KR101079775B1 - Preparation Method of Electroconductive Nanofiber through Electrospinning followed by Electroless Plating - Google Patents

Abstract

The present invention comprises the steps of: a) preparing an electrospinning liquid containing a polymer having a fiber forming ability and an electroless plating catalyst; b) electrospinning the electrospinning liquid to prepare nanofibers having a diameter of 10 nm to 5 μm; and c) electroless plating the nanofibers.
According to the present invention, it is possible to significantly reduce the time and cost required for manufacturing the electrically conductive fibers, less cracks due to flexibility, it is possible to manufacture electrically conductive nanofibers that can maintain the electrical conductivity as much as the metal.

Description

Preparation method of electroconductive nanofiber through electrospinning followed by electroless plating

The present invention relates to a method for producing electrically conductive nanofibers through electrospinning followed by electroless plating, specifically, a) preparing an electrospinning solution including a polymer having a fiber forming ability and an electroless plating catalyst; b) electrospinning the electrospinning liquid to prepare nanofibers having a diameter of 10 nm to 5 μm; and c) electroless plating the nanofibers.

Electroless plating is a technique for coating a metal material on the surface of various materials, and has been used in textiles, fibers, and polymer films in various papers and patents. This technology is fundamentally intended to impart conductivity to non-conductive materials, and plated fibers and polymer films can be used for electromagnetic shielding, flexible electrodes, wearable computers, antistatic agents and sensors.

In general, plated fabric is mainly used as an electromagnetic shielding material, in particular, a flexible and light product is currently produced by coating on a fabric such as polyester.

Until now, a method of imparting a conductive function to a fiber includes a method of mixing a conductive material with a spinning solution in the manufacture of yarns of chemical fibers, a method of coating a conductive material by sputtering, or an organic conductive material (conductive polymer (pyrrole, PEDOT) ), Conductive ink, paint) and the like, and a method of manufacturing metal fibers.

Among them, a method of incorporating a conductive material may not have good conductivity as compared to a method of forming a metal film, and a method of coating an organic conductive material may be poor in touch and dark in color.

On the other hand, the method of forming a metal film on the surface of the fiber by the vacuum deposition method, the sputtering method, the electroless plating method, etc. is excellent in conductivity and has a metallic-specific gloss, so that it can be used as smart clothing, electromagnetic shielding agent and the like.

However, in the case of the vacuum deposition method and the sputtering method, it is difficult to cause irregularities on the surface and to coat a metal film of a predetermined thickness or more, and it is frequently used when manufacturing a conductive film because only one surface of the metal film can be raised in one treatment process. Electroless plating is used to impart conductivity to fibers and the like because the thickness is adjustable and three-dimensional plating coating is possible.

Until now, the electroless plating method is a method of catalyzing the fabric and the electrons generated when the reducing agent is oxidized on the surface of the catalyst to attach metal on the catalyst by reducing the metal ions. The continuous metal attachment was used.

At this time, the pretreatment is a process for initiating a chemical reaction with a metal on the surface of the fiber, and attaching a metal nucleus to the surface of the fiber so as to increase the bonding strength with the metal film by surface treating the fiber surface. ), Sensitizing, activating, accelerating and the like. These processes require catalysts such as palladium chloride or silver nitrate, which leads to lengthy processes and increased costs. In addition, in the case of the fabric used as a base material, the surface area is smaller than that of the nanofiber, and the diameter of the fiber is large, so that the plating metal coated on the individual fiber is easily dropped, deformed, and denatured by various factors, causing a sharp decrease in conductivity. Resulted.

When the plated metal is dropped from ordinary fibers without post-treatment such as adhesive coating, the metal powder is released into the air, which may cause humans to absorb it by breathing or stick to the body and cause skin diseases such as allergies. have.

When used as an electromagnetic shielding material, there is a limit to the density of the fabric, the shielding rate associated with it also has some limitations. Electromagnetic waves smaller than the space between the fabrics of the plated fibers are allowed to pass through, and several layers must be used to prevent them.

Accordingly, the present inventors have made diligent research efforts to overcome the problems of the prior art, when manufacturing nanofibers by electrospinning, including an electroless plating catalyst, and electroless plating on the nanofibers thus prepared To reduce the time and cost of the manufacturing process, less cracking due to flexibility, it was confirmed that the metal-plated nanofibers capable of maintaining the electrical conductivity as much as the metal, and completed the present invention.

Therefore, the main object of the present invention is to reduce the process time and cost, to reduce the damage caused by the drop-out phenomenon, to produce a conductive metal fiber with a high metal density, and to plated metal plating nano which is durable by physical force and harmless to human body It is to provide a fiber manufacturing method.

