JP2001187306A - Filter material and air filter using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a filter material good in bending aptitude at the time of processing as a filter, having flame retardancy and low in gas generation and to provide an air filter using the filter. SOLUTION: The filter material is a laminated body of a sheet obtained by subjecting a flame retardant fiber and a heat adhesive fiber to wet type paper manufacturing and a PTFE porous membrane and the material has the flame retardancy of section 3 by JIS L1091A-1 method and also the total gas generation of BHT and DBP of <=10 μg/g at heating at 120 deg.C for 20 min based on gas chromatography mass spectrometry, and the air filter is obtained by using the filter material.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a filter medium and an air filter using the same. More specifically, the present invention relates to a flame-retardant and low-gas-generating filter medium composed of a laminate of a wet-type papermaking sheet and a polytetrafluoroethylene porous membrane, and a HEPA (High) such as a clean room using the filter medium. The present invention relates to an air filter suitable as an Efficiency Particulate Air (ULF) filter or an ULPA (Ultra Low Penetration Air) filter.

[0002]

2. Description of the Related Art High-performance air filter media used for HEPA filters and ULPA filters in clean rooms and the like have conventionally been prepared by mixing chopped strand glass fibers and micro glass fibers, forming them by a wet papermaking method, and then adding a binder. The filter media made by this method is made of glass fiber, so when used in the semiconductor field or biotechnology field, a small amount of acid, alkali, etc. There is a problem that the surface of the glass fiber is eroded by contact with water, and a small amount of boron, phosphorus or the like leaks from the filter medium, resulting in deterioration of the performance of products such as semiconductors and bio-based products in the electronic field. Further, there is a drawback that the filter medium has no elasticity and the glass fiber is broken and falls off during folding or when an impact is applied. Further, when the used filter media is discarded, the incombustible garbage problem is serious because almost no volume reduction occurs even when incinerated.

[0003] In order to solve such a problem, a non-woven fabric made by melt-blowing using polypropylene or the like as a raw material without using any glass fiber is applied to a non-woven fabric by electrification by applying a high DC voltage to collect. Electret filter media with improved efficiency have been disclosed (JP-A-5-7713, JP-A-6-128858,
Japanese Patent Publication No. 5-10962. The electret filter medium produced by this method has an advantage that the pressure loss can be suppressed to a low level because the collection efficiency is enhanced by electrostatic attraction, and that the medium can be combusted. However, under the following conditions, there is a concern that the collection efficiency is reduced. When exposed to organic solvents such as alcohol under high temperature and high humidity conditions. When dust accumulates on the filter media. Therefore, in the semiconductor industry, etc., it has not actually been used for important parts.

In order to solve the above problems, a filter medium using a polytetrafluoroethylene (hereinafter abbreviated as PTFE) porous membrane has been developed. However, this P
Since the TFE porous membrane has a very thin and flexible thickness of 1 to 50 μm, it is extremely difficult to use it alone as a filter medium. Therefore, usually, a support layer for reinforcement is laminated and used. For example, JP-A-9-206568
In Japanese Unexamined Patent Application Publication No.
A reinforcing material and a reinforcing support layer are laminated on a porous membrane.

However, in these publications,
No mention is made of the flame retardancy of the reinforcing material or the support for reinforcement and the suppression of the amount of gas generated therefrom, in order not to deteriorate the air permeability and to improve the foldability when processing as a filter. In addition, the reinforcing material and the reinforcing support are used, and as a result, problems such as poor flame retardancy and a large amount of gas generated from the filter arise. Therefore, a filter medium that suppresses the amount of gas generated by using a reinforcing material made of a nonwoven fabric and heat-treating the same has been proposed (Japanese Patent Application Laid-Open No. 11-137931), but does not mention flame retardancy at all. No flame retardancy has been obtained with the air filter media.

On the other hand, a flame-retardant filter using a flame-retardant fiber and impregnated with a flame retardant has been disclosed for use as a range hood or a ventilation fan filter for a kitchen (Japanese Patent Laid-Open No. 11-169617). However, the use of this filter is quite different, and does not mention gas generation. As described above, a filter medium and a filter that have flame retardancy and generate a small amount of gas have not been found yet.

