JPH0142353B2 - - Google Patents

Description

[Detailed Description of the Invention] The present invention relates to an improved silver plating method for preventing radiation in stainless steel thermos flasks (hereinafter referred to as stainless steel thermos flasks), and involves vacuum heating treatment and hydrogen reduction treatment on the outer surface of stainless steel. This invention relates to a silver plating method that allows an extremely thin and spotless silver plating film to be directly formed on the outer surface of stainless steel using an electroless plating method using a two-liquid or three-liquid method.

In recent years, from the perspective of improving the strength of thermos flasks, metal thermos flasks with inner and outer containers made of stainless steel have been developed and widely used.

Generally, in thermos flasks, it is necessary to reduce heat loss due to radiation in order to increase the heat insulation effect, and stainless steel thermos flasks have traditionally had heat loss on both or either the outer surface of the inner tank and the inner surface of the outer tank. Radiation loss is prevented by plating one side with aluminum or nickel, or by polishing the surfaces of the inner and outer tanks with extremely high precision to increase their reflectance. In terms of radiation loss prevention performance,
Silver plating is far superior to aluminum or nickel plating. However, with current electroless plating technology, it is difficult to form a thin, spotless silver plating film on the outer surface of stainless steel, and no matter how chemically or mechanically the stainless steel surface is treated, the film thickness remains The current situation is that the plating can only be large and extremely patchy, making it impossible to put it to practical use. As a result, as mentioned above, a method of plating with aluminum, nickel, etc. instead of silver has been adopted.

On the other hand, as an improvement to the above-mentioned high-precision polishing method and measures to prevent radiation loss due to nickel plating, etc., there is a method of further applying silver plating on top of nickel plating, etc., and a method of fixing a thin glass layer to the surface of stainless steel and A method of applying silver plating has been developed, and thermos flasks are known in which the heat insulating effect is further improved by this method.

However, the method of applying silver plating on top of nickel plating, etc., or the method of fixing a thin glass layer to the stainless steel surface and applying silver plating on top of it, both significantly increase the number of processing steps, making it difficult to reduce the manufacturing cost of thermos flasks. The problem is that it is difficult to plan. Furthermore, if a glass layer is present or the plating layer is thick, degassing becomes more difficult and the degree of vacuum is likely to decrease due to the release of gas molecules.

The present invention aims to solve the above-mentioned problems in preventing radiation from stainless steel thermos flasks. The purpose of this invention is to provide a method for silver plating stainless steel thermos flasks that enables the formation of a thin and spotless silver plating film using electroless plating, thereby reducing manufacturing costs and significantly reducing radiation loss. It is something to do.

Generally, when manufacturing a stainless steel thermos flask, the inner and outer chambers are baked in order to maintain the degree of vacuum in the vacuum insulation space G constant over a long period of time. In other words, the inner and outer vessels are placed in a vacuum furnace and heated at high temperature in vacuum for a certain period of time to forcefully release the gas molecules inside the stainless steel, thereby preventing the degree of vacuum from changing over time. be. In the baking process, the inventor of the present application
Focusing on cleaning the outer surface of stainless steel, we conducted electroless silver plating experiments on numerous test pieces with different heating temperatures and degrees of vacuum, and based on the results, we first performed preliminary silver plating in a vacuum heating furnace. We discovered that it is possible to form an extremely thin and uniformly thick silver film with excellent reflectance using an electroless plating method on test pieces that have been heat-treated and then subjected to hydrogen reduction treatment at a temperature above a certain value. It is something that

In the present invention, after preliminary heat treatment of the inner tank and the outer tank in a vacuum heating furnace, the inner tank and the outer tank are heated to 200°C or higher in a hydrogen-containing gas atmosphere to perform a hydrogen reduction treatment. The basic structure is to directly apply silver plating to the hydrogen-reduced outer surface of the inner tank and/or the inner surface of the outer tank using two-component or three-component electroless plating. This structure makes it possible to form a thin, uniformly thick silver plating film with excellent reflectance and adhesion on stainless steel, which was previously thought to be technically impossible. It becomes possible.

Hereinafter, details will be explained based on an embodiment of the present invention shown in FIGS. 1 and 2.

FIG. 1 is a longitudinal sectional view of a stainless steel thermos flask according to the present invention, in which 1 is a stainless steel inner tank, 2 is a stainless steel outer tank, 3 is a heat insulating stopper, and 4
5 is a vacuum exhaust port, 5 is a sealing plate, and 6 is a vacuum insulation space. The inner and outer tanks 1 and 2 are formed using stainless steel (SUS304) plates with a thickness of 0.5 mm, and the outer surface of the inner tank 1 is coated with a silver coating 7 to prevent radiation loss. Formed and fixed using liquid electroless plating. In this embodiment, the silver film 7 is formed only on the outer surface of the inner tank 1, but the outer tank 2
Of course, it may be formed only on the inner surface side of the tank, or may be formed on both the inner and outer tanks.

