JP2007321252A - Sheet for adsorption of boron compound - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a boron-adsorption sheet composed of ultrafine filament nonwoven fabric having good adsorptivity of boron compounds and provide a method for producing the sheet and use of the sheet. <P>SOLUTION: The sheet for the adsorption of boron compounds is a nonwoven fabric composed of filaments comprising (i) a modified polyvinyl alcohol containing 1-20 mol% ethylene unit and (ii) other thermoplastic polymer, wherein the modified polyvinyl alcohol (i) occupies ≥10% of the fiber surface and ≥1 mass% of the nonwoven fabric. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a boron compound-adsorbing sheet used for removing boron and / or boron compounds, using a long-fiber nonwoven fabric comprising thermoplastic polyvinyl alcohol having low crystallinity as a component, and preferred embodiments thereof. It is related with the filter which is an example, and also the manufacturing method of the sheet | seat.

  Conventionally, a filter made of glass fiber is used in air purification in a clean room or the like. This glass fiber contains boron, reacts with hydrofluoric acid in a clean room, and a boron compound is released into the room. In recent years, the need for work in highly clean spaces in the semiconductor, liquid crystal, and medical fields has increased. Especially in semiconductor manufacturing plants, it is necessary to keep chemical substances in clean rooms to the ppb level. Efficient removal is required.

  In response to such demands, chemical filters using ion exchange resins have been proposed, but efficient removal of boron compounds other than boric acid is difficult. In addition, since the ion exchange resin takes a bead-like form, when used as a filter, it is necessary to fix the beads to the base sheet using an adhesive, which is sufficient in terms of surface area, handleability, and moldability. is not.

  On the other hand, the adsorption filter in the fiber sheet state is excellent in moldability, easy to handle, and has an advantage that the fibrous adsorbent has excellent adsorption performance due to its large surface area compared to the granular adsorbent.

From this point of view, Patent Document 1 discloses a boron removing filter having a hydroxyl group and a gas cleaning method using the same. Namely, in order to remove contaminants such as boron and boron compounds volatilized from the HEPA filter for clean room or trimethylamine generated from the ion exchange fiber, it is made of a polyvinyl alcohol fiber, particularly a resin having the same ion exchange group as the polyvinyl alcohol. It is described that it is preferable to use a short fiber non-woven fabric or a paper made from the short fiber.
However, in the case of a short fiber nonwoven fabric or papermaking paper, fiber waste is generated from the nonwoven fabric or paper, so that it is not suitable for a clean room. Furthermore, in the case of such a nonwoven fabric or papermaking, it discovered that PVA which comprises a fiber did not adsorb | suck a boron compound as expected.

  Patent Document 2 describes that a nonwoven fabric obtained by melt-blowing ethylene-modified polyvinyl alcohol is used as a boron adsorption filter. However, in the case of this non-woven fabric, the form stability is low in a high humidity atmosphere, and since it is water-soluble, it cannot be used for a water treatment filter, and when the constituent fibers are made extremely fine to enhance the performance, There is a problem that the form stability under a high humidity condition is further lowered, the sheet is swollen and contracted, and the pressure loss is increased.

JP-A-10-192623 JP 2001-62218 A

  As described in the above document, it is well known that the hydroxyl group of the polyvinyl alcohol fiber is coordinated to boron in the boron compound to form a complex. In addition, since the hydroxyl group and boron in the non-crystalline region form a complex, it is preferable to use a polyvinyl alcohol fiber having a crystallinity as low as possible, thereby exhibiting high adsorption performance.

  In order to further improve the performance, it is effective to increase the surface area of the polyvinyl alcohol, and it is possible to improve the adsorption and removal efficiency of the boron compound and to extend the life. The means for improving the surface area is achieved by making the fineness of the sheet-constituting fibers finer.

  As a method for producing an ultrafine fiber sheet, a method is also known in which a composite fiber sheet made of a polymer of two or more components is processed and the fiber constituting the sheet is divided in the length direction to make it ultrafine. Two or more kinds of components exist in the nonwoven fabric. By removing one component using chemicals, it is possible to obtain an ultrafine fiber sheet consisting of only one component, but the component other than the component to be removed is unfavorably affected, so the composite fiber is composed. In many cases, combinations of components to be limited are limited.

  On the other hand, polyvinyl alcohol (hereinafter sometimes abbreviated as PVA) is a water-soluble polymer, and it is known that the degree of water-solubility can be changed by its basic skeleton, molecular structure, form, and various modifications. . Moreover, it has been confirmed that PVA is biodegradable. Currently, PVA and PVA fibers having such basic performance are attracting a lot of attention because how to harmonize the synthetic material with the natural world has become a major issue in terms of the global environment.

  The purpose of the present invention is to have a high adsorption performance for boron compounds compared to conventional PVA fibers, and even to form stability and strength under high humidity conditions even when the constituent fibers are made extremely fine. The object is to provide an excellent sheet for adsorbing boron compounds.

  The present invention comprises a non-woven fabric composed of long fibers composed of a modified PVA (A) containing 1 to 20 mol% of ethylene units and another thermoplastic polymer (A), and the non-woven fabric includes a modified PVA (A) Is a boron compound-adsorbing sheet characterized in that it is present in an amount of 1% by mass or more based on the mass of the nonwoven fabric in a state in which 10% or more of the fiber surface is occupied.

And, preferably, the average fineness of the long fibers is 0.5 dtex or less and the modified PVA (a) is present in the amount of 1 to 30% by mass relative to the mass of the nonwoven fabric, or the modified PVA (a) is a plasticizer. Is contained.
Furthermore, the present invention is a boron adsorption filter having the boron compound adsorption sheet, specifically, a boron adsorption chemical filter or a boron adsorption liquid filter, and the boron is disposed downstream of the glass fiber sheet. A boron adsorption filter in which adsorption sheets are laminated.

