JP3476997B2 - Resin chromate treated metal plate - Google Patents

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to corrosion resistance of zinc-based plated steel sheet, aluminum-based plated steel sheet, zinc alloy sheet, aluminum alloy sheet, or steel sheet, particularly corrosion resistance when the treatment film is damaged by processing or scratching. Excellent, and
The present invention relates to a resin chromate-treated metal plate with less elution of chromium into an alkaline degreasing liquid or a water-soluble rolling oil.

[0002]

2. Description of the Related Art Chromate treatment has hitherto been known as a rust-preventing treatment for zinc-based plated steel sheets, aluminum-based plated steel sheets, zinc alloys, aluminum alloys, or steel sheets. An electrolytic chromate or a reactive chromate containing valent chromium as a main component, and 6
There is a coating chromate which contains a valent chromium and is dried without being washed with water after coating. In recent years, chromate-treated metal plates have come to be widely used for home appliances, building materials, automobiles, etc., and various performances have been demanded by consumers. For example, uniformity of appearance, fingerprint resistance, adhesion with paint,
Examples include the corrosion resistance of flat plate materials when used bare, the corrosion resistance of processed parts and scratches, and the poor solubility of chromium in alkaline degreasing.

As a known technique for making chromate insoluble, for example, as described in JP-A-3-215683, a method of heating a chromate film at a high temperature of 200 ° C. or higher is known. . However,
According to this method, hexavalent chromium is reduced during drying and
Since it becomes valent chromium and almost no hexavalent chromium remains in the film, the corrosion resistance at the processed part and the scratched part is 6
Significantly inferior to chromate containing valent chromium. Also,
JP-A-4-358082 and JP-A-5-28754
As can be seen in Japanese Patent Publication No. 8, a resin such as polyacrylic acid or a reducing agent such as alcohol is added to the chromate treatment bath,
A method of reducing and fixing hexavalent chromium and crosslinking trivalent chromium in a resin is also known.

According to this method, the corrosion resistance of the chromate film is improved by helping the barrier effect of the resin.
Since the self-healing action due to the elution of hexavalent chromium does not function at the damaged portion of the barrier film such as a scratch, the problem of corrosion resistance of the processed part and the scratch remains. In order for the chromate-treated metal plate to be widely used in the future as well, despite the fact that chromium insolubility is a necessary elemental technology,
It has been impossible to achieve this while maintaining the level of the required performance up to now, especially the high corrosion resistance in the processed part and the scratched part.

[0005]

DISCLOSURE OF THE INVENTION The present invention solves the above-mentioned technical problems and is excellent in corrosion resistance at a processed portion and a scratched portion, and reduces the amount of chromium eluted into an alkaline degreasing liquid or a water-soluble rolling oil. An object of the present invention is to provide a resin chromate-treated metal plate.

[0006]

The gist of the present invention is a zinc-based plated steel sheet, an aluminum-based plated steel sheet, a zinc alloy plate,
On either surface of aluminum alloy plate or steel plate,
The invention is characterized in that a water-dispersible resin emulsion and a resin chromate film containing a chromic acid compound as a main component are formed, and in the resin chromate film, a chrome pool containing a chromic acid compound and lacking emulsion particles is dispersed. It is on a resin chromate-treated metal plate. The depth of the chromium pool may be equal to or larger than the particle size of the resin particle emulsion. Further, the missing portion of the emulsion particles forming the chrome pool does not need to penetrate the coating, and the upper portion or /
The emulsion particles may remain in the lower part. The area ratio of the chromium pool is preferably 5% or more and 60% or less on any cut surface when the resin chromate-treated coating is cut in the horizontal direction with respect to the treated surface. Also, the distribution density of the chrome pool is preferably 10 points or more per 5 μm × 5 μm on any cut surface.

