JP3183630B2 - Electrogalvanized steel sheet - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrogalvanized steel sheet having a bright surface tone, a beautiful surface appearance with a high gloss, and an excellent appearance without unevenness in the color tone; A galvanizing bath additive; and a method for producing the steel sheet. In detail, the electrogalvanized steel sheet of the present invention is a steel sheet having high brightness and glossiness, having a uniform color tone of the plating appearance, and further having an excellent appearance without glittering luster, such as home appliances and It is extremely useful in that it can be used for OA products and the like without painting.

[0002]

2. Description of the Related Art Electrogalvanized steel sheets exhibit excellent corrosion resistance as a result of the galvanized film having a sacrificial anticorrosion effect on the base steel sheet. Widely used as materials.

[0003] Conventionally, electrogalvanized steel sheets have been used mainly as a base material for coatings, taking advantage of their excellent corrosion resistance. Therefore, in the final product state, the surface of the galvanized steel sheet is concealed by a topcoat paint, resulting in the appearance of the plated surface. Was rarely a problem. However, in recent years, users have requested that the finishing coating process be omitted. There is a sharp increase in the tendency to use the product as it is naked (unpainted). In such a case, the surface appearance of the galvanized layer appears as the appearance of the final product as it is, so that it is extremely important to control the surface appearance of the galvanized itself. In particular, regarding the color tone of the plating surface, not only is there no unevenness in the color appearance of the plating due to the difference in the partial color tone of the plating surface, but also the color tone of the plating surface is bright (that is, has a high brightness) and the glossiness is high. Recently, highly plated steel sheets have been strongly desired.

[0004] Among them, it is considered that unevenness in the appearance of a part of the plating surface is caused by an uneven state of the surface of the original plate (steel plate). The thickness of the oxide film layer on the surface of the steel sheet is not uniform, or Ni, S contained in steel
When elements such as i, Mn, and C are locally segregated and concentrated on the surface of the steel sheet, the growth mechanism of zinc plating changes, and regions having different plating crystal morphologies and crystal orientations are formed. As a result, a minute change occurs in the amount of visible light reflected on the plating surface, and this is recognized as unevenness in color appearance of the plating. Such uneven color tone on the plating surface
Small and width and length: about several mm, large
The width: about several hundred mm, the length: about several tens of meters, and its generation position, form, and number of generation are completely unspecified.

[0005] In addition to the uneven color appearance of the plating due to the unevenness of the surface properties of the base steel sheet, when the ferrite crystal grain size on the steel sheet surface is large, the galvanized crystal formed thereon becomes coarse. This may cause a problem such as a contract glittering phenomenon in which the appearance after plating looks glittering.

[0006] As described above, it is considered that the unevenness of the color appearance and the glittering of the plating are caused by microscopic change of the electrogalvanized crystal due to the state of the surface of the original sheet. However, the surface properties of the original sheet are completely uniform. Alternatively, arbitrarily controlling is extremely difficult on an industrial scale. Under such circumstances, many methods for improving the appearance color tone of the surface of the electrogalvanized steel sheet have been disclosed.

[0007] Among them, Japanese Patent Application Laid-Open No. 7-7679 discloses a method for improving the uneven color appearance of the plating caused by the original plate.
No. 2, JP-A-7-76793, JP-A-7-76794
JP-A-7-238387, JP-A-7-31687
No. 8, JP-A-7-278880, and the like.

Each of these publications is composed of a plating layer having a two-layer structure. The plating conditions and types of the lower layer are variously changed to hide the minute non-uniformity on the surface of the original plate. The electrogalvanized surface applied to the upper layer is not affected by the surface of the original plate. For example, Japanese Patent Application Laid-Open No. 7-76792 discloses a method for uniformly forming a zinc plating crystal by applying the same zinc plating layer to the lower layer as the upper layer and controlling the plating conditions of the zinc plating layer. Japanese Patent Application Laid-Open No. Hei 7-3167878 discloses a method for forming a lower zinc plating layer using a galvanizing bath containing a method of forming a lower zinc plating layer at a high current density. . Japanese Patent Application Laid-Open No. 7-76793 discloses a method of applying a Ni plating layer as a method of applying a lower plating layer using a plating type which is less likely to be affected by the surface of a plating original sheet, and Japanese Patent Application Laid-Open No. 7-238387 discloses a Ni-P JP-A-7-27888 discloses a method of applying an amorphous lower plating layer such as Co-P or the like.
No. 0 contains polyoxyalkylene derivatives and Pb, Sn, S
There is disclosed a method of adding a substance that suppresses a hydrogen generation reaction such as b into a plating bath or applying these substances to the surface of a plating original sheet in advance.

