MARES, Ladislav (Sramkova 22, Liberec, 460 10, CZ)
| CLAIMS 1. A method for deposition of functional layer of polymeric nanofibres on a surface of a substrate, at which on the surface of the substrate an auxiliary layer of polymeric material in the form of nanofibres and/or nanoparticles and/or microfibres and/or microparticles is deposited electrostatically, characterised in that, the nanofibres and/or nanoparticles and/or microfibres and/or microparticles of the auxiliary layer of polymeric material are during deposition and/or after deposition on the substrate dissolved on their surfaces, due to which they adhere well to the substrate, and subsequently on nanofibres and/or nanoparticles and/or microfibres and/or microparticles of the auxiliary layer of polymeric material, being dissolved on their surfaces, the functional layer of polymeric nanofibres is deposited, which adheres well to the auxiliary layer of polymeric material. 2. The method according to the claim 1 , characterised in that, the nanofibres and/or nanoparticles and/or microfibres and/or microparticles of the auxiliary layer of polymeric material are dissolved on their surfaces by vapours of a solvent. 3. The method according to the claim 1 or 2, characterised in that, the nanofibres and/or nanoparticles and/or microfibres and/or microparticles of the auxiliary layer of polymeric material are dissolved on their surfaces by aerosol of a solvent. 4. The method according to any of the previous claims, characterised in that, for the nanofibres and/or nanoparticles and/or microfibres and/or microparticles of the auxiliary' layer of polymeric material are dissolved on their surfaces by increased temperature. 5. The method according to any of the previous claims, characterised in that, the nanofibres of the functional layer of polymeric nanofibres are during their contact with nanofibres^ and/or nanoparticles and/or microfibres and/or microparticles of the auxiliary layer of polymeric material dissolved on surfaces by the solvent contained in nanofibres and/or nanoparticles and/or microfibres and/or microparticles of the auxiliary layer of polymeric material. 6. The method according to any of the previous claims, characterised in that, the nanofibres of the functional layer of polymeric nanofibres are during their contact with nanofibres and/or nanoparticles and/or microfibres and/or microparticles of the auxiliary layer of polymeric material dissolved on surfaces by increased temperature of nanofibres and/or nanoparticles«and/or microfibres and/or microparticles of the auxiliary layer of polymeric material. |
Technical field
The invention relates to a method for deposition of functional layer of polymeric nanofibres on a surface of a substrate, by which on the surface of the substrate an auxiliary layer of polymeric material in the form of nanofibres and/or nanoparticles and/or microfibres and/or microparticles is deposited electrostatically.
Background art
One of the greatest problems up to now obstructing an adequate utilisation of polymeric nanofibres in an industrial scale is their low adhesion to substrate materials, on which are these nanofibres during their production through electrostatic spinning deposited and in combination with which they should be used. These substrate materials are depending on requirements and the intended manner of utilisation e.g. filtration, papers of various types, textiles of spunbond, meltblown, scrim, reemay type, etc., but also any other materials not only with smooth but also with rugged surface. The international patent application WO 03045875 discloses a composite comprising substrate material, on which by means of chemical bond the layer of nanofibres is attached. This chemical bond is created so that surface of the substrate material is still before deposition of the layer of nanofibres partially etched by suitable solvent, which subsequently partially dissolves also the deposited nanofibres. Once the solvent is evaporated, a relatively strong and resistant bond of nanofibrous layer to the substrate is secured. The substantial disadvantage of this solution is a very limited range of applicable substrates and polymers for production of nanofibres as their bond is conditioned by usage of such a solvent which is able to dissolve both the substrate material as well as the material of polymeric nanofibres deposited or just being deposited on the substrate. The solution according to WO 03045875 is due to mentioned disadvantages, with exception of small number of certain combinations of substrate materials and materials of nanofibres, not suitable for industrial applicability.
