JP2002018243A - Method for manufacturing filter paper for air filter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To stably and efficiently manufacture filter paper for an air filter with a transmissivity of 0.03% or less and a pressure loss of <225 Pa by preventing the accumulation of the eluted matter from glass fibers generated by circulating and reusing used papermaking water, in a method for forming filter paper from a fiber material containing fibers by a wet papermaking process using acidic papermaking water. SOLUTION: In the method for manufacturing filter paper for the air filter, used papermaking water is subjected to ultrafiltration membrane separation treatment to be circulated and used.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a filter paper for an air filter, and more particularly to a method of wet-making a fiber material mainly composed of glass fiber to obtain a transmittance of 0.03% or less and a pressure loss of less than 225 Pa. And a method for producing a high-performance filter paper for an air filter. In addition, the object to be purified by the filter paper for an air filter of the present invention includes other gases other than air.

[0002]

2. Description of the Related Art Conventionally, filter paper for an air filter has been used to create a clean space such as a clean room, a biological clean room, a clean bench or the like in the electronic precision industry. The filter paper for an air filter is generally manufactured by dispersing fine glass fibers in water and wet-making the same.

[0003] In this wet papermaking, dilution water (hereinafter, referred to as "papermaking water") used at the time of dispersion of glass fibers and papermaking is an acidic water adjusted to a pH of about 3 with dilute sulfuric acid. Water. That is, in wet papermaking,
Such acidic papermaking water is used to promote the opening of the fiber mass and maintain a good dispersion state.
Such wet papermaking using acidic papermaking water is generally called "acid papermaking".

[0004] The used papermaking water generated in this acidic papermaking cannot be discharged to the outside as it is for environmental protection. For this reason, it is generally recycled in terms of reducing wastewater treatment costs, reducing the cost of sulfuric acid used for preparing papermaking water, and effectively reusing water resources (for example, Ken-ichi Ota, “Paper Pulp Technology Times”). 29 (9) 5
7 (1986)).

[0005] By the way, the required performance of the filter paper for an air filter is that the collection efficiency is 99.97% or more in order to highly collect fine particles in the air to create high-purity air. The high performance is a ratio (transmittance) of the fine particles permeating the filter paper for a filter of 0.03% or less.

[0006] In order to perform efficient processing, it is desired that the airflow resistance is low, that is, the pressure loss is low. In general, in a filter paper for an air filter having a transmittance of 0.03% or less, it is considered practically good if the pressure loss is 260 Pa or less. Further, from the viewpoint of energy saving, a lower one is required, and the target value is less than 225 Pa.

[0007]

However, in the prior art, the pressure loss is 225P when the transmittance is 0.03% or less.
It is difficult to stably produce filter paper for an air filter less than a, and after a lapse of time from the start of production, the pressure loss gradually increases even with the same transmittance, and 2 to 4 hours have passed since the start of production. There is a problem that the pressure loss of the filter paper for an air filter obtained at the time when the pressure exceeds 225 Pa.

The reason why the pressure loss increases is as follows.

That is, in acidic papermaking, a glass component flows out of glass fiber, which is a papermaking material, when exposed to acidic conditions, and the eluted substance (hereinafter referred to as "eluted matter") is formed as fine particles as fine particles. The fine particles of the eluate are accumulated in the papermaking water by circulating and recycling the used papermaking water. The eluate accumulated in the papermaking water adheres to the glass fibers that are made during papermaking. This eluate is spherical particles having a diameter of 5 μm or less, and when attached to filter paper, hinders the passage of air and increases pressure loss, but does not contribute to improvement in transmittance.

Therefore, when producing filter paper for an air filter under the condition of setting the transmittance to 0.03% or less, if the papermaking water is fresh, a filter paper for an air filter having a pressure loss of less than 225 Pa can be obtained. By repeatedly using the water, the eluate is accumulated, and the pressure loss of the obtained filter paper for an air filter exceeds 225 Pa even if the transmittance is 0.03% or less. In addition, the pressure loss is 22
In order to make it less than 5 Pa, the amount of glass fiber making which contributes to the transmittance corresponding to the amount of adhered eluate is reduced, and the transmittance of 0.03% or less cannot be achieved.

[0011] That is, comparing the pressure loss due to the presence or absence of the eluted matter with the same transmittance, the results are as follows: filter paper with no eluted matter attached: low pressure loss Filter paper with eluted matter attached: high pressure loss In addition, comparing the transmittance with the presence or absence of eluate at the same pressure loss, filter paper with no eluate attached: low transmittance (good) Filter paper with eluate attached: high transmittance (poor) Is the result.

If the used papermaking water is not reused, the problem caused by the eluate of glass fiber can be avoided. In this case, however, a large amount of acidic wastewater is neutralized and then discharged. As well as soaring wastewater treatment costs,
A large amount of water and acid corresponding to the amount of wastewater are required, which is industrially disadvantageous.

