EP2607528A1 - Adhesion optimisation of fibres produced by means of dispersion electro-spinning through variation of the softening point of the latex polymer - Google Patents

Abstract

Producing fiber webs by dispersion electrospinning of primary or secondary aqueous latex polymeric dispersions, comprises (i) adding 0.5-15 wt.% water soluble matrix polymers to particle dispersions before spinning, where the matrix polymer is chosen such that it does not cause flocculation of the latex polymer, and (ii) electro-spinning at 0-100[deg] C, where the latex polymer particles have a diameter = 200 nm, the softening point of the latex polymer comprising the particles is at least 20[deg] C below the spinning temperature, and the aqueous dispersions contain 5-50 wt.% particles. Independent claims are also included for: (1) preparing the primary aqueous latex polymer particles by an emulsion polymerization, comprising (a) flushing a reaction vessel with a protective gas including argon and nitrogen, (b) providing degassed water, (c) adding at least one monomer, (d) adding a surfactant, (e) vigorously stirring the mixture, (f) adding a free radical initiator, (g) further stirring for 15-180 minutes at a reduced stirring rate, and (h) optionally cooling the reaction mixture to room temperature and stopping the stirring process, where the steps (a) to (g) are carried out at 0-100[deg] C; and (2) electrospun fiber webs obtainable by the above mentioned method.

Description

The present invention provides a process for making electrospun fiber webs having improved adhesion and fiber webs obtainable therefrom.

Description and introduction of the general field of the invention

The present invention relates to the fields of macromolecular chemistry, polymer chemistry and materials science.

State of the art

A major problem with the use of nanofibers is the poor adhesion of the fibers to substrates as well as the fibers to each other within the nanofiber web. This leads to mechanically unstable coatings.

In previously used methods of adhesion improvement carried out by pretreatment of the substrate or by aftertreatment of the produced nonwovens. This requires an additional step in production.

An important point to improve adhesion is the formation of bonds between the electrospun fibers themselves and the fibers as well as the substrate.

The question arose as to whether the formation of such contact points can be promoted by a suitable choice of the polymers used.

Processes for the preparation of nanofibres and mesofibres from aqueous colloidal dispersions of at least one water-insoluble and at least one water-soluble polymer have been described for the first time in US Pat WO 2006/089522 A1 described. The WO 2008/022993 A2 represents an evolution of the WO 2006/089522 A1 in the WO 2008/022993 A2 Surfactants are added to the spinning solution to improve the properties of the fibers. The WO 2009/010443 A2 again represents an evolution of the WO 2008/022993 A2 in the WO 2009/010443 A2 For example, the properties of the electrospun fibers are further improved by using a water-insoluble polymer whose glass transition temperature is at most 15 ° C below or above the process temperature for electrospinning. However, no latex polymer particles are spun in all three mentioned publications.

For the first time, the present invention provides the ability to produce electrospun fiber webs with improved adhesion optimization that do not require an additional operation to improve adhesion to substrates.

task

The object of the invention is to provide a process for the production of electrospun fiber webs with improved adhesion and fiber webs obtainable therefrom.

Solution of the task

• die Erweichungspunkte der Latexpolymere, aus denen die Partikel bestehen, mindestens 20°C unterhalb der Spinntemperatur liegen,
• die wässrigen Dispersionen der Partikel 5 bis 50 Gew.-% Partikel enthalten,
• den Partikeldispersionen vor dem Spinnen 0,5 bis 15 Gew.-% eines wasserlöslichen Matrixpolymers zugegeben wird, wobei das Matrixpolymer so gewählt wird, dass es das Latexpolymer nicht zur Ausflockung bringt, und
• das Elektrospinnen bei Temperaturen von 0 bis 100°C durchgeführt wird.

The object to provide a process for the production of electrospun fiber webs with improved adhesion is achieved according to the invention by a process for producing fiber webs by dispersion electrospinning primary or secondary aqueous latex polymer dispersions, characterized in that

• the softening points of the latex polymers constituting the particles are at least 20 ° C. below the spinning temperature,
• the aqueous dispersions of the particles contain 5 to 50% by weight of particles,
• 0.5 to 15% by weight of a water-soluble matrix polymer is added to the particle dispersions prior to spinning, the matrix polymer being chosen so as not to flocculate the latex polymer, and
• the electrospinning is carried out at temperatures of 0 to 100 ° C.

It has surprisingly been found that the adhesion of nonwoven fabrics made by the dispersion electrospinning process is significantly improved when aqueous primary or secondary particle dispersions of latex polymers are used in which the softening point of the latex polymer is well below the electrospinning temperature.
According to the invention, "softening point significantly below the processing temperature" means that the softening point is at least 20 ° C. below the processing temperature.

The process according to the invention, the fiber webs obtainable therefrom and the use of these fibers are explained below.

The invention is not limited to one of the embodiments described below, but can be modified in many ways.

All of the claims, the description and the drawings resulting features and advantages, including design details, spatial arrangements and method steps may be essential to the invention both in itself and in a variety of combinations.

A dispersion in the sense of the present invention, in accordance with textbook knowledge, denotes a mixture of at least two immiscible phases, one of the at least two phases being liquid. Depending on the state of matter of the second or further phase, dispersions are subdivided into aerosols, emulsions and suspensions, the second or further phase being gaseous in the case of aerosols, solid in the case of emulsions and solid in the case of suspensions. Suspensions and emulsions are preferably used in the process according to the invention. The colloidal polymer dispersions preferably used according to the invention are also referred to in the technical language as latex.

