JPH02149699A - Composite-plated steel sheet having superior formability - Google Patents

Abstract

PURPOSE:To obtain a composite-plated steel sheet having superior formability by forming a specified amt. of a composite Zn or Zn alloy plating layer on the surface of a steel sheet by electroplating in a Zn or Zn alloy plating bath contg. a specified amt. of an adduct of melamine to (iso)cyanuric acid. CONSTITUTION:A composite Zn or Zn alloy plating layer is formed on at least one side of a steel sheet by 1-100g/m<2> by electroplating in a Zn or Zn alloy plating bath contg. an adduct of melamine to (iso)cyanuric acid suspended by >=1g/l to obtain a composite-plated steel sheet. This surface-treated steel sheet has superior lubricity at the time of press forming, satisfactory chemical treatability, adhesion to a coating film and high corrosion resistance.

Description

Detailed Description of the Invention (Industrial Field of Application) The present invention relates to a surface-treated steel sheet for forming, which has particularly excellent lubricity during press forming, as well as corrosion resistance and paintability.
Furthermore, it relates to a composite electroplated steel sheet with excellent coating film adhesion.

(Prior Art) Surface-treated steel sheets for forming processing, such as surface-treated steel sheets for automobiles, undergo a pressing process on the way to the final product. Generally, in press forming of a steel plate, the lubricity of the surface of the steel plate that comes into contact with the mold is important. When this lubricity is lost, the plating film seizes, resulting in forming defects such as breakage of the base steel plate. or,
The plating film may be baked and adhered to the mold, and pressing may be performed while the film material is deposited, causing problems such as indentation flaws in the plated steel sheet.

Conventionally, in order to ensure the lubricity of a steel plate, a measure has been taken to apply a liquid lubricant (so-called lubricating oil) to the steel plate.

Furthermore, a thin film of fatty acid metal soap has been formed on the surface of the steel sheet, or the surface of the steel sheet has been coated with a polymeric substance such as fluororesin or vinyl resin.

However, since the press-formed steel plate then undergoes a chemical conversion treatment process and a painting process to become the final product, the oils and fats adhering to the steel plate must be completely removed before these processes. For this purpose, degreasing is usually performed using an aqueous solution of an alkaline detergent, but degreasing becomes insufficient due to deterioration of this degreasing solution, and problems such as uneven chemical conversion on the surface of the steel sheet may occur after the chemical conversion treatment process. . Furthermore, handling large amounts of oils and fats significantly worsens the working environment.

In order to solve these problems, attempts have been made to impart self-lubricating properties to the steel sheet by applying composite plating to obtain a surface-treated steel sheet that can be press-formed as is without lubrication with oil or the like.

Nickel-molybdenum sulfide composite plating (METAL FINISHING (November 1967) by VEST et al.
)] and the zinc-graphite composite plating disclosed in JP-A No. 52-24941 are typical examples. Molybdenum sulfide and graphite are layered solid lubricants that have lubricity due to their cleavage structure. By performing electroplating while suspending these as dispersed particles in a Ni or Zn plating bath, a self-lubricating plating film in which these particles are eutectoid is formed on the surface of the steel sheet.

However, materials with high specific gravity such as molybdenum sulfide and graphite (
3-5) Inorganic substances are difficult to maintain in a suspended state in a plating bath, which is disadvantageous in obtaining a composite film in which they are uniformly dispersed.

In addition, when chemical conversion treatment is performed on the resulting film, the chemical conversion reaction starts with the elution of the plating film, so if chemically inert graphite or molybdenum sulfide is dispersed and eutectoid, the part may become inactive sites, causing uneven chemical formation. As a result, the adhesion of the coating film becomes insufficient.

Regarding paint film adhesion of plated steel sheets, it is well known that composite plating with organic polymer particles eutectoid improves paint film adhesion due to its affinity with the polymer used for coating. be. [Naito et al., Metal surface technology (Vol. 3)
0. p, 584.1979)) (Problems to be Solved by the Invention) The object of the present invention is to provide a method that does not have the drawbacks of the conventional methods described above, has excellent lubricity during press molding, has good chemical conversion treatment properties, and has good coating film adhesion. The object of the present invention is to provide a surface-treated steel sheet having high corrosion resistance and high corrosion resistance.