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention is described in detail below. In order to provide a resin chromate-treated metal plate having a small amount of eluted chromium and having a self-repairing function, the present inventors have constituted the chromate film mainly with the insoluble trivalent chromium,
It was considered effective to disperse a small amount of a chromic acid compound containing a larger amount of partially soluble hexavalent chromium. This is because by taking such a film structure, the total elution amount of hexavalent chromium in the degreasing liquid etc. is significantly reduced compared to the conventional one, and a small amount of dispersed hexavalent chromium elutes in the processed part and the scratched part. , Because it is expected to fulfill the self-repairing function.

Therefore, the inventors of the present invention first treat a metal plate by a known method using a series of resin chromate baths containing a commercially available acrylic emulsion resin and a chromic acid compound having a reduced rate as a main component. The performance was examined, but it was found that the reduction of the chromium elution amount and the corrosion resistance of the worked part and the scratch part were not compatible. At this time, when the structure of the treated film was examined,
In such a resin chromate film, the chromic acid compound is present as a continuous film almost uniformly so as to surround the periphery of the resin emulsion particles, and the reduction rate of this continuous film is the same as the dissolution rate of chromium and the processed part and scratches. It was found that it is a controlling factor of corrosion resistance in the parts.

Therefore, the present inventors made the continuous film surrounding the resin particles mainly composed of the hardly soluble trivalent chromium, but allowed a small amount of the soluble chromate compound containing hexavalent chromium to coexist in the resin chromate film. Therefore, as a result of diligent examination of the method, it is necessary to control the stabilization method of the emulsion, the type and concentration of the functional group of the emulsion resin particles, the state of existence of the chromic acid compound in the treatment bath, and the drying condition of the resin chromate film. As a result, it was found that the emulsion particles are missing and the chromium pool containing the chromic acid compound can be dispersed in the resin chromate film at various area ratios and densities. A transmission electron micrograph of a cut surface of such a resin chromate film is shown in FIG.
A schematic diagram of the cross-sectional structure is shown in FIG. Reference numeral 1 is emulsion resin particles, 2 is chrome accumulation, 3 is a chromic acid compound, 4
Is a metal plate. As a result of investigating the performance of the resin chromate-treated metal plate prepared in this way, it was found that, as expected, the reduction of the chromium elution amount and the corrosion resistance of the worked part and the scratch part are highly compatible.

Therefore, in the present invention, the chromium pool is dispersed in the resin chromate film. The depth of the chromium pool may be equal to or larger than the particle size of the emulsion resin particles. Further, the missing portion of the emulsion particles forming the chrome pool does not need to penetrate the film, and the emulsion particles may remain above or / and below. It is necessary that the size of the chromium pool is equal to or larger than 5 emulsion resin particles. If it is smaller than this, the hexavalent chromium is reduced due to the contact between the chromium compound and the resin particles, and the concentration of hexavalent chromium in the chromium reservoir is reduced, which is not preferable. Usually, the size is about 10 to 30 resin particles,
Many of them are about 1 micron in length.

The larger the amount of chrome accumulation, the better the corrosion resistance of the processed part and the scratched part. However, when the resin chromate film is cut in the horizontal direction with respect to the treated surface, the area ratio of the chrome accumulation on any cut surface. When it exceeds 60%, the secondary adhesion of the paint is impaired. On the other hand, when the area ratio is less than 5%, the effect on the processed portion and the scratch corrosion resistance is not remarkable. In addition, the higher the density of the chromium pool, the longer the self-repairing function in the processed part and the scratched part. It is desirable that the distribution density is 10 points or more per 5 μm × 5 μm in the range of 5 to 60% in the area ratio of any cut surface of the chromium pool.

Although the mechanism of formation of chromium pools is not clear, it is considered that the main causes are pseudo-aggregation of emulsion resin particles in a resin chromate bath and non-uniform evaporation of water in the drying process. For example, chromium puddle is generally less likely to form when the emulsion is stabilized by a low molecular weight surfactant. It is considered that this is because the low molecular weight surfactant becomes a factor for inhibiting contact between the resin particles in the resin chromate bath, and pseudo-aggregation of the resin particles does not easily occur.

