DRAWN SILICONE MEMBRANES

Abstract

The invention relates to a method for producing thin, porous membranes from crosslinkable silicone compositions (S), in which: in a first step, a mixture of the silicone 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 silicone 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) in 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.

Claims

1. A process for producing thin porous membranes from crosslinkable silicone compositions (S), wherein a first step comprises forming a mixture from the silicone compositions (S) with a pore-former (P) and optionally solvent (L), a second step comprises introducing the mixture into a mold and vulcanizing the silicone composition (S), and removing any solvent present (L), where a crosslinked membrane with pores is formed, a third step comprises removing the pore-former (P) from the crosslinked membrane, and a fourth step comprises opening the pores of the membrane by drawing.

2. The process as claimed in claim 1, wherein an addition-crosslinkable silicone composition (S) is used, comprising (A) polyorganosiloxane containing at least two alkenyl groups per molecule and having a viscosity at 25 C. of 0.2 to 1000 Pa.Math.s, (B) SiH-functional crosslinking agent, (C) hydrosilylation catalyst, and (I) inhibitor.

3. The process as claimed in claim 2, wherein the polyorganosiloxane (A) containing alkenyl groups has a composition of the average general formula (1)
R.sup.1.sub.xR.sup.2.sub.ySiO.sub.(4-x-y)/2 (I) in which R.sup.1 is a monovalent, optionally halogen- or cyano-substituted C.sub.1-C.sub.10 hydrocarbon radical which comprises aliphatic carbon-carbon multiple bonds and is optionally bonded to silicon via an organic divalent group, R.sup.2 is a monovalent, optionally halogen- or cyano-substituted C.sub.1-C.sub.10 hydrocarbon radical which is free from aliphatic carbon-carbon multiple bonds and is SiC-bonded, x is a non-negative number such that there are at least two radicals R.sup.1 in each molecule, and y is a non-negative number such that (x+y) lies in the range from 1.8 to 2.5.

4. The process as claimed in one or more of claims 2 and 3, wherein the organosilicon compound (B) has a composition of the average general formula (4)
H.sub.aR.sup.3.sub.bSiO.sub.(4-a-b)/2 (4), in which R.sup.3 is a monovalent, optionally halogen- or cyano-substituted hydrocarbon radical which is free from aliphatic carbon-carbon multiple bonds and is SiC-bonded, and a and b are non-negative integers with the proviso that 0.5<(a+b)<3.0 and 0<a<2, and that there are at least two silicon-bonded hydrogen atoms per molecule.

5. The process as claimed in one or more of claims 2 to 4, wherein the hydrosilylation catalyst (C) is selected from metals and their compounds from the group consisting of platinum, rhodium, palladium, ruthenium, and iridium.

6. The process as claimed in one or more of claims 2 to 5, wherein the silicone composition (s) comprises at least one filler (D).

7. The process as claimed in one or more of claims 1 to 6, wherein the pore-former (P) is selected from monomeric, oligomeric, and polymeric glycols.

8. The process as claimed in one or more of claims 1 to 7, wherein 20 to 2000 parts by weight of pore-former (P) are added, based on 100 parts by weight of silicone composition (S).

9. The process as claimed in one or more of claims 1 to 8, wherein the drawing takes place biaxially.

10. A membrane producible by the process as claimed in one or more of claims 1 to 9.

11. The use of a membrane as claimed in claim 10 for separating mixtures, in sticking-plasters or as textile membrane.

Description

EXAMPLE 1

Producing a Liquid Silicone Rubber Solution with Additional Solvent

[0124] 26.67 g of silicone composition base material, 13.33 g of vinylpolymer 20000 and 66.08 g of toluene are introduced, together with a KOMET PTFE magnetic stirring rod, into a 250 ml laboratory glass flask, with dissolution overnight on a roller bed. 3.618 g of crosslinker H014, 0.4 g of inhibitor PT 88 and 0.04 g of catalyst EP are weighed out into the homogeneous solution and dissolved with stirring. This is followed by slow dropwise addition of 70.49 g of triethylene glycol with vigorous stirring, and by continuation of stirring until the resulting mixture is homogeneous.

EXAMPLE 2

Not Inventive: Producing Porous Silicone Rubber Membranes on PTFE Foil

[0125] The polymer solution from Example 1 is introduced into a PE beaker, homogenized for 1 minute at 2500 rpm and 0% vacuum and degassed for 1 minute at 2500 rpm and 100% vacuum in a SpeedMixer DAC 400.1 V-DP. A film 250 m thick is subsequently applied slowly by hand, using a box-type film-drawing frame, onto a Teflon glass fiber foil, and the solvent is evaporated off in a circulating air drying cabinet at 110 C., with simultaneous vulcanization of the film. After the vulcanization, the crosslinked silicone film comprising pore-former is placed into a water bath at room temperature for at least 8 hours and the polymer membrane is dried at room temperature.

