Process for the production of a structured film

Abstract

The present invention relates to a process for the formation of a structured film, a structured film as such, an article comprising the structured film, a device for the continuous formation of such a structured film and a composite comprising the structured film.

Claims

1. A process for the formation of a structured porous film comprising: a) applying a porous film onto an elastic substrate in a stretched state such that a reversible adhesion of the porous film on the stretched substrate occurs, b) relaxing the substrate with the applied film thereon to obtain a structured porous film, and c) removing the structured porous film from the substrate.

2. The process according to claim 1, further comprising applying a backer material to the structured porous film.

3. The process according to claim 1, wherein the porous film comprises a member selected from fluoropolymer, a polyvinylalcohol, a polyurethane and combinations thereof.

4. The process according to claim 3, wherein the porous film comprises a member selected from polytetrafluoroethylene (PTFE) a modified PTFE, a fluorothermoplastic, a fluoroelastomer and combinations thereof.

5. The process according to claim 1, wherein the porous film has a thickness between 0.5 μm and 250 μm.

6. The process according to claim 1, wherein the substrate comprises a member selected from a polysiloxane, fluorosilicone a rubber and combinations thereof.

7. The process according to claim 1, wherein the substrate is stretched at a processing ratio of at least 110% in at least one direction.

8. The process according to claim 1, wherein the elastic substrate is stretched at a processing ratio of at most 1100% in at least one direction.

9. A structured porous film obtained by the process according to claim 1.

10. The structured film according to claim 9, wherein structures in the structured film have a height of at least two times the thickness of a non-structured film, and wherein the structure density in at least one direction is at least 1/mm.

11. A structured porous film comprising a porous film reversibly adhered to an elastic substrate, wherein structures in the porous film have a height at least two times the thickness of a non-structured film and the structure density in at least one direction is at least 1/mm.

12. The structured porous film according to claim 11, wherein the structure density in at least one direction is at least 2/mm.

13. The structured porous film according to claim 12, wherein the structure height is from 2 μm to 2000 μm.

14. The structured porous film according to claim 13, wherein the area increase factor of the structured film is at least 1.8.

15. An article comprising a structured porous film according to claim 11, wherein said elastic substrate is removed.

16. The article according to claim 15, wherein the article is a vent or a filter.

17. A structured porous film obtained by the process of claim 1, wherein said structured porous film has applied thereto a backer material to form a composite, and wherein said composite has an asymmetric airflow of at least 30%.

18. A composite comprising a structured film obtained by the process of claim 1 and having an asymmetric airflow of at least 30%.

19. A structured porous film consisting of: a porous film having structures in the porous film that have a height at least two times the thickness of a non-structured film and the structure density in at least one direction is at least 1/mm, wherein said porous film has a multi-layered structure.

20. The structured porous film according to claim 19, wherein the structure density in at least one direction is at least 2/mm.

21. The structured porous film according to claim 20, wherein the structure height is from 2 μm to 2000 μm.

22. A structured porous film comprising: a porous film having structures therein that have a height at least two times the thickness of the non-structured film and the structure density in at least one direction is at least 1/mm, wherein said structures are permanent in said porous film separate from a substrate.

23. The structured porous film according to claim 22, wherein the structure density in at least one direction is at least 2/m.

24. The structured porous film according to claim 22, wherein the structure height is from 2 μm to 2000 μm.

25. The structured porous film according to claim 24, wherein the area increase factor of the structured film is at least 1.8.

26. The structured porous film according to claim 22, wherein said porous film has a multi-layered structure.

27. The structured porous film according to claim 11, wherein said porous film has a multi-layered structure.

28. The composite of claim 18, wherein said composite is in the form of a vent or filter.

Description

(1) The present invention will be further illustrated by the examples described below, and by reference to the following figures:

(2) FIG. 1a) to d) show a schematic drawing of an exemplary device for performing the process of the invention involving biaxial stretching in a non-continuous manner.

(3) FIG. 2 shows a schematic drawing of a first embodiment of a device for performing the process of the invention involving transverse uniaxial stretching in a continuous manner.