[0007]

SUMMARY OF THE INVENTION Under such circumstances, the present invention provides a filter medium which has good foldability when processed as a filter, has flame retardancy, and has low gas generation. And an air filter using the same.

[0008]

Means for Solving the Problems The inventors of the present invention have conducted intensive studies to achieve the above object, and as a result, have made a wet papermaking of a fiber mixture containing flame-retardant fibers and heat-adhesive fibers as essential components. It has been found that the object of the present invention can be achieved by a filter medium having a specific flame retardant property and a gas generating property, which is a laminated body of a sheet and a porous PEFE membrane, and completes the present invention based on this finding. Reached.

That is, the present invention provides a laminate of a sheet formed by wet papermaking of a fiber mixture containing flame-retardant fibers and heat-adhesive fibers as essential components, and a PTFE porous membrane,
Flame retardancy according to JIS L1091A-1 method is category 3, and 2,6-di-acid when heated at 120 ° C for 20 minutes.
tert-butyl-4-methylphenol (hereinafter referred to as BH
T) and dibutyl phthalate (hereinafter abbreviated as DBP) in total, and provide a filter medium characterized in that the total gas generation is 10 μg / g or less based on gas chromatography mass spectrometry. is there. The present invention also provides an air filter using the above filter medium.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION The filter medium of the present invention comprises a laminate of a sheet obtained by wet-making a fiber mixture containing flame-retardant fibers and heat-adhesive fibers as essential components, and a porous PTFE membrane. is there. And in the present invention, the filter medium is
The flame retardancy determined by measuring the carbonization time, residual flame time, residual dust time and carbonized area according to the JIS L1091A-1 method (45 ° micron burner method) is category 3. Further, the total gas generation amount of BHT and DBP when heated at 120 ° C. for 20 minutes is 10 μg / g or less based on gas chromatography mass spectrometry. The method of measuring the gas generation amount will be described later in detail.

In the wet papermaking sheet of the filter medium of the present invention, the flame-retardant fiber used as one of the essential components only has to have an LOI value of 26 or more measured according to the flame retardancy test method JIS K7201A-1. There is no particular limitation, and various types can be used.

Examples of such flame-retardant fibers include poly-p-phenylene terephthalamide, poly-p-benzamide, poly-p-phenylene benzobisthiazole, poly-p-phenylene benzobisoxazole, polyamide hydrazine, and polyhydrazine. Hydrazine and poly-p-
At least one selected from phenylene terephthalamide-3,4-diphenyl ether terephthalamide fibers, or flame-retardant acrylic fibers, polyclar fibers and polyvinyl chloride fibers obtained by copolymerizing pinyl chloride and / or vinylidene chloride At least one member selected from among them is preferable. Among these, particularly preferred flame-retardant fibers are flame-retardant acrylic fibers, polyvinyl chloride fibers and polyvinyl chloride fibers obtained by copolymerizing vinyl chloride and / or vinylidene chloride.

The flame-retardant acrylic fibers obtained by copolymerizing vinyl chloride and / or vinylidene chloride more preferably contain an antimony compound or a halogen atom. The reason for this is that if halogen atoms are present in the polymer, hydrogen decomposition is generated by thermal decomposition of the polymer itself. Increase. Further, when antimony pentoxide is present as an antimony compound, for example, carbon dioxide generated by the reaction with the polymer further improves the flame retardancy. Therefore, flame retardancy can be maintained even when used in combination with flammable heat-bondable fibers.

The fiber diameter and the fiber length of the flame-retardant fiber are not particularly limited, but the fiber diameter is usually 0.5 to 5.
0 denier, preferably 1.0 to 2.0 denier, and the fiber length is usually 1 to 10 mm, preferably 3 to 7 m
m. The content of the flame-retardant fibers in the sheet is usually in the range of 30 to 90% by weight, preferably 50 to 85% by weight. If the content is less than 30% by weight, good flame retardancy cannot be obtained, and if it exceeds 90% by weight, the tensile strength and stiffness of the sheet become insufficient.

