EP3558500A1

EP3558500A1 - Drawn silicone membranes

Info

Publication number: EP3558500A1
Application number: EP17710497.3A
Authority: EP
Inventors: Christian ANGER; Barbara Moser; Richard Weidner
Original assignee: Wacker Chemie AG
Current assignee: Wacker Chemie AG
Priority date: 2017-03-03
Filing date: 2017-03-03
Publication date: 2019-10-30
Also published as: WO2018157941A8; US20200001241A1; WO2018157941A1; KR102324520B1; KR20190075134A; CN110049811A; JP2020509098A; JP6862559B2

Abstract

The invention relates to a method for producing thin, porous membranes from crosslinkable silicon compositions (S), in which: in a first step, a mixture of the silicon compositions (S) with a pore forming agent (P) and, where appropriate, solvent (L) is formed; in a second step, the mixture is placed in a mould and the silicon composition (S) is vulcanised and any solvent (L) present is removed, producing a crosslinked membrane with pores; in a third step, the pore forming agent (P) is removed from the crosslinked membrane; and in a fourth step, the pores of the membrane are opened by stretching. The invention also relates to the membranes produced in this manner and to the use thereof for separating mixtures, in wound plasters, as packaging materials and as textile membranes.

Description

Stretched silicone membranes

The invention relates to a process for preparing expanded microporous silicone membranes, as well as the membranes obtainable therewith and their use.

Membranes are thin porous moldings and are used for the separation of mixtures. Another application arises in the text area, e.g. as a breathable and water repellent membrane. Coagulated asymmetric microporous polyurethane membranes are often used (Loeb-Sourirajan method). Alternative microporous membranes are based on biaxially stretched polytetrafluoroethylene.

The preparation of porous silicone membranes according to the Loeb-Souriraj on process is known. For example, in JP55225703 the preparation of a porous silicone membrane from a

Silicon carbonate copolymer taught. By this method, only anisotropic pore size along the

Film layer thickness obtained. In addition, you also always need a separate precipitation bath.

DE102010001482 further teaches the preparation of isotropic

Silicon membranes by means of an evaporation-induced

Phase separation. A disadvantage of this method, however, is the fact that for this process thermoplastic

Silicone elastomers are necessary, whereby the so accessible membranes are much less temperature stable than

comparable thin silicone rubber films. Furthermore, thermoplastic silicone elastomers have an undesirable

so-called "cold flow *, whereby the porous membranes change their membrane structure under continuous load.

In contrast, US2004234786 describe silicone rubber membranes starting from aqueous emulsions or

DE102007022787 Fiber-reinforced silicone rubber membranes, A disadvantage of these methods, however, is that only non-porous membranes are accessible, which can be used as a water barrier layer, but have no appreciable water vapor permeability advantageous if, instead of, in these

Patent patents mentioned silicone copolymers, even thin porous membranes based on pure silicone rubbers

which, because of their crosslinked structure, are thermally stable and non-flowable, ie exhibit no "cold flow." The production of isotropic porous silicone membranes would also be advantageous.

The invention relates to a method for producing thin porous membranes of crosslinkable

Silicone compositions (S) in which

in a first step a mixture of the

Silicone compositions (S) with a pore-forming agent (P) and optionally solvent (L) is formed,

in a second step, the mixture is brought into a mold and the silicone composition (S) is vulcanized and optionally present solvent (L) is removed, wherein a

crosslinked membrane with pores,

in a third step the pore former (P) from the

cross-linked membrane is removed and

in a fourth step, the pores of the membrane are opened by stretching. Surprisingly, it was found that pores in

Membranes made of crosslinked silicone rubber can be irreversibly opened by stretching and the stretched membranes have a symmetrical, isotropic distribution. In addition, the layer thickness after stretching and the

Relax the membranes unexpectedly larger than before stretching. It is possible to use known silicone rubbers. The process of stretching is crucial here, as the

Diffusion of, for example, water vapor can be accelerated many times over.

Such a process for the preparation of porous silicone membranes has not previously been described and was not expected in this way.

