JP6901273B2 - Pre-plating method and plating method for rare earth magnets - Google Patents

Description

The present invention relates to a rare earth magnet plating pretreatment method and a plating treatment method. Specifically, the present invention relates to a rare earth magnet plating pretreatment method and a plating treatment for forming a corrosion-resistant metal film having good adhesion and appearance on the surface of the rare earth magnet. Regarding the method.

R-TM-B (R: rare earth element, TM: transition metal, B: boron) permanent magnets represented by Nd-Fe-B permanent magnets are used for various purposes because they have high magnetic properties. It is widely used mainly in the fields of electrical and electronic equipment. In particular, the R-TM-B permanent magnet developed as a high-performance permanent magnet has excellent magnetic characteristics, and is therefore suitably used in response to high performance and miniaturization of electric and electronic devices.

However, rare earth magnets have a problem that they are easily oxidized in a short time in the atmosphere containing moisture. This oxidation not only forms an oxide on the surface, but also causes intergranular corrosion along the internal grain boundaries.

As a means for preventing the oxidation of the rare earth magnet, it has been proposed to perform surface treatment on the rare earth magnet. For example, the surface treatment includes the formation of a resin film and the formation of a plating film. The resin film is formed by spraying or electrodeposition coating, and is simple and low cost. However, since the resin itself contains water, sufficient corrosion resistance cannot be obtained in a high temperature and high humidity environment. The formation of a plating film has been praised for its excellent corrosion resistance. However, vapor phase plating such as the vacuum vapor deposition method and the ion plating method is expensive and has a problem that it is difficult to form a plating layer in a groove or the like.

Therefore, as the surface treatment of the rare earth magnet, film formation by electroless plating such as Ni or Cu or electrolytic plating is adopted. In order to form a film by this electroless plating or electroplating, it is necessary to pretreat the rare earth magnet in advance.

For example, Patent Document 1 describes a corrosion-resistant rare earth magnet in which the surface of a sintered magnetic material is sequentially subjected to a plating pretreatment step, an activation treatment step, a smut removal step, a Cu plating step, and a Ni-P plating step. The manufacturing method is described.

Here, in Patent Document 1, the pretreatment step is defined as removing rust, solvent degreasing, alkaline degreasing, and pickling to remove rust on the surface of rare earth magnets and stains on oils and fats. Further, the activation treatment step is performed to improve the adhesion between the plating film and the magnet, and hydrochloric acid, sulfuric acid and the like are exemplified as the activation liquid. The smut removal step is a step of removing a small amount of impurities remaining by being physically attracted or magnetically attracted to the surface of the magnet from the surface of the magnet. Specific methods include removal by brushing and water. , Air spray removal, and ultrasonic removal are exemplified.

Further, in Patent Document 2, the surface of the magnetic alloy is surface-adjusted with an alkaline solution having a pH of 8 or more composed of an organic complex compound and / or an inorganic complex compound and a buffer, and then an organic carboxylate (including an oxycarboxylate). A method for surface treatment of a magnetic alloy which is de-smuted with an alkaline solution having a pH of 8 or more composed of an inorganic tin compound and a peroxide and then forming an oxidation-resistant film is described.

On the other hand, various plating films formed on magnetic alloys have been proposed. For example, in Patent Document 2, a metal plating film is formed by electroless copper plating, electrolytic copper plating and electrolytic nickel plating, alkaline electroless nickel plating and electrolytic nickel plating.

Further, Patent Document 3 describes a rare earth permanent magnet having a two-layer electroless plating layer composed of a permanent magnet body, a substituted Cu plating layer formed on the surface thereof, and a thicker electroless Ni-P plating layer. .. According to the rare earth permanent magnet described in Patent Document 3, it is said that the magnetic characteristics are less deteriorated, the adhesion is improved, and the magnetism resistance is high.

However, even if a metal film such as Ni is formed after pretreatment such as removing smut as described in Patent Document 1 and Patent Document 2, the adhesion and appearance are good, and the corrosion resistance is excellent. It cannot be said that the film has been obtained. Further, even if the surface of the rare earth magnet is subjected to the electroless plating treatment and the electroplating treatment as shown in Patent Documents 2 and 3, the adhesion and appearance are good as in the case of the above-mentioned pretreatment. Therefore, a metal plating film having excellent corrosion resistance has not been obtained.

Japanese Unexamined Patent Publication No. 3-283607 Japanese Unexamined Patent Publication No. 8-3783 Japanese Unexamined Patent Publication No. 2003-249405

Therefore, an object of the present invention is to provide a plating pretreatment method and a plating treatment method for a rare earth magnet having a metal plating film having good adhesion and appearance and excellent corrosion resistance on the surface.

Therefore, as a result of diligent research, the present inventors have come up with the idea of solving the above-mentioned problems by adopting the plating pretreatment method and the plating treatment method for rare earth magnets described below.

Rare earth magnet plating pretreatment method according to the present invention: The rare earth magnet plating pretreatment method according to the present invention is a rare earth magnet plating pretreatment when a metal film is formed on the surface of the rare earth magnet by electroless plating or electrolytic plating. In this method, after performing the alkaline degreasing treatment step, the acid activity treatment is performed at least in two steps of the first acid treatment step and the second acid treatment step, and after each of these steps, ultrasonic vibration of 20 to 150 kHz is performed. It is characterized in that the smut is removed by ultrasonic water washing in which the surface to be plated of the rare earth magnet is brought into contact with water at 20 to 50 ° C. to which the above-mentioned material is added for 1 to 5 minutes.

In the method for pre-treating a rare earth magnet according to the present invention, in the first acid treatment step, the surface to be plated of the rare earth magnet is subjected to one or two of nitric acid, sulfuric acid, hydrochloric acid, and phosphoric acid or salts thereof. It is preferable to immerse the substance in an acid solution containing 15 to 150 mL / L for 50 to 600 seconds.

In the method for pre-treating a rare earth magnet according to the present invention, in the second acid treatment step, the surface to be plated of the rare earth magnet is subjected to one or two of nitric acid, sulfuric acid, hydrochloric acid, and phosphoric acid or salts thereof. It is preferable to immerse in an acid solution containing 20 to 100 mL / L and having an acid concentration of 20 to 100 mL / L for 30 to 600 seconds.

Plating treatment method for rare earth magnets according to the present invention: The plating treatment method for rare earth magnets according to the present invention is for forming a metal film on the surface of a rare earth magnet treated by the above-mentioned pre-plating method by electroless plating. It is a plating treatment method for rare earth magnets and includes two types of plating treatment steps. The two types of plating treatment steps are an alkali electroless nickel plating treatment step and an electroless nickel plating treatment step, and the alkali electroless nickel The plating bath used in the plating treatment step is characterized by containing a nickel salt and an organic carboxylic acid and / or a salt thereof.

In the method for plating a rare earth magnet according to the present invention, it is preferable that the plating bath further contains a reducing agent and a stabilizer and has a pH of 9 to 10.

