JPH0372908A - Filter medium for air filter - Google Patents

Abstract

PURPOSE:To form a filter medium for air filter having excellent mechanical strength by superposing a filter layer consisting of glass fiber only on the side of void layer of a porous membrane comprising a fine-pore layer having fine pores which have openings perpendicular to the surface of the membrane and a void layer. CONSTITUTION:A porous membrane made from organic polymer, comprising a fine-pore layer having pores which have openings substantially perpendicular to the surface of the membrane and which have average pore diameter of 0.2-10mum and an opening ratio of 35-95% and a void layer having pore diameters larger than those of pores of the fine-pore layer is formed. A filter layer consisting of glass fiber only is superposed on the side of the void layer of the porous membrane to obtain a filter medium for air filter. For superposing a filter layer on a porous membrane, when thermoplastic material is employed in forming a porous membrane, the porous membrane is heated in a spotlike manner and pressed onto the filter layer so that the membrane is easily contacted with the said layer.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a high-performance filter medium for air purification that realizes a highly clean environment.

[Conventional technology]

Hitherto, HJICPA filters made of glass fibers, FA filters, and the like have been known as high-performance filter media for air purification to achieve a highly clean environment. However, with a filter made only of glass fibers, fine particles originating from the glass rod fibers fall off and flow into the permeating gas, making it difficult to improve air cleanliness.

In addition, as a solution to the problem caused by such falling particles, glass iIt, &! A filter medium in which a porous membrane made of polytetrafluoroethylene was laminated on the air outflow side of the layer was developed in Japanese Patent Application Laid-open No. 6
This is disclosed in Japanese Patent Laid-Open No. 2-2770.9 and Japanese Utility Model Application No. 6l-t32020, and furthermore, filter media in which a mesh cloth body or a hull is interposed in the intermediate part are disclosed in Japanese Patent Laid-Open No. 63-16017 and Japanese Unexamined Utility Model Publication No. 63-16017. It is disclosed in Publication No. 16019/1983.

[Problems to be Solved by the Invention] However, Kei discovered that the filter medium made of the glass edge 1aIII and the polytetrafluoroethylene porous membrane had not been sufficiently studied for the structure of the porous membrane, and the life of the entire filter medium was shortened. The problem is that it cannot be made longer.

In addition, porous membranes made of polytetrafluoroethylene have insufficient mechanical strength and are not thermoplastic, so they do not have sufficient processing properties and cannot be thermally melted and bonded to glass fiber layers. That's a problem.

Organic polymer porous membrane B consisting of a void layer having pores
Glass tJ on the void layer side! The filtration layer A consisting of fibers is 8
The filter medium for air filters is made up of two layers.

As the filtration layer made only of glass fibers, a well-known glass fiber filter paper known for use in air filtration can be used. The fiber diameter, dispersion state, filling rate, layer thickness, etc. can be appropriately selected and used.

Porous membrane BFi made of organic polymer, pores opening substantially perpendicular to the membrane surface (hereinafter referred to as "straight pores")
Straight pores (straight pores) and pores with larger diameters than straight pores, straight pores have a curvature ratio of 1.0 to 1.2 in any cut plane perpendicular to the membrane surface.
pores with a change ratio of 0.6 to 1.7. Here, the curvature ratio is the L/LsO ratio when the curved casing or straight line passing through the center of the hole appearing on the cut surface is L, and the thickness of the straight hole layer is L8. means. In addition, the change ratio is the width of the hole applied to the outer nine surfaces of the membrane (straight hole opening surface) for one straight hole appearing on the cut surface.If the change ratio is smaller than the above range, the pressure loss will increase. This is undesirable, and the distance between holes that are larger than the above range and adjacent to each other becomes extremely small, making it difficult to increase the aperture ratio. If the curve ratio is larger than the above range, the pressure loss will increase, which is not preferable.

Of course, the portion where the curvature ratio, housing, or change ratio of the pores deviates from the above range is not a straight pore, and in this asymmetric membrane, the diameter of the pores that connect the straight pore layer and the void layer usually gradually decreases from the interface between the two layers. It has a structure in which the voids increase sharply or rapidly in the side direction of the void layer.

