JP2006263597A - Corrosion prevention method for cut end surface of precoated steel sheet - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent the corrosion of a cut end surface of a precoated steel sheet by allowing a repair coating film 8 covering the cut end surface 6 of a precoated steel sheet to have a function of retaining an aqueous solution including the rust preventive ions eluted from an under coating film 2. <P>SOLUTION: The repair coating film 8 formed of a repair coating material compounded with coarse grains or secondary particles 7 of a large surface area as aggregate is formed on the cut end surface 6 of the cut sheet cut out for the precoated steel sheet provided with the under coating film 2, a top coating film 3, and a rear surface coating film 4. The rust preventive ion-containing aqueous solution oozing from the under coating film 2 is guided by the coarse grains or secondary particles 7 and is held in the repair coating film 8 and therefore, the cut end surface 6 not covered with the coating films 2 to 4 is also effectively prevented from corrosion. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an anticorrosion method in which a cut end surface of a precoated steel sheet is painted by a relatively simple method, and corrosion growth starting from the cut end surface where the base steel is exposed is suppressed.

Coated steel sheets used for exterior materials, interior materials, cover materials, and the like are being switched from post-coats that are coated after being formed into a target shape to pre-coated steel sheets that can be omitted on the user side. A pre-coated steel sheet is an advantageous material in that the productivity is remarkably higher than that of the post-coating, and the corrosion resistance, surface properties, appearance, and the like are excellent.
The pre-coated steel plate is supplied to the user in a coil shape or a cut plate shape, and is formed into a target shape by cutting, punching, drawing or the like on the user side. Since the plating layer and the base steel are exposed at the end face of the precoated steel sheet produced by cutting, rust is likely to be generated at the cut end face as compared with a flat portion having a sound coating film. Patent Document 1 [0010] introduces that the use of a back coating containing calcium chromate or strontium chromate in an epoxy resin improves the corrosion resistance of the cut end surface by elution of chromium from the back coating.
Japanese Patent Laid-Open No. 7-185452

In the case of thin pre-coated steel sheets, the chromium that elutes from the back coating film may spread over the entire cut end face, but the base steel remains in a bare state without coming into contact with the eluted chromium as the pre-coated steel sheet becomes thicker. Easy to be. For example, when a precoated steel plate having a thickness of more than 0.8 mm is used as an exterior building material, the degree of exposure of the base steel at the cut end surface is large, and corrosion may proceed starting from red rust generated on the exposed base steel.
In order to prevent corrosion of the end face, it is effective to preliminarily paint the cut end face exposed in the final product with a repair paint. For example, in patent document 2, the antirust coating film is given to the cut end surface by pressing the coating pad which impregnated the sponge and the nonwoven fabric with the coating material to the cut end surface. However, in general repair paints, the repaired portion tends to corrode prematurely because of its low rust prevention ability, and long-term corrosion inhibition of the cut end face cannot be expected.
Japanese Patent Laid-Open No. 9-285758

The anticorrosive ability of the repair paint is improved by blending an anticorrosive pigment such as calcium chromate or strontium chromate that elutes as chromate ions. Although elution of chromate ions is effective for rust prevention of the cut end face, when the repair coating film gets wet with rainwater, the rust preventive pigment dissolves and the rust prevention ability decreases. Although it can recover the rust-proof ability that has been reduced by applying twice, it is forced to be costly and cumbersome to store and handle.
The present invention has been devised to solve such a problem, and by using the anticorrosive pigment dispersed in the undercoat film for corrosion prevention of the cut end face, it is a simple method and can be applied to the cut end face over a long period of time. An object of the present invention is to provide a high-quality pre-coated steel sheet that suppresses corrosion.

  The present invention is directed to a pre-coated steel sheet in which an undercoating film containing an eluting rust preventive pigment and a top coat film for imparting a color tone are provided on one or both sides of the original plate, and does not contain a rust preventive pigment (service coat). ) May be provided on the back side. A pre-coated steel plate is cut into a predetermined size cut plate, a plurality of cut plates are stacked, and then a repair paint is applied to the cut end surface of the pre-coated steel plate and dried.

