JP2006089871A - Method for producing nonwoven fabric - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for producing a nonwoven fabric excellent in an ion-permeating property, a gas-permeating property, a liquid-permeating property, etc. and applicable to various applications. <P>SOLUTION: The method for producing the nonwoven fabric comprises a fiber web-forming step for forming a fiber web by using a thermoplastic resin fiber composed of a thermoplastic resin and a heat-resistant fiber composed of a resin having a high melting point or carbonization temperature higher than the melting point of the thermoplastic resin fiber, a aggregation step for melting only the thermoplastic resin fiber to lose a fiber form, aggregating the melted thermoplastic resin in intersecting points of the heat-resistant fiber and forming aggregated fiber web by blowing hot air to the fiber web and a coagulating step for coagulating the aggregated thermoplastic resin under pressure-free conditions. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a method for producing a nonwoven fabric.

  Conventionally, non-woven fabrics have various properties by appropriately selecting and combining fibers, fiber web forming methods, fiber web bonding methods, and post-processing, and thus have been applied to various applications.

  For example, one application utilizing the electrical insulation performance, which is one of the characteristics of a nonwoven fabric, is an electrical double layer capacitor separator application. In other words, an electric double layer capacitor has a structure in which a pair of electrodes is immersed in an ionic solution. When a voltage is applied to the electrodes, ions of the opposite sign to the electrodes are distributed in the vicinity of the electrodes, and the layer of ions is formed. On the other hand, charges of opposite sign to ions are accumulated inside the electrode. Therefore, if a load is connected between the electrodes, the charge inside the electrodes is discharged, and the ions distributed in the vicinity of the electrodes are separated from the vicinity of the electrodes and return to the neutralized state. In such an electric double layer capacitor, if a pair of electrodes come into contact with each other, it is difficult to form an ion layer in the vicinity of the electrodes. Therefore, a separator is disposed between the pair of electrodes.

  As a separator for an electric double layer capacitor made of such a nonwoven fabric, “a liquid crystalline property having a melting point or a thermal decomposition temperature of 250 ° C. or more, an average fiber length of 0.3 mm to 2 mm, and at least a part of which is fibrillated to a fiber diameter of 1 μm or less. There has been proposed a separator for an electric double layer capacitor which is a nonwoven fabric containing polymer fibers and has a porosity of 68% to 85% (Patent Document 1). This separator for an electric double layer capacitor is actually manufactured by forming a wet fiber web containing a core-sheath composite fiber composed of a polyester core component and a modified polyester sheath component, and then bringing it into contact with a heating drum. Although this separator is excellent in electrical insulation performance, a film is formed by press-fusing the core-sheath composite fiber, so that the internal resistance is high and the ion permeability is poor.

With respect to the separator for an electric double layer capacitor made of such a nonwoven fabric, the applicant of the present application “has a fibril-containing fiber and a fine polyester fiber having a fineness of 0.45 dtex (decitex) or less, and an areal density of 20 to 40 g. in / ^{m 2,} a thickness of 30 to 50 [mu] m, apparent density exceeds the 0.5 g / cm ^3, was proposed an electric double layer separator for capacitor "consisting of 0.8 g / cm ³ or less of the nonwoven fabric (Patent Document 2). This separator for an electric double layer capacitor was actually manufactured by heating and pressurizing a wet fiber web with a thermal calendar having a temperature lower than the melting point of the fine polyester fiber. This separator for electric double layer capacitors has a low internal resistance and superior ion permeability compared to the electric double layer capacitor of Patent Document 1 because the fine polyester fiber is not melted and does not form a film. However, there has been a demand for a separator for an electric double layer capacitor that has a lower internal resistance and further improved ion permeability.

  As described above, the nonwoven fabric is excellent in various performances such as separation performance, liquid retention performance, wiping performance, and concealment performance, but conversely, it has poor ion permeability, gas permeability, or liquid permeability and is applicable to various applications. There were cases where it would be an obstacle. For example, in addition to the above separators for electric double layer capacitors, gas or liquid filter materials, lithium ion secondary battery separators, alkaline secondary battery separators, laminate substrates, electrode support materials, wiping When applied to materials, medical base materials, and fixing unit cleaning sheets for copying machines, etc., the performance is inferior, and there are cases where it cannot be applied.

JP 2002-266281 A (Claim 1, Claim 7, Claim 12, Examples, etc.) JP 2002-270471 A (Claim 1, Claim 4, Examples, etc.)

  The present invention has been made to solve the above-described problems, and an object of the present invention is to provide a method for producing a nonwoven fabric that is excellent in ion permeability, gas permeability, liquid permeability, and the like and can be applied to various uses.

  The present inventors have pursued the causes of poor ion permeability, gas permeability, liquid permeability, etc. as described above. In addition to the dense structure of the nonwoven fabric, the fibers are pressure-fused to form a film. It has been found that this is caused by maintaining the fibrous form by pressure bonding. The present invention has been made based on this finding.

  The invention according to claim 1 of the present invention is a fiber using a thermoplastic resin fiber made of a thermoplastic resin and a heat resistant fiber made of a resin having a melting point or a carbonization temperature higher than the melting point of the thermoplastic resin fiber. A fiber web forming step for forming a web, and by blowing hot air against the fiber web, only the thermoplastic resin fibers are melted to disappear the fiber form, and the melted thermoplastic resin is used as an intersection of the heat resistant fibers. A non-woven fabric manufacturing method comprising a coagulation step of coagulating to form an aggregate fiber web and a coagulation step of coagulating the aggregated thermoplastic resin under no pressure ”.

