WO2024235447A1 - Silicone elastomer for dielectric actuators, having prolonged service life - Google Patents

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

Silicone elastomer for dielectric actuators with extended

lifespan

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.

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.

US2015315347A (= corresponding EP2931792) describes a method for producing thin silicone films which are particularly suitable for applications in the field of dielectric converters due to the high thickness precision achieved through the type of production. Various silicone base materials can be used.

US2015344671A (= corresponding EP2938679) describes silicones with functional groups that can increase the electrical permittivity. This increases the energy density of converters in relation to the layer thickness, but the breakdown voltage and thus the load capacity is 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 lifetime of actuators or generators, which also have low breakdown field strengths in the range between 54 and 65.4 V/pm .

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

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

The present invention therefore relates to silicone-based dielectric elastomer actuators (DEA) with an equibiaxial pre-stretch 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

- (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 radicals 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 having 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 (A1) / (A2) > 1.5.

The service life 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 cross-linked in a layer of about 20 pm. The method of producing this thin layer is not important; all methods known to the state of the art 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, such as carbon black or nanoscale carbon fibers. After pre-stretching, the elastomer preferably has a thickness in the test of between 10 gm and 20 gm.

The specification of the service life in [h] refers to the failure of 50 % of the samples ( t50% according to Weibull ).

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

In order to keep the number of pages of the description of the present invention from being too extensive, only the preferred embodiments of the individual features are listed below.

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

The silicone-based DEAs 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 .

Another object of the present invention is a process for producing silicon-based, dielectric Elastomer actuators (DEA) with a service life of at least 30 hours at 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 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 radicals 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% by weight of a reinforcing filler having an average surface area of between 50 and 400 m ² /g, provided 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 cross-linking, and the ratio of (Al) to (A2) is at least 1.5, and thus (Al) / (A2) > 1.5.

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 test purposes, all technologies are suitable for producing thin layers, such as spin coating, roller application, dip coating, spraying, doctor blade application, box doctor blade application or slot nozzle application. For industrial purposes, doctor blade, chamber doctor blade and slot nozzle application are preferred, and chamber doctor blade and slot nozzle application are particularly preferred. In addition, it is crucial that the silicone elastomer composition (X), depending on the selected layer thickness, does not contain any particles that are larger than two thirds of the silicone elastomer layer thickness. For a 30 gm layer, this means that no particles should be contained that are 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.

Due to the required absence of particles, the entire process of material and actuator manufacturing must 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 carried out by all techniques known in the art. Examples of this are strainers using strainer sieves (wire nets, wire mesh), filter candles made of a wide variety of materials (metal, plastic, ceramic, etc.), filtration techniques such as magnetic filtration, pressure filtration using filter presses, backwash filters, pressure filters, etc. with or without filter aids such as activated carbon, metal oxides, etc. Another example of the removal of particles from the silicone elastomer composition (X) is centrifugation, whereby all of the processes mentioned or possible can be carried out in a batch process or continuously.

The process for producing the elastomer actuators from the silicone elastomer composition (X) is preferably carried out under clean room 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 only stored and processed in clean rooms of class ISO 5 (ISO 1466-1) and better. Preferably in clean rooms of class ISO 4 and better.

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

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 constituents 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 contains the components (Al), (A2), (B), (C), (D) and (E).

components (Al) and (A2)

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

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

The addition-crosslinking silicone elastomer compositions (X) according to the invention preferably contain at least one aliphatically unsaturated organosilicon compound as constituents (Al) 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.

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)

R ¹ aR ² bSiO (4-ab) /2 (I) used, whereby

R ¹ independently of one another, identical or different, is an organic or inorganic radical free from aliphatic carbon-carbon bonds,

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 R ² radicals are present per molecule.

The radical R ¹ can be mono- or polyvalent radicals, where the polyvalent radicals, such as bivalent, trivalent and tetravalent radicals, then connect several, such as two, three or four, siloxy units of the formula (I) to one another.

