JP3461741B2 - Pre-coated steel sheet with excellent corrosion resistance - Google Patents

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a precoated steel sheet having excellent corrosion resistance, and particularly to a precoated steel sheet containing no poisonous hexavalent chromium.

[0002]

2. Description of the Related Art For home electric appliances, building materials, automobiles, etc., prepainted steel coated with a colored organic film has come to be used in place of conventional postpainted products that have been painted after processing. . This steel sheet is obtained by coating a rustproof steel sheet and a plated steel sheet with an organic coating, and has the characteristics of good workability and good corrosion resistance while having an aesthetic appearance.

For example, Japanese Unexamined Patent Publication (Kokai) No. 8-168723 discloses a technique for obtaining a precoated steel sheet having excellent workability, stain resistance and hardness by defining the structure of the coating. On the other hand, Japanese Unexamined Patent Publication No. 3-100180 discloses a precoated steel sheet whose end surface corrosion resistance is improved by using a specific chromate treatment liquid. These precoated steel sheets have corrosion resistance, workability and paint adhesion due to the combined effect of chromate treatment and an organic coating film containing a chromium-based rust-preventive pigment. It is used for general purpose now.

When a chromium-based rust preventive pigment is added to the coating film, it is common to add it to the lower layer coating film and then provide the upper layer coating film thereon. By this, the elution of hexavalent chromium outside the coating film is prevented. On the other hand, JP-A-7-51620 discloses a pigment that supplies phosphate ions onto a surface-treated steel sheet that has been treated with zinc phosphate,
A precoated steel sheet having good corrosion resistance by providing a coating layer mixed with a pigment that supplies vanadate ions is disclosed, but a precoated steel sheet having a coating layer subjected to chromate treatment and further added with a chromium-based rust preventive pigment. The corrosion resistance is inferior to that of, so that it is rarely actually used. Further, the rust preventive pigment in the precoated steel sheet is added to the lower layer coating film in the same manner as when the chromium-based rust preventive pigment is used.

[0005]

The hexavalent chromium contained in the chromate treatment and the chromium-based pigment is water-soluble,
The elution has the property of repairing scratches on the coating film that have occurred in the coating film. Therefore, it has been used to date for imparting corrosion resistance. However, due to the toxicity problem of hexavalent chromium which may be eluted from an organic film containing a chromate treatment and a chromium-based rust preventive pigment, demands for a chromium-free rust preventive treatment and a non-chrome organic film have recently been increased.

Therefore, it is an object of the present invention to provide a non-chrome precoated steel sheet having excellent corrosion resistance in order to meet such demands.

[0007]

According to the present invention, a steel plate or a plated steel plate has an undercoating layer on at least one surface thereof, and a lower rust-preventive coating layer containing a rust-preventive pigment thereon, and further on top of that. By a precoated steel sheet having an upper rust-preventive coating layer containing a rust-preventive pigment which simultaneously contains an ion source releasing vanadate and an ion source releasing phosphate.

The rust preventive pigment contained in the lower rust preventive coating film is also preferably a rust preventive pigment containing both an ion source releasing vanadate ions and an ion source releasing phosphate ions. The amount of the rust preventive pigment contained in the upper and lower rust-preventive coating layers, which simultaneously contains the vanadate ion-releasing ion source and the phosphate ion-releasing ion source, is 1 with respect to 100 parts by weight of the dry coating resin. It is preferable that the amount is -100 parts by weight.

The undercoat layer of the precoated steel sheet of the present invention is
A water-based organic resin containing no chromic acid is highly desirable from the viewpoint that the non-chromization of the precoated steel sheet is completely achieved.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION The anticorrosion treatment of a precoated steel sheet of the present invention was developed for the purpose of preventing the corrosion of a steel sheet and a plated steel sheet, and includes cold rolled steel sheet, hot rolled steel sheet, hot dip galvanized steel sheet, and electrogalvanized sheet. Steel sheet, hot-dip galvanized steel sheet,
Commonly known steel plates and plated steel plates such as aluminum plated steel plates, aluminum-zinc alloyed plated steel plates, and stainless steel plates can be applied.

The steel sheet and the plated steel sheet can be subjected to usual treatments such as washing with hot water and degreasing with alkali before the surface treatment. The precoated steel sheet of the present invention contains a rust preventive pigment in a rust preventive coating layer, and the rust preventive pigment contained in the upper rust preventive coating layer is an ion source releasing vanadate ion and an ion releasing phosphate ion. It is characterized by including sources at the same time.