  The invention according to claim 2 of the present invention further comprises “a crystallization step of crystallizing the thermoplastic resin by heat treatment after the aggregation step”. Method.

  The invention according to claim 3 of the present invention is “the method for producing a nonwoven fabric according to claim 1 or 2, wherein in the agglomeration step, hot air is blown so that the hot air permeates the fiber web”. .

  The invention according to claim 4 of the present invention is as follows: “The heat-resistant fiber is made of a resin having a melting point or carbonization temperature of 300 ° C. or higher, the thermoplastic resin fiber is 200 ° C. or higher, and lower than the melting point or carbonization temperature of the heat-resistant fiber. It is made of a thermoplastic resin having a melting point, "the method for producing a nonwoven fabric according to any one of claims 1 to 3,".

  The invention according to claim 5 of the present invention is as follows: "The amount of thermoplastic resin fibers is 10 to 60 mass% of the entire fiber web, and the nonwoven fabric according to any one of claims 1 to 4 is manufactured. Method.

  The invention according to claim 6 of the present invention is “the method for producing a nonwoven fabric according to any one of claims 1 to 5, wherein the thermoplastic resin fiber is made of a polyester resin”.

  The invention according to claim 7 of the present invention is “a method for producing a nonwoven fabric according to any one of claims 1 to 6, wherein the heat-resistant fiber includes a heat-resistant fiber having fibrils”. It is.

  The invention according to an eighth aspect of the present invention is as described in any one of the first to seventh aspects, wherein the heat-resistant fiber includes a wholly aromatic polyamide fiber or a wholly aromatic polyester fiber. Is a method for producing a nonwoven fabric.

  The invention according to claim 9 of the present invention is "the method for producing a nonwoven fabric according to any one of claims 1 to 8, wherein the fineness of the thermoplastic resin fiber is 0.45 dtex or less". is there.

  The invention according to claim 10 of the present invention is “the method for producing a nonwoven fabric according to any one of claims 1 to 9, wherein the nonwoven fabric is used as a separator for an electric double layer capacitor”.

  According to the invention of claim 1 of the present invention, hot air is blown to extinguish the fiber form of the thermoplastic resin fiber, and aggregate and solidify at the intersection of the heat-resistant fiber in a non-fiber state. A space occupied by the plastic resin fibers is formed. Therefore, a nonwoven fabric excellent in ion permeability, gas permeability, liquid permeability, etc. can be manufactured.

  According to the invention of claim 2 of the present invention, since the thermoplastic resin is crystallized, even if it is used for applications where external force is applied at high temperature, the structural change hardly occurs and the desired performance can be exhibited. A nonwoven fabric excellent in stability can be produced.

  According to the invention of claim 3 of the present invention, since the hot air is blown so that the hot air permeates the fiber web, the heat is sufficiently transmitted, and the fiber form of the thermoplastic resin fiber is easily extinguished. There is an effect that the thermoplastic resin is pushed apart by permeation, and the thermoplastic resin is easily moved to the intersection of the heat-resistant fibers and easily aggregated.

  According to the invention of claim 4 of the present invention, since both the heat resistant fiber and the thermoplastic resin fiber are excellent in heat resistance, a nonwoven fabric applicable to various uses can be produced.

  According to the invention concerning Claim 5 of this invention, since it is excellent in mechanical strength, the easy-to-handle nonwoven fabric can be manufactured.

  According to the invention concerning Claim 6 of this invention, it is excellent in heat resistance and can manufacture the nonwoven fabric applicable to various uses.

  According to the invention according to claim 7 of the present invention, since a nonwoven fabric having a dense structure can be produced, a nonwoven fabric excellent in various performances such as electrical insulation, separation performance, liquid retention performance, wiping performance, or concealment is produced. it can.

  According to the invention concerning Claim 8 of this invention, the nonwoven fabric which is excellent in heat resistance and can be applied to the use which requires heat resistance can be manufactured.

  According to the invention of claim 9 of the present invention, since the thermoplastic resin fiber is thin, the thermoplastic resin fiber is not in a fiber form, and the uniform dispersibility of the heat resistant fiber by forming a space is not impaired. A nonwoven fabric solidified uniformly throughout the nonwoven fabric can be produced.

  According to the invention concerning Claim 10 of this invention, the nonwoven fabric for separators for electric double layer capacitors which is low in internal resistance and excellent in ion permeability can be manufactured.

  In the manufacturing method of the nonwoven fabric of this invention, the thermoplastic resin fiber which consists of a thermoplastic resin is used so that it may melt | dissolve with the heat | fever of a hot air, a fiber form may be lose | disappeared, and it can aggregate at the intersection of a heat resistant fiber.

  The thermoplastic resin fiber only needs to be composed of a thermoplastic resin having a melting point lower than the melting point or carbonization temperature of the heat-resistant fiber described later (preferably a melting point lower by 20 ° C. or more, more preferably a melting point lower by 30 ° C. or more). Although not particularly limited, for example, polyester resins (polyethylene terephthalate, polybutylene terephthalate, polytrimethylene terephthalate, etc.), polyamide resins (nylon 6, nylon 66, etc.), polyphenylene sulfide resins, polyvinyl chloride resins, polyurethane resins , Polyolefin resins (polypropylene, polyethylene, poly-4-methylpentene-1, etc.), polyvinylidene chloride resins, and the like. Among these thermoplastic resins, it is preferable to be made of a thermoplastic resin having a melting point of 200 ° C. or higher (preferably 210 ° C. or higher, more preferably 220 ° C. or higher) so as to be excellent in heat resistance. Examples of thermoplastic resins having a melting point of ℃ or higher include polyester resins (polyethylene terephthalate, polybutylene terephthalate, polytrimethylene terephthalate, etc.), polyamide resins (nylon 6, nylon 66, etc.), polyphenylene sulfide resins, polyvinyl chloride resins, A polyurethane resin, poly-4-methylpentene-1, etc. can be mentioned, Among these, the polyester resin excellent in heat resistance is suitable.