In the wet papermaking sheet, the heat-adhesive fiber used as another essential component is usually used to improve the tensile strength, tear strength and stiffness (hardness) of the sheet. At the same time, it also plays a role in increasing the adhesive strength when producing a laminate with the PTFE porous membrane.

In the step of producing the sheet, the heat-adhesive fibers and the intersections with other fibers are adhered to each other in a drying step, thereby increasing the various strengths. In the drying step, it is necessary to heat the fiber to a temperature equal to or higher than the melting point of the heat-adhesive fiber.
Within the range of 0 ° C. However, in the case of the dryer of the air dryer type, there is an apparatus in which the hot air temperature reaches 200 ° C. or more, but there is no problem if the temperature of the entire sheet can be controlled to be about 90 to 150 ° C.

In the case of Melty 4080 shown below, the core has a melting point of about 260 ° C. and the sheath has a melting point of about 110 ° C. Therefore, at a temperature of 110 ° C. or higher, the low-melting polyester in the sheath softens and melts. The strength of the sheet is improved by bonding the fibers in contact with the softened or melted sheath. In consideration of sheet productivity and economy, the temperature of the cylinder dryer for drying is 10 to 2 times lower than the melting point of the sheath.
It is preferably about 0 ° C. higher, in this case 120 to 130 ° C.
Is desirable.

Since the melting point of the heat-adhesive fiber is preferably about 70 to 130 ° C. since it is desirable to reduce the load on the dryer and to perform fusion with a small amount of heat energy, the temperature of the dryer is 90 to 150 ° C. Is preferable. Excessive heating exceeding 150 ° C. not only wastes heat energy but also makes it difficult for the melted portion of the heat-adhesive fiber to drip and stay at the intersection of the fibers, which in turn causes a decrease in sheet strength. . In addition, excessive melting may cause troubles such as sticking of the sheet to the cylinder dryer and sticking of the molten material to the roll immediately after the dryer.

The heat-adhesive fiber not only plays a role of improving the strength of the sheet, but also serves to improve the heat-adhesive fiber during heat lamination or hot embossing when forming a laminate of the sheet and the PTFE porous film. It functions to soften and melt to increase the adhesive strength with the porous film.

Examples of the heat-adhesive fibers include conjugate fibers such as a core-sheath type (core-shell type) and a side-by-side type (side-by-side type). For example, a combination of polypropylene (core) and polyethylene (sheath) (trade name: Daiwabo NBF-H: manufactured by Daiwa Spinning Co., Ltd.), a combination of polypropylene (core) and ethylene vinyl alcohol (sheath) (trade name: Daiwabo NBF-E: Combination of polypropylene (core) and polyethylene (sheath) (trade name: Chisso ESC: manufactured by Chisso), combination of high-melting polyester (core) and low-melting polyester (sheath) (trade name: Melty 4080) : Unitika Ltd.)
And the like. In addition, vinylon binder fiber (V
Hot water melting type such as PB107-1 (manufactured by Kuraray Co., Ltd.) can also be used.

The diameter of the heat-adhesive fiber is not particularly limited, but is preferably from 0.3 to 5 denier, more preferably from 0.5 to 2 denier. If the fiber diameter is less than 0.3 denier, the pressure loss of the sheet increases, which causes the life of the filter to be shortened. If the fiber diameter exceeds 5 denier, cavities are formed in the stepwise fiber diameter distribution of the fibers in the sheet, and although the pressure loss of the filter medium decreases, the collection efficiency may decrease. Further, the area of fusion with other fibers is reduced, and the strength of the sheet is not improved much. The fiber length of this heat-adhesive fiber is usually in the range of 1 to 10 mm, preferably 3 to 7 mm. The content of the heat adhesive fiber in the sheet is usually 5 to 60% by weight, preferably 10 to 50% by weight.
% By weight. If the content is less than 5% by weight, good tensile strength and stiffness cannot be obtained, and if it exceeds 60% by weight, the flame retardancy of the sheet becomes insufficient.

