JPH03143514A - Filter medium - Google Patents

Abstract

PURPOSE:To obtain the filter medium capable of removing fine particles in fluid with high efficiency by forming the medium with a polyvinyl acetal resin porous body having a three-dimensional reticular structure of <=40mum average pore diameter and >=60% porosity and having >=70mol% degree of acetalization. CONSTITUTION:An aq. soln. of completely or partially saponified PVA is prepared, and starch grains extracted from rice, wheat, etc., and the aldehydes (ordinarily formaldehyde) as a cross-linking agent are added to the soln., slowly agitated and uniformly mixed. An acid catalyst such as sulfuric acid is added to the obtained liq. mixture and sufficiently agitated, and the mixture is injected into a mold and heated to cause a cross-linking reaction. The reaction product is discharged from the mold and dipped in a concd. liq. mixture of the cross linking agent and acid catalyst for a long time to promote the cross-linking reaction. The obtained reaction product is sufficiently washed with water to remove the unreacted cross-linking agent, acid catalyst and remaining starch to obtain a filter medium having uniform fine open cells and a three-dimensional reticular structure. The fine dust in air and the impurity fine particles in liq. are efficiently removed by this filter medium.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a filter medium suitable for precision filtration that can efficiently remove particulates contained in gas and liquid.

(Prior art) In recent years, the requirements for clean rooms have become increasingly sophisticated. For example, the so-called HEPA class is 0.3μ
This is a strict method that captures 99.97% or more of the microparticles of m. Traditionally, paper filters have been used to remove fine dust from the air. This filter is made of ultrafine glass am or synthetic Iam nonwoven fabric, and among them, glass fiber nonwoven fabric has been mainly used because it is relatively rigid and can improve trapping performance but does not easily increase ventilation resistance. However, these nonwoven fabrics suffer from the shedding of microparticles and microfibers generated during manufacturing.
・There is a drawback that the water flows out to the permeation side.

On the other hand, membrane filters and sintered metal bodies are known as filters for separating fine particles from liquids. However, all of these have drawbacks such as low porosity, which causes a large pressure loss when fluid passes through, and membrane filters that have a large area are difficult to manufacture, and sintered metal bodies have a wide pore size distribution. .

Therefore, it is possible to use a synthetic resin porous body as a filter medium, but it is extremely difficult to manufacture one with high porosity and small pore size, and specifically, one with an average pore size of 60 μm or less is still unsatisfactory. The current situation is that this has not been obtained.

(Problems to be Solved by the Invention) An object of the present invention is to provide a filter medium that can remove fine dust in the air and contaminant particles in a liquid with high precision and efficiency, and also has good workability.

(Means for Solving the Problems) This is achieved by a filter medium made of a porous polyvinyl acetal resin having a mole of 70 or more.

The polyvinyl acetal (hereinafter abbreviated as "rVAtJ") based resin of the present invention is a polyvinyl alcohol (hereinafter "PVAtJ") based resin.
AJ) is subjected to a crosslinking reaction with an aldehyde in the presence of a catalyst, and the degree of acetalization, which indicates the degree of crosslinking, is 70 mol% or more, preferably 80 mol% or more. If the degree of acetalization is lower than TO mortarization, the material will have poor water resistance and will have soft physical properties in a wet state, and will lack shape retention and three-dimensional stability as a filter medium, making it impractical.

The filter medium of the present invention has an average pore diameter of 40 μm or less, preferably 50 μm or less, more preferably 20 μm or less,
It has a three-dimensional network structure with a porosity of 60% or more, preferably 70% or more, and more preferably 80% or more. If the pore size is larger than 40 μm, the capture rate of fine particles will be low, and if the porosity is too small, the pressure loss due to filtration will be large.

Since the pores of the filter medium of the present invention have a three-dimensional network structure,
Although the pore diameter is extremely small, the porosity is high and the ventilation resistance is low. In addition, gas or liquid containing contaminant particles passing through the filter medium passes through a labyrinth of complex pores, during which time the contaminant particles are subject to inertial effects and diffusion effects.

This will be captured by interactions such as the blocking effect, the tactile effect, and the electrostatic effect. Therefore, it is possible to capture fine particles having a particle size that is smaller than or equal to the average pore diameter, and it is possible to achieve filtration accuracy comparable to that of a membrane filter or a sintered metal body with low pressure loss.

Further, the filter medium of the present invention is a material with excellent workability, and can be cut or sliced by ordinary means such as scissors or a knife, and its shape and thickness can be relatively easily formed.

The filter medium of the present invention can be manufactured, for example, as follows. That is, completely or partially saponified PV gum is made into an aqueous solution, starch granules and aldehydes as a crosslinking agent are added thereto, and the mixture is heated at a temperature of 50°C or less, preferably 25 to 40°C for 1 hour or more, preferably 2 Mix evenly with slow stirring for ~5 hours.

As the starch granules, for example, starch granules extracted and purified from rice, wheat, etc. are suitable. Formaldehyde is usually used as the aldehyde.

