JPH07249514A - Bond magnet and its manufacture - Google Patents

Abstract

PURPOSE:To provide a bond magnet which is free from deterioration in magnetic characteristic and is coated with a plated film that can be mass-produced in a relatively short time. CONSTITUTION:A bond magnet is coated with a surface layer 4 composed of a electroplated film deposited in an acidic plating bath of <=4.0 in pH on a surface base layer 3 which is deposited in a plating bath of <=80 deg.C in temperature and >=6.0 in pH.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a bond magnet used in a stepping motor for a floppy disk drive, a spindle motor for a hard disk drive, etc., and a method for manufacturing the same.

[0002]

2. Description of the Related Art In recent years, as electronic devices have become lighter, thinner, shorter, and smaller, the electronic parts constituting them have tended to become smaller. This tendency is also seen in motors, which requires smaller and more complex magnets to be built in. Against this background, there is an increasing demand for bonded magnets that can meet the needs for downsizing and complicated shapes. The conventional bonded magnet and its manufacturing method will be described below. The bond magnet is a composite magnetic material containing magnetic powder and a binder as main components, and its manufacturing method is generally compression molding, injection molding, extrusion molding, or rolling molding. Ferrite-based, SmCo-based, and NdFeB-based magnetic powders are generally used as magnetic powders, but NdFeB-based magnetic powders are predominant in applications that require particularly high magnetic properties. Also, as a binder, an organic binder is advantageous because of its superiority in molding processing.
Particularly in applications where high magnetic properties are required, thermosetting resins, which are suitable for compression molding and capable of producing high-density products, are mainly used.

Among such bonded magnets, NdFeB
It is essential to form a corrosion-resistant coating on the surface of the bonded magnet, since many of them contain iron, which easily becomes an oxide. Further, in a bonded magnet molded by compression molding, it is essential to form a film on the surface of the bonded magnet in order to prevent the loss of magnetic powder. Furthermore, in the case of bonded magnets that require decorative functions such as medical supplies, it is necessary to form a film on the surface of the bonded magnets in order to give it a beautiful appearance. The components of these coatings are precious metals, epoxy-based resins, fluorine-based resins, silicone-based resins, etc., and the forming method is electrolytic plating, electroless plating or vacuum deposition for metal coatings, and electrodeposition coating or resin coating for resin coatings. Spray painting is common.

[0004]

However, there are problems in each of the above conventional configurations. First, there is a problem that electroless plating, vacuum deposition and electrodeposition coating are not practical because of high cost, and spray coating has a problem that a practically durable resin film cannot be formed on the edge portion of the bond magnet. On the other hand, electroplating is low cost and can form a sufficient film on the edge of the bond magnet, so it seems to be the most suitable method for forming a film on the bond magnet at this time, but it is still improving. There are still issues to be solved. First, in electroplating using an acid plating bath, a plating film having a sufficient thickness can be obtained, but the plating solution that has entered through the pores on the surface of the bonded magnet oxidatively deteriorates the magnetic metal, resulting in deterioration of magnetic properties. There is. On the other hand, when an alkaline plating bath is used, there is a problem that the oxidation deterioration of the magnetic metal by the plating solution is slight, but it takes too much processing time to obtain a film thickness that can be practically used.

The present invention solves the above-mentioned conventional problems and provides a bond magnet to which a plating method which is excellent in mass productivity without deteriorating the magnetic characteristics of the bond magnet and relatively short treatment time required for film formation. The manufacturing method is provided.

[0006]