(4) FIG. 3 shows a schematic drawing of a first embodiment of a device for performing the process of the invention involving uni- or biaxial stretching in a continuous manner.

(5) FIG. 4 shows a schematic drawing of a first embodiment of a device for performing the process of the invention involving biaxial stretching in a continuous manner.

(6) FIG. 5 shows a schematic drawing of a first embodiment of a device for performing the process of the invention involving uniaxial stretching in a continuous manner.

(7) FIG. 6 shows a schematic drawing of a second embodiment of a device for performing the process of the invention involving uniaxial stretching in a continuous manner.

(8) FIG. 7 shows a SEM image of a side view of the film of Comparative Example 1A.

(9) FIG. 8 shows a SEM image (top view) showing the structures of the film of Example 1C.

(10) FIG. 9 shows a SEM image showing a side view of Example 1C. The structured porous film is supported on a backer material.

(11) In FIG. 10, the determination of the structure density of the structured film of Example 1C is shown (left hand image). In the right hand image, a surface topography is shown.

(12) FIG. 11 is a SEM image (top view) of the structures film of Example 1D.

(13) FIG. 12 is a SEM image showing a side view of the structured film of Example 1D which is supported on a backer material.

(14) In FIG. 13, the determination of the structure density of the film of Example 1D is shown (left hand image). In the right hand image, a surface topography of the film is shown.

(15) FIG. 14 is a SEM image (top view) of the structured film of Example 1E.

(16) FIG. 15 is a SEM image showing a side view of the structured film of Example 1E which is supported on a backer material.

(17) In FIG. 16, the determination of the structure density of the film of Example 1E is shown (left hand image). In the right hand image, a surface topography is shown.

(18) FIG. 17 is a SEM image (top view) of the structured film of Example 1F.

(19) FIG. 18 is a SEM image showing a side view of the structured film of Example 1F which is supported on a backer material.

(20) FIG. 19 is a SEM image (top view) of the structured film of Example 1G.

(21) FIG. 20 is a SEM image showing a side view of the structured film of Example 1G which is supported on a backer material.

(22) FIG. 21 is a SEM image (top view) of the structured film of Example 1H.

(23) FIG. 22 is a SEM image (top view) of the structured film of Example 1I.

(24) FIG. 23 is a SEM image showing a side view of the structured film of Example 1I which is supported on a backer material.

(25) FIG. 24 is a SEM image (top view) of the film of reference Example 2A.

(26) FIG. 25 is a SEM image (top view) of the structured film of Example 2B.

(27) FIG. 26 is a SEM image (top view) of the structured film of Example 2C.

(28) FIG. 27 is a scheme of the experimental set-up for filtration Example 4.

(29) FIG. 28 is a SEM image (top view) of the structured film of Example 6B.

(30) In FIG. 29, the determination of the structure density of the film of Example 6B is shown (left hand image). In the right hand image, a surface topography of the film is shown.

(31) FIG. 30 is a SEM image (top view) of the structured film of Example 3.

MEASUREMENT METHODS

(32) a) Rigidity Measurements

(33) Rigidity of the porous films may be measured according to ASTM D-2923-08, procedure B. Although this method is indicated to be suitable for polyolefin film, it may also be used for films made of other materials.

(34) For measuring the rigidity, a Handle-O-Meter test device (Thwing-Albert Instrument Company) may be used.

(35) b) ATEQ Airflow

(36) Airflow is measured using an ATEQ airflow meter at a pressure of 70 mbar.

(37) c) Gurley Number

(38) Gurley numbers [s] were determined using a Gurley Densometer according ASTM D 726-58.

(39) The results are reported in terms of Gurley Number which is the time in seconds for 100 cubic centimeters of air to pass through 6.54 cm.sup.2 of a test sample at a pressure drop of 1.215 kN/m.sup.2 of water.

(40) d) Structure Height

(41) Topography images were created with an areal confocal 3d measurement system “μsurf explorer” (Nanofocus AG). Such topographic images are e.g. given on the right hand side of FIGS. 10, 13, 16, and 30.

