JP6942067B2 - Electrolytic nickel plating method including heat treatment step - Google Patents

Description

The present invention relates to an electroplating and heat treatment method for nickel, and more particularly to an electroplating and heat treatment method for increasing the hardness of a nickel plating film.

Since the plating film is thin and it is difficult to measure various mechanical properties, it is generally measured using a Vickers hardness tester or a micro Vickers hardness tester specified in JIS Z 2244 to express the mechanical properties of plating. Vickers hardness is used. Hv is used as a symbol for Vickers hardness, and it is expressed as "Hv is 150". In general, the wear resistance tends to improve as the hardness of the material increases, so it is important to improve the wear resistance.
The Vickers hardness of the electrolytic nickel plating film is usually about 400 or less, but the hardness is higher in the film plated with a plating solution to which a brightener is added. As a result of examining various compounds as additives for electrolytic nickel plating, it was reported that when sodium allylsulfonate, which has been conventionally used as a brightener, was used, a plating film having a film hardness Hv of about 600 was obtained. (Non-Patent Document 1).
As described above, in the case of electrolytic nickel plating, the Hv is limited to about 600 even with the optimum selection of brightener. Further, it has been generally said that the hardness of the electrolytic nickel plating film does not increase even if it is heat-treated, and the hardness of the electrolytic nickel plating film currently produced industrially is 600 or less.

There is also a method called alloy plating to increase the hardness of the nickel plating film. It is said that alloy plating such as nickel-cobalt plating can have a hardness of about Hv700, and nickel-tungsten carbide composite plating can have a hardness of about Hv800, but the management of the plating process becomes complicated and the cost increases.

In the case of electroless plating, it is said that a considerable amount of phosphorus, boron, etc. are co-deposited in the plating film, which also increases the hardness. Actually, the hardness of the film obtained by electroless nickel-phosphorus plating is about 600, and the hardness of the electroless nickel-boron plating film is about 700, but if these are heat-treated at a temperature of 300 ° C or higher, Vickers hardness is said to improve to about 1000 and 1100, respectively. However, electroless plating performs plating by chemically reducing the metal ions contained in the plating solution, so there is a life due to the consumption of the reducing agent, and the plating solution must be discarded every time a certain amount of plating is performed. Therefore, the cost is significantly higher than that of electroplating.
In electrolytic nickel plating, hypophosphate or the like is added to a watt bath or sulfamic acid bath, phosphorus is co-deposited in the nickel film to be electrodeposited, and the nickel plating film co-deposited with phosphorus is heat-treated. There is also research to increase the hardness of the plating film. However, this method of adding hypophosphorous acid requires time and effort to control the process to distribute phosphorus as uniformly as possible, and phosphorus is not a cheap element, so the cost increases, so it is aimed at practical use. No research has been done. Further, the above method imitates the method of increasing the hardness by evaporating phosphorus and boron in the conventional electroless nickel plating and further performing a heat treatment at 300 ° C. or higher, which is similar to alloy plating. ing. On the other hand, even if the electrolytic nickel plating film performed without adding hypophosphorous acid or the like is heat-treated at 300 ° C. or higher, the hardness does not increase and the heat treatment effect cannot be obtained.

As described above, electrolytic nickel plating has the great advantage that the cost is significantly low because it does not require large-scale equipment and the processing process is less complicated, but the film hardness is only up to about Hv600 even if a brightener is used. It is said that it does not rise, and there was a tendency to avoid it from the viewpoint of durability and wear resistance.
Under such circumstances, it is of great practical significance if a high-hardness nickel plating film can be obtained without significantly changing the usual electrolytic nickel plating equipment and without changing the composition of the plating film.

