KR20110068008A - Nano web and method for manufacturing the same - Google Patents

Abstract

PURPOSE: Nano web and a manufacturing method thereof are provided to improve functions of the nanoweb by forming the nanoweb with high porosity and voids of big structure. CONSTITUTION: A manufacturing method of nano web includes the following steps: manufacturing a polyelectrolyte solution; manufacturing nanofiber(1) thorugh electrospinning; manufacturing nano fiber aggregate from nano fiber; measuring a thickness of the nano fiber aggregate with a non-contact type method; and converting the polyamic acid nanofiber aggregate into the nano fiber aggregate. The nano fiber is manufactured in an electric file of 850-3500 V / cm.

Description

Nano web and method for manufacturing the same

The present invention relates to a nano web and a method of manufacturing the same, and more particularly, to a nano web and a method of manufacturing the nanofibers are converging each other.

The porous membrane can be used in various fields such as electrolyte membranes, secondary battery membranes, filters, fuel cell membranes, artificial medical tubes such as artificial blood vessels, semiconductor membranes and water purification membranes. Porous membranes usable in these fields require not only porosity but also chemical resistance, heat resistance and mechanical properties.

As a material satisfying these required properties, expanded polytetrafluoroethylene (ePTFE) films are mainly used. However, since ePTFE has a weak mechanical strength and manufactures a film using fluorine, there is a problem in that it threatens the environment and the cost is high and the economy is inferior. In addition, since ePTFE has a low porosity and a small pore diameter, ePTFE has a poor ability to support functional conductors, and has a limited performance improvement when used in fuel cell membranes.

Accordingly, various materials are being developed to replace ePTFE, including polyimide films. Such a polyimide film has advantages of excellent heat resistance and chemical resistance, but is poorly soluble in common organic solvents, and thus has poor processability and imparts porosity to the film. Therefore, a polyimide film has a thin, uniform thickness, high porosity, and large pores. There is a problem that is difficult to manufacture.

In addition, the thickness measurement of the conventional porous membrane was measured by a contact method that directly measures the thickness of the porous membrane between the gauge, this contact measurement method has the advantage of easy measurement, but the measured thickness of the membrane according to the pressing force There may be a problem that the measurement error is large, depending on the skill of the measurer. If the thickness of the film thus prepared cannot be accurately measured, it is difficult to produce a film having a uniform thickness. In particular, the stack for the fuel cell is made of a stack of hundreds to thousands of electrolyte membranes, if the electrolyte membrane does not have a uniform thickness, there is a problem that the degree of integration is inferior and thus the efficiency is reduced.

Accordingly, there is a demand for the development of a technology capable of quickly and accurately measuring the thickness of the prepared porous membrane regardless of the external environment.

Accordingly, the present invention relates to a nano web and a method for manufacturing the same, which can prevent problems caused by the above limitations and disadvantages of the related art.

An advantage of the present invention is to provide a nano-web and a method for producing the nano-web having a thin, high porosity and large pores by producing a nano-web through electrospinning at the optimum conditions.

It is another object of the present invention to provide a nanoweb and a method of manufacturing the same having a uniform thickness according to the precise measurement of the thickness of the nanoweb by a non-contact method.

In order to achieve the above advantages, and in accordance with the object of the present invention, as an aspect of the present invention, a process for preparing a polyamic acid solution; Preparing nanofibers by electrospinning the polyamic acid solution; Preparing nanofiber aggregates from the nanofibers; And it provides a method for producing a nano-web comprising the step of measuring the thickness of the nanofiber aggregate using a non-contact method.

As another aspect of the present invention, there is provided a polyamic acid nanofiber having an average diameter of 100 to 5,000 nm; And a nanoweb comprising the nano-agglomerates having the polyamic acid nanofibers intertwined with each other to form a three-dimensional network and having a porosity of 50 to 99% and an average thickness of 5 to 40 μm.

According to the present invention by the above configuration has the following effects.