On the other hand, in a so-called soap-free emulsion which does not use a low molecular weight surfactant, chromium pools are more likely to be formed. In the soap-free emulsion, the contact inhibition resistance between resin particles is relatively small, and it is considered that emulsion resin particles are pseudo-aggregated in the bath, that is, dozens of particles are gathered and loosely bound. When it is applied on a metal plate, the resin particles will not be evenly arranged, but will be arranged in a cluster of pseudo-aggregation units. In the gaps between these pseudo-aggregation units, the evaporation rate of water is higher than that of the surroundings during the drying process, and the flow of resin particles to that portion is hindered. On the other hand, it is presumed that the chromic acid compound having a low viscosity flows into this, and as a result, a chromium pool lacking the resin particles is generated.

The content of soluble hexavalent chromium in the chromic acid compound contained in the chromium pool is estimated to be higher than the content of hexavalent chromium in the continuous film of chromic acid compound surrounding the emulsion resin particles. The reason is,
In a continuous film, the area of contact with a reducing resin is large, and the reduction of the chromic acid compound gradually progresses even after coating and drying, whereas there is no contact with the resin in the chromium pool and the reduction Is suppressed.

The area ratio and distribution density of the chromium pool are
It varies depending on the type and concentration of the functional groups of the emulsion resin particles, the state of existence of the chromic acid compound in the resin chromate bath, and the drying conditions of the resin chromate film. The existing state of the chromic acid compound in the bath is the kind and amount of ions coordinating around chromium and the association state of the chromium complex, which changes depending on the temperature history of the treatment bath and coexisting added ions. Among the factors controlling the formation of chromium pools as described above, the type and concentration of the functional groups of the resin and the state of the chromic acid compound present in the bath determine the size of the pseudo-aggregate of the resin particles in the bath and the strength of the aggregation. It seems to determine the quality.

Of these, the effect of the type and concentration of the functional group of the resin on the pseudo-aggregation of the resin particles in the bath will be described first. The functional groups of the resin that may emulsion resin particles are quasi aggregated in the resin chromate bath, -COOH having proton donating, -SO ₃ H, -PO
Examples include (OH) ₂ , hydrolyzable and easily oxidizable ester groups, amide groups, alcohol amide groups, alcoholic hydroxyl groups and glycidyl groups. It is possible to use two or more of these together. In addition, the relationship between the concentration and characteristics of these functional groups and the formation of pseudo-aggregates is generally such that the more functional groups contained in a compound having a low glass transition temperature are present on the surface of resin particles, The size increases and the strength of aggregation increases. In addition, until reaching the steady state, pseudo-aggregation gradually progresses after the bath is built. In addition, the higher the bath temperature, the faster this process.

The resin that can be used is not particularly limited as long as it is a water-dispersible emulsion, but industrially, for example, epoxy resin, acrylic resin, polyurethane resin, styrene.
Examples thereof include maleic acid resin, phenol resin, polyolefin resin, a mixture of two or more kinds thereof, and a copolymer with another resin. In particular, vinyl resin emulsions represented by acrylic resins, that is, acrylic resin emulsions, (meth) acrylic acid and its ester copolymers, glycidyl group-modified acrylic compounds, aromatic vinyl compounds, and olefins such as ethylene and butadiene. , One of urethane modified acrylic compounds or 2
Those obtained by further copolymerizing at least one species are suitable. Although the form of the emulsion depends on the combination with the functional group, emulsion polymerization using a low molecular weight surfactant or soap-free polymerization without using a surfactant can be used. Is more desirable. The size of the resin emulsion particles can be appropriately selected, but usually the particle size is 0.0
It is common to use the one having a range of 5 to 0.5 μm.

Next, the relationship between the presence state of the chromic acid compound in the bath and the pseudo aggregation of the resin emulsion will be described. Chromate compounds themselves aggregate under certain conditions. Generally, such agglomeration is called gelation, and the resin particles are also taken into the network of the chromic acid compound to form a much stronger aggregate than the pseudoaggregation of the resin particles. Therefore,
In order to cause the resin particles to pseudo-aggregate, it is necessary to select conditions under which aggregation of the chromic acid compound itself does not occur.

