JP2008240165A - Method for providing nonwoven fabric of electrostatic spinning with strength - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a technology for improving strength of a nonwoven fabric of electrostatic spinning composed of fibers of submicron order. <P>SOLUTION: The method for providing a nonwoven fabric of electrostatic spinning with strength comprises keeping the nonwoven fabric at ≥60°C and ≤120°C in an atmosphere at ≥60°C in a state in which the nonwoven fabric of electrostatic spinning is in contact with water. The nonwoven fabric of electrostatic spinning is preferably an acrylic resin. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a technique for imparting strength to an electrospun nonwoven fabric composed of extremely fine fibers of the order of submicrons.

  There are many known techniques for producing non-woven fabrics that do not weave the fibers. Direct spinning methods such as the spunbond method and melt-blow method, or pre-spun fibers are made into sheets with a card machine as short fibers. There are a dry method, a wet method in which short fibers are dispersed and formed in water, and an air lay method in which fibers are dispersed and conveyed by an air stream to form a sheet. Among these, the direct spinning method is widely used as a filter for filtering a gas or a liquid because relatively thin fibers can be obtained as constituent fibers of the obtained nonwoven fabric.

  On the other hand, the raw material components for constituting the fiber are dissolved or dispersed in a solvent or the like, and an electrostatic force is applied to this and discharged from a thin tube such as a syringe to generate fine fibers, which are collected. In recent years, the electrospinning technique for forming a sheet has attracted attention rapidly because a nonwoven fabric composed of sub-micron fibers (hereinafter referred to as an electrospun nonwoven fabric) can be easily obtained.

  Conventionally, as such an electrospinning technique, for example, in US Pat. No. 2,048,651 (hereinafter referred to as Patent Document 1), a high voltage is applied or the liquid polymer is spun into a spinning space. An apparatus including a liquid reservoir having a nozzle part that can be supplied to the substrate and a counter electrode for accumulation having a flat plate shape or a roll shape, and a manufacturing method are disclosed. In this publication technique, the fibers spun by the electric field from the nozzle portion are collected on the collecting counter electrode, and then the collected fiber aggregate is collected by a scraping device or the like.

  However, in the technique according to Patent Document 1 described above, since fibers are directly accumulated on the counter electrode for accumulation by the force of an electric field, a paper-like fiber aggregate is formed by electrostatic force with the counter electrode for accumulation due to charged fibers. It was difficult to recover as a low-density cotton-like fiber aggregate. In addition, even when a scraping device is provided on the electrode, the fiber aggregate after scraping is not bulky, and in a field where it is preferable to use it as a bulky fiber aggregate, it may necessarily exhibit satisfactory characteristics. In some cases, for example, the accumulated fibers are firmly bonded to each other.

  In order to solve such problems of the prior art, for example, in Japanese Patent Application Laid-Open No. 2004-238799 (hereinafter referred to as Patent Document 2) proposed by the present applicant, an electrospinning method, in which a polymer solution to be spun is spun It proposes a technique including a step of supplying to a space, a step of irradiating ions having a polarity opposite to that of the supplied and formed fiber, and a step of collecting the spun fiber. Further, this document technology is opposed to the polymer supply unit that can supply the polymer solution to the spinning space, the charge applying unit that can apply a charge to the polymer solution, and the polymer supply unit described above. The opposite electrode that can electrically attract the fibers formed by the supply of, and the fibers flying between the polymer supply unit and the opposite electrode, ions of the opposite polarity to the charge of the fibers An electrostatic spinning device including means capable of irradiating and a fiber recovery device capable of recovering the spun fiber is also disclosed.

