JPH0243911A - Gas filter - Google Patents

Abstract

PURPOSE:To enhance particle removal performance by forming a gas filter of a porous membrane of the polymer having the pores vertical to the membrane surface and the average hole diameter thereof, wherein the ratio of major to minor diameter, being within a specified range. CONSTITUTION:A gas filter is formed of a porous membrane of the polymer capable of being formed into a film which has pores substantially vertical to at least one side of the membrane surface. The aforesaid pore having an average hole diameter of 0.5-10mum, the ratio of major to minor diameter being 1.0-2.0 and a coefficient of hole diameter variation being 0-50% is present at an opening rate of 35-75%, the hole rate of the porous membrane being 50-90% as a whole. As the polymer capable of being formed into the aforesaid film, poly vinylidene fluoride or polytetrafluoroethylene copolymer is used in this example. The gas filter thus formed is small in pressure loss yet excellent in the particle removal performance.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to a gas filter or its pre-filter used for removing particulates mixed in gas for the purpose of air purification, dust collection, dust removal, etc. .

[Prior Art] Conventional gas filters or their pre-filters include inorganic and organic non-woven fabrics, wine membrane filters, and membrane filters.

[Problem to be solved by the invention]

However, the above-mentioned membrane filters, etc. have large pore diameters and have a mechanism that traps them internally, so their removal performance is unreliable.
Although the reliability of the removal performance was slightly improved, the asymmetric structure
The problem with any homogeneous structure is that the pressure loss is large.

[Issues (i-Means to solve)]

The gist of the present invention is that pores opened substantially perpendicularly to the membrane surface on at least one surface have an average pore diameter of (L5
~10 μm The ratio of major axis/breadth axis is 1.0 to 2.0, the total pore size variation coefficient is 0 to 50%, and the porosity is 55 to 75%, and the porosity of the entire porous membrane is 50 to 75%. The gas filter consists of a porous membrane of 90% film-formable polymer.

Porous B used in the gas filter of the present invention! X is
At least one surface has pores that are opened substantially perpendicular to the membrane surface, but pores that are opened substantially perpendicular to the membrane surface (hereinafter referred to as "straight pores") are defined as pores that are opened substantially perpendicular to the membrane surface. The hearing path ratio is 1.0 to 1.2 on any vertical cut plane.
refers to a hole with a change ratio of [16 to 1.7].

Here, the blood flow ratio is defined as the S line or straight line kt passing through the center 2 of the hole for one hole appearing on the cut surface,
Thickness kt of a porous layer consisting of straight pores (hereinafter referred to as "straight pore layer"). This refers to the ratio of t7t0 when the paper is closed.

In addition, the change ratio is defined as the width of the hole on the surface of one straight hole appearing on the cut surface, and
Width id of the hole at any position inside the straight hole layer
The ratio t of a/a is called.

If the change ratio is smaller than the above range, the fractionation accuracy will be lowered, which is undesirable, and if it is larger than the range, it will be difficult to increase the pore area ratio since the distance between adjacent holes is extremely small, which is not preferable.

If the blood flow ratio is larger than the above range, the F flow resistance will increase and the transmittance will decrease, which is not favorable.

Note that the portion where the blood flow ratio or change ratio of the pores deviates from the above range is naturally not a straight pore. For example, in an asymmetric membrane consisting of a straight pore layer and a void j-, the diameter of the pore in the void layer differs from the interface between both layers. It has a structure that increases gradually or rapidly.

It is more preferable that the change ratio is 0.7 to 1.5, and α
It is particularly preferable that the weight is 8 to 1.2. Also, the blood line ratio is 1
, 0 to 1.1, preferably 1.0 to 1.
05 is particularly preferred.

In this porous membrane, the pores present on the surface of the straight pore layer (hereinafter referred to as "cross-face pores") are circular or elliptical in shape, and rarely have a major axis/minor axis ratio of 50%. Also, the average pore diameter r1 aett moa is enclosed. Here,
The arithmetic average value of the major axis and minor axis of each surface pore is called the pore diameter of the surface pore, and the average pore diameter of the surface pore is N 1vA.
is called the arithmetic mean value of the pore diameters of the surface pores. Normal NO value is 10
0 is adopted. In addition, the pore diameter variation coefficient refers to a value expressed by the following formula regarding the pore diameter of surface pores.

