JPH10183359A - Treatment of electroless plating bath - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a treatment method for an electroless plating bath capable of easily, surely and inexpensively removing phosphorus acid ions from the aged electroless plating bath in which a large amt. of the phosphorus acid ions accumulate without introducing impurities therein, capable of easily recovering nickel sulfate from the formed and separated nickel phosphite and capable of effectively utilizing the plating bath components or the phosphorus acid ions as a reaction medium. SOLUTION: The operations to adding the nickel sulfate to the electroless plating bath which is prepd. by using a water-soluble nickel salt, its complexing agent and sodium hypophosphite as a reducing agent as essential components and in which the phosphite accumulates to form and settle the nickel phosphite, removing the nickel phosphite to regenerate the electroless plating bath and reusing the bath are repeated. Sulfuric acid or the sulfuric acid and sodium sulfate are added to the separated nickel phosphite to form the nickel sulfate and sodium phosphite or sodium hypophosphite from nickel phosphite and the resulted nickel sulfate is recovered.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION The present invention occurs when an electroless plating bath such as an electroless nickel plating bath using hypophosphorous acid or hypophosphite such as sodium hypophosphite as a reducing agent is regenerated. The present invention relates to a method for treating an electroless plating bath, which can effectively treat nickel phosphite and enables the electroless plating bath to be used repeatedly without waste.

[0002]

2. Description of the Related Art Electroless plating using sodium hypophosphite as a reducing agent, particularly electroless nickel plating (electroless Ni-P plating), has been widely used in various fields. ing. In this type of electroless plating, plating is performed by reducing metal ions by the reducing action of hypophosphite ions and precipitating them on the object to be plated.

Accordingly, as the plating proceeds, the metal ions and hypophosphite ions in the plating bath decrease, and the deposition rate decreases and the composition of the precipitate (for example, Ni and P in a Ni-P plating bath). Alloy composition) changes. For this reason,
Insufficient metal ions and hypophosphite ions are appropriately replenished, the concentration of these ions is returned to the initial level, and plating is continued.

However, as described above, the hypophosphite ion
When reducing metal ions by reduction, hypophosphorous acid
The ions are oxidized to form phosphite ions (H_TwoPO _Three ^-)But
It forms and accumulates gradually in the plating bath.

This phosphite ion (H_TwoPO _Three ^-)
A small amount has little effect on plating, but a large amount
For example, 50 to 100 g / L or more, especially 150 g /
If it exceeds L, the plating may be affected.
Problems with the adhesion between the plating object and the plating film
Deposits in the plating film and adversely affects its uniformity and corrosion resistance.
To dissolve the plating bath,
There is a case.

Therefore, when performing electroless Ni-P plating, three to ten turns (one turn is the first electroless Ni-P plating)
The total amount of nickel ions contained in the -P plating bath was consumed or precipitated. For example, if 6 g / L of nickel ions were present in the first electroless Ni-P plating bath, 6 g / L The case where nickel ions are consumed or precipitated is defined as one turn. Therefore, in this case, 3 to 10 turns mean that the nickel ions have been consumed or precipitated at 18 to 60 g / L. ) After use, electroless Ni-P
The fact is that the plating bath was discarded.

[0007] Accordingly, the life of the electroless Ni-P plating bath is relatively short, and the waste liquid treatment accompanying the disposal of the electroless Ni-P plating bath has become an industrial problem. Although a method for regenerating an electrolytic Ni-P plating bath has been proposed, the conventional regenerating method requires a complicated treatment method, harmful impurity ions are mixed into the regenerated plating bath, and equipment cost is reduced. Due to problems such as high cost, it has not been widely implemented.

[0008] From such a point, the present inventors have previously included hypophosphorous acid or a salt thereof as a water-soluble nickel salt, a complexing agent and a reducing agent, and reduced the concentration of hypophosphorous acid or a salt thereof by plating. The water-soluble nickel salt was added to the aging solution of the electroless nickel plating bath containing 100 g / L or more of the phosphite ion generated by oxidation in an amount of 0.5 to 1 mol of the phosphite ion.
A method for regenerating an electroless nickel plating bath, characterized in that nickel phosphite is formed and precipitated by adding it in a molar ratio of not less than 1, and this precipitate is removed (Japanese Patent Laid-Open No. 5-2 / 1993).
No. 47660).