As the repair coating, an organic solvent-based coating containing coarse particles or secondary particles having a large surface area as an aggregate is used. Aggregates with irregularities on the surface are used, and the roughness can be defined by the specific surface area of the powder, but a coarse or secondary particle having a specific surface area of 10 m ² / g or more is preferred.
The coarse particles include zeolite with irregularities on the surface, and the secondary particles include silica secondary particles in which fine primary particles are aggregated, alumina secondary particles, and the like. The coarse particles or secondary particles are preferably subjected to a hydrophilic treatment with a silane coupling agent, a water-soluble polymer, a surfactant or the like prior to blending into the paint.

  Even if a rust preventive pigment is added to the paint used for repairing the cut end face, a decrease in the rust preventive ability due to the dissolution of the rust preventive pigment from the repair coating film cannot be avoided. Then, the present inventors examined using the rust preventive pigment dispersed in the undercoat film of the precoated steel sheet for corrosion prevention of the cut end face. The rust preventive pigment elutes in a wet environment and becomes a corrosion protection film to protect the substrate. For example, in a chromium-based rust preventive pigment, corrosion resistance is imparted by precipitation of chromate, which is a reaction product of eluted chromate ions and plating components, steel components, and corrosive factors, onto the substrate surface.

  The anti-corrosive pigment blended in the undercoat is not only for the steel plate surface in contact with the undercoat, but also for the anticorrosion of the cut end face because the aqueous solution containing the eluted metal ions flows in the in-plane direction and is sent to the cut end face. Also work. However, the eluted metal ions are not supplied to the cut end surface far from the undercoat coating film, and the supply of the eluted metal ions becomes insufficient as the precoated steel plate becomes thicker. In addition, the rust preventive pigment that has just flowed out flows out from the cut end face by contact with rainwater, and the proportion consumed without working to prevent corrosion increases.

  When the rust preventive pigment that has flowed out to the cut end face is retained on the cut end face and the rust preventive pigment can flow along the in-plane direction of the cut end face, the anticorrosive pigment blended in the undercoat film is effectively prevented from being corroded on the cut end face. Available to: From such a viewpoint, as a result of investigating and examining the required characteristics of the repair coating film provided on the cut end face, it was found that it is effective to disperse coarse particles or secondary particles having a large surface area as an aggregate. It can be explained as follows that the rust preventive pigment is properly distributed on the cut end face due to the dispersion of coarse particles or secondary particles.

The pre-coated steel sheet using the coating original plate 1 in which the plating layer 1b is provided on the base steel 1a is provided with the undercoating film 2 and the overcoating film 3 on the surface that becomes the outer surface of the product, and the back surface coating film (service coat) on the back surface that becomes the inner surface of the product. ) 4 is provided (FIG. 1). Instead of the back coating film 4, the undercoating film 2 and the top coating film 3 may be provided on the back side. The rust preventive pigment 5 is not normally dispersed in the top coating film 3 or the back coating film 4 but is dispersed only in the undercoating film 2.
The precoated steel sheet is stored, transported and handled as a cut sheet cut to a predetermined size, but the base steel is exposed on the cut end face 6 without the coating films 2 to 4 and is in a state of being easily rusted. Therefore, a repair coating in which coarse particles or secondary particles are dispersed is obtained by applying and drying a repair paint containing coarse particles having a large surface area (FIG. 2a) or secondary particles (FIG. 2b) as aggregate 7 on the cut end face. The cut end face 6 is covered with a film 8.

Unlike ordinary aggregates having a smooth surface, the surface of coarse particles or secondary particles such as zeolite, silica secondary particles, and alumina secondary particles is not covered with the binder resin of the paint. The surface portion of the aggregate 7 not covered with the binder resin allows the flow of the aqueous solution containing rust-preventing ions that has flowed in the in-plane direction from the undercoat coating 2 to the cut end surface 6. That is, the rust-preventing ion-containing aqueous solution sequentially moves from one aggregate 7 to the adjacent aggregate 7 due to the surface tension between the uncoated surface portion of the aggregate 7 and the rust-preventing ion-containing aqueous solution.
Since the preferential flow path of the rust-preventing ion-containing aqueous solution is formed in the repair coating film 8 by the aggregate 7 dispersed in the repair coating film 8, the pre-coated steel plate using the thick coating original plate 1 covers the entire cut end surface 6. The aqueous solution containing rust-preventing ions is supplied, and the rust-preventing pigment elution layer 9 is formed. Since the rust-preventing ions react with the corrosive factor and the reaction product having a corrosion inhibiting action is deposited on the cut end face, the cut end face is protected from corrosion. On the other hand, since the rust-preventing ion-containing aqueous solution is repelled by the binder resin of the repair coating 8 in the coating film portion without the aggregate 7, the ratio of the rust-preventing ion-containing aqueous solution flowing out from the repair coating 8 in contact with rainwater is reduced. The anticorrosion sustainability for the cut end face 6 is improved.