  Furthermore, the present invention removes a part of the modified PVA (a) by treating the spunbonded nonwoven fabric composed of the composite long fiber composed of the modified PVA (a) and another thermoplastic polymer (a) with hot water. It is a manufacturing method of the boron compound adsorption | suction sheet | seat characterized by doing.

  The long fibers constituting the present invention have the above-mentioned special modified PVA (A) on the fiber surface, but this modified PVA (A) has more non-crystalline regions compared to PVA constituting ordinary PVA fibers, High adsorption capacity for boron compounds. And it is preferable as a boron adsorption filter that such modified PVA (a) exists firmly on the fiber surface, and in the present invention, from the composite fiber of the modified PVA component (a) and another thermoplastic resin (a). By using a method of extracting and removing a part of the modified PVA (a) with hot water, the non-woven fabric constituent fiber becomes extremely fine, and the modified PVA (a) exists firmly on the fiber surface, and boron adsorption capacity Will increase more.

Hereinafter, the present invention will be described in detail.
In the present invention, the modified PVA (a) needs to contain 1 to 20 mol% of ethylene units, and preferably contains 3 to 20 mol% of ethylene units. When PVA with an ethylene unit of less than 1 mol% is used, if spinning is performed after spinning, the latent heat of fusion often exceeds 100 J / g, the non-crystalline region decreases, and the boron adsorption capacity decreases. . On the other hand, when the ethylene unit exceeds 20 mol%, the amount of hydroxyl group is reduced, the boron adsorption part is reduced, the water performance is lowered, and it is difficult to partially remove the modified PVA (a) from the composite fiber. It becomes.

  The ratio of the modified PVA (a) present in the nonwoven fabric of the present invention (the nonwoven fabric after being treated with hot water to dissolve and remove a part of the modified PVA) is 1% by mass or more based on the mass of the nonwoven fabric. It is necessary, preferably 1 to 30% by mass, more preferably 1 to 10% by mass. When the ratio of the modified PVA is less than 1% by mass, the boron adsorption capacity is lowered because the absolute amount of the PVA component in the nonwoven fabric is small. On the other hand, if it exceeds 30% by mass, the dimensional stability may be insufficient under high humidity, and the PVA may not be sufficiently removed, so that it may be difficult to reduce the size.

  In the present invention, it is necessary that the modified PVA (A) is exposed on the fiber surface, and the ratio thereof is 10% or more with respect to the total sheet surface area (that is, the total surface area of the nonwoven fabric constituting long fibers). It is necessary and it is preferable that it is 30 to 100%, and it is more preferable that it is 50 to 100%. When it is less than 10%, it becomes difficult for the boron compound and the PVA hydroxyl group to come into contact with each other, and the performance of efficiently adsorbing the boron compound decreases.

  Furthermore, the heat of fusion ΔH of the PVA constituting the long-fiber nonwoven fabric obtained in the present invention (that is, the nonwoven fabric treated with hot water after dissolving and removing a part of the modified PVA) is preferably 100 J / g or less. 50 to 80 J / g is more preferable. When it exceeds 100 J / g, the PVA means that there are few amorphous regions, and it is difficult to obtain the target boron adsorption ability.

  In the present invention, as described above, modified PVA (a) containing 1 to 20 mol% of ethylene units is used. This modified PVA (A) can be melt-spun. In general PVA and PVA having functional groups that are not suitable for melt spinning by post-modification, melt spinning and thermal decomposition temperature are close to each other, so melt spinning cannot be performed (that is, not thermoplastic). Various modifications are necessary for melt spinning, whereas the modified PVA (A) used in the present invention can be melt-spun without any special modification.

  200-800 are preferable, as for the viscosity average polymerization degree (henceforth abbreviated as polymerization degree) of modified PVA (a), 230-600 are more preferable, and 250-500 are especially preferable. PVA used for ordinary fibers has a higher degree of polymerization, and higher strength fibers are obtained. Therefore, those having a degree of polymerization of 1500 or more are common, for example, those having a degree of polymerization of about 1700 or about 2100. Usually used. In view of this, it can be said that the polymerization degree of PVA used in the present invention is extremely low and is a special one. When the degree of polymerization is less than 200, sufficient spinnability cannot be obtained at the time of spinning, and as a result, a satisfactory composite fiber may not be obtained. On the other hand, if the degree of polymerization exceeds 800, the melt viscosity is too high to allow the polymer to be discharged from the spinning nozzle, and a satisfactory composite fiber may not be obtained.

The degree of polymerization (P) of the modified PVA (a) is measured according to JIS-K6726. That is, after the PVA is completely re-saponified and purified, the intrinsic viscosity [η] (dl / g) measured in water at 30 ° C. is obtained by the following formula.
P = ([η] × 10 ³ /8.29) ^{(1 / 0.62)}

  The saponification degree of the modified PVA (a) used in the present invention is preferably in the range of 90 to 99.99 mol%, more preferably 92 to 99.9 mol%, and particularly preferably 94 to 99.8 mol%. When the degree of saponification is less than 90 mol%, the thermal stability of PVA is poor, and stable composite melt spinning may not be performed due to thermal decomposition or gelation. On the other hand, PVA having a saponification degree larger than 99.99 mol% is difficult to produce stably.

  The modified PVA (a) can be obtained by saponifying the vinyl ester unit of the vinyl ester-ethylene copolymer. Vinyl compound monomers for forming vinyl ester units include vinyl formate, vinyl acetate, vinyl propionate, vinyl valenate, vinyl caprate, vinyl laurate, vinyl stearate, vinyl benzoate, vinyl pivalate and Examples thereof include vinyl versatate. Among these, vinyl acetate is preferable from the viewpoint of obtaining PVA with high productivity.

