JP2000308805A - Filter paper for air filter and its production - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the formation of the film of a binder containing a thermosensitive solidification type resin in the surface layer part of filter paper for an air filter and to improve a dust holding capacity by bonding glass fibers by using the binder. SOLUTION: The glass fibers of the filter paper for the air filter are bonded by using the thermosensitive solidification type resin binder. An aqueous slurry is first prepared by dispersing the glass fibers into water and papermaking of the aqueous slurry is executed by a wet papermaking process, by which wet paper is obtained. Next, the thermosensitive solidification type resin binder is adhered to the wet paper and is then dried. At this time, the concentration of the thermosensitive solidification type resin binder liquid in an emulsion is preferably 0.1 to 10 wt.%. Dimethyl polysiloxane may be incorporated at 0.05 to 0.5 wt.% into the binder liquid in order to impart water repellence thereto at need. Further, the content of the thermosensitive solidification type resin in the filter paper after drying is preferably 1 to 10 wt.%.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a filter paper for an air filter, and more particularly to a filter paper for an air filter having an excellent dust retention capacity and a method for producing the same.

[0002]

2. Description of the Related Art Filter paper for an air filter is used for collecting airborne particulates in a clean space such as a clean room such as an electronic precision industry, a biological clean room, or a clean bench. Such filter paper for air filters is generally prepared by dispersing fine glass fibers in water and wet-making the paper.Then, in order to prevent re-scattering of the fibers and maintain strength during processing, and to impart other properties, a resin solution or resin emulsion is used. It is manufactured by immersing in a liquid and then drying.

As the above resin binder, an acrylic resin, a urethane resin, a polyvinyl alcohol resin or an epoxy resin is used as a main component, and wax and silicon are added as assistants. On the other hand, it is 1 to 10% by weight.

[0004] In general, a filter is composed of a pre-filter, an intermediate filter, a HEPA,
Filters are set in order to improve the filtration efficiency. Here, as for the performance required for the filter paper used for the intermediate filter, importance is attached to the retention capacity of the collected dust (DHC: Dust Holding Capacitty) in addition to the filtration efficiency.

As a means for increasing the DHC of the intermediate filter, the thickness of the fiber diameter is sequentially changed in the thickness direction of the filter, and a density gradient is provided in the thickness direction. A multilayer papermaking method is adopted in which sheets having different fiber diameters are separately made and stacked. A cationic emulsion binder is used to prevent the formation of a resin film at the fiber intersection. (JP-A-9-14
1023) has been proposed.

[0006]

In the above-mentioned prior art and the production of the filter, when the filter paper impregnated with the binder resin emulsion is dried, the temperature of the surface of the filter paper is higher than that of the inside and the water on the surface is high. Because of the rapid evaporation of the emulsion particles, the emulsion particles move to the surface following the flow of water, and as a result, are present at a high concentration on the surface of the filter paper.
As the drying proceeds further, the emulsion particles start binding,
Form a film. That is, since a film will be formed on the surface layer, dust will be collected only on the surface layer,
The dust will not be retained in the inner layer of the filter paper,
This may cause a reduction in the filter's ability to retain dust. Further, in the above prior art, a cationic emulsion binder is used in order to prevent a resin film from being formed on the paper filter paper, but the prevention of resin film formation is not sufficient, and DHC is not so high. .

It is an object of the present invention to provide a filter paper for an air filter having an excellent dust retention capacity by preventing the formation of a binder film formed on a surface layer portion.

[0008]

The above object of the present invention is achieved by the following constitution. That is, the present invention is a filter paper for an air filter, in which glass fibers are bound using a thermosetting resin binder.

In the present invention, the filter paper for an air filter is manufactured as follows. An aqueous slurry is prepared by dispersing glass fibers in water, and papermaking is performed using this aqueous slurry by a wet papermaking method to obtain a wet paper. The glass fiber used is a glass short fiber having an average diameter of 0.1 to 2 μm and / or several to several tens of glass filaments having an average diameter of 0.3 to 10 μm. cm chopped strands cut into cm lengths are used, and the composition of these fibers is:
There is no particular limitation, and for example, borosilicate glass, high silica glass, E glass, or the like is used.

In order to improve the dispersibility of the glass fibers in the slurry during wet papermaking, it is preferable to add a small amount of acid to water to adjust the pH of the slurry to about 2 to 5.

As the acid used for adjusting the pH of the slurry,
Inorganic acids such as hydrochloric acid, sulfuric acid and nitric acid are used, and in addition, organic acids such as acetic acid can also be used.

