Silicone elastomer for dielectric actuators, having prolonged service life

Abstract

The present invention relates to the use of silicone elastomers, obtainable from defined, addition-crosslinking organopolysiloxane compositions in dielectric elastomer actuators (DEA), which allow substantially prolonged service life as compared to prior art DEAs.

Description

[0001] Silicone elastomer for dielectric actuators with extended

[0002] life

[0003] The present invention relates to the use of silicone elastomers obtainable from defined, addition-curing organopolysiloxane compositions in dielectric elastomer actuators (DEA), which enable DEA with a significantly extended service life compared to the prior art.

[0004] For the characterization, comparison and evaluation of dielectric layers or transducers based on electroactive polymers, the combination of the elastic modulus [MPa] and the breakdown field strength [V / pm] has been used in the state of the art, since the breakdown field strength is considered a measure of the electrical load capacity of the dielectric layer and is used as a decisive criterion for the lifetime.

[0005] US2015315347A (= corresponding EP2931792) describes a process for producing thin silicone films, which, due to their high thickness precision and the manufacturing process, are particularly suitable for applications in the field of dielectric converters. Various silicone base materials can be used.

[0006] US2015344671A (= corresponding EP2938679) describes silicones with functional groups that can increase electrical permittivity. While this increases the energy density of converters relative to the layer thickness, the breakdown voltage and thus the load capacity are lower than with polydimethylsiloxane-based layers that do not contain the described groups. The same applies to the service life. US2022017701A (= corresponding EP3892686) claims special silicone elastomer mixtures, but without reference to the service life of actuators or generators, which also have low breakdown field strengths in the range between 54 and 65.4 V / pm.

[0007] In the state of the art, there is currently no disclosure of a correlation between the service life and the ingredients used.

[0008] There is still a great need for materials that are suitable for increasing the lifetime of actuators compared to the state of the art.

[0009] The present invention therefore relates to silicone-based dielectric elastomer actuators (DEA) with an equibiaxial pre-stretching by a factor of 1.3, measured at a permanently applied direct voltage of 90 V / pm at a temperature of 85 ° C and 85% relative humidity, characterized in that they contain a dielectric made of silicone, which is produced by crosslinking an addition-crosslinking silicone elastomer composition (X) containing

[0010] - (Al ) 20 to 60 wt . % of at least one organopolysiloxane having an average molecular weight Mw of at most 40 , 000 g / mol with at least two aliphatically unsaturated radicals per molecule ,

[0011] - (A2) 1 to 40 wt . % of at least one organopolysiloxane having an average molecular weight Mw of at least 85,000 g / mol with at least two aliphatically unsaturated radicals per molecule, - (B) 0.1 to 10 wt.% of at least one organohydrogenpolysiloxane having at least three silicon-bonded hydrogen atoms,

[0012] - (C) 5 to 30 wt.% of at least one alkenyl group-containing silicone resin having at least one branching point,

[0013] - (D) at least one hydrosilylation catalyst,

[0014] (E) 5 to 30 wt.% of a reinforcing filler with an average surface area of ​​between 50 and 400 m 2 / g, with the proviso that the sum of all components always adds up to 100 wt.%, the Si-H / Si-vinyl ratio of (B) to (Al) , (A2 ) ,

[0015] (C) and (E) is chosen to be between 0.5 and 3 to ensure cross-linking, and the ratio of (Al) to (A2) is at least 1.5, and thus (A1) / (A2) > 1.5.

[0016] The lifetime was determined under a static electric field at a continuous voltage of 90 V / pm under various combinations of temperature and humidity. A sample of the elastomer is crosslinked in a layer which is approximately 20 pm. The method of production of this thin layer is not important; all known state of the art processes can be used, such as spin coating, doctor blade application or slot die application. After production, the samples are equibiaxially stretched by a certain factor (e.g. 1.3 or 1.7) and an electrically conductive electrode is applied to both sides to create a capacitor-like structure. The electrode can also be applied using various methods, e.g. using pad printing. The electrode material consists of conductive particles, for example carbon black or nanoscale carbon fibers.After pre-stretching, the elastomer preferably has a thickness in the test between 10 gm and 20 gm .

[0017] The lifetime in [h] refers to the failure of 50% of the samples (t50% according to Weibull).

[0018] A detailed disclosure of this determination method, sample preparation and evaluation can be found in the following scientific article: Fabio Beco Albuquerque and Herbert Shea 2021 Smart Mater . Struct . 30 125022 . There are various methods for producing thin films such as application by spin coating, doctor blade, slot die or other techniques known in the art.

[0019] In order to avoid making the number of pages of the description of the present invention too extensive, only the preferred embodiments of the individual features are listed below.

[0020] However, the knowledgeable reader should understand this type of disclosure to mean that every combination of different preference levels is explicitly disclosed and explicitly desired.

[0021] The silicone-based DEA according to the invention preferably contain a silicone dielectric with a thickness of 10 to 100 gm, and a thickness accuracy of ±5%, measured on an area of ​​200 cm 2 .

