JPS635938A - Coated steel plate - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field 1] The present invention relates to a coated steel plate using an aluminum-zinc alloy plated steel plate as a substrate.

E Background technology] As an aluminum-zinc alloy plated steel sheet,
A steel plate plated with an alloy of 55.0% by weight of AI, 43.4% by weight of Zn, and 1.6% by weight of Si as shown in Publication No. 6-7161, and 4 to 5% by weight of AI. Most of the rest is a steel plate plated with a metal alloy mainly consisting of Zn and La and Ce, with AI at 4 to 5% by weight, and most of the rest is an alloy of Zn and 0.1% by weight of Mg. Steel plates plated with These aluminum-zinc alloy coated steel sheets were developed with the aim of having greater durability than the conventionally widely used galvanized steel sheets, and can be used bare (unpainted) or painted for roofing or other purposes. It is rapidly becoming popular for applications such as building materials such as walls, agricultural facilities, electrical equipment, automobiles, and industrial equipment. In other words, if the thickness of the plating layer of aluminum-zinc alloy plated steel sheet is the same as that of galvanized steel sheet, for example, A1 is 55.0.
In the case of alloy-plated steel sheets containing 43.4% by weight of Zn and 1.6% by weight of Si, the corrosion resistance is 3 to 6 times higher, and low aluminum alloys with 4 to 7% by weight of AI have a proven track record of corrosion resistance. Coated steel sheets are said to have nearly twice the corrosion resistance of galvanized steel sheets, and therefore aluminum-zinc alloy coated steel sheets, especially coated steel sheets using aluminum-zinc alloy coated steel sheets as substrates, are rapidly becoming popular. There is.

However, in the case of a painted steel sheet that is coated using an aluminum-zinc alloy coated steel sheet as a substrate, compared to a painted steel sheet that is painted using a galvanized steel sheet as a substrate,
The cut end is electrochemically disadvantageous, and there is a problem that blistering of the coating film tends to occur at the cut end in a corrosive atmosphere. Therefore, in order to solve this problem, Japanese Patent Application Laid-Open No. 58-120784 ``Painted Steel Sheet Using Aluminum-Zinc Alloy Plated Steel Sheet as a Substrate'' and Japanese Patent Application Laid-Open No. 59-14
As disclosed in Publication No. 942 "Painted Steel Sheets," chromic acid-based rust preventive pigments such as strontium chromate, which have low water solubility, and chromic acid-based rust preventive pigments, such as calcium chromate, which have high water solubility, are used in the undercoat paint. Rust-preventive pigments are mixed and added, or romic acid-based rust-preventive pigments such as strontium chromate, barium chromate, zinc potassium chromate, etc. are added in high concentrations, which improves the coating film. This is to prevent the occurrence of blisters. Although these measures can improve the blistering of the coating film at the cut end, they are not sufficient.

On the other hand, when painting an aluminum-zinc alloy plated steel sheet, surface treatment is performed by chemical conversion treatment in order to improve the adhesion of the paint film. When performing chemical conversion treatment using a phosphoric acid-based chemical conversion treatment solution such as zinc phosphate or iron phosphate, the aluminum in the plating layer of the aluminum-zinc alloy plated steel sheet dissolves in the phosphoric acid.
When this concentration reaches a certain level, the formation of a chemical conversion coating may be inhibited and the adhesion of the coating may decrease. Therefore, chromic acid-based chemical conversion treatment liquids such as chromic acid-based or mixed chemical conversion treatment liquids of chromic acid and silica gel, or chemical conversion treatment liquids containing chromic acid, silica gel, and phosphoric acid are used. The adhesion of the film can be increased to the same level or higher than that of a galvanized iron plate.

However, when using such a romic acid-based chemical conversion treatment liquid, there is a problem that the scratch resistance of the paint film is inferior to that when using a phosphoric acid-based chemical conversion treatment liquid such as zinc phosphate or iron phosphate. .

