JPH09155127A - Filter media - Google Patents

Abstract

(57) [Abstract] [Problem] A feature of the wet papermaking method is that it has a possibility of being incinerated to cope with future environmental problems, or its weight after incineration is much smaller than that of a filter medium using conventional glass fibers. An object of the present invention is to provide a filter medium having a uniform texture, low pressure loss, high filtration efficiency, high strength, and being flexible and capable of being independently incorporated into a filter. SOLUTION: The web is formed by a wet papermaking method using an aqueous dispersion of ultrafine fibers, skeletal fibers having an average diameter larger than that of the ultrafine fibers, and expandable particles, the expandable particles after the foaming treatment. Is formed by forming voids in the layers of the web. Preferably,
The ultrafine fibers are micro glass fibers having an average fiber diameter of 3 μm or less. In addition, at least a part of the fibrillated organic fibers has a fiber diameter of 1 μm or less.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a clean room air filter used in the fields of semiconductor manufacturing industry, pharmaceutical manufacturing industry, food industry, hospital, etc., filter media for office air conditioners, home air conditioners and the like, and an engine. The present invention relates to a filter medium for liquid filtration such as oil, fuel and water treatment.

[0002]

2. Description of the Related Art Conventionally, clean room air filters have been manufactured by a wet papermaking method using glass fibers such as chopped strand glass fibers and ultrafine glass fibers. Glass fibers have poor disintegration and dispersibility, and in order to improve them, as shown in the 19th Paper and Pulp Symposium Abstracts, pages 9 to 19 (1984), sulfuric acid water (pH 3.2 or less) is used. The glass fiber sheet was manufactured by the wet papermaking method using

However, the method of manufacturing a glass fiber sheet with sulfuric acid acid has a problem that the glass surface is leached by the acid and the glass fiber becomes brittle in addition to the problems of work safety and corrosion of each device. there were. Further, when formed into a sheet, Na ₂ SO ₄ and Na produced by the neutralization reaction between sodium and sulfuric acid on the glass surface are formed.
Since a strong electrolyte such as Cl adheres to the surface of the glass fiber, when used as a filter material for an air filter for electronics, which dislikes the presence of a conductive substance, the sulfuric acid,
The strong electrolyte was scattered and became a serious problem.

On the other hand, a filter medium composed of glass fibers is treated as an incombustible material and cannot be incinerated, resulting in coarse dust, which is regarded as a problem for future environmental measures. A reduction in quantity is being considered. However, the use of glass fiber is unavoidable at present due to the problem of filtration performance.

For this reason, a filter medium produced by the melt blown method without using any glass fiber has been developed. However, this method has a drawback that it is fragile because of its weak strength and it is soft and poor in processability. There is. Therefore, it is extremely rare to use the filter medium produced by the melt blown method alone, and generally, it is used by laminating it with a strong nonwoven fabric such as a nonwoven fabric produced by the spunbond method or a woven or knitted fabric. However, there was a problem in terms of cost and performance.

To solve this problem, Japanese Patent Laid-Open No. 2-9
Japanese Patent No. 1262 discloses ultrafine fibers and 10 to 10% of the ultrafine fibers.
Disclosed is one in which the strength is increased while maintaining the performance of an ultrafine fiber by randomly mixing with a composite fiber containing a thermoplastic component having a melting point of 200 ° C. lower. Also,
The publication describes that a melt blow method is particularly preferable as a method for obtaining an ultrafine fiber nonwoven fabric. If it is attempted to obtain it by the wet papermaking method, the composite fibers will be melted in the drying process of the nonwoven fabric and strength will not be expressed until it is cooled, and the nonwoven fabric will stick to the surface of the cylinder dryer, resulting in delamination of the nonwoven fabric. , Or surface peeling will occur.
Even if a non-woven fabric can be manufactured, the non-woven fabric is not stiff and it is difficult to incorporate it into a filter by itself.

Further, JP-A-3-249249 discloses that the strength is improved by controlling the ratio between the weight average molecular weight (Mw) and the number average molecular weight (Mn). However, the manufacturing method disclosed here is limited to the melt blowing method.

On the other hand, as one using expansive small spheres,
Japanese Patent Laid-Open No. 58-115160 discloses a spunbonded nonwoven fabric impregnated with a solution containing vinylidene sulfide side (foaming agent). However, since this method is a fiber layer formed by the spunbond method,
A sheet with a good texture (uniformity of fiber dispersion) cannot be obtained. Also, even if this sheet is impregnated with a dispersion liquid in which expandable particles are dispersed and the sheet is heated to expand the expandable particles, the fibers are firmly and mechanically entangled to each other to such an extent that the heat treatment alone cannot easily unwind. Therefore, when the expandable particles are foamed, the fibers in the entangled state are pressed and separated, so that the sheet acts as a resistance against foaming. Therefore, not only the foaming becomes nonuniform but also the foaming efficiency is poor, so that it is necessary to increase the amount of the expandable particles used.