[0022] A further subject of the present invention is a process for producing silicone-based, dielectric elastomer actuators (DEA), with a service life of at least 30 hours at an equibiaxial pre-strain by a factor of 1.3, measured at a permanently applied direct voltage of 90 V / pm at a temperature of 85 °C and 85% relative humidity, characterized in that the dielectric contained is produced by crosslinking an addition-crosslinking silicone elastomer composition (X), wherein the silicone elastomer composition (X)

[0023] - (Al) 20 to 60 wt.% of at least one organopolysiloxane having an average molecular weight Mw of not more than 40,000 g / mol with at least two aliphatically unsaturated radicals per molecule,

[0024] - (A2) 1 to 40 wt.% of at least one organopolysiloxane having an average molecular weight M wof at least 85,000 g / mol with at least two aliphatically unsaturated residues per molecule,

[0025] - (B) 0.1 to 10 wt.% of at least one organohydrogenpolysiloxane having at least three silicon-bonded hydrogen atoms,

[0026] - (C) 5 to 30 wt.% of at least one alkenyl group-containing silicone resin having at least one branching point,

[0027] - (D) at least one hydrosilylation catalyst,

[0028] (E) 5 to 30 wt.% of a reinforcing filler with an average surface area of ​​between 50 and 400 m 2 / g, with the proviso that the sum of all components always adds up to 100 wt.%, the Si-H / Si-vinyl ratio of (B) to (Al), (A2), (C) and (E) is chosen so that it is between 0.5 and 3 in order to ensure crosslinking, and the ratio of (Al) to (A2) is at least 1.5, and thus (Al) / (A2) > 1.5.

[0029] For the production of dielectric elastomer actuators (DEA), thin elastomer layers in the range between 10 gm and 100 gm are first produced from the silicone elastomer compositions (X) according to the invention, which serve as the basis for the dielectric. For testing purposes, all technologies for producing thin layers are suitable, such as spin coating, roller application, dip coating, spraying, doctor blade application, box-type doctor blade application, or slot die application. For industrial purposes, doctor blade, chambered doctor blade, and slot die application are preferred, with chambered doctor blade and slot die application being particularly preferred. Furthermore, it is crucial that the silicone elastomer composition (X), depending on the selected layer thickness, does not contain any particles larger than two-thirds of the silicone elastomer layer thickness. For a 30 gm layer, this means that it should not contain any particles larger than 20 gm.The number of particles between 20 and 30 gm for this layer thickness is, in a preferred embodiment, less than 100 ppm and particularly preferably less than 10 ppm.

[0030] Due to the required freedom from particles, care must be taken throughout the material and actuator manufacturing process to ensure that the processes are carried out under controlled conditions with regard to the environment and the ambient air (filtered air, clean rooms). The removal of any particles contained in the silicone elastomer composition (X) can in principle be achieved using all techniques known to the state of the art. Examples include straining using strainer screens (wire nets, wire mesh), filter candles made from a wide variety of materials (metal, plastic, ceramic, etc.), filtration techniques such as magnetic filtration, pressure filtration using filter presses, backwash filters, pressure nutsches, etc. with or without filter aids such as activated carbon, metal oxides, etc.Another example for the removal of particles from the silicone elastomer composition (X ) is centrifugation, whereby all mentioned or possible processes can be carried out in a batch process or continuously.

[0031] The process for producing the elastomer actuators from the silicone elastomer composition (X) preferably takes place under cleanroom conditions in which particles larger than 5 pm do not occur. For the design of the production plant, this means that the uncrosslinked silicone composition, after removal of any particles it may contain, is stored and processed only in cleanrooms of class ISO 5 (ISO 1466-1) or better. Preferably in cleanrooms of class ISO 4 or better.

[0032] The addition-crosslinking silicone elastomer compositions (X) according to the invention can be one-component silicone compositions as well as two-component silicone compositions.

[0033] In the case of two-component silicone elastomer compositions (X), the two components of the addition-crosslinking silicone elastomer composition (X) according to the invention can contain all components in any combination, generally with the proviso that one component does not simultaneously contain siloxanes with aliphatic multiple bonds, siloxanes with Si-bonded hydrogen and catalyst, i.e. essentially not simultaneously contain the components (A1), (A2), (B), (C), (D) and (E).

[0034] Components (Al) and (A2)

[0035] The compounds (A1) and (A2) used in the addition-crosslinking silicone elastomer compositions (X) according to the invention are selected such that (A1) and (A2) have at least two aliphatically unsaturated radicals.

[0036] The addition-crosslinking silicone elastomer composition (X) according to the invention usually contains 20-60 wt.%, preferably 25-55 wt.% and particularly preferably 30-50 wt.% (Al) and 1-40 wt.%, preferably 2-30 wt.% and particularly preferably 5-20 wt.% (A2).

[0037] The addition-crosslinking silicone elastomer compositions (X) according to the invention preferably contain at least one aliphatically unsaturated organosilicon compound as constituents (A1) and (A2), it being possible to use all aliphatically unsaturated organosilicon compounds previously used in addition-crosslinking compositions, such as, for example, silicone block copolymers with urea segments, silicone block copolymers with amide segments and / or imide segments and / or ester-amide segments and / or polystyrene segments and / or silarylene segments and / or carborane segments and silicone graft copolymers with ether groups.

[0038] As organosilicon compounds (Al) or (A2) which have SiC-bonded radicals with aliphatic carbon-carbon multiple bonds, preferably linear or branched organopolysiloxanes comprising units of the general formula (I)

[0039] R 1 aR 2 bSiO (4-ab) / 2 (I) is used, where

[0040] R 1 independently of one another, identically or differently, an organic or inorganic radical free from aliphatic carbon bonds,

[0041] R 2 independently of one another, identically or differently, denote a monovalent, substituted or unsubstituted, SiC-bonded hydrocarbon radical having at least one aliphatic carbon-carbon multiple bond, a is 0, 1, 2 or 3, and b is 0, 1 or 2, with the proviso that the sum a + b is less than or equal to 3 and at least 2 radicals R 2 per molecule.