Next, a thermosetting resin binder is adhered to the obtained wet paper. The method of attaching the binder is not particularly limited. For example, a wet paper is immersed in an emulsion of a thermosetting resin, and the excess resin is removed by suction.
And the like.

Here, the thermosetting resin used as the binder is a thermoplastic or thermosetting resin in which resin particles dispersed in a dispersion medium in the form of an emulsion become gelled by heating. The heating temperature is referred to as the cloud point). Examples of the type of resin include urethane resin, acrylic resin, methacrylic resin, polyvinyl alcohol resin, and epoxy resin. Among these, a heat-coagulable polyurethane, for example, a thermo-coagulable polyether-type polyurethane is most preferably used. ;water,
(Solids concentration 40% by weight) is commercially available.

Since the thermosetting coagulable resin binder has a relatively low cloud point, the resin particles dispersed in the dispersion medium are:
When heated at a relatively low temperature, for example, about 50 ° C., it solidifies and becomes gel-like and adheres to the surface of the fiber constituting the wet paper, so that the dispersion medium (water) moves toward the surface of the wet paper. It does not move, and the formation of the resin film on the surface layer portion of the wet paper web hardly occurs. Therefore, the binder binds the glass fibers constituting the filter paper in a state of being substantially uniformly distributed in the thickness direction of the filter paper, and the dust is collected and retained even in the inner layer portion of the filter paper, and the dust of the filter is removed. Retention capacity is increased.

The concentration of the thermosetting resin binder liquid in the emulsion is desirably 0.1 to 10% by weight. If the concentration is less than 0.1% by weight, the adhering rate to wet paper is poor, and the amount of resin necessary for bonding glass fibers to each other does not adhere.
There is no difference compared to the case of 0% by weight, but the cost is high. The binder liquid may contain 0.05 to 0.5% by weight of dimethylpolysiloxane in order to impart water repellency, if necessary, in addition to the thermosetting resin.

After the wet paper is treated with the heat-sensitive coagulation type emulsion binder, the wet paper is dried by a heating drying oven or the like. Drying is performed at a temperature of 110 to 250 ° C for 3 to
Desirably, it is 20 minutes.

The content of the thermosetting resin in the dried filter paper is desirably 1 to 10% by weight. Content is 1
If the amount is less than 10% by weight, the fiber-to-fiber bonding is not sufficient, and the mechanical strength of the filter paper is low. If the amount exceeds 10% by weight, the dust holding capacity tends to decrease, and the cost increases. The basis weight (weight per unit area) of the filter paper is usually 20 to 200.
g / m ² .

[0018]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of the present invention and comparative examples will be described. Example 1 Short glass fibers having an average diameter of 1 μm, short glass fibers having an average diameter of 2 μm, and an average diameter of 6 μm and a length of 13
The glass chopped strands of 10 mm, 30 parts and 60 parts by weight were dispersed in sulfuric acid acidic water at a pH of 4, respectively, and then wet-laid with a paper machine. The obtained wet paper was immersed in an emulsion liquid having a weight composition shown in Table 1 below as a binder liquid, and was then suctioned and drained, and then dried at 140 ° C. for 10 minutes. The obtained paper has a basis weight of 64 g / m ² and a binder adhesion amount of 6% by weight.
Met. In addition, "Bondick 1510" (dispersion medium: water) manufactured by Dainippon Ink and Chemicals, Ltd. is used as a thermo-coagulation type polyether polyurethane, and "Dick Silicon" manufactured by Dainippon Ink and Chemicals, Inc. is used as dimethylpolysiloxane. Conch "was used.

[0019]

[Table 1]

[Comparative Example 1] The same fiber composition as in Example 1, except that the binder solution used in Example 1 was replaced with a composition shown in Table 2 below, and the basis weight was 64 g / m ² by the papermaking / drying method. As a result, paper having a binder adhesion amount of 6% by weight was obtained.
The cationic acrylate copolymer is a copolymer of an acrylate ester, a cation-modified acrylate ester, and a monomer. The product name is “Boncoat SFC Series” manufactured by Dainippon Ink and Chemicals, Inc. The same dimethylpolysiloxane as in Example 1 was used.

[0021]

[Table 2]

[Comparative Example 2] The same fiber composition as in Example 1, except that the binder solution used in Example 1 was replaced with a composition shown in Table 3 below, and the basis weight was 64 g / m ² by the papermaking and drying method. As a result, paper having a binder adhesion amount of 6% by weight was obtained.
The anionic acrylate copolymer is a copolymer of an acrylate ester and a monomer, and is commercially available under the trade name “Boncoat R-3” manufactured by Dainippon Ink and Chemicals, Inc.
020 "and the same dimethylpolysiloxane as in Example 1.