US 2005/0192622 further discloses several other methods how to increase adhesion of layer of polymeric nanofibres to the substrate. One of them consists in that on the substrate a primary layer of polymeric material in the form of droplets is first deposited through electrostatic spraying , on which subsequently the covering layer of polymeric nanofibres is ^ deposited through electrostatic spinning The primary layer is before deposition of the covering layer, during it or after it dissolved in a suitable manner, for example by dipping into the solvent or by exposition to an increased temperature, while it binds the covering layer of nanofibres to the substrate after drying. Nevertheless this procedure shows a number of disadvantages, out of which the most ultimate one consists in that the material of covering layer of nanofibres must always feature a higher melting point or a higher resistance against the used solvent than the material of the primary layer, in order to melt only the material of the primary layer and not the material of the covering layer through application of the increased temperature or the solvent , and thus keeping its nanofibrous morphology. This requirement restricts, similarly like in case of WO 03045875, very distinctly the applicable materials and their combinations, and in a real practice reduces applicability of this procedure. ' Moreover, during dipping into the solvent it is not possible either to observe or to control the rate of dissolved material of the primary layer, which leads either to insufficient dissolution of material of the primary layer and its too fast drying, or on the contrary to excessive dissolution of material of the primary layer and its turning into more or less continuous film, and' due to this to worsened permeability and further characteristics of the prepared composite. Of course, this further restricts its
1 practical applicability. Moreover, during this procedure it is not possible to secure that the primary as well as the covering layer of polymeric material is not separated from the substrate? ( Due to fast drying neither one of the above mentioned solutions is suitable for utilisation during electrostatic spinning of polymer melts.
The goal of the invention is to propose a method for deposition of a layer of polymeric nanofibres on a surface of an arbitrary substrate, which would remove or at least reduce disadvantages of the prior art, secure a sufficient adhesion of layer of nanofibres to the substrate and which would be applicable even in case of electrostatic spinning of polymer melts.
Principle of the invention/
Goals of the invention have been achieved by a method for deposition of functional layer of polymeric nanofibres on a surface of a substrate at which on the surface of the substrate an auxiliary layer of polymeric material in the form of nanofibres and/or nanoparticles and/or microfibres and/or microparticles is deposited electrostatically, ' ,}. whose principle consists in that the nanofibres and/or nanoparticles aήd/or microfibres and/or microparticies of the auxiliary layer of polymeric material are during deposition and/or after deposition on the substrate dissolved on their, surfaces, thanks to which they adhere well to the substrate. Subsequently on nanofibres and/or nanoparticles and/or microfibres and/or microparticles dissolved on their surfaces the functional layer of polymeric nanofibres is, deposited, which adheres well to the auxiliary layer of polymeric material. Through r .this a high adhesion of the functional layer of nanofibres in principle to aηy . surface and material is secured.
For small material in the auxiliary layer it is convenient to use for surface dissolution of nanofibres and/or nanoparticles and/or microfibres and/or; " , microparticles of the auxiliary layer of polymeric material vapours of the solyent. At its greater quantity, aerosol of the solvent may be used. < , .'; ;
For certain types of polymeric material it is more convenient, or eventhe only variant, to use ' for the surface dissolution of nanofibres and/or nanoparticles and/or ' microfibres and/or microparticles an increased temperature. At the same;time it is possible to combine increased temperature with delivery of vapours or aerosol of the solvent for reaching the best result and faster dissolution.
After deposition of polymeric nanofibres of the functional layer on surface dissolved nanofibres and/or nanoparticles and/or microfibres and/or microparticles of the auxiliary layer of polymeric material there may also occur their surface dissolution, by which even greater strength of binding of the functional layer, the auxiliary layer and the substrate is ensured. Polymeric nanofibres of the functional layer are at the same time on their surface dissolved due to residues of the solvent in nanofibres and/or nanoparticles and/or microfibres and/or .^m jcroparticles of the auxiliary layer of polymeric material or their increased temperature.
Examples of embodiment
For performance of . the method for deposition of -functional layer of polymeric nanofibres on the surface of any substrate * according to the invention, after a simple structural modification, a device for electrostatic spinning of polymeric solutions, working on any of the known principles may be utilised.
Principle of the invention [ will be further explained on an example of the deviceaccording to CZ PV 2006-243, which comprises in one spinning chamber two spinning electrodes of elongated cylindric shape and against them arranged collecting electrode, which induces with each of the spinning electrodes just one electrostatic spinning field. These electrostatic spinning fields are at the same time mutually separated by insulating plates, while through both of them the substrate material, for example a planar textile is moving, , on whose surface in each electrostatic field a layer of polymeric nanofibres is being deposited. This arrangement enables to spin in each of the electrostatic fields any polymeric matrix with arbitrary required parameters of surface density, diameter of nanofibres etc. ; ,^ *
When performing the, method according to the invention, in the first electrostatic spinning field on, the substrate textile there is evenly deposited an auxiliary layer of polymeric material in a form of a layer of polymeric nanofibres, whose surface density varies, in dependence on the type of polymeric matrix, content of a solvent in it, speed of motion of the substrate textile and requirements on the resultant product, from 0,05 up to 1 g/m 2 , usually in the range from 0,1 to 0,7 g/m 2 , nevertheless in specific examples of embodiment the surface density of the auxiliary layer may be increased even above 1 g/m 2 . Electrostatic spinning upon usage of rotating cylindric spinning electrode simultaneously secures uniform distribution of polymeric material of the auxiliary layer on the substrate textile. The purpose of the auxiliary layer is to increase the adhesion between the substrate textile and the functional layer of nanofibres.