(Means for Solving the Problems) The present inventors have discovered that organic materials have a lower specific gravity and are advantageous for uniform dispersion as dispersion particles for composite plating, and that the above-mentioned "
Although polymer resins are used in the paper entitled "Materials Technology," since not only resins but also organic substances can be expected to have good coating film adhesion, we have investigated the lubricity and coating film properties of composite plating using dispersed particles of various organic substances. Performance such as adhesion and corrosion resistance was investigated. As a result, it has been found that an adduct of melamine and (iso)cyanuric acid is most effective in achieving the above objective as dispersed particles for zinc-based composite plating.

Here, the gist of the present invention is to provide an adduct of melamine and cyanuric acid (hereinafter referred to as MC) on at least one side of a steel plate.
(abbreviated as A) is Ig/j! A deposit of 1 to 1 formed from a zinc or zinc alloy plating bath suspended in the above amount
This is a composite plated steel sheet with excellent formability and has a composite zinc-based electroplated film layer of 00 g/+w''.

In the present invention, the base material steel sheet includes not only cold-rolled steel sheets, but also zinc, zinc alloy, and other various plated steel sheets. That is, by further applying the composite electroplating of the present invention on a conventionally plated steel sheet, press formability and coating film adhesion can be improved.

Further, the electroplating film of the plated steel sheet of the present invention may be either pure zinc plating or zinc alloy plating (hereinafter, these will be collectively referred to as zinc-based plating). There is no particular restriction on the zinc content in the case of zinc alloy plating, and as shown in Examples, the zinc content may be 50% or less (eg, 15%).

(Function) The electroplated steel sheet of the present invention has MC on one or both sides.
1 to 100 g of composite zinc-based plating film layer eutectoided by A
It is formed with an adhesion amount of 7 m''. Note that this adhesion amount is the amount per one side.

MCA has a layered structure in which melamine, which is a triazine ring-type heterocyclic compound, and cyanuric acid and/or isocyanuric acid are alternately bonded secondary to each other through hydrogen bonds, It is a white powder with an average particle size of 1 to 2-2, which has self-lubricating properties due to its cleavable lamellar structure, similar to graphite etc. [Hirae, Materials Technology (Vo.
l, 4. p, 429° (1986)), therefore,
Good lubricity can be imparted to the plating film during press molding.

In addition, since MCA is a crystalline organic substance rather than a polymer resin, it has good water wettability and has a relatively low specific gravity.
It has been found that it has the advantage of being easy to disperse uniformly in a plating bath.

moreover,? ICA is chemically stable and can be dispersed in acidic or alkaline zinc-based plating baths without chemical change, and does not adversely affect the corrosion resistance of the formed plating film. However, since it is an organic substance and has a certain degree of polarity due to its chemical structure, it has an affinity for the resin components of paints, unlike graphite and molybdenum disulfide.
It improves the adhesion of the plating film and is less likely to cause uneven chemical formation.

? In order for ICA to achieve the desired effect mentioned above, it is necessary that the MCA, which is compositely eutectoided into the zinc-based plating film, be exposed on the surface of the plating film and firmly fixed in the plating film. is necessary. This was confirmed as follows.

FIG. 1 is an FT-IR spectrum diagram of MCA (melamine cyanurate, manufactured by Nissan Chemical Industries, Ltd.) powder measured using an FT-IR (Fourier transform infrared spectrophotometer).

On the other hand, Figure 2 shows the same MCA powder as Log/j! MCA-containing Zn-
Ni alloy electroplated steel sheet (Ni 12.Owt%, with
Diffuse reflection type FT-IR measured after thoroughly brushing and washing the plated surface with an amount of 20g/l1z)
It is a spectrum diagram.

Comparing the spectrograms of FIG. 1 and FIG. 2, it can be seen that the peaks match at various wave numbers. That is, MCA is Zn
, a composite eutectoid plating film with Ni is obtained, and MC
It can be seen that part of the A particle is exposed on the surface. Furthermore, the MCA is firmly fixed in the plating film to the extent that it can withstand brushing and washing with water.

Due to the cleavability of the MCA particles exposed on the surface, the surface of the steel sheet exhibits good lubricity during press forming. Furthermore, due to the affinity between MCA and coating resin, the composite plated steel sheet of the present invention has good coating film adhesion.