Through the use of isotropic symmetric microporous

Silicone membranes can be achieved high water vapor permeabilities, as for example in

Textile membrane applications are needed. Furthermore, due to the symmetrical isotropic distribution of the pores the

mechanical stability of this significantly increased. This brings with it the advantage of very high water columns. water

Penetrates such silicone membranes only above 1 bar water pressure.

Preference is given to cross-linking the silicone compositions (S) to membranes via covalent bonds, as described e.g. by

Condensation reactions, additions or radical

Mechanisms arise. Particularly preferred networking is liquid, ie with viscosities up to 300,000 MPa, gel or highly viscous, ie viscosities over 2 000 000 MPa, silicones such as those marketed by Wacker Chemie AG under the brand name ELASTOSIL ^®.

As silicone compositions (S) are preferred

Liquid silicone (LSR) used. A preferred liquid silicone (LSR) is one

addition-crosslinkable silicone composition (S) containing

(A) at least two alkenyl groups per molecule containing polyorganosiloxane having a viscosity at 25 ° C from 0.2 to

1000 Pa-s,

(B) SiH functional crosslinking agent

(C) hydrosilylation catalyst

(I) and inhibitor.

0

The alkenyl group-containing polyorganosiloxane (A) preferably has a composition of the average general formula (1)

on, in the

R ^{1 is} a monovalent, optionally halogen or

cyano-substituted, optionally bonded via an organic divalent group to silicon

Hydrocarbon radical containing aliphatic carbon-carbon multiple bonds,

R ^{2 is} a monovalent, optionally halogen or

cyanosubstituted, via SiC-bonded

Hydrocarbon radical that is free of aliphatic carbon-carbon multiple bonds

x is such a nonnegative number that at least two residues

R ^{1 are present} in each molecule, and

y is a non-negative number such that (x + y) is in the range of 1.8 to 2.5. The alkenyl groups R ¹ are accessible to an addition reaction with a SiH-functional crosslinking agent (B).

Usually, 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.

Organic divalent groups, via which the alkenyl groups may be bonded to silicon of the polymer chain, consist for example of oxyalkylene units, such as those of

general formula (2)

in the

m the values 0 or 1, in particular 0,

n values from 1 to 4, in particular 1 or 2 and

o mean values of 1 to 20, in particular from 1 to 5.

The oxyalkylene units of the general formula (2) are bonded to the left of a silicon atom.

The radicals R ¹ may be bonded in any position of the polymer chain, in particular on the terminal silicon atoms.

Examples of unsubstituted radicals R ² 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, hexyl, such as the n-hexyl, heptyl, such as the n-heptyl, octyl, 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; Alkenyl radicals, such as the vinyl, allyl, η-5-hexenyl, 4-vinylcyclohexyl and the 3-norbornenyl radical; Cycloalkyl radicals, such as cyclopentyl, cyclohexyl, 4-ethylcyclohexyl, cycloheptyl radicals,

Norbornyl radicals and methylcyclohexyl radicals; Aryl radicals, such as the phenyl, biphenylyl, naphthyl radical; Alkaryl radicals, such as o-, m-, p-tolyl radicals and ethylphenyl radicals; Aralkyl radicals, like the

Benzyl, the alpha and the ß-phenylethyl.

Examples of substituted hydrocarbon radicals as radicals R ² are halogenated hydrocarbons, such as chloromethyl, 3-chloropropyl, 3-bromopropyl, 3, 3, 3-trifluoropropyl and

5,5,5,4,4,3,3-heptafluoropentyl radical and the chlorophenyl, dichlorophenyl and Trifluortolylrest.

R ² preferably has 1 to 6 carbon atoms.

Particularly preferred are methyl and phenyl.

Component (A) may also be a mixture of various

Alkenyl groups containing polyorganosiloxanes, which, for example, in the alkenyl group content, the nature of

Alkenyl group or structurally different.

The structure of the alkenyl-containing polyorganosiloxanes (A) may be linear, cyclic or branched. The content of tri- and / or tetrafunctional units leading to branched polyorganosiloxanes is typically very low, preferably at most 20 mol%, in particular at most 0.1 mol%.