  As the coating original plate 1, various types of plated steel plates, stainless steel plates, ordinary steel plates, low alloy steel plates and the like are used. Especially, a stainless steel plate and a Zn-Al-Mg alloy plating steel plate are the suitable coating original plates from long-term durability, end surface corrosion resistance, intensity | strength, cost, etc. Pre-coating treatments such as degreasing, surface adjustment, and chemical conversion treatment are applied according to the type of coating original plate. As the chemical conversion treatment, in addition to the chromate treatment and the phosphate treatment, a chromium-free treatment for forming a chemical conversion film such as a titanium-based, zirconium-type, or silica-based material having a small environmental load can be employed.

  An undercoat paint is applied to the original plate 1 that has been pre-painted and dried to form an undercoat paint film 2. The undercoat paint is prepared by blending a chromium-based or non-chromium-based anticorrosive pigment with a base resin such as epoxy or polyester. If necessary, extender pigments, aggregates and the like may be added. Various rust preventive pigments can be used as long as they elute in an aqueous solution, and the rust preventive pigments having an average particle size of 0.01 to 10 μm are improved by making the rust preventive pigments finer, thereby improving the dissolution of rust preventive ions from the cut end face. Is preferred.

  Examples of chromium-based rust preventive pigments include zinc chromate, strontium chromate, barium chromate, calcium chromate, and non-chromium rust preventive pigments include magnesium phosphate, zinc phosphate, calcium phosphate, aluminum polyphosphate, and modified silica. , Calcium carbonate, titanium oxide, etc. If necessary, multiple types of anti-corrosion pigments are added to the paint. The addition amount of the rust preventive pigment is adjusted so that the rust preventive pigment 5 is dispersed in the dried undercoat coating film 2 at a ratio of 5 to 70% by mass (preferably 20 to 60% by mass). If the amount of dispersion is less than 5% by mass, the amount of the rust preventive pigment 5 necessary for anticorrosion of the cut end face 6 is insufficient. Conversely, if the amount of dispersion exceeds 70% by mass, the film formability is adversely affected.

  The undercoat paint is applied to the original plate 1 that has been pretreated, and is baked by heating and drying at a temperature equal to or higher than the curing start temperature of the undercoat film, for example, a surface temperature of 200 ° C. Specifically, heating and drying conditions of 190 to 380 ° C. × 15 to 90 seconds are employed. The coating amount of the undercoat paint is adjusted to an amount that forms the undercoat film 2 having a dry film thickness of 2 to 15 μm. If the film thickness is less than 2 μm, there is a concern that the film formability and the rust-preventing effect may be reduced.

  The top coating is prepared by blending a color pigment or dye with a base resin such as polyester, epoxy-modified polyester, fluorine, acrylic, or urethane. Color pigments or dyes include titanium oxide, carbon black, cyanine blue, cyanine green, iron oxide, and the like, and metallic pigments such as aluminum powder and bright powder can also be used. Add various additives such as antibacterial agents, fungicides, insect repellents, non-adhesive agents, lubricants, antifouling agents, matting agents, UV absorbers, etc. as needed, aggregates, extender pigments, powders, etc. May be.

  The top coat is applied onto the undercoat coating 2, and is baked by heating and drying at a temperature equal to or higher than the curing start temperature of the top coat, for example, the surface temperature: 230 ° C. Specifically, heating and drying conditions of 220 to 450 ° C. × 15 to 90 seconds are employed. The coating amount of the top coating is adjusted to the amount by which the top coating film 3 is formed with a dry film thickness of 5 to 30 μm. If the film thickness is less than 5 μm, the concealability and durability may be inferior. Conversely, if the film thickness exceeds 30 μm, the molding processability is lowered and the cost is increased.

  The back coating is applied to the back side of the coating original plate 1 that has been pre-treated. The back coating can be applied simultaneously with the undercoat or topcoat on the front side. The baking temperature is set to be equal to or higher than the curing start temperature of the back coating film, and is baked by heating and drying at the baking temperature of the undercoat or topcoat. The coating amount of the back surface coating is adjusted to an amount by which the back coating film 4 having a dry film thickness of 1 to 10 μm is formed. If the film thickness is less than 1 μm, the film formability may be lowered, and if the film thickness exceeds 10 μm, the cost tends to increase.