[0009] However, the nickel phosphite separated in this manner is not considered to be used effectively, and no effective reuse cycle of the electroless plating bath has been proposed at present. there were.

[0010] An object of the present invention is to effectively treat nickel phosphite generated when an electroless plating bath using hypophosphorous acid or a salt thereof as a reducing agent is regenerated, and in particular to use the electroless nickel plating bath without waste. An object of the present invention is to provide a method for treating an electroless plating bath that can be used repeatedly.

[0011]

SUMMARY OF THE INVENTION In order to achieve the above object, the present invention provides an electroless plating bath in which hypophosphorous acid or a salt thereof is used as a reducing agent and phosphite ions are accumulated. A nickel phosphite is formed by adding a water-soluble nickel salt to the mixture, and separated from the plating bath. Sulfuric acid or sulfuric acid and sodium sulfate are added to the separated nickel phosphite to form nickel phosphite. To a nickel sulfate and phosphorous acid or monosodium phosphite, and recovering the obtained nickel sulfate.

The present invention also provides a method for treating an electroless nickel plating bath, which comprises, as main components, a water-soluble nickel salt, a complexing agent thereof, and sodium hypophosphite as a reducing agent. It is necessary to add nickel sulfate to the electroless nickel plating bath in which nickel has been accumulated to form and precipitate nickel phosphite, remove the nickel phosphite, regenerate the electroless nickel plating bath, and reuse it. At the same time, sulfuric acid or sulfuric acid and sodium sulfate are added to the separated nickel phosphite to convert the nickel phosphite into nickel sulfate and phosphorous acid or monosodium phosphite, and the obtained nickel sulfate is recovered. And a method for treating an electroless nickel plating bath.

[0013] In this case, nickel sulfate recovered by adding sulfuric acid or sulfuric acid and sodium sulfate to the nickel phosphite is added to a plating bath for converting the phosphite to nickel phosphite. It is effective to use it as a raw material. Further, cooling the plating bath from which the nickel phosphite has been removed to a temperature lower than room temperature,
It is recommended to deposit and precipitate sodium sulfate from this plating bath and remove it from the viewpoint of repeated use of the electroless nickel plating bath. This sodium sulfate is preferably used as a sodium sulfate raw material added to convert nickel phosphite to monosodium phosphite.

That is, the present inventor has found that by adding sulfuric acid or sulfuric acid and sodium sulfate to nickel phosphite, nickel phosphite becomes nickel sulfate and phosphorous acid or monosodium phosphite. It has been found that the obtained nickel sulfate can be reused as a water-soluble nickel salt for forming an electroless plating bath or as a water-soluble nickel salt for precipitating nickel phosphite, and can be recycled. Things.

Hereinafter, the present invention will be described in more detail.
The electroless plating bath to be treated according to the present invention contains, as a main component, a water-soluble salt of a metal to be electrolessly deposited, a complexing agent thereof, and a hypophosphorous acid or a salt thereof as a reducing agent. Sulfate, sodium hypophosphite, and any type may be used as long as it is a type that can be continuously used by replenishing sodium hydroxide as a pH adjuster. For example, a single plating of electroless nickel, cobalt, copper, etc. Baths include alloy plating baths such as electroless nickel-cobalt, nickel-copper, nickel-tungsten, and cobalt-tungsten, and are particularly suitably applied to electroless nickel and nickel alloy plating baths. These electroless plating baths may be any of an acidic type, a neutral type, and an alkaline type, and may have a known composition.
In particular, it is preferably applied to an acidic bath having a pH of 3.5 to 6.5.