Most preferably, the use is vinyl groups

containing polydimethylsiloxanes whose molecules of the

general formula (3) where the nonnegative integers p and q satisfy the following relations: p-> 0.50 <(p + q) <20000, preferably 200 <(p + q) <1000, and 0 <(p + 1) / ( p + q) <0.2. In particular, p = 0.

The viscosity of the polyorganosiloxane (A) at 25 ° C is preferably 0.5 to 500 Pa-s, in particular 1 to 100 Pa-s, most preferably 1 to 50 Pa-s. The at least two SiH functions per molecule containing organosilicon compound (B) preferably has a

Composition of the average general formula (4) in the

R ^{3 is} a monovalent, optionally halogen or

Cyanosubstituierten over Sic-bound CI - CIQ - hydrocarbon radical, which is free of aliphatic

Means carbon-carbon multiple bonds and a and b are nonnegative integers,

with the proviso that 0.5 <(a + b) <3, 0 and 0 <a <2, and that at least two silicon-bonded hydrogen atoms are present per molecule.

Examples of R ³ are the radicals indicated for R ² . R ³ preferably has 1 to 6 carbon atoms. Particularly preferred are methyl and phenyl. Preferred is the use of an organosilicon compound (B) containing three or more SiH bonds per molecule. When using only two SiH bonds per molecule containing organosilicon compound (B), the use of a polyorganosiloxane (A), which has at least three alkenyl groups per molecule is recommended. The hydrogen content of the organosilicon compound (B), which refers exclusively to the hydrogen atoms bonded directly to silicon atoms, is preferably in the range of 0.002 to 1.7% by weight of hydrogen, preferably 0.1 to 1.7% by weight of hydrogen ,

The organosilicon compound (B) preferably contains

at least three and at most 600 silicon atoms per molecule. Preferred is the use of organosilicon compound (B) containing 4 to 200 silicon atoms per molecule.

The structure of the organosilicon compound (B) may be linear, branched, cyclic or network-like.

Particularly preferred organosilicon compounds (B) are linear polyorganosiloxanes of the general formula (5)

in which

R ^{4 has} the meanings of R ³ and

the nonnegative integers c, d, e and f following

Meet relations: and

The SiH-functional organosilicon compound (B) is

preferably in such an amount in the crosslinkable

Silicon compound contain that the molar ratio of SiH groups to alkenyl groups at 0.5 to 5, especially at 1.0 to 3.0.

As hydrosilylation catalyst (C) it is possible to use all known catalysts which catalyze the hydrosilylation reactions taking place in the crosslinking of addition-crosslinking silicone compositions.

As hydrosilylation catalysts (C) in particular metals and their compounds from the group platinum, rhodium,

Palladium, ruthenium and iridium used.

Preferably, platinum and platinum compounds are used.

Particular preference is given to those platinum compounds which are known in

Polyorganosiloxanes are soluble. As soluble

Platinum compounds, for example, the platinum-olefin

Complexes of the formulas (PtCl2-olefin) 2 and H (PtCl3-01efin) can be used, preferably alkenes having 2 to 8

Carbon atoms, such as ethylene, propylene, isomers of butene and octene, or cycloalkenes having 5 to 7 carbon atoms, such as cyclopentene, cyclohexene and cyclohepten used. Other soluble platinum catalysts are the platinum-cyclopropane complex of the formula (PtCl2C3Hg) 2, the

Reaction products of hexachloroplatinic acid with alcohols, ethers and aldehydes or mixtures thereof or the

Reaction product of hexachloroplatinic acid with

Methylvinylcyclotetrasiloxane in the presence of sodium bicarbonate in ethanolic solution. Particular preference is given to complexes of platinum with vinylsiloxanes, such as sym-divinyltetramethyldisiloxane.

The hydrosilylation catalyst (C) can be used in any desired form, for example also in the form of Hydrosilylation catalyst containing microcapsules, or polyorganosiloxane particles.

The content of hydrosilylation catalysts (C) is

preferably chosen such that the addition-crosslinkable

Silicone composition (S) has a Pt content of 0.1 to 200 ppm by weight, in particular from 0.5 to 40 ppm by weight.