In any of the above methods, the surface of the original plate is concealed by some method so that the surface of the original zinc plate is not affected by the unevenness of the surface of the original plate. It is not a method of directly acting on the plating crystal itself. In addition, since the thickness of the lower plating layer formed by these methods is very thin, when the surface defect of the plating original plate is large, the above-described concealing action is hardly expected, and the uppermost layer surface is formed. The crystal morphology of the plating surface cannot be sufficiently controlled. Furthermore,
In these publications, there is no description about the brightness, and the effect of improving the brightness is not completely known.

As a method of improving the plating color tone other than the above, Japanese Patent Publication No. 3-31795 discloses a method of defining the ferrite crystal grain size (crystal grain size) on the surface of an original plate for plating. However, in all plating base sheets,
It is very difficult to control the entire surface within the preferred ferrite crystal grain size range specified in the above-mentioned gazette. This leads to a disadvantage that uneven color tone is generated. In addition, there is no description regarding the brightness improvement in this publication.

On the other hand, as a method for improving the brightness, Japanese Patent Publication No. 36559/1993 discloses a method of adding a nonionic polyacrylamide to a plating bath. This method has been made in view of the circumstances that "all conventional brighteners have no effect at high current density, and the permissible current density is further reduced by increasing the weight." Applies to use in Its composition is
A conventional brightener having a large amount of a compound having a cationic group which is easily adsorbed on the cathode is one in which a polymer (nonionic polyacrylamide) having a different effect is added to a plating bath. Even when electrogalvanizing is performed at a high current density of 450 A / dm ^2, the growth of coarse crystal grains is suppressed, and the plating is smooth without gloss and high in whiteness (same as lightness in the case of galvanized steel sheet). An object is to provide an electrogalvanized steel sheet having a surface. However, this method is intended to be used under a high current density, as its purpose, and has no effect under the usual plating conditions of less than 100 A / dm ² , and there is a problem in practicality. . Further, it is completely unknown whether or not the nonionic polyacrylamide used in the publication has an effect of improving unevenness in color appearance of plating.

[0012] In addition, as an electrogalvanized steel sheet having a high lightness and having no uneven plating appearance caused by a base plate, JP-A-8-41679 discloses a steel sheet provided with a Sn plating layer below a zinc plating layer. Is disclosed. However, according to the publication, between the plating base plate and the galvanized layer, Sn, which is a metal more noble than zinc or iron, is concentrated and present as a pure Sn layer. There is a problem that it deteriorates and the original performance of the plated steel sheet is impaired. Further, there is no description in the publication regarding the effect of improving glossiness.

As described above, although galvanized steel sheets having a bright plating surface tone and high glossiness, and electrogalvanized steel sheets having no unevenness in plating appearance color tone or glittering gloss have been particularly desired in recent years, these galvanized steel sheets have been demanded. At present, a plated steel sheet having all the required characteristics has not been developed yet.

[0014]

DISCLOSURE OF THE INVENTION The present invention has been made in view of the above circumstances, and its object is to provide a high brightness and glossiness and to reduce the surface condition of an original plating plate. It is an object of the present invention to provide an electrogalvanized steel sheet having an excellent appearance without causing unevenness in the color tone of the plating appearance, and further having an excellent appearance without glittering luster. Furthermore, an object of the present invention is to provide an electrogalvanizing bath additive for improving brightness and gloss, which can provide such a galvanized steel sheet; and to efficiently produce the electrogalvanized steel sheet using the additive. It is to provide a method that can be performed.

[0015]

Means for Solving the Problems The electrogalvanized steel sheet according to the present invention which can solve the above-mentioned problems is that the surface of the electrogalvanized steel sheet is obtained by a method according to JIS Z8722 (condition d, with an optical trap). Brightness: 70 or more, glossiness obtained by the method of JIS Z8741 (60-degree specular gloss method): 30 or more and having no uneven color tone, specifically, 30 mm on the surface of the electrogalvanized steel sheet When any two points are taken at intervals, the difference in brightness between the two points is within 5 and the difference in gloss is within 15 (the method of measuring brightness and gloss is the same as before). However, it has a gist. In the present invention, brightness and glossiness are measured using "SZS- # 90" manufactured by Nippon Denshoku Co., Ltd. Among the above electrogalvanized steel sheets, those having no glitter are very useful because they have an even better appearance, and such steel sheets are also included in the scope of the present invention.