In this case, the electroless nickel plating bath contains a carboxylic acid such as nickel sulfate, citric acid, succinic acid, malic acid, acetic acid, lactic acid and salts thereof, other known complexing agents for nickel, and hypophosphorous acid. Those containing sodium as a main component are used. The concentration of these components is in a normal range, for example, nickel sulfate is 0.05 to 0.3 mol / L,
The amount of the complexing agent can be in the range of 1 to 5 mol / L per mol of nickel sulfate, and the amount of sodium hypophosphite can be in the range of 10 to 90 g / L. In addition, a stabilizer, a pH adjuster and the like can be added to this plating bath, and the pH of the electroless nickel plating bath can be made alkaline or acidic. However, the plating solution for continuous use has a pH of 3. 5 to 6.5, especially 4 to 6
It is usual that

The plating method using this electroless nickel plating bath can also adopt a usual method, but as the plating reaction progresses, the nickel ions and hypophosphite ions in the plating bath decrease and the pH decreases. . For this reason, nickel sulfate, as a supplement to the plating bath, continuously or intermittently,
While adding sodium hypophosphite, a pH increasing agent such as sodium hydroxide is added to maintain the nickel ion concentration, the hypophosphite ion concentration and the pH in the plating bath at predetermined concentrations. Thereby, good electroless plating can be performed for a long period of time. However, when phosphite ions generated by oxidation of hypophosphite ions accumulate in the plating bath, removal treatment is performed.

That is, the processing method of the present invention has the following
By using a plating bath, hypophosphite ion H_TwoPO _Two ^-
Consumption (oxidation) of phosphite (phosphite ion H_TwoP
O _Three ^-) Accumulated plating bath (in this case, the regeneration time is
It is appropriately selected and is not limited, but usually 50 g /
L or more, preferably 100 g / L or more, especially 15 g / L or more.
0g / L or more, and sometimes 200g / L or more
Plating bath), and is deposited from the above electroless plating bath.
Or the same as the constituent metal of the electroless plating film
Is the same metal as at least one of them when two or more are
Sulfate, for example, sulfuric acid for electroless nickel plating bath
Nickel is converted to metal ions in the plating bath
Add so that the concentration is higher than the concentration.

In this case, the amount added in this treatment may be higher than the metal ion concentration (normal plating control metal ion concentration) in the normal plating operation of the plating bath, but is preferably the plating control metal ion. It is preferable to add so that the concentration is more than 1 and 10 times by weight or less, preferably 1.2 to 10 times by weight, particularly 1.5 to 6 times by weight, in terms of formation and precipitation of poorly soluble phosphite. It is suitable.
The addition of the above-mentioned additive such as nickel sulfate is preferably 0.5 mol or more, preferably 1 mol or more, per 1 mol of phosphite ions.

In addition, an operation of raising the temperature of the electroless plating bath to a temperature higher than the plating operation temperature (normal plating control temperature) together with the addition of the additive, and changing the electroless plating bath to pH (normal Plating control pH)
It is preferable to perform one or both of the operations of raising the pH to a higher pH in order to more effectively generate and precipitate the hardly soluble nickel phosphite.

In this case, it is preferable that the former operation is performed at 5 ° C. or higher than the normal plating control temperature. For example, a common acidic electroless nickel plating bath is often plated at 90 ° C.
The temperature is raised to 5 ° C. or higher, particularly 97 ° C. or higher, and in some cases, to the boiling point. In the latter operation, it is preferable to raise the pH by 0.1 or more, particularly 1 or more, from the normal plating management pH,
For example, in the case of an acidic electroless plating bath having a pH of 4 to 6, it is preferable to set the pH as high as described above in the range of pH 4.5 to 12, preferably pH 7 to 10, particularly pH 8 to 9.

In addition, this pH adjustment is performed by adjusting the poorly soluble phosphite
This is important because nickel is effectively produced and precipitated.
You. That is, when electroless nickel plating is performed,
Hypophosphite ion H PO _Three ^2-Phosphorous by oxidation of
Acid ion H_TwoPO _Three ^-Is formed, which is dependent on the pH of the bath.
Therefore H_ThreePO _ThreeOr H PO _Three ^2-Changes to This place
If Ni²⁺To form poorly soluble nickel phosphite
Is precipitated by HPO _Three ^2-Because, as above
It adjusts the pH.

H_TwoPO _Two ^-+ H_TwoO = H_TwoPO _Three ^-+ 2H⁺+ 2e NaH_TwoPO_Three+ NaOH = Na_TwoHPO_Three+ H_TwoO Na_TwoHPO_Three+ NiSO_Four= NiHPO_Three+ Na_TwoSO_Four

As a method for increasing the pH of the plating bath, a method of adding an alkali hydroxide such as sodium hydroxide and a method of adding a metal hydroxide and a carbonate can be used. In the latter case, in the treatment for increasing the pH, since the pH is increased by the addition, the amount of addition of the metal ion may be smaller than in the treatment for adding the above-mentioned additive.

