JPH09316681A - Water-soluble organic additive in electrogalvanizing bath and production of electrogalvanized steel sheet and surface-treated glavanized steel sheet excellent in appearance uniformity - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress the generation of a minute part nonuniform in appearance on a plating surface due to microscopic nonuniformity of the surface of a steel sheet by using a water-soluble org. high molecular compd. electrochemically easy to decompose and chemically inert to the surface of an anode as an additive. SOLUTION: A polyoxyalkylene derivative shown by the general formula R2 -O-(R1 -O)n -R2 and having 10<3> -10<5> mol.wt. is preferably used as the water-soluble org. high molecular compd. In the formula, R2 is a lower alkylene, and R2 is hydrogen or a lower alkylene. A steel sheet is electrogalvanized in a galvanizing bath contg. 1-500ppm of the derivative to form a zinc plating layer on the surface at 10g/m<2> , and an electrogalvanized steel sheet excellent in appearance uniformity is obtained. Further, the service life of the electrode is not shortened, and the waste water is easily treated since the derivative is decomposed when plating is finished and not present in the plating soln.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention can provide a uniform plating appearance and can prolong the life of the electrode because it is chemically inert to the surface of the anode. The present invention relates to a water-soluble organic additive in an electrogalvanizing bath which is decomposable and therefore decomposes at the end of plating and does not remain in a plating solution (thus, wastewater treatment is easy). Furthermore, the present invention uses the above-mentioned water-soluble organic additive, and there is no difference or unevenness in the partial color tone (microscopic appearance color tone) / gloss of the plating appearance due to the microscopic nonuniformity of the surface of the original plating plate. The present invention relates to an electrogalvanized steel sheet having a uniform appearance and a method for producing a surface-treated electrogalvanized steel sheet. The plated steel sheet obtained by the method of the present invention,
Since it has excellent uniformity of plating appearance even without applying a coating treatment, it is extremely useful as various vehicle bodies such as automobiles, outer panel materials such as home electric appliances and OA equipment, or building materials.

[0002]

2. Description of the Related Art Galvanized steel sheets have excellent corrosion resistance because the galvanized film exerts a sacrificial anticorrosion action on the base steel sheet, and is therefore used as an outer plate material for automobiles and household electric appliances or as a building material. Widely used. The following two methods are widely used as a method for producing such a galvanized steel sheet.

Hot dip galvanizing method: That is, by continuously dipping and running a steel strip in a hot dip galvanizing bath,
A method of forming a galvanized film on the surface of a steel sheet. Electrogalvanizing method: That is, a method in which a steel sheet is continuously immersed and run in an acidic solution containing zinc ions, and zinc ions are electrodeposited on the surface of the steel sheet by an electrochemical reaction to deposit a plating film.

Of these methods, the hot dip galvanizing method has the advantage of being excellent in corrosion resistance because a galvanized film with a high adhesion amount can be easily formed, but on the other hand, the steel sheet is dipped in a hot dip zinc bath. Since the treatment is performed, dross present in the bath may adhere to the galvanized surface, or the spangle pattern generated during solidification as a plating film may remain unevenly, resulting in uniform plating surface appearance. In that respect, there are some difficulties.

However, in most cases, the conventional galvanized steel sheet has been used as a so-called coating base steel sheet, in which the surface of the galvanized steel sheet is used after being coated with some coating. Since some of the defects are completely covered by the overcoating applied thereon, the fact that the above-mentioned surface appearance defect in the hot-dip galvanized steel sheet has hardly been regarded as a problem.

On the other hand, in the electrogalvanizing method, the electric power cost increases in proportion to the coating amount, so that there is an economical problem in that a high coating amount causes an increase in manufacturing cost. Since there are no defects on the plated surface appearance such as dross defects and residual spangle patterns due to the plating method, it is useful in that a galvanized product having a beautiful appearance can be obtained.

However, in recent years, with the progress of the omission of the coating process on the user side, after the desired molding process, it is often used as it is without coating (that is, the plating appearance is left as it is) without coating. That is, by subjecting galvanized steel sheets to various chromate treatments and chemical conversion treatments such as organic or inorganic coating treatments, not only corrosion resistance but also workability, fingerprint resistance, weldability, groundability (conductivity), etc. There is an increasing number of cases in which special chemical treatment galvanized steel sheets that combine the above performance are used without any coating.

Then, the appearance of the plated surface during the production of the galvanized steel sheet appears as it is in the appearance of the final product.
The appearance defects on the galvanized surface, which have not been regarded as a problem in the past, cannot be ignored, and the requirements for the appearance quality of the galvanized surface become very strict.

In such an uncoated bare application, it is unsuitable to use a hot-dip galvanized steel sheet that does not give a very good surface appearance, and therefore it is inevitable that electrogalvanization will give a beautiful surface appearance. Steel plates will be used frequently. However, as the field of application for naked applications has expanded, the fact is that even the surface quality of conventional electrogalvanized steel sheets is no longer able to satisfy the demands of consumers. It has become necessary to improve even the fine appearance unevenness that occurs on the galvanized surface.

In general, the appearance of an electrogalvanized steel sheet is easily affected by the surface of the steel sheet which is the material to be plated. For example, if the thickness of the oxide film layer on the surface of the steel sheet is not uniform, there will be a difference in the appearance color tone after the galvanized film is formed between the thick part and the thin part of the film, and uneven appearance will be observed. There are cases. In addition, Ni, Si, Mn, C contained in the steel sheet
Even if there is a part where elements such as
Similarly, the appearance unevenness after the galvanized film is formed is generated.

By the way, such non-uniformity of the fine surface appearance that occurs on the plated surface of the electrogalvanized steel sheet is due to micro-nonuniformity of the electrogalvanized crystal itself, but the causes thereof are complex and diverse. Therefore, it was difficult to solve the problem easily.

[0012] Specifically, a minute unevenness in appearance such as a partial change in color tone or a minute flow pattern means that locally and irregularly different color tone regions are generated on the plating surface, or the length and shape are different. It is a phenomenon that streaky irregularities occur irregularly, and these are defects and stains in minute areas existing on the steel plate surface which is the original plate to be plated, concentration of elements in the steel, as described above.
This is due to the microscopic non-uniformity of the electrogalvanized crystal due to the non-uniformity of the oxide film thickness, etc., but it is extremely difficult as a practical problem to make the surface quality of such a steel sheet industrially uniform.