(42) The height of the structures is the maximum distance between a height peak and a height dip (valley) of a representative sample evaluated via image analysis.

(43) e) Structure Density

(44) To determine the structure density in x (e.g. transverse) direction and y (e.g. longitudinal or machine) direction, 3D topography or SEM images were analysed. Multiple measurements per axis are made and averaged out to determine structure density in perpendicular directions x and y.

(45) Lines in x and y directions were applied on the images. All structure edges crossing a line were marked. Multiple measurements were taken and averaged. This procedure is depicted in the left hand side pictures of FIGS. 10, 13, 16, and 30.

(46) The structure density where evaluated using following formula: (As 2 edges define one structure, the average edge number is divided by 2)

(47) Structure density in direction x=(average number of edges x/2)/evaluated sample width x

(48) Structure density in direction y=(average number of edges y/2)/evaluated sample width y

(49) For example, this procedure yields for the structured film of Example 1E as shown in FIG. 13, left hand side, the following structure densities:

(50) Direction x: (18+13+13)/3/2/4.29 mm=1.5/mm

(51) Direction y: (10+12+16)/3/2/4.28 mm=1.5/mm

(52) f) Further Properties

(53) Further properties, such as bubble point, water entry pressure, pore size, and porosity, were measured as indicated in US 2007/0012624, unless otherwise indicated.

EXAMPLES

(54) A) Device

Example D1

(55) FIG. 1 shows a typical and simple device for carrying out the process of the invention and obtaining the structured porous film of the invention in a non-continuous manner, wherein an elastic carrier (a) is inflated to stretch the elastic carrier (a) and a film (d) is applied at a stretched state. The inner pressure is reduced by opening a valve and so that the substrate is relaxed and, thereby, the structured film (c) is formed on the elastic carrier (a).

Example D2

(56) FIG. 2 shows a schematic illustration of a further embodiment of a continuous processing method and device of the invention wherein an rotatable elastic carrier belt (a) is fixed to two rotating elements that induce and release transverse stretch to the silicone substrate along a circular motion. A film (d) is applied via pressure roll (h) on the stretched elastic carrier belt (a). The film moves on the stretched elastic carrier belt (a) and a structured film (c) is formed during relaxation of the elastic carrier belt (a). Optionally, a backer material (e) is preheated with e.g. an IR heater (g) and applied via pressure roll (b) on the structured film (c) to form a composite (f) comprising a structured film (c) and a backer material (e).

Example D3

(57) FIG. 3 shows a schematic illustration of a further embodiment of a continuous processing method and device of the invention wherein a rotatable elastic carrier belt (a) rotates between two rolls with a surface velocity ratio.

(58) To induce stretch in the elastic carrier (a) the surface velocity of roll 2 is lower than surface velocity of roll 1. This ratio causes the elastic carrier belt (a) to change its stretch state from relaxed to stretched during rotation. The elastic carrier (a) is fixed on the sides with clamps (i) that run in a rail (g) so that they can change their distance depending on the stretch ratio in the elastic carrier (a) where they are fixed to while keeping the elastic carrier (a) at a constant width.

(59) In another version of this process the rails (g) form an angle so that the elastic carrier belt (a) is in addition to the longitudinal stretch, stretched in the transverse direction with changing its width repeatable during rotation.

(60) A film (d) is applied on the stretched elastic carrier via pressure roll (b).

(61) A structured film (c) is formed on the elastic carrier (a). A backer material (e) is provided and laminated to the structured film (c) on the elastic carrier (a) via pressure roll (h) to form a composite material (f) comprising the structured film (c).

Example D4

(62) FIG. 4 shows a schematic illustration of a further embodiment of a continuous processing method and device of the invention wherein a rotatable elastic carrier belt (a) rotates between two rolls with a surface velocity ratio.

(63) To induce stretch in the elastic carrier (a) the surface velocity of roll 2 is lower than surface velocity of roll 1. This ratio causes the elastic carrier belt (a) to change its stretch state from relaxed to stretched during rotation.