In the method for plating a rare earth magnet according to the present invention, it is preferable that the reducing agent is phosphoric acid and / or a salt thereof, and the stabilizer is lead nitrate.

In the method for plating a rare earth magnet according to the present invention, it is preferable that the organic carboxylic acid is citric acid.

According to the rare earth magnet plating pretreatment method and the plating treatment method according to the present invention, it is possible to obtain a rare earth magnet having a metal plating film having good adhesion and appearance and excellent corrosion resistance on the surface.

Hereinafter, modes for carrying out the present invention will be described.

[About the plating pretreatment method for rare earth magnets according to the present invention]
The rare earth magnet plating pretreatment method according to the present invention is a rare earth magnet plating pretreatment method for forming a metal film on the surface of a rare earth magnet by electroless plating or electrolytic plating. In the method for pre-plating a rare earth magnet according to the present invention, after performing an alkaline degreasing treatment step, an acid activity treatment is carried out in at least two steps of a first acid treatment step and a second acid treatment step, and after each of these steps. Remove the smut by washing with ultrasonic water. The method for pre-plating the rare earth magnet according to the present invention will be specifically described below.

<About rare earth magnets>
Rare earth magnets are represented by R-TM-B system (rare earth elements including R: Y, TM: transition metals, B: boron), and the rare earth elements include at least one kind such as samarium, neodymium, praseodymium, and formium. Yttrium can be mentioned. Examples of the transition metal include iron and cobalt.

<Alkaline degreasing treatment>
The alkaline degreasing treatment removes dirt from oils and fats on the surface of the rare earth magnet, and is performed by immersing the rare earth magnet in an alkaline degreasing treatment liquid. The components of the alkaline degreasing solution are not particularly limited, and for example, those containing sodium hydroxide, sodium carbonate, sodium cyanide, sodium metasilicate and the like can be used, and as a commercial product, an alkaline degreasing agent (trade name K). -340, Japan Kanigen Co., Ltd.) is exemplified. Here, as the immersion conditions for the rare earth magnet, it is preferable that the alkali concentration of the alkaline degreasing solution is 5 to 200 g / L, the temperature is 20 to 90 ° C., and the immersion time is 2 to 30 minutes. Further, before this alkaline degreasing treatment, a solvent degreasing treatment using trichloroethylene or the like may be performed.

<About acid activity treatment>
In the present invention, the surface to be plated of a rare earth magnet is subjected to an alkali degreasing treatment and then an acid activity treatment. The acid activity treatment removes the oxide film and alkali film on the surface of the rare earth magnet, improves the adhesion between the rare earth magnet and the metal plating film, prevents the invasion of impurities, and improves the corrosion resistance of the metal plating film. It is done for the purpose of making it. Here, this acid activity treatment is carried out in at least two steps of a first acid treatment step and a second acid treatment step.

1. 1. About the first acid treatment step The first acid treatment step aims at removing the oxide film and the alkali film on the surface of the rare earth magnet. Here, the first acid treatment liquid used in the first acid treatment step sufficiently activates the magnet surface by containing one or two of nitric acid, sulfuric acid, hydrochloric acid, and phosphoric acid or salts thereof. It is preferable to make it. Examples of the phosphoric acid include phosphorus compounds such as hypophosphorous acid, phosphorous acid, and orthophosphorus acid.

Then, in the first acid treatment step, it is preferable to immerse the surface to be plated of the rare earth magnet in an acid solution having an acid concentration of 15 to 150 mL / L for 50 to 600 seconds. Here, if the acid concentration in the acid solution is less than 15 mL / L or the immersion time is less than 50 seconds, the magnet surface is not sufficiently activated, resulting in poor adhesion of the plating film, which is not preferable. Further, when the acid concentration in the acid solution exceeds 150 mL / L or the immersion time exceeds 600 seconds, smut or sandy precipitates (components in which the magnet, which is a sintered alloy, remains intergranular corrosion) on the magnet surface. This is not preferable because it causes adhesion of the plating film due to adhesion).

Further, in the first acid treatment step, it is more preferable that the temperature of the acid solution for immersing the surface to be plated of the rare earth magnet is 10 to 50 ° C. By setting the temperature of the acid solution used in the first acid treatment step to 10 to 50 ° C., activation of the surface to be plated is promoted, and abnormal etching is less likely to occur.

2. About the second acid treatment step The purpose of the second acid treatment step is to improve the adhesion between the rare earth magnet and the metal plating film, prevent the ingress of impurities, and improve the corrosion resistance of the metal plating film. It is something to do. Here, the second acid treatment liquid used in the second acid treatment step contains one or two of nitric acid, sulfuric acid, hydrochloric acid, and phosphoric acid or salts thereof, similarly to the first acid treatment liquid. However, it is preferable for sufficiently activating the magnet surface. Examples of the phosphoric acid include phosphorus compounds such as hypophosphorous acid, phosphorous acid, and orthophosphorus acid.

Then, in the second acid treatment step, it is preferable to immerse the surface to be plated of the rare earth magnet in an acid solution having an acid concentration of 20 to 100 mL / L for 30 to 600 seconds. Here, if the acid concentration in the acid solution is less than 20 mL / L, surface activation that sufficiently improves the adhesion of the plating film does not occur, which is not preferable. If the acid concentration in the acid solution exceeds 100 mL / L, abnormal etching occurs on the magnet surface, which is not preferable. Further, if the immersion time is less than 30 seconds, surface activation does not occur uniformly and sufficiently, which is not preferable. If the immersion time exceeds 600 seconds, abnormal etching occurs due to an increase in work man-hours and excessive surface activation, which is not preferable.

Further, in the second acid treatment step, it is more preferable that the temperature of the acid solution in which the surface to be plated of the rare earth magnet is immersed is 10 to 50 ° C. By setting the temperature of the acid solution used in the second acid treatment step to 10 to 50 ° C., it is possible to reduce insufficient activation on the surface to be plated and prevent abnormal etching.

The first acid treatment step and the second acid treatment step in the present invention have been described above, but in the rare earth magnet plating pretreatment method according to the present invention, the first acid treatment step and the second acid treatment step are further followed. An acid treatment step can also be provided. In the rare earth magnet plating pretreatment method according to the present invention, even if three or more stages of acid treatment steps are provided, the same effect as when two steps of acid treatment steps are provided can be obtained, but in this case, man-hours are required. Will lead to an increase in. Here, in the acid treatment steps of the third and subsequent steps, the acid concentration can be gradually lowered and the treatment time can be gradually shortened as compared with the acid treatment step of the second step (second acid treatment step).

<About ultrasonic water washing>
In the present invention, after the above-mentioned alkaline degreasing treatment and acid activity treatment, ultrasonic water washing is performed to remove the smut. Ultrasonic washing removes impurities physically or magnetically attached to the surface of the rare earth magnet, whereby the adhesion between the rare earth magnet and the metal plating film can be improved. The water used for ultrasonic washing can be tap water, ion-exchanged water, or the like, and is not particularly limited. Further, the method of ultrasonic water washing is not particularly limited, and a rare earth magnet can be immersed.