The chromic acid compound usable in the present invention includes chromic anhydride and reduced chromic acid obtained by partially reducing chromic acid with starch or the like, or potassium dichromate, ammonium dichromate, sodium dichromate, potassium chromate. , Chromate such as ammonium chromate and sodium chromate, and chromate. Of these, chromic anhydride or reduced chromic acid obtained by partially reducing chromic anhydride is preferably used from the viewpoints of bath stability, film-forming property, and economy. Further, in order to prevent the chromic acid compound from aggregating in the bath, it is effective to add an acid such as phosphoric acid, boric acid, sulfuric acid or nitric acid. Especially phosphoric acid is most effective. The amount added is not particularly specified, but in order to ensure the stability of the bath under conditions where the bath temperature is higher than room temperature and is maintained for a long time, the chromic acid concentration in the bath (calculated as CrO ₃ ) At least 1.2
It is advantageous to add more than twice as much phosphoric acid (as H ₃ PO ₄ ).

On the other hand, the drying conditions determine the area ratio and distribution density of the final chromium pool. Generally, the higher the evaporation rate of water due to the short-time drying in a high temperature atmosphere, the higher the distribution density of chromium pools. The drying temperature can be appropriately selected according to the drying method and the film-forming property of the emulsion resin particles, but is 3 to 15 in high-speed processing in a continuous line.
Assuming a short-time drying of about a second, it is necessary to reach a maximum plate temperature of 50 ° C or higher. On the other hand, since the chromate compound coexisting in the resin chromate film is not excessively reduced, The temperature is preferably 180 ° C or lower. Therefore, the range of the heating rate under this condition is approximately 2 to 50 ° C /
It becomes sec.

In addition to the resin emulsion and the chromic acid compound, an inorganic sol such as silica, alumina, titania and zirconia, a fluoride and the like can be contained in the chromate treatment bath and the film, if necessary. The thickness of the resin chromate film specified in the present invention can be appropriately selected, but is usually about 0.1 to 5 μm. If it is less than 0.1 μm, the effect as a continuous film cannot be obtained, and if it is 5 μm or more, the effect is saturated.

As the metal plate to which the present invention can be applied, a galvanized steel plate, a zinc-nickel plated steel plate, a zinc-iron plated steel plate, a zinc-chrome plated steel plate, a zinc-titanium plated steel plate, a zinc-magnesium plated steel plate, a zinc- Manganese-plated steel sheet, zinc-based electroplating such as zinc-aluminum-plated steel sheet, hot-dip galvanized steel sheet, vapor-phase plated steel sheet, aluminum-plated steel sheet, and a small amount of different metal elements or impurities in these plating layers, such as cobalt,
Molybdenum, tungsten, nickel, titanium, chromium, aluminum, manganese, iron, magnesium, lead,
It includes a plated steel sheet containing antimony, tin, copper, cadmium, arsenic, etc., and / or a plating layer in which an inorganic substance such as silica or alumina or an organic additive is dispersed. Alternatively, it can be applied to multilayer plating in which two or more kinds of these platings are laminated, and further to multilayer plating in which these platings are combined with other platings such as iron plating and iron-phosphorus plating. Further, an aluminum plate and an aluminum alloy plate added with silicon, copper, magnesium, iron, manganese, chromium, titanium, zinc or the like as an alloying element or impurities, a zinc or zinc alloy plate, or a steel plate can also be used.

As a chromate treatment method for a metal plate,
A general coating method such as coating with a roll coater, coating with a ringer roll, coating with dipping and air knife squeezing, coating with a bar coater, or spraying can be used. Further, the treatment can be carried out by one-step treatment with a treatment bath in which a resin emulsion is mixed with a chromic acid compound and other additives, and once drying. In order to observe the fine structure of the resin chromate film, by coating and drying the resin chromate-treated metal plate in the horizontal direction with respect to the treated surface with an ultra microtome,
A slice having a thickness of about 50 to 200 nm was prepared and analyzed with a transmission electron microscope.