[Object of the Invention] The present invention has been made in view of the above points, and is capable of preventing the occurrence of blistering of the coating film at the cut end in a corrosion-resistant atmosphere, and also provides scratch-resistant properties such as scratch resistance. The object of the present invention is to provide a coated steel sheet using an aluminum-zinc alloy plated steel sheet as a substrate, which has excellent properties.

[Disclosure of the Invention 1 The coated steel sheet according to the present invention is an undercoat in which a rust preventive pigment mainly composed of chromate is blended on the surface of an aluminum-zinc alloy plated steel sheet that has been chemically treated with a chromic acid-based chemical conversion treatment liquid. A coating film of paint is formed, and a topcoat film of an unsaturated polyester topcoat containing glass fibers surface-treated with a silane coupling agent is formed on the surface of this undercoat film. The present invention will be described in detail below.

As the aluminum-zinc alloy plating, any of those mentioned above can be used, and first, a chemical conversion treatment is applied to the surface of this aluminum-zinc alloy plated steel sheet. In carrying out the chemical conversion treatment, in the present invention, a chemical conversion treatment liquid such as a chromic acid type, a system containing chromic acid and silica gel, a system containing chromic acid, silica gel, and phosphoric acid is used to improve the adhesion of the coating film. Among these, chromic acid-based or mixed chemical conversion treatment liquids of chromic acid and silica gel are sufficient, but
A chemical conversion treatment solution containing chromic acid, silica gel, and phosphoric acid is most suitable;
rOz), silica sol (Si02), phosphorus 1! (H, P
The weight ratio of O,) is 1 for phosphoric acid and 1 for chromic acid.
~3, It is preferable to set the silica sol to 1 to 3, and the coating and removal of the chemical conversion treatment liquid is 5 to 60 g/m2 in dry state.
It is preferable to set the drying temperature to about 60~60℃.
It is preferable to set the temperature to about 100°C, but of course the temperature is not limited to this. After performing the chemical conversion treatment in this manner, an undercoat paint is applied to the surface of the aluminum-zinc alloy plated steel sheet.

Undercoat paints include epoxy, epoxy urethane, polyester, and polymeric polyester paints that contain rust-preventing pigments based on chromates such as strontium chromate, calcium chromate, barium chromate, and zinc-potassium chromate. It is preferable that titanium oxide, mica powder, etc. be further blended into this undercoat paint. The amount of the anticorrosive pigment mainly composed of chromate in the resin system of the undercoating paint is preferably 15 to 60% by weight based on the nonvolatile components. If the amount is less than 15% by weight, the effect of preventing blistering at the cut end of the topcoat paint film by blending the rust preventive pigment will be insufficient, and if it exceeds 60% by weight, the blistering prevention effect will be improved. This cannot be expected, and on the contrary, the adhesion of the undercoat to the aluminum-zinc alloy plated steel sheet deteriorates, resulting in deterioration of bending workability, such as peeling of the paint film during bending. The coating thickness of this undercoat paint on the aluminum-zinc alloy plated steel sheet is preferably 3 to 10 microns in terms of dry coating thickness. Thickness is 3
If it is less than μ, the effect of preventing blistering at the cut end of the top coat film will be insufficient, and the scratch resistance of the top coat film will also decrease.

In this case, the reduction in scratch resistance can be suppressed by adding titanium oxide or mica powder. Also, the thickness is 10
If it exceeds μ, bending workability tends to deteriorate. After the undercoat is applied to the surface of the aluminum-zinc alloy plated steel sheet to form an undercoat film, a topcoat containing glass fiber is applied to the surface.