Then, in ultrasonic water washing, it is preferable that the surface to be plated of the rare earth magnet is brought into contact with water subjected to ultrasonic vibration of 20 to 150 kHz for 1 to 5 minutes. Here, when the frequency of ultrasonic vibration is less than 20 kHz or exceeds 150 kHz, a special device is required and there is no great merit, so that it is not suitable as a condition for ultrasonic water washing. Further, if the time for contacting the surface to be plated of the rare earth magnet with the water subjected to ultrasonic vibration is less than 1 minute, the water washing is not sufficiently performed and the smut cannot be sufficiently removed. If the time for contacting the surface to be plated of the rare earth magnet with the water subjected to ultrasonic vibration exceeds 5 minutes, the work man-hours will increase, which is not preferable.

Further, in ultrasonic water washing, it is more preferable that the temperature of the water used is 20 to 50 ° C. By setting the temperature of the water used in the ultrasonic water washing to 20 to 50 ° C., it is possible to prevent insufficient washing with water and effectively prevent abnormal etching on the magnet surface.

[About the plating treatment method for rare earth magnets according to the present invention]
The method for plating a rare earth magnet according to the present invention is a method for plating a rare earth magnet when forming a metal film on the surface of the rare earth magnet treated by the above-mentioned pre-plating method by electroless plating. The rare earth magnet plating treatment method according to the present invention includes an alkali electroless nickel plating treatment step and an electroless nickel plating treatment step, and the plating bath used in the alkali electroless nickel plating treatment step includes a nickel salt and an organic carboxyl. Contains acid and / or a salt thereof. Hereinafter, the plating treatment method for the rare earth magnet according to the present invention will be specifically described.

<About electroplating>
In the present invention, after the above-mentioned plating pretreatment, two types of electroless plating treatments are applied to the surface of the rare earth magnets to form a nickel plating film as a means for preventing the oxidation of the rare earth magnets. In the electroless plating treatment in the present invention, an alkaline electroless nickel plating treatment step and an electroless nickel plating treatment step are carried out as two types of electroless plating treatments. By carrying out these two types of plating treatment steps, it is possible to perform plating precipitation without applying a catalyst, and it is possible to obtain the effect of efficiently precipitating the film thickness. Here, by performing the alkaline electroless nickel plating treatment and the electroless nickel plating treatment in this order, the precipitation of nickel is promoted and the self-decomposition of the plating bath does not occur, so that it is not necessary to add a catalyst. ..

1. 1. Alkaline electroless nickel plating treatment step In the rare earth magnet plating treatment method according to the present invention, the plating bath used in the alkaline electroless nickel plating treatment step contains a nickel salt, an organic carboxylic acid and / or a salt thereof. .. Here, by containing the nickel salt in the plating bath, the adhesion of the nickel plating film can be improved. The nickel salt preferably contains neither sulfuric acid nor chlorine, and nickel acetate, nickel carbonate, nickel nitrate, nickel hydroxide and the like can be preferably used. In particular, it is industrially desirable to use nickel carbonate as the nickel salt, and by using nickel carbonate, the adhesion of the nickel plating film can be further improved. Further, by containing the organic carboxylic acid and / or a salt thereof in the plating bath, it is possible to stabilize nickel precipitation. Examples of the organic carboxylic acid include citric acid, lactic acid, malic acid, succinic acid, malonic acid, acetic acid and the like. In particular, by using citric acid as the organic carboxylic acid, it is possible to further stabilize nickel precipitation.

Further, the plating bath used in the alkaline electroless nickel plating treatment step further contains a reducing agent and a stabilizer, and the pH is preferably 9 to 10. Here, by further containing a reducing agent in the plating bath, nickel can be sufficiently precipitated. By using phosphoric acid and / or a salt thereof as the reducing agent, nickel precipitation can be promoted, which is preferable. Examples of the phosphoric acid include phosphorus compounds such as hypophosphorous acid and phosphorous acid, and hypophosphorous acid is particularly preferable. Further, by further containing a stabilizer in the plating bath, abnormal decomposition can be suppressed. Examples of the stabilizer include heavy metal stabilizers such as lead, bismuth, cadmium, titanium, and antimony, and sulfur-based stabilizers such as thiosulfate, thiourea, and thiodiglycolic acid, which are known in electroless nickel plating. Polyvalent metal oxide stabilizers such as iodate, molybdate, vanadinate, and stannate can be used. These stabilizers may be used alone or in combination of two or more. In particular, by using lead as the stabilizer, self-decomposition of the plating bath can be suppressed.

The plating bath used in the alkaline electroless nickel plating treatment step is stable because the pH is 9 or more, so that an abnormal reaction with the reducing agent occurs on the surface in contact with the magnet and the magnet does not dissolve. It becomes possible to deposit nickel. Further, when the pH is 10 or less, the problem that nickel salt precipitation or nickel precipitation is stopped and a film cannot be formed does not occur. Further, by setting the plating bath at 20 to 70 ° C., the effect of uniformizing and stabilizing nickel precipitation can be obtained. Incidentally, in the alkaline electroless nickel plating treatment step, the method of adjusting the pH of the plating bath to 9 to 10 is not particularly limited, and for example, a pH adjuster such as ammonia and other additives are included in the plating bath. Can be used.

The plating bath used in the alkaline electroless nickel plating treatment step has been described above. Specifically, the concentration of the nickel salt in the plating bath is preferably 4 to 5 g / L as metallic nickel. The bath composition of the plating bath excluding the nickel salt was 5 to 30 g / L of citric acid, 20 to 40 g / L of sodium hypophosphate, 0.0001 to 0.05 g / L of sodium thiosulfate, and 0 lead. It is preferably 0005 to 0.005 g / L.

2. Electroless nickel plating treatment step In the rare earth magnet plating treatment method according to the present invention, the film thickness of the electroless nickel film can be further increased by performing the electroless nickel plating treatment step. As the plating bath used in the electroless nickel plating treatment step, a bath containing a normal nickel salt such as nickel sulfate or nickel hypophosphate or a reducing agent such as phosphorus or boron is used.

<About metal plating film>
Even if the surface of the rare earth magnet treated by the above-mentioned pretreatment method for plating the rare earth magnet according to the present invention is subjected to electrolytic plating treatment or electroless plating treatment by a conventionally known method, the adhesion and appearance of the rare earth magnet are obtained. It is possible to form a metal plating film having good corrosion resistance and excellent corrosion resistance. However, by forming a nickel plating film on the surface of the rare earth magnet under the above-mentioned plating treatment conditions, it is possible to form a nickel plating film having better adhesion and appearance and excellent corrosion resistance. The plating film may be a single layer or a plurality of layers, and can be arbitrarily selected depending on the purpose.

The plating pretreatment method and the plating treatment of the rare earth magnet according to the present invention have been described above, but examples of the present invention will be shown below, and the present invention will be described in more detail. The present invention is not limited to these examples.