FIG. 2 shows the manufacturing process of a stainless steel thermos flask by the silver plating method according to the present invention,
A is the molding process for the inner and outer tanks, B is the chemical cleaning process for the inner and outer tanks, C is the pre-heat treatment process, D is the hydrogen reduction process, E is the pre-rinsing process, F is the plating process, and G is the plating process. A post-rinsing process, H is a post-heat treatment process, and I is an assembly/vacuum sealing process.

The inner and outer tanks 1 and 2 formed into a predetermined shape in the molding process A are sent to a cleaning process B, where they are first subjected to chemical treatments such as degreasing. The inner and outer tanks 1 and 2 that have undergone chemical cleaning treatment such as degreasing are then sent to preheat treatment step C, where they are heated at a temperature of 100°C to 700°C in a vacuum furnace that constitutes step C. ^10-1 to ^10-4 torr
Heat treated for about 5 to 20 minutes under vacuum.

After completing the preheat treatment in the vacuum heating furnace, the inside of the vacuum heating furnace is made into an atmosphere of a mixed gas consisting of 5% hydrogen and 95% inert gas, and the temperature inside the furnace is increased to 100%.
℃~700℃, inner/outer tank 1 for about 20~60 minutes,
By holding 2 in this state, the so-called hydrogen reduction treatment is performed on the outer surface of each. By performing the hydrogen reduction treatment, the surface of the stainless steel plate becomes almost completely clean, resulting in an extremely high-grade clean surface that cannot be obtained with conventional chemical or mechanical cleaning treatments such as pickling and pap polishing. It will be done. In this embodiment, the chemical cleaning step B and the preheat treatment step C are used as preliminary treatment steps, but it goes without saying that these may be omitted.

The inner and outer tanks 1 and 2 that have left the hydrogen reduction treatment process D are
It is then sent to a rinsing step E, where a rinsing solution consisting of tin and a suitable hydrating agent is added, such as that manufactured by London Laboratories, USA.
A so-called rinsing process is performed using RBL, an RNA processing solution (trade name). By performing the rinsing treatment, the stainless steel surface becomes hydrophilic, and
Silver adheres to the surface using the tin as a core, making it easier to form the silver plating film 7 and further improving its adhesive strength. Furthermore, the above
After processing with RBL and RNA processing solution, a final rinse is performed with pure water. If you do this,
This is advantageous in that the amount of gas degassed in the post-heat treatment step H, which will be described later, is reduced and the quality of the plating solution is maintained.

After the rinsing process, the inner and outer tanks are sent to a plating process F, where they are plated with silver using an electroless plating method. In the first embodiment of the present application, a silver solution and a reducing solution are used as a plating solution in a volume ratio of 1:1.
A so-called two-component plating solution mixed in step 1 is used, and the components of the silver solution and reducing solution are as follows.

Silver liquid Silver nitrate 3.5 g Ammonia water Amount required to redissolve the precipitate Water 60 ml Sodium hydroxide 2.5 g Reducing liquid 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, 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,
Boil for about 10 minutes, cool to room temperature, and adjust by adding alcohol. Temperature 15-30
By immersing the outer surface of the inner tank for a predetermined period of time, e.g. 1 to 2 minutes, in the plating solution at a temperature of 0.degree. C., an extremely thin and uniformly thick silver plating film 7 is formed and fixed on the outer surface of the inner tank. become. The same applies to the silver plating on the inner surface of the outer tank, and by filling the outer tank 2 with the plating liquid and draining it after storing it for a predetermined time, a similar silver plating film 7 can be firmly formed. Become.

The plating solution is not limited to those mentioned 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 ATA, product name ATS)
etc. are most suitable for implementing the present invention.

Further, in the first embodiment, a two-component electroless plating is used, but it goes without saying that a three-component plating solution may be used. For example, the silver liquid (product name MS-1L) and reducing solution (product name MA-260L) manufactured by London Laboratory, Inc.
Mix at a ratio of 1:1 and add neutralizing liquid (trade name) to this.
By using a three-component plating solution made by adding a small amount of KDR), the outer surface of the inner tank is immersed for 1 to 2 minutes in the plating solution at a temperature of 50°C to 70°C.
A silver plating film may also be formed.