As the top coat 9 paint, an unsaturated polyester resin paint such as an unsaturated polyester resin paint or a silicone unsaturated polyester resin paint is used, and glass fiber is blended in this top coat paint. Here, the special public service in the 1970s
Publication No. 25485 "Pre-coated steel plate" and Special Publication No. 1973-
As disclosed in Publication No. 8128 [Coating for pre-coated steel sheets containing flaky glass], paints may contain fibers, flakes, beads (fibers are used in the present invention from the viewpoint of coating performance). By adding and using E plus C1f lath, the strength and hardness of the coating film can be increased, and the scratch resistance and abrasion resistance can be improved. Therefore, in the present invention, glass fiber is blended into the unsaturated polyester resin-based top coat to increase the strength and hardness of the top coat, thereby improving scratch resistance and abrasion resistance. It is. However, since the surface of glass fiber is generally covered with hydrophilic polar groups such as OH groups, it has poor wettability with paint and does not mix well with the paint, making it difficult to uniformly disperse it in the paint film. If only added, the coating film becomes porous and becomes more permeable to moisture, which may reduce the adhesion between the metal substrate and the coating film and elute zinc ions, leading to a decrease in corrosion resistance.

Therefore, in the present invention, the surface of the glass fiber is treated with a silane coupling agent to improve the compatibility of the glass fiber with the paint resin. In the case of unsaturated polyester resin paints such as unsaturated polyester resin paints and silicone unsaturated polyester resin paints, by treating the surface of the glass fibers with a silane coupling agent, the bond between the glass fibers and the paint resin can be reduced. By imparting wettability to the glass fibers and uniformly dispersing them in the coating film, it is possible to improve the water permeability, moisture permeability, gas resistance, etc. of the coating film, and also to improve the corrosion resistance. It is possible.

As a silane coupling agent, the chemical structure is CH2
= Vinyl type represented by CHS + (OCH3)3, epoxy type represented by O, methacryloxy type represented by H30, mercapto type represented by HS C3H6S i(OCH3)3, and other chloro A propyl type etc. can be used.

Top coats of unsaturated polyester resin paints are composed of unsaturated polyester resins or silicone unsaturated polyester resins, pigments, solvents, and the like. The amount of glass fibers surface-treated with a silane coupling agent added to the top coating is preferably set to 8 to 40 parts by weight per 100 parts by weight of the paint. If the blending amount is less than 8% by weight, the effect of improving the scratch resistance by improving the hardness of the top coat film due to the blending of glass fibers cannot be obtained, and
If it exceeds 0% by weight, the elongation of the coating film will be extremely reduced and the bending processability will be poor. Further, as the glass #a fiber, E glass, C glass, etc. can be used, but it is preferable that the diameter of the glass fiber is set to 3 to 30 μm, and the fiber length is set to 3 to 100 μm, respectively. The film thickness of unsaturated polyester resin-based top coat paint is 20~
It is applied so that it is as thin as 35 μm, but if the diameter of the glass fibers becomes larger than this, the glass fibers may be arranged on the surface of the coating film, causing cracks in the coating film during processing, or glass fibers may be missing from the coating film. If the diameter of the glass fiber is smaller than this, the effect of improving the strength of the coating film will not be sufficient. Furthermore, if the fiber length of the glass fiber is longer than this, the glass fibers cannot be uniformly dispersed in the paint, and if the fiber length of the glass fiber is shorter than this, the effect of improving the strength of the paint film will not be sufficient. be. By blending and stirring the glass fibers in this way, it is made into a paint, which is then applied onto the undercoat film applied to the aluminum-zinc alloy plated holly steel sheet to form a topcoat film, resulting in a finished coated steel sheet. It is something.

Here, in order to test the moisture permeability of the top coat, glass fibers with a diameter of 13μ and a fiber length of 30 to 50μ, which had been surface-treated with a silane coupling agent, were used at 0% by weight, 10% by weight,
It was added to an unsaturated polyester resin paint at four levels of 20% and 30% by weight, and this was applied to a fluororesin clear coated board using a bar coater to a dry film thickness of 50μ, and allowed to set for 5 to 10 minutes. After the coating, baking was performed for 10 minutes in an electric furnace at an ambient temperature of 140° C., and the coating film was peeled off from the coated plate to obtain a test free film. Then, a moisture permeability test was conducted on this film in accordance with JISZ 0208 at a temperature of 40° C.±0.5° C. and a humidity of 90±2% RH for 20 hours and 72 hours. As shown in Table 1, the amount of glass fiber added is 1
Up to about 0% by weight, it has no relation to moisture permeability, and when it exceeds 10% by weight, it can be seen that the moisture permeability decreases as the amount added increases.