As Inihibtor (I), for example, ethynylcyclohexanol can be used.

The silicone composition (S) may contain at least one filler (D). Non-reinforcing fillers (D) with a BET surface area of up to 50 m ² / g are, for example, quartz, diatomaceous earth, calcium silicate, zirconium silicate, zeolites, metal oxide powders, such as aluminum, titanium, iron, or

Zinc oxides or their mixed oxides, barium sulfate, calcium carbonate, gypsum, silicon nitride, silicon carbide, boron nitride, glass and plastic powder. Reinforcing fillers, ie fillers having a BET surface area of at least 50 m ² / g, in particular 100 to 400 m ² / g, are, for example, pyrogenically prepared

Silica, precipitated silica, aluminum hydroxide, carbon black, such as furnace and acetylene black, and large BET surface area silicon-aluminum mixed oxides.

The stated fillers (D) may be rendered hydrophobic, for example by treatment with organosilanes,

Organosilazanes or siloxanes or by etherification of hydroxyl groups to alkoxy groups. It can be a kind of

Filler (D), it can also be a mixture of at least two fillers (D) can be used.

Preferably, the silicone compositions (S) contain

at least 3% by weight, more preferably at least 5% by weight, in particular at least 10% by weight and at most 40% by weight of filler fraction (D).

The silicone compositions (S) may optionally contain, as further component (E), possible additives in a proportion of 0 to 70% by weight, preferably 0.0001 to 40% by weight. These additives may be, for example, resinous polyorganosiloxanes other than the polyorganosiloxanes (A) and (B), coupling agents, pigments, dyes, plasticizers, organic polymers, heat stabilizers and inhibitors. These include additives such as dyes and pigments. In addition, thixotropic components, such as finely divided silica or other commercially available

Thixotropieadditive be included. Also, as a further constituent (E) for better crosslinking, preferably at most 0.5% by weight, particularly preferably at most 0.3% by weight, in particular <0.1% by weight, of peroxide may be present.

As suitable pore formers (P) it is possible to use all organic low molecular weight compounds immiscible with silicones.

Examples of pore formers (P) are monomeric, oligomeric and polymeric glycols. Preference is given to glycols of the general formula (6)

R5-0 [(CH ₂ ) _g O] _h -R5 (6), used in the

R ^{5 is} hydrogen, methyl, ethyl or propyl,

g values from 1 to 4, in particular 1 or 2 and

h is from 1 to 20, in particular from 1 to 5. Preferred examples of glycols are ethylene glycol,

Diethylene glycol, triethylene glycol, tetraethylene glycol,

Propylene glycol, dipropylene glycol, monomethyl diethylene glycol, dimethyl diethylene glycol, trimethyl diethylene glycol

5 low molecular weight polyglycols such as polyethylene glycol 200,

Polyethylene glycol 400, polypropylene glycol 425 and

Polypropylene glycol 725.

The pore formers (P) are used in amounts of preferably from 20 to 2000 parts by weight, more preferably from 30 to 300

Parts by weight, in particular from 50 to 200 parts by weight in each case based on 100 parts by weight of silicone composition (S) is added. Examples of solvents (L) are ethers, in particular aliphatic ethers, such as dimethyl ether, diethyl ether, methyl t-butyl ether, diisopropyl ether, dioxane or tetrahydrofuran, esters, in particular aliphatic esters, such as ethyl acetate or butyl acetate, ketones, in particular aliphatic ketones, such as acetone or Methyl ethyl ketone, sterically hindered alcohols, especially aliphatic alcohols such as i-propanol, t-butanol, amides such as DMF, aromatic hydrocarbons such as toluene or xylene, aliphatic hydrocarbons such as pentane, cyclopentane, hexane, cyclohexane, heptane, chlorinated hydrocarbons such

Methylene chloride or chloroform.

Solvent or solvent mixtures having a boiling point or boiling range of up to 120 ° C at 0.1 MPa are preferred.

Preferably, the solvents (L) are to

aromatic or aliphatic hydrocarbons.