The rust preventive pigment may release both phosphate ions and vanadate ions in an environment where water and oxygen are present. Phosphate ion rarely exists alone in water, and exists in various forms, for example, as a polycondensation polymer, but it is understood that even in such a case, it is included in the concept of “phosphate ion”. It is also understood that vanadate ions also include polymerized vanadate ions.

The rust preventive pigment suitable for use in the present invention is obtained by firing and pulverizing a mixture containing a phosphoric acid compound, a vanadic acid compound, and optionally a network modifying ion source and / or a substance on glass. It is preferable that the phosphoric acid compound used in the present invention acts on the vanadium compound by heating to form a calcined organism that is not a simple mixture, such as orthophosphoric acid, condensed phosphoric acid, orthophosphate or condensed phosphate of various metals. , Phosphorus pentoxide, phosphate minerals, commercially available complex phosphate pigments, or mixtures thereof. Specific examples of such a phosphoric acid compound include phosphate minerals such as monetite, torphyrite, witlockite, xenotime, starcolite, struvite, and orthorite. Specific examples of commercially available composite phosphoric acid pigments include polyphosphoric acid silica and the like. Examples of condensed phosphoric acid include polyphosphoric acid and metaphosphoric acid. As the condensed phosphate, for example, metaphosphate, tetrametaphosphate, hexametaphosphate,
Pyrophosphate, acidic pyrophosphate, tripolyphosphate,
Alternatively, a mixture thereof may be used. The metal species forming the phosphate is not particularly limited, and alkali metal,
Examples thereof include alkaline earth metals, metal species of other typical elements, and transition metals. Examples of preferable metals include magnesium, calcium, strontium, barium, titanium, zirconium, manganese, iron, cobalt, nickel, zinc, aluminum and the like.

The vanadium compound used in the present invention is vanadium
Any of compounds with valence of 0, 2, 3, 4, 5
One or more can be used, of which pentavalent vanadium compounds
It is desirable to include one or more of The form is metal,
Oxides, hydroxides, metal oxyacid salts, halides, sulfuric acid
And vanadyl compounds. Vanadium compound
Specific examples of the product include vanadium (II) compounds, for example,
Vanadium (II) oxide, vanadium (II) hydroxide, etc.
Nadium (III) compounds such as vanadium (III) oxide (V
₂O₃) Etc., vanadium (IV) compounds such as vanadium oxide
Um (IV) (V ₂O_Four), Vanadyl halide (VOX
₂) Etc., vanadium (V) compounds such as vanadium oxide
(V) (V₂O_Five) Etc., vanadates, for example, various
Metal orthovanadate, metavanadate or pi
Rovanadate, vanadyl halide (VOX₃)etc,
Also, a mixture of these may be mentioned. Vanadic acid metal
The seeds include the same as those shown for phosphate.

The amount of the rust-preventive pigment contained in the upper rust-preventive coating layer, which simultaneously contains the vanadate ion-releasing ion source and the phosphate ion-releasing ion source, is such that the dry coating resin 10
It is preferably 1 to 100 parts by weight with respect to 0 parts by weight. When it is less than 1 part by weight, the corrosion resistance is poor, and when it is 100 parts by weight or more, the workability of the coating film is deteriorated, which is not suitable. A coloring pigment may be added to the upper rust-preventive coating layer together with the rust-preventive pigment in order to improve the design. Titanium oxide (T
iO ₂ ), zinc oxide (ZnO), zirconium oxide (Z
rO ₂ ), calcium carbonate (CaCO ₃ ), barium sulfate (BaSO ₄ ), alumina (Al ₂ O ₃ ), kaolin clay, carbon black, iron oxide (Fe ₂ O ₃ , Fe)
Inorganic pigments such as ₃ O ₄ ) and generally known coloring pigments such as organic pigments can be used. The amount of the color pigment added is arbitrary, and several types can be mixed according to the desired color and the required amount can be added. However, the rust-preventive pigment itself, which includes an ion source that releases vanadate ions and an ion source that releases phosphate ions at the same time, is white. It is possible to obtain the appearance of the white coating film used.