Further, in JP-A-1-135513, in the examples, a sheet made of fibers having a fiber diameter of 1.5 denier and 14 denier is prepared, and then the expandable small spheres and the adhesive resin are applied to the sheet. Impregnation with an aqueous dispersion containing is described. Since the sheet of this method is not mechanically entangled, the sheet acts as a resistance to foaming is reduced, but since the expansive small spheres are added by the method of impregnation, the expansive small spheres are provided. Is not uniformly dispersed in the layer of the sheet, and expandable small spheres foamed by heating are unevenly present in the layer of the sheet.Thus, when the sheet is used as an air filter material, the thickness and There will be large fluctuations in efficiency, resulting in poor performance.

In Japanese Patent Laid-Open No. 3-260152, a heat-melting adhesive is used for the fibers constituting the sheet,
Since the method of applying the foaming agent is the impregnation method as in JP-A-1-135513, a uniform sheet cannot be obtained.

In order to solve these problems, attempts have been made to produce a high-performance filter medium by using not only glass fibers but also organic fibers by a wet papermaking method. However, when the filter medium is manufactured by the wet papermaking method, the filter medium is generally densified in the drying step because the filter medium shrinks in the thickness direction. This high density increases the pressure loss of the filter medium,
Furthermore, there is a problem that the filtration performance is not as high as expected. In order to reduce this pressure loss, actions such as reducing the thickness of the filter medium and reducing the density of the filter medium can be improved. However, reducing the thickness of the filter medium decreases the strength and also reduces the uniformity of the filter medium. There is a risk of In order to reduce the density of the filter media, actions such as adding thick fibers and weakening the press in the papermaking process as much as possible can be considered, but if thick fibers are added, the filtration performance will decrease. In the present situation, high efficiency filter media have not yet been obtained by using the wet papermaking method.

[0012]

In view of the present situation, an object of the present invention is to incinerate in order to cope with future environmental problems, or to reduce the weight after incineration as compared with a filter medium using a conventional glass fiber. An object of the present invention is to provide a filter medium which is very small and has a uniform texture which is a characteristic of a wet papermaking method, has low pressure loss, high filtration efficiency, high strength, and is flexible and can be independently incorporated into a filter. .

[0013]

[Means for Solving the Problems] As a result of intensive studies to solve these problems, the inventors have invented the filter medium of the present invention. That is, the filter medium of the present invention is a web produced by a wet papermaking method using an aqueous dispersion composed of ultrafine fibers, skeletal fibers having an average diameter larger than that of the ultrafine fibers, and expandable particles. The expandable particles are characterized by forming voids in the layer of the web.

In the filter material of the present invention, the ultrafine fibers are preferably micro glass fibers having an average fiber diameter of 3 μm or less.

More preferably, at least a part of the ultrafine fibers is an organic fiber fibrillated to a fiber diameter of 1 μm or less.

Further, preferably, the whole amount or a part of the skeleton fiber having an average diameter larger than that of the ultrafine fiber is an organic fiber having a crimping property.

In the filter medium of the present invention, the compounding ratio of the expandable particles in the filter medium is preferably 3 to 10% by weight.

The present invention will be described in detail below. The ultrafine fibers used in the present invention are preferably fibers having an average fiber diameter of 5 μm or less, but are not particularly limited, and include organic fibers, inorganic fibers, fillers and the like. Among them, the ultrafine fibers are microglass fibers having an average fiber diameter of 3 μm or less, or at least a part thereof is a fiber diameter of 1 μm.
Fibrillated organic fibers are preferred below.

The micro glass fiber is an ultrafine glass fiber produced by a steam spraying method, a spinning method, a flame insertion method, a rotary method or the like, and an average fiber diameter thereof is generally 5
It means that the thickness is less than μm. In the present invention, 3
μm or less is more preferable.