[0042] For rest R 1 They can be monovalent or polyvalent radicals, with the polyvalent radicals, such as bivalent, trivalent and tetravalent radicals, then linking several, such as two, three or four, siloxy units of the formula (I) to one another.

[0043] More examples for R 1 are the monovalent radicals -F, -CI, - Br, OR 6 , -CN, -SCN, -NCO and SiC-bonded, substituted or unsubstituted hydrocarbon radicals, which may be interrupted by oxygen atoms or the group -C(O)-, as well as divalent radicals bonded to Si on both sides according to formula (I). If radical R 1 SiC-bonded, substituted hydrocarbon radicals, preferred substituents are halogen atoms, phosphorus-containing radicals, cyano radicals, -OR 6 , -NR 6 -, NR 6 2, -NR 6 -C (0) -NR 6 2, — C(O)— NR 6 2, -C(O)R 6 , -C(O)OR 6, -SO2-Ph and - CeFs. Where R 6 independently of one another, identically or differently, denote a hydrogen atom or a monovalent hydrocarbon radical having 1 to 20 carbon atoms and Ph equals the phenyl radical.

[0044] Examples of residues R 1are alkyl radicals, such as the methyl, ethyl, n-propyl, iso-propyl, n-butyl, iso-butyl, tert-butyl, n-pentyl, iso-pentyl, neo-pentyl, tert-pentyl radical, hexyl radicals, such as the n-hexyl radical, heptyl radicals, such as the n-heptyl radical, octyl radicals, such as the n-octyl radical and iso-octyl radicals, such as the 2,2,4-trimethylpentyl radical, nonyl radicals, such as the n-nonyl radical, decyl radicals, such as the n-decyl radical, dodecyl radicals, such as the n-dodecyl radical, and octadecyl radicals, such as the n-octadecyl radical, cycloalkyl radicals, such as cyclopentyl, Cyclohexyl, cycloheptyl and methylcyclohexyl radicals, aryl radicals such as the phenyl, naphthyl, anthryl and phenanthryl radicals, alkaryl radicals such as o-, m-, p-tolyl radicals, xylyl radicals and ethylphenyl radicals, and aralkyl radicals such as the benzyl radical, the α- and β-phenylethyl radicals.

[0045] Examples of substituted radicals R 1are haloalkyl radicals, such as the 3, 3, 3-trifluoro-n-propyl radical, the 2, 2, 2, 2', 2', 2'-hexafluoroisopropyl radical, the heptafluoroisopropyl radical, haloaryl radicals, such as the o-, m- and p-chlorophenyl radical, - (CH2) -N (R 6 ) C (0) NR 6 2, (CH2) oC (0) NR 6 2, - (CH2)OC (0) R 6 , - (CH2)OC (0)OR 6 , - (CH2) OC (0) NR 6 2,

[0046] - (CH2) -C (0) - (CH2) P C (O) CH3, - (CH2) -O-C0-R 6 , - (CH2) -NR 6 - (CH2) P -NR 6 2,

[0047] - (CH2) OO- (CH2) P CH (OH) CH2OH, - (CH2) o (OCH2CH2) P 0R 6 , - (CH2) o -SO2-Ph and - (CH2) oO-CeFs, where R 6 and Ph has the meaning given above and o and p are identical or different integers between 0 and 10.

[0048] Examples for R 1Equally divalent radicals which are Si-bonded on both sides according to formula (I) are those which are derived from the monovalent examples given above for radical RI in that an additional bond occurs through substitution of a hydrogen atom. Examples of such radicals are - (CH2)-, and Ph, o and p have the meaning given above.

[0049] Preferably, the residue R 1 a monovalent, SiC-bonded, optionally substituted hydrocarbon radical having 1 to 18 carbon atoms and free from aliphatic carbon-carbon multiple bonds, particularly preferably a monovalent, SiC-bonded hydrocarbon radical having 1 to 6 carbon atoms and free from aliphatic carbon-carbon multiple bonds, in particular the methyl or phenyl radical.

[0050] For rest R 2It can be any group that is amenable to an addition reaction (hydrosilylation) with a SiH-functional compound.

[0051] If Rest R 2 SiC-bonded, substituted hydrocarbon radicals, the substituents are halogen atoms, cyano radicals and -OR 6 preferred, where R 6 has the meaning given above .

[0052] Preferably, the residue R 2 alkenyl and alkynyl groups having 2 to 16 carbon atoms, such as vinyl, allyl, methallyl, 1-propenyl, 5-hexenyl, ethynyl, butadienyl, hexadienyl, cyclopentenyl, cyclopentadienyl, cyclohexenyl, vinylcyclohexylethyl, divinylcyclohexylethyl, norbornenyl, vinylphenyl and styryl radicals, with vinyl, allyl and hexenyl radicals being particularly preferably used.

[0053] The molecular weight M wof the component (Al) should be on average not more than 40,000 g / mol, the molecular weight M w of component (A2 ) should be on average greater than 85,000 g / mol. M w means the mass average molecular weight. (A1) has a preferred average molecular weight Mw of at most 30,000 g / mol and particularly preferably of at most 20,000 g / mol. (A2) has a preferred average molecular weight Mw of at least 90,000 g / mol and particularly preferably of at least 95,000 g / mol.