  Moreover, as a polymer which can apply the technique of the patent document 2 mentioned above, a polyvinylidene fluoride (PVDF), a polyvinylidene fluoride-hexafluoropropylene copolymer, a polyacrylonitrile (PAN), a polyacrylonitrile-methacrylate copolymer, a polymethacryl Methyl acid, polyvinyl chloride, polyvinylidene chloride-acrylate copolymer, polyethylene, polypropylene, nylon 12, nylon-4,6 and other nylons, aramid, polybenzimidazole, polyvinyl alcohol, cellulose, cellulose acetate, cellulose acetate butyrate Rate, polyvinylpyrrolidone-vinyl acetate, poly (bis- (2- (2-methoxy-ethoxyethoxy)) phosphazene) (poly (bis- (2- (2-methoxy-ethyetheth xy)) phosphazene); MEEP), polypropylene oxide, polyethyleneimide (PEI), polysuccinic acid ethylene (poly (ethylene succinate)), polyaniline, polyethylene sulfide, polyoxymethylene-oligo-oxyethylene (poly (oxymethylene-oligo-oxyethylene) )), SBS copolymer, polyhydroxybutyric acid, polyvinyl acetate, polyethylene terephthalate, polyethylene oxide, collagen, polylactic acid, polyglycolic acid, poly D, L-lactic acid-glycolic acid copolymer, polyarylate, polypropylene fumarate (Poly (propylene fumarates)), biodegradable polymers such as polycaprolactone, polypeptides Various polymers such as biopolymers such as proteins, coal tar pitch, pitch systems such as petroleum pitch, etc. that can be melted or dissolved in an appropriate solvent, copolymers and mixtures thereof, and various metal alkoxides are hydrolyzed. There is a disclosure that a threadable sol solution can be used.

  Further, the present applicant has disclosed in Japanese Patent Application Laid-Open No. 2005-194675 (hereinafter referred to as Patent Document 3) an electrostatic spinning technique using a solvent of a spinning stock solution mainly having a solubility in water of 100 g / 100 ml or more. A technology capable of stably producing a fiber assembly with less variation in fiber diameter by spinning in an atmosphere controlled to a predetermined humidity with a relative humidity of 40% or less and a humidity fluctuation range of ± 2% or less. Proposed.

  On the other hand, as a technique for improving the strength of the fiber itself, for example, in Japanese Patent Application Laid-Open No. 2001-55620 (hereinafter referred to as Patent Document 4), it is composed of an acrylonitrile-based polymer containing at least 98% by weight of acrylonitrile, and exceeds 3 g / d. Acrylic fibers having a tensile strength, a tensile elongation of 50% or more, and a knot strength / tensile strength of 0.9 or more have been proposed. In this publication, an acrylonitrile-based polymer containing at least 98% by weight of acrylonitrile is spun by a wet or dry-wet spinning method, washed with water and stretched, and then first in a wet and heat atmosphere at 110 to 130 ° C. There is also disclosed a method for producing acrylic fibers, which is characterized by giving a total shrinkage of 25 to 40% by performing a relaxation wet heat treatment and then a relaxation drying treatment.

US Pat. No. 2,048,651 (pages 2 and 3 and FIG. 2) Japanese Patent Laying-Open No. 2004-238749 ([Claims], [0026] and [FIG. 1]) JP-A-2005-194675 ([Claims], [0006], [Example] and [FIG. 4]) JP 2001-55620 A ([Claims])

  As described above, various proposals have been made for the electrospinning technology as an electrospun nonwoven fabric having various characteristics as its application expands. In addition, as disclosed in Patent Document 4, a technique for imparting strength to the fiber itself is also known, but the fiber constituting the electrospun nonwoven fabric has a fiber diameter on the order of submicrons, for example, about several hundred nm. For this reason, it is impossible to perform post-treatment as a single fiber. For this reason, in providing the strength of the electrospun nonwoven fabric derived from an extremely thin fiber diameter, unsolved problems still remain.

  The invention according to the present application has been made as a result of intensive studies by the present applicant in view of the above-described technical background. Therefore, the object of the present invention is to provide a technique capable of improving the strength of an electrospun nonwoven fabric. There is to do.

  In order to achieve this object, according to the method for imparting strength to an electrospun nonwoven fabric according to the present invention, the nonwoven fabric is subjected to 60 ° C. in a temperature atmosphere of 60 ° C. or more in a state where the electrospun nonwoven fabric is in contact with moisture. It is characterized in that it is maintained at a temperature not lower than 120 ° C. and not higher than 120 ° C.

  In carrying out the above-described present invention, it is preferable that the above-described electrospun nonwoven fabric is an acrylic resin.

  By adopting the configuration of the present invention, an electrospun nonwoven fabric having excellent strength can be provided.