The thickness of the upper rust-preventive coating layer is preferably 1 to 25 μm, and if it is less than 1 μm, the corrosion resistance deteriorates, and
If it exceeds μm, the processability of the coating film is poor. As the base resin for the upper rust preventive coating layer, generally known resins such as polyester resin, urethane resin, acrylic resin, epoxy resin and melamine resin can be used.

The upper rust-preventive coating layer can be applied by a generally known application method such as roll coating, curtain flow coating, air spray, airless spray, dipping, bar coating and brush coating. In the pre-coated steel sheet of the present invention, the lower rust-preventive coating layer also uses a rust-preventive pigment that simultaneously contains an ion source that releases vanadate ions and a phosphate ion in the rust-preventive pigment, and in addition to good corrosion resistance, It is also environmentally friendly and suitable.

The rust-preventive pigment contained in the lower rust-preventive coating layer which simultaneously contains an ion source releasing vanadate ions and an ion source releasing phosphate ions is the one used in the above-mentioned upper rust-preventing coating layer. The same as can be used. The base resin for the lower rust preventive coating layer may be the same as that used for the upper rust preventive coating layer. Similar to the upper rust-preventing coating layer, the amount of the rust-preventing pigment containing the ion source releasing vanadate ions and the ion source releasing phosphate ions in the lower rust-preventing coating layer is 100 wt. It is preferably 1 to 100 parts by weight with respect to parts. When it is less than 1 part by weight, the corrosion resistance is poor, and when it is 100 parts by weight or more, the workability of the coating film is deteriorated, which is not suitable.

The thickness of the lower rust-preventive coating film layer is preferably 1 to 25 μm, and if it is less than 1 μm, the corrosion resistance becomes poor, and
If it exceeds μm, the processability of the coating film is poor. The coating method of the lower rust-preventive coating layer is a generally known coating method, for example, low coating,
It can be performed by air spray, airless spray, dipping, bar coating, brush coating and the like.

In the precoated steel sheet of the present invention, it is more preferable to use a water-soluble resin containing no hexavalent chromium in the undercoat layer because the precoated steel sheet has good corrosion resistance and can completely achieve dechromization. . A suitable water-soluble resin used for the undercoat layer includes a resin which is originally water-insoluble but can be in a state in which the insoluble resin is finely dispersed in water (water-dispersible resin), such as an emulsion or a suspension.

Resins usable as such water-soluble resins include polyolefin resins, acrylic olefin resins, polyurethane resins, acrylic resins, polycarbonate resins, epoxy resins, polyester resins, phenol resins, and other thermosetting resins. Examples of the resin include a resin, and a crosslinkable resin is more preferable. Particularly preferred resins are acrylic olefin resins, polyurethane resins, and mixed resins of both. You may mix and use 2 or more types of these water-soluble resins.

Further, it is said that a phosphoric acid compound, tannic acid, silica, a silane coupling agent, etc. are effective in the corrosion resistance and coating adhesion in the undercoating layer using a water-soluble resin. It does not depart from the invention to add generally known additives. When the water-soluble resin is used, the thickness of the undercoat layer is 0.1 μm as a dry film thickness.
It is preferably m or more. If it is less than 0.1 μm, the rust preventive power is insufficient. On the other hand, if the film thickness is too thick, it is uneconomical as a base treatment layer and is inconvenient for coating. Therefore, the upper limit of the film thickness is preferably 40 μm or less.

The method of applying the undercoat layer is not particularly limited, and generally known coating methods such as roll coating, air spraying, airless spraying and dipping can be employed.

[0024]

[Example] The coated amount of galvanized steel sheet is 20 g / side.
0.6 mm thick electrogalvanized steel sheet with both sides plated at m ² , and the amount of galvanized coating is 60 g / m per side
FC-364S (manufactured by Nippon Parkerizing Co., Ltd.) with a hot dip galvanized steel sheet having a thickness of 0.6 mm and plated on both sides with ²
It was degreased by immersing it in an aqueous solution having a concentration of 2% by weight and a temperature of 60 ° C. for 10 seconds, washed with water, and then dried. Then, a water-soluble resin or chromate treatment shown in Table 3 was applied as a base treatment layer by a roll coater and dried in a hot air drying oven. The ultimate plate temperature during drying was 150 ° C.

