JP3282517B2 - Resin chromate treated Zn-based plated steel sheet with excellent blackening resistance - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to a method for imparting blackening resistance to Zn-based steel sheets such as Zn-coated steel sheets and Zn-based alloy-coated steel sheets having a resin chromate film on the surface of the plating film while maintaining high corrosion resistance. Related to technology.

[0002]

2. Description of the Related Art Chromate treatment is a technique which is widely used as a primary rust preventive treatment or a coating base treatment for plated steel sheets such as Zn-plated steel sheets, Zn-based alloy-plated steel sheets, and Al-plated steel sheets.

[0003] The basis of the chromate treatment is to form a chemical conversion treatment layer mainly composed of Cr ³⁺ on the plating film by reacting Cr ⁶⁺ in the treatment solution with the plating film.
At the time of this treatment, when an appropriate amount of additives is added to the treatment liquid, these are taken into the chemical conversion treatment layer. Certain additives incorporated in this way are known to be effective in improving properties or imparting new functions, and are used industrially.

For example, when an inorganic colloid such as silica sol or phosphoric acid is added alone or in combination under certain conditions, the corrosion resistance is remarkably improved or the whiteness of the appearance is improved as compared with the case where no inorganic colloid is added.

When a resin is added to form a so-called resin chromate film, various functions such as lubricity, insulation and fingerprint resistance can be imparted depending on the type of the resin. For example, if lubricity is imparted by this method, a chromate-treated steel sheet that can withstand roll forming and pressing required for building materials and home appliances can be manufactured.

[0006] A resin-chromated Zn-plated steel sheet used without painting for applications such as building materials and home appliances requires not only corrosion resistance but also good appearance. However, when the chromate-treated Zn-plated steel sheet is stored in an unpainted state, particularly when stored in a high-temperature and humid environment, the surface is partially or entirely blackened over time, so-called black. In some cases, strange phenomena occur, which causes a problem that the commercial value is significantly impaired in appearance. For example, a resin chromate-treated Zn-based plated steel sheet for building materials, which is often stored in a piled state, often turns black in a high-temperature and wet environment in summer. In particular, a resin-chromated Zn-plated steel sheet having a single-layer resin chromate film as a chemical conversion treatment layer is liable to blackening.

[0007] The cause of the blackened, chromate-treated Zn-based plated steel sheet to appear black is that moisture or oxygen passes through the chemical conversion treatment layer during storage, and oxides, hydroxides, hydrated oxides, etc. are formed on the surface of the plating film. It is thought to be because it is in a form that easily generates or absorbs or scatters visible light.

[0008] The technique relating to the resin chromate treatment of a single layer of a Zn-based plated steel sheet proposed from the viewpoint of blackening suppression is as follows. (1) JP-A-5-287548 (hereinafter referred to as Prior Art 1) This publication mainly contains an aqueous resin polymerized with reduced chromic acid, phosphoric acid, a water-soluble polymer polyol, and an anionic emulsifier. Apply the chromate treatment solution to the surface of the metal material and heat dry to form a hardly soluble chromate film with high corrosion resistance, paint adhesion and blackening resistance, and gel even when mixed with silica sol-based chromate treatment solution Is disclosed.

(2) JP-A-6-192850 (hereinafter referred to as prior art 2) This publication discloses reduced chromic acid, water-dispersible urethane resin,
Non-ionic emulsifier, silicone-modified polyether-based defoamer, treatment liquid containing polymer resin powder, excellent dispersibility of polymer resin powder and pigment, and excellent resistance to blackening during press working. A technique relating to the composition of a chromate treatment liquid is disclosed.

[0010]

However, these prior arts have the following problems.

In other words, the technique disclosed in Prior Art 1 is effective in suppressing gelation due to mixing of the processing liquids in a situation where the processing liquid needs to be exchanged with a silica sol-based chromate processing liquid, Under severe humid environment, blackening cannot be sufficiently suppressed.

The black discoloration which is a problem in the prior art 2 is the black discoloration of the chromate film when the temperature of the mold rises during press working, and is stored in the above-described, particularly, a high-temperature and humid environment. No consideration has been given to blackening, which is a problem in such cases.