Primary dispersions or "primary latices" are the direct result of heterophase polymerizations. Primary aqueous (polymer) dispersions are formed predominantly by emulsion polymerization, ie the particles are formed during the synthesis of the polymer molecules in water. Such dispersions have been used successfully for electrospinning, but are not known for biodegradable polymers.
Secondary dispersions are prepared by the conversion of polymers obtained in any other way into the dispersed state. So-called "artificial latices" are obtained by dispersing a polymer or a solution of a polymer in water. If a polymer solution is used, the emulsion formed first, for example be converted by evaporation of the solvent in a further step in a polymer dispersion.
In the context of the present invention, these artificial latices are referred to as secondary aqueous dispersions according to the general usage of the art. In the formation of the secondary dispersion, the polymer molecules are already present, as opposed to the primary dispersion, but no polymerization takes place.

As a natural example, plastic dispersions have the latex in the latex of the rubber plants. The synthetic products, plastic dispersions or emulsion polymers are referred to as polymer latices. For the preparation, monomeric, polymerizable liquids are emulsified in water with the aid of emulsifiers. Mycelles, accumulations of emulsifier molecules in the aqueous phase form into spherical dressings, which open up about 100 monomers in the interior. Then the monomers are polymerized by addition of initiators and heat.

The matrix polymer embeds the latex polymer fibers. Betten means that the matrix fixes the latex particles in the fiber and stabilizes them mechanically and thermally.

Upon evaporation, the latex particles approach each other until the flocculation point is reached. The strong capillary forces which now occur between the particles cause their deformation and, further, a complete coalescence to form a closed polymer film. The film formation from a plastic dispersion is highly dependent on the composition and the temperature. The minimum film-forming temperature (MFT) is the temperature at which a plastic dispersion just dries to a crack-free film. In addition, the so-called white point (WP) also has a certain significance in practice, namely the temperature at which the layer which has not yet become a closed film dressing changes into a cracked layer in the event of an increase in the drying temperature.

From the large number of test methods that are common for characterizing the mechanical film properties, the tensile and the torsional vibration test are of particular importance.

Polymers are macromolecules. Due to the size of the macromolecules, their regular arrangement in a crystal is severely hampered for kinetic reasons and sometimes even completely prevented. Therefore, the melting behavior of polymers differs significantly from the behavior of low molecular weight compounds. Instead of a clear melting point, many polymers have wide melting ranges, and sometimes only gradual softening is observed instead of melting. The heat of fusion also varies greatly from polymer to polymer. If the crystal formation of the macromolecules is completely prevented, instead of a melting temperature only a softening point is found (or instead of a freezing point a solidification point), the so-called glass point, below which the polymer is present as an amorphous solid, ie glassy. The glass transition temperature T _g is always lower than the melting temperature T _m .

In the context of the present invention, "fusion of the fibers at the contact points" means that the fibers physically fuse together at the contact points.

As electrospinnbare dispersions secondary or primary polymer dispersions with particle diameters less than or equal to 200 nm can be used. Particularly advantageous particle diameters are less than or equal to 150 nm. Advantageously, the polydispersity index (PDI) of the particles used is between 0.025 and 0.8. It is known to the person skilled in the art that it is possible to determine the PDI of nanoparticles, for example via dynamic light scattering.

Filming of the fibers is prevented by the choice of a stabilizing water-soluble matrix polymer having a glass transition temperature above the processing temperature. According to the present invention, the glass transition temperature must be at least 20 ° C above the processing temperature. In this case, the matrix polymer should stabilize the fibers sufficiently to prevent film formation, but allow a fusion of the fibers at contact points.
Advantageously, between 10 to 25 wt .-% of the fibers of the water-soluble matrix polymer, since then the fibers are both sufficiently stable and can melt at the contact points.
It is known to the person skilled in the art that when electrospinning polymer solutions which contain more than one type of polymer, the proportion of the respective polymer type in the spinning solution is not equal to the proportion of this type of polymer in the finished fiber or in the finished nonwoven fabric. If the spinning solution according to the present invention contains 0.5 to 15% by weight of matrix polymer, 10 to 25% by weight of the finished fibers consist of this matrix polymer.

Suitable water-soluble matrix polymers are selected from polyvinyl alcohol, polyvinylformamide, polyvinylamine, polycarboxylic acid, polyacrylamide, polyitaconic acid, poly (2-hydroxyethyl acrylate), poly (N-isopropylacrylamide), polysulfonic acid, polymethacrylamide, polyalkylene oxides; Poly-N-vinylpyrrolidone; hydroxymethylcelluloses; hydroxyethylcelluloses; hydroxypropyl; carboxymethyl; maleic; alginates; collagens; Gelatin, poly (ethyleneimine), polystyrenesulfonic acid; Combinations composed of two or more of the monomeric units constituting the above-mentioned polymers, copolymers composed of two or more of the monomer units constituting the aforementioned polymers, graft copolymers composed of two or more of the monomeric units constituting the aforementioned polymers, star polymers composed of two or more of them above-mentioned polymer-forming monomer units, highly branched polymers composed of two or more of the above-mentioned polymers forming monomer units and dendrimers composed of two or more of the above-mentioned polymers forming monomer units.
In an advantageous embodiment of the present invention polyvinyl alcohol (PVA) is used as the matrix polymer, wherein a 10 to 25% aqueous PVA solution used is used and the proportion of PVA in the spinning solution is 5 wt .-%.

