JP7576006B2 - Plating solution purification filters - Google Patents

Description

The present invention relates to a filter for purifying a plating solution and an adsorbent for purifying a plating solution.

Filters containing activated carbon are widely used for purifying liquids, not just for water purification. For example, Patent Document 1 discloses an activated carbon-containing filter used for purifying an alkali-resistant plating solution.

On the other hand, in addition to the plating components, various additives are added to plating solutions to improve the plating finish. For example, polymeric organic compounds such as polyethylene glycol, polyvinyl alcohol, and gelatin are added as additives to plating solutions used for electrolytic plating. It is known that these polymeric organic compounds gradually decompose in the solution each time electrolytic plating is performed, turning into low molecular weight decomposition products that act as impurities. If the decomposition products increase in the plating solution, problems will occur in the plating finish, so the decomposition products must be removed.

For example, Patent Document 2 discloses a method for using an activated carbon-containing filter to remove decomposition products from a plating solution and reuse the plating solution.

However, according to the inventors' investigations, when an acidic copper foil plating solution is used, and the decomposition products are adsorbed and removed using an activated carbon-containing filter (hereinafter referred to as "regenerated plating solution"), plating finish problems such as uneven plating can occur.

The inventors investigated the cause of this defect and found that a high chlorine concentration in the acidic copper foil plating solution promotes the dissolution of the anode metal and metallic copper into the plating solution, causing uneven plating, and that chlorine dissolves from the activated carbon-containing filter into the regenerated plating solution.

Furthermore, it was found that the activated carbon-containing filter removes not only decomposition products but also necessary additives consisting of high molecular weight organic compounds from the regenerated plating solution, which also causes defects in the plating finish.

The present invention has been made in consideration of the above circumstances, and its purpose is to provide a filter for purifying a plating solution that can efficiently remove decomposition products generated from additives from the plating solution while suppressing the removal of the additives, and can also suppress the elution of chlorine into the plating solution, and to provide an activated carbon adsorbent for obtaining this filter for purifying a plating solution.

JP 2012-61390 A JP 2005-240108 A

After extensive investigation, the inventors have discovered that the above object can be achieved by the following invention.

The plating solution purification filter according to one aspect of the present invention includes a molded body containing an adsorbent made of activated carbon and having an iodine adsorption amount per unit mass of 930 to 1,300 mg/g, and the chloride ion concentration of the filtrate collected after filtering raw water having a chloride ion concentration of 6.0 to 9.0 mg/L, a pH of 6.9 to 7.5, and an electrical conductivity of 90 to 130 μS/cm for 1 minute is equal to or less than the chloride ion concentration of the raw water.

An adsorbent for purifying a plating solution according to another aspect of the present invention is an adsorbent for purifying a plating solution made of activated carbon, and has an iodine adsorption amount per unit mass of 1000 to 1400 mg/g, an ash content of the activated carbon of 0.5 mass% or less, and a chloride content of the activated carbon of 0.0030 mass% or less.

FIG. 1 is a perspective view of a mold for preparing a molded body of a filter for refining a plating solution according to this embodiment. FIG. 2 is a perspective view showing an example of a molded body of this embodiment obtained using the mold frame of FIG. FIG. 3 is a diagram for explaining how to cut out a sample when measuring the specific surface area, etc., of the activated carbon in the molded body.

The following describes specific embodiments of the present invention, but the present invention is not limited to these.

(Filter for refining plating solution)
The filter for purifying a plating solution of the present embodiment includes a molded body containing an adsorbent made of activated carbon and having an iodine adsorption amount per unit mass of 930 to 1,300 mg/g, and the chloride ion concentration of filtrate collected after filtering raw water having a chloride ion concentration of 6.0 to 9.0 mg/L, a pH of 6.9 to 7.5, and an electrical conductivity of 90 to 130 μS/cm for 1 minute is equal to or lower than the chloride ion concentration of the raw water.

This configuration makes it possible to efficiently remove decomposition products generated from the additives from the plating solution while suppressing removal of the additives, and also to suppress the dissolution of chlorine into the plating solution.

This is believed to be because, by specifying the lower limit of the amount of iodine adsorption per unit mass of the molded body, it is possible to ensure the removal of decomposition products generated from the additives from the plating solution, and, by specifying the upper limit of the amount of iodine adsorption, it is possible to suppress the removal of the additives from the plating solution.

It is also believed that by using the plating solution purification filter of this embodiment to filter raw water and keep the chloride ion concentration of the filtrate below a predetermined value, it is possible to suppress the dissolution of chlorine into the plating solution.

The iodine adsorption amount per unit mass of the molded body contained in the plating solution purification filter of this embodiment (hereinafter also referred to as "molded body iodine adsorption amount") is 930 to 1300 mg/g. If the molded body iodine adsorption amount is less than 930 mg/g, the decomposition products cannot be sufficiently removed from the plating solution, which has a negative effect on the plating formed. On the other hand, if the molded body iodine adsorption amount is greater than 1300 mg/g, not only the decomposition products but also the additives are removed from the plating solution, and the plating cannot be formed sufficiently. The molded body iodine adsorption amount is preferably 940 mg/g or more, and more preferably 950 mg/g or more. In addition, the molded body iodine adsorption amount is preferably 1290 mg/g or less, and more preferably 1200 mg/g or less. In this embodiment, the iodine adsorption capacity of the molded product is measured and calculated according to the method for determining "iodine adsorption performance" specified in JIS K 1474:2014 (activated carbon test method), as described in the examples below.

