JP5662270B2 - Beautiful electrogalvanized steel strip - Google Patents

Description

  The present invention is excellent in appearance quality compared to conventional electrogalvanized steel strips, although it can be efficiently manufactured by conventional electrogalvanizing equipment, and is used for home appliances, civil engineering / building materials, automobiles, etc. In particular, the present invention relates to a beautiful electrogalvanized steel strip and a chromium-free coated steel strip provided with a chromium-free coating on the electrogalvanized steel strip.

  Since the electrogalvanized steel strip is excellent in sacrificial anticorrosive action, it has been conventionally used in a wide range of industrial fields such as home appliances, civil engineering / building materials, and automobiles. Especially in recent years, the trend of reducing environmentally hazardous substances has been strengthened, and organic or inorganic chromium-free coating has been applied instead of the conventional chromate film as the upper layer of the electrogalvanized steel strip to provide further corrosion resistance and fingerprint resistance. Chrome-free coated electrogalvanized steel strip is used. These steel strips are required to be excellent in surface appearance (surface unevenness, color tone variation) because there are many examples where they are used without coating taking advantage of their excellent corrosion resistance and fingerprint resistance. In recent years, due to the increase in the size of parts such as thin TV panels, the demand for beautification of the surface appearance has become increasingly important.

  There are various possible causes for surface appearance defects (surface unevenness, color variation) of the electrogalvanized steel strip. The main cause is the orientation and size of the galvanized crystals deposited on the electrogalvanized steel strip. Since it is partially different, the reflectance of light is different for each part, and is visually recognized as a surface appearance defect (surface unevenness, color variation, mainly brightness variation).

  The reason why the direction and size of the electrodeposited galvanized crystals are partially different is considered as follows. Zinc-plated crystals have the property of growing in a certain direction and size (epitaxial growth) by electrodeposition, and it is known that the crystal precipitation form is greatly influenced by the electrodeposition conditions and the condition of the base steel strip surface. However, if there are non-uniform parts (for example, A part and B part) such as oxide film, dirt, impurity elements, and base crystal grain size on the surface of the plating base material (cold rolled steel strip), The direction and size of the galvanized crystal on the outermost surface of the final electrogalvanized steel strip will grow in a certain direction and size (separate directions and sizes in part A and B). Will be different for each part.

  Therefore, in order to prevent surface appearance defects (surface unevenness, color variations) of the electrogalvanized steel strip, (1) oxide film and dirt on the base metal (cold rolled steel strip) surface, impurity elements, crystal grain size, etc. (2) It is necessary to suppress the property that the electrodeposited crystal of galvanizing grows in a certain direction and size (epitaxial growth).

  Various methods have been proposed so far to eliminate non-uniform parts such as oxide film, dirt, impurity elements, and crystal grain size on the surface of the base metal (cold rolled steel strip). For example, a method of performing pre-electroplating or displacement plating before performing electrogalvanization can be mentioned.

For example, JP-A-8-134688 discloses a method of applying a plating layer made of Co and Ni to a lower layer of electrogalvanizing. Japanese Patent Application Laid-Open No. 9-202993 discloses a method of applying 0.5 to 100 mg / m ² of Cu or Co or an alloy plating layer thereof to the lower layer of electrogalvanizing. Furthermore, Japanese Patent Application Laid-Open No. 2000-192282 discloses a method of applying a 1 to 5 g / m ² 0.02 to ² wt% Sn—Zn alloy plating layer to a lower layer of electrogalvanizing.

  However, the method of forming a plating layer with a different chemical composition below the electrogalvanized steel strip is a plating bath for forming a plating layer with a different chemical composition, an energizing device for electrodepositing plating, etc. This is not desirable when considering commercial productivity.

In recent years, in order to increase the annealing efficiency of a base material (cold rolled steel strip), a method of air-water cooling (cooling by water spray) after annealing at a high temperature has become common. Since the steel strip surface is oxidized when air-water cooling is performed, it is also common to remove the oxide film by pickling and to perform Ni plating after cooling. In this method, a Ni plating layer is formed on the surface of the steel strip. In this case, the amount of Ni plating deposited is generally as low as ¹ to 20 mg / m ² , so that uneven adhesion occurs (Ni Often adhere to the surface of the steel strip in islands). If there is uneven adhesion on the Ni plating, the growth of electrogalvanized crystals deposited on the upper layer is affected by the amount of adhesion of the Ni plating, which in turn has the disadvantage of promoting the uneven surface of the plating.

  Various methods have also been proposed for the method (2) of suppressing the property that the galvanized electrodeposited crystal grows in a certain direction and size (epitaxial growth). The main method is to add other metal components, anions, organic substances, etc. to the electrogalvanizing bath.

  For example, JP-A-8-158090 discloses a method for producing an electrogalvanized steel strip in which polyoxyalkylene having an average molecular weight of 1000 to 100,000 or an alkyl ether thereof is present in a concentration range of 1 to 500 ppm in a plating bath. In JP-A-8-188899, the total amount of at least one selected from the group consisting of Sn, In, Bi, and Sb on a base steel strip having an average crystal grain size of 38 μm or less on the surface is set to 0. An electrogalvanizing method using a plating bath containing 0008 to 0.05 wt% is disclosed in Japanese Patent Application Laid-Open No. 9-256192 using a steel strip having a surface average ferrite grain size of 38 μm or less as a base material. There is provided a method for producing an electrogalvanized steel strip excellent in uniformity in appearance in which electrogalvanization is performed in a zinc plating bath containing 100 to 5000 ppm of ions. Japanese Patent Application Laid-Open No. 2000-192282 discloses a method for producing an electrogalvanized steel strip that is electroplated using an acidic zinc plating solution to which 1 to 50 g / l diallyldimethylammonium chloride-sulfur dioxide copolymer (PAS) is added. Are each disclosed.