According to one aspect of the invention, the present invention comprises the steps of: a) preparing an electrospinning liquid comprising a polymer having a fiber forming ability and an electroless plating catalyst; b) electrospinning the electrospinning liquid to prepare nanofibers having a diameter of 10 nm to 5 μm; c) providing a method for producing metal-plated nanofibers comprising electroless plating the nanofibers.

In the metal plating nanofiber production method of the present invention, when preparing the electrospinning liquid, it is preferable to dissolve a polymer having an ability to form a fiber and an electroless plating catalyst in an organic solvent. At this time, the organic solvent is methyl ethyl ketone, chloroform, chloroform, dichloromethane, methylpyrrolidinone (NMP), dimethyl sulfoxide (DMSO), Dimethylformamide (DMF), methanol, ethanol, propanol, butanol, t-butyl alcohol, isopropyl alcohol (isoPA, 2-propanol), benzyl alcohol, tetra Tetrafurfuran (THF), ethyl acetate, butyl acetate, propylene glycol diacetate, propylene glycol methyl ether acetate (PGMEA), acetonitrile ( acetonitrile, trifluoroacetonitrile, ethylene glycol, dimethylacetamide (DMAC), acetone, pyridine It is pyrrolidine and preferred to use a Dean (pyrrolidine), may be used alone or in combination thereof.

In the metal plating nanofiber production method of the present invention, the average molecular weight of the polymer having a fiber forming ability is preferably 5,000 to 1,000,000, more preferably 10,000 to 300,000. Such polymers include polyvinylidene fluoride (PVDF), polyvinylidene fluoride copolymer, polyurethane (polyurethane), nylon, polyvinylacetate (PVAc), polyvinyl alcohol (PVA), polyethylene-vinylacetate copolymer ( PEVAc) or cellulose acetate is preferably used, and these may be used alone or in combination.

In the metal plating nanofiber manufacturing method of the present invention, the electroless plating catalyst refers to a material that acts as a nucleus when the metal ions of the plating solution undergo a reduction process during the electroless plating, and such catalysts include Ti, Sn, It is preferable to use a salt of Au, Pt, Pd, Ni, Cu, Ag, Al, Zn or Fe, and these may be used alone or in combination.

In the metal plating nanofiber manufacturing method of the present invention, the electroless plating is preferably electroless plating with Ti, Sn, Au, Pt, Pd, Ni, Cu, Ag, Al, Zn or Fe metal, these alone Or it can mix and use.

In the metal plating nanofiber production method of the present invention, electroless plating is preferably performed using a plating solution having a concentration of 0.1 to 100 g / 100 ml of a metal salt or ion. Since the solubility varies depending on the metal to be plated, it is necessary to adjust the concentration accordingly.

In the metal plating nanofiber manufacturing method of the present invention, it is preferable to electroless plate using a plating solution of 1 to 500 times the weight of the nanofiber of step b). Since the degree of absorption of the plating liquid varies depending on the polymer constituting the nanofibers, it is necessary to adjust the plating liquid accordingly.

In the metal plating nanofiber production method of the present invention, it is preferable that the electrospinning solution further comprises a metal chloride selected from the group consisting of chlorides of Ca, K and Fe.

In the metal-plating nanofiber manufacturing method of the present invention, it is preferable to modify the nanofiber of step b) by a surface treatment method selected from the group consisting of plasma surface treatment, corona surface treatment and ultraviolet surface treatment to electroless plating. .

In the metal plating nanofiber production method of the present invention, electroless plating is preferably performed using a plating solution to which a surfactant is added.

In the metal plating nanofiber production method of the present invention, it is preferable to electrolessly plate by applying a positive pressure or a negative pressure.

In the metal-plating nanofiber manufacturing method of the present invention, after the step c), the plated nanofibers are heated for 5 to 20 minutes at a temperature higher than 20 degrees Celsius higher than the melting point of the nanofibers to melt the nanofibers, It is preferable to further include the step of improving the adhesion between the nanofiber and the metal plating layer by cooling to room temperature.

In the metal plating nanofiber manufacturing method of the present invention, after the step c), it is preferable to further include the step of coating the surface of the plated nanofiber with a coating agent.

In the metal-plating nanofiber manufacturing method of the present invention, after the step c), the step of polymerizing the monomer solution containing a polymerization initiator to the coated nanofibers to coat the polymer protective film on the surface of the plated nanofibers Alternatively, the method may further include gas phase polymerization by applying the polymerization initiator solution to the plated nanofibers and exposing the monomer to vapor.