  The fineness of the thermoplastic resin fiber is not particularly limited, but is preferably 0.45 dtex or less. Thermoplastic resin fibers are made to disappear by hot air and aggregate at the intersection of heat-resistant fibers, but the thinner the thermoplastic resin fibers are, the smaller the space formed by the thermoplastic resin fibers being out of fiber form. This is because the thermoplastic resin can be agglomerated and coagulated uniformly throughout the nonwoven fabric without decreasing the uniform dispersibility of the heat-resistant fibers. A more preferred fineness is 0.35 dtex or less, a further preferred fineness is 0.25 dtex or less, and a most preferred fineness is 0.15 dtex or less. The lower limit of the fineness of the thermoplastic resin fiber is not particularly limited, but is preferably about 0.01 dtex. This “fineness” refers to a value obtained by the A method defined in JIS L 1015.

  The fiber length of the thermoplastic resin fiber varies depending on the fiber web forming method and is not particularly limited, but is preferably about 1 to 160 mm. In the case of producing a wet nonwoven fabric excellent in the uniform dispersibility of fibers, the fiber length of the thermoplastic resin fibers is preferably 1 to 25 mm, more preferably 3 to 20 mm. This fiber length refers to the length obtained by the method B (corrected staple diagram method) of JIS L 1015.

  The amount of the thermoplastic resin fiber is preferably 10% by mass or more, more preferably 20% by mass or more of the entire fiber web so that a nonwoven fabric having excellent mechanical strength can be produced. On the other hand, it is preferably 60% by mass or less, more preferably 50% by mass or less, and still more preferably 40% by mass or less from the relationship with the heat resistant fiber described later. The thermoplastic resin fibers may be two or more types of thermoplastic resin fibers that differ in resin composition, fineness, and / or fiber length. When two or more kinds of thermoplastic resin fibers are used, the total mass is preferably within the above range.

  In the present invention, in addition to the thermoplastic resin fibers as described above, the melting point of the thermoplastic resin fibers is higher (preferably higher than 20 ° C., more preferably higher than 30 ° C. so that the nonwoven fabric form can be maintained. A heat-resistant fiber made of a resin having a high melting point or carbonization temperature is used. The heat-resistant fiber only needs to be made of a resin having a melting point or carbonization temperature higher than that of the thermoplastic resin fiber, and the same thermoplastic resin fiber as the above-described thermoplastic resin fiber can also be used. However, it is preferable to use heat-resistant fibers made of a resin having a melting point or a carbonization temperature of 300 ° C. or higher so that it has excellent heat resistance and can be applied to various applications. More specifically, examples of the “resin having a melting point of 300 ° C. or higher” include polytetrafluoroethylene and polyphenylene sulfide, and the “resin having a carbonization temperature of 300 ° C. or higher” includes a meta-based resin. Examples include wholly aromatic polyamides, para-based wholly aromatic polyamides, polyamide imides, aromatic polyether amides, polybenzimidazoles, and wholly aromatic polyesters. Among these, wholly aromatic polyamides (meta-type wholly aromatic polyamides, para-type wholly aromatic polyamides) or wholly aromatic polyesters are excellent because of their excellent heat resistance. The preferable wholly aromatic polyamide heat-resistant fiber and / or wholly aromatic polyester heat-resistant fiber preferably occupies 50 mass% or more of the heat-resistant fiber so as to be excellent in heat resistance. It is more preferable to occupy 70 mass% or more, more preferably 90 mass% or more of the heat-resistant fiber, and most preferably 100 mass% of the heat-resistant fiber.

  “Melting point” in the present invention refers to a temperature obtained from a differential thermal analysis curve (DTA curve) obtained by differential thermal analysis specified in JIS K 7121, and “carbonization temperature” refers to heat specified in JIS K 7120. The temperature obtained by gravimetric measurement.

  Nonwoven fabrics produced using heat-resistant fibers, particularly wholly aromatic polyamide heat-resistant fibers and / or wholly aromatic polyester heat-resistant fibers, can be suitably used as separators for electric double layer capacitors. For example, in an electric double layer capacitor using an organic electrolyte, if an individual material (for example, a collector electrode, an electrode, a separator, etc.) contains moisture, an electric double layer capacitor having a high withstand voltage or an electric double layer having a high energy density. Since it is difficult to manufacture a multilayer capacitor, it is necessary to sufficiently dry individual materials. A nonwoven fabric (separator for electric double layer capacitor) manufactured using such a heat-resistant fiber, a collector electrode, and After the electrodes are assembled, they can be simultaneously dried at a temperature of 150 ° C. or higher, so that an electric double layer capacitor having a high withstand voltage and an electric double layer capacitor having a high energy density can be easily manufactured. Nonwoven fabrics manufactured using such heat-resistant fibers have excellent thermal stability, and the mechanical strength hardly changes even at a temperature of 150 ° C. or higher. The electric double layer capacitor can be manufactured without impairing the electrical insulation performance.