First, since the nano-web according to the present invention has a high porosity and a large pore structure, the nano web has a better performance than the porous membrane in the form of a film.

Second, according to the present invention, since the thickness of the nanoweb can be measured quickly and accurately, there is an effect of producing a thin and uniform nanoweb.

Third, according to the present invention, the polyimide nanoweb prepared by the imidation reaction of the polyamic acid precursor is excellent in workability and excellent in heat resistance and fire resistance.

Therefore, such a nanoweb can be used in various fields such as electrolyte membranes, secondary battery membranes, filters, fuel cell membranes, artificial medical tubes such as artificial blood vessels, semiconductor membranes and water purification membranes.

The 'contact' thickness measurement used in the present invention means measuring the thickness directly by using a gauge, and the 'non-contact' thickness measurement means measuring the thickness of the light transmission or reflection and indirectly measuring the thickness thereof. do.

The term “nano fiber” used in the present invention refers to an ultrafine fiber having an average diameter of several thousand nm or less, and is produced by electrospinning.

The term “nano web” used in the present invention is a collection of ultrafine fibers such as the “nano fibers” and means that it is produced by electrospinning.

Nanofibers can be produced by a variety of methods, for example, electrospinning, direct spinning, composite spinning, flash spinning, and the like can be manufactured by various methods. Among these, electrospinning can produce nanofibers through a simple process using a simple facility, and since all materials that can be dissolved in a solvent can be spun, there are advantages of manufacturing ultrafine fibers of various materials.

Hereinafter, the present invention will be described in detail.

The manufacturing method of the nanoweb 10 of this invention is demonstrated concretely.

First, a polyamic acid solution is prepared. The process of preparing the polyamic acid solution may include a process of preparing a polyamic acid polymer and a process of dissolving the polyamic acid polymer in a solvent.

The polyamic acid polymer may be prepared through conventional methods. That is, the polyamic acid polymer may be prepared by mixing diamine in an organic solvent in a nitrogen atmosphere and adding and polymerizing dianhydride. The dianhydride may be pyromellyrtic dianhydride (PMDA), benzophenonetetracarboxylic dianhydride (BTDA), ODPA (4,4'-oxydiphthalic anhydride), BPDA (biphenyltetracarboxylic dianhydride), or SIDA (bis (3,4-dicarboxyphenyl) dimethylsilane dianhydride The diamine may be used by selecting one of ODA (4,4'-oxydianiline), p-PDA (p-penylene diamine), or o-PDA (openylene diamine).

The polyamic acid solution may be prepared by dissolving the polyamic acid polymer in a solvent. The solvent is m-cresol, N-methyl-2-pyrrolidone (NMP), dimethylformamide (DMF), dimethylacetamide (DMAc), dimethylsulfoxide (DMSO), acetone, diethylacetate, tetrahydro It may be at least one of furan (THF), chloroform, γ-butyrolactone.

The polyamic acid solution may have a concentration of 5 to 20%. If the concentration of the polyamic acid solution is less than 5%, the viscosity during the spinning process is too low to form the nanofibers (1), or the polyamic acid nanofibers (1) having a uniform diameter cannot be prepared, whereas When the concentration of the polyamic acid solution exceeds 20%, the viscosity is too high during the spinning process, so that the binding force of the solution is too large and the discharge pressure is rapidly increased, the spinning may not be performed or the processability may be lowered.

Next, the nanofibers 1 are prepared by electrospinning the polyamic acid solution. That is, in a solution tank in which a polyamic acid solution, which is a spinning solution, is stored, a predetermined amount of the spinning solution is supplied to a spinning unit using a metering pump, and the spinning solution is discharged through a nozzle installed under the spinning unit, and then scattered toward the focusing unit. Nanofibers (1) can be produced by the process of making.