FIG. 1 is an observation example of a resin chromate film formed by this method, in which the arrangement of resin emulsion particles is not uniform, and it is observed that there are missing portions with a size of several μm. FIG. 2 shows the portion of the chromium pool defined in the present invention in FIG. Since the chromium compound is present in the chromium pool at a high concentration, the transmission of the electron beam is suppressed, and it is observed as a dark area in the transmission electron micrograph. Therefore, in order to measure the area ratio of the chromium pool, it is effective to perform a binary image processing on the transmission electron micrograph to calculate the area ratio of the dark portion. The area ratio and distribution density of the chromium pool were determined by actually measuring at least 10 places in an area of 5 μm × 5 μm or more using a photograph as shown in FIG.

[0025]

EXAMPLES The present invention will now be described with reference to examples. (1) Type of metal plate: GI using the following five types as metal plates to be chromated; hot-dip galvanized steel plate (coating adhesion amount 90 g / m
² ) EG: Electrogalvanized steel sheet (coating weight 20g / m
² ) SZ: hot-dip zinc-aluminum plated steel sheet (coating weight 120 g / m ² , AL / Zn = 5/95) GA: alloyed hot-dip galvanized steel sheet (coating weight 45 g)
/ M ² , Fe / Zn = 15/85) AL: Hot-dip aluminized steel sheet (coating weight 100 g /
m ² ) (2) Kind of chromic acid: Chromic anhydride partially reduced was used. The concentration of chromic acid is 20 to _{5 in} terms of CrO _3.
It was set to 0 g / l.

(3) Type of resin emulsion: The following resin emulsions were used. The concentration of the resin emulsion in the bath is 3 to 7 of the chromic acid concentration (converted to CrO ₃ ) in terms of solid content.
Doubled For comparison, water-soluble polyacrylic acid (symbol X) was also used. A: Acrylic-epoxy emulsion obtained by copolymerizing propyl acrylate, butyl acrylate, methacrylic acid, and glycidyl methacrylate without using a low molecular weight surfactant. B: Methyl methacrylate, butyl acrylate, methacrylic acid having a low molecular weight. Acrylic Emulsion C Copolymerized Without Surfactant: Acrylic Emulsion D Copolymerized Methyl Methacrylate, Butyl Acrylate, Methacrylic Acid, Hydroxyethyl Acrylate Without Using Low Molecular Weight Surfactant D: Aromatic vinyl emulsion E copolymerized with vinylphenol, styrene and methacrylic acid E: olefin-acrylic emulsion F copolymerized with butadiene, acrylic acid and hexyl acrylate F: low molecular weight methacrylic acid and styrene Aromatic vinyl was emulsion polymerization in the presence of a surface active agent based emulsion X: water-soluble polyacrylic acid

(4) Other additives: Phosphoric acid (P) was added, and colloidal silica (S) was also added in part. The addition amount of phosphoric acid is 1.5 times or more the chromic acid concentration, and the addition amount of colloidal silica (converted to SiO ₂ )
Was set to 0.5 to 1.5 times the chromic acid concentration. (5) Chromate treatment method: Coating treatment was performed using a roll coater.

(6) Control of area ratio and distribution density of chromium pool: particle size of resin emulsion particles, kind and concentration of functional group, temperature history of chromate treatment bath and amount of phosphoric acid in treatment bath, drying after coating By controlling the rate of temperature rise in the process, samples were prepared in which chromium pools were dispersed in the resin chromate film at various area ratios and distribution densities. As an example, the invention example 1 in Table 1 will be described in detail. The resin particle size is about 150 nm, the functional groups are carboxyl groups (concentration: 10% by weight as methacrylic acid) and hydroxyl groups (concentration: 5% by weight as hydroxyethyl acrylate), and chromic acid (concentration 30 g / l ) 2
A double amount of phosphoric acid and a 5-fold amount of resin emulsion were added, and after application of the bath, the mixture was left at room temperature for 1 week and then applied. The drying plate temperature was 60 ° C., and the temperature rising rate was 2 ° C./sec.