Further, the electrogalvanizing bath additive for improving brightness and gloss according to the present invention, which can solve the above problems, includes a metal salt of naphthenic acid, an aniline derivative, a lower alkanoyl compound, and an organic peroxide. At least one selected from the group consisting of: Here, the metal salt of naphthenic acid is cobalt naphthenate, the aniline derivative is dimethylaniline, the lower alkanoyl compound is methyl ethyl ketone, and the organic peroxide is methyl ethyl ketone peroxide belonging to a condensation type peroxide of a carbonyl compound. This is a preferred embodiment of the present invention.

Further, the method for producing an electrogalvanized steel sheet according to the present invention, which can solve the above-mentioned problems, includes the steps of: preparing a metal salt of naphthenic acid, an aniline derivative, a lower alkanoyl compound, and an organic solvent in an electrogalvanizing bath; At least one member selected from the group consisting of oxides in a total amount of 1.0
It has a gist in the addition of 〜100 ppm. Here, those in which the metal salt of naphthenic acid is cobalt naphthenate, the aniline derivative is dimethylaniline, the lower alkanoyl compound is methyl ethyl ketone, and the organic peroxide is methyl ethyl ketone peroxide are preferred embodiments of the method of the present invention. .

[0018]

BEST MODE FOR CARRYING OUT THE INVENTION The inventors of the present invention have conducted intensive studies to provide an electrogalvanized steel sheet having both high brightness and glossiness and an excellent appearance without unevenness in plating appearance color tone and glitter. It has been found that the intended purpose can be achieved by adding at least one selected from the group consisting of a metal salt of naphthenic acid, an aniline derivative, a lower alkanoyl compound, and an organic peroxide to an electrogalvanizing bath. Was. That is, the electrogalvanizing bath additive for improving brightness and gloss of the present invention is at least one selected from the group consisting of a metal salt of naphthenic acid, an aniline derivative, a lower alkanoyl compound, and an organic peroxide. .

These compounds have not heretofore been known as brighteners, and have been found to have, for the first time, an effect of improving brightness and glossiness according to the present invention.

Here, the lightness and glossiness will be described.
There is no correlation between glossiness and lightness, such that increasing glossiness inevitably increases lightness. That is, incident light, reflected light, and absorbed light on the surface of the electrogalvanized steel sheet are represented by the following relationship: incident light = specular reflection light + diffuse reflection light + surface absorption light. Among these, an index representing “specular reflection light” is “glossiness”, and “brightness” is an index representing reflected light excluding regular reflection light, that is, “diffuse reflection light”. Therefore,
If the incident light is the same, increasing the gloss (that is, increasing the specular reflection) results in a relative decrease in diffuse reflection and a decrease in brightness. The conventional brightener is intended only to increase the specular reflection light, and the glossiness is certainly improved, but the brightness tends to decrease. On the other hand, the additive of the present invention has a glossiness such as "increase the specular reflection light to increase the glossiness, and at the same time increase the diffuse reflection light by reducing the surface absorption light, thereby increasing the brightness". This is different from the conventional brightener in that the effect of improving brightness is obtained at once.

Japanese Unexamined Patent Publication No. Hei 8-74089 is an example of an electrogalvanized steel sheet having excellent lightness (= white light). This publication is made in view of the finding that "it is effective to reduce the light absorption on the plating surface in order to increase the lightness".
By reducing the thickness to less than μm, light absorption is reduced as much as possible and lightness is improved. However, this publication mainly aims at improving the brightness, and with respect to the gloss, there is only a passive description that "a large decrease in the gloss results in a decrease in the appearance of the plating surface, which is not preferable". There is no idea of positively improving the glossiness as in the present invention. Moreover, there is no description about unevenness in plating appearance color tone. As described above, Japanese Patent Application Laid-Open No. 8-74089 mainly aims at improving the brightness, and does not aim at improving the glossiness in addition to the improvement of the brightness as in the present invention. Both are clearly distinguished from each other in that there is no description about the improvement in uneven color tone. Moreover, according to the above-mentioned publication, glycine and aspartic acid are added in a large amount of 1 to 20 g / L in obtaining such a steel sheet. This may adversely affect other properties such as properties (this point will be confirmed in Examples described later). On the other hand, the electrogalvanized steel sheet of the present invention is obtained by adding the above-described plating bath additive to a plating bath. As described above, the addition amount is 1.0 to
Since the amount is 100 ppm, which is a very small amount as compared with the case of the above-mentioned publication, there is no possibility of adversely affecting plating adhesion and the like, so that it has a remarkable effect as compared with the above-mentioned publication.