In this porous membrane, the pores (hereinafter referred to as "surface pores") existing on the outer surface of the membrane of the straight pore layer are circular or elliptical, and the ratio of the major axis to the minor axis is 1.0 to 2.0. It is desirable that the pore diameter variation coefficient is 0 to 50. Also,
The average pore diameter is in the range of 12 to 10μ.Here, the arithmetic average value of the major and minor diameters of each inner pore is called the pore diameter of the surface pore, and the average pore diameter of the surface pore is N It refers to the arithmetic average value of the pore diameters of surface pores.The value of N is usually 100.The pore diameter variation coefficient refers to the value expressed by the following formula for the pore diameter of the surface pores.

(Standard deviation/average pore diameter)xlooo (correspondence) Average pore diameter is 0.
If the diameter is smaller than 2 μm, the collection efficiency is high, but the pressure loss will also be extremely high, which is not preferable. If the diameter is larger than 10 μm, the collection efficiency is low and it is not practical. Average pore size is 5μ
It is preferably less than m, and particularly preferably less than 3 μm. It is more preferable that the pore diameter variation coefficient is D to 40.

The ratio of the major axis to the minor axis and the average pore diameter can be measured using a scanning electron microscope.

Considering the filtration efficiency ε pressure loss, the thickness of the straight pore layer may be about 1 to 50 μm, and more preferably about 3 to 20 μm.

Further, the thickness of the entire porous membrane B may be about 10 to 200 μm.

In addition, the aperture ratio refers to the ratio of the total area of the surface pores to the surface area of the outer surface of the membrane, and the aperture ratio is 35 to 95.1, and if the aperture ratio is less than 35'1, pressure loss occurs. is undesirable because it becomes high, and it is undesirable if it exceeds 954 because the strength of the porous membrane decreases and it becomes easily damaged. It is more preferable that the aperture ratio is between 40 and 804! Yes.

The porosity (vot'6) of the entire porous membrane B is 50 to 95
If the porosity is smaller than the above range, the pressure loss will increase, which is undesirable, and if it is larger than the range, the mechanical properties of the porous membrane B will deteriorate, which is not preferable.

It is more preferable that the porosity of the entire porous membrane B is 65 to 95 pores.

Among these, the porosity can be determined using a mercury porosimeter.

The mechanical strength of porous membrane B has a breaking strength of 10f151 due to issues such as ease of handling during lamination processing and strength during folding processing.
It is preferable that the width is greater than the width of the casing.

If it is smaller than the above range, defects may occur in the film, resulting in decreased reliability, which is not desirable.

The organic polymer used as the material for porous membrane B is not particularly limited,
For example, fluoropolymers such as polyvinylidene fluoride and trifluoroethylene, poly(meth)acrylic esters such as polysulfone, polyethersulfone, polycarbonate, polyetherimide, polyethylene terephthalate, polymethyl methacrylate, and polybutyl (meth)acrylate; acrylonitrile, cellulose acetate,
Cellulose esters such as cellulose nitrate, polyolefins such as polyethylene, poly-4-methyl-1-pentene, polybutadiene, polyvinyl acetate, polystyrene,
Polymers such as poly-α-methylstyrene, poly-4-vinylpyridine, polyvinylpyrrolidone, polyvinyl chloride, polyvinylidene chloride, silicone-based polymer polyphenylene oxide, and copolymers thereof can be mentioned.

However, thermoplastic organic polymers are preferred from the viewpoint of handling properties during lamination processing and adhesion processing properties through thermal fusion. Among these, (meth)acrylic ester polymers alone or blends of (meth)acrylic ester polymers and other polymers are suitable for delicately controlling the structure of the porous membrane. The other polymer is preferably a fluorinated polyolefin or a copolymer of two or more fluorinated olefins.

Such a porous membrane B can be manufactured by a wet coagulation method or a combination of a wet coagulation method and a charged particle irradiation method, but a preferred method is the steam coagulation method described in JP-A-63-267406. can.

The filter medium for air filters of the present invention is one in which the above-mentioned filtration layer A and porous membrane B are laminated, but for HHP mukras, the pressure loss (ΔPj
It is preferable that k+B ) and collection efficiency (R) be in a range that satisfies the following formula.

Pressure loss ΔPA+B≦60 wtz H2O (IIA
Speed 5.3 cm/sea) Collection efficiency RA+B≧9
9.974 (linear velocity: 5.3 crn/sea, 0.3 μm particles) When used as a high-performance filter medium of the ULFA class, it is preferably within the following range.