Conventionally, as a measure for improving the appearance of an electrogalvanized steel sheet in a broad sense, the manufacturing conditions of a material to be plated (pickling condition after hot rolling, electrolytic cleaning condition after cold rolling) , Annealing conditions, etc.), electrolytic zinc plating pretreatment conditions (electrolytic degreasing conditions, pickling conditions), electrolytic zinc plating conditions, plating posttreatment conditions, etc. have been proposed.

Of these, for example, JP-A-61-147894
JP-A-4-124295 and JP-A-4-124295 disclose iron group ions (F
e, Ni and / or Co ions) or Sn ions are added first to deposit these metal ions on the steel sheet, and the deposited metal elements serve as growth nuclei for zinc plating crystals to grow on the zinc. It discloses a method of making zinc-plated crystals fine and smooth by microdispersing the initial deposition of ions. However, these methods have a problem that a sufficient crystal refining effect is not recognized.

JP-A-4-74887 and JP-A-4-74887
Japanese Patent No. 74888 discloses that an acidic zinc plating bath containing a predetermined conductive auxiliary agent is used to perform lower layer plating on the surface of a steel sheet at a predetermined current density, and then another acidic zinc plating bath is used to provide a predetermined current density. Discloses a method of forming an upper plating layer.

According to this method, the upper electrogalvanized layer is formed by preferentially orienting the smooth (0002) plane, so that absorption of visible light on the plated surface is suppressed, and electrozinc having high brightness and gloss. It is said that it will be possible to obtain plated steel sheets. However, these methods basically lack the effect of suppressing the generation of fine non-uniform portions on the plated surface due to microscopic non-uniformity on the steel sheet surface.

Further, in Japanese Patent Publication No. 39-24027, Japanese Patent Publication No. 55-41306, Japanese Patent Publication No. 61-127887, Japanese Patent Publication No. 61-127891, Japanese Patent Publication No. 63-14890, etc., an electrogalvanizing bath is used. It is intended to obtain an electrogalvanized steel sheet having an excellent surface appearance by incorporating therein an organic compound having various functional groups and various molecular weights at a predetermined concentration.
These methods are for adsorbing an organic compound added to the plating bath on the surface in the process of electrodeposition of zinc ions to suppress the deposition reaction of electrogalvanizing, and to obtain a smooth plating appearance. As a result, a plating appearance with high glossiness can be obtained.

That is, the excellent plating surface appearance intended in these publications means that the surface glossiness of the electrogalvanized layer is increased, and the fine non-uniformity of the plating surface, which is a problem in the present invention. It is not possible to expect even control of the occurrence of parts. That is, a satisfactory effect cannot be always expected for the improvement of the fine nonuniformity portion of the plating appearance caused by the microscopic nonuniformity of the surface of the steel plate which is the original plate to be plated. Also, when the glossiness of the electrogalvanized surface increases,
In some cases, the appearance of electrogalvanizing on the surface of the steel sheet may become more conspicuous due to microscopic nonuniformity, and some improvement measures must be taken.

Further, when the surface gloss of the electrogalvanized steel sheet becomes high, the surface flaws produced during the forming process tend to be conspicuous on the contrary, so that the improvement of the gloss results in good results for all applications. is not. In the present invention, since it is desired to improve only the fine appearance nonuniformity of the plated surface as it is with a product having a conventional semi-glossy or matte surface glossiness, only the improvement of the glossiness of the plated surface is required. These methods, which are intended to be, are not always the best bet.

Incidentally, among the above publications, JP-A-61-1278
Japanese Patent Laid-Open No. 91-91 discloses a method of obtaining a smooth plated surface in which a (0002) plane of an electrogalvanized crystal is suppressed from being preferentially grown to be randomly crystallized to leave some surface irregularities. It is completely unknown whether this phenomenon can suppress the generation of fine appearance uneven portions on the plated surface, which are caused by microscopic unevenness on the surface of the base steel sheet.

Japanese Patent Publication No. 3-31795 discloses a method for obtaining an electrogalvanized steel sheet having a good appearance and gloss by defining the ferrite grain size (crystal grain size) of the surface of the base steel sheet and the pH of the electrogalvanizing bath. Is disclosed. Specifically, the ferrite grain size of the steel material surface is 10 to 35 μm,
The expansion rate is 1.0 to 2.0 and the pH of the plating bath is
Of 1.0 to 2.5 is a method of improving the plating appearance. In this publication, attention is paid to the fact that electrogalvanized crystals grow epitaxially corresponding to the individual ferrite crystal grains on the surface of the base steel sheet, and the base material has a large ferrite crystal grain size (that is, a small ferrite crystal grain size). By using a steel sheet, it is intended to reduce the epitaxial growth unit of the obtained electrogalvanized crystal and, as a result, to obtain a smooth and fine plated surface having high gloss.

In the method for adjusting the ferrite crystal grain size on the surface of the steel sheet as described above, no sharp and sharp change in the glossiness of zinc plating with respect to the crystal grain size of the steel sheet is observed, but in reality, the ferrite crystal grain on the surface of the steel sheet is not changed. It is difficult to control the particle size to a suitable range for all applications.

Further, when the surface of the steel sheet having different ferrite grain sizes is partially used, it may cause the appearance of electrogalvanizing to have a partially different color tone and gloss. However, even if adopted, fine nonuniformity of the appearance of the electrogalvanized surface due to the microscopic nonuniformity of the surface of the steel sheet is not improved.

The method of producing an electrogalvanized steel sheet having an excellent surface appearance disclosed in Japanese Patent Laid-Open No. 63-100193 is a method of forming a thin oxide film on the surface of a base steel sheet before performing the electrogalvanizing treatment to form a plated surface. It suppresses glare in the appearance and gives a fine and smooth plating appearance.

The reason for the improvement of the surface appearance brought about by this method is the same as that described in JP-B-3-31795, and the crystal grains on the surface of the base steel sheet and the electrogalvanized crystal are in a heteroepitaxial relationship. Focusing on this point, an oxide film having a predetermined thickness is formed in advance on the surface of the base steel sheet in order to grow plated crystals randomly without being affected by the crystal grains on the surface of the base steel sheet. However, this method inevitably lowers the processing adhesion of the electrogalvanized film due to the oxide film treatment, and cannot be applied to products that are subjected to a high degree of molding after plating.

