JPH0755283B2 - Air filter paper - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an air filter paper, and more particularly to an air filter paper used for controlling fine particles in the air in a clean space such as a so-called clean room, biological clean room or clean bench.

[0002]

2. Description of the Related Art In order to efficiently collect submicron particles, a conventional filter paper of this type is generally manufactured by adding a suitable binder to fine micro glass fibers, wet-making the paper, and then drying the paper. The particle collection efficiency (for particles of 0.1 to 3 μm) and pressure loss of these filter papers are about 99.98% and 34 to 34% at a wind speed of 5.3 cm / sec, respectively.
It was about 40 mm W.G.

In recent years, it has been required to further increase the collection efficiency, and therefore, microglass fibers having a smaller fiber diameter are used as the constituent fibers of the filter paper or the thickness of the filter paper is increased. Was attempted, but neither was practical because the pressure loss increased. Therefore, as a filter paper having both mechanical particle collecting effect and particle collecting effect by electrostatic force, wool fiber coated with colophony on the surface of wool fiber and mechanically charged by friction force, wool fiber, cellulose fiber -It has been devised to charge the phenolic resin by mixing short fibers such as polyolefin fibers with crushed liquid of the phenolic resin and molding. However, since these are mechanically charged, the structure is complicated and the manufacture is not easy.
There was also a problem in the persistence and stability of the collection effect due to charging.

Further, as a constituent fiber of the filter paper, an electret fiber, for example, a synthetic resin film is made into an electret by a high voltage electric discharge machining, and a fiber obtained by chopping this into an extremely fine width or a synthetic fiber is subjected to a high voltage electric discharge machining. There is also a filter paper using an electretized one. However, even these filter papers have a drawback that the initial collection efficiency rapidly decreases with the passage of time.

[0005]

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and its object is to:
An object of the present invention is to provide an air filter paper of the type described at the beginning, which has a particle collection efficiency improved significantly while maintaining a pressure loss comparable to that of a conventional air filter paper of this type. Another object of the present invention is to provide an air filter paper of the same kind in which the initial particle collection efficiency lasts for a long period of time.

Another object of the invention is to provide an air filter paper of the same kind which is simple in construction and easy to manufacture.

[0007]

The present invention is used for controlling airborne fine particles in a clean space , and all or a major part of the constituent fibers constituting the filter paper is glass fiber. In addition, in the air filter paper obtained by the wet papermaking method, the fluorine-containing resin is attached to the surface of the constituent fibers, and the amount of the fluorine-containing resin adhered is 0.1 to 10% by weight based on the constituent fibers. , Attached
The fluorine-containing resin makes the surface of the constituent fibers electrically polar.
Cause airborne charged particles in the air to
It is an air filter paper characterized in that it is also collected .

As the constituent fibers of the filter paper, any fibers conventionally used can be used, but in the present invention, microglass fibers are mainly used, and those having an average fiber diameter of about 0.1 to 10 μm are suitable. Is. Further, in order to improve the strength, chemical resistance, etc. of the filter paper, fine denier aromatic polyamide fibers, carbon fibers and the like can be mixed and used in an appropriate amount (about 1 to 10% by weight).

In the present invention, the fluorine-containing resin means polytetrafluoroethylene (PTFE, tetrafluoroethylene resin), tetrafluoroethylene-hexafluoropropylene copolymer (FEP), polychlorotrifluoroethylene (PCTFE), perfluoroethylene. A resin containing a fluorine atom such as a fluoroalkyl group-containing resin. Since PTFE has excellent heat resistance, chemical resistance, solvent resistance, etc., it is used as a gasket, packing, and coating material. FEP and PCTFE have the same chemical stability as PTFE and are easy to process. Therefore, FEP and PCTFE are used for the same purpose as PTFE, although other properties are somewhat inferior. Perfluoroalkyl group-containing resin is a base resin (acrylic resin, urethane resin, etc.) containing a large number of fluoroalkyl groups, and coating this on a solid surface significantly reduces the surface energy. It is used as a water repellent and an oil repellent.