As described above, the plating bath additive of the present invention is very useful in that it not only has an excellent improving effect on both lightness and glossiness, but also can eliminate uneven color tone and glitter. . In addition, Japanese Patent Application Laid-Open
The same thing as described in comparison with -74089 can be said in comparison with a conventional brightener. That is,
With the conventional brightener, a sufficient gloss improvement effect could not be obtained unless several g to several tens g / L were added to the plating bath, whereas when the plating bath additive of the present invention was used, , At least one of these additives in a total amount of only 1.0 to 1
By adding only 00 ppm (a content of several hundreds to several thousandths is better than in the case of adding a brightener), a gloss effect equal to or higher than that of a conventional brightener can be obtained, and the brightness It is very surprising that the improvement effect was also obtained. Furthermore, the fact that the addition amount of the plating bath additive can be extremely reduced in this manner is also very useful in that other characteristics such as plating adhesion are not adversely affected. That is, since a conventional additive such as a brightener is added in a large amount to the plating bath, it is often co-deposited in the plating layer, and the surface properties are often significantly deteriorated. As a result, not only the expected effect is not obtained, but also the properties such as plating adhesion are adversely affected. On the other hand, the plating bath additive of the present invention can obtain the desired effect even if the addition amount is extremely small, and does not cause the above-mentioned adverse effects such as the reduction in plating adhesion.

The plating bath additives used in the present invention include, as metal salts of naphthenic acid, cobalt naphthenate, lead naphthenate, zinc naphthenate, iron naphthenate, manganese naphthenate (preferably cobalt naphthenate); aniline Derivatives include aniline, dimethylaniline, pentamethylaniline and the like (preferably dimethylaniline); lower alkanoyl compounds have 1 to 1 carbon atoms
6 alkanoyl compounds, for example, methyl ethyl ketone, acetone, diethyl ketone, methyl vinyl ketone and the like (preferably methyl ethyl ketone); and organic peroxides include, for example, condensed peroxides of carbonyl compounds (eg, methyl ethyl ketone peroxide, acetylacetone peroxide) , Methyl isobutyl ketone peroxide, preferably methyl ethyl ketone peroxide), acyl peroxide (eg, diacetyl peroxide,
Dipropionyl peroxide, phthaloyl peroxide, etc.),
And dialkyl peroxide (for example, dibutyl peroxide and the like). These compounds may be used alone in the plating bath, or two or more of them may be used in combination.

Although the mechanism of action of the compound is not known in detail, the compound added to the plating bath is adsorbed to the zinc growth point during the growth of the zinc plating crystal, and This is considered to suppress continuous coarse growth. Such an effect of suppressing the coarse growth of zinc-plated crystals occurs uniformly in all places, eliminating the "non-uniform region of the plating crystal morphology" which is the cause of uneven color appearance of the plating and miniaturizing the plating crystals. Therefore, it is considered that the effect of improving brightness and glossiness can be achieved together.

The electrogalvanized steel sheet obtained by adding the above-described plating bath additive of the present invention to a plating bath has a surface defined by JIS Z87.
Brightness obtained by method 22 (condition d, with light trap): 70 or more (preferably 75 or more, more preferably 8 or more)
0 or more), JIS Z8741 (60-degree specular gloss method)
Satisfies the glossiness of 30 or more (preferably 40 or more, more preferably 50 or more) and has no color tone unevenness, specifically, the surface of the electrogalvanized steel sheet at an arbitrary interval of 30 mm. When two points are taken, the difference in brightness between the two points is within 5 and the difference in gloss is within 15 (the method of measuring brightness and gloss is the same as before), and the surface appearance It is very good.

As described above, in the present invention, the use of the above-described plating bath additive of the present invention has succeeded for the first time in improving both the brightness and the glossiness of an electrogalvanized steel sheet. And the electrogalvanized steel sheet of the present invention, in addition to the improvement of the lightness and glossiness described above, does not have uneven color tone, and further satisfies the required characteristics such as no glittering luster. Requirements (ie,
It is a steel sheet that satisfies all of the following requirements: improved brightness, improved gloss, no uneven color tone, and no glitter.

As described above, the unevenness of the color tone (the area where the color is changed) is small and has a width and length of about several mm as described above, and is large and has a width of about several hundred mm and a length of several hundred. Some exist up to about 10 m. However, uneven color tone can be recognized by the naked eye only when the optical characteristics such as brightness and glossiness are rapidly changing at the boundary between the normal area and the uneven color tone area. Even if the optical characteristics of the portion change gradually and continuously, it is not recognized as uneven tone by the naked eye. From such a viewpoint, in the present invention, as a scale of “steel plate without uneven color tone”, “30 mm
When any two points are taken at intervals, the difference in brightness between the two points is within 5 (preferably within 3), and the difference in gloss is 15
Satisfies the condition (preferably within 5) "(the methods for measuring the brightness and gloss are the same as described above). It is also confirmed in Examples described later that the results of evaluating the uneven plating color tone on such a scale correspond to the results of evaluating the uneven plating color tone by visual observation. Here, the interval between the two points was set to 30 mm because the minimum measurement area of the color tone measuring device [Nippon Denshoku Co., Ltd. "SZS- $ 90"] for measuring these optical characteristics was 10 mm x 10 mm.
mm.

