PROCESS FOR PRODUCING STRUCTURED POLYMER SURFACES

Abstract

The invention relates to a process for the production of a structured surface on a polymeric material. In the production process, the polymeric material is brought into contact with a surface-structuring mold which comprises, on a first side, channels of length at least 10 m, open toward the first side, and then the removal of the surface-structuring mold from the polymeric material, where the structured surface is obtained on the polymeric material. The polymeric material is brought into contact with the surface-structuring mold at ambient pressure.

Claims

1.-16. (canceled)

17. A process for structuring of a surface of a polymeric material by a surface-structuring mold which comprises a first side and a second side, where the first side of the surface-structuring mold comprises channels of length at least 10 .sub.lam open toward the first side, comprising the steps of: i) providing the polymeric material, ii) bringing the polymeric material provided in step i) into contact with the first side of the surface-structuring mold, iii) removing the surface-structuring mold from the polymeric material to give a structured surface on the polymeric material, where the step ii) is carried out at ambient pressure, where the ambient pressure is in the range from 600 to 1100 mbar, where the polymeric material comprises at least one polymer with glass transition temperature T.sub.G and, in step ii), the polymeric material is brought into contact at a first temperature T.sub.1, which is above the last transition temperature T.sub.G of the at least one polymer, with the first side of the surface-structuring mold, and where the polymeric material is brought into contact with the first side of the surface-structuring mold with an application pressure in the range from 0 to 25 kPa.

18. The process according to claim 17, wherein the channels are additionally open toward the second side, and are continuous between the first side and the second side, and permit fluid exchange between the first side and the second side of the surface-structuring mold.

19. The process according to claim 17, wherein the polymeric material comprises at least one polymer selected from the group consisting of polyethylene, polypropylene, polystyrene, copolymers of polystyrene, polyesters, polyamides, polycarbonates, and polyurethane.

20. The process according to claim 17, wherein, in step ii), the polymeric material is brought into contact with the first side of the surface-structuring mold for a time of at most one minute.

21. The process according to claim 17, wherein the thickness of the material provided in step i) is in the range from 30 m to 100 mm.

22. The process according to claim 17, wherein the structured surface obtained in step iii) on the polymeric material comprises crinite structures which comprise a large number of tiny hairs.

23. The process according to claim 22, wherein the length of the tiny hairs of the crinite structures of the structured surface of the polymeric material is in the range from 50 to 300 m.

24. The process according to claim 22, wherein the diameter of the tiny hairs of the crinite structures of the structured surface of the polymeric material is in the range from 0.1 to 50 m.

25. The process according to claim 22, wherein the ratio of the length of the tiny hairs of the crinite structures of the structured surface of the polymeric material to the diameter of the tiny hairs of the crinite structures of the structured surface of the polymeric material is in the range from 2 to 400.

26. The process according to claim 18, wherein, during step ii), and during step iii), fluid exchange via the channels is possible between the first side of the surface-structuring mold and the environment on the second side of the surface-structuring mold.

27. The process according to claim 17, wherein the first side of the surface-structuring mold is opposite to the second side of the surface-structuring mold.

28. The process according to claim 17, wherein the diameter of the channels of the surface-structuring mold is in the range from 0.1 to 50 m.

29. The process according to claim 17, wherein the surface-structuring mold has been produced from a metal, a metal alloy, a ceramic, glass, silicon, or a polymer.

30. A process for structuring of a surface of a polymeric material by a surface-structuring mold which comprises a first side and a second side, where the first side of the surface-structuring mold comprises channels open toward the first side, comprising the steps of: I) providing the polymeric material, II) bringing the polymeric material provided in step I) into contact with the first side of the surface-structuring mold for a contact time of at most one minute, III) removing the surface-structuring mold from the polymeric material to give a structured surface on the polymeric material.

Description

[0153] The examples below provide further explanation of the process of the invention, but said process is not restricted thereto.

EXAMPLES

[0154] Polymeric Material

[0155] A polyethylene film (HDPE film) of thickness 500 m was provided by pressing HDPE polymer pellets between two heated press platens at 150 C. for 5 minutes in a press mask of thickness 500 m. After a press phase lasting 5 minutes with a 20 kN load the platens were cooled in the press, and the resultant HDPE film was removed once a temperature close to room temperature had been reached.