  However, among the methods of adding other metal ion components, anions, organic substances, etc. to the electrogalvanizing bath, if the additive component has the property of eutectoid with zinc (mainly metal ions), When the current density applied to the steel strip changes due to the change in speed due to the electrodeposition of the plating, the amount of eutectoid changes with the change in the current density, the brightness of the plating changes due to the change in the amount of eutectoid, On the contrary, there was a problem that unevenness was sometimes promoted. In addition, when the metal ion component is eutectoidally formed as a metal during galvanization, it is not preferable in that a small local battery is partially formed and the corrosion resistance is lowered.

  On the other hand, when the additive component does not co-deposit with zinc (anion, organic matter, etc.), it is necessary to control the concentration in the bath to a certain level, but the method for analyzing the concentration in the bath quickly and accurately However, there is a disadvantage that it is difficult and expensive as compared with metal ions. Unlike the pickling bath before plating, etc., the electrogalvanizing bath is generally used permanently without reconstructing the bath and replenishing components consumed by electrodeposition or taking out. Therefore, if the concentration in the bath cannot be quickly and accurately analyzed and insufficient components cannot be replenished, the amount of additional components (anions, organic substances, etc.) necessary for the effect will be insufficient, and the brightness of the plating will change, which will cause unevenness. There was a drawback of promoting.

  As another method for suppressing the property that the galvanized electrodeposited crystal grows in a certain direction and size (epitaxial growth), various organic substances can be used in a degreasing solution or pickling solution that is implemented as a pretreatment for galvanizing. A method of adding an inorganic substance has also been proposed.

  For example, JP-A-9-59788 discloses a primary amine (excluding benzylamine), secondary amine, tertiary amine, and quaternary ammonium in a pickling solution before electrogalvanizing. Disclosed is a method of containing at least one nitrogen-containing organic compound that forms a cation in an acidic liquid, selected from the group consisting of salts and heterocyclic compounds.

  JP-A-2002-309393 discloses the production of an electrogalvanized steel strip in which a base steel strip before plating is brought into contact with an acidic aqueous solution containing 5 ppm or more of a water-soluble polymer having an amino group having an average molecular weight of 1,000 to 200,000. A method is disclosed.

  Japanese Patent Application Laid-Open No. 2003-64493 discloses a pickling accelerator having a reducing action on an oxide film of a plating base steel strip and an organic compound having a carbonyl group or a thiocarbonyl group that can dissolve and remove the oxide film. A method of performing pickling before plating using a pickling solution containing a compound is disclosed. JP-A-2003-64493 further discloses a method of adding colloidal silica into the pickling solution before plating.

  However, according to the knowledge of the present inventors, in any of these methods, when the Ni plating layer does not exist as the first layer on the surface of the steel strip, or when the amount of adhesion is small even if the Ni plating layer exists, Although the effect is shown, it was insufficient when the variation of the adhesion amount of the Ni plating layer was large, particularly when the variation of the adhesion amount of the Ni plating layer exceeded 10% of the average adhesion amount.

JP-A-8-134688 JP 9-202993 A JP 2000-192282 A JP-A-8-158090 JP-A-8-188899 JP-A-9-256192 JP 2000-192282 A JP 9-59788 A Japanese Patent Laid-Open No. 2002-309393 JP 2003-64493 A

  The present invention has been made in view of the above circumstances, and an object thereof is to provide an electrogalvanized steel strip free from surface appearance defects (surface unevenness, color variation). In particular, a Ni plating layer is formed on the surface of the steel strip as the first layer, and even if there is a variation in the amount of adhesion on the plating layer, there is no surface appearance defect (surface unevenness, color variation) electrogalvanized steel strip Is to provide.

  In order to solve the above-mentioned problems, the present inventors have conducted intensive studies, and as a result, even if a Ni plating layer with a variation in the amount of adhesion exists on the surface of the steel strip, a galvanized crystal is deposited on this surface. In order to suppress the epitaxial growth of steel and, as a result, to suppress unevenness in the surface appearance of the electrogalvanized steel strip, one or more amine compounds and an S (sulfur) -containing functional group are provided between the Ni plating layer and the electrogalvanizing layer. Obtaining knowledge that it is effective to provide a layer made of an organic compound having a group, the present invention has been made.

In the present invention, at least one surface of a steel strip is measured under 10 parts of 10 mm square ( 1 cm ² ) continuous in the width direction of the steel strip under an electrogalvanized layer at an arbitrary portion. An electrogalvanized steel strip having a Ni plating layer having an average adhesion amount of 1 to 30 mg / m ^2, which is a 10 mm square ( 1 cm) continuous in the width direction of the steel strip at an arbitrary portion of the surface of the electrogalvanized layer ² ) An electrogalvanized steel strip characterized in that the ratio of the brightness difference between the maximum brightness and the minimum brightness to the average brightness when the brightness (L value) at 10 locations is measured is 2% or less.