As disclosed in the publication, 100
It is technically very difficult to continuously perform uniform oxide film treatment in the width direction and longitudinal direction of the steel sheet in the range of ~ 300 Å. If the thickness of the oxide film is thin, the effect of improving the appearance will not be exhibited. If the thickness becomes too thick, the processing adhesion of the electrogalvanized steel sheet will drop sharply. The most problematic point is that if the thickness of the oxide film is unevenly formed on the surface of the steel sheet, the unevenness causes changes in the crystal grains of electrogalvanizing, which rather deteriorates the appearance of the plated surface. .

Japanese Unexamined Patent Publication (Kokai) No. 57-110692 is intended to obtain an electrogalvanized steel sheet having an excellent plated surface appearance by removing stains on the plated surface and non-plated surface and preventing discoloration. , Specifically, an alkaline aqueous solution having a pH of 12 or more or a pH after the galvanizing treatment
It is a method of wetting the steel sheet surface with an acidic aqueous solution of 2.5 or less. However, even with this method, the uneven appearance of the plated surface due to the microscopic unevenness of the surface of the base steel sheet cannot be improved.

JP-A-7-76792, JP-A-7-76
793, JP-A-7-76794, JP-A-7-238.
387, JP-A-7-243083, JP-A-7-27.
8880, JP-A-7-278881 and JP-A-7-278881
No. 316878 describes a method for improving stains on the appearance of plating caused by microscopic defects on the surface of a base steel sheet and a plating film configuration. The electrogalvanized steel sheets disclosed in these publications all form a two-layer electrogalvanized plating film, and as a lower plating film, zinc or a zinc-based galvanic film obtained under various conditions is used. A desired plating layer made of alloy plating or a metal element other than zinc or an alloy is first applied to the surface of the steel sheet, and a normal electrogalvanized layer is further formed thereon. In these inventions, it is the various lower-layer zinc plating layers that are directly applied to the steel plate surface that have the effect of reducing the plating surface appearance stains due to minute defects on the steel plate surface, and the addition of organic substances to the plating bath and high By adopting the plating current density, the crystal grains of the lower zinc-plated layer are made finer or amorphized to shield the non-uniformity of the surface of the base steel sheet, and the steel sheet is applied to the ordinary electrogalvanized surface of the upper layer. It is designed not to have an adverse effect due to microscopic defects on the surface.

However, since the thickness of the lower layer plating film formed by these methods is very thin, it is difficult to expect the above-mentioned shielding effect when the surface defects of the base steel sheet are significant.
Further, the concealment effect of the lower plating layer cannot be effectively exhibited unless it is an electrogalvanized layer or a metal and alloy plated layer other than zinc obtained only under certain specific conditions, and thus strict control of lower plating treatment conditions is required. However, there are difficulties on an industrial scale.

[0030]

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and an object thereof is to obtain a fine appearance of the electrogalvanized surface due to microscopic nonuniformity of the surface of the base steel sheet. It is possible to surely suppress the generation of uniform parts and obtain an electrogalvanized steel sheet with a uniform plating appearance, without degrading the life of the electrode, and further disintegrating at the end of plating and remaining in the plating solution. It is an object of the present invention to provide a water-soluble organic additive in an electrogalvanizing bath, which has characteristics such as not being used (and therefore, wastewater treatment is also easy).

Another object of the present invention is to use a single electrogalvanized layer directly on the surface of a steel sheet by using the above-mentioned organic additive, instead of a complicated two-layer type plating structure conventionally proposed. The present invention is intended to provide a method for producing an electrogalvanized steel sheet that can be applied.

Still another object of the present invention is to provide a method for producing a surface-treated steel sheet having a chromate film formed on the surface of the above electrogalvanized steel sheet for the purpose of improving corrosion resistance and the like, as well as corrosion resistance and fingerprint resistance. , For the purpose of improving lubricity,
An object of the present invention is to provide a method for producing a surface-treated electrogalvanized steel sheet in which an organic or inorganic thin film clear film having a uniform plating appearance is formed on the chromate film.

[0033]

The water-soluble organic additive in the electrogalvanizing bath according to the present invention, which has been able to achieve the above object, is electrochemically easily decomposable, and at the same time with respect to the anode surface. The gist is that it is composed of a chemically inactive water-soluble organic polymer compound and gives a uniform plating appearance. Such a water-soluble organic polymer compound has a molecular weight of 10 ³ to 1 represented by the following general formula.
It is preferably a polyoxyalkylene derivative of 0 ⁵ . R ₂ —O— (R ₁ —O) n—R ₂ provided that R ₁ : lower alkylene group R ₂ : H or lower alkyl group, respectively.

The method for producing an electrogalvanized steel sheet according to the present invention, which has been able to achieve the above-mentioned object, means that when the galvanized layer is formed on the surface of the steel sheet by the electroplating method, the polyoxyalkylene derivative is 500
performed galvanized with zinc plating bath to ppm content, weight per unit area: those having the gist where to form the galvanized layer of 10 g / m ² Ultra to 100 g / m ^2.

Further, in the method for producing a surface-treated electrogalvanized steel sheet according to the present invention, the surface of the plating layer of the electrogalvanized steel sheet satisfying the above requirements is subjected to a chromate treatment mainly containing a Cr compound to obtain a steel sheet surface. To sequentially form a zinc plating layer and a chromate film on the steel sheet, and by further applying an organic or inorganic clear film on the chromate film, a zinc plating layer, a chromate film and a clear film are sequentially formed on the steel sheet surface. Each point has its own gist. Here, it is 5 in terms of metal Cr adhesion amount.
It is a preferred embodiment of the present invention to control the amount of solid content to be 0.3 to 2.0 g / m ² when performing a chromate treatment of up to 200 mg / m ² or applying a clear film.

[0036]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, embodiments of the present invention will be described in detail with the background of the present invention. We have
In view of the problems of the conventional techniques as described above, the cause of the uneven microscopic appearance occurring on the plated surface of the electrogalvanized steel sheet was investigated. As a result, it was confirmed that the portion visually recognized as the nonuniform portion had a slight change in glossiness and brightness as compared with other normal portions. That is, the amount of reflected light (regular reflection amount and diffuse reflection amount) with respect to the visible light incident on the electrogalvanized surface is different between the microscopically nonuniform portion and the macroscopic normal portion. It was concluded that it was recognized as a difference in color tone, that is, a microscopic appearance defect part.

