JPH0354198B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Field of Application] In the membrane separation technology required in fields such as the pharmaceutical industry and the electronic industry, the present invention is directed to a thin film of metal or alloy made into regular ultra-fine porosity by track etching. For details, see He ⁺ , O ⁺ ions, N ⁺
This invention relates to a porous thin film in which an amorphous metal thin film is subjected to track etching using any one of ions, F ⁺ ions, α particles, protons, and deuterons as high-speed charged particles. The invention also relates to a method for producing this porous thin film. [Prior Art] Membrane separation techniques proposed around the world include precision filtration, dialysis, electrodialysis, reverse osmosis, ultrafiltration, gas separation, and controlled release. For example, for filters in the electronic industry, there is a growing demand for highly efficient separation membranes. That is, with the shift to VLSI and ULSI semiconductors, high precision and tolerance, such as circuit line width on the order of 0.1μ, are required. Microfilter technology has been gaining importance in recent years as a means of removing ultrafine particles and microorganisms that pose a hindrance, or of preventing contamination caused by them. As one of the highly efficient separation membranes that meet this requirement, ultrathin membranes made of polymeric materials are irradiated with neutrons from nuclear reactors to produce micropores on the order of 1 or 1/10 microns, with a maximum of ¹⁰⁸ micropores per ^cm2 . A technique called track etching, in which the holes are etched with a chemically corrosive solution, was proposed, and it came into the spotlight as a new material for membrane filters as filter elements. This method takes advantage of the fact that neutrons break the bonds between atoms in a polymeric material, and the tracks left behind are enlarged by the use of a corrosive solution. Track etching, which has already been developed, has been applied to thin polymer films (polycarbonate membranes), but has not yet been applied to other metal-based or ceramic-based materials, and its technical potential was unknown. Conventional techniques have relied on ultrasonic perforation and laser beam perforation to form micropores on the order of microns in thin films of metals or alloys (hereinafter only the former will be used). As will be clear from the comparative examples described below, laser beam drilling has an incomparably low number of holes and requires time for the laser beam to pass through, which is disadvantageous both physically and methodically. The same may be said of ultrasonic drilling. [Problems to be solved by the invention] Track-etched polycarbonate membranes have superior filter properties compared to cellulose-based membranes, but because the material is polymeric, the following problems occur. There is. In organic solvents, it swells, changes the pore size, and becomes prone to cracking. Also, for electrical insulation,
It becomes charged and becomes easily clogged. In recent years, although there has been a demand for more durable and more efficient separation membranes in fields such as the pharmaceutical industry and the electronics industry, the demand has not been met. [Object of the Invention] Therefore, the object of the present invention is to solve the drawbacks of the conventional polymeric membranes as described above.
The object of the present invention is to provide a metal thin film that has regular ultrafine porosity through track etching. [Means for Solving the Problems] Amorphous metal thin films generally have superior mechanical strength, electrical conductivity, heat resistance, corrosion resistance, and chemical resistance when compared to polymer thin films. Selecting an amorphous amorphous metal thin film as a workpiece, the present invention provides a porous amorphous metal suitable for constructing filters and the like having regular micropores using a track etching method.
Rather than using expensive and large-scale equipment such as nuclear reactors, we utilize commercially available equipment and select metal-based thin films, which generally have better heat resistance and strength than polymeric materials, as workpieces. After continuing to search for various technologies that would enable track etching, we used He ⁺ , O ⁺ , N ⁺ , and F ⁺ element ions, α particles, protons, and deuterons as the irradiation source, and used a thin film of amorphous metal as the workpiece. As a result, we have now proposed a technique that can accurately realize track etching on a metal-based thin film using an inexpensive and compact device. [Function] The present invention will be explained in detail below, starting with the manufacturing method. Although the thin film used as the workpiece is usually amorphous, the part through which the irradiated charged particles pass through is crystalline.In the case of crystalline, it is made of metal or metal, which has a higher corrosiveness to chemical corrosive liquids than amorphous. A thin film of alloy is used. That is, Figure 4 shows the corrosion rate of Fe-Cr based alloy as an example of such an alloy in 1N saline solution at 30°C.