In the coated steel sheet obtained as described above, since the surface of the aluminum-galvanized steel sheet is chemically treated using a chromic acid-based chemical conversion treatment liquid, this chemical conversion film is used to connect the substrate and the coating. In addition to improving adhesion with the film, the use of an undercoat containing anti-corrosion pigments mainly consisting of chromate improves the adhesion between the undercoat and the topcoat and the substrate. As a result, the synergistic effect of the chromic acid-based chemical conversion treatment and the undercoat paint containing a rust-preventing pigment mainly composed of chromate ensures a high degree of adhesion between the substrate and the paint film. , it is possible to prevent the occurrence of paint film blistering at the cut end. When chemical conversion treatment is performed using a chromic acid-based chemical conversion treatment liquid, there is a tendency for the scratch resistance of the paint film to decrease, but the glass fiber added to the top coat increases the hardness of the paint film and makes it resistant to scratches. This prevents deterioration in adhesion properties and improves scratch resistance, etc. Furthermore, at this time, glass fibers are surface-treated with a silane coupling agent and then added to an unsaturated polyester resin top coat. Because of this, the action of the silane coupling agent improves the wettability of the glass fibers with the resin in the unsaturated polyester resin top coat, and the glass fibers do not become highly permeable to water. The present invention will now be illustrated by examples in order to effectively demonstrate the improvement in coating film strength and coating film hardness by blending.

K19 thickness is 0.4mm, 55.0%Al-43.4%Zn-
An aluminum-galvanized steel plate coated with 1.6% Si alloy plating at 80 g/m2 (one side) was used as the substrate.
A chromic acid group chemical conversion treatment solution containing a weight ratio of chromic acid silica gel and phosphoric acid = 2:2:1 was applied to the surface of this substrate at a treatment coating amount of 50 mg/m2 (one side), and then heated at 90°C for 20 seconds. The aluminum-galvanized steel sheet was chemically treated by drying under the following conditions.

Next, an epoxy resin undercoat containing 25% by weight of strontium chromate and 25% by weight of calcium chromate as antirust pigments was applied to the chemically converted surface of the aluminum-galvanized steel sheet. The coating was done by roll coating so that the dry coating thickness was 4 μm.
An undercoat film was formed by drying at 00°C for 60 seconds.

Furthermore, an unsaturated polyester resin top coat (Superlac DIFF-60 matte, blue, manufactured by Nippon Paint Co., Ltd.) was applied, and the diameter was 13 μm, the fiber length was 30 to 50 μm, and the surface was treated with an epoxy-type silane coupling agent. 20 parts by weight of lath fibers were added to 100 parts by weight of the paint, and this was applied onto the undercoat film of an aluminum-galvanized steel plate. The application is dry! ! ! This was applied by roll coating to a film thickness of 20 μm, and dried at 200° C. for 60 seconds to form a top coat, thereby obtaining a coated aluminum-zinc coated steel sheet.

The same procedure as in the example was carried out except that the amount of lath fiber added to the top coat paint was set at 5 parts by weight per 100 parts by weight of the paint.
A painted aluminum-galvanized steel sheet was obtained.

A coated aluminum-zinc coated steel sheet was obtained in the same manner as in the example except that the amount of glass fiber added to the top coat was set at 60 parts by weight per 100 parts by weight of the paint.

A coated aluminum-galvanized steel plate was obtained in the same manner as in the example except that glass fibers having a diameter of 1 μm were used as the glass fibers added to the top coat.

1j [(Glass fiber added to the top coat paint has a diameter of 50μ
A coated aluminum-galvanized steel sheet was obtained in the same manner as in the example except that the same material was used.

