JP2007015202A - Composite structure and filter using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a composite structure that excels in deodorant and antibacterial properties and efficiently removes harmful substances, and a filter using it. <P>SOLUTION: The composite structure is formed by laminating an ultrafine fiber and a fiber structure. The ultrafine fiber has a diameter of 1-1,000 nm, the fiber composing the fiber structure has a diameter of 1-100 μm, and an inorganic material that decomposes substances by photoexcitation is supported on the composite structure. The filter using the composite structure is also provided. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a composite structure formed by laminating ultrafine fibers and a fiber structure, and a filter using the same. The present invention also relates to a composite structure that can be suitably used for filters, masks, and the like that remove harmful chemical substances contained in indoor air and wastewater.

  Conventionally, in order to impart a deodorant and antibacterial function to a fiber fabric, one having a photocatalyst layer has been proposed (for example, Patent Document 1).

In contrast, the market demands a high level of deodorization and antibacterial functions, and there is a demand for efficient removal of harmful substances. However, conventionally, as a substrate for supporting such a photocatalyst, a woven fabric or a non-woven fabric made of general-purpose synthetic fibers such as polyester has been used, and there is a limit to the amount of photocatalyst that can be supported on these, and a filter that removes harmful chemical substances. When used in applications such as sheet and sheet, there is a drawback that the performance is not sufficiently exhibited.
Japanese Patent Laid-Open No. 10-1879

  An object of the present invention is to solve the above-described problems of the background art and provide a composite structure excellent in deodorization and antibacterial performance and efficiently removing harmful substances, and a filter using the same.

  As a result of intensive studies to achieve the above-mentioned object, the present inventors have supported an inorganic substance (photocatalyst) that decomposes a substance by photoexcitation on a fiber structure in which ultrafine fibers with extremely fine nano-levels are laminated. When this was used as a filter, it was found that it exhibited excellent antibacterial deodorization performance that was not possible in the past, and that it could efficiently remove harmful substances.

  Thus, according to the present invention, a composite structure is formed by laminating ultrafine fibers and a fiber structure, the diameter of the ultrafine fibers being 1 to 1000 nm, and the diameter of the fibers constituting the fiber structure being 1 to 100 μm. And a composite structure characterized in that an inorganic material that decomposes a substance by photoexcitation is supported on the composite structure.

  In the present invention, a structure in which ultrafine fibers having a specific fineness and a fiber structure are laminated is suitable for decomposing while adsorbing harmful substances. In particular, a photocatalyst is applied to ultrafine fibers having a very large specific surface area. When gaseous harmful substances and the like are caused to flow through the composite structure by being supported, the contact efficiency is extremely high, so that the harmful substances can be efficiently decomposed. Thereby, the composite structure of this invention can exhibit the outstanding antimicrobial and deodorizing effect.

  The composite structure of the present invention is a composite structure formed by laminating ultrafine fibers and a fiber structure. In the present invention, the diameter of the ultrafine fiber is 1-1000 nm, the diameter of the fiber constituting the fiber structure is 1-100 μm, and the composite structure carries an inorganic material (photocatalyst) that decomposes the substance by photoexcitation. It is important to be. In this way, especially when the photocatalyst is supported on an ultrafine fiber with a very large specific surface area, when the composite structure such as a gaseous harmful substance is flowed to the composite structure, the contact efficiency becomes high and the harmful substance is efficiently decomposed. Can do. In addition, the laminated structure of the ultrafine fibers and the fiber structure as described above is suitable for decomposing while adsorbing harmful substances, and can maintain a high air permeability for a long time with little decrease in pressure loss. It also has merit.

  Therefore, in the present invention, the diameter of the ultrafine fiber single fiber needs to be 1-1000 nm, preferably 10-800 nm. When the diameter of the single fiber is less than 1 nm, the strength of the composite structure is reduced. On the other hand, when the diameter of the single fiber exceeds 1000 nm, functions such as high deodorization and antibacterial performance, which are the objects of the present invention. Cannot be obtained.

Also, the basis weight of the microfine fibers 0.001~1.0g / ^{m 2,} preferably it is desirable to 0.001 to 0.5 g / ^{m 2.} If it is less than 0.001 g / m ² , it tends to be difficult to uniformly coat the fine fiber on the surface of the fiber structure. On the other hand, if it exceeds 0.5 g / m ² , sufficient air permeability cannot be obtained. There is a tendency.