Latex and matrix polymers are combined so that the matrix polymer does not flocculate the latex polymer. Which combinations of latex and Matrexpolymer are suitable, can be easily determined experimentally. The person skilled in the art can carry out these experiments without departing from the scope of the patent claims.

Weakly crosslinked latex polymer particles, or polymers that can be crosslinked during the spinning process or after the spinning process, are particularly suitable because of the increased thermal stability. "
By "weakly crosslinked" is meant in the context of the present invention, a degree of crosslinking less than 5%.
Crosslinking can occur before, during or after electrospinning. Advantageously, it takes place during electrospinning. If the crosslinking takes place after electrospinning, this is a crosslinking of the fibers.

The processing temperature of the polymer dispersions to be used according to the invention in electrospinning is between the melting and boiling point of the water, i. between 0 ° C and 100 ° C. Temperatures between 20 ° C and 30 ° C are advantageous.

1. a) Spülen des Reaktionsgefäßes mit einem Schutzgas, ausgewählt aus Argon und Stickstoff,
2. b) Vorlegen entgasten Wassers,
3. c) Zugabe des mindestens einen Monomers,
4. d) Zugabe eines Tensids,
5. e) starkes Rühren der Mischung,
6. f) Zugabe eines Radikalstarters,
7. g) Weiterrühren für 15 bis 180 min. bei verringerter Rührgeschwindigkeit,
8. h) optional Abkühlen des Reaktionsgemisches auf Raumtemperatur und Beenden des Rührens,

wobei die Schritte a) bis g) bei Temperaturen zwischen 0 °C und 100 °C durchgeführt werden.If primary aqueous latex dispersions are used in the process according to the invention for the production of nonwoven fabrics, these dispersions are prepared by an emulsion polymerization comprising the steps

1. a) rinsing the reaction vessel with an inert gas selected from argon and nitrogen,
2. b) presenting degassed water,
3. c) adding the at least one monomer,
4. d) addition of a surfactant,
5. e) strong stirring of the mixture,
6. f) addition of a radical initiator,
7. g) Continue stirring for 15 to 180 min. at reduced stirring speed,
8. h) optionally cooling the reaction mixture to room temperature and stopping the stirring,

wherein the steps a) to g) are carried out at temperatures between 0 ° C and 100 ° C.

Working with protective gas and the use of degassed water is imperative in the preparation of primary aqueous dispersions of latex polymer particles, since the production must be free of oxygen.

According to the method described above, the latex polymer particles are prepared by radical polymerization of the corresponding monomers. The primary latex polymers are homo- and copolymers of polystyrenes, polyvinyl chlorides, polyvinylidene fluorides, poly-α-methylstyrenes, polymethacrylates, polyacrylates, polyacrylonitriles, polymethacrylonitriles, polybutadiene, neoprene, polyisoprene, polyvinyl acetates, polytetrafluoroethylene, polyesters, polyethers, polycarbonates, polyurethanes, polyamides, Polyureas, polyamideimides, polyimides, polylactides, polyesteramides, polyimidazoles, polyketones, poly (p-xylylenes) polyolefins, polyetherketones, polysulfones, polythiazoles, polyoxazoles, polyarylenylenes, polysilanes, polysiloxanes, ormocerenes. The preparation of these particles is carried out by radical polymerization of the corresponding monomers by means of radical polymerization. At least one type of monomer is used in the process according to the invention for the preparation of the primary particles, but it is also possible to use two or more types of monomer.

In principle, ionic and nonionic surfactants can be used in the process according to the invention for the preparation of the primary latex polymer particles. Advantageously, an ionic surfactant is used, since ionic surfactants stabilize the fibers better than nonionic. An anionic surfactant is particularly preferably used.

• Alkylcarboxylate R-COO-Na⁺, mit R = gesättigter oder ungesättigter, linearer Alkylrest, je nach Fettsäuretyp
• Alkylbenzolsulfonate (ABS): C_nH_2n+1-C₆H₄-SO₃-Na⁺, zum Beispiel Natriumdodecylbenzolsulfonat
• sekundäre Alkansulfonate (SAS): C_nH_2n+1-SO₃-Na⁺
• Fettalkoholsulfate (FAS): H₃C-(CH₂)_n-CH₂-O-SO₃-Na⁺ [n = 8-16], zum Beispiel Natriumlaurylsulfat

Suitable anionic surfactants are, for example, carboxylates, sulfates and sulfates. Examples include:

• Alkylcarboxylates R-COO-Na ⁺ , with R = saturated or unsaturated, linear alkyl radical, depending on the fatty acid type
• Alkylbenzenesulfonates (ABS): C _n H _{2n + 1} -C ₆ H ₄ -SO ₃ -Na ⁺ , for example, sodium dodecylbenzenesulfonate
• secondary alkanesulfonates (SAS): C _n H _{2n + 1} -SO ₃ -Na ⁺
• Fatty Acid Sulfates (FAS): H ₃ C- (CH ₂ ) _n -CH ₂ -O-SO ₃ -Na ⁺ [n = 8-16], for example, sodium lauryl sulfate

Suitable cationic surfactants are, for example, quaternary ammonium compounds, e.g. DSDMAC (distearyldimethylammonium chloride) or 2-methacryloxy-ethyldodecyldimethylammonium bromide.