The above-mentioned fluorine-containing resin includes a solution type obtained by dissolving the resin in a solvent, an emulsion type obtained by emulsion polymerization, and a solid type such as powder and granules. It can be used in the invention. As the fluorine-containing resin used in the present invention, a resin having a high fluorine content is preferable, and a resin having a high electronegativity of fluorine is preferably used.

If the amount of the fluorine-containing resin attached is less than 0.1% by weight with respect to the constituent fibers, the effect will be small, so
It is preferably at least wt%. Although there is no particular upper limit of the amount of adhesion, if the amount is too large, the effect is not so great and the cost is rather increased, so about 0.1 to 10% by weight is appropriate. Incidentally, a binder is usually added to increase the strength of the filter paper, but it is not always necessary to add the binder in the present invention. However, if added, low-melting point organic fibers such as polyvinyl alcohol (PVA) fibers, polyamide fibers, and polyester fibers, or acrylic resins are preferable. The amount of the binder added is generally about 1 to 10% by weight based on the constituent fibers of the filter paper, and is determined according to the predetermined pressure loss and strength.

The reason why the particle collection efficiency is increased by the adhesion of the fluorine-containing resin is that the fluorine atom has a large electronegativity, that is, the ability to attract an electron when the atom chemically bonds. Polarity is generated,
It is presumed that this is because the floating charged particles in the air are electrically collected. By the way, the electronegativity of fluorine is
4.0 is the highest of all elements, followed by oxygen and chlorine 3.
5, nitrogen is 3.0.

The method for producing the above-mentioned filter paper is a method in which a slurry in which the constituent fibers of the filter paper are dispersed in water is wet-processed, the wet paper is treated with a fluorine-containing resin and then dried. The step of wet-making the slurry obtained by dispersing the constituent fibers of the filter paper in water is the same as the conventional method. As the constituent fibers, it is possible to use a mixture of the above-mentioned fibers having different types and fiber diameters according to the required collection efficiency and strength.

Further, in the step of treating the wet paper web with the fluorine-containing resin, the treatment with the fluorine-containing resin means that the wet paper is placed in a fluorine-containing resin solution or emulsion so as to adhere the fluorine-containing resin to the surfaces of the constituent fibers. It means dipping in, or spraying or applying them onto the surface of the wet paper. The concentration of this fluorine-containing resin solution or emulsion should be 0.1-
It is preferably 2% by weight, particularly about 0.1 to 1% by weight. If it is less than 0.1% by weight, the fluorine-containing resin is hard to adhere to the wet paper, while if it exceeds 2% by weight, the effect is not improved and the cost is increased.

The above treatment may be carried out at a normal temperature for producing the filter paper, and heating or cooling is not particularly required. The step of drying the wet paper web may be the same as a conventional method. At this stage, the wet paper is dried and the fluorine-containing resin is fixed. When a binder is added, its crosslinking reaction is related to temperature, so the strength of the filter paper changes depending on the drying temperature. In this case, it is preferable to set the drying temperature to about 120 to 130 ° C. in consideration of the balance between strength and energy cost.

By the way, in order to improve the dispersibility of the fibers when the constituent fibers of the filter paper are dispersed in water, a small amount of acid can be added to the water to make it acidic. As the acid to be added, inorganic acids such as hydrochloric acid, sulfuric acid and nitric acid, and organic acids such as formic acid and acetic acid can be used. The pH value of the acid-added solution is preferably about 2-5. The lower the pH value, the better the dispersibility of the fiber, but if the pH value is less than 2, the fiber strength will be adversely affected and the machine will also be corroded. On the other hand, if the pH value exceeds 5, the effect is small and the meaning of adding an acid becomes dilute.