When carrying out this method of raising the pH, the plating bath may be at room temperature, but at a temperature of 40 to 90 ° C., particularly 50 to 70 ° C.
It is preferred that the temperature be raised to 0 ° C. and left.

In each of the above treatments, if necessary, the mixture is allowed to stand with stirring to form and precipitate a poorly soluble phosphite. In this case, the standing time is 30 minutes to 24 hours, particularly 1 to 5 hours. Is preferred.

Separation and removal of the formed precipitate can be carried out by a conventional method such as filtration. In this case, it is preferable to perform filtration at a high temperature, and a separate tank and a plurality of filtration devices are installed near the plating tank, and precipitation can be performed and filtration can be performed while one of the tanks is stopped. Alternatively, filtration may be performed in a separate tank.

The regenerated electroless plating bath can be used for plating again after adjusting the metal ion concentration, hypophosphite ion concentration, pH and the like. When acid ions are accumulated, by performing the regeneration treatment as described above, the acid ions can be used repeatedly, so that the life of the electroless plating bath can be extended.

On the other hand, the separated nickel phosphite NiH
For PO ₃ , sulfuric acid or sulfuric acid and sodium sulfate are added thereto. This gives the following reaction i from nickel phosphite
Or, according to ii, nickel sulfate and phosphorous acid or monosodium phosphite are produced.

NiHPO ₃ + H ₂ SO ₄ = NiSO ₄ + H ₃ PO ₃ ... I NiHPO ₃ + ／ H ₂ SO ₄ + 1 / 2Na ₂ SO ₄ = NiSO ₄ + NaH ₂ PO ₃ ... Ii

In this treatment, the amount of sulfuric acid used in the reaction of i is 0.5 to 0.5 mol per mol of nickel phosphite.
Preferably it is 1.2 mol, especially 0.7 to 1.0 mol. When the amount of sulfuric acid is too small, there is a disadvantage that dissolution of nickel phosphite is delayed.When the amount is too large, after separating nickel sulfate and phosphorous acid, a large amount of a pH adjuster is required when reused. Occurs.

The sulfuric acid used in this treatment is 5
It is desirable to use 硫酸 20% by weight, especially 10-15% by weight of dilute sulfuric acid.

On the other hand, in the case of the reaction (ii), sulfuric acid and sodium sulfate are used in an equivalent amount, and the total amount thereof is 0.5 to 1.2 mol, particularly 0.7 to 1.0 mol per mol of nickel phosphite. It is preferable to make it 1.0 mol.
Sodium sulfate is 2 to 20% by weight, especially 5 to 1%.
It can be used by dissolving it in 5% by weight of dilute sulfuric acid.

Sulfuric acid or sulfuric acid and sodium sulphate are added to nickel phosphite to produce nickel sulphate and phosphorous acid or monosodium phosphite, and the resulting nickel sulphate and phosphorous acid or monosodium phosphite are separated. As a specific method of separation, ordinary crystallization treatment utilizing the difference in solubility between nickel sulfate and phosphorous acid or monosodium phosphite in water may be performed.

The nickel sulfate separated as described above can be used as a component of a plating bath. However, when used without particular purification, it is used to precipitate and form the above nickel phosphite. It is recommended to use as raw material nickel sulfate. Phosphorous acid or monosodium phosphite is discharged out of the system.

Here, the above nickel sulfate is converted to nickel phosphite.
As raw material nickel sulfate for precipitation and formation of kel
When using, the sulphate nit
Preferably, Kel is used. That is, the reaction i
Phosphorous acid, a strong acid, adheres to the nickel sulfate
May be present. Reuse such nickel sulfate
Then, in the reaction to produce nickel phosphite,
Sodium hydroxide to neutralize attached phosphorous acid
Although the amount of use of the system increases, it was obtained by the reaction of ii.
In the case of nickel sulfate, the phosphorous acid
It is not necessary to neutralize thorium even if it is attached.
For producing a modified nickel phosphite NiSO_Four+ NaH_TwoPO_Three+ Na OH = NiHPO_Three+ N
a_TwoSO_Four+ H_TwoO  Use the required amount of sodium hydroxide
Just fine.