Examples of the fibrillated organic fibers, at least a portion of which has a fiber diameter of 1 μm or less, include those treated by the following method. 1) A method of causing a synthetic polymer solution to flow into a poor solvent for the polymer while applying a shearing force to precipitate fibrous fibrils (fibrid method, Japanese Patent Publication No. 35-11851). 2) A method of precipitating fibrils by shearing while polymerizing a synthetic monomer (polymerization shearing method, Japanese Patent Publication No. Sho 47-2)
No. 1898). 3) mixing two or more incompatible polymers, melt-extruding,
Alternatively, spinning, cutting, and fibrillating into a fibrous form by mechanical means (split method, Japanese Patent Publication No. 35-9651). 4) mixing two or more incompatible polymers, melt-extruding,
Alternatively, a method of spinning, cutting and immersing in a solvent to dissolve one of the polymers to form fibrils in a fibrous state (polymer blend dissolution method, US Pat. No. 3,382,305). 5) A method in which the synthetic polymer is explosively ejected from the high pressure measurement to the low pressure measurement at a temperature higher than the boiling point of the solvent and then fibrillated into a fibrous form (flash spinning method, Japanese Patent Publication No. 36-1646).
No. 0). 6) A method in which fibers are cut into an appropriate fiber length, dispersed in water, and fibrillated using a homogenizer, a beater or the like (JP-A-56-100801, JP-A-59-99-1).
2011 publication).

Specific examples of the fibrillated organic fiber include KY-400S (manufactured by Daicel Chemical Industries) obtained by fibrillating poly-p-phenylene terephthalamide fiber with a homogenizer, and pulp with a homogenizer. Serish KY-100S (manufactured by Daicel Chemical Industries), PC-310S obtained by fibrillating a linter with a homogenizer.
KY-410S (manufactured by Daicel Chemical Industries, Ltd.) in which acrylic fibers were fibrillated with a homogenizer, KY-420S (manufactured by Daicel Chemical Industries) in which polyethylene fibers were fibrillated with a homogenizer, and polypropylene fibers. KY-430 fibrillated with a homogenizer
S (manufactured by Daicel Chemical Industries, Ltd.). Further, a fiber obtained by fibrillating cellulose staple (trade name: Lyocell) manufactured by Courtes Co., Ltd. with a beater such as a beater or a disc refiner can be used.

The skeletal fibers having an average diameter larger than that of the ultrafine fibers used in the present invention (hereinafter referred to as skeletal fibers) are blended in order to form a uniform void by forming a network with the ultrafine fibers on the papermaking wire. It

The fiber diameter of the skeleton fiber is not particularly limited, but it is important that it is thicker than the ultrafine fibers in order to form a network with the ultrafine fibers on the papermaking wire.
However, the fiber diameter is preferably 50 μm or less in consideration of the operability at the time of papermaking by the wet papermaking method and the collection efficiency of the filter medium,
It is more preferably 30 μm or less.

The material of the skeletal fiber is not particularly limited, but for example, synthetic fibers such as polyethylene fiber, polypropylene fiber, polyamide fiber, polyester fiber, acrylic fiber, vinylon fiber, natural pulp with a small amount of film, hemp pulp, cotton linter, Examples include lint and regenerated cellulose.

The skeleton fibers are not limited to one kind of fiber diameter, and it is also possible to use fibers having two or more kinds of fiber diameters together, and the fiber diameters are sequentially changed from ultrafine fibers to skeleton fibers having two or more kinds of fiber diameters. By mixing different fibers, a uniform void is formed inside the filter medium, so that the filter medium has excellent collection efficiency.

Further, in the case where the skeleton fiber contains all or a part of crimpable organic fibers, it is possible to reduce the density of the filter medium and widen the space volume inside the filter medium while maintaining the network with the ultrafine fibers. It plays a role in balancing collection efficiency and life.

The expandable particles are particles in which a thermally expansive gas is included. Examples of the thermally expansive gas include ethane, ethylene, propane, butane and isobutane.
Examples of the resin used for the outer wall of the expandable particles include polystyrene, polyvinyl chloride, polyvinylidene chloride, and copolymers thereof. Particularly when vinylidene chloride-acrylonitrile copolymer is used for the outer wall and isobutane is used for the thermally expansive gas, the degree of expansion of the particles,
It is preferable in terms of retaining ultrafine fibers.

Since the expandable particles are mixed in the aqueous dispersion together with the ultrafine fibers and the skeletal fibers having an average diameter larger than that of the ultrafine fibers, they are uniformly distributed between the fibers when the web is formed. There is. Therefore, by radially adhering the ultrafine fibers contained in the filter medium to the outer wall of the expandable particles that have been softened when heated above the foaming temperature, it is possible to lengthen the path of air containing dust that passes through the filter medium. It increases the efficiency of collection by increasing the chances of contact with the fibers.

When further heated, the outer wall of the expandable particles expands into a thin film due to the expansion of the gas contained therein to form voids in the layer of the filter medium, and then the gas is released, and the outer wall melts to form the layer of the filter medium. While maintaining the voids inside, it acts as an adhesive that firmly fixes the surface of the ultrafine fibers and skeleton fibers, the intersections of the ultrafine fibers and the skeleton fibers, and the intersections of the skeleton fibers and the ultrafine fibers. It also plays a role in improving the overall hardness (waist).