The pre-coated steel sheet sent out from the continuous coating line is wound into a coil shape and conveyed to the next process, and is cut into a cut plate of a predetermined size in the next process. Alternatively, the pre-coated steel plate coming out from the continuous coating line may be cut into a cut plate while running. A plurality of cut plates are stacked on top of each other to be piles that can be stored and transported.
On the side surface of the pile, there is a cut end face 6 with no coatings 2 to 4 and exposed base steel. Therefore, the cut end face 6 is covered with the repair coating film 8 by applying the repair paint to the pile side surface and baking it.

The repair paint is prepared by blending an aggregate, a color pigment, and a solvent with a base resin such as alkyd, modified alkyd, acrylic, or urethane.
For the aggregate 7, coarse particles or secondary particles having a large surface area are used. Coarse (FIG. 2a) The specific surface area: 10 m ² / g or more synthetic zeolites are active alumina, active carbon, secondary particles specific surface area silica, alumina and the like are aggregated in (Figure 2b): 10m ² / There are more than g particles. When secondary particles are used, secondary particles having an average particle size of 1 μm or more in the paint are preferred because the secondary particles need to maintain a certain degree of aggregation during the paint dispersion process. Secondary particles having a particle size of less than 1 μm are not preferable because the dispersibility of the aggregate with respect to the base resin is increased, and the flow of the rust-preventing ion-containing aqueous solution is suppressed between the aggregates.

  The amount of aggregate blended into the repair coating is determined in the range of 20 to 120% by mass with respect to the resin solid content. When the blending amount is less than 20% by mass, the flow between the aggregates of the rust-preventing ion-containing aqueous solution is suppressed, which is not preferable. However, excessive blending exceeding 120% by mass means a decrease in the amount of base resin or solvent added, and the coating tends to become unstable. In order for the rust-preventing ion-containing aqueous solution to easily flow between the aggregates, it is preferable that the surfaces of the coarse particles or secondary particles are subjected to a hydrophilic treatment with a silane coupling agent, a water-soluble polymer, a surfactant, or the like.

Examples of the colorant blended in the repair coating include titanium oxide, carbon black, cyanine blue, cyanine green, iron oxide, and aluminum powder. If necessary, extender pigments and the like may be added to the repair paint.
The repair paint is applied to the cut end face 6 by spraying or the like, and a repair coating film 8 is formed by drying at room temperature. The coating amount of the repair paint is adjusted to an amount for forming the repair coating film 8 having a dry film thickness of 5 to 300 μm. When the film thickness is less than 5 μm, the corrosion resistance is insufficient, and when the film thickness exceeds 300 μm, there is a concern about an increase in cost.

Plate thickness: A hot-dip galvanized steel sheet having a zinc adhesion amount of 70 g / m ^{2 made} of a cold-rolled steel sheet having a thickness of 1.6 mm was used as a coating original sheet. Apply degreasing and coating chromate treatment to both front and back sides of the original coating 1, apply an undercoat paint based on epoxy resin or polyester resin, and blend coarse particles or secondary particles with a specific surface area of 10 m ² / g or more, and dry Film thickness: An undercoat film 2 of 7 μm was formed. Synthetic zeolite, activated alumina, and activated carbon were used as coarse particles, and silica powder and alumina powder were used as secondary particles, and silane coupling treatment was performed prior to blending.

Simultaneously with the undercoat coating, a back coating was applied to the back surface of the coating original plate 1 to form a back coating film 4 having a dry film thickness of 5 μm. For the formation of the undercoat coating film 2 and the back coating film 4, heating and drying conditions of 350 ° C. × 90 seconds were employed.
Next, a top coat was applied on the undercoat film 2, and a top film 3 having a dry film thickness of 15 μm was formed by heating and drying at 380 ° C. for 90 seconds.