The effect of improving the performance of the filter paper due to the adhesion of the fluorine-containing resin is not affected by the addition of this acid.

[0018]

[Effect of the Invention] Air filter paper of the present invention, while maintaining the conventional pressure drop comparable to this type air filter paper, the constituent fibers
Due to the electrical polarity created on the surface, it floats in the air.
Since it is possible to electrically collect the loosely charged particles, it is possible to significantly improve the particle collection efficiency, and it is possible to maintain the particle collection efficiency for a long time. This improvement in particle collection efficiency is very significant as an air filter paper for clean space. Further, since the air filter paper of the present invention has a structure in which the above-mentioned fluorine-containing resin is attached to the surface of the constituent fibers of the filter paper mainly composed of glass fiber, the structure is simple and the manufacture is easy.

Therefore, it is used as an air supply filter for a clean room or clean bench of the semiconductor industry, precision industry, etc., a biological clean room of a hospital operating room, a pharmaceutical factory, etc., or an exhaust gas purification filter for a nuclear facility, a biological hazard facility, etc. Is useful as Further, the air filter paper of the present invention forms wet paper using a slurry obtained by dispersing the constituent fibers of the filter paper mainly composed of glass fiber in water, and drying the wet paper to fix the fluorine-containing resin. Since it can be formed by means of the above, no special dispersion liquid, equipment, etc. are required for manufacturing, and therefore the air filter paper can be manufactured very easily and the manufacturing cost can be kept low, which is suitable for mass production. Is.

Therefore, the air filter paper of the present invention has industrially excellent effects.

[0021]

The present invention will be described in more detail with reference to the following examples. However, the present invention is not limited to these examples. Example 1 As the constituent fibers of the filter paper, three kinds of fiber diameters (0.35 μm, 0.4
Microglass fiber mixed fibers (5 μm, 3.2 μm) and 2% by weight of the aromatic polyamide fibers were put in water, and the fibers were dispersed in water by stirring.
At this time, in order to improve the dispersibility of the fibers, sulfuric acid was added to this slurry to make it acidic (pH = 4).

Next, the above slurry was wet-processed using a TAPPI standard square sheet machine. On the other hand, an acrylic acid ester copolymer aqueous emulsion was used as a binder, and a tetrafluoroethylene resin aqueous emulsion was used as a fluorine-containing resin to mix the two, and the concentration of the binder and the fluorine-containing resin in water was 2% by weight and respectively.
A treatment liquid was prepared by diluting and adjusting the concentration to 0.3% by weight. Then, the wet paper web was immersed in the treatment liquid at room temperature for about 10 seconds, then pulled up and dried at 130 ° C.

The collection efficiency of this filter paper was 99.9961% (four nines), and the pressure loss was 36.2 mm WG (Water Gauge). The change in collection efficiency is as shown in the figure, and the pressure loss is from the initial value (36.2 mm WG) to the final value (109.5 mm WG).
It is clear that the collection efficiency has not deteriorated even though the collection efficiency has increased to about 3 times. Comparative Example In Example 1, the wet paper after wet papermaking was directly dried under the same conditions without being immersed in the treatment liquid containing the tetrafluoroethylene resin aqueous emulsion.

The collection efficiency of this filter paper was 99.971% (three-nine), and the pressure loss was 36.0 mm WG. Example 3 Wet papermaking was carried out in the same manner as in Example 1 using the same microglass fiber mixed fibers and aromatic polyamide fibers as the constituent fibers of the filter paper as in Example 1 (however, pH of slurry = 3).
.