In addition, in the case of the second embodiment of the present application, the above-mentioned MS-1L
The specific formulation of MA-260L and KDR is to first add water.
MS-1L (20c.c.) and MA-260L (20c.c.) into 200c.c.
Mix and then KDR (10c.c.) into another water 200c.c.
Silver plating is carried out by mixing the two and finally mixing and stirring the two, and silver plating is carried out by keeping the plating solution at around 60℃ and immersing the inner tank in it for 2 to 3 minutes. ing.

After completing the silver plating process F, the inner and outer tanks 1 and 2 undergo a post-rinsing process G in which the silver plating film 7 is rinsed with pure water and RNA treatment solution (trade name of London Laboratories, Inc., USA). The material is sent to a post-heat treatment step H, where a vacuum furnace is used to degas the inside of the plating layer. The post-heat treatment H is performed at a relatively low temperature and under a high degree of vacuum in view of the heat resistance of the silver plating film 7, and the adsorbed gas molecules in the plating layer are almost completely degassed by the heat treatment. will be done.

After finishing the post-heat treatment H, the inner and outer tanks 1 and 2 are finally sent to the assembly/vacuum sealing process I, in which a sealing plate 5 is brazed to the vacuum exhaust port 4 on the bottom of the outer tank 2 in a vacuum furnace, or
Alternatively, the vacuum insulation space 6 is sealed off by closing the exhaust port 4 by electron beam welding. Note that the post-heat treatment step H and the vacuum sealing step I are usually performed in the same vacuum furnace, and the inside of the space 6 is
It is maintained at a vacuum level of about 10 ^-3 to ^{10 -5} torr.

In each of the embodiments of the present application, the plating process F using the electroless plating method is described as described above, but silver plating using the so-called electrolytic plating method may also be adopted. According to steps C and D, direct silver plating on stainless steel using an electrolytic plating method, which has been conventionally considered impossible, becomes possible.

According to the silver plating method according to the present invention, it is possible to easily form and fix an extremely thin silver plating film 7 with a uniform thickness and no spots on the surface of a stainless steel material. For example, when stainless steel is treated with a conventional surface treatment method that combines degreasing with hydrochloric acid and ultrasonic cleaning, and then silver plated with so-called electroless plating or electrolytic plating. However, the film is thick and extremely uneven, and the thickness is uneven and the adhesion is weak, and furthermore, the reflectance is extremely low and only a silver plating film 7 can be formed that cannot be put to practical use. On the other hand, according to the present invention, it is possible to obtain a silver plating film 7 having extremely excellent properties in terms of thickness, unevenness, adhesion, reflectance, aging, etc., and the silver efficiency is also higher than that of plating on glass. The value is approximately the same or slightly better than that in the case where

In addition, the thermos according to the present invention with an internal volume of 2.2 mm (outer tank inner diameter 121 mmφ, inner tank inner diameter 100 mmφ, vacuum insulation space thickness 10 mm, inner and outer tank stainless steel plate thickness 0.5 mm, only the outer surface of the inner tank is silver-plated, electronic According to a heat retention test using vacuum sealing using beam welding, hot water (2.2) with a boiling temperature of 95°C reaches 67°C after 24 hours. On the other hand, a thermos bottle with the same capacity that uses conventional surface polishing and plating processing such as aluminum, has a
After an hour, the temperature becomes 62°C to 63°C, which shows a temperature difference of about 4°C to 5°C.

Furthermore, according to the plating method of the present invention, manufacturing costs can be significantly reduced compared to silver plating on a glass film or two-layer plating.

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

[Brief explanation of drawings]

FIG. 1 is a longitudinal sectional view of a stainless steel thermos flask according to the present invention. FIG. 2 is a manufacturing process diagram of a thermos flask according to the present invention. 1...Inner tank, 2...Outer tank, 3...Insulation plug, 4...
...Vacuum exhaust port, 5...Sealing plate, 6...Vacuum insulation space, 7...Silver film, A...Molding process, B...Chemical cleaning process, C...Preheat treatment process, D...Hydrogen reduction Treatment process, E... Pre-rinsing process, F...
Plating process, G... Post-rinsing process, H...
... Post-heat treatment process, I... Assembly/vacuum sealing process.

Claims (1)

[Claims] 1. In the silver plating treatment of a thermos flask whose inner and outer tanks are made of stainless steel plates, the inner and outer tanks are first preheated in a vacuum heating furnace, and then the inner and outer tanks are heated to contain hydrogen. Hydrogen reduction treatment is performed by heating to 200℃ or higher in a gas atmosphere, and after the hydrogen reduction treatment, silver plating is directly applied to the outer surface of the inner tank and/or the inner surface of the outer tank using an electroless plating method. A method for silver plating a thermos flask made of stainless steel plate.