JP6963954B2 - Wet non-woven fabric manufacturing method - Google Patents

Description

The present invention relates to a method for producing a wet non-woven fabric containing fibrillated heat-resistant fibers.

As a heat-resistant non-woven fabric, a wet non-woven fabric containing fibrillated heat-resistant fibers is known. Hereinafter, "wet non-woven fabric containing fibrillated heat-resistant fiber" may be abbreviated as "fibrillated heat-resistant fiber-containing non-woven fabric". For example, in recent years, the use of lithium-ion batteries has expanded to applications such as electric vehicles in addition to conventional portable devices. In applications such as electric vehicles, lithium-ion batteries, which are larger than those of mobile devices, are used.

As the lithium ion battery separator, a porous film made of polyolefin such as polyethylene or polypropylene is often used, but in a large lithium ion battery, a heat resistant separator is used.

As the heat-resistant separator, a fibrillated heat-resistant fiber-containing non-woven fabric is used as a separator as it is, and a fibrillated heat-resistant fiber-containing non-woven fabric is used as a base material, and the base material, a porous membrane made of an organic polymer, and a porous material containing inorganic particles are contained. It is known that a film (coating layer) or the like is combined to form a separator.

As an embodiment in which the fibrillated heat-resistant fiber-containing non-woven fiber is used as it is as a separator, it contains heat-resistant pulp fibers (fibrillated heat-resistant fibers) having a melting point or carbonization temperature of 300 ° C. or higher, and thermoplastic fibers having a melting point of 200 ° C. or higher. A separator for a lithium ion secondary battery made of a non-woven fabric (see, for example, Patent Document 1), containing at least one type of fibrillated organic fiber (fibrillated heat-resistant fiber) having a fiber diameter of 1 μm or less, and , Non-fibrillated fiber Separator for electrochemical element (see, for example, Patent Document 2) containing one or more kinds of organic fibers of 0.5 dtex or less, melting point or thermal decomposition temperature of 250 ° C. or more, at least a part. Electrochemical consisting of a fibrillated polymer (fibrillated heat-resistant fiber) having a fiber diameter of 1 μm or less and a weight average fiber length in the range of 0.2 mm to 2 mm, and a non-woven fabric containing an organic fiber having a fineness of 3.3 dtex or less. A separator for an element (see, for example, Patent Document 3) is disclosed.

As a base material used in a mode in which a fibrillated heat-resistant fiber-containing non-woven fabric is used as a base material, and the base material is combined with a porous film made of an organic polymer, a porous film (coating layer) containing inorganic particles, or the like to form a separator. , A wet non-woven fabric containing fibrillated heat-resistant fibers and synthetic short fibers as essential components (see, for example, Patent Document 4) is disclosed.

A base material comprising a non-woven fabric containing synthetic resin short fibers and fibrillated lyocell fibers as essential fibers, and further comprising a fibrillated heat-resistant fiber (see, for example, Patent Document 5), an oriented crystallized polyester-based non-woven fabric. A non-woven fabric containing 30% by mass or more of fibers, and a base material more preferably containing fibrillated heat-resistant fibers (see, for example, Patent Document 6) is disclosed.

In the base materials disclosed in Patent Documents 1 to 6, the fibrillation treatment of the fibrillated heat-resistant fiber is disclosed. However, there is no mention of a method for dissociating or dispersing fibrillated heat-resistant fibers. In particular, when a commercially available product is used as the fibrillated heat-resistant fiber, which is obtained by removing the medium from the slurry of the fibrillated heat-resistant fiber by applying a mechanical shearing force to obtain a powdery granular composition, the solid content concentration is high. It has been increased to 20 to 35% by mass, and there is a problem that powdery undissolved matter remains in the usual dissociation method or dispersion treatment. When the powdery undissociated material is contained in the wet non-woven fabric, the thickness becomes uneven, and when an attempt is made to provide a coating layer containing inorganic particles, the coating layer unevenness occurs, and the separator and the electrode In some cases, the contact of the particles becomes non-woven, causing a problem that the battery characteristics deteriorate. In addition, when a wet non-woven fabric is manufactured by the wet papermaking method, when the wet paper is picked up from the papermaking wire to the wet blanket, the problem that powdery undissolved matter is peeled off from the papermaking wire, contact with the wet blanket or the top blanket. In some cases, there may be a problem that the powdery undissolved material is peeled off, and a problem that the powdery granular undissolved material is peeled off on the surface of the Yankee dryer. ..