• Polyalkylenglycolether (Fettalkoholethoxylate (FAEO))
  
           CH₃-(CH₂)₁₀-₁₆-(O-C₂H₄)_1-25-OH
  
  
• Fettalkoholpropoxylate (FAPO) CH₃-(CH₂)_10-16-(0-C₃H₆)_1-25-OH
• Alkylglucoside wie Polysorbat 20 (Tween 20)
• Alkylpolyglucoside (APG) CH₃-(CH₂)_10-16-(O-Glykosid)_1-3-OH
• Oktylphenolethoxylate C₈H₁₇-(C₆H₄-(O-C₂H₄)_1-25-OH, z.B. Octoxinol-9 (Triton X-100)
• Nonylphenolethoxylate C₉H₁₉-(C₆H₄)-(0-C₂H₄)_1-25-OH, z.B. Nonoxinol-9

Suitable nonionic surfactants are, for example

• Polyalkylene glycol ethers (fatty alcohol ethoxylates (FAEO))
  
  CH ₃ - (CH ₂ ) ₁₀ - ₁₆ - (OC ₂ H ₄ ) _1-25 -OH
  
  
• Fatty alcohol propoxylates (FAPO) CH ₃ - (CH _{2) 10-16} - (0-C ₃ H _{6) 1-25} -OH
• Alkyl glucosides such as polysorbate 20 (Tween 20)
• Alkyl polyglucosides (APG) CH ₃ - (CH _{2) 10-16} - (O-glycoside) _1-3 -OH
• Octylphenolethoxylates C ₈ H ₁₇ - (C ₆ H ₄ - (OC ₂ H ₄ ) _1-25 -OH, eg octoxinol-9 (Triton X-100)
• Nonylphenolethoxylates C ₉ H ₁₉ - (C ₆ H ₄ ) - (O-C ₂ H ₄ ) _1-25 -OH, eg nonoxinol-9

• einem anorganischen Peroxid, z.B. Wasserstoffperoxid oder Peroxodisulfate, wie die Mono- oder Di-Alkalimetall- oder Ammoniumsalze der Peroxodischwefelsäure, wie beispielsweise deren Mono- und Di-Natrium-, -Kalium- oder Ammoniumsalze oder
• einem organisches Peroxid, z.B. einem Alkylhydroperoxide, beispielsweise tert.-Butyl-, p-Menthyl- oder Cumylhydroperoxid, oder
• einer Azoverbindung, z.B. 2,2-Azobis-(N,N'-dimethylen-isobutyramidin)dihydrochlorid, 2,2'-Azobis-(2-amidinopropan)dihydrochlorid, 2,2'-Azobis[2-(2-imidazolin-2-yl)propan]dihydrochlorid, 4,4'-Azobis-[4-cyanovaleriansäure).

The radical starter is selected from

• an inorganic peroxide, for example hydrogen peroxide or peroxodisulfates, such as the mono- or di-alkali metal or ammonium salts of peroxodisulfuric acid, for example their mono- and di-sodium, potassium or ammonium salts or
• an organic peroxide, for example an alkyl hydroperoxide, for example tert-butyl, p-menthyl or cumyl hydroperoxide, or
• an azo compound, eg 2,2-azobis (N, N'-dimethylene-isobutyramidine) dihydrochloride, 2,2'-azobis (2-amidinopropane) dihydrochloride, 2,2'-azobis [2- (2-imidazoline) 2-yl) propane] dihydrochloride, 4,4'-azobis [4-cyanovaleric acid].

The reaction temperature in the preparation of the primary latex polymer particles may be between the melting and boiling points of the water, ie between 0 ° C and 100 ° C. Advantageously, it is at 60 to 70 ° C. If potassium peroxodisulfate is used as radical initiator, the reaction temperature is advantageously between 45 and 95 ° C.
If the steps a) to g) are carried out at temperatures above room temperature, the reaction mixture is cooled to room temperature in step g).

The stirring speed can be varied in the case of the apparatus described in the embodiments 1.1 to 1.3 between 250 and 2,500 rev / min.

In the preparation of the dispersions, the reaction temperature is advantageously 45 to 95 ° C.

The person skilled in the art is aware that he can control the particle size via the stirring speed. "Particle size" is used synonymously with "average particle diameter". Which stirring speed is required for the desired particle size depends, as is known, also on the size and geometry of the reaction apparatus used and on the type of stirring device. The skilled person can easily and without going beyond the scope of the claims determine which stirring speed he must set in his Appartur to obtain the desired particle size.

Furthermore, the particle size is controlled by the amount of surfactant added. The more surfactant added, the lower the particle size obtained. The person skilled in the art can easily determine which particle size he receives as a function of the amount of surfactant added.

Advantageously, the polydispersity index (PDI) of the particles used is between 0.025 and 0.8.