The mixing ratio of the expandable particles to be mixed with the filter medium can be changed depending on the use of the filter medium, but it is preferably in the range of 3 to 10% by weight of the filter medium, and more preferably,
It is in the range of 4 to 7% by weight. When the compounding ratio of the expandable particles is small, the filter medium does not expand sufficiently to form a dense filter medium and the strength of the filter medium becomes weak.

On the other hand, when the blending ratio of the expandable particles is excessive, the strength of the filter medium is increased and the collection efficiency is improved, but the air permeability is deteriorated because voids inside the filter medium are filled more than necessary. The pressure loss becomes high and the life becomes short.

Materials that can be used for the filter medium of the present invention are not limited to ultrafine fibers, skeletal fibers and expandable particles, and organic synthetic fibers, natural fibers, binder fibers and the like used for nonwoven fabrics can be used as long as the performance is not impaired. There is no problem even if it is mixed.

Examples of the binder fiber include core-sheath type (core-shell type) and parallel type (side-by-side type) composite fibers. For example, a combination of polypropylene (core) and polyethylene (sheath) (trade name: Daiwabo NBF-H: manufactured by Daiwa Boshoku), a combination of polypropylene (core) and ethylene vinyl alcohol (sheath) (trade name: Daiwabo NBF-E: Yamato) Made by spinning),
Examples include a combination of polypropylene (core) and polyethylene (sheath) (trade name: Chisso ESC: manufactured by Chisso), a combination of high-melting polyester (core) and low-melting polyester (sheath) (trade name: Melty 4080: manufactured by Unitika), etc. To be In addition, vinylon binder fiber (VPB107
× 1: Hot water melting type such as Kuraray) can also be used.

The fiber diameter of the binder fiber is not particularly limited, but is preferably 0.3 to 5 denier, more preferably 1 to 2 denier. When the fiber diameter is less than 0.3 denier, the pressure loss of the filter medium becomes high and the life of the filter becomes short. Further, when the fiber diameter exceeds 5 denier, the area of fusion with other fibers is reduced and the strength of the filter medium is not improved so much.

In the filter medium of the present invention, it is important that the ultrafine fibers, skeleton fibers and expandable particles are uniformly dispersed in the filter medium in order to improve the performance. It is desirable to manufacture by a wet papermaking method that can simultaneously mix and disperse.

As a method for producing a nonwoven fabric such as a filter medium, in addition to the wet papermaking method, a nonwoven fabric (4) (fiber engineering)
Vol. 43, No. 11 (1990), a mixed fiber method, a carding method, a random webbing method, a spunbond method, a vertical stacking method, etc. may be mentioned. However, these methods are usually methods for mainly processing long fibers having a fiber length of 50 mm or more and continuous thread-like fibers, and ultrafine fibers, skeletal fibers, and expandable particles are mixed and dispersed at the same time to prepare a filter medium. Is very difficult. if,
When attempting to produce this filter medium by these methods, it is conceivable that a sheet is produced in advance only with ultrafine fibers and skeletal fibers, and this sheet is impregnated with a dispersion liquid in which expandable particles are dispersed and dried. At the stage of sheet production, the fiber length of the ultrafine fibers is so short that they may fall off, or sufficient entanglement may not be obtained and the sheet may be cut. Even if a sheet is obtained, a sheet having a good texture (uniformity of fiber dispersion) cannot be obtained. Even if a filter medium is obtained by impregnating this sheet with a dispersion liquid in which the expandable particles are dispersed and drying it, the expandable particles are not uniformly dispersed in the filter medium, and the performance of the filter medium becomes poor.

When a filter material is prepared by the wet papermaking method, it is necessary to uniformly disperse the ultrafine fibers, the skeletal fibers and the expandable particles in the dispersed water. Therefore, it is necessary to add a dispersant such as a surfactant to the dispersed water. Is desirable.

Surfactants include anionic, cationic,
It is classified as nonionic and bisexual. Examples of the anionic surfactant include carboxylic acid salts, sulfuric acid ester salts, sulfonic acid salts, and phosphoric acid ester salts. Examples of the cationic surfactant include an amine salt and an ammonium salt. Examples of the nonionic surfactant include an ether type, an ester type, and an amino ether type.
Examples of the amphoteric surfactant include a betaine type. Of these, those having good fiber dispersibility may be appropriately selected and used. Further, even if it is out of this range, there is no problem as long as it has good fiber dispersibility.

In order to improve the dispersion stability of the fibers that are uniformly mixed and dispersed, an anionic polyacrylamide-based viscous agent is added to the fiber dispersion liquid or the papermaking white water to form the filter medium after wet papermaking. Will improve further.