More specifically, the electrogalvanized steel strip of the present invention having the above-described features is a 10 mm square ( 1 cm) continuously in the width direction of the steel strip at an arbitrary portion in order from the bottom on at least one surface of the steel strip. ² ) The average adhesion amount when measuring the adhesion amount at 10 locations is 1 to 30 mg / m ² , and the ratio of the difference between the maximum adhesion amount and the minimum adhesion amount to the average adhesion amount is 10% or more And a first layer composed of a Ni plating layer, and an organic compound having at least one amine compound and an S (sulfur) -containing functional group, and the adhesion amount is 0.002 mg / m ^{2 in} total of these organic compounds. As mentioned above, it has the 2nd layer which is 1 mg / m < ² > or less, and the 3rd layer which consists of an electrogalvanized layer containing 95 mass% or more of Zn.

  The amine compound is preferably at least one compound selected from polyethyleneimine and derivatives thereof, and the organic compound having an S-containing functional group is preferably at least one compound selected from thiourea and derivatives thereof.

  Preferably, the second layer adsorbs the amine compound and the organic compound having the S-containing functional group on the surface of the steel strip by immersing in an acidic liquid containing the amine compound and the organic compound having the S-containing functional group. It is a layer formed by this.

In addition to the amine compound and the organic compound having an S-containing functional group, the acidic liquid preferably contains a compound that promotes removal of iron and nickel oxides.
The compound that promotes the removal of the iron and nickel oxides is preferably at least one compound selected from saturated lower carboxylic acids and salts thereof.

  From another aspect, the present invention provides the above electrogalvanized plating having a chromium-free coating as an upper layer of the electrogalvanized layer or a fourth layer of the upper layer of the third layer on at least one surface of a steel strip. It is a chromium-free coated steel strip based on a steel strip.

  According to the present invention, a beautiful electrogalvanized steel strip or a chromium-free electrogalvanized steel strip can be obtained even when the variation in the amount of adhesion of the first layer of Ni plating is 10% or more. Therefore, the present invention is applied to an electrogalvanized steel strip manufactured by a method in which pickling and thin nickel plating are performed before electrogalvanizing using a cold-rolled steel strip cooled at high temperature and air-water cooled as a base material. In addition to the excellent corrosion resistance and fingerprint resistance characteristic of electrogalvanized steel strip, it has a beautiful appearance with extremely suppressed surface unevenness and color variation, so it can be used without painting. In particular, it has an advantage in applications.

Hereinafter, the present invention will be described more specifically by taking specific embodiments thereof as examples. However, the following description is for illustrative purposes and does not limit the present invention.
Electro-galvanized steel strip according to the present invention, in at least one surface of the strip, below the electro-galvanized layer, measuring the adhesion amount of 1 cm ² by 10 positions continuous in the width direction of the steel strip in any part An electrogalvanized steel strip having a Ni plating layer with an average adhesion amount of 1 to 30 mg / m ² , and continuous in the width direction of the steel strip at any part of the surface of the electrogalvanized layer The ratio of the brightness difference between the maximum brightness and the minimum brightness when the brightness (L value) at 10 locations of 1 cm ² is measured is 2% or less. As long as it has this feature, the steel strip of the base material, the electrogalvanizing and the pretreatment method are not particularly limited.

  The electrogalvanized steel strip having the above-described features according to the present invention includes, on at least one surface of the steel strip, a first layer made of a Ni plating layer, a second layer made of a specific organic compound, and an electrogalvanized layer. Since this can be realized by having the third layer, this embodiment will be described below.

  The steel strip used as the base material is not limited, and the present invention can be applied to any steel strip that is generally used as a base material for electrogalvanizing. If it is the range of general carbon steel, it is applicable irrespective of the component in steel, intensity | strength, and the annealing method (box annealing or continuous annealing). In addition, as a base material, it is desirable to use a cold-rolled steel strip that has been annealed after cold rolling because of its excellent workability. A hot-rolled pickled steel strip that has been washed can also be applied.

  The cold-rolled steel strip may be obtained by annealing after cold rolling by high-temperature annealing and air-water cooling excellent in productivity. In this case, as described above, since the steel strip surface is oxidized, the removal of the oxide film by pickling and the thin Ni plating called nickel strike plating are generally performed. This Ni plating can constitute the first layer described below.

  The thin Ni plating layer of the first layer serves to improve the adhesion between the steel strip (preferably an annealed cold rolled steel strip) of the plating base material and the electrogalvanizing. That is, when a small amount of Ni is present on the surface of the base steel strip so as not to cover the entire base steel strip, when the second layer of electrogalvanizing precipitates, the deposition of electrogalvanizing starts from this Ni Since Ni and Zn have good plating adhesion, it is considered that the adhesion with the base steel strip of electrogalvanization is improved.

The purpose of applying Ni plating is different from the purpose of uniformly covering the entire base steel strip to improve the corrosion resistance, and depositing a small amount of Ni on the surface of the steel strip in islands. The purpose is to assist the deposition of electrogalvanizing as a starting point. Therefore, since the adhesion amount of Ni plating is not uniform when viewed microscopically, it is expressed as an average adhesion amount when a continuous range of 1 cm ² is measured.

