JPS59197597A - Preparation of nickel plated steel plate for welded can excellent in corrosion resistance after coating - Google Patents

Abstract

PURPOSE:To prepare an Ni-plated steel for a welded can excellent in corrosion resistance after coating, by applying two-stage cathode electrolytic treatment due to specific current density to a steel plate having an Ni-plated surface in a chromic anhydride aqueous solution. CONSTITUTION:Ni-electroplating is applied to the surface of a steel plate as a can material in an Ni-amount of 0.15-1.0g/m<2>. In the next step, this steel plate is subjected to cathodic electrolytic treatment in an aqueous solution containing CrO3 and NH4F so as to bring an F<->/Cr<+6> ratio to 1/100-1/10 and to adjust CrO3 content to 10-80g/l at current density of 7.5A/dm<2> or less to form a chromatic film. Subsequently, cathodic electrolytic treatment is further applied to said steel plate in the same aqueous solution at current density of 15A/dm<2> to perform the precipitation plating of metal chromium for eliminating pinholes in the Ni-plating film and the chromate film in an amount of 20mg/m<2> or less. By this method, an Ni-plated steel plate excellent in weldability and good in corrosion resistance after coating is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for manufacturing a nickel-plated steel plate for welded cans that has excellent corrosion resistance after coating, and is particularly suitable for can materials that can be welded by seam welding such as Sudronitsta welding or spot welding. The present invention aims to provide a preferable method for producing nickel-plated steel sheets that have excellent corrosion resistance after painting.

Although can-making methods for obtaining can bodies have diversified in recent years, can-making methods by air resistance welding, such as the Sudronik welding method, have significantly developed and become popular. By the way, it is important that the can materials used in can manufacturing methods using these welding techniques not only have excellent weldability, but also excellent corrosion resistance, especially corrosion resistance after painting. Although tin-plated steel sheets (tin plate) have been used as materials for welded cans, the tin plate has the following problems when used in the above-mentioned can manufacturing method.

That is, one of the reasons for the development of the above-mentioned can manufacturing method is the reduction in the price of can bodies, but since the price of tin for furiki is high, it is difficult to respond immediately to this reduction in the price of can bodies.

On the other hand, efforts are being made to reduce the amount of tin deposited and make it thinner, but tin, which is effective for weldability, becomes alloyed with the base iron by heating during paint baking, resulting in poor strength of the welded part when the welding current is small. On the other hand, when the welding current is large, dust occurs in the welded area, making it difficult to obtain welding with a preferable optimum current, and even if it is obtained, the range is very narrow and stable operation cannot be performed. Furthermore, blisters are generated in areas where the Chichi-tin alloy layer is formed due to the corrosive aqueous solution that enters through the paint film, causing iron to be leached through the paint film, and in the can, holes are formed in the steel plate at the defective parts of the paint film. The corrosion resistance after painting is significantly inferior, such as the phenomenon observed, and it is not possible to reduce the price of the can body.

As a material for reducing the price of can bodies, ultra-thin nickel-plated steel sheets and their manufacturing method were developed using the Special Publication No. 36-1.
0064, 36-15252, JP-A-55-1380
96, 56-169788, and 57-2895, these are nickel plating with a thickness of about 0.3μ or less) and the cathode is placed in an aqueous solution containing chromic anhydride, chromate, or dichromate. It is electrolytically treated to form a chromate film. Also, apart from this, JP-A-57-28
96, 57-3569.7, and 57-35698 are S04-
Chromate treatment by cathodic electrolysis in an aqueous solution containing chromic anhydride, chromate, or dichromate with a ratio of 2/Cr" of 1/40 or less or a F-/Cr ratio of 1/10 or less. In some cases, high-temperature water treatment is required to further improve the properties of this chromate film.However, even if the nickel-plated steel sheets obtained by these known techniques have good weldability, the Corrosion resistance is not sufficient. In other words, nickel metal itself generally has good corrosion resistance and good weldability, but no matter how good the nickel plating layer is, pinholes still exist and the base iron is exposed. Therefore, chromate treatment is required to avoid elution of iron and nickel metal itself from these pinholes, and since this chromate film is very thin, pinholes also exist in this film, and nickel plating 1~ It is impossible to completely eliminate pinholes, and the nickel plating layer has an exposed layer structure.In other words, a steel plate with such coating grooves must be painted and immersed in a corrosive water bath. Then, a chemical reaction occurs in the corrosive aqueous solution that penetrates through the growth film, and the exposed bare steel becomes a local anode and is anodically dissolved, while the surrounding nickel becomes a local cathode, reducing hydrogen and oxygen and forming a blister. (paint film blistering) occurs.Furthermore, in the defective areas of the paint film, exposed pinholes in the base steel become local anodes and create holes in the steel, so corrosion resistance after painting is not sufficient. However, the method according to JP-A No. 57-2897 has a nickel plating of 0.3μ or less, followed by S 0.2-/Cr+6(7
) 7.5 A/d 7F in an aqueous solution of so4::-proprietary chromic acid with a ratio of 1/40 or less! ”~25/d
The amount of metallic chromium is 10 μ/ni or less by the cathodic electrolytic treatment of d and the high temperature water treatment with a pH of 4.0 or more at 65 to 100° C., and the amount of chromate coating is 20 mg/xr in total with the metal chromium layer in terms of Cr. ? The following method has been proposed, and the nickel-plated steel sheet obtained by this technique has good corrosion resistance after coating, but does not have sufficient weldability. In other words, there are two layers: a nickel plating layer, a metallic chromium layer and a chromate film.
The layer formed is a steel sheet with few pinholes and has good corrosion resistance after painting, but although the wax in the metal chromium layer is small, it is a coating similar to chromic acid treated steel sheet (TFS). Therefore, in the can manufacturing method using electric resistance welding, dust often occurs in the welded area, resulting in poor weldability.

