JPH0142354B2 - - Google Patents

Description

Detailed Description of the Invention The present invention aims to directly plate the surface of stainless steel with silver, gold, platinum, or other metals using an electroless plating method to form a thin and spotless plating film on the stainless steel. This relates to a method for pre-plating steel.

Stainless steel has excellent corrosion resistance and acid resistance, and in general, special protective treatments such as plating are rarely applied to its surface. In industrial applications related to electronics, catalysts, bioreactors, etc., it is often necessary to plate the surface of stainless steel with various metals such as silver, gold, platinum, palladium, iridium, and osmium. be.

However, with current plating technology, it is generally difficult to directly apply silver plating, gold plating, etc. to the outer surface of stainless steel. In other words, even if the outer surface of stainless steel is subjected to mechanical or chemical pretreatment, it can be directly plated using an electroless plating method.
In practice, it has not been possible to obtain a high-quality plating film that is thin and completely free of spots.

Conventionally, when performing electroless plating on stainless steel, a film of a metal such as nickel, which can be plated relatively easily on stainless steel, is first formed on the outer surface of the stainless steel as a base layer, and then a film is formed on the outer surface of the stainless steel. Furthermore, a two-layer plating method that includes silver plating, etc. is being used, but the plating process becomes complicated, which increases the plating cost, and depending on the application, the plating film becomes too thick, which is undesirable. was left behind.

The present inventors focused on the fact that even with conventional mechanical or chemical surface treatment methods, a film of silver, etc. is partially formed on the surface of stainless steel, even if it is incomplete, and electroless plating. We have conducted extensive research into a pretreatment method that can directly form a good plating film, and have arrived at the pretreatment method of the present invention.

To specifically explain the method of the present invention, as a result of various plating experiments conducted on a large number of test pieces with different surface treatment methods and treatment conditions, it was found that hydrogen was formed on the outer surface of stainless steel under certain temperature conditions. We have found that test pieces heat-treated in a gas-containing atmosphere can be plated with extremely high quality using an electroless method.

The present invention provides a plating pretreatment method that can easily form a thin and spotless plating film of silver, gold, platinum, or other metals directly on stainless steel with high plating efficiency using an electroless plating method. When plating silver, gold, platinum, or other metals directly onto the surface of stainless steel using an electroless plating method, the plated portion of the stainless steel surface is heated to a temperature of 200°C or higher in an atmosphere containing hydrogen gas. Then, the surface is heat-treated.

With this configuration, it is possible to directly form an excellent plating film on stainless steel with a thin, even and uniform thickness, which was almost impossible to achieve technologically until now. It is possible to significantly reduce costs.

EMBODIMENT OF THE INVENTION Hereinafter, the details will be explained based on one embodiment of the present invention shown in the drawings.

FIG. 1 is an explanatory diagram of the plating pretreatment method according to the present invention, in which a stainless steel plated body P formed by cutting, press working, etc. is first subjected to preliminary treatment such as degreasing. Thereafter, heat treatment is performed at a temperature of 200° C. to 700° C. for about 20 to 60 minutes in a heating furnace 1 filled with hydrogen.

That is, after storing the object P to be plated in the furnace 1,
The heater 2 is energized to raise the temperature inside the furnace, and the vacuum pump 3 is used to exhaust the air inside the furnace.
After setting the furnace temperature to 200°C to 400°C and the vacuum level to 10 ^-1 to ^{10 -2} torr, valve 4 was closed, vacuum pump 3 was stopped, valve 5 was opened, and 5% hydrogen stored in cylinder 6 was released. A hydrogen-containing gas 7 consisting of 95% of an inert gas such as argon and the like is introduced into the furnace to replace the atmosphere with the hydrogen-containing gas 7. After creating a hydrogen-containing gas atmosphere inside the furnace, the temperature inside the furnace was raised to 200℃~700℃, and the temperature was increased to about 20℃~700℃.
The object to be processed P is heat-treated in a reducing gas atmosphere for 60 minutes. As a result of this operation, the surface of the stainless steel is probably subjected to so-called hydrogen reduction treatment, and the oxide film etc. are almost completely removed.As a result, the outer surface of the object to be treated P is subjected to conventional chemical or mechanical treatments such as pickling and polishing. It is presumed that this results in an extremely high-grade clean surface that cannot be obtained through surface treatment.