In addition, when using the composite structure of this invention for a filter, the fabric weight of a microfiber can be suitably changed according to the structure of the filter unit which installs it. Specifically, when used in a vertical flow unit that allows gaseous harmful chemicals to flow vertically (cross-sectional direction of the composite structure) with respect to the surface of the composite structure as shown in FIG. In order to reduce the pressure loss, the basis weight of the ultrafine fibers is preferably in the range of 0.001 to 0.1 g / m ² . On the other hand, when used in a parallel flow unit that allows gaseous hazardous chemicals to flow parallel to the composite structure surface as shown in FIG. 2 (in the direction of the composite structure surface), the contact efficiency between the gaseous harmful chemicals and the composite structure In order to improve the weight, the basis weight of the ultrafine fiber is preferably in the range of 0.001 to 0.5 g / m ² .

  The ultrafine fibers are preferably formed from one or more polymers by electrospinning. This electrospinning method will be described in detail later.

  In the present invention, any polymer capable of forming the ultrafine fiber having the fineness described above by the electrospinning method or the like may be used as the polymer constituting the ultrafine fiber. In particular, acrylonitrile and aromatic polyamides, particularly aromatic polyamides based mainly on polymetaphenylene isophthalamide are preferred in that they can be put into practical use as moldability, filters, etc., and can also provide other performance such as heat resistance. .

  Next, the fiber structure used in the present invention refers to a woven or knitted fabric, a nonwoven fabric, a paper-like material, or the like. The fibers constituting the fiber structure include natural fibers such as cotton and hemp, inorganic fibers such as glass fibers, carbon fibers, and metal fibers, and polyamide fibers, polyester fibers, aromatic polyamide fibers, acrylic fibers, Synthetic fibers such as polyvinyl chloride fiber, polyolefin fiber, and polyacrylonitrile fiber can be mentioned. When high heat resistance and chemical resistance are required for the composite fiber structure, inorganic fiber or aromatic polyamide is used for synthetic fiber. Fiber is more preferred.

  In addition, as described above, in the case of ultrafine fibers of a polyacrylonitrile-based polymer, a heat-resistant fiber having a heat resistance of 1000 ° C. or higher, for example, glass fiber, carbon fiber, metal fiber, etc., is selected as the fiber structure to be laminated. Thus, after laminating them, it becomes possible to fire at 1000 ° C. or higher, and polyacrylonitrile ultrafine fibers can be carbonized to form a composite structure further improving the adsorption performance of gaseous harmful chemical substances and the like. it can.

  The diameter of the fiber constituting the fiber structure is preferably 1 to 100 μm, more preferably 3 to 50 μm. If the diameter of the fiber is less than 1 μm, the entire fiber structure tends to have a clogged structure, and it becomes difficult to obtain sufficient air permeability, and the antibacterial and deodorizing effects tend to be reduced. On the other hand, when it exceeds 100 μm, the inter-fiber voids become large, and the collection efficiency, antibacterial effect, and deodorizing effect tend to be reduced due to a decrease in the chance of collision of the particles to be collected with the fibers.

  The shape of the fiber may be any shape such as a short fiber yarn, a long fiber yarn, a split yarn, or a tape yarn.

In the present invention, the ultrafine fiber of the composite structure needs to carry an inorganic material that decomposes a substance by photoexcitation. Here, the inorganic material that decomposes a substance by photoexcitation is an inorganic material selected from TiO ₂ , ZnO, SnO ₂ , SrTiO ₃ , WO ₃ , Bi ₂ O ₃ , Fe ₂ O _3, etc. A substance that exhibits a photoexcitation effect by visible light.

  In the present invention, the binder for supporting the inorganic material on the surface of the ultrafine fiber is preferably a silicone resin in which at least a part of the organic group bonded to the silicon atom is substituted with a hydroxyl group. The silicone resin is, for example, methyltrimethoxysilane, ethyltrimethoxysilane, phenyltrimethoxysilane, methyltriethoxysilane, ethyltriethoxysilane, phenyltriethoxysilane, methyltriisopropoxysilane, ethyl as organoalkoxysilane. Triisopropoxysilane, phenyltriisopropoxysilane, dimethyldiethoxysilane, diethyldiethoxysilane, phenylmethyldimethoxysilane, diphenyldimethoxysilane, dimethyldiethoxysilane, diethyldiethoxysilane, phenylmethyldiethoxysilane, dimethyldiisopropoxy Examples include silane, diethyldiisopropoxysilane, phenylmethyldiisopropoxysilane, and mixtures thereof.