Next, a method for producing the electrogalvanized steel sheet of the present invention will be described. The production method of the present invention is a method for preparing an electrogalvanizing bath from the above-mentioned plating bath additives of the present invention (that is, a metal salt of naphthenic acid, an aniline derivative, a lower alkanoyl compound, and an organic peroxide). At least one) in a total amount of 1.0 to 100
ppm is added.

Here, the above-mentioned plating bath additives may be used alone or in combination of two or more.
In short, it is necessary to add 1.0 to 100 ppm in total. If the addition amount is less than 1.0 ppm, the effect of uniformly reducing the size of the plating crystals is poor, and the effect of reducing unevenness in the color appearance of the plating and the effect of improving the brightness and gloss are insufficient.
It is preferably at least 3 ppm, more preferably at least 5 ppm. On the other hand, if it exceeds 100 ppm, a phenomenon called plating burn occurs, and both lightness and glossiness decrease.
Preferably 80 ppm or less, more preferably 50 ppm
It is as follows.

As described above, according to the production method of the present invention, the amount of the above additive to be added to the plating bath is reduced to several hundredths to several thousandths as compared with the conventional brightener. Since it can be reduced, it is possible to obtain an excellent galvanized steel sheet that can improve the brightness and whiteness without causing any adverse effects such as a decrease in plating adhesion, and has no unevenness in the color tone and glitter of the plating appearance. Very useful in that it can be obtained.

In the production method of the present invention, the type and amount of the plating bath additive are specified, and other requirements are not particularly specified, but are preferable for the purpose of obtaining even more excellent characteristics. Plating conditions and plating compositions are described below.

First, the current density in the case of performing electrogalvanizing is preferably 20 A / dm ² or more. 20A
If it is less than / dm ² , coarse growth of zinc-plated crystals is likely to occur, and satisfactory plating appearance and the effect of improving brightness and gloss cannot be sufficiently obtained. The higher the current density is, the more useful it is because the growth nucleation amount of zinc plating increases.However, if the current density is too high, there is a delay in the rate of supplying zinc ions from the plating bath to the zinc deposition point. As a result, the plating appearance deteriorates due to plating burns. Therefore, it is preferable to adjust the current density within a range where plating burn does not occur,
It is recommended to adjust to the range of 30 to 200 A / dm ² .

The pH of the plating bath is 0.5 to 0.5 from the viewpoint of increasing the current efficiency and suppressing the plating burn phenomenon.
It is preferred to be in the range of 2.0. When the pH is in a strongly acidic region of less than 0.5, a large amount of hydrogen is generated and the loss of current efficiency is increased. On the other hand, when the pH exceeds 2.0, particularly when plating is performed at a high current density of 100 A / dm ² or more, the plating burn phenomenon easily occurs, and the plating appearance is impaired.

The composition of the plating bath is not particularly limited as long as it contains zinc ions as a main component. However, in order to ensure sufficient current efficiency, the ZnSO ₄ .7H ₂ O concentration is 5%.
0-600 g / L, more preferably 150-500 g / L
Adjustment to the range of L is recommended. When the concentration is low, the phenomenon of plating burn tends to occur when plating is performed at a high current density.On the other hand, when the concentration is too high, a zinc compound is precipitated, which may cause clogging of a pipe. This causes the steel sheet to be pressed by the precipitates.

In the plating bath, Na ₂ SO ₄ , (NH ₄ ) ₂ is used in order to increase conductivity and reduce power consumption.
A conductive auxiliary agent such as SO ₄ , KCl, or NaCl may be added, or a metal ion such as Ni, Co, Fe, or Cr may be added for the purpose of improving blackening resistance and corrosion resistance of the plating layer. . Regarding a preferable relative flow rate of the plating solution, if the rate is too low, the supply of zinc ions is delayed particularly at a high current density, which may cause deterioration in appearance due to plating burn.
It is preferable to maintain the above. Here, the relative flow velocity means a difference between the liquid flow velocity and the passing speed in consideration of the flow direction of the liquid and the passing direction of the steel plate as the plating original plate.

The amount of galvanized coating applied by electrogalvanizing is not limited at all, and may be appropriately determined in consideration of the degree of corrosion resistance required according to the use. However, if the coating weight is less than 1 g / m ² , the original corrosion resistance of zinc plating cannot be sufficiently exhibited, while if the coating weight is excessively increased beyond 100 g / m ² , only the power cost increases. Is useless.