  Hereinafter, the method technique of the present invention will be described in detail with specific embodiments. First, the electrospun non-woven fabric referred to in the present application includes, for example, constituent fibers of various resins disclosed in Patent Document 2 and the like, and a known device disclosed in the same publication or the above-mentioned Patent Document 3 can be used. . Specifically, as a result of intensive studies by the present inventors, it has been found that the following resins that are fiber reinforced under wet heat are suitable. Among them, a polymer having polyacrylonitrile as a main component in the main chain, such as homopolymerized polyacrylonitrile, a copolymer having vinyl acetate or a carboxylic acid ester as a copolymerization component, and the like are preferable. The chemical species of the copolymer component is not particularly limited, and examples thereof include the following monomers. That is, acrylic acid esters represented by methyl acrylate, ethyl acrylate, isopropyl acrylate, n-butyl acrylate, 2-ethylhexyl acrylate, 2-hydroxyethyl acrylate, hydroxypropyl acrylate, and the like, methyl methacrylate , Ethyl methacrylate, isopropyl methacrylate, n-butyl methacrylate, n-hexyl methacrylate, cyclohexyl methacrylate, lauryl methacrylate, 2-hydroxyethyl methacrylate, hydroxypropyl methacrylate, diethylaminoethyl methacrylate, etc. Methacrylic acid esters, acrylic acid, methacrylic acid, maleic acid, itaconic acid, acrylamide, N-methylol acrylamide, diacetone acrylamide, styrene, vinyl toluene Emissions, vinyl acetate, vinyl chloride, vinylidene chloride, vinyl bromide, vinylidene bromide, unsaturated monomers such as vinyl fluoride, vinylidene fluoride. Furthermore, p-sulfophenyl methallyl ether, methallyl sulfonic acid, allyl sulfonic acid, styrene sulfonic acid, 2-acrylamido-2-methylpropane sulfonic acid, and alkalis thereof are expected in the hope of secondary effects such as dyeability improvement. A metal salt or the like may be used. The proportion of the chemical species to be copolymerized with acrylonitrile described above can be 40% by weight or less, preferably 20% by weight or less, and more preferably 10% by weight. Random copolymers, alternating copolymers, periodic copolymers can be used. It may be a copolymer having an arbitrary regularity such as a polymer or a block copolymer.

  Next, the gist of the present invention is that the electrospun non-woven fabric and moisture are exposed to a predetermined temperature atmosphere in contact with each other. First, the state where the electrospun nonwoven fabric is in contact with moisture means that the electrospun nonwoven fabric immediately after being obtained by the above-mentioned apparatus is immersed in water at room temperature in advance and then exposed to a predetermined temperature atmosphere, or strength. Any of the cases in which the electrospun nonwoven fabric before the application treatment is exposed to water vapor having a predetermined temperature condition may be used. At this time, strength is given when the electrospun nonwoven fabric in the contact state is exposed to a predetermined temperature, but according to the experiments of the inventors of the present application, this exposure time is extremely high. The purpose is achieved in a short time and depends mainly on the temperature to be exposed, but it can be 1 minute or more, preferably 3 minutes or more.

  Further, according to the verification by the present inventor, it is preferable that the temperature condition to which the electrospun nonwoven fabric is exposed in the above contact state with moisture is in the range of 60 ° C. or more and 120 ° C. or less. It is difficult to give sufficient strength at a temperature below 60 ° C., and it is difficult to expect improvement in strength at temperatures higher than 120 ° C. However, after exposure to water, when exposed to a high temperature atmosphere with sufficient moisture adhered to the surface of the constituent fibers of the electrospun non-woven fabric, the heat decomposition temperature of the polymer forming the constituent fibers is equal to or lower than the thermal decomposition temperature described above as an example. When the acrylic resin is a polymer, the temperature can be about 180 ° C. or lower. That is, the temperature condition of the exposure atmosphere is substantially maintained at about 100 ° C. due to the evaporation of the moisture adhering to the fibers, so that it is possible to impart the same strength as in the above-described preferable temperature range.

  Examples of the present invention will be described below. It should be noted that the following numerical conditions, arrangement relations, and other aspects are only specific examples given to the extent that the present invention can be easily understood, and the present invention is not limited to these specific conditions. Absent.

(Preparation of electrospun nonwoven fabric)
In order to verify the method according to the present invention, an apparatus similar to the apparatus disclosed in Patent Document 3 (see FIG. 4) is used. That is, one end of a polytetrafluoroethylene tube was connected to the syringe, and a stainless steel nozzle having an inner diameter of 0.5 mmφ was attached to the other end of the tube. Next, a high-voltage power source was connected to the nozzle, and a metal drum (diameter 20 cmφ) grounded with conductive silicone rubber was installed at a position facing the nozzle and about 8 cm away from the nozzle. The syringe can be connected to a microfeeder for discharging and supplying the spinning solution at a constant speed to constitute an electrostatic spinning device.