In this case, the intensity of the electric field between the radiating part and the focusing part may be 850 to 3,500 V / cm. If the strength of the electric field is less than 850 V / cm, since the spinning solution is not continuously discharged, the nanoweb 10 of uniform thickness cannot be manufactured, and the formed nanofibers 1 are scattered at high speed. Since the focused polymer cannot be smoothly focused, the discharged polymer solution may not be sufficiently fibrous, and thus, the nanoweb 10 may be difficult to form. On the other hand, when the intensity of the electric field is more than 3,500V / cm, the scattered nanofibers (1) may not be accurately seated in the focusing portion may not form a normal nanoweb (10).

Next, a nanofiber (1) aggregate is prepared from the nanofibers (1). That is, the nanofibers 1 assembly is manufactured through a process in which the nanofibers 1 manufactured under the above conditions are entangled with each other in the focusing portion to form an irregular and discontinuous three-dimensional network structure.

In addition, the process of manufacturing the nanofiber (1) aggregate may be performed including a heat treatment process. That is, the surface of the nanofiber 1 assembly may be smoothed and the thickness may be uniform by heat-treating the nanofiber 1 assembly manufactured through the spinning process using a device such as a hot press. The aggregate of nanofibers (1) formed in the converging portion may have an uneven surface due to the formation of loops on the surface. Loops formed on the surface of the nanofibers (1) aggregate are subjected to high temperature and pressure by a hot plate such as a hot press. It becomes flat and even, so that the surface of the nanofiber (1) aggregate is smoother and the thickness of the nanofiber (1) aggregate is uniform.

Next, a polyimide nanofiber (1) aggregate is prepared through a process of imidizing the polyamic acid nanofiber (1) aggregate. The step of imidation can be carried out through a heat imidation step, a chemical imidation step, or a step using a combination of heat imidation and chemical imidization.

The chemical imidization may be performed through a process of treating the polyamic acid nanofibers (1) aggregate with a dehydrating agent such as acetic anhydride and an imidization catalyst such as tertiary amines such as pyridine. The thermal imidization may be performed through a process of heating the polyamic acid nanofibers (1) to a temperature of 80 to 400 ℃. The imidization using the chemical imidization and thermal imidization processes is a process of activating the dehydrating agent and the imidization catalyst by treating the polyamic acid nanofibers (1) with a dehydrating agent and an imidizing catalyst, followed by heat treatment. It can be done through. As described above, when the chemical imidization step and the thermal imidation step are performed in parallel, the polyamic acid nanofiber (1) aggregate can be imided more smoothly.

Through such an imidization process, polyimide nano aggregates having an imidation ratio of 90% or more can be produced.

Optionally, the above-described heat treatment process and thermal imidation process may be performed simultaneously using the same apparatus.

Next, the thickness of the nanofiber (1) aggregate is measured using a non-contact method. Thus, the thickness and thickness uniformity of the prepared nanofiber (1) assembly can be measured, and if the difference between the expected thickness and the actual thickness is severe, the thickness is adjusted by changing the spinning conditions. In this way, the thickness of the nanofiber (1) aggregate can be managed within a predetermined range through a process of measuring the thickness of the nanofiber (1) aggregate, thereby obtaining a nanofiber (1) aggregate having a uniform thickness. Can be.

The thickness of the conventional nanofiber (1) aggregate was measured by a contact method of directly measuring the nanofiber (1) aggregate as a sample between the gauges using a thickness gauge. However, such a contact method has an advantage of easy measurement, but the measured thickness of the film may vary according to the pressing force, and there is a problem that the measurement error increases according to the skill of the measurer.

The present invention indirectly measures the thickness of the nanofiber (1) aggregate. In other words, instead of measuring the thickness of the nanofiber (1) aggregate directly by contact method, the nanofibers (through a non-contact method of measuring the color difference of the nanofiber (1) aggregate using a spectrophotometric apparatus and converting the thickness therefrom) 1) Measure the thickness of the aggregates. In more detail, a reference sample having a known thickness is prepared in advance, a b value, which is a measure of yellow color of the reference sample, is measured using a spectrophotometer, and a linear regression line is obtained through data on the b value for each thickness. The thickness of the nanofiber (1) aggregate is measured by measuring the b value of the nanofiber (1) aggregate actually manufactured and converting the thickness from the measured b value using the linear regression line.

