POROUS THERMOPLASTIC MEMBRANES

Abstract

The present invention is directed to a membrane, comprising a polyurethane (PU1), wherein the polyurethane (PU1) is based on 80 to 100% by weight of a mixture of at least one diol (D1) and at least one polyisocyanate (I1), and 0 to 20% by weight of at least one compound (C1) with at least two functional groups which are reactive towards isocyanate groups. Furthermore, the present invention is directed to a process for preparing a membrane, comprising providing a solution (L1) at least comprising a polyurethane (PU1) and preparing a membrane from solution (L1) using phase inversion; as well as the use of a membrane according to the present invention for coating a woven article.

Claims

1-16. (canceled)

17. A membrane, comprising a polyurethane (PU1), wherein the polyurethane (PU1) comprises: 80 to 100% by weight of a mixture of at least one diol (D1) and at least one polyisocyanate (I1), and 0 to 20% by weight of at least one compound (Cl) with at least two functional groups which are reactive towards isocyanate groups, wherein the membrane has pores with an average pore diameter in the range of from 0.001 ?m to 0.8 ?m, determined using Hg porosimetry according to DIN 66133, wherein the pore size distribution has a gradient over the diameter of the membrane.

18. The membrane according to claim 17, wherein the membrane comprises a further polyurethane (PU2) which is based on at least one polyol (P2), at least one diol (D2) and at least one polyisocyanate (I2)

19. The membrane according to claim 17, wherein the compound (C1) is a polyol.

20. The membrane according to claim 17, wherein the compound (C1) is selected from the group of divalent residues of an oligo- or polysiloxane of the formula
-[Ak-O].sub.q-Ak-Si(R.sub.2)[OSi(R.sub.2)].sub.pOSi(R.sub.2)-Ak-[O-Ak].sub.q- (1) wherein Ak represents C.sub.2-C.sub.4 alkylene, R represents C.sub.1-C.sub.4 alkyl, and each of p, q and q independently is a number selected from the range 0-50.

21. The membrane according to claim 17, wherein the membrane has a thickness in the range from 5 to 100 ?m.

22. The membrane according to claim 17, wherein the membrane has a liquid entry pressure in the range of 1 to 5 bar.

23. The membrane according to claim 17, wherein the diol (D1) is selected from the group consisting of ethane diol, butane diol and hexane diol.

24. The membrane according to claim 17, wherein the polyisocyanate is selected from the group consisting of diphenylmethanediisocyanate (MDI), toluenediisocyanate (TDI) and hexamethylenediisocyanate (HDI).

25. A process for preparing a membrane, comprising: preparing a membrane from a solution (L1) at least comprising a polyurethane (PU1) using phase inversion, wherein the membrane has pores with an average pore diameter in the range of from 0.001 ?m to 0.8 ?m, determined using Hg porosimetry according to DIN 66133, and wherein the pore size distribution has a gradient over the diameter of the membrane.

26. The process according to claim 25, wherein the solution (L1) comprises at least one additive selected from the group consisting of mono-, di- or trialkanols bearing no further functional groups like iso-propanol, ethylene glycol, propylene glycol or propylenetriol (glycerin).

27. The process according to claim 25, wherein the preparing comprises: forming a film from solution (L1); and bringing the film in contact with a mixture (L2).

28. The process according to claim 27, wherein the mixture (L2) comprises water.

29. A process for coating a woven article, comprising coating the article with the membrane according to claim 17.

Description

BRIEF DESCRIPTION OF THE FIGURES

[0151] FIG. 1 shows SEM pictures of the membrane obtained according to example 1 of the invention. FIG. 1(a) is a picture of the bottom surface, FIG. 1(b) is a SEM picture of the cross section of the membrane and FIG. 1(c) is a picture of the surface of the membrane. The pictures show that the membrane has a pore size gradient with small pores in the top layer (surface/skin) and bigger pores towards the bottom of membrane.

[0152] Examples will be used below to illustrate the invention. The examples which follow are for illustration of the invention, but are not in any way restricting as regards the subject matter of the present invention.