If solvents (L) are used, they are amounts of preferably 1 to 300 parts by weight, especially preferably 10 to 200 parts by weight, in particular 20 to 100 parts by weight, in each case based on 100 parts by weight

Silicone composition (S). The silicone compositions (S), pore formers (P), and optionally solvents (L) are in the first step preferably under high shear, for example with a Turrax ^® or Speedmixer ^® to a homogeneous mixture

processed.

Preferably, the mixture is included in the first step

Temperatures of at least 0 ° C, more preferably at least 10 ° C, in particular at least 20 ° C and at most 60 ^o C,

more preferably produced at most 50 ° C.

Preferably, the homogeneous mixture contains at most 1

Part by weight, more preferably at most 0.1 parts by weight of surfactants, in each case based on 100 parts by weight

Silicone composition (S), especially no surfactants.

In the second step, the mixture is preferably applied to a thin membrane e.g. by doctoring.

To produce the membranes, the mixture is preferably applied to a substrate in the second step.

Preferred geometrical embodiments of the producible thin porous membranes are films, hoses, fibers,

Hollow fibers, mats, wherein the geometric shape is not bound to any solid forms, but largely depends on the substrates used. The applied to substrates mixtures are preferably processed into films. The substrates preferably contain one or more substances from the group comprising metals, metal oxides, polymers or glass. The substrates are basically none

bound geometric shape. Preferably, however, the use of substrates in the form of plates, films, textile surface substrates, woven or preferably nonwoven nets or particularly preferably in the form of nonwoven webs are used. Substrates based on polymers contain, for example, polyamides, polyimides, polyetherimides, polycarbonates,

Polybenzimidazoles, polyethersulfones, polyesters, polysulfones, polytetrafluoroethylenes, polyurethanes, polyvinylchlorides,

Cellulose acetates, polyvinylidene fluorides, polyether glycols, polyethylene terephthalate (PET), polyaryl ether ketones,

Polyacrylonitrile, polymethyl methacrylates, polyphenylene oxides, polycarbonates, polyethylenes or polypropylenes. Preference is given to polymers having a glass transition temperature Tg of at least 80 ° C. Contain substrates based on glass

For example, quartz glass, lead glass, float glass or soda-lime glass.

Preferred mesh or nonwoven substrates include glass, carbon, aramid, polyester, polyethylene, polypropylene,

Polyethylene / Polypropylene Copolymer - or

Polyethylene terephthalate fibers.

The layer thickness of the substrates is preferably> 1 μπι, particularly preferably> 10 .mu.m, very particularly preferably> 100 μπι and preferably <2 mm, more preferably <100 .mu.m, most preferably <50 μπι. Most preferred ranges for the layer thickness of the substrates are the ranges formable from the above values. The thickness of the porous membranes is determined primarily by the coating height. All technically known forms of the order of the mixture on substrates can be used for the production of the porous membranes.

The application of the mixture to the substrate is carried out preferably by means of a doctor blade, by meniscus coating, casting, spraying, dipping, screen printing, gravure printing,

Transfer coating, gravure coating or spin on disk. The mixtures thus applied have film thicknesses of preferably> 10, particularly preferably ≥ 100 μm, in particular> 200 ≦ and preferably ≦ 10,000 μm, more preferably ≦ 5000 μm, in particular ≦ 1000 μm. Most preferred areas for the

Film thicknesses are the areas formulated from the above values.

Preferably, the mixture is added in the second step

Temperatures of at least 0 ° C, more preferably at least 10 ° C _{/ more} preferably at least 20 ° C and at most 60 ° C,

most preferably at most 50 ° C brought into a mold.

Subsequently, in the third step, the vulcanization of the formed mixture.

If low-boiling solvent (L) is used, it is advantageous if this is prevented by vulcanization by e.g.

Evaporation is removed from the mixture.

In a preferred embodiment, the solvent (L) is evaporated at the same time as the vulcanization. The crosslinking of the mixture is preferably carried out by irradiation with light or heating, preferably at 30 to 250 ° C, in particular at 150-210 ° C. The pore-forming agent (P) can in the third step on all the

Professional common methods are to remove species from the membrane. Examples are extraction, evaporation, a successive solvent exchange or simple washing out of the

Pore-forming agent (P) with solvent. Suitable solvents include, for example, water and those mentioned above

Solvent (L).