The reaction time required to prepare the primary aqueous latex polymer particles is between 15 and 180 minutes. The end of the reaction, i. the end of particle formation, as known in the art, can be determined by measuring the internal temperature. After consumption of all monomers, the polymerization reaction ends and the temperature subsequently drops.

If, on the other hand, secondary aqueous latex polymer particle dispersions are used in the process according to the invention for producing fibrous webs, the polymers on which the particles are based are selected from polyesters, polyethers, polycarbonates, polyurethanes, polyamides, polyureas, polyamideimides, polyimides, polylactides, polyesteramides, polyimidazoles, polyketones, polyurethanes. (-p-xylylenes) polyolefins, polyether ketones, polysulfones, polythiazoles, polyoxazoles, polyarylenylenes, polysilanes, polysiloxanes, ormocerenes, natural polymers, cellulose, cellulose acetate and collagen.
Electrospinning itself is known. In this case, a solution of the spinning polymer is exposed to a serving as an electrode edge a high electric field. For example, this can be done by extruding the solution to be spun in an electric field under low pressure through a cannula connected to one pole of a voltage source. The result is a flow of material directed at the counterelectrode, which solidifies on the way to the counterelectrode. This creates a disordered fiber fleece.
Optionally, the spinning solution may contain other components in addition to the polymer or polymer blend.

In electrospinning, a voltage of 10 to 30 kV is applied to the cannula. Advantageous are about 20 kV. A voltage of 0 to 30 kV is applied to the counterelectrode, advantageously 10 kV. The diameter of the cannula is advantageously 0.5 to 1.2 mm; in Embodiment 2, it was 0.9 mm. Cannula or cannulas and counterelectrode are at a distance of 5 to 50 cm from each other; in Example 2, it was 20 cm. The feed of the syringe plunger should in the embodiment 2 and Fig. 3 shown device between 0.1 and 2 ml of spinning solution per hour; in example 2 it was 2 mL / h. The solvent used in the process according to the invention is water. The concentration of the particles in the spinning solution is 5 to 50 wt .-%, preferably 20 wt .-%. The concentration of the water-soluble matrix polymer in the spinning solution is 1 to 10%, advantageously 5% by weight.
The diameters of the fibers in the fiber webs obtainable by the process according to the invention are between 200 and 1200 nm.

Optionally, during the spinning process between the nozzle and the counter electrode, a frame made of a conductive material can be introduced, for example a rectangular frame. In this case, the fibers are deposited in the form of an oriented nonwoven on this frame. This process for producing oriented meso- and nanofiber nonwovens is known to the person skilled in the art and can be applied without departing from the scope of the patent claims.

The diameter of the fibers obtained is preferably 200 nm to 1200 nm. Fiber diameters between 200 nm and 700 nm are particularly preferred.

The person skilled in the art knows how to adjust the fiber diameter. For example, the fiber diameter becomes larger the more viscous, i. the more concentrated the polymer solution to be spun. The higher the flow rate of the spinning solution per unit time, the larger the diameter of the obtained electrospun fibers. Furthermore, the fiber diameter depends on the surface tension and the conductivity of the spinning solution. This is known to the person skilled in the art and he can apply this knowledge without departing from the scope of the patent claims.

Nonwovens made of different fibers can be produced by parallel and / or layered electrospinning processes.
In parallel spinning two needles and a counter electrode are used, the two needles advantageously have a distance of 1 to 20 cm from each other. The remaining parameters are adjusted with a single cannula, as in electrospinning.

In an advantageous embodiment of the method according to the invention, a single aqueous dispersion of primary or secondary latex polymer particles electrospun. The spinning takes place inevitably using a single cannula.

In a further advantageous embodiment of the process according to the invention, two aqueous dispersions of primary or secondary latex polymer particles are electrospun. As described in the method according to the invention, a water-soluble matrix polymer is added to each of the two particle dispersions prior to spinning, it being possible to use two identical or two different latex polymers and, independently of this, two identical or two different matrix polymers for the two dispersions. The spinning of two aqueous dispersions of primary or secondary latex polymer particles takes place by means of parallel and / or layered electrospinning.

By parallel and / or guided layer-wise electrospinning processes also the bonding fibers can be incorporated into mixed fiber webs with fibers consisting of other polymers and achieve in this way an adhesion improvement.

Both in electrospinning with a single cannula and in parallel and / or layered spinning dispersions are advantageously used with particle diameters between 50 nm and 200 nm. The fibers obtained after electrospinning have diameters of 200 nm to 1200 nm.

The electrospinning with a cannula and the parallelspinning are in the Fig. 3 or 4 shown.

• durch Bestrahlen,
• durch physikalische Verknüpfung, z.B. durch ionische Wechselwirkungen, Kristallite oder Phasenseparation in Blockcopolymeren,
• durch chemische Verknüpfung, z.B. durch die Bildung von Estern, Amiden, Ethern,
• durch thermische Behandlung,
• während des Spinnprozesses durch die Verdampfung des Wassers
• durch Behandlung der Fasern mit geeigneten Reagenzien, z.B. durch difunktionelle Moleküle, die mit funktionellen Gruppen des Polymers reagieren.

