METHOD AND APPARATUS FOR PRODUCING A NANOSTRUCTURED OR MICROSTRUCTURED FOIL BY EXTRUSION COATING OR EXTRUSION CASTING

Abstract

A method for extrusion coating or extrusion casting, a polymer sheet (4, 5) produced thereby, a roller (2) for use in extrusion coating or extrusion casting, and an apparatus comprising said roller (2), in which micro- and/or nanostructures provided on the surface of the roller (2) are transferred to the polymer sheet (4, 5), and which is applicable to the extrusion coating or extrusion casting of all types of thermoplastic polymer.

Claims

1-20. (canceled)

21. A method for producing a microstructured thermoplastic polymer coating on a carrier foil, the coating comprising at least one microstructured surface area, said method comprising: providing an extrusion coating roller for an industrial polymer extrusion coating process using a thermoplastic polymer; applying a surface comprising a microstructured non-thermoplastic polymer foil on the said extrusion coating roller, thereby forming a microstructured extrusion coating roller; maintaining the temperature of the said microstructured extrusion coating roller below the solidification temperature of the said thermoplastic polymer; moving the carrier foil at a fixed velocity between the microstructured extrusion coating roller and a counter pressure roller by rotating the microstructured extrusion coating roller at a fixed rotational velocity; and continuously applying a melt of said thermoplastic polymer between the said moving carrier foil and the said rotating microstructured extrusion coating roller, whereby said thermoplastic polymer melt is solidified upon contact with said microstructured extrusion coating roller maintained at a temperature below the solidification temperature of the said thermoplastic polymer melt thereby forming a solid microstructured thermoplastic polymer coating on said carrier foil.

22. The method according to claim 21, wherein microstructures are produced on both sides of the carrier foil by using both the microstructured extrusion coating roller and a microstructured counter pressure roller.

23. The method according to claim 21, wherein an aspect ratio of the said microstructures is more than 0.25.

24. The method according to claim 21, wherein the said microstructured surface is applied by mounting microstructured shims on the said extrusion coating roller.

25. The method according to claim 21, wherein the microstructured surface is applied by coating the said extrusion coating roller with a material which is subsequently microstructured.

26. The method according to claim 25, wherein the said material is a polymer composite precursor which is microstructured by embossing to form a solid microstructured polymer composite material, and wherein said polymer composite precursor may be cured during embossing.

27. The method according to claim 26, wherein the said polymer composite materials for the said microstructures on the roller: comprise inorganic particles selected from the group consisting of: metal/metalloid particles, metal/metalloid oxide particles, metal/metalloid nitride particles, metal/metalloid carbide particles, metal metalloid sulfide particles, metal/metalloid phosphate particles, or mixtures thereof; and/or comprise inorganic particles having particle sizes with a largest feature having a size preferably below 2 micrometers.

28. The method according to claim 25, wherein the said polymer composite materials for the said microstructures on the roller contain inorganic particles with a volume content of more than 0.1% by volume.

29. The method according to claim 25, wherein the said polymer composite materials for the said microstructures on the roller contain inorganic particles having a covalently bonded compatibilization molecule agent containing an organic moiety, a siloxy moiety, a sulfide moiety, a sulphate moiety, a phosphate moiety, an amine moiety, a carboxyl moiety, a hydroxyl moiety, or a combination thereof.

30. The method according to claim 21, wherein the said microstructured non-thermoplastic polymer foil on the said extrusion coating roller is provided as at least one foil that is glued to the surface of a roller using a thermoplastic.

31. The method according to claim 21, wherein the fixed rotational velocity at which the microstructured extrusion coating roller rotates is at least 10 m/min.

32. A method for producing a microstructured amorphous thermoplastic polymer foil comprising at least one microstructured surface area, said method comprising: providing an extrusion roller for an industrial polymer extrusion casting process using a thermoplastic polymer; applying a surface comprising a microstructured non-thermoplastic polymer foil or coating on the said extrusion roller, thereby forming a microstructured extrusion roller; maintaining the temperature of the said microstructured extrusion roller below the solidification temperature of the said thermoplastic polymer; and continuously applying a melt of said thermoplastic polymer between the said microstructured extrusion roller and a counter pressure roller, wherein the microstructured extrusion roller is rotated at a fixed rotational velocity, whereby said thermoplastic polymer melt is solidified upon contact with said microstructured extrusion roller maintained at a temperature below the solidification temperature of the said thermoplastic polymer melt, thereby forming a solid microstructured thermoplastic polymer foil.

