JP2755425B2 - Filter materials for high-performance air filters - Google Patents

Description

The present invention relates to a high performance air filter (HEPA filter) for efficiently removing fine dust contained in a gas and obtaining a clean gas. Things.

More specifically, the present invention relates to a HEPA filter which does not contain glass, does not deteriorate in performance due to contact with chemical vapor such as hydrofluoric acid, does not generate glass dust, and can reduce the volume by incineration.

(B) Conventional Techniques and Problems As a filter medium for a high-performance filter for removing fine particles contained in a gas, glass is widely used because a small-diameter filter medium can be manufactured relatively inexpensively. .
However, in the case of filter media using glass microfibers, it is inevitable that fine glass fibers contained in the filter media fall off during use.
Because dust from the filter media itself due to the vibration of the filter media is inevitable, use in high-performance filter media that dislikes dust generation and in applications that pose a safety and health problem, such as food use, is restricted. Problems such as limited use in applications that may be exposed to elemental acid vapor due to lack of resistance to oxygen, and limited use in nuclear power applications due to the inability to reduce the volume by incineration. there were.

For this reason, a filter medium using fibrillated organic fibers has been developed as a solution to the drawbacks of the filter medium using ultrafine fibers of glass (JP-A-59-92011, JP-A-63-2011). JP-232-232, JP-A-63-236512, Japanese Patent Application
No. 63-249078, Japanese Patent Application No. 63-306363). Although the filter medium using these fibrillated organic fibers has sufficient sheet strength as a filter medium due to the entanglement of the fibrillated fibers, the strength against rubbing or the like at the time of manufacturing the filter unit is not sufficient. Peeling and brushing are inevitable.

Even in the filter material for HEPA filter using micro glass, there is a spalling or raising of fibers due to rubbing or the like during processing of the filter unit, and this defect is avoided by applying a latex binder.

However, in filter media for HEPA filters containing fibrillated organic fibers, the prevention of fiber spalling and napping by applying a latex binder significantly increases the pressure loss even when the amount of binder attached is minimized. In addition, a reduction in collection efficiency is inevitable.

The present invention relates to HEPA using fibrillated organic fibers.
The purpose of the present invention is to prevent the fibers from peeling or raising due to rubbing or the like during processing of the filter and to minimize the increase in pressure loss.

(C) Means for Solving the Problems As a result of various studies as a method for solving these problems, the above problems were solved by providing a protective layer composed of a thin porous sheet containing partially fusible fibers. We have found that we can do this and completed the present invention.

That is, according to the present invention, a part or all of the fiber has a fiber diameter of 1 μm.
a protective layer having a basis weight of 5 g / m ² or more containing 30% by weight or more of partially fusible fibers having a diameter of 2 μm or more at least on the downstream side of the filtration layer containing an organic fiber fibrillated to m or less. And a filter material for a high-performance air filter.

Some or all of the fibers used in the filtration layer of the present invention are, for example, fibrillated organic fibers having a fiber diameter of 1 μm or less. 1) A synthetic polymer solution is allowed to flow into a poor solvent for the polymer while applying a shearing force. And fibril precipitation (Fibrid method, Japanese Patent Publication No. 35-11851). 2) A method in which fibrils are deposited by shearing while polymerizing a synthetic monomer (polymerization shearing method, Japanese Patent Publication No. 47-21898).
3) A method in which two or more incompatible polymers are mixed, melt-extruded or spun, cut, and fibrillated into fibrils by mechanical means (split method, Japanese Patent Publication No. 35-9651). ), 4) A method of mixing two or more incompatible polymers, melt-extruding or spinning, slicing in a solvent after cutting, dissolving one polymer, and fibrillating into a fibrous form (polymer blend dissolution method) 5) A method in which a synthetic polymer is explosively ejected from the high-pressure side to the low-pressure side 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. 36-16460). 6) A method of blending a polyester polymer with an alkali-soluble component incompatible with the polyester, shaping the resulting mixture with an alkali, subjecting the mixture to beating, and fibrillating into a fibrous form. No.56-315 7) Highly crystalline and highly oriented fibers such as Kevlar fibers are cut into appropriate fiber lengths, dispersed in water, and homogenized.
Fibrillation using a beater, a sand mill or the like (JP-A-56-100801, JP-A-59-92011, US
-4761203), specific examples of which are fibrillated Kevlar fibers with a homogenizer (MFC-400, manufactured by Daicel), and fibril fibers made of acrylonitrile homopolymer (Cashimilon). FCA, manufactured by Asahi Kasei Kogyo Co., Ltd.) using a refiner or the like, and polyester pulp obtained by an alkali weight reduction beating method.