The water-soluble resin used as the undercoating layer contains ammonium phosphate in an amount of 12% with respect to the treatment liquid.
50 ppm and tannic acid (manufactured by Fuji Chemical Industry Co., Ltd .: tannic acid AL) were added to the treatment liquid at 10,000 ppm. Next, the components shown in Table 2 were mixed to prepare an anticorrosive pigment, and the components shown in Table 3 were baked under the conditions shown in the same table and then pulverized to obtain a phosphate ion source and vanadate. A rust preventive pigment containing both ion sources was prepared. Next, the prepared primer coating containing the rust preventive pigment was applied as a lower rust preventive coating layer by a roll coater, and cured and dried in an induction heating furnace in which hot air was blown so that the reached plate temperature was 220 ° C.

Commercially available polyester-based primer coatings, epoxy resin-based primer coatings, urethane resin-based primer coatings are used as the primer coatings, and if necessary, chromium-based rust preventive pigments to be described later are prepared. The anticorrosion pigment was changed to the one used. Next, on the lower rust-preventive coating layer, the top coating was further applied as the upper rust-preventing coating layer with a roller curtain coater, and cured by an induction heating furnace with hot air blow so that the reached plate temperature was 220 ° C. Dried.

Commercially available polyester clear paints, epoxy resin clear paints, urethane resin clear paints were used as the top paints, and those prepared by adding the rust-preventive pigment prepared later were used. The plate was water-cooled after each curing and drying process. The following evaluation was performed on the precoated steel sheet thus produced. 1. Adhesion of coating film The plate after coating was put in a 1 mm square grid on the coated surface with a cutter knife and extruded by 7 mm with an Erichsen tester so that the coated surface was convex, and then a tape peeling test was performed. JIS-K5400.8.2, and J for how to insert crosses, how to extrude Erichsen, and how to peel off tape.
It was carried out according to the method described in IS-K5400.8.5. Further, the evaluation after peeling the tape is performed according to JIS-K5400.
The evaluation example shown in 8.5 was used, and a rating of 10 was given as ◯, a rating of 6 to less than 10 was given as Δ, and a rating of less than 6 was given as x. 2. Bending test of coating film The coated plate was bent by 180 °, and the coating film in the processed portion was observed with a 10 times magnifying glass to check for cracks in the coating film. In addition, an adhesive tape was attached to the processed portion, and the remaining state of the coating film was visually observed when the adhesive tape was peeled off vigorously. The bending process was performed in a 20 ° C. atmosphere with a 0.6 mm spacer interposed therebetween. The evaluation of coating film cracking is ○ when there is no coating film cracking, Δ when there is some cracking in the coating film,
When there was a clear crack in the coating film visually, it was evaluated as x. Further, the evaluation of the coating film residual state after peeling with a tape is ○ when the coating film is not peeled at all and remains on the plated steel sheet, Δ when the coating film is partially peeled, and almost the bending portion When peeling was observed over the entire surface, it was evaluated as x. 3. The plate after corrosion resistance coating was subjected to a salt spray test by the method described in JIS-K5400.9.1. The test time was 120 hours for the electrogalvanized steel sheet and 240 hours for the hot-dip galvanized steel sheet. The evaluation method of the coating film of the cross cut part is
When the maximum swelling width on one side of the cross cut was less than 1 mm, it was evaluated as ○, when 1 mm or more and less than 3 mm, Δ, and when 3 mm or more. In addition, the above-mentioned salt spray test was also carried out on a flat plate manufactured so that the return (burr) at the time of cutting came to the evaluation surface side of the coated steel plate (to be the lower burr),
The swelling width of the coating film from the end face was observed. The evaluation method of the end face is ◯, 3 mm when the swelling width from the end face is within 3 mm.
△ when above 5 mm or less × when above 5 mm
It was evaluated. 4. Due to the structure of the toxic pre-coated steel sheet, those that do not contain hexavalent chromium that is environmentally toxic at all are ○, because the outermost surface of the pre-coated steel sheet that contains hexavalent chromium is coated with a resin that does not contain hexavalent chromium, If the hexavalent chromium is less likely to elute outside the coating film, it contains Δ, chromium, and the coating film coated on the outermost surface of the precoated steel sheet also contains hexavalent chromium,
Those that might be eluted out of the coating film were evaluated as x.