Next, an acid catalyst such as sulfuric acid or the like is added to the resulting mixed solution, and the mixture is thoroughly stirred, then poured into a mold, and heated to carry out a crosslinking reaction. The reaction product obtained here has a degree of acetalization of 50NTo molar, is soft and weak in a wet state, and lacks dimensional stability. Subsequently, this reaction product was taken out from the mold, and the concentrations of the crosslinking agent and the acid catalyst were 15 to 25 times each! ! It is immersed in a high-concentration mixed solution of about kCs, and the crosslinking reaction is further carried out for a long time at a temperature of 40 to 700°C. Subsequently, the obtained reaction product was thoroughly washed with water,
Unreacted crosslinking agent, acid catalyst, remaining starch, etc. are removed, and the filter medium of the present invention having uniform, fine, continuous pores can be obtained. The obtained filter medium is a PvAt-based resin porous material with an acetalization degree of 70 molar or more, and an average pore diameter of 5 to 5.
It has pores with a three-dimensional network structure of 40 μm and a porosity of 60 to 85 volumes.

(Effects of the Invention) The filter medium of the present invention has uniform and fine continuous pores, has a high porosity, has a small pressure loss during filtration, has excellent dimensional stability, and has good chemical resistance.

Furthermore, the filter medium of the present invention does not have the phenomenon of shedding of microparticles or microfibers that occurs in filter media made of glass fiber nonwoven fabric, and can easily be obtained with a wide area, and can be cut or sliced into desired shapes and thicknesses. It can also be bent easily, so it is suitable for gases.

It is extremely suitable for various high-precision filtration of liquids.

The filter medium of the present invention is suitable as a HEPA class filter medium that captures 119.97% or more of 0.311 m fine particles, which have been extremely difficult to manufacture in the past.

Hereinafter, the present invention will be described in detail with reference to Examples, but before that, methods for measuring various characteristic values in this specification will be described.

Atmospheric dust collection rate〉 Atmospheric dust floating in the ambient air was collected using a filter medium, and was determined from the amount of atmospheric dust before and after filtration. Measurement is 200mm x 200m
A filter medium of size m was attached to the filtration test device, and the flow rate was 50
Ambient air was flowed for 2 minutes at 0 cc/min, and the number of atmospheric dust before and after filtration was measured using a particle counter KO-Of (manufactured by Rion ■), which was set to measure atmospheric dust of 0.3 μm or more.

The atmospheric dust collection rate was determined using the following formula.

<Liquid filtration test> The test filter medium was inserted into a 47 mm glass filter holder, fixed with a clip, attached to a suction bottle, and vacuum suctioned with an aspirator to obtain the following particulate dispersion stock solution.
The mixture was filtered for 1 minute at a suction speed of 1 minute to obtain a filtrate. The resulting filtrate and stock solution were each 70 mJi! The number of fine particles contained in the liquid is measured using a liquid automatic particle counter MODEL 470G (
HIAO/ROYCO) was used to count five types of particle sizes, and the capture rate (%) in each particle size range was determined from the following formula.

(Here, A is the number of particles in 70 mj of stock solution, B is 70 mj of filtrate.
A! (number of particles in) Fine particle dispersion stock solution: 0.1 g of JIS-81 test powder (Kanto loam powder, average particle size 8 μm) specified in JIS Z-8901 was dispersed in 21 water.

(Example 1) Partially saponified PVA with a degree of polymerization IT00 was dissolved in hot water,
A 1440 mg PVA aqueous solution with a concentration of 20''!/1% by weight was prepared and the temperature was adjusted to 45°C.Next, rice starch asoy was added to 540 mJ of water and stirred to form a dispersion, which was prepared first. In addition to the PVA aqueous solution prepared, 380 ml of a 37% formaldehyde aqueous solution was added, and the mixture was aged for 3 hours while slowly stirring while maintaining the liquid temperature at 32°C.

After aging, 290 ml of 50% sulfuric acid was added, water was further added to adjust the liquid volume to 31%, and the mixture was stirred and mixed uniformly. The resulting mixture was poured into a mold made of vinyl chloride and heated at approximately 60°C for 40 minutes.
A crosslinking reaction was carried out for a period of time. The obtained reaction product was removed from the mold, immersed in a mixed solution of 15% formaldehyde and 26% sulfuric acid, and reacted at 46°C for 3 days, and then thoroughly washed with water to remove unreacted formaldehyde, sulfuric acid, After removing starch and the like, it was dried to obtain a PVAt-based resin porous body. Next, this was cut to a thickness of 1.3 mm to obtain a sheet-like filter medium.

The obtained filter medium had an acetalization degree of 82 mol%.

It was a PYAt resin porous body having a porosity of 85, a mean pore diameter of 70 μm, and continuous pores in a three-dimensional network structure with a small pore size distribution, and had good dimensional stability.

The characteristic values of this filter medium as a gas filter medium were as shown in Table 1. Commercially available (7) HEPA gas 5 liters as a comparative example
The results for a fiber filter paper AF-992 (Toyo Roshi fR) are shown. Further, the characteristic values as a liquid filter medium were as shown in Table 2.

Table (Example 2) A PvAt-based MB porous body was prepared in the same manner as in Example 1 except that wheat starch was used instead of the rice starch used in Example 1, and cut into 2.0 mm thick pieces. An inventive filter medium was obtained.

The average pore diameter of the obtained filter medium was 30 μm, and the characteristic values as a liquid filter medium were as shown in Table 2.

Claims (1)

[Claims] A filter material made of a porous polyvinyl acetal resin having a three-dimensional network structure with an average pore diameter of 40 μm or less, a porosity of 60% or more, and a degree of acetalization of 70 mol% or more.