(64) A film (d) is applied on the stretched elastic carrier via pressure roll (b).

(65) A structured film (c) is formed on the elastic carrier (a). A backer material (e) is provided and preheated with an IR heater (f) to melt an adhesive component and laminated to the structured film (c) on the elastic carrier (a) via pressure roll (h) to form a composite material (g) comprising the structured film (c).

(66) The elastic carrier (a) and consequently the film (d) in this process are contracted in the machine direction while an expansive force acts in the transverse direction depending on the Poisson's ratio of the elastic carrier material.

Example D5

(67) FIG. 5 shows a schematic illustration of a further embodiment of a continuous processing method and device of the invention wherein a roll of elastic carrier material (a) is provided. The roll is at least stretched in one direction, before the film (d) is applied with a pressure roll (b). In this case the elastic carrier is hold by clamps (e) on the sides and the clamps increase their distance in the machine direction to stretch the elastic carrier. After applying the film the stretch is released. A structured film (c) is formed on the elastic carrier. The clamps release the elastic carrier at the end of the process.

(68) As shown in the image the elastic carrier with the structured film is spooled on a roll. This roll can then be used for further processes, e.g. a coating step, after which the elastic carrier is removed from the coated structured film. Another method would be to remove the structured film from the elastic carrier before the elastic carrier is spooled on a roll.

Example D6

(69) FIG. 6 shows a schematic illustration of a further embodiment of a continuous processing method and device of the invention wherein a roll of elastic carrier material (a) is provided. The roll is stretched in machine direction, before the film is applied. A ratio between the surface velocity of roll 1 and roll 2 stretches the elastic carrier (a). A film (d) is applied on the stretched elastic carrier via pressure roll (b). The stretch is released, with roll 3 having a lower surface velocity than roll 2, to form a structured film (c). Usually surface velocity of roll 1 equals approximately the surface velocity of roll 1. The elastic carrier (a) and consequently the film (d) in this process are contracted in the machine direction while an expansive force acts in the transverse direction depending on the Poisson's ratio of the elastic carrier material.

(70) B) Process/Structured Porous Films

(71) In the following examples, a Bicomponent Copolyester Spunbond was used as “standard backer material”. To adhere the backer material to the membrane samples a polyurethane hot melt web adhesive (Article Number: D6C8F 10 g/m.sup.2; Company: Protechnic (France)) was used. The web adhesive was pre-applied to the backer material in a heat press at 120° C. and 5 psi (0.34 bar) areal pressure at 15 seconds dwell time.

Example 1

(72) An ePTFE membrane was made by processes known in the art, for example U.S. Pat. No. 3,953,566. The membrane had an average matrix tensile strength of 10 N/mm.sup.2 in machine direction and 25 N/mm.sup.2 in transverse direction, an airflow of 8 Gurley seconds, a bubble point of 1.5 bar, a thickness of 35 μm, mass/area of 17 g/m.sup.2, and mean flow pore size of 0.18 μm.

Reference Example 1A (Not Structured)

(73) The membrane was placed on a sheet of 1 mm Elastosil RT620 silicone (Wacker silicones). Component A and B where mixed and poured onto a 15 cm by 40 cm rectangular glass plate with 1 mm thick aluminum profiles at the edges. A small glass plate was moved on the aluminum profiles to evenly distribute the silicone on the glass plate to obtain a 1 mm thick sheet after 3 hour curing time at room temperature.

(74) The backer material with pre-adhered adhesive layer was placed on top of the membrane, the adhesive layer facing towards the membrane. A 10 mm thick, 150 mm diameter silicone sheet (Elastosil RT620) was preheated in an oven to reach 150° C. The upper silicone sheet was placed on top of the backer material. An aluminium rod with a diameter of 80 mm and a mass of 5 kg was placed on top of the upper silicone sheet for 10 s to create a bond between the membrane sample and the backer material.

(75) After 10 s the rod and upper silicone sheet were removed and the sample was cooled for 3 min before removing from the lower silicone sheet material.