In the present invention, the amount of adhesion of the first Ni plating layer is 1 mg / m ² or more and 30 mg / m ^{2 in} terms of the average amount of adhesion when 10 sites of 1 cm ² are continuously measured in the width direction of the steel strip. m ² or less. When the average adhesion amount of the Ni plating layer is less than 1 mg / m ² , the adhesion of electrogalvanization is insufficient, and for example, the adhesion of electrogalvanization when deep drawing is performed becomes insufficient. On the other hand, when the average adhesion amount of the Ni plating layer exceeds 30 mg / m ² , it is necessary to reduce the line speed during production, which is disadvantageous in terms of cost.

When an attempt is made to perform such low adhesion amount Ni plating on the steel strip of the plating base material, a difference in the adhesion amount of Ni plating occurs in the width direction of the steel strip due to various reasons. If there is such a difference in the amount of Ni plating deposited, the size and orientation of the galvanized crystals deposited on the Ni plating are different, so that a beautiful electrogalvanized steel strip cannot be obtained. For this reason, in the past, the difference in adhesion amount, which is the difference between the maximum adhesion amount and the minimum adhesion amount in the Ni plating adhesion amount when measuring the adhesion amount at 10 locations in 1 cm ² increments in the width direction of the steel strip. It was necessary to keep the ratio below 10%. To that end, it was necessary to devise measures such as reducing the line speed during steel strip production, which hindered productivity.

In the present invention, the ratio of the difference between the maximum adhesion amount and the minimum adhesion amount when measuring the adhesion amount at 10 locations of 1 cm ² continuously in the width direction of the steel strip is as high as 10% or more and high production. Even in the case of a steel strip manufactured with the property, it is possible to obtain a stable and beautiful electrogalvanized steel strip and chromium-free electrogalvanized steel strip. Therefore, the ratio of the difference in the adhesion amount of the first Ni plating layer is preferably 10% or more. This is because the effect of the present invention becomes clearer when there is such a large difference in adhesion amount. The proportion of the difference in adhesion amount may exceed 50%, for example, and may reach 100% or more. The upper limit of this ratio is not particularly limited, but generally it is preferably within 150%.

  The first Ni plating layer is formed by electroplating. The Ni plating may be performed by any method as long as the steel strip is immersed in an aqueous solution containing nickel ions and Ni is deposited at a predetermined amount of current. Although general Ni strike plating is performed using a chloride bath containing nickel chloride, the first layer can be formed by employing such a normal strike plating method. Ni plating is preferably performed immediately after pickling after continuous annealing when the base steel strip is an annealed cold rolled steel strip, but after a while or immediately before the electrogalvanized steel strip. It is also possible to implement.

  Conventionally, electrogalvanizing is performed on the first Ni plating layer. In the present invention, the second layer is an organic material having at least one amine compound and at least one S-containing functional group. A layer made of two types of organic compounds, called compounds, is formed before electrogalvanizing. Forming this second layer is a feature of the present invention.

  An amine compound is characterized in that it is easily coordinated to a nickel atom by physical adsorption selectively as a cationic amine in an aqueous solution. On the other hand, an organic compound having an S-containing functional group has a feature that a lone pair of a sulfur atom is easily selectively coordinated to an iron atom by chemical adsorption.

  By forming a second layer composed of at least one of an amine compound and an organic compound having an S-containing functional group, the Ni plating layer of the first layer is unevenly and partly covered with an island shape. However, the amine compound is selectively adsorbed on Ni on the surface of the steel strip, and the organic compound having an S-containing functional group is selectively adsorbed on Fe, so that the entire surface of the steel strip constitutes the second layer. The crystal orientation of zinc coated with an organic compound and electrodeposited on the upper layer is constant over the entire surface of the steel strip, and it is possible to produce a beautiful electro-galvanized steel strip with no unevenness.

  On the other hand, in the case where the second layer is formed only from the amine compound, this organic compound is likely to be selectively adsorbed onto Ni. It is considered that the second layer is difficult to be formed in a portion where the amount of adhering is small. Therefore, unevenness of the electrogalvanization of the third layer occurs.

  Further, when the second layer is formed only from an organic compound having an S-containing functional group, this organic compound is likely to be selectively adsorbed to Fe, so that the portion of the first Ni plating layer with a large amount of adhesion is used. It is considered that the second layer is hardly formed on the top. As a result, the third layer of electrogalvanizing is also uneven.

  Thus, since both an amine compound and an organic compound having an S-containing functional group are necessary, even if two or more amine compounds are used or only two or more compounds having an S-containing functional group are used, The effects of the invention cannot be achieved reliably.

The adhesion amount of the amine compound and the organic compound having an S-containing functional group in the second layer is 0.002 mg / m ² or more and 1 mg / m ² or less in total. If the adhesion amount is less than 0.002 mg / m ^2, the change in the crystal orientation of zinc electrodeposited on the upper layer is not sufficient, and a beautiful non-uniform electrogalvanized steel strip cannot be obtained. On the other hand, when the adhesion amount exceeds 1 mg / m ² , the adhesion of the electrogalvanized electrodeposited on the upper layer is lowered. Further, in order to obtain a high adhesion amount, the concentration of the treatment liquid must be increased, which is not preferable in terms of cost.

  Examples of the amine compound include various aliphatic, alicyclic and aromatic amine compounds, and heterocyclic compounds containing N as a hetero atom, and it is preferable to use a water-soluble compound. Since organic compounds having a large number of amino groups in the molecule are preferred, polyamines, especially polyalkylene polyamines such as polyethyleneimine and derivatives thereof are most preferred because of their great effects.

