JPS639980B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a nickel-plated steel sheet having excellent coating film adhesion to ultraviolet-cured paints.

The key point is to control the composition of the chromate film applied to the plated steel sheet as a post-treatment and the composition of the surface oil applied thereon so as to provide optimum adhesion to the ultraviolet curing paint.

(Conventional technology) In recent years, from the viewpoint of energy saving and low pollution, "ultraviolet curable paints" (hereinafter referred to as "ultraviolet curable paints") that use ultraviolet rays to cure the coating film have been developed.
(abbreviated as UV paint) are being applied in various fields.
In particular, the coating on the outside of cans (white coat for printing) is the most advanced in practical application because it is thin and has few problems with corrosion resistance and other problems. Epoxy acrylate, polyester-modified epoxy, and the like having unsaturated double bonds in the molecule are used as UV paints.
The biggest drawback of UV paints is their poor adhesion to the substrate, which is due to large volumetric shrinkage during curing. In order to overcome this drawback, efforts have been made to improve the coating composition, such as increasing the molecular weight of the prepolymer and reducing the amount of reactive diluent mixed.

On the other hand, the material to be coated is a tin-plated steel plate or a nickel-plated steel plate. Nickel-plated steel sheets have been developed in recent years to replace tin-plated steel sheets as a material for welded cans, and are usually produced by cathodic electrolysis from a nickel sulfate + nickel chloride bath. Both tin-plated steel sheets and nickel-plated steel sheets undergo chromate electrolytic post-treatment to improve corrosion resistance and paint adhesion, and a surface oil is applied on top of this. Cottonseed oil and dioctyl sebacate are used as surface oils, and acetyltributyl citrate and the like are also used for tin-plated steel sheets.

From the perspective of the material to be coated, the adhesion of UV paint is affected by the chromate film composition and oil film, and
It is known that this change can also be caused by dry baking before UV painting. For example, a paper titled "Influence of surface properties of tin-plated steel sheets on the performance of ultraviolet curable inks and lacquers" presented by Herwig et al. at the 2nd International Tin-Plated Steel Sheet Conference (EJ
HelWig and MJBlack; “Effect of Tinplate
Surface properties on performance of UV―
Cured Inks and Lacquers”；Proc.2ndlnter.
Tinplate Conf. p. 407 (1980) London) states that tributyl citrate exhibits more stable UV paint adhesion than cottonseed oil or dioctyl sebagate on tin-plated steel sheets, and that it forms a chromate film that provides good adhesion. Conditions (PH and temperature of electrolyte) are presented. However, the relationship between the detailed structure of the product's surface and UV paint adhesion is not clear. Moreover, the chromate film formed on the nickel-plated steel sheet is different from that on the tin-plated steel sheet, and it was completely unclear what type of surface oil had superior UV adhesion. Furthermore, in the can manufacturing field, there is generally a baking process (infrared rays or hot air heating) for the inner surface paint prior to UV painting (outer surface), so the heating (pre-baking, dry baking) at this time can cause the oil and chromate film to become separated. The reaction results in a surface composition that is different from that before dry firing, and this controls adhesion, resulting in a wide difference in adhesion depending on the dry firing conditions. For example, during preliminary dry firing, there is severe adhesion deterioration at the contact area with the stainless steel support (called a wicket) that supports the nickel plated board (UV coating peeling occurs on the shape of the wicket).
This was known, but the cause was unknown. In other words, in order to always obtain stable UV paint adhesion regardless of the baking conditions, it is necessary to accurately understand the structure of the chromate film, including the composition of the oil, but no research has been conducted from this perspective to date. do not have. The reason for this is that the oil film and chromate film are extremely thin, each at a few tens of angstroms, and their composition
This is because there was no way to accurately know the structure. However, in recent years, with the development of surface analysis instruments such as Auger electron spectroscopy (AFS) and X-ray photoelectron spectroscopy (ESCA), it has become possible to quantify the chemical composition of surfaces on the order of Å, and these devices are now being utilized in a variety of fields. . Among these, ESCA is characterized by the analysis of the extreme surface layer containing organic matter, and can be applied to the analysis of the composition of chromate films containing surface oil.