The filter material of the present invention may be a wet paper machine for producing general paper or wet non-woven fabric, for example, a fourdrinier paper machine, a cylinder paper machine or a slanted wire paper machine, which is a single layer.
It may be a multilayer of two or more layers in which the same model or different models are combined. In the case of two or more layers, the life of the filter medium is improved by making the upstream side a rough layer and the downstream side a dense layer.

A dryer such as a cylinder drier, a through drier or an infrared drier can be used for drying, and the drying temperature must be equal to or higher than the foaming temperature of the expandable particles.

However, the filter material of the present invention is not limited to that obtained by a wet paper machine, but includes all of expandable particles, ultrafine fibers, skeleton fibers, or a fiber sheet, woven fabric,
It can be laminated with non-woven fabrics, films, membranes and the like.

The filter material of the present invention has good strength and stiffness when dried, but in order to further improve the strength and stiffness depending on the application, it is possible to add various binders after wet papermaking and drying. is there.

As the binder to be used, acrylic latex, vinyl acetate latex, urethane latex, epoxy latex, SBR latex, phenol resin, and cationic polyacrylamide which is a water-soluble paper strength agent having a cationic group, amphoteric Polyacrylamide, cationic acrylamide, amphoteric acrylamide,
Examples thereof include cationic polyamide, amphoteric polyamide, polyamide polyamine, cationic starch, cationic guar gum, amphoteric guar gum, polyamide epiclohydrin, cationic PVA and the like. Cationic polyacrylamide and amphoteric polyacrylamide are preferable, and these can be used alone or in combination of two or more kinds.

After wet papermaking and drying, the amount of binder applied is less than 20% by weight based on the basis weight of the filter medium. 2
If it exceeds 0% by weight, not only the strength and stiffness are strengthened, but the collection performance is deteriorated and the pressure loss is increased to shorten the life of the filter.

Further, in order to impart water repellency and flame retardancy to the sheet, a water repellent and a flame retardant may be added depending on the use.

[0047]

In the filter material of the present invention, the expandable particles are mixed in the aqueous dispersion together with the ultrafine fibers and the skeletal fibers having an average diameter larger than that of the ultrafine fibers. It is distributed between the fibers. Therefore, by radially adhering the ultrafine fibers contained in the filter medium to the outer wall of the expandable particles softened when heated above the foaming temperature, it is possible to lengthen the path of air containing dust that passes through the filter medium. It increases the efficiency of collection by increasing the chances of contact with the fibers. When further heated, the outer wall of the expandable particles expands into a thin film due to the expansion of the gas contained therein and expands to form a void in the layer of the filter medium, and then the gas is released, and the outer wall melts to form a void in the layer of the filter medium. While maintaining, the surface of the ultrafine fibers and the skeleton fibers, the intersections of the ultrafine fibers and the skeleton fibers, and the adhesives that firmly fix the intersections of the skeleton fibers and the ultrafine fibers, so the waist of the entire filter medium ( It also plays a role of improving hardness. Further, since the air permeability can be ensured by the voids in the filter medium layer formed of the expandable particles, it is possible to provide a filter medium having high strength and being flexible and capable of being incorporated into a filter independently.

[0048]

The present invention will be specifically described below with reference to examples, but the present invention is not limited to these examples.
In the examples, “parts” and “%” indicate “parts by weight” and “% by weight”, respectively.

Example 1 A sodium acrylate type anionic surfactant (Nippon Acrylic Chemical; Primal 850) was added to a 2 m ³ dispersion tank so as to be 1% of the total fiber, and the fiber diameter was about 0.
65 μm micro glass fiber (Shurler; # 10
6), polyester fiber (made by Teijin) having a fiber diameter of about 12.5 μm × fiber length of 5 mm, and expandable particles (made by Matsumoto Yushi-Seiyaku Co., Ltd .; Matsumoto Mike Sphere F-30, foaming start temperature: about 100 ° C.) each 1
Blended in a ratio of 5: 80: 5, and dispersed at a concentration of 0.2%, 30
After dispersing for a minute, paper is made with a cylinder paper machine so as to have a dry weight of 70 g / m ² and then dried with an air through dryer at 150 ° C., and then an acrylic latex (made by Nippon Acrylic,
Primal HA-16) was impregnated with 5 g / m ² and dried at 150 ° C. to obtain a filter medium.

Example 2 A sodium acrylate type anionic surfactant (Nippon Acrylic Chemical; Primal 850) was added to a 2 m ³ dispersion tank so as to be 1% of the total fiber, and the fiber diameter was about 2.
7 μm micro glass fiber (made by Schuller; # 11
0), a polyester fiber (made by Teijin) having a fiber diameter of about 12.5 μm × fiber length of 5 mm, and expandable particles (made by Matsumoto Yushi-Seiyaku Co., Ltd .; Matsumoto Microsphere F-1300, foaming start temperature: about 100 ° C.): 20: After mixing at a ratio of 75: 5 and dispersing at a dispersion concentration of 0.2% for 30 minutes, after making a paper with a cylinder paper machine so that the dry weight becomes 70 g / m ² , after drying with an air-through dryer at 150 ° C. , Acrylic latex (Nippon Acrylic; Primal HA-16) impregnated with 5 g / m ²
It was dried at ℃ and a filter medium was obtained.

