JP2949130B2 - Method for producing porous metal filter - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a method for producing a porous metal filter having fine pores, particularly in the semiconductor industry and the field of microelectronics.
The present invention relates to a method of manufacturing a filter for removing high-pressure gas or liquid contaminant fine particles used in a semiconductor manufacturing process and purifying a high-purity gas or liquid.

[Conventional technology]

2. Description of the Related Art Conventionally, in the purification of high-pressure gas or liquid used in a semiconductor manufacturing process, a porous fluororesin film has been used to remove contaminant fine particles of about 0.01 μm to 0.1 μm.

However, the porous fluororesin membrane has no problem in its function of removing contaminating fine particles, but has some problem in heat resistance. That is, it cannot cope with the use of purification of gas or liquid having a high pressure of 170 ° C. or higher.

Further, in order to meet the above requirements, metal and ceramic filters have been studied. However, in the case of a ceramic filter which is a sintered product, there is a limit in the pore diameter due to its production, and it is very difficult to remove fine particles of 0.01 μm to 0.1 μm. Problem also arises.

On the other hand, in the case of a metal filter obtained by sintering metal powder, (a) sintering of a molded body by press molding or (b) plasticizing and kneading the metal powder and an organic binder of 15 to 30% by weight, followed by molding and sintering. Manufactured by the method.

However, in the method (a), the porous filter becomes heterogeneous, and the generated pore diameter is large.

In the method (b), it is difficult to use a large amount of an organic binder and to knead the fine particles with a fine particle of 1 μm or less with the binder. In general, a porous filter having a pore diameter for using metal particles of 5 μm or more is impossible. It is.

[Problems to be solved by the invention]

As described above, the conventional porous filter has a problem in terms of heat resistance, or it is difficult to form a porous body having fine pores necessary for capturing fine particles of 0.01 μm to 0.1 μm.

An object of the present invention is to solve the above-mentioned problems of the prior art,
From high pressure gas or liquid at high temperature of 170 ℃ or more
It is an object of the present invention to provide a method for producing a porous metal filter body capable of removing contaminating extremely fine particles of about μm and purifying a high-quality gas or liquid having no extractable substance for a long period of time.

[Means for solving the problem]

The present invention relates to a method for producing a filter by sintering a metal powder, kneading a composite powder obtained by coating a metal powder with acrylic fine particles with a wax binder, molding, calcining, and sintering. It is a manufacturing method.

It is known that when metal powder and organic fine particles are mixed, the metal powder is coated with the organic fine particles. The metal powder coated with the organic fine powder has better dispersibility of each powder and better fluidity than the powder not coated.

The acrylic fine particles have a particle size of 0.01 to 12.0 μm, preferably
0.1 to 0.5 μm is effective.

The acrylic fine particles used in the present invention exist stably up to 200 ° C, and decompose to monomers at 250 ° C or higher,
Since it evaporates, it is convenient as an organic binder.

When the metal powder coated with acrylic fine particles and the wax binder are kneaded at 80 to 150 ° C., the wax melts, but the acrylic fine particles have a high melting point. is there. Therefore, a uniformly dispersed metal powder dispersion is produced.

The dispersion state of the metal powder and the acrylic fine particles need not necessarily cover the metal powder with the acrylic fine particles, but may be in a state of being dispersed. If the diameter of the metal fine particles is D and the diameter of the acrylic fine particles is d, D / d may be 4 or more.

Further, the ratio of the metal powder to the acrylic fine particles is preferably 5 or more, preferably 50 or more per one metal powder, in order to enhance the dispersibility.

The dispersion of the metal powder and the acrylic fine powder may be a simple mixing, or preferably a uniform dispersion using a ball mill or a mixing mill. Thereby, each metal powder particle is coated with the acrylic fine particles, and the fluidity is improved.

The metal powder thus prepared is mixed with a wax-based binder and kneaded at 70 to 200 ° C, preferably 80 to 150 ° C, in a molten state of paraffin wax. At this time, since the acrylic fine particles do not melt, the metal powder maintains a good dispersion state.

The amount of paraffin to be mixed is 2 to 50% by weight, preferably 5 to 30% by weight based on the metal powder, and under these conditions, a homogeneous kneaded product is produced.

If the temperature at the time of compression molding of the kneaded product is lower than 70 ° C., the wax does not melt, so that a satisfactory molded product cannot be formed. On the other hand, if the molding temperature exceeds 150 ° C., the paraffin wax becomes syrupy and uniform molding becomes difficult. Generally, a molding pressure of 10 to 100 kg / cm ² is sufficient.