Subsequently the nanofibres of the auxiliary layer of polymeric materialare depending on the type of polymeric matrix and its quantity in the auxiliary layer dissolved on their surfaces by action of vapours of a solvent, aerosol of the solvent, increased temperature or by combination of any of these factors. Through an easy ^ setting of quantity of solvent brought into contact with the auxiliary layer, of polymeric material and/or setting of increased temperature, possibly also -the course of reaching it, also the quantity of dissolved material of the ^ auxiliary layer of polymeric material can be easily controlled. At only surface dissolution, the nanofibres of the auxiliary layer of polymeric material preserve their original shape and the even distribution on the substrate textile, nevertheless they adhere to -it more closely, while a part of polymeric material of the auxiliary layer may at the* same time may penetrate into the inner structure of the substrate textile. By this a high adhesion of the auxiliary layer of polymeric material to the substrate textile is secured, without expressive influence on; characteristics of composite created in such a way, because relatively small quantity of polymeric material in the auxiliary layer and only surface dissolution of nanofibres ensures, that a continuous film impervious to air is not created on the surface of the substrate textile, and that the substrate textile keeps even after deposition and surface dissolution of nanofibres of auxiliary layer of polymeric material in principle its parameters, especially as regards to its air permeability and pressure drop. At greater quantity of polymeric material in the auxiliary layer, for the purpose to prevent forming of polymeric film a stream of 'air or other suitable gas may be used. At the same time this can also promote the surface dissolution of polymeric nanofibres of the auxiliary layer, as it can be pre-heated to the required temperature and/or it may serve to carry and/or to deflect the vapours and/or aerosol of the solvent.
The means for bringing the vapours and/or aerosol of the solvent to the auxiliary layer of polymeric material formed of nanofibres and/or means for increasing its temperature are preferably installed in vicinity of exit of the substrate textile from the first electrostatic spinning field and/or entrance of the substrate textile into the, second electrostatic spinning field and/or between them, possibly for portions of the path of the substrate textile. Preferably each of them is controllable independently on others, so that in each moment there is achieved just the required quantity of vapours and/or aerosol and/or thermal energy brought to the substrate textile and to the auxiliary layer of polymeric material. , ^
In other examples, when for the surface dissolution of nanofibres of the auxiliary layer of polymeric, material the vapours and/or aerosol of solvent are used, they may be applied to the substrate textile still before depositing the auxiliary layer of polymeric .material and so the nanofibres of auxiliary layer do not become dry after deposition on the substrate textile or dissolve on their surfaces immediately after their deposition.
Next to this, the nanofibres of the auxiliary layer may be dissolved on their surfaces by action of vapours and/or aerosol of the solvent and/or increased temperature stilh-b ' efore their deposition on the substrate textile, during their deposition. This* is especially advantageous in cases, when the used polymeric material of^the auxiliary layer becomes due to its chemical properties and/or conditions in electrostatic spinning field diyquickly, and so on the substrate textile already would be deposited totally or nearly totally solidified nanofibres.
Immediately after' the- surface dissolution of nanofibres of the auxiliary layer of polymeric material, the substrate textile with the auxiliary layer is brought into the second electrostatic field, where on these nanofibres a functional layer of polymeric nanofibres with parameters, which are given by the considered utilisation of the final product, is deposited. Rests of solvent in the auxiliary layer of polymeric material and/or its increased temperature further causes partial dissolution of polymeric nanofibres of the functional layer on their surface, due to which the functional layer adheres well to the auxiliary layer of polymeric material and to the substrate textile, so that after evaporation of the solvent and/or reduction of the temperature, sufficiently high adhesion is achieved between the substrate textile, the auxiliary layer of polymeric material and the functional layer. " This enables utilisation of the final product in applications, where the functional layer of nanofibres increases or improves properties of the substrate textile and is subjected to mechanical stress, for example in filtration of liquid ' s/ in surface treatment of products, etc.