Fibers other than the fibrillated organic fibers used in the filtration layer of the present invention include wood pulp, hemp pulp,
Examples include espart, cotton fiber, synthetic fiber such as polyester fiber, vinylon fiber, acrylic fiber, polyethylene fiber, polypropylene fiber, polyamide fiber and rayon fiber, and recycled fiber. Among these fibers, synthetic fibers are preferably used from the viewpoints of dust generation and chemical resistance.

As the filtration layer of the present invention, Japanese Patent Application No. 63-249078 and Japanese Patent Application No. 63-3063 filed by the inventor as a part of the inventor.
The filter material shown in No. 63 is preferably used.

The partially fusible fiber having a diameter of 2 μm or more used in the protective layer of the present invention is a composite fiber composed of two components: a component that is melt-bonded by heat treatment, hot water treatment, and the like, and a component that does not melt by these treatments. , Sheath and core ty
pe), fibers having a structure such as side-by-side (Side by side type), and specific examples thereof include core-sheath type binder fibers (type 4080, type 2080 (all manufactured by Unitika), Daiwabo NBF, Daiwabo UBF (hereinafter Daiwa Spinning Co., Ltd.), ET fiber (Chisso)), parallel binder fiber (ES fiber,
EA fiber (all manufactured by Chisso Corporation) and the like.

The blending amount of these partially fusible fibers must be 30% by weight or more from the viewpoint of surface strength and adhesion strength to the filtration layer, and below this, sufficient surface strength and adhesion strength cannot be obtained. In addition, the basis weight of the protective layer must be at least 5 g / m ^{2 in} production. The upper limit of the basis weight of the protective layer is not particularly limited, but is preferably 50 g / m ² or less from the viewpoint of cost, pressure loss, and workability.

The fibers other than the partially fusible fibers used in the protective layer of the present invention include synthetic fibers such as polyester fibers, vinylon fibers, nylon fibers, acrylic fibers, polyethylene fibers, polypropylene fibers, polyamide fibers, rayon fibers, and wood. Natural fibers such as pulp, hemp pulp, espart, and cotton fibers, and regenerated and semi-synthetic fibers such as rayon fibers and acetate fibers.

Among these fibers, synthetic fibers are preferably used from the viewpoints of dust generation and chemical resistance. Further, it is preferable to contain 3 to 30% by weight of ultrafine fibers having a fiber diameter of 1 to 5 μm from the viewpoint of preventing the fibrillated fibers from falling off.

In the filter material of the present invention, inorganic fibers such as glass fiber which breaks or breaks during production, processing and use to generate very fine dust are not preferred, and the constituent fiber components of the filter material are all organic fibers. It is preferable that all of them are synthetic fibers.

If necessary, the filter medium of the present invention may contain a water-repellent agent such as a fluorine-based or silicon-based water-repellent agent, a viscous agent,
Additives such as a retention aid, a surfactant and a dyeing agent can be blended.

The filter medium of the present invention is preferably water-repellent,
For example, it is preferable to apply a water repellent dispersion to the filter medium by a method such as spraying or impregnation, and then dry the filter medium.

The filter material of the present invention is produced by a paper machine for producing general paper or wet nonwoven fabric, for example, a fourdrinier paper machine, a round mesh paper machine, an inclined wire paper machine or the like.

The method of laminating the filter layer and the protective layer of the filter material of the present invention to integrate them is not particularly limited.
The layers are stacked (combined) and dried and heat-treated, or the filtration layer and the protective layer are separately formed and dried, and then laminated and bonded between hot rolls to be integrated. .

The protective layer may be provided only on the downstream side of the filtration layer in order to prevent the fibers in the filtration layer from dropping to the downstream side of the filtration layer. However, if there is a problem in processing, it is provided on both the upstream side and the downstream side. No problem.