According to the present invention, as a result of studying a method for solving the above-mentioned conventional problems, first, an underlayer was formed on the surface of the bonded magnet by a plating bath at a relatively low temperature and in a neutral to alkaline range. The inventors conceived a method of forming an electrolytic plating film of the following, and forming an electrolytic plating film by an acidic plating bath having a high film growth rate on the bonded magnet surface with the underlying layer closing the pores. The bonded magnet of the present invention and the manufacturing method thereof based on such an idea are composed of the following eight items. An electrolytic plating film deposited as a surface layer by an acidic plating bath having a pH of 4.0 or less, and an electrolytic plating film deposited as a surface underlayer at a plating bath temperature of 80 ° C. or less and a plating bath pH of 6.0 or more Bond magnet with. The total thickness of the surface layer and the surface underlayer is 30 to 7
The bonded magnet as described, which is 0 μm. The bonded magnet according to the above, wherein the underlayer on the surface has a thickness of 1 to 30 μm. The plating bath used for the deposition of the surface underlayer is a copper cyanide bath, copper pyrophosphate bath, high zinc cyanide bath, medium zinc cyanide bath, low zinc cyanide bath, zincate bath, cadmium cyanide bath, potassium At least one or more of a low concentration tin bath, a potassium high concentration tin bath, a sodium tin bath, a tin-cobalt alloy stannate bath, a tin-cobalt alloy pyrophosphoric acid bath, and a tin-nickel alloy pyrophosphoric acid bath, or a description Bond magnet. After forming the electrolytic plating film as the base of the surface layer under the conditions that the plating bath temperature is 80 ° C. or lower and the plating bath pH is 6.0 or higher, the electrolytic plating serving as the surface layer is subjected to an acidic plating bath of pH 4.0 or lower. A method for producing a bonded magnet which is formed. The total thickness of the surface layer and the surface underlayer is 30 to 7
The method for producing a bonded magnet as described above, wherein the bonded magnet has a thickness of 0 μm. The method for producing a bonded magnet as described above, wherein the surface underlayer has a thickness of 1 to 30 μm. The plating bath used for the deposition of the surface underlayer is a copper cyanide bath, copper pyrophosphate bath, high zinc cyanide bath, medium zinc cyanide bath, low zinc cyanide bath, zincate bath, cadmium cyanide bath, potassium At least one of a low-concentration tin bath, a high-potassium tin bath, a sodium-based tin bath, a tin-cobalt alloy stannous bath, a tin-cobalt alloy pyrophosphate bath, and a tin-nickel alloy pyrophosphate bath was prepared. Or a method for producing the bonded magnet as described above.

[0007]

According to this structure, the pores of the bonded magnet are blocked by the electrolytic plating film deposited by the plating bath having a bath temperature of 80 ° C. or less and in the neutral to alkaline range, and the blocked underlayer. A surface layer formed by an acidic plating bath is formed on the electrolytic plating film. Since the plating bath used for forming the underlayer has a bath temperature of 80 ° C. or lower and a pH of 6.0 or higher, even if the plating bath penetrates into the pores on the surface of the bonded magnet and remains, it does not cause oxidative deterioration of the magnetic metal. It is minor. On the other hand, the pH used to form the surface layer
Since an acidic plating bath having a pH of 4.0 or less has a high film growth rate, an electrolytic plating film having a sufficient thickness can be formed in a short time.

[0008]

EXAMPLES The details of the present invention will be described below based on examples. FIG. 1 is an explanatory diagram showing a cross-sectional structure near the surface of a bonded magnet. The bonded magnet is obtained by binding magnetic powder 1 with a binder resin, and numerous voids 2 are present on the surface thereof. When such a bonded magnet is immersed in a plating bath to form an electrolytic plating film, the plating solution enters the pores 2 and remains. When the plating bath is an acid plating bath, the residual plating solution causes significant oxidative deterioration of the magnetic powder 1, and the effect on the magnetic properties of the bonded magnet cannot be ignored. In order to prevent the acidic plating solution from entering the pores 2, the present invention deposits on the surface of the bonded magnet at a bath temperature of 80 ° C. or lower and a plating bath pH of 6.0 or higher as shown in FIG. Electroplated film is formed to form the underlayer 3, and then p is formed on the underlayer 3 as shown in FIG.
The surface layer 4 is formed by forming an electrolytic plating film deposited by an acidic plating bath of H4.0 or less. The neutral or alkaline plating bath used to form the underlayer has a slight degree of oxidative deterioration of the magnetic metal even if it penetrates and remains in the pores on the surface of the bonded magnet, while the acidic plating bath used to form the surface layer forms a film. Since the growth rate is high, it is possible to provide a bonded magnet that suppresses deterioration of magnetic properties to a minimum and that also satisfies industrial mass productivity.