  As a polymerization method of the vinyl ester-ethylene copolymer used as a raw material of the modified PVA (a) used in the present invention, known methods such as a bulk polymerization method, a solution polymerization method, a suspension polymerization method, and an emulsion polymerization method are available. Can be mentioned. Among them, a bulk polymerization method or a solution polymerization method in which polymerization is performed without solvent or in a solvent such as alcohol is usually employed. Examples of alcohol used as a solvent during solution polymerization include lower alcohols such as methyl alcohol, ethyl alcohol, and propyl alcohol. As initiators used for copolymerization, α, α′-azobisisobutyronitrile, 2,2′-azobis (2,4-dimethyl-valeronitrile), benzoyl peroxide, n-propyl peroxycarbonate And known initiators such as azo initiators or peroxide initiators. Although there is no restriction | limiting in particular about superposition | polymerization temperature, The range of 0 to 200 degreeC is suitable.

  The content ratio of alkali metal ions in the modified PVA (A) used in the present invention is preferably 0.00001 to 0.05 parts by mass in terms of sodium ion with respect to 100 parts by mass of the modified PVA (A), and 0.0001 to 0.03 parts by mass is more preferable, and 0.0005 to 0.01 parts by mass is particularly preferable. Those having an alkali metal ion content of less than 0.00001 parts by mass are industrially difficult to produce. On the other hand, when the content of alkali metal ions is more than 0.05 parts by mass, polymer decomposition, gelation and yarn breakage at the time of composite melt spinning are remarkable, and it may not be possible to fiberize stably. Examples of the alkali metal ion include potassium ion and sodium ion.

  In the present invention, the method for containing a specific amount of alkali metal ions in the modified PVA (a) is not particularly limited, and a method of adding an alkali metal ion-containing compound after polymerizing the modified PVA (a), vinyl ester When the ethylene copolymer is saponified in a solvent, an alkaline substance containing an alkali ion is used as a saponification catalyst so that an alkali metal ion is added to the modified PVA (a), and the saponified modified PVA ( A method of controlling the content of alkali metal ions contained in the modified PVA (a) by washing a) with a washing solution can be mentioned, but the latter method is preferred. The content of alkali metal ions can be determined by atomic absorption method.

  Examples of the alkaline substance used as the saponification catalyst include potassium hydroxide and sodium hydroxide. The molar ratio of the alkaline substance used for the saponification catalyst is preferably from 0.004 to 0.5, particularly preferably from 0.005 to 0.05, based on the vinyl acetate unit. The saponification catalyst may be added all at the beginning of the saponification reaction, or may be added additionally during the saponification reaction.

Examples of the saponification solvent include methanol, methyl acetate, dimethyl sulfoxide, dimethylformamide and the like. Among these solvents, methanol is preferable, methanol whose water content is controlled to 0.001 to 1% by mass is more preferable, methanol whose water content is controlled to 0.003 to 0.9% by mass is more preferable, and water content is Methanol controlled to 0.005 to 0.8% by mass is particularly preferable. Examples of the cleaning liquid include methanol, acetone, methyl acetate, ethyl acetate, hexane, water, and the like. Among these, methanol, methyl acetate, water alone or a mixed liquid is more preferable.
Although it sets so that the content rate of an alkali metal ion may be satisfy | filled as a quantity of a washing | cleaning liquid, 300-10000 mass parts is preferable with respect to 100 mass parts of modified PVA (a) normally, and 500-5000 mass parts is more. preferable. As washing | cleaning temperature, 5-80 degreeC is preferable and 20-70 degreeC is more preferable. The washing time is preferably 20 minutes to 100 hours, more preferably 1 hour to 50 hours.

  Further, it is effective to add a plasticizer to the modified PVA (a) for the purpose of adjusting the melting point and melt viscosity and lowering the crystal orientation, as long as the objects and effects of the present invention are not impaired. As the plasticizer, all conventionally known plasticizers can be used, but diglycerin, polyglycerin alkyl monocarboxylic acid esters, and glycols added with ethylene oxide and propylene oxide are preferably used. Among these, the compound which added 1-30 mol% of ethylene oxide with respect to 1 mol of sorbitol is preferable.

  Specific examples of the other thermoplastic resins (a) that are integrated with the modified PVA (a) used in the present invention to constitute long fibers include, for example, polyethylene terephthalate, polytrimethylene terephthalate, polybutylene terephthalate, polyhexamethylene. Aromatic polyesters such as terephthalate, polylactic acid, polyethylene succinate, polybutylene succinate, polybutylene succinate adipate, polyhydroxybutyrate-polyhydroxyvalylate copolymer, aliphatic polyester such as polycaprolactone and copolymers thereof , Nylon 6, Nylon 66, Nylon 610, Nylon 10, Nylon 12, Nylon 6-12 and other aliphatic polyamides and copolymers thereof, Polypropylene, Polyethylene, Polybutene, Polymethylpentene Refin and its copolymers, water-insoluble ethylene-vinyl alcohol copolymer containing 25 to 70 mol% of ethylene units, polystyrene, polydiene, chlorine, polyolefin, polyester, polyurethane, polyamide, fluorine At least one type can be selected from the elastomers of the system.

  From the viewpoint of easy composite spinning with the modified PVA (a) suitably used in the present invention, the above-mentioned polyethylene terephthalate, polylactic acid, nylon 6, nylon 66, polypropylene, polyethylene, and ethylene units are contained in an amount of 25 mol% to 70 mol%. An ethylene-vinyl alcohol copolymer is preferred. Of course, these thermoplastic resins (a) may be homopolymers or copolymers. However, it must be a fiber-forming resin.