1. Fiber length is 1 to 1 as lath wL miscellaneous added to top coat paint.
A coated aluminum-galvanized steel plate was obtained in the same manner as in the example except that a 2μ thick plate was used.

Ratio 1 J□ Added to top coat paint, but the fiber length is 130
A coated aluminum-galvanized steel plate was obtained in the same manner as in the example except that a steel plate having a thickness of ~150 μm was used.

A coated aluminum-galvanized steel sheet was obtained in the same manner as in the example except that the glass fibers added to the top coat were not treated with a coupling agent.

A coated aluminum-galvanized steel sheet was obtained in the same manner as in the example except that a top coat without glass fiber was used.

Comparison 1 - Painted aluminum was prepared in the same manner as in the example except that an undercoat without anti-rust pigment was used.
A galvanized steel sheet was obtained.

Painted aluminum-zinc was prepared in the same manner as in the example except that an undercoat prepared by blending 5% by weight of strontium chromate and 5% by weight of calcium chromate as anti-rust pigments was used. A plated steel plate was obtained.

Saitoseyu 1Y 40% by weight of strontium chromate as a rust-preventive pigment,
A coated aluminum-galvanized steel sheet was obtained in the same manner as in the example except that an undercoat containing 40% by weight of calcium chromate was used.

A 225 galvanized iron plate with a thickness of 0.41fiI6 was used as a substrate, and a coating amount of 1.0g7m2 of zinc phosphate-based chemical conversion treatment liquid (Bonderai 103, manufactured by Nippon Parkerizing Co., Ltd.) was applied to the surface of this substrate. Galvanized iron sheets were chemically treated by dipping in Next, an epoxy resin undercoat containing 10% by weight of strontium chromate as a rust-preventive pigment was applied to the chemical conversion-treated surface of the galvanized iron plate. Coating was carried out by roll coating so that the dry coating thickness was 4 μm, and an undercoat coating film was formed by drying at 200°C for 60 seconds. Furthermore, 100 parts by weight of glass fibers, which have a diameter of 13 μm and a fiber length of 30 to 50 μm and are not treated with a coupling agent, are added to the unsaturated polyester resin topcoat paint (Superlac DIFF-60 matte, blue, manufactured by Nippon Paint Co., Ltd.). 20 parts by weight was applied to the undercoat film of a galvanized iron plate. The coating was carried out by roll coating so that the dry film thickness was 20 μm, and the coating was dried at 200° C. for 60 seconds to form a top coat, thereby obtaining a coated galvanized iron plate.

A coated galvanized iron plate was obtained in the same manner as in Comparative Example 12, except that a coating material containing no glass fiber was used as the K-1 shade topcoat paint.

Painted aluminum was prepared in the same manner as in the example except that 10 parts by weight of strontium chromate was added as a rust preventive pigment to K1 to prepare an undercoat, and a topcoat without glass fiber was used. A galvanized steel sheet was obtained.

The painted aluminum-galvanized steel sheets and painted galvanized iron sheets obtained in the above Examples and Comparative Examples 1 to 14 were tested for scratch resistance, workability, and corrosion resistance. The results are shown in Table 2. Here, the "pencil hardness" in the "scratch resistance" of the second attenuation was tested based on JIS D 0202. In addition, "coin scratch" in "scratch resistance" is tested by scratching the surface of the coating film at a 45-degree angle with a 10 yen coin, and is evaluated on a five-point scale based on the degree of scratches that occur on the coating film. “5” indicates that the undercoat film has not been reached, and “5” indicates that the undercoat film has reached 10%.
4", when reaching 30% undercoat film, "3", 70%
The case where the undercoat film was reached was indicated as "2", and the case where 100% undercoat film was achieved was indicated as [1], respectively.