As described above, the pores on the surface of the bonded magnet are practically sealed by the electrolytic plating film deposited under the conditions of the plating bath temperature of 80 ° C. or lower and the plating bath pH of 6.0 or higher as the underlayer on the surface. It is a feature of the present invention that the invasion of the acidic plating solution, which must be used to obtain a uniform film thickness, is prevented. In addition, by forming this underlayer, conductivity can be imparted to the entire surface of the bonded magnet prior to the formation of the thick film surface layer by the acid plating bath, which causes problems when forming an electrolytic plating film by the conventional acid plating bath. However, it is possible to remarkably reduce the number of pinholes that are concentrated in a portion having poor conductivity such as a binder portion or a void portion on the surface of the bonded magnet.

The bonded magnets to which the plating method of the present invention is applied are mainly those containing magnetic powder that is easily oxidized and deteriorated by contact with an acidic plating bath.
A typical example is dFeB magnetic powder. N
Other than the dFeB system, those containing other rare earth system magnetic powder such as SmFeN system and SmCo system can be mentioned. Further, since electrolytic plating is performed, it is premised that the magnetic powder has conductivity. However, when a treatment for imparting conductivity to the surface is performed, such as applying a conductive paste or electroless plating, Ba-based ferrite, Sr It is also possible to use oxide-based magnetic powders such as system-based ferrite and MnZn-based ferrite. The above-mentioned treatment of a bonded magnet made of ferrite is effective in applications where appearance is important. The surface of these magnetic particles may be treated with a silane-based or titanate-based coupling agent or the like in order to improve dispersibility. The magnetic powder content is preferably 50 to 98 wt%. 97wt which can obtain a high-density molded product for applications requiring high magnetic properties
% Or more is more preferable, but if the amount exceeds 98 wt%, the binder becomes insufficient and the strength of the bonded magnet itself is significantly reduced.

As the main component of the binder, general-purpose ones such as epoxy resin and nylon resin can be used. Generally, an epoxy resin is used for compression molding, and a nylon resin is used for injection molding, extrusion molding, and roll molding.
When the main component is a thermosetting resin, a general curing agent can be used. It is also effective to add an appropriate curing accelerator if necessary. It is possible to add a plasticizer and a lubricant as appropriate for improving the moldability, but in order to maintain the strength of the bonded magnet itself, the addition amount thereof is 5 to 50 wt.
It is preferably in the range of%.

The electrolytic plating film serving as an underlayer formed on the surface of the bonded magnet must be treated under the conditions of a plating bath temperature of 80 ° C. or lower and a plating bath pH of 6.0 or higher. Become. When forming a copper film, a copper cyanide bath, copper pyrophosphate bath, or the like, when forming a zinc film, a high-zinc cyanide bath, medium zinc cyanide bath,
A low-zinc cyanide bath, a zincate bath, etc., and a cadmium cyanide bath, etc., to form a cadmium film,
In order to form a tin film, a low-potassium tin bath,
In order to form a tin-cobalt alloy film, a high-concentration potassium bath, a sodium-based tin bath, etc. forms a tin-nickel alloy film by a tin-cobalt alloy stannate bath, a tin-cobalt alloy pyrophosphate bath, etc. For this purpose, a tin-nickel alloy pyrophosphate bath or the like can be used.
In particular, a zinc bath is suitable in the present invention because the formed plating film itself has a sacrificial corrosion effect. The treatment temperature may be 80 ° C. or lower, but it is preferably 50 ° C. or lower in order to suppress deterioration of magnetic properties. More preferably, the temperature is 45 ° C. or lower. Treatment pH
Has a tradeoff with temperature, but it is necessary that pH is 6.0 or higher. The pH is preferably 6.5 or higher.
When the treatment temperature is 50 ° C. or higher, pH = 7.0 or higher is preferable. Further, the thickness thereof needs to be 1 μm or more in order to suppress the deterioration of the magnetic properties due to electrolytic plating in an acid bath or the like to be subsequently performed, but if it is 30 μm or more, there is a problem in mass productivity. Considering suppression of deterioration of magnetic properties and mass productivity, the range of 5 to 10 μm is preferable. If necessary, the surface of the bonded magnet may be washed or polished or treated with a silane-based or titanate-based coupling agent before forming the electrolytic plating film as the underlayer.