Pressure loss Δ' A+B≦80wH20 (linear speed 5.3
cm/sea) Collection efficiency RA+B≧99.9999 (linear speed 5.5
cm/sec *α5pm particles) In this way, the level of collection efficiency of the air filter medium can be selected appropriately depending on the purpose of use, but the pressure loss ΔPA+B is 50 wsJo or less for both HKPA class and ULPA class. It is more preferable.

Among them, the pressure loss (ΔPA-1-B) and collection efficiency (RA+B) of a laminate such as the filter medium for air filters of the present invention are determined by the pressure loss N of the filtration layer and porous membrane B alone, ΔPB,
It is known that the relationship between the collection efficiencies RA and RB is expressed by the following formula, and that it agrees well with experimental values.

△Pmu+B=ΔPmu+ΔPB RA+l1=t 1-(1-R,/100)x(1-
RB/100))xlo.

Therefore, to obtain a specific ΔP %R, M+B
Various examples can be given of the combination of the filtration layer A and the porous membrane B in M+B, and usually a combination in which the collection efficiency of each of the filtration layer A and the porous membrane B is 80 or more is adopted. Considering filter life, it is preferable that porous membrane B has a structure with lower pressure loss and lower collection efficiency than filtration NIA.
The method of type A can be adopted as the method for laminating the filtration layer A and the porous membrane B according to the present invention, but if a thermoplastic material is used for the porous membrane B, the porous membrane B is heated in spots. However, it can be easily adhered to the filtration layer A by pressure bonding.

In addition, if necessary, a network C having heat-fusible fibers described below may be used.
may be sandwiched between the filtration mA and the porous gB and heat-pressed.

In addition, in the present invention, the filtration layer A is provided on the void layer side of the porous membrane B.
The reason why these are laminated is to ensure that fine particles passing through the insertion layer A and fibers falling off from the filtration layer A are filtered in advance through the void layer of the porous membrane B, and then through the straight pore layer. This also has the effect of suppressing a decrease in the aperture ratio of the porous membrane B during processing of the fr layer.

As the network C, known heat-fusible fibers can be used. The heat-fusible fibers include components such as polyethylene, propylene-based copolymers, or polyester-based copolymers that can be melt-bonded by heat treatment or moist heat treatment at a relatively low temperature of about 150°C or less, and the heating of these components. Composite type m-ya consisting of two precepts with a high melting point component such as polyester or polypropylene, which melts and bends due to treatment, can be mentioned.

If the willow material for air filters of the present invention is >V, heat-sealable lI1. Reticular protection NjI with fibers
D may be arranged in a laminated manner, and as the net-like protective layer, the same one as the net-like body 0 can be used.

〔Example〕

The present invention will be explained below with reference to Examples. In the examples, we used 1000 to 5000 times magnified photographs taken with a scanning electronic W4 microscope to measure the film thickness, the thickness of the straight pore layer, the major and minor axes of each of the 100 surface pores, and the cut surface. L g -4 (16) was measured for the 100 S holes that appeared, and the pore diameter variation coefficient, curvature ratio, and change ratio were determined according to the above-mentioned formula.

The porosity was measured by the area method, and the porosity was measured by a mercury porosimeter.

Pressure loss is 1 for air filter media! [Punch out a disk shape with a diameter of 47 m and incorporate it into a holder, and blow air at a linear velocity of S.
, 3 cm/sec by actually measuring the transmembrane pressure difference.

The collection efficiency is determined by punching out the air filter material into a disc shape with a diameter of 25 cm, inserting it into a holder, connecting it to a particle counter, and collecting indoor air at a linear velocity of 5.3 cm/s.
EC for 2 minutes, and (L3~(15 μm particle permeation number n) was measured. On the other hand, before and after that, the average value no of the measured values measured without passing through the air filter medium was calculated (1-
→x1oo(4EQ) The value expressed as 0.3 μm particle collection efficiency.

Examples 1 and 2 As the glass fiber periphery for the filtration layer A, a commercially available one having the performance shown in Table 1 was used, and the porous membrane B was prepared as follows.
Built.

Tetrafluoroethylene/vinylidene fluoride 20/
Copolymer 4 consisting of s o (mot/mot)
0 part was dissolved in 60 parts of methyl methacrylate, and further IC
2,2'-azobis(2-methylpropionitrile) α
Add 3 parts of 0.03 parts, hold at 60°C for 15 hours, then
Methyl methacrylate was polymerized by holding at ℃ for 2 hours to obtain a polymer composition.

