Device for production of layer of nanofibres through electrostatic spinning of polymer matrices

Technical field The invention relates to the device for production of layer of nanofibres through electrostatic spinning of polymer matrices in electrostatic field of a high intensity induced by difference of potentials between the spinning electrode and the collecting electrode, which comprises endless belt mounted at least on two stretching shafts, out of which at least one is coupled with a drive, while between the spinning electrode and the collecting electrode is in vicinity of the collecting electrode performed the guidance of substrate material is.

Background art

The device for production of layer of nanofibres through electrostatic spinning of polymer matrices comprises the spinning electrode and the collecting electrode, which is usually formed of a rod or metal plate connected to opposite pole of high voltage source than the spinning electrode or is grounded.

EP 1059106 and US 4.143.196 disclose the device at which the collecting electrode comprises electrically conductive smooth belt, on which the produced layer of nanofibres is deposited, which is subsequently removed from the belt of the collecting electrode and is transported outside the device. In EP

1059106 a section of the belt, on which the layer of nanofibres is deposited, is horizontal, while in US 4.143.196 a section of the belt, on which the layer of nanofibres is deposited, is vertical. This device does not solve depositing of layer of nanofibres on the substrate material, neither the transport of substrate material in the space between the spinning electrode and the collecting electrode. The belt collecting electrodes according to the background art are used for direct depositing of nanofibres into a layer of nanofibres and for transport of this layer of nanofibres outside the space between the spinning electrode and the collecting electrode.

According to CZ PUV 2007-18612 the collecting electrode formed of a body of cylindric shape is in contact with substrate material, which through the spinning device is guided basically horizontally. Nevertheless the disadvantage of this solution is an increased friction of substrate material against surface of the collecting electrode, when especially at fine substrate materials consisting of little mutually fixed fibres, which are for example fine webs, damage of substrate material occurs or may occur, especially in cases when the device comprises more spinning units, thus also more collecting electrodes and the substrate material must be strongly stretched so that its slacking is prevented. The goal of the invention is to reduce or eliminate the disadvantages of the background art.

Principle of the invention

The goal of the invention has been reached by the device for production of layer of nanofibres through electrostatic spinning of polymer matrices according to the invention, whose principle consists in that the guidance of substrate material is formed of hold-down means of substrate material, which are performed on endless belt of the collecting electrode.

The hold-down means of substrate material performed on the endless belt serve to secure a good contact of substrate material with surface of the collecting electrode and an steady speed in motion of substrate material through the spinning space. A good contact of substrate material with surface of the collecting electrode is a basic prerequisite for uniform depositing of nanofibres into a layer of nanofibres on the substrate material. To improve hold-down of substrate material on surface of the cylindric body of the collecting electrode it is advantageous, if the hold-down means are formed of openings in the belt of the collecting electrode, and the space behind the belt in direction from the spinning electrode to the collecting electrode is coupled with a source of underpressure. To improve transport of substrate material formed especially of fine web of relatively great thickness it is advantageous, if the endless belt of the

collecting electrode is provided on its outer side with tips, that are able to extend into the substrate material and to exit from it again, thus exactly determine the speed of motion of substrate material, its position and also its stretching between the collecting electrodes of individual one after another arranged spinning units. The tips form the hold-down means and on the belt are used either independently or in combination with openings and under pressure behind the belt of the collecting electrode.

To improve the spinning effect it is advantageous, if the tips are made of electrically conductive material and their length corresponds to thickness of the substrate material. The conductive tips on belt of the collecting electrode create irregularities of electrostatic field between the spinning electrode and the collecting electrode and so contribute to formation of Taylor cones from polymer solution on the spinning electrode, thus also to formation of nanofibres. At sufficient density of tips made of electrically conductive material it is advantageous, if these tips are mounted in body made of electrically nonconducting material and at least in position against the spinning electrode the tips are connected to the high voltage source of opposite polarity than the spinning electrode or grounded. Electrostatic field in this case is induced between the tips and the spinning electrode. The produced nanofibres are carried from the spinning electrode towards the tips of the collecting electrode and they deposit on the substrate material.