(Standard deviation/average pore diameter) Therefore, it is not preferable, and the pore diameter variation coefficient is 50.
If it is larger than %, the fractionation characteristics will deteriorate, which is not preferable.

If the average pore diameter is smaller than α5 μm, sufficient transmittance cannot be obtained, so it is not preferable, and if it is larger than 10 μm, it is not practical. It is more preferable that the pore size variation coefficient is 0 to 40.

R'tl Regarding the straight pores, the ratio between the thickness Lo of the straight pore layer and the average pore diameter of the surface pores is not particularly limited, but the value of t0/D may be approximately α1 or more,
It is preferably about 15 or more, more preferably about 1.0 or more, and particularly preferably about 3 or more.

The length/breadth ratio and average pore diameter can be measured by scanning electron microscopy.

Here, the porosity refers to the ratio of the total surface pore area to the membrane external interface area, and the porosity is 35 to 75%. If the porosity is less than 35%, the fluid permeability will be low, which is undesirable, and if it exceeds 75%, the strength of the porous membrane will decrease and it will be easily damaged, which is undesirable.

Porous membranes used in the gas filter of the present invention include homogeneous membranes consisting only of the straight pore layer, and asymmetric membranes consisting of a straight pore layer on one side and a void layer having a larger pore diameter than the straight pores on the other side. Examples include those having a heterogeneous membrane structure consisting of straight pore layers on both sides and a void layer inside.

The thickness of the straight hole layer is not particularly limited, but is approximately α0
It is preferably about 1 to 50 μm, and in the case of a homogeneous membrane, the value can be from 5 μm to several μm depending on the diameter of the straight pores and the purpose of the membrane.

In asymmetric membranes and heterogeneous membranes, the thickness of the straight pore layer can similarly be α01 μm to about 1 tin, and the total film thickness can be about 5 μm to several square meters.

As mentioned above, the gas filter made of the porous membrane of the present invention can have various pore structures, but since it is easy to increase the fluid permeability and is easy to handle, the gas filter made of the porous membrane of the present invention has a straight surface. Is the hole JfI larger than the hole with a straight hole layer on the other side? It is particularly preferable to use a non-named membrane composed of a void layer having a void layer.

If it is larger than the above range, the mechanical properties of the porous membrane will deteriorate, which is not preferable.

Note that the porosity can be determined using a mercury porosimeter.

The polymer that can be formed into a film in the present invention refers to a polymer that is soluble in organic bath agents and insoluble in water, and whose solution can be spread. Polyvinylidene fluoride as the column,
Fluoropolymers such as polytetrafluoroethylene copolymers and trifluoroethylene, poly(meth)acrylics such as polysulfone, polyethersulfone, polycarbonate, polyetherimide, polyethylene terephthalate, polymethyl methacrylate, and polybutyl (meth)acrylate. Cellulose esters such as acid esters, polyacrylonitrile, cellulose acetate, cellulose nitrate,
Polyolefins such as polyethylene, poly-4-methyl-1-pe/tene, polybutadiene, polyvinyl acetate, polystyrene, poly-α-methylstyrene, poly-4-vinylpyridine, polyvinylpyrrolidone, polyvinyl chloride,
Examples include polymers such as polyvinylidene chloride, silicone polymers, polyphenylene oxide, and copolymers of these. Can be used selectively.

In addition, in the present invention, the polymer (including copolymer) can be used not only as a single system but also as a blend of 241 or more polymers that are compatible with each other.

Such a blend has the advantage that the structure of the porous membrane can be delicately controlled by utilizing the different solubility of the polymer components in a certain solvent. Examples of such blends include polymer alloys of vinylidene fluoride and tetrafluoroethylene copolymers and polyalkyl (meth)acrylates, polyvinyl chloride and polyalkyl (meth)acrylates, polystyrene and polybutadiene, and styrene-acrylonitrile copolymers. Examples include blends of coalescence and polyphenylene oxide.

Various methods can be used to manufacture the gas filter of the present invention, and a particularly preferred method and module structure of the gas filter can be various forms. Examples include those that are fixed in a holder, or those that are cut into a disk shape and incorporated into a membrane holder.

The gas filter of the present invention may be used by laminating a plurality of filters with the same or different pore diameters.
It may also be used in a laminated structure with other gas filters.