Examples of the organic compound having an S-containing functional group include a compound having a thiocarbonyl group (> C═S) group or a thiol (—SH), and a heterocyclic compound containing S as a hetero atom, which is also water-soluble. It is preferable to use a chemical compound. Of these, thiourea and its derivatives are preferable because of their great effects. In the case also contain further amino groups (-NH ₂₎ as thiourea, the amino group is poor in reactivity, exhibits no adsorption effect on Fe. Therefore, thiourea and its derivatives, in a broad sense, thiocarbonyl groups, thiol groups, or organic compounds having both an -S- moiety and an amino group are treated as organic compounds having an S-containing functional group in the present invention.

  As a second layer, a method of forming a layer composed of two kinds of organic compounds, that is, an amine compound and an organic compound having an S-containing functional group is not particularly limited, but the steel strip having the Ni plating layer described above as the first layer, It is immersed in a solution, preferably an aqueous solution, in which one or more amine compounds and one or more organic compounds having an S-containing functional group are dissolved. A method of adsorbing these compounds on the surface of the Ni plating layer, a method of using this solution to adsorb electrically or electrostatically while energizing a steel strip, and applying this solution by spraying or other methods, The method of drying etc. is possible. The solvent is preferably water, but more preferably an acidic solution as described below.

  The most preferable method for forming the second layer is one or more amine compounds and S in a pickling bath (that is, an acid solution) used in a pickling treatment generally performed as a pretreatment for electrogalvanizing. At least one organic compound having a functional group contained is added, and at the same time as pickling, the surface of the steel strip (this surface has a thin Ni plating layer, but Ni plating adheres unevenly in islands) This is a method of forming a second layer composed of an amine compound and an organic compound having an S-containing functional group by adsorbing these organic compounds to a partly exposed iron). By adding an amine compound and an organic compound having an S-containing functional group to the pickling bath, dissolving or suspending these compounds in the pickling bath, and passing a steel strip in the pickling bath, pickling is performed. The second layer is formed by firmly adsorbing an organic compound having an amine compound and an S-containing functional group on the surface of the steel strip by coordination with Ni or Fe.

  Immediately after fresh metal iron or nickel is exposed on the surface of the Ni strip of the steel strip by pickling, amine compounds and organic compounds having S-containing functional groups are most easily coordinated and adsorbed to iron or nickel. The present inventors have clarified through experiments that it is easy to form a second layer that is easy, stable and uniform. This method is very efficient because it does not require modification of an existing electrogalvanized steel strip production facility or an additional process, and can be produced only with the existing facility.

The addition amount of the amine compound and the organic compound having an S-containing functional group to the pickling bath is such that the adhesion amount of these organic compounds remaining on the steel strip surface after pickling treatment and subsequent water washing is 0.002 mg in total. / M ² or more and 1 mg / m ² or less.

The ratio of the amine compound and the organic compound having an S-containing functional group is not particularly limited, but both the amine compound and the organic compound having an S-containing functional group have a minimum adhesion amount of 0.002 mg / m ² or more. It is preferable to do.

  The type of the pickling bath is not particularly limited, but is generally an acid bath based on hydrochloric acid or sulfuric acid. Except for adding an amine compound and an organic compound having an S-containing functional group in accordance with the present invention, the pickling treatment can be performed under conditions commonly used for pickling treatment of electrogalvanized steel strip.

  Accelerates the removal of iron and nickel oxides present on the surface of steel strips in acidic liquids (eg pickling baths) containing amine compounds and organic compounds with S-containing functional groups used to form the second layer When the compound to be added is added at the same time, the oxides of iron and nickel are removed, and the organic compounds having amine compounds and S-containing functional groups are easily adsorbed by iron and nickel on the steel strip. It can be expected that the crystal orientation of the electrogalvanizing is further uniformized.

As an example of the compound that promotes the removal of iron and nickel oxides formed on the surface of the steel strip, a suitable one can be selected from a kind of compound generally called a pickling accelerator. Although various inorganic and organic compounds have been known so far as pickling accelerators, saturated lower carboxylic acids are particularly preferred for use in the present invention. The carboxylic acid may be either a monocarboxylic acid or a di- or polycarboxylic acid. Examples of suitable saturated lower carboxylic acids are formic acid, acetic acid, propionic acid, oxalic acid, malonic acid and the like.

  Some thiols and amines are called pickling accelerators. However, according to the study by the present inventors, the effect of promoting the removal of the iron and nickel oxides described above was not necessarily recognized. Therefore, in the present invention, these are regarded as amine compounds or organic compounds having an S-containing functional group, and at the same time, it is preferable to add a compound that promotes the removal of iron and nickel oxides as described above.

  Here, the compound (= pickling accelerator) that promotes the removal of iron and nickel oxides present on the surface of the steel strip means that the compound is added to the acid bath and pickled more than when it is not added. It is a compound that promotes. The method for confirming whether pickling is promoted is to investigate the acid pickling reduction amount of the compound-free acid (weight reduction when a steel strip of a certain size is immersed in an acid solution of a certain concentration and temperature for a certain period of time). Then, the amount of pickling loss when a certain amount of a compound is added is investigated, and if the amount of pickling loss when a compound is added is large, the compound is defined as a pickling accelerator.

