JPH06254317A - Production of high performance filter paper - Google Patents

Abstract

PURPOSE:To provide a production method of filter paper for high performance air filter by a wet sheet making method without raising pressure drop of the filter paper with high collecting efficiency. CONSTITUTION:In the case that water used at the time of wet type sheet production with a sheet making machine 3 is recycled and reused, fine fiber generated at the time of glass fiber production and also at the time of the sheet production is removed by filtering the water with a microfilter device 5. The possibility to choke a space of the glass fiber constituting the filter paper with the fine fiber not contributing to collection efficiency of atmospheric dust is removed by removing the fine glass fiber in the water.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a high-performance filter paper, and more particularly to a method for producing a filter paper for a high-performance air filter capable of making paper without increasing pressure loss.

[0002]

2. Description of the Related Art Conventionally, filter papers for high-performance air filters used in clean rooms and the like have been manufactured by a wet papermaking method, which is a method of papermaking mainly glass fibers with a fiber diameter of submicron unit in an aqueous system. (Japanese Patent Laid-Open No. 61-
26670, JP-A-2-251214). The glass fiber having a fiber diameter of submicron unit is a cotton-like aggregate, and in order to disintegrate and disperse this into a single fiber, a force for disintegrating from the outside is applied by a pulper or beater. For this reason, the glass fiber is damaged and the shape thereof is reduced even if the size is large or small.

Further, from the viewpoints of recent increasing demands for environmental protection, resource saving and energy saving, it is customary to circulate and reuse water used for wet papermaking of glass fibers. Usually, in a wet papermaking method using natural cellulose, for example, wood pulp, the quality of the desired papermaking is not adversely affected by water used for circulation, but wet papermaking of filter paper for high-performance air filters Therefore, since the water to be recycled and reused contains minute glass fibers, the recycling and papermaking of such water will have a significant impact on the quality of the air filter obtained. .

[0004]

SUMMARY OF THE INVENTION According to the above-mentioned prior art, when glass fibers, which are cotton-like aggregates, are disintegrated and dispersed into single fibers by a pulper or beater, the glass fibers are damaged and the fiber length becomes extremely short. In addition, minute glass fibers accumulate in the water for reuse that is circulated and reused, and this is partly mixed in the filter paper for high-performance filters that have been made into paper. Thus, the minute short glass fibers fill the voids between the fibers and increase the ventilation resistance (so-called pressure loss). Further, if the glass fiber becomes extremely short and becomes granular, the surface area becomes small and it does not contribute to the collection efficiency of atmospheric dust. Therefore, an object of the present invention is to provide a method for producing a filter paper for a high performance air filter by a wet papermaking method without increasing the pressure loss of the filter paper having a high collection efficiency.

[0005]

The above objects of the present invention can be achieved by the following constitutions. That is, it is a method for producing a high-performance filter paper in which fine fibers generated during glass fiber production and during glass fiber wet papermaking are removed by microfiltration of water for circulation and reuse during wet papermaking of glass fiber.

[0006]

[Function] By circulating the water used for wet papermaking and removing the fine glass fibers in the water during reuse, the fine fibers that do not contribute to the collection efficiency of atmospheric dust may block the glass fiber voids constituting the filter paper. Disappears.

[0007]

EXAMPLE An example of the present invention will be described. FIG. 1 shows a schematic diagram of the wet papermaking process for glass fiber and the microfiltration process of water for use in this embodiment. The glass fiber raw material and the water used in the upper tank 1 are mixed by the mixer 2 and supplied to the paper machine 3. The paper machine 3 shown in FIG. 1 is an inclined paper machine (may be a Fourdrinier paper machine), and the glass fibers after papermaking are guided to a drying step. The water discharged from the paper machine 3 is guided to the lower tank 4, where replenishing water consisting of clean water corresponding to the filtration residue in the microfiltration device 5 is replenished, and is pressurized by the pressurizing pump 6 to be supplied to the microfiltration device 5. Sent to. Micro filtration device 5
The circulating water filtered in step 1 is circulated and supplied to the upper tank 1 by the liquid feed pump 7.

In the process shown in FIG. 1, when a high-performance filter paper having a high collection efficiency is produced from glass fibers by a papermaking method, as described in the section of the prior art, the disaggregation and dilution of the raw glass fibers are carried out. It is customary to circulate and reuse the water used for the purpose from the viewpoint of environmental protection, energy saving, and resource saving, and the glass fiber with a diameter of submicron unit, which is a raw material for high-performance filter paper, is manufactured. In addition to originally containing fine fibers derived from the method, since it is a cotton-like aggregate, it is damaged and micronized during disaggregation. Table 1 shows the shape distribution of these fine fibers.

[0009]

[Table 1]

Further, FIG. 2 shows the transition of the concentration of the suspension in the water and the pressure loss of the filter paper during the papermaking process of the filter paper for a high performance air filter from glass fiber, and FIG. 3 shows the particles. The relationship between the size of the diameter and the filtration method is shown. According to the study by the present inventors, it has been found that it is necessary to adjust the amount of minute glass fibers accumulated in the water to be about 5 ppm or less, preferably 2 ppm or less.