33. A microstructured thermoplastic foil made according to the method of claim 32.

34. A roller for extrusion coating or extrusion casting, comprising microstructures on at least a part of its outer surface, wherein the microstructures are formed from a non-thermoplastic polymer.

35. The roller according to claim 34, the roller being a cooling roller.

36. The roller according to claim 34, wherein the microstructures are formed in a polymer sheet, the polymer sheet being affixed to the outer surface of the roller.

37. The roller according to claim 34, wherein the microstructures are formed as at least one polymer shim, the at least one polymer shim being affixed to the outer surface of the roller.

38. An apparatus for extrusion coating, comprising at least one roller according to claim 34.

39. An apparatus for extrusion casting of thermoplastic polymer sheets having microstructures on both sides of the sheet, comprising two rollers according to claim 34, wherein the two rollers are arranged such that the thermoplastic polymer sheet is formed therebetween.

Description

BRIEF DESCRIPTION OF THE FIGURES

[0092] FIG. 1 shows a schematic diagram of an extrusion coating apparatus and process

[0093] FIG. 2 shows a schematic diagram of an extrusion casting apparatus and process

[0094] FIG. 3 shows a flow chart of a method for making the micro or nanostructured foil.

DETAILED DESCRIPTION

[0095] The method and apparatus according to the invention will now be described in more detail with regard to the accompanying figures. The figures show one way of implementing the present invention and are not to be construed as being limiting to other possible embodiments falling within the scope of the attached claim set.

[0096] FIG. 1 shows one embodiment of the technique. A carrier foil (1) is passed between the micro or nanostructured roller (2) and a counter roller (3). An amorphous or semicrystalline thermoplastic melt is deposited between the micro or nanostructured roller (2) and the carrier foil (1). The micro or nanostructured roller is kept at a temperature below the solidification temperature of said amorphous or semicrystalline thermoplastic melt. The micro or nanostructured roller and the counter roller rotate as indicated by the arrows, thereby moving the carrier foil while laminating the thermoplastic melt to the carrier foil. Upon contact between the amorphous or semicrystalline thermoplastic melt (4) and the micro or nanostructured roller (2), a simultaneous cooling and shaping of the amorphous or semicrystalline thermoplastic melt occurs, thereby forming a micro or nanostructured and solid amorphous or semicrystalline thermoplastic coating which is laminated to the carrier foil, thereby forming a carrier foil comprising a micro or nanostructured amorphous or semicrystalline thermoplastic coating. The cooling times using a polymeric structure on said extrusion roller are much longer relative to a metal-coated nanostructured extrusion cooling roller, hence improving replication quality significantly (5).

[0097] FIG. 2 shows another embodiment of the technique. An amorphous or semicrystalline thermoplastic melt is (1) is passed between the micro or nanostructured extrusion roller (2) and a counter roller (3). The micro or nanostructured roller is kept at a temperature below the solidification temperature of the amorphous or semicrystalline thermoplastic melt. The micro or nanostructured roller and the counter roller rotate as indicated by the arrows, thereby moving and shaping the amorphous or semicrystalline thermoplastic melt. Upon contact between the amorphous or semicrystalline thermoplastic melt (1) and the micro or nanostructured roller (2), a simultaneous cooling and shaping of the amorphous or semicrystalline thermoplastic melt occurs, thereby forming a micro or nanostructured and solid thermoplastic foil (4).

[0098] FIG. 3 shows a flow chart of a method for making the micro or nanostructured foil. First an initial extrusion coating roller for an industrial polymer extrusion coating process using an amorphous or semicrystalline thermoplastic material is provided (11), then a micro or nanostructured surface on the said extrusion coating roller is applied (12) thereby forming a micro or nanostructured extrusion coating roller (13) which is maintained at a the temperature below the solidification temperature of the said amorphous or semicrystalline thermoplastic material. A carrier foil is placed between the rotating micro or nanostructured extrusion coating roller and a rotating counter pressure roller, thereby being moved at a given velocity corresponding to the rotational velocity of the rotating micro or nanostructured extrusion coating roller (14). By continuously applying a melt of said amorphous or semicrystalline thermoplastic material between the said moving carrier foil and the said rotating micro or nanostructured extrusion roller, the said amorphous or semicrystalline thermoplastic melt is solidified after contact with said micro or nanostructured extrusion coating roller maintained at a temperature below the solidification temperature of the said amorphous or semicrystalline thermoplastic melt thereby forming a solid micro or nanostructured amorphous or semicrystalline thermoplastic coating on said carrier foil (15).