In the plating solution purification filter of this embodiment, the chloride ion concentration of the filtrate (hereinafter simply referred to as "filtrate") collected after filtering the raw water for 1 minute using the filter is equal to or lower than the chloride ion concentration of the raw water. If the chloride ion concentration of the filtrate is higher than that of the raw water, chlorine will dissolve in the plating solution from which decomposition products have been removed by filtration, adversely affecting the plating formed. However, the plating solution purification filter of this embodiment can suppress the adverse effects of chlorine on the plating. The difference between the chloride ion concentration of the filtrate and that of the raw water (the value obtained by subtracting the chloride ion concentration of the raw water from the chloride ion concentration of the filtrate) is preferably -0.5 mg/L or less. In this embodiment, the chloride ion concentrations of the raw water and the filtrate are measured by the ion chromatography method described in the examples described later.

Here, the reason why the chloride ion concentration of the filtered water is higher than that of the raw water is due to chlorine or chlorides (hereinafter referred to as "chlorine, etc.") contained in the activated carbon that constitutes the molded body. Activated carbon, especially that made from plant-based carbonaceous materials such as coconut shells, contains a certain amount of chlorine, etc. as impurities. The chlorine, etc. contained in the activated carbon can be reduced by washing the activated carbon with acid to reduce impurities other than chlorine, etc., and then subjecting it to a heat treatment. However, if the activated carbon contains more chlorine, etc. than its adsorption capacity allows, the chloride ion concentration of the filtered water may be higher than that of the raw water.

In the plating solution purification filter of this embodiment, the electrical conductivity of the filtrate collected after filtering the raw water for 1 minute using the filter is preferably equal to or less than the electrical conductivity of the raw water plus 5 μS/cm (the value obtained by subtracting the electrical conductivity of the raw water from the electrical conductivity of the filtrate is equal to or less than 5 μS/cm). The electrical conductivity of the filtrate increases due to impurities such as metal components and chlorine eluted from the molded body. If the electrical conductivity of the filtrate is higher than the value obtained by adding 5 μS/cm to the electrical conductivity of the raw water, metal components eluted from the activated carbon and chlorine, etc. will be eluted into the plating solution from which decomposition products have been removed by filtration, which may have an adverse effect on the plating formed. The difference between the electrical conductivity of the filtrate and the electrical conductivity of the raw water (the value obtained by subtracting the electrical conductivity of the raw water from the electrical conductivity of the filtrate) is more preferably equal to or less than 3 μS/cm, and even more preferably equal to or less than 1 μS/cm. There is no particular limit to the lower limit of the electrical conductivity of the filtrate, but if the electrical conductivity is too low, the cost of the molded body will be excessively high. Therefore, the difference between the electrical conductivity of the filtrate and the electrical conductivity of the raw water is preferably -7 μS/cm or more, and more preferably -6 μS/cm or more. In this embodiment, the electrical conductivity of the raw water and the filtrate is measured using a pH meter "F-74" and a Tou pH electrode "9615S-10D" (both manufactured by Horiba Advanced Techno Co., Ltd.).

Here, the raw water used for the evaluation of the chloride ion concentration and the electrical conductivity has a chloride ion concentration of 6.0 to 9.0 mg/L, a pH of 6.9 to 7.5, and an electrical conductivity of 90 to 130 μS/cm. This raw water can be purified water obtained by filtering tap water using activated carbon for water purification. The chloride ion concentration, pH, and electrical conductivity of the purified water are measured, and if all of the items are within the above ranges, the purified water can be used as is as the raw water for evaluation. If the chloride ion concentration of the purified water is lower than the above range, it can be increased by adding sodium chloride (NaCl), and if the chloride ion concentration of the purified water is higher than the above range, it can be decreased by adding ion-exchanged water. If the electrical conductivity of the purified water is lower than the above range, it can be increased by adding sodium sulfate (Na ₂ SO ₄ ), and if the electrical conductivity of the purified water is higher than the above range, it can be decreased by adding ion-exchanged water. As the activated carbon for water purification used for adjusting the raw water, a commercially available product can be used.

In the plating solution purification filter of this embodiment, the number of times of methylene blue circulation adsorption is preferably 4 to 12 times. The number of times of methylene blue circulation adsorption refers to the number of times (the number of times methylene blue is added plus 1) that 2 L of methylene blue aqueous solution with an initial concentration of about 120 mg/L is circulated through the plating solution purification filter, and if the concentration of the methylene blue aqueous solution 30 minutes after the start of the circulation is 2 mg/L or less, methylene blue is added to the initial concentration and the circulation is continued until the concentration of the methylene blue aqueous solution 30 minutes after the addition of methylene blue exceeds 2 mg/L.

If the number of times methylene blue is circulated is less than four, the decomposition products cannot be sufficiently removed from the plating solution, which adversely affects the plating formed. On the other hand, if the number of times methylene blue is circulated is more than 12, not only the decomposition products but also the additives are removed from the plating solution, which makes it impossible to form a sufficient plating. The number of times methylene blue is circulated is preferably five or more, and more preferably six or more. The number of times methylene blue is circulated is preferably 11 or less, and more preferably 10 or less. In this embodiment, the number of times methylene blue is circulated is measured by the method described in the examples below.

In the plating solution purification filter of this embodiment, the ratio of the volume of pores with diameters of 1.0 nm to 1.5 nm measured by the MP method to the total pore volume of the activated carbon measured at a pore volume calculation relative pressure of 0.990 (hereinafter referred to as the "1 nm pore volume ratio") is preferably 2.3% or more. If the 1 nm pore volume ratio is less than 2.3%, decomposition products cannot be sufficiently removed from the plating solution, which has an adverse effect on the plating formed. The 1 nm pore volume ratio is preferably 2.8% or more, and more preferably 3.0% or more. In this embodiment, the 1 nm pore volume ratio is measured by the method described in the Examples below.

