JPH10264300A - High anticorrosive precoat steel plate - Google Patents

Abstract

PROBLEM TO BE SOLVED: To raise the anticorrosion property in a plane part and anticorrosion property in a cut part of a cold rolled steel plate by forming a primer layer on one surface of a chromate-treated film being specified in an adhering quantity and component, coating a finish coat thereon, and coating a primer on the other surface. SOLUTION: The chromate treatment film layer is formed by coating a baking type chromate composition containing water soluble chromic compound and zinc powder on the entire surface of a cold rolled steel plate subjected to a degreasing and descaling treatment, and its adhering quantity is 0.2-14 g/m<2> . On a chromate treatment film at the surface side, a finish coat is coated via the primer, and a primer is coated on a chromate-treated film at the rear side. Herein, selected for the primer are primers of urethane, polyester, epoxy modified urethane, and epoxy modified polyester. A polyester coating is employed for finish coating.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a high corrosion-resistant precoated steel sheet, and more particularly to a high corrosion-resistant precoated steel sheet using a cold-rolled steel sheet as a substrate, which is suitably used for home electric appliances, automobile parts, building members and the like. .

[0002]

2. Description of the Related Art Conventionally, in the consumer electronics and building materials industries, a finished steel sheet has been degreased, subjected to a chemical conversion treatment, and then subjected to a final coating.

[0003] However, in order to avoid problems caused by soaring labor costs, steel sheets coated with zinc or zinc-based alloy are outsourced to a coated steel sheet manufacturer, and the coated steel sheet manufacturer supplies a phosphate-based chemical treating agent or A chemical conversion treatment with a chromate-based chemical conversion treatment agent was performed, followed by a primer treatment as needed, and finally a top coat was applied. Then, pre-coated steel sheets manufactured by painted steel sheet manufacturers have been supplied to the home appliance industry, the building material industry, and the like.

[0004] In recent years, pre-coated steel sheets based on cold-rolled steel sheets have been studied for the purpose of cost reduction due to problems such as a delay in economic recovery and a further rise in labor costs. Here, the cold-rolled steel sheet is galvanized,
Alternatively, it refers to a steel sheet that has not been subjected to zinc-based alloy plating.

In general, the performance required for a precoated steel sheet is considered to be important not only in workability, stain resistance, and chemical resistance, but also in corrosion resistance between a flat portion and a cut portion such as a cut end portion that appears when the precoated steel sheet is cut. .

[0006] However, the cost of the precoated steel sheet based on the cold-rolled steel sheet is greatly reduced, but a chemical conversion treatment agent (for example, the above-mentioned zinc phosphate-based chemical conversion agent) conventionally used for galvanized steel sheet is used. Treatment agents, chromate-based chemical conversion treatment agents, etc.) could not sufficiently impart the corrosion resistance of the plane portion and the cut portion. That is, the generation of red rust in the flat part and the cut part was remarkably fast.

[0007] On the other hand, there is also a paint in which a chromium-based rust-preventive pigment is added to a primer to improve corrosion resistance. However, when a paint containing such a conventional chromium-based rust-preventive pigment is used as a primer for a galvanized steel sheet, a large rust-preventive effect can be exhibited, but a sufficient rust-preventive effect can be obtained for a cold-rolled steel sheet. The inability to demonstrate this has been clarified by the inventors' research.

Further, as can be seen in Zincrometal (trade name), JP-A-54-61277, JP-A-1-14867 and JP-A-1-20059,
There are cold-rolled coated steel sheets obtained by applying a paint containing zinc powder to a cold-rolled steel sheet. These cold-rolled steel sheets exhibit a red rust preventing ability in a plane portion, but do not have a sufficient effect of suppressing red rust by a sacrificial protective action on an end face.

An object of the present invention is to solve the above-mentioned problems and to provide a pre-coated steel sheet which is made of a cold-rolled steel sheet and which has excellent corrosion resistance at a flat portion and at an end portion (cut portion). .

Another object of the present invention is to provide a precoated steel sheet having both high anticorrosion properties and excellent workability.