Next, regarding the electrolytic plating film formed on the underlayer, an acidic plating bath having a pH of 4.0 or less is selected from the viewpoint of mass productivity. For example, copper sulfate bath, matte Ni
Bath, Watt bath, Sulfamic acid bath, Wood strike bath, Immersion Ni bath, Hexavalent Cr low concentration bath, Hexavalent Cr
Sargent bath, hexavalent Cr fluoride containing bath, fluorinated Cd plating bath, sulfuric acid Sn plating bath, borofluoride Sn
Plating bath, Borofluoride Pb plating bath, Sulfamic acid P
b plating bath, methanesulfonic acid Pb plating bath, borofluoric acid solder plating bath, phenolsulfonic acid solder plating bath, alkanol sulfonic acid solder plating bath, chloride F
e plating bath, sulfate Fe plating bath, borofluoride Fe plating bath, sulfamate Fe plating bath, Sn-Co alloy fluoride bath, Sn-Ni alloy fluoride bath, etc. can be appropriately selected depending on the anode metal species. Brightening agent, leveler agent, anti-pitting agent, satin forming agent, anode dissolving agent, PH
Additives such as buffers and stabilizers can also be added.

Regarding the thickness of the electrolytic plating film formed by the acidic plating bath, it is necessary that the total thickness including the underlayer is 30 μm or more. Below that, practical rust preventive properties and mechanical strength cannot be obtained. Further, as a post-process, a washing process with water, a washing process with hot water, a sealing treatment process and the like can be added depending on the purpose.

Next, an example of the bonded magnet of this embodiment and a method of manufacturing the same will be described. (Examples 1 to 4) 32 mesh NdFeB-based isotropic magnetic powder (MQP-B manufactured by General Motors) 97w
A magnetic powder compound consisting of t% and an epoxy adhesive of 3 wt% was press-molded at a molding pressure of 5 t / cm ² and cured at 180 ° C. for 1 hour in an argon atmosphere and 30 mm × 5 mm ×
A 3 mm rectangular parallelepiped bonded magnet was obtained. This bonded magnet is electroplated by using the neutral or alkaline plating baths shown in (Table 1) to (Table 4), and further electrolyzed on the electrolytic plating film by using the acidic plating bath shown in (Table 5). Nickel plated. In this way, the surface layer has a pH of 4.
The electrolytic nickel plating film deposited by an acidic plating bath of 0 or less is used as a surface underlayer at a plating bath temperature of 80.
A bonded magnet having an electrolytic plating film deposited at a temperature of ℃ or less and a plating bath pH of 6.0 or more was produced. As a comparative example, a single-layer electrolytic plating film was formed on the above-mentioned 30 mm × 5 mm × 3 mm rectangular parallelepiped bonded magnet by using the acidic plating bath shown in Table 5 without forming an underlayer, and the underlayer was formed. A bonded magnet was prepared.

[0016]

[Table 1]

[0017]

[Table 2]

[0018]

[Table 3]

[0019]

[Table 4]

[0020]

[Table 5] The characteristics of the obtained isotropic bonded magnet are shown in (Table 6).

[0021]

[Table 6] As is clear from this (Table 6), the bonded magnets of Examples 1 to 4 showed no deterioration in magnetic properties and higher corrosion resistance than the bonded magnets of Comparative Examples having only a single-layer coating by an acidic plating bath. You can see that you also have. The inventors of the present invention have conducted a study on a bonded magnet having a plating film composed of an underlayer and a surface layer by changing the pH of the plating bath for forming the underlayer. As a result, the pH is less than 6.0 and the plating bath temperature is It was confirmed that if the temperature exceeds 80 ° C, it becomes difficult to suppress the generation of rust.