Examples 1B-1E

(76) Biaxial Processing:

(77) The elastic substrate of a device according to FIG. 1 is stretched to the desired processing ratio with air inflation. The processing ratio is given in Table 1 below.

(78) After reaching the desired stretched state, a valve is closed to keep the processing ratio on a constant state. The film sample is applied on the stretched elastic substrate and a force is applied with a rubber roller to adhere the film sample to the elastic substrate.

(79) After sufficient adhesion is achieved, the air valve is opened to release the inner pressure that stretches the elastic substrate.

(80) A typical processing time was 3 seconds for Elastosil RT620 inflated to a processing ratio of 200%. The elastic substrate retracts back to its original unstretched, flat shape. The adhered film retracts with the elastic substrate, but is structured after the process.

(81) A standard backer material was applied in the same manner as in Reference Example 1.

(82) Examples 1B to 1E show variations in the processing ratio of the elastic substrate and therefore variations in the amount of retraction on the elastic substrate and consequently on the retracted film.

Example 1F, 1H and 1I

(83) For Examples 1F, 1H and 1I in addition structuring of the film has been done by using elastic substrates which a structured surface, which is in the following denoted as “microstructure 1”, “microstructure 2”, and “microstructure 3”, respectively.

(84) For this purpose, the film to be stretched was placed on a sheet comprising microstructured surfaces which were produced as described below:

(85) Microstructure 1

(86) Mold surface was covered with Sandpaper P180 (grit size after FEPA (European Federation of Abrasive Producers) norm), Art.-Nr.: 2871000 “Bogen Schleifpapier Nass-/Trocken” from Wolfcraft GmbH.

(87) Microstructure 2

(88) Mold surface was covered with Sandpaper Vitex P60 (grit size after FEPA (European Federation of Abrasive Producers) norm), Art.-Nr.: KK114F VSM from Vereinigte Schmirgel- and Maschinen-Fabriken AG.

(89) Microstructure 3

(90) Cast silicone surface was covered with micropunched Polyethylen film to create a microstructured surface.

(91) A standard backer material was applied in the same manner as in Reference Example 1.

Examples 1G and 1I

(92) Continuous Transverse Processing:

(93) The membrane sample was placed on a continuous rotating belt of 2 mm thickness.

(94) In Example 1G ECOFLEX 0010 silicone having a smooth, non-patterned surface (Smooth on, Inc.) was used as elastic substrate. Component A and B where mixed and poured onto a 15 cm by 80 cm rectangular glass plate with 2 mm thick aluminum profiles at the edges. A small glass plate was moved on the aluminum profiles to evenly distribute the silicone on the glass plate to obtain a 1 mm thick sheet after 3 hour curing time at room temperature.

(95) In Example 1I Elastosil RT 620 silicone with a dot surface microstructure was used as substrate.

(96) The substrate sheet was clamped in rotating system that stretches and releases stretch of the silicone sheet along a circular motion as described in Example D2. A roll of the standard backer material with pre-adhered adhesive (polyurethane hot melt web adhesive) layer was provided and pre-heated to 130° C. with heated air and then pressed onto the structured film with a pressure roll to form a composite.

(97) Properties of the films of Examples 1A to 1I are given in Table 1.

(98) TABLE-US-00001 TABLE 1 Example Example Example Example Example 1A (ref.) 1B 1C Example 1D 1E Example 1F Example 1G 1H Example 1I processing type — biaxial biaxial biaxial biaxial biaxial transverse biaxial transverse Processing ratio 100 125 150 200 300 200 200 200 200 (%) processing temp. 20 20 20 20 20 20 20 20 20 (° C.) elastic substrate — Elastosil Elastosil Elastosil Elastosil Elastosil ECOFLEX Elastosil Elastosil RT620 RT620 RT620 RT620 RT620 0010 RT620 RT620 elastic substrate — smooth smooth smooth smooth Micro- smooth Micro- Micro- surface structure 1 structure 2 structure 3 airflow ATEQ - up 32.40 11.80 40.10 58.70 105.90 85.70 55.20 57.50 42.20 (l/h) airflow ATEQ - 33.40 10.80 43.10 67.00 101.80 51.70 54.60 56.20 24.90 down (l/h) structure height — 204 681 827 890 551 301 334 466 (μm) structure density, — — 1.4/mm 1.7/mm 1.5/mm 2.5/mm 3.1/mm 3.3/mm 0.8/mm direction x structure density, — — 1.5/mm 1.5/mm 1.5/mm 2.5/mm 0.0/mm 3.3/mm 0.8/mm direction y Area increase 1 1.6 2.25 4 9 4 2 4 2 factor (calc. from proc. ratio(s))