Next, the manufacturing method of the long-fiber nonwoven fabric used for the boron compound adsorption sheet of this invention is demonstrated.
In addition, as a manufacturing method of a nonwoven fabric, the fiber of a nonwoven fabric raw material is disperse | distributed to water, the dispersion liquid is made into paper, and the nonwoven fabric is manufactured (what is called wet nonwoven fabric), The fiber about 30-50 mm in length was used as the web. Later, a method of entanglement by jetting a needle punch or high pressure fluid to make a nonwoven fabric (so-called dry nonwoven fabric), a method of collecting fibers obtained by blowing a molten polymer liquid by gas and making a nonwoven fabric (so-called melt blown method), There are various methods such as a method in which continuous fibers obtained by stretching a molten polymer liquid with a gas are directly collected on a collecting surface to make a nonwoven fabric (so-called spunbond method). Bond method is used. By using the spunbond method, it is possible to obtain a feature that high productivity and a high-strength nonwoven fabric made of long fibers can be produced.
The long-fiber nonwoven fabric used in the present invention can be efficiently produced by using a so-called spunbond nonwoven fabric production method in which the melt spinning step and the nonwoven fabricization step are directly connected. That is, the modified PVA (a) is melt-kneaded with a melt extruder, the other thermoplastic resin (a) is melt-kneaded with another melt extruder, and both melted resins are separately guided to the spinning head, and the respective flow rates are adjusted. After weighing and merging both resins, discharge from the spinning nozzle hole, cool the discharged yarn with a cooling device, and then use a suction device such as an air jet nozzle to achieve the desired fineness In addition, the fiber is pulled and thinned by a high-speed air stream at a speed corresponding to a yarn take-up speed of 1000 to 6000 m / min, and then deposited on a movable collection surface while being opened to form a nonwoven web. Subsequently, the composite continuous fiber nonwoven fabric containing the modified PVA (a) as one component is obtained by partially pressing and winding the web.

  In the present invention, the fiberizing conditions constituting the long-fiber nonwoven fabric depend on the type of modified PVA (A) used, the type of other thermoplastic resin (A), the composite shape of the fiber cross section, and the properties of the target nonwoven fabric. It is preferable to set appropriately, and it is desirable to determine the fiberizing conditions mainly while paying attention to the following points.

The spinneret temperature is preferably Mp + 10 ° C. to Mp + 80 ° C. when the melting point of the polymer having a high melting point among the polymers constituting the composite fiber is Mp, the shear rate (γ) is 500 to 25000 sec ⁻¹ , and the draft (V) is 50 to 50 ° C. Spinning at 2000 is preferred. Further, when viewed from the combination of the polymers to be composite-spun, a polymer having a close melt viscosity as measured by the die temperature at the time of spinning and the shear rate at the time of passing through the nozzle, for example, at a melt spinning die temperature at a shear rate of 1000 sec ⁻¹ . From the viewpoint of spinning stability, it is preferable to perform composite spinning with a combination having a difference in melt viscosity within 2000 poise.

The melting point of the polymer in the present invention is the peak temperature of the main endothermic peak observed with a differential scanning calorimeter (DSC: for example, TA 3000 manufactured by Mettler). The shear rate (γ) is calculated as γ = 4Q / πr ³ where r (cm) is the nozzle radius and Q (cm ³ / sec) is the amount of polymer discharged per single hole. The draft V is calculated by V = (A · πr ² / Q) × (5/3) where the take-up speed is A (m / min).

When the PVA fiber of the present invention is produced, if the spinneret temperature is lower than Mp + 10 ° C., the melt viscosity of the polymer is too high, and the spinning / thinning property due to high-speed air current is inferior. Stable spinning cannot be performed because the polymer is easily thermally decomposed. Further, the shear rate is easily Dan'ito lower than 500 sec ^-1, spinnability becomes high back pressure of the nozzle and higher than 25000Sec ^-1 deteriorates. When the draft is lower than 50, unevenness in fineness becomes large and stable spinning is difficult, and when the draft is higher than 2000, the yarn is easily broken.

  In the present invention, when the discharged yarn is pulled and thinned using a suction device such as an air jet nozzle, it is pulled and thinned by a high-speed air stream at a speed corresponding to a yarn take-up speed of 1000 to 6000 m / min. Is preferred. The conditions for taking up the yarn by the suction device are appropriately selected depending on the melt viscosity of the molten polymer discharged from the spinning nozzle hole, the discharge speed, the spinning nozzle temperature, the cooling conditions, etc., but if it is less than 1000 m / min, the cooling of the discharged yarn is performed. Adhesion between adjacent yarns may occur due to solidification delay, and the orientation and crystallization of the yarn does not progress. The resulting nonwoven fabric is coarse and low in mechanical strength, which is not preferable. On the other hand, if it exceeds 6000 m / min, the warp / thinning property of the discharged yarn cannot be followed, and the yarn will be cut, making it impossible to produce a stable long fiber nonwoven fabric.

  Further, when stably producing the PVA-based long fiber nonwoven fabric of the present invention, the distance between the spinning nozzle hole and the suction device such as an air jet nozzle is the same as the PVA used, the composition, and the spinning conditions described above. However, it is preferably 30 to 200 cm, more preferably 35 to 120 cm, and even more preferably 40 to 100 cm. When the interval is smaller than 30 cm, fusion between adjacent yarns may occur due to a delay in cooling and solidification of the discharged yarn, and the orientation / crystallization of the yarn does not progress, and the resulting nonwoven fabric is rough. The mechanical strength is low, which is not preferable. On the other hand, if it exceeds 200 cm, the cooling and solidification of the discharged yarn has progressed too much, and the warp and thinning properties of the discharged yarn cannot follow, and the yarn is cut. It cannot be manufactured.