Example 3 A sodium acrylate type anionic surfactant (Nippon Acrylic Chemical; Primal 850) was added to a 2 m ³ dispersion tank so as to be 1% with respect to all fibers, and the fiber diameter was about 0.
A fibrillated fiber of 5 μm of aromatic polyamide (manufactured by Daicel Chemical Industries; KY-400S), fiber diameter of about 7.2 μm
× Polyester fiber having a fiber length of 5 mm (manufactured by Teijin), expandable particles (manufactured by Matsumoto Yushi-Seiyaku Co., Ltd .; Matsumoto Microsphere F-30, foaming initiation temperature: about 100 ° C) were mixed at a ratio of 10: 85: 5, respectively. Disperse at a dispersion concentration of 0.2% for 30 minutes, then make a dry weight of 70 g / m ² using a cylinder paper machine, then 150
After drying with an air-through dryer at ℃, 5g / m ^{2 of} acrylic latex (Nippon Acrylic, Primal HA-16) was impregnated and dried at 150 ° C to obtain a filter medium.

Example 4 A sodium acrylate-based anionic surfactant (Nippon Acrylic Chemical; Primal 850) was added to a 2 m ³ dispersion tank so as to be 1% of the total fiber, and the fiber diameter was about 0.
65 μm micro glass fiber (Shurler; # 10
6), polyester fiber having a fiber diameter of about 12.5 μm × fiber length of 5 mm (manufactured by Teijin), expandable particles (manufactured by Matsumoto Yushi-Seiyaku Co., Ltd .; Matsumoto Microsphere F-30, foaming initiation temperature: about 100 ° C.) 15: 82: 3 in a ratio of 0.2% dispersion and 3
After dispersing for 0 minutes, paper was made with a cylinder paper machine to a dry weight of 70 g / m ² , and dried with an air-through dryer at 150 ° C., and then 5 g of acrylic latex (made by Japan Acrylic; Primal HA-16). / m ² impregnation, 150
It was dried at ℃ and a filter medium was obtained.

Example 5 A sodium acrylate type anionic surfactant (Nippon Acrylic Chemical; Primal 850) was added to a 2 m ³ dispersion tank so as to be 1% with respect to all fibers, and the fiber diameter was about 0.
65 μm micro glass fiber (manufactured by Schuler; # 10
6), polyester fiber having a fiber diameter of about 12.5 μm × fiber length of 5 mm (manufactured by Teijin), expandable particles (manufactured by Matsumoto Yushi-Seiyaku Co., Ltd .; Matsumoto Microsphere F-30, foaming initiation temperature: about 100 ° C.) 15: After mixing at a ratio of 75:10 and dispersing at a dispersion concentration of 0.2% for 30 minutes, after making a paper with a cylinder paper machine so that the dry weight becomes 70 g / m ² , after drying with an air-through dryer at 150 ° C. , Acrylic latex (Nippon Acrylic; Primal HA-16) impregnated with 5 g / m ²
It was dried at ℃ and a filter medium was obtained.

Example 6 A sodium acrylate type anionic surfactant (Nippon Acrylic Chemical; Primal 850) was added to a 2 m ³ dispersion tank so as to be 1% with respect to all fibers, and the fiber diameter was about 0.
3 μm micro glass fiber (Shurler; # 10
0), fibrillated fibers of aromatic polyamide having a fiber diameter of about 0.5 μm (manufactured by Daicel Chemical Industries; KY-400S),
Acrylic fiber (made by Mitsubishi Rayon) with a fiber diameter of about 3.9 μm × fiber length of 3 mm, fiber diameter of about 14.3 μm × fiber length of 5 mm
Crimped polyester fiber (made by Teijin), expandable particles (made by Matsumoto Yushi-Seiyaku Co., Ltd .; Matsumoto Microsphere F-1300, foaming start temperature: about 100 ° C) are mixed at a ratio of 15: 10: 30: 35: 10, respectively. Then, after dispersing for 30 minutes at a dispersion concentration of 0.2%, after making paper with a cylinder paper machine so that the dry weight becomes 70 g / m ² ,
After drying with an air-through dryer at 150 ° C, acrylic latex (made by Nippon Acrylic; Primal HA-1
6) was impregnated with 5 g / m ² and dried to obtain a filter material for HEPA filter (high performance air filter).