Optionally, the fibers obtained by the process according to the invention can be crosslinked. The networking can be done, for example

• by irradiation,
• by physical linkage, eg by ionic interactions, crystallites or phase separation in block copolymers,
• by chemical linkage, for example by the formation of esters, amides, ethers,
• by thermal treatment,
• during the spinning process by the evaporation of the water
• by treating the fibers with suitable reagents, for example by difunctional molecules which react with functional groups of the polymer.

Suitable crosslinkers are generally monomers which contain two, optionally also three or more ethylenic double bonds which are capable of copolymerization and which are not conjugated in the 1,3-positions. Suitable crosslinkers are compounds having two or more ethylenically unsaturated groups, such as diacrylates or dimethacrylates of at least dihydric saturated alcohols, e.g. Ethylene glycol diacrylate, ethylene glycol dimethacrylate, 1,2-propylene glycol diacrylate, 1,2-propylene glycol dimethacrylate, butanediol-1,4-diacrylate, butanediol-1,4-dimethacrylate, hexanediol diacrylate, neopentyl glycol diacrylate, neopentyl glycol dimethacrylate, 3-methylpentanedi diacrylate and 3-methylpentanediol dimethacrylate. Also, the acrylic and methacrylic acid esters of alcohols having more than two OH groups can be used as crosslinking agents, e.g. Trimethylolpropane triacrylate or trimethylolpropane trimethacrylate. Another class of crosslinkers are diacrylates or dimethacrylates of polyethylene glycols or polypropylene glycols having molecular weights of from 200 to 9,000, respectively.

In addition to the homopolymers of ethylene oxide or propylene oxide, it is also possible to use block copolymers of ethylene oxide or propylene oxide or copolymers of ethylene oxide and propylene oxide which contain the ethylene oxide and propylene oxide units randomly distributed. The oligomers of ethylene oxide or propylene oxide are also suitable for the preparation of the crosslinkers, for example diethylene glycol diacrylate, diethylene glycol dimethacrylate, triethylene glycol diacrylate, triethylene glycol dimethacrylate, tetraethylene glycol diacrylate and / or tetraethylene glycol dimethacrylate.

Also suitable as crosslinking agents are vinyl acrylate, vinyl methacrylate, vinyl itaconate, divinyl adipate, butanediol divinyl ether, trimethylolpropane trivinyl ether, allyl acrylate, allyl methacrylate, pentaerythritol triallyl ether, triallyl sucrose, pentaallylsucrose, methylenebis (meth) acrylamide, divinylethyleneurea, divinylpropyleneurea, divinylbenzene, divinyldioxane, triallylcyanourate, tetraalllylsilane, tetravinylsilane and bis- or Polyacrylsiloxane.

Preferred crosslinkers are e.g. Divinyl compounds such as divinyl benzene, diallyl and triallyl compounds such as diallyl maleate, diallyl fumarate, diallyl phthalate, triallyl cyanurate or triallyl isocyanurate, polyallyl compounds such as polyallyl methacrylate, allyl esters of acrylic and methacrylic acid, dihydrodicyclopentadienyl acrylate (DCPA), divinyl esters of dicarboxylic acids such as succinic acid and the adipic acid, diallyl and divinyl ethers of functional alcohols such as ethylene glycol and butane-1,4-diol such as Ethylene glycol dimethacrylate, pentaerythritol tetraacrylate. Furthermore, the acrylic acid ester of tricyclodecenyl alcohol is suitable as a crosslinker.

Crosslinking can occur before, during or after electrospinning. Advantageously, it takes place during electrospinning.
Optionally, the water-soluble polymer can be removed after crosslinking. This is advantageously done by treatment with water.

The person skilled in methods of linking polymers are known. He can apply them without departing from the scope of the claims.

The object of providing electrospun fiber webs with improved adhesion is achieved according to the invention by nonwoven webs obtainable by the process according to the invention.

The adhesion can be improved by subsequent heat or pressure treatment. Which of the two types of treatment is chosen depends on the substrate: If heat treatment is required, it must be heat-stable and pressure-stable during pressure treatment. For three-dimensional substrates, a pressure treatment is not suitable; in all other cases it is easy to see whether heat or pressure treatment achieve better results. The person skilled in the art knows how to determine the heat or pressure stability of a substrate. He can apply this knowledge without departing from the scope of the claims.

The nonwoven fabrics obtainable by the process according to the invention can be used for functional textiles and for filtration.

LIST OF REFERENCE NUMBERS

1

voltage source

2

capillary

3

syringe

4

dope

5

counter electrode

6

fiber formation

7

fiber mat

Figure legends Fig.1

Fig. 1 shows a SEM image of the fibers prepared from Dispersion 1. The white bar at the bottom of the picture is 10 μm.

Fig. 2

Fig. 2 shows a SEM image of the fibers prepared from Dispersion 1. The white bar at the bottom of the picture is 10 μm.

Fig. 3

Fig. 3 shows a schematic representation of a device suitable for carrying out the electrospinning process.

The device comprises a syringe 3, at the tip of which is a capillary nozzle 2. This capillary nozzle 2 is connected to a pole of a voltage source 1. The syringe 3 receives the solution 4 to be spun. Compared to the Output of the capillary nozzle 2 is arranged at a distance of about 20 cm connected to the other pole of the voltage source 1 counter electrode 5 , which acts as a collector for the fibers formed.