  The composite form of the composite fiber is not particularly limited, but considering the dispersibility and uniformity of the fiber diameter after ultrafinening, a sea-island type (for example, a cross-sectional shape as shown in FIG. 1) composed of sea components and island components, orange Those having a cross-sectional shape type (for example, a cross-sectional shape as shown in FIG. 2), a fan-shaped shape, or a multi-layer bonded type shape arranged in a strip shape are preferable. When the composite cross-sectional shape is a sea-island type, the number of island components that are the ultrafine fiber forming component (A) is preferably in the range of 2 to 800 in terms of productivity, more preferably in the range of 10 to 200. is there. In addition, when the cross-sectional shape of the composite fiber has a cross-sectional shape type of a mandarin orange, a fan shape, or a bonded type shape, the ultrafine fiber forming component (A) constituting the composite fiber is modified by the modified PVA (A) It is preferable from the point of productivity that it is divided | segmented into 2-20 pieces. When used for a filter, since the fineness of the fiber is important, a sea-island shape in which a thin fiber can be easily obtained is preferable.

  When producing a composite fiber spunbonded nonwoven fabric comprising the thermoplastic resin (a) and modified PVA (a) used in the present invention, the mass ratio of the thermoplastic polymer (a) and modified PVA (a) depends on the purpose. However, 5/95 to 95/5 is preferable, and 10/90 to 90/10 is more preferable. If it is outside the preferred range, the combined effect may not appear.

  Further, as long as the purpose and effect of the present invention are not impaired, the thermoplastic resin (a) and the modified PVA (a) may be optionally provided with a stabilizer such as a copper compound, a colorant, an ultraviolet absorber, and a light stabilizer. Antioxidants, antistatic agents, flame retardants, plasticizers, lubricants, crystallization rate retarders can be added during the polymerization reaction or in subsequent steps. Addition of an organic stabilizer such as hindered phenol, a copper halide compound such as copper iodide, and an alkali metal halide compound such as potassium iodide as heat stabilizers improves the melt retention stability during fiberization. Therefore, it is preferable.

  Further, if necessary, fine particles having an average particle size of 0.01 μm or more and 5 μm or less are added to the thermoplastic resin (i) at a polymerization reaction or in a subsequent step at 0.05% by mass or more and 10% by mass or less. Can do. The type of fine particles is not particularly limited, and for example, inert fine particles such as silica, titanium oxide, calcium carbonate, and barium sulfate can be added, and these may be used alone or in combination of two or more. In particular, inorganic fine particles having an average particle diameter of 0.02 μm or more and 1 μm or less, such as silica, are preferably added. In this case, spinnability and stretchability are improved.

  In spunbond sheeting, after thinning by high-speed air flow at a speed corresponding to the take-up speed of the yarn, it is deposited on a movable collection surface while opening the fiber to form a nonwoven web, Subsequently, a composite continuous fiber nonwoven fabric can be obtained by partially thermocompressing and winding the web. Furthermore, if necessary, a sheet having various textures and physical properties can be obtained by performing bonding and entanglement processing and performing web processing according to the purpose. The bonding method may be a method using hot embossing or a heat flat calender. The entanglement method may be a method using a needle punch or a method using a high-pressure water entanglement process.

As a basis weight of the web, a range of 5 to 500 g / m ² is preferable in terms of productivity and post-processing property of the nonwoven fabric. Further, the thickness of the suction-thinned web-forming composite fiber is preferably in the range of 0.2 to 8 dtex from the viewpoint of productivity.

In the present invention, the thermoplastic polymer (A) can be made extremely fine by extracting and removing the modified PVA (A) from the composite fiber spunbonded nonwoven fabric with water. There are no particular restrictions on the method of extracting the modified PVA (a) from the composite spunbonded nonwoven fabric with water, such as continuous multi-stage washing tanks, circular, beam, zicker, Wiens dyeing machines, vibratory washers, relaxers, etc. Arbitrary methods, such as a method of using a hot water treatment facility and a method of injecting a high-pressure water stream, can be appropriately selected. The extraction water may be neutral, and may be an alkaline aqueous solution, an acidic aqueous solution, or an aqueous solution to which a surfactant or the like is added. The thickness of the ultrafine fiber after extracting and removing the modified PVA is preferably 0.5 dtex or less, more preferably 0.2 dtex or less and 0.01 dtex or more.
Moreover, in this invention, as a fabric weight of a nonwoven fabric, the range of 5-500 g / m < ² > is preferable at the point of productivity and post-processability.

  When the modified PVA (A) is extracted and removed from the composite fiber spunbonded nonwoven fabric with water, a removal treatment must be performed so that a part of the modified PVA (A) remains in the sheet. For that purpose, these conditions are determined in advance so that the amount of water used for the removal treatment, the treatment method, the treatment time, the treatment temperature, etc. are variously changed and the residual amount of PVA defined in the present invention is obtained. Is preferred.

  The modified PVA (A) used in the present invention has biodegradability and is decomposed into water and carbon dioxide when treated with activated sludge or buried in soil. The activated sludge method is preferable for the treatment of the waste liquid after dissolving PVA. When the PVA aqueous solution is continuously treated with activated sludge, it is decomposed in 2 days to 1 month. Moreover, since PVA used for this invention has low combustion heat and the load with respect to an incinerator is small, you may incinerate PVA by drying the waste_water | drain which melt | dissolved PVA.

  Furthermore, the spunbonded nonwoven fabric of the present invention may be subjected to post-processing treatment such as electrification processing, plasma discharge treatment or hydrophilization treatment by corona discharge treatment according to the purpose.

  In addition, the spunbond nonwoven fabric obtained in the present invention is not only used alone, but can also be used by laminating with other long fiber nonwoven fabrics, short fiber nonwoven fabrics, woven fabrics, knitted fabrics, etc. In this case, practical functions can be further imparted.