The electroplated copper sheet of the present invention is produced by electroplating a base steel sheet using a zinc-based plating bath containing %A cloudy MCA at a rate of 1 g/l or more. The amount of MCA added is Ig/j! If the amount is less than 30g/Il, sufficient lubricity and film adhesion cannot be obtained.On the other hand, if the amount added exceeds 30g/Il,
Since the effect of MCA addition is saturated and no further performance improvement can be obtained, the economically preferable upper limit of the amount of MCA added is 30 g/l.

Any conventional zinc-based electroplating bath may be used, and either an alkaline bath such as a cyanide bath or an acidic bath such as a chloride bath can be used, but a sulfuric acid acid bath is preferred when performing continuous plating.

MCA powder is added to this basic plating bath, and electroplating is performed while maintaining the MCA powder in a suspended state by appropriate stirring. Stirring is performed, for example, by mechanical stirring, ultrasonic stirring, or a combination of both.

If desired, a suitable surfactant may be added as a dispersion aid, but this is usually not necessary, and the plating conditions may be the same as conventional ones and do not require any particular changes.

The amount of adhesion of the MCA eutectoid composite plating film on the plated steel sheet of the present invention is 1 to 100 g/n? It is. Adhesion amount is 1g/
If it is less than rd, the corrosion resistance as a zinc-based plating film will be insufficient, and the composite plating will not have sufficient lubricity. On the other hand, if the adhesion amount exceeds 100 g/rrl,
Molding processability deteriorates.

The present invention will be illustrated below with reference to Examples.

Large construction group (i) Electroplating Commercially available cold-rolled steel sheets and various zinc-based plated steel sheets (electrogalvanization, alloyed hot-dip galvanization (Fe 17%), Z
n-13%Ni and Zn-15%Fe alloy electroplating, and Zn-55%AQ and Zn-5%AQ alloy hot-dip galvanized steel sheets) were used as base steel sheets, and after alkaline degreasing and water washing by the usual method, Various sulfuric acid acid electroplating baths (ZnSZ) to which various amounts of MCA (manufactured by Nissan Chemical Industries, Ltd.: melamine cyanurate, average particle size 1-) were added
Single-sided plating was performed using a n-Nis Zn-Pa bath under the following conditions. The plating bath was stirred using a magnetic stirrer, and under these conditions the MCA powder could be maintained in a suspended state without settling.

fa) Plating bath composition (Zn plating) Zn5Oa・7HzO: 400 g/INazSO
4: 100 g/1 (Zn-Fe plating) Zn5O, -7HtO: 5-300 g/lF
e5Ot ・/l1! O: 200-400 g/
INazSOa: 100 g/j! (
Zn-Ni plating] ZnSO4・78zO: 100-250 g/l
N15Oa・6H2O: 100-250 g/β1
JalsO4: 100 g/j! (BL plating conditions: pH 1.8, bath temperature 50°C, current density 60 A/da) Type of base steel sheet, composition and amount of plating film on the resulting matted steel sheet, and amount of MCA added to the plating bath are shown in Table 1 below.

(11) Painting Each plated steel plate obtained was subjected to phosphate chemical conversion treatment under the conditions shown in (al) below, and then (b) to +dl below.
Automotive paint was applied to the plated surface under the conditions shown below.

fal chemical conversion treatment A dipping type zinc phosphate chemical conversion treatment liquid for automobiles (manufactured by Nippon Bariki Rising Co., Ltd.: PB13080) was used, and the liquid temperature was 43°C.
The sample was immersed in water for 120 seconds.

fbl Cation Electrodeposition Coating A common cationic electrodeposition paint for automobiles (manufactured by Nippon Paint Co., Ltd.: U-80) was applied at a voltage of 300V for an electrodeposition time of 3 minutes, and then the coating film was baked at 180°C for 30 minutes.

Coating film thickness: 20ts.

After applying FCL intermediate coating melamine alkyd paint for general automobiles, drying (140℃, 25 minutes) Coating film thickness: 40p Drying (140℃, 25 minutes) Coating film thickness: 40p (iii) Test method according to (i) above Corrosion resistance of each unpainted plated steel plate obtained,
Workability, powdering resistance, chimping resistance, and secondary adhesion (paint film adhesion) after coating according to (ii) above were evaluated by the following test method.