Further examples of R ¹ are the monovalent radicals -F, -Cl, - Br, OR ⁶ , -CN, -SCN, -NCO and SiC-bonded, substituted or unsubstituted hydrocarbon radicals which can be interrupted by oxygen atoms or the group -C(O)-, as well as divalent radicals which are Si-bonded on both sides according to formula (I). If the radical R ¹ is a SiC-bonded, substituted hydrocarbon radical, 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 , -SO ₂ -Ph and - CeFs. R ⁶ independently, identically or differently, denote a hydrogen atom or a monovalent Hydrocarbon residue with 1 to 20 carbon atoms and Ph equal to the phenyl residue.

Examples of radicals R ¹ 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, 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.

Examples of substituted radicals R ¹ are 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, - (CH 2 ) -N (R ⁶ ) C (0) NR ⁶ 2, (CH ₂ ) oC (0) NR ⁶ 2, - (CH ₂ ) OC (0) R ⁶ , - (CH ₂ ) OC (0) OR ⁶ , - (CH ₂ ) OC (0) NR ⁶ 2,

- (CH ₂ ) -C (0) - (CH ₂ ) _P C (0) CH ₃ , - (CH ₂ ) -0-C0-R ⁶ , - (CH ₂ ) -NR ⁶ - (CH ₂ ) _P -NR ⁶ ₂ ,

- (CH ₂ ) OO- (CH ₂ ) _P CH (OH) CH2OH, - (CH ₂ ) o (OCH2CH2) _P 0R ⁶ , - ( CH ₂ ) _o -S0 ₂ -Ph and - (CH2) oO-CeFs, where R ⁶ and Ph have the meanings given above and o and p are identical or different integers between 0 and 10.

ist, und Ph, o und p die voranstehend genannte Bedeutung haben. Examples of R ¹ divalent radicals bonded to Si on both sides according to formula (I) are those which are derived from the monovalent examples given above for radical RI by an additional bond being formed by substitution of a hydrogen atom. Examples of such radicals are - (CH2)-,

and Ph, o and p have the meaning given above.

The radical R ¹ is preferably 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.

The residue R ² can be any group that is accessible to an addition reaction (hydrosilylation) with a SiH-functional compound.

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

The radical R ² preferably comprises 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.

The molecular weight M _w of the component (Al) should be on average not more than 40,000 g/mol, the molecular weight M _w of the Constituent (A2) should be on average greater than 85,000 g/mol. M _w here means the mass average of the molar masses. (Al) has a preferred average molar mass Mw of at most 30,000 g/mol and particularly preferably of at most 20,000 g/mol. (A2) has a preferred average molar mass Mw of at least 90,000 g/mol and particularly preferably of at least 95,000 g/mol.

For example, the components (Al) and (A2) can be an alkenyl-functional oligo- or polysiloxane, or a high-polymer polydimethylsiloxane (number average determined by NMR) having chain-based or terminal Si-bonded vinyl groups. The structure of the molecules forming components (Al) 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, with those of the formulas R ¹ SiO3/2, R ² SiO3/2 and S1O4/2 being preferred. Of course, mixtures of different siloxanes that satisfy the criteria of components (Al) and (A2) can also be used.

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

component (B)

All hydrogen-functional organosilicon compounds can be used as organosilicon compounds (B) which also have previously been used in addition-curable compositions.

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).

As organopolysiloxanes (B) containing Si-bonded hydrogen atoms, preferably linear, cyclic or branched organopolysiloxanes consisting of units of the general formula (III)

R ¹ cH _d SiO(4-cd)/2 (III) is used, where

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.

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

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

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 also 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 ¹ has the meaning given above. Branched and network-like polysiloxanes additionally contain trifunctional and/or tetrafunctional units, with those of the formulae R ¹ SiO3/2 , HS1O3/2 and S1O4/2 being preferred, where R ¹ has the meaning given above.

Of course, mixtures of different siloxanes which 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, and 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.

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

The components (Al), (A2) and (B) used according to the invention are commercially available products or according to chemically

process can be produced.