During operation of the device, a voltage between 18 kV and 35 kV is set at the electrodes 2 and 5 , and the spinning solution 4 is discharged through the capillary nozzle 2 of the syringe 3 at a low pressure. Due to the electrostatic charge of the polymer molecules in the solution due to the strong electric field of 0.9 to 2 kV / cm, a material flow directed towards the counterelectrode 5 , which solidifies on the way to the counterelectrode 5 with fiber formation 6 , arises as a result on the counter electrode 5 fibers 7 with diameters in the micron and nanometer range.

Fig. 4

Schematic representation of a parallel electrospinning process.

Two different polymer solutions A and B are spun by means of two side by side syringes 2A and 2B . The cannulas of both syringes are connected to a high voltage source 1 . The distance of the syringes is chosen so that the exiting material flows 3A and 3B overlap. On the movable counter electrode 5 , the nonwoven fabric 4 , consisting of two different fiber types, collected.

embodiments Embodiment 1 Preparation of the dispersions 1.1 Preparation of the dispersion 1 with photocrosslinkable particles with a glass transition point of -60 ° C.

In a laboratory reactor (1 l reaction vessel) with connection to the argon line and bubble counter 205 ml (1441 mmol) of butyl methacrylate and 19.5 g (73 mmol) of 4-methacryloyl-oxy-benzophenone under argon flow in 250 ml of deionized and degassed water. To this mixture was added 1.72 g (6 mmol) of sodium dodecyl sulfate

The reaction dispersion was heated with vigorous stirring (1000 rpm) with a 75 ° C water bath. When the reaction temperature reached 65 ° C., the reaction was started by adding 0.68 g (2.5 mmol) of K ₂ S ₂ O ₈ suspended in a little water (5 ml). The stirring speed was reduced to 250 rpm.
After 45 minutes, the water bath was removed and the reaction mixture cooled to room temperature.
The mean particle diameter was 78 nm.

1.2 Preparation of Dispersion 2 with Crosslinked Particles with a Glass Point of 35 ° C

Allyl methacrylate (54 mL, 500 mmol, 1 eq), methyl methacrylate (160.4 mL 1500 mmol, 3 eq) and butyl methacrylate (143.4 mL 1000 mmol, 1 eq.) Were placed in a reactor vessel with stirrer motor and stirring blade with connection to the argon line and bubble counter ) with vigorous stirring (1000 rpm) under argon flow in 1000 mL of deionized and degassed water. To this mixture was added sodium dodecylsulfate (2.29 g, 8 mmol).
The reaction dispersion was heated with a 75 ° C water bath, then by addition of potassium peroxodisulfate suspended in some water (1.36 g, 5 mmol) started the reaction. The reaction temperature was 65 ° C.
After 45 minutes, the water bath was removed and the reaction mixture cooled to room temperature.
The mean particle diameter was 93 nm.

1.3 Preparation of the dispersion 3 with a glass transition point of -60 ° C.

In a laboratory reactor (1 l reaction vessel) with connection to the argon line and bubble counter, 215 ml (1500 mmol) of butyl methacrylate were added under argon flow into 250 ml of deionized and degassed water. To this mixture was added 1.72 g (6 mmol) NaDS.

The reaction dispersion was heated with vigorous stirring (1000 rpm) with a 75 ° C water bath. When the reaction temperature reached 65 ° C., the reaction was started by adding 0.68 g (2.5 mmol) of K ₂ S ₂ O ₈ suspended in a little water (5 ml). The stirring speed was reduced to 250 rpm.
After 45 minutes, the water bath was removed and the reaction mixture cooled to RT.
The mean particle diameter was 65 nm.

Embodiment 2: Electrospinning the dispersions

The electrospinning solutions were prepared with a 60 ° C aqueous 25 wt.% Polyvinylalkol solution (Mowiol 56-98) in a ratio of 20% latex particles and 5% PVA.

The substrate used was a mixed fiber fleece made of 55% viscose, 20% polypropylene, 15% polyester and 10% shredded cotton.

The latex particles containing dispersions 1 to 3 mentioned in Example 1 were electro-spun into non-woven fabrics. For this purpose, electrospinning solutions were prepared with a 60 ° C aqueous 25 wt .-% polyvinyl alcohol solution (Mowiol 56-98) prepared in a ratio of 20% latex particles and 5% PVA. The nonwoven fabrics of Dispersions 1 to 3 were spun onto a mixed fiber nonwoven (substrate) of 55% viscose, 20% polypropylene, 15% polyester and 10% shredded cotton.

• Dispersion 1: 350 nm,
• Dispersion 2: 364 nm,
• Dispersion 3: 584 nm.

The thickness of the fiber webs spun from the dispersions 1 to 3 was 20 g / m ² .
Fiber diameter:

• Dispersion 1: 350 nm,
• Dispersion 2: 364 nm,
• Dispersion 3: 584 nm.

Embodiment 3 Adhesion of the fibers

The adhesion of the fibers is determined by the so-called Tesatest. In this standard adhesion test, an adhesive film strip is applied to the layer at a uniform pressure and pulled off abruptly. The adhesion is assessed by looking at the demolition image. It was assessed whether the fracture took place on the substrate or in the non-woven fabric, and it was also assessed whether fibers not covered by the Tesafilm were entrained.

3.1 fibers from dispersion 1

Fibers from dispersion 1 were spun onto the substrate as described in Example 2. The fibers were irradiated after spinning for 30 minutes with a medium pressure mercury vapor lamp (TQ 150, Heraeus).