Japanese Unexamined Patent Publication No. 2006-19191 International Publication No. 01/93350 Pamphlet Japanese Unexamined Patent Publication No. 2004-146137 Japanese Unexamined Patent Publication No. 2012-3873 International Publication No. 2011/046066 Pamphlet Japanese Unexamined Patent Publication No. 2012-134024

The subject of the present invention is in view of the above circumstances, and it is possible to obtain a wet non-woven fabric containing fibrillated heat-resistant fibers, which is excellent in uniformity, has no defects, and is excellent in coatability. It is an object of the present invention to provide a method for producing a wet non-woven fabric.

As a result of diligent research to solve the above problems, the following inventions were found.

(1) In a method for producing a wet non-woven fabric containing fibrillated heat-resistant fibers, a wet papermaking method is used in which the fibrillated heat-resistant fibers are dispersed in water using a high-speed rotary shear type disperser. to produce a wet-laid nonwoven fabric, high-speed rotation shearing type dispersing machine, a manufacturing method of wet-laid nonwoven fabric, wherein a disperser der Rukoto having a ring-shaped blade with a fine slit rotating at a high speed on a part of the structure.

According to the method for producing a wet nonwoven fabric of the present invention, it is possible to provide a wet nonwoven fabric containing fibrillated heat-resistant fibers, which has excellent uniformity, no defects, and excellent coatability.

The method for producing a wet nonwoven fabric of the present invention is characterized in that a wet nonwoven fabric is produced by a wet papermaking method using a slurry in which fibrillated heat-resistant fibers are dispersed in water using a high-speed rotary shear type disperser.

In the present invention, fibrillated heat resistant fibers are used. Examples of fibrillated heat-resistant fibers include total aromatic polyamide, total aromatic polyester, polyimide, polyamideimide, polyether ether ketone, polyphenylene sulfide, polybenzoimidazole, poly-p-phenylene benzobisthiazole, and poly-p-phenylene benzo. A fibrillated fiber made of a heat-resistant resin such as bisoxazole or polytetrafluoroethylene is used. Among these, total aromatic polyamide is preferable because it has a high affinity with the electrolytic solution and is easily fibrillated.

The fibrillated heat-resistant fiber is a refiner, beater, mill, grinder, a rotary homogenizer that applies shearing force by a high-speed rotary blade, and a high-speed rotating cylindrical inner blade and a fixed outer blade. A double-cylindrical high-speed homogenizer that generates shear force between them, an ultrasonic crusher that is miniaturized by the impact of ultrasonic waves, and a pressure difference of at least 21 MPa is applied to the fiber suspension to allow it to pass through a small-diameter orifice to achieve high speed. It can be obtained by treating the fibers with a high-pressure homogenizer or the like that applies a shearing force or a cutting force to the fibers by colliding them and rapidly decelerating them.

The slurry concentration of the fibrillated heat-resistant fiber is often 0.001% by mass to 2% by mass, and the medium is removed from the slurry from the aspect of transportation to increase the concentration to obtain a powdery granular composition. I have something to do. Examples of the method for removing the medium include a liquid removal treatment, for example, filtration, squeezing, centrifugation and the like, a drying treatment and a combination thereof.

When the concentration is increased in this way to obtain a powder-granular composition, the fibrillated heat-resistant fibers are in a powdered state because several fibrillated heat-resistant fibers are entangled and solidified. Even if it is dispersed in water for a long time in the powder state, the powder state is not solved, and when a wet non-woven fabric is produced by a wet paper machine, it becomes a big drawback and the uniformity of the wet non-woven fabric is impaired. In addition, when a wet non-woven fabric is combined with a porous film made of an organic polymer, a porous film containing inorganic particles (coating layer), etc., uneven coating layer, uncoated parts, voids, etc. may occur, which improves workability. It may be significantly impaired.