  The amount of the photocatalyst supported is 0.1 to 10% by weight, preferably 4 to 8% by weight, based on the weight of the composite structure. If the amount is less than 0.1% by weight, the ability to adsorb and decompose gaseous harmful chemicals is insufficient. On the other hand, if the amount exceeds 10% by weight, voids between fibers are easily crushed by an excess photocatalyst. Problems such as increased loss are likely to occur.

  As a method for manufacturing the composite structure described above, the following method can be employed. That is, as a method of laminating ultrafine fibers on the fiber structure, the above-described electrospinning method can be preferably employed. In the electrospinning method, a high voltage is applied to a polymer solution to spray the solution to form ultrafine fibers. The thickness of the ultrafine fiber depends on the applied voltage, the solution concentration, and the spray scattering distance. By producing ultrafine fibers continuously on a substrate, a thin film having a three-dimensional structure with a three-dimensional network can be obtained. For example, new properties and functions are expected to be improved by making the functional thin film that has been studied so far into a three-dimensional structure. In addition, this method makes it possible to increase the thickness of the membrane like a fabric such as a nonwoven fabric, and a nonwoven fabric having a submicron network can be manufactured.

  Specifically, a powder of a polymer mainly composed of polyacrylonitrile is dissolved in a solvent N, N-dimethylformamide at a weight ratio of 0.1 to 20% by weight, and the applied voltage is in the range of 0.1 to 30 kV. It can be obtained by selecting optimum conditions and spinning on the fiber structure.

  Here, a solvent having a low boiling point and a high polarity is preferable as the solvent for dissolving the polymer powder containing polyacrylonitrile as a main component. For example, N-methyl-2-pyrrolidone, N, N-dimethylformamide, N, N-dimethylacetamide, tetramethylurea, N-methylcaprolactam, N-methylbiperidine and the like are exemplified, but preferably N, N- Select dimethylformamide.

  In addition, if the polymer concentration (viscosity) is decreased to reduce the viscosity, the absolute amount of the polymer to be charged decreases, and the deformation of the solution does not easily occur due to the decrease in the amount of charge of the polymer. It becomes a film. On the other hand, if the concentration is high, ultrafine fibers can be easily formed due to an increase in the charge amount of the polymer, but the amount of solvent decreases and the evaporation rate increases, so that solidification proceeds rapidly and the fiber diameter increases.

  Considering the above, it is preferable to select N, N-dimethylformamide as a solvent and make the polymer concentration 10 to 15% by weight in the production of polyacrylonitrile microfibers.

  As another example, in the case of an aromatic polyamide ultrafine fiber, 1-50 kV of a solution in which an aromatic polyamide containing polymetaphenylene isophthalamide as a main component is dissolved in a solvent at a concentration of 0.1 to 20% by weight. A method is preferably employed in which an aromatic polyamide ultrafine fiber is formed by applying a voltage to spin, and then laminated on the fiber structure.

  The solvent for dissolving the aromatic polyamide fiber is preferably a polar solvent having a low boiling point and a high polarity. For example, N, N-dimethylacetamide, N-methyl-2-pyrrolidone, N, N-dimethylformamide, tetramethylurea, N-methylcaprolactam, N-methylbiperidine and the like are exemplified, and in particular, N, N-dimethylacetamide, N -Methyl-2-pyrrolidone is preferred.

  Further, by adding an alkali metal salt to the solution, it becomes easy to be charged and the spinning state is very stable. Examples of the alkali metal salt include lithium chloride, calcium chloride, sodium chloride, potassium chloride, and magnesium chloride, with lithium chloride and calcium chloride being particularly preferable. As addition amount of said alkali metal salt, 0.1 to 1.0 weight% is preferable with respect to the weight of a solvent.

  The ultrafine fiber may have fine pores on the fiber surface in order to improve the contact opportunity with the gaseous harmful chemical substance. From this point of view, when the ultrafine fibers are laminated in a non-woven shape, it is preferable to select a spinning condition for electrospinning to make the structure bulky.