According to another aspect of the present invention, the present invention provides a metal-plated nanofiber prepared by the above method.

Hereinafter, the present invention will be described more specifically.

Compared with general fabrics and fibers, nanofibers produced by electrospinning are known to have a large surface area. In addition, nanofibers have a very small diameter, so two-dimensional products such as webs made of nanofibers have a very high tissue density. When various metals are coated on the nanofibers through electroless plating, plating fibers having a very high density and surface area can be obtained (see FIG. 1). Webs made of these metal-plated nanofibers can be produced in a variety of thicknesses ranging from a few micrometers to several millimeters, and the thickness of the plated metal can be from a few nanometers to several micrometers.

Low levels of metal thickness and randomly shaped nanofibers (see FIGS. 2 and 7) are durable to external deformations such as bending, and thus can be easily used for flexible displays, wearable computers, and clothing heating wires that require flexibility.

In addition, such a metal-plated nanofiber web exhibits a net effect between nanofibers, so that even if the metal is dropped, the metal-plated nanofiber web can be caught inside the fiber without being released to the outside, thereby significantly reducing the respiratory and skin diseases caused by the dropped metal. .

Until now, in order to impart conductivity through electroless plating to fabrics or fibers, an etching process that maximizes adhesion by giving irregularities to the surface and a catalyst treatment process (sensitization, activation, acceleration, etc.) were required to attach metal to the surface. .

However, in the present invention, in the manufacture of the fiber (more specifically, electrospinning), the catalyst is spun together with the polymer solution so that the catalyst can be located in or on the fiber, thereby increasing the cost of conventional processes and palladium chloride. Can be used efficiently, and the etching and catalytic treatment process can be omitted.

The catalyst located on the surface acts as a nucleus when the metal ions in the plating solution undergo a reduction process so that metal can be produced only at the fiber surface. In the conventional electroless plating, the catalysts physically attached to the fibers are melted into the plating solution and some metal ions are reduced in the plating solution, and thus have high efficiency.

Nanofiber webs have a much smaller pore size than ordinary woven and knitted fabrics, and thus the plating solution is not easily absorbed. Therefore, when electroless plating is performed without a special pretreatment process, plating occurs only on the web surface (see FIG. 4), and the thickness of the metal becomes thick and has a plate shape, which is easily deformed and torn due to external force, causing cracks to fall off. It happens very well.

To compensate for this, the following methods can be used.

In the electrospinning step, there is a method of using a metal chloride having excellent absorption (wetness) when preparing the electrospinning solution. For example, metal chlorides such as FeCl ₃ and CaCl ₂ have an effect of totally hydrophilizing the fiber through moisture absorption, so that the plating solution using water can be easily absorbed.

In addition, there is a method of surface-modifying the nanofibers prepared by electrospinning with plasma, corona or ultraviolet (UV). Polyvinyl fluoride, polystyrene, etc. are basically excellent in water repellency. Therefore, when plating the nanofibers using these materials as the base material of the fiber, the surface treatment method as described above is used to impart hydrophilicity of the surface, so that the plating solution in the aqueous solution can be evenly spread on the nanofibers.

In addition, there is a method of applying negative pressure or positive pressure when electroless plating the nanofibers prepared by electrospinning. After impregnating the nanofibers in the plating liquid, air is removed from the pores using negative pressure to fill the space with the plating liquid. Alternatively, if a positive pressure is applied to a device such as a roller or a press, the plating liquid pushes the air to fill the pores. When the positive pressure or the negative pressure is applied, it is preferable to apply a positive pressure of about 5 atmospheres or a negative pressure (vacuum) of about 10 mmHg or less.

There is also a method of electroless plating nanofibers by adding a surfactant to the plating solution. When surfactant is added, the surface tension of the plating liquid is reduced, so that the plating liquid can evenly penetrate into the pores of the nanofibers.

Such methods of uniformly plating the nanofibers, that is, using metal chlorides, modifying the surface of the nanofibers, adding positive or negative pressures, and adding a surfactant to the plating solution, respectively, may be used alone or in combination. It can be applied in parallel.

The metal plated on the surface of the nanofiber has some durability by external force, but the possibility of dropping out by excessive force cannot be excluded. Therefore, in some cases, a method of increasing durability is required, and the following method may be used.

There is a method of melting a polymer material, which is a base material of nanofibers, and using the same as an adhesive. That is, it can be said to be a method of melting the polymer material inside the metal film of the plated nanofibers to improve the adhesion to the plated metal. The melting point does not affect metals above thousands of degrees because the temperature required to melt the polymer material does not exceed 300 degrees Celsius. In addition, the molten polymer material increases fluidity, closely adheres to the metal, and cools it to room temperature again, thereby solidifying the adhesion between the plated metal material and the polymer material to prevent the metal from falling off.