(7) Measurement of Area Ratio and Distribution Density of Chromium Reservoir: The chromate-treated metal plate after coating and drying was cut by using an ultramicrotome at room temperature in the horizontal direction with respect to the treated surface. A piece of resin chromate film,
Area of 5 μm at a magnification of 20000 by a transmission electron microscope
Photographs were taken at 10 fields of view of × 5 μm or more, the area ratio and distribution density of the chromium pool were measured, and the average value was obtained.

(8) Performance evaluation method 1) Chromium elution rate: The alkaline degreasing solution was sprayed on the test material for 3 minutes at room temperature and then washed with water for 1 minute. Determined by X-ray analysis. ◎: Chromium elution rate less than 5% ◯: Chromium elution rate 5% or more and less than 10% △: Chromium elution rate 10% or more and less than 20% ×: Chromium elution rate 20% or more

2) Corrosion resistance of processed part: The specimen was subjected to Erichsen processing to a height of 7 mm and then subjected to a salt spray test to measure the white rust occurrence area ratio in the processed part. The test period is GI,
EG, SZ, AS was 6 days, AL was 9 days. ◎: White rust occurrence rate of less than 5% ◯: White rust occurrence rate of 5% or more and less than 10% △: White rust occurrence rate of 10% or more and less than 20% ×: White rust occurrence rate of 20% or more

3) Paint adhesion: A melamine alkyd paint was applied to the sample in an amount of 20 μm, dried, and then dried in boiling water at 30 μm.
It was soaked for a minute. Immediately a cross-cut test (1 mm cross-cut 10 x 1
The peeled area ratio of the coating film was examined by (0, tape peeling). ⊚: Peeling rate less than 5% ◯: Peeling rate 5% or more and less than 10% Δ: Peeling rate 10% or more and less than 20% ×: Peeling rate 20% or more performance evaluation results are shown in Tables 1 and 2. As is clear from the table, by dispersing a predetermined amount of chromium pool in the coating, excellent corrosion resistance of the processed part, paint adhesion,
Moreover, the amount of chromium elution is small.

[0033]

[Table 1]

[0034]

[Table 2]

[0035]

According to the present invention, the resin chromate-treated metal plate can be used for alkaline degreasing or the like while maintaining high corrosion resistance at the processed portion and the scratched portion, which is the original function of chromate treatment.
The elution amount of valent chromium can be reduced.

[Brief description of drawings]

Fig. 1 Transmission electron micrograph of cut surface of resin chromate film

FIG. 2 is a diagram showing a chromium pool portion defined by the present invention in FIG. 1;

FIG. 3 is a schematic diagram of a cross-sectional structure of a resin chromate film.

[Explanation of symbols]

1 Emulsion resin particles 2 Chrome pool 3 Chromic acid compound 4 metal plate

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁷ Identification code FI C23C 28/00 C23C 28/00 C (56) References JP-A-55-58375 (JP, A) (58) Fields investigated ( Int.Cl. ⁷ , DB name) C23C 22/27 B05D 7/14 B05D 7/24 301 B32B 15/18 C23C 28/00

Claims (3)

(57) [Claims] 1. A zinc-based plated steel plate, an aluminum-based plated steel plate, a zinc alloy plate, an aluminum alloy plate, or a steel plate, on which surface a water-dispersible resin emulsion and a resin chromate film containing a chromic acid compound as a main component are formed. A resin chromate-treated metal plate, which is formed and has dispersed therein a chromium pool containing a chromate compound, in which emulsion particles are missing, in the resin chromate film. 2. When the resin chromate-treated film is cut in the horizontal direction with respect to the treated surface, the area ratio of the chrome pool is 5% or more and 60% or less on any cut surface. The resin chromate-treated metal plate described. 3. The resin chromate treatment according to claim 2, wherein when the resin chromate treatment film is cut in the horizontal direction with respect to the treated surface, the density of chromium pools on any cut surface is 10 points or more per 5 μm × 5 μm. Metal plate.