  Furthermore, as a method for supporting the photocatalyst on the obtained composite fiber on the composite structure, particularly the ultrafine fiber through the above-mentioned binder, spray coating method, roll coating method, spin coating method, flow coating method, dip coating method Other known coating methods can be exemplified. In particular, the dip coating method is preferable for uniformly applying the photocatalyst to the surface of the ultrafine fiber. The thickness of the photocatalyst layer can be adjusted by the concentration, and is adjusted according to the basis weight of the ultrafine fiber composite filter. Furthermore, the photocatalyst used preferably has an average primary particle size of 0.1 μm or less, and the optimum concentration of the photocatalyst solution is preferably in the range of 1 to 4% by weight.

  The composite structure thus obtained is preferably used for applications that require the adsorption and decomposition of harmful chemical substances contained in the air and water, such as a filter for purifying indoor air and a filter for purifying wastewater. Hazardous chemical substances adhering to a filter or the like cannot be completely removed from the atmosphere and water by simply adsorbing them, so they must be decomposed at the same time while being adsorbed. It was found that gas adsorption and decomposition easily occur due to the lamination of the fiber structure.

In addition, in terms of the ability of photocatalysts to decompose gaseous hazardous chemicals, the amount of photocatalyst supported increases even when the amount of ultrafine fibers stacked is small compared to fibers used in general filters. As the specific surface area is increased, the photocatalytic activity is remarkably increased, and the decomposition efficiency is remarkably improved. For example, nitrogen oxides (NO _x ) such as nitrogen monoxide (NO) and nitrogen dioxide (NO ₂ ) generated and generated when ammonia gas is treated, ammonium ions (NH 4 ⁺ ) and nitrate ions detected from a filter When the concentration of (NO 3 ⁻ ) is measured, a filter in which ultrafine fibers are laminated exhibits a high decomposition ability.

  Hereinafter, the present invention will be described in more detail based on examples. In addition, each physical property in an Example is calculated | required with the following method.

Ammonia gas (10 ppm in Example 1 and Comparative Example 1 below, 100 ppm in Example 2 and Comparative Example 2) as a harmful chemical substance is placed inside the filter unit in which the composite structure shown in FIGS. The gas concentration at the gas outlet in the evaluation apparatus was measured at regular intervals while flowing at 0.0 L / min and irradiating with an ultraviolet lamp (intensity ² mW / m ² ). For the ammonia gas concentration and NO _x concentration, a gas detector tube was used, and at the same time, in order to confirm the progress of decomposition, decomposition products (ammonium ions (NH4 ⁺ ), nitrate ions (NO3 ⁻ ) remaining in the filter after the test were used. ) Was measured by ion chromatography. Moreover, about the removal performance of ammonia, it calculated as a removal rate using following Formula. It can be said that the higher the removal rate after a certain period of time, the better the performance. (Tables 1 and 3)
(Removal rate) = [1− (ammonia concentration after a fixed time / initial ammonia concentration)] × 100
Furthermore, the degree of progress of decomposition was calculated as the mass balance of nitrogen from the measurement results obtained by the gas detector tube and the ion chromatography. (Table 2)

[Example 1]
A polyester fiber non-woven fabric (fiber diameter: 25 μm, basis weight: 11.2 g / m ² ) was dissolved in a weight ratio of 11:89 with a polymer powder containing polyacrylonitrile as a main component and solvent N, N-dimethylformamide. the polymer solution was prepared, the fiber diameter under applied voltage 20kV by electrospinning method are laminated basis weight 0.5 g / ^{m 2} to about 200nm polyacrylonitrile ultrafine fibers, the composite structure (basis weight 11.7 g / ^{m 2)} Produced. A solution prepared by mixing this composite structure with a mixed solvent of isopropyl alcohol and methanol (weight ratio 50/50) and 4% photocatalytic titanium dioxide slurry solution (Pal titanium 3607; manufactured by Nihon Parkerizing Co., Ltd.) at 50/50. A composite structure (weight per unit area: 12.4 g / m ² ) carrying a photocatalyst was prepared.

  Next, a vertical flow unit that allows gaseous harmful chemicals to flow perpendicularly (cross-sectional direction of the composite structure) to the surface of the composite structure as shown in FIG. 1 and parallel to the surface of the composite structure as shown in FIG. Four composite structures (20 cm square) carrying the above-mentioned photocatalyst were installed in a parallel flow unit in which a gaseous harmful chemical substance flows in the (composite structure surface direction), and a gas decomposition performance test was performed. The results are shown in Tables 1 and 2.