[0011]

A first means for solving the above problems is a baking type chromate composition containing a degreased and descaled cold-rolled steel sheet, a water-soluble chromate compound and zinc powder. Is coated on the surface of the cold-rolled steel sheet and then baked to form an adhesion amount of 0.2 to 1
A chromate conversion coating layer of 4 g / m ² , a primer formed on one surface of both surfaces of the cold-rolled steel sheet of the chromate conversion coating, which is treated as a front side, and a surface of the primer formed on the one surface A topcoat paint painted on, having a primer coated on the other surface of the chromate conversion coating, which is treated as the back side of both surfaces of the cold-rolled steel sheet, wherein the primer is a urethane-based primer, a polyester-based primer, or an epoxy. A modified urethane-based primer, and at least one primer selected from the group consisting of epoxy-modified polyester-based primers, wherein the overcoat is a high corrosion-resistant precoated steel sheet characterized by being a polyester-based paint, and The second means for degreasing and descaling is And cold-rolled steel sheet, which is formed by baking the baking-type chromate composition containing a water-soluble chromic acid compound and zinc powder after coating the surface of the cold-rolled steel sheet, the adhesion amount 0.2~14g / m ² The chromate conversion coating layer, and the chromate conversion coating, a topcoat paint coated on one surface treated as the front side of both surfaces of the cold-rolled steel sheet, and the chromate conversion coating, as the back side of both surfaces of the cold-rolled steel sheet. A primer coated on the other surface to be handled, wherein the primer is at least one primer selected from the group consisting of a urethane-based primer, a polyester-based primer, an epoxy-modified urethane-based primer, and an epoxy-modified polyester-based primer. High corrosion resistance, characterized in that the top coating is a polyester coating A third means for solving the above-mentioned problem is a pre-coated steel sheet, wherein the film thickness of the primer in the first means or the second means is 1 to 15 μm. A fourth means for solving the above-mentioned problems is a high corrosion resistance pre-coated steel sheet, wherein the first means or the second means wherein the film thickness of the top coat in the first means or the second means is 5 to 30 μm. Means of high corrosion resistance pre-coated steel sheet.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION A high corrosion-resistant precoated steel sheet according to the present invention comprises a cold rolled steel sheet as a base material, a chromate conversion coating layer formed on both surfaces thereof, and a chromate conversion layer on a side which is regarded as a front side surface. On the conversion coating, via a primer,
Alternatively, it has a top coat coated without a primer, and a primer coated on the chromate conversion coating on the back side and the side to be viewed.

This cold-rolled steel sheet is not particularly limited as long as it is not subjected to plating treatment and is a degreased and descaled rolled steel sheet.

The chromate conversion coating layer is formed by applying a baking type chromate composition containing a water-soluble chromate compound and zinc powder to the entire surface of the cold-rolled steel sheet, especially the front side and the back side, and then baking. It is formed. When the chromate conversion coating layer is formed on the front side and the back side of the cold rolled steel sheet, the chromate conversion coating existing on the front side and the back side even if the cut end face is exposed by cutting the cold rolled steel sheet. The sacrificial protection action is provided by the zinc powder in the layer, which prevents corrosion of the cut end face. As described above, it is important to form a chromate conversion coating layer on both surfaces of the cold-rolled steel sheet, such as the front and back side surfaces of the cold-rolled steel sheet. If the chromate conversion coating layer is formed only on one side of the cold-rolled steel sheet, or if the chromate conversion coating layer is not formed on both sides, the cut end face of the cold-rolled steel sheet is easily corroded. Thus, the object of the present invention cannot be achieved.

The baking type chromate composition is not particularly limited as long as it contains the water-soluble chromate compound and zinc powder.

The water-soluble chromic acid compound is not particularly limited, and includes compounds known per se.
For example, chromic anhydride, chromic acid, water-soluble metal salts of chromate, bichromate and the like can be mentioned. Of these, chromic anhydride is preferably used, and calcium chromate, magnesium chromate, zinc dichromate, potassium dichromate, sodium dichromate, magnesium dichromate, calcium dichromate and the like are also preferable. Can be used.

The zinc powder may be in any shape, but is preferably in the form of flakes (also referred to as flakes), and particularly preferably has an average thickness of 0.01 to 1 μm.
Preferably, the length is 0.1 to 0.5 μm and the length of the longest part is 20.
It is preferable that the flakes have a size of not more than μm, preferably not more than 15 μm. The zinc powder may be used together with the aluminum powder.