[0023]

[Table 3]

With respect to the filter papers obtained in the above Examples and Comparative Examples, pressure loss and collection efficiency were measured by the following methods.
Table 4 shows the results. Filter paper pressure loss (mmAq) The passage resistance when air was passed through the filter paper at a passing air velocity of 5.3 cm / sec was measured with a manometer. Filter paper collection efficiency (%) Dioctyl phthalate (DOP particles) having an average particle diameter of about 0.3 μm is generated and passed through the filter paper, and the number of DOP particles on the upstream and downstream sides of the filter paper is measured with a laser particle counter. Then, the value of 100 × (the number of DOP particles on the downstream side) / (the number of DOP particles on the upstream side) was calculated as the collection efficiency (%).

Next, using this filter paper, the outer diameter 61
A medium-performance filter of 0 × 610 × 290 mm, rated air volume of 56 m ³ / min, filter paper area of 10 m ² was assembled, and the initial pressure loss, the initial collection efficiency, and the dust holding capacity were measured. The results are shown in Table 4.

Initial pressure loss of filter (mmAq) The air pressure of the filter was 56 m ³ / min, and the pressure loss at the initial stage was measured by a manometer.

Initial collection efficiency of filter (%) Air having a rated air flow (56 m ³ / min) is passed through the filter.
DOP with an average particle diameter of 0.3 μm in the air upstream of the filter
The particles are supplied, and the number of DOP particles on the upstream side and the downstream side of the filter is measured by a laser particle counter,
In the initial stage, 100 × (the number of DOP particles on the downstream side) /
The value of (the number of DOP particles on the upstream side) was calculated as the collection efficiency (%).

Dust holding capacity (g / m ² ) Air with a rated air volume (56 m ³ / min) is passed through the filter.
Continue supplying JIS 15 class dust at a rate of 70 mg / m ³ from the upstream side, and the pressure loss value gradually increases to 30 mmH
_The unit of filter paper area (m ² )
Per unit weight (g).

[0029]

[Table 4] ================================ Example 1 Comparative Example 1 Comparative Example 2 --------------------------- filter paper properties pressure loss _{(initial) 2.8mmH 2 O 3.0mmH 2 O 3.2mmH} 2 O catching collecting efficiency (initial) 53% 52% 52% filter characteristic initial pressure loss _{12mmH 2 O 13mmH 2 O 13mmH 2} O initial trapping efficiency of 55% 53% 52% dust retention capacity ^{61g / m 2 49g / m 2} 41g / m 2 ===============================

Comparing the above example of Table 4 with the comparative example,
It can be seen that the filter produced by the filter paper of the present invention has a significantly higher dust retention capacity than the comparative example.

The filter paper for the air filter of the present invention is used for an air conditioner, a semiconductor clean room, a biological room,
Used in hospital operating rooms, cleaning processes in pharmaceutical factories, and clean spaces in research facilities.

[0032]

According to the filter paper for an air filter of the present invention,
An air filter with small pressure loss, excellent collection efficiency, and excellent dust retention capacity can be obtained.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) D21H 19/24 D21H 19/24 Z // C08J 5/04 CFF C08J 5/04 CFF (C08L 75/08 83 : 04) F term (reference) 4D019 AA01 BA04 BB05 BC20 CB06 4F072 AA02 AA07 AB09 AB15 AB31 AD43 AD47 AG02 AH03 AH31 AJ04 AK02 AL01 4J002 CK041 CP032 DL006 FA046 GD05 4L055 AF04 AG85 AG86 AG97 AH36 AH37 A3737H

Claims (5)

[Claims] 1. A filter paper for an air filter, wherein glass fibers are bound using a binder containing a thermosetting resin. 2. The filter paper for an air filter according to claim 1, wherein the binder further contains dimethylpolysiloxane in addition to the thermosetting resin. 3. The air filter according to claim 2, wherein the binder contains 0.1 to 10% by weight of thermosetting coagulated polyether type polyurethane, 0.05 to 0.5% by weight of dimethylpolysiloxane, and the balance of water. For filter paper. 4. The filter paper for an air filter according to claim 1, wherein the binder contains 1 to 10% by weight in solid content. 5. An aqueous slurry is prepared by dispersing glass fibers in water, a wet paper is formed by using the aqueous slurry by a wet papermaking method, and a binder containing a thermosetting resin is attached to the wet paper. And drying after that.