Next, the molded product is degreased in a temperature range from room temperature to 500 ° C. In this case, if the heating rate is increased to more than 5 ° C./min, foaming, cracking or deformation is exceeded, so that a satisfactory molded product cannot be obtained. On the other hand, at 0.05 ° C./min or less, it is too slow and not practical. From this, the heating rate is 0.
05 ° C to 5 ° C / min is preferred.

In particular, at around 80 to 100 ° C. where the wax softens, around 200 ° C. at which the decomposition of the wax binder starts, and around 350 ° C. at which the acrylic fine particles decompose, the molded body is easily deformed. It is preferable to keep the temperature constant. In addition, since the decomposition of the binder is completed at 400 to 450 ° C., if the temperature is maintained for about 30 minutes to 5 hours to completely remove the binder, there is an advantage that carbon does not remain in the product. The binder removal is preferably performed in an inert gas such as nitrogen or argon in order to prevent oxidation of the metal.

The degreased molded body undergoes a sintering reaction in a reducing atmosphere such as hydrogen gas or ammonia or in a vacuum, and performs a sintering reaction while removing the surface oxidation state. The sintering reaction is carried out at a temperature corresponding to 30 to 80% of the melting point of the metal to be used, whereby the sintering reaction is performed. In this case, when the particles of the metal powder are large, a sintering temperature closer to the melting point is required, and the sintering temperature is extremely low for fine particles of 1 μm or less.

At a temperature corresponding to 80% or more of the melting point of the metal, sintering proceeds excessively, and the particles are fused to form closed pores, which makes the porous material unsuitable.

According to observation with an electron microscope, the dispersion of each of the particles in the porous body obtained in the present invention was better than that of the porous body manufactured using only the wax binder.

 Hereinafter, the composition of the raw material in the present invention will be described.

(A) Acrylic fine particles This component is a thermoplastic resin, and is almost complete spherical and fine particles of uniform size. By dry-blending with metal powder, it adheres to the powder surface due to the charging phenomenon, improves the dispersion of the metal powder, and acts as a binder during powder molding. Acrylic fine particles exist stably up to 200 ° C and rapidly decompose at 250 ° C or higher, especially at 300 to 400 ° C. By combining them with paraffin wax, the thermal decomposition temperature of the binder can be increased, and when removing binder, Thermal decomposition of the binder gradually progressed,
Deformation of the molded body due to rapid thermal decomposition of the binder is prevented.

The acrylic fine particles contain a methacrylate polymer and a copolymer thereof as a main component.

(B) Paraffin wax This component improves the fluidity of the blended mixture during molding and improves the wettability between the raw material powder and the binder,
Has the effect of homogenizing the blended mixture.

(C) Metal powder The metal powder used is a metal powder having an average diameter of 0.05 μm to 50 μm. When the average particle diameter is reduced to 1 μm or less, the specific surface area of the powder relatively increases. A relatively large amount of acrylic fine powder and paraffin wax to be blended is required.

〔The invention's effect〕

As described above, according to the present invention, a sinterable metal powder and acrylic fine particles are mixed, and a composite powder having a metal powder surface substantially coated with acrylic fine particles is kneaded with a wax binder, molded, and then degreased. , Sintered, enhances the dispersibility of metal powder with a small particle size, and prevents the deformation of the compact by gradually decomposing these binders according to the pyrolysis temperature range of acrylic fine particles and wax. Is done.
For this reason, it is possible to obtain a porous filter having fine pores with few closed pores. Therefore, by using the porous metal filter obtained by the method of the present invention as a filter in a semiconductor manufacturing process or the like, for example, a temperature of 40
High-pressure gas or liquid contaminant fine particles of 0.01 μm to 0.1 μm in a high temperature state such as 0 ° C. can be removed, and a high-quality gas or liquid can be purified. Moreover, there is no extractable substance. Therefore, the effect of contributing to the manufacture and development of semiconductor products is extremely large.

〔Example〕

Hereinafter, the present invention will be described in more detail with reference to Examples and Comparative Examples.

Example 1 As a raw metal powder, a substantially spherical, average particle size of 3 to 7 was used.
Nickel fine powder (INCO # 123) having a μm and a specific surface area of 0.34 to 0.40 m ² / g was used. 230 g of this nickel fine powder and 11.5 g of acrylic fine powder were mixed in a ball mill for 10 hours. The acrylic fine powder was a substantially spherical methacrylate polymer having an average particle diameter of 0.4 μm (Soken Chemical MP1000). After removing this mixture from the ball mill,
Add 11.5 g of paraffin wax (Chukyo Yushi E914) and add 60 ml of twin-screw kneader (Toyo Seiki, Labo Plastomill)
And mixed at 130 ° C.
Driving continued for 0 minutes. The plasticized mixture was taken out of the kneader, cooled to room temperature, solidified, crushed, and compacted at 100 ° C for 15 minutes with a small compression molding machine.
A disk-shaped molded product having a diameter of 13 mm and a thickness of 3 mm was prepared.