In the present invention, when producing a wet non-woven fabric, a slurry in which fibrillated heat-resistant fibers are dispersed in water using a high-speed rotary shear type disperser is used. In the present invention, the "high-speed rotary shear type disperser" means that a slurry containing fibrillated heat-resistant fibers is passed between a rotor having a dispersion blade and rotating and a stator having a dispersion blade, and the slurry is contained. This is a disperser that applies shearing force to the fibrillated heat-resistant fibers to disperse them. Specific devices include a single disc refiner, a double disc refiner, a conical refiner, and the like.

Further, in order to obtain a slurry in which powdery undissolved fibrillated heat-resistant fibers are dispersed uniformly and efficiently, a high-speed rotary shear type disperser uses a ring-shaped blade having fine slits that rotate at high speed. It is effective to have a high-speed rotary shear disperser that is part of the structure. In a high-speed rotary shear disperser having a ring-shaped blade with fine slits that rotate at high speed as part of its structure, the hydrodynamic shock wave generated between the slits is an undissolved powder of fibrillated heat-resistant fibers. Works effectively on. Specific examples of the device include a top finer (manufactured by Aikawa Iron Works), a VF pump (manufactured by Shinhama Pump Mfg. Co., Ltd.), and a milder (manufactured by Pacific Kiko Co., Ltd.).

When obtaining a slurry in which powdery and granular undissolved products of fibrillated heat-resistant fibers are dispersed using the above disperser, the slurry concentration, processing time, the number of rotations of the rotor of the disperser, and the clearance between the stator and the rotor are obtained. By adjusting the above, the dispersibility of the fibrillated heat-resistant fiber can be appropriately adjusted.

In the present invention, the wet non-woven fabric may contain fibers other than fibrillated heat-resistant fibers. Examples of fibers other than fibrillated heat-resistant fibers include synthetic resin short fibers, cellulose fibers, pulped or fibrillated cellulose fibers, fibrids made of synthetic resin, pulped products made of synthetic resin, and inorganic fibers.

Synthetic resin short fibers include polyolefin, polyester, polyvinyl acetate, ethylene-vinyl acetate copolymer, polyamide, acrylic, polyvinyl chloride, polyvinylidene chloride, polyvinyl ether, polyvinyl ketone, polyether, polyvinyl alcohol, diene, polyurethane. , Non-fibrillated short fibers made of synthetic resins such as phenol, melamine, furan, urea, aniline, unsaturated polyester, fluorine, silicone and derivatives thereof. Examples of the inorganic fiber include glass, alumina, silica, ceramics, rock wool and the like. The cellulose fiber may be either natural cellulose or regenerated cellulose. By containing fibers other than fibrillated heat-resistant fibers, the tensile strength and piercing strength of the wet non-woven fabric are increased.

The synthetic resin short fiber may be a fiber (single fiber) made of a single resin, or may be a composite fiber made of two or more kinds of resins. Further, the synthetic resin short fibers contained in the wet nonwoven fabric of the present invention may be used alone or in combination of two or more. Examples of the composite fiber include a core sheath type, an eccentric type, a side-by-side type, a sea island type, an orange type, and a multiple bimetal type.

The fineness of the fibers used in the wet non-woven fabric is preferably 0.01 dtex or more and 0.6 dtex or less, and more preferably 0.02 dtex or more and 0.3 dtex or less. When the fineness of the fibers used in the wet non-woven fabric exceeds 0.6 dtex, the number of fibers in the thickness direction decreases, so that the pore size distribution of the wet non-woven fabric becomes wide. In addition, it becomes difficult to reduce the thickness, and the strength characteristics tend to decrease. When the fineness of the fiber used for the wet non-woven fabric is less than 0.01 dtex, the fiber becomes very expensive and stable production of the fiber becomes difficult, or when the wet non-woven fabric is produced by the wet papermaking method, the dehydration property is lowered. In some cases.