In the present invention, the fiber mixture containing the flame-retardant fiber and the heat-adhesive fiber is made into a paper by wet papermaking, and the fiber mixture contains a fiber having a fiber diameter of 10 μm or less. preferable. For that purpose, for example, it is advantageous to make a part of the flame-retardant fibers have a fiber diameter of 10 μm or less. Fibers having a fiber diameter of 10 μm or less give a moderate tensile strength to an undried sheet after wet papermaking by forming a network with other fibers during wet papermaking,
This not only enables the sheet to be smoothly fed to the drying zone, but also has the effect of increasing the collection efficiency of the dried sheet. In particular, poly-p-phenylene terephthalamide, poly-p-benzamide, poly-p-phenylene benzobisthiazole, poly-p-phenylene benzobisoxazole, polyamide hydrazine, polyhydrazine, poly-
Fibers made of p-phenylene terephthalamide-3, 4-diphenylether terephthalamide, PTFE, etc. are very rigid, so that even when beaten with a homogenizing device or the like, the fibers are split vertically without being cut. As the fibers become finer (fibrillation), when applied to a filter medium, the pressure loss can be kept low and the collection efficiency can be increased. Further, since the material is flame-retardant, it is suitable for a flame-retardant filter medium.

In order to increase the collection efficiency, there is no flame retardancy, even if the fiber is made of rayon, polyester, polyethylene, polypropylene, polyacrylonitrile, nylon, wood pulp or the like having a fiber diameter of 10 μm or less. Can be blended within a range that does not inhibit the above.

Specific examples of fibers having a fiber diameter of 10 μm or less include KY-400S (manufactured by Daicel Chemical Industries, Ltd.) in which poly-p-phenylene terephthalamide fibers are fibrillated in a homogenizer, and pulp is fibrils in a homogenizer. Serish KY-100S (manufactured by Daicel Chemical Industries),
PC-310 in which linter is fibrillated by homogenizer
S (manufactured by Daicel Chemical Industries), KY-410S (manufactured by Daicel Chemical Industries) in which acrylic fibers are fibrillated by a homogenizer, KY-420S (manufactured by Daicel Chemical Industries) in which polyethylene fibers are fibrillated by a homogenizer, polypropylene fibers KY-430 fibrillated with a homogenizer
S (manufactured by Daicel Chemical Industries, Ltd.). Further, fibers obtained by fibrillating cellulose staple (trade name: Lyocell) of Coatles Co., Ltd. with a beater such as a beater, a disc refiner, or a PFI mill may be used. The content of fibers having a fiber diameter of 10 μm or less in the sheet is as follows:
It is preferably in the range of 1 to 40% by weight, more preferably 3% by weight.
~ 35% by weight.

In the present invention, a sheet is prepared by wet-papermaking a fiber mixture containing the above-mentioned flame-retardant fiber and heat-adhesive fiber as essential components. The above-mentioned fiber mixture is commonly used for general nonwoven fabrics. Other fibers can be blended, if desired, as long as the object of the present invention is not impaired.

The wet papermaking method is not particularly limited, and a conventionally known method can be used. First, the fiber mixture is poured into dispersing water in a dispersing tank such as a pulper so that the solid content concentration is preferably 2% by weight or less, more preferably 1% by weight or less, and the mixture is sufficiently stirred to be uniform. Disperse in. This stirring and dispersion treatment also has the purpose of opening the bundled fibers, but at the same time, removes oils, plasticizers, antioxidants, etc. that remain near the fiber surface, which is the source of generated gases such as BHT and DBP. It is to leave from.

In this dispersion treatment, it is desirable to use a surfactant in order to uniformly disperse the fibers. However, it is possible to select the amount and type of use in consideration of the influence on the amount of gas generated after sheet production. It is important.

By adding an anionic polyacrylamide-based thickener to the fiber dispersion in order to improve the dispersion stability of the uniformly mixed and dispersed fibers, the formation of the sheet after wet papermaking is further improved. .