Detailed Description of an Embodiment

[0099] In a first example a ø300 mm, 600 mm wide extrusion roller was mounted with 100 μm thin PET polymer foil with a diffraction grating topography. A polyethylene melt was extrusion coated onto a PET carrier foil at a velocity of 30 m/min, resulting in the production of a foil covered with diffraction gratings defined in the polyethylene coating laminated to the PET carrier foil.

[0100] In a second example a 0300 mm, 600 mm wide extrusion roller is coated with a 2 μm layer of Norland Adhesive grade NOA 63, which is structured by step-and-repeat embossing and ultra-violet exposure of a self cleaning nanostructure on a PDMS stamp that is transparent or semi-transparent to ultra-violet light. The nanostructured adhesive coating on the roller is used for the extrusion coating process. A stretchable laminate foil with a hotmelt backing is used as carrier foil and a polypropylene thermoplastic melt is applied to the carrier foil at 60 m/min. Thereby 0.6 m.sup.2/s of self cleaning foil is produced. The produced foil is laminated to transport vehicles in order to make them self cleaning.

[0101] In a third example a 850 mm long, 600 mm wide sheet of stainless steel having a thickness of 0.4 mm was coated with a 2 μm layer of heat curable imprint polymer grade mr-I 9000M from micro resist technology GmbH, which was structured by step-and-repeat embossing and flash heating of a nickel shim having a microlens array microstructure. The microstructured polymer coating on the roller was used for the extrusion coating process. A stretchable laminate foil with a hotmelt backing was used as carrier foil and a polystyrene thermoplastic melt was applied to the carrier foil at 60 m/min. Thereby 0.6 m.sup.2/s of microlens array foil with excellent optical transmission was produced. The produced foil can be used in optical sensors to focus the incoming light onto the light-sensitive parts of the sensor array.

[0102] In a fourth example a 01000 mm, 2500 mm wide piece of non-thermoplastic polymer foil having an inverse drag reduction microstructure is fixed to the surface of a suitable extrusion roller by use of a suitable adhesive. The microstructured roller is used for the extrusion coating process. A stretchable laminate foil with a hotmelt backing is used as carrier foil and a polypropylene thermoplastic melt is applied to the carrier foil at 60 m/min. Thereby 0.6 m.sup.2/s of drag reduction foil is produced. The foil is laminated to cover a ship hull, thereby reducing the drag on the ship, and hence reducing CO2 emissions or increasing the top speed.

[0103] In a fifth example 01000 mm, 2500 mm wide extrusion roller is coated with a 2 μm layer of UV-curable resist grade mr-UVCur06 from micro resist technology GmbH, which is structured by step-and-repeat embossing and ultra-violet light exposure of a yoghurt repellent microstructure on a PDMS stamp which has been coated with an anti-adhesive promoter. The nanostructured roller is used for the extrusion coating process. A cardboard foil is used as carrier foil and a polypropylene thermoplastic melt is applied to the carrier foil at 200 m/min. Thereby 5 m.sup.2/s of food repellent cardboard foil is produced, which is used for yoghurt packaging, ensuring that the yoghurt packaging may be completely emptied, thereby reducing food waste.