As described above, the electrogalvanized steel sheet of the present invention is intended to be used in a bare state without the finish coating. However, in actual use, corrosion resistance, scratch resistance, For the purpose of further improving various performances such as fingerprint resistance and workability, it is also effective to apply one or more chemical conversion treatments to the surface of the galvanized layer. Examples of the chemical conversion treatment layer include a chromate film treatment layer, a phosphate film treatment layer, and a clear film treatment layer.

Of these, the chromate film treatment includes a reaction type chromate film treatment, a coating type chromate treatment, an electrolytic chromate treatment and the like. Corrosion resistance, scratch resistance,
In order to improve properties such as blackening resistance, various oxides such as silica and organic silane compounds, and further, phosphoric acid,
It is recommended to perform a chromate treatment containing various reaction accelerators such as nitric acid, fluoride and silicon fluoride.

Further, regarding the thin film clear film treatment applied on the chromate film, when the film is mainly composed of an organic resin, an epoxy resin, a polyester resin,
Polyurethane resin, ethylene copolymer resin containing ethylenically unsaturated carboxylic acid as a polymerization component, polyvinyl resin, polyamide resin, fluorine resin and other organic resin components as main components, or more corrosion resistance and lubricity ,
In order to improve properties such as scratch resistance, workability, weldability, electrodeposition coating properties, coating film adhesion, etc., as necessary, various oxide particles such as silica, inorganic pigments such as various phosphates, and wax particles. And a treatment liquid containing an organic silane compound, a naphthenate or the like.

When the coating is mainly composed of an inorganic substance, it is mainly composed of a silicate such as sodium silicate, potassium silicate, lithium silicate, or the like, or has a film-forming property, corrosion resistance and lubrication. Inorganic pigments such as various oxide particles such as colloidal silica and various phosphates as necessary to improve properties such as resistance, scratch resistance, workability, weldability, electrodeposition coating properties, and coating film adhesion , A treatment liquid containing wax particles, an organic silane compound and the like can be applied.

The amount of the chemical conversion film deposited is not particularly limited, but is preferably controlled in the range of 5 to 300 mg / m ^{2 in} consideration of the effects such as improvement of corrosion resistance and economy. For the same reason, it is recommended that the preferable thickness of the organic film layer and the inorganic film layer be 0.1 to 20 μm.

Incidentally, the brightness and brightness difference defined in the present invention,
The values of gloss and gloss difference are not limited to the untreated electro-galvanized steel sheet, but also to the above-mentioned chromate film-treated steel sheet, phosphate film-treated steel sheet, and furthermore, the thin film clear film treatment is applied on the chromate film. It can also be applied effectively to steel plates that have been used.

Hereinafter, the present invention will be described in more detail with reference to Examples. However, the following Examples do not limit the present invention, and all changes and implementations without departing from the spirit of the present invention will be described. Within the technical scope of

[0044]

[Embodiment] In the following method, Ni, Ni
A cold-rolled steel sheet having a non-uniformly concentrated portion of an impurity element such as Si or Mn or a non-uniformly formed portion of an oxide film was intentionally produced.

First, an Al-killed hot-rolled steel sheet was manufactured using a steel slab extracted at a high temperature of 1250 ° C. from a soaking furnace while intentionally making the rough descaling conditions in the hot rolling process nonuniform. Next, using the hot-rolled steel sheet, an Al-killed cold-rolled steel sheet obtained through a process of hydrochloric acid pickling → cold rolling → box annealing was used as a plating base sheet. As the box annealing method, a tight annealing method in which steel sheets were brought into close contact with each other and annealed was used,
The permeation amount of the reducing atmosphere gas was changed by intentionally changing the degree of adhesion (adhesion pressure) between the steel sheets in a part of the surface of the steel sheet.

In the cold-rolled steel sheet thus obtained, no irregularities are found on the surface of the cold-rolled steel sheet as it is visually observed, but the cold-rolled steel sheet is analyzed by AES analysis or EPMA surface analysis. When the surface of the rolled steel sheet is observed in detail, the oxide film layer formed on the surface clearly has uneven portions, and unavoidable impurities or additive elements in the steel such as Ni, Si, and Mn are partially removed. It was confirmed that the surface was thickened.