The content of the water-soluble chromate compound in the baking type chromate composition is 1 to 12% by weight, preferably 2 to 8% by weight, based on the finally obtained baking type chromate composition. %. The content ratio of the zinc powder in the baking type chromate composition is 10 to 40% by weight, and preferably 15 to 30% by weight, based on the finally obtained baking type chromate composition.

The baking type chromate composition may further contain boric acid or boron oxide, a cobalt salt, a nickel salt, an oxohydroxy low molecular weight ether, Conditioner,
A wetting agent, water, an organic solvent and the like are blended.

As the boric acid, generally available orthoboric acid is suitable. If necessary, metaboric acid and tetraboric acid can be used instead of or together with the orthoboric acid. When boric acid and / or boron oxide is blended, its content in the baking type chromate composition is generally 0 to 9% by weight, preferably 0.5 to 5% by weight, based on the whole baking type chromate composition.
5% by weight. When the content of boric acid and / or boron oxide is within the above range, it is possible to obtain a composition exhibiting a more excellent anticorrosion action in both saline and freshwater environments.

The cobalt salt and the nickel salt may contain either of them in the baking type chromate composition, or may contain both of them, and may contain any of the cobalt salt and the nickel salt. In this case, plural kinds of cobalt salts or plural kinds of nickel salts may be used in combination.

In any case, the compounding amount of the cobalt salt and / or the nickel salt is usually 0 to 12% by weight, preferably 1 to 10% by weight based on the whole baking type chromate composition.
It is.

As the oxohydroxy low molecular weight ether, glycol and its low molecular weight ether type polymer can be used, and specifically, ethylene glycol, propylene glycol, diethylene glycol, tetraethylene glycol, dipropylene glycol, triethylene glycol Glycol, tripropylene glycol, diacetone alcohol and similar homologs and mixtures thereof can be mentioned.

When these oxohydroxy low-molecular-weight ethers are contained, they act as a reducing agent on the water-soluble chromic acid compound to convert it into a chromic acid polymer,
In addition, when the baking type chromate composition is applied to the surface of the cold-rolled steel sheet and then heated, it is volatilized gradually in the course of forming the coating film, thereby preventing the solvent and the like from evaporating to a boiling point, and providing uniform chromate. The formation of the coating can be facilitated.

The pH adjuster is effective when used when the water-soluble chromic acid compound is strongly acidic. This pH
The adjusting agent is used to adjust the pH of the mixed solution to between 3.0 and 6.0, and is usually used to oxidize metals such as lithium, strontium, calcium, barium, magnesium, zinc, and cadmium. Material and hydroxide. This pH adjuster adjusts the pH of the stoving type composition to between 3.0 and 6.0, keeps the storage stability of the stoving type chromate composition in the best condition, and reduces the zinc powder and the acids in the liquid. It is possible to prevent the adhesiveness of the coating layer from deteriorating due to a sudden reaction and the appearance from being darkened.

The wetting agent is used to help suspend and disperse the zinc powder. Examples of the wetting agent include a nonionic surfactant, particularly an alkylphenol polyethoxy adduct, such as "Nopco 1592" (registered trademark) manufactured by Diamond Shamrock, USA.

There is no particular limitation on the water, and there is no particular limitation on the organic solvent. However, considering the danger of fire and the adverse effect on the health of workers, it is preferable to use water without using an organic solvent as the solvent.

The baking type chromate composition according to the present invention can be prepared by mixing the above components by a known method, for example, using a high-speed stirrer or the like.

As a preferred baking type chromate composition,
Metals such as chromic anhydride, zinc and aluminum, pH adjusters such as metal oxides and hydroxides, cobalt salts and / or salts described in JP-B-60-50228 and JP-B-4-83889. Nickel salt,
Compositions containing oxohydroxy low molecular weight ethers such as polyglycols and a solvent (for example, commercially available and available as Dacrodip (registered trademark)) can be mentioned.

This baking type chromate composition usually contains a water-soluble chromic acid compound such as chromic anhydride and a first component containing water as the main components, a metal powder such as zinc powder and oxohydroxy low molecular weight ether. Provided to the user as a combination with a second component as well as a thickener.