The present invention solves the above-mentioned conventional problems and provides a method for wet-making a fiber material containing glass fibers by using acidic paper-making water. An object of the present invention is to provide a method for manufacturing an air filter filter paper, which stably and efficiently manufactures an air filter paper having a transmittance of 0.03% or less and a pressure loss of less than 225 Pa while preventing the accumulation of eluate.

[0014]

The method for producing a filter paper for an air filter according to the present invention is a method for producing a filter paper for an air filter by wet-forming a fiber material containing glass fibers using acidic papermaking water. The method for recycling and recycling used papermaking water is characterized in that the used papermaking water is subjected to ultrafiltration membrane separation treatment and then recycled.

In order to prevent the accumulation of eluted substances from the glass fibers in the papermaking water after the used papermaking water is circulated and reused, it is sufficient to remove the eluted substances and recycle the used water. As described above, the eluate from the glass fiber that causes an increase in the pressure loss of the filter paper is spherical fine particles having a diameter of 5 μm or less, and it is not easy to remove such fine particles selectively and efficiently. .

In the present invention, a semipermeable ultrafiltration (UF) membrane separation device that allows water to permeate but does not allow fine particles to pass through is used to efficiently remove the eluate in the used papermaking water.

There is almost no impurity other than the eluate in the used papermaking water, and the water from which the eluate has been removed by the UF membrane separator has basically the same water quality as new papermaking water. By using water, it is possible to obtain a high-performance filter paper for an air filter which does not have a problem of an increase in pressure loss due to the attachment of the eluate.

Although a continuous centrifugal separator having a rotation speed of 10,000 times / min or more can remove the eluate, a UF membrane separator is advantageous in terms of simplicity of the device.

[0019]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, an embodiment of a method for producing a filter paper for an air filter according to the present invention will be described in detail.

The material mainly composed of glass fiber used for wet papermaking in the present invention may be composed of only glass fiber, and may be a mixed material of glass fiber and another material such as heat-resistant silica fiber. There may be.

When glass fibers are used in combination with ultrafine glass fibers and glass long fibers, it is possible to increase the strength by entanglement of the ultrafine glass fibers with the skeleton of the glass long fibers,
It is preferable in that a binder is not required for wet papermaking, and among these, as the ultrafine glass fiber, it is possible to obtain an ultrafine fiber having an average fiber diameter of 0.8 μm or less, particularly 0.5 to 0.7 μm. This is preferable in terms of improving the strength of the filter paper and collecting efficiency. When high heat resistance is required for the obtained filter paper for an air filter, the ultrafine glass fiber may be replaced with an ultrafine silica fiber.

On the other hand, as glass long fibers (hereinafter sometimes referred to as “chopped strands”), 600 to 1000 strands having an average fiber diameter of 8 to 12 μm are cut into an average fiber length of 5 to 15 mm. Are preferred.

Such a chopped strand is preferably used in an amount of 5 to 30% by weight based on the total of the ultrafine glass fiber and the long glass fiber. If the content of the chopped strands is less than 5% by weight, the skeletal portion is reduced, and the strength of the obtained filter paper is insufficient. If the content is more than 30% by weight, the ratio of ultrafine glass fibers bridging the skeletal portion is relatively reduced. In addition, the entanglement is reduced, so that the strength of the obtained filter paper is lowered, and the collection efficiency is also poor.

When high heat resistance is required for the obtained filter paper for an air filter, the glass composition of the chopped strand is preferably an E glass composition having excellent heat resistance, but is not limited thereto, and the heat resistance is not sufficient. Any other glass composition, for example, an S glass composition, may be used.

In the present invention, wet papermaking is carried out according to a conventional method using such ultrafine glass fibers or ultrafine silica fibers and chopped strands in a predetermined ratio.

The water p for papermaking used in this wet papermaking is
H is from 2.5 to 4.5, preferably around 3.0. By using such acidic papermaking water, the dispersibility of the fiber is enhanced, and a good papermaking with high strength and no variation in collection efficiency can be manufactured.

This papermaking water is circulated and reused after use. In the present invention, in circulating and reusing the papermaking water, the used papermaking water is subjected to membrane separation treatment with a UF membrane separator to remove eluted substances. This membrane permeate is recycled and reused.

There is no particular limitation on the type of the UF membrane separator used, and there is no particular limitation on the membrane shape (flat membrane, hollow fiber membrane, etc.). It is preferable to completely and efficiently eliminate the eluate.

The method of the present invention can be easily carried out by providing a UF membrane separator in a circulation pipe of used papermaking water.

It is needless to say that chemicals generally used for wet papermaking such as a binder and a fixing agent may be added to the papermaking water.

The basis weight (weight) of the paper thus obtained is preferably about 90 to 110 g / m ² from the viewpoints of collection efficiency and strength.

The obtained paper is made into a product by attaching a binder according to a conventional method.

The filter paper for an air filter of the present invention is generally sandwiched between a plurality of fold-folded separators, and is used as a filter medium for an air filter.

Although the present invention is applied to the production of filter paper for high-performance air filters having a transmittance of 0.03% or less, the filter paper for medium-performance air filters having a transmittance of about 1 to 95% or a filter having a transmittance of 0 to 95% is used. It can be effectively applied to ultra high performance air filter paper of 0.001% or less.