"Bendability" of "Workability" is 4 with a thickness of 0 and 4 am.
Bend the test piece at a 180 degree angle with two steel plates in between.
The test was conducted by adhering cellophane tape to the folded part and determining the degree of adhesion of the paint film to the cellophane tape when it was peeled off. A case where the coating film adhesion was 30% or less was indicated as "Δ", and a case where the adhesion to the cellophane tape exceeded 30% was indicated as [x]. "Fit Edge Creep Resistance" in "Corrosion Resistance" is determined by sealing the three side edges and the front and back sides of the test piece with polyester tape, and placing the test piece with the edge side exposed on a salt water spray tester (JIS K 54
00) for 1000 hours, the test was conducted by evaluating the blister state of the coating film from the unsealed exposed end face, and the maximum blister length was displayed. "Corrosion resistance" [Salt spray test 400 hr J] The test piece as a flat plate (displayed in the "flat part"), 0.4III1
A test piece made by sandwiching two steel plates of 1 thickness and bending at an angle of 180 degrees (indicated by "2T bending part"), an NT cutter (
Using test pieces with cross-shaped scratches reaching from the painted surface to the board (indicated in "Cross cut section"), the end face of each test piece was sealed with polyester tape and this was subjected to the salt spray test fi (JISK5400). The test was conducted by exposing it for 4000 hours and evaluating its appearance.
``◎'' indicates that there is no abnormality on the paint surface, ``rOJ'' indicates that the occurrence of paint film blisters or white rust is less than 30%, and ``◎'' indicates that the occurrence of paint film blisters or white rust exceeds 30%.
Δ", and those with red rust are indicated as "x".

The results in Table 2 confirm that the examples are excellent in all of the scratch resistance, workability, and corrosion resistance. On the other hand, in Comparative Example 7, in which glass fibers were not surface-treated with a coupling agent, and in Comparative Example 9, in which an undercoat was used that did not contain anti-corrosion pigments, the corrosion resistance was poor, and the top coat did not contain glass fibers. It is confirmed that Comparative Example 8, which was not coated, had low surface hardness and poor scratch resistance.

[Effect of the Invention J As described above, the present invention provides an undercoat coating containing a rust-preventing pigment mainly composed of chromate on the surface of an aluminum-zinc alloy plated steel sheet that has been chemically treated with a chromic acid-based chemical conversion treatment liquid. A coating film is formed, and on the surface of this undercoat coating, a top coating film of an unsaturated polyester resin top coating containing glass fibers that has been surface-treated with a silane coupling agent is formed. Therefore, the adhesion between the substrate and the coating film can be highly improved by the combination of chromic acid-based chemical conversion treatment and an undercoat containing a rust-preventing pigment mainly composed of chromate. It is possible to prevent the occurrence of paint film blistering, and even though the chemical conversion treatment is performed using a chromic acid-based chemical conversion treatment liquid, the hardness of the paint film is reduced by the glass fibers blended into the top coat. In this case, the glass fibers are surface-treated with a silane coupling agent and then treated with unsaturated polyester. It is blended into the resin-based top coat, and the action of the silane coupling agent improves the wettability of the glass fibers with the resin in the unsaturated polyester resin top coat.
It is possible to effectively exhibit the effect of improving coating film hardness by incorporating glass fiber without increasing water permeability.

Claims (4)

[Claims] (1) On the surface of an aluminum-zinc alloy plated steel sheet that has been chemically treated with a chromic acid-based chemical conversion treatment liquid, a coating film of an undercoat containing a rust-preventing pigment mainly composed of chromate is formed. A coated steel sheet characterized in that a top coat film of an unsaturated polyester resin top coat compounded with glass fibers surface-treated with a silane coupling agent is formed on the surface of the base coat film. (2) The undercoat paint contains 15 to 60% by weight of a chromate-based rust preventive pigment based on the non-volatile content in the undercoat paint, as set forth in claim 1. Painted steel plate. (3) Glass fiber has a diameter of 3 to 30μ and a fiber length of 3
Claim 1, characterized in that the diameter is 100μ.
Coated steel plate according to item 2 or item 2. (4) The coated steel sheet according to any one of claims 1 to 3, wherein the content of glass fiber in the unsaturated polyester resin top coat is 8 to 40% by weight.