The fiber length of the fibers used in the wet non-woven fabric is preferably 1 mm or more and 10 mm or less, and more preferably 1 mm or more and 5 mm or less. If the fiber length exceeds 10 mm, the formation may be poor. On the other hand, when the fiber length is less than 1 mm, the mechanical strength of the wet nonwoven fabric becomes low, and the wet nonwoven fabric may be damaged when the coating layer is formed.

The wet non-woven fabric of the present invention is produced by a wet papermaking method. In the wet papermaking method, first, fibrillated heat-resistant fibers and, in some cases, other fibers to be used in combination are uniformly mixed and dispersed in water to form a slurry, and then screens (removal of foreign substances, lumps, etc.) are performed. , A slurry having a final fiber concentration adjusted to 0.01 to 0.50% by mass is obtained. The slurry is made with a paper machine to obtain wet paper. In order to make the dispersibility of the fibers uniform, chemicals such as a dispersant, an antifoaming agent, a hydrophilic agent, a polymer viscous agent, and a mold release agent may be added in the process.

As the paper machine, for example, a paper machine that uses a paper machine such as a long net, a circular net, or an inclined wire alone, or a combination paper machine in which two or more paper machines of the same type or different types are installed online is used. be able to. Further, when the wet non-woven fabric has a multi-layer structure of two or more layers, a laminating method of laminating wet papers made by each paper machine or a method of laminating wet papers made by each paper machine, or after forming one layer, fibers are put on the layer. A wet non-woven fabric can be produced by a casting method or the like in which dispersed slurries are cast and laminated. When the slurry in which the fibers are dispersed is cast, the previously formed layer may be in a wet paper state or a dry state. Further, two or more dried layers can be heat-sealed to form a wet non-woven fabric having a multi-layer structure.

In the present invention, when the wet nonwoven fabric has a multi-layer structure, it may have a multi-layer structure in which the fiber composition of each layer is the same, or a multi-layer structure in which the fiber composition of each layer is different. In the case of a multi-layer structure, the fiber concentration of the slurry can be lowered by lowering the basis weight of each layer, so that the texture of the wet non-woven fabric is improved, and as a result, the uniformity of the texture of the wet non-woven fabric is improved. Further, even if the formation of each layer is uneven, it can be compensated by laminating. Further, the papermaking speed can be increased, and the effect of improving the operability can be obtained.

In the wet papermaking method, a sheet-shaped wet papermaking non-woven fabric is obtained by drying the wet paper produced by the papermaking net with a Yankee dryer, an air dryer, a cylinder dryer, a suction drum type dryer, an infrared type dryer or the like. When the wet paper is dried, it is brought into close contact with a heat roll such as a Yankee dryer and heat-pressure dried, so that the smoothness of the adhered surface is improved. Hot pressure drying means drying by pressing wet paper against the hot roll with a touch roll or the like. The surface temperature of the heat roll is preferably 100 to 180 ° C, more preferably 100 to 160 ° C, and even more preferably 110 to 160 ° C. The pressure is preferably 50 to 1000 N / cm, more preferably 100 to 800 N / cm.

The present invention will be described below with reference to examples, but the present invention is not limited to these examples. In the examples, the percentages (%) and parts are all based on mass unless otherwise specified. The coating amount is the dry coating amount. Examples 1 and 2 are reference examples.

Examples 1 to 6 and Comparative Examples 1 to 4
(Dispersion treatment of fibrillated heat resistant fibers)
Commercially available fibrillated heat-resistant fibers (Daicel FineChem, Tiara (registered trademark) KY-400S and Teijin, Twaron (registered trademark) 1094) were dispersed using the equipment under the conditions shown in Table 1. A slurry of fibrillated heat resistant fibers was obtained.