This shows the influence of the content. The figure shows that when Cr exceeds 6%, amorphous Fe-Cr alloys are not corroded in the same saline solution, but crystalline ones are significantly corroded. That is, Fe
- For use of Cr-based alloys according to the invention, preferably at least 6% Cr, otherwise
A material with a Cr content close to 6% must be selected to maintain the distinct difference in corrosivity between amorphous and crystalline materials. The reason for this is that when micropores are formed by irradiated charged particles, the pore walls and their surrounding areas change from amorphous to crystalline, and this crystalline substance is properly treated with the corrosive liquid later. This is because it is necessary for the initial fine pores to develop into approximately cylindrical or truncated conical shapes after dissolution. This is because if even amorphous material were to be etched, the truncated micropores would lose their initial micropore shape due to etching. Fe−Cr
Examples of amorphous-forming elements in the base alloy include non-metallic elements such as P, C (however, the C content is greater than or equal to that contained in the steel), and B. Examples include F ₇₄ P ₁₃ C ₇ Cr ₆ . Amorphous alloys have better corrosion resistance than crystal alloys.
Although the heat resistance has been improved, F ₇₄ P ₁₃ C ₇ Cr ₆ has even better H ₂ SO ₄ resistance than stainless steel.
This characteristic is also exhibited by thin films. The thickness of the thin film is preferably about 0.5 μm to 20 μm. Fast charged ions of He ⁺ , O ⁺ , N ⁺ , F ⁺ ions, protons, and deuterons are most commercially preferred in the present invention as irradiation sources. That is, irradiation with these nonmetal element ions can be easily performed using a commercially available ion accelerator such as Vendegraf or Minicyclotron. The charge of irradiated ions is about 1 to 80 MeV,
The ion current on the thin film is 10 ^-8 to 1 μA, but these conditions can be adjusted as appropriate depending on the transfer speed and thickness of the thin film. The number of ions actually irradiated, that is, the number of micropores, can be calculated from the ion current value and the ion charge using the following formula, and the pore values described later are based on this calculation. This formula is: 1μQ=10 ¹³ (pieces) ......(1) B=V×W (cm ² /sec) ......(2) C=A/B (μQ) ......(3) D =C×10 ¹³ (pieces) ......(4) However, in the above formula; A (μA)...Ion current, W (cm)...Ion beam width, V (cm)...... Thin film transfer speed, B (cm ² / sec): irradiation area per second, C (μQ): irradiation amount per unit area (cm ² ), D (pieces): number of tracks, Show each. The procedure for irradiating the metal or alloy thin film with the specified high-speed charged particles will be explained with reference to FIG. 1, which shows an apparatus.
In a commercially available ion accelerator such as a minicyclotron, a chamber C and an accelerator A are connected through an introduction tube B, and members A, B, and C are each maintained in a vacuum.