When the above-described second layer is formed using a pickling bath or an acidic solution, washing is performed after the treatment with the pickling bath or the acidic solution. This washing with water may be performed according to a conventional method.
After forming the second layer composed of the amine compound and the organic compound having an S-containing functional group as described above, an electrogalvanized layer containing 95% or more of Zn is formed as the third layer above the second layer. The method for forming the electrogalvanized layer may be the same as the conventional electrogalvanizing method. The electrogalvanizing bath used may be a sulfuric acid bath or a hydrochloric acid bath. The composition of the plating bath is not limited.

  If the Zn ion concentration of the plating bath is a concentration that is generally used for electrogalvanizing, an electrogalvanized layer can be formed. However, in a commercially produced electrogalvanizing bath, generally, a considerable proportion of Fe ions eluted from the base steel strip is usually dissolved, and other impurity metal ions are also dissolved in a small amount. Therefore, the Zn content of the electrogalvanized layer formed as the third layer is 95% or more. When the Zn content of the electrogalvanized layer is lower than 95%, the surface appearance and corrosion resistance are lowered.

The current density at the time of depositing the Zn plating layer by electrogalvanizing is not particularly defined, and may be the same as that generally used for the production of the electrogalvanized steel strip. In general, the current density is about 10 to 100 A / dm ^2. The energization method may be continuous energization or intermittent pulse energization.

The adhesion amount of the electrogalvanized layer containing 95% or more of Zn formed as the third layer is not particularly limited, but is preferably 5 g / m ² or more and 100 g / m ² or less. If the adhesion amount of the electrogalvanized layer is not more than 5 g / m ² , sufficient corrosion resistance imparting effect cannot be obtained. In addition, electrogalvanization tends to deposit unevenly, and if the amount of adhesion is small, it becomes uneven and the surface appearance tends to be impaired. Therefore, the amount of adhesion is preferably 5 g / m ² or more. On the other hand, if the adhesion amount of the electrogalvanized layer exceeds 100 g / m ² , the corrosion resistance imparting effect is saturated and the amount of electricity used is increased, which is uneconomical.

Thus, an electrogalvanized layer having a Zn content of 95% by mass or more is formed as a third layer on the first Ni plating layer and the second organic compound layer described above. The ratio of the brightness difference between the maximum brightness and the minimum brightness to the average brightness is 2% or less when measuring the lightness (L value) at 10 locations of 1cm ² each in the width direction of the steel strip at any part of the surface of the steel sheet Thus, an electrogalvanized steel strip having a beautiful appearance with extremely suppressed surface unevenness and color variation can be obtained. This lightness difference is preferably 1% or less, more preferably 0.5% or less. The smaller the brightness difference, the smaller the surface unevenness and color variation, and the more beautiful the appearance is.

  By providing a chromium-free film as the fourth layer on the electrogalvanized layer having a Zn content of 95% or more formed as the third layer, a third layer is formed on the first layer and the second layer. Further, the beautiful appearance of the electrogalvanized film can be further enhanced.

  The kind of the chromium-free coating of the fourth layer is not particularly limited, and various types of chromium-free coatings proposed for forming an upper layer of electrogalvanizing can be used. A typical chromium-free film is a transparent or translucent thin organic resin film, inorganic film, or organic-inorganic composite film having a thickness of about 1 μm. Examples of the organic resin film include resin films such as urethane resin, polyester resin, epoxy resin, acrylic resin, polyimide resin, and silicone resin. Examples of the inorganic coating include a silica coating (eg, formed from ethyl silicate or a hydrolyzate thereof), a lithium silicate coating, an aluminum phosphate coating, and the like. When an organic resin is contained in the inorganic film, an organic-inorganic composite film is obtained.

  When the fourth layer of chromium-free coating is present, if there is a difference in Zn crystal size or orientation in the third electrogalvanized layer, the brightness difference in this part is greatly promoted and the surface appearance It has the property of making it stand out as a difference. When a thin transparent chrome-free film as the fourth layer is present on the third electrogalvanized layer, the surface brightness decreases by about 10 points in terms of L value compared to the case up to the third layer. If there is a lightness difference in the third layer, the bright part and dark part of the third layer are equally reduced by about 10 points, so that the lightness difference thus generated becomes a region of lightness difference that is easily recognized by human eyes. It is believed that there is.

  In the present invention, the brightness difference in the third electrogalvanized layer is as small as 2% or less, so even if the brightness becomes more clearly visible to the naked eye by the formation of a chromium-free film, the unevenness of the appearance is still present. And color variations are not noticeable, and a beautiful appearance is maintained. The ratio of the difference in brightness obtained in the same manner as described above after forming the fourth layer is also preferably within 2%, more preferably within 1%.

  The method for forming the chromium-free film of the fourth layer is not particularly limited. There are generally used methods such as a method of applying with a roll coater, a method of applying with a spray and then squeezing with a roll to control the thickness, a method of applying with a spray and then washing away unnecessary components by washing with water. Dry or bake as necessary after application. The thickness of the chromium-free film is not limited. Typically, it is around 1 μm, but depending on the film material, it can be made thinner or thicker. In general, the thickness is preferably 3 μm or less. The chromium-free coating of the fourth layer is optionally selected from one or more selected from rust preventive components, weather resistance imparting components, lubricity imparting components, coating strengthening components (crosslinking agents, silane coupling agents), etc. An appropriate amount may be contained.