In addition, there is a method of forming a protective layer on the plated nanofiber surface when the metal coating does not need to be exposed to the outside, that is, when used for a purpose such as a shield. Because nanofibers generally have pores, materials with fine particles can move inside. Therefore, the sprayed on the plated nanofibers can be used to spray a polymer solution having a film-forming ability, or by impregnating the plated nanofibers in the polymer solution to form a protective film on the plating layer. In addition, there is a method of attaching a polymerization initiator to the plated nanofibers by spraying or solution impregnation, followed by gas phase or liquid phase polymerization of a polymer having film forming ability. When the polymer is moved into the pores of the nanofibers in a gas or liquid state, polymerization occurs by a polymerization initiator attached to the nanofibers, thereby forming a polymer protective film.

Portable devices requiring flexible electrodes are currently using or studying metal thin films or conductive polymer films. In the case of a metal thin film, cracking may occur in many deformations, and the density is high, which causes a problem in weight reduction. In the case of the conductive polymer film, it is not yet reliable and does not show the conductivity as much as the metal.

When the metal-plated nanofibers are manufactured using the manufacturing method of the present invention, the occurrence frequency of cracks caused by external force and / or folding is low, and the electrically conductive nanofibers can maintain the conductivity as much as the metal. It can be produced by saving a considerable amount, and these electrically conductive nanofibers are expected to replace the conductive polymer and metal thin film.

1 is a schematic view showing a nanofiber and a catalyst composite (A) prepared by electrospinning an electrospinning solution in which a polymer and a metal salt catalyst are dissolved, and the metal plating nanofibers (B) of the present invention prepared by electroless plating them.
2 is a view illustrating the cause of durability of the metal-plated nanofibers of the present invention by external force (bending).
Figure 3 is a block diagram showing a schematic process for producing a metal-plated nanofibers in a preferred embodiment of the present invention.
Figure 4 is a scanning electron micrograph showing the form plated only on the surface during electroless plating of the PVDF nanofiber web prepared by electrospinning using only DMAc / acetone (6/4) mixed solution of PVDF (compare before and after plating) ).
5 is a preferred embodiment of the present invention by impregnating a silver plating solution with an electrospun nanofiber web using a DMAc / acetone (6/4) mixed solution in which a catalyst (SnCl ₂ ) is mixed in PVDF, and then positive pressure is applied thereto. Scanning electron microscopy shows that the plating solution is evenly distributed in the web and then electroless plated to uniformly plated silver only on the surface of the nanofiber up to the inside of the nanofiber web.
FIG. 6 is a scanning electron micrograph in a state where the electroless silver plated nanofibers of FIG. 5 are folded at 180 degrees. FIG.
FIG. 7 is a scanning electron micrograph in which the electroless silver plated nanofibers of FIG. 4 are folded at 180 degrees, and cracks are observed.

Hereinafter, the present invention will be described in more detail with reference to Examples. Since these examples are only for illustrating the present invention, the scope of the present invention is not to be construed as being limited by these examples.

Example.

In a 6: 4 mixture of dimethylacetamide (DMAC) and acetone, polyvinylidene fluoride (PVDF, Kynar 761) and SnCl ₂ , one of the fluorine-based polymers, were 12 and 1wt% (w / v) added to concentration and dissolved for about a day with stirring at a temperature of 60 ° C. The solution was placed in a syringe and electrospinned by applying a high voltage of about 23 kV. At this time, the used syringe needle was 19G, the spinning distance from the syringe needle to the drum-type current collector was 10cm, the discharge rate of the solution was 1ml / h, the spinning time was 4 hours, the diameter of the drum-type current collector was 12.5cm, The rotational speed of the current collector was about 60 rpm.

In order to generate silver ions, 1.2 g of AgNO ₃ and 0.8 g of NaOH were dissolved in 100 ml of distilled water, and a few drops of aqueous ammonia were added to obtain a clear solution (A). In addition, an aqueous glucose solution (B) at a concentration of 5 g / l was prepared to reduce silver ions to a metal form.

The solution A was impregnated with a nanofiber web prepared by electrospinning at a ratio of 100 ml: 1 g and a pressure (positive pressure) was applied through a roller to evenly distribute the plating solution. Thereafter, solution B was mixed with solution A in a volume ratio of 1: 3 and stirred for 30 minutes in a bath at 15 degrees Celsius so that the nanofiber web was electroless silver plated. The silver plated nanofiber web was then washed with distilled water and dried. The nanoweb gradually became gray or white in the early black plating.