  As such a heat-resistant fiber, it is preferable to include a heat-resistant fiber having fibrils. By including heat-resistant fibers having fibrils, a nonwoven fabric having a dense structure can be produced, and the nonwoven fabric is also excellent in various properties such as electrical insulation, separation performance, liquid retention performance, wiping performance, and concealment performance. Can be manufactured. Since the higher the content ratio, the higher the content ratio of such heat-resistant fibers, the better the various performances. Therefore, it is preferable that 50% by mass or more of the heat-resistant fibers be heat-resistant fibers having fibrils. More preferably, 70 mass% or more of the heat-resistant fiber is blended so as to be a heat-resistant fiber having fibrils, and more preferably 90 mass% or more of the heat-resistant fiber is blended so as to be heat-resistant fibers having fibrils. It is most preferable to blend only heat-resistant fibers having fibrils as heat-resistant fibers. The “heat-resistant fiber having fibrils” refers to a heat-resistant fiber in which innumerable fine fibers (fibrils) are generated from one heat-resistant fiber by mechanical shearing force or the like.

  When heat-resistant fibers that are not fibrillated are included, heat-resistant fibers having a fineness of 0.3 dtex or less are preferably used so that a nonwoven fabric having a dense structure can be produced. It is more preferable to use. On the other hand, the freeness of the fibrillated heat-resistant fibers is preferably 300 mlCSF or less, more preferably 200 mlCSF or less, so that a nonwoven fabric having a dense structure can be produced. More preferably, heat resistant fibers of 100 ml CSF or less are used. In addition, it is preferable that the freeness of the fibrillated heat-resistant fiber is 50 mlCSF or more. This “freeness” means a value measured by a JIS P8121 Canadian standard freeness tester.

  The fiber length of the non-fibrillated heat resistant fiber varies depending on the fiber web forming method and is not particularly limited, but is preferably about 1 to 160 mm. When manufacturing a wet nonwoven fabric excellent in uniform fiber dispersibility, the fiber length of heat-resistant fibers that are not fibrillated is preferably from 1 to 25 mm, more preferably from 3 to 20 mm.

  The amount of such heat-resistant fibers is preferably 40 mass% or more, more preferably 50 mass% or more, and still more preferably 60 mass% or more of the entire fiber web so that the heat resistance is excellent. On the other hand, from the relationship with the thermoplastic resin fiber described above, it is preferably 90 mass% or less, and more preferably 80 mass% or less. The heat-resistant fiber may contain two or more types of heat-resistant fibers that differ from each other by at least one point selected from the resin composition, the presence or absence of fibrils, the fineness, the freeness, and the fiber length. When two or more types of heat resistant fibers are included, the total mass is preferably within the above range.

  A fiber web forming step of forming a fiber web using such heat-resistant fibers and thermoplastic resin fibers is performed. The method for forming the fiber web is not particularly limited, and examples thereof include a dry method such as an air lay method and a card method, or a wet method. Among these, it is preferable to form by a wet method that makes it easy to produce a nonwoven fabric that is excellent in various performances such as separation performance, liquid retention performance, wiping performance, and concealment performance because the fibers are uniformly dispersed. These fiber webs can be formed by a conventionally known method.

  For example, suitable wet fiber webs include a horizontal long net method, an inclined wire type short net method, a circular net method, a forward flow net / reverse flow net combination method, a forward flow net / circular former combination method, a reverse flow net It can be formed by a method such as a circle network former combination method, a short network / circle network combination method, or a long network / circle network combination method. In addition, when forming a fiber web by a wet method, two or more wet fiber webs having the same or different fiber orientation are laminated, and a laminated wet fiber web (in particular, a laminated wet fiber web having different fiber orientations of adjacent fiber webs). Is preferably formed. This is because such a laminated wet fiber web has a small pore diameter, and can produce a nonwoven fabric that is further excellent in various performances such as electrical insulation performance, separation performance, liquid retention performance, wiping performance, and concealment performance. More specifically, the wet fiber webs made by the same type of net are laminated, or the wet fiber webs made by different types of nets (for example, short net and circular net, long net and circular net) are laminated. Laminated wet fiber webs can be manufactured, and when wet fiber webs made with different types of nets are laminated, laminated wet fiber webs with different fiber orientations can be formed. Further, when the wet wet fiber web that has been made is dried, it is preferably dried at a temperature at which the thermoplastic resin fibers do not melt.

  Next, an aggregation step is performed. In this agglomeration step, hot air is blown against the fiber web to melt only the thermoplastic resin fibers to eliminate the fiber form, and to agglomerate the melted thermoplastic resin at the intersections of the heat-resistant fibers. Is a step of forming. When sufficient heat is applied to melt the thermoplastic resin fiber, the molten thermoplastic resin is in the most stable state without forming a film of the thermoplastic resin derived from the thermoplastic resin fiber. They found that they can be agglomerated at the intersections of heat-resistant fibers.

  The hot air is blown with hot air at a temperature at which the thermoplastic resin fiber melts but the heat resistant fiber does not melt or carbonize. That is, hot air having a temperature equal to or higher than the melting point of the thermoplastic resin fiber and lower than the melting point of the heat-resistant fiber or the carbonization temperature is blown.