In the plating solution purification filter of this embodiment, the average pore diameter of the activated carbon measured by the MP method is preferably 1.70 nm or more and 1.92 nm or less. If the average pore diameter of the activated carbon is less than 1.70 nm, the decomposition products cannot be sufficiently removed from the plating solution, which has a negative effect on the plating formed. On the other hand, if the average pore diameter of the activated carbon is greater than 1.92 nm, not only the decomposition products but also the additives are removed from the plating solution, and the plating cannot be formed sufficiently. The average pore diameter of the activated carbon is preferably 1.71 nm or more, and more preferably 1.74 nm or more. The average pore diameter of the activated carbon is preferably 1.91 nm or less, and more preferably 1.88 nm or less. In this embodiment, the average pore diameter of the activated carbon is measured by the method described in the examples below.

(Activated carbon)
The activated carbon used as an adsorbent in the molded body of the filter for refining a plating solution of the present embodiment preferably has an iodine adsorption amount per unit mass of 1000 to 1400 mg/g, an ash content of 0.5 mass% or less, and a chloride content of 0.0030 mass% or less.

If the amount of iodine adsorption per unit mass of activated carbon (hereinafter also referred to as "activated carbon iodine adsorption") is less than 1000 mg/g, even if a filter for purifying a plating solution made using this activated carbon is used, it is not possible to sufficiently remove decomposition products from the plating solution, which has a negative effect on the plating formed. On the other hand, if the amount of iodine adsorption of activated carbon is greater than 1400 mg/g, not only the decomposition products but also the additives are removed from the plating solution by using a filter for purifying a plating solution made using this activated carbon, and the plating cannot be formed sufficiently. The amount of iodine adsorption of activated carbon is preferably 1050 mg/g or more, and more preferably 1060 mg/g or more. In addition, the amount of iodine adsorption of activated carbon is preferably 1390 mg/g or less, and more preferably 1380 mg/g or less. In this embodiment, the amount of iodine adsorption of activated carbon is measured and calculated by the same method as the above-mentioned molded body iodine adsorption amount.

If the ash content of the activated carbon exceeds 0.5% by mass, the ash will dissolve into the plating solution filtered using a plating solution purification filter made from this activated carbon, adversely affecting the plating formed. To prevent the ash from dissolving into the plating solution, the ash content of the adsorbent is preferably 0.4% by mass or less, and more preferably 0.3% by mass or less.

If the chloride content of the activated carbon exceeds 0.0030% by mass, chloride will dissolve into the plating solution filtered using a plating solution purification filter made from this activated carbon, adversely affecting the plating formed. In order to prevent chloride from dissolving into the plating solution, the chloride content of the activated carbon is preferably 0.0029% by mass or less, and more preferably 0.0020% by mass or less.

The activated carbon used in this embodiment can be, for example, activated carbon obtained by subjecting a carbonaceous material to at least one of carbonization and activation.

When carbonization of a carbonaceous material is required, it can be performed, for example, at 400 to 800°C, preferably 500 to 800°C, and more preferably 550 to 750°C, while blocking oxygen or air. Either gas activation or chemical activation can be used as the activation method, and both may be combined. Gas activation, which leaves less impurities behind, is particularly preferred. Gas activation can be performed by reacting the carbonized carbonaceous material with an activation gas (e.g., water vapor, carbon dioxide gas, etc.) at, for example, 750 to 1100°C, preferably 800 to 980°C, and more preferably 850 to 950°C. Considering the safety of the work and the reactivity of the carbonaceous material, the activation gas is preferably a water vapor-containing gas containing 10 to 40% by volume of water vapor. There are no particular limitations on the activation time and the heating rate, and they can be selected appropriately depending on the type, shape, and size of the carbonaceous material selected.

The carbonaceous material is not particularly limited, but examples thereof include plant-based carbonaceous materials (e.g., plant-derived materials such as wood, sawdust, charcoal, fruit shells such as coconut shells and walnut shells, fruit seeds, pulp manufacturing by-products, lignin, and blackstrap molasses), mineral-based carbonaceous materials (e.g., mineral-derived materials such as peat, lignite, brown coal, bituminous coal, anthracite, coke, coal tar, coal pitch, petroleum distillation residue, and petroleum pitch), synthetic resin-based carbonaceous materials (e.g., synthetic resin-derived materials such as phenolic resin, polyvinylidene chloride, and acrylic resin), and natural fiber-based carbonaceous materials (e.g., natural fibers such as cellulose, and natural fiber-derived materials such as recycled fibers such as rayon). These carbonaceous materials can be used alone or in combination of two or more types. Among these carbonaceous materials, coconut shells and phenolic resins are preferred from the viewpoint of obtaining a molded body having the above-mentioned characteristics, and coconut shells are more preferred.

After activation, the activated carbon may be washed to remove ash and chemicals, especially when using plant-based carbonaceous materials such as coconut shells or mineral-based carbonaceous materials. An acid is used for washing, and hydrochloric acid is preferred as the acid because of its high cleaning efficiency. After pickling, the acid is thoroughly washed away with water.

The activated carbon of this embodiment may be in any form, such as powder, particles, or fibers (thread, woven fabric (cloth), felt), etc., and may be appropriately selected depending on the application, but particles are preferred because they have high adsorption performance per volume.

The particle size of the activated carbon in this embodiment is not particularly limited, but the 50% particle size (D50) in the cumulative particle size distribution based on volume is preferably about 120 to 170 μm, more preferably about 125 to 165 μm, and even more preferably about 130 to 160 μm. If the activated carbon has a particle size in this range, it becomes easier to obtain a molded body that can efficiently remove decomposition products generated from the additives from the plating solution while suppressing the removal of the additives. In this embodiment, the above D50 value is a value measured by a laser diffraction/scattering method, and can be measured, for example, by a wet particle size distribution measuring device (Microtrac MT3300EX II) manufactured by Nikkiso Co., Ltd.