Japanese Unexamined Patent Publication No. 5-112898 Japanese Patent No. 4942098 Japanese Patent No. 4991472 Japanese Patent No. 5858428

Keisuke Kishimoto et al. "Surface Technology" Vol.54, No.10, 2003 p.710-713 "Effects of various additives on the characteristics of electrodeposited nickel film" Takatoshi Kase "Metal Surface Technology" vol.12, No.2 (1961) p.53-58. "A few properties of brighteners and electrodeposits in bright nickel plating"

The present invention provides a technique for obtaining a nickel plating film having a level of hardness that cannot be obtained by conventional electrolytic nickel plating, without significantly changing the equipment of ordinary electrolytic nickel plating and without changing the composition of the plating film. It is intended to be provided. Specifically, a method for obtaining a high-hardness nickel electrolytic plating film is provided by examining a plating method and heat treatment conditions when performing nickel plating using a normal electrolytic nickel plating solution to which a brightener is added.

By the way, an electroplating technique using air bubbles has been known as a technique for obtaining a plating film having gloss and few pinholes, and plating in which the surface tension is adjusted to 45 dyn / cm or less by adding a surfactant. A method of plating while generating fine bubbles (microbubbles) having a diameter of 10 to 1000 μm (for example, 100 μm) in a bath (Patent Document 1), or a method of plating in a foam layer formed by continuously generating bubbles (Patent Document 1). Patent Document 2) and the like were known.
The present inventors have also developed a technique for obtaining a glossy plating film with few pinholes by electroplating in a foam layer of a plating solution to which a brightener is added together with a surfactant (Patent Documents). 3,4). These techniques mainly focus on plating in foam as an aggregate of only bubbles.

In developing a method for obtaining a high-hardness nickel electrolytic plating film, the present inventors recall using an electroplating method while generating these bubbles, and increase the hardness in the case of conventional electrolytic nickel plating. It was decided to consider applying heat treatment, which had a negative view on the effect.
Specifically, an appropriate amount of each of a primary brightener and a secondary brightener is added to the nickel electrolytic plating solution, and a small amount of sodium dodecyl sulfate (SDS) is added as a surfactant to form microbubbles having a diameter of 500 microns or less. Electrolytic nickel plating was performed while feeding and dispersing in the plating solution and stirring, and then the test piece was heat-treated at 200 ° C. for 1 hour.
As a result, the Vickers hardness (Hv) measured on the plated surface was able to provide a nickel plating film with a high hardness close to 800, rather than 600, which was conventionally unattainable with electro-nickel plating.
Next, when experiments were conducted on the case where the addition of a small amount of the surfactant was omitted and the case where the microbubbles were omitted, a nickel-plated coating having a high hardness of about 750 could be provided.
With the above findings, the present invention could be completed.
The hardness values described here are values measured from the surface side using a Micro Vickers hardness tester FM-ARS9008 manufactured by Future Tech Co., Ltd. with a test load of 50 gf and a holding time of 15 seconds. The hardness may be measured on the side surface of the plating film. In this case, the plating film is thickly plated to a thickness of several tens of μm, the object to be plated is cut, the cross section is polished, and then the hardness is measured. taking measurement. Therefore, not only is the orientation of the crystals in the plating film the same as when the plating film is thin, but it also gives a strong history of cutting and polishing. Therefore, the hardness measured from the surface side of the plating film of a dozen μm. Cannot be compared with.

The present invention is a method for obtaining a high-hardness nickel plating film, which uses a nickel plating solution obtained by adding appropriate amounts of a primary brightener and a secondary brightener to an electrolytic plating solution of nickel, and performs electrolytic nickel plating while stirring. Provided is a method including a step of performing the process and a step of heat-treating the obtained nickel-plated product at 100 ° C. or higher and lower than 300 ° C.
The present invention is a method for obtaining a nickel plating film having a higher level of hardness, and in the electrolytic plating step, a nickel plating solution to which a small amount of surfactant is added together with a primary brightener and a secondary brightener is used. Provided is a method, or a method of performing plating by stirring while feeding microbubbles having a maximum diameter of 500 microns or less.
In order to obtain the highest hardness nickel plating film, an electrolytic plating solution containing a primary brightener, a secondary brightener and a surfactant is used, microbubbles are sent in, and electrolytic nickel plating is performed with stirring, and then electrolytic nickel plating is performed. , It is preferable to provide a step of performing heat treatment.