  In this way, the thermoplastic resin formed by melting the thermoplastic resin fibers by the action of hot air also acts at the pressure when hot air is blown, and aggregates at the intersection of the heat resistant fibers, but at this stage other than hot air blowing When pressure is applied to the fiber, aggregation at the fiber intersection of the thermoplastic resin is hindered, and the thermoplastic resin is fixed in a state close to the fiber state, that is, in a state where the thermoplastic resin is continuous in a linear or curved shape, or heat resistant. Since it is fixed in the state of a film around the intersection of the fibers and tends to deteriorate various performances such as ion permeability, gas permeability, and liquid permeability, it is preferable not to apply pressure other than hot air blowing.

  In this agglomeration step, the thermoplastic resin fibers in the fiber web are melted by blowing hot air, but the thermoplastic resin fibers are efficiently melted and the melted thermoplastic resin is the intersection of the heat resistant fibers. It is preferable to blow the hot air so that the hot air permeates the fiber web so as to easily aggregate. This is because the thermoplastic resin is pushed out by permeation of hot air, and the thermoplastic resin is easily moved to the intersection of the heat-resistant fibers to be aggregated.

  And the coagulation | solidification process, ie, the coagulation | solidification process which coagulates the aggregated thermoplastic resin under no pressure, is implemented. This coagulation step may be any method as long as the aggregated thermoplastic resin coagulates, and is not particularly limited, but a method of blowing or circulating a gas below the melting point of the thermoplastic resin, or There is a method of leaving it in a gas below the melting point of the thermoplastic resin. If pressure is applied in this coagulation step, a film is formed over a wide range centering on the intersection of heat resistant fibers, and various performances such as ion permeability, gas permeability, or liquid permeability tend to be deteriorated. , Under no pressure. The term “under no pressure” in the present invention means that no pressure is applied other than the gas blowing pressure and the gas circulation pressure.

  The present invention can produce a non-woven fabric as described above, but if it further comprises a crystallization step of crystallizing the thermoplastic resin by heat treatment after the aggregation step, an external force is applied at high temperatures. Even if it uses for, the nonwoven fabric excellent in thermal stability which can exhibit desired performance with a little structural change can be manufactured. In addition, this crystallization process may be implemented after implementing a solidification process, and can also be implemented simultaneously with a solidification process.

  The heat treatment for crystallizing the thermoplastic resin is not particularly limited as long as it is a heat treatment for crystallizing the thermoplastic resin, but a method of blowing or circulating hot air at a temperature lower than the melting point of the thermoplastic resin is used. Can be mentioned. The heat treatment temperature is not particularly limited as long as it is a heat treatment for crystallizing the thermoplastic resin, and varies depending on the composition of the thermoplastic resin. When the thermoplastic resin is made of a suitable polyester, the temperature is preferably 130 to 230 ° C. In the case of polyester, crystallization tends to be insufficient at less than 130 ° C., and when it exceeds 230 ° C., it approaches the extrapolated dissolution start temperature (temperature at which the resin begins to melt), and the polyester begins to remelt, It is because the state of polyester will change, More preferably, it is 150-220 degreeC. In addition, the heat treatment in this crystallization step is preferably carried out under no pressure in any stage so that the thermoplastic resin does not form a linear or curved continuous film. Note that “crystallize” means that a crystallization peak is not drawn on a DSC curve drawn by differential scanning calorimetry of the manufactured nonwoven fabric.

  Although a nonwoven fabric can be manufactured as mentioned above, there may be variations in thickness. Also, the apparent density, tensile strength and / or tear strength may not be within the desired range. In such a case, it is preferable to perform the calendar process (calendar process) at a temperature lower than the softening temperature of the thermoplastic resin fibers (preferably a temperature lower by 20 ° C. or more) to solve the above problems. The pressure in the calendar process is not particularly limited because it varies depending on the degree of thickness variation, desired apparent density, desired tensile strength, desired tear strength, and the like. This pressure and temperature can be appropriately set by repeating the experiment. The “softening temperature” refers to a temperature that gives a starting point of a melting endothermic curve obtained by using a differential scanning calorimeter and raising the temperature from room temperature at a heating temperature of 10 ° C./min.

  Moreover, when applying the nonwoven fabric manufactured by the manufacturing method of this invention to various uses, you may implement post-processing in order to improve the adaptability to each use. For example, when used for separators for electric double layer capacitors, separators for lithium secondary batteries, separators for alkaline secondary batteries, hydrophilic treatment (for example, sulfonation) In order to enhance the trapping ability of dust etc. when used for affinity imparting treatment such as treatment, corona discharge treatment, grafting treatment, fluorine gas treatment, surfactant imparting treatment, etc.), gas or liquid filter media use or wiping use In order to increase the adhesion to the metal film when used for the electretization treatment, the substrate application for laminates, the affinity imparting treatment for increasing the affinity with the varnish, and the electrode support material application Water-repellent / oil-repellent treatment to suppress the permeation of contaminated liquids, and fixing parts for copiers, etc. When used in sheet applications it can be carried out applying the process of the release agent, and the like.

  The nonwoven fabric produced by the production method of the present invention is in a state in which the heat-resistant fibers as described above are fixed by a thermoplastic resin solidified in a non-fiber state at the fiber intersection. Therefore, the nonwoven fabric is excellent in ion permeability, gas permeability, liquid permeability, and the like. In other words, the thermoplastic resin does not form a linear or curved continuous film extending long like a fiber, and is in a state of being fixed at a point rather than a surface, so that it is ion permeable, gas permeable, or liquid It is a nonwoven fabric excellent in permeability and the like. The state in which the heat resistant fiber is fixed by the thermoplastic resin solidified in a non-fiber state at the fiber intersection is reflected in the air permeability. That is, when the film is formed, the air permeability is lowered, but the nonwoven fabric produced by the production method of the present invention has a high air permeability because the film is not formed. More specifically, the air permeability of the nonwoven fabric produced by the production method of the present invention can be 120 s / 100 ml or less, more preferably 100 s / 100 ml or less. This “air permeability” is a value measured in a state where an adapter having a diameter of 5 mm is attached to a Gurley tester (B type) specified in JIS P8111.