The SEM image of fibers from Dispersion 1 (see Fig. 1 ) shows a more compact fiber structure than fibers of dispersion 2 (see embodiment 3.2 and Fig. 2 ) with stabilizing fusing points at the contact points of the fibers.

The nonwoven made from Dispersion 1 has a compact structure, the fibers can not be separated from each other. The adhesion on the substrate is good, the fibers can not be detached from the substrate without aids. The Tesatest results in a adhesion failure of the fiber web from the substrate. No fibers underneath the tesa film were lifted off.

3.2 fibers from dispersion 2

Fibers from dispersion 2 were spun onto the substrate as described in Example 2. The fibers were irradiated after spinning for 30 minutes with a medium pressure mercury vapor lamp (TQ 150, Heraeus).

The SEM image of fibers from Dispersion 2 shows that these fibers have a loose fiber structure. The individual fibers lie loosely on top of each other and show no fusion. The SEM uptake of fibers from Dispersion 2 is in Fig. 2 shown.

The fibers prepared from dispersion 2 show a cotton-like structure. The fibers show no adhesion to each other or to the substrate and can easily be lifted off the substrate. When performing the Tesatestes the uppermost fiber layers are lifted, the connection of the fibers with each other is too weak to entrain lower fiber layers.

3.3 fibers from dispersion 3

By a parallel Elektrospinnpinnprozess of 20 wt.% Polyamide 6 in formic acid with dispersion 3, a mixed fiber fleece was prepared and compared with a fleece of pure polyamide 6 (reference fleece).

The lack of adhesion of the electrospun polyamide 6 fibers can be seen by the complete detachment of the electrospun web during the Tesatestes.

The Tesatest results in a significantly better adhesion of the fibers in the mixed fiber fleece. The break between substrate and electrospun fibers occurs exclusively at the points below the Tesastreifens.

Embodiment 4 Pressure treatment of a layer-spun fiber mat

By a layer-wise Elektrospinnpinnprozess of 20 wt.% Polyamide 6 in formic acid and dispersion 3, a mixed fiber fleece was made with a total of 6 layers, wherein the first layer of dispersion 3 was. The resulting nonwoven fabric was compared with a nonwoven made of pure polyamide 6 (comparative nonwoven).

The lack of adhesion of both untreated electrospun webs is evidenced by the complete detachment of the electrospun web during the Tesatestes.

The fibers were then subjected to a pressure treatment of 20 bar for 60 s. The web consisting of polyamide completely dissolved from the substrate even after the treatment during the tesate test. The mixed fiber nonwoven made of polyamide and dispersion 3, however, shows a significantly improved adhesion. When performing Tesatest the break between substrate and electrospun fibers occurs only at the points below the Tesastreifens.

Claims (14)

Process for the production of fiber webs by dispersion electrospinning primary or secondary aqueous latex polymer dispersions, characterized in that the latex polymer particles have diameters less than or equal to 200 nm, the softening points of the latex polymers constituting the particles are at least 20 ° C. below the spinning temperature, the aqueous dispersions of the particles contain 5 to 50% by weight of particles, 0.5 to 15% by weight of a water-soluble matrix polymer is added to the particle dispersions prior to spinning, the matrix polymer being chosen such that it does not flocculate the latex polymer, and - The electrospinning is carried out at temperatures of 0 to 100 ° C. A method according to claim 1, characterized in that primary aqueous latex polymer dispersions are used. A method according to claim 1, characterized in that secondary aqueous latex polymer dispersions are used. A method according to any one of claims 1 to 3, characterized in that 10 to 25 wt .-% of the fibers consist of the water-soluble matrix polymer. A method according to any one of claims 1 to 4, characterized in that the electrospinning is carried out at temperatures between 20 ° C and 30 ° C. A method according to any one of claims 1 to 5, characterized in that a single aqueous dispersion of primary or secondary latex polymer particles is electrospun. A method according to any one of claims 1 to 5, characterized in that two aqueous dispersions of primary or secondary latex polymer particles are electrospun. A method according to claim 7, characterized in that the two aqueous dispersions of primary or secondary latex polymer particles are spun in parallel and / or in layers. A method according to any one of claims 1 to 8, characterized in that the particles or the fibers obtainable from them before, during or after spinning are crosslinked. A process for the preparation of primary aqueous latex polymer particles according to claims 1, 2 and 4 to 9 by an emulsion polymerization comprising the steps a) rinsing the reaction vessel with an inert gas selected from argon and nitrogen, b) presenting degassed water, c) adding the at least one monomer, d) addition of a surfactant, e) strong stirring of the mixture, f) addition of a radical initiator, g) Continue stirring for 15 to 180 min. at reduced stirring speed, h) optionally cooling the reaction mixture to room temperature and stopping the stirring,
wherein the steps a) to g) are carried out at temperatures between 0 ° C and 100 ° C. A method according to claim 11, characterized in that in step d) an anionic surfactant is used. Electrospun fiber webs obtainable by a process according to claims 1 to 9. Electrospun fiber webs according to claim 12, characterized in that they are subjected to a heat or pressure treatment. Use of the fiber webs according to one of claims 12 and 13 for functional textiles and for filtration.

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