  The spunbonded nonwoven fabric obtained in this way dissolves and removes most of the modified PVA (a) from the composite cross section, turns the composite long fibers into ultrafine long fiber bundles, and leaves part of the modified PVA (a). Therefore, even if the modified PVA (a) is extracted and removed from the composite fiber, the bonding force between the modified PVA and other thermoplastic polymer is strong, and a part of the modified PVA is extremely elongated. Since it remains on the surface of the fiber and the fiber surface is coated with the residual modified PVA (a), and the modified PVA has a very high boron compound adsorption capacity, the resulting boron compound adsorption capacity is greatly improved. And can be suitably used as a filter. In addition, water-soluble PVA is generally easily affected by water and humidity, and easily contracts under high humidity conditions, and undergoes a shape change. However, in the present invention, ultrafine fibers are thermoplastic resin (a). ) Is not affected by water or humidity.

  As a method for producing a long-fiber non-woven fabric whose surface is coated with PVA, the long-fiber non-woven fabric is impregnated with or coated with an aqueous solution of the modified PVA (a), and dried to allow the modified PVA to exist on the surface of the long-fiber non-woven fabric constituent fiber. There is also a method, and in the present invention, a long-fiber nonwoven fabric obtained by such a method is also included, but the long-fiber nonwoven fabric obtained by such a method has a modified PVA (a) present on the surface of the nonwoven fabric. It is easy to drop off from the surface and cannot be said to be a suitable method for obtaining the sheet of the present invention.

  EXAMPLES Next, although an Example demonstrates this invention concretely, this invention is not limited to these Examples. In the examples, each physical property value was measured as follows. In addition, unless otherwise indicated, the part and% in an Example are related with mass.

[Analysis method of PVA]
The analysis method of PVA followed JIS-K6726 unless otherwise specified.
The amount of modification was determined by measurement with a 500 MHz 1H-NMR (JEOL GX-500) apparatus using modified polyvinyl ester or modified PVA.
The content of alkali metal ions was determined by atomic absorption method.

[Melting point]
The melting point of PVA was increased to 250 ° C. at a temperature rising rate of 10 ° C./min in nitrogen using DSC (Mettler, TA3000), cooled to room temperature, and again to 270 ° C. at a temperature rising rate of 10 ° C./min. The temperature at the top of the endothermic peak indicating the melting point of PVA when the temperature was raised was examined.

[Spinning state]
The melt spinning state was observed and evaluated according to the following criteria.
◎: Extremely good, ○: Good, △: Somewhat difficult

[Nonwoven fabric state]
The obtained nonwoven fabric was visually observed and touched and evaluated according to the following criteria.
◎: Uniform and extremely good, ○: Almost homogeneous and good, △: Slightly difficult

[Ratio of modified PVA on nonwoven fabric surface]
The constituent elements and bonding state of the nonwoven fabric surface were analyzed by X-ray photoelectron spectroscopy (XPS), and the proportion of PVA was calculated from the results.

[Ratio of modified PVA in nonwoven fabric]
A 30 cm × 30 cm sample was immersed in 2000 cc of water in an autoclave and heat-treated at 120 ° C. for 1 hour. After the treatment, remove the sheet from hot water and squeeze it lightly. The water-soluble thermoplastic PVA (a) in the sheet is completely extracted and removed by a total of 3 repeated treatments. From the mass change before and after the treatment, the ratio of the water-soluble thermoplastic PVA (a) in the sheet was determined.

[ΔH of PVA component of nonwoven fabric]
The ΔH of the PVA component was determined by using DSC (Mettler, TA3000), and ΔH when the temperature was raised to 250 ° C. at a temperature rising rate of 80 ° C./min in nitrogen.

[Average fiber diameter]
100 fibers were randomly selected from an enlarged photograph of the sample taken at a magnification of 1000 times with a microscope, the fiber diameters were measured, and the average value was taken as the average fiber diameter.

[Unit weight]
Measured according to JIS L1906 “General long fiber nonwoven fabric test method”.

[Thickness]
Measured according to JIS L1906 “General long fiber nonwoven fabric test method”.

[Boron removal efficiency]
Using contaminated air with a boron concentration of 10 ng / m ³ for a filter with a filtration area of 100 cm ² and absorbing this in ultrapure water, the inductively coupled plasma mass spectrometer is used to determine the boron removal efficiency. It was.

Reference example 1
[Production of ethylene-modified PVA]
A 100 L pressure reactor equipped with a stirrer, nitrogen inlet, ethylene inlet and initiator addition port was charged with 29.0 kg of vinyl acetate and 31.0 kg of methanol, heated to 60 ° C., and then nitrogen bubbling for 30 minutes. The inside was replaced with nitrogen. Next, ethylene was introduced and charged so that the reactor pressure was 5.6 kg / cm ² (5.5 × 10 ⁵ Pa). Prepare a 2.8 g / L solution of 2,2'-azobis (4-methoxy-2,4-dimethylvaleronitrile) (AMV) dissolved in methanol as an initiator, and perform nitrogen replacement by bubbling with nitrogen gas. did. After adjusting the temperature inside the polymerization tank to 60 ° C., 170 ml of the initiator solution was injected to start polymerization. During the polymerization, ethylene was introduced, the reactor pressure was maintained at 5.6 kg / cm ² (5.5 × 10 ⁵ Pa), the polymerization temperature was maintained at 60 ° C., and the initiator solution was used at 610 ml / hr. Polymerization was carried out with continuous addition of AMV. After 9.5 hours, when the polymerization rate reached 68%, the polymerization was stopped by cooling. After the reaction vessel was opened to remove ethylene, nitrogen gas was bubbled to completely remove ethylene. Next, unreacted vinyl acetate monomer was removed under reduced pressure to obtain a methanol solution of polyvinyl acetate.