[0126] The undrawn membrane from Example 2 is shown in FIG. 1. The pores are predominantly pushed-in and not symmetrically isotropically distributed.

EXAMPLE 3

Producing Porous Silicone Rubber Membranes on PTFE Foil

[0127] The polymer solution from Example 1 is introduced into a PE beaker, homogenized for 1 minute at 2500 rpm and 0% vacuum and degassed for 1 minute at 2500 rpm und 100% vacuum in a SpeedMixer DAC 400.1 V-DP. A film 250 m thick is subsequently applied slowly by hand, using a box-type film-drawing frame, onto a Teflon glass fiber foil, and the solvent is evaporated off in a circulating air drying cabinet at 110 C., with simultaneous vulcanization of the film. After the vulcanization, the crosslinked silicone film comprising pore-former is placed into a water bath at room temperature for at least 8 hours. After the washed-off polymer film has dried, the pores are opened by biaxial drawing.

[0128] The drawn membrane from Example 3 is shown in FIG. 2. The pores are predominantly spherical in shape and are symmetrically isotropically distributed.

EXAMPLE 4

Determining the Water Vapor Permeability Performance of Biaxially Drawn Silicone Membranes

[0129] The water vapor permeability is determined by the JIS 1099 A1 method.

[0130] The water vapor permeability is 5642 g/m.sup.2*24 h at a layer thickness of 100 m.

EXAMPLE 5

Not Inventive: Determining the Water Vapor Permeability Performance of Undrawn Silicone Membranes

[0131] The water vapor permeability is determined by the JIS 1099 A1 method.

[0132] The water vapor permeability is 2.542 g/m.sup.2*24 h at a layer thickness of 500 m.

EXAMPLE 6

Pressure Testing

[0133] To test the mechanical stability of the membrane under pressure, the membrane is placed for 3 days between two rubber rollers which press against one another with an applied pressure of 7 kg weight. The morphology of the membrane is retained even under pressure.

EXAMPLE 7

Producing a Liquid Silicone Rubber Solution with Additional Solvent

[0134] 40.00 g of silicone composition base material and 66.42 g of toluene are introduced, together with a KOMET PTFE magnetic stirring rod, into a 250 ml laboratory glass flask, with dissolution overnight on a roller bed. 3.84 g of crosslinker H014, 0.4 g of inhibitor PT 88 and 0.04 g of catalyst EP are weighed out into the homogeneous solution and dissolved with stirring. This is followed by slow dropwise addition of 70.49 g of triethylene glycol with vigorous stirring, and by continuation of stirring until the resulting mixture is homogeneous.

EXAMPLE 8

Not Inventive: Producing Porous Silicone Rubber Membranes on PTFE Foil

[0135] The polymer solution (Example 7) is introduced into a PE beaker, homogenized for 1 minute at 2500 rpm and 0% vacuum and degassed for 1 minute at 2500 rpm and 100% vacuum in a SpeedMixer DAC 400.1 V-DP. A film 250 m thick is subsequently applied slowly by hand, using a box-type film-drawing frame, onto a Teflon glass fiber foil, and the solvent is evaporated off in a circulating air drying cabinet at 110 C., with simultaneous vulcanization of the film. After the vulcanization, the crosslinked silicone film comprising pore-former is placed into a water bath at room temperature for at least 8 hours and the polymer membrane is dried at room temperature.

EXAMPLE 9

Producing Porous Silicone Rubber Membranes on PTFE Foil

[0136] Place the polymer solution (Example 7) into a PE beaker, homogenize for 1 minute at 2500 rpm and 0% vacuum and degass for 1 minute at 2500 rpm and 100% vacuum in a SpeedMixer DAC 400.1 V-DP. A film 250 m thick is subsequently applied slowly by hand, using a box-type film-drawing frame, onto a Teflon glass fiber foil, and the solvent is evaporated off in a circulating air drying cabinet at 110 C., with simultaneous vulcanization of the film. After the vulcanization, the crosslinked silicone film comprising pore-former is placed into a water bath at room temperature for at least 8 hours. After the washed-off polymer film has dried, the pores are opened by biaxial drawing.

EXAMPLE 10

Determining the Water Vapor Permeability Performance of Biaxially Drawn Silicone Membranes

[0137] The water vapor permeability is determined by the JIS 1099 A1 method.

[0138] The water vapor permeability of the membrane from Example 9 is 3895 g/m.sup.2*24 h at a layer thickness of 55 m.

Example 11

Not Inventive: Determining the Water Vapor Permeability Performance of Undrawn Silicone Membranes

[0139] The water vapor permeability is determined by the JIS 1099 A1 method.

[0140] The water vapor permeability of the membrane from Example 8 is 1767 g/m.sup.2*24 h at a layer thickness of 54 m.