Further, when the crystal morphology of the electrogalvanized surface was investigated, the microscopic appearance nonuniformity generation portion and other normal portions often had different zinc plating crystal morphology. It was estimated that the degree of epitaxy with the steel sheet during growth was different.

As described above, the cause of the non-uniform microscopic appearance that occurs on the plated surface of the electrogalvanized steel sheet is that the morphology (size or orientation) of the plated crystals formed on the steel sheet surface is uneven or coarse. Therefore, the inventors of the present invention considered that, as a countermeasure against this, if the zinc plating crystal is made fine and the orientation of the crystal is made random, the defect of non-uniform microscopic appearance can be eliminated. . That is, by controlling the crystal growth of the electrogalvanized layer by some means, regardless of the properties and morphology of the steel plate surface that is the original plate, if it is possible to give a certain property, specifically, the crystal size and crystal orientation, We thought that it would be possible to suppress the occurrence of microscopic uneven appearance on the plating surface.

Therefore, first, the zinc-plated crystal is miniaturized,
As a method of randomizing the orientation of the plated crystals, we investigated how to increase the precipitation overvoltage during electrogalvanizing. Specifically, while varying the ferrite crystal grain size variously, various intentionally manufactured cold-rolled steel sheets were used so that the surface texture becomes microscopically non-uniform, and the current density during electrogalvanization was changed. The obtained zinc-plated crystals and the zinc-plated appearance were investigated by increasing the number.

As a result, according to this method, it was confirmed by experiments that the above-mentioned defects of non-uniform microscopic appearance could be eliminated. However, in consideration of continuous production in an actual operation line, the precipitation overvoltage is lower than that at present. It was concluded that there is a limit in terms of equipment or manufacturing cost, and it is difficult to put it into practical use if it is significantly raised.

A method of converting the electrogalvanized coating into a two-layer type (multilayer type) galvanized coating, that is, the galvanized lower layer portion which is first electrodeposited on the surface of the steel sheet is plated under high precipitation overvoltage, After that, by performing the upper layer zinc plating treatment under normal conditions, a large increase in manufacturing cost is prevented,
Although a method of improving the quality of the plating appearance to some extent is conceivable, it is inevitable that the electroplating equipment is complicated and the management of the plating adhesion amount is complicated, and it is difficult to say that this is a preferable method.

Then, the present inventors next prepared an electroplated steel sheet in a zinc plating bath containing various organic compounds, and investigated the effect of suppressing the occurrence of microscopic uneven appearance on the plated surface. . As a result, they have found that by adding a water-soluble organic compound having a certain specific functional group or molecular weight at a predetermined concentration, microscopic nonuniformity on the galvanized surface can be reduced or eliminated.

The first organic compound added to the plating bath in order to increase the glossiness of electrogalvanizing has hitherto been the first.
, Secondary, tertiary aliphatic amines, cationic quaternary aliphatic or aromatic ammonium salts, polyacrylamides, copolymers of polyacrylamide and cationic organic compounds, glucose, dextrin, Carbonyl amide substitution products of polyalkylene compounds are well known,
It has been found that among these, there is an organic compound capable of reducing not only the effect of increasing the glossiness of zinc plating but also the non-uniformity of the microscopic appearance of the plating surface, depending on the type and amount added.

However, the object of the present invention is to prevent the occurrence of microscopic non-uniform portions on the galvanized surface on the premise that the color tone of the appearance of the conventional galvanized steel sheet is not significantly changed. Therefore, the method of adding a so-called organic brightening agent that causes the glossiness of the obtained electrogalvanized surface to change significantly, even if it is possible to prevent the occurrence of microscopically nonuniform parts on the galvanized surface. However, it should be excluded from the gist of the present invention.

Under such constraint conditions, the present inventors further studied to narrow down various water-soluble organic compounds that can reduce or eliminate the occurrence of microscopic nonuniformity on the galvanized surface. It was

By the way, in order to produce an electrogalvanized steel sheet in a continuous production line, it is necessary to install an anode with respect to a cathode (steel sheet) in an electrolytic reaction in an acidic zinc plating bath. As this anode, an insoluble anode such as an iridium oxide electrode or a Pb alloy electrode is generally used.
However, it has been found that the water-soluble organic compound added to the galvanizing bath has the effect of significantly deteriorating the insoluble electrode such as iridium oxide in the continuous electrolytic reaction for a long time. Although the reason for this is not clear, it is presumed that various functional groups contained in the water-soluble organic compound are adsorbed on the electrode surface or an oxidation-reduction reaction occurs to accelerate the reduction of the iridium oxide film. It

For any reason, the above-mentioned insoluble anode is expensive, and an increase in the wear rate accelerates the replacement time, which leads to an increase in the manufacturing cost, which adversely affects the continuous productivity, and also increases the plating power due to the wear. And increase the power cost.

As described above, suppressing the occurrence of non-uniform microscopic appearance of the electrogalvanized surface by adding a water-soluble organic compound to the galvanizing bath has a problem that the insoluble electrode is adversely affected. It turns out that

In addition, in the process of manufacturing in a continuous line on an industrial scale, the zinc plating bath or the diluted solution of the zinc plating bath is inevitably continuously little by little, or periodically a large amount at a time. Will be drained to. Usually, in order to drain the galvanizing bath or its diluted solution to rivers or the sea, prescribed pretreatment is required. Specifically, neutralization treatment, heavy metal precipitation removal treatment, and eutrophication elements such as phosphorus. And the removal treatment of

In particular, when an organic compound is contained in the waste water, the COD value and BOD value in the waste water rise, the water quality deteriorates, and the environment is destroyed. It is necessary to remove organic compounds contained in water. However, when an organic compound having a highly hydrophilic functional group is used, it is not easy to remove it to a desired low concentration level by the simple method as described above.
Therefore, the activated sludge method, that is, after thoroughly blowing air into water containing organic compounds, aerobic bacteria are used to treat and decompose organic compounds in water, and aerobic bacteria grown by eutrophication. A method of aggregating the bacterial cells and removing them by filtering is widely used. However, since this activated sludge method has a very high treatment cost, the production cost of the electrogalvanized steel sheet increases significantly.

The addition of the water-soluble organic compound to the galvanizing bath in this way brings about new problems such as selection of a method for treating the organic compound remaining in the wastewater and an increase in cost due to the treatment method. I have it.