  Methanol was added to the obtained polyvinyl acetate solution to adjust the concentration to 50%, and 2.0 kg of polyvinyl acetate in methanol (1.0 kg of polyvinyl acetate in the solution) was added to 0.47 kg (polyvinyl acetate). Saponification was performed by adding an alkaline solution (NaOH in 10% methanol) having a molar ratio (MR) of 0.10 to the vinyl acetate unit in vinyl acetate. About 5 minutes after the addition of alkali, the gelled system was pulverized by a pulverizer and allowed to stand at 60 ° C. for 3 hours to proceed saponification, and then 0.5% acetic acid water / methanol = 20/80. 10.0 kg of the mixed solution was added to neutralize the remaining alkali. After confirming the end of neutralization using a phenolphthalein indicator, 20.0 kg of a mixed solution of water / methanol = 20/80 was added to the white solid PVA obtained by filtration, and the mixture was allowed to wash at room temperature for 3 hours. After repeating the above washing operation three times, 10.0 kg of methanol was further added, and the mixture was left to wash at room temperature for 3 hours. Then, PVA obtained by centrifugal drainage was left in a dryer at 70 ° C. for 2 days to obtain dry PVA (PVA-1).

  The saponification degree of the obtained ethylene-modified PVA was 99.1 mol%. Further, after the modified PVA was incinerated, the sodium content measured by an atomic absorption photometer using a material dissolved in an acid was 0.0012 parts by mass with respect to 100 parts by mass of the modified PVA.

  In addition, after removing the unreacted vinyl acetate monomer after polymerization, a methanol solution of polyvinyl acetate obtained by precipitation in n-hexane and reprecipitation purification by dissolving with acetone was performed three times, and then dried under reduced pressure at 80 ° C. for 3 days. To obtain purified polyvinyl acetate. When the polyvinyl acetate was dissolved in DMSO-d6 and measured at 80 ° C. using 500 MHz proton NMR (JEOL GX-500), the ethylene content was 8.7 mol%. After saponifying the above methanol solution of polyvinyl acetate at an alkali molar ratio of 0.5, the pulverized product was allowed to stand at 60 ° C. for 5 hours to allow saponification to proceed, followed by methanol soxhlet for 3 days, and then at 80 ° C. And purified under reduced pressure for 3 days to obtain purified ethylene-modified PVA. It was 340 when the average degree of polymerization of this PVA was measured according to JIS K6726 of the usual method. Further, a cast film having a thickness of 10 microns was prepared by preparing a 5% aqueous solution of the purified modified PVA. After the film was dried under reduced pressure at 80 ° C. for 1 day, the melting point of PVA was measured by the above-described method using DSC (Mettler, TA3000) and found to be 212 ° C. (Table 1).

  The PVA obtained above was melt-extruded at a set temperature of 220 ° C. and a screw rotation speed of 200 rpm using a Nippon Steel Works twin screw extruder (30 mmφ) to produce pellets.

Example 1
The PVA (PVA-1) pellet obtained by the above reference example was added with the compound shown in Table 1 as a plasticizer (PVA-2), and this PVA2, polypropylene having a melt flow rate of 35 and a melting point of 160 ° C. Prepare, melt and knead each polymer with a separate extruder so that the mass ratio of the composite long fiber constituting the nonwoven fabric to the fiber cross section perpendicular to the fiber axis is PP / PVA = 80/20 Guided to a 230 ° C. core-sheath type (sheath: PVA) composite spinning pack, discharged from the spinneret under conditions of a nozzle diameter of 0.35 mmφ × 1008 holes, a discharge amount of 1050 g / min, and a shear rate of 2500 sec ⁻¹ While being cooled with cooling air at 20 ° C, the ejector is located at a distance of 80 cm from the nozzle and is pulled fine at a take-up speed of 2300 m / min with high-speed air. , And the opened filaments group to form a collecting deposited so long fiber web on the collecting conveyor onto which is rotating endlessly. In the spinning state, no breakage was observed, and the cross-sectional shape was extremely good.

Next, the web was passed between a concavo-convex pattern embossing roll heated to 140 ° C. and a flat roll under a linear pressure of 50 kg / cm, and the embossed part was subjected to thermocompression bonding, whereby a single fiber fineness of 3.8 dtex was obtained. A core-sheath type composite continuous fiber nonwoven fabric having a basis weight of 51 g / m ² was obtained. The obtained non-woven fabric was homogeneous and very good. The production conditions of the composite long fiber nonwoven fabric are shown in Table 2. Table 3 shows the results of measuring the performance of the obtained spunbonded nonwoven fabric. From Table 3, it can be seen that the boron removal performance is very good.

Examples 2 and 3
Using the PVA used in Example 1, the die for composite spinning described in Table 2 and the thermoplastic polymer, employing the spinning conditions described in Table 2, and the appropriate nozzle-ejector distance and line net speed. A non-woven web composed of composite long fibers was obtained under exactly the same conditions as in Example 1, except that the composite long fiber nonwoven fabric was subjected to partial thermocompression bonding at the embossing treatment temperature shown in Table 2. The mass ratio of the composite fiber component was adjusted by changing the amount of polymer introduced into the pack. Production conditions and production results are shown in Tables 2 and 3. When the boron removal performance of the obtained spunbonded nonwoven fabric was evaluated, it showed good performance.

Example 4
Using the PVA used in Example 1, the die for composite spinning described in Table 2 and the thermoplastic polymer, employing the spinning conditions described in Table 2, and the appropriate nozzle-ejector distance and line net speed. A non-woven web composed of composite long fibers was obtained under exactly the same conditions as in Example 1, except that the composite long fiber nonwoven fabric was subjected to partial thermocompression bonding at the embossing treatment temperature shown in Table 2. The mass ratio of the composite fiber component was adjusted by changing the amount of polymer introduced into the pack. Moreover, the sea-island type composite fiber was led so that the thermoplastic polymer became an island component and PVA became a sea component.