Example 2

(99) An ePTFE membrane was made by processes known in the art for example U.S. Pat. No. 5,814,405 or DE 69617707. The membrane had an average ATEQ airflow of 54 l/hr (at 12 mbar test pressure), a WEP (Water Entry Pressure) of 28 psi (1.93 bar), a bubble point of 8.2 psi (0.57 bar), an average Gurley number of 2.8 Gurley seconds and a mass/area of 10 g/m.sup.2. The membrane had an average transverse direction rigidity of 29.7 g/m and average machine direction rigidity of 9.8 g/m, measured according to ASTM D2923-08 Method B, using a Handle-O-Meter test device (Thwing-Albert Instrument Company) at 20° C.

(100) In this example, the standard backer material was applied in the same manner as in Reference Example 1. In Examples 2B and 2C, different processing types as indicated have been used. Results are given in Table 2 below.

(101) TABLE-US-00002 TABLE 2 Example 2A Example 2B Example 2C (reference) (inventive) (inventive) processing type — biaxial transverse Processing ratio (%) 100 200 200 processing 20 20 20 temperature (° C.) elastic substrate — Elastosil RT620 ECOFLEX 0010 elastic substrate — smooth smooth surface airflow ATEQ - up 94.50 28.70 138.00 (l/h) airflow ATEQ - 92.80 27.60 136 down (l/h) Structure height — 144 169 (μm) Structure density — 4.4/mm 7.5/mm direction x Structure density — 0.6/mm 0.0/mm direction y

Example 3

(102) An ePTFE membrane was made by processes known in the art, for example in US 2007/0012624 A1. The membrane had an average max load of 6N in machine direction and 7N in transverse direction and an average mass/area of 0.3 g/m.sup.2.

(103) The elastic substrate used was Elastosil RT620 and had a thickness of 250 μm. The substrate was stretched to a processing ratio of 200%. There was no visible structuring occurring in the sample. The sample was directly transferred to a pressure sensitive electrical conductive tape to examine the resulted structure in SEM analysis.

(104) The determined structure density in direction x was 270.8/mm, and in direction y was 354.2/mm. As, thus, the structure density is very high, this explains why no visible structures could be seen on the sample.

Example 4—Filtration Examples

Example 4A

(105) A three layer composite ePTFE membrane was made by processes described in U.S. Pat. No. 7,306,729. The composite membrane had an average matrix tensile strength of 13798 (PSI) (95.1 MPa) an ATEQ airflow of 74.9 L/h, a bubble point of 34.8 psi (2.34 bar), a porosity of 81%, a thickness of 1.6 mil, mass/area of 16.7 g/m.sup.2, and pore size of 0.147 microns. This membrane was rendered hydrophilic and water wettable by coating with polyvinyl alcohol by processes known in the art such as those described in U.S. Pat. No. 5,874,165.

Example 4C

(106) A monolithic ePTFE membrane was made by processes known in the art for example U.S. Pat. No. 3,953,566 or U.S. Pat. No. 5,814,405. The membrane had an average matrix tensile strength of 18726 (PSI) (129.1 MPa), an ATEQ airflow of 10.2 L/h, a bubble point of 32 psi (2.21 bar), a porosity of 88%, a thickness of 1.99 mil, mass/area of 13 g/m.sup.2, and mean flow pore size of 0.184 microns.