Next, after the distributed processing as described above,
After the fibers dispersed in water are further diluted with water to about 0.01 to 0.5% by weight, various paper machines conventionally used in the production of general paper and wet-laid nonwoven fabrics, such as fourdrinier paper machines, The paper is made using a net paper machine, an inclined wire paper machine, or the like. By further diluting as described above, the cleaning effect of the fiber is increased. For example, when the paper is made at 0.01% by weight, it is washed with about 10,000 times more water than the untreated case. In addition, oils, plasticizers, and the like, which easily come off near the fiber surface, are washed away. When making paper, white water (dewatered water) is usually circulated and used. However, the concentration of oils and plasticizers in the white water increases due to circulation, and it may adhere again to the fiber. It is desirable to use

The purpose of drying after papermaking is to increase the strength of the sheet by heating it to a temperature higher than the melting point of the heat-adhesive fiber blended in the sheet, thereby increasing the strength of the sheet. However, the amount of gas generated from the sheet after drying is reduced. Also plays a role. It is considered that the temperature is 80 ° C. or less even when the sheet is used after being processed into a filter medium or a filter, for example, even under extremely severe conditions in a clean room or the like. In this case, heating the sheet at a temperature exceeding 80 ° C. releases oil, plasticizer, antioxidant, and the like remaining in the fiber in advance at this stage, so that the amount of gas generated under the conditions actually used is obtained. It plays the role of reducing It is important that the drying temperature is equal to or higher than the melting point of the heat-adhesive fiber, as described above, and is preferably in the range of 90C to 150C. However, in the case of an air-hood type dryer or the like, or in the case where the papermaking speed is extremely high and a sufficient amount of heat cannot be given to the sheet, the heating may not exceed 150 ° C at all. As the dryer, for example, a cylinder dryer, a through dryer, an infrared dryer, or the like can be used. The basis weight of the sheet thus obtained is usually 10
To 100 g / m ^2, preferably in the range of 15 to 50 g / m ^2.

The sheet used in the filter medium of the present invention may be wet-laid and dried in order to further improve the strength and stiffness depending on the application, and then, after taking into consideration the effects of flame retardancy and the amount of generated gas, various types of binders are used. Can be provided.

As the binder, for example, acrylic latex, vinyl acetate latex, urethane latex, epoxy latex, polyester latex, SBR latex, NBR latex,
Epoxy resin binder, phenolic resin burner, polyvinyl alcohol, starch, paper strength agents generally used in the papermaking process, and the like, these alone,
Alternatively, it can be used in combination with a crosslinking agent.

After the wet papermaking and drying treatment, the amount of the binder to be applied is usually 20% by weight based on the basis weight of the sheet.
It is as follows. If it exceeds 20% by weight, the strength and stiffness are increased, but the trapping performance is reduced, and the pressure loss is increased, and the life may be shortened. In order to further impart water repellency and further flame retardancy to the sheet depending on the use, a water repellent and a flame retardant may be added.

The filter medium of the present invention comprises a laminate of the sheet thus obtained and the porous PTFE membrane, and the number of laminates is not particularly limited as long as it is two or more. It can be appropriately selected according to the application. For example, in the case of a filter medium for an ultra-high performance air filter (ULPA),
Five layers of sheet / PTFE porous membrane / sheet / PTFE porous membrane / sheet can be laminated and used.

The thickness, pore diameter, porosity and the like of the porous PTFE membrane are not particularly limited and may be appropriately selected depending on the intended use of the obtained filter medium.
１００100 μm, preferably 1-50 μm.

As a laminating method, there is a method using an adhesive. However, when an adhesive is used, the micropores of the filter medium are buried, and as a result, pressure loss may increase and the life may be shortened. Lamination is preferred. Although the heat-adhesive fiber blended in the sheet according to the present invention is softened and melted once in the drying step (90 to 150 ° C.) at the time of sheet production, and the intersections of the fibers or other fibers are bonded, When a temperature higher than the temperature heated in the drying step is applied during the heat lamination, it is softened and melted again, so that it adheres at the intersection of the heat-fused fiber and the porous film. Therefore, it is preferable that the temperature of the heat lamination be higher than the temperature of the drying step in producing the sheet. Considering heat energy cost and adhesiveness,
A range from 50 to 180 ° C is preferred. However, when the adhesiveness is poor or when the lamination speed is very fast and heat is hardly conducted to the sheet, it is advantageous to treat at a temperature exceeding 180 ° C.