  About about 50 m of the obtained composite long fiber nonwoven fabric, the PVA component was extracted using a continuous multi-stage washing tank (treatment at a residence time of 3 minutes at 85 ° C.). The proportion of PVA in the nonwoven fabric after extraction and removal was 7%. Production conditions and production results are shown in Tables 2 and 3. When the boron removal performance of the obtained spunbonded nonwoven fabric was evaluated, it showed good performance.

Example 5
An ultrafine spunbonded nonwoven fabric was obtained under the same conditions as in Example 4 except that the PVA extraction treatment conditions shown in Table 2 were used. The proportion of PVA in the nonwoven fabric after extraction and removal was 1%. Production conditions and production results are shown in Tables 2 and 3. When the boron removal performance of the obtained spunbonded nonwoven fabric was evaluated, it showed good performance.

Comparative Example 1
The PVA (PVA-1) pellets are heated and melt-kneaded with an extruder, led to a spinning pack at 230 ° C., with a nozzle diameter of 0.35 mmφ × 1008 holes, a discharge amount of 655 cm 3 / min, and a shear rate of 2,600 sec−1. The ejector is discharged from the spinneret under conditions, and the spinning filament group is cooled with a cooling air of 20 ° C., and the ejector located at a distance of 60 cm from the nozzle is pulled up at a take-up speed of 2500 m / min with a high-speed air, and is drawn with a draft 520 The opened filament group was collected and deposited on an endlessly rotating collection conveyor device to form a long fiber web.

  Next, this web is passed between a concavo-convex pattern embossing roll heated to 150 ° C. and a flat roll under a linear pressure of 50 kg / cm, and the embossed part is subjected to thermocompression bonding, whereby the single fiber fineness is 3.4 decitex long. A long-fiber non-woven fabric having a basis weight of 48 g / m @ 2 was obtained. The production conditions and production results of the long fiber nonwoven fabric are shown in Table 2 and Table 3. Moreover, as a result of leaving this sheet in a 100% humidity atmosphere for 50 hours, 13% shrinkage occurred in the area, and the dimensional stability was insufficient.

Comparative Example 2
A spunbonded nonwoven fabric was obtained under the same conditions as in Comparative Example 1 except that PVA (PVA-3) described in Table 1 was used and a sheet was formed under the conditions described in Table 2. Production conditions and production results are shown in Tables 2 and 3. When the boron removal performance of the obtained spunbonded nonwoven fabric was evaluated, ethylene units were not introduced into the PVA of the nonwoven fabric component, so that the crystallinity was high and the intended performance could not be obtained.

Comparative Example 3
Using the PVA used in Comparative Example 2, using the composite spinneret of the type shown in Table 2, a thermoplastic polymer, adopting the spinning conditions shown in Table 2, the nozzle-ejector distance and the line net speed as appropriate. A non-woven web composed of composite long fibers was obtained under exactly the same conditions as in Example 1, except that the composite long fiber nonwoven fabric was subjected to partial thermocompression bonding at the embossing treatment temperature shown in Table 2. The mass ratio of the composite fiber component was adjusted by changing the amount of polymer introduced into the pack. Production conditions and production results are shown in Tables 2 and 3. When the boron removal performance of the obtained spunbonded nonwoven fabric was evaluated, sufficient performance was not obtained as in Comparative Example 2.

Comparative Example 4
A spunbonded nonwoven fabric was obtained under the same conditions as in Comparative Example 1 except that PVA (PVA-4) described in Table 1 was used and a sheet was formed under the conditions described in Table 2. Production conditions and production results are shown in Tables 2 and 3. When the boron removal performance of the obtained spunbonded nonwoven fabric was evaluated, sufficient performance was not obtained.

Comparative Example 5
An ultrafine composite spunbonded nonwoven fabric was obtained under exactly the same conditions as in Example 3 except that PVA was extracted under the conditions described in Table 2. The proportion of PVA in the nonwoven fabric after extraction and removal was 0.0002%. Production conditions and production results are shown in Tables 2 and 3. When the boron removal performance of the obtained spunbonded nonwoven fabric was evaluated, the PVA component was hardly present in the nonwoven fabric, so that sufficient performance was not obtained.

Fiber sectional view showing an example of the composite form of the composite fiber used in the present invention Fiber sectional view showing an example of the composite form of the composite fiber used in the present invention

Explanation of symbols

1 Water-soluble thermoplastic polyvinyl alcohol 2 Thermoplastic polymer

Claims (6)

  It consists of a non-woven fabric composed of long fibers composed of a modified polyvinyl alcohol (A) containing 1 to 20 mol% of ethylene units and another thermoplastic polymer (A), and the modified polyvinyl alcohol (A) is a fiber. A boron compound-adsorbing sheet, which is present in an amount of 1% by mass or more based on the mass of the nonwoven fabric in a state of occupying 10% or more of the surface.   The boron compound adsorbing sheet according to claim 1, wherein the average fineness of the long fibers is 0.5 dtex or less and the modified polyvinyl alcohol (a) is present in an amount of 1 to 30% by mass relative to the mass of the nonwoven fabric.   The boron compound adsorption sheet according to claim 1 or 2, wherein the modified polyvinyl alcohol (a) contains a plasticizer.   A boron adsorption filter comprising the boron compound adsorption sheet according to claim 1.   The filter which laminated | stacked the sheet | seat for boron adsorption | suction in any one of Claims 1-3 in the downstream of the glass fiber sheet. A part of the modified polyvinyl alcohol (a) is removed by treating the spunbonded nonwoven fabric composed of the composite long fiber composed of the modified polyvinyl alcohol (a) and other thermoplastic polymer (a) with hot water. A method for producing a boron compound adsorption sheet.

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