In a likewise preferred embodiment of the invention, in the third step, the pore-forming agent (P) is passed through

Extraction removed.

The extraction is preferably carried out with a

Solvent which does not destroy the formed porous structure but is well miscible with the pore-forming agent (P). Particularly preferred is the use of water as

Extractant. The extraction is preferred

Temperatures between 20 ° C and 100 ° C instead. The preferred duration of the extraction can be determined for the respective system in a few experiments. The duration of the extraction is preferably at least 1 second to several hours. The process can also be repeated several times.

Preferably, after the third step, the membrane is dried by the solvent, preferably at temperatures

between 20 ° C and 120 ° C, preferably at pressures of 0.0001 MPa to 0.1 MPa. Stretching in the fourth step opens the pores of the membrane. The stretching is preferably carried out at 0 ° C to 100 ° C, more preferably at 10 ° C to 50 ° C. The stretching in the fourth step can be performed monoaxially or biaxially. Preferably, the stretching is biaxial.

Preference is given to the production of membranes with a

uniform symmetric isotropic pore distribution along the cross section. Particularly preferred is the preparation

Microporous membranes with pore sizes from 0.1 μm to 20 μπ \.

The membranes preferably have an isotropic pore distribution. The membranes produced by the process exhibit in

Generally a porous structure. The free volume is preferably at least 5 vol .-%, more preferably

at least 20% by volume, in particular at least 35% by volume and at most 90% by volume, particularly preferably at most 80% by volume, in particular not more than 75% by volume.

The membranes thus obtained may e.g. for the separation of

Mixtures are used. Alternatively, the membranes can be removed from the substrate and then used directly without further support or optionally on others

Substrates, such as nonwovens, fabrics or films are applied, preferably at elevated temperatures and under application of pressure, for example in a hot press or in a

Laminator. In order to improve the adhesion to the other substrates, adhesion promoters can be used.

The finished membranes have layer thicknesses of preferably at least 1 .mu.m, more preferably at least 10 μπι, in particular at least 50 μπι, preferably at most 10000 microns, more preferably at most 2000 microns, especially at most 1000 μηι, most preferably at most 100 on.

The membranes thus obtained can be used directly as membrane,

preferably be used for the separation of mixtures.

Furthermore, the porous membranes can also be used in wound plasters. Likewise preferred is the use of the porous membranes in packaging materials, in particular in the packaging of foods which, for example, undergo further maturing processes after production. Particularly preferred is the use of the membranes as textile membranes, in particular as breathable and / or water-repellent

Layer in the construction of textile laminates.

All the above symbols of the above formulas each have their meanings independently of each other. In all

Formulas is the silicon atom tetravalent.

In the following examples, unless stated otherwise, all amounts and percentages are by weight, all pressures are 101.3 kPa (abs.) And all temperatures and viscosity data are at 25 ° C.

Determination of viscosities:

Unless stated otherwise, the viscosities are determined by the method of rotational viscometry according to DIN EN 53019

certainly. Unless otherwise stated, all apply

Viscosity data at 25 ° C and atmospheric pressure of 0.1013 MPa.

Silicones used:

Base mass silicone composition: Terminally vinyl-functionalized polydimethylsiloxane

(Viscosity 1000 mPas)

Pyrogenic silica H-polymer 1000:

Si-H functionalized silicone / Si-H content 0.11 mmol / g

Crosslinker HO14:

Si-H functional siloxane / Si-H content 1.5 mmol / g

Inhibitor PT 88: ethynylcyclohexanol

Cat EP: Platinum-Containing Hydrosilylation Catalyst Vinyl Polymer 20000: Terminally Vinyl-Functionalized

Polydimethylsiloxane (viscosity 20000 mPas)

Example 1: Preparation of a liquid silicone rubber solution with additional solvent

26.67 g of matrix silicone composition, 13.33 g of vinyl polymer 20000 and 66.08 g of toluene are placed in a 250 ml laboratory glass bottle together with a PTPE magnetic stir bar KOMET and dissolved on a roll bar overnight. 3.618 g of crosslinker H014, 0.4 g of inhibitor PT 88 and 0.04 g of catalyst EP are weighed into the homogeneous solution and dissolved with stirring.