That is, the present invention is as follows.
[1] A method for obtaining a high-hardness nickel-plated film by an electrolytic plating heat treatment method for nickel.
(1) A step of preparing an electrolytic nickel plating solution by adding a surfactant together with a primary brightener and a secondary brightener.
Here, the primary brighteners include sodium 1,5 naphthalenedisulfonate (DNS), sodium 1,3,6-naphthalenetrisulfonate (TNS); p-toluenesulfonamide (PTSA); orthobenzene / sulfonamide (Orthobenzene / sulfonamide). Saccharin) or a sodium salt thereof; at least one compound selected from, or a mixture thereof.
The secondary brightener is at least one compound selected from formaldehyde (formalin); sodium allylsulfonate; butynediol; ethylene cyanhydrin; propargyl alcohol, gelatin, and thiourea, or a mixture thereof .
(2) A step of feeding microbubbles having a maximum diameter distribution of bubbles of 500 microns or less into an electrolytic nickel plating solution and forming a nickel film on the surface of the object to be plated while stirring.
(3) A step of heat-treating a plated product on which an electrolytic nickel film is formed at a temperature of 100 ° C. or higher and lower than 300 ° C. for 5 minutes or longer.
A method for obtaining a high-hardness nickel-plated coating, which comprises.

Conventionally, the upper limit of the Vickers hardness of the electrolytic nickel plating film is about 600, but according to the present invention, it has become possible to obtain a nickel plating film having a Vickers hardness of about 700 to 800.

Effect of heat treatment temperature on the hardness of electrolytic nickel-plated pieces

1. 1. Plating device The electroplating device for carrying out the present invention is not particularly limited, and for example, a plating tank made of stainless steel or the like equipped with a stirrer, a DC power supply, and an anode conducting on the positive electrode side of the DC power supply. It is necessary that the device is equipped with a cathode, which is a member to be plated that conducts to the negative electrode side, and is further equipped with equipment capable of forming microbubbles when the microbubbles are sent. There are various methods for generating microbubbles, such as swirling shear, pressure foaming, cavitation, and venturi, but the equipment is not limited to any of these methods and can form microbubbles of the required size. All you need is.
The object to be plated to be subject to electrolytic nickel plating of the present invention is generally a metal such as iron or copper, but plastic, ceramic or the like may be used as long as the surface is conductive or a substance to which it is imparted. good.

2. Heat treatment equipment There are no special restrictions on the equipment that performs heat treatment, and an electric furnace or the like that can appropriately control the temperature may be used.
The heat treatment of the plating film is generally used to prevent hydrogen embrittlement of the material due to the plating treatment, improve the adhesion of the plating film to special metals, improve the mechanical properties, etc., and microscopic distortion due to heat treatment. It was said that the hardness of the plating film decreases with heating due to the relaxation of the plating, the formation and coarsening of undistorted crystals by recrystallization, the release of occluded gas, and the condensation of impurities.
In electroless nickel plating, the hardness of the plating film is greatly increased by heat treatment at 300 ° C or higher, but it is said that the hardness does not increase even if the same heat treatment is applied to the film obtained by electrolytic plating. The nickel plating film obtained by electrolytic plating is not heat-treated.

3. 3. Plating solution Sulfamic acid bath and strike bath (wood bath) are available as plating solutions used for electrolytic nickel plating, but the watt bath containing nickel sulfate, nickel chloride, and boric acid as the main components is the most common and practical. And you can use this. The plating film obtained by using the watt bath has good adhesion to the substrate, is semi-glossy and has corrosion resistance, and a mirror-glossy film is also formed with a plating solution obtained by adding a brightener to the watt bath. It is known that the hardness of the plating film increases to about Hv600 when a brightener is used.