At the time of use, the user mixes the first component, the second component, and the thickener, and applies a predetermined amount to the surface of the cold-rolled steel sheet on which the chromate conversion coating is to be provided. The application amount is
Usually, it is an amount necessary for finally forming a coating layer of several microns or more.

In the baking, a cold-rolled steel sheet coated with a baking type chromate composition is treated with a hot air circulation furnace (IDG combustion furnace or electric furnace), a far infrared heating furnace, an infrared heating furnace, a high frequency induction heating furnace, or a combination thereof. The heating is performed by a method selected from the following. Heating is 180 ° C
At least 0.2 seconds at the above temperature, preferably 2 seconds or more.
0.5 seconds or more at a temperature of 00 ° C. or more, more preferably 2 seconds or more.
It is preferable to carry out at a temperature of 60 ° C. or more for 0.5 seconds or more.

That is, preferred chromate conversion coatings include 10 to 40% of flaky zinc powder, a mixture of flaky zinc powder and flaky aluminum powder, flaky zinc alloy powder, A mixture of flaky zinc alloy powder and flaky aluminum alloy powder, a mixture of flaky zinc powder and flaky aluminum alloy powder, and a mixture of flaky zinc alloy powder and flaky aluminum powder At least one metal powder selected from the group consisting of 1 to 12% of a water-soluble chromic acid compound, 0 to 9% of a boric acid compound, 0 to 4% of p
H regulators, 0-12% nickel and / or cobalt salts, 7-30% polyglycols such as oxohydroxy low molecular weight ethers, 0-4% surfactants,
The remainder is formed by painting and baking the entire surface of a cold-rolled steel sheet with a composition comprising water or a water-compatible organic solvent or a mixture of both.

The amount of the chromate conversion coating is 0.2 g / m ^{2 to} 14 g / m ² , preferably ² g / m ^{2 to} 14 g / m 2.
10 g / m ² . When the adhesion amount is 0.2 g / m ² or less, the effect of suppressing red rust in a corrosive environment becomes insufficient. Also,
If the amount exceeds 14 g / m ² , cracks tend to occur in the chromate conversion coating layer during bending, which adversely affects the workability of the coated steel sheet.

The high corrosion-resistant precoated steel sheet according to the present invention is provided with a top coat paint with or without a primer, on the chromate conversion coating on the side to be regarded as the front side. A primer is applied on the chromate conversion coating on the side considered to be the back side.

As the primer, at least one primer selected from the group consisting of a urethane-based primer, a polyester-based primer, an epoxy-modified urethane-based primer, and an epoxy-modified polyester-based primer is employed. The film thickness of the primer is usually 1 to 15 μm.

As the top coating, a polyester coating is used. The film thickness of the top coat is usually 5 to 5.
30 μm.

By employing a polyester-based coating as the top coating, a sealing effect can be imparted to the precoated steel sheet, moisture and oxygen can be effectively blocked, and a synergistic effect with the chromate conversion coating layer can be obtained. A precoated steel sheet that can maintain corrosion resistance for a long time can be provided. Further, by applying the polyester-based paint, cracks, peeling, and the like, which may occur at the time of processing such as bending in a precoated steel sheet having only a chromate conversion coating layer, can be effectively prevented.

In particular, at least one primer selected from the group consisting of a urethane-based primer, a polyester-based primer, an epoxy-modified urethane-based primer, and an epoxy-modified polyester-based primer, and the polyester-based paint, which is the top coat, are used. Thus, a coating film having excellent workability and excellent sealing properties can be realized.

The high corrosion-resistant precoated steel sheet according to the present invention is characterized in that a specific top coat is applied to the chromate conversion coating on the side to be regarded as the front side with or without a specific primer. By coating and applying a specific primer on the chromate conversion coating on the back side and the side to be considered, cracks, peeling etc. can be effectively prevented even if bending processing is performed, so workability and It has excellent sealing properties and can maintain corrosion resistance on the surface subjected to bending or the like for a long period of time.

Hereinafter, the present invention will be specifically described based on examples.

Example 1 As a test substrate, a 0.35 mm-thick cold-rolled steel sheet which had been washed with alkali degreasing, polished on both sides with Scotch Brightberry Fine, and descaled was used.