In embodiment according to the claim 6 the tips are made of electrically nonconducting material and they are mounted on belt made from electrically conductive material, which is connected to high voltage source of opposite polarity than the spinning electrode or grounded. This embodiment is suitable for substrate materials formed of thin webs of electrically conductive material or of material, at which the electric conductivity was increased by some of the known methods. At such thin webs it is sufficient, when the electrostatic field is induced between the spinning electrode and surface of the belt of the collecting electrode, with which the web is in contact.

Description of the drawing

Exemplary embodiment of the device according to the invention and the collecting electrode according to the invention is schematically represented on enclosed drawings, where Fig. 1 shows the spinning device with the collecting electrode containing the rotatably mounted smooth belt with openings with assigned source of underpressure is assigned, Fig. 2 another variant of the device at which the endless belt of the collecting electrode is provided with tips.

Examples of embodiment Exemplary embodiment of the device for production of layer of nanofibres through electrostatic spinning of polymer matrices in electrostatic field of high intensity according to the invention is represented in Fig. 1. Polymer matrix is formed of any electrostatic spinnable form of polymer possibly with various additives or mixture of polymers, that may also be added with various additives, while usually the electrostatic spinnable form is solution or melt. In the spinning chamber 1 there is arranged the spinning unit, which comprises the spinning electrode 2 and against it arranged the collecting electrode 3. Between the spinning electrode 2 and the collecting electrode 3 electrostatic field of high intensity is induced in a known manner. In the spinning chamber 1 in a known manner, not described in detail, the passage for substrate material 4 is created, which is unwound in the known not represented unwinding device and into the spinning chamber 1 it is brought by feeding rollers 51., 52. From the spinning chamber ± the substrate material 4 is taken away by the draw-off rollers 61., 62, behind which it is in a known not represented manner wound in the not represented winding device. The spinning electrode 2 may be created in any known manner, while in the represented example of embodiment is represented the rotating spinning electrode formed of rotating cylindric body, whose surface section extends into reservoir of polymer matrix being subjected to spinning.

The collecting electrode 3 contains the endless belt 3J. made of electrically conductive material, which in the spinning chamber λ_ is mounted on a pair of stretching shafts 32, 33. In the belt 3J. the openings 311 are performed. The endless belt 3J. forms between the stretching shafts 32, 33 two

sections, the guiding section, which is in contact with the substrate material, and the reversible section. Between the guiding section and reversible section of endless belt 31_ and stretching shafts 32, 33 the underpressure chamber 34 is arranged, whose inner space is coupled with a known not represented source of underpressure, while the underpressure chamber 34 is positioned behind the guiding section of the belt 3J. in direction from the spinning electrode 2 to the collecting electrode 3. Belt 3J. of the collecting electrode 3 in a known not represented manner is connected to the high voltage source of opposite polarity than the spinning electrode 3 or grounded. At least one of the stretching shafts 32, 33 of the collecting electrode is coupled with a not represented drive, which ensures its forced rotation in direction corresponding to the direction of motion of substrate material 4, while the rotation speed is by some of the known methods regulated according to the speed of motion of the substrate material 4. The substrate material 4 is guided on a guiding section of endless belt 31.. During the spinning process the substrate material 4 moves through the spinning chamber 1 between the spinning electrode 2 and the collecting electrode 3, while it is in contact with surface of the guiding section of the endless belt 3J[ of the collecting electrode. The air or other gas from the space of spinning chamber 1_is sucked in through the openings 311 in the endless belt 31. by the underpressure chamber 34, thus the substrate material 4 is kept in contact with surface of the guiding section of the endless belt 3J. and during the spinning process the nanofibres are deposited on it. Suction of the air or other gas from the space of the spinning chamber 1 contributes also to depositing of produced nanofibres to the substrate material 4. The formed layer 41 of nanofibres is taken away together with the substrate material by means of a pair of the draw-off rollers 61., 62.