The sulfuric acid used in the above reactions i and ii consumes and requires a running cost.
As for the sodium sulfate used in the above reaction, a product (waste) obtained by treating the plating bath waste liquid can be used, as described later, so that there is substantially no cost even if consumed. Therefore,
In the case of the reaction (ii), the amount of sulfuric acid involved in the cost can be reduced to half of that in the case of the reaction (i), which not only can reduce the processing cost, but also leads to the reduction of wastes, and increases the economic and environmental effects. be able to.

On the other hand, the plating bath after the nickel phosphite is separated is regenerated and reused as described above. In such a regenerated and reused plating bath, sodium sulfate is gradually accumulated. To go.

That is, in the case of an electroless nickel plating bath, those containing nickel sulfate, a complexing agent, and sodium hypophosphite as main components are widely used. Phosphite ion, p
In order to replenish and adjust H, nickel sulfate, sodium hypophosphite, and sodium hydroxide as a pH adjuster are continuously used while being replenished. Therefore, as described above, phosphite ions accumulate in the plating bath, and sodium ions and sulfate ions also accumulate. In this case, since sodium sulfate has high solubility, it does not particularly affect the plating film.

However, the phosphite ions accumulated according to the above-mentioned method are precipitated as nickel phosphite by adding nickel sulfate, and the precipitate is removed to regenerate the electroless nickel plating bath and to repeat reuse. Finally, the solubility exceeds the solubility limit of sodium sulfate, and its crystals precipitate, which adversely affects the properties of the plating film.

Therefore, after the nickel phosphite is removed as described above, the electroless nickel plating bath is cooled, if necessary, to a temperature lower than room temperature to precipitate and precipitate sodium sulfate. It is recommended that the phosphite ions accumulate in the plating bath be effectively removed, so that the plating bath can be regenerated and reused, and a large amount can be accumulated by such repeated use. Sodium sulfate can be easily and reliably removed without introducing impurity ions, so that the plating bath has a longer life and the electroless plating bath can be used repeatedly for a longer period of time.

Here, the amount of the accumulated sodium sulfate before the treatment is performed is appropriately selected.
At 200 g / L or more, especially at 400 g / L or more, before the solubility limit of sodium sulfate is reached. The cooling temperature is not particularly limited, but is 0 to 15 ° C, particularly 0 to 5 ° C. If it is too low, the entire plating bath will crystallize, and if it is too high, the amount that can be removed at one time will be small. Further, as a method for removing the precipitated sodium sulfate, an ordinary crystallization method can be used.

In this case, the sodium sulfate removed from the plating bath can be used for the above-mentioned reaction ii when obtaining nickel sulfate from nickel phosphite.

In the plating bath from which sodium sulfate has been removed, the bath composition is adjusted in the same manner as described above, and the plating bath is reused.

Next, the recycling flow of the electroless nickel plating bath based on the method of the present invention will be described with reference to the drawings.

In the figure, A is a plating area, and B is a reproduction area. In the figure, reference numeral 1 denotes an electroless nickel plating bath containing an electroless nickel plating bath, which is mainly composed of nickel sulfate, a complexing agent thereof, and sodium hypophosphite as a reducing agent. It is contained as. The pH is usually 3.5 to 6.5, especially 4 to 6
It is adjusted to.

In this electroless nickel plating bath, as the plating proceeds, the concentration of nickel ions and hypophosphite ions decreases, and the pH decreases.
In the above, nickel sulfate and sodium hypophosphite are added and their concentrations are adjusted to a predetermined concentration, and a pH adjuster (usually sodium hydroxide) is added to adjust the pH to a predetermined value. Return to tank 1. Note that this replenishment may be performed continuously or intermittently in the replenishment adjustment tank 2. In some cases, the replenishment may be directly performed in the plating tank 1 without providing the replenishment adjustment tank 2.

Further, as described above, when the above electroless nickel plating bath is replenished and plated continuously, the amount of phosphite ions increases. The bath in which the phosphite ion has been increased in this manner is regenerated in the regeneration zone B.