In summary of the above contents, a method for improving the appearance non-uniformity of the galvanized surface by adding a water-soluble organic compound to the galvanizing bath is as follows: Adverse effect on insoluble anode,
It causes various problems such as complicated wastewater treatment and increased manufacturing cost.

Therefore, as a result of studies by the present inventors for the purpose of solving the above problems, among the water-soluble organic compounds added to the zinc plating bath, it has an excellent effect of uniform plating appearance and, at the same time, plating It decomposes in a relatively short time in the bath, the decomposition products evaporate without remaining in the plating bath, are spontaneously released to the outside of the plating bath, and have the property of being chemically inert to the anode surface. It was found that there is a substance, and the use of such an organic compound is the main gist of the present invention.

That is, the water-soluble organic additive in the electrogalvanizing bath of the present invention is electrochemically degradable (that is, under electrogalvanizing conditions and under electric current), and at the same time with respect to the anode surface. It is composed of a chemically inert water-soluble organic polymer compound and gives a uniform plating appearance. In this way, it has the effect of eliminating microscopic non-uniformity of the plating surface without increasing the gloss of zinc plating, and decomposes in a relatively short time in an acidic zinc plating bath to become a gas component and evaporate outside the bath. In addition to the properties described above, those that are chemically inert to the surface of the anode are included in the scope of the present invention. In the following description, a polyoxyalkylene derivative represented by the following general formula, which is a typical example of the present invention, will be described. R ₂ —O— (R ₁ —O) n—R ₂ provided that R ₁ : lower alkylene group R ₂ : H or lower alkyl group, respectively.

The above polyoxyalkylene derivative naturally has the above-mentioned properties, but since the low-molecular organic compound produced by decomposition does not harm the human body and does not contain halogen, it pollutes the atmosphere. It is very useful in that it does not cause ozone destruction.

Here, the molecular weight of the polyoxyalkylene derivative must be 10 ³ to 10 ⁵ .
When it is less than 10 ^3, the effect of preventing microscopic nonuniformity of the electrogalvanized surface is poor, while when it exceeds 10 ⁵ , the stability of the electrogalvanized gloss is poor. Fluctuations in glossiness due to fluctuations in concentration in the plating bath may be recognized, and uneven plating appearance such as a new flow pattern of the plating bath may occur on the plating surface. It is preferably 10 ³ to 10 ⁴ .

The lower alkylene used in the present invention may be any one having 1 to 6 carbon atoms, for example, straight chain or branched chain such as methylene, ethylene, propylene, butylene, tertiary butylene, pentylene and hexylene. Chain alkylene. Preferred is alkylene having 1 to 4 carbon atoms, and more preferred is 1 to 3 alkylene.

Further, the lower alkyl used in the present invention may be one having 1 to 6 carbon atoms, for example, straight chain such as methyl, ethyl, propyl, butyl, tertiary butyl, pentyl, hexyl or the like. Branched chain alkyl is mentioned. Preferable is alkyl having 1 to 4 carbon atoms, and more preferable is alkyl having 1 to 3 carbon atoms.

Note that n in the formula is R ₁ , R to be selected.
It is determined by the relationship between the _two types and the molecular weight specified in the present invention, and a suitable integer can be appropriately selected within a range satisfying the above molecular weight range.

Examples of such polyoxyalkylene derivatives include polyoxyethylene, polyoxypropylene, polyoxyethylene polyoxypropylene glycol, polyoxyethylene alkyl ether, polyoxypropylene alkyl ether, polyoxyethylene polyoxypropylene alkyl ether. Etc.
Among them, polyoxyethylene, polyoxypropylene, and polyoxyethylene polyoxypropylene glycol have a more excellent action.

Next, a method for producing an electrogalvanized steel sheet using the above polyoxyalkylene derivative will be described. First, the concentration of the polyoxyalkylene derivative added to the galvanizing bath must be 1 to 500 ppm. If the concentration in the bath is less than 1 ppm,
Since the effect of miniaturizing the zinc plating crystal and randomizing the crystal orientation is poor, it is not possible to effectively exert the effect of preventing the occurrence of microscopic nonuniformity of the electrogalvanized surface, and it decomposes and evaporates in a short time in the zinc plating bath. As a result, the concentration becomes almost 0, and it is difficult to maintain the effect. On the other hand, when the concentration in the bath exceeds 500 ppm, not only the effect of preventing microscopic non-uniformity on the plating surface is saturated, but also uneven plating appearance such as a new flow pattern accompanying the flow of the plating bath on the plating surface and plating discoloration It is not preferable because the deterioration of glossiness easily occurs due to. The derivative used in the present invention is
Since it decomposes and disappears in the bath over time, the lower limit of 10 ppm or more and the upper limit of 300 ppm or less are preferable in consideration of the action duration and the like.

Examples of the plating bath to which these organic compounds are added include sulfuric acid baths, chloride baths, and various organic acid baths. When an insoluble anode such as an iridium oxide electrode or various Pb alloy electrodes is used. Considering the operational stability during production, the productivity, the production cost, etc. in the continuous line, it is preferable to use the sulfuric acid plating bath.

The composition of the acidic zinc plating bath is not particularly limited. For example, in the case of a sulfuric acid bath, the zinc ion concentration is ZnS.
Be O ₄ · 7H ₂ O converted at 50~600g / L is recommended, more preferably 150~500g / L. When it is less than 50 g / L, the plating current efficiency is lowered, while when it is more than 600 g / L, the zinc compound is precipitated to cause a surface defect such as a flaw on the plating surface,
There is a risk of depositing on the piping of the plating bath circulation system, resulting in clogging of the piping. Further, if the concentration is excessively increased, the loss due to dragout of the plating bath also increases, leading to an increase in chemical costs, which is not preferable.

In order to reduce the power consumption, it is recommended to add a conductivity aid to the plating bath to increase the conductivity of the zinc plating bath. The type and concentration of the conductivity aid is not limited at all, and sodium sulfate, aluminum sulfate, magnesium sulfate, ammonium sulfate,
It is possible to use a commonly used conductivity aid such as potassium chloride or sodium chloride in a desired concentration.

