JPH0811167B2 - Method for treating waste liquid in which inorganic particles are dispersed - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a treatment method for removing inorganic particles contained in a liquid, particularly waste water.

[Conventional technology]

In recent years, with the progress of electronics, in manufacturing a small semiconductor device such as an LSI, a large number of thin disk-shaped substrates are manufactured by sequentially cutting a round bar-shaped semiconductor material in a thin thickness. By the way, in this case, the cutting is performed while water is applied to the cutting portion, and a large amount of chips of the semiconductor material having a diameter of about 0.3 to 1 μm generated by the cutting enter the water. It is necessary to collect chips and pure water from this wastewater, and especially when the material of the semiconductor substrate is gallium arsenide, it cannot be discharged directly because it contains harmful substances. To be done.

This wastewater filtering device is disclosed in JP-A-60-82113 and JP-A-62-1213.
As disclosed in 0-175511, as compared with the conventional cartridge system, as a system capable of continuously performing liquid filtration for a long time without troublesome replacement work, a filter medium having a hollow portion at the center is provided. A method has been devised in which a filter is wound in a roll shape, and when it is clogged, a surface filter medium is separately wound and filtration is always performed with a new filter medium. In such a high-performance liquid filtration, a filter medium having 1) high removal efficiency, 2) low initial pressure loss, and 3) high tensile strength must be used.

Until now, no filter medium has all of the features 1), 2) and 3).

[Problems to be solved by the invention]

The liquid filter media that have been developed so far are sintered metal particles, cellulose, synthetic resin, paper made from fibers such as asbestos, and so-called pore type in which a synthetic resin film is perforated. The filtration principle of these filter media is to create pores smaller than the particle size of the particles to be removed,
This prevents the particles from passing and removes them. However, there is a limit to reducing the diameter of the sintered metal due to the limitation based on the size of the metal particles, and for the pore type, there is a limit to reducing the diameter of the pores, so that the required performance is satisfied. It was not possible to make a filter medium with both high removal efficiency and low initial pressure drop.

On the other hand, in the case of fiber-making paper, it is necessary to shorten the fiber length (generally 1 cm or less) in order to make paper, and therefore the tensile strength of the sheet was low. When a binder was applied to the sheet in order to increase the tensile strength, both the removal efficiency and the initial pressure drop performance were significantly reduced, and none of them satisfied all the above three requirements.

SUMMARY OF THE INVENTION The object of the present invention is therefore to provide a method for industrially advantageously removing inorganic particles from an effluent using a high-performance and high-strength liquid filter medium. In particular, the filter medium used in the present invention is excellent in removal efficiency and initial pressure loss, and also has high tensile strength, so that continuous filtration by a roll system is possible instead of the conventional cartridge system, It greatly contributes to improvement of performance and prevention of pollution by highly purifying cleaning water of the semiconductor element.

[Means for solving problems]

The method for treating the waste liquid in which the inorganic particles are dispersed according to the present invention is a waste liquid in which the inorganic particles having a particle diameter of 5.0 μm or less are dispersed, in which ultrafine fibers having an average single yarn fiber diameter of 0.3 to 3.0 μm are randomly entangled, The bulk density exceeds 0.35 / cm ³ , the tensile strength in the longitudinal direction is at least 200 g / cm width, and the filtration cylinder traverse is formed by winding the nonwoven fabric by the melt blow method with a basis weight of 20 to 100 g / m ² in multiple layers around the perforated pipe. Liquid is passed from the outer peripheral surface to the inside in the direction along the surface, the outer peripheral surface is peeled off after a period of time to expose a new non-woven fabric filter surface to the surface, and the inorganic particles are substantially removed. This is a method of treating waste liquid in which particles are dispersed.

The melt-blowing method is disclosed in, for example, Japanese Patent Laid-Open No. 50-46972, in which a thermoplastic polymer is melted and discharged from an orifice, and heated high-speed gas is sprayed from slits on both sides of the orifice to discharge the discharged material. This is a process of obtaining ultrafine fibers by thinning. The fiber web obtained by this melt-blowing method is a non-woven fabric in which ultrafine fibers are randomly intertwined with each other. In the nonwoven fabric used in the present invention, it is important that the ultrafine fibers are not in the form of fiber bundles but are separated substantially in the form of single fibers.

According to the study of the present inventors, in the non-woven fabric in which the ultrafine fibers are present in the form of a fiber bundle, the function as the ultrafine fibers is hardly exerted, and only the filter performance which is not much different from the thick fiber non-woven fabric is obtained. I understood. That is, it was found that the minute space formed by the random entanglement of ultrafine fibers is the point to increase the removal rate, and by using a non-woven fabric with a fiber aggregate structure separated into substantially single fibers, high-performance removal is possible. A low pressure drop was achieved in combination with the rate.
The melt blow method is most suitable for obtaining the random ultrafine fiber nonwoven fabric which does not substantially contain fiber bundles.