Using the cold-rolled steel sheet, electrogalvanizing was performed in the following procedure. In addition, in plating bath, Tables 2-4
Were added. <Procedure of electrogalvanizing> Alkaline immersion degreasing: 3% by weight sodium orthosilicate, 60 ° C. × 5 seconds Alkaline electrolytic degreasing: 3% by weight sodium orthosilicate, 60 ° C. × 5 seconds, 50 A / dm ² , PR electrolytic method Rinse acid wash: 5 wt% aqueous solution of sulfuric acid, 40 ° C. × 3 seconds washing galvanized: as washed with water and dried below <galvanized conditions> plating bath _{composition: ZnSO 4 · 7H 2 O 300~400g} / L Na 2 SO 4 50 _{~100g / L H 2 SO 4 10~} 40g / L · current density: 10~150A / dm ² · plating bath temperature: 60 ° C.-plating solution flow rate: 0.5 to 2 m / sec electrode (anode): Pb alloy Electrode ・ Amount of plating: 10-80 g / m ² (per side)

With respect to the electrogalvanized steel sheet thus obtained, the lightness of the galvanized surface was measured by the method specified in JIS Z8722 (condition d, with a light trap), and the glossiness was specified in JIS Z8741. It was measured by the 60-degree specular gloss method and evaluated according to the following criteria. <Brightness> ：: 80 or more ○: 70 or more and less than 80 △: 60 or more and less than 70 ×: less than 60 <Glossiness> ：: 50 or more ○: 30 or more and less than 50 △: 20 or more and less than 30 ×: less than 20

Further, the color tone unevenness was evaluated in the following manner. First, if the color tone unevenness of the plating appearance can be confirmed even by a slight visual inspection, the vicinity of the boundary between the color tone unevenness part and the normal part is sandwiched, and the lightness and glossiness at two points 30 mm apart are measured, and the lightness between the two points is measured. The absolute values of the difference and the gloss difference were determined. On the other hand, when the unevenness in the color appearance of the plating was hardly discriminated visually, two arbitrary points were taken on the plating surface at intervals of 30 mm, and the lightness difference and the gloss difference between the two points were measured. For each of the measurement results, the plating color tone unevenness was evaluated based on the criteria shown in Table 1.

[0050]

[Table 1]

The glitter was visually observed and evaluated according to the following criteria. <Glittering Gloss> ◎: Not observed at all. ：: Slightly recognized but hardly noticeable. X: It remarkably occurs and is very conspicuous. Furthermore, regarding the plating adhesion, the plated steel sheet was subjected to a 180-degree close contact bending test with the plated surface outside, and then a cellophane adhesive tape was attached to the bent portion and adhered to the tape when vigorously peeled off. The zinc was visually observed and evaluated according to the following criteria. ◎: No zinc adhered to the tape. ○: 有 り Very slight. Δ: 〃 Clearly recognized. ×: 著 し く Notable. Tables 2 to 4 also show the types and amounts of the additives used and the evaluation results thereof.

[0052]

[Table 2]

[0053]

[Table 3]

[0054]

[Table 4]

As is clear from the results shown in the table, examples satisfying the requirements of the method of the present invention (Nos. 3 to 6, 9 to 11, 14 to 1).
6, 19-23, 26-31, 34-39, 42-4
7, 50-54, 57-60, 63-66) can simultaneously achieve high lightness and glossiness, and have no unevenness in plating color tone or glitter due to uneven surface of the original plate. It turns out that it is hardly noticeable. Furthermore, the plating adhesion was also excellent. Among them, Nos. 63 to 66 are examples in which a plurality of additives of the present invention were added, and it was confirmed that similar results were obtained also in these examples.

On the other hand, examples which do not satisfy the requirements of the present invention have the following disadvantages. First, No.1
Is an example in which the additive of the present invention is not added to the plating bath, but both lightness and glossiness are low, and the plating appearance is dark and glossless, and uneven plating color tone and glitter are also observed. .

Nos. 2, 8, 13, 18, 25, 3
3, 41, 49, 56, and 62 are examples in which the additive concentration of the additive is lower than the lower limit of the method of the present invention, but the lightness and glossiness are low, and uneven plating color tone and glitter are clearly observed. .

Further, Nos. 7, 12, 17, 24, 32, 4
Nos. 0, 48, 55, 61 and 67 are examples in which the additive concentration exceeds the upper limit of the method of the present invention, but the color tone unevenness and the glittering luster are not so conspicuous, but the lightness and glossiness are very low. It was hard to say that it had a low and beautiful appearance. In addition, the tendency of the plating adhesion to generally decrease was observed.