Further, the pH of the plating bath does not affect the operation of the present invention at all, but in the electrogalvanizing process which is industrially produced at a high current density, if the pH is too low, plating is performed. Causes a decrease in current efficiency,
On the other hand, if the pH is too high, the plating appearance phenomenon is likely to occur due to the plating burn phenomenon, so that the pH is 0.5 to 2.0.
It is preferable that More preferably 1.0 to 1.5
It is.

The flow velocity of the plating bath is not particularly limited, but if the flow velocity is low, the plating appearance may be deteriorated due to the phenomenon of plating burn when plating at a high current density, and the flow rate is 0.5 m.
It is desirable to manage at / sec or more. As for the plating current density, it is preferable that the plating current density is as large as possible in consideration of industrial productivity, but if it is too large, the plating appearance may be deteriorated due to a plating burn phenomenon. Therefore, if productivity and the like are taken into consideration, 50 to 300 A / It is recommended that the range is dm ² .

The galvanized steel obtained by the method of the present invention
The amount of plating on the plate is over 10 to 100 g / m^Two To do
And are required. 10g / m^Two Below, the electric zinc plated
It is inferior in corrosion resistance, which is the basic property required for steel sheets. Corrosion resistance
A plated steel sheet that does not have excellent properties is superior to other characteristics.
Even if it is used, its utility value is extremely low at the actual usage level.
Therefore, even in the present invention, the above lower limit
Those below the value are harmful to achieving the purpose of the present invention.
However, from the viewpoint of corrosion resistance, this lower limit
Was defined. Particularly in the present invention,
And form a single zinc-plated layer instead of a two-layer structure
By trying to obtain the desired characteristics,
Therefore, it is necessary to set this lower limit value. Better
15g / m to obtain corrosion resistance^Two It is preferable to be above
And more preferably 20 g / m ^Two That is all. one
100g / m^Two Corrosion resistance even when attached excessively over
And the appearance improvement effect is saturated, which is economically wasteful.
You. Preferably 60 g / m^Two Or less, and more preferably
Is 40 g / m^Two It is the following. Specifically, the product required
Considering various performance such as corrosion resistance and uniformity of appearance and manufacturing cost
It is set appropriately while considering.

As in the present invention, polyoxyalkylene
By adding the derivative to the plating bath, the surface appearance can be made uniform.
A method of manufacturing electrogalvanized steel sheets with excellent integrity was proposed.
(Japanese Patent Laid-Open No. 7-278880). This way
Suppresses hydrogen generation reaction on the surface of steel sheet
After applying the lower plating layer that has adsorbed the substance
The desired galvanized layer is applied on the
The plated steel sheet has a single-layer structure in that it has a two-layer structure.
This is different from the steel sheet of the present invention. Further, in the same publication, the above hydrogen
The current effect can be improved by adding a reaction suppressor to the plating bath.
The lower layer plating is intended to prevent the rate from decreasing.
The basis weight of the wood layer is 1 g / m^Two 10 g / m or more ^Two Defined below
In addition, in order to obtain an excellent appearance improving effect,
And the relative flow velocity is strictly controlled. However,
The authors confirmed by experiments that, unexpectedly, the prescribed
Add a concentration of polyoxyalkylene derivative to the plating bath
However, no decrease in current efficiency was observed.
By using a single layer structure instead of a complicated two layer structure
It has been found that excellent uniform plating appearance can be obtained.
Was. However, in the present invention, the basic characteristics required for plated steel sheets are
The coating weight of the plating layer is 1 to provide corrosion resistance
> 0 to 100 g / m^Two And against this,
In the above publication, the polyoxyalkylene derivative is adsorbed.
The coating weight of the lower plating layer is 1 to 10 g / m^Two In that
Both are further different. Thus, the present invention and the above publication
Is derived from polyoxyalkylene as an additive in the plating bath
Although it agrees with the point that the body is used,
It can be seen that there are significant differences. Furthermore, the same publication
That was not recognized at all, that is, polyoxyal
The xylene derivative is electrochemically easily degradable, so
When it finishes, it decomposes and does not remain in the plating solution.
Wastewater treatment is also easy) and for the anode surface
Since it is chemically inert, it does not cause a reduction in electrode life.
We found new knowledge such as
Before adding the water-soluble organic compound to the plating bath
According to the present invention, all the inconveniences described above can be eliminated.
Is extremely useful.

In continuously producing electrogalvanized steel sheet by adding the water-soluble organic additive of the present invention represented by the above polyoxyalkylene derivative to the plating bath, the organic additive is easily decomposed electrochemically. Because of its nature, it is necessary to properly control the concentration in the bath. Specifically, when microscopic non-uniformity of the zinc plating surface occurs or is likely to occur, immediately add a predetermined amount of a predetermined organic compound to the zinc plating bath and control the concentration of the organic compound in the bath. By doing so, it is possible to prevent appearance defects due to microscopic unevenness of the plating appearance. After that, when returning to a steel plate coil lot with good surface properties again, the addition of an organic compound becomes unnecessary, so the organic compound remaining in the plating bath at that time spontaneously decomposes and evaporates, and It is released outside the bath and waits for it to disappear from the bath.

As described above, the water-soluble organic additive of the present invention is not always allowed to be present in the galvanizing bath, but is added to the bath only when or when it is necessary.
The supply to the plating bath and the control of the concentration in the bath are stopped at the stage when they are no longer needed, and thereafter, they are spontaneously eliminated from the plating bath over time, thereby raising the object of the present invention. It was possible to solve all the problems such as the adverse effect on the insoluble anode due to the addition of the organic compound, the complicated wastewater treatment, and the accompanying increase in manufacturing cost.

The rate of decomposition and evaporation of the water-soluble organic additive of the present invention in the plating bath varies depending on the molecular weight of the organic compound used and the type of functional group, and the temperature and flow rate of the acidic zinc plating bath, It naturally depends on the stirring condition, the type and concentration of trace impurities in the bath, the presence or absence of an oxidizer, and the like. In the present invention, the decomposition evaporation rate is not particularly specified, so that the concentration control in the bath and the replenishment timing are appropriately changed according to the decomposition evaporation rate so that the action of the present invention can be effectively exhibited. Just go.

Specifically, for example, in the case of using one having a relatively slow decomposition and evaporation rate in the plating bath, once the plating bath is replenished to a predetermined concentration, the concentration becomes substantially zero. It takes half a day to several days, and there is no need to supplement the organic compound in the process.

