METHOD AND DEVICE FOR PRODUCING NANO FILMS

Abstract

A method for producing films or more precisely stated, mats and plates out of nanofibers, in particular films or mats and plates out of cellulose nanofibers, wherein nanofiber material is dispersed in solvent; the solids content is between 1 and 4% by volume and the resulting slurry is applied by means of an application device to a conveyor belt that is moving in the conveying direction and then the poured-on slurry is pre-dried and the pre-dried slurry, after the pre-drying, is subjected to the main drying and after the achievement of a predetermined moisture content, is removed from the conveyor belt.

Claims

1. A method for producing films or mats and plates out of cellulose nanofibers, comprising: dispersing nanofiber material in solvent, resulting in a slurry having a solids content between 1 and 4% by volume; pouring the resulting slurry onto a conveyor belt that is moving in a conveying direction; pre-drying the slurry that has been poured on the conveyor belt using infrared heating elements that are arranged longitudinally and/or transversely or diagonally to the conveying direction of the conveyor belt; after the pre-drying, subjecting the pre-dried slurry to a main drying performed with middle-wave and/or short-wave infrared heating elements with a high power density, wherein the infrared heating elements are controlled individually or in groups, and selectively removing solvent vapor and removing moisture in the main drying by supplying air and/or other gases that are diffusely directed into a region of the main drying; and after achieving a predetermined moisture content, removing the slurry from the conveyor belt.

2. The method according to claim 1, wherein the nanofiber material is dispersed in a solvent selected from at least one of the group consisting of: water an organic solvent, and alcohol.

3. The method according to claim 1, wherein the slurry is poured onto the conveyor belt and applied using a doctor blade, a profiled doctor blade, a bar with an indentation ground into it, a blade-shaped nozzle, a slot nozzle, a slide-die nozzle, or a volume-controlled application nozzle.

4. The method according to claim 1, wherein the slurry is poured onto a smooth conveyor belt.

5. The method according to claim 1, comprising heating the conveyor belt to 40 to 95 C.

6. The method according to claim 1, comprising carrying out the pre-drying in a housing with a controlled gas supply or air supply.

7. The method according to claim 1, wherein the infrared heating elements are individually controllable.

8. The method according to claim 1, comprising adjusting a gas flow or air flow during the main drying with regard to a relative humidity and/or flow speed of the slurry.

9. The method according to claim 1, wherein after the main drying, the dried slurry material is remoistened to a desired moisture content.

10. A device for performing a method for producing films from cellulose nanofibers, comprising: a conveyor belt; a plurality of rollers for conveying the conveyor belt along a longitudinal direction in a loop in the form of an upper and lower run; an application device for applying a film slurry onto a region of the conveyor belt; a pre-drying unit, following the application device in a conveying direction of the conveyor belt, wherein the pre-drying unit comprises infrared heating elements that act on the poured-on slurry; and following the pre-drying unit in the conveying direction of the conveyor belt, a main drying unit with infrared heating elements; wherein in the region of the conveyor belt in which the conveyor belt supports the slurry, the conveyor belt is held by rollers, at least some of the rollers are heatable.

11. The device according to claim 10, wherein the main drying unit is followed in the conveying direction by a remoistening unit.

12. The device according to claim 10, further comprising a dispersing device, which comprises a receptacle and an agitating device; wherein the agitating device can agitate at more than 1,000 revolutions per minute.

Description

BRIEF DESCRIPTION OF THE DRAWING

[0048] The invention and in particular, the apparatus used, will be explained by way of example based on a drawing. The sole FIGURE here shows a very schematic side view of a corresponding apparatus.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0049] The apparatus according to the invention for producing nanofilms 1 has a dispersing unit 2; the dispersing unit 2 has a receptacle 3 and an agitating or whipping mechanism 4. In addition, the dispersing unit 2 has a supply for nanofiber material and a supply for corresponding solvents. The agitating or whipping device 4 in this case is preferably an electromotive device 4 with a corresponding agitating or whipping mechanism 5; the agitating or whipping mechanism 5 and the motor 4 are embodied so that rotation speeds of more than 1,000 revolutions per minute can be achieved and in addition, the agitating mechanism mixes and disperses the entire contents.