Japanese Utility Model Publication No. 55-41292 discloses a high-performance air filter made of a non-woven fabric composed of entangled bundles of ultrafine fiber bundles, each of which is a bundle of ultrafine fibers. This non-woven fabric can suppress pressure loss as compared with a non-woven fabric in which ultrafine fibers are separated into single fibers, but on the other hand, the collection efficiency is significantly reduced. Even if mechanical treatment such as rubbing, tapping, rubbing, etc., of the non-woven fabric of this publication can be partially defibrated, only a part of the fibers can be defibrated, and the non-woven fabric used in the present invention has a high degree. A defibrated state is not achieved.

The average fiber diameter of the melt-blown ultrafine fibers used in the present invention is 0.3 to 3.0 μm, preferably 0.5 to 2.0 μm.
If it exceeds 3.0 μm, the removal efficiency will be extremely reduced,
It is not suitable as a high performance filter used in the present invention.
On the other hand, if it is less than 0.3 μm, the tensile strength of the nonwoven fabric is lowered and the pressure loss becomes too large, so that the object of the present invention cannot be achieved.

Although the diameter of the fiber obtained by the melt-blowing method is extremely small, it is difficult to accurately measure the length of the fiber,
The average length of the fibers is 30 mm or more, usually 100 mm to several hundred mm. The relatively long fiber length is a factor of the high tensile strength of the nonwoven fabric used in the present invention.

The material of the ultrafine fibers may be any melt-blown thermoplastic polymer, for example, polyester,
Polyamide, polyolefin and blends thereof,
Examples thereof include copolymers. Polyester, particularly polyethylene terephthalate, which has a large heat shrinkage rate, is preferable because it is easy to obtain a high bulk density and a large tensile strength.

The bulk density of the nonwoven fabric used in the present invention should be greater than 0.35 g / cm ³ , preferably 0.60 g / cm ³ or less, more preferably 0.55 g / cm ³ or less. The bulk density is an important factor that contributes to not only removal efficiency and initial pressure loss but also tensile strength of the nonwoven fabric. If the bulk density is too large, the removal efficiency and the tensile strength are increased, but the initial pressure loss becomes too large, which is not preferable. On the other hand, if it is 0.35 g / cm ³ or less, it is preferable in that the initial pressure loss is small, but on the other hand, the tensile strength is low and it is not suitable.

As a method of obtaining a nonwoven fabric having such a high bulk density, a method of strongly pressing the meltblown web at a temperature not higher than the glass transition point of the fiber and a width of 5 kg / cm or more is preferable. Pressing under these conditions does not cause heat fusion between fibers, and improves filtration performance and strength.

The tensile strength in one direction (length direction) of the nonwoven fabric used in the present invention is at least 200 g / cm, preferably 300 g / cm or more, more preferably 500 g / cm or more. Only when it is stronger than this, it becomes possible to use it as a filter medium for a roll type continuous filtration device. When the non-woven fabric is a random non-woven fabric in which ultrafine fibers are separated into single fibers instead of fiber bundles, it becomes extremely difficult to maintain high tensile strength of the non-woven fabric. The present inventor uses a melt-blown ultrafine fiber to obtain an ultrafine fiber having a relatively long fiber length, and increases the bulk density of this ultrafine fiber nonwoven fabric to a value greater than 0.35 g / cm ³ to increase the degree of entanglement between the fibers. By increasing it, this high strength could be achieved while satisfying high filter performance (high removal efficiency, low pressure loss).

The nonwoven fabric used in the present invention has a collection efficiency of 70% or more, preferably 80% or more. The collection efficiency here is 0.3μ
It is a value measured with m dioctyl terephthalate (DOP) particles. With this collection efficiency, 99% or more of the cutting waste in the wastewater having a particle size of 0.3 μm or more can be removed. The initial pressure loss of the non-woven fabric used in the present invention is 50 mm or less at a wind speed of 4 cm / sec., Preferably 30 mmH ₂ O.
It is as low as below.

The nonwoven fabric used in the present invention preferably has a basis weight of 20 to 100 g / m ² . If it is less than 20 g / m ² , the tensile strength will decrease,
On the other hand, if it exceeds 100 g / m ² , the initial pressure loss may become too large.

The above-mentioned non-woven fabric is usually wound in multiple layers around the peripheral surface of a cylindrical porous tube to form a filter cylinder having a hollow at the center and used for filtration. The wastewater to be filtered is filtered by passing it from the outside to the inside of the filter cylinder or from the inside of the filter cylinder to the outside in the radial direction along the cross section of the filter cylinder.