4. Brighteners Brightening nickel-plated brighteners include primary brighteners and secondary brighteners (Non-Patent Document 2).
In the present invention, a compound generally known as a brightener may be used, or a commercially available brightener may be used.
(4-1) Primary brightener The primary brightener is said to have a function of imparting gloss by refining the crystal particles in the plating film. Since the structure whose size is about one digit below the wavelength of visible light is mainly controlled, it is often not possible to obtain mirror gloss, and it is also called a semi-gloss agent.
As the sulfur-based compounds utilized in the primary brightener, 1 aromatic sulfonic acids, 5-naphthalene disulfonic acid sodium salt (DNS); p aromatic sulfonamides - toluenesulfonic ami de; ortho benzene aromatic sulfonic imides -Sulfonamide (saccharin) and its sodium salt; etc. In general, the Sakkari down or sodium naphthalene disulfonic acid (DNS) is used.
The primary brightener used in the present invention may be a simple substance of these compounds or a mixture thereof, or a mixture thereof with some additives added thereto, and is a commercially available primary brightener prepared as a primary brightener. You may.

The amount of the primary brightener added to the plating solution in the present invention may be any amount within the range recommended as a normal addition amount. When the specific compounds shown here or a mixture thereof is used as the primary brightener, the amount of the primary brightener or a mixture thereof is usually 3 to 9 mmol (3 to 9 mmol / L) per 1 liter of the plating solution. It is said that a range of degrees is appropriate, and in the present invention as well, the amount may be increased or decreased as appropriate within such a range. When a commercially available primary brightener supplied in the form of a solution is used, the amount may be appropriately increased or decreased within the range recommended by the primary brightener manufacturer.

(4-2) Secondary brightener The secondary brightener is used to smooth a small area that cannot be reached by the primary brightener, thereby obtaining a mirror surface gloss.
As its mechanism of action, sulfur compounds, which are primary brighteners such as saccharin adsorbed on the surface, control crystallization at a level one digit below the wavelength of light to perform rough smoothing, and secondary such as butynediol. It is believed that the brightener smoothes the fine irregularities generated by the crystal particles when it is reduced to butanediol on the plated surface to give it luster.
The material utilized for the secondary brightener, such as aldehyde formaldehyde (formalin), etc. A sodium Rirusuruhon acid allyl or vinyl compounds, such as butynediol acetylene compounds, such as ethylene cyanohydrin nitriles, other propargyl alcohol, a gelatin, and the like thiourea. Since unsaturated alcohols such as butynediol and propargyl alcohol are generally used, the secondary brightener is also referred to as an unsaturated alcohol component.
The secondary brightener used in the present invention may be a compound thereof, a mixture thereof, or a mixture thereof to which a slight additive is added, or a commercially available secondary brightener prepared as a secondary brightener. You may use it.

The amount of the secondary brightener added to the plating solution in the present invention may be any amount within the range recommended as a normal addition amount. When the specific compounds shown here or a mixture thereof is used as the secondary brightener, the amount of the secondary brightener or a mixture thereof is usually in the range of about 0.4 to 1.8 mmol per 1 liter of the plating solution. It is said that 0.4 to 1.8 mmol / L) is appropriate, and in the present invention as well, the amount may be appropriately increased or decreased within such a range. When a commercially available secondary brightener supplied in the form of a solution is used, the amount may be appropriately increased or decreased within the range recommended by the secondary brightener manufacturer.