(D) Action Since the filter layer of the present invention does not contain any latex binder or other adhesive having a film-forming property in the filter layer, an increase in pressure loss and a decrease in trapping efficiency due to the film formation of the binder are prevented. There is no.

Further, since the filter medium of the present invention is made of organic fibers, there is no damage to the fibers, no dust is generated from the inside, the protective layer does not hinder the filtration performance, and the filter layer and the protective layer are the protective layer. Because it is point bonded by the partially fusible fiber inside and is completely integrated,
It is possible to prevent the filter material fibers from peeling off or fluffing due to rubbing or the like during processing without lowering the filtering performance.

(E) Examples Hereinafter, the present invention will be described with reference to Examples, but the present invention is not limited thereto.

% And parts in Examples and Comparative Examples mean weight% and parts by weight, respectively. In addition, the pressure loss and the dust collection efficiency in Examples and Comparative Examples were measured by the following methods, with the side having the protective layer as the downstream side.

Pressure loss: The ventilation resistance when air was passed through the filter at a flow rate of 4.75 cm / sec was determined by a water column manometer.

Dust collection efficiency: Dioctyl phthalate particles having an average particle size of 0.3 μm are generated, and air containing the particles is flowed at a flow rate of 5.
After passing through the filter medium at 3 cm / sec, the number of particles in the air sampled before and after the filter medium was measured using a light scattering particle counter (KC-11, manufactured by Rion Co., Ltd.), and the following equation was used. Was calculated.

Examples 1 and 2 Fiber diameter 1 μm in an aqueous solution in which a nonionic surfactant (Emanone 3299, polyoxyethylene fatty acid ester type, manufactured by Kao Corporation) was dissolved so as to be 3.0% based on the total fiber weight.
18% Kevlar fine fiber (MFC-400, manufactured by Daicel) as an organic fiber fibrillated to less than m, polyester fiber (0.1 denier x 3 mm, diameter of about 3 μm, manufactured by Asahi Kasei Corporation)
8%, Y type vinylon fiber (Kuraray Co., 2 denier × 6m
m, maximum projected diameter of about 20 μm) to prepare an aqueous slurry by mixing 74%, and form a sheet from this slurry to a basis weight of 75 g / m ² using a standard square handmade paper machine, and then lightly It was pressed and dried to form a filter layer. An aqueous slurry composed of 100% of polyester binder fiber (type 4080, 2 denier × 5 mm, manufactured by Unitika) was prepared as a partially fusible fiber, and a basis weight of 25 g / gram was obtained from this slurry using a standard square handmade paper machine. After forming a sheet so as to obtain m ² and 50 g / m ² , the sheet was lightly pressed and dried to obtain protective layers of Examples 1 and 2, respectively.

The filter layer and the protective layer were overlapped and lightly hot-pressed with a hot roll to obtain filter material sheets of Examples 1 and 2, respectively. Table 1 shows the physical properties of the sheet and the filter performance. The resulting filter material sheet exhibited practically no problematic filter performance as a HEPA filter, and no fuzzing or peeling of fibers was observed on the surface provided with the protective layer.

Comparative Example 1 A filter medium comprising only the filtration layer of Example 1 was prepared, and a filter sheet of Comparative Example 1 was obtained. Table 1 shows the physical properties and filtration performance of this filter material. The obtained filter material sheet exhibited the same filtering performance and volume reduction as those of Example 1, but the fibers on the surface were easily raised by rubbing with a finger, and the fibers were peeled off.

Comparative Example 2 An acrylic binder (HA-16,
(Rohm & Haas Co., Ltd.) diluent was impregnated and dried to a solid content of 0.5 g / m ² to obtain a filter material sheet of Comparative Example 2. Table 1 shows the physical properties and filtration performance of this filter material. Although the obtained filter material sheet prevented fluffing of the fiber on the surface and did not show any peeling of the fiber, the collection efficiency was lower than that of the filter material of Example 1 and Comparative Example 1, and the pressure loss was reduced. The rise is remarkable,
The performance was inferior.