  Moreover, the thermoplastic resin is not unevenly distributed in the thickness direction of the nonwoven fabric produced by the production method of the present invention. By not being unevenly distributed in this way, if the amount of the thermoplastic resin is the same, a nonwoven fabric excellent in ion permeability, gas permeability, liquid permeability, etc. can be produced. Such a state is difficult to manufacture even if the heat-resistant fibers are bonded with an emulsion type adhesive. That is, when dried to bond with an emulsion type adhesive, the adhesive also moves (so-called migration) to the nonwoven fabric surface as the liquid (usually water) evaporates.

In addition, even if the nonwoven fabric manufactured through the above crystallization processes does not draw a crystallization peak, even if DSC curve is drawn by differential scanning calorimetry. In other words, because the thermoplastic resin is sufficiently crystallized, it resists external forces even at high temperatures, maintains the fixed state of the heat-resistant fibers, suppresses structural changes in the nonwoven fabric, and achieves the desired performance (tensile strength, tearing). It is a nonwoven fabric with excellent thermal stability that can exhibit strength and the like. Differential scanning calorimetry is performed under the following conditions in accordance with JIS K 7121 (heat flux differential scanning calorimetry) to draw a DSC curve.
1. Shape, size and mass of the test piece (nonwoven fabric);
A circular nonwoven fabric having a diameter of 6.4 mm is used as a test piece. The test piece is weighed to the second decimal place using an electronic balance with 5 mg as a guide.
2. Inflow rate of nitrogen gas; 50 ml / min.
3. Heating rate: 10.0 deg / min.
4). Measurement start temperature; room temperature (25 ° C)

The basis weight, thickness and apparent density of the nonwoven fabric produced by the production method of the present invention vary depending on the application and are not particularly limited, but the basis weight is 15 to 150 g / m ² , the thickness is 20 to 700 μm, and the appearance The density can be 0.2 to 0.75 g / cm ³ . The “weight per unit area” refers to the basis weight obtained based on the method specified in JIS P 8124 (paper and paperboard—basis weight measurement method), and the “thickness” is a measured value according to the method specified in JIS B 7502, that is, The value measured with an external micrometer at 5 N load is used. Furthermore, “apparent density (D, unit: g / cm ³ )” is the basis weight (W, unit: g / cm ² ) and thickness (T, unit: quotient divided by cm), that is, a value obtained from the following equation.
D = W / T

For example, when using the nonwoven fabric manufactured with the manufacturing method of this invention as a separator for electric double layer capacitors, a fabric weight is 10-60 g / m < ² >, thickness is 17-55 micrometers, and an apparent density is 0.32-. It is preferably 0.6 g / cm ³ . The nonwoven fabric (electric separator for an electric double layer capacitor) satisfying such physical properties is excellent in ion permeability due to many voids. That is, if the basis weight of the nonwoven fabric is less than 10 g / m ² , the strength tends to be weak. If the basis weight exceeds 60 g / m ² , the volume occupied by the nonwoven fabric (electric double layer capacitor separator) in a certain volume is increased. This is because the energy density tends to be too high to increase the energy density, and a more preferable basis weight is 15 to 30 g / m ² . Further, if the thickness of the nonwoven fabric (electric double layer capacitor separator) is less than 17 μm, it will be difficult to exert sufficient electrical insulation properties, and there will be a tendency to become unstable such as leakage current. When the thickness exceeds 55 μm, the volume occupied by the separator in a constant volume increases, and the energy density tends not to be increased. Therefore, a more preferable thickness is 20 to 50 μm. Furthermore, when the apparent density of the nonwoven fabric is less than 0.32 g / cm ³ , the mechanical strength tends to be weak and tends to be difficult to handle. When the apparent density exceeds 0.6 g / cm ³ , the nonwoven fabric is dense. This is because the structure tends to be too thin and the ion permeability tends to deteriorate, so a more preferable apparent density is 0.35 to 0.55 g / cm ³ . In addition, although the nonwoven fabric (electric double layer capacitor separator) has a large amount of voids having the basis weight, thickness, and apparent density as described above, the tensile strength in at least one direction is 10 N / 15 mm width or more. It is preferable that the material has a high tensile strength and is easy to handle. The direction having such tensile strength may be any direction, but the nonwoven fabric (electric double layer capacitor separator) may be wound with the electrode while applying tension to the longitudinal direction to form an electrode group. Therefore, the tensile strength in the longitudinal direction of the nonwoven fabric (electric double layer capacitor separator) is preferably 10 N / 15 mm width or more. “Tensile strength” refers to the tensile strength measured in accordance with JIS P-8113 after taking a rectangular sample (width: 15 mm, length: 200 mm) from a nonwoven fabric (electric double layer capacitor separator). . Furthermore, the nonwoven fabric (electric double layer capacitor separator) preferably has a tear strength of 0.11 N or more despite having many voids having the basis weight, thickness, and apparent density as described above. This is because the tear strength does not cause breakage during the formation of the electrode group and during the drying process after the formation. This “tear strength” is obtained by taking a rectangular sample (width: 75 mm, length: 150 mm) from a non-woven fabric (electric double layer capacitor separator) and then applying the JIS L-1096 8.15.4C method (trapezoid method). The value measured according to this.

