JPH0214431B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for silver plating stainless steel. Silver plating has traditionally been applied to various items such as jewelry, but products made from ordinary steel such as mild steel have the problem of rusting when the silver plating wears out after long-term use. Therefore, attempts have been made to use stainless steel as a material, but it has been impossible to directly silver plate the stainless steel surface. On the other hand, in recent years, attempts have been made to apply silver plating to metal thermos flasks in the same way as glass thermos flasks, taking advantage of the fact that silver plating has a small radiation coefficient. Stainless steel, which is used as a metal material for metal tribo bottles, has the advantages of excellent corrosion resistance, strong mechanical strength, and low thermal conductivity, but like other metal materials, the inner container When creating a high vacuum in the space formed between the inner container and the outer container, there is a problem in that gas is released from the inside and the degree of vacuum gradually decreases. Even if an attempt was made to form a silver mirror plating like in a heavy container, it was impossible to cause a silver mirror reaction. As a method for silver plating stainless steel, for example, in Japanese Patent Publication No. 57-22571, a glassy layer containing silicon dioxide as a main component is formed on the surface of stainless steel, and a silver mirror reaction is applied on the glassy layer. The method of silver plating is also
JP-A-57-75621 proposes a method of applying nickel plating to the surface of stainless steel and then silver plating thereon by silver mirror reaction. Stainless steel vacuum double containers coated with silver plating using these methods can obtain sufficient heat retention for practical purposes due to the action of the glass layer or nickel plating layer and the silver mirror layer, and can maintain heat retention for a long period of time. However, the glassy layer interposed between the stainless steel base and the silver mirror layer tends to become uneven, resulting in variations in product quality, and in the case of nickel plating, the inner and outer bottles are Since each member, for example, the body member, neck member, and bottom member, must be plated and then joined, the manufacturing process is complicated and requires a large number of man-hours. The present invention was made to solve these problems, and aims to provide a method for silver plating stainless steel that can form a homogeneous and high-quality silver plating. The method of silver plating stainless steel is characterized by firing in a neutral atmosphere and then causing a silver mirror reaction through the oxide film formed on the surface of the stainless steel by firing. That is, in the present invention, although it is impossible to cause a silver mirror reaction with the raw material of stainless steel,
When the surface is moderately oxidized, an oxide film made of ferric oxide is formed on the surface, and this oxide film promotes the silver mirror reaction, making it possible to form a silver plating layer with good adhesion. It was completed based on knowledge. In a preferred embodiment of the present invention, in order to promote the silver mirror reaction, after the oxide film is formed and prior to the silver mirror reaction, the surface of the oxide film is wetted and activated with an activating solution containing a stannous halide as a main component. What is done is done. In another preferred embodiment, in order to ensure strong adhesion of the silver plating layer to the stainless steel surface, the firing treatment is performed at 250 to 550°C for 5 to 120 minutes.
It is preferably carried out at 300 to 450°C for 10 to 60 minutes. According to the method of the present invention, silver plating on stainless steel is performed by first oxidizing the stainless steel surface by firing treatment and then causing a silver mirror reaction, but the degree of oxidation on the stainless steel surface is
It is preferable that the glossiness of the stainless steel surface after firing is 10 to 50 lower than the glossiness of the polished surface before firing. This is because oxidation that reduces the gloss level to less than 10 cannot cause a silver mirror reaction on the stainless steel surface, and excessive oxidation that reduces the gloss level to more than 50 makes it difficult to cause a silver mirror reaction. Because it will be. The reason why this phenomenon occurs is that in unfired or similar conditions, ferric oxide is not sufficiently formed and the silver mirror reaction is inhibited, and if it is excessively oxidized, there is no ferric oxide on the surface and almost no ferric oxide exists on the surface. It is presumed that this is because only chromium oxide is left. Usually, the change in the glossiness falls within the above range as long as the firing is carried out under the firing conditions, so there is no need to particularly measure the glossiness after firing. The silver plating layer is formed on the stainless steel surface with the oxide film interposed therebetween, and this can be formed by a method similar to that used for manufacturing glass rubble bottles. That is, in order to accelerate the silver precipitation rate and to deposit it uniformly, the oxide film is activated by wetting it with an activating solution containing stannous halide as a main component, and then treated with a silver mirror solution. Ru. Although the activation treatment can be omitted, it is desirable to perform it in order to shorten the time required to form the silver plating layer. Further, as the silver mirror solution, one used for manufacturing glass rub bottles may be used. Examples of the present invention will be described below. Example 1 A 0.3 mm thick stainless steel (SUS304) test piece (50 mm x 150 mm) was prepared, buffed, baked in air at 350°C for 30 minutes, and then 10 ppm
of tin chloride to activate its surface. After washing with water, it was immersed in a silver mirror solution prepared according to the following formulation at 20°C for 5 minutes to cause a silver mirror reaction, and when washed with water and dried, a good silver plating layer could be formed. (Prescription of silver mirror solution) Dissolve 10g of silver nitrate in a small amount of water and add 28%
Add 500ml of ammonia water and water to make 4800ml,
An aqueous solution in which 10g of sodium hydroxide is further dissolved
Add 200ml to make the total volume 5000ml, and use this as Solution A. Separately, 0.25 ml of concentrated nitric acid was added to an aqueous solution of 20 g of sucrose dissolved in 50 ml of water and boiled. After adding 5 ml of a 37% formaldehyde aqueous solution to this,
Add water to bring the total volume to 5000ml, and use this as Solution B. The above liquid A and liquid B are mixed at a volume ratio of 1:1 to obtain a silver mirror liquid. In order to examine the adhesion of the plating layer thus formed, I rubbed it strongly with my fingertips, but there was no peeling at all. The gloss of the test piece surface after buffing and degreasing was 122, and the gloss after firing was 101, which was 21 lower than before firing. This gloss value is calculated using a digital variable angle gloss meter (Model: UGV-) manufactured by Suga Test Instruments Co., Ltd.
4D), based on the measurement method specified in JIS Z8741, with an incident angle of 60° and the standard sample's glossiness of 91.1 set to 1/4 of that, 22.8. Comparative Example 1 When the unfired test piece prepared in Example 1 was treated in the same manner as in Example 1 using the activating solution and silver mirror solution, a silver plating layer could be formed on the surface of the test piece. Nakatsuta. Examples 2 to 7 and Reference Examples 1 to 3 After firing the test pieces prepared in Example 1 under various firing conditions shown in Table 1, the glossiness was measured, while using the silver mirror solution prepared in Example 1. Electroless plating was performed under the same conditions. The results are shown in Table 1 together with the results of Comparative Example 1.