As described above, after the color difference of the nanofiber (1) aggregate is obtained using light, the thickness of the nanofiber (1) aggregate can be measured quickly and accurately by obtaining the thickness of the nanofiber (1) aggregate therefrom. As such, by accurately measuring the thickness of the nanofiber aggregates in a non-contact manner, the nanofiber aggregates of uniform thickness can be obtained by precisely controlling the manufacturing process of the nanofiber aggregates.

The nanoweb 10 of the present invention will be described in detail. 1 illustrates a nano web 10 according to an embodiment of the present invention. As shown in FIG. 1, the nanoweb 10 of the present invention includes a nano-assembly in which the polyamic acid nanofibers 1 and the polyamic acid nanofibers 1 are entangled with each other to form a three-dimensional network.

The polyamic acid nanofibers 1 may have an average diameter of 100 to 2,000 nm. When the average diameter of the polyamic acid nanofibers (1) is less than 100 nm, the diameter is too small to control the process and the shape stability may be poor, while the average diameter of the polyamic acid nanofibers (1) is 2,000 nm When exceeding, the diameter may be too large to make it difficult to manufacture the nano-web 10 having a thin thickness and excellent pore characteristics.

The nano aggregate may have a porosity of 50 to 99% and an average pore (2) of 0.5 to 3.0 ㎛. If the porosity of the nano-assembly is less than 50%, the performance of a product manufactured using the same cannot be improved, whereas if the porosity of the nano-assembly exceeds 99%, the morphological stability of the nanoweb 10 is reduced. Since fairness may be reduced. On the other hand, when the average pore (2) of the nano-assembly is less than 0.5 ㎛, the performance of the product manufactured using this cannot be improved, while the average web (2) of the nano-assembly is more than 3.0 ㎛ nanoweb The shape stability of (10) may be lowered and the processability may be lowered, and the performance of the product manufactured using the same may be lowered.

Since the conventional porous ePTFE film or polyimide film is manufactured by imparting a pore to the film, the porosity is low and the pore size is small, so that the performance is low, and there is a problem that it is not easy to manufacture a thin thickness.

On the other hand, since the porous nanoweb 10 of the present invention is manufactured by electrospinning, the thickness of the porous nanoweb 10 can be easily controlled, and thus, the thickness is thin. Accordingly, the product using the nano-web 10 of the present invention can increase the degree of integration can be greatly improved efficiency.

In addition, the porous nanoweb 10 of the present invention has a high porosity and a large average pore size because the nanofibers are entangled with each other to form a three-dimensional network structure. Accordingly, the fuel cell membrane and the like manufactured using the nanoweb 10 of the present invention can greatly improve the performance.

The nanoweb 10 of the present invention may include the polyimide nanoweb 10 produced by the imidation reaction of the polyamic acid nanoweb 10 described above. The polyimide nano web 10 preferably has a porosity and an average pore diameter of the polyamic acid nano web 10 described above. It is preferable that the polyimide nanoweb 10 has an imidation ratio of 90% or more. If the imidation ratio is less than 90%, since the heat resistance and chemical resistance are inferior, there may be a limit to use in a product requiring morphological stability at high temperature and insoluble property in an organic solvent.

The nano web 10 of the present invention may be 10 or more times of wear, measured by the provision of KS K ISO 12947-4: 2008 according to the Textile-Martindale method, which indirectly shows the wear strength. When the nanoweb 10 has the thickness and porosity described above, the nanoweb 10 may have a wear frequency of 10 to 20 times.

The provision of KS K ISO 12947-4: 2008 according to the Textile-Martindale method is a method of measuring the wear strength of cloth, and measures the number of wears until the appearance changes, and the increase in the number of wears is the nano web. Since the nanofibers constituting (10) are strongly concentrated, interlayer peeling between the nanofibers does not occur easily. Therefore, the nano web 10 having the wear strength of 10 or more times thus has excellent durability because the interlayer peeling does not occur easily.