This molded product was degreased in a degreasing furnace under an N ₂ atmosphere. At this time, the temperature was raised from room temperature to 80 ° C at a rate of
Temperature rise rate 0.1 ° C / min from 200 ° C to 200 ° C, hold at 200 ° C for 2 hours, temperature increase rate from 200 ° C to 350 ° C 0.1 ° C / min, hold at 350 ° C for 2 hours, temperature rise from 350 ° C to 500 ° C Speed, 0.2 ° C / min, 500
It was a condition of holding at 5 ° C. for 5 hours.

This fat body is further set in a firing furnace, and hydrogen is 10% by volume.
Was fired under a nitrogen stream containing. The firing conditions were as follows: the temperature was raised at 5 ° C./min, and the temperature was maintained at 800 ° C. for 3 hours.

The apparent porosity of the obtained sintered body is 28.4%, apparent density
At 8.83, the porous body had a maximum pore size of 1.6 μm according to the bubble point method (ASTM: F316).

Comparative Example 1 A reaction was carried out in the same manner as in Example 1, except that 21.7 g of paraffin wax was used without using acrylic fine particles.

Apparent porosity of the obtained sintered body is 7.2%, apparent density
At 8.00, the maximum pore size according to the bubble point method was 1.2 μm.

The sintered body obtained here has a small apparent porosity and a small apparent density as compared with Example 1, so that the inside has a high proportion of closed pores, and the number of holes is small even by observation with an electron microscope. Did not.

(Examples 2 to 5) A sintered body was manufactured in the same manner as in Example 1 except that the weight ratio of wax / acrylic fine particles and the sintering temperature were as shown in Table 1, and the results were shown in Table 1. Show.

Example 6 As a metal fine powder, a spherical fine powder having an average particle size of 0.5 μm (Sumitomo Metal Mining SNP-110) was used.

Spherical polymethyl methacrylate fine powder (Nippon Paint Microgel YKC-2) having an average particle size of 0.05 μm was used as the acrylic fine powder. As the paraffin wax, a good fluidity grade (Chukyo Yushi NE-119) was used.

Degreasing was performed in the same manner as in Example 1 except that 196 g of nickel fine powder, 11.8 g of acrylic fine powder, and 14.9 g of paraffin wax were used. Sintering was performed under the same conditions as in Example 1 except that the sintering temperature was 550 ° C.

The resulting sintered body has an apparent porosity of 38.5% and an apparent density of 8.
70, the maximum pore size of the obtained sintered body was 0.11 μm.

Claims (10)

(57) [Claims] 1. A method of mixing a sinterable metal powder and acrylic fine particles, kneading a composite powder having the metal powder surface substantially coated with acrylic fine particles with a wax binder, molding, degreased and sintered. A method for producing a porous metal filter body, comprising: 2. The method according to claim 1, wherein the acrylic fine particles have a particle size of 0.01 μm to 1.0 μm.
The method for producing a porous metal filter according to claim 1, wherein the porous metal filter has a particle diameter of m. 3. The method for producing a porous metal filter according to claim 1, wherein the acrylic fine particles are mainly composed of a methacrylate polymer or a copolymer thereof. 4. The method according to claim 1, wherein the composite powder and the wax binder
The method according to claim 1, wherein the kneading is performed within a temperature range of 150 ° C. 5. The porous metal filter according to claim 1, wherein D / d is 4 or more, where D is the particle diameter of the metal powder and d is the particle diameter of the acrylic fine particles. Production method. 6. The mixing ratio between the metal powder and the acrylic fine particles is as follows:
The method for producing a porous metal filter according to claim 1, wherein the number of the acrylic fine particles is 50 or more per one metal powder. 7. The method according to claim 1, wherein the wax binder is a paraffin wax. 8. The mixing ratio of the composite powder and the wax binder is such that the weight of the wax is 5 to the weight of the metal powder in the composite powder.
The method for producing a porous metal filter according to claim 1, wherein the content is from 30 to 30% by weight. 9. The metal porous filtration according to claim 1, wherein the kneaded product of the composite powder and the wax is molded at a molding temperature of 70 to 150 ° C. and a molding pressure of 10 to 100 kg / m ^2. How to make the body. 10. A heating rate in an inert gas atmosphere of 0.05 to
The method for producing a porous metal filter according to claim 1, wherein the degreasing is performed by maintaining the temperature at 5 ° C / min at a predetermined temperature for 30 minutes to 5 hours.