The stainless steel constituting the body P to be plated may be of any type as long as it is generally known as stainless steel, and may be any type of stainless steel such as ferritic, martensitic, austenitic, etc. The method of the invention can be applied.

In this embodiment, cleaning treatment is performed as a pretreatment, but the pretreatment may be omitted depending on the surface condition of the stainless steel.

Further, in this embodiment, the object to be processed P was heated by the indirect heater 2, but the heating method may be any method such as high/low frequency induction heating, resistance heating, infrared heating, etc. Any type of equipment for placing the hydrogen atmosphere may be used.

In the example, before replacing the hydrogen-containing gas, the inside of the device was once evacuated and then the hydrogen-containing gas was introduced. There is no problem.

In this example, the heat treatment of the object P to be plated in a hydrogen atmosphere is carried out in a so-called batch method.
It is also possible to use a continuous heat treatment method.

In the heat treatment operation in the hydrogen gas-containing atmosphere, if the temperature inside the furnace is lower than 200°C, the thickness of the plating film becomes uneven and spots are likely to occur, and formation of a high-quality plating film cannot be expected. do not have. This phenomenon is
It is presumed that this is because oxides are not sufficiently reduced when the temperature is below 200°C.

In addition, when so-called intergranular corrosion becomes a particular problem during heat treatment of austenitic stainless steel, etc., it is desirable to set the heat treatment temperature to 400° C. or lower.

FIG. 2 shows an example of a silver plating process employing the pretreatment method for plating according to the present invention, in which a stainless steel object P to be plated formed into an appropriate shape is subjected to a cleaning process A. After performing preliminary treatment such as degreasing, the material is sent to heat treatment step B in a hydrogen gas-containing atmosphere, and is subjected to preheat treatment for plating in the heating furnace 1 as described above.

After the heat treatment in the hydrogen gas-containing atmosphere, the plated object P is subsequently sent to the rinsing process C, where a rinsing liquid consisting of tin and a suitable hydrating agent is applied, for example, manufactured by London Laboratory Co., Ltd. in the United States. Perform a so-called rinsing treatment using RBL treatment solution (trade name) and RNA treatment solution (trade name). By performing the rinsing treatment, the surface of the stainless steel becomes hydrophilic, and silver adheres to the surface using tin as a core, making it easier to form a silver plating film. Furthermore, after the treatment with the RBL and RNA treatment solution, the membrane is finally rinsed lightly with pure water. This rinsing treatment step C may be omitted.

After the rinsing process, the object P to be plated is sent to a plating process D, where it is plated with silver using an electroless plating method. A so-called two-component plating solution in which a silver solution and a reducing solution were mixed at a volume ratio of 1:1 was used as the plating solution, and the components of the silver solution and the reducing solution were as follows.

Silver solution Silver nitrate 3.5 g Ammonia water Amount required to redissolve the precipitate Water 60 ml Sodium hydroxide 2.5 g Reducing solution Glucose 45 g Tartaric acid 4 g Alcohol 100 ml Water 1000 ml To prepare the above silver solution, add ammonia water to 3.5 g of silver nitrate, and add ammonia water to 3.5 g of silver nitrate. Add aqueous ammonia until the formed precipitate is redissolved. Next, add 2.5 g of sodium hydroxide and 60 ml of water to 60 ml of this silver solution, and adjust by adding ammonia water again until the black solution becomes clear. In addition, the adjustment of the reducing solution is performed using water.
After sequentially dissolving glucose and tartaric acid in 1000ml,
This is done by boiling for about 10 minutes, cooling to room temperature, and then adding alcohol. 1 to 2 objects P to be plated are placed in the plating solution at a temperature of 15 to 30°C.
By dipping for a minute, an extremely thin and uniformly thick silver plating film was formed on the surface of the object P to be processed.