A polymer solution was prepared by dissolving 70 parts of this polymer composition in 950 parts of methyl ethyl ketone, and then cast onto a glass plate to a thickness of 250 μm in an area of approximately 20 α squares using a film-forming applicator. A thin film of coalescent solution was formed.

The next one is already 3kl? Open the valve of the piping containing saturated steam of icm*, set the steam flow rate to 5.0 kg/hr, place the thin film at a position 20cIP1 from the steam nozzle, and let the steam flow contact the surface for 2 minutes. The polymer was allowed to coagulate. Next, the thin film was peeled off from the glass plate and washed by immersing it in running water for 1 hour. Further, the thin film-like material was placed in a vacuum dryer at 60° C. for 1 hour to dry it.

The porous membrane B1 thus obtained had the performance shown in Table 2, and was an asymmetric membrane having a straight pore layer on one surface side.

Porous membrane B thus obtained! and the filtration layer Al or Mu3 are stacked on top of each other with the straight pore layer of the porous membrane facing outward, and are heat-sealed and bonded at points of about 1-diameter at intervals of 1 in both the vertical and horizontal directions. A filter medium for an air filter was obtained.

This filter medium exhibited the performance shown in Table 3, and no dust was observed from the filter medium during the evaluation.

Example 3 Instead of setting the water vapor flow rate to 50kg/hr, the water vapor flow rate was 35.5k/hr.
porous membrane Bh having the properties shown in Table 2, produced in the same manner as in Example 1, with g/hr and other conditions; filtration WA+ shown in Table 1; and heat fusion properties of diameter α 32 m made of polyethylene and polyethylene terephthalate. A fiber network O (the mesh space is 3gH x 5m) is connected to a network C
was used as an intermediate layer, and the porous membrane B was laminated so that the straight pore layer was on the outside, and bonded under pressure at a temperature of 100° C. to obtain a filter medium for an air filter.

The filter media shown in Table 3 showed the performance shown in Table 3, and no dust was observed.

Table 1 [Effects of the Invention] The cotton material of the present invention has excellent characteristics in that it does not generate glass fine particles and the increase in pressure loss due to clogging is slow.

In addition, a filter medium using a porous membrane made of a thermoplastic polymer can improve the adhesion state at the interface with the glass IB fiber layer, and the breaking strength of the porous membrane is above a specified value. has excellent handling and processability, and can be used as a filter medium with excellent mechanical strength.

Claims (8)

[Claims] (1) A filter material for an air filter having a filtration layer A made only of glass fibers and a porous membrane B made of an organic polymer, wherein the porous membrane B has an average pore diameter of 0.2 to 10 μm and an aperture ratio of 3.
The filtration layer A is porous, consisting of a microporous layer having pores opening substantially perpendicularly to the membrane surface of 5 to 95%, and a void layer having pores with a larger pore diameter than the pores of this microporous layer. Membrane B
A filter material for air filters that is laminated on the void layer side of the air filter. (2) The filter medium for an air filter according to claim 1, wherein the porous membrane B is made of a thermoplastic organic polymer. (3) The air filter medium according to claim 2, wherein the thermoplastic organic polymer is a (meth)acrylic ester polymer alone or a blend of a (meth)acrylic ester polymer and another polymer. (4) The filter medium for an air filter according to claim 3, wherein the other polymer is a fluorinated polyolefin or a copolymer of two or more fluorinated olefins. (5) The filter medium for an air filter according to any one of claims 1 to 4, wherein the network C having partially fusible fibers is arranged between the filtration layer A and the porous membrane B. (6) The filter medium for an air filter according to any one of claims 1 to 4, wherein the net-like protective layer D having partially fusible fibers is disposed on the outer surface side of the porous membrane B. (7) Pressure loss for air flow rate of 5.3/sec is 60
Below mmH_2O, the collection efficiency of 0.3 μm particles is 99
．． The filter material for an air filter according to any one of claims 1 to 6, which has a content of 97% or more. (8) The filter medium for an air filter according to any one of claims 1 to 6, which has a pressure loss of 80 mmH_2O or less at an air flow rate of 5.3 cm/sec and a collection efficiency of 0.3 μm particles of 99.9999% or more.