[0013] As described above, the technology for suppressing the blackening of a Zn-based plated steel sheet having a single-layer resin chromate film with time has hardly been clarified.

[0014] The present invention has been made in view of such circumstances, and even while having a single layer, while maintaining good corrosion resistance,
It is an object of the present invention to provide a resin chromate-treated Zn-based plated steel sheet having excellent blackening resistance.

[0015]

The present invention provides excellent blackening resistance by limiting the amount of a nonionic emulsifier (nonionic emulsifier) contained per 1 g of a water-dispersible resin in a resin chromate film. Resin-plated Zn-plated steel sheet, the gist of which is water-dispersible resin,
In a chromate-treated Zn-based plated steel sheet containing a nonionic emulsifier and a Cr compound and having a chromate film formed directly on the surface of the Zn-based plating film, the content of the nonionic emulsifier is 10 per 1 g of the water-dispersible resin. Resin chromate treated Zn-based plated steel sheet with excellent blackening resistance of up to 65 mg.

The present inventors have conducted intensive studies to solve the above-mentioned problems of resin-chromate-treated steel sheets based on Zn-plated steel sheets such as Zn-plated steel sheets and Zn-based alloy-plated steel sheets. It was found that the type and the amount of the emulsifier almost inevitably existed in E. coli were closely related to blackening over time.

Most water-dispersible resins (including emulsion-type water-dispersible resins) contain anionic or nonionic emulsifiers used in the process of emulsion polymerization, and therefore contain these resins. These emulsifiers are inevitably present in the resin chromate treatment liquid. Further, as disclosed in Prior Art 2 and Japanese Patent Application Laid-Open No. 5-279867, to suppress gelation of the resin in the resin chromate treatment liquid, to improve continuous coating properties and storage stability, An emulsifier may be added to the treatment liquid when preparing the resin chromate treatment liquid.

In general, anionic emulsifiers lack an effect of suppressing gelation. Therefore, its content in the resin chromate treatment solution is controlled to such an extent that the minimum amount required during the emulsion polymerization of the water-dispersible resin remains, and gelation of the resin in the treatment solution is mainly suppressed by the nonionic emulsifier. There is a need to.

The concentration of the nonionic emulsifier in the treatment liquid has a lower limit concentration necessary for preventing gelation. When the concentration is further increased beyond the lower limit, the blackening resistance is first deteriorated, and when the concentration is further increased, the curing of the chromate film is hindered. The degradation of blackening resistance is due to the excess free nonionic emulsifier compared to the amount required to suppress gelation of the resin, and the formation of Cr ⁶⁺ and plating film on the plating film surface necessary for the formation of a chromate film. Presumably, it has the effect of inhibiting the chromate reaction.

As a result of a detailed study of the relationship between the deterioration of the blackening resistance and the content of the nonionic emulsifier with respect to the water-dispersible resin, an appropriate range of the content of the nonionic emulsifier in the resin chromate film was obtained. Is 10 to 65 per g of water-dispersible resin
mg and more preferably in the range of 13-26 mg / g of resin.

Examples of the nonionic emulsifier include polyoxyethylene alkyl ether, polyoxyethylene alkyl phenyl ether, polyoxyethylene alkyl ester, sorbital alkyl ester, polyoxyethylene solital alkyl ester, and polyoxyethylene polyoxypropylene. A nonionic surfactant such as a block polymer can be used.

The smaller the content of the anionic emulsifier, the better. However, if the content of the anionic emulsifier is small, the effect of the present invention of preventing blackening is not impaired. For example, when the content of nonionic emulsifier is 25 mg per 1 g of resin, blackening does not occur even if the amount of anionic emulsifier required for emulsion polymerization of the water-dispersible resin is up to about 5 mg per 1 g of resin. Absent.

When it is necessary to use an anionic emulsifier in combination, a carboxylate such as soap; a sulfate such as sodium alkyl sulfate or sodium alkyl allyl ether sulfate; a sulfonate such as sodium alkylbenzene sulfonate; Anionic surfactants such as acid ester salts can be used.