Component (C):

Resins are used as components (C) which are selected from: -MQ-siloxane resins, composed of M units of the formula R ⁹ 3SiO]_/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, composed of ^ ^the 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

R ⁹ represents saturated hydrocarbon radicals having 1-40 carbon atoms which are optionally substituted by halogens, and where at least 2 of the radicals R per molecule represent alkenyl radicals having 1-10 carbon atoms.

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 are alkenyl radicals having 1-10 carbon atoms. The hydrocarbon radicals R ⁹ can be halogen-substituted, linear, cyclic, branched, aromatic, saturated or unsaturated.

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 radicals; alkaryl radicals, such as o-, m-, p-tolyl radicals and ethylphenyl radicals; aralkyl radicals, such as benzyl, alpha- and ß-phenylethyl radicals.

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

The hydrocarbon radicals R ⁹ preferably have 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.

The alkenyl groups R ⁹ are accessible 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 used.

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).

component (D)

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-like structure. The low molecular weight platinum complexes of the organopolysiloxanes include 1,3-diethenyl-1,1,3,3-tetramethyldisiloxane complexes with platinum. Further examples are platinum phosphite complexes or platinum phosphine complexes. For example, for light- or UV-curing compositions, alkylplatinum complexes such as derivatives of cyclopentadienyltrimethylplatinum ( IV ), cyclooctadienyldimethylplatinum ( 11 ) or diketonato complexes such as bisacetylacetonatoplatinum ( I I ) can be used to start the addition reaction with the aid of light. These compounds can be encapsulated in a resin matrix.

The concentration of component (D) is sufficient to catalyze the hydrosilylation reaction of components (A1), (A2) and (B) and (C) when acted upon to generate the heat required in the process described herein. The amount of Component (D) may contain 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 low if the platinum group metal content is less than 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).

component (E)

A further component of the addition-crosslinking silicone compositions (X) are reinforcing fillers (E). Preference is given to pyrogenic or precipitated silicas with BET surface areas between 50 m ² /g and 400 m ² /g, with pyrogenic and precipitated silicas with BET surface areas between 100 m ² /g and 200 m ² /g being preferred. The silica fillers mentioned can be hydrophilic in nature or can be 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% by weight, preferably 10 to 25% by weight.

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

Preferred fillers (E) have 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.%, as a result of a surface treatment. Particularly preferred are crosslinkable addition-crosslinking silicone elastomer compositions (X) which are characterized in that the filler (E) is a surface-treated silica, comprising 0.01 to 2% by weight of 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 component (E) is preferably used as a single filler or likewise preferably as a mixture of several finely divided fillers.

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).

component (F)

The addition-crosslinking silicone elastomer composition (X) according to the invention can optionally contain further additives as constituents in a proportion of up to 70% by weight, preferably 0.0001 to 40% by weight. These additives can be, for example, inactive fillers, resinous polyorganosiloxanes which are different from 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 the electrical properties, dispersing aids, solvents, adhesion promoters, pigments, dyes, plasticizers, organic polymers, heat stabilizers, etc. These include additives such as quartz powder, diatomaceous earth, clays, chalk, lithopone, carbon black, graphite, metal oxides, metal carbonates, sulfates, metal salts of carboxylic acids, metal dusts, fibers such as glass fibers, plastic fibers, plastic powders, metal dusts, dyes, pigments, etc.

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 for example, copper, gold, nickel or silver; silicon carbide; tungsten carbide; zinc oxide and a combination thereof. Thermally conductive fillers are known in the art and are 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 different particle size distributions can be used.

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 fluid such as linear, branched and cyclic polydimethylsiloxanes and combinations of these solvents (F). The optimum concentration of a particular solvent (F) in the addition-curing silicone elastomer composition (X) can be determined by Routine tests can easily determine this. Depending on the weight of the compound, the amount of solvent (F) can be between 0 and 95 wt.% or between 1 and 95 wt.%.