In Example 1, as a pretreatment for plating a rare earth magnet, after performing an alkali degreasing treatment step, an acid activity treatment is carried out in two steps of a first acid treatment step and a second acid treatment step, and after each of these steps, super The adhesion of the plating film when the smut was removed by sonic washing was confirmed.

In this Example 1, a rare earth magnet (neodymium magnet "Product No .: N50M" manufactured by Shin-Etsu Chemical Co., Ltd.) is used as a test body, and the test body is immersed in an alkaline degreasing solution having an alkali concentration of 50 g / L and a temperature of 50 ° C. for 10 minutes. After performing the alkaline degreasing treatment step of immersing, ultrasonic water washing was performed by applying ultrasonic vibration of 38 kHz for 2 minutes. Next, the test piece was subjected to a first acid treatment step of immersing the test piece in an acid solution (room temperature) of 60% nitric acid of 50 mL / L for 160 seconds, and then ultrasonically washed with water under the same conditions as described above. Further, after performing a second acid treatment step of immersing the test piece in an acid solution (25 ° C.) of 36% hydrochloric acid of 50 mL / L for 160 seconds, ultrasonic water washing was performed under the same conditions as described above. Here, as the above-mentioned alkaline degreasing agent, "Product No .: K-340" manufactured by Japan Kanigen Co., Ltd. was used. Further, for ultrasonic water washing, "Product No .: 64200" manufactured by Kaijo Co., Ltd. was used as an apparatus.

Then, after performing the above-mentioned pretreatment on the test piece, it is plated with an alkaline electroless nickel plating solution (temperature: 50 ° C., pH: 10) for 15 minutes, and then further manufactured by Japan Kanigen Co., Ltd. The plating treatment was performed for 25 minutes using an electroless nickel plating solution (temperature: 88 ° C.) of "trade name: SEK-797". Here, as the alkaline electroless nickel plating solution, one containing a nickel salt and an organic carboxylic acid was used. Specifically, as the nickel salt, nickel carbonate having a concentration of 4.5 g / L was used as metallic nickel. Moreover, 20 g / L citric acid was used as the organic carboxylic acid. In the alkaline electroless nickel plating solution, the bath composition excluding the nickel salt and the organic carboxylic acid is 30 g / L of sodium hypophosphate, 0.001 g / L of sodium thiosulfate, and 0.001 g / L of lead. The composition was used.

In Example 1, the adhesion of the plating film thus formed on the surface of the test piece was evaluated according to JIS Z 1522. To confirm the adhesion of the plating film in Example 1, 100 squares are formed on the surface of the rare earth magnet at 2 mm intervals, and a peeling test is performed with an adhesive tape (“Product No .: CT-18” manufactured by Nichiban Co., Ltd.). It was evaluated from the residual rate of.

Table 1 shows the results of confirming the adhesion of the plating film under the above conditions. Table 1 shows the results of Examples 2 and 3 and Comparative Examples 1 to 9 in addition to Example 1. Here, the confirmation of the adhesion of the plating film was evaluated by the residual ratio of the squares after the peeling test. The adhesion of the plating film was evaluated as "○" for those having no missing squares and "x" for those with even a part of the squares missing.

In Example 2, as in Example 1, as a pretreatment for plating a rare earth magnet, an alkali degreasing treatment step is performed, and then an acid activity treatment is performed in two steps, a first acid treatment step and a second acid treatment step. After each of these steps, the adhesion of the plating film when the smut was removed by ultrasonic water washing was confirmed. The results of this confirmation are shown in Table 1.

In Example 2, the same plating pretreatment and plating treatment as in Example 1 were performed except that a neodymium magnet (product number: N48M) manufactured by Shin-Etsu Chemical Co., Ltd. was used as a test body. Therefore, the description of these processes will be omitted.

In Example 3, similarly to Example 1, as a pretreatment for plating a rare earth magnet, an alkali degreasing treatment step is performed, and then an acid activity treatment is performed in two steps of a first acid treatment step and a second acid treatment step. After each of these steps, the adhesion of the plating film when the smut was removed by ultrasonic water washing was confirmed. The results of this confirmation are shown in Table 1.

In Example 3, the same pre-plating and plating treatments as in Example 1 were performed except that a samarium-cobalt magnet (product number: R26H) manufactured by Shin-Etsu Chemical Co., Ltd. was used as a test body. Therefore, the description of these processes will be omitted.

In Example 4, based on the results obtained in Examples 1 to 3, when the frequency of ultrasonic vibration applied to the surface of the test piece in ultrasonic washing is changed, the state and adhesion of the plating film are affected. We confirmed the impact.

In Example 4, the same test body as in Example 1 was used, except that the frequency of ultrasonic water washing performed on the test body was changed to 25 kHz, and the same pretreatment and plating treatment as in Example 1 were performed. .. Therefore, the description of these processes will be omitted.

Table 2 shows the results of confirming the state and adhesion of the plating film under the above conditions. Table 2 shows the results of Examples 5 and 6 in addition to Example 4. Here, the confirmation of the state of the plating film was visually evaluated. The state of the plating film was evaluated as "⊚" for uniform gloss, "○" for non-uniform gloss, "Δ" for partially matte gloss, and "x" for matte gloss. Further, the adhesion of the plating film was evaluated under the same conditions as in Example 1.

In Example 5, as in Example 4, when the frequency of ultrasonic vibration applied to the surface of the test piece was changed in ultrasonic water washing, the effect on the state and adhesion of the plating film was confirmed. .. The results of this confirmation are shown in Table 2.

In Example 5, the same test body as in Example 1 was used, except that the frequency of ultrasonic water washing performed on the test body was changed to 45 kHz, and the same pretreatment and plating treatment as in Example 1 were performed. .. Therefore, the description of these processes will be omitted.

In Example 6, as in Example 4, when the frequency of ultrasonic vibration applied to the surface of the test piece was changed in ultrasonic water washing, the effect on the state and adhesion of the plating film was confirmed. .. The results of this confirmation are shown in Table 2.

In Example 6, the same test body as in Example 1 was used, except that the frequency of ultrasonic water washing performed on the test body was changed to 100 kHz, and the same pretreatment and plating treatment as in Example 1 were performed. .. Therefore, the description of these processes will be omitted.

In Example 7, based on the results obtained in Examples 1 to 3, when the conditions of the first acid treatment step (acid concentration of the acid solution, immersion time) were changed, the adhesion and appearance of the plating film were improved. We confirmed the impact.

In Example 7, the same test as in Example 1 except that in the first acid treatment step performed on the test piece, the acid concentration of the acid solution was set to 10 mL / L and the immersion time of the test piece was changed to 600 sec. Using the body, the same pretreatment and plating treatment as in Example 1 were performed. Therefore, the description of these processes will be omitted.