Then added dropwise with vigorous stirring slowly 70.49 g of triethylene glycol and stirred until a homogeneous mixture. Example 2 - not According to the Invention: Production of Porous Silicone Rubber Membranes on PTFE Film

The polymer solution from Example 1 is placed in a PE beaker, homogenized for 1 minute at 2500 rpm and 0% vacuum and for 1 min. At 2500 rev / min and 100% vacuum on SpeedMixer DAC 400.1 V-DP degassed. Then slowly by hand with a Kastenfilmziehrahmen a 250 micron thick film on a Teflon ^ -Glasfaser film, the solvent is evaporated at 110 ° C in a convection oven and vulcanized simultaneously the film. After vulcanization, the crosslinked silicone film containing pore-forming agent is placed in a water bath at room temperature for 8 hours and the polymer membrane is dried at room temperature. The unstretched membrane of Example 2 is shown in FIG. The pores are predominantly indented and not symmetrically distributed isotropically.

Example 3: Production of porous silicone rubber membrane on PTFE film

The polymer solution of Example 1 is placed in a PE beaker, homogenized for 1 minute at 2500 rpm and 0% vacuum and degassed for 1 minute at 2500 rpm and 100% vacuum on the SpeedMixer DAC 400.1 V-DP. Then you slowly by hand with a box Filmziehrahmen a 250 pm thick film on a

Teflon ^® glass fiber film, the solvent is evaporated at 110 ° C in a convection oven and simultaneously vulcanized the film. After vulcanization, the crosslinked silicone film containing pore-forming agent is placed in a water bath at room temperature for 8 hours. After drying the washed out

Polymer film, the pores are opened by biaxial stretching.

The stretched membrane of Example 3 is shown in FIG. The pores are predominantly spherical in shape and symmetrically distributed isotropically.

Example 4 Determination of the Performance of Biaxially Stretched Silicone Membranes with Respect to Water Vapor Permeability The water vapor transmission is determined by the method JIS 1099 AI.

The water vapor permeability is 5642 g / m ² * 24 h at a layer thickness of 100 microns.

Example 5 - not according to the invention: determination of the performance of unstretched silicone membranes with respect to

Water vapor permeability

The water vapor permeability is determined by the method JIS 1099 AI.

The water vapor permeability is 2542 g / m ² * 24 h with a layer thickness of 50 μm.

Example 6: Pressure test

To test the mechanical stability of the membrane under pressure, the membrane is placed for 3 days between two rubber rollers, which press each other with a contact pressure of 7 kg weight. The morphology of the membrane is maintained under pressure.

Example 7: Preparation of a Plüssigsiliconkautschuk solution with additional solvent

40.00 g of matrix silicone composition and 66.42 g of toluene are placed together with a PTFE magnetic stir bar KOMET in a 250 ml laboratory glass bottle and dissolved overnight on a roll bar. 3.84 g of crosslinker H014, 0.4 g of inhibitor PT 88 and 0.04 g of catalyst EP are weighed into the homogeneous solution and dissolved with stirring. Then added dropwise with vigorous stirring slowly 70.49 g of triethylene glycol and stirred until a homogeneous mixture.

Example 8 - not According to the Invention: Preparation of Porous Silicone Rubber Membranes on PTPE Polie The polymer solution (Example 7) is placed in a PE beaker, homogenized for 1 minute at 2500 rpm and 0% vacuum and degassed for 1 min. At 2500 rpm and 100% vacuum on SpeedMixer DAC 400.1 V-DP. Then, by hand, slowly applying a 250 μm thick film to a Teflon * glass fiber film by hand with a box-film-drawing frame, the solvent is evaporated at 110 ° C

Convection oven and vulcanized simultaneously the film. After vulcanization, the crosslinked silicone film containing pore-forming agent is allowed to stand at room temperature for at least 8

Placed in a water bath for hours and dried the polymer membrane at room temperature.