The cold rolled steel sheet was subjected to a chromate conversion coating treatment. Dacrodip (registered trademark) having the following composition was used as the baking type chromate treatment composition used in this treatment.

<Composition of dacrodip> Chromic anhydride content 6% by weight Flake-like zinc powder content 27% by weight pH adjuster 3% by weight Polyglycols 20% by weight Surfactant 1% by weight Water balance Using a roll coater Dacrodip was applied to the entire surface of the test substrate. The coated test substrate is placed in an electric heating hot air circulating furnace to heat the test substrate. When the surface temperature of the test substrate reaches 300 ° C. in the furnace, the test substrate is taken out of the furnace and cooled. did. The time from when the test substrate was heated to when its surface temperature reached 300 ° C. was 90 seconds. A part of the cold rolled steel sheet after baking was cut out and the weight of the chromate conversion coating was measured to be 0.2 g / m ² .

Next, the primer was coated with a film having a thickness of 15 μm.
Is applied on the chromate conversion coating layer formed on both sides of the test substrate with a roll coater so that the applied test substrate is placed in an electrically heated hot air circulating furnace as in the case of the dacro dip, and the furnace The surface temperature of the test substrate within 2
Bake to 40 ° C. Further, a top coat is applied to the surface (otenmen) by a roll coater so that the film thickness becomes 10 μm, and then placed in an electric heating type hot air circulating furnace, where the surface temperature of the test substrate reaches 240 ° C. I baked it.

As a primer, a urethane-based primer (product name: Appliance Primer manufactured by Lilly, USA)
As a top coat, a polyester top coat (pre-color # 320 white, manufactured by Nippon Oil & Fat) used for home appliances was used. The precoated steel sheet thus obtained was evaluated by the following method. The results are shown in Table 1.

<Corrosion Resistance> The corrosion resistance of the flat portion was determined by passing a cross cut reaching a cold rolled steel sheet as a base material through a coating film on the surface (omotenmen), and then spraying salt water on the cross cut formation surface. At the time after 240 hours have passed since spraying,
The evaluation was made based on the maximum blister width of the coating film in the cross cut portion and the occurrence of red rust. The corrosion resistance of the end face was evaluated by cutting red rust after 72 hours after spraying salt water after cutting so that the burr was on the back face.

<Maximum blister width> ○: One-side blister width 1 mm or less △: One-side blister width 1 to 5 mm ×: One-side blister width 5 mm or more <Situation of red rust generation> ○: No red rust generation Δ: Partial red rust generation ×: Significant red rust Occurrence <Workability> 20 mm across a spacer of 0.35 mm thickness
After 180 degree bending at ℃,
Observation was performed using a 0-magnifying loupe. The evaluation was performed by changing the number of spacers and showing the number of spacers at the time when cracks did not occur. The display method was 0T when there was no spacer, and 1T when there was no spacer. Evaluation of workability was performed on the surface (omotenmen).

Example 2 The procedure of Example 1 was repeated except that the weight of the chromate conversion coating layer was 2 g / m ² , the thickness of the primer was 10 μm, and the thickness of the top coat was 15 μm. A precoated steel sheet was produced. The precoated steel sheet thus obtained was evaluated in the same manner as in Example 1. The results are shown in Table 1.

Example 3 The same procedure as in Example 1 was performed except that the weight of the chromate conversion coating layer was 14 g / m ² , the thickness of the primer was 1 μm, and the thickness of the top coat was 30 μm. A precoated steel sheet was produced. The precoated steel sheet thus obtained was evaluated in the same manner as in Example 1. The results are shown in Table 1.

(Example 4) A polyester primer NP26 (manufactured by NOF Corporation) was used as a primer, the adhesion weight of the chromate conversion coating layer was 2 g / m ² , the thickness of the primer was 10 μm, and the thickness of the top coat was A precoated steel sheet was produced in the same manner as in Example 1 except that the thickness was changed to 15 μm. The precoated steel sheet thus obtained was evaluated in the same manner as in Example 1. The results are shown in Table 1.

Example 5 In Example 1, the surface of the test substrate on which the chromate conversion coating layer was formed (Omotenmen)
A primer was applied only to the back surface of the test base material without applying a primer, and a pre-coated steel sheet was prepared in the same manner as in Example 1 except that the top coat was directly applied to the front surface (omotenmen). Produced. The precoated steel sheet thus obtained was evaluated in the same manner as in Example 1. The results are shown in Table 1.