On the other hand, the acrylic ester copolymer aqueous emulsion was diluted to adjust its concentration to 2% by weight. Separately, the solution type tetrafluoroethylene resin was adjusted to a concentration of 1.5% by weight. Then, at room temperature, the wet paper is first dipped in a diluting solution of an acrylic acid ester copolymer aqueous emulsion, and then dipped in a tetrafluoroethylene resin solution.
It was dried at 0 ° C. The immersion time was set to about 10 seconds in both cases.
In this case, the collection efficiency was 99.9965% (four nines), the pressure loss was 35.4 mmW.G., and there was no decrease in the collection efficiency. Examples 4 and 6 Using tetrafluoroethylene-hexafluoropropylene copolymer (FEP) as the fluorine-containing resin, Example 1
Filter paper was produced in the same manner as in Steps 3 and 3. Examples 7 and 9 Polychlorotrifluoroethylene (PCTFE) was used as the fluorine-containing resin, and filter papers were produced in the same manner as in Examples 1 and 3. Examples 10 and 12 Using a perfluoroalkyl group-containing resin (used as a water repellent) as the fluorine-containing resin, Example 1
Filter paper was produced in the same manner as in Steps 3 and 3. Example 13 Microglass fiber mixed fibers having the same three kinds of fiber diameters as in Example 1 were put into water, and sulfuric acid was further added to the mixture to make it acidic (pH = 3) and stirred. Next, this slurry was wet-processed.

On the other hand, the acrylic acid ester copolymer aqueous emulsion was diluted to adjust the concentration to 2% by weight. Separately, powdered perfluoroalkyl group-containing resin
It was dissolved in 1,1-trichloroethane and adjusted to a concentration of 1.5% by weight. Then, at room temperature, the wet paper web was first dipped in a dilute solution of an acrylic acid ester copolymer aqueous emulsion, then dipped in a perfluoroalkyl group-containing resin solution, and then dried at 130 ° C. The immersion time was set to about 10 seconds in both cases.

Embodiments 4, 6, 7, 9, 10, 12, 13 described above
Table 1 shows the measurement results of the pressure loss and the collection efficiency in.
It should be noted that no deterioration in collection efficiency was observed in Examples 4, 6, 7, 9, 10, 12, and 13. The air filter paper according to this example has a particle collection efficiency of the conventional three-nine (about 99.98) while maintaining a pressure loss comparable to that of the conventional air filter paper of this type.
%) To four nines (about 99.996%).

In the above Examples 1 to 13 and Comparative Example, the pressure loss, the collection efficiency, and the change in the collection efficiency were determined by the following method. Pressure loss (mm WG): The ventilation resistance when air was passed through the filter paper at a wind speed of 5.3 cm / sec was measured with a water column manometer. Collection efficiency (%): Dioctyl phthalate (DOP) particles with an average particle size of about 0.2 μm are generated and passed through a filter paper, and the particle size distribution of DOP smoke on the upstream side and the downstream side of the filter paper is measured by PMS laser aerosol. Measurement was performed with a spectrometer, and the collection efficiency was calculated for particles of 0.1 to 3 μm.

Change in collection efficiency: Average particle size of about 0.2μ
A DOP smoke of about m is loaded through the filter paper at a speed of 5.3 cm / sec, the number of outflow particles is measured every hour, and the DO
The change in the number of outflow particles with respect to the P loading time was obtained.

[0030]

[Table 1]

[Brief description of drawings]

FIG. 1 is a graph showing changes in collection efficiency in Example 1 of the present invention.

Continuation of the front page (51) Int.Cl. ⁶ Identification number Office reference number FI Technical display location D01F 9/08 A D21H 13/40 17/34 27/08 F24F 7/06 C

Claims (1)

[Claims] 1. An air filter paper which is used for controlling fine particles in the air in a clean space and which constitutes all or a major part of the constituent fibers of the filter paper and which is obtained by a wet papermaking method. with fluorine-containing resin is deposited on the surface of the fibers is 0.1 to 10 wt% adhesion amount of the fluorine-containing resin to the constituent fibers, the fluorine-containing resin by adhering, constituting fiber
It creates an electrical polarity on the surface of the fiber, which
An air filter paper characterized in that it also electrically collects airborne charged particles .