Table 3 shows the results of confirming the adhesion and appearance of the plating film under the above conditions. Table 3 shows the results of Examples 8 to 13 in addition to Example 7. Here, the confirmation of the adhesion of the plating film was evaluated under the same conditions as in Example 1. The appearance of the plating film was visually evaluated under the same conditions as in Example 4. Based on the above, the evaluation of the adhesion and appearance of the plating film is uniform in appearance and good adhesion is "◎", cloudiness is also seen in appearance but good adhesion is "○", and the appearance is uniform but good adhesion. The defect was marked with "Δ", and the appearance was cloudy and the poor adhesion was marked with "x".

In Example 8, similarly to Example 7, when the conditions of the first acid treatment step (acid concentration of the acid solution, immersion time) were changed, the effect on the adhesion and appearance of the plating film was confirmed. went. The results of this confirmation are shown in Table 3.

In Example 8, the same test as in Example 1 except that in the first acid treatment step performed on the test piece, the acid concentration of the acid solution was set to 20 mL / L and the immersion time of the test piece was changed to 300 sec. Using the body, the same pretreatment and plating treatment as in Example 1 were performed. Therefore, the description of these processes will be omitted.

In Example 9, as in Example 7, when the conditions of the first acid treatment step (acid concentration of the acid solution, immersion time) were changed, the effect on the adhesion and appearance of the plating film was confirmed. went. The results of this confirmation are shown in Table 3.

In Example 9, the same test as in Example 1 except that in the first acid treatment step performed on the test piece, the acid concentration of the acid solution was set to 20 mL / L and the immersion time of the test piece was changed to 60 sec. Using the body, the same pretreatment and plating treatment as in Example 1 were performed. Therefore, the description of these processes will be omitted.

In Example 10, as in Example 7, it was confirmed that when the conditions of the first acid treatment step (acid concentration of the acid solution, immersion time) were changed, the effect on the adhesion and appearance of the plating film was confirmed. went. The results of this confirmation are shown in Table 3.

In Example 10, the same test as in Example 1 except that in the first acid treatment step performed on the test piece, the acid concentration of the acid solution was set to 50 mL / L and the immersion time of the test piece was changed to 60 sec. Using the body, the same pretreatment and plating treatment as in Example 1 were performed. Therefore, the description of these processes will be omitted.

In Example 11, as in Example 7, when the conditions of the first acid treatment step (acid concentration of the acid solution, immersion time) were changed, the effect on the adhesion and appearance of the plating film was confirmed. went. The results of this confirmation are shown in Table 3.

In Example 11, the same test as in Example 1 except that in the first acid treatment step performed on the test piece, the acid concentration of the acid solution was set to 100 mL / L and the immersion time of the test piece was changed to 60 sec. Using the body, the same pretreatment and plating treatment as in Example 1 were performed. Therefore, the description of these processes will be omitted.

In Example 12, as in Example 7, when the conditions of the first acid treatment step (acid concentration of the acid solution, immersion time) were changed, the effect on the adhesion and appearance of the plating film was confirmed. went. The results of this confirmation are shown in Table 3.

In Example 12, the same test as in Example 1 except that in the first acid treatment step performed on the test piece, the acid concentration of the acid solution was set to 100 mL / L and the immersion time of the test piece was changed to 300 sec. Using the body, the same pretreatment and plating treatment as in Example 1 were performed. Therefore, the description of these processes will be omitted.

In Example 13, similarly to Example 7, when the conditions of the first acid treatment step (acid concentration of the acid solution, immersion time) were changed, the effect on the adhesion and appearance of the plating film was confirmed. went. The results of this confirmation are shown in Table 3.

In Example 13, the same test as in Example 1 except that the acid concentration of the acid solution was set to 200 mL / L and the immersion time of the test body was changed to 30 sec in the first acid treatment step performed on the test body. Using the body, the same pretreatment and plating treatment as in Example 1 were performed. Therefore, the description of these processes will be omitted.

In Example 14, based on the results obtained in Examples 1 to 3, when the conditions of the second acid treatment step (acid concentration of the acid solution, immersion time) were changed, the adhesion and appearance of the plating film were improved. We confirmed the impact.

In Example 14, the same test as in Example 1 except that in the second acid treatment step performed on the test piece, the acid concentration of the acid solution was set to 10 mL / L and the immersion time of the test piece was changed to 600 sec. Using the body, the same pretreatment and plating treatment as in Example 1 were performed. Therefore, the description of these processes will be omitted.

Table 4 shows the results of confirming the adhesion and appearance of the plating film under the above conditions. Table 4 shows the results of Examples 15 to 20 in addition to Example 14.

In Example 15, as in Example 14, it was confirmed that when the conditions of the second acid treatment step (acid concentration of the acid solution, immersion time) were changed, the effect on the adhesion and appearance of the plating film was confirmed. went. The results of this confirmation are shown in Table 4.

In Example 15, the same test as in Example 1 except that the acid concentration of the acid solution was set to 20 mL / L and the immersion time of the test body was changed to 300 sec in the second acid treatment step performed on the test body. Using the body, the same pretreatment and plating treatment as in Example 1 were performed. Therefore, the description of these processes will be omitted.

In Example 16, as in Example 14, it was confirmed that when the conditions of the second acid treatment step (acid concentration of the acid solution, immersion time) were changed, the effect on the adhesion and appearance of the plating film was confirmed. went. The results of this confirmation are shown in Table 4.

In Example 16, the same test as in Example 1 except that in the second acid treatment step performed on the test piece, the acid concentration of the acid solution was set to 20 mL / L and the immersion time of the test piece was changed to 60 sec. Using the body, the same pretreatment and plating treatment as in Example 1 were performed. Therefore, the description of these processes will be omitted.

In Example 17, as in Example 14, it was confirmed that when the conditions of the second acid treatment step (acid concentration of the acid solution, immersion time) were changed, the effect on the adhesion and appearance of the plating film was confirmed. went. The results of this confirmation are shown in Table 4.

In Example 17, the same test as in Example 1 except that in the second acid treatment step performed on the test piece, the acid concentration of the acid solution was set to 50 mL / L and the immersion time of the test piece was changed to 60 sec. Using the body, the same pretreatment and plating treatment as in Example 1 were performed. Therefore, the description of these processes will be omitted.

In Example 18, as in Example 14, it was confirmed that when the conditions of the second acid treatment step (acid concentration of the acid solution, immersion time) were changed, the effect on the adhesion and appearance of the plating film was confirmed. went. The results of this confirmation are shown in Table 4.

In Example 18, the same test as in Example 1 except that in the second acid treatment step performed on the test piece, the acid concentration of the acid solution was set to 100 mL / L and the immersion time of the test piece was changed to 60 sec. Using the body, the same pretreatment and plating treatment as in Example 1 were performed. Therefore, the description of these processes will be omitted.

In Example 19, as in Example 14, it was confirmed that when the conditions of the second acid treatment step (acid concentration of the acid solution, immersion time) were changed, the effect on the adhesion and appearance of the plating film was confirmed. went. The results of this confirmation are shown in Table 4.

In Example 19, the same test as in Example 1 except that in the second acid treatment step performed on the test piece, the acid concentration of the acid solution was set to 100 mL / L and the immersion time of the test piece was changed to 300 sec. Using the body, the same pretreatment and plating treatment as in Example 1 were performed. Therefore, the description of these processes will be omitted.