Hereinafter, the present invention will be described with reference to experimental examples.
(1) Preparation of test pieces of electrogalvanized steel strip and chromium-free coated steel strip Hereinafter, in all tests, steel plates cut into 170 mm x 170 mm from cold-rolled annealed steel strip of ordinary steel (0.8 mm thickness) Electroplating was carried out while flowing the plating solution in one direction at a predetermined flow rate using a small flow cell that was used as a plating base material and simulated the flow state of an actual continuous electroplating line.

First, the steel sheet cut out from the steel strip was degreased by performing electrolytic degreasing at a current density of 10 A / dm ² in a 10% NaOH aqueous solution at 30 ° C. for 5 minutes and then washing with water for 2 minutes.

  This degreased steel plate was subjected to nickel plating on both surfaces under the conditions shown in Table 1 to form a first Ni plating layer. The adhesion amount of Ni was adjusted to a predetermined adhesion amount by adjusting the current density and the energization time. In the continuous electroplating of the steel strip, the flow direction of the liquid in the plating bath is parallel to the rolling direction of the steel strip, and thus is perpendicular to the width direction of the steel strip. In order to simulate this state, in the experiment in this example, the steel plate was set and plated so that the rolling direction of the steel plate was parallel to the flow direction of the plating bath.

A steel plate subjected to Ni plating is continuous at a 10 mm square (1 cm ² ) in the direction perpendicular to the liquid flow direction in the Ni plating bath (as described above, this direction corresponds to the width direction of the steel strip in continuous strip plating). The amount of Ni deposited at each location was measured by the fluorescent X-ray method using the amount of Ni deposited as measured by the atomic absorption method after pickling.

  The average value of the measured Ni deposits at 10 locations was defined as the average deposit. Further, the ratio (%) of the difference in adhesion amount (= maximum adhesion amount−minimum adhesion amount) with respect to the average adhesion amount from the maximum adhesion amount and the minimum adhesion amount at 10 locations was determined as the adhesion amount variation. The results are summarized in Table 4.

  The steel plate on which the first Ni plating layer is formed is dipped in a pickling solution having the composition shown in Table 2 for 5 seconds at 25 ° C., then washed with water (spray), pickled, and simultaneously pickled. A second layer comprising an amine compound and an organic compound having an S-containing functional group was formed on both sides of the substrate. In Table 2, “N-containing compound” and “S-containing compound” mean an organic compound having an amine compound and an S-containing functional group, respectively.

  About each steel plate which formed the 2nd layer, the content rate (mass%) of N atom and S atom was measured from the intensity | strength of N and S calculated | required using Shimadzu Corporation ESCA3200. In addition, the same steel plate (formed only with the first layer) is pickled under the same conditions with the same pickling solution to which neither an amine compound nor an organic compound having an S-containing functional group is added. The strength of N and S was measured by the method, and the adhesion amount of the amine compound and the organic compound having the S-containing functional group in the second layer was determined from the difference from the measured value at that time. The results are summarized in Table 4.

  The steel sheet on which the second layer was formed by the above method was electrogalvanized under the conditions shown in Table 3, and an electrogalvanized layer serving as the third layer was formed on both surfaces of the steel sheet. Since the plating bath used was newly constructed every time of the test, the Zn content of the electrogalvanized layer was 99% or more, substantially 100%. Further, similarly to the formation of the first layer, the steel plate was set and plated such that the rolling direction of the steel plate was parallel to the flow direction of the plating bath.

  The adhesion amount of the electrogalvanized layer was determined by immersing a test piece obtained by cutting the plated steel sheet into a predetermined size and immersing it in dilute hydrochloric acid containing an inhibitor, dissolving only the electrogalvanized, It was determined by the method (mass difference before and after pickling).

  For some steel plates, after electrogalvanizing to form the third layer, a chrome-free urethane resin paint (clear paint) is applied to one side of the steel sheet, and the bar coater is adjusted so that the film thickness after baking is about 1 μm. The film was baked at a maximum plate temperature (PMT) of 100 ° C. and allowed to cool to room temperature to form a fourth layer of a chromium-free film.

  The adhesion amount of the 4th layer was calculated | required from the measurement result in the fluorescent X ray using the analytical curve created with the organic resin (chromium free urethane resin) of the known film thickness measured beforehand by the gravimetric method. The results are shown in Table 4.

(2) Performance investigation (2-1) Plating unevenness About the electrogalvanized steel sheet having the first to third layers or the chromium-free coated steel sheet having the first to fourth layers created above, In 10 areas of 10 mm square (1 cm ² ) continuous in the direction corresponding to the width direction (that is, the direction perpendicular to the liquid flow direction in the electrogalvanizing bath), the color difference meter SM- manufactured by Suga Test Instruments Co., Ltd. The brightness (L value) of the Hunter color system is measured by 7-IS-2B, and the average brightness, the minimum brightness, the maximum brightness, and the brightness variation (lightness difference (= maximum brightness-minimum brightness) from the 10 measured values. ) To the average brightness (%)) was calculated.

The following ratings were given in light of the degree of variation in brightness and the degree of plating unevenness that could be visually confirmed.
○: Lightness variation is ≦ 2% (unevenness is not visually recognized)
X: Lightness variation is> 2% (unevenness is observed visually).