The direction of gas flow is not particularly limited, but if the pore structure is asymmetrical, according to the void j-'1 rule, it is better to move toward the dense layer side because clogging will be slower and the life will be longer. preferable.

〔Example〕

The present invention will be explained below with reference to examples. In addition to the actual rows, enlarged photographs of 1000 to 500 mm dark using a scanning microscope were used to determine the film thickness, the thickness of the straight pore layer, the major and minor axes of each of the 100 surface pores, and the information that appeared on the cut surface. Lo Lo * d * do for 100 holes
', and the pore diameter variation coefficient, curve ratio, and change ratio were determined according to the above formula.

The porosity is determined by the area method, and the porosity is determined by the mercury porosimeter.
It was measured from this. Also, the air permeability is 10p for the transmembrane pressure,
Measured by combining s and i.

Particulate removal performance is achieved by cutting a gas filter into a disk shape with a diameter of 47 mm and incorporating it into a holder, and connecting it to a particle counter to control indoor air at 5 G Owt /
Suction was carried out for 2 minutes at min, and the number n of particles passing through of 113 μm or more was measured, while +1 f! :15μm
The particle collection efficiency was defined as the above. In addition, the pressure loss was measured by actually measuring the differential pressure applied to the gas filter using a U-shaped water column differential pressure gauge.

1 voice] 1 Tetrafluoroethylene/vinylidene fluoride 20/
80 (1fIo4/mot') was ffi-dissolved in 40 parts of methyl methacrylate and held at 85° C. for 15 minutes in a nitrogen atmosphere to polymerize methyl methacrylate to obtain a polymer composition *. A polymer solution was prepared by dissolving 100 parts of this polymer composition in 1,900 parts of methyl ether ketone, and then it was spread on a glass plate to a thickness of 254 μm using an applicator for making a film. The valve of the pipe containing saturated steam of 9/σ2 was opened at 9° where the thin film was formed, and the surface of the thin film was brought into contact with the saturated steam for 20 seconds to solidify the polymer.

In addition, water vapor was supplied under the same conditions and 1cr1 was removed from the thin film material.
When we measured the temperature at the position one position before us, it was 83°C.

Also, the actual value of the water vapor flow rate at this time is 267? /min
and the spray width at the position 50 crs from the nozzle (diameter 1
The amount of water vapor supplied per unit area calculated from the area of 177 cm-'' of 5αφ) was 25~/6θC-force.

Next, after drying by blowing air at 25° C. for 1 minute, the polymer was peeled off from the glass plate to obtain a porous membrane (gas filter) with an asymmetric structure. The surface of the porous membrane and a cross section perpendicular to the membrane surface were observed using a scanning electron microscope.

On the surface that has been in contact with steam, circular or elliptical micropores with uniform pore diameters and a ratio of major axis/minor axis of 2.0 or less can be seen, and in the cross section perpendicular to the membrane surface on the surface side, pore size changes. A straight hole with almost no holes was planted. Further, a void layer was observed from the inside of the membrane to the other surface, and the pore size of the voids on the surface was 10 to 50 μm.

The curvature ratio and change ratio of the straight pores are set as 6111, and the ratio of the major axis / minor axis of the pores existing on the surface of the nutrate pore layer,
The average pore diameter, pore diameter variation coefficient, and porosity were all measured, and the porosity of the entire porous membrane was also measured.

Furthermore, [Collection efficiency and pressure drop of particles larger than L5 μm? The results are shown in Table 1.

Examples 2 and 3 The amount of water vapor supplied was 17 tq/sea −, respectively.
cm” (Example 2), and 9.84/soa・c
m'' (Example 5), and other conditions were the same as in Example 1 to produce a porous membrane f!: Its structural performance, etc. were measured and are shown in Table 1.

In either case, it is an asymmetric membrane consisting of straight pores and a void layer, and the pore size of the voids on the surface is approximately 10
It fell at ~100 μm.

/ / [Effects of the Invention] Although the gas filter of the present invention has a small pressure loss, its particle removal performance is poor.

Claims (1)

[Claims] The pores are formed substantially perpendicularly to the membrane surface on at least one surface, and have an average pore diameter of 0.5 to 10 μm, a length/breadth ratio of 1.0 to 2.0, and a pore diameter variation coefficient of 0. ~50
A gas filter comprising a porous membrane of a film-formable polymer, which has a porosity of 35 to 75% as % and a porosity of the entire porous membrane of 50 to 90%.