The present invention was devised in view of the above-mentioned circumstances, and the surface of the steel plate has a thickness of 0.15 to 1.0 ft'/
sr? After confirming the nickel plating film of F-/C
A chromate film is formed by cathodic electrolytic treatment at a current density If of 7.5 A/dm' or less in an aqueous chromic acid anhydride solution of 10 to BOf'/l containing F- with an r+' ratio of 1/100 to 1/10. After forming, a current density of 15 A/dt? 1′ or more, cathode 1 solution treatment and metallic chromium 20trq/lr? It is characterized by the following:

That is, to further explain the present invention, the present invention has N
The i-plated layer minimizes the exposed parts of the steel to improve corrosion resistance, and cathodic electrolysis treatment is performed in an aqueous solution of F-rich chromic acid anhydride to create a chromate film with few pinholes and no metallic chromium. This method improves the corrosion resistance after painting without impairing weldability by simultaneously depositing metallic chromium and chromate films to eliminate pinholes once formed and further improve corrosion resistance.

To explain the details of each process in the present invention, nickel plating is carried out to minimize the exposed parts of steel and improve corrosion resistance, and the plating method is different from ordinary electrolytic nickel plating. Any method may be adopted, and the details of the method are not particularly specified.

However, in the present invention, the amount of nickel plating is 0.15 to 1.0'.
? /rr? However, 0.15t/rr? Below this, the exposed area of the steel becomes large and corrosion resistance is insufficient even after subsequent cathodic electrolytic treatment. On the other hand, 1, Qr/y+? The above methods are effectively the same, but the cost disadvantage increases.

As mentioned above, even if the weldability is good when steel is simply plated with nickel, as a material for cans, the corrosion resistance and paint adhesion after painting are extremely poor. Therefore, in the present invention, following nickel plating, F- is 1/100 of Cr +6.
10~s o y7t8 contained at a ratio of ~1/10
After forming a chromate film by cathodic electrolytic treatment in an aqueous solution of chromic acid anhydride with a current density of 7.5 A/dn or less, the current density is 12 A/dm' or more, preferably 15 A/dn in the same solution. ? With the above, cathodic electrolysis treatment is performed to form a layer consisting of a chromate film and metallic chromium. In other words, the formation of such a layer significantly improves the corrosion resistance after painting without impairing weldability, but if the F- ion coating is less than 1/100 of the Cr+ 6 ion in this treatment bath, A chromate film with few pinholes could not be obtained, and Kin
Even when 4-chromium and chromate films are deposited simultaneously, pinholes cannot be eliminated. Also this F
- If the amount of ions is more than 1/10 of the Cr ions, the chromate film will become non-uniform, which is undesirable.On the other hand, if the chromic acid concentration is 10 to 80 t/l and less than 10171, the conductivity of the bath will be low. , it is difficult to perform high current density treatment in the latter stage, and at the same time, the bath tends to change over time, which poses operational problems.In addition, at 809/ or higher, the chromate film tends to dissolve, making it difficult to create a chromate film with few pinholes. cannot be obtained stably.

