforated steel frame, measuring 55 x 20 x 20 cm, the inner walls of which were covered with polyester fabric. The cover, also consisting of a perforated steel plate covered with polyester fabric, was fixed onto the frame to form a closed mold that was permeable to gas (Figure 4). After 45 minutes at 23°C, the resulting foam was removed. As can be seen in Figure 5, there was no significant deformation of the foam block obtained according to the invention. The shape of the block perfectly matched the shape defined by the mold. The density of the foam was 0.135 g / mL.

Claims

1. 1. A method for preparing a silicone foam, comprising the steps of: a) preparing a silicone composition capable of forming a foam by releasing a gas; b) introducing the silicone composition into a closed mold; and c) crosslinking and / or curing the silicone composition to obtain a silicone foam. Including, the walls of the mold are permeable to gases at least during all or part of the process for crosslinking and / or curing the silicone composition; The silicone composition capable of forming a silicone foam is a composition that crosslinks by polyaddition and generates hydrogen during the foaming reaction, A method for preparing a silicone foam, wherein the walls of the mold are composed of two adjacent materials, one of which is a hard outer material to ensure the mechanical strength of the mold, is permeable to gases, and is a screen or perforated plate, and the other is an inner material that is permeable to gases and impermeable to liquids.

2. The silicone composition capable of forming a silicone foam is a composition that crosslinks by polyaddition, At least two silicon-bonded C per molecule 2 ~C 12 at least one organopolysiloxane A containing alkenyl groups; at least one organopolysiloxane B having at least two SiH motifs per molecule, a catalytically effective amount of at least one hydrosilylation catalyst C, and at least one pore-forming agent D containing hydroxyl groups 2. The method for preparing the silicone foam of claim 1, wherein the composition comprises:

3. 3. The method for preparing a silicone foam according to claim 2, wherein the pore-forming agent D containing hydroxyl groups is selected 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.

4. 4. The method for preparing a silicone foam according to claim 3, wherein the pore former D is water.

5. The silicone composition comprises (by weight relative to the total weight of the silicone composition): a. 40% to 80% by weight of at least two silicon-bonded C groups per molecule 2 ~C 12 at least one organopolysiloxane A containing alkenyl groups; b. 1% to 20% of at least one organopolysiloxane B having at least two SiH motifs per molecule; c. 2 ppm to 400 ppm by weight of a hydrosilylation catalyst C selected from platinum compounds (amount calculated by weight of platinum metal); d. 0.3 wt% to 2.5 wt% of Pore Former D; e. At least 3% by weight of a material having a specific surface area of ​​100 m 2 / g to 300m 2 / g of fumed silica, f. at least 6% by weight of at least one inorganic filler that is quartz powder; and g. 0.4% to 5% by weight of at least one heat and / or fire resistant additive A method for preparing the silicone foam of any one of claims 2 to 4, comprising:

6. 5. A method for preparing a silicone foam according to claim 1, wherein the inner material, which is permeable to gases and impermeable to liquids, is a soft material.

7. 7. The method for preparing a silicone foam according to claim 6, wherein the inner material is a woven, knitted or nonwoven fibrous material.

8. The following steps: a) preparing a silicone composition capable of forming a foam by releasing a gas; b) introducing the silicone composition into a closed mold, the walls of which are made up of two adjacent materials, one being a rigid outer material ensuring the mechanical strength of the mold, which is permeable to gases and is a screen or perforated plate, and the other being an inner material which is permeable to gases and impermeable to liquids; 5. A method for preparing a silicone foam according to claim 1, comprising the step of: c) crosslinking and / or curing the silicone composition to obtain a silicone foam.

9. 5. The method for preparing a silicone foam according to claim 1, wherein the method is carried out at atmospheric pressure.

10. 5. The method for preparing a silicone foam according to any one of claims 1 to 4, wherein the method is carried out at room temperature.

11. A method for producing an article from a silicone foam obtained by the method according to any one of claims 1 to 4.

12. The method of claim 11, wherein the article is an article in the construction, transportation, electrical insulation or home appliances sectors.

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