[0035]

The present invention will be described more specifically below with reference to examples and comparative examples.

The specifications of the glass fiber, chopped strand and binder used in the following Examples and Comparative Examples are as follows. [Extra fine glass fiber] Nippon Sheet Glass Co., Ltd. “306” Average fiber diameter 0.6 μm [Chopped strand] Nippon Sheet Glass Co., Ltd. “RES06GP12W” Average fiber diameter 9 μm Number of bundled fibers 600 to 1000 Average fiber length 6 mm [Binder The following acrylate copolymer and dimethylpolysiloxane were used. Acrylic ester copolymer: "Pontcoat SFC" manufactured by Dainippon Ink and Chemicals, Inc. Dimethylpolysiloxane: "Dick Silicone" manufactured by Dainippon Ink and Chemicals, Inc.

The papermaking water used was as follows. [Papermaking water] New water: normal industrial water Circulating water: HEP that recycles used papermaking water
A (pressure loss: 260 to 230 Pa, transmittance: 0.03% or less) A papermaking water (pH 3.0) in the filter paper manufacturing process was collected 4 hours after the start of papermaking (eluate concentration: about 900 ppm). The changes over time in the concentration of the eluate in the water for circulating papermaking and the pressure loss of the filter paper obtained in this wet papermaking system are as shown in FIGS. 1 (a) and 1 (b). Reclaimed water: Membrane permeated water (eluate concentration 1 to 5 p) obtained by separating the above circulating water by UF membrane separation using an ultrafilter (polysulfone flat membrane type: average pore diameter 10 nm) manufactured by DDS, Denmark.
pm).

The test method and criteria for the manufactured filter paper for an air filter are as follows. [Pressure loss (Pa)] The passage resistance when air was passed through the filter paper at a passing air velocity of 5.3 cm / sec was measured by a manometer. Judgment criterion: O was less than 225 Pa, and X was 225 Pa or more. [Transmittance (%)] Dioctyl phthalate (DOP) particles having an average particle diameter of 0.3 μm are generated and passed through a filter paper, and the number ratio of DOP particles on the upstream and downstream sides of the filter paper is measured by a laser particle counter. And the transmittance were calculated. Judgment criteria: 0.03% or less was evaluated as ○, and that exceeding 0.03% was evaluated as ×. [Strength (N)] Measured according to JIS P 8113. Judgment criteria: 9.8 N or more was evaluated as O, and less than 9.8 N as X.

Examples 1 and 2 and Comparative Examples 1 to 5 Using 90% of ultra-fine glass fibers and 10% of chopped strands as glass fiber materials, the fibers were defibrated with a Tappi standard disintegrator, and the pH of 3.0 was obtained as shown in Table 1. JIS with papermaking water
In P8209, a hand-made sheet having a basis weight of 95 g / m ² was prepared. Thereafter, the sheet was impregnated with a binder solution to allow the binder to adhere. The amount of the binder attached is 5% by weight based on the glass fiber. Thereafter, this sheet was dried at 160 ° C. for 15 minutes using a hot air drier to obtain a sample. The evaluation results of the filter paper performance are shown in Table 1.

[0040]

[Table 1]

Table 1 shows that according to the present invention, a filter paper for an air filter having a low transmittance and a low pressure loss can be obtained by using used papermaking water.

[0042]

As described above in detail, according to the method for producing a filter paper for an air filter of the present invention, in a method for wet-making a fiber material containing glass fibers using acidic paper-making water, the used paper-making water is used. Prevents the accumulation of effluent from glass fiber due to re-use by circulation, and in spite of lower pressure loss than conventional products in filter paper performance,
It is possible to stably and efficiently produce a filter paper for an air filter having an equivalent transmittance or an excellent transmittance even though the pressure loss is equal to that of a conventional product, over a long period of time.

According to the present invention, a high-performance air filter paper having a transmittance of 0.03% or less and a pressure loss of less than 225 Pa can be stably and efficiently produced over a long period of time.

[Brief description of the drawings]

FIG. 1 (a) is a graph showing the change over time in the concentration of eluted substances in circulating papermaking water of a wet papermaking system in which circulating water was collected in Examples and Comparative Examples, and FIG. 1 (b) is obtained. 4 is a graph showing a change over time in pressure loss of a filter paper.

Claims (3)

[Claims] 1. A method for producing a filter paper for an air filter by wet-fabricating a fiber material containing glass fibers using acidic papermaking water, wherein the method comprises the step of recycling used papermaking water. A method for producing a filter paper for an air filter, wherein water for papermaking is subjected to an ultrafiltration membrane separation treatment and then recycled. 2. The method for producing a filter paper for an air filter according to claim 1, wherein the water for papermaking has a pH of 2.5 to 4.5. 3. The method for producing a filter paper for an air filter according to claim 1, wherein the transmittance of the obtained filter paper for an air filter is 0.03% or less and the pressure loss is less than 225 Pa.