The air filter of the present invention is obtained by using the filter medium thus produced, and includes, for example, a medium-performance air filter, a HEPA filter, and a ULPA.
Used as a filter. INDUSTRIAL APPLICABILITY The air filter of the present invention is flame-retardant and generates a small amount of gas, and can be suitably used, for example, in a clean room.

[0038]

Next, the present invention will be described in more detail with reference to examples, but the present invention is not limited to these examples.

Example 1 Poly-p-phenylene terephthalamide fiber having a fiber diameter of 10 μm or less (Twaron 1097 manufactured by Nippon Aramid Co., Ltd.), flame-retardant acrylic fiber (Super Balzer manufactured by Mitsubishi Rayon Co., Ltd.), A heat-adhesive fiber (trade name: Melty 4080, 2d × 5 mm: manufactured by Unitika) and vinylon binder fiber (VPB107-1: manufactured by Kuraray Co., Ltd.) are blended at a weight ratio of 10: 65: 20: 5, respectively, to the dispersion water. After dispersing at a solid concentration of 0.2% by weight of the fiber for 30 minutes, it is further diluted with water to 0.04% by weight and dried to a dry weight of 30%.
The paper was made with a 25 cm square hand-made paper machine so as to obtain g / m ² and then dried with a cylinder dryer at a temperature of 130 ° C. to obtain a sheet for lamination.

Next, a 10 μm-thick PTFE porous membrane (Microtex NT) was placed between the two laminated sheets thus obtained.
F1432: manufactured by Nitto Denko Corporation) and heat-laminated to obtain a filter medium.

Comparative Example 1 A commercially available spunbonded non-woven fabric made of polyester / polyethylene core-sheath fibers (core: polyester, sheath: polyethylene) (Elves S0303WDO manufactured by Unitika, basis weight 30 g / m ² ), PTFE porous A filter film was obtained by sandwiching a porous membrane (Microtex NTF1432: manufactured by Nitto Denko Corporation) and heat laminating.

The filter media prepared in Example 1 and Comparative Example 1 were evaluated by the following evaluation methods, and the results are shown in Table 1. <Flame retardancy> Flammability test method for textile products (JIS L10
The carbonization time, residual flame time, residual dust time, and carbonization area were measured by the A-1 method (45 ° micro burner method) of 91) to determine Category 1, Category 2, and Category 3. (Category 1 has poor flame retardancy and Category 3 has the best flame retardancy.)

<Gas generation amount> Generated gas sampling method JHS-100 purge &
Using a trap-type Curie-point headspace sampler, the gas generated by heating the sample at 120 ° C. for 20 minutes is adsorbed on an adsorbent (Tenax TA: manufactured by GL Science), and the adsorbed gas is heated at 358 ° C. for 10 seconds. The gas was analyzed by gas chromatography (GC 6890 and 5890, manufactured by HP) to calculate the total amount (μg / g) of BHT and DBP.

Gas Chromatography Measurement Conditions Column: DB-1 manufactured by J & W Co. 0.25 mmφ × 30 m Column temperature: 45 ° C. (3 minutes) → 10 ° C. (1 minute) → 260
° C (10 minutes) Inlet temperature: 200 ° C Detector: FDI Purge gas: Helium

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

<Collection efficiency> The collection efficiency (%) was determined by generating DOP aerosol (dioctyl phthalate, particle size: 0.3 μm) particles and blowing air containing these particles at a wind speed of 5.3 cm.
Per second, sample air before and after the filter media,
The concentration of each particle was measured by a multi-dust counter and calculated by the following equation 1. A (%) = {(BC) / B} × 100 (Equation 1) A: Collection efficiency B: Number of particles before filtration C: Number of particles after filtration