  The nonwoven fabric produced by the production method of the present invention is not only excellent in electrical insulation performance, separation performance, liquid retention performance, wiping performance, or concealment performance, which are basic performance of the nonwoven fabric, but is also in conflict with performance. Since it is excellent in ion permeability, gas permeability, liquid permeability, etc., and also in thermal stability, it can be used for various applications. For example, separators for electric double layer capacitors, separators for lithium secondary batteries, separators for alkaline secondary batteries, gas or liquid filter materials, base materials for laminated plates, electrode support materials, wiping materials, medical It can be suitably used for a base material for a printer, a cleaning sheet for a fixing portion of a copying machine or the like.

  In particular, when the nonwoven fabric produced by the production method of the present invention is used as a separator for an electric double layer capacitor, (1) a stable electric double layer capacitor in which leakage current is difficult to occur because of excellent electrical insulation. (2) Even if the separator for the electric double layer capacitor, the collector electrode, and the electrode group are assembled by assembling the electrode group and then dried together at a high temperature to remove moisture, the separator of the present invention Since the mechanical strength can be maintained even at high temperatures, it is possible to produce an electric double layer capacitor having a high withstand voltage and an electric double layer capacitor having a high energy density without breaking the separator. (3) Non-intersection of heat resistant fibers Due to the solidification of the thermoplastic resin in the fiber state, there are many voids and excellent ion permeability, so the internal resistance is low and the capacity is large. The non-woven fabric produced by the production method of the present invention is used for an electric double layer capacitor in order to produce various effects such as the ability to produce an electric double layer capacitor, and (4) the ability to produce an electric double layer capacitor having a high energy density in a constant volume. It can be suitably used as a separator.

  Examples of the present invention will be described below, but the present invention is not limited to the following examples.

Example 1
Heat-resistant fiber having fibrils made of para-type wholly aromatic polyamide (product name: Twaron 1094, manufactured by Teijin, carbonization temperature: 500 ° C. or higher, freeness (CSF): 150 ml), and a fineness of 0. A polyester fiber (melting point: 260 ° C., softening temperature: 253 ° C.) having 11 dtex and a fiber length of 3 mm was prepared.

  Next, a slurry was formed in which the heat-resistant fiber (freeness (CSF): 90 ml) in which the heat-resistant fiber was promoted to be fibrillated by a refiner was dispersed in a mass ratio of 70:30. Thereafter, the slurry is supplied to each net to a paper machine equipped with a forward flow net, an inclined wire type short net, a forward flow net, and a Yankee dryer, and each wet fiber web is formed, and each wet fiber web is laminated. The laminated wet fiber web was formed, and then the laminated wet fiber web was dried by a Yankee dryer set at a temperature of 120 ° C. to form a three-layer wet fiber web in which the fiber orientation was unidirectional, random, and unidirectional. (Fabric web forming step). The surface of this three-layer wet fiber web was in the state shown in FIG. 1, and the cross section was in the state shown in FIG.

  Next, a speed of 15 m / min. While transporting the three-layer wet fiber web, hot air at a temperature of 280 ° C. is blown from both sides thereof, and the hot air is transmitted through the three-layer wet fiber web, thereby melting only the polyester fiber and eliminating the fiber form. The melted polyester resin was agglomerated at the intersections of the heat resistant fibers to form an agglomerated fiber web (the agglomeration step). This aggregation process was performed under no pressure.

  Next, the aggregated fiber web was air-cooled at room temperature under no pressure to coagulate the aggregated polyester resin to produce a coagulated nonwoven fabric (the coagulation step).

  Thereafter, the solidified nonwoven fabric was passed through a dryer heated to a temperature of 220 ° C. under no pressure for 3 seconds to crystallize the polyester resin, thereby producing a crystallized nonwoven fabric (the crystallization step).

Next, this crystallized nonwoven fabric was pressed with a calendar at room temperature (linear pressure: 20 N / cm) to produce a wet nonwoven fabric having a basis weight of 15 g / m ² , a thickness of 33 μm, and an apparent density of 0.45 g / cm ³ . As shown in FIG. 3, the surface of the wet nonwoven fabric was in a state in which the polyester resin fibers disappeared and the polyester resin solidified in a non-fiber state at the intersection of the heat resistant fibers. Moreover, as shown in FIG. 4, the cross section of this wet nonwoven fabric was not unevenly distributed in the thickness direction of the wet nonwoven fabric, and was distributed uniformly. When the differential scanning calorimetry of this wet nonwoven fabric was measured, a DSC curve as shown in FIG. 5 was drawn, and no crystallization peak was drawn. Furthermore, the physical properties of the wet nonwoven fabric were as follows.
(1) Tensile strength in the longitudinal direction: 10.7 N / 15 mm width (2) Elongation in the longitudinal direction: 2.5%
(3) Tear strength: 0.21N
(4) Air permeability: 51s / 100ml

(Comparative Example 1)
A three-layer wet fiber web produced in exactly the same manner as in Example 1 was pressed (linear pressure: 50 N / cm) with a pair of thermal calenders set at a temperature of 220 ° C., with a basis weight of 15 g / m ² , a thickness of 25 μm, A wet nonwoven fabric with an apparent density of 0.6 g / cm ³ was produced. As shown in FIG. 6, the surface of this wet nonwoven fabric maintained the fiber form although the polyester fiber did not form a film. The physical properties of this wet nonwoven fabric were as follows.
(1) Tensile strength in the longitudinal direction: 4.6 N / 15 mm width (2) Elongation in the longitudinal direction: 1.7%
(3) Tear strength: 0.30N
(4) Air permeability: 130s / 100ml

(Production of electric double layer capacitor)
First, an aluminum thin plate as a collecting electrode, granular activated carbon, carbon black, and polytetrafluoroethylene as an electrode are mixed and kneaded, an electrode prepared by a rolling method, a wet nonwoven fabric of Example 1 and Comparative Example 1 as a separator, and insulation A sheet was prepared.