On the other hand, when a material having a very high decomposition evaporation rate is used, its concentration becomes substantially zero within 1 to several hours after addition to the plating bath, so that the surface texture is microscopically determined. If non-uniform cold-rolled steel sheet coils are continuously threaded for a long period of time, or if it is expected that they will be threaded, it is necessary to estimate the time required to complete the threading in advance. Accordingly, additional supply may be appropriately made while analyzing the residual concentration in the plating bath.

At the actual operation level, the life of the water-soluble organic additive in the plating bath is preferably 1 hour to several days, more preferably, considering the ease of controlling the concentration in the bath. 1 to 12 hours.

Although the production conditions in the present invention have been described above, in actual use, the decomposition evaporation rate of the additive in the plating bath, which is determined by the type of the water-soluble organic additive to be used, the plating conditions, etc. After taking into consideration, it is desirable to appropriately adjust the initial addition amount, the bath concentration range, the presence or absence of additional replenishment, and the like.

Further, in the present invention, for the purpose of improving the performance such as corrosion resistance, lubricity, fingerprint resistance, and scratch resistance at the actual operation level, after the above-mentioned electrogalvanization, chromate treatment is performed to perform chromate treatment. To form a film,
Alternatively, it is desirable to further form a thin film clear film mainly composed of an organic resin or an inorganic resin on the chromate film.

The chromate film formed on the galvanized layer may be a so-called reactive chromate film, a coating chromate film, an electrolytic chromate film, or a combination thereof. May be. Specifically, a chromate film containing a Cr compound as a main component is formed, but if necessary, various oxides such as silica are used for the purpose of improving performance such as corrosion resistance, scratch resistance, and blackening resistance. Or an organic silane compound may be contained, or it is also recommended to further contain various reaction accelerators such as phosphates, nitrates, fluorides and silicon fluorides. When performing the chromate treatment, it is preferable to control the amount so that the amount of metal Cr deposited is 5 to 200 mg / m ² .

Further, when a clear film mainly containing an organic resin or an inorganic resin is applied after the chromate treatment, these compounds are added in an amount of 0.3-2.
It is preferable to control so as to be 0 g / m ² . Here, when the film is mainly composed of an organic resin, an epoxy resin, a polyester resin, a polyurethane resin,
A resin mainly containing an organic resin component such as an ethylene copolymer resin containing an ethylenically unsaturated carboxylic acid as a polymerization component, a polyvinyl resin, a polyamide resin, or a fluorine resin is preferable. Further, if necessary, various oxide particles such as silica and various phosphates for the purpose of improving performance such as corrosion resistance, lubricity, scratch resistance, workability, weldability, electrodeposition coating property, and coating adhesion. Inorganic pigments, wax particles, organic silane compounds, naphthenates and the like may be contained.

On the other hand, when the film is mainly composed of an inorganic resin, it is preferably composed mainly of a silicate such as sodium silicate, potassium silicate or lithium silicate.
Further, various oxide particles such as colloidal silica or various oxide particles may be used as necessary for the purpose of improving performance such as film-forming property, corrosion resistance, lubricity, scratch resistance, processability, weldability, electrodeposition coating property, and coating adhesion. Inorganic pigments such as phosphates, wax particles, and organic silane compounds may be contained.

Further, in the present invention, it is also effective to perform alkaline degreasing, alkaline electrolytic degreasing and acid treatment on the base steel sheet before the electrogalvanizing treatment for the purpose of cleaning and activating the surface of the base steel sheet.

Hereinafter, the present invention will be described in more detail with reference to examples. However, the present invention is not limited to the following examples, and is appropriately modified within a range compatible with the gist of the above and the following. It is, of course, possible to add and carry out, and all of them are included in the technical scope of the present invention.

[0082]

【Example】

Example 1 A cold-rolled steel plate to be a plating original plate was produced as follows.
First, an Al-killed hot-rolled steel sheet was manufactured by intentionally making the rough descaling mill conditions in the hot rolling process nonuniform by using a steel slab that was sufficiently held in a soaking furnace and then subjected to high temperature extraction at 1250 ° C. .

Next, using the hot rolled steel sheet, an Al-killed cold rolled steel strip coil (0.8 ^t x 1250 ^w mm x L) obtained through a hydrochloric acid pickling-tandem cold rolling-annealing process was produced. Then, it was tested as a plating original plate.

With this cold-rolled steel sheet as it is, it is not possible to recognize the occurrence of microscopic non-uniformity on the surface of the cold-rolled steel sheet as long as it is visually observed, but the cold-rolled steel sheet cannot be observed by AES analysis or EPMA surface analysis. When the surface of the rolled steel sheet is investigated in detail, the oxide film layer formed on the surface clearly has microscopic nonuniformity, and inevitable impurity elements or additive elements in the steel such as Ni, Si, and Mn. Was confirmed to be locally concentrated on the surface.

After producing several coils of cold-rolled steel sheet coils in which microscopically non-uniform portions were intentionally provided on such a surface, these coils were used together with cold-rolled steel sheet coils having good surface properties. An electrogalvanized steel sheet was continuously manufactured on an electroplating line in the same manner as described above.

[Procedure for producing galvanized steel sheet] (1) Alkaline aqueous solution immersion degreasing: 3% by weight caustic soda aqueous solution, 60 ° C, 2 seconds (2) Alkaline aqueous solution electrolytic degreasing: 3% by weight caustic soda aqueous solution, 60 ° C, 2 seconds , 20 ± 10 A / dm ² (3) Washing with water (4) Pickling: 5 ± 2 wt% sulfuric acid aqueous solution, 40 ° C, 2 seconds (5) Washing with water (6) Electrogalvanizing: As below (7) Washing with water (below (8) to (10) post-treatments are carried out on some of them.) (8) Chromate treatment: Reactive chromate treatment, Cr equivalent adhesion amount 20 ± 5 mg / m ² (9) Washing with water (10) Thin film organic Resin coating treatment: Cross-linked polyethylene resin (colloidal silica and wax particles added) Solid content amount 0.6 ± 0.2 g / m ² (11) Dry