(Problem to be solved by the invention) In order to solve the problem of poor adhesion of UV paint, the present inventors applied the above-mentioned ESCA to clarify the influence of the material surface on adhesion, and Based on this, we have developed a steel plate for can making that has excellent adhesion to UV paint.

(Means for Solving the Problems) The present invention provides that the adhesion of UV paint to chromate-treated nickel-plated steel sheets is affected by the degree of hydration of the chromate film and the concentration of polar groups in the oil applied to the surface. Therefore, in order to improve the adhesion of UV paint, the hydration degree N of the chromate film (represented by the general formula Cr ₂ O ₃ NH ₂ O) is 1.5 or more,
Concentration of polar groups (ester carbonyl groups) in surface oil,
n _CO is the nonpolar group (carbon hydrogen group) concentration, n _CH
The surface should be designed so that the hydration degree N is at least 8% and the relationship between the hydration degree N and the polar group concentration ratio (n _CO /n _CH ) is 0.24N + 2.6 (n _CO /n _CH )≧1. It is something to do.

(Function) First, the present inventors investigated the cause of poor adhesion of UV paint.

The can-making steel sheets to which UV paint is applied are chromate-treated nickel-plated steel sheets, or multi-layer plating steel sheets with a nickel base and a thin plating on top, and these are coated with surface oil. It is used in a state where Therefore, UV
After the paint was applied and cured, the paint film at the peeled interface and the metal side were examined using ESCA, and it was determined that the peeling occurred at the interface between the chromate film containing the oil film and the paint film, and therefore the oil film was detected. It was revealed that both the composition of the chromate film and the composition of the chromate film can affect adhesion.

Next, we focused on the hydration degree and coverage of the chromate film composition as well as the polar concentration of the oil film, and investigated the dry baking method, various surface activation treatments (flame treatment, UV pre-irradiation),
A number of samples with different surface conditions and compositions were prepared depending on the type of oil and solvent cleaning, and the relationship with adhesion was investigated. As a result, it was found that adhesion was determined by the concentration of polar groups in the oil and the degree of hydration of the chromate film, and that the higher the concentration of polar groups and the higher the degree of hydration, the better the adhesion. This relationship is shown in FIG.

In the present invention, the degree of hydration of the chromate film and the concentration of polar groups in the oil are determined based on the above-mentioned ESCA measurement data. The present invention quantitatively defines the surface composition of a material to be coated, and therefore, the method of quantifying it has an important meaning and will be described in detail below.

Chromate treated nickel plated steel plate surface
When measured with ESCA, 4 of Cr, O, Ni and C
The elements are detected, but C can be separated into a hydrocarbon group (I _CH ) and an ester carbonyl group (I _CO ) depending on its peak shape, as shown in Figure 2, and Cr and Ni can be separated from their peak positions. Trivalent hydrated chromium oxide (Cr ₂ O ₃ , NH ₂ O) and nickel oxide (Ni ₂ OC)
It is fixed as . The reason why the oil film is made of a compound containing an ester bond is that dioctyl sebacate or cottonseed oil, which has an ester carbonyl group in the molecule, is generally used as the surface oil.

Now, the surface element concentration can be determined as follows according to the usual quantitative analysis procedure. i.e. i, j
When the peak intensity (height or area is used) of an element is I _i and I _j , the ratio ni/nj of the atomic concentration (number of atoms per unit volume) is given by equation (1).

n _i /n _j =I _i /I _j ×σ _j λ _j S _j /σ _i λ _i S _i (1) Here, σ _i and σ _j are the ionization cross sections of elements i and j, and the ionization cross section of C is When the area σ _c is 1.00, σ _p =
2.85 σ _Cr = 7.60 σ _Ni = 1392. λ _j and λ _j are the escape depths of electrons and are determined from λ∝E ^0.75 _K (E _K is the kinetic energy of the electron). S is the detection efficiency (device function) that depends on the kinetic energy of electrons, and is the detection efficiency (device function) of this device (VG
ESCA), S _C = 1.3, S _Cr = 1.85, S _p = 1.8,
S _Ni =2.6. Using these values, from equation (1),
ni/nj is required. However, since C consists of a hydrocarbon group (285.0eV) and an ester group (288.6eV), the sum of the respective peak intensities (I _CH +
Take I _CO = I _C ). n _p /n _C =k, n _Cr /n _C =k ₂ ,
If n _Ni /n _C = k ₃ , then n _C +n _O +n _Cr +n _Ni = 1, so n _C = 1/1 + k ₁ + k ₂ + k ₃ - (2) n _p = k ₁ /1 + k ₁ + k ₂ +k ₃ -(3) n _Cr =k ₂ /1+k ₁ +k ₂ +k ₃ -(4) n _Ni =k ₃ /1+k ₁ +k ₂ +k ₃ -(5) The atomic concentration percent of all elements can be determined as follows. . In addition, the concentration of hydrocarbon C (n _CH ) and the concentration of ester C (n _CO ) are respectively n _CH = n _C ×
(I _CH /I _C ), n _CO = n _C × (I _CO /I _C ).