In Example 20, as in Example 14, it was confirmed that when the conditions of the second acid treatment step (acid concentration of the acid solution, immersion time) were changed, the effect on the adhesion and appearance of the plating film was confirmed. went. The results of this confirmation are shown in Table 4.

In Example 20, the same test as in Example 1 except that in the second acid treatment step performed on the test piece, the acid concentration of the acid solution was set to 200 mL / L and the immersion time of the test piece was changed to 30 sec. Using the body, the same pretreatment and plating treatment as in Example 1 were performed. Therefore, the description of these processes will be omitted.

In Example 21, two types of electroless plating treatments, an alkaline electroless nickel plating treatment step and an electroless nickel plating treatment step, are performed as a plating treatment method for the rare earth magnet, and the plating used in the alkali electroless nickel plating treatment step is performed. The adhesion of the plating film obtained when the bath contained the nickel salt and the organic carboxylic acid was confirmed.

In Example 21, the same test body as in Example 1 was used in the pre-plating treatment of the test body, except that both the first acid treatment step and the second acid treatment step in the acid activity treatment were carried out for 150 seconds. The same pre-plating and plating treatments as in Example 1 were performed. Therefore, the description of these processes will be omitted.

Table 5 shows the results of confirming the adhesion of the plating film under the above conditions. Table 5 shows the results of Examples 22 and 23 and Comparative Example 10 in addition to Example 21.

In Example 22, similarly to Example 21, an alkali electroless nickel plating treatment step and an electroless nickel plating treatment step are performed as a plating treatment method for the rare earth magnet, and a plating bath used in the alkali electroless nickel plating treatment step is performed. However, the adhesion of the plating film obtained when the nickel salt and the organic carboxylic acid were contained was confirmed. The results of this confirmation are shown in Table 5.

In Example 22, the same test piece as in Example 2 was used, except that in the plating pretreatment of the test piece, both the first acid treatment step and the second acid treatment step in the acid activity treatment were carried out for 150 seconds. The same pre-plating and plating treatments as in Example 1 were performed. Therefore, the description of these processes will be omitted.

In Example 23, as in Example 21, an alkali electroless nickel plating treatment step and an electroless nickel plating treatment step are performed as a plating treatment method for the rare earth magnet, and a plating bath used in the alkali electroless nickel plating treatment step is performed. However, the adhesion of the plating film obtained when the nickel salt and the organic carboxylic acid were contained was confirmed. The results of this confirmation are shown in Table 5.

In Example 23, the same test piece as in Example 3 was used, except that in the plating pretreatment of the test piece, both the first acid treatment step and the second acid treatment step in the acid activity treatment were carried out for 150 seconds. The same pre-plating and plating treatments as in Example 1 were performed. Therefore, the description of these processes will be omitted.

In Example 24, based on the results obtained in Examples 21 to 23, two types of electroless plating treatments, an alkali electroless nickel plating treatment step and an electroless nickel plating treatment step, are performed as a plating treatment method for rare earth magnets. When this was done, the effect of the pH value of the plating bath used in the alkaline electroless nickel plating treatment step on the precipitation and adhesion of the plating film was confirmed.

In Example 24, in the electroless plating treatment of the test piece, the same test piece as in Example 1 was used except that the pH value of the plating bath used in the alkaline electroless nickel plating treatment step was set to "8.5". The same pre-plating and plating treatments as in Example 1 were performed. Therefore, the description of these processes will be omitted.

Table 6 shows the results of confirming the precipitation and adhesion of the nickel plating film formed under the above conditions. Table 6 shows the results of Examples 25 to 28 in addition to Example 24. Here, the evaluation of the precipitation property of the plating film was performed visually. The evaluation of the precipitation property of the plating film is "○" when the unprecipitated part of the plating is not confirmed, "△" when the unprecipitated part of the plating is confirmed even in part, and the precipitated part of the plating is hardly confirmed. Was set to "x". Further, the adhesion of the plating film was evaluated under the same conditions as in Example 1.

In Example 25, as in Example 24, when two types of electroless plating treatments, an electroless nickel plating treatment step and an electroless nickel plating treatment step, are performed as the plating treatment method for the rare earth magnet. The effect of the pH value of the plating bath used in the alkaline electroless nickel plating treatment step on the precipitation and adhesion of the plating film was confirmed. The results of this confirmation are shown in Table 6.

In Example 25, in the electroless plating treatment of the test piece, the same test piece as in Example 1 was used except that the pH value of the plating bath used in the alkaline electroless nickel plating treatment step was set to "9.0". The same pre-plating and plating treatments as in Example 1 were performed. Therefore, the description of these processes will be omitted.

In Example 26, as in Example 24, when two types of electroless plating treatments, an electroless nickel plating treatment step and an electroless nickel plating treatment step, are performed as the plating treatment method for the rare earth magnet. The effect of the pH value of the plating bath used in the alkaline electroless nickel plating treatment step on the precipitation and adhesion of the plating film was confirmed. The results of this confirmation are shown in Table 6.

In Example 26, in the electroless plating treatment of the test piece, the same test piece as in Example 1 was used except that the pH value of the plating bath used in the alkaline electroless nickel plating treatment step was set to "9.5". The same pre-plating and plating treatments as in Example 1 were performed. Therefore, the description of these processes will be omitted.

In Example 27, as in Example 24, when two types of electroless plating treatments, an electroless nickel plating treatment step and an electroless nickel plating treatment step, are performed as the plating treatment method for the rare earth magnet. The effect of the pH value of the plating bath used in the alkaline electroless nickel plating treatment step on the precipitation and adhesion of the plating film was confirmed. The results of this confirmation are shown in Table 6.

In this Example 27, the same test body as in Example 1 was used, and the same pre-plating treatment and plating treatment as in Example 1 were performed. Therefore, the description of these processes will be omitted. The pH value of the plating bath used in the alkaline electroless nickel plating treatment step in Example 27 is "10.0" as in Example 1.

In Example 28, as in Example 24, when two types of electroless plating treatments, an electroless nickel plating treatment step and an electroless nickel plating treatment step, are performed as the plating treatment method for the rare earth magnet. The effect of the pH value of the plating bath used in the alkaline electroless nickel plating treatment step on the precipitation and adhesion of the plating film was confirmed. The results of this confirmation are shown in Table 6.

In Example 28, in the electroless plating treatment of the test piece, the same test piece as in Example 1 was used except that the pH value of the plating bath used in the alkaline electroless nickel plating treatment step was set to "10.5". The same pre-plating and plating treatments as in Example 1 were performed. Therefore, the description of these processes will be omitted.

Comparative example

[Comparative Example 1]
In Comparative Example 1, in order to make a comparison with Examples 1 to 3, one of the first acid treatment step and the second acid treatment step is performed after performing the alkaline degreasing treatment step as the plating pretreatment for the rare earth magnet. The adhesion of the plating film was confirmed when the above treatment was not applied. The results of this confirmation are shown in Table 1.