The scanning electron micrograph of the obtained silver plated nanoweb is shown in FIG. 5, and the 4-probe conductivity measurement resulted in a very high conductivity of 10 ⁴ S / cm or more.

In order to evaluate the flexibility of the silver-plated nanoweb, scanning electron micrographs were obtained in the fully folded state as shown in FIG. 6, and almost no cracks were generated.

In addition, the PVDF nanofiber web electrospun without incorporating SnCl ₂ was electroless silver plated without pretreatment with positive or negative pressure to prepare a nanofiber web, and after the web was completely folded, it was confirmed by a scanning electron microscope. As shown, many cracks were observed, and at the same time, the electrical conductivity also decreased rapidly.

Claims (16)

a) preparing an electrospinning liquid containing a polymer having a fiber forming ability and an electroless plating catalyst;
b) electrospinning the electrospinning liquid to prepare nanofibers having a diameter of 10 nm to 5 μm;
c) electroless plating the nanofibers. The method of claim 1, wherein the electrospinning liquid is prepared by dissolving a polymer having a fiber forming ability and an electroless plating catalyst in an organic solvent. The method of claim 2, wherein the organic solvent is methyl ethyl ketone, chloroform, dichloromethane, methylpyrrolidinone (NMP), dimethyl sulfoxide (dimethyl sulfoxide, DMSO). ), Dimethylformamide (DMF), methanol, ethanol, propanol, butanol, t-butyl alcohol, t-butyl alcohol, isopropylalcohol (iPA, 2-propanol), benzyl alcohol , Tetrahydrofuran (THF), ethyl acetate, ethyl acetate, butyl acetate, propylene glycol diacetate, propylene glycol methyl ether acetate (PGMEA), aceto Nitrile (acetonitrile), trifluoroacetonitrile, ethylene glycol, dimethylacetamide (DMAC), acetone, pyridine yridine) and pyrrolidine. The method of manufacturing metal-plated nanofibers, characterized in that it is selected from the group consisting of. The method of claim 1, wherein the polymer having a fiber forming ability is polyvinylidene fluoride (PVDF), polyvinylidene fluoride copolymer, polyurethane (polyurethane), nylon, polyvinylacetate (PVAc), polyvinyl alcohol (PVA ), Polyethylene-vinylacetate copolymer (PEVAc), cellulose acetate is selected from the group consisting of metal-plated nanofiber manufacturing method. The method of claim 1, wherein the electroless plating catalyst is metal-plated nanofiber production, characterized in that selected from the group consisting of salts of Ti, Sn, Au, Pt, Pd, Ni, Cu, Ag, Al, Zn and Fe Way. The method of claim 1, wherein the electroplating method of metal plating nanofibers is characterized by electroless plating with a metal selected from the group consisting of Ti, Sn, Au, Pt, Pd, Ni, Cu, Ag, Al, Zn and Fe. The method for producing metal-plated nanofibers according to claim 1, wherein the electroless plating is carried out using a plating solution having a concentration of 0.1 to 100 g / 100 ml of a metal salt or ion. The method of claim 1, wherein the electroplating method using a plating solution of 1 to 500 times the weight of the nanofibers of the step b). The method of claim 1, wherein the electrospinning solution further comprises a metal chloride selected from the group consisting of chlorides of Ca, K and Fe. The method of claim 1, wherein the nano-fiber of step b) metal plating nanofiber manufacturing, characterized in that the electroless plating by modifying the surface treatment method selected from the group consisting of plasma surface treatment, corona surface treatment and ultraviolet surface treatment Way. The metal plating nanofiber manufacturing method according to claim 1, wherein the plating solution is electrolessly plated using a plating solution to which a surfactant is added. [Claim 2] The method of claim 1, wherein electroless plating is performed by applying a positive pressure or a negative pressure. The method of claim 1, further comprising: heating the plated nanofibers at a temperature of 20 degrees Celsius or more higher than the melting point of the nanofibers for at least 20 minutes to melt the nanofibers, and then cooling them to room temperature. Metal-plated nanofiber manufacturing method, characterized in that. The method of claim 1, wherein after the step c), further comprising the step of coating the surface of the plated nanofibers with a coating agent. The method of claim 1, wherein after the step c), a monomer solution including a polymerization initiator is coated on the plated nanofibers to polymerize the polymer protective film on the surface of the plated nanofibers, or the polymerization initiator solution is plated. Method for producing a metal-plated nanofiber, characterized in that further comprising vapor-phase polymerization by applying to the nanofiber after exposure to the monomer vapor. Metal-plated nanofibers prepared by the method of claim 1.

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