Now, through the above procedure, we can find the atomic percent of each element (and component) that makes up the surface.
The degree of hydration (N) and coverage (α) of hydrated chromium oxide can be determined by the following method.
That is, the surface structure can generally be expressed as αCr ₂ O ₃ NH ₂ O+(1−α)Ni ₂ O ₃ —(6). The atomic concentration of oxygen (n _p ′) in this molecular formula is calculated from equation (4) as follows:
Since there are fewer ester bonds, no′=n ₀ −2n _CO
becomes. Here, when n ₀ '/n _Cr =X and n _Ni /n _Cr =Y, N and α can be obtained from the following equations (7) and (8).

N=2X−3Y−3 ―(7) α=1/Y+1 ―(8) According to the above calculation, the hydrated chromium oxide layer of the nickel-plated steel sheet is It was found that it can be characterized as follows. On the other hand, since the properties of oil can be evaluated by its polar group concentration ratio (n _CO /n _CH ), the present inventors evaluated the surface of an oil-coated nickel-plated steel sheet based on the above three characteristic values, that is, the polar group concentration ratio of oil.
It was decided to define it by n _CO /n _CH (=I _CO /I _CH ), the degree of hydration (N) of the chromate film, and its coverage (α). n and α vary depending on the chromate treatment conditions and dry firing conditions, N = 1.5 ~ 4.6, α = 0.75 ~
It was in the range of 0.91. Although N and α generally decrease due to dry firing, there is an interaction with surface oil.

In addition, n _CO /n _CH generally increases during dry baking (oil oxidation), but n CO /n increases in areas where air circulation is poor in the oven (such as the contact area with the stainless steel wick mentioned _above ). _CH does not change and oxidation of the oil is less likely to occur. Furthermore, pretreatment such as flame heating increases n _CO /n _CH , but UV pre-irradiation, solvent cleaning, etc. do not change much. When we investigated the adhesion of UV paint by changing the surface composition under the various conditions listed above, we found that adhesion was determined by the degree of hydration (N) and the concentration of polar groups (n _CO /n _CH ), and that chromate There was almost no relationship between coverage (α) in the range of 0.75 to 0.91.

This result is shown in the relationship shown in FIG. 1 mentioned above. In Figure 1, the horizontal axis shows the concentration of polar groups in oil;
The vertical axis indicates the degree of hydration of the chromate film, where O indicates good adhesion and X indicates poor adhesion. The reason why adhesion becomes poor when the degree of hydration is low is because there are fewer all bonds (-OH...) that increase adhesion through hydrogen bonding, and even if the concentration of polar groups in the oil is somewhat high, adhesion may be poor. Become. This lower limit is approximately N=1.5.
On the other hand, even if the degree of hydration is above this value, if the polar group concentration of the oil is low, good adhesion cannot be obtained. Taking into account that it changes depending on the dry firing conditions, it is necessary to ensure a polar group concentration (n _CO /n _CH ×100) of 8% or more. The broken line in the figure is 0.24N+
2.60 (n _CO /n _CH ) = 1, but N≧1.5,
Even if n _CO /n _CH ×100≧8% is ensured, adhesion is still poor in the range below and to the left of the broken line. Therefore, the surface composition to obtain good adhesion regardless of the dry firing conditions is N≧1.5 and n _CO /n _CH ≧0.08.
and 0.24N+2.60 (n _CO /n _CH )≧1 or more.

That is, a chromate-treated nickel-plated steel sheet having a surface composition within the above range exhibits good UV paint adhesion regardless of the presence or absence of dry firing and the presence or absence of wicket contact. Examples of the present invention will be described below.