In cathodic electrolytic treatment, two-stage treatment with different current densities @
It is essential. That is, initially 7.5 A, 'an? A chromate film containing no metallic chromium is formed at the following current density, and then treated in the same night at a current density of 12 A/dm or more, preferably 15 A/di or more, to remove metallic chromium by 1/1 Form below ♂. 7.5A/drr in 1st stage processing? If the treatment is carried out at a current density above, a chromate film containing metallic chromium will be directly formed on the Nj plating layer, resulting in good corrosion resistance after painting but significantly poor weldability. On the other hand, 7.5A/
drrr? When only the first stage treatment is performed at the following current density, the weldability is good because it does not contain metallic chromium, but the corrosion resistance after painting is poor. 1st with different current density. It is possible to significantly improve post-painting corrosion resistance without impairing weldability only when the second stage treatment is also carried out, and although the detailed reason for this difference cannot be clearly elucidated, Ni After forming a chromate film that does not contain metallic chromium on the plating layer, cathodic electrolysis treatment is performed at a current density that causes metallic chromium to precipitate, and metallic chromium is deposited at a current that causes metallic chromium to be deposited directly on the N1 plating layer. Compared to those treated with cathodic electrolysis at a high density, the deposited state of metallic chromium is different from the original, without impairing weldability, and the chromate coating has fewer pinholes and has good corrosion resistance after painting. It was confirmed that it could be done.

Similarly, in the present invention, since the sulfuric acid radical inevitably contained in the chromic anhydride has a sQ4/CrO3 ratio of 1500 or less, there are no particular restrictions. Also, during cathode electrolytic treatment, C
rs+ is generated, but the chromic anhydride concentration is 10 to 8.
In the range of Oy/t, the film formation V has no influence, so it is not particularly specified. Similarly, in the present invention, fluorides such as HF, 'NH4F, and NaF can be used for supplying F- ions.

Processed by the above method, the metal chromium is 41 to /R or less, and the chromate film amount is 5 to 20 /1 in terms of chromium.
1? range. The amount of metallic chromium is 10m7/n? or the amount of chromate film is 2 in terms of chromium.
0η/n? If it exceeds this, weldability will deteriorate and the amount of chromate film will be 5 m9/lt in terms of chromium. If it is less than that, the corrosion resistance after painting will be poor.

Specific examples of the method of the present invention will be described below.

Example 1 Cold-rolled steel plate for tinplate with plate thickness of 0.21 am (temper 1T)
4) 30? /l NaOH solution at 80°C, IOA
/drr? After electrolytic degreasing for 1 second at a current density of
Electrolytic pickling was performed for 1 second at a current density of /dm'. After washing with water, perform Ni plating under the conditions shown in (a) below, and then perform cathodic electrolytic treatment under the conditions shown in (b) after washing with water,
Further, after washing with water and drying, the surface was coated with DO8 oil in the usual manner.

(a) Ni plating bath composition NiSO4・6H! 0 24or/zN i
C14・6T (20459/lH, BO4301/) Bath pH 2.5 Bath temperature 50℃ Flow density 30A/dm' Processing time
1.0'sec plating amount
0.8r/a (b) Cathode electrolytic treatment bath composition Cr O330S'/1 NH4F 1.5t/l.

(F/Cr11=1/20.25) Bath temperature 45°C Current density and processing time: 1st stage 6 A/dtr? X
1.5 s e c: 2nd stage 25 A/d+y? X
O,3sec Film property Metallic chromium amount 8/
? ? ? Chromate film amount 13Tq/i Example 2 Example I After performing the same pretreatment as in Example 1 on the same cold rolled steel sheet as in Example 1, Ni was applied under the conditions shown in the following (a).
After plating, cathodic electrolytic treatment was carried out under the conditions shown in (after water washing), and after washing and drying, oiling was carried out in the same manner as in Example 1.

(a) Ni plating bath composition Ni5O4・6I (20250t/1Na2
so, LOOP/1T(3B0,501/
Bath pH 3.0 Bath temperature 60℃ Current density 10A/drr? Processing time: 1.5 seconds Plating amount: 0.4f/rr? (b) Cathode electrolytic treatment bath composition Cry36o＼f/L NaF O,4? /l (F:/Ct" = 1/86) Bath temperature 40°C Current density x processing time 1st stage 5 A/arri" x
1.5 seconds 2nd stage '30A/dm"Xo, 1 second coating maximum amount of metal chromium 4~/R chromate coating g
111ng/d Example 3 The same cold-rolled steel sheet as in Example 1 was subjected to the same pretreatment as in Example 1, then Ni plating was performed under the conditions shown in (a) below, and after washing with water ( Under the conditions shown in (b): The sample was subjected to a chemical treatment, and after washing with water and drying, it was coated with oil in the same manner as in Example 1.

(a) Ni plating bath composition NiSO4・6H20240? /1NiC1
2.6H2045f/7 I (3BO330?/ hammered,) H2,0 Bath temperature 50℃ Turtle flow density If 30A/dm' Processing time 0.8 seconds Plating amount
o, 6g/F (ro) Negative electrolytic treatment bath composition CrO3' 151/LNH4F
1.0 y/1 (F7'CP=1/27) Bath temperature 45℃ Current density x processing time 1st stage 71/d i x 1.0 seconds 2nd stage 15A/d door x 0.3 seconds Coating amount Amount of metallic chromium 2■/Amount of pure chromate film 13 mg/lr? Comparative Example I Up to Comparative Example 1, the same treatment as in Example 1 was performed, and after washing with water, cathodic electrolysis treatment was performed under the following conditions, followed by washing with water, drying, and applying oil in the same manner as in Example 1.