[0156] A polyethylene film (LDPE film) of thickness about 200 m was used, as is obtainable commercially from Goodfellow.

[0157] A polypropylene film (PP film) of thickness 500 m was provided by, in a manner analogous to that for the HDPE film, melting Moplen HP 400 H pellets (LyondeliBasell Industries Holdings) between two heated press platens at 220 C. for 5 minutes in a press mask of thickness 500 m. After a press phase lasting 5 minutes with a 20 kN load the platens were cooled in the press, and the resultant PP film was removed once a temperature close to room temperature had been reached.

[0158] A polystyrene film (PS film) of thickness 500 m was obtained by, in a manner analogous to that for the HDPE film, melting PS 158 K pellets (Styrolution) between two heated press platens at 190 C. for 5 minutes in a press mask of thickness 500 m. After a press phase lasting 5 minutes with a 20 kN load the platens were cooled in the press, and the resultant PS film was removed once a temperature close to room temperature had been reached.

[0159] Sheet-Like Shaping Mold

[0160] Four different Isopore polycarbonate membranes of thickness in each case 20 m and with average channel diameters of 0.6 m, 1.2 m, 3.0 m, and 10 m from Merck Millipore were used. The channels were continuous and open toward both sides.

[0161] Other systems used were a polycarbonate membrane with average channel diameters of 1 m from Whatman, and a polycarbonate membrane with average channel diameters of 5 m from Sterlitech. The thickness of the membranes was 20 m, and the channels were continuous and open toward both sides.

[0162] Other systems used were nickel foils of thickness 14 m with average channel diameters of 4 m and with an average distance of 8 m between the channels, and also a nickel foil of thickness 10 m with channel diameters of 7 m and an average distance of 11 m between the channels from Temicon GmbH, Dortmund. The channels were continuous and open toward both sides.

[0163] Nickel foil was also used in the form of two-layer laminate with non-continuous pores and total thickness of 27 m. The thickness of the shaping layer was 5 m, with round channels (length of channels: 5 m, average channel diameter: 1.5 m, average distance between channels: 3 m). The outer layer was likewise composed of nickel, thickness 22 m, and had no pores.

[0164] Structured silicon wafer produced by microlithography. The total thickness of the surface-structuring mold was 500 m. The channels were closed toward one side and had square cross section with edge length 88 m. The average distance between the channels was 40 m. The length of the channels was 20 m.

[0165] Characterization

[0166] The morphology of the structured surfaces of the polymeric materials and of lateral views of cross sections of the polymeric materials was studied by means of scanning electron microscopy using secondary electron detection for topographic imaging. An ElectroScan 2020 ESEM was used here, and the acceleration voltage used was 23 kV. The images were obtained by gold-sputtering to render the surfaces of the polymeric materials conductive.

[0167] The wetting behavior of the resultant structured surfaces was determined by measuring the contact angle with water. A Dataphysics OCA20 goniometer was used for this purpose with water droplets of volume 10 L. Droplets of lower volume could not be deposited on the extremely water-repellent structured surfaces. The angle at which the water droplets rolled off the structured surface was determined, this being the angle by which the polymeric material had to be inclined from horizontal to cause the droplet to move. The determination was achieved by increasing the angle of inclination stepwise, starting from a horizontal orientation with initial value 0. All of the measurements were made at room temperature under ambient conditions. The stated values are in each case the average value of 5 measurements at various locations on the polymeric material.

Inventive Example 1

Structuring of an HDPE Film by Means of Polycarbonate Membranes, General Specification

[0168] The HDPE film (22 cm) was heated on a hotplate to 150 C., and the polycarbonate membrane was placed thereon under atmospheric pressure and loaded with a weight of 100 g. This corresponds to an application pressure of 2.5 kPa, After 15 s, the polymeric material, together with the surface-structuring mold, was removed from the hotplate and allowed to cool at room temperature (23 C.). When the temperature of the HDPE film was about 40 C., the membrane was pulled away manually from the HDPE film, and after cooling to room temperature the structured surface of the HDPE film was analyzed. Table 1 collates the analysis data.

TABLE-US-00001 TABLE 1 Angle of Diameter of Diameter of Length of crinite contact with Water roll-off channels crinite structuring structuring water angle Example (m) (m) (m) (degrees) (degrees) 1a 0.6 0.5 84 163 <10 1b 1.0 0.8 65 n.a.* <5 1c 1.2 0.7 69 150 <10 1d 3 1.0 110 158 <10 1e 5 4.0 32 151 <10 1f 10 10 16 160 15 *No determination possible, because it was impossible to retain the drop on the surface.