As the water-dispersible resin, acrylic resin, urethane resin, polyester resin, polyolefin resin,
Epoxy resin or the like can be used.

The amount of the water-dispersible resin in the chromate film is preferably in the range of 1 to 5 g / m ² . This is because if it is less than 1 g / m ² , important scratch resistance cannot be secured during steel plate processing, and if it exceeds 5 g / m ² , film peeling is likely to occur when subjected to severe processing.

Sources of the Cr compound include chromate, ammonium chromate, chromate (eg, zinc chromate, sodium chromate, barium chromate, etc.), and bichromate (eg, ammonium bichromate, etc.) ) Can be used.

The adhesion amount of the Cr compound in the chromate film is as follows:
The range is preferably 10 to 100 mg / m ^{2 in} terms of metal Cr per one side of the steel sheet. This coating weight is insufficient in corrosion resistance is less than 10 mg / m ^2, When it exceeds 100 mg / m ^2, not only can not be obtained improving corrosion resistance effect corresponding to the amount, color and color unevenness This is because corrosion resistance is likely to be degraded due to abnormalities such as appearance and cohesive failure of the chromate film during steel plate processing.

The chromate film of the present invention may contain a compound which promotes the reaction between the plating film and Cr ⁶⁺ such as phosphoric acid or a sulfuric acid compound or a fluorine compound as long as the effects of the present invention are not impaired. .

The Zn-based plating according to the present invention can be used in addition to pure zinc.
In addition to Fe, Ni, Co, Mn, Cr, Al, Mo, Si, Sn, Pb, Nb
And metals or oxides such as Ta, hydroxides, or
Widely includes Zn-based alloy plating containing a predetermined amount of one or more selected from organic substances and the like.

The Zn-based plated steel sheet of the present invention has the above-mentioned Zn-based plated film on a steel sheet as a base material,
The method for forming the film is not particularly limited, and includes a film formed by a known method such as a hot-dip plating method, an electroplating method, and a vapor phase plating method.

[0031]

BEST MODE FOR CARRYING OUT THE INVENTION The resin-chromated Zn-plated steel sheet of the present invention has a water-dispersible resin, a Cr compound and a water-dispersible resin in an amount of 10 to 65 mg per 1 g of the surface of the Zn-based plated film. This is a steel sheet obtained by applying a chromate treatment solution containing a nonionic emulsifier and then drying to form a chromate film. As a method for applying the chromate treatment liquid, an application type treatment using a roll coater is desirable.

[0032]

EXAMPLES Examples of the present invention will be described below in comparison with comparative examples.

The following Example 1 was applied to the surface of a Zn-based plated steel sheet.
A resin chromate-treated steel sheet having a resin chromate film formed by the method described in Example 2 was prepared, and the amounts of the Cr compound, resin and emulsifier attached to the prepared steel sheet are shown below.
After measurement by the methods (1) and (2), the blackening resistance was evaluated by the test method (3) shown below. (1) Measurement of the amount of attached Cr compound after film formation The amount of attached Cr compound (the amount of metal Cr conversion) after film formation was measured by the calibration curve method of X-ray fluorescence analysis.

(2) Measurement of Attached Amount of Resin and Emulsifier The amount of attached resin was measured by a calibration curve method of a fluorescent X-ray analysis method. The amount of the emulsifier in the resin chromate film was determined from the amount of the emulsifier added to the amount of the resin added in the step of adjusting the resin solution and the measured amount of the resin adhered.

(3) Blackening resistance test The stack was left standing in an environment at a temperature of 80 ° C and a humidity of 95% for 10 days, and the L value after the test (lightness index in the color difference formula of Hunter of JIS Z8730 (1980) 6.3.2) ) Was evaluated for blackening resistance. The evaluation criteria are as follows. ○: L value change is less than 2 △: L value change is 2 to 5 ×: L value change is more than 5

The types of Zn-plated steel sheet, water-dispersible resin, and nonionic emulsifier studied in the following Examples 1 and 2 are as follows. (1) Zn-plated steel sheet electrical Zn plated steel sheet (plating species symbol: EG): the coating weight per one side 20 g / m ² melt Zn plated steel sheet (plating species symbol: GI): a coating weight per one side 40 g / m ² Alloy Hot-dip Zn-plated steel sheet (Plating type symbol: GA): 45 g / m ² per coating weight per side 5% Al-Zn alloy coated steel sheet (Plating type symbol: GF): 60 g / m ² per coating weight