In Comparative Example 1, in the plating pretreatment of the test piece, the same test piece as in Example 1 was used except that the first acid treatment step was not performed, and the same plating pretreatment and plating treatment as in Example 1 were performed. Therefore, the description of these processes will be omitted.
[Comparative Example 2]
In Comparative Example 2, as in Comparative Example 1, after performing the alkaline degreasing treatment step as the plating pretreatment for the rare earth magnet, either the first acid treatment step or the second acid treatment step is not performed. The adhesion of the plating film was confirmed. The results of this confirmation are shown in Table 1.

In Comparative Example 2, in the plating pretreatment of the test piece, the same test piece as in Example 1 was used except that the second acid treatment step was not performed, and the same plating pretreatment and plating treatment as in Example 1 were performed. Therefore, the description of these processes will be omitted.

[Comparative Example 3]
In Comparative Example 3, in order to make a comparison with Examples 1 to 3, after performing an alkaline degreasing treatment step as a plating pretreatment for the rare earth magnet, there are two steps of a first acid treatment step and a second acid treatment step. When the acid activity treatment was performed, the adhesion of the plating film was confirmed when the smut was not removed by ultrasonic water washing after all these steps. The results of this confirmation are shown in Table 1.

In Comparative Example 3, in the plating pretreatment of the test piece, the smut was not removed by ultrasonic water washing after each step of the alkaline degreasing treatment step, the first acid treatment step, and the second acid treatment step. Using the same test piece as in No. 1, the same pre-plating treatment and plating treatment as in Example 1 were performed. Therefore, the description of these processes will be omitted.

[Comparative Example 4]
In Comparative Example 4, similarly to Comparative Example 3, as a pretreatment for plating the rare earth magnet, an alkali degreasing treatment step is performed, and then an acid activity treatment is performed in two steps of a first acid treatment step and a second acid treatment step. In this case, the adhesion of the plating film was confirmed when the smut was not removed by ultrasonic water washing after all these steps. The results of this confirmation are shown in Table 1.

In Comparative Example 4, in the plating pretreatment of the test piece, the same test piece as in Example 1 was used except that the smut was not removed by ultrasonic water washing after the alkaline degreasing treatment step and the first acid treatment step. The same pre-plating and plating treatments as in Example 1 were performed. Therefore, the description of these processes will be omitted.

[Comparative Example 5]
In Comparative Example 5, similarly to Comparative Example 3, as a pretreatment for plating a rare earth magnet, an alkali degreasing treatment step is performed, and then an acid activity treatment is performed in two steps of a first acid treatment step and a second acid treatment step. In this case, the adhesion of the plating film was confirmed when the smut was not removed by ultrasonic water washing after all these steps. The results of this confirmation are shown in Table 1.

In Comparative Example 5, in the plating pretreatment of the test piece, the same test piece as in Example 1 was used except that the smut was not removed by ultrasonic water washing after the alkaline degreasing treatment step, and the same pre-plating treatment as in Example 1. And plating treatment was performed. Therefore, the description of these processes will be omitted.

[Comparative Example 6]
In Comparative Example 6, similarly to Comparative Example 3, as a pretreatment for plating a rare earth magnet, an alkali degreasing treatment step is performed, and then an acid activity treatment is performed in two steps of a first acid treatment step and a second acid treatment step. In this case, the adhesion of the plating film was confirmed when the smut was not removed by ultrasonic water washing after all these steps. The results of this confirmation are shown in Table 1.

In Comparative Example 6, in the plating pretreatment of the test piece, the same test piece as in Example 1 was used except that the smut was not removed by ultrasonic water washing after the first acid treatment step and the second acid treatment step. The same pre-plating and plating treatments as in Example 1 were performed. Therefore, the description of these processes will be omitted.

[Comparative Example 7]
In Comparative Example 7, similarly to Comparative Example 3, as a pretreatment for plating a rare earth magnet, an alkali degreasing treatment step is performed, and then an acid activity treatment is performed in two steps of a first acid treatment step and a second acid treatment step. In this case, the adhesion of the plating film was confirmed when the smut was not removed by ultrasonic water washing after all these steps. The results of this confirmation are shown in Table 1.

In Comparative Example 7, in the pre-plating treatment of the test body, the same test body as in Example 1 was used except that the smut was not removed by ultrasonic water washing after the first acid treatment step, and the same pre-plating as in Example 1. Treatment and plating treatment were performed. Therefore, the description of these processes will be omitted.

[Comparative Example 8]
In Comparative Example 8, similarly to Comparative Example 3, as a pretreatment for plating the rare earth magnet, an alkali degreasing treatment step is performed, and then an acid activity treatment is performed in two steps of a first acid treatment step and a second acid treatment step. In this case, the adhesion of the plating film was confirmed when the smut was not removed by ultrasonic water washing after all these steps. The results of this confirmation are shown in Table 1.

In Comparative Example 8, in the pre-plating treatment of the test body, the same test body as in Example 1 was used except that the smut was not removed by ultrasonic water washing after the second acid treatment step, and the same pre-plating as in Example 1. Treatment and plating treatment were performed. Therefore, the description of these processes will be omitted.

[Comparative Example 9]
In Comparative Example 9, similarly to Comparative Example 3, as a pretreatment for plating a rare earth magnet, an alkali degreasing treatment step is performed, and then an acid activity treatment is performed in two steps of a first acid treatment step and a second acid treatment step. In this case, the adhesion of the plating film was confirmed when the smut was not removed by ultrasonic water washing after all these steps.

In Comparative Example 9, in the plating pretreatment of the test piece, the same test piece as in Example 1 was used except that the smut was not removed by ultrasonic water washing after the alkaline degreasing treatment step and the second acid treatment step. The same pre-plating and plating treatments as in Example 1 were performed. Therefore, the description of these processes will be omitted.

[Comparative Example 10]
In Comparative Example 10, in order to make a comparison with Examples 21 to 23, it is obtained when only the electroless nickel plating treatment step is performed without performing the alkali electroless nickel plating treatment step as the plating treatment method for the rare earth magnet. The adhesion of the plating film was confirmed.

In Comparative Example 10, the same rare earth magnet as in Example 21 was used as the test body, and the same pre-plating treatment as in Example 21 was performed in the plating pretreatment of the test body. Further, in Comparative Example 10, in the plating treatment of the test piece, the same electroless nickel plating treatment step as in Example 21 was performed without performing the alkaline electroless nickel plating step. Therefore, the description of these processes will be omitted.