(binder)
The molded body of this embodiment preferably contains a fibrous binder. The fibrous binder is not particularly limited as long as it can be shaped by entangling the activated carbon, can be mixed with the activated carbon after pickling, and has acid resistance to enable the filter to be used in an acidic plating solution, and can be widely used regardless of whether it is a synthetic product or a natural product. Examples of such binders include acrylic fibers, polyethylene fibers, polypropylene fibers, polyacrylonitrile fibers, cellulose fibers, nylon fibers, aramid fibers, and pulp. The fiber length of the fibrous binder is preferably 4 mm or less.

Two or more of these fibrous binders may be used in combination. It is particularly preferable to use polyacrylonitrile fiber or cellulose pulp as the binder. This can further increase the density and strength of the molded body and suppress performance degradation.

In this embodiment, the water permeability of the fibrous polymer binder is about 10 to 150 mL in terms of CSF value. In this embodiment, the CSF value is a value measured in accordance with JIS P 8121-2:2012 (Pulp - Freeness test method - Part 2: Canadian standard freeness method). The CSF value can be adjusted, for example, by fibrillating the binder.

If the CSF value of the fibrous polymer binder is less than 10 mL, liquid permeability may not be achieved and pressure loss may increase. On the other hand, if the CSF value exceeds 150 mL, the powdered activated carbon may not be sufficiently retained, resulting in a molded body with low strength and poor adsorption performance.

The mixing ratio of activated carbon and fibrous binder in the molded body of this embodiment is preferably about 4.0 to 6.0 parts by mass of fibrous binder per 100 parts by mass of activated carbon, from the viewpoints of the adsorption effect of decomposition products in the plating solution, moldability, etc. If the amount of fibrous binder is less than 4.0 parts by mass, there is a risk that sufficient strength cannot be obtained and the molded body cannot be molded. Furthermore, if the amount of fibrous binder exceeds 6.0 parts by mass, there is a risk that the adsorption performance will decrease. It is more preferable to mix 4.5 to 5.5 parts by mass of fibrous binder.

(Modification of Filter for Refining Plating Solution)
The filter for refining a plating solution according to the present embodiment may be a cylindrical filter having a center core in addition to the molded body. The cylindrical shape has the advantage of being able to reduce the resistance to liquid passage.

The core that can be used in this embodiment is not particularly limited as long as it can be inserted into the hollow portion of a cylindrical molded body and reinforce the molded body, but for example, a trical pipe, a netron pipe, a ceramic filter, or a cylindrical nonwoven fabric laminated pipe is preferable. Furthermore, nonwoven fabric can be wrapped around the outer periphery of the core.

The plating solution refining filter of this embodiment may also have a nonwoven fabric wrapped around the outer periphery of a cylindrical molded body, and may also have gaskets bonded to both end faces of the molded body.

(How to use filters for refining plating solutions)
The plating solution purification filter of the present embodiment is used by immersing it in a plating solution tank that contains a plating solution. By circulating the plating solution through the filter, it is possible to adsorb and remove decomposition products generated from the additives while suppressing removal of the additives in the plating solution.

(Method for manufacturing molded body)
The molded body included in the filter for refining a plating solution according to the present embodiment can be manufactured by any method, and is not particularly limited. The slurry suction method is preferred in terms of efficient manufacturing.

As an example, the manufacturing method of the cylindrical molded body of this embodiment is described in detail below, but the present invention is not limited to this.

Specifically, for example, a cylindrical molded body can be obtained by a manufacturing method including a slurry preparation process in which powdered activated carbon and a fibrous binder are dispersed in water to prepare a slurry, a suction filtration process in which the slurry is filtered while being suctioned to obtain a preformed body, a drying process in which the preformed body is dried to obtain a dried molded body, and, if necessary, a grinding process in which the outer surface of the molded body is ground.

(Slurry preparation process)
In this embodiment, in the slurry preparation step, a slurry is prepared by dispersing powdered activated carbon and a fibrous binder in a solvent so that, for example, the fibrous binder is 4.5 to 5.5 parts by mass per 100 parts by mass of activated carbon, and the solid content concentration is 4.0 to 6.0% by mass (particularly preferably 4.5 to 5.5% by mass). The solvent is not particularly limited, but it is preferable to use water or the like. If the solid content concentration of the slurry is too high, there is a problem that the dispersion is likely to become non-uniform and the molded body is likely to have spots. On the other hand, if the solid content concentration is too low, not only will the molding time be long and the productivity will decrease, but the density of the molded body will increase, and clogging will easily occur due to the capture of turbid components.

(Suction filtration process)
Next, in the suction filtration step, for example, as shown in Fig. 1, a core as described above is attached to a cylindrical molding frame 1 having a large number of small suction holes 3 on the surface of a core body 2 and flanges 4, 4' attached to both ends, and the core is immersed in the slurry contained in a container, and the slurry is filtered while being sucked from the inside of the frame 1 through a filtrate discharge port 5, thereby attaching the slurry to the frame 1. As a suction method, a conventional method such as a method of sucking using a suction pump or the like can be used. The preform 7 is compressed to a predetermined diameter while attached to the frame 1.

(Drying process)
After the preform 7 is molded by the suction filtration process, the flanges 4, 4' at both ends of the mold 1 are removed, and the core 2 is pulled out to obtain the preform 7 having a hollow cylindrical shape. In the drying process, the preform 7 removed from the mold 1 is dried in a dryer or the like to obtain the molded body 6 (the molded body of this embodiment) shown in Fig. 2.

The drying temperature is, for example, about 100 to 150°C (particularly 110 to 130°C), and the drying time is, for example, about 4 to 24 hours (particularly 8 to 16 hours). If the drying temperature is too high, the fibrous binder may be altered or melted, leading to a decrease in the filtering performance and strength of the molded body 6. If the drying temperature is too low, the drying time may be long or drying may be insufficient.

(Grinding process)
If necessary, after the drying step, a grinding step can be performed to further adjust the outer diameter of the filter or to reduce unevenness on the outer peripheral surface. The grinding means used in this embodiment is not particularly limited as long as it can grind (or polish) the outer surface of the dried molded body 6, and a conventional grinding method can be used, but from the viewpoint of grinding uniformity, a method using a grinding machine that rotates and grinds the molded body 6 itself is preferred.