Hereinafter, the effects of the present invention will be described in more detail with reference to Examples and Comparative Examples. These examples are merely to aid the understanding of the present invention and do not limit the scope of the present invention.

B value measurement according to the thickness of nano web

The polyamic acid was dissolved in dimethylformamide to make a 10% by weight polyamic acid solution, and the polyamic acid solution was discharged through a single nozzle installed in an electrospinning apparatus to form a nanofiber (1) and the formed nanofiber (1) Concentrating them to the focusing unit, by controlling the discharge time to produce a nano-web having a variety of thickness.

The nano webs prepared as described above were cut into 100 cm × 500 cm to prepare a sample, and the thickness and b value of the 1 cm × 1 cm point were measured from the upper left corner of the sample to the left and right directions. The b value was measured continuously and the results were averaged to calculate the final thickness and b value. At this time, the thickness was measured directly by using a thickness measuring device (model name: G, brand name: PEACOCK) that is a contact measuring instrument, and spectroscopic side device (model name: SF 600, brand name: Datacolor), which is a non-contact measuring instrument. B value was measured, and the number of measurements per sample was 20 times.

Table 1 shows the direct thickness and the b value measured in this way.

division Direct thickness (㎛) b value Sample 1 15 5.2 Sample 2 18 6.9 Sample 3 24 9.8 Sample 4 26 10.1 Sample 5 27 10.3

As shown in Table 1 above, it can be seen that the direct thickness of the nanoweb and the b value correlate.

Example  One

The polyamic acid was dissolved in dimethylformamide to make a 10% by weight polyamic acid solution, and the polyamic acid solution was discharged through a single nozzle installed in an electrospinning apparatus to form a nanofiber (1) and the formed nanofiber (1) The polyamic acid nano webs 10 were prepared by focusing them on a focusing unit. At this time, the viscosity of the polyamic acid solution used was 180 poise, the intensity of the electric field applied between the spinneret and the focusing unit installed below the single nozzle was 2,500 v / cm.

Example  2 to 5

In Example 1 described above, the polyamic acid nanoweb was prepared by the same method as Example 1, except that the intensity of the electric field applied between the radiating part and the focusing part was changed to 3600, 3400, 900, and 700 v / cm, respectively. (10) were prepared.

The physical properties of the polyamic acid nano webs 10 prepared by Examples 1 to 5 were measured by the following method, and the results are shown in Table 2 below.

Measuring Porosity (%)

The porosity can be measured from the ratio of the pore 2 in the total volume in the porous nano web 10, the density of the nanofiber (1) raw polymer, the volume of the nano web (10), the nano web (10) Using the weight of) was obtained by the following equation.

Porosity (%) = (density of nano web / density of nano fiber raw material polymer) × 100 = [(weight of nano web / volume of nano web) / density of nano fiber raw material polymer] × 100

Average Fiber diameter (Μm)

Samples were prepared from each of the polyamic acid nano webs 10 prepared by the examples, and images of the samples having a predetermined magnification were obtained by using an electron scanning microscope image (model name: JSM6700F, trade name: JEOL) device, and the center of the image was obtained. The average fiber diameter was calculated by averaging 10 values starting from the nanofibers (1) closest to the point.

Wear count measurement

The number of wear was measured to indirectly check the interlaminar peel strength. Samples were prepared from each of the polyamic acid nano webs 10 prepared by the examples, and the number of wear was measured according to the provisions of KS K ISO 12947-4: 2008 according to the Textile-Martindale method. In this case, since the strength of the polyamic acid nano web 10 is weak, the wear felt is a plain weave fabric woven from 70 denier nylon 6 fibers.

division Average fiber diameter (㎛) Porosity (%) Wear Example 1 1.5 94.4 18 Example 2 1.1 97.8 10 Example 3 1.3 96.4 13 Example 4 1.7 94.6 10 Example 5 1.8 94.7 5

Example  6

The polyamic acid nanoweb 10 obtained in Example 1 was heat-treated for 20 minutes in a hot press maintained at 200 ° C to prepare a polyimide nanoweb 10 having an imidation ratio of 99%.