Comparative Example 1 A sodium acrylate type anionic surfactant (Nippon Acrylic Chemical; Primal 850) was added to a 2 m ³ dispersion tank so as to be 1% of the total fiber, and the fiber diameter was about 0.
65 μm micro glass fiber (Shurler; # 10
6), a polyester fiber (made by Teijin) having a fiber diameter of about 12.5 μm and a fiber length of 5 mm is blended at a ratio of 15:85,
Disperse at 0.2% dispersion concentration for 30 minutes, then dry weight 7
After making paper with a cylinder paper machine so as to be 0 g / m ² , after drying with an air-through dryer at 150 ° C, 5 g of acrylic latex (made by Nippon Acrylic; Primal HA-16)
It was impregnated with / m ² and dried at 150 ° C. to obtain a filter medium.

Comparative Example 2 A sodium acrylate-based anionic surfactant (Nippon Acrylic Chemical; Primal 850) was added to a 2 m ³ dispersion tank so as to be 1% of the total fiber, and the fiber diameter was about 1
2.5 μm x 5 mm fiber length polyester fiber (manufactured by Teijin), expandable particles (manufactured by Matsumoto Yushi-Seiyaku; Matsumoto Microsphere F-3)
0, foaming start temperature: about 100 ° C.) in a ratio of 95: 5, and dispersed at a dispersion concentration of 0.2% for 30 minutes, and then dried with a cylinder paper machine to a dry weight of 70 g / m ^2. After papermaking,
After drying with an air-through dryer at 150 ° C, acrylic latex (made by Nippon Acrylic; Primal HA-1
6) was impregnated with 5 g / m ² and dried at 150 ° C. to obtain a filter medium.

Comparative Example 3 A sodium acrylate type anionic surfactant (Nippon Acrylic Chemical; Primal 850) was added to a 2 m ³ dispersion tank so as to be 1% with respect to the total fiber, and the fiber diameter was about 0.
65 μm micro glass fiber (Shurler; # 10
6), expandable particles (Matsumoto Yushi-Seiyaku; Matsumoto Microsphere F-3)
0, foaming initiation temperature: about 100 ° C.) in a ratio of 95: 5, and dispersed at a dispersion concentration of 0.2% for 30 minutes, and then dried with a cylinder paper machine so that the dry weight becomes 70 g / m ^2. After papermaking,
An attempt was made to dry with an air-through dryer at 150 ° C, but the strength of the filter medium was weak and no filter medium was obtained.

Comparative Example 4 After paper making with the same composition as in Example 1 and drying with an air-through dryer at 90 ° C. lower than the foaming start temperature of the expandable particles, an acrylic latex (Nippon Acrylic; Primal HA-16). Was impregnated with 5 g / m ² and dried at 90 ° C. to obtain a filter medium.

Comparative Example 5 A sodium acrylate type anionic surfactant (Nippon Acrylic Chemical; Primal 850) was added to a 2 m ³ dispersion tank so as to be 1% with respect to all fibers, and the fiber diameter was about 6 μm.
m × fiber length 6 mm (made by Asahi Fiber Glass), fiber diameter about 12.5 μm × fiber length 5 mm, polyester fiber (made by Teijin), expandable particles (made by Matsumoto Yushi-Seiyaku; Matsumoto Microsphere F-30, (Foaming start temperature: about 100 ° C.) at a ratio of 15: 80: 5, respectively, and a dispersion concentration of 0.2% gives 3
After dispersing for 0 minutes, after making paper with a cylinder paper machine so that the dry weight becomes 70 g / m ² , after drying with an air-through dryer at 150 ° C., 5 g of acrylic latex (Nippon Acrylic; Primal HA-16) / m ² impregnation, 150
It was dried at ℃ and a filter medium was obtained.

Comparative Example 6 A sodium acrylate-based anionic surfactant (Nippon Acrylic Chemical; Primal 850) was added to a 2 m ³ dispersion tank so as to be 1% of the total fiber, and the fiber diameter was about 0.
3 μm micro glass fiber (Shurler; # 10
0), fibrillated fibers of aromatic polyamide having a fiber diameter of about 0.5 μm (manufactured by Daicel Chemical Industries; KY-400S),
Acrylic fiber (made by Mitsubishi Rayon) with a fiber diameter of about 3.9 μm × fiber length of 3 mm, fiber diameter of about 14.3 μm × fiber length of 5 mm
16.7: 1 crimped polyester fibers (made by Teijin)
It was mixed in a ratio of 1.1: 33.3: 38.9, dispersed at a dispersion concentration of 0.2% for 30 minutes, and then dried at a weight of 70 g / m ^2.
After making a paper with a cylinder paper machine so as to be dried, it is dried with an air-through dryer at 150 ° C, and then impregnated with acrylic latex (Nippon Acrylic; Primal HA-16) at 5 g / m ² and dried to obtain a filter material for HEPA filter. Obtained.