[Table] As is clear from the above description, according to the present invention, there is no need for a complicated process unlike in the case of conventional silver plating on a stainless steel surface with a glassy layer or nickel plating layer interposed therebetween. Simply, after firing,
Since a silver plating layer can be formed by carrying out a silver mirror reaction, excellent effects such as improved workability and the ability to manufacture a high quality silver plating layer at low cost can be obtained. Incidentally, when the present invention is applied to the production of stainless steel rubble bottles, the manufacturing cost can be significantly reduced compared to the method in which nickel metal is used, and a rubble bottle with heat retention performance comparable to that of glass rubble bottles can be obtained. I was able to do that. This will be explained with reference to the attached drawings. In the drawings, 1 is an inner bottle made of stainless steel, 2 is an outer bottle made of stainless steel, and both are attached at the mouth part 3 by brazing, welding, or other means. The inner bottle 1 is joined to form a double wall structure.
The space 4 formed between the outer bottle 2 and the outer bottle 2 is evacuated and made into a vacuum. A tip tube 5, which serves as an exhaust port for evacuating the space 4, is connected to the bottom 2b of the outer bottle 2 by brazing or the like.
A bottom cover 6 is attached to the bottom part 2b with adhesive to protect the bottom part 2b. On the other hand, according to the present invention, in order to improve the heat retention ability of the stainless steel vacuum double container, the walls of the inner and outer bottles forming the space 4, that is, the outer surface of the inner bottle 1 and the inner surface of the outer bottle 2, are provided with grooves. As shown in FIG. 2, an oxide film 7 is formed, and a silver mirror layer 8 is laminated thereon. This stainless steel thermos flask was manufactured as follows. That is, first, the inner bottle 1 is manufactured from a 0.5 mm thick stainless steel plate (SUS304), and the shoulder member 2c, body member 2a, and bottom member 2b of the outer bottle 2 are manufactured from 0.6 mm thick stainless steel plate, and then the inner bottle 1 and the shoulder member 2c of the outer bottle 2 are welded at their mouth portions 3, and this is baked in air at 350° C. for 30 minutes.
Next, separately from this, the body member 2a and bottom member 2b of the outer bottle are welded to form an integrated assembly, which is then welded to the fired inner bottle 1 to form a double wall structure, and the outer bottle bottom 2b
An aqueous solution containing 10 ppm of stannous chloride is injected into the space 4 from the tip tube 5 connected to the inner bottle 1 to activate the outer surface of the inner bottle 1, and after discharging the aqueous solution, it is washed with water. Next, the silver mirror solution prepared in Example 1 was added to the tip tube 5.
As in the case of a glass thermos flask, the double bottle is held horizontally in the axial direction and poured into the space while rotating at high speed to precipitate silver mirror and form the silver mirror layer shown in FIG. After that, it is washed with water, dried, and vacuum treated in the same manner as for glass thermos flasks, and the tip is melt-sealed. Attach the bottom cover 6 to the bottom of the double bottle obtained in this way.
Join them to obtain a thermos flask with an internal capacity of 0.75. In order to investigate the heat retention ability of this thermos flask, we measured it under the following conditions using the test method specified in JIS S2005, and the heat retention effect for 6 hours and 24 hours was 82.5℃ and 59.9℃, respectively.
It was hot. [Test conditions] Pouring temperature: 95℃ Hot water amount: Full Stopper: Sealed stopper (45mmφ) Ambient temperature: 20℃

[Brief explanation of drawings]

Figure 1 is a longitudinal cross-sectional view of a stainless steel thermos flask manufactured by applying the method of the present invention, and Figure 2 is A of Figure 1.
It is an enlarged view of the part. DESCRIPTION OF SYMBOLS 1... Inner bottle, 2... Outer bottle, 4... Space, 5... Chip tube, 6... Bottom cover, 7... Oxide film, 8... Silver mirror layer.

Claims (1)

[Claims] 1. A method for silver plating stainless steel, which is characterized by firing stainless steel in an oxidizing atmosphere, and then causing a silver mirror reaction through an oxide film formed on the surface of the stainless steel by firing treatment. . 2 Prior to the silver mirror reaction, the first halogenated
2. The method according to claim 1, wherein the oxide film surface is activated by wetting it with an activating liquid containing tin as a main component. 3. The method according to claim 1 or 2, wherein stainless steel is fired at 250 to 550°C for 5 to 120 minutes in an oxidizing atmosphere.