[0054] For example, components (A1) and (A2) can be an alkenyl-functional oligo- or polysiloxane, or a highly polymeric polydimethylsiloxane (number average determined by NMR) containing chain-based or terminal Si-bonded vinyl groups. The structure of the molecules forming components (A1) and (A2) is not fixed; in particular, the structure of a higher molecular weight, i.e., oligomeric or polymeric siloxane can be linear, cyclic, branched, or resinous, network-like. Linear and cyclic polysiloxanes are preferably composed of units of the formula R 1 3SiOi / 2, R 2 R 1 2SiOi / 2, R 2 R 1 SiOi / 2 and R 1 2SiO2 / 2, where R 1 and R 2 have the meaning given above. Branched and network-like polysiloxanes additionally contain trifunctional and / or tetrafunctional units, where those of the formulas R 1SiO3 / 2, R 2 SiO3 / 2 and SiO4 / 2 are preferred. Of course, mixtures of different siloxanes that satisfy the criteria of components (Al) and (A2) can also be used.

[0055] Particularly preferred as components (A1) and (A2) is the use of vinyl-functional, essentially linear polydiorganosiloxanes with the stated molecular weights.

[0056] Component (B)

[0057] All hydrogen-functional organosilicon compounds which have previously been used in addition-crosslinkable compositions can be used as organosilicon compound (B).

[0058] The addition-crosslinking silicone elastomer composition (X) according to the invention usually contains 0.1 to 10 wt.% (B), preferably 1-8 wt.% (B) and particularly preferably 2-7 wt.% (B).

[0059] As organopolysiloxanes (B) which have Si-bonded hydrogen atoms, preferably linear, cyclic or branched organopolysiloxanes comprising units of the general formula (III)

[0060] R 1 cH d SiO(4-cd) / 2 (III) is used, where

[0061] R 1 has the meaning given above, c is 0, 1, 2 or 3 and d is 0, 1 or 2, with the proviso that the sum of c + d is less than or equal to 3 and at least two Si-bonded hydrogen atoms are present per molecule.

[0062] The organopolysiloxane (B) used according to the invention preferably contains Si-bonded hydrogen in the range from 0.04 to 1.7 percent by weight (wt.%), based on the total weight of the organopolysiloxane (B).

[0063] The molecular weight of component (B) can vary within wide limits, approximately between 10 2 and 10 6g / mol. For example, component (B) can be a relatively low-molecular SiH-functional oligosiloxane, such as tetramethyldisiloxane, but also a high-polymer polydimethylsiloxane containing chain- or terminal SiH groups, or a silicone resin containing SiH groups.

[0064] The structure of the molecules forming component (B) is also not fixed; in particular, the structure of a higher molecular weight, i.e. oligomeric or polymeric SiH-containing siloxane can be linear, cyclic, branched or even resinous, network-like. Linear and cyclic polysiloxanes (B) are preferably composed of units of the formula R 1 3SiOi / 2 , HR 1 2SiOi / 2 , HR 1 SiO2 / 2 and R 1 2SiO2 / 2 , where R 1has the meaning given above. Branched and network-like polysiloxanes additionally contain trifunctional and / or tetrafunctional units, where those of the formulas R 1 SiO3 / 2 , HS1O3 / 2 and S1O4 / 2 are preferred, where R 1 has the meaning given above .

[0065] Of course, mixtures of different siloxanes that satisfy the criteria of component (B) can also be used. Particular preference is given to the use of low molecular weight SiH-functional compounds such as tetrakis(dimethylsiloxy)silane and tetramethylcyclotetrasiloxane, as well as higher molecular weight, SiH-containing siloxanes such as poly(hydrogenmethyl)siloxane and poly(dimethylhydrogenmethyl)siloxane with a viscosity at 25 °C of 10 to 20,000 mPa*s (shear d = 1 s -1 ), or analogous SiH-containing compounds in which some of the methyl groups are replaced by 3,3,3-trifluoropropyl or phenyl groups.

[0066] To adjust the mechanical properties of the cured silicone film, preferably as (B) a, w-Si-H functional polyorganosiloxanes with a dynamic viscosity of 10 - 100,000 mPa - s (shear d = 1 s -1 ) are used. Component (B) is preferably present in the crosslinkable silicone compositions (X) according to the invention in an amount such that the molar ratio of SiH groups to aliphatically unsaturated groups from (A) is from 0.5 to 3, particularly preferably between 0.8 and 2.0.

[0067] The components (A1), (A2) and (B) used according to the invention are commercially available products or according to chemically

[0068] process can be produced.

[0069] Component (C):

[0070] Resins selected from: -MQ-siloxane resins, composed of M units of the formula R 93SiO]_ / 2 and Q units of the formula S1O4 / 2 -MT-siloxane resins, composed of M units of the formula R 9 3SiOj_ 2 and T units of the formula R 9 SiC>3 2, and -MTQ-siloxane resins, built from ^ er Formula R 9 3SiOj_ / 2 and T- units of the formula R 9 SiC>3 / 2 and Q units of the formula S1O4 / 2 or a mixture of two or more such resins, where

[0071] R 9 optionally halogen-substituted saturated hydrocarbon radicals having 1-40 carbon atoms, and wherein at least 2 of the radicals R per molecule are alkenyl radicals having 1-10 carbon atoms.

[0072] Preferably at least 0.1 mol%, particularly preferably at least 0.5 mol%, in particular at least 2 mol% and preferably at most 20 mol%, in particular at most 10 mol% of the radicals R 9 Alkenyl radicals with 1-10 carbon atoms. The hydrocarbon radicals R 9can be halogen-substituted, linear, cyclic, branched, aromatic, saturated or unsaturated.