When the filter cylinder is formed as described above and the take-up shaft of this non-woven fabric is provided outside, and when drainage is passed from the outer peripheral surface of the filter cylinder to the inside for filtration, clogging occurs after a predetermined period has passed. When starting, the nonwoven fabric is wound around an external winding shaft, and a new nonwoven fabric filter medium surface is exposed on the surface, whereby continuous filtration can be performed.

As the waste water, a dispersion of inorganic particles having a particle size of 5.0 μm or less, particularly 0.3 to 1.0 μm is treated. Examples of such inorganic particles include chips such as silicon wafers and gallium / arsenic wafers.

〔Example〕

Next, a specific example of the drainage treatment method of the present invention will be described in more detail.

The bulk density is a value obtained by dividing the weight per unit area by the thickness. The thickness was measured using a dial thickness gauge H (Peacock type: Ozaki Seisakusho). Further, the tensile strength is a value measured using a Tensilon under the conditions of a width of 2 cm, a gripping length of 10 cm, and a pulling speed of 10 cm / min for each of the widths of 1 cm.

Example 1. Polyethylene terephthalate was spun by a melt blow method and wound into a web having a basis weight of 50 g / m ² , a width of 1 m and a length of 600 m. The average single fiber diameter of this web (measured by photographing with a scanning electron microscope) was 1.5 μm. The web was pressed at room temperature (25 ° C.) with a pressure of 10 kg / cm width and continuously wound. The bulk density of this nonwoven fabric was 0.45 g / cm ³ , and the tensile strength was 670 g / cm in the length direction and 350 g / cm in the width direction.
The collection efficiency of DOP was 90%, and the initial pressure loss was 20 mmH ₂ O. This non-woven fabric is wound in multiple layers around a porous cylindrical tube to form a filter cylinder having a hollow portion in the center, and a take-up shaft for this non-woven fabric (filter material) is provided on the outside of the filter cylinder from the outer peripheral surface of the filter cylinder. The water to be treated was supplied in the direction of the inner peripheral surface for filtration. As the water to be treated, when discharged water containing approximately 30,000 to 50,000 pieces of silicon cutting chips per 10 cc was filtered through a flow rate of 25 l / min, the number of cutting chips in the drainage was 100 per 10 cc (particle size 0.3
˜1.0 μm) was obtained.

After clogging, the nonwoven fabric filter material was wound around the winding shaft and a new filter material surface was exposed on the surface, so that filtration could be continuously continued.

Example 2. Polypropylene melt-blown to have a basis weight of 70 g / m ² , width
A web having a length of 1 m, a length of 600 m and an average single fiber diameter of 0.8 μm was obtained. This web is pressed at a pressure of 15 kg / cm width at room temperature to obtain a bulk density of 0.53 g / cm ³ , a tensile strength of 740 g / cm in the longitudinal direction,
A non-woven fabric having a width direction of 560 g / cm and a DOP collection efficiency of 99.9% was obtained.
When this non-woven fabric was subjected to the same discharge treatment test as in Example 1, the removal rate was 99.9% or more, which was extremely good.

〔The invention's effect〕

The non-woven fabric having a bulk density of more than 0.35 g / cm ^{3 in} which melt-blown ultrafine fibers having an average single-filament fiber diameter of 0.3 to 3.0 μm are randomly entangled, and the meltblown ultrafine fibers are separated into substantially single fibers. It has excellent filter performance due to the micro space based on the entangled structure, and high tensile strength based on the highly entangled structure of the relatively long fiber length of meltblown fiber. As a result, a filter medium for liquid treatment having three excellent properties of high removal efficiency, low initial pressure loss, and high tensile strength can be obtained. This filter medium is most suitable as a filter medium for a roll type filter that can continuously perform liquid filtration for a long time without a troublesome replacement operation, as compared with the conventional cartridge type. Material (silicon wafer,
This is a filter medium effective for removing chips (diameter of about 0.3 to 1 μm) of gallium / arsenic wafers) and for collecting pure water, and the industrial significance of the present invention is great.

Claims (2)

[Claims] 1. Drainage in which inorganic particles having a particle diameter of 5.0 μm or less are dispersed is randomly entangled with ultrafine fibers having an average single-filament fiber diameter of 0.3 to 3.0 μm, and has a bulk density exceeding 0.35 / cm ³ and a length. Direction tensile strength is at least 200g / cm width, and areal weight 20 ~ 1
A non-woven fabric filter surface made by wrapping multiple layers of non-woven fabric with a melt blown method of 00 g / m ² around the perforated pipe in a direction along the cross section of the filter cylinder from the outer peripheral surface to the inside, and then peeling off the outer peripheral surface after a certain period of time. Is exposed to the surface to substantially remove the inorganic particles, and a method for treating drainage liquid in which inorganic particles are dispersed. 2. The drainage treatment method according to claim 1, wherein the non-woven fabric can collect at least 70% or more of dioctoctyl phthalate particles having a particle diameter of 0.3 μm.