The above Examples 1 to 6 and Comparative Examples 1 to 6
The filter material produced in 1. was evaluated by the following evaluation methods, and the results are shown in Table 1 below.

<Pressure Loss> The pressure loss (Pa) was measured by an underwater manometer to measure the ventilation resistance when air was passed through the filter medium at a wind speed of 5.3 cm / sec.

<Collection efficiency> The collection efficiency (%) is as follows: DOP aerosol (dioctyl phthalate, particle size: 0.3 μm) particles are generated, and the air containing the particles is swept at a velocity of 5.3 cm.
Per second, sample air before and after the filter media,
Each particle concentration was measured with a multi-dust counter and calculated from the following formula 1.

[0064]

[Equation 1] Collection efficiency = {(number of particles before filtration-number of particles after filtration) / number of particles before filtration} × 100

<Ash content after incineration> The ash content (%) after incineration is
The weight was calculated from the weight before and after being incinerated by heating the filter medium in an electric furnace at 900 ° C. for 2 hours, using the following formula 2.

[0066]

[Formula 2] Ash = (weight of filter medium after incineration / weight of filter medium before incineration) × 100

<Tensile Strength> Tensile Strength (kgf / 25m
m) is a tensilon measuring machine (manufactured by Orientec, HTM, which cuts the filter medium in the longitudinal direction into a width of 25 mm and a length of 160 mm.
-100) and the average value of 6 measurements was shown.

<Filter Workability> Filter workability refers to workability when the filter medium is folded into a bellows shape and incorporated into a unit.

[0069]

[Table 1]

Since the filter media of Examples 1 to 5 are blended with the expandable particles, they are elastic, have good filter processability and good collection efficiency.

An electron micrograph of the cross section of the filter medium of Example 6 is shown in FIG. It can be seen from the cross-sectional photograph that voids formed by the expandable particles are present in the layer of the filter medium. In addition, after the outer wall of the expandable particles after forming voids by foaming becomes a thin film, it breaks and acts as an adhesive that is entangled at the intersections of the fibers, increasing the rigidity (hardness) of the filter medium and improving the filter processability. HE with good collection efficiency
It was a filter material that could be used for a PA filter.

The filter material of Comparative Example 1 did not contain expandable particles and thus had a weak stiffness and poor filter processability. The filter medium of Comparative Example 2 has a low collection efficiency because it does not contain ultrafine fibers. The filter medium of Comparative Example 3 could not be obtained because no skeletal fiber was added. The filter medium of Comparative Example 4 was
Since it was dried at a temperature lower than the foaming start temperature of the expandable particles, the expandable particles did not foam, so the waist was weak,
The filter processability was poor. The filter medium of Comparative Example 5 has a low collection efficiency because the fiber diameter of the glass fiber exceeds 5 μm.

An electron micrograph of a cross section of the filter medium of Comparative Example 6 is shown in FIG. The cross-sectional photograph shows that there are no large voids in the layer of the filter medium, the thickness is thinner and the density is higher than in Example 6, so the air permeability is low and the pressure loss is high.
Since the outer wall of the expandable particles does not have an adhesive effect, the waist was weak and the filter processability was poor.

[0074]

The filter medium of the present invention has a very small weight after incineration and has a uniform texture which is a characteristic of the wet papermaking method.
It has low pressure drop, high filtration efficiency, high strength, and is flexible and can be incorporated into the filter alone.

[Brief description of the drawings]

FIG. 1 is an electron micrograph of a cross section of a filter medium showing an example of the present invention.

FIG. 2 is an electron micrograph of a cross section of a filter medium showing a comparative example other than the present invention.

Claims (5)

[Claims] 1. A web produced by a wet papermaking method using an aqueous dispersion comprising ultrafine fibers, skeletal fibers having a larger average diameter than ultrafine fibers, and expandable particles, the foamability after foaming treatment. A filter medium, characterized in that particles form voids in a layer of the web. 2. The filter medium according to claim 1, wherein the ultrafine fibers are microglass fibers having an average fiber diameter of 3 μm or less. 3. An ultrafine fiber, at least a part of which has a fiber diameter of 1.
The filter medium according to claim 1, wherein the filter medium is an organic fiber fibrillated to a size of less than or equal to μm. 4. The whole or a part of the skeletal fiber having an average diameter larger than that of the ultrafine fiber is an organic fiber having a crimping property, which is characterized in that. Filter material. 5. The compounding ratio of the expandable particles in the filter medium is 3 to.
It is 10 weight%, The filter medium as described in any one of Claims 1-4.