[0073] Examples of unsubstituted radicals R 9 are alkyl radicals, such as the methyl, ethyl, n-propyl, iso-propyl, n-butyl, iso-butyl, tert. -butyl, n-pentyl, iso-pentyl, neo-pentyl, tert. -pentyl radical, hexyl radicals, such as the n-hexyl radical, heptyl radicals, such as the n-heptyl radical, octyl radicals, such as the n-octyl radical and iso-octyl radicals, such as the 2,2,4-trimethylpentyl radical, nonyl radicals, such as the n-nonyl radical, decyl radicals, such as the n-decyl radical; Cycloalkyl radicals, such as cyclopentyl, cyclohexyl, 4-ethylcyclohexyl, cycloheptyl, norbornyl and methylcyclohexyl radicals; aryl radicals, such as phenyl, biphenylyl and naphthyl; alkaryl radicals, such as o-, m-, p-tolyl and ethylphenyl radicals; aralkyl radicals, such as benzyl, alpha- and ß-phenylethyl radicals.

[0074] Examples of substituted hydrocarbon radicals as radicals R 9are halogenated hydrocarbons, such as the chloromethyl, 3-chloropropyl, 3-bromopropyl, 3,3,3-trifluoropropyl and 5,5,5,4,4,3,3-hexafluoropentyl radicals as well as the chlorophenyl, dichlorophenyl and trifluorotolyl radicals.

[0075] Preferably, the hydrocarbon radicals R 9 1 to 6 carbon atoms, particularly preferred are alkyl radicals and phenyl radicals. Preferred halogen substituents are fluorine and chlorine. Particularly preferred monovalent hydrocarbon radicals R 9 are methyl, ethyl, phenyl.

[0076] The alkenyl groups R 9 are amenable to an addition reaction with the SiH functions of component (B). Alkenyl groups with 2 to 6 carbon atoms, such as vinyl, allyl, methallyl, 1-propenyl, 5-hexenyl, ethynyl, butadienyl, hexadienyl, cyclopentenyl, cyclopentadienyl, cyclohexenyl, preferably vinyl and allyl, are usually used.

[0077] The addition-crosslinking silicone elastomer composition (X) according to the invention usually contains 5 to 30 wt.% (C), preferably 6 to 30 wt.%, more preferably 7 to 25 wt.% (C) and particularly preferably 7 to 15 wt.% (C).

[0078] Component (D)

[0079] All catalysts known in the art can be used as the hydrosilylation catalyst (D). Component (D) can be a platinum group metal, for example platinum, rhodium, ruthenium, palladium, osmium, or iridium, an organometallic compound, or a combination thereof. Examples of component (D) are compounds such as hexachloroplatinic(IV) acid, platinum dichloride, platinum acetylacetonate, and complexes of said compounds encapsulated in a matrix or a core-shell structure. Low-molecular-weight platinum complexes of organopolysiloxanes include 1,3-diethenyl-1,1,3,3-tetramethyldisiloxane complexes with platinum. Further examples are platinum phosphite complexes or platinum phosphine complexes.For light- or UV-curing compositions, alkyl platinum complexes such as derivatives of cyclopentadienyltrimethylplatinum (IV), cyclooctadienyldimethylplatinum (II), or diketonato complexes such as bisacetylacetonatoplatinum (II) can be used to initiate the addition reaction with the aid of light. These compounds can be encapsulated in a resin matrix.

[0080] The concentration of component (D) is sufficient to catalyze the hydrosilylation reaction of components (A1), (A2), (B), and (C) when exposed to generate the heat required in the process described herein. The amount of component (D) can be between 0.1 and 1000 parts per million (ppm), 0.5 and 100 ppm, or 1 and 25 ppm of the platinum group metal, depending on the total weight of the components. The cure rate may be slow if the platinum group metal content is below 1 ppm. The use of more than 100 ppm of the platinum group metal is uneconomical or reduces the storage stability of the silicone elastomer composition (X).

[0081] Component (E)

[0082] Another component of the addition-curing silicone compositions (X) are reinforcing fillers (E). Preference is given to fumed or precipitated silicas with BET surface areas between 50 m 2 / g and 400 m 2 / g, where pyrogenic and precipitated silicas with BET surface areas between 100 m 2 / g and 200 m 2 / g are preferred. The silica fillers mentioned may be hydrophilic in nature or hydrophobized by known methods. The content of actively reinforcing filler in the crosslinkable silicone elastomer composition (X) according to the invention is in the range from 5 to 30 wt.%, preferably 10 to 25 wt.%.

[0083] The crosslinkable addition-curing silicone elastomer compositions (X) are particularly preferably characterized in that the filler (E) is surface-treated. The surface treatment is achieved by the methods known in the prior art for hydrophobizing finely divided fillers.

[0084] Preferred fillers (E) have, as a result of a surface treatment, a carbon content of at least 0.01 to a maximum of 20 wt. %, preferably between 0.1 and 10 wt. %, particularly preferably between 0.5 and 5 wt. %. Particularly preferred are crosslinkable addition-crosslinking silicone elastomer compositions (X) characterized in that the filler (E) is a surface-treated silica containing 0.01 to 2 wt. % Si-bonded, aliphatically unsaturated groups. These are, for example, Si-bonded vinyl groups. In the addition-crosslinking silicone compositions (X) according to the invention, the constituent (E) is preferably used as a single filler or likewise preferably as a mixture of several finely divided fillers.

[0085] The addition-crosslinking silicone elastomer composition (X) according to the invention usually contains 5 to 30 wt.% (E), preferably 7-25 wt.% (E) and particularly preferably 10-20 wt.% (E).