EXAMPLES

1. Preparation of the Polyurethane (Hardphase)

1.1 Compounds Used

[0153] The following compounds were used:

TABLE-US-00001 Molecular Abbreviation Compound weight [g/mol] Iso 1 4,4Methylenediphenylendiisocyanate 250.26 g/mol Iso 2 m-Tolylidenediisocyanate(T80) 174.2 g/mol Iso 3 Hexamethylene-1,6-diisocyanate 168.2 g/mol KV 1 1,2-ethane diol 62.07 g/mol KV 2 1,4-butane diol 90.12 g/mol KV 3 diethylenglykole (2,2Oxi-diethanol) 106.12 g/mol KV 4 1,6-hexane diol 118.2 g/mol

1.2 Examples

(a) Polyurethane (Hardphase) Type 1

[0154] In a 21 tin container, the chain extender (KV) was dispensed. Subsequently, the isocyanate Iso1 or Iso2 was added under gentle stirring and the reaction mixture was carefully heated to 70? C. with heated air. The mixture was stirred until a temperature of 90? C. was reached. Then, the reaction mixture was poured into a flat bowl and heated for 10 minutes at 125? C. on a heating plate. The slab obtained was tempered in a heating oven for 15 hours at 80? C.

(b) Polyurethane (Hardphase) Type 2

[0155] In a 21 tin container, the chain extender (KV) was dispensed and heated to 80? C. Subsequently, the isocyanate Iso3 was added and the mixture was stirred at 220 rpm until a temperature of 110? C. was reached. Then, the reaction mixture was poured into a flat bowl and heated for 10 minutes at 125? C. on a heating plate. The slab obtained was tempered in a heating oven for 15 hours at 80? C.

[0156] The material obtained was cut into pieces and milled to a granulate.

1.3 Composition of the Materials Prepared

[0157]

TABLE-US-00002 Isocyanate Amount Iso Diol Amount KV total amount Hardphase (Iso) [g] (KV) [g] [g] 1 Iso 1 480.8 KV 1 119.2 600 2 Iso 1 441.1 KV 2 158.9 600 3 Iso 1 421.3 KV 3 178.7 600 4 Iso 1 407.5 KV 4 192.5 600 5 Iso 2 737.3 KV 1 262.7 1000 g 6 Iso 2 197.72 KV 2 102.29 2 ? 300 g 7 Iso 2 186.43 KV 3 113.57 2 ? 300 g 8 Iso 2 178.73 KV 4 121.27 2 ? 300 g 9 Iso 3 219.13 KV 1 80.87 2 ? 300 g 10 Iso 3 195.34 KV 2 104.67 2 ? 300 g 11 Iso 3 183.94 KV 3 116.05 2 ? 300 g 12 Iso 3 176.12 KV 4 123.81 2 ? 300 g

2. Preparation of Membranes

2.1 Abbreviations and Compounds Used in the Examples

[0158]

TABLE-US-00003 NMP N-Methylpyrrolidone GLY Glycerin DMAc Dimethylacetamide LEP liquid entry pressure WDD water vapour permeability

2.2 Testing Methods

[0159] The liquid entry pressure (LEP) of the membranes was tested according DIN EN 20811 using a pressure cell with a diameter of 60 mm using ultrapure water (salt-free water, filtered by a Millipore UF-system) up to 4 bar (40 000 mm water column). The LEP is defined as pressure value when the liquid water starts to permeate the membrane. A high LEP allows the membrane to resist to a high liquid water column and is desired.

[0160] The water vapour permeability (WDD) was measured with a cup method at 38? C. and 90% relative humidity according to DIN 53122. For a given membrane thickness absolute WDD values are reported. High WDD values are desired and allow high flow rates of water vapour.

[0161] The pore size distribution was determined using Hg porosimetry. The measurements were conducted according to DIN 66133.