[0104] In a sixth example 8 identical pieces of non-thermoplastic polymer micro-Fresnel foil having a size of 800 mm by 1250 mm were fixed to a steel sheet having a size of 3200 mm by 2500 mm in a fully covering pattern using a suitable adhesive. The micro-Fresnel structure was characterized by having parallel lines of triangular wedges where one side is perpendicular to the surface plane and has a depth of 40 μm and a pitch between the lines of 300 μm. The foil sheet was used as a cliché, ie a polymer shim, on a suitable steel roller and fixed to the said roller using methods common in the printing industry. The micro-Fresnel structured roller was used for the extrusion coating process. A previously produced foil having an anti-reflective structure was used as carrier foil, such that the unstructured side was towards the melt, and a transparent and ageing resistant thermoplastic melt was applied to the carrier foil at 20 m/min. The side of the foil having the micro-Fresnel structures was coated using Aluminium metal sputtering, after which the Aluminium layer is extrusion coated with a protection layer. Thereby 50 m.sup.2/min of solar concentrating foil was produced, which can be used for concentrating solar light for a heating application, to produce central heating for district heating in a city and off-setting the need for fossil fuels.

[0105] In a seventh example a stainless steel sheet is prepared with holes and fixtures similar to a shim for a flexo-print printing press. The sheet having a size of 3100 mm long and 2500 mm wide and a thickness of 0.3 mm is spray-coated with a 1 μm layer of ultra-violet curable imprint resist by mixing it with a suitable solvent. The resist is structured by step-and-repeat embossing and ultra-violet exposure by use of a transparent PDMS stamp having an optically varying diffractive pattern in the shape and design of a company logo. The step-and-repeat pattern is hexagonal. The steel sheet is mounted directly on the suitable cooling roller and is used for the extrusion coating process. A pre-metallized laminate foil with a hotmelt backing is used as carrier foil and a Surlyn ionomer thermoplastic melt is applied to the carrier foil at 100 m/min. Thereby 250 m.sup.2/min of packaging foil with bright optically varying logos on the one side is produced without the need for inks or pigments. The foil is used for anti-counterfeit protection of pharmaceutical tablets in a blister-pack.

[0106] In an eighth example a Poly-acrylo-nitrile (PAN) melt is blown extruded at 240 C with cooling roller and counter roller maintained at 70 C. The cooling roller comprises a non-thermoplastic polymer coating having decorative structures thereon, and has a width of 1.5 m. A 20 μm thin PAN-foil comprising decorative structures is produced at a rate of 0.5 m/s, giving a productivity of 0.75 m.sup.2/s of decorative foil used for plastic bags.

[0107] In a ninth example a 30 μm thick polystyrene (PS) foil is extrusion cast between a pair of rollers having thereon a nanostructured non-thermoplastic polymer coating, resulting in a PS foil with structures on both sides. The rollers comprise cell active structures, resulting in a PS foil comprising structures which have a biological activity. The PS foil is corona treated in line, and cut out in small, hexagonal pieces with a dimension of 30 μm*100 μm*100 μm. The hexagonal pieces are then used as micro beads in adherent cell proliferation reactors with the main purpose of inducing a more natural cell behavior and the secondary purpose of vastly increasing the available surface area for the cells.