[0086] Component (F)

[0087] The addition-crosslinking silicone elastomer composition (X) according to the invention may optionally contain further additives as constituents in a proportion of up to 70% by weight, preferably 0.0001 to 40% by weight. These additives may be, for example, inactive fillers, resinous polyorganosiloxanes other than the siloxanes (A1), (A2), (B), and (C), non-reinforcing fillers, fungicides, fragrances, rheological additives, corrosion inhibitors, oxidation inhibitors, light stabilizers, flame-retardants, and agents for influencing electrical properties, dispersing aids, solvents, adhesion promoters, pigments, dyes, plasticizers, organic polymers, heat stabilizers, etc.These include additives such as quartz flour, diatomaceous earth, clays, chalk, lithopone, carbon black, graphite, metal oxides, metal carbonates, metal sulfates, metal salts of carboxylic acids, metal dusts, fibers such as glass fibers, plastic fibers, plastic powders, metal dusts, dyes, pigments, etc.

[0088] These components (F) can also be thermally or electrically conductive. Examples of thermally conductive fillers are aluminum nitride; aluminum oxide; barium titanate; beryllium oxide; boron nitride; diamond; graphite; magnesium oxide; particulate metal such as copper, gold, nickel or silver; silicon carbide; tungsten carbide; zinc oxide and a combination thereof. Thermally conductive fillers are known in the art and commercially available. For example, CB-A20S and Al-43-Me are alumina fillers in various particle sizes commercially available from Showa-Denko, and AA-04, AA-2 and AA18 are alumina fillers commercially available from Sumitomo Chemical Company. Silver fillers are commercially available from Metalor Technologies USA Corp, of Attleboro, Massachusetts, USA. Boron nitride fillers are commercially available from Advanced Ceramics Corporation, Cleveland, Ohio, USA.Reinforcing fillers include silica and short fibers such as KEVLAR® short fibers. A combination of fillers with different particle sizes and particle size distributions can be used.

[0089] Examples of further optional components (F) include one or more solvents and one or more inhibitors. However, care must be taken to ensure that the solvent (F) does not have any adverse effects on the overall system. Suitable solvents (F) are known in the art and are commercially available. The solvent (F) can, for example, be an organic solvent having 3 to 20 carbon atoms. Examples of solvents (F) include aliphatic hydrocarbons such as nonane, decalin and dodecane; aromatic hydrocarbons such as mesitylene, xylene and toluene; esters such as ethyl acetate and butyrolactone; ethers such as n-butyl ether and polyethylene glycol monomethyl ester; ketones such as methyl isobutyl ketone and methyl pentyl ketone; silicone fluids such as linear, branched and cyclic polydimethylsiloxanes and combinations of these solvents (F).The optimal concentration of a particular solvent (F) in the addition-curing silicone elastomer composition (X) can be easily determined by routine testing. Depending on the weight of the compound, the amount of solvent (F) can range between 0 and 95 wt.% or between 1 and 95 wt.%.

[0090] The addition-curing silicone elastomer composition (X) may optionally additionally contain inhibitors and stabilizers. Inhibitors and stabilizers serve to specifically adjust the processing time, initiation temperature, and crosslinking rate of the addition-curing silicone composition (X) according to the invention. These inhibitors and stabilizers are very well known in the field of addition-curing compositions. Examples of common inhibitors are acetylenic alcohols, such as 1-ethynyl-1-cyclohexanol, 2-methyl-3-butyn-2-ol, and 3-methyl-2-butyn-2-ol.5-Dimethyl-l-hexyn-3-ol, 3-methyl-l-dodecyn-3-ol, polymethylvinylcyclosiloxanes such as 1, 3, 5, 7-tetravinyltetramethyltetracyclosiloxane, low molecular weight silicone oils with methylvinyl-SiOi / 2 groups and / or R2vinylSiOi / 2 end groups, such as divinyltetramethyldisiloxane, tetravinyldimethyldisiloxane, trialkyl cyanurates, alkyl maleates such as diallyl maleates, dimethyl maleate and diethyl maleate, alkyl fumarates such as diallyl fumarate and diethyl furmarate, organic hydroperoxides such as cumene hydroperoxide, tert. Butyl hydroperoxide and pinane hydroperoxide, organic peroxides, organic sulfoxides, organic amines, diamines and amides, phosphanes and phosphites, nitriles, triazoles, diaziridines, and oximes. The effect of these inhibitor additives depends on their chemical structure, so the concentration must be determined individually. Inhibitors and inhibitor mixtures are preferably used in amounts of 0.00001 wt.% to 5 wt.%.%, based on the total weight of the mixture, preferably 0.00005 to 2 wt.% and particularly preferably 0.0001 to 1 wt.%.

[0091] Activation for crosslinking can be achieved thermally, via IR radiation, or via UV radiation. For room-temperature curing systems, room temperature is sufficient for curing, so no additional energy input is required. Microwave or ultrasound activation is also possible.

[0092] In UV-crosslinking systems, the catalyst (D) of the hydrosilylation reaction of the addition-crosslinking silicone elastomer composition (X) is activated by irradiation in order to achieve crosslinking. All light sources known from the prior art can be used, such as, for example, LEDs, mercury vapor lamps, doped mercury vapor lamps, xenon lamps or lasers. Preferably, wavelengths between 250 and 800 nm are used, with particular preference being given to wavelengths between 300 and 500 nm. The light sources can be arranged as desired, and the distance between the light source and the silicone composition (X) to be crosslinked can vary between a few millimeters and several centimeters.