(2-2) Plating adhesion The electrogalvanized steel sheet formed up to the third layer (electrogalvanizing) by the above method was punched into a circle having a diameter of 90 mm, and its mass was measured to be W1. Molding oil was applied to the steel sheet, and after performing cylindrical molding with an inner diameter of 50 mm, a shoulder R of 5 mm, and a height of 25 mm, solvent degreasing was performed. A cellophane tape was applied to the outer surface of the cylindrical wall surface portion of the obtained molding material, and then peeled off. The mass was measured again to obtain W2. The value of W1-W2 was recorded as the amount of peeling of plating, and evaluated as follows.

○: Plating peeling amount ≦ 5 mg (no substantial peeling of plating)
×: Plating peeling amount> 5 mg (with substantial peeling of plating)
The test results are shown in Table 5.

  As can be seen from Tables 3 to 5, in the inventive examples, the lightness difference was within 2%, the lightness variation was small, and no visual unevenness was observed. In Nos. 8 and 9 with the chrome-free coating, the brightness was about 10% lower than the other examples without this coating, but the difference in brightness remained within 2%, giving it a beautiful appearance. Was holding.

  On the other hand, in No. 10 in which the adhesion amount of the second layer composed of an amine compound and an organic compound having an S-containing functional group was too small, the brightness difference exceeded 2%, and the appearance was visually uneven. On the other hand, in No. 11 in which the amount of the second layer deposited was too large, the appearance was good, but the adhesion of the electrogalvanized layer was lowered. Further, even with No. 12 in which the amount of the first Ni plating layer deposited was too small, the adhesiveness of the electrogalvanized layer also decreased.

Claims (9)

On at least one surface of the steel strip, the average amount of deposit when 10 deposits of 10 mm square ( 1 cm ² ) continuous in the width direction of the steel strip at an arbitrary portion under the electrogalvanized layer is measured. An electrogalvanized steel strip having a Ni plating layer of 1 to 30 mg / m ² , each 10 mm square ( 1 cm ² ) continuous in the width direction of the steel strip at any part of the surface of the electrogalvanized layer An electrogalvanized steel strip characterized in that the ratio of the brightness difference between the maximum brightness and the minimum brightness when the brightness (L value) at 10 locations is measured is 2% or less. On at least one surface of the steel strip, the average amount of deposit when 10 deposits of 10 mm square ( 1 cm ² ) continuous in the width direction of the steel strip at an arbitrary portion under the electrogalvanized layer is measured. A chrome-free coated electrogalvanized steel strip having a chrome-free coating applied to an upper layer of an electrogalvanized steel strip having a Ni-plated layer of 1 to 30 mg / m ² , wherein any portion of the surface of the chrome-free coating The ratio of the lightness difference between the maximum lightness and the minimum lightness when measuring 10 lightness (L value) at 10 mm square ( 1 cm ² ) continuous in the width direction of the steel strip to the average lightness is 2% or less. Features a chrome-free coated electrogalvanized steel strip. On at least one surface of the steel strip, the average amount of deposit is 1 to 30 mg when the amount of deposit is measured in 10 mm squares ( 1 cm ² ) in 10 mm square ( 1 cm ² ) continuously in any part in the width direction in order from the bottom. / M ² , and the ratio of the difference between the maximum adhesion amount and the minimum adhesion amount at that time to the average adhesion amount is 10% or more, a first layer composed of a Ni plating layer, and each one or more amine compounds and A second layer composed of an organic compound having an S (sulfur) -containing functional group, the adhesion amount of which is 0.002 mg / m ² or more and 1 mg / m ² or less in terms of the total amount of these organic compounds, and 95% by mass or more of Zn The electrogalvanized steel strip according to claim 1, further comprising a third layer made of an electrogalvanized layer containing On at least one surface of the steel strip, the average amount of deposit is 1 to 30 mg when the amount of deposit is measured in 10 mm squares ( 1 cm ² ) in 10 mm square ( 1 cm ² ) continuously in any part in the width direction in order from the bottom. / M ² , and the ratio of the difference between the maximum adhesion amount and the minimum adhesion amount at that time to the average adhesion amount is 10% or more, a first layer composed of a Ni plating layer, and each one or more amine compounds and A second layer composed of an organic compound having an S (sulfur) -containing functional group, the adhesion amount of which is 0.002 mg / m ² or more and 1 mg / m ² or less in terms of the total amount of these organic compounds, and 95% by mass or more of Zn The chromium-free-coated electrogalvanized steel strip according to claim 2, comprising a third layer made of an electrogalvanized layer containing bismuth and a fourth layer made of a chromium-free coating.   The electrogalvanized steel strip according to claim 3 or 4, wherein the amine compound is at least one compound selected from polyethyleneimine and derivatives thereof.   The electrogalvanized steel strip according to any one of claims 3 to 5, wherein the organic compound having an S-containing functional group is at least one compound selected from thiourea and derivatives thereof.   The second layer is formed by adsorbing an amine compound and an organic compound having an S-containing functional group on the surface of the steel strip by dipping in an acidic solution containing an amine compound and an organic compound having an S-containing functional group. The electrogalvanized steel strip according to any one of claims 3 to 6, which is a formed layer.   The electrogalvanized steel strip according to claim 7, wherein the acidic liquid contains a compound that promotes removal of oxides of iron and nickel in addition to an amine compound and an organic compound having an S-containing functional group.   The electrogalvanized steel strip according to claim 8, wherein the compound that promotes removal of iron and nickel oxides is at least one compound selected from saturated lower carboxylic acids and salts thereof.