Among the filtration methods shown in FIG. 3, a chemical treatment method such as coagulation sedimentation, which is equivalent to the conventional filtration method, is used for removing fine fibers for the purpose of reusing water for papermaking. Although it is a good method, it is not preferable because it may interfere with the production of filter papers for high-performance air filters due to the influence of residual chemicals in the treated water. Also, regarding the reverse osmosis method, although the water obtained by this has no problem at all, there is a problem in terms of treatment capacity, and if it is attempted to secure the required amount of water, the equipment cost will become enormous and economical. Can not be established. Therefore, when reusing the water used in the filter paper making for the high performance air filter of this example, microfiltration (usually filtering a filter having a size of 0.1 μm or more) and ultrafiltration can be used to improve the It was judged that the quality of the performance filter medium could be secured and it was economically advantageous.

The performance of a high-performance filter paper produced by microfiltration of papermaking water will be described with reference to Examples. The glass fiber used as the raw material yarn is CMLF306-C ₄ (manufactured by Nippon Glass Fiber Co., Ltd., nominal fiber diameter (average fiber diameter) 0.6 μm).
mφ) and CMLF208-C ₄ (Nippon Glass Fiber Co., Ltd.)
Made: Nominal fiber diameter 0.8 μmφ) and RES06X-GP0
640DE (manufactured by Nippon Glass Fiber Co., Ltd .: nominal fiber diameter 6 μm)
φ × 6 mm) and RES13X-GP0640DE (manufactured by Nippon Glass Fiber Co., Ltd .: nominal fiber diameter 6 μm φ × 13 mm), using Boncoat SFC-55 (manufactured by Dainippon Ink and Chemicals, Inc .: acrylic adhesive) as a binder. I was there.
The reason why four kinds of glass fibers are used in combination is to exert the function as a high performance filter paper. Then, water adjusted to pH 3 was used as water for wet papermaking. Filtration at the time of reuse of water after the glass fiber papermaking was performed by a microfiltration method. A polysulfone flat membrane type (manufactured by itself) having an average pore diameter of 0.9 μm was used as the microfiltration material. Further, the filtration treatment performance was based on the DOP efficiency value and the pressure loss value as indexes. Here, as the DOP efficiency value, a measured value (percentage) of the collection efficiency of 0.3 μm particles of DOP at a surface wind velocity of 5.3 cm / sec was used. Further, the pressure loss value is a value (water column value) obtained by measuring the pressure loss when the air is blown at a surface wind velocity of 5.3 cm / sec with a fine differential pressure gauge.

Further, as a comparative example, a filter paper was made from the same raw material as in this example, and the water used was untreated,
Experiments were carried out for reuse (Comparative Example 1) and sand filtration of water after use (Comparative Example 2). The sand filtration method was an upward flow type, and an area load of 5 m / H, a sand filtration layer thickness of 1 m, an effective sand diameter of 0.45 mm, and a self-made sand filtration layer with a uniform coefficient of 1.3 were used. Area load: Numerical value obtained by converting the amount of water passing through the filter bed per cross-sectional area of the filter bed. Sand effective diameter: The size of the sand grain that 10% passes when the sand is sieved, expressed in mm. The value obtained by dividing the size of the sand grains when 60% of the material passed through the sieve is divided by the above-mentioned effective diameter. Uniformity coefficient = (diameter for 60% passage) / (diameter for 10% passage) As is clear from the above equation. It can be said that the closer the uniformity coefficient is to 1.0, the more uniform the sand particle diameters are. Table 2 shows the results of the experiments of Examples and Comparative Examples 1 and 2.

[0014]

[Table 2]

As shown in Table 2, this embodiment can be used for a high-performance air filter having a high collection efficiency without increasing the pressure loss as compared with the comparative example even if the water is circulated and reused. A simple filter paper can be manufactured. In this way, the reason why the filtration with high collection efficiency can be produced in the case of this example is that the minute glass fibers in the water for circulation and reuse are removed, and therefore the collection efficiency of such atmospheric dust is It is considered that this is because the microfibers that do not contribute have no possibility of blocking the glass fiber voids constituting the filter paper, and do not increase the pressure loss of the filter paper.

The microfibers that block the glass fiber voids that compose the filter paper accumulate in the water for reuse by circulating and reuse the wet papermaking water, and after the equilibrium state is reached, they are mixed in the papermaking filter paper. Therefore, even if the water is not circulated and reused, the same effect as that obtained when the water is subjected to the microfiltration treatment can be obtained. However, in this case, the amount of water used becomes huge, which is economically disadvantageous. If the water is not reused, it cannot be simply discarded, which requires post-treatment, which increases the economic burden. Therefore,
The method for producing filter paper by wet papermaking that does not circulate and reuse water is applicable only to regions where papermaking water is available at a very low cost and environmental regulations are very loose.

[0017]

According to the present invention, it is possible to manufacture a filter paper having a high collection efficiency without increasing the pressure loss.

[Brief description of drawings]

FIG. 1 is a schematic view of a glass fiber wet papermaking process and a water microfiltration process according to an embodiment of the present invention.

FIG. 2 is a graph showing changes over time in pressure loss of filter paper and concentration of suspended substances in water when the water is circulated and reused in the wet papermaking of glass fiber without treatment.

FIG. 3 is a diagram showing a relationship between a particle size of a filtration target and an effective filtration method.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Upper tank, 2 ... Mixer, 3 ... Paper machine, 4 ... Lower tank, 5 ... Micro filtration device, 6 ... Pressurizing pump, 7 ... Liquid sending pump

Claims (1)

[Claims] 1. Production of a high-performance filter paper characterized by removing fine fibers generated during glass fiber production and during glass fiber wet papermaking by microfiltering water for circulation and reuse for wet papermaking of glass fiber Method.