[0093] The silicone films and deelectrics produced with the silicone elastomer composition (X) according to the invention described have the advantage over the prior art that EAPs equipped therewith show a service life that is at least 1.2 times longer.

[0094] The silicone elastomers produced from the silicone elastomer compositions (X) according to the invention have the further advantage in thin layers of less than 100 pm that their breakdown voltage in generators and actuators is at least 70 V / pm, preferably at least 80 V / pm and particularly preferably at least 90 V / pm, i.e. significantly better than dielectric electroactive polymers according to the prior art.

[0095] Particularly in applications as EAPs in actuators or generators, the elastomers used are subjected to considerable stress, as they undergo several million vibration cycles over their lifetime. A further advantage of the silicone elastomers produced from the silicone compositions (X) according to the invention is their very high resistance to continuous loads.

[0096] Examples:

[0097] In the examples described below, all parts and percentages are by weight unless otherwise stated. Unless otherwise stated, the following examples are carried out at a pressure of the ambient atmosphere, i.e. approximately 1000 hPa, and at room temperature, i.e. 25°C, or at a temperature which occurs when the reactants combine at room temperature without additional heating or cooling. In the following, all viscosity data refer to a temperature of 25°C. The following examples illustrate the invention without having any limiting effect.

[0098] The following abbreviations are used:

[0099] Example

[0100] No. Number

[0101] Time t

[0102] hour h rF relative humidity

[0103] PDMS polydimethylsiloxane

[0104] Wt . % Weight percent , w / w

[0105] The lifetime was determined under a static electric field at a continuous voltage load of 90 V / pm under various combinations of temperature and humidity. A sample of the elastomer is cross-linked in a layer which is approximately 20 pm. The method of production of this thin layer is not important; all state-of-the-art processes can be used, such as spin coating, doctor blade application or slot die application. After production, the samples are equibiaxially stretched by a certain factor (e.g. 1.3 or 1.7) and an electrically conductive electrode is applied to both sides to create a capacitor-like structure. The electrode can also be applied using various methods, e.g. using pad printing. The electrode material consists of conductive particles, for example carbon black or nanoscale carbon fibers.After pre-stretching, the elastomer preferably has a thickness in the test between 10 pm and 20 pm.

[0106] The lifetime in [h] refers to the failure of 50% of the samples (t50% according to Weibull).

[0107] Silicone formulation 1 (comparative example 1)

[0108] Component A: 50 wt.% of a linear, vinyl-terminated organopolysiloxane with an average molecular weight of 16,500 g / mol

[0109] Component B: 27 wt.% of a linear, Si-H terminated organopolysiloxane and 3.0 wt.% of a Si-H comb crosslinker

[0110] Component D: 10 ppm based on the metal of a Karstedt-type platinum catalyst

[0111] Component E: 20 wt.% of a hydrophobic, pretreated silica with a BET surface area of ​​130 m2 / g

[0112] The ratio of Si-bonded hydrogen atoms to Si-bonded

[0113] alkylene groups is 1.1.

[0114] Silicone formulation 2 (comparative example 2)

[0115] Component A1: 49 wt.% of a linear, vinyl-terminated organopolysiloxane with an average molecular weight of 16,500 g / mol Component A2: 14 wt.% of a linear, vinyl-terminated organopolysiloxane with an average molecular weight of 70,500 g / mol Component B: 23 wt.% of a linear, Si-H terminated organopolysiloxane and 3.0 wt.% of a Si-H comb crosslinker Component C: 4 wt.% of a silicone resin containing M and Q units, where some of the M groups carry a vinyl group,

[0116] Component D: 10 ppm based on the metal of a Karstedt-type platinum catalyst

[0117] Component E: 20 wt.% of a hydrophobic, pretreated silica with a BET surface area of ​​130 m 2 / G

[0118] The ratio of Si-bonded hydrogen atoms to Si-bonded alkylene groups is 1.1.

[0119] Silicone formulation 3 (according to the invention)

[0120] Component A1: 38 wt.% of a linear, vinyl-terminated organopolysiloxane with an average molecular weight of 16,500 g / mol Component A2: 6 wt.% of a linear, vinyl-terminated organopolysiloxane with an average molecular weight of 90,000 g / mol Component B: 26 wt.% of a linear, Si-H terminated organopolysiloxane and 5.0 wt.% of a Si-H comb crosslinker Component C: 7.0 wt.% of a silicone resin which contains M and Q units, where some of the M groups carry a vinyl group.

[0121] Component D: 10 ppm based on the metal of a Karstedt-type platinum catalyst

[0122] Component E: 18 wt.% of a hydrophobic, pretreated silica with a BET surface area of ​​130 m2 / g. The ratio of Si-bonded hydrogen atoms to Si-bonded alkylene groups is 1.1.

[0123] Silicone formulation 4 (according to the invention)

[0124] Component A1: 31 wt.% of a linear, vinyl-terminated organopolysiloxane with an average molar mass of 16,500 g / mol Component A2: 18 wt.% of a linear, vinyl-terminated organopolysiloxane with an average molar mass of 95,000 g / mol Component B: 18 wt.% of a linear, Si-H terminated organopolysiloxane and 5.0 wt.% of a Si-H comb crosslinker Component C: 8.0 wt.% of a silicone resin which contains M and Q units, where some of the M groups carry a vinyl group.