(Example) Example 1 A nickel-plated steel plate with a nickel coating amount of 600 mg/m ² was obtained by cathodic electrolysis in a nickel sulfate + nickel chloride mixed bath, and then chromic acid was added to 60 g/m2 of sulfuric acid.
Cathodic electrolysis was performed at a current density of 20 A/dm ² in a treatment bath of 400 ppm to form a film mainly composed of hydrated chromium oxide with a Cr deposition amount of 8 mg/dm ² , washed with hot water at 90°C, and dried with hot air. did. Furthermore, acetyl tributyl citrate having a high ester carbonyl concentration was applied as a surface oil at 4 mg/m ² . Then, as pre-baking, the plated plate was placed upright on a stainless steel support and baked at 210°C for 10 minutes. When the surface in contact with the support (places with poor air flow) was measured using ESCA, the concentration of polar groups in the oil film (n _CO /n _CH ×
A surface with a composition of 20.2% 100) and a degree of hydration (N) of 3.6 was obtained. In addition, the values were 22.8% and 3.5 at locations that did not come into contact with the support, respectively.
A UV prepolymer containing epoxy acrylate as the main component was roll applied to the surface of the plating board at a weight of 180 mg/dm ² after drying, followed by UV irradiation (10 KW, 1.3 seconds) to form a coating film. . The adhesion of the UV coating thus obtained was excellent at all locations, regardless of the contact with the support, and it did not peel off at all when peeled off with a scratch tape.

Example 2 A nickel-plated steel plate was obtained under the same conditions as in Example 1, and then 60 g of chromic acid was added to sulfuric acid.
Cathodic electrolysis was performed at a current density of 20 A/dm ² in a treatment bath of 400 ppm to form a film mainly composed of hydrated chromium oxide with a Cr deposition amount of 8 mg/dm ² , washed with hot water at 50°C, and dried with hot air. . Furthermore, 4 mg/m ² of dioctyl sebacate was applied as a surface oil. Then, as a pre-baking, the plated plate was placed against a stainless steel support and baked at 210°C for 10 minutes. Then, the part that came into contact with the support (the part with poor air circulation) was heat-treated with the flame of a gas burner. After that, the surface of the contact area was measured using ESCA, and the concentration of polar groups in the oil film (n _CO /n _CH ×100) was 22.6℃, and the degree of hydration (N) was
A surface with a composition of 2.6 was obtained. The surface area of the portion that did not come into contact with the support was 20.8% and 28, respectively. A UV coating film was formed on the surface of the plating board in the same manner as in Example 1. The film adhesion of this product was excellent in all cases, regardless of the contact with the support. On the other hand, when gas burner treatment was not performed, the surface of the contact part with the support was (n _CO /n _CH ) x 100 = 7.5%, N = 2.1, and peeling of the UV coating was observed in this part.

[Brief explanation of the drawing]

Figure 1 shows the relationship between the adhesion of UV-cured coating, the degree of hydration of hydrated chromium oxide (N), and the surface oil polar group concentration ratio (n _CO /n _CH ). . The broken line in the figure indicates 0.24N+2.60n _CO /n _CH =1. Figure 2 shows an X-ray photoelectron spectrometer (ESCA) on the surface of a chromate-treated nickel-plated steel plate.
The spectra of C, Cr and Ni are shown. From the peak shift of C, the atomic concentration of the polar group concentration of the surface oil can be determined from the peak intensity of 285 electron volts indicating a hydrocarbon group and the peak intensity of 288.6 electron volts corresponding to a carboxy group.

Claims (1)

[Claims] 1 A chromate-treated nickel-plated steel sheet, in which the degree of hydration N of the hydrated chromium oxide film represented by the general formula Cr ₂ O ₃ NH ₂ O is 1.5 or more, and the polar group (ester bond) of the surface oil film is The ratio of the atomic concentration (n _CO ) to the concentration of nonpolar groups (hydrocarbons) (n _CH ) (n _CO /n _CH ×100) is 8% or more and 0.24N
A steel plate for can making having excellent adhesion to ultraviolet curing paint, characterized by having a surface composition satisfying +2.60 (n _CO /n _CH )≧1.