The plating solution is not limited to those described above, and may be of any composition as long as it utilizes a two-component silver mirror reaction.For example, the plating solution manufactured by London Laboratory, Inc. Two-component plating liquid (product name: ATS, product name: ATA)
etc. are most preferred.

Further, in the above embodiment, a two-component electroless plating solution was used, but it goes without saying that a known three-component plating solution may be used. For example, a silver solution (product name: MS-1L) and a reducing solution (product name: MA-260L) manufactured by London Laboratory, Inc. are mixed in a 1:1 ratio, and this is mixed with a neutralizing solution (product name:
By using a three-component plating solution made by adding a small amount of KDR), the outer surface of the inner tank is immersed in the plating solution at a temperature of 50℃ to 70℃ for 1 to 2 minutes.
A silver film may also be formed. The specific preparation of silver solution (MS-1L), reducing solution (MA-260L), and neutralizing solution (KDR) is as follows: First, add 20 c.c. (MS-1 L) to 200 c.c. of water. (MA−260L) Mix 20c.c.
Next, 10 c.c. of (KDR) was mixed into another 200 c.c. of water, and finally the two were mixed and stirred. The plating solution was maintained at 60° C., and the object P was immersed therein for 2 to 3 minutes to carry out silver plating.

When the plating treatment is completed, the treated body P is sent to a finishing step E, and the outer surface of the silver plating film is rinsed using the RNA treatment solution and pure water.

In the above embodiments of plating, silver plating using an electroless method was explained, but the method invention of the present application
It can also be applied to plating metals that are generally considered difficult to directly plate on stainless steel, such as gold, platinum, palladium, ossium, iridium, etc. In this case, the plating process is exactly the same as that for silver plating, except that the plating solution used in the plating process D is different.

For example, when performing gold plating, 10g of gold chloride
30 ml of a gold liquid made by mixing 5 g of sodium chloride and 800 ml of water, and 70 ml of a reducing liquid formed by mixing 22.5 g of tartaric acid, 300 g of caustic soda, 380 ml of alcohol, and 600 ml of water to prepare a plating solution. The object P to be processed may be immersed in the liquid for 2 to 3 minutes.
When plating with palladium, the plating solution may be a mixture of 5.4 g of tetramine palladium chloride, 33.6 g of sodium EDTA, 350 g of ammonia, and 0.3 g of hydrazine.

In addition, in the examples of each of the above-mentioned plating, plating with silver, gold, etc. by an electroless method is described,
Of course, the method invention of the present application can also be applied to electroplating of silver, gold, etc.

As mentioned above, the present invention heat-treats stainless steel under constant temperature conditions in an atmosphere containing hydrogen gas, thereby making it possible to directly plate stainless steel by an electroless method, which had been considered technically difficult until now. This means that the surface of stainless steel is coated with extremely thin silver, platinum, gold, iridium, etc. with a uniform thickness and no spots.
It is possible to form a plating film of metals such as palladium, osmium, etc., and the plating cost can be significantly reduced compared to conventional two-layer plating.

Furthermore, the specular light reflectance on the surface of the plating film is approximately the same value as in the case of conventional two-layer plating, and there is no deterioration in the physical or chemical properties of the film.

As mentioned above, the present invention has excellent practical utility.

[Brief explanation of drawings]

FIG. 1 is an explanatory diagram of a pretreatment method for plating according to the present invention. FIG. 2 is a process diagram of silver plating stainless steel using the pretreatment method for plating according to the present invention. 1... Heating furnace in an atmosphere containing hydrogen gas, 2... Heater, 4, 5... Valve, 3... Vacuum pump, 6
...Cylinder, P...Object to be plated, 7...Reducing gas, A...Cleaning process, B...Heat treatment process in an atmosphere containing hydrogen gas, C...Rinse treatment process, D...
Plating process, E...finishing process.

Claims (1)

[Claims] 1. A pre-plating method for stainless steel, which, when performing electroless plating on the surface of stainless steel, heat-treats the plated portion of the stainless steel surface to a temperature of 200°C or higher in an atmosphere containing hydrogen gas.