  Next, after forming an electrode group by stacking an insulating sheet, a collector electrode, an electrode, a separator (one sheet), an electrode, and a collector electrode in this order, this electrode group is processed into a wound shape with a load of 500 g. Produced.

  Next, after drying the cylindrical electrode group at a temperature of 200 ° C. for 50 hours, the cylindrical electrode group was impregnated under reduced pressure with an electrolytic solution in which tetraethylammonium tetrafluoroborate was dissolved in propylene carbonate in a glow box, and then the container And the container was sealed to manufacture a wound capacitor. This wound type capacitor produced 10 pieces each using the wet nonwoven fabric of Example 1, and using the wet nonwoven fabric of Comparative Example 1.

(Measurement of internal resistance)
The wound capacitor produced by the above method was charged to 2.5 V for 5 minutes at a constant current of 10 A, held for 5 minutes, and then the internal resistance value was measured from the charge / discharge curve obtained by the discharging operation.

  As a result, the wound capacitor using the wet nonwoven fabric of Example 1 as a separator was excellent in ion permeability showing a low resistance value in the range of 33 to 35 mΩ, whereas the wet nonwoven fabric of Comparative Example 1 was used. The wound type capacitor used as the separator had a resistance value in the range of 38 to 42 mΩ and was slightly inferior in ion permeability.

(Measurement of voltage maintenance rate)
The wound capacitor produced by the above method was applied to 2.5 V (initial voltage: Vi) and then left for 72 hours, and the remaining voltage (Vr) after being left was measured. From this result, the voltage maintenance ratio (Vk) was calculated from the following equation.
Vk = (Vr / Vi) × 100 = 40 Vr

  As a result, the wound type capacitor using the wet nonwoven fabric of Example 1 as a separator all showed a high voltage maintenance rate of 85% or more, whereas the wet nonwoven fabric of Comparative Example 1 was used as a separator. The four wound capacitors had a low voltage maintenance ratio, with four showing a voltage maintenance ratio of 40% or less.

  From these results, it was found that the separator using the nonwoven fabric produced by the production method of the present invention has good ion permeability and good electrical insulation. It was also found that the polyester resin is excellent in thermal stability and can maintain a fixed state of the heat-resistant fiber even when dried at a temperature of 200 ° C. for 50 hours.

Electron micrograph of the surface of the three-layer wet fiber web in Example 1 Electron micrograph of the cross section of the three-layer wet fiber web in Example 1 Electron micrograph of wet nonwoven fabric surface in Example 1 Electron micrograph of a wet nonwoven fabric cross section in Example 1 DSC curve of wet nonwoven fabric in Example 1 Electron micrograph of wet nonwoven fabric surface in Comparative Example 1

Explanation of symbols

1 Heat resistant fiber 2 Polyester fiber

Claims (10)

A fiber web forming step of forming a fiber web using a thermoplastic resin fiber made of a thermoplastic resin and a heat resistant fiber made of a resin having a melting point or a carbonization temperature higher than the melting point of the thermoplastic resin fiber,
By blowing hot air against this fiber web, only the thermoplastic resin fibers are melted to extinguish the fiber form, and the molten thermoplastic resin is aggregated at the intersections of the heat resistant fibers to form an aggregate fiber web An agglomeration step,
A coagulation step of coagulating the agglomerated thermoplastic resin under no pressure;
The manufacturing method of the nonwoven fabric characterized by comprising. The method for producing a nonwoven fabric according to claim 1, further comprising a crystallization step of crystallizing the thermoplastic resin by heat treatment after the aggregation step. The method for producing a nonwoven fabric according to claim 1 or 2, wherein in the aggregating step, the hot air is blown so that the hot air passes through the fiber web. The heat-resistant fiber is made of a resin having a melting point or carbonization temperature of 300 ° C. or higher, and the thermoplastic resin fiber is made of a thermoplastic resin having a melting point of 200 ° C. or higher and lower than the melting point or carbonization temperature of the heat-resistant fiber. The manufacturing method of the nonwoven fabric in any one of Claims 1-3 which do. The method for producing a nonwoven fabric according to any one of claims 1 to 4, wherein the amount of thermoplastic resin fibers is 10 to 60 mass% of the entire fiber web. The method for producing a nonwoven fabric according to any one of claims 1 to 5, wherein the thermoplastic resin fibers are made of a polyester resin. The method for producing a nonwoven fabric according to any one of claims 1 to 6, wherein the heat-resistant fiber includes a heat-resistant fiber having fibrils. The method for producing a nonwoven fabric according to any one of claims 1 to 7, wherein the heat-resistant fiber includes a wholly aromatic polyamide fiber or a wholly aromatic polyester fiber. The method for producing a nonwoven fabric according to any one of claims 1 to 8, wherein the fineness of the thermoplastic resin fiber is 0.45 dtex or less. The method for producing a nonwoven fabric according to any one of claims 1 to 9, wherein the nonwoven fabric is used as a separator for an electric double layer capacitor.

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