[Summary]
From Table 1, in the plating pretreatment of rare earth magnets, after performing the alkaline degreasing treatment step, the acid activity treatment is performed in two steps of the first acid treatment step and the second acid treatment step, and after each of these steps, ultrasonic waves are used. In Examples 1 to 3 in which the smut was removed by washing with water, the adhesion of the plating film was confirmed according to the cross-cut method, and as a result, no peeling was observed in the plating film of the test piece. On the other hand, after performing the alkaline degreasing treatment step, Comparative Examples 1 and 2 in which the acid activity treatment was not performed in two steps of the first acid treatment step and the second acid treatment step, and the alkaline degreasing treatment step were performed. Later, with respect to Comparative Examples 3 to 9 in which the acid activity treatment was performed in two steps of the first acid treatment step and the second acid treatment step and the smut was not removed by ultrasonic water washing after all these steps, the cloth was used. As a result of confirming the adhesion of the plating film according to the cutting method, a defect was found in a part of the grid. Based on the above results, in the pre-plating treatment of rare earth magnets, after performing the alkaline degreasing treatment step, the acid activity treatment is carried out in two steps, the first acid treatment step and the second acid treatment step, and after each of these steps, super It was found that the adhesion of the plating film can be effectively improved by removing the smut by sonic washing.

From Table 2, Examples 4 to 6 in which the frequency of ultrasonic vibration applied to the surface of the test piece in the above-mentioned ultrasonic water washing was set to the condition (20 to 150 kHz) specified in the present invention were completely defective in the plating film of the test piece. As a result of confirming the adhesion of the plating film according to the cross-cut method, no peeling was observed in the plating film of the test piece. Based on the above results, it is possible to set the frequency condition of ultrasonic vibration of ultrasonic water washing performed after performing alkaline degreasing treatment and acid activity treatment in the pre-plating treatment of rare earth magnets within the condition range specified in the present invention. It was found to be more preferable in improving the adhesion of the plating film.

From Table 3, in the above-mentioned first acid treatment step, the condition of the acid concentration of the acid solution (15 to 150 mL / L) and the condition of the time of immersion in the acid solution (50 to 600 seconds) specified in the present invention are satisfied. Compared with Examples 7 and 13 which do not satisfy all of these conditions, Examples 8 to 12 are generally better in terms of adhesion and appearance of the plating film as a result of confirming the adhesion of the plating film according to the cross-cut method. The result was obtained. From the above results, it is more preferable that the conditions specified in the present invention are satisfied in the first acid treatment step performed in the plating pretreatment of the rare earth magnet in order to have good adhesion and appearance on the surface of the rare earth magnet. Do you get it.

From Table 4, in the above-mentioned second acid treatment step, the condition of the acid concentration of the acid solution (20 to 100 mL / L) and the condition of the time of immersion in the acid solution (30 to 600 seconds) specified in the present invention are satisfied. Compared with Examples 14 and 20 which do not satisfy all of these conditions, Examples 15 to 19 are generally better in terms of adhesion and appearance of the plating film as a result of confirming the adhesion of the plating film according to the cross-cut method. The result was obtained. From the above results, it is more preferable that the conditions specified in the present invention are satisfied in the second acid treatment step performed in the pre-plating treatment of the rare earth magnet in order to have good adhesion and appearance on the surface of the rare earth magnet. Do you get it.

From Table 5, in the plating treatment of rare earth magnets, two types of plating treatment steps, an alkali electroless nickel plating treatment step and an electroless nickel plating treatment step, are performed, and a nickel salt and an organic substance are added to the alkaline electroless nickel plating treatment liquid. As a result of confirming the adhesion of the plating film in Examples 21 to 23 containing the carboxylic acid according to the cross-cut method, no peeling was observed in the plating film of the test piece. On the other hand, in Comparative Example 10 in which the alkali electroless nickel plating treatment step was not performed, as a result of confirming the adhesion of the plating film according to the cross-cut method, a defect was found in a part of the squares. Based on the above results, in the plating treatment of rare earth magnets, two types of plating treatment steps, an alkaline electroless nickel plating treatment step and a non-electroless nickel plating treatment step, are performed, and a nickel salt is added to the alkaline electroless nickel plating treatment liquid. It was found that the stable formation of the plating film and the improvement of the adhesion can be achieved by using the one containing the organic carboxylic acid and the organic carboxylic acid.

From Table 6, in Examples 25 to 27 that satisfy the pH value condition (pH 9 to 10) of the plating bath used in the above-mentioned alkaline electroless nickel plating treatment step, compared with Examples 24 and 28 that do not satisfy this condition. Nickel could be sufficiently deposited on the surface of the test piece evenly, and good results were obtained regarding the precipitation property of the plating film. Based on the above results, regarding the alkaline electroless nickel plating treatment liquid used in the plating treatment of rare earth magnets, satisfying the conditions specified in the present invention is more necessary for the plating film to be evenly and stably deposited on the surface of the rare earth magnets. It turned out to be preferable.

According to the method for pre-plating a rare earth magnet according to the present invention, a rare earth magnet having a metal plating film having good adhesion and appearance and excellent corrosion resistance can be obtained. Since this rare earth magnet has such an advantage, it is used for various purposes, and is particularly preferably used in the fields of electric and electronic devices.

Claims (7)

A pretreatment method for rare earth magnets when forming a metal film on the surface of rare earth magnets by electroless plating or electrolytic plating.
After performing the alkaline degreasing treatment step, the acid activity treatment was carried out in at least two steps of the first acid treatment step and the second acid treatment step, and after each of these steps, ultrasonic vibration of 20 to 150 kHz was applied 20 to 20 to A pretreatment method for plating a rare earth magnet, which comprises removing smut by ultrasonic water washing in which the surface to be plated of the rare earth magnet is brought into contact with water at 50 ° C. for 1 to 5 minutes. In the first acid treatment step, the surface to be plated of the rare earth magnet contains one or two of nitric acid, sulfuric acid, hydrochloric acid, and phosphoric acid or salts thereof, and the acid concentration is 15 to 150 mL / L. The pretreatment method for plating a rare earth magnet according to claim 1, wherein the rare earth magnet is immersed in a liquid for 50 to 600 seconds. In the second acid treatment step, the surface to be plated of the rare earth magnet contains one or two of nitric acid, sulfuric acid, hydrochloric acid, and phosphoric acid or salts thereof, and the acid concentration is 20 to 100 mL / L. The pretreatment method for plating a rare earth magnet according to claim 1 or 2 , wherein the rare earth magnet is immersed in a liquid for 30 to 600 seconds. A method for plating a rare earth magnet when forming a metal film on the surface of the rare earth magnet treated by the plating pretreatment method according to any one of claims 1 to 3 by electroless plating.
Equipped with two types of plating processes
The two types of plating treatment steps are an alkaline electroless nickel plating treatment step and an electroless nickel plating treatment step.
A method for plating a rare earth magnet, wherein the plating bath used in the alkali electroless nickel plating treatment step contains a nickel salt and an organic carboxylic acid and / or a salt thereof. The method for plating a rare earth magnet according to claim 4 , wherein the plating bath further contains a reducing agent and a stabilizer and has a pH of 9 to 10. The method for plating a rare earth magnet according to claim 5 , wherein the reducing agent is phosphoric acid and / or a salt thereof, and the stabilizer is lead nitrate. The method for plating a rare earth magnet according to any one of claims 4 to 6 , wherein the organic carboxylic acid is citric acid.