(Example 6) The same procedure as in Example 1 was carried out except that the adhesion weight of the chromate conversion coating layer was 2 g / m ² , the thickness of the primer was 10 μm, and the thickness of the top coat was 5 μm. A precoated steel sheet was produced. The precoated steel sheet thus obtained was evaluated in the same manner as in Example 1. The results are shown in Table 1.

(Comparative Example 1) The same procedure as in Example 1 was carried out except that dacrodip was applied so that the adhesion weight of the chromate conversion coating layer was 0.1 g / m ² . The evaluation was performed in the same manner as described above. The results are shown in Table 1.

Comparative Example 2 The procedure of Example 1 was repeated except that the weight of the chromate conversion coating layer was 20 g / m ² , the thickness of the primer was 1 μm, and the thickness of the top coat was 30 μm. A precoated steel sheet was produced. The precoated steel sheet thus obtained was evaluated in the same manner as in Example 1. The results are shown in Table 1.

(Comparative Example 3) A test piece was prepared in such a manner that the weight of the chromate conversion coating layer was 2 g / m ² , the thickness of the primer was 10 μm, and the thickness of the top coat was 15 μm. Epoxy primer-NP was used as a primer. The pre-coated steel sheet thus obtained is
Evaluation was performed in the same manner as in Example 1 above.
The results are shown in Table 1.

Comparative Example 4 A commercially available cold-rolled steel sheet treated with zinc phosphate (adhesion weight: 2 g / m ² ) was coated in the same manner as in Example 1 to prepare a comparative material. The evaluation was performed in the same manner as described above. The results are shown in Table 1.

[0058]

[Table 1]

[0059]

As described above, the pre-coated steel sheet according to the present invention has excellent corrosion resistance in the flat portion, the end face portion, and the workability despite the fact that the cold-rolled steel plate is the base material. INDUSTRIAL APPLICABILITY The present invention is very effective in reducing the cost of precoated steel sheets, and can be used for home appliances, furniture, building materials, and the like.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁶ Identification code FI C23C 28/00 C23C 28/00 C

Claims (4)

[Claims] 1. A degreased and descaled cold-rolled steel sheet, and a baking type chromate composition containing a water-soluble chromic acid compound and zinc powder coated on the surface of the cold-rolled steel sheet and then baked. , Adhesion amount 0.2-1
A chromate conversion coating layer of 4 g / m ² , a primer formed on one surface of both surfaces of the cold-rolled steel sheet of the chromate conversion coating, which is treated as a front side, and a surface of the primer formed on the one surface A topcoat paint painted on, having a primer coated on the other surface of the chromate conversion coating, which is treated as the back side of both surfaces of the cold-rolled steel sheet, wherein the primer is a urethane-based primer, a polyester-based primer, or an epoxy. A highly corrosion-resistant precoated steel sheet, which is at least one kind of primer selected from the group consisting of a modified urethane primer and an epoxy-modified polyester primer, wherein the top coat is a polyester paint. 2. A degreased and descaled cold-rolled steel sheet, and a baking type chromate composition containing a water-soluble chromic acid compound and zinc powder coated on the surface of the cold-rolled steel sheet and then baked. , Adhesion amount 0.2-1
A chromate conversion coating layer of 4 g / m ² , a topcoat paint coated on one surface of the chromate conversion coating that is treated as a front side of both surfaces of the cold-rolled steel sheet, and both surfaces of the cold conversion steel plate of the chromate conversion coating Having a primer painted on the other surface treated as the back side,
The primer is at least one primer selected from the group consisting of a urethane-based primer, a polyester-based primer, an epoxy-modified urethane-based primer, and an epoxy-modified polyester-based primer, and the top-coat paint is a polyester-based paint. Corrosion resistant pre-coated steel sheet. 3. The high corrosion-resistant precoated steel sheet according to claim 1, wherein the primer film layer according to claim 1 or 2 has a thickness of 1 to 15 μm. 4. The highly corrosion-resistant precoated steel sheet according to claim 1, wherein the thickness of the overcoating material according to claim 1 or 2 is 5 to 30 μm.