The addition-crosslinking silicone elastomer composition (X) can optionally additionally contain inhibitors and stabilizers. Inhibitors and stabilizers serve to specifically adjust the processing time, initiation temperature and crosslinking rate of the addition-crosslinking silicone composition (X) according to the invention. These inhibitors and stabilizers are very well known in the field of addition-crosslinking compositions. Examples of common inhibitors are acetylenic alcohols such as 1-ethynyl-l-cyclohexanol, 2-methyl-3-butyn-2-ol and 3,5-dimethyl-l-hexyn-3-ol, 3-methyl-l-dodecin-3-ol, polymethylvinylcyclosiloxanes such as 1,3,5,7-tetravi- nyltetramethyltetracyclosiloxane, 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 added in a proportion of 0.00001% by weight to 5% by weight, based on the total weight of the mixture, preferably 0.00005 to 2% by weight and particularly preferably 0.0001 to 1% by weight.

The activation for cross-linking can be thermal, via IR radiation or via UV radiation. For room temperature cross-linking systems, the room temperature is the most important for curing. sufficient so that no additional energy supply is required. Microwave activation or activation by ultrasound is also possible.

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.

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

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.

Especially in applications as EAPs in the field of actuators or generators, the elastomers used are subjected to great stress, as they undergo several million vibration cycles over the course of their service life. Another The advantage of the silicone elastomers produced from the silicone compositions (X) according to the invention is a very high resistance to long-term loads.

Examples:

In the examples described below, all parts and percentages are by weight unless otherwise stated. Unless otherwise stated, the examples below 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 is reached when the reactants combine at room temperature without additional heating or cooling. All viscosity data below refer to a temperature of 25 °C. The following examples illustrate the invention without having a limiting effect.

The following abbreviations are used:

Example

No. Number

time t

hour h rF relative humidity

PDMS polydimethylsiloxane

Wt . % Weight percent , w/w

The service life 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 cross-linked in a layer which is approximately 20 pm. The method of producing this thin layer is not important; all methods known from the state of the art can be used, such as, for example, Spin coating, doctor blade application or slot die application. After production, the samples are stretched equibiaxially 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, such as carbon black or nanoscale carbon fibers. After pre-stretching, the elastomer preferably has a thickness in the test between 10 pm and 20 pm.

The specification of the service life in [h] refers to the failure of 50 % of the samples (t50% according to Weibull).

Silicone formulation 1 (comparative example 1)

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

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

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

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.

Silicone formulation 2 (comparative example 2)

Component Al: 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 part of the M groups carries a vinyl group,

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

Component E: 20 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.

Silicone formulation 3 (according to the invention)

Component Al: 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, whereby some of the M groups carry a vinyl group.

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

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.

Silicone formulation 4 (according to the invention)

Component Al: 31 wt.% of a linear, vinyl-terminated organopolysiloxane with an average molecular weight of 16,500 g/mol Component A2: 18 wt.% of a linear, vinyl-terminated organopolysiloxane with an average molecular weight 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, whereby some of the M groups carry a vinyl group.

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

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.

Silicone formulation 5 (according to the invention)

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

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

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 : Lifetime at 20 ° C, 90 % RH and 90 V/pm operating voltage

Tabelle 3 : Lebensdauer bei 85 °C, 85 % rF und 100 V/pm Betriebs¬Table 2 : Lifetime at 20 °C, 30 % RH and 100 V/pm operating voltage

Table 3: Lifetime at 85 °C, 85 % RH and 100 V/pm operating

Tension

Claims

patent claims 1. Silicone-based dielectric elastomer actuators (DEA) with a service life of at least 30 hours at an equibiaxial pre-stretch 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 radicals 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 having an average surface area 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 . 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 contained. 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. Process for the production of 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) - (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 radicals 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% by weight of a reinforcing filler with an average surface area between 50 and 400 m ² /g, provided 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 cross-linking, and the ratio of (Al) to (A2) is at least 1.5, and thus (Al) / (A2) > 1.5. 6. Process 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 nozzle 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 nozzle application.