That is, an electroless dyne with increased phosphite ions
Transfer the nickel plating bath to storage tank 3 and add sodium hydroxide
To adjust the pH of the plating bath to 7 to 10, especially 8 to 9.
Adjust, H_TwoPO _Three ^-To H PO _Three ^2-And

Next, in order to adjust the pH as described above,
The bath was transferred to the phosphorous acid separation tank 4, where the temperature was 30-1.
Add nickel sulfate at 00 ° C, especially 70-90 ° C
And phosphite ion H PO _Three ^2-To nickel phosphite N
iHPO_ThreeAnd is separated. Phosphorous acid
The plating bath from which the ions have been separated is
Transfer to sodium silicate separation tank 6 and remove excess sodium sulfate
(Note that this sodium sulfate is mainly
Also based on nickel and sodium hydroxide sodium hydroxide
Is removed). Here, the separation of sodium sulfate
Is to cool the plating bath below room temperature, preferably to 0-5 ° C.
Crystallization of sodium sulfate and separation
Can be done by In addition, sodium sulfate in the plating bath
This operation can be omitted if the thorium content is low.
it can.

The plating bath from which sodium sulfate has been separated is supplied with nickel sulfate, sodium hypophosphite, and, if necessary, a complexing agent in the regeneration adjustment supply tank 7 to adjust the pH. It is transferred to the tank 2, the composition of the plating bath is readjusted if necessary, and then returned to the plating tank 1.

On the other hand, the nickel phosphite NiHPO ₃ separated in the phosphite separation tank 4 is transferred to a nickel phosphite treatment tank 8, to which sulfuric acid or sulfuric acid and sodium sulfate are added, and nickel phosphite is added. Dissolved in sulfuric acid, transferred to a nickel sulfate separation tank 9 and separated into nickel sulfate and phosphorous acid or monosodium phosphite by the above-described method. It is sent to a tank 4 and used as a raw material nickel sulfate for converting phosphite ions to nickel phosphite, and phosphite or monosodium phosphite is discharged out of the system. In this case, when sulfuric acid and sodium sulfate are added to nickel phosphite for treatment, sodium sulfate separated and removed in the sodium sulfate separation tank 6 can be used.

Therefore, the nickel sulfate used as a reaction medium and possibly sodium sulfate as a reaction medium when removing phosphite ions can be re-used by the above method, so that the operation cost of electroless nickel plating is significantly reduced. Moreover, there is no contamination of the plating bath by different components. Further, according to the above-mentioned flow, the troublesome plating waste solution of waste solution treatment containing a large amount of complexing agent is substantially eliminated, and there is no waste of complexing agent, waste solution treatment cost is reduced, and it is effective as an environmental conservation measure. is there.

[0054]

The present invention will be described below in more detail with reference to Examples, but the present invention is not limited to the following Examples.

An electroless nickel plating bath having the following composition was prepared. Nickel sulfate 5.0 g / L (N
As ^{_{i 2+) NaH 2 PO 2 ·}} H 2 O 25.0 g / L sodium acetate 18.0 g / L malic acid ^{40.0 g / L Pb 2+ 0.3mg /} L (NaH 2 PO 3 0 g / L) pH 4.5

Using the above electroless nickel plating bath, nickel sulfate, NaH ₂ PO ₂ .H ₂ O, and NaOH (or H ₂ SO ₄ ) as a pH adjuster were added at predetermined intervals to the above Ni ²⁺ concentration, NaH ₂ PO ₂・ Plating is performed at 90 ° C. while replenishing so that the H ₂ O concentration and the pH become 4.5 and, if necessary, while replenishing sodium acetate, malic acid, and Pb ²⁺ appropriately.
Further, when the phosphite ion is increased to a predetermined value or more, after performing the same nickel sulfate addition treatment as described later and performing a phosphite ion removal operation, plating is performed in the same manner as above, and then the plating bath is analyzed. Was done. The results are as follows.

[0057] _{^{Ni 2+ 5.0 g / L NaH 2}} PO 2 · H 2 O 25.0 g / L NaH 2 PO 3 205 g / L Na 2 SO 4 · 7H 2 O 430 g / L Pb 2+ 0 0.3mg / L

Next, this plating bath was left at 5 ° C. for 1 hour, and the crystallized sodium sulfate was removed by filtration.
The obtained plating bath was analyzed and the following results were obtained.