[Comparative Example 1]
Except for not laminating polyacrylonitrile microfibers, a solution prepared by mixing a mixed solvent of isopropyl alcohol and methanol and a 4% photocatalyst titanium dioxide slurry solution was applied to the polyester fiber nonwoven fabric in the same manner as in Example 1, and the photocatalyst was applied. A supported nonwoven fabric was produced. Subsequently, the gas decomposition performance test of this nonwoven fabric was implemented like Example 1. FIG. The results are shown in Tables 1 and 2.

[Example 2]
Polyester fiber non-woven fabric (fineness 0.2 dtex: 0.3 dtex: 1.2 dtex = 35: 50: 15 mixing ratio, basis weight 7.5 g / m ² ) powdered body mainly composed of polymetaphenylene isophthalamide and chlorinated A polymer solution in which lithium and a solvent N, N-dimethylacetamide are dissolved at a weight ratio of 10: 89: 1 is prepared, and an aromatic polyamide ultrafine fiber having a fiber diameter of 65 nm is applied under an applied voltage of 20 kV by an electrospinning method. 0.5 g / m ^{2 was} laminated to produce a composite structure (weight per unit area: 8.0 g / m ² ). Prepared by mixing 50/50 with a mixed solvent of isopropyl alcohol and methanol (weight ratio 50/50) and 4% photocatalytic titanium dioxide slurry solution (Pal titanium 3607; manufactured by Nihon Parkerizing Co., Ltd.) to the obtained composite structure. The resulting solution was applied at 1.0 g / m ² to prepare a composite structure carrying a photocatalyst. Next, four composite structures (20 cm square) carrying the above-mentioned photocatalyst in a vertical flow unit that allows gaseous harmful chemicals to flow vertically (in the direction of the cross section of the composite structure) with respect to the surface of the composite structure as shown in FIG. ) Installed and conducted a gas decomposition performance test. The results are shown in Table 3.

[Comparative Example 2]
Except for not laminating aromatic polyamide ultrafine fibers, a solution prepared by mixing a mixed solvent of isopropyl alcohol and methanol with a 4% photocatalytic titanium dioxide slurry solution was applied to a polyester fiber nonwoven fabric in the same manner as in Example 2. A nonwoven fabric carrying a photocatalyst was prepared. Subsequently, the gas decomposition performance test of this nonwoven fabric was implemented like Example 2. FIG. The results are shown in Table 3.

  In the present invention, the structure in which the ultrafine fibers having a specific diameter and the fiber structure described above are laminated is suitable for decomposing while adsorbing harmful substances, and is particularly suitable for ultrafine fibers having a very large specific surface area. When gaseous harmful substances and the like are caused to flow through the composite structure due to the support, the contact efficiency is extremely high and the harmful substances can be efficiently decomposed. Thereby, the composite structure of this invention exhibits the outstanding antibacterial and deodorizing effect, and can be preferably used for a filter, a mask, etc. In particular, when a filter using the above-mentioned fiber structure is used, it exhibits extremely high antibacterial and deodorizing performances that have not been achieved in the past.

It is the schematic which shows an example of the vertical flow unit apparatus which evaluates the gas decomposition | disassembly performance of a filter. It is the schematic which shows an example of the parallel flow unit apparatus which evaluates the gas decomposition | disassembly performance of a filter.

Explanation of symbols

1: UV lamp 2: Photocatalyst carrying composite structure 3: Test gas filling port 4: Test gas discharge port 5: Gas flow

Claims (6)

  A composite structure formed by laminating ultrafine fibers and a fiber structure, wherein the diameter of the ultrafine fibers is 1 to 1000 nm, the diameter of the fibers constituting the fiber structure is 1 to 100 μm, and the composite structure A composite structure characterized in that an inorganic material that decomposes a substance by photoexcitation is supported on the body. The composite structure of claim 1, wherein the basis weight of the fiber structure is in a range of 0.001~1.0g / ^{m 2.}   The composite structure according to claim 1, wherein the amount of the inorganic material supported is 0.1 to 10% by weight based on the weight of the composite structure.   The composite structure according to claim 1, wherein the ultrafine fiber is an ultrafine fiber made of a polyacrylonitrile-based polymer.   The composite structure according to claim 1, wherein the ultrafine fiber is an ultrafine fiber made of polymetaphenylene isophthalamide-based aromatic polyamide.   A filter using the composite structure according to claim 1.

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