The grinding process is not limited to the method using a grinding machine. For example, the molded body 6 fixed to a rotating shaft may be ground with a fixed flat grinding wheel. In this method, the generated grinding swarf tends to accumulate on the grinding surface, so it is effective to grind while blowing air.

The molded body thus obtained can be used as the filter for purifying a plating solution of this embodiment. For example, after producing the molded body by the above-mentioned production method, the molded body can be cut into a desired size and shape depending on the amount of plating solution to be processed, etc., to obtain a filter for purifying a plating solution. Furthermore, if necessary, a core may be inserted into the hollow part of the molded body, a cap may be attached to the tip part of the molded body, or a nonwoven fabric may be wrapped around the outer periphery of the molded body.

(Adsorbent for refining plating solution)
The adsorbent for purifying a plating solution according to another embodiment of the present invention is an adsorbent for purifying a plating solution made of activated carbon, in which the iodine adsorption amount per unit mass is 1000 to 1400 mg/g, the ash content of the activated carbon is 0.5 mass% or less, and the chloride content of the activated carbon is 0.0030 mass% or less. The reasons for specifying the iodine adsorption amount, the ash content, and the chloride content are the same as the reasons for specifying these items of the activated carbon described above.

By using the adsorbent for purifying a plating solution according to this embodiment, it is possible to efficiently remove decomposition products generated from the additives from the plating solution while suppressing the removal of the additives, and it is also possible to suppress the elution of chlorine and ash into the plating solution. The adsorbent for a plating solution according to this embodiment can be used in the above-mentioned filter for purifying a plating solution.

As mentioned above, this specification discloses various aspects of the technology, the main technologies of which are summarized below.

The filter for purifying a plating solution according to one embodiment of the present invention includes a molded body containing an adsorbent made of activated carbon and having an iodine adsorption amount per unit mass of 930 to 1,300 mg/g, and the chloride ion concentration of the filtrate collected after filtering raw water having a chloride ion concentration of 6.0 to 9.0 mg/L, a pH of 6.9 to 7.5, and an electrical conductivity of 90 to 130 μS/cm for 1 minute is equal to or less than the chloride ion concentration of the raw water.

This configuration makes it possible to provide a filter for purifying a plating solution that can efficiently remove decomposition products generated from the additives while suppressing the removal of the additives, and can also suppress the elution of chlorine into the plating solution.

The above-mentioned plating solution purification filter may have an electrical conductivity of the filtered water that is equal to or less than the electrical conductivity of the raw water plus 5 μS/cm. This makes it possible to suppress the elution of metal components and the like into the plating solution, and to form high-quality plating.

In the above-mentioned plating solution purification filter, the molded body may contain a fibrous binder. This makes it difficult for the molded body to lose its shape, and it is possible to efficiently remove decomposition products generated from the additives from the plating solution while stably suppressing the removal of the additives over a long period of time.

In the above-mentioned plating solution purification filter, the activated carbon may be made from coconut shells. This allows the plating solution purification filter to be manufactured at low cost.

The plating solution purification filter may have a methylene blue circulation adsorption count of 4 to 12 times. This allows the decomposition products generated from the additives to be efficiently removed from the plating solution while suppressing the removal of the additives.

The plating solution purification filter may have a ratio of the volume of pores of the activated carbon having a diameter of 1.0 nm or more and 1.5 nm or less, measured by the MP method, to the total pore volume of the activated carbon measured at a pore volume calculation relative pressure of 0.990, of 2.3% or more. This makes it possible to efficiently remove decomposition products generated from the additives from the plating solution while suppressing removal of the additives.

The plating solution purification filter may have an average pore size of the activated carbon measured by the MP method of 1.70 nm or more and 1.92 nm or less. This makes it possible to efficiently remove decomposition products generated from the additives from the plating solution while suppressing removal of the additives.

Another aspect of the present invention is an adsorbent for purifying a plating solution, which is made of activated carbon and has an iodine adsorption amount per unit mass of 1000 to 1400 mg/g, an ash content of the activated carbon of 0.5 mass% or less, and a chloride content of the activated carbon of 0.0030 mass% or less.

This configuration makes it possible to provide an adsorbent for plating solution purification to obtain a filter for plating solution purification that can efficiently remove decomposition products generated from additives while suppressing removal of the additives, and can also suppress the elution of chlorine into the plating solution.

The present invention will be described in more detail below with reference to examples, but these examples are not intended to limit the present invention in any way.

First, we will explain the manufacturing methods for the activated carbon, molded bodies, and filters prepared in each example shown in Tables 1 to 3.

[Raw materials for molded bodies]
(Granular activated carbon)
The raw material for granular activated carbons 1 to 11 was coconut shells. The coconut shell char carbonized at 400°C to 600°C was activated with steam at 900°C to 950°C. The activation time was adjusted so as to achieve the target amount of iodine adsorption. The activated carbon after activation was designated as granular activated carbon 11.

The activated carbon was washed with dilute hydrochloric acid, then washed with ion-exchanged water, and dried at 120°C to obtain granular activated carbon. The washed and dried activated carbon was designated granular activated carbon 7 to 9.

The washed and dried activated carbon was further heat-treated in LPG combustion gas with a heat treatment temperature of 700°C and a water vapor partial pressure of approximately 40%. The heat-treated activated carbon was designated granular activated carbon 1 to 6 and 10.

(Activated carbon fiber)
Phenol resin was used as the raw material for the fibrous activated carbon 1. Phenol-based resin fiber ("KT-2800" manufactured by Gun-ei Chemical Industry Co., Ltd.) was heat-treated in LPG combustion gas at 980° C. to obtain the fibrous activated carbon 1 (2 denier, 800,000 fibers).