In another variant^, the method according to the invention the substrate textile with surface dissolved , nanofibres of the auxiliary layer of polymeric material is brought into the second electrostatic field after the temperature of the substrate textile with the ( auxiliary layer is reduced and/or concentration of rests of solvent in it is reduced, through which the dissolution of polymeric nanofibres of the functional layer is completely removed or reduced in a required rate.
This can be besides also prevented e.g. ' by usage of different polymeric materials with different chemical and/or physical properties for preparation of nanofibres of the auxiliary layer and nanofibres of the functional layer.
Deposition of the auxiliary layer in the form of polymeric nanofibres through electrostatic spinning ensures its uniformity all over the whole surface of the substrate textile, thus , ' also uniform adhesion of the functional layer of nanofibres to it. This solution is simultaneously structurally as well as operationally the simplest one, as it does not requires installation and operation of elements other than of twσ identical spinning electrodes in combination with which, only one collecting' electrode may be utilised.
The quantity of polymeric material in the auxiliary layer is so small, that in principle it does not play any role in what formations it is to be found. Therefore for creation and deposition ι of the auxiliary layer of polymeric material even other methods of electrostatic spinning than those utilising some of the above mentioned spinning electrodes, or generally even other principles than the electrostatic spinning, may be used. So the auxiliary layer of polymeric material may be created, next' to electrostatic spinning, e.g. through electrostatic spraying when the polymeric material moves towards the substrate textile in the form of nano-droplets and/or micro-droplets of polymeric matrix, which are by gradual solidification transformed into nanoparticles and/or microparticles of polymeric material, but also through any other procedure, which ensures positioning of the required quantity of polymeric material on the surface of the substrate textile, this either in the form of nanofibres, microfibres, nanoparticles, microparticles or their mixtures.
The functional layer of nanofibres may be created also through any~ technique of electrostatic spinning, e.g. through spinning from the nozzle (nozzles) nevertheless the 'electrostatic spinning upon usage of elongated cylindric electrode described e.g. in CZ patent 294274 seems to be the most useful at present. Utilisation 5 of this spinning electrode, possibly of the rotating cord spinning electrode according to WO 2008028428, static cord spinning electrode according to CZ PV 2007 - 485 or spinning electrode created according to CZ PV 2008,,-,, 442 directly of the polymeric matrix subject to spinning with free surface, secures at the same time, that the-functional layer of nanofibres will be uniform -^over its entire surface.* Due to this reason it is advantageous to use any of these spinning electrodes also for creating the auxiliary layer of polymeric material. After then, for both spinning electrodes one common collecting electrodehmay be used, possibly for each of them any number of any known type -df collecting electrodes may be used, according to the requirements on properties and parameters of the given electrostatic spinning field. • ' ' U 1 -
The functional layer of nanofibres may be created of polymeric nanofibres of any electrostatically spinnable polymer in the form of solution or polymer melt, possibly the ,, nanofibres of the functional layer may contain various active substances,;, like e.g. particles of photodynamic sensitizers according to CZ PV 2006-432, particles of low-molecular substance, or metal nanoparticles according to CZ PV 2005-225, etc., which spreads possibilities of their utilisation even on further applications outside filtration.
Upon usage of the invention it is possible, with good results, to deposit the layer of functional nanofibres in principle on any substrate, not only on the textile described in example, of embodiment. The auxiliary layer of nanofibres and their surface dissolution, possibly in combination with surface dissolution of nanofibres of the functional layer, secures a sufficient adhesion of the functional layer in principle to any surface and material. The functional layer of nanofibres may be therefore deposited not only on planar units such as filtration paper or filtration textile, but also, on .surfaces in principle of any products from any material, both finished or designed for further processing.
The described procedure eliminates disadvantages of the background art in such a manner that it enables any combination of polymeric material of auxiliary layer with material of the functional layer of nanofibres, simultaneously secures a high adhesion .of .the auxiliary layer to the substrate immediately after depositing the auxiliary layer or during it. The auxiliary layer as well as the functional layer of nanofibres jat the same time may be prepared both from the same polymeric material, orjjom various polymeric materials, without necessity to seek for suitable combinations of their properties, especially their resistance towards the given solvent or melting point. This of course not only substantially spreads the portfolio of applicable polymeric materials almost without limitation, but also significantly reduces financial as well as technological demands of the whole process.
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