[0050] Sufficiently dispersed material or more precisely, the slurry produced by means of this, can be transferred to a storage receptacle 6; the storage receptacle 6 has corresponding supply devices for supplying the slurry from the dispersing unit 2 to the storage receptacle 6. The storage receptacle 6 likewise has an agitating mechanism 7, which has a drive 8 and a corresponding agitator 9; these components are dimensioned so that they keep the slurry in the dispersed, non-separated state.

[0051] By means of a hose system 10, a corresponding pump 11, and a corresponding downstream hose 12, the slurry can be correspondingly supplied to an application device 13. The application device 13 in this case is a doctor blade and in this case, extends across the width of the system. The slurry is poured from the application device 13 onto a conveyor belt 14, which moves in accordance with the arrow direction 15. To tension the conveyor belt 14, at least one first roller 16 and one last roller 17 are provided; between the rollers 16, 17, there can be a plurality of additional support and heating rollers 18. The rollers 16, 17 in this case rest with a partial circumference against the belt 14, while the other rollers 18 preferably rest against the belt 14 in a supporting fashion over only a relatively narrow region of the belt.

[0052] The rollers 16, 17, 18 are preferably all embodied as heatable, in particular electrically heatable; belt 14 temperatures of between 40 and 85 can be set.

[0053] After the application device 13, there is a pre-drying device 19; the pre-drying device 19 is composed of a plurality of IR heating elements 20 arranged longitudinally relative to the travel direction 15 of the belt 14 and a plurality of IR heating elements 21 arranged transversely relative to the travel direction of the belt 14.

[0054] Naturally, it is also possible to position the heating elements 20, 21 obliquely or at an angle to the travel direction 15 of the belt 14.

[0055] It is also possible to embody the IR heating elements at different distances from the belt surface.

[0056] In the vicinity of the pre-drying 19, it is also possible for there to be a housing (not shown) around the entire pre-drying unit 19, which shields the pre-drying unit from the outside atmosphere and the uncontrolled access by this atmosphere, but does provide a selective ventilation, e.g. a transverse ventilation by means of corresponding nozzles and corresponding opposing suction devices.

[0057] The pre-drying unit 19 is followed by the drying unit 22; the drying unit has at least one, but preferably a plurality of infrared heating elements 23, which can be arranged similarly to the heating elements of the pre-drying unit, but can also be infrared heating elements that operate in particular spots and that can preferably be individually controlled.

[0058] Preferably, the surface temperature of the slurry is measured and the heating intensity by means of the infrared heating elements can be adapted to a desired surface temperature, which can particularly vary from the entrance of the drying unit to the exit from the drying unit.

[0059] In order to set a defined vapor pressure above the slurry 24, the drying unit 22 can also have a surrounding housing, which prevents the uncontrolled access by the surrounding atmosphere, but permits an appropriate supply of air or another gas. The air or the gas, whose relative humidity is adjusted so that it is able to absorb a particular quantity of moisture from the slurry 24, is guided so that it flows through the region above the slurry 24.

[0060] In this case, it is important that the flow travels in a diffuse fashion and is not aimed directly at the surface since a direct flow against the surface can produce waves in the very moist slurry in the region of the entrance to the drying unit 22 and at the exit, can produce cracks in the slurry material, which is then already correspondingly thin and film-like.

[0061] The drying unit 22 is followed by a remoistening device 25, which can be embodied as a fog or humidity chamber or which brings about a defined remoistening in some other way.

[0062] To achieve this, it is possible to measure the moisture content of the slurry, preferably in a contactless way, and to regulate the moistening in a corresponding way.

[0063] The film 26 that is produced by means of this is removed from the last roller 17, possibly with a corresponding removing blade (not shown), and is supported by a support roller 27. It then travels over a spreader roller 28 to a winder 29, where it is correspondingly wound.

[0064] Since during the film can develop a static charge during production, after the removal of the film 26 from the conveyor belt 14, an air ionization device or another device 30 for reducing or eliminating the charge can be provided.

[0065] In order to correspondingly guide and tension the conveyor belt, it is possible for other rollers 31, particularly in the form of tension rollers 31, to be correspondingly provided in the region of the lower run of the belt.

[0066] The invention has the advantage that for the first time, it is possible in a reproducible, high-quality method to produce a nanofiber film with a high degree of uniformity with regard to the thickness over both its length and width; the production is carried out in widths of 1 m and more and at speeds of 50 m per minute, which enables the method to be used commercially.