Comparative example  One

A commercially available ePTFE porous film (manufacturer: WL Gore, trade name: Teflon) having a thickness of 15 μm was used.

The physical properties of the polyimide nanoweb 10 prepared in Example 6 and the ePTFE porous film of Comparative Example 1 were measured by the following method and are shown in Table 3 below.

Porosity and average pore measurement

It measured by the method mentioned above.

Heat resistance measurement

Differential scanning calorimetry (model name: DSC-Q100, manufacturer: TA Instrument, temperature rising rate of 10 ℃ / min, 0 ~ 400 ℃ temperature range) to polyimide nano webs (10) and ePTFE porous film to indirectly check the heat resistance Melt temperature (Tm) was measured.

Chemical resistance measurement

The chemical resistance of the polyimide nano webs 10 and the ePTFE porous film is measured by first measuring the dry weight of the sample left in a vacuum oven set at 50 ° C. for at least 24 hours, and then immersing the dry sample in dimethylformamide. After removing 1 hour, washed 5 times in a large amount of distilled water and left for 24 hours in a vacuum oven set at 50 ℃ after measuring the dry weight, the weight change calculated by the weight difference of the sample before and after drying is less than ± 10% The organic solvent was evaluated to have chemical resistance.

division Porosity (%) Average pore size (㎛) Melting temperature (℃) Chemical resistance Example 6 86.4 1.53 More than 400 has exist Comparative Example 1 33.3 0.25 327 has exist

1 illustrates a nanoweb according to an embodiment of the present invention.

DESCRIPTION OF THE RELATED ART [0002]

1: nanofiber 2: voids

10: Nano Web

Claims (9)

Preparing a polyamic acid solution; Preparing nanofibers by electrospinning the polyamic acid solution; Preparing nanofiber aggregates from the nanofibers; And Method of manufacturing a nano-web comprising the step of measuring the thickness of the nanofiber aggregate using a non-contact method. The method of claim 1, The polyamic acid solution is a method for producing a nano-web, characterized in that 5 to 20% by weight. The method of claim 1, The manufacturing method of the nanofibers is a method of manufacturing a nano-web, characterized in that the electric field of 850 to 3500 V / cm is applied between the radiating portion and the focusing portion of the electrospinning apparatus. The method of claim 1, Method for producing a nano-web characterized in that it further comprises an imidization process for converting the polyamic acid nanofiber aggregates into polyimide nanofiber aggregates. The method of claim 1, The step of measuring the thickness of the nanofiber aggregates comprises the step of measuring the color difference of the nanofiber aggregates using a spectrophotometric apparatus. The method of claim 5, The process of measuring the color difference of the nanofiber aggregate comprises the step of measuring the b value which is a measure of yellow and converting the thickness of the nanofiber aggregate through the b value. Polyamic acid nanofibers having an average diameter of 100 to 5,000 nm; And The polyamic acid nanofibers are entangled with each other to form a three-dimensional network, the nanoweb comprising a nano aggregate having a porosity of 50 to 99% and an average thickness of 5 to 40 ㎛. The method of claim 7, wherein The nano-web is characterized in that the wear strength measured by the regulation of KS K ISO 12947-4: 2008 according to the textile-Martindale method 10 times or more. 8. The method according to claim 6 or 7, Including the polyimide nano-assembly having an imidation rate of 90% or more by the imidization reaction of the polyamic acid nano-assembly, The polyimide nanofibers have an average diameter of 100 to 5,000nm, the polyimide nanofiber aggregate has a porosity of 50 to 99% and an average thickness of 5 to 40 ㎛.

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