The evaluation results will be described below. Examples 1 to 23, 25 to 27, 31, 32, 34, 37 of the present invention
Nos. 39 to 39 are pre-coated steel sheets conventionally used in general (providing a lower layer rust-preventive coating film to which a rust-preventive pigment is added on a chromate-treated layer, and further, an upper-layer coating layer to which no rust-preventive pigment is added. Compared with Comparative Examples 5 and 7), the pre-coated steel sheet provided with No. 1 is preferable since it does not contain chromium at all, has less toxicity, and has excellent corrosion resistance. In Example 24, since the amount of the rust preventive pigment added to the upper rust preventive coating film layer is small, the corrosion resistance is equivalent to that of the conventional precoated steel sheet (Comparative Examples 5 and 7), but it does not contain chromium at all and has low toxicity. Is preferred. Example 29 has the same level of corrosion resistance as the conventional precoated steel sheet (Comparative Examples 5 and 7) because the amount of the rust preventive pigment added to the lower rust preventive coating film is small, but does not contain chromium at all and has low toxicity. Is preferred. In Example 33, the adhesion amount of the base treatment layer was small, so that the conventional precoated steel sheet (Comparative Examples 5 and 7) was used.
And corrosion resistance are at the same level, but do not contain chromium at all,
It is preferable because it has low toxicity. In Example 28, since the amount of the rust-preventive pigment added to the upper rust-preventive coating film layer was too large, the workability of the coating film and the adhesion of the processed portion were inferior as compared with the conventional precoated steel sheet (Comparative Example 5.7). It is suitable because it has good corrosion resistance, contains no chromium, and has low toxicity. In Example 30, since the amount of the rust-preventive pigment added to the lower rust-preventive coating film is too large, the workability of the coating film and the adhesion of the processed portion are inferior to those of the conventional precoated steel sheet (Comparative Example 5.7), but the corrosion resistance is low. It is suitable because it has a good viscosity, contains no chromium, and has low toxicity.

Since Examples 35, 36 and 40 contain chromium in the undercoating layer or the lower rust-preventive coating film, they have the same toxicity as the conventional precoated steel sheets (Comparative Examples 5 and 7), but are excellent in corrosion resistance and suitable. Is. On the other hand, Comparative Examples 1, 2, and 6 are not suitable because chromium is likely to be eluted on the surface of the precoated steel sheet and toxicity is high. Further, in Comparative Examples 2 and 3, the corrosion resistance and toxicity are the same level as those of the conventional precoated steel sheets (Comparative Examples 5 and 7), and there is no effect.

[0030]

Industrial Applicability According to the present invention, it is possible to provide a precoated steel sheet having excellent coating film adhesion, coating film processability, and corrosion resistance, without using hexavalent chromium, which is environmentally toxic. . Therefore, it can be said that the present invention has an extremely high industrial value.

[0031]

[Table 1]

[0032]

[Table 2]

[0033]

[Table 3]

[0034]

[Table 4]

[0035]

[Table 5]

[0036]

[Table 6]

─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Hiroyasu Furukawa 1 Kimitsu City, Chiba Prefecture Nippon Steel Stock Company Kimitsu Works (56) Reference JP-A-7-52309 (JP, A) 7-51620 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) C23C 22/42 B05D 7/14 B32B 15/08 C23C 22/40

Claims (5)

(57) [Claims] 1. An ion which has a surface treatment layer on at least one surface of a steel plate or a plated steel plate, has a lower rust-preventive coating layer containing a rust-preventive pigment thereon, and further releases vanadate ions. A precoated steel sheet having an upper rust-preventive coating film layer containing a rust-preventive pigment that simultaneously contains a source and an ion source that releases phosphate ions. 2. The rust preventive pigment contained in the lower rust preventive coating layer is also
The precoated steel sheet according to claim 1, which is a rust-preventive pigment that simultaneously contains an ion source that releases vanadate ions and an ion source that releases phosphate ions. 3. An addition amount of a rust preventive pigment contained in the upper rust preventive coating film layer, which simultaneously contains an ion source releasing vanadate ion and an ion source releasing phosphate ion, is 100 parts by weight of dry coating resin. It is 1-100 weight part with respect to, The pre-coated steel plate of Claim 1 or 2 characterized by the above-mentioned. 4. The amount of the rust preventive pigment contained in the lower rust preventive coating layer, which simultaneously contains an ion source releasing vanadate ion and an ion source releasing phosphate ion, is 100 parts by weight of dry coating resin. The pre-coated steel sheet according to any one of claims 1 to 3, wherein the pre-coated steel sheet is 1 to 100 parts by weight. 5. The precoated steel sheet according to claim 1, wherein the base treatment layer is made of a resin containing no hexavalent chromium.