Fluorinated heat-resistant fiber 4.0 parts by mass and fineness 0.06 dtex, fiber length 3 mm oriented crystallized polyethylene terephthalate (PET) synthetic resin short fiber 56.0 mass 40.0 parts by mass of unstretched PET-based synthetic resin short fibers (softening point 120 ° C., melting point 230 ° C.) for a single component type binder having a fineness of 0.2 dtex and a fiber length of 3 mm were dispersed in water with a pulper. A uniform papermaking slurry having a concentration of 0.1% by mass was prepared, a wet paper web was obtained using an inclined paper machine, and dried with a cylinder dryer having a surface temperature of 135 ° C. to obtain a sheet. The obtained sheet was subjected to a steel roll in which one roll was chrome-plated, a resin roll having a hardness of Shore D92 in the other roll, and a thermal calendar device having a surface temperature of 195 ° C. and a linear pressure of 100 kN / m. , Calendar treatment was performed to obtain wet non-woven fabrics of Examples 1 to 6 and Comparative Examples 1 and ² having a basis weight of 10 g / m 2 and a thickness of 15 μm.

The wet non-woven fabrics produced in Examples and Comparative Examples were evaluated as follows, and the results are shown in Table 2.

(Evaluation of the number of defects)
A 20 cm × 50 cm wet non-woven fabric was observed with transmitted light, the number of undissociated fibers present in the sample was counted, and converted into the number of defects per unit square meter.

(Evaluation of coatability)
100 parts of boehmite having a D50 particle size of 0.9 μm and a specific surface area of 5.5 m ² / g is mixed with 120 parts of a 0.3% aqueous solution of carboxymethyl cellulose sodium salt having a viscosity of 200 mPa · s at 25 ° C. of the 1 mass% aqueous solution. Stir well, then 300 parts of a 0.5% aqueous solution of carboxymethyl cellulose sodium salt having a viscosity of 7000 mPa · s at 25 ° C., a styrene butadiene rubber (SBR) binder (manufactured by JSR Corporation, trade name:). TRD2001) (solid content concentration 48%) was mixed and stirred to prepare a coating solution. On one side of the wet non-woven fabric ^{, a coating liquid was applied and dried with a wire bar so that the coating amount was 12 g / m 2,} and it was confirmed whether or not there were coating spots.

By comparing Examples 1 and 2 with Comparative Examples 1 to 4, a wet non-woven fabric is produced by a wet papermaking method using a slurry in which fibrillated heat-resistant fibers are dispersed in water using a high-speed rotary shear type disperser. By doing so, it can be seen that a wet non-woven fabric containing fibrillated heat-resistant fibers having a small number of defects, excellent uniformity, and excellent coatability can be provided.

By comparing Examples 1 and 2 with Examples 3 to 6, the high-speed rotary shear type disperser is a disperser having a ring-shaped blade having fine slits rotating at high speed as a part of the structure. , The granular undissolved product of the fibrillated heat-resistant fiber can be dispersed more efficiently and more uniformly. Then, it can be seen that it is possible to provide a wet non-woven fabric having a smaller number of defects, better uniformity, and better coatability.

By comparing Examples 3 and 4 with Examples 5 and 6, the high-speed rotary shear type disperser is a disperser having a ring-shaped blade having fine slits rotating at high speed as a part of the structure. Even when the treatment concentration is high, the fibrillated heat-resistant fibers can be dispersed. Then, it can be seen that a wet non-woven fabric having a small number of defects, excellent uniformity, and excellent coatability can be provided.

The wet non-woven fabric obtained by the method for producing a wet non-woven fabric of the present invention can be suitably used for battery separators, filter media, wipers, insulating papers and the like.

Claims (1)

In a method for producing a wet non-woven fabric containing fibrillated heat-resistant fibers, a wet non-woven fabric is produced by a wet papermaking method using a slurry in which the fibrillated heat-resistant fibers are dispersed in water using a high-speed rotary shear type disperser. produced, high speed shearing type dispersing machine, a manufacturing method of wet-laid nonwoven fabric, wherein a disperser der Rukoto having a ring-shaped blade with a fine slit rotating at a high speed on a part of the structure.