[0047]

[Table 1]

The laminating sheet used in the filter medium produced in Example 1 has a dispersion step in water which is a characteristic of wet papermaking in a fiber state, and is dispersed about 500 times in water here. As a result, it is diluted and washed, and further diluted 5 times (total 2500 times) to form a sheet, so that oils, plasticizers, and the like, which easily come off near the fiber surface, are washed away. BHT, DB together with the evaporation of water in the drying process
Gases such as P are also released from the sheet, and BHT, DBP, etc. remaining in the obtained sheet are reduced, and a PTFE porous film is sandwiched between two sheets for lamination to form a filter material by heat lamination. Even in this case, since the sheet was sandwiched between the lamination sheets having a small amount of gas generation, the flame retardancy was classified into Category 3, and the amount of gas generation was very small.

The filter medium of Comparative Example 1 was a commercially available polyester /
This is a filter material obtained by heat laminating a PTFE porous membrane between two spunbonded nonwoven fabrics made of polyethylene core-sheath fibers. The flame retardancy was very poor in Category 1. In addition, since the spunbonded nonwoven fabric does not have a step of dispersing in water, the amount of generated gas is large.

Example 2 The composition of Example 1 was applied to a 450 mm-wide circular mesh test paper machine.
30 g / m weight ^TwoPT between two sheets for lamination
FE porous membrane (Microtex NTF1432: Nittoden)
(Manufactured by Kosha Co., Ltd.).
5mm) x (305mm in width) x (150mm in depth)
The filter was assembled with 61 pleats. filter
Pleating processability and morphological stability when incorporating into
Was.

[0051]

EFFECTS OF THE INVENTION The filter medium of the present invention is diluted into about 2500 to 10000 times the sheet-forming process in water, which is a characteristic of wet papermaking in the fiber state, and is made into a sheet. Oils, plasticizers, and the like near the surface that are easily released are washed away. Further, in the drying step, water evaporates and B
Gases such as HT and DBP are also released from the sheet, so that BHT, DBP and the like remaining in the filter medium are reduced. In addition, since a sheet having essential flame-retardant fibers and a porous PTFE membrane are used, the flame retardancy is good in Category 3.

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Kojiro Nagatsuka 5-33-1, Ontacho, Higashimurayama-shi, Tokyo F-term in Oshitari Research Laboratories Co., Ltd. 4D019 AA01 BA13 BB05 BB08 BB10 BC11 BD01 CA02 DA03 DA06

Claims (6)

[Claims] 1. A laminate of a sheet obtained by wet paper-making a fiber mixture containing a flame-retardant fiber and a heat-adhesive fiber as essential components, and a polytetrafluoroethylene porous membrane,
Flame retardancy according to JIS L1091A-1 method is category 3, and 2,6-di-acid when heated at 120 ° C for 20 minutes.
A filter medium characterized in that the total gas generation amount of tert-butyl-4-methylphenol and dibutyl phthalate is 10 μg / g or less based on gas chromatography mass spectrometry. 2. The flame-retardant fiber is poly-p-phenylene terephthalamide, poly-p-benzamide, poly-p-
2. The fiber according to claim 1, which is at least one selected from phenylene benzobisthiazole, poly-p-phenylene benzobisoxazole, polyamide hydrazine, polyhydrazine and poly-p-phenylene terephthalamide-3,4-diphenyl ether terephthalamide fiber. Filter media described. 3. The flame-retardant fiber is at least one selected from flame-retardant acrylic fibers, polyvinyl chloride fibers, and polyvinyl chloride fibers obtained by copolymerizing vinyl chloride and / or vinylidene chloride. 2. The filter medium according to 1. 4. The filter medium according to claim 1, wherein the fiber mixture contains fibers having a fiber diameter of 10 μm or less. 5. The drying temperature in wet papermaking is 90-15.
The filter medium according to any one of claims 1 to 4, wherein the temperature is 0 ° C. 6. An air filter using the filter medium according to any one of claims 1 to 5.