Bath composition Cry, 30g/LNLF
1.51/l (F7'CF6 = 1/20.25) Bath temperature
45゛℃ Tortoise current density x treatment time 6A/am"xl, 3 seconds Coating amount Metallic chromium amount Or; 4/n?Fucrose coating amount 11ki/n? Comparative example 2 Same treatment as Example 1 until Ni plating After washing with water, cathodic electrolysis treatment was performed under the following conditions, and after washing with water and drying, oiling was performed in the same manner as in Example 1.

Bath composition Cr 0.30g/1 NH4F t5y/l (F/Cs6 = 1/20.25) Bath temperature 45°C ゛Sleep flow density x treatment time 15A/d silence x 1.5 seconds Film discharge Metallic chromium Amount ioη arm chromate coating amount 127η/rr? Comparative Example 3 The same treatment as in Example 1 was carried out up to Ni plating, and after washing with water, cathodic electrolysis treatment was carried out under the following conditions, and after washing with water, drying and washing, the same oiling as in Example 1 was carried out.

Bath composition Cr03 30? /1m temperature
45℃ at, flow density change x processing time 15A/dze x 1.5 seconds Coating amount Chromate coating amount 8mti/rr? The following tests were carried out for each Example 1.23 and Comparative Example 1.2.3 of this proposal, and the corrosion resistance, paint adhesion, and weldability are summarized in Table 1 below. 'f Riro on the street.

■ Corrosion resistance test ■ Blister resistance test Coat 50 coats of epoxy phenol paint on the surface of the sample per di, bake at 210℃ for 13 minutes, cut into 60rs x 90mm (after sealing the cut surface and back side) 1 in 5% NaCl aqueous solution
After 30 minutes of retort treatment at 30°C and subsequent immersion in the same aqueous solution at 38°C for 96 hours, did the surface appearance change? @Festival.

■Pitting corrosion resistance test Epoxyphenol paint 't50. W/drr? After baking at 210°C for 13 minutes, 60° x 9°r! After cutting it into 1.5 mm lengths, securing the cuts with diamond cutter coating IIQ, and sealing the cut surface and back side, 1.5% citric acid and 1.5% Na
After immersing a portion in the C1 aqueous solution at 38°C for 10 days, changes in surface appearance were observed.
1■、■ Iron elution test after painting Apply epoxy phenol paint to the surface of the sample at a thickness of 50■/dm, bake it at 210℃ for 13 minutes, cut it into 55MX55 glue, and leave a sample width of 25d. After alcohol, 1.5% citric acid and 1,5
% NaCl aqueous solution (100 d) at 38°C for 20 days, the elution of iron was measured.

■、(Metal adhesion test sample surface was coated with 5QLv/dynF epoxy phenol paint, baked at 210℃ for 13 minutes, cut into 5×100 pieces, and nylon After heat and pressure bonding with a type of adhesive, the samples were retorted in a 3% NaCl aqueous solution at 120°C for 90 minutes, and a T-peel test was conducted using a tensile test of 1fi to evaluate paint adhesion based on beer strength 1 set.

Weldability test samples were heat treated in air at 210°C for 13 minutes, and welding was performed using a Sutronic welding machine by changing the welding flow. Weldability was evaluated based on the current range.

In other words, according to the above results, it was confirmed that the products of the present invention exhibited superior results in terms of weldability, paint adhesion, and post-painting corrosion resistance compared to the comparative examples. Ta.

According to the present invention as described above, can materials that can be welded by seam welding such as Sudronik bath welding or spot welding have good paint adhesion and excellent corrosion resistance after welding. Nickel plated steel &
This invention can be manufactured appropriately and has great industrial effects.

Patent applicant Nippon Kokan Co., Ltd. Inventor Yutaka Watanabe Text
Masa Kojima, Toshihiro Muroma Yamamoto, Patent Attorney Haku) I(-1)

Claims (1)

[Claims] A nickel plating film of 0.15 to 1.0 t/d is applied to the surface of the steel plate, and then the F-/Cr'' ratio is 1/100.
10~s o t7 containing F- consisting of ~l/10
A current density of 7.5 A /
After forming a chromate film by cathodic decomposition treatment at a temperature below dm', a current density of 15 A was applied to the above 7 in a chromic acid solution @liquid.
/dyr? With the above, negative electrolytic treatment was performed to remove 204% of metallic chromium.
A method for producing a nickel-plated steel sheet for welded cans having excellent corrosion resistance after painting, characterized in that the coating is applied to a coating of less than /R.