(2) Water-dispersible resin Acrylic resin emulsion Urethane resin emulsion Polyester resin emulsion Polyolefin resin emulsion Epoxy resin emulsion

(3) Nonionic emulsifier polyoxyethylene alkyl ether polyoxyethylene alkyl phenyl ether polyoxyethylene alkyl ester sorbital alkyl ester polyoxyethylene solital alkyl ester polyoxyethylene polyoxypropylene block polymer

(Example 1) Cr-plated steel sheet
O ₃ is 3 g / l in terms of metal Cr, acrylic resin emulsion (water-dispersible resin) is 225 g / l, and polyoxyethylene alkyl ether (nonionic emulsifier) is contained in the proportions shown in Table 1.
A treatment liquid having a Cr reduction ratio of 30% was applied by a roll coater method, and heated by a hot air drying furnace until the steel sheet temperature reached 80 ° C. to dry the treatment liquid to form a resin chromate film. At this time, the adhesion amounts of the Cr compound and the water-dispersible resin were adjusted to 20 mg / m ² and 1.5 g / m ² , respectively, by a coating roll. When the concentration of the nonionic emulsifier was less than 10 mg / m ² , a steel sheet having a uniform chemical conversion treatment film could not be produced because the resin gelled in the treatment solution.

The effect of the content of the nonionic emulsifier on blackening resistance was evaluated for the prepared steel sheet. Show evaluation results
Figure 1 shows.

[0041]

[Table 1]

As is clear from Table 1, the invention examples in which the content of the nonionic emulsifier with respect to the water-dispersible resin is within the range of the present invention are compared with the comparative examples in which this content is out of the range of the present invention. , All show good blackening resistance.

Example 2 Under the same conditions as in Example 1, a steel sheet was prepared in which the types of the water-dispersible resin and the nonionic emulsifier were changed. As a water-dispersible resin, urethane resin, polyester resin, polyolefin resin, epoxy resin, as a nonionic emulsifier, polyoxyethylene alkyl phenyl ether, polyoxyethylene alkyl ester,
Sorbital alkyl esters, polyoxyethylene sorbital alkyl esters, and polyoxyethylene polyoxypropylene block polymers were newly investigated.

The prepared steel sheet was evaluated for blackening resistance. Table 2 shows the steel sheets subjected to the evaluation and the evaluation results.

[0045]

[Table 2]

As can be seen from Table 2, regardless of the type of the water-dispersible resin and the emulsifier, the invention examples in which the content of the nonionic emulsifier with respect to the water-dispersible resin is within the range of the present invention are as follows. All of them show good resistance to blackening as compared with Comparative Examples outside the range of the present invention.

The steel sheet of the invention obtained as described above has excellent corrosion resistance.

[0048]

According to the present invention, it is possible to obtain a resin-chromate-treated Zn-plated steel sheet which is excellent in blackening resistance while maintaining good corrosion resistance. The steel sheet of the present invention is particularly effective when used in applications requiring excellent blackening resistance, such as building materials used in a high-temperature and high-humidity environment in summer, where blackening is likely to occur.

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-6-192850 (JP, A) JP-A-6-192849 (JP, A) JP-A-5-279867 (JP, A) JP-A-56-1982 29679 (JP, A) JP-A-3-215683 (JP, A) JP-A-3-215681 (JP, A) JP-A-3-215682 (JP, A) (58) Fields investigated (Int. ⁷ , DB name) C23C 22/00-22/86

Claims (1)

(57) [Claims] 1. A chromate-treated Zn-plated steel sheet containing a water-dispersible resin, a nonionic emulsifier, and a Cr compound and having a chromate film directly formed on the surface of the Zn-based plating film, wherein the nonionic emulsifier is contained. A resin chromate-treated Zn-plated steel sheet having excellent blackening resistance, wherein the amount is 10 to 65 mg per 1 g of the water-dispersible resin.