2.3 Examples: Preparation of Porous Membranes Using N-Methylpyrrolidone as Polymer Solvent

[0162] General Procedure

[0163] Into a three neck flask equipped with a magnetic stirrer there were added 71 ml of N-methylpyrrolidone 1, 10 g glycerin as second dope additive and 19 g of TPU hardphase. The mixture was heated under gentle stirring at 60? C. until a homogeneous clear viscous solution, usually referred to as dope solution was obtained. The solution was degassed overnight at room temperature. Clear and transparent polymer solutions were obtained.

[0164] After that the membrane solution was reheated at 60? C. for 2 hours and casted onto a glass plate with a casting knife (150 microns) at 60? C. using an Erichsen Coating machine operating at a speed of 5 mm/min. The membrane film was allowed to rest for 30 seconds before immersion in a water bath at 25? C. for 10 minutes. After the membrane had detached from the glass plate, the membrane was carefully transferred into a water bath for 12 h. After several washing steps with water the membrane was stored wet until characterization regarding liquid entry pressure (LEP) and water vapour permeability (WDD) started. Table 1 summarizes the membrane properties.

2.4 Comparative Examples: Preparation of Non-Porous Films Using N-Methylpyrrolidone as Polymer Solvent

[0165] General Procedure

[0166] Into a three neck flask equipped with a magnetic stirrer there were added 81 ml of N-methylpyrrolidone 1, and 19 g of TPU hardphase. The mixture was heated under gentle stirring at 60? C. until a homogeneous clear viscous solution, usually referred to as dope solution was obtained. The solution was degassed overnight at room temperature. Clear and transparent polymer solutions were obtained.

[0167] After that the membrane solution was reheated at 60? C. for 2 hours and casted onto a glass plate with a casting knife (150 microns) at 60? C. using an Erichsen Coating machine operating at a speed of 5 mm/min. The membrane film was allowed to rest for 30 seconds before immersion in a water bath at 25? C. for 10 minutes. After the membrane had detached from the glass plate, the membrane was carefully transferred into a water bath for 12 h. After several washing steps with water the membrane was stored wet until characterization regarding liquid entry pressure (LEP) and water vapour permeability (WDD) started. Table 1 summarizes the membrane properties.

TABLE-US-00004 TABLE 1 Compositions and properties of membranes prepared; thickness in [?m], LEP in [bar], WDD in [g/m.sup.2 * d]. TPU Hardphase No. Thickness LEP WDD Example 1 BUMDI 2 50 4 1224 Example 2 HEXMDI 4 50 4 950 Comparative 1 BuMDI 2 30 4 158 Comparative 2 HEXMDI 4 30 4 97

[0168] Porous membranes produced according to the invention show improved water vapour permeability characteristics (WDD) over membranes known from the art. At the same time porous TPU membranes produced according to the invention show comparable liquid entry pressure properties (LEP) compared to membranes known from the art.

3. Pore Size Distribution of the Membranes

[0169] The pore size distribution of the membrane obtained according to example 1 according to the invention was determined using Hg porosimetry according to DIN 66133.

[0170] The results of the Hg porosimetry are summarized in table 2.

TABLE-US-00005 TABLE 2 Tabular report Hg porosimetry Pore diameter (?m) Incremental pore area (m.sup.2/g) 0.500 0.024 0.100 18.938 0.050 28.181 0.010 7.337 0.004 2.576

[0171] The average pore diameter accounts for 0.14445 ?m and the median pore diameter (area) at 2.4575 psi and 29.570 m.sup.2/g accounts 0.08706 ?m.

[0172] The membrane obtained according to example 1 of the invention was also tested using scanning electron microscopy (SEM). Both surfaces (bottom and top) of the membrane as well as a cross section of the membrane were examined.

[0173] The measurements as shown in FIG. 1 show that the membrane has a pore size gradient with small pores in the top layer (skin) and bigger pores towards the bottom of membrane. FIG. 1(a) is a picture of the bottom surface, FIG. 1(b) is a SEM picture of the cross section of the membrane and FIG. 1(c) is a picture of the surface of the membrane.