(fibrous binder)
As the fibrous binder, "Fibrillated acrylic pulp Bi-PUL/F" manufactured by Nippon Exlan Kogyo Co., Ltd. was used.

[Production of Molded Body]
(Slurry using granular activated carbon)
Granular activated carbons 1 to 10 were pulverized in a ball mill and then classified using a JIS standard sieve with an upper mesh of 80 mesh and a lower mesh of 325 mesh to obtain powdered activated carbons having the particle size (D50) shown in Table 2.

0.11 kg of the fibrous binder (solid content: 55 mL of CSF) was added to 2.0 kg of the powdered activated carbon, and the mixture was stirred and dispersed in tap water to prepare 30 L of slurry.

(Slurry using fibrous activated carbon)
1 kg of fibrous activated carbon 1 was added to 0.055 kg (CSF = 55 mL) of the above fibrous binder in terms of solid content and 100 L of tap water, and the mixture was placed in a small beater and beaten to form a slurry so that the density of the molded body for measuring the beaten density was 0.22 g/mL.

The density of the molded body for measuring the beaten density, which was made from the beaten slurry, was measured as follows. A 300-mesh wire mesh was wrapped around the central axis (core) of a mold (frame) with an outer diameter of 40 mm and an outer diameter flange spacing of 50 mm, which has a number of small suction holes (diameter 3 mm, pitch 5 mm) as shown in Figure 1, so that the outer diameter was 18 mm. The slurry was sucked using this mold to make a cylindrical molded body for measuring the beaten density, and the density (beaten density) of the molded body was calculated from the weight and dimensions after drying.

(Molding of slurry)
The obtained slurry was sucked into a mold (frame) having a shape as shown in Figure 1, an outer diameter of 63 mm, a center axis (core) diameter of 30 mm, and a flange-to-flange length of 245 mm, and equipped with a center axis filter (MF filter manufactured by Asahi Textile Industries Co., Ltd., nominal mesh size 30 μm, inner diameter 30 mm, outer diameter 33 mm, length 245 mm) until the outer diameter of the preform molded body obtained by sucking the slurry became approximately 65 mm, which was approximately 2 mm larger than the outer diameter of the mold.

The resulting preform was then compressed and molded (rolling molding) by pressing it down with a plate while rotating until it had the same outer diameter as the mold, and then removed from the mold and dried to complete a cylindrical molded body as shown in Figure 2. A single layer of nonwoven fabric (Spunbond nonwoven fabric "Elves T0703WDO" manufactured by Unitika Ltd.) was wrapped around the outer periphery of the completed molded body, and packings made by punching out a 2 mm thick foamed polyethylene sheet into a doughnut shape with an outer diameter of 63 mm and an inner diameter of 30 mm were attached to both ends of the molded body with a 0.5 mm thick hot melt adhesive, and the length was adjusted to 250 mm to complete a filter for purifying plating solution. This molded body or filter was used in Tests No. 1 to 12.

Next, we will explain how to evaluate the activated carbon and molded bodies prepared in each example shown in Tables 1 to 3, as well as how to evaluate the filtered water obtained in each example.

[Ash and chloride content in activated carbon, iodine adsorption amount on activated carbon]
The amount of iodine adsorption (activated carbon iodine adsorption amount) of the activated carbon before mixing with the binder was measured according to the measurement method for "iodine adsorption performance" specified in JIS K 1474: 2014 (activated carbon test method). The ash content and chloride content in the activated carbon were also measured according to the method specified in the above JIS.

[Measurement of metal (Na, K) content in activated carbon]
10 mL of concentrated nitric acid (1.38) was added to 0.1 g of a sample of activated carbon before mixing with the binder, and microwaves were applied using a parallel scale-up microwave synthesis device (CEM's "Microwave MARS6") to produce an activated carbon decomposition liquid.

The elemental contents in the decomposition liquid obtained were measured using a multi-type ICP emission spectrometer (Shimadzu Corporation, ICPE-9820). The elemental contents in the activated carbon were calculated based on the obtained elemental contents. The Na and K contents shown in Table 1 are the values calculated in this way per 1 kg of activated carbon.

[Measurement of activated carbon particle size]
The particle size (D50) of each activated carbon after pulverization in a ball mill was measured by the laser diffraction measurement method described below. That is, the activated carbon to be measured was placed in ion-exchanged water together with a surfactant, ultrasonic vibration was applied to prepare a uniform dispersion, and the particle size distribution was measured using a particle size distribution measuring device (Microtrac MT3300EX-II manufactured by Microtrac-Bell). As the surfactant, "Polyoxyethylene (10) octylphenyl ether" manufactured by Wako Pure Chemical Industries, Ltd. was used. The analysis conditions are shown below.

(Analysis conditions)
Number of measurements: Average value of 3 measurements Measurement time: 30 seconds Distribution display: Volume particle size classification: Standard Calculation mode: MT3000II
Solvent name: WATER
Upper measurement limit: 2000μm, lower measurement limit: 0.021μm
Residual ratio: 0.00
Passing ratio: 0.00
Residual ratio setting: Ineffective particle transmittance: Absorbing particle Refractive index: N/A
Particle shape: N/A
Solvent refractive index: 1.333
DV value: 0.0882
Transmittance (TR): 0.800-0.930
Extended filter: Invalid Flow rate: 70%
Ultrasonic output: 40W
Ultrasonic time: 180 seconds

[Measurement of specific surface area, pore volume, and average pore diameter of activated carbon in molded body]
The molded body before the attachment of the peripheral nonwoven fabric and packing was arbitrarily cut with a cutter knife at a position 115 mm from the end face in the longitudinal direction to a volume of about 6 mL as shown in Figure 3. The cut sample was placed in a crucible and heated at 700 ° C in a nitrogen atmosphere for 1 hour, and then cooled to room temperature in a nitrogen atmosphere to prepare a sample for measuring the specific surface area and pore volume. Using this sample, the specific surface area and pore volume of the activated carbon in the molded body were calculated by the following method.