Table 4 summarizes the results of studies conducted with the addition of a conventional brightener, each of which has the following disadvantages. First, Nos. 68 to 76 are examples using dextrin and polyacrylamide which are conventional brighteners. Even if these brighteners were used and the addition concentration in the plating bath was variously changed, good brightness and glossiness could not be both provided. Specifically, when the additive concentration (1.0 to 100 ppm) specified by the method of the present invention is added, satisfactory results cannot be obtained in any of lightness, glossiness, uneven plating color tone, and glitter. . When the additive concentration is set to 500 ppm, the glossiness and the glitter are improved, but the effect of improving the brightness and the uneven color tone of the plating is insufficient. Further increase the concentration to 1000 ppm, 500
At 0 ppm, plating burns occur, lightness and gloss are both reduced, and a large amount of additives are eutectoid in the plating layer, resulting in a significant decrease in plating adhesion.

Nos. 77 to 86 are conventional examples using glycine and aspartic acid. In the low addition region where the addition concentration in the plating bath is as low as 1.0 to 100 ppm, good results cannot be obtained with respect to any of brightness, glossiness, unevenness in plating appearance color tone, and glitter. Further, when the addition concentration is 1 to 10 g / L, although the brightness is improved, the effect of improving the gloss is poor, and the improvement in uneven color tone and glittering of the plating appearance is still insufficient. When the additive concentration was further increased to 20 g / L, the lightness and glossiness tended to decrease again.

In the above embodiment, an experiment was performed using a plated original plate having uneven color tone. However, it is needless to say that similar results can be obtained when an original plate having no uneven color tone is used.

[0062]

The electrogalvanized steel sheet of the present invention has high brightness and gloss, and is excellent in appearance without unevenness in color and appearance of plating due to the surface condition of the base plate.

The electrogalvanizing bath additive for improving brightness and gloss of the present invention is very useful for obtaining the above-mentioned plated steel sheet. That is, the above additive was slightly added to the plating bath for 1: 1.
By simply adding 0 to 100 ppm, the effect of improving the glossiness and lightness can be obtained, and a very excellent steel sheet having no uneven color tone and glittering of the plating appearance can be obtained, and the quality of the plating appearance can be significantly improved. it can. Moreover, unlike the case where a conventional brightener is added, it is extremely useful in that a large amount of the brightener is not added to the plating bath and adverse effects such as a decrease in plating adhesion do not occur.

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-61-127891 (JP, A) JP-A-4-124295 (JP, A) JP-A-9-67695 (JP, A) JP-A-8- 158090 (JP, A) JP-A-9-3684 (JP, A) JP-A-8-74089 (JP, A) JP-A-6-2193 (JP, A) JP-A-7-331483 (JP, A) JP-A-8-188899 (JP, A) JP-A-8-260182 (JP, A) JP-B-3-31795 (JP, B2) (58) Fields investigated (Int. Cl. ⁷ , DB name) C25D 3/22 C25D 5/26

Claims (12)

(57) [Claims] 1. A method according to JIS Z8722 (condition d, with a light trap), wherein the surface of an electrogalvanized steel sheet has a brightness of 70 or more, and JIS Z8741
(Gloss degree obtained by the method of (60 ° specular gloss method): 30 or more, and 30 mm on the surface of the electrogalvanized steel sheet
If any two points are taken at intervals, the difference in brightness between the two points will be
5 or less, and the difference in gloss is 15 or less (brightness and gloss
Galvanized steel sheet measuring method of time is characterized that you meet the same) as before. 2. The electrogalvanized steel sheet according to claim 1, wherein the steel sheet has no glitter. 3. A metal salt of naphthenic acid, an aniline derivative,
An electrogalvanizing bath additive for improving brightness and gloss, which is at least one selected from the group consisting of lower alkanoyl compounds and organic peroxides. 4. The additive according to claim 3 , wherein the metal salt of naphthenic acid is cobalt naphthenate. 5. The additive according to claim 3 , wherein the aniline derivative is dimethylaniline. 6. The additive according to claim 3 , wherein said lower alkanoyl compound is methyl ethyl ketone. 7. The additive according to claim 3 , wherein said organic peroxide is methyl ethyl ketone peroxide. 8. A method of manufacturing a galvanized steel sheet according to claim 1 or 2, in the electroplating galvanizing bath, metal salts, aniline derivatives of the naphthenic acids, lower alkanoyl compounds, and organic peroxides A method for producing an electrogalvanized steel sheet, comprising adding at least one selected from the group consisting of 1.0 to 100 ppm in total. 9. The method according to claim 8 , wherein the metal salt of naphthenic acid is cobalt naphthenate. 10. The method according to claim 8 , wherein the aniline derivative is dimethylaniline. 11. The method according to claim 8 , wherein the lower alkanoyl compound is methyl ethyl ketone. 12. The method according to claim 8 , wherein the organic peroxide is methyl ethyl ketone peroxide.