JPH0213024B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for continuously vacuum-depositing zinc Zn onto steel materials, particularly steel strips. Conventionally, when vacuum depositing Zn on steel strip, Zn
Because of the low adhesion to the steel strip, it is said that it is necessary to keep the deposition pressure as low as possible and the temperature of the steel strip as high as possible, and the deposition pressure is 10 ^-4 to ^{10 -6} Torr. It was considered appropriate. However, 10 ^-4 ~ which is said to be appropriate
Of course, in a vacuum of 10 ^-6 Torr, even in a vacuum with a higher pressure of 10 ^-2 Torr, many large-capacity vacuum pumps are required to maintain the vacuum, and the vacuum container also has a large amount of leakage. However, since it is necessary to reduce the amount of gas emitted, there is a drawback that both equipment costs and operating costs are high. Also, something like this
When the temperature of the steel strip is raised to 200℃ or higher under a vacuum with a low pressure such as 10 ^-4 to ^{10 -6} Torr, the evaporation occurs.
The temperature of the steel strip increases due to the condensation and solidification latent heat generated when Zn vapor is deposited on the steel strip, and
There was a drawback that Zn evaporated from the steel strip again, so-called re-evaporation, and the re-evaporated Zn vapor adhered and deposited on the drive part or sealing device in the vacuum chamber, causing problems in operation. Conventionally, in order to prevent this re-evaporation, the steel strip was cooled during deposition.
A method to prevent temperature rise due to the latent heat of Zn, or by providing a protective cover to protect Zn from drive parts and sealing devices.
Methods have been considered to prevent adhesion, but steel strips are cooled in a vacuum, which has low cooling efficiency and cannot be cooled rapidly.Furthermore, preventing adhesion with a cover is difficult because Zn is on the underside. Since it is a large metal, it can penetrate into the back side of the cover and adhere to drive parts, etc., and has disadvantages such as low adhesion prevention effect. In view of the above circumstances, the present inventors investigated the deposition pressure and temperature of the deposited object from the viewpoint of preventing re-evaporation of deposited zinc. As a result, the inventors found that the adhesion of the deposited film even under relatively high pressure vacuum conditions. We have found an optimal range that ensures high performance, low re-evaporation, and allows easy and inexpensive vapor deposition on an industrial scale. That is, the present invention provides a method for vacuum evaporating zinc onto a steel material, in which the surface of the steel material to be deposited is subjected to a reduction treatment, and the temperature (T°K) and deposition pressure (PTorr) of the material to be deposited are set as below. This is a vacuum evaporation method for zinc, which is characterized in that the evaporation is performed while adjusting the evaporation within a range that satisfies the following relationship. This will be explained in detail with reference to FIG. 1, which summarizes the experimental results of the present invention. The curve in Figure 1: 1 is
This is a plot of the temperature of Zn (T°K) and the saturated vapor pressure of Zn (P _s Torr) at that temperature.
It is expressed as [logP _s =-(6850/T)-0.755logT+11.24]. Usually, the evaporation rate of metal in vacuum is determined by equation (1). G=C・√・(P _s − P)…(1) G: Evaporation rate C: Constant M: Atomic weight of evaporated metal T: Temperature of evaporated metal P _s :〃 Saturated vapor pressure at temperature T P: Vapor deposition pressure ( In equation 1), when P approaches _Ps , the evaporation rate decreases, and if P= _Ps , no evaporation occurs at all. In reality, when P≒P _s , equation (1) does not apply, and some amount of evaporation will occur due to diffusion, but the amount is very small and if P>P _s , practically no evaporation occurs. Re-evaporation is not a problem. That is, in the region to the left of curve 1, re-evaporation is not a problem, and curve 1 is the limit line where re-evaporation becomes a problem. Therefore, in order to avoid re-evaporation, it is sufficient to lower the temperature of the object to be deposited and increase the deposition pressure, but an experiment was then conducted to find the limit values. As a result, it was found that the adhesion of the deposited Zn film was good when the temperature of the object to be deposited was 80°C or higher, and as shown in Figure 1, straight line 2, this was found to be unrelated to the deposition pressure. . That is, the straight line 2 is the limit line on the low temperature side where the adhesion of the film can be ensured. However, it has become clear that the substrate temperature is preferably 200°C or higher in order to obtain a film with higher performance such as film toughness. On the other hand, as shown in Figure 1, straight line 3, if the temperature of the deposited material exceeds 400℃, Fe-Zn alloy is formed and the film performance is inhibited.