5. Surfactants As surfactants, generally versatile and inexpensive sodium dodecyl sulfate (also referred to as SDS or sodium lauryl sulfate) is preferable, and it is often used in practice, but other anionic surfactants. Agents, cationic surfactants, nonionic surfactants, amphoteric surfactants and the like can also be used.
Anionic surfactants are typically alkyl sulfates such as sodium dodecyl sulfate (SDS), but others include α-olefin sulfonates, alkylbenzene sulfonates, their phosphate esters, and perfluoroolefins. Examples thereof include sulfonates, perfluoroalkylbenzene sulfonates, perfluoroether sulfonates and the like. Examples of the cation of the salt of these anionic anionic surfactants include sodium, potassium, diethyldimethylammonium, tetramethylammonium and the like.
Examples of the nonionic surfactant include C4-C25 alkylphenol-based surfactants, C4-C20 alkanol-based carbon atoms, and polyalkylene glycol-based surfactants. Examples of the cationic surfactant include lauryltrimethylammonium salt, lauryldimethylethylammonium salt, dimethylbenzyllaurylammonium salt and the like.
Examples of zwitterionic surfactants include sulfated or sulfonated adducts of the condensation product of betaine, sulfobetaine, ethylene oxide and / or propylene oxide with alkylamines or diamines.

When adding a surfactant to the plating solution, the amount to be added must be 1/10 or more of the critical micelle concentration, but there is a problem even if an amount that becomes the critical micelle concentration or higher is added. There is no. Although it depends on the type of surfactant, in the case of SDS, 0.1 to 10 g / L is preferably added, and 0.5 to 5 g / L is added.

6. Microbubbles Microbubbles are generated by mounting equipment for generating microbubbles in a plating tank and operating the equipment (Patent Document 1 and the like). There are various types of equipment for generating microbubbles, such as pressure / swirl, pressure foaming, swirl / shear, cavitation, and venturi, but any of them may be used.
The size of the bubbles of the microbubbles needs to be the peak value of the distribution of the diameters of the bubbles, that is, the maximum diameter of about 500 μm or less.

Before starting plating, it is necessary to send gas to the nozzle so that a certain amount of microbubbles are present in the plating solution. For that purpose, for example, about 0.1 to 0.2 liters of gas may be sent to the nozzle for about 2 to 3 minutes per minute for 1 liter of the plating solution, but the gas flow rate may be increased and the time may be shortened. , You may slow it down and lengthen the time.
Microbubbles have a small buoyancy, and a considerable amount of microbubbles stay in the plating solution during plating, for example, 10 minutes. Therefore, microbubbles may be continuously generated during plating, and the microbubbles may be generated. The generation may be slowed down or stopped.

Hereinafter, embodiments of the present invention will be described in more detail based on Examples. However, the embodiments of the present invention are not limited to these examples.
Other terms and concepts in the present invention are based on the meanings of terms commonly used in the art, and various techniques used to carry out the present invention particularly include techniques whose sources are clearly stated. Except for this, those skilled in the art can easily and surely carry out the procedure based on known documents and the like. In addition, various analyzes were performed by applying the methods described in the instruction manuals, catalogs, etc. of the analytical instruments or reagents used mutatis mutandis.
The contents of the prior art documents, patent gazettes and patent application specifications cited in the present specification shall be referred to as the description contents of the present invention.

( Experimental Example 1 : Comparative Example ) Electrolytic nickel plating method including heat treatment step (1-1) Electrolytic nickel plating step and heat treatment step 240 parts of nickel sulfate, 45 parts of nickel chloride and 30 parts of boric acid are dissolved in 1000 parts of water. The pH was adjusted to 4-5. To this, 16 mmol of saccharin as a primary brightener and 5.8 mmol of butynediol as a secondary brightener per 1 L of plating solution were added to prepare a nickel plating solution used in this example.
Place the prepared plating solution in a plating tank equipped with a stirrer and a nozzle for creating microbubbles of the cyclone method (Venturi method), and while continuing stirring while generating microbubbles, ^{Halcel with an average current density of 5 A / dm 2} for 10 minutes. Electrolytic nickel plating was performed on the iron plate.
After completion of plating, the prepared plating test piece was washed with water and dried, and then the hardness was measured. The hardness of the plating film was measured at three points by changing the position with a Micro Vickers hardness tester, and the average value was calculated.
Further, the test piece plated under the same conditions was heat-treated in an electric furnace at 200 ° C. for 1 hour. The hardness of the plating test piece after the heat treatment was measured by the same method.