[Electrogalvanizing Conditions] Plating Cell: Horizontal Horizontal Plating Cell Plating Bath Composition: ZnSO ₄ 7H ₂ O 350 ± 50 g / L Na ₂ SO ₄ 80 ± 20 g / L H ₂ SO ₄ 30 ± 5 g / L ・ Current density: 100 A / dm ²・ Plating bath temperature: 60 ° C ・ Plating bath flow rate: 1.5 m / sec ・ Electrode (anode): Iridium oxide electrode ・ Amount of plating: 20 g / m ² (per surface) ・ Plating Addition of polyoxyalkylene derivative to the bath Additive: Polyoxyethylene polyoxypropylene glycol Addition concentration: 50 ppm as initial addition concentration

The surface of the obtained electrogalvanized steel sheet (including the chromate-treated material and the thin-film organic film-treated material) was continuously visually observed in the outgoing-side inspection section of the electrogalvanizing line to obtain a microscopic appearance. The frequency of occurrence of non-uniform parts was evaluated according to the following criteria.・ Generation of non-uniform microscopic appearance (degree of microscopic unevenness of surface appearance) ○: No microscopic non-uniformity of appearance is shown, showing a good appearance △: 〃 Occurs a little and stands out × : 〃 Significant occurrence, very noticeable

The results are shown in FIG. In the figure, (1),
(5) to (7), (8) and (11) are coils with normal surface properties, and the plating surface appearance is uniform even if polyoxyethylene polyoxypropylene glycol is not added to the plating bath. Is. On the other hand, (2) to (4),
(9) and (10) are coils with microscopic non-uniformity on the surface, so if plating is performed without adding the above-mentioned additional substances in the plating bath, non-uniform appearance will occur. Is.

As is apparent from FIG. 1, when a cold-rolled steel sheet coil having microscopically non-uniform portions on its surface is used as an original plate, by adding a polyoxyalkylene derivative to the plating bath, the electric Galvanized as it is [Coil No. (2)] or chromate treatment [Coil No. (3)]
A cold-rolled steel sheet coil with normal surface texture, with no occurrence of microscopically non-uniformity in the plating appearance even after post-plating treatment of thin film organic coating [Coil No. (4)] It can be seen that when used, the same excellent plating appearance as that of [Coil No. (1) and (5) to (7)] can be obtained. The concentration of the polyoxyalkylene derivative in the plating bath decreased with time after the addition, and the concentration became almost 0 about 2 hours after the addition.

On the other hand, when the polyoxyalkylene derivative was not added to the plating bath, the galvanized steel sheet using the cold-rolled steel sheet coil having a microscopically nonuniform portion on the surface had a plating appearance. , Plating appearance failure occurred [Coil No. (9)].

Incidentally, in the case where the post-plating treatment is chromate treatment and thin film organic coating treatment [Coil No. (10)], only zinc plating is performed [Coil No.
(9)], the defective plating appearance tended to be more noticeable.

Example 2 In the electrogalvanized steel sheet produced in the same manner as in Example 1, the amount of polyoxyethylene polyoxypropylene glycol added to the plating bath and the zinc coating deposition amount were changed variously as shown in Table 1. In each case, the occurrence of microscopic nonuniformity and the corrosion resistance were evaluated.

Of these, the occurrence of microscopically nonuniform portions was evaluated in the same manner as in Example 1, and the corrosion resistance was evaluated as follows.
A salt spray test based on JIS Z2371 was carried out, and the red rust resistance was evaluated according to the following criteria. ⊚: Red rust occurred in the test time of 36 hours or more ○: 〃 24 hours or more and less than 36 hours 〃 △: 〃 12 hours or more and less than 24 hours 〃 ×: 〃 less than 12 hours 〃 These results are shown in Table 1.

[0095]

[Table 1]

The following can be considered from the results of the table. Nos. A to F, H to J, and O to S are all examples satisfying the requirements specified in the present invention, and it is understood that no microscopic nonuniform portion is generated and the corrosion resistance is excellent. .
On the other hand, those that do not satisfy the requirements of the present invention,
The following problems are involved. No. G is an example in which the addition amount of the additive is large, but for this reason, a plating appearance defect due to plating burn (not due to the plated steel sheet) occurred. No. K and L are examples in which the amount of the additive added was small, but the plating appearance deteriorated. No. M and N are examples in which the amount of zinc plating adhered is small, but the corrosion resistance deteriorates.

[0097]

EFFECTS OF THE INVENTION The present invention is constituted as described above, and in producing an electrogalvanized steel sheet, it is easily decomposable electrochemically and is water-soluble which is chemically inert to the surface of the anode. By using a water-soluble organic additive composed of an organic polymer compound that gives a uniform plating appearance, it is possible to reliably suppress the occurrence of uneven plating appearance areas and obtain an electrogalvanized steel sheet having a uniform plating appearance. In addition, the life of the electrode could be extended and the wastewater could be easily treated.

[Brief description of drawings]

FIG. 1 is an explanatory diagram showing a result of an example.

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Masatoshi Iwai 1 Kanazawa-cho, Kakogawa-shi, Hyogo Kobe Steel, Ltd. Inside the Kakogawa Works

Claims (6)

[Claims] 1. A water-soluble organic polymer compound which is electrochemically easily decomposable and chemically inert to the surface of the anode, and which gives a uniform plating appearance. Water-soluble organic additive in electrogalvanizing bath. 2. The water-soluble organic additive according to claim 1, wherein the water-soluble organic polymer compound is a polyoxyalkylene derivative represented by the following general formula and having a molecular weight of 10 ³ to 10 ⁵ . R ₂ —O— (R ₁ —O) n—R ₂ provided that R ₁ : lower alkylene group R ₂ : H or lower alkyl group, respectively. 3. When forming a galvanized layer on the surface of a steel sheet by an electroplating method, electrogalvanization is performed in a galvanizing bath containing 1 to 500 ppm of the polyoxyalkylene derivative according to claim 2, and the basis weight is: 10 g / m
^A method for producing an electrogalvanized steel sheet having excellent plating appearance uniformity, which comprises forming a galvanized layer of more than ^{2 to} 100 g / m ² . 4. The manufacturing method according to claim 3, wherein a sulfuric acid-based zinc plating bath is used. 5. Production of a surface-treated electrogalvanized steel sheet excellent in uniformity of plating appearance, which comprises subjecting the electrogalvanized steel sheet obtained by the method according to claim 3 or 4 to chromate treatment. Method. 6. A surface-treated electrogalvanized steel sheet excellent in uniformity of plating appearance, characterized by forming a clear film on the surface-treated electrogalvanized steel sheet obtained by the method according to claim 5. Production method.