It has also become clear that the limit should not be exceeded. That is, straight line 3 is the limit line where alloying occurs. Regarding the deposition pressure, as long as it is permissible in terms of film performance, higher pressures are more advantageous in terms of equipment costs and operation.As a result of various tests, it was found that deposition up to 30 Torr is possible without impeding film performance. It became clear. However, as shown by straight line 4 in Figure 1, when the deposition pressure exceeds 30 Torr, intense boiling occurs in the evaporation source, and as a result, molten Zn scatters in the form of a splash, leaving granular particles on the object to be deposited.
It has become clear that Zn adheres to the surface, resulting in poor evaporation. Straight line 4 is the limit line where boiling of the evaporation source occurs. On the other hand, on the low pressure side, there is no limit to film performance, but as shown by straight line 5 in Figure 1,
When the pressure is lower than 10 ^-2 Torr, as mentioned above, the vacuum system becomes expensive, the temperature range of the material to be deposited to prevent re-evaporation becomes narrower, and the basis weight of Zn is limited. . For example, if the material to be deposited is
In the case of a 0.3 mmt steel strip, only a maximum of 80 g/m ² can be deposited, and if the weight exceeds this, the temperature at the end of the deposition becomes a region where re-evaporation becomes a problem. Straight line 5 is a limit line where the cost of the vacuum system and the range of the basis weight of Zn become a problem. As explained above, the present invention improves film performance, equipment, and operation by performing vapor deposition at the vapor deposition pressure and temperature of the material to be vaporized within the shaded area surrounded by straight lines and curves 1 to 5 in FIG. All of the above provide a problem-free vapor deposition method. In other words, the present invention has great industrial value in that it enables the vacuum deposition of Zn at high pressures such as 10 ^-2 to 30 Torr, which can make the exhaust system inexpensive. It's a method. Note that the steel plate is pretreated by some method as reduction treatment, but this pretreatment method is not particularly limited, and any method such as gas reduction treatment, ion bombardment, electron beam irradiation, etc. may be used. However, gas reduction treatment is suitable industrially. Example 1 Zn was vapor-deposited onto a mild steel plate using a batch-type vapor deposition apparatus having a bell jar with an inner diameter of 450φ. Zn evaporated from a graphite crucible is 0.3mmt×70mm×
Vapor deposition was performed on a 120 mm substrate by varying the deposition pressure and substrate temperature. As a pre-evaporation treatment, after degreasing with solvent in the air, it was placed in the evaporation equipment and heated at 700℃ in _H2 gas.
Reduction treatment was performed for 5 min. After vapor deposition under various conditions, film adhesion was evaluated by bending the film closely at 180°, applying Scotch tape to the bent part, peeling it off, and observing whether or not there was any peeling. Moreover, the presence or absence of Fe--Zn alloy layer formation was determined by observing the cross section with an optical microscope. The film thickness was measured using an electrolytic film thickness meter. The film thickness was deposited at each pressure level under conditions such that it would be 10μ in the absence of re-evaporation, and the presence or absence of re-evaporation was determined from the difference between the target film thickness and the measured value. The implementation results are shown in Table 1. In Table 1, each column is

[Table] shows the adhesion, 〇: Good adhesion, 〓: Good adhesion, but there are small cracks at the bent part, ×: Poor adhesion, -: Not evaluated because film thickness = 0. , is shown. The film thickness term indicates re-evaporation, and A
indicates alloying.

【table】

Claims (1)

[Claims] 1. In a method of vacuum evaporating zinc onto a steel material, the surface of the steel material to be deposited is subjected to reduction treatment, and the temperature (T°K) and deposition pressure (PTorr) of the material to be deposited are adjusted. A method for vacuum vapor deposition of zinc, characterized in that the vapor deposition is adjusted within a range that satisfies the following relationship. 353≦T≦673 10 ^-2 ＜P≦30 logP≧−(6850/T)−0.755logT＋11.24