Example 3 70% polyester binder fiber (type 4080, 2 denier x 5 mm, manufactured by Unitika), 25% polyester fiber (Tepyrus TM04N SD, 0.5 denier x 5 mm, manufactured by Teijin Limited)
And an aqueous slurry composed of 5% of polyester fiber (Tepyrus TK04N SD, 0.1 denier x 3 mm, manufactured by Teijin Limited) was prepared from the slurry to a basis weight of 10 g / m ² using a standard square handmade paper machine. After forming the sheet, a filter sheet of Example 3 was obtained in the same manner as in Example 1 except that the sheet was lightly pressed and dried to form a protective layer. Table 1 shows the physical properties and filtration performance of this sheet. The obtained filter material sheet had a lower pressure loss and a higher collection efficiency than the filter material sheet of Comparative Example 2, and no fuzzing or peeling of fibers was observed on the surface provided with the protective layer.

Example 4 An aqueous dispersion of a fluorine-based water- and oil-repellent (Sumiraze FP210, manufactured by Sumitomo Chemical Co., Ltd.) was added to the filter sheet of Example 3 in solid content.
The filter material was impregnated to a concentration of 0.5 g / m ² and dried to obtain a filter material sheet of Example 4. Table 1 shows the physical properties and filtration performance of this sheet. The obtained filter material sheet had a lower pressure loss and a higher collection efficiency than the filter material sheet of Comparative Example 2, and no fuzzing or peeling of fibers was observed on the surface provided with the protective layer. The water repellency was also sufficient.

Example 5 Kevlar fine fibers (MFC-400, Daicel Co., Ltd.) were dissolved in an aqueous solution in which a nonionic surfactant (Emanone 3299, polyoxyethylene fatty acid ester type, manufactured by Kao Corporation) was dissolved so as to be 3.0% based on the total fiber weight. 18%, polyester fiber (0.1 denier x 3 mm, diameter of about 3 μm, made by Asahi Kasei Corporation) 8
%, Y type vinylon fiber (Kuraray Co., 2 denier × 6mm,
An aqueous slurry is prepared by mixing 74% of the maximum projected diameter (approximately 20 μm), and a filtration layer sheet is formed from this slurry to a basis weight of 75 g / m ² using a standard square handmade paper machine. 70% polyester binder fiber (type 4080, 2 denier × 5 mm, manufactured by Unitika), 25% polyester fiber (Tepilus TM04N SD, 0.5 denier × 5 mm, manufactured by Teijin Limited), and polyester fiber (Tepilus TK04N SD, 0.1 denier × 3 mm, manufactured by Teijin Ltd.) A protective layer sheet made from an aqueous slurry composed of 5% using a standard square hand-made paper machine so as to have a basis weight of 10 g / m ² was superposed in a wet state.
The resultant was dried with a cylinder dryer to obtain a filter material sheet of Example 5. Table 1 shows the physical properties and filtration performance of this sheet. Compared with the filter sheet of Comparative Example 2, the obtained filter sheet had a lower pressure loss, a higher collection efficiency, and no fuzzing or peeling of fibers was observed on the surface provided with the protective layer.

Example 6 The protective layer of Example 1 was superimposed on the side of the filter sheet of Example 5 where the protective layer was not provided, and lightly heated with a hot roll to obtain a filter sheet of Example 6 having protective layers on both sides. . Table 1 shows the physical properties and filtration performance of this sheet. The resulting filter material sheet exhibited practically no problematic filter performance as a HEPA filter, and no fuzzing or peeling of fibers was observed on the surface provided with the protective layer.

(F) Effects of the Invention Since the filter medium of the present invention is composed of only flexible organic fibers, it is a drawback of the filter medium using glass fibers, such as self-dusting property and mixing of fine glass into the filter. A filter material for HEPA filters that can avoid problems such as low volume reduction by incineration, weakness to hydrofluoric acid, etc., and has no fuzzing or peeling off of fibers due to rubbing during processing, and has good pressure loss and collection efficiency. is there.

Claims (1)

(57) [Claims] 1. A partially fusible fiber having a diameter of 2 μm or more is contained in an amount of 30% by weight or more on at least a downstream side of a filtration layer containing an organic fiber in which a part or all of the fiber has a fiber diameter of 1 μm or less. A filter medium for a high-performance air filter containing no glass fiber, comprising a protective layer having a basis weight of 5 g / m2 or more.