[0125] Component D: 10 ppm based on the metal of a Karstedt-type platinum catalyst

[0126] Component E: 20 wt.% of a hydrophobic, pretreated silica with a BET surface area of ​​130 m2 / g. The ratio of Si-bonded hydrogen atoms to Si-bonded alkylene groups is 1.1.

[0127] Silicone formulation 5 (according to the invention)

[0128] Component A1: 19 wt.% of a linear, vinyl-terminated organopolysiloxane with an average molecular weight of 16,500 g / mol Component A2: 14 wt.% of a linear, vinyl-terminated organopolysiloxane with an average molecular weight of 110,000 g / mol Component B: 16 wt.% of a linear, Si-H terminated organopolysiloxane and 5.0 wt.% of a Si-H comb crosslinker Component C: 10.0 wt.% of a silicone resin which contains M and Q units, where some of the M groups carry a vinyl group.

[0129] Component D: 10 ppm based on the metal of a Karstedt-type platinum catalyst

[0130] Component E: 18 wt.% of a hydrophobic, pretreated silica with a BET surface area of ​​130 m 2 / g The ratio of Si-bonded hydrogen atoms to Si-bonded alkylene groups is 1.1. Table 1: Lifespan at 20 ° C, 90 % RH and 90 V / pm operating voltage

[0131] Table 2 : Lifespan at 20 °C, 30 % RH and 100 V / pm operating voltage Table 3 : Lifespan at 85 °C, 85 % RH and 100 V / pm operating

[0132] Tension

Claims

Patent claims 1. Silicone-based dielectric elastomer actuators (DEA) with a service life of at least 30 hours at an equibiaxial pre-strain by a factor of 1.3, measured at a permanently applied direct voltage of 90 V / pm and at a temperature of 85 °C and 85% relative humidity, characterized in that they contain a dielectric made of silicone, which is produced by crosslinking an addition-crosslinking silicone elastomer composition (X) containing - (Al) 20 to 60 wt.% of at least one organopolysiloxane having an average molecular weight Mw of not more than 40,000 g / mol with at least two aliphatically unsaturated radicals per molecule, - (A2) 1 to 40 wt.% of at least one organopolysiloxane having an average molecular weight M w of at least 85,000 g / mol with at least two aliphatically unsaturated residues per molecule, - (B) 0.1 to 10 wt.% of at least one organohydrogenpolysiloxane having at least three silicon-bonded hydrogen atoms, - (C) 5 to 30 wt.% of at least one alkenyl group-containing silicone resin having at least one branching point, - (D) at least one hydrosilylation catalyst, (E) 5 to 30 wt.% of a reinforcing filler with an average surface area of ​​between 50 and 400 m 2 / G, with the proviso that the sum of all components always adds up to 100 wt%, the Si-H / Si-vinyl ratio of (B) to (Al), (A2), (C) and (E) is chosen to be between 0.5 and 3 to ensure cross-linking, and the ratio of (Al) to (A2) is at least 1.5, and thus (Al) / (A2) > 1.

5.

2. Silicone-based dielectric elastomer actuators (DEA) according to claim 1, wherein the silicone dielectric has a thickness of 10 to 100 pm, and a thickness accuracy of ±5%, measured on an area of ​​200 cm 2 has.

3. Silicone-based dielectric elastomer actuators (DEA) according to claim 1, wherein as (B) at least one a,w-Si-H functional polyorganosiloxane with a dynamic viscosity of 10 - 100,000 mPa-s (d = 1 s -1 ) is included.

4. Silicone-based dielectric elastomer actuators (DEA) according to claim 1, wherein (Al) has an average molecular weight Mw of at most 30,000 g / mol and (A2) of at least 85,000 g / mol.

5. A process for the production of silicone-based dielectric elastomer actuators (DEA) with a lifetime of at least 30 hours at an equibiaxial pre-strain by a factor of 1.3, measured at a permanently applied direct voltage of 90 V / pm at a temperature of 85 °C and 85% relative humidity, characterized in that the dielectric contained is produced by crosslinking an addition-crosslinking silicone elastomer composition (X), wherein the silicone elastomer composition (X) - (Al) 20 to 60 wt.% of at least one organopolysiloxane having an average molecular weight Mw of not more than 40,000 g / mol with at least two aliphatically unsaturated radicals per molecule, - (A2) 1 to 40 wt.% of at least one organopolysiloxane having an average molecular weight M w of at least 85,000 g / mol with at least two aliphatically unsaturated residues per molecule, - (B) 0.1 to 10 wt.% of at least one organohydrogenpolysiloxane having at least three silicon-bonded hydrogen atoms, - (C) 5 to 30 wt.% of at least one alkenyl group-containing silicone resin having at least one branching point, - (D) at least one hydrosilylation catalyst, (E) 5 to 30 wt.% of a reinforcing filler with an average surface area of ​​between 50 and 400 m 2 / g, contains, with the proviso that the sum of all components always adds up to 100% by weight, the Si-H / Si-vinyl ratio of (B) to (Al), (A2), (C) and (E) is chosen to be between 0.5 and 3 to ensure crosslinking, and the ratio of (Al) to (A2) is at least 1.5, and thus (Al) / (A2) > 1.

5.

6. The method according to claim 5, characterized in that the DEA is manufactured from thin elastomer layers in the range between 10 pm and 100 pm, which are produced from the silicone elastomer compositions (X) according to the invention by means of doctor blade, chamber doctor blade and slot die application.

7. Process according to claim 5, characterized in that the 10 pm to 100 pm thin elastomer layers are produced by means of chamber doctor blade and slot die application.

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