In embodiment according to the Fig. 2 the endless belt 3J. of the collecting electrode is provided with the tips 312 on the outer side. Embodiment of the tips 312 and the belt 3J. of the collecting electrode may be various according to the technological conditions of spinning, according to the kind of the polymer matrix subjected to spinning, according to the application of the produced layer of nanofibres, etc. The tips 312 are designated especially for

improvement of transport of the substrate material 4 formed especially of fine webs of a low linear cohesion at relatively high thickness. When the substrate material 4 passes around the collecting electrode 3 the tips 312 extend into the substrate material 4 and they penetrate it at least partially and subsequently exit from the substrate material 4 again. By this the tips 312 exactly determine the speed of motion of substrate material 4, its position and stretching of substrate material 4 between the collecting electrodes 3 of individual one after another arranged spinning units.

In embodiment according to Fig. 2 the belt 3J. of the collecting electrode 3 is made of electrically conductive material as well as the tips 312. Length of the tips 312 corresponds to thickness of substrate material 4 or it is smaller. The peaks of the tips 312 during passage through the spinning space remain inside the substrate material 4 or they are to be found in area of its surface, on which the nanofibres are deposited. At low concentration of the tips 312 arranged in the belt 3J. the electrostatic field between the spinning electrode 2 and the collecting electrode 3 is induced between the active part of the spinning electrode 2 and against it positioned section of the belt 3J. of the collecting electrode 3, while in the place of the tips 312 electrostatic field is induced between the peak of the tip 312 and the active section of the spinning electrode 2. On the peak of electrically conductive tip 312 the brought charge is concentrated into a point singular charge, which contributes to producing of nanofibres especially in initial phase of the spinning process. The produced nanofibres are deposited on surface of substrate material 4. At high concentration of the tips 312 electrostatic field is induced between the active section of the spinning electrode 2 and peaks of the tips 312 to be found in the given moment against this active section of the spinning electrode 2. At this embodiment the peaks of tips 312 form the grid of singular charges. The produced nanofibres are deposited on surface of the substrate material 4.

In not represented embodiment the belt 31_ of the collecting electrode 3 is made of electrically nonconducting material and in it there are mounted the tips

312 made of electrically conductive material, while the dimensions of the tips

312 are identical as at the previous embodiment. The tips 312 are connected to

high voltage source of opposite polarity than the spinning electrode 2 or grounded. Electrostatic field is induced between the peaks of the tips 312 and the active section of the spinning electrode 2 and the produced nanofibres are deposited on surface of the substrate material 4. In advantageous embodiment of the collecting electrode 3 formed of the endless belt 3J_ made of electrically nonconducting material with the tips 312 made of electrically conductive material, are to the high voltage source connected only those tips, whose peaks are to be found against the spinning electrode 2. At this embodiment the stretching shafts 3_1, 32 of the endless belt 3_1 may be mounted outside the spinning chamber λ_. Also the reversible section of the endless belt 3J. may pass outside of the spinning chamber ±.

In not represented embodiment the belt 3J. of the collecting electrode 3 is made of electrically conductive material and in it the tips 312 made of electrically nonconducting material are mounted. In case of installation of such collecting electrode 3 into the spinning unit of the device according to the invention, electrostatic field is induced between the active section of the spinning electrode 2 and against it positioned section of the belt 3J. of the collecting electrode, while the tips 312 exert only function of transportation and maintaining of position of the substrate material 4 and they may be longer than the thickness of the substrate material 4.

All embodiments of the endless belt 3_1 of the collecting electrode 3 equipped with tips 312 may be provided with openings 3_H in the belt 31., while to the rear side of the belt 3J. the underpressure chamber 34 is assigned. The openings 311 are performed between the tips 312 and serve to sticking of the substrate material_4 to the belt 31. of the collecting electrode 3.

List of referential markings

1 spinning chamber

2 spinning electrode

3 collecting electrode

31 endless belt

311 openings in the belt

312 tips

32, 33 stretching shafts

34 underpressure chamber

4 substrate material

41 layer of nanofibres

51 , 52 feeding rollers

61 , 62 draw-off rollers