The specific surface area S1 (m ² /g) was determined by measuring the nitrogen adsorption isotherm at 77K using a high-precision fully automatic gas adsorption apparatus ("BELSORP-mini" manufactured by Microtrack-Bell Corporation) and by the BET method.

The total pore volume V1 (mL/g) was determined from the amount of nitrogen adsorbed using the high-precision fully automatic gas adsorption apparatus. Specifically, the nitrogen adsorption amount (V) measured using the high-precision fully automatic gas adsorption apparatus at a pore volume calculation relative pressure of 0.990 was converted to the volume of liquid nitrogen (Vp) using the following formula (1), and the obtained value of Vp was taken as the total pore volume V1 (mL/g). In formula (1), Mg is the molecular weight of the adsorbate (nitrogen) (28.013), and ρg (g/cm ³ ) is the density of the adsorbate (nitrogen) (0.808 g/cm ³ ).
Vp=V×Mg/(22414×ρg)…(1)

The average pore diameter D1 (nm) was calculated from the total pore volume V1 (mL/g) and the specific surface area S1 (m ² /g) according to the following formula (2), assuming that the pores were cylindrical.
D1=(V1/S1)×4×1000…(2)

The nitrogen gas adsorption isotherm was analyzed using the MP method, and the total pore volume (mL/g) of pores with diameters in the range of 1.0 to 1.5 nm was calculated. NGCB-BEL.t was used for the reference curve.

[Molded body iodine adsorption amount]
A sample is cut out at the same position and size as the sample used for measuring the specific surface area of the activated carbon in the molded body. The cut out sample is cut into sample pieces of different sizes and dried at 115°C for 3 hours. After drying, the weight of the sample cooled in a desiccator is measured, and each sample piece is loosened with a spatula to remove lumps, and used as a sample for measuring the iodine adsorption amount of the molded body. Using these samples, the iodine adsorption amount of the molded body was measured according to the measurement method for "iodine adsorption performance" specified in JIS K 1474:2014 (activated carbon test method).

[Methylene Blue (MB) Circulation Number]
The cylindrical molded body wrapped with nonwoven fabric was cut to a thickness of 16.3 mm, and gaskets were attached to both ends with hot melt to prepare a sample filter for measuring the number of MB circulations. The gasket was made by punching out a 2 mm thick foamed polyethylene sheet into a doughnut shape with an outer diameter of 63 mm and an inner diameter of 30 mm. The aqueous solution for measuring the number of MB circulations (aqueous MB solution) was made by adding methylene blue (MB) to ion-exchanged water to a concentration of about 120 mg/L. The column in which the sample filter was set was a homemade one with an inner diameter of 70 mm, with a structure that allowed both ends of the sample filter to be sealed with ribs.

A sample filter was set in the column, and 2 L of MB aqueous solution was circulated through the sample OUT-IN at 20°C and a flow rate of 0.56 L/min. If the MB concentration in the MB aqueous solution 30 minutes after the start of the flow was 2 mg/L or less, further MB was added so that the concentration was approximately 120 mg/L. This procedure was repeated until the MB concentration 30 minutes after the MB addition exceeded 2 mg/L. The number of repetitions (the number of MB additions plus 1) until the MB concentration 30 minutes after the start of the flow or the MB addition exceeded 2 ppm was defined as the MB circulation number.

The pump used for circulating the solution was Yamato Scientific's "Digital Pump 07522-20." The concentration of MB in the MB aqueous solution was measured using an ultraviolet-visible spectrophotometer (Shimadzu Corporation's "UV-1800") at a wavelength of 665 nm, after diluting the MB aqueous solution with ion-exchanged water.

[Raw water]
The raw water for filtration was prepared by filtering tap water through activated carbon for water purification and adjusting the water temperature to 20±3° C. The pH of the raw water was 6.9 to 7.5. The chloride ion concentration and electrical conductivity of the raw water used in each example were as shown in Table 3.

[Measurement of chloride ion concentration in raw water and filtered water]
A filter for purifying plating solution, which includes a molded body, a nonwoven fabric wound around the outer periphery of the molded body, and packings bonded to both ends of the molded body, was set in a plastic housing ("1PA" manufactured by Advantec Co., Ltd.), raw water was passed through at a flow rate of 10 L/min, 100 ml of the filtrate was sampled 1 minute after the filtrate, which was obtained by filtering the raw water, started to come out of the outlet of the plastic housing, and the chloride ion concentration was measured under the following conditions using an ion chromatograph ("INTEGRION" manufactured by Thermo Fisher Scientific Co., Ltd.). 100 ml of unfiltered raw water was also sampled, and the chloride ion concentration was measured in the same manner. When the chloride ion concentration of the filtrate was equal to or lower than the chloride ion concentration of the raw water, the chlorine elution judgment was "○" (acceptable), and when the chloride ion concentration of the filtrate was higher than the chloride ion concentration of the raw water, the chlorine elution judgment was "×" (not acceptable).

(Ion Chromatography Conditions)
Column: AS23 4×250 mm and AS23 4×50 mm
Suppressor: AERS 500 Carbonate 4mm
Eluent: 4.5 M sodium carbonate + 0.8 mM sodium bicarbonate solution (ultrapure water)

[Measurement of electrical conductivity of raw water and filtered water]
The electrical conductivity of the filtered water and raw water sampled for measuring the chloride ion concentration was measured using a pH meter ("LAQUA F-74" and "Tou pH electrode 9615S-10D" manufactured by Horiba Advanced Techno Co., Ltd.).