The obtained coated steel sheet was cut into a size of 65 mm × 150 mm with a mechanical shear, and a repair coating film 8 having a dry film thickness of 5 to 300 μm was formed by spraying a repair paint on the cut end face and drying at room temperature. The repair paint was prepared by blending aggregate: 20 to 120% by mass, coloring pigment: 100 to 0% by mass, extender pigment: 8% by mass, and solvent: 20% by mass based on the alkyd resin.
After the repair coating, the corrosion resistance of the cut end surface was investigated by a salt spray test based on JIS K5600. After the spraying of salt water was continued for 500 hours, the cut end face was observed, and the test piece in which corrosion slightly stopped was evaluated as excellent corrosion resistance (◯), and the test piece in which corrosion progressed markedly was evaluated as poor corrosion resistance (×).
As can be seen from the test results in Table 1, it can be seen that the cut end face is effectively anticorrosive by providing a repair coating film in which the coarse or secondary particles defined in the present invention are dispersed. On the other hand, in the comparative example where the repair coating film is too thin or the aggregate content is too small, considerable corrosion occurred on the cut end face.

  A modified alkyd resin, an acrylic resin or a urethane resin was used as the base of the repair paint, and the repair paint was prepared by blending secondary particles of silica powder as an aggregate. The repair coating was applied to the cut end face in the same manner as in Example 1 to form a repair coating film, and then the corrosion resistance of the cut end face was investigated by the same corrosion test. As can be seen from the results of the investigation in Table 2, it can be seen that the corrosion resistance of the cut end face is improved by the dispersion of the aggregate in any repair coating film formed using any base resin.

Hot-dip galvanized steel sheet, hot-dip Zn-5% Al alloy-plated steel sheet, hot-dip Zn-55% Al alloy-plated steel sheet, Zn-Al-Mg alloy-plated steel sheet, hot-dip aluminum-plated steel sheet and electrogalvanized steel sheet (Each plated steel plate has a coating weight of 70 g / m ² per side) is used as the coating base plate, and the repair coating film is cut in the same manner as in Example 1 with a repair paint containing synthetic zeolite as an aggregate and modified alkyd resin. Formed.
The cut end surface corrosion resistance of the coated steel sheet after the repair coating was investigated by the same salt spray test as in Example 1. As can be seen from the investigation results in Table 3, the corrosion resistance of the cut end face is improved by providing the repair coating film according to the present invention on the cut end face regardless of the type of the plated steel sheet used as the coating original plate. confirmed.

  As described above, when a repair paint in which coarse particles having a large surface area or secondary particles 7 are blended as an aggregate is applied to the cut end face 6 of the pre-coated steel sheet and dried, the rust-preventing ions that have dissolved from the undercoat film 2 are removed. A repair coating 8 capable of retaining the aqueous solution contained on the cut end face 6 is formed. The coarse particles or secondary particles 7 dispersed in the repair coating 8 form a preferential channel of the rust-preventing ion-containing aqueous solution in the repair coating 8 and spread the rust-preventing ion-containing aqueous solution over the entire cut end face 6. And preventing the aqueous solution containing rust-preventing ions from flowing out of the repair coating 8 into the rainwater. Thus, the precoat steel plate in which the cut end face is anticorrosive is used in a wide range of fields as an exterior material, interior material, cover material, etc. utilizing a beautiful surface.

Schematic diagram showing the cut end face of a pre-coated steel sheet coated with a repair coating Schematic diagram of a repair paint containing coarse particles (a) or secondary particles (b) as an aggregate

Claims (5)

Cut and stacked pre-coated steel sheets that are colored with a top coat film provided through an undercoat film containing an rust-preventing pigment that can be eluted, into a cut plate of a predetermined size,
An organic solvent-based repair coating containing coarse particles or secondary particles with a large surface area as an aggregate is applied to the cut end surfaces of the stacked precoated steel sheets, and the cut end surfaces are covered with a repair coating in which the coarse particles or secondary particles are dispersed. A method for anticorrosion of a cut end surface of a precoated steel sheet, characterized by covering. The cut end face anticorrosion method according to claim 1, wherein a repair paint containing an aggregate having a specific surface area of 10 m ² / g or more is used.   The cutting end face anticorrosion method according to claim 1, wherein a repair coating is used in which a hydrophilized zeolite, silica secondary particles and / or alumina secondary particles are blended as an aggregate.   The cut end face anticorrosion method according to claim 1, wherein the anticorrosive pigment contained in the undercoat film of the precoated steel sheet is one or more of a chromium anticorrosive pigment and a non-chromium anticorrosive pigment.   The cutting end surface anticorrosion method according to claim 1, wherein a zinc-based plated steel plate or an aluminum-based plated steel plate is used as a coating original plate.

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