Corrosion resistance was evaluated by making a cross cut on the plated surface of a plated steel plate test piece that reached the base steel plate, performing a salt water spray n test according to JIS Z 23/L for 500 hours, and measuring the maximum bulge width of the cross cut part.

Workability (press formability) was determined by taking a disk-shaped blank with a diameter of 9 cm from a steel plate immediately after plating, and molding it into a cylindrical shape with a diameter of 50++ m and a depth of 28 cm, with the plated side facing outward. The steel plate was drawn and evaluated based on the presence or absence of breakage. ○ indicates no breakage, and × indicates breakage.

Powdering resistance was determined by performing a test in which the plating film on the side wall of the cylindrical deep-drawn product obtained in the processability test was peeled off using adhesive tape, and the amount of peeling was visually measured. It was evaluated based on the criteria.

5: No peeling at all 4: The area ratio to which peeling pieces are attached to the total area of the tape is less than 10% 3: The area ratio is 10% or more and less than 30% 2: The area ratio is 30% or more, The above area ratio is less than 50%
% or more chipping resistance is measured by adding 2 diamond grains of 10a+g to the plated surface of a plated steel sheet specimen at a low temperature of -20℃.
It was made to collide at a speed of 10 Kg+/h, an adhesive tape peel test was performed on the collision point, and the peel diameter was measured and evaluated.

The secondary adhesion after painting was determined by immersing the painted steel plate in ion-exchanged water at 50°C for 10 days, then making cuts in 2+1- squares and performing a tape peeling test on all squares (100
Evaluation was made based on the number of peeled squares with respect to squares). ○
indicates a peeling grid of 5 or less, Δ indicates a peeling grid of 6 to 15, and x indicates a peeling grid of 16 or more.

The test results are also shown in Table 1. In Table 1, the comparative examples are:
MCA powder was not added or the amount added was Ig.
This is an example where it was less than /nf.

As can be seen from the results in Table 1, the plated steel sheet according to the present invention achieved satisfactory performance in all test items of corrosion resistance, workability (press formability and powdering resistance), chipping resistance, and secondary adhesion. It shows. On the other hand, none of the comparative plated steel sheets showed good results in all test items. In addition, when comparing the present invention example and the comparative example, which have the same conditions except for the presence or absence of MCA addition, it is found that MC
It can be seen that the composite plating of A improves all the properties tested.

(Effects of the Invention) As described above, the composite electroplated steel sheet on which the MCA of the present invention is eutectoid has a plating film with self-lubricating properties, so it exhibits sufficient lubricity during press forming. Molding can be carried out smoothly without any lubrication treatment. Since MC^ exhibits lubricity based on its cleavable lamellar structure, its lubrication effect is much higher than that of a composite plated steel sheet eutectoided with a polymer resin such as polytetrafluoroethylene, which does not have such properties.

On the other hand, compared to conventional self-lubricating composite plated steel sheets in which inorganic lubricants such as graphite and molybdenum disulfide are eutectoid, since the dispersed particles are organic crystals, it is easier to maintain the suspended state of the dispersed particles. Moreover, unlike inorganic lubricants, it is less likely to cause uneven chemical formation and has the effect of improving paint film adhesion. Furthermore, the chemical stability of MCA improves the corrosion resistance of the plating film, and it is less prone to scratches as shown by the chipping resistance test results.

As can be seen from the above, the plated steel sheet of the present invention exhibits performance particularly suitable for use in automobile bodies, but it can also be used as a self-lubricating steel sheet with high corrosion resistance for other uses, either painted or unpainted. Can be used.

[Brief explanation of the drawing]

Figure 1 is an FT-IR spectrum diagram of MCA powder manufactured by Nissan Chemical Industries; and Figure 2 is a diffuse reflection type FT of the plated surface of a composite plated steel sheet prepared from a Zn-Ni plating bath in which the same MCA powder was dispersed. - IR spectrum diagram.

Claims (1)

[Claims] Formed on at least one side of a steel sheet from a zinc or zinc alloy plating bath in which an adduct of melamine and (iso)cyanuric acid is suspended in an amount of 1 g/l or more, the coating weight is 1 to 100.
Composite plated steel sheet with excellent formability, having a composite zinc-based electroplating film layer of g/m^2.