(1-2) Effect of heat treatment step The Vickers hardness of the plating film of the test piece without heat treatment was 583, which was almost the same as the hardness obtained by ordinary nickel electrolytic plating, whereas after heat treatment The hardness of the plating film is 722, which shows that it is considerably high.

(1-3) Effect of blending surfactant When plating treatment is performed using the nickel plating solution shown in this experimental example (1-1) under the same plating conditions in which microbubbles coexist, and in the nickel plating solution. The same heat treatment as in (1-1) was performed when the plating treatment was performed using a plating solution containing sodium dodecyl sulfate at a ratio of 0.1% by weight under the condition that microbubbles did not coexist and only stirring was performed. Processed.
When the hardness of the plating film before and after the heat treatment was measured under the same measurement conditions as in (1-1), the hardness of both after the heat treatment was almost the same. That is, it was found that by adding a small amount of surfactant to the plating solution, the same effect as in the case of coexistence of microbubbles can be obtained.

(Example 1 ) Plating process and heat treatment process in the coexistence of microbubbles with a surfactant-containing plating solution
To the nickel plating solution prepared in the same manner as in Experimental Example ( 1-1), 0.1% by weight of sodium dodecyl sulfate was further added as a surfactant. Using the prepared plating solution, electrolytic nickel plating was performed on the Halcel iron plate under the same conditions as in Experimental Example 1 while stirring in the presence of microbubbles. The Vickers hardness of the obtained plating test piece after washing and drying with water was 622.
Further, the hardness of the test piece plated under the same conditions after heat treatment at 200 ° C. for 1 hour was 794, and the hardness after heat treatment was significantly increased.

(Example 2 ) Effect of heat treatment temperature on the hardness of electrolytic nickel plating film 100 ° C., 150 ° C., 200 ° C., 250 ° C. with respect to the test piece after the plating treatment step obtained in Example 1. The heat treatment step was carried out for 1 hour at a different temperature of 300 ° C. The hardness of the plating film is 718 at 100 ° C, 744 at 150 ° C, 794 at 200 ° C, and 791 at 250 ° C, all of which are significantly higher than the hardness 622 before heat treatment, and the higher the temperature, the higher the hardness. It tended to be higher, but unlike the case of electroless nickel plating, it decreased to 443 at 300 ° C. (Fig. 1)

Claims (1)

A method for obtaining a high-hardness nickel-plated film by an electrolytic plating heat treatment method for nickel.
(1) A step of preparing an electrolytic nickel plating solution by adding a surfactant together with a primary brightener and a secondary brightener.
Here, the primary brighteners include sodium 1,5 naphthalenedisulfonate (DNS), sodium 1,3,6-naphthalenetrisulfonate (TNS); p-toluenesulfonamide (PTSA); orthobenzene / sulfonamide (Orthobenzene / sulfonamide). Saccharin) or a sodium salt thereof; at least one compound selected from, or a mixture thereof.
Here, the primary brightener is at least one compound selected from formaldehyde (formalin); sodium allylsulfonate; butynediol; ethylene cyanhydrin; propargyl alcohol, gelatin, and thiourea, or a mixture thereof .
(2) A step of feeding microbubbles having a peak value of the diameter distribution of bubbles of 500 microns or less into the electrolytic nickel plating solution and forming a nickel film on the surface of the object to be plated while stirring.
(3) A step of heat-treating a plated product on which an electrolytic nickel film is formed at a temperature of 100 ° C. or higher and lower than 300 ° C. for 5 minutes or longer.
A method for obtaining a high-hardness nickel-plated coating, which comprises.

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