[Polyethylene glycol (PEG) removal performance evaluation]
The PEG removal performance evaluation was carried out for the purpose of evaluating the filter's ability to remove decomposition products from the plating solution. In the PEG removal performance evaluation test, the plating solution was replaced with ion-exchanged water, the additive (high molecular weight organic compound) added to the plating solution was replaced with polyethylene glycol 20,000 (PEG20000), and the decomposition products (low molecular weight organic compounds) generated from the additives in the plating solution were replaced with polyethylene glycol 400 (PEG400).

To assess PEG removal performance, a sample filter similar to the one used to measure MB circulation frequency was used.

Two types of aqueous PEG solutions were used: PEG 20000 or PEG 400 was added to ion-exchanged water so that the TOC concentration was approximately 1,650 mg/L.

A sample filter was placed in the column, and 5 L of PEG aqueous solution was circulated through the sample at OUT-IN at a flow rate of 0.5 L/min at 20°C. The TOC concentration in the PEG aqueous solution was measured 3 hours after the start of the flow, and the removal rates of PEG 20000 and PEG 400 from the PEG aqueous solution before the flow was started were calculated.

Since it is preferable for the plating solution purification filter of the present invention to remove only decomposition products without removing additives as much as possible, PEG20000, which corresponds to additives, is deemed to pass if it has a removal rate of 25% or less, and PEG400, which corresponds to decomposition products, is deemed to pass if it has a removal rate of 25% or more. Those that met both the PEG20000 removal rate of 25% or less and the PEG400 removal rate of 25% or more were given a removal performance rating of "○" (acceptable), and those that did not were deemed to pass were deemed to pass an "×" (not acceptable).

The pump used for circulating the liquid was Yamato Scientific's "Digital Pump 07522-20." The TOC concentration in the PEG aqueous solution was measured using a total organic carbon meter (Shimadzu Corporation's "TOC-Lcsh ASI-L").

[Plating finish judgment]
Using the plating solution filtered through a plating refinement filter, plate-shaped nickel test pieces were copper-plated, and the finished product was visually inspected. Products that could be used as plated products were rated as "Good", products that could be used as plated products were rated as "Good", and products that were unusable due to uneven color or thickness were rated as "Poor".

The measurement and evaluation results for each of the above items are shown in Tables 1 to 3. Table 1 shows the measurement and evaluation results for the activated carbon before crushing or beating. Table 2 shows the measurement and evaluation results for the filter and the activated carbon in the filter. Table 3 shows the measurement results for the raw water and the filtered water, an evaluation of the filter performance, and an evaluation of the plating finish.

(Discussion)
The filter for purifying a plating solution of this embodiment (an example of the present invention) was able to efficiently remove PEG 400 from a PEG solution while suppressing the removal of PEG 20000, and was also able to suppress the elution of chlorine into the PEG solution, demonstrating excellent removal performance. Furthermore, when plating was performed using a plating solution filtered through the filter for purifying a plating solution of this embodiment, the result was excellent in the finish.

In contrast, the plating solution refining filter of the comparative example was inferior in terms of removal performance or suppression of chlorine elution. Furthermore, when plating was performed using a plating solution filtered through the plating solution refining filter of the comparative example, the finish was inferior.

From the above, it was confirmed that the plating solution refining filter of the present invention can efficiently remove decomposition products generated from additives from the plating solution while suppressing the removal of additives from the plating solution, and can also suppress the elution of chlorine into the plating solution. In addition, when the plating solution refining filter of the present invention is used, the finished plated product obtained is good, confirming its usefulness as a plating solution refining filter.

This application is based on Japanese Patent Application No. 2018-245928, filed on December 27, 2018, the contents of which are incorporated herein by reference.

In order to express the present invention, the present invention has been properly and sufficiently described above through the embodiments with reference to specific examples, etc., but it should be recognized that a person skilled in the art can easily modify and/or improve the above-mentioned embodiments. Therefore, as long as the modification or improvement made by a person skilled in the art is not at a level that deviates from the scope of the claims described in the claims, the modification or improvement is interpreted as being included in the scope of the claims.

The present invention has broad industrial applicability in the technical fields of filters for purifying plating solutions and adsorbents for purifying plating solutions.

Claims (5)

A filter for purifying a plating solution,
The present invention is provided with a molded body containing an adsorbent made of activated carbon and having an iodine adsorption amount per unit mass of 930 to 1300 mg/g,
raw water having a chloride ion concentration of 6.0 to 9.0 mg/L, a pH of 6.9 to 7.5, and an electrical conductivity of 90 to 130 μS/cm is filtered for 1 minute, and the chloride ion concentration of filtrate collected is equal to or lower than the chloride ion concentration of the raw water;
The activated carbon has a chloride content of 0.0030% by mass or less,
A plating solution purification filter in which the number of times of methylene blue circulation adsorption is 4 to 12 times, which is the number of times (the number of times methylene blue was added plus 1) that a cycle of circulating and passing 2 L of an aqueous methylene blue solution having an initial concentration of 120 mg/L through the plating solution purification filter and continuing circulation and passing the solution if the concentration of the aqueous methylene blue solution 30 minutes after the start of passing the solution is 2 mg/L or less, is repeated until the concentration of the aqueous methylene blue solution 30 minutes after the addition of the methylene blue exceeds 2 mg/L . The filter for purifying a plating solution according to claim 1, wherein the electrical conductivity of the filtered water is equal to or less than the electrical conductivity of the raw water plus 5 μS/cm. The filter for refining a plating solution according to claim 1 or 2, wherein the molded body contains a fibrous binder. 4. The filter for refining a plating solution according to claim 1, wherein a ratio of a volume of pores having a diameter of 1.0 nm or more and 1.5 nm or less of the activated carbon measured by an MP method to a total pore volume of the activated carbon measured at a pore volume calculation relative pressure of 0.990 is 2.3% or more . The filter for refining a plating solution according to any one of claims 1 to 4 , wherein the activated carbon has an average pore size measured by an MP method of 1.70 nm or more and 1.92 nm or less.

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