Example 9: Production of porous silicone rubber membrane on PTFE film

Place the polymer solution (Example 7) in a PE beaker, 1

Homogenize at 2500 rpm and 0% vacuum and degas for 1 min at 2500 rpm and 100% vacuum on SpeedMixer DAC 400.1 V-DP. Then, by hand, slowly applying a 250 μm thick film to a Teflon * glass fiber film by hand with a box-film-drawing frame, the solvent is evaporated at 110 ° C

Given hours in a water bath. After drying the

washed out polymer film, the pores are opened by biaxial stretching.

Example 10 Determination of the Performance of Biaxially Stretched Silicone Membranes with Respect to Water Vapor Permeability

The water vapor permeability is determined by the method JIS 1099 AI.

The water vapor permeability of the membrane of Example 9 is 3895 g / m2 * 24h with a layer thickness of 55 μm. Example 11 - not according to the invention: determination of the performance of unstretched silicone membranes with respect to

Water vapor permeability

The water vapor permeability is determined by the method JIS 1099 AI.

The water vapor permeability of the membrane of Example 8 is 1767 g / m2 * 24h at a layer thickness of 54 μπι.

Claims

claims

1. Process for the preparation of thin porous membranes

crosslinkable silicone compositions (S), in which

in a first step a mixture of the

in a second step, the mixture is placed in a mold and the silicone composition (S) vulcanized and

optionally present solvent (L) is removed, forming a crosslinked membrane with pores,

in a third step, the pore-forming agent (P) is removed from the crosslinked membrane and

in a fourth step, the pores of the membrane are opened by stretching.

2. The method of claim 1, wherein a

addition-crosslinkable silicone composition (S) is used, containing

(A) containing at least two alkenyl groups per molecule

Polyorganosiloxane having a viscosity at 25 ° C of 0.2 to

1000 Pa-s,

(B) SiH functional crosslinker,

(C) hydrosilylation catalyst and

(I) inhibitor.

3. The method of claim 2, wherein the alkenyl groups

containing polyorganosiloxane (A) a composition of average general formula (1) has, in the R ^{1 is} a monovalent, optionally halogen or cyano-substituted, optionally bonded via an organic divalent group of silicon

Hydrocarbon radical containing aliphatic carbon-carbon multiple bonds,

R ^{2 is} a monovalent, optionally halogen or

cyano-substituted, over Sic-bonded

Hydrocarbon radical that is free of aliphatic carbon-carbon multiple bonds

x is such a nonnegative number that at least two residues

R ^{1 are present} in each molecule, and

y is a non-negative number such that (x + y) is in the range of 1.8 to 2.5.

4. The method according to one or more of claims 2 and 3, wherein the organosilicon compound (B) a

Composition of the average general formula

has, in the

R ^{3 is} a monovalent, optionally halogen or

cyanosubstituted, via SiC-bonded

Hydrocarbon radical that is free of aliphatic

Means carbon-carbon multiple bonds and a and b are nonnegative integers,

with the proviso that 0.5 <(a + b) <3, 0 and 0 <a <2, and that at least two silicon-bonded hydrogen atoms are present per molecule. Method according to one or more of claims 2 to 4, wherein the hydrosilylation catalyst (C) is selected from metals and their compounds from the group of platinum, rhodium, palladium, ruthenium and iridium.

Method according to one or more of claims 2 to 5, wherein the silicone composition (S) contains at least one filler (D).

Method according to one or more of claims 1 to 6, wherein the pore-forming agent (P) is selected from monomeric, oligomeric and polymeric glycols.

Method according to one or more of claims 1 to 7, in which 20 to 2000 parts by weight of pore-forming agent (P), based on 100 parts by weight of silicone composition (S) are added.

Method according to one or more of claims 1 to 8, wherein the stretching is biaxial.

, Membranes producible by the process according to one or more of claims 1 to 9. 11. Use of the membranes according to claim 10 for the separation of mixtures, in wound plasters or as textile membranes.