[0108] Further aspects of the invention are set out in the following clauses: [0109] 1. A method for producing a nanostructured amorphous thermoplastic polymer coating on a carrier foil comprising at least one nanostructured or microstructured surface area, said method comprising at least the following steps: [0110] providing an initial extrusion coating roller for an industrial polymer extrusion coating process using an amorphous thermoplastic material [0111] applying a surface comprising a nanostructured non-thermoplastic polymer foil or coating on the said extrusion coating roller, thereby forming a nanostructured extrusion coating roller [0112] maintaining the temperature of the said nanostructured extrusion coating roller below the glass transition temperature of the said amorphous thermoplastic material [0113] moving a carrier foil between the rotating nanostructured extrusion coating roller and a rotating counter pressure roller at a given velocity corresponding to the rotational velocity of the rotating high aspect ratio nanostructured extrusion coating roller [0114] continuously applying a melt of said amorphous thermoplastic material between the said moving carrier foil and the said rotating nanostructured extrusion roller, whereby said amorphous thermoplastic melt is solidified upon contact with said nanostructured extrusion coating roller maintained at a temperature below the glass transition temperature of the said amorphous thermoplastic melt thereby forming a solid nanostructured amorphous thermoplastic coating on said carrier foil. [0115] 2. A method for producing a nanostructured amorphous thermoplastic polymer coating on a carrier foil comprising at least one nanostructured or microstructured surface area, said method comprising at least the following steps: [0116] providing an initial extrusion coating roller for an industrial polymer extrusion coating process using an amorphous thermoplastic material [0117] applying a surface comprising a nanostructured non-thermoplastic polymer foil or coating on the said extrusion coating roller, thereby forming a nanostructured extrusion coating roller [0118] maintaining the temperature of the said nanostructured extrusion coating roller below the glass transition temperature of the said amorphous thermoplastic material [0119] continuously applying a melt of said amorphous thermoplastic material between the said counter roller and the said rotating high aspect ratio nanostructured extrusion roller, whereby said amorphous thermoplastic melt is solidified upon contact with said high aspect ratio nanostructured extrusion roller maintained at a temperature below the solidification temperature of the said amorphous thermoplastic melt thereby forming a solid high aspect ratio nanostructured thermoplastic foil. [0120] 3. A method according to clause 1 or 2, where the aspect ratio of the said nano or microstructure is above 2, more preferably above 1.5, more preferably above 1, more preferably above 0.75, even more preferably above 0.5, and most preferable more than 0.25. [0121] 4. A method according to any previous clause, where high aspect ratio nanostructures are produced on both sides of the cast foil by using both a high aspect ratio nanostructured extrusion roller and a high aspect ratio nanostructured counter roller. [0122] 5. A method according to any previous clause where the said high aspect ratio nanostructured surface is applied by mounting high aspect ratio nanostructured shims on the said initial extrusion coating roller. [0123] 6. A method according to any previous clause where the high aspect ratio nanostructured surface is applied by coating the said initial extrusion coating roller with a material which is subsequently high aspect ratio nanostructured. [0124] 7. A method according to clause 6 where the said material is a polymer or polymer composite precursor which is nanostructured by embossing to form a solid high aspect ratio nanostructured ceramic material and where said polymer or polymer composite precursor may be cured during embossing. [0125] 8. A method according to any of the previous clauses where the said polymer composite materials for the said high aspect ratio nanostructures on the roller or shim [0126] comprising inorganic metal/metalloid particles, metal/metalloid oxides, metal/metalloid nitrides, metal/metalloid carbides, metal metalloid sulfides, metal/metalloid phosphates, or mixtures thereof [0127] having particle sizes with the largest feature having a size preferably below 2 micrometers, more preferably below 200 nm, even more preferably below 20 nm, most preferably having a size below 2 nm [0128] having geometries ranging from spherical to elongated to flat. [0129] 9. A method according to any of the previous clauses where the said polymer composite materials for the said high aspect ratio nanostructures on the roller or shim contain inorganic particles with a volume content of more than 0.1% by volume, preferably more than 0.25% by volume, even more preferably more than 1% by volume, even more preferably more than 5% by volume, even more preferably more than 20% by volume, and most preferably more than 50% by volume. [0130] 10. A method according to any of the previous clauses where the said polymer composite materials for the said high aspect ratio nanostructures on the roller or shim contain inorganic particles having a covalently bonded compatibilization molecule agent containing an organic moiety, a siloxy moiety, a sulfide moiety, a sulphate moiety, a phosphate moiety, an amine moiety, a carboxyl moiety, a hydroxyl moiety, or a combination thereof. [0131] 11. A method according to any of the previous clauses where the said high aspect ratio nanostructures are provided as one or a plurality of foils that is glued to the surface of a roller or a shim using a thermoplastic or thermoset adhesive [0132] 12. An amorphous thermoplastic foil according to clause 2 or a foil with a high aspect ratio nanostructured amorphous thermoplastic coating according to clause 1 made by any of the previous clauses.

[0133] Although the present invention has been described in connection with the specified embodiments, it should not be construed as being in any way limited to the presented examples. The scope of the present invention is set out by the accompanying claim set. In the context of the claims, the terms “comprising” or “comprises” do not exclude other possible elements or steps. Also, the mentioning of references such as “a” or “an” etc. should not be construed as excluding a plurality. The use of reference signs in the claims with respect to elements indicated in the figures shall also not be construed as limiting the scope of the invention. Furthermore, individual features mentioned in different claims, may possibly be advantageously combined, and the mentioning of these features in different claims does not exclude that a combination of features is not possible and advantageous.

[0134] All patent and non-patent references cited in the present application are also hereby incorporated by reference in their entirety.