In the chamber C, a thin film 1 as a workpiece is continuously run by thin film feed rolls D, D so as to be substantially orthogonal to the high-speed charged particles. As an example, the running speed is about 1 cm/sec,
This has a relative relationship with the material and thickness of the thin film 1, and the irradiation conditions of high-speed charged particles, and is not constant, but the irradiation is made for a time necessary to provide the required number of micropores. In order to amplify the energy of high-speed charged particles from accelerator A, a nuclear-reactive substance 2 such as Be is provided at the open end of introduction tube B, and one side of this substance 2 is closely held on thin film 1 (Figure 2). If this is adopted, high-speed charged particles with low energy density but with higher energy than the nuclear-reactive substance 2 can fly out and effectively form holes in the thin film 1 in close contact with the nuclear-reactive substance 2. In this example, the thin film 1 and the feed rollers D and D may be placed in the atmosphere unlike the previous case, but the surface of the thin film 1 that receives the irradiation is in close contact with the substance 2 to prevent the irradiation action from energy loss. Make sure you can receive it. Instead of He ⁺ , O ⁺ , N ⁺ , F ⁺ ions, alpha particles from isotopes such as Co ₆₀ or proton and deuteron irradiation using the same ion accelerator are equally effective. The chemical corrosive solution varies depending on the material of the thin film, but hot saline, hot hydrochloric acid aqueous solution, hot nitric acid aqueous solution, etc. are used as examples. This corrosive liquid and the thin film 1 are removed using a method in which the treated thin film 1 is immersed in a liquid tank (not shown) filled with the corrosive liquid using a dipping roll and then continuously pulled up. It is desirable to provide a convection means that gently applies the liquid to the thin film 1 so as to flow in the direction in which the fine pores of the thin film 1 are formed, and that makes the temperature distribution in the tank as uniform as possible. By doing so, the pore walls 11 of the unidirectional and orderly array of fine pores 10 that are initially drilled in the thickness direction of the thin film 1 by the irradiation, or their nearby portions 11, are affected by the impact caused by the constant-velocity charged particles. It changes from an amorphous substance to a stable crystal quality,
Since this immediately melts away when it comes into contact with the corrosive liquid, the pore diameter gradually expands while maintaining the initial shape of the fine pores 10, which is approximately cylindrical or truncated conical, resulting in an overall uniform shape. 10 micro holes with a hole diameter on the order of 1 digit micron to 1/10 digit micron.
are formed in large numbers [see Figure 3 A and B].
As already mentioned, the amorphous metal or alloy that is the material of the thin film 1 of the present invention exhibits a significantly higher corrosive property against the corrosive liquid when it changes to a crystalline state. , while ensuring corrosion prevention in other amorphous materials, thereby establishing micropores 10 with sharp boundaries. The number of micropores 10 is determined by the current i of the irradiated thin film 1.
As already mentioned, the number of ions, that is, the number of micropores, is calculated from the measured value and the ion charge. According to the invention, the hole
The number of holes/cm ² can be adjusted to 10 ⁴ to 10 ⁸ and the hole diameter can be adjusted to 12 to 0.05 μm, respectively. Furthermore, if the micropores become clogged, they can be almost completely cleaned by ultrasonic cleaning. The present invention will be explained in detail below using examples. Example 1 (a) Workpiece: An alloy of Fe ₇₄ P ₁₃ C ₇ Cr ₆ was made into a piece of 15 μm thick, 20 mm wide, and 10 cm long using the single roll method.
Amorphous amorphous alloy thin film (b) High-speed charged particles……From Van de Graff
Irradiation with 2 MeV He ⁺ ions with a beam width of 20 mm and an ion current of 0.001 μA (c) Thin film traveling speed: 1 cm/sec (d) Chemical corrosive solution: 20% HCl aqueous solution at 40°C (e) Results ......As a result of etching the material treated using the apparatus shown in Figure 1 under the conditions of (a) to (c) using (d), approximately cylindrical micropores with a pore diameter of 0.1 μm were formed.
A porous thin film with a pore number of 10 ⁸ /cm ² was obtained. Example 2 (a) Workpiece: Amorphous alloy thin film of Fe ₇₄ P ₁₃ C ₇ Cr ₆ alloy with a thickness of 17 μm, width of 20 mm, and length of 10 cm (b) High-speed charged particles: 17 MeV generated by a small AVF cyclotron Deuteron irradiation with a beam width of 10 mm and an ion current of 0.0001 μA (c) Thin film traveling speed...1 cm/sec (d) Chemical corrosive solution...40℃, 20% HCl aqueous solution (e) Results... As a result of etching the material treated using the apparatus shown in Figure 1 under the conditions of (a) to (c) using (d), approximately cylindrical micropores with a pore diameter of 0.3 μm were formed.
A porous thin film with 10 ⁷ /cm ² was obtained. Comparison with prior art (comparative example) Taking drilling by _CO2 gas laser as an example, the output
150W, energy 0.015J/pulse, number of pulses
A 140μm thick laser is used with a 625pps CO ₂ gas laser.