Further, polyacrylonitrile (homopolymer) having a weight average molecular weight of 500,000 was dissolved in dimethylformamide (DMF) as a solvent to prepare a spinning solution A having a concentration of 10% by mass. This spinning solution A was put in the above-described syringe, and the spinning solution was discharged at a rate of 1 (mL / hour) in a direction perpendicular to the direction of gravity. This semi-solidified fiber was collected and collected by the above-mentioned metal drum rotating at a constant speed at a peripheral speed of 6 (m / min) on the surface. At this time, by applying a voltage of +15 kV from a high voltage power source to the nozzle, an electric field was applied to the spinning solution to make the fibers extremely fine. The electrospun non-woven fabric A thus accumulated and prepared on the surface of the metal drum was unified to an average fiber diameter of 350 (nm) (as observed by an electron microscope) and an area density of 5 (g / m ² ). In addition, when the nonwoven fabric was integrated and formed, the fiber distribution was made uniform by reciprocatingly swinging at a speed of 20 (cm / min) in a direction orthogonal to the distance between the nozzle and the metal drum. The nonwoven fabric was prepared in an environment at a temperature of 25 ° C. and a relative humidity of 23% ± 2%. In the measurement evaluation described below, the electrospun nonwoven fabric A was prepared and used under the same conditions using the above-described apparatus. .

  Furthermore, the oil “Bonnel MVPD122” (trade name, manufactured by Mitsubishi Rayon Co., Ltd.) made of a commercially available copolymerized PAN obtained by copolymerizing an acrylic ester and acrylonitrile is removed with alcohol and water, and DMF is used as a solvent. A spinning solution B having a concentration of 14% by mass was prepared. Electrospinning was performed using this spinning solution B under the same conditions as described above, and an electrospun nonwoven fabric B having the same average fiber diameter and surface density as described above was prepared.

(Measurement of tensile strength)
In order to evaluate the reinforcing method in this example, the strength evaluation of the electrospun nonwoven fabric after various processing conditions described later was performed by the following method. First, a rectangular measurement sample was collected from an electrospun nonwoven fabric sample under the condition of 50 (mm) × 15 (mm) width. Note that “vertical” in the dimension conditions of the measurement sample is a direction along the cylindrical outer peripheral surface of the metal drum described above. This sample is fixed to a chuck of a tensile strength tester “Tensilon TM-111-100” (Orientec Co., Ltd., trade name), and the constant distance is 20 mm between chucks and the tensile speed is 50 (mm / min). The maximum tension (tensile strength) up to rupture was measured. As an evaluation result, this tensile strength was divided by the surface density of the electrospun nonwoven fabric, and the strength of each electrospun nonwoven fabric was compared.

  Hereinafter, processing conditions for each sample of each example and comparative example subjected to actual evaluation will be described. First, the electrospun non-woven fabric A described above is moistened by exposing it to a 4-level saturated steam environment with a set temperature difference of 20 ° C. in a temperature range of 60 to 120 ° C. for 10 minutes using a commercially available autoclave. Heat treatment was performed to evaluate the strength improvement effect. In addition, after these wet heat treatments, drying is performed at 150 ° C. for 30 minutes with a hot air drier for the purpose of removing the spinning solvent DMF and moisture. Measurement samples of Example 1 to Example 4 were obtained. In addition, in order to evaluate the influence of the wet heat treatment time, an evaluation sample of Example 5 exposed to wet heat by an autoclave at 100 ° C. for 30 minutes was obtained, and only the above drying was performed on the electrospun nonwoven fabric A as a control. An evaluation sample of Comparative Example 1 was obtained. Furthermore, as Comparative Example 2, an autoclave treatment was performed for 30 minutes under a temperature condition of 40 ° C. lower than that in the series of examples, and an evaluation sample was obtained.

  Further, in order to verify the wet heat condition treatment at 140 ° C. exceeding the preferred temperature range of the present invention, a stainless steel sealable pressure resistant container is separately prepared as Comparative Example 3, and water and the electrospun nonwoven fabric A are contained in the container. Were placed in a constant temperature dryer, and the temperature was raised to 140 ° C. The treatment time at this time was 10 minutes after the temperature inside the pressure vessel was monitored and the target temperature reached 140 ° C.