Inventive Example 2

Structuring of an LDPE Film by Means of Polycarbonate Membranes, General Specification

[0169] The LDPE film (22 cm) was heated on a hotplate to 140 C., and the polycarbonate membrane was placed thereon under atmospheric pressure and loaded with a weight of 100 g. This corresponds to an application pressure of 2.5 kPa. After 40 s, the polymeric material, together with the surface-structuring mold, was removed from the hotplate and allowed to cool at room temperature (23 C.). When the temperature of the LDPE film was about 40 C., the membrane was pulled away manually from the LDPE film, and after cooling to room temperature the structured surface of the LDPE film was analyzed. Table 2 collates the analysis data.

TABLE-US-00002 TABLE 2 Diameter Diameter Length of Angle of Water of of crinite crinite contact with roll-off channels structuring structuring water angle Example (m) (m) (m) (degrees) (degrees) 2a 0.6 0.5 12 144 15 2b 1.2 1.0 11 140 15 2c 3 2.5 11 142 15 2d 10 9 3 103 n.a.** **No determination possible; even at an angle of inclination of 90, droplet adheres on the surface.

Inventive Example 3

Modification of an Polypropylene Film by Means of Polycarbonate Membranes, General Specification

[0170] The PP film (22 cm) was heated on a hotplate to 190 C., and the polycarbonate membrane was placed thereon under atmospheric pressure, without weight loading. After 5 s, the polymeric material, together with the surface-modification mold, was removed from the hotplate and allowed to cool at room temperature (23 C.). When the temperature of the PP film was about 40 C., the membrane was pulled away manually from the PP film, and after cooling to room temperature the structured surface of the PP film was analyzed. Table 3 collates the analysis data.

TABLE-US-00003 TABLE 3 Diameter Diameter Length of Angle of Water of of crinite crinite contact with roll-off channels structuring structuring water angle Example (m) (m) (m) (degrees) (degrees) 3a 0.6 0.4 20 165 <10 3b 1.2 0.6 10 n.a.* <5 3c 3 1.7 7 163 <10 3d 10 9.4 5 119 n.a.** *No determination possible, because it was impossible to retain the drop on the surface. **No determination possible; even at an angle of inclination of 90, droplet adheres on the surface.

Inventive Example 4

Structuring of a PP Film by Means of a Nickel Foil, General Specification

[0171] The PP film (22 cm) was heated on a hotplate to 190 C., and the nickel foil was placed thereon under atmospheric pressure and loaded with a weight of 100 g. This corresponds to an application pressure of 2.5 kPa. After 60 s, the polymeric material, together with the surface-structuring mold, was removed from the hotplate and allowed to cool at room temperature (23 C.). When the temperature of the PP film was about 40 C., the nickel foil was pulled away manually from the PP film, and after cooling to room temperature the structured surface of the PP film was analyzed. Table 4 collates the analysis data.

TABLE-US-00004 TABLE 4 Diameter Diameter Length of Angle of Water of of crinite crinite contact with roll-off channels structuring structuring water angle Example (m) (m) (m) (degrees) (degrees) 4 4 4 10 150 20

Inventive Example 5

Structuring of an HDPE Film by Means of a Nickel Foil, General Specification

[0172] The HDPE film (22 cm) was heated on a hotplate to 150 C., and the nickel foil was placed thereon under atmospheric pressure and loaded with a weight of 100 g. This corresponds to an application pressure of 2.5 kPa. After 15 s, the polymeric material, together with the surface-structuring mold, was removed from the hotplate and allowed to cool at room temperature (23 C.). When the temperature of the HDPE film was about 40 C., the nickel foil was pulled away manually from the HDPE film, and after cooling to room temperature the structured surface of the HDPE film was analyzed. Table 5 collates the analysis data.