When a Fe ₇₄ P ₁₃ C ₇ Cr ₆ alloy film was laser-perforated, 500 circular holes/cm ² were perforated in 10 seconds. A comparison between the comparative example and Examples 1 and 2 shows that the number of holes drilled by laser drilling is incomparably smaller than that of the present invention, and the time required to complete the holes is much longer, resulting in improved productivity. It turns out that it is incomparably disadvantageous in terms of porosity. Example 3 (a) Workpiece (1) Fe ₇₄ P ₁₃ C ₇ Cr ₆ amorphous alloy thin film (2) Polycarbonate thin film (b) Drilling method (1) Track etching method A After deuteron irradiation from a small AVF cyclotron, chemical Etching. (2) Track etching method B Chemically etches after irradiating alpha particles from a nuclear reactor. (3) Laser perforation method (comparison) Perforation is performed using a CO ₂ gas laser. (c) Results In the track etching method, the irradiation amount of charged particles was varied on the workpiece so that the etching holes were 10 ⁴ to 10 ⁸ /cm ² . In addition, the laser drilling method takes about 100 times as much work time as the track etching method, resulting in a hole of 10 ⁴ /cm ^2.
The diameter of the hole drilled and its density are
Obtained by SEM. In addition, in order to evaluate the filter characteristics of the produced porous thin film, we processed it into the shape of a membrane filter and investigated its lifespan when it was used to separate photosensitive liquids for semiconductor manufacturing. Also used in semiconductor manufacturing for similar purposes.
We also investigated the lifespan when used in _N2 gas filters. These results are shown in Table 1.

〔Effect of the invention〕

From the above explanation, the present invention can provide a porous amorphous metal thin film having a pore diameter of 0.05 to 12 μm and a micropore density of 10 ⁴ to 10 ⁸ /cm ² , which is different from that of a polymer thin film. When this thin film metal is used as a filter for constructing a clean room, for example, it can exhibit excellent filter properties because it has mechanical strength, wear resistance, corrosion resistance, and electrical conductivity. In addition, according to the present invention, instead of a nuclear reactor, H ⁺ , O ⁺ , N ⁺ , and F ⁺ ion irradiation (in addition to α particles, protons, and deuterons) is performed using a commercially available accelerator. Since the track hole can be formed by irradiation), the device is compact and costs can be reduced.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram showing one embodiment of an apparatus for carrying out the method of the present invention, FIG. 2 is a schematic diagram of another embodiment of the apparatus,
Figures 3A and 3B are schematic diagrams showing the shape of micropores in the thin film of the present invention. It is a corrosion characteristic diagram of an alloy. (Explanation of symbols) 1... thin film of amorphous metal or alloy, 10... micropore, 11... pore wall and its immediate vicinity, 2... nuclear reactive substance, A... ion accelerator, B... introduction tube , C... closed chamber, D... thin film feeding roll.

Claims (1)

[Scope of Claims] 1. Consisting of a thin film of amorphous metal, this thin film has fine pores that have regular unidirectionality throughout the thickness, have a pore diameter of 0.05 to 12 μm, and have a substantially cylindrical to truncated conical shape. A porous amorphous metal thin film having a distribution density of 10 ⁴ to 10 ⁸ /cm ² . 2. Selecting as a workpiece a thin film of amorphous metal or alloy, which has significantly greater chemical corrosivity than amorphous amorphous material when it changes to a crystalline state, and applying He ⁺ , O ⁺ , N ⁺ ,
irradiating high-speed charged particles selected from F ⁺ , α particles, protons, and deuterons from substantially orthogonal directions to form a large number of unidirectional micropores through the thickness of the thin film; A method for producing a porous amorphous metal thin film, which comprises treating the thin film with a chemical etchant to align the micropores into a substantially cylindrical or truncated conical shape. 3. The manufacturing method according to claim 2, wherein irradiation with high-speed charged particles is continuously applied while the thin film is traveling at a constant speed. 4. The manufacturing method according to claim 3, wherein the irradiation with high-speed charged particles is performed using an ion accelerator such as a Vendegraph or a minicyclotron.