(Examples 5 to 13) NdFeB type isotropic magnetic powder (MQ manufactured by General Motors) that passed 32 mesh
P-B) A magnetic powder compound consisting of 97 wt% of epoxy adhesive and 3 wt% of epoxy adhesive was press-molded at a molding pressure of 5 t / cm ² and cured under an argon atmosphere at 180 ° C. for 1 hour to obtain a cubic bond magnet having a side of 5 mm. . This bonded magnet was subjected to electrolytic plating using the alkaline plating bath shown in (Table 1), and further electrolytic nickel plating was performed thereon using the acidic plating bath shown in (Table 5). In this way
An electrolytic plating film deposited as a surface layer by an acidic plating bath having a pH of 4.0 or less, and an electrolytic plating film deposited as a base layer of the surface layer at a plating bath temperature of 80 ° C. or less and a plating bath pH of 6.0 or more A bonded magnet having a film was prepared, and several kinds of underlayer and surface layer having different film thicknesses were obtained. As a comparative example, a bonded magnet without a base layer was prepared by forming a single-layer electrolytic plating film using the acidic plating bath (Table 5) without forming a base layer on the above cubic bonded magnet with a side of 5 mm. Was produced. The characteristics of the obtained isotropic bonded magnet are shown in (Table 7).

[0023]

[Table 7] As is clear from this (Table 7), the bonded magnets of Examples 5 to 13 showed no deterioration in magnetic properties and higher corrosion resistance than the bonded magnets of Comparative Examples having only the single-layer coating by the acidic plating bath. Example 5, in which the thickness of the underlayer is 1 μm or more, and the total thickness of the surface layer and the underlayer on the surface is 30 μm or more.
It can be seen that 6, 9, 10, 11, and 12 have extremely excellent corrosion resistance.

[0024]

As described above in detail, according to the present invention,
Has an electrolytic plating film without deteriorating magnetic properties,
Further, it becomes possible to obtain a bonded magnet which is excellent in mass productivity, and the corrosion resistance of the bonded magnet is dramatically improved, so that the industrial value of the present invention is extremely high.

[Brief description of drawings]

FIG. 1 is an explanatory diagram showing a cross-sectional structure near the surface of a bonded magnet.

FIG. 2 is an explanatory view showing a state in which an electrolytic plating film serving as an underlayer is formed on the surface of the bonded magnet.

FIG. 3 is an explanatory view showing a state in which an electrolytic plating film serving as a surface layer is formed on a base layer formed on the surface of a bonded magnet.

[Explanation of symbols]

 1 Magnetic powder 2 Porosity 3 Underlayer 4 Surface layer

Claims (8)

[Claims] 1. An electrolytic plating film deposited as a surface layer by an acidic plating bath having a pH of 4.0 or less, and a surface plating layer having a plating bath temperature of 80 ° C. or less and a plating bath pH of 6.0 or more. Bonded magnet with electroplated film. 2. The bonded magnet according to claim 1, wherein the total thickness of the surface layer and the surface underlayer is 30 to 70 μm. 3. The bonded magnet according to claim 1, wherein the surface underlayer has a thickness of 1 to 30 μm. 4. A plating bath used for depositing a surface underlayer is a copper cyanide bath, copper pyrophosphate bath, high zinc cyanide bath, medium zinc cyanide bath, low cyanide zinc bath, zincate bath, cyan. At least one or more of a cadmium bromide bath, a low potassium tin bath, a high potassium tin bath, a sodium tin bath, a tin-cobalt alloy stannate bath, a tin-cobalt alloy pyrophosphate bath, and a tin-nickel alloy pyrophosphate bath. The bonded magnet according to claim 1, 2, or 3. 5. A plating bath temperature of 80 ° C. or lower, a plating bath p
Under the condition that H is 6.0 or more, after forming the electrolytic plating film which becomes the base of the surface layer, the electrolytic plating which becomes the surface layer is adjusted to pH.
A method for producing a bonded magnet, which is formed by an acidic plating bath of 4.0 or less. 6. The method for producing a bonded magnet according to claim 5, wherein the total thickness of the surface layer and the surface underlayer is 30 to 70 μm. 7. The method for producing a bonded magnet according to claim 5, wherein the thickness of the underlayer on the surface is set to 1 to 30 μm. 8. A plating bath used for depositing a surface underlayer is a copper cyanide bath, a copper pyrophosphate bath, a high zinc cyanide bath, a medium zinc cyanide bath, a low zinc cyanide bath, a zincate bath, and a cyanide bath. At least one or more of a cadmium bromide bath, a low potassium tin bath, a high potassium tin bath, a sodium tin bath, a tin-cobalt alloy stannate bath, a tin-cobalt alloy pyrophosphate bath, and a tin-nickel alloy pyrophosphate bath. The method for producing a bonded magnet according to claim 5, 6 or 7, wherein