Preparation of the Structured Film of Examples 4A and 4C

(107) The elastic substrate (ECOFLEX 0030) of a device shown in FIG. 1 was stretched to a processing ratio of 200% for Example 4A and 150% for Example 4C with air inflation.

(108) After reaching the desired stretch ratio a valve was closed to keep the stretch ratio on a constant state. The film sample of Example 4A was applied on the elastic substrate and a force is applied with a rubber roller to adhere the film sample to the elastic substrate.

(109) After sufficient adhesion was achieved the air valve was opened to release the inner pressure that stretches the elastic carrier. Therefore the elastic substrate retracts back to its original flat shape. The adhered sample retracts with the elastic substrate, and was structured after the process.

(110) A polypropylene Fiberweb was used as backer material for the structured film. To adhere the backer material to the structured film samples, a polyurethane hot melt web adhesive (Article Number: D6C8F 10 g/m.sup.2; Company: Protechnic (France)) was used. The web adhesive was pre-applied to the backer material in a heatpress at 120° C. and 5 psi (0.34 bar) areal pressure at 15 seconds dwell time.

(111) The film of Example 4C was processed in the same way as that of Example 4A. In Example 4A, in addition, an acrylic glass plate was laid on top of the film during retraction to guide more uniform wrinkle formation.

Comparative Examples 4B and 4D

(112) For Comparative Examples 4B and 4D the membranes of Examples 4A and 4C, respectively, were placed on a non-stretched 2 mm thick sheet of ECOFLEX 0030 silicone (Smooth on, Ltd.). Component A and B are mixed and poured onto a 15 cm by 40 cm rectangular glass plate with 2 mm thick aluminum profiles at the edges. A small glass plate was moved on the aluminum profiles to evenly distribute the silicone on the glass plate to obtain a 2 mm thick sheet after 3 hour curing time at room temperature.

(113) The backer with pre-adhered adhesive layer was placed on top of the film, the adhesive layer facing towards the membrane. Pressure was applied with a mechanical heatpress at 130° C. for 15 s dwell time to create a bond between the film and the backer material. After 3 min cooling the sample was removed from the silicone carrier.

(114) Particle Filtration Capacity Test

(115) A 3 ppm suspension of 300 nm polystyrene latex nanospheres was made by diluting a 1 wt % stock solution of nanospheres (Poly Sciences Nanobead NIST Traceable Particle Size Standard PN 64015) in a solution of water and surfactant (Triton X100 Sigma Aldrich in MilliQ de-ionized water). Membrane filter discs and a non-woven support were die cut to a diameter of 25 mm, and loaded into a 25 mm diameter swinnex filter holder (sterlitech PN 540100 PP 25 Polypropylene In-Line Filter Holder).

(116) The filter holder was then attached to a switching 4 way switching valve manifold with an off position and 3 inlet feeds for wet out, rinse, and polystyrene latex suspension. The three inlet feeds were housed in attached pressure vessels (regulated to a set pressure of 5 psi (0.34 bar) with compressed gas). The filtrate from the filter outlet was collected on a balance attached to a PC logging mass data with time.

(117) These data were then processes using a density of (1 g/cm.sup.3) to convert mass to volume (V) and a time stamp to calculate the flow rate (change in Volume (V)/time (t)) and permeability (Volume (V)/(time (t)×filter area (a)×pressure (p)). Data were also plotted in the t/V vs. t form to calculate the expected maximum process volume before clogging (Vmax) using a least squares fit to the line in the t/V vs t plot using the standard method (slope=1/Vmax), (F. Badmington, M. Payne, R. Wilkins, E. Honig, Vmax testing for practical microfiltration train scale-up in biopharmaceutical processing, Pharmaceut. Tech., 19 (1995) 64).

(118) The switching valve allows the sample to be wet out with isopropyl alcohol, flushed a solution of water and surfactant (1 wt % Triton X100 in water described above) solution, and then challenged with the 3 ppm polystyrene latex suspension. Hydrophobic membrane samples were wet with 10 ml of alcohol, flushed with 100 ml of surfactant water solution, and then challenged, with 3 ppm latex beads. Hydrophilic samples were challenged with 3 ppm latex solution with no prewet. Area values for the Comparative Examples 4B and 4D were based on the inner diameter of the o-ring, and for inventive examples 4A and 4C were based on measurement of the unfolded area of the sample measured from a digital picture.