TABLE-US-00005 TABLE 5 Diameter Diameter Length of Angle of Water of of crinite crinite contact with roll-off channels structuring structuring water angle Example (m) (m) (m) (degrees) (degrees) 5a 4 4 10 140 30 5b 7 7 14 135 65

Inventive Example 6

Structuring of a PS Film by Means of a Nickel Foil, General Specification

[0173] The PS film (22 cm) was heated on a hotplate to 230 C., and the nickel foil was placed thereon under atmospheric pressure and loaded with a weight of 100 g, corresponding to an application pressure of 2.5 kPa. After 60 s, the polymeric material, together with the surface-structuring mold, was removed from the hotplate and allowed to cool at room temperature (23 C.). When the temperature of the PS film was about 40 C., the nickel foil was pulled away manually from the PS film, and after cooling to room temperature the structured surface of the PS film was analyzed. Table 6 collates the analysis data.

TABLE-US-00006 TABLE 6 Diameter Diameter Length of Angle of Water of of crinite crinite contact with roll-off channels structuring structuring water angle Example (m) (m) (m) (degrees) (degrees) 6 4 4 12 165 10

Inventive Example 7

Structuring of a Polymer Film by Means of Polycarbonate Membranes, and then Removal of the Membrane by Means of Solvent

[0174] The polymeric materials (22 cm) were heated on a hotplate. The HDPE film was heated to 150 C., and the PP film was heated to 190 C. The polycarbonate membrane was placed thereon at atmospheric pressure, and in the case of the HDPE film loaded with a weight of 100 g, corresponding to an application pressure of 2.5 kPa; no weight loading was used in the case of the PP film. After 15 s (HDPE film) or after 5 s (PP film) the polymeric materials, together with the surface-structuring mold, were removed from the hotplate and cooled to 23 C. The polymeric materials, together with the polycarbonate membrane, were then immersed in dichloromethane as solvent, whereupon the polycarbonate membrane dissolved. After complete removal of the polycarbonate, the PE film or the PP film was dried, and the structured surfaces of the polymeric materials were analyzed. Table 7 collates the analysis data.

TABLE-US-00007 TABLE 7 Diameter of Length of Angle of Water Diameter of crinite crinite contact roll-off channels structuring structuring with water angle Example Polymer (m) (m) (m) (degrees) (degrees) 7a HDPE 0.6 0.6 9 177 <10 7b HDPE 1.2 1.2 11 n.a.* <5 7c HDPE 3 3 14 168 10 7d HDPE 5 5 10 109 n.a.** 7e HDPE 10 10 17 117 n.a.** 7f PP 0.6 0.6 3.5 160 10 7g PP 1.2 1.2 3.8 170 10 7h PP 3 3 3.6 150 n.a.** 7i PP 5 5 5.2 108 n.a.** 7j PP 10 10 5.1 106 n.a.** *No determination possible, because it was impossible to retain the drop on the surface. **No determination possible; even at an angle of inclination of 90, droplet adheres on the surface.

Comparative Example 8

Structuring of an HDPE Film by Means of a Nickel Foil with Channel Length 5 m

[0175] The HDPE film (22 cm) was heated at atmospheric pressure on a hotplate to 150 C., and the nickel foil was placed thereon and loaded with a weight of 100 g. This corresponds to an application pressure of 2.5 kPa. After 15 s, the polymeric material, together with the surface-structuring mold, was removed from the hotplate and allowed to cool at room temperature (23 C.). When the temperature of the HDPE film was about 40 C., the nickel foil was pulled away manually from the HDPE film, and after cooling to room temperature the structured surface of the HDPE film was analyzed. It was not possible to obtain any structures of the invention on the surface.

Inventive Example 9

Structuring of an HDPE Film by Means of a Structured Silicon Wafer with Channel Length 20 m

[0176] The HDPE film (22 cm) was heated on a hotplate to 150 C., and the structured silicon wafer was placed thereon under atmospheric pressure and loaded with a weight of 100 g, corresponding to an application pressure of 2.5 kPa. After 15 s, the polymeric material, together with the surface-structuring mold, was removed from the hotplate and allowed to cool at room temperature (23 C.). When the temperature of the HDPE film was about 40 C., the surface-structuring mold was pulled away manually from the HDPE film, and after cooling to room temperature the structured surface of the HDPE film was analyzed. Crinite structures of the invention were obtained on the structured surface. The average length of the crinite structures was 40 m. The angle of contact with water on the structured surface was determined as 160, and the roll-off angle was 5. The average diameter of the tiny hairs, determined by scanning electron microscopy and measurement of the tiny hairs on the scaled micrographs, was 0.9 m.