  Instead of the autoclave, Example 6 was performed under the same conditions as in Examples 1 to 4 and Example 5, except that the electrospun nonwoven fabric A was wet-heat treated with high-temperature steam ejected from the nozzle. Such an evaluation sample was obtained. At this time, the steam temperature in contact with the electrospun nonwoven fabric was 84 ° C., and the contact time with the steam was 30 minutes.

  Next, instead of the treatment with autoclave and high-temperature steam, the electrospun nonwoven fabric A was immersed in distilled water at room temperature, then heated with a hot air dryer at a temperature of 100 ° C. for 10 minutes, and further at 150 ° C. described above for 30 minutes. The sample which concerns on Example 7 was obtained by performing the drying process of a minute. Moreover, the sample which concerns on Example 8 was obtained on the conditions same as Example 7 except having set the temperature of the hot air dryer to 150 degreeC, and performing heat processing. Moreover, as a control for the sample, a sample of Comparative Example 4 was obtained under the same conditions except that it was air-dried at room temperature after being immersed in the distilled water.

  Subsequently, instead of the electrospun nonwoven fabric A, the sample of Example 9 was prepared under the same conditions as in Example 3 except that the electrospun nonwoven fabric B prepared by the copolymerized PAN was used. Prepared. Further, a sample of Comparative Example 5 was obtained as a control for this sample.

  Table 1 below shows the preparation conditions, processing conditions, and measurement results of the 14 types of evaluation samples described above. In the figure, in the column of strength measurement results, the tensile strength per unit surface density is clearly shown, and in order to facilitate understanding of the relative strength imparting effect, different electrostatic spinning of constituent resins The percentage of the measurement result of the comparative example sample that serves as a reference for each nonwoven fabric is calculated and shown in parentheses.

  As can be understood from the above [Table 1], in the case of polyacrylonitrile in which the constituent resin is a homopolymer, it was carried out for Comparative Example 1 in which only the heat treatment relating to the solvent removal of DMF was performed without contacting with moisture. Strength improvement was recognized in all of Examples 1 to 5. Moreover, with respect to these five example samples to which the method of the present invention was applied, no substantial improvement in strength was observed in the sample of Comparative Example 2 in which the temperature condition was 40 ° C. when contacted with moisture. Furthermore, from a comparison between Example 3 and Example 5, when an autoclave was used, it became clear that the heat treatment by the method of the present invention was sufficient for 10 minutes. In addition, it can be understood from Comparative Example 3 that when the temperature is higher than the above-described preferable temperature range, the effect of improving the strength is not recognized, and the above-described preferable temperature range is an appropriate condition. That is, when an autoclave is used as the method of the present invention, the heating temperature in the state of contact with water is at least in the range of 60 to 120 ° C. and 10 minutes or more as a condition for providing efficient strength. It was confirmed that the temperature atmosphere is preferable.

  Further, in Example 6 in which steam treatment was performed as a system opened under atmospheric pressure, and Example 7 in which the moisture and fibers were brought into contact with each other by being immersed in water at room temperature, the atmosphere was at a predetermined temperature. From comparison with Comparative Example 3, it was confirmed that the same strength as that of a sealed and pressurized atmosphere such as an autoclave could be imparted. Further, Example 8 shows that when heated in contact with water, the temperature may be as high as 120 ° C. or higher. This is considered to be because the electrospun nonwoven fabric itself is maintained at approximately 100 ° C. due to the influence of latent heat due to the evaporation of water that has permeated the electrospun fiber sheet even when the ambient temperature is a constant temperature of 120 ° C. or higher. .

  Further, from the comparison between Example 9 and Comparative Example 5 in which the resin composition of the electrospun nonwoven fabric is copolymerized PAN, the effect of the present invention is not limited to so-called homopolymerized PAN, but acrylonitrile and acrylic. It was also confirmed by PAN copolymerized with acid. From these facts, the method of the present invention can be applied to various acrylic resins containing these specific PANs.

Claims (2)

Strength imparting of an electrospun nonwoven fabric, characterized in that the electrospun nonwoven fabric is maintained at a temperature of 60 ° C. or higher and 120 ° C. or lower in a temperature atmosphere of 60 ° C. or higher in a state where the electrospun nonwoven fabric is in contact with moisture. Method. The method for imparting strength to an electrospun nonwoven fabric according to claim 1, wherein the electrospun nonwoven fabric is made of an acrylic resin.