[0059] _{^{Ni 2+ 5.0 g / L NaH 2}} PO 2 · H 2 O 24.3 g / L NaH 2 PO 3 203 g / L Na 2 SO 4 · 7H 2 O 110 g / L Pb 2+ 0 0.3mg / L

Further, nickel sulfate was added to this plating bath at pH 4.5 so as to have a concentration of 30 g / L.
The mixture was kept at 5 ° C. for 1 hour to remove the formed precipitate. The analysis results of the obtained plating bath are as follows.

[0061] _{^{Ni 2+ 9.0 g / L NaH 2}} PO 2 · H 2 O 7.3 g / L NaH 2 PO 3 99 g / L Na 2 SO 4 · 7H 2 O 106 g / L Pb 2+ 0 .1 mg / L

For the above plating bath, Ni ²⁺ 5.0 g /
_{L, NaH 2 PO 2 · H} 2 O25.0g / L, pH4.5
Then, plating was performed at 90 ° C. for 30 minutes. A 5 × 10 cm mild steel plate was used as the object to be plated, and the plating bath volume was 1 liter. As a result of visually observing the appearance of the obtained plating film, a good appearance of electroless nickel-
Phosphorus alloy plating film is obtained, there is no roughness on the surface,
No iron rust was observed even after being left in the washing water for 60 minutes.

[0063]

According to the present invention, phosphite ions can be easily, reliably and inexpensively removed from an aged electroless plating bath in which a large amount of phosphite ions have accumulated without introducing impurities. At the same time, nickel sulfate can be easily recovered from the formed and separated nickel phosphite, and can be effectively used as a plating bath component or a reaction medium for removing phosphite ions.

[Brief description of the drawings]

FIG. 1 is a flow sheet illustrating an embodiment of the present invention.

[Explanation of symbols]

 A Plating area B Regeneration area 1 Plating tank 2 Replenishment adjustment tank 3 Storage tank 4 Phosphorous acid separation tank 5 Storage tank 6 Sodium sulfate separation tank 7 Regeneration adjustment supply tank 8 Nickel phosphite treatment tank 9 Nickel sulfate separation tank 10 Nickel sulfate recovery tank

Claims (5)

[Claims] 1. A method for producing and precipitating nickel phosphite by adding a water-soluble nickel salt to an electroless plating bath in which phosphite ions are accumulated, using hypophosphorous acid or a salt thereof as a reducing agent.
This was separated from the plating bath, and sulfuric acid or sulfuric acid and sodium sulfate were added to the separated nickel phosphite to convert the nickel phosphite into nickel sulfate and phosphorous acid or monosodium phosphite. A method for treating an electroless plating bath, comprising recovering nickel sulfate. 2. A method according to claim 1, wherein nickel sulfate is added to an electroless nickel plating bath containing a water-soluble nickel salt, a complexing agent thereof, and sodium hypophosphite as a reducing agent as main components and phosphite accumulated therein. Nickel phosphite is formed and precipitated, and the nickel phosphite is removed to regenerate the electroless nickel plating bath and reuse is repeated, and sulfuric acid or sulfuric acid is added to the separated nickel phosphite. A method for treating an electroless nickel plating bath, comprising adding nickel phosphite to nickel sulphate and phosphorous acid or monosodium phosphite by adding sodium phosphite and sodium sulfate. 3. A nickel sulfate raw material, wherein nickel sulfate recovered by adding sulfuric acid or sulfuric acid and sodium sulfate to the nickel phosphite is added to a plating bath to convert the phosphite into nickel phosphite. 3. The processing method according to claim 2, wherein the processing method is used as: 4. The plating bath from which the nickel phosphite has been removed is cooled to a temperature lower than room temperature to precipitate and precipitate sodium sulfate from the plating bath and remove it. Processing method. 5. The treatment according to claim 4, wherein the nickel sulfate precipitated, precipitated and removed by the cooling is used as a sodium sulfate raw material added to convert nickel phosphite to monosodium phosphite. Method.