(119) The results for the testings of Example 4 are given in Table 3:

(120) TABLE-US-00003 TABLE 3 Vmax Average Vmax Increase flow rate Area Area increase Example (ml) factor (ml/s) (cm.sup.2) factor 4A (structured) 2000 3.4 0.8 14.4 3.8 4B (flat) 588 0.3 3.8 4C (structured) 1667 1.8 0.2 8.9 2.3 4D (flat) 909 0.3 3.8

(121) The “Area increase factor” was determined by dividing the area of the structured film by the area of the backer. The area of the structured film was measured after removing the structured film from the backer by heating the sample to melt the adhesive and after successive unfolding the removed film.

Example 5

(122) A three layer composite ePTFE membrane was made by processes described in U.S. Pat. No. 7,306,729. The composite membrane had an average matrix tensile strength of 13768 PSI (94.9 MPa), an ATEQ airflow of 74.9 L/h, a bubble point of 34.8 psi (2.40 bar), a porosity of 81%, a thickness of 1.6 mil, mass/area of 16.7 g/m.sup.2, and a pore size of 0.147 microns. This membrane was rendered hydrophilic and water wettable by coating with polyvinyl alcohol by processes known in the art such those as described in U.S. Pat. No. 5,874,165A.

(123) For Reference Example 5A and Examples 5B and 5C, a standard backer material as described above has been applied as in Reference Example 1.

(124) Examples 5B and 5C have been processed by standard biaxial processing on a device as shown in FIG. 1. For Example 5C, in addition a hot air gun was pointed with a distance of 4 cm to the applied sample. After heating for a time needed to achieve the desired temperature, measured with an IR heater pointed on the material, the sample was pressed against a carrier with a rubber roll and shrunk back as described. The valve was completely opened so that the process was below 1 second to avoid cooling at processing.

(125) Results are given in Table 4:

(126) TABLE-US-00004 TABLE 4 Example 5A (reference) Example 5B Example 5C processing type — biaxial biaxial processing ratio (%) 100 200 200 processing temperature — 20 140 (° C.) elastic substrate — Elastosil Elastosil RT620 RT620 elastic substrate surface — smooth smooth airflow ATEQ at 68.8 240.2 213.00 70 mbar - up (l/h) airflow ATEQ at 74.4 180.2 213.60 70 mbar - down (l/h) structure height (μm) — — — structure density — 1.0/mm 2.9/mm direction x structure density — 1.2/mm 3.2/mm direction y

Example 6

(127) A layer of electrospun PVA (polyvinyl alcohol) nanofibers was deposited on to a polypropylene spunbond non-woven by free surface electrospinning via processes and solution conditions described in U.S. Pat. No. 7,585,437 B2 using an elmarco nanospider. The PVA nanofiber layer was removed from the spun bond intact by careful peeling. The layer as removed had a basis weight of 1.7 g/m.sup.2, a fiber diameter of 250 nm and an ATEQ air flow of 219 l/h.

(128) A standard backer material as described above has been used and applied as in Reference Example 1.

(129) Example 6B has been processed by using standard biaxial processing. In addition, in Example 6B an acrylic glass plate was placed on top of the film at the retraction to guide more uniform winkle formation.

(130) Results are given in Table 5.

(131) TABLE-US-00005 TABLE 5 Example 6A (reference) Example 6B processing type — biaxial processing ratio (%) 100 200 processing temperature (° C.) 20 20 elastic substrate — Elastosil RT620 elastic substrate surface — smooth airflow ATEQ at 70 mbar - up 142.40 393.80 (l/h) airflow ATEQ at 70 mbar - down 150